太阳中微子——物质世界的“隐士”

 曾有前辈物理学家说:做科学研究首要的一件事是要分清楚哪些是真问题,哪些是假问题,哪些是成熟的问题,哪些是不成熟的问题;如果分得清这些问题,做研究就会事半功倍,如果分不清楚它们,就会事倍功半,甚至做无用功。然而,物理学的发展过程中从不缺乏曲折和戏剧性,也从不缺乏各种迷惑人的问题,它们有的是装扮成真问题的假问题,有些是看起来像是假问题的真问题。     

谈“原始问题”与能力培养

把物理问题划分为“抽象问题”和“原始问题”两类，探讨如何求解“原始问题”，以提高解决实际问题的能力。     

关于高中物理教学中学生问题意识培养的几点思考

物理学家海森堡曾经说过：“提出正确的问题,往往等于解决了问题的大半。”问题是思维的起点,是创新的源泉。本文着重讨论了培养学生问题意识的意义,以及如何培养学生问题意识的策略。     

奇异性核物理前沿问题

简要评述奇异性核物理的几个前沿问题,包括Λ超核能谱精细结构与ΛN相互作用提取问题,自由YN势的改进问题、K核问题、Σ超子-核势问题、Λ超子-Λ超子相互作用强度问题、中子星内部奇异粒子成分问题等。     

多组分放射性衰变曲线的辨识

多组分放射性衰变曲线的辨识问题在许多工程技术领域中经常出现。对于二元组分问题，早已 有了很好的解决办法，但对于多元组分问题，仍没有令人满意的算法。为此提出了一个新算法，道德将问题化为一个常微分方程的反问题，进一步应用等价的积分方程与多项式求根的技巧使问题得到解决。数值实验表明该方法对于多元组分问题能得到好的结果。     

各向异性的悬臂梁负担均布载荷的弯曲问题

柱体是工程结构中常常遇到的结构单位。按照载荷情况的不同,主要的柱体问题有下面三类:(1)柱体的扭转问题;(2)悬臂梁在其悬空端负担一个横向载荷的问题;(3)悬臂梁负担均布载荷的问题。在各向同性的场合,前两问题首先由圣维南建立一般性的理论。第三个问题则首先由米恰耳创立一般性的理论。米恰耳将所设问题化为一个平面形变问题。在任意各向异性的场合,前两问题已由列赫尼茨基建立了一般性的理论。本文的目的在建立任意各向异性的悬臂梁负担均布载荷的一般理论。我们利用列赫尼茨基的方法和结果,将所设问题化为一个广义平面形变问题,后者的一般性的解法,亦已经由列赫尼茨基建立。     

关于几个典型的刚体运动问题中被动力作用的教学讨论

在存在约束的动力学问题中,有关被动力作用的分析一直是大学物理教学中的薄弱环节,因而可能导致学生对这类问题的错误理解和求解。本文结合小球与匀质细杆碰撞问题、摩擦轮问题和旋转轮摩擦加速问题等3个典型问题讨论了大学物理教学中的被动力在刚体运动中的作用,即特别是小球与匀质悬挂杆的碰撞问题。讨论力求便于学生理解,因此推导尽量简单。文章认为,讨论有约束的刚体动力学问题时必须强调约束是通过被动力对刚体的运动带来作用。这是使学生正确理解和求解刚体动力学问题的关键之一。     

适应法象差自动校正程序中若干问题的处理

本文讨论了适应法象差自动校正程序中几个问题的处理方法,这些问题主要是:象差参数的选择问题;变量尺度问题;线性检查和步长控制问题;按给定公差自动排除相关象差的问题;并介绍了一个适应法程序的流程图。     

巧用开普勒第三定律解决天体运动问题

在天体运行中,会有绕同一个中心天体运动的行星或卫星问题;卫星与它所绕行的天体的同步问题;卫星在轨期间的变轨问题;卫星之间的追及和相遇问题。应用开普勒第三定律是解决这些问题的重要途径。     

气冷引线热平衡方程的求解方法

给出了在气冷引线最佳化问题中求解热平衡方程的方法。在寻求终解的过程中,既要解决诸多参量中包含非独立参量的问题,又要解决特解表达式的定义域中既有自变量又有因变量的问题,还要解决多解函数中确定真解定义域的问题。上述问题的解决为最终求出引线温度分布并解决引线最佳化问题奠定了基础。     

Cumulants and moments

We introduce a ¹-algebra of terminating sequences. The set of normalized linear functionals on this algebra is then equipped with a quasi-multiplication and thus with a multiplication. A state corresponds to a sequence of moments. With it we associate its sequence of cumulants. The quasi-multiplication relates cumulants and moments in a very easy way. We give necessary and sufficient conditions for a sequence to be a sequence of moments and necessary and sufficient conditions for a sequence to be a sequence of cumulants.     

Measuring Light Field of Light Source with High Directional Resolution Using Mirrored Ball and Pinhole Camera

This paper presents a method of measuring a light field of a light source with high directional resolution using a mirrored ball and a pinhole camera. The light field describes a spatial and directional distribution of radiances from the light source. The directional distribution is expanded by a reflection on the mirrored ball, and the radiances are measured by a charge-coupled device (CCD) camera with a pinhole lens. The light source is laterally moved by a robot arm to measure the directionally expanded light field, and each pixel on a CCD can obtain the radiances from the light source through the pinhole lens with high directional resolution. The light field is estimated from the pixel value and the position of each pixel using a ray tracing technique. The light field of a krypton lamp was experimentally measured by the proposed method, and the accuracy of the measurement was evaluated against the irradiances measured by a spectro-radiometer at sample points.     

Scintillation properties of dark hollow beams in a weak turbulent atmosphere

The on-axis scintillation index for a circular dark hollow beam (DHB) propagating in a weak turbulent atmosphere is formulated, and the scintillation properties of a DHB are investigated in detail. The scintillation index for a DHB reduces to the scintillation index for a Gaussian beam, an annular beam and a flat-topped beam under certain conditions. It is found that the scintillation index of a DHB is closely related to the beam parameters and can be lower than that of a Gaussian beam, an annular beam and a flat-topped beam in a weak turbulent atmosphere at smaller waist sizes and longer propagation lengths. PACS 42.25.Bs; 42.68.Ay     

On reconstructing photon statistics by on/off detectors: Toward the multi-partite case

The propagation of pulses of the pump and its second harmonic in a quadratically nonlinear medium whose linear properties are characterized by a negative refractive index at the pump frequency and by a positive refractive index at the harmonic frequency is considered theoretically. In the case of a low intensity of the interacting waves, the pump and second-harmonic pulses propagate in the opposite directions, but sufficiently powerful pulses can form a simulton—a solitary two-frequency wave propagating in a certain direction as a single whole. Solutions to a set of equations are found which describe the steady-state propagation of a solitary wave and of a nonlinear periodic (cnoidal) wave.     

Atomic quantum gases in Kagomé lattices

We demonstrate the possibility of creating and controlling an ideal and trimerized optical Kagomé lattice, and study the low temperature physics of various atomic gases in such lattices. In the trimerized Kagomé lattice, a Bose gas exhibits a Mott transition with fractional filling factors, whereas a spinless interacting Fermi gas at 2/3 filling behaves as a quantum magnet on a triangular lattice. Finally, a Fermi-Fermi mixture at half-filling for both components represents a frustrated quantum antiferromagnet with a resonating-valence-bond ground state and quantum spin liquid behavior dominated by a continuous spectrum of singlet and triplet excitations. We discuss the method of preparing and observing such a quantum spin liquid employing molecular Bose condensates.     

The Klein-Gordon and the Dirac Oscillators in a Noncommutative Space

We study the Dirac and the Klein-Gordon oscillators in a noncommutative space. It is shown that the Klein-Gordon oscillator in a noncommutative space has a similar behaviour to the dynamics of a particle in a commutative space and in a constant magnetic field. The Dirac oscillator in a noncommutative space has a similar equation to the equation of motion for a relativistic fermion in a commutative space and in a magnetic field, however a new exotic term appears, which implies that a charged fermion in a noncommutative space has an electric dipole moment.     

Atom-dimer scattering for confined ultracold fermion gases

We solve the three-body problem of a quasi-one-dimensional ultracold Fermi gas with parabolic confinement length a (perpendicular) and 3D scattering length a. On the two-body level, there is a Feshbach-type resonance at a (perpendicular)/a approximately 1.46, and a dimer state for arbitrary a (perpendicular)/a. The three-body problem is shown to be universal, and described by the atom-dimer scattering length a(ad) and a range parameter b(ad). In the dimer limit a (perpendicular)/a>1, we find a repulsive zero-range atom-dimer interaction. For a (perpendicular)/a<-1, however, the potential has long range, with a(ad)>0 and b(ad)>a(ad). There is no trimer state, and despite a(ad)=0 at a( perpendicular)/a approximately 2.6, there is no resonance enhancement of the interaction.     

Instability of traveling waves in an optical waveguide

Instability of traveling IR waves within a waveguide structure is discussed. A practical model of a traveling wave amplifier of a solid state is proposed, utilizing an optical waveguide. The mechanism of instability is interpreted in terms of an interaction between a plasmon wave and a circuit one under a constraining boundary condition. Properties of the traveling amplification and related problems are discussed, with appropriately suggested semiconductor materials and device designs. The features of the amplifier are a simple structure, a low DC biasing power dissipation for room-temperature operation, unidirectionality, and a wide wavelength range from IR or submillimeter order, suited to various applications.     

单电子在含有双能级原子的空腔中的输运行为

本文构造了一个含有双能级原子的空腔系统,用来模拟一个含有双能级量子点的微腔系统, 并研究其对电子输运行为的影响.通过对该系统输运方程的求解,给出了系统输运系数的具体表达式,然后通过调整空腔及原子的本征特性以及两者的耦合性质,研究了电子在腔体中的输运行为对腔体本征属性的依赖关系. 这些结果可以为如何操控电子在微观结构器件中的输运特性提供一定的理论支持.     

Comparisons of predicted steady-state levels in rooms with extended- and local-reaction bounding surfaces

A combined beam-tracing and transfer-matrix model for predicting steady-state sound-pressure levels in rooms with multilayer bounding surfaces was used to compare the effect of extended- and local-reaction surfaces, and the accuracy of the local-reaction approximation. Three rooms—an office, a corridor and a workshop—with one or more multilayer test surfaces were considered. The test surfaces were a single-glass panel, a double-drywall panel, a carpeted floor, a suspended-acoustical ceiling, a double-steel panel, and glass fibre on a hard backing. Each test surface was modeled as of extended or of local reaction. Sound-pressure levels were predicted and compared to determine the significance of the surface-reaction assumption. The main conclusions were that the difference between modeling a room surface as of extended or of local reaction is not significant when the surface is a single plate or a single layer of material (solid or porous) with a hard backing. The difference is significant when the surface consists of multilayers of solid or porous material and includes a layer of fluid with a large thickness relative to the other layers. The results are partially explained by considering the surface-reflection coefficients at the first-reflection angles.