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 ‘building blocks’ 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$N$-Log$S$, 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$_0$. 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

A Comparison of Curve Fitting Algorithms for Flame Atomic Absorption Spectrometry

A comparison of six commercially available curve fitting algorithms for calibration in flame atomic absorption spectrometry (FAAS) has been made. Programs using the algorithms were written in BAsrc for a microcomputer and, where possible, tested against the commercial version. Calibration curves for magnesium, chromium and nickel produced by the algorithms were compared, on the basis of the sum of squares of the percentage deviations and its root mean square, with each other and with linear interpolation and manual fitting. The standard deviations of the goodness of fit parameters were calculated to indicate significant differences between the fits obtained. With the exception of the simple parabola, linear interpolation and manual methods, which were significantly poorer, the algorithms performed similarly. In general the errors in curve fitting were well below 5% for the commercial algorithms

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