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991.
We study the problem of how to minimize the cost of maintaining consistency among at least N copies of an object in an enviroment where the mix of read and write operations can vary. Quorum consensus requires that
read and write operations must assemble appropriate quorums before an operation can succeed. The cost of an operation is proportional
to the size of a quorum, and the objective is obviously to minimize the cost while still maintaining consistency. It is known
that the quorum size can be reduced by organizing a number of copies into logical structures such as grids and hierarchies.
In this paper, we show (a) how methods based on grids and hierarchies can be treated in a common framework, and (b) how these
hierarchies can be optimized so as to minimize the cost of consensus. Of course, the optimal solution depends upon the mix
of read and write operations that is present. Consequently, given N copies of an object and a ratio of write operations F, our algorithms determine the optimal values for the number of levels
in the hierarchy and the read/write quorum sizes at each level. The algorithms, which run in O(N
1.63) and O(N
2) time, were tested, and the results are reported and discussed.
Received September 1, 1992/February 16, 1995 相似文献
992.
Rovee-Collier Carolyn; Bhatt Ramesh S.; Chazin Sharon 《Canadian Metallurgical Quarterly》1996,22(5):1178
The effects of set size and novelty on visual pop-out in 6-month-old infants was assessed in a perceptual-identification (memory reactivation) paradigm in which infants, trained and tested in their own homes, viewed a mobile containing a unique novel or familiar object amidst different numbers of familiar or novel distractors, respectively. Unique objects of both types popped out at all set sizes except the largest, where there was modest evidence that familiar distractors speeded processing (Experiment 1). When the proportion of familiar targets in a display of intermediate set size was increased, however, infants no longer detected the familiar target (Experiment 2). These findings offer additional support for the proposition that visual pop-out in infants and adults is the same phenomenon. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
993.
C Prabhakar G Madhusudhan K Sahadev CM Reddy MR Sarma GO Reddy R Chakrabarti CS Rao TD Kumar R Rajagopalan 《Canadian Metallurgical Quarterly》1998,8(19):2725-2730
Novel compounds having a dual pharmacophore were synthesised and evaluated for their insulin sensitiser and anti-inflammatory properties in different animal models. 相似文献
994.
M. S. Sodha Ashvini Kumar A. Srivastava G. N. Tiwari 《Energy Conversion and Management》1980,20(3):181-190
This paper presents an analysis of periodic heat flux through a roof, on which a solar still has been placed. It is seen that on a typical hot day in Delhi, for high reflectivity of the bottom of the basin (on account of deposits or otherwise) the daily heat flux in the room gets reduced by 40% and the production of distilled water is 0.6 kg/m2 day; the produced swings in the heat flux also get reduced in magnitude. For a typical cold day in Delhi, if a black dye is mixed with basin water the daily heat flux in the room increases by a factor of two and the yield of the distillate becomes 5.0 kg/m2 day. 相似文献
995.
This paper obtains lower and upper bounds for decomposable multi-component complex systems. Some particular cases are discussed. 相似文献
996.
Arun Kumar Patwardhan 《国际钢铁研究》1982,53(7):283-287
Structural investigations in extra low carbon mar steels with nominal compositions A1 (4 Mn-1.0 Si), A2 (4 Mn-1.0 Si – 0.042 Nb), A3 (~ 5 Mn-1.5 Si), A4 (2.6 Mn-1.0 Si) and A5 (~ 5 Mn-2.5 Si) in the heat treated condition by X-ray diffraction technique (Debye-Scherrer method) for identifying strengthening mechanisms. Results on the formation of M23C6 type carbide either singly (in most cases) or in combination with austenite. Discussion pertaining to 1. identification of factors promoting the structural changes and, 2. their likely effect on mechanical properties. 相似文献
997.
A maintained system is considered which can exit from the operable state to two states: failed and less productive. Profit equations are developed to study the system behaviour and a condition is derived under which the system can be profitably operated in a less productive state. A numerical example has been included to illustrate the results. 相似文献
998.
Chitosan chemistry and pharmaceutical perspectives 总被引:44,自引:0,他引:44
999.
A couple of non-convex search strategies, based on the genetic algorithm, are suggested and numerically explored in the context
of large-deflection analysis of planar, elastic beams. The first of these strategies is based on the stationarity of the energy
functional in the equilibrium state and may therefore be considered weak. The second approach, on the other hand, attempts
to directly solve the governing differential equation within an optimisation framework and such a solution may be thought
of as strong. Several numerical illustrations and verifications with ‘exact’ solutions, if available, are provided
For communication 相似文献
1000.
Surface-modified superparamagnetic nanoparticles for drug delivery: preparation, characterization, and cytotoxicity studies 总被引:10,自引:0,他引:10
Superparamagnetic iron oxide nanoparticles have been used for many years as magnetic resonance imaging (MRI) contrast agents or in drug delivery applications. In this study, a novel approach to prepare magnetic polymeric nanoparticles with magnetic core and polymeric shell using inverse microemulsion polymerization process is reported. Poly(ethyleneglycol) (PEG)-modified superparamagnetic iron oxide nanoparticles with specific shape and size have been prepared inside the aqueous cores of AOT/n-Hexane reverse micelles and characterized by various physicochemical means such as transmission electron microscopy (TEM), infrared spectroscopy, atomic force microscopy (AFM), vibrating sample magnetometry (VSM), and ultraviolet/visible spectroscopy. The inverse microemulsion polymerization of a polymerizable derivative of PEG and a cross-linking agent resulted in a stable hydrophilic polymeric shell of the nanoparticles. The results taken together from TEM and AFM studies showed that the particles are spherical in shape with core-shell structure. The average size of the PEG-modified nanoparticles was found to be around 40-50 nm with narrow size distribution. The magnetic measurement studies revealed the superparamagnetic behavior of the nanoparticles with saturation magnetization values between 45-50 electromagnetic units per gram. The cytotoxicity profile of the nanoparticles on human dermal fibroblasts as measured by standard 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay showed that the particles are nontoxic and may be useful for various in vivo and in vitro biomedical applications. 相似文献