740 research outputs found
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
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
Ruled Laguerre minimal surfaces
A Laguerre minimal surface is an immersed surface in the Euclidean space
being an extremal of the functional \int (H^2/K - 1) dA. In the present paper,
we prove that the only ruled Laguerre minimal surfaces are up to isometry the
surfaces R(u,v) = (Au, Bu, Cu + D cos 2u) + v (sin u, cos u, 0), where A, B, C,
D are fixed real numbers. To achieve invariance under Laguerre transformations,
we also derive all Laguerre minimal surfaces that are enveloped by a family of
cones. The methodology is based on the isotropic model of Laguerre geometry. In
this model a Laguerre minimal surface enveloped by a family of cones
corresponds to a graph of a biharmonic function carrying a family of isotropic
circles. We classify such functions by showing that the top view of the family
of circles is a pencil.Comment: 28 pages, 9 figures. Minor correction: missed assumption (*) added to
Propositions 1-2 and Theorem 2, missed case (nested circles having nonempty
envelope) added in the proof of Pencil Theorem 4, missed proof that the arcs
cut off by the envelope are disjoint added in the proof of Lemma
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
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.
Drugâdrug interactions in pediatric oncology patients
BackgroundDrugâdrug interactions (DDIs) can negatively affect pharmacotherapy. However, pediatric DDI studies are scarce. We undertook an exploratory study to investigate prevalence and clinical relevance of DDIs between cytostatic and noncytostatic drugs in outpatient pediatric oncology patients.ProcedureAfter informed consent and inclusion, the following information was collected: currently prescribed noncytostatic and cytostatic drugs, comorbidities, and use of overâtheâcounter (OTC) drugs, complementary and alternative medicines (CAMs), and dietary supplements. All medication was screened for DDIs according to two databases: MicromedexÂź Solutions and the Dutch drug database GâStandard. The researcher presented DDIs with an associated potential for adverse outcome and a proposal for intervention to three independent experts. If the experts considered a DDI to be potentially clinically relevant and requiring intervention, the physician was notified.ResultsSeventyâthree patients were included (median age 8.9 years). A total of 67 different DDIs were counted (66 in MicromedexÂź Solutions, 14 in GâStandard, and 13 DDIs in both databases). The medication reviews resulted in 35 interventions related to 11 different DDIs. The majority of DDIs concerned noncytostatic drugs (25/35) and one third occurred between cytostatic and noncytostatic drugs (10/35). The use of QTcâintervalâprolonging drugs resulted in one intervention. The use of OTC drugs, CAM, or dietary supplements did not lead to DDIs.ConclusionsThis study resulted in a selection of 11 potentially clinically relevant DDIs for 73 outpatients in our pediatric oncology department. Interventions were formulated in close collaboration between physicians and clinical pharmacists. Future research should focus on assessing DDIs concerning QTcâinterval prolongation.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137518/1/pbc26410_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137518/2/pbc26410.pd
Rotating Shallow Water Dynamics: Extra Invariant and the Formation of Zonal Jets
We show that rotating shallow water dynamics possesses an approximate
(adiabatic-type) positive quadratic invariant, which exists not only at
mid-latitudes (where its analogue in the quasigeostrophic equation has been
previously investigated), but near the equator as well (where the
quasigeostrophic equation is inapplicable). Deriving the extra invariant, we
find "small denominators" of two kinds: (1) due to the triad resonances (as in
the case of the quasigeostrophic equation) and (2) due to the equatorial limit,
when the Rossby radius of deformation becomes infinite. We show that the "small
denominators" of both kinds can be canceled. The presence of the extra
invariant can lead to the generation of zonal jets. We find that this tendency
should be especially pronounced near the equator. Similar invariant occurs in
magnetically confined fusion plasmas and can lead to the emergence of zonal
flows.Comment: 29 pages, 4 figure
Kinetics of a Network of Vortex Loops in He II and a Theory of Superfluid Turbulence
A theory is developed to describe the superfluid turbulence on the base of
kinetics of the merging and splitting vortex loops. Because of very frequent
reconnections the vortex loops (as a whole) do not live long enough to perform
any essential evolution due to the deterministic motion. On the contrary, they
rapidly merge and split, and these random recombination processes prevail over
other slower dynamic processes. To develop quantitative description we take the
vortex loops to have a Brownian structure with the only degree of freedom,
which is the length of the loop. We perform investigation on the base of
the Boltzmann type kinetic equation for the distribution function of
number of loops with length . By use of the special ansatz in the collision
integral we have found the exact power-like solution to kinetic equation in the
stationary case. This solution is not (thermodynamically) equilibrium, but on
the contrary, it describes the state with two mutual fluxes of the length (or
energy) in space of sizes of the vortex loops. The term flux means just
redistribution of length (or energy) among the loops of different sizes due to
reconnections. Analyzing this solution we drew several results on the structure
and dynamics of the vortex tangle in the turbulent superfluid helium. In
particular, we evaluated the mean radius of the curvature and the full rate of
the reconnection events. We also studied the evolution of the full length of
vortex loops per unit volume-the so-called vortex line density. It is shown
this evolution to obey the famous Vinen equation. The properties of the Vinen
equation from the point of view of the developed approach had been discussed.Comment: 34 pages, 9 Postscript figures, [aps,preprint,12pt]{revtex4
Heavy quark supermultiplet excitations
Lorentz covariant wave functions for meson and baryon supermultiplets are
simply derived by boosting representations corresponding to
multiquark systems at rest.Comment: 12 pages (Revtex), UTAS-PHYS-93-4
Application of heavy-quark effective theory to lattice QCD: I. Power Corrections
Heavy-quark effective theory (HQET) is applied to lattice QCD with Wilson
fermions at fixed lattice spacing a. This description is possible because
heavy-quark symmetries are respected. It is desirable because the ultraviolet
cutoff in current numerical work and the heavy-quark mass are
comparable. Effects of both short distances, a and , are captured fully
into coefficient functions, which multiply the operators of the usual HQET.
Standard tools of HQET are used to develop heavy-quark expansions of lattice
observables and, thus, to propagate heavy-quark discretization errors. Three
explicit examples are given: namely, the mass, decay constant, and semileptonic
form factors of heavy-light mesons.Comment: 41 pp., no figs; Phys Rev D version, improving argument that an HQET
holds for all m_Q
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