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  • Articles  (20)
  • Springer  (20)
  • 2000-2004  (9)
  • 1980-1984  (11)
  • 1950-1954
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  • Articles  (20)
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  • 1
    Electronic Resource
    Electronic Resource
    Semiclassical calculations with nuclear model potentials in the ħ-resummation approach (1984)
    Springer
    The European physical journal 315 (1984), S. 341-347 
    Details
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The single-particle densityρ(r) of a system of fermions can be calculated in a tractable way as the Laplace inverse of the Bloch density describing the system. The complex integrals involved can be solved very easily by the saddle-point method. The semiclassical nature of this approach is illustrated in the simple example of the single-particle level density of a harmonic oscillator potential. It is then applied to calculate the total energy of particles in different mean field potentials. The exact Bloch density being generally unknown, different approximate forms are used in our calculations which correspond to a partial resummation of the Wigner-Kirkwoodħ-expansion. The resulting local densities reproduce the exact density distributions on the average, without quantal oscillations. They are well defined everywhere, even beyond the classical turning point, in contrast to the original Wigner-Kirkwood approach.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01438459
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  • 2
    Electronic Resource
    Electronic Resource
    Partial resummation ofℏ-expansion of the Bloch density for non local potentials (1980)
    Springer
    The European physical journal 296 (1980), S. 87-90 
    Details
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Wigner-Kirkwoodℏ-expansion of the Wigner transform of the Bloch density can be resummed in the case of non local potentials if we keep only up to second order derivatives of the Wigner transform of the non-local potential with respect to the phase space variables. We also investigate a second approximation to the Bloch density where care has been taken with respect to a consistentℏ expansion. For a one dimensional example we calculate the smooth part of the density and the corresponding energy demonstrating that both approximations to the Bloch-density yield well defined average densitiesand energies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01415620
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  • 3
    Electronic Resource
    Electronic Resource
    β-structures of polypeptides with L- and D-residues (1980)
    Springer
    Journal of molecular evolution 15 (1980), S. 231-238 
    Details
    ISSN: 1432-1432
    Keywords: β-structure ; Poly-DL-peptides ; Kinetics of hydrolysis ; Enantiomer enrichment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary It was previously shown that nuclei ofβ-sheets surrounded by unordered segments are formed in polypeptide chains built up with alternating hydrophobic and hydrophilic residues and containing both L- and D-enantiomers. It was also established that segments of residues having the same configuration tend to segregate in these nuclei when the starting composition of stereomonomers departs from the racemic mixture. Soft acidic hydrolysis of these polymers has been studied. Kinetic measurements show two pseudo first order rate constants, in agreement with the existence of two conformational species. The unordered part of the chains is hydrolyzed more rapidly, allowing the isolation of aβ-fraction enriched in one enantiomer. Thus, a plausible process of enrichment in enantiomer during prebiotic evolution has been described, which however does not explain the preference of one enantiomer over the other one.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01732950
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  • 4
    Electronic Resource
    Electronic Resource
    Prebiotic synthesis and organization of biopolymer-like macromolecules (1984)
    Springer
    Origins of life and evolution of the biospheres 14 (1984), S. 229-236 
    Details
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Prebiotic synthesis of bio-oligomers containing more than five units are examined with respect to chemical divergence and physical dispersion of the products. Experiments are presented which support a possible pathway running from a primitive mixture of amino acids to peptides organized into stereospecific β-sheet surfaces. This pathway includes selective condensation of amino acids through the racemization-free N-carboxyanhydride polymerization, specific aggregation of alternating sequences with hydrophilic and hydrophobic residues and enantioselection of homochiral sequences.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00933662
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  • 5
    Electronic Resource
    Electronic Resource
    Identification of Olfactory Stimulants for Anopheles gambiae from Human Sweat Samples (2000)
    Springer
    Journal of chemical ecology 26 (2000), S. 1367-1382 
    Details
    ISSN: 1573-1561
    Keywords: Anopheles gambiae ; behavior ; electroantennogram ; human sweat ; identification ; malaria mosquito ; indole ; geranyl acetone ; 6-methyl-5hepten-2-one ; 1-dodecanol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The behavioral and electroantennogram (EAG) responses of female Anopheles gambiae mosquitoes to pooled samples of freshly collected human sweat and human sweat incubated for 42–52 hr were tested. No behavioral or EAG response was obtained to pooled fresh sweat samples, whereas incubated pooled sweat samples produced a behavioral as well as an EAG response. GC-MS analysis of the headspace composition of the fresh sweat revealed ethanol (15.1% of the total amount of volatiles trapped), acetic acid (10.9%), and 3-hydroxy-2-butanone (9.5%) as the most abundant compounds; a wide range of ethyl esters was present as well. None of the ethyl esters was detected in the headspace collections from incubated sweat, while the relative amounts of ethanol, acetic acid, and 3-hydroxy-2-butanone were strongly reduced. In the latter collections, indole (27.9%), 1-dodecanol (22.4%), and 3-methyl-1-butanol (10%) were present in high amounts, while they were absent or present in only minor amounts in the headspace collections from fresh sweat. Geranyl acetone (6%) and 6-methyl-5-hepten-2-one (1.9%) were relatively abundant in both the fresh and incubated headspace samples. EAG responses were observed in response to indole, 6-methyl-5-hepten-2-one, and geranyl acetone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005475422978
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  • 6
    Electronic Resource
    Electronic Resource
    Experimental Evaluation of a Model for Oxygen Exchange in a Pulsating Intravascular Artificial Lung (2000)
    Springer
    Annals of biomedical engineering 28 (2000), S. 160-167 
    Details
    ISSN: 1573-9686
    Keywords: Respiratory support ; Artificial lung ; Intravenous oxygenation ; Hollow fibers ; Gas transfer ; Gas exchange ; IMO
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Intravascular oxygenation and carbon dioxide removal remains a potentially attractive means for respiratory support in patients with acute or chronic respiratory failure. Our group has been developing an intravascular hollow fiber artificial lung that uses a pulsating balloon located within the fiber bundle to augment gas transfer. We previously reported on a simple compartmental model for simulating O2 exchange in pulsating intravascular artificial lungs. In this study we evaluate the O2 exchange model with gas exchange and PO2 measurements performed on an idealized intravascular artificial lung (IIVAL) tested in a water perfusion loop. The IIVAL has well-defined bundle geometry and can be operated in balloon pulsation mode, or a steady perfusion mode for determining the mass transfer correlation required by the model. The O2 exchange rates and compartmental O2 tensions measured with balloon pulsation in the IIVAL are within 10% of model predictions for flow and pulsation conditions relevant to intravascular oxygenation. The experiments confirmed that a significant buildup of PO2 occurs within the fiber bundle, which reduces the O2 exchange rate. The agreement between experiments and predictions suggests that the model captures the cardinal processes dictating gas transfer in pulsating intravascular artificial lungs. © 2000 Biomedical Engineering Society. PAC00: 8780-y, 8710+e
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.240
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  • 7
    Electronic Resource
    Electronic Resource
    Enantiomer enrichment in early peptides (1981)
    Springer
    Origins of life and evolution of the biospheres 11 (1981), S. 135-142 
    Details
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract The two main ordered conformations of polypeptides, the α-helix and the β-sheet, were considered as possible asymmetric supports for stereoselection processes leading to the enrichment in one enantiomer. α-Helices can accomodate residues of both chirality distributed in the same chain, whereas the formation of β-sheets arises from the association of chain segments containing at least seven residues of the same chirality. When the residue composition departs from the racemic mixture, one handedness of the helix is favored, whereas the β-sheet nuclei become predominantly of a unique chirality. Taking into account these observations, processes of enrichment specific for α-and β-structures were envisaged theoretically as well as experimentally.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00928004
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  • 8
    Electronic Resource
    Electronic Resource
    Non-adiabatic effects in the time dependent level crossing problem (1984)
    Springer
    The European physical journal 319 (1984), S. 159-165 
    Details
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We discuss the exact solution of the time-dependent Schrödinger equation for a system of two crossing levels with a residual interaction. In contrast to the familiar Landau-Zener (LZ) solution used in most applications, we allow for more general boundary conditions; in particular we treat explicitly the case of afinite interval around the crossing point. The exact jumping probability is shown to be extremely sensitive to these boundary conditions; in many realistic cases it is found to be smaller than the LZ value by several orders of magnitude. We also compare the exact excitation energy to the one obtained in the usual cranking approach.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01415629
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  • 9
    Electronic Resource
    Electronic Resource
    The nuclear surface as a collective variable (1984)
    Springer
    The European physical journal 319 (1984), S. 205-213 
    Details
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In heavy nuclei where the thickness of the diffused edge is relatively small, a certain sharp effective surface can be defined which characterizes the shape of the nucleus, and it can be considered as a collective dynamic variable. It is shown that the problem of fluid dynamics can be simplified by reducing it to simple linearized equations for the dynamics in the nuclear interior and boundary conditions set at the effective dynamic sharp surface of the density distribution. These conditions are derived from the fluid dynamical equations. Transitional densities obtained from this simple model are compared with the numerical solution of fluid dynamical equations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01415634
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  • 10
    Electronic Resource
    Electronic Resource
    Validity of the semiclassical kinetic energy density functional for deformed nuclear shapes (1980)
    Springer
    The European physical journal 297 (1980), S. 247-256 
    Details
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We investigate the semiclassical kinetic energy density functionalτ[ρ] for deformed nuclear shapes. Using Strutinsky-averaged quantities as reference, we demonstrate that the functionalτ[ρ] is able to reproduce the averaged kinetic energies very accurately, even at very large deformations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01892805
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