Probing the Binary Black Hole Merger Regime with Scalar Perturbations

We present results obtained by scattering a scalar field off the curved background of a coalescing binary black hole system. A massless scalar field is evolved on a set of fixed backgrounds, each provided by a spatial hypersurface generated numerically during a binary black hole merger. We show that the scalar field scattered from the merger region exhibits quasinormal ringing once a common apparent horizon surrounds the two black holes. This occurs earlier than the onset of the perturbative regime as measured by the start of the quasinormal ringing in the gravitational waveforms. We also use the scalar quasinormal frequencies to associate a mass and a spin with each hypersurface, and observe the compatibility of this measure with the horizon mass and spin computed from the dynamical horizon framework.Comment: 10 Pages and 6 figure

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

Mapping the magic numbers in binary Lennard-Jones clusters

Using a global optimization approach that directly searches for the composition of greatest stability, we have been able to find the particularly stable structures for binary Lennard-Jones clusters with up to 100 atoms for a range of Lennard-Jones parameters. In particular, we have shown that just having atoms of different size leads to a remarkable stabilization of polytetrahedral structures, including both polyicosahedral clusters and at larger sizes structures with disclination lines.Comment: 5 pages, 5 figure

Frequency noise and intensity noise of next-generation gravitational-wave detectors with RF/DC readout schemes

The sensitivity of next-generation gravitational-wave detectors such as Advanced LIGO and LCGT should be limited mostly by quantum noise with an expected technical progress to reduce seismic noise and thermal noise. Those detectors will employ the optical configuration of resonant-sideband-extraction that can be realized with a signal-recycling mirror added to the Fabry-Perot Michelson interferometer. While this configuration can reduce quantum noise of the detector, it can possibly increase laser frequency noise and intensity noise. The analysis of laser noise in the interferometer with the conventional configuration has been done in several papers, and we shall extend the analysis to the resonant-sideband-extraction configuration with the radiation pressure effect included. We shall also refer to laser noise in the case we employ the so-called DC readout scheme.Comment: An error in Fig. 10 in the published version in PRD has been corrected in this version; an erratum has been submitted to PRD. After correction, this figure reflects a significant difference in the ways RF and DC readout schemes are susceptible to laser noise. In addition, the levels of mirror loss imbalances and input laser amplitude noise have also been updated to be more realistic for Advanced LIG

Forest ecosystem changes from annual methane source to sink depending on late summer water balance

Forests dominate the global carbon cycle, but their role in methane (CH4) biogeochemistry remains uncertain. We analyzed whole-ecosystem CH4 fluxes from 2 years, obtained over a lowland evergreen forest in Maine, USA. Gross primary productivity provided the strongest correlation with the CH4 flux in both years, with an additional significant effect of soil moisture in the second, drier year. This forest was a neutral to net source of CH4 in 2011 and a small net sink in 2012. Interannual variability in the summer hydrologic cycle apparently shifts the ecosystem from being a net source to a sink for CH4. The small magnitude of the CH4 fluxes and observed control or CH4 fluxes by forest productivity and summer precipitation provide novel insight into the CH4 cycle in this globally important forest ecosystem.Organismic and Evolutionary Biolog

Sodium nitroglycerin induces middle cerebral artery vasodilatation in young, healthy adults

© 2018 The Authors Experimental Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society New Findings: What is the central question of this study? Nitric oxide causes dilatation in peripheral vessels; however, whether nitric oxide affects basal cerebral artery dilatation has not been explored. What is the main finding and its importance? This study demonstrated that vasodilatation occurs in the right middle cerebral artery in response to exogenous nitric oxide. However, blood velocity decreased and, therefore, overall cerebral blood flow remained unchanged. This study provides new insight into the role of nitric oxide in cerebral blood flow control. Abstract: Recent evidence indicates that basal cerebral conduit vessels dilate with hypercapnia, with a nitric oxide (NO) mechanism explaining one way in which parenchymal cerebral arterioles dilate. However, whether NO affects basal cerebral artery dilatation remains unknown. This study quantified the effect of an exogenous NO donor [sodium nitroglycerin (NTG); 0.4 mg sublingual spray] on the right middle cerebral artery (rMCA) cross-sectional area (CSA), blood velocity and overall blood flow. Measures of vessel CSA (7 T magnetic resonance imaging) and MCA blood velocity (transcranial Doppler ultrasound) were made at baseline (BL) and after exogenous NTG or placebo (PLO) administration in young, healthy individuals (n = 10, two males, age range 20–23 years). The CSA increased in the rMCA [BL, 5.2 ± 1.2 mm2; PLO, 5.4 ± 1.5 mm2; NTG, 6.6 ± 1.5 mm2, P \u3c 0.05; mean ± SD]. Concurrently, rMCA blood velocity decreased from BL during NTG compared with PLO (BL, 67 ± 10 cm s−1; PLO, 62 ± 10 cm s−1; NTG, 59 ± 9.3 cm s−1, P \u3c 0.05; mean ± SD]. However, total MCA blood flow did not change with NTG or PLO [BL, 221 ± 37.4 ml min−1; PLO, 218 ± 35.0 ml min−1; NTG, 213 ± 46.4 ml min−1). Therefore, exogenous NO mediates a dilatory response in the rMCA, but not in its downstream vascular bed

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

Central Versus Peripheral Cardiovascular Risk in Metabolic Syndrome

Individuals with metabolic syndrome (MetS; i.e., three of five of the following risk factors (RFs): elevated blood pressure, waist circumference, triglycerides, blood glucose, or reduced HDL) are thought to be prone to serious cardiovascular disease and there is debate as to whether the disease begins in the peripheral vasculature or centrally. This study investigates hemodynamics, cardiac function/morphology, and mechanical properties of the central (heart, carotid artery) or peripheral [total peripheral resistance (TPR), forearm vascular bed] vasculature in individuals without (1–2 RFs: n = 28), or with (≥3 RFs: n = 46) MetS. After adjustments for statin and blood pressure medication use, those with MetS had lower mitral valve E/A ratios (<3 RFs: 1.24 ± 0.07; ≥3 RFs: 1.01 ± 0.04; P = 0.025), and higher TPR index (<3 RFs: 48 ± 2 mmHg/L/min/m2; ≥3 RFs: 53 ± 2 mmHg/L/min/m2; P = 0.04). There were no differences in heart size, carotid artery measurements, cardiovagal baroreflex, pulse-wave velocity, stroke volume index, or cardiac output index due to MetS after adjustments for statin and blood pressure medication use. The use of statins was associated with increased inertia in the brachial vascular bed, increased HbA1c and decreased LDL cholesterol. The independent use of anti-hypertensive medication was associated with decreased predicted VO2max, triglycerides, diastolic blood pressure, interventricular septum thickness, calculated left ventricle mass, left ventricle posterior wall thickness, and left ventricle pre-ejection period, but increased carotid stiffness, HDL cholesterol, and heart rate. These data imply that both a central cardiac effect and a peripheral effect of vascular resistance are expressed in MetS. These data also indicate that variance in between-group responses due to pharmacological treatments are important factors to consider in studying cardiovascular changes in these individuals