Zero-Point Fluctuations and the Quenching of the Persistent Current in Normal Metal Rings

The ground state of a phase-coherent mesoscopic system is sensitive to its environment. We investigate the persistent current of a ring with a quantum dot which is capacitively coupled to an external circuit with a dissipative impedance. At zero temperature, zero-point quantum fluctuations lead to a strong suppression of the persistent current with decreasing external impedance. We emphasize the role of displacement currents in the dynamical fluctuations of the persistent current and show that with decreasing external impedance the fluctuations exceed the average persistent current.Comment: 4 pages, 2 eps figure

Zero-point fluctuations in the ground state of a mesoscopic normal ring

We investigate the persistent current of a ring with an in-line quantum dot capacitively coupled to an external circuit. Of special interest is the magnitude of the persistent current as a function of the external impedance in the zero temperature limit when the only fluctuations in the external circuit are zero-point fluctuations. These are time-dependent fluctuations which polarize the ring-dot structure and we discuss in detail the contribution of displacement currents to the persistent current. We have earlier discussed an exact solution for the persistent current and its fluctuations based on a Bethe ansatz. In this work, we emphasize a physically more intuitive approach using a Langevin description of the external circuit. This approach is limited to weak coupling between the ring and the external circuit. We show that the zero temperature persistent current obtained in this approach is consistent with the persistent current calculated from a Bethe ansatz solution. In the absence of coupling our system is a two level system consisting of the ground state and the first excited state. In the presence of coupling we investigate the projection of the actual state on the ground state and the first exited state of the decoupled ring. With each of these projections we can associate a phase diffusion time. In the zero temperature limit we find that the phase diffusion time of the excited state projection saturates, whereas the phase diffusion time of the ground state projection diverges.Comment: 12 pages, 5 figure

A critical appraisal of guidelines for the management of knee osteoarthritis using Appraisal of Guidelines Research and Evaluation criteria

Clinical practice guidelines have been elaborated to summarize evidence related to the management of knee osteoarthritis and to facilitate uptake of evidence-based knowledge by clinicians. The objectives of the present review were summarizing the recommendations of existing guidelines on knee osteoarthritis, and assessing the quality of the guidelines using a standardized and validated instrument – the Appraisal of Guidelines Research and Evaluation (AGREE) tool. Internet medical literature databases from 2001 to 2006 were searched for guidelines, with six guidelines being identified. Thirteen clinician researchers participated in the review. Each reviewer was trained in the AGREE instrument. The guidelines were distributed to four groups of three or four reviewers, each group reviewing one guideline with the exception of one group that reviewed two guidelines. One independent evaluator reviewed all guidelines. All guidelines effectively addressed only a minority of AGREE domains. Clarity/presentation was effectively addressed in three out of six guidelines, scope/purpose and rigour of development in two guidelines, editorial independence in one guideline, and stakeholder involvement and applicability in none. The clinical management recommendation tended to be similar among guidelines, although interventions addressed varied. Acetaminophen was recommended for initial pain treatment, combined with exercise and education. Nonsteroidal anti-inflammatory drugs were recommended if acetaminophen failed to control pain, but cautiously because of gastrointestinal risks. Surgery was recommended in the presence of persistent pain and disability. Education and activity management interventions were superficially addressed in most guidelines. Guideline creators should use the AGREE criteria when developing guidelines. Innovative and effective methods of knowledge translation to health professionals are needed

Suppression of level hybridization due to Coulomb interactions

We investigate an ensemble of systems formed by a ring enclosing a magnetic flux. The ring is coupled to a side stub via a tunneling junction and via Coulomb interaction. We generalize the notion of level hybridization due to the hopping, which is naturally defined only for one-particle problems, to the many-particle case, and we discuss the competition between the level hybridization and the Coulomb interaction. It is shown that strong enough Coulomb interactions can isolate the ring from the stub, thereby increasing the persistent current. Our model describes a strictly canonical system (the number of carriers is the same for all ensemble members). Nevertheless for small Coulomb interactions and a long side stub the model exhibits a persistent current typically associated with a grand canonical ensemble of rings and only if the Coulomb interactions are sufficiently strong does the model exhibit a persistent current which one expects from a canonical ensemble.Comment: 19 pages, 6 figures, uses iop style files, version as publishe

Quantum Coherence of the Ground State of a Mesoscopic Ring

We discuss the phase coherence properties of a mesoscopic normal ring coupled to an electric environment via Coulomb interactions. This system can be mapped onto the Caldeira-Leggett model with a flux dependent tunneling amplitude. We show that depending on the strength of the coupling between the ring and the environment the free energy can be obtained either by a Bethe ansatz approch (for weak coupling) or by using a perturbative expression which we derive here (in the case of strong coupling). We demonstrate that the zero-point fluctuations of the environment can strongly suppress the persistent current of the ring below its value in the absence of the environment. This is an indication that the equilibrium fluctuations in the environment disturb the coherence of the wave functions in the ring. Moreover the influence of quantum fluctuations can induce symmetry breaking seen in the polarization of the ring and in the flux induced capacitance

Management recommendations for knee osteoarthritis: how usable are they?

OBJECTIVES: Despite the availability of practice guidelines for the management of knee osteoarthritis, inadequacies in practices of clinicians and patients have been found, leading to suboptimal outcomes. Literature has shown that simply disseminating management recommendations does not lead to adherence. Research suggests that barriers to use should be identified and addressed to improve adherence. The objective of this study was to identify barriers to use of conservative management recommendations for knee osteoarthritis by patients, general practitioners and physiotherapists. METHODS: Following systematic reviews of evidence and guidelines, 12 key management recommendations were elaborated on four themes: medication, exercise, self-management and occupation. Focus groups were separately done with patients with knee osteoarthritis, general practitioners and physiotherapists to assess barriers to the use of recommendations. RESULTS: Patients and general practitioners appeared generally fatalistic with regards to knee osteoarthritis, with physiotherapists being more positive regarding long-term improvement of knee osteoarthritis. For medication, discrepancies were found between recommendations and views of clinicians. Both patients and general practitioners appeared ambivalent towards exercise and activity, recognizing its usefulness but identifying it at the same time as a cause of knee osteoarthritis. Patients and general practitioners appeared to consider weight loss particularly difficult. DISCUSSION/CONCLUSIONS: Barriers specific to each knee osteoarthritis management recommendation and stakeholder group were identified. Recommendations to address these barriers were elaborated. Results of this study can be used to develop implementation strategies to overcome identified barriers, with the goal of facilitating the use of guideline recommendations and improving outcomes