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Full-Text Articles in Physics

Workshop Addresses Aviation Community, Jennifer Meehan, Joseph Kunches Aug 2012

Workshop Addresses Aviation Community, Jennifer Meehan, Joseph Kunches

Jennifer (Jinni) Meehan

No abstract provided.


The Second Annual Space Weather Community Operations Workshop: Advancing Operations Into The Next Decade, Jennifer Meehan, Jared Fulgham, Kent Tobiska Jul 2012

The Second Annual Space Weather Community Operations Workshop: Advancing Operations Into The Next Decade, Jennifer Meehan, Jared Fulgham, Kent Tobiska

Jennifer (Jinni) Meehan

No abstract provided.


Double Layer In Ionic Liquids: Overscreening Versus Crowding, Martin Z. Bazant, Brian D. Storey, Alexei A. Kornyshev Jul 2012

Double Layer In Ionic Liquids: Overscreening Versus Crowding, Martin Z. Bazant, Brian D. Storey, Alexei A. Kornyshev

Brian Storey

We develop a simple Landau-Ginzburg-type continuum theory of solvent-free ionic liquids and use it to predict the structure of the electrical double layer. The model captures overscreening from short-range correlations, dominant at small voltages, and steric constraints of finite ion sizes, which prevail at large voltages. Increasing the voltage gradually suppresses overscreening in favor of the crowding of counterions in a condensed inner layer near the electrode. This prediction, the ion profiles, and the capacitance-voltage dependence are consistent with recent computer simulations and experiments on room-temperature ionic liquids, using a correlation length of order the ion size.


Mixture Segregation Within Sonoluminescence Bubbles, Brian D. Storey, Andrew J. Szeri Jul 2012

Mixture Segregation Within Sonoluminescence Bubbles, Brian D. Storey, Andrew J. Szeri

Brian Storey

This paper concerns a relaxation of the assumption of uniform mixture composition in the interior of sonoluminescence bubbles. Intense temperature and pressure gradients within the bubble drive relative mass diffusion which overwhelms diffusion driven by concentration gradients. This thermal and pressure diffusion results in a robust compositional inhomogeneity in the bubble which lasts several orders of magnitude longer than the temperature peak or light pulse at the main collapse of the bubble. This effect has important consequences for control of sonoluminescence, gas dynamics, sonochemistry, and the physics of light production.


Tension-Induced Straightening Transition Of Self-Assembled Helical Ribbons, Yevgeniya V. Zastavker, Brice Smith, George B. Benedek Jun 2012

Tension-Induced Straightening Transition Of Self-Assembled Helical Ribbons, Yevgeniya V. Zastavker, Brice Smith, George B. Benedek

Yevgeniya V. Zastavker

Helical ribbons with pitch angles of either 11° or 54° self-assemble in a wide variety of quaternary surfactant-phospholipid/fatty acid-sterol-water systems. By elastically deforming these helices, we examined their response to uniaxial forces. Under sufficient tension, a low pitch helix reversibly separates into a straight domain with a pitch angle of 90° and a helical domain with a pitch angle of 16.5°. Using a newly developed continuum elastic free energy model, we have shown that this phenomenon can be understood as a first order mechanical phase transition.


A Depth-Averaged Electrokinetic Flow Model For Shallow Microchannels, Hao Lin, Brian D. Storey, Juan G. Santiago Mar 2012

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–Brinkman–Forchheimer-type …


Instability Of Electro-Osmotic Channel Flow With Streamwise Conductivity Gradients, Jose Santos, Brian D. Storey Mar 2012

Instability Of Electro-Osmotic Channel Flow With Streamwise Conductivity Gradients, Jose 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 …


Nonlinear Electrokinetics At Large Voltages, Martin Z. Bazant, Mustafa Sabri Kilic, Brian D. Storey, Armand Ajdari Mar 2012

Nonlinear Electrokinetics At Large Voltages, Martin Z. Bazant, Mustafa Sabri Kilic, Brian D. Storey, Armand Ajdari

Brian Storey

Part of Focus on Micro- and Nanofluidics The classical theory of electrokinetic phenomena assumes a dilute solution of point-like ions in chemical equilibrium with a surface whose double-layer voltage is of order the thermal voltage, kBT/e=25 mV. In nonlinear 'induced-charge' electrokinetic phenomena, such as ac electro-osmosis, several volts 100kBT/e are applied to the double layer, and the theory breaks down and cannot explain many observed features. We argue that, under such a large voltage, counterions 'condense' near the surface, even for dilute bulk solutions. Based on simple models, we predict that the double-layer capacitance decreases and the electro-osmotic mobility saturates …


Steric Effects On Ac Electro-Osmosis In Dilute Electrolytes, Brian D. Storey, Lee Edwards, Mustafa Sabri Kilic, Martin Z. Bazant Mar 2012

Steric Effects On Ac Electro-Osmosis In Dilute Electrolytes, Brian D. Storey, Lee 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 the ions and …


Rayleigh-Taylor Instability Of Violently Collapsing Bubbles, Hao Lin, Brian D. Storey, Andrew J. Szeri Mar 2012

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 bubbles. …


Bulk Electroconvective Instability At High Péclet Numbers, Brian D. Storey, Boris Zaltzman, Isaak Rubinstein Mar 2012

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, …


Field-Amplified Sample Stacking And Focusing In Nanofluidic Channels, Jess M. Sustarich, Brian D. Storey, Sumita Pennathur Mar 2012

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 …


Heat-Capacity And Magnetic Measurements On The Y(Ni2-XCoX)B2C System, C. C. Hoellwarth, P. Klavins, R. N. Shelton Mar 2012

Heat-Capacity And Magnetic Measurements On The Y(Ni2-XCoX)B2C System, C. C. Hoellwarth, P. Klavins, R. N. Shelton

Chance Hoellwarth

We have performed field-and temperature-dependent magnetization, resistivity, and heat-capacity measurements on polycrystalline samples of the Y(Ni2-xCox)B2C system with 0.0≤x≤0.4. Values of Tc ,x0,Hc2,ΘD,λ and N(Ed) were determined for various samples. We observe that ΘD increases with x, while all the other parameters decrease with x. The Tc vs x data can be described using the BCS theory and the measured values of N(Ef)and ΘD. The results suggest that the decrease in Tc is due to the decrease in N(Ef), in agreement with the results from band structure calculations.


Exposing Students To The Idea That Theories Can Change, Chance Hoellwarth, Matthew J. Moelter Feb 2012

Exposing Students To The Idea That Theories Can Change, Chance Hoellwarth, Matthew J. Moelter

Chance Hoellwarth

No abstract provided.


A Direct Comparison Of Conceptual Learning And Problem Solving Ability In Traditional And Studio Style Classrooms, Chance Hoellwarth, Matthew J. Moelter, Randall D. Knight Feb 2012

A Direct Comparison Of Conceptual Learning And Problem Solving Ability In Traditional And Studio Style Classrooms, Chance Hoellwarth, Matthew J. Moelter, Randall D. Knight

Chance Hoellwarth

We present data on student performance on conceptual understanding and on quantitative problem-solving ability in introductory mechanics in both studio and traditional classroom modes. The conceptual measures used were the Force Concept Inventory and the Force and Motion Conceptual Evaluation. Quantitative problem-solving ability was measured with standard questions on the final exam. Our data compare three different quarters over the course of 2 years. In all three quarters, the normalized learning gain in conceptual understanding was significantly larger for students in the studio sections. At the same time, students in the studio sections performed the same or slightly worse on …