Ca(NO3)2•4H2O-catalysed Biginelli Reaction: One-pot Synthesis of 1,2,3,4-Tetrahydropyrimidin-2-ones/pyrimidine-2-thiones under Solvent-free Conditions

The synthesis of 1,2,3,4-dihydropyrimidinone/thione derivatives was achieved in good to excellent yields using calcium(II) nitrate as catalyst to promote the Biginelli three-component condensation reaction from a diversity of aromatic aldehydes, β-keto compounds and urea or thiourea. The reaction was carried out under solvent-free conditions.     

Square-wave adsorptive stripping voltammetry of menadione (vitamin K(3))

Menadione (vitamin K₃) undergoes a reversible two-electron transfer involving the quinone structure in acidic medium. As demonstrated by using cyclic voltammetry, the reduced form is more strongly adsorbed than the oxidized one. Stripping voltammetry of an adsorbed layer has been applied to the determination of this molecule after preconcentration of the reduced compound and scanning the potential towards less negative values. Adsorption, which is highly effective when stirring is used, approaches an equilibrium process in quiescent solution, as evidenced by a loss of part of the adsorbed material when stirring is stopped. A square-wave mode has been selected owing to its high sensitivity (the current is 20 times that for the differential pulse mode), but also to its high scan-rate, which minimizes the slow desorption process occurring during the scan. A concentration range from 2 × 10⁻¹⁰ to 5 × 10⁻⁷ M is easily investigated, the detection limit being 1.3 × 10⁻¹⁰ M. The influence of several operational parameters has also been considered.     

Sidelobe Level Reduction in Linear Array Pattern Synthesis Using Particle Swarm Optimization

The design of nonuniformly spaced linear array antennas using Particle Swarm Optimization method is considered. The purpose is to match a desired radiation pattern and improve the performance of these arrays in terms of sidelobe level. This performance criterion determines how well the system is suitable for wireless communication applications and interference reduction. Two approaches are considered: in the first, the design of element placement with the constraint of array length being imposed is performed. The second is based on element position perturbation starting from a uniform element distribution. Many examples are treated to show the effectiveness of the designs and the effect some other parameters might have on the overall performance of the array.     

Capacity Optimization of MIMO Wireless Communication Systems Using a Hybrid Genetic-Taguchi Algorithm

The purpose of this paper is to use a hybrid Taguchi-genetic algorithm to optimize the capacity of MIMO systems with different linear array geometrical configurations at both communication ends (Transmitter and Receiver). The method combines the traditional genetic algorithm, known to have a powerful global exploration capability, and the Taguchi method, which can exploit the optimum offspring and thus, enhance the genetic algorithm. The idea is to use the spatial channel model where the effect of mutual coupling is considered. Each array geometrical configuration has its own contribution in the total channel matrix depending on its physical parameters. The end result is to find out which combination(s) produce the highest capacity value.     

A new worm propagation threat in BitTorrent: modeling and analysis

Peer-to-peer (P2P) networking technology has gained popularity as an efficient mechanism for users to obtain free services without the need for centralized servers. Protecting these networks from intruders and attackers is a real challenge. One of the constant threats on P2P networks is the propagation of active worms. Recent events show that active worms can spread automatically and flood the Internet in a very short period of time. Therefore, P2P systems can be a potential vehicle for active worms to achieve fast worm propagation in the Internet. Nowadays, BitTorrent is becoming more and more popular, mainly due its fair load distribution mechanism. Unfortunately, BitTorrent is particularly vulnerable to topology aware active worms. In this paper we analyze the impact of a new worm propagation threat on BitTorrent. We identify the BitTorrent vulnerabilities it exploits, the characteristics that accelerate and decelerate its propagation, and develop a mathematical model of their propagation. We also provide numerical analysis results. This will help the design of efficient detection and containment systems.     

Rapid access to novel 2-alkylthiopyrimidine derivatives and attempt of their Tacrine analogs synthesis

A variety of novel 2-alkylthiopyrimidines were synthesized through simple condensation of arylidenemalononitriles with different 2-alkylthiouronium halide derivatives catalyzed by anhydrous potassium carbonate (K₂CO₃). The reactions have been carried out under mild conditions in i-PrOH, and the products were obtained in moderate to good yields with a simple work-up method. Subsequently, some examples of these compounds have been converted into Tacrine analogs by applying the Friedländer reaction.     

Structural Stabilities and Elastic Thermodynamic Properties of SrTe Compound and SrTe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ca<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Alloy Under High Pressure

The effect of pressure on the structural, elastic, and thermodynamic properties of SrTe in both B1 (rocksalt) and B2 (CsCl-type) phases and the SrTe_1?x Ca _x alloys with Ca dopant concentrations at x = 0.16667, 0.20, 0.33333, 0.42857, 0.44444 and 0.50 have been investigated using the two new gradient-corrected functional developed by Perdew, J.P.; Burke, K.; Ernzerhof named Density-Gradient Expansion for Exchange in Solids (PBEsol) and generalized Wu–Cohen (WC), in a significant range of pressure from 0 GPa to 30 GPa. The structure parameters, elastic stiffness constants c _ij , the bulk modulus (B), Kleinman parameter (\( \xi \)), shear anisotropies A _shear are also determined. Furthermore, as reported in this study, the aggregate elastic modulus (B, G, E), Poisson’s ratio (ν) and the Lame’s coefficients (λ) are estimated. On the other hand, the ductility, brittleness, longitudinal, transverse sound velocities and the Debye temperature Θ_D(T) are also obtained. Importantly, our results are in reasonable agreement with the available theoretical and experimental data. To the best of our knowledge, this is the first study of the effect of the composition on the properties of the SrTe_1?x Ca _x alloys which may encourage other works for the confirmation of the reported results.     

AlCl3-promoted reaction of cycloalkanones with hydrazones: a convenient direct synthesis of 4,5,6,7-tetrahydro-1H-indazoles and their analogues

The AlCl₃-promoted reactions of cycloalkanones with hydrazones are described. This approach represents a mild and operationally simple method to access 2,3-diaryl-4,5,6,7-tetrahydro-1H-indazoles and their analogues in good to moderate yields.     

A cooperative Bayesian and lower bound estimation in dynamic framed slotted ALOHA algorithm for RFID systems

A novel estimation scheme that combines Bayesian and lower bound estimating radio frequency identification tag population size is proposed. The developed methodology is based on the fusion between the Bayesian and lower bound estimating techniques. It turns out that the fusion rule is built up thanks to an existing linear relationship between the cited techniques. Simulation results show that the developed technique significantly improves the accuracy of the estimating tag quantity and presents less estimation error. Also, the resulting advanced dynamic framed slotted ALOHA protocol considerably improves the performance and efficiency of the radio frequency identification anti‐collision compared with the most recent protocols using others estimating methods.