Modeling and testing of energy absorbing lightweight materials and structures for automotive applications

As a consequence of the increasing demands in automotive industry concerning crashworthiness and passive safety, the concern for energy management and safety demands also increases. The goal of energy management is to reduce the forces and stresses on an occupant or a pedestrian during a crash event; in some cases it may be possible to reduce the forces by a factor of two. This requires usage of new advanced materials in automotive components. Energy absorbing foams and other lightweight materials like plastics and polymer composites are increasingly used in automotive industry. Hence, extensive study of energy absorbing behavior of these materials as well as the automotive components is needed for further improvements in numerical modeling and crash simulations. The paper enlightens recent advances in investigation of mechanical properties and energy absorption ability of the mentioned lightweight materials as well as modeling with finite element codes for crash simulations.     

Learning and clustering of fuzzy cognitive maps for travel behaviour analysis

In modern society, more and more attention is given to the increase in public transportation or bike use. In this regard, one of the most important issues is to find and analyse the factors influencing car dependency and the attitudes of people in terms of preferred transport mode. Although the individuals’ transport behavioural modelling is a complex task, it has a notable social and economic impact. Thus, in this paper, fuzzy cognitive maps are explored to represent the behaviour and operation of such complex systems. This soft-computing technique allows modelling how the travellers make decisions based on their knowledge of different transport modes properties at different levels of abstraction. These levels correspond to the hierarchy perception including different scenarios of travelling, different benefits of choosing a specific travel mode, and different situations and attributes related to those benefits. We use learning and clustering of fuzzy cognitive maps to describe travellers’ behaviour and change trends in different abstraction levels. Cluster estimations are done before and after the learning of the maps, in order to compare people’s way of thinking if only considering an initial view of a transport mode decision for a daily activity, and when they really have a deeper reasoning process in view of benefits and consequences. The results of this study will help transportation policy decision makers in better understanding of people’s needs and consequently will help them actualizing different policy formulations and implementations.     

Interplay between Endothelin and Erythropoietin in Astroglia: The Role in Protection against Hypoxia

We show that, under in vitro conditions, the vulnerability of astroglia to hypoxia is reflected by alterations in endothelin (ET)-1 release and capacity of erythropoietin (EPO) to regulate ET-1 levels. Exposure of cells to 24 h hypoxia did not induce changes in ET-1 release, while 48–72 h hypoxia resulted in increase of ET-1 release from astrocytes that could be abolished by EPO. The endothelin receptor type A (ETA) antagonist BQ123 increased extracellular levels of ET-1 in human fetal astroglial cell line (SV-FHAS). The survival and proliferation of rat primary astrocytes, neural precursors, and neurons upon hypoxic conditions were increased upon administration of BQ123. Hypoxic injury and aging affected the interaction between the EPO and ET systems. Under hypoxia EPO decreased ET-1 release from astrocytes, while ETA receptor blockade enhanced the expression of EPO mRNA and EPO receptor in culture-aged rat astroglia. The blockade of ETA receptor can increase the availability of ET-1 to the ETB receptor and can potentiate the neuroprotective effects of EPO. Thus, the new therapeutic use of combined administration of EPO and ETA receptor antagonists during hypoxia-associated neurodegenerative disorders of the central nervous system (CNS) can be suggested.     

Study of the X-ray optical anisotropy of materials via X-ray interferometry

A new method for studying the X-ray optical anisotropy of materials which is based on the X-ray interferometric technique of measurement is described. Unlike the existing methods, in which the sample under study is placed in the path of one of the interfering beams, the test samples in the proposed method are placed directly in the path of two interfering beams; this eliminates the effect of other factors on the displacement of the interference moirefringes. In this method, moirefringes simultaneously occur during the same exposure both in the absence and in the presence of samples with different orientations of the optical axes. A relative displacement of moirefringes is observed in three different columns of the same beam, which makes it possible not only to simultaneously observe and immediately identify the presence of X-ray optical anisotropy but also to measure the values of refractive indexes n _o and n _e for a given sample (n _o is the refractive index for an emission with the polarization perpendicular to the principal cross section, and n _e is the refractive index for a beam with the polarization in the plane of the principal section and parallel to the optical axis). The new method is used to record the X-ray optical anisotropy of a cellophane film and to measure the values of refractive indexes n _o and n _e for cellophane. It is found that the cellophane film is an X-ray optically positive anisotropic medium.     

On the Fixed-Parameter Tractability of the Maximum Connectivity Improvement Problem

Theory of Computing Systems - In the Maximum Connectivity Improvement (MCI) problem, we are given a directed graph G = (V,E) and an integer B and we are asked to find B new edges to be added to G...