A new perspective on GCRT J1745-3009

Two WSRT observations were performed and five archival VLA data were reduced in order to redetect the enigmatic radio transient GCRT J1745-3009. The source was not redetected. We were, however, able to extract important new information from the discovery dataset. Our reanalysis excludes models that predict symmetric bursts, but the transient white dwarf pulsar is favoured. Although we now have more contraints on the properties of this source, we are still unsure about its basic model.Comment: 11 pages, 5 figure

"Community Development Banking, A Proposal to Establish a Nationwide System of Community Development Banks"

This brief proposes that the establishment of a nationwide system of community development banks (CDBs) would advance the capital development of the economy. The proposal is based on the notion that a critical function of the financial system is not being adequately performed by existing institutions for low-income citizens, inner-city minorities, and entrepreneurs who seek modest financing for small businesses. The primary goals of the CDBs are to deliver credit, payment, and savings opportunities to communities not well served by banks and to provide financing throughout a designated area for businesses too small to attract the interest of the investment banking and normal commercial banking communities.

Engineering model 8-cm thruster subsystem

An Engineering Model (EM) 8 cm Ion Thruster Propulsion Subsystem was developed for operation at a thrust level 5 mN (1.1 mlb) at a specific impulse 1 sub sp = 2667 sec with a total system input power P sub in = 165 W. The system dry mass is 15 kg with a mercury-propellant-reservoir capacity of 8.75 kg permitting uninterrupted operation for about 12,500 hr. The subsystem can be started from a dormant condition in a time less than or equal to 15 min. The thruster has a design lifetime of 20,000 hr with 10,000 startup cycles. A gimbal unit is included to provide a thrust vector deflection capability of + or - 10 degrees in any direction from the zero position. The EM subsystem development program included thruster optimization, power-supply circuit optimization and flight packaging, subsystem integration, and subsystem acceptance testing including a cyclic test of the total propulsion package

Actively Contracting Bundles of Polar Filaments

We introduce a phenomenological model to study the properties of bundles of polar filaments which interact via active elements. The stability of the homogeneous state, the attractors of the dynamics in the unstable regime and the tensile stress generated in the bundle are discussed. We find that the interaction of parallel filaments can induce unstable behavior and is responsible for active contraction and tension in the bundle. Interaction between antiparallel filaments leads to filament sorting. Our model could apply to simple contractile structures in cells such as stress fibers.Comment: 4 pages, 4 figures, RevTex, to appear in Phys. Rev. Let

Numerical studies of the 2 and 3D gauge glass at low temperature

We report results from Monte Carlo simulations of the two- and three-dimensional gauge glass at low temperature using parallel tempering Monte Carlo. In two dimensions, we find strong evidence for a zero-temperature transition. By means of finite-size scaling, we determine the stiffness exponent theta = -0.39 +/- 0.03. In three dimensions, where a finite-temperature transition is well established, we find theta = 0.27 +/- 0.01, compatible with recent results from domain-wall renormalization group studies.Comment: 3 pages, 3 figures. Proceedings of "2002 MMM Conference", Tampa, F

Multidimensional methods for hyperbolic problems

The numerical solution of multidimensional wave-propagation problems is considerably more complex than solutions for one-dimensional problems, but improving a method`s accuracy produces more significant increases in efficiency. This is particularly true for first-order accurate methods. Higher-order methods, which are already comparatively efficient, are especially difficult to construct on irregular meshes. The passive-scalar advection equation provides an ideal vehicle for investigating the relationships between accuracy, efficiency, and physical acceptability for a variety of finite-difference schemes. Development and analysis of methods for this equation provide insight into solving more complicated problems involving material and/or neutron transport. We found that three approaches to two-dimensional upwind differencing led to schemes equivalent to the dimensionally split Lax-Wendroff method. Assuming stability, we were able to prove that both the split-Lax-Wendroff and a new two-dimensional, predictor-corrector scheme yielded second-order convergence on nonuniform tensor-product grids, despite first-order discretization errors for such grids. We were able to prove that in some cases, Roe`s upwinding for triangulations (which is locally inconsistent) converges with first-order accuracy. The sensitivity of fourth-order accurate, conservative, mimetic methods to the roughness of nonuniform grid-spacing was explored analytically and numerically in one-dimension and for logically-rectangular two-dimensional grids. We also considered the application of a novel set of unknowns towards conservative second-order methods on irregular polyhedral grids. Queried, we noted that convergent, stable, split schemes for ill-posed problems could not exist. This prompted us to reconsider conditions implying that splitting is stable for the differential operators and for related difference methods

"Community Development Banks"

The Clinton/Gore proposal for the creation of a network of 100 community development banks (CDBs) to revitalize communities is bold, and will contribute to the success of the U.S. economy. Banks are essential institutions in any community, and the establishment of a bank is often a prerequisite for the investment process. For this reason, the creation of banks in communities lacking such institutions is important to the welfare of these communities. The vitality of the American economy depends on the continual creation of new and initially small firms. Because it is in the public interest to foster the creation of new entrants into industry, trade, and finance, it is also in the public interest to have a set of strong, independent, profit-seeking banking institutions that specialize in financing smaller businesses. When market forces fail to provide a service that is needed and potentially profitable, it is appropriate for government to help create the market. Community development banks fall into such a category. They do not require a government subsidy, and after start-up costs, the banks are expected to be profitable. The primary perspective of this concept paper is that the main function of the financial structure is to advance the capital development of the economy-to increase the real productive capacity and wealth-producing ability of the economy. The second assumption is that capital development is encouraged by the provision of a broad range of financial services to various segments of the U.S. economy, including consumers, small and large businesses, retailers, developers, and all levels of government. The third is that the existing financial structure is particularly weak in servicing small and start-up businesses, and in servicing certain consumer groups. The fourth is that this problem has become more acute because of a decrease in the number of independent financing alternatives and a rise in the size distribution of financing sources, which have increased the financial system's bias toward larger transactions. These are assumptions that appear to be supported by the evidence: they are also incorporated in other proposals that advance programs to develop community development banking.

A powerful bursting radio source towards the Galactic Centre

Transient astronomical sources are typically powered by compact objects and usually signify highly explosive or dynamic events. While radio astronomy has an impressive record of obtaining high time resolution observations, usually it is achieved in quite narrow fields-of-view. Consequently, the dynamic radio sky is poorly sampled, in contrast to the situation in the X- and gamma-ray bands in which wide-field instruments routinely detect transient sources. Here we report a new transient source, GCRT J1745-3009, detected in 2002 during a moderately wide-field radio transient monitoring program of the Galactic center (GC) region at 0.33 GHz. The characteristics of its bursts are unlike those known for any other class of radio transient. If located in or near the GC, its brightness temperature (~10^16 K) and the implied energy density within GCRT J1745-3009 vastly exceeds that observed in most other classes of radio astronomical sources, and is consistent with coherent emission processes rarely observed. We conclude that GCRT J1745-3009 is the first member of a new class of radio transient sources, the first of possibly many new classes to be identified through current and upcoming radio surveys.Comment: 16 pages including 3 figures. Appears in Nature, 3 March 200

An automated archival VLA transients survey

In this paper we present the results of a survey for radio transients using data obtained from the Very Large Array archive. We have reduced, using a pipeline procedure, 5037 observations of the most common pointings - i.e. the calibrator fields. These fields typically contain a relatively bright point source and are used to calibrate `target' observations: they are therefore rarely imaged themselves. The observations used span a time range ~ 1984 - 2008 and consist of eight different pointings, three different frequencies (8.4, 4.8 and 1.4 GHz) and have a total observing time of 435 hours. We have searched for transient and variable radio sources within these observations using components from the prototype LOFAR transient detection system. In this paper we present the methodology for reducing large volumes of Very Large Array data; and we also present a brief overview of the prototype LOFAR transient detection algorithms. No radio transients were detected in this survey, therefore we place an upper limit on the snapshot rate of GHz frequency transients > 8.0 mJy to rho less than or equal to 0.032 deg^-2 that have typical timescales 4.3 to 45.3 days. We compare and contrast our upper limit with the snapshot rates - derived from either detections or non-detections of transient and variable radio sources - reported in the literature. When compared with the current Log N - Log S distribution formed from previous surveys, we show that our upper limit is consistent with the observed population. Current and future radio transient surveys will hopefully further constrain these statistics, and potentially discover dominant transient source populations. In this paper we also briefly explore the current transient commissioning observations with LOFAR, and the impact they will make on the field.Comment: Accepted for publication in MNRA

Precision measurement of the half-life and the decay branches of 62Ga

In an experiment performed at the Accelerator Laboratory of the University of Jyvaskyla, the beta-decay half-life of 62Ga has been studied with high precision using the IGISOL technique. A half-life of T1/2 = 116.09(17)ms was measured. Using beta-gamma coincidences, the gamma intensity of the 954keV transition and an upper limit of the beta-decay feeding of the 0+_2 state have been extracted. The present experimental results are compared to previous measurements and their impact on our understanding of the weak interaction is discussed.Comment: 7 pages, 7 figures, submitted to EPJ