86 research outputs found

    Cluster-resolved dynamic scaling theory and universal corrections for transport on percolating systems

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    For percolating systems, we propose a universal exponent relation connecting the leading corrections to scaling of the cluster size distribution with the dynamic corrections to the asymptotic transport behaviour at criticality. Our derivation is based on a cluster-resolved scaling theory unifying the scaling of both the cluster size distribution and the dynamics of a random walker. We corroborate our theoretical approach by extensive simulations for a site percolating square lattice and numerically determine both the static and dynamic correction exponents.Comment: 6 pages, 5 figures, 1 tabl

    Universality of finite-size corrections to the number of critical percolation clusters

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    Monte-Carlo simulations on a variety of 2d percolating systems at criticality suggest that the excess number of clusters in finite systems over the bulk value of nc is a universal quantity, dependent upon the system shape but independent of the lattice and percolation type. Values of nc are found to high accuracy, and for bond percolation confirm the theoretical predictions of Temperley and Lieb, and Baxter, Temperley, and Ashley, which we have evaluated explicitly in terms of simple algebraic numbers. Predictions for the fluctuations are also verified for the first time.Comment: 13 pages, 2 figs., Latex, submitted to Phys. Rev. Let

    Lagrangian predictability of high-resolution regional models: the special case of the Gulf of Mexico

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    The Lagrangian prediction skill (model ability to reproduce Lagrangian drifter trajectories) of the nowcast/forecast system developed for the Gulf of Mexico at the University of Colorado at Boulder is examined through comparison with real drifter observations. Model prediction error (MPE), singular values (SVs) and irreversible-skill time (IT) are used as quantitative measures of the examination. Divergent (poloidal) and nondivergent (toroidal) components of the circulation attractor at 50m depth are analyzed and compared with the Lagrangian drifter buoy data using the empirical orthogonal function (EOF) decomposition and the measures, respectively. Irregular (probably, chaotic) dynamics of the circulation attractor reproduced by the nowcast/forecast system is analyzed through Lyapunov dimension, global entropies, toroidal and poloidal kinetic energies. The results allow assuming exponential growth of prediction error on the attractor. On the other hand, the <it>q</it>-th moment of MPE grows by the power law with exponent of 3<it>q</it>/4. The probability density function (PDF) of MPE has a symmetrical but non-Gaussian shape for both the short and long prediction times and for spatial scales ranging from 20km to 300km. The phenomenological model of MPE based on a diffusion-like equation is developed. The PDF of IT is non-symmetric with a long tail stretched towards large ITs. The power decay of the tail was faster than 2 for long prediction times

    Directed polymers and interfaces in random media : free-energy optimization via confinement in a wandering tube

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    We analyze, via Imry-Ma scaling arguments, the strong disorder phases that exist in low dimensions at all temperatures for directed polymers and interfaces in random media. For the uncorrelated Gaussian disorder, we obtain that the optimal strategy for the polymer in dimension 1+d1+d with 0<d<20<d<2 involves at the same time (i) a confinement in a favorable tube of radius RSLνSR_S \sim L^{\nu_S} with νS=1/(4d)<1/2\nu_S=1/(4-d)<1/2 (ii) a superdiffusive behavior RLνR \sim L^{\nu} with ν=(3d)/(4d)>1/2\nu=(3-d)/(4-d)>1/2 for the wandering of the best favorable tube available. The corresponding free-energy then scales as FLωF \sim L^{\omega} with ω=2ν1\omega=2 \nu-1 and the left tail of the probability distribution involves a stretched exponential of exponent η=(4d)/2\eta= (4-d)/2. These results generalize the well known exact exponents ν=2/3\nu=2/3, ω=1/3\omega=1/3 and η=3/2\eta=3/2 in d=1d=1, where the subleading transverse length RSL1/3R_S \sim L^{1/3} is known as the typical distance between two replicas in the Bethe Ansatz wave function. We then extend our approach to correlated disorder in transverse directions with exponent α\alpha and/or to manifolds in dimension D+d=dtD+d=d_{t} with 0<D<20<D<2. The strategy of being both confined and superdiffusive is still optimal for decaying correlations (α<0\alpha<0), whereas it is not for growing correlations (α>0\alpha>0). In particular, for an interface of dimension (dt1)(d_t-1) in a space of total dimension 5/3<dt<35/3<d_t<3 with random-bond disorder, our approach yields the confinement exponent νS=(dt1)(3dt)/(5dt7)\nu_S = (d_t-1)(3-d_t)/(5d_t-7). Finally, we study the exponents in the presence of an algebraic tail 1/V1+μ1/V^{1+\mu} in the disorder distribution, and obtain various regimes in the (μ,d)(\mu,d) plane.Comment: 19 page

    Seal Bomb Noise as a Potential Threat to Monterey Bay Harbor Porpoise

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    Anthropogenic noise is a known threat to marine mammals. Decades of research have shown that harbor porpoises are particularly sensitive to anthropogenic noise, and geographic displacement is a common impact from noise exposure. Small, localized populations may be particularly vulnerable to impacts associated with displacement, as animals that are excluded from their primary habitat may have reduced foraging success and survival, or be exposed to increased threats of predation or bycatch. Seal bombs are underwater explosives used in purse seine fisheries to deter marine mammals during fishery operations. Pinnipeds are believed to be the primary target for seal bomb use, however there may be indirect impacts on harbor porpoises. Active purse seine fishing using seal bombs in the greater Monterey Bay area may, at times, span the entire range of the Monterey Bay harbor porpoise stock, which may lead to negative impacts for this population. In this contribution, we review anthropogenic noise as a threat to harbor porpoises, with a focus on the potential for impacts from seal bomb noise exposure in the Monterey Bay region

    Прикроватный анализ кислотно-основного состояния

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    Laboratory service is one of the most hang-the-expense items in the cost of treatment of patients in an intensive care unit. Isolated acid-base balance (ABB) impairments are rare in clinical practice. These impairments are generally combined and they frequently cause a drastic change in the pH value of blood. Early detection of their origin and its elimination are of profound importance in these situations. Miniaturization of analyzers has made it possible to conduct some investigations and particularly to determine ABB just in the intensive care unit or operating suite. The attached software permits creation of a database and transmission of information to the laboratory network. One year’s experience has indicated that the quality of reagents and reference substances allows real-time determination of the values of ABB with a high degree of accuracy and reproducibility at a patient’s bed. Лабораторная служба является одной из самых затратных статей расхода в лечении пациентов. В клинической практике редко встречаются нарушения КОС в изолированном виде. Обычно эти расстройства являются сочетанными и нередко влекут за собой резкое изменение величины рН крови. В таких ситуациях крайне важным является раннее выявление первопричины и ее устранение. Миниатюризация анализаторов позволила проводить некоторые исследования и, в частности, определение КОС непосредственно в отделении интенсивной терапии или в операционной. Прилагаемое программное обеспечение позволяет создавать базу данных результатов и передавать информацию в лабораторную сеть. Годовой опыт использования анализаторов показал, что качество реагентов и калибровочных материалов позволяет с высокой точностью и воспроизводимостью определять показатели КОС у постели больного в режиме реального времени.

    Critical behavior of the long-range Ising chain from the largest-cluster probability distribution

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    Monte Carlo simulations of the 1D Ising model with ferromagnetic interactions decaying with distance rr as 1/r1+σ1/r^{1+\sigma} are performed by applying the Swendsen-Wang cluster algorithm with cumulative probabilities. The critical behavior in the non-classical critical regime corresponding to 0.5<σ<10.5 <\sigma < 1 is derived from the finite-size scaling analysis of the largest cluster.Comment: 4 pages, 2 figures, in RevTeX, to appear in Phys. Rev. E (Feb 2001

    Transcatheter mitral valve edge-to-edge repair in patients with severe mitral regurgitation: data from the MitraClip Russia Trial

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    Aim. To study the immediate and short-term outcomes of transcatheter mitral valve edge-to-edge repair with the MitraClip NT in patients with severe mitral regurgitation as part of the MitraClip Russia prospective single-center study.Material and methods. The study included 16 patients (men, 10; women, 6) with mean age of 70,1±2,1 years (mean Euroscore II, 6,90±5,56%; STS, 6,33±3,94%). Immediate technical success was defined as successful access, delivery, and removal of the device, and adequate placing the clip(s) to reduce the mitral regurgitation to grade 2 or below without the need for device- or procedure-related reintervention.Results. Immediate technical success was achieved in all patients. The average number of implanted clips per 1 patient was 1,7. In 1 patient (6,3%), a clip was attached to one mitral leaflet, which required an non-scheduled implantation of a second clip. In hospital mortality was 6,3%: a 92-year-old patient on the 3rd day after the operation had a sudden cardiac arrest followed by coma, hemispheric ischemic stroke and death on the 6th day. An autopsy revealed an iatrogenic atrial septal defect. Echocardiography performed on the 10th and 30th day after surgery showed a decrease in mitral regurgitation grade in 15 patients, while grade 3 residual mitral regurgitation did not reveal in any patient.Conclusion. Transcatheter mitral valve edge-to-edge repair with the MitraClip is a minimally invasive method for treating severe symptomatic mitral regurgitation (degenerative and functional). The results demonstrate high immediate efficacy and an acceptable safety profile in high surgical risk patients. Based on the analysis of death causes, the authors conclude that it is necessary to include initial pulmonary hypertension above 75 mm Hg as a relative contraindication to this procedure. The study limitations are the small sample size and short follow-up period

    Statistical signatures of critical behavior in small systems

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    The cluster distributions of different systems are examined to search for signatures of a continuous phase transition. In a system known to possess such a phase transition, both sensitive and insensitive signatures are present; while in systems known not to possess such a phase transition, only insensitive signatures are present. It is shown that nuclear multifragmentation results in cluster distributions belonging to the former category, suggesting that the fragments are the result of a continuous phase transition.Comment: 31 pages, two columns with 30 figure
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