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41.
Competition between languages or cultural traits diffusing in the same geographical area is studied combining the model of Abrams and Strogatz with a model of human dispersal on an inhomogeneous substrate. Also, the effect of population growth is discussed. It is shown through numerical simulations that the final configuration of the languages can be strongly affected by geographical and historical factors. These factors are not related to the dynamics of culture transmission, but rather to initial population distributions as well as geographical boundaries and inhomogeneities, which modulate the diffusion process. 相似文献
42.
The interaction between two paramagnetic metal centers, a [3Fe-4S](+) cluster and a [NiFe] center, is investigated in the hydrogenase from Desulfovibrio vulgaris Miyazaki F by pulsed ELDOR (electron-electron double resonance). The distance between the metal centers is known from X-ray crystallography. The experimental dipolar spin-spin interaction deviates from the value expected for two point-dipoles located at the centers of the metal clusters. An extended spin-coupling model accounting for the spin coupling in the [3Fe-4S](+) cluster yields the observed interaction under the assumption of a particular magnetic coupling scheme for the three Fe ions. These results demonstrate that pulsed ELDOR can be used to gain insight into the inner structure of a multinuclear metal cluster. 相似文献
43.
We demonstrate the influence of vectorial coupling on the synchronization behavior of complex systems. We study two semiconductor lasers subject to delayed optical feedback which are unidirectionally coherently coupled via their optical fields. Our experimental and numerical results demonstrate a characteristic synchronization scenario in dependence on the relative feedback phase leading cyclically from chaos synchronization to almost uncorrelated states, and back to chaos synchronization. Finally, we reveal the influence of the feedback phase on the dynamics of the solitary delay system. 相似文献
44.
We generalize the modal interpretation of quantum mechanics so that it may be applied to composite systems represented by arbitrary density operators. We discuss the interpretation these density operators receive and relate this to the discussion about the interpretation of proper and improper mixtures in the standard interpretation. 相似文献
45.
The biosynthesis of the eremophilane sesquiterpenoid PR toxin is shown to involve an 1,2-hydride migration from C(5) to C(4) of the molecule. 相似文献
46.
Pieter Maaskant 《Mikrochimica acta》1989,97(1-2):31-39
Crystal fragments of biotite, garnet, and spinel were mounted together in one block which afterwards was sawn into several pieces; each piece was coated with SiO2 of varying thickness, up to 7.9m. Electron probe microanalysis was carried out at various accelerating voltages of the major elements present, using the non-SiO2-coated minerals as reference standard.Calibration curves, depth below the surface versus ratios of X-ray yields, have been established with the ultimate goal to use them for a (semi)-quantification of elements present in subsurface phases in quartz, a common host mineral in rocks. 相似文献
47.
We study the kinetics of crystal nucleation of an undercooled Lennard-Jones liquid using various path-sampling methods. We obtain the rate constant and elucidate the pathways for crystal nucleation. Analysis of the path ensemble reveals that crystal nucleation occurs along many different pathways, in which critical solid nuclei can be small, compact, and face centered cubic, but also large, less ordered, and more body centered cubic. The reaction coordinate thus includes, besides the cluster size, also the quality of the crystal structure. 相似文献
48.
R.H.?BirknerEmail author J.?Kaiser W.?Els?sser C.?Jung 《Applied physics. B, Lasers and optics》2004,79(8):963-967
We demonstrate the interplay between the intensity noise and the spatial emission characteristics of resonant-cavity light-emitting diodes. First, we find that the total aperture intensity noise exhibits a sub-shot noise behavior in a quite large pumping regime. Second, we investigate the angular, spectral, and spatial emission characteristics of the devices by controlling the shape and width of the angular intensity distribution via temperature detuning of the quantum well wavelength and the cavity resonance wavelength. Finally, the angular and aperture resolved intensity noise exhibit a super-shot noise behavior in contrast to that of the total emission. We explain this difference with anticorrelations between various radial components which increase with the temperature-tuned extension of the spatial emission. PACS 85.60.Jb; 42.50.L; 23.20.En 相似文献
49.
50.
We demonstrate a novel optical dipole trap that is based on enhancement of the optical power density of a Nd:YAG laser beam in a resonator. The trap is particularly suited for experiments with ultracold gases, as it combines a potential depth of the order of 1 mK with storage times of several tens of seconds. We study the interactions in a gas of fermionic lithium atoms in our trap and observe the influence of spin-changing collisions and off-resonant photon scattering. A key element in reaching long storage times is the use of an ultralow-noise laser. The dependence of storage time on laser noise is investigated. 相似文献