1,524 research outputs found
Frame-dragging, disk warping, jet precessing, and dipped X-ray lightcurve of Sw J1644+57
The X-ray transient source Sw J1644+57 recently discovered by Swift is
believed to be triggered by tidal disruption of a star by a rapidly spinning
supermassive black hole (SMBH). For such events, the outer disk is very likely
misaligned with respect to the equatorial plane of the spinning SMBH, since the
incoming star before disruption most likely has an inclined orbital plane. The
tilted disk is subject to the Lense-Thirring torque, which tends to twist and
warp due to the Bardeen-Petterson effect. The inner disk tends to align with
the SMBH spin, while the outer region tends to remain in the stellar orbital
plane, with a transition zone around the Bardeen-Petterson radius. The
relativistic jet launched from the spinning SMBH would undergo precession. The
5-30 day X-ray lightcurve of Sw J1644+57 shows a quasi-periodic (2.7-day)
variation with noticeable narrow dips. We numerically solve a warped disk and
propose a jet-precessing model by invoking a Blandford-Znajek jet collimated by
a wind launched near the Bardeen-Petterson radius. Through simulations, we show
that the narrow dips in the X-ray lightcurve can be reproduced for a range of
geometric configurations. From data we infer that the inclination angle of the
initial stellar orbit is in the range of from the SMBH
equatorial plane, that the jet should have a moderately high Lorentz factor,
and that the inclination angle, jet opening angle, and observer's viewing angle
are such that the duty cycle of the line-of-sight sweeping the jet cone is
somewhat less than 0.5.Comment: 8 pages, 8 figures; Accepted for publication in Ap
Protein Arrays: Issues to Be Addressed
Protein arrays are fast becoming established as a means to monitor protein expression
levels and investigate protein interactions and function. They present particular technical
demands that will need to be solved in order to achieve the maximum capability of efficient
and sensitive protein analysis in the high throughput setting of functional genomics. The
following resumé of some major issues around this new technology was made as the
chairperson’s introduction to the workshop session on peptide and protein chips
Stoichiometric and catalytic C-C and C-H bond formation with B(C6F5)3 via cationic intermediates
This work showcases a new catalytic cyclization reaction using a highly Lewis acidic borane with concomitant C−H or C−C bond formation. The activation of alkyne‐containing substrates with B(C6F5)3 enabled the first catalytic intramolecular cyclizations of carboxylic acid substrates using this Lewis acid. In addition, intramolecular cyclizations of esters enable C−C bond formation as catalytic B(C6F5)3 can be used to effect formal 1,5‐alkyl migrations from the ester functional groups to unsaturated carbon–carbon frameworks. This metal‐free method was used for the catalytic formation of complex dihydropyrones and isocoumarins in very good yields under relatively mild conditions with excellent atom efficiency
Stöchiometrische und katalytische C-C- und C-H-Bindungsbildung mit B(C6 F5 )3 über kationische Zwischenstufen
Diese Arbeit beschreibt eine neuartige katalytische Cyclisierung unter Verwendung eines stark Lewis-sauren Borans mit einhergehender C-H- oder C-C-Bindungsbildung. Die Aktivierung von Molekülen mit C-C-Dreifachbindungen unter Verwendung von B(C6F5)3 ermöglicht erstmals eine entsprechende Lewis-Säure-katalysierte, intramolekulare Cyclisierung von Carbonsäuren. Darüber hinaus zeigen die Ester dieser Carbonsäuren mit katalytischen Mengen B(C6F5)3 eine formale 1,5-Migration der Estergruppen unter Knüpfung einer C-C-Bindung. Unter Verwendung dieser neuen metallfreien Methode konnten anspruchsvolle Dihydropyrone und Isocumarine in hohen Ausbeuten unter milden Bedingungen sowie mit hoher Atomökonomie synthetisiert werden
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Estimated Impact of Achieving Optimal Cardiovascular Health Among US Adults on Cardiovascular Disease Events
Background Better cardiovascular health (CVH) scores are associated with lower risk of cardiovascular disease (CVD). However, estimates of the potential population-level impact of improving CVH on US CVD event rates are not currently available. Methods and Results Using data from the National Health and Nutrition Examination Survey 2011 to 2016 (n=11 696), we estimated the proportions of US adults in CVH groups. Levels of 7 American Heart Association CVH metrics were scored as ideal (2 points), intermediate (1 point), or poor (0 points), and summed to define overall CVH (low, 0-8 points; moderate, 9-11 points; or high, 12-14 points). Using individual-level data from 7 US community-based cohort studies (n=30 447), we estimated annual incidence rates of major CVD events by levels of CVH. Using the combined data sources, we estimated population attributable fractions of CVD and the number of CVD events that could be prevented annually if all US adults achieved high CVH. High CVH was identified in 7.3% (95% CI, 6.3%-8.3%) of US adults. We estimated that 70.0% (95% CI, 56.5%-79.9%) of CVD events were attributable to low and moderate CVH. If all US adults attained high CVH, we estimated that 2.0 (95% CI, 1.6-2.3) million CVD events could be prevented annually. If all US adults with low CVH attained moderate CVH, we estimated that 1.2 (95% CI, 1.0-1.4) million CVD events could be prevented annually. Conclusions The potential benefits of achieving high CVH in all US adults are considerable, and even a partial improvement in CVH scores would be highly beneficial
Living Supramolecular Polymerisation of Perylene Diimide Amphiphiles by Seeded Growth under Kinetic Control
Canadian Initiatives to Prevent Hypertension by Reducing Dietary Sodium
Hypertension is the leading risk for premature death in the world. High dietary sodium is an important contributor to increased blood pressure and is strongly associated with other important diseases (e.g., gastric cancer, calcium containing kidney stones, osteoporosis, asthma and obesity). The average dietary sodium intake in Canada is approximately 3400 mg/day. It is estimated that 30% of hypertension, more than 10% of cardiovascular events and 1.4 billion dollars/year in health care expenses are caused by this high level of intake in Canada. Since 2006, Canada has had a focused and evolving effort to reduce dietary sodium based on actions from Non Governmental Organizations (NGO), and Federal and Provincial/Territorial Government actions. NGOs initiated Canadian sodium reduction programs by developing a policy statement outlining the health issue and calling for governmental, NGO and industry action, developing and disseminating an extensive health care professional education program including resources for patient education, developing a public awareness campaign through extensive media releases and publications in the lay press. The Federal Government responded by striking a Intersectoral Sodium Work Group to develop recommendations on how to implement Canada’s dietary reference intake values for dietary sodium and by developing timelines and targets for foods to be reduced in sodium, assessing key research gaps with funding for targeted dietary sodium based research, developing plans for public education and for conducting evaluation of the program to reduce dietary sodium. While food regulation is a Federal Government responsibility Provincial and Territorial governments indicated reducing dietary sodium needed to be a priority. Federal and Provincial Ministers of Health have endorsed a target to reduce the average consumption of sodium to 2300 mg/day by 2016 and the Deputy Ministers of Health have tasked a joint committee to review the recommendations of the Sodium Work Group and report back to them
Role of right posterior parietal cortex in maintaining attention to spatial locations over time
Recent models of human posterior parietal cortex (PPC) have variously emphasized its role in spatial perception, visuomotor control or directing attention. However, neuroimaging and lesion studies also suggest that the right PPC might play a special role in maintaining an alert state. Previously, assessments of right-hemisphere patients with hemispatial neglect have revealed significant overall deficits on vigilance tasks, but to date there has been no demonstration of a deterioration of performance over time--a vigilance decrement--considered by some to be a key index of a deficit in maintaining attention. Moreover, sustained attention deficits in neglect have not specifically been related to PPC lesions, and it remains unclear whether they interact with spatial impairments in this syndrome. Here we examined the ability of right-hemisphere patients with neglect to maintain attention, comparing them to stroke controls and healthy individuals. We found evidence of an overall deficit in sustaining attention associated with PPC lesions, even for a simple detection task with stimuli presented centrally. In a second experiment, we demonstrated a vigilance decrement in neglect patients specifically only when they were required to maintain attention to spatial locations, but not verbal material. Lesioned voxels in the right PPC spanning a region between the intraparietal sulcus and inferior parietal lobe were significantly associated with this deficit. Finally, we compared performance on a task that required attention to be maintained either to visual patterns or spatial locations, matched for task difficulty. Again, we found a vigilance decrement but only when attention had to be maintained on spatial information. We conclude that sustaining attention to spatial locations is a critical function of the human right PPC which needs to be incorporated into models of normal parietal function as well as those of the clinical syndrome of hemispatial neglect
Epigenetic regulation of adaptive responses of forest tree species to the environment
Epigenetic variation is likely to contribute to the phenotypic plasticity and adaptative capacity of plant species, and may be especially important for long-lived organisms with complex life cycles, including forest trees. Diverse environmental stresses and hybridization/polyploidization events can create reversible heritable epigenetic marks that can be transmitted to subsequent generations as a form of molecular “memory”. Epigenetic changes might also contribute to the ability of plants to colonize or persist in variable environments. In this review, we provide an overview of recent data on epigenetic mechanisms involved in developmental processes and responses to environmental cues in plant, with a focus on forest tree species. We consider the possible role of forest tree epigenetics as a new source of adaptive traits in plant breeding, biotechnology, and ecosystem conservation under rapid climate chang
Electronic phase transitions in PrCaMnO epitaxial thin films revealed by resonant soft x-ray scattering
We report the study of magnetic and orbital order in
PrCaMnO epitaxial thin films grown on
(LaAlO)-(SrAlTaO) (LSAT) (011). In
a new experimental approach, the polarization and energy dependence of resonant
soft x-ray scattering are used to reveal significant modifications of the
magnetic order in the film as compared to the bulk, namely (i) a different
magnetic ordering wave vector, (ii) a different magnetic easy axis and (iii) an
additional magnetic reordering transition at low temperatures. These
observations indicate a strong impact of the epitaxial strain on the spin
order, which is mediated by the orbital degrees of freedom and which provides a
promising route to tune the magnetic properties of manganite films. Our results
further demonstrate that resonant soft x-ray scattering is a very suitable
technique to study the magnetism in thin films, to which neutron scattering
cannot easily be applied due to the small sample volume.Comment: 5 pages, 3 figure
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