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51.
52.
Wireless Sensor Networks (WSNs) has been attracting lots of interest in recent years. In such networks sensors data are collected
over multi-hop routes at one or multiple base-stations (gateway nodes) for processing. In many WSN applications such as disaster
management and combat field surveillance, rapid response to detected events is necessary and thus data latency should be minimal.
Given the sensor’s energy and radio range constraints, direct communication with the gateway is inefficient and often infeasible
for most deployed sensors. An intuitive approach to limit data latency is to increase the population of gateways and place
them in the vicinity of sensors. However, gateway nodes are typically costly and thus it is desired to limit their count.
Therefore, there is a need to balance between such conflicting requirements. In this paper, we pursue an integrated approach
to asset planning in WSNs so that the data latency is minimized. The goal is to determine the least number of gateways and
identify where to place them in the network in order to achieve a certain delay bound on data delivery. We formulate an optimization
model for the asset planning problem and present effective algorithms for solving it. The proposed solution scheme employs
contemporary search heuristics such as k-means and genetic algorithms. Validation results confirm the effectiveness of our approach in achieving the desired design
goals. 相似文献
53.
Web caching has been the solution of choice to web latency problems. The efficiency of a Web cache is strongly affected by the replacement algorithm used to decide which objects to evict once the cache is saturated. Numerous web cache replacement algorithms have appeared in the literature. Despite their diversity, a large number of them belong to a class known as stack‐based algorithms. These algorithms are evaluated mainly via trace‐driven simulation. The very few analytical models reported in the literature were targeted at one particular replacement algorithm, namely least recently used (LRU) or least frequently used (LFU). Further they provide a formula for the evaluation of the Hit Ratio only. The main contribution of this paper is an analytical model for the performance evaluation of any stack‐based web cache replacement algorithm. The model provides formulae for the prediction of the object Hit Ratio, the byte Hit Ratio, and the delay saving ratio. The model is validated against extensive discrete event trace‐driven simulations of the three popular stack‐based algorithms, LRU, LFU, and SIZE, using NLANR and DEC traces. Results show that the analytical model achieves very good accuracy. The mean error deviation between analytical and simulation results is at most 6% for LRU, 6% for the LFU, and 10% for the SIZE stack‐based algorithms. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
54.
Samia Dabbou Faten Brahmi Ameni Taamali Manel Issaoui Youssef Ouni Mohamed Braham Mokhtar Zarrouk Mohamed Hammami 《Journal of the American Oil Chemists' Society》2010,87(10):1199-1209
The effects of the contents of lipids, pigments, α-tocopherol and phenols were studied in relation to the antioxidant capacity
of five virgin olive oils obtained from five olive cultivars planted in Tunisia (Arbequina, Koroneiki, Leccino, Oueslati and
Chemchali). The antioxidant capacities were evaluated by two different radical scavenging activities: radical scavenging activity
by the DPPH assay (RSA-DPPH) and total antioxidant status by the ABTS test (TAA-ABTS). The highest contents of antioxidant
compounds (75.96, 10.34, 6.32, 15.39 and 241.52 mg kg−1 for oleic acid, O/L ratio, carotenes, chlorophylls and total phenols, respectively) were found for the Koroneiki cultivar
except for α-tocopherol and o-diphenols, which had the highest contents (369 and 160.7 mg kg−1, respectively) in the Leccino and Chemchali cultivars (cvs). Furthermore, the highest antioxidant capacity in virgin olive
oil was observed in the Koroneiki cultivar (0.24 mmol TE kg−1) followed by the Chemchali and Leccino cvs (0.22 and 0.13 mmol TE kg−1) for the TAA-ABTS test. However, the RSA-DPPH activity was higher for the Chemchali cultivar (19.9%) than for the Koroneiki
and Leccino cvs (18.4 and 13.5%, respectively). Correlation between these capacities and the oil composition revealed that
they were mainly influenced by the carotene content, followed by chlorophyll and phenolic contents where the ABTS test was
more pronounced. Then, the antioxidant capacity of the virgin olive oils was correlated with polar components and the lipid
profile which are important for its shelf life. 相似文献
55.
Mahmoud A. Abd El-Ghaffar Nivin M. Ahmed Elham A. Youssef 《Journal of Coatings Technology and Research》2010,7(6):703-713
This work presents a method of preparing single-, double-, and triple-cation ferrite pigments by employing simple chemical
techniques to study their corrosion protection properties. The prepared pigments were characterized using X-ray diffraction
and scanning electron microscopy. All prepared ferrite pigments were evaluated using ASTM methods. Anticorrosive paint formulations
were performed using different prepared pigment loadings. The physico-mechanical and corrosion properties of dry paint films
were examined. The tests revealed that the prepared ferrite pigments show excellent anticorrosive behavior, and that the best
among them in performance are zinc and zinc magnesium. Calcium, zinc–calcium, and zinc–magnesium–calcium ferrites show better
performance in high pigment loadings, while magnesium ferrite pigments show good results only in low pigment loading. 相似文献
56.
Mohammad A. Khanfar Diaa T. A. Youssef Prof. Khalid A. El Sayed Prof. 《ChemMedChem》2010,5(2):274-285
The microfilament cytoskeleton protein actin plays an important role in cell biology and affects cytokinesis, morphogenesis, and cell migration. These functions usually fail and become abnormal in cancer cells. The marine‐derived macrolides latrunculins A and B, from the Red Sea sponge Negombata magnifica, are known to reversibly bind actin monomers, forming 1:1 stoichiometric complexes with G‐actin, disrupting its polymerization. To identify novel therapeutic agents for effective treatment of metastatic breast cancer, several semisynthetic derivatives of latrunculin A with diverse steric, electrostatic, and hydrogen bond donor and acceptor properties were rationally prepared. Analogues were designed to modulate the binding affinity toward G‐actin. Examples of these reactions are esterification, acetylation, and N‐alkylation. Semisynthetic latrunculins were then tested for their ability to inhibit pyrene‐conjugated actin polymerization, and subsequently assayed for their antiproliferative and anti‐invasive properties against MCF7 and MDA‐MB‐231 cells using MTT and invasion assays, respectively. 相似文献
57.
The production of cationised cotton fabrics, via Sandene 8425, 1, 1-dimethyl-3-hydroxy azetidinium chloride and 1, 1-diethyl-3-hydroxy azetidinium chloride, greatly enhances the exhaustion and fixation of acid dyes. This paper shows that these dyes can be used in the absence of salt in a neutral medium. Wash fastness, light fastness and other properties were studied. 相似文献
58.
Chen (Computers and Electrical Engineering, vol. 30, 2004) illustrated that Tseng et al.’s authenticated encryption schemes, with message linkages for message flows, do not achieve their claimed integrity and authenticity properties. Furthermore, Chen presented some modified schemes to repair these flaws. In this paper, we show that the modified schemes proposed by Chen are not secure. In particular, we present an attack that allows a dishonest referee, in case of a dispute, to decrypt all the future and past authenticated ciphertext between the contended parties. We also present a simple fix to prevent this attack. 相似文献
59.
H. Bahmanpour K. M. Youssef R. O. Scattergood C. C. Koch 《Journal of Materials Science》2011,46(19):6316-6322
Copper alloys with different amounts of zinc were synthesized via high energy ball milling at liquid nitrogen and room temperature.
Bulk samples were produced in situ by controlling the milling temperature. It is shown that temperature plays an important
role in formation of artifact-free consolidated samples via its effect on defect formation and annihilation during the milling
process. The mechanical behavior of Cu–Zn nanocrystalline alloys was examined using Vickers microhardness and tensile tests.
The nanostructure of the alloys was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The
hardness results of processed alloys vary as a function of the alloying elements. Considering typical low ductility of nanocrystalline
materials, the improved ductility with the high strength observed in these alloys suggests that they are artifact-free and
may have several deformation mechanisms, which may include dislocation activity and nano-twinning. 相似文献
60.
Hamdy M. Youssef 《热应力杂志》2013,36(12):1293-1309
A problem of thermoelastic interactions in an elastic infinite layer 0 ≤ x ≤ h with an elevated temperature field arising from ramp-type heating and loading has been constructed. The governing equations are written in a unified system from which the field equations for coupled thermoelasticity as well as for generalized thermoelasticity can be easily obtained as particular cases. Due attention has been paid to the finite rise times of temperature and stress. The problem has been solved analytically by using a state-space approach. Solutions from the derived analytical expressions have been computed for a specific situation. The solution for the half-space when (h → ∞) has been found also. Numerical results for the temperature distribution and thermal stress are represented graphically. A comparison was made among the results predicted by the theories. 相似文献