Decoherent Histories and Non-adiabatic Quantum Molecular Dynamics

The role of quantum coherence loss in mixed quantum-classical dynamical systems is explored in the context of the theory of quantum decoherence introduced recently by Bittner and Rossky. (J. Chem. Phys. {\bf 103}, 8130 (1995)). This theory, which is based upon the consistent histories interpretation of quantum mechanics, introduces decoherence in the quantum subsystem by carefully considering the relevant time and length scales over which one must consider the effects of phase interference between alternative histories of the classical subsystem. Such alternative histories are an integral part of any quantum-classical computational scheme which employ transitions between discrete quantum states; consequently, the coherences between alternative histories have a profound effect on the transition probability between quantum states. In this paper, we review the Bittner-Rossky theory and detail a computational algorithm suitable for large-scale quantum molecular dynamics simulations which implements this theory. Application of the algorithm towards the relaxation of a photoexcited aqueous electron compare well to previous estimates of the excited state survival time as well as to the experimental measurements.Comment: 22 pages, 3 figure

The M\"obius function of generalized subword order

Let P be a poset and let P* be the set of all finite length words over P. Generalized subword order is the partial order on P* obtained by letting u \leq w if and only if there is a subword u' of w having the same length as u such that each element of u is less than or equal to the corresponding element of u' in the partial order on P. Classical subword order arises when P is an antichain, while letting P be a chain gives an order on compositions. For any finite poset P, we give a simple formula for the Mobius function of P* in terms of the Mobius function of P. This permits us to rederive in a easy and uniform manner previous results of Bjorner, Sagan and Vatter, and Tomie. We are also able to determine the homotopy type of all intervals in P* for any finite P of rank at most 1.Comment: 29 pages, 4 figures. Incorporates referees' suggestions; to appear in Advances in Mathematic

Equality of P-partition generating functions

To every labeled poset (P,\omega), one can associate a quasisymmetric generating function for its (P,\omega)-partitions. We ask: when do two labeled posets have the same generating function? Since the special case corresponding to skew Schur function equality is still open, a complete classification of equality among (P,\omega) generating functions is likely too much to expect. Instead, we determine necessary conditions and separate sufficient conditions for two labeled posets to have equal generating functions. We conclude with a classification of all equalities for labeled posets with small numbers of linear extensions.Comment: 24 pages, 19 figures. Incorporates minor changes suggested by the referees. To appear in Annals of Combinatoric

Structural and Electronic Properties of the Interface between the High-k oxide LaAlO3 and Si(001)

The structural and electronic properties of the LaAlO3/Si(001) interface are determined using state-of-the-art electronic structure calculations. The atomic structure differs from previous proposals, but is reminiscent of La adsorption structures on silicon. A phase diagram of the interface stability is calculated as a function of oxygen and Al chemical potentials. We find that an electronically saturated interface is obtained only if dopant atoms segregate to the interface. These findings raise serious doubts whether LaAlO3 can be used as an epitaxial gate dielectric.Comment: 4 pages, 5 figure

Financial intermediation, monetary policy, and equilibrium business cycles

Business cycles ; Monetary theory ; Financial institutions

Inside Money and Monetary Neutrality

This paper examines the interaction between the financial and real sectors of the economy within the framework of a stochastic, rational expectation model that distinguishes between inside and outside money. The model also can be used to study the impact of variations in the degree of intermediation, measured by the elasticity of bank deposit supply. In contrast to earlier work which emphasized confusion between monetary and real shocks, we focus on the role played by confusion between inside and outside money and temporary and permanent base money disturbances. Financial sector disturbances, as well as temporary shocks tothe monetary base, are shown to have real effects even when private agents have complete information. When contemporaneous information on economic disturbances is incomplete, permanent shocks to the monetary base also have real effects. If our model is correct, it is invalid to reject equilibrium models of the business cycle on the grounds that anticipated money affects output. We argue that this result is robust in the sense that many "reasonable" models which incorporate inside money would yield a non-neutrality of portfolio and temporary base money supply shocks.

QCD Splitting/Joining Functions at Finite Temperature in the Deep LPM Regime

There exist full leading-order-in-alpha_s numerical calculations of the rates for massless quarks and gluons to split and join in the background of a quark-gluon plasma through hard, nearly collinear bremsstrahlung and inverse bremsstrahlung. In the limit of partons with very high energy E, where the physics is dominated by the Landau-Pomeranchuk-Migdal (LPM) effect, there are also analytic leading-log calculations of these rates, where the logarithm is ln(E/T). We extend those analytic calculations to next-to-leading-log order. We find agreement with the full result to within roughly 20% for E(less) >~ 10 T, where E(less) is the energy of the least energetic parton in the splitting/joining process. We also discuss how to account for the running of the coupling constant in the case that E/T is very large. Our results are also applicable to isotropic non-equilibrium plasmas if the plasma does not change significantly over the formation time associated with particle splitting.Comment: 20 pages, 6 figures. Changes from v3: Typos fixed in the subscripts of various Casimir factor

Phase-field Crystals with Elastic Interactions

We report on a novel extension of the recent phase-field crystal (PFC) method introduced in [Elder et al., Phys. Rev. Lett., Vol. 88, 245701:1-4 (2002)], which incorporates elastic interactions as well as crystal plasticity and diffusive dynamics. In our model, elastic interactions are mediated through wave modes that propagate on time scales many orders of magnitude slower than atomic vibrations but still much faster than diffusive times scales. This allows us to preserve the quintessential advantage of the PFC model: the ability to simulate atomic-scale interactions and dynamics on time scales many orders of magnitude longer than characteristic vibrational time scales. We demonstrate the two different modes of propagation in our model and show that simulations of grain growth and elasto-plastic deformation are consistent with the microstructural properties of nanocrystals.Comment: 4 pages, 6 figure

Climate Change: An Agenda for Global Collective Action

Over the past decade, and especially over the past few years, climate change has emerged as one of the most important issues facing the international community. A global consensus now exists that climate change represents a significant potential threat to the world's well-being. But there is disagreement about how and when to address that threat. To motivate the discussion of both the timing and magnitude of emissions mitigation policy, the paper begins with an overview of the underlying science and economics. Understanding the uncertainties and differences in the timing of costs and benefits of climate change mitigation helps frame the extensive discussion of political economy issues that we examine in the second section. Specifically, we explore the interaction of economic and political concerns in enforcing emissions commitments and encouraging developing country participation within the "voluntaristic" framework entailed by the current system of global governance. Given these political economy constraints, in the third section we evaluate the Kyoto Protocol and alternative formulations to climate change policy. We conclude that modifications to the Kyoto framework are required to advance the effort to address climate change. At the very least, a thorough re-examination of alternative frameworks may prove helpful in building a global consensus behind a more effective strategy. The final section concludes with a discussion of one promising approach to addressing climate change: a flexible hybrid system that combines a permit trading program with the ability of governments to sell additional permits at a given maximum price.Environment, Technology and Industry, Regulatory Reform, Other Topics

Community Efforts to Expand Dental Services for Low-Income People

Examines low-income patients' limited access to dental care, as well as state and community efforts to expand services, including changing Medicaid and State Children's Health Insurance Program reimbursement rates and licensing laws for preventive care