Dancing "atoms" and "molecules" of luminous gas-discharge spots

Highly localized, dynamic particle-like excitations are observed in a dc-driven, quasi-two-dimensional gas-discharge system. These localized excitations undergo a transition from isolated to aggregated state as the discharge current is increased. Although they provide us a macroscopic analogue of microscopic atoms and molecules, they are quite distinct from the latter in the point that they exhibit a rich variety of complex dynamics. The fact that these localized excitations can show synchronous dynamics even in distant places, together with recent theoretical studies, indicates that a global coupling plays an important role on the dynamics of such localized excitations.     

"没有"与"为零"的区别--兼谈"能量"概念的物理意义

笔者最近有机会听了一些老师的初中物理课，在一些老师的“内能”概念教学实践中，笔者发现他们总是在想方设法运用各种教学手段强调如下两个教学要点：     

Observation of "Stick" and "Handle" intermediates along the fullerene road

The hypothesis that fullerenes grow in a carbon plasma by the addition of C2 units (the "fullerene road") has been widely acclaimed as the most plausible mechanism for formation of larger fullerenes including C60 and C70. Calculations suggest that the association of C2 with fullerenes proceeds through two classes of intermediates, "sticks" and "handles." Here we report the observation of these species using high-resolution ion-mobility measurements for C(n) cations generated by laser vaporization of graphite and laser desorption of C60. Sticks with up to eight-atom chains have also been found.     

"引力"七问

1 引力是什么 牛顿在17世纪就认识到宇宙中任何地方的一切物体的引力作用方式是相同的,且两物体间的吸引力与它们的质量的乘积成比例,与它们距离的平方成反比,即著名的"引力的平方反比律."爱因斯坦在20世纪初发表的广义相对论是研究物质在空间和时间中如何进行引力相互作用的理论,它将平方反比律解释成时空因物质和能量的存在而发生畸变的结果,并把牛顿理论包含在内.     

一种“类耗散系统”中的“类Ⅴ型阵发”

一类不连续不可逆保面积映象可以展示类似耗散的行为,因此可称其为“类耗散系统”.在一种类耗散系统中观察到了椭圆周期轨道及其周围的椭圆岛与映象不连续边界碰撞而消失的现象.周期轨道消失后,经过一系列过渡椭圆周期轨道之后,系统的行为由一个混沌类吸引子主导.在混沌类吸引子刚刚出现时,混沌时间序列呈现层流相与湍流相的无规交替.这一切都与不连续耗散系统中发生的Ⅴ型阵发的相应性质十分相似,因此可称为“类Ⅴ型阵发”.然而,当混沌类吸引子刚刚出现时,仅可以找到最后一个过渡椭圆岛的“遗迹”,并不存在它的“鬼魂”,因此类Ⅴ型阵发不遵从Ⅴ型阵发的特征标度规律.反之,混沌类吸引子的鬼魂却存在于最后一个过渡椭圆周期轨道的类瞬态过程中,因此在类Ⅴ型阵发导致混沌运动的临界点之前,由此“类瞬态混沌奇异集”中逃逸的规律就成为标志这一种临界现象的标度律.这与Ⅴ型阵发又根本不同. 关键词： 类耗散性 类混沌吸引子 类Ⅴ型阵发     

“Hopf/homoclinic”簇放电和“SubHopf/homoclinic"簇放电之间的同步

以修正过的Morris-Lecar神经元模型为例,讨论了“Hopf/homoclinic”簇放电和“SubHopf/homoclinic"簇放电之间的同步行为.首先,分别考察了同一拓扑类型的两个耦合簇放电神经元的同步行为,发现“Hopf/homoclinic”簇放电比“SubHopf/homoclinic”簇放电达到膜电位完全同步所需要的耦合强度小,即前者比后者更容易达到膜电位完全同步.其次,对这两个不同拓扑类型的簇放电神经元的耦合同步行为进行了讨论.通过数值分析发现随着耦合强度的增加,两种不同类型的簇放电首先达到簇放电同步,然后当耦合强度足够大时甚至可以达到膜电位完全同步,并且同步后的放电类型更接近容易同步的簇放电类型,即“Hopf/homoclinic”簇放电.然而令人奇怪的是此时慢变量并没有达到完全同步,而是相位同步;慢变量之间呈现为一种线性关系.这一点和现有文献的结果截然不同.     

Ccontrolling the Transition Between "Higher" and "Lower" State of OB in Coherent Atomic Medium

We present a new experimental demonstration that the threshold points and shape of OB hysteresis curve in a four-level Rb atomic system inside an optical cavity were controllably changed by optical signals.Tuning the triggering optical signal to two different transitions of the atomic system we found that the OB threshold points shift toward different direction and at the same time the shape of the OB curve is also changed.For a given intensity of probe laser the OB system can be reliably inversed from its lower stable state to upper state under the triggering of a suitably tuned optical pulse signal (we named it up-controlling signal).More interesting, the inversed OB state does not drop to its initial lower stable state after the triggering pulse signal has passed, but moves to the upper branch of the initial OB curve and stably stays there until another optical signal tuned on other atomic transition (named down-controlling signal) coming.The result shows that there is the ability of information storage in the OB system.The experiments are reasonably explained with the change of cavity resonant condition resulting from the enhanced third-order nonlinearity in multilevel atomic system owing to atomic coherence.     

Dissociation of perceptual judgments of "what" and "where" in an ambiguous auditory scene

Whenever an acoustic scene contains a mixture of sources, listeners must segregate the mixture in order to compute source content and/or location. Some past studies have explored whether perceived location depends on which sound elements are perceived within a source. However, no direct comparisons have been made of "what" and "where" judgments for the same sound mixtures using the same listeners. The current study tested if the sound elements making up an auditory object predict that object's perceived location. Listeners were presented with an auditory scene containing competing "target" and "captor" sources, each of which could logically contain a "promiscuous" tone complex. In separate blocks, the same listeners matched the perceived spectro-temporal content ("what") and location ("where") of the target. Generally, as the captor intensity decreased, the promiscuous complex contributed more to both what and where judgments of the target. However judgments did not agree either quantitatively or qualitatively. For some subjects, the promiscuous complex consistently contributed more to the spectro-temporal content of the target than to its location while for some it consistently contributed more to target location. These results show a dissociation between the perceived spectro-temporal content of an auditory object and where that object is perceived.     

浅议"做功"

关于功的概念高中物理的定义是:作用在物体上的力与物体在力的方向上产生的位移之积即为该力对物体所作的功.     

“淇淇”辞世

本刊在1999年第18卷第2期曾刊登了应崇福院士所著“南下访‘淇淇’”一文。据媒体报道,“淇淇”已于今年（2002年）7月14日辞世。消息传出后,原饲养单位两天内收到各界表示关注的电子邮件、传真、电话等40余份（见《光明日报》2002年7月17日A2版）。     

指南针从"理"到"文"——从物理学出发进行"文理综合"的探索

编者按:目前在我国掀起了新的基础教育改革浪潮,提出了新的教育理念,制定了课程标准,新编写的教材已在少数地方试用.面临这种形势制约改革成败的重要问题之一--新的评价体系,亟待改革完善.此文既涉及课程的构建,也涉及评价和测量.发表此文意在引起广大读者对这些问题的关注,并积极参加讨论.     

"神舟"号飞船的微重力测量

航天器在太空自由漂移时出现失重状态．当存在各种干扰力时，呈现微重力状态．失重状态使得物体各部分之间不产生压力作用或者形变作用，对此开展的研究称之为微重力科学．微重力用微重力加速度的值度量．准稳态加速度来自大气阻力、潮汐力、太阳辐射压等，分析得到“神舟”号飞船的准稳态加速度在10^-7g0以下．瞬变加速度和振动加速度可用石英挠性加速度计检测．“神舟”号飞船的微重力测量仪器具有三轴检测、守时、统计分析、依照预先注入的指令准实时传送微重力统计数据或原始数据的能力．该仪器带宽为(0．06—100)Hz，分辨率5μg0，量程(-10— 10)mg0，沿飞行轴线还有一个放大为(-150— 150)mg0的量程．该仪器对“神舟一号”到“神舟五号”各艘飞船轨道运行段实施全过程连续监测，准实时提供了飞船各种动作发生的时刻及引起的加速度量值，为飞船飞行控制、有效载荷动作监测和空间微重力科学实验分析提供了有效服务。     

"功"的教学设计与构思

【教学课题】 普通高中课程标准实验教科书《物理·必修2》（人教社2006年第2版）第七章第2节“功”． 【设计思想】 学生对“功”并不陌生,他们已经知道做功的两个必要因素、功的计算公式和单位等知识．本节课新增的内容主要有功的计算的一般表达式、正功和负功的物理意义、合力做功和分力做功的关系等．通过对教材的分析发现,这些新内容完全可以在原有知识的基础上,运用学生已经掌握的力的合成与分解等方法得出．为此,笔者一改以知识主线安排教学内容的传统做法,依据新课程基于建构主义教学理念,     

Melting of "porous" vortex matter

Bitter decoration and magneto-optical studies reveal that in heavy-ion irradiated superconductors, a "porous" vortex matter is formed when vortices outnumber columnar defects. In this state ordered vortex crystallites are embedded in the "pores" of a rigid matrix of vortices pinned on columnar defects. The crystallites melt through a first-order transition while the matrix remains solid. The melting temperature increases with density of columnar defects and eventually turns into a continuous transition. At high temperatures a sharp kink in the melting line is found, signaling an abrupt change from crystallite melting to melting of the rigid matrix.