A centrifugo-magnetically actuated gas micropump

This paper describes a novel gas micropump on a centrifugal microfluidic platform. The pump is integrated on a passive and microstructured polymer disk which is sealed with an elastomer lid featuring paramagnetic inlays. The rotational motion of this hybrid disk over a stationary magnet induces a designated sequence of volume displacements of the elastic lid, leading to a net transport of gas. The pumping pressure scales linearly with the frequency, with a maximum observable pressure of 4.1 kPa. The first application of this rotary device is the production of gas-liquid flows by pumping ambient air into a continuous centrifugal flow of liquid. The injected gas volume segments the liquid stream into a series of liquid compartments. Apart from such multi-phase flows, the new pumping technique supplements a generic air-to-liquid sampling method to centrifugal microfluidic platforms

Leverage and productivity growth in emerging economies: Is there a threshold effect?

While credit is essential for investment, innovation and economic growth, there are risks to unfettered credit booms. The present paper provides an innovative micro-economic approach to identify the threshold leverage beyond which corporate indebtedness becomes “excessive”. In particular, the paper hypothesizes a non-linear relationship in that moderate leverage could boost growth while very high leverage could restrict total factor productivity growth, through increased likelihood of financial distress and bankruptcy. Estimates of a threshold model for a group of emerging CEE countries confirm the non-linear relationship, after controlling for various firm, industry and financial market characteristics.Financial support from ESRC grant RES-062-23-0986 is gratefully acknowledge

Statistical eigen-inference from large Wishart matrices

We consider settings where the observations are drawn from a zero-mean multivariate (real or complex) normal distribution with the population covariance matrix having eigenvalues of arbitrary multiplicity. We assume that the eigenvectors of the population covariance matrix are unknown and focus on inferential procedures that are based on the sample eigenvalues alone (i.e., "eigen-inference"). Results found in the literature establish the asymptotic normality of the fluctuation in the trace of powers of the sample covariance matrix. We develop concrete algorithms for analytically computing the limiting quantities and the covariance of the fluctuations. We exploit the asymptotic normality of the trace of powers of the sample covariance matrix to develop eigenvalue-based procedures for testing and estimation. Specifically, we formulate a simple test of hypotheses for the population eigenvalues and a technique for estimating the population eigenvalues in settings where the cumulative distribution function of the (nonrandom) population eigenvalues has a staircase structure. Monte Carlo simulations are used to demonstrate the superiority of the proposed methodologies over classical techniques and the robustness of the proposed techniques in high-dimensional, (relatively) small sample size settings. The improved performance results from the fact that the proposed inference procedures are "global" (in a sense that we describe) and exploit "global" information thereby overcoming the inherent biases that cripple classical inference procedures which are "local" and rely on "local" information.Comment: Published in at http://dx.doi.org/10.1214/07-AOS583 the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

Race and “Hotspots” of Preventable Hospitalizations

Abstract Preventable hospitalizations (PHs) are those for ambulatory care-sensitive conditions that indicate insufficiencies in local primary healthcare. PH rates tend to be higher among African Americans, in urban centers, rural areas and areas with more African American residents. The objective of this study is to determine geographic clusters of high PH rates (“spatial clusters”) by race. Data from Maryland hospitals were utilized to determine the rates of PHs in zip code tabulation areas (ZCTAs) by race in 2010. Geographic clusters of ZCTAs with higher than expected PH rates were identified using Scan Statistic and Anselin’s Local Moran’s I. 10 PH spatial clusters were observed among the total population with an average PH rate of 3,046.6 per 100,000 population. Among whites, the average PH rate was 3,339.9 per 100,000 in 11 PH spatial clusters. Only five PH spatial clusters were observed among African Americans with a higher average PH rate (3,710.8 per 100,000). The locations and other characteristics of PH spatial clusters differed by race. These results can be used to target resources to areas with high PH rates. Because PH spatial clusters are observed in differing locations for African Americans, approaches that include cultural tailoring may need to be specifically targeted

Black men, English suits and a Corner Office: Education and the making of a West-Cameroon Civil Service 1954-1972

Abstract: Within the perspective of postcolonial state building in Africa, the study hinges on the colonial education, manpower and development nexus to examine the state of preparedness of the Trust Territory of the British Southern Cameroons with regards to an indigenous political and economic leadership as the British and Nigerian colonial authorities were leaving the territory. It discusses the quantity and quality of manpower produced by the British colonial education system that was on hand to take over the mantle of leadership as the territory gained independence. The study asserts that, the forming West Cameroon state was ill-disposed to its own endeavours due to lacks in a sufficiently qualified personnel and could thus not implement its own policies; the roots being a poorly developed colonial educational system. This had significant effects on the socio-economic development of the federal state of West Cameroon. The paper has relied on archival data and some critical secondary literature to present the argument

Halo-Galaxy Lensing: A Full Sky Approach

The halo-galaxy lensing correlation function or the average tangential shear profile over sampled halos is a very powerful means of measuring the halo masses, the mass profile, and the halo-mass correlation function of very large separations in the linear regime. We reformulate the halo-galaxy lensing correlation in harmonic space. We find that, counter-intuitively, errors in the conventionally used flat-sky approximation remain at a % level even at very small angles. The errors increase at larger angles and for lensing halos at lower redshifts: the effect is at a few % level at the baryonic acoustic oscillation scales for lensing halos of $z\sim 0.2$, and comparable with the effect of primordial non-Gaussianity with $f_{\rm NL}\sim 10$ at large separations. Our results allow to readily estimate/correct for the full-sky effect on a high-precision measurement of the average shear profile available from upcoming wide-area lensing surveys.Comment: 12 pages, 4 figure