Water adsorption on amorphous silica surfaces: A Car-Parrinello simulation study

A combination of classical molecular dynamics (MD) and ab initio Car-Parrinello molecular dynamics (CPMD) simulations is used to investigate the adsorption of water on a free amorphous silica surface. From the classical MD SiO_2 configurations with a free surface are generated which are then used as starting configurations for the CPMD.We study the reaction of a water molecule with a two-membered ring at the temperature T=300K. We show that the result of this reaction is the formation of two silanol groups on the surface. The activation energy of the reaction is estimated and it is shown that the reaction is exothermic.Comment: 12 pages, 6 figures, to be published in J. Phys.: Condens. Matte

Software Support Cost Estimating Models: A Comparative Study of Model Content and Parameter Sensitivity

This research entailed a comparison of five software estimating models: PRICE-S, SEER-SEM, SoftCost-OO, SoftEst, and SPR KnowledgePLAN. The objective was to research the differences of the software models as related to software support cost. The following major question areas were addressed: (1) How do the differences between the models impact the resulting cost estimates? (2) To what degree can we explain and adjust for the differences between cost models? All items were for flight avionics of a manned aircraft. The differences between the models significantly impact the resulting estimates. Over the five models evaluated, a range of over $60 million occurred during a twenty year estimate. The researchers can explain the differences in the models due to the different algorithms used, but were not able to normalize the models to achieve equivalent estimates. The researchers feel a typical user will not be able to normalize separate models and should, therefore, concentrate on learning one or two models in detail. Different models are more appropriate depending on the task or project being estimated

Mechanical and electrochemical deterioration mechanisms in the tribocorrosion of Al alloys in NaCl and in NaNO3 solutions

Tribocorrosion of Al-Si-Cu-Mg alloys was investigated in 0.05 M NaCl and 0.1 M NaNO3 solutions under severe sliding and controlled electrochemical conditions. A simple galvanic coupling model was developed to analyze and quantitatively predict the evolution potential of the open circuit potential during tribocorrosion. According to this model and the obtained results, galvanic coupling was established in the NaNO3 solution within the wear track between passive and mechanically depassivated areas. In the NaCl solution, galvanic coupling was established between the whole depassivated wear track and the surrounding area. This difference was attributed to different mechanical properties of the passive surfaces.The research team was financially supported by the Portuguese Foundation for Science and Technology (FCT-Portugal), under a PhD scholarship (SFRH/BD/27911/2006). The authors thank also to Dr. Edith Ariza (University of Minho) and Pierre Mettraux (EPFL) for SEM analysis

Effect of Al2Cu precipitates size and mass transport on the polarisation behaviour of age-hardened Al–Si–Cu–Mg alloys in 0.05M NaCl

The electrochemical behaviour of age-hardened Al–Si–Cu–Mg alloys was investigated in a 0.05 M NaCl solution under controlled mass transport conditions using a rotating disk electrode. This work aimed at getting better understanding of the effect of the alloy microstructure, in particular the size distribution of Al2Cu phase, on the corrosion behaviour of the alloy. Three different size distributions of the Al2Cu phase were obtained through appropriate heat treatments. The cathodic reduction of oxygen was found to occur mainly on the Al2Cu phases acting as preferential cathodes. Small sized Al2Cu phases were found to promote at high rotation rates a transition from a 4 electron to a 2 electron dominated oxygen reduction mechanisms.The research team was financially supported by the Portuguese Foundation for Science and Technology (FCT-Portugal), under a PhD scholarship (SFRH/BD/27911/2006). The authors thank also to Drs. Edith Ariza (University of Minho) and Pierre Mettraux (EPFL) for SEM analysis

Distributional and classical solutions to the Cauchy Boltzmann problem for soft potentials with integrable angular cross section

This paper focuses on the study of existence and uniqueness of distributional and classical solutions to the Cauchy Boltzmann problem for the soft potential case assuming $S^{n-1}$ integrability of the angular part of the collision kernel (Grad cut-off assumption). For this purpose we revisit the Kaniel--Shinbrot iteration technique to present an elementary proof of existence and uniqueness results that includes large data near a local Maxwellian regime with possibly infinite initial mass. We study the propagation of regularity using a recent estimate for the positive collision operator given in [3], by E. Carneiro and the authors, that permits to study such propagation without additional conditions on the collision kernel. Finally, an $L^{p}$-stability result (with $1\leq p\leq\infty$) is presented assuming the aforementioned condition.Comment: 19 page

Cooling process for inelastic Boltzmann equations for hard spheres, Part II: Self-similar solutions and tail behavior

We consider the spatially homogeneous Boltzmann equation for inelastic hard spheres, in the framework of so-called constant normal restitution coefficients. We prove the existence of self-similar solutions, and we give pointwise estimates on their tail. We also give general estimates on the tail and the regularity of generic solutions. In particular we prove Haff 's law on the rate of decay of temperature, as well as the algebraic decay of singularities. The proofs are based on the regularity study of a rescaled problem, with the help of the regularity properties of the gain part of the Boltzmann collision integral, well-known in the elastic case, and which are extended here in the context of granular gases.Comment: 41 page

Influence of SiC reinforcement particles on the tribocorrosion behaviour of Al–SiCp FGMs in 0.05M NaCl solution

The main aim of this work was to study and understand the influence of SiC particles on the corrosion and tribocorrosion of Al-matrix composite materials. For that, Al–SiCp functionally graded composites were produced by centrifugal casting and different SiCp contents were achieved. Their mechanical properties were improved by age-hardening heat treatments. The tribocorrosion behaviour was studied in 0.05M NaCl solutions using a reciprocating motion tribometer involving an alumina ball sliding against the Al-based samples. Above critical SiC particles' content the matrix alloy surface was found to be protected against wear by SiC particles protruding from the surface. Below this threshold content, the SiC reinforcement was inefficient and the wear rate of the composite was the same as the non-reinforced alloy.The research team was financially supported by the Portuguese Foundation for Science and Technology (FCT-Portugal) under a PhD scholarship (SFRH/BD/27911/2006). The authors also thank Dr Edith Ariza (University of Minho) and Pierre Mettraux (EPFL) for SEM analysis

Predictive models of syncope causes in an outpatient clinic

The investigation of unexplained syncope remains a challenging clinical problem. In the present study we sought to evaluate the diagnostic value of a standardized work-up focusing on non invasive tests in patients with unexplained syncope referred to a syncope clinic, and whether certain combinations of clinical parameters are characteristic of rhythmic and reflex causes of syncope. METHODS AND RESULTS: 317 consecutive patients underwent a standardized work-up including a 12-lead ECG, physical examination, detailed history with screening for syncope-related symptoms using a structured questionnaire followed by carotid sinus massage (CSM), and head-up tilt test. Invasive testings including an electrophysiological study and implantation of a loop recorder were only performed in those with structural heart disease or traumatic syncope. Our work-up identified an etiology in 81% of the patients. Importantly, three quarters of the causes were established non invasively combining head-up tilt test, CSM and hyperventilation testing. Invasive tests yielded an additional 7% of diagnoses. Logistic analysis identified age and number of significant prodromes as the only predictive factors of rhythmic syncope. The same two factors, in addition to the duration of the ECG P-wave, were also predictive of vasovagal and psychogenic syncope. These factors, optimally combined in predictive models, showed a high negative and a modest positive predictive value. CONCLUSION: A standardized work-up focusing on non invasive tests allows to establish more than three quarters of syncope causes. Predictive models based on simple clinical parameters may help to distinguish between rhythmic and other causes of syncop

Integral representation of the linear Boltzmann operator for granular gas dynamics with applications

We investigate the properties of the collision operator associated to the linear Boltzmann equation for dissipative hard-spheres arising in granular gas dynamics. We establish that, as in the case of non-dissipative interactions, the gain collision operator is an integral operator whose kernel is made explicit. One deduces from this result a complete picture of the spectrum of the collision operator in an Hilbert space setting, generalizing results from T. Carleman to granular gases. In the same way, we obtain from this integral representation of the gain operator that the semigroup in L^1(\R \times \R,\d \x \otimes \d\v) associated to the linear Boltzmann equation for dissipative hard spheres is honest generalizing known results from the first author.Comment: 19 pages, to appear in Journal of Statistical Physic