A Compact Microchip-Based Atomic Clock Based on Ultracold Trapped Rb Atoms

We propose a compact atomic clock based on ultracold Rb atoms that are magnetically trapped near the surface of an atom microchip. An interrogation scheme that combines electromagnetically-induced transparency (EIT) with Ramsey's method of separated oscillatory fields can achieve atomic shot-noise level performance of 10^{-13}/sqrt(tau) for 10^6 atoms. The EIT signal can be detected with a heterodyne technique that provides noiseless gain; with this technique the optical phase shift of a 100 pW probe beam can be detected at the photon shot-noise level. Numerical calculations of the density matrix equations are used to identify realistic operating parameters at which AC Stark shifts are eliminated. By considering fluctuations in these parameters, we estimate that AC Stark shifts can be canceled to a level better than 2*10^{-14}. An overview of the apparatus is presented with estimates of duty cycle and power consumption.Comment: 15 pages, 11 figures, 5 table

Relocation remembered: Perspectives on senior transitions in the living environment

The experience of aging may necessitate transitions in living environments, either through adaptations to current residences or relocations to more supportive environments. For over a half century, the study of these transitions has informed the work of researchers, health and mental health providers, policymakers, and municipal planners. In the 1970s and ‘80s, knowledge about these transitions advanced through Lawton & Nahemow’s ecological theory of competence and environmental press, Wiseman’s behavioral model of relocation decision-making, and Litwak & Longino’s developmental perspective on senior migrations. This paper revisits influential theoretical frameworks which contribute to our understanding of senior transitions in living environments. These seminal works are shown to inform recent studies of relocation and gerontology. This paper concludes with a call for a view on housing transitions that reflects the contemporary context

Single-Particle Density of States of a Superconductor with a Spatially Varying Gap and Phase Fluctuations

Recent experiments have shown that the superconducting energy gap in some cuprates is spatially inhomogeneous. Motivated by these experiments, and using exact diagonalization of a model d-wave Hamiltonian, combined with Monte Carlo simulations of a Ginzburg-Landau free energy functional, we have calculated the single-particle density of states LDOS$(\omega,r)$ of a model high-T$_c$ superconductor as a function of temperature. Our calculations include both quenched disorder in the pairing potential and thermal fluctuations in both phase and amplitude of the superconducting gap. Most of our calculations assume two types of superconducting regions: $\alpha$, with a small gap and large superfluid density, and $\beta$, with the opposite. If the $\beta$ regions are randomly embedded in an $\alpha$ host, the LDOS on the $\alpha$ sites still has a sharp coherence peak at $T = 0$, but the $\beta$ component does not, in agreement with experiment. An ordered arrangement of $\beta$ regions leads to oscillations in the LDOS as a function of energy. The model leads to a superconducting transition temperature $T_c$ well below the pseudogap temperature $T_{c0}$, and has a spatially varying gap at very low $T$, both consistent with experiments in underdoped Bi2212. Our calculated LDOS$(\omega,r)$ shows coherence peaks for $T T_c$, in agreement with previous work considering phase but not amplitude fluctuations in a homogeneous superconductor. Well above $T_c$, the gap in the LDOS disappears.Comment: 37 pages, 12 figures. Accepted by Phys. Rev. B. Scheduled Issue: 01 Nov 200

Magneto-Gas Kinetic Method for Nonideal Magnetohydrodynamics Flows: Verification Protocol and Plasma Jet Simulations

In this work, the gas-kinetic method (GKM) is enhanced with resistive and Hall magnetohydrodynamics (MHD) effects. Known as MGKM (for MHD–GKM), this approach incorporates additional source terms to the momentum and energy conservation equations and solves the magnetic field induction equation. We establish a verification protocol involving numerical solutions to the one-dimensional (1D) shock tube problem and two-dimensional (2D) channel flows. The contributions of ideal, resistive, and Hall effects are examined in isolation and in combination against available analytical and computational results. We also simulate the evolution of a laminar MHD jet subject to an externally applied magnetic field. This configuration is of much importance in the field of plasma propulsion. Results support previous theoretical predictions of jet stretching due to magnetic field influence and azimuthal rotation due to the Hall effect. In summary, MGKM is established as a promising tool for investigating complex plasma flow phenomena

Impediments to Effective Interactions Between Multipurpose Water Districts and Other Governmental Institutions in Urbanizing Areas

Water institutions are highly diffused throughout society. These institutions interact with one another in various ways. As water needs and services expand, collaborative and cooperative arrangements are commonly sought as a means of meeting common goals of providing a safe, dependable adn least cost water supply to particular constituencies. Of the many different institutions involved in the development, managment, distribution, and use of water, perhaps the most significant in terms of extensive interactions with other institutions is the kind that is typified by Water Conservancy Districts and Metropolitan Water Districts in Utah. The statutory and operating framework of counterpart organizations in Arizona, Colorado, Nebraska, Oregon, and South Dakota are compared in this report. Significant differences in procedures for creation and termination, selection of officers, powers and legal rights, opportunity for input to policy formulation, sources of financiing, planning responsibility, and coordination are identified. Interstate comparisons provide the backdrop for more specific examination of the interactions of districts in Utah with other organizations and agencies. The results indicate that districts have tended to embrace large scale projects as solutions to projected water shortages. The continuing and long term financial obligation constrains the districts flexibility to adjust to alternative supply options that may become visible to retail users as demand patterns change during the drawn out construction schedules of large projects. Because the Conneville Unit of the Central Utah Project is presently engaged in a large and active investigative and construction program, and is negotiating water purchase contracts, examples of some of the kinds of impediments to effective institutional interaction were more readily identified in that region by those interviewed. In situations where institutional differences occur, their mediation could be more readily effected if districts were more directly linked to general purpose government and particularly to state oversight. State government might promote more harmonious coordination of district operations by inviting periodic full and open appraisal of district plans and policies in a search for mid-course corrections that might better serve the public interest without abrogating contractual commitments

Supernova 2010ev: A reddened high velocity gradient type Ia supernova

Aims. We present and study the spectroscopic and photometric evolution of the type Ia supernova (SN Ia) 2010ev. Methods. We obtain and analyze multi-band optical light curves and optical-near-infrared spectroscopy at low and medium resolution spanning from -7 days to +300 days from the B-band maximum. Results. A photometric analysis shows that SN 2010ev is a SN Ia of normal brightness with a light curve shape of $\Delta m_{15}(B)=1.12 \pm 0.02$ and a stretch s = $0.94 \pm 0.01$ suffering significant reddening. From photometric and spectroscopic analysis, we deduce a color excess of $E(B - V) = 0.25 \pm 0.05$ and a reddening law of $R_v = 1.54 \pm 0.65$. Spectroscopically, SN 2010ev belongs to the broad-line SN Ia group, showing stronger than average Si II {\lambda}6355 absorption features. We also find that SN 2010ev is a high-velocity gradient SN, with a value of $164 \pm 7$ km s$^{-1}$ d$^{-1}$. The photometric and spectral comparison with other supernovae shows that SN 2010ev has similar colors and velocities to SN 2002bo and SN 2002dj. The analysis of the nebular spectra indicates that the [Fe II] {\lambda}7155 and [Ni II] {\lambda}7378 lines are redshifted, as expected for a high velocity gradient supernova. All these common intrinsic and extrinsic properties of the high velocity gradient (HVG) group are different from the low velocity gradient (LVG) normal SN Ia population and suggest significant variety in SN Ia explosions.Comment: 16 pages, 13 figures, 7 tables. Accepted to A&

Adherence to Best Practices for Stated Preference Valuation within the U.S. Marine Ecosystem Services Literature

Non-market economic values derived from stated preference (SP) methods are often of interest for policy analysis and evaluation, program design, green accounting, and damage assessments and are increasingly in demand with adoption of ecosystem-based management approaches that emphasize accounting for ecosystem services and their values. A recent guidance prescribes a set of twenty-three best practices guidelines (BPGs) to follow when conducting a SP study to ensure the validity of the results and maximize its ability to provide reliable economic value information. In this article, we evaluate adherence to these guidelines within the U.S. SP marine ecosystem service valuation literature. Our results suggest adherence by the literature to the guidelines is heterogeneous with none of the studies examined adhering to all guidelines and some guidelines being adhered to better than others. Evidence points to adherence differences between older and more recent studies, between studies using different SP valuation methods, and between studies valuing recreation ecosystem services and ones valuing other ecosystem services. Furthermore, a citation analysis suggests studies addressing elements embodied in the BPGs tend to have more citations all else being equal. We discuss several challenges to valuing marine ecosystem services and areas for improvement and inquiry

Thermal divergences on the event horizons of two-dimensional black holes

The expectation value of the stress-energy tensor \langleT_{\mu\nu}\rangle of a free conformally invariant scalar field is computed in a general static two-dimensional black hole spacetime when the field is in either a zero temperature vacuum state or a thermal state at a nonzero temperature. It is found that for every static two-dimensional black hole the stress-energy diverges strongly on the event horizon unless the field is in a state at the natural black hole temperature which is defined by the surface gravity of the event horizon. This implies that both extreme and nonextreme two-dimensional black holes can only be in equilibrium with radiation at the natural black hole temperature.Comment: 13 pages, REVTe

Magnetic White Dwarfs from the SDSS II. The Second and Third Data Releases

Fifty-two magnetic white dwarfs have been identified in spectroscopic observations from the Sloan Digital Sky Survey (SDSS) obtained between mid-2002 and the end of 2004, including Data Releases 2 and 3. Though not as numerous nor as diverse as the discoveries from the first Data Release, the collection exhibits polar field strengths ranging from 1.5MG to ~1000MG, and includes two new unusual atomic DQA examples, a molecular DQ, and five stars that show hydrogen in fields above 500MG. The highest-field example, SDSSJ2346+3853, may be the most strongly magnetic white dwarf yet discovered. Analysis of the photometric data indicates that the magnetic sample spans the same temperature range as for nonmagnetic white dwarfs from the SDSS, and support is found for previous claims that magnetic white dwarfs tend to have larger masses than their nonmagnetic counterparts. A glaring exception to this trend is the apparently low-gravity object SDSSJ0933+1022, which may have a history involving a close binary companion.Comment: 20 pages, 4 figures Accepted for publication in the Astronomical Journa

Design and Testing of a Feed-Forward Control System for Deployable Vortex Generators Dependent on Angle of Attack

A vortex generator (VG hereafter) is a common feature of an aircraft wing that disturbs the flow on the leading edge of the wing, thus energizing the boundary layer and reducing flow separation. For an aircraft experiencing flow separation, VGs can increase the lift-to-drag ratio of the wing and prevent stall; however, if flow separation isn’t an issue, the unnecessary frontal area of the VGs has the potential to produce parasitic drag. This study seeks to determine whether the use of a deployment system can improve the performance of VG’s by raising or lowering them depending on the angle of attack of the wing. Using wind tunnel testing, a feed-forward control deployment system was developed which improved the lift to drag ratio for some angles of attack, and it was determined that further development could potentially produce a system with significant improvements in aircraft efficiency