巴西科学家破解"潜水艇悖论"

一艘以接近光速行进的潜水艇 ,它究竟是会浮在海里还是会最后沉下去 ?这是一个悖论 ,是由爱因斯坦相对论引出的著名的“潜水艇悖论”。巴西圣保罗州立大学的科学家马察斯最近宣布彻底破解了这个悖论。他在新一期美国《物理评论D》杂志上发表的研究结论认为 ,那艘潜水艇最终将沉入水底。根据爱因斯坦的相对论 ,物体的长度在运动方向上会产生收缩。举例来说 ,一列以近光速飞跑的火车 ,在站台上静止的观察者眼中会变短 ;而在火车上的乘客看来 ,以接近光速后退着的站台却收缩了。而所谓“潜水艇悖论”指的是这样一种理论假想情况 :首先假设一艘…     

科学发现的逻辑验证

R演算是一个关于逻辑连接词符号和量词符号的演算系统．它是一个根据事实反驳对科学理论进行修正的符号演算系统．文中以狭义相对论和生物进化论为例，使用R演算，对这两个科学理论的发现过程，在数理逻辑层面进行了验证．验证的结果表明：对Einstein时代的物理学而言，狭义相对论是唯一而且正确的选择．对Darwin时代的生物学而言，在接受自然选择原理等前提下，R演算可以推导出3种不同的，但逻辑上合理的进化论方案．Darwin提出的进化论是其中一种．有趣的是三者中的另一种，现在看来它具有一定的包容性．     

美成功发射验证爱因斯坦相对论的卫星

经过45年酝酿和开发，耗资7．5亿美元的美国“引力探测器B”卫星，日前从加利福尼亚州范登堡空军基地成功升空，它的使命是以前所未有的精度对爱因斯坦1916年提出的广义相对论进行验证。     

水滑石晶体生长机理

从“生长基元”角度出发,研究了水滑石晶体生长机理,结果表明水滑石生长形态符合负离子配位多面体生长模型．采用Raman光谱分析了镁铝水滑石、铜镁铝类水滑石、铜锌镁铝类水滑石生长溶液拉曼位移,发现镁铝水滑石层板生长基元是[Mg-（0H）6]^4-,[Al-（0H）6]^3-;含铜锌类水滑石的生长基元是[Mg-（0H）6]^4-（M=Zn^2＋,Cu^2-）,[Mg-（0H）6]^4-,[A1-（0H）6]^3-,水滑石的生长是生长基元先叠合为金属板层,然后再吸附阴离子A”及H：0,依此循环而组成层状化合物．水滑石生长基元所处生长环境不同,会使生长形态不同,以至形成不同外形的水滑石．文章还分析了为什么含铜类水滑石较难合成的原因．     

氢化非晶硅薄膜喇曼及椭偏表征

用等离子体增强化学气相沉积（PECVD）方法制备氢化非晶硅（a—Si：H）薄膜,利用喇曼散射谱、椭偏透射谱和暗电导测试,通过改变辉光放电前SiH4气体温度,研究了气体温度对薄膜非晶网络结构和光电性能的影响．结果表明,随着辉光放电前SiH4气体温度从室温提高到433K,a-Si：H薄膜的短程有序和中程有序程度提高,折射率和吸收系数增强,同时,暗电导提高2个数量级．a—Si：H薄膜非晶网络结构的变化是其暗电导提高的主要原因．     

水平梯度表面能材料表面上的液滴运动

通过化学气相沉积的方法（CVD），利用十二烷基三氯硅烷（C12H25Cl3Si）在硅基板表面上的自扩散方式，形成单分子自聚合薄膜，在硅基板上制取了梯度表面能表面．采用原子力显微镜对梯度表面能材料表面微观结构进行了测量．通过躺滴法，获得了梯度表面能材料水平表面上的微量液滴接触角的分布，并以此表征材料表面能的分布．使用高速摄像仪对液滴在水平放置的梯度表面能材料表面上的运动规律进行了测量．实验表明：水平放置的梯度表面能材料表面可驱使液滴从憎水侧向亲水侧迁移，单个液滴的运动速度最大可达40mm／s,液滴在梯度表面能材料表面的运动一般可分为加速运动区和减速运动区；当液滴峰值速度较小而减速运动较大时，液滴运动会呈现蠕动的现象．     

对“辐射热力学的新进展——辐射有效能 光量子等效温度 光量子熵常数”一文的讨论

陈则韶等人在“辐射热力学的新进展——辐射有效能 光量子等效温度 光量子熵常数”（中文版见中国科学E辑：技术科学,2009,39（4）：609～617;英文版见Sci China Ser E-Tech Sci,2008,51（8）：1096—1109）一文中,通过赋予单个光子以有效能和熵等宏观热力学参数,提出了光子等效温度和光子熵常数概念．本文证明若将这些概念及其推论用于宏观热力学系统,将得到违背宏观热力学定律的结论,说明光子等效温度和光子熵常数概念是错误的．     

后工业化时代城市老工业区发展更新策略——以瑞士“苏黎世西区”为例

本文对“苏黎世西区”城市老工业区改造进行了详细介绍和分析，提出系统综合的目标设定、广泛协作的论证决策以及融合共生的设计思想是其获得成功的关键，值得借鉴和学习．文章结合我国老工业区改造的现状，提出了建议．     

青藏铁路主动冷却路基的工程效果

在全球变暖的背景下,高温冻土区的建筑必须改变单纯依靠热阻（增加路堤高度、采用保温材料）的消极“保”温方法,而采用“冷却路基”的积极“降”温措施．通过局地因素对多年冻土分布影响的分析得到如下启示：可以通过改变路基的结构和填料调控传热,以达到冷却路基的目的．青藏铁路的实践表明：通过遮阳板调控辐射,通过块石层、通风管、热管调控对流,通过“热半导体”材料调控传导,通过这些调控方式的组合,均可有效地降低路基下多年冻土的地温,保证路基的稳定．冷却路基方法是高温冻土区工程建筑应对全球转暖的有效措施．     

世界研究开发动态与评论

中法研究让血癌细胞“改邪归正”获进展　　记者从刚刚在巴黎结束的中法医学研讨会上了解到 ,中法两国专家合作研究用新方法使导致白血病的恶性细胞“改邪归正” ,这一研究已经取得了显著进展。在此基础上开发的新药在动物试验中有效率达到 85 %。这项成果是上海第二医科大学与法国巴黎圣路易医院合作取得的。据出席本次会议的中国工程院院士、上海第二医科大学教授王振义介绍 ,白血病俗称血癌 ,许多白血病患者因缺乏有效的治疗方法或化疗药物引起毒副反应而无法救治。因此 ,上海第二医科大学从上世纪 80年代就开始研究用“诱导恶性细胞凋亡…     

Popper’s response to Dingle on special relativity and the problem of the observer

Dingle contended that Einstein’s special theory of relativity was physically impossible for the simple reason that it required clocks to be simultaneously faster and slower than each other. McCrea refuted Dingle using an operationalist argument. An operational response did not satisfy Popper, who wrote an unpublished essay to counter Dingle’s claim. Popper developed an analysis that avoided operationalism by using a system of coinciding clocks, contending that this system showed that special relativity withstood Dingle’s criticism that it was not a symmetrical and consistent physical theory. However, Popper mistakenly included an asymmetric calculation in his analysis. Once this is corrected, the amended result supports Dingle’s position. Popper went on to argue that to avoid determinism, special relativity had to be reconciled with absolute time; this too supports Dingle. Popper’s failure to refute Dingle calls into question his claim that ‘the observer’ is superfluous to special relativity.     

Is electromagnetic field momentum due to the flow of field energy?

Momentum and energy conservation require electromagnetic field momentum and energy to be treated as physically real, even in static fields. This motivates the conjecture that field momentum might be due to the flow of a relativistic mass density (defined as energy density divided by the square of the speed of light).This article investigates the velocity of such a mass flow and finds a conflict between two different definitions of it, both of which originally seem plausible if the flow is to be taken as real. This investigation is careful to respect the transformation rules of special relativity throughout.The paper demonstrates that the consensus definition of the flow velocity of electromagnetic energy is inconsistent with the transformation rules of special relativity, and hence is incorrect. A replacement flow velocity is derived which is completely consistent with those transformation rules.The conclusion is that these conflicting definitions of flow velocity cannot be resolved in a way that is consistent with special relativity and also allows electromagnetic field momentum density to be the result of relativistic mass flow. Though real, field momentum density cannot be explained as the flow of a relativistic mass density.As a byproduct of the study, it is also shown that there is a comoving system in which the electromagnetic energy-momentum tensor is reduced to a simple diagonal form, with two of its diagonal elements equal to the energy density and the other two diagonal elements equal to plus and minus a single parameter derived from the electromagnetic field values, a result that places constraints on possible fluid models of electromagnetism.     

The case for black hole thermodynamics part II: Statistical mechanics

I present in detail the case for regarding black hole thermodynamics as having a statistical-mechanical explanation in exact parallel with the statistical-mechanical explanation believed to underlie the thermodynamics of other systems. (Here I presume that black holes are indeed thermodynamic systems in the fullest sense; I review the evidence for that conclusion in the prequel to this paper.) I focus on three lines of argument: (i) zero-loop and one-loop calculations in quantum general relativity understood as a quantum field theory, using the path-integral formalism; (ii) calculations in string theory of the leading-order terms, higher-derivative corrections, and quantum corrections, in the black hole entropy formula for extremal and near-extremal black holes; (iii) recovery of the qualitative and (in some cases) quantitative structure of black hole statistical mechanics via the AdS/CFT correspondence. In each case I briefly review the content of, and arguments for, the form of quantum gravity being used (effective field theory; string theory; AdS/CFT) at a (relatively) introductory level: the paper is aimed at readers with some familiarity with thermodynamics, quantum mechanics and general relativity but does not presume advanced knowledge of quantum gravity. My conclusion is that the evidence for black hole statistical mechanics is as solid as we could reasonably expect it to be in the absence of a directly-empirically-verified theory of quantum gravity.     

On miracles and spacetime

What have recently been dubbed two ‘miracles’ of general relativity—(1) that all non-gravitational interactions are locally governed by Poincaré invariant dynamical laws; and (2) that, in the regime of experimental practice in which curvature effects may be ignored, the local Poincaré symmetries of the dynamical laws governing matter fields coincide with the local Poincaré symmetries of the dynamical metric field—remain unaccounted for in that theory. In this paper, I demonstrate that these two ‘miracles’ admit of a natural explanation in one particular successor theory to general relativity—namely, perturbative string theory. I argue that this point has important implications when considering both the ‘chronogeometricity’ (that is, the object in question being surveyed by rods and clocks built from matter fields) and spatiotemporal status of the dynamical metric field in both general relativity and perturbative string theory.     

Physically locating the present: A case of reading physics as a contribution to philosophy

By means of an example, special relativity and presentism, I argue for the importance of reading history of physics as a contribution to philosophy, and for the fruitfulness of this approach to doing integrated history and philosophy of science. Within philosophy of physics, presentism is widely regarded as untenable in the light of special relativity. I argue that reading Newton's Principia as a contribution to philosophy reveals a law-constitutive approach to the unity of what there is, from which an alternative approach to presentism within physics emerges. This view respects the methodological and epistemological commitments of philosophy of physics in “taking special relativity seriously”, but proposes an alternative approach to the status of spacetime (as epistemic) and to the ground of what is real (law-constitution). While this approach to presentism does not preserve all of the contemporary presentist desiderata, it offers the possibility that the spatiotemporal extent of an existing thing is less than its entire history as represented in the block universe. I argue that the approach warrants further philosophical investigation.     

Heuristics versus norms: On the relativistic responses to the Kaufmann experiments

The aim of this article is to provide a historical response to Michel Janssen’s (2009) claim that the special theory of relativity establishes that relativistic phenomena are purely kinematical in nature, and that the relativistic study of such phenomena is completely independent of dynamical considerations regarding the systems displaying such behavior. This response will be formulated through a historical discussion of one of Janssen's cases, the experiments carried out by Walter Kaufmann on the velocity-dependence of the electron's mass. Through a discussion of the different responses formulated by early adherents of the principle of relativity (Albert Einstein, Max Planck, Hermann Minkowski and Max von Laue) to these experiments, it will be argued that the historical development of the special theory of relativity argues against Janssen's historical presentation of the case, and that this raises questions about his general philosophical claim. It will be shown, more specifically, that Planck and Einstein developed a relativistic response to the Kaufmann experiments on the basis of their study of the dynamics of radiation phenomena, and that this response differed significantly from the response formulated by Minkowski and Laue. In this way, it will be argued that there were, at the time, two different approaches to the theory of relativity, which differed with respect to its relation to theory, experiment, and history: Einstein's and Planck's heuristic approach, and Minkowski's and Laue's normative approach. This indicates that it is difficult to say, historically speaking, that the special theory of relativity establishes the kinematical nature of particular phenomena. Instead, it will be argued that the theory of relativity should not be seen as a theory but rather as outlining an approach, and that the nature of particular scientific phenomena is something that is open to scientific debate and dispute.     

Drawing the line between kinematics and dynamics in special relativity

Special relativity is preferable to those parts of Lorentz's classical ether theory it replaced because it shows that various phenomena that were given a dynamical explanation in Lorentz's theory are actually kinematical. In his book, Physical Relativity, Harvey Brown challenges this orthodox view. I defend it. The phenomena usually discussed in this context in the philosophical literature are length contraction and time dilation. I consider three other phenomena in the same class, each of which played a role in the early reception of special relativity in the physics literature: the Fresnel drag effect, the velocity dependence of electron mass, and the torques on a moving capacitor in the Trouton–Noble experiment. I offer historical sketches of how Lorentz's dynamical explanations of these phenomena came to be replaced by their now standard kinematical explanations. I then take up the philosophical challenge posed by the work of Harvey Brown and Oliver Pooley and clarify how those kinematical explanations work. In the process, I draw attention to the broader importance of the kinematics–dynamics distinction.     

Poincaré's Contributions to Relativistic Dynamics

In this paper I concentrate on the dynamic aspects of the special theory of relativity (in the non-Minkowski formalism), and not on the kinematic part of the story as is usually done. Following up the dynamic story leads to a new point of view as to Poincaré's important role in the development of special relativity. Much of Poincaré's dynamic work did not enter into Einstein's 1905 theory, since Einstein was mainly occupied with kinematics. However, the dynamic part is most fundamental in the development of the special theory of relativity after 1905. In this paper I consider the main developments of relativistic dynamics in which I demonstrate that much response to Poincaré's dynamic research can be found. I argue that Poincaré's dynamic work assisted in departing from Einstein's electrodynamic theory towards relativistic dynamics (independent of electrodynamics).     

Time isotropy,Lorentz transformation and inertial frames

Homogeneity of Euclidean space and time, spatial isotropy, principle of relativity and the existence of a finite speed limit (or its variants) are commonly believed to be the only axioms required for developing the special theory of relativity (Lorentz transformations). In this paper, however, it is pointed out that the Lorentz transformation for a boost cannot actually be derived without the explicit assumption of time isotropy (viz. time-reversal symmetry) which is logically independent of the other postulates of relativity. Postulating time isotropy also restores the symmetry between space and time in the postulates of relativity (i.e. time and space share the same symmetries then). Time isotropy also helps explain naturally one key general feature of the fundamental physical laws, viz. their time-reversal symmetry. But inertial frames are defined in influential texts as frames having space-time homogeneity and spatial isotropy only. Inclusion of time isotropy in that definition is thus suggested.     

Symmetry and asymmetry in electrodynamics from Rowland to Einstein

Halfway through the paper in which he laid down the foundations for the theory of special relativity, Einstein concludes that “the asymmetry mentioned in the Introduction … disappears.” Making asymmetry disappear has proved to be one of Einstein's many significant moves in his annus mirabilis of 1905. This elimination of asymmetry has led many commentators to claim that Einstein was motivated by either an aesthetic or an epistemic argument which gives priority to symmetry over asymmetry. Following closely the development of electrodynamics in the period from 1880 to 1905 and the usage of the related terms reciprocity and symmetry, we suggest a different way of understanding Einstein's motivation and the path he took. In contrast to the received view, we argue that Einstein responded to a debate in the literature on electrodynamics and that he was concerned neither with an aesthetic nor with an epistemic argument; rather, his reasoning was physical in the best sense, and most original. We will show that by providing a new perspective on the relation between electricity and magnetism, Einstein succeeded in bringing the discussion of symmetry in electrodynamics to an end.