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  • 1990-1994  (38)
  • 1980-1984
  • 1991  (38)
  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 881-889 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Significant improvements in CdTe/CdS solar cell efficiency are commonly observed as a result of a postdeposition CdCl2 dip followed by a 400 °C heat treatment during cell processing which increases CdTe grain size. In this paper, we investigate the electronic mechanisms responsible for CdCl2-induced improvement in cell performance along with possible performance-limiting defects resulting from this process in molecular-beam epitaxy-grown polycrystalline CdTe/CdS solar cells. Current density-voltage-temperature (J-V-T) analysis revealed that the CdCl2 treatment changes the dominant current transport mechanism from interface recombination/tunneling to depletion region recombination, suggesting a decrease in the density and dominance of interface states due to the CdCl2 treatment. It is shown that the change in transport mechanism is associated with (a) an increase in heterojunction barrier height from 0.56 to 0.85 eV, (b) a decrease in dark leakage current from 4.7×10−7 A/cm2 to 2.6×10−9 A/cm2 and, (c) an increase in cell Voc from 385 to 720 mV. The CdCl2 also improved the optical response of the cell. Substantial increases in the surface photovoltage and quantum efficiency accompanied by a decrease in the bias dependence of the spectral response in the CdCl2-treated structures indicate that the CdCl2 treatment improves carrier collection from the bulk as well as across the heterointerface. However, deep level transient spectroscopy measurements detected a hole trap within the CdTe depletion region of the CdCl2-treated devices at Ev + 0.64 eV which is attributed to the formation of VCd-related defects during the annealing process after the CdCl2 dip. J-V-T analysis demonstrated that this trap is the probable source of dominant recombination in the CdCl2-treated cells. An inverse correlation was found between the density of the Ev + 0.64 eV trap and cell Voc, suggesting that the heat treatment with CdCl2 may eventually limit the CdTe/CdS cell performance unless the formation of this defect complex is controlled or eliminated.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 95 (1991), S. 6075-6078 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 113 (1991), S. 5475-5476 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 113 (1991), S. 3106-3114 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Using a polyclonal antiserum raised against the C-terminal heptapeptide of pro-enkephalin A, we have isolated the opioid heptapeptide Tyr-Gly-Gly-Phe-Met-Arg-Phe (MERF) from ovine median eminence and mapped its distribution in that structure. MERF-immunoreactivity was confined to the pars externa (neurosecretory zone) where it colocalized with corticotrophin-releasing factor in the majority of terminals. No larger, N-terminally extended forms of MERF were detected in median eminence extracts suggesting that pro-enkephalin is fully processed to its constituent enkephalin congeners, and that the bioactive products, including MERF, act at the level of the hypothalamus in regulating anterior pituitary function.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 14 (1991), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Very little attention has been directed at the responses of tropical plants to increases in global atmospheric CO2 concentrations and the potential climatic changes. The available data, from greenhouse and laboratory studies, indicate that the photosynthesis, growth and water use efficiency of tropical plants can increase at higher CO2 concentrations. However, under field conditions abiotic (light, water or nutrients) or biotic (competition or herbivory) factors might limit these responses. In general, elevated atmospheric CO2 concentrations seem to increase plant tolerance to stress, including low water availability, high or low temperature, and photoinhibition. Thus, some species may be able to extend their ranges into physically less favourable sites, and biological interactions may become relatively more important in determining the distribution and abundance of species. Tropical plants may be more narrowly adapted to prevailing temperature regimes than are temperate plants, so expected changes in temperature might be relatively more important in the tropics. Reduced transpiration due to decreased stomatal conductance could modify the effects of water stress as a cue for vegetative or reproductive phenology of plants of seasonal tropical areas. The available information suggests that changes in atmospheric CO2 concentrations could affect processes as varied as plant/herbivore interactions, decomposition and nutrient cycling, local and geographic distributions of species and community types, and ecosystem productivity. However, data on tropical plants are few, and there seem to be no published tropical studies carried out in the field. Immediate steps should be undertaken to reduce our ignorance of this critical area.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    European journal of neuroscience 3 (1991), S. 0 
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: We have investigated the projection from the substantia nigra to the pontomedullary reticular formation in the rat using both retrograde and anterograde neuroanatomical tracers. Injections of a conjugate of wheatgerm agglutinin with horseradish peroxidase into the medullary or pontomedullary reticular formation resulted in the retrograde labelling of a continuous band of cells extending from the caudal half of the dorsolateral substantia nigra into the retrorubral field. Injections of the anterograde tracer Phaseolus vulgaris leukoagglutinin (PHA-L) into either the dorsolateral substantia nigra or the caudally adjacent retrorubral field revealed a descending projection to the lateral medullary and pontomedullary brainstem, which terminated mainly within the lateral (parvicellular) reticular formation. The anterograde PHA-L fibre labelling ran throughout the rostrocaudal extent of the parvicellular reticular formation and extended into the caudally continuous region, the medullary dorsal and medullary ventral reticular formation, where it tapered off. Also labelled, although more lightly, were the rostral and ventrolateral regions of the nucleus of the solitary tract and the magnocellular reticular formation. Electron microscopy established that the PHA-L-labelled fibres formed synaptic contacts with nerve cell bodies and dendrites in the parvicellular reticular formation. It is suggested that one role of this nigroreticular pathway might be to connect the basal ganglia with brainstem premotor neurons that influence orofacial musculature.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    International journal of food science & technology 26 (1991), S. 0 
    ISSN: 1365-2621
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Diced steer flank and brisket were flaked at a nominal temperature of -4.0°C to investigate the effects of rotational speed (3360 or 5250 r.p.m.), two different impeller designs, aperture size (1.5, 6.1 and 19.0mm) and number of cutting stations on the resulting particle size distribution, measured using video image analysis. Changes in ice content and enthalpy were also calculated from measurements of temperature before and after flaking.The amount of ice which melted, and the corresponding enthalpy change, was significantly greater for the smaller aperture sizes, and the higher speeds.Of the four factors investigated, the most important influence on particle size was that of aperture size. However, under some conditions, the number of cutting stations and the rotational speed also influenced the resulting particle size characteristics, most notably in producing thinner particles.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Grass and forage science 46 (1991), S. 0 
    ISSN: 1365-2494
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Preliminary studies were carried out on the effect of stocking rate during late autumn on a continuously stocked Lolium perenne-dominated sward at an upland site in central Scotland. Measurements were made of L. perenne tiller population density on 29 September and 2 November and of L. perenne net production, mean sward height and total herbage mass in early and late October and early and late November. Stocking rates were 12 ewes per ha during October and 8 and 16 ewes per ha during November. Sward height and herbage mass declined with time and more rapidly at the higher stocking rate. L. perenne growth per tiller and per unit area was influenced by time but not by stocking rate and was closely related to the 5·5°C soil temperature at 10 cm depth. Tiller senescence was greatly reduced at the higher stocking rate and/or the consequentially lower sward height and herbage mass. Tiller net production was therefore sustained at a positive level on the higher stocked sward throughout November while on the lower stocked sward it fell below zero early in November.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Sedimentology 38 (1991), S. 0 
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The Poacher's Point Formation is located within the Etosha Pan, northern Namibia. It contains Pleistocene stromatolites, ooids and silica nodules. The stromatolites were constructed by cyanobacteria in very lowenergy lacustrine conditions. The internal structure of the oncoids is complex and subdivided into shells by unconformities. Each unconformity-bounded shell probably represents stromatolite growth during a distinct lacustrine event. Shallower conditions are represented by colloform growth and deeper water by smooth oncoid mat morphology. The unconformities represent hiatuses of unknown duration. At least six stromatolite growth shells are recognized. Silica concretions which may have developed during shallowing lake stages are also present. The lack of clastic material in the carbonate lithologies suggests that the lake waters may have accumulated from collecting rainwater or have been spring fed. The lowest bed of the succession is a saline clay which represents a seasonally flooded salt pan deposited in an arid to semi-arid climate similar to that of today. The overlying carbonates represent sedimentation during a series of transient lacustrine events, representing intermittent wetter periods. Finally, due to progressive aridity, the lacustrine succession was terminated by calcrete development.
    Type of Medium: Electronic Resource
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