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Statistical Quantities (statistical + quantity)

Distribution by Scientific Domains

Engineering	40%
Chemistry	40%

Selected Abstracts

PIV measurement and turbulence scale in turbulent combustion

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 7 2006
Kazuhiro Yamamoto
Abstract We have investigated turbulent combustion by PIV (Particle Image Velocimetry) technique. Comparing with LDV data, the validity of PIV measurements has been confirmed. Particularly, the conditions of sampling number and spatial resolution have been shown to yield reliable data using PIV. Based on the velocity fields in cold flow and combustion, the interaction between flame and flow has been discussed. It was observed that the flow field is changed by combustion and the turbulence is reduced. In order to determine statistical quantities such as mean velocity and RMS of velocity fluctuation, a sampling number of 1000 is needed. Moreover, the velocity correlation coefficient was evaluated to obtain the integral length scale of the flow. For both cold flow and combustion, the PIV estimated scale is very close to that of LDV based on the assumption of Taylor's hypothesis. As a result, the spatial resolution in this study is about 6 times smaller than the integral length scale. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(7): 501,512, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20129 [source]

Assessment of non-Fickian subgrid-scale models for passive scalar in a channel flow

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 1 2005
E. Montreuil
Abstract In order to assess new subgrid-scale (SGS) models for a passive scalar, several large eddy simulations of a turbulent channel flow with passive scalar, for various Prandtl numbers ranging from 0.1 to 2.0 are carried out. These models are not based on the classical Fickian approximation and do not necessarily induce an alignment between the SGS heat flux vector and the gradient of the resolved temperature. Five SGS models are investigated on two grids. To validate the simulations, statistical quantities such as mean temperature, temperature variance and turbulent heat flux are compared with available data obtained by direct numerical simulation (DNS). The SGS dissipation is computed for different models in order to analyse its behaviour. The turbulence structures based on instantaneous velocity and temperature are described to study the correlations between these two fields. Among the assessed models, those consisting in Fickian and non-Fickian parts seem to be full of promise. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Molecular surface electrostatic potentials in relation to noncovalent interactions in biological systems

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2001
Peter Politzer
Abstract Noncovalent interactions are predominantly electrostatic in nature. It follows that an effective tool for their investigation and elucidation is the electrostatic potential on the molecular surface. We have shown that a variety of condensed phase macroscopic properties can be expressed quantitatively in terms of certain site-specific and global statistical quantities that characterize the overall pattern of the surface potential. We are now extending this approach to interactions in biological systems. Several applications will be discussed, including initial qualitative studies of dioxins, a series of anticonvulsants and some tetracyclines, the nucleotide bases, and a recent quantitative treatment of the anti-HIV activities of three groups of reverse transcriptase inhibitors. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001 [source]

Flow of particles suspended in a sheared viscous fluid: Effects of finite inertia and inelastic collisions

AICHE JOURNAL, Issue 10 2010
Micheline Abbas
Abstract We investigate in this article the macroscopic behavior of sheared suspensions of spherical particles. The effects of the fluid inertia, the Brownian diffusion, and the gravity are neglected. We highlight the influence of the solid-phase inertia on the macroscopic behavior of the suspension, considering moderate to high Stokes numbers. Typically, this study is concerned with solid particles O (100 ,m) suspended in a gas with a concentration varying from 5% to 30%. A hard-sphere collision model (with elastic or inelasic rebounds) coupled with the particle Lagrangian tracking is used to simulate the suspension dynamics in an unbounded periodic domain. We first consider the behavior of the suspension with perfect elastic collisions. The suspension properties reveal a strong dependence on the particle inertia and concentration. Increasing the Stokes number from 1 to 10 induces an enhancement of the particle agitation by three orders of magnitude and an evolution of the probability density function of the fluctuating velocity from a highly peaked (close to the Dirac function) to a Maxwellian shape. This sharp transition in the velocity distribution function is related to the time scale which controls the overall dynamics of the suspension flow. The particle relaxation (resp. collision) time scale dominates the particulate phase behavior in the weakly (resp. highly) agitated suspensions. The numerical results are compared with the prediction of two statistical models based on the kinetic theory for granular flows adapted to moderately inertial regimes. The suspensions have a Newtonian behavior when they are highly agitated similarly to rapid granular flows. However, the stress tensors are highly anisotropic in weakly agitated suspensions as a difference of normal stresses arises. Finally, we discuss the effect of energy dissipation due to inelastic collisions on the statistical quantities. We also tested the influence of a simple modeling of local hydrodynamic interactions during the collision by using a restitution coefficient which depends on the local impact velocities. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source]

Random Deposition as a Growth Mode in Atomic Layer Deposition,

CHEMICAL VAPOR DEPOSITION, Issue 3 2004
R.L. Puurunen
Abstract Despite the increasing number of successful applications of material growth by atomic layer deposition (ALD), the description of many physicochemical processes that occur during ALD growth is still incomplete. The way the material is arranged on the surface during ALD growth, called the ALD growth mode, defines important material properties, such as when the substrate gets fully covered by the ALD-grown material, and the surface roughness. This work initiates the theoretical description of ALD growth modes by describing the random deposition growth mode, both qualitatively and quantitatively, by using the growth per cycle as a statistical quantity. [source]