Superconducting magnesium diboride films on Silicon with Tc0 about 24K grown via vacuum annealing from stoichiometric precursors

Superconducting magnesium diboride films with Tc0 ~ 24 K and sharp transition \~ 1 K were successfully prepared on silicon substrates by pulsed laser deposition from a stoichiometric MgB2 target. Contrary to previous reports, anneals at 630 degree and a background of 2x10^(-4) torr Ar/4%H2 were performed without the requirement of Mg vapor or an Mg cap layer. This integration of superconducting MgB2 films on silicon may thus prove enabling in superconductor-semiconductor device applications. Images of surface morphology and cross-section profiles by scanning electron microscopy (SEM) show that the films have a uniform surface morphology and thickness. Energy dispersive spectroscopy (EDS) reveals these films were contaminated with oxygen, originating either from the growth environment or from sample exposure to air. The oxygen contamination may account for the low Tc for those in-situ annealed films, while the use of Si as the substrate does not result in a decrease in Tc as compared to other substrates.Comment: 5 pages, 4 figures, 15 references; due to file size limit, images were blure

On narrowing coated conductor film: emergence of granularity-induced field hysteresis of transport critical current

Critical current density Jc in polycrystalline or granular superconducting material is known to be hysteretic with applied field H due to the focusing of field within the boundary between adjacent grains. This is of concern in the so-called coated conductors wherein superconducting film is grown on a granular, but textured surface of a metal substrate. While previous work has mainly been on Jc determined using induced or magnetization currents, the present work utilizes transport current via an applied potential in strip geometry. It is observed that the effect is not as pronounced using transport current, probably due to a large difference in criterion voltage between the two types of measurements. However, when the films are narrowed by patterning into 200-, 100-, or 80-micron, the hysteresis is clearly seen, because of the forcing of percolation across higher-angle grain boundaries. This effect is compared for films grown on ion-beam-assisted-deposited (IBAD) YSZ substrate and those grown on rolling-assisted-biaxially-textures substrates (RABiTS) which have grains that are about ten times larger. The hysteresis is more pronounced for the latter, which is more likely to have a weak grain boundary spanning the width of the microbridge. This is also of concern to applications in which coated conductors will be striated in order to reduce of AC losses.Comment: text-only: 10 pages, plus 5 figures on 5 page

A continuous compositional-spread technique based on pulsed-laser deposition and applied to the growth of epitaxial films

A novel continuous-compositional spread technique based on the non-uniformity of the deposition rate typically observed in Pulsed Laser Deposition (PLD) is introduced. The approach uses the spatial variations in the deposition-rate naturally occurring in PLD; therefore, there is no need for the masks typically used in combinatorial techniques. Consequently, combinatorial materials synthesis can be carried out under optimized film growth conditions (e.g. at high temperature). Additionally, lifting the need for post-annealing renders this method applicable to heat-sensitive materials and substrates (e.g. films of transparent oxides on polymer substrates). Composition determination across the sample and mapping of physical properties onto the ternary phase diagram is achieved via a simple algorithm using the parameters that describe the deposition-rate profiles. Results are shown for the high-temperature growth of crystalline perovskites (including (Ba,Sr)TiO3 and the formation of a metastable alloy between SrRuO3 and SrSnO3) and the room-temperature growth of transparent conducting oxides.Comment: 6 pages, accepted for publication in Rev. Sci. Inst

Gastric intramucosal pH-guided therapy in patients after elective repair of infrarenal abdominal aneurysms: is it beneficial?

Objective: To determine if gastric intramucosal pH (pHi)-guided therapy reduces the number of complications and length of stay in the intensive care unit (ICU) or the hospital after elective repair of infrarenal abdominal aortic aneurysms. Design: Prospective, randomized study. Setting: Surgical intensive care unit (SICU) of a University Hospital. Patients: Fifty-five consecutive patients randomized to group 1 (pHi-guided therapy) or to group 2 (control). Interventions: Patients of group 1 with a pHi of lower than 7.32 were treated by means of a prospective protocol in order to increase their pHi to 7.32 or more. Measurements and results: pHi was determined in both groups on admission to the SICU and thereafter at 6-h intervals. In group 2, the treating physicians were blinded for the pHi values. Complications, APACHE II scores, duration of endotracheal intubation, fluid and vasoactive drug treatment, treatment with vasoactive drugs, length of stay in the SICU and in the hospital and hospital mortality were recorded. There were no differences between groups in terms of the incidence of complications. We found no differences in APACHE II scores on admission, the duration of intubation, SICU or hospital stay, or hospital mortality. In the two groups the incidence of pHi values lower than 7.32 on admission to the SICU was comparable (41 % and 42 % in groups 1 and 2, respectively). Patients with pHi lower than 7.32 had more major complications during SICU stay (p<0.05), and periods more than 10 h of persistently low pHi values (< 7.32) were associated with a higher incidence of SICU complications (p<0.01). Conclusions: Low pHi values (<7.32) and their persistence are predictors of major complications. Treatment to elevate low pHi values does not improve postoperative outcome. Based on these data, we cannot recommend the routine use of gastric tonometers for pHi-guided therapy in these patients. Further studies are warranted to determine adequate treatment of low pHi values that results in beneficial effects on the patient's postoperative course and outcom

Bone strength loss during long-term bed rest is related to bone loading history

Bed rest studies are an accepted model for simulating bone loss due to microgravity during space flights. In a previous 60 days bed rest study, we investigated the loss of bone mass and the microstructural degeneration at the distal radius and tibia using a high-resolution (HR) pQCT device1. In combination with micro-finite element (micro-FE) analyses, it was possible to also quantify the loss of strength during bed rest2. In that study large variations in loss of bone strength were found between subjects. For some subjects no loss of strength was found whereas for others strength was reduced by 6.5%. Although these values are small and thus may not increase the risk of fracture, it may cause premature age-related osteoporosis and understanding the fundamental nature of the skeletal response to unloading is of great interest to develop countermeasures for overcoming the adverse effects of microgravity during spaceflights. In this study we investigate if the variation in loss of bone strength between subjects as observed in the earlier bed rest study could be related to their activity level prior to the bed rest. Since we expect that subjects that were more active would be more affected by the disuse, we hypothesized that the loss of bone strength is positively correlated to the physical activity of the subjects. As the activity level of the subjects prior to the bed rest study was not known, we used a recently developed method to estimate the bone loading history based on the bone architecture and correlated that with the loss in bone strength measured in the bed rest study to test our hypothesis