音叉振动阻尼系数的测定与研究

利用计算机的声卡采集音叉振动信号,研究了振动衰减过程中阻尼系数的大小,得出了阻尼系数不是常数,而是与音叉振幅成线性关系的初步结论,并用共振态下策动力振幅对音叉振幅的关系验证了这一结论.根据阻尼系数与振幅的关系解释了两种传统方法测量结果差别很大的原因.     

介子波函数中非微扰效应的一个讨论

本文应用背景场方法计算了与介子分布振幅矩相关的两点关联函数的算符乘积展开. 其结果表明非微扰效应大小依赖于介子的自旋和夸克质量.     

液体对微振动的放大效应

根据表面波声光效应的原理,实验上建立了固体表面微振动的激光衍射测量系统.当激光斜入射到微振动引起的液体表面波上,观察到了清晰、反衬度非常高的衍射图样.利用MATLAB软件对拍摄的衍射图样进行扫描,得到了衍射光斑的光强分布图,并根据衍射图样宽度与表面波振幅的解析关系式,求出了液体表面波的振幅,其大小在微米量级.改变样品池中液体的深度,测得不同深度下液体表面波的振幅,给出了表面波振幅与液体深度之间的解析关系,并发现了液体对微振动的放大效应.利用液体对微振动的放大效应,求出了固体表面微振动的振幅,实现了固体表面微振动的探测.     

液体对微振动的放大效应

根据表面波声光效应的原理,实验上建立了固体表面微振动的激光衍射测量系统.当激光斜入射到微振动引起的液体表面波上,观察到了清晰、反衬度非常高的衍射图样.利用MATLAB软件对拍摄的衍射图样进行扫描,得到了衍射光斑的光强分布图,并根据衍射图样宽度与表面波振幅的解析关系式,求出了液体表面波的振幅,其大小在微米量级.改变样品池中液体的深度,测得不同深度下液体表面波的振幅,给出了表面波振幅与液体深度之间的解析关系,并发现了液体对微振动的放大效应.利用液体对微振动的放大效应,求出了固体表面微振动的振幅,实现了固体表面微振动的探测.     

方形光阑限制高斯光束的传输变换

对基模高斯光束经方形光阑限制光学系统的光斑传输变换规律进行了论述．对于任一共轴光学系统,在不考虑有效光阑前面元件的衍射和变换时,考察入射光经有效光阑和其后面的元件发生衍射,根据柯林斯公式,对于非成像光学系统,采用稳相法得到出射光场的振幅分布;对于成像光学系统,根据像传递原理得到出射光场的振幅分布,最后得出出射光斑大小由有效光阑边长与光阑处高斯光束腰斑大小比较决定的结论．     

电磁驱动的固定弦振动的理论分析

对电磁驱动的弦线波动方程进行分析,得到了严格的理论解。很好地解释了实际中出现的几个现象,并且讨论了驻波振幅与磁场和讯号源的依赖关系。结果表明：驻波振劝的振幅与讯号源的电压或电流正比,与磁场的关系依赖于电磁阴尼和空气阻尼的相对大小。     

光折变多重存储的栅自增强读出特性研究

研究了光折变重存储读出时折射率栅自增强特性与记录晶体厚度、记录时的光强比以及写入的折射率栅振幅之间的关系.结果表明记录晶体的厚度大于某一值,才有自增强效应;较小的参物光强比具有较大的自增强效果,能获得较大的读出衍射效率;自增强读出所能达到的最大衍射效率与写入的栅振幅大小无关,而读出时衍射效率增加的速率与写入的栅振幅成反比.     

壁温周期变化引起的一维热声波的数值模拟

本文采用可压缩流动的SIMPLE算法对壁温周期变化引起的气体中的一维热声波的产生和传播进行了数值模拟,分析了其中的流动和换热规律.计算结果表明,壁面温度周期变化可以产生大振幅的热声波,当其达到准平衡状态时温度产生稳态的超温现象,超温幅度的大小和极值的位置随着加热温度的振幅和频率变化而不同.超温现象导致冷壁面的温度梯度增大,强化了介质与冷壁面间的换热.     

弛豫媒质中有限束超声波的非线性传播畸变理论

文中提出弛豫媒质中有限束非线性声波方程,并采用微扰法求得由非线性传播畸变产生的高次谐波的一般解.研究表明,对高斯型声波,其谐波畸变解可以解析给出,而且其径向分布始终维持高斯函数.虽然其频散量大小会影响各次谐波的振幅,但其相速的变化却仍与对在频率的小振幅波相同.文中还用Blackstock算子将所得的结果应用于任何吸收-频散媒质,包括只能从经验得到其吸收与频率关系的一些生物媒质.     

论菲涅耳公式对半波损失的解释

本文对一般教科书中直接用菲涅耳公式解释电磁波的半波损失问题提出质疑,认为平行于入射面的反射波、折射波与入射波的电矢量振动的振幅一般不在同一直线上,由菲涅耳公式给出的反射波、折射波与入射波电矢量振动的振幅之比,只能描述其相应振幅之比的大小随入射角和折射角变化的关系,而不能反映其相应振幅间的位相随入射角和折射角变化的关系.笔者认为若将平行于入射面的电矢量振动的振幅分解为平行于界面法线和垂直于界面法线的两个坐标分量,然后根据边界条件导出相应振幅坐标分量之比随入射角和折射角变化的关系。便可以较为严格地解释电磁波在界面反射中发生半波损失的物理实质。 关于电磁波的半波损失在其有关学术领域中一直是一个众说纷纭的问题,近年来,在国内举行的有关学术讨论会中,对该问题的争论重新激烈起来,其争论的焦点在于如何用菲涅耳公式解释电磁波传播至两不同介质的界面时,发生半波损失现象的物理实质。 所谓半波损失,其实质是位相突变π,即电磁波经界面反射后,反射波的电矢量振动的振幅与入射波的振幅反向,亦有π的位相差。反射波位相的改变取决于具体问题的边界条件。振幅反向即位相差为π。对应半波长(λ/2)的光程改变。并非反射过程中真实失去λ/2的光程。 经典电磁理论认为,     

Calculation of multiloop amplitudes in the theory of closed oriented superstrings

Multiloop superstring amplitudes are obtained upon integrating local amplitudes with respect to modular parameters of the Schottky supergroup and with respect to vertex coordinates in the nonsplit (1|1) complex supermanifold. Ambiguities in this integration are removed by the condition requiring that the local symmetries of the amplitudes under discussion be conserved. Local superstring amplitudes are calculated by summing local fermion-string amplitudes. The resulting superstring amplitudes are free from divergencies. The vacuum amplitude is zero, in just the same way as the one-, two-, and three-point massless-boson amplitudes are. The amplitudes in question vanish after integration of corresponding local amplitudes with respect to interaction-vertex coordinates and with respect to the limiting points of the Schottky supergroup, with the exception of those (3|2) points that are fixed by SL(2) symmetry.     

Relations of loop partial amplitudes in gauge theory by Unitarity cut method

It is well known that under the color-decomposition, one-loop amplitude of gluons contains partial amplitudes of single and double trace structures, and particularly all partial amplitudes of double trace structure can be expressed as a linear combination of partial amplitudes of single trace structure. Using unitarity cut method, we prove that this result is the natural consequence of tree-level Kleiss-Kuijf relation. Generalizing the unitarity cut method to two-loop (triple cut in this case), we show that, unlike the one-loop case, partial amplitudes of double and triple trace structures cannot be expressed as a linear combination of partial amplitudes of leading-color single trace structure. For partial amplitudes of subleading-color single trace structure, we have shown a very non-trivial Kleiss-Kuijf relation for six and seven-point amplitudes, which is one new result of our paper and cannot be obtained by U(1)-decoupling method. Mysteriously, when we consider the case of eight points, Kleiss-Kuijf relation must be modified for subleading-color single trace partial amplitudes.     

Decay amplitudes and resonances

The structure of a type of decay amplitudes, which we considered recently and its connection to scattering amplitudes (of arbitrary arrangement channel cases), to conventional decay amplitudes, and to the energy distribution is worked out in detail. The meaning of unperturbed energies in usual approaches is clarified. Our considerations include the case of overlapping resonances. Sum rules for transition amplitudes, such as are of interest for neutral kaon decays, are rigorously derived. The exact interrelations between various approaches are shown.     

Complete and effectively complete inclusive experiments

The experiments required to meadure all the independent amplitudes in any single-particle inclusive process with experimentally available incident particles are determined, and the amplitude (or combination of amplitudes) obtained from each measurement is given. Various kinematic regions are considered, and the measurements which determine the subset of amplitudes expected to be important in each region are found. The prospects of a meaningful separation of exchanged naturalities are also investigated and found to be difficult, due to a kinematic suppression of certain amplitudes.     

Recursion relations and scattering amplitudes in the light-front formalism

The fragmentation functions and scattering amplitudes are investigated in the framework of light-front perturbation theory. It is demonstrated that, the factorization property of the fragmentation functions implies the recursion relations for the off-shell scattering amplitudes which are light-front analogs of the Berends–Giele relations. These recursion relations on the light-front can be solved exactly by induction and it is shown that the expressions for the off-shell light-front amplitudes are represented as a linear combinations of the on-shell amplitudes. By putting external particles on-shell we recover the scattering amplitudes previously derived in the literature.     

Pion-Nucleon Interaction and Two-Pion-Exchange Three-Nucleon Forces

We compare the πN scattering amplitudes that underlie 2π-exchange three-nucleon forces (TBFs) with the experimental πN amplitudes in the form of partial-wave phase shifts and subthreshold invariant amplitudes. The amplitudes of the Tucson-Melbourne and Brazil TBFs when taken on-pion-mass-shell predict scattering lengths at threshold and phase shifts (slightly) above threshold which are in good agreement with the experimental amplitudes, except for the S-waves. Partial wave amplitudes from separable potentials, recently employed in a 2π-TBF calculation, were continued below threshold, summed into invariant amplitudes, and compared with the experimental amplitudes in this kinematic region, which is most relevant to the kinematics of TBFs. The separable-potential invariant amplitudes, in contrast to those of TM and Brazil TBFs, do not compare well quantitatively with the experimental amplitudes in this region but have a similar qualitative behaviour. The very small TBF effect in the triton of the separable-potential amplitude appears to be due to the πNN vertex function rather than the πN amplitude itself. Received April 27, 1994; revised August 2, 1994; accepted for publication August 31, 1994     

Hidden analytic relations for two-loop Higgs amplitudes in QCD

We compute the Higgs plus two-quark and one-gluon amplitudes(H→qqg) and Higgs plus three-gluon amplitudes(H→3 g) in the Higgs effective theory with a general class of operators.By changing the quadratic Casimir CF to CA,the maximally transcendental parts of the H→ qqg amplitudes turn out to be equivalent to that of the H→3 g amplitudes,which also coincide with the counterparts in N=4 SYM.This generalizes the so-called maximal transcendentality principle to the Higgs amplitudes with external quark states,thus the full QCD theory.We further verify that the correspondence applies also to two-loop form factors of more general operators,in both QCD and scalar-YM theory.Another interesting relation is also observed between the planar H→qqg amplitudes and the minimal density form factors in N=4 SYM.     

General formalism in collinear regime for pseudoscalar meson production in NN collisions

The spin structure of the matrix element for the pseudoscalar meson production processes in nucleon-nucleon collisions is established in the collinear kinematical regime in terms of 3 independent scalar amplitudes. This result is valid for any reaction mechanism and for any energy of the colliding and the produced particles. The complete experiment for the full reconstruction of all 3 complex amplitudes must contain two different classes of polarization experiments. The polarization transfer coefficients can be used to determine the moduli of all 3 amplitudes, whereas the spin correlation coefficients for + collisions are sensitive to the relative phases of different amplitudes. Received: 13 August 2001 / Accepted: 20 September 2001     

Off-mass shell dual amplitudes (II)

A new method for continuing dual model amplitudes off the mass shell was recently proposed. This paper explores some of the properties of the resulting amplitudes. It is demonstrated that one-current amplitudes contain fixed poles in the J-plane at positions that are correlated with the asymptotic power behavior of form factors. The two-point function is explicitly calculated and shown to fall asymptotically as a power provided that a certain condition involving the dimension of space-time and a parameter (that is believed to be correlated with the leading Regge intercept) is satisfied. Certain formulas required for future investigation of more complicated amplitudes are also derived.     

Spin dependence of the parity non-conserving neutron-nucleus interaction

We show that the spin dependence of the parity violating amplitudes can provide a clue to the precise origin of the large parity non-conserving effects observed in neutron scattering on nuclei. The polarization asymmetries for longitudinal and transverse polarization of the incoming neutrons allow the separation of these spin amplitudes. In the mechanism of parity admixing of the virtually excited compound nucleus states, the spin dependence of the weak amplitudes is determined by the spin dependence of the strong interaction amplitudes for the elastic channel of the decay of the p-wave resonance