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  • Springer  (22)
  • American Association for the Advancement of Science (AAAS)  (3)
  • 2000-2004  (15)
  • 1990-1994  (10)
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  • 1
    Electronic Resource
    Electronic Resource
    Modulating the hydroxylamine accumulation in the hydrogenation of substituted nitroarenes using vanadium-promoted RNi catalysts (2000)
    Springer
    Topics in catalysis 13 (2000), S. 205-212 
    Details
    ISSN: 1572-9028
    Keywords: hydrogenation of aromatic nitro compounds ; Raney nickel ; vanadium promoter ; modified catalysts ; aryl hydroxylamine ; chloronitrobenzene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The effect of vanadium promotion of Raney nickel on aryl hydroxylamine accumulation in the catalytic hydrogenation of electron deficient aromatic nitro compounds was investigated. High accumulation of 70–80% was observed with unmodified Raney nickel. Vanadium promoters were able to modulate the accumulation and depending on the modifier used, an increase (up to 86%) or a decrease (down to 11%) was found. Higher rates were obtained in the former (up to a factor 1.3), lower ones in the latter case (down to a factor 0.1) compared to the unmodified system. Supported or unsupported NH4VO3 was usually the most efficient modifier for obtaining low accumulation and reasonable rates, but the optimum concentration and modification procedure had to be determined for every substrate separately. In cases of low accumulation, the vanadium promoters worked as disproportionation catalysts. Dehalogenation was not significantly influenced by the presence of promoters: in all cases dehalogenation took only place after both the nitro arene and aryl hydroxylamine compound had been consumed completely.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009050804228
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  • 2
    Electronic Resource
    Electronic Resource
    Chromium doped manganites: evidence for electronically phase-separated systems (2000)
    Springer
    The European physical journal 18 (2000), S. 233-240 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 75.30.Vn Colossal magnetoresistance - 78.70.Dm X-ray absorption spectra - 75.25.+z Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: X-ray absorption spectroscopy (XAS) and soft-X-ray magnetic circular dichroism (SXMCD) at the Mn L2,3-, Cr L2,3- and O-K edges of Sm0.5Ca0.5Mn1-xCrxO3 ( ) bulk polycrystalline samples have been performed at T=20 K below the ferromagnetic Curie temperature. We show the existence of a magnetic sublattice on each of the probed cations. Considering an electronically phase-separated system, results are compared with magnetization and resistivity measurements and a tentative correlation with magnetoresistance properties on such doped compounds is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100510070053
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  • 3
    Electronic Resource
    Electronic Resource
    Enantioselective Homogeneous Hydrogenation of Monosubstituted Pyridines and Furans (2000)
    Springer
    Monatshefte für Chemie 131 (2000), S. 1335-1343 
    Details
    ISSN: 1434-4475
    Keywords: Keywords. Homogeneous catalysis; Enantioselective hydrogenation; Heterocyclic arenes; Rh diphosphine complexes.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary.  The first case of an enantioselective hydrogenation of monosubstituted pyridines and furans with homogeneous rhodium diphosphine catalysts with low but significant enantioselectivities and catalyst activities is reported. Best enantioselectivities (ees of 24–27%) were obtained for the hydrogenation of 2- and 3-pyridine carboxylic acid ethyl ester and 2-furan carboxylic acid with catalysts prepared in situ from [Rh(nbd)2]BF4 and the chiral ligands diop, binap, or ferrocenyl diphosphines of the josiphos type. Turnover numbers (ton) were in the order of 10–20, turnover frequencies (tof) usually 1–2 h−1. Diphosphines giving 6- or 7-ring chelates led to higher ees than 1,2-diphosphines; otherwise, no clear correlation between ligand properties and catalytic performance was found. In some experiments black precipitates were observed at the end of the reaction, indicating the decomposition of the homogeneous catalysts for certain ligand/metal/substrate combinations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007060070013
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  • 4
    Electronic Resource
    Electronic Resource
    Boundary conditions for quantum mechanics on cones and fields around cosmic strings (1991)
    Springer
    Communications in mathematical physics 139 (1991), S. 103-139 
    Details
    ISSN: 1432-0916
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Abstract We study the options for boundary conditions at the conical singularity for quantum mechanics on a two-dimensional cone with deficit angle ≦ 2π and for classical and quantum scalar fields propagating with a translationally invariant dynamics in the 1+3 dimensional spacetime around an idealized straight infinitely long, infinitesimally thin cosmic string. The key to our analysis is the observation that minus-the-Laplacian on a cone possesses a one-parameter family of selfadjoint extensions. These may be labeled by a parameterR with the dimensions of length—taking values in [0, ∞). ForR=0, the extension is positive. WhenR≠0 there is a bound state. Each of our problems has a range of possible dynamical evolutions corresponding to a range of allowedR-values. They correspond to either finite, forR=0, or logarithmically divergent, forR≠0, boundary conditions at zero radius. Non-zeroR-values are a satisfactory replacement for the (mathematically ill-defined) notion of δ-function potentials at the cone's apex. We discuss the relevance of the various idealized dynamics to quantum mechanics on a cone with a rounded-off centre and field theory around a “true” string of finite thickness. Provided one is interested in effects at sufficiently large length scales, the “true” dynamics will depend on the details of the interaction of the wave function with the cone's centre (/field with the string etc.) only through a single parameterR (its “scattering length”) and will be well-approximated by the dynamics for the corresponding idealized problem with the sameR-value. This turns out to be zero if the interaction with the centre is purely gravitational and minimally coupled, but non-zero values can be important to model nongravitational (or non-minimally coupled) interactions. Especially, we point out the relevance of non-zeroR-values to electromagnetic waves around superconducting strings. We also briefly speculate on the relevance of theR-parameter in the application of quantum mechanics on cones to 1+2 dimensional quantum gravity with massive scalars.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02102731
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  • 5
    Electronic Resource
    Electronic Resource
    U(1)×SU(2)-gauge invariance of non-relativistic quantum mechanics, and generalized Hall effects (1992)
    Springer
    Communications in mathematical physics 148 (1992), S. 553-600 
    Details
    ISSN: 1432-0916
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Abstract We show that the non-relativistic quantum mechanics of particles with spin coupled to an electromagnetic field has a naturalU(1)×SU(2) gauge invariance. Ward identities reflecting this gauge invariance combined with an assumption of incompressibility of a system of such particles in an appropriate external field and for suitable values of the particle density permit us to determine the form of the effective action of the system as a functional of small fluctuations in the electromagnetic field, in the large-distance-, adiabatic limit. In this limit, the action is found to have a universal form. We present explicit results for two-dimensional, incompressible electron fluids and apply them to derive the equations of linear response theory, describing a variety of generalized Hall effects. Sum rules for the Hall conductivities, magnetic susceptibilities and other quantities of physical interest are found.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02096549
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  • 6
    Electronic Resource
    Electronic Resource
    High-pressure freezing of soybean nodules leads to an improved preservation of ultrastructure (1992)
    Springer
    Planta 188 (1992), S. 155-163 
    Details
    ISSN: 1432-2048
    Keywords: Bradyrhizobium ; Electron microscopy ; Glycine (root nodules) ; High-pressure freezing ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract High-pressure freezing of chemically untreated nodules of soybean (Glycine max (L.) Merr.), in sharp contrast to chemical fixation and prefixation, appears to preserve the ultrastructure close to the native state. This is supported by the observation that the peribacteroid membrane of high-pressure-frozen samples is tightly wrapped around the bacteroids, a finding that is fully consistent with the current views on the physiology of oxygen and metabolite transport between plant cytosol and bacteroids. In soybean root nodules, the plant tissue and the enclosed bacteria are so dissimilar that conventional aldehyde-fixation procedures are unable to preserve the overall native ultrastructure. This was demonstrated by high-pressure freezing of nodules that had been pre-fixed in glutaraldehyde at various buffer molalities: no buffer strength tested preserved all ultrastructural aspects that could be seen after high-pressure freezing of chemically untreated nodules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00216809
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  • 7
    Electronic Resource
    Electronic Resource
    Transport of volatile chlorinated hydrocarbons in unsaturated aggregated media (1993)
    Springer
    Water, air & soil pollution 68 (1993), S. 291-305 
    Details
    ISSN: 1573-2932
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Transport of volatile hydrocarbons in soils is largely controlled by interactions of vapours with the liquid and solid phase. Sorption on solids of gaseous or dissolved compounds may be important. Since the contact time between a chemical and a specific sorption site can be rather short, kinetic or mass-transfer resistance effects may be relevant. An existing mathematical model describing advection and diffusion in the gas phase and diffusional transport from the gaseous phase into an intra-aggregate water phase is modified to include linear kinetic sorption on gas-solid and water-solid interfaces. The model accounts for kinetic mass transfer between all three phases in a soil. The solution of the Laplace-transformed equations is inverted numerically. We performed transient column experiments with 1,1,2-Trichloroethane, Trichloroethylene, and Tetrachloroethylene using air-dry solid and water-saturated porous glass beads. The breakthrough curves were calculated based on independently estimated parameters. The model calculations agree well with experimental data. The different transport behaviour of the three compounds in our system primarily depends on Henry's constants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00479409
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  • 8
    Electronic Resource
    Electronic Resource
    Two-dimensional spin freezing in Y1−z Ca z Ba2Cu3−x Fe x O7 (1993)
    Springer
    Hyperfine interactions 77 (1993), S. 277-299 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Hyperfine electric and magnetic interactions in Y1−z Ca z Ba2Cu3−x Fe x O6+y compounds have been studied for different rates of Fe and Ca substitution (x=0.09 and 0.24;z=0.24;y=0−1) by57Fe Mössbauer spectroscopy of powder samples obtained by different thermal treatments. Calculations of the Fe3+ EFG tensor have been performed for different coordination polyhedra in Cu1 and Cu2 sites. Variations of the direction, amplitude and of the sign of the principal component of the EFG are reported versus the iron displacement from the ideal Cu sites inside the pyramidal and tetrahedral coordination polyhedra. Calculated ΔE Q and η values are compared with the experimental ones. For the Cu2 site, faithfully probed in both oxygen-depleted and oxygen-saturated samples by fairly large fraction of residing iron atoms, the mutual orientations of the axes of the principal EFG component and that of easiest magnetization are deduced from interrelations between quadrupole parameters for paramagnetic quadrupolar and magnetic Zeeman Mössbauer spectra. In the desoxygenated samples, the coexistence of a long range 2D antiferromagnetic order and of a spin-glass order has been evidenced. For the oxygen-saturated samples, the two-dimensional spin-glass order is observed belowT f =10 K. The Mössbauer spectra under applied fields at 4.2 K show an easy polarization of the spins in the Cu2 sites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02320318
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  • 9
    Electronic Resource
    Electronic Resource
    Damage processes in Fe 3 O 4 magnetic insulator irradiated by swift heavy ions. Experimental results and modelisation (2001)
    Springer
    The European physical journal 24 (2001), S. 291-295 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 61.80.Jh Ion radiation effects – 75.60.-d Domain effects, magnetization curves, and hysteresis – 85.70.Ge Ferrite and garnet devices
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: The behavior of the magnetic properties of magnetite Fe3O4 irradiated by swift heavy ions is investigated by magnetization measurements. Although there is no induced structural phase transformation, both coercive field and saturation magnetization are sensitive to ion irradiation and exhibit different behaviors depending on the ion fluence range. In the low fluence regime, the coercive field increases, which is evidence for a strong pinning of magnetic domain boundaries by the induced defects. The magnetization shows a decrease in the saturation value and tends to reorient perpendicularly to the ion track axis. At high fluence, the initial magnetic properties of the sample are nearly restored. The changes in the magnitude and the direction of magnetization are interpreted by magnetostrictive effects related to the stress induced by irradiation. A phenomenological model is applied to reproduce the fluence evolution of the saturation magnetization, assuming relaxation of the stress induced around the core of defects of the tracks by overlapping effects at high fluence. The results are compared to those obtained in the case of yttrium iron garnet Y3Fe5O12.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s10051-001-8676-3
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  • 10
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    Differentiation of embryonic stem cell lines generated from adult somatic cells by nuclear transfer (2001)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2001-04-28
    Description: Embryonic stem (ES) cells are fully pluripotent in that they can differentiate into all cell types, including gametes. We have derived 35 ES cell lines via nuclear transfer (ntES cell lines) from adult mouse somatic cells of inbred, hybrid, and mutant strains. ntES cells contributed to an extensive variety of cell types, including dopaminergic and serotonergic neurons in vitro and germ cells in vivo. Cloning by transfer of ntES cell nuclei could result in normal development of fertile adults. These studies demonstrate the full pluripotency of ntES cells.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Wakayama, T -- Tabar, V -- Rodriguez, I -- Perry, A C -- Studer, L -- Mombaerts, P -- New York, N.Y. -- Science. 2001 Apr 27;292(5517):740-3.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉The Rockefeller University, New York, NY 10021, USA. teru@advancedcell.com〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11326103" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Blastocyst/*cytology ; *Cell Differentiation ; Cell Line ; Cell Lineage ; Chimera ; Cloning, Organism ; Crosses, Genetic ; Dopamine/metabolism ; Embryo Transfer ; Female ; Germ Cells/*cytology ; Male ; Mice ; Mice, Inbred C57BL ; Mice, Inbred DBA ; Mice, Inbred ICR ; Mice, Nude ; Neurons/*cytology ; *Nuclear Transfer Techniques ; Serotonin/metabolism ; Stem Cells/*cytology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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