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

Binary Black Holes: Spin Dynamics and Gravitational Recoil

We present a study of spinning black hole binaries focusing on the spin dynamics of the individual black holes as well as on the gravitational recoil acquired by the black hole produced by the merger. We consider two series of initial spin orientations away from the binary orbital plane. In one of the series, the spins are anti-aligned; for the second series, one of the spins points away from the binary along the line separating the black holes. We find a remarkable agreement between the spin dynamics predicted at 2nd post-Newtonian order and those from numerical relativity. For each configuration, we compute the kick of the final black hole. We use the kick estimates from the series with anti-aligned spins to fit the parameters in the \KKF{,} and verify that the recoil along the direction of the orbital angular momentum is $\propto \sin\theta$ and on the orbital plane $\propto \cos\theta$, with $\theta$ the angle between the spin directions and the orbital angular momentum. We also find that the black hole spins can be well estimated by evaluating the isolated horizon spin on spheres of constant coordinate radius.Comment: 15 pages, 10 figures, replaced with version accepted for publication in PR

Gravitational recoil from spinning binary black hole mergers

The inspiral and merger of binary black holes will likely involve black holes with both unequal masses and arbitrary spins. The gravitational radiation emitted by these binaries will carry angular as well as linear momentum. A net flux of emitted linear momentum implies that the black hole produced by the merger will experience a recoil or kick. Previous studies have focused on the recoil velocity from unequal mass, non-spinning binaries. We present results from simulations of equal mass but spinning black hole binaries and show how a significant gravitational recoil can also be obtained in these situations. We consider the case of black holes with opposite spins of magnitude $a$ aligned/anti-aligned with the orbital angular momentum, with $a$ the dimensionless spin parameters of the individual holes. For the initial setups under consideration, we find a recoil velocity of V = 475 \KMS a. Supermassive black hole mergers producing kicks of this magnitude could result in the ejection from the cores of dwarf galaxies of the final hole produced by the collision.Comment: 8 pages, 8 figures, replaced with version accepted for publication in Ap

From Physics Model to Results: An Optimizing Framework for Cross-Architecture Code Generation

Starting from a high-level problem description in terms of partial differential equations using abstract tensor notation, the Chemora framework discretizes, optimizes, and generates complete high performance codes for a wide range of compute architectures. Chemora extends the capabilities of Cactus, facilitating the usage of large-scale CPU/GPU systems in an efficient manner for complex applications, without low-level code tuning. Chemora achieves parallelism through MPI and multi-threading, combining OpenMP and CUDA. Optimizations include high-level code transformations, efficient loop traversal strategies, dynamically selected data and instruction cache usage strategies, and JIT compilation of GPU code tailored to the problem characteristics. The discretization is based on higher-order finite differences on multi-block domains. Chemora's capabilities are demonstrated by simulations of black hole collisions. This problem provides an acid test of the framework, as the Einstein equations contain hundreds of variables and thousands of terms.Comment: 18 pages, 4 figures, accepted for publication in Scientific Programmin

Hyperlipidemia: a new therapeutic target for diabetic neuropathy

Abstract Emerging data establish dyslipidemia as a significant contributor to the development of diabetic neuropathy. In this review, we discuss how separate metabolic imbalances, including hyperglycemia and hyperlipidemia, converge on mechanisms leading to oxidative stress in dorsal root ganglia (DRG) sensory neurons. We conclude with suggestions for novel therapeutic strategies to prevent or reverse diabetes-induced nerve degeneration.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/78728/1/j.1529-8027.2009.00237.x.pd

Polymer brush lubrication of the silicon nitride-steel contact: a colloidal force microscopy study

A greener lubrication solution for the steel–silicon nitride hybrid contact is proposed. The utilisation of surface-initiated (SI) activators-regenerated-by-electron-transfer (ARGET) atom-transfer radical polymerisation (ATRP) is employed to produce an oleophilic polymer brush which is based on methyl methacrylate. The current study presents the synthesis and characterisation of poly methyl methacrylate brushes. X-ray photoelectron spectroscopy, contact angle, gel permeation chromatography and atomic force microscopy were used to characterise the initiators and brushes. The lubricating effects of the polymer brushes under dry and swollen states were elucidated by lateral force microscopy with a steel colloid with a normal load in the nanoscale range. By testing in water and in poly α-olefin (PAO) this work shows that the frictional response of surface initiated polymers is highly dependent on the interaction between polymer brushes and fluid

Fermion absorption cross section of a Schwarzschild black hole

We study the absorption of massive spin-half particles by a small Schwarzschild black hole by numerically solving the single-particle Dirac equation in Painleve-Gullstrand coordinates. We calculate the absorption cross section for a range of gravitational couplings Mm/m_P^2 and incident particle energies E. At high couplings, where the Schwarzschild radius R_S is much greater than the wavelength lambda, we find that the cross section approaches the classical result for a point particle. At intermediate couplings we find oscillations around the classical limit whose precise form depends on the particle mass. These oscillations give quantum violations of the equivalence principle. At high energies the cross section converges on the geometric-optics value of 27 \pi R_S^2/4, and at low energies we find agreement with an approximation derived by Unruh. When the hole is much smaller than the particle wavelength we confirm that the minimum possible cross section approaches \pi R_S^2/2.Comment: 11 pages, 3 figure

ER Stress in Diabetic Peripheral Neuropathy: A New Therapeutic Target

Significance: Diabetes and other diseases that comprise the metabolic syndrome have reached epidemic proportions. Diabetic peripheral neuropathy (DPN) is the most prevalent complication of diabetes, affecting ?50% of diabetic patients. Characterized by chronic pain or loss of sensation, recurrent foot ulcerations, and risk for amputation, DPN is associated with significant morbidity and mortality. Mechanisms underlying DPN pathogenesis are complex and not well understood, and no effective treatments are available. Thus, an improved understanding of DPN pathogenesis is critical for the development of successful therapeutic options. Recent Advances: Recent research implicates endoplasmic reticulum (ER) stress as a novel mechanism in the onset and progression of DPN. ER stress activates the unfolded protein response (UPR), a well-orchestrated signaling cascade responsible for relieving stress and restoring normal ER function. Critical Issues: During times of extreme or chronic stress, such as that associated with diabetes, the UPR may be insufficient to alleviate ER stress, resulting in apoptosis. Here, we discuss the potential role of ER stress in DPN, as well as evidence demonstrating how ER stress intersects with pathways involved in DPN development and progression. An improved understanding of how ER stress contributes to peripheral nerve dysfunction in diabetes will provide important insight into DPN pathogenesis. Future Directions: Future studies aimed at gaining the necessary insight into ER stress in DPN pathogenesis will ultimately facilitate the development of novel therapies. Antioxid. Redox Signal. 21, 621?633.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140287/1/ars.2013.5807.pd

Binary Black Hole Encounters, Gravitational Bursts and Maximum Final Spin

The spin of the final black hole in the coalescence of nonspinning black holes is determined by the ``residual'' orbital angular momentum of the binary. This residual momentum consists of the orbital angular momentum that the binary is not able to shed in the process of merging. We study the angular momentum radiated, the spin of the final black hole and the gravitational bursts in a series of orbits ranging from almost direct infall to numerous orbits before infall that exhibit multiple bursts of radiation in the merger process. We show that the final black hole gets a maximum spin parameter $a/M_h \le 0.78$, and this maximum occurs for initial orbital angular momentum $L \approx M^2_h$.Comment: Replaced with version to appear in PR

Implementation of standard testbeds for numerical relativity

We discuss results that have been obtained from the implementation of the initial round of testbeds for numerical relativity which was proposed in the first paper of the Apples with Apples Alliance. We present benchmark results for various codes which provide templates for analyzing the testbeds and to draw conclusions about various features of the codes. This allows us to sharpen the initial test specifications, design a new test and add theoretical insight.Comment: Corrected versio