Basic concepts of synergetics

The paper presents a brief outline of microscopic as well as of macroscopic synergetics. In microscopic synergetics we start from evolution equations for microscopic variables or densities in which fluctuating forces and control parameters are included. When control parameters are changed, the systems are studied close to instability points. The concepts of order parameters, enslaving, critical fluctuations, and critical slowing down are presented. In macroscopic synergetics unbiased estimates on distribution functions and underlying processes are made based on observed moments or correlation functions. In such a case, a Fokker-Planck equation or a corresponding Langevin equation may be derived.     

品味物理概念

有些物理概念需要剖析细节才能深入理解,本文以爱因斯坦扩散系数、电磁波纵波分量对光子静止质量的影响以及状态的最小体积等为例,分析物理教学中的有趣问题.     

Fundamental concepts of quantum chaos

We review the fundamental concepts of quantum chaos in Hamiltonian systems. The quantum evolution of bound systems does not possess the sensitive dependence on initial conditions, and thus no chaotic behaviour occurs, whereas the study of the stationary solutions of the Schrödinger equation in the quantum phase space (Wigner functions) reveals precise analogy of the structure of the classical phase portrait. We analyze the regular eigenstates associated with invariant tori in the classical phase space, and the chaotic eigenstates associated with the classically chaotic regions, and the corresponding energy spectra. The effects of quantum localization of the chaotic eigenstates are treated phenomenologically, resulting in Brody-like level statistics, which can be found also at very high-lying levels, while the coupling between the regular and the irregular eigenstates due to tunneling, and of the corresponding levels, manifests itself only in low-lying levels.     

Overview of plasma-based accelerator concepts

An overview is given of the physics issues relevant to the plasma wakefield accelerator, the plasma beat-wave accelerator, the laser wakefield accelerator, including the self-modulated regime, and wakefield accelerators driven by multiple electron or laser pulses. Basic properties of linear and nonlinear plasma waves are discussed, as well as the trapping and acceleration of electrons in the plasma wave. Formulas are presented for the accelerating field and the energy gain in the various accelerator configurations. The propagation of the drive electron or laser beams is discussed, including limitations imposed by key instabilities and methods for optically guiding laser pulses. Recent experimental results are summarized     

Dynamical Localization Simulated on Actual Quantum Hardware

Quantum computers are invaluable tools to explore the properties of complex quantum systems. We show that dynamical localization of the quantum sawtooth map, a highly sensitive quantum coherent phenomenon, can be simulated on actual, small-scale quantum processors. Our results demonstrate that quantum computing of dynamical localization may become a convenient tool for evaluating advances in quantum hardware performances.     

A Flawed Argument Against Actual Infinity in Physics

In “Nonconservation of Energy and loss of Determinism II. Colliding with an Open Set” (2010) Atkinson and Johnson argue in favour of the idea that an actual infinity should be excluded from physics, at least in the sense that physical systems involving an actual infinity of component elements should not be admitted. In this paper I show that the argument Atkinson and Johnson use is erroneous and that an analysis of the situation considered by them is possible without requiring any type of rejection of the idea of infinity.     

Nuclear multifragmentation: Basic concepts

We present a brief overview of nuclear multifragmentation reaction. Basic formalism of canonical thermodynamical model based on equilibrium statistical mechanics is described. This model is used to calculate basic observables of nuclear multifragmentation like mass distribution, fragment multiplicity, isotopic distribution and isoscaling. Extension of canonical thermodynamical model to a projectile fragmentation model is outlined. Application of the projectile fragmentation model for calculating average number of intermediate mass fragments and the average size of the largest cluster at different Z _bound, differential charge distribution and cross-section of neutron-rich nuclei of different projectile fragmentation reactions at different energies are described. Application of nuclear multifragmentation reaction in basic research as well as in other domains is outlined.     

New concepts for controlled homoepitaxy

On the basis of a kinetic growth model we discuss new methods to grow atomically flat homoepitaxial layers in a controlled way. The underlying principle of these methods is to change the growth parameters during growth of an atomic layer in such a way that nucleation on top of a growing layer is suppressed, and thus, layer-by-layer growth is achieved. Experimentally, this can be realized by changing the substrate temperature or deposition rate during monolayer growth in a well-defined way. The same can be achieved at constant temperature and deposition rate by simultaneous ion bombardment during the early stages of growth of a monolayer, or by adding suitable surfactants to the system. Model experiments on Ag(111) and on Cu(111) using thermal energy atom scattering and scanning tunneling microscopy demonstrate the success of these methods.     

Dynamic concepts in neutron polarization

A new method of polarizing a neutron beam is proposed, which in contrast to conventional polarizers allows to make use of 100% of the incident intensity. It exploits the fact, that neutrons of different spin states differ in velocity after they have passed through an arrangement of crossed static and time-dependent magnetic fields. Provided the neutrons initially being sufficiently monochromatic, the two spin states can be separated in momentum space and be forced to point into the same spatial direction by means of a momentum-dependent spin rotation procedure. With presently available magnetic field technology (or nuclear pseudomagnetism) this dynamic method is applicable at continuous sources to polarize highly monochromatic thermal neutrons as those obtained by perfect crystal diffraction. The method seems to be particularly powerful, however, in the production of polarized cold and ultra-cold neutrons, where energy spreads of 1% and more are admissible. It is shown that at pulsed sources even polychromatic neutrons can be polarized with this technique.     

斯特林循环的理想和实际效率的讨论

套用大学物理热循环效率的计算公式于理想斯特林热机时,会出现原理上的差错,这是由斯特林热机的特殊设计造成.本文首先从热机效率的基本公式出发,阐述斯特林热机的工作原理,从中看到斯特林热机独特的设计原理使其效率的计算不同于基本公式的原因;其次给出实际斯特林热机工作时热损耗的来源分析;最后结合有关论文的结论,给出工质为范德瓦耳斯气体时的效率与体积比的关联.     

腔内有双折射滤光片的激光实际线宽

在研制高效宽带增益激光非线性频率转化的实验中发现,由双折射滤光片透过率计算出的激光输出频谱宽度比激光器实际频谱宽度要大一个数量级左右.考虑到激光模式竞争和均匀增宽效应,理论上提出了一个精确计算激光器实际频谱线宽的模型.用该模型模拟的带不同厚度双折射滤光片的调Q运转钛宝石激光器的光谱宽度与实验结果一致,这为优化设计双折射滤光片及该类激光器提供了依据.     

Fundamental concepts of the theory of dislocations

The fundamental concepts of the theory of dislocations are given in an exact way and some theorems are proved.

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In conclusion the author would like to thank Professor M. Valouch and Professor L. Zachoval for the interest they took in this work and for remarks and advice which helped to improve it.     

基于AFI的快速发射场B1+成像方法

该文提出了一种基于实际翻转角成像(Actual Flip-angle Imaging,AFI)的快速发射场测量方法(Fast AFI,FAFI),将多次激发平面回波成像(Multi-shot Echo Planar Imaging,Multi-shot EPI)的采集方式运用于AFI发射场(B_1~+)测量中,充分利用AFI序列中采集的等待时间,高倍数加速了水模和人体头部、腹部及盆腔的发射场测量.该文在水模和人体(n=16)实验中,验证了采用FAFI序列得到的B_1~+测量结果与AFI结果的一致性.FAFI序列大幅加速了发射场测量,为实现动态B_1~+匀场(B_1~+shimming)和快速局部激发提供了高效的发射场测量方法.     

Phase-shifting in-line digital holography on a digital micro-mirror device

A digital phase-shifting in-line holographic system based on the single coherence beam is developed. A series of phase-shifting fringes are generated by computer and outputted by a digital micro-mirror device (DMD). These fringes modulate the coherence beam because of the intensity modulation ability of DMD. In this work, the reconstructed conjugate image would not appear because of applying the phase-shifting algorithm. And calibration for the value of the optical phase shift is not necessary. An experiment based on a lens-less digital in-line micro-holographic setup with a phase grating specimen is conducted to demonstrate the validity of the present method.