1,060 research outputs found
The Klein-Gordon equation on the toric AdS-Schwarzschild black hole
We consider the Klein-Gordon equation on the exterior of the toric anti de-Sitter Schwarzschild black hole with Dirichlet, Neumann and Robin boundary con- ditions at I. We define a non-degenerate energy for the equation which controls the renormalised H1 norm of the field. We then establish both decay and integrated de- cay of this energy through vector field methods. Finally we demonstrate the necessity of ‘losing a derivative’ in the integrated energy estimate through the construction of a Gaussian beam staying in the exterior of the event horizon for arbitrary long co- ordinate time
Universal properties of the near-horizon optical geometry
We make use of the fact that the optical geometry near a static
non-degenerate Killing horizon is asymptotically hyperbolic to investigate
universal features of black hole physics. We show how the Gauss-Bonnet theorem
allows certain lensing scenarios to be ruled in or out. We find rates for the
loss of scalar, vector and fermionic `hair' as objects fall quasi- statically
towards the horizon. In the process we find the Lienard-Wiechert potential for
hyperbolic space and calculate the force between electrons mediated by
neutrinos, extending the flat space result of Feinberg and Sucher. We use the
enhanced conformal symmetry of the Schwarzschild and Reissner-Nordstrom
backgrounds to re-derive the electrostatic field due to a point charge in a
simple fashion
On the backreaction of frame dragging
The backreaction on black holes due to dragging heavy, rather than test,
objects is discussed. As a case study, a regular black Saturn system where the
central black hole has vanishing intrinsic angular momentum, J^{BH}=0, is
considered. It is shown that there is a correlation between the sign of two
response functions. One is interpreted as a moment of inertia of the black ring
in the black Saturn system. The other measures the variation of the black ring
horizon angular velocity with the central black hole mass, for fixed ring mass
and angular momentum. The two different phases defined by these response
functions collapse, for small central black hole mass, to the thin and fat ring
phases. In the fat phase, the zero area limit of the black Saturn ring has
reduced spin j^2>1, which is related to the behaviour of the ring angular
velocity. Using the `gravitomagnetic clock effect', for which a universality
property is exhibited, it is shown that frame dragging measured by an
asymptotic observer decreases, in both phases, when the central black hole mass
increases, for fixed ring mass and angular momentum. A close parallelism
between the results for the fat phase and those obtained recently for the
double Kerr solution is drawn, considering also a regular black Saturn system
with J^{BH}\neq 0.Comment: 18 pages, 8 figure
The Ghost in the Machine: Inferring Machine-Based Strategies from Observed Behavior
We introduce a procedure to infer the repeated-game strategies that generate actions in experimental choice data. We apply the technique to set of experiments where human subjects play a repeated Prisoner's Dilemma. The technique suggests that two types of strategies underly the data
Phased Array Feed Calibration, Beamforming and Imaging
Phased array feeds (PAFs) for reflector antennas offer the potential for
increased reflector field of view and faster survey speeds. To address some of
the development challenges that remain for scientifically useful PAFs,
including calibration and beamforming algorithms, sensitivity optimization, and
demonstration of wide field of view imaging, we report experimental results
from a 19 element room temperature L-band PAF mounted on the Green Bank
20-Meter Telescope. Formed beams achieved an aperture efficiency of 69% and
system noise temperature of 66 K. Radio camera images of several sky regions
are presented. We investigate the noise performance and sensitivity of the
system as a function of elevation angle with statistically optimal beamforming
and demonstrate cancelation of radio frequency interference sources with
adaptive spatial filtering.Comment: 19 pages, 13 figure
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Use of Photocell Readouts in the Development of High Resolution Scintillator Systems
Photomultiplier-based scintillator spectrometers are the systems of choice for a multitude of X-ray and gamma radiation measurement applications. Despite widespread use, they have numerous shortcomings. The most serious is the relatively poor energy resolution that makes isotope identification problematic particularly in the case of trace quantities. Energy resolution in scintillator/photomultiplier tube (PMT) spectrometers is governed by a combination of the crystal intrinsic resolution that includes non-linearity effects, photomultiplier statistics, and the variability in the probability of a scintillation photon generating a photoelectron at the photocathode. It is evident that energy resolution in these systems is linked to both the physics of light generation in the scintillator, as well as the characteristics of the PMT. PMTs also present design problems especially in the case of handheld and portable instruments due to their considerable weight and volume. Additionally, PMTs require well-regulated high voltage and are vulnerable to magnetic fields
Early Analysis of Japanese: Fujitani Nariakira's Ayuishoo
Fujitani Nariakira was a pioneering linguist of Edo Japan. In the early stages of kokugogaku development, he conducted groundbreaking analyses of the language. In Ayuishoo, one of his primary works, he details an elaborate analysis of particles and auxiliary verbs. He provides the first systematic classification of word types, based on function. He also provides an analysis of the conjugation system. In Ayuishoo, he gives a detailed analysis of over 200 linguistic elements, explaining the meaning and use of each item, cites poetry showing applications of each, and shows how each is manifested in the colloquial Japanese of his time. In all, he includes over 600 poems, drawing from over 70 sources from Japanese literature. His work spans studies of language, linguistics and literature. His methodology and his work are also applicable in the pedagogy of teaching premodern Japanese today. This paper discusses Ayuishoo and its significance
Performance of polarimetric beamformers for phased array radio telescopes
The results of four recently introduced beamforming schemes for phased array systems are discussed, each of which is capable to provide high sensitivity and accurate polarimetric performance of array-based radio telescopes. Ideally, a radio polarimeter should recover the actual polarization state of the celestial source, and thus compensate for unwanted polarization degradation effects which are intrinsic to the instrument. In this paper, we compare the proposed beamforming schemes through an example of a practical phased array system (APERTIF prototype) and demonstrate that the optimal beamformer, the max-SLNR beamformer, the eigenvector beamformer, and the bi-scalar beamformer are sensitivity equivalent but lead to different polarization state solutions, some of which are sub-optimal
Efficient Prediction of Array Element Patterns Using Physics-Based Expansions and a Single Far-Field Measurement
A method is proposed to predict the antenna array beam through employing a relatively small set of physics-based basis functions-called characteristic basis function patterns (CBFPs)-for modeling the embedded element patterns. The primary CBFP can be measured or extracted from numerical simulations, while additional (secondary) CBFPs are derived from the primary one. Furthermore, each numerically generated CBFP, which is typically simulated/measured for discrete directions only, can in turn be approximated by analytical basis functions with fixed expansion coefficients to evaluate the resulting array pattern at any angle through interpolation. This hierarchical basis reduces the number of unknown expansion coefficients significantly. Accordingly, the CBFP expansion coefficients can be determined through a single far-field measurement of only a few reference sources in the field of view. This is particularly important for multibeam array applications where only a limited number of reference sources are available for predicting the beam shape. Furthermore, this instantaneous beam calibration is fast, i.e., potentially capable to speed up the array calibration by one or two orders of magnitude, which is particularly important if the antenna radiation characteristics are subject to drifts
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