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Search Results: 1 - 10 of 477628 matches for " Richard A. Morrison "
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Stability Analysis of the Helmholtz Oscillator with Time Varying Mass
Richard A. Morrison
Mathematics , 2007,
Abstract: We study the effects of periodically time varying mass on the stability of the Helmholtz oscillator, which, when linearised, takes the form of Ince's equation and exhibits parametric resonance. The resonance regions in the parameter space are mapped and we use the Melnikov function to demonstrate that the parametric instability does not affect the qualitative dynamics of the nonlinear system.
An Approach to Enhance the Conservation-Compatibility of Solar Energy Development
D. Richard Cameron, Brian S. Cohen, Scott A. Morrison
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0038437
Abstract: The rapid pace of climate change poses a major threat to biodiversity. Utility-scale renewable energy development (>1 MW capacity) is a key strategy to reduce greenhouse gas emissions, but development of those facilities also can have adverse effects on biodiversity. Here, we examine the synergy between renewable energy generation goals and those for biodiversity conservation in the 13 M ha Mojave Desert of the southwestern USA. We integrated spatial data on biodiversity conservation value, solar energy potential, and land surface slope angle (a key determinant of development feasibility) and found there to be sufficient area to meet renewable energy goals without developing on lands of relatively high conservation value. Indeed, we found nearly 200,000 ha of lower conservation value land below the most restrictive slope angle (<1%); that area could meet the state of California’s current 33% renewable energy goal 1.8 times over. We found over 740,000 ha below the highest slope angle (<5%) – an area that can meet California’s renewable energy goal seven times over. Our analysis also suggests that the supply of high quality habitat on private land may be insufficient to mitigate impacts from future solar projects, so enhancing public land management may need to be considered among the options to offset such impacts. Using the approach presented here, planners could reduce development impacts on areas of higher conservation value, and so reduce trade-offs between converting to a green energy economy and conserving biodiversity.
RU486 Reversal of Cortisol Repression of 1,25-Dihydroxyvitamin D3 Induction of the Human Osteocalcin Promoter  [PDF]
Nigel A. Morrison
Open Journal of Endocrine and Metabolic Diseases (OJEMD) , 2013, DOI: 10.4236/ojemd.2013.31009
Abstract:

In conditions of corticosteroid excess, such as Cushing’s syndrome, a reduction in serum osteocalcin is observed and bone loss occurs. The human osteocalcin gene is induced by 1,25-dihydroxyvitamin D3 derivatives and repressed by glucocorticoids. In this paper we show that cortisol, a natural glucocorticoid, represses both basal and vitamin D induced activity of the human osteocalcin promoter. Furthermore, we address the specific question as to whether the anti-progestin anti-glucocorticoid RU486 is able to antagonize the inhibitory effect of cortisol on osteocalcin gene expression. We show that RU486 has agonist activity alone, in that it is able to repress the basal promoter activity of the osteocalcin gene and antagonist activity, reversing incompletely the cortisol mediated repression of 1,25-dihydroxyvitamin D3 induction.

A Legacy of Derogation: Prejudice toward Aboriginal Persons in Canada  [PDF]
Todd G. Morrison, Melanie A. Morrison, Tomas Borsa
Psychology (PSYCH) , 2014, DOI: 10.4236/psych.2014.59112
Abstract:

Interpersonal prejudice toward Aboriginal men and women has, to date, received little attention from Canadian social psychologists. The present study sought to address this omission by examining the correlates of Old-Fashioned Prejudice (O-PATAS) and Modern Prejudice (M-PATAS) toward Aboriginal persons. Data from two samples (Sample 1: n = 280, 71.6% females; Sample 2: n = 163, 70.9% females) were used. As predicted, in Sample 1, respondents evidenced greater levels of modern prejudice than old-fashioned prejudice, and both forms correlated positively with social dominance orientation, right-wing authoritarianism and negativity toward other stigmatized groups (specifically, gay men and overweight persons). For Sample 2, modern prejudice toward Aboriginal people correlated negatively with empathy as well as self-reported contact with Aboriginal people. However, no association was observed between scores on the M-PATAS and a multifaceted measure of religiosity.

Best Practice Recommendations for Using Structural Equation Modelling in Psychological Research  [PDF]
Todd G. Morrison, Melanie A. Morrison, Jessica M. McCutcheon
Psychology (PSYCH) , 2017, DOI: 10.4236/psych.2017.89086
Abstract: Although structural equation modelling (SEM) is a popular analytic technique in the social sciences, it remains subject to misuse. The purposes of this paper are to assist psychologists interested in using SEM by: 1) providing a brief overview of this method; and 2) describing best practice recommendations for testing models and reporting findings. We also outline several resources that psychologists with limited familiarity about SEM may find helpful.
Identifying subtypes of patients with neovascular age-related macular degeneration by genotypic and cardiovascular risk characteristics
Michael Feehan, John Hartman, Richard Durante, Margaux A Morrison, Joan W Miller, Ivana K Kim, Margaret M DeAngelis
BMC Medical Genetics , 2011, DOI: 10.1186/1471-2350-12-83
Abstract: We identified a sample of patients with neovascular AMD, that in previous studies had been shown to be at elevated risk for the disease through environmental factors such as cigarette smoking and genetic variants including the complement factor H gene (CFH) on chromosome 1q25 and variants in the ARMS2/HtrA serine peptidase 1 (HTRA1) gene(s) on chromosome 10q26. We conducted a multivariate segmentation analysis of 253 of these patients utilizing available epidemiologic and genetic data.In a multivariate model, cigarette smoking failed to differentiate subtypes of patients. However, four meaningfully distinct clusters of patients were identified that were most strongly differentiated by their cardiovascular health status (histories of hypercholesterolemia and hypertension), and the alleles of ARMS2/HTRA1 rs1049331.These results have significant personalized medicine implications for drug developers attempting to determine the effective size of the treatable neovascular AMD population. Patient subtypes or clusters may represent different targets for therapeutic development based on genetic pathways in AMD and cardiovascular pathology, and treatments developed that may elevate CV risk, may be ill advised for certain of the clusters identified.The current medical literature is increasing weekly with studies identifying DNA variants and their possible interaction with environmental factors that may have impact on risk of disease. The growth of such studies has been spurred by the promise of understanding the genetic and environmental basis of complex diseases, and the possibility of identifying therapeutically responsive targets for drug development. Enormous numbers of DNA variants have been associated with diseases and traits and this number will only grow as it becomes economically feasible to sequence an individual patient's entire genome[1].One key data interpretation challenge lies in how best to assess the phenotypic heterogeneity and risk factor heterogeneity with
Backward-propagating MeV electrons from $10^{18}$ W/cm$^2$ laser interactions with water
John T. Morrison,Enam A. Chowdhury,Kyle D. Frische,Scott Feister,Vladimir M. Ovchinnikov,John A. Nees,Chris Orban,Richard R. Freeman,W. Melvyn Roquemore
Physics , 2015, DOI: 10.1063/1.4916493
Abstract: We present an experimental study of the generation of $\sim$MeV electrons opposite to the direction of laser propagation following the relativistic interaction at normal incidence of a $\sim$3 mJ, $10^{18}$ W/cm$^2$ short pulse laser with a flowing 30 $\mu$m diameter water column target. Faraday cup measurements record hundreds of pC charge accelerated to energies exceeding 120 keV, and energy-resolved measurements of secondary x-ray emissions reveal an x-ray spectrum peaking above 800 keV, which is significantly higher energy than previous studies with similar experimental conditions and more than five times the $\sim$110 keV ponderomotive energy scale for the laser. We show that the energetic x-rays generated in the experiment result from backward-going, high-energy electrons interacting with the focusing optic and vacuum chamber walls with only a small component of x-ray emission emerging from the target itself. We also demonstrate that the high energy radiation can be suppressed through the attenuation of the nanosecond-scale pre-pulse. These results are supported by 2D Particle-in-Cell (PIC) simulations of the laser-plasma interaction that exhibit beam-like backward-propagating MeV electrons.
Presenilin 2 Is the Predominant γ-Secretase in Microglia and Modulates Cytokine Release
Suman Jayadev,Amanda Case,Alison J. Eastman,Huy Nguyen,Julia Pollak,Jesse C. Wiley,Thomas M?ller,Richard S. Morrison,Gwenn A. Garden
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0015743
Abstract: Presenilin 1 (PS1) and Presenilin 2 (PS2) are the enzymatic component of the γ-secretase complex that cleaves amyloid precursor protein (APP) to release amyloid beta (Aβ) peptide. PS deficiency in mice results in neuroinflammation and neurodegeneration in the absence of accumulated Aβ. We hypothesize that PS influences neuroinflammation through its γ-secretase action in CNS innate immune cells. We exposed primary murine microglia to a pharmacological γ-secretase inhibitor which resulted in exaggerated release of TNFα and IL-6 in response to lipopolysaccharide. To determine if this response was mediated by PS1, PS2 or both we used shRNA to knockdown each PS in a murine microglia cell line. Knockdown of PS1 did not lead to decreased γ-secretase activity while PS2 knockdown caused markedly decreased γ-secretase activity. Augmented proinflammatory cytokine release was observed after knockdown of PS2 but not PS1. Proinflammatory stimuli increased microglial PS2 gene transcription and protein in vitro. This is the first demonstration that PS2 regulates CNS innate immunity. Taken together, our findings suggest that PS2 is the predominant γ-secretase in microglia and modulates release of proinflammatory cytokines. We propose PS2 may participate in a negative feedback loop regulating inflammatory behavior in microglia.
Implications of high level pseudogene transcription in Mycobacterium leprae
Diana L Williams, Richard A Slayden, Amol Amin, Alejandra N Martinez, Tana L Pittman, Alex Mira, Anirban Mitra, Valakunja Nagaraja, Norman E Morrison, Milton Moraes, Thomas P Gillis
BMC Genomics , 2009, DOI: 10.1186/1471-2164-10-397
Abstract: Gene expression analysis identified transcripts from 49% of all M. leprae genes including 57% of all ORFs and 43% of all pseudogenes in the genome. Transcribed pseudogenes were randomly distributed throughout the chromosome. Factors resulting in pseudogene transcription included: 1) co-orientation of transcribed pseudogenes with transcribed ORFs within or exclusive of operon-like structures; 2) the paucity of intrinsic stem-loop transcriptional terminators between transcribed ORFs and downstream pseudogenes; and 3) predicted pseudogene promoters. Mechanisms for translational "silencing" of pseudogene transcripts included the lack of both translational start codons and strong Shine-Dalgarno (SD) sequences. Transcribed pseudogenes also contained multiple "in-frame" stop codons and high Ka/Ks ratios, compared to that of homologs in M. tuberculosis and ORFs in M. leprae. A pseudogene transcript containing an active promoter, strong SD site, a start codon, but containing two in frame stop codons yielded a protein product when expressed in E. coli.Approximately half of M. leprae's transcriptome consists of inactive gene products consuming energy and resources without potential benefit to M. leprae. Presently it is unclear what additional detrimental affect(s) this large number of inactive mRNAs has on the functional capability of this organism. Translation of these pseudogenes may play an important role in overall energy consumption and resultant pathophysiological characteristics of M. leprae. However, this study also demonstrated that multiple translational "silencing" mechanisms are present, reducing additional energy and resource expenditure required for protein production from the vast majority of these transcripts.Bacterial pseudogenes are inactivated, presumably nonfunctional genes that can accumulate in the genomes of bacterial species, especially those undergoing processes such as niche selection or host specialization [1,2]. When a bacterial gene is under low se
An Integrated Model of Multiple-Condition ChIP-Seq Data Reveals Predeterminants of Cdx2 Binding
Shaun Mahony ,Matthew D. Edwards ,Esteban O. Mazzoni,Richard I. Sherwood,Akshay Kakumanu,Carolyn A. Morrison,Hynek Wichterle,David K. Gifford
PLOS Computational Biology , 2014, DOI: doi/10.1371/journal.pcbi.1003501
Abstract: Regulatory proteins can bind to different sets of genomic targets in various cell types or conditions. To reliably characterize such condition-specific regulatory binding we introduce MultiGPS, an integrated machine learning approach for the analysis of multiple related ChIP-seq experiments. MultiGPS is based on a generalized Expectation Maximization framework that shares information across multiple experiments for binding event discovery. We demonstrate that our framework enables the simultaneous modeling of sparse condition-specific binding changes, sequence dependence, and replicate-specific noise sources. MultiGPS encourages consistency in reported binding event locations across multiple-condition ChIP-seq datasets and provides accurate estimation of ChIP enrichment levels at each event. MultiGPS's multi-experiment modeling approach thus provides a reliable platform for detecting differential binding enrichment across experimental conditions. We demonstrate the advantages of MultiGPS with an analysis of Cdx2 binding in three distinct developmental contexts. By accurately characterizing condition-specific Cdx2 binding, MultiGPS enables novel insight into the mechanistic basis of Cdx2 site selectivity. Specifically, the condition-specific Cdx2 sites characterized by MultiGPS are highly associated with pre-existing genomic context, suggesting that such sites are pre-determined by cell-specific regulatory architecture. However, MultiGPS-defined condition-independent sites are not predicted by pre-existing regulatory signals, suggesting that Cdx2 can bind to a subset of locations regardless of genomic environment. A summary of this paper appears in the proceedings of the RECOMB 2014 conference, April 2–5.
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