Preventing Sybil attacks in P2P file sharing networks based on the evolutionary game model

In cooperative Peer-to-Peer (P2P) networks, a number of users, called Free-riders, try to receive service from others without cooperating with them. Some others, called Sybil nodes, break the rules of the system by colluding and showing fake identities. P2P networks are highly vulnerable to these attacks. In previous research, no method has been suggested to counter these two attacks simultaneously. In the proposed method, a new centrality relationship has been used in the incentive mechanism to deal with both problems at the same time. In this regard, the more varied the nodes receiving service from a peer are, the better the peer reputation will be. The results show that the longer the network life goes on, the more free-riders are detected, and the number of services delivered to the collusive nodes will also be reduced. © 201

Unital Design Based Sink Location Service for Wireless Sensor Networks

In wireless sensor networks (WSNs), providing source node with sink position is an essential principle for geographic routing protocols. Previous works have only focused on the problem of sink localization in a 2-D sensing field while that of 3-D WSNs has received little attention. Providing sink location service with low control overhead and energy consumption is a challenging issue in 3-D WSNs area. In this paper, we propose a unital design based sink location service (UDSL) for WSNs. In this scheme, sink location announcement (SLA) and sink location query (SLQ) packets are forwarded along two paths or blocks. The node located at the intersection of the two paths sends the sink position to the source. In the proposed method, SLA and SLQ messages are constructed using unital design blocks. For this purpose, a mapping from unital design to sink location service has been proposed. However, this basic mapping does not guarantee an intersection of paths,therefore, we propose an enhanced UDSL providing 100 probability of intersection. In order to analyze the proposed scheme's performance, extensive WSNs simulations and experiments have been conducted. The results indicate that UDSL provides reasonable performance in terms of hop counts, path length, and energy consumption for providing sink location service. © 2013 IEEE

Effect of nearest neighbor repulsion on the low frequency phase diagram of a quarter-filled Hubbard-Holstein chain

We have studied the influence of nearest-neighbor (NN) repulsion on the low frequency phase diagram of a quarter-filled Hubbard-Holstein chain. The NN repulsion term induces the apparition of two new long range ordered phases (one $4k_F$ CDW for positive $U_{eff} = U-2g^2/\omega$ and one $2k_F$ CDW for negative $U_{eff}$) that did not exist in the V=0 phase diagram. These results are put into perspective with the newly observed charge ordered phases in organic conductors and an interpretation of their origin in terms of electron-molecular vibration coupling is suggested.Comment: 10 pages, 10 figure

TCLAB: A New Topology Control Protocol in Cognitive MANETs Based on Learning Automata

The mobility of the nodes and their limited energy supply in mobile ad hoc networks (MANETs) complicates network conditions. Having an efficient topology control mechanism in the MANET is very important and can reduce the interference and energy consumption in the network. Indeed, since current networks are highly complex, an efficient topology control is expected to be able to adapt itself to the changes in the environment drawing upon a preventive approach and without human intervention. To accomplish this purpose, the present paper proposes a learning automata-based topology control method within a cognitive approach. This approach deals with adding cognition to the entire network protocol stack to achieve stack-wide and network-wide performance goals. In this protocol, two cognitive elements are embedded at each node: one for transmission power control, and the other for channel control. The first element estimates the probability of link connectivity, and then, in a non-cooperative game of learning automata, it sets the proper power for the corresponding node. Subsequently, the second element allocates efficient channel to the corresponding node, again using learning automata. Having a cognitive network perspective to control the topology of the network brings about many benefits, including a self-aware and self-adaptive topology control method and the ability of nodes to self-adjust dynamically. The experimental results of the study show that the proposed method yields more improvement in the quality of service (QoS) parameters of throughput and end-to-end delay more than do the other methods. © 2017, Springer Science+Business Media, LLC

Residual design of sink localization algorithms for wireless sensor networks

Geographic routing protocols in wireless sensor networks require providing location information of sinks to source nodes. Most studies have only focused on two-dimensional (2D) sensing field, but the real-world applications of sensor networks are in a three-dimensional (3D) environment. This paper presents a new scheme based on residual design principles for 3D networks. In this scheme, sink location announcement (SLA) and sink location query (SLQ) packets are forwarded along two blocks. The node located at the intersection of the two blocks sends the sink position to the source. In the proposed method, SLA and SLQ messages constructed using residual design blocks. For this purpose, the mapping from residual design to sink location service have been proposed. In order to analyze proposed algorithm's performance, a series of simulations have been conducted using the NS-2 network simulator. Simulation results indicate that proposed algorithm can significantly reduce the communication overhead and energy consumption. © 2019 - IOS Press and the authors

TCLAB: A New Topology Control Protocol in Cognitive MANETs Based on Learning Automata

The mobility of the nodes and their limited energy supply in mobile ad hoc networks (MANETs) complicates network conditions. Having an efficient topology control mechanism in the MANET is very important and can reduce the interference and energy consumption in the network. Indeed, since current networks are highly complex, an efficient topology control is expected to be able to adapt itself to the changes in the environment drawing upon a preventive approach and without human intervention. To accomplish this purpose, the present paper proposes a learning automata-based topology control method within a cognitive approach. This approach deals with adding cognition to the entire network protocol stack to achieve stack-wide and network-wide performance goals. In this protocol, two cognitive elements are embedded at each node: one for transmission power control, and the other for channel control. The first element estimates the probability of link connectivity, and then, in a non-cooperative game of learning automata, it sets the proper power for the corresponding node. Subsequently, the second element allocates efficient channel to the corresponding node, again using learning automata. Having a cognitive network perspective to control the topology of the network brings about many benefits, including a self-aware and self-adaptive topology control method and the ability of nodes to self-adjust dynamically. The experimental results of the study show that the proposed method yields more improvement in the quality of service (QoS) parameters of throughput and end-to-end delay more than do the other methods. © 2017, Springer Science+Business Media, LLC

Charge transport in the “emeraldine” form of polyaniline

The conductivity and the dielectric constant of the “emeraldine” form of polyaniline is studied in a wide range of frequency (dc, 10 1–10 5 Hz, 6.5×10 9 Hz), temperature (20K–340K) and protonation level (x ≡[C1]/[N] =0.0–0.5). Two distinct behaviors are observed: Firstly, for low protonation (x ≤ 0.13), hopping of charges between polarons and bipolarons leads to dipolar relaxation ( ϵ RF (T)). Oscillation of polarons around pinning centers is suggested to be responsible for the high frequency dielectric constant of low protonated samples. Secondly, for intermediate to highly protonated samples (x > 0.22), the presence of “metallic islands” is apparent. Oscillation of charge carriers within the coherence length contributes to ϵ μω (T=0). The intrinsic conductivity within the islands is estimated to be of the order of 250 S/cm. The T-dependence of the dielectric constant indicates an increase of the coherence length with increasing temperature. The role of localization and the nature of “textured metallic islands” are discussed

Highly conducting polyacetylene

“New”-(CH)x and “ARA” (i.e.AdditionalReducingAgent)-(CH)x have been synthesized at room temperature. “New”-(CH)x is formed by polymerizing acetylene on flat polymeric or glass substrates using an AlEt3/Ti (n-BuO)4 catalyst in silicone oil which has previously been heat-treated. Additional reducing agents may be added to the catalyst after its thermal treatment to produce “ARA”-(CH)x. The stretch-oriented “New”-(CH)x polymerized on glass and “ARA”-(CH)x polymerized on polyethylene can be p-doped with I2/CCl4 to give conductivities of ∼50,000 and ∼75,000 S/cm respectively. Optical absorption, photoinduced infrared absorption, magnetic susceptibility and conductivity studies on selected forms of the above doped and undoped types of (CH)x are discussed. The electronic structure of highly conducting “New”-and “ARA”-(CH)x is observed to be essentially identical to that of conventional Shirakawa-(CH)x

Polímeros condutores intrínsecos e seu potencial em blindagem de radiações eletromagnéticas Intrinsically conducting polymers and their potencial in electromagnetic interference shielding

A procura por novos materiais que possuam propriedades magnéticas e dielétricas adequadas ao uso em absorvedores de radiação eletromagnética é de grande importância. Dentre os materiais em estudo, os polímeros condutores têm sido aplicados como centros de absorção de radiação, devido à possibilidade de variação da sua condutividade com a freqüência da radiação das ondas incidentes, sendo esta pesquisa o estado da arte no processamento de materiais absorvedores de radiação (MAR). O objetivo deste trabalho é apresentar a ampla faixa de propriedades dos polímeros condutores, correlacionando-as com o potencial de aplicação destes materiais como aditivos no processamento de MAR. Uma breve análise dos resultados obtidos com uma blenda de EPDM contendo 30-80 %(m/m) de PAni-DBSA e espessuras de 1 e 3 mm, analisadas na faixa de 8-12 GHz, mostra que o material absorveu na faixa de 50 a 90% da radiação incidente.<br>The search for new materials possessing magnetic and dieletric properties adequated to be used as radar absorbing materials has been of great importance. Among the materials under study, conducting polymers have been applied due to the possibility of variation of their conductivity with the frequency of the incident radiation. These research areas have been considered the state of the art in the processing of radar absorbing materials. The aim of this work is to present the large range of properties of the conducting polymers and their correlation with the potential application of these materials as electromagnetic radiation absorbers. Some results are also presented on blends of EPDM and 30-80% (w/w) of PAni-DBSA with thickness of 1 and 3 mm, analysed in the range of 8-12 GHz, which absorbed in the range of 50-90% of incident radiation

Electronic instabilities and irradiation effects in the (TMTTF)2X series

The paper presents a single-crystal ESR study of a series of pristine and X-ray irradiated (TMTTF)2X salts, where TMTTF is tetramethyltetrathiafulvalene and X is either a centro-symmetrical (SbF6 and Br) or a non-centro-symmetrical (ReO4, ClO4, BF4, SCN and NO3) monovalent anion. Besides standard line-width and spin-susceptibility measurements, the analysis of the asymmetry of the ESR line shape allows to obtain simultaneous information on the electrical conductivity. This whole set of data is used to determine the charge and spin gaps related to the charge ordering (CO) and anion ordering (AO) ground states and their evolution as a function of X-ray irradiation damages. We show in particular that the sensibility of (TMTTF)2X salts to irradiation depends upon the nature of the anion X and that the CO ground state is drastically affected by irradiation damages at the difference of the AO ground state. We also present evidence of a CO transition and of a decoupling between the AO transition and the opening of a spin gap in (TMTTF)2NO3