Theoretical Investigation of the Size Effect on the Oxygen Adsorption Energy of Coinage Metal Nanoparticles

Catalysis Letters - This study evaluates the finite size effect on the oxygen adsorption energy of coinage metal (Cu, Ag and Au) cuboctahedral nanoparticles in the size range of 13 to 1415 atoms...     

The Intergenerational Transmission of Perfectionism: Parents' Psychological Control as an Intervening Variable.

The present study investigated the role of parental (adaptive and maladaptive) intrapersonal perfectionism as a predictor of parental psychological control and the role of parents' psychological control in the intergenerational transmission of perfectionism in a sample of female late adolescents and their parents. First, parental maladaptive perfectionism, but not parental adaptive perfectionism, significantly predicted parents' psychological control even when controlling for parents' neuroticism. This relationship was found to be stronger for fathers than for mothers. Second, a significant direct relationship was found between mothers' and daughters' maladaptive perfectionism but not between fathers' and daughters' maladaptive perfectionism. Third, process analyses showed that, for both mothers and fathers, psychological control is an intervening variable in the relationship between parents' and daughters' maladaptive perfectionism. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Strategies for Reducing Stress in Ultrasonic Cutting Systems

Abstract:  Ultrasonic cutting is an established technology in the cutting of food products. As the high-cost components of an ultrasonic cutting system are the ultrasonic generator and transducer, some designs have concentrated on running several cutting blades from a single power source. This strategy is undoubtedly economic, but problems remain with reliability. Blade failure during cutting is a common problem in ultrasonic systems and therefore strategies are proposed to reduce stress levels at the failure locations. Many alternative blade profiles are investigated using finite element (FE) models, which are validated by experimental modal analysis (EMA) using a 3D laser Doppler vibrometer (LDV). Combining three strategies can reduce the stress level at the failure location on cutting blades. The first investigates the blade profile at the failure location with the aim of incorporating sufficient gain at reduced stress levels. The second concentrates on detuning the block horn and blades in order to move the longitudinal node away from the highest stressed section of the blade. Finally, a redesign of the block horn is studied in order to eliminate the effects of blade flexural vibrations in the longitudinal cutting mode.     

On the modelling of bubbly flow in vertical pipes

To qualify CFD codes for two-phase flows, they have to be equipped with constitutive models standing for the interaction between the gaseous and the liquid phases. In case of bubbly flow this particularly concerns the forces acting on the bubbles and bubble coalescence and break-up. Applying a two fluid approach, besides the drag forces describing the momentum exchange in flow direction, the non-drag forces acting perpendicular to the flow direction play an important role for the development of the flow structure. Gas–liquid flow in vertical pipes is a very good object for studying the corresponding phenomena. Here, the bubbles move under clear boundary conditions, resulting in a shear field of nearly constant structure where the bubbles rise for a comparatively long time. The evolution of the flow within the pipe depends on a very complex interaction between bubble forces and bubble coalescence and break-up, e.g. the lift-force, which strongly influences the radial distribution of the bubbles, changes its sign depending on the bubble diameter. The consequence is the radial separation of small and large bubbles. Neglecting this phenomenon, models are not able to describe the correct flow structure. Extensive experiments measuring the radial gas volume fraction distribution, the bubble size distribution and the radial residence of bubbles dependent on their size were determined for different distances from the gas injection. Basing on these experiments the applicability and the limits for the simulation of bubble flow with current CFD-codes are demonstrated, using the simulation of vertical pipe flow with CFX-4 as an example. Using a simplified model focusing particularly on the radial phenomena described above, parametric studies were conducted. They give an indication for necessary improvements of the codes. Finally a possible way for the improvement of the CFD-codes is shown.     

Weakest pre-condition reasoning for Java programs with JML annotations

This paper distinguishes several different approaches to organising a weakest pre-condition (WP) calculus in a theorem prover. The implementation of two of these approaches for Java within the LOOP project is described. This involves the WP-infrastructures in the higher order logic of the theorem prover PVS, together with associated rules and strategies for automatically proving JML specifications for Java implementations. The soundness of all WP-rules has been proven on the basis of the underlying Java semantics. These WP-calculi are integrated with the existing Hoare logic, and together form a verification toolkit in PVS: typically one uses Hoare logic rules to break a large verification task up into smaller parts that can be handled automatically by one of the WP-strategies.     

Source code verification of a secure payment applet

This paper discusses a case study in formal verification and development of secure smart card applications. An elementary Java Card electronic purse applet is presented whose specification can be simply formulated as “in normal operation, the applet’s balance field can only be decreased, never increased”. The applet features a challenge-response mechanism which allows legitimate terminals to increase the balance by putting the applet into a special operation mode. A systematic approach is used to guarantee a secure flow of control within the applet: appropriate transition properties are first formalized as a finite state machine, then incorporated in the specification, and finally formally verified using the Loop translation tool and the PVS theorem prover.     

Simulations in Coalgebra

A new approach to simulations is proposed within the theory of coalgebras by taking a notion of order on a functor as primitive. Such an order forms a basic building block for a “lax relation lifting”, or “relator” as used by other authors. Simulations appear as coalgebras of this lifted functor, and similarity as greatest simulation. Two-way similarity is then similarity in both directions. In general, it is different from bisimilarity (in the usual coalgebraic sense), but a sufficient condition is formulated (and illustrated) to ensure that bisimilarity and two-way similarity coincide. Also, a distributive law is identified which ensures that similarity on a final coalgebra forms a dcpo structure.     

AN EVALUATION OF THE ECONOMICS OF FUEL CELLS IN URBAN BUSES

One of the contenders for a clean source of on-board electric power in a vehicle is the fuel cell: an electrochemical device that transforms the chemical energy stored in a fuel directly into electricity. While less widely known and less far advanced than batteries, fuel cells hold a considerable potential to provide the power for a novel generation of non-polluting vehicles. At present, fuel cell technology is entering the stage of commercialization, which is an appropriate moment to try and assess its economic potential in the field of transport. Based on a review of the present state of the technology, concentrating on the solid polymer fuel cell, a model is set up of a fleet of urban buses, widely regarded as one of the earliest applications of fuel cells in transport. Under the central assumption that the fuel cell stack cost is $300 per kilowatt, the fuel cell bus is found to be around 30% more expensive than its diesel counterpart. However, there are considerable cost reductions possible through economies of scale in the production of hydrogen, the fuel required for the solid polymer fuel cell. Remarkably, these economies of scale allow the cost of the fuel cell bus to drop below that of the diesel. What is more, the fleet size required for this—more than 25 vehicles—is by no means prohibitive. In a trade-off analysis, the possibility is investigated of reducing the cost by allowing one parameter to deteriorate, if this permits another one to improve. In particular, it is found that cheaper (mass-) production techniques for the fuel cell at the expense of reduced efficiency make economic sense if a relative drop in the efficiency of 1% is accompanied by a cost reduction of at least 1⋅06%—something that is likely to be attainable. A scenario for a direct methanol fuel cell, assuming a cost per kilowatt three times as high as for the solid polymer fuel cell, results in a slightly higher overall cost, without being able to offer the same economies of scale in fuel provision. The social costs are calculated also, taking into account the environmental externalities associated with the whole system including the fuel supply chain. The inclusion of externalities fails to shift the balance decisively in favour of the fuel cell, partly because of a cancellation effect between the diesel tax, which has to be excluded in a social cost calculation, and the externalities, which are added in. The main outcome is therefore that in order to succeed in the marketplace, the principal task for the developers of fuel cells is a further reduction of the cost. © 1997 by John Wiley & Sons, Ltd.