Anomalous tunneling of bound pairs in crystal lattices

A novel method of solving scattering problems for bound pairs on a lattice is developed. Two different break ups of the hamiltonian are employed to calculate the full Green operator and the wave function of the scattered pair. The calculation converges exponentially in the number of basis states used to represent the non-translation invariant part of the Green operator. The method is general and applicable to a variety of scattering and tunneling problems. As the first application, the problem of pair tunneling through a weak link on a one-dimensional lattice is solved. It is found that at momenta close to \pi the pair tunnels much easier than one particle, with the transmission coefficient approaching unity. This anomalously high transmission is a consequence of the existence of a two-body resonant state localized at the weak link.Comment: REVTeX, 5 pages, 4 eps figure

Shear band dynamics from a mesoscopic modeling of plasticity

The ubiquitous appearance of regions of localized deformation (shear bands) in different kinds of disordered materials under shear is studied in the context of a mesoscopic model of plasticity. The model may or may not include relaxational (aging) effects. In the absence of relaxational effects the model displays a monotonously increasing dependence of stress on strain-rate, and stationary shear bands do not occur. However, in start up experiments transient (although long lived) shear bands occur, that widen without bound in time. I investigate this transient effect in detail, reproducing and explaining a t^1/2 law for the thickness increase of the shear band that has been obtained in atomistic numerical simulations. Relaxation produces a negative sloped region in the stress vs. strain-rate curve that stabilizes the formation of shear bands of a well defined width, which is a function of strain-rate. Simulations at very low strain-rates reveal a non-trivial stick-slip dynamics of very thin shear bands that has relevance in the study of seismic phenomena. In addition, other non-stationary processes, such as stop-and-go, or strain-rate inversion situations display a phenomenology that matches very well the results of recent experimental studies.Comment: 10 pages, 10 figure

Generalized stacking fault energy surfaces and dislocation properties of aluminum

We have employed the semidiscrete variational generalized Peierls-Nabarro model to study the dislocation core properties of aluminum. The generalized stacking fault energy surfaces entering the model are calculated by using first-principles Density Functional Theory (DFT) with pseudopotentials and the embedded atom method (EAM). Various core properties, including the core width, splitting behavior, energetics and Peierls stress for different dislocations have been investigated. The correlation between the core energetics and dislocation character has been explored. Our results reveal a simple relationship between the Peierls stress and the ratio between the core width and atomic spacing. The dependence of the core properties on the two methods for calculating the total energy (DFT vs. EAM) has been examined. The EAM can give gross trends for various dislocation properties but fails to predict the finer core structures, which in turn can affect the Peierls stress significantly (about one order of magnitude).Comment: 25 pages, 12 figure

On the reduction of the CSP dichotomy conjecture to digraphs

It is well known that the constraint satisfaction problem over general relational structures can be reduced in polynomial time to digraphs. We present a simple variant of such a reduction and use it to show that the algebraic dichotomy conjecture is equivalent to its restriction to digraphs and that the polynomial reduction can be made in logspace. We also show that our reduction preserves the bounded width property, i.e., solvability by local consistency methods. We discuss further algorithmic properties that are preserved and related open problems.Comment: 34 pages. Article is to appear in CP2013. This version includes two appendices with proofs of claims omitted from the main articl

VALSARTAN IN EVERYDAY CLINICAL PRACTICE IN RUSSIA: ANTIHYPERTENSIVE EFFICACY AND INFLUENCE ON SEXUAL FUNCTION IN PATIENTS WITH ARTERIAL HYPERTENSION

Aim. To study antihypertensive efficacy and safety of valsartan-based therapy (Diovan, Novartis Pharma) as well as patient’s compliance and influence of treatment on several aspects of sexual function.Material and methods. 114 doctors from 81 medical institutions of Russia participated in this prospective multicenter observation study. 650 hypertensive patients (average age 53,9±0,4 y.o.) were enrolled. The evaluation of therapy efficacy was based on analysis of systolic (SBP) and diastolic (DBP) blood pressure (BP) changes. Safety and compliance of treatment was also analyzed. The evaluation of sexual function was performed with 5 universal questions selected form the International Index of Erectile Function. These questions could be asked in both men and women. The valsartan dose was 80-320 mg OD. A combination of the valsartan with hydrochlorothiazide (12,5-25 mg/d), amlodipine (5-10 mg/d) or any other antihypertensive was allowed.Results. Significant similar decrease of SBP and DBP was observed in smoking and non-smoking patients (37,5/18,5 and 37,6/15,9 mm Hg respectively, р<0,01 vs baseline). 312 patients (56,9% men, 43,1% women) completed sexual function survey. After 12 weeks of treatment the number of patients without sexual activity and with 1-2 successful sexual attempts in the last 4 weeks significantly decreased from 22 to 16% and from 44 to 30% respectively (р<0,05). Significant increase in the number of patients with 5-6 and 7-10 successful sexual attempts was observed (from 7 to 20% and from 0 to 7% respectively, р<0,05). The treatment resulted in significant increase in the number of patients, who characterized their sexual life satisfaction as “very satisfied” (from 11 to 25%, р<0,01).Conclusion. During the course of effective antihypertensive treatment there was a significant increase in sexual function and general satisfaction with sexual life in patients with arterial hypertension, which could have favorable long-term consequences in increased compliance to the antihypertensive therapy