5,799 research outputs found
Antimatter propulsion, status and prospects
The use of advanced propulsion techniques must be considered if the currently envisioned launch date of the manned Mars mission were delayed until 2020 or later. Within the next thirty years, technological advances may allow such methods as beaming power to the ship, inertial-confinement fusion, or mass-conversion of antiprotons to become feasible. A propulsion system with an ISP of around 5000 s would allow the currently envisioned mission module to fly to Mars in 3 months and would require about one million pounds to be assembled in Earth orbit. Of the possible methods to achieve this, the antiproton mass-conversion reaction offers the highest potential, the greatest problems, and the most fascination. Increasing the production rates of antiprotons is a high priority task at facilities around the world. The application of antiprotons to propulsion requires the coupling of the energy released in the mass-conversion reaction to thrust-producing mechanisms. Recent proposals entail using the antiprotons to produce inertial confinement fusion or to produce negative muons which can catalyze fusion. By increasing the energy released per antiproton, the effective cost, (dollars/joule) can be reduced. These proposals and other areas of research can be investigated now. These short term results will be important in assessing the long range feasibility of an antiproton powered engine
The Quiescent Optical and Infrared Counterpart to EXO 0748-676 = UY Vol
We present optical and infrared photometry of the low-mass X-ray binary EXO
0748-676 in quiescence for the first time in 24 years since it became X-ray
active in 1985. We find the counterpart at average magnitudes of R=22.4 and
J=21.3. We monitored the source approximately nightly through 2008 November to
2009 January. During this time there was considerable night-to-night optical
variability but no long term trends were apparent. The night-to-night
variability reveals a periodicity of P=0.159331+/-0.000012d, consistent with
the X-ray orbital period to within 0.01%. This indicates that the quiescent
optical modulation is indeed orbital in nature rather than a superhump.
Interestingly, the modulation remains single-peaked with a deep minimum
coincident with the times of X-ray eclipse, and there is no indication of a
double-peaked ellipsoidal modulation. This indicates that even in `quiescence'
emission from the accretion disk and/or X-ray heated inner face of the
companion star dominate the optical emission, and implies that obtaining an
accurate dynamical mass estimate in quiescence will be challenging.Comment: Accepted for publication by the Astrophysical Journal Letter
Requirement for the NF-kappa B family member Re1A in the development of secondary lymphoid organs
The transcription factor nuclear factor (NF)-kappaB has been suggested to be a key mediator of the development of lymph nodes and Peyer's patches. However, targeted deletion of NF-kappaB/ Rel family members has not yet corroborated such a function. Here we report that when mice lacking the RelA subunit of NF-kappaB are brought to term by breeding onto a tumor necrosis factor receptor (TNFR)1-deficient background, the trice that are born lack lymph nodes, foyer's patches, and an organized splenic microarchitecture, and have a profound defect in T cell-dependent antigen responses. Analyses of TNFR1/1RelA-deficient embryonic tissues and of radiation chimeras suggest that the dependence on RelA is manifest not in hematopoietic cells but rather in radioresistant stromal cells needed for the development of secondary lymphoid organs
Adjustment to a low-control situation: Reexamining the role of coping responses
The aim of the study was to test a revised conceptualization of the role of coping in adjustment to a low-control stressor-women's adjustment to a failed in vitro fertilization (NF) attempt. Data were collected prior to the IVF treatment (Time I) and twice after the failed NF attempt (1 to 2 weeks after finding out the results, n = 171, and fi weeks later, n = 139). Initial adjustment was assessed at Time I, whereas measures of coping and both self-report and partner ratings of adjustment were obtained at Times ? and 3. As predicted, escapist strategies and problem-management strategies (mainly at Time ?) were associated with poor adjustment, whereas problem-appraisal coping was associated with better adjustment., There was also support for the proposed positive relationship between adjustment and emotional approach coping (on self-report adjustment)
On the Optical -- X-ray correlation from outburst to quiescence in Low Mass X-ray Binaries: the representative cases of V404 Cyg and Cen X-4
Low mass X-ray binaries (LMXBs) show evidence of a global correlation of
debated origin between X-ray and optical luminosity. We study for the first
time this correlation in two transient LMXBs, the black hole V404 Cyg and the
neutron star Cen X-4, over 6 orders of magnitude in X-ray luminosity, from
outburst to quiescence. After subtracting the contribution from the companion
star, the Cen X-4 data can be described by a single power law correlation of
the form , consistent with disk reprocessing. We
find a similar correlation slope for V404 Cyg in quiescence (0.46) and a
steeper one (0.56) in the outburst hard state of 1989. However, V404 Cyg is
about times optically brighter, at a given keV X-ray
luminosity, compared to Cen X-4. This ratio is a factor of 10 smaller in
quiescence, where the normalization of the V404 Cyg correlation also changes.
We show that once the bolometric X-ray emission is considered and the known
main differences between V404 Cyg and Cen X-4 are taken into account (a larger
compact object mass, accretion disk size, and the presence of a strong jet
contribution in the hard state for the black hole system) the two systems lie
on the same correlation. In V404 Cyg, the jet dominates spectrally at
optical-infrared frequencies during the hard state, but makes a negligible
contribution in quiescence, which may account for the change in its correlation
slope and normalization. These results provide a benchmark to compare with data
from the 2015 outburst of V404 Cyg and, potentially, other transient LMXBs as
well.Comment: Accepted on ApJ, 12 pages, 4 figures, 4 table
A continental rift model for the La Grande greenstone belt
Stratigraphic relationships and the geochemistry of volcanic rocks contrain the nature and timing of the tectonic and magmatic processes in the pre-deformational history of the La Grande greenstone belt in the Superior Province of north-central Quebec. The lowermost supracrustals in this belt are obscured by syntectonic granitoid intrusives. The supracrustal succession in the western part of the belt consists of a lower sequence of immature clastic sediments and mafic volcanoclastics, overlain by pillowed and massive basalts. Further east, along tectonic strike, a lower sequence of mafic volcanoclastics and immature clastic sediments is overlain by a thick sequence of pillowed and massive basalts, and resedimented coarse clastic sediments and banded iron formation. These are overlain by assive basaltic andesites, andesites and intermediate volcanoclastics intercalated with immature clastic sediments. In contrast, in the eastern part of the belt lenses of felsic volcanics and volcanoclastics occur at the base of the succession and pillowed and massive basalts are overlain by komatiites at the top. The La Grande greenstone belt can be explained as the product of continental rifting. The restricted occurence of komatiites, and eastwardly directed paleocurrents in clastic sediments in the central part of the belt are consistent with rifting commencing in the east and propagating westward with time. The increase in depth of emplacement and deposition with time of the lower three units in the central part of the belt reflects deposition in a subsiding basin. These supracrustal rocks are believed to represent the initial rift succession
Circulatory arrest for traumatic brachiocephalic artery pseudoaneurysm repair
Blunt traumatic injuries to the brachiocephalic artery require surgical management. The operative technique used depends on the location of the injury, the patient\u27s hemodynamic stability, and the surgeon\u27s experience. Perfusion strategy can facilitate vascular control of the aortic arch and branch vessels. This report presents an urgent repair of a proximal posterior blunt traumatic brachiocephalic artery injury under circulatory arrest, with an excellent outcome
A single center experience with coronary endarterectomy and vein patch reconstruction
Background: To evaluate the medium and late term outcomes of coronary artery bypass grafting with pull-through coronary endarterectomy using a saphenous vein patch for bypass distal anastomosis site.
Methods: Retrospective review of all coronary artery bypass graft (CABG) procedures performed from January 1, 2000 through June 30, 2013 with and without concomitant coronary endarterectomy (CE), was carried out at the Veterans Affairs Medical Center in Washington DC. Patients who underwent concomitant valve operations were excluded. Primary outcome was overall survival, with analyses performed examining CE as well as the use of cardiopulmonary bypass. Secondary outcomes included 30-day mortality and post-operative MI.
Results: 1255 CABG operations were performed, 10 of which included CE. All CE procedures were performed with saphenous vein patch. 7 involved left anterior descending artery (LAD) CE with left internal mammary artery (LIMA) conduits. The remaining 3 were diagonal branch artery (D1) CE with saphenous vein bypass conduits. 1-year survival was 70%. 5-year survival was 43% out of 7 patients.
Conclusions: Pull-through CE with saphenous vein patch is a safe alternative technique for patients with diffuse coronary artery disease. Perioperative events and intermediate outcomes are favorable, although long-term survival is less than patients without CE
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