Photoluminescence investigation of GaN films grown by metalorganic chemical vapor deposition on (100) GaAs

GaN films were grown on (100) GaAs substrates by metalorganic chemical vapor deposition and were found to be of (200) cubic or (111) cubic/(0002) hexagonal phase. Their photoluminescence characteristics remained invariant with material phase. We report assignment of band‐edge photoluminescence near 3.36 eV and 3.15–3.31 eV in apparently cubic GaN to intrinsic/bound excitons and phonon‐assisted, donor‐acceptor pair recombination respectively, on the basis of observed temperature and intensity dependences. A free exciton energy of 3.375 eV is deduced at 6.5 K. © 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69757/2/JAPIAU-77-4-1705-1.pd

Relating Statistical Image Differences and Degradation Features

Document images are degraded through bilevel processes such as scanning, printing, and photocopying. The resulting image degradations can be categorized based either on observable degradation features or on degradation model parameters. The degradation features can be related mathematically to model parameters. In this paper we statistically compare pairs of populations of degraded character images created with different model parameters. The changes in the probability that the characters are from different populations when the model parameters vary correlate with the relationship between observable degradation features and the model parameters. The paper also shows which features have the largest impact on the image

Hierarchically coupled ultradian oscillators generating robust circadian rhythms

Ensembles of mutually coupled ultradian cellular oscillators have been proposed by a number of authors to explain the generation of circadian rhythms in mammals. Most mathematical models using many coupled oscillators predict that the output period should vary as the square root of the number of participating units, thus being inconsistent with the well-established experimental result that ablation of substantial parts of the suprachiasmatic nuclei (SCN), the main circadian pacemaker in mammals, does not eliminate the overt circadian functions, which show no changes in the phases or periods of the rhythms. From these observations, we have developed a theoretical model that exhibits the robustness of the circadian clock to changes in the number of cells in the SCN, and that is readily adaptable to include the successful features of other known models of circadian regulation, such as the phase response curves and light resetting of the phase

Ezrin, a membrane cytoskeleton cross-linker protein, as a marker of epithelial damage in asthma

RATIONALE: Bronchial epithelial cell damage occurs in patients with bronchial asthma. Ezrin, a membrane-cytoskeleton protein, maintains cellular morphology and intercellular adhesion and protects the barrier function of epithelial cells. OBJECTIVES: To study the role of ezrin in bronchial epithelial cells injury and correlate its expression with asthma severity. METHODS: Levels of ezrin were measured in exhaled breath condensate (EBC) and serum in asthma patients and bronchoalveolar lavage fluid (BALF) from a mouse model of asthma by ELISA. The regulation of IL-13 on ezrin protein levels was studied in primary bronchial epithelial cells (PBECs). Ezrin knockdown using shRNA was studied in human bronchial epithelial 16HBE cells. RESULTS: Ezrin levels were decreased in asthmatic EBC (392.7±34.99 vs 150.5±10.22 pg/ml, p<0.0001) and serum (700.7±55.59 vs 279.2±25.83pg/ml, p<0.0001) compared to normal subjects. Levels were much lower in uncontrolled (p<0.001) and partly-controlled patients (p<0.01) compared to well-controlled subjects. EBC and serum ezrin levels correlated with lung function in asthma patients and serum ezrin levels were negatively correlated with serum IL-13 and periostin. IL-13-induced down-regulation of ezrin expression in PBECs was significantly attenuated by the JAK2 (Janus tyrosine kinase 2) inhibitor TG101348. Ezrin knockdown changed 16HBE cell morphology, enlarged intercellular spaces and increased their permeability. Ezrin expression was decreased in the lung tissue and BALF of 'asthmatic' mice and negatively correlated with BALF IL-13 level. CONCLUSIONS: Ezrin down-regulation is associated with IL-13-induced epithelial damage and might be a potential biomarker of asthma control

Identification of disease-causing genes using microarray data mining and gene ontology

Background: One of the best and most accurate methods for identifying disease-causing genes is monitoring gene expression values in different samples using microarray technology. One of the shortcomings of microarray data is that they provide a small quantity of samples with respect to the number of genes. This problem reduces the classification accuracy of the methods, so gene selection is essential to improve the predictive accuracy and to identify potential marker genes for a disease. Among numerous existing methods for gene selection, support vector machine-based recursive feature elimination (SVMRFE) has become one of the leading methods, but its performance can be reduced because of the small sample size, noisy data and the fact that the method does not remove redundant genes. Methods: We propose a novel framework for gene selection which uses the advantageous features of conventional methods and addresses their weaknesses. In fact, we have combined the Fisher method and SVMRFE to utilize the advantages of a filtering method as well as an embedded method. Furthermore, we have added a redundancy reduction stage to address the weakness of the Fisher method and SVMRFE. In addition to gene expression values, the proposed method uses Gene Ontology which is a reliable source of information on genes. The use of Gene Ontology can compensate, in part, for the limitations of microarrays, such as having a small number of samples and erroneous measurement results. Results: The proposed method has been applied to colon, Diffuse Large B-Cell Lymphoma (DLBCL) and prostate cancer datasets. The empirical results show that our method has improved classification performance in terms of accuracy, sensitivity and specificity. In addition, the study of the molecular function of selected genes strengthened the hypothesis that these genes are involved in the process of cancer growth. Conclusions: The proposed method addresses the weakness of conventional methods by adding a redundancy reduction stage and utilizing Gene Ontology information. It predicts marker genes for colon, DLBCL and prostate cancer with a high accuracy. The predictions made in this study can serve as a list of candidates for subsequent wet-lab verification and might help in the search for a cure for cancers