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  • Springer  (422)
  • American Institute of Physics (AIP)  (61)
  • Wiley-Blackwell
  • 2000-2004  (147)
  • 1985-1989  (372)
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  • 1
    ISSN: 1432-1327
    Keywords: Metal substitution Cerium binding Lactoferrin Crystal structure Transferrin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. Proteins of the transferrin family play a key role in iron homeostasis through their extremely strong binding of iron, as Fe3+. They are nevertheless able to bind a surprisingly wide variety of other metal ions. To investigate how metal ions of different size, charge and coordination characteristics are accommodated, we have determined the crystal structure of human lactoferrin (Lf) complexed with Ce4+. The structure, refined at 2.2 Å resolution (R=20.2%, R free=25.7%) shows that the two Ce4+ ions occupy essentially the same positions as do Fe3+, and that the overall protein structure is unchanged; the same closed structure is formed for Ce2Lf as for Fe2Lf. The larger metal ion is accommodated by small shifts in the protein ligands, made possible by the presence of water molecules adjacent to each binding site. The two Ce4+ sites are equally occupied, indicating that the known difference in the pH-dependent release of Ce4+ arises from a specific protonation event, possibly of the His ligand in one of the binding sites. Comparing the effects of binding Ce4+ with those for the binding of other metal ions, we conclude that the ability of transferrins to accommodate metal ions other than Fe3+ depends on an interplay of charge, size, coordination and geometrical preferences of the bound metal ion. However, it is the ability to accept the six-coordinate, approximately octahedral, site provided by the protein that is of greatest importance.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1572-9591
    Keywords: Fusion energy ; international collaboration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract This report was prepared by a Working Group at the request of the U.S. Department of Energy, Office of Fusion Energy Sciences in 1997. The report addresses technical opportunities for mutually beneficial collaboration between the United States and other international fusion research programs. A number of outstanding opportunities are discussed.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Behavioral ecology and sociobiology 23 (1988), S. 105-108 
    ISSN: 1432-0762
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The loud and elaborate songs of male songbirds are throught to serve in territorial defense and to stimulate reproductive behavior in the female. We report here that in contrast to several other species, song alone is inadequate to induce sexual (lordosis) behavior in female indigo and lazuli buntings (Passerina cyanea and P. amoena); they require a more elaborate stimulus configuration to develop the full expression of sexual receptivity as indicated by a stereotyped copulation solicitation display. A live male must be present near the female, singing must ensue, and in addition a second and unique vocal utterance must be heard by the female; this is a soft buzzy-sounding vocalization, audible for no more than a few meters, not recognized previously as a critical arousal signal of the male songbird repertoire. Females also utter similar soft sounds in an intimate vocal exchange with the male leading to solicitation of copulation.
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  • 4
    ISSN: 1573-5117
    Keywords: microstratification ; thin layer sampler ; heterogeneous water column ; chemocline ; stratification ; meromixis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A series of inexpensive, pneumatic thin layer water samplers is described. They can be operated from small boats, and permit sampling at 2.5 cm intervals with little or no disturbance of stratified systems such as oxyclines or redoxclines of meromictic lakes, or microstratification of flagellates in sheltered epilimnia. Some models permit replicate sampling at closely-spaced intervals in a two-dimensional array. Their performance abilities are illustrated with examples of microstratification.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Plant systematics and evolution 151 (1986), S. 175-186 
    ISSN: 1615-6110
    Keywords: Angiosperms. — Nectar ; amino acids ; pollinators ; sample size ; phylogenetic constraint ; evolutionary significance. — Flora of California
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Approximately 1 500 angiosperm species, in previous papers, have been sampled for the assessment of the amino acids (a. a.) in their nectar. We reaffirm that the findings provide statistically significant data linking differences in the concentration with pollinator type. Flowers that are pollinated by animals that have alternative sources of protein-building a. a.’s show lower a. a. concentration than those that are not. There is a tendency for woody plant nectar a. a.’s to be less concentrated than those of herbaceous plants, but there can be “phylogenetic constraints” which may reduce the correlations of a. a. concentration with pollinator type and with life form. The individual a. a.’s form complements which are qualitatively extremely constant within species. Proline is a normal constituent of many nectars and does not necessarily indicate contamination of the nectar by pollen. Criticism of our findings byGottsberger & al. (1984) is answered by reference to our previous publications and those of other workers, and to the presentation of data from California native species, not published previously. All previous postulates are borne out by these new data with the exception of positive correlations of a. a. concentration with “primitive” and “advanced” floral characteristics taken one at a time, which appear to be inconsistent and are affected strongly by the nature of the family in which they occur. Summary data are provided for families and genera which indicate that high or low a. a. concentration can typify certain families and genera of both relatively “primitive” and relatively “advanced” nature. Needs for future research on an ecosystem basis are quoted.
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  • 6
    ISSN: 1615-6110
    Keywords: Angiosperms ; Leguminosae ; Mimosoideae ; Acacia terminalis ; Bee- and bird-pollination ; extrafloral nectaries ; intraspecific variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Intraspecific variation has been found for several pollination-related characteristics in two isolated populations of the self-incompatible treeAcacia terminalis: floral characteristics including colour and flowering time; style length; size and colour of extrafloral nectaries on the leaf petioles; chemical components of the extrafloral nectar; different taxa of bee pollinators; and frequency differences in bird pollinators. These differences possibly reflect the evolution of two different pollination syndromes within this species.
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  • 7
    Publication Date: 1985-03-01
    Print ISSN: 0018-8158
    Electronic ISSN: 1573-5117
    Topics: Biology
    Published by Springer
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 6566-6572 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present an improved version of our recent algorithm [B. Paizs, G. Fogarasi, and P. Pulay, J. Chem. Phys. 109, 6571 (1998)] for optimizing the geometries of large molecules. The approximate Cholesky factorization technique has been generalized to the case of redundant coordinates, and an alternative approach involving use of the B†B matrix in the iterative coordinate back transformation is described. The generalized full Cholesky factors of B†B are very sparse and the corresponding force and geometry transformations are fast and numerically stable, permitting us to apply this technique for internal coordinate geometry optimization of molecules containing thousands of atoms. As an example we present optimization data on alpha-helical alanine polypeptides, and various globular proteins. Results for the alanine polypeptides indicates that internal coordinate optimization is clearly superior to the first-order Cartesian optimization techniques generally used in force field calculations. The largest system investigated is alpha-helical Ac-(Ala)999-NH2 containing 9999 atoms, which was successfully optimized using less than a megaword of memory. Optimization of various globular proteins shows that our procedure can easily deal with highly redundant (including full primitive) coordinate sets. © 2000 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3277-3281 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We point out that the creation of a soliton pulse train in a nonlinear-dispersive system can be used for the generation of high-power microwave bursts. A modulated transmission line with an appropriate nonlinear dielectric is proposed. The nonlinear wave evolution is analyzed and requirements for the dielectric material are found. Problems associated with the material are discussed. Low-power experimental demonstrations of these concepts are presented.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 761-765 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An electron channeling study has been done on large grained YBa2Cu3Ox samples. Selected area channeling patterns (SACP) were used to examine several dozen grains on electropolished surfaces and it was demonstrated that (a) the twin planes observed in polarized optical light microscopy lie parallel to {110} crystal planes, and (b) the long flat sides of high aspect ratio grains are formed by basal planes, and the shorter sides are formed by either (010), (100), or {110} planes. A majority of the large grains examined were found to contain subgrains, misaligned by 0.5°–1° and ranging in size from less than 3 to 20 μm. The origin of the subgrains is not understood.
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