Formation of diffuse and spark discharges between two needle electrodes with the scattering of particles

The development of a nanosecond discharge in a pin-to-pin gap filled with air at atmospheric pressure has been studied with high temporal and spatial resolutions from a breakdown start to the spark decay.Positive and negative nanosecond voltage pulses with an amplitude of tens of kilovolts were applied.Time-resolved images of the discharge development were taken with a fourchannel Intensified Charge Coupled Device(ICCD)camera.The minimum delay between the camera channels could be as short as≈0.1 ns.This made it possible to study the gap breakdown process with subnanosecond resolution.It was observed that a wide-diameter streamer develops from the high-voltage pointed electrode.The ionization processes near the grounded pin electrode started when the streamer crossed half of the gap.After bridging the gap by the streamer,a diffuse discharge was formed.The development of spark leaders from bright spots on the surface of the pointed electrodes was observed at the next stage.It was found that the rate of development of the spark leader is an order of magnitude lower than that of the wide-diameter streamer.Long thin luminous tracks were observed against the background of a discharge plasma glow.It has been established that the tracks are adjacent to brightly glowing spots on the electrodes and are associated with the flight of small particles.

Electromagnetic Scattering of a High-Order Bessel Trigonometric Beam by Typical Particles

The scattering of an electromagnetic high-order Bessel trigonometric beam by several typical homogeneous dielec- tric particles is investigated. The incident beam is represented by the vector expressions in Cartesian coordinates. The scattering problems involving homogeneous dielectric particles are formulated with the surface integral equation method. As an example, the effects of the beam＇s parameters on the differential scattering cross section for a sphere are analyzed in detail. Then the numerical results for the scattering of a high-order Bessel trigonometric beam by three typical nonspherieal particles, including a spheroid, a cylinder, and a cube, are presented.

Quark-Quark Scattering

Scattering process always reveal valuable information. For example scattering of alpha particle in Rutherford＇s well known experiment revealed the existence of nucleus. Physicists have been studying collision process both experimentally as well as theoretically to know much about particle Physics. It is believed that the quark-quark scattering results are same as those of lepton-lepton systems and they are mass independent. The aim of this work was to calculate amplitude cross section for heavy quarks. Our results reveal a mass dependence of these results for heavy quarks.

Light Focusing through Scattering Media by Particle Swarm Optimization

We demonstrate light focusing through scattering media by introducing particle swarm optimization for modulat- ing the phase wavefront. Light refocusing is simulated numerically based on the angular spectrum method and the circular Gaussian distribution model of the scattering media. Experimentally, a spatial light modulator is used to control the phase of incident light, so as to make the scattered light converge to a focus. The influence of divided segments of input light and the effect of the number of iterations on light intensity enhancement are investigated. Simulation results are found to be in good agreement with the theoretical analysis for light refocusing.

Advances in Atmospheric Radiation:Theories,Models,and Their Applications.PartⅠ:Atmospheric Gas Absorption and Particle Scattering

Atmospheric radiation is a major branch of atmospheric physics that encompasses the fundamental theories of atmospheric absorption,particle scattering(aerosols and clouds),and radiative transfer.Specifically,the simulations of atmospheric gaseous absorption and scattering properties of particles are the essential components of atmospheric radiative transfer models.Atmospheric radiation has important applications in weather,climate,data assimilation,remote sensing,and atmospheric detection studies.In PartⅠ,a comprehensive review of the progress in the field of gas absorption and particle scattering research over the past 30 years with a particular emphasis on the contributions from Chinese scientists is presented.The review of gas absorption includes the construction of absorption databases,the impact of different atmospheric absorption algorithms on radiative calculations,and their applications in weather and climate models and remote sensing.The review on particle scattering starts with the theoretical and computational methods and subsequently explores the optical modeling of aerosols and clouds in remote sensing and atmospheric models.Additionally,the paper discusses potential future research directions in this field.

Optical spectra of plasmon-exciton core-shell nanoparticles:an anisotropic classical model eliminates discrepancies in experiments

The optical properties of hybrid core-shell nanostructures composed of a metallic core and an organic shell of molecular J-aggregates are determined by the electromagnetic coupling between plasmons localized at the surface of the metallic core and Frenkel excitons in the shell.In cases of strong and ultra-strong plasmon-exciton coupling,the use of the traditional isotropic classical oscillator model to describe the J-aggregate permittivity may lead to drastic discrepancies between theoretical predictions and the available experimental spectra of hybrid nanoparticles.We show that these discrepancies are not caused by limitations of the classical oscillator model itself,but by considering the organic shell as an optically isotropic material.By assuming a tangential orientation of the classical oscillators of the molecular J-aggregates in a shell,we obtain excellent agreement with the experimental extinction spectra of TDBC-coated gold nanorods,which cannot be treated with the conventional isotropic shell model.Our results extend the understanding of the physical effects in the optics of metal-organic nanoparticles and suggest an approach for the theoretical description of such hybrid systems.

Resonant surface plasmons of a metal nanosphere treated as propagating surface plasmons

On the assumption that the resonant surface plasmons on a spherical nanoparticle are formed by standing waves of two counter-propagating surface plasmon waves along the surface, by using Mie theory simulation, we find that the dispersions of surface plasmon resonant modes supported by silver nanospheres match with those of the surface plasmons on a semiinfinite medium-silver interface very well. This suggests that the resonant surface plasmons of a metal nanosphere can be treated as a propagating surface plasmon wave.

FUNDAMENTAL RESEARCH ON RADIOFREQUENCY ABLATION OF RAT BRAIN TISSUE BASED ON NEAR-INFRARED SPECTROSCOPY AND MIE THEORY

Near-infrared spectroscopy(NIRS)technology and Mie theory are utilized for fundamental research on radiofrequency ablation of biological tissue.Firstly,NIRS is utilized to monitor rats undergoing radiofrequency ablation surgery in real time so as to explore the relationship between reduced scattering coefficient(μ_(s)')and the degree of thermally induced tissue coagulation.Then,Mie theory is utilized to analyze the morphological structure change of biological tissue so as to explore the basic mechanism of the change of optical parameters caused by thermally induced tissue coagulation.Results show that there is a close relationship between μ_(s)' and the degree of thermally induced tissue coagulation;the degree of thermal coagulation can be obtained by the value of μ_(s)';when biological tissue thermally coagulates,the average equivalent scattering particle decreases,the particle density increases,and the anisotropy factor decreases.

Effects of the inlet particle spatial distribution on the performance of a gas-solid cyclone separator

The present study was aimed at the inlet particle spatial distribution of a gas-solid separator with high solid loading and investigated its effects on cyclone performance and the inner flow pattern.The flow fields of a cyclone with different rectangular particle flow areas on the inlet surface were numerically simulated using a four-way coupling method.The simulated results indicate that reducing the inlet particle flow area and lowing the inlet particle position can effectively reduce the scattered particles inside the cyclone separator and enhance the separation performance.Vertically gathering the particles to the centerline can also weaken the particle back-mixing.The particles near the roof account for the swirling particle ceiling phenomenon.The inlet particle spatial distribution affects the pressure drop mainly by affecting the gas tangential velocity in the cylinder body.Moreover,compared to the hori-zontal particle distribution on the inlet surface,the vertical particle distribution has greater effects on cyclone performance.

Inversion of particle size distribution from light-scattering data using a modified regularization algorithm

A modified regularization algorithm with a more proper operator was proposed for the inversion of particle size distribution （PSD） from light-scattering data in a laser particle sizer based on the Mie scattering principle. The Generalized Cross-Validation （GCV） method and the L-curve method were used for deter- mining the regularization parameter. The Successive Over-Relaxation （SOR） iterative method was used to increase the exactness and stability of the converged result. The simulated results based on the modified algorithm are in a good agreement with the experimental data measured for nine standard particulate samples, their mixtures as well as three natural particulate materials with irregular shapes, indicating that this modified regularization method is not only feasible but also effective for the simulation of PSD from corresponding light-scattering data.

From micro-to nanosized particles:Selected characterization methods and measurable parameters

Airborne micro- and nanoparticles-aerosols - play an important role in many natural phenomena and in a variety of industrial processes, as well as the public health issue. They may be of natural or anthropogenic origin; their presence in an environment might be intentional or due to undesirable release. In any case, merely the particle detection and characterization, ideally in real-time, provide an insight into the potential burden allowing also controlling and abatement measures. Due to the broad size range it is not possible to characterize the entire particle spectrum with only one method. This contribution discusses selected optical techniques based on elastic light scattering, which are suitable for characterization of micrometer sized particles and particular electrical techniques allowing measurement of nanoparticles. It is shown that combination of instruments measuring different properties of the same nanoparticles offers derivative parameters contributing to more complete characterization of aerosols

A Numerical Study of Quantum Decoherence

The present paper provides a numerical investigation of the decoherence effect induced on a quantum heavy particle by the scattering with a light one.The time dependent two-particle Schr¨odinger equation is solved by means of a time-splitting method.The damping undergone by the non-diagonal terms of the heavy particle density matrix is estimated numerically,as well as the error in the Joos-Zeh approximation formula.

XFEL data analysis for structural biology

X-ray Free Electron Lasers （XFELs） have advanced research in structure biology, by exploiting their ultra-short and bright X-ray pulses. The resulting ＂diffraction before destruction＂ experimental approach allows data collection to outrun radiation damage, a crucial factor that has often limited resolution in the structure determination of biological molecules. Since the first hard X-ray laser （the Linac Coherent Light Source （LCLS） at SLAC） commenced operation in 2009, serial femtosecond crystallography （SFX） has rapidly matured into a method for the structural analysis of nano- and micro-crystals. At the same time, single particle structure determination by coherent diffractive imaging, with one particle （such as a virus） per shot, has been under intense development. In this review we describe these applications of X-ray lasers in structural biology, with a focus particularly on aspects of data analysis for the computational research community. We summarize the key problems in data analysis and model reconstruction, and provide perspectives on future research using computational methods.