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Papers by Sarah Beskok

Transactions of the Asme Serie C Journal of Heat Transfer, Jun 1, 2003

Numerical simulations of laminar, forced convection heat transfer for reciprocating, twodimension... more Numerical simulations of laminar, forced convection heat transfer for reciprocating, twodimensional channel flows are performed as a function of the penetration length, Womersley (␣) and Prandtl (Pr) numbers. The numerical algorithm is based on a spectral element formulation, which enables high-order spatial resolution with exponential decay of discretization errors, and second-order time-accuracy. Uniform heat flux and constant temperature boundary conditions are imposed on certain regions of the top surface, while the bottom surface is kept insulated. Periodicity of velocity and temperature fields is imposed on the side boundaries, while the flow is driven by an oscillating pressure gradient. These sets of boundary conditions enable time-periodic solution of the problem. Instantaneous and time-averaged surface and bulk temperature distributions, and Nusselt number variations are presented. For high ␣ flows, the temperature field is significantly affected by the Richardson's annular effect. Overall, forced convection increases by increasing the penetration length, ␣ and Pr. Corresponding steady-flow simulations are performed by matching the volumetric flowrate. For the limited parameter space investigated in this paper, steady unidirectional forced convection is more effective than the reciprocating flow forced convection.

Http Dx Doi Org 10 1080 104077802317221366, Nov 30, 2010

ABSTRACT

Analytical Chemistry, Mar 1, 2009

We demonstrate negative dielectrophoresis (DEP) trapping of particles from high-conductivity medi... more We demonstrate negative dielectrophoresis (DEP) trapping of particles from high-conductivity media using a novel planar microelectrode that allows electrothermal enhancement of DEP traps. DEP force and electrothermal flow motion are investigated using a scaling analysis, numerical simulations, and experiments. Results show that the DEP trapping is enhanced by lateral transport of particles toward the capture zones due to electrothermal flow, whereas DEP trapping occurred only in limited spatial ranges without the flow motion. The electrothermally enhanced DEP will broaden the limit of electrokinetic manipulations in high-conductivity media. By providing patterned trapping zones that can act as target-specific attachment/detection sites, the presented device allows development of biosensor applications for rapid detection of pathogens and other microorganisms within a practical range of buffer conductivity.

Abstract Flow past a cylinder with a flexible splitter plate is modeled by the coupling of incomp... more Abstract Flow past a cylinder with a flexible splitter plate is modeled by the coupling of incompressible Navier-Stokes equations with the membrane equation. The fluid/structure coupling is achieved by an Arbitrary Eulerian Lagrangian (ALE) formulation, which allows``arbitrary&quot; motion of the fluid/plate interface. The interaction is accomplished by incorporating the instantaneous pressure distribution on the flexible plate with the resultant deformation, velocity and acceleration of the fluid/plate interface. The fluid/structure ...

Abstract Electroosmotically driven flows in micro-channels are analyzed analytically and numerica... more Abstract Electroosmotically driven flows in micro-channels are analyzed analytically and numerically by using a high-order h/p type spectral element simulation suite, Nektar. The high-resolution characteristic of the spectral element method enables us to resolve the sharp electric double layers with successive p-type mesh refinements. For electric double layers that are much smaller than the channel height, the Helmholtz Smoluchowski velocity is used to develop semi-analytical relations for the velocity and the pressure distributions in micro ...

We simulate the electrophoretic motion of individual microtubules in microchannels in order to ob... more We simulate the electrophoretic motion of individual microtubules in microchannels in order to obtain their anisotropic mobility and compare with recent experimental results (van den Heuvel et al., PNAS, 2007). We include for comparison simulation results for a circular cylinder with a similar``effective&amp;#x27;&amp;#x27;radius, in order to examine how the surface roughness of microtubules affects the electrical double layer, the externally applied field, and hence the electrophoretic mobility. The simulation method is based on the smoothed profile method ( ...

Volume 10: Micro- and Nano-Systems Engineering and Packaging, 2013

ABSTRACT In this paper, the performance of a PDMS-based microfluidic device is thoroughly charact... more ABSTRACT In this paper, the performance of a PDMS-based microfluidic device is thoroughly characterized for detecting continuous static and dynamic loads. This device comprises of a single PDMS rectangular microstructure and a set of electrolyte-enabled distributed transducers. It is fabricated by a standard fabrication process well developed for PDMS-based microfluidic devices. One potential application of this device is to measure spatially-varying mechanical properties of heterogeneous soft materials, through quasi-static, stress relaxation and dynamic mechanical analysis (DMA) tests. Thus, the response of this device to three types of inputs: static, step and sinusoidal, is examined with a custom experimental setup. For the first time, the capability of using a polymer-based microfluidic device to detect sinusoidal inputs is reported. The characterized results demonstrate the potential of using this device to measure soft materials.

Biophysical Journal, 2014

Electromanipula/on of cells, which includes dielectrophoresis, electrorota/on, and electrophoresi... more Electromanipula/on of cells, which includes dielectrophoresis, electrorota/on, and electrophoresis, as a label free cell manipula/on and characteriza/on tool has gained par/cular interest recently. However, the applicability of electromanipula/on to biological cells is limited to cells suspended in special types of media containing lower amounts of salts in comparison to physiological buffers. Impedance measurements of cells are o?en performed in low conduc/ve buffers, mainly due to parasi/c capacitance that occurs at the electrode electrolyte interface. One might ques/on the use of electromanipula/on buffers as it results in lower membrane ac/vity and possible increased cellular death. Therefore, in this study, effects of electromanipula/on buffers with varying salt concentra/ons on cellular viability and membrane ac/vity was studied for a human T--cell leukemia cell line (Jurkat). Cellular viability was measured in vitro using an MTT cell viability assay. Cellular death was also measured using the trypan blue dye exclusion method. Membrane capacitance and conductance was measured by impedance spectroscopy over a range of extracellular salt concentra/ons. We described the cell membrane conductance at different extracellular salt concentra/ons using a quan/ta/ve model. Even though membrane conductance measurements by impedance spectroscopy is indica/ve of number and ac/vity of ion channels even performed at low extracellular salt levels; results indicate that cells in electromanipula/on buffers have reduced viability. Strategies to increase metabolic ac/vity by changing buffer composi/on while s/ll retaining the performance of impedance spectroscopy and electromanipula/on are also presented.

Electrophoresis, 2015

Electromanipulation of cells as a label-free cell manipulation and characterization tool has gain... more Electromanipulation of cells as a label-free cell manipulation and characterization tool has gained particular interest recently. However, the applicability of electromanipulation, particularly dielectrophoresis (DEP), to biological cells is limited to cells suspended in buffers containing lower amounts of salts relative to the physiological buffers. One might question the use of low conductivity buffers (LCBs) for DEP separation, as cells are stressed in buffers lacking physiological levels of salt. In LCB, cells leak ions and undergo volume regulation. Therefore, cells exhibit time-dependent DEP response in LCB. In this work, cellular changes in LCB are assessed by dielectric spectroscopy, cell viability assay, and gene expression of chondrocytes and Jurkats. Results indicate leakage of ions from cells, increases in cytoplasmic conductivity, membrane capacitance, and conductance. Separability factor, which defines optimum conditions for DEP cell separation, for the two cell types ...

Journal of Micromechanics and Microengineering, 2003

The bulging of microfluidic systems during pressure-driven flow is potentially a major considerat... more The bulging of microfluidic systems during pressure-driven flow is potentially a major consideration for polydimethylsiloxane (PDMS)-based devices. Microchannel cross-sectional areas can change drastically as a function of flow rate and downstream microchannel position. Such geometrical flexibility leads to difficulties in predicting convective/diffusive transport for these systems. We have previously introduced a non-dimensional parameter, κ, for characterizing convection and diffusion behavior

Journal of Heat Transfer, 2001

The micro heat spreader (MHS) is a micro-fluidic device designed for thermal management of microe... more The micro heat spreader (MHS) is a micro-fluidic device designed for thermal management of microelectronic components. It connects two reservoirs by a set of micro-channels (Fig. 1). The bottom surfaces of the reservoirs are membranes that are driven with a phase difference of π, either by electrostatic or piezoelectric actuation. The idea is to minimize the chip surface temperature by oscillatory flow forced convection and mixing. Numerical simulations are performed for an MHS device with channel to reservoir expansion ratio H/h 25. The ...

International Journal of Computational Engineering Science, 2001

Performance analysis of a reversible micro-pump system is obtained by numerical simulations. The ... more Performance analysis of a reversible micro-pump system is obtained by numerical simulations. The unsteady incompressible Navier-Stokes equations are solved in a moving micro-pump system using a spectral h/p element algorithm, employing an arbitrary Lagrangian Eulerian (ALE) formulation on structured/unstructured meshes. The performance of the micro-pump is evaluated as a function of the Reynolds number and the geometric parameters. The volumetric flowrate is shown to increase as a function of the Reynolds number. The unsteady traction forces on the pump membrane and the vorticity dynamics within the pump cavity are presented.

Computers & Fluids, 2014

The objective of the present paper is to provide a challenging and well-defined validation test c... more The objective of the present paper is to provide a challenging and well-defined validation test case for fluid-structure interaction (FSI) in turbulent flow to close a gap in the literature. The following list of requirements are taken into account during the definition and setup phase. First, the test case should be geometrically simple which is realized by a classical cylinder flow configuration extended by a flexible structure attached to the backside of the cylinder. Second, clearly defined operating and boundary conditions are a must and put into practice by a constant inflow velocity and channel walls. The latter are also evaluated against a periodic setup relying on a subset of the computational domain. Third, the material model should be widely used. Although a rubber plate is chosen as the flexible structure, it is demonstrated by additional structural tests that a classical St. Venant-Kirchhoff material model is sufficient to describe the material behavior appropriately. Fourth, the flow should be in the turbulent regime. Choosing water as the working fluid and a medium-size water channel, the resulting Reynolds number of Re = 30, 470 guarantees a sub-critical cylinder flow with transition taking place in the separated shear layers. Fifth, the test case results should be underpinned by a detailed validation process. For this purpose complementary numerical and experimental investigations were carried out. Based on optical contactless measuring techniques (particle-image velocimetry and laser distance sensor) the phase-averaged flow field and the structural deformations were determined. These data were compared with corresponding numerical predictions relying on large-eddy simulations and a recently developed semi-implicit predictor-corrector FSI coupling scheme. Both results were found to be in close agreement showing a quasi-periodic oscillating flexible structure in the first swiveling FSI mode with a corresponding Strouhal number of about St FSI = 0.11.

Biophysical Journal, 2013

have further influence in the binding of the drug to form transport and regulatory complexes. Our... more have further influence in the binding of the drug to form transport and regulatory complexes. Our findings point out that BSAn has more potency than BSA agent in delivering anticancer drug emodin.

Proceedings of ASME IMECE Meeting, MEMS, 2000

Ann Arbor

FEBRUARY 2002 VOLUME 11 NUMBER 1 JMIYET (ISSN 1057-7157) ... 2 An Extraction-Based Verification M... more FEBRUARY 2002 VOLUME 11 NUMBER 1 JMIYET (ISSN 1057-7157) ... 2 An Extraction-Based Verification Methodology for MEMS B. Baidya, SK Gupta, and T. Mukherjee ... 12 Measurements and Modeling of Two-Phase Flow in Microchannels With Nearly Constant Heat Flux Boundary Conditions L. Zhang, J.-M. Koo, L. Jiang, M. Asheghi, KE Goodson, JG Santiago, and TW Kenny ... 20 Design Considerations of Rectangular Electrostatic Torsion Actuators Based on New Analytical Pull-in Expressions O. Degani and Y. Nemirovsky ... 27 The Strain Gradient Effect in ...

RLE Progress report, 1997

RefDoc Refdoc est un service / is powered by. www.cnrs.fr www.inist.fr Bookmark and Share. Découv... more RefDoc Refdoc est un service / is powered by. www.cnrs.fr www.inist.fr Bookmark and Share. Découvrir / Discover. Refdoc. EXPORT. Mendeley to Mendeley. EndNote to EndNote. INIST-CNRS. 2, Allée du Parc de Brabois CS 10310 F-54519 Vandoeuvre-lès-Nancy Cedex France Phone: +33 (0)3 83 50 46 64 Fax: +33 (0)3 83 50 46 66. Nous contacter Contact us. Faire une nouvelle recherche Make a new search. Commander ce document, ok. Order this document, ok. Titre du document / Document title. Computational prototyping tools and techniques. ...

APS Meeting Abstracts, Nov 1, 1999

Electroosmotically driven flows in micro-channels are analyzed analytically and numerically by us... more Electroosmotically driven flows in micro-channels are analyzed analytically and numerically by using a high-order h/p type spectral element simulation suite, Nektar. The high-resolution characteristic of the spectral element method enables us to resolve the sharp electric double layers with successive p-type mesh refinements. For electric double layers that are much smaller than the channel height, the Helmholtz Smoluchowski velocity is used to develop semi-analytical relations for the velocity and the pressure distributions in micro ...