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in creator/contributor: "Griffiths, S.K."  
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Exchange front stability in packed-column chromatography

Description: Exchange front deformation in gas-phase chromatography may sometimes impair column performance. Such deformation can arise from column heterogeneities or from the unstable growth of small disturbances inherently present in the flow field. Here we examine the fundamental stability of a planar traveling exchange front subject to a small sinusoidal perturbation in the front position. The analysis includes the disparity between fluid and front velocities characteristic of exchange chromatography, a… more
Date: April 1, 1993
Creator: Griffiths, S. K. & Nilson, R. H.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

Condensation pressures in small pores: An analytical model based on density functional theory

Description: Adsorption and condensation are critical to many applications of porous materials including filtration, separation, and the storage of gases. Integral methods are used to derive an analytical expression describing fluid condensation pressures in slit pores bounded by parallel plane walls. To obtain this result, the governing equations of Density Functional Theory (DFT) are integrated across the pore width assuming that fluid densities within adsorbed layers are spatially uniform. The thickness,… more
Date: February 1, 1999
Creator: Nilson, R. H. & Griffiths, S. K.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

Hydrodynamic dispersion of a neutral non-reacting solute in electroosmotic flow

Description: Analytical methods are employed to determine the axial dispersion of a neutral non-reacting solute in an incompressible electroosmotic flow. In contrast to previous approaches, the dispersion is obtained here by solving the time-dependent diffusion-advection equation in transformed spatial and temporal coordinates to obtain the two-dimensional late-time concentration field. The coefficient of dispersion arises as a separation eigenvalue, and its value is obtained as a necessary condition for sa… more
Date: June 1, 1999
Creator: Griffiths, S. K. & Nilson, R. H.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

Band spreading in two-dimensional microchannel turns for electrophoretic or electroosmotic species transport

Description: Analytical and numerical methods are employed to investigate species transport by electrophoretic or electroosmotic motion in the curved geometry of a two-dimensional turn. Closed-form analytical solutions describing the turn-induced diffusive and dispersive spreading of a species band are presented for both the low and high Peclet number limits. The authors find that the spreading due to dispersion is proportional to the product of the turn included angle and the Peclet number at low Peclet nu… more
Date: March 1, 2000
Creator: Griffiths, S. K. & Nilson, R. H.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Electroosmotic fluid motion and late-time solute transport at non-negligible zeta potentials

Description: Analytical and numerical methods are employed to determine the electric potential, fluid velocity and late-time solute distribution for electroosmotic flow in a tube and channel when the zeta potential is not small. The electric potential and fluid velocity are in general obtained by numerical means. In addition, new analytical solutions are presented for the velocity in a tube and channel in the extremes of large and small Debye layer thickness. The electroosmotic fluid velocity is used to ana… more
Date: December 1, 1999
Creator: Griffiths, S. K. & Nilson, R. H.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

The influence of feature sidewall tolerance on minimum absorber thickness for LIGA x-ray masks

Description: Minimizing mask absorber thickness is an important practical concern in producing very small features by the LIGA process. To assist in this minimization, the authors have developed coupled numerical models describing both the exposure and development of a thick PMMA resist. The exposure model addresses multi-wavelength, one-dimensional x-ray transmission through multiple beam filters, through the mask substrate and absorber, and the subsequent attenuation and photon absorption in the PMMA resi… more
Date: February 1, 1999
Creator: Griffiths, S. K.; Hruby, J. M. & Ting, A.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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A locally analytic density functional theory describing adsorption and condensation in microporous materials

Description: The fluid density distribution within microscopic pores is determined by solving integral equations relating to the local chemical potential to the Van der Waals attractions and hard sphere repulsions of surrounding material. To avoid resolving the density distribution on sub-molecular scales, the governing equations are averaged over zones of molecular size using analytic functions to represent local density variations within each zone. These local density profiles range form singularities to … more
Date: February 1, 1997
Creator: Nilson, R. H. & Griffiths, S. K.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

Processing solid propellants for recycling

Description: Rapid evolution in the structure of military forces worldwide is resulting in the retirement of numerous weapon systems. Many of these systems include rocket motors containing highly energetic propellants based on hazardous nitrocellulose/nitroglycerin (NC/NG) mixtures. Even as the surplus quantities of such material increases, however, current disposal methods -- principally open burning and open detonation (OB/OD) -- are coming under close scrutiny from environmental regulators. Environmental… more
Date: May 1, 1994
Creator: Whinnery, L. L.; Griffiths, S. K.; Handrock, J. L. & Lipkin, J.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Optimum conditions for composites fiber coating by chemical vapor infiltration

Description: A combined analytical and numerical method is employed to optimize process conditions for composites fiber coating by chemical vapor infiltration (CVI). For a first-order deposition reaction, the optimum pressure yielding the maximum deposition rate at a preform center is obtained in closed form and is found to depend only on the activation energy of the deposition reaction, the characteristic pore size, and properties of the reactant and product gases. It does not depend on the preform specifi… more
Date: April 1997
Creator: Griffiths, S. K. & Nilson, R. H.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

Deposition uniformity, particle nucleation and the optimum conditions for CVD in multi-wafer furnaces

Description: A second-order perturbation solution describing the radial transport of a reactive species and concurrent deposition on wafer surfaces is derived for use in optimizing CVD process conditions. The result is applicable to a variety of deposition reactions and accounts for both diffusive and advective transport, as well as both ordinary and Knudsen diffusion. Based on the first-order approximation, the deposition rate is maximized subject to a constraint on the radial uniformity of the deposition … more
Date: June 1, 1996
Creator: Griffiths, S. K. & Nilson, R. H.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

In situ bioremediation: A network model of diffusion and flow in granular porous media

Description: In situ bioremediation is a potentially expedient, permanent and cost- effective means of waste site decontamination. However, permeability reductions due to the transport and deposition of native fines or due to excessive microorganism populations may severely inhibit the injection of supplemental oxygen in the contamination zone. To help understand this phenomenon, we have developed a micro-mechanical network model of flow, diffusion and particle transport in granular porous materials. The mo… more
Date: April 1997
Creator: Griffiths, S. K.; Nilson, R. H. & Bradshaw, R. W.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

Modeling electrodeposition for LIGA microdevice fabrication

Description: To better understand and to help optimize the electroforming portion of the LIGA process, we have developed one and two-dimensional numerical models describing electrode-position of metal into high aspect-ratio molds. The one-dimensional model addresses dissociation, diffusion, electromigration, and deposition of multiple ion species. The two-dimensional model is limited to a single species, but includes transport induced by forced flow of electrolyte outside the mold and by buoyancy associated… more
Date: February 1, 1998
Creator: Griffiths, S. K.; Nilson, R. H. & Bradshaw, R. W.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

Conditions for similitude between the fluid velocity and electric field in electroosmotic flow

Description: Electroosmotic flow is fluid motion driven by an electric field acting on the net fluid charge produced by charge separation at a fluid-solid interface. Under many conditions of practical interest, the resulting fluid velocity is proportional to the local electric field, and the constant of proportionality is everywhere the same. Here the authors show that the main conditions necessary for this similitude are a steady electric field, uniform fluid and electric properties, an electric Debye laye… more
Date: April 1, 1999
Creator: Cummings, E. B.; Griffiths, S. K.; Nilson, R. H. & Paul, P. H.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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