Quantitative analysis of 3D hydrodynamic focusing of microparticles by digital holographic microscopy

In the field of life sciences, the monitoring of biological samples has become a great concern to control the ecosystem evolution. However, their characterization is often time-consuming because the typical size of the organisms/particles of interest is several orders of magnitude smaller than the size of the sample under observation. Optical visualization systems require, then, high magnifications that severely limit the depth of focus and consequently decrease the sampling rate. To tackle this issue, the most straightforward technique consists in focusing the samples to fit the observation field of view by means of so-called "sheath flows". This expedient allows for increasing the overall flow rate, inversely related to the sampling time. In this article, a cost-effective 3D hydro-focusing device is presented. Several flow rates have been tested for both sample and sheath flows, and a thorough investigation of the shape of the focused streamlines conducted in order to validate the prototype design. The 3D position of the sampled micro-objects has been located by digital holographic microscopy and their distribution in cross-sections downstream the injection nozzle compared to numerical simulations. A maximum constriction—ratio between the part of the cross-sections where particles are present with and without focusing sheath flow—of 4.4 % has been observed confirming the potentiality of the technique. Also, a successful match between experiment and numerical simulation has been noted.     

Analytic investigation of the anode zone of a higher-pressure glow discharge

The structure of the glow-discharge anode sheath is investigated analytically in the one-dimensional formulation within the framework of a diffusion-drift approximation. Charged particle recombination reduces significantly the anode potential drop and the width of the anode zone. Given fairly heavy current, which is typical of anode spots, the contribution of the diffusion processes becomes significant because of the reduced width of the anode sheath. Analytical estimates of the anode potential drop and the width of the anode sheath which satisfactorily describe the results of numerical calculations are obtained. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.2, pp. 172–180, March–April, 1994.     

Transmission characteristics of EM wave in a finite thickness plasma

One of the key factors for solving the problems of re-entry communication interruption is electromagnetic(EM) wave transmission characteristics in a plasma.Theoretical and experimental studies were carried out on specific transmission characteristics for different plasma sheath characteristic under thin sheath condition in re-entry state.The paper presents systematic studies on the variations of wave attenuation characteristics versus plasma sheath thickness L,collision frequency ν,electron density n e and wave working frequency f in a φ 800 mm high temperature shock tube.In experiments,L is set to 4 cm and 38 cm.ν is 2 GHz and 15 GHz.n e is from 1×10 10 cm(-3) to 1×10 13 cm(-3),and f is set to 2,5,10,14.6 GHz,respectively.Meanwhile,Wentzel-Kramers-Brillouin(WKB) and finite-difference time-domain(FDTD) methods are adopted to carry out theoretical simulation for comparison with experimental results.It is found that when L is much larger than EM wavelength λ(thick sheath) and ν is large,the theoretical result is in good agreement with experimental one,when sheath thickness L is much larger than λ,while ν is relatively small,two theoretical results are obviously different from the experimental ones.It means that the existing theoretical model can not fully describe the contribution of ν.Furthermore,when L and λ are of the same order of magnitude(thin sheath),the experimental result is much smaller than the theoretical values,which indicates that the current model can not properly describe the thin sheath effect on EM attenuation characteristics.     

Mathematical analysis of the radiation from a magnetic line source on a cylindrically capped wedge covered by a plasma sheath

Summary Radial eigenfunctions appropriate for the dielectric (or plasma) layered medium and air are used to obtain an exact solution of the problem of radiation from a magnetic line source (or a slotted antenna) on a conducting infinite wedge with a cylindrical cap covered by a dielectric (or plasma) sheath. In order to satisfy the boundary conditions at the interfaces between the dielectric (or plasma) and the air, it is necessary to expand the radial eigenfunctions of one medium in terms of those of the other.This method can be used to solve any other two dimensional diffraction or radiation problem involving a cylindrically capped wedge surrounded by a dielectric (or plasma) sheath.     

Deformation of rock in the explosion of a cylindrical charge in a coaxial cavity filled with liquid

A study is made of the effect of a water sheath around a cylindrical explosive charge on the parameters of shock waves in rocks. A coupled problem for the detonation-product-water-rock system is examined within the framework of continuum mechanics. A binomial isentropic equation is used for the detonation products, water is modeled by a Tate-type equation, and the rock is modeled by an elastoplastic medium which undergoes dilatation. A numerical solution is obtained by a finite-difference scheme. The dependence of the wave processes in the rock and the dimensions of the crushing zone on the radius of the water sheath is studied with the use of sandstone and siltstone as examples. Institute of Hydromechanics, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Prikladnaya Mekhanika, Vol. 35, No. 3, pp. 83–88, March, 1999.     

Strength evaluation of a cement sheath adjacent to a production wellbore

A model for predicting the strength of a cement sheath adjacent to a production wellbore without consideration of internal and temperature stresses is proposed based on solutions of the Lamé problems for one- and two-layer tubes and the Huber–Mises yield criterion using the model of a perfectly plastic isotropic body.     

Optimization of Forced Convection Heat Transfer in a Composite Porous Medium Channel

The optimization of heat transfer for forced convection in a composite porous channel was studied. We investigated the question where should one place, in the core or in the sheath, the material with high permeability and high-thermal conductivity and where should one place the material with low permeability and low-thermal conductivity, to maximize heat transfer from the walls. We also investigated the optimal heat transfer situation when one has the freedom to vary the relative volumes of the core and the sheath.     

The influence of a magnetic field, parallel to the cathode, on the second cathode sheath of a low-pressure arc discharge

Summary The influence on the second sheath of a magnetic field, directed parallel to the indirectly heated cathode of a low pressure gas discharge is described.The phenomena are in accordance with the existing picture of the discharge mechanism, based on beam-plasma space-charge interaction.     

A Geometric Level-Set Formulation of a Plasma-Sheath Interface

In this paper, we present a new geometric level-set formulation of a plasma-sheath interface arising in plasma physics. We formally derive the explicit dynamics of the interface from the Euler-Poisson equations and study the local-time evolution of the interface and sheath in some special cases.     

The MHD properties of ambipolar diffusion and quasi—Ambipolar diffusion in a plasma column

In the present paper, based on the conservation law of mass and momentum for ion and electron, the distribution of velocity, density of ions and electrons along radial direction are solved numerically. Furthermore, the comparison between MHD properties of ambipolar and quasi-ambipolar diffusion is made. The numerical calculation is carried out for argon plasma. The results show that the ion density, ratio of ion and electron velocity at the cathode sheath boundary surface increase with the intensity of magnetic induction, meanwhile, the distance between sheaths decreases as well as the radial velocity of ion and electron at the anode sheath boundary. The ion density varies in accord with experiment qualitatively^[1]. All parameters mentioned above are not sensitive to magnetic field in ambipolar diffusion.     

Two-dimensional spreading of a cloud of conducting gas in a magnetic field self-similar solution

A self-similar solution of the problem on the spreading in a magnetic field of a cloud of conducting gas, having the shape of a cylinder of noncircular cross section, is constructed. The cylindrical surface of the gas is restrained by a nonconducting sheath that spreads according to a prescribed law. The shape of the transverse cross section of the cylindrical cloud is determined from the solution. Cross sections obtained for a concrete case are represented in graphic form.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 29–36, March–April, 1973.In conclusion the author thanks V. I. Khonichev for assistance with the numerical calculations.     

考虑水泥环完整性的油气井最大允许井口压力计算方法

在最大允许井口压力计算方法中考虑水泥环的完整性,以厚壁圆筒的弹塑性分析理论为基础,建立了套管-水泥环-地层组合体力学模型,将(内层)水泥环内壁发生破坏作为环空允许带压的限制条件。基于Drucker-Prager与拉伸破坏准则计算了某实例井各环空的最大允许井口压力,并将其结果与采用API RP 90标准推荐做法的计算结果进行了对比。计算结果表明:如果环空带压值增大,对于套管-水泥环-地层组合体而言,垂深最深与最浅处的水泥环内壁将最有可能率先发生破坏;采用本文方法的计算结果有可能会小于依据API RP 90标准的计算结果,依据API RP 90标准计算得到A、B环空的最大允许井口压力分别为17.04MPa和6.39MPa,而采用本文方法计算得到A、B环空的最大允许井口压力分别为15.1MPa和17.5MPa。     

双螺旋辊式新型磨浆机螺旋套磨损机理的研究

利用金相组织分析和电子显微分析技术,结合生产实际,对已磨损的输料段和磨浆段的螺旋套进行磨损表面形貌分析,探讨螺旋套磨损机理.结果表明:输料段正螺旋套能够将纸浆料旋转送入机壳内,不承受较大的挤压应力,但由于纸浆料中含有腐蚀介质,其主要的磨损失效形式以腐蚀磨损为主,磨料磨损为辅;磨浆段反螺旋套本身无正输送能力,浆料在正输送组件作用下形成高压区,纤维与浆料之间产生较大摩擦力,导致纤维分离,进而使之分丝帚化和压溃,浆料水分降低,其主要的磨损失效形式为高应力磨料磨损,并伴有腐蚀磨损.     

Electrical probe diagnostics for the laminar flame quenching distance

A simplified theory, previously developed for the general case of weakly ionized gas flow, is used to predict electrical probe response when the flame is quenched on the probe surface. This theory is based on the planar model of space charge sheaths around the measuring electrode. For the flame quenching case, by assuming that the sheath thickness is comparable with the thermal boundary layer thickness, probe current can be related to flame quenching distance. The theoretical assumptions made to obtain the analytical formulation of probe current were experimentally proved by using direct visualization and high-frequency PIV. The direct visualization method was also used to validate the results of flame quenching distance values obtained with electrical probe. The electrical probe diagnostics have been verified for both head-on and sidewall flame quenching regimes and for stoichiometric methane/air and propane/air mixtures in a pressure range of 0.05–0.6 MPa.     

外支架对移植静脉力学特性的影响

自体静脉移植是动脉粥样硬化等血管阻塞疾病的主要治疗手段之一,但移植静脉重建引起的再狭窄严重影响通畅率。研究表明,静脉和动脉之间几何尺寸与力学性质的不同以及力学环境的差异是吻合口再狭窄的主要原因。在动脉环境下,静脉桥路被严重扩张,桥路的内半径要比宿主动脉的大很多,这不仅大大提高了桥路管壁中的应力水平,而且也促使吻合口附近涡流的形成。管壁中增高的周向应力和由于涡流引起的紊乱的切应力是静脉桥路再狭窄的主要原因。为了提高静脉桥路的通畅率,外支架的技术日益引起人们的重视。外支架除了可以加强静脉桥路壁强度,降低管壁中的周向应力外,还可以消除吻合口附近的涡流,从而起到保护作用。本文将综述外支架保护静脉桥路的研究历史以及目前现状。     

Experiments with gas-filled triodes

Summary In this paper experiments are described showing the different types of electrical discharges in a gas-filled triode. The determining parameters are the following: the cathode emission, the spacing of cathode, grid and anode, the diameter of the meshes of the grid, the potentials of the grid and the anode, the gas pressure and the differential ionization function of the gas. The anode voltage may be concentrated in a space charge sheath. If this space charge sheath is located at the grid, the anode current may be modulated with moderate grid potentials. If not, much larger voltages are required for modulation.     

Evolution of ion–ion acoustic instability in multi-ion plasma sheaths

Nonlinear Dynamics - The generation of ion-acoustic solitary waves is investigated in a nonuniform multicomponent collisional plasma sheath containing cold ions and Boltzmann electrons to probe the...     

Interaction of a supersonic flow with a transverse jet injected through a circular aperture in a plate

A flow pattern created by the interaction of a supersonic flow with a transverse sonic or supersonic jet injected normally to the direction of the main flow through a circular aperture in a plate is considered. The pressure rises in front of the jet owing to the retarding action of the incident flow. The boundary layer building up on the wall in front of the injection nozzle is accordingly detached. The flow pattern in the region of interaction between the jet and the external flow is illustrated in Fig. 1. The three-dimensional zone of detachment thus formed deflects the incident flow from the wall, and in front of the jet a complicated system of sharp jumps in contraction develops. A three-dimensional system of jumps also develops in the jet itself.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No, 5, pp. 193–197, September–October, 1970.     

Atomization of a Powder by a Swirling Flow with a Recirculation Zone

The problem of the motion of a swirling flow in an axisymmetric channel with permeable walls is investigated numerically. Various flow regimes including those with the formation of recirculation zones are obtained. The problem of atomization of a powder by a swirling flow for the purpose of obtaining a finely dispersed mixture is considered. Particle concentration distributions in the flow are calculated, the formation of characteristic deposition zones is demonstrated, and the unsteady process of particle transfer is investigated with allowance for deposition on the lateral surface of the channel.