Search PubMed⌕ Search

Biomedical subjects

M A Moore

Publications and source records attributed to M A Moore.

At least 19 recordsLinked to original sources
PubMed2006

Interface free energies in p-spin glass models.

The replica method is used to calculate the interface free energy associated with the change from periodic to antiperiodic boundary conditions in finite-dimensional p-spin glass models in the phase which at mean-field level has one-step replica symmetry breaking (1RSB). In any finite dimension the interface free energy is exponentially small for a large system. This result implies that, in finite dimensions, the 1RSB state does not exist, as it is destroyed by thermal excitation of arbitrarily large droplets. The implications of this for the theory of structural glasses are discussed.

Journal Article↗
PubMed2006

Thermodynamic glass transition in finite dimensions.

Using an effective potential method, a replica formulism is set up for describing supercooled liquids near their glass transition. The resulting potential is equivalent to that for an Ising spin glass in a magnetic field. Results taken from the droplet picture of spin glasses are then used to provide an explanation of the main features of fragile glasses.

Journal Article↗
PubMed2004

Complexity of vector spin glasses.

We study the annealed complexity of the m-vector spin glasses in the Sherrington-Kirkpatrick limit. The eigenvalue spectrum of the Hessian matrix of the Thouless-Anderson-Palmer free energy is found to consist of a continuous band of positive eigenvalues in addition to an isolated eigenvalue and (m-1) null eigenvalues due to rotational invariance. Rather surprisingly, the band does not extend to zero at any finite temperature. The isolated eigenvalue becomes zero in the thermodynamic limit, as in the Ising case (m=1), indicating that the same supersymmetry breaking recently found in Ising spin glasses occurs in vector spin glasses.

Journal Article↗
PubMed2004

Complexity of Ising spin glasses.

We compute the complexity [logarithm of the number of Thouless-Anderson-Palmer (TAP) states] associated with minima and index-one saddle points of the TAP free energy. Higher-index saddles have smaller complexities. The two leading complexities are equal, consistent with the Morse theorem on the total number of turning points, and have the value given by Bray and Moore [J. Phys. C, ()]]. In the thermodynamic limit, TAP states of all free energies become marginally stable.

Journal Article↗
PubMed2004

Generalized Bose-Einstein phase transition in large-m component spin glasses.

It is proposed to understand finite dimensional spin glasses using a 1/m expansion, where m is the number of spin components. It is shown that this approach predicts a replica symmetric state in finite dimensions. The point about which the expansion is made, the infinite-m limit, has been studied in the mean-field limit in detail and has a very unusual phase transition, rather similar to a Bose-Einstein phase transition but with N(2/5) macroscopically occupied low-lying states.

Journal Article↗
PubMed2003

Free energy fluctuations in Ising spin glasses.

The sample-to-sample fluctuations of the free energy in finite-dimensional Ising spin glasses are calculated, using the replica method, from higher order terms in the replica number n. It is shown that the Parisi symmetry breaking scheme does not give the correct answers for these higher order terms. A modified symmetry breaking scheme with the same stability is shown to resolve the problem.

Journal Article↗
PubMed2003

Corrections to scaling are large for droplets in two-dimensional spin glasses.

The energy of a droplet of linear extent l in the droplet theory of spin glasses goes as l(theta) for large l. It is shown by numerical studies of large droplets in two-dimensional systems that this formula needs to be modified by the addition of a scaling correction l(-omega) in order to accurately describe droplet energies at the length scales currently probed in numerical simulations. Using this simple modification, it is now possible to explain many results which have been found in simulations of three-dimensional Ising spin glasses with the droplet model.

Journal Article↗
PubMed2003

Interface energies in ising spin glasses.

The replica method has been used to calculate the interface free energy associated with the change from periodic to antiperiodic boundary conditions in finite-dimensional spin glasses. At mean-field level the interface free energy vanishes, but after allowing for fluctuation effects, a nonzero interface free energy is obtained which is significantly different from numerical expectations.

Journal Article↗
PubMed2003

Provision of hepatitis B vaccination for primary care dental staff in Scotland.

OBJECTIVES: All dental surgeons should be protected from hepatitis B virus (HBV) infection by immunisation, ideally administered and monitored via occupational health services (OHS). This study examined relevant OHS systems in place for dental primary care healthcare workers (DHCW) across all Health Board Areas (HBAs) in Scotland. It also explored the DHCWs' knowledge of, and access to, these systems in three HBAs. METHODS: Data from senior staff in all Scottish Health Boards and Primary Care Trusts were collected by self-completing questionnaires. Information from DHCWs was collected via telephone interviews with General Dental Practitioners (GDPs) and Community Dental Officers (CDOs) in each of Ayrshire and Arran, Highland and Lothian Health Boards. RESULTS: Thirteen of the 15 HBAs had robust HBV vaccination and monitoring systems. However, only 7/15 (47%) of these covered all DHCWs. Seven HBAs provided vaccination and monitoring for CDOs only, leaving GDPs to undertake these responsibilities for themselves. Of the 105 DHCWs approached, 82 gave an interview. These interviews highlighted major differences between HBAs in relation to access of DHCWs to OHS and indicated that CDOs had greater access than GDPs to OHS. Overall, 31% of DHCWs were not satisfied with the OHS available. CONCLUSION: In order to safeguard both staff and patients, significant further work is required to ensure that all DHCWs have access to appropriate OHS support for provision and monitoring of immunisation procedures and related functions such as management of sharps injuries.

Chi-Square Distribution↗
PubMed2002

p-Spin model in finite dimensions and its relation to structural glasses.

The p-spin spin-glass model has been studied extensively at mean-field level because of the insights which it provides into the mode-coupling approach to structural glasses and the nature of the glass transition. We demonstrate explicitly that the finite-dimensional version of the three-spin model is in the same universality class as an Ising spin glass in a magnetic field. Assuming that the droplet picture of Ising spin glasses is valid we discuss how this universality may provide insights into why structural glasses are either "fragile" or "strong."

Journal Article↗
PubMed2002

Why temperature chaos in spin glasses is hard to observe.

The overlap length of a three-dimensional Ising spin glass on a cubic lattice with Gaussian interactions has been estimated numerically by transfer matrix methods and within a Migdal-Kadanoff renormalization group scheme. We find that the overlap length is large, explaining why it has been difficult to observe spin glass chaos in numerical simulations and experiment.

Journal Article↗
PubMed2002

Aspect-ratio scaling and the stiffness exponent theta for Ising spin glasses.

We introduce the technique of aspect-ratio scaling to study the scale dependence of interfacial energies in Ising spin glasses, and we show how one can use it to determine the stiffness exponent theta in a clean way, with results that are independent of the domain-wall-forcing boundary conditions imposed on the system. In space dimension d = 2 we obtain theta = -0.282(3) for a Gaussian distribution of exchange interactions.

Journal Article↗
PubMed2001

Numerical solution of the mode-coupling equations for the Kardar-Parisi-Zhang equation in one dimension.

We have studied the Kardar-Parisi-Zhang equation in the strong coupling regime in the mode-coupling approximation. We solved numerically in dimension d=1 for the correlation function at wave vector k. At large times t we found the predicted stretched exponential decay consistent with our previous saddle point analysis [Phys. Rev. E 63, 057103 (2001)], but we also observed that the decay to zero occurred in an unexpected oscillatory way. We have compared the results from mode coupling for the scaling functions with the recent exact results from Prähofer and Spohn (e-print cond-mat/0101200) for d=1 who also find an oscillatory decay to zero.

Journal Article↗
PubMed2001

Crosslink formation in porcine valves stabilized by dye-mediated photooxidation.

Bovine pericardial and porcine valve materials stabilized by dye-mediated photooxidation have shown potential for bioprosthetic valve use. Previously, in vitro and in vivo stability of these materials was demonstrated through enzymatic, chemical, extraction, rat subcutaneous, and functional challenges. Here, we examine the stability of photooxidized porcine aortic valves through amino acid, crosslink, and hydrothermal isometric tension analysis. Photooxidation reduced intact histidine residues from 17.0 to 0 residues per 1000, indicating the photooxidative alteration of this amino acid. Diphenyl borinic acid-derivitized hydrolyzates of proteins were separated by high-performance liquid chromatography, which identified several amino acid crosslinks that appeared with photooxidation that were absent in untreated controls. Thermal relaxation analysis indicated a significantly higher (p < 0.0002) thermal stability for photooxidized porcine cusps than that of untreated controls, with mean relaxation times for untreated cusps of 14,000 +/- 4650 versus 22,900 +/- 2480 s for photooxidized cusps. In summary, porcine aortic valve tissue treated by dye-mediated photooxidation contains new chemical species and exhibits properties consistent with intermolecular crosslink formation, which explain the increased biostability of this material and its potential for use in bioprosthetic devices.

Amino Acids↗
PubMed2001

Inhibition of both paracrine and autocrine VEGF/ VEGFR-2 signaling pathways is essential to induce long-term remission of xenotransplanted human leukemias.

Antiangiogenic agents block the effects of tumor-derived angiogenic factors (paracrine factors), such as vascular endothelial growth factor (VEGF), on endothelial cells (EC), inhibiting the growth of solid tumors. However, whether inhibition of angiogenesis also may play a role in liquid tumors is not well established. We recently have shown that certain leukemias not only produce VEGF but also selectively express functional VEGF receptors (VEGFRs), such as VEGFR-2 (Flk-1, KDR) and VEGFR1 (Flt1), resulting in the generation of an autocrine loop. Here, we examined the relative contribution of paracrine (EC-dependent) and autocrine (EC-independent) VEGF/VEGFR signaling pathways, by using a human leukemia model, where autocrine and paracrine VEGF/VEGFR loops could be selectively inhibited by neutralizing mAbs specific for murine EC (paracrine pathway) or human tumor (autocrine) VEGFRs. Blocking either the paracrine or the autocrine VEGF/VEGFR-2 pathway delayed leukemic growth and engraftment in vivo, but failed to cure inoculated mice. Long-term remission with no evidence of disease was achieved only if mice were treated with mAbs against both murine and human VEGFR-2, whereas mAbs against human or murine VEGFR-1 had no effect on mice survival. Therefore, effective antiangiogenic therapies to treat VEGF-producing, VEGFR-expressing leukemias may require blocking both paracrine and autocrine VEGF/VEGFR-2 angiogenic loops to achieve remission and long-term cure.

Animals↗
PubMed2001

Clonal variation in phenotype and life span of human embryonic fibroblasts (MRC-5) transduced with the catalytic component of telomerase (hTERT).

Expression of telomerase (hTERT) in certain cell types has been shown to extend cellular life span without malignant transformation. We studied the phenotype of 26 telomerase-transduced fibroblast clones (TTFC) generated from a mass culture of hTERT retrovirally transduced MRC-5 cells. About two-thirds of the transduced clones senesced at the expected time or shortly thereafter, despite high levels of expression of telomerase and telomere length maintenance. The remaining one-third of the clones were "immortalized" (followed for over 200 cumulative population doublings). All clones maintained a nontransformed phenotype: contact inhibition, anchorage dependency, lack of tumor formation in nude mice, dose dependency to serum and growth factors, low expression of a matrix metalloproteinase associated with metastatic invasion (MMP-9) and high expression of its inhibitor TIMP-1, and no cytogenetic abnormalities by G-banding. In addition, fibroblast-specific biological parameters, such as colony size, production of collagenase, and response to MMC and gamma radiation were tightly regulated at the clonal and subclonal levels.

Animals↗
PubMed2001

Effect of cellulose acetate materials on the oxidative burst of human neutrophils.

Following adverse clinical events involving seven patients undergoing renal dialysis using 12-year-old cellulose acetate hemodialyzers, this in vitro study was proposed in an effort to characterize the inflammatory response to the constituent cellulose acetate (CA) fiber materials. Chemiluminescence (CL) and apoptosis assays were used to determine whether human neutrophils were activated by CA fiber materials and/or are sensitive to degradation/alteration of these fibers over time. Furthermore, the study examined in vitro assays with human neutrophils using a CA film, the solvents used in the film preparation and CA resin. The film could be cut to identical sized pieces in an effort to compare hemodialysis material effects in standardized amounts. For the CL assays, 60-min exposure was followed by secondary stimulation with n-formyl-met-leu-phe (fMLP) or phorbol-12-myristate-13-acetate (PMA). Short-term exposure (60-min postintroduction to CA materials) increased the inflammatory response as measured by the respiratory burst of neutrophils (p < or =.05), with CA fiber exposure significantly compared with cells alone. There was a trend toward an increased response with exposure to older fibers with secondary PMA stimulation. Apoptosis was increased 12% with exposure to the more aged fibers versus 2% with the new fibers. The fiber storage component, glycerol, significantly inhibited the oxidative response (p < or =.001; > or =80% suppression with concentrations of 5-20%). The solvents used in film preparation, N,N-dimethylacetamide and tetrahydrofuran, produced greater than a 70% and 60% suppression, respectively, of CL activity for all concentrations > or =1%. More work is needed to determine the specific nature of the interaction of inflammatory cells with CA materials, but early evidence suggests that neutrophils are activated by CA and display an altered response to more aged fibers.

Adult↗