Radiation model for nanoparticle: extension of classical Brownian motion concepts

Emissive power per unit area of a blackbody has been modeled as a function of frequency using quantum electrodynamics, semi-classical and classical approaches in the available literature. Present work extends the classical lumped-parameter systems model of Brownian motion of nanoparticle to abstract an emissive power per unit area model for nanoparticle radiating at temperature greater than absolute zero. The analytical model developed in present work has been based on synergism of local deformation leading to local motion of nanoparticle due to photon impacts. The work suggests the hypothesis of a free parameter f′ characterizing the damping coefficient of resistive forces to local motion of nanoparticle and the manipulation of which is possible to realize desired emissivity from nanoparticles. The model is validated with the well established Planck’s radiation law.     

Molecular dynamics simulations of structural disordering and forming defects in a milling process for selenium

In our previous paper, structural changes of selenium powders ground by a planetary ball mill at various rotational speeds were investigated for the nanostructural modification of particles using mechanical grinding process. The experimental results indicated that the amorphisation of Se by grinding accompanies lattice strain, and the lattice strain arises from impact energy which is more than an energy related to intermolecular interaction. In this paper, molecular dynamics simulations of selenium have been carried out under compressing conditions of various pressure strengths for obtaining information of the lattice strain at atomic level. Then, dynamical behaviour of atomic configuration has been discussed in this process. The structural disordering and formation of the structural defects were estimated by deviations of bond length and angle and the number of created defects before and after compressing from simulated results. The disordering took place during compressing at various pressure strengths, and the disordered atoms return to their initial positions at lower pressure. Stable disordered state and defects after the compression can however remain by compression at more than a certain pressure strength mainly associated with binding energy of selenium.     

Improvements on the third generation of electron momentum spectrometer

The significant modifications to our recently constructed electron momentum spectrometer have been implemented. Compared with our previous report, the energy and the angle resolutions are significantly improved and reach △E = 0.45 eV, △θ = ±0.53° and △φ = ±0.84°, respectively. Moreover, the details of data reduction and the relation between azimuthal angle range and the sensitivity are discussed.     

Modelling of spreading process: effect from hydrogen bonds

Lubricant spreading on solid substrates has drawn considerable attention not only for the microscopic wetting theory but also for the dramatic application in head-disk interface of magnetic storage drive systems. Molecular dynamic simulation based on a coarse-grained bead-spring model has been used to study such a spreading process. The spreading profiles indicate that the hydrogen bonds among lubricant molecules and the hydrogen bonds between lubricant molecules and polar atoms of solid substrates will complicate the spreading process in a tremendous degree. The hydrogen bonds among lubricant molecules will strengthen the lubricant combination intensity, which may hinder most molecules from flowing down to the substrates and diffusing along the substrates. And the hydrogen bonds between lubricant molecules and polar atoms of solid substrates will confine the lubricant molecules around polar atoms, which may hinder the molecules from diffusing along the substrates and cause precursor film to vanish.     

Enhancement of water permeation across nanochannels by partial charges mimicked from biological channels

In biological water channel aquaporins （AQPs）, it is believed that the bipolar orientation of the single-file water molecules inside the channel blocks proton permeation but not water transport. In this paper, the water permeation and particularly the water-selective behaviour across a single-walled carbon nanotube （SWNT） with two partial charges adjacent to the wall of the SWNT are studied by molecular dynamics simulations, in which the distance between the two partial charges is varied from 0.14 nm to 0.5 nm and the charges each have a quantity of 0.5 e. The two partial charges are used to mimic the charge distribution of the conserved non-pseudoautosomal （NPA） （asparagine/proline/alanine） regions in AQPs. Compared with across the nanochannel in a system with one ＋1 ε charge, the water permeation across the nanochannel is greatly enhanced in a system with two ＋0.5 e charges when charges are close to the nanotube, i.e. the two partial charges permit more rapid water diffusion and maintain better bipolar order along the water file when the distance between the two charges and the wall of SWNT is smaller than about 0.05 nm. The bipolar orientation of the single-file water molecules is crucial for the exclusion of proton transfer. These findings may serve as guidelines for the future nanodevices by using charges to transport water and have biological implications because membrane water channels share a similar single-file water chain and positive charged region at centre and provide an insight into why two residues are necessitated in the central region of water channel protein.     

Simulation of plasma doping process by using the localized molecular dynamics method

Plasma doping is the candidate for semiconductor doping. Accurate simulation of the doping technology is needed for the advanced integrated circuit manufacturing. In this paper, the plasma doping process simulation is performed by using the localized molecular dynamics method. Models that involve the statistics of the implanted compositions, angles and energies are developed. The effect of the model on simulation results is studied. The simulation results about the doping concentration profile are supported by experimental data.     

红外视景仿真技术及其研究进展

从红外视景仿真技术意义出发，介绍了其所包含的几个基本部分；从目标辐射建模、背景辐射建模和大气建模三方面，总结了国内外红外视景仿真技术发展历程和状况。其中列举了国外多个典型红外视景仿真软件和几个较完善红外辐射模型，并统计了2000年以来国内高校在红外视景仿真方面的研究情况。统计数据表明，多个发达国家的红外视景仿真技术已逐步趋于成熟和产品化，而国内尚未开发出功能较完善的红外视景仿真系统，只能仿真较简单场景。     

Time resolution of the bunch-shape detector with a thin-wire emission target

The time resolution of a new bunch-length detector based on the radio frequency (RF) scanning of the produced secondary electrons is calculated. A dedicated Monte-Carlo code by means of SIMION software is developed for accurate simulation of spread in the investigated secondary electrons transit times and image width. In calculation the initial energy distribution of electrons and the actual structure of accelerating and focusing electric fields were considered. It is shown that by using a thin-wire emission target a femtosecond time precision could be achieved using moderate applied voltages.     

Inflow conditions for spatial direct numerical simulation of turbulent boundary layers

The inflow conditions for spatial direct numerical simulation (SDNS) of turbulent boundary layers should reflect the characteristics of upstream turbulence, which is a puzzle. In this paper a new method is suggested, in which the flow field obtained by using temporal direct numerical simulation (TDNS) for fully developed turbulent flow (only flow field for a single moment is sufficient) can be used as the inflow of SDNS with a proper transformation. The calculation results confirm that this method is feasible and effective. It is also found that, under a proper time-space transformation, all statistics of the fully developed turbulence obtained by both temporal mode and spatial mode DNS are in excellent agreement with each other, not only qualitatively, but also quantitatively. The normal-wise distributions of mean flow profile, turbulent Mach number and the root mean square (RMS) of the fluctuations of various variables, as well as the Reynolds stresses of the fully developed turbulence obtained by using SDNS, bear similarity in nature. Supported by the National Natural Science Foundation of China (Grant No. 90205021), the China Postdoctoral Science Foundation (Grant No. 20060400707), and the Foundation for the Author of National Excellent Doctoral Dissertation of China (Grant No. 200328), and partially supported by Liu-Hui Center of Applied Mathematics, Nankai University and Tianjin University     

Entropy and equilibrium property of QCD-instanton induced final state in deep-inelastic scattering

The scaling and additivity properties of Rényi entropy in rapidity space of the instanton final state (IFS) and current jet identified by the r-sorting method from the QCDINS Monte Carlo event sample are to saturation with decreasing phase space scale. Furthermore, it is found that the additivity of H2 holds well for the IFS in narrow rapidity windows at different positions. These results indicate that the IFS produced in the instanton-induced process of deep inelastic scattering has reached local equilibrium.