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Biomedical subjects

Douglas Smith

Publications and source records attributed to Douglas Smith.

12 recordsLinked to original sources
PubMed2006

Improved rate control for electron-beam evaporation and evaluation of optical performance improvements.

A new deposition-rate-control and electron-beam-gun (e-gun) strategy was developed that significantly reduces the growth-rate variations for e-beam-deposited SiO2 coatings. The resulting improvements in optical performance are evaluated for multilayer bandpass filters. The adverse effect of uneven silica-source depletion on coating spectral performances during long deposition runs is discussed.

Journal Article↗
PubMed2006

Exact solution to plane-wave scattering by an ideal "left-handed" wedge.

An exact analytical solution to the problem of plane-wave diffraction by a penetrable left-handed medium (LHM) epsilon = micro = -1 wedge of arbitrary angle (subject to valid physical constraints) is presented. Standard analysis involving discontinuous angular eigenfunctions and even/odd symmetry decomposition resulted in a discrete spectrum leading to a series solution resembling the traditional perfect electric conductor wedge solution but exhibiting the expected negative refraction phenomenology. Numerical results are presented, some of which seemed paradoxical but are explainable by classical means. A new type of illusory edge radiation is observed and explained. Also, a novel edge-launched interface standing wave is observed on the directly illuminated side. The exact analytical solution is verified by comparison with finite-difference time-domain simulation on causal LHM materials.

Journal Article↗
PubMed2005

Swine in biomedical research: creating the building blocks of animal models.

The opportunities for utilizing swine biomedical models are immense, particularly in models that address lifestyle issues (nutrition, stress, alcohol, drugs of abuse, etc.). However, in order to fully capitalize upon the promise, there needs to be a more general recognition of these cofactors, such as nutrition, as key modulators of phenotype via genomic, epigenetic, and postgenomic mechanisms. Furthermore, increased interactions between nutrition scientists and clinical and fundamental researchers in other disciplines, including developmental biology, immunology, neuroscience, oncology, and cardiovascular and gastrointestinal physiology, are required. Closing discussions focused on the need for future conferences at more frequent intervals to support interactions between the various disciplines. This was especially critical because of the global distribution of investigators.

Animals↗
PubMed2005

Prevalence of elevated pulmonary arterial pressures measured by echocardiography in a multicenter study of patients with systemic sclerosis.

OBJECTIVE: To estimate the prevalence of elevated pulmonary arterial pressures (PAP) as a correlate for pulmonary arterial hypertension (PAH) in patients with systemic sclerosis (SSc) in rheumatology centers in Canada. METHODS: During the one-year study period (June 2002-May 2003), charts of patients with SSc were reviewed to determine demographics, SSc characteristics, percentage of patients with a PAH diagnosis, and the site criteria for such diagnosis. Subjects with no PAH that had symptoms of dyspnea and/or fatigue were invited to undergo Doppler echocardiography to estimate their systolic PAP (sPAP). RESULTS: A total of 539 patients with SSc (age 56 yrs +/- 13 SD, 84% female, 41% with diffuse SSc, 58% limited SSc, SSc disease duration 9 yrs +/- 7 SD) at 8 rheumatology centers were reviewed. Twenty-three percent of patients were diagnosed with elevated sPAP based on the site diagnosis criteria (i.e., > 30 mm Hg or > 35 mm Hg). From the non-PAH, not recently screened patients that had symptoms of dyspnea or fatigue, a total of 89 patients underwent a Doppler echocardiograph; 40% had sPAP > 35 mm Hg. CONCLUSION: Elevated PAP are common in both limited and diffuse SSc disease, occurring in 21% of limited and 26% of diffuse SSc patients. During the screening most patients had mild PAP elevations that would require further assessments such as right heart catheterization to diagnose PAH where appropriate. A high index of suspicion is important and routine echocardiography in symptomatic patients may allow earlier diagnosis of PAH and intervention. The proportion of SSc patients with mild to moderate elevations of PAP who will develop significant PAH is unknown and longterm studies are needed to address the natural progression.

Adolescent↗
PubMed2004

Evolutionary conservation and selection of human disease gene orthologs in the rat and mouse genomes.

BACKGROUND: Model organisms have contributed substantially to our understanding of the etiology of human disease as well as having assisted with the development of new treatment modalities. The availability of the human, mouse and, most recently, the rat genome sequences now permit the comprehensive investigation of the rodent orthologs of genes associated with human disease. Here, we investigate whether human disease genes differ significantly from their rodent orthologs with respect to their overall levels of conservation and their rates of evolutionary change. RESULTS: Human disease genes are unevenly distributed among human chromosomes and are highly represented (99.5%) among human-rodent ortholog sets. Differences are revealed in evolutionary conservation and selection between different categories of human disease genes. Although selection appears not to have greatly discriminated between disease and non-disease genes, synonymous substitution rates are significantly higher for disease genes. In neurological and malformation syndrome disease systems, associated genes have evolved slowly whereas genes of the immune, hematological and pulmonary disease systems have changed more rapidly. Amino-acid substitutions associated with human inherited disease occur at sites that are more highly conserved than the average; nevertheless, 15 substituting amino acids associated with human disease were identified as wild-type amino acids in the rat. Rodent orthologs of human trinucleotide repeat-expansion disease genes were found to contain substantially fewer of such repeats. Six human genes that share the same characteristics as triplet repeat-expansion disease-associated genes were identified; although four of these genes are expressed in the brain, none is currently known to be associated with disease. CONCLUSIONS: Most human disease genes have been retained in rodent genomes. Synonymous nucleotide substitutions occur at a higher rate in disease genes, a finding that may reflect increased mutation rates in the chromosomal regions in which disease genes are found. Rodent orthologs associated with neurological function exhibit the greatest evolutionary conservation; this suggests that rodent models of human neurological disease are likely to most faithfully represent human disease processes. However, with regard to neurological triplet repeat expansion-associated human disease genes, the contraction, relative to human, of rodent trinucleotide repeats suggests that rodent loci may not achieve a 'critical repeat threshold' necessary to undergo spontaneous pathological repeat expansions. The identification of six genes in this study that have multiple characteristics associated with repeat expansion-disease genes raises the possibility that not all human loci capable of facilitating neurological disease by repeat expansion have as yet been identified.

Animals↗
PubMed2004

Macrophage surface expression of annexins I and II in the phagocytosis of apoptotic lymphocytes.

When cells undergo apoptosis, or programmed cell death, they expose phosphatidylserine (PS) on their surface. Macrophages that efficiently phagocytose apoptotic cells also express PS on their surface, although at a lower level. The PS exposed on both cells is required for phagocytosis, because uptake is inhibited by masking PS on either cell with annexin V, a PS-binding protein. The inhibition is not additive, suggesting that the exposed PS molecules on the two cells participate in a common process. We asked whether this dual requirement reflects bridging of the target cell and macrophage by bivalent, PS-binding annexins. Monoclonal antibodies (mAbs) against annexins I or II stained a variety of live phagocytes. Apoptotic Jurkat T lymphocytes and human peripheral T lymphocytes, but not apoptotic thymocytes, were stained by anti-annexin I but not II. Phagocytosis of apoptotic targets was inhibited by mAbs to annexins I or II, or by pretreatment of macrophages with the same mAbs. Pretreatment of apoptotic thymocytes had no effect, whereas pretreating Jurkat cells with anti-annexin I or removing annexin I with EGTA was inhibitory. Annexin bridging is vectorial, because annexin is bound to PS molecules on targets but not on macrophages, suggesting annexins serve as both ligand and receptor in promoting phagocytosis.

Animals↗
PubMed2004

Genome sequence of the Brown Norway rat yields insights into mammalian evolution.

The laboratory rat (Rattus norvegicus) is an indispensable tool in experimental medicine and drug development, having made inestimable contributions to human health. We report here the genome sequence of the Brown Norway (BN) rat strain. The sequence represents a high-quality 'draft' covering over 90% of the genome. The BN rat sequence is the third complete mammalian genome to be deciphered, and three-way comparisons with the human and mouse genomes resolve details of mammalian evolution. This first comprehensive analysis includes genes and proteins and their relation to human disease, repeated sequences, comparative genome-wide studies of mammalian orthologous chromosomal regions and rearrangement breakpoints, reconstruction of ancestral karyotypes and the events leading to existing species, rates of variation, and lineage-specific and lineage-independent evolutionary events such as expansion of gene families, orthology relations and protein evolution.

Animals↗
PubMed2004

Two theorems on electromagnetic bistatic scattering.

For an axially incident plane wave, two theorems are stated in which sufficient conditions are imposed on the constitutive parameters epsilon and mu of a three-dimensional scatterer to ensure the identity of scattering patterns in orthogonal planes, both near and far zone, such as E and H planes. The theorems represent an extension of existing scattering theorems that apply to bodies of revolution. The theorems are proven analytically, and the results are validated through detailed finite-difference-time-domain and method-of-moments computer simulations on a few noncanonical complex shapes characterized by quite general causal permittivity epsilon and permeability mu functions. The selected materials have Lorentzian functional forms and encompass ordinary materials as well as left-handed materials as special cases.

Journal Article↗
PubMed2003

Population size estimation in Yellowstone wolves with error-prone noninvasive microsatellite genotypes.

Determining population sizes can be difficult, but is essential for conservation. By counting distinct microsatellite genotypes, DNA from noninvasive samples (hair, faeces) allows estimation of population size. Problems arise because genotypes from noninvasive samples are error-prone, but genotyping errors can be reduced by multiple polymerase chain reaction (PCR). For faecal genotypes from wolves in Yellowstone National Park, error rates varied substantially among samples, often above the 'worst-case threshold' suggested by simulation. Consequently, a substantial proportion of multilocus genotypes held one or more errors, despite multiple PCR. These genotyping errors created several genotypes per individual and caused overestimation (up to 5.5-fold) of population size. We propose a 'matching approach' to eliminate this overestimation bias.

Alleles↗
PubMed2002

High-dose cyclophosphamide for refractory autoimmune hemolytic anemia.

High-dose cyclophosphamide, without stem cell rescue, has been used successfully to treat aplastic anemia and other autoimmune disorders. To determine the safety and efficacy of high-dose cyclophosphamide among patients with severe refractory autoimmune hemolytic anemia, we treated 9 patients with cyclophosphamide (50 mg. kg(-1). d(-1) for 4 days) who had failed a median of 3 (range, 1-7) other treatments. The median hemoglobin before treatment was 6.7 g/dL (range, 5-10 g/dL). The median time to reach an absolute neutrophil count of 500/microL or greater was 16 days (range, 12-18 days). Six patients achieved complete remission (normal untransfused hemoglobin for age and sex), and none have relapsed after a median follow-up of 15 months (range, 4-29 months). Three patients achieved and continue in partial remission (hemoglobin at least 10 g/dL without transfusion support). High-dose cyclophosphamide was well tolerated and induced durable remissions in patients with severe refractory autoimmune hemolytic anemia.

Adult↗