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51.
52.
利用全量子理论的方法,研究了存在相位退相干时多光子T-C模型中两个二能级原子与二项式光场相互作用系统中两原子的布居数反转。讨论了相位退相干系数、二项式光场系数、最大光子数、跃迁光子数对原子布居数反转的影响。结果表明:相位退相干减少了原子布居数反转的振幅、破坏了原子的量子特性。改变跃迁光子数,可以改变原子间布居数反转演化周期及演化强度。当二项式光场的最大光子数增大时,原子布居差的崩塌-回复现象就会逐渐消失。相位退相干因子不变时, 二项式光场从相干态过渡到数态过程中,原子布居的振荡频率由大变小,周期性的崩塌与回复现象逐渐消失。 相似文献
53.
We investigate the thermoelectric properties of GaN with p-and n-type doping by the first principles calculation and the semi-classical Boltzmann theory. We find that the power factors (S2σof p-type GaN (-3500 W/mK2) is about twice that of the n-type (-1750 W/mK2), which indicates the thermoelectric properties of p-type GaN would be better. Thermal conductivity of GaN crystal decreases rapidly as the temperature increases, but it is still too large for thermoelectric applications. The figure of merit (ZT) estimated at 1500 K is 0.134 for p-type GaN crystal and 0.062 for the n-type. 相似文献
54.
Let (R, m) be a Noetherian, one-dimensional, local ring, with |R/m|=∞. We study when its associated graded ring G(m) is Buchsbaum; in particular, we give a theoretical characterization for G(m) to be Buchsbaum not Cohen–Macaulay. Finally, we consider the particular case of R being the semigroup ring associated to a numerical semigroup S: we introduce some invariants of S, and we use them in order to give a necessary and a sufficient condition for G(m) to be Buchsbaum. 相似文献
55.
Laser ablation coupled to mass quadrupole spectrometry (LAMQS) has been used to prepare thin films of aluminum oxide deposited on Si substrates starting from commercial Al2O3 polycrystalline targets. X-ray photoemission (XPS) and reflection electron energy loss spectroscopy (REELS) have allowed the investigation of the electronic properties of the produced films. In particular, it was found that the Al/O atomic ratio assumes a value very near to 0.7 (stoichiometric ratio) only for films deposited normally with respect to the target surface, while films grown at larger deposition angles are more rich in oxygen content.The composition, the mass density, the optical energy gap, the complex dielectric function and refraction index of the films have been calculated and compared with the results obtained from our starting target material and with the literature. The morphology of the deposited samples has been analyzed by the AFM technique. 相似文献
56.
L. Torrisi G. Mondio A. M. Mezzasalma D. Margarone F. Caridi T. Serafino A. Torrisi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,54(2):225-232
Physical analyses by laser ablation coupled to mass quadrupole spectrometry (LAMQS), energy dispersive X-ray fluorescence
(EDX) induced by electron beam, scanning electron microscopy (SEM) and surface profilometry analysis (SPA) are applied to
the investigation of two silver tetradrachms from Messana, in order to compare their elemental composition and structure.
Quantitative analysis of the elemental composition and of the silver isotopic ratios have been carried out analyzing the surface
patina of the two samples. Significant differences in the sulfur, chlorine and copper content, in the isotopic ratios and
in the morphological aspects have been measured. The obtained results are presented and discussed from the point of view of
the physical techniques useful to establish the differences between apparently true and false coins. 相似文献
57.
58.
Rong Jian SA Ke Chen WU* Ping LIU Chen Sheng LIN Chao Yong MANG State Key Laboratory of Structural Chemistry Fujian Institute of Research on the Structure of Matter Chinese Academy of Sciences Fuzhou The Graduate school of the Chinese Academy of Sciences Beijing 《中国化学快报》2002,(12)
A series of tri-nuclear transition metal clusters with incomplete cubane-like configurations have been studied by TDDFT method. The calculations show that they have enormously large second-order polarizabilities () and are potential nonlinear optical materials for infrared double frequency conversion1. In this paper some tetra-nuclear transition metal clusters with cubane-like configurations, MCu3X4 (PPh3)3 (M=W, Mo; X= S, O, Cl, Se, Br), were studied by TDDFT method for a reference… 相似文献
59.
Let G be a graph with n(G) vertices and m(G) be its matching number.The nullity of G,denoted by η(G),is the multiplicity of the eigenvalue zero of adjacency matrix of G.It is well known that if G is a tree,then η(G) = n(G)-2m(G).Guo et al.[Jiming GUO,Weigen YAN,Yeongnan YEH.On the nullity and the matching number of unicyclic graphs.Linear Alg.Appl.,2009,431:1293 1301]proved that if G is a unicyclic graph,then η(G)equals n(G)-2m(G)-1,n(G)-2m(G),or n(G)-2m(G) +2.In this paper,we prove that if G is a bicyclic graph,then η(G) equals n(G)-2m(G),n(G)-2m(G)±1,n(G)-2m(G)±2or n(G)-2m(G) + 4.We also give a characterization of these six types of bicyclic graphs corresponding to each nullity. 相似文献
60.
A phenomenological theory for polarization flop in spiral multiferroic TbMnO<Subscript>3</Subscript>
A phenomenological Landau theory has been used to explain magnetic field-driven polarization flop in TbMnO 3. The Néel wall-like magnetic structure in spiral multiferroics induces a space-dependent internal magnetic field which exerts a torque on spins to rotate bc-spiral to ab-spiral. The external magnetic field is argued to be competing with easy axis anisotropy and the system stabilizes when anisotropy is minimum. With the help of Landau free energy with DM magnetoelectric coupling and a general ansatz for magnetization, the phenomenon of polarization flop has been explained. Relation between Tflop and critical magnetic field has been established and found to be in good agreement with the experiment. This could be an indication that anisotropy of the system is temperature- and magnetic field-dependent. 相似文献