Josephson current in unconventional superconductors through an Anderson impurity

Josephson current for a system consisting of an Anderson impurity weakly coupled to two unconventional superconductors is studied and shown to be driven by a surface zero energy (mid-gap) bound-state. The repulsive Coulomb interaction in the dot can turn a $\pi$ junction into a 0-junction. This effect is more pronounced in p-wave superconductors while in high-temperature superconductors with $d_{x^2-y^2}$ symmetry it can exit for rather large artificial centers at which tunneling occurs within a finite region.Comment: 4 pages 3.eps figure

Preparation of facilities for fundamental research with ultracold neutrons at PNPI

The WWR-M reactor of PNPI offers a unique opportunity to prepare a source for ultracold neutrons (UCN) in an environment of high neutron flux (about 3*10^12 n/cm^2/s) at still acceptable radiation heat release (about 4*10^-3 W/g). It can be realized within the reactor thermal column situated close to the reactor core. With its large diameter of 1 m, this channel allows to install a 15 cm thick bismuth shielding, a graphite premoderator (300 dm^3 at 20 K), and a superfluid helium converter (35 dm^3). At a temperature of 1.2 K it is possible to remove the heat release power of about 20 W. Using the 4pi flux of cold neutrons within the reactor column can bring more than a factor 100 of cold neutron flux incident on the superfluid helium with respect to the present cold neutron beam conditions at the ILL reactor. The storage lifetime for UCN in superfluid He at 1.2 K is about 30 s, which is sufficient when feeding experiments requiring a similar filling time. The calculated density of UCN with energy between 50 neV and 250 neV in an experimental volume of 40 liters is about 10^4 n/cm^3. Technical solutions for realization of the project are discussed.Comment: 10 pages, more detail

Forest Protection and Permanence of Reduced Emissions

Tropical forests are essential for climate change mitigation. As awareness grows over the use of credits from reduced emissions from deforestation and forest degradation (REDD+) and other nature-based climate solutions within both voluntary and compliance carbon markets, key concerns about the long-term durability of the reductions, or their permanence, arise for countries, corporations, regulators and policy makers. The paper seeks to analyze an efficient means of distribution and application of different policy pathways to slow down and stop deforestation and explore the longevity of reductions via modeling. The impact of policies like REDD+ most likely will have a time limitation. At some point tropical nations will take more responsibility to protect forests. REDD+ should constitute an initial intervention that will help tropical nations shock to a zero-deforestation trajectory. To establish conditions of permanence, we conduct numerical analyses using a model based on a cellular automata algorithm that learns from historical deforestation patterns and other spatial features in the Brazilian state of Mato Grosso. The model simulates future deforestation, first applying policy to reduce deforestation and then relaxing the policy intervention. Our simulations show that policies that are successful in reducing deforestation and related emissions from business as usual may have long-term positive consequences on an avoided deforestation trajectory even after potential policy reversals. Some accumulated gains could be lost but sizable benefits will remain, assuring permanence of emissions reduction during the policy implementation and potentially even after policies are relaxed. Hence, permanence depends both on the probability of policy reversals and the risk of emissions rebounding. Our results are important for advancing the understanding around the unsettled debate on the permanence of avoided emissions. Further, this paper argues that as policies to prevent deforestation or reduce emissions otherwise are reversible, permanence should be understood and discussed in a probabilistic and time-dependent framework

Fano effect of a strongly interacting quantum dot in contact with superconductor

The physics of a system consisting of an Aharonov Bohm (AB) interferometer containing a single level interacting quantum dot (QD) on one of its arms, and attached to normal (N) and superconducting (S) leads is studied and elucidated. Here the focus is directed mainly on N-AB-S junctions but the theory is capable of studying S-AB-S junctions as well. The interesting physics comes into play under the conditions that both the Kondo effect in the QD and the the Fano effect are equally important.It is found the conductance of the junction is suppressed as the Fano effect becomes more dominant.Comment: 4 pages, Talk to be given at the NATO Conference MQO, Bled, Slovenia 7-10 September 200

Magnetization plateaux in dimerized spin ladder arrays

We investigate the ground state magnetization plateaux appearing in spin 1/2 two-leg ladders built up from dimerized antiferromagnetic Heisenberg chains and dimerized zig-zag interchain couplings. Using both Abelian bosonization and Lanczos methods we find that the system yields rather unusual plateaux and exhibits massive and massless phases for specific choices or ``tuning'' of exchange interactions. The relevance of this behavior in the study of NH_4CuCl_3 is discussed.Comment: 9 pages, RevTeX, 11 postscript figure

Evidence for topological nonequilibrium in magnetic configurations

We use direct numerical simulations to study the evolution, or relaxation, of magnetic configurations to an equilibrium state. We use the full single-fluid equations of motion for a magnetized, non-resistive, but viscous fluid; and a Lagrangian approach is used to obtain exact solutions for the magnetic field. As a result, the topology of the magnetic field remains unchanged, which makes it possible to study the case of topological nonequilibrium. We find two cases for which such nonequilibrium appears, indicating that these configurations may develop singular current sheets.Comment: 10 pages, 5 figure

Random forest for gene selection and microarray data classification

A random forest method has been selected to perform both gene selection and classification of the microarray data. In this embedded method, the selection of smallest possible sets of genes with lowest error rates is the key factor in achieving highest classification accuracy. Hence, improved gene selection method using random forest has been proposed to obtain the smallest subset of genes as well as biggest subset of genes prior to classification. The option for biggest subset selection is done to assist researchers who intend to use the informative genes for further research. Enhanced random forest gene selection has performed better in terms of selecting the smallest subset as well as biggest subset of informative genes with lowest out of bag error rates through gene selection. Furthermore, the classification performed on the selected subset of genes using random forest has lead to lower prediction error rates compared to existing method and other similar available methods

Anisotropic transport in the two-dimensional electron gas in the presence of spin-orbit coupling

In a two-dimensional electron gas as realized by a semiconductor quantum well, the presence of spin-orbit coupling of both the Rashba and Dresselhaus type leads to anisotropic dispersion relations and Fermi contours. We study the effect of this anisotropy on the electrical conductivity in the presence of fixed impurity scatterers. The conductivity also shows in general an anisotropy which can be tuned by varying the Rashba coefficient. This effect provides a method of detecting and investigating spin-orbit coupling by measuring spin-unpolarized electrical currents in the diffusive regime. Our approach is based on an exact solution of the two-dimensional Boltzmann equation and provides also a natural framework for investigating other transport effects including the anomalous Hall effect.Comment: 10 pages, 1 figure included. Discussion of experimental impact enlarged; error in calculation of conductivity contribution corrected (cf. Eq. (A14)), no changes in qualitative results and physical consequence

Neighborhood Health Care Access and Sexually Transmitted Infections among Women in the Southern United States: A Cross-Sectional Multilevel Analysis

Introduction: The United States has experienced an increase in reportable sexually transmitted infections (STIs) while simultaneously experiencing a decline in safety net services for STI testing and treatment. This multilevel study assessed relationships between neighborhood-level access to health care and STIs among a predominantly Human Immunodeficiency Virus (HIV)-seropositive cohort of women living in the south. Methods: This cross-sectional multilevel analysis included baseline data from HIV-seropositive and HIV-seronegative women enrolled in the Women's Interagency HIV Study sites in Alabama, Florida, Georgia, Mississippi, and North Carolina between 2013 and 2015 (N = 666). Administrative data (eg, United States Census) described health care access (eg, percentage of residents with a primary care provider, percentage of residents with health insurance) in the census tracts where women lived. Sexually transmitted infections (chlamydia, gonorrhea, trichomoniasis, or early syphilis) were diagnosed using laboratory testing. Generalized estimating equations were used to determine relationships between tractlevel characteristics and STIs. Analyses were conducted using SAS 9.4. Results: Seventy percent of participants were HIV-seropositive. Eleven percent of participants had an STI. A 4-unit increase in the percentage of residents with a primary care provider was associated with 39% lower STI risk (risk ratio, 0.61, 95%confidence interval, 0.38-0.99). The percentage of tract residents with health insurance was not associated with STIs (risk ratio, 0.98, 95% confidence interval, 0.91-1.05). Relationships did not vary by HIV status. Conclusions: Greater neighborhood health care access was associated with fewer STIs. Research should establish the causality of this relationship and pathways through which neighborhood health care access influences STIs. Structural interventions and programs increasing linkage to care may reduce STIs

Associations between county-level voter turnout, county-level felony voter disenfranchisement, and sexually transmitted infections among women in the Southern United States

Purpose: Voting may play a critical role in the allocation of social and structural resources to communities, which in turn shapes neighborhood environments, and ultimately, an individual's sexually transmitted infection (STI) risk. We assessed relationships among county-level voter turnout and felony voter disenfranchisement, and STIs. Methods: This cross-sectional multilevel analysis included 666 women in Alabama, Florida, Georgia, Mississippi, and North Carolina enrolled in the Women's Interagency HIV Study between 2013 and 2015. Having a baseline bacterial STI (chlamydia, gonorrhea, trichomoniasis, or early syphilis) was determined by laboratory testing. We used generalized estimating equations to test relationships between county-level voter turnout in the 2012 general election, county-level percentage of felony disenfranchised voters, and STI prevalence. Results: Eleven percent of participants had an STI. Higher voter turnout corresponded to lower STI prevalence (prevalence ratio = 0.84, 95% confidence interval = 0.73–0.96 per 4 percentage point higher turnout). Greater felony voter disenfranchisement corresponded to higher STI prevalence (prevalence ratio = 1.89, 95% confidence interval = 1.10–3.24 per 4 percentage point higher disenfranchisement). Conclusions: STI prevalence was inversely associated with voter turnout and positively associated with felony voter disenfranchisement. Research should assess causality and mechanisms through which civic engagement shapes sexual health. Expanding political participation, including eliminating discriminatory voting laws, could influence sexual health