55,906 research outputs found
Anomalies in the gravitational recoil of eccentric black-hole mergers with unequal mass ratios
No full textThe radiation of linear momentum imparts a recoil (or "kick") to the center of mass of a merging black-hole binary system. Recent numerical relativity calculations have shown that eccentricity can lead to an approximate 25% increase in recoil velocities for equal-mass, spinning binaries with spins lying in the orbital plane ("superkick" configurations) [U. Sperhake et al. Phys. Rev. D 101, 024044 (2020)]. Here we investigate the impact of nonzero eccentricity on the kick magnitude and gravitational-wave emission of nonspinning, unequal-mass black hole binaries. We confirm that nonzero eccentricities at merger can lead to kicks which are larger by up to similar to 25% relative to the quasicircular case. We also find that the kick velocity v has an oscillatory dependence on eccentricity, which we interpret as a consequence of changes in the angle between the infall direction at merger and the apoapsis (or periapsis) direction
Avulsion of the left internal mammary artery graft after minimally invasive coronary surgery: fatal complication or medical error? A case report
No full textMinimally invasive direct coronary artery bypass (MIDCAB) is performed through a left anterior mini-thoracotomy without the use of a cardiopulmonary bypass and offers greater potential for more rapid recovery, reduced pain and a decreased need for blood transfusion than conventional coronary artery bypass grafting. Few major complications of the MIDCAB procedure have been reported in the literature since the first intervention was performed in 1995, but the most serious one is avulsion of the left internal mammary artery (LIMA) graft near the site of anastomosis with the left; anterior descending coronary artery. Forensic issues regarding the role of the surgeon in causing this life-threatening emergency condition have not been discussed. We report here the case of a 48-year-old man who died 18 days after a MIDCAB of massive thoracic bleeding due to the avulsion of the LIMA graft. We discuss the probable etiopathogenesis of this fatal complication from a forensic point of view
Avulsion of the left internal mammary artery graft after minimally invasive coronary surgery: fatal complication or medical error? A case report
No full textMinimally invasive direct coronary artery bypass (MIDCAB) is performed through a left anterior mini-thoracotomy without the use of a cardiopulmonary bypass and offers greater potential for more rapid recovery, reduced pain and a decreased need for blood transfusion than conventional coronary artery bypass grafting. Few major complications of the MIDCAB procedure have been reported in the literature since the first intervention was performed in 1995, but the most serious one is avulsion of the left internal mammary artery (LIMA) graft near the site of anastomosis with the left anterior descending coronary artery. Forensic issues regarding the role of the surgeon in causing this life-threatening emergency condition have not been discussed. We report here the case of a 48-year-old man who died 18 days after a MIDCAB of massive thoracic bleeding due to the avulsion of the LIMA graft. We discuss the probable etiopathogenesis of this fatal complication from a forensic point of view
Non-linear numerical schemes in general relativity
No full textAvailable from British Library Document Supply Centre-DSC:DXN051489 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo
Dynamic cosmic strings II: numerical evolution of excited cosmic strings
No full textAn implicit, fully characteristic, numerical scheme for solving the field equations of a cosmic string coupled to gravity is described. The inclusion of null infinity as part of the numerical grid allows us to apply suitable boundary conditions on the metric and matter fields to suppress unphysical divergent solutions. The code is tested by comparing the results with exact solutions, checking that static cosmic string initial data remain constant when evolved, and undertaking a time dependent convergence analysis of the code. It is shown that the code is accurate, stable and exhibits clear second order convergence. The code is used to analyze the interaction between a Weber-Wheeler pulse of gravitational radiation with the string. The interaction causes the string to oscillate at frequencies proportional to the masses of the scalar and vector fields of the string. After the pulse has largely radiated away the string continues to ring but the oscillations slowly decay and eventually the variables return to their static values
Dynamic cosmic strings. I
No full textThe field equations for a time dependent cylindrical cosmic string coupled to gravity are reformulated in terms of geometrical variables defined on a (2+1)-dimensional spacetime by using the method of Geroch decomposition. Unlike the 4-dimensional spacetime the reduced case is asymptotically flat. A numerical method for solving the field equations which involves conformally compactifying the space and including null infinity as part of the grid is described. It is shown that the code reproduces the results of a number of vacuum solutions with one or two degrees of freedom. In the final section the interaction between the cosmic string and a pulse of gravitational radiation is briefly described. This is fully analyzed in the sequel
Comment on "Kerr Black Holes as Particle Accelerators to Arbitrarily High Energy"
No full textA Comment on the Letter by Máximo Bañados, Joseph Silk, and Stephen M. West [Phys. Rev. Lett. 103, 111102 (2009)]
Nonlinear radial oscillations of neutron stars
No full textThe effects of nonlinear oscillations in compact stars are attracting considerable current interest. In order to study such phenomena in the framework of fully nonlinear general relativity, highly accurate numerical studies are required. A numerical scheme specifically tailored for such a study is based on formulating the time evolution in terms of deviations from a stationary equilibrium configuration. Using this technique, we investigate over a wide range of amplitudes nonlinear effects in the evolution of radial oscillations of neutron stars. In particular, we discuss mode coupling due to nonlinear interaction, the occurrence of resonance phenomena, shock formation near the stellar surface as well as the capacity of nonlinearities to stabilize perturbatively unstable neutron star models
A Dynamic Subfilter-scale Stress Model for Large Eddy Simulations Based on Physical Flow Scales
No full textWe propose a new definition of the length scale in an eddy-viscosity model for large-eddy simulations (LES). This formulation extends and generalizes a previous proposal [Piomelli, Rouhi and Geurts, Proc. ETMM10, 2014], in which the LES length scale was expressed in terms of the integral length-scale of turbulence determined by the flow characteristics and explicitly decoupled from the simulation grid; this approach was named Integral Length-Scale Approximation (ILSA). As in the original ILSA, the model coefficient was determined by the user, and required to maintain a desired contribution of the unresolved, subfilter scales (SFS) to the global transport. We propose a local formulation (local ILSA) in which the model coefficient is local in space, allowing a precise control over SFS activity as a function of location. This new formulation preserves the properties of the global model; application to channel flow and backward-facing step verifies its features and accuracy
Large-eddy simulation of a separated flow with a sub-filter scale model based on the integral length-scale
No full textA new sub-filter scale model for large-eddy simulations, which uses a length-scale proportional to the integral scale of the turbulence instead of the grid resolution to parametrize the modelled stresses, will be assessed in the prediction of the flow of a boundary-layer over a rough surface, which includes separation and reattachment
- …
