弦振动实验装置的改进

弦振动实验装置的改进郑稷（重庆师范专科学校６３２１６８）弦振动实验是力学实验中一个重要而典型的实验．该实验的主要内容是研究弦振动的基频与弦长（其他条件不变）和基频与张力（其他条件不变）的关系．实验方法有两种：（１）采用振动频率固定的振动体，通过改变弦...     

用打点计时器作弦振动实验

在传统的普物实验教材中,常用电动音叉与一端固定的弦来作“弦的振动实验”,如图1所示。实验时常用方法是固定弦长L,改变张力T,或改变张力T的同时调节弦长L,使弦上产生基频或某次谐频共振。由于张力T改变时,弦线的线密度将随之改变,这会给实验带来误差。另外,实验中策动源频率不可改变,使实验的“自由度”受到一定限制。用音频振荡器(可用音讯——1甲型)的功率输出去驱动打点计时器(可用中学物理实验用的)作弦的振动实验可以固定弦长和张力,而改变策动源的频率(频率的大小可以由刻度盘读出,也可以用频率计测出)。     

弦长对弦振动实验的影响研究

弦振动实验中,在固定端施加张力不变的前提下,改变弦长度。利用振动频率与驻波波长的关系,得到弦的线密度。通过比较不同弦长下得到的弦的线密度与弦质量长度比结果的比较,讨论了弦长对弦线密度测量结果的影响,分析了弦振动实验中合理选择弦长的必要性。     

弦振动实验数据处理与分析

通过对大量实验数据进行分析,同时采用Matlab软件对数据进行系统处理,并且利用Ori-gin软件作图并进行拟合,简单形象地展现了数据间的关系.以此为基础,分析总结了弦振动形成驻波的规律,并且对实验仪器进行了一定的测评.     

关于弦振动实验中的驻波解

利用波的合成所形成的驻波现象来检测波的参量:波速、波长和频率并进而研究一些物理现象,在大学物理实验中是有启发和实际意义的。本刊曾先后刊载了黄涛和郝乃澜的两篇文章,对弦振动实验中的有关问题进行了探讨。但不得不指出的是郝文在定解问题的处理、推导和得出结论时,     

弦振动实验装置的改进

弦振动实验装置的改进刘全跃（皖南医学院芜湖２４１００１）一、问题的提出弦振动研究实验是普通物理实验的一个基本内容，通过这个实验可加深对横波的产生、传播以及所形成驻波的理解，并可学会一种测量频率的方法——驻波法，实验中常用的振源是电动音叉；然而传统的弦...     

弦振动实验的改进

分析了弦音计实验在精确度及操作性上存在的不足,对实验做了以下改进:将水平仪的水准器直接安装在弦音计的杠杆中,将接收线圈放在适当位置,利用单片机直接读取共振频率.通过改进实验精确度更高,操作更快捷.     

用弦的振动分析电贝司发声原理

本文通过弦的振动对电贝司的发声原理做了分析，内容涉及到间高、泛音、音色等方面，特别是为不同的弹奏技法产生的不同音色找到了一些解释。     

弦振动实验中的倍频共振现象

本文在张力正弦变化的模型下讨论了有纵向策动时弦的振动，从功、能角反出发分析了出现驻波时需要满足倍频关系的实质，以简化的周期性张力模型为基础讨论了策动为纵向时发生共振的条件. 这些讨论对低年级学生解决弦振动实验中遇到的疑难问题会有帮助     

非齐次边界条件时的半无界弦自由振动问题

基于达朗贝尔公式,讨论了半无界弦自由振动时的非齐次边界条件的延拓问题.结果表明:对半无界弦自由振动时的非齐次边界条件的延拓,理论上可有多种方法,尽管延拓表达式不同,但不会影响最终结果.文中最后还给出了两种相对简单的延拓方法.     

对弦振动实验中振源的改进

设计制作了一种振源．将其应用于弦振动实验时,不但能像电动音叉作振源那样,可以验证弦线上驻波波长与弦线张力、密度的关系,而且还可以验证电动音叉作振源所不能验证的弦线上驻波波长与驻波频率的关系．     

The covariant perturbative string spectrum

We provide generating functions for the perturbative massive string spectrum which are covariant with respect to the SO(9)$\mathit{SO}(9)$ little group, and which contain all the representation theoretic content of the spectrum. Generating functions for perturbative bosonic, Type II, Heterotic and Type I string theories are presented, and generalizations are discussed.     

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。     

负载弦之演示教具

介绍一自制的负载弦教具，5颗沿铀向充磁的圆柱状钐钴磁铁穿在细钓鱼线上，作为负载弦之负载质点，再以可调频率的交流电磁化马蹄形电磁铁，使得马蹄形电磁铁对圆柱状钐钴磁铁施与周期性的引力及斥力，启动负载弦的各个简正模式．此自制的负载弦教具可定量演示教科书中理论计算的结果．     

Investigation of quasi-realistic heterotic string models with reduced Higgs spectrum

Quasi-realistic heterotic-string models in the free fermionic formulation typically contain an anomalous U(1) that leads to supersymmetry breaking. Supersymmetry is restored by imposing F- and D-flatness on the vacuum. A three generation free fermionic standard-like model which did not admit stringent F- and D-flat directions has been presented (Cleaver et al. in Phys. Rev. D 78, 046009, 2008) and it was argued that all the moduli in that model were fixed. The particular property of that model was the reduction of the untwisted Higgs spectrum by a combination of symmetric and asymmetric internal dimension boundary conditions with respect to the internal fermions associated with the compactified dimensions. This reduction occurred without the need or presence of flat directions. In this paper we extend the analysis of free fermionic models with reduced Higgs spectrum to models with the same internal space but with modified gauge groups: SO(10) or flipped SU(5) subgroup. We show that all the models studied in this paper do admit stringent flat directions. Currently, the only examples of models that do not admit stringent flat directions are the standard-like models of Cleaver et al. (Phys. Rev. D 78, 046009, 2008). We comment on the relationship between flat directions and reduced Higgs in free fermionic models as well as the possible connection between moduli stabilization and model phenomenology.     

High frequency vibration analysis by the complex envelope vectorization

The complex envelope displacement analysis (CEDA) is a procedure to solve high frequency vibration and vibro-acoustic problems, providing the envelope of the physical solution. CEDA is based on a variable transformation mapping the high frequency oscillations into signals of low frequency content and has been successfully applied to one-dimensional systems. However, the extension to plates and vibro-acoustic fields met serious difficulties so that a general revision of the theory was carried out, leading finally to a new method, the complex envelope vectorization (CEV). In this paper the CEV method is described, underlying merits and limits of the procedure, and a set of applications to vibration and vibro-acoustic problems of increasing complexity are presented.     

Rotating QCD string and the meson spectrum

The spectra of light–light and heavy–light mesons are described by spinless Salpeter equation and Dirac equation respectively, which predict linear dependence of the meson mass squared M² on angular momentum J and number of radial nodes n. Both spectra are computed by the WKB method and shown to agree with exact numerical data within few percent even for the lowest levels. The drawback of Salpeter and Dirac equation is that (inverse) Regge slopes do not coincide with the string ones, 2πσ and πσ respectively, because the string dynamics is not taken into account properly. The lacking string rotation is introduced via effective Hamiltonian derived from QCD which generates linear Regge trajectories for light mesons with the correct string slope.     

Gluelump spectrum in the QCD string model

The spectrum of gluons in the adjoint source field is computed analytically using the QCD string Hamiltonian, containing only one parameter — string tension, fixed by meson and glueball spectrum. Spin splitting is shown to be small. A good agreement is observed with specially generated gluelump states measured on the lattice. The important role of gluelumps defining the behaviour of field-strength correlators is stressed and correspondence with earlier computations of the latter is established.