Solar cell performance, mathematical model Quarterly report, 1 Dec. 1969 - 28 Feb. 1970

Mathematical model for performance prediction of silicon solar cell in space environmen

A Constant Spectral Index for Sagittarius A* During Infrared/X-ray Intensity Variations

We report the first time-series of broadband infrared (IR) color measurements of Sgr A*, the variable emission source associated with the supermassive black hole at the Galactic Center. Using the laser and natural guide star AO systems on the Keck II telescope, we imaged Sgr A* in multiple near-infrared broadband filters with a typical cycle time of ~3 min during 4 observing runs (2005-2006), two of which were simultaneous with Chandra X-ray measurements. In spite of the large range of dereddened flux densities for Sgr A* (2-30 mJy), all of our near-IR measurements are consistent with a constant spectral index of alpha = -0.6+-0.2. Furthermore, this value is consistent with the spectral indices observed at X-ray wavelengths during nearly all outbursts; which is consistent with the synchrotron self-Compton model for the production of the X-ray emission. During the coordinated observations, one IR outburst occurs <36 min after a possibly associated X-ray outburst, while several similar IR outbursts show no elevated X-ray emission. A variable X-ray to IR ratio and constant infrared spectral index challenge the notion that the IR and X-ray emission are connected to the same electrons. We, therefore, posit that the population of electrons responsible for both the IR and X-ray emission are generated by an acceleration mechanism that leaves the bulk of the electron energy distribution responsible for the IR emission unchanged, but has a variable high-energy cutoff. Occasionally a tail of electrons >1 GeV is generated, and it is this high-energy tail that gives rise to the X-ray outbursts. One possible explanation for this type of variation is from the turbulence induced by a magnetorotational instability, in which the outer scale length of the turbulence varies and changes the high-energy cutoff.Comment: 11 pages, 7 figures (color), Accepted for publication in ApJ. Resolution (Fig 1&2) downgraded for astro-ph. For full resolution, see http://casa.colorado.edu/~hornstei/sgracolor.pd

Multinationals Do It Better: Evidence on the Efficiency of Corporations’ Capital Budgeting

This paper examines the effectiveness of multinational enterprises’ capital budgeting decisions as compared to the decisions of purely domestic enterprises. This is an important question because of multinationals’ role in allocating capital globally. Answering this question may also shed light on whether multinationals are indeed better managed than are purely domestic firms. We examine this question empirically using the deviation of a firm’s estimated marginal Tobin’s q from an appropriate benchmark as an indicator of effective resource allocation. We find that multinationals make more efficient capital budgeting decisions than do purely domestic firms. The result stems from multinational enterprises’ exercising greater restraint on over-investment, but is not due to looser liquidity constraints. In obtaining the result, we account for the impact of institutional ownership, managerial ownership, and managerial entrenchment. We also test whether multinationals’ greater capital budgeting efficiency might be due to their investment locations, since they might thereby be monitored by more agents and also may be more successful in resisting pressures from special interest groups and governments to adopt practices that are not consistent with firm value maximization. We do not find support for the monitoring and bargaining hypotheses. Our observations therefore suggest that multinationals may be intrinsically better managed firms than are purely domestic firms

Metacarpophalangeal Pattern Profile Analysis in Sotos Syndrome

The metacarpophalangeal pattern profile (MCPP) was analyzed on 16 Sotos syndrome patients. A mean Sotos syndrome profile was produced. Correlation studies confirm clinical homogeneity of Sotos syndrome individuals. Discriminant analysis of Sotos syndrome patients and normal individuals produces a function of two MCPP variables and age, which may provide a useful tool for diagnosis

The two states of Sgr A* in the near-infrared: bright episodic flares on top of low-level continuous variability

In this paper we examine properties of the variable source Sgr A* in the near-infrared (NIR) using a very extensive Ks-band data set from NACO/VLT observations taken 2004 to 2009. We investigate the variability of Sgr A* with two different photometric methods and analyze its flux distribution. We find Sgr A* is continuously emitting and continuously variable in the near-infrared, with some variability occurring on timescales as long as weeks. The flux distribution can be described by a lognormal distribution at low intrinsic fluxes (<~5 mJy, dereddened with A_{Ks}=2.5). The lognormal distribution has a median flux of approximately 1.1 mJy, but above 5 mJy the flux distribution is significantly flatter (high flux events are more common) than expected for the extrapolation of the lognormal distribution to high fluxes. We make a general identification of the low level emission above 5 mJy as flaring emission and of the low level emission as the quiescent state. We also report here the brightest Ks-band flare ever observed (from August 5th, 2008) which reached an intrinsic Ks-band flux of 27.5 mJy (m_{Ks}=13.5). This flare was a factor 27 increase over the median flux of Sgr A*, close to double the brightness of the star S2, and 40% brighter than the next brightest flare ever observed from Sgr~A*.Comment: 14 pages, 6 figures, accepted for publication in Ap

An open-source probabilistic record linkage process for records with family-level information: Simulation study and applied analysis

Research with administrative records involves the challenge of limited information in any single data source to answer policy-related questions. Record linkage provides researchers with a tool to supplement administrative datasets with other information about the same people when identified in separate sources as matched pairs. Several solutions are available for undertaking record linkage, producing linkage keys for merging data sources for positively matched pairs of records. In the current manuscript, we demonstrate a new application of the Python RecordLinkage package to family-based record linkages with machine learning algorithms for probability scoring, which we call probabilistic record linkage for families (PRLF). First, a simulation of administrative records identifies PRLF accuracy with variations in match and data degradation percentages. Accuracy is largely influenced by degradation (e.g., missing data fields, mismatched values) compared to the percentage of simulated matches. Second, an application of data linkage is presented to compare regression model estimate performance across three record linkage solutions (PRLF, ChoiceMaker, and Link Plus). Our findings indicate that all three solutions, when optimized, provide similar results for researchers. Strengths of our process, such as the use of ensemble methods, to improve match accuracy are discussed. We then identify caveats of record linkage in the context of administrative data

Tributes to Professor Alice Brumbaugh

Tributes to Professor Alice Brumbaugh upon her retirement from the University of Maryland School of Law

Accretion models of Sgr A*

The supermassive black hole in the center of our Galaxy, Sgr A*, is unique because the angular size of the black hole is the largest in the sky thus providing detailed boundary conditions on, and much less freedom for, accretion flow models. In this paper I review advection-dominated accretion flow (ADAF; another name is radiatively inefficient accretion flow) models for Sgr A*. This includes the developments and dynamics of ADAFs, and how to explain observational results including the multi-waveband spectrum, radio polarization, IR and X-ray flares, and the size measurements at radio wavebands.Comment: 9 pages, 6 figures; invited talk presented at the "Galactic Center Workshop 2006: From the Center of the Milky Way to Nearby Low-Luminosity Galactic Nuclei", April 18-22, 2006; Bad Honnef, German

Evidence for X-ray synchrotron emission from simultaneous mid-IR to X-ray observations of a strong Sgr A* flare

This paper reports measurements of Sgr A* made with NACO in L' -band (3.80 um), Ks-band (2.12 um) and H-band (1.66 um) and with VISIR in N-band (11.88 um) at the ESO VLT, as well as with XMM-Newton at X-ray (2-10 keV) wavelengths. On 4 April, 2007, a very bright flare was observed from Sgr A* simultaneously at L'-band and X-ray wavelengths. No emission was detected using VISIR. The resulting SED has a blue slope (beta > 0 for nuL_nu ~ nu^beta, consistent with nuL_nu ~ nu^0.4) between 12 micron and 3.8 micron. For the first time our high quality data allow a detailed comparison of infrared and X-ray light curves with a resolution of a few minutes. The IR and X-ray flares are simultaneous to within 3 minutes. However the IR flare lasts significantly longer than the X-ray flare (both before and after the X-ray peak) and prominent substructures in the 3.8 micron light curve are clearly not seen in the X-ray data. From the shortest timescale variations in the L'-band lightcurve we find that the flaring region must be no more than 1.2 R_S in size. The high X-ray to infrared flux ratio, blue nuL_nu slope MIR to L' -band, and the soft nuL_nu spectral index of the X-ray flare together place strong constraints on possible flare emission mechanisms. We find that it is quantitatively difficult to explain this bright X-ray flare with inverse Compton processes. A synchrotron emission scenario from an electron distribution with a cooling break is a more viable scenario.Comment: ApJ, 49 pages, 9 figure

Circulating miR-181 is a prognostic biomarker for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a relentless neurodegenerative disease of the human motor neuron system, where variability in progression rate limits clinical trial efficacy. Therefore, better prognostication will facilitate therapeutic progress. In this study, we investigated the potential of plasma cell-free microRNAs (miRNAs) as ALS prognostication biomarkers in 252 patients with detailed clinical phenotyping. First, we identified, in a longitudinal cohort, miRNAs whose plasma levels remain stable over the course of disease. Next, we showed that high levels of miR-181, a miRNA enriched in neurons, predicts a greater than two-fold risk of death in independent discovery and replication cohorts (126 and 122 patients, respectively). miR-181 performance is similar to neurofilament light chain (NfL), and when combined together, miR-181 + NfL establish a novel RNA–protein biomarker pair with superior prognostication capacity. Therefore, plasma miR-181 alone and a novel miRNA–protein biomarker approach, based on miR-181 + NfL, boost precision of patient stratification. miR-181-based ALS biomarkers encourage additional validation and might enhance the power of clinical trials