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  • Oxford University Press  (170,467)
  • American Institute of Physics (AIP)  (139,455)
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  • 1
    Publication Date: 2021-03-15
    Description: In a recent work we computed the relative frequencies with which strong shocks (4.0≤Mw〈5.0), widely felt by the population were followed in the same area by potentially destructive main shocks (Mw≥5.0) in Italy. Assuming the stationarity of the seismic release properties, such frequencies can be tentatively used to estimate the probabilities of potentially destructive shocks after the occurrence of future strong shocks. This allows us to set up an alarm-based forecasting hypothesis related to strong foreshocks occurrence. Such hypothesis is tested retrospectively on the data of a homogenized seismic catalogue of the Italian area against a purely random hypothesis that simply forecasts the target main shocks proportionally to the space-time fraction occupied by the alarms. We compute the latter fraction in two ways a) as the ratio between the average time covered by the alarms in each area and the total duration of the forecasting experiment (60 years) and b) as the same ratio but weighted by the past frequency of occurrence of earthquakes in each area. In both cases the overall retrospective performance of our forecasting algorithm is definitely better than the random case. Considering an alarm duration of three months, the algorithm retrospectively forecasts more than 70% of all shocks with Mw5.5 occurred in Italy from 1960 to 2019 with a total space-time fraction covered by the alarms of the order of 2%. Considering the same space-time coverage, the algorithm is also able to retrospectively forecasts more than 40% of the first main shocks with Mw5.5 of the seismic sequences occurred in the same time interval. Given the good reliability of our results, the forecasting algorithm is set and ready to be tested also prospectively, in parallel to other ongoing procedures operating on the Italian territory.
    Description: This paper benefitted from funding provided by the European Union within the ambit of the H2020 project RISE (No. 821115), which in particular fully financed the PhD grant of one of the authors (E.B.).
    Description: Published
    Description: 1192–1206
    Description: 6T. Studi di pericolosità sismica e da maremoto
    Description: JCR Journal
    Keywords: Earthquake interaction ; Statistical seismology ; forecasting, ; prediction ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 2
    Publication Date: 2020-10-16
    Description: This article has been accepted for publication in Geophysical Journal International ©: The Authors 2019. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. Uploaded in accordance with the publisher's self-archiving policy.
    Description: The active tectonic processes in convergent margins confer a high degree of complexity to the crust. Determining the thermal structure is, therefore, key to better elucidate the nature of those processes. In order to reconstruct the thermal structure of the crust beneath the Italian peninsula, we combine the most recent and accurate shear-wave velocity model that is currently available with thermodynamic modelling, assuming a global average crustal composition with no lateral variations. Our model, presented in terms of Moho temperature and crustal thermal gradients, shows a very good agreement with the known thermal anomalies associated with the backarc spreading related to the Apennine subduction. Importantly, we envisage a new anomalous region of high Moho temperatures in NW Italy (T 〉 800 degrees C at 30 km), at the transition between the Alps and Apennine orogens. The lowest temperatures of our model, corresponding to geothermal gradients 〈 19 degrees C km(-1), are obtained in the still active but slow-convergent portion of the northern Apennine. Moho temperatures increase moving southwards along the Apennine chain, an observation that is coherent with the evidence of ceasing subduction and consequent rebalancing of the depressed isotherms along the slab. Our results suggest that a thermal structure in different tectonic settings can be inferred with acceptable uncertainties based on absolute seismic velocity models. In this sense, our approach can be extended to any other region.
    Description: Published
    Description: 239–247
    Description: 1T. Struttura della Terra
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 3
    Publication Date: 2020-11-20
    Description: Siwi caldera, in the Vanuatu arc (Tanna island), is a rare volcanic complex where both persistent eruptive activity (Yasur volcano)and rapid block resurgence (Yenkahe horst) can be investigated simultaneously during a post-caldera stage. Here we provide new constraints on the feeding system of this volcanic complex, based on a detailed study of the petrology, geochemistry and volatile content of Yasur^Siwi bulk-rocks and melt inclusions, combined with measurements of the chemical composition and mass fluxes of Yasur volcanic gases. Major and trace element analyses of Yasur^ Siwi volcanic rocks, together with literature data for other volcanic centers, point to a single magmatic series and possibly long-lived feeding of Tanna volcanism by a homogeneous arc basalt. Olivine-hosted melt inclusions show that the parental basaltic magma, which produces basaltic-trachyandesites to trachyandesites by 50^70% crystal fractionation, is moderately enriched in volatiles ( 1wt % H2O, 0·1wt % S and 0·055 wt % Cl). The basaltic-trachyandesite magma, emplaced at between 4^5 km depth and the surface, preserves a high temperature (1107 158C) and constant H2O content ( 1wt %) until very shallow depths, where it degasses extensively and crystallizes. These conditions, maintained over the past 1400 years of Yasur activity, require early water loss during basalt differentiation, prevalent open-system degassing, and a relatively high heat flow ( 109W). Yasur volcano releases on average 13·4 103 tons d 1 of H2O and 680 tons d 1 of SO2, but moderate amounts of CO2 (840 tons d 1), HCl (165 tons d 1), and HF (23 tons d 1). Combined with melt inclusion data, these gas outputs constrain a bulk magma degassing rate of 5 107 m3 a 1, about a half of which is due to degassing of the basaltic-trachyandesite. We compute that 25 km3 of this magma have degassed without erupting and have accumulated beneath Siwi caldera over the past 1000 years, which is one order of magnitude larger than the accumulated volume uplift of the Yenkahe resurgent block. Hence, basalt supply and gradual storage of unerupted degassed basaltictrachyandesite could easily account for (or contribute to) the Yenkahe block resurgence.
    Description: Published
    Description: 1077-1105
    Description: 2.3. TTC - Laboratori di chimica e fisica delle rocce
    Description: 2.4. TTC - Laboratori di geochimica dei fluidi
    Description: JCR Journal
    Description: restricted
    Keywords: Vanuatu arc ; Yasur ; gas fluxes ; volatiles ; melt inclusions ; resurgent block ; volcano thermal budget ; 04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases ; 04. Solid Earth::04.08. Volcanology::04.08.03. Magmas
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 4
    Publication Date: 2020-12-15
    Description: This article has been accepted for publication in Geophysical Journal International ©: The Authors 2015. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. Uploaded in accordance with the publisher's self-archiving policy.
    Description: ectonic earthquake swarms challenge our understanding of earthquake processes since it is difficult to link observations to the underlying physical mechanisms and to assess the hazard they pose. Transient forcing is thought to initiate and drive the spatio-temporal release of energy during swarms. The nature of the transient forcing may vary across sequences and range from aseismic creeping or transient slip to diffusion of pore pressure pulses to fluid redistribution and migration within the seismogenic crust. Distinguishing between such forcing mechanisms may be critical to reduce epistemic uncertainties in the assessment of hazard due to seismic swarms, because it can provide information on the frequency–magnitude distribution of the earthquakes (often deviating from the assumed Gutenberg–Richter relation) and on the expected source parameters influencing the ground motion (for example the stress drop). Here we study the ongoing Pollino range (Southern Italy) seismic swarm, a long-lasting seismic sequence with more than five thousand events recorded and located since October 2010. The two largest shocks (magnitude M w = 4.2 and M w = 5.1) are among the largest earthquakes ever recorded in an area which represents a seismic gap in the Italian historical earthquake catalogue. We investigate the geometrical, mechanical and statistical characteristics of the largest earthquakes and of the entire swarm. We calculate the focal mechanisms of the M l 〉 3 events in the sequence and the transfer of Coulomb stress on nearby known faults and analyse the statistics of the earthquake catalogue. We find that only 25 per cent of the earthquakes in the sequence can be explained as aftershocks, and the remaining 75 per cent may be attributed to a transient forcing. The b-values change in time throughout the sequence, with low b-values correlated with the period of highest rate of activity and with the occurrence of the largest shock. In the light of recent studies on the palaeoseismic and historical activity in the Pollino area, we identify two scenarios consistent with the observations and our analysis: This and past seismic swarms may have been ‘passive’ features, with small fault patches failing on largely locked faults, or may have been accompanied by an ‘active’, largely aseismic, release of a large portion of the accumulated tectonic strain. Those scenarios have very different implications for the seismic hazard of the area.
    Description: Published
    Description: 1553–1567
    Description: 4T. Sismicità dell'Italia
    Description: JCR Journal
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  • 5
    Publication Date: 2021-01-18
    Description: The horizontal to vertical spectral ratio (HVSR) of seismic noise is often used to investigate site effects, and it is usually assumed to be a stable feature of the site considered. Here we show that such an assumption is not always justified, and may lead to incorrect conclusions. The HVSR analysis was performed on ambient seismic noise recordings lasting from weeks to months at many sites in Calabria, Italy. Results show a variety of site effects, from the resonance of a shallow sedimentary layer to the polarized amplification of horizontal ground motion associated with topographic effects. We describe the results of seven sites whose HVSR is characterized by dual content: one that is persistent, and another appearing only occasionally. Two sites very near the coast of the Tyrrhenian sea and five sites in the Calabrian Arc mountains show the most remarkable results. The shape of the HVSR changes significantly at these sites when the amplitude of background noise increases in a broad frequency band during periods of bad weather. The occasional contribution to the HVSR consists of one or more peaks, depending on the site, that appear only when the amplitude of ambient noise is higher than usual. The seven sites where we observe the HVSR variability are all located in complex geological environments, on mountains, ridges or foothills. A variation of the HVSR correlated with the day–night cycle is also observed at some of these sites.
    Description: Published
    Description: 2162–2171
    Description: 1T. Struttura della Terra
    Description: JCR Journal
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  • 6
    Publication Date: 2021-02-10
    Description: The 2007 caldera-forming eruption of Piton de la Fournaise (PdF) erupted the largest volume of magma (210 Mm3)recorded at this volcano in at least three centuries. Major and trace element and Sr^Nd isotope data for bulk-rocks, groundmasses and olivine phenocrysts have been combined with melt inclusion data (major, trace and volatile elements) to track magma evolution over the whole eruptive sequence. We show that each eruptive phase had a distinctive geochemical and petrological signature and that caldera collapse on 5 April was preceded by a marked shift in bulk magma composition and crystal content and size. Aphyric basalt erupted at the beginning of the sequence (February 2007) had relatively high Sr isotope ratio (87Sr/86Sr ¼ 0·70420^0·704180) and low Nd isotopic ratio(143Nd/144Nd ¼ 0·51285^0·51286). Olivine-basalts extruded on2^5 April just before caldera collapse are less enriched in radiogenic Sr (87Sr/86Sr ¼ 0·70412^0·70416), but characterized by the same Nd isotopic composition. This magma is interpreted as a new deep input, which pressurized the shallow PdF plumbing system and triggered the 2007 activity. Post-collapse oceanite lavas represent the main volume of magma extruded in 2007. Their bulk-rocks and groundmasses have 87Sr/86Sr (0·70418) intermediate between those of February and 5 April, and similar to those of the March 2007 and 2001^2006 lavas.We show that the Steady State Basalts (SSB) commonly erupted at PdF are hybrid melts, which result from multistep mixing between ‘alkaline’and ‘transitional’end-members. Our results lead us to propose a new model of the PdF plumbing system to reconcile the petrological, geochemical and geophysical observations: (1) the shallow portion (above sea level) of the PdF plumbing system hosts several small sills, in which magma experiences variable degrees of degassing, cooling and crystallization; (2) oceanite lavas result from the withdrawal of shallow harrisitic mushes stored at low pressures (548 MPa; 51800^2400 m depth) below both the volcano summit and its eastern flank; (3) water degassing plays a major role in fast magma crystallization at shallow depths. Multistep ascent and periodic extrusion of the shallow magmas is promoted by injections of deeper and hotter basaltic magma, containing up to 1·3 wt % H2O and 1630 ppm S. In 2007, the new deep input was the ultimate source of the large excess in sulfur degassing detected by satellites. Lateral draining and intrusion of magma below the eastern flank of the volcano are the cause of major volcano deformation, flank sliding and summit caldera collapse.
    Description: Published
    Description: 1287-1315
    Description: 2V. Struttura e sistema di alimentazione dei vulcani
    Description: 3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici
    Description: 4V. Processi pre-eruttivi
    Description: 6A. Geochimica per l'ambiente e geologia medica
    Description: JCR Journal
    Keywords: Piton de la Fournaise ; plumbing system ; magma reservoir ; caldera collapse ; melt inclusions ; volatile budget ; isotope geochemistry ; basalt
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 7
    Publication Date: 2021-02-23
    Description: The preparation, initiation, and occurrence dynamics of earthquakes in Italy are governed by several frequently unknown physical mechanisms and parameters. Understanding these mechanisms is crucial for developing new techniques and approaches for earthquake monitoring and hazard assessments. Here, we develop a first-order numerical model simulating quasi-static crustal interseismic loading, coseismic brittle episodic dislocations, and postseismic relaxation for extensional and compressional earthquakes in Italy based on a common framework of lithostatic and tectonic forces. Our model includes an upper crust, where the fault is locked, and a deep crust, where the fault experiences steady shear.
    Description: Published
    Description: 627–645
    Description: 2T. Deformazione crostale attiva
    Description: JCR Journal
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  • 8
    Publication Date: 2021-03-24
    Description: The 2016–17 central Italy earthquake sequence began with the first mainshock near the town of Amatrice on August 24 (MW 6.0), and was followed by two subsequent large events near Visso on October 26 (MW 5.9) and Norcia on October 30 (MW 6.5), plus a cluster of 4 events with MW 〉 5.0 within few hours on January 18, 2017. The affected area had been monitored before the sequence started by the permanent Italian National Seismic Network (RSNC), and was enhanced during the sequence by temporary stations deployed by the National Institute of Geophysics and Volcanology and the British Geological Survey. By the middle of September, there was a dense network of 155 stations, with a mean separation in the epicentral area of 6–10 km, comparable to the most likely earthquake depth range in the region. This network configuration was kept stable for an entire year, producing 2.5 TB of continuous waveform recordings. Here we describe how this data was used to develop a large and comprehensive earthquake catalogue using the Complete Automatic Seismic Processor (CASP) procedure. This procedure detected more than 450,000 events in the year following the first mainshock, and determined their phase arrival times through an advanced picker engine (RSNI-Picker2), producing a set of about 7 million P- and 10 million S-wave arrival times. These were then used to locate the events using a non-linear location (NLL) algorithm, a 1D velocity model calibrated for the area, and station corrections and then to compute their local magnitudes (ML). The procedure was validated by comparison of the derived data for phase picks and earthquake parameters with a handpicked reference catalogue (hereinafter referred to as ‘RefCat’). The automated procedure takes less than 12 hours on an Intel Core-i7 workstation to analyse the primary waveform data and to detect and locate 3000 events on the most seismically active day of the sequence. This proves the concept that the CASP algorithm can provide effectively real-time data for input into daily operational earthquake forecasts, The results show that there have been significant improvements compared to RefCat obtained in the same period using manual phase picks. The number of detected and located events is higher (from 84,401 to 450,000), the magnitude of completeness is lower (from ML 1.4 to 0.6), and also the number of phase picks is greater with an average number of 72 picked arrival for a ML = 1.4 compared with 30 phases for RefCat using manual phase picking. These propagate into formal uncertainties of ± 0.9km in epicentral location and ± 1.5km in depth for the enhanced catalogue for the vast majority of the events. Together, these provide a significant improvement in the resolution of fine structures such as local planar structures and clusters, in particular the identification of shallow events occurring in parts of the crust previously thought to be inactive. The lower completeness magnitude provides a rich data set for development and testing of analysis techniques of seismic sequences evolution, including real-time, operational monitoring of b-value, time-dependent hazard evaluation and aftershock forecasting.
    Description: Published
    Description: 555–571
    Description: 3T. Fisica dei terremoti e Sorgente Sismica
    Description: JCR Journal
    Keywords: 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 9
    Publication Date: 2021-05-12
    Description: erratum paper
    Description: Published
    Description: 1090-1092
    Description: 1T. Struttura della Terra
    Description: JCR Journal
    Keywords: Theoretical seismology ; Seismic attenuation ; Seismic noise ; Surface waves ; Free oscillations ; Seismic interferometry ; 04.06. Seismology ; 04.01. Earth Interior
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 10
    Publication Date: 2021-05-12
    Description: This article has been accepted for publication inGeophysical Journal International ©The Author(s) 2020. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
    Description: Determining the crustal structure of ocean island volcanoes is important to understand the formation and tectonic evolution of the oceanic lithosphere and tectonic swells in marine settings, and to assess seismic hazard in the islands. The Azores Archipelago is located near a triple junction system and is possibly under the influence of a mantle plume, being at the locus of a wide range of geodynamic processes. However, its crustal structure is still poorly constrained and debated due to the limited seismic coverage of the region and the peculiar linear geometry of the islands. To address these limitations, in this study we invert teleseismic Rayleigh wave ellipticity measurements for 1-D shear wave speed (VS) crustal models of the Azores Archipelago. Moreover, we test the reliability of these new models by using them in independent moment tensor inversions of local seismic data and demonstrate that our models improve the waveform fit compared to previous models. We find that data from the westernmost seismic stations used in this study require a shallower Moho depth (∼10 km) than data from stations in the eastern part of the archipelago (∼13–16 km). This apparent increase in the Moho depth with increasing distance from the mid-Atlantic ridge (MAR) is expected. However, the rate at which Moho deepens away from the MAR is greater than that predicted from a half-space cooling model, suggesting that local tectonic perturbations have modified crustal structure. The 1-D VS models obtained beneath the westernmost seismic stations also show higher wave speeds than for the easternmost stations, which correlates well with the ages of the islands except Santa Maria Island. We interpret the relatively low VS profile found beneath Santa Maria Island as resulting from underplating, which agrees with previous geological studies of the island. Compared to a recent receiver function study of the region, the shallow structure (top ∼2 km) in our models shows lower shear wave speed, which may have important implications for future hazard studies of the region. More generally, the new seismic crustal models we present in this study will be useful to better understand the tectonics, seismicity, moment tensors and strong ground motions in the region.
    Description: Published
    Description: 1232–1247
    Description: 5T. Sismologia, geofisica e geologia per l'ingegneria sismica
    Description: JCR Journal
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  • 11
    Publication Date: 2021-05-12
    Description: The island of Pantelleria, located in the Sicily Channel Rift Zone (Italy), has been the site of violent peralkaline silicic magmatism alternating with minor effusive to low-intensity Strombolian erup- tions of basaltic composition. The basaltic rock suites exposed on the island were sampled to in- vestigate the plumbing system dynamics through the study of chemical stratigraphy and temporal records of olivine crystals. Our petrographic and geochemical observations, together with the com- positional variability of olivine, suggest different evolutionary histories for basaltic magmas erupted over two major periods divided by the 􏰃45 ka Green Tuff (GT) eruption. Core-to-rim com- positional traverses across olivine crystals document different types of zoning. We recognized oliv- ine zones affected by Fo oscillations at very fine scales in the inner cores, rims and/or in intermedi- ate portions of crystals and used them to reconstruct the residence and passage of crystals through different magmatic environments, with P–T–ƒO2 and compositional characteristics con- strained by thermodynamic modeling. The sequence of magmatic environments evidenced by oliv- ine zoning indicate that the pre-GT volcanic period was dominated by injection at shallow crustal levels (􏰃300–200 MPa) of primitive melts, initially moving from a deep storage zone at the crust- mantle boundary. Supply of this magma significantly decreased after the GT eruption, while the dy- namics of magma transfer within the upper portion of the plumbing system were greatly enhanced. The diffusive relaxation of olivine zoning provided the timing of storage and migration of a crystal through different environments. For magmas feeding the ancient (〉45 ka) basaltic activ- ity we retrieved transfer histories that are much longer (up to 􏰃3 years) if compared with those cal- culated for the post-GT basalts (1–9 months). The compositional and temporal dataset presented in this study supports the idea that the GT eruption and the subsequent collapse of the volcanic edi- fice could have caused major changes to the internal structural setting of Pantelleria, creating more favorable conditions for the migration of magmas in the upper portions of the plumbing system.
    Description: Published
    Description: egaa05
    Description: 2V. Struttura e sistema di alimentazione dei vulcani
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 12
    Publication Date: 2021-05-12
    Description: Ischia, a volcanic island located 18 miles SW of Naples (Southern Italy), is a densely populated active caldera that last erupted in AD 1302. Melt inclusions in phenocrysts of the Vateliero and Cava Nocelle shoshonite^latite eruptive products (6th to 4th centuries BC) constrain the structure and nature of the Ischia deep magmatic feeding system.Their geochemical characteristics make Ischia a natural borehole for probing the physico-chemical conditions of magma generation in mantle contaminated by slab-derived fluids or melts, largely dominated by CO2.Volatile concentrations in olivine-hosted melt inclusions require gas^melt equilibria at between 3 and 18 km depth. In agreement with what has already been demonstrated at the other neighboring Neapolitan volcanoes (Procida, Campi Flegrei caldera and Somma^Vesuvius volcanic complex), a major crystallization depth at 8^10 km has been identified.The analyzed melt inclusions provide clear evidence for CO2-dominated gas fluxing and consequent dehydration of magma batches stagnating at crustal discontinuities. Gas fluxing is further supported by selective enrichment in K owing to fluid-transfer during magma differentiation.This takes place under oxidized conditions (Fe3þ /Fe 0·3) that can be fixed by an equimolar proportion of divalent and trivalent iron in the melt if post-entrapment crystallization of the host olivine is discarded.The melt inclusion data, together with data from the literature for other Neapolitan volcanoes, show that magmatism and volcanism in the Neapolitan area, despite differences in composition and eruption dynamics, are closely linked to supercritical CO2-rich fluids. These fluids are produced by devolatilization of subducting terrigenous^pelagic metasediments and infiltrate the overlying mantle wedge, generate magmas and control their ascent up to eruption. Geochemical characteristics of Ischia and the other Neapolitan volcanoes reveal that the extent of fluid or melt contamination of the pre-subduction asthenospheric mantle wedge was similar among these volcanoes. However, differences in the isotopic compositions of the erupted magmas (more enriched in radiogenic Sr at Ischia, Campi Flegrei and Somma^Vesuvius with respect to Procida) and the amount of H2O in the plumbing system of these volcanoes (almost double at Ischia, Campi Flegrei and Somma^Vesuvius than at Procida) reflect the different flow-rates of deep slab-derived fluids or melts through the mantle wedge, which, in turn, control the amount of generated magma.The high bulk permeability of the lithosphere below Ischia, Campi Flegrei and Somma^Vesuvius, determined by the occurrence of intersecting NW^SE and NE^SW regional fault systems, favours fluid ascent and accumulation at crustal levels, with consequent larger magma production and storage than at Procida, located along the NE^SW system.
    Description: Published
    Description: 951-984
    Description: 2V. Struttura e sistema di alimentazione dei vulcani
    Description: 3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici
    Description: 4V. Processi pre-eruttivi
    Description: 6A. Geochimica per l'ambiente e geologia medica
    Description: JCR Journal
    Keywords: CO2-fluxing ; melt inclusions ; redox state ; trachybasalts
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 13
    Publication Date: 2021-06-21
    Description: Sulphur behaviour and variations in redox conditions during magma differentiation and degassing in the Mt Etna (Italy) volcanic system have been explored by integrating the study of olivine-hosted melt inclusions (MIs) with an experimental survey of sulphur solubility in hydrous basaltic magmas. Sulphur solubility experiments were performed at conditions relevant to the Etnean plumbing system (1200 C, 200MPa and oxygen fugacity between NNOþ0 2 and NNOþ1 7, with NNO being the nickel–nickel oxide buffer), and their results confirm the important control of oxygen fugacity (fO2) on S abundance in mafic magmas and on S partitioning between fluid and melt phases (DSfluid/melt). The observed DSfluid/melt value increases from 5164 to 14666 when fO2 decreases from NNOþ1 760 5 to NNOþ0 3. Based on the calculated DSfluid/melt and a careful selection of previously published data, an empirical model is proposed for basaltic magmas to predict the variation of DSfluid/melt values with variations in P (25–300 MPa), T (1030–1200 C) and fO2 (between NNO– 0 8 and NNOþ2 4). Olivine-hosted melt inclusions (Fo89-91) from tephra of the prehistoric (4 ka BP) sub-plinian picritic eruption, named FS (‘Fall Stratified’), have been investigated for their major element compositions, volatile contents and iron speciation (expressed as Fe3þ/PFe ratio). These primitive MIs present S content from 235677 to 34456168 ppm, and oxygen fugacity values, estimated from Fe3þ/PFe ratios, range from NNOþ0 760 2 to NNOþ1 660 2. Iron speciation has also been investigated in more evolved and volatile-poorer Etnean MIs. The only primitive melt inclusion from the Mt Spagnolo eruption (4–15 ka BP) presents a S content of 1515649ppm and an estimated fO2 of NNOþ1 460 1. The more evolved MIs (from 2002–2003, 2006, 2008–2009 and 2013 eruptions) have S content lower than 500 ppm, and their Fe3þ/RFe ratios result in fO2 between NNO– 0 960 1 and NNOþ0 460 1. Redox conditions and S behaviour in Etnean magmas during degassing and fractional crystallization were modelled coupling MELTS code with our empirical DSfluid/melt model. Starting from an FS-type magma composition and upon decrease of T and P, fractional crystallization of olivine, clinopyroxene, spinel and plagioclase causes a significant fO2 decrease. The fO2 reduction, in turn, causes a decrease in sulphur solubility and an increase in DSfluid/melt, promoting S exsolution during magma ascent, which further enhances the reduction of fO2. For the evolved MIs of 2002–2013 eruptions, magma differentiation may therefore have played a crucial role in decreasing redox conditions and favouring efficient S degassing. Differently, during the unusual FS eruption, only limited melt evolution is observed and S exsolution seems to have been triggered by a major pressure decrease accompanied by H2O and CO2 exsolution during fast magmatic ascent.
    Description: Published
    Description: egaa095
    Description: 4V. Processi pre-eruttivi
    Description: JCR Journal
    Keywords: melt inclusions ; sulphur solubility experiments ; XANES ; Mt. Etna ; 04.08. Volcanology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 14
    Publication Date: 2020-10-16
    Description: The behaviour of tsunami waves at any location depends on the local morphology of the coasts, the encountered bathymetric features, and the characteristics of the source. However, the importance of accurately modelling the geometric properties of the causative fault for simulations of seismically induced tsunamis is rarely addressed. In this work, we analyse the effects of using two different geometric models of the subduction interface of the Calabrian Arc (southern Italy, Ionian Sea) onto the simulated tsunamis: a detailed 3-D subduction interface obtained from the interpretation of a dense network of seismic reflection profiles, and a planar interface that roughly approximates the 3-D one. These models can be thought of as representing two end-members of the level of knowledge of fault geometry. We define three hypothetical earthquake ruptures of different magnitudes (Mw 7.5, 8.0, 8.5) on each geometry. The resulting tsunami impact is evaluated at the 50-m isobath in front of coastlines of the central and eastern Mediterranean. Our results show that the source geometry imprint is evident on the tsunami waveforms, as recorded at various distances and positions relative to the source. The absolute differences in maximum and minimum wave amplitudes locally exceed one metre, and the relative differences remain systematically above 20 per cent with peaks over 40 per cent. We also observe that tsunami energy directivity and focusing due to bathymetric waveguides take different paths depending on which fault is used. Although the differences increase with increasing earthquake magnitude, there is no simple rule to anticipate the different effects produced by these end-member models of the earthquake source. Our findings suggest that oversimplified source models may hinder our fundamental understanding of the tsunami impact and great care should be adopted when making simplistic assumptions regarding the appropriateness of the planar fault approximation in tsunami studies. We also remark that the geological and geophysical 3-D fault characterization remains a crucial and unavoidable step in tsunami hazard analyses.
    Description: Published
    Description: 1805–1819
    Description: 3T. Sorgente sismica
    Description: 6T. Studi di pericolosità sismica e da maremoto
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 15
    Publication Date: 2021-04-14
    Description: The scaling of earthquake parameters with seismic moment and its interpretation in terms of self- similarity is still debated in the literature. We address this question by examining a worldwide compilation of corner frequency-based and elastic rebound theory (ERT)-based fault slip, area and stress drop values for earthquakes ranging in magnitude from -0.7 to 7.8. We find that corner frequency estimates of slip (and stress drop) scale differently than those inferred from the ERT approach, where the latter deviates from the generally accepted constant stress drop behavior of so- called self-similar scaling models. We also find that average slips from finite-source models are consistent with corner frequency scaling, whereas peak slip values are more consistent with the ERT scaling. The different scaling of corner frequency- and ERT-based estimates of slip and stress drop with earthquake size is interpreted in terms of heterogeneity of the rupture process. ERT-based estimates of stress drop decrease with seismic moment suggesting a self-affine behavior. Despite the inferred heterogeneity at all scales, we do not observe a clear effect on the Brune stress drop scaling with earthquake size.
    Description: Published
    Description: 1771–1781
    Description: 2T. Deformazione crostale attiva
    Description: JCR Journal
    Keywords: Earthquake dynamics ; Earthquake source observations ; Dynamics and mechanics of faulting ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 16
    Publication Date: 2020-11-26
    Description: So far, the role of appendicularians in the biogeochemical cycling of organic matter has been largely overlooked. Appendicularians represent only a fraction of total mesozooplankton biomass, however these ubiquitous zooplankters have very high filtration and growth rates compared to copepods, and produce numerous fecal pellets and filtering houses contributing to export production by aggregating small marine particles. To study their quantitative impact on biogeochemical flux, we have included this group in the biogeochemical flux model, using a recently developed ecophysiological model. One-dimensional annual simulations of the pelagic ecosystem including appendicularians were conducted with realistic surface forcing for the year 2000, using data from the DyFAMed open ocean station. The appendicularian grazing impact was generally low, but appendicularians increased detritus production by 8% and export production by 55% compared to a simulation without appendicularians. Therefore, current biogeochemical models lacking appendicularians probably under, or misestimate the detritus and export production by omitting the pathway from small-sized plankton to fast sinking detritus. Detritus production and export rates are 60% lower than the estimates from mesotrophic sites, showing that appendicularians’ role is lower but still significant in oligotrophic environments. The simulated annual export at 200 m exceeds sediment trap values by 44%, suggesting an intense degradation during the sinking of appendicularian detritus, supported by observations made at other sites. Thus, degradation and grazing of appendicularian detritus need better quantification if we are to accurately assess the role of appendicularia in export flux.
    Description: EU-FP6 project SESAME GOCE-036949
    Description: Published
    Description: 855-872
    Description: 3.7. Dinamica del clima e dell'oceano
    Description: JCR Journal
    Description: reserved
    Keywords: BFM ; zooplankton ; 03. Hydrosphere::03.01. General::03.01.01. Analytical and numerical modeling ; 03. Hydrosphere::03.01. General::03.01.07. Physical and biogeochemical interactions ; 03. Hydrosphere::03.04. Chemical and biological::03.04.01. Biogeochemical cycles ; 03. Hydrosphere::03.04. Chemical and biological::03.04.04. Ecosystems
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 17
    Publication Date: 2020-11-11
    Description: This article has been accepted for publication in Geophysical Journal International ©: 2021 The Author(s) 2020. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
    Description: In this short paper we show how to use the classical maximum likelihood estimation procedure for the b-value of the Gutenberg–Richter law for catalogues with different levels of completeness. With a simple correction, that is subtracting the relative completeness level to each magnitude, it becomes possible to use the classical approach. Moreover, this correction allows to adopt the testing procedures, initially made for catalogues with a single level of completeness, for catalogues with different levels of completeness too.
    Description: Published
    Description: 337–339
    Description: 6T. Studi di pericolosità sismica e da maremoto
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 18
    Publication Date: 2020-12-21
    Description: This article has been accepted for publication in Geophysical Journal International. Published by Oxford University Press on behalf of the Royal Astronomical Society.
    Description: The classical procedure of the Probabilistic Seismic Hazard Analysis (PSHA) requires a Poissonian distribution of earthquakes. Seismic catalogs follow a Poisson distribution just after the application of a declustering algorithm that leaves only one earthquake for each seismic sequence (usually the stronger, i.e. the main shock). Removing earthquakes from the seismic catalogs leads to underestimation of the annual rates of the events and consequently associate with low seismic hazard as indicated by several studies. In this study, we aim investigating the performance of two declustering methods on the Italian instrumental catalog and the impact of declustering on estimation of the b-value and on the seismic hazard analysis. To this end, first the spatial variation in the seismicity rate was estimated from the declustered catalogs using the adaptive smoothed seismicity approach, considering small earthquakes (Mw≥3.0). We then corrected the seismicity rates using new approach that allows for counting all events in the complete seismic catalog by simply changing the magnitude frequency distribution. The impact of declustering on seismic hazard analysis is illustrated using PSHA maps in terms of peak ground acceleration (PGA) and spectral acceleration (SA) in 2 s, with 10% and 2% probability of exceedance in 50 years, for Italy. We observed that the hazard calculated from the declustered catalogs was always lower than the hazard computed using the complete catalog. These results are in agreement with previous results obtained in different parts of the world.
    Description: Published
    Description: 1174–1187
    Description: 6T. Studi di pericolosità sismica e da maremoto
    Description: JCR Journal
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  • 19
    Publication Date: 2021-05-12
    Description: We have constructed a 3-D shear wave velocity (Vs) model for the crust and uppermost mantle beneath the Middle East using Rayleigh wave records obtained from ambient-noise cross-correlations and regional earthquakes. We combined one decade of data collected from 852 permanent and temporary broad-band stations in the region to calculate group-velocity dispersion curves. A compilation of 〉54 000 ray paths provides reliable group-velocity measurements for periods between 2 and 150 s. Path-averaged group velocities calculated at different periods were inverted for 2-D group-velocity maps. To overcome the problem of heterogeneous ray coverage, we used an adaptive grid parametrization for the group-velocity tomographic inversion. We then sample the period-dependent group-velocity field at each cell of a predefined grid to generate 1-D group-velocity dispersion curves, which are subsequently inverted for 1-D Vs models beneath each cell and combined to approximate the 3-D Vs structure of the area. The Vs model shows low velocities at shallow depths (5–10 km) beneath the Mesopotamian foredeep, South Caspian Basin, eastern Mediterranean and the Black Sea, in coincidence with deep sedimentary basins. Shallow high-velocity anomalies are observed in regions such as the Arabian Shield, Anatolian Plateau and Central Iran, which are dominated by widespread magmatic exposures. In the 10–20 km depth range, we find evidence for a band of high velocities (〉4.0 km s–1) along the southern Red Sea and Arabian Shield, indicating the presence of upper mantle rocks. Our 3-D velocity model exhibits high velocities in the depth range of 30–50 km beneath western Arabia, eastern Mediterranean, Central Iranian Block, South Caspian Basin and the Black Sea, possibly indicating a relatively thin crust. In contrast, the Zagros mountain range, the Sanandaj-Sirjan metamorphic zone in western central Iran, the easternmost Anatolian plateau and Lesser Caucasus are characterized by low velocities at these depths. Some of these anomalies may be related to thick crustal roots that support the high topography of these regions. In the upper mantle depth range, high-velocity anomalies are obtained beneath the Arabian Platform, southern Zagros, Persian Gulf and the eastern Mediterranean, in contrast to low velocities beneath the Red Sea, Arabian Shield, Afar depression, eastern Turkey and Lut Block in eastern Iran. Our Vs model may be used as a new reference crustal model for the Middle East in a broad range of future studies.
    Description: Published
    Description: 1349-1365
    Description: 1T. Struttura della Terra
    Description: JCR Journal
    Keywords: 04.01. Earth Interior ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 20
    Publication Date: 2021-07-23
    Description: Marine aquaculture holds great promise for meeting increasing demand for healthy protein that is sustainably produced, but reaching necessary production levels will be challenging. The ecosystem approach to aquaculture is a framework for sustainable aquaculture development that prioritizes multiple-stakeholder participation and spatial planning. These types of approaches have been increasingly used to help guide sustainable, persistent, and equitable aquaculture planning, but most countries have difficulties in setting or meeting longer-term development goals. Scenario analysis (SA) for future planning uses similar approaches and can complement holistic methods, such as the ecosystem approach to aquaculture framework, by providing a temporal analogue to the spatially robust design. Here we define the SA approach to planning in aquaculture, outline how SA can benefit aquaculture planning, and review how this tool is already being used. We track the use of planning tools in the 20 International Council for the Exploration of the Sea member nations, with particular attention given to Norway’s development goals to 2050. We conclude that employing a combination of an ecosystem framework with scenario analyses may help identify the scale of development aquaculture goals over time, aid in evaluating the feasibility of the desired outcomes, and highlight potential social-ecological conflicts and trade-offs that may otherwise be overlooked.
    Repository Name: EPIC Alfred Wegener Institut
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  • 21
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    Unknown
    Oxford University Press
    In:  EPIC3Journal of Experimental Botany, Oxford University Press, ISSN: 0022-0957
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
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  • 22
    Publication Date: 2017-04-04
    Description: Crystal-rich lithic clasts occurring in volcanic deposits are key tools to understand processes of storage, cooling, and fractionation of magmas in pre-eruptive volcanic systems. These clasts, indeed, represent snapshots of the magma-chamber/host-rock interface before eruptions and provide information on crystallization, differentiation, and degrees of interaction between magma and wall-rocks. In this study, with the aim to shed light on magma-carbonate interaction and CO2 emission in volcanic areas, we focused on the petrology of cumulate and skarn rocks by using as case study a suite of mafic and calcite-bearing lithic clasts from the Colli Albani Volcanic District. By means of phase relations, bulk rock chemistry, phase compositions, and stable isotope data we have recognized different types of cumulates and skarns. Cumulates containing either clinopyroxene±olivine associated with Cr-bearing spinel or glass+phlogopite have been divided in primitive and differentiated, respectively. Primitive cumulates originate at the interface between a relatively primitive magma and carbonate-bearing rocks and show evidences of olivine instability (i.e. heteradcumulate texture) due to carbonate assimilation. Differentiated cumulates, characterized by Ca-rich olivines, phlogopite, and glass containing calcite, form from a differentiated magma in a system open to CaO-contamination. Skarns has been divided in exoskarns, characterized by xenomorphic texture and abundant calcite, and endoskarns, characterized by hypidiomorphic texture, Ca-Tschermak-rich mineral phases, and interstitial glass. Exoskarns formed by means of solid state reactions in a dolostone protolith whereas endoskarns crystallized at subliquidus temperature from a silicate melt that experienced exoskarns assimilation. Our study evidences that magma-carbonate interaction can not be considered a one step process exhausting just after the formation of skarn shells. Magma and carbonate rocks, when in contact, continuously interact leading to the formation of exoskarns, endoskarns, cumulates (primitive and differentiated ones), and differentiated melts. Finally, by means of oxygen and carbon isotope compositions of calcite in equilibrium with skarns, we demonstrate that carbonate assimilation represents a source of massive CO2 degassing mechanism due to the consumption of calcite and removing of CO2 during the decarbonation process.
    Description: Sapienza Universita' di Roma INGV-DPC [Project V 3.1, Colli Albani].
    Description: Published
    Description: 2307-2332
    Description: 2.3. TTC - Laboratori di chimica e fisica delle rocce
    Description: JCR Journal
    Description: reserved
    Keywords: magma/carbonate interaction ; CO2 degassing ; c umulate and skarn ; Colli Albani ; 04. Solid Earth::04.04. Geology::04.04.05. Mineralogy and petrology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 23
    Publication Date: 2020-06-17
    Description: Petrological and geochemical (major element, trace element, Sr–Nd isotope) data for recent (〈5 kyr old) basalts that sporadically erupt on the western flank of Piton de la Fournaise (PdF), one of the most active volcanoes on Earth, allow the tracking of magma transfer and evolution from mantle to crustal depths. In the western peripheral area of PdF we document the broadly synchronous eruptions of (1) primitive olivine and olivine–clinopyroxene transitional basalts with tholeiitic affinity 30 that are closely associated in space with (2) transitional olivine basalts with alkaline affinity, and (3) hybrid lavas, intermediate between the ‘alkaline’ and the ‘tholeiitic’ end-members. The composition of the latter overlaps with that of the lavas frequently erupted from the conduit system feeding the main summit cone. AlphaMELTS modelling, and fluid inclusion and clinopyroxene barometry, constrain the conditions of magma storage at 10–30 km, and the ascent of magma from the upper 35 mantle to the shallow crustal plumbing system. Variable degrees of mantle melting, together with minor source heterogeneity and contamination with cumulate-derived partial melts, contribute to the diversity of PdF magmas. However, all these processes do not represent the dominant factors that produce the large variability we found in major element composition. Indeed, the composition of basalts erupted from PdF peripheral centers is strongly controlled by polybaric olivine–clinopyr- 40 oxene fractionation at pressures higher than 3 kbar. Crystal textures and geochemical modelling suggest that fast magma ascent is critical to prevent clinopyroxene dissolution. Conversely, longlasting magma stagnation promotes pyroxene resorption and magma differentiation. ‘Central’ eruptions occurring close to the PdF summit cone emit variably more evolved melts, which result from olivine–clinopyroxene–plagioclase differentiation at intermediate–shallow pressure (〈3 kbar and in most cases 〈1 kbar). Deep and extensive magma mixing before injection into the crustal magma conduit system, located below the summit region, results in the apparent homogeneity of basalts erupted from the central area. As regards ‘peripheral’ eruptions, deep-seated stagnation of basaltic melts and differentiation at the mantle–crust transition zone (c. 4 kbar) produces a range of 5 magma compositions. We demonstrate that rapid magma ascent from deep-seated reservoirs can bypass the central plumbing system. The eruptions of these magmas both in the central area and on the densely populated flanks have major consequences in terms of volcanic hazard at PdF.
    Description: Published
    Description: 1717–1752
    Description: 2V. Struttura e sistema di alimentazione dei vulcani
    Description: JCR Journal
    Keywords: transitional basalts ; clinopyroxene crystallization and resorption ; mantle–crust underplating
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 24
    Publication Date: 2017-04-04
    Description: Stromboli is known for its persistent degassing and rhythmic strombolian activity occasionally punctuated by paroxysmal eruptions. The basaltic pumice and scoria emitted during paroxysms and strombolian activity, respectively, differ in their textures, crystal contents and glass matrix compositions, which testify to distinct conditions of crystallization, degassing and magma ascent. We present here an extensive dataset on major elements and volatiles (CO2, H2O, S and Cl) in olivine-hosted melt inclusions and embayments from pyroclasts emplaced during explosive eruptions of variable magnitude. Magma saturation pressures were assessed from the dissolved amounts of H2O and CO2 taking into account the melt composition evolution. Both pressures and melt inclusion compositions indicate that (1) Ca-basaltic melts entrapped in high-Mg olivines (Fo89–90) generate Stromboli basalts through crystal fractionation, and (2) the Stromboli plumbing system can be imaged as a succession of magma ponding zones connected by dikes. The 7–10 km interval, where magmas are stored and differentiate, is periodically recharged by new magma batches, possibly ranging from Ca-basalts to basalts, with a CO2-rich gas phase. These deep recharges promote the formation of bubbly basalt blobs, which are able to intrude the shallow plumbing system (2–4 km), where CO2 gas fluxing enhances H2O loss, crystallization and generation of crystal-rich, dense, degassed magma. Chlorine partitioning into the H2O–CO2-bearing gas phase accounts for its efficient degassing (≥69%) under the open-system conditions of strombolian activity. Paroxysms, however, are generated through predominantly closed-system ascent of basaltic magma batches from the deep storage zone. In this situation crystallization is negligible and sulfur exsolution starts at ≤170 MPa. Chlorine remains dissolved in the melt until lower pressures, only 16% being lost upon eruption. Finally, we propose a continuum in explosive eruption energy, from strombolian activity to large paroxysmal events, ultimately controlled by variable pressurization of the deep feeding system associated with magma and gas recharges.
    Description: Published
    Description: 603-626
    Description: 2.3. TTC - Laboratori di chimica e fisica delle rocce
    Description: 3.5. Geologia e storia dei vulcani ed evoluzione dei magmi
    Description: JCR Journal
    Description: reserved
    Keywords: Stromboli ; melt inclusions ; magmatic volatiles ; CO2 fluxing ; magma degassing ; 04. Solid Earth::04.04. Geology::04.04.05. Mineralogy and petrology ; 04. Solid Earth::04.08. Volcanology::04.08.03. Magmas
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 25
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    Oxford University Press
    In:  EPIC3Ocean Acidification, Oxford, Oxford University Press, pp. 291-311, ISBN: 978-0-19-959109-1
    Publication Date: 2014-04-15
    Repository Name: EPIC Alfred Wegener Institut
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  • 26
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    Oxford University Press
    In:  EPIC3Journal of Plankton Research, Oxford University Press, 34(5), pp. 399-415, ISSN: 0142-7873
    Publication Date: 2019-07-17
    Description: This study investigates the relationships between the spring phytoplankton community and environmental factors in the Brazil-Malvinas confluence region. Phytoplankton community composition was determined by the high performance liquid chromatography/CHEMTAX approach, complemented with microscopic examination. Abiotic factors included temperature, salinity, dissolved inorganic macronutrients (ammonium, nitrite, nitrate, phosphate and silicate), water column stability and upper mixed layer depth (UMLD). These environmental variables were reasonably informative to explain the variability of the phytoplankton communities (44% of variation explained). Cluster and canonical correspondence analyses allowed discrimination of four zones (coastal, Sub-Antarctic, tropical and intermediate zones), also identifiable in the T–S diagrams and in the nutrient spatial distribution patterns. The presence of nutrient-rich Sub-Antarctic waters was a major oceanographic feature, associated with diatoms and dinoflagellates. However, in the Sub-Antarctic zone, biomass was particularly low, probably as a result of grazing pressure, as suggested by chemical and biological indicators. In contrast, in oligotrophic tropical waters, phytoplankton was mainly composed by small nanoflagellates and cyanobacteria. A large intermediate zone was also dominated by nanoflagellates, mainly Phaeocystis antarctica, probably favored by strong water column stability. The coastal zone exhibited fairly similar conditions to those in the intermediate zone, but with deeper UMLD, a favorable condition for diatom growth. These results emphasize the importance of the properties of water masses and also biological processes such as grazing in structuring phytoplankton communities in the region.
    Repository Name: EPIC Alfred Wegener Institut
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  • 27
    Publication Date: 2022-05-25
    Description: © The Author(s), 2013. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Conservation Physiology 1 (2013): cot006, doi:10.1093/conphys/cot006.
    Description: Large whales are subjected to a variety of conservation pressures that could be better monitored and managed if physiological information could be gathered readily from free-swimming whales. However, traditional approaches to studying physiology have been impractical for large whales, because there is no routine method for capture of the largest species and there is presently no practical method of obtaining blood samples from free-swimming whales. We review the currently available techniques for gathering physiological information on large whales using a variety of non-lethal and minimally invasive (or non-invasive) sample matrices. We focus on methods that should produce information relevant to conservation physiology, e.g. measures relevant to stress physiology, reproductive status, nutritional status, immune response, health, and disease. The following four types of samples are discussed: faecal samples, respiratory samples (‘blow’), skin/blubber samples, and photographs. Faecal samples have historically been used for diet analysis but increasingly are also used for hormonal analyses, as well as for assessment of exposure to toxins, pollutants, and parasites. Blow samples contain many hormones as well as respiratory microbes, a diverse array of metabolites, and a variety of immune-related substances. Biopsy dart samples are widely used for genetic, contaminant, and fatty-acid analyses and are now being used for endocrine studies along with proteomic and transcriptomic approaches. Photographic analyses have benefited from recently developed quantitative techniques allowing assessment of skin condition, ectoparasite load, and nutritional status, along with wounds and scars from ship strikes and fishing gear entanglement. Field application of these techniques has the potential to improve our understanding of the physiology of large whales greatly, better enabling assessment of the relative impacts of many anthropogenic and ecological pressures.
    Description: This work was supported by the United States Office of Naval Research (award #N000141110435 to K.E.H., award #N000141110540 to R.M.R., and award #N0001412WX20890 to L.C.Y. and C.E.D.); the United Kingdom Natural Environmental Research Council (supporting A.J.H.); the National Center for Research Resources, a component of the United States National Institutes of Health (NIH; supporting C.E.D.); the NIH Roadmap for Medical Research (UL1 RR024146 supporting C.E.D.); The Hartwell Foundation (supporting C.E.D.) and the 2012 Marine Mammal Breath Workshop, which was funded by the National Oceanic and Atmospheric Administration’s Marine Mammal Health and Stranding Response Program.
    Keywords: Blow ; Biopsy dart ; Cetacea ; Faecal samples ; Non-invasive ; Visual health assessment
    Repository Name: Woods Hole Open Access Server
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  • 28
    Publication Date: 2022-05-25
    Description: © 2010 The Authors. This article is distributed under the terms of the Creative Commons Attribution-Noncommercial License. The definitive version was published in ICES Journal of Marine Science: Journal du Conseil 67 (2010): 365-378, doi:10.1093/icesjms/fsp262.
    Description: A commercial acoustic system, originally designed for seafloor applications, has been adapted for studying fish with swimbladders. The towed system contains broadband acoustic channels collectively spanning the frequency range 1.7–100 kHz, with some gaps. Using a pulse-compression technique, the range resolution of the echoes is ~20 and 3 cm in the lower and upper ranges of the frequencies, respectively, allowing high-resolution imaging of patches and resolving fish near the seafloor. Measuring the swimbladder resonance at the lower frequencies eliminates major ambiguities normally associated with the interpretation of fish echo data: (i) the resonance frequency can be used to estimate the volume of the swimbladder (inferring the size of fish), and (ii) signals at the lower frequencies do not depend strongly on the orientation of the fish. At-sea studies of Atlantic herring demonstrate the potential for routine measurements of fish size and density, with significant improvements in accuracy over traditional high-frequency narrowband echosounders. The system also detected patches of scatterers, presumably zooplankton, at the higher frequencies. New techniques for quantitative use of broadband systems are presented, including broadband calibration and relating target strength and volume-scattering strength to quantities associated with broadband signal processing.
    Description: The research was supported by the US Office of Naval Research, grants number N00014-04-1-0440 and N00014-04-1-0475, NOAA/CICOR cooperative agreement NA17RJ1223, NOAA/ National Marine Fisheries Service, and the J. Seward Johnson Chair of the WHOI Academic Programs Office.
    Keywords: Acoustic scattering ; Broadband ; Echosounder ; Fish ; Resonance
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  • 29
    Publication Date: 2022-05-25
    Description: © The Author(s), 2012. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nucleic Acids Research 40 (2012): W82-W87, doi:10.1093/nar/gks418.
    Description: Amplicon sequencing of the hypervariable regions of the small subunit ribosomal RNA gene is a widely accepted method for identifying the members of complex bacterial communities. Several rRNA gene sequence reference databases can be used to assign taxonomic names to the sequencing reads using BLAST, USEARCH, GAST or the RDP classifier. Next-generation sequencing methods produce ample reads, but they are short, currently ∼100–450 nt (depending on the technology), as compared to the full rRNA gene of ∼1550 nt. It is important, therefore, to select the right rRNA gene region for sequencing. The primers should amplify the species of interest and the hypervariable regions should differentiate their taxonomy. Here, we introduce TaxMan: a web-based tool that trims reference sequences based on user-selected primer pairs and returns an assessment of the primer specificity by taxa. It allows interactive plotting of taxa, both amplified and missed in silico by the primers used. Additionally, using the trimmed sequences improves the speed of sequence matching algorithms. The smaller database greatly improves run times (up to 98%) and memory usage, not only of similarity searching (BLAST), but also of chimera checking (UCHIME) and of clustering the reads (UCLUST). TaxMan is available at http://www.ibi.vu.nl/programs/taxmanwww/.
    Description: University of Amsterdam under the research priority area ‘Oral Infections and Inflammation’ (to B.W.B.); National Science Foundation [NSF/BDI 0960626 to S.M.H.]; the European Union Seventh Framework Programme (FP7/ 2007-2013) under ANTIRESDEV grant agreement no 241446 (to E.Z.).
    Repository Name: Woods Hole Open Access Server
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  • 30
    Publication Date: 2022-05-25
    Description: © The Author(s), 2013. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Briefings in Bioinformatics 15 (2014): 783-787, doi:10.1093/bib/bbt010.
    Description: The extremely high error rates reported by Keegan et al. in ‘A platform-independent method for detecting errors in metagenomic sequencing data: DRISEE’ (PLoS Comput Biol 2012;8:e1002541) for many next-generation sequencing datasets prompted us to re-examine their results. Our analysis reveals that the presence of conserved artificial sequences, e.g. Illumina adapters, and other naturally occurring sequence motifs accounts for most of the reported errors. We conclude that DRISEE reports inflated levels of sequencing error, particularly for Illumina data. Tools offered for evaluating large datasets need scrupulous review before they are implemented.
    Description: National Institutes of Health [1UH2DK083993 to M.L.S.]; National Science Foundation [BDI- 096026 to S.M.H.].
    Keywords: Next-generation sequencing ; Sequencing error ; Adapter ligation ; PCR ; Quality score
    Repository Name: Woods Hole Open Access Server
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  • 31
    Publication Date: 2022-05-25
    Description: © The Authors, 2010. This article is distributed under the terms of the Creative Commons Attribution-Noncommercial License. The definitive version was published in Journal of Plankton Research 32 (2010): 1355-1368, doi:10.1093/plankt/fbq062.
    Description: Increasing availability and extent of biological ocean time series (from both in situ and satellite data) have helped reveal significant phenological variability of marine plankton. The extent to which the range of this variability is modified as a result of climate change is of obvious importance. Here we summarize recent research results on phenology of both phytoplankton and zooplankton. We suggest directions to better quantify and monitor future plankton phenology shifts, including (i) examining the main mode of expected future changes (ecological shifts in timing and spatial distribution to accommodate fixed environmental niches vs. evolutionary adaptation of timing controls to maintain fixed biogeography and seasonality), (ii) broader understanding of phenology at the species and community level (e.g. for zooplankton beyond Calanus and for phytoplankton beyond chlorophyll), (iii) improving and diversifying statistical metrics for indexing timing and trophic synchrony and (iv) improved consideration of spatio-temporal scales and the Lagrangian nature of plankton assemblages to separate time from space changes.
    Description: This study was supported by NSF grants to R.J.: OCE-0727033, 0815838 and 0732152. NSF grants to A.C.T.: OCE-0535386, 0815051 and 0814413. NSF grant to J.A.R.: OCE 0815336.
    Keywords: Plankton ; Phenology ; Life history ; Climate change
    Repository Name: Woods Hole Open Access Server
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  • 32
    Publication Date: 2022-05-25
    Description: © The Authors, 2010. This article is distributed under the terms of the Creative Commons Attribution-Noncommercial 2.5 License. The definitive version was published in Genome Biology and Evolution 2 (2010): 304, doi:10.1093/gbe/evq022.
    Description: Reduction of various biological processes is a hallmark of the parasitic lifestyle. Generally, the more intimate the association between parasites and hosts the stronger the parasite relies on its host's physiology for survival and reproduction. However, some systems have been held to be indispensable, for example, the core pathways of carbon metabolism that produce energy from sugars. Even the most hardened anaerobes that lack oxidative phosphorylation and the tricarboxylic acid cycle have retained glycolysis and some downstream means to generate ATP. Here we describe the deep-coverage genome resequencing of the pathogenic microsporidiian, Enterocytozoon bieneusi, which shows that this parasite has crossed this line and abandoned complete pathways for the most basic carbon metabolism. Comparing two genome sequence surveys of E. bieneusi to genomic data from four other microsporidia reveals a normal complement of 353 genes representing 30 functional pathways in E. bieneusi, except that only 2 out of 21 genes collectively involved in glycolysis, pentose phosphate, and trehalose metabolism are present. Similarly, no genes encoding proteins involved in the processing of spliceosomal introns were found. Altogether, E. bieneusi appears to have no fully functional pathway to generate ATP from glucose. Therefore, this intracellular parasite relies on transporters to import ATP from its host.
    Description: This work was supported by grants from the Canadian Institutes for Health Research (MOP-84265), the National Institutes of Health (NIH AI31788, R21 AI52792, and R21 AI064118), and the National Science Foundation (MCB- 0135272). N.C. is a Scholar of the Canadian Institute for Advanced Research and is supported by a fellowship from the Swiss National Science Foundation (NSF) (PA00P3- 124166). D.E. is supported by the Swiss NSF. P.J.K. is a Fellow of the Canadian Institute for Advanced Research and a Senior Scholar of the Michael Smith Foundation for Health Research.
    Keywords: Microsporidia ; Parasite ; Glycolysis ; Carbon metabolism ; Reduction ; Evolution
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  • 33
    Publication Date: 2022-05-25
    Description: Author Posting. © The Authors, 2014. This article is posted here by permission of The Royal Astronomical Society for personal use, not for redistribution. The definitive version was published in Geophysical Journal International 197 (2014): 697-704, doi:10.1093/gji/ggu048.
    Description: After the 1960 M9.5 Valdivia, Chile earthquake, three types of geodetic observations were made during four time periods at nearby locations. These post-seismic observations were previously explained by post-seismic afterslip on the downdip extension of the 1960 rupture plane. In this study, we demonstrate that the post-seismic observations can be explained alternatively by volumetric viscoelastic relaxation of the asthenosphere mantle. In searching for the best-fitting viscosity model, we invert for two variables, the thickness of the elastic lithosphere, He, and the effective Maxwell decay time of the asthenosphere mantle, TM, assuming a 100-km-thick asthenosphere mantle. The best solutions to fit the observations in four sequential time periods, 1960–1964, 1960–1968, 1965–1973 and 1980–2010, each yield a similar He value of about 65 km but significantly increasing TM values of 0.7, 6, 10 and 80 yr, respectively. We calculate the corresponding viscoelastic Coulomb stress increase since 1960 on the future rupture plane of the 2010 M8.8 Maule, Chile earthquake. The calculated viscoelastic stress increase on the 2010 rupture plane varies gradually from 13.1 bars at the southern end to 0.1 bars at the northern end. In contrast, the stress increase caused by an afterslip model has a similar spatial distribution but slightly smaller values of 0.1–3.2 bars on the 2010 rupture plane.
    Description: This work was supported by a MIT/WHOI Joint Program Student Fellowship and a Graduate Student Fellowship from the WHOI Deep Ocean Exploration Institute (MD), as well as NSF Grant OCE-1141785 and a Deerbrook Foundation Award (JL).
    Keywords: Seismic cycle ; Transient deformation ; Seismicity and tectonics ; Subduction zone processes ; Dynamics: seismotectonics ; South America
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  • 34
    facet.materialart.
    Unknown
    Oxford University Press
    In:  EPIC3Geophysical Journal International, Oxford University Press, 193(3), pp. 1399-1414, ISSN: 0956-540X
    Publication Date: 2019-07-16
    Description: The Boreas Basin is located in the Norwegian-Greenland Sea between Northeast Greenland and Svalbard. Towards the east, it is bounded by the ultraslow mid-ocean Knipovich Ridge. Here, we present a 340-km-long seismic refraction line acquired during the expedition ARK-XXIV/3 of research vessel Polarstern in 2009, using 18 ocean bottom seismometers. It crosses the central Boreas Basin from the Knipovich Ridge to the Northeast Greenland margin. Thus, the line provides the first reliable crustal structure information of this basin. In addition, the gravity data acquired parallel to the seismic refraction line are used to calculate a 2.5-D gravity model. The P-wave velocity model shows an unusual ∼3-km-thin oceanic crust with seismic velocities less than 6.3 km s−1, indicating the absence of a significant oceanic layer 3. Mantle velocities vary between 7.5 kms−1 in the uppermost mantle and 8.0 km s−1 at approximately 15 km depth. The low velocities within the upper mantle may be explained by 13 per cent serpentinisation, which is negligible at about 15 km depth. Furthermore, the S-wave velocity model shows low Vp/Vs ratios in the mantle, indicating a highly serpentinised mantle at shallow depths. The gravity model has crustal densities between 2.3 and 2.9 g cm−3, which also point towards the absence of a significant thick oceanic layer 3. The results of our seismic refraction line and other geophysical data indicate that the entire Boreas Basin opened at ultraslow spreading rates since at least ∼28 Ma. No evidence for an extinct spreading ridge in the centre of the Boreas Basin was found.
    Repository Name: EPIC Alfred Wegener Institut
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  • 35
    facet.materialart.
    Unknown
    Oxford University Press
    In:  EPIC3The Natural History of the Crustacea, Vol. 6: Reproductive Biology, New York, U.S.A., Oxford University Press, 30 p., pp. 277-306, ISBN: 9780190688554
    Publication Date: 2021-02-24
    Description: Due to an exceptional variety of habitats, body plans, and lifestyles, crustaceans exhibit a wide array of mating systems. Some groups engage in simple, pure- search polygamous systems in which males usually search for receptive females. In other groups, males defend valuable resources to attract and/ or guard females to ensure paternity. Some species have developed highly complex systems of harem defense polygyny and monogamy, even cases of sub- and eusociality are reported. The expression of mating systems does not seem to be uniformly correlated to taxonomic affiliation, but is rather diverse within certain groups, suggesting that the evolution of mating systems is largely facilitated by the lifestyle of the species. Despite the broad range of mating systems in crustaceans, and although some groups have been studied comparably well, there remains a lack of knowledge about the behavioral and sexual biology of many species. In the light of the high diversity of lifestyles, mating systems, and habitats of certain groups, crustacean species would be ideal models to unravel the evolution of reproductive strategies and social behaviors.
    Repository Name: EPIC Alfred Wegener Institut
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  • 36
    Publication Date: 2022-05-26
    Description: © The Author(s), 2013. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Genome Biology and Evolution 5 (2013): 2368-2381, doi:10.1093/gbe/evt179.
    Description: The dinoflagellates are an evolutionarily and ecologically important group of microbial eukaryotes. Previous work suggests that horizontal gene transfer (HGT) is an important source of gene innovation in these organisms. However, dinoflagellate genomes are notoriously large and complex, making genomic investigation of this phenomenon impractical with currently available sequencing technology. Fortunately, de novo transcriptome sequencing and assembly provides an alternative approach for investigating HGT. We sequenced the transcriptome of the dinoflagellate Alexandrium tamarense Group IV to investigate how HGT has contributed to gene innovation in this group. Our comprehensive A. tamarense Group IV gene set was compared with those of 16 other eukaryotic genomes. Ancestral gene content reconstruction of ortholog groups shows that A. tamarense Group IV has the largest number of gene families gained (314–1,563 depending on inference method) relative to all other organisms in the analysis (0–782). Phylogenomic analysis indicates that genes horizontally acquired from bacteria are a significant proportion of this gene influx, as are genes transferred from other eukaryotes either through HGT or endosymbiosis. The dinoflagellates also display curious cases of gene loss associated with mitochondrial metabolism including the entire Complex I of oxidative phosphorylation. Some of these missing genes have been functionally replaced by bacterial and eukaryotic xenologs. The transcriptome of A. tamarense Group IV lends strong support to a growing body of evidence that dinoflagellate genomes are extraordinarily impacted by HGT.
    Description: J.H.W. was supported by the NSF IGERT Program in Comparative Genomics at the University of Arizona (grant number DGE-0654435). This work was supported by grants from the National Science Foundation (grant numbers OCE-0723498, EF-0732440) and funding provided by the BIO5 Institute at the University of Arizona to J.D.H.
    Keywords: Gene innovation ; Alexandrium tamarense Group IV ; Phylogenetic profile ; Phylogenomics ; De novo transcriptome assembly ; Mitochondrial metabolism
    Repository Name: Woods Hole Open Access Server
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  • 37
    Publication Date: 2022-05-26
    Description: Author Posting. © Author, 2014. This article is posted here by permission of The Royal Astronomical Society for personal use, not for redistribution. The definitive version was published in Geophysical Journal International 198 (2014): 622-636, doi: 10.1093/gji/ggu121.
    Description: The robust statistical model of a Gaussian core contaminated by outlying data that underlies robust estimation of the magnetotelluric (MT) response function has been re-examined. The residuals from robust estimators are systematically long tailed compared to a distribution based on the Gaussian, and hence are inconsistent with the robust model. Instead, MT data are pervasively described by the alpha stable distribution family whose variance and sometimes mean are undefined. A maximum likelihood estimator (MLE) that exploits the stable nature of MT data is formulated, and its two-stage implementation in which stable parameters are first fit to the data and then the MT responses are solved for is described. The MLE is shown to be inherently robust, but differs from the conventional robust estimator because it is based on a model derived from the data, while robust estimators are ad hoc, being based on the robust model that is inconsistent with actual data. Propriety versus impropriety of the complex MT response was investigated, and a likelihood ratio test for propriety and its null distribution was established. The Cramér-Rao lower bounds for the covariance matrix of proper and improper MT responses were specified. The MLE was applied to exemplar long period and broad-band data sets from South Africa. Both are shown to be significantly stably distributed using the Kolmogorov–Smirnov goodness of fit and Ansari-Bradley non-parametric dispersion tests. Impropriety of the MT responses at both sites is pervasive, hence the improper Cramér-Rao bound was used to estimate the MLE covariance. The MLE is shown to be nearly unbiased and well described by a Gaussian distribution based on bootstrap simulation. The MLE was compared to a conventional robust estimator, establishing that the standard errors of the former are systematically smaller than for the latter and that the standardized differences between them exhibit excursions that are both too frequent and too large to be described by a Gaussian model. This is ascribed to pervasive bias of the robust estimator that is to some degree obscured by their systematically large confidence bounds. Finally, a series of topics for further investigation is proposed.
    Description: This work was supported by NSF grant EAR0809074.
    Keywords: Time series analysis ; Numerical approximations and analysis ; Fractals and multifractals ; Probability distributions ; Magnetotellurics
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  • 38
    Publication Date: 2022-05-26
    Description: © The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Plankton Research 36 (2014): 943-955, doi:10.1093/plankt/fbu029.
    Description: The mechanisms by which phytoplankton cope with stressors in the marine environment are neither fully characterized nor understood. As viruses are the most abundant entities in the global ocean and represent a strong top-down regulator of phytoplankton abundance and diversity, we sought to characterize the cellular response of two marine haptophytes to virus infection in order to gain more knowledge about the nature and diversity of microalgal responses to this chronic biotic stressor. We infected laboratory cultures of the haptophytes Haptolina ericina and Phaeocystis pouchetii with CeV-01B or PpV-01B dsDNA viruses, respectively, and assessed the extent to which host cellular responses resemble programmed cell death (PCD) through the activation of diagnostic molecular and biochemical markers. Pronounced DNA fragmentation and activation of cysteine aspartate-specific proteases (caspases) were only detected in virus-infected cultures of these phytoplankton. Inhibition of host caspase activity by addition of the pan-caspase inhibitor z-VAD-fmk did not impair virus production in either host–virus system, differentiating it from the Emiliania huxleyi-Coccolithovirus model of haptophyte–virus interactions. Nonetheless, our findings point to a general conservation of PCD-like activation during virus infection in ecologically diverse haptophytes, with the subtle heterogeneity of cell death biochemical responses possibly exerting differential regulation on phytoplankton abundance and diversity.
    Description: Funding to J.L.R, R.-A.S. and A.L. was provided by the Norwegian Research Council for the “VIPMAP” (nr. 186142) and “HAPTODIV” (nr. 190307) projects, and by the European Research Council Advanced Grant ERC-AG-LS8 “Microbial Network Organisation” (MINOS, project number 250254). J.L.R. received a FRIBIO overseas research fellowship from the Norwegian Research Council. K.D.B. and B.V.M. were supported by funding from the United States National Science Foundation (OCE-1061883).
    Keywords: Caspase ; DNA fragmentation ; IETD ; Phycodnaviridae ; z-VAD-fmk ; Haptophyte
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  • 39
    Publication Date: 2022-05-26
    Description: © The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Genome Biology and Evolution 6 (2014): 2210-2217, doi:10.1093/gbe/evu177.
    Description: The alpha subunits of voltage-gated calcium channels (Cavs) are large transmembrane proteins responsible for crucial physiological processes in excitable cells. They are assisted by three auxiliary subunits that can modulate their electrical behavior. Little is known about the evolution and roles of the various subunits of Cavs in nonbilaterian animals and in nonanimal lineages. For this reason, we mapped the phyletic distribution of the four channel subunits and reconstructed their phylogeny. Although alpha subunits have deep evolutionary roots as ancient as the split between plants and opistokonths, beta subunits appeared in the last common ancestor of animals and their close-relatives choanoflagellates, gamma subunits are a bilaterian novelty and alpha2/delta subunits appeared in the lineage of Placozoa, Cnidaria, and Bilateria. We note that gene losses were extremely common in the evolution of Cavs, with noticeable losses in multiple clades of subfamilies and also of whole Cav families. As in vertebrates, but not protostomes, Cav channel genes duplicated in Cnidaria. We characterized by in situ hybridization the tissue distribution of alpha subunits in the sea anemone Nematostella vectensis, a nonbilaterian animal possessing all three Cav subfamilies common to Bilateria. We find that some of the alpha subunit subtypes exhibit distinct spatiotemporal expression patterns. Further, all six sea anemone alpha subunit subtypes are conserved in stony corals, which separated from anemones 500 MA. This unexpected conservation together with the expression patterns strongly supports the notion that these subtypes carry unique functional roles.
    Keywords: Voltage-gated calcium channel ; Ion channel ; Cnidaria ; Nematostella vectensis ; Evolution of nervous system
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  • 40
    Publication Date: 2022-05-26
    Description: © The Author(s), 2012. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nucleic Acids Research 40 (2012): 7132-7149, doi:10.1093/nar/gks467.
    Description: The capacity of microorganisms to respond to variable external conditions requires a coordination of environment-sensing mechanisms and decision-making regulatory circuits. Here, we seek to understand the interplay between these two processes by combining high-throughput measurement of time-dependent mRNA profiles with a novel computational approach that searches for key genetic triggers of transcriptional changes. Our approach helped us understand the regulatory strategies of a respiratorily versatile bacterium with promising bioenergy and bioremediation applications, Shewanella oneidensis, in minimal and rich media. By comparing expression profiles across these two conditions, we unveiled components of the transcriptional program that depend mainly on the growth phase. Conversely, by integrating our time-dependent data with a previously available large compendium of static perturbation responses, we identified transcriptional changes that cannot be explained solely by internal network dynamics, but are rather triggered by specific genes acting as key mediators of an environment-dependent response. These transcriptional triggers include known and novel regulators that respond to carbon, nitrogen and oxygen limitation. Our analysis suggests a sequence of physiological responses, including a coupling between nitrogen depletion and glycogen storage, partially recapitulated through dynamic flux balance analysis, and experimentally confirmed by metabolite measurements. Our approach is broadly applicable to other systems.
    Description: Office of Science (BER), U.S. Department of Energy [DE-FG02-07ER64388 to D.S. and DE-FG02- 08ER64511 to M.H.S.]; National Aeronautics and Space Administration, NASA Astrobiology Institute [NNA08CN84A to D.S.].
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  • 41
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4546-4550 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The properties of high-resistivity InP with resistivity up to 107 Ω cm, obtained by thermal diffusion of Cu at 800 °C for over 20 h into undoped and p-type InP samples, are investigated. Hall-effect measurements showed that the compensation mechanism in the slowly cooled sample is different from that in the quickly cooled samples. Photoluminescence was quenched in the quickly cooled samples when annealed at 350 °C and the anneal temperature at which the sample resistivity and carrier mobility reached the maximum. It is shown that the electrical compensation in the slowly cooled sample could be understood by a simple deep-level compensation model. However, the semi-insulating behavior of the quickly cooled samples appears to be consistent with an internal Schottky depletion model associated with the Cu precipitates. The photoluminescence quenching is due to the Cu precipitates acting as effective nonradiative recombination centers.
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  • 42
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4551-4556 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Iron pyrite thin films prepared by flash evaporation of pyrite powder have been annealed at different temperatures in a sulfur atmosphere. We present some results on the influence of the annealing temperature (from 250 to 450 °C) on the optical and electrical properties of three groups of samples with different thicknesses ((approximately-equal-to)0.3, 0.6, and 1 μm, respectively). Sulfuration temperature has a clear influence on the optical absorption and electrical resistivity of the films, with some differences in their behavior depending on the film thickness. In light of the available present knowledge of pyrite thin films, interpretation of the obtained results is difficult, it suggests that the shape of the optical absorption curves (and their absorption edge) at low photon energies is determined by the density of point defects, which decreases on increasing the annealing temperature. On the other hand, the electrical resistivity seems to be influenced by both the film grain size and point defect density.
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  • 43
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 839-847 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Self-consistent nonequilibrium fluid models of both the two-dimension (2D) and one-dimension (1D) are presented. In the 2D simulations, the models evaluate the quantitative effects of both radial and axial flow dynamics inside a cylindrically symmetric parallel-plate geometry. The 1D model assumes that the radius of the electrode is much larger than the electrode gap and the moment distributions are uniform along the radial direction. The models are based on the first three moments of the Boltzmann equation and Poisson's equation. Radio frequency (rf) glow discharge simulations from those two fluid models are presented and compared in this study. The comparisons are presented in terms of plasma density, electric field, mean energy, and ionization rate. Results of the 1D fluid model are close to those at the center of the reactor from the 2D simulations. Nonuniform profiles along the radial direction are obtained from the 2D simulations due to the radial dynamics. Higher electron mean energy in the middle region of the radial sheath is observed. The maximum ionization rate is located in the radial sheath region and agrees with the experimental observation.
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  • 44
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 825-831 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper a model of charged particle behavior in a low-pressure oxygen plasma is developed, and compared with experimental results. Agreement is excellent. It is demonstrated that the extremely high temperature ((approximately-greater-than)1 eV) of electrons in these plasmas results in diffusion totally dominating the transport of charged species. It is also shown that charged particle recombination on the walls of a quartz reactor is insignificant. Finally, the influence of the electron temperature profile must be fully considered for accurate results. This work complements an earlier model of radical behavior in these plasmas. Both are needed to fully understand materials modification in these plasmas, which has been shown to involve a synergism between radicals and charged species.
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  • 45
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 853-861 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Large particles (tens of nm to tens of μm in diameter) are problematic in low-pressure (〈1 Torr) plasma processing (etching, deposition) discharges because they can contaminate the product and can perturb electron transport. Although the source of these particles has been studied by a number of groups, a definitive explanation is still lacking. In this paper, we theoretically investigate the role of negative ions in the formation of large clusters, the precursors to particles, in low-pressure plasmas. We find that the formation of particles requires a critically large cluster. Forming the critically large cluster requires longer residence times in the plasma than is usually possible if clustering involves only neutral particles. We propose that negatively charged intermediates, which are trapped in electropositive plasmas, increase the average residence time of clusters to allow the growth of critically large clusters.
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  • 46
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 868-871 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Swift heavy ion irradiation-induced defects have been studied in n-type germanium at room temperature using deep level transient spectroscopy. Several electron traps have been observed after irradiation. The corresponding energies have been determined to be at Ec−0.22, Ec−0.275, Ec−0.29, Ec−0.32, and Ec−0.465 eV. The isochronal annealing behavior of these traps has been studied in detail between room temperature and 200 °C. Comparison of our results with previously published ones allowed an identification of these defects with complexes like divacancies or associations of vacancies with impurities.
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  • 47
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 862-867 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The temporal behavior of the cathode sheath in 30 kHz 0.4–1 Torr H2 discharges has been investigated by optical emission spectroscopy. Analysis of the Stark splitting of plasma-induced H Balmer delta emission was used to measure the electric field with spatial and temporal resolution in the instantaneous cathode sheath. The location of the plasma/sheath boundary was determined from the position of the maximum of the H2 d 3Πu→a 3Σg+ (0,0) Q1 emission at 622.5 nm. Both methods showed that the sheath width increases as the cathode voltage becomes more negative, whereas the width remains constant as the applied voltage drops off. Analysis of the electric-field profile provided information on the time evolution of the ion density close to the electrode during the cathode half-cycle, in agreement with recent numerical calculations. At the beginning of the anodic half-cycle an intense flash of plasma-induced emission was observed, localized within 3 mm from the electrode.
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  • 48
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 877-883 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hollow glass fibers can guide x rays because glancing-angle collisions with a smooth glass surface are highly reflective. Surface roughness decreases this reflectivity. We have developed relatively simple expressions for the effects of surface roughness on x-ray scattering, and we relate our results to the theoretical efficiency of x-ray lenses formed from bundles of hollow glass fibers.
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  • 49
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 884-890 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Positron lifetime spectroscopy and two-dimensional angular correlation of annihilation radiation have been used to investigate grown-in vacancy structures in synthetic crystalline α-SiO2, synthetic fused quartz, and in a 60-μm-thick chemical-vapor-deposited amorphous SiO2 film. For α-SiO2 a ∼300 ps lifetime component suggests trapping by either silicon monovacancies or by oxygen divacancies (or both). The vacancies are neutral and present at a concentration level of 1017/cm3. The positron bulk lifetime for α-SiO2 is estimated to be ∼238 ps in good agreement with semiempirical predictions. In the fused quartz significant positronium formation is found (80%) and the remaining positrons annihilate in voids yielding a lifetime of ∼500 ps. The amorphous SiO2 film contains a mixture of small vacancy clusters and voids and ∼30% of the positrons form positronium. Heat treatment above 950 °C results in a substantial reduction in defect concentration, but up to 1100 °C a small vacancy cluster contribution persists. The positron data indicate that positronium formation in the fused quartz and in the amorphous film takes place in the voids.
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  • 50
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 872-876 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: X-ray photoelectron spectroscopy has been used to study the surface composition and chemistry of two perovskites: SrTiO3 and Pb(Zr,Ti)O3 (commonly known as PZT). It is seen that ion bombardment, which is a common surface modification technique, can cause substantial changes in these oxides. The PZT surface undergoes surface depletion of lead along with chemical reduction of the Pb2+ ion to its metallic state. The Zr/(Ti+Zr) ratio also changes with sputtering, but the total oxygen to cation ratio is unchanged. On the other hand, the surface stoichiometry of SrTiO3 is almost unaffected by ion bombardment. In all the perovskites, irrespective of whether the composition changes or not, a substantial amount of surface Ti is reduced to a lower valency state on sputtering. Most of this component is restored back to the original Ti4+ state when Ni is evaporated on these surfaces, indicating that the reduced state is associated with a damaged outermost surface that can be repaired with an adsorbate. The implication of these results to the bonding properties of these materials have been discussed.
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  • 51
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4102-4104 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The spin pinning in the oxide surface layer has been observed directly, and it is considered a possible reason why the oxide layer leads to the decrease of the specific saturation magnetization for fine iron particles. The pinning depth has been estimated by means of a Mössbauer effect under an applied field of 6 T in a thermal-cycle process. The Debye temperature of the oxide layer and the temperature dependence of f2/f1 have been obtained, where f1 and f2 are the Mössbauer recoilless fractions for the inner α-Fe core and the oxide layer, respectively. Furthermore, the estimation for the thickness of an oxide layer has been improved.
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  • 52
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4105-4112 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A theory of collective translational vibrations of 90° domain walls (DWs) in ferroelectric ceramics is presented. Vibrational motions of DWs forming a regular domain structure of a representative grain are assumed to be completely correlated but independent of DW oscillations in other grains. A dynamic mechanical stress field appearing in a ceramic because of DW vibrations is calculated. In contrast to former studies, this calculation takes into account effects due to the lagging of sound waves emitted by oscillating DWs and gives a general expression for the dynamic mechanical restoring force acting on DWs. From this expression we derive the equation of sustained forced DW vibrations in an oscillating external electric field that is valid for a wide frequency range including microwave frequencies. A general solution of this equation is found, which enables us to compute numerically the dependencies of amplitude and phase of DW vibrations on the frequency ω of the applied electric field. It is shown that in the low-frequency range ω〈ω*=ct/g (ct=velocity of transverse sound wave, g=grain size) the general equation of DW vibrations can be reduced to a simplified equation that includes the static restoring force, the inertial reaction, and the radiation reaction self-force of the DWs emitting sound waves. Analytic expressions are derived for the DW effective mass and for the factors characterizing the static restoring force and the radiation reaction. The contribution of DW vibrations to the complex dielectric constants of ferroelectric ceramics is calculated. It is predicted that at very high frequencies ω(very-much-greater-than)ω* the DW contribution to the real part of permittivity strongly decreases due to clamping of DWs. In this frequency range a peak of dielectric losses should also arise being caused by the emission of sound waves from oscillating DWs. It is emphasized that the above effects can be correctly described on the base of the general equation of DW vibrations only.
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  • 53
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4121-4124 
    ISSN: 1089-7550
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    Topics: Physics
    Notes: A phenomenological model has been applied in an attempt to explain the inability of the ordered regions in the lead magnesium niobate family of relaxor ferroelectrics to coarsen. This approach is based on the concept that the free energy is lowered by an embryonic decomposition along a non-neutral direction. It is proposed that the excess free energy associated with the formation of the non-neutral phase is offset by the distortability of the perovskite structure toward the pyrochlore. The lack of coarsening is then explained as a balance of the electrostatic energy and gradient energy terms, following an earlier published report. This model is then applied to the La-modified (donor-doped) lead magnesium niobate, to explain the dependence of the size of the ordered regions on the degree of doping as observed by other workers.
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  • 54
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4113-4120 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Charge injection leading to catastrophic breakdown has been used to study the dielectric properties of the buried oxide layer in silicon implanted with high-energy oxygen ions. Current versus gate bias, current versus time, and capacitance versus gate bias were used to characterize, at various temperatures, MOS metal-oxide-semiconductor capacitors with areas in the 1×10−4–1×10−2 cm2 range fabricated with commercially available single- or triple-implant separation by implanted oxygen silicon wafers. The data show that injected charge accumulates in the buried oxide at donorlike oxide traps ultimately leading to catastrophic breakdown. Both Poole–Frenkel and Fowler–Nordheim conduction, as well as impact-ionization mechanisms, have been identified in the oxide. The charge and field to breakdown in the best buried oxides are, respectively, near 1 C cm−2 and 10 MV cm−1, similar to the thermally grown oxide parameters. Cumulative distributions of these parameters measured over a large number of capacitors show that the frequency of breakdown events caused by extrinsic defects is scaled with the capacitor area. Intrinsic and extrinsic defect distributions are broader than with thermally grown oxides.
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  • 55
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4125-4129 
    ISSN: 1089-7550
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    Topics: Physics
    Notes: Zinc (Zn) is doped into GaSe single crystals grown by the Bridgman technique in a wide range from 0.005 to 0.5 at. % to the stoichiometric melt. Radiative recombination mechanisms have been investigated by using photoluminescence (PL) measurements. The PL spectra in Zn-doped samples at 77 K are dominated by three emission bands at 1.75, 1.63, and 1.27 eV. The 1.63 and 1.27 eV emission bands are enhanced with the increase in the amount of Zn. In addition to the results of Hall effect measurements, it is found that the 1.63 and 1.27 eV emission bands are associated with the acceptor levels at 0.12 and 0.3 eV above the valence band, respectively. For the 1.27 eV emission band, the temperature dependences of the PL intensity, peak energy, and half-width are characterized by the configurational coordinate model.
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  • 56
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4598-4607 
    ISSN: 1089-7550
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    Topics: Physics
    Notes: High-field effects in metal-oxide-semiconductor capacitors have been studied in detail. A comprehensive set of experiments, stressing identically fabricated capacitors on both P-type and N-type silicon, both in accumulation and in inversion, has been made to study defect generation in the oxide at high fields. There is clear experimental evidence that both bulk hole and electron traps are generated under all stress conditions. High-field prebreakdown properties depend mainly upon the dynamics of generation of traps, trapping and detrapping at these and in previously existing traps. It has been found that of several processes, some dominate, depending upon the type of silicon and polarity during stressing, and this is also true for the final breakdown mechanism. In this paper the dominant mechanisms are identified for each of the field stress conditions that have been studied.
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  • 57
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    Notes: The heavy-hole and light-hole excitons of a CdTe epilayer, pseudomorphically grown on an InSb epilayer by molecular beam epitaxy, are studied with a diamond anvil cell as a function of applied hydrostatic pressure via photoluminescence (PL) and photomodulated reflectivity (PR) spectroscopies. They are compared with the excitonic features in the simultaneously measured PL spectra of a sample of bulk CdTe. Under applied pressure, the lattice mismatch-induced splitting between the light-hole and heavy-hole related transitions increases in a continuous and reversible manner because of the additional pressure-induced compression due to the difference in the compressibilities of CdTe and InSb. The unusually large strain sustained by the CdTe epilayer under pressure is discussed in the light of various models. The PR signal vanishes after the InSb epilayer goes through a structural phase transition at approximately 20 kbar, while the PL signal persists until it is irreversibly quenched by the CdTe epilayer undergoing a structural phase transition at approximately 30 kbar. For pressures between 20 and 30 kbar, the behavior of the CdTe epilayer is similar to that of the bulk sample; the strain appears to have been relaxed due to the structural phase transition which has taken place in InSb. Values of the first- and second-order pressure coefficients for bulk CdTe and for the CdTe epilayer as well as values of the hydrostatic and shear deformation potentials are obtained at 14 and 80 K and compared with previously quoted values.
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  • 58
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    Notes: This article discusses a low-temperature photoluminescence (PL) and electroabsorption (EA) study of GaxIn1−xAs/Ga0.22In0.78As0.48P0.52 single quantum well (QW) samples prepared by gas-source molecular beam epitaxy. The linewidth of PL emitted from these single QW samples increases monotonically with increasing QW strain. EA measurements on the same samples reveal a multipeaked response on the high energy side of the PL spectrum. The energy separation of the EA features corresponds to that expected for differences in QW thickness of one monolayer. The observed PL broadening results from PL emanating from different regions of the same well, differing in thickness, while the Stokes shift results from migration of excitons to wider well regions. Spectral features are lost at large strain which is attributed to strain-enhanced roughening of the QW surface during the crystal deposition.
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  • 59
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4153-4157 
    ISSN: 1089-7550
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    Topics: Physics
    Notes: We report photoluminescence (PL) results obtained on p-type ZnSe epilayers grown by molecular beam epitaxy. As an acceptor dopant, we used an active nitrogen beam produced by a free radical nitrogen source. On the basis of a detailed analysis of PL data we propose a simple semiquantitative method for a quick and contactless evaluation of the net acceptor concentration in p-type ZnSe. In particular, we show that the intensity ratio of the donor–acceptor pair (DAP) emission to the acceptor-bound exciton (I1) emission strongly depends on both the excitation power and the quality of the sample, and because of that it cannot by itself be regarded as a good measure of the net acceptor concentration. On the other hand, the intensity of the DAP emission under saturation excitation shows a simple direct proportionality to the net acceptor concentration, thus providing a reliable tool for determining the relative doping level in p-type ZnSe films.
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  • 60
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4158-4162 
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    Topics: Physics
    Notes: Polymer films containing 4-alkoxy-3-chlorobenzoic acid heated to 140 °C showed two optically different states at room temperature depending on the cooling rate. If after heating the film cooled rapidly, it froze in the transparent state. In contrast, it reverted to the light scattering state when cooled slowly. Cycles between the two optical states were reproducible, therefore these films may offer potential as a rewritable recording material. The reversibility in the optical transmittance may be caused by a reversible change in the crystal size of the acid in the polymer matrix.
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  • 61
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 963-968 
    ISSN: 1089-7550
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    Topics: Physics
    Notes: Ultraviolet pulsed laser induced oxidation kinetics of crystalline germanium (c-Ge) is determined from real-time optical measurements in conjunction with absolute measurements of the oxygen incorporation performed by nuclear reaction analysis. Although the oxidation process can be triggered at laser fluences initially below the melting threshold of c-Ge, it is strongly activated when surface melting occurs and therefore the fast oxidation process observed is mainly a thermally activated process. Because an optical coupling between the oxide layer and the c-Ge underneath, the growth kinetics is complex and leads to nonconstant rates. The oxygen incorporation reaches a saturation value which depends both on the laser fluence and the oxygen pressure. The results show that the oxygen incorporation is limited by an overlapped laser-induced material removal process rather than by the diffusion length of oxygen species.
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  • 62
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4651-4659 
    ISSN: 1089-7550
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    Topics: Physics
    Notes: We have investigated melt-spun Pr-Co alloys with the objective of optimizing their permanent magnet characteristics. Among a variety of elemental additives studied, carbon was found capable of significantly improving the properties, the coercivity in particular. For binary Pr-Co systems optimum values of the remanence, Br=5.7 kG, intrinsic coercivity, Hci=5.8 kOe, and energy product, (BH)max=4.7 MG Oe, were obtained from the Pr16Co84 composition. These values were enhanced to Br=5.8 kG, Hci=16.5 kOe, and (BH)max=7.4 MG Oe for Pr18Co76C6. In both cases the melt-spun ribbons were principally composed of PrCo5. The 16.5 kOe coercivity of the carbon-containing ribbons is the highest ever reported for a PrCo5-based material. Two new rare earth-cobalt phases were tentatively identified during the course of this work: PrCo7 (hexagonal TbCu7 structure) and PrCo2Cx (cubic MgCu2 structure). Survey results for other melt-spun, RCo5-based alloys are also described.
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  • 63
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4643-4650 
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    Topics: Physics
    Notes: The microstructural origin of magnetic anisotropy in a magnetron in-line sputter-deposited CoPtCr/Cr magnetic thin-film disk was examined by mapping magnetic properties and microstructure. The film coercivity (Hc), remanence-thickness product (Mrδ), and coercivity squareness (S*) were determined as a function of radial (r) and angular (θ) co-ordinates using a transfer curve magnetometer. The observed variations in Hc, Mrδ, and S* across the disk were 85 Oe, 0.15 emu/cm2, and 0.03, respectively. The angular variation in magnetic properties showed a sinusoidal pattern with the maxima corresponding to the regions where the tracks were parallel (θ=270°) to the pallet movement direction. High-resolution scanning transmission electron microscopy showed subtle differences in the Co-alloy grain morphology and crystallographic orientation between θ=270° and θ=360° locations. The grains were equiaxed in general except for a small fraction of grains elongated in the direction of pallet movement. Lattice images clearly showed that about 45% of the Co-alloy grains had in-plane c axes and a preferred alignment of the c axes along the texture groove. A greater preference for the c axes to lie along the texture line was observed for the θ=270° location. A coherency stress-based model is proposed to explain the preferred c-axis alignment. While the crystalline anisotropy appears to be the main factor responsible for the magnetic anisotropy, both crystalline and shape anisotropies contribute to the magnetic anisotropy variations.
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  • 64
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    Journal of Applied Physics 74 (1993), S. 4664-4672 
    ISSN: 1089-7550
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    Topics: Physics
    Notes: Insulating barium titanate films were successfully grown on Ti-deposited silicon substrates using the hydrothermal method. The film thickness was 35 and 49 nm for films treated at 200 and 250 °C, respectively, in a 0.25 M Ba(OH)2 solution for 8 h. The BaTiO3 films did not reach the Ti/Si interface. X-ray photoelectron spectroscopy revealed OH-free and nearly carbon-free films, which was corroborated using Auger electron spectroscopy (AES) depth analysis. AES revealed that the oxygen and barium concentrations are correlated throughout the film, and the existence of a diffuse BaTiO3/Ti interface. A discussion on the film growth mechanism is made using existing information on the subject.
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    Journal of Applied Physics 74 (1993), S. 4660-4663 
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    Topics: Physics
    Notes: Magnetoresistance, antiferromagnetic coupling, and crystallographic orientation of Co/Cu superlattices with intentionally mixed interfaces have been studied as a function of the thickness of the mixed region. The antiferromagnetic coupling is weakened, and spin-independent scattering of free electrons is enhanced with increasing thickness of the mixed region, although the morphology and the superlattice period remain unchanged. Saturation magnetoresistance is reduced from 27% to 4% as the result of the formation of a 0.15 nm mixed region at the interfaces. Moreover, the crystallographic orientation of Co/Cu superlattices is also found to be varied by formation of the mixed region. Giant magnetoresistance, antiferromagnetic coupling, and the crystallinity of Co/Cu superlattices are governed by the events in the thin region at the interfaces less than 1 monolayer.
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    Journal of Applied Physics 74 (1993), S. 4685-4690 
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    Topics: Physics
    Notes: The effects on the reflectance spectra of zinc oxide powders, of heat treatment, and of mechanical grinding were investigated for both undoped and aluminum-doped ZnO. A broad absorptance band at 390–400 nm was induced in the undoped powders both by heating in air and by grinding. From a comparison with electron paramagnetic resonance data from the literature, the band could be related to oxygen vacancies. It was found that aluminum doping suppresses the band formation induced by grinding; however, the doping does not suppress the band formation induced by heat treatment.
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    Journal of Applied Physics 74 (1993), S. 4673-4680 
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    Topics: Physics
    Notes: Hydrogenated amorphous carbon films were prepared from CH4, H2, and Ar mixtures by plasma enhanced chemical vapor deposition. Films with various physical properties resulting from various deposition conditions were utilized for this study. The varying deposition parameters included H2 flow rates, Ar flow rates, total pressures, substrate temperatures, and power densities. A systematic study regarding the relationship between deposition conditions and the microstructures, optical, and thermal properties was conducted. Furthermore, how the optical and thermal properties related to the microstructures was analyzed. Fourier transform infrared spectroscopy was employed in this paper for determining the hydrogen concentration and the amounts of tetrahedral and trigonal bondings associated with C—H bond and their relative ratio while the optical properties were measured by optical spectrophotometer. Additionally, photothermal deflection spectroscopy was applied for the measurements of thermal diffusion length.
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    Journal of Applied Physics 74 (1993), S. 4681-4684 
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    Topics: Physics
    Notes: The relationship between the magnitude of the piezoelectric field and the degree of lattice constant mismatch is investigated via low-temperature photoluminescence measurements of the quantum-confined Stark effect for a series of (111)B Al0.15Ga0.85As-InyGa1−yAs pseudomorphic quantum well heterostructures. The experimental strain-induced electric field values agree well with theoretical calculations for indium mole fractions in the range 0.037≤y≤0.09. In addition, an anomalous saturation of the photoluminescence transition energy is observed at values of applied voltage greater than that required to nullify the piezoelectric field, despite the indication from separate electroreflectance measurements that the net electric field within the quantum well reverses polarity under similar electrical biasing conditions.
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    Journal of Applied Physics 74 (1993), S. 7044-7047 
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    Topics: Physics
    Notes: Laser assisted particle removal (LAPR) is an innovative laser cleaning technique which can remove various particles from solid surfaces via laser induced explosive evaporation of a chosen energy transfer medium, e.g., water. An Ar+ ion continuous-wave laser (488 nm) was used to study the CO2 laser pumped explosive evaporation of water adsorbed on a Si substrate. The probe laser beam was parallel to the sample surface at different displacements and interacted with the ejected material upon pulsed CO2 laser irradiation in analogy with the time resolved laser beam deflection experiments on laser induced vaporization of copper by Guo et al. [Opt. Commun. 77, 381 (1990)]. Using CO2 laser energies which are much greater than the LAPR thresholds, we observed the generation and propagation of a shock wave at supersonic speeds followed by a water vapor/aerosol/particle cloud at a much slower speed. From the evolution of the shock wave, the total conversion efficiency of the incident laser beam into the shock wave has been determined using a self-similar approximation.
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    Journal of Applied Physics 74 (1993), S. 2681-2685 
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    Topics: Physics
    Notes: Two types of YBa2Cu3Oy-La0.7Ca0.3MnOz-YBa2Cu3Oy (YBCO-LCMO-YBCO) coplanar-type junctions with a 0.2 μm gap were fabricated by electron-beam lithography and Ar-ion-beam milling. One is a junction in which a current flows into the a-b plane (ferromagnetic spin arrangement) of the LCMO and then passes through the channel along the c axis (antiferromagnetic arrangement), and the other is a junction in which the current only passes through the a-b plane. In the former junction the current-voltage characteristics show nonlinearity which suggests a superconductive linkage, while the latter has linear characteristics. This anisotropy of the proximity effect is attributed to anisotropy of the spin structure, because the LCMO film has a small anisotropy of the normal decay length in the a-b plane and along the c axis.
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    Journal of Applied Physics 74 (1993), S. 2701-2704 
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    Topics: Physics
    Notes: RFe2 laves phase intermetallic compounds are promising materials for magnetostrictive applications. To obtain a larger magnetostriction in a low magnetic field, the influence of boron addition on the giant magnetostriction of an amorphous (SmFe2) (1−x) at. % B (x) at. % alloy has been examined. In the amorphous alloy, the saturation magnetostriction anomalously increases, while the saturation magnetization decreases with the increase in x. The highest saturation magnetostriction of −670×10−6 at 10 kOe and its effective magnetostriction of −490×10−6 at 0.3 kOe can be obtained for amorphous (SmFe2) 99.26 at. % B 0.74 at. % alloy. This effective giant magnetostriction obtained in a low magnetic field is larger than those reported in previous researches. I attribute this anomalous giant magnetostriction in a low magnetic field to the increment of elastic energy in the amorphous (SmFe2) (1−x) at. % B (x) at. % alloy.
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    Journal of Applied Physics 74 (1993), S. 2725-2730 
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    Topics: Physics
    Notes: Effects of interfaces such as metal/polymer interfaces and polymer/polymer interfaces on the space-charge distribution in multiply low-density polyethylene have been investigated using a pulsed electroacoustic method. It has been found that the heterocharge was dominant in an artificial interface existing in a polyethylene sample. The time dependence of the heterocharge distribution in the interface on applied voltages and polarity was studied. From these charge distributions, the modified electrical field was calculated based on Poisson's equation. The calculated result indicated that the actual field was stronger than the applied uniform field at the artificial interface. A new data display method for a three- or two-dimensional plot is employed to display all measurement data on one plot in which the space charge becomes visible so that the results can be easily and conveniently understood.
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    Journal of Applied Physics 74 (1993), S. 7078-7084 
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    Topics: Physics
    Notes: The thermal diffusivity measurement through pulsed photodeflection in a modified collinear configuration is presented and discussed; comparison between theory and experiment is also shown.
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    Journal of Applied Physics 74 (1993), S. 7094-7100 
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    Topics: Physics
    Notes: A theory is presented to explain the observed electron emission characteristics of a hollow-cathode-based plasma source. The theory is compared with measurements made in a laboratory vacuum facility and is used to predict emission characteristics when the source plasma expands into an ambient space plasma. Crucial to understanding the observed emission current-voltage characteristic of hollow-cathode-type devices is the recognition of the role of emission current, not just the current in the main discharge circuit, in ionization of the neutral gas flowing through the device. This ionization can lead to breakdown of the sort that is familiar in many gas discharge devices. Equally crucial to understanding the low impedance capability of the device in coupling spacecraft to an ambient space plasma is recognition of the role of escaping as well as trapped source electrons in the formation of the space potential profile. The presence of these electrons, according to the theory, results in space electron emission current-voltage characteristics which are well approximated by those observed in laboratory chambers.
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    Journal of Applied Physics 74 (1993), S. 4729-4736 
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    Topics: Physics
    Notes: The neutral and charged species emitted by pulsed-laser irradiation of polytetrafluoroethylene (PTFE) at 248 nm in vacuum have been examined. In particular, the species and properties of the emission products produced at typical fluence regimes used in the pulsed-laser deposition of PTFE thin films have been characterized. The relative intensities of the major products as well as their dependence on laser fluence are presented, and a simple model is used to fit the observed fluence dependence. Evidence that the major neutral component, the monomer (C2F4), is formed from a thermally activated unzipping reaction is presented. The ionic species are derived from the neutral decomposition products, apparently ionized by electron collisions in the weak plasma generated at the target surface.
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    Journal of Applied Physics 74 (1993), S. 4737-4740 
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    Topics: Physics
    Notes: Impurity doping in InP layer grown by metalorganic vapor-phase epitaxy using tertiarybutylphosphine and organic doping sources is presented. Diethylzinc and diethylselenide were used as the p-type and n-type doping sources, respectively. Electrical properties and surface morphology of the impurity-doped layers together with their growth condition dependence were investigated. Good controllability and reproducibility of the doping level were confirmed. The maximum doping levels of 1.8×1018 and 1×1019 cm−3 were successfully attained for p-InP and n-InP, respectively. These results promise further safe metalorganic vapor-phase epitaxy by using organic compounds for all precursors.
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    Journal of Applied Physics 74 (1993), S. 3103-3110 
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    Topics: Physics
    Notes: In a previous report [G. P. Watson, D. G. Ast, T. J. Anderson, and Y. Hayakawa, Appl. Phys. Lett. 58, 2517 (1991)] we demonstrated that the motion of misfit dislocations in InGaAs, grown by organometallic vapor phase epitaxy on patterned GaAs substrates, can be impeded even if the strained epitaxial layer is continuous. Trenches etched into GaAs before growth are known to act as a barrier to misfit dislocation propagation [E. A. Fitzgerald, G. P. Watson, R. E. Proano, D. G. Ast, P. D. Kirchner, G. D. Pettit, and J. M. Woodall, J. Appl. Phys. 65, 2220 (1989)] when those trenches create discontinuities in the epitaxial layers; but even shallow trenches, with continuous strained layers following the surface features, can act as barriers. By considering the strain energy required to change the length of the dislocation glide segments that stretch from the interface to the free surface, a simple model is developed that explains the major features of the unique blocking action observed at the trench edges. The trench wall angle is found to be an important parameter in determining whether or not a trench will block dislocation glide. The predicted blocking angles are consistent with observations made on continuous 300 and 600 nm thick In0.04Ga0.96As films on patterned GaAs. Based on the model, a structure is proposed that may be used as a filter to yield misfit dislocations with identical Burgers vectors or dislocations which slip in only one glide plane.
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 3126-3130 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Near-surface regions of Cd1−xMnxTe and Hg1−xCdxTe epilayers (down to tens of angstroms) on (001) GaAs substrates have been characterized by extremely asymmetric Bragg reflection topography (EABRT) with the laboratory x-ray source condition and a Lang camera, using x-ray grazing incidence angles less than the critical angle for total external reflection. The experimental topographs obtained in the present work illustrate the potential of the EABRT technique for nondestructive characterization of near-surface regions of crystals. The resolution of an image in EABRT is discussed in detail.
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 3144-3149 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The enthalpies of formation of metastable fcc Ag-Cu solid solutions, produced by ball milling of elemental powders, were determined by differential scanning calorimetry. Experimental thermodynamic data for these metastable alloys and for the equilibrium phases are compared with both calculation of phase diagrams (CALPHAD) and atomistic simulation predictions. The atomistic simulations were performed using the free-energy minimization method (FEMM). The FEMM determination of the equilibrium Ag-Cu phase diagram and the enthalpy of formation and lattice parameters of the metastable solid solutions are in good agreement with the experimental measurements. CALPHAD calculations made in the same metastable regime, however, significantly overestimate the enthalpy of formation. Thus, the FEMM is a viable alternative approach for the calculation of thermodynamic properties of equilibrium and metastable phases, provided reliable interatomic potentials are available. The FEMM is also capable of determining such properties as the lattice parameter which are not available from CALPHAD calculations.
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  • 80
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 3150-3155 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The diffusion of δ-function-shaped B- and Sb-dopant spikes in thin Si films grown by solid-phase-epitaxy [(SPE), growth of amorphous film by molecular-beam epitaxy (MBE) at room temperature and subsequent regrowth in situ] during annealing in vacuum is compared to diffusion in films grown by low-temperature (LT) MBE. Diffusion temperatures from 750 to 900 °C, and two-dimensional concentrations of 0.7–1.6×1014 cm−2 have been investigated. The diffusive behavior of dopants in SPE films is found to be qualitatively different from that in films grown by LTMBE. This is related to the vacancylike defects that are intrinsic to growth by SPE but not to growth by LTMBE. Dopant profiles widen significantly during SPE regrowth, making the achievement of δ-function dopant spikes impossible. After a vacuum anneal the diffusion coefficients for both n- and p-type dopants are lower in SPE films than the corresponding values in films grown by LTMBE by up to one order of magnitude. The diffused depth profile of the dopant in LTMBE films shows the characteristic deviation from a pure Gaussian that is expected due to the concentration dependence of diffusion, i.e., a flat top and steep shoulders. In contrast, dopant depth profiles of SPE-grown material show after diffusion a central spike and relatively flat shoulders. The width of the central spike is, after an initial transient that it was not possible to resolve, independent of diffusion time and temperature. This indicates that the SPE material is defective, with the defects acting as traps during diffusion.
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  • 81
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 3162-3171 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ultrathin GaAs wires as thin as 15–40 nm and about 2 μm long have been grown on a GaAs substrate by metal-organic vapor-phase epitaxy. The wires, which consist of whiskers, are grown between 380 and 550 °C using trimethylgallium and arsine (AsH3) as source materials. It is found that the wire growth direction is parallel to the [111] arsenic dangling-bond direction and can be perfectly controlled by the crystallographic orientation of the GaAs substrate surface. From transmission electron microscopic analysis it is revealed that the crystal structure of the wire coincides with the zinc-blende type for the growth temperature range of 460–500 °C, but it changes to the wurtzite type at 420 °C and temperatures higher than 500 °C. It is also found that the wires have a twin-type structure around the [111] growth axis for zinc blende and [0001] growth axis for wurtzite. Photoluminescence study of these wires shows that the luminescence peak energy shifts to a higher energy as the wire width decreases from 100 to about 35 nm. In terms of luminescence polarization it is confirmed that the luminescence intensity parallel to the wires is four times greater than that perpendicular to the wires. These results clearly indicate the quantum-size effect of carriers confined in the wire. As a preliminary application to devices, a p-n junction has been formed along the GaAs wire. Light emission by current injection to the p-n junction wires has been observed in continuous operation at room temperature.
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  • 82
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 3181-3188 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The existence of partially correlated roughness in multilayer thin films is demonstrated using x-ray diffraction diffuse-intensity distribution measurements. The method is generally applicable and produces, in addition to values of magnitudes of interfacial roughness and its lateral correlation length, a measure of the cross correlation between interfaces separated by intermediate ones. A simple phenomenological model can describe roughness in W/C multilayers prepared under standard conditions. A cumulative roughness function is used to show that the wavelength range in which the interfacial roughness predominates in these layers lies between 50 A(ring) and 2000 A(ring) and that the long-wavelength roughness replicates better than the short-wavelength roughness.
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  • 83
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 3194-3203 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Film-substrate interactions of YBa2Cu3O7−x (YBCO) thin films grown by pulsed laser deposition on alkaline earth fluoride substrates were investigated. X-ray photoelectron spectroscopy, atomic force microscopy, and x-ray-diffraction measurements showed that the quality of the film and amount of chemical reaction between film and substrate were dependent on the substrate material and deposition temperature. The reaction of YBCO films with CaF2 and MgF2 substrates forms BaF2 and calcium or magnesium oxide species. The reacted film is insulating and has a microscopically rough surface. No reaction was detected in films deposited on BaF2 and SrF2. Physical and thermodynamic properties which may explain the observed order of reactivity are examined.
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  • 84
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 3215-3218 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We analyze the role of coherent terahertz radiation on the ultrafast electron dynamics of laser excited photoconductors. Generation of electromagnetic radiation is included within the framework of the usual hot carrier transport theory. A Monte Carlo scheme is used to study the resulting changes in the nonequilibrium electronic energy and transient drift velocity. Our results reveal a density dependent decrease in both quantities, due to reductions in the internal electric fields caused by radiative energy outflow. At densities above 2×1017 cm−3, we obtain a decrease in the transient velocity and expect delays in the onset of phonon emission.
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  • 85
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 3219-3223 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The steady state and transient drift velocity of holes in silicon have been investigated using Monte Carlo techniques. The valence band is modeled by warped nonparabolic heavy and light hole bands, and a spherical spin-orbit band. The nonparabolicity of the heavy and light hole bands is included using piecewise continuous functions. The calculated velocities are in better agreement with experimental steady state drift velocity values compared to previous Monte Carlo calculations using only a heavy hole band. Transient calculations show the magnitude of the velocity overshoot for holes is smaller than electrons in silicon but is significantly higher than the steady state drift velocity when high fields are applied.
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  • 86
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 7264-7268 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dc and ac conductivity of single crystal and glass of Li2B4O7 have been measured at various temperatures. It has been shown that these materials are mixed conductors in which electronic and ionic conduction coexist. In the single crystals, both the electronic conduction and ionic conduction along the c axis are much smaller than that perpendicular to the c axis. The anisotropy in the electronic conduction is considered to be due to the conduction by the π electron of the BO3 layer located on the (001) crystallographic plane. The anisotropy in the ionic conduction is also considered to be due to the diffusion of Li ions and/or protons between the BO3 layers. The thermal activation energies of the electronic conduction were 0.65 eV for glass, 1.61 eV for the crystal parallel to the c axis, and 0.78 eV for the crystal perpendicular to the c axis. The activation energy of the ionic conduction was 0.46 eV for the crystal perpendicular to the c axis.
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 2968-2970 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is shown that a combination of low-temperature photoluminescence and luminescence excitation spectroscopies together with appropriate modelization can provide the precise information needed for a thorough control of interdiffusion in quantum well structures. A fit of observed and calculated transition energies up to five energy levels, using the interdiffusion length as a unique parameter, is considered. The potentiality of this procedure to fully characterize the interdiffusion process is illustrated by considering the examples of lightly and heavily intermixed GaAs-AlGaAs multiquantum wells.
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 2977-2979 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A photoluminescence study has been made on an oxygen-containing Si fine structure fabricated by a gas evaporation technique. Transmission electron micrographs have shown that the fine structure is composed of nonspherical particles aggregated together in chain-like or cluster-like structures. The luminescence from the samples after oxidation treatment is bright blue as viewed with the naked eye, the spectra having a peak at about 470 nm or shorter wavelength. A peculiar temperature dependence of the emission peak indicates that the emission is strongly correlated with some structural change in the fine structure.
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 2983-2985 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Superconducting YBa2Cu3O7−δ thin films with Tc=89.5 K were deposited on MgLaAl11O19 (11¯0) substrates by pulsed laser deposition. X-ray diffraction patterns indicate that the YBa2Cu3O7−δ films were epitaxial films, with the c axis perpendicular to the substrate surfaces. Microstrip resonators of YBa2Cu3O7−δ thin films deposited on MgLaAl11O19 substrates were fabricated. The loaded quality factor of the resonator was 1007 at 77 K and 4.28 GHz. As a new substrate for high Tc oxide superconducting films, MgLaAl11O19 substrates are especially suitable for superconducting-microwave applications.
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 1469-1472 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Barrier penetration is attributed to energy fluctuations expected from the uncertainty principle. Numerical simulations are made by calculating the traversal time and action for a large number of possible velocity profiles. Distributions of traversal time are determined by assuming that the probability of each velocity profile decreases exponentially with the action of the fluctuation it requires. Distributions of traversal times are reported for rectangular barriers having different sizes. For large barriers the distributions are leptokurtic and centered at the semiclassical traversal time T0 = d(square root of)m/[2(V0−E)], where d and V0 are the length and height of the barrier and m and E are the mass and energy of the particle. The kurtosis decreases and the mode shifts to shorter durations with decreasing barrier size.
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  • 91
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 7306-7310 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have found that a nonquantizing weakly p-doped InP/Ga0.47In0.53As/InP heterostructure exhibits a photovoltage as high as 2 V at 120 K for moderate light excitation power densities of a few mW/cm2. The back electrical contact is ohmic and the front rectifying contact is established through a thin silver layer. We have monitored as a function of reverse bias applied to the structure the internal photoemission current and also the external photoemission current, due to electrons emitted into vacuum after lowering the surface work function by cesium and oxygen adsorption. Both of these dependences exhibit strong effects of the excitation power density. The dependence of the photovoltage as a function of external bias is obtained using photoreflectance. As shown by a simple model, this gigantic photovoltage arises from accumulation of photoexcited carriers in the Ga0.47In0.53As layer because of the existence of energy barriers with the neighboring InP layers. The different electron and hole transfer probabilities across these barriers result in a strong change of the potential of the Ga0.47In0.53As layer under light excitation.
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 7315-7320 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We propose a new method of making heavily doped n-type GaAs to a very shallow depth using sulfur hexafluoride (SF6) plasma treatment of the GaAs surface. Semi-insulating GaAs substrate implanted with Si was exposed to a sulfur containing SF6 plasma and capped with silicon nitride anneal cap. During a subsequent anneal step at an elevated temperature to electrically activate the implanted Si, the sulfur diffused into GaAs to a shallow depth of ∼600 A(ring) resulting in further enhancement of net carrier concentration. With this technique the carrier concentration near the surface region was almost doubled compared to samples with Si implantation only. The enhanced carrier concentration improved the wafer-scale variation of ohmic contact resistance using AuGeNi contact metals from 0.089±0.073 to 0.049±0.017 Ω mm. The surface chemistry of SF6 plasma treated GaAs surface was characterized by x-ray photoelectron spectroscopy and Auger electron spectroscopy, and the results were compared with the carrier-concentration profiles and ohmic contact resistance.
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 7329-7339 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron coincidence spectroscopy in an ultrahigh vacuum scanning transmission electron microscope has been used to study the generation pathways for secondary (SE) and Auger electrons (AE) excited by high-energy incident electrons. Energy and momentum transfer of inelastically scattered 100 keV primary electrons have been correlated with energy selected SE and AE for both thin 〈111〉 oriented Si crystals and amorphous C films. Coincidence spectra from the valence excitation region indicate that bulk plasmon decay is not the primary production channel for SE in Si(111) and that SE result partially from the decay of ionizations from deep in the valence band. Energy deposition by the primary beam is responsible for SE production at excitation energies above the valence region. At most one SE is emitted from the entrance surface of a thin film for each inelastically scattered 100 keV primary electron. An enhancement in both the SE yield and generation probability is observed at the C K ionization edge. Correlations between energy loss electrons in the vicinity of the C K ionization edge and energy selected SE near the C KLL AE energy show a very sharp threshold in the generation probability. High-momentum transfer (spatially localized) inelastic scattering events are more efficient at creating SE than low-momentum transfer events. The high-spatial resolution obtained in SE images is explained using the Heisenberg uncertainty principle and the scattering angle dependence of the SE generation probability.
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 3061-3064 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A steep plasma edge in infrared reflectivity spectra of Hg1−xCdxTe and HgSe:Fe has been observed. It is predicted that the edge is sensitive to the variation of carrier concentration, which indicates the possibility of developing a fast light-controlled switch for infrared radiation as well as a new approach of infrared modulation and detection. The modulation gain in power and detectivity limited by the generation-recombination process has been calculated and compared with the photoconductive counterpart.
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 3065-3070 
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    Topics: Physics
    Notes: The transfer of energy between the plasma and the iron anode and the evaporation of metal were taken into account in modeling a short free-burning arc in argon at atmospheric pressure. The presence of metal vapor in the plasma modifies the electrical conductivity and the radiated power and leads to arc cooling in the anode region. In return, the arc cooling modifies the rate of vaporization of the anode and thus the calculated concentration of iron vapor in the arc.
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 3080-3083 
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    Topics: Physics
    Notes: Six samples of congruently melting lithium niobate (∼Li0.95Nb1.01O3) have been examined by powder x-ray diffraction for the occurrence of niobium antisite defects (niobium on lithium sites). Contrary to current thinking, we have found no evidence for the occurrence of high concentrations of such defects, which also require the presence of Nb site vacancies. Rather, it was found that the number of antisite defects is close to the minimum that is required to sustain charge neutrality in a model of the type ([Li1−xNbx/5][Nb]O3), where the Nb site is fully occupied.
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 3071-3079 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The plasma plume induced by pulsed CO2 laser irradiation of a Ti target at power densities up to 4×108 W cm−2 was studied by emission spectroscopy. Time- and space-resolved measurements were performed by varying laser intensity, laser temporal pulse shape, ambient gas pressure, and the nature of the ambient gas. Experimental results are discussed by comparison with usual models. We show that shock wave and plasma propagation depend critically on the ratio Ivap/Ii, Ivap being the intensity threshold for surface vaporization and Ii the plasma ignition threshold of the ambient gas. Spectroscopic diagnostics of the helium breakdown plasma show maximum values of electron temperature and electron density in the order of kTe∼10 eV and ne=1018 cm−3, respectively. The plasma cannot be described by local thermodynamic equilibrium modeling. Nevertheless, excited metal atoms appear to be in equilibrium with electrons, hence, they can be used like a probe to measure the electron temperature. In order to get information on the role of the plasma in the laser-surface interaction, Ti surfaces were investigated by microscopy after irradiation. Thus an enhanced momentum transfer from the plasma to the target due to the recoil pressure of the breakdown plasma could be evidenced.
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 3084-3090 
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    Topics: Physics
    Notes: Crystallization temperatures of a-Si:H films deposited on GaAs substrates by a glow-discharge method increased with an increase in the concentration of As doped into the a-Si:H films. Crystallization of a-Si:H films with an As concentration of 2×1020 cm−3 started at a temperature of about 1050 °C. These a-Si:H films also had a large amounts of H and SiH3.
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 3091-3098 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The conductivity and the impurity profiles of InP implanted with dopant ions (Si,Be) or non dopant ions (B,H,N,O,P) have been investigated. Experiments have been done in substrates with and without Fe doping. Low-temperature, short-time annealing of implanted Si and Be reveals an n-type distribution of carriers which cannot be accounted for on the basis of implant activation. In order to examine the contribution without the carriers originating from the dopant ions, the behavior of electrically inactive B, H, N, O, and P, implants was investigated. Implantation of these ions into semi-insulating InP introduced n-type doping in the 1×1016 cm3 range after an anneal above 450 °C. For H, O, N, and P ions, the n-type conductivity could be eliminated by annealing at higher temperatures. However, boron anneals up to 750 °C did not eliminate the n-type conductivity. The n-type carrier profiles tracked the ion profiles. The carrier profile is influenced by the redistribution of the Fe during annealing; however, the Fe motion cannot explain the n-type conductivity. This conductivity may be due to a complex formed above 450 °C.
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 3099-3102 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated proton implantation enhanced intermixing of GaAs/AlGaAs quantum wells for H+ doses ranging from 5×1013 to 1×1016 ions/cm2. Implantation of 20 keV H+ followed by a high temperature rapid thermal anneal leads to enhanced diffusion of Al into the GaAs quantum well. Shifts of electron–heavy hole recombination energies due to compositional changes were observed using room temperature cathodoluminescence. Diffusion lengths of longer than 2 nm were calculated from energy shifts in a 5 nm well and were found to vary with both implanted dose and anneal time, as expected if the enhanced interdiffusion is caused by implantation introduced defects.
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