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101.
102.
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
103.
It is shown that unless complex modes are included in the mode-matching analysis to determine the resonant frequencies of dielectric-loaded resonators, some resonant frequencies could be missed. Field distributions, mode charts, and mode coefficients of dielectric-loaded resonators in which complex modes exist are presented. Experimental measurements for the verification of the computed results are presented and show good agreement with theory 相似文献
104.
A numerical-integral equation approach is used to explore plane-wave scattering from a nonplanar surface with a sinusoidal height profile for the case of the magnetic field parallel to the surface ridges (TM polarization). The results are compared to those found previously by the authors for the TE polarization. The TM case is more sensitive to the height of the sinusoid and shows shape resonate effects which are characterized by a large increases in the surface current. A "Brewster angle" complete null of the specular reflection is also present and tends to be broader and more strongly emphasizes the anomalies which occur at the Rayleigh wavelengths. The failure of two anomalies to coalesce at the crossing of two Rayleigh wavelength conditions is also explored. 相似文献
105.
Dye removal from wastewater using activated carbon developed from sawdust: adsorption equilibrium and kinetics 总被引:13,自引:0,他引:13
Malik PK 《Journal of hazardous materials》2004,113(1-3):81-88
Mahogany sawdust was used to develop an effective carbon adsorbent. This adsorbent was employed for the removal of direct dyes from spent textile dyeing wastewater. The experimental data were analysed by the Langmuir and Freundlich models of adsorption. Equilibrium data fitted well with the Langmuir model. The rates of adsorption were found to conform to the pseudo-second-order kinetics with good correlation. The equilibrium adsorption capacity of the sawdust carbon was determined with the Langmuir equation as well as the pseudo-second-order rate equation and found to be >300 mg dye per gram of the adsorbent. The most ideal pH for adsorption of direct dyes onto sawdust carbon was found to be 3 and below. The results indicate that the Mahogany sawdust carbon could be employed as a low cost alternative to commercial activated carbon in the removal of dyes from wastewater. 相似文献
106.
Anthony D. Caunt John A. Licchelli Ian W. Parsons Robert N. Haward Malik R.Y. Al-Hillo 《Polymer》1983,24(1):121-125
Reduction of TiCl4 with organomagnesiums either in the presence of preformed MgCl2, or concurrently with the formation of MgCl2 from chlorocarbons, yields materials which are active catalysts for the polymerization of propene and ethene. Transformation of these materials to a violet allotrope by heating with TiCl4 gives materials much more active for propene polymerization, albeit stereoregulation is still not good. interestingly, these transformed materials show little advantage for ethene polymerization except at high temperatures. Use of a Lewis base does not give high stereoregulation with propene; although some advantage is gained activity is greatly diminished by this. 相似文献
107.
Osama Zaki Keith Brown John Fletcher David Lane 《Engineering Applications of Artificial Intelligence》2007,20(8):1112-1124
This paper demonstrates the use of multi-agent systems (MAS), firstly as a modelling technique for dynamic physical systems and secondly as the basis for a generic and powerful diagnostic system, which can support heterogeneous distributed systems. First an overview of the diagnostic techniques including those offered by the two communities fault detection and isolation (FDI ) and DX (based on intelligent techniques) is given. The use of digital signal processing (DSP) as a significant technique for improved fault diagnosis is illustrated. A rule-based engine is used to control the behaviours of the agents and also as a tool for diagnosis. Finally, the integration of DSP agents and the rule-based engine into MAS is demonstrated using a real-life application, a class-AB amplifier (a power electronic circuit). It is shown that the integration of DSP agents and rules into MAS provides a powerful tool for prognosis and for detection of abrupt (short and open circuit) and incipient faults. 相似文献
108.
Costas Busch Malik Magdon-Ismail Marios Mavronicolas 《Journal of Parallel and Distributed Computing》2007
In bufferless networks the packets cannot be buffered while they are in transit; thus, once injected, the packets have to move constantly. Bufferless networks are interesting because they model optical networks. The objective of this work is to demonstrate that efficient bufferless packet switching is achievable in particular, interesting network topologies. 相似文献
109.
Determination of the dopant weight fraction in polyaniline films using a quartz-crystal microbalance
The electrical conductivity of polyaniline depends on factors such as degree of oxidation, type of protonation, and dopant weight fraction. The last of these factors is connected with the loss of mass during the deprotonation of polyaniline, and can thus conveniently be determined in situ by the use of a quartz microbalance. This is illustrated in the present paper which concerns the determination of the weight fraction of acid in thin polyaniline films prepared by the chemical oxidation of aniline in the aqueous solutions of sulfuric and phosphoric acids. It is illustrated that the deprotonation-reprotonation processes are fast, complete, and reversible. Polyaniline has sulfate counter-ions in 0.1 M sulfuric acid while, in 0.5-1 M sulfuric acid, hydrogen sulfate counter-ions are present. The quartz microbalance involving polyaniline films can be used in the sensing of the acidity. 相似文献
110.
Salah M Ramadan Ahmed El Sherbini Mahmoud Marie Mohamed Zaki 《Wireless Personal Communications》2007,41(1):57-75
One of the challenging tasks in Personal Communication Services (PCS) is to efficiently maintain the location of PCS subscribers
who move from one region to another (hereafter called mobile users). When a mobile user receives a call, the network has to
quickly determine its current location. The existing location management scheme suffers from high signaling traffic in locating
the mobile users. Two-level forwarding pointer scheme has been proposed from per-user forwarding pointer scheme to reduce
the cost of signaling traffic. In this paper, we enhance the two-level forwarding pointer scheme. When a mobile user moves
from its current Registered Area (RA), which is served by Mobile Switching Center (MSC), to another RA the local switch that
acts as a parent of those two MSCs maintains this movement in its memory (hereafter called cache entry). A cache entry is
used to locate rapidly the mobile user instead of querying the Home Location Register (HLR) and waiting for its reply. HLR
is centralized in the network and far away from the mobile users so that the signaling traffic crossing it is expensive. Sometimes
the cache entry may be failed to reach the mobile user then a two-level forwarding pointers will be created from the corresponding
Visitor Location Register (VLR), attached to its MSC, through a correct path to locate the mobile user. Thus, there is a saving
in cost of querying the underlying HLR. The analytical results indicate that such proposal efficiently reduces the signaling
traffic cost for all values of Call to Mobility Ratio (CMR), this is especially considerable when CMR ≥1, without any increase
in the call setup delay.
Salah M. Ramadan (samohra@yahoo.com) received the BS and MS degrees from Computers Engineering Department, Al-Azhar University, Cairo, Egypt,
in 1995 and 2002, respectively. From 2002, he was a Ph.D. student in Computers Engineering Department at Al-Azhar University
and is currently pursuing the Ph.D. degree, where he is a research assistant in the Wireless Networks Branch. His research
interests include traffic management in ATM networks, routing protocols, mobility management in PCS networks, and mobile computing.
He is currently an instructor in Cisco Academy, Egypt.
Ahmed M. El-Sherbini (Sherbini@mcit.gov.eg) received the Ph.D. in Electrical and Communication Engineering, Case Western University, U.S.A. March
1983 and M.Sc. in Communication Engineering, Cairo University, Giza, Egypt, June 1980. (M. Sc. Research Studies at the Ecole
Nationale Superieure des Telecommunications (ENST), Paris, France). He is the Director, National Telecommunication Institute
– Ministry of Communications and Information Technology, Egypt and Professor of Electrical and Communication Engineering Dept.
Faculty of Engineering, Cairo University, Egypt.
M. I. Marie received his B.Sc., M.Sc. and Ph.D. in electronic and communication engineering from Cairo University on 1972, 1981, 1985,
respectively. Now he is a professor of communications at Computer and System Engineering department Al-Azhar University, Cairo,
Egypt. His fields of interest includes digital communication, computer networks and protocols development.
M. Zaki (azhar@mailer.scu.eun.eg) is the professor of software engineering, Computer and System Engineering Department, Faculty of
Engineering, Al-Azhar University at Cairo. He received his B.Sc. and M.Sc. degrees in electrical engineering from Cairo University
in 1968 and 1973 respectively. He received his Ph.D. degrees in computer engineering from Warsaw Technical University, Poland
in 1977. His fields of interest include artificial intelligence, soft computing, and distributed system. 相似文献