Structural Organization of syndiotactic polystyrene films crystallized in the β form

Syndiotactic polystyrene (sPS) films were obtained either by casting or by melt crystallization in the β form. Different thermal treatments of the melt led to mixed α and β forms. The structural organization was investigated by x-rays, transport properties, and Fourier transform infrared analysis. The β form is characterized by chains in zigzag planar conformation. For samples prevalently in β form, the fraction of impermeable phase, derived from sorption measurements, was found coincident with the fraction of crystalline phase derived from x-rays. In samples with mixed α and β forms, however, a fraction of mesophase is also present. The β form of sPS is stable to dichloromethane, whereas the α form is transformed into a crystalline form with the chains in helical conformation. Nevertheless, when the relative fraction of β form is lower than a critical value, it also dissolves in liquid dichloromethane, undergoing the conformational transition into the helical form.     

A normal form for excitable media

We present a normal form for traveling waves in one-dimensional excitable media in the form of a differential delay equation. The normal form is built around the well-known saddle-node bifurcation generically present in excitable media. Finite wavelength effects are captured by a delay. The normal form describes the behavior of single pulses in a periodic domain and also the richer behavior of wave trains. The normal form exhibits a symmetry preserving Hopf bifurcation which may coalesce with the saddle node in a Bogdanov-Takens point, and a symmetry-breaking spatially inhomogeneous pitchfork bifurcation. We verify the existence of these bifurcations in numerical simulations. The parameters of the normal form are determined and its predictions are tested against numerical simulations of partial differential equation models of excitable media with good agreement.     

Form Invariance and Conserved Quantity for Non-holonomic Systems with Variable Mass and Unilateral Constraints

The paper studies the form invariance and a type of non-Noether conserved quantity called Mei conserved quantity for non-holonomic systems with variable mass and unilateral constraints.Acoording to the invariance of the form of differential equations of motion under infinitesimal transformations,this paper gives the definition and criterion of the form invariance for non-holonomic systems with variable mass and unilateral constraints.The condition under which a form invariance can lead to Mei conservation quantity and the form of the conservation quantity are deduced.An example is given to illustrate the application of the results.     

光斑的形状因子及其在光纤定解问题中的应用

通过比较面光源与多极子点源两种辐射场,定义了光斑的形状因子,它决定于光斑上的源强分布.给出了形状因子的确定方法,求出了几种常见光斑的形状因子.把形状因子应用于光纤理论,补充了入射端面上的定解条件,完整地设定了定解问题.利用形状因子简单讨论了光纤端面的源强分布对光纤模式特性的影响 关键词： 光纤光学 多极子面光源 形状因子     

Effects of rebinding rate and asymmetry in unbinding rate on cargo transport by multiple kinesin motors

Many intracellular transports are performed by multiple molecular motors in a cooperative manner.Here,we use stochastic simulations to study the cooperative transport by multiple kinesin motors,focusing mainly on effects of the form of unbinding rate versus force and the rebinding rate of single motors on the cooperative transport.We consider two forms of the unbinding rate.One is the symmetric form with respect to the force direction,which is obtained according to Kramers theory.The other is the asymmetric form,which is obtained from the prior studies for the single kinesin motor.With the asymmetric form the simulated results of both velocity and run length of the cooperative transport by two identical motors and those by a kinesin-1 motor and a kinesin-2 motor are in quantitative agreement with the available experimental data,whereas with the symmetric form the simulated results are inconsistent with the experimental data.For the cooperative transport by a faster motor and a much slower motor,the asymmetric form can give both larger velocity and longer run length than the symmetric form,giving an explanation for why kinesin adopts the asymmetric form of the unbinding rate rather than the symmetric form.For the cooperative transport by two identical motors,while the velocity is nearly independent of the rebinding rate,the run length increases linearly with the rebinding rate.For the cooperative transport by two different motors,the increase of the rebinding rate of one motor also enhances the run length of the cooperative transport.The dynamics of transport by N(N=3,4,5,6,7 and 8)motors is also studied.     

Form factors in the projected linear chiral sigma model

Several nucleon form factors are computed within the framework of the linear chiral soliton model. To this end variational means and projection techniques applied to generalized hedgehog quark-boson Fock states are used. In this procedure the Goldberger-Treiman relation and a virial theorem for the pion-nucleon form factor are well fulfilled demonstrating the consistency of the treatment. Both proton and neutron charge form factors are correctly reproduced, as well as the proton magnetic one. The shapes of the neutron magnetic and of the axial form factors are good but their absolute values at the origin are too large. The slopes of all the form factors at zero momentum transfer are in good agreement with the experimental data. The pion-nucleon form factor exhibits to great extent a monopole shape with a cut-off mass ofΛ=690 MeV. Electromagnetic form factors for the vertexγNΔ and the nucleon spin distribution are also evaluated and discussed.     

Exploring light-cone sum rules for pion and kaon form factors

We analyze the higher-twist effects and the SU(3)-flavor symmetry breaking in the correlation functions used to calculate form factors of pseudoscalar mesons in the QCD light-cone sum rule approach. It is shown that the Ward identities for these correlation functions yield relations between twist-4 two- and three-particle distribution amplitudes. In addition to the relations already obtained from the QCD equations of motions, we have found a new one. With the help of these relations, the twist-4 contribution to the light-cone sum rule for the pion electromagnetic form factor is reduced to a very simple form. Simultaneously, we correct a sign error in an earlier calculation. The updated light-cone sum rule prediction for the pion form factor at intermediate momentum transfers is compared with the recent Jefferson Lab data. Furthermore, from the correlation functions with strange-quark currents the kaon electromagnetic form factor and the weak transition form factors are predicted with accuracy. Received: 30 June 2002 / Published online: 7 October 2002 RID="a"     

Euclidean Majorana and Weyl Spinors

The complex form algebra of Schwinger functions of a Dirac field on a Euclidean R ^d with arbitrary dimension d is decomposed into the form algebras of Majorana spinors and of Weyl spinors. The existence of real form algebras is investigated. The reality condition leads to severe restrictions in the case of Majorana forms which do not agree with the results of classical field theory. For all real form algebras Euclidean spinors are constructed as elements of a measure space.     

Parity Violation in Electron Quasi-Elastic Scattering

Parity violating electron scattering on a nucleus in the quasi-elastic region is investigated within a relativistic single particle model from ²⁰⁸Pb and with the incident electron energy up to 1 GeV. We discuss the effect of nucleon electromagnetic form factors by comparing the standard Sachs form factors with the parameterized form recently adjusted to the world data. The effect of the strangeness is also investigated through the recent results of the strangeness form factors, and we separately calculate the asymmetries of longitudinal and transverse response functions.     

Tail,zeros and space-like region behaviour of the electromagnetic pion form factor

Combining the real and imaginary parts of the pion form factor from the resonant region, given by a simple formula obtained by means of the dispersion relation method, with some special assumptions in the asymptotic region and sum rules, the time-like region form factor tail is predicted. Further, the existence of form factor zeros is investigated and on the basis of numerical results one can conclude that zeros of the pion form factor exist. By means of the unsubtracted dispersion relation, the predicted space-like region behaviour of the form factor is found to be in excellent agreement with the existing experimental data.     

光学自由曲面数控化加工方法

在光学系统中，为了满足特殊的成像要求，需要使用自由曲面光学零件，但由于自由曲面是一类非常复杂的曲面，用传统的光学加工方法很难加工。本文概要介绍了光学非球面的多种加工方法，探索了这些方法加工光学自由曲面的可能性，提出了用数控化加工方法加工光学自由曲面，并利用这种方法加工了一块自由曲面透镜。     

二噻吩乙烯桥连-环糊精二聚体光致变色性质

合成了以可光控的二噻吩乙烯分子为桥连单元的β-环糊精二聚体作为潜在的可调受体化合物．该化合物显示了显著的光致变色特性，即以254 nm的紫外光照射，开环体会立即发生光环化反应生成粉红色的闭环体；而有色的闭环体用大于460 nm的可见光照射后又会发生开环反应．同时还研究了正向光环化反应的反应动力学．此外，还以四苯磺基卟啉（TSPP）为客体化合物进行了荧光滴定，研究开/闭环体之间包合能力的差异，发现闭环体对TSPP的包合稳定常数是开环体的5倍．     

单面完整约束力学系统的形式不变性

研究单面完整约束力学系统的形式不变性.根据运动微分方程的形式在无限小变换下的不变性，给出了单面完整约束力学系统形式不变性的定义和判据，建立了系统的形式不变性与Noether对称性、Lie对称性之间的关系，并举例说明结果的应用. 关键词： 分析力学 单面约束 形式不变性 Lie对称性 Noether对称性 守恒量     

Nucleon form factors in a projected chiral soliton model with dynamical confinement

We calculate nucleon form factors in the framework of a chiral chromodielectric model. The model state describing the nucleon is an angular momentum and isospin eigenstate with obtained by means of Peierls-Yoccoz projection from the hedgehog. We present results for the electromagnetic form factors and also for the axial form factors of the nucleon. There is a fairly good agreement with the data for small momentum transfers. For high momentum transfers (i.e. q² > 0.1 GeV² the agreement becomes poorer. As a general rule the calculated form factors fall too rapidly.     

Electron density in the oxygen discharge plasma

The electron density in two forms of the oxygen plasma positive column is determined. These two forms differ in the gradient of the potential of the axial electrical field. The electron density is measured by means of a microwave toroidal resonator. In the form with higher gradient (so-called “H” form), a lower electron density than in the form with lower gradient (so-called “T” form) is found. The electron density in the two types of oxygen discharge plasma, which differ in cathode fall, is measured too.     

Non-Noether Conserved Quantity for Relativistic Nonholonomic System with Variable Mass

Using form invariance under special infinitesimal transformations in which time is not variable, the non-Noether conserved quantity of the relativistic nonholonomic system with variable mass is studied. The differential equations of motion of the system are established. The definition and criterion of the form invariance of the system under infinitesimal transformations are studied. The necessary and sufficient condition under which the form invariance is a Lie symmetry is given. The condition under which the form invariance can be led to a non-Noether conserved quantity and the form of the conserved quantity are obtained. Finally, an example is given to illustrate the application of the result.     

升温在位红外研究物理老化对间规聚苯乙烯结晶行为的影响

通过在位红外光谱测量研究了物理老化对非晶和δ晶型的间规聚苯乙烯（ＳＰＳ）升温结晶过程的影响。发现对于晶样品来说,在物理老化前后,其结晶（即非晶→α晶型）的温度区间变化不大;但对于δ晶型的样品而言其物理老化后的晶型转变（即δ晶型→γ晶型）温度区间是１０４～１２７℃,与未物理老化的晶型转变温度区间９０～１１２℃相比,转变温度升高了约１４℃,这充分说明了物理老化使溶致型的δ晶型更加稳定,其溶剂与晶体的结     

Electromagnetic properties of relativistic quarks in confining potentials

We investigate electromagnetic properties of the quark core of nucleons in a model with massless quarks in confining potentials. We find quark core rms radii of 0.6 fm or smaller to be compatible with form factor data corrected for pion cloud effects. Relations between the magnetic form factor and the axial vector or pseudoscalar form factors will also be discussed.     

pH-Induced Changes in the Secondary Structure of Cytochrome c: an Infrared Spectroscopic Study

The infrared spectra of 3mM solutions of horse heart cytochrome c were recorded as a function of pD(corresponding to acid high spin form, acidic low spin form, native form, lysine form, the so-termed “strained lysine form” as well as the so-termed “A state” of cytochrome c). An analysis of the pH-induced changes in the secondary structure was performed based on changes in the conformation-sensitive amide I bands of this protein. In lysine and strained lysine forms, the contents of random structure increase at the expense of α-helix. In acidic low. spin form (pH4–2.5), cytochrome c was almost unfolded. The proportion of α-helix had a substantial decrease while the contents of both random structure and 3₁₀-helices got a rise. In acidic high spin form (when pH is below 2.5), a further decrease of pD gave no rise to a continued unfolding in cytochrome c but made it refold to the “A state” with properties similar to those of a molten globular state. Adding enough KC1 to the cytochrome c solution(pD2.2 with 0.5MKC1 and pD3.0 with 1.5 MKCl) in which cytochrome c was nearly fully unfolded also led to the formation of A state of cytochrome c. The compositions of all types of secondary structures in A state were evaluated. The behavior of 3₁₀-helices in acidic high/low spin form indicated they might be intermediates between α-helices and random structure in acidic solution as proposed by Miick et al.