1,287 research outputs found

    Performance evaluation of WMN-GA for different mutation and crossover rates considering number of covered users parameter

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    Node placement problems have been long investigated in the optimization field due to numerous applications in location science and classification. Facility location problems are showing their usefulness to communication networks, and more especially from Wireless Mesh Networks (WMNs) field. Recently, such problems are showing their usefulness to communication networks, where facilities could be servers or routers offering connectivity services to clients. In this paper, we deal with the effect of mutation and crossover operators in GA for node placement problem. We evaluate the performance of the proposed system using different selection operators and different distributions of router nodes considering number of covered users parameter. The simulation results show that for Linear and Exponential ranking methods, the system has a good performance for all rates of crossover and mutation.Peer ReviewedPostprint (published version

    A testbed for MANETs: Implementation, experiences and learned lessons

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    In this paper, we present the implementation, experiences and lessons learned of our tesbed for Ad-hoc networks and Mobile Ad hoc Networks (MANETs). We used OLSR protocol for real experimental evaluation. We investigate the effect of mobility and topology changing in the throughput of a MANET. We study the impact of best-effort traffic for Mesh Topology and Linear Topology. In this work, we consider eight experimental models and we assess the performance of our testbed in terms of throughput, round trip time and packet loss. We found that some of the OLSR's problems can be solved, for instance the routing loop, but this protocol still has the self-interference problem. Also, there is an intricate interdependence between MAC layer and routing layer. We carried out the experiments considering stationary nodes of an Ad-hoc network and the node mobility of MANETs. We found that throughput of TCP was improved by reducing Link Quality Window Size (LQWS). For TCP data flow, we got better results when the LQWS value was 10. Moreover, we found that the node join and leave operations increase the packet loss. The OLSR protocol has a good performance when the source node is moving. However, the performance is not good when the relay nodes are moving.Peer ReviewedPostprint (published version

    Anhydrous alteration of Allende chondrules in the solar nebura I: Description and alteration of chondrules with known oxygen-isotopic compositions

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    Anhydrous alteration of eleven Allende chondrules with already-known oxygen isotopic compositions were studied in detail with reference to a dark inclusion and the matrix from Allende. Anhydrous alteration of chondrules includes three processes different from each other, formation of secondary olivine zonation, replacement of groundmassic plagioclase or glass by nepheline and/or sodalite, and replacement of phenocrystic enstatite by ferroan olivine. The degrees of each process are different among chondrules. A positive correlation in degrees between replacement of groundmassic plagioclase or glass and phenocrystic enstatite is recognized, suggesting that these two processes took place at the same time by reactions with a nebular gas at temperatures probably lower than 800K. The secondary olivine zonation may have formed prior to and in the early stage of the replacement of groundmassic plagioclase and phenocrystic enstatite. The anhydrous alteration of Allende dark inclusions was caused in a nebular gas having an oxygen isotopic composition along the Allende inclusion mixing line, but Allende chondrules have experienced the anhydrous alteration in a gas reservoir having an oxygen isotopic composition along the Allende chondrule mixing line. Therefore, the anhydrous alteration of chondules and dark inclusions took place in different nebular gas reservoirs prior to the accretion of the Allende parent body

    Comparative study of anhydrous alteration of chondrules in reduced and oxidized CV chondrites

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    Chondrules in three CV chondrites of the reduced subgroup (Leoville, Efremovka and Vigarano) were studied to explore the effect of anhydrous alteration, in comparison to those in Allende of the oxidized subgroup. The alteration consists of secondary olivine zonation, replacement of low-Ca pyroxene by ferroan olivine, and replacement of primary groundmass by nepheline and sodalite. The highest degree of alteration occurs in chondrules of Allende. Leoville chondrules show only olivine zonation and seem not to have experienced replacement of pyroxene and groundmass. Some chondrules in Efremovka have replacement textures of groundmass and show olivine zonation. On the other hand, many chondrules in Vigarano were subjected to all types of alteration. Thus, chondrules even in reduced CV chondrites do not completely preserve their primary features, although the degree of alteration for the reduced CVs varies, and is lower on the whole than that of Allende. The differences between CV chondrites of the oxidized and reduced subgroups appear to be determined by the degree of secondary alteration and oxidation of Fe. The alterations took place prior to the final consolidation with the matrix on the CV parent body

    Mineralogy and petrology of an unusual Belgica-7904 carbonaceouschondrite: Genetic relationships among the components

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    Belgica-7904 (B-7904) carbonaceous chondrite consists of abundant chondrules, various clasts, isolated minerals, and a dehydrated phyllosilicate matrix. Chondrules are divided into magnesian and ferroan types. Magnesian type has forsterite phenocryst, often with pyroxene, plagioclase, and unusual Cr-rich ovoid, which set in a dehydrated phyllosilicate groundmass. Kamacite is abundantly included in the forsterite phenocrysts, and is rarely associated with schreibersite. Ferroan type consists mainly of ferroan olivine phenocryst and dehydrated phyllosilicate groundmass with phosphate, instead of schreibersite in magnesian type. Clasts in B-7904 are classified into seven types. These include matrix-like clasts, phyllosilicate-rich clasts, hortonolite-rich clasts (aggregates of ferroan olivine and opaque minerals), Mn-rich olivine-bearing clasts containing schreibersite, Mn-rich forsterite, and Mn-rich chromite, forsterite-spinel clasts like amoeboid olivine inclusions (AOI\u27s) in C3 chondrites, kamacite-rich clasts, and sulfide-rich clasts consistsing of troilite, pentlandite, taenite, and Co-rich metal. Mineralogical study suggests that magnesian chondrules, phyllosilicate-rich clasts, and Mn-rich olivine-bearing clasts formed under reducing conditions, whereas ferroan chondrules, hortonolite-rich clasts, and the matrix originated under oxidizing conditions. Thus, the components of B-7904 originated in different reservoirs with contrasting fO_2 and fS_2 in the solar nebula, and were later mixed. Glass inclusion in chondrules, which occur in olivine phenocrysts and dehydrated phyllosilicate groundmasses, contains CaO, whereas phyllosilicates in the groundmass are nearly free from CaO. Thus, CaO was mainly lost from these chondrules during hydrous alteration, although some CaO remains as abundant phosphate in ferroan chondrules. All of the CaO lost from the chondrules and clasts appears to have been concentrated in the matrix as Ca-carbonates. The oxidation reaction to form magnetite and magnesiowustite from kamacite also took place in a magnesian chondrule at about 660K and 10^ bars oxygen partial pressure, which is much higher than an oxygen partial pressure (10^ bars) of the canonical solar gas with a total gas pressure of 10^ bars at 600K. This suggests that magnesian chondrules were oxidized by a nebular gas of non-solar composition, probably after mixing with ferroan chondrules. All phyllosilicates in B-7904 were dehydrated by intense heating, and the unequilibrated mineral assemblages and the magmatic temperatures retained in some of the chondrules suggest that the heating took place for a short duration, probably by shock heating

    Anhydrous alteration of Allende chondrules in the solar nebura II: Alkali-Ca exchange reactions and formation of nepheline,sodalite and Ca-rich phases in chondrules

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    Fifty-eight Allende chondrules were studied to investigate secondary anhydrous alteration of chondrules. Nepheline and sodalite replace anorthite-normative cryptocrystalline groundmass and plagioclase. These reactions presumably took place by replacement of Ca of the anorthite component by 2 (Na, K) introduced from chondrules, and are called alkali-Ca exchange reactions. The degree of the reaction is variable among chondrules; a few chondrules display the reaction in the peripheral parts only. In contrast, the primary groundmass in some other chondrules was totally replaced by nepheline and sodalite. Most of the Allende chondrules were subjected to the alkali-Ca exchange reaction. Some Ca-rich phases such as hedenbergite, andradite, grossular, kirschsteinite and wollastonite, rarely occur intimately with nepheline and sodalite in groundmass. These Ca-rich phases are also secondary products in chondrules. During the alkali-Ca exchange reaction, part of the CaO released from anorthite was used to form the Ca-rich phases in chondrules. Since the abundance of the Ca-rich phases is too low, CaO was mostly lost from chondrules during the alkali-Ca exchange reaction. CAIs and chondrules in oxidized CV chondrites include similar secondary minerals, suggesting that both of them were subjected to the alkali-Ca exchange reaction under similar conditions

    Anhydrous alteration of Allende chondrules in the solar nebula III: Alkali-zoned chondrules and heating experiments for anhydrous alteration

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    The groundmass of some chondrules in Allende shows chemical zonation from alkali-poor and CaO-rich cores to alkali-rich and CaO-poor rims, and the zonation was defined to be original groundmass (zone I), continuous zoning region (zone II), and discontinuously high-Na and low-Ca zone (zone III). The zonation was formed after chondrule solidification and prior to accretion on the Allende parent body, and was probably produced by reactions with an oxidized nebular gas in equilibrium with nepheline, sodalite, high-Ca pyroxene, and ferroan olivine. Heating experiments using synthetic glass beads were conducted, and zonation similar to the alkali-zoned chondrules was formed. The experimental results suggests that the reaction temperature and duration for the Allende alkali-zoned chondrules were about 600°-400℃ and 1-10^4 years, respectively

    Performance evaluation of wireless sensor networks for mobile event and mobile sink

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    Extending lifetime and energy efficiency are important objectives and challenges in-Wireless Sensor Networks (WSNs). In large scale WSNs, when the nodes are near to the sink they consume much more energy than the nodes far from the sink. In our previous work, we considered that the sink node was stationary and only event node was moving in the observation field. In this work, we consider both cases when the sink node and event node are moving. For the simulations, we use TwoRayGround and Shadowing radio models, lattice topology and AODV protocol. We compare the simulation results for the cases when the sink node and event node are mobile and stationary. The simulation results have shown that the goodput of TwoRayGround is better than Shadowing in case of mobile event, but the depletion of Shadowing is better than TwoRayGround in case of mobile event. The goodput in case of mobile sink is better than stationary sink when the transmission rate is lower than 10pps. For TwoRayGround radio model, the depletion in case of mobile sink is better than stationary sink when the number of nodes is increasedPeer ReviewedPostprint (published version
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