On codimension two flats in Fermat-type arrangements

In the present note we study certain arrangements of codimension $2$ flats in projective spaces, we call them "Fermat arrangements". We describe algebraic properties of their defining ideals. In particular, we show that they provide counterexamples to an expected containment relation between ordinary and symbolic powers of homogeneous ideals.Comment: 9 page

Assessing Laws and Legal Authorities for Obesity Prevention and Control

This is the first paper in a two part series on the laws and legal authorities for obesity prevention and control, which resulted from the National Summit on Legal Preparedness for Obesity Prevention and Control in 2008. In this paper, the authors apply the “laws and legal authorities” component of the Centers for Disease Control and Prevention (CDC) legal framework on public health legal preparedness to demonstrate the essential role that law can play in the fight against obesity. Their analysis identified numerous laws and policies in the three vital domains of healthy lifestyles, healthy places, and healthy societies. For example, in terms of healthy lifestyles, governments can impact nutrition through: food subsidies, taxation, and bans; food marketing strategies; and nutritional labeling and education. With regard to healthy places, state and local governments can apply zoning laws and policy decisions to change the environment to encourage healthy eating and physical activity. Governments can promote healthy societies through laws and legal authorities that affect the ability to address obesity from a social perspective (such as antidiscrimination law, health care insurance and benefit design, school and day care for children, and surveillance). This paper describes instances of how current laws and legal authorities affect the public health goal of preventing obesity in both positive and negative ways. It also highlights the progressive use of laws at every level of government (i.e., federal, state, and local) and the interaction of these laws as they relate to obesity prevention and control. In addition, general gaps in the use of law for obesity prevention and control are identified for attention and action. (These gaps serve as the basis for the companion paper, which delineates options for policymakers, practitioners, and other key stakeholders in the improvement of laws and legal authorities for obesity prevention and control.

Bulk and contact-sensitized photocarrier generation in single layer TPD devices

In this paper, we report on the photoelectronic properties of TPD studied in sandwich geometry. In particular, we have obtained from both forward and reverse bias measurements the "mew-tau" product for holes in TPD. "mew" is the hole mobility and "tau" the carrier trapping time. The "mew-tau" product is a measure of the electronic quality of the material and allows a quantitative comparison of different samples. We have carried out numerical simulations to understand the photocurrent in these structures. We show that in reverse bias, the photocurrent (PC) is due to bulk. The carrier generation is governed by field assisted exciton dissociation at electric fields greater than 10^6 V/cm. At lower fields the generation of carriers occurs spontaneously in the bulk of the sample. In forward bias, the photocurrent is due to exciton dissociation at the ITO contact. We also obtain a "mew-tau" product for holes from forward bias PC measurements which is in agreement with the value obtained from reverse bias measurements. Based on our experiments, we demonstrate that TPD in a sandwich structure is a good candidate for cheap large area solar blind UV detector arrays.Comment: Submitted to J. Appl. Phy

Virtual Conference and Meeting Systems: Resources for Online Connections

Librarians have always tried to stretch the limits of applicable technologies to create effective connections among researchers and resources. We thrive on the tools and tactics that help us do this, and we are always on the prowl for newer, better alternatives. This is one of the best ways we have of keeping high service standards in the face of shrinking budgets and skeletal staffing. Fortunately, there have never been so many technologies to choose from, and there have never been so many challenges calling out for technological intervention. Hosting online instruction sessions is, for example, an excellent opportunity for libraries to benefit from new technologies. As the private sector has known for some time, good virtual conferencing systems can save time and money by reducing the need for travel, and they provide surprising flexibility for online training. Facing increasing demands to provide library-related instruction for classes held off-campus and online, we undertook a search for the best products to serve academic needs and budgets. What follows are the results of our investigation: a small selection of some of the most popular, the most cost-effective, and the most useful systems available. This list is by no means complete, however. It seems that there are new entries to the market almost every day, each with its own strengths. We hope the entries below will help you get started on your own search for the best of the many alternatives

Rotational Effects of Twisted Light on Atoms Beyond the Paraxial Approximation

The transition probability for the emission of a Bessel photon by an atomic system is calculated within first order perturbation theory. We derive a closed expression for the electromagnetic potentials beyond the paraxial approximation that permits a systematic multipole approximation . The matrix elements between center of mass and internal states are evaluated for some specially relevant cases. This permits to clarify the feasibility of observing the rotational effects of twisted light on atoms predicted by the calculations. It is shown that the probability that the internal state of an atom acquires orbital angular momentum from light is, in general, maximum for an atom located at the axis of a Bessel mode. For a Gaussian packet, the relevant parameter is the ratio of the spread of the atomic center of mass wave packet to the transversal wavelength of the photon.Comment: 10 pages, no figure

Aharonov-Casher oscillations of spin current through a multichannel mesoscopic ring

The Aharonov-Casher (AC) oscillations of spin current through a 2D ballistic ring in the presence of Rashba spin-orbit interaction and external magnetic field has been calculated using the semiclassical path integral method. For classically chaotic trajectories the Fokker-Planck equation determining dynamics of the particle spin polarization has been derived. On the basis of this equation an analytic expression for the spin conductance has been obtained taking into account a finite width of the ring arms carrying large number of conducting channels. It was shown that the finite width results in a broadening and damping of spin current AC oscillations. We found that an external magnetic field leads to appearance of new nondiagonal components of the spin conductance, allowing thus by applying a rather weak magnetic field to change a direction of the transmitted spin current polarization.Comment: 16 pages, 6 figure

Quantum Mechanical Properties of Bessel Beams

Bessel beams are studied within the general framework of quantum optics. The two modes of the electromagnetic field are quantized and the basic dynamical operators are identified. The algebra of these operators is analyzed in detail; it is shown that the operators that are usually associated to linear momentum, orbital angular momentum and spin do not satisfy the algebra of the translation and rotation group. In particular, what seems to be the spin is more similar to the helicity. Some physical consequences of these results are examined.Comment: 17 pages, no figures. New versio

Dissipative dynamics of topological defects in frustrated Heisenberg spin systems

We study the dynamics of topological defects of a frustrated spin system displaying spiral order. As a starting point we consider the SO(3) nonlinear sigma model to describe long-wavelength fluctuations around the noncollinear spiral state. Besides the usual spin-wave magnetic excitations, the model allows for topologically non-trivial static solutions of the equations of motion, associated with the change of chirality (clockwise or counterclockwise) of the spiral. We consider two types of these topological defects, single vortices and vortex-antivortex pairs, and quantize the corresponding solutions by generalizing the semiclassical approach to a non-Abelian field theory. The use of the collective coordinates allows us to represent the defect as a particle coupled to a bath of harmonic oscillators, which can be integrated out employing the Feynman-Vernon path-integral formalism. The resulting effective action for the defect indicates that its motion is damped due to the scattering by the magnons. We derive a general expression for the damping coefficient of the defect, and evaluate its temperature dependence in both cases, for a single vortex and for a vortex-antivortex pair. Finally, we consider an application of the model for cuprates, where a spiral state has been argued to be realized in the spin-glass regime. By assuming that the defect motion contributes to the dissipative dynamics of the charges, we can compare our results with the measured inverse mobility in a wide range of temperature. The relatively good agreement between our calculations and the experiments confirms the possible relevance of an incommensurate spiral order for lightly doped cuprates.Comment: 22 pages, 7 figures, final published versio

Analysis of measurement errors for a superconducting phase qubit

We analyze several mechanisms leading to errors in a course of measurement of a superconducting flux-biased phase qubit. Insufficiently long measurement pulse may lead to nonadiabatic transitions between qubit states $|1>$ and $|0>$, before tunneling through a reduced barrier is supposed to distinguish the qubit states. Finite (though large) ratio of tunneling rates for these states leads to incomplete discrimination between $|1>$ and $|0>$. Insufficiently fast energy relaxation after the tunneling of state $|1>$ may cause the repopulation of the quantum well in which only the state $|0>$ is supposed to remain. We analyze these types of measurement errors using analytical approaches as well as numerical solution of the time-dependent Schr\"{o}dinger equation.Comment: 14 pages, 14 figure

A study of Feshbach resonances and the unitary limit in a model of strongly correlated nucleons

A model of strongly interacting and correlated hadrons is developed. The interaction used contains a long range attraction and short range repulsive hard core. Using this interaction and various limiting situations of it, a study of the effect of bound states and Feshbach resonances is given. The limiting situations are a pure square well interaction, a delta-shell potential and a pure hard core potential. The limit of a pure hard core potential are compared with results for a spinless Bose and Fermi gas. The limit of many partial waves for a pure hard core interaction is also considered and result in expressions involving the hard core volume. This feature arises from a scaling relation similar to that for hard sphere scattering with diffractive corrections. The role of underlying isospin symmetries associated with the strong interaction of protons and neutrons in this two component model is investigated. Properties are studied with varying proton fraction. An analytic expression for the Beth Uhlenbeck continuum integral is developed which closely approximates exact results based on the potential model considered. An analysis of features associated with a unitary limit is given. In the unitary limit of very large scattering length, the ratio of effective range to thermal wavelength appears as a limiting scale. Thermodynamic quantities such as the entropy and compressibility are also developed. The effective range corrections to the entropy vary as the cube of this ratio for low temperatures and are therefore considerably reduced compared to the corrections to the interaction energy which varies linearly with this ratio. Effective range corrections to the compressibility are also linear in the ratio.Comment: 39 pages, 15 figures, 2 table