3-d resistive MHD simulations of magnetic reconnection and the tearing mode instability in current sheets

Magnetic reconnection plays a critical role in many astrophysical processes where high energy emission is observed, e.g. particle acceleration, relativistic accretion powered outflows, pulsar winds and probably in dissipation of Poynting flux in GRBs. The magnetic field acts as a reservoir of energy and can dissipate its energy to thermal and kinetic energy via the tearing mode instability. We have performed 3d nonlinear MHD simulations of the tearing mode instability in a current sheet. Results from a temporal stability analysis in both the linear regime and weakly nonlinear (Rutherford) regime are compared to the numerical simulations. We observe magnetic island formation, island merging and oscillation once the instability has saturated. The growth in the linear regime is exponential in agreement with linear theory. In the second, Rutherford regime the island width grows linearly with time. We find that thermal energy produced in the current sheet strongly dominates the kinetic energy. Finally preliminary analysis indicates a P(k) 4.8 power law for the power spectral density which suggests that the tearing mode vortices play a role in setting up an energy cascade.Comment: 4 pages, 8 figures, accepted for publication in the International Journal of Modern Physics D, proceedings of HEPRO meeting, held in Dublin, in September 200

A multi-flow model for microquasars

We present a new picture for the central regions of Black Hole X-ray Binaries. In our view, these central regions have a multi-flow configuration which consists in (1) an outer standard accretion disc down to a transition radius r_J, (2) an inner magnetized accretion disc below r_J driving (3) a non relativistic self-collimated electron-proton jet surrounding, when adequate conditions for pair creation are met, (4) a ultra relativistic electron-positron beam. This accretion-ejection paradigm provides a simple explanation to the canonical spectral states, from radio to X/gamma-rays, by varying the transition radius r_J and disc accretion rate independently. Large values of r_J and low accretion rate correspond to Quiescent and Hard states. These states are characterized by the presence of a steady electron-proton MHD jet emitted by the disc below r_J. The hard X-ray component is expect to form at the jet basis. When r_J becomes smaller than the marginally stable orbit r_i, the whole disc resembles a standard accretion disc with no jet, characteristic of the Soft state. Intermediate states correspond to situations where r_J ~ r_i. At large accretion rate, an unsteady pair cascade process is triggered within the jet axis, giving birth to flares and ejection of relativistic pair blobs. This would correspond to the luminous intermediate state, with its associated superluminal motions.Comment: 12 pages, 3 figures. Proceedings of ``High Energies in the Highlands'', Fort-William, 27 June-1 July 200

The Male Army Nurse Corps Officer Experience in the Vietnam Conflict

Background: A considerable amount of research has been conducted on the wartime experiences of female nurses who served in the Vietnam conflict and as a result, much is known about their experiences and the impact that their service had on their personal and professional lives. The same, however, is not true for male nurses. Anecdotal evidence suggests that the experiences of male Army Nurse Corps (ANC) Officers may have been substantially different from that of their female colleagues, thus making the impact of the experience on them potentially different. Overall Objective: This study explores and interprets the lived experiences of a purposive sample (n=17) of male nurses who served in the Vietnam conflict. The specific aims are: Aim 1: Explore the study participants’ perceptions prior to entry into the Army Nurse Corps. Aim 2: Identify the accounts of their experiences during their deployment to Vietnam. Aim 3: Describe the impact that service in Vietnam had on their professional and personal lives after their return to the United States. Aim 4: Generate hypotheses for future studies utilizing male nurses who served in Vietnam as the study population with potential for comparison with nurses in subsequent conflicts. Methods: Interpretive phenomenological analysis was used to identify and assess the perceptions and attitudes of a purposive sample of 17 US Army Nurse Corps (ANC) officers who served one tour of duty in Vietnam from 1965 to 1971. Qualitative data were collected through semi-structured four-part interviews with study participants, average age 26.2 years at time of deployment, who were recruited through military Internet sites. Interviews were recorded, transcribed, coded, analyzed, and interpreted to gain insight into the experiences of male ANC officers prior to, during, and following their deployment to Vietnam. Results: There are clearly identifiable differences in the experiences of males nurses who served in Vietnam when compared to their female colleagues. These include differences in access to basic nursing education, the threat of the draft, and being assigned positions in Vietnam at least partly because they were male. However, participants deny a negative impact, and though a few experienced PTSD, most identified their war experience as a value to professional advancement. As demonstrated in the findings of this study, this group appear to be a well-adjusted successful cohort with little negative long-term impact that they associate with their time in Vietnam, though perhaps a selective sample. Various themes emerged across interviews, notably, resilience following repeated trauma, empathy for others, downplaying the significance of their individual contributions, and pride in their involvement in wartime nursing. Discussion: This study represents the first identified systematic study utilizing male nurses in the US military who served in the Vietnam Conflict as the study population. Given the impact the experience of providing nursing care in a combat area has been shown to have on individuals, expanding the knowledge to include this cohort increases our understanding of this phenomena. Findings of this study: 1) represent the lived experiences of a select sample of male ANC nurses who served in the Vietnam Conflict and the consequences of their service; 2) provide information useful in the selection, training, and aftercare of individuals who provide nursing care under combat conditions; 3) provide insight into the long term effects of providing conflict nursing care; and 4) generate hypotheses for further studies. There are clearly some identifiable differences in the experiences of male nurses who served in Vietnam when compared to their female colleagues. These include differences in access to basic nursing education, the threat of the draft, and being assigned positions in Vietnam at least partly because they were male. However, in their interpretation of their experiences, these factors appear to have had limited negative impact on this cohort of male ANC officers. Their self described success in navigating extreme emotional situations that were physically and professionally challenging and largely viewing them as an opportunity for growth illustrates the resilience discernible throughout the interviews. Study participants emerged, largely, as highly functioning individuals. This characteristic is illustrated, in part, by their significant career success. As demonstrated in the findings of this study, participants describe themselves as a well adjusted and successful cohort with some negative impact that they associate with their time in Vietnam. Future studies of this population would likely expand these findings by utilizing more inclusive sampling methodology. Given the complete lack of preparation study participants received when transitioning from Vietnam back to the United States, future studies regarding the long term efficacy of transitioning programs afforded returning nurses in current conflicts would be beneficial

Early Ambulation for Colorectal Enhanced Recovery Patients in a Surgical Specialties Unit

Early ambulation is a key concept in surgical recovery and overall improvement of medical conditions. The initiation of Enhanced Recovery programs (ERP) for surgical procedures have used evidence-based research to bundle best practices for a quicker and more effective recovery. The author evaluated the consistency of early ambulation on a surgical specialties unit using the ERP method. Through process improvement methods, data and practice were evaluated to show inconsistencies in documentation, data report abstraction, and understanding of complete collaborative bundle components

Intrinsic Variability and Field Statistics for the Vela Pulsar: 2. Systematics and Single-Component Fits

Individual pulses from pulsars have intensity-phase profiles that differ widely from pulse to pulse, from the average profile, and from phase to phase within a pulse. Widely accepted explanations do not exist for this variability or for the mechanism producing the radiation. The variability corresponds to the field statistics, particularly the distribution of wave field amplitudes, which are predicted by theories for wave growth in inhomogeneous media. This paper shows that the field statistics of the Vela pulsar (PSR B0833-45) are well-defined and vary as a function of pulse phase, evolving from Gaussian intensity statistics off-pulse to approximately power-law and then lognormal distributions near the pulse peak to approximately power-law and eventually Gaussian statistics off-pulse again. Detailed single-component fits confirm that the variability corresponds to lognormal statistics near the peak of the pulse profile and Gaussian intensity statistics off-pulse. The lognormal field statistics observed are consistent with the prediction of stochastic growth theory (SGT) for a purely linear system close to marginal stability. The simplest interpretations are that the pulsar's variability is a direct manifestation of an SGT state and the emission mechanism is linear (either direct or indirect), with no evidence for nonlinear mechanisms like modulational instability and wave collapse which produce power-law field statistics. Stringent constraints are placed on nonlinear mechanisms: they must produce lognormal statistics when suitably ensemble-averaged. Field statistics are thus a powerful, potentially widely applicable tool for understanding variability and constraining mechanisms and source characteristics of coherent astrophysical and space emissions.Comment: 11 pages, 12 figures. Accepted by Monthly Notices of the Royal Astronmical Society in April 200

Search For Oxygen in Cool DQ White Dwarf Atmospheres

We report new infrared spectroscopic observations of cool DQ white dwarfs by using Coolspec on the 2.7m Harlan-Smith Telescope. DQs have helium-rich atmospheres with traces of molecular carbon thought to be the result of convective dredge-up from their C/O interiors. Recent model calculations predict that oxygen should also be present in DQ atmospheres in detectable amounts. Our synthetic spectra calculations for He-rich white dwarfs with traces of C and O indicate that CO should be easily detected in the cool DQ atmospheres if present in the expected amounts. Determination of the oxygen abundance in the atmosphere will reveal the C/O ratio at the core/envelope boundary, constraining the important and uncertain ^{12}C(alpha,gamma)^{16}O reaction rate.Comment: 2 pages, 2 figures, to appear in proceedings of the 13th European Workshop on White Dwarf