Efficient generation and optimization of stochastic template banks by a neighboring cell algorithm

Placing signal templates (grid points) as efficiently as possible to cover a multi-dimensional parameter space is crucial in computing-intensive matched-filtering searches for gravitational waves, but also in similar searches in other fields of astronomy. To generate efficient coverings of arbitrary parameter spaces, stochastic template banks have been advocated, where templates are placed at random while rejecting those too close to others. However, in this simple scheme, for each new random point its distance to every template in the existing bank is computed. This rapidly increasing number of distance computations can render the acceptance of new templates computationally prohibitive, particularly for wide parameter spaces or in large dimensions. This work presents a neighboring cell algorithm that can dramatically improve the efficiency of constructing a stochastic template bank. By dividing the parameter space into sub-volumes (cells), for an arbitrary point an efficient hashing technique is exploited to obtain the index of its enclosing cell along with the parameters of its neighboring templates. Hence only distances to these neighboring templates in the bank are computed, massively lowering the overall computing cost, as demonstrated in simple examples. Furthermore, we propose a novel method based on this technique to increase the fraction of covered parameter space solely by directed template shifts, without adding any templates. As is demonstrated in examples, this method can be highly effective..Comment: PRD accepte

A Lower Bound Technique for Communication in BSP

Communication is a major factor determining the performance of algorithms on current computing systems; it is therefore valuable to provide tight lower bounds on the communication complexity of computations. This paper presents a lower bound technique for the communication complexity in the bulk-synchronous parallel (BSP) model of a given class of DAG computations. The derived bound is expressed in terms of the switching potential of a DAG, that is, the number of permutations that the DAG can realize when viewed as a switching network. The proposed technique yields tight lower bounds for the fast Fourier transform (FFT), and for any sorting and permutation network. A stronger bound is also derived for the periodic balanced sorting network, by applying this technique to suitable subnetworks. Finally, we demonstrate that the switching potential captures communication requirements even in computational models different from BSP, such as the I/O model and the LPRAM

Ethnic enclaves and the economic success of immigrants - evidence from a natural experiment

Recent immigrants tend to locate in ethnic "enclaves" within metropolitan areas. The economic consequence of living in such enclaves is still an unresolved issue. We use an immigrant policy initiative in Sweden, when government authorities distributed refugee immigrants across locales in a way that may be considered exogenous. This policy initiative provides a unique natural experiment, which allows us to estimate the causal effect on labor market outcomes of living in enclaves. We find substantive evidence of sorting across locations. When sorting is taken into account, living in enclaves improves labor market outcomes; for instance, the earnings gain associated with a standard deviation increase in ethnic concentration is in the order of four to five percent.Immigration; Enclaves; Labor market outcomes

Settlement Policies and the Economic Success of Immigrants

Many developed countries, e.g. the UK, Germany, and Sweden, use or have used settlement policies to direct the inflow of new immigrants away from immigrant dense metropolitan areas. We evaluate a reform of Swedish immigration policy that featured dispersion of refugee immigrants across the country, but also a change in the approach to labor market integration. We focus exclusively on how immigrants fared because of the policy. The results indicate that immigrants experienced fairly substantial long run losses because of the policy. We also find that only a smaller share of this effect was associated with the dispersion of immigrants across regions. The larger share of the impact appears to stem from a common component that affected immigrants regardless of where they were located. Our somewhat speculative reading of this result is that it can be traced to a shift in emphasis of integration policy from a policy focusing on labor market assimilation to one of income support.Immigration; Settlement policies; Labor market outcomes

How Important is Access to Jobs? Old Question - Improved Answer.

We study the impact of job proximity on individual employment and earnings. The analysis exploits a Swedish refugee dispersal policy to obtain exogenous variation in individual locations. Using very detailed data on the exact location of all residences and workplaces in Sweden, we find that having been placed in a location with poor job access in 1990-91 adversely affected employment in 1999. Doubling the number of jobs in the initial location in 1990-91 is associated with 2.9 percentage points higher employment probability in 1999. Considering that the 1999 employment rate was 43 percent among the refugees, this is a considerable effect. The analysis suggests that residential sorting leads to underestimation of the impact of job access.Job access, endogenous location, natural experiment

Sorting and separation of microparticles by surface properties using liquid crystal-enabled electro-osmosis

Sorting and separation of microparticles is a challenging problem of interdisciplinary nature. Existing technologies can differentiate microparticles by their bulk properties, such as size, density, electric polarizability, etc. The next level of challenge is to separate particles that show identical bulk properties and differ only in subtle surface features, such as functionalization with ligands. In this work, we propose a technique to sort and separate particles and fluid droplets that differ in surface properties. As a dispersive medium, we use a nematic liquid crystal (LC) rather than an isotropic fluid, which allows us to amplify the difference in surface properties through distinct perturbations of LC order around the dispersed particles. The particles are placed in a LC cell with spatially distorted molecular orientation subject to an alternating current electric field. The gradients of the molecular orientation perform two functions. First, elastic interactions between these pre-imposed gradients and distortions around the particles separate the particles with different surface properties in space. Second, these pre-imposed patterns create electro-osmotic flows powered by the electric field that transport the sorted particles to different locations thus separating them. The demonstrated unique sorting and separation capability opens opportunities in lab-on-a-chip, cell sorting and bio-sensing applications

Ethnic Enclaves and Welfare Cultures – Quasi-Experimental Evidence

We examine peer effects in welfare use among immigrants to Sweden by exploiting a governmental refugee placement policy. We distinguish between the quantity of contacts—the number of individuals of the same ethnicity—and the quality of contacts – welfare use among members of the ethnic group. OLS regressions suggest that both these factors are positively related to individual welfare use. Instrumental variables estimations yield the conclusion that only the quality of contacts matter. An increase of the fraction of the ethnic group on welfare by 10 percent raises the individual probability of welfare use by almost 7 percent.immigrants, welfare use, ethnic concentration, welfare cultures, immigration

How Important is Access to Jobs? Old Question - Improved Answer

We study the impact of job proximity on individual employment and earnings. The analysis exploits a Swedish refugee dispersal policy to get exogenous variation in individual locations. Using very detailed data on the exact location of all residences and workplaces in Sweden, we find that having been placed in a location with poor job access in 1990-91 adversely affected employment in 1999. Doubling the number of jobs in the initial location in 1990-91 is associ­ated with 2.9 percentage points higher employment probability in 1999. The analysis suggests that residential sorting leads to underestimation of the impact of job access.Spatial Mismatch; Endogenous Location; Natural Experiment