动量、动能与牛顿的力——动力学的基础概念与图像

1 引子:"不变性"是认识自然的基础 在人类探索自然的过程中,无论是将其归因于"造物主的完美",还是基于"实用主义的必须",有一条基本的信念始终贯穿其中,那就是宇宙中一定存在某些永恒不变的东西,它或许是组成世界的元素,又或许是物体上承载的某种性质,亦或是支配事物运行变化的法则.     

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当年伽利略用自制的望远镜开启了人类认识宇宙的新纪元,400年后的今天,一架30米的巨型望远镜将造在夏威夷岛上的冒纳凯阿火山上。望远镜的分块式主镜直径接近100英尺(约合30米),建成后将成为世界上最大的光学望远镜。该项目简称"TMT",预计造价10亿美元,计划10年完成。这只巨大的"天眼"将使得天文学家能比过去更清晰地看到暗弱的天体,为人类带来更多有关宇宙的更新、更深层的信息并有望做出重大突破性发现。     

眼见为实(上):磁畴成像

看到了,才相信安得物理论虚实,眼见为真定认知。只是江山多乱序,此峰难断彼峰斯。1引子自然科学,之所以在人类认识和实践中具有崇高信誉和地位,笔者以为有两个运行要素是重要的:严密的分析推演逻辑和眼见为实的理念。前者太过高深,笔者不敢谬论;后者即为本篇学习体会之主角。眼见为实,即"Seeing is believing",通俗一些即"看到了,才相信"。刚开始我们也许只能看到局部,如瞎子摸象,然后我们相信局部并推演全局.     

上海光源在化学领域中的应用

<正>化学作为一门历史悠久而又富有活力的基础学科,成为人类用以认识和改造物质世界的主要方法和手段之一。在现代,很多人称化学为一门"中心科学",因为它是不少自然学科的核心,如材料科学、纳米技术、生物学、环境生态学等。作为一门以实验为基础的学科,化学在与物理学、生物学、地理学、天文学等学科的相互渗透中,得到了迅速的发展,又进一步推动了其他学科和技术的发展。具体     

迈向火星的第一步——中国科学院物理研究所“火星，我们来了”主题讨论侧记

<正>"日月安属?列星安陈?"——屈原《天问》千年以来,人类在仰望火星。古代的人们时常在夜空中望见一颗红色的行星,亮度常变而轨迹复杂。"荧荧火光,离离乱惑",被称为"荧惑"的火星在某些天象中或许是某种灾祸的化身。现代科学告诉我们,火星是地球的近邻,位于地球的外侧,无论是自转周期还是季节性气候变化,火星与地球都有着很大的相似之处。火星不仅引发了人们科学观测和科学研究的巨大兴趣,也成为许多科幻小说、     

核能应用的物理学基础

 能源是维持人类生存和发展的重要物质条件。随着世界人口的不断增加、人类生产和生活条件的不断改善,人类对能源的需求量也在不断地上升。然而,目前世界上的常规能源,如水力、风力、煤炭、石油和天然气等资源都是有限的,煤炭、石油和天然气的世界储量最多还可开采100到200年,到21世纪中叶,世界将面临能源匮乏的严重局面。因此寻找和开发新能源一直是人类的一项重要任务。在20世纪30年代,随着人们对原子核研究的深入,人们认识到在原子核内蕴藏着巨大的可开发的能量,并开始了和平利用原子核能的研究。现在世界上已建成的裂变核电站有300多座,其发电量约占世界总发电量的14。     

拉普拉斯妖的出现——“拉普拉斯妖”随笔之五

一 中文字典里的"妖"字,往往与"精"、"怪"、"魔"、"孽"等字连在一起组成一个名词.这些名词或指姿色迷人的女子,或指害人索命的鬼魅,或指凶狠残忍的魔怪,有时也指呼风唤雨,撒豆成兵,具有某种超常能力怪异反常的"什么东西".总之,"妖"是非物质世界的一种"存在",与"妖"字相连,大多充满着荒诞和邪恶.     

激光在军事上的广泛应用

 激光作为人类认识世界和改造世界的武器,使得人类对大自然的认识和改造能力得到了提高,而且在科学技术、工农业生产、人类生活等领域引起了一次深刻的变革。它使光学这个古老的科学分支变得面貌一新,在物理、化学、医学、军事等方面得到了广泛的应用,本文主要介绍激光在军事上的应用。一、激光致盲武器激光致盲武器的射击对象是人眼以及光学和光电装置等目标。它一般由激光器、精密瞄准跟踪系统、光束控制和发射系统组成。激光器是激光武器的核心,用于产生起致盲作用的激光光束,如二氧化碳激光器,平均输出功率一般在1000～10000W之间.     

南极往事——中国科学院物理研究所“我国南极科学考察事业回顾与展望”主题讨论侧记

正"为了你在乎的东西值得冒险"。——《南极大冒险》南极,白雪皑皑的神秘王国,冰封千里的冰雪世界,探险家们梦寐以求的圣地。作为地球上最寒冷的冰雪天险,人类涉足南极的历史不过一百余年。随着人们对南极大陆了解的深入,人们逐渐发现南极地区是地球上具有独特地理环境、     

谁能聆听“上帝”的声音?——反谈科学发现的逻辑

 在人类探索自然奥秘的历程中,有过无数传奇般的故事。类似“苹果落地”之类的传说,虽然家喻户晓,未必引人深思,连日来翻检史籍,发现这样两件科学史案例,在常人看来,这两件科学事件相去多年,似乎无甚关联,可是,认真追寻下去,我仿佛隐隐约约看到了“上帝”的影子;它促使我们不断在想:人类究竟能在何种程度上认识神奇的大自然?如果真的存在一个上帝的话,那么究竟是谁能聆听上帝的声音? 这两件科学事件其实都很著名,一是勒维烈通过数学计算,预见到海王星的存在;另一件则是科学巨匠爱因斯坦创立广义相对论。     

关于"太阳在银河系中所受引力与到银心距离r的关系"的讨论

讨论了银道面内的引力场强分布和太阳在银河系中所受引力与到银心距离r的关系，指出引力场强g并不是与r的平方成反比，这是由于银河系的大小和形状不能忽略造成的．强调了万有引力定律的适用条件．     

On the calculation of the bremsstrahlung in the region of the plasma frequency

On the basis of the classical theory of radiation produced in incomplete Coulomb interaction, a formula is derived for the coefficient of the bremsstrahlung of fully ionized plasma. In the region of rectilinear approximation a comparison is made with the results of the quantum formula derived from the Born approximation. Furthermore, the influence of dispersion upon the emission coefficient is taken into account; some relations for the region of dispersion are given.     

Dependence of the Intensity of the Spectral Lines and the Composition of the Sample and the Plasma Parameters of the Unipolar Arc

The investigation was made of the dependence of the intensity of Tl, Ga, Mo, Mg, Mn, Sn, Bi, Ni, Zn, Pt and Au spectral lines and the plasma parameters (temperature T, electron concentration n_e, degree of 6 ionnization α) from concentration of lithium additive.     

On the predictability of the positions of the convergence zones in the ocean

The disagreement between the experimental and calculated positions of the first convergence zone are known from many publications. The most probable cause for such a disagreement, namely, the incorrect specification of the input data for the calculations, is considered. The lack of simultaneity between the hydrological surveys of the region and the acoustic experiments is emphasized. The experimental data obtained by the author in five ocean regions are presented. These data characterize the diurnal variability of the distance from the source to the nearest boundary of the convergence zone. The relations proposed by different researchers for calculating the sound speed from the temperature, salinity, and hydrostatic pressure are analyzed. It is shown that these relations lead to a substantial difference in the estimated depth dependence of the hydrostatic gradient of the sound speed. The position of the first convergence zone is calculated for the propagation conditions determined by vertical temperature and salinity profiles with the subsequent recalculation of these profiles into sound speed profiles by using eight different formulas known from the literature. It is shown that different formulas lead to different values of the distance to the first zone; this difference is substantially greater than that between the calculations and experiment. The necessity of improving the recalculation relations in view of the experimental data on sound propagation in natural oceanic waveguides, including the data on the actual positions of the convergence zones, is emphasized.     

Extracting the wavefunction of the LSP at the LHC

We consider associated production of squarks and gluinos with the lightest supersymmetric particle (LSP), or states nearly degenerate in mass with it. Though sub-dominant to pair production of color SU(3)-charged superpartners, these processes are directly sensitive to the wavefunction composition of the lightest neutralinos. Exploiting event-shape variables - including some introduced here for the first time - we are able to identify the composition of the LSP by selecting events involving a single high-pT jet recoiling against missing transverse energy. We illustrate the proposed technique on a set of benchmark cases and propose methods for applying these results in more realistic experimental environments.     

Set the controls for the heart of the Sun

In this paper we describe experiments conducted with high-power lasers that are attempting to replicate, for a very short time and in miniature, conditions found in the Sun. Experiments to date have reached conditions in the outer part of the Sun. To reach the Sun's centre requires compression of material to very much greater than solid density and heating to over ten million degrees. To achieve this, a new class of experiments and a new generation of high-power lasers are required.     

On the Question of the Source of the Apokamp

Technical Physics - The object of this work is the apokamp—a new type of plasma jet, which is formed from a bright offshoot emerging at the bending point of a channel of a high-voltage...