7,907 research outputs found
Space telescope phase B definition study. Volume 2A: Science instruments, f24 field camera
The analysis and design of the F/24 field camera for the space telescope are discussed. The camera was designed for application to the radial bay of the optical telescope assembly and has an on axis field of view of 3 arc-minutes by 3 arc-minutes
Local Density of States and Angle-Resolved Photoemission Spectral Function of an Inhomogeneous D-wave Superconductor
Nanoscale inhomogeneity seems to be a central feature of the d-wave
superconductivity in the cuprates. Such a feature can strongly affect the local
density of states (LDOS) and the spectral weight functions. Within the
Bogoliubov-de Gennes formalism we examine various inhomogeneous configurations
of the superconducting order parameter to see which ones better agree with the
experimental data. Nanoscale large amplitude oscillations in the order
parameter seem to fit the LDOS data for the underdoped cuprates. The
one-particle spectral function for a general inhomogeneous configuration
exhibits a coherent peak in the nodal direction. In contrast, the spectral
function in the antinodal region is easily rendered incoherent by the
inhomogeneity. This throws new light on the dichotomy between the nodal and
antinodal quasiparticles in the underdoped cuprates.Comment: 5 pages, 9 pictures. Phys. Rev. B (in press
The Preemption of Collective State Antitrust Enforcement In Telecommunications
The dichotomy between the levels of government provided murky guidance to telecommunications firms on what behavior is anticompetitive and what decisions firms will have to spend years defending. Despite T-Mobile and Sprint agreeing to sell off several subsidiaries, helping to create a new competitor, and surviving a gamut of regulatory reviews, these companies still could not merge. At this point, preventing the deal would cause irreversible harm to the merging parties.
The conflicts that arose in the T-Mobile-Sprint merger could have been solved through the preemption of collective state antitrust enforcement in the telecommunications market, which would balance the twin goals of promoting the consumer and aggregate social welfares. The telecommunications market is subject to substantial federal scrutiny and regulation, which limits competitive choices to an abnormal degree and causes the market to suffer extraordinary damage when collective states interject themselves as enforcers. Limiting state antitrust activities is not a novel concept, with a variety of studies arguing that the inefficiencies and competing interests associated with state action substantially hamper state antitrust enforcement of national markets. This Comment does not presume to redefine the antitrust system in its entirety, but narrowly applies the possibility of preempting state action to the telecommunications market
Fermion Soliton Stars with Asymmetric Vacua
Fermion soliton stars are a motivated model of exotic compact objects in
which a nonlinear self-interacting real scalar field couples to a fermion via a
Yukawa term, giving rise to an effective fermion mass that depends on the fluid
properties. Here we continue our investigation of this model within General
Relativity by considering a scalar potential with generic asymmetric vacua.
This case provides fermion soliton stars with a parametrically different
scaling of the maximum mass relative to the model parameters, showing that the
special case of symmetric vacua, in which we recover our previous results,
requires fine tuning. In the more generic case studied here the mass and radius
of a fermion soliton star are comparable to those of a neutron star for natural
model parameters at the GeV scale. Finally, the asymmetric scalar potential
inside the star can provide either a positive or a negative effective
cosmological constant in the interior, being thus reminiscent of gravastars or
anti-de Sitter bubbles, respectively. In the latter case we find the existence
of multiple, disconnected, branches of solutions.Comment: 9 pages, 7 figures. v2: matches version accepted in PR
Defending OC-SVM based IDS from poisoning attacks
Machine learning techniques are widely used to detect intrusions in the cyber security field. However, most machine learning models are vulnerable to poisoning attacks, in which malicious samples are injected into the training dataset to manipulate the classifier's performance. In this paper, we first evaluate the accuracy degradation of OC-SVM classifiers with 3 different poisoning strategies with the ADLA-FD public dataset and a real world dataset. Secondly, we propose a saniti-zation mechanism based on the DBSCAN clustering algorithm. In addition, we investigate the influences of different distance metrics and different dimensionality reduction techniques and evaluate the sensitivity of the DBSCAN parameters. The ex-perimental results show that the poisoning attacks can degrade the performance of the OC-SVM classifier to a large degree, with an accuracy equal to 0.5 in most settings. The proposed sanitization method can filter out poisoned samples effectively for both datasets. The accuracy after sanitization is very close or even higher to the original value.</p
Transporting Bits or Transporting Energy: Does it matter? A comparison of the sustainability of local and remote computing
This document presents the results of a study of the sustainability of data management and data movement between data centres, the ultimate goal being to minimize the CO2 footprint
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