Mode Interactions in Four-frequency Degeneracy-lifted Ring Lasers

Abstract

A non-planar ring cavity, with a non-reciprocal bias in the form of the longitudinal Zeeman effect on the gain medium, has been used to demonstrate four-mode bidirectional operation in a He-Ne ring laser at 632·8 nm. It has also been shown that this ring system is sensitive to rotation.     

3-mode Interactions with O(2) Symmetry and a Model for Taylor-Couette flow

We analyse the bifurcations of a general ordinary dififerential equation where is equivariant under an action of the group O(2) on. The equation represents the most general nonlinear local interaction of three O(2)-symmetric modes:a steady-state mode with mode-number k, and two periodic (Hopf) modes with mode-numbers l and m. The parameter λ is a bifurcation parameter, and α₁, α₂are unfolding parameters that split the individual modes apart. The system is assumed to be in Birkhoff normal form, so that f also commutes with an action of the 2-torus T². We discuss the existence and stability of bifurcating branches and how these break the O(2) × T² symmetry.Depending on the precise mode-numbers k l m we find up to 31 symmetry classes of possible solutions including six that combine all three modes, and thus cannot be found in any 2-mode interaction. We also discuss the possible occurrence of Sacher-Naimark torus bifurcations, providing a further 10 solution types, and 'slow drift'bifurcations.

This 10-dimensional system can occur generically in O(2)-symmetric bifurcation problems having two extra parameters, and in principle is applicable to a wide range of physical systems. The discussion here is motivated by the observed pattern formation in the Taylor–Couette system, the flow of a fluid contained between coaxial rotating cylinders. It arises by seeking a 'hidden organizing centre' that combines two previous mode-interaction models of this system: a 6-dimensional Hopf–steady-state model due to Chossat and looss (1985) and Golubitsky and Stewart (1986), and an 8-dimensional Hopf–Hopf model due to Chossat, Demay and looss (1987). We interpret the general results on the 10-dimensional system in the context of Taylor–Couette flow, giving schematic pictures of the associated flow patterns. The model incorporates almost all of the observed non-chaotic flows in the Taylor–Couette experiment into a single finite-dimensional dynamical system. It predicts the possible occur- rence of four new flow patterns (corresponding to four of the six possible solutions that combine all three modes). Theseform invariant 3-tori, and may be described as superimposed twisted vortices, superimposed wavy vortices, and two types of twisted wavy vortices. Possible torus bifurcations from states in the 10-dimensional model include various modulated spirals, three types of modulated twisted vortices, three types of modulated wavy vortices, modulated superimposed spirals, modulated interpenetrating spirals, modulated superimposed ribbons, and modulated interpenetrating ribbons. However, whether any of these new states and torus bifurcations can actually occur in Taylor–Couette flow at suitable parameter values, and if so whether they can occur stably, depend upon more detailed numerical calculations than we have performed     

Detection of Receptor-Ligand Interactions With an GHz Impedance Biosensor System

Nanogap impedance biosensors with an electrode separation of 75 nm have been used for the specific detection of biological interactions. Different model systems, such as thrombin-anti-thrombin antibody, and Rev-peptide-anti-Rev aptamer are presented to demonstrate the detectability of different molecular masses at varying concentrations. In order to improve the signal-to-noise ratio, the use of reference sensors has been explored. The interaction of prostate specific antigen (PSA) with an anti-PSA antibody is shown to demonstrate the detection at concentrations as low as 10 nM.     

A Sliding Mode Flux-Linkage Controller With Integral Compensation for Switched Reluctance Motor

A novel flux-linkage controller using sliding mode technique with integral compensation (SM-I) is proposed for torque ripple minimization of a switched reluctance motor (SRM). The proposed SM-I controller inherits the advantages of proportion–integration (PI) and conventional SM controller. These make it feasible for the flux-linkage controller to reduce torque ripple by correctly selecting the flux ramps in the limit of available dc-link voltage. Moreover, since the controller is not model-based, it avoids the complexity of mathematical modeling and is easily implemented. Experimental results demonstrate that the proposed controller performs better and can be used as an alternative for nonlinear SRM drive systems.      

松散粉粒物品软包装冲击力学模型

通过对松散粉粒物品软包装冲击过程力学模型的建立与研究,得到冲击状态下包装袋受力的数学表达式。为包装袋的设计提供了较为满意的依据。     

Symmetry considerations in CdSe nanocrystals

Semiconductor nanocrystals or quantum dots show a wide range of physical properties depending on their size or shape. In this paper, we show that symmetry is also an important characteristic that can lead to different electronic and optical properties. We use pseudopotential density-functional theory, within a real space approach, and address the sensitivity of electronic and optical properties with respect to the symmetry point groups associated to CdSe nanocrystals.     

Tests of a Two-Photon Technique for Measuring Polarization Mode Dispersion With Subfemtosecond Precision

An investigation is made of a recently introduced quantum interferometric method capable of measuring polarization mode dispersion (PMD) on sub-femtosecond scales, without the usual interferometric stability problems associated with such small time scales. The technique makes use of the extreme temporal correlation of orthogonally polarized pairs of photons produced via type-II phase-matched spontaneous parametric down-conversion. When sent into a simple polarization interferometer these photon pairs produce a sharp interference feature seen in the coincidence rate. The PMD of a given sample is determined from the shift of that interference feature as the sample is inserted into the system. The stability and resolution of this technique is shown to be below 0.2 fs. We explore how this precision is improved by reducing the length of the down-conversion crystal and increasing the spectral band pass of the system.     

不同微波遥感模态和不同数据组合的等湿度区域分布与土壤湿度的反演

论述了主动、被动和主动被动相结合的3种微波遥感模态反演土壤湿度的方法和特点。为了采用人工神经网络方法反演出土壤湿度，在随机粗糙面双谱散射模型的基础上计算了裸土壤表面的散射系数和发射率，分析了3种不同的微波遥感模态和不同数据组合的等湿度区域分布的特点，从而确定了适合于各个微波遥感模态的输入数据组合。反演结果表明，只要选择适当的人工神经网络输入数据组合，采用3种模态中的任何一种微波遥感模态反演土壤湿度都是可行的，并具有较好的反演精度，结果对于微波遥感反演土壤湿度方案的选取具有指导意义。     

可装配性设计中的零件对称度的自动识别

可装配性设计——DFA(Design for assembly)是改善产品装配性能，减少产品装配费用的主要途径。零件对称度自动识别是DFA的重要内容，也是产品装配几何特征识别的关键技术之一，受到国内外许多专家和学者的广泛关注。笔者在分析以往国内外研究成果的基础上，提出了对称度分治识别算法——DCSR(Divide and Conquer-based Symmetry Recognition Method)。该算法将三维几何实体的对称度识别转化为二维问题，降低了几何计算的复杂性；通过利用几何相关性，提高了算法的效率。DCSR已用于笔者研发的产品可装配性设计支持系统——DFAS中，已在实际应用中得到验证。     

Doping-Dependent Superconducting Symmetry in Hubbard Systems

The d-wave superconducting state is studied by using a generalized Hubbard model, in which a next-nearest-neighbor correlated-hopping interaction (t ₃) is included. The results obtained within the BCS framework suggest the existence of a critical hole concentration, below which a d_x ^{2-y 2}-wave superconducting gap is observed. However, above this critical concentration the maxima of the single-particle excitation energy gap are rotated by /4 and no real nodes exist, as observed in tunneling experiments. In this study, the parameters estimated by first-principle calculations for cuprate superconductors are used.     

Symmetry and structure: an overview

The many aspects of symmetry are reviewed as a unifying principle in science. Discrete symmetry groups dictate the structures of physical objects and continuous space-time symmetries are the generators of special relativity and quantum operators. Internal symmetry and gauge invariance provide the basis of quantum theory and the electromagnetic field. Approximate global symmetries underpin the formulation of conservations and natural laws in terms of field densities and conserved currents. Symmetry breaking elucidates phenomena such as phase transition, nucleation and crystal growth, superconductivity, the arrow of time and chirality.     

Symmetry of secondary ferroics. II

In an earlier paper (Part I), the symmetry requirements for the secondary ferroic phenomena of ferrobielectricity, ferrobimagnetism and ferromagnetoelasticity and ferromagnetoelectricity were considered, and examples of materials illustrating the behavior discussed. In this second paper, the phenomena of ferrobielasticity and ferroelastoelectricity are considered. It is shown that there are 5 ferrobielastics, 15 ferroelastoelectric and 10 ferrobielastic-ferroelastoelectric species in which the primary ferroic effects are forbidden by symmetry. For α-quartz and other secondary ferroics it is suggested that the orientation of twin or domain walls which effect state switching under stress are dictated by strain compatibility between the contiguous domain states involved.     

Symmetry of secondary ferroics. I

Although at present there are only a few well documented examples, secondary ferroic phenomena may prove to be rather common, since the symmetry requirements are not especially stringent. In this paper, the conditions for ferrobielectricity, ferrobimagnetism, ferromagnetoelasticity and ferromagnetoelectricity are discussed. It is shown that ferrobielectricity can be expected in antiferroelectric ferroelastic classes with substantial dielectric anisotropy. Nickel oxide and other antiferromagnetic ferroelastics with anisotropic magnetic susceptibility show ferrobimagnetism. Evidence for ferromagnetoelastic domains is found in CoF₂ and FeCO₃, while Cr₂O₃ shows ferromagnetoelectric switching. Of the 90 magnetic point groups, 35 are potentially ferromagnetoelastic and 40 potentially ferromagnetoelectric. In a companion paper (Part II) to be published, symmetry restrictions for ferrobielasticity and ferroelastoelectricity will be considered, and the conditions which determine the orientation of domain walls in secondary ferroics examined.     

Gravity from Symmetry Breaking Phase Transition

Journal of Low Temperature Physics - The paper is devoted to the memory of Dmitry Diakonov. We discuss gravity emerging in the fermionic vacuum as suggested by Diakonov 10 years ago in his paper...     

Current Mode Monolithic Active Pixel Sensor With Correlated Double Sampling forCharged Particle Detection

A monolithic active pixel sensor operating in current mode for charged particle detection is described. The sensing element in each pixel is an n-well/p-sub diode with a PMOS transistor integrated in an n-well. The drop of the n-well potential from the collection of charge modulates the transistor channel current. Each pixel features two current mode memory cells. The subtraction of distant-in-time samples frees the signal of fixed pattern noise (FPN) and of the correlated low-frequency temporal noise components, resulting in extraction of the particle footprint. The subtraction circuits are placed at each column end. A transimpedance amplifier, integrating in sequence two current samples and subtracting the results in an arithmetic operation, was adopted. The integrated version of the transimpedance amplifier, designed with a maximized conversion gain, is burdened by a risk of an early saturation, imperiling its operation, if the dispersions of the dc current component are too big. The degree of dispersions could not be estimated during the design. Some number of columns is available as a backup with the direct current readout. An external realization of the subtracting circuit, based on the same principle, is used to process direct output columns. The concept of the data acquisition setup developed, the tested performance of an array of cells, and the processing circuitry are described     

Symmetry properties of two-dimensional anisotropic photonic crystals

A theoretical study of two-dimensional photonic crystals made of anisotropic material is presented. Detailed computation principles including a treatment of the TE and TM polarizations are given for a photonic crystal made of either uniaxially or biaxially anisotropic materials. These two polarizations can be decoupled as long as any one of the principal axes of the anisotropic material is perpendicular to the periodic plane of the photonic crystal. The symmetry loss due to the anisotropy of the material and the variation of the Brillouin zones relative to the tensor orientations are also analyzed. Furthermore, the symmetry properties of the two-dimensional photonic band structure are studied, and the resulting effect on the photonic bandgap and the dispersion properties of photonic crystal are analyzed as a function of the orientation of the anisotropic material.     

Symmetry of Two-Electron States in Unconventional Superconductors

A group-theoretical approach is developed to constructing two-electron states in the basis of one-electron states of crystals. Such states correspond to Cooper pairs in superconductors and pseudogap states (at T* > T _c ). The theory is applied to unconventional superconductors: heavy-fermion and high-T _c materials. Comparison of theoretical results with experimental data is used to gain insight into the structure of two-electron states in these materials.     

Symmetry properties of the causal heat equations

Symmetry properties of the causal (hyperbolic) heat equations are studied. Symmetry groups of two variants of hyperbolic equations are calculated. The results obtained are analysed and compared with known properties of the classical heat equation. These findings may be considered as possible arguments in favour of one of the causal heat conduction models.