Nonlinear saturation of electrostatic waves: mobile ions modify trapping scaling

The amplitude equation for an unstable electrostatic wave in a multi-species Vlasov plasma has been derived. The dynamics of the mode amplitude $\rho(t)$ is studied using an expansion in $\rho$; in particular, in the limit $\gamma\rightarrow0^+$, the singularities in the expansion coefficients are analyzed to predict the asymptotic dependence of the electric field on the linear growth rate $\gamma$. Generically $|E_k|\sim \gamma^{5/2}$, as $\gamma\rightarrow0^+$, but in the limit of infinite ion mass or for instabilities in reflection-symmetric systems due to real eigenvalues the more familiar trapping scaling $|E_k|\sim \gamma^{2}$ is predicted.Comment: 13 pages (Latex/RevTex), 4 postscript encapsulated figures which are included using the utility "uufiles". They should be automatically included with the text when it is downloaded. Figures also available in hard copy from the authors ([email protected]

Metastability of solitary roll wave solutions of the St. Venant equations with viscosity

We study by a combination of numerical and analytical Evans function techniques the stability of solitary wave solutions of the St. Venant equations for viscous shallow-water flow down an incline, and related models. Our main result is to exhibit examples of metastable solitary waves for the St. Venant equations, with stable point spectrum indicating coherence of the wave profile but unstable essential spectrum indicating oscillatory convective instabilities shed in its wake. We propose a mechanism based on ``dynamic spectrum'' of the wave profile, by which a wave train of solitary pulses can stabilize each other by de-amplification of convective instabilities as they pass through successive waves. We present numerical time evolution studies supporting these conclusions, which bear also on the possibility of stable periodic solutions close to the homoclinic. For the closely related viscous Jin-Xin model, by contrast, for which the essential spectrum is stable, we show using the stability index of Gardner--Zumbrun that solitary wave pulses are always exponentially unstable, possessing point spectra with positive real part.Comment: 42 pages, 9 figure

Thrombolysis in Patients Aged over 80 Years Is Equally Effective and Safe

BACKGROUND: Despite stroke's high prevalence in the elderly, intravenous thrombolysis is licensed in Europe only for patients younger than 80 years old. We aimed to compare the functional outcomes and complication rates in patients older versus younger than 80 years old treated with intravenous thrombolysis. METHODS: A retrospective observational study of patients who received intravenous thrombolysis in a stroke unit between January 1, 2009, and June 30, 2012, was conducted. Variables were compared between 2 subgroups (≤80 and >80 years). RESULTS: Overall, 512 patients underwent intravenous thrombolysis, of which 13.1% were over 80 years. The mean age was 65.4 years in the younger subgroup and 82.9 years in the older subgroup. Prior independence rates did not differ between the subgroups. Prevalence of atrial fibrillation and cardioembolic stroke was higher in the older subgroup (P = .004 and .026). Only 3% of the elderly with atrial fibrillation were taking oral anticoagulants. Symptoms-to-needle time was lower in the older subgroup (P = .048). Stroke severity was higher in patients over 80 years (P = .026). There was significant improvement in the National Institutes of Health Stroke Scale score 7 days after intravenous thrombolysis (P < .001) in both subgroups. The proportion of patients with 3 months' favorable outcome and independence, hemorrhagic transformation, and mortality rates were similar in both subgroups. CONCLUSIONS: Elderly patients' benefits and outcomes from intravenous thrombolysis treatment were identical to the younger subgroup without excess hemorrhagic transformation or mortality. These results favor the use of intravenous thrombolysis in patients over 80 years.info:eu-repo/semantics/publishedVersio

On scattering of solitons for the Klein-Gordon equation coupled to a particle

We establish the long time soliton asymptotics for the translation invariant nonlinear system consisting of the Klein-Gordon equation coupled to a charged relativistic particle. The coupled system has a six dimensional invariant manifold of the soliton solutions. We show that in the large time approximation any finite energy solution, with the initial state close to the solitary manifold, is a sum of a soliton and a dispersive wave which is a solution of the free Klein-Gordon equation. It is assumed that the charge density satisfies the Wiener condition which is a version of the ``Fermi Golden Rule''. The proof is based on an extension of the general strategy introduced by Soffer and Weinstein, Buslaev and Perelman, and others: symplectic projection in Hilbert space onto the solitary manifold, modulation equations for the parameters of the projection, and decay of the transversal component.Comment: 47 pages, 2 figure

Coercivity and stability results for an extended Navier-Stokes system

In this article we study a system of equations that is known to {\em extend} Navier-Stokes dynamics in a well-posed manner to velocity fields that are not necessarily divergence-free. Our aim is to contribute to an understanding of the role of divergence and pressure in developing energy estimates capable of controlling the nonlinear terms. We address questions of global existence and stability in bounded domains with no-slip boundary conditions. Even in two space dimensions, global existence is open in general, and remains so, primarily due to the lack of a self-contained $L^2$ energy estimate. However, through use of new $H^1$ coercivity estimates for the linear equations, we establish a number of global existence and stability results, including results for small divergence and a time-discrete scheme. We also prove global existence in 2D for any initial data, provided sufficient divergence damping is included.Comment: 29 pages, no figure

On the Stability of Periodic Solutions of the Generalized Benjamin-Bona-Mahony Equation

We study the stability of a four parameter family of spatially periodic traveling wave solutions of the generalized Benjamin-Bona-Mahony equation to two classes of perturbations: periodic perturbations with the same periodic structure as the underlying wave, and long-wavelength localized perturbations. In particular, we derive necessary conditions for spectral instability to perturbations to both classes of perturbations by deriving appropriate asymptotic expansions of the periodic Evans function, and we outline a nonlinear stability theory to periodic perturbations based on variational methods which effectively extends our periodic spectral stability results.Comment: 27 pages, 3 figure

Algebro-Geometric Solutions of the Boussinesq Hierarchy

We continue a recently developed systematic approach to the Bousinesq (Bsq) hierarchy and its algebro-geometric solutions. Our formalism includes a recursive construction of Lax pairs and establishes associated Burchnall-Chaundy curves, Baker-Akhiezer functions and Dubrovin-type equations for analogs of Dirichlet and Neumann divisors. The principal aim of this paper is a detailed theta function representation of all algebro-geometric quasi-periodic solutions and related quantities of the Bsq hierarchy.Comment: LaTeX, 48 page

Subjetividad, cuerpo propio y arraigo terreno : Una relectura desde Hannah Arendt del debate Ricoeur-Parfit

En el presente trabajo nos proponemos abordar algunos de los desafíos que enfrentan los procesos de constitución de la subjetividad en el mundo contemporáneo. Nos serviremos para ello de los desarrollos de Paul Ricoeur sobre la identidad en Sí mismo como otro y de las consideraciones de Hannah Arendt en torno de La condición humana hacia la segunda mitad del siglo XX. En el primer apartado, reconstruimos someramente las críticas de Ricoeur a la concepción reduccionista de Derek Parfit, con el objeto de mostrar las dos condiciones básicas de la existencia humana sobre las que se sustenta la cuestión de la identidad: el arraigo terreno y la experiencia del cuerpo propio. Ricoeur advierte que los casos ficcionales de Parfit conducen a una situación de indecibilidad, en la medida en que suponen una aproximación a la identidad entendida meramente como mismidad, al tiempo que desconocen esas dos condiciones de la existencia humana. Sin embargo, ni la Tierra ni el cuerpo propio, pueden ser reducidos a meros objetos físicos, sino que se encuentran a la base de la posibilidad de nuestras experiencias de la espacialidad y temporalidad de los objetos físicos. No obstante, a partir del análisis de Hannah Arendt es posible advertir que algunos sucesos del siglo pasado han erosionado estas condiciones, volviéndolas problemáticas. En este contexto, en el segundo apartado examinamos el enfoque arendtiano, bajo la hipótesis de que permite reconsiderar las críticas de Ricoeur a Parfit, a través de situaciones históricas concretas del siglo pasado, que han de diversa manera impactado en los procesos de subjetivación De este modo, no pretendemos en absoluto dar por saldada la controversia entre ambos filósofos, sino más bien poner de manifiesto, recurriendo a la mediación del análisis de Arendt, algunos de los desafíos que enfrenta la constitución de la subjetividad en las sociedades contemporáneas.Facultad de Humanidades y Ciencias de la Educació

Hipertensão arterial sistémica em idade pediátrica

The definition of hypertension (HT) in the pediatric age group is based on the normal distribution of blood pressure (BP) in healthy children. Normal BP is defined as being below the 90th percentile for gender, age and height, and hypertension as equal to or higher than the 95th percentile on at least three separate occasions. If the values are above the 90th percentile but below the 95th percentile, the child should be considered prehypertensive. Ambulatory BP monitoring is useful in the assessment of BP levels in the young. P values in children and adolescents have creased in the last decade, in parallel with increases in body mass index, and HT now has a prevalence of 2-5%. Obesity in childhood and adolescence is one of the main predictors of HT in adulthood, but it is also associated with other cardiovascular risk factors such as dyslipidemia, abnormal glucose metabolism, insulin resistance, inflammation and impaired vascular function. Left ventricular hypertrophy is the most prominent evidence of target organ damage caused by hypertension in children and adolescents. The goal for antihypertensive treatment is to reduce BP below the 95th percentile. Weight control, with regular physical activity and dietary changes, is the primary therapy for obesity-related hypertension. Weight loss decreases not only BP but also other cardiovascular risk factors. The indications for use of antihypertensive drugs are: symptomatic hypertension, secondary hypertension, established hypertensive target organ damage, stage 2 hypertension and failure of nonpharmacologic measures