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Biomedical subjects

R Epstein

Publications and source records attributed to R Epstein.

At least 19 recordsLinked to original sources
PubMed2006

Test of thermal transport models through dynamic overpressure stabilization of ablation-front perturbation growth in laser-driven CH foils.

Heat-flow-induced dynamic overpressure at the perturbed ablation front of an inertial confinement fusion target can stabilize the ablative Richtmyer-Meshkov-like instability and mitigate the subsequent ablative Rayleigh-Taylor (RT) instability. A series of experiments was performed on the OMEGA laser to quantify the dynamic overpressure stabilization during the shock transit. Analysis of the experimental data using hydrocode simulations shows that the observed oscillatory evolution of the ablation-front perturbations depends on Dc, the size of the thermal conduction zone, and the fluid velocity in the blowoff region Vb1 that are sensitive to the thermal transport model used. We show that the simulations match the experiment well when the time dependence of the heat-flux inhibition is taken into account using a recently developed nonlocal heat-transport model [V. N. Goncharov et al., Phys. Plasmas 13, 012702 (2006)].

Journal Article↗
PubMed2004

Dependence of shell mix on feedthrough in direct drive inertial confinement fusion.

The mixing of cold, high-density shell plasma with the low-density, hot spot plasma by the Rayleigh-Taylor instability in inertial confinement fusion is experimentally shown to correlate with the calculated perturbation feedthrough from the ablation surface to the inner shell surface. A fourfold decrease in the density of shell material in the mix region of direct drive implosions of gas filled spherical plastic shells having predicted convergence ratios approximately 15 was observed when laser imprint levels were reduced and the initial shell was thicker, corresponding to a reduction in the feedthrough rms level by a factor of 6. Shell mix is also shown to limit the spherical compression of the implosion.

Journal Article↗
PubMed2003

Effects of energy availability on immediate and delayed emotional reactions to work events.

This study focuses on daily work events as proximal stimuli for discrete emotional reactions and suggests that availability of energy resources required for coping with goal-disruptive events, or for capitalizing on new opportunities offered by goal-enhancing events, influences intensity of emotional reactions. Using experience-sampling methodology with a sample of hospital residents, it is shown that negative emotion and fatigue following disruptive events are intensified when only limited energy resources are available due to current workload. However, positive emotions, promoted by goal-enhancing events, are mitigated due to inability to capitalize on new opportunities or challenges. Aftereffects of work events reveal that the energizing effect of goal-enhancing events mitigates end-of-day fatigue and negative emotion on high-workload days, although the effect of disruptive events is diminished by the end of such days, apparently because of lesser conspicuity against a background of high workload. Theoretical and practical implications are discussed.

Adult↗
PubMed2002

Shell mix in the compressed core of spherical implosions.

The Rayleigh-Taylor instability in its highly nonlinear, turbulent stage causes atomic-scale mixing of the shell material with the fuel in the compressed core of inertial-confinement fusion targets. The density of shell material mixed into the outer core of direct-drive plastic-shell spherical-target implosions on the 60-beam, OMEGA laser system is estimated to be 3.4(+/-1.2) g/cm(3) from time-resolved x-ray spectroscopy, charged-particle spectroscopy, and core x-ray images. The estimated fuel density, 3.6(+/-1) g/cm(3), accounts for only approximately 50% of the neutron-burn-averaged electron density, n(e)=2.2(+/-0.4)x10(24) cm(-3).

Journal Article↗
PubMed2001

Long-term sleep disturbances in adolescents after minor head injury.

It has been demonstrated that patients in the acute phase after minor head injury (MHI) complain of sleep disturbances. The purpose of the present study was to characterize the long-term effects of MHI on sleep in adolescents. Nineteen adolescents who had suffered MHI 3 years before the study and had complained of sleep disturbances completed a sleep questionnaire and were investigated in the sleep laboratory by whole-night polysomnographic recordings and were actigraphically monitored for 5 days at home. Questionnaire results revealed severe complaints regarding sleep behavior. Polysomnographic recordings revealed that in comparison with controls, MHI was associated with lower sleep efficiency (79.8 +/- [9.8]% vs 87.7 +/- [6.8]%; P < 0.005), with more wake time (10.6 +/- [9.0]% vs 3.4 +/- [4.4]%; P < 0.005), and with more awakenings lasting more than 3 minutes (2.1 +/- [1.5] vs 0.6 +/- [0.8]; P < 0.005). These findings were confirmed by actigraphic monitoring that revealed lower sleep efficiency (90 +/- [5]% vs 94 +/- [3]%; P < 0.05), more minutes of wake time (49 +/- [21] min vs 28 +/- [15] min; P < 0.05), and a trend toward more awakenings longer than 5 minutes (1.8 +/- [0.8] vs 1.2 +/- [0.8]; P = 0.063). Our data demonstrated that 3 years after MHI without any discernible clinical sequel, adolescents still complain of sleep disturbances that could be confirmed by both polysomnographic and actigraphic monitoring.

Adolescent↗
PubMed2001

Sleep-wake monitoring in women suffering from anorexia nervosa.

There is evidence that some Anorexia Nervosa (AN) patients have sleep abnormalities. No studies of their sleep-wake cycles in a natural environment have yet been reported. The purpose of this study was to evaluate an objective and subjective sleep-wake cycle of AN patients compared to a healthy age-equated control group (CON). Twenty-one AN female and sixteen CON female subjects were recruited. Sleep-wake patterns were monitored using ambulatory monitoring mini-actigraphs for one week. Each subject completed self-report questionnaires. The self-report questionnaires revealed significantly more sleep disturbances in AN than CON, whereas the ambulatory sleep data revealed no significant differences between the two groups in sleep-wake cycle.

Journal Article↗
PubMed2001

Daily and yearly burnout symptoms in Israeli shift work residents.

Burnout is a syndrome of physical and emotional exhaustion that develops among individuals who are open to public demands. In view of their heavy work load and sleep deprivation, we decided to evaluate the impact of long working hours on burnout and psychological status among a sample of residents during the first 2 years of their residency. Seventy-eight residents participated in the study, all residents completed self-administered questionnaires, and their sleep-wake cycle was monitored by a wrist-worn actigraph for a period of 5-7 days. The questionnaires included a short form suitable for Experience Sampling Method (ESM), and a longer background Questionnaire. The results revealed that sleep duration, Work Load and the interaction between them, explain the Negative Mood the day after the night shift. However, positive mood, and fatigue were not affected by sleep duration or workload. In general, after one year of residency, residents become more stressed, less involved in the job, and had a high level of burnout and psychosomatic symptoms. However, after the second year, the burnout symptoms were almost the same as at the beginning except for the level of stress that remained high. Sleep duration was unrelated to the burnout symptoms.

Adult↗
PubMed2001

Can we consider medical residents as shift workers?

Although medical residents are characterized by long working hours, night shifts and high levels of work load, it is unclear if their work schedule can be classified as shift work, or if it has a similar impact on residents' well-being. The present paper compared the profile of complaints about sleep or daytime functioning of medical residents to that of rotating shift workers and day workers, of similar ages. Sixty-one residents (aged: 32.2 +/- 2.2 years), after 2 years of residency, participated in the study. The two control groups with a similar age range (26-40 years) were chosen, and included 94 rotating shift workers and 146 day workers. All subjects completed self-administered questionnaires on their sleep habits, and their sleep-wake cycle was monitored by a wrist-worn actigraph. Ten percent of the residents complained about difficulties falling asleep, 34% complained about morning tiredness, 14% complained about mid-sleep awakening, and 20% about prolonged fatigue. The residents slept significantly less than the day workers, and their sleep efficiency was significantly higher. When examining their subjective complaints profile, residents complained more than day workers and their answers were more similar to those of rotating shift workers, therefore they can be considered to be characterized as shift workers.

Activities of Daily Living↗
PubMed2000

Sleep-wake cycles in women with binge eating disorder.

OBJECTIVE: Binge eating disorder (BED) is a new diagnostic category in the 4th ed. of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV). The majority of studies on sleep characteristics in overweight women have used nonbinging obese women. The aim of this study was to evaluate sleep characteristics in obese BED patients in comparison to non-BED obese (OB) and nonbinging normal weight (NW) women. METHOD: Eighteen females with BED, 13 OB, and 16 NW women were recruited. Sleep-wake patterns were monitored for 1 week using mini-actigraphs and self-report questionnaires. RESULTS: Their ambulatory sleep data revealed that BED and OB subjects had significantly lower sleep efficiency, had more wake during sleep, and had less zero activity than the NW group. The self-report questionnaires presented significantly more sleep disturbances in the BED and OB groups than in the NW group. DISCUSSION: The objective results support the subjective sleep disturbances reported by the two obese groups, the BED and the OB. A possible explanation for these findings could be weight-related physical discomfort or the existence of breathing disorders in sleep. Further research, for example, overnight polysomnography recordings and follow-up treatment, is required.

Adult↗
PubMed2000

The neural-cognitive basis of the Jamesian stream of thought.

William James described the stream of thought as having two components: (1) a nucleus of highly conscious, often perceptual material; and (2) a fringe of dimly felt contextual information that controls the entry of information into the nucleus and guides the progression of internally directed thought. Here I examine the neural and cognitive correlates of this phenomenology. A survey of the cognitive neuroscience literature suggests that the nucleus corresponds to a dynamic global buffer formed by interactions between different regions of the brain, while the fringe corresponds to a set of mechanisms in the frontal and medial temporal lobes that control the contents of this global buffer. A consequence of this account is that there might be conscious imagistic representations that are not part of the nucleus. I argue that phenomenology can be linked to psychology and neuroscience and a meaningful way that illuminates both.

Cognition↗
PubMed2000

Substantive thoughts about substantive thoughts: a reply to Galin.

In his commentary, David Galin raises several important issues that deserve to be addressed. In this response, I do three things. First, I briefly discuss the relation between the present work and the metaphoric theories of thought developed by cognitive lin- guists such as Lakoff and Johnson (1998). Second, I address some of the confusions that seem to have arisen about my use of the terms "substantive thought" and "nucleus." Third, I briefly discuss some of the directions that Galin suggests for further research.

Cognition↗
PubMed2000

Actigraphic monitoring (actigraphy) of circadian locomotor activity in schizophrenic patients with acute neuroleptic-induced akathisia.

BACKGROUND: Actigraphy is a quantitative method for measurement of motor activity. In the present study we used actigraphy to examine diurnal variations in locomotor activity of schizophrenic patients with neuroleptic-induced akathisia (NIA). METHOD: Thirty-two schizophrenic patients, 16 with NIA and 16 without (DSM-IV criteria) underwent 24-h actigraphic monitoring. Clinical assessments of NIA were conducted with Barnes Akathisia Scale (BAS) at 08:00, 12:00, 16:00 and 20:00. Sleep parameters (duration, latency, continuity and efficacy) were assessed by actigraphy. Sleep quality was evaluated by a self-rated sleep questionnaire. RESULTS: NIA patients demonstrated persistent higher daytime motor activity from 11:30 to 14:15 and from 18:00 to 21:00 than controls. There were no differences between the groups in nighttime motor activity, confirming clinical observations that NIA tends to disappear during sleep. Subject's sleep assessments were similar in the two groups. CONCLUSIONS: Actigraphy seems to be a reliable, non-invasive, method of measuring motor activity in patients with NIA. Its sensitivity and specificity as an objective quantitative diagnostic instrument in patients with NIA merits further investigation.

Adult↗
PubMed2000

Formal perceptual evaluation of voice quality in the United Kingdom.

This document is a position statement on the formal perceptual evaluation of voice quality in the United Kingdom (UK). It addresses a number of clinical issues pertaining to the complexity of voice quality analysis. There is also a brief description of the three formal perceptual protocols most commonly used in the UK: The Vocal Profile Analysis (VPA), GRBAS and The Buffalo III Voice Profile. Potential clinical problems with perceptual voice quality evaluation are highlighted. Problems associated with the lack of defined terminology, limitless variety of voice quality, general lack of reliability data and difficulties in determining specificity and sensitivity are discussed. A practical guide for selecting an evaluation scheme is described. The conclusion is that the GRBAS scheme should be recommended as the absolute minimum standard for practising UK voice clinicians. However, there is a clear need to develop a more satisfactory perceptual rating scheme that is clinically realistic, theoretically sound, internationally acceptable and has proven reliability.

Female↗
PubMed1999

Naturalistic sleep monitoring in women suffering from bulimia nervosa.

OBJECTIVE: Eating disorders may be associated with alterations in sleep. There is evidence that some bulimia nervosa (BN) patients have sleep abnormalities. No studies of their sleep-wake cycles in a natural environment have as yet been reported. The purpose of this study was to evaluate an objective and subjective sleep-wake cycle of BN compared to a healthy age-equated control group (CON). METHOD: Twenty-nine BN female and eighteen CON subjects were recruited. Sleep-wake patterns were monitored using ambulatory monitoring, mini-actigraphs (Min-Act), for 1 week. Each subject completed self-report questionnaires. RESULTS: The self-reporting questionnaires revealed that BN complained of significantly more sleep disturbances than CON. The ambulatory sleep data revealed significant differences between BN and CON in sleep onset and offset time. DISCUSSION: BN had sleep onset and sleep offset of 1 hr later, which may be connected to binge-purge patterns during the day. It is suggested that future research should focus on BN after remission.

Adolescent↗
PubMed1999

Left-handedness and achievements in foreign language studies.

Studies of brain lateralization lend support to the hypothesis that language-motor functions in left-handers are differently organized from those in right-handers. However, the implications of these differences regarding cognitive functioning are as yet subject to controversy. This concerns all hypotheses raised and empirical data collected over the years. Although it was suggested that left-handers are at higher risk of having language and reading deficits, empirical data from clinical and nonclinical populations are inconclusive at the present time. No effort, however, has been invested in examining possible differences in academic studies of foreign languages according to handedness. Here we report data indicating inferior achievements of left-handed native Hebrew speakers in studies of English as a foreign language. Left-handed pupils significantly more than right-handers were placed in lower level English classes and had more difficulties in applying orthographic-phonological mapping rules in reading English words and pseudowords. However, left-handers' difficulties in this task were not correlated with their performance in a word recognition task. It is thus suggested that the "common symptom" of poor word reading in left-handers indicates different processing failures in different left-handers, some of which impede the buildup of an internal representational system of mapping orthography to phonology and some of which concern mainly the precision of word production.

Achievement↗
PubMed1999

The parahippocampal place area: recognition, navigation, or encoding?

The parahippocampal place area (PPA) has been demonstrated to respond more strongly in fMRI to scenes depicting places than to other kinds of visual stimuli. Here, we test several hypotheses about the function of the PPA. We find that PPA activity (1) is not affected by the subjects' familiarity with the place depicted, (2) does not increase when subjects experience a sense of motion through the scene, and (3) is greater when viewing novel versus repeated scenes but not novel versus repeated faces. Thus, we find no evidence that the PPA is involved in matching perceptual information to stored representations in memory, in planning routes, or in monitoring locomotion through the local or distal environment but some evidence that it is involved in encoding new perceptual information about the appearance and layout of scenes.

Adolescent↗