First principles study of structural,magnetic and electronic properties of CrAs

Abstract

We report ab initio density functional calculations of the structural and magnetic properties, and the electronic structure of CrAs. To simulate the observed pressure-driven experimental results, we perform our analysis for different volumes of the unit cell, showing that the structural, magnetic and electronic properties strongly depend on the size of the cell. We find that the calculated quantities are in good agreement with the experimental data, and we review our results in terms of the observed superconductivity.     

Fracture control parameters for NiTi based shape memory alloys

In this paper new fracture control parameters for Nickel–Titanium (NiTi) based shape memory alloys (SMAs) are proposed, based on a recent literature analytical model on fracture mechanics of SMAs. In fact, the stress induced martensitic transformation, occurring in the crack tip region of NiTi alloys, causes a complex and unusual stress distribution with respect to common engineering materials. For this reason two different stress intensity factors (SIFs) have been defined to describe the stress distribution in both transformed and untransformed regions, i.e. in the martensitic and austenitic phases, respectively. Systematic studies have been carried out to analyze the effects of the main thermo-mechanical parameters of NiTi alloys on the two proposed SIFs, i.e. on the crack tip stress distribution, and comparisons with linear elastic fracture mechanics have been illustrated. Finally, the proposed model was used to analyze different loading conditions of a commercial superelastic NiTi alloys, which demonstrated a marked effect of the temperature on the crack tip stress distribution.     

Exploiting Free‐Energy Minima to Design Novel EphA2 Protein–Protein Antagonists: From Simulation to Experiment and Return

The free‐energy surface (FES) of protein–ligand binding contains information useful for drug design. Here we show how to exploit a free‐energy minimum of a protein‐ligand complex identified by metadynamics simulations to design a new EphA2 antagonist with improved inhibitory potency.     

Non isobaric boundary layers related to Marangoni flows

Summary The paper deals with the dissipative layers, called Marangoni boundary layers, that can be formed, along the interface of two immiscible fluids, in surface driven flows. Under the hypothesis that the flow fields of the two interfacing fluids are uncoupled, similar solutions are studied for the case in which an external pressure gradient is present. The similarity class is derived and the pertinent equations are solved numerically by mean of an algorithm based on a Quasi-Linearization Technique.

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Sommario Si considerano Strati Limiti che possono formarsi, lungo l'interfaccia di due fluidi immiscibili, in flussi indotti da gradienti di tensione superficiale, noti come strati limiti alla Marangoni. Soluzioni simili vengono derivate per il caso in cui sia presente un gradiente di pressione esterno, nell'ipotesi che i campi di moto nei due fluidi interfaccianti siano disaccoppiati. Le equazioni sono integrate numericamente con un algoritmo basato su una tecnica di Quasi-Linearizzazione.

     

Stresses and momenta in electromagnetic materials

The notion of energy–momentum, or energy–stress, pertains typically to electromagnetism. Eshelby transferred such a notion into elasticity in 1951 and, afterward, into continuum mechanics, in order to account for the force acting on a material defect. Similarities and differences between the Maxwell tensor of electromagnetism and the Eshelby tensor are shown and commented hereby. Basing on a Lagrangian approach to electromagnetic materials, canonical momenta are shown to emerge in a natural way. On the basis of these canonical quantities, one can introduce the material momentum (or pseudomomentum) along with the classical momentum and the material stress (Eshelby stress) along with the Maxwell stress, which is a Cauchy-like stress.     

The Effect of Grafting Zirconia and Ceria onto Alumina as a Support for Silicotungstic Acid for the Catalytic Dehydration of Glycerol to Acrolein

The effect of ceria and zirconia grafting onto alumina (α and θ–δ phases) as supports for silicotungstic acid for the dehydration of glycerol to acrolein was studied. 30 % Silicotungstic acid (STA) supported on 5 % zirconia/δ,θ‐alumina was the best catalyst, producing 85 % selectivity to acrolein at 100 % glycerol conversion, and it showed stable activity without using oxygen as a co‐feed. The catalyst produced a STA of 90 g_(acrolein) kg_(cat)^?1 h^?1, which was greater than the STA simply supported on δ,θ‐alumina, which only demonstrated 75 % selectivity towards acrolein. The effect of grafting on the support material was investigated by means of nitrogen adsorption, ammonia temperature‐programmed desorption, thermogravimetric analysis, Raman spectroscopy, and powder X‐ray diffraction. A pulsed‐field gradient (PFG) NMR technique was also used to study diffusion processes associated with the catalysts. Diffusion studies of the grafted catalysts showed that zirconia contributes to the formation of more tortuous pathways within the pore structure, leading to the diminution of acid strength and making the catalyst less susceptible to coke formation.     

A two-stage solution approach for the Directed Rural Postman Problem with Turn Penalties

In this paper, we consider the Directed Rural Postman Problem with Turn Penalties (DRPP-TP). A solution is a tour that traverses all required arcs of the graph. The total cost of the tour is the sum of the lengths of the traversed arcs plus the penalties associated with the turns. One solution approach involves transforming the arc routing problem into an equivalent node routing problem. An alternative direct approach (without graph transformation) that involves two stages has been proposed in the literature. In the first part of this paper, we investigate the applicability of the direct approach. We identify several characteristics of the input instance that make this approach effective and present several limitations of this approach. In the second part of this paper, we describe an integer linear program that is combined with a local search algorithm. This combination produces high-quality solutions to the DRPP-TP in a reasonable amount of computing time.     

Regularizing properties of a class of matrices including the optimal and the superoptimal preconditioners

In this work, given a positive definite matrix A, we introduce a class of matrices related to A, which is obtained by suitably combining projections of its powers onto algebras of matrices simultaneously diagonalized by a unitary transform. After a detailed theoretical study of some spectral properties of the matrices of this class, which suggests their use as regularizing preconditioners, we prove that such matrices can be cheaply computed when the matrix A has a Toeplitz structure. We provide numerical evidence of the advantages coming from the employment of the proposed preconditioners when used in regularizing procedures.     

Autonomous systems,dynamical systems,LPTI symmetries,topology of trajectories,and periodic solutions

In the case of autonomous dynamical systems, it is better to base symmetry considerations on trajectories than on full solutions. In this setting topological arguments can be used; a special role is played in this context by time-independent Lie-point symmetries. As an application of this approach, we obtain results on the existence of stationary and/or periodic solutions.     

The Poincaré-Lyapounov-Nekhoroshev Theorem

We give a detailed and mainly geometric proof of a theorem by N. N. Nekhoroshev for hamiltonian systems in n degrees of freedom with k constants of motion in involution, where 1≤k≤n. This state's persistence of k-dimensional invariant tori, and local existence of partial action-angle coordinates, under suitable nondegeneracy conditions. Thus it admits as special cases the Poincaré-Lyapounov theorem (corresponding to k=1) and the Liouville-Arnold one (corresponding to k=n) and interpolates between them. The crucial tool for the proof is a generalization of the Poincaré map, also introduced by Nekhoroshev.