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## Full-Text Articles in Mechanical Engineering

Argon Rectification And The Cause Of Light Emission In Single-Bubble Sonoluminescence, Brian D. Storey, Andrew J. Szeri

#### Argon Rectification And The Cause Of Light Emission In Single-Bubble Sonoluminescence, Brian D. Storey, Andrew J. Szeri

*Brian Storey*

In single-bubble sonoluminescence, repeated brief flashes of light are produced in a gas bubble strongly driven by a periodic acoustic field. A startling hypothesis has been made by Lohse and co-workers [Phys. Rev. Lett. 78, 1359 (1997)] that the non-noble gases in an air bubble undergo chemical reaction into soluble products, leaving only argon. In the present work, this dissociation hypothesis is supported by simulations, although the associated temperatures of about 7000 K seem too low for bremsstrahlung, which has been proposed as the dominant light emission mechanism. This suggests that emission from water vapor and its reaction products, heretofore ...

Shape Stability Of Sonoluminescence Bubbles: Comparison Of Theory To Experiments, Brian D. Storey

#### Shape Stability Of Sonoluminescence Bubbles: Comparison Of Theory To Experiments, Brian D. Storey

*Brian Storey*

Single bubble sonoluminescence (SBSL) is the brief flash of light emitted from a single, stable, acoustically forced bubble. In experiments, the maximum pressure amplitude with which a bubble may be forced is limited by considerations of spherical stability. The traditional linear stability analysis predicts a threshold for SBSL at a much lower pressure amplitude than experimental observations. This work shows that if one constructs an accurate model of the radial dynamics, the traditional linear stability analysis predicts a boundary that is in excellent agreement with experimental data.

Field-Amplified Sample Stacking And Focusing In Nanofluidic Channels, Jess M. Sustarich, Brian D. Storey, Sumita Pennathur

#### Field-Amplified Sample Stacking And Focusing In Nanofluidic Channels, Jess M. Sustarich, Brian D. Storey, Sumita Pennathur

*Brian Storey*

Nanofluidic technology is gaining popularity for bioanalytical applications due to advances in both nanofabrication and design. One major obstacle in the widespread adoption of such technology for bioanalytical systems is efficient detection of samples due to the inherently low analyte concentrations present in such systems. This problem is exacerbated by the push for electronic detection, which requires an even higher sensor-local sample concentration than optical detection. This paper explores one of the most common preconcentration techniques, field-amplified sample stacking, in nanofluidic systems in efforts to alleviate this obstacle. Holding the ratio of background electrolyte concentrations constant, the parameters of channel ...

Rayleigh-Taylor Instability Of Violently Collapsing Bubbles, Hao Lin, Brian D. Storey, Andrew J. Szeri

#### Rayleigh-Taylor Instability Of Violently Collapsing Bubbles, Hao Lin, Brian D. Storey, Andrew J. Szeri

*Brian Storey*

In a classical paper Plesset has determined conditions under which a bubble changing in volume maintains a spherical shape. The stability analysis was further developed by Prosperetti to include the effects of liquid viscosity on the evolving shape modes. In the present work the theory is further modified to include the changing density of the bubble contents. The latter is found to be important in violent collapses where the densities of the gas and vapor within a bubble may approach densities of the liquid outside. This exerts a stabilizing influence on the Rayleigh–Taylor mechanism of shape instability of spherical ...

Electrohydrodynamic Instabilities In Microchannels With Time Periodic Forcing, David A. Boy, Brian D. Storey

#### Electrohydrodynamic Instabilities In Microchannels With Time Periodic Forcing, David A. Boy, Brian D. Storey

*Brian Storey*

In microfluidic applications it has been observed that flows with spatial gradients in electrical conductivity are unstable under the application of sufficiently strong electric fields. These electrohydrodynamic instabilities can drive a nonlinear flow despite the low Reynolds number. Such flows hold promise as a simple mechanism for mixing fluids. In this work, the effect of a time periodic electric field on the instability is explored. The case where an electric field is applied across a diffuse interface of two fluids with varying electrical conductivity is considered. Frequency-dependent behavior is found only in the regime where the instability growth rates are ...

Bistability In A Simple Fluid Network Due To Viscosity Contrast, John B. Geddes, Brian D. Storey, David Gardner, Russell T. Carr

#### Bistability In A Simple Fluid Network Due To Viscosity Contrast, John B. Geddes, Brian D. Storey, David Gardner, Russell T. Carr

*Brian Storey*

We study the existence of multiple equilibrium states in a simple fluid network using Newtonian fluids and laminar flow. We demonstrate theoretically the presence of hysteresis and bistability, and we confirm these predictions in an experiment using two miscible fluids of different viscosity—sucrose solution and water. Possible applications include blood flow, microfluidics, and other network flows governed by similar principles.

Bulk Electroconvective Instability At High Péclet Numbers, Brian D. Storey, Boris Zaltzman, Isaak Rubinstein

#### Bulk Electroconvective Instability At High Péclet Numbers, Brian D. Storey, Boris Zaltzman, Isaak Rubinstein

*Brian Storey*

Bulk electroconvection pertains to flow induced by the action of a mean electric field upon the residual space charge in the macroscopic regions of a locally quasielectroneutral strong electrolyte. For a long time, controversy has existed in the literature as to whether quiescent electric conduction from such an electrolyte into a uniform charge-selective solid, such as a metal electrode or ion exchange membrane, is stable with respect to bulk electroconvection. While it was recently claimed that bulk electroconvective instability could not occur, this claim pertained to an aqueous, low-molecular-weight electrolyte characterized by an order-unity electroconvection Péclet number. In this paper ...

Instability Of Electro-Osmotic Channel Flow With Streamwise Conductivity Gradients, J. Jobim Santos, Brian D. Storey

#### Instability Of Electro-Osmotic Channel Flow With Streamwise Conductivity Gradients, J. Jobim Santos, Brian D. Storey

*Brian Storey*

This work considers the stability of an electro-osmotic microchannel flow with streamwise electrical conductivity gradients, a configuration common in microfluidic applications such as field amplified sample stacking. Previous work on such flows has focused on how streamwise conductivity gradients set a nonuniform electro-osmotic velocity which results in dispersion of the conductivity field. However, it has been known for many years that electric fields can couple with conductivity gradients to generate unstable flows. This work demonstrates that at high electric fields such an electrohydrodynamic instability arises in this configuration and the basic mechanisms are explored through numerical simulations. The instability is ...

Steric Effects On Ac Electro-Osmosis In Dilute Electrolytes, Brian D. Storey, Lee R. Edwards, Mustafa Sabri Kilic, Martin Z. Bazant

#### Steric Effects On Ac Electro-Osmosis In Dilute Electrolytes, Brian D. Storey, Lee R. Edwards, Mustafa Sabri Kilic, Martin Z. Bazant

*Brian Storey*

The current theory of alternating-current electro-osmosis (ACEO) is unable to explain the experimentally observed flow reversal of planar ACEO pumps at high frequency (above the peak, typically 10–100 kHz), low salt concentration (1–1000 μM), and moderate voltage (2–6 V), even taking into account Faradaic surface reactions, nonlinear double-layer capacitance, and bulk electrothermal flows. We attribute this failure to the breakdown of the classical Poisson-Boltzmann model of the diffuse double layer, which assumes a dilute solution of pointlike ions. In spite of low bulk salt concentration, the large voltage induced across the double layer leads to crowding of ...

A Depth-Averaged Electrokinetic Flow Model For Shallow Microchannels, Hao Lin, Brian D. Storey, Juan G. Santiago

#### A Depth-Averaged Electrokinetic Flow Model For Shallow Microchannels, Hao Lin, Brian D. Storey, Juan G. Santiago

*Brian Storey*

Electrokinetic flows with heterogeneous conductivity configuration occur widely in microfluidic applications such as sample stacking and multidimensional assays. Electromechanical coupling in these flows may lead to complex flow phenomena, such as sample dispersion due to electro-osmotic velocity mismatch, and electrokinetic instability (EKI). In this work we develop a generalized electrokinetic model suitable for the study of microchannel flows with conductivity gradients and shallow-channel geometry. An asymptotic analysis is performed with the channel depth-to-width ratio as a smallness parameter, and the three-dimensional equations are reduced to a set of depth-averaged equations governing in-plane flow dynamics. The momentum equation uses a Darcy ...