Raman scattering at 532 and 355 nm in atmospheric pressure propane/air flames,with and without liquid fuels

We discuss an experimental investigation of Raman scattering spectroscopy in the vicinity of a simulated reacting liquid fuel spray. Spray flames are known to produce interference from droplet elastic scattering, laser-induced fluorescence, and laser-induced incandescence of soot. The goal in this work is to evaluate various experimental approaches to this challenging problem. We evaluate Raman scattering from both 532 and 355 nm beams (second and third harmonics of Nd : YAG), at various polarization orientations and over various lifetimes. We discuss tradeoffs between the various approaches and identify operating regimes in which such Raman measurements are possible. Perhaps the most compelling finding of this work is that the third harmonic of Nd : YAG holds more promise for measurement in high-pressure, combusting spray environments than has been previously thought. PACS 42.62.Fi; 47.55.Dz; 47.70.Fw     

Thermographic studies of plastered mosaics

In this work, different mosaics covered with various plasters (of thickness and composition) were evaluated in lab by means of various thermography approaches with the intention of detecting the tesserae beneath the plastered surface. Thermal images, as well as the thermal contrast curves between plain plastered surfaces and plastered mosaics were recorded. Results from the assessment are presented and discussed, indicating that images seeing through the mortar–plaster on plastered mosaic surfaces can be obtained using numerous thermography approaches.     

Linear and nonlinear vibrations analysis of viscoelastic sandwich beams

In this paper, numerical models are proposed for linear and nonlinear vibrations analyses of viscoelastic sandwich beams with various viscoelastic frequency dependent laws using the finite element based solution. Real and various complex eigenmodes approaches are investigated as Galerkin bases. Based on harmonic balance method, simplified and general approaches are developed for nonlinear vibration analysis. Analytical frequency-amplitude and phase-amplitude relationships are elaborated based on the numerically computed complex eigenmodes. The equivalent loss factors and frequencies as well as the forced harmonic response and phase curves are performed for sandwich beams with various boundary conditions and frequency dependent viscoelastic laws.     

Numerical approaches to fractional calculus and fractional ordinary differential equation

Nowadays, fractional calculus are used to model various different phenomena in nature, but due to the non-local property of the fractional derivative, it still remains a lot of improvements in the present numerical approaches. In this paper, some new numerical approaches based on piecewise interpolation for fractional calculus, and some new improved approaches based on the Simpson method for the fractional differential equations are proposed. We use higher order piecewise interpolation polynomial to approximate the fractional integral and fractional derivatives, and use the Simpson method to design a higher order algorithm for the fractional differential equations. Error analyses and stability analyses are also given, and the numerical results show that these constructed numerical approaches are efficient.     

Microscopic Studies on the Nucleus 28O

The ground-state properties of the nucleus ²⁸O are studied in relativistic and nonrelativistic mean-field approaches. It is shown by these calculations without any adjusting parameters that ²⁸O is a weakly bound nucleus and exhibits neutron halos. The differences among various mean-field approaches have been compared and discussed.     

一维无限深势阱定态波函数动量展开讨论

一维无限深势阱定态的动量概率分布存在两种"互相矛盾"的结论.为帮助学生理解两种结论的异同,锻炼严谨的科学作风和解决复杂问题的能力,笔者在量子力学理论教学中指导学生利用Python等现代科学计算工具,将一维无限深势阱定态波函数动量展开的讨论进行数值求解与可视化,绘制了不同观点以及不同情形下粒子的动量概率分布图.以此为基础讨论了不同计算结果的物理含义,揭示了两种结论的内在联系.此创新性的举措不仅有效加深了学生对于该重要问题的理解,还促进了学生专业知识、科学能力和综合素质的全面培养.     

Decay amplitudes and resonances

The structure of a type of decay amplitudes, which we considered recently and its connection to scattering amplitudes (of arbitrary arrangement channel cases), to conventional decay amplitudes, and to the energy distribution is worked out in detail. The meaning of unperturbed energies in usual approaches is clarified. Our considerations include the case of overlapping resonances. Sum rules for transition amplitudes, such as are of interest for neutral kaon decays, are rigorously derived. The exact interrelations between various approaches are shown.     

Constrained radar waveform optimization for a cooperative radar-communication system

The coexistence of radar-sensing and communication systems research has received a surge of interest in recent times to tackle the issue of spectrum inadequacy. Designing an optimized radar waveform for a coexistence scenario has been a challenging task for accomplishing the convergence of radar-sensing and communication functionalities, without degrading the performance at either end. This paper proposes a novel global optimization-based Spatial Branch and Bound (SBnB) approach to optimize the phase coefficients of a Non-Linear Frequency Modulated (NLFM) waveform in a CRCS framework. In addition, the Modified-Power Ratio Constraint-Cramér–Rao Lower Bound (M-PRC-CRLB), a local optimization-based approach is proposed to optimize the phase coefficients of an NLFM waveform. The spectral energy distribution and auto-correlation characteristics of an NLFM waveform are comprehensively investigated for various values of polynomial order (N) and at different threshold Signal-to-Noise-Ratio (SNR) values. To compare the proposed waveform design approaches (M-PRC-CRLB, SBnB) with the existing waveform design approaches namely, Minimum Estimation Error Variance (MEEV) and PRC- CRLB, a Peak-to-Side-Lobe-Ratio (PSLR), and Integrated-Side-Lobe-Ratio (ISLR) are evaluated at various polynomial orders and threshold SNR values. Furthermore, the performance of a CRCS is assessed using the radar estimation rate and communication data rate. The simulation results reveal that the proposed optimized radar waveform design approaches provide improved performance compared to the existing radar waveform design approaches in terms of radar estimation rate. Further, the proposed global optimization-based SBnB approach achieves a comparable performance of the communication data rate. In addition, the proposed approaches accomplish enhanced spectral utilization, controlled side-lobe energy levels, reduced range-domain ambiguities, and a higher information rate in a CRCS.     

Quantum memories

We perform a review of various approaches to the implementation of quantum memories, with an emphasis on activities within the quantum memory sub-project of the EU integrated project “Qubit Applications”. We begin with a brief overview over different applications for quantum memories and different types of quantum memories. We discuss the most important criteria for assessing quantum memory performance and the most important physical requirements. Then we review the different approaches represented in “Qubit Applications” in some detail. They include solid-state atomic ensembles, NV centers, quantum dots, single atoms, atomic gases and optical phonons in diamond. We compare the different approaches using the discussed criteria.     

Gain and saturation in semiconductor lasers

Several approaches have been developed for modelling the gain and saturation behaviour of semiconductor lasers, and this study includes a historical review of these various approaches. Special attention is given to rate equation models and to the possibility of so-called gain nonlinearities that might affect the CW and modulation performance of semiconductor lasers. Discussions are mainly limited to the GaAs/GaAIAs and InGaAsP/InP systems, for which the gain and gain nonlinearities have been most extensively studied.     

Experimental Evaluation of Undersampling Schemes for Electron Tomography of Nanoparticles

One of the emerging challenges in the field of 3D characterization of nanoparticles by electron tomography is to avoid degradation and deformation of the samples during the acquisition of a tilt series. In order to reduce the required electron dose, various undersampling approaches have been proposed. These methods include lowering the number of 2D projection images, reducing the probe current during the acquisition, and scanning a smaller number of pixels in the 2D images. A comparison is made between these approaches based on tilt series acquired for a gold nanoparticle.     

激光聚变研究进展

本文综合评述近年来发展很快的激光惯性约束聚变研究取得的新进展,包括驱动器、激光聚变物理及实现激光聚变的不同途径。重点分析不同驱动内爆方式的特点、取得的成就和遇到的困难。最后是今后的展望。     

Extreme Sub-radiance: Can Quantum Effects Generate Dramatically Longer Atomic Lifetimes?

The prolongation of lifetimes for an excited atom due to the presence of nearby atoms in the ground state is shown to follow simply from unitarity of the time evolution. We also discuss possible approaches to the detection and the overcoming of various technical obstacles.     

The simulation of a free-electron laser amplifier with a ribbon relativistic electron beam

An amplifier based on a high-power free-electron planar laser operating at a wavelength of 4 mm is simulated. The system is built around the U-3 accelerator, which forms a ribbon relativistic electron beam with an energy of up to 1 MeV and a total operating current of up to 2 kA. The simulation uses various approaches, including the direct numerical simulation of the Maxwell equations and particle motion equations by means of the PIC-code KARAT. The approaches are shown to give close results.     

Comparison of various approaches to the calculation of optically induced forces

Various approaches used for the calculation of optically induced forces applied to a transparent optical medium imbedded in a close plane optical resonator are analyzed. The forces are calculated by means of analysis of a change in the eigen frequency and energy stored in the resonator at various positions of the medium. It is shown that results obtained are identical to those calculated by means of approaches based on the Maxwell stress tensor, based on an analysis of a change in the momentum of light. An exception is for results obtained on the base of last versions of the Lorentz density force.     

Developments in excited-state density functional theory

This article discusses the reasons behind the apparent lack of success of density functional theory (DFT), during the past three decades, with excited states of many-electron systems. It describes various variational and non-variational approaches developed so far for dealing with this problem. Those include Theophilou’s equiensemble approach, extended to unequally weighted ensembles by Gross et al., Fritsche’s wavefunction partitioning approach, local scaling transformation theory by Kryachko et al., the work-function formalism developed by Harbola and Sahni, etc. Through intimate connections between time-dependence and excited states, under a perturbation, various time-dependent (TD) DFT approaches to excited states, e.g., a quantum fluid dynamical approach, a TD density-functional response theory and a TD optimized effective potential approach, are also reviewed.     

Canonical nonequilibrium ensembles and subdynamics

A method for constructing a canonical nonequilibrium ensemble for systems in which correlations decay exponentially has recently been proposed by Coveney and Penrose. In this paper, we show that the method is equivalent to the subdynamics formalism, developed by Prigogine and others, when the dimension of the subdynamic kinetic subspace is finite. The comparison between the two approaches helps to clarify the nature of the various operators used in the Brussels formalism. We discuss further the relationship between these two approaches, with particular reference to a simple discrete-time dynamical system, based on the baker's transformation, which we call the baker's urn.     

消毒灭菌的电离辐射与电磁辐射等物理技术比较分析北大核心CSCD

消毒灭菌技术广泛应用于食品工业、医疗领域、水处理等方面。相对于传统化学和热效应的消毒灭菌方法,γ射线、X射线、电子束、微波、低温等离子体、紫外线、高压脉冲电场等物理手段具有不污染环境、消毒灭菌温度低、没有化学残留物等优点而日益受到重视。但这些物理技术手段各有不同,本文首先介绍了γ射线、X射线、电子束、微波、低温等离子体、紫外线、高压脉冲电场等消毒灭菌的技术原理,然后对比了各自优缺点和应用领域。每种方法都有优势和不足,应针对不同的消毒灭菌对象而选择不同的方式。最后,展望了消毒灭菌的发展方向,提出了消毒灭菌在家庭日常消毒、医疗垃圾处理、有人状态下的室内空气消毒等方面的迫切需求。     

Comparative Analysis of Interaction Modes of Two Droplets and of a Large Population in an Aerosol Cloud

Doklady Physics - A comparative analysis of experimental results obtained by various investigators using two different experimental approaches is presented: the phenomenological approach (the...