Bondi Accretion in the Spherically Symmetric Johannsen-Psaltis Spacetime

The Johannsen-Psaltis spacetime explicitly violates the no hair theorem. It describes rotating black holes with scalar hair in the form of parametric deviations from the Kerr metric. In principle, black hole solutions in any modified theory of gravity could be written in terms of the Johannsen-Psaltis metric. We study the accretion of gas onto a static limit of this spacetime. We utilise a recently proposed pseudo-Newtonian formulation of the dynamics around arbitrary static, spherically symmetric spacetimes. We obtain a potential that generalises the Paczy\'nski-Wiita potential to the static Johannsen-Psaltis metric. We also perform a fully relativistic analysis of the geodesic equations in the static Johannsen-Psaltis spacetime. We find that positive values of the scalar hair parameter, $\epsilon_{3}$, lower the accretion rate and vice versa. Similarly, positive (negative) values of $\epsilon_{3}$ reduce (increase) the gravitational acceleration of radially infalling massive particles.Comment: 13 Pages, 1 figure, submitted to CQ

Ownership and rent-seeking behavior in specialty health care practices

Specialty health care practices are unique in that they exhibit a wide range of ownership types, from large corporations controlled by third parties to those directly owned by practitioners (physicians, therapists, etc.). Many of these practices also employ licensed assistants whose labor is partially substitutable with those of the practitioners. This paper presents a theoretical model that examines the impact that different levels of ownership have on rent-seeking behavior and efficiency within specialty practices. Our primary focus is on whether lower levels of ownership induce practitioners to extract larger economic rents by substituting their services for those of their assistants. We find that if the practitioners are not required to be technically efficient then they unambiguously respond to lower ownership with rent-seeking. However, requiring the firm to be technically (but not allocatively) efficient, may be sufficient to mitigate this incentive.efficiency

COFFEE -- An MPI-parallelized Python package for the numerical evolution of differential equations

COFFEE (ConFormal Field Equation Evolver) is a Python package primarily developed to numerically evolve systems of partial differential equations over time using the method of lines. It includes a variety of time integrators and finite differencing stencils with the summation-by-parts property, as well as pseudo-spectral functionality for angular derivatives of spin-weighted functions. Some additional capabilities include being MPI-parallelisable on a variety of different geometries, HDF data output and post processing scripts to visualize data, and an actions class that allows users to create code for analysis after each timestep.Comment: 12 pages, 1 figure, accepted to be published in Software

Synchronous wearable wireless body sensor network composed of autonomous textile nodes

A novel, fully-autonomous, wearable, wireless sensor network is presented, where each flexible textile node performs cooperative synchronous acquisition and distributed event detection. Computationally efficient situational-awareness algorithms are implemented on the low-power microcontroller present on each flexible node. The detected events are wirelessly transmitted to a base station, directly, as well as forwarded by other on-body nodes. For each node, a dual-polarized textile patch antenna serves as a platform for the flexible electronic circuitry. Therefore, the system is particularly suitable for comfortable and unobtrusive integration into garments. In the meantime, polarization diversity can be exploited to improve the reliability and energy-efficiency of the wireless transmission. Extensive experiments in realistic conditions have demonstrated that this new autonomous, body-centric, textile-antenna, wireless sensor network is able to correctly detect different operating conditions of a firefighter during an intervention. By relying on four network nodes integrated into the protective garment, this functionality is implemented locally, on the body, and in real time. In addition, the received sensor data are reliably transferred to a central access point at the command post, for more detailed and more comprehensive real-time visualization. This information provides coordinators and commanders with situational awareness of the entire rescue operation. A statistical analysis of measured on-body node-to-node, as well as off-body person-to-person channels is included, confirming the reliability of the communication system

Flexible dual-diversity wearable wireless node integrated on a dual-polarised textile patch antenna

A new textile wearable wireless node, for operation in the 2.45 GHz industrial, scientific and medical (ISM) band, is proposed. It consists of a dual-polarised textile patch antenna with integrated microcontroller, sensor, memory and transceiver with receive diversity. Integrated into a garment, the flexible unit may serve for fall detection, as well as for patient or rescue-worker monitoring. Fragile and lossy interconnections are eliminated. They are replaced by very short radiofrequency signal paths in the antenna feed plane, reducing electromagnetic compatibility and signal integrity problems. The compact and flexible module combines sensing and wireless channel monitoring functionality with reliable and energy-efficient off-body wireless communication capability, by fully exploiting dual polarisation diversity. By integrating a battery, a fully autonomous and flexible system is obtained. This novel textile wireless node was validated, both in flat and bent state, in the anechoic chamber, assessing the characteristics of the integrated system in free-space conditions. Moreover, its performance was verified in various real-world conditions, integrated into a firefighter garment, and used as an autonomous body-centric measurement device

The non-linear perturbation of a black hole by gravitational waves. II. Quasinormal modes and the compactification problem

Recently, Friedrich's Generalized Conformal Field Equations (GCFE) have been implemented numerically and global quantities such as the Bondi energy and the Bondi-Sachs mass loss have been successfully calculated directly on null-infinity. Although being an attractive option for studying global quantities by way of local differential geometrical methods, how viable are the GCFE for study of quantities arising in the physical space-time? In particular, how long can the evolution track phenomena that need a constant proper physical timestep to be accurately resolved? We address this question by studying the curvature oscillations induced on the Schwarzschild space-time by a non-linear gravitational perturbation. For small enough amplitudes, these are the well approximated by the linear quasinormal modes, where each mode rings at a frequency determined solely by the Schwarzschild mass. We find that the GCFE can indeed resolve these oscillations, which quickly approach the linear regime, but only for a short time before the compactification becomes ``too fast'' to handle numerically.Comment: 19 pages, 8 figures, submitted to CQ