7,507 research outputs found
Irreversible flow of vortex matter: polycrystal and amorphous phases
We investigate the microscopic mechanisms giving rise to plastic depinning
and irreversible flow in vortex matter. The topology of the vortex array
crucially determines the flow response of this system. To illustrate this
claim, two limiting cases are considered: weak and strong pinning interactions.
In the first case disorder is strong enough to introduce plastic effects in the
vortex lattice. Diffraction patterns unveil polycrystalline lattice topology
with dislocations and grain boundaries determining the electromagnetic response
of the system. Filamentary flow is found to arise as a consequence of
dislocation dynamics. We analize the stability of vortex lattices against the
formation of grain boundaries, as well as the steady state dynamics for
currents approaching the depinning critical current from above, when vortex
motion is mainly localized at the grain boundaries. On the contrary, a
dislocation description proves no longer adequate in the second limiting case
examined. For strong pinning interactions, the vortex array appears completely
amorphous and no remnant of the Abrikosov lattice order is left. Here we obtain
the critical current as a function of impurity density, its scaling properties,
and characterize the steady state dynamics above depinning. The plastic
depinning observed in the amorphous phase is tightly connected with the
emergence of channel-like flow. Our results suggest the possibility of
establishing a clear distinction between two topologically disordered vortex
phases: the vortex polycrystal and the amorphous vortex matter.Comment: 13 pages, 16 figure
Effectiveness and process evaluation in obesity and type 2 diabetes prevention programs in children: a systematic review and meta-analysis
Background: Obesity in children is one of the most severe public health challenges of the current century and Type 2 Diabetes Mellitus (T2DM) frequency is also escalating. More so, the importance of process evaluation (PE) in complex interventions is increasingly recognized. The present review, aims to identify the effectiveness in terms of body composition parameters in a generation of articles to prevent obesity and T2DM in children. We hypothesise that those studies reporting PE applying the latest implementation guidelines suggested by the researchers would potentially show positive changes in body composition compared to those not reporting it. Additionally, we will evaluate the implementation degree of PE in those articles considering it and describe the PE subcomponents. Lastly, we aim to assess the intervention target used and its results.
Methods: A literature review was performed in parallel by 2 independent reviewers. A final number of 41 studies were selected for inclusion criteria.
Results: Meta-analysis of BMI and zBMI found non-significant effects of the proposed interventions. Sub-group analysis revealed only a significant effect in studies which performed PE. Moreover, PE was reported in 42% effective studies and 57% non-effective studies. Fidelity and satisfaction were the most implemented PE subcomponents, although there was a generally low grade of PE use (7/41). The highest proportion of effectiveness (83%) was shown in interventions of physical activity alone while the intervention most used was 3-arm target (diet, PA and BS).
Conclusions: Overall, obesity and T2DM prevention studies included in this review are not effective in terms of BMI and zBMI. Those studies performing PE reported to be effective in terms of BMI, while studies not reporting PE did not have positive results in terms of BMI and zBMI. In addition, none of the intervention studies included all PE indicators and most studies, which included PE in their interventions, did not provide full report of the PE components, according to the guidelines used for the present review. PROSPERO registration number: CRD42018093667
Kosterlitz-Thouless transition in three-state mixed Potts ferro-antiferromagnets
We study three-state Potts spins on a square lattice, in which all bonds are
ferromagnetic along one of the lattice directions, and antiferromagnetic along
the other. Numerical transfer-matrix are used, on infinite strips of width
sites, . Based on the analysis of the ratio of scaled mass
gaps (inverse correlation lengths) and scaled domain-wall free energies, we
provide strong evidence that a critical (Kosterlitz-Thouless) phase is present,
whose upper limit is, in our best estimate, . From analysis
of the (extremely anisotropic) nature of excitations below , we argue that
the critical phase extends all the way down to T=0. While domain walls parallel
to the ferromagnetic direction are soft for the whole extent of the critical
phase, those along the antiferromagnetic direction seem to undergo a softening
transition at a finite temperature. Assuming a bulk correlation length varying,
for , as , , we attempt finite-size scaling plots of our finite-width
correlation lengths. Our best results are for . We propose a
scenario in which such inconsistency is attributed to the extreme narrowness of
the critical region.Comment: 11 pages, 6 .eps figures, LaTeX with IoP macros, to be published in J
Phys
Heat exchange between two interacting nanoparticles beyond the fluctuation-dissipation regime
We show that the observed non-monotonic behavior of the thermal conductance
between two nanoparticles when they are brought into contact is originated by
an intricate phase space dynamics. Here it is assumed that this dynamics
results from the thermally activated jumping through a rough energy landscape.
A hierarchy of relaxation times plays the key role in the description of this
complex phase space behaviour. Our theory enables us to analyze the heat
transfer just before and at the moment of contact.Comment: 4 pages, 1 figure, approved for publication in Physical Review
Letter
Synthesis, Photochemical, and Redox Properties of Gold(I) and Gold(III) Pincer Complexes Incorporating a 2,2′:6′,2″-Terpyridine Ligand Framework
Reaction of [Au(C6F5)(tht)] (tht = tetrahydrothiophene) with 2,2′:6′,2″-terpyridine (terpy) leads to complex [Au(C6F5)(η1-terpy)] (1). The chemical oxidation of complex (1) with 2 equiv of [N(C6H4Br-4)3](PF6) or using electrosynthetic techniques affords the Au(III) complex [Au(C6F5)(η3-terpy)](PF6)2 (2). The X-ray diffraction study of complex 2 reveals that the terpyridine acts as tridentate chelate ligand, which leads to a slightly distorted square-planar geometry. Complex 1 displays fluorescence in the solid state at 77 K due to a metal (gold) to ligand (terpy) charge transfer transition, whereas complex 2 displays fluorescence in acetonitrile due to excimer or exciplex formation. Time-dependent density functional theory calculations match the experimental absorption spectra of the synthesized complexes. In order to further probe the frontier orbitals of both complexes and study their redox behavior, each compound was separately characterized using cyclic voltammetry. The bulk electrolysis of a solution of complex 1 was analyzed by spectroscopic methods confirming the electrochemical synthesis of complex 2
Depinning and critical current characteristics of topologically defected vortex lattices
We discuss the role of dislocation assemblies such as grain boundaries in the
dynamic response of a driven vortex lattice. We simulate the depinning of a
field-cooled vortex polycrystal and observe a general enhancement of the
critical current as well as a distinct crossover in the characterisitic of this
quantity as a function of pinning density. The results agree with analytical
predictions for grain boundary depinning. The dynamics of grain boundaries thus
proves an essential mechanism underlying the flow response of defected vortex
lattices and the corresponding transport properties of the superconducting
material. We emphasize the connection between the topological rearrangements of
the lattice and its threshold dynamics. Our theory encompasses a variety of
experimental observations in vortex matter as well as in colloidal crystals.Comment: 7 Figure
Searching for New Physics in Leptonic Decays of Bottomonium
New Physics can show up in various well-known processes already studied in
the Standard Model, in particular by modifying decay rates to some extent. In
this work, I examine leptonic decays of vector resonances of
bottomonium below production, subsequent to a magnetic dipole
radiative structural transition of the vector resonance yielding a pseudoscalar
continuum state, searching for the existence of a light Higgs-like neutral
boson that would imply a slight but experimentally measurable breaking of
lepton universality.Comment: LaTeX, 12 pages, 1 EPS figur
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