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  • 1
    Digitale Medien
    Digitale Medien
    A class of colliding waves in metric-affine gravity, nonmetricity and torsion shock waves (2000)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 41 (2000), S. 6369-6380 
    Details
    ISSN: 1089-7658
    Quelle: AIP Digital Archive
    Thema: Mathematik , Physik
    Notizen: By using our recent generalization of the colliding waves concept to metric–affine gravity theories, and also our generalization of the advanced and retarded time coordinate representation in terms of Jacobi functions, we find a general class of colliding wave solutions with fourth degree polynomials in metric-affine gravity. We show that our general approach contains the standard second degree polynomial colliding wave solutions as a particular case. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1287429
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  • 2
    Digitale Medien
    Digitale Medien
    Artificial neural networks for parameter estimation in geophysics [ Received ] (2000)
    Oxford BSL : Blackwell Science Ltd
    Geophysical prospecting 48 (2000), S. 0 
    Details
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: Artificial neural systems have been used in a variety of problems in the fields of science and engineering. Here we describe a study of the applicability of neural networks to solving some geophysical inverse problems. In particular, we study the problem of obtaining formation resistivities and layer thicknesses from vertical electrical sounding (VES) data and that of obtaining 1D velocity models from seismic waveform data. We use a two-layer feedforward neural network (FNN) that is trained to predict earth models from measured data. Part of the interest in using FNNs for geophysical inversion is that they are adaptive systems that perform a non-linear mapping between two sets of data from a given domain. In both of our applications, we train FNNs using synthetic data as input to the networks and a layer parametrization of the models as the network output. The earth models used for network training are drawn from an ensemble of random models within some prespecified parameter limits. For network training we use the back-propagation algorithm and a hybrid back-propagation–simulated-annealing method for the VES and seismic inverse problems, respectively. Other fundamental issues for obtaining accurate model parameter estimates using trained FNNs are the size of the training data, the network configuration, the description of the data and the model parametrization. Our simulations indicate that FNNs, if adequately trained, produce reasonably accurate earth models when observed data are input to the FNNs.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2478.2000.00171.x
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  • 3
    Digitale Medien
    Digitale Medien
    Sex differences in behaviour as an indirect consequence of mating system (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 57 (2000), S. 0 
    Details
    ISSN: 1095-8649
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: A considerable literature has been devoted to documenting differences between the sexes. However, relatively little attention has hitherto been directed towards those differences that arise as an indirect consequence of mating system even though they can have profound implications for the daily lives of the animals involved. In this review we focus on differences in the non-reproductive behaviour of fish and relate these to sexual dimorphism in size and morphology, and to variance in fitness between the sexes. In line with our expectation, differences in distributional ecology, schooling, aggression, predator avoidance and foraging are exaggerated in sexually dimorphic species and polygamous mating systems. Nonetheless, the behaviour of males and females may also differ in sexually monomorphic and monogamous species. We conclude by highlighting promising directions for further research.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1095-8649.2000.tb02196.x
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  • 4
    Digitale Medien
    Digitale Medien
    The negative effect of nitrate on gametogenesis is independent of nitrate assimilation in Chlamydomonas reinhardtii (2000)
    Springer
    Planta 211 (2000), S. 287-292 
    Details
    ISSN: 1432-2048
    Schlagwort(e): Key words: Chlamydomonas ; Gametogenesis ; Nitrate reductase mutants ; Nitrate signal
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract.  The effect of nitrate on gamete differentiation as well as on the expression of genes involved in gametogenesis, nitrogen scavenging, and nitrate assimilation has been analyzed in wild-type and mutant strains of Chlamydomonas reinhardtii. Nitrate prevented gamete formation from wild-type strains and caused a strong reduction in the number of zygotes recovered in genetic crosses between nitrate-assimilation-deficient mutants, thus suggesting that nitrate by itself is providing a negative regulatory signal for the sexual differentiation of the alga. Addition of nitrate at low concentrations to wild-type cells, after an initial period of nitrogen starvation, resulted in a drastic decrease in transcript levels of both nitrate-assimilation genes (NIA1 and NRT2;1) and genes induced after N-starvation (NCG2 and NCG4). This strong effect of nitrate was due to its assimilation products since it was not evident in nitrate-assimilation mutants. A slight negative effect of nitrate on NCG4 expression was only observed in the mutant. Nitrate by itself was also found to provide a negative signal for the expression of gamete-specific genes (GAS3 and GAS18) in mutants incapable of assimilating nitrate.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004250000291
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  • 5
    Digitale Medien
    Digitale Medien
    Volcanic history of El Chichón Volcano (Chiapas, Mexico) during the Holocene, and its impact on human activity (2000)
    Springer
    Bulletin of volcanology 62 (2000), S. 90-104 
    Details
    ISSN: 1432-0819
    Schlagwort(e): Stratigraphy ; Evolution ; El Chichón ; México
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie
    Notizen: 2 abundance and depletion in MgO, CaO, TiO2, as well as trace and rare earth elements. This suggests segregation of olivine and orthopyroxene from the melt. Since human settlements in southeast Mexico and Central America can be traced as far back as approximately 2500 years BP, most of these events probably affected human activity. In fact, there are reports of pottery shards and other artifacts in deposits from the eruption of 1250 BP. Pottery fragments in deposits of an eruption that took place 2500 BP are also reported in this paper. Thus, the impact of the volcano on human activities has been frequent, with most of the repose intervals lasting between 100 to 600 years. The impact of the eruptions was probably of greater than local extent, because airfall tephra could reach distant sites and possibly even affect weather. The eruptive history of El Chichón also offers clues in the investigation of the Maya civilization. Several researchers have considered the volcano as an important factor in the answer to some intriguing questions such as the extensive use of volcanic ash in Late Classic Maya ceramics or, of greater importance, the causes of the collapse of the Classic Maya civilization.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004459900064
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  • 6
    Digitale Medien
    Digitale Medien
    Two hydrochlorides of 7-methyl-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene (2000)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. e255-e256 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The X-ray structure determinations of the two title compounds, namely 7-methyl-7,17-diaza-3,11-diazoniabicyclo[11.3.1]heptadeca-1(17),13,15-triene dichloride monohydrate, C14H26N42+·2Cl−·H2O, (I), and 7-methyl-17-aza-3,7,11-triazoniabicyclo[11.3.1]heptadeca-1(17),13,15-triene 2.826-chloride 0.174-nitrate, C14H27N43+·2.826Cl−·0.174NO3−, (II), are reported. Protonation occurs at the secondary amine N atoms in (I) and at all three amine N atoms in (II) to which the Cl− ions are linked via N—H...Cl hydrogen bonds. The macrocyclic hole is quite different in both structures, as is observed by comparing particularly the N3...N4 distances [2.976 (4) and 4.175 (4) Å for (I) and (II), respectively]. In (II), a Cl− ion alternates with an NO3− ion in a disordered structure.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270100006065
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  • 7
    Digitale Medien
    Digitale Medien
    Structural analysis of WW domains and design of a WW prototype (2000)
    [s.l.] : Nature America Inc.
    Nature structural biology 7 (2000), S. 375-379 
    Details
    ISSN: 1072-8368
    Quelle: Nature Archives 1869 - 2009
    Thema: Biologie , Medizin
    Notizen: [Auszug] Two new NMR structures of WW domains, the mouse formin binding protein and a putative 84.5 kDa protein from Saccharomyces cerevisiae, show that this domain, only 35 amino acids in length, defines the smallest monomeric triple-stranded antiparallel β-sheet protein domain that is stable in the ...
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1038/75144
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  • 8
    Digitale Medien
    Digitale Medien
    A simplification of the protein assay method of Ramsay et al. for the quantification of Thiobacillus ferrooxidans in the presence of ferric precipitates (2000)
    Springer
    Applied microbiology and biotechnology 53 (2000), S. 722-725 
    Details
    ISSN: 1432-0614
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Abstract A variation on Ramsay's method for microbial protein determination has been developed in order to quantify Thiobacillus ferrooxidans attached to ferric precipitates or in aqueous suspensions containing such precipitates. Some modifications have been introduced to provide a method that is more sensitive, simple and rapid. A linear standard curve is presented to permit a direct correlation between the protein concentration (mg/l) and the cell concentration (106 cells/ml). An application of this method has been demonstrated in the quantification of biomass immobilized on the surface of polyurethane foam particles in a packed bed reactor, several experiments having been conducted to establish the best conditions for the quantification studies.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002530000321
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  • 9
    Digitale Medien
    Digitale Medien
    Comparative study of the kinetics of the thermal decomposition of synthetic and natural siderite samples (2000)
    Springer
    Physics and chemistry of minerals 27 (2000), S. 495-503 
    Details
    ISSN: 1432-2021
    Schlagwort(e): Key words Thermal decomposition ; Kinetics ; Siderite ; CRTA
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: Abstract The mechanism of the thermal decomposition of two siderites (a pure synthetic and a natural Mg-containing sample) has been determined from comparison of the results obtained from linear heating rate (TG) and constant rate thermal analysis (CRTA) experiments in high vacuum. The thermal decomposition of the synthetic siderite takes place approximately 200 K below the decomposition temperature of the natural sample. The mechanism and the product of the thermal decomposition are different for the siderite samples. In fact, an A2 kinetic model describes the thermal decomposition of the synthetic siderite, whereas the thermal decomposition of the natural sample obeys an F1 kinetic law. Decomposition products of the synthetic siderite are iron and magnetite, those of the natural siderite are wüstite and minor magnetite.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002690000093
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  • 10
    Digitale Medien
    Digitale Medien
    Crystal structures and voltammetric behavior of three copper(II) complexes derived from bulky Schiff bases (2000)
    Springer
    Transition metal chemistry 25 (2000), S. 511-517 
    Details
    ISSN: 1572-901X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Three Schiff base copper(II) complexes have been prepared and characterized by elemental analysis, mass spectra, i.r., electronic spectra, μeff and X-ray crystal structures. Cyclic voltammetry studies on the complexes indicate a dependence of the cathodic potentials upon electronic effects, but independence on the solid state structure.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1007028814788
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