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We designed a new microfluidic method, multiorifice flow fractionation (MOFF), for continuous size-based separation of spherical microparticles. This method utilizes inertial lift force and momentum-change-induced inertial force generated in a series of contraction/expansion microchannels. The particles were concentrated gradually along the walls of microchannels by those inertial forces as they passed through the channels. The particle trajectory was defected from the carrier fluid by means of numerous sudden turns formed in a multiorifice channel. The inertial force was induced by this trajectory mismatching between fluid and particle that resulted from the momentum change. The trajectory mismatching induces the lateral drift of the equilibrium position of particle distribution, and its extent is variable according to particle size and flow rate. In the case of polydispersion, the size-based particle separation could be achieved in the specific range of the channel Reynolds number ([Re.sub.c]). It was found that, at [Re.sub.c] of 63-91, large polymer particles (~15 [micro]m) were aligned along the centerline of outlet channel, whereas small particles (~7 [micro]m) remained near both sidewalls. This method has potential in continuous separation without using a sheath flow. 10.1021/ac9005765

Given a large and complex network, we would like to find the best partition of this network into a small number of clusters. This question has been addressed in many different ways. Here we propose a strategy along the lines of optimal prediction for the Markov chains associated with the dynamics on these networks. We develop the necessary ingredients for such an optimal partition strategy, and we compare our strategy with the previous ones. We show that when the Markov chain is lumpable, we recover the partition with respect to which the chain is lumpable. We also discuss the case of well-clustered networks. Finally, we illustrate our strategy on several examples. partitioning | lumpability | MNCut | k means

The efflorescence relative humidity (ERH) of the particles containing a mixture of sodium chloride and sodium sulfate is studied. The results show that the ERH values increase with the increasing mole fraction of sodium sulfate.

The study report on the micellization of a diblock copolymer in dilute solution explored by dissipative particle dynamics is presented. Results reveal that weight-average aggregation number of micelles reduces with increasing the soluble-block length.

Abstract: The kinetics of heavy metal desorption from a naturally contaminated soil were investigated in the presence of Triton X-100 in combination with [I.sup.-], [SCN.sup.-], or [I.sup.-]/[SCN.sup.-]. Different kinetic equations [...]

The collision sequence of N-beads sliding along a friction less hoop gives rise to a dynamical system that can be studied via matrix products. The problem for general N and some basic theorems regarding the eigenvalues of the collision matrices and their products are formulated.

The mesoscopic models of amphiphilic surfactants that are able to describe the complex phase behavior of phospholipids bilayers are studied. The models can be simulated very efficiently to study the bilayer properties as function of temperature and surfactant characteristics.

A study on synthesis of copper nanoparticles within the AOT reverse micelle system, the bulk organic phase influences both the particle growth rate and ultimate particle size obtained is demonstrated. An interaction energy model is also applied to describe the forces between the metallic copper nanoparticles coated with AOT surfactant.

The study was done to observe the addition of the stable radical, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl(4-OH-TEMPO), to the reaction mixture in the photolysis of 7-silanaorbornadiene in solution, which resulted in the decrease of the magnetic field effect detected for the yield of stable reaction product tetraphenylnaphthalene (TPN).

The fundamental characteristics of motion of a droplet ejected from a nozzle with 26 [micro]m aperture have been carefully investigated. Droplets ejected are periodically charged and deflected by the deflection field. The behavior of charged and uncharged droplets in air is examined by a CCD camera, and from its images velocities and deflection distances are calculated. The results indicate that droplet train is decelerated linearly by the aerodynamic resistance, which is much smaller than the Stokes resistance for a single particle. It was found that there are two types of coalescence: one is due to Coulomb force between a charged and an uncharged droplet and the other is due to purely aerodynamic effect which is caused by the vacancy of the train. Deflected charge droplets showed complicated motion because of Coulomb and aerodynamic effects when they are proceeding in air. A factor to the Stokes resistance is shown to be between 0.5 and 0.6. Thus, the aerodynamic resistance for the train of droplets is much smaller than for the single particle. Index Terms--Electrostatics, charged droplet, particle motion, aerodynamic effect, inkjet, nozzle, droplet train, deflection, Stokes resistance, coalescence.

Polydisperse samples of Au nanoparticles protected with monolayers of hexanethiolate ligands (C6 MPCs) and with mixed monolayers of hexanethiolate and mercaptoundecanoic acid (C6/MUA MPCs) have been chromatographically separated using C8 120-[Angstrom] columns and acetone/ toluene mobile phase. The spectral details of eluted peaks and of quantized double-layer charging features in the differential pulse voltammetry of collected fractions were used to show that the elution orders of C6 MPC mixtures and of C6/MUA MPC mixtures were different For C6 MPCs, the smallest MPCs were eluted first, whereas the smallest C6/MUA MPCs were eluted last. The reversal of order of elution was rationalized in terms of intermolecular interactions with the stationary phase, dominant for the C6 MPC, being suppressed by the heightened polarity of the monolayer surface of the C6/MUA MPCs, making a size exclusion mechanism dominant. The range of apparent core diameters of the separated nanoparticles was 1.3-2 nm.

The paper presents an algebraic scheme to construct hierarchical divergence-free basis for velocity in incompressible fluids. A reduced system of equations is solved in the corresponding subspace by an appropriate iterative method. The basis is constructed from the matrix representing the incompressibility constraints by computing algebraic decompositions of local constraint matrices. A recursive strategy leads to a hierarchical basis with desirable properties such as fast matrix-vector products, a well-conditioned reduced system, and efficient parallelization of the computation. The scheme has been extended to particulate flow problems in which the Navier-Stokes equations for fluid are coupled with equations of motion for rigid particles suspended in the fluid. Experimental results of particulate flow simulations have been reported for the SGI Origin 2000.

The propagator of a particle in a one-dimensional box is quite different from the propagator for infinite space. It has a complicated but regular structure of everywhere dense singularities. We investigate the case of periodic boundary conditions both numerically and theoretically, leaving the slightly more complicated case of reflecting boundary conditions to the suggested problems. The singularity structure is shown to match up with the fractional revivals observed by many authors in wave packet studies. [DOI: 10.1119/1.1509415]

Based on Jourdain's variational equation proposed in 1909, we deduce a minimal set of general equations of motion for nonholomic dynamical systems of particles and rigid bodies. This equation of motion for the system, which differs slightly from the Gibbs--Appell equation, appears to be the same as the equation derived by Kane in 1961. Since the same equation was established by Appell in 1903 on the basis of D'Alembert's principle, the newly derived equation is named Appell's equation. [DOI: 10.1119/1.1514239]

The quantum mechanical formalism for the position and momentum of a particle on a one-dimensional lattice is developed. Some mathematical features characteristic of finite-dimensional Hilbert spaces are compared with the infinite-dimensional case. The construction of an unbiased basis for state determination is discussed. [DOI: 10.1119/11.1514208]

Studies of the interaction between a pulsed C[O.sub.2] laser and micrometer-sized aqueous and organic particles by use of light-scattering methods and step-scan Fourier-transform infrared (FTIR) spectroscopy are reported. Visible two-color extinction experiments indicate primary particle shattering, accompanied by a high fraction of vaporization, followed by secondary particle evaporation. The extent of the latter depends on the pulse intensity and particle composition. Angle-resolved light-scattering investigations provide insight into the aerosol size distribution and temperature following the pulsed heating event. The time dependence of the vapor plume, monitored with step-scan FTIR spectroscopy, confirms that a large fraction of the initial particle is quickly evaporated during the shattering event, followed by secondary fragment evaporation and thermal expansion.

Several possibilities for the use of elastic light scattering in the backscatter range (scattering angle [??] > 140 deg) for determination of size, velocity, and refractive index of spherical particles are investigated. First the phase Doppler technique is considered. Numerical simulations of light scattering with the Lorenz-Mie theory are used to show that the phase Doppler technique is unsuitable for such backscatter configurations, except for special measurement conditions. The time-shift (or pulse-displacement) technique is then considered by use of the Fourier-Lorenz-Mie theory. Simulations show that up to four fractional signals can be obtained by use of the technique in backscatter, corresponding to the scattering order or modes: surface wave (long path), reflection, second-order refraction (inner path), and a mixture of second-order refraction (outer path) and surface wave (short path). Signal characteristics as a function of particle size, refractive index, and particle ellipticity are studied. Suggestions for a practical measurement instrument are put forward.

An optical levitation and translation method for a microscopic particle by use of the resultant force induced by multiple light beams is studied. We show dependence of the radiation pressure force on the illuminating distribution by numerical calculation, and we find that the strongest axial force is obtained by a specific spacing period of illuminating beams. Extending the optical manipulation technique by means of vertical-cavity surface-emitting laser (VCSEL) array sources [Appl. Opt. 40, 5430 (2001)], we are the first, to our knowledge, to demonstrate levitation of a particle and its translation while levitated by using a VCSEL array. The vertical position of the target particle can be controlled in a range of a few tens of micrometers with an accuracy of 2 [micro]m or less. The analytical and experimental results suggest that use of multiple beams is an effective method to levitate a particle with low total illumination power. Some issues on the manipulation method that uses multiple beams are discussed.

This paper addresses the question of what happens to a particle in a box that is initially in the ground state, when the box is split into two slightly unequal halves. If the splitting is done sufficiently slowly, it is found that the particle always ends up in the bigger half of the box, regardless of how small the difference in sizes of the two halves may be. Approximate analytical expressions that describe the process are derived, and an optical analogy is presented. [DOI: 10.1119/1.1446854]

The steady-state sheath between a Maxwellian plasma source and a dielectric surface was simulated numerically in the collisionless hypothesis. A method of nonphysical numerical time evolution was investigated to extend the electrostatic Particle-In-Cell method to a large range of ion masses at low cost in calculation time. Secondary electron emission effects were also considered and all of these results for a Maxwellian plasma were validated by comparison with previous analytical models in the entire range of ion masses and with other numerical simulations in the case of light ions. The occurrence of instabilities resulting from the interaction between the ion and the secondary electron flows was also investigated. The numerical times method was thus validated and its limitations characterized. It is now available to simulate arbitrary distribution functions of electrons, secondary electrons, and ions at low cost in calculation time. Index Terms--Particle-In-Cell, plasma, secondary electron emission, sheath, two-stream instability.

This review analyzes particle-based, gas-kinetic, and fluid dynamic models to interpret the motion in self-driven many-particle systems. Aspects of universality and spin systems are discussed along with the application of the findings to other systems, such as bacterial colonies, flocks of birds, and stock market dynamics.

A model to estimate the extent of intraparticle, or perfusive, electroosmotic flow (EOF) in CEC capillaries packed with macroporous particles has been developed. Nucleosil packings (d(sub p)= 7 (mu)m) having nominal pore sizes of 500, 1000, and 4000 angstroms were studied. Intraparticle pores ranging from 50 to 10 000 angstroms in diameter were partitioned into 995 intervals of 10 angstroms. Using pore size distribution data for the sorbents obtained by mercury intrusion porosimetry, fractions of the total column void volume contributed by pores in the range of interest were determined. The average channel diameter of the interstitial space was estimated from the d(sub p) of the packing; its fraction of total column volume was determined from the interstitial porosity. Estimations of relative EOF velocity in the intraparticle and interstitial channels were made by treating the channels as parallel cylindrical capillary tubes. Relative EOF values were combined with the volume fraction data and used as weighting factors in calculating an effective particle diameter (d(sub p,eff)) for each set of conditions (i.e., packing type, ionic strength of eluent). Values of d(sub p,eff) generated by the model correctly predict the trends observed in the experimental data. At the lowest ionic strength, plate height correlated inversely with the pore size of packing (h(sub 4000) angstroms < h(sub 1000) angstroms < h(sub 500) angstroms). Rate curves for each column tended toward lower plate heights with increasing eluent ionic strength before converging at some limiting point. The point of convergence was reached at moderate ionic strengths for the larger pore media (1000 and 4000 angstroms) and higher ionic strength for the 500 angstroms.

We recently developed a new method for simple determination of particle magnetic susceptibility using analytical magnetapheresis. This new method does not require laborious calibration plots and trial susceptibility values as do previous analytical magnetapheresis methods. The new method is based on balancing channel flow rates and magnetically induced flow rates for particle deposition in analytical magnetapheresis. The maximal flow rate for complete particle deposition was determined experimentally and set to equal the magnetically induced flow rate for determining particle magnetic susceptibility. This magnetic susceptibility determination generally takes less than 20 min. Several magnetically susceptible and ion-labeled particles were tested using this new method. The carrier magnetic susceptibilities were varied, and erbium ion-labeled particles were studied experimentally, resulting in successful susceptibility determinations of erbium ion-labeled particles and yeasts. The precision of each measurement was generally approximately 10%. Experimental determination of particle magnetic susceptibilities differed by less than 10% from reference measurements taken using a superconducting quantum interference device magnetometer. This method can determine minimal susceptibilities on the order of 10(super -9) cgs. The minimum number of erbium labeling ions per particle required for complete deposition of silicas and yeasts was found to be 6.7 x 109. Analytical magnetapheresis shows good potential for use in simple determination of particle magnetic susceptibilities and should become a useful technique.

This paper presents a model for the normal force-displacement relation of spherical particles in contact with each other based on the continuum theory of elastoplasticity. Research reveals that the model applies to granular flow simulations and allows for an accurate prediction of the contact force level in plastics.

This article reviews history and development of the two-electron atoms theory from the time of Bohr-Sommerfeld quantization with reference to their spectra and the latter's impact on the doubly excited resonance states of the atoms. Regular and chaotic classical two-electron dynamics are analyzed in terms of their doubly excited states.

By scattering light from small particles, their geometrical Structure and their state of motion can be measured. An experiment is described for measuring the diffusivity of small particles undergoing Brownian motion using the technique called photon correlation spectroscopy or dynamic light scattering. The necessary experimental apparatus and the related theory are discussed. Photon correlation spectroscopy is a powerful tool for studying the dynamical behavior of fluids near critical points, and a discussion is given of this phenomenon. The same experimental technique also can be used to study laminar or turbulent flows, and the associated theory is introduced to enable such experiments to be interpreted.

A simple one-dimensional model is presented for the motion of a Brownian particle. It is shown how the collisions between a Brownian particle and its surrounding molecules lead to the Langevin equation, the power spectrum of the stochastic force, and the equipartition of kinetic energy.

Results demonstrate that onset of crack propagation in thick and thin particulate composite specimens occurs at the crack tip element with the same applied strain. Data further indicate that damage initiation, growth and saturation manifest near the crack tip.

A study was conducted to analyze the numerical simulation of particle trajectories and deposition efficiency of a single rectangular-shaped fiber in an electric field. The potential air flow was examined using the boundary-element method. Deposition efficiencies were computed for different values of the Stokes number and the nondimensional electric number. A differential equation was determined and utilized to examine particle movement.

Quasiparticle transmission through a superconductor is characterized by the influence of hole-like and electron-like particles on each other. Quasiparticles which were introduced into the superconductor convert themselves into Cooper pairs by Andreev reflection, and the tunneling factor is influenced by the Fermi energy of the particles. The real part of the tunneling factor is much larger than the imaginary part for the quasiparticles.

An analysis of planetary formation when the parent materials are distributed as centimeter sized particles reveals that the particles settle toward the midplane on a layer of mass density gas. Vertical profiles of particle density is determined by nonlinear, coupled interactions between the particles and the nebula. During this stage the planetesimals, the forerunners of planets, form.

Pinning down the large-scale magnetic field of the Galactic Centre--which provides our closest view of a galactic nucleus--within the uncertainty (greater than two orders of magnitude) implied by existing, rival [...], The amplitude of the magnetic field near the Galactic Centre has been uncertain by two orders of magnitude for several decades. On a scale of ~100 parsecs (pc), fields of ~1,000 microgauss (µG; refs 1-3) have been reported, implying a magnetic energy density more than 10,000 times stronger than typical for the Galaxy. Alternatively, the assumption of pressure equilibrium between the various phases of the Galactic Centre interstellar medium (including turbulent molecular gas, the contested (4) 'very hot' plasma, and the magnetic field) suggests fields of ~100 µG over ~400 pc size scales (5). Finally, assuming equipartition, fields of only ~6 µG have been inferred from radio observations (6) for 400 pc scales. Here we report a compilation of previous data that reveals a downward break in the region's non-thermal radio spectrum (attributable to a transition from bremsstrahlung to synchrotron cooling of the in situ cosmic-ray electron population). We show that the spectral break requires that the Galactic Centre field be at least ~50 µG on 400 pc scales, lest the synchrotron-emitting electrons produce too much γ-ray emission, given other existing constraints (7). Other considerations support a field of 100 µG, implying that over 10% of the Galaxy's magnetic energy is contained in only [??] 0.05% of its volume.

The fluctuations in the number of particles of the ideal gas are calculated using the canonical and the grand canonical ensembles. The two results differ by a factor which accounts for the relative size of the total volume and the subvolume where the canonical ensemble fluctuations are calculated. This factor gives a simple example of explicit finite-size effects, because it arises from considering a fixed number of particles in the canonical ensemble. Our simulation results for the isothermal compressibility of the hard disk fluid with a finite number of particles are improved by applying this correction.

A microfluidic continuous flow lab-on-a-chip structure is described for combined reaction and separation implementation. A formula is derived thereby setting the limitations of the structure, relating the desired duration of the particles in the reaction site to the particle size under the condition of a narrow spatial particle distribution along the separation site.