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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
    Search for catalytic properties of simple polypeptides (1987)
    Springer
    Origins of life and evolution of the biospheres 17 (1987), S. 381-390 
    Details
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Simple polypeptides were used as possible supports for nucleotide polymerization, in the absence of any preformed polynucleotide template. Sequential copolymers of alanine and glycine, water soluble polypeptides based on arginine and poly(Glu-SerGlu) have been tested. No catalytic effect has been found although poly(Glu-Ser-Glu) favors the 2′–5′ internucleotide linkage. More interestingly, polypeptides containing arginine residues strongly accelerate the hydrolysis of oligoadenylic acids. The influence of pH, temperature, nature of the buffer and polypeptide sequence was investigated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02386476
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  • 6
    Electronic Resource
    Electronic Resource
    Selective emergence and survival of early polypeptides in water (1987)
    Springer
    Origins of life and evolution of the biospheres 17 (1987), S. 367-379 
    Details
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Oligopeptides essential to primitive cells could not be obtained just by raising the background noise of organic compounds produced by a prebiotic chemistry working at random. Selection pathways were required. Experimental evidence is given for selective condensation of amino acids in water as well as for selective resistance to degradation. It is shown that N-carboxyanhydrides are good candidates for chemical selection in water. They are formed when active esters of amino acids are left in the presence of bicarbonate ions or when N,N'-carbonyldiimidazole is used as condensing agent. Polymerization of a mixture of proteinaceous and non-proteinaceous amino acids leads to an enrichment in the proteinaceous ones plusα-aminobutyric acid. Selective resistance toward degradation ofβ-pleated sheet conformation is used to exemplify a possible accumulation of homochiral sequences made of hydrophilic and strong hydrophobic residues. Amino acids with branched aliphatic side-chains are selected but those having short linear aliphatic side-chains such asα-aminobutyric acid or norvaline are not.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02386475
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  • 7
    Electronic Resource
    Electronic Resource
    Simplified method for wetland habitat assessment (1989)
    Springer
    Environmental management 13 (1989), S. 207-213 
    Details
    ISSN: 1432-1009
    Keywords: Wetlands ; Assessment technique ; Environmental impact ; Habitat evaluation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract This article presents a wetland habitat assessment technique (HAT) using birds as indicators of habitat quality. The technique is quick, simple, inexpensive, and lends itself to screening large numbers of wetlands. HAT can provide input to more extensive evaluation techniques. Measures of species diversity and rarity are used to assess the quality of the wetland. By applying the notion of ecologically optimum size, the technique addresses the issue of economic efficiency. Results of field testing HAT on 11 tidally influenced wetlands are presented to illustrate HAT's utility. Application of HAT in a variety of situations is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868367
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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    Influence of simple polypeptides on nucleotide polymerization (1986)
    Springer
    Origins of life and evolution of the biospheres 16 (1986), S. 452-453 
    Details
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02422129
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  • 10
    Electronic Resource
    Electronic Resource
    Emergence and survival of protein-like peptides in water (1986)
    Springer
    Origins of life and evolution of the biospheres 16 (1986), S. 486-486 
    Details
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02422150
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