1,118 research outputs found
Strong ExB shear flows in the pedestal region in H-mode plasma
We report the first experimental observation of stationary zonal flows in the
pedestal region of the H-mode plasma in the H-1 toroidal heliac. Strong peaks
in E_r shear mark the top and foot of the density pedestal. Strong m=n=0
low-frequency (f < 0.6 kHz) zonal flows are observed in regions of increased
E_r, suggesting substantial contribution of zonal flows to the spatial
modulation of E_r radial profiles. Radial localization of zonal flows is
correlated with a region of zero magnetic shear and low-order (7/5) rational
surfaces.Comment: 4 pages, 5 figure
Self-organization in turbulence as a route to order in plasma and fluids
Transitions from turbulence to order are studied experimentally in thin fluid
layers and magnetically confined toroidal plasma. It is shown that turbulence
self-organizes through the mechanism of spectral condensation. The spectral
redistribution of the turbulent energy leads to the reduction in the turbulence
level, generation of coherent flow, reduction in the particle diffusion and
increase in the system's energy. The higher order state is sustained via the
nonlocal spectral coupling of the linearly unstable spectral range to the
large-scale mean flow. The similarity of self-organization in two-dimensional
fluids and low-to-high confinement transitions in plasma suggests the
universality of the mechanism.Comment: 5 pages, 4 figure
Action minimizing fronts in general FPU-type chains
We study atomic chains with nonlinear nearest neighbour interactions and
prove the existence of fronts (heteroclinic travelling waves with constant
asymptotic states). Generalizing recent results of Herrmann and Rademacher we
allow for non-convex interaction potentials and find fronts with non-monotone
profile. These fronts minimize an action integral and can only exists if the
asymptotic states fulfil the macroscopic constraints and if the interaction
potential satisfies a geometric graph condition. Finally, we illustrate our
findings by numerical simulations.Comment: 19 pages, several figure
Magneto-optical Kerr Effect Studies of Square Artificial Spin Ice
We report a magneto-optical Kerr effect study of the collective magnetic
response of artificial square spin ice, a lithographically-defined array of
single-domain ferromagnetic islands. We find that the anisotropic inter-island
interactions lead to a non-monotonic angular dependence of the array coercive
field. Comparisons with micromagnetic simulations indicate that the two
perpendicular sublattices exhibit distinct responses to island edge roughness,
which clearly influence the magnetization reversal process. Furthermore, such
comparisons demonstrate that disorder associated with roughness in the island
edges plays a hitherto unrecognized but essential role in the collective
behavior of these systems.Comment: Physical Review B, Rapid Communications (in press
Stochastic dynamics and control of a driven nonlinear spin chain: the role of Arnold diffusion
We study a chain of non-linear, interacting spins driven by a static and a
time-dependent magnetic field. The aim is to identify the conditions for the
locally and temporally controlled spin switching. Analytical and full numerical
calculations show the possibility of stochastic control if the underlying
semi-classical dynamics is chaotic. This is achievable by tuning the external
field parameters according to the method described in this paper. We show
analytically for a finite spin chain that Arnold diffusion is the underlying
mechanism for the present stochastic control. Quantum mechanically we consider
the regime where the classical dynamics is regular or chaotic. For the latter
we utilize the random matrix theory. The efficiency and the stability of the
non-equilibrium quantum spin-states are quantified by the time-dependence of
the Bargmann angle related to the geometric phases of the states.Comment: Journal-ref: to appear in J.Phys.
Mycophenolic acid versus azathioprine as primary immunosuppression for kidney transplant recipients
Background Modern immunosuppressive regimens after kidney transplantation usually use a combination of two or three agents of different classes to prevent rejection and maintain graft function. Most frequently, calcineurinâinhibitors (CNI) are combined with corticosteroids and a proliferationâinhibitor, either azathioprine (AZA) or mycophenolic acid (MPA). MPA has largely replaced AZA as a first line agent in primary immunosuppression, as MPA is believed to be of stronger immunosuppressive potency than AZA. However, treatment with MPA is more costly, which calls for a comprehensive assessment of the comparative effects of the two drugs. Objectives This review of randomised controlled trials (RCTs) aimed to look at the benefits and harms of MPA versus AZA in primary immunosuppressive regimens after kidney transplantation. Both agents were compared regarding their efficacy for maintaining graft and patient survival, prevention of acute rejection, maintaining graft function, and their safety, including infections, malignancies and other adverse events. Furthermore, we investigated potential effect modifiers, such as transplantation era and the concomitant immunosuppressive regimen in detail. Search methods We searched Cochrane Kidney and Transplant's Specialised Register (to 21 September 2015) through contact with the Trials' Search Coâordinator using search terms relevant to this review. Selection criteria All RCTs about MPA versus AZA in primary immunosuppression after kidney transplantation were included, without restriction on language or publication type. Data collection and analysis Two authors independently determined study eligibility, assessed risk of bias and extracted data from each study. Statistical analyses were performed using the randomâeffects model and the results were expressed as risk ratio (RR) for dichotomous outcomes and mean difference (MD) for continuous outcomes with 95% confidence intervals (CI). Main results We included 23 studies (94 reports) that involved 3301 participants. All studies tested mycophenolate mofetil (MMF), an MPA, and 22 studies reported at least one outcome relevant for this review. Assessment of methodological quality indicated that important information on factors used to judge susceptibility for bias was infrequently and inconsistently reported. MMF treatment reduced the risk for graft loss including death (RR 0.82, 95% CI 0.67 to 1.0) and for deathâcensored graft loss (RR 0.78, 95% CI 0.62 to 0.99, P < 0.05). No statistically significant difference for MMF versus AZA treatment was found for allâcause mortality (16 studies, 2987 participants: RR 0.95, 95% CI 0.70 to 1.29). The risk for any acute rejection (22 studies, 3301 participants: RR 0.65, 95% CI 0.57 to 0.73, P < 0.01), biopsyâproven acute rejection (12 studies, 2696 participants: RR 0.59, 95% CI 0.52 to 0.68) and antibodyâtreated acute rejection (15 studies, 2914 participants: RR 0.48, 95% CI 0.36 to 0.65, P < 0.01) were reduced in MMF treated patients. Metaâregression analyses suggested that the magnitude of risk reduction of acute rejection may be dependent on the control rate (relative risk reduction (RRR) 0.34, 95% CI 0.10 to 1.09, P = 0.08), AZA dose (RRR 1.01, 95% CI 1.00 to 1.01, P = 0.10) and the use of cyclosporin A microâemulsion (RRR 1.27, 95% CI 0.98 to 1.65, P = 0.07). Pooled analyses failed to show a significant and meaningful difference between MMF and AZA in kidney function measures. Data on malignancies and infections were sparse, except for cytomegalovirus (CMV) infections. The risk for CMV viraemia/syndrome (13 studies, 2880 participants: RR 1.06, 95% CI 0.85 to 1.32) was not statistically significantly different between MMF and AZA treated patients, whereas the likelihood of tissueâinvasive CMV disease was greater with MMF therapy (7 studies, 1510 participants: RR 1.70, 95% CI 1.10 to 2.61). Adverse event profiles varied: gastrointestinal symptoms were more likely in MMF treated patients and thrombocytopenia and elevated liver enzymes were more common in AZA treatment. Authors' conclusions MMF was superior to AZA for improvement of graft survival and prevention of acute rejection after kidney transplantation. These benefits must be weighed against potential harms such as tissueâinvasive CMV disease. However, assessment of the evidence on safety outcomes was limited due to rare events in the observation periods of the studies (e.g. malignancies) and inconsistent reporting and definitions (e.g. infections, adverse events). Thus, balancing benefits and harms of the two drugs remains a major task of the transplant physician to decide which agent the individual patient should be started on
Topological Alterations of the Structural Brain Connectivity Network in Children with Juvenile Neuronal Ceroid Lipofuscinosis
BACKGROUND AND PURPOSE: We used diffusion MR imaging to investigate the structural brain connectivity networks in juvenile neuronal ceroid lipofuscinosis, a neurodegenerative lysosomal storage disease of childhood. Although changes in conventional MR imaging are typically not visually apparent in children agedPeer reviewe
A heavy quark effective field lagrangian keeping particle and antiparticle mixed sectors
We derive a tree-level heavy quark effective Lagrangian keeping
particle-antiparticle mixed sectors allowing for heavy quark-antiquark pair
annihilation and creation. However, when removing the unwanted degrees of
freedom from the effective Lagrangian one has to be careful in using the
classical equations of motion obeyed by the effective fields in order to get a
convergent expansion on the reciprocal of the heavy quark mass. Then the
application of the effective theory to such hard processes should be sensible
for special kinematic regimes as for example heavy quark pair production near
threshold.Comment: LaTeX, 14 pages, 1 EPS figure
Letter to the Editor concerning âA systematic review of controlled trials on visual stress using intuitive overlays or colorimeter"
yesWe read with interest the review written by Evans and Allen, and published in the Journal of Optometry, in July, 2016
The HQET/NRQCD Lagrangian to order alpha/m^3
The HQET/NRQCD Lagrangian is computed to order alpha/m^3. The computation is
performed using dimensional regularization to regulate the ultraviolet and
infrared divergences. The results are consistent with reparametrization
invariance to order 1/m^3. Some subtleties in the matching conditions for NRQCD
are discussed.Comment: Two terms added to Lagrangian. Explicit value of G^3 coefficient
given. Some references added, and TeX problems fixed. (18 pages, uses revtex
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