PubMed Health⌕ Search

Biomedical subjects

D Stroud

Publications and source records attributed to D Stroud.

At least 19 recordsLinked to original sources
PubMed2005

Surface-enhanced plasmon splitting in a liquid-crystal-coated gold nanoparticle.

We show that, when a gold nanoparticle is coated by a thin layer of nematic liquid crystal, the nanoparticle surface has a strong effect on the director orientation, but, surprisingly, this deformation can enhance the surface plasmon splitting. We consider three plausible liquid crystal director configurations in zero electric field: boojum pair (north-south pole configuration), baseball (tetrahedral), and homogeneous. From the discrete dipole approximation, we find that the surface plasmon splitting is largest for the boojum pair, and this result is in good agreement with experiment.

Journal Article↗
PubMed2005

Synchronization in disordered Josephson junction arrays: small-world connections and the Kuramoto model.

We study synchronization in disordered arrays of Josephson junctions. In the first half of the paper, we consider the relation between the coupled resistively and capacitively shunted junction (RCSJ) equations for such arrays and effective phase models of the Winfree type. We describe a multiple-time-scale analysis of the RCSJ equations for a ladder array of junctions with non-negligible capacitance in which we arrive at a second order phase model that captures well the synchronization physics of the RCSJ equations for that geometry. In the second half of the paper, motivated by recent work on small-world networks, we study the effect on synchronization of random, long-range connections between pairs of junctions. We consider the effects of such shortcuts on ladder arrays, finding that the shortcuts make it easier for the array of junctions in the nonzero voltage state to synchronize. In two-dimensional (2D) arrays we find that the additional shortcut junctions are only marginally effective at inducing synchronization of the active junctions. The differences in the effects of shortcut junctions in 1D and 2D can be partly understood in terms of an effective phase model.

Journal Article↗
PubMed2003

Scaling properties of random walks on small-world networks.

Using both numerical simulations and scaling arguments, we study the behavior of a random walker on a one-dimensional small-world network. For the properties we study, we find that the random walk obeys a characteristic scaling form. These properties include the average number of distinct sites visited by the random walker, the mean-square displacement of the walker, and the distribution of first-return times. The scaling form has three characteristic time regimes. At short times, the walker does not see the small-world shortcuts and effectively probes an ordinary Euclidean network in d dimensions. At intermediate times, the properties of the walker shows scaling behavior characteristic of an infinite small-world network. Finally, at long times, the finite size of the network becomes important, and many of the properties of the walker saturate. We propose general analytical forms for the scaling properties in all three regimes, and show that these analytical forms are consistent with our numerical simulations.

Journal Article↗
PubMed2002

Extensive mosaic structure revealed by the complete genome sequence of uropathogenic Escherichia coli.

We present the complete genome sequence of uropathogenic Escherichia coli, strain CFT073. A three-way genome comparison of the CFT073, enterohemorrhagic E. coli EDL933, and laboratory strain MG1655 reveals that, amazingly, only 39.2% of their combined (nonredundant) set of proteins actually are common to all three strains. The pathogen genomes are as different from each other as each pathogen is from the benign strain. The difference in disease potential between O157:H7 and CFT073 is reflected in the absence of genes for type III secretion system or phage- and plasmid-encoded toxins found in some classes of diarrheagenic E. coli. The CFT073 genome is particularly rich in genes that encode potential fimbrial adhesins, autotransporters, iron-sequestration systems, and phase-switch recombinases. Striking differences exist between the large pathogenicity islands of CFT073 and two other well-studied uropathogenic E. coli strains, J96 and 536. Comparisons indicate that extraintestinal pathogenic E. coli arose independently from multiple clonal lineages. The different E. coli pathotypes have maintained a remarkable synteny of common, vertically evolved genes, whereas many islands interrupting this common backbone have been acquired by different horizontal transfer events in each strain.

Acute Disease↗
PubMed2002

Characterizing the structure of small-world networks.

We give exact relations for small-world networks (SWN's) which are independent of the "degree distribution," i.e., the distribution of nearest-neighbor connections. For the original SWN model, we illustrate how these exact relations can be used to obtain approximations for the corresponding basic probability distribution. In the limit of large system sizes and small disorder, we use numerical studies to obtain a functional fit for this distribution. Finally, we obtain the scaling properties for the mean-square displacement of a random walker, which are determined by the scaling behavior of the underlying SWN.

Community Networks↗
PubMed2000

Genetic analysis of Escherichia coli K1 gastrointestinal colonization.

Strains of Escherichia coli expressing the K1 polysaccharide capsule colonize the large intestine of newborn infants, and are the leading cause of Gram-negative septicaemia and meningitis in the neonatal period. We used signature-tagged mutagenesis (STM) to identify genes that E. coli K1 requires to colonize the gastrointestinal (GI) tract. A total of 2140 mTn5 mutants was screened for their capacity to colonize the GI tract of infant rats, and 16 colonization defective mutants were identified. The mutants have transposon insertions in genes affecting the synthesis of cell surface structures, membrane transporters, transcriptional regulators, enzymes in metabolic pathways, and in genes of unknown function, designated dgc (defective in GI colonization). Three dgcs are absent from the whole genome sequence of E. coli K-12, although related sequences are found in other pathogenic strains of E. coli and in Shigella flexneri. Additionally, immunohistochemistry was used to define the nature of the colonization defect in five mutants including all dgc mutants. STM was successfully applied to examine the factors involved in E. coli K1 colonization, and the findings are relevant to the pathogenesis of other enteric infections.

Animals↗
PubMed2000

Exact results and scaling properties of small-world networks

We study the distribution function for minimal paths in small-world networks. We derive its general form, which we verify numerically, and also discuss its scaling properties. Using the general form of this distribution function, we derive exact expressions for the average minimal distance &lmacr; and its variance sigma(2). Finally, we study the limit of large system sizes and obtain some approximate results.

Journal Article↗
PubMed1998

Total body nitrogen predicts long-term mortality in haemodialysis patients--a single-centre experience.

BACKGROUND: It has been estimated that 30-50% of adult haemodialysis patients have moderate to severe malnutrition. We have previously shown that estimation of total body nitrogen, expressed as a nitrogen index (NI) by in vivo neutron activation analysis (IVNAA) is an accurate tool for estimating total body protein in dialysis patients. It is not clear whether the nitrogen index is predictive of mortality and morbidity in dialysis patients. METHODS: We studied the long-term predictive value of nutritional assessment by IVNAA and serum albumin on mortality and morbidity (including infection episodes requiring hospital admission, ischaemic heart disease (IHD), cerebrovascular or peripheral vascular disease (PVD). Seventy-six chronic haemodialysis patients were initially studied between 1989 and 1991, with a minimum follow-up of 5 years. The mean age of the patients was 48.3 years (range 21-76). Patients were divided into two groups, group I, n = 22, had a NI < or = 0.8 (NI < or = 0.8 represents protein malnutrition) and group II, n = 54, had a NI > 0.8. RESULTS: Fifteen patients in group II died in the follow-up period compared to nine from group I (P < 0.05), but NI < or = 0.8 did not predict vascular or infective morbidity. Serum albumins < or = 35 g/day did predict over all mortality (P < 0.05) as well as infection episodes (P < 0.001). When patients above the age of 50 years were analysed, NI did predict mortality (P < 0.05) but serum albumin did not, while the age of> 50 itself was a strong predictor of mortality (P < 0.001). CONCLUSION: We conclude that NI < or = 0.8 is predictive of long-term mortality. This reinforces the view that low body protein stores are predictive of increased mortality in dialysis patients and that the serum albumin is predictive of mortality because of its reflection of protein stores.

Adult↗
PubMed1997

Detection of anaplastic lymphoma kinase (ALK) and nucleolar protein nucleophosmin (NPM)-ALK proteins in normal and neoplastic cells with the monoclonal antibody ALK1.

The t(2;5)(p23;q35) translocation, associated with anaplastic large-cell lymphoma (ALCL), results in the production of the nucleolar protein nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) protein. This report describes an immunocytochemical study of the distribution of ALK and NPM-ALK proteins using a new monoclonal antibody, ALK1, that recognizes a formalin resistant epitope in both the 80-kD NPM-ALK chimeric and the 200-kD normal human ALK proteins. Cytoplasmic and nuclear labeling was seen in the t(2;5)+ SU-DHL-1 and Karpas 299 cell lines. Normal ALK protein expression was restricted to the central nervous system (in scattered neurons, glial cells, and endothelial cells). Two hundred and thirty-nine cases of lymphoma and 80 nonhematopoietic tumors were immunostained. Antibody ALK1 labeled 53.4% (39 of 73 cases) of CD30+ ALCL. A case of ALCL with a t(1;2) translocation was ALK1+. Three cases of CD30- ALCL with prominent nucleoli showed a unique pattern of coarse granular cytoplasmic labeling. All other tumors, including Hodgkin's disease and lymphomatoid papulosis, were ALK1-. These results indicate that reliable immunostaining of routine biopsy material for NPM-ALK and ALK proteins is feasible. Such analysis is of diagnostic importance, especially because t(2;5)+ ALCL cases have a good prognosis with appropriate treatment.

Adolescent↗