A solidification model for prediction of castability in the precipitation-strengthened nickel-based superalloys

The Scheil equation was used to model the solidification path, microsegregation of alloying elements in the interdendritic regions, solidification temperature ranges, and to predict the formation of secondary structures and the castability behavior of as-cast superalloys. 4 experimental alloys with pre-specified γ-Ti,Nb,Al,Mo composition containing different Nb, Ti and Al contents were designed using vacuum induction melting furnace. The produced as-cast superalloys were characterized using optical and scanning electron microscopy equipped with energy dispersive X-ray spectrometer and TG–DSC analysis. The experiments showed logic conformity to the modeling results. The model and experiment confirmed the highest segregation behavior for Ti and Nb. All the experimental superalloys indicated the remarkable tendency to form secondary eutectic structures at the last stages of solidification. Superalloy with chemical composition of γ-3.5%Mo,1.8%Al,4%Ti,2.9%Nb showed the shorter solidification temperature range and the best castability.     

Morphological,Electrical, and Chemical Changes in Cyclically Contacting Polycrystalline Silicon Surfaces Coated with Perfluoroalkylsilane Self-Assembled Monolayer

The evolution of morphology, electrical properties, and chemical composition has been studied in cyclically contacting polycrystalline silicon (polysilicon) surfaces coated with perfluoroalkylsilane self-assembled monolayer (SAM). The microinstrument used is a MEMS cantilever that is repeatedly actuated out-of-plane to impact a landing pad and is then moved in-plane to enable nondestructive in situ inspection of the impacted area. Analyses show that a device with a monolayer coating exhibits signs of surface degradation after a much higher number of cycles than its uncoated counterpart. A sharp increase in contact resistance between the cantilever and landing pad is observed at ~10 billion cycles for a coated device, versus ~25 million cycles for an uncoated device. Likewise, the onset of grain fracture in the landing pad occurs at ~25 billion cycles for the SAM-coated device, versus ~3 billion cycles for its uncoated counterpart. The effectiveness of the monolayer coating diminishes after more than 100 billion contact cycles as the SAM layer is removed, and the polysilicon substrate becomes susceptible to adhesive wear.     

Cyclic bond behaviour of plain bars. Part I: Experimental investigation

In recent years there has been wide use of non-linear dynamic analysis for the evaluation of existing structures in areas of high seismic risk. In the simulation of the cyclic behaviour of elements in reinforced concrete (RC) its bonding performance cannot be ignored. There are numerous numerical models developed in recent decades which can explicitly account for the slip between reinforcing bars and the surrounding concrete through the definition of the local hysteretic bond–slip relationship. As for plain bars, commonly used in reinforced concrete buildings before the 1970s, there are almost no references to hysteretic bond mechanisms.This paper describes the results of a series of monotonic and cyclic pull-out tests aimed at the assessment of the bond performances of plain round bars. Monotonic behaviour is characterized by a first ascending branch, up to the maximum bond strength; in this phase, as the slip increases, chemical–physical adhesion and micro-interlocking between the cement paste and the indentations of the bar surface progressively activate. During post-peak phase the only frictional contribute is present, gradually degrading towards a minimum value as the slip increases. The two parameters, maximum bond strength and minimum frictional bond, in spite of the high variability shown, seem to reflect well the literature indications about bond performances of plain bars. In cyclic field, where the only frictional mechanism is present, experimental results show a significant degradation of bond capacities. Hysteretic cycles show a singular shape, characterized by a reloading phase showing a slight reduction for slip values approaching zero and a subsequent increase in bond stress towards the maximum imposed slip. Bond stresses in cyclic field show a high variability, but it is generally possible to recognize a decreasing trend both with the number of cycles and with the maximum imposed slip.     

One year of ICTP diploma courses on-line using the automated EyA recording system

The 12-month pre-Ph.D. ICTP Diploma Courses in the fields of Condensed Matter Physics, High Energy Physics, Mathematics, Earth System Physics and Basics Physics have been recorded using the automated, low cost recording system called EyA developed in-house. We discuss the technical details on how these recordings were implemented, together with some web usage statistics and students feedback. As yet, no similar endeavor has been made to put on-line a complete high-level Diploma Programme, due to the high costs involved when using alternative recording solutions. These recordings are freely available on the website www.ictp.tv.     

Removal of exhausted oils by adsorption on mixed Ca and Mg oxides

Adsorption tests were performed on two different exhausted oils to reduce their polluting and health hazard potential: a "water-insoluble oil", utilised for automotive engine lubrication, and an "emulsified" oil, used as coolant for metal-cutting tools. Dolomite, a low-cost recovery material, was used to prepare two effective adsorbents: (a) a mixed Ca and Mg oxide obtained by thermal decomposition of dolomite at 1800 degrees C, and (b) an activated material obtained by submitting this product to chemical treatment with HCl. Preliminary tests carried out with an excess of the former material showed that the insoluble oil was adsorbed with lower yield (Y = 0.40) than the soluble (emulsified) oil (Y = 0.60). The material activation with HCl remarkably improved the adsorption of soluble oil organic fraction (Y > 0.90), while only a little increase in the removal yield was observed for the insoluble oil (Y = 0.44). The results presented and discussed in this work pointed out that the products of dolomite calcination can successfully replace the conventional adsorbing materials in the removal of organic pollutants, with particular concern to exhausted soluble oils, which cannot usually be recycled, thus reducing the operational costs of their treatment.     

The intriguing role of spanish language vocabulary knowledge in predicting English reading comprehension.

This study explored a holistic model of English reading comprehension among a sample of 135 Spanish-English bilingual Latina and Latino 4th-grade students This model took into account Spanish language reading skills and language of initial literacy instruction. Controlling for language of instruction, English decoding skill, and English oral language proficiency, the authors explored the effects of Spanish language alphabetic knowledge, fluency, vocabulary knowledge, and listening comprehension on English reading comprehension. Results revealed a significant main effect for Spanish vocabulary knowledge and an interaction between Spanish vocabulary and English fluency, such that faster English readers benefited more from Spanish vocabulary knowledge than their less fluent counterparts. This study demonstrates the existence of literary skills transfer from the 1st to the 2nd language, as well as limits on such transfer. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Simon effect with and without awareness of the accessory stimulus.

The authors investigated whether a Simon effect could be observed in an accessory-stimulus Simon task when participants were unaware of the task-irrelevant accessory cue. In Experiment 1A a central visual target was accompanied by a suprathreshold visual lateral cue. A regular Simon effect (i.e., faster cue-response corresponding reaction times [RTs]) was found. Experiment 1B demonstrated that this effect cannot be attributed to perceptual grouping of the target and cue. Experiments 2A, 2B, and 2C showed a reverse Simon effect (i.e., faster noncorresponding RTs) when participants were not aware of the cue. In this condition, the Simon effect would occur relative to the reorientation of attention from the cue, which would initially capture attention, toward the target. This conclusion is supported by the results of Experiments 3A and 3B, in which the reorientation of attention was induced by having the target flash after its onset. With suprathreshold cues either a reverse or regular Simon effect was observed by using a 100-ms or ≥200-ms onset flashing interval, respectively, whereas with subthreshold cues a reverse Simon effect was found irrespective of the interval length. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A super-peer model for resource discovery services in large-scale Grids

As deployed Grids increase from tens to thousands of nodes, peer-to-peer (P2P) techniques and protocols can be used to implement scalable services and applications. The super-peer model is a novel approach that helps the convergence of P2P models and Grid environments and can be used to deploy a P2P information service in Grids. A super-peer serves a single physical organization in a Grid, and manages metadata associated to the resources provided by the nodes of that organization. Super-peers connect to each other to form a peer network at a higher level. This paper examines how the super-peer model can handle membership management and resource discovery services in a multi-organizational Grid. A simulation analysis evaluates the performance of a resource discovery protocol; simulation results can be used to tune protocol parameters in order to increase search efficiency.     

Quantitative Assessment of a Peer-to-peer Cooperative Infrastructure Using Stochastic Well-Formed Nets

Traditional support tools for software engineers, normally based on a client-server architecture, are unsuitable to deal with the new issues emerging from the current (and future) cooperative work scenarios (where connectivity is intrinsically transient, the number of interacting partners dynamically changes, etc.). This paper presents a quantitative assessment of a fully decentralized, peer-to-peer, cooperative infrastructure. Stochastic Well-Formed Nets (SWNs) modelling the new peer-to-peer architecture, and a traditional (client-server) one, are developed and analysed: we used SWNs for their ability to directly exploit the symmetries intrinsically present in the modelled systems, thus greatly reducing the complexity of the analysis. The main goal is to compare the impact of the two alternative protocols on the collaborative work. Together with the performance figures of interest, methodological issues concerning the choice of the most appropriate model abstraction level, the adoption of a compositional modelling approach, and the management of the model complexity are also discussed.     

CAD tools for aesthetic engineering

The role of computers and of computer-aided design tools for the creation of geometrical shapes that will be judged primarily by aesthetic considerations is reviewed. Examples are the procedural generation of abstract geometrical sculpture or the shape optimization of constrained curves and surfaces with some global ‘cost’ functional. Different possibilities for such ‘beauty functionals’ are discussed. Moreover, rapid prototyping tools based on layered manufacturing now add a new dimension to the visualization of emerging designs. Finally, true interactivity of the CAD tools allows a more effective exploration of larger parts of the design space and can thereby result in an actual amplification of the creative process.