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  • 2020-2023  (9)
  • 1995-1999  (682)
  • 1975-1979  (93)
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  • 1
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    Pleistocene depositional environments and links to cryosphere-ocean interactions on the eastern Ross Sea continental slope, Antarctica (IODP Hole U1525A) (2022)
    In:  EPIC3Marine Geology, 443, pp. 106674, ISSN: 00253227
    Details
    Publication Date: 2022-04-12
    Description: The repeated proximity of West Antarctic Ice Sheet (WAIS) ice to the eastern Ross Sea continental shelf break during past ice age cycles has been inferred to directly influence sedimentary processes occurring on the continental slope, such as turbidity current and debris flow activity; thus, the records of these processes can be used to study the past history of the WAIS. Ross Sea slope sediments may additionally provide an archive on the history and interplay of density-driven or geostrophic oceanic bottom currents with ice-sheet-driven depositional mechanisms. We investigate the upper 121 m of Hole U1525A, collected during International Ocean Discovery Program (IODP) Expedition 374 in 2018. Hole U1525A is located on the southwestern external levee of the Hillary Canyon (Ross Sea, Antarctica) and the depositional lobe of the nearby trough-mouth fan. Using core descriptions, grain size analysis, and physical properties datasets, we develop a lithofacies scheme that allows construction of a detailed depositional model and environmental history of past ice sheet-ocean interactions at the eastern Ross Sea continental shelf break/slope since ~2.4 Ma. The earliest Pleistocene interval (~2.4- ~ 1.4 Ma) represents a hemipelagic environment dominated by ice-rafting and reworking/deposition by relatively persistent bottom current activity. Finely interlaminated silty muds with ice-rafted debris (IRD) layers are interpreted as contourites. Between ~1.4 and ~0.8 Ma, geostrophic bottom current activity was weaker and turbiditic processes more common, likely related to the increased proximity of grounded ice at the shelf edge. Silty, normally-graded laminations with sharp bases may be the result of flow-stripped turbidity currents overbanking the canyon levee during periods when ice was grounded at or proximal to the shelf edge. A sandy, IRD- and foraminifera-bearing interval dated to ~1.18 Ma potentially reflects warmer oceanographic conditions and a period of stronger Antarctic Slope Current flow. This may have enhanced upwelling of warm Circumpolar Deep Water onto the shelf, leading to large-scale glacial retreat at that time. The thickest interval of turbidite interlamination was deposited after ~1 Ma, following the onset of the Mid-Pleistocene Transition, interpreted as a time when most ice sheets grew and glacial periods were longer and more extreme. Sedimentation after ~0.8 Ma was dominated by glacigenic debris flow deposition, as the trough mouth fan that dominates the eastern Ross Sea continental slope prograded and expanded over the site. These findings will help to improve estimations of WAIS ice extent in future Ross Sea shelf-based modelling studies, and provide a basis for more detailed analysis of the inception and growth of the WAIS under distinct oceanographic conditions.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 2
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    Bottom current control on sediment deposition between the Iselin Bank and the Hillary Canyon (Antarctica) since the late Miocene: An integrated seismic-oceanographic approach (2021)
    In:  EPIC3Deep Sea Research Part I: Oceanographic Research Papers, 176, pp. 103606, ISSN: 09670637
    Details
    Publication Date: 2022-04-12
    Description: In this paper we analyze how oceanic circulation affects sediment deposition along a sector of the Ross Sea continental margin, between the Iselin Bank and the Hillary Canyon, and how these processes evolved since the Late Miocene. The Hillary Canyon is one of the few places around the Antarctic continental margin where the dense waters produced onto the continental shelf, mainly through brine rejection related to sea ice production, flow down the continental slope and reach the deep oceanic bottom layer. At the same time the Hillary Canyon represents a pathway for relatively warm waters, normally flowing along the continental slope within the Antarctic Slope Current, to reach the continental shelf. The intrusion of warm waters onto the continental shelf produces basal melting of the ice shelves, reduces their buttressing effect and triggers instabilities of the ice sheet that represent one of the main uncertainties in future sea level projections. For this study we use seismic, morpho-bathymetric and oceanographic data acquired in 2017 by the R/V OGS Explora. Seismic profiles and multibeam bathymetry are interpreted together with age models from two drilling sites (U1523 and U1524) of the International Ocean Discovery Program (IODP) Expedition 374. Oceanographic data, together with a regional oceanographic model, are used to support our reconstruction by showing the present-day oceanographic influence on sediment deposition. Regional correlation of the main seismic unconformities allows us to identify eight seismic sequences. Seismic profiles and multibeam bathymetry show a strong influence of bottom current activity on sediment deposition since the Early Miocene and a reduction in their intensity during the mid-Pliocene Warm Period. Oceanographic data and modelling provide evidence that the bottom currents are related to the dense waters produced on the Ross Sea continental shelf and flowing out through the Hillary Canyon. The presence of extensive mass transport deposits and detachment scarps indicate that also mass wasting participates in sediment transport. Through this integrated approach we regard the area between the Iselin Bank and the Hillary Canyon as a Contourite Depositional System (ODYSSEA CDS) that offers a record of oceanographic and sedimentary conditions in a unique setting. The hypotheses presented in this work are intended to serve as a framework for future reconstructions based on detailed integration of lithological, paleontological, geochemical and petrophysical data.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev , info:eu-repo/semantics/article
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  • 3
    Electronic Resource
    Electronic Resource
    Stark effect and Stark-ladder effect in Al0.4Ga0.6As/GaAs asymmetric coupled multiple quantum wells (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 2486-2494 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoluminescence (PL) measurements at 10 K were performed in order to investigate the influence of electric fields on the exciton states in Al0.4Ga0.6As/GaAs asymmetric coupled multiple quantum wells (ACMQW) grown by molecular-beam epitaxy. The coupling of the electronic energy levels in the wells led to an enhancement of the quantum-confined Stark effect. The PL intensity decreased as the electric field increased. Calculated values of the intersubband transition energies were in good agreement with the experimental values for the ACMQW, and these values showed a similar behavior as those for the step quantum well. When the external applied field was very strong, Stark-ladder transitions were observed, and the measured dependence of the field-induced energy shifts of the Stark-ladder transitions for the ACMQW agreed with theory. These results indicate that the Stark effect and the Stark-ladder transitions in a unique ACMQW based on the AlxGa1−xAs/GaAs structure were observed simultaneously. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358777
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  • 4
    Electronic Resource
    Electronic Resource
    Carrier lifetimes in dielectric cap disordered GaAs/AlGaAs multiple quantum well with SiN capping layers (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 3438-3440 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Time resolved photoluminescence (PL) characteristics of a SiN cap disordered GaAs/AlGaAs multiple quantum well (MQW) structure exhibit a decrease in carrier lifetime in conjunction with an increase in quantum well disordering (QWD) as the SiN capping layer thickness is increased. The decrease in carrier lifetime is attributed to enhanced carrier trapping due to the defects introduced during dielectric cap quantum well disordering and the relaxation of the momentum conservation during radiative recombination by QWD. Potential applications of these effects on high speed optical devices such as laser diodes (LD's) and optical modulators are discussed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115272
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  • 5
    Electronic Resource
    Electronic Resource
    Moisture Sorption Characteristics of Composite Foods Filled with Chocolate (1999)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of food science 64 (1999), S. 0 
    Details
    ISSN: 1750-3841
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: We compared the moisture sorption isotherms (MSI's) and their temperature dependence of composite foods with those of crust and filling. The MSI were determined on cracker, cookie, chocolate, and two types of composite foods such as CFI (cracker/chocolate/cracker) and CF2 (cookie/chocolate/cookie) at 20,30, and 40°C and 11–85% relative humidity, and fitted into the Guggenheim-Anderson-de Boer (GAB) equation. Chocolate had the lowest monolayer (mo) value, equilibrium moisture content (EMC), and sorption energy levels, followed by cookie and cracker. The CFI had higher EMC values and sorption energy than CF2. The GAB mo values and C1 values decreased with temperature, while C2 values increased with temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2621.1999.tb15887.x
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  • 6
    Electronic Resource
    Electronic Resource
    Synthesis and properties of poly(ethylene glycol) macromer/β-chitosan hydrogels (1997)
    Springer
    Journal of materials science 8 (1997), S. 537-541 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Semi-interpenetrating polymer network (semi-IPN) hydrogels composed of β-chitosan and poly(ethylene glycol) diacrylate macromer (PEGM) were synthesized and characterized for the application as potential biomedical materials. The mixture of PEGM and β-chitosan, dissolved in water including a small amount of acetic acid, was cast to prepare hydrogel films, followed by a subsequent crosslinking with 2,2-dimethoxy-2-phenylacetophenone as a non-toxic photoinitiator by ultraviolet irradiation. Photocrosslinked hydrogels exhibited relatively high equilibrium water content in the range 77–83% which is mainly attributed to the free water content rather than to the bound water, hydrogen bonded with components in semi-IPN hydrogels. The crystallinity, thermal properties and mechanical properties of semi-IPN hydrogels were studied. All the photocrosslinked hydrogels revealed a remarkable decrease in crystallinity. The glass transition temperatures, Tg, of crosslinked PEGM segment in semi-IPNs increased compared with poly(ethylene glycol) itself. However, with increasing β-chitosan content their Tg decreased owing to the higher degree of crosslinking. The tensile strengths of semi-IPNs in dry state were rather high, but those of hydrogels in wet state decreased drastically.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018594614087
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  • 7
    Electronic Resource
    Electronic Resource
    Preparation of CuInSe2 thin films by selenization of co-sputtered Cu–In precursors (1998)
    Springer
    Journal of materials science 9 (1998), S. 361-366 
    Details
    ISSN: 1573-482X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract CuInSe2 thin films have been prepared by high Se vapor selenization of co-sputtered Cu–In alloy precursors within a partially closed graphite container. Cu–In alloys with different compositions were investigated. X-ray diffraction (XRD) analysis of the films showed mainly CuIn2 and Cu11In9 phases and the Cu11In9 peak intensity was found to increase as the alloy composition tended towards Cu-rich. A linear dependence of the alloy composition on the Cu/In deposition power was observed from energy dispersive analysis by X-rays (EDX). A three-fold volume expansion was exhibited by all the CuInSe2 films after selenization at 500–550 °C. Scanning electron microscopy (SEM) analysis of the films showed large and densely packed crystal structures with sizes above 5 μm. The CuInSe2 films exhibited single phase chalcopyrite structure with preferential orientation in the (1 1 2) direction. The EDX composition analyses of the films showed Cu/In ratio ranging from 0.43 to 1.2, and Se/(Cu+In) ratios from 0.92 to 1.47. The measured film resistivities varied from 10-1 to 105 Ωcm. The Cu–In alloy precursors with Cu/In ratio less than 0.70 were found to form CuIn3Se5 a defect chalcopyrite compound. All films were Se rich, with the exception of samples with very high Cu content.© 1998 Kluwer Academic Publishers
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008936210166
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  • 8
    Electronic Resource
    Electronic Resource
    The Brevibacterium albidum gene encoding the arginine tRNACCG complements the growth defect of an Escherichia coli strain carrying a thermosensitive mutation in the rnpA gene at the nonpermissive temperature (1997)
    Springer
    Molecular genetics and genomics 254 (1997), S. 464-468 
    Details
    ISSN: 1617-4623
    Keywords: Key words Brevibacterium albidum  ;  Arginine tRNACCG  ;  Escherichia colirnpA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The Escherichia colirnpA gene encodes C5 protein, the protein component of RNase P. The rnpA49 mutation renders the C5 protein thermosensitive, which results in thermosensitivity of RNase P function. The chromosomal DNA region from Brevibacterium albidum that complements the rnpA49 mutation was analysed. The gene capable of complementing the growth defect of an rnpA49 mutant strain at nonpermissive temperature was identified as the gene for an arginine tRNA with anticodon CCG by a deletion analysis combined with complementation assays. Transcription of the arginine tRNA gene carried on a multicopy plasmid was correlated with the complementation of the rnpA49 mutation, indicating that the gene product is indeed responsible for complementation of the rnpA49 mutation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004380050440
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  • 9
    Electronic Resource
    Electronic Resource
    Exact Algorithm for the Surrogate Dual of an Integer Programming Problem: Subgradient Method Approach (1998)
    Springer
    Journal of optimization theory and applications 96 (1998), S. 363-375 
    Details
    ISSN: 1573-2878
    Keywords: Integer programming ; surrogate dual ; nondifferentiable optimization ; subgradient method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract One of the critical issues in the effective use of surrogate relaxation for an integer programming problem is how to solve the surrogate dual within a reasonable amount of computational time. In this paper, we present an exact and efficient algorithm for solving the surrogate dual of an integer programming problem. Our algorithm follows the approach which Sarin et al. (Ref. 8) introduced in their surrogate dual multiplier search algorithms. The algorithms of Sarin et al. adopt an ad-hoc stopping rule in solving subproblems and cannot guarantee the optimality of the solutions obtained. Our work shows that this heuristic nature can actually be eliminated. Convergence proof for our algorithm is provided. Computational results show the practical applicability of our algorithm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022622231801
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  • 10
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    Double parton scattering inp¯pcollisions ats=1.8TeV (1997)
    American Physical Society
    Details
    Publication Date: 1997-10-01
    Print ISSN: 0556-2821
    Electronic ISSN: 1089-4918
    Topics: Physics
    Published by American Physical Society
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