Solving Dynamic Discrete Choice Models Using Smoothing and Sieve Methods

We propose to combine smoothing, simulations and sieve approximations to solve for either the integrated or expected value function in a general class of dynamic discrete choice (DDC) models. We use importance sampling to approximate the Bellman operators defining the two functions. The random Bellman operators, and therefore also the corresponding solutions, are generally non-smooth which is undesirable. To circumvent this issue, we introduce a smoothed version of the random Bellman operator and solve for the corresponding smoothed value function using sieve methods. We show that one can avoid using sieves by generalizing and adapting the `self-approximating' method of Rust (1997) to our setting. We provide an asymptotic theory for the approximate solutions and show that they converge with root-N-rate, where $N$ is number of Monte Carlo draws, towards Gaussian processes. We examine their performance in practice through a set of numerical experiments and find that both methods perform well with the sieve method being particularly attractive in terms of computational speed and accuracy

Superconducting fluctuations in organic molecular metals enhanced by Mott criticality

Unconventional superconductivity typically occurs in materials in which a small change of a parameter such as bandwidth or doping leads to antiferromagnetic or Mott insulating phases. As such competing phases are approached, the properties of the superconductor often become increasingly exotic. For example, in organic superconductors and underdoped high-$T_\mathrm{c}$ cuprate superconductors a fluctuating superconducting state persists to temperatures significantly above $T_\mathrm{c}$. By studying alloys of quasi-two-dimensional organic molecular metals in the $\kappa$-(BEDT-TTF)$_2$X family, we reveal how the Nernst effect, a sensitive probe of superconducting phase fluctuations, evolves in the regime of extreme Mott criticality. We find strong evidence that, as the phase diagram is traversed through superconductivity towards the Mott state, the temperature scale for superconducting fluctuations increases dramatically, eventually approaching the temperature at which quasiparticles become identifiable at all.Comment: 19 pages, 4 figures, 1 tabl

Studying the Density of States of buried interfaces in organic semiconductor thin films using electronic sum frequency generation

Abstract: New nanostructured semiconductor materials such as nanocrystals and organic semiconductors constitute an attractive platform for optoelectronics design due to the ease of their processability and highly tunable properties. Incorporating these new nanostructured materials into electrical circuits requires forming junctions between them and other layers in a device, yet the change in dielectric properties about these junctions can strongly perturb the electronic structure of the two layers. Specifically, the morphology of the interface between two materials greatly affect their ability to transfer charge and energy through the system, and the method through which this energy travels across a junction is poorly understood. To study these processes, an interfacial technique is required that measures the Density of States (Dos) at buried interfaces in working devices. In this thesis, we adapt an interface-selective optical technique, electronic sum frequency generation (ESFG), to study the dynamics of energy transfer across interfaces in these materials. We begin by developing “direct” detected ESFG to study the electronic states and morphology at the interface of thin films made from known organic semiconductor materials. Using direct ESFG, we examine the differences in the DoS at an interface in an organic thin film relative to its bulk. Through polarization optics, we study morphological changes in the film caused at the junction of the OSC and substrate. To account for interference from multiple ESFG active interfaces present in a thin film, we use a modeling system to separate contributions to the measured ESFG signal from the air exposed and buried interface of interest. We then adapt the direct detected ESFG to “heterodyne” detected ESFG (HD-ESFG), which significantly increases the detection ability of the ESFG spectrometer. Additionally, HD-ESFG allows us to measure the phase of the materials response, which direct ESFG cannot. This phase information can give a better understanding of the morphology at the interface and additional inputs for thin film interference modeling to better deconvolute the signal from the buried interface.Chemistr

Prospectus, April 21, 2010

A WORD WITH RICHARD EDWARDS OF MARGOT & THE NUCLEAR SO AND SO\u27S; Melinda Gates calls for closer attention to community-college graduation rates; Chuck Shepherd’s News of the Weird; Musically united, we stand; Marking the green revolution; Blagojevich? Quite sane; When Armageddon lives next door; Letter to the Editor; Bankrupting Your Student Loans: A book on how to save yourself from years of poverty; Time for a relationship checkup: How healthful are yours?; Prospectus Pick: Meadowbrook Park; Tragedy and triumph: Substance-free dorm gives students help with rehab; The Health Care reform and what it means for you; Get ready for what’s next; NFL draft turns into three-day affair; Volcanic ash and airplaneshttps://spark.parkland.edu/prospectus_2010/1012/thumbnail.jp

Prospectus, July 14, 2010

PITCHFORK MUSIC FESTIVAL, HERE WE COME!; Things you need to do before the summer ends; Chuck Shepherd’s News of the Weird; It s all about the beats; Respiratory Care: Nothing to cough at; Back to the nest puts families to the test: More than the economy is at play as more young adults move back in with Mom and Dad; Put academics first; U.S. public libraries: We lose them at our peril; A Goodbye from a staff writer...; Be prepared for injuries outdoors; Parkland’s Transition Tour helps adults go back to school; Smart gadgets may one day anticipate our needs; Steinbrenner dead at 80 after reported heart attack; In harm’s wayhttps://spark.parkland.edu/prospectus_2010/1017/thumbnail.jp

Prospectus, February 24, 2010

OVER A DOZEN POSSIBLY INVOLVED IN LOCAL BOOK THEFT RING; Postal Service asks for designs of an electric postal van; Student looks to help Parkland facilities go “green”; Chuck Shepherd’s News of the Weird; Women who rock the music industry; Women who rock the music industry; Olympic medals contain recycled metals; Mend No Child Left Behind, don’t end it; Responsibility; Letter to the Editor; Ask MNN: What is the greenest take-out container?; Sexual Assault on Campus: increasing education to prevent date rape and other sex-related crimes; Prospectus Pick: Lefabuleux destin d’Amelie Poulain; Hall of Fame inductees awarded for greatness; Parkland teacher feature: Martha Bowser-Kienerhttps://spark.parkland.edu/prospectus_2010/1005/thumbnail.jp

Prospectus, February 17, 2010

PARKLAND\u27S GRAPHIC DESIGN PROGRAM SHOWS PROMISE; Artist, producer RJD2 to revisit C-U music scene; Chuck Shepherd’s News of the Weird; There’s no place like home; Parkland teacher feature: Amy Donohue; Saving antibiotics so antibiotics can save us; What Westminster doesn’t show; Letter to the Editor; Talk It Out: Resolving Conflicts on Campus; Bet you’ll watch some of the Olympics along the way; Prospectus Pick: Vampire Weekend\u27s “Contra”; Breaking barriershttps://spark.parkland.edu/prospectus_2010/1004/thumbnail.jp

Prospectus, October 21, 2009

https://spark.parkland.edu/prospectus_2009/1028/thumbnail.jp