Multi-soliton complexes

In this paper we introduce the concept of multi-soliton complexes (MSC). A particular example of a MSC is an incoherent soliton in a multimode fiber or in a photorefractive crystal, but there are many examples in other areas of physics. We discuss a variety of profiles of MSCs, their unusual collisional properties, the possibility of a MSC on a background and some other interesting properties of MSCs. Some of their features are also shared by single solitons, but there are many differences between the properties of the two types. (c) 2000 American Institute of Physics.     

Stochastic resonance in thermally activated reactions: Application to biological ion channels

At the molecular level many thermally activated reactions can be viewed as Poisson trains of events whose instantaneous rates are defined by the reaction activation barrier height and an effective collision frequency. When the barrier height depends on an external parameter, variation in this parameter induces variation in the event rate. Extending our previous work, we offer a detailed theoretical analysis of signal transduction properties of these reactions considering the external parameter as an input signal and the train of resulting events as an output signal. The addition of noise to the system input facilitates signal transduction in two ways. First, for a linear relationship between the barrier height and the external parameter the output signal power grows exponentially with the mean square fluctuation of the noise. Second, for noise of a sufficiently high bandwidth, its addition increases output signal quality measured as the signal-to-noise ratio (SNR). The output SNR reaches a maximum at optimal noise intensity defined by the reaction sensitivity to the external parameter, reaction initial rate, and the noise bandwidth. We apply this theory to ion channels of excitable biological membranes. Based on classical results of Hodgkin and Huxley we show that open/closed transitions of voltage-gated ion channels can be treated as thermally activated reactions whose activation barriers change linearly with applied transmembrane voltage. As an experimental example we discuss our recent results obtained with polypeptide alamethicin incorporated into planar lipid bilayers.(c) 1998 American Institute of Physics.     

Gauge-invariant sub-structures of tree-level double-emission exact QCD spin amplitudes

In this note we discuss possible separations of exact, massive, tree-level spin amplitudes into gauge-invariant parts. We concentrate our attention on processes involving two quarks entering a color-neutral current and, thanks to the QCD interactions, two extra external gluons. We will search for forms compatible with parton-shower languages, without applying approximations or restrictions on phase space regions. Special emphasis will be put on the isolation of parts necessary for the construction of evolution kernels for individual splittings and to some degree for the running coupling constant as well. Our aim is to better understand the environment necessary to optimally match hard matrix elements with parton-shower algorithms. To avoid complications and ambiguities related to regularization schemes, we ignore, at this point, virtual corrections. Our representation is quite universal: any color-neutral current can be used; in particular, our approach is not restricted to vector currents only. This work is partially supported by RTN European Programme, MRTN-CT-2006-035505 (HEPTOOLS, Tools and Precision Calculations for Physics Discoveries at Colliders).     

Stern-Gerlach Experiment’s Interpretations and Noether’s Theorem

In this paper we suggest that theories treating two interacting objects in a different manner (for instance electromagnetic field of a laser classically, and the interacting atom as a quantum object) should be called “mixed”. Mixed theories are not so rare in Physics. One just should look at the whole area of Atomic, Molecular and Optical Physics in which mixed theories are often used, and, also, theories including quantum object interacting with classical surroundings that are the subject of our present discussion: the field of Quantum decoherence, when applied to resolving the dilemma should classical trajectories be used in explaining the Stern-Gerlach experiment or not. Consequently we are proving one improved corollary to Noether’s theorem, stating that mixed theories are not supporting the law of conservation of angular momentum and spin, as they are not based on the isotropy of space-time.     

Some minimal notes on notation and minima: A comment on “How particular is the physics of the free energy principle?” by Aguilera,Millidge, Tschantz,and Buckley

We comment on a technical critique of the free energy principle in linear systems by Aguilera, Millidge, Tschantz, and Buckley, entitled “How Particular is the Physics of the Free Energy Principle?” Aguilera and colleagues identify an ambiguity in the flow of the mode of a system, and we discuss the context for this ambiguity in earlier papers, and their proposal of a more adequate interpretation of these equations. Following that, we discuss a misinterpretation in their treatment of surprisal and variational free energy, especially with respect to their gradients and their minima. In sum, we argue that the results in the target paper are accurate and stand up to rigorous scrutiny; we also highlight that they, nonetheless, do not undermine the FEP.     

Images of synchronized chaos: Experiments with circuits

Synchronization of oscillations underlies organized dynamical behavior of many physical, biological and other systems. Recent studies of the dynamics of coupled systems with complex behavior indicate that synchronization can occur not only in case of periodic oscillations, but also in regimes of chaotic oscillations. Using experimental observations of chaotic oscillations in coupled nonlinear circuits we discuss a few forms of cooperative behavior that are related to the regimes of synchronized chaos. This paper is prepared under the request of the editors of the special focus issue of Chaos and contains the materials for the lecture at the International School in Nonlinear Science, "Nonlinear Waves: Synchronization and Patterns," Nizhniy Novgorod, Russia, 1995. The main goal of the paper is to outline the collection of examples that illustrate the state of the art of chaos synchronization. (c) 1996 American Institute of Physics.     

物理教学中让学生感知科学探索过程,提高认知水平,培养物理思维能力

物理学是培养学生逻辑思维能力的一门科学.在物理科学研究中,为了发现科学规律,很多科学家进行了艰苦而卓有成效的探索.在课堂教学上,作为教师,应该抓住机会向学生讲授科学家们是如何探索科学问题的,包括探索过程中的思维方法、试验过程.本文以波粒二象性、法拉第电磁感应定律、太空探索等为例,具体讲解这些探索过程中的思维方法和实验过程,通过这些,让学生感知科学探索过程,提高学生的认知水平,激发学生的学习兴趣,掌握正确的思维方式和科学方法,培养创新能力.     

项目化学习下CUPT备赛模式与实践——以南京师范大学队为例

在中国大学生物理学术竞赛(CUPT)10年的关键性时间节点,本文介绍了以南京师范大学CUPT代表队10年备赛经验所形成的备赛模式,论述了南京师范大学以项目化学习理论(Project Based Learning)为基础、依托CUPT培养本科创新性人才的实践探索,对备赛模式中的特色进行详细阐释,以期在已有模式及成果的基础上继续发挥CUPT对本科创新性人才培养的积极作用.     

2011 Asia Pacific Few-Body Conference Summary Remarks

These remarks represent the author’s personal perspective regarding ideas presented at this fifth Asia Pacific Conference on Few-Body Problems in Physics. They are not intended as a comprehensive summary of what we witnessed during this week of stimulating presentations and intense discussions. However, these remarks do characterize some of the physics we heard and some of the key questions raised. The ideas presented will hopefully outlive the rapporteurs who brought their work and that of others to our attention here in the International Hall of the Sungkyunkwan University in Seoul, Republic of Korea. Finally, we bid adieu to our friend, colleague, and mentor, John A. Tjon.     

从统计物理学看复杂网络研究

从统计物理学来看,网络是一个包含了大量个体及个体之间相互作用的系统。本文从统计物理学的角度整理与总结了复杂网络目前的主要研究结果,并对将来的研究工作做了一个展望。文章把网络分为三个层次———无向网络、有向网络与加权网络,对不同网络的静态几何量研究的现状分别做了综述,并结合网络机制模型设计与评价的需要,提出了新的有待研究的静态几何量;对网络机制模型做了总结与分析,提出了有待解决的关于双向幂律网络的机制模型的问题;部分地概括了网络演化性质,网络的结构稳定性以及网络上的动力学模型的研究。然后,以我们目前正在进行的两个方面的工作—科学家网络和产品生产关系网络—为例,粗略地介绍了网络研究在一些实际问题中的应用。最后,作为一个简单的补充和索引,我们整理了复杂网络研究中部分常用的解析与数值计算的方法。     

从统计物理学看复杂网络研究

从统计物理学来看，网络是一个包含了大量个体及个体之间相互作用的系统。本文从统计物理学的角度整理与总结了复杂网络目前的主要研究结果，并对将来的研究工作做了一个展望。文章把网络分为三个层次——无向网络、有向网络与加权网络，对不同网络的静态几何量研究的现状分别做了综述，并结合网络机制模型设计与评价的需要，提出了新的有待研究的静态几何量；对网络机制模型做了总结与分析，提出了有待解决的关于双向幂律网络的机制模型的问题；部分地概括了网络演化性质，网络的结构稳定性以及网络上的动力学模型的研究。然后，以我们目前正在进行的两个方面的工作—科学家网络和产品生产关系网络一为例，粗略地介绍了网络研究在一些实际问题中的应用。最后，作为一个简单的补充和索引，我们整理了复杂网络研究中部分常用的解析与数值计算的方法。     

Dynamics of three types of annual plants competing for water and light

We present and discuss a Monte Carlo model describing the dynamics of three types of annual plants which have different tolerances to shade and drought. External conditions (water and light) fluctuate around some values which are our control parameters and which decide how many resources the system receives. The plants compete with their nearest neighbours for the resources, however not in the same way. We show that for certain ranges of the control parameters a coexistence of the three species is observed. We discuss how the characteristics of the the plants — their number, germination, biomass or the number of nearest neighbours, depend on the two control parameters characterising external conditions. We show that elimination is done at the level of adult plants, not seedlings. We find also cooperative behaviour of plants in difficult conditions, as observed in field studies and we propose an explanation for this fact. Apart from plants tolerating shade but requiring more water and those tolerating drought but needing more light, which are common in nature, we introduce a third species with intermediary demands. We investigate under what conditions this new species could dominate and whether the total number of plants, regardless of their type, is larger with or without the intermediate plant. We show that in our model, like in nature, systems with two kinds of plants with opposite characteristics are, in general, as effective as a system with an additional third type of plants. We show that two contradictory hypotheses made by biologists, concerning the demands of plants in drought and shade, could be both true, however in different regimes.     

Lecture notes on shear viscosity in heavy ion collisions

These notes are a summary of a lecture delivered at the 30th Erice School in Nuclear Physics and provide an elementary introduction to shear viscosity as it is applied to heavy ion collisions. After a qualitative review of the ideal and viscous space-time evolutions, I calculate the elliptic flow and discuss how viscosity affects the results.     

Response to "Comment on 'Finding finite-time invariant manifolds in two-dimensional velocity fields' " [Chaos 11, 427 (2001)

Lapeyre, Hua, and Legras have recently suggested that the detection of finite-time invariant manifolds in two-dimensional fluid flows, as described by Haller and Haller and Yuan, can be substantially improved. In particular, they suggested (a) a change of coordinates to strain basis before the application of Theorem 1 of Haller and (b) the use of a nondimensionalized time computed from Theorem 1. Here we discuss why these proposed steps will not result in a significant overall improvement. We verify our arguments in a more detailed computation of the example analyzed in Lapeyre, Hau, and Legras (the Kida ellipse), as well as in a two-dimensional barotropic turbulence simulation. While in both of these examples the techniques suggested by Lapeyre, Hau, and Legras reveal additional thin regions of hyperbolicity near vortex cores, they also lead to an overall loss of detail in the global computation of finite-time invariant manifolds. (c) 2001 American Institute of Physics.     

Efficient noncausal noise reduction for deterministic time series

We present a simple noncausal noise reduction algorithm for time series that consist of noisy measurements of the state vectors of a deterministic (chaotic) nonlinear system. The underlying dynamical system is assumed to be known and to operate in discrete time. The noise reduction algorithm is an iterative scheme for finding exact deterministic orbits close to the measured noisy orbits. Furthermore, we discuss cases where the solution is not the original orbit but homoclinic to it. (c) 2001 American Institute of Physics.     

"Green" noise in quasistationary stochastic systems

We consider the behavior of stochastic systems driven by noise with a zero value of spectral density at zero frequency ("green" noise). For this purpose we propose the version of the Krylov-Bogoliubov averaging method to study the systems which are not stationary in the case of an external white noise. We use the ergodicity of a nonlinear random function in the method, and obtain equations for any approximation of the theory. In particular, it is shown in the first approximation that there is an effective potential to describe the averaged motion of the system. We consider a phase-locked loop as an example and show that metastable states are possible. The lifetime of these states essentially increases if the form of a green noise spectrum becomes sharper in the low-frequency region. The high stability of the system driven by green noise is confirmed by numerical simulation. It is important that the theoretical result obtained by the averaging method and the one obtained in the simulation coincide with sufficient accuracy. In conclusion, we discuss some of the unsolved green noise problems. (c) 2001 American Institute of Physics.     

Application of phototransferred thermoluminescence (PTTL) for dose re-assessment in routine dosimetry using MTS-N (LiF:Mg,Ti) thermoluminescent detectors

Erasure of the thermoluminescence (TL) signal on detector readout is considered to be a disadvantage of TL dosimetry, as post-readout dose reassessment is then impossible in principle. A method of dose reassessment based on phototransferred thermoluminescence (PTTL) has been developed at the Institute of Nuclear Physics, Polish Academy of Sciences (IFJ PAN) and applied to MTS-N (LiF:Mg,Ti) detectors. We demonstrate the possibility of applying PTTL for dose reassessment in MTS-N TL detectors routinely applied in the dosimetric service at IFJ PAN. Readings of TL detectors exposed to relatively high doses by the customers of our dosimetry service can now be reassessed using our automatic readers. A major obstacle in applying the PTTL method at lower exposures is the presence of residual dose accumulated in LiF:Mg,Ti detectors after many field exposure and readout cycles. Since most of the TL detectors in our service have been already used for a long time (e.g. for over 10 years in the case of some detector batches), we find that our PTTL method of dose reassessment is possible only in detectors which had received doses exceeding 5 mSv.     

On the biological effects of cosmic rays: Epidemiological studies

Summary Determining the biological effects of cosmic rays and other natural ionizing radiations, could possibly help us in shedding light on the more general problem of low-dose ionizing-radiation effects. In this work we provide a survey of the most recent studies available on epidemiological methods: we discuss the main difficulties in using these methods, as well as the discrepancies in their results. Work presented as a poster at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

普通物理综合设计实验课教学方法改革初探

开设普通物理综合设计实验课程目的在于培养学生动手能力、分析问题解决问题能力和创新能力。本文以首都师范大学物理系开设的普通物理综合设计实验为例讨论了具体的教学方法和过程,首先通过设计大量的预习思考题提高学生预习的针对性和预习效果,通过分组讨论来理解实验原理,并给出设计思路,最后通过实际实验锻炼学生的动手能力。该方法取得了良好的教学效果。