PIN versus Avalanche photodiode gain optimization in zero cross correlation optical code division multiple access system

In this paper, we show details of zero cross correlation (ZCC) code development and investigate performance by measuring bit-error-rates compared to other optical code division multiple access (OCDMA) codes using Avalanche photodiode (APD) and PIN photodetector. We present a configuration to determine how optical OCDMA systems can be applied with PIN and APD photodetector. Analysis of Avalanche photodiode gain optimization is discussed in ZCC code system. We also present analytical and numerical theoretical results for data transmission of spectrally encoded incoherent OCDMA signal and how signal-noise is being affected by using these two photodetectors.     

Recovering boundary data: The Cauchy Stokes system

This paper is concerned with the severely ill-posed Cauchy–Stokes problem. We are interested in a data completion problem which is exploited to detect small leaks to control water loss Kim et al. (2008) [1]. This inverse problem is rephrased into an optimization one: An energy-like error functional is introduced. We prove that the optimality condition of the first order is equivalent to solving an interfacial equation which turns out to be a Cauchy-Steklov-Poincaré operator. Numerical trials highlight the efficiency of the method.     

Extrudate swell of linear and branched polyethylenes: ALE simulations and comparison with experiments

Extrudate swell is a common phenomenon observed in the polymer extrusion industry. Accurate prediction of the dimensions of an extrudate is important for appropriate design of dies for profile extrusion applications. Prediction of extrudate swell has been challenging due to (i) difficulties associated with accurate representation of the constitutive behavior of polymer melts, and (ii) difficulties associated with the simulation of free surfaces, which requires special techniques in the traditionally used Eulerian framework. In a previous work we had argued that an Arbitrary Lagrangian Eulerian (ALE) based finite element formulation may have advantages in simulating free surface deformations such as in extrudate swell. In the present work we reinforce this argument by comparing our ALE simulations with experimental data on the extrudate swell of commercial grades of linear polyethylene (LLDPE) and branched polyethylene (LDPE). Rheological behavior of the polymers was characterized in shear and uniaxial extensional deformations, and the data was modeled using either the Phan–Thien Tanner (PTT) model or the eXtended Pom–Pom (XPP) model. Additionally, flow birefringence and pressure drop measurements were done using a 10:1 contraction–expansion (CE) slit geometry in a MultiPass Rheometer. Simulated pressure drop and contours of the principal stress difference were compared with experimental data and were found to match well. This provided an independent test for the accuracy of the ALE code and the constitutive equations for simulating a processing-like flow. The polymers were extruded from long (L/D = 30) and short (L/D = 10) capillaries dies at 190 °C. ALE simulations were performed for the same extrusion conditions and the simulated extrudate swell showed good agreement with the experimental data.     

3D simulation of radionuclide transport in porous media

We present an efficient and easily implementable finite volume method simulating radionuclide transport through highly heterogeneous grounds in three space dimensions. The numerical concentration of the transported chemicals are proved to remain nonnegative and stable. Then, we run a realistic test case in which some radioactive iodine I¹²⁹ particles are released from a leak in an underground nuclear waste disposal site. The question of whether the radionuclide invades the underground and reach the ground surface is investigated. Because of the 3D nature of the problem, a particular emphasis is made on the control of CPU time. Copyright © 2009 John Wiley & Sons, Ltd.     

Chemoselective Bromination in a Two-Step Substitution Under the Influence of Tetrachlorosilane and N-Bromosuccinimide

The synthesis of gem dibromide carbonyl compounds via a cheep and readily available combined reagent from tetrachlorosilane and N-bromosuccinimide (TCS-NBS).     

Method of synthesizing adamantyl-substituted phenols based on 1,3-dehydroadamantane

The possibility of obtaining adamantyl-substituted phenols by the reaction of 1,3-dehydroadamantane with phenols in the presence of catalytic amounts of sulfuric acid was studied.     

An efficient hash-based authenticated key agreement scheme for multi-server architecture resilient to key compromise impersonation

During the past decade, rapid advances in wireless communication technologies have made it possible for users to access desired services using hand-held devices. Service providers have hosted multiple servers to ensure seamless online services to end-users. To ensure the security of this online communication, researchers have proposed several multi-server authentication schemes incorporating various cryptographic primitives. Due to the low power and computational capacities of mobile devices, the hash-based multi-server authenticated key agreement schemes with offline Registration Server (RS) are the most efficient choice. Recently, Kumar-Om presented such a scheme and proved its security against all renowned attacks. However, we find that their scheme bears an incorrect login phase, and is unsafe to the trace attack, the Session-Specific Temporary Information Attack (SSTIA), and the Key Compromise Impersonation Attack (KCIA). In fact, all of the existing multi-server authentication schemes (hash-based with offline RS) do not withstand KCIA. To deal with this situation, we propose an improved hash-based multi-server authentication scheme (with offline RS). We analyze the security of the proposed scheme under the random oracle model and use the ‘‘Automated Validation of Internet Security Protocols and Applications’’ (AVISPA) tool. The comparative analysis of communication overhead and computational complexity metrics shows the efficiency of the proposed scheme.     

Synthesis and Thermal Properties of Biodegradable Poly(ester‐urethane)s Based on Chemo‐Synthetic Poly[(R,S)‐3‐hydroxybutyrate]

A series of telechelic oligo[(R,S)‐3‐hydroxybutyrate]‐diols (PHB‐diols) was synthesized from ethyl (R,S)‐3‐hydroxybutyrate (ethyl (HB)) and four different aliphatic diols, namely, 1,4‐butanediol, 1,6‐hexanediol, 1,8‐octanediol and 1,10‐decanediol by transesterification and condensation in bulk. The structures of the synthesized oligomers were confirmed by ¹H NMR spectroscopy and MALDI‐TOF mass spectroscopy. The use of 1,4‐butanediol results in an oligoester with hydroxyl functionality of approximately 2. In the case of the higher aliphatic diols, the number average functionalities were found to be lower than 2. These differences were ascribed to side reactions which occur during polymerization, yielding unreactive end groups. Other novel families of biodegradable poly(ester‐urethane)s were synthesized either from PHB‐diol alone, or PHB‐diol mixed with poly(ε‐caprolactone)‐diol (PCL‐diol), poly(butylene adipate)‐diol (PBA‐diol) or poly(diethylene glycol adipate)‐diol (PDEGA‐diol). In each case, 1,6‐hexamethylene diisocyanate was used as a nontoxic connecting agent. The homopolymers prepared from PCL‐diol, PBA‐diol and PDEGA‐diol were also synthesized for the sake of comparison. All the prepared copolymers possess high molecular weight with glass transition temperature (T_g) values varying from –54 to –23°C. Some of the prepared copoly(ester‐urethane)s are partially crystalline with melting temperatures (T_m's) varying from 37 to 56°C.     

Modeling and simulation of an ATM backbone network

We present a simulation model to analyze the performance of a Mesh ATM backbone network: using the proposed model, we study the performance of a fully connected network topology. Then we assess the impact of different routing schemes on network performance. Copyright © 2000 John Wiley & Sons, Ltd.     

Effect of SnSb Particle Size on Creep Behaviour under Power Law Regime of Sn-10%Sb Alloy

Sn-10 %Sb alloy was casted from the liquid state, drawn into wires of 0.55 mm in diameter or rolled into sheet of 0.2 mm thick. The as received as well as the heat treated specimens were examined by metallurgical microscope. Room temperature creep tests at constant loads were also carried out. The results obtained show that increasing annealing temperature, T_a, affects the structure and properties of the alloy. The increase of T_a leads to smaller SnSb particle size, therefore results in increasing its mechanical strength as measured by the decrease in steady state creep rate of specimen. The stress exponent parameter (m) calculated from the equation ϵ_S= A s_m was found to have higher values than usual and to decrease by increasing annealing temperature which was related to the associated decrease of the SnSb particle size.