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R Rosner

Publications and source records attributed to R Rosner.

At least 19 recordsLinked to original sources
PubMed2006

Multiscale character of the nonlinear coherent dynamics in the Rayleigh-Taylor instability.

We report nonlinear solutions for a system of conservation laws describing the dynamics of the large-scale coherent structure of bubbles and spikes in the Rayleigh-Taylor instability (RTI) for fluids with a finite density ratio. Three-dimensional flows are considered with general type of symmetry in the plane normal to the direction of gravity. The nonlocal properties of the interface evolution are accounted for on the basis of group theory. It is shown that isotropic coherent structures are stable. For anisotropic structures, secondary instabilities develop with the growth rate determined by the density ratio. For stable structures, the curvature and velocity of the nonlinear bubble have nontrivial dependencies on the density ratio, yet their mutual dependence on one another has an invariant form independent of the density ratio. The process of bubble merge is not considered. Based on the obtained results we argue that the large-scale coherent dynamics in RTI has a multiscale character and is governed by two length scales: the period of the coherent structure and the bubble (spike) position.

Journal Article↗
PubMed2005

Model flames in the Boussinesq limit: the case of pulsating fronts.

We extend earlier work on the nonlinear behavior of premixed flames in a gravitationally stratified medium, subject to the Boussinesq approximation, in two dimensions. The main result is that the nature of the traveling burning front is largely determined by the form of the adopted boundary conditions on the side walls: while symmetric boundary conditions lead to stably scalloped traveling wave solutions, loss of symmetry leads to the development of pulsating fronts. However, despite differences in geometrical features, the symmetric and asymmetric systems obey the same scaling behavior for the average effective flame speed.

Journal Article↗
PubMed2004

Kelvin-Helmholtz instability for relativistic fluids.

We reexamine the stability of an interface separating two nonmagnetized relativistic fluids in relative motion, showing that, in an appropriate reference frame, it is possible to find analytic solutions to the dispersion relation. Moreover, we show that the critical value of the Mach number, introduced by compressibility, is unchanged from the nonrelativistic case if we redefine the Mach number as M= [beta/ (1- beta(2) )(1/2) ] [ beta(s) / (1- beta(2)(s) )(1/2) ](-1) , where beta and beta(s) are, respectively, the speed of the fluid and the speed of sound (in units of the speed of light).

Journal Article↗
PubMed2003

Model flames in the Boussinesq limit: the effects of feedback.

We have studied the fully nonlinear behavior of premixed flames in a gravitationally stratified medium, subject to the Boussinesq approximation. The key results include the establishment of criteria for when such flames propagate as simple planar flames, elucidation of scaling laws for the effective flame speed, and a study of the stability properties of these flames. The simplicity of some of our scaling results suggests that analytical work may further advance our understandings of buoyant flames.

Journal Article↗
PubMed2002

Explosive energy release in magnetic shocks.

We show that a magnetic shock whose initial density and/or magnetic perturbation exceeds the Hugoniot limit may lead to substantial and rapid energy release in low beta plasmas (such as occur in the magnetospheres of neutron stars). We illustrate this effect for a fast Magnetohydrodynamic perturbation, as well as for large density perturbations which can be naturally created in low beta plasmas. Using the Riemann solution and simulations, we show that slow modes of finite magnitudes and Alfvénic perturbations can generate strong density perturbations. These perturbations develop into shocks, resulting in efficient energy release.

Journal Article↗
PubMed2002

Shear instability of fluid interfaces: stability analysis.

We examine the linear stability of fluid interfaces subjected to a shear flow. Our main object is to generalize previous work to an arbitrary Atwood number, and to allow for surface tension and weak compressibility. The motivation derives from instances in astrophysical systems where mixing across material interfaces driven by shear flows may significantly affect the dynamical evolution of these systems.

Journal Article↗
PubMed2001

Plasmoid impacts on neutron stars and highest energy cosmic rays.

Particle acceleration by electrostatic polarization fields that arise in plasmas streaming across magnetic fields is discussed as a possible acceleration mechanism of highest energy ( greater, similar10(20) eV) cosmic rays. Specifically, plasmoids arising in planetoid impacts onto neutron star magnetospheres are considered. We find that such impacts at plausible rates may account for the observed flux and energy spectrum of the highest energy cosmic rays.

Journal Article↗
PubMed2001

Interface imprinting by a rippled shock using an intense laser.

Perturbation imprinting at a flat interface by a rippled shock has been observed in a laser hydrodynamics experiment. A strong shock was driven through a three-layer target, with the first interface rippled, and the second flat. The chosen thickness of the second layer gave instability growth with opposite phases at the two interfaces, consistent with two-dimensional simulations and rippled shock theory.

Journal Article↗
PubMed2001

Between search and research: how to find your way around? Review of the article "Thought Field Therapy- soothing the bad moments of Kosovo".

This article is based on a review of the article, "Thought Field Therapy-Soothing the Bad Moments of Kosovo," (Johnson, Shala, Sejdijaj, Odell, & Dabishevici [2001]). As it is assumed that it is the intention of the reviewed article to prove the effectiveness of TFT, the information given is evaluated in terms of how well this goal is attained. However, as a sample description is not provided and minimal methodological standards, such as some kind of standardized diagnostical procedure, are not met, it is not possible to appraise issues central to any empirical study. Furthermore the design of the study is not in accordance with the goal of the study, as any control for expectancy effects, natural remission, or even a comparison with other successful psychotherapeutic procedures is missing. The study provides very limited evidence for the effectiveness of TFT.

Albania↗
PubMed2000

Vicarious emotional experience and emotional expression in group psychotherapy.

Emotional arousal is a key concept in most theories of change. To be able to understand the role of emotional expression better, two treatments, cognitive therapy (CT) and focused expressive psychotherapy (FEP; a manualized form of Gestalt therapy), with opposite process assumptions about the expression of emotions were compared. Additionally vicarious emotional experience in the sense of an underlying emotional contagion was examined. Clients suffering from major depression were rated for the expression of emotion in three randomly selected sessions of a 20-session treatment course. While the types of emotions generally experienced by CT clients and FEP clients did not differ significantly, differences in the subgroups of active and observing-group members were found. This indicated that the process assumptions made by the respective treatments were only valid for the actively participating clients and not for the observing group members. Emotional contagion as a process was not supported.

Adult↗
PubMed2000

Evidence for topological nonequilibrium in magnetic configurations

We use direct numerical simulations to study the evolution, or relaxation, of magnetic configurations to an equilibrium state. We use the full single-fluid equations of motion for a magnetized, nonresistive, but viscous fluid; and a Lagrangian approach is used to obtain exact solutions for the magnetic field. As a result, the topology of the magnetic field remains unchanged, which makes it possible to study the case of topological nonequilibrium. We find two cases for which such nonequilibrium appears, indicating that these configurations may develop singular current sheets.

Journal Article↗
PubMed1999

Historiography and historians of neuroscience: towards diversity in the ISHN.

This article introduces and critiques the historiographical tradition of the history of the neurosciences as it has been established in the International Society for the History of the Neurosciences (ISHN). The founding members of the ISHN were practitioner-historians, practitioners of the neurosciences with an interest in the great moments, ideas and controversies in the history of their field. The historiographical precedent set by these clinician-historians emphasized those aspects of history most interesting to them. Academic historians bring a different approach to the history of neurosciences, particularly an interest in studying the intellectual and cultural contexts of both the inherited and the forgotten ideas about the nervous system. Their approach to history has not been well presented in the ISHN, in part because the current historiographical tradition does not address their interests. This article highlights the methodological and epistemological differences between academic and practitioner-historians and discusses the difficulties that other historical societies have faced in trying to bring them together. The article then suggests ideas for symposia that might facilitate an interdisciplinary dialogue and a revised historiographical tradition that speaks to the needs of both academic and historians and practitioner historians.

Historiography↗
PubMed1995

On the possibility of coherently stimulated recombination and cosmological structure generation: recombination instability.

Possible instabilities during cosmological recombination may produce an epoch of nonlinear density growth and fractal-like structural patterns out to the horizon scale at that epoch (approximately 200 Mpc today). With this motivation, we examine the consequences of the change in effective radiative recombination reaction rate coefficients produced by intense stimulated emission. The proton-electron recombination is considered as a natural laser, leading to the formation of spatially nonuniform distributions of neutral matter earlier than the recombination epoch.

Journal Article↗
PubMed1995

On the possibility of coherently stimulated recombination and cosmological structure generation: cosmological consequences.

Given a specific physical mechanism for instabilities during cosmological recombination discussed in an earlier paper, we examine the nonlinear growth of density structures to form fractal-like structural patterns out to the horizon scale at that epoch (approximately 200 Mpc today). A model for such fractal patterns is presented. Such effects could explain observed large-scale structure patterns and the formation of objects at high z, while keeping microwave background anisotropies at the observed minimal levels. We also discuss possible microwave background implications of such a transition and note a potentially observable spectral signature at lambda approximately 0.18 mm as well as a weak line near the peak in the microwave background.

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PubMed1995

Base-rate estimates of criminal behavior by homeless mentally ill persons in New York City.

OBJECTIVES: The study aimed to estimate the prevalence of homelessness among mentally disordered offenders entering the criminal justice and forensic mental health systems, to compare base rates of arrest for violent and nonviolent criminal charges among homeless and domiciled persons with mental illness, and to examine patterns in the categories of victims chosen by these two groups. METHODS: The authors analyzed data from structured psychiatric interviews and criminal and psychiatric records of 77 homeless defendants and 107 domiciled defendants referred for psychiatric examination by the criminal and supreme courts in Manhattan over a six-month period. RESULTS: Mentally disordered defendants had 40 times the rate of homelessness found in the general population, and 21 times the rate in the population of mentally ill persons in the city. The overall rate of criminal offenses was 35 times higher in the homeless mentally ill population than in the domiciled mentally ill population. The rate of violent crimes was 40 times higher and the rate of nonviolent crimes 27 times higher in the homeless population. Homeless defendants were significantly more likely to have been charged with victimizing strangers. CONCLUSIONS: Homeless mentally ill persons appear to be grossly overrepresented among mentally disordered defendants entering the criminal justice and forensic mental health systems and to have a higher base rate of arrest for both violent and nonviolent crimes than domiciled mentally ill persons.

Adult↗
PubMed1995

Obsessional harassment and erotomania in a criminal court population.

The criminal behaviors of harassment and menacing are difficult to control, and of increasing concern to the general public and local law enforcement officials. In 1992, the New York State Legislature modified the Penal Law, responding to public fears and concerns that stalking behavior may become violent. Some persons charged with these types of offenses are suffering from psychiatric disorders. Among these disorders are those classified as Delusional Disorders. According to both DSM-III-R (1987-1993) and DSM-IV (1994), there are five specific types of Delusional Disorder: erotomanic, grandiose, jealous, persecutory and somatic. This type of disorder tends to be chronic. Forty eight cases of persons charged with harassment and menacing in the New York County Criminal and Supreme Court and referred for evaluation to the Forensic Psychiatry Clinic between January 1987 and January 1994 are reviewed. When cases of erotomania and other affectionate/amorous complaints were compared with persecutory/angry forms of harassing behavior, there was a great deal of similarity. When all harassers were compared to the Clinic population as a whole, major differences in ethnicity, age, educational level and sex were noted. Findings are presented regarding incidence, other demographic data, recidivism, violence and clinical diagnosis. The researchers conclude that erotomania does exist, however, there are other psychiatric disorders which can also be diagnosed in individuals accused of harassing and menacing behavior. From the point of view of the victim and the criminal justice system, the similarities in behavior patterns are more important than the different diagnoses.

Adult↗