552 research outputs found
Persistent currents in carbon nanotubes
Persistent currents driven by a static magnetic flux parallel to the carbon
nanotube axis are investigated. Owing to the hexagonal symmetry of graphene the
Fermi contour expected for a 2D-lattice reduces to two points. However the
electron or hole doping shifts the Fermi energy upwards or downwards and as a
result, the shape of the Fermi surface changes. Such a hole doping leading to
the Fermi level shift of (more or less) 1eV has been recently observed
experimentally. In this paper we show that the shift of the Fermi energy
changes dramatically the persistent currents and discuss the electronic
structure and possible currents for zigzag as well as armchair nanotubes.Comment: 8 text pages, 6 figures, to appear in Physics Letters
The microwave induced resistance response of a high mobility 2DEG from the quasi-classical limit to the quantum Hall regime
Microwave induced resistance oscillations (MIROs) were studied experimentally
over a very wide range of frequencies ranging from ~20 GHz up to ~4 THz, and
from the quasi-classical regime to the quantum Hall effect regime. At low
frequencies regular MIROs were observed, with a periodicity determined by the
ratio of the microwave to cyclotron frequencies. For frequencies below 150 GHz
the magnetic field dependence of MIROs waveform is well described by a
simplified version of an existing theoretical model, where the damping is
controlled by the width of the Landau levels. In the THz frequency range MIROs
vanish and only pronounced resistance changes are observed at the cyclotron
resonance. The evolution of MIROs with frequency are presented and discussed.Comment: 4 pages, presented at EP2DS, to be published in Physica
Quasiexcitons in Incompressible Quantum Liquids
Photoluminescence (PL) has been used to study two-dimensional incompressible
electron liquids in high magnetic fields for nearly two decades. However, some
of the observed anomalies coincident with the fractional quantum Hall effect
are still unexplained. We show that emission in these systems occurs from
fractionally charged "quasiexciton" states formed from trions correlated with
the surrounding electrons. Their binding and recombination depend on the state
of both the electron liquid and the involved trion, predicting discontinuities
in PL and sensitivity to sample parameters.Comment: 4 pages, 4 figure
Frequency quenching of microwave induced resistance oscillations in a high mobility two-dimensional electron gas
The frequency dependence of microwave-induced resistance oscillations (MIROs)
has been studied experimentally in high-mobility electron GaAs/AlGaAs
structures to explore the limits at which these oscillations can be observed.
It is found that in dc transport experiments at frequencies above 120 GHz,
MIROs start to quench, while above 230 GHz, they completely disappear. The
results will need to be understood theoretically but are qualitatively
discussed within a model in which forced electronic charge oscillations
(plasmons) play an intermediate role in the interaction process between the
radiation and the single-particle electron excitations between Landau levels.Comment: final version: total 13 pages including 6 figures (6 pages in journal
format
Systematic assessment of the quality of osteoporosis guidelines
BACKGROUND: Numerous agencies have developed clinical practice guidelines for the management of postmenopausal osteoporosis. The study objective was to conduct a systematic assessment of the quality of osteoporosis guidelines produced since 1998. METHODS: Guidelines were identified by searching MEDLINE (1998+), the world wide web, known guideline developer websites, bibliographies of retrieved guidelines, and through consultation with content experts. Each guideline was then assessed by three independent appraisers using the 'Appraisal Instrument for Clinical Guidelines' (version 1) by Cluzeau. RESULTS: We identified 26 unique guidelines from 1998–2001 and 21 met our inclusion criteria. Of the 21 guidelines reviewed, 8 were developed by medical societies, 6 by national groups, 6 by government agencies, and 1 by an international group. Twelve of the guidelines were published, 7 were organizational reports, and 2 were accessible only from the web. Half or more of the 20 items assessing the rigor of guideline development were met by 15% (median quality score 23%, range 5–80%, (95% CI 16.5, 34.7)), 81% met at least half of the 12 items assessing guideline content and context (median score 58%, range 17–83%, (95% CI 50.8, 65.5)), and none met half or more of the items assessing guideline application (median score 0%, range 0–47%, (95% CI -0.5 to 12.6)). Eight guidelines described the method used to assess the strength of evidence, and in 6 there was an explicit link between recommendations and the supporting evidence. Ten guidelines were judged not suitable for use in practice, 10 were acceptable with modification, and one was acceptable for use without modification. CONCLUSION: The methodological quality of current osteoporosis guidelines is low, although their scores for clinical content were higher. Virtually no guidelines covered dissemination issues. Few guidelines were judged as acceptable for use in their current format
When it is time to hang up the keys: the driving and dementia toolkit – for persons with dementia (PWD) and caregivers – a practical resource
A unified approach to nonlocal impulsive differential equations with the measure of noncompactness
Appropriate disclosure of a diagnosis of dementia : identifying the key behaviours of 'best practice'
Background: Despite growing evidence that many people with dementia want to know their diagnosis, there is wide variation in attitudes of professionals towards disclosure. The disclosure of the diagnosis of dementia is increasingly recognised as being a process rather than a one-off behaviour. However, the different behaviours that contribute to this process have not been comprehensively defined. No intervention studies to improve diagnostic disclosure in dementia have been reported to date. As part of a larger study to develop an intervention to promote appropriate disclosure, we sought to identify important disclosure behaviours and explore whether supplementing a literature review with other methods would result in the identification of new behaviours. Methods: To identify a comprehensive list of behaviours in disclosure we conducted a literature review, interviewed people with dementia and informal carers, and used a consensus process involving health and social care professionals. Content analysis of the full list of behaviours was carried out. Results: Interviews were conducted with four people with dementia and six informal carers. Eight health and social care professionals took part in the consensus panel. From the interviews, consensus panel and literature review 220 behaviours were elicited, with 109 behaviours over-lapping. The interviews and consensus panel elicited 27 behaviours supplementary to the review. Those from the interviews appeared to be self-evident but highlighted deficiencies in current practice and from the panel focused largely on balancing the needs of people with dementia and family members. Behaviours were grouped into eight categories: preparing for disclosure; integrating family members; exploring the patient's perspective; disclosing the diagnosis; responding to patient reactions; focusing on quality of life and well-being; planning for the future; and communicating effectively. Conclusion: This exercise has highlighted the complexity of the process of disclosing a diagnosis of dementia in an appropriate manner. It confirms that many of the behaviours identified in the literature (often based on professional opinion rather than empirical evidence) also resonate with people with dementia and informal carers. The presence of contradictory behaviours emphasises the need to tailor the process of disclosure to individual patients and carers. Our combined methods may be relevant to other efforts to identify and define complex clinical practices for further study.This project is funded by UK Medical Research Council, Grant reference number G0300999
Measurements of fiducial and differential cross sections for Higgs boson production in the diphoton decay channel at s√=8 TeV with ATLAS
Measurements of fiducial and differential cross sections are presented for Higgs boson production in proton-proton collisions at a centre-of-mass energy of s√=8 TeV. The analysis is performed in the H → γγ decay channel using 20.3 fb−1 of data recorded by the ATLAS experiment at the CERN Large Hadron Collider. The signal is extracted using a fit to the diphoton invariant mass spectrum assuming that the width of the resonance is much smaller than the experimental resolution. The signal yields are corrected for the effects of detector inefficiency and resolution. The pp → H → γγ fiducial cross section is measured to be 43.2 ±9.4(stat.) − 2.9 + 3.2 (syst.) ±1.2(lumi)fb for a Higgs boson of mass 125.4GeV decaying to two isolated photons that have transverse momentum greater than 35% and 25% of the diphoton invariant mass and each with absolute pseudorapidity less than 2.37. Four additional fiducial cross sections and two cross-section limits are presented in phase space regions that test the theoretical modelling of different Higgs boson production mechanisms, or are sensitive to physics beyond the Standard Model. Differential cross sections are also presented, as a function of variables related to the diphoton kinematics and the jet activity produced in the Higgs boson events. The observed spectra are statistically limited but broadly in line with the theoretical expectations
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