Prototype selection for parameter estimation in complex models

Parameter estimation in astrophysics often requires the use of complex physical models. In this paper we study the problem of estimating the parameters that describe star formation history (SFH) in galaxies. Here, high-dimensional spectral data from galaxies are appropriately modeled as linear combinations of physical components, called simple stellar populations (SSPs), plus some nonlinear distortions. Theoretical data for each SSP is produced for a fixed parameter vector via computer modeling. Though the parameters that define each SSP are continuous, optimizing the signal model over a large set of SSPs on a fine parameter grid is computationally infeasible and inefficient. The goal of this study is to estimate the set of parameters that describes the SFH of each galaxy. These target parameters, such as the average ages and chemical compositions of the galaxy's stellar populations, are derived from the SSP parameters and the component weights in the signal model. Here, we introduce a principled approach of choosing a small basis of SSP prototypes for SFH parameter estimation. The basic idea is to quantize the vector space and effective support of the model components. In addition to greater computational efficiency, we achieve better estimates of the SFH target parameters. In simulations, our proposed quantization method obtains a substantial improvement in estimating the target parameters over the common method of employing a parameter grid. Sparse coding techniques are not appropriate for this problem without proper constraints, while constrained sparse coding methods perform poorly for parameter estimation because their objective is signal reconstruction, not estimation of the target parameters.Comment: Published in at http://dx.doi.org/10.1214/11-AOAS500 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

Combustion Dynamics Characteristics and Fuel Pressure Modulation Responses of a Three-Cup Third-Generation Swirl-Venturi Lean Direct Injection Combustion Concept

This paper presents the combustion dynamic data and fuel modulation response of a three-cup Lean Direct Injection combustor developed by Woodward, FST. The test was conducted at the NASA Glenn Research Center CE-5 flame tube test facility. The facility provided inlet air up to 922 K and pressure up to 19.0 bar. At the low-power configuration, the combustion noise was quiet. Large combustion pressure oscillations were observed with the High-power configuration at an off design condition, with low inlet air temperature and pressure conditions and a high equivalence ratio (about T3=600 K, P3 = 800 kPa, and ER =0.46). The noise amplitude was as high as 1.5 psi at around 220 Hz. As inlet air pressure and temperature increased, this combustion instability decreased. Fuel modulated signals were produced with the WASK fuel modulator located in the fuel line upstream of the center cup pilot fuel-air mixer. The amplitudes of the modulated signals detected in the combustor were low. Only less than 0.13% (0.06 psi) of the input energy was detected, and the signal amplitudes decreased as the modulated frequencies increased. Interaction between the modulated signals and the combustion noise varied with operating conditions. At a condition with low combustion noise around 150 hz, modulating a signal at around the same frequency would increase the combustion noise from 0.2 psi to as high as 0.6 psi, whereas at a condition with a high combustion instability around 250 hz, the modulated signal did not seem to have much effect on the combustion noise

The Globular Cluster System of the Coma cD Galaxy NGC 4874 from Hubble Space Telescope ACS and WFC3/IR Imaging

We present new HST optical and near-infrared (NIR) photometry of the rich globular cluster (GC) system of NGC 4874, the cD galaxy in the core of the Coma cluster (Abell 1656). NGC 4874 was observed with the HST Advanced Camera for Surveys in the F475W (g) and F814W (I) passbands and the Wide Field Camera 3 IR Channel in F160W (H). The GCs in this field exhibit a bimodal optical color distribution with more than half of the GCs falling on the red side at g-I > 1. Bimodality is also present, though less conspicuously, in the optical-NIR I-H color. Consistent with past work, we find evidence for nonlinearity in the g-I versus I-H color-color relation. Our results thus underscore the need for understanding the detailed form of the color-metallicity relations in interpreting observational data on GC bimodality. We also find a very strong color-magnitude trend, or "blue tilt," for the blue component of the optical color distribution of the NGC 4874 GC system. A similarly strong trend is present for the overall mean I-H color as a function of magnitude; for M_814 < -10 mag, these trends imply a steep mass-metallicity scaling with $Z\propto M_{\rm GC}^{1.4\pm0.4}$, but the scaling is not a simple power law and becomes much weaker at lower masses. As in other similar systems, the spatial distribution of the blue GCs is more extended than that of the red GCs, partly because of blue GCs associated with surrounding cluster galaxies. In addition, the center of the GC system is displaced by 4+/-1 kpc towards the southwest from the luminosity center of NGC 4874, in the direction of NGC 4872. Finally, we remark on a dwarf elliptical galaxy with a noticeably asymmetrical GC distribution. Interestingly, this dwarf has a velocity of nearly -3000 km/s with respect to NGC 4874; we suggest it is on its first infall into the cluster core and is undergoing stripping of its GC system by the cluster potential.Comment: 24 pages, 20 figures, accepted for publication in Ap

Multicollinearity in Regression Analyses Conducted in Epidemiologic Studies

The adverse impact of ignoring multicollinearity on findings and data interpretation in regression analysis is very well documented in the statistical literature. The failure to identify and report multicollinearity could result in misleading interpretations of the results. A review of epidemiological literature in PubMed from January 2004 to December 2013, illustrated the need for a greater attention to identifying and minimizing the effect of multicollinearity in analysis of data from epidemiologic studies. We used simulated datasets and real life data from the Cameron County Hispanic Cohort to demonstrate the adverse effects of multicollinearity in the regression analysis and encourage researchers to consider the diagnostic for multicollinearity as one of the steps in regression analysis

Volatile Compounds Produced by Irradiation of Commercial Hams and Frankfurters

Low-dose irradiation (1.6 kGy) of commercially- produced cured, sliced ham and frankfurters resulted in off-odors and off-flavors following the irradiation treatment. Lipid oxidation was not affected by irradiation but gas chromatography/mass spectrometry analysis showed that several new volatile compounds were produced in the products by irradiation processing. These included heptane, trans-1-butyl-2- methylcyclopropanone, 2-octene toluene and 2- butanone. Changes in odor and flavor of irradiated ham and frankfurters resulting from production of volatile compounds must be controlled before irradiation will be accepted by the industry or by consumers as a means of improved the microbial safety of these products

Combined Metformin and Resveratrol Confers Protection Against UVC-Induced DNA Damage in A549 Lung Cancer Cells via Modulation of Cell Cycle Checkpoints and DNA Repair

Aging in humans is a multi-factorial cellular process that is associated with an increase in the risk of numerous diseases including diabetes, coronary heart disease and cancer. Aging is linked to DNA damage, and a persistent source of DNA damage is exposure to ultraviolet (UV) radiation. As such, identifying agents that confer protection against DNA damage is an approach that could reduce the public health burden of age-related disorders. Metformin and resveratrol have both shown effectiveness in preventing several age-related diseases; using human A549 cells, we investigated whether metformin or resveratrol, alone or combined, prevent UVC-induced DNA damage. We found that metformin inhibited UVC-induced upregulation of p53, as well as downregulated the expression of two DNA damage markers: γH2AX and p-chk2. Metformin also upregulated DNA repair as evidenced by the increase in expression of p53R2. Treatment with metformin also induced cell cycle arrest in UVC-induced cells, in correlation with a reduction in the levels of cyclin E/cdk2/Rb and cyclin B1/cdk1. Compared to metformin, resveratrol as a single agent showed less effectiveness in counteracting UVC-elicited cellular responses. However, resveratrol displayed synergism when combined with metformin as shown by the downregulation of p53/γH2AX/p-chk2. In conclusion, the results of the present study validate the effectiveness of metformin, alone or with the addition of resveratrol, in reducing the risk of aging by conferring protection against UV-induced DNA damage

The virtual peripheral nerve academy: education for the identification and treatment of peripheral nerve disorders

Millions of people around the globe suffer peripheral nerve injuries caused by trauma and medical disorders. However, medical school curricula are profoundly deficient in peripheral nerve education. This lack of knowledge within the healthcare profession may cause inadequate patient care. We developed the Virtual Peripheral Nerve Academy (VPNA) as a reusable virtual learning environment to provide medical students with detailed education on the peripheral nervous system (PNS). Students are introduced to the PNS through virtual 3D rendering of the human body, wherein they visualize individual nerves through dissection and observe normal motor and sensory function associated with each nerve. PNS structures that are absent from traditional texts are included in this visualization, ranging from the innervation of joints to the normal anatomic variation required for differential diagnosis of pain after an injury. Detailed modules on peripheral nerve disorders allow students to observe pathophysiological mechanisms, associated symptomatology, and appropriate treatments. Students are briefed on a patient clinical case, then interact with a patient avatar to learn the appropriate diagnostics, including physical exam maneuvers and electrodiagnostic testing. Interactive modules on peripheral nerve surgeries detail surgical techniques. The VPNA data and analytics dashboards allow medical students and course instructors to assess skill improvement and identify specific learning needs. The built-in learner management system and availability on both computer-based and virtual reality platforms facilitate integration into any existing medical school curricula. Ultimately, this immersive technology enables every medical student to learn about the peripheral nervous system and gain competency in treating real-life nerve pathologies