Synthesis, optical and morphological characterization of soluble main chain 1,3,4-oxadiazole copolyarylethers—potential candidates for solar cells applications as electron acceptors

New copoly(arylether)s containing substituted terphenyl, quinquephenyl, fluorene and anthracene moieties with aromatic 1,3,4-oxadiazole units were prepared and the resulting copolymers are soluble in common organic solvents. Investigation of their optical properties revealed that they emit blue and yellow light. Moreover, their photovoltaic response was studied in blends with poly(3-hexylthiophene) (P3HT) as the electron donor. Despite the low power conversion efficiencies it was shown that photo-induced electron transfer does take place and the performances are higher than a single layer P3HT device. In addition, an anthracene-fluorene-oxadiazole main chain copolymer (PAFOXD) was also examined in a single layer photovoltaic device and gave one of the highest reported open-circuit voltage (V_oc) values in the literature (0.89 V). Finally, a detailed morphological study of the blends and the PAFOXD surface using the atomic force microscopy (AFM) technique, revealed the effect of solvent selection to the preparation of thin films exhibiting the desired performance characteristics.     

Scalable total BETI based solver for 3D multibody frictionless contact problems in mechanical engineering

A total BETI (TBETI) based domain decomposition algorithm with the preconditioning by a natural coarse grid of the rigid body motions is adapted for the solution of multibody frictionless contact problems of linear elastostatics and proved to be scalable, i.e., the cost of the solution is asymptotically proportional to the number of variables. The analysis admits floating bodies. The proofs combine the original results by Langer and Steinbach on the scalability of BETI for linear problems and our development of optimal quadratic programming algorithms for bound and equality constrained problems. The theoretical results are verified by numerical experiments. The power of the method is demonstrated on the analysis of ball bearings.     

An editing tool that manages device associations in an in-home environment

The forthcoming home environment will comprise numerous computationally enhanced artifacts that are autonomous, but interconnected via an invisible web of network-based services. The approach presented in this paper is to enable end users to make their own applications by linking such artifacts, which are treated as reusable components. A key requirement to achieve this is the availability of editing tools that meet the needs of different classes of users. A tool of this kind designed for end users is presented in this paper, together with the outcome of user evaluation sessions.     

Interrelation of Flooding and Complete Dispersion in Agitated Gas‐Liquid Contactors

Despite the fact that the complete dispersion characteristics in agitated gas‐liquid contactors are operationally important, the flooding‐loading transition is widely used as a design criterion, due to its experimental convenience and accuracy. Moreover, limited data are available in the literature on the interrelation of the flooding‐loading and the loading‐complete dispersion transitions, although several investigators have worked on these two transition stages. Thus, knowledge of the interrelation between these two stages would be of theoretical and practical importance. In this work, the dependence of the stirrer speed at complete dispersion, n_CD, on the stirrer speed at flooding, n_F, was experimentally studied, in coalescing and non‐coalescing systems, using Rushton turbines of two different diameters. The experimental results, having an accuracy of < 5 %, are given in the form of a dimensionless correlation.     

Location-Aided Handover in Heterogeneous Wireless Networks

The concept of being always online, regardless of the time and place, has been one of the hot topics in the commercial and scientific forums during the last years. The term itself is not solidly defined, however it is often used to refer to user's ability to get the same services via changing variety of underlying networks. In order to really work, this kind of multiaccess in heterogeneous networks still requires research, technological achievements and even compromises. The key to successfully implement the multiaccess is vertical handover that allows the application services to be seamlessly transferred between different networks.     

Cellular Network Performance Analysis: Handoff Algorithms Based on Mobile Location and Area Information

Mobile world's rapid growth has spurred development of new protocols and new algorithms to meet changing operation requirements such as mobile networking, and quality-of-service support. A key requirement in the bearer capabilities is the handover. The freedom to be able to make and receive calls anywhere, at any time, creating a totally new dimension in human communications has frequently been advertised as the main advantage of new wireless systems. Handovers are a key concept in providing this mobility. It makes it possible for a user to travel from one cell to another while having a seamless connection. Network operators give emphasis to optimize handover, since it is strongly related to dropped calls, network overload and subsequently users' criticism. The ability of a cellular network to perform efficient handovers is crucial to offer attractive services as real-time applications or streaming media as planned in third generation networks. Since signal propagation and pathloss are complex in nature, we can expect unnecessary and wrong handoff executions. Both UMTS and those of the second generation (GSM) systems will require redefined handoff algorithms of active connections as the smooth mobility support and continuous connection are essential issues for obtaining high performance and increasing user satisfaction. In this paper we present a set of intelligent algorithms using the mobile terminal (MT) location information and area awareness to assist safe handoff decisions. The implemented algorithms are validated by means of cellular network simulators that clearly show the impact of these techniques to major system performance metrics.     

Wireless Personal Communications special issue on Cellular and Wireless Location Based Technologies and Services

Wireless Personal Communications -     

Environmentally Friendly Precision Machining

Material removal processing has been investigated both theoretically and experimentally to a certain extent. The demands for environmentally friendly processes impose new parameters such as the use of minimal quantity or even the complete omission of cutting fluids. Therefore, the related processes need to be newly studied in order to be optimized for specific cutting conditions. Cutting fluids are used in material removal processes mainly for lubrication, reduction of the temperature in the cutting region, and increase of tool life. However, cutting fluids are associated with skin and breathing problems of the machine operators. Furthermore, after their disposal and if, as in most cases, recycling is not possible, they may become polluting agents in soil and water when inappropriately handled. In this paper the case of hard cutting, a process that can be performed without the use of a cutting fluid, is investigated. A discussion on the technological parameters involved is given and experimental data are presented in order to point out the environmental as well as the economical benefits emerging from the use of such a technology.     

Vortex depth in unbaffled single and multiple impeller agitated vessels

Although vortex formation is usually an undesirable phenomenon in the process industry, satisfactory process conditions and results can also be obtained in unbaffled agitated vessels in the presence of a vortex. This fact and especially the low power requirements in these systems, with their immediate relevance to the energy problem in the process industry, show the true importance of vortex formation in agitated vessels. This article reviews the literature results and the correlations proposed for the prediction of vortex depth in unbaffled agitated vessels with various types of single and multiple impeller systems and presents a critical discussion on the basis of a theoretical analysis.