对《用排列对比方法讲解相对论》一文的一些意见

本刊2010年第5期第14页《用排列对比方法讲解相对论》一文,希望达到用时少、效果好的目标,这个愿望很好,只是其中有些提法值得商榷.(1)第14页左栏倒数第8行"真空中光速不变"     

用复平面几何法阐述狭义相对论

本文采用具有虚轴的空一时坐标系统，可以简洁而直观地阐述和计算洛仑兹空间一时间变换一般式、特例以及适度（加速度）、质量变换式和相对论多普勒效应．各变换式的推导都直接在空一时坐标中进行，即只用到基本假设而无需利用其它变换结果，文中引入的若干概念和一阶（二阶）导致变换式在阐述中是有用的。     

用三角函数表示相对论物理量

本文中“时空角” 是通过ｖ＝ｃ（ｓｉｎ）定义的．这导致了用简单的实三角函数表示的洛伦兹变换式，并获得了对于粒子与相应德布罗意波的重要的相对论物理量的图解关系．许多相对论的关系式是利用通常的三角恒等式与公式得到的．     

用改进L-P法研究一维相对论振子振动方程

采用改进的Ｌ－Ｐ法研究一维相对率振子动方程的近似解，此法克服了参数摄动法易出现长期项，而建立补充方程和须解微分方程的弊病。     

用时空代数推导狭义相对论的任意方向加速度变换

时空代数(Space-time Algebra,STA)是定义在4维实Minkowski矢量空间M~4上的16维几何代数(Geometric Algebra,也称为Clifford代数)Cl_(1,3),是一个可结合的代数环,它提供了不依赖于特定标架描述四维时空的方法.本文采用时空代数,给出推导狭义相对论中沿任意方向作相对运动的惯性系之间加速度变换的一种简单方法.     

关于相对论动量定义式的推导方法

指出部分大学物理教材中，用完全非弹性碰撞方法推导相对论动量定义式时，必须附加系统质量守恒这一“预期论据”，从而存在着违反逻辑规则等问题．     

相对论高次谐波的蒙特卡罗模拟

根据相对论条件下的经典电磁辐射理论,采用蒙特卡罗计算方法对类氢离子在强激光场下辐射的高次谐波进行了模拟计算,获得了相对论领域内激光参数（频率、脉冲波形、强度等）对高次谐波影响的各种计算结果,并对结果进行了理论分析。     

相对论高次谐波的蒙特卡罗模拟

 根据相对论条件下的经典电磁辐射理论,采用蒙特卡罗计算方法对类氢离子在强激光场下辐射的高次谐波进行了模拟计算,获得了相对论领域内激光参数（频率、脉冲波形、强度等）对高次谐波影响的各种计算结果,并对结果进行了理论分析。     

“三重”探究建构相对论时空观

从学生的实际出发,设计“三重”探究,即“学史”探究、“实验”探究、“应用”探究,让学生从“绝对时空观”的前概念中建构起新的相对论时空观．     

用科学探究的方法进行新课教学的尝试——“向心力、向心加速度”的教学

现代教育理论认为"科学探究是科学学习的核心","学科学的中心环节是探究.学生们应该在积极地参与科学探究的过程中逐渐对自然界有所认识.对从学生们所亲历的事物中产生的一些实际问题进行探究,是科学教学所要采取的主要做法","通过做科学(即‘科学探究'活动)来学科学".在<高中物理(试验修订本)>的使用中我们越来越体会到上述教育思想在新教材的编写中已有比较明显的体现.科学探究是以科学方法为指导的,为此加强科学方法的教育也就成了新教材的重要特点之一.     

Strong-Coupled Relativity Without Relativity

GR can be interpreted as a theory of evolving 3-geometries. A recent such formulation, the 3-space approach of Barbour, Foster and Ó'Murchadha, also permits the construction of a limited number of other theories of evolving 3-geometries, including conformal gravity and strong gravity. In this paper, we use the 3-space approach to construct a 1-parameter family of theories which generalize strong gravity. The usual strong gravity is the strong-coupled limit of GR, which is appropriate near singularities and is one of very few regimes of GR which is amenable to quantization. Our new strong gravity theories are similar limits of scalar-tensor theories such as Brans–Dicke theory, and are likewise appropriate near singularities. They represent an extension of the regime amenable to quantization, which furthermore spans two qualitatively different types of inner product.We find that these strong gravity theories permit coupling only to ultralocal matter fields and that they prevent gauge theory. Thus in the classical picture, gauge theory breaks down (rather than undergoing unification) as one approaches the GR initial singularity.     

物理试题应该怎么讲

常听人说：物理难学．学生往往有这样的体验：书上的例题看得懂,老师讲课听得懂,但自己做题,往往做不出．物理解题难的一个重要原因是能否掌握解题的规律和方法．下面就一些物理题的解法做一些归纳．     

Quantitative Evaluation Methods of In-Line X-Ray Phase Contrast Techniques

By revealing the relationship between edge visibility and imaging parameters in in-line phase contrast imaging （PCI）, we propose a method to quantitatively measure the contribution of absorption and phase shift from acquired images. We also prove that edge visibility will grow with the increasing source-object distance and object-detector distance. The result is validated by relative phase factor and by experiments conducted on a microfocus x-ray source. This method provides a new approach to evaluate in-line PCI images and is helpful for deciding imaging parameters.     

Relativizing Relativity

Special relativity theory is generalized to two or more maximal signalling speeds. This framework is discussed in three contexts: (i) as a scenario for superluminal signalling and motion, (ii) as the possibility of two or more light cones due to the a birefringent vacuum, and (iii) as a further extension of conventionality beyond synchrony.     

Third Relativity

It seems likely that quantum dynamical law doesnot have a separate objective existence, but is oneaspect of the quantum process of nature, amatter-spacetime-dynamics unity, and is not onlyvariable, but may be the only variable. This is oneresult of a systematic application of the criteria fora group contraction given by Inonu and Wigner (1952).They point out that nonsemisimplicity is circumstantial evidence for a group contraction in which somecoupling coefficient has been taken to a singular limit.In their example, the coupling coefficient is c and thegroup contraction c passes from special to Galilean relativity.     

Spinor Relativity

Spinor relativity is a unified field theory, which derives gravitational and electromagnetic fields as well as a spinor field from the geometry of an eight-dimensional complex and ‘chiral’ manifold. The structure of the theory is analogous to that of general relativity: it is based on a metric with invariance group GL(ℂ²), which combines the Lorentz group with electromagnetic U(1), and the dynamics is determined by an action, which is an integral of a curvature scalar and does not contain coupling constants. The theory is related to physics on spacetime by the assumption of a symmetry-breaking ground state such that a four-dimensional submanifold with classical properties arises. In the vicinity of the ground state, the scale of which is of Planck order, the equation system of spinor relativity reduces to the usual Einstein and Maxwell equations describing gravitational and electromagnetic fields coupled to a Dirac spinor field, which satisfies a non-linear equation; an additional equation relates the electromagnetic field to the polarization of the ground state condensate.     

茶叶中咖啡因提取条件优化及方法对比

对索氏、超声波及微波提取咖啡因的条件进行优化与对比.利用正交试验优化提取条件,对结果进行比较,索氏法提取率最高.最佳条件为:95％乙醇、提取60min、低温升华80min,平均提取率为79.8mg/5g.该方法简单,易于操作,具有一定的实际意义.