Multimode lasers as analogs of complex biological systems (a survey)

Simulating the activity of complex biological systems, in particular, the human brain, is a topical problem the solution of which is necessary both for understanding their functioning and for developing new classes of computational system based on operating principles of the brain. Some features and analogies that can be found in the operation of laser systems and brain and used for developing new generation computational systems are discussed. The appropriateness of such analogies is justified by the fact that both laser systems and the brain are open (interacting with the environment) dissipative spatially distributed nonlinear systems. Therefore, laser optical systems and, in particular, systems with dissipative optical solitons offer an opportunity to experimentally and theoretically model some important cognitive brain functions. One of particularities of the brain operation is the ability to manipulate images. Proceeding from this, in this work, problems related to generation and amplification with laser of spatial structures (images), as well as to amplification of signals coming to it from outside are discussed.     

Classical analog to topological nonlocal quantum interference effects

The two main features of the Aharonov-Bohm effect are the topological dependence of accumulated phase on the winding number around the magnetic fluxon, and nonlocality-local observations at any intermediate point along the trajectories are not affected by the fluxon. The latter property is usually regarded as exclusive to quantum mechanics. Here we show that both the topological and nonlocal features of the Aharonov-Bohm effect can be manifested in a classical model that incorporates random noise. The model also suggests new types of multiparticle topological nonlocal effects which have no quantum analog.     

Topological defect motifs in two-dimensional Coulomb clusters

We study the distribution of topological defects in two-dimensional Coulomb clusters with parabolic lateral confinement. The minima hopping algorithm based on molecular dynamics is used to efficiently locate the ground-?and low-energy metastable states, and their structure is analysed by means of the Delaunay triangulation. The size, structure and distribution of geometry-induced lattice imperfections strongly depends on the system size and the energetic state. Besides isolated disclinations and dislocations, classification of defect motifs includes defect compounds-grain boundaries, rosette defects, vacancies and interstitial particles. Proliferation of defects in metastable configurations destroys the orientational order of the Wigner lattice.     

三聚化非厄密晶格中具有趋肤效应的拓扑边缘态

近年来,探索新的拓扑量子结构、深入分析各种多聚化拓扑晶格中的新奇物理性质已经成为热点.并且,多聚化拓扑模型在量子光学等领域的研究也愈发深入,拥有广阔的发展前景.本文聚焦于研究三聚化非厄密晶格中的新奇拓扑特性.首先,若晶胞内最近邻正反向耦合不相等,三聚化模型中的体态和边缘态出现趋肤效应.其中,随着最近邻耦合正反系数差的增大,拓扑保护的边缘态的宽度和简并度均可被调制,边缘态数量也会减少.其次,当在考虑次近邻耦合的影响时,随着次近邻耦合系数在适当范围内变化,系统本征能谱的上下能隙及其中具有趋肤效应的边缘态也会发生不对称的变化.此外,当适当改变两种耦合系数,三聚化非厄密模型的体态和边缘态的局域程度也会随之发生变化.     

原子光刻

与光子和电子不同,原子的激发亚稳态具有方便操作的内能态结构,这使利用内能态的光学淬灭原理实现光刻技术成为现实.基于原子光学的中性原子束光刻技术是下一代光刻技术(the next generation lithography, NGL)的一种, 它可分两种途径实现：激光驻波原子直沉积技术和亚稳态中性原子光刻技术.前者可以实现图案的纳米尺度特征、大面积平行沉积和高分辨率;后者结合有效的抗蚀剂,同样可以实现纳米图形制造,在基板上获得的尖锐边缘分辨率目前可达40 nm.两种途径的原理相差甚远,但最终获得的结果相似.     

Dirac semimetal in three dimensions

We show that the pseudorelativistic physics of graphene near the Fermi level can be extended to three dimensional (3D) materials. Unlike in phase transitions from inversion symmetric topological to normal insulators, we show that particular space groups also allow 3D Dirac points as symmetry protected degeneracies. We provide criteria necessary to identify these groups and, as an example, present ab initio calculations of β-cristobalite BiO(2) which exhibits three Dirac points at the Fermi level. We find that β-cristobalite BiO(2) is metastable, so it can be physically realized as a 3D analog to graphene.     

Possible reaction coordinates in the metastable states of sodiumnitroprusside Na2[Fe(CN)5NO]2H2O: a discussion based on neutron diffraction- and spectroscopic measurements

The metastable states of sodiumnitroprusside are extremely stable at temperatures below 200 K. It is possible to allocate structural changes measured by neutron diffraction to measured spectroscopic parameters, but the amount of the structural change is relatively small for a reaction co-ordinate as the metastable states have an extremely long lifetime. New hypotheses for related systems try to explain such a phenomena in two ways: The first way is a bending of the NO-bond in the metastable state, the second one an exchange of the oxygen and nitrogen atoms in the NO-bond (which can be regarded as an bending). As such changes would be possible also from our density functional calculations, we re-investigated our neutron diffraction data using the new models. However, our results are not compatible with one of these models. On the contrary, the neutron diffraction data show partially opposite tendencies. We compare both models with EXAFS measurements, with vibrational spectroscopic results and the data found by M?ssbauer spectroscopy. We propose a potential scheme for all three states (GS, and ) extracted from absorption and thermodynamic data to explain the electronic and energetic rearrangement, and the population dynamics. Received: 23 June 1997 / Accepted: 13 October 1997     

Predication of topological states in the allotropes of group-IV elements

Three-dimensional (3D) topological insulators (TIs) have been studied for approximately fifteen years, but those made from group-IV elements, especially Ge and Sn, seem particularly attractive owing to their nontoxicity, sizable intrinsic spin–orbit coupling (SOC) strength and natural compatibility with the current semiconductor industry. However, group-IV elemental TIs have rarely been reported, except for the low temperature phase of α-Sn under strain. Here, based on first-principles calculations, we propose new allotropes of Ge and Sn, named T5-Ge/Sn, as desirable TIs. These new allotropes are also highly anisotropic Dirac semimetals if the SOC is turned off. To the best of our knowledge, T5-Ge/Sn are the first 3D allotropes of Ge/Sn that possess topological states in their equilibrium states at room temperature. Additionally, their isostructures of C and Si are metastable indirect and direct semiconductors. Our work not only reveals two promising TIs, but more profoundly, we justify the advantages of group-IV elements as topological quantum materials (TQMs) for fundamental research and potential practical applications, and thus reveal a new direction in the search for desirable TQMs.     

Dynamics of Electronic States and Magnetoabsorption in 3D Topological Insulators in a Quantizing Magnetic Field

Quantum states have been calculated analytically; the dynamics of a wave packet in a magnetic field has been investigated, and the optical absorption coefficient has been calculated for surface states in 3D topological insulators of the Bi₂Te₃ family. We have detected a qualitative effect of the hexagonal warping of the spectrum on the structure of wavefunctions at the Landau levels, its manifestation in the features of the wave packet dynamics in a quantizing magnetic field, as well as in the frequency dependence of the optical absorption coefficient, in which new peaks that are absent in the isotropic model of the spectrum appear depending on the polarization of the incident wave. The effects considered here can be manifested in the optical and transport experiments with topological insulators, which makes it possible to determine the parameters of their band structure.     

Intrinsic stability of quasicrystals under the generation of Frenkel pairs

Under irradiation metastable quasicrystals undergo a phase transition to an amorphous state. This transition can be reversed by annealing. As in normal crystalline materials the phase transition is considered to be triggered by generation and recombination of vacancies and interstitial atoms (Frenkel pairs). We have classified the possible Frenkel defects in a metastable monatomic quasicrystal with respect to geometric and energetic properties. With numerical simulation we have studied the behaviour of the quasicrystal under a load of Frenkel defects for various defect concentrations. We find three ranges of behaviour: up to 5% defects per atom the structure remains icosahedral, in a middle range it stays disordered icosahedral or it becomes either disordered or perfect crystalline, depending on the implementation of the defects. If there are more than 10% defects the structure becomes irreversibly amorphous. We finally compare our results with experimental data.     

Construction and Application of Functional Brain Network Based on Entropy

Functional brain network (FBN) is an intuitive expression of the dynamic neural activity interaction between different neurons, neuron clusters, or cerebral cortex regions. It can characterize the brain network topology and dynamic properties. The method of building an FBN to characterize the features of the brain network accurately and effectively is a challenging subject. Entropy can effectively describe the complexity, non-linearity, and uncertainty of electroencephalogram (EEG) signals. As a relatively new research direction, the research of the FBN construction method based on EEG data of fatigue driving has broad prospects. Therefore, it is of great significance to study the entropy-based FBN construction. We focus on selecting appropriate entropy features to characterize EEG signals and construct an FBN. On the real data set of fatigue driving, FBN models based on different entropies are constructed to identify the state of fatigue driving. Through analyzing network measurement indicators, the experiment shows that the FBN model based on fuzzy entropy can achieve excellent classification recognition rate and good classification stability. In addition, when compared with the other model based on the same data set, our model could obtain a higher accuracy and more stable classification results even if the length of the intercepted EEG signal is different.     

Efficiency of electrical manipulation in two-dimensional topological insulators

We investigate the efficiency of electrical manipulation in a two-dimensional topological insulator by inspecting the electronic states of a lateral electrical potential superlattice in the system. The spatial distribution of the electron density in the system can be tuned by changing the strength of the externally applied lateral electrical superlattice potential. This provides us the information about how efficiently one can manipulate the electron motion inside a two-dimensional topo- logical insulator. Such information is important in designing electronic devices, e.g., an electric field effect transistor made of the topological insulator. The electronic states under various conditions are examined carefully. It is found that the dispersion of the mini-band and the electron distribution in the potential well region both display an oscillatory behavior as the potential strength of the lateral superlattice increases. The probability of finding an electron in the potential well region can be larger or smaller than the average as the potential strength varies. These features can be attributed to the coupled multiple-band nature of the topological insulator. In addition, it is also found that these behaviors are not sensitive to the gap parameter of the two-dimensional topological insulator model. Our study suggests that the electron density manipulation via electrical gating in a two-dimensional topological insulator is less effective and more delicate than that in a traditional single-band semiconductor.     

Neutrinos produced by ultrahigh-energy photons at high redshift

Some of the proposed explanations for the origin of ultrahigh-energy cosmic rays invoke new sources of energetic photons (e.g., topological defects, relic particles, etc.). At high redshift, when the cosmic microwave background has a higher temperature but the radio background is low, the ultrahigh-energy photons can generate neutrinos through pair production of muons and pions. The resulting diffuse background of 10(17) eV neutrinos can be detected by future experiments.     

Topological particle field theory,general coordinate invariance and generalized Chern-Simons actions

We show that recently proposed generalized Chern-Simons action can be identified with the field theory action of a topological point particle. We find the crucial correspondence which makes it possible to derive the field theory actions from a special version of the generalized Chern-Simons actions. We provide arguments that the general coordinate invariance in the target space and the flat connection condition as a topological field theory can be accommodated in a very natural way. We propose series of new gauge invariant observables.     

A network analysis of the Chinese stock market

In many practical important cases, a massive dataset can be represented as a very large network with certain attributes associated with its vertices and edges. Stock markets generate huge amounts of data, which can be use for constructing the network reflecting the market’s behavior. In this paper, we use a threshold method to construct China’s stock correlation network and then study the network’s structural properties and topological stability. We conduct a statistical analysis of this network and show that it follows a power-law model. We also detect components, cliques and independent sets in this network. These analyses allows one to apply a new data mining technique of classifying financial instruments based on stock price data, which provides a deeper insight into the internal structure of the stock market. Moreover, we test the topological stability of this network and find that it displays a topological robustness against random vertex failures, but it is also fragile to intentional attacks. Such a network stability property would be also useful for portfolio investment and risk management.     

Nucleation of Topological Dipoles¶in Nematic Liquid Crystals

A topological dipole is a pair of point defects with opposite topological charges. In this paper we show by example how the nucleation of such a dipole within a smooth field can drive a metastable state into a stable one. Building on our previous work, we construct a mathematical model for the dynamics of both monopoles and dipoles in a capillary filled with a nematic liquid crystal. Though our analysis is fit for liquid crystals, a similar mechanism is also likely to apply to the field theory for other ordered media. Received: 10 July 1997 / Accepted: 25 June 1998     

Composite solitons in SU(3) spin–orbit-coupling Bose gases

We study solitons in a spin-1 Bose–Einstein condensates with SU(3) spin–orbit coupling. We obtain the ground state and the metastable solution for solitons with attractive interactions by the imaginary-time evolution method. Compared with the SU(2) spin–orbit coupling, it is found that the solitons in SU(3) spin–orbit coupling show a new feature due to breaking the symmetry. The solitons called the composite solitons have mixing manifolds of ferromagnetic and antiferromagnetic states. This has stimulated people to study the topological excitation properties of SU(3) spin–orbit coupling and it is expected to find new quantum phases.     

磁性外尔半金属材料研究现状与展望

外尔半金属是拓扑半金属家族中的一员。理想的外尔半金属费米面附近有且仅有非简并价带和导带形成的孤立能带交叉点,其低能激发准粒子可以用描述手性外尔费米子的外尔方程来刻画。在三维固体中形成外尔半金属态需要破缺时间反演、中心反演以及它们的组合对称操作。外尔点(即能带交叉点)具有拓扑稳定性和确定的手性或磁荷,且左右手性外尔点需成对出现。非磁性外尔半金属TaAs家族材料的发现,使得研究具有手征性的电子态,及其导致的新物性、新现象成为可能。与非磁性外尔半金属相比,磁性外尔半金属可以仅仅具有一对外尔点,是最简单的外尔半金属,有利于物理机理的分析。磁性外尔半金属可用于实现具有本征磁性的量子反常霍尔效应,提供了通过外磁场来调控外尔点及其相关效应的新手段。文章介绍了磁性外尔半金属的理论模型、拓扑数计算等基本原理,简要回顾了一些典型材料的理论计算和实验研究进展,并介绍了磁性拓扑量子化学理论和磁性拓扑材料的高通量计算,最后讨论了磁性外尔半金属的发展前景和未来的研究方向。     

一级相变时的红外特征辐射–熔融结晶和蒸气冷凝或沉淀

本文报道了一种新的物理现象–一级相变时 (熔融结晶, 蒸气冷凝或沉淀)的红外特征辐射. 实验结果根据相应的理论模型来进行分析. 此理论模型是基于一个论断, 那就是粒子(原子, 分子, 团簇)从高能级亚稳态 (气态或液态) 向低能级稳态 (液态或结晶态) 相变时释放出一个或多个光子. 这些光子的能量取决于相变潜热和新相粒子的结合特性. 对所有研究过的物质来说, 这种能量集中在红外区. 这就是为什么这种辐射被称作红外特征辐射. 在雾和云的形成过程中, 水发生了结晶、冷凝、升华, 从而产生了大量红外辐射留在了大气中. 因而, 该研究的结果必然对大气现象有很重要的影响: 它是地球冷却的因素之一; 冰雹云的形成伴随着强烈的红外辐射, 这种辐射可用来表征高能相转化为低能相的过程, 可以作为一种气象预警. 红外特征辐射似乎可以用来解释木星的呈红色现象. 它可以用于大气储能, 就此, 继风能、水能、太阳能、地热能后, 红外特征辐射成为生态学上第五种纯净的能源. 关键词： 熔体结晶 蒸气结晶 特鲁藤规则 大气蓄能     

高光谱成像技术在中医证候客观诊断中的应用

因高光谱成像技术具有灵敏度高、蕴含图谱信息丰富等特点,使其有望被作为突破口来解决中医证候诊断缺乏客观指标的困境。鉴于舌与证候之间存在复杂且模糊的映射关系,针对当前舌信息采集方式的局限性以及现有处理模式存在将混合信息体割裂提取以致重要内涵丢失的缺陷,提出了一种新思路:采用高光谱技术进行舌象采集并将舌体交叠混合的图谱信息作为一个整体进行分析,结合多种线性与非线性数据挖掘算法以黑箱模式关联证候,提取特异性光谱指标群。并将所提取的光谱指标群综合临床的生理、生化及中医症征指标,从多角度分析病因病机的机理,找到一种证候客观诊断的新模式。