Universal Magnetic Fluctuations with a Field Induced Length Scale

We calculate the probability density function for the order parameter fluctuations in the low temperature phase of the 2D-XY model of magnetism near the line of critical points. A finite correlation length, \xi, is introduced with a small magnetic field, h, and an accurate expression for \xi(h) is developed by treating non-linear contributions to the field energy using a Hartree approximation. We find analytically a series of universal non-Gaussian distributions with a finite size scaling form and present a Gumbel-like function that gives the PDF to an excellent approximation. We propose the Gumbel exponent, a(h), as an indirect measure of the length scale of correlations in a wide range of complex systems.Comment: 7 pages, 4 figures, 1 table. To appear in Phys. Rev.

Finite size scaling in the 2D XY-model and generalized universality

In recent works (BHP), a generalized universality has been proposed, linking phenomena as dissimilar as 2D magnetism and turbulence. To test these ideas, we performed a MC study of the 2D XY-model. We found that the shape of the probability distribution function for the magnetization M is non Gaussian and independent of the system size --in the range of the lattice sizes studied-- below the Kosterlitz-Thoules temperature. However, the shape of these distributions does depend on the temperature, contrarily to the BHP's claim. This behavior is successfully explained by using an extended finite-size scaling analysis and the existence of bounds for M.Comment: 7 pages, 5 figures. Submitted to Phys. Rev. Lett. Details of changes: 1. We emphasized in the abstract the range of validity of our results. 2. In the last paragraph the temperature dependence of the PDF was slightly re-formulate

About the Functional Form of the Parisi Overlap Distribution for the Three-Dimensional Edwards-Anderson Ising Spin Glass

Recently, it has been conjectured that the statistics of extremes is of relevance for a large class of correlated system. For certain probability densities this predicts the characteristic large $x$ fall-off behavior $f(x)\sim\exp (-a e^x)$, $a>0$. Using a multicanonical Monte Carlo technique, we have calculated the Parisi overlap distribution $P(q)$ for the three-dimensional Edward-Anderson Ising spin glass at and below the critical temperature, even where $P(q)$ is exponentially small. We find that a probability distribution related to extreme order statistics gives an excellent description of $P(q)$ over about 80 orders of magnitude.Comment: 4 pages RevTex, 3 figure

Universal energy distribution for interfaces in a random field environment

We study the energy distribution function $\rho (E)$ for interfaces in a random field environment at zero temperature by summing the leading terms in the perturbation expansion of $\rho (E)$ in powers of the disorder strength, and by taking into account the non perturbational effects of the disorder using the functional renormalization group. We have found that the average and the variance of the energy for one-dimensional interface of length $L$ behave as, $_{R}\propto L\ln L$, $\Delta E_{R}\propto L$, while the distribution function of the energy tends for large $L$ to the Gumbel distribution of the extreme value statistics.Comment: 4 pages, 2 figures, revtex4; the distribution function of the total and the disorder energy is include

Higher correlations, universal distributions and finite size scaling in the field theory of depinning

Recently we constructed a renormalizable field theory up to two loops for the quasi-static depinning of elastic manifolds in a disordered environment. Here we explore further properties of the theory. We show how higher correlation functions of the displacement field can be computed. Drastic simplifications occur, unveiling much simpler diagrammatic rules than anticipated. This is applied to the universal scaled width-distribution. The expansion in d=4-epsilon predicts that the scaled distribution coincides to the lowest orders with the one for a Gaussian theory with propagator G(q)=1/q^(d+2 \zeta), zeta being the roughness exponent. The deviations from this Gaussian result are small and involve higher correlation functions, which are computed here for different boundary conditions. Other universal quantities are defined and evaluated: We perform a general analysis of the stability of the fixed point. We find that the correction-to-scaling exponent is omega=-epsilon and not -epsilon/3 as used in the analysis of some simulations. A more detailed study of the upper critical dimension is given, where the roughness of interfaces grows as a power of a logarithm instead of a pure power.Comment: 15 pages revtex4. See also preceding article cond-mat/030146

STOPP/START interventions to improve medicines management for people aged 65 years and over: a realist synthesis

Background Drug-related problems and potentially inappropriate prescribing impose a huge burden on patients and the health-care system. The most widely used tools for appropriate prescription in older adults in England and in other European countries are the Screening Tool of Older People’s Prescriptions (STOPP)/Screening Tool to Alert to the Right Treatment (START) tools. STOPP/START tools support medicines optimisation for older adults. Objectives To identify, test and refine the programme theories underlying how interventions based on the STOPP/START tools are intended to work, for whom, in what circumstances and why, as well as the resource use and cost requirements or impacts. Design A realist synthesis. Setting Primary care, hospital care and nursing homes. Patients Patients aged ≥ 65 years. Interventions Any intervention based on the use of the STOPP/START tools. Review methods Database and web-searching was carried out to retrieve relevant evidence to identify and test programme theories about how interventions based on the use of the STOPP/START tools work. A project reference group made up of health-care professionals, NHS decision-makers, older people, carers and members of the public was set up. In phase 1 we identified programme theories about STOPP/START interventions on how, for whom, in what contexts and why they are intended to work. We searched the peer-reviewed and grey literature to identify documents relevant to the research questions. We interviewed experts in the field in our reference group to gain input on our list of candidate context–mechanism–outcome configurations, to identify additional context–mechanism–outcome configurations and to identify additional literature and/or relevant concepts. In phase 2 we reviewed and synthesised relevant published and unpublished empirical evidence and tested the programme theories using evidence from a larger set of empirical studies. Results We developed a single logic model structured around three key mechanisms: (1) personalisation, (2) systematisation and (3) evidence implementation. Personalisation: STOPP/START-based interventions are based on shared decision-making, taking into account patient preferences, experiences and expectations (mechanisms), leading to increased patient awareness, adherence, satisfaction, empowerment and quality of life (outcomes). Systematisation: STOPP/START tools provide a standardised/systematic approach for medication reviews (mechanisms), leading to changes in professional and organisational culture and burden/costs (outcomes). Evidence implementation: delivery of STOPP/START-based interventions is based on the implementation of best evidence (mechanisms), reducing adverse outcomes through appropriate prescribing/deprescribing (outcomes). For theory testing, we identified 40 studies of the impact of STOPP/START-based interventions in hospital settings, nursing homes, primary care and community pharmacies. Most of the interventions used multiple mechanisms. We found support for the impact of the personalisation and evidence implementation mechanisms on selected outcome variables, but similar impact was achieved by interventions not relying on these mechanisms. We also observed that the impact of interventions was linked to the proximity of the selected outcomes to the intervention in the logic model, resulting in a clearer benefit for appropriateness of prescribing, adverse drug events and prescription costs. Limitations None of the available studies had been explicitly designed for evaluating underlying causal mechanisms, and qualitative information was sparse. Conclusions No particular configuration of the interventions is associated with a greater likelihood of improved outcomes in given settings. Study registration This study is registered as PROSPERO CRD42018110795. Funding This project was funded by the National Institute for Health Research (NIHR) Health Services and Delivery Research programme and will be published in full in Health Services and Delivery Research; Vol. 9, No. 23. See the NIHR Journals Library website for further project information

Diffuse scattering

Diffuse neutron scattering covers a wide range of phenomena related to short range nuclear and magnetic orderings. Although it is “a priori” simple to measure, the underlying physics is often quite complex. Extracting useful and reliable information requires careful corrections and calibrations, and appropriate models of analysis, specifics for each physical case. This paper yields a partial and subjective glance on this specific subject, showing studies about chemical orderings in binary alloys and magnetic correlations in frustrated “spin ices” as examples

Changes in air quality in Mexico City, London and Delhi in response to various stages and levels of lockdowns and easing of restrictions during COVID-19 pandemic

The impacts of COVID-19 lockdown restrictions have provided a valuable global experiment into the extent of improvements in air quality possible with reductions in vehicle movements. Mexico City, London and Delhi all share the problem of air quality failing WHO guideline limits, each with unique situations and influencing factors. We determine, discuss and compare the air quality changes across these cities during the COVID-19, to understand how the findings may support future improvements in their air quality and associated health of citizens. We analysed ground-level PM10, PM2.5, NO2, O3 and CO changes in each city for the period 1st January to August 31, 2020 under different phases of lockdown, with respect to daily average concentrations over the same period for 2017 to 2019. We found major reductions in PM10, PM2.5, NO2 and CO across the three cities for the lockdown phases and increases in O3 in London and Mexico City but not Delhi. The differences were due to the O3 production criteria across the cities, for Delhi production depends on the VOC-limited photochemical regime. Levels of reductions were commensurate with the degree of lockdown. In Mexico City, the greatest reduction in measured concentration was in CO in the initial lockdown phase (40%), in London the greatest decrease was for NO2 in the later part of the lockdown (49%), and in Delhi the greatest decrease was in PM10, and PM2.5 in the initial lockdown phase (61% and 50%, respectively). Reduction in pollutant concentrations agreed with reductions in vehicle movements. In the initial lockdown phase vehicle movements reduced by up to 59% in Mexico City and 63% in London. The cities demonstrated a range of air quality changes in their differing geographical areas and land use types. Local meteorology and pollution events, such as forest fires, also impacted the results