Novel polymeric flame retardant plasticizers for poly(vinyl chloride)

Polyphosphate esters have been used as polymeric flame retardant plasticizers in poly(vinyl chloride); thermal and flammability studies were carried out to evaluate their efficiencies as fire retardants. A comparison is also made on the fire retardancy of the conventional simple phosphates with that of the polyphosphates as novel fire retardant plasticizers for PVC.

Reactivity of pyridinium poly(hydrogen fluoride) towards silicon tetrachloride, trichlorosilane and tris(amino)silanes

The reaction of silicon tetrachloride (SiCl4), trichlorosilane (HSiCl3) and tris(amino)silanes[(R2N)3SiH] with pyridinium poly(hydrogen fluoride) (PPHF) gives rise to hexafluorosilicatesalts in good yields. They have been characterized as pyridinium hexafluorosilicate(C5H5NH)2SiF6 (in the case of SiCl4 and HSiCl3) and the corresponding dialkyl ammoniumhexafluorosilicate (R2NH2)2SiF6 salts [for tris(amino)silanes] (where R2N=pyrrolidino,piperidino, hexamethyleneimino, morpholino, N-methylpiperazino and diethylamino). Theinteresting features of these reactions are the cleavage of Si---Cl, Si---H and Si---N bondsat room temperature by PPHF and fluorination of the silicon moiety to a hexa-coordinateddoubly charged anionic species. These compounds have been characterized by NMR (1H,29Si, 19F) and IR spectroscopy, and by chemical analysis.

A Shapley Value-Based Approach to Discover Influential Nodes in Social Networks

Our study concerns an important current problem, that of diffusion of information in social networks. This problem has received significant attention from the Internet research community in the recent times, driven by many potential applications such as viral marketing and sales promotions. In this paper, we focus on the target set selection problem, which involves discovering a small subset of influential players in a given social network, to perform a certain task of information diffusion. The target set selection problem manifests in two forms: 1) top-k nodes problem and 2) lambda-coverage problem. In the top-k nodes problem, we are required to find a set of k key nodes that would maximize the number of nodes being influenced in the network. The lambda-coverage problem is concerned with finding a set of k key nodes having minimal size that can influence a given percentage lambda of the nodes in the entire network. We propose a new way of solving these problems using the concept of Shapley value which is a well known solution concept in cooperative game theory. Our approach leads to algorithms which we call the ShaPley value-based Influential Nodes (SPINs) algorithms for solving the top-k nodes problem and the lambda-coverage problem. We compare the performance of the proposed SPIN algorithms with well known algorithms in the literature. Through extensive experimentation on four synthetically generated random graphs and six real-world data sets (Celegans, Jazz, NIPS coauthorship data set, Netscience data set, High-Energy Physics data set, and Political Books data set), we show that the proposed SPIN approach is more powerful and computationally efficient. Note to Practitioners-In recent times, social networks have received a high level of attention due to their proven ability in improving the performance of web search, recommendations in collaborative filtering systems, spreading a technology in the market using viral marketing techniques, etc. It is well known that the interpersonal relationships (or ties or links) between individuals cause change or improvement in the social system because the decisions made by individuals are influenced heavily by the behavior of their neighbors. An interesting and key problem in social networks is to discover the most influential nodes in the social network which can influence other nodes in the social network in a strong and deep way. This problem is called the target set selection problem and has two variants: 1) the top-k nodes problem, where we are required to identify a set of k influential nodes that maximize the number of nodes being influenced in the network and 2) the lambda-coverage problem which involves finding a set of influential nodes having minimum size that can influence a given percentage lambda of the nodes in the entire network. There are many existing algorithms in the literature for solving these problems. In this paper, we propose a new algorithm which is based on a novel interpretation of information diffusion in a social network as a cooperative game. Using this analogy, we develop an algorithm based on the Shapley value of the underlying cooperative game. The proposed algorithm outperforms the existing algorithms in terms of generality or computational complexity or both. Our results are validated through extensive experimentation on both synthetically generated and real-world data sets.

Electron-beam irradiation effects on poly(ethylene-co-vinyl acetate) polymer

Poly(ethylene-co-vinyl acetate) (EVA) films were irradiated with a 1.2MeV electron beam at varied doses over the range 0-270kGy in order to investigate the modifications induced in its optical, electrical and thermal properties. It was observed that optical band gap and activation energy of EVA films decreased upon electron irradiation, whereas the transition dipole moment, oscillator strength and number of carbon atoms per cluster were found to increase upon irradiation. Further, the dielectric constant, the dielectric loss, and the ac conductivity of EVA films were found to increase with an increase in the dose of electron radiation. The result further showed that the thermal stability of EVA film samples increased upon electron irradiation.

Poly-ols Based Sol-Gel Synthesis of Zinc Oxide Thin Films

We demonstrate that the structural and optical properties of a sol-gel deposited zinc oxide thin film can be tuned by varying the composition of the sol, consisting of ethylene glycol and glycerol. A systematic study of the effect of the composition of sol on the mean grain size, thickness, and defect density of the zinc oxide film is presented. About 20% glycerol content in the sol is observed to improve the quality of the film, as evaluated by X-ray diffraction and photoluminescence studies. Thus, optimizing the composition of the sol for about 60 nm thick ZnO film using 20% glycerol resulted in the zinc oxide film that is about 80% transparent in visible spectrum, exhibiting electrical resistivity of about 18 Omega cm and field-effect mobility of 0.78 cm(2)/(V s). (C) 2010 The Electrochemical Society. DOI: 10.1149/1.3515894] All rights reserved.

Algorithms for Routing and Centralized Scheduling in IEEE 802.16 Mesh Networks

IEEE 802.16 standards for Wireless Metropolitan Area Networks (WMANs) include a mesh mode of operation for improving the coverage and throughput of the network. In this paper, we consider the problem of routing and centralized scheduling for such networks. We first fix the routing, which reduces the network to a tree. We then present a finite horizon dynamic programming framework. Using it we obtain various scheduling algorithms depending upon the cost function. Next we consider simpler suboptimal algorithms and compare their performances.

Mobile Base Stations Placement and Energy Aware Routing in Wireless Sensor Networks

Increasing network lifetime is important in wireless sensor/ad-hoc networks. In this paper, we are concerned with algorithms to increase network lifetime and amount of data delivered during the lifetime by deploying multiple mobile base stations in the sensor network field. Specifically, we allow multiple mobile base stations to be deployed along the periphery of the sensor network field and develop algorithms to dynamically choose the locations of these base stations so as to improve network lifetime. We propose energy efficient low-complexity algorithms to determine the locations of the base stations; they include i) Top-K-max algorithm, ii) maximizing the minimum residual energy (Max-Min-RE) algorithm, and iii) minimizing the residual energy difference (MinDiff-RE) algorithm. We show that the proposed base stations placement algorithms provide increased network lifetimes and amount of data delivered during the network lifetime compared to single base station scenario as well as multiple static base stations scenario, and close to those obtained by solving an integer linear program (ILP) to determine the locations of the mobile base stations. We also investigate the lifetime gain when an energy aware routing protocol is employed along with multiple base stations.

Efficient and Fair Scheduling of Uplink and Downlink in IEEE 802.16 OFDMA Networks

We develop new scheduling algorithms for the IEEE 802.16d OFDMA/TDD based broadband wireless access system, in which radio resources of both time and frequency slots are dynamically shared by all users. Our objective is to provide a fair and efficient allocation to all the users to satisfy their quality of service.

A non-cooperative game-theoretic approach to channel assignment in multi-channel multi-radio wireless networks

Channel assignment in multi-channel multi-radio wireless networks poses a significant challenge due to scarcity of number of channels available in the wireless spectrum. Further, additional care has to be taken to consider the interference characteristics of the nodes in the network especially when nodes are in different collision domains. This work views the problem of channel assignment in multi-channel multi-radio networks with multiple collision domains as a non-cooperative game where the objective of the players is to maximize their individual utility by minimizing its interference. Necessary and sufficient conditions are derived for the channel assignment to be a Nash Equilibrium (NE) and efficiency of the NE is analyzed by deriving the lower bound of the price of anarchy of this game. A new fairness measure in multiple collision domain context is proposed and necessary and sufficient conditions for NE outcomes to be fair are derived. The equilibrium conditions are then applied to solve the channel assignment problem by proposing three algorithms, based on perfect/imperfect information, which rely on explicit communication between the players for arriving at an NE. A no-regret learning algorithm known as Freund and Schapire Informed algorithm, which has an additional advantage of low overhead in terms of information exchange, is proposed and its convergence to the stabilizing outcomes is studied. New performance metrics are proposed and extensive simulations are done using Matlab to obtain a thorough understanding of the performance of these algorithms on various topologies with respect to these metrics. It was observed that the algorithms proposed were able to achieve good convergence to NE resulting in efficient channel assignment strategies.

Second harmonic generation in poled molecularly doped polymer films : Push-pull butadienes in poly(methyl methacrylate) and polystyrene

We report second harmonic generation in a new class of organic materials, namely donor-acceptor substituted all-trans butadienes doped in poly(methyl methacrylate) or polystyrene and oriented by corona poling at elevated temperatures. Second harmonic measurements were made at room temperature. The observed d33 coefficients are greater than those of potassium dihydrogen phosphate or 4-dimethylamino-4'-nitrostilbene doped in similar polymer matrices. Rotational diffusion coefficients estimated from the decay characteristics of the second harmonic intensity in the polymer films indicate that the polymer matrix plays a major role in stabilizing the dopants in a nonlinear optics conducive environment.

Synthesis and studies of Rh(I) catalysts within and across poly(alkyl aryl ether) dendrimers

In order to study the efficiencies of catalytic moieties within and across dendrimer generations, partially and fully functionalized dendrimers were synthesized. Poly(alkyl aryl ether) dendrimers from zero to three generations, presenting 3 to 24 peripheral functionalities, were utilized to prepare as many as 12 catalysts. The dendrimer peripheries were partially and fully functionalized with triphenylphosphine in the first instance. A rhodium(I) metal complexation was performed subsequently to afford multivalent dendritic catalysts, both within and across generations. Upon synthesis, the dendritic catalysts were tested in the hydrogenation of styrene, in a substrate-to-catalyst ratio of 1:0.001. Turn-over-numbers were evaluated for each catalyst, from which significant increases in the catalytic activities were identified for multivalent catalysts than monovalent catalysts, both within and across generations. (C) 2010 Elsevier B.V. All rights reserved.

Dendritic Poly(ether imine) Based Gene Delivery Vector

The nonviral vector based gene delivery approach is attractive due to advantages associated with molecular-level modifications suitable for optimization of vector properties. In a new class of nonviral gene delivery systems, we herein report the potential of poly(ether Mine) (PETIM) dendrimers to mediate an effective gene delivery function. PETIM dendrimer, constituted with tertiary amine branch points, n-propyl ether linkers and primary amines at their peripheries, exhibits significantly reduced toxicities, over a broad concentration range. The dendrimer complexes pDNA effectively, protects DNA from endosomal damages, and delivers to the cell nucleus. Gene transfection studies, utilizing a reporter plasmid pEGFP-C1 and upon complexation with dendrimer, showed a robust expression of the encoded protein. The study shows that PETIM dendrimers are hitherto unknown novel gene delivery vectors, combining features of poly(ethylene imine)-based polymers and dendrimers, yet are relatively nontoxic and structurally precise.

A study of the reaction of divalent transition metal chlorides with pyridinium poly(hydrogen fluoride), ppht, and the effect of potassium hydrogen fluoride on fluorination and complexation

Studies of the reaction of metal chlorides, MCl2 (M = Mn, Co, Ni, Cu, Zn) with PPHF at room temperature have shown that Mn, Co and Zn form the corresponding metal fluorides, MF2, while Ni and Cu form their dipyridine metal(II) dichloride complexes. Nickel and copper complexes further undergo fluorination and complexation by potassium hydrogen fluoride in PPHF to form KNiF3 and KCuF3.

Improving fault detection and reliability in FDDI networks

FDDI (Fibre Distributed Data Interface) is a 100 Mbit/s token ring network with two counter rotating optical rings. In this paper various possible faults (like lost token, link failures, etc.) are considered, and fault detection and the ring recovery process in case of a failure and the reliability mechanisms provided are studied. We suggest a new method to improve the fault detection and ring recovery process. The performance improvement in terms of station queue length and the average delay is compared with the performance of the existing fault detection and ring recovery process through simulation. We also suggest a modification for the physical configuration of the FDDI networks within the guidelines set by the standard to make the network more reliable. It is shown that, unlike the existing FDDI network, full connectivity is maintained among the stations even when multiple single link failures occur. A distributed algorithm is proposed for link reconfiguration of the modified FDDI network when many successive as well as simultaneous link failures occur. The performance of the modified FDDI network under link failures is studied through simulation and compared with that of the existing FDDI network.

Bayesian Decentralized Spectrum Sensing in Cognitive Radio Networks

This paper considers the problem of spectrum sensing, i.e., the detection of whether or not a primary user is transmitting data by a cognitive radio. The Bayesian framework is adopted, with the performance measure being the probability of detection error. A decentralized setup, where N sensors use M observations each to arrive at individual decisions that are combined at a fusion center to form the overall decision is considered. The unknown fading channel between the primary sensor and the cognitive radios makes the individual decision rule computationally complex, hence, a generalized likelihood ratio test (GLRT)-based approach is adopted. Analysis of the probabilities of false alarm and miss detection of the proposed method reveals that the error exponent with respect to M is zero. Also, the fusion of N individual decisions offers a diversity advantage, similar to diversity reception in communication systems, and a tight bound on the error exponent is presented. Through an analysis in the low power regime, the number of observations needed as a function of received power, to achieve a given probability of error is determined. Monte-Carlo simulations confirm the accuracy of the analysis.