Michigan Technological University

About: Michigan Technological University is a education organization based out in Houghton, Michigan, United States. It is known for research contribution in the topics: Population & Volcano. The organization has 8023 authors who have published 17422 publications receiving 481780 citations. The organization is also known as: MTU & Michigan Tech.

Multiframe blind deconvolution of astronomical images

Abstract: Maximum-likelihood estimation techniques are presented for the problem of forming object estimates from turbulence-degraded images when the point-spread functions are unknown. The inability of unconstrained maximum-likelihood methods to form meaningful estimates is acknowledged, and iterative algorithms are derived for estimating the object by using both a penalized maximum-likelihood method and a physically meaningful parameterization of the point-spread functions by phase errors distributed over an aperture.

Dependence of energy gap on x and T in Zn 1 − x Mn x Se: The role of exchange interaction

Abstract: Photoluminescence and reflectivity measurements have been carried out on ${\mathrm{Zn}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Se solid solutions in the complete range of crystal compositions, 0\ensuremath{\le}x\ensuremath{\le}0.55. The features of the photoluminescence and reflectivity data near the band edge enabled us to determine values of the fundamental band gap as a function of Mn molar fraction x and temperature (8 K\ensuremath{\le}T\ensuremath{\le}300 K). The energy gap in crystals with compositions in the vicinity of the zinc-blende--wurtzite structural transition (0.2\ensuremath{\lesssim}x\ensuremath{\lesssim}0.3) exhibited a scatter of values, probably associated with the presence of various polytypes (as evidenced by transmission-electron-microscopy measurements). The dependence of ${E}_{g}$ on x is anomalous for 0\ensuremath{\le}x\ensuremath{\le}0.2, showing a minimum in the ${E}_{g}$ vs x curve. A simple model (in terms of second-order perturbation theory in s-d and p-d interactions) relates this minimum to a maximum observed in the magnetic susceptibility as a function of x. For samples with x\ensuremath{\gtrsim}0.35, the ${E}_{g}$ dependence on T shows an onset of an additional blue shift as the temperature is lowered below \ensuremath{\sim}150 K. This onset, though not reproduced by our simple calculation, appears to be also related to the presence of s-d and p-d interactions.

Physical aging of epoxy polymers and their composites

Abstract: Exposure to extended periods of sub-Tg temperatures causes physical changes in the molecular structure of epoxy resins and epoxy-based materials to occur. These physical aging mechanisms include the reduction in free volume and changes to the molecular configuration. As a result, mechanical, thermodynamical, and physical properties are affected in ways that can compromise the reliability of epoxy-based engineering components and structures. In this review, the physical changes in the molecular structure of epoxies are described, and the influence of these changes on the bulk-level response is detailed. Specifically, the influence of physical aging on the quasistatic mechanical properties, viscoelasticity, fracture toughness, thermal expansion coefficient, volume relaxation, enthalpy relaxation, endothermic peak temperature, fictive temperature, and moisture/solvent absorption capability is reviewed. Also discussed are relationships between relaxation functions, crosslink density, composite reinforcement, and epoxy/copolymer blending and the physical aging response of epoxies. Finally, the concepts of thermal and mechanical rejuvenation are discussed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

Joint analysis of two microarray gene-expression data sets to select lung adenocarcinoma marker genes

Abstract: Due to the high cost and low reproducibility of many microarray experiments, it is not surprising to find a limited number of patient samples in each study, and very few common identified marker genes among different studies involving patients with the same disease. Therefore, it is of great interest and challenge to merge data sets from multiple studies to increase the sample size, which may in turn increase the power of statistical inferences. In this study, we combined two lung cancer studies using micorarray GeneChip®, employed two gene shaving methods and a two-step survival test to identify genes with expression patterns that can distinguish diseased from normal samples, and to indicate patient survival, respectively. In addition to common data transformation and normalization procedures, we applied a distribution transformation method to integrate the two data sets. Gene shaving (GS) methods based on Random Forests (RF) and Fisher's Linear Discrimination (FLD) were then applied separately to the joint data set for cancer gene selection. The two methods discovered 13 and 10 marker genes (5 in common), respectively, with expression patterns differentiating diseased from normal samples. Among these marker genes, 8 and 7 were found to be cancer-related in other published reports. Furthermore, based on these marker genes, the classifiers we built from one data set predicted the other data set with more than 98% accuracy. Using the univariate Cox proportional hazard regression model, the expression patterns of 36 genes were found to be significantly correlated with patient survival (p < 0.05). Twenty-six of these 36 genes were reported as survival-related genes from the literature, including 7 known tumor-suppressor genes and 9 oncogenes. Additional principal component regression analysis further reduced the gene list from 36 to 16. This study provided a valuable method of integrating microarray data sets with different origins, and new methods of selecting a minimum number of marker genes to aid in cancer diagnosis. After careful data integration, the classification method developed from one data set can be applied to the other with high prediction accuracy.

Auditor Tenure and the Ability to Meet or Beat Earnings Forecasts

Abstract: We examine the relation between auditor tenure and a firm's ability to use discretionary accruals to meet or beat analysts' earnings forecasts. Regulators have long expressed concern over the use of earnings management to attain earnings targets. These concerns are compounded by lingering questions over whether long-term auditor-client relationships impair an auditor's ability to independently stem such practices. The profession counter-argues that mandatory auditor rotation reduces auditors' familiarity with the client and adversely affects audit quality. Consistent with both arguments, we find that firms with both short (two to three years) and long (13-15 years or more) tenure are more likely to report levels of discretionary accruals that allow them to meet or beat earnings forecasts. The results suggest that while regulatory mandates for periodic auditor turnover have negative effects, sustained long term auditor-client relationships may be also detrimental to audit quality. The generalizability of our results may not extend to firms that are not covered by analysts, as these firms do not face the same public pressure to manage earnings in order to meet or beat expectations.