Detection and localization of continuous gravitational waves with pulsar timing arrays: the role of pulsar terms

A pulsar timing array is a Galactic-scale detector of nanohertz gravitational waves (GWs). Its target signals contain two components: the `Earth term' and the `pulsar term' corresponding to GWs incident on the Earth and pulsar respectively. In this work we present a Frequentist method for the detection and localization of continuous waves that takes into account the pulsar term and is significantly faster than existing methods. We investigate the role of pulsar terms by comparing a full-signal search with an Earth-term-only search for non-evolving black hole binaries. By applying the method to synthetic data sets, we find that (i) a full-signal search can slightly improve the detection probability (by about five percent); (ii) sky localization is biased if only Earth terms are searched for and the inclusion of pulsar terms is critical to remove such a bias; (iii) in the case of strong detections (with signal-to-noise ratio $\gtrsim$ 30), it may be possible to improve pulsar distance estimation through GW measurements.Comment: 12 pages, 9 figures, typos corrected. To match the published version. Code implementing this method is available at the PPTA Wiki pag

Tomographic approach to resolving the distribution of LISA Galactic binaries

The space based gravitational wave detector LISA is expected to observe a large population of Galactic white dwarf binaries whose collective signal is likely to dominate instrumental noise at observational frequencies in the range 10^{-4} to 10^{-3} Hz. The motion of LISA modulates the signal of each binary in both frequency and amplitude, the exact modulation depending on the source direction and frequency. Starting with the observed response of one LISA interferometer and assuming only doppler modulation due to the orbital motion of LISA, we show how the distribution of the entire binary population in frequency and sky position can be reconstructed using a tomographic approach. The method is linear and the reconstruction of a delta function distribution, corresponding to an isolated binary, yields a point spread function (psf). An arbitrary distribution and its reconstruction are related via smoothing with this psf. Exploratory results are reported demonstrating the recovery of binary sources, in the presence of white Gaussian noise.Comment: 13 Pages and 9 figures high resolution figures can be obtains from http://www.phys.utb.edu/~rajesh/lisa_tomography.pd

An observational study of clinicoetiological profile of stroke patients in a new tertiary care hospital in North Odisha, India

Background: Stroke is one of the leading causes of morbidity and mortality in India. The objective was to study the clinical profile, risk factors, neurological characters, pattern of brain stroke, areas of brain affected as per CT scan findings in patients with stroke.Methods: This observational study was carried out from June 2018 to Jan 2019 of all new patients admitted with stroke in Pandit Raghunath Murmu Medical College and Hospital, Baripada, Mayurbhanj, Odisha, India.Results: The incidence of stroke is maximum in 46-60 years of age group. The average age+SD was 59.3+13.5 in our study. 274 (46.52%) patients had ischemic stroke and 315 (53.48%) patients had hemorrhagic stroke. The male to female ratio was 1.46:1. Anterior circulation (86.42%) was the most common territory involved in the brain. The most common risk factor was hypertension with 77.76% followed by dyslipidemia (53.99%). The most common clinical presentation was hemiplegia (85.23%).Conclusions: The incidence of stroke is maximum in 46-60 years of age group. The average age+SD was 59.3+13.5 in our study. 274 (46.52%) patients had ischemic stroke and 315 (53.48%) patients had hemorrhagic stroke. The male to female ratio was 1.46:1. Anterior circulation (86.42%) was the most common territory involved in the brain. The most common risk factor was hypertension with 77.76% followed by dyslipidemia (53.99%). The most common clinical presentation was hemiplegia (85.23%).

Kinetic characteristics of ions in an inertial electrostatic confinement device

The kinetic analyses are quite important when it comes to understand the particle behavior in any device as they start to deviate from continuum nature. In the present study, kinetic simulations are performed using Particle-in-Cell (PIC) method to analyze the behavior of ions inside a cylindrical Inertial Electrostatic Confinement Fusion (IECF) device which is being developed as a tabletop neutron source. Here, the lighter ions, like deuterium are accelerated by applying an electrostatic field between the chamber wall (anode) and the cathode (cylindrical gridded wire), placed at the center of the device. The plasma potential profiles obtained from the simulated results indicate the formation of multiple potential well structures inside the cathode grid depending upon the applied cathode potential (from $-1$ to $-5~kV$). The ion density at the core region of the device is found to be of the order of $10^{16}~m^{-3}$, which closely resembles the experimental observations. Spatial variation of Ion Energy Distribution Function (IEDF) has been measured in order to observe the characteristics of ions at different cathode voltages. Finally, the simulated results are compared and found to be in good agreement with the experimental profiles. The present analysis can serve as a reference guide to optimize the technological parameters of the discharge process in IECF devices.Comment: 11 pages, 11 figure

Comparative larval biology of three Macrobrachium species under controlled conditions

Three large sized Macrobrachium species-. viz. Macrobrachium rosenbergi;, M malcolmsonii and M gangelicum are available in Indian riverine systems. The study on the seed production and growout of these species are being carried out to develop technologies for commercial application. Hence, the knowledge on comparative larval biology of the three species is extremely important to give a new line for developing hatchery technology for large-scale seed production in different agro-climatic conditions. The present communication deals with comparative study of larval growth and seed production of the three larger species

Variability of signal to noise ratio and the network analysis of gravitational wave burst signals

The detection and estimation of gravitational wave burst signals, with {\em a priori} unknown polarization waveforms, requires the use of data from a network of detectors. For determining how the data from such a network should be combined, approaches based on the maximum likelihood principle have proven to be useful. The most straightforward among these uses the global maximum of the likelihood over the space of all waveforms as both the detection statistic and signal estimator. However, in the case of burst signals, a physically counterintuitive situation results: for two aligned detectors the statistic includes the cross-correlation of the detector outputs, as expected, but this term disappears even for an infinitesimal misalignment. This {\em two detector paradox} arises from the inclusion of improbable waveforms in the solution space of maximization. Such waveforms produce widely different responses in detectors that are closely aligned. We show that by penalizing waveforms that exhibit large signal-to-noise ratio (snr) variability, as the corresponding source is moved on the sky, a physically motivated restriction is obtained that (i) resolves the two detector paradox and (ii) leads to a better performing statistic than the global maximum of the likelihood. Waveforms with high snr variability turn out to be precisely the ones that are improbable in the sense mentioned above. The coherent network analysis method thus obtained can be applied to any network, irrespective of the number or the mutual alignment of detectors.Comment: 13 pages, 6 figure

A Spin-Mechanical Device for Detection and Control of Spin Current by Nanomechanical Torque

We propose a spin-mechanical device to control and detect spin currents by mechanical torque. Our hybrid nano-electro-mechanical device, which contains a nanowire with a ferromagnetic-nonmagnetic interface, is designed to measure or induce spin polarized currents. Since spin carries angular momentum, a spin flip or spin transfer process involves a change in angular momentum--and hence, a torque--which enables mechanical measurement of spin flips. Conversely, an applied torque can result in spin polarization and spin current.Comment: 6 pages, 2 figure