2,203 research outputs found
The OPERA trial : a protocol for the process evaluation of a randomised trial of an exercise intervention for older people in residential and nursing accommodation
Background: The OPERA trial is large cluster randomised trial testing a physical activity intervention to address
depression amongst people living in nursing and residential homes for older people. A process evaluation was
commissioned alongside the trial and we report the protocol for this process evaluation. Challenges included the
cognitive and physical ability of the participants, the need to respect the privacy of all home residents, including
study non-participants, and the physical structure of the homes. Evaluation activity had to be organised around the
structured timetable of homes, leaving limited opportunities for data collection. The aims of this process evaluation
are to provide findings that will assist in the interpretation of the clinical trial results, and to inform potential
implementation of the physical activity intervention on a wider scale.
Methods/design: Quantitative data on recruitment of homes and individuals is being collected. For homes in the
intervention arm, data on dose and fidelity of the intervention delivered; including individual rates of participation
in exercise classes are collected. In the control homes, uptake and delivery of depression awareness training is
monitored. These data will be combined with qualitative data from an in-depth study of a purposive sample of
eight homes (six intervention and two control).
Discussion: Although process evaluations are increasingly funded alongside trials, it is still rare to see the findings
published, and even rarer to see the protocol for such an evaluation published. Process evaluations have the
potential to assist in interpreting and understanding trial results as well as informing future roll-outs of
interventions. If such evaluations are funded they should also be reported and reviewed in a similar way to the
trial outcome evaluation
Nanomechanical resonators operating as charge detectors in the nonlinear regime
We present measurements on nanomechanical resonators machined from
Silicon-on-Insulator substrates. The resonators are designed as freely
suspended Au/Si beams of lengths on the order of 1 - 4 um and a thickness of
200 nm. The beams are driven into nonlinear response by an applied modulation
at radio frequencies and a magnetic field in plane. The strong hysteresis of
the magnetomotive response allows sensitive charge detection by varying the
electrostatic potential of a gate electrode.Comment: 8 pages, 6 figure
Polarization insensitivity of AlGaAs/GaAs interdiffused quantum wells
Modeling is used to show that interdiffusion can generate a polarization independent parabolic-like quantum well. Criteria to achieve the parabolic-like quantum wells by interdiffusion are discussed. The results indicated that interdiffused quantum wells can produce equal eigen-state spacing, polarization insensitive Stark shift and modulation characteristics similar to an ideal parabolic quantum well. The design process to obtain polarization insensitive ON- and OFF- states in the parabolic-like interdiffused quantum wells is discussed. The predicted modulation depth is comparable to those measured using parabolic quantum wells. The diffused quantum wells have the advantage of using an as-grown rectangular quantum well with post-growth annealing to tailor its confinement profile. These features suggest that the interdiffused quantum well structure can be use to produce polarization insensitive electro-absorptive modulation.published_or_final_versio
Interdiffusion contributions in optimized surface-acoustic-wave quantum-well modulators
The electro-absorption of AlGaAs/GaAs diffused quantum well (DFQW) modulator using surface acoustic wave (SAW) QW interactions was studied theoretically. The modulator was also optimized through the use of both the steeper potential at the device surface for modulation and a long λSAW and a low power SAW. The non-uniform feature of the SAW induced potential was also taken into account in optimizing the device structure. Interdiffusion took place into the W stack to modify modulation performance so that λop and the optical properties of the optimized structure can be further modified. The modulation efficiency of an incident optical field depended on the guiding properties in the QW active region.published_or_final_versio
Fully compressible simulation of low-speed premixed reacting flows
Low speed premixed combustion flows in industrial applications are generally simulated using the "incompressible" Navier-Stokes algorithms, which belong to the family of fractional step methods, or segregated methods. The approximations used for the combustion modelling in the framework of the segregated mathematical formulation, often represent important limitations for applying the combustion numerical simulation to a wider class of problems of engineering interest. Recent developments of preconditioning techniques allow to apply the same complete system of Navier-Stokes equations to a wide variety of fluid flow problems characterized by the whole range of Reynolds, Mach, Grashof, Prandtl and Damkoeler numbers. The present work describes the development of a fully "compressible" mathematical model for the simulation of low-speed turbulent premixed reactive flows. Issues on flow and fluid compressibility as well as on the two mathematical alternative formulations, are discussed. Also discussed are issues related to coupling the flamelet premixed combustion model (based on the solution of a transport equation for the progress variable) with one-equation turbulence models, instead of the classical two-equation K – ε model. In this work the model by Spalart & Allmaras is used. The several advantages brought about by the use of the fully compressible formulation are discussed based on the results obtained on a test case taken from literature
Local Versus Global Thermal States: Correlations and the Existence of Local Temperatures
We consider a quantum system consisting of a regular chain of elementary
subsystems with nearest neighbor interactions and assume that the total system
is in a canonical state with temperature . We analyze under what condition
the state factors into a product of canonical density matrices with respect to
groups of subsystems each, and when these groups have the same temperature
. While in classical mechanics the validity of this procedure only depends
on the size of the groups , in quantum mechanics the minimum group size
also depends on the temperature ! As examples, we apply our
analysis to a harmonic chain and different types of Ising spin chains. We
discuss various features that show up due to the characteristics of the models
considered. For the harmonic chain, which successfully describes thermal
properties of insulating solids, our approach gives a first quantitative
estimate of the minimal length scale on which temperature can exist: This
length scale is found to be constant for temperatures above the Debye
temperature and proportional to below.Comment: 12 pages, 5 figures, discussion of results extended, accepted for
publication in Phys. Rev.
A comparison of electrochemical degradation of phenol on boron doped diamond and lead dioxide anodes
This work compares two electrode materials used to mineralize phenol contained in waste waters. Two disks covered with either boron doped diamond (BDD) or PbO2 were used as anodes in a one compartment flow cell under the same hydrodynamic conditions. Efficiencies of galvanostatic electrolyses are compared on the basis of measurements of Total Organic Carbon (TOC) and Chemical Oxygen Demand (COD). Galvanostatic electrolyses were monitored by analysis of phenol and of its oxidation derivatives to evaluate the operating time needed for complete elimination of toxic aromatics. The experimental current efficiency is close to the theoretical value for the BDD electrode. Other parameters being equal, phenol species disappeared at the same rate using the two electrode materials but the BDD anode showed better efficiency to eliminate TOC and COD. Moreover, during the electrolysis less intermediates are formed with BDD compared to PbO2 whatever the current density. A comparison of energy consumption is given based on the criterion of 99% removal of aromatic compounds
Correlated tunneling in intramolecular carbon nanotube quantum dots
We investigate correlated electronic transport in single-walled carbon
nanotubes with two intramolecular tunneling barriers. We suggest that below a
characteristic temperature the long range nature of the Coulomb interaction
becomes crucial to determine the temperature dependence of the maximum G_max of
the conductance peak. Correlated sequential tunneling dominates transport
yielding the power-law G_max ~ T^{\alpha_{end-end}-1}, typical for tunneling
between the ends of two Luttinger liquids. Our predictions are in agreement
with recent measurements
Magnetotransport in Two-Dimensional Electron Systems with Spin-Orbit Interaction
We present magnetotransport calculations for homogeneous two-dimensional
electron systems including the Rashba spin-orbit interaction, which mixes the
spin-eigenstates and leads to a modified fan-chart with crossing Landau levels.
The quantum mechanical Kubo formula is evaluated by taking into account
spin-conserving scatterers in an extension of the self-consistent Born
approximation that considers the spin degree of freedom. The calculated
conductivity exhibits besides the well-known beating in the Shubnikov-de Haas
(SdH) oscillations a modulation which is due to a suppression of scattering
away from the crossing points of Landau levels and does not show up in the
density of states. This modulation, surviving even at elevated temperatures
when the SdH oscillations are damped out, could serve to identify spin-orbit
coupling in magnetotransport experiments. Our magnetotransport calculations are
extended also to lateral superlattices and predictions are made with respect to
1/B periodic oscillations in dependence on carrier density and strength of the
spin-orbit coupling.Comment: 8 pages including 8 figures; submitted to PR
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