The minimum norm method for the determination of the charge density from elastic electron scattering data

Unphysical behavior in the QR algorithm based least squares determination of the expansion coefficients of the charge density obtained from limited information about the charge form factor occurs when the spread of the singular values in the matrix relating these quantities becomes too large. Setting the smallest singular values equal to zero in the singular value decomposition used in the minimum norm method yields a much more reasonable determination of the charge density. Increasing the size of the basis without increasing the range of the prior information about the charge form factor leads to ambiguities in the determination of the charge density. Numerical results in an analytic model are presented.     

Relationship Between the Proton Charge Form Factor and the Quark-Quark Interaction

We demonstrate how the parameterized proton elastic charge form factor may be used to determine the quark-quark interaction assuming a constituent-quark model of the nucleon and non-relativistic kinematics. The relation between the hypercentral component of the three-quark bound-state wave function and the charge density is obtained by using an Abel-type integral equation. To a high degree of accuracy, this component fixes the hypercentral potential, from which the quark-quark interaction may be determined exactly via another Abel transform. We find that the presence of the meson cloud makes it impossible to determine the long-range behaviour of the quark-quark potential. However, our results indicate that the Gari-Krüpelmann and dipole parametrizations of the form factor both generate potentials that are singular at short distances, indicating a degree of sensitivity of the form factor to the quark-quark interaction at small distances. We also generalize our technique to systems of arbitrarily large number of particles. Received June 21, 1994; revised October 3, 1994; accepted for publication November 24, 1994     

The conductivity of the two component system of the chessboard type

The effective conductivity of the sample with a chessboard structure is found. The corner points are singular for the electric field and charge density. The effective conductivity, charge density and electric potential are expressed in terms of a Weierstrass elliptic function. The results are valid for films and for cylindrical samples with the same cross-section structure. We confirm the conjecture of Dykhne about the value of the effective conductivity for the chessboard structure.     

Effects of contact resistance on the evaluation of charge carrier mobilities and transport parameters in amorphous zinc tin oxide thin-film transistors

Accurate determination of the charge transport characteristics of amorphous metal-oxide transistors requires the mitigation of the effects of contact resistance. The use of additional electrodes as voltage probes can overcome contact resistance-related limitations and yields accurate charge carrier mobility values, trap depths and temperature and carrier density dependencies of mobility as well as trap depths. We show that large differences in measured charge carrier mobility values are obtained when such contact resistances are not factored out. Upon exclusion of the contact resistance, the true temperature dependence of charge carrier mobility appears in the form of two clearly distinct mobility regimes. Analyzing these revealed mobility regions leads to a more accurate determination of the underlying transport physics, which shows that contact resistance-related artefacts yield incorrect trends of trap depth with gate voltage, potentially leading to a misconstruction of the charge transport picture. Furthermore, a comparison of low- and high-mobility samples indicates that the observed effects are more general.     

Empirical transverse charge densities in the nucleon and the nucleon-to-delta transition

Using only the current empirical information on the nucleon electromagnetic form factors we map out the transverse charge density in proton and neutron as viewed from a light front moving towards a transversely polarized nucleon. These charge densities are characterized by a dipole pattern, in addition to the monopole field corresponding with the unpolarized density. Furthermore, we use the latest empirical information on the N-->Delta transition form factors to map out the transition charge density which induces the N-->Delta excitation. This transition charge density in a transversely polarized N and Delta contains both monopole, dipole and quadrupole patterns, the latter corresponding with a deformation of the N and Delta charge distribution.     

Proton electromagnetic-form-factor ratios at low Q2

We study the ratio R identical with muG_{E}(Q2)/G_{M}(Q2) of the proton at very small values of Q2. Radii commonly associated with these form factors are not moments of charge or magnetization densities. We show that the form factor F2 is correctly interpretable as the two-dimensional Fourier transformation of a magnetization density. A relationship between the measurable ratio and moments of true charge and magnetization densities is derived and used to show that the magnetization density extends further than the charge density, in contrast with expectations based on the measured reduction of R as Q2 increases.     

Determining the mobility of ions by transient current measurements at high voltages

We present polarization and transient current experiments that allow an independent determination of the charge carrier density and the mobility of ions in polymer electrolytes at low charge carrier density. The method relies on a complete depletion of ions in the bulk electrolyte achieved by applying high voltages. Based on a qualitative model for the charge dynamics in this nonlinear regime, the method is exemplarily applied to a system of polymethylmethacrylate doped with small amounts of a lithium salt. The independently obtained values for the ionic mobility, the charge carrier density, and the conductivity are consistent for all salt concentrations studied. Criteria for the applicability of the method are discussed.     

Charge form factor and cluster structure of the 6Li nucleus

The charge form factor of the 6Li nucleus is considered on the basis of its cluster structure. The charge density of ⁶Li is presented as a superposition of two terms. One of them is a folded density and the second one is a sum of the ⁴He and deuteron densities. Using the available experimental data for ⁴He and deuteron charge form factors, a satisfactory agreement of the calculations within the suggested scheme is obtained with the experimental data for the charge form factor of ⁶Li, including those in the region of large transferred momenta.      

圆筒状DBD放电特性模拟研究

用XOOPIC软件对同轴圆筒状反应装置DBD放电特性进行了二维模拟研究。在频率为20kHz、正弦电压幅值为5kV的大气压氩气放电中,再现了微放电通道形成和发展过程,其微放电的寿命约为4ns。获得了电子、离子、介质表面电荷密度和电场强度随空间和时间的分布,发现在高压线圈的位置附近电子、离子和介质表面电荷密度存在极值。与典型平板介质阻挡放电相比,微放电中的电子密度、场强增加2~3个数量级。     

Effect of coma on the focusing of an apertured singular beam

Effect of coma on the intensity distribution and encircled energy of a singular beam, at the focal plane of a lens, is evaluated numerically by using Fresnel–Kirchhoff diffraction integral for two different values of topological charge. Results show lateral shift and flattening of the dark core. It is noticed that the singular beam with double topological charge is affected more by comatic aberration in comparison to the beam with single topological charge. We also verified our results by using optical transfer function approach.     

The three-body force in the trinucleons

The status of three-body forces in nuclear physics within the context of the trinucleon system is reviewed. The theoretical approaches of the Hannover. Brazilian, Tuscon-Melbourne, and Urbana-argonne groups to modeling the three-nucleon force are outlined and compared. Results of numerical calculations based upon contemporaryNN forces alone plus those utilizing these three-body interactions are summarized for various bound-state observables and the Fourier transform of the charge density (the charge form factor in the impulse approximation) as well as selected continuum observables. Uncertainties in our experimental knowledge of theNN force, which significantly affect conclusions about the size of nuclear three-body force effects. are discussed.     

Empirical transverse charge densities in the deuteron

Using the recent empirical information on the deuteron electromagnetic form factors we map out the transverse charge density in the deuteron as viewed from a light front moving towards the deuteron. The charge densities for a transversely polarized deuteron are characterized by monopole, dipole and quadrupole patterns.     

Correlation anomalies of the atomic form factor in the X-ray region of elastic scattering

The role of electron correlations in the ground state of the Ne atom in the determination of the absolute values and shape of its form factor is studied. It is found that the correlation effects change the Hartree–Fock values of the atomic form factor within the range from -0.15 to +0.15%.     

Short time propagation of a singular wave function: Some surprising results

The Schrödinger evolution of an initially singular wave function was investigated. First it was shown that a wide range of physical problems can be described by initially singular wave function. Then it was demonstrated that outside the support of the initial wave function the time evolution is governed to leading order by the values of the wave function and its derivatives at the singular points. Short-time universality appears where it depends only on a single parameter—the value at the singular point (not even on its derivatives). It was also demonstrated that the short-time evolution in the presence of an absorptive potential is different than in the presence of a nonabsorptive one. Therefore, this dynamics can be harnessed to the determination whether a potential is absorptive or not simply by measuring only the transmitted particles density.     

EFFECTS OF MODE LOCALIZATION ON INPUT-OUTPUT DIRECTIONAL PROPERTIES OF STRUCTURES

The singular-value decomposition (SVD) is employed to study the effects of localization phenomena on input-output relationships, and power and energy transmission ratios of structures. For weakly and strongly coupled systems, existence of strong localization of singular vectors and abrupt veering of singular value loci are shown. Occurrence of strong localization causes abrupt changes in input-output directional properties. In contrast to eigenvalues, singular values do not veer away by introducing a disorder in weakly coupled systems. In particular, the use of singular values and vectors is computationally advantageous in considering multiple load cases. While eigenvalue-based analyses give information about the resonance frequencies and vibration modes of a structure, singular values of the structure are related to the forced response characteristics and give the dynamic behavior in the frequency domain. Representative examples in structural dynamics are presented.     

IWD-Hankel-SVD模型下玉米叶片光谱铜污染信息预测

近年来在工业化和城镇化快速发展的地区,由重金属污染导致的环境问题尤为突出,特别是农业重金属污染更为社会所关注,因此,探索快速便捷的重金属污染甄别与监测方法极为重要。高光谱遥感作为新兴的重金属污染监测技术已有了深入研究。提出了固有波长尺度分解（IWD）概念和方法,并结合Hankel矩阵和奇异值分解（SVD）等建立了植被重金属污染程度预测的IWD-Hankel-SVD模型,该模型分为单变量模型和多变量模型。单变量模型主要是通过重金属污染的植被光谱IWD处理来获取光谱信息固有旋转分量（PRC）以提取最佳PRC的有效特征波段;在对各特征波段所构建的Hankel矩阵进行奇异值分解（SVD）基础上,依据获得该模型的奇异熵实现重金属污染信息预测。多变量模型是以植物叶绿素浓度相对值、单变量模型奇异熵作为参数实现重金属污染的信息预测。根据不同重金属Cu2+胁迫梯度下玉米植株污染的叶片光谱和叶绿素浓度以及叶片中Cu2+含量测定的数据,首先对不同浓度Cu2+胁迫下玉米叶片光谱进行IWD分析,获得能够较好保留原始输入光谱信息的最佳PRC,并从中提取到有效特征波段553~680,681~780,1 266~1 429,1 430~1 631,1 836~1 913和1 914~2 111 nm;然后对每一个特征波段构造其Hankel矩阵并进行SVD处理,以求取单变量的IWD-Hankel-SVD模型奇异熵;最后通过各特征波段所对应模型奇异熵与玉米叶片中Cu2+含量的相关分析,得到依据1 266~1 429和1 836~1 913 nm特征波段计算出奇异熵与玉米叶片中Cu2+含量的决定系数R2均高达0.9左右,说明这两个特征波段用于IWD-Hankel-SVD模型的Cu污染程度预测更具优越性和解释能力。同时,再把玉米叶片中叶绿素浓度相对值、1 266~1 429和1 836~1 913 nm特征波段相应模型奇异熵作为参数,采用偏最小二乘回归分析,得出多变量IWD-Hankel-SVD模型的玉米叶片Cu污染程度预测能力更强,决定系数R2达到0.9476,证明了多变量模型更具有鲁棒性和稳健性。     

Electron bunch interaction with a monochromatic electromagnetic wave

A technique of modulation of the charge density in a bunch when it interacts with a linearly polarized laser beam is developed. Solution of the problem is based on the numerical method for determination of interaction time of different electrons in the bunch flying through the interaction region, with use of an integral of motion of an electron in the monochromatic electromagnetic field. It is shown that in the terahertz frequency range, at high values of the field strength, sufficiently harddriving modulation of the charge density in the bunch may be obtained. High efficiency of the bunch charge density modulation is demonstrated in plots for different electrodynamical parameters.     

Model dependence of charge densities determined from electron scattering

A new method is used to analyze recent experiments on electron scattering on ³He in the high momentum transfer region. The accuracy of the new measurements is very high so that the charge density can be determined with much higher accuracy than before. We find that further reduction of the error in charge density can only be achieved by a more accurate measurement of the region 3 < q < 6 fm^?1. Continuing the previous work of Hetherington and Borysowicz, a very useful approximate relation is derived between the error of charge density and the error of measurements of form factor. We find that linear expansion methods lead to similar results as the present method. They require, however, stronger asymptotic assumptions about ?(r).     

Isovector coupling channel and central properties of the charge density distribution in heavy spherical nuclei

The influence of the isovector coupling channel on the central depression parameter and the central value of the charge density distribution in heavy spherical nuclei was studied. The isovector coupling channel leads to about 50% increase of the central depression parameter, and weakens the dependency of both central depression parameter and central density on the asymmetry, impressively contributing to the semibubble form of the charge density distribution in heavy nuclei, and increasing the probability of larger nuclei with higher proton numbers and higher neutron-to-proton ratios stable.