Sequence of phase transitions induced in an array of Josephson junctions by their crossover to pi-state

We show that the transition of Josephson junctions between the conventional and pi states caused by the decrease in temperature induces in a regular two-dimensional array of such junctions not just a single phase transition between two phases with different ordering but a sequence of two, three or four phase transitions. The corresponding phase diagrams are constructed for the cases of bipartite (square or honeycomb) and triangular lattices.Comment: 5 pages, v2: as published in EP

Electron Transport in Granular Metals

We consider thermodynamic and transport properties of a long granular array with strongly connected grains (inter-grain conductance g>>1.) We find that the system exhibits activated behavior of conductance and thermodynamic density of states ~exp(-T*/T) where the gap, T*, is parametrically larger than the energy at which conventional perturbation theory breaks down. The scale T* represents energy needed to create a long single-electron charge soliton propagating through the array.Comment: 4 pages, 1 figur

Chiral Correction to the Spin Fluctuation Feedback in two-dimensional p-wave Superconductors

We consider the stability of the superconducting phase for spin-triplet p-wave pairing in a quasi-two-dimensional system. We show that in the absence of spin-orbit coupling there is a chiral contribution to spin fluctuation feedback which is related to spin quantum Hall effect in a chiral superconducting phase. We show that this mechanism supports the stability of a chiral p-wave state.Comment: 8 pages. The final version is accepted for publication in Europhys Let

Estimation of changes in spermogram and index of sperm DNA fragmentation in patients with premature ejaculation receiving Neurodoz biocomplex

Background. An incidence of premature ejaculation (PE) in men of reproductive age of 24–45 years is 23 %. The treatment of PE is based on antidepressants from the group of selective serotonin re-uptake inhibitors. However, drugs of this group have gametotoxic action.Objective. Evaluate the effectiveness of Neurodoz biocomplex, its effect on the parameters of spermogram and sperm DNA integrity in patients with PE.Materials and methods. The study involved 16 patients with PE and normozoospermia aged from 26 to 35 years. Ejaculate and sperm DNA fragmentation were assessed by Halosperm (Halotech®) method before and after the therapy. Duration of treatment was 2 months. Evaluation of efficacy was based on the duration of sexual intercourse, as well as on the visual analogue scale and the questionnaire data of patients with premature ejaculation.Results. In 8 weeks there was a decrease in ejaculate volume from to 3.6 ± 1.1 down to 3.2 ± 1.1 mL (p = 0.312) and an increase in the concentration of sperm (34.2 ± 9.8) × 106 up to (35.6 ± 9.7) × 106 (p = 0.688). Sperm motility (category a + b) increased from 36.6 ± 4.3 to 37.2 ± 4.5 % (p = 0.703), the percentage of morphologically normal forms increased from 14.6 ± 1.4 up to 14.8 ± 1.1 (p = 0.656). DNA fragmentation of sperm has decreased from 15.6 ± 2.7 down to 15.4 ± 2.7 % (p = 0.635). Duration of intravaginal latency increased from 101.8 ± 34.4 (45–150) up to 217.3 ± 28.9 (190–280) sec (p < 0.001). An overall score according to the premature ejaculation questionnaire decreased from 13.9 ± 3.0 (9–20) down to 4.4 ± 1.9 (0–7) (p < 0.001). Visual analogue scale symptoms improved from 7.3 ± 1.7 (5–10) to 2.6 ± 1.2 (0–4) (p < 0.001).Conclusion. Neurodoz is an effective and safe agent for PE correction. Giving an absence of negative impact of biocomplex on spermatogenesis in patients with normozoospermia, it is possible to administer it to men who are trying to conceive. Further study is necessary in order to assess an impact of the drug on semen parameters in subfertile patient

Powers of Hamilton cycles in pseudorandom graphs

We study the appearance of powers of Hamilton cycles in pseudorandom graphs, using the following comparatively weak pseudorandomness notion. A graph $G$ is $(\varepsilon,p,k,\ell)$-pseudorandom if for all disjoint $X$ and $Y\subset V(G)$ with $|X|\ge\varepsilon p^kn$ and $|Y|\ge\varepsilon p^\ell n$ we have $e(X,Y)=(1\pm\varepsilon)p|X||Y|$. We prove that for all $\beta>0$ there is an $\varepsilon>0$ such that an $(\varepsilon,p,1,2)$-pseudorandom graph on $n$ vertices with minimum degree at least $\beta pn$ contains the square of a Hamilton cycle. In particular, this implies that $(n,d,\lambda)$-graphs with $\lambda\ll d^{5/2 }n^{-3/2}$ contain the square of a Hamilton cycle, and thus a triangle factor if $n$ is a multiple of $3$. This improves on a result of Krivelevich, Sudakov and Szab\'o [Triangle factors in sparse pseudo-random graphs, Combinatorica 24 (2004), no. 3, 403--426]. We also extend our result to higher powers of Hamilton cycles and establish corresponding counting versions.Comment: 30 pages, 1 figur

Biomechanical control-based locomotor function rehabilitation technology for children with cerebral palsy

Locomotor functions of children with special needs by the example of infantile cerebral palsy have bee

Simplicity out of complexity: band structure for W20_{20}O58_{58} superconductor

The band structure, density of states, and the Fermi surface of a recently discovered superconductor, oxygen-deficient tungsten oxide WO$_{2.9}$ that is equivalent to W$_{20}$O$_{58}$, studied within the density functional theory (DFT) in the generalized gradient approximation (GGA). Here we show that despite the extremely complicated structure containing 78 atoms in the unit cell, the low-energy band structure is quite feasible. Fermi level is crossed by no more than 10 bands per one spin projection (and even 9 bands per pseudospin projection when the spin-orbit coupling is considered) originating from the $d$-orbitals of tungsten atoms forming zigzag chains.Comment: 6 pages, 5 figure

Phase transitions in the antiferromagnetic XY model with a kagome lattice

The ground state of the antiferromagnetic XY model with a kagome lattice is characterized by a well developed accidental degeneracy. As a consequence the phase transition in this system consists in unbinding of pairs of fractional vortices. Addition of the next-to-nearest neighbors (NNN) interaction leads to stabilization of the long-range order in chirality (staggered chirality). We show that the phase transition, related with destruction of this long-range order, can happen as a separate phase transition below the temperature of the fractional vortex pairs unbinding only if the NNN coupling is extremely weak, and find how the temperature of this transition depends on coupling constants. We also demonstarte that the antiferromagnetic ordering of chiralities and, accordingly, the presence of the second phase transition are induced by the free energy of spin wave fluctuations even in absence of the NNN coupling.Comment: 10 pages (Revtex) + 8 figures (in 2 postscript files

Backflow and dissipation during the quantum decay of a metastable Fermi liquid

The particle current in a metastable Fermi liquid against a first-order phase transition is calculated at zero temperature. During fluctuations of a droplet of the stable phase, in accordance with the conservation law, not only does an unperturbed current arise from the continuity at the boundary, but a backflow is induced by the density response. Quasiparticles carrying these currents are scattered by the boundary, yielding a dissipative backflow around the droplet. An energy of the hydrodynamic mass flow of the liquid and a friction force exerted on the droplet by the quasiparticles have been obtained in terms of a potential of their interaction with the droplet.Comment: 5 pages (REVTeX), to be published in Phys. Rev.