47,008 research outputs found
Quantifying the Morphologies and Dynamical Evolution of Galaxy Clusters. I. The Method
We describe and test a method to quantitatively classify clusters of galaxies
according to their projected morphologies. This method will be subsequently
used to place constraints on cosmological parameters ( and the power
spectrum of primordial fluctuations on scales at or slightly smaller than that
of clusters) and to test theories of cluster formation. We specifically address
structure that is easily discernible in projection and dynamically important to
the cluster. The method is derived from the two-dimensional multipole expansion
of the projected gravitational potential and yields dimensionless {\it power
ratios} as morphological statistics. If the projected mass profile is used to
characterize the cluster morphology, the power ratios are directly related to
the cluster potential. However, since detailed mass profiles currently exist
for only a few clusters, we use the X-ray--emitting gas as an alternative
tracer of cluster morphology. In this case, the relation of the power ratios to
the potential is qualitatively preserved. We demonstrate the feasibility of the
method by analyzing simulated observations of simple models of X-ray clusters
using the instrument parameters of the ROSAT PSPC. For illustrative purposes,
we apply the method to ROSAT PSPC images of A85, A514, A1750, and A2029. These
clusters, which differ substantially in their X-ray morphologies, are easily
distinguished by their respective power ratios. We discuss the suitability of
this method to address the connection between cluster morphology and cosmology
and to assess whether an individual cluster is sufficiently relaxed for
analysis of its intrinsic shape using hydrostatic methods. Approximately 50
X-ray observations of Abell clusters with the PSPC will be amenable to
morphological analysis using the method of this paper.Comment: To appear in ApJ October 20, 1995. 29 pages (7 figures missing),
PostScrip
Cross-border intellectual property rights: contract enforcement and absorptive capacity
This paper studies cross-border intellectual property rights (IPR) as a North-South contract using a Nash bargaining approach and distinguishes between the outcome and its actual enforcement. The absorptive capacity of the Southern country to exploit technology transfer plays a key role in the negotiated level of IPRs and its post-treaty enforcement. The optimal level of IPR protection relates positively to absorptive capacity. This provides a rationale for the longer time-frame provided to least developed countries in Article 66 of TRIPS to implement its provisions. In addition, monitoring is only effective in preventing contract violation up to a critical level of absorptive capacity. We relate this to the US Trade Representative “Special 301” report, which flags countries that deny adequate IPR protection as “priority watch list”. While disputes with less developed economies are promptly resolved, emerging economies, where most losses from copyright piracy originates from, continue to remain on the list.
TEC enhancement due to energetic electrons above Taiwan and the West Pacific
The energetic electrons of the inner radiation belt during a geomagnetic
disturbance can penetrate in the forbidden range of drift shells located at the
heights of the topside equatorial ionosphere (<1000 km). A good correlation was
previously revealed between positive ionospheric storms and intense fluxes of
quasi-trapped 30-keV electrons at ~900 km height in the forbidden zone. In the
present work, we use statistics to validate an assumption that the intense
electron fluxes in the topside equatorial ionosphere can be an important source
of the ionization in the low-latitude ionosphere. The data on the energetic
electrons were obtained from polar orbiting satellites over the periods of the
62 strong geomagnetic storms from 1999 to 2006. Ionospheric response to the
selected storms was determined using global ionospheric maps of vertical total
electron content (VTEC). A case-event study of a major storm on 9 November 2004
provided experimental evidence in support to the substantial ionization effect
of energetic electrons during positive ionospheric storms at the low latitudes.
Statistical analysis of nine magnetic storms indicated that the VTEC increases
coincided with and coexisted with intense 30-keV electron fluxes irrespective
of local time and phase of geomagnetic storm. We concluded that extremely
intense fluxes of the 30-keV electrons in the topside low-latitude ionosphere
can contribute ~ 10 - 30 TECU to the localized positive ionospheric storms.Comment: 15 pages, 4 figures, 1 table accepted for publication in Terrestrial,
Atmospheric and Oceanic Sciences (TAO), Dec. 2012 A special issue on
"Connection of solar and heliospheric activities with near-Earth space
weather: Sun-Earth connection
A New Approximate Fracture Mechanics Analysis Methodology for Composites with a Crack or Hole
A new approximate theory which links the inherent flaw concept with the theory of crack tip stress singularities at a bi-material interface was developed. Three assumptions were made: (1) the existence of inherent flaw (i.e., damage zone) at the tip of the crack, (2) a fracture of the filamentary composites initiates at a crack lying in the matrix material at the interface of the matrix/filament, and (3) the laminate fails whenever the principal load-carrying laminae fails. This third assumption implies that for a laminate consisting of 0 degree plies, cracks into matrix perpendicular to the 0 degree filaments are the triggering mechanism for the final failure. Based on this theory, a parameter bar K sub Q which is similar to the stress intensity factor for isotropic materials but with a different dimension was defined. Utilizing existing test data, it was found that bar K sub Q can be treated as a material constant. Based on this finding a fracture mechanics analysis methodology was developed. The analytical results are correlated well with test results. This new approximate theory can apply to both brittle and metal matrix composite laminates with crack or hole
Myriad phases of the Checkerboard Hubbard Model
The zero temperature phase diagram of the checkerboard Hubbard model is
obtained in the solvable limit in which it consists of weakly coupled square
plaquettes. As a function of the on-site Coulomb repulsion U and the density of
holes per site, x, we demonstrate the existence of at least 16 distinct phases.
For instance, at zero doping, the ground state is a novel d-wave Mott insulator
(d-Mott), which is not adiabatically continuable to a band insulator; by doping
the d-Mott state with holes, depending on the magnitude of U, it gives way to a
d-wave superconducting state, a two-flavor spin-1/2 Fermi liquid (FL), or a
spin-3/2 FL.Comment: 4 pages, 2 figures, minor revisions, published in Phys. Rev. B as a
Rapid Communicatio
Combining Stream Mining and Neural Networks for Short Term Delay Prediction
The systems monitoring the location of public transport vehicles rely on
wireless transmission. The location readings from GPS-based devices are
received with some latency caused by periodical data transmission and temporal
problems preventing data transmission. This negatively affects identification
of delayed vehicles. The primary objective of the work is to propose short term
hybrid delay prediction method. The method relies on adaptive selection of
Hoeffding trees, being stream classification technique and multilayer
perceptrons. In this way, the hybrid method proposed in this study provides
anytime predictions and eliminates the need to collect extensive training data
before any predictions can be made. Moreover, the use of neural networks
increases the accuracy of the predictions compared with the use of Hoeffding
trees only
Strain modification in coherent Ge and SixGe1–x epitaxial films by ion-assisted molecular beam epitaxy
We have observed large changes in Ge and SixGe1–x layer strain during concurrent molecular beam epitaxial growth and low-energy bombardment. Layers are uniformly strained, coherent with the substrate, and contain no dislocations, suggesting that misfit strain is accommodated by free volume changes associated with injection of ion bombardment induced point defects. The dependence of layer strain on ion energy, ion-atom flux ratio, and temperature is consistent with the presence of a uniform dispersion of point defects at high concentration. Implications for distinguishing ion-surface interactions from ion-bulk interactions are discussed
Charge Transport Scalings in Turbulent Electroconvection
We describe a local-power law scaling theory for the mean dimensionless
electric current in turbulent electroconvection. The experimental system
consists of a weakly conducting, submicron thick liquid crystal film supported
in the annulus between concentric circular electrodes. It is driven into
electroconvection by an applied voltage between its inner and outer edges. At
sufficiently large voltage differences, the flow is unsteady and electric
charge is turbulently transported between the electrodes. Our theoretical
development, which closely parallels the Grossmann-Lohse model for turbulent
thermal convection, predicts the local-power law . and are dimensionless
numbers that are similar to the Rayleigh and Prandtl numbers of thermal
convection, respectively. The dimensionless function , which is
specified by the model, describes the dependence of on the aspect ratio
. We find that measurements of are consistent with the theoretical
model.Comment: 12 pages, 7 figures, Submitted to Phys. Rev. E. See also
http://www.physics.utoronto.ca/nonlinea
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