Velocity Filtration Research Articles

Variations of the elemental composition distribution over the thickness of YBa2Cu3O7-δ thin films obtained by pulsed laser deposition from one target

Epitaxial YBa2Cu3O7‒δ (YBCO) films 150–200 and 300 nm thick, respectively, were deposited on SrTiO3 (100) substrates by pulsed laser deposition at different conditions: with and without using the velocity filtration technique. The films have T(R = 0) in the range of 77.4–87 R(T) depending on the conditions of deposition from one target with YBa2Cu3O6.8 composition. The films contain Zn, Sr, Pd, Ag and Ti impurity elements obtained from the target (a total of no more than 2 at. %). Data of the film resistance temperature dependences, X-ray phase analysis, analysis of X-ray fluorescence (XRF) spectra and study of the surface relief by SEM methods revealed the nonuniform distributions of impurity and matrix Y, Ba, Cu elements over the film depth. Impurity concentrations near the surface lead to the formation of faceted spiral pyramids on the surface, which probably evolve into large elongated particles according to the Ostwald mechanism. This knowledge is practically important for optimizing pulsed laser deposition technologies and creating 2D instruments and devices for studying physical phenomena.

Filtering Efficiency and Design Properties of Medical- and Non-Medical-Grade Face Masks: A Multiscale Modeling Approach

Approved medical face masks have been shown to prevent the spread of respiratory droplets associated with coronavirus transmission in specific settings. The primary goal of this study was to develop a new strategy to assess the filtering and transmissibility properties of medical- and non-medical-grade face masks. In this study, we designed and assessed the filtering efficiency of particles through six different masks with a diverse set of fabrics, textures (woven and non-woven), fiber diameters, and porosity. The filtering and transmissibility properties of face mask layers individually and in combination have been assessed using mathematical analyses and new experimental data. The latter provided velocity profiles and filtration efficiencies for which the data were shown to be predictable. The filtration efficacy and pressure drop across each fabric have been tested using an aerosol particle spray and scanning electron microscopy. To assess clinical significance, the temperature and humidity of the masks were tested on a group of healthy volunteers spanning various age ranges (9–79 years old), utilizing an embedded temperature sensor disc. Also, a mask filter model was developed using fluid dynamic simulations (Solidworks Flow) to evaluate the aerodynamic dispersion of respiratory droplets. Overall, the FFP2 and FFP3 masks demonstrated the highest filtration efficiencies, each exceeding 90%, a feature of multi-layered masks that is consistent with simulations demonstrating higher filtering efficiencies for small particles (<5 µm). The velocity and temperature simulations of all six masks revealed a low air velocity (~1 m/s) inside the mask and a temperature variation of approximately 3 °C during the breathing cycle.

Temperature inversion in a gravitationally bound plasma: Case of the solar corona

The temperature of the solar atmosphere increases from thousands to millions of degrees moving from the lower layer (chromosphere) to the outermost one (corona), while the density drops accordingly. The mechanism behind this phenomenon, known as a temperature inversion, is still unknown. In this work, we model a coronal loop as a collisionless plasma confined in a semicircular tube that is subject to the Sun’s gravity and in thermal contact with a fully collisional chromosphere behaving as a thermostat at the loop’s feet. By using kinetic N-particle simulations and analytical calculations, we show that rapid, intermittent, and short-lived heating events in the chromosphere drive the coronal plasma towards a non-equilibrium stationary state. The latter is characterized by suprathermal tails in the particles’ velocity distribution functions, exhibiting temperature and density profiles strikingly similar to those observed in the atmosphere of the Sun. These results suggest that a million-Kelvin solar corona can be produced without the local deposition of heat in the upper layer of the atmosphere that is typically assumed by standard approaches. We find that suprathermal distribution functions in the corona are self-consistently produced instead of postulated a priori, in contrast to classical kinetic models based on a velocity filtration mechanism.

Numerical investigation on the effect of porosity distribution on the flame characteristics

The low velocity filtration combustion of a lean methane/air mixture in the fixed bed reactors is numerically investigated using the system scale method. The effect of porosity on the flame characteristics, such as temperature profile, flame displacement speed and flame shape is examined in this study. For comparison, porosity is considered in two forms, i.e., volumetric average porosity (VAP) and porosity spatial distribution function (PSDF). The simulation results show that, local distribution of porosity primarily affects the flame shape, while having minimal impact on the peak flame temperature and mean flame displacement velocity. Quantitative analysis indicates that the flame displacement velocity obtained using VAP is closer to the experimental data compared to the PSDF. However, the simulation with PSDF explicitly captures the flame front bending caused by local porosity variation. Velocity and temperature fields suggests that flame front bending predominantly depends on the local flame displacement speed (LFDS), which is the vector sum of local interstitial airflow speed and the laminar flame speed of the combustible gas. The radial difference in LFDS, which is associated with uniformity in velocity and temperature fields, serves as the main driving force for flame front instability. The inclusion of PSDF enables a more accurate prediction of flame front development by capturing the preferential flow near the wall.

Structure, Morphology, Transport, and Mechanism of Oxygen Loss in YBa-=SUB=-2-=/SUB=-Cu-=SUB=-3-=/SUB=-O-=SUB=-7-delta-=/SUB=- Thin Films Obtained by Pulsed Laser Deposition with Velocity Filtration in Erosion Plume

We report the study of YBa2Cu3O7-delta films, synthesized on SrTiO3(100) substrates by pulsed laser deposition with velocity filtration, using X-ray diffractometry, transport measurements, and scanning electron microscopy. We have revealed the dependence of the structure of 100-200 nm thick YBa2Cu3O7-delta films on deposition time and velocity of particles in erosion plume, set by velocity filter. After deposition, the films, or their part, close to the substrate, consisted of 3-10-nm crystals with oxygen index delta=0.08, the same as in the target. For deposition time from 10 to 60 min, we observed the growth of regular pyramids with triangular and quadrangular bases from 20 to 500 nm in size at the base and spiral pyramids with polygonal bases on the film surface. The maximum oxygen loss up to delta=0.35 and T(R=0) up to 77.4 K coincided with the appearance of spiral pyramids up to 100 nm-high. These findings evidence in favor of oxygen depletion of the top layers of YBa2Cu3O7-delta thin films through the formation and growth of oxygen-deficient pyramids on their surface. The oxygen index in the range of delta=0.08-0.15 in both nanocrystals and regular pyramids of 20-300 nm in size provided T(R=0)=84-87 K and the width of superconducting transition Delta T=2.5-3.5 K. Keywords: pulsed laser deposition, surface morphology, film transport properties, film evolution, SrTiO3.

Структура, морфология, транспорт и механизм потери кислорода в тонких пленках YBa-=SUB=-2-=/SUB=-Cu-=SUB=-3-=/SUB=-O-=SUB=-7-delta-=/SUB=-, полученных импульсным лазерным напылением со скоростной фильтрацией эрозионного факела

We report the study of YBa2Cu3O7‒delta films, synthesized on SrTiO3(100) substrates by pulsed laser deposition with velocity filtration, using X-ray diffractometry, transport measurements, and scanning electron microscopy. We have revealed the dependence of the structure of 100-200 nm thick YBa2Cu3O7‒delta films on deposition time and velocity of particles in erosion plume, set by velocity filter. After deposition, the films, or their part, close to the substrate, consisted of 3‒10-nm crystals with oxygen index delta = 0.08, the same as in the target. For deposition time from 10 to 60 min, we observed the growth of regular pyramids with triangular and quadrangular bases from 20 to 500 nm in size at the base and spiral pyramids with polygonal bases on the film surface. The maximum oxygen loss up to delta = 0.35 and T (R = 0) up to 77.4 K coincided with the appearance of spiral pyramids up to 100 nm-high. These findings evidence in favor of oxygen depletion of the top layers of YBa2Cu3O7‒delta thin films through the formation and growth of oxygen-deficient pyramids on their surface. The oxygen index in the range of delta = 0.08‒0.15 in both nanocrystals and regular pyramids of 20‒300 nm in size provided T(R = 0) =84‒87 K and the width of superconducting transition DeltaT = 2.5‒3.5 K.

Transport and Morphological Characteristics of Thin YBa2Cu3O7 – x Films Obtained by Pulsed Laser Deposition with Velocity Filtration of the Laser Erosion Plume

Transport and Morphological Characteristics of Thin YBa2Cu3O7 – x Films Obtained by Pulsed Laser Deposition with Velocity Filtration of the Laser Erosion Plume

Characteristics of solar wind suprathermal halo electrons

A suprathermal halo population of electrons is ubiquitous in space plasmas, as evidence of their departure from thermal equilibrium even in the absence of anisotropies. The origin, properties, and implications of this population, however, are poorly known. We provide a comprehensive description of solar wind halo electrons in the ecliptic, contrasting their evolutions with heliospheric distance in the slow and fast wind streams. At relatively low distances less than 1 AU, the halo parameters show an anticorrelation with the solar wind speed, but this contrast decreases with increasing distance and may switch to a positive correlation beyond 1 AU. A less monotonic evolution is characteristic of the high-speed winds, in which halo electrons and their properties (e.g., number densities, temperature, plasma beta) exhibit a progressive enhancement already distinguishable at about 0.5 AU. At this point, magnetic focusing of electron strahls becomes weaker and may be counterbalanced by the interactions of electrons with wave fluctuations. This evolution of halo electrons between 0.5 AU and 3.0 AU in the fast winds complements previous results well, indicating a substantial reduction of the strahl and suggesting that significant fractions of strahl electrons and energy may be redistributed to the halo population. On the other hand, properties of halo electrons at low distances in the outer corona suggest a subcoronal origin and a direct implication in the overheating of coronal plasma via velocity filtration.

Effect of Periodic Permeability of Lung Tissue on Fluid Velocity and Nonspherical Nanoparticle Filtration

Nonspherical nanoparticles are toxic and extremely hazardous to human health. If these particles are inhaled, it will either deposit in throat and primer airways or flow with the air stream for a long time and cause various lung diseases such as bronchitis, emphysema, chronic obstructive pulmonary disease and asthma etc. To analyze the flow of these particles through lung we considered periodic permeability of lung and calculated filtration efficiency of lung under oscillatory boundary condition. We used generalized Navier–Stokes equation for flow dynamics of air and Newton equation of motion for flow dynamics of particles. Filtration efficiency of lung is also calculated for needle prolate particles at different value of mean permeability of porous lung. Finite difference numerical scheme is used to solve the nonlinear differential equations and MATLAB is used to find the solution computationally at very fine grid. Effect of mean permeability of media, aspect ratio of particle, Reynolds number, frequency of oscillation are analyzed on the flow of air and particles. Result shows that the filtration efficiency varies inversely with the value of mean permeability of porous lung.

Fabrication and Electrical Characteristics of Asymmetric Rings Made of HTS YBCO Films Obtained by Pulsed Laser Deposition

HTS YBCO films 200–400 nm thick are fabricated by pulsed laser deposition, both without filtration and in the regimes of velocity filtration of particles of an ablation plume. Using AFM and SEM, it is established that the size of large particles in the plane of films during deposition without filtration ranges from 60 to 1000 nm. After filtration, the maximum particle size in the film plane is less than 500 nm. Two types of irregularities are found on the surface after deposition: irregularities obtained from rounded particles and irregularities from faceted crystals. Using the methods of electron lithography and etching with argon ions through a mask, micro- and nanostructures are fabricated from HTS films. A correlation has been found between the characteristic dimensions of the irregularities on the surface of the films and the available lateral resolution of the microstructures obtained. For structures from HTS films that are asymmetric rings with a characteristic line width of 800 nm, the temperature dependences of the superconducting transition are determined and their asymmetric I–V characteristics are observed.

Chemical control of quartz suspensions aggregative stability

ABSTRACTThis article studies the influence of zeta potential on the fluidization of quartz suspensions and the possibility of its chemical control by changing the aggregative stability of the system using a reagent whose main component is the reaction product of amines and phosphoric esters. It is shown that aggregation of quartz, when treated by the specified chemical system, takes place due to an electrokinetic potential decrease resulting from reduction in the thickness of the diffuse portion of the electrical double layer around the quartz particles. It was found that chemical treatment of the quartz suspension contributes to a significant increase in fluidization onset velocity and fluid filtration coefficient. The article also proposed a correction to the Richardson–Zaki equation to take into account the aggregation of quartz particles. In order to explain the filtration properties of treated sand, a model was developed that takes into account the influence of aggregation on the porosity of the porous medium. The results presented here can be of use when developing oil fields composed of poorly consolidated sandstones.

Experimental Study on the Influence of DPF Micropore Structure and Particle Property on Its Filtration Process

A single layer filtration system was developed to investigate the filtration and regeneration performance of diesel particle filter (DPF). The particle layer thickness was directly measured online to analyze the different filtration stages. The influence of particle property on particle layer stage performance was also investigated. The results indicate that the filtration velocity can greatly affect the deep bed filtration stage, and the deposited particle layer can be compressed even in very low filtration velocity and higher filtration velocity trends to form denser particle layer. Optimizing the pore structure can effectively shorten the deep bed filtration stage and reduce the pressure drop eventually. An empirical function was proposed to relate the pore structure and the initial increment rate of pressure drop, which presented that reducing the pore size distribution range (3σ) can result in low DPF filtration pressure drop. The filtration stage could be further divided into four stages, and the value of particle layer thickness ranging within 15~20 μm has been found to be critical number for the shift from the transient stage to the cake filtration stage. Particle with large primary diameter and BET surface was beneficial to form loose particle layer.

Velocity filtration and temperature inversion in a system with long-range interactions

Temperature inversion due to velocity filtration, a mechanism originally proposed to explain the heating of the solar corona, is demonstrated to occur also in a simple paradigmatic model with long-range interactions, the Hamiltonian mean-field model. Using molecular dynamics simulations, we show that when the system settles into an inhomogeneous quasi-stationary state in which the velocity distribution has suprathermal tails, the temperature and density profiles are anticorrelated: denser parts of the system are colder than dilute ones. We argue that this may be a generic property of long-range interacting systems.

TYPE III RADIO BURSTS IN CORONAL PLASMAS WITH KAPPA PARTICLE DISTRIBUTIONS

We present the first simulations of type III bursts produced in the corona with suprathermal non-Maxwellian background particles, as inferred from solar wind data and proposed by theories for the corona and solar wind. The coronal background particles are assumed to follow kappa ({kappa}) distributions. The predicted f{sub p} emission of type III bursts is sensitive via the {kappa} index to the presence of suprathermal background particles, where f{sub p} is the local plasma frequency. The simulations show that (1) the speeds v{sub b} of type III beams are much larger (e.g., v{sub b} Almost-Equal-To 0.58c for {kappa} = 5) and so type III bursts drift much faster for low {kappa} ({<=}5) background plasmas than for Maxwellian backgrounds (producing v{sub b} < 0.3c), and (2) f{sub p} emission generated in a {kappa}-distributed background corona has a larger total bandwidth than in a Maxwellian background, for similar onset frequencies. Type III beams are thus more persistent, i.e., extending over larger distances, in {kappa}-distributed corona. Consequently, observations of fast-drifting coronal type III bursts and associated fast electron beams suggest that the ambient electrons in the corona are {kappa}-distributed, at least when such bursts are observed. These results support, from the new viewpointmore » of nonthermal radio emission, the occasional presence of suprathermal background electrons in the corona and the associated mechanisms (e.g., 'velocity filtration') for coronal heating and solar wind acceleration. The new results also help resolve longstanding issues regarding the speeds and persistence of type III beams, and the production of remotely observable levels of f{sub p} emission despite severe losses during propagation.« less

Study on Filtration Performance of Rotary Disc Filter with Different Filter Discs

Rotary disc filter is widely used in industrial water treatment. There are two methods to improving the filtration efficiency, which are the higher filtration velocity and lower filtration pressure drop; while the type of the filter disc plays an important role on the performance of filtration, In order to know how the filter disc affect performance of filtration, simplified model was used. On this basis, rectangular and triangular type was numerically simulated with the CFD software Fluent, DPM model, then the flow field configuration, velocity magnitude, pressure drop through the filter medium and the distribution of the particles were obtained. Then, the simulation results were analyzed and the conclusion was achieved that was under the same operation condition and porous parameters. Filter disc with a triangular type has greater advantages than the one with a rectangular type in the aspects of lower pressure drop, velocity distribution uniformity and particle distribution, which can highly improve the filtration efficiency.

Experimental investigation on low velocity filtration combustion in porous packed bed using gaseous and liquid fuels

This paper presents an experimental study on the characteristics of the filtration combustion of premixed gas as well as the pulse combustion of liquid fuel spray in a porous medium burner (PMB), with the latter as emphasis. The experimental system consists of combustor, primary combustion chamber (PCC), gas supply system, fuel supply system and the data acquisition system, which employs methane/air and liquid diesel oil as fuel respectively. The combustion phenomena of both fuels are observed, and the combustion characteristics are investigated through the spatial distribution and temporal evolution of the axial temperature in the burner. The influences of equivalence ratio and the inlet air velocity on the filtration combustion with low velocity are discussed. On the other hand, the influences of air flow rate and fuel injection quantity on the pulse combustion of diesel oil are studied. The experiment proves the self-sustained pulse combustion of a liquid fuel (diesel oil) within a porous ceramic burner, which suggests the feasibility of the porous medium engine (PME).

Identification of in Vitro Autophosphorylation Sites and Effects of Phosphorylation on the Arabidopsis CRINKLY4 (ACR4) Receptor-like Kinase Intracellular Domain: Insights into Conformation, Oligomerization, and Activity

Arabidopsis CRINKLY4 (ACR4) is a receptor-like kinase (RLK) that consists of an extracellular domain and an intracellular domain (ICD) with serine/threonine kinase activity. While genetic and cell biology experiments have demonstrated that ACR4 is important in cell fate specification and overall development of the plant, little is known about the biochemical properties of the kinase domain and the mechanisms that underlie the overall function of the receptor. To complement in planta studies of the function of ACR4, we have expressed the ICD in Escherichia coli as a soluble C-terminal fusion to the N-utilization substance A (NusA) protein, purified the recombinant protein, and characterized the enzymatic and conformational properties. The protein autophosphorylates via an intramolecular mechanism, prefers Mn(2+) over Mg(2+) as the divalent cation, and displays typical Michaelis-Menten kinetics with respect to ATP with an apparent K(m) of 6.67 ± 2.07 μM and a V(max) of 1.83 ± 0.18 nmol min(-1) mg(-1). Autophosphorylation is accompanied by a conformational change as demonstrated by circular dichroism, fluorescence spectroscopy, and limited proteolysis with trypsin. Analysis by nanoliquid chromatography and mass spectrometry revealed 16 confirmed sites of phosphorylation at Ser and Thr residues. Sedimentation velocity and gel filtration experiments indicate that the ICD has a propensity to oligomerize and that this property is lost upon autophosphorylation.

Deposition of smooth high-T c superconducting films with a solid-state YAG: Nd3+ laser

A method is presented for the deposition of smooth epitaxial high-T c superconducting films using a pulsed infrared YAG: Nd3+ laser and velocity filtration. This method is based on the removal of drops and solid particles from the flow of deposited substance with a fast shutter made of a rotating disk. The deposited smooth homogeneous YBa2Cu3O7−δ films have a critical temperature T c > 90 K. The surface concentration of drops is less than 3 × 102 cm−2, and their amount is decreased by more than six orders of magnitude.

The purification of protein in cross-flow microfiltration of microbe/protein mixtures

The use of cross-flow microfiltration to purify BSA from yeast/BSA binary suspension is studied. The yeast cake properties, the BSA rejection coefficient and the filtration flux under various operating conditions, such as cross-flow velocity, filtration pressure and suspension pH value, are measured and discussed. The experimental results show that the filter cake plays the major role in determining the filtration resistance, the filtration flux as well as the BSA rejection. The filtration rate increases with the increase of cross-flow velocity, while decreases with the increase of filtration pressure or suspension pH. The BSA rejection coefficient is mainly determined by the sweeping effect on the cake surface and the cake mass. An increase in cross-flow velocity, filtration pressure or suspension pH, causes the BSA rejection coefficient to be higher. Theoretical models are derived to predict the filtration flux and the BSA rejection coefficient at the pseudo-steady state under various conditions. The calculated results agree fairly well with experimental data. On the viewpoint of protein recovery and protein purification flux, pH 3.0, high cross-flow velocity and low filtration pressure is the optimum operating condition for purification of BSA from the binary suspension using cross-flow microfiltration

Exospheric distributions of minor ions in the solar wind

We investigate the acceleration of heavy solar wind ions on the basis of an exospheric Lorentzian model and show that the heavy ions can flow faster than the protons when their temperatures in the corona are more than proportional to their mass. The Lorentzian kinetic exospheric model [Pierrard and Lemaire, 1996], initially developed only for electrons and protons of the solar wind in a monotonic potential energy, is here generalized for the case of a nonmonotonic potential energy and applied to the heavy solar wind ions. We study how the mass, the charge, and the coronal temperature of the heavy ions influence their motion. The present work indicates that the temperature of the ions in the corona characterizing the dispersion of their velocities is a crucial factor determining their bulk velocity at large radial distances. Pierrard and Lamy [2003] showed that the velocity filtration effect can produce very high values of ion temperatures in the solar corona, considering that ion velocity distribution functions are enhanced with suprathermal tails in the low corona. We show that for sufficiently high ion temperatures at the exobase, our exospheric model can account for large bulk speeds of the heavy solar wind ions and for their relative abundances at 1 AU.