5,343 research outputs found
Fine Grained Component Engineering of Adaptive Overlays: Experiences and Perspectives
Recent years have seen significant research being carried out into peer-to-peer (P2P) systems. This work has focused on the styles and applications of P2P computing, from grid computation to content distribution; however, little investigation has been performed into how these systems are built. Component based engineering is an approach that has seen successful deployment in the field of middleware development; functionality is encapsulated in âbuilding blocksâ that can be dynamically plugged together to form complete systems. This allows efficient, flexible and adaptable systems to be built with lower overhead and development complexity. This paper presents an investigation into the potential of using component based engineering in the design and construction of peer-to-peer overlays. It is highlighted that the quality of these properties is dictated by the component architecture used to implement the system. Three reusable decomposition architectures are designed and evaluated using Chord and Pastry case studies. These demonstrate that significant improvements can be made over traditional design approaches resulting in much more reusable, (re)configurable and extensible systems
New and Old Tests of Cosmological Models and Evolution of Galaxies
We describe the classical cosmological tests, such as the Log-Log,
redshift-magnitude and angular diameter tests, and propose some new tests of
the evolution of galaxies and the universe. Most analyses of these tests treat
the problem in terms of a luminosity function and its evolution which can lead
to incorrect conclusions when dealing with high redshift sources. We develop a
proper treatment in three parts. In the first part we describe these tests
based on the isophotal values of the quantities such as flux, size or surface
brightness. We show the shortcomings of the simple point source approximation
based solely on the luminosity function and consideration of the flux limit. We
emphasize the multivariate nature of the problem and quantify the effects of
other selection biases due to the surface brightness and angular size
limitations. In these considerations the surface brightness profile plays a
critical role. In the second part we show that considerable simplification over
the complicated isophotal scheme is achieved if these test are carried out in
some sort of metric scheme, for example that suggested by Petrosian (1976).
This scheme, however, is limited to well resolved sources. Finally, we describe
the new tests, which use the data to a fuller extent than the isophotal or
metric based tests, and amount to simply counting the pixels or adding their
intensities as a function of the pixel surface brightness, instead of dealing
with surface brightness, sizes and fluxes of individual galaxies. We show that
the data analysis and its comparison with the theoretical models of the
distributions and evolution of galaxies has the simplicity of the metric test
and utilizes the data more fully than the isophotal test.Comment: 29 pages including 8 figures.
http://www-bigbang.stanford.edu/~vahe/papers/finals/newtest.ps. To appear in
ApJ, Oct. 199
The Relationship of Perceived Social Support, Health Status, and Quality of Life in Female Systemic Lupus Erythematosus Patients
This study was designed to explore the relationship among perceived social support, health status, and quality of life in a sample of female systemic lupus erythematosus (SLE) patients. A strong positive correlation was found between perceived social support and quality of life. Negative correlations were found between perceived health status and perceived social support, and perceived health status and quality of life. Last, a negative correlation was found between objective health status and quality of life. In multiple regression analyses, perceived social support explained a significant amount of variance in the quality of life variable in conjunction with both observed health status and perceived health status. This study has important implications for workers in the health care industry. It is important for health care providers to pay attention to not only the physical, but also to the psychosocial components of health care delivery in relation to SLE patients. Because there is no known cure for SLE, attention needs to be focused on helping the SLE patient improve her life quality. This study has shown that both perceived health status and quality of life are related to social support and suggests that when working with patients with chronic illness such as SLE, the introduction of social support information may prove to be a very important component to a holistic treatment of mind and body
Spin-Coupled Local Distortions in Multiferroic Hexagonal HoMnO3
Local structural measurements have been performed on hexagonal HoMnO3 in
order to ascertain the specific changes in bond distances which accompany
magnetic ordering transitions. The transition from paramagnetic to the
antiferromagetic (noncollinear) phase near ~70 K is dominated by changes in the
a-b plane Mn-Mn bond distances. The spin rotation transition near ~40 K
involves both Mn-Mn and nearest neighbor Ho-Mn interactions while the low
temperature transition below 10 K involves all interactions, Mn-Mn, Ho-Mn
(nearest and next nearest) and Ho-Ho correlations. These changes in bond
distances reveal strong spin-lattice coupling. The similarity in magnitude of
the change in J(Mn-Mn) and J(Ho-Mn) enhances the system frustration. The
structural changes are interpreted in terms of a model of competing spin order
and local structural distortions. Density functional calculations are used to
estimate the energies associated with ionic displacements. The calculations
also reveal asymmetric polarization of the charge density of Ho, O3 and O4
sites along the z-axis in the ferroelectric phase. This polarization
facilitates coupling between Ho atoms on neighboring planes normal to the
z-axis.Comment: 8 figure
Improved Parameters and New Lensed Features for Q0957+561 from WFPC2 Imaging
New HST WFPC2 observations of the lensed double QSO 0957+561 will allow
improved constraints on the lens mass distribution and hence will improve the
derived value of H. We first present improved optical positions and
photometry for the known components of this lens. The optical separation
between the A and B quasar images agrees with VLBI data at the 10 mas level,
and the optical center of the primary lensing galaxy G1 coincides with the VLBI
source G' to within 10 mas. The best previous model for this lens (Grogin and
Narayan 1996) is excluded by these data and must be reevaluated.
Several new resolved features are found within 10\arcsec of G1, including an
apparent fold arc with two bright knots. Several other small galaxies are
detected, including two which may be multiple images of each other. We present
positions and crude photometry of these objects.Comment: 7 pages including 2 postscript figures, LaTeX, emulateapj style. Also
available at
http://www.astro.lsa.umich.edu:80/users/philf/www/papers/list.htm
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Current Calibration Practices for Flame Atomic Absorption Spectrometry - 1. Initial Results from a Survey
Information about 309 different routine analyses by flame atomic absorption spectrometryhas been obtained from a questionnaire survey. The information is analysed according to themethods of overcoming interferences, the methods of curve fitting and the reasons forchoosing a particular calibration method. The results indicate that most methods suffer frominterference effects and that the addition of matrix modifiers or the matching of standards isthe most popular approach to overcoming these effects. Manual curve fitting procedures arestill widely used and 5-point calibrations are the most used. No clear cut reasons for choice ofcalibration strategy emerge from this preliminary analysis of the returns to date
Analytical Aspects of Absorption Spectroelectrochemistry at a Platinum Electrode- II: Quantitative Basis and Study of Organic Compounds
The theoretical basis for a new spectroelectrochemical technique, in which a narrow lightbeamis passed at grazing incidence over a plane electrode surface, has been derived. Agreement betweentheoretical and experimental behaviour has been obtained for a number of organic molecules withwell-defined redox behaviour. The advantages of this technique over other spectroelectrochemical techniquesare discussed with respect to potential applications in quantitative analysis and electrochemicalstudies
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