Friction and wear on the atomic scale

Friction force microscopy experiments have been performed under ultrahigh vacuum conditions. Within a small force regime (below 1 nN), friction without wear is observed as a function of velocity on ionic crystals and metals. The results are discussed in the framework of a refined version of the Tomlinson model, which includes thermal activation. Higher normal forces lead to abrasive wear. The debris extracted from ionic crystals can be characterized with high lateral resolution. The dependence of wear rate on velocity and normal force is investigated.     

ARMIDA TM: Multimedia Applications across ATM-Based Networks Accessed via Internet Navigation

ARMIDA TM (Applications Retrieving Multimedia Information Distributed over ATM) is a prototypical system for experimental applications based on the interactive retrieval of multimedia information from remote data bases over ATM networks. ARMIDA TM aims at being compliant with the specifications issued by the Digital Audio Visual Council (DAVIC) for interactive multimedia services and applications, as well as at representing a sample implementation of the system specified in DAVIC 1.0. The present paper illustrates the way ARMIDA TM works to provide these applications, by describing the system hardware and software architecture and its main components, with a particular concern towards the way they interact to implement the required functionality.     

The impact of the dependence structure in risk management: a focus on credit-risk

The aim of the paper is to discuss the important role of the dependence structure in risk management. Therefore, we focus on credit-risk and propose an innovative model to value the credit risk of a portfolio. This new approach (HYC for short) is based on a hierarchical hybrid copula and involves a clusterization of the portfolio in several risk's classes. The HYC model is classified as hybrid because the computation of the loss cdf depends on the class's cardinality: for large groups one is justified to apply a limiting approach, while for small ones one applies a procedure preserving the granularity of the group itself. In order to appreciate the impact of the dependence structure in credit-risk evaluation, a VaR analysis based on the HYC loss function is here compared to the CreditMetrics approach in an in-sample exercise and to the empirical VaR in an out-of sample exercise aimed to test the forecasting effectiveness of the model. This comparison allows us to appreciate over/under-valuation of the capital detained from the financial institution. Moreover, the impact of an enlargement of the dependence structure is discussed with respect to the systemic/contagious effects in the context of a portfolio optimisation with constraint on a sub-portfolio's risk.     

Optimization‐based adaptive sliding mode control with application to vehicle dynamics control

This paper presents the design of a new adaptive optimization‐based second‐order sliding mode control algorithm for uncertain nonlinear systems. It is designed on the basis of a second‐order sliding mode control with optimal reaching, with the aim of reducing the control effort while maintaining all the positive aspects in terms of finite‐time convergence and robustness in front of matched uncertainties. These features are beneficial to guarantee good performance in case of vehicle dynamics control, a crucial topic in the light of the increasing demand of semiautonomous and autonomous driving capabilities in commercial vehicles. The new proposal is theoretically analyzed, as well as verified relying on an extensive comparative study, carried out on a realistic simulator of a 4‐wheeled vehicle, in the case of a lateral stability control system.     

Synthesis and characterisation of a porous Al scaffold sintered from NaAlH<Subscript>4</Subscript>

A simple and cost-effective method for the synthesis of a porous Al scaffold has been optimised using only NaAlH₄ and TiCl₃. The starting materials were compacted into a pellet and sintered under dynamic vacuum to remove the Na and H₂. The sintering conditions, such as vacuum level, temperature, and time, were the key factors that influenced both the extraction of Na and H₂ from the pellet and the overall porosity. Quantitative phase analysis by X-ray diffraction revealed that after the sintering process, the as-prepared porous Al scaffold consisted primarily of Al. Morphological observations conducted by scanning electron microscopy showed that the scaffold exhibited an open network of pores with a small number of mesopores and no formation of micropores. The specific surface area of the scaffold was determined to be 7.9 ± 0.1 and 6.0 ± 0.5 m²/g by the Brunauer–Emmet–Teller method and from small-angle X-ray scattering measurements, respectively. The total porosity of the Al scaffold was 44.6%.     

3D Scaffolds to Study Basic Cell Biology

Mimicking the properties of the extracellular matrix is crucial for developing in vitro models of the physiological microenvironment of living cells. Among other techniques, 3D direct laser writing (DLW) has emerged as a promising technology for realizing tailored 3D scaffolds for cell biology studies. Here, results based on DLW addressing basic biological issues, e.g., cell‐force measurements and selective 3D cell spreading on functionalized structures are reviewed. Continuous future progress in DLW materials engineering and innovative approaches for scaffold fabrication will enable further applications of DLW in applied biomedical research and tissue engineering.     

Translation-based approaches for solving disjunctive temporal problems with preferences

Disjunctive Temporal Problems (DTPs) with Preferences (DTPPs) extend DTPs with piece-wise constant preference functions associated to each constraint of the form l ≤ x ? y ≤ u, where x,y are (real or integer) variables, and l,u are numeric constants. The goal is to find an assignment to the variables of the problem that maximizes the sum of the preference values of satisfied DTP constraints, where such values are obtained by aggregating the preference functions of the satisfied constraints in it under a “max” semantic. The state-of-the-art approach in the field, implemented in the native DTPP solver Maxilitis, extends the approach of the native DTP solver Epilitis. In this paper we present alternative approaches that translate DTPPs to Maximum Satisfiability of a set of Boolean combination of constraints of the form l?x ? y?u, ? ∈{<,≤}, that extend previous work dealing with constant preference functions only. We prove correctness and completeness of the approaches. Results obtained with the Satisfiability Modulo Theories (SMT) solvers Yices and MathSAT on randomly generated DTPPs and DTPPs built from real-world benchmarks, show that one of our translation is competitive to, and can be faster than, Maxilitis (This is an extended and revised version of Bourguet et al. 2013).     

Onion under Microscope: An in-depth analysis of the Tor Web

World Wide Web - Tor is an open source software that allows accessing various kinds of resources, known as hidden services, while guaranteeing sender and receiver anonymity. Tor relies on a free,...     

Honeycomb supports with high thermal conductivity for gas/solid chemical processes

The scope of this review article is to address the use of novel monolithic catalysts with high thermal conductivity in externally cooled tubular reactors for gas/solid exothermic chemical processes in place of conventional packed beds of catalyst pellets.

After discussing the analysis and the implications of heat conduction in honeycomb monolith structures, we review herein simulation studies and experimental investigations showing that near-isothermal reactor operation can be achieved even under very high thermal loads by adopting specific materials and designs of the honeycomb supports associated with high effective radial thermal conductivities. For such monoliths, the limiting thermal resistance is located at the interface between the monolith and the inner tube wall (“gap resistance”). Recent measurements of the “gap” heat transfer coefficient point to very large values (>400 W/(m² K)), which are controlled both by the tube–monolith clearance at the actual operating conditions and by the thermal conductivity of the process gas.