Transitions to the Continuum: Three Different Approaches

We present three different derivations of the transition probabilities to the continuum. It is shown that calculations, performed as a direct application of the postulates of orthodox quantum mechanics (OQM), do not yield results consistent with experiments. Traditional treatments are summarized and criticized. The relation of the transitions to the continuum with the traditional quantum measurement problem is pointed out; we sum up and comment some contributions concerning this issue. It is shown that an approach based on the notion of spontaneous projections yields expressions of the transition probabilities similar to those obtained in the traditional way and new predictions which could be submitted to experimental tests.     

物理发现中的"殊途同归"

在物理学发展的道路上，一个自然现象或物理问题往往会有许多科学者不约而同地去进行探索，正如猎手们把箭同时射向猎物一样．这就使得物理学发现史上会出现这样的现象：多个科学者在事先互相并不了解的情况下，各自从同一条思路，或从不同的思路，完全独立地发现同一个物理学成果．这就是物理发现中的“殊途同归”现象．     

Nuclear Level Mixing: From a Curiosity to Applications in Nuclear Physics, Solid State Physics and Gamma Optics

The history of “Nuclear Level Mixing” is closely related to the research that Prof. Coussement performed during the last 25 years. In particular, the impact of this quantum mechanical concept on different research fields will be discussed. Without going in detail, we aim to give the reader an idea of how one single concept may lead to different discoveries. This revised version was published online in July 2006 with corrections to the Cover Date.     

做好三个"难做"的物理演示实验的诀窍

在高中物理教学中，“水波的干涉”、“布朗运动”和“静电实验”是三个较难做好的演示实验．“水波的干涉”实验的主要问题是看不到明显而规则的强弱条纹；“布朗运动”实验的主要问题是要么显微镜中看到的是黑洞洞的一片，要么镜头被沾湿弄脏；“静电实验”的主要问题是漏电，一漏电什么也做不成．这三个实验其实都有诀窍，如果我们能像刑警“破案”一样仔细分析每个实验做不成的原因，问题就可以解决．     

物理教学中培养创新能力的途径

从科学方法渗透、鼓励学生质疑、发散思维的训练、解决实际问题的能力训练、实验教学的改革等方面阐述了在物理教学中培养创新能力的途径.     

Incorporating Instantaneous Parts in the LFD Yukawa Model

We have treated the box diagram as an example to get a better understanding of the influence of the instantaneous parts. The expressions of the kernels are derived using the light-front time-ordered (LFTO) box diagrams corresponding to the covariant box diagram. Knowing the expressions for the kernels we discuss the divergences in these expressions. We will show that the zero modes do not cause any problems neither in the propagating LFTO-diagrams nor in the instantaneous diagrams. The logarithmic ultraviolet divergence, , is present in all LFTO-diagrams and cannot be removed by adding propagating and instantaneous diagrams.     

The Ideas Behind the Different Approaches to Quantum Cosmology

In this review work I present an overview aboutthe main ideas behind the different approaches toquantum cosmology and their physical meaning. Inparticular I use the Bianchi type IX cosmological modelin order to exemplify the concepts.     

Majorana: From Atomic and Molecular, to Nuclear Physics

In the centennial of Ettore Majorana’s birth (1906–1938?), we re-examine some aspects of his fundamental scientific production in atomic and molecular physics, including a not well known short communication. There, Majorana critically discusses Fermi’s solution of the celebrated Thomas–Fermi equation for electron screening in atoms and positive ions. We argue that some of Majorana’s seminal contributions in molecular physics already prelude to the idea of exchange interactions (or Heisenberg–Majorana forces) in his later works on theoretical nuclear physics. In all his papers, he tended to emphasize the symmetries at the basis of a physical problem, as well as the limitations, rather than the advantages, of the approximations of the method employed.     

Majorana and the Quasi-Stationary States in Nuclear Physics

A complete theoretical model describing artificial disintegration of nuclei by bombardment with α-particles, developed by Majorana as early as 1930, is discussed in detail jointly with the basic experimental evidences that motivated it. By following the quantum dynamics of a state resulting from the superposition of a discrete state with a continuum one, whose interaction is described by a given potential term, Majorana obtained (among the other predictions) the explicit expression for the integrated cross section of the nuclear process, which is the directly measurable quantity of interest in the experiments. Although this is the first application of the concept of quasi-stationary states to a Nuclear Physics problem, it seems also that the unpublished Majorana work anticipates by several years the related seminal paper by Fano on Atomic Physics.     

The Nuclear Quadrupole Interaction in High Temperature Superconductors

Abstract

Since their discovery in 1986 [11], the high temperature superconducting (HTS) copper oxides have presented a continuing challenge to both experiment and theory. The identification of the underlying mechanism (or mechanisms) responsible for their superconductivity remains an unanswered question. Numerous theories have been proposed ranging from phonon-mediated pairing of the charge carriers, similar to the Bardeen–Cooper–Schrieffer (BCS) [2] theory developed for conventional low-temperature superconductors, to novel concepts independent of phonons [3–-l0]. For conventional superconductors the variation of the transition temperature T_c , with isotopic mass M (from BCS theory T_c ～ M^?a ) was an important verification of the contribution of electron-phonon interactions to electron pairing. Measurements of this effect of HTS cuprates resulted in isotope shifts much smaller than predicted by theory [ll-14], raising doubts about the role of phonons. However, Barbee [15] argued that the size of the isotope shift is not a unique indicator of phonon-mediated pairing. Since the HTS materials contain Cu ions with partially filled 3d shells, many of the alternative theories of HTS have focused on magnetic interactions and associated spin fluctuations [3–10]. The reader is referred to Ref. 16 for the details of other theories that have been proposed and to the article by Schrieffer and Anderson [17) for an overview discussion of the theory of high temperature superconductivity.     

Categorizing Different Approaches to the Cosmological Constant Problem

We have found that proposals addressing the old cosmological constant problem come in various categories. The aim of this paper is to identify as many different, credible mechanisms as possible and to provide them with a code for future reference. We find that they all can be classified into five different schemes of which we indicate the advantages and drawbacks     

有感于高三物理概念教学

在高三复习课后布置的作业中有这样一道题目:在一条倾斜的静止不动的传送带上,有一铁块正在匀速向下滑动,途中传送带突然改成向上加速运动,铁块由上端滑到底端所用的时间与传送带不动相比较     

The sixth Conference on Advanced Topics in the Interdisciplinary Fields of Particle Physics,Nuclear Physics and Cosmology

The sixth Conference on Advanced Topics in the Interdisciplinary Fields of Particle Physics, Nuclear Physics and Cosmology was held on July 22-27,     

The sixth Conference on Advanced Topics in the Interdisciplinary Fields of Particle Physics, Nuclear Physics and Cosmology

The sixth Conference on Advanced Topics in the Interdisciplinary Fields of Particle Paysics.Nuclear Paysic8and Cosmology was held on July 22-27,2007 in Lijiang,Yunan Province.Over 70 scientists who were activelv working in the fields attended the conference and 42 physicists gave talks.9 papers have been selected to be published in the proceedings.     

The Few-Body Approximation in Nuclear,Atomic, and Molecular Physics

The quantum theory of few-body scattering based on Faddeev-Yakubovsky integral and differential equa¬tions is applied to calculations of various processes (elastic, inelastic, atom exchange, and dissociative) in nuclear, atomic, and molecular physics. Analytical solutions of these equations are presented for various limiting cases. The methods used for solving the integral and differential systems of equations are discussed.     

Application of Hadron-Hadron Nuclear Interaction Parametrization Model in the Study of Superhigh Energy Cosmic Rays

Under the assumption of mixed primary cosmic ray composition and using a hadron-hadron interaction parametrization model to describe hadron-hadron nuclear interaction,the behavior of superhigh energy cosmic ray particles in the atmosphere is simulated,and the simulated results compared with experimental data of Mt.emulsion chamber in details.The influences from the mean transverse momentum value of secondary particles in fragmentation region on simulated results are discussed also in details.     

The Lattice Solid Model to Simulate the Physics of Rocks and Earthquakes: Incorporation of Friction

The particle-based lattice solid model developed to study the physics of rocks and the nonlinear dynamics of earthquakes is refined by incorporating intrinsic friction between particles. The model provides a means for studying the causes of seismic wave attenuation, as well as frictional heat generation, fault zone evolution, and localisation phenomena. A modified velocity–Verlat scheme that allows friction to be precisely modelled is developed. This is a difficult computational problem given that a discontinuity must be accurately simulated by the numerical approach (i.e., the transition from static to dynamical frictional behaviour). This is achieved using a half time step integration scheme. At each half time step, a nonlinear system is solved to compute the static frictional forces and states of touching particle-pairs. Improved efficiency is achieved by adaptively adjusting the time step increment, depending on the particle velocities in the system. The total energy is calculated and verified to remain constant to a high precision during simulations. Numerical experiments show that the model can be applied to the study of earthquake dynamics, the stick–slip instability, heat generation, and fault zone evolution. Such experiments may lead to a conclusive resolution of the heat flow paradox and improved understanding of earthquake precursory phenomena and dynamics.     

Nuclear Physics Programs for the Future RIBs Facility in Korea

We present nuclear physics programs based on the planned experiments using rare isotope beams (RIBs) for the future Korean Rare Isotope Beams Accelerator facility(KRIA). This ambitious facility has both an Isotope Separation On Line (ISOL) and fragmentation capability for producing RIBs and accelerating beams of wide range mass of nuclides with energies of a few to hundreds MeV per nucleon. Low energy RIBs at Elab = 5 to 20 MeV per nucleon are for the study of nuclear structure and nuclear astrophysics toward and beyond the drip lines while higher energy RIBs produced by inflight fragmentation with the reaccelerated ions from the ISOL enable to explore the neutron drip lines in intermediate mass regions. The planned programs have goals for investigating internal structures of the exotic nuclei toward and beyond the nucleon drip lines by addressing the following issues: how the shell structure evolves in areas of extreme proton to neutron imbalance; whether the isospin symmetry maintains in isobaric mirror nuclei at and beyond the drip lines; how two-proton radioactivity affects abundances of the elements; what the role of the continuum states including resonant states above protondecay threshold in exotic nuclei is in astrophysical nuclear reaction processes, and how the nuclear reaction rates triggered by unbound proton-rich nuclei make an effect on rapid proton capture processes in a very hot stellar plasma.     

与原子科学共传奇——钱三强院士在发展原子能科学中经历的几件事

多年来,作者为了编撰杰出科学家、我国原子能事业创始人、国家"两弹一星"功勋奖章获得者钱三强先生的年谱和传记,对他经历过的一些与原子科学有关的事件,进行过比较广泛而深入的调查研究,其中许多情况令人感慨.