"机械能守恒定律是否遵从相对性原理"辨

从两个层次上的相对性原理出发,对“机械能守恒定律是否遵从相对性原理”进行了剖析;并对究竟把什么称作机械能守恒定律更为合理,提出了一些看法。     

编者的话

本刊围绕机械能守恒定律是否遵从相对性原理的问题引发了一场争论[1～ 8] ,争论的焦点最后转向什么是相对性原理以及它与协变性要求的关系问题 .关于相对性原理 ,我们查到爱因斯坦本人有关狭义相对论的著述中有 3段话 :表述Ａ　自然界规律对于洛伦兹变换是协变的[9] .表述Ｂ　如果Ｓ是惯性系 ,则相对于Ｓ作匀速运动而无转动的其他参考系Ｓ′也是惯性系 ,自然界规律对于所有惯性系都是相同的[10 ] .表述Ｃ　自然规律同参照系的运动状态无关 ,至少在参照系没有加速运动时是这样[11] .朗道在他的《场论》中[12 ] 写得更明确 :所有自然规律在所…     

相对论问答录之一

<正>问题一、狭义相对论建立在哪两条公理的基础之上?狭义相对论建立在"相对性原理"和"光速不变原理"这两条公理的基础之上。相对性原理是说,物理规律在所有惯性系中都相同。需要强调,这里所说的相对性原理已经是伽利略相对性原理的推广。伽利略相对性原理只针对     

从洛仑兹力定律讨论B与E的相对性

本文从洛仑兹力定律来讨论Ｂ、Ｅ的相对性；即在一个惯性系中表现为磁场力，而在另一惯性系中则表现为电场力，或者两种场力同时并存．这些场力、完全遵从力的相对论的变换规律．     

小谈广义相对论--"从低速到高速"之五

我们已介绍过狭义相对论；在那里爱因斯坦把牛顿的相对性原理推广到包括电磁现象，但还是指惯性系说的；各个参考系是相对做匀速运动的惯性参考系．对加速参考系又该如何呢？爱因斯坦在马赫思想的影响下提出：物理规律对所有参考系，不管是惯性系还是加速系，都应该是一样的．这个进一步推广了的相对性原理叫“广义相对性原理”．它是爱因斯坦广义相对论的一个基本原理．     

再论光速不变原理和洛伦兹变换

根据相对性原理和光速不变原理不仅可以得到洛伦兹变换关系,而且可以证明运动的相对性条件,即爱因斯坦条件成立.同时表明在相对性原理假设下,光速不变原理、间隔不变性和洛伦兹变换关系这三者等价.     

用相对性原理理解电场和磁场

电场和磁场是用来描述电荷之间相互作用的两种效应,不同参照系的观察者可以观测到不同的电场和磁场的比例。就像一个硬币的两个面,只有将电场和磁场看成一个整体,电磁场基本理论才能与相对性原理相互自洽,电场和磁场仅仅只是相互为相对论效应。本文通过3个熟悉的例子进一步说明相对性原理的重要性,只有物理规律才与参照系无关,如何解释物理规律是与参照系相关的。从这个意义上说,电场、磁场是人们"发明"来解释电荷之间相互作用的物理规律。     

从引力场方程的建立到引力波的直接探测

1引力场方程的建立1905年,爱因斯坦在对时间概念经过长久思考后,提出了两个基本公设:(1)相对性原理(伽利略的相对性原理的推广):物理规律在所有惯性系中都具有相同的形式.(2)光速不变原理:在所有的惯性系中,光在真空中的速度c是恒定的,它不依赖于发光物体的运动速度.在此基础上,建立了狭义相对论.1905年后,爱因斯坦企图把引力现象归纳在狭义相对论的范畴之     

《从零学相对论》连载

第1讲 狭义相对论的引入 相对性原理是牛顿力学的一个重要出发点.然而,麦克斯韦(以下简称麦氏)的电磁理论问世之后,相对性原理曾一度遭遇过严峻的挑战,最终导致狭义相对论的诞生.因此,要介绍狭义相对论的引入动机,有必要讲清以下三个问题: 1.什么是相对性原理? 2.麦氏电磁理论为何曾一度对相对性原理提出过严峻挑战? 3.上述挑战如何诱发爱因斯坦创立狭义相对论?     

相对性原理及其对自然界定律的协变性要求--机械能守恒定律协变性疑难的解答

阐明狭义相对性原理的准确含义,批出它并不要求自然界每条定律都单独协变,但要求每条定律至少属于一个协变集合,给出最小协变集的求法。表明机械能守恒定律满足狭义相对性原理及其对自然界定律的协变性要求,还指出一切社会科学定律也都满足狭义相对性原理。     

Study on the radiation problem caused by electron beam loss in accelerator tubes

The beam dynamic code PARMELA was used to simulate the transportation process of accelerating electrons in S-band SW linacs with different energies of 2.5, 6 and 20 MeV. The results indicated that in the ideal condition, the percentage of electron beam loss was 50% in accelerator tubes. Also we calculated the spectrum, the location and angular distribution of the lost electrons. Calculation performed by Monte Carlo code MCNP demonstrated that the radiation distribution of lost electrons was nearly uniform along the tube axis, the angular distributions of the radiation dose rates of the three tubes were similar, and the highest leaking dose was at the angle of 160° with respect to the axis. The lower the energy of the accelerator, the higher the radiation relative leakage. For the 2.5 MeV accelerator, the maximum dose rate reached 5% of the main dose and the one on the head of the electron gun was 1%, both of which did not meet the eligible protection requirement for accelerators. We adopted different shielding designs for different accelerators. The simulated result showed that the shielded radiation leaking dose rates fulfilled the requirement.     

Analysis of Laser-generated Rayleigh wave on viscoelastic materials

In order to understand the viscoelasticity of material, this research has been conducted to study the propagation characteristics of viscoelastic Rayleigh wave theoretically. A model is presented for the pulsed laser generation of ultrasound on viscoelastic medium surface. Referred to the Kelvin model, the frequency equation and the normal displacement of viscoelastic Rayleigh wave were derived, the influence of the viscoelastic modulus on dispersion and attenuation was discussed. From the theoretical calculation, it is shown that the effect of viscoelasticity on the attenuation of Rayleigh wave is more than that on its dispersion. In the case of a weak viscosity, the attenuation of viscoelastic Rayleigh wave is directly proportional to viscosity modulus; the effect of shear viscosity on the attenuation is much more than that of bulk viscosity. The transient response of viscoelastic Rayleigh wave was also simulated using Laplace and Hankel inversion transform, which are showed in good agreement with the theoretic predictions. The model provides a useful tool for the determination of viscoelastic parameters of medium.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Synergistic effects on iodine release in potassium iodide solution by combination of ultrasound and visible light irradiations

Iodine release in potassium iodide solution has been investigated under the irradiations of ultrasound and visible light respectively and simultaneously. We have observed that the amount of iodine liberated under the combined irradiation of ultrasound and visible light is larger than the sum of that under the respective irradiations of ultrasound and visible light, indicating a synergistic effect of ultrasound and visible light irradiations. Based on the investigation of the reaction kinetics of iodine liberated, we have ascribed the synergistic effect to the perfect stirring of the photochemical reactor induced by the applying simultaneous ultrasound. The ideal stirring can result in the homogenization of the primary light effect in the whole reaction medium, which induces the acceleration of the photochemical reaction. On behavior of our knowledge, there are few reports on the investigations of utilizing the combination of ultrasonic energy and light energy to accelerate the reaction yield and rate as well as the kinetics of the reaction.     

Region of interest and pixel-by-pixel analysis of dynamic contrast enhanced magnetic resonance imaging parameters and time-intensity curve shapes: a comparison in chondroid tumors

Dynamic contrast enhanced (DCE) MRI is widely acknowledged to be a helpful tool in the diagnosis and differentiation of tumors. In common clinical settings, the dynamic changes described by the time-intensity curves (TICs) are evaluated to find patterns of atypical tissue behavior, i.e., areas characterized by rapid contrast wash-in and wash-out. Despite the ease of this approach, there is no consensus about the specificity of the TIC shapes in discriminating tumor grades. We explore a new way of looking at TICs, where these are not averaged over a selected region of interest (ROI), but rendered pixel-by-pixel. In this way, the characteristic of the tissue is not given as a single TIC classification but as a distribution of the different TIC patterns. We applied this method in a group of patients with chondroid tumors and compared its outcome with the outcome of the standard ROI-based averaged TIC analysis. Furthermore, we focused on the problem of ROI selection in these tumors and how this affects the outcome of the TIC analysis. Finally, we investigated what relationship exists between the "standard" DCE-MRI parameter maximum enhancement (ME) and the TIC shape. CONCLUSIONS: We demonstrate that, where the ROI approach fails to show the presence of areas of rapid contrast wash-in and wash-out, the pixel-by-pixel approach reveals the coexistence of a heterogeneous pattern of TIC shapes. Secondly, we point out the differences in the DCE MRI parameters and tumor volume that can result when selecting the tumor based on DCE parameter maps or post-contrast T1-weighted images. Finally, we show that ME maps and TIC shape maps highlight different tissue areas and, therefore, the use of the ME maps is not appropriate for the correct identification of areas of atypical TICs.     

A study on the best irradiation dose of X-ray for Hep-2 cells by Fourier transform infrared spectroscopy

Fourier transform infrared spectroscopy (FTIR) was employed to study the human epidermis larynx carcinoma cell lines (Hep-2) which were irradiated by different doses of X-ray.The results show that (1) the irradiation of X-ray damages the structure of the CH3 groups of the thymine in DNA,which restrains the reproduction of Hep-2 cells effectively,(2) the 8 Gy dose of X-ray irradiation changes the framework and the relative contents of some proteins,lipids and the nucleic acid molecules intercellular in the greatest degree,and (3) the 8 Gy dose of X-ray irradiation is the best irradiation dose for lowering the degree of the cancerization of Hep-2 cells according to the criteria for the degree of the cancerization reported recently.Meanwhile,the apoptosis of these cells were detected by using flow cytometry (FCM) primarily.It shows that the apoptotic ratio of the Hep-2 cells depends on the irradiation dose to some extent,but is not linearly.And the apoptotic ratio of the 12 Gy dose group is the maximum (20.36%),but the apoptotic ratios of the 2 to 8 Gy dose groups change little.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.