Particles Of Different Densities Research Articles

LDL particle size: an important drug target?

Low density lipoprotein (LDL) is the main carrier of plasma cholesterol and a major component of atherosclerotic plaque [1]. Lowering LDL cholesterol reduces coronary events and mortality from coronary artery disease (CAD) [2–4], however, the relation between LDL cholesterol concentration and (CAD) is complex. Many patients with CAD have plasma LDL cholesterol concentrations in the normal rangefor the general population [5]. Thus, it could be that coronary risk goes beyond LDL cholesterol concentration to the characteristics of the LDL particles themselves. The purpose of this communication is to address the issue of whether LDL particle size and density influences its atherogenecity and how this might be modified by drug therapy.

A generalized empirical description for particle slip velocities in liquid fluidized beds

An empirical equation for calculating the slip velocity of a species in any homogeneous suspension is proposed. The Richardson and Zaki (1954, Trans. Inst. Chem. Engng, 32, 35–53) and Lockett and Al-Habbooby (1973, Trans. Inst. Chem. Engng 51, 281–292; 1974, Powder Technol., 10, 67–71) equations are special cases of the proposed equation, and arise when all species are of the same density. Therefore, the main value of the proposed equation is in describing the slip velocities of particles in suspensions containing species of different density. In this short note results from one experimental system are presented, and shown to be consistent with the model. The model is also consistent with the explanation used by Moritomi et al. (1982) to account for phase inversion in fluidized beds. The model is appealing in its simplicity, and should find favour in the design and control of process equipment. The new model predicts the strong segregation effects observed in suspensions containing particles of different density, and hence represents an immediate improvement on the Lockett and Al-Habbooby equation. Its application is expected to cover all homogeneous suspensions, in which the particles are all more dense than the suspension. At this stage its validation has been limited to low concentrations of dense particles settling through a fluidized bed of low density particles as occurs in a Teetered Bed Separator, and to phase inversion conditions in fluidized beds. It is hoped that this note might lead to a much more extensive validation of the model by workers using vastly different particle species.

降雨領域評価に基づくTRMMマイクロ波放射計降雨推定方法

Recent studies based on aircraft observations made over ocean by radar and multi-channel passive microwave radiometer, each with a field of view(fov)of a few kilometers, indicate significant problems in relating the radar derived rain rate with the brightness temperature measurements of the microwave radiometer. We arrive at a similar conclusion from extensive observations of rain rate made by ship-borne radars and rain rate deduced from observations of the satellite-borne, multi-channel Special Sensor Microwave Imager(SSM/I) radiometer, which has a much larger fov(∼30 km). The principal reason for these problems is that the signal due to rain drops contained in the radiometer measurements is non-linearly mixed with that of other hydrometeors that could be present in the radiometer fov. These other hydrometeors include liquid droplets, and dry and melting ice and snow particles of different densities, sizes, and shapes in clouds. Observations made by SSM/I are not adequate to uncouple the rain signal satisfactorily from such a non-linear mix of signals on the scale of the radiometer footprint. These problems are complicated further by meteorological conditions, which can significantly alter the amount and spatial distributiion of these other hydrometeors. For these reasons an empirical method is developed to estimate area-average rain rate in a mesoscale region of about 300×300 km2, based on SSM/I data. One parameter of this empirical method fR relates to the fractional rain area in a mesoscale region, while the second parameter, χ, reflects in a weak way the scattering and emission properties of the hydrometeors in that region. This method requires tuning with the help of radar data. Over the TOGA-COARE area, the rain rates retrieved from this method can reproduce the radar observed rain rates with a correlation coefficient of about 0.85. Furthermore, monthly total rainfall estimated from this method for the TOGA-COARE area has an error of about 13 %. This rain retrieval method is applicable to the Tropical Rainfall Measuring Mission(TRMM), in which multi-channel dual-polarization microwave radiometer observations over a 760 km wide swath are overlapped with those of radar, which has a swath of 220 km.

An Excel program for computing the dynamic properties of particles in Newtonian fluids

Grain sizes of natural sediments can be determined by direct measurement of orthogonal axis dimensions, or alternatively by sieve or settling tube analysis. As these different techniques do not always give compatible results, published equations for modelling the hydrodynamic or aerodynamic behavior of particles have limited application. In this paper, an Excel program, which allows input from all three methods, is presented. The program calculates the settling velocity of spheres and ellipsoids as well as the critical shear stress at incipient grain motion in unidirectional fluid flow. Additional information includes the shape entropy of the particles, the drag coefficient, Reynolds numbers, and critical shear velocity. As the equations apply to particles of different densities in various liquids or gases, the program can be used for unusual situations such as modelling sediment entrainment on other planets.

Collection efficiencies of large water drops collecting aerosol particles of various densities

A laboratory experiment to study the effect of the density of aerosol material on collection efficiency of water drops, is conducted with MgS0 4 and MnCl 2 particles. When compared with the earlier results for NaCl and other particles, our observations show that the collection efficiency of water drops increases wish increase in impaction parameter, irrespective of whether the change in impaction parameter is caused by the change in the density of particles or the size of particles/water drop. Our results are correlated through the aerodynamical diameter parameter and with earlier experimental results of other investigators for particles of different densities. The agreement between our experimental results and the theory of Slinn (1983, Precipitation Scavenging in Atmospheric Sciences and Power Production, Chap. 11. Division of Biomedical Environmental Research, U.S. Department of Energy) increases with the increase in the density or size of the particles. Moreover, our experimental results confirm the prediction of Slinn's theory that inertial impaction mechanism is dominant for smaller particles if their density is higher.

Settling behaviour of concentrated dispersions and some volcanological applications

Experiments have been carried out on the settling of non-aggregating, poorly sorted aqueous dispersions laced with lowdensity particles in order to gain insight into the sedimentation behaviour of volcaniclastic flows which contain pumice. Two poorly sorted dispersions of silicon carbide particles with continuous size distributions were studied; plastic beads were added as a light component. Experiments were carried out at solids concentrations between 10 and 60 vol%. Dispersions of low concentration generated normally graded deposits in which particles of different densities were in approximate hydraulic equivalence. Above a critical concentration (45 to 60% depending on the grain-size distribution) particle segregation was suppressed, and the dispersion settled to form a virtually ungraded bed. Hindered settling at intermediate concentrations generated normally graded deposits with elutriation pipes, “floating” rafts of plastic, and capping layers of fines elutriated by escaping pore fluid. Buoyancy forces resulted in strong hydraulic inequivalence between light and dense components in the deposits from intermediate concentrations. Two mechanisms of elutriation-pipe growth were observed. At intermediate concentrations, pipes grew progressively upwards in the deposit as the latter aggraded, whereas at high concentrations they nucleated and grew uniformly throughout the whole dispersion. Elutriation pipes form readily during sedimentation of some poorly sorted aqueous dispersions; the presence of elutriation pipes cannot be used alone to distinguish between deposits of epiclastic and pyroclastic flows. Reverse grading of pumice, pumice rafts, elutriation pipes, and layers of elutriated fines should characterise deposits from pumice-rich submarine mass flows. Despite differences in the fluid phase, the experiments also have implications for fluidization mechanisms in pyroclastic flows. Hindered settling of a concentrated, poorly sorted dispersion is a type of self-fluidization in which the sedimentation of large particles causes a sufficiently strong vertical fluid flux to fluidize or elutriate smaller ones. Hindered settling is intrinsic to all pyroclastic flows as they spread out and deflate across the landscape, and may reinforce other gas sources as an effective fluidization mechanism during emplacement of type 2 and type 3 ignimbrites and of coignimbrite lag breccias.

Suspension of Solid Particles

The results of agitator speed measurements for complete suspension of solid particles reported earlier were completed by new measurements in larger vessel and with smaller particles and with particles of different density. Good agreement between earlier and new results justifies the applicability of the correlation proposed for calculation of critical agitator speed.

Numerical simulation of polydisperse sedimentation: equal-sized spheres

This paper describes the results of numerical simulations for polydisperse sedimentation of equal-sized spheres, e.g. particles of different density. Using the Stokesian dynamics algorithm, mobility matrices are computed for random particle configurations and ensemble averages taken to calculate the mean mobility matrices. It is shown that the settling velocities of individual particles species may be expressed in terms of two scalar functions of total volume fraction. These are the selfmobility Mo, (∼ short-time self-diffusion coefficient) and the interaction mobility MI. This latter quality is related to the velocity of a force-free tracer particle in a suspension of identical particles subjected to a unit force. Numerical values for Mo and MI are calculated for a range of volume fractions from ϕ = 0.025 to 0.50. All results show excellent agreement with the dilute theory of Batchelor. Simple algebraic expressions are given which well correlate the numerical results.

On transport of suspended particulates in tube flow.

Blood cells suspended in shear flows exhibit much larger dispersive motions than those predicted by the Stokes-Einstein formula for Brownian diffusion. The lateral migration and the erratic motions of the 8 microns red blood cells (RBC) is thought to be analogous to a diffusive process. It is shown that the often cited convective-diffusion theory may not be an adequate model for describing the transverse migration of suspended cells in blood flow. A comprehensive review of both the classical theory and of contemporary work in particle transport is presented, with particular emphasis on low Reynolds number tube flows. The mechanisms of Taylor dispersion, the effects of Brownian perturbations on translational and rotational motions of the suspended particles in shear fields, and the influence of integratable and chaotic advections, are individually examined. The classical experiment by Segre and Silberberg (1962) lead us to believe that particle hydrodynamics may play an important role in transverse migrations. In this light, we have further examined the hydrodynamic aspects of the so-called "tubular pinch" effect, the lateral migration of rigid spheres. We have also discussed the transverse motions of liquid drops, and the reversibility of the organization of suspensions in transport. The convective accelerations in the entrance region of a tube can produce relative velocities between fluid medium and various type of particulates if there is a difference in density. The deformable RBC, an "active-type" particle, can provide feedback to the flow from both mass and momentum considerations; the more rigid platelet, a "passive-type" particle, will experience a much smaller relative velocity as compared to the RBC. We may expect that particles of different densities are transported to different equilibrium annular positions before entering the fully developed flow region. The erratic, lateral movement of suspended particulates in steady laminar tube flow can be described by the usual Lagrangian coordinates.

A study of segregation in a gas-solid fluidized bed: Particles of different density

Segregation and mixing of large particles (≈4 mm) of different density are studied. An experimental technique is developed based upon division of the bed into slices before the gas supply is turned off. Three binary systems (polyethylene, alumina and glass) have been studied, varying the mixture composition and the gas velocity. Concentration and voidage profiles along the bed height are measured. Results are described according to the Gibilaro—Rowe model.

Cell manipulation in ultrasonic standing wave fields

AbstractParticles suspended in either travelling or standing wave fields experience non‐zero time averaged radiation forces. In a standing wave field such forces can result in migration of the particles to preferred positions separated by distances of half an acoustic wavelength. Radiation forces also give rise to either interparticle attraction or repulsion and can exert a torque on suspended particles. The forces depend on some or all of the following properties (i.e. particle size and shape, sound frequency, the square of the sound pressure amplitude) and on the differences between the density and compressibility of the particles and those of the suspending phase. The forces acting on suspended particles are analysed and threshold pressures for the migration of particles to half‐wavelength separations are derived. It is shown that appropriate choice of sound pressure amplitude should lead either to separation of particles of different densities and compressibilities in the sound field or to concentration of mixed samples essentially at the same location. Experimental observations of ultrasonic radiation force effects on cells are reviewed as are applications of radiation forces to effect cell concentration in electrofusion procedures and the use of ultrasound to support cells away from solid surfaces. Examples of cell concentration, cell alignment and cell‐cell interaction are presented.

Cell manipulation by radiation forces

Particles suspended in acoustic fields experience nonzero time averaged radiation forces that can cause particle movement, interparticle attraction or repulsion, and can exert a torque on suspended particles. In a standing wave, such field forces result in migration of the particles to positions separated by half an acoustic wavelength. The forces depend on some or all of the following properties: particle size and shape, sound frequency, the square of the sound‐pressure amplitude, and the differences between the density and compressibility of the particles and those of the suspending phase. Threshold pressure for the vertical migration of particles to half‐wavelength separations is derived. It is shown that appropriate choice of sound‐pressure amplitude should lead either to the separation of particles of different densities and compressibilities or to the concentration of mixed samples essentially at the same location. Applications of radiation forces to bring cells together in suspension for cell electrofusion procedures and the use of ultrasound to support cells away from solid surfaces are described. Examples of cell concentration, cell sedimentation, cell alignment, and cell‐cell interaction are also presented.

Role of settling, entrainment and dispersive equivalence and of interstice trapping in placer formation

Grain-scale placer mineral concentrating processes are reviewed. Early explanations of localized enrichment of heavy particles in terms of sorting associated with the settling equivalence of clasts of differing density have been superseded. Entrainment equivalence is shown to be a more appropriate concentrating factor in both fluvial and littoral sedimentary environments. The vertical shuffling of particles of different density that is associated with dispersive equivalence is an ancillary process that presents appropriate particles for entrainment sorting. However, the role of entrapment of comparatively small grains in the interstices of the stream bed or the beach face is shown to be more important that hitherto envisaged. This depositional enrichment is controlled by the relative sizes of the bed sediment pores and the ingressing particles. Local vertical changes in framework particle size dictate patterns of interstice clogging and hence the quantity of placer mineral rich matrix passing into the bed.

Preparation and application of monodisperse polymer particles

AbstractThe swelling capacity of aqueous dispersions of particles (or droplets) containing a relatively low molecular weight, highly water‐insoluble compound (Y) may be more than a thousand times higher than that of particles consisting of polymer only. The rate, and also the degree of swelling, may furthermore be increased by having the swelling substance, which usually is a low molecular weight, slightly water soluble substance, present in a finely dispersed form. A two‐step swelling process has been described. In a first step, relatively small monodisperse polymer particles are swollen with a component Y and then with monomer or monomer mixtures, followed by polymerization. The method allows preparation of highly monodisperse particles of more than 50 μm diameter with a standard deviation of less than 2%. The particles may be prepared as core and shell particles of different density and with various surface layers, or as macroporous particles. The new particles have found application as standards in immunoassays and, most important up to now, in liquid chromatography. An extension of the process allows the production of monodisperse magnetizable particles which have found application in cell separation of cancer cells from normal cells.

A comprehensive interpretation of solid layer inversion in liquid fluidised beds

Solid mixing and segregation in liquid fluidised beds containing binary mixtures of spherical particles of different density and size has been studied for a range of liquid velocities, bulk bed compositions and particle properties. It was shown that a bed of denser particles expands with liquid velocity independently of the presence of the lighter particles. When the bulk volume fraction of the lighter particles is high and the liquid velocity is relatively low, the bed forms two layers, i.e. the upper layer consisting almost entirely of the lighter and the lower mixed layer consisting of both components in which the volume of the lighter increases with liquid velocity. A completely mixed bed is obtained at a certain velocity and then a further increase of the velocity causes “layer inversion”. The liquid velocity at which complete mixing occurs depends on the bulk bed composition, and at that velocity the volume fraction of the lighter in the lower mixed layer is constant regardless of the bulk bed composition. It is shown that layer inversion occurs for a given particle mixture when the liquid velocity passes through a value at which the volume fraction of the lighter in the lower layer becomes equal to the bulk bed composition; or for a given velocity, when the bulk bed composition becomes equal to the fraction of the lighter component which exists in the lower layer. The dependency of the fraction on the liquid velocity and the particle properties is examined to some extent.

Mixing of solid particles of different density in a horizontal batch mixer. Measurement of axial diffusion coefficients

Axial diffusion coefficients of tracer particles were obtained by the method of impulse response. The results show that the diffusion coefficients of the particles of different densities are larger than those of identical particles. The assumption of completely reflecting barriers for the end walls is inapplicable to the mixing of heterogeneous particle systems.

Motion and Segregation of Solid Particles of Different Density in a Horizontal Drum Mixer

Motion and Segregation of Solid Particles of Different Density in a Horizontal Drum Mixer

Application of a solid-phase radioimmunoassay and immune electron microscopy for hepatitis A in diagnosis and research

With crude virus suspensions from stool and antibodies from hepatitis-A patients, a solid-phase radioimmunoassay (RIA) for detection of hepatitis virus A (HVA) had antibodies against hepatitis virus A (anti-HVA) has been developed. Examples for the application of this test are demonstrated. Virus particles from the stools of the two patients were further characterized. Serologically, they were identical or very similar to the MS-1 strain. Isopycnic CsCl-gradient centrifugation of both strains revealed two peaks, but the particles of different densities did not differ in size or serologically. A modification of the RIA was also useful for determination of IgM antibodies in patients' sera fractionated by sucrose-density centrifugation. The application of the RIA method for serologic epidemiology is demonstrated by a comparison of anti-HVA prevalence in German and non-German women residing in Germany.

Myelin consists of a continuum of particles of different density with varying lipid composition : major differences are found between normal mice and quaking mutants

Mouse brain myelin consists of a continuum of particles of different densities, as shown by sucrose density gradient centrifugation. In normal animals most of the material (65 per cent) is concentrated between 0.6 and 0.7 M sucrose (the maximum being found at 0.66 M sucrose, corresponding to 23 per cent). The density differences among various myelin fractions are related to their protein/lipid ratios, as lighter fractions contain less protein and more lipid. Lipid analysis shows a decrease in the amount of every lipid from the lightest to the heaviest fraction: the light fraction is richer in phosphatidyl-ethanolamine, phosphatidyl-serine and cerebrosides. The distribution is highly abnormal in purified myelin from Quaking mutant ; very low quantities of myelin with normal density are found, but unexpected large amount of high density particles are found, possibly related to a "pre-myelin" material (oligodendrogial) processes which are not maturing into normal myelin).

The polypeptide composition of avian infectious bronchitis virus particles

SummaryEgg grown avian infectious bronchitis virus (IBV) centrifuged on sucrose density gradients was found to consist of a major virus peak of density 1.17 to 1.18 g/cm3 and occasionally two minor virus peaks of density 1.21 to 1.22 g/cm3 and 1.13 g/cm3. Three different IBV strains were examined and no morphological differences were detected between virus particles of different densities or from different strains. The polypeptides of the different density virus particles from the three IBV strains were analysed on polyacrylamide gels. In all cases 7 polypeptides were observed, although there were differences in the proportions of these polypeptides in particles of different densities and those from the different strains. The polypeptides have been called VP1 (molecular weight 130,000), VP2 (105,000), VP3 (97,000), VP4 (81,000), VP5 (74,000), VP6 (51,000) and VP7 (33,000). Additional polypeptides were produced if slightly harsher treatments were used.