3,850 research outputs found
Study of flight management requirements during SST low visibility approach and landing operations. Volume 1 - Definition of baseline SST landing system
Baseline instrument landing system for low visibility approach and landing of supersonic transport
Robustness of Binary Black Hole Mergers in the Presence of Spurious Radiation
We present an investigation into how sensitive the last orbits and merger of
binary black hole systems are to the presence of spurious radiation in the
initial data. Our numerical experiments consist of a binary black hole system
starting the last couple of orbits before merger with additional spurious
radiation centered at the origin and fixed initial angular momentum. As the
energy in the added spurious radiation increases, the binary is invariably
hardened for the cases we tested, i.e. the merger of the two black holes is
hastened. The change in merger time becomes significant when the additional
energy provided by the spurious radiation increases the Arnowitt-Deser-Misner
(ADM) mass of the spacetime by about 1%. While the final masses of the black
holes increase due to partial absorption of the radiation, the final spins
remain constant to within our numerical accuracy. We conjecture that the
spurious radiation is primarily increasing the eccentricity of the orbit and
secondarily increasing the mass of the black holes while propagating out to
infinity.Comment: 12 pages, 12 figure
Altered cortical activation patterns associated with baroreflex unloading following 24 h of physical deconditioning
Cardiovascular arousal is associated with patterned cortical activity changes. Head-down-tilt bed rest (HDBR) dimishes the baroreflex-mediated cardiac control. The present study tested the hypothesis that HDBR deconditioning would modify the forebrain organization for heart rate (HR) control during baroreflex unloading. Heart rate variability (HRV), blood pressure and plasma hormones were analysed at rest, whereas HR and cortical autonomic activation patterns (functional magnetic resonance imaging) were measured during graded and randomly assigned lower body negative pressure treatments (LBNP, -15 and -35 mmHg) both before (Pre) and after (Post) a 24 h HDBR protocol (study 1; n= 8). An additional group was tested before and following diuretic-induced hypovolaemia (study 2; n= 9; spironolactone, 100 mg day-1 for 3 days) that mimicked the plasma volume lost during HDBR (-15% in both studies; P \u3c 0.05). Head-down bed rest with hypovolaemia did not affect baseline HR, mean arterial pressure, HRV or plasma catecholamines. Head-down bed rest augmented the LBNP-induced HR response (P \u3c 0.05), and this was associated with bed-rest-induced development of the following changes: (i) enhanced activation within the genual anterior cingulate cortex and the right anterior insular cortex; and (ii) deactivation patterns within the subgenual regions of the anterior cingulate cortex. Diuretic treatment (without HDBR) did not affect baseline HR and mean arterial pressure, but did reduce resting HRV and elevated circulating noradrenaline and plasma renin activity (P \u3c 0.05). The greater HR response to LBNP following diuretic (P \u3c 0.05) was associated with diminished activation of the right anterior insula. Our findings indicate that 24 h of HDBR minimized the impact of diuretic treatment on baseline autonomic and cardiovascular variables. The findings also indicate that despite the similar augmentation of HR responses to LBNP and despite similar pre-intervention cortical activation patterns, HDBR and diuretic treatment produced different effects on the cortical responses, with HDBR affecting anterior cingulate cortex and right insula regions, whereas diuretic treatment affected primarily the right insula alone, but in a direction that was opposite to HDBR. The data indicate that physical deconditioning can induce rapid functional changes within the cortical circuitry associated with baroreflex unloading, changes that are distinct from diuretic-induced hypovolaemia. The results suggest that physical activity patterns exert a rapid and notable impact on the cortical circuitry associated with cardiovascular control. © 2012 The Physiological Society
Cortical Circuitry Associated With Reflex Cardiovascular Control in Humans: Does the Cortical Autonomic Network Speak or Listen During Cardiovascular Arousal
Beginning with clinical evidence of fatal cardiac arrhythmias in response to severe stress, in epileptic patients, and following stroke, the role of the cerebral cortex in autonomic control of the cardiovascular system has gained both academic and clinical interest. Studies in anesthetized rodents have exposed the role of several forebrain regions involved in cardiovascular control. The introduction of functional neuroimaging techniques has enabled investigations into the conscious human brain to illuminate the temporal and spatial activation patterns of cortical regions that are involved with cardiovascular control through the autonomic nervous system. This symposia report emphasizes the research performed by the authors to understand the functional organization of the human forebrain in cardiovascular control during physical stressors of baroreceptor unloading and handgrip exercise. The studies have exposed important associations between activation patterns of the insula cortex, dorsal anterior cingulate, and the medial prefrontal cortex and cardiovascular adjustments to physical stressors. Furthermore, these studies provide functional anatomic evidence that sensory signals arising from baroreceptors and skeletal muscle are represented within the insula cortex and the medial prefrontal cortex, in addition to the sensory cortex. Thus, the cortical pathways subserving reflex cardiovascular control integrate viscerosensory inputs with outgoing traffic that modulates the autonomic nervous system. © 2012 Wiley Periodicals, Inc.
Methods and considerations for the analysis and standardization of assessing muscle sympathetic nerve activity in humans.
The technique of microneurography and the assessment of muscle sympathetic nerve activity (MSNA) are used in laboratories throughout the world. The variables used to describe MSNA, and the criteria by which these variables are quantified from the integrated neurogram, vary among studies and laboratories and, therefore, can become confusing to those starting to learn the technique. Therefore, the purpose of this educational review is to discuss guidelines and standards for the assessment of sympathetic nervous activity through the collection and analysis of MSNA. This review will reiterate common practices in the collection of MSNA, but will also introduce considerations for the evaluation and physiological inference using MSNA
Methods and considerations for the analysis and standardization of assessing muscle sympathetic nerve activity in humans
© 2015 Elsevier B.V.. The technique of microneurography and the assessment of muscle sympathetic nerve activity (MSNA) are used in laboratories throughout the world. The variables used to describe MSNA, and the criteria by which these variables are quantified from the integrated neurogram, vary among studies and laboratories and, therefore, can become confusing to those starting to learn the technique. Therefore, the purpose of this educational review is to discuss guidelines and standards for the assessment of sympathetic nervous activity through the collection and analysis of MSNA. This review will reiterate common practices in the collection of MSNA, but will also introduce considerations for the evaluation and physiological inference using MSNA
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Effects of a Magazine’s Move to Online-only: Post-print Audience Attention and Readership Retention Revisited
For financial reasons, newspapers and magazines are increasingly going online-only. By doing so, some have returned to profitability, but with what consequences for their audiences? To expand the scant evidence base, we conducted a case study of the UK’s New Musical Express (NME) magazine. By analyzing quantitative audience data from official industry sources, we estimate total time spent with the NME by its British audience fell dramatically post-print—by 72%. This fall mirrors that suffered by The Independent newspaper, which went online-only two years earlier. We also report that the NME’s official net weekly and monthly readership increased post-print, although these results are difficult to compare with The Independent’s because the two titles differed in their print publication frequencies. We conclude that the attention periodicals attract via their print editions is unlikely to immediately transfer to their online editions should they go online-only. Building a fuller theory of print platform cessation, however—one that also encompasses changes in readership/reach—requires more comparable data. This case study provides further evidence to suggest that though, for newspapers and magazines, a post-print existence may be less costly, it is also more constrained, with much of the attention they formerly enjoyed simply stripped away
Long term study of the seismic environment at LIGO
The LIGO experiment aims to detect and study gravitational waves using ground
based laser interferometry. A critical factor to the performance of the
interferometers, and a major consideration in the design of possible future
upgrades, is isolation of the interferometer optics from seismic noise. We
present the results of a detailed program of measurements of the seismic
environment surrounding the LIGO interferometers. We describe the experimental
configuration used to collect the data, which was acquired over a 613 day
period. The measurements focused on the frequency range 0.1-10 Hz, in which the
secondary microseismic peak and noise due to human activity in the vicinity of
the detectors was found to be particularly critical to interferometer
performance. We compare the statistical distribution of the data sets from the
two interferometer sites, construct amplitude spectral densities of seismic
noise amplitude fluctuations with periods of up to 3 months, and analyze the
data for any long term trends in the amplitude of seismic noise in this
critical frequency range.Comment: To be published in Classical and Quantum Gravity. 24 pages, 15
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Initial Data and Coordinates for Multiple Black Hole Systems
We present here an alternative approach to data setting for spacetimes with
multiple moving black holes generalizing the Kerr-Schild form for rotating or
non-rotating single black holes to multiple moving holes. Because this scheme
preserves the Kerr-Schild form near the holes, it selects out the behaviour of
null rays near the holes, may simplify horizon tracking, and may prove useful
in computational applications. For computational evolution, a discussion of
coordinates (lapse function and shift vector) is given which preserves some of
the properties of the single-hole Kerr-Schild form
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