Fast randomized algorithm for 2-hops clustering in vehicular ad-hoc networks

Vehicular Ad-Hoc Networks (VANETs) enable inter vehicle wireless communication as well as communication with road side equipment. Warning messages can be exchanged among nearby vehicles, helping to predict dangerous situations, and thus improving road safety. Such safety messages require fast delivery and minimal delay to local areas, in order for them to be effective. Therefore, a fast and efficient channel access scheme is required. A feasible solution, derived from the Mobile Ad-Hoc Networks (MANETs) field, groups nodes into smaller manageable sections called clusters. Such an approach can be beneficial for locally delivering messages under strict time constraints. In this paper, a Hierarchical Clustering Algorithm (HCA) is presented. HCA is a distributed randomized algorithm, which manages channel access by forming three hierarchy clusters. The proposed channel access scheme enables delay bounded reliable communication. Unlike other common clustering algorithm for VANETs, HCA does not require the knowledge of the vehicles’ locations. This feature guarantees accurate operation even when localization systems such as GPS are not available. The running time and message complexity were analyzed and simulated. Simulation results show that the algorithm behaves well especially under realistic mobility patterns; therefore, it is a suitable solution for channel access scheme for VANETs.     

Geometric Frustration in Molecular Crystals

Unlike Lego bricks that perfectly assemble next to one another, solid assemblies of organic compounds often include some inevitable misfit between constituents, giving rise to geometric frustration. In order to fit into the assembly the molecular building blocks must distort, at some finite energetic cost. In cases where this distortion at the ground state is uniform across all the units in the assembly, the associated geometric frustration is said to be locally resolved. Such locally resolved frustration carries little implications on the morphology and response properties of the assembled structure. However, in many cases, for small enough assemblies there are non-local compromises that are more energetically favorable. These conformations are associated with non-uniform distortions and highly cooperative response between the molecular constituents. The cooperative nature of frustrated assemblies may result in growth arrest, tendency to form filaments, exotic response properties and large morphological variations during the growth of the assembly. Almost a century ago German mineralogist Ferdinand Bernauer discovered that a large fraction of small organic compounds could form twisted molecular crystals. These are straight and narrow needle-like structures with mesoscopic pitch, a crystalographically impossible structure. Recent revived interest in twisted molecular crystals discovered even more compounds that form these exotic assemblies and led to their study by modern means. Electron microscopy revealed straight faceted structures with sharp diffraction peaks in selected area electron diffraction, much like regular crystals. Moreover, the pitch of the molecular crystals varied with size, with thicker crystals exhibiting less twist. In this work we review twisted molecular crystals as frustrated assemblies. In this approach twist emerges from the preferred morphology at the constituent scale, and gets attenuated with size by the incompatibility of twist and large-scale crystalline order. We discuss two distinct mechanisms that produce twisted molecular crystals, and provide a prediction for the twist decay as a function of the crystals’ spatial dimensions.     

Homogeneous Desulfurization of Thiols and Sulfides by Yb[N(SiMe3)2]2.2 THF. Relevance to Heterogeneous and Biological Desulfurizations and the Synthesis of Lanthanide(II) Sulfides

Yb[N(SiMe₃)₂]₂·2THF was found to desulfurize thiols (RSH) and dibenzyl sulfide. With thiols, the extent of desulfurization was a function of the relative stability of the corresponding radical, R·. Radicals were also involved in the desulfurization of dibenzyl sulfide. A unified mechanism involving a series of one-electron redox steps leading to the generation of organic radical intermediates has been proposed.     

Faulty Plant Reconfiguration Based on Disturbance Decoupling Methods

The disturbance decoupling problem by dynamic measurement feedback (DDDPM) for discrete‐time nonlinear control systems is considered in this paper. The mathematical approach known under the name “the algebra of functions” is used to derive an algorithm that finds, whenever possible, a measurement feedback which solves the DDDPM. Finally, the applicability of the DDDPM in fault tolerant control (FTC) is discussed.     

The end of cheap oil: Current status and prospects

This paper, analyses the factors impacting the price of crude oil in order to examine the likely evolution of the oil market and attempts to answer the question, whether cheap oil is already a thing of the past. Based on data made publicly available mostly by the major oil companies, it examines the effects of demand and supply, the evolution of world oil reserves, the trends in new discoveries of new oilfields, the evolution of world Gross Domestic Product (GDP), and the depletion of oil resources. The analysis concludes that the world peak in conventional oil production—the point beyond which oil production will irreversibly start declining—is approaching and will be reached, even according to the most optimistic scenarios, before 2040 and quite possibly much sooner. If the appropriate solutions for substituting crude oil and for conserving the use of energy are not implemented in time, then the current upward trend in oil prices is bound to continue.     

The effect of solids on the electrochemical treatment of olive mill effluents

The electrochemical oxidation of an olive mill effluent over Ti–Pt anodes was studied. The effluent had an average total chemical oxygen demand (COD) value of 234 g L^?1, soluble COD of 61 g L^?1, soluble phenolic content 3.4 g L^?1, total solids of 80 g L^?1 and pH = 5.1. Experiments were conducted in a 10 L vessel with the effluent recirculating at 1 L s^?1. The applied current was varied between 5 and 20 A, the salinity between 1 and 4% NaCl, and experiments were performed with the effluent diluted with water to achieve the desired initial concentration. Emphasis was given to the effect of the presence of solids as well as of varying operating conditions on process performance as assessed in terms of COD, color and phenols removal. In general, degradation of phenols occurred relatively fast with conversion increasing with increasing applied current and decreasing initial organic loading and this was accompanied by low COD removal levels and moderate decolorization. The presence of solids had practically no effect on phenols removal, which, in most cases, was complete in less than about 180 min of reaction. However, oxidation in the presence of solids resulted in a substantial solid fraction being dissolved and this consequently increased sample color and the soluble COD content. The solid content typically found in olive mill effluents may partially impede its treatment by electrochemical oxidation, thus requiring more severe operating conditions and greater energy consumption. Copyright © 2007 Society of Chemical Industry     

Irreducibility, reduction and transfer equivalence of nonlinear input–output equations on homogeneous time scales

The purpose of this paper is to present a necessary and sufficient condition for irreducibility of nonlinear input–output delta differential equations. The condition is presented in terms of the common left divisor of two differential polynomials describing the behaviour of the system defined on a homogenous time scale. The concept of reduction is explained. Subsequently, the definition of transfer equivalence based upon the notion of an irreducible differential form of the system is introduced, inspired by the analogous definition for continuous-time systems.     

On classical state space realisability of quadratic input–output differential equations

This article studies the realisability property of continuous-time quadratic input–output (i/o) equations in the classical state space form. Constraints on the parameters of the quadratic i/o model are suggested that lead to realisable models. The complete list of second- and third-order realisable i/o quadratic models is given and two subclasses of the n-th order realisable i/o quadratic systems are suggested. Our conditions rely basically upon the property that certain combinations of coefficients of the i/o equations are zero or not zero. We provide explicit state equations for realisable second-order quadratic i/o equations, and for one realisable subclass of quadratic i/o equations of arbitrary order.     

On realizability of neural networks-based input-output models in the classical state-space form

This paper proves that the typical neural network-based input/output model does not have a state-space realization and suggests the Additive Nonlinear Auto-Regressive with eXogenous input (ANARX) structure as an excellent choice for neural-network-based input-output models. The advantage of the ANARX model is that the time-steps in the argument are pair-wise decomposed, which allows the ANARX model to be realized in state space, and to be linearized via dynamic output feedback. Moreover, accessibility of the state-space realization has been proved.     

Accommodation to defects in the discrete dynamic systems

Consideration was given to adaptation of the nonlinear dynamic systems to faults. The problem of accommodation by generating a control law enabling complete decoupling from the fault-generated actions was solved within this framework. The proposed approach was obtained in continuation of its earlier counterpart and for a wider class of systems enabled solution of the problem of accommodation and established a simpler—static, in particular,—solution.