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Full-Text Articles in Physical Sciences and Mathematics

Computerizing Efficient Estimation Of A Pathwise Differentiable Target Parameter, Mark J. Van Der Laan, Marco Carone, Alexander R. Luedtke Oct 2015

Computerizing Efficient Estimation Of A Pathwise Differentiable Target Parameter, Mark J. Van Der Laan, Marco Carone, Alexander R. Luedtke

Alex Luedtke

Frangakis et al. (2015) proposed a numerical method for computing the efficient influence function of a parameter in a nonparametric model at a specified distribution and observation (provided such an influence function exists). Their approach is based on the assumption that the efficient influence function is given by the directional derivative of the target parameter mapping in the direction of a perturbation of the data distribution defined as the convex line from the data distribution to a pointmass at the observation. In our discussion paper Luedtke et al. (2015) we propose a regularization of this procedure and establish the validity …

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Capacity Planning With Financial And Operational Hedging In Low‐Cost Countries, Lijian Chen, Shanling Li, Letian Wang Sep 2015

Capacity Planning With Financial And Operational Hedging In Low‐Cost Countries, Lijian Chen, Shanling Li, Letian Wang

Lance (Lijian) Chen

The authors of this paper outline a capacity planning problem in which a risk-averse firm reserves capacities with potential suppliers that are located in multiple low-cost countries. While demand is uncertain, the firm also faces multi-country foreign currency exposures. This study develops a mean-variance model that maximizes the firm’s optimal utility and derives optimal utility and optimal decisions in capacity and financial hedging size. The authors show that when demand and exchange rate risks are perfectly correlated, a risk- averse firm, by using financial hedging, will achieve the same optimal utility as a risk-neutral firm. In this paper as well, …

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A Simulation-Based Approach To Solve A Specific Type Of Chance Constrained Optimization, Lijian Chan Sep 2015

A Simulation-Based Approach To Solve A Specific Type Of Chance Constrained Optimization, Lijian Chan

Lance (Lijian) Chen

We solve the chance constrained optimization with convex feasible set through approximating the chance constraint by another convex smooth function. The approximation is based on the numerical properties of the Bernstein polynomial that is capable of effectively controlling the approximation error for both function value and gradient. Thus, we adopt a first-order algorithm to reach a satisfactory solution which is expected to be optimal. When the explicit expression of joint distribution is not available, we then use Monte Carlo approach to numerically evaluate the chance constraint to obtain an optimal solution by probability. Numerical results for known problem instances are …

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Re-Solving Stochastic Programming Models For Airline Revenue Management, Lijian Chen, Tito Homem-De-Mello Sep 2015

Re-Solving Stochastic Programming Models For Airline Revenue Management, Lijian Chen, Tito Homem-De-Mello

Lance (Lijian) Chen

We study some mathematical programming formulations for the origin-destination model in airline revenue management. In particular, we focus on the traditional probabilistic model proposed in the literature. The approach we study consists of solving a sequence of two-stage stochastic programs with simple recourse, which can be viewed as an approximation to a multi-stage stochastic programming formulation to the seat allocation problem. Our theoretical results show that the proposed approximation is robust, in the sense that solving more successive two-stage programs can never worsen the expected revenue obtained with the corresponding allocation policy. Although intuitive, such a property is known not …

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Ancillary Service Capacity Optimization For Both Electric Power Suppliers And Independent System Operator, Lijian Chen, Dengfeng Sun, Guang Li Sep 2015

Ancillary Service Capacity Optimization For Both Electric Power Suppliers And Independent System Operator, Lijian Chen, Dengfeng Sun, Guang Li

Lance (Lijian) Chen

Ancillary Services (AS) in electric power industry are critical to support the transmission of energy from generators to load demands while maintaining reliable operation of transmission systems in accordance with good utility practice. The ancillary services are procured by the independent system operator (ISO) through a process called the market clearing process which can be modeled by the partial equilibrium from the ends of ISO. There are two capacity optimization problems for both Market participants (MP) and Independent System Operator (ISO). For a market participant, the firm needs to determine the capacity allocation plan for various AS to pursue operating …

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Capacity-Driven Pricing Mechanism In Special Service Industries, Lijian Chen, Suraj M. Alexander Sep 2015

Capacity-Driven Pricing Mechanism In Special Service Industries, Lijian Chen, Suraj M. Alexander

Lance (Lijian) Chen

We propose a capacity driven pricing mechanism for several service industries in which the customer behavior, the price demand relationship, and the competition are significantly distinct from other industries. According our observation, we found that the price demand relationship in these industries cannot be modeled by fitted curves; the customers would neither plan in advance nor purchase the service strategically; and the competition would be largely local. We analyze both risk neutral and risk aversion pricing models and conclude the proposed capacity driven model would be the optimal solution under mild assumptions. The resulting pricing mechanism has been implemented at …

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Fast Super-Resolution With Affine Motion Using An Adaptive Wiener Filter And Its Application To Airborne Imaging, Russell C. Hardie, Kenneth J. Barnard, Raúl Ordóñez May 2015

Fast Super-Resolution With Affine Motion Using An Adaptive Wiener Filter And Its Application To Airborne Imaging, Russell C. Hardie, Kenneth J. Barnard, Raúl Ordóñez

Raúl Ordóñez

Fast nonuniform interpolation based super-resolution (SR) has traditionally been limited to applications with translational interframe motion. This is in part because such methods are based on an underlying assumption that the warping and blurring components in the observation model commute. For translational motion this is the case, but it is not true in general. This presents a problem for applications such as airborne imaging where translation may be insufficient. Here we present a new Fourier domain analysis to show that, for many image systems, an affine warping model with limited zoom and shear approximately commutes with the point spread function …

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Research In Mathematics Educational Technology: Current Trends And Future Demands, Shannon O. Driskell, Robert N. Ronau, Christopher R. Rakes, Sarah B. Bush, Margaret L. Niess, David K. Pugalee May 2015

Research In Mathematics Educational Technology: Current Trends And Future Demands, Shannon O. Driskell, Robert N. Ronau, Christopher R. Rakes, Sarah B. Bush, Margaret L. Niess, David K. Pugalee

Shannon O.S. Driskell

This systematic review of mathematics educational technology literature identified 1356 manuscripts addressing the integration of educational technology into mathematics instruction. The manuscripts were analyzed using three frameworks (Research Design, Teacher Knowledge, and TPACK) and three supplementary lenses (Data Sources, Outcomes, and NCTM Principles) to produce a database to support future research syntheses and meta-analyses. Preliminary analyses of student and teacher outcomes (e.g., knowledge, cognition, affect, and performance) suggest that the effects of incorporating graphing calculator and dynamic geometry technologies have been abundantly studied; however, the usefulness of the results was often limited by missing information regarding measures of validity, reliability, …

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Prospective Teachers' Use Of Representations In Solving Statistical Tasks With Dynamic Statistical Software, Hollylynne Lee, Shannon O. Driskell, Suzanne R. Harper, Keith R. Leatham, Gladis Kersaint, Robin L. Angotti May 2015

Prospective Teachers' Use Of Representations In Solving Statistical Tasks With Dynamic Statistical Software, Hollylynne Lee, Shannon O. Driskell, Suzanne R. Harper, Keith R. Leatham, Gladis Kersaint, Robin L. Angotti

Shannon O.S. Driskell

This study examined a random stratified sample (n=62) of prospective teachers' work across eight institutions on three tasks that utilized dynamic statistical software. Our work was guided by considering how teachers may utilize their statistical knowledge and technological statistical knowledge to engage in cycles of investigation. Although teachers did not tend to take full advantage of dynamic linking capabilities, they utilized a large variety of graphical representations and often added statistical measures or other augmentations to graphs as part of their analysis.

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Trials Of The Urban Ecologist, Rebecca W. Dolan, Tim Carter, Travis J. Ryan, Carmen M. Salsbury, Thomas E. Dolan, Marjorie Hennessy Feb 2015

Trials Of The Urban Ecologist, Rebecca W. Dolan, Tim Carter, Travis J. Ryan, Carmen M. Salsbury, Thomas E. Dolan, Marjorie Hennessy

Travis J. Ryan

A group of scientists describe some of the obstacles encountered and insights gained while carrying out ecological research in and around the city of Indianapolis.

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Laminar Flow Of Two Miscible Fluids In A Simple Network, Casey Karst, Brian Storey, John B. Geddes Sep 2013

Laminar Flow Of Two Miscible Fluids In A Simple Network, Casey Karst, Brian Storey, John B. Geddes

Brian Storey

When a fluid comprised of multiple phases or constituents flows through a network, nonlinear phenomena such as multiple stable equilibrium states and spontaneous oscillations can occur. Such behavior has been observed or predicted in a number of networks including the flow of blood through the microcirculation, the flow of picoliter droplets through microfluidic devices, the flow of magma through lava tubes, and two-phase flow in refrigeration systems. While the existence of nonlinear phenomena in a network with many inter-connections containing fluids with complex rheology may seem unsurprising, this paper demonstrates that even simple networks containing Newtonian fluids in laminar flow …

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Causes Of Uprooting And Breakage Of Specimen Giant Sequoia Trees, Douglas D. Piirto, W. Wayne Wilcox, John R. Parmeter, Jr., David L. Wood Feb 2013

Causes Of Uprooting And Breakage Of Specimen Giant Sequoia Trees, Douglas D. Piirto, W. Wayne Wilcox, John R. Parmeter, Jr., David L. Wood

Douglas D. Piirto

A study of the causes of uprooting and stem failure in old-growth giant sequoia (Sequoia gigantea [Lindl.] Decne) indicated many factors, depending upon the type of failure (by root, stem, or earth). Advanced decay and fire scars were the most frequently associated with failure. In 21 of 33 study trees, one-third or more of the roots were judged too decayed to provide support. Twenty-seven study trees possessed basal fire scars, and 26 fell toward the scarred side. Nine Basidiomycetes, including Fomes annosus, Poria albipellucida, Poria incrassata, and Armillaria mellea, were associated with decayed wood. Carpenter ants were found in or …

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Editorial: Social Implications Of Technology- “Il Buono, Il Brutto, Il Cattivo”, Katina Michael Aug 2012

Editorial: Social Implications Of Technology- “Il Buono, Il Brutto, Il Cattivo”, Katina Michael

Professor Katina Michael

Late last year, IEEE SSIT was invited to put together a paper for the centennial edition of Proceedings of the IEEE that was published in May 2012. The paper titled, “Social Implications of Technology: The Past, the Present, and the Future,” brought together five members of SSIT with varying backgrounds, and two intense months of collaboration and exchange of ideas. I personally felt privileged to be working with Karl D. Stephan, Emily Anesta, Laura Jacobs and M.G. Michael on this project.

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

Workshop Addresses Aviation Community, Jennifer Meehan, Joseph Kunches

Jennifer (Jinni) Meehan

No abstract provided.

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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.

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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.

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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.

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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.

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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 …

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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 …

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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 …

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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 …

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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. …

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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, …

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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 …

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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.

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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.

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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 …

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Distribution Changes Of American Martens And Fishers In Eastern North America, 1699–2001 - Chapter 4, William Krohn Dec 2011

Distribution Changes Of American Martens And Fishers In Eastern North America, 1699–2001 - Chapter 4, William Krohn

William B. Krohn

This chapter provides an example of the type of technical analysis that can be done with information in Early Maine Wildlife by Krohn and Hoving (2010).

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Reverse Drag Revisited: Why Footwall Deformation May Be The Key To Inferring Listric Fault Geometry, Phillip G. Resor, David D. Pollard Dec 2011

Reverse Drag Revisited: Why Footwall Deformation May Be The Key To Inferring Listric Fault Geometry, Phillip G. Resor, David D. Pollard

Phillip G Resor

Although reverse drag, the down warping of hanging wall strata toward a normal fault, is widely accepted as an indicator of listric fault geometry, previous studies have shown that similar folding may form in response to slip on faults of finite vertical extent with listric or planar geometry. In this study we therefore seek more general criteria for inferring subsurface fault geometry from observations of near-surface deformation by directly comparing patterns of displacement, stress, and strain around planar and listric faults, as predicted by elastic boundary element models. In agreement with previous work, we find that models with finite planar, …

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