Oscillating two-stream instability of a plasma wave in a plasmachannel

A long wavelength Langmuir wave (ω₀, k₀), propagating through a parabolic plasma density channel, can decay into a low-frequency mode (ω,k&oarr;) and two short wavelength Langmuir wave sidebands (ν_1,2,k&oarr;_1,2 ), via two-stream instability where ω_1,2=ω∓ω₀ and k&oarr;_1,2=k&oarr;∓k&oarr;₀. Depending on the mode number n, the growth rate maximizes in the range γ_max≃0.1ω_pi-0.4ω_pi for the range of k from 0.1(ω_pi/c_s) to 0.2(ω_pi/c_x) for ν₀~ν_th where ν₀ and ν_th are the oscillatory and thermal velocities of electrons, ω_pi is the ion plasma frequency on the axis, and c_s is the sound speed. The growth rate increases with the width a of the plasma density channel. It decreases with the mode number. The instability may be relevant to laser based charged particle accelerators     

Nanoparticle in a quantum crystal with a narrow vacancy band

Vacancy-assisted diffusion of a neutral probe nanoparticle with a radius R_p of a few lattice constants in a quantum crystal with a narrow vacancy band is considered. The diffusion coefficient of the probe D_p(T) in such a crystal should fall exponentially near T_melt, and it can go through a maximum at temperatures T_tr, where the transition from thermally activated hopping of localized vacancies to a proper band motion of delocalized vacancions takes place, under the condition that the mean free path of the vacancions l_v(T) at T_tr is less than R_p and increases with lowering the temperature quicker than the inverse value of the relative concentration of vacancies X_v(T). Below T_tr, where l_v is much longer than the probe diameter, the value of D_p should fall proportionally to X_v(T).     

Towards a realistic Einstein-Gauge cosmology

We present the cosmological solutions in the six-dimensional Einstein-gauge theory to which is added a matter term. The general behavior of the scale factors of the ordinary (R₃) and extra (R₂) dimensions can be depicted in four stages. Stage 1: Both R₃ and R₂ expand. Stage 2: R₂ is a constant and R₃ is an inflationary solution. Stage 3: R₂ recollapses towards its minimum value, R₃ will continue to increase monotonically. Stage 4: R₂ stabilizes at R_KK and R₃ expands in the usual FRW way, while the four-dimensional cosmological constant becomes zero.     

Multipartite Entanglement of a Tetrahedron Lattice

Three-dimensional Heisenberg model in the form of a tetrahedron lattice is investigated. The concurrence and multipartite entanglement are calculated through 2-concurrence C and 4-concurrence C4. The concurrence C and multipartite entanglement G4 depend on different coupling strengths Ji and are decreased when the temperature T is increased. For a symmetric tetrahedron lattice, the concurrence C is symmetric about J1 when J~ is negative while the multipartite entanglement G4 is symmetric about J1 when J2 〈 2. For a regular tetrahedron lattice, the concurrence G of ground state is 1/3 for ferromagnetic case while G = 0 for antiferromagnetic ca.se. However, there is no multipartitc entanglement since C4=0 in a regular tetrahedron lattice. The external magnetic field 13 can increase the maximum value of the concurrence GB and induce two or three peaks in Cn. There is a peak in the multipartite entanglement G4 B when G4B is varied as a function of the temperature T. This peak is mainly induced by the magnetic field B.     

Quantitative determination of anti-structured defects applied to alloys of a wide chemical range

Anti-structured defects bridge atom migration among heterogeneous sublattices facilitating diffusion but could also result in the collapse of ordered structure.Component distribution Ni_(75)Al_xV_(25-x) alloys are investigated using a microscopic phase field model to illuminate relations between anti-structured defects and composition,precipitate order,precipitate type,and phase stability.The Ni_(75)Al_xV_(25-x) alloys undergo single Ni_3V(stage Ⅰ),dual Ni_3Al and Ni_3V(stage Ⅱ with Ni_3V prior;and stage Ⅲ with Ni_3Al prior),and single Ni_3Al(stage Ⅳ) with enhanced aluminum level.For Ni_3V phase,anti-structured defects(V_(Ni1),Niy,except V_(Ni2)) and substitution defects(Al_(Ni1),Al_(Ni2),Al_v) exhibit a positive correlation to aluminum in stage I,the positive trend becomes to negative correlation or smooth during stage Ⅱ.For Ni_3 Al phase,anti-structured defects(Al_(Ni),Ni_(Al)) and substitution defects(V_(Ni),V_(Al)) have a positive correlation to aluminum in stage Ⅱ,but Ni_(Al) goes down since stage Ⅲ and lasts to stage Ⅳ.V_(Ni) and V_(Al) fluctuate when Ni_3Al precipitates prior,but go down drastically in stageⅣ.Precipitate type conversion of single Ni_3V/dual(Ni_3V+Ni_3Al) affects Ni_3V defects,while dual(Ni_3V+Ni_3Al)/single Ni_3 Al has little effect on Ni_3Al defects.Precipitate order swap occurred in the dual phase region affects on Ni_3Al defects but not on Ni_3V.     

The Necessary and Sufficient Conditions for a Universal Conservation of a State of a Unitary Quantum Circuit

By A. Peres and A. Stern's opinions a computational process evolves along a cyclic logic orbit defined by the sequence ψ₀→ψ₁→ … →ψ_M-1→ψ₀. It begins from a start position and returns to the same position after a computation. A. Stern thought that if we could design such a circuit, its operations can be extended to including nonconservative behavior associated with the external perturbations or internal quantum errors. A. Peres did not discuss how to make φ_M-1=φ₀. A. Stern proposed only a necessary condition for a conservation of a state of a quantum circuit. In this paper we present a necessary and sufficient condition for a universal conservation of a state of a quantum circuit. We also find all operators which can allow the conservation.     

Probability of a ductile fracture

The present paper studies ductile fracture by a random fractal and calculates the fracture probability q of a ductile fracture. The fracture probability q is sensitive to the number n (microvoid size) and the probability p of forming microvoids. There are two critical probabilities p_c1 and p_c2. When pp_c2 = 1-1/n², the fracture probability q is 100%, the ductile fracture occurs with probability 1; when p_c2 > p>p_c1, there is a positive probability q (1>q>0), the fracture probability q increases with increasing probability p and/or decreasing number n; when p<p_c1, the fracture probability q is zero (in fact less than 0.00001), the fracture does not occur. The critical probabilities p_c1 and p_c2 increase with increasing n. When 1-1/n²>p>1-1/n, though a ductile fracture does not occur, there is at least a macrovoid which passes through the transverse plane of the specimen.     

Motion of Chern-Simons number at high temperatures under a chemical potential

I investigate the evolution of finite temperature, classical Yang-Mills field equations under the influence of a chemical potential for Chern-Simons number N_cs. The rate of N_cs diffusion,, Γ_d, and the linear response of N_cs to a chemical potential, Γ_μ, are both computed; the relation Γ_d = 2Γ_μ is satisfied numerically and the results agree with the recent measurement of Γ_d by Ambjørn and Krasnitz. The response of N_cs under chemical potential remains linear at least to μ = 6T, which is impossible if there is a free energy barrier to the motion of N_cs. The possibility that the result depends on lattice artefacts via hard thermal loops is investigated by changing the lattice action and by examining elongated rectangular lattices; provided that the lattice is fine enough, the result is weakly if at all dependent on the specifics of the cutoff. I also compare SU(2) with SU(3) and find Γ_SU(3) 7(_{s/w)⁴ΓSU(2)}.     

Kinetics of a Migration－Driven Aggregation－Fragmentation Process

We propose a reversible model of the migration-driven aggregation-fragmentation process with the symmetric migration rate kernels K(k;j)=K'(k;j)=λkj^υ and the constant aggregation rates I₁, I₂ and fragmentation rates J₁, J₂. Based on the mean-field theory, we investigate the evolution behavior of the aggregate size distributions in several cases with different values of index υ. We find that the fragmentation reaction plays a more important role in the kinetic behaviors of the system than the aggregation and migration. When J₁=0 and J₂ =0, the aggregate size distributions a_k(t) and b_k(t) obey the conventional scaling law, while when J₁>0 and J₂>0, they obey the modified scaling law with an exponential scaling function. The total mass of either species remains conserved.     

高次柱面反射型太阳能聚光镜的光学设计

提出了一种新型高效太阳能聚光镜, 这种聚光镜用一组特定系数, a₂, a₄, a₆, a₈, a₁₀, a₁₂, a₁₄, a₁₆ 与 C的高次柱面内壁的一部分作为反射镜. 利用高次柱面方程和光反射定律, 推导出了在高次柱面内壁上太阳反射光束的方向矢量与高次柱面系数C, a₂,a₄, a₆, a₈, a₁₀, a₁₂, a₁₄, a₁₆的关系, 通过优化设计这些系数, 可以使入射到高次柱面内壁上的太阳光束反射后全部聚焦在一条与柱面母线平行的宽度很窄的线段上, 形成线聚光. 这组特定系数用粒子群优化算法求得, 并经计算机模拟证明其聚焦效果. 用这组特定系数的高次柱面作为聚光镜, 其对光的压缩比可达148倍, 其线性光斑可作为一种强光源或高温光源. 高次柱面反射镜可由金属或玻璃直接磨制而成, 也可由高次柱面骨架和铺设在骨架上的镀铝聚酯薄膜构成. 关键词： 太阳能聚光镜 高次柱面 多项式系数优化 线性聚焦     

Alternating-current relaxation of a rotating metallic particle

Based on a first-principles approach,we establish an alternating-current(AC) relaxation theory for a rotating metallic particle with complex dielectric constant ε_α=ε_α-iσ_α/ω_0.Here εα is the real part,σ_α the conductivity,ω_0 the angular frequency of an AC electric field,and i=-1~(1/2).Our theory yields an accurate interparticle force,which is in good agreement with the existing experiment.The agreement helps to show that the relaxations of two kinds of charges,namely,surface polarized charges(described by ε_α) and free charges(corresponding to σ_α),contribute to the unusually large reduction in the attracting interparticle force.This theory can be adopted to determine the relaxation time of dynamic particles in various fields.     

Analytical solutions for a doubly driven two-level atom

We have deduced analytical solutions of an energy level diagram of the doubly driven/dressed atom for a two-level atom exposed to a strong near-resonant bichromatic laser field in a special case, i.e., the bichromatic field with frequencies ω1 and ω2, and Rabi frequencies ?1 and ?2, in which the first coupling field of ?1 acts on the bare atomic levels, and then the resulting singly dressed states are driven by the second coupling field of ?2, thus resulting in the doubly dressed atom.We have measured the probe absorption spectra of a doubly driven two-level atom. The system consists of 52S1/2, F= 2 and 5~2P_(3/2), F'= 3 states of ~(87)Rb atoms in a magneto-optical trap(MOT) as well as the cooling/trapping beams and an additional coupling field. As for the spectroscopic properties of the doubly driven two-level atom, theoretical analytical solutions are in general agreement with the experimental spectrum as a whole.     

{Cu3}单分子磁体在磁场中的热纠缠

本文研究单分子磁体Na₉[Cu₃Na₃(H₂O)₉ (α-AsW₉O₃₃)₂]·26H₂O中三角自旋 环在磁场作用下的热纠缠性质, 利用数值计算求出任意两个Cu²⁺离子量子比特之间的配对纠缠度, 分别记为C₁₂, C₂₃和C₁₃. 研究结果表明, 磁场的方向和大小以及温度对配对纠缠度具有重要影响, 而且参数的变化对C₁₂, C₂₃和C₁₃的影响也是各不相同. 给出外加三个不同方向的磁场时, 配对纠缠度C₁₂, C₂₃和C₁₃各自对应的临界温度T_c随磁场强度的变化图, 由此可以得到单分子磁体三角自旋环中存在纠缠态的参数范围. 通过选择适当的磁场方向和大小以及温度等实验参数, 可以有效地调节和提高单分子磁体中的配对纠缠度. 关键词： 配对纠缠 单分子磁体 三角自旋环     

The Conductance of a Mesoscopic Ring with a Quantum Dot

Employing the generalized Landauer-type formula and equations-of-motion technique, we present an analysis of the conductance for a mesoscopic ring with a quantum dot embedded in one of its arms. An explicit expression is obtained for the conductance of the device. The conductance, which is a function of single particle energy E' in the dot and the flux Φ through the ring, can be divided into three parts, G₁, G₂ and G₃. The second part G₂ is the most important term because it reflects the AB effect with a period of h/e. G₂ disappears in the vicinity of a conductance resonance of the system, which leads to a sudden phase shift by π. Moreover, under the condition of single-level approximation for the dot, we find that all resonances are in phase, which is in agreement with a recent experiment done by Yacoby et al. (Phys. Rev. Lett. 74 (1995) 4047).     

Shadows and observational appearance of a new family of Ayón-Beato-García black holes

In this paper, we study the shadows and observational appearance of the Ayón-Beato-García (ABG) black hole, which is surrounded by a thin disk accretion. For a four-dimensional ABG black hole, as the charge q increases, the event horizon r₊, radius r_p and impact parameter b_p of the photon sphere decrease, while the maximum value of effective potential V_eff increases. However, as the term γ associated with nonlinear electrodynamics increases, the related physical quantities r₊, r_p and b_p increase, but the maximum value of V_eff decreases. When the light ray reaches the vicinity of the ABG black hole, one can observe the trajectories of the light rays appearing as three types, i.e., direct emission, lens ring and photon ring. Furthermore, the shadows and the observational appearance of the ABG black hole are studied. The results show that the charge q and the term γ have a great influence on the shape and intensity of the black hole shadow. When the relevant state parameters change or the emission model changes, it can be argued that it is the direct emission that plays a decisive role in the total observed intensity of the ABG black hole, while the contribution of the lens ring to the total observed intensity is small and the photon ring makes almost no contribution.     

Boson Representations of Subalgebra Chain for Quantum Algebra (Cl)q with q a Root of Unity

The method of q-deformed boson realization is extended to the caee that q is a root of unity. By using thb method, many irreducible and indecomposable representations of each su balgebra in a su balgebra chain of the quantum universal enveloping algebra (quan tum algebra) (C_l)_q are obtained on the q-deformed Fock space and its quotient space. AB an example, the representations of (C₃)_q are constructed in explicit forms. Besides, by embedding (A₁)_q = (C_l)_q, into the subalgebra chain, a new realisation of (A₁)_q and its representations are obtained.     

The Fractional Parentage Coefficients for a Double-j Fermion System

The coefficients of fractional parentage (CFPs) for a double-j fermion system are defined. The CFPs are given when the wave functions are classified according to the group chains U(N) ⊃ U(N₁) × U(N₂) ⊃ SP(N₁)× SP(N₂) ⊃O(3₁)×O(3₂) ⊃ O(3) and U(N) ⊃ SP(N) ⊃ SP(N₁)× SP(N₂) ⊃ O(3₁)× O(3₂) ⊃ O(3). Using these CFPs many repeating calculations can be avoided.     

Influence of sodium ion dynamics on the 23Na quadrupolar interaction in sodalite: a high-temperature 23Na MAS NMR study

High-temperature ²³Na MAS NMR experiments up to 873 K for a number of different sodalites (Na₈[AlSiO₄]₆(NO₃)₂, Na₈[AlSiO₄]₆(NO₂)₂, Na₈[AlSiO₄]₆I₂, Na_7.9[AlSiO₄]₆(SCN)_7.9 · 0.5H₂O, Na₈[AlGeO₄]₆(NO₃)₂, and Na₇[AlSiO₄]₆(H₃O₂) · 4H₂O) were carried out. The spectra of the first five sodalites consist of a quadrupolar MAS pattern with different quadrupolar coupling constants. The quadrupolar interaction for the thiocyanate sodalite, the nitrate aluminosilicate, and germanate sodalite decreases strongly passing a coalescence state on heating, while the quadrupolar interaction of the iodide and nitrite sample shows nearly no change. The basic hydrosodalite shows an asymmetric lineshape at room temperature and, between 350 and 370 K, a second line due to the evaporation of cage-water emerges. The linewidth increases with rising temperature. The temperature dependence of the quadrupolar interaction seems to be a function of the sodalite β-cage expansion. Two conceivable jump mechanisms are proposed for a tetrahedral two-site jump between occupied and unoccupied tetrahedral sites.     

一种电光可调的铌酸锂/钠基表面等离子体定向耦合器

为了满足日益增加的集成光子器件设计的需求,本文研究了一种铌酸锂/钠表面等离子体波导(Li Nb O3/Na surface plasmonic waveguide, LNSPW),并利用LNSPW构成电光可调的定向耦合器(directional coupling,DC).利用有限元方法 (finite element method, FEM)对波导的模式特性和耦合器的耦合特性进行了分析.结果表明,随着波导尺寸的增大,传播长度可达约200μm,归一化有效模场面积小于0.4.通过调节耦合间距(W_gap)、耦合长度(L_C)和工作波长(λ)等参数,铌酸锂钠表面等离子体波导构建的定向耦合结构可实现3 d B耦合.当W_gap=100 nm和L_C=17μm时, DC在V₀=53 V时可实现3 d B耦合,且具有较好的方向性和隔离度.LNSPW的研究为实现可调的DC提供了一种可行的方案,在集成电光可调器件研究领域有潜在的应用前景.除此之外, LNSPW还可广泛应用于非线性光学、光信号处理及光全...     

Long-distance super-exchange and quantum magnetic relaxation in a hybrid metal–organic framework

The hybrid metal–organic framework [(CH3)2NH2]Fe(HCOO)3with a perovskite-like structure exhibits a variety of unusual magnetic behaviors at low temperatures. While the long-distance super-exchange through the Fe-O–CH-O–Fe exchange path leads to a canted antiferromagnetic ordering at TN～ 19 K, a second transition of magnetic blocking develops at TB～ 9 K. The stair-shaped magnetization hysteresis loops below TBresemble the behaviors of resonant quantum tunneling of magnetization in single-molecular quantum magnets. Moreover, the magnetic relaxation also exhibits several features of resonant quantum relaxation, such as the exponential law with a single characteristic relaxation time, and the nonmonotonic dependence of relaxation rate on the applied magnetic field with a much faster relaxation around the resonant fields. The origin of quantum tunneling behaviors in the [(CH3)2NH2]Fe(HCOO)3metal–organic framework is discussed in terms of magnetic phase separation due to the modification of hydrogen bonding on the long-distance super-exchange interaction.