神经元网络在τ→ρVτ极化分析中的应用

在LEP/L3的τ→ρV_τ极化物理分析中,用人工神经元网络法选择事例,获得了比较高的选择效率.详细研究表明,网络本身不会引入明显的系统偏差.使用在Z⁰能区采集到的8977个τ⁺τ^－对事例,得到τ→ρVτ道的极化率P_τ=－0.129±0.050±0.050.本文介绍在这一工作中使用的神经网络训练方法和技巧.     

反应物振动激发对O(3P)+D2→OD+D立体动力学的影响

运用准经典轨线方法,基于Roger的³A"势能面,在碰撞能为104.5 kJ/mol时对O(³P)+D₂反应的立体动力学性质进行了理论研究. 详细讨论与产物矢量相关的的极化分布函数以及四个极化微分反应截面进行了. 结果表明,产物OD的立体动力学性质对反应物分子H_{2相似文献}   

用高斯分布法计算非晶态聚合物聚氯乙烯主转变过程中的动态力学弛豫时间谱分布

对非晶态聚合物聚氯乙烯PVC进行不同频率升温扫描的动态力学弛豫谱测量,发现主转变内耗峰(α峰)峰形及其他峰参数均随频率变化。本文根据连续分布谱的理论讨论PVC主转变内耗峰弛豫时间τ的分布情况,并通过高斯分布时方法,计算出PVC主转变弛豫过程中弛豫时间常数τ₀和激活能△H对弛豫时间τ的贡献权重。指出τ₀和△H在PVC主转变过程中都有明显的分布。     

反质子与核非弹性碰撞中的自旋效应

A(p,p)A*非弹性碰撞过程,若反质子的光学势包含了自旋轨道耦合势,它在碰撞过程中不但能激发正常宇称态,也能激发反常的宇称态,以及非弹性过程的极化度.本文在DWIA框架下导出了微分截面(dσ/dΩ)_f,i,极化度P(θ).并对入射能量为46.8MeV和179.7MeV ¹²C(p,p)¹²C*的2⁺,3^－和1⁺态微分截面、极化度进行严格的分波方法计算.计算与实验符合很好.由于反常宇称态的非弹过程已被测得,表明反质子光学势的自旋效应不容忽视.     

Quasi-classical Trajectory Study of the Intramolecular Isotope Effect in the Reaction O(3P)+H2/HD

利用准经典轨线方法在BMS1解析势能面上研究了反应O(³P)+H₂体系的动力学性质. 主要研究了同位素效应对该反应体系的积分截面、产物转动态分布、微分截面、产物角动量的取向和定向以及对极化微分截面的影响. 对于微分截面,还考虑了反应物初始振动量子数对微分截面的影响. 对反应O+HD与O+H₂产生OH的转动发布进行比较,发现前者OH的转动激发更为明显. 微分截面的结果表明,振动量子数和同位素对散射方向有一定影响. 同位素取代对产物的取向和定向以及极化微分截面的影响也比较明显. 对以上结果利用已有的理论模型进行了分析,得到了合理的解释.     

用14MeV中子轰击铌伴生γ射线研究

利用脉冲化的T(d,n)⁴He中子源、伴随粒子方法、Ge(Li)探测器和飞行时间技术测量了14.9MeV中子和铌反应在30°—140°之间七个角度上的分立γ射线谱;由高分辨γ谱分析程序识别了79条谱线;初步确定了62条谱线所由产生的反应类型和跃迁能级,其中有40条谱线是在由中子诱发的核反应中首次发现的.定出了每条谱线在七个角度上的微分产生截面,结果表明该反应中的伴生γ发射基本上是各向同性的.     

20Na的β+延发α粒子测量

利用兰州放射性次级束流线提供的²⁰Na束流,通过²⁰Naβ^{+ 20}Ne→¹⁶O+α过程,测量了²⁰Na的衰变半衰期T_1/2及衰变α粒子能谱.结果表明,除了E_d≥2.688MeV的9条较高激发能级的衰变α粒子外,实验中还观察到衰变能量E_d为0.890和1.054MeV,1.991MeV,2.424和2.457MeV的²⁰Ne低激发能级的3条α谱线.     

Ce(Ⅳ)和Ce(Ⅲ)化合物系列的X射线光电子能谱研究

用XPS研究了标称四价铈盐系列:硫酸铈铵、硫酸铈、二苯基羟乙酸铈、碘酸铈、过氧化铈、二氧化铈以及三价铈盐系列:草酸亚铈、硫酸亚铈、二苯基羟乙酸亚铈、碘酸亚铈和氯化亚铈.结果表明,上述标称四价铈盐都属于混合价化合物,其Ce3d电子能谱呈现Ce⁴⁺和Ce³⁺的二组谱线结构的混合.在真空中加热后CeO₂的Ols电子能谱有两个氧峰,这说明 Ce(4f⁰)O(2p^π)←→Ce(4f¹)O(2p^n-1) 类型价态波动的可能性较大.三价铈盐的3d谱线的低结合能端约3.5—4eV处则存在摔落伴峰.     

BaTiO3和Ce:BaTiO3单晶的高温喇曼散射研究

从室温至180℃测量了BaTiO₃和Ce:BaTiO₃单晶的偏振喇曼谱,在X(ZZ)Y几何配置下发现了三条频率分别为986,1204和1480cm^-1的新谱线.根据喇曼散射截面的温度依赖关系,确认这些新谱线对应二阶喇曼散射,而A₁(TO)谱中位于275和514cm^-1处的非对称宽峰则属于一阶喇曼散射.在此基础上,对立方相BaTiO₃的喇曼谱和结构相变机制进行了讨论.通过比较B     

Z0共振峰线形的拟合

本文描述了拟合Z⁰峰线形的整个过程;讨论了Z⁰能区e⁺e^－→ff反应截面的各种辐射修正;给出了截面测量中系统误差的主要来源及其在拟合中的考虑;并以Z⁰的一个轻子衰变道τ⁺τ^－(γ)为例,说明拟合Z⁰峰线形得到Z⁰质量、衰变总宽度及τ⁺τ^－(γ)道衰变分宽度的方法.文中还对不同的理论计算程序作了简单的分析和比较.     

Azimuthal distributions in radiative decay of a polarized τ lepton

We investigate various distributions over emitted photon angles, especially over the azimuthal angle, in the one-meson radiative decay of the polarized τ lepton, τ^– → π^–γν_τ. In connection with this, the photon phase space is discussed in more detail because it is nontrivial in the case of a polarized τ lepton. The decay matrix element contains both the inner bremsstrahlung and the resonance (structural) contributions. The azimuthal dependence of some observables are calculated. They are the asymmetry of the differential decay width caused by the τ-lepton polarization, the Stokes parameters of the emitted photon itself, and the correlation parameters describing the influence of τ-lepton polarization on the photon Stokes parameters. A numerical estimation is done in the τ-lepton rest frame for an arbitrary direction of the τ-lepton polarization 3-vector. The vector and axial-vector form factors describing the structure-dependent part of the decay amplitude are determined using the chiral effective theory with resonances (RχT). It is found that the features of the azimuthal distributions allows separating various terms in the spin-dependent contribution. The so-called up–down and right–left asymmetries are also calculated.     

25MeV/u40Ar+197Au反应中高激发热核的时空演化

报道了25MeV/u⁴⁰Ar+¹⁹⁷Au反应中从两粒子相对动量关联函数提取的发射时间随空间大小演化的规律.结果表明，即使发射源质量数减小50%，对计算的关联函数及提取的发射时间影响仍然很小.在短发射时间(τ≤100fm/c)情况下，较小的核物质密度，导致提取的发射时间变小.因此，在正常核物质密度参数下提取的τ值可作为发射时间的上限值.在长发射时间(τ≥300fm/c)情况下发射时间不随空间大小变化，提取的τ即为实际的发射时间. 关键词：     

光谱位相干涉仪参数的优化选取

模拟研究了光谱位相相干直接电场重构法的三个主要参数：时间延迟τ、频率剪切量Ω和展宽器色散φ之间的相互关系.研究结果表明：不同的待测脉冲，具有不同的最佳时间延迟τ；而τ的改变所引起的Ω的改变又限制了τ的选取范围；在此情况下只有适当调整φ才能在τ的较宽的范围内保证测量精度. 关键词： 光谱位相相干直接电场重构法 飞秒脉冲测量 光谱相干     

Analytic Approximation for Process e++e－→τ++τ－ Cross Section Near Threshold

In the structure function approach,we calculate the threshold behaviours for e⁺+e^－→τ⁺+τ^－,which including QED radiative corrections from initial correction,vacuum polarization effect,Coulomb effect and final state correction.This theoretical prediction for threshold behaviours of τ-pair production is useful for BES new measurement of lepton τ mass.     

Uncertainties in τ polarization measurement at SLC/LEP and QED/electroweak radiative corrections

We discuss the τ polarization measurement at SLC/LEP energies as a data point in the precision tests of the Glashow-Salam-Weinberg model. Theoretical and experimental uncertainties of this measurement are examined and it is concluded that apart from left-right asymmetry measurement, and for typical values of the parameters of the Standard Model, the τ polarization offers the best probe of the couplings of leptons to the Z⁰. In particular, the dependence of the τ polarization on the top and Higgs masses is discussed. The interplay of QED initial state bremsstrahlung and other classes of radiative corrections is also discussed.     

Magnetoelectric effect in samarium molybdate

This paper reports on the nonlinear magnetoelectric effect (MEE) in the orthorhombic ferroelectric ferroelastic β′ phase of samarium molybdate Sm₂(MoO₄)₃ observed in magnetic fields up to 20 T and temperatures from 4.4 to 0.43 K. The magnetic-field-induced electric polarization in Sm₂(MoO₄)₃ is an order of magnitude larger than that in isomorphic Gd₂(MoO₄)₃. This provides support for the magnetostriction mechanism proposed by us for the MEE in rare-earth molybdates. The polarization in Sm₂(MoO₄)₃ was found to fall off with time. The relaxation time constant τ increases with decreasing temperature from τ=10² s at T=4.4 K to τ≈10³ s at T=0.43 K.     

Conductivity of Wigner liquid

The conductivity of two-dimensional electron systems with low carrier concentration is considered on the basis of the previously suggested model (Fermi liquid with a soft mode) under the assumption that the equilibrium in each of the (fermion and boson) subsystems is established faster than the impurity relaxation and the relaxation between the subsystems (hydrodynamic approximation). The conductivity of the system depends on three characteristic times: τ₁(τ₂) is determined by the fermion (boson) impurity scattering and τ₁₂ is determined by the friction between the subsystems; the respective temperature dependences are obtained. The conductivity is related to the relaxation time τ in the usual way, and τ obeys the relationship τ^?1=τ ₁ ^?1 +(τ₂+τ₁₂)^?1. It follows from the results obtained that the resistivity of pure samples should increase with temperature and tend towards saturation.     

On the wave functions of an exactly solvable model of interacting fermions with spin 1/2 in an external field

It is shown that hyperbolic systems of Sutherland spin 1/2 particles in an external field with the Morse potential characterized by parameter τ² have a discrete part of their spectrum in the case of a particular constraint on the τ, parameter of two-particle interaction λ, and the number of particles. The ground state is described by a Jastrow wave function. The results known for systems with an interaction inversely proportional to the squared distance between particles are reproduced in the limit τ → ∞.     

Measuring picosecond excited‐state lifetimes at synchrotron sources

A new analysis method for the short excited‐state lifetime measurement of photosensitive species in crystals is described. Based on photocrystallographic techniques, this method is an alternative to spectroscopic methods and is also valid for non‐luminescent excited species. Two different approaches are described depending on the magnitude of the lifetime τ. For very short lifetimes below the width of the synchrotron pulse, an estimated τ can be obtained from the occurrence of the maximal system response as a function of the pump–probe delay time Δt. More precise estimates for both short and longer lifetimes can be achieved by a refinement of a model of the response as a function of the pump–probe delay time. The method also offers the possibility of the structure determination of excited species with lifetimes in the 40–100 ps range.     

Time Domain Optical Spectrometry with Fiber Optic Waveguides

Abstract

The transit time, τ, of a light pulse in a fiber optic waveguide is a function not only of the fiber length but also of the frequency content of the pulse and, to some extent, the electric and magnetic field distributions within the fiber. Thus, we can write τ = τ(L, γ, μ, v) where L is the fiber length and γ is the wavelength. The integers and v index the mode of propagation which is excited. The purpose of this article is to review a number of ways the various transit time effects in optical fibers can be used to measure optical spectra in the time domain. Conventional spectrometers disperse the light spatially. The spectrum is measured either with an array of detectors or, if a single detector is used, by mechanically scanning some element of the spectrometer. The instruments described in this review use optical fibers to selectively delay the wavelength components of a modulated light source so that these components arrive sequentially at a single detector. If the light source is already pulsed, these instruments have the same inherent capability as a multiple detector spectrometer in terms of measurement time or signal-to-noise ratio. For a steady source, special modulation schemes can be used to improve the signal collection and reduce the effective dead time required to measure the dispersed light.