排序方式: 共有56条查询结果,搜索用时 15 毫秒
1.
We use tools of the equilibrium statistical mechanics of disordered systems to study analytically the statistical properties of an ecosystem composed of N species interacting via random mutual interactions, as well as via deterministic self-interactions of order p>/=2. We show that the main effect of increasing the order of the interactions among the species is to make the system less competitive, in the sense that the fraction of extinct species is greatly reduced. In addition, we find that for p>2 there is a threshold value which gives a lower bound to the concentration of the surviving species, preventing then the existence of rare species and, consequently, increasing the robustness of the ecosystem to external perturbations. 相似文献
2.
3.
The electro-optical Kerr effect induced by a slowly varying electric field in liquid helium at temperatures below the lambda point is investigated. The Kerr constant of liquid helium is measured to be (1.43+/-0.02(stat)+/-0.04(sys)) x 10(-20) (cm/V)(2) at T=1.5 K. Within experimental uncertainty, the Kerr constant is independent of temperature in the range T=1.5 K to 2.17 K, which implies that the Kerr constant of the superfluid component of liquid helium is the same as that of normal liquid helium. Pair and higher correlations of He atoms in the liquid phase account for about 23% of the measured Kerr constant. Liquid nitrogen was used to test the experimental setup; the result for the liquid nitrogen Kerr constant is (4.38+/-0.15) x 10(-18) (cm/V)(2). Kerr effect can be used as a noncontact technique for measuring the magnitude and mapping out the distribution of electric fields inside these cryogenic insulants. 相似文献
4.
5.
Streptomyces omiyaensis SSM 5670 was characterized by its ability to use compression moulded samples of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) as its sole carbon source. Biodegradation of PHBV in liquid mineral salts medium was investigated using scanning electron microscopy, gravimetric measurements, capillary viscometry, tensile testing and wide angle X-ray spectroscopy. The biodegradation of PHBV proceeds via surface erosion mechanism, resulting in the formation of pits by microbial attack. PHBV specimens lost about 45% of their original weight after 45 days of exposure. During the degradation process the elastic modulus reduces less than 10%. The formation of pores and microcracks initiated at the degraded pits determines the reduction of the elongation and stress at break. However, the true stress at break is practically independent of the degradation time. No significant changes of PHBV molecular weight or crystallinity were observed during biodegradation. The polymer chain cleavage occurred only at the specimen surface and does not discriminate between crystalline and amorphous states. 相似文献
6.
Voronov DL Anderson EH Gullikson EM Salmassi F Warwick T Yashchuk VV Padmore HA 《Optics letters》2012,37(10):1628-1630
Diffraction efficiency of multilayer-coated blazed gratings (MBG) strongly depends on the perfection of the sawtooth-shaped layers in the overall composite structure. Growth of multilayers on sawtooth substrates should be carefully optimized to reduce groove profile distortion and, at the same time, to avoid significant roughening of multilayer interfaces. In this work, we report on a way to optimize growth of sputter-deposited Mo/Si multilayers on sawtooth substrates through variation of the sputtering gas pressure. We believe a new record for diffraction efficiency of 44% was achieved for an optimized MBG with groove density of 5250 lines/mm at the wavelength of 13.1 nm. 相似文献
7.
M. U. Belyi A. S. Kolesnik B. A. Okhrimenko V. P. Yashchuk 《Journal of Applied Spectroscopy》1989,50(5):523-529
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 50, No. 5, pp. 808–814, May, 1989. 相似文献
8.
Troitskii B. B. Domrachev G. A. Semchikov Yu. D. Khokhlova L. V. Anikina L. I. Denisova V. N. Novikova M. A. Marsenova Yu. A. Yashchuk L. M. 《Russian Journal of General Chemistry》2002,72(8):1276-1281
Fullerene-C60 inhibits thermal and thermooxidative degradation of copolymers of methyl methacrylate with styrene, butyl acrylate, glycidyl methacrylate, and hydroxyethyl methacrylate. 相似文献
9.
Seltzer SJ Michalak DJ Donaldson MH Balabas MV Barber SK Bernasek SL Bouchiat MA Hexemer A Hibberd AM Kimball DF Jaye C Karaulanov T Narducci FA Rangwala SA Robinson HG Shmakov AK Voronov DL Yashchuk VV Pines A Budker D 《The Journal of chemical physics》2010,133(14):144703
Many technologies based on cells containing alkali-metal atomic vapor benefit from the use of antirelaxation surface coatings in order to preserve atomic spin polarization. In particular, paraffin has been used for this purpose for several decades and has been demonstrated to allow an atom to experience up to 10?000 collisions with the walls of its container without depolarizing, but the details of its operation remain poorly understood. We apply modern surface and bulk techniques to the study of paraffin coatings in order to characterize the properties that enable the effective preservation of alkali spin polarization. These methods include Fourier transform infrared spectroscopy, differential scanning calorimetry, atomic force microscopy, near-edge x-ray absorption fine structure spectroscopy, and x-ray photoelectron spectroscopy. We also compare the light-induced atomic desorption yields of several different paraffin materials. Experimental results include the determination that crystallinity of the coating material is unnecessary, and the detection of C[Double Bond]C double bonds present within a particular class of effective paraffin coatings. Further study should lead to the development of more robust paraffin antirelaxation coatings, as well as the design and synthesis of new classes of coating materials. 相似文献
10.
Allison M Fox Mike Anderson Corinne Reid Tim Smith Dorothy VM Bishop 《BMC neuroscience》2010,11(1):1-15