Dynamical fermions as a global correction

In the simplified setting of the Schwinger model we present a systematic study on the simulation of dynamical fermions by global accept/reject steps that take into account the fermion determinant. A family of exact algorithms is developed, which combine stochastic estimates of the determinant ratio with the exploitation of some exact extremal eigenvalues of the generalized problem defined by the `old' and the `new' Dirac operator. In this way an acceptable acceptance rate is achieved with large proposed steps and over a wide range of couplings and masses.Comment: 39 pages, 9 figures, small changes in the text, Fig.5 and Tab.2 (incl. 1 corrected typo

Center vortex model for the infrared sector of Yang-Mills theory - Quenched Dirac spectrum and chiral condensate

The Dirac operator describing the coupling of continuum quark fields to SU(2) center vortex world-surfaces composed of elementary squares on a hypercubic lattice is constructed. It is used to evaluate the quenched Dirac spectral density in the random vortex world-surface model, which previously has been shown to quantitatively reproduce both the confinement properties and the topological susceptibility of SU(2) Yang-Mills theory. Under certain conditions on the modeling of the vortex gauge field, a behavior of the quenched chiral condensate as a function of temperature is obtained which is consistent with measurements in SU(2) lattice Yang-Mills theory.Comment: 36 LaTeX pages, 13 ps figures included via epsf; minor reformulations and added cross-referencing for the purpose of clarit

Quantum Monte Carlo simulations of a particle in a random potential

In this paper we carry out Quantum Monte Carlo simulations of a quantum particle in a one-dimensional random potential (plus a fixed harmonic potential) at a finite temperature. This is the simplest model of an interface in a disordered medium and may also pertain to an electron in a dirty metal. We compare with previous analytical results, and also derive an expression for the sample to sample fluctuations of the mean square displacement from the origin which is a measure of the glassiness of the system. This quantity as well as the mean square displacement of the particle are measured in the simulation. The similarity to the quantum spin glass in a transverse field is noted. The effect of quantum fluctuations on the glassy behavior is discussed.Comment: 23 pages, 7 figures included as eps files, uses RevTeX. Accepted for publication in J. of Physics A: Mathematical and Genera

Two-Sided Matching for mentor-mentee allocations—Algorithms and manipulation strategies

In scenarios where allocations are determined by participant’s preferences, Two-Sided Matching is a well-established approach with applications in College Admissions, School Choice, and Mentor-Mentee matching problems. In such a context, participants in the matching have preferences with whom they want to be matched with. This article studies two important concepts in Two-Sided Matching: multiple objectives when finding a solution, and manipulation of preferences by participants. We use real data sets from a Mentor-Mentee program for the evaluation to provide insight on realistic effects and implications of the two concepts. In the first part of the article, we consider the quality of solutions found by different algorithms using a variety of solution criteria. Most current algorithms focus on one criterion (number of participants matched), while not directly taking into account additional objectives. Hence, we evaluate different algorithms, including multi-objective heuristics, and the resulting trade-offs. The evaluation shows that existing algorithms for the considered problem sizes perform similarly well and close to the optimal solution, yet multi-objective heuristics provide the additional benefit of yielding solutions with better quality on multiple criteria. In the second part, we consider the effects of different types of preference manipulation on the participants and the overall solution. Preference manipulation is a concept that is well established in theory, yet its practical effects on the participants and the solution quality are less clear. Hence, we evaluate the effects of three manipulation strategies on the participants and the overall solution quality, and investigate if the effects depend on the used solution algorithm as well

STRATEGIC ANALYSIS OF TRAIT COMMERCIALIZATION IN GENETICALLY MODIFIED (GM) GRAINS: THE CASE OF GM WHEAT

The prospective commercialization of GM traits leads to several strategic questions for agbiotechnology and seed firms. Important issues addressed in this study include the method of trait commercialization by agbiotechnology firms and variety production decisions by seed firms. Specifically, agbiotechnology firms must decide whether to license their traits to seed firms, to purchase a seed firm, or to not license or release their traits. These issues are highly strategic. The purpose of this study was to determine equilibrium strategies of agbiotechnology and seed firms regarding the prospective commercialization of two GM traits. Two game theory models were developed to examine equilibrium strategies in two different scenarios. In the first model, both agbiotechnology firms had commercialization strategies of licensing and not licensing. In the second model, the first moving agbiotechnology firm was allowed to have a strategic option to purchase a seed firm as a commercialization strategy. The second agbiotechnology firm remained with two strategies, licensing and not licensing. These models were applied to the case of Roundup Ready® (RR) and fusarium resistant (FR) HRS wheat, although the general structure of the models could be used to analyze other crops and traits. Studies on trait commercialization and stacking are lacking the public literature. This study uses game theory models to develop likely situations that may occur regarding the prospective commercialization of GM traits.genetically modified grains, wheat, Crop Production/Industries, Research and Development/Tech Change/Emerging Technologies,

HIV and tuberculosis in India

The global impact of the converging dual epidemics of tuberculosis (TB) and human immunodefi ciency virus (HIV) is one of the major public health challenges of our time. The World Health Organization (WHO) reports 9.2 million new cases of TB in 2006 of whom 7.7% were HIV-infected. Tuberculosis is the most common opportunistic infection in HIV-infected patients as well as the leading cause of death. Further, there has been an increase in rates of drug resistant tuberculosis, including multi-drug (MDRTB) and extensively drug resistant TB (XDRTB), which are diffi cult to treat and contribute to increased mortality. The diagnosis of TB is based on sputum smear microscopy, a 100-year old technique and chest radiography, which has problems of specifi city. Extra-pulmonary, disseminated and sputum smear negative manifestations are more common in patients with advanced immunosuppression. Newer diagnostic tests are urgently required that are not only sensitive and specifi c but easy to use in remote and resource-poor settings. Treatment of HIV-TB co-infection is complex and associated with high pill burden, overlapping drug toxicities, risk of immune reconstitution infl ammatory syndrome (IRIS) and challenges related to adherence. From a programmatic point of view, screening of all HIV-infected persons for tuberculosis and vice-versa will help identify co-infected patients who require treatment for both infections. This requires good coordination and communication between the TB and AIDS control programs, in India

Essays on Matching Markets

The thesis consists of three chapters in the theory of matching markets. In Chapter 2, I study a central authority's ability to commit to a publicly announced mechanism in a one-to-one agent-object matching model. The authority announces a strategy-proof mechanism and then privately selects a mechanism to initiate a matching. An agent's observation in form of the final matching has an innocent explanation (Akbarpour and Li, 2020), if given the agent's reported preferences, there is a combination with other agents' preferences leading to an identical observation under the announced mechanism. The authority can only commit up to safe deviations (Akbarpour and Li, 2020)---mechanisms that produce only observations with innocent explanations. For efficient or stable announcements, I show that no safe deviation exists if and only if the announced mechanism is dictatorial. I establish that the Deferred Acceptance (DA) Mechanism (Gale and Shapley, 1962) implies commitment to stability. Moreover, group strategy-proof and efficient announcements allow commitment to efficiency only if they are dictatorial. In Chapter 3, we study The Efficiency Adjusted Deferred Acceptance Matching Rule (EDA) which is a promising candidate mechanism for public school assignment. A potential drawback of EDA is that it could encourage students to game the system since it is not strategy-proof. However, to successfully strategize, students typically need information that is unlikely to be available to them in practice. We model school choice under incomplete information and show that EDA is regret-free truth-telling, which is a weaker incentive property than strategy-proofness and was introduced by (Fernandez, 2020). We also show that there is no efficient matching rule that weakly Pareto dominates a stable matching rule and is regret-free truth-telling. Note that without modifications the EDA as introduced by (Kesten, 2010) weakly Pareto dominates a stable matching rule, but it is not efficient. In Chapter 4, I study agents’ incentives in a one-to-one object allocation model where agents are envious. Among all agents whose assignment is tracked by some agent, the agent envies those who are matched to an object she prefers to her own assignment. Given a mechanism and agents’ actions, agent i’s envy towards agent j at object x under the induced matching is inevitable if i has no action where she does not envy j at x, given one keeps the actions of other agents unchanged. A matching mechanism is envyproof, if for each market and agent, any envy under truthful revelation of preferences is inevitable. Envy-proofness is a concept that is stronger than strategy-proofness. I show that the Top Trading Cycle (TTC) Mechanism is envy-proof. Moreover, the unique strategy-proof and stable mechanism, the Deferred Acceptance Mechanism, is not envy-proof