Search Results - (Author, Cooperation:C. Westphal)

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  1. 1
    L. A. Garibaldi ; I. Steffan-Dewenter ; R. Winfree ; M. A. Aizen ; R. Bommarco ; S. A. Cunningham ; C. Kremen ; L. G. Carvalheiro ; L. D. Harder ; O. Afik ; I. Bartomeus ; F. Benjamin ; V. Boreux ; D. Cariveau ; N. P. Chacoff ; J. H. Dudenhoffer ; B. M. Freitas ; J. Ghazoul ; S. Greenleaf ; J. Hipolito ; A. Holzschuh ; B. Howlett ; R. Isaacs ; S. K. Javorek ; C. M. Kennedy ; K. M. Krewenka ; S. Krishnan ; Y. Mandelik ; M. M. Mayfield ; I. Motzke ; T. Munyuli ; B. A. Nault ; M. Otieno ; J. Petersen ; G. Pisanty ; S. G. Potts ; R. Rader ; T. H. Ricketts ; M. Rundlof ; C. L. Seymour ; C. Schuepp ; H. Szentgyorgyi ; H. Taki ; T. Tscharntke ; C. H. Vergara ; B. F. Viana ; T. C. Wanger ; C. Westphal ; N. Williams ; A. M. Klein
    American Association for the Advancement of Science (AAAS)
    Published 2013
    Staff View
    Publication Date:
    2013-03-02
    Publisher:
    American Association for the Advancement of Science (AAAS)
    Print ISSN:
    0036-8075
    Electronic ISSN:
    1095-9203
    Topics:
    Biology
    Chemistry and Pharmacology
    Computer Science
    Medicine
    Natural Sciences in General
    Physics
    Keywords:
    Animals ; Bees/physiology ; Crops, Agricultural/*growth & development ; Flowers/physiology ; Fruit/*growth & development ; Insects/*physiology ; *Pollination
    Published by:
    http://www.aaas.org/

    Latest Papers from Table of Contents or Articles in Press
  2. 2
    Barbeta, V. B. ; Westphal, C. H. ; Jardim, R. F. ; Maple, M. B. ; Obradors, X.

    [S.l.] : American Institute of Physics (AIP)
    Published 1993
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Systematic studies of transport and magnetic properties on polycrystalline Nd1.85Ce0.15CuO4−y specimens under applied magnetic fields as high as 8 kOe have revealed strong evidence of granularity in this system. Electrical resistivity measurements show two superconducting transitions. One of the transitions occurs at higher temperature and is almost insensitive to applied magnetic field and current density, while the other one occurs at lower temperature and is strongly modified by the application of magnetic field and changes in the current density. In the low-field limit (H〈100 Oe), a drastic broadening of the superconducting transition is observed. Magnetic susceptibility χac measurements show similar features. There are two well-defined contributions to the diamagnetic signal below 20 K which are particularly evident in the resistive component of χac where two peaks can be identified. The application of an applied magnetic field shifts both peaks towards low temperatures. All the results can be satisfactorily explained in terms of weakly linked Josephson junctions between superconducting islands. The islands have a superconducting transition at higher temperature, and the long-range order phase coherence is achieved through Josephson coupling at lower temperatures.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.352539

    Articles: DFG German National Licenses
  3. 3
    Escote, M. T. ; Westphal, C. H. ; Jardim, R. F.

    [S.l.] : American Institute of Physics (AIP)
    Published 2000
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Polycrystalline samples of LnNi0.3Co0.7O3 (Ln=La, Pr) were prepared through sol-gel precursors. The samples were subjected to several heat treatments at temperatures ranging from 650 to 1000 °C and under oxygen pressure as high as 70 bar. Characterizations of x-ray powder diffraction XRD magnetization M(T), and ac magnetic susceptibility χac(T) were performed on these compounds. The results of XRD showed that samples of LaNi0.3Co0.7O3 crystallize in a rhombohedral distorted perovskite structure (R3¯c) and that PrNi0.3Co0.7O3 compounds displayed an orthorhombically distorted structure (Pbnm). The temperature dependence of M(T) revealed the presence of a sharp cusp occurring at temperatures TP∼60 and ∼ 30 K for Ln=La and Pr, respectively. Below TP, the M(T) curves taken after different thermal cycles, i.e., field cooled and zero-field cooled processes, are histories dependent on the magnitude of M(T) decreasing with increasing applied magnetic field. We have also observed that TP decreases with increasing applied magnetic field. Measurements of χac(T) at zero applied magnetic field in all samples studied revealed one peak anomaly occurring at temperatures Tf=58 and 30 K for La and Pr, respectively. In fact, increasing frequency over four orders of magnitude results in a shift of the peak anomaly to higher temperatures, as expected for a spin-glass system. Also, a broadening of the peak anomaly is observed with the application of an external magnetic field and it evolves in two peaks at H as high as ∼ 500 Oe. Thus the χac(T) curves reveal two well-defined peaks: one, which is essentially frequency independent and another that is shifted to higher temperatures with increasing frequency. The origin of these magnetic behaviors is discussed. © 2000 American Institute of Physics.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.372563

    Articles: DFG German National Licenses
  4. 4
    Kaduwela, A. P. ; Xiao, H. ; Thevuthasan, S. ; Westphal, C. ; Van Hove, M. A. ; Fadley, C. S.

    [S.l.] : American Institute of Physics (AIP)
    Published 1994
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Magnetic circular dichroism (MCD) in x-ray absorption represents an exciting new technique for studying and imaging magnetic systems. However, there are to date relatively few studies of dichroism in the inherent process involved: photoelectron emission. We will here illustrate that photoelectron diffraction (PD) theory provides a fruitful way of analyzing dichroism data for both nonmagnetic and magnetic systems. Circular dichroism (CD) has been observed in core-level photoemission from nonmagnetic systems: C 1s from CO/Pd(111) and Si 2p from Si(100). For CO/PD(111), chirality in the experimental geometry is readily discernible, but for Si(100), it is more difficult to define the chirality with simple vector relationships. PD effects implicitly contain all information on such core-level dichroism, and we will present multiple-scattering simulations of the observations to date. We will also discuss the role of such CD effects in core-level MCD measurements, using Fe 2p emission from magnetically aligned Fe(110) as an example. The analysis of such MCD data has so far been qualitative. We will present a more quantitative analysis including final-state effects such as the interference of l±1 photoelectron channels and spin-dependent scattering and diffraction.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.358229

    Articles: DFG German National Licenses
  5. 5
    Jardim, R. F. ; Westphal, C. H. ; Cohenca, C. H. ; Ben-Dor, L. ; Maple, M. B.

    [S.l.] : American Institute of Physics (AIP)
    Published 1996
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    We have performed measurements of ac magnetic susceptibility χac as a function of temperature and magnetic field on polycrystalline specimens of Sm2−xCexCuO4−y (0.15≤x≤0.18) prepared from a sol-gel precursor. All the samples studied show a striking double resistive superconducting transition. One of the resistive transitions occurs at a higher temperature Tci and the other one at a lower Josephson-coupling temperature Tcj. Magnetic measurements reveal the appearance of superconductivity below Tcj which is evident from the resistive component χ″ which peaks only at Tcj. Measurements made on pellets and crushed samples with average grain size ∼1 μm show essentially the same features. This suggests that Josephson coupling occurs inside physical grains with dimensions close to 5 μm. We have also utilized the behavior of the peak in the χ″ component as a function of applied magnetic fields to build a H vs T phase diagram for these compounds. Some interesting features were observed in this H vs T phase diagram: (1) a Hα, α=2/3, dependence at low applied magnetic fields (H≤2 kOe) and high temperatures, and (2) an abrupt increase in the magnitude of the exponent at high fields and low temperatures. The behavior at low fields and high temperatures suggests that the magnetic response of the system is mainly controlled by a disordered Josephson network. Possible connections between these two different behaviors are discussed. © 1996 American Institute of Physics.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.361947

    Articles: DFG German National Licenses
  6. 6
    Jardim, R. F. ; Westphal, C. H. ; Cohenca, C. H. ; Ben-Dor, L. ; Maple, M. B.

    [S.l.] : American Institute of Physics (AIP)
    Published 1994
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    A systematic study of transport and magnetic properties of polycrystalline Sm2−xCexCuO4−y (0.15≤x(very-much-less-than)0.18) specimens obtained from a sol-gel precursor reveals a striking double resistive superconducting transition. One of the resistive transitions takes place at a temperature Tci and is almost insensitive to Ce concentration, applied magnetic field, and current density, while the other transition occurs at a lower temperature Tcj and is very sensitive to Ce content, applied magnetic field, and current density. Alternating-current magnetic susceptibility χac measurements reveal two interesting features. There is only one contribution to the diamagnetic signal below ∼20 K, which is particularly evident in the resistive component χ‘ of χac where a peak at Tcj can be identified. The application of an applied magnetic field shifts the χ‘ peak to lower temperatures and reveals a spin-glass-like behavior. All the results can be satisfactorily explained in terms of weakly linked Josephson junctions between small superconducting islands. The small islands have a superconducting transition at a higher temperature Tci, and the long-range phase coherence is achieved through Josephson coupling at lower temperatures Tcj. All the results suggest a superconducting glass state in a disordered Josephson network.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.356849

    Articles: DFG German National Licenses
  7. 7
    Jardim, R. F. ; Westphal, C. H. ; Becerra, C. C. ; Paduan-Filho, A.

    [S.l.] : American Institute of Physics (AIP)
    Published 1997
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    We have studied the structural, magnetic, and transport properties of polycrystalline (Nd1−xGdx)1.85Ce0.15CuO4−y; x=0.0, 0.05, 0.10, 0.25, and 0.50; produced under different atmospheres and cooling rates after the reduction process. From x-ray analysis the T′-structure is preserved for all samples studied. We also found that quenched samples in argon atmosphere exhibit superconductivity below ∼22 K. The temperature dependence of the electrical resistivity ρ(T) displays a striking double resistive superconducting transition with no evidence of a zero resistance state down to 1.5 K. The electrical resistivity has a (approximate)20% drop at the upper critical temperature Tci followed by a plateau down to a lower temperature Tcj. While Tci is both weakly dependent on the Gd content and external applied magnetic field, the behavior of ρ(T) at low temperatures is strongly sensitive to the Gd concentration, excitation current, and applied magnetic fields. Also, the behavior of ρ(T) below (approximate)3 K is almost field independent. The magnetic susceptibility data χ(T) reveal superconductivity below Tci and a reentrantlike behavior at low temperatures where the magnitude of χ(T) increases rapidly with decreasing temperature. These observations are similar to those observed in granular Ga films close to the nonmetallic side of the superconductor-insulator transition. We argue that these compounds can be understood within the framework of a superconducting granular model. © 1997 American Institute of Physics.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.365137

    Articles: DFG German National Licenses
  8. 8
    Staff View
    ISSN:
    0039-6028
    Source:
    Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics:
    Physics
    Type of Medium:
    Electronic Resource
    URL:
    http://linkinghub.elsevier.com/retrieve/pii/0039-6028(91)90593-H

    Articles: DFG German National Licenses
  9. 9
    Staff View
    ISSN:
    0039-6028
    Source:
    Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics:
    Physics
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1016/0039-6028(92)91321-2

    Articles: DFG German National Licenses
  10. 10
    Staff View
    ISSN:
    0039-6028
    Source:
    Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics:
    Physics
    Type of Medium:
    Electronic Resource
    URL:
    http://linkinghub.elsevier.com/retrieve/pii/0039-6028(91)90967-W

    Articles: DFG German National Licenses
  11. 11
    Westphal, C. ; Frosch, D.

    Amsterdam : Elsevier
    Staff View
    ISSN:
    0022-5320
    Source:
    Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics:
    Biology
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1016/S0022-5320(84)90126-6

    Articles: DFG German National Licenses
  12. 12
    Frosch, D. ; Westphal, C.

    Amsterdam : Elsevier
    Staff View
    ISSN:
    0892-0354
    Source:
    Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics:
    Electrical Engineering, Measurement and Control Technology
    Natural Sciences in General
    Type of Medium:
    Electronic Resource
    URL:
    http://linkinghub.elsevier.com/retrieve/pii/0892-0354(89)90002-6

    Articles: DFG German National Licenses
  13. 13
    Staff View
    ISSN:
    0042-207X
    Source:
    Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics:
    Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Physics
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1016/0042-207X(90)90281-3

    Articles: DFG German National Licenses
  14. 14
    Staff View
    ISSN:
    0167-2584
    Source:
    Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics:
    Physics
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1016/0167-2584(91)90388-8

    Articles: DFG German National Licenses
  15. 15
    Staff View
    ISSN:
    0167-2584
    Source:
    Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics:
    Physics
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1016/0167-2584(91)90840-N

    Articles: DFG German National Licenses
  16. 16
    Staff View
    ISSN:
    0304-8853
    Source:
    Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics:
    Physics
    Type of Medium:
    Electronic Resource
    URL:
    http://linkinghub.elsevier.com/retrieve/pii/0304-8853(92)90793-N

    Articles: DFG German National Licenses
  17. 17
    Staff View
    ISSN:
    0304-8853
    Source:
    Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics:
    Physics
    Type of Medium:
    Electronic Resource
    URL:
    http://linkinghub.elsevier.com/retrieve/pii/0304-8853(92)91511-Q

    Articles: DFG German National Licenses
  18. 18
    Frosch, D. ; Westphal, C. ; Bachhuber, K.

    Amsterdam : Elsevier
    Staff View
    ISSN:
    0304-3991
    Source:
    Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics:
    Electrical Engineering, Measurement and Control Technology
    Natural Sciences in General
    Physics
    Type of Medium:
    Electronic Resource
    URL:
    http://linkinghub.elsevier.com/retrieve/pii/0304-3991(85)90007-5

    Articles: DFG German National Licenses
  19. 19
    Staff View
    ISSN:
    0304-8853
    Source:
    Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics:
    Physics
    Type of Medium:
    Electronic Resource
    URL:
    http://linkinghub.elsevier.com/retrieve/pii/0304-8853(92)90289-Z

    Articles: DFG German National Licenses
  20. 20
    Staff View
    ISSN:
    0304-8853
    Source:
    Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics:
    Physics
    Type of Medium:
    Electronic Resource
    URL:
    http://linkinghub.elsevier.com/retrieve/pii/0304-8853(92)91546-6

    Articles: DFG German National Licenses