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Biomedical subjects

M Rappaport

Publications and source records attributed to M Rappaport.

At least 19 recordsLinked to original sources
PubMed2004

Vortex nanoliquid in high-temperature superconductors.

Using a differential magneto-optical technique to visualize the flow of transport currents, we reveal a new delocalization line within the reversible vortex liquid region in the presence of a low density of columnar defects. This line separates a homogeneous vortex liquid, in which all the vortices are delocalized, from a heterogeneous "nanoliquid" phase, in which interconnected nanodroplets of vortex liquid are caged in the pores of a solid skeleton formed by vortices pinned on columnar defects. The nanoliquid phase displays high correlation along the columnar defects but no transverse critical current.

Journal Article↗
PubMed2003

Melting of "porous" vortex matter.

Bitter decoration and magneto-optical studies reveal that in heavy-ion irradiated superconductors, a "porous" vortex matter is formed when vortices outnumber columnar defects. In this state ordered vortex crystallites are embedded in the "pores" of a rigid matrix of vortices pinned on columnar defects. The crystallites melt through a first-order transition while the matrix remains solid. The melting temperature increases with density of columnar defects and eventually turns into a continuous transition. At high temperatures a sharp kink in the melting line is found, signaling an abrupt change from crystallite melting to melting of the rigid matrix.

Journal Article↗
PubMed2002

Negative mass instability for interacting particles in a 1D box: theory and application.

We demonstrate that the synchronization effect observed [Pedersen et al., Phys. Rev. Lett. 87, 055001 (2001)]], when a bunch of ions oscillates between two mirrors in an electrostatic ion beam trap, can be explained as a negative mass instability. We derive simple necessary conditions for the existence of a regime in which this dispersionless behavior occurs and demonstrate that in this regime, the ion trap can be used as a high resolution mass spectrometer.

Journal Article↗
PubMed2002

Long-range spatial correlations in the exciton energy distribution in GaAs/AlGaAs quantum wells.

Variations in the width of a quantum well (QW) are known to be a source of broadening of the exciton line. Using low temperature near-field optical microscopy, we have exploited the dependence of exciton energy on well width to show that in GaAs QWs, these seemingly random well-width fluctuations actually exhibit well-defined order-strong long-range correlations appearing laterally, in the plane of the QW, as well as vertically, between QWs grown one on top of the other. We show that these fluctuations are correlated with the commonly found mound structure on the surface. This is an intrinsic property of molecular beam epitaxial growth.

Journal Article↗
PubMed2001

'Inverse' melting of a vortex lattice.

Inverse melting is the process in which a crystal reversibly transforms into a liquid or amorphous phase when its temperature is decreased. Such a process is considered to be very rare, and the search for it is often hampered by the formation of non-equilibrium states or intermediate phases. Here we report the discovery of first-order inverse melting of the lattice formed by magnetic flux lines in a high-temperature superconductor. At low temperatures, disorder in the material pins the vortices, preventing the observation of their equilibrium properties and therefore the determination of whether a phase transition occurs. But by using a technique to 'dither' the vortices, we were able to equilibrate the lattice, which enabled us to obtain direct thermodynamic evidence of inverse melting of the ordered lattice into a disordered vortex phase as the temperature is decreased. The ordered lattice has larger entropy than the low-temperature disordered phase. The mechanism of the first-order phase transition changes gradually from thermally induced melting at high temperatures to a disorder-induced transition at low temperatures.

Journal Article↗
PubMed2000

Imaging the vortex-lattice melting process in the presence of disorder

General arguments suggest that first-order phase transitions become less sharp in the presence of weak disorder, while extensive disorder can transform them into second-order transitions; but the atomic level details of this process are not clear. The vortex lattice in superconductors provides a unique system in which to study the first-order transition on an inter-particle scale, as well as over a wide range of particle densities. Here we use a differential magneto-optical technique to obtain direct experimental visualization of the melting process in a disordered superconductor. The images reveal complex behaviour in nucleation, pattern formation, and solid-liquid interface coarsening and pinning. Although the local melting is found to be first-order, a global rounding of the transition is observed; this results from a disorder-induced broad distribution of local melting temperatures, at scales down to the mesoscopic level. We also resolve local hysteretic supercooling of microscopic liquid domains, a non-equilibrium process that occurs only at selected sites where the disorder-modified melting temperature has a local maximum. By revealing the nucleation process, we are able to experimentally evaluate the solid-liquid surface tension, which we find to be extremely small.

Journal Article↗
PubMed1997

Implementation of the Patient Self-Determination Act (PSDA) in nursing homes in New York City.

OBJECTIVE: To examine implementation of the Patient Self Determination Act (PSDA), verbal directives, procedures for determination of resident' decision-making capacity, and role of ethics committees in nursing homes in New York City. DESIGN: Telephone survey. PARTICIPANTS: Social workers in 109 (69%) nursing homes in New York City. MEASUREMENT: An 80-item instrument addressing: (1) social worker knowledge of the PSDA; (2) informing residents about advance directives (living wills and durable power of attorney for health care [health care proxies]); (3) determination of decision-making capacity to be informed about advance directives; (4) estimates of advance directives executed; (5) perceptions of PSDA effect; (6) ethics committees; (7) follow-up and documentation; and (8) staff and community education. MAIN RESULTS: Virtually all social workers in nursing homes stated that they made what they perceived to be a "serious effort" to inform residents about advance directives and to have residents execute directives (preferentially a health care proxy). More residents were thought to have executed a directive pursuant to the PSDA law than before the Act went into effect. Social workers in most homes informed residents about directives through face-to-face discussions. Most homes, however, did not inform residents who were thought to lack decision-making capacity about their right to execute a directive. Only 37% of homes had written procedures to determine a resident's decision-making capacity to be informed about directives; most homes relied on physician and social work assessments. Voluntary homes differed significantly from proprietary homes in that they were larger, more likely to have an ethics committee, and more aggressive in their implementation of the PSDA. Forty-five percent of homes with an ethics committee had written procedures for determination of resident decision-making capacity compared with 26% of homes without a committee. Overall, 24% of residents were thought to have executed an advance directive. The number of directives per bed did not vary significantly by facility size, ownership, religious affiliation, or whether they did or did not have an ethics committee. CONCLUSIONS: The fact that social workers in nursing homes speak with most residents about advance directives has the potential to improve resident understanding around end of life decisions. The practice of not informing residents about advance directives when they are perceived to lack decision-making capacity is problematic given that most homes have no clear procedures for determining residents' cognitive capacity to execute a directive. There is a need to replicate the benefits achieved by homes with ethics committees in implementing the PSDA in other homes.

Advance Directives↗
PubMed1994

Effects of stimulus intensity and duration on posterior tibial nerve somatosensory-evoked potential patterns obtained under anesthesia.

STUDY DESIGN: This study analyzed systematic changes in stimulus intensity and duration on the latencies and amplitudes of somatosensory-evoked potential peaks obtained upon posterior tibial nerve stimulation of orthopedic patients under anesthesia. OBJECTIVES: To examine the effects of systematic stimulus changes on somatosensory-evoked potential patterns and to compare the sensitivity of different peaks. SUMMARY OF BACKGROUND DATA: Previous studies primarily examined the effects of either stimulus intensity or stimulus duration but not their interactions. METHODS: Nine orthopedic patients were tested using three stimulus intensities and three stimulus durations. Five peak latencies and four amplitudes were measured. Data consisted of frequency of peak occurrences under each condition and analyses of variances of peak latencies and amplitudes. RESULTS: Three latencies yielded stable findings (P40, N50, P60). Peak latencies under anesthesia were not affected by stimulus intensity or duration. Amplitudes, however, were affected differentially. P40-N50 increased with increases in stimulus intensity or stimulus duration, but no significant interaction effects were found. N50-P60 showed no significant changes associated with stimulus intensity or duration. CONCLUSION: Under combined isoflurane/nitrous oxide anesthesia, somatosensory-evoked potential patterns obtained upon stimulation of the posterior tibial nerves showed no significant changes in major peak latencies with changes in stimulus intensity or duration. However, changes in amplitude were found. Stimulus intensity-duration interaction effects were observed, described, and interpreted.

Adult↗
PubMed1992

An epidemiological study of obsessive-compulsive disorder and related disorders in Israeli adolescents.

Five hundred and sixty-two, 16- to 17-year-old consecutive inductees into the Israeli Army, constituting a random sample of their cohort, were screened for obsessive-compulsive disorder (OCD), Tourette's syndrome, transient tics (TT), chronic multiple tics (CMT), and attention-deficit hyperactive disorder (ADHD). Two child psychiatrists interviewed the subjects, using screening items from structured interviews that implement DSM-III-R diagnostic criteria. For OCD, a point prevalence of 3.6% was found, 3.9% for ADHD, 1.8% for CMT, and 1.6% for TT. For ADHD, TT, and CMT, but not for OCD, there was a significantly higher prevalence for males than for females. Among the OCD individuals, there was an elevation of TT, CMT, and Tourette's syndrome relative to the population rates.

Adolescent↗
PubMed1992

Effects of anesthesia and stimulus intensity on posterior tibial nerve somatosensory evoked potentials.

Under anesthesia peak latencies occurring up to 75 milliseconds after stimulus onset upon somatosensory evoked potential testing of the somatosensory evoked potential testing of the posterior tibial nerve were not affected by stimulus intensity (between 5 and 19 ma) or by length of time under isoflurane and nitrous oxide up to over 2 hours. When pre- and postoperative tests on patients who were not under anesthesia were compared with results under anesthesia, no significant latency differences were found in relation to stimulus intensity for peaks N30, P40 and N50. For peaks P60 and N75, however, significantly increased latencies were seen during anesthesia, more pronounced and consistent for N75. Amplitudes, however, were affected by both stimulus intensity and anesthesia duration. A curvilinear relationship was found during early anesthesia. Maximum amplitudes were found at 7 or 11 ma stimulus intensity levels, depending upon which peak was analyzed, with lesser amplitudes occurring at both lower and higher stimulus intensity levels. Stimulus intensity and anesthesia interacted such that maximum amplitude occurred, in general, at 11 ma after short duration anesthesia (6') and at 7 ma after long duration anesthesia (125'). Under long duration anesthesia amplitudes were significantly diminished, mostly at the 11 ma intensity level. At 15 and 19 ma intensity levels peak amplitudes remained relatively constant regardless of anesthesia duration and therefore are the intensities to use to monitor changes during prolonged surgeries. When preoperative during prolonged surgeries. When preoperative and postoperative tests were compared to tests under anesthesia, there was a decrease in amplitude under anesthesia, greater for long than short duration anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Effects of stimulus intensity on posterior tibial nerve somatosensory evoked potentials.

Relationships between stimulus intensity and peak latencies and amplitudes in posterior tibial nerve somatosensory evoked potential patterns were evaluated in ten healthy subjects. Eight intermediate latency peaks between 30 and 125 milliseconds (ms) after stimulus onset and seven amplitudes were analyzed. In general, there was a decrease in latency with each increase in stimulus intensity over a five step intensity range between 5 and 19 milliamps (mA) for most peaks. Similarly, increases in amplitudes generally occurred with increases in stimulus intensity for most peaks. Later peaks N105 and P115 as well as amplitudes P90-N105 and N105-P115 were least sensitive to stimulus intensity changes. The greatest changes in peak latency and amplitude occurred as stimulus intensity was increased from 7 to 11 mA. Beyond 11 mA relatively little change was observed in either peak latencies or amplitudes. Under anesthesia, by contrast, there was no stimulus intensity-peak latency interaction and beyond 11 mA there were decreases in amplitudes. Possible reasons for these findings are discussed.

Adult↗
PubMed1992

Evaluation of coma and vegetative states.

The Coma/Near-Coma (CNC) scale was designed to measure small clinical changes in patients with severe traumatic and nontraumatic brain injuries who were functioning at very low levels characteristic of near-vegetative and vegetative states. In 20 patients followed for 16 weeks the scale identified 25% who ultimately showed modest improvement. Interrater reliability was high (r = .95); validity was supported by significant correlations between CNC- and brain-multimodality evoked potential abnormality scores as well as between scores on the CNC and the Disability Rating Scale. The CNC scale was easily learned and it could be completed quickly and cost effectively. Staff found it useful in recognizing among relatively homogeneous low-level patients those most likely to respond to further rehabilitation care. The CNC appears to be useful for justifying ongoing intensive rehabilitation and for preventing premature transfer to lower levels of care.

Adolescent↗
PubMed1991

Passive P300 response in traumatic brain injury patients.

Severe traumatic brain injury (TBI) patients in a vegetative state were exposed to passive P300 (PP300) evoked potential tests under two conditions: two auditory tones (unimodality condition), and a flash and auditory tone (bimodality condition). A third non-P300 condition using a single repetitive auditory tone was also presented. Patients produced PP300 responses under all three conditions, even though the severity of their clinical condition did not allow them to respond to even simple commands. No peak latency differences were found. PP300 amplitude was significantly larger under the bimodality stimulus condition than either the unimodality or non-P300 condition. The PP300 amplitude under the unimodality condition, in turn, was larger than the P300-like response in the non-P300 condition. This replicates earlier findings with normal subjects. PP300 responses appear to be a tool that might find utility in evaluating TBI patients. Results raise questions about the neuropsychological/neurophysiological nature of the PP300 response.

Adolescent↗
PubMed1991

Short and long latency auditory evoked potentials in traumatic brain injury patients.

Short latency auditory nerve and brainstem evoked responses (BAERs) and long latency cortical auditory evoked responses (CAERs) in 75 long-term traumatic brain injury (TBI) cases were compared. CAERs were found to be significantly correlated with clinical disability as measured by the Disability Rating Scale, while BAERs were not. Also, BAER patterns were consistently and significantly less abnormal and less sensitive to overall dysfunction than CAER patterns. Findings support previous observations that BAERs have relatively little utility for evaluating in surviving TBI patients the degree of overall brain impairment. In general, long latency AEP patterns are better able to reflect the extent and severity of brain dysfunction and overall clinical condition than are short latency AEP patterns in long-term severe TBI patients, and these patterns should be obtained routinely in the evaluation of such patients.

Adolescent↗
PubMed1991

Dermatomal somatosensory evoked potentials in brachial plexus injuries.

The dermatomally stimulated somatosensory evoked potential is an essentially painless, noninvasive procedure that can add useful information to the diagnosis of the site and extent of brachial plexus injuries. In this study, 13 patients with unilateral brachial plexus injuries who had previously undergone conventional electromyographic testing underwent somatosensory evoked potential recording with median, ulnar, radial, musculocutaneous nerve and C5, C6, C7, C8 and T1 dermatomal stimulation. There was no significant difference in the peak latencies, interpeak latencies, or amplitudes of the major peaks between the normal values and the values from the affected levels. However, analysis for absence or presence of major peaks from side-to-side was useful in supporting the data from electromyographic and radiologic studies, as well as in providing more specific information as to the level of injury and extent of injury in two of the cases. The accurate diagnosis can provide the information needed to determine patient treatment as well as plan the rehabilitation program of the patient. The dermatomal somatosensory evoked potential can be a useful supplement to the assessment of the patient with a brachial plexus injury.

Adult↗
PubMed1990

P300 response under active and passive attentional states and uni- and bimodality stimulus presentation conditions.

P300 evoked potential patterns were evaluated for two active and two passive attentional states in which stimuli were presented in either one or two sensory modalities. Latency to an infrequent auditory tone was shortest when counting the frequent stimulus, longer when counting the infrequent stimulus, longer still under a passive condition, and longest in a non-P300 condition. P300 amplitudes identifiable in the passive attentional state were enhanced when stimuli were from two, rather than from one, sensory modality. Implications for understanding the mechanism of attention are discussed. Preliminary findings in traumatic brain injury patients suggest that passive P300 responses may be useful in assessing the extent and severity of brain dysfunction.

Adolescent↗
PubMed1990

Effects of stimulus intensity on direct recordings of eighth nerve auditory evoked responses.

Effects of auditory stimulus intensity on auditory nerve and brainstem evoked potential patterns recorded simultaneously from the scalp and directly from the eighth nerve were compared for an anesthetized patient undergoing surgery for macrovascular decompression. Replicable robust potentials were readily obtained from a recording electrode on the eighth nerve less than half a second after as few as 15 stimulations. Less robust and less readable evoked potential patterns were obtained from scalp recordings after 30 seconds and about 900 stimulations. It was observed in the direct auditory evoked response (DAER) that there is a systematic decrease in peak latencies with each 10 dB increase in stimulus intensity between 60 and 90 dB nHL. Also, with each 10 dB increase in stimulus intensity there is an increase in amplitude of the DAER action potential between 70 and 90 dB nHL but not between 60 and 70 dB.

Acoustic Stimulation↗