Coherent transport in Josephson-Junction rhombi chain with quenched disorder

We consider a chain of Josephson-junction rhombi (proposed originally by Doucot and Vidal) in quantum regime. In a regular chain with no disorder in the maximally frustrated case when magnetic flux through each rhombi \Phi_r is equal to one half of superconductive flux quantum \Phi_0, Josephson current is due to correlated transport of pairs of Cooper pairs, i.e. charge is quantized in units of $4e$. Sufficiently strong deviation \delta\Phi =|\Phi_r-\Phi_0/2| > \delta\Phi^c from the maximally frustrated point brings the system back to usual $2e$-quantized supercurrent. For a regular chain \delta\Phi^c was calculated by us previously. Here we present detailed analysis of the effect of quenched disorder (random stray charges and random fluxes piercing rhombi) on the pairing effect.Comment: 21 pages, 5 figure

Non-Abelian symmetries and disorder: a broad non-ergodic regime and anomalous thermalization

Symmetries play a central role in single-particle localization. Recent research focused on many-body localized (MBL) systems, characterized by new kind of integrability, and by the area-law entanglement of eigenstates. We investigate the effect of a non-Abelian $SU(2)$ symmetry on the dynamical properties of a disordered Heisenberg chain. While $SU(2)$ symmetry is inconsistent with the conventional MBL, a new non-ergodic regime is possible. In this regime, the eigenstates exhibit faster than area-law, but still a strongly sub-thermal scaling of entanglement entropy. Using exact diagonalization, we establish that this non-ergodic regime is indeed realized in the strongly disordered Heisenberg chains. We use real-space renormalization group (RSRG) to construct approximate excited eigenstates, and show their accuracy for systems of size up to $L=26$. As disorder strength is decreased, a crossover to the thermalizing phase occurs. To establish the ultimate fate of the non-ergodic regime in the thermodynamic limit, we develop a novel approach for describing many-body processes that are usually neglected by RSRG, accessing systems of size $L>2000$. We characterize the resonances that arise due to such processes, finding that they involve an ever growing number of spins as the system size is increased. The probability of finding resonances grows with the system size. Even at strong disorder, we can identify a large lengthscale beyond which resonances proliferate. Presumably, this eventually would drive the system to a thermalizing phase. However, the extremely long thermalization time scales indicate that a broad non-ergodic regime will be observable experimentally. Our study demonstrates that symmetries control dynamical properties of disordered, many-body systems. The approach introduced here provides a versatile tool for describing a broad range of disordered many-body systems.Comment: 25 pages, 21 figure

Resistance of two-dimensional superconducting films

We consider the problem of finite resistance R in superconducting films with geometry of a strip of width W near zero temperature. The resistance is generated by vortex configurations of the phase field. In the first type of process, quantum phase slip, the vortex world line in 2+1 dimensional space-time is spacelike (i.e., the superconducting phase winds in time and space). In the second type, vortex tunneling, the world line is timelike (i.e., the phase winds in the two spatial directions) and connects opposite edges of the film. For moderately disordered samples, processes of the second type favor a train of vortices, each of which tunnels only across a fraction of the sample. Optimization with respect to the number of vortices yields a tunneling distance of the order of the coherence length ξ , and the train of vortices becomes equivalent to a quantum phase slip. Based on this theory, we find the resistance ln R ∼ − gW/ξ , where g is the dimensionless normal-state conductance. Incorporation of quantum fluctuations indicates a quantum phase transition to an insulating state for g 1

Exploring lipophilic antioxidants accumulation in field-grown low temperature-stressed Ephedra monosperma

The seasonal patterns of changes in the content of lipophilic antioxidants $\beta$-carotene ($\beta$-Car), zeaxanthin (Zx), $\alpha$-tocopherol ($\alpha$-Toc), plastoquinone (PQ)/plastoquinol ($PQH_{2}$) were studied in the assimilating shoots of evergreen shrub Ephedra monosperma J.G. Gmel ex C.A. Mey under natural conditions of Central Yakutia. The shortening of the photoperiod and the seasonal decrease in temperature induced a 1.4-fold increase in $\alpha$-Toc content. The fall in the average daily temperature from 0.1 to $-8.1^{\circ}C$ in October led to a decrease in the content of $\beta$-Car as a result of the accumulation of rhodoxanthin (Rhd). In this period a sharp increase in the content of Zx retained overnight was also detected. In winter, elevated content of Zx and $\alpha$-Toc persisted. During September, the content of PQH2 increased by 2.5 times and PQ by 1.4 times (compared to July). The beginning of exposure to freezing average daily temperatures from -3 to $-5^{\circ}C$ led to the depletion of the total PQ pool by 18%. However, the content of $PQ_{tot}$ in the winter months was 1.5 times higher than at the end of July. The results revealed different timing and temperature ranges of variation for individual antioxidants during the development of frost resistance in ephedra

New opportunities for identifying the risk of cardiovascular events in young people: the role of familial hypercholesterolemia

A search was made for publications on modern methods for determining cardiovascular risk in young people with positive family history for early cardiovascular events. The use of various screening options allows timely identification of patients with heterozygous familial hypercholesterolemia who have a high cardiovascular risk. The most effective method is cascade screening. Cardiovascular risk assessment systems that include a family history of early cardiovascular events and lipid profiles in individuals under 40 years of age provide prevention of atherosclerosis. In the diagnosis of risk, the lipoprotein (a) is of particular clinical importance, elevated concentrations of which are associated with a high risk of vascular damage and an unfavorable course of atherosclerosis