2,651 research outputs found

    Replica theory for fluctuations of the activation barriers in glassy systems

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    We consider the problem of slow activation dynamics in glassy systems undergoing a random first order phase transition. Using an effective potential approach to supercooled liquids, we determine the spectrum of activation barriers for entropic droplets. We demonstrate that fluctuations of the configurational entropy and of the liquid glass surface tension are crucial to achieve an understanding of the barrier fluctuations in glassy systems and thus are ultimatively responsible for the broad spectrum of excitations and heterogeneous dynamics in glasses. In particular we derive a relation between the length scale for dynamic heterogeneity and the related barrier fluctuations. Diluted entropic droplets are shown to have a Gaussian distribution of barriers, strongly suggesting that non-Gaussian behavior results from droplet-droplet interactions.Comment: 16 pages, 9 eps figure

    New Formalism for Numerical Relativity

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    We present a new formulation of the Einstein equations that casts them in an explicitly first order, flux-conservative, hyperbolic form. We show that this now can be done for a wide class of time slicing conditions, including maximal slicing, making it potentially very useful for numerical relativity. This development permits the application to the Einstein equations of advanced numerical methods developed to solve the fluid dynamic equations, {\em without} overly restricting the time slicing, for the first time. The full set of characteristic fields and speeds is explicitly given.Comment: uucompresed PS file. 4 pages including 1 figure. Revised version adds a figure showing a comparison between the standard ADM approach and the new formulation. Also available at http://jean-luc.ncsa.uiuc.edu/Papers/ Appeared in Physical Review Letters 75, 600 (1995

    Cosmic Swarms: A search for Supermassive Black Holes in the LISA data stream with a Hybrid Evolutionary Algorithm

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    We describe a hybrid evolutionary algorithm that can simultaneously search for multiple supermassive black hole binary (SMBHB) inspirals in LISA data. The algorithm mixes evolutionary computation, Metropolis-Hastings methods and Nested Sampling. The inspiral of SMBHBs presents an interesting problem for gravitational wave data analysis since, due to the LISA response function, the sources have a bi-modal sky solution. We show here that it is possible not only to detect multiple SMBHBs in the data stream, but also to investigate simultaneously all the various modes of the global solution. In all cases, the algorithm returns parameter determinations within 5σ5\sigma (as estimated from the Fisher Matrix) of the true answer, for both the actual and antipodal sky solutions.Comment: submitted to Classical & Quantum Gravity. 19 pages, 4 figure

    Double-Stranded RNA Attenuates the Barrier Function of Human Pulmonary Artery Endothelial Cells

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    Circulating RNA may result from excessive cell damage or acute viral infection and can interact with vascular endothelial cells. Despite the obvious clinical implications associated with the presence of circulating RNA, its pathological effects on endothelial cells and the governing molecular mechanisms are still not fully elucidated. We analyzed the effects of double stranded RNA on primary human pulmonary artery endothelial cells (hPAECs). The effect of natural and synthetic double-stranded RNA (dsRNA) on hPAECs was investigated using trans-endothelial electric resistance, molecule trafficking, calcium (Ca2+) homeostasis, gene expression and proliferation studies. Furthermore, the morphology and mechanical changes of the cells caused by synthetic dsRNA was followed by in-situ atomic force microscopy, by vascular-endothelial cadherin and F-actin staining. Our results indicated that exposure of hPAECs to synthetic dsRNA led to functional deficits. This was reflected by morphological and mechanical changes and an increase in the permeability of the endothelial monolayer. hPAECs treated with synthetic dsRNA accumulated in the G1 phase of the cell cycle. Additionally, the proliferation rate of the cells in the presence of synthetic dsRNA was significantly decreased. Furthermore, we found that natural and synthetic dsRNA modulated Ca2+ signaling in hPAECs by inhibiting the sarco-endoplasmic Ca2+-ATPase (SERCA) which is involved in the regulation of the intracellular Ca2+ homeostasis and thus cell growth. Even upon synthetic dsRNA stimulation silencing of SERCA3 preserved the endothelial monolayer integrity. Our data identify novel mechanisms by which dsRNA can disrupt endothelial barrier function and these may be relevant in inflammatory processes

    A Transiting Hot Jupiter Orbiting a Metal-Rich Star

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    We announce the discovery of Kepler-6b, a transiting hot Jupiter orbiting a star with unusually high metallicity, [Fe/H] = +0.34 +/- 0.04. The planet's mass is about 2/3 that of Jupiter, Mp = 0.67 Mj, and the radius is thirty percent larger than that of Jupiter, Rp = 1.32 Rj, resulting in a density of 0.35 g/cc, a fairly typical value for such a planet. The orbital period is P = 3.235 days. The host star is both more massive than the Sun, Mstar = 1.21 Msun, and larger than the Sun, Rstar = 1.39 Rsun.Comment: 12 pages, 2 figures, submitted to the Astrophysical Journal Letter

    Layperson perception of reflux-related symptoms

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    OBJECTIVE: To assess for differences of intended meaning in the description of reflux-related symptoms among otolaryngology patients and clinicians. STUDY DESIGN: Cross-sectional survey-based study. SETTING: Five tertiary, academic otolaryngology practices. METHODS: Between June 2020 and July 2022, a questionnaire consisting of 20 common descriptors of reflux-related symptoms within four domains (throat-, chest-, stomach-, and sensory-related symptoms) was completed by patients. Attending otolaryngologists at five academic medical centers then completed the same survey. The primary outcome was to assess differences in patient and clinician perceptions of reflux-related symptoms. Differences based on geographic location was a secondary outcome. RESULTS: A total of 324 patients and 27 otolaryngologists participated. Patients selected a median of six terms compared with 10.5 for otolaryngologists ( CONCLUSION: There are differences between otolaryngologists and their patients in the interpretation of the symptoms of reflux. Patients tended to have a narrower interpretation of reflux with symptoms primarily limited to classic stomach-related symptoms, while clinicians tended to have a broader definition of reflux that included extra-esophageal manifestations of disease. This has important counseling implications for the clinician, as patients presenting with reflux symptoms may not comprehend the relationship of those symptoms to reflux disease

    Relational Particle Models. II. Use as toy models for quantum geometrodynamics

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    Relational particle models are employed as toy models for the study of the Problem of Time in quantum geometrodynamics. These models' analogue of the thin sandwich is resolved. It is argued that the relative configuration space and shape space of these models are close analogues from various perspectives of superspace and conformal superspace respectively. The geometry of these spaces and quantization thereupon is presented. A quantity that is frozen in the scale invariant relational particle model is demonstrated to be an internal time in a certain portion of the relational particle reformulation of Newtonian mechanics. The semiclassical approach for these models is studied as an emergent time resolution for these models, as are consistent records approaches.Comment: Replaced with published version. Minor changes only; 1 reference correcte
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