Radio Detection of 18 Rass BL Lac Objects

We present the radio detection of 18 BL Lac objects from our survey of over 575 square degrees of sky. These 18 objects are located within 20 arcsec of the X-ray position, of which 11 have a measured red-shift. All candidates are radio emitters above ~1 mJy and fall within the range of existing samples on the two colour, alpha_ro vs alpha_ox, diagram with a transitional population of three (3) evident. Two unusual sources have been identified, a candidate radio quiet BL Lac, RX J0140.9-4130, and an extreme HBL, RX J0109.9-4020, with Log(nu_peak)~19.2. The BL Lac Log(N)-Log(S) relation is consistent with other samples and indicates the ROSAT All Sky Survey (RASS) could contain (2000+-400) BL Lac objects.Comment: 14 pages, 6 figures, accepted for publication in Serbian Astronomical Journa

Perturbation analysis of the limit cycle of the free van der Pol equation

A power series expansion in the damping parameter, epsilon, of the limit cycle of the free van der Pol equation is constructed and analyzed. Coefficients in the expansion are computed in exact rational arithmetic using the symbolic manipulation system MACSYMA and using a FORTRAN program. The series is analyzed using Pade approximants. The convergence of the series for the maximum amplitude of the limit cycle is limited by two pair of complex conjugate singularities in the complex epsilon-plane. A new expansion parameter is introduced which maps these singularities to infinity and leads to a new expansion for the amplitude which converges for all real values of epsilon. Amplitudes computed from this transformed series agree very well with reported numerical and asymptotic results. For the limit cycle itself, convergence of the series expansion is limited by three pair of complex conjugate branch point singularities. Two pair remain fixed throughout the cycle, and correspond to the singularities found in the maximum amplitude series, while the third pair moves in the epsilon-plane as a function of t from one of the fixed pairs to the other. The limit cycle series is transformed using a new expansion parameter, which leads to a new series that converges for larger values of epsilon

Child Care and Mothers' Employment Decisions

Rising female labor force participation and recent changes to the welfare system have increased the importance of child care for all women and, particularly, the less-skilled. This paper focuses on the child care decisions of women who differ by their skill level and the role that costs play in their work decision. After reviewing government child-care programs targeted at less-skilled women, we present a descriptive analysis of current utilization and child care costs. We emphasize differences across skill groups, showing that the least-skilled women both use less costly paid care and are more likely to use unpaid care. We then survey the existing evidence regarding the responsiveness of female labor supply to child care costs, reviewing both econometric studies and demonstration projects that include child care components. To investigate variation in the response to child care cost across skill levels, we implement models similar to this past literature. We conclude that while the overall elasticity of labor force participation with respect to the market price of child care is between -0.05 and -0.35, this elasticity is larger for the least skilled women and declines with skill. Throughout the paper, we reflect upon the implications of our analysis for welfare reform.

Atomic-phase interference devices based on ring-shaped Bose-Einstein condensates: Two ring case

We theoretically investigate the ground-state properties and quantum dynamics of a pair of adjacent ring-shaped Bose-Einstein condensates that are coupled via tunneling. This device, which is the analogue of a symmetric superconducting quantum interference device, is the simplest version of what we term an Atomic-Phase Interference Device (APHID). The two-ring APHID is shown to be sensitive to rotation.Comment: 8 page

Equilibrium properties of the Skylab CMG rotation law

The equilibrium properties of the control moment gyroscopes of the Skylab are discussed. A rotation law is developed to produce gimbal rates which distribute the angular momentum contributions among the control moment gyroscopes to avoid gimbal stop encounters. The implications for gimbal angle management under various angular momentum situations are described. Conditions were obtained for the existence of equilibria and corresponding stability properties

Magnetically generated spin-orbit coupling for ultracold atoms

We present a new technique for producing two- and three-dimensional Rashba-type spin-orbit couplings for ultracold atoms without involving light. The method relies on a sequence of pulsed inhomogeneous magnetic fields imprinting suitable phase gradients on the atoms. For sufficiently short pulse durations, the time-averaged Hamiltonian well approximates the Rashba Hamiltonian. Higher order corrections to the energy spectrum are calculated exactly for spin-1/2 and perturbatively for higher spins. The pulse sequence does not modify the form of rotationally symmetric atom-atom interactions. Finally, we present a straightforward implementation of this pulse sequence on an atom chip

Structural analyses for the modification and verification of the Viking aeroshell

The Viking aeroshell is an extremely lightweight flexible shell structure that has undergone thorough buckling analyses in the course of its development. The analytical tools and modeling technique required to reveal the structural behavior are presented. Significant results are given which illustrate the complex failure modes not usually observed in simple models and analyses. Both shell-of-revolution analysis for the pressure loads and thermal loads during entry and a general shell analysis for concentrated tank loads during launch were used. In many cases fixes or alterations to the structure were required, and the role of the analytical results in determining these modifications is indicated

A comparison of the UK Standard Assessment Procedure and detailed simulation of solar energy systems for dwellings

The drive to reduce worldwide Carbon Emissions directly associated with dwellings and to achieve a zero carbon home dictates that Renewable Energy Technologies will have an increasingly large role in the built environment. Created by the Building Research Establishment (BRE), the Standard Assessment Procedure (SAP) is the UK Government's approved methodology for assessing the energy ratings of dwellings. This paper presents an evaluation of the advantage given to SAP ratings by the domestic installation of typical Photovoltaic (PV) and Solar Domestic Hot Water (SDHW) systems in the UK. Comparable PV and SDHW systems will also be simulated with more detailed modelling packages. Results suggest that calculation variances can exist between the SAP methodology and detailed simulation methods, especially for higher performance systems that deviate from the default efficiency parameters

Enhanced vaccine control of epidemics in adaptive networks

We study vaccine control for disease spread on an adaptive network modeling disease avoidance behavior. Control is implemented by adding Poisson distributed vaccination of susceptibles. We show that vaccine control is much more effective in adaptive networks than in static networks due to an interaction between the adaptive network rewiring and the vaccine application. Disease extinction rates using vaccination are computed, and orders of magnitude less vaccine application is needed to drive the disease to extinction in an adaptive network than in a static one

Properties of the Scalar Universal Equations

The variational properties of the scalar so--called ``Universal'' equations are reviewed and generalised. In particular, we note that contrary to earlier claims, each member of the Euler hierarchy may have an explicit field dependence. The Euler hierarchy itself is given a new interpretation in terms of the formal complex of variational calculus, and is shown to be related to the algebra of distinguished symmetries of the first source form.Comment: 15 pages, LaTeX articl