Renormalization Group Study of the Intrinsic Finite Size Effect in 2D Superconductors

Vortices in a thin-film superconductor interact logarithmically out to a distance on the order of the two-dimensional (2D) magnetic penetration depth $\lambda_\perp$, at which point the interaction approaches a constant. Thus, because of the finite $\lambda_\perp$, the system exhibits what amounts to an {\it intrinsic} finite size effect. It is not described by the 2D Coulomb gas but rather by the 2D Yukawa gas (2DYG). To study the critical behavior of the 2DYG, we map the 2DYG to the massive sine-Gordon model and then perform a renormalization group study to derive the recursion relations and to verify that $\lambda_\perp$ is a relevant parameter. We solve the recursion relations to study important physical quantities for this system including the renormalized stiffness constant and the correlation length. We also address the effect of current on this system to explain why finite size effects are not more prevalent in experiments given that the 2D magnetic penetration depth is a relevant parameter.Comment: 8 pages inRevTex, 5 embedded EPS figure

Critical-point scaling function for the specific heat of a Ginzburg-Landau superconductor

If the zero-field transition in high temperature superconductors such as YBa_2Cu_3O_7-\delta is a critical point in the universality class of the 3-dimensional XY model, then the general theory of critical phenomena predicts the existence of a critical region in which thermodynamic functions have a characteristic scaling form. We report the first attempt to calculate the universal scaling function associated with the specific heat, for which experimental data have become available in recent years. Scaling behaviour is extracted from a renormalization-group analysis, and the 1/N expansion is adopted as a means of approximation. The estimated scaling function is qualitatively similar to that observed experimentally, and also to the lowest-Landau-level scaling function used by some authors to provide an alternative interpretation of the same data. Unfortunately, the 1/N expansion is not sufficiently reliable at small values of N for a quantitative fit to be feasible.Comment: 20 pages; 4 figure

Diatom Abundance and Diversity Across the Arcata Wastewater Treatment Plant and Wildlife Sanctuary

Wastewater management is an essential component of modern society that is necessary for reducing human environmental impact, particularly in aquatic ecosystems. In Humboldt County, California, the Arcata Wastewater Treatment Plant and Wildlife Sanctuary (Arcata Marsh) is a model for other wastewater treatment plants worldwide to treat waste naturally, reducing the use of chemicals. This wastewater is then discharged into the Humboldt Bay. It is well known how treatment helps remove harmful waste materials, but it has not been investigated how phytoplankton diversity is affected before, during, and after treatment. Phytoplankton are primary producers that are responsible for carbon sequestration and production of oxygen, and are an essential food source for higher trophic-level organisms. When nutrient levels are high, such as in human waste water, it can lead to single species proliferation, thus resulting in lower diversity and higher abundance of other species in the community. This can have negative consequences on the higher trophic levels that consume them and also creates “dead-zones\u27\u27 where aerobic species are unable to survive. In this study, pre-treatment water and post-treatment water were sampled and observed for diversity and abundance of diatoms, a quantifiable subphylum of phytoplankton. It was hypothesized that successful treatment would result in higher diversity of diatoms in post-treatment waters than that of pretreatment waters. This study found 30 morphologies across all sample sites, with abundance of 2-4 species being significantly greater in pre-treatment ponds than post-treatment ponds. There were no significant trends in diversity across the ponds

The Current-Temperature Phase Diagram of Layered Superconductors

The behavior of clean layered superconductors in the presence of a finite electric current and in zero-magnetic field behavior is addressed. The structure of the current temperature phase diagram and the properties of each of the four regions will be explained. We will discuss the expected current voltage and resistance characteristics of each region as well as the effects of finite size and weak disorder on the phase diagram. In addition, the reason for which a weakly non-ohmic region exists above the transition temperature will be explained.Comment: 8 pages (RevTeX), 4 encapsulated postscript figure

Renormalization group approach to layered superconductors

A renormalization group theory for a system consisting of coupled superconducting layers as a model for typical high-temperature superconducters is developed. In a first step the electromagnetic interaction over infinitely many layers is taken into account, but the Josephson coupling is neglected. In this case the corrections to two-dimensional behavior due to the presence of the other layers are very small. Next, renormalization group equations for a layered system with very strong Josephson coupling are derived, taking into account only the smallest possible Josephson vortex loops. The applicability of these two limiting cases to typical high-temperature superconductors is discussed. Finally, it is argued that the original renormalization group approach by Kosterlitz is not applicable to a layered system with intermediate Josephson coupling.Comment: RevTeX, 15 pages, 4 figures can be obtained from the author by conventional mail; accepted for publication in Phys. Rev.

3D Lowest Landau Level Theory Applied to YBCO Magnetization and Specific Heat Data: Implications for the Critical Behavior in the H-T Plane

We study the applicability of magnetization and specific heat equations derived from a lowest-Landau-level (LLL) calculation, to the high-temperature superconducting (HTSC) materials of the YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO) family. We find that significant information about these materials can be obtained from this analysis, even though the three-dimensional LLL functions are not quite as successful in describing them as the corresponding two-dimensional functions are in describing data for the more anisotropic HTSC Bi- and Tl-based materials. The results discussed include scaling fits, an alternative explanation for data claimed as evidence for a second order flux lattice melting transition, and reasons why 3DXY scaling may have less significance than previously believed. We also demonstrate how 3DXY scaling does not describe the specific heat data of YBCO samples in the critical region. Throughout the paper, the importance of checking the actual scaling functions, not merely scaling behavior, is stressed.Comment: RevTeX; 10 double-columned pages with 7 figures embedded. (A total of 10 postscript files for the figures.) Submitted to Physical Review

Heterojunction bipolar transistor technology for data acquisition and communication

Heterojunction Bipolar Transistor (HBT) technology has emerged as one of the most promising technologies for ultrahigh-speed integrated circuits. HBT circuits for digital and analog applications, data conversion, and power amplification have been realized, with speed performance well above 20 GHz. At Rockwell, a baseline AlGaAs/GaAs HBT technology has been established in a manufacturing facility. This paper describes the HBT technology, transistor characteristics, and HBT circuits for data acquisition and communication

Plasma Magnetohydrodynamics and Energy Conversion

Contains reports on five research projects.U. S. Air Force. Aeronautical Systems Division (Contract AF33(615)-1083)National Science Foundation (Grant GK-19

Thoracic transplantation

Note on Sources: The articles in this supplement are based on the reference tables in the 2002 OPTN/SRTR Annual Report, which are not included in this publication. Many relevant data appear in figures and tables directly referred to in the article; other tables from the Annual Report that serve as the basis for this article include the following: Tables 1.5, 1.6, 1.12, 1.13, 11.1–11.4, 11.8, 11.9, 12.1–12.4, 12.7–12.9, 13.1–13.4, and 13.7–13.9. All of these tables are also available online at http://www.ustransplant.org.The Scientific Registry of Transplant Recipients (SRTR) is funded by contract #231-00-0116 from the Health Resources and Services Administration (HRSA). The views expressed herein are those of the authors and not necessarily those of the US Government. This is a US Government-funded work. There are no restrictions on its use.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/91976/1/2003 AJT Thoracic Transplantation.pd

Selection of patients for heart transplantationin the current era of heart failure therapy

AbstractObjectivesWe sought to assess the relationship between survival, peak exercise oxygen consumption (Vo2), and heart failure survival score (HFSS) in the current era of heart failure (HF) therapy.BackgroundBased on predicted survival, HF patients with peak Vo2<14 ml/min/kg or medium- to high-risk HFSS are currently considered eligible for heart transplantation. However, these criteria were developed before the widespread use of beta-blockers, spironolactone, and defibrillators—interventions known to improve the survival of HF patients.MethodsPeak Vo2and HFSS were assessed in 320 patients followed from 1994 to 1997 (past era) and in 187 patients followed from 1999 to 2001 (current era). Outcomes were compared between these two groups of patients and those who underwent heart transplantation from 1993 to 2000.ResultsSurvival in the past era was 78% at one year and 67% at two years, as compared with 88% and 79%, respectively, in the current era (both p < 0.01). One-year event-free survival (without urgent transplantation or left ventricular assist device) was improved in the current era, regardless of initial peak Vo2: 64% vs. 48% for peak Vo2<10 ml/min/kg (p = 0.09), 81% vs. 70% for 10 to 14 ml/min/kg (p = 0.05), and 93% vs. 82% for >14 ml/min/kg (p = 0.04). Of the patients with peak Vo2of 10 to 14 ml/min/kg, 55% had low-risk HFSS and exhibited 88% one-year event-free survival. One-year survival after transplantation was 88%, which is similar to the 85% rate reported by the United Network for Organ Sharing for 1999 to 2000.ConclusionsSurvival for HF patients in the current era has improved significantly, necessitating re-evaluation of the listing criteria for heart transplantation