Low cost management of replicated data in fault-tolerant distributed systems

Many distributed systems replicate data for fault tolerance or availability. In such systems, a logical update on a data item results in a physical update on a number of copies. The synchronization and communication required to keep the copies of replicated data consistent introduce a delay when operations are performed. A technique is described that relaxes the usual degree of synchronization, permitting replicated data items to be updated concurrently with other operations, while at the same time ensuring that correctness is not violated. The additional concurrency thus obtained results in better response time when performing operations on replicated data. How this technique performs in conjunction with a roll-back and a roll-forward failure recovery mechanism is also discussed

Approximate initial data for binary black holes

We construct approximate analytical solutions to the constraint equations of general relativity for binary black holes of arbitrary mass ratio in quasicircular orbit. We adopt the puncture method to solve the constraint equations in the transverse-traceless decomposition and consider perturbations of Schwarzschild black holes caused by boosts and the presence of a binary companion. A superposition of these two perturbations then yields approximate, but fully analytic binary black hole initial data that are accurate to first order in the inverse of the binary separation and the square of the black holes' momenta.Comment: 13 pages, 4 figures, added comparison to numerical calculations, accepted to PR

How to deal with the growing incentives competition

The use of subsidies to attract investment costs government billions of dollars annually, making regulation urgent. While comprehensive limitations such as the EU’s are not likely soon, we should improve transparency, have major stakeholders promote incentive rules within preferential trade areas, strengthen WTO notifications, and ban relocation subsidies where possibl

Interpreting Spectral Energy Distributions from Young Stellar Objects. I. A grid of 200,000 YSO model SEDs

We present a grid of radiation transfer models of axisymmetric young stellar objects (YSOs), covering a wide range of stellar masses (from 0.1Msun to 50Msun) and evolutionary stages (from the early envelope infall stage to the late disk-only stage). The grid consists of 20,000 YSO models, with spectral energy distributions (SEDs) and polarization spectra computed at ten viewing angles for each model, resulting in a total of 200,000 SEDs. [...]. These models are publicly available on a dedicated WWW server: http://www.astro.wisc.edu/protostars/ . In this paper we summarize the main features of our models, as well as the range of parameters explored. [...]. We examine the dependence of the spectral indices of the model SEDs on envelope accretion rate and disk mass. In addition, we show variations of spectral indices with stellar temperature, disk inner radius, and disk flaring power for a subset of disk-only models. We also examine how changing the wavelength range of data used to calculate spectral indices affects their values. We show sample color-color plots of the entire grid as well as simulated clusters at various distances with typical {\it Spitzer Space Telescope} sensitivities. We find that young embedded sources generally occupy a large region of color-color space due to inclination and stellar temperature effects. Disk sources occupy a smaller region of color-color space, but overlap substantially with the region occupied by embedded sources, especially in the near- and mid-IR. We identify regions in color-color space where our models indicate that only sources at a given evolutionary stage should lie. [...].Comment: 69 pages, 28 figures, Accepted for publication in ApJS. Preprint with full resolution figures available at http://www.astro.wisc.edu/protostars

Tax Increment Financing in Missouri: An Analysis of Determinants, Competitive Dynamics, Equity, and Path Dependency

Tax increment financing (TIF) has been a popular and controversial economic development tool for several decades. This research considers the determinants of competitive dynamics, equity, and path dependency on TIF use. We use logistic and ordinary least squares regressions on the approval, number, and value of TIFs in Missouri to flesh out the way the determinants contribute to TIF approval, value, and frequency of use. This study finds that there are competitive dynamics that affect TIF use: being adjacent to another city that uses TIFs increases the likelihood that a city will approve a TIF. The study finds evidence that TIF adoption patterns contribute to intermunicipal inequality, and provides some support for the importance of path dependency on TIF use

Trumpet slices of the Schwarzschild-Tangherlini spacetime

We study families of time-independent maximal and 1+log foliations of the Schwarzschild-Tangherlini spacetime, the spherically-symmetric vacuum black hole solution in D spacetime dimensions, for D >= 4. We identify special members of these families for which the spatial slices display a trumpet geometry. Using a generalization of the 1+log slicing condition that is parametrized by a constant n we recover the results of Nakao, Abe, Yoshino and Shibata in the limit of maximal slicing. We also construct a numerical code that evolves the BSSN equations for D=5 in spherical symmetry using moving-puncture coordinates, and demonstrate that these simulations settle down to the trumpet solutions.Comment: 11 pages, 6 figures, submitted to PR