Phonon Diodes and Transistors from Magneto-acoustics

By sculpting the magnetic field applied to magneto-acoustic materials, phonons can be used for information processing. Using a combination of analytic and numerical techniques, we demonstrate designs for diodes (isolators) and transistors that are independent of their conventional, electronic formulation. We analyze the experimental feasibility of these systems, including the sensitivity of the circuits to likely systematic and random errors.Comment: 5 pages, 4 figure

Learning salience amoung [sic] features through contingency in the CEL framework

Determining which features in an environment are salient given a task, salience assignment, is a central problem in Machine Learning. A related phenomenon, contingency (the conditions under which relative salience among environmental features is acquired), is central to learning and memory in animal psychology. This paper presents an analysis of a set of empirical data on contingency and an algorithm for the salience assignment problem. The algorithm presented is implemented in a working computer program which interacts with a simulated environment to produce contingent associative learning corresponding to relevant behavioral data. The model also makes specific empirical predictions that can be experimentally tested

Quantum Monte Carlo for minimum energy structures

We present an efficient method to find minimum energy structures using energy estimates from accurate quantum Monte Carlo calculations. This method involves a stochastic process formed from the stochastic energy estimates from Monte Carlo that can be averaged to find precise structural minima while using inexpensive calculations with moderate statistical uncertainty. We demonstrate the applicability of the algorithm by minimizing the energy of the H2O-OH- complex and showing that the structural minima from quantum Monte Carlo calculations affect the qualitative behavior of the potential energy surface substantially.Comment: 7 pages, 4 figure

New and Noteworthy Plants of Texas

Rhexia alifanus (Melastomataceae) and Rhynchospora inundatum (Cyperaceae), both previously reported in the state, are documented as part of the flora of the state. Ratibida pinnata (Asteraceae), Tradescantia fluminensis (Commelinaceae) and Saccharum ravennae (Poaceae) are reported as new to Texas. Phytologia 92(2): 249-255 (August 2, 2010).Waller Creek Working Grou

Umbral Moonshine and the Niemeier Lattices

In this paper we relate umbral moonshine to the Niemeier lattices: the 23 even unimodular positive-definite lattices of rank 24 with non-trivial root systems. To each Niemeier lattice we attach a finite group by considering a naturally defined quotient of the lattice automorphism group, and for each conjugacy class of each of these groups we identify a vector-valued mock modular form whose components coincide with mock theta functions of Ramanujan in many cases. This leads to the umbral moonshine conjecture, stating that an infinite-dimensional module is assigned to each of the Niemeier lattices in such a way that the associated graded trace functions are mock modular forms of a distinguished nature. These constructions and conjectures extend those of our earlier paper, and in particular include the Mathieu moonshine observed by Eguchi-Ooguri-Tachikawa as a special case. Our analysis also highlights a correspondence between genus zero groups and Niemeier lattices. As a part of this relation we recognise the Coxeter numbers of Niemeier root systems with a type A component as exactly those levels for which the corresponding classical modular curve has genus zero.Comment: 181 pages including 95 pages of Appendices; journal version, minor typos corrected, Research in the Mathematical Sciences, 2014, vol.

Stress effects on the Raman spectrum of an amorphous material: theory and experiment on a-Si:H

Strain in a material induces shifts in vibrational frequencies, which is a probe of the nature of the vibrations and interatomic potentials, and can be used to map local stress/strain distributions via Raman microscopy. This method is standard for crystalline silicon devices, but due to lack of calibration relations, it has not been applied to amorphous materials such as hydrogenated amorphous silicon (a-Si:H), a widely studied material for thin-film photovoltaic and electronic devices. We calculated the Raman spectrum of a-Si:H \ab initio under different strains $\epsilon$ and found peak shifts $\Delta \omega = \left( -460 \pm 10\ \mathrm{cm}^{-1} \right) {\rm Tr}\ \epsilon$. This proportionality to the trace of the strain is the general form for isotropic amorphous vibrational modes, as we show by symmetry analysis and explicit computation. We also performed Raman measurements under strain and found a consistent coefficient of $-510 \pm 120\ \mathrm{cm}^{-1}$. These results demonstrate that a reliable calibration for the Raman/strain relation can be achieved even for the broad peaks of an amorphous material, with similar accuracy and precision as for crystalline materials.Comment: 12 pages, 3 figures + supplementary 8 pages, 4 figure

Aviation security and terrorism: a review of the economic issues

Following the terrorist attacks on September 11, 2001, the passage of the Aviation and Transportation Act mandated a substantial increase in resources devoted to aviation security. This paper summarizes the specific changes stemming from this legislation. In addition, the paper examines the economic issues underlying the regulation and provision of aviation security. The fact that security at one airport can affect the well being of those at other airports and elsewhere, an example of a network externality (spillover), provides an economic justification for governmental involvement in aviation security. A fundamental question is whether the federal role should be restricted to setting and monitoring security standards or whether the role should also include the financing and implementation of security. A controversial change is that the federal government has assumed responsibility from the airlines and airports for the actual provision of aviation security. Proponents of this change argue that, relative to private provision, public provision reduces the incentives to reduce quality through cost reductions. On the other hand, a public agency might not provide security services efficiently because it can operate in a more-or-less monopolistic way. Furthermore, a public agency might provide an excessive amount of security and incur unnecessary expenses because it is likely to be judged on its security record and not on all the attributes encompassed by air transportation services for consumers. Thus, economic theory does not provide a clear answer to what is likely to be a continuing source of controversy - the appropriate scope of governmental involvement in aviation security.Economic conditions ; War - Economic aspects

The Effect of Inheritance Receipt on Retirement

This paper uses the receipt of an inheritance to measure the effect of wealth shocks on retirement. Using the Health and Retirement Study (HRS), we first document that inheritance receipt is common among older workers %u2013 one in five households receives an inheritance over an eight-year period, with a median value of about $30,000. We find that inheritance receipt is associated with a significant increase in the probability of retirement. In particular, we find that receiving an inheritance increases the probability of retiring earlier than expected by 4.4 percentage points, or 12 percent relative to the baseline retirement rate, over an eight-year period. Importantly, this effect is stronger when the inheritance is unexpected and thus more likely to represent an exogenous shock to wealth.