167 research outputs found
Magnetic levitation force between a superconducting bulk magnet and a permanent magnet
The current density in a disk-shaped superconducting bulk magnet and the
magnetic levitation force exerted on the superconducting bulk magnet by a
cylindrical permanent magnet are calculated from first principles. The effect
of the superconducting parameters of the superconducting bulk is taken into
account by assuming the voltage-current law and the material law. The magnetic
levitation force is dominated by the remnant current density, which is induced
by switching off the applied magnetizing field. High critical current density
and flux creep exponent may increase the magnetic levitation force. Large
volume and high aspect ratio of the superconducting bulk can enhance the
magnetic levitation force further.Comment: 18 pages and 8 figure
Vortex Plastic Motion in Twinned Superconductors
We present simulations, without electrodynamical assumptions, of
, and , in hard superconductors, for a variety
of twin-boundary pinning potential parameters, and for a range of values of the
density and strength of the pinning sites. We numerically solve the overdamped
equations of motion of up to 10^4 flux-gradient-driven vortices which can be
temporarily trapped at pinning centers. These simulations relate
macroscopic measurements (e.g., M(H), ``flame'' shaped profiles) with
the underlying microscopic pinning landscape and the plastic dynamics of
individual vortices
Critical currents, flux-creep activation energy and potential barriers for the vortex motion from the flux creep experiments
We present an experimental study of thermally activated flux creep in a
superconducting ring-shaped epitaxial YBCO film as well as a new way of
analyzing the experimental data. The measurements were made in a wide range of
temperatures between 10 and 83 K. The upper temperature limit was dictated by
our experimental technique and at low temperatures we were limited by a
crossover to quantum tunneling of vortices. It is shown that the experimental
data can very well be described by assuming a simple thermally activated
hopping of vortices or vortex bundles over potential barriers, whereby the
hopping flux objects remain the same for all currents and temperatures. The new
procedure of data analysis also allows to establish the current and temperature
dependencies of the flux-creep activation energy U, as well as the temperature
dependence of the critical current Ic, from the flux-creep rates measured at
different temperatures. The variation of the activation energy with current,
U(I/Ic), is then used to reconstruct the profile of the potential barriers in
real space.Comment: 12 pages, 13 Postscript figures, Submitted to Physical Review
Patterned nanostructure in AgCo/Pt/MgO(001) thin film
The formation of patterned nanostructure in AgCo/Pt/MgO(001) thin film is
simulated by a technique of combining molecular dynamics and phase-field
theory. The dislocation (strain) network existing in Pt/MgO is used as a
template whose pattern is transferred to AgCo phase in spinodal decomposition,
resulting in regular arrays of Co islands that are attracted by the
dislocations. The influence of various factors, such as component concentration
and film thickness, is studied. It is found that the spinodal decomposition of
AgCo in this system is mainly characterized by a competition between a
surface-directed layer structure and the strain-induced patterned structure,
where the patterned Ag-Co structure only dominates in a small range near the
interface (less than 10 atomic layers). However, if the interlayer diffusion
can be minimized by controlling film growth conditions, it is shown that the
patterned structure can be formed throughout the entire film.Comment: 8 pages, 12 figure
An RCT to Increase Breast and Colorectal Cancer Screening
Introduction
Adherence to breast and colorectal cancer screenings reduce mortality from these cancers, yet screening rates remain suboptimal. This 2 × 2 RCT compared 3 theory-based interventions to usual care to simultaneously increase breast and colon cancer screening in women who were nonadherent to both screenings at study entry.
Design
RCT.
Setting/participants
Women (n=692) who were nonadherent to both breast and colon cancer screenings and aged 51–75 years were recruited. Enrollment, intervention delivery, and data collection were completed between 2013 and 2017, and data analyzed in 2018.
Intervention
The randomized intervention included the following 4 groups: 3 intervention arms (personally tailored messages using a web-based intervention, phone delivery by a trained navigator, or both) compared with usual care. Women at an average risk for colon cancer were allowed to select either colonoscopy or stool test as their preferred colon cancer screening. Mammography was promoted for breast cancer screening.
Main outcome measures
Outcome data at 6 months included self-report and medical records for screening activity.
Results
All intervention arms significantly increased receipt of either a mammogram or stool test compared with control (web: p<0.0249, phone: p<0.0001, web + phone: p<0.0001). When considering receipt of both mammogram and stool test, all intervention arms were significantly different from usual care (web: p<0.0249, phone: p<0.0003, web + phone: p<0.0001). In addition, women who were adherent to mammography had a 4.5 times greater odds of becoming adherent to colonoscopy.
Conclusions
The tailored intervention simultaneously supporting both breast and colon cancer screenings significantly improved rates of obtaining one of the screenings and increased receipt of both tests
Biochemical evidence for an alternate pathway in N-linked glycoprotein biosynthesis
Asparagine-linked glycosylation is a complex protein modification conserved among all three domains of life. Herein we report the in vitro analysis of N-linked glycosylation from the methanogenic archaeon Methanococcus voltae. Using a suite of synthetic and semisynthetic substrates, we show that AglK initiates N-linked glycosylation in M. voltae through the formation of α-linked dolichyl monophosphate N-acetylglucosamine, which contrasts with the polyprenyl diphosphate intermediates that feature in both eukaryotes and bacteria. Notably, AglK has high sequence homology to dolichyl phosphate β-glucosyltransferases, including Alg5 in eukaryotes, suggesting a common evolutionary origin. The combined action of the first two enzymes, AglK and AglC, afforded an α-linked dolichyl monophosphate glycan that serves as a competent substrate for the archaeal oligosaccharyl transferase AglB. These studies provide what is to our knowledge the first biochemical evidence revealing that, despite the apparent similarity of the overall pathways, there are actually two general strategies to achieve N-linked glycoproteins across the domains of life.National Institutes of Health (U.S.) (Grant GM039334
Perpendicular Magnetic Anisotropy in FePt Patterned Media Employing a CrV Seed Layer
A thin FePt film was deposited onto a CrV seed layer at 400°C and showed a high coercivity (~3,400 Oe) and high magnetization (900–1,000 emu/cm3) characteristic of L10 phase. However, the magnetic properties of patterned media fabricated from the film stack were degraded due to the Ar-ion bombardment. We employed a deposition-last process, in which FePt film deposited at room temperature underwent lift-off and post-annealing processes, to avoid the exposure of FePt to Ar plasma. A patterned medium with 100-nm nano-columns showed an out-of-plane coercivity fivefold larger than its in-plane counterpart and a remanent magnetization comparable to saturation magnetization in the out-of-plane direction, indicating a high perpendicular anisotropy. These results demonstrate the high perpendicular anisotropy in FePt patterned media using a Cr-based compound seed layer for the first time and suggest that ultra-high-density magnetic recording media can be achieved using this optimized top-down approach
Cost-effectiveness of a mailed educational reminder to increase colorectal cancer screening
<p>Abstract</p> <p>Background</p> <p>Colorectal cancer (CRC) screening rates are low in many areas and cost-effective interventions to promote CRC screening are needed. Recently in a randomized controlled trial, a mailed educational reminder increased CRC screening rates by 16.2% among U.S. Veterans. The aim of our study was to assess the costs and cost-effectiveness of a mailed educational reminder on fecal occult blood test (FOBT) adherence.</p> <p>Methods</p> <p>In a blinded, randomized, controlled trial, 769 patients were randomly assigned to the usual care group (FOBT alone, n = 382) or the intervention group (FOBT plus a mailed reminder, n = 387). Ten days after picking up the FOBT cards, a 1-page reminder with information related to CRC screening was mailed to the intervention group. Primary outcome was number of returned FOBT cards after 6 months. The costs and incremental cost-effectiveness ratio (ICER) of the intervention were assessed and calculated respectively. Sensitivity analyses were based on varying costs of labor and supplies.</p> <p>Results</p> <p>At 6 months after card distribution, 64.6% patients in the intervention group returned FOBT cards compared with 48.4% in the control group (P < 0.001). The total cost of the intervention was 2.49 per patient, and the ICER was 13.50 to $16.50 per additional patient screened for CRC.</p> <p>Conclusions</p> <p>A simple mailed educational reminder increases FOBT card return rate at a cost many health care systems can afford. Compared to other patient-directed interventions (telephone, letters from physicians, mailed reminders) for CRC screening, our intervention was more effective and cost-effective.</p
Mycobacterium tuberculosis Glucosyl-3-Phosphoglycerate Synthase: Structure of a Key Enzyme in Methylglucose Lipopolysaccharide Biosynthesis
Tuberculosis constitutes today a serious threat to human health worldwide, aggravated by the increasing number of identified multi-resistant strains of Mycobacterium tuberculosis, its causative agent, as well as by the lack of development of novel mycobactericidal compounds for the last few decades. The increased resilience of this pathogen is due, to a great extent, to its complex, polysaccharide-rich, and unusually impermeable cell wall. The synthesis of this essential structure is still poorly understood despite the fact that enzymes involved in glycosidic bond synthesis represent more than 1% of all M. tuberculosis ORFs identified to date. One of them is GpgS, a retaining glycosyltransferase (GT) with low sequence homology to any other GTs of known structure, which has been identified in two species of mycobacteria and shown to be essential for the survival of M. tuberculosis. To further understand the biochemical properties of M. tuberculosis GpgS, we determined the three-dimensional structure of the apo enzyme, as well as of its ternary complex with UDP and 3-phosphoglycerate, by X-ray crystallography, to a resolution of 2.5 and 2.7 Å, respectively. GpgS, the first enzyme from the newly established GT-81 family to be structurally characterized, displays a dimeric architecture with an overall fold similar to that of other GT-A-type glycosyltransferases. These three-dimensional structures provide a molecular explanation for the enzyme's preference for UDP-containing donor substrates, as well as for its glucose versus mannose discrimination, and uncover the structural determinants for acceptor substrate selectivity. Glycosyltransferases constitute a growing family of enzymes for which structural and mechanistic data urges. The three-dimensional structures of M. tuberculosis GpgS now determined provide such data for a novel enzyme family, clearly establishing the molecular determinants for substrate recognition and catalysis, while providing an experimental scaffold for the structure-based rational design of specific inhibitors, which lay the foundation for the development of novel anti-tuberculosis therapies
Chemical Approaches To Perturb, Profile, and Perceive Glycans
Glycosylation is an essential form of post-translational modification that regulates intracellular and extracellular processes. Regrettably, conventional biochemical and genetic methods often fall short for the study of glycans, because their structures are often not precisely defined at the genetic level. To address this deficiency, chemists have developed technologies to perturb glycan biosynthesis, profile their presentation at the systems level, and perceive their spatial distribution. These tools have identified potential disease biomarkers and ways to monitor dynamic changes to the glycome in living organisms. Still, glycosylation remains the underexplored frontier of many biological systems. In this Account, we focus on research in our laboratory that seeks to transform the study of glycan function from a challenge to routine practice
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