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981.
The structures of the modulated phases of K2SeO4, Rb2ZnCl4, Rb2ZnCl4 and Cs2CdBr4 are compared. Both commensurate and incommensurate modulations are considered. Clear common features can be derived between the polarization vectors of their primary harmonic modulations. Even distortions with very different modulation wavevectors present a clear correlation. 相似文献
982.
A time-dependent box model is developed to calculate oxygen isotope compositions of bone phosphate as a function of environmental and physiological parameters. Input and output oxygen fluxes related to body water and bone reservoirs are scaled to the body mass. The oxygen fluxes are evaluated by stoichiometric scaling to the calcium accretion and resorption rates, assuming a pure hydroxylapatite composition for the bone and tooth mineral. The model shows how the diet composition, body mass, ambient relative humidity and temperature may control the oxygen isotope composition of bone phosphate. The model also computes how bones and teeth record short-term variations in relative humidity, air temperature and δ18O of drinking water, depending on body mass. The documented diversity of oxygen isotope fractionation equations for vertebrates is accounted for by our model when for each specimen the physiological and diet parameters are adjusted in the living range of environmental conditions. 相似文献
983.
Probing complex RNA structures by mechanical force 总被引:2,自引:0,他引:2
Harlepp S Marchal T Robert J Léger JF Xayaphoummine A Isambert H Chatenay D 《The European physical journal. E, Soft matter》2003,12(4):605-615
RNA secondary structures of increasing complexity are probed combining single molecule stretching experiments and stochastic unfolding/refolding simulations. We find that force-induced unfolding pathways cannot usually be interpreted by solely invoking successive openings of native helices. Indeed, typical force-extension responses of complex RNA molecules are largely shaped by stretching-induced, long-lived intermediates including non-native helices. This is first shown for a set of generic structural motifs found in larger RNA structures, and then for Escherichia colis 1540-base long 16S ribosomal RNA, which exhibits a surprisingly well-structured and reproducible unfolding pathway under mechanical stretching. Using out-of-equilibrium stochastic simulations, we demonstrate that these experimental results reflect the slow relaxation of RNA structural rearrangements. Hence, micromanipulations of single RNA molecules probe both their native structures and long-lived intermediates, so-called kinetic traps, thereby capturing -at the single molecular level- the hallmark of RNA folding/unfolding dynamics.Received: 15 September 2003, Published online: 5 February 2004PACS:
87.15.-v Biomolecules: structure and physical properties - 82.37.Rs Single molecule manipulation of proteins and other biological molecules - 87.15.Aa Theory and modeling; computer simulation 相似文献
984.
F. Pétrélis F. Lund 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,35(3):291-294
We investigate the effect of a localized magnetic field on the propagation of sound in an infinite fluid described by the magnetohydrodynamic equations (MHD). An externally imposed magnetic field will scatter an acoustic wave, and the scattered wave is related to the spatial structure of the magnetic field. Measuring it is thus a non-intrusive probe for the magnetic field. Simple examples likely to be encountered in practice are worked out, and estimates are given that suggest the practical feasability of this diagnostic tool in current MHD experiments.Received: 1 May 2003, Published online: 15 October 2003PACS:
42.25.Fx Diffraction and scattering - 47.65.+a Magnetohydrodynamics and electrohydrodynamics - 52.35.Dm Sound waves 相似文献
985.
The solar gravitational deflection angle of a graviton is calculated through the scattering cross section of the graviton by the sun and shown to be equal to the light deflection angle as calculated from the null geodesic equation of general relativity. 相似文献
986.
H. Jirari R. Mélin N. Stefanakis 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(1):125-139
We consider the proximity effect in multiterminal ferromagnet/superconductor (FSF) hybrid structures in which two or three
electrodes are connected to a superconductor. We show that two competing effects take place in these systems: (i) pair breaking
effects due to the response to the exchange field induced in the superconductor; (ii) a reduction of the superconducting order
parameter at the interface that takes place already in NS junctions. We focus on this second effect that dominates if the
thickness of the S layer is small enough. We consider several single-channel electrodes connected to the same site. We calculate
the superconducting order parameter and the local density of state (LDOS). With two ferromagnetic electrodes connected to
a superconductor we find that the superconducting order parameter in the ferromagnetic alignment is larger than the superconducting
order parameter in the antiferromagnetic alignment ( > ), in agreement with [Eur. Phys. J. B 25, 373 (2002)]. If a third spin polarized electrode is connected to a superconductor we find that - can change sign as the transparency of the third electrode increases. This can be understood from the fact that the superconducting
order parameter is reduced if pair correlations among the ferromagnetic electrodes increase. If the two ferromagnetic electrodes
are within a finite distance we find Friedel oscillations in the Gorkov function but we still obtain > . 相似文献
987.
PROMETHEE multi-criteria methods are based on fuzzy evaluations of the differences between pairs of alternatives for each criterion. PROMETHEE II associates a crisp number to each action. PROMETHEE III associates an interval to each action and two actions are considered indifferent when they are very close to each other. PROMETHEE V applies Integer Linear Programming in order to select the subset of alternatives that maximizes the sum of PROMETHEE II scorings, subject to a set of constraints. In order to make the model more realistic, this paper proposes that some constraints are soft and some coefficients are estimated by fuzzy numbers. Fuzzy Integer Linear Programming is applied, using the PROMETHEE III scorings as objective function coefficients, in order to find the subsets of non-outranked alternatives that best satisfy the soft constraints. The new model is more realistic and fits better the fuzzy philosophy of PROMETHEE. The method is illustrated with an example. 相似文献
988.
989.
S. Tzortzakis G. Méchain G. Patalano M. Franco B. Prade A. Mysyrowicz 《Applied physics. B, Lasers and optics》2003,76(5):609-612
We report the first observation of the attachment of two single plasma filaments created collinearly in the atmosphere by
IR femtosecond laser pulses. The linked filamentary structure is electrically conductive and emits sub-THz radiation over
its entire length. Concatenation is achieved only for a specific time ordering between the two initial laser pulses. The pulse
producing the filament closer to the laser source must be retarded with respect to the other pulse. This special time ordering
is attributed to the acceleration of light in a self-guided pulse.
Received: 4 March 2003 / Published online: 14 May 2003
RID="*"
ID="*"Corresponding author. Fax: +33-1/6931-9996, E-mail: stzortz@ensta.fr 相似文献
990.
We have measured the thermal conductivity of liquid 3He in 98% aerogel at ultralow temperatures. Aerogel introduces disorder on a scale comparable to the superfluid coherence length. At low pressures the liquid in the aerogel shows normal-state behavior with conductivity linear in temperature. At pressures above approximately 6 bars the onset of superfluidity suppresses the conductivity and the thermal conductivity again tends towards linear behavior in the very low temperature limit, providing strong evidence that here the liquid 3He in the aerogel is behaving as a gapless superfluid. 相似文献