4He+在Al和Si单晶晶面沟道中的半波长及阻止本领

采用高分辨探测系统,在不同的入射角θ_in和出射角θ_out的条件下,测量了1—2MeV⁴He⁺入射在Al(100)面和Si(110),(100)面中的背散射能谱。得到了背散射能谱振荡峰的间距ΔE与cosθ_in/cosθ_out的直线关系,从而获得了1—2MeV⁴He⁺在这三个晶面中的振荡半波长及阻止本领。实验得到的半波长与理论计算值在误差范围内一致,晶面沟道方向的阻止本领略大于随机方向的阻止本领。 关键词：     

Higher Harmonics and Transport Coefficients of Plasmas in Circulary Polarized Magnetic Fields and Additional Electromagnetic Fields

With the methods of kinetic theory on the basis of the Boltzmann and Fokker-Planck kinetic equations the behaviour of a Lorentz plasma in a circularly polarized (rotating) magnetic field (rotation frequency ω), an alternating electric field (frequency ω′) and additional constant electromagnetic fields is investigated. By means of a generalized Fourier expansion it is shown that the above fields create in the plasma currents of the frequencies 0, ω′, ω–ω′,ω, ω+ω′, 2ω–ω′, 2ω, and 2ω+ω′. Transport coefficients are calculated explicitly and the validity of Onsager reciprocity relations and that of Kronig-Kramers relations is discussed. The special case of the electric field induced by the rotating magnetic field is treated separately. Finally, problems of plasma containment are discussed.     

π p forward elastic scattering near 1 GeV/c

We have measured the differential cross section of the reaction π⁻p→π⁻p in the range 0.92 ? cos θ_c.m. ? 0.99 at 15 momenta between 0.875 and 1.580 GeV/c. The results we report complete the available data; previous measurements of this reaction do not extend beyond cos θ_c.m.=0.90. We compare our experimental results with dispersion relation predictions. A comparison of our results for B, the slope of the differential cross section, with earlier results shows many discrepancies.     

The effect of nanoparticles on the surface hydrophobicity of polystyrene

The surface hydrophobicity of polystyrene-nanoparticle nanocomposites has been investigated as a function of the nanoparticle content. The addition of hydrophobically coated nanoparticles in polystyrene increased the contact angle θ of a water drop with respect to that on polystyrene surface due to change of surface composition and/or surface roughness. When the nanoparticles dispersed well in the polymer, cos θ decreased linearly with increasing amount of nanoparticles indicating a composite surface consisting of smooth polystyrene regions and rough nanoparticle regions. In case of formation of nanoparticle aggregates in polystyrene, cos θ decreased sharply at a critical concentration of nanoparticles. The observed behaviour was modeled in terms of a transition from Wenzel regime to Cassie-Baxter regime at a critical roughness length scale below which the Laplace pressure prevented the penetration of the water drop into the surface undulations. We argue that multiple length scales are needed below the critical roughness length scale to increase the contact angle further by decreasing the fraction of surface area of solid material (increasing the fraction of surface area of air) underlying the water drop.     

相干态的叠加态的量子统计性质

本文研究了相干态的叠加态的量子统计性质.结果表明,相干态的叠加态仅存在奇次幂的高阶压缩效应,而不存在偶次幂的高阶压缩效应.给出了高阶压缩和高阶反聚束效应与叠加系数间的函数关系.高阶压缩要求叠加系数的辐角取值满足cosθ>exp(-2|α|²),而高阶反聚束效应则要求0.5π<θ<1.5π.奇偶相干态的有关结果均作为特例应包含在本文的一般结论之中.     

Application of Fourier Slice Theorem in Wigner Operator Theory and New Complete Representation

By applying the Fourier slice theorem, S_θ(λ) =∫_{-\infty }^{\infty }P_θ(t)e^-iλt=F(λcosθ,λsinθ), where P_θ(t) is a projection of f( x,p) =∫∫_{-\infty}^{\infty }F( u,v) e^i(ux+vp)ldudv along lines of constant, to the Wigner operator we are naturally led to projection operator (pure state), which results in a new complete epresentation. The Weyl orderimg formalism of the Wigner operator is used in the derivation.     

Rigorous absolute bounds for pion-pion scattering (1). Solving a first extremum problem

This paper is the first of a series of three where we reconsider the derivation of rigorous absolute bounds for strong interactions. It is devoted to the solution of a preliminary extremum problem. From the knowledge, at a given physical energy s and unphysical angle cos θ₀ > 1, of the absorptive part A (s, cos θ₀) of the elastic scattering amplitude for two spinless particles, we find, by exploiting the unitarity condition, the least upper bound of the modulus |F(s, cos θ₁)| of the scattering amplitude for the same energy s and various angles θ₁. Upper (but not least upper) bounds given by previous authors are numerically compared with ours.     

Construction of a unitary analytic scattering amplitude: (IV). Many two-body channels

We extend previous results concerning the existence of unitary amplitudes that correspond to a given differential cross section to the many-channel case. We use cos θ analyticity and show that all of the one-channel results may be adapted to the more general problem. A new constraint, the commutavity of the dispersive and absorptive parts, is shown to be automatic in all but exceptional singular cases.     

Magnetic resonance imaging of electroconvection in a polar organic solvent

Molecular motion in the polar organic solvent nitrobenzene induced by an electric field is studied by magnetic resonance imaging. Rf pulse sequences that correlate images obtained at two different times under conditions of both continuous and pulsed electric fields are introduced. The resultant image correlation spectra indicate that the time scale of motion in a 9.6 kV/cm electric field is tens of milliseconds. Comparison of the results to an analytic solution for the Fokker-Planck probability function for one-dimensional bounded diffusion yields an electric field dependent effective diffusion coefficient for perdeuterated nitrobenzene of D = 1.08 x 10(-5) cm(2)/s + (3.33 x 10(-3) cm(4)/kV(2)s) E(2) at room temperature. Characteristics of this electroconvection and its consequences for combining multidimensional nuclear magnetic resonance with electrical orientation are also discussed.     

Angular distributions of auger electron emission: Clean and gas-adsorbed polycrystalline Ni surfaces

The excitation angle (β) and emission angle (θ) dependences of the Ni M₂,₃VV (61 eV) and Ni L₃VV (850 eV) Auger emissions from clean polycrystalline Ni surfaces, and the S L₂, ₃ M₂, ₃M₂, ₃ (150 eV) Auger emission from S-adsorbed poly-Ni surfaces have been investigated. In the case of Ni (61 eV) and S Auger emissions, the β-dependence shows the $\text{1}\text{cos β}$ distribution, while a significant deviation from $\text{1}\text{cos β}$ is observed for Ni (850 eV) Auger emission. The cosθ distribution and the intermediate between isotropic and cosθ distributions are observed for Ni (61 eV), and for Ni (850 eV) and S Auger emissions, respectively. Those results have been found to be in fairly good agreement with the calculations based on the simple continuum model without consideration of the diffraction effect and the inherent anisotropic emission.     

A Quantum Mechanical Gauge Model and a Possible Dynamical Solution of the StrongCPProblem

A model describing a quantum mechanical particle on a circle with minimal electromagnetic interaction with a space independent vector potential, and with a potential −M cos(?−θ_M) so that it mimics the massive Schwinger model, is discussed as a prototype of mechanisms and infrared structures which characterize gauge quantum field theories in positive gauges and QCD in particular. The functional integral representation in terms of the field variables which enter in the Lagrangean displays non-standard features, like a complex functional measure (failure of Nelson positivity), a crucial rôle of the boundary conditions, and the decomposition intoθsectors already in finite volume. In the infinite volume limit, one essentially recovers the standard picture whenM=0 (“massless fermions”), but one meets substantial differences forM≠0: for generic boundary conditions, independently of the Lagrangean angle of the topological term, the infinite volume limit selects the sector withθ=θ_Mand provides a natural “dynamical” solution of the strong CP problem. In comparison with previous approaches, the strategy discussed here allows us to exploit the consequences of theθdependence of the free energy density, with a unique minimum atθ=θ_M.     

Obtaining of preset electrostatic fields in a quasi-electrode system

A method for obtaining electrostatic fields of a preset form in a quasi-electrode cylindrical system is considered. “Distributed” electrodes (filamentary conductors) make it possible to solve the inverse boundary-value problem, viz., to preset an azimuthal electric potential distribution over the cylinder surface for obtaining the required field in the cylinder, thus ensuring a larger working region as compared to an obviously electrode system.     

Winkelverteilung der Kernphotoreaktion3He (γ,p)2H

The angular distribution of the photonuclear reaction³He(γ,p)²H was measured with an exitation energyE _x=16 to 27 MeV using a 32.5 MeV betatron. In agreement with a theoretical calculation of Böschet al. we found for the coefficients of the distributionf(θ)=b (a/b+sin²θ(1+β·cosθ+γ·cos²θ)) the values:a/b≦0.14; β=0.77 (+0.14; ?0.07); γ≦0.30. This was the first attempt to use spark chambers as a detection device for photonuclear reactions in the low energy range. We found it to be a promising new facility.     

Grover量子搜索算法的一般化多相位匹配

一个量子系统将不可避免地受到不可预知的微扰影响,据此断定文献中的Grover量子搜索算法的实验实现是在三维复子空间中完成的.同时证明在二维复子空间中,对任意给定的初始态|γ0＞=cosβ0| α＞+sinβ0eiζ|β＞(β0是较小的正实数,ζ是任意的一个实数),存在解集Fj={(θj,θj-1,…,θ1),(φj,φj-1,…,φ1)}(整数j≥2)使得目标态能以100％的最大成功概率找到,其中相位旋转角θj和φl是不为2k’π的实数(1≤l≤j,k’为任意整数).如果只要求目标态以较高的成功概率找到,那么当一个无序数据库中目标态和非目标态的总个数足够大时,对于相对较小的正整数j,解集Fj可表示为j∑l=1θl=j∑l=1φl的形式.     

Hot electrons in silicon dioxide: Ballistic to steady-state transport

Hot electron transport in silicon dioxide is examined with emphasis on current experimental and theoretical results. For oxide layers thicker than 100 Å, steady-state transport has been shown to control the carrier flow at all fields studied. The transition from a nearly thermal electron distribution at electric fields less than approximately 1.5 MV/cm to significantly hot distributions with average energies between 2 and 6 eV at higher fields of up to 16 MV/cm is discussed. The significance of nonpolar phonon scattering in controlling the dispersive transport at higher electric fields, thereby preventing runaway and avalanche breakdown, is reviewed. The transition from ballistic to steady-state transport on very thin oxides layers of less than 100 Å in thickness and the observation of single phonon scattering events are also discussed.     

Drastic influence of plasma quasi-static electric fields on satellites of helium forbidden lines

The emission spectrum has been calculated of helium- and alkali-like quantum systems in plasma with quasi-monochromatic electric field E₀ cos ωt. It was demonstrated that taking into account even relatively weak quasi-static plasma electric fields S could drastically alter the known Baranger-Mozer results, concerning the intensities of the forbidden line satellites. The way for the correction of Baranger-Mozer-type diagnostics of the field E₀ cos ωt is pointed out. It was also found that intensive satellites of a new type appear at the distance ±ω from the allowed line.     

Relaxation time of a Brownian rotator in a potential with nonparabolic barriers

The extension of the Kramers theory of the escape rate of a Brownian particle from a potential well to the entire range of damping proposed by Mel’nikov and Meshkov [V.I. Mel’nikov, S.V. Meshkov, J. Chem. Phys. 85 (1986) 1018] is applied to the inertial rotational Brownian motion of a fixed axis rotator in a potential V(θ)=−K₁cos2θ−K₂cos4θ, where θ is the angle specifying the orientation of the rotator and K₁ and K₂ are constants. It is shown that in the neighbourhood of K₁∼4K₂ (flat barrier), the Mel’nikov-Meshkov method must suitably be adapted so that the effect of a nonparabolic barrier top can be correctly accounted for in the calculation of the relaxation time. The results obtained are compared with numerical calculations of the longest relaxation time (inverse smallest nonvanishing eigenvalue) using a matrix continued fraction algorithm and reasonable agreement is obtained for K₁≥4K₂ and all values of the dissipation parameter.     

Na原子斯塔克态寿命的实验测定

在１２５０￣２０００Ｖ／ｃｍ的静电场变化范围内，用可调谐激发实现Ｎａ原子在ｎ＝１７，ｍ＝０斯塔克族各能态布局，采用延迟脉冲场电离方法测量了各斯塔克能态在不同外电场下的寿命，讨论了外电场强度和环境黑体辐射对斯塔克态寿命的影响。     

The computation of Karplus equation coefficients and their components using self-consistent field and second-order polarization propagator methods

The Karplus equation has been investigated by ab initio computation of the spin-spin coupling constants for a series of rotated ethane geometries. The couplings have been calculated at the self-consistent field (SCF) level as well as using the second-order polarization propagator approximation (SOPPA) and the second-order polarization propagator approximation with coupled cluster singles and doubles amplitudes (SOPPA(CCSD)) and have been compared with results of previous calculations. The four principal components of the coupling constants rather than just the Fermi-contact have been calculated, and the common supposition that the Fermi-contact term is totally dominant has been confirmed. The derivatives of the orbital paramagnetic and orbital diamagnetic terms are significant but opposite in sign for the case of this rotation in ethane. It is found that the coefficients in the Karplus equation are largely overestimated at the SCF level, whereas the SOPPA(CCSD) results are in good agreement with coefficients derived from experimental coupling constant data or the results of multi-configurational self-consistent field (MCSCF) calculations. It is further observed that extending the Fourier series in the Karplus equation to include cos(3θ) and cos(4θ) terms neither significantly improves the quality of the fit nor significantly changes the values of the other coefficients. In order to simulate the Abraham and Pachler equation, calculations varying the nuclear charge on hydrogen have been performed. These will allow an abstract but flexible prediction of the effect of electronegative substituents.