Pattern Synthesis of Nonuniformly Spaced Arrays Based on Unit Circle Representation and Taguchi Method

Unit circle representation techniques such as Schelkunoff null placement method have been extensively used to synthesize uniformly spaced linear arrays. In this work, it is attempted to extend the unit circle representation approach to synthesize nonuniformly spaced linear arrays with some desired null directions and minimum achievable sidelobe level. The problem is formulated as an optimization task upon which Taguchi method is employed to solve for the set of element positions. Illustrative examples are included to demonstrate the design effectiveness and flexibility for modern wireless communication system applications.     

Mathematical and numerical modeling of the non-associated plasticity of soils—Part 1: The boundary value problem

The soil is characterized by the influence of the hydrostatic stress, which leads to a yield surface with a shape of a pyramid for Mohr–Coulomb criteria and a shape of a cone for Drucker–Prager one. These materials are also characterized by a non-associated plasticity where the plastic yielding rule does not follow the normality rule. The usual mechanical models use two independent functions to describe this particular collapse. Unfortunately, this manner broke the model formulation. The purpose of this work is to present a consistent formulation of the non-associated plasticity of soil. The frame of the mathematical analysis is the concept of the implicit standard material. The cornerstone of this new idea is the construction of a single function called the bipotential playing in the same time the roles of the yield surface and the plastic potential. The bipotential concept is then intended to involve the constitutive law, cover the normality rule even for the non-associated soil and the proof of the solution existence. The formulation was initially performed for the case of a regular point out of the cone apex and in present, it is extended to the irregular point located at the apex. The paper presents firstly the implicit standard material method. Then, the methodology to build a full model for the boundary value problem is detailed. Particular expressions and relations are sufficiently explained and discussed. Attention is made to the evolution problem and the variational principles related to the elastic–plastic behavior.     

A DMAP-catalyzed mild and efficient synthesis of 1,2-dihydroquinazolines via a one-pot three-component protocol

An efficient and simple method for the synthesis of 1,2-dihydroquinazolines catalyzed by 4-(N,N-dimethylamino)pyridine (DMAP) from readily available aromatic or heteroaromatic aldehydes, 2-aminobenzophenone, and ammonium acetate under mild conditions is described. The scope and limitations of the method are discussed.     

Velocity profiles of water flowing past solid glass surfaces using fluorescent nanoparticles and molecules as velocity probes

Measurements of the velocity profile of water flowing on a glass surface using fluorescent nanoparticles and single fluorescent molecules as velocity probes show that the no slip boundary condition holds down to at least 10 nm from the surface. For water flowing on a hydrophobic solid surface, silanized glass, the no slip boundary condition fails, and a slip length of 45 nm is measured. These velocity measurements are complemented with atomic force microscopy measurements of dissipation on a small sphere oscillating near the surface with results in agreement with the velocity profiles.     

Structural, electronic and elastic properties of Ti2TlC, Zr2TlC and Hf2TlC

Using First-principle calculations, we have studied the structural, electronic and elastic properties of M₂TlC, with M = Ti, Zr and Hf. Geometrical optimization of the unit cell is in good agreement with the available experimental data. The effect of high pressures, up to 20 GPa, on the lattice constants shows that the contractions are higher along the c-axis than along the a axis. We have observed a quadratic dependence of the lattice parameters versus the applied pressure. The band structures show that all three materials are electrical conductors. The analysis of the site and momentum projected densities shows that bonding is due to M d-C p and M d-Tl p hybridizations. The M d-C p bonds are lower in energy and stiffer than M d-Tl p bonds. The elastic constants are calculated using the static finite strain technique. We derived the bulk and shear moduli, Young’s modulus and Poisson’s ratio for ideal polycrystalline M₂TlC aggregates. We estimated the Debye temperature of M₂TlC from the average sound velocity. This is the first quantitative theoretical prediction of the elastic properties of Ti₂TlC, Zr₂TlC, and Hf₂TlC compounds that requires experimental confirmation.      

Reliable and energy aware query-driven routing protocol for wireless sensor networks

Wireless sensor networks become very attractive in the research community, due to their applications in diverse fields such as military tracking, civilian applications and medical research, and more generally in systems of systems. Routing is an important issue in wireless sensor networks due to the use of computationally and resource limited sensor nodes. Any routing protocol designed for use in wireless sensor networks should be energy efficient and should increase the network lifetime. In this paper, we propose an efficient and highly reliable query-driven routing protocol for wireless sensor networks. Our protocol provides the best theoretical energy aware routes to reach any node in the network and routes the request and reply packets with a lightweight overhead. We perform an overall evaluation of our protocol through simulations with comparison to other routing protocols. The results demonstrate the efficiency of our protocol in terms of energy consumption, load balancing of routes, and network lifetime.     

Gestion de clés et sécurité multipoint: étude et perspectives

Multicast routing is an efficient communication mechanism for group-oriented applications. Several such applications need security guarantees: authentication, integrity confidentiality and access control. Techniques implementing these security services for point-to-point communications can not be directly used in a group communication settings. Consequently, group communication security has been extensively studied. Much current research has been dedicated to key management, which is a building block for all security mechanisms. In this paper, we describe the different existing approaches for managing keys within a group. We discuss the advantages and drawbacks of key management protocols existing in the literature and present a classification and a comparative study of these protocols. We also provide some criticisms and future directions.     

Mathematical and numerical modeling of the non-associated plasticity of soils—Part 2: Finite element analysis

The method of the implicit standard material has allowed the formulation of a consistent mathematical model of the boundary value problem for the non-associated plasticity of soil. The mean accomplished steps are the achievement of the bipotential function, the recovering of the stress–strain relationship under a normality rule, introduction of the bifunctional and the proof of the solution existence. Here the mathematical model is discretized by the finite element method. First, the stress update scheme was formulated, the tangent matrix is explicitly derived and then the non-linear system is solved by the Newton–Raphson method where a new algorithm using a symmetrical tangent matrix is improved. This is in opposition to conventional non-associated plasticity, which uses a non-symmetric tangent matrix. Through the numerical examples we show the feasibility and the efficiency of the algorithm. It is also seen that we perform some studies of the numerical solutions, particularly the comparison between associated and non-associated limit load.