875 research outputs found
Suppression of 2D superconductivity by the magnetic field: quantum corrections vs superconductor-insulator transition
Magnetotransport of superconducting Nd_{2-x}Ce_xCuO_{4+y} (NdCeCuO) films is
studied in the temperature interval 0.3-30 K. The microscopic theory of the
quantum corrections to conductivity, both in the Cooper and in the diffusion
channels, qualitatively describes the main features of the experiment including
the negative magnetoresistance in the high field limit. Comparison with the
model of the field-induced superconductor-insulator transition (SIT) is
included and a crossover between these two theoretical approaches is discussed.Comment: 5 pages, 4 figures. Submitted to JETP Letter
Theoretical Description of Resistive Behavior near a Quantum Vortex-Glass Transition
Resistive behaviors at nonzero temperatures (T > 0) reflecting a quantum
vortex-glass (VG) transition (the so-called field-tuned
superconductor-insulator transition at T=0) are studied based on a quantum
Ginzburg-Landau (GL) action for a s-wave pairing case containing microscopic
details. The ordinary dissipative dynamics of the pair-field is assumed on the
basis of a consistency between the fluctuation conductance terms excluded from
GL approach and an observed negative magnetoresistance. It is shown that the VG
contribution, G_{vg}(B=B_{vg}, T \to 0),to 2D fluctuation conductance at the VG
transition field B_{vg} depends on the strength of a repulsive-interaction
between electrons and takes a universal value only in the ordinary dirty limit
neglecting the electron-repulsion. Available resistivity data near B_{vg} are
discussed based on our results, and extensions to the cases of a d-wave pairing
and of 3D systems are briefly commented on.Comment: Explanation of data in strongly disordered case, as well as Fig.2 and
3, was renewed, and comments on recent publications were added. To appear in
J.Phys.Soc. Jp
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Predictors of Stunting, Wasting and Underweight among Tanzanian Children Born to HIV-Infected Women.
Children born to human immunodeficiency virus (HIV)-infected women are susceptible to undernutrition, but modifiable risk factors and the time course of the development of undernutrition have not been well characterized. The objective of this study was to identify maternal, socioeconomic and child characteristics that are associated with stunting, wasting and underweight among Tanzanian children born to HIV-infected mothers, followed from 6 weeks of age for 24 months. Maternal and socioeconomic characteristics were recorded during pregnancy, data pertaining to the infant's birth were collected immediately after delivery, morbidity histories and anthropometric measurements were performed monthly. Multivariate Cox proportional hazards methods were used to assess the association between potential predictors and the time to first episode of stunting, wasting and underweight. A total of 2387 infants (54.0% male) were enrolled and followed for a median duration of 21.2 months. The respective prevalence of prematurity (<37 weeks) and low birth weight (<2500 g) was 15.2% and 7.0%; 11.3% of infants were HIV-positive at 6 weeks. Median time to first episode of stunting, wasting and underweight was 8.7, 7.2 and 7.0 months, respectively. Low maternal education, few household possessions, low infant birth weight, child HIV infection and male sex were all independent predictors of stunting, wasting and underweight. In addition, preterm infants were more likely to become wasted and underweight, whereas those with a low Apgar score at birth were more likely to become stunted. Interventions to improve maternal education and nutritional status, reduce mother-to-child transmission of HIV, and increase birth weight may lower the risk of undernutrition among children born to HIV-infected women
Perspective on Reversible to Irreversible Transitions in Periodic Driven Many Body Systems and Future Directions For Classical and Quantum Systems
Reversible to irreversible (R-IR) transitions arise in numerous periodically
driven collectively interacting systems that, after a certain number of driving
cycles, organize into a reversible state where the particle trajectories
repeat, or remain irreversible with chaotic motion. R-IR transitions were first
systematically studied for periodically sheared dilute colloids, and appear in
a wide variety of both soft and hard matter systems, including amorphous
solids, crystals, vortices in type-II superconductors, and magnetic textures.
In some cases, the reversible transition is an absorbing phase transition with
a critical divergence in the organization time scale. R-IR systems can store
multiple memories and exhibit return point memory. We give an overview of R-IR
transitions including recent advances in the field, and discuss how the general
framework of R-IR transitions could be applied to a much broader class of
periodically driven nonequilibrium systems, including soft and hard condensed
matter systems, astrophysics, biological systems, and social systems. Some
likely candidate systems are commensurate-incommensurate states, systems
exhibiting hysteresis or avalanches, and nonequilibrium pattern forming states.
Periodic driving could be applied to hard condensed matter systems to see if
R-IR transitions occur in metal-insulator transitions, semiconductors, electron
glasses, electron nematics, cold atom systems, or Bose-Einstein condensates.
R-IR transitions could also be examined in dynamical systems where
synchronization or phase locking occurs. We discuss the use of complex periodic
driving such as changing drive directions or multiple frequencies as a method
to retain complex multiple memories. Finally, we describe features of classical
and quantum time crystals that could suggest the occurrence of R-IR transitions
in these systems.Comment: 25 pages, 27 figure
Multi-instrument Evaluation of a Real-time PCR Assay for Identification of Atlantic Salmon: A Case Study on the Use of a Pre-packaged Kit for Rapid Seafood Species Identification
Protecting the seafood supply chain from species substitution is critical for economic, health, and conservation reasons. DNA-based methods represent an effective means to detect species substitution, but current methods can be time consuming or costly, and require specialized instruments and operators. Real-time PCR provides an alternative that can be performed quickly, and in some cases even on-site. The use of commercial kits reduces the expertise required by the operator and therefore increases accessibility to testing. This potentially increases the likelihood of adoption into the supply chain, but only if the kits are robust across multiple operators, instruments, and samples. In this study, the InstantID™ Atlantic salmon kits were tested on a variety of instruments with market samples of fresh, frozen, smoked, and canned Atlantic salmon. Results were repeatable across all samples and instruments tested. This kit, and others like it that have undergone appropriate evaluation, represents a means for expanded access to testing for industry or regulators to screen seafood for species authenticity. Portable equipment can bring testing on-site, further reducing analysis time
Teratogenic risk and contraceptive counselling in psychiatric practice: analysis of anticonvulsant therapy
<p>Background:
Anticonvulsants have been used to manage psychiatric conditions for over 50 years. It is recognised that some, particularly valproate, carbamazepine and lamotrigine, are human teratogens, while others including topiramate require further investigation. We aimed to appraise the documentation of this risk by psychiatrists and review discussion around contraceptive issues.</p>
<p>Methods:
A retrospective review of prescribing patterns of four anticonvulsants (valproate, carbamazepine, lamotrigine and topiramate) in women of child bearing age was undertaken. Documented evidence of discussion surrounding teratogenicity and contraceptive issues was sought.</p>
<p>Results:
Valproate was most commonly prescribed (n=67). Evidence of teratogenic risk counselling at medication initiation was sub-optimal – 40% of individuals prescribed carbamazepine and 22% of valproate. Documentation surrounding contraceptive issues was also low- 17% of individuals prescribed carbamazepine and 13% of valproate.</p>
<p>Conclusion:
We found both low rates of teratogenic risk counselling and low rates of contraception advice in our cohort. Given the high rates of unplanned pregnancies combined with the relatively high risk of major congenital malformations, it is essential that a detailed appraisal of the risks and benefits associated with anticonvulsant medication occurs and is documented within patients’ psychiatric notes.</p>
The Upper Critical Field in Disordered Two-Dimensional Superconductors
We present calculations of the upper critical field in superconducting films
as a function of increasing disorder (as measured by the normal state
resistance per square). In contradiction to previous work, we find that there
is no anomalous low-temperature positive curvature in the upper critical field
as disorder is increased. We show that the previous prediction of this effect
is due to an unjustified analytical approximation of sums occuring in the
perturbative calculation. Our treatment includes both a careful analysis of
first-order perturbation theory, and a non-perturbative resummation technique.
No anomalous curvature is found in either case. We present our results in
graphical form.Comment: 11 pages, 8 figure
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