Exact Gravitational Wave Signatures from Colliding Extreme Black Holes

The low-energy dynamics of any system admitting a continuum of static configurations is approximated by slow motion in moduli (configuration) space. Here, following Ferrell and Eardley, this moduli space approximation is utilized to study collisions of two maximally charged Reissner--Nordstr{\"o}m black holes of arbitrary masses, and to compute analytically the gravitational radiation generated by their scattering or coalescence. The motion remains slow even though the fields are strong, and the leading radiation is quadrupolar. A simple expression for the gravitational waveform is derived and compared at early and late times to expectations.Comment: 6 page

Letting Kids Be Kids: Employing a Developmental Model in the Study of Domestic Minor Sex Trafficking

As American society has become increasingly aware of the plight of sex trafficked American children, attention has shifted from delinquency to victimhood (Mitchell, Finkelhor, & Wolak, 2010) with a corresponding awareness of the trauma that victims endure. This reconceptualization is incomplete without a larger understanding of the developmental vulnerabilities that leave children uniquely susceptible to recruitment and exploitation. Since the average age of entry into the commercial sex trade within the United States is 12-14 (Estes & Weiner, 2001), an exploration of the particular vulnerabilities of young teenagers--separation from parents; the process of identity formation; yearning for love and attention; susceptibility to peer pressure; cognitive and neurological changes; etc.—is essential to understanding the current epidemic of sex trafficking of minors. This article will not only elucidate these developmental liabilities and the corresponding increased risk for psychological distress among adolescents but it will also reveal the unique developmental advantages that facilitate growth and healing among adolescents. Such knowledge will explain why early adolescents are targeted and will consider how society can combat trafficking through reduction of risk factors, prevention and intervention programs, political action, and an appreciation of teenagers’ strengths

Is there a breakdown of effective field theory at the horizon of an extremal black hole?

© 2017, The Author(s). Linear perturbations of extremal black holes exhibit the Aretakis instability, in which higher derivatives of a scalar field grow polynomially with time along the event horizon. This suggests that higher derivative corrections to the classical equations of motion may become large, indicating a breakdown of effective field theory at late time on the event horizon. We investigate whether or not this happens. For extremal Reissner-Nordstrom we argue that, for a large class of theories, general covariance ensures that the higher derivative corrections to the equations of motion appear only in combinations that remain small compared to two derivative terms so effective field theory remains valid. For extremal Kerr, the situation is more complicated since backreaction of the scalar field is not understood even in the two derivative theory. Nevertheless we argue that the effects of the higher derivative terms will be small compared to the two derivative terms as long as the spacetime remains close to extremal Kerr.SH is supported by the Blavatnik Postdoctoral Fellowship. SH is grateful to the Albert Einstein Institute, Potsdam for hospitality during the completion of this work. Part of this work was completed while HSR was a participant in the “Geometry and Relativity” programme at the Erwin Schr¨odinger Institute, Vienna

Post-ISCO Ringdown Amplitudes in Extreme Mass Ratio Inspiral

An extreme mass ratio inspiral consists of two parts: adiabatic inspiral and plunge. The plunge trajectory from the innermost stable circular orbit (ISCO) is special (somewhat independent of initial conditions). We write an expression for its solution in closed-form and for the emitted waveform. In particular we extract an expression for the associated black-hole ringdown amplitudes, and evaluate them numerically.Comment: 21 pages, 5 figures. v4: added section with numerical evaluation of the ringdown amplitude

Binocular vision enhances a rapidly evolving affordance priming effect: Behavioural and TMS evidence

Extensive research has suggested that simply viewing an object can automatically prime compatible actions for object manipulation, known as affordances. Here we explored the generation of covert motor plans afforded by real objects with precision (‘pinchable’) or whole-hand/power (‘graspable’) grip significance under different types of vision. In Experiment 1, participants viewed real object primes either monocularly or binocularly and responded to orthogonal auditory stimuli by making precision or power grips. Pinchable primes facilitated congruent precision grip responses relative to incongruent power grips, and vice versa for graspable primes, but only in the binocular vision condition. To examine the temporal evolution of the binocular affordance effect, participants in Experiment 2 always viewed the objects binocularly but made no responses, instead receiving a transcranial magnetic stimulation pulse over their primary motor cortex at three different times (150, 300, 450 ms) after prime onset. Motor evoked potentials (MEPs) recorded from a pinching muscle were selectively increased when subjects were primed with a pinchable object, whereas MEPs from a muscle associated with power grips were increased when viewing graspable stimuli. This interaction was obtained both 300 and 450 ms (but not 150 ms) after the visual onset of the prime, characterising for the first time the rapid development of binocular grip-specific affordances predicted by functional accounts of the affordance effect

Motor‐evoked potentials reveal a motor‐cortical readout of evidence accumulation for sensorimotor decisions

Many everyday activities require time-pressured sensorimotor decision making. Traditionally, perception, decision, and action processes were considered to occur in series, but this idea has been successfully challenged, particularly by neurophysiological work in animals. However, the generality of parallel processing requires further elucidation. Here, we investigate whether the accumulation of a decision can be observed intrahemispherically within human motor cortex. Participants categorized faces as male or female, with task difficulty manipulated using morphed stimuli. Transcranial magnetic stimulation, applied during the reaction-time interval, produced motor-evoked potentials (MEPs) in two hand muscles that were the major contributors when generating the required pinch/grip movements. Smoothing MEPs using a Gaussian kernel allowed us to recover a continuous time-varying MEP average, comparable to an EEG component, permitting precise localization of the time at which the motor plan for the responding muscle became dominant. We demonstrate decision-related activity in the motor cortex during this perceptual discrimination task, suggesting ongoing evidence accumulation within the motor system even for two independent actions represented within one hemisphere

Numerical characterization of cohesive and non-cohesive 'sediments' under different consolidation states using 3D DEM triaxial experiments

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Elyashiv, H., Bookman, R., Siemann, L., ten Brink, U., & Huhn, K. Numerical characterization of cohesive and non-cohesive 'sediments' under different consolidation states using 3D DEM triaxial experiments. Processes, 8(10), (2020): 1252, doi:10.3390/pr8101252.The Discrete Element Method has been widely used to simulate geo-materials due to time and scale limitations met in the field and laboratories. While cohesionless geo-materials were the focus of many previous studies, the deformation of cohesive geo-materials in 3D remained poorly characterized. Here, we aimed to generate a range of numerical ‘sediments’, assess their mechanical response to stress and compare their response with laboratory tests, focusing on differences between the micro- and macro-material properties. We simulated two endmembers—clay (cohesive) and sand (cohesionless). The materials were tested in a 3D triaxial numerical setup, under different simulated burial stresses and consolidation states. Variations in particle contact or individual bond strengths generate first order influence on the stress–strain response, i.e., a different deformation style of the numerical sand or clay. Increased burial depth generates a second order influence, elevating peak shear strength. Loose and dense consolidation states generate a third order influence of the endmember level. The results replicate a range of sediment compositions, empirical behaviors and conditions. We propose a procedure to characterize sediments numerically. The numerical ‘sediments’ can be applied to simulate processes in sediments exhibiting variations in strength due to post-seismic consolidation, bioturbation or variations in sedimentation rates.This research received no external funding