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AbstractIn the dry environments of high-temperature gas reactors, aerosols and dust particles can be highly nonspherical and even chainlike agglomerates, and are highly charged. To elucidate the role of both shape and charge on particle dynamics, we have explored numerical solutions of the Poisson equation for arbitrary geometries. In this paper, we describe the general computational framework, and report results for condensation/evaporation for several different cases, including chainlike agglomerates. We find that the shape factor based on the volume equivalent sphere approximation underestimates the actual condensation rate on the agglomerate, in addition to not accounting for the local condensation rates.

The aim of this study was to characterize levels of serum biomarkers in patients with severe refractory cardiogenic shock (SRCS) and to document temporal changes in these levels during restoration of circulation.

Percutaneous ventricular assist devices (pVADs) are being increasingly used in patients with cardiogenic shock. They offer a means of instituting rapid and adequate cardiac support in patients with cardiogenic shock unresponsive to inotropesvasopressors and intraaortic balloon pumps (IABPs). However, there is considerable debate on the appropriate use of these devices given the difficulty of conducting randomized trials in patients with cardiogenic shock, lack of clear guidelines on indications, device selection, and cost-effective care of patients implanted with these devices.

AbstractAn experimental system was constructed in accordance with the standard ASTM C835-06 to measure the total hemispherical emittance (emissivity) of structural materials of interest in very high temperature reactor (VHTR) systems. First, data were acquired for 304 stainless steel as well as for oxidized and unoxidized nickel, and good reproducibility and agreement with the literature was found. Emissivity of Hastelloy X was then measured under different conditions that included (a) “as received” (original sample) from the supplier, (b) with increased surface roughness, (c) oxidized, and (d) graphite coated. Measurements were made over a wide range of temperatures. Hastelloy X, as received from the supplier, was cleaned before additional roughening of the surface and coating with graphite. The emissivity of the original samples (cleaned after received) varied from ~0.18 to 0.28 in the temperature range of 473 to 1498 K. The apparent emissivity increased only slightly as the roughness of the surface increased (without corrections for the increased surface area due to the increased surface roughness). When Hastelloy X was coated with graphite or was oxidized, however, its emissivity was observed to increase substantially. With a deposited graphite layer on the Hastelloy, increases from 0.2 to 0.53 at 473 K and from 0.25 to 0.6 at 1473 K were observed—a finding that has strong favorable safety implications in terms of decay heat removal in postaccident VHTR environments. Initial oxidation of Hastelloy X surfaces was observed to notably increase the emissivity of the Hastelloy X but was not observed to progress significantly beyond the initial oxidation even with more prolonged exposure. Since there is likely to be initial surface oxidation of any Hastelloy X used in the construction of VHTRs, this represents an essentially neutral finding in terms of the safety implications in postaccident VHTR environments.

Rotary oscillations of several axi‐symmetric bodies in axi‐symmetric viscous flows with slip are investigated. A numerical method based on the Green's function technique is used wherein the relevant Helmholtz equation, as obtained from the unsteady Stokes equation, is converted into a surface integral equation. The technique is benchmarked against a known analytical solution, and accurate numerical results for local stress and torque on spheres and spheroids as function of the frequency parameter and the slip coefficients are obtained. It is found that in all cases, slip reduces stress and torque, and increasingly so with the increasing frequency parameter. The method discussed here can be potentially extended to the realistic case of an oscillating disk viscometer. Copyright © 2003 John Wiley & Sons, Ltd.

The diffusion of boron into polycrystalline diamond films was carried out at 1000°C. Experiments were conducted at different electric field strengths through a diamond-boron-diamond (DBD) matrix for different times at a vacuum of 686 Torr. During the experiments hydrogen was flowing into the reactor at a rate of 11 sccm. The results showed that the best conditions to diffuse boron into diamond occurred at 200 V and 8 h. The diffusion coefficient of boron in diamond was calculated using the experimental data and was found to be 3.50 X 10-14cm2/s at 1000°C. The diamond films showed a dramatic reduction in electrical resistivity from more than 1013Ω cm to 50 Ω cm.

Quantifying the role of surface shape and physicochemical surface conditions on the interfacial reactivity of particles and substrates is fundamental to a multitude of natural and engineered surface adsorption phenomena. We consider continuum/jump regime adsorption at the gas or liquid interface of arbitrary regular solid surfaces with heterogeneous surface features. In particular, the 3-D boundary value problem (based on Laplace's diffusion equation) is converted into a 2-D integral equation for the adsorbate concentration at the particle surface. This accommodates numerical descretization via the implementation of 2-D Gauss–Legendre quadratures on an arrangement of high- and low-adsorption patch trace sites constructed to completely cover the particle surface. A generalized computer program is developed to solve the resulting linear algebra problem for the unkown local adsorption current densities. We investigate the role of various distributions of high- and low-adsorption sites for a generalized class of spheres which includes the DNA-like shaped twisted spheres. The biological implications of the role of surface curvature on interfacial adsorption/reactivity at particle surfaces are also discussed.

Equilibrium adsorption isotherms are reported for radon and water vapor on two commercial activated carbons: coconut shell Type PCB and hardwood Type BD. The isotherms of the water vapor were measured gravimetrically at 298 K. The isotherms of radon from dry nitrogen were obtained at 293, 298, and 308 K while the data for the mixture of radon and water vapor were measured at 298 K. The concentrations of radon in the gas and solid phases were measured simultaneously, once the adsorption equilibrium and the radioactive equilibrium between the radon and its daughter products were established. The shape of the isotherms was of Type III for the radon and Type V for the water vapor, according to Brunauer's classification. The adsorption mechanism was similar for both the radon and the water vapor, being physical adsorption on the macropore surface area in the low pressure region and micropore filling near saturation pressure. The uptake capacity of radon decreased both with increasing temperature and relative humidity. The heat of adsorption data indicated that the PCB- and the BD-activated carbons provided a heterogeneous surface for radon adsorption. The equilibrium data for radon were correlated with a modified Freundlich equation.

Temperature and relative humidity can influence the adsorption capacity of radon on activated carbon to a great extent, depending on the physical properties of the carbon. Experiments were carried out to measure the radon uptake by an activated carbon in the presence of water vapor in a specially designed adsorption apparatus. The radon concentrations in the gas and solid phases were measured simultaneously once the adsorption equilibrium and the radioactive equilibrium between the radon daughter products were reached. The experiments in the presence of water vapor were carried out using two approaches. In one case the activated carbon was preequilibrated with water vapor prior to exposing it to radon. In the other case the carbon was exposed to a mixture of water vapor and radon. The uptake capacity for radon decreased substantially when both components were introduced together compared to when carbon was preequilibrated with water.

In diffuse reflectance spectroscopy the Kubelka-Munk equations have been used extensively. These equations provide simple solutions to the inverse problem of obtaining information on the scattering and absorption cross sections from reflected light. Proof is provided that the basic Kubelka-Munk equationdr(x)sdx=r2(x)-2ar(x)+1should be replaced by the equationdr(x)sdx=r2(x)-2(2a-1)r(x)+1and that the Kubelka-Munk functionks=(1-R∞)22R∞should be replaced by the functionks=(1-R∞)24R∞.Here r(x) is the reflectance; sis the scattering cross section (cm−1); a= (k+ s)/ s, where kis the absorption cross section (cm−1); and R∞is the reflection coefficient of an infinitely thick sample. We note, however, that because of a redefinition of acarried out by Kubelka and Munk in the process of their calculations, the scattering cross section scalculated from their expressionsd=112(1R∞-R∞)(coth-112(1R∞+R∞)-r(d)12(1R∞+R∞)-coth-112(1R∞+R∞)12(1R∞+R∞))is correct. But the Kubelka-Munk theory still overestimates kby a factor of two.

In the elementary solution method of the BGK model (Cercignani, 1962), the function [image omitted] plays a central role. In this paper some highly accurate values for the related integrals Qn (n=0 to 10) and Fn (n-0 to 20) are reported. As a consequence, numerically exact results (up to 15 significant digits) for the viscous slip, the thermal creep slip and some higher order slip coefficients are also given.

Adsorption isotherms of water vapor on molecular sieve 13X were obtained at 288, 298, and 308 K. The isotherms were of Type 1 and exhibited hysteresis upon desorption. The heat of adsorption data indicated that water was held on the surface by physical forces and the molecular sieve 13X provided a heterogeneous surface for the water vapor. The equilibrium data were correlated by the Polanyi potential theory and the theory of the pore volume filling proposed by Dubinin and co-workers.

The problem of planar condensation/evaporation of a monatomic vapor is solved based on the linearized Boltzmann equation. Accurate numerical results for the pressure and temperature jumps, and the macroscopic profiles for the density and temperature are reported for rigid sphere molecular interaction. Variational expressions for the jumps for several different molecular force laws are evaluated. For rigid spheres, these agree well with the numerical results but are otherwise found to be relatively insensitive to the intermolecular force laws.

It is shown that the work of Cercignani and Tironi on Maxwell's boundary conditions method can be improved in a simple and logical way. The technique for improvement is illustrated by a study of the linearized plane Couette flow problem and it is found that the proposed modification yields results that are identical with some highly accurate variational results.

A theoretical and experimental study of the phenomenon of diffusion slip in a binary gas mixture is presented. To provide some physical insight, a very general variational expression given earlier by Loyalka is rederived via the use of a method developed recently. The case of Maxwellian diffuse specular reflection is considered in some detail and the inadequacies of previous theoretical results based on the early arguments of Maxwell, kinetic models and simple intermolecular force laws are discussed. Although in general, the variational results (or the equivalent results given here) together with the assumptions of Lennard Jones potential and diffusive reflection give a satisfactory agreement with the available experimental data, it is found that for isobaric (isotopic) mixtures, in the choice of the intermolecular and gas-surface interaction parameters special care should be taken in that the results are quite sensitive to small variations in the values of these parameters.