Detection and Mitigation of Impulsive Interference on OFDM Signals Based on Spectrum Sensing,Blanking and Symbol Retransmission

The increasing number of wireless devices and systems operating on the same area leads to significant interference problems that need to be solved. This paper deals with detection and mitigation of the interference generated by an impulsive noise source on an orthogonal frequency division multiplexing system. The idea proposed here is to overcome the interference problem by exploiting the transmission of two replicas of the symbol affected by interference, that are suitably combined at the receiver after a blanking operation of the corrupted samples. An energy detection based sensing scheme is used to reveal the presence of interference. The proposed method allows to efficiently remove the interference without affecting the useful information and exploiting profitably the diversity gain against noise through the soft combining approach. Performance in terms of bit error rate and throughput is compared with the case without mitigation and with the classical blanking method showing a significant improvement. The reduction of the transmission rate, due to the retransmissions, is well compensated by the improvement of the data reliability that leads to an increase of useful data correctly received.     

Wetting of SiC by Al-Ti alloys and joining by in-situ formation of interfacial Ti3Si(Al)C2

Two pressureless and reliable procedures for brazing SiC-based materials have been designed. The joining was obtained by the in-situ formation of a Ti₃Si(Al)C₂ MAX phase using simple Al-Ti interlayers. Wettability studies were conducted using several Al-Ti alloys in contact with SiC at 1500?°C. The interfacial microstructures and thermodynamic analysis demonstrated that liquid Al₃Ti in contact with SiC formed a well-bonded Ti₃Si(Al)C₂ interfacial layer. These findings guided the design of two joining methods: one consisted of the simple infiltration of Al₃Ti into the brazing seam, while an Al₃Ti paste/Ti/Al₃Ti paste interlayer assembly was designed for the second process. Sound interfaces without cracks were obtained in both processes. The average shear strength was very high, 296?MPa, for the infiltration method; the drawback was the presence of residual Al. Joining through Al₃Ti/Ti/Al₃Ti interlayers avoided the presence of low-temperature melting phases, with lower shear strength: 85 or 89?MPa depending on the testing method.     

Ni-56Si合金对SiC陶瓷的润湿和铺展

采用座滴法考察了不同温度和气氛下Ni-56Si合金对SiC陶瓷的润湿和铺展行为。分析了固化后的液滴/SiC衬底界面和液滴表面的微结构和相组成。结果表明:该润湿体系于1350℃下在真空、1个大气压的静态或流动的Ar+5%(体积分数)H2的混合气3种气氛中均可获得优良的润湿性。在真空条件下,其铺展最快达到平衡,1350℃时的润湿性明显优于1100℃和1200℃,且在1100℃时的铺展过程与1350℃和1200℃有显著不同,即存在2种不同的铺展机制,这与SiC表面的润湿壁垒(SiO2层)的消除动力学有关。界面微结构分析进一步证实该系统的非反应润湿特性。     

Attacking Fair-Exchange Protocols: Parallel Models vs. Trace Models

Most approaches to formal protocol verification rely on an operational model based on traces of atomic actions. Modulo CSP, CCS, state-exploration, Higher Order Logic or strand spaces frills, authentication or secrecy are analyzed by looking at the existence or the absence of traces with a suitable property.We introduced an alternative operational approach based on parallel actions and an explicit representation of time. Our approach consists in specifying protocols within a logic language ( AL _SP), and associating the existence of an attack to the protocol with the existence of a model for the specifications of both the protocol and the attack.In this paper we show that, for a large class of protocols such as authentication and key exchange protocols, modeling in AL _SP is equivalent - as far as authentication and secrecy attacks are considered - to modeling in trace based models.We then consider fair exchange protocols introduced by N. Asokan et al. showing that parallel attacks may lead the trusted third party of the protocol into an inconsistent state. We show that the trace based model does not allow for the representation of this kind of attacks, whereas our approach can represent them.     

Stochastic Flow Analysis for Predicting River Scour of Cohesive Soils

Damage to bridge crossings during flood events endangers the lives of the traveling public and causes costly disruptions to traffic flow. The most common causes of bridge collapse are scouring of the streambed and banks and erosion of highway embankments. This study couples a synthetic river flow simulation technique with a scour model for cohesive soils and determines the expected scour depth for a given lifetime of the bridge. A fractionally differenced autoregressive integrated moving average model generates synthetic streamflow sequences of the same length as the expected lifetime of the bridge. The scour model predicts the progression of scour depth through time in a multilayered soil. The model is used to determine the scour depth associated with different replicates of the synthetic flow sequences of the same length as the lifetime of the bridge. The probability distribution of scour depth is estimated by repeating this simulation procedure over a number of independent realizations of streamflow series for a given life of the bridge. This approach provides a framework for the probabilistic design and risk analysis of bridge foundations subjected to scour.     

Diclofenac-hydrotalcite: In vitro and in vivo release experiments

Solutions of the anti-inflammatory drug diclofenac in ethanol and ethanol–water were prepared and mixed with hydrotalcite and hydrotalcite heated at 500 °C. Hydrotalcite pretreated at 500 °C showed a higher adsorption of diclofenac. Diclofenac-hydrotalcites were used for in vitro release experiments to evaluate the percutaneous absorption of diclofenac, using sets of eight Franz cells with membranes of stratum corneum epidermis obtained from human skin; a 2% diclofenac hydroalcoholic gel was used for comparison. Hydrotalcite pretreated at 500 °C is less suitable for release procedures, despite its higher adsorption capacity, whereas diclofenac adsorbed from ethanolic solution by untreated hydrotalcite presents the most efficient sample and shows the best permeation profiles. This sample was selected for the in vivo experiments. Ten healthy volunteers participated on the in vivo experiments: the diclofenac-hydrotalcite appeared to be useful for an efficient application on human skin as inhibitor of the UV-induced erythemas, also better than the usual gel samples.     

An efficient interpreter for the lambda-calculus

A call-by-need reduction algorithm for the LAMBDA-calculus is presented. Call-by-need is as efficient as call-by-value and is equivalent to call-by-name in languages without side effects. The algorithm, which is the core of a running system, is presented by illustrating successive transformations of a straightforward implementation of the classical definition of reduction in the LAMBDA-calculus. All notions and algorithms are introduced as LISP code.