Impact of modulated multiple optical feedback time delays on laser diode chaos synchronization

By studying laser diodes subject to multiple time-delayed optical feedback, we demonstrate that the signatures of time delays in the autocorrelation function of the laser output can be erased in systems incorporating modulated feedback time delays. This property enhances the suitability of such laser systems highly suitable for secure chaos-based communication systems. Chaos synchronization properties of a laser-based modulated multiple time-delayed system are also reported for the first time.     

Interaction of “extremely diluted solutions” with aqueous solutions of hydrochloric acid and sodium hydroxide: A calorimetric study at 298 K

The “extremely diluted solutions” (EDS) have revealed a really intriguing behaviour, characterized by multiple independent variables. Because of their behaviour, EDS can be described as far-from-equilibrium systems, capable of auto-organizing as a consequence of little perturbations.

We measured the heats of mixing of basic and acid solutions with such EDS and their electrical conductivity, comparing with the analogous heats of mixing and electrical conductivity of the untreated solvent.

In particular, calorimetric titrations have been performed with NaOH or HCl solutions at various concentrations. Plots of the excess heat as a function of the concentration of titrant reveal differences and similarities between the two. By analysing these plots we were able to formulate new hypotheses about the supramolecular organization of the solvent water, when subject to mechanical perturbations stemming from the EDS preparation protocol, that is comprised of an iterative process of successive dilutions and succussions.     

基于大脑模板的MRI扫描自动定位方法

在大脑磁共振成像(MRI)影像学的数据采集中,通常先扫描一幅定位图像,并根据解剖学先验知识手动调整合适的扫描定位参数,再进行后续的正式扫描.该文实现了一种直接以大脑模板为参照的自动定位的方法:首先采集一幅中等分辨率的快速三维定位图像,然后通过与模板的配准确定定位参数,并应用到后续序列的扫描,以保证不同被试在图像采集时采用与模板一致的空间定位.该方法一方面便于不同被试的图像数据之间进行系统性比较与参照,帮助诊断者快速定位病灶,也可在后续常用的基于体素分析过程最大化数据的利用效率.另一方面,针对单个体多次扫描之间的自动定位,该文进一步使用迭代方法,通过多次"扫描、配准、自动定位"步骤,逐步减小图像配准算法的误差.实验证明,该文基于大脑模板的自动定位方法能够确保不同被试之间和同一被试之内在图像数据采集时的空间定位高度一致性,其中同一被试内多次扫描的空间定位误差1.0 mm和1.0o.     

Non-Gaussian diffusion MRI assessment of brain microstructure in mild cognitive impairment and Alzheimer’s disease

We report the first application of a novel diffusion-based MRI method, called diffusional kurtosis imaging (DKI), to investigate changes in brain tissue microstructure in patients with mild cognitive impairment (MCI) and AD and in cognitively intact controls. The subject groups were characterized and compared in terms of DKI-derived metrics for selected brain regions using analysis of covariance with a Tukey multiple comparison correction. Receiver operating characteristic (ROC) and binary logistic regression analyses were used to assess the utility of regional diffusion measures, alone and in combination, to discriminate each pair of subject groups. ROC analyses identified mean and radial kurtoses in the anterior corona radiata as the best individual discriminators of MCI from controls, with the measures having an area under the ROC curve (AUC) of 0.80 and 0.82, respectively. The next best discriminators of MCI from controls were diffusivity and kurtosis (both mean and radial) in the prefrontal white matter (WM), with each measure having an AUC between 0.77 and 0.79. Finally, the axial diffusivity in the hippocampus was the best overall discriminator of MCI from AD, having an AUC of 0.90. These preliminary results suggest that non-Gaussian diffusion MRI may be beneficial in the assessment of microstructural tissue damage at the early stage of MCI and may be useful in developing biomarkers for the clinical staging of AD.     

Two charges on plane in a magnetic field I. “Quasi-equal” charges and neutral quantum system at rest cases

Low-lying bound states for the problem of two Coulomb charges of finite masses on a plane subject to a constant magnetic field B$B$ perpendicular to the plane are considered. Major emphasis is given to two systems: two charges with the equal charge-to-mass ratio (quasi-equal charges) and neutral systems with concrete results for the hydrogen atom and two electrons (quantum dot).     

Generalized Noether's theorem. I. theory

This article is a theoretical investigation of generalized Noether's theorem, which, though unconcerned with considerations such as coordinate transformations, symmetry, and invariance, is the basic mechanism of conventional Noether's theorem, its extensions, and its inverse. The generalized theorem is a completely new approach to the subject—formally, conceptually, and practically. It is an association, for a set of field equations, of field variations with conserved currents. The theorem is stated from two points of view and analyzed with regard to its interpretation and its formal and conceptual relation to conventional Noether's theorem and extensions, transformation groups, and Hamilton's principle. The inverse theorem is also treated. The role of coordinate transformations in conventional Noether's theorem is analyzed.     

Reverse draining of a magnetic soap film — Analysis and simulation of a thin film equation with non-uniform forcing

We analyze and classify equilibrium solutions of the one-dimensional thin film equation with no-flux boundary conditions and in the presence of a spatially dependent external forcing. We prove theorems that shed light on the nature of these equilibrium solutions, guarantee their validity, and describe how they depend on the properties of the external forcing. We then apply these results to the reverse draining of a one-dimensional magnetic soap film subject to an external non-uniform magnetic field. Numerical simulations illustrate the convergence of the solutions towards equilibrium configurations. We then present bifurcation diagrams for steady state solutions. We find that multiple stable equilibrium solutions exist for fixed parameters, and uncover a rich bifurcation structure to these solutions, demonstrating the complexity hidden in a relatively simple looking evolution equation. Finally, we provide a simulation describing how numerical solutions traverse the bifurcation diagram, as the amplitude of the forcing is slowly increased and then decreased.     

Comment on “The structure of monolayer SiO2 on Mo(1 1 2): A 2-D [Si-O-Si] network or isolated [SiO4] units?”

In a recent paper by Chen and Goodman [M. Chen, D.W. Goodman, Surf. Sci. 600 (2006) L255] the structure of SiO₂ films epitaxially grown on Mo(1 1 2) has been revisited. This structure has been the subject of several experimental and theoretical studies but it is still controversial, with some authors claiming that it is formed by isolated [SiO₄] units and others in favor of a two-dimensional [Si-O-Si] network. With this Comment we want do underline some aspects of the discussion, in particular related to the theoretical work performed so far on this subject, which in our opinion have not been properly represented in Ref. [M. Chen, D.W. Goodman, Surf. Sci. 600 (2006) L255].     

Nonequilibrium Green’s function method for quantum thermal transport

This review deals with the nonequilibrium Green’s function (NEGF) method applied to the problems of energy transport due to atomic vibrations (phonons), primarily for small junction systems. We present a pedagogical introduction to the subject, deriving some of the well-known results such as the Laudauer-like formula for heat current in ballistic systems. The main aim of the review is to build the machinery of the method so that it can be applied to other situations, which are not directly treated here. In addition to the above, we consider a number of applications of NEGF, not in routine model system calculations, but in a few new aspects showing the power and usefulness of the formalism. In particular, we discuss the problems of multiple leads, coupled left-right-lead system, and system without a center. We also apply the method to the problem of full counting statistics. In the case of nonlinear systems, we make general comments on the thermal expansion effect, phonon relaxation time, and a certain class of mean-field approximations. Lastly, we examine the relationship between NEGF, reduced density matrix, and master equation approaches to thermal transport.     

多调制延时耦合半导体激光器的混沌同步与编码

数值研究了非相干光反馈与非相干光注入半导体激光器的多调制延时混沌同步,由于该系统是基于非相干注入的,所以不需要接收激光器的频率与发送激光器频率完全匹配。通过对非相干光反馈半导体激光器输出自相关函数的研究,发现在多调制延时系统中,延时标识可以被隐藏,这一特性可以提高系统的安全性,非常适用于混沌保密通信系统。分别利用混沌移位键控(CSK)及混沌隐藏(CMS)编码方法考查了单向耦合和双向耦合系统的通信性能。     

The effect of nearby bubbles on array gain

The coherent processing of signals from multiple hydrophones in an array offers improvements in angular resolution and signal-to-noise ratio. When the array is steered in a particular direction, the signals arriving from that direction are added in phase, and any signals arriving from other directions are not. Array gain (AG) is a measure of how much the signal arriving from the steering direction is amplified relative to signals arriving from all other directions. The subject of this paper is the manner in which the AG of an acoustic array operating in water that contains air bubbles is affected by scattering from nearby bubbles. The effects of bubbles on acoustic attenuation and dispersion are considered separately from their effects on AG. Acoustic measurements made in bubbly water using the AB Wood tank at the Institute of Sound and Vibration Research, University of Southampton, in June 2008 show that as bubble density increases, relative phase shifts in individual hydrophone signals increase and signal correlation among the hydrophones is reduced. A theory and numerical simulation linking bubble density at the hydrophone to the AG is in good agreement with the measurements up to the point where multiple scattering becomes important.     

30 Years of sonochemistry links with China

Most scientists consider that sonochemistry became recognised as a discrete subject in the 1980’s – some 40 years ago which coincidentally is when my own interests in the subject began. This review briefly outlines how I first became involved in sonochemistry and then in its development. However its main theme is the way in which my links with China through sonochemistry have developed from their beginnings in 1990. This was the subject of my presentation at AOSS4 and involves a range of topics which started with the extraction of natural products and surface treatment but later expanded to include therapeutic ultrasound and environmental protection.     

Chaos synchronization and encoding in coupled semiconductor lasers of multiple modulated time delays

We numerically investigate the synchronization performance of unidirectionally and bidirectionally coupled chaotic semiconductor lasers subject to multiple modulated time delays optical feedbacks. Moreover, by studying the autocorrelation function of the coherent feedback semiconductor laser output, we find that the signatures of time delays can be erased in systems incorporating modulated feedback time delays, which largely improve the system security. Finally, chaos masking switching (CMS) is utilized to examine the communication ability. Numerical results indicate that the messages could be successfully recovered both in unidirectionally and bidirectionally coupled lasers, which confirms the possibility of applying multiple modulated delay system in optical chaos secure communication.     

Formation energy and geometry of vacancies at BN and B<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>C<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>N<Subscript><Emphasis Type="Italic">z</Emphasis></Subscript> nanocones

We have studied, through ab initio calculations, the stability of 60° and 120° boron nitride nanocones containing mono and multiple boron, nitrogen, and carbon vacancies. The stability of the vacancies as well as the structures reconstruction mechanism have been investigated. Our results indicate that the stability of the cones presenting such vacancies strongly depends on growth conditions. We have also found that multiple vacancies display formation energies that are comparable, and in some cases, even lower to the ones presented by monovacancies. Therefore, our results allow us to conclude that the formation energy does not depend on the vacancy size. Finally, for 120° cones, we can verify that the stability of the boron and nitrogen vacancies depends on the position where the atom has been removed.     

Multiple coincidences in surface structure determinations

We show that when the adsorbate is a weak scatterer of electrons, agreement of calculated LEED spectra with experiment is subject to approximate multiple coincidences in the vertical adsorbate-substrate spacing, with a periodicity of about 0.7 Å. Scrutiny of low energy spectra and the appearance of a compression or expansion of the theoretical energy scale with respect to experiment provide means to distinguish between the coincidences.     

A quantum spherical <Emphasis Type="Italic">p</Emphasis>-spin glass model: Low-temperature behavior

Low-temperature slow dynamics, aging, and temperature and field shifts are studied analytically and numerically for a quantum p-spin (p = 3) glass model interacting with internal quantum environment and external magnetic fields. It is demonstrated that the correlation function and the real part of susceptibility are subject to aging and restoration (rejuvenation) under little changes of temperature and field. The examined effects are briefly analyzed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 42–48, January, 2007.     

Multiple two-variable <Emphasis Type="Italic">p</Emphasis>-adic <Emphasis Type="Italic">q-L</Emphasis>-function and its behavior at <Emphasis Type="Italic">s</Emphasis> = 0

The objective of this paper is to construct a multiple p-adic q-L-function of two variables which interpolates multiple generalized q-Bernoulli polynomials. By using this function, we solve a question of Kim and Cho. We also define a multiple partial q-zeta function which is related to the multiple q-L-function of two variables. Finally, we give a finite-sum representation of the multiple p-adic q-L-function of two variables and prove a multiple q-extension of the generalized formula of Diamond and Ferrero-Greenberg.     

Statistical mechanics of gravitating systems ... <Emphasis Type="Italic">and some curious history of Chandra’s rare misses!</Emphasis>

Chandra’s academic life had several phases each culminating in a monograph describing that subject. I shall deal with aspects of his work in the two earliest phases. I shall describe the overall structure of statistical mechanics of gravitating systems, the relevance of isothermal sphere in the mean-field approximation and issues related to collisional relaxation and dynamical friction in self-gravitating system of particles. There are several curious features in the history of these topics which I comment upon.     

Aspirin abolishes spontaneous oto-acoustic emissions

Spontaneous oto-acoustic emissions (OAEs) were measured prior to, during, and following administration of aspirin. The dose schedule was three 325-mg tablets every 6 h for a total of 16 doses (3.75 days). In every subject studied, all spontaneous OAEs gradually diminished and then disappeared during the drug regimen. Emissions that were initially small disappeared within 14-20 h of beginning the drug regimen (3-4 doses), while initially large emissions took 40-70 h (7-12 doses) to disappear completely. In contrast, the initial size of an emission appeared unrelated to the time required for it to recover to full strength once drug administration ceased. The recovery process was highly idiosyncratic, with the emissions of some subjects returning to full strength within 24 h, while for other subjects, full recovery required several days. In two subjects having multiple emissions in the same ear, the relative sizes of the different emissions often changed greatly during the disappearance and recovery phases. When small frequency shifts appeared for these subjects, they appeared--and were in the same direction--for each of the multiple emissions. In a related experiment, the spontaneous emission was unchanged in one subject who took a drug that inhibits the intracellular entry of calcium ions (verapamil).