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  • Articles: DFG German National Licenses  (29)
  • 1995-1999  (28)
  • 1965-1969  (1)
  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This work shows preliminary results on the study of FexMn0.6−xAl0.40 alloys. It includes measurements of the temperature dependence of the ac susceptibility, zero field cooled magnetization, and Mössbauer spectroscopy. From the results obtained, the occurrence of reentrant spin glass behavior from a spin glass phase to an antiferromagnetic one for 0.2≤x≤0.35 and from a spin glass phase to a ferromagnetic one for the x=0.55 sample is proposed. Also, a normal spin glass transition was detected in the Fe range corresponding to 0.35≤x≤0.5. These results allow us to construct a magnetic phase diagram for the alloy series. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 353-359 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The microstructural differences of YBa2Cu3O7−δ (YBCO) films prepared by in situ magnetron sputtering on (100)-SrTiO3 and (100)-LaAlO3 substrates have been investigated. A detailed analysis of the film orientation by means of Raman spectroscopy has been developed, showing that a certain amount of a-axis oriented grains always nucleate on the LaAlO3 surface, at the optimal deposition conditions for c-axis epitaxy. High-resolution electron microscopy has been used to show the epitactic nature of the YBCO films and has provided evidence for the orientational differences. A clear correlation between the degree of misorientation and the surface microstructure has been shown by atomic force microscopy and scanning tunneling microscopy, the bulk structure of these samples being reflected by their surface morphology. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 4316-4323 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Resistance heating of the gasket strip in a gem-anvil high pressure cell was successful in obtaining sample temperatures up to 1100 °C, under pressures up to 4.0 GPa. The heating capabilities, as well as the mechanical and chemical stability, of several different gasket strips (two Ni-based alloys, Ta, Pt/Rh, and a Re/Mo alloy) with different design shapes, and two different single-crystal anvil materials (diamond and cubic zirconia) were investigated. Two gasket-strip designs were found to provide optimum uniform heating conditions while decreasing the required current needed to achieve 1100 °C. Two anvil systems were investigated to reduce the temperature increase of the pressure cell body. Cubic zirconia anvils reduced the cell-body temperature to 100 °C at sample temperatures up to 1100 °C. However, zirconia anvils often failed during heating and almost always failed during cooling. Diamond anvils with cubic zirconia mounting plates also permitted temperatures up to 1100 °C to be reached without anvil failure. However, the cell-body temperature increased to 300 °C. A sealed vacuum-type chamber was employed to eliminate the problem with gasket and anvil oxidation. The optimized operating parameters reported here provide a routine method for high temperature-high pressure studies. The method was used to densify and sinter nanosize amorphous silicon nitride and γ-alumina powders at high temperatures and high pressures.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 3540-3543 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This work describes the characteristics of a bench station designed for both the control of the operational parameters of a unitary, low temperature fuel cell and the data acquisition for performance evaluation. The controlled parameters are the current through the cell, the pressure and the flow of the reactants, and the temperature of the cell and of the gaseous reactants. The system measures the potential drop across the cell and the potential of each electrode with respect to a reference, as a function of the current, which is varied on a predetermined interval. The program plots the results and fits the experimental curve to a theoretical expression, which allows the determination of the cell resistance and the Tafel kinetic parameters of the cell reactions. The test station provides a rapid route to the work with single/half cells in the evaluation of materials and fuel cell performance. The computer controlled procedures, data acquisition, and analyses proposed here substitute with advantages time consuming manual procedures. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford BSL : Blackwell Science Ltd
    Freshwater biology 36 (1996), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. The breakdown of oak (Quercus robur L.), chestnut (Castanea sativa Miller) and eucalypt (Eucalyptus globulus Labill.) litter enclosed in 5-mm mesh bags was compared between first-order headwaters (two with native riparian forest and two with eucalypt plantations) and a third-order reach of Agüera stream. Weight loss and dynamics of phosphorus and nitrogen in litter were studied for a period of 155 days.2. Among the different sites, processing rates ranged from 0.0045 to 0.0080 day–1 for chestnut leaf litter, from 0.0036 to 0.0051 day–1 for oak, and from 0.0027 to 0.0158 day–1 for eucalypt.3. The availability of nutrients in water clearly influenced nitrogen and phosphorus dynamics in litter. In headwater reaches, net immobilization was not observed and losses of phosphorus and nitrogen followed mass loss. However, there was an enrichment of litter at the low reach, where influence of human settlements—located upstream—could lead to a greater availability of phosphorus in water.4. The enhancement of litter decay by the exogenous nutrient supply depended on leaf quality, as only the processing rate of eucalypt increased at the nutrient-rich site.5. The processing rates differed little among headwaters, suggesting that riparian forest type, i.e. deciduous forest v eucalypt plantations, did not affect litter decay in the stream.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 759 (1995), S. 0 
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 53 (1998), S. 0 
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The reef fish community of the Mexican Caribbean and the factors governing its structure are poorly known. Using canonical correspondence analysis (CCA), the relationship between fish community species composition and abundance, and environmental variables was investigated at three Mexican Caribbean reefs. These reefs are separated by c. 70 km: Boca Paila, located in the northern Sian Ka'an Biosphere Reserve; Tampalam, in the southern portion of said reserve; and Majahual, an unprotected area near the Mexico/Belize border. One hundred and thirty-four fish species belonging to 41 families were identified by underwater visual census. Their quantitative data, and 15 environmental variables collected during 60 sample transects, were analysed. The sample stations were distributed among the three reefs, and covered five dominant habitat types: reef lagoon, back reef, reef crest, reef front and reef slope. The variables estimated were: temperature, depth, current direction, current intensity, vertical relief, visibility, topographical complexity and substratum coverage (percent of sand, seagrass, algae, rock and rubbles, gorgonians, massive coral, branching coral and encrusting coral). Ordination diagrams with points based on fish species, sample sites, and environmental variables, showed a pattern mainly determined by degree of reef site complexity. Habitat scale environmental factors defined element distribution in three main areas: (a) reef fish species associated with lagoon and back reef sites of low topographical complexity; (b) species associated with intermediate complexity reef crest sites; and (c) species associated with high complexity reef front and reef slope sites. Nearly 52% of the variation in fish species data was explained by environmental variables in the direct and simultaneous ordination analysis. Topographical complexity was the most important variable, but depth, encrusting coral coverage, and vertical relief also had significant effect on fish species. Use of multivariate statistical methods proved valuable in deciphering the reef fish community structure patterns in the southern Mexican Caribbean. The current study provides a base for future reef fish research and regional tourism and fisheries management.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Anatomia, histologia, embryologia 25 (1996), S. 0 
    ISSN: 1439-0264
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: HGCs were found in the head epidermis, yolk sac and pharynx epithelium of trout embryos. These cells usually appear in clusters, closely related positionally to neighbouring cells. The differentiation and specialization of HGCs seem to be mainly dependent on cell-cell interactions, which provides, in part, the positional information necessary for the cells to differentiate and localize in the appropriate place. The final secretory process is the result of a sequence of events by which the maturation of enzymatic granules occurs. The electron-density of the granules varies according to the proximity of the secretory stage. Exocytosis of the secretory granules were observed. After secretion, each HGC undergoes cellular death by apoptosis (programmed cell death).
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1432-2323
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. Three cases are reported of reuse of a transplanted liver graft after early death of the first recipient due to cerebral hemorrhage. The good condition of the donors; the excellent biochemical evolution of the graft in the first recipients; total ABO compatibility and donor-recipient crossmatch; the absence of positivity to hepatitis B virus (HBV), hepatitis C virus (HCV), and bacteriologic cultures; and early death made reuse possible. The shortage of donors in relation to patients on the waiting list and the poor clinical condition of the second recipients made it necessary to adopt the decision to reuse the graft in an attempt to save their lives. The evolution of the patients and the reused grafts was satisfactory, and there were no complications that could be attributed to the fact that the graft had been transplanted before.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 148 (1995), S. 233-242 
    ISSN: 1432-1424
    Keywords: Paracellular flow ; Malpighian tubules ; Secretion ; Epithelial transport ; Water transport ; Convective flow
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Lumen to bath J 12/C 1 and bath to lumen J 21/ C 2 fluxes per unit concentration of 19 probes with diameters (d m) ranging from 3.0–30.0 Å (water, urea, erythritol, mannitol, sucrose, raffinose and 13 dextrans with d m 9.1–30.0 Å) were measured during volume secretion (J v ) in the upper segment of the Malpighian Tubule of Rhodnius by perfusing lumen and bath with 14C or 3H-labeled probes. J net=(J 12/C 1 − J 21/C 2) was studied as a function of J v · J v was varied by using different concentrations of 5-hydroxy tryptamine. J net for 3H-water was not different from J v We found: (i) A strong correlation between J net and J v for 8 probes d m =3.0–11.8 Å (group a probes), indicating that the convective component of J net is more important than its diffusive component and than unstirred layers effects which are negligible. Therefore group a probes are solvent dragged as they cross the epithelium, (ii) There is no correlation between J net and J v for 11 probes with d m=11.8–30 Å (group b). Therefore these probes must cross the epithelium by diffusion and not by solvent drag, (iii) In a plot of J net/J v vs. d m group a probes show a steep linear relation with a slope = −0.111, while for group b probes the slope is −0.002. Thus there is a break between groups a and b in this plot. We tried to fit the data with models for restricted diffusion and convention through cylindrical or parallel slit pathways. We conclude that (i) group a probes are dragged by water through an 11.0 Å-wide slit, (ii) Most of J v must follow an extracellular noncytosolic pathway, (iii) Group b probes must diffuse through a 42 Å-wide slit, (iv) A cylindrical pathway does not fit the data.
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