1,720,964 research outputs found
Two-dimensional Lorentz process for magnetotransport: Boltzmann-Grad limit
No full textWe study a system of charged, noninteracting classical particles moving in a Poisson distribution of hard-disk scatterers in two dimensions, under the effect of a magnetic field perpendicular to the plane. We prove that, in the low-density (Boltzmann- Grad) limit, the particle distribution evolves according to a generalized linear Boltzmann equation, previously derived and solved by Bobylev et al. (Phys. Rev. Lett. 75 (1995) 2, J. Stat. Phys. 87 (1997) 1205-1228, J. Stat. Phys. 102 (2001) 1133-1150). In this model, Boltzmann's chaos fails, and the kinetic equation includes non-Markovian terms. The ideas of (Phys. Rev. 185 (1969) 308-322) can be however adapted to prove convergence of the process with memory
Re: Atrioventricular septal defect with common atrioventricular junction, common arterial trunk and severe coartation of the aorta in a patient with Down's syndrome.
No full textExistence and stability of weak solutions of the Vlasov-Poisson system in localised Yudovich spaces
Full text linkWe consider the Vlasov-Poisson system both in the repulsive (electrostatic potential) and in the attractive (gravitational potential) cases. Our first main theorem yields the analog for the Vlasov-Poisson system of Yudovich’s celebrated well-posedness theorem for the Euler equations: we prove the uniqueness and the quantitative stability of Lagrangian solutions f = f ( t , x , v ) whose associated spatial density ρ f = ρ f ( t , x ) is potentially unbounded but belongs to suitable uniformly-localised Yudovich spaces. This requirement imposes a condition of slow growth on the function p ↦ ‖ ρ f ( t , ⋅ ) ‖ L p uniformly in time. Previous works by Loeper, Miot and Holding-Miot have addressed the cases of bounded spatial density, i.e. ‖ ρ f ( t , ⋅ ) ‖ L p ≲ 1 , and spatial density such that ‖ ρ f ( t , ⋅ ) ‖ L p ∼ p 1 / α for α ∈ [ 1 , + ∞ ) . Our approach is Lagrangian and relies on an explicit estimate of the modulus of continuity of the electric field and on a second-order Osgood lemma. It also allows for iterated-logarithmic perturbations of the linear growth condition. In our second main theorem, we complement the aforementioned result by constructing solutions whose spatial density sharply satisfies such iterated-logarithmic growth. Our approach relies on real-variable techniques and extends the strategy developed for the Euler equations by the first and fourth-named authors. It also allows for the treatment of more general equations that share the same structure as the Vlasov-Poisson system. Notably, the uniqueness result and the stability estimates hold for both the classical and the relativistic Vlasov-Poisson systems
Mean field evolution of fermions with Coulomb interaction
Full text linkWe study the many body Schrödinger evolution of weakly coupled fermions interacting through a Coulomb potential. We are interested in a joint mean field and semiclassical scaling, that emerges naturally for initially confined particles. For initial data describing approximate Slater determinants, we prove convergence of the many-body evolution towards Hartree–Fock dynamics. Our result holds under a condition on the solution of the Hartree–Fock equation, that we can only show in a very special situation (translation invariant data, whose Hartree–Fock evolution is trivial), but that we expect to hold more generally
EMOTIONAL FLUCTUATIONS OF BLOOD PRESSURE IN ADOLESCENTS: INFLUENCE OF THE REPETITION OF THE MEASUREMENT
No full textBackground. The optimal methodology to measure blood pressure (BP) in children remains controversial. Particularly relevant is the concern that anxiety may trigger a rising in BP during the first measurement, while the second and/or the third reading is lower because the child is more relaxed. However, experimental data concerning the pattern of repeated readings of BP are almost non existent. Therefore we accurately examined, by a repeated measures ANOVA design, the pressor response of a large group of healthy children, during the adolescent growth, to three consecutive BP measurements separated by one minute.
Method. From a larger group of 719 well-being children aged 5-15 years examined in our hospital between July 2004 and March 2005, a cohort of 145 age-eligible children (11-14 years) was selected for this study. In each subject, BP readings were carried out in the supine position placing size-appropriate cuffies on the right arm and by making use of an oscillometric monitor, whose reliability is unaffected by the enviromental noise. Anthropometric parameters also were acquired. Data were analysed with a PC based statistic package (SPSS for Windows) testing the within-subjects differences.
Results and conclusions. Data from the study are shown in the figure
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
From the Hartree dynamics to the Vlasov equation
Full text linkWe consider the evolution of quasi-free states describing fermions in the mean field limit, as governed by the nonlinear Hartree equation. In the limit of large , we study the convergence towards the classical Vlasov equation. For a class of regular interaction potentials, we establish precise bounds on the 0rate of convergence
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