6,084 research outputs found
Spontaneous, collective coherence in driven, dissipative cavity arrays
We study an array of dissipative tunnel-coupled cavities, each interacting
with an incoherently pumped two-level emitter. For cavities in the lasing
regime, we find correlations between the light fields of distant cavities,
despite the dissipation and the incoherent nature of the pumping mechanism.
These correlations decay exponentially with distance for arrays in any
dimension but become increasingly long ranged with increasing photon tunneling
between adjacent cavities. The interaction-dominated and the
tunneling-dominated regimes show markedly different scaling of the correlation
length which always remains finite due to the finite photon trapping time. We
propose a series of observables to characterize the spontaneous build-up of
collective coherence in the system.Comment: 9 pages, 4 figures, including supplemental material (with 4 pages, 1
figure). This is a shorter version with some modifications in the
supplemental material (a gap in the proof was closed and calculations
significantly generalized and improved
Collective resonances in plasmonic crystals: Size matters
Periodic arrays of metallic nanoparticles may sustain Surface Lattice
Resonances (SLRs), which are collective resonances associated with the
diffractive coupling of Localized Surface Plasmon Resonances (LSPRs). By
investigating a series of arrays with varying number of particles, we traced
the evolution of SLRs to its origins. Polarization resolved extinction spectra
of arrays formed by a few nanoparticles were measured, and found to be in very
good agreement with calculations based on a coupled dipole model. Finite size
effects on the optical properties of the arrays are observed, and our results
provide insight into the characteristic length scales for collective plasmonic
effects: for arrays smaller than 5 x 5 particles, the Q-factors of SLRs are
lower than those of LSPRs; for arrays larger than 20 x 20 particles, the
Q-factors of SLRs saturate at a much larger value than those of LSPRs; in
between, the Q-factors of SLRs are an increasing function of the number of
particles in the array.Comment: 4 figure
Unmasking quality: exploring meanings of health by doing art
This paper arises from a presentation at the ‘Quality in Healthcare’ symposium at Cumberland Lodge, England, in 2013. MK, CR and SH conceived the paper and led the writing of the manuscript. JF, JL-D, AC, DE contributed substantially to the intellectual content of the paper through providing critical commentary and interpretation. All authors read and approved the final manuscript
Semiclassical Coherent States propagator
In this work, we derived a semiclassical approximation for the matrix
elements of a quantum propagator in coherent states (CS) basis that avoids
complex trajectories, it only involves real ones. For that propose, we used
the, symplectically invariant, semiclassical Weyl propagator obtained by
performing a stationary phase approximation (SPA) for the path integral in the
Weyl representation. After what, for the transformation to CS representation
SPA is avoided, instead a quadratic expansion of the complex exponent is used.
This procedure also allows to express the semiclassical CS propagator uniquely
in terms of the classical evolution of the initial point, without the need of
any root search typical of Van Vleck Gutzwiller based propagators. For the case
of chaotic Hamiltonian systems, the explicit time dependence of the CS
propagator has been obtained. The comparison with a
\textquotedbl{}realistic\textquotedbl{} chaotic system that derives from a
quadratic Hamiltonian, the cat map, reveals that the expression here derived is
exact up to quadratic Hamiltonian systems.Comment: 13 pages, 2 figure. Accepted for publication in PR
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mHealth: providing a mindfulness app for women with chronic pelvic pain in gynaecology outpatient clinics: qualitative data analysis of user experience and lessons learnt
OBJECTIVES: To determine whether a pre-existing smartphone app to teach mindfulness meditation is acceptable to women with chronic pelvic pain (CPP) and can be integrated into clinical practice within the National Health Service (NHS) CPP pathways, and to inform the design of a potential randomised clinical trial.
DESIGN: A prestudy patient and public involvement (PPI) group to collect feedback on the acceptability of the existing app and study design was followed by a three-arm randomised feasibility trial. In addition, we undertook interviews and focus groups with patients and staff to explore app usability and acceptability. We also obtained participant comments on the research process, such as acceptability of the study questionnaires.
SETTING: Two gynaecology clinics within Barts Health NHS, London, UK.
PARTICIPANTS: Patients with CPP lasting ≥6 months with access to smartphone or personal computer and understanding of basic English.
INTERVENTION: The intervention was mindfulness meditation content plus additional pain module delivered by a smartphone app. Active controls received muscle relaxation content from the same app. Passive (waiting list) controls received usual care.
MAIN OUTCOME MEASURES: Themes on user feedback, app usability and integration, and reasons for using/not using the app.
RESULTS: The use of the app was low in both active groups. Patients in the prestudy PPI group, all volunteers, were enthusiastic about the app (convenience, content, portability, flexibility, ease of use). Women contributing to the interview or focus group data (n=14), from a 'real world' clinic (some not regular app users), were less positive, citing as barriers lack of opportunities/motivation to use the app and lack of familiarity and capabilities with technology. Staff (n=7) were concerned about the potential need for extra support for them and for the patients, and considered the app needed organisational backing and peer acceptance.
CONCLUSION: The opinions of prestudy PPI volunteers meeting in their private time may not represent those of patients recruited at a routine clinic appointment. It may be more successful to codesign/codevelop an app with typical users than to adapt existing apps for use in real-world clinical populations.
TRIAL REGISTRATION NUMBER: ISRCTN10925965
Intercomparisons of HIRDLS, COSMIC and SABER for the detection of stratospheric gravity waves
Colocated temperature profiles from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC), High Resolution Dynamics Limb Sounder (HIRDLS) and the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) mission are compared over the years 2006–2007 to assess their relative performances for the detection of stratospheric gravity waves. Two methods are used, one based on a simple comparison of the standard deviations and correlation coefficients of high-pass filtered profiles from each instrument, and the other based on Stockwell transform analyses of the profiles for vertical wavelength and temperature perturbation scales. It is concluded, when allowing for their different vertical resolution capabilites, that the three instruments reproduce each other's results for magnitude and vertical scale of perturbations to within their resolution limits in approximately 50 % of cases, but with a positive frequency and temperature bias in the case of COSMIC. This is possibly indicative of a slightly higher vertical resolution being available to the constellation than estimated
Collaborative working within UK NHS secondary care and across sectors for COPD and the impact of peer review : qualitative findings from the UK National COPD Resources and Outcomes Project
Introduction: We investigated the effects on collaborative work within the UK National Health Service (NHS) of an intervention for service quality improvement: informal, structured, reciprocated, multidisciplinary peer review with feedback and action plans. The setting was care for chronic obstructive pulmonary disease (COPD).
Theory and methods: We analysed semi-structured interviews with 43 hospital respiratory consultants, nurses and general managers at 24 intervention and 11 control sites, as part of a UK randomised controlled study, the National COPD Resources and Outcomes Project (NCROP), using Scott’s conceptual framework for action (inter-organisational, intra-organisational, inter-professional and inter-individual). Three areas of care targeted by NCROP involved collaboration across primary and secondary care.
Results: Hospital respiratory department collaborations with commissioners and hospital managers varied. Analysis suggested that this is related to team responses to barriers. Clinicians in unsuccessful collaborations told ‘atrocity stories’ of organisational, structural and professional barriers to service improvement. The others removed barriers by working with government and commissioner agendas to ensure continued involvement in patients’ care. Multidisciplinary peer review facilitated collaboration between participants, enabling them to meet, reconcile differences and exchange ideas across boundaries.
Conclusions: The data come from the first randomised controlled trial of organisational peer review, adding to research into UK health service collaborative work, which has had a more restricted focus on inter-professional relations. NCROP peer review may only modestly improve collaboration but these data suggest it might be more effective than top-down exhortations to change when collaboration both across and within organisations is required
Nonmonotonic Evolution of the Blocking Temperature in Dispersions of Superparamagnetic Nanoparticles
We use a Monte Carlo approach to simulate the influence of the dipolar
interaction on assemblies of monodisperse superparamagnetic
nanoparticles. We have identified a critical
concentration c*, that marks the transition between two different regimes in
the evolution of the blocking temperature () with interparticle
interactions. At low concentrations (c < c*) magnetic particles behave as an
ideal non-interacting system with a constant . At concentrations c > c*
the dipolar energy enhances the anisotropic energy barrier and
increases with increasing c, so that a larger temperature is required to reach
the superparamagnetic state. The fitting of our results with classical particle
models and experiments supports the existence of two differentiated regimes.
Our data could help to understand apparently contradictory results from the
literature.Comment: 13 pages, 7 figure
Independent nonclassical tests for states and measurements in the same experiment
We show that one single experiment can test simultaneously and independently
both the nonclassicality of states and measurements by the violation or
fulfillment of classical bounds on the statistics. Nonideal measurements
affected by imperfections can be characterized by two bounds depending on
whether we test the ideal measurement or the real one.Comment: 9 pages, 3 figures. Proceedings of 17th CEWQO 201
Proposal of a method for fluorimetric analysis of malvin in red wines
A fluorimetric method for the quantitative determination of malvin (malvidin 3,5-diglucoside) in red wines is described. The method is based on previous fractionation of the wine in a Polyclar AT column and later formation of a fluorophore, by oxidation of the malvin. The proposed method has good precision and accuracy and when applied to hybrid red wines affords results significantly comparable with those obtained by HPLC
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