256 research outputs found
Numerical Study of the Spin-Flop Transition in Anisotropic Spin-1/2 Antiferromagnets
Magnetization processes of the spin-1/2 antiferromagnetic model in two
and three spatial dimensions are studied using quantum Monte Carlo method based
on stochastic series expansions. Recently developed operator-loop algorithm
enables us to show a clear evidence of the first-order phase transition in the
presence of an external magnetic field. Phase diagrams of closely related
systems, hard core bosons with nearest-neighbor repulsions, are also discussed
focusing on possibilities of phase-separated and supersolid phases.Comment: 4 pages, Revtex version 4, with 4 figures embedded, To appear in
Phys. Rev.
Multi-layered Ruthenium-modified Bond Coats for Thermal Barrier Coatings
Diffusional approaches for fabrication of multi-layered Ru-modified bond coats for thermal
barrier coatings have been developed via low activity chemical vapor deposition and high activity
pack aluminization. Both processes yield bond coats comprising two distinct B2 layers, based on
NiAl and RuAl, however, the position of these layers relative to the bond coat surface is reversed
when switching processes. The structural evolution of each coating at various stages of the
fabrication process has been and subsequent cyclic oxidation is presented, and the relevant
interdiffusion and phase equilibria issues in are discussed. Evaluation of the oxidation behavior of
these Ru-modified bond coat structures reveals that each B2 interlayer arrangement leads to the
formation of α-Al 2 O 3 TGO at 1100°C, but the durability of the TGO is somewhat different and in
need of further improvement in both cases
Specific heat of quasi-2D antiferromagnetic Heisenberg models with varying inter-planar couplings
We have used the stochastic series expansion (SSE) quantum Monte Carlo (QMC)
method to study the three-dimensional (3D) antiferromagnetic Heisenberg model
on cubic lattices with in-plane coupling J and varying inter-plane coupling
J_perp < J. The specific heat curves exhibit a 3D ordering peak as well as a
broad maximum arising from short-range 2D order. For J_perp << J, there is a
clear separation of the two peaks. In the simulations, the contributions to the
total specific heat from the ordering across and within the layers can be
separated, and this enables us to study in detail the 3D peak around T_c (which
otherwise typically is dominated by statistical noise). We find that the peak
height decreases with decreasing J_perp, becoming nearly linear below J_perp =
0.2J. The relevance of these results to the lack of observed specific heat
anomaly at the ordering transition of some quasi-2D antiferromagnets is
discussed.Comment: 7 pages, 8 figure
Seabird sensitivity mapping tool: project report [issue number 3]
This project builds upon the existing evidence base for seabird habitat use at sea to develop a fast, user-friendly tool to estimate the sensitivities of key seabird species to ORDs in all British Isles shelf seas. The tool produces estimates for the sensitivity and exposure of all at sea locations in UK waters for 13 seabird species (Atlantic puffin, Common guillemot, Razorbill, Black-legged kittiwake, European shag, European storm petrel, Great skua, Herring gull, Lesser black-backed gull, Northern gannet, Northern fulmar, Great black-backed gull and Red-throated diver) in both the breeding and non-breeding seasons, based on GPS tracking and at sea survey data
Criticality in coupled quantum spin-chains with competing ladder-like and two-dimensional couplings
Motivated by the geometry of spins in the material CaCuO, we study a
two-layer, spin-half Heisenberg model, with nearest-neighbor exchange couplings
J and \alpha*J along the two axes in the plane and a coupling J_\perp
perpendicular to the planes. We study these class of models using the
Stochastic Series Expansion (SSE) Quantum Monte Carlo simulations at finite
temperatures and series expansion methods at T=0. The critical value of the
interlayer coupling, J_\perp^c, separating the N{\'e}el ordered and disordered
ground states, is found to follow very closely a square root dependence on
. Both T=0 and finite-temperature properties of the model are
presented.Comment: 9 pages, 11 figs., 1 tabl
Gamma rays from colliding winds of massive stars
Colliding winds of massive binaries have long been considered as potential sites of non-thermal high-energy photon production. This is motivated by the detection of non-thermal spectra in the radio band, as well as by correlation studies of yet unidentified EGRET gamma-ray sources with source populations appearing in star formation regions. This work re-considers the basic radiative processes and its properties that lead to high energy photon production in long-period massive star systems. We show that Klein-Nishina effects as well as the anisotropic nature of the inverse Compton scattering, the dominating leptonic emission process, likely yield spectral and variability signatures in the gamma-ray domain at or above the sensitivity of current or upcoming gamma ray instruments like GLAST-LAT. In addition to all relevant radiative losses, we include propagation (such as convection in the stellar wind) as well as photon absorption effects, which a priori can not be neglected. The calculations are applied to WR140 and WR147, and predictions for their detectability in the gamma-ray regime are provided. Physically similar specimen of their kind like WR146, WR137, WR138, WR112 and WR125 may be regarded as candidate sources at GeV energies for near-future gamma-ray experiments. Finally, we discuss several aspects relevant for eventually identifying this source class as a gamma-ray emitting population. Thereby we utilize our findings on the expected radiative behavior of typical colliding wind binaries in the gamma-ray regime as well as its expected spatial distribution on the gamma-ray sky
Predictions of total and total reaction cross sections for nucleon-nucleus scattering up to 300 MeV
Total reaction cross sections are predicted for nucleons scattering from various nuclei. Projectile energies to 300 MeV are considered. So also are mass variations of those cross sections at selected energies. All predictions have been obtained from coordinate space optical potentials formed by full folding effective two-nucleon (NN) interactions with one body density matrix elements (OBDME) of the nuclear ground states. Good comparisons with data result when effective NN interactions defined by medium modification of free NN t matrices are used. Coupled with analyses of differential cross sections, these results are sensitive to details of the model ground states used to describe nuclei
Dialysis initiation, modality choice, access, and prescription: conclusions from a Kidney Disease: Improving Global Outcomes (KDIGO) Controversies Conference
Globally, the number of patients undergoing maintenance dialysis is increasing, yet throughout the world there is significant variability in the practice of initiating dialysis. Factors such as availability of resources, reasons for starting dialysis, timing of dialysis initiation, patient education and preparedness, dialysis modality and access, as well as varied \u201ccountry-specific\u201d factors significantly affect patient experiences and outcomes. As the burden of end-stage kidney disease (ESKD) has increased globally, there has also been a growing recognition of the importance of patient involvement in determining the goals of care and decisions regarding treatment. In January 2018, KDIGO (Kidney Disease: Improving Global Outcomes) convened a Controversies Conference focused on dialysis initiation, including modality choice, access, and prescription. Here we present a summary of the conference discussions, including identified knowledge gaps, areas of controversy, and priorities for research. A major novel theme represented during the conference was the need to move away from a \u201cone-size-fits-all\u201d approach to dialysis and provide more individualized care that incorporates patient goals and preferences while still maintaining best practices for quality and safety. Identifying and including patient-centered goals that can be validated as quality indicators in the context of diverse health care systems to achieve equity of outcomes will require alignment of goals and incentives between patients, providers, regulators, and payers that will vary across health care jurisdictions
The Earth: Plasma Sources, Losses, and Transport Processes
This paper reviews the state of knowledge concerning the source of magnetospheric plasma at Earth. Source of plasma, its acceleration and transport throughout the system, its consequences on system dynamics, and its loss are all discussed. Both observational and modeling advances since the last time this subject was covered in detail (Hultqvist et al., Magnetospheric Plasma Sources and Losses, 1999) are addressed
Canagliflozin and Renal Outcomes in Type 2 Diabetes and Nephropathy
BACKGROUND
Type 2 diabetes mellitus is the leading cause of kidney failure worldwide, but few
effective long-term treatments are available. In cardiovascular trials of inhibitors
of sodium–glucose cotransporter 2 (SGLT2), exploratory results have suggested
that such drugs may improve renal outcomes in patients with type 2 diabetes.
METHODS
In this double-blind, randomized trial, we assigned patients with type 2 diabetes
and albuminuric chronic kidney disease to receive canagliflozin, an oral SGLT2
inhibitor, at a dose of 100 mg daily or placebo. All the patients had an estimated
glomerular filtration rate (GFR) of 30 to <90 ml per minute per 1.73 m2
of bodysurface area and albuminuria (ratio of albumin [mg] to creatinine [g], >300 to
5000) and were treated with renin–angiotensin system blockade. The primary
outcome was a composite of end-stage kidney disease (dialysis, transplantation, or
a sustained estimated GFR of <15 ml per minute per 1.73 m2
), a doubling of the
serum creatinine level, or death from renal or cardiovascular causes. Prespecified
secondary outcomes were tested hierarchically.
RESULTS
The trial was stopped early after a planned interim analysis on the recommendation of the data and safety monitoring committee. At that time, 4401 patients had
undergone randomization, with a median follow-up of 2.62 years. The relative risk
of the primary outcome was 30% lower in the canagliflozin group than in the
placebo group, with event rates of 43.2 and 61.2 per 1000 patient-years, respectively (hazard ratio, 0.70; 95% confidence interval [CI], 0.59 to 0.82; P=0.00001).
The relative risk of the renal-specific composite of end-stage kidney disease, a
doubling of the creatinine level, or death from renal causes was lower by 34%
(hazard ratio, 0.66; 95% CI, 0.53 to 0.81; P<0.001), and the relative risk of endstage kidney disease was lower by 32% (hazard ratio, 0.68; 95% CI, 0.54 to 0.86;
P=0.002). The canagliflozin group also had a lower risk of cardiovascular death,
myocardial infarction, or stroke (hazard ratio, 0.80; 95% CI, 0.67 to 0.95; P=0.01)
and hospitalization for heart failure (hazard ratio, 0.61; 95% CI, 0.47 to 0.80;
P<0.001). There were no significant differences in rates of amputation or fracture.
CONCLUSIONS
In patients with type 2 diabetes and kidney disease, the risk of kidney failure and
cardiovascular events was lower in the canagliflozin group than in the placebo group
at a median follow-up of 2.62 years. (Funded by Janssen Research and Development;
CREDENCE ClinicalTrials.gov number, NCT02065791.
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