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  • Springer  (539,955)
  • American Institute of Physics (AIP)  (46,193)
  • Blackwell Publishing Ltd  (39,436)
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  • 101
    Publication Date: 2017-04-04
    Description: Large variations of the CO2 flux through the soil were observed between November 2002 and January 2006 at Mt. Etna volcano. In many cases, the CO2 flux was strongly influenced by changes in air temperature and atmospheric pressure. A new filtering method was then developed to remove the atmospheric influences on soil CO2 flux and, at the same time, to highlight the variations strictly related to volcanic activity. Successively, the CO2 corrected data were quantitatively compared with the spectral amplitude of the volcanic tremor by cross correlation function, cross-wavelet spectrum and wavelet coherence. These analyses suggested that the soil CO2 flux variations preceded those of volcanic tremor by about 50 days. Given that volcanic tremor is linked to the shallow (a few kilometer) magma dynamics and soil CO2 flux related to the deeper (*12 km b.s.l.) magma dynamics, the “delayed similarity” between the CO2 flux and the volcanic tremor amplitude was used to assess the average speed in the magma uprising into the crust, as about 170–260 m per day. Finally, the large amount of CO2 released before the onset of the 2004–2005 eruption indicated a deep ingression of new magma, which might have triggered such an eruption.
    Description: In press
    Description: N/A or not JCR
    Description: reserved
    Keywords: Mt. Etna ; Soil CO2 flux ; Volcanic tremor ; Cross-wavelet spectrum ; Wavelet coherence ; Cross correlation function ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 05. General::05.02. Data dissemination::05.02.01. Geochemical data ; 05. General::05.02. Data dissemination::05.02.02. Seismological data
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 102
    Publication Date: 2017-04-04
    Description: New Sr and Nd isotope data for whole rocks, glasses and minerals are combined to reconstruct the nature and origin of mixing end-members of the 200 km3 trachytic to phonolitic Campanian Ignimbrite (Campi Flegrei, Italy) magmatic system. The least-evolved magmatic end-member shows equilibrium between host glass and the majority of the phenocrysts and is less radiogenic in Sr and Nd than the most-evolved magma. On the contrary, only the Fe-rich pyroxene from the most-evolved erupted magma is in equilibrium with the matrix glass, while all other minerals are in isotopic disequilibrium. These magmas mixed prior to and during the Campanian Ignimbrite eruption and minerals were freely exchanged between the magma batches. Combining the results of the geochemical investigations on magma end-members with geophysical and geological data, we develop the following scenario. In stage 1, a parental, less differentiated magma rose into the middle crust, and evolved through combined crustal assimilation and crystal fractionation. In stage 2, the differentiated magma rose to shallower depth, fed the pre-Campanian Ignimbrite activity and evolved by further open-system processes into the most-evolved and most-radiogenic Campanian Ignimbrite end-member magma. In stage 3, new trachytic magma, isotopically distinct from the pre-Campanian Ignimbrite magmas, rose from ca. 6 km to shallower depth, recharged the most-evolved pre-Campanian Ignimbrite magma chamber, and formed the large and stratified Campanian Ignimbrite magmatic system. During the course of the Campanian Ignimbrite eruption, the two layers were tapped separately and/or simultaneously, and gave rise to the range of chemical and isotopic values displayed by the Campanian Ignimbrite pumices, glasses and minerals.
    Description: Published
    Description: 285-300
    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: Campanian Ignimbrite ; Radiogenic isotopes ; Mixing process ; 04. Solid Earth::04.08. Volcanology::04.08.03. Magmas ; 04. Solid Earth::04.08. Volcanology::04.08.05. Volcanic rocks
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 103
    Publication Date: 2017-04-04
    Description: This paper shows the results of a detailed reprocessing of aeromagnetic data,obtained by the downward projection to the seabed. The area of interest is centered over the Tyrrhenian Basin,whose bathymetric –topographic lay-out is characterized by a somewhat irregular trend.The origin of the intense depth variations depends on the Tyrrhenian structural setting,that is associated with the presence of several tectonic lineaments,seamounts or volcanic islands.The data were characterized by good quality and dense sam- pling,but they have been reprocessed in order either to solve some problems in the original compilation,and to reduce the distor- tion of the geomagnetic anomaly field caused by the difference of distance between the survey level and the magnetic source.The reprocessed magnetic map is proposed as an e ffective analysis tool for the Tyrrhenian area that is characterized by high susceptibility lithotypes.Downward projection of the aeromagnetic data by BTM algorithm increases the de finition of the anomalous magnetic signal without distortions in the geometric pattern of the field,thus showing a more stable and effective association between the magnetic anomalies and their geological sources.This effect is particularly true for high frequency anomalies that are directly comparable after the topographic projection because the depth filtering effect is attenuated.Moreover,the BTM method has been applied for the first time to a regional scale survey that shows substantial advantages because no fictitious anomalies in the high frequency sector of the spectrum were generated.This has been a typical effect of the traditional downward projection methods widely used before.The final result is a BTM anomaly map that is able to show the structural connections between the geological magnetic sources of the Tyrrhenian Sea area.
    Description: Published
    Description: 265-277
    Description: reserved
    Keywords: Potential methods,marine geomagnetism,downward continuation,Tyrrhenian Sea ; 04. Solid Earth::04.02. Exploration geophysics::04.02.04. Magnetic and electrical methods
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 104
    Publication Date: 2017-04-04
    Description: During 1991−93 at Mount Etna, long-period (LP) events occurring in swarms characterized the evolution of the eruption. The presence of multiplets i.e. groups of events with similar waveform signatures, has been recognized within this activity. Traditional techniques for locating LP events do not allow obtaining reliable hypocenters, which have only succeeded in placing earthquakes in a roughly 1 km2 area slightly east of the Mt. Etna Northeast Crater. Hypocenters have been relocated in two steps: the absolute location has been improved using Thurber’s code and a complex 3D velocity model; a highly precise relative location has been applied on multiplets to define the source geometry. 3D locations and high precision analysis suggest that during the 1991−93 eruption the resonator producing LP events was a part of the uppermost Northeast Crater conduit, measuring 210 meters in height and 45−50 meters in diameter.
    Description: Published
    Description: 663-674
    Description: reserved
    Keywords: waveform correlation ; stacked events ; 1991−93 eruption ; conduct geometry ; Mt. Etna Northeast Crater ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous
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  • 105
    Publication Date: 2017-04-04
    Description: The use of a hand-held thermal camera during the 2002–2003 Stromboli effusive eruption proved essential in tracking the development of flow field structures and in measuring related eruption parameters, such as the number of active vents and flow lengths. The steep underlying slope on which the flow field was emplaced resulted in a characteristic flow field morphology. This comprised a proximal shield, where flow stacking and inflation caused piling up of lava on the relatively flat ground of the vent zone, that fed a medial–distal lava flow field. This zone was characterized by the formation of lava tubes and tumuli forming a complex network of tumuli and flows linked by tubes. Most of the flow field was emplaced on extremely steep slopes and this had two effects. It caused flows to slide, as well as flow, and flow fronts to fail frequently, persistent flow front crumbling resulted in the production of an extensive debris field. Channel-fed flows were also characterized by development of excavated debris levees in this zone (Calvari et al. 2005). Collapse of lava flow fronts and inflation of the upper proximal lava shield made volume calculation very difficult. Comparison of the final field volume with that expecta by integrating the lava effusion rates through time suggests a loss of ~70% erupted lava by flow front crumbling and accumulation as debris flows below sea level. Derived relationships between effusion rate, flow length, and number of active vents showed systematic and correlated variations with time where spreading of volume between numerous flows caused an otherwise good correlation between effusion rate, flow length to break down. Observations collected during this eruption are useful in helping to understand lava flow processes on steep slopes, as well as in interpreting old lava–debris sequences found in other steep-sided volcanoes subject to effusive activity.
    Description: Published
    Description: JCR Journal
    Description: reserved
    Keywords: Lava flow field ; Morphology ; Tumuli ; Lava tubes ; Effusion rate ; Rheology ; Stromboli volcano ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
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  • 106
    Publication Date: 2017-04-04
    Description: The southernmost sector of the Italian peninsula is crossed by an almost continuous seismogenic belt capable of producing M ~ 7 earthquakes and extending from the Calabrian Arc, through the Messina Straits, as far as Southeastern Sicily. Though large earthquakes occurring in this region during the last Millennium are fairly well known from the historical point of view and seismic catalogues may be considered complete for destructive and badly damaging events (IX £ Io £ XI MCS), the knowledge and seismic completeness of moderate earthquakes can be improved by investigating other kinds of documentary sources not explored by the classical seismological tradition. In this paper, we present a case study explanatory of the problem, regarding the Ionian coast between the Messina Straits and Mount Etna volcano, an area of North-eastern Sicily lacking evidence of relevant seismic activity in historical times. Now, after a systematic analysis of the 18th century journalistic sources (gazettes), this gap can be partly filled by the rediscovery of a seismic sequence that took place in 1780. According to the available catalogues, the only event on record for this year is a minor shock (Io = VI MCS, Mw = 4.8) recorded in Messina on March 28, 1780. The newly discovered data allow to reinstate it as the mainshock (Io = VII–VIII MCS, Mw = 5.6) of a significant seismic period, which went on from March to June 1780, causing severe damage along the Ionian coast of North-eastern Sicily. The source responsible for this event appears located offshore, 40-km south of the previous determination, and is consistent with the Taormina Fault suggested by the geological literature, developing in the low seismic rate zone at the southernmost termination of the 1908 Messina earthquake fault.
    Description: Published
    Description: reserved
    Keywords: Historical seismology ; Macroseismic data ; MCS-EMS intensity scales ; 1780 Seismic sequence ; Seismotectonics ; NE Sicily ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics ; 04. Solid Earth::04.06. Seismology::04.06.05. Historical seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 107
    Publication Date: 2017-04-04
    Description: The catastrophic events that occurred in May 1998 in the area of Sarno (Southern Italy) highlight the destructive potential of debris flows, even when they are of relatively low magnitude. More than 130 people were killed and severe property damage took place when volcaniclastic debris flows triggered by heavy rainfall inundated various towns located in piedmont areas. This work investigates the suitability of LAHARZ, a GIS-assisted method for the automatic delineation of lahar inundation areas, for reproducing the May 1998 flows at Sarno. It was found that recalibration of the empirical relationship employed by LAHARZ is required in order to realistically hind-cast the inundation areas of considered events. The potential for further improvements in prediction outputs for this type of geomorphic setting is discussed, taking into account the observed lower mobility of these small volcaniclastic debris flows as compared to lahars of similar size.
    Description: Published
    Description: JCR Journal
    Description: reserved
    Keywords: Sarno ; LAHARZ ; Debris flows ; Lahars ; Debris flow modelling ; Hazard assessment ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
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  • 108
    Publication Date: 2017-04-04
    Description: Bulk atmospheric deposition of major cations (Na, K, Ca, Mg) and anions (Cl, F, SO4) were measured at 15 sites around an active volcano, Mount Etna, from 2001 to 2003. Their composition indicates several natural sources, among which deposition of plume-derived volcanogenic gas compounds is prevalent for F, Cl and S. Plume-derived acidic compounds are also responsible for the prevailing acidic composition of the samples collected on the summit of the volcano (pH in the 2.45–5.57 range). Cation species have complex origin, including deposition of plume volcanogenic ash and aerosols and soil-dust wind re-suspension of either volcanic or carbonate sedimentary rocks. Variation of the deposition rates during the March 2001– March 2003 period, coupled with previous measurements from 1997 to 2000 (Appl Geochem 16:985–1000, 2001), were compared with the variation of SO2 flux, volcanic activity and rainfall. The deposition rate was mainly controlled by rainfall. Commonly, about 0.1–0.9% of HF, HCl and SO2 emitted by the summit crater’s plume were deposited around the volcano. We estimate that ∼2 Gg of volcanogenic sulphur were deposited over the Etnean area during the 2002–2003 flank eruption, at an average rate of ∼24 Mg day−1 which is two orders of magnitude higher than that typical of quiescent degassing phases.
    Description: Published
    Description: 255-265
    Description: JCR Journal
    Description: open
    Keywords: Volcanic degassing ; Etna volcano ; Impact of volcanic eruptions ; S deposition rates ; Halogen deposition rates ; Bulk deposition chemistry ; Environmental volcanology ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
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  • 109
    Publication Date: 2017-04-04
    Description: Forward Looking Infrared Radiometer (FLIR) cameras offer a unique view of explosive volcanism by providing an image of calibrated temperatures. In this study, 344 eruptive events at Stromboli volcano, Italy, were imaged in 2001–2004 with a FLIR camera operating at up to 30 Hz. The FLIR was effective at revealing both ash plumes and coarse ballistic scoria, and a wide range of eruption styles was recorded. Eruptions at Stromboli can generally be classified into two groups: Type 1 eruptions, which are dominated by coarse ballistic particles, and Type 2 eruptions, which consist of an optically-thick, ash-rich plume, with (Type 2a) or without (Type 2b) large numbers of ballistic particles. Furthermore, Type 2a plumes exhibited gas thrust velocities (〉15 m s−1) while Type 2b plumes were limited to buoyant velocities (〈15 m s−1) above the crater rim. A given vent would normally maintain a particular gross eruption style (Type 1 vs. 2) for days to weeks, indicating stability of the uppermost conduit on these timescales. Velocities at the crater rim had a range of 3–101 m s−1, with an overall mean value of 24 m s−1. Mean crater rim velocities by eruption style were: Type 1= 34 m s−1, Type 2a=31 m s−1, Type 2b=7 m s−1. Eruption durations had a range of 6–41 s, with a mean of 15 s, similar among eruption styles. The ash in Type 2 eruptions originates from either backfilled material (crater wall slumping or ejecta rollback) or rheological changes in the uppermost magma column. Type 2a and 2b behaviors are shown to be a function of the overpressure of the bursting slug. In general, our imaging data support a broadening of the current paradigm for strombolian behavior, incorporating an uppermost conduit that can be more variable than is commonly considered.
    Description: NSF grant no. EAR-0207734, NERC grant no. NER/B/S/2001/00707, the USGS Volcano Hazards Program and the Geophysical Institute at the University of Alaska Fairbanks
    Description: Published
    Description: 769-784
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: JCR Journal
    Description: reserved
    Keywords: Stromboli volcano ; volcano monitoring ; thermal imaging ; eruption dynamics ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 110
    Publication Date: 2017-04-04
    Description: An immersed boundary technique suitable for the solution of multiphase compressible equations of gas–particle flows of volcanic origin over complex 2D and 3D topographies has been developed and applied. This procedure combines and extends different existing methods designed for incompressible flows. Furthermore, the extension to compressible multiphase flows is achieved through a flux correction term in the mass continuity equations of the immersed cells that accounts for density variations in the partial volumes. The technique is computationally accurate and inexpensive, if compared to the use and implementation of the finite-volume technique on unstructured meshes. The first applications that we consider are the simulations of pyroclastic density currents generated by the collapse of a volcanic column in 2D axisymmetric geometry and by a dome explosion in 3D. Results show that the immersed boundary technique can significantly improve the description of the no-slip flow condition on an irregular topography even with relatively coarse meshes. Although the net effect of the present technique on the results is difficult to quantify in general terms, its adoption is recommended any time that cartesian grids are used to describe the large-scale dynamics of pyroclastic density currents over volcano topographies.
    Description: Published
    Description: 183-198
    Description: 3.6. Fisica del vulcanismo
    Description: JCR Journal
    Description: reserved
    Keywords: Pyroclastic density currents ; Compressible flows ; Cartesian grids ; Finite-volume method ; Immersed boundary method ; Numerical simulation ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 111
    Publication Date: 2017-04-04
    Description: The Campania Region (southern Italy) is characterized by the frequent occurrence of volcaniclastic debris flows that damage property and loss of life (more than 170 deaths between 1996 and 1999). Historical investigation allowed the identification of more than 500 events during the last four centuries; in particular, more than half of these occurred in the last 100 years, causing hundreds of deaths. The aim of this paper is to quantify debris-flow hazard potential in the Campania Region. To this end, we compared several elements such as the thickness distribution of pyroclastic fall deposits from the last 18 ka of the Vesuvius and Phlegrean Fields volcanoes, the slopes of relieves, and the historical record of volcaniclastic debris flows from A.D. 1500 to the present. Results show that flow occurrence is not only a function of the cumulative thickness of past pyroclastic fall deposits but also depends on the age of emplacement. Deposits younger than 10 ka (Holocene eruptions) apparently increase the risk of debris flows, while those older than 10 ka (Late Pleistocene eruptions) seem to play a less prominent role, which is probably due to different climatic conditions, and therefore different rates of erosion of pyroclastic falls between the Holocene and the Late Pleistocene. Based on the above considerations, we compiled a large-scale debris-flow hazard map of the study area in which five main hazard zones are identified: very low, low, moderate, high, and very high.
    Description: Published
    Description: 157-167
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: 5.4. TTC - Sistema Informativo Territoriale
    Description: JCR Journal
    Description: reserved
    Keywords: Debris flows ; Explosive eruptions ; Hazard mapping ; Vesuvius volcano ; Erosion ; Campania region ; Southern Italy ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 112
    Publication Date: 2017-04-04
    Description: More than ca 100 km3 of nearly homogeneous crystal-poor phonolite and ca 100 km3 of slightly zoned trachyte were erupted 39 ka during the Campanian Ignimbrite super eruption, the most powerful in the Neapolitan area. Partition coefficient calculations, equilibrium mineral assemblages, glass compositions and texture were used to reconstruct compositional, thermal and pressure gradients in the pre-eruptive reservoir as well as timing and mechanisms of evolution towards magma chamber overpressure and eruption. Our petrologic data indicate that a wide sill-like trachytic magma chamber was active under the Campanian Plain at 2.5 kbar before CI eruption. Thermal exchange between high liquidus (1199 C) trachytic sill and cool country rocks caused intense undercooling, driving a catastrophic and fast (102 years) in situ fractional crystallization and crustal assimilation that produced a water oversaturated phonolitic cap and an overpressure in the chamber that triggered the super eruption. This process culminated in an abrupt reservoir opening and in a fast single-step high decompression. Sanidine phenocrysts crystal size distributions reveal high differentiation rate, thus suggesting that such a sill-like magmatic system is capable of evolving in a very short time and erupting suddenly with only short-term warning.
    Description: Published
    Description: On line First
    Description: 2.3. TTC - Laboratori di chimica e fisica delle rocce
    Description: 3.6. Fisica del vulcanismo
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: JCR Journal
    Description: reserved
    Keywords: Campanian Ignimbrite ; Super eruption ; Crystal size distribution ; Partition coefficients ; 04. Solid Earth::04.04. Geology::04.04.04. Marine geology ; 04. Solid Earth::04.04. Geology::04.04.05. Mineralogy and petrology ; 04. Solid Earth::04.08. Volcanology::04.08.05. Volcanic rocks
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  • 113
    Publication Date: 2017-04-04
    Description: We present an updated geological evolution of Mount Etna volcano based on new 40Ar/39Ar age determinations and stratigraphic data integrating the previous K/Ar ages. Volcanism began at about 500 ka ago through submarine eruptions on the Gela–Catania Foredeep basin. About 300 ka ago fissure-type eruptions occurred on the ancient alluvial plain of the Simeto River forming a lava plateau. From about 220 ka ago the eruptive activity was localised mainly along the Ionian coast where fissure-type eruptions built a shield volcano. Between 129 and 126 ka ago volcanism shifted westward toward the central portion of the present volcano (Val Calanna–Moscarello area). Furthermore, scattered effusive eruptions on the southern periphery of Etna edifice occurred until about 121 ka ago. The stabilization of the plumbing system on the Valle del Bove area is marked by the building of two small polygenic edifices, Tarderia and Rocche volcanoes. Their eruptive activity was rather coeval ending 106 and 102 ka ago, respectively. During the investigated time-span volcanism in Etna region was controlled by a main E–W extensional tectonic related to the reactivation of Malta Escarpment fault system in eastern Sicily.
    Description: Published
    Description: On line First
    Description: 3.5. Geologia e storia dei sistemi vulcanici
    Description: JCR Journal
    Description: reserved
    Keywords: Mount Etna ; 40Ar/39Ar dating ; 04. Solid Earth::04.04. Geology::04.04.99. General or miscellaneous
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  • 114
    Publication Date: 2017-04-03
    Description: The aim of this study is to shed light ontwo important destructive seismicsequences, about 20 years apart (1138–1139and 1156–1159), which hit the northernsector of the Dead Sea transform faultsystem (DSTFS), in the easternMediterranean region. Although some ofthese earthquakes were already known to thescholarly tradition, the interpretationsprovided until today have largely beenpartial and characterised by uncertaintiesand discrepancies among the variousauthors. Our study has developed throughresearch into the original Arabic, Syriac,Armenian and Latin texts and a criticalanalysis relating to a territory fragmentedby the presence of the Christian-Latinstates. This analysis has allowed us toshed light on the already existing, albeitoften uncertain, information and to add newelements of these two important series ofearthquake shocks to our knowledge base.As regards the first seismic sequence(October 1138–June 1139), apart from havingdefined the date with greater accuracy,eight new locations affected have beenidentified, unknown to previous studies.The shocks jolted a vast area withdestructive effects, including theterritory of Aleppo (modern Halab, Syria)and the western part of the region ofEdessa (modern Urfa, Turkey).The second seismic sequence (September1156–May 1159) was much longer anddevastating, and hit a huge area, includedbetween the present-day territories ofnorth-western Syria, northern Lebanon andthe region of Antioch (modern Antakya, insouthern Turkey). A detailed analysis ofthe primary sources has allowed toreconstruct the series of shocks withchronological detail of the effects,improving our previous knowledge. Lastly,the authors formulate an hypothesis as tothe possible seismogenic zones affected.
    Description: Published
    Description: 105-127
    Description: 3.10. Sismologia storica e archeosismologia
    Description: JCR Journal
    Description: reserved
    Keywords: Historical earthquakes ; seismic sequences ; Lebanon ; Syria ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous ; 04. Solid Earth::04.06. Seismology::04.06.05. Historical seismology
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  • 115
    Publication Date: 2017-04-04
    Description: The recent seismological literature recorded three strong earthquakes in Algeria, Libya and Tunisia between 1656 and 1694 AD. The historical evidence for these derives from European sources only (gazettes, journalistic pamphlets, missionary literature). Considering the kind of sources involved, their likely biases and the geographical distances that divided their places of production from the places that they spoke about, it is possible that some of these accounts could be less than reliable, and therefore have little use as materials from which to assess earthquake parameters. To answer these doubts, we have retrieved, cross-checked and critically analysed the original historical sources quoted in previous compilations and studies.
    Description: Unpublished
    Description: 3.10. Sismologia storica e archeosismologia
    Description: open
    Keywords: Historical Seismology ; North Africa Earthquakes ; Early journalistic sources ; 04. Solid Earth::04.06. Seismology::04.06.05. Historical seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: book chapter
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  • 116
    Publication Date: 2017-04-04
    Description: For 5 months before the 2001 Mt. Etna eruption, a progressive gravity decrease was measured along a profile of stations on the southern slope of the volcano. Between January and July 2001, the amplitude of the change reached 80 μGal, while the wavelength of the anomaly was of the order of 15 km. Elevation changes observed through GPS measurements during a period encompassing the 5-month gravity decrease, remained within 4–6 cm over the entire volcano and within 2–4 cm in the zone covered by the microgravity profile. We review both gravity and elevation changes by a model assuming the formation of new cracks, uniformly distributed in a rectangular prism. The inversion problem was formulated following a global optimization approach based on the use of Genetic Algorithms. Although it is possible to explain the observed gravity changes by means of the proposed analytical formulation, the results show that calculated elevation changes are significantly higher than those observed. Two alternative hypotheses are proposed to account for this apparent discrepancy: (1) that the assumptions behind the analytical formulation, used to invert the data, are fallacious at Etna, and thus, numerical models should be utilized; (2) that a second process, enabling a considerable mass decrease to occur without deformation, acted together with the formation of new cracks in the source volume.
    Description: Published
    Description: 553–562
    Description: 2.6. TTC - Laboratorio di gravimetria, magnetismo ed elettromagnetismo in aree attive
    Description: JCR Journal
    Description: reserved
    Keywords: Gravity ; Elastic modeling ; 04. Solid Earth::04.03. Geodesy::04.03.05. Gravity variations
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  • 117
    Publication Date: 2017-04-04
    Description: This work presents a methodology to study the interannual variability associated with summertime months in which extremely hot temperatures are frequent. Daily time series of maximum and minimum temperature fields (T max and T min, respectively) are used to define indexes of extreme months based on the number of days crossing thresholds. An empirical orthogonal function (EOF) analysis is applied to the monthly indexes. EOF loadings give information about the geographical areas where the number of days per month with extreme temperatures has the largest variability. Correlations between the EOF principal components and the time series of other fields allow plotting maps highlighting the anomalies in the large scale circulation and in the SSTs that are associated with the occurrence of extreme events. The methodology is used to construct the “climatology” of the extremely hot summertime months over Europe. In terms of both interannual and intraseasonal variability, there are three regions in which the frequency of the extremely hot days per month homogeneously varies: north-west Europe, Euro-Mediterranean and Eurasia region. Although extremes over those regions occur during the whole summer (June to August), the anomalous climatic conditions associated with frequent heatwaves present some intraseasonal variability. Extreme climate events over the north-west Europe and Eurasia are typically related to the occurrence of blocking situations. The intraseasonal variability of those patterns is related to the amplitude of the blocking, the relative location of the action centre and the wavetrain of anomalies downstream or upstream of the blocking. During June and July, blocking situations which give extremely hot climate conditions over north-west Europe are also associated with cold conditions over the eastern Mediterranean sector. The Euro-Mediterranean region is a transition area in which extratropical and tropical systems compete, influencing the occurrence of climate events: blockings tend to be related to extremely hot months during June while baroclinic anomalies dominate the variability of the climate events in July and August. We highlight that our method could be easily applied to other regions of the world, to other fields as well as to model outputs to assess, e.g. the potential change of extreme climate events in a warmer climate.
    Description: Published
    Description: 77-98
    Description: 3.7. Dinamica del clima e dell'oceano
    Description: JCR Journal
    Description: open
    Keywords: Extreme events ; Heatwaves ; Temperature anomalies ; climate variability ; 01. Atmosphere::01.01. Atmosphere::01.01.02. Climate
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 118
    Publication Date: 2017-04-04
    Description: The main purpose of this paper is to introduce a Bayesian event tree model for eruption forecasting (BET_EF). The model represents a flexible tool to provide probabilities of any specific event at which we are interested in, by merging all the relevant available information, such as theoretical models, a priori beliefs, monitoring measures, and any kind of past data. BET_EF is based on a Bayesian procedure and it relies on the fuzzy approach to manage monitoring data. The method deals with short- and long-term forecasting, therefore it can be useful in many practical aspects, as land use planning, and during volcanic emergencies. Finally, we provide the description of a free software package that provides a graphically supported computation of short- to long-term eruption forecasting, and a tutorial application to the recent MESIMEX exercise at Vesuvius.
    Description: Published
    Description: 623-632
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: JCR Journal
    Description: partially_open
    Keywords: eruption forecasting ; event tree ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 119
    Publication Date: 2017-04-04
    Description: Fluorine is one of the many environmental harmful elements released by volcanic activity. The content of total, oxalate extractable and water extractable fluorine was determined in 96 topsoils of three active volcanic systems of southern Italy (Mt. Etna, Stromboli and Vulcano). Total fluorine content (FTOT) ranges from 112 to 7430 mg kg-1, F extracted with oxalate (FOX) ranges from 16 to 2320 mg kg-1 (2 – 93 % of FTOT) and F extracted with distilled water (FH2O) ranges from 1.7 to 159 mg kg-1 (0.2 – 40 % of FTOT). Fluorine in the sampled topsoils derives both from the weathering of volcanic rocks and ashes and from enhanced deposition due to volcanic gas emissions either from open-conduit passive degassing (Mt. Etna and Stromboli) or from a fumarolic field (Vulcano). Fluorine accumulation in the studied soils does generally not present particular environmental issues except for a few anomalous sites at Vulcano where measured contents could be dangerous both for vegetation and for grazing animals.
    Description: Published
    Description: 413-423
    Description: 4.5. Degassamento naturale
    Description: JCR Journal
    Description: reserved
    Keywords: soil fluorine ; oxalate extractable F ; water extractable F ; environmental impact of volcanic F ; Sicily ; 04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 120
    Publication Date: 2017-04-04
    Description: The Chimaera gas seep, near Antalya (SW Turkey), has been continuously active for thousands of years and it is known to be the source of the first Olympic fire in the Hellenistic period. New and thorough molecular and isotopic analyses including methane (approximately 87% v/v; δ to the power of 13 C1 from -7.9‰ to -12.3‰; δ to the power of 13 D1 from -119‰ to -124‰), light alkanes (C2 + C3 + C4 + C5 = 0.5%; C6+: 0.07%; δ to the power of 13 C2 from -24.2‰ to -26.5‰; δ to the power of 13 C3 from -25.5‰ to -27‰), hydrogen (7.5–11%), carbon dioxide (0.01–0.07%; δ to the power of 13 CCO2: -15‰), helium (approximately 80 ppmv; R/Ra: 0.41) and nitrogen (2–4.9%; δ to the power of 15 N from -2‰ to -2.8‰) converge to indicate that the seep releases a mixture of organic thermogenic gas, related to mature type III kerogen occurring in Palaeozoic and Mesozoic organic-rich sedimentary rocks, and abiogenic gas produced by low-temperature serpentinization in the Tekirova ophiolitic unit. Methane is not related to mantle or magma degassing. The abiogenic fraction accounts for about half of the total gas released, which is estimated to be well beyond 50 ton year to the power of -1. Ophiolites and limestones are in contact along a tectonic dislocation leading to gas mixing and migration to the Earth’s surface. Chimaera represents the biggest emission of abiogenic methane on land discovered so far. Deep and pressurized gas accumulations are necessary to sustain the Chimaera gas flow for thousands of years and are likely to have been charged by an active inorganic source.
    Description: Published
    Description: 263-273
    Description: 3.8. Geofisica per l'ambiente
    Description: JCR Journal
    Description: reserved
    Keywords: abiogenic methane ; isotopic composition ; ophiolites ; seep ; serpentinization ; 03. Hydrosphere::03.04. Chemical and biological::03.04.05. Gases
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 121
    Publication Date: 2017-04-04
    Description: In eastern Elba Island (Tuscany, Italy), a shallow crustal level felsic, tourmaline-bearing, dyke-sill swarm of Late Miocene age is associated with abundant tourmaline-quartz hydrothermal veins and metasomatic masses. Development of these veins and masses in the host rocks demonstrates multiple hydro-fracturing by magmatic, boron-rich saline fluid. Tourmalines in felsic dykes are schorl, whereas in veins and metasomatic masses, tourmaline composition ranges from schorl-dravite through dravite to uvite. This compositional shift is evidence for an increasing contribution to the magmatic boron-rich fluids by a Mg-Ca-Ti-rich external component represented by biotite-rich and amphibolite host rocks. This system can be envisaged as an exposed proxy of the high temperature hydrothermal system presently active in the deepest part of the Larderello-Travale geothermal field (Tuscany).
    Description: Published
    Description: 318-326
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: 3.5. Geologia e storia dei sistemi vulcanici
    Description: JCR Journal
    Description: reserved
    Keywords: Hydro-fractures ; geothermal systems ; Magmatism ; southern Tuscany ; 04. Solid Earth::04.01. Earth Interior::04.01.99. General or miscellaneous ; 04. Solid Earth::04.04. Geology::04.04.09. Structural geology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 122
    Publication Date: 2017-04-04
    Description: While the seismicity of the Southern Alps is high in the Eastern sector, corresponding to the Veneto and Friuli regions, it decreases towards West up to the Adda River. In the sector between the Lessini Mts. and Eastern Friuli the damaging earthquakes are clustered in a well defined seismic belt, where seismogenic sources responsible for earthquakes with Mw 6 have been defined in recent works. In contrast, the knowledge of the Southalpine sector West of this area is sparser; the area experienced some earthquakes with Mw〉5.5 and varied events with 4.8≤Mw≤5.5 the distribution of which is, apparently, random. For the area roughly defined by the basins of the Adda River to the West and the middle Adige River to the East, this paper reappraises the background knowledge of the earthquakes occurred before 1700. The investigation and the results are presented according to two successive periods, up to 1995 and from 1995 on. In the research performed up to 1995, the most important achievements concerned two different aspects: i) the assessement of several “fake quakes”, some of which were the object of paradigmatic case-histories; ii) the resizing and relocation of several, presumed damaging earthquakes. Though this round of investigation changed significantly the picture of the seismicity with respect to the Seventies, the research continued. For the period from 1995 on, the discussion focuses on the reliability of the available information; material that received little or no consideration before, new historical findings and comments to the seismological interpretation as in the most recent literature are also presented. This part includes also the discussion of archaeoseismological evidence of damage related to past earthquakes.
    Description: Published
    Description: 93-129
    Description: 3.10. Sismologia storica e archeosismologia
    Description: reserved
    Keywords: historical seismology ; Adda and Middle Adige River Basins ; Southern Alps ; archaeoseismology ; 04. Solid Earth::04.06. Seismology::04.06.05. Historical seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: book chapter
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  • 123
    Publication Date: 2017-04-04
    Description: National seismic risk maps are an important risk mitigation tool as they can be used for the prioritization of regions within a country where retrofitting of the building stock or other risk mitigation measures should take place. The production of a seismic risk map involves the convolution of seismic hazard data, vulnerability predictions for the building stock and exposure data. The seismic risk maps produced in Italy over the past 10 years are compared in this paper with recent proposals for seismic risk maps based on state-of-the-art seismic hazard data and mechanics-based vulnerability assessment procedures. The aim of the paper is to open the discussion for the way in which future seismic risk maps could be produced, making use of the most up-to-date information in the fields of seismic hazard evaluation and vulnerability assessment.
    Description: Italian Ministry of Research and Higher Education (MIUR—Ministero dell’Università e della Ricerca) through the financing of the project AIRPLANE (Advancing Interdisciplinary Research PLAtform on volcanoes aNd Earthquakes)
    Description: In press
    Description: 4.2. TTC - Scenari e mappe di pericolosità sismica
    Description: JCR Journal
    Description: reserved
    Keywords: Seismic risk ; Seismic hazard ; 04. Solid Earth::04.06. Seismology::04.06.11. Seismic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 124
    Publication Date: 2017-04-03
    Description: The Valtiberina region (central Italy) has a seismic record going back to the Middle Ages and including five Io 〉 VIII MCS earthquakes, the earliest of which (1352, 1389, 1458). though recently and extensively studied, remain rather poorly known. This makes it all the more important to ensure that the later ones (1789, 1917) are as throughly studied as possible. The 1789 earthquake is listed by the current Italian catalogue (CPTI Working Group 2004) with Io VIII-IX MCS and Mm 5.8. These parameters were assessed from a database of 28 macroseismic intensity data points (Castelli et al. 1996), which is less than plentiful for a late 18th century earthquake. An analysis of the historical context of the 1789 earthquake and its influence on the production of contemporary accounts evidences a few research paths that previous studies either did not or could not take. Following them, the macroseismic database of the 1789 earthquake can be noticeably improved, providing the catalogue compiler with a mean to check the reliability of its current parameters.
    Description: Published
    Description: 249-260
    Description: 5.1. TTC - Banche dati e metodi macrosismici
    Description: open
    Keywords: Historical Seismicity ; 1789 Valtiberina Earthquake ; 04. Solid Earth::04.06. Seismology::04.06.05. Historical seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: book chapter
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  • 125
    Publication Date: 2017-04-04
    Description: We consider the process of slow extrusion of very viscous magma that forms lava domes. Dome-building eruptions are commonly associated with hazardous phenomena, in- cluding pyroclastic flows generated by dome collapses, explosive eruptions and volcanic blasts. These eruptions commonly display fairly regular alternations between pe- riods of high and low or no activity with time scales from hours to years. Usually hazardous phenomena are asso- ciated with periods of high magma discharge rate, thus, understanding the causes of pulsatory activity during ex- trusive eruptions is an important step towards forecasting volcanic behavior, especially the transition to explosive ac- tivity when magma discharge rate increases by a few orders of magnitude. In recent years the risks have increased be- cause the population density in the vicinity of many active volcanoes has increased.
    Description: Published
    Description: 3.6. Fisica del vulcanismo
    Description: open
    Keywords: Volcanic Eruptions ; Cyclicity ; During Lava ; 04. Solid Earth::04.01. Earth Interior::04.01.99. General or miscellaneous ; 04. Solid Earth::04.08. Volcanology::04.08.04. Thermodynamics ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: book chapter
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  • 126
    Publication Date: 2017-04-04
    Description: We show the magnetic model of the Selli-Vavilov region. The Selli Line is known as the northwestern edge of the southern Tyrrhenian basin. The tectonic evolution of the Tyrrhenian basin is dominated by a Tortonian - Quaternary extension through the eastward movement of the Apennine subduction system. This migration has generated a diffuse stretching of the continental crust with the emplacement of new oceanic material. This latter occurred in several localized zones where the eastward retreating of the Ionian subduction system produced a strong depletion of the crust with formation of basins and correlated spreading. Nowadays the presence of oceanic crust is confirmed through direct drilling investigation but a complete mapping of the oceanic crustal distribution is still lacking. The Selli-Vavilov region shows a differentiated crustal setting where seamount structures, the oceanic basement portions and continental crust blocks are superimposed. To this aim, a 2D inversion of the magnetic data of this region was conducted to define buried structures. The magnetic susceptibility pattern was computed by solving the least squares problem of the misfit between the predicted and real data for separated wavebands. This method produced two 2D models of the high and low frequency fields of the Selli-Vavilov region. The two apparent susceptibility maps provide different information for distinct ranges of depth. The results of the inversions were also combined with seismic data of the Selli region highlighting the position of the highly-magnetized buried bodies. The results confirm a role for the Selli Line as a deep crustal boundary dividing the Sardinian passive domain from the easternmost active region where different oceanic structures are located. The Selli Line has worked as a detachment fault system which has moved eastward. Finally, the Selli-Vavilov region may be interpreted as a tectonic result due to a passive asymmetrical rift occurred between the Tortonian and Pliocene.
    Description: Published
    Description: 251-266
    Description: 2.6. TTC - Laboratorio di gravimetria, magnetismo ed elettromagnetismo in aree attive
    Description: 3.4. Geomagnetismo
    Description: 3.5. Geologia e storia dei sistemi vulcanici
    Description: JCR Journal
    Description: reserved
    Keywords: Geomagnetism ; Tectonics ; Geodynamics ; Inversion ; Oceanic crust ; Volcanic structure ; 04. Solid Earth::04.05. Geomagnetism::04.05.04. Magnetic anomalies ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics ; 05. General::05.01. Computational geophysics::05.01.03. Inverse methods
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 127
    Publication Date: 2017-04-04
    Description: Cross-spectral analysis of ULF wave measurements recorded at ground magnetometer stations closely spaced in latitude allows accurate determinations of magnetospheric field line resonance (FLR) frequencies. This is a useful tool for remote sensing temporal and spatial variations of the magnetospheric plasma mass density. The spatial configuration of the South European GeoMagnetic Array (SEGMA, 1.56 〈 L 〈 1.89) offers the possibility to perform such studies at low latitudes allowing to monitor the dynamical coupling between the ionosphere and the inner plasmasphere. As an example of this capability we present the results of a cross-correlation analysis between FLR frequencies and solar EUV irradiance (as monitored by the 10.7-cm solar radio flux F10.7) suggesting that changes in the inner plasmasphere density follow the short-term (27-day) variations of the solar irradiance with a time delay of 1–2 days. As an additional example we present the results of a comparative analysis of FLR measurements, ionospheric vertical soundings and vertical TEC measurements during the development of a geomagnetic storm.
    Description: Published
    Description: 25-27
    Description: 1.6. Osservazioni di geomagnetismo
    Description: 1.7. Osservazioni di alta e media atmosfera
    Description: 3.9. Fisica della magnetosfera, ionosfera e meteorologia spaziale
    Description: JCR Journal
    Description: reserved
    Keywords: ULF waves ; Field line resonance ; Remote sensing ; Solar activity ; Plasmasphere ; Ionosphere ; 01. Atmosphere::01.02. Ionosphere::01.02.02. Dynamics ; 01. Atmosphere::01.02. Ionosphere::01.02.04. Plasma Physics ; 01. Atmosphere::01.03. Magnetosphere::01.03.03. Magnetospheric physics ; 05. General::05.07. Space and Planetary sciences::05.07.01. Solar-terrestrial interaction
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 128
    Publication Date: 2017-04-04
    Description: Following the 2001 and 2002–2003 flank eruptions, activity resumed at Mt. Etna on 7 September 2004 and lasted for about 6 months. This paper presents new petrographic, major and trace element, and Sr–Nd isotope data from sequential samples collected during the entire 2004–2005 eruption. The progressive change of lava composition allowed defining three phases that correspond to different processes controlling magma dynamics inside the central volcano conduits. The compositional variability of products erupted up to 24 September is well reproduced by a fractional crystallization model that involves magma already stored at shallow depth since the 2002–2003 eruption. The progressive mixing of this magma with a distinct new one rising within the central conduits is clearly revealed by the composition of the products erupted from 24 September to 15 October. After 15 October, the contribution from the new magma gradually becomes predominant, and the efficiency of the mixing process ensures the emission of homogeneous products up to the end of the eruption. Our results give insights into the complex conditions of magma storage and evolution in the shallow plumbing system of Mt. Etna during a flank eruption. Furthermore, they confirm that the 2004–2005 activity at Etna was triggered by regional movements of the eastern flank of the volcano. They caused the opening of a complex fracture zone extending ESE which drained a magma stored at shallow depth since the 2002–2003 eruption. This process favored the ascent of a different magma in the central conduits, which began to be erupted on 24 September without any significant change in eruptive style, deformation, and seismicity until the end of eruption.
    Description: Published
    Description: 781–793
    Description: 2.3. TTC - Laboratori di chimica e fisica delle rocce
    Description: JCR Journal
    Description: reserved
    Keywords: Geochemistry ; Isotopic compositions ; Magma feeding system ; Magma mixing ; Mt. Etna ; 04. Solid Earth::04.08. Volcanology::04.08.03. Magmas ; 04. Solid Earth::04.08. Volcanology::04.08.05. Volcanic rocks
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 129
    Publication Date: 2019-01-30
    Description: Within the framework of the European LESSLOSS Project “Risk Mitigation for Earthquakes and Landslides”, finite-fault seismological models have been proposed for the computation of earthquake scenarios for three urban areas: Istanbul (Turkey), Lisbon (Portugal) and Thessaloniki (Greece). For each case study, ground motion scenarios were developed for the two most probable events with different return periods (generally 50 and 500 years), locations and magnitudes that were derived from historical and geological data. The ground motion simulations were performed in the frequency band of engineering interest (0.5-20 Hz) by two numerical finite-fault methods: a hybrid deterministic-stochastic method, DSM, used for all of the cases investigated, and a non-stationary stochastic finite-fault simulation method, RSSIM, applied only in the case of Lisbon. In the present study, the results with respect to bedrock and surface are presented in terms of peak ground acceleration (PGA) for the city of Lisbon and the surrounding area, using earthquake scenarios from the onshore source area of the Lower Tagus Valley, and from the offshore source area of the Marques de Pombal fault, which is one of the possible sources of the 1755 Lisbon earthquake. Site effects are evaluated by means of a properly designed equivalent stochastic non-linear one-dimensional ground response analyses of stratified soil profile units. The requirements of the users (e.g., engineers, local administrators) constrain the choice of the scenario that can be adopted as input for disaster scenario predictions and loss modelling; in the case of Lisbon, the maximum values of shaking were assumed as the criteria for the reference scenarios.
    Description: Published
    Description: 233-243
    Description: 3T. Storia Sismica
    Description: open
    Keywords: Simulating Earthquake Scenarios ; European LESSLOSS project ; The Case of Lisbon ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: book chapter
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  • 130
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    Springer
    In:  EPIC3The Andes - Active Subduction Orogeny, Frontiers in Earth Sciences, Springer, pp. 3-27, ISBN: 978-3-540-24329-8
    Publication Date: 2014-04-15
    Description: We quantitatively analyse the spatial pattern of deformation partitioning and of temporal accumulation of deformation in the Central Andes (15–26° S) with the aim of identifying those mechanisms responsible for initiating and controlling Cenozoic plateau evolution in this region. Our results show that the differential velocity between upper plate velocity and oceanic plate slab rollback velocity is crucial for determining the amount and rate of shortening, as well as their lateral variability at the leading edge of the upper plate. This primary control is modulated by factors affecting the strength balance between the upper plate lithosphere and the Nazca/South American Plate interface. These factors particularly include a stage of reduced slab dip (33 to 20 Ma) that accelerated shortening and an earlier phase (45 to 33 Ma) of higher trenchward sediment flux that reduced coupling at the plate interface, resulting in slowed shortening and enhanced slab rollback. Because high sediment flux and transfer of convergence into upper plate shortening constitute a negative feedback, we suggest that interruption of this feedback is critical for sustaining high shortening transfer, as observed for the Andes. Although we show that climate trends have no influence on the evolution of the Central Andes, the position of this region in the global arid belt in a low erosion regime is the key that provides this interruption; it inhibits high sediment flux into the trench despite the formation of relief from ongoing shortening. Along-strike variations in Andean shortening are clearly related to changes of the above factors. The spatial pattern of distribution of deformation in the Central Andes, as well as the synchronization of fault systems and the total magnitude of shortening, was mainly controlled by large-scale, inherited upper plate features that constitute zones of weakness in the upper plate leading edge. In summary, only a very particular combination of parameters appears to be able to trigger plateau-style deformation at a convergent continental margin. The combination of these parameters (in particular, differential trench-upper plate velocity evolution, high plate interface coupling from low trench infill, and the lateral distribution of weak zones in the upper plate leading edge) was highly uncommon during the Phanerozoic. This led to very few plateau-style orogens at convergent margins like the Cenozoic Central Andes in South America or, possibly, the Laramide North American Cordillera.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Inbook , peerRev
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  • 131
    Publication Date: 2021-05-19
    Description: Metal concentrations of 37 soil samples taken from mining areas (abandoned mine pits and transport routes) in Kpogamé and Hahotoé (southern Togo) range from 0.2-43 ppm for Cd, 15-115 ppm for Pb, 182-1,029 ppm for Cr, 18-356 ppm for Cu, 15-342 pm for Ni, 90-513 ppm for V, 35-536 ppm for Zn, 80-469 ppm for Zr and 266-3,161 ppm for Sr. The tropical alteration of the ore waste plays an important role in the distribution of trace elements in the studied soils. Because the alteration affects the element mobility, generally old abandoned mining areas, which , together with soils near the transport routes, show a higher degree of contamination. Under low pH and oxidising conditions in studied soils Cd, Ni and Zn are generally easily mobilised and are thus available to the environment.
    Description: Published
    Keywords: Heavy metals ; Pollution ; Heavy metals ; Mining ; Phosphorite ; Pollution
    Repository Name: AquaDocs
    Type: Journal Contribution
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  • 132
    Publication Date: 2022-05-25
    Description: © 2008 The Author. This is an open-access article distributed under the terms of the Creative Commons Attribution Noncommercial License. The definitive version was published in Environmental Fluid Mechanics 8 (2008): 551-560, doi:10.1007/s10652-008-9076-5.
    Description: Experiments are reviewed in which a two-layer salt-stratified tank of water was mixed by turbulence. The density profile began as a single step and evolved to a smooth mixed profile. The turbulence was generated by many excursions of a horizontally moving vertical rod with Richardson number Ri 〉 0.9 and Reynolds Number Re 〉 600. There was almost perfect collapse of all the profiles to one universal profile as a function of a similarity variable. We develop a theoretical model for a simple mixing law with a buoyancy flux that is a function of internal Richardson number Rii. A similarity equation is found. A flux law that increases with small Rii and decreases with large Rii is considered next. Since no analytical solution is known, the similarity concept is tested by numerically integrating the equations in space and time. With buoyancy flux monotonically increasing with internal Richardson number, the similarity approach is valid for a profile starting from a slightly smoothed step. However, a shock forms for a mixing law with higher initial Rii (so that buoyancy flux decreases with Richardson number) and the similarity approach is invalid for those initial conditions.
    Keywords: Turbulence ; Mixing ; Stratified ; Similarity solution ; Layered fluid
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 133
    Publication Date: 2022-05-25
    Description: Author Posting. © Annual Reviews, 2003. This article is posted here by permission of Annual Reviews for personal use, not for redistribution. The definitive version was published in Annual Review of Environment and Resources 28 (2003): 521-558, doi:10.1146/annurev.energy.28.011503.163443.
    Description: Agriculture and industrial development have led to inadvertent changes in the natural carbon cycle. As a consequence, concentrations of carbon dioxide and other greenhouse gases have increased in the atmosphere and may lead to changes in climate. The current challenge facing society is to develop options for future management of the carbon cycle. A variety of approaches has been suggested: direct reduction of emissions, deliberate manipulation of the natural carbon cycle to enhance sequestration, and capture and isolation of carbon from fossil fuel use. Policy development to date has laid out some of the general principles to which carbon management should adhere. These are summarized as: how much carbon is stored, by what means, and for how long. To successfully manage carbon for climate purposes requires increased understanding of carbon cycle dynamics and improvement in the scientific capabilities available for measurement as well as for policy needs. The specific needs for scientific information to underpin carbon cycle management decisions are not yet broadly known. A stronger dialogue between decision makers and scientists must be developed to foster improved application of scientific knowledge to decisions. This review focuses on the current knowledge of the carbon cycle, carbon measurement capabilities (with an emphasis on the continental scale) and the relevance of carbon cycle science to carbon sequestration goals.
    Description: The National Center for Atmospheric Research is supported by the National Science Foundation.
    Keywords: Carbon sequestration ; Measurement techniques ; Climate ; Kyoto protocol
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 134
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    Unknown
    Annual Reviews
    Publication Date: 2022-05-25
    Description: Author Posting. © Annual Reviews, 2006. This article is posted here by permission of Annual Reviews for personal use, not for redistribution. The definitive version was published in Annual Review of Fluid Mechanics 38 (2006): 395-425, doi:10.1146/annurev.fluid.38.050304.092129.
    Description: Over the past four decades, the combination of in situ and remote sensing observations has demonstrated that long nonlinear internal solitary-like waves are ubiquitous features of coastal oceans. The following provides an overview of the properties of steady internal solitary waves and the transient processes of wave generation and evolution, primarily from the point of view of weakly nonlinear theory, of which the Korteweg-de Vries equation is the most frequently used example. However, the oceanographically important processes of wave instability and breaking, generally inaccessible with these models, are also discussed. Furthermore, observations often show strongly nonlinear waves whose properties can only be explained with fully nonlinear models.
    Description: KRH acknowledges support from NSF and ONR and an Independent Study Award from the Woods Hole Oceanographic Institution. WKM acknowledges support from NSF and ONR, which has made his work in this area possible, in close collaboration with former graduate students at Scripps Institution of Oceanography and MIT.
    Keywords: Solitary waves ; Nonlinear waves ; Stratified flow ; Physical Oceanography
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  • 135
    Publication Date: 2022-05-25
    Description: This paper is not subject to U.S. copyright. The definitive version was published in Geo-Marine Letters 29 (2009): 395-404, doi:10.1007/s00367-009-0159-1.
    Description: A program of geophysical mapping and vibracoring was conducted to better understand the geologic evolution of Apalachicola Bay. Analyses of the geophysical data and sediment cores along with age control provided by 34 AMS 14C dates on marine shells and wood reveal the following history. As sea level rose in the early Holocene, fluvial deposits filled the Apalachicola River paleochannel, which extended southward under the central part of the bay and seaward across the continental shelf. Sediments to either side of the paleochannel contain abundant wood fragments, with dates documenting that those areas were forested at 8,000 14C years b.p. As sea level continued to rise, spits formed of headland prodelta deposits. Between ~6,400 and ~2,500 14C years b.p., an Apalachicola prodelta prograded and receded several times across the inner shelf that underlies the western part of the bay. An eastern deltaic lobe was active for a shorter time, between ~5,800 and 5,100 14C years b.p. Estuarine benthic foraminiferal assemblages occurred in the western bay as early as 6,400 14C years b.p., and indicate that there was some physical barrier to open-ocean circulation and shelf species established by that time. It is considered that shoals formed in the region of the present barrier islands as the rising sea flooded an interstream divide. Estuarine conditions were established very early in the post-glacial flooding of the bay.
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  • 136
    Publication Date: 2022-05-25
    Description: © 2009 The Authors. This article is distributed under the terms of the Creative Commons Attribution Noncommercial License. The definitive version was published in Marine Biology 156 (2009): 1049-1056, doi:10.1007/s00227-009-1149-6.
    Description: Behavioral observations using a remotely operated vehicle (ROV) in the Gulf of California in March, 2003, provided insights into the vertical distribution, feeding and anatomy of the rare and delicate ctenophore Thalassocalyce inconstans. Additional archived ROV video records from the Monterey Bay Aquarium Research Institute of 288 sightings of T. inconstans and 2,437 individual observations of euphausiids in the Gulf of California and Monterey Canyon between 1989 and 2005 were examined to determine ctenophore and euphausiid prey depth distributions with respect to temperature and dissolved oxygen concentration [dO]. In the Gulf of California most ctenophores (96.9%) were above 350 m, the top of the oxygen minimum layer. In Monterey Canyon the ctenophores were more widely distributed throughout the water column, including the hypoxic zone, to depths as great as 3,500 m. Computer-aided behavioral analysis of two video records of the capture of euphausiids by T. inconstans showed that the ctenophore contracted its bell almost instantly (0.5 s), transforming its flattened, hemispherical resting shape into a closed bi-lobed globe in which seawater and prey were engulfed. Euphausiids entrapped within the globe displayed a previously undescribed escape response for krill (‘probing behavior’), in which they hovered and gently probed the inner surfaces of the globe with antennae without stimulating further contraction by the ctenophore. Such rapid bell contraction could be effected only by a peripheral sphincter muscle even though the presence of circumferential ring musculature was unknown for the Phylum Ctenophora. Thereafter, several live T. inconstans were collected by hand off Barbados and microscopic observations confirmed that assumption.
    Description: Supported by the David and Lucile Packard Foundation and NOAA Grant #NA06OAR4600091.
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  • 137
    Publication Date: 2022-05-25
    Description: © 2008 The Authors. This is an open-access article distributed under the terms of the Creative Commons Attribution Noncommercial License. The definitive version was published in Environmental Fluid Mechanics 8 (2008): 495-509, doi:10.1007/s10652-008-9107-2.
    Description: Estuarine turbulence is notable in that both the dissipation rate and the buoyancy frequency extend to much higher values than in other natural environments. The high dissipation rates lead to a distinct inertial subrange in the velocity and scalar spectra, which can be exploited for quantifying the turbulence quantities. However, high buoyancy frequencies lead to small Ozmidov scales, which require high sampling rates and small spatial aperture to resolve the turbulent fluxes. A set of observations in a highly stratified estuary demonstrate the effectiveness of a vessel-mounted turbulence array for resolving turbulent processes, and for relating the turbulence to the forcing by the Reynolds-averaged flow. The observations focus on the ebb, when most of the buoyancy flux occurs. Three stages of mixing are observed: (1) intermittent and localized but intense shear instability during the early ebb; (2) continuous and relatively homogeneous shear-induced mixing during the mid-ebb, and weakly stratified, boundary-layer mixing during the late ebb. The mixing efficiency as quantified by the flux Richardson number Rf was frequently observed to be higher than the canonical value of 0.15 from Osborn (J Phys Oceanogr 10:83–89, 1980). The high efficiency may be linked to the temporal–spatial evolution of shear instabilities.
    Description: The funding for this research was obtained from ONR Grant N00014-06-1-0292 and NSF Grant OCE-0729547.
    Keywords: Turbulence ; Estuaries ; Shear instability ; Buoyancy flux
    Repository Name: Woods Hole Open Access Server
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  • 138
    Publication Date: 2022-05-25
    Description: © 2009 The Authors. This is an open-access article distributed under the terms of the Creative Commons Attribution Noncommercial License. The definitive version was published in JARO - Journal of the Association for Research in Otolaryngology 10 (2009): 497-509, doi:10.1007/s10162-009-0174-y.
    Description: The dynamic displacement of the semicircular canal cupula and modulation of afferent nerve discharge were measured simultaneously in response to physiological stimuli in vivo. The adaptation time constant(s) of normal cupulae in response to step stimuli averaged 36 s, corresponding to a mechanical lower corner frequency for sinusoidal stimuli of 0.0044 Hz. For stimuli equivalent to 40–200 deg/s of angular head velocity, the displacement gain of the central region of the cupula averaged 53 nm per deg/s. Afferents adapted more rapidly than the cupula, demonstrating the presence of a relaxation process that contributes significantly to the neural representation of angular head motions by the discharge patterns of canal afferent neurons. We also investigated changes in time constants of the cupula and afferents following detachment of the cupula at its apex—mechanical detachment that occurs in response to excessive transcupular endolymph pressure. Detached cupulae exhibited sharply reduced adaptation time constants (300 ms–3 s, n = 3) and can be explained by endolymph flowing rapidly over the apex of the cupula. Partially detached cupulae reattached and normal afferent discharge patterns were recovered 5–7 h following detachment. This regeneration process may have relevance to the recovery of semicircular canal function following head trauma.
    Description: Financial support was provided by the NIDCD R01 DC06685 (Rabbitt) and NASA GSRP 56000135 & NSF IGERT DGE- 9987616 (Breneman).
    Keywords: Vestibular ; Inner ear micromechanics ; Cupula regeneration ; Angular motion sensation ; Afferent response dynamics
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  • 139
    Publication Date: 2022-05-25
    Description: First published online as a Review in Advance on October 24, 2005. (Some corrections may occur before final publication online and in print)
    Description: Author Posting. © Annual Reviews, 2005. This article is posted here by permission of Annual Reviews for personal use, not for redistribution. The definitive version was published in Annual Review of Physiology 68 (2006): 22.1-22.29, doi:10.1146/annurev.physiol.68.040104.105418.
    Description: Superfast muscles of vertebrates power sound production. The fastest, the swimbladder muscle of toadfish, generates mechanical power at frequencies in excess of 200 Hz. To operate at these frequencies, the speed of relaxation has had to increase approximately 50-fold. This increase is accomplished by modifications of three kinetic traits: (a) a fast calcium transient due to extremely high concentration of sarcoplasmic reticulum (SR)-Ca2+ pumps and parvalbumin, (b) fast off-rate of Ca2+ from troponin C due to an alteration in troponin, and (c) fast cross-bridge detachment rate constant (g, 50 times faster than that in rabbit fast-twitch muscle) due to an alteration in myosin. Although these three modifications permit swimbladder muscle to generate mechanical work at high frequencies (where locomotor muscles cannot), it comes with a cost: The high g causes a large reduction in attached force-generating cross-bridges, making the swimbladder incapable of powering low-frequency locomotory movements. Hence the locomotory and sound-producing muscles have mutually exclusive designs.
    Description: This work was made possible by support from NIH grants AR38404 and AR46125 as well as the University of Pennsylvania Research Foundation.
    Keywords: Parvalbumin ; Ca2+ release ; Ca2+ uptake ; Cross-bridges ; Adaptation ; Sound production ; Whitman Center
    Repository Name: Woods Hole Open Access Server
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  • 140
    Publication Date: 2022-02-16
    Description: The role of mud volcanoes (MVs) as a source of methane(CH4) flux to the atmosphere and the ocean has been increasingly recognised in the last several years (Milkov 2000; Dimitrov 2002, 2003; Etiope and Klusman 2002; Kopf 2002, 2003; Milkov et al. 2003; Etiope and Milkov 2004). In one of the most recent papers, Kopf (2003) claims to report a reliable estimate of the global CH4 emission from MVs. However, the significance and usefulness of the estimate presented by Kopf (2003) are rather poor. The used dataset is smaller than in previous studies (although the author makes a reverse claim), and some previously published works are misquoted and misinterpreted. Numerous arithmetic mistakes made during simple calculations and data manipulations lead to confusing results and conclusions. In this comment, we highlight some of the most significant problems with the estimates published by Kopf (2003).
    Description: Published
    Description: 490-492
    Description: 4.5. Degassamento naturale
    Description: JCR Journal
    Description: reserved
    Keywords: Methane ; mud volcanoes ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 141
    Publication Date: 2022-02-16
    Description: A new estimate of global methane emission into the atmosphere from mud volcanoes (MVs) on land and shallow seafloor is presented. The estimate, considered a lower limit, is based on 1) new direct measurements of flux, including both venting of methane and diffuse microseepage around craters and vents, and 2) a classification of MV sizes in terms of area (km2) based on a compilation of data from 120 MVs. The methane flux to the atmosphere is conservatively estimated between 6 and 9 Mt y)1. This emission from MVs is 3–6% of the natural methane sources and is comparable with ocean and hydrate sources, officially considered in the atmospheric methane budget. The total geologic source, including MVs, seepage from seafloor, microseepage in hydrocarbon-prone areas and geothermal sources, would amount to 35–45 Mt y)1. The authors believe it is time to add this parameter in the Intergovernmental Panel on Climate Change official tables of atmospheric methane sources.
    Description: Published
    Description: 997-1002
    Description: 4.5. Degassamento naturale
    Description: JCR Journal
    Description: reserved
    Keywords: Methane ; Mud volcanoes ; 03. Hydrosphere::03.04. Chemical and biological::03.04.05. Gases
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  • 142
    Publication Date: 2022-06-09
    Description: Results of geological, geomechanical and seismometric investigations aiming at the analysis of the seismic response in a carbonate ridge of the Nera River valley (Central Apennines – Italy) are discussed. Geological and geomechanical surveys were aimed at defining the stratigraphic and structural setting of the outcropping formations and the jointing conditions of the rock mass. Velocimetric records of both ambient noise and small-magnitude earthquakes were analysed in order to identify amplification conditions. The analysis was carried out in the time domain, through directional energy evaluation, and in the frequency domain, through H/V spectral ratios and spectral ratios with respect to a reference station. A local amplification factor was estimated from Housner intensity. The study revealed a significant seismic amplification in a fault zone. This effect was observed in intensely jointed and mylonitic rock masses, located inside moderately jointed rock masses, and is the result of specific geometries and significant impedance contrasts. A map of fault zones prone to amplification of ground motion was constructed, taking into account the jointing conditions of the rock masses and the structural setting of the investigated ridge. The study relied on an integrated methodological approach, which combined the available data under union and intersection criteria.
    Description: Published
    Description: 416-449
    Description: JCR Journal
    Description: reserved
    Keywords: jointed rock masses ; velocimetric records ; seismic amplification ; trapped waves ; Central Italy ; 04. Solid Earth::04.06. Seismology::04.06.09. Waves and wave analysis
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  • 143
    Publication Date: 2022-05-24
    Description: Various authors, analysing the set of accelerograms recorded at Gubbio Piana (GBP) (central Italy), have demonstrated that strong amplification occurs at this accelerometric station, which is installed within an alluvial basin. In particular, Ambraseys et al. [(2005a), Bull Earthq Eng 3:1–53; (2005b), Bull Earth Eng 3:55–73] observed that the strong motion peaks at GBP greatly exceed the median values predicted by the attenuation relationships they derived for Europe. In this work, we analyse and discuss some characteristics of the ground motion recorded at the GBP station. We show that the ground motion parameters, such as peak-ground acceleration and peak-ground velocity, are strongly influenced by the presence of locally induced surface waves that produce both a lengthening of the significant shaking duration and an increase in the peak values with respect to a nearby bedrock site. The basin-induced surface waves are observed in the three components of motion and their effects on the peak values are particularly evident in the vertical component. In the frequency domain, the energy of the surface waves is mostly restricted to the frequency band 0.4–0.8Hz for both the horizontal and vertical components. The horizontal and vertical Fourier amplitudes are also very similar, and this indicates that the H/V spectral ratio technique is not applicable to describing the site response due to the propagation of seismic wave in a complex 2D/3D geological structure. Finally, a preliminary polarization analysis shows that the directions of polarization, as well as the degree of elliptical polarization, exhibit a strong variability with time, that may be related to a complex propagation of Love and Rayleigh waves within the basin.
    Description: Published
    Description: JCR Journal
    Description: reserved
    Keywords: Strong motion ; Alluvial basin effects ; Site effects ; Gubbio plain ; 04. Solid Earth::04.06. Seismology::04.06.04. Ground motion
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  • 144
    Publication Date: 2022-05-30
    Description: Scientific investigations in Antarctica are, for many different reasons, a challenging and fascinating task. Measurements, observations and field operations must be carefully planned well in advance and the capacity of successfully meeting the goals of a scientific project is often related to the capacity of forecasting and anticipating the many different potential mishaps. In order to do that, experience and logistic support are crucial. On the scientific side, the team must be aware of its tasks and be prepared to carry out observations in a hostile environment: both technology and human resources have to be suitably selected, prepared, tested and trained. On the logistic side, nations, institutions and any other organisation involved in the expeditions must ensure the proper amount of competence and practical support. The history of modern Italian Antarctic expeditions dates back to the middle 80’s when the first infrastructures of “Mario Zucchelli Station”, formerly Terra Nova Bay Station, were settled at Terra Nova Bay, Northern Victoria Land. Only a few years later, the first geodetic infrastructures were planned and built. Italian geodetic facilities and activities were, ever since, being constantly maintained and developed. Nowadays, the most remarkable geodetic infrastructures are the permanent Global Positioning System (GPS) station (TNB1) installed at Mario Zucchelli and the GPS geodetic network Victoria Land Network for DEFormation control (VLNDEF) entirely deployed on an area extending between 71° S and 76° S and 160° E and 170° E. These facilities do not only allow carrying out utmost geodetic investigations but also posses interesting capacities on the international multidisciplinary scientific scenario. In order to fully exploit their potentiality, management and maintenance of the infrastructure are crucial; nevertheless, in order to perform high quality scientific research, these abilities must be coupled with the knowledge concerning a proper use and a correct processing of the information that these infrastructures can provide. This work focuses on the different methods that can be applied to process the observations that are performed with GPS technique in Northern Victoria Land, aiming at reaching the highest accuracy of results and assuring the larger significance and versatility of the processing outcomes. Three software were used for the analysis, namely: Bernese v.5.0, Gipsy/Oasis II and Gamit/Globk. The working data sets are (i) the permanent GPS station TNB1 observations continuously performed since 1998 and (ii) the five episodic campaigns performed on the sites of VLNDEF. The two infrastructures can be regarded as neat examples of standard geodetic installation in Antarctica. Therefore, the technological solutions that were adopted and applied for establishing the GPS permanent station and the VLNDEF geodetic network as well as the data processing strategies and the data analysis procedures that were tested on their observation will be illustrated in detail. The results will be presented, compared and discussed. Furthermore, their potentials and role in geodetic research will be carefully described; their versatility will also be highlighted in the foreground of a multidisciplinary Antarctic international scientific activity.
    Description: Published
    Description: 37-72
    Description: 1.8. Osservazioni di geofisica ambientale
    Description: reserved
    Keywords: Antarctica ; Geodesy ; Geodetic Infrastructures ; GPS ; 01. Atmosphere::01.01. Atmosphere::01.01.08. Instruments and techniques
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 145
    Publication Date: 2022-05-24
    Description: In the framework of the SESAME project one of the taskswas the compilation of all available ambient noise measurements within urban environments affected by historical or/and recent strong earthquakes in Europe. The aim of such a task was to give an answer to the question; “How does horizontal-to-vertical ambient noise spectral ratio compare with damage in modern cities?”. For this purpose five European urban areas, namely, Angra do Heroismo (Portugal), Fabriano and Palermo (Italy), Thessaloniki and Kalamata (Greece) were selected for which spatial damage information was available either in terms of modified Mercalli intensity or in EMS98 damage grades. The geological setting of the examined sites as well as the causative earthquakes are satisfactorily known. Ambient noise recordings compiled for all examined sites have been homogeneously processed by a technique developed and agreed upon SESAME project. Using a standard multivariate statistical analysis, namely, factor analysis and canonical correlation, the horizontal-to-vertical ambient noise spectral ratio (HVNSR) is correlated with damage pattern observed within examined urban areas. Results show that, in some cases (Thessaloniki, Palermo), the HVNSR seems to be able to differentiate between areas previously shown to be associated with higher damage. In other cases however (Angra do Heroismo, Fabriano, Kalamata), the correlation is not statistically significant indicating thus the complex character of the parameters involved, implying that currently there is no a straightforward way that a value of HVNSR can correctly predict the extent to which a given region will be associated with increased damage.
    Description: Published
    Description: 109–140
    Description: 4.1. Metodologie sismologiche per l'ingegneria sismica
    Description: JCR Journal
    Description: reserved
    Keywords: Ambient noise ; Site effect ; Macroseismic intensity ; Factor and canonical analysis ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous
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  • 146
    Publication Date: 2022-05-24
    Description: The concerted effort to collect earthquake damage data in Italy over the past 30 years has led to the development of an extensive database from which vulnerability predictions for the Italian building stock can be derived. A methodology to derive empirical vulnerability curves with the aforementioned data is presented herein and the resulting curves have been directly compared with mechanics-based vulnerability curves. However, it has been found that a valid comparison between the empirical and analytical vulnerability curves is not possible mainly due to a number of shortcomings in the database of surveyed buildings. A detailed discussion of the difficulties in deriving vulnerability curves from the current observed damage database is thus also presented.
    Description: DPC — Dipartimento della Protezione Civile MIUR – Ministero dell’Università e della Ricerca - project AIRPLANE
    Description: Published
    Description: 485–504
    Description: 4.2. TTC - Scenari e mappe di pericolosità sismica
    Description: JCR Journal
    Description: reserved
    Keywords: vulnerability curves ; damage data ; 04. Solid Earth::04.06. Seismology::04.06.11. Seismic risk
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  • 147
    Publication Date: 2022-05-26
    Description: © 2009 The Authors. This is an open-access article distributed under the terms of the Creative Commons Attribution Noncommercial License. The definitive version was published in Coral Reefs 28 (2009): 327-337, doi:10.1007/s00338-009-0466-z.
    Description: Design and decision-making for marine protected areas (MPAs) on coral reefs require prediction of MPA effects with population models. Modeling of MPAs has shown how the persistence of metapopulations in systems of MPAs depends on the size and spacing of MPAs, and levels of fishing outside the MPAs. However, the pattern of demographic connectivity produced by larval dispersal is a key uncertainty in those modeling studies. The information required to assess population persistence is a dispersal matrix containing the fraction of larvae traveling to each location from each location, not just the current number of larvae exchanged among locations. Recent metapopulation modeling research with hypothetical dispersal matrices has shown how the spatial scale of dispersal, degree of advection versus diffusion, total larval output, and temporal and spatial variability in dispersal influence population persistence. Recent empirical studies using population genetics, parentage analysis, and geochemical and artificial marks in calcified structures have improved the understanding of dispersal. However, many such studies report current self-recruitment (locally produced settlement/settlement from elsewhere), which is not as directly useful as local retention (locally produced settlement/total locally released), which is a component of the dispersal matrix. Modeling of biophysical circulation with larval particle tracking can provide the required elements of dispersal matrices and assess their sensitivity to flows and larval behavior, but it requires more assumptions than direct empirical methods. To make rapid progress in understanding the scales and patterns of connectivity, greater communication between empiricists and population modelers will be needed. Empiricists need to focus more on identifying the characteristics of the dispersal matrix, while population modelers need to track and assimilate evolving empirical results.
    Description: Work by CB Paris was supported by the National Science Foundation grant NSF-OCE 0550732. Work by M-A Coffroth and SR Thorrold was supported by the National Science Foundation grant NSF-OCE 0424688. Work by TL Shearer was supported by an International Cooperative Biodiversity Group grant R21 TW006662-01 from the Fogarty International Center at the National Institutes of Health.
    Keywords: Connectivity ; Larval dispersal ; Marine protected areas ; Resilience ; Replacement ; Genetics
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  • 148
    facet.materialart.
    Unknown
    Springer
    In:  Primate Biogeography, Progress and Prospects vol. 77 no. 2, pp. 135-138
    Publication Date: 2024-01-12
    Keywords: primates ; biogeography
    Repository Name: National Museum of Natural History, Netherlands
    Type: info:eu-repo/semantics/review
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  • 149
    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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  • 150
    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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  • 151
    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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  • 152
    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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  • 153
    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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  • 154
    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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  • 155
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 862-867 
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    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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  • 156
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 877-883 
    ISSN: 1089-7550
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    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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  • 157
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 884-890 
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    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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  • 158
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 872-876 
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    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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  • 159
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4102-4104 
    ISSN: 1089-7550
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    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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  • 160
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4105-4112 
    ISSN: 1089-7550
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    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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  • 161
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    Journal of Applied Physics 74 (1993), S. 4121-4124 
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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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  • 162
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    Journal of Applied Physics 74 (1993), S. 4113-4120 
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    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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  • 163
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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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  • 164
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    Journal of Applied Physics 74 (1993), S. 4598-4607 
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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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  • 165
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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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  • 166
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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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  • 167
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    Journal of Applied Physics 74 (1993), S. 4153-4157 
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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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  • 168
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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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  • 169
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 963-968 
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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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  • 170
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    Journal of Applied Physics 74 (1993), S. 4651-4659 
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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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  • 171
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    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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    Journal of Applied Physics 74 (1993), S. 4664-4672 
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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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  • 181
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 7078-7084 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    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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  • 182
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 7094-7100 
    ISSN: 1089-7550
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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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  • 183
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4729-4736 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    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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  • 184
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4737-4740 
    ISSN: 1089-7550
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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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  • 185
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 3103-3110 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    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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  • 186
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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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  • 187
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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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  • 188
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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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  • 189
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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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  • 190
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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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  • 191
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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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  • 192
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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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  • 193
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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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  • 194
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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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  • 195
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 2968-2970 
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    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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  • 197
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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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  • 198
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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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  • 199
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 7306-7310 
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    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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