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Alike web spam has been a major issue to almost every aspect of the current World Wide Web, social spam has led to a serious threat to the utilities of online social media, particularly in informat...

Twitter is widely used by the social media users to share their thoughts, experiences and breaking news. Due to huge user base and quick delivery of information, posts of Twitter users reach millions of people within few seconds. During extreme events and social crisis, emergency responders utilize local information posted by the Twitter users to combat the chaotic situation. Even news media cite Twitter as their source of information a number of times. With these applications, it is necessary to understand how information reaches individuals at Twitter network. There are mainly two ways by which Twitter users receive an information: (i) through internal links within Twitter network, and (ii) through sources out of Twitter network that are newspapers, radio and televisions. Existing research mainly utilized internal links for modeling information diffusion at Twitter and very few studies considered external influence. There is a study which quantifies the effects of internal and external sources on the mentions of URLs in users’ tweets. In this paper, authors have utilized retweets, URLs and hashtags to quantify internal and external influence on information diffusion at Twitter. The analysis of 880 K tweets clearly represents that the diffusion of 79% tweets is internally influenced and only remaining 21% can be attributed to the influence of external sources.

The development of vehicles and portable advancements for wireless connectivity among vehicles has carried new difficulties to the Internet of Vehicles (IoV). So as to precisely find vehicles and rapidly process information for reducing the pressure of reliable communication, grouping techniques are desirable in order to ensure that portable stations and terminals residing at roadsides can easily make use of maximum transmission opportunity. In literature, vast amount of researchers have considered grouping paradigm for reliable information dissemination, yet we have incorporated the data reputation-based stable and secure grouping strategy into an optimization problem that provides the QoS upper bounds for better system performance. Our proposed grouping paradigm is modeled into a simulative platform considering the mobility simulator SUMO and network simulator NS3 aiming to reduce overhead.

Internet of things is a fast-growing field of industry as a lot of IoT applications are introduced in the market. Its popularity is also growing because of its ease of use and its applications serving in vast domains. The demand for IoT deployment over a large scale is increasing at a swift pace. A lot of issues and challenges have worked on, and a lot remains to be explored and solved. It has become a focus of research. A considerable number of researches have contributed a lot in the field of IoT. However, still it is lagging in the security domain, so is the reason for concern for many researchers. There are few other concerns in IoT which are related to the security goals, requirements, challenges, and issues. This paper provides an overview of IoT along with presenting various privacy and security issues in it. The paper also shows how the security in IoT differs from the security in conventional systems. Various lightweight encryption techniques for IoT, limitations of IoT, IoT technologies, and architectures are discussed and compared in the paper.

Internet of vehicles (IoV) is considered one of the biggest innovations in the transportation world. IoV technology alludes to the advancement and deployment of an effective platform that takes into account the growth, expansion, integration of new technologies, and complex human interactions. The versatile mobile cellular systems are equipped for giving incredible coverage to vehicular clients, yet the prerequisite of stringent real-time security services cannot continuously be ensured in mobile systems. Consequently, the heterogeneous vehicular system (Het-VANET), which incorporates cellular systems with DSRC, develops as a promising answer to meet the correspondences necessities of the intelligent transportation system (ITS). In heterogeneous-IoV (HET-IoV), connectivity and near-field communications create enormous new interactive features which are presuming as to provide promising proposal to transform the operation and role for industrial systems such as transportation systems and manufacturing systems. The main motivation behind HET-IoV concept is to give advance connectivity, the pervasive presence of things and make efficient use of radio resources for these networks. Subsequently, the quick evolution of computing and communications technologies gives rise to vehicles with powerful computing abilities that are not limited to service recipients but also advocated service providers. This results with the idea of vehicular cloud computing (VCC) that collectively uses computational, communicative, and storage resources inside vehicle equipment, for example, on-board units, communications devices, or mobile user equipment arrived by passengers. Vehicular cloud computing (VCC) provides a new management mechanism for big data that enables the processing of data and the mining of valuable knowledge from it. Regardless, to the best of our knowledge, these works don’t have a point by point examination of the new VCC perspective, which incorporates absolutely new applications, difficulties, and research issues. To associate this gap, this chapter gives an audit on the compromise of Cloud and IoV. Starting by portraying fundamentals of IoV, heterogeneous vehicular access technologies and VCC analyze their characteristics, coordination, and challenges. In addition, it also provides a state-of-art picture of the heterogeneous vehicular communication model. Because of the reception of vehicular cloud, they both perform a powerful innovation by managing storage, on-demand retrieving of data, data dissemination in sparse environments, and security, with an attention on recent research challenges.

As the traffic density keeps on increasing, the efficient and safer traffic management is the bottleneck issue nowadays. This resulted in developing intelligent transport system. The dedicated short-range communication (DSRC) is an enabling technology for the success of intelligent transportation system (ITS). Recently, endeavors have been developed to create communication for vehicle to everything (V2X) utilizing IEEE 802.11p. This system confronts difficulties while ensuring network stability and guaranteeing the system’s adaptability with the increase in traffic. Therefore, simulative investigations have been done to evaluate the optimum physical and medium access control layer parameters like packet reception ratio and packet update delay in both city and highway scenarios. Moreover, realistic conditions for city have been created by using Rician fading model and for highway using random waypoint mobility model is used. The simulation findings conclude that evaluations done for these MAC protocols in highway scenario show better results for different vehicle density as compared to evaluations done in city scenarios.

A distributed strategy is proposed for finding relocation overhead associated with movement of each node during cascaded relocation process.A criteria is given for selecting suitable node to relocate during cascaded movement.The performance of the scheme is evaluated and compared with other baseline approaches through example networks.The approach is validated analytically and through ns-2 based simulation. In wireless sensor networks, hostile deployment terrains make resource constrained sensor nodes vulnerable to failures. Sometimes, even a single node failure can partition a network into many disjoint segments and can fail the application mission completely. Since, in most scenarios manual intervention is not possible and hence network must have self-healing capability by detecting and recovering faults at its own. In this paper, a distributed connectivity restoration (DCR) scheme is proposed which on node failure(s) reconstructs the network topology by using cascaded node movements enabling self-healing capability in the network. The DCR is based on partial network information including topological overhead associated with each node. The selection of befitting nodes to be relocated during cascaded movement is done strategically by using partial network information such that the relocation and message overheads are reduced. Ns-2 based simulation experiments are performed to evaluate the performance of the proposed scheme and is compared with other baseline approaches. Display Omitted

Due to autonomous operation and constrained resources, nodes of a wireless sensor network are susceptible to failures. Due to multiple node failures, network topology may change or partition into many disconnected segments causing data/query path breakage. Early detection and recovery of faults is desirable in most scenarios. Also, due to limited battery life of a node, the solution must consume minimum possible energy for prolonged network operation. Hence in this paper, we propose a Fault Detection and Recovery scheme which is an energy efficient fault detection and recovery strategy that achieves minimum data loss by efficiently replacing faulty node on the present route or by finding full or partial alternate paths. Topology is managed by constructing a virtual grid over the entire network which helps in managing dynamically changing network topology easily and makes failure detection and recovery effective. It also helps to create energy efficient path between a source and a sink by finding s...

Internet of vehicles (IoVs) nowadays has opened the door to a myriad of advancements in safety, mobility, and in environmental aspects. Although, due to core challenges like high mobility, variable density, frequent fragmentation and the hostile terrain types in vehicles, there is a greater need to improve data dissemination interfaces for the IoV. To mitigate these challenges, this paper proposes an efficient group based topology management vehicular data dissemination (TVDD) scheme that focuses on improving the stability of groups and meeting users' quality of service (QoS) requirements. Continuous service availability is achieved by grouping vehicles in intra-grouping and inter-grouping domains. Group heads (GHs) are selected for avoiding continuous connectivity voids by optimising the stability factor. Furthermore, for holistic data delivery a hybrid data forwarding approach based on LTE-V is proposed. Simulations are carried out using network simulator (NS3) and mobility simulator simulation mobility (SUMO). Encouraging results are obtained in terms of grouping overhead, grouping stability and packet delivery ratio stable data delivery.

Generally, fault detection approaches pursue high detection accuracy, but neglect energy consumption due to the high volume of messages exchanged. Therefore, in this work we propose a reactive distributed scheme for detecting faulty nodes. The scheme is able to detect transient and permanent faulty nodes accurately by exchanging fewer messages. In existing fault detection schemes, nodes exchange too many messages after every specific interval to detect suspicious node. However, in the proposed scheme comparatively much less messages are exchanged within a limited geographical area around the suspicious node only and that too when the node suspects its own readings. In the proposed scheme, each node exploits the temporal correlation in its own readings to detect any suspicious behavior. In order to confirm its status, the suspicious node communicates with its immediate neighbors who may be locally good or possible faulty with a certain level of confidence. Thus, the scheme utilizes the strength of both spatial and temporal correlation to find faulty nodes. Also, a confidence level is assigned to each correlated neighbor of suspicious node in order to enhance the detection accuracy. The ns-2 based simulation results show that our scheme performs better by reducing communication overhead and by detecting faulty nodes with high accuracy as compared to existing approaches.

WLANs are prone to flooding denial-of-service DoS attacks. Present research work proposes a novel method to enhance WLAN security by restricting flooding DoS effect on the access point AP. Each node in the proposed method listens transmission of other neighbouring nodes and sends at regular interval a linked list to AP, containing the identifiers IDs of all nodes from which it hears. AP stores the linked list information and runs location-based coordinate calculation LBCC algorithm. LBCC finds the expected coordinates of each node and probable location area with the expected coordinates as centre. Flooding DoS attack by the attacker is restricted at the AP using node’s probable location area. The method is validated by simulation experimentations with varying topologies. Further, geometrical analysis of the method is also provided.

In recent years, wireless sensor networks (WSN's) have gained much attention due to its various applications in military, environmental monitoring, industries and in many others. All these applications require some target field to be monitored by a group of sensor nodes. Hence, coverage becomes an important issue in WSN's. This paper focuses on full coverage issue of WSN's. Based on the idea of some existing and derived theorems, Position and Hop-count Assisted (PHA) algorithm is proposed. This algorithm provides full coverage of the target field, maintains network connectivity and tries to minimize the number of working sensor nodes. Algorithm works for communication range less than root three times of sensing range and it can be extended for arbitrary relation between communication range and sensing range. By using hop-count value, three-connectivity in the network is maintained. Also, neighbors information is used to create logical tree structure which can be utilized in routing, redundant data removal and in other areas. Simulation results show that PHA algorithm outperforms layered diffusion-based coverage control algorithm by providing better area coverage and activating fewer nodes.

The IEEE 802.11i standard provides authentication and security at the Medium Access Control layer in wireless local area networks (WLANs). It involves an authentication process followed by a four-way handshake to evolve a key for securing data sessions. The standard suffers under denial-of-service (DoS) attacks. These attacks often block the ongoing communication process and deprive services to the legitimate users. These are easy to conduct while maintaining anonymity of the attackers. It hence becomes imperative to learn about the attacks and their solutions in IEEE 802.11i-protected WLANs so that future research proposals and solutions to mitigate the attack may develop. The paper presents a review of DoS attacks and existing solutions pertaining to the IEEE 802.11i security standard. Copyright © 2014 John Wiley & Sons, Ltd.

Due to the rapid exchange of information and large user base of social networking sites, these are focused for gathering the latest information or news from people over the world. Anyone having an internet connected device can share thoughts or update on real-time events. Social media helps reporters as well as common men in sharing useful information, but at the same time, it also leads to deliberate or accidental spread of rumors, i.e. pieces of information having uncertain truth at the time of posting. During social crisis, people access these platforms to get relevant information. In the rush of being early responders to a critical event users post the information even without checking its veracity and that further used by other users to fill-in their informational gap. So flagging out the unverified information can be useful in maintaining a distance from spreading the information that may end up being false. The openness of online social networking platforms (i.e. Twitter or Facebook), presence of machine learning and NLP (Natural Language Processing) based techniques give us a chance to inspect the conduct of people in posting rumorous information. In this work, we summarize and present the efforts and achievements so far to combat the spread of rumorous information. These efforts composed of analyzing the content of rumors, properties of users who share rumors and network structure that favor the spread of such information.

Authentication per frame and symmetric key based encryption is an implicit necessity for security in Wireless Local Area Networks (LANs). We propose a novel symmetric key based secure WLAN communication scheme. The scheme provides authentication per frame, generates new secret key for encryption of each frame and involves less message exchanges for maintaining the freshness of key and initial vector (IV). It enhances wireless security by utilizing key hiding concept for sharing the symmetric secret key and IV. The shared secret encryption key and IV are protected using counters and then mixed with each other before sending. We prove security of the scheme in Canetti–Krawczyk model.

Authentication is one of the essential tools available for security in WLANs. Access control authentication mechanisms provides entity authentication, access into the network and key evolving for data frames protection. Secure WLAN Authentication Scheme (SWAS) is one such access control authentication mechanism. It provides entity authentication along with per frame authentication. All the participating entities in the scheme i.e. STA, AP and AS authenticate each other. The scheme makes use of cryptographic measure like delegation, key management, encryption and MIC for securing the scheme. The security properties of the scheme need to be validated for effectiveness. In this paper, a formal tool i.e. Protocol Composition Logic (PCL) is used for proving the authentication property of the scheme. General Terms Networks, Security, WLAN

Topology management is a critical issue in the context of wireless sensor networks. There are different factors by which topology of a network may be affected. Maintaining this topology in uncontrolled mobility of nodes and make it to work efficiently is a tedious task. In this paper, we propose an efficient topology management strategy based upon geographical forwarding information. Simulation experimentation reveals that geographically inspired virtual grid [GIVG] achieves significant improvements compared to other approaches in terms of energy consumption and communication overheads.

In wireless sensor networks (WSNs), nodes near to sink communicate more than the nodes at farther away from the sink. This load imbalance causes an energy hole around sink and affects overall network lifetime. Therefore, a corona model based approach is proposed to enhance network's lifetime by balancing energy depletion rate across network and avoiding energy hole around sink. The approach balances energy depletion in inter-corona as well as in intra-corona. In inter-corona, the balance in energy depletion rate is achieved by assigning decreasing communication ranges from outermost to innermost coronas whereas in intra-corona, the balance is achieved by dynamically tuning relay load over nodes during data transmission. The relay load tuning considers current relay load and remaining energy of nodes. The proposed scheme works well for uniformly and non-uniformly deployed networks. To validate the results, the approach is compared with baseline approaches through ns-2 based simulation.

Measurements of effective thermal conductivity ( λ e ) and effective thermal diffusivity ( χ e ) of twin pellets of Zn x Te 100− x ( x = 5, 10, 30 and 50) chalcogenide materials, prepared under load of 5 tons (equivalent pressure ≈433 MPa) have been made simultaneously at room temperature using transient plane source (TPS) technique. Specific heat per unit volume ( C p ) has also been determined from the so obtained data of λ e and χ e . The material has been prepared by melt quenching method. The results indicate that both the values of λ e and χ e increase logarithmically with increasing Zn concentration. This behaviour of λ e and χ e with zinc concentration can be explained by change of bond formation from covalent to ionic in this system. An effort has also been made to predict these values by an empirical relation. X-ray diffraction (XRD) studies for structural investigation of ZnTe have also been carried out and found to be polycrystalline in nature.

Polypyrrole (pure) and polypyrrole doped with different protonic acids (HCl and H3PO4) have been synthesized using NaOH as reducing agent in aqueous HCl medium and ammonium persulphate (APS) as an oxidant, respectively. These pure and doped samples were named as S1, S2, and S3 for further investigations. These pure and doped samples were annealed at 200oC for 4 hr. The amorphous nature of these annealed and as-prepared polypyrrole samples was confirmed by XRD. FTIR spectra and SEM images of all the samples were taken at room temperature, which indicate: significant change in annealed samples. To calculate the energy band gap of all the samples, the absorption spectra were recorded by USB-2000 spectrophotometer at room temperature in the wavelength range 300–800 nm. From the analysis of absorption spectra, optical band gap of as-prepared samples (S1–S3) was determined to be 2.64, 2.43, and 2.29 eV, respectively and for annealed samples A1–A3 values obtained were 2.30, 2.25, and 2.17 eV. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers

A thin film of zinc selenide (ZnSe) was deposited onto a clean glass substrate using a vacuum evaporation technique. This thin film was characterized through X-ray diffraction, which indicated that the film was polycrystalline in nature. Absorption and transmission spectra of this thin film were recorded using a spectrophotometer. The energy band gap, refractive index and extinction coefficient were determined using these spectra. It was found that the energy band gap of ZnSe film was 2.55 eV. It was also observed that the refractive index and extinction coefficient of the film decreased with the increase of wavelength. The conductivity of this thin film was determined by current–voltage measurement using an electrometer over the temperature range from room temperature to 413 K. It was observed that conductivity increased with increase in temperature. This is explained on the basis of structural changes occurring due to the change in grain size and the increase in carrier density.

The CdS nanoparticles of different sizes are synthesized by a simple chemical method. Here, CdS nanoparticles are grown through the reaction of solution of different concentration of CdCl2 with H2S. X-ray diffraction pattern confirms nano nature of CdS and has been used to determine the size of particle. Optical absorption spectroscopy is used to measure the energy band gap of these nanomaterials by using Tauc relation. Energy band gap ranging between 3.12 eV to 2.47 eV have been obtained for the samples containing the nanoparticles in the range of 2.3 to 6.0 nm size. A correlation between the band gap and size of the nanoparticles is also established.

The thin films of Cd1-x Zn x S (x = 0, 0.2, 0.4, 0.6, 0.8 and 1) have been prepared by the vacuum evaporation method using a mechanically alloyed mixture of CdS and ZnS. The structural, optical and electrical properties have been investigated through the X-ray diffractometer, spectrophotometer and Keithley electrometer. The X-ray diffraction patterns of these films show that films are polycrystalline in nature having preferential orientation along the (002) plane. In the absorption spectra of these films, absorption edge shifts towards lower wavelength with the increase of Zn concentration. The energy band gap has been determined using these spectra. It is found that the energy band gap increases with increasing Zn concentration. The electrical conductivity of so prepared thin films has been determined using a I–V characteristic curve for these films. The result indicates that the electrical conductivity decreases with increasing Zn content and increases with temperature. An effort has also been made to o...

A flame retardant composition was prepared from phosphorus-melamine-urea-formaldehyde (PMUF) reaction. The flame retardancy of rigid polyurethane foam (RPUF) was studied by impregnating it with various concentrations of PMUF. Optimum impregnation time, retention and density of RPUF samples with PMUF were also studied. The morphology, elemental analysis, and thermal stability of RPUF and RPUF-PMUF samples were studied with scanning electron microscopy (SEM), CHNS analyzer, and energy dispersive X-rays (EDX) and, thermogravimetric analysis (TGA), derivative thermogravimetric (DTG), differential thermal analysis (DTA), respectively. The deposition of PMUF on the cell walls and surfaces was exhibited by decreased cell size from 357 to 285 (±5) μm. CHNS and EDX studies show the introduction of phosphorus and nitrogen into the RPUF-PMUF samples. The degradation of RPUF and RPUF-PMUF samples was occurred through two and three stages in nitrogen and air, respectively. RPUF-PMUF samples are decomposed comparatively at lower temperature than RPUF which is resulted into large amount of high temperature stable char residue. This char residue acts as insulating blanket and protects RPUF-PMUF from fire. Fire performance and smoke density of RPUF and RPUF-PMUF samples were investigated with BS: 4735, ASTM D2863 and ASTM E662, respectively. RPUF-PMUF samples demonstrate reduced extent burnt from 125 to 27 mm, burning rate 2.23–0.44 mm/s and percent mass loss (PML) from 100 to 8.82%. Oxygen index was also increased from 17.8 to 23.8. Dm results obtained during smoke density tests show that RPUF-PMUF generates less and delayed smoke than RPUF under flaming and nonflaming mode. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Using a Dynamic Mechanical Analyzer (DMA), mechanical properties like modulus and phase transition temperature of polyester composites of banana fibers (treated and untreated) are measured simultaneously. The shifting of phase transition temperature is observed in some treatments. The performance of the composite depends to a large extent on the adhesion between polymer matrix and the reinforcement. This is often achieved by surface modification of the matrix or the filler. Banana fiber was modified chemically to achieve improved interfacial interaction between the fiber and the polyester matrix. Various silanes and alkalies were used to modify the fiber surface. Chemical modification was found to have a profound effect on the fiber/matrix interaction, which is evident from the values of phase transition temperatures. Of the various chemical treatments, simple alkali treatment with 1% NaOH was found to be the most effective.

In-network aggregation is a technique in which queries are propagated in the network and in response phase information is processed at aggregator node only. In wireless sensor network, nodes are deployed in a particular area for sensing certain parameters like sound vibration, humidity, temperature etc. Information sensed by nodes may be highly correlated and redundant. It is not energy efficient to send correlated, redundant data to the sink. In wireless sensor network, correlation (spatial or temporal or spatiotemporal) among sensor readings may be exploited to reduce battery consumption and increase network lifetime. In this paper we propose an approach that handles multiplicity of sinks and shares information among sinks.

A thick film of aniline-formaldehyde copolymer and PMMA is synthesized via dispersion of aniline-formaldehyde copolymer powder as filler particles in PMMA with two different concentrations. Variation of the complex elastic modulus and mechanical loss factor (tanδ) with temperature is studied. It is observed that the complex elastic modulus decreases with temperature owing to thermal expansion of films. On the other hand, tanδ increases up to a characteristic temperature beyond which it shows a decreasing trend toward melting. Transition temperature T g of sample S1 (pure PMMA) is found to be 80°C. In sample S2 (1 wt % aniline formaldehyde copolymer), the peak of tanδ at a lower temperature (66°C) corresponds to glass transition temperature T g of the PMMA matrix, while the peak of tanδ at a higher temperature (107.8°C) corresponds to T g of a polymer chain restricted by filler particles of aniline-formaldehyde copolymer. A further increase (10 wt % aniline-formaldehyde copolymer) in the concentration of filler particles of aniline-formaldehyde copolymer results in a more compact structure and a shift of T g to a higher temperature, 122.2°C. This shift in the glass transition temperature of thick films of aniline-formaldehyde copolymer and PMMA is dependent upon the concentration of filler particles in the sample.

Formulations for rigid polyurethane foams (RPUFs) based on crude 4,4'-diphenylmethane diisocyanate, polyether polyol, triethylenediamine, 1,4-butane diol, poly(siloxane ether), methylene chloride, and water were studied. The stoichiometric ratios of various foam ingredients and their effects on physical properties such as the cream time, gel time, tack-free time, and density of the RPUF samples were studied. The results indicated that the rate of RPUF formation increased with the catalyst (triethylenediamine and tin) and water content. The density of the RPUF samples blown with water, methylene chloride, and a mixture of water and methylene chloride decreased from 240.1 to 33.4 kg/m 3 with an increase in the blowing agent contents. However, the RPUF density increased with increasing contents of 1,4-butane diol. The cell morphology and thermal properties of the RPUF samples were investigated with scanning electron microscopy, thermogravimetric analysis, derivative thermogravimetry, and differential thermal analysis. Scanning electron microscopy results revealed an average increase in the cell size of the RPUF samples from 162 to 278 μm with increased water content. A thermal behavior study indicated that the RPUF samples decomposed in nitrogen and degraded in air through two and three weight-loss stages, respectively. Foam pyrolysis in nitrogen and combustion in air led to 15 and 0% char residue, respectively. The results indicated that the thermal stability of the RPUFs was better in nitrogen than in an air atmosphere.

The II-VI polycrystalline semiconducting materials have come under increased scrutiny because of their wide use in the cost reduction of devices for photovoltaic applications.Cd1−XZnXTe is one of the II-VI ternary semiconductor materials whose bandgap can be tailored to any value between 1.48–2.26 eV as X varies from 0 to 1. It is promising material for high-efficiency solar cells, switching, and other optoelectronic devices. Polycrystalline thin film ofCd1−XZnXTe with variable composition (0≤X≤1) has been deposited on ultraclean glass substrates by screen printing method followed by sintering process. The optical and structural properties ofCd1−XZnXTe thin films have been examined. The optical bandgap of these films is studied using reflection spectra in wavelength range of 350–900 nm by using double beam spectrophotometer. The structure of sample was determined from X-ray diffraction patterns. The films were polycrystalline in nature having wurtzite (Hexagonal) structure over the whole range studied. The lattice parameters vary almost linearly with the composition parameterX, following Vegard's law. Sintering is a very simple and viable method compared to other cost-intensive methods. The results of the present investigation will be useful in characterizing the material CdZnTe for its applications in photovoltaics.

Currently available fault detection approaches generally pursue high fault detection performance but neglect energy consumption due to high volume of messages exchanged during fault detection process. Therefore, in this work we propose a reactive distributed scheme for detecting faulty nodes. The scheme is able to detect transient and permanent faulty nodes accurately with very less false alarm rate. In our scheme, all nodes individually analyze their measured data for detecting any suspicious behavior through utilizing temporal correlation. If a node finds itself suspicious of possessing faulty data, only then it exchanges its readings with the nodes in same geographical area rather than exchanging too much messages after every specific interval as in other DFDs. The scheme utilizes the strength of both spatial and temporal correlation to find faulty nodes and reduces the message overhead during fault detection. The ns-2 based simulation results show that our scheme performs better by reducing communication overhead and detects faulty nodes with high accuracy as compared to existing DFD.

In wireless sensor networks (WSNs), sensor nodes are deployed densely in large numbers to increase the quality of services (QoS). However, QoS is significantly affected by faults in such networks. The probability of faults in WSNs increases with increase of sensor nodes. In order to provide better QoS, it is essential that faulty nodes should be diagnosed and handled timely without affecting the underlying work of the network. In this paper, our main focus is on diagnosing transient and permanent fault by communicating an optimal number of messages. We propose a mechanism to diagnose such faults without degrading the throughput of WSNs. The proposed approach is reactive in nature, which during fault diagnosis generates traffic smoothly in the network due to which the network never degrades its performance. Scheme also allows faults to occur during diagnosis process. The result shows that our scheme diagnoses faults correctly and efficiently and is able to maintain the desired throughput during fault diagnosis.

Since sensor nodes in wireless sensor networks (WSNs) are deployed randomly in hostile and ill-disposed environments, failures occur more frequently and unexpectedly as compared to other traditional networks. These frequent faults and failures in the network are major attributes towards poor quality of services (QoS). Therefore, for providing better QoS, such failures should be identified and recovered timely. On the other hand, wireless sensor nodes are resource constrained battery operated devices. Therefore, the failure diagnosis and recovery procedure should be energy efficient. In this work, we propose an energy efficient mechanism to diagnose and recover failures. At first, we propose a very low false alarming rate consensus based failure identification mechanism for diagnosing failures in the network. Secondly, an energy efficient coverage preserving failure recovery (CPFR) mechanism is proposed for recovering failures and maintaining an adequate coverage. The ns-2 based result shows that proposed scheme is able to diagnose failures with very low false alarming rate and is also able to recover failures by maintaining coverage above a threshold.

Samples of selenium rich Se85Cd15−xZnx (x = 0, 3, 7, 11 and 15) system in bulk form have been prepared using a technique of slow cooling of the melt. Measurements of effective thermal conductivity (λe) and effective thermal diffusivity (χe) of Se85Cd15−xZnx pellets, prepared at constant load of 10 tons, have been carried out from room temperature to 200 °C using the transient plane source technique. The variation in λe and χe of Se85Cd15−xZnx with the concentration of zinc and temperature is explained on the basis of structure modifications of the samples and the mean free path of the phonons due to scattering from defects and voids.

Pure polypyrrole and polypyrrole in salt form were synthesized using NaOH as reducing agent in aqueous HCl, respectively. Electrical conduction in these pure and doped polypyrrole samples was studied through the I-V characteristics of these materials. I-V characteristic curves for both pure and doped polypyrrole were found to be linear. The conductivity of chlorine-doped polypyrrole is about 104 times that of pure polypyrrole. An attempt has been made to study the dependence of conductivity on temperature, in order to understand the application of these systems. It has been observed from the variation of conductivity vs. temperature curve in both the samples that the conductivity increases with the increase in temperature. This behaviour is indicative of semiconducting nature of the samples with a variation in electrical conductivity of each, which is a strong function of doping and temperature of the environment. Activation energies for both the samples have been found to be in millielectron-volt range, 101.94 meV and 121.68 meV for pure and doped polypyrrole, respectively. An effort has also been made to understand the charge transport in these conductive polymers through models.

Chemical method has been used to prepare cadmium sulphide by using cadmium, hydrochloric acid and H2S. The reflection spectra of covered and uncovered sintered films of CdS have been recorded by ‘Hitachi spectrophotometer’ over the wavelength range 300–700 nm. The energy band gaps of these films have been calculated from reflection spectra. It is found that the energy band gap of both films is same as 2.41 eV. It is indicated that energy band gap of these films does not change. This value of band gap is in good agreement with the value reported by other workers. The measurement of photocurrent has also been carried out using Keithley High Resistance meter/ Electrometer. This film shows the high photosensitivity and high photocurrent decay. Thus so obtained films are suitable for fabrication of photo detectors and solar cells.

Measurements of I – V characteristics and DC electrical conductivity of Se 85− x Te 15 Sb x (where x = 2, 4, 6, 8 and 10) glassy thin pellets, prepared by well established melt quenching technique in bulk (pellets of diameter 12 mm and thickness ≈1 mm were prepared under a constant load of 5 tons), have been carried out at room temperature using Keithley High Resistance Meter/Electrometer 6517A. For the recording of I – V characteristics, this equipment was used in FVMI (Force Voltage Measure Current) mode. It is found evident from the I – V characteristics that the glass containing 4 at. wt.% of Sb has the minimum resistance allowing maximum current through the sample as compared to the other at. wt.% of Sb contents e.g. 2, 6, 8 and 10. At 4 at. wt.% of Sb, conductivity rises to 76% of the value obtained for 2 at. wt.% of Sb. Composition dependence of DC conductivity is discussed in terms of the bond formation between Se and Sb at different compositions. The conduction mechanism is discussed qualitatively on the basis of Poole–Frenkel conduction mechanism. Also the linear relation between ln ( I ) and V 1/2 verifies that the conduction mechanism is of Poole–Frenkel type for both low and high voltage range. The deviation of ohmic behaviour at lower voltage range towards the non-ohmic at higher voltage range is due to the high voltage induced temperature effects in the sample.

TheI—Vcharacterization and the electrical resistivity of selenium rich Se85Cd15-xZnx (x = 0, 3, 7, 11 and 15) system at room temperature have been studied. Samples were obtained using melt cooling technique. So prepared samples were then characterized in terms of their crystal structure and lattice parameter using X-ray diffraction method. The materials were found to be poly crystalline in nature, having zinc blend structure over the whole range of zinc concentration. The measurements ofI—V bdcharacteristics have been carried out at different temperatures from room to 140°C. The electrical resistivity of the samples with composition at room temperature has been found to vary between maximum 2.7 x 108 Ωm and minimum 7.3 x 105 Ωm and shows a maximum at 3 at. wt.% of Zn. The carrier activation energy of the samples with composition has also been determined and found to vary from 0.026 eV to 0.111 eV.

Simultaneous measurements of effective thermal conductivity (λe) and effective thermal diffusivity (χe) of four samples S1 (polyaniline mixed with 100% Ni), S2 (polyaniline mixed with 90% Ni and 10% Al), S3 (polyaniline mixed with 80% Ni and 20% Al) and S4 (polyaniline mixed with 70% Ni and 30% Al) of polyaniline mix with metal Ni and Al in different percentage have been made using transient plane source technique. In the temperature range from room temperature to 170 °C. Both λe and χe increase with increase in temperature. Addition of aluminium concentration at the cost of nickel in the composite increases the value of λe and χe over the entire range of temperature under investigation. It has been found that the values of λe and χe are maximum when 70% of Ni and 30% of Al are mixed in polyaniline matrix. This behaviour is also predicted by an empirical relation, which is obtained from polynomial fit of the experimental data and is explained on the basis of bond formation between metal (Ni and Al) and nitrogen of polyaniline matrix.

Recently, mobile collector or sink mobility has become an important research topic in WSNs. Data collector mobility can improve the performance of WSNs. Mobile sinks are mounted on some vehicles, animals or people moving randomly to collect information sensed by the sensor nodes where the data sink trajectories are changing or random. In the scenarios where the trajectories of the mobile collectors are fixed or predetermined, the efficient data collection problems are concerned to improve the performance of the network. Therefore, in this paper we propose an intelligent mobile data gathering scheme which dynamically changes its DGT (Data Gathering Tour) in between by utilizing information from NIT (Neighbor Information Table). Each CH (Cluster Head) learns about its neighbors whether they have data to send or not and thus creates a NIT. Based on the information in NIT at a CH, MDC (Mobile data Collector) decides its further course of action. Hence, the path travelled is dynamically pruned using this information at each cluster head. Simulation results show significant energy savings when this scheme is applied to various data collection scenarios in which different CHs are deployed as opposed to scenarios when no dynamic path pruning and data filtering is used.

The paper reports influence of samarium substitution on the properties of a PZT composition near MPB. Samarium (Sm) was varied from 0 to 0.02/FU. The samples were prepared by standard double sinter...

In recent years, Wireless Sensor Networks (WSNs) have gained much attention because of its varying applications from catastrophic region to industrial and household region. In few applications, sensors are deployed in extreme environmental conditions. Hence, node access is not possible in that scenario. Therefore, a large number of sensor nodes are deployed in the target field so that node replacement problem is eliminated. Also, coverage is a very important parameter because it measures how effectively a target field is monitored by the sensor network. This paper focuses on the coverage issue in wireless sensor networks. Initially, three different types of coverage issues are discussed. Then, full coverage issue is examined by considering different points such as node type, deployment type, relation of communication range to sensing range, strategy used to detect full coverage and positioning based/independent algorithms. Some applications of wireless sensor networks are given. Finally, research challenges in the field of area coverage are discussed.

Measurements of thermophysical properties of Zn x Te 100− x ( x = 5, 10, 30 and 50) chalcogenide material in pellet form have been made in the temperature range from room temperature (15 °C) to 200 °C and in cooling cycle from 200 °C to 15 °C using transient plane source (TPS) technique. In heating mode the values of effective thermal conductivity ( λ e ) and effective thermal diffusivity ( χ e ) increase from 15 °C to 200 °C. During the cooling mode λ e and χ e decrease slightly in the temperature range from 200 °C to 160 °C below which λ e and χ e remain almost constant at all temperatures. Such type of behaviour shows thermal hysteresis in this sample, which can be explained on the basis of the change in structure of the material. XRD studies suggest that the material is polycrystalline in nature.