Effect of Sample Configuration on Droplet-Particles of TiN Films Deposited by Pulse Biased Arc Ion Plating

Orthogonal experiments are used to design the pulsed bias related parameters,including bias magnitude, duty cycle and pulse frequency,during arc ion deposition of TiN films on stainless steel substrates in the case of samples placing normal to the plasma flux.The effect of these parameters on the amount and the size distribution of droplet-particles are investigated,and the results have provided sucient evidence for the physical model,in which particles reduction is due to the case that the particles are ne...     

Control of Self-assembled Particles on Thin YSZ Film Deposited by PLD

The laser ablation characteristics of yttria-stabilized zirconia (YSZ) films have been investigated as a function of several parameters by pulsed laser deposition (PLD). Particles ejection which compromises the quality of films was analyzed in detail. Self-assembled particles that aligned along the grain boundaries were found in the as-deposited YSZ films on CeO₂/Ni–W templates for the first time, to our knowledge. A simple physical model was proposed to explain this unique phenomenon. We believe this model may supply some clues to attain a particle-free, smooth, and high crystalline buffer layers for HTS layer.     

Effect of particle-particle interaction on dielectrophoretic single particle trap in a sudden contraction flow

Dielectrophoretic(DEP) force is significant in manipulating tiny objects in micro/nano scale. To study the effect of electric interaction force on particle manipulation, a microstructure consisting of a pair of strip electrodes and a sudden contraction micro-channel was constructed. Besides DEP force and hydrodynamic force acting on single particle, the numerical model also involved electric interaction force and force moment on two particles. The analyses revealed that the particle-particle interaction force was in the same order as that of DEP force on single trapped particle. The interaction force resulted in trapping single particle failure under continuous DEP force.Thus, pulsed DEP force, turning on/off DEP force at a given time interval, was suggested. During the "off" period,the velocity difference of the two particles located at sudden contraction micro-channel enlarged the gap between them and further weakened the particle-particle interaction. By a proof-of-concept experiment, both the trapping behavior of single particle and that of two particles were in good agreement with the model.With carefully controlled parameters, the reliable function of retaining single particle was realized by pulsed DEP.     

Simulated pulsed flow of gas and particles in a horizontal oppose-pulsed gas jets of bubbling fluidized bed

Flow behavior of gas and particles with a horizontal oppose-pulsed gas jets are simulated by means of a three dimensional Computational Fluid Dynamics (CFD) model with the kinetic theory of granular flow in a gas-particles bubbling fluidized bed. The effects of amplitudes and frequencies on the hydrodynamics of gas and particles are analyzed. The simulation results are presented in terms of phase velocity vector plot, volume fraction of phases, granular temperature, power spectrum and Reynolds stresses in the bed. Results show that the impingement caused by the oppose-pulsed gas jets oscillates with the variation of pulsed gas velocity. The impingement zone with the high solid volume fraction reciprocates from the left side to the right side through the bed center with the variation of pulsed jet gas velocities. The lateral velocity and gas turbulent kinetic energy, granular temperature and Reynolds stresses of gas and particles are larger near the pulsed gas jets than that at the center of the bed. The large dispersion coefficients of particles using the horizontal oppose-pulsed gas jets enhance the mixing of particles in gas-solid fluidized bed.     

Experimental and numerical determination of mechanical properties of polygonal wood particles and their flow analysis in silos

Responding to a lack in the literature, mechanical properties of polygonal wood particles are determined for use in a discrete element model (DEM) for flow analysis in silos, and some methods are proposed for determining such parameters. The parameters arrived at here have also formed part of the input to the SPOLY software, developed in-house to compute the DEM model with spheropolyhedron elements. The model is validated using a 2D physical model, where “prismatic” particles with polygonal cross sections are placed inside a silo with variable aperture and hopper angle. Validation includes comparison of flow-rates computed by SPOLY, displacement profiles, and clogging thresholds with experimental results. The good agreement that emerges will encourage future use of miniature triaxial tests, grain-surface profilometry, inclined slope tests, and numerical analysis of the intragranular stresses—toward a direct construction of the contact-deformation relations required in realistic DEM modelling of particle flow with angular-shaped particles.     

Determination of the optical-breakdown threshold under irradiation of condensed inclusions by pulsed laser radiation

On the basis of the thermal approach, a mathematical model of the optical breakdown on condensed inclusions exposed to pulsed laser radiation is developed. As individual stages of the process, we consider the particle heating and evaporation, the formation of a vapor aureole and its ionization, as well as the propagation of shock waves in the space surrounding the particle. The threshold characteristics of the laser-beam parameters sufficient for initiating an optical breakdown on metal and dielectric particles, as well as on dielectric liquid drops are determined. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 6, pp. 106–117, November–December, 2005.     

Miniaturized flow fractionation device assisted by a pulsed electric field for nanoparticle separation

Electric field flow fractionation (EFFF) is a powerful separation technique based on an electrical field perpendicular to a pressure-driven flow. Previous studies of microelectric field flow fractionation (micro-EFFF) indicate that separation performance was limited due to a weak effective electric field caused by polarization layers on the electrode surfaces. In this work, we report on a micro-EFFF device that uses a pulsed voltage scheme to overcome these limitations. The device was fabricated in indium tin oxide (ITO)-coated glass with ITO as electrodes. The effective electric field for pulsed voltage operation was found to be 50-fold stronger when compared with constant voltage operation. A strong influence of pulsed voltage frequency on nanoparticle retention times was observed. Using pulsed voltage, improved separation of polystyrene particles of different surface charge and particle size is demonstrated. Pulsed voltage also offers more parameters compared to the constant voltage mode, e.g., pulse frequency, duty cycle, and waveform to optimize the retention behavior of analytes.     

A Model of Quasibrittle Fracture Caused by Pulsed Loading

We study the stress-strain state formed in a plate containing a stationary crack of finite length subjected to pulsed loading, develop a model of quasibrittle fracture caused by loads of this type, and deduce analytic expressions for the stress-strain state near the tip of the stationary crack in the plate. The proposed model admits rigorous physical justification and enables one to describe the development of brittle and quasibrittle fracture processes in materials with cracklike defects under dynamic and static loads within the framework of the same approach. The results of numerical simulation are in good qualitative agreement with the experimentally established regularities of the behavior of the critical parameters of fracture processes.     

Pulsed laser technique application to liquid and gaseous flows and the scattering power of seed materials

Mie scattering computations have been performed for light scattered by small particles from a pulsed sheet of laser illumination and collected and imaged by a camera lens. From these computations the smallest particles that can be photographed in various fluid measurement situations, including air and water, have been determined in terms of system parameters such as laser power, light sheet geometry, f/No., and photographic film properties. The particle scattering requirements of the individual particle image mode and the speckle mode are compared.     

Optical properties of carbon-containing titanium oxide nanocomposites obtained by the pulsed plasma chemical method

This paper presents the results of an experimental investigation on the optical properties of the TiO₂ and Ti_xC_yO_z nanopowders, produced by the pulsed plasma chemical method. Pulsed plasma chemical synthesis is realized on the laboratory stand, including a plasma chemical reactor (6 l) and TEA-500 electron accelerator. The parameters of the electron beam are as follows: 400–450 keV electron energy, 60 ns half-amplitude pulse duration, up to 200 J pulse energy, and 5 cm beam diameter. In TiO₂ sample, obtained using the pulsed plasma chemical method, the particles can be divided into two groups: 100–500 nm large spherical particles and tiny complex particles (sized less than 100 nm). For TixCyOz sample, the morphology of the particles is mainly presented with irregular fragment shape. The average size of the particles is ranged from 200 to 300 nm. The band gap for all synthesized samples is within 2.94–3.35 eV.     

Light interactions with gold nanorods and cells: implications for photothermal nanotherapeutics

Gold nanorods (AuNR) can be tailored to possess an intense and narrow longitudinal plasmon (LP) absorption peak in the far-red to near-infrared wavelength region, where tissue is relatively transparent to light. This makes AuNRs excellent candidates as contrast agents for photoacoustic imaging, and as photothermal therapeutic agents. The favorable optical properties of AuNR which depend on the physical parameters of shape, size and plasmonic coupling effects, are required to be stable during use. We investigate the changes that are likely to occur in these physical parameters in the setting of photothermal therapeutics, and the influence that these changes have on the optical properties and the capacity to achieve target cell death. To this end we study 3 sets of interactions: pulsed light with AuNR, AuNR with cells, and pulsed light with cells incubated with AuNR. In the first situation we ascertain the threshold value of fluence required for photothermal melting or reshaping of AuNR to shorter AuNR or nanospheres, which results in drastic changes in optical properties. In the second situation when cells are exposed to antibody-conjugated AuNR, we observe using transmission electron microscopy (TEM) that the particles are closely packed and clustered inside vesicles in the cells. Using dark-field microscopy we show that plasmonic interactions between AuNRs in this situation causes blue-shifting of the LP absorption peak. As a consequence, no direct lethal damage to cells can be inflicted by laser irradiation at the LP peak. On the other hand, using irradiation at the transverse peak (TP) wavelength in the green, at comparative fluences, extensive cell death can be achieved. We attribute this behavior on the one hand to the photoreshaping of AuNR into spheres and on the other hand to clustering of AuNR inside cells. Both effects create sufficiently high optical absorption at 532 nm, which otherwise would have been present at the LP peak. We discuss implications of these finding on the application of these particles in biomedicine.     

A model of polymer composite structure with intermediate layer

In real structures isothermal planes may be distorted, and it is necessary to take this into account while carrying out the calculations of thermal conductivity λ_k of a material. The distortion depends on thermal conductivities of constituent particles and the matrix. With computer speeds already available, we can calculate temperature fields of the structural elements and to evaluate the thermal conductivity of the material. A structural model of polymeric compositions with solid particles with a shell and with microspheres is proposed. It is possible to evaluate the influence of a particle distribution order and particle spacing on the properties of compositions using structural elements. The model is suitable for the estimation with the use of corresponding coefficients of general regularities in compositions which are different by physical nature and yet are represented by analogous mathematical expressions (Fourier, Fick and Ohm laws). Solutions of integral equations for the structural element provide relative magnitudes and are, therefore, simple to use when evaluating other physical parameters of a composition. The application of the model is illustrated by examples.     

A discrete element method-based approach to predict the breakage of coal

Pulverization is an essential pre-combustion technique employed for solid fuels, such as coal, to reduce particle sizes. Smaller particles ensure rapid and complete combustion, leading to low carbon emissions. Traditionally, the resulting particle size distributions from pulverizers have been determined by empirical or semi-empirical approaches that rely on extensive data gathered over several decades during operations or experiments, with limited predictive capabilities for new coals and processes. This work presents a Discrete Element Method (DEM)-based computational approach to model coal particle breakage with experimentally characterized coal physical properties. The effect of select operating parameters on the breakage behavior of coal particles is also examined.     

Dynamics of acceleration of millimeter-sized pellets in railgun accelerators with external magnetic field

A physical model of the acceleration of small (1–3 mm) solid pellets in a railgun with a plasma piston and an external pulsed magnetic field is proposed. For the typical operating parameters of the railgun, the effect of the erosion of electrodes, drag force, and dimensions of a body on its final velocity has been studied. It is shown that the saturation of velocity of 1- to 2-mm pellets occurs at short distances (15–20 cm) and is mainly governed by the capture of a portion of the erosion mass by the plasma piston.     

介质阻挡稳态丝状放电数值模拟

本文采用流体模型对纯Ne介质阻挡放电(DBD)中的丝状放电现象进行了研究.通过模拟获得了放电过程中电流、带电粒子等物理参数的时间空间分布及丝状放电的形成.结果表明,在pd值较低及方波驱动电压条件下,初始均匀的DBD中将逐渐形成多个稳定的丝状放电通道,而且所有通道的丝状放电同时进行,形成单个放电电流脉冲.同时模拟结果表明,在辉光放电范围内,升高pd值,丝状放电的数量将减少.     

Particle characterization and separation by a coupled acoustic-gravity field

A coupled acoustic-gravity field is proposed as a novel external field for particle separation and characterization. When a standing plane ultrasound wave is generated, particles move to the node of the wave along the ultrasound force gradient. If the particles also undergo a sedimentation force, they aggregate at the equilibrium position, where these two forces are balanced. The equilibrium position, which is determined by the density and compressibility of a medium and particles, characterizes the particles. The local ultrasound energy, which is necessary for quantitative discussions, is evaluated by using a standard particle, the physical parameters of which are unambiguously determined; aluminum particles are used in the present study. The local ultrasound energy makes possible the determination of the compressibility of unknown materials. Nonporous particles of inorganic and polymeric materials, the particle sizes of which range from 3 to 100 microm, follow a derived model, suggesting that the local ultrasound energy and a derived model be valid. The proposed external field can be used for separation of particles having different acoustic natures.     

Evaluation and extension of physical property-porosity models based on minimum solid area

Physical property-porosity models based on minimum solid areas of idealized stackings of either: (1) spherical particles partially bonded (e.g. sintered), or (2) spherical pores in a solid matrix are shown to agree with appropriate physical property data for bodies whose porosity is reasonably represented by such stackings. Appropriate physical properties are those determined mainly by local stress or flux, e.g. elastic properties, strengths, and electrical and thermal conductivity. The minimum solid areas are, respectively, the: (1) bond (e.g. neck) area between particles defining pores smaller than the particles, or (2) minimum web thickness between adjacent pores being more than or equal to the surrounding particles (e.g. bubbles in a foam). Combinations of the models for mixtures of basic porosity types and changes in basic model parameters (e.g. stacking) over the significant porosity range covered, are shown to agree with the literature (mainly mechanical) property data for bodies of appropriate porosity combinations. Areas of further development and testing are noted.     

Individual detection of single-nanometer-sized particles in liquid by photothermal microscope

We have developed a thermal lens microscope for liquid-phase and surface microanalyses. By applying the thermal lens microscope to particle detection, we succeeded in detecting a pulsed photothermal signal from single-nanometer-sized particles in liquid and counting them individually. The samples were polystyrene latex particles (190 and 80 nm in diameter) and colloidal Ag particles (10 nm in diameter). To verify that the detected pulsed signals corresponded to the single-particle photothermal effects, we confirmed the items as described below using 190-nm polystyrene particles. First, no pulsed signal was generated under irradiation by either the excitation beam or the probe beam. Second, the pulse counts were proportional to the expectation value of the particles in the detection volume and zero for ultrapure water blank. Third, the pulse counts' distribution in a series of unit times had a Poisson distribution when the expectation value of the sample was much less than 1. Then, we demonstrated counting 80-nm polystyrene particles and 10-nm Ag particles in water. The pulsed signals were clearly distinguished from noise, and the signal-to-noise ratio was as large as 5. Finally, we discussed differences between the conventional thermal lens effect and the single-particle photothermal effect. Individual nanometer-sized particle detection by photothermal effect was the first demonstration.     

Matrix assisted pulsed laser evaporation of biomaterial thin films

In this paper, processing of biomaterial thin films using a novel physical vapor deposition process known as matrix assisted pulsed laser evaporation (MAPLE) is reviewed. The matrix assisted pulsed laser evaporation process provides excellent control over several film parameters, including thickness, roughness, homogeneity, and reliability. Deposition of dexamethasone thin films, poly (d, l) lactic acid/dexamethasone bilayer thin films, and chitosan thin films is reviewed. The results highlight the expanding role of matrix assisted pulsed laser evaporation process in biomaterials, drug delivery, and tissue engineering.     

低频脉冲超声对大鼠骨骼肌疲劳的恢复效果研究

建立大鼠的运动疲劳模型,研究低频脉冲超声对骨骼肌运动疲劳的恢复效果,通过对肌肉组织的物理(体重)和生化(肌酸激酶(Creatine Kinase,CK),血尿素氮(Blood Urea Nitrogen,BUN),肌酐,丙二醛和钙离子)指标分析,研究低频脉冲超声与大鼠骨骼肌疲劳恢复效果的相关性。结果表明,在进行超声照射后,大鼠血清中的CK值和BUN值较疲劳组得到一定的缓解,体重存在一定范围的上升。初步的实验表明低频脉冲超声对缓解肌肉的疲劳有一定的促进作用。