1,091 research outputs found
Phonon-phonon interactions in transition metals
In this paper the phonon self energy produced by anharmonicity is calculated
using second order many body perturbation theory for all bcc, fcc and hcp
transition metals. The symmetry properties of the phonon interactions are used
to obtain an expression for the self energy as a sum over irreducible triplets,
very similar to integration in the irreducible part of the Brillouin zone for
one particle properties. The results obtained for transition metals shows that
the lifetime is on the order of 10^10 s. Moreover the Peierls approximation for
the imaginary part of the self energy is shown to be reasonable for bcc and fcc
metals. For hcp metals we show that the Raman active mode decays into a pair of
acoustic phonons, their wave vector being located on a surface defined by
conservation laws.Comment: 14 pages, 3 figure
A new experimental procedure for characterizing quantum effects in small magnetic particle systems
A new experimental procedure is discussed, which aims at separating thermal
from quantum behavior independently of the energy barrier distribution in small
particle systems.
Magnetization relaxation data measured between 60 mK and 5 K on a sample of
nanoparticles is presented. The comparison between experimental data and
numerical calculations shows a clear departure from thermal dynamics for our
sample, which was not obvious without using the new procedure presented here.Comment: LaTeX source, 6 pages, 5 PostScript figure
Clinical Judgment Analysis
SUMMARY Judgment is central to the practice of medicine and occurs between making clinical observations and taking clinical decisions. Clinical judgment analysis has developed as a method of making statistically firm models of doctors' judgments. Computed models reveal the differential importance attached to items of clinical, social, or other data which are determinants of clinical decisions. These models can both reveal the causes of conflicts of judgment and may help resolve them in a way that unaided discussion cannot. Revealing experts' models to students speeds learning of diagnostic skills. Clinical judgment analysis offers a method of probing the judgments not just of students and doctors but also of patients who have shown systematic differences in their perceptions of risk and benefit. The power and relevance of clinical trials can be improved by the consistent application of judgment policies generated from both the trialists and those who will use their result
Non-monotonic field-dependence of the ZFC magnetization peak in some systems of magnetic nanoparticles
We have performed magnetic measurements on a diluted system of gamma-Fe2O3
nanoparticles (~7nm), and on a ferritin sample. In both cases, the ZFC-peak
presents a non-monotonic field dependence, as has already been reported in some
experiments,and discussed as a possible evidence of resonant tunneling. Within
simple assumptions, we derive expressions for the magnetization obtained in the
usual ZFC, FC, TRM procedures. We point out that the ZFC-peak position is
extremely sensitive to the width of the particle size distribution, and give
some numerical estimates of this effect. We propose to combine the FC
magnetization with a modified TRM measurement, a procedure which allows a more
direct access to the barrier distribution in a field. The typical barrier
values which are obtained with this method show a monotonic decrease for
increasing fields, as expected from the simple effect of anisotropy barrier
lowering, in contrast with the ZFC results. From our measurements on
gamma-Fe2O3 particles, we show that the width of the effective barrier
distribution is slightly increasing with the field, an effect which is
sufficient for causing the observed initial increase of the ZFC-peak
temperatures.Comment: LaTeX file 19 pages, 9 postscript figures. To appear in Phys. Rev. B
(tentative schedule: Dec.97
The value of clinical judgement analysis for improving the quality of doctors' prescribing decisions
Background Many initiatives are taken to improve prescribing decisions. Educational strategies for doctors have been effective in at least 50% of cases. Some reflection on one's own performance seems to be a common feature of the most effective strategies. So far, such reflections have mainly focused on the observed outcomes of the doctors' decisions, i.e. on what doctors do in practice. Studies in other fields have shown that another form of feedback based on the analysis of judgements may be useful as well. Objectives The objectives of the study were to discuss the principles underlying clinical judgement analysis, give examples of its use in the medical context, and discuss its potential for improving prescribing decisions. Results Clinical judgement analysis can look behind the outcome of a decision to the underlying decision process. Carefully constructed or selected case material is required for this analysis. Combining feedback on outcomes with feedback based on clinical judgement analysis offers doctors insight both in what they do, and why or when they do it. It may reveal determinants of decision making which are not available through unaided introspection. Interventions using this combination of feedback for improving doctors' prescribing behaviour have been (partly) successful in 4 cases and unsuccessful in one case. Conclusions Clinical judgement analysis gives doctors a structured reflection on the decision-making policy, and can help them to improve their future decisions. It may be especially useful for groups of doctors who try to work towards a consensus policy. The approach is not very helpful when simple decision rules are appropriate
Small Angle Scattering by Fractal Aggregates: A Numerical Investigation of the Crossover Between the Fractal Regime and the Porod Regime
Fractal aggregates are built on a computer using off-lattice cluster-cluster
aggregation models. The aggregates are made of spherical particles of different
sizes distributed according to a Gaussian-like distribution characterised by a
mean and a standard deviation . The wave vector dependent
scattered intensity is computed in order to study the influence of the
particle polydispersity on the crossover between the fractal regime and the
Porod regime. It is shown that, given , the location of the
crossover decreases as increases. The dependence of on
can be understood from the evolution of the shape of the center-to-center
interparticle-distance distribution function.Comment: RevTex, 4 pages + 6 postscript figures, compressed using "uufiles",
published in Phys. Rev. B 50, 1305 (1994
Active video games and health indicators in children and youth: a systematic review
BACKGROUND: Active video games (AVGs) have gained interest as a way to increase physical activity in children and youth. The effect of AVGs on acute energy expenditure (EE) has previously been reported; however, the influence of AVGs on other health-related lifestyle indicators remains unclear. OBJECTIVE: This systematic review aimed to explain the relationship between AVGs and nine health and behavioural indicators in the pediatric population (aged 0â17 years). DATA SOURCES: Online databases (MEDLINE, EMBASE, psycINFO, SPORTDiscus and Cochrane Central Database) and personal libraries were searched and content experts were consulted for additional material. DATA SELECTION: Included articles were required to have a measure of AVG and at least one relevant health or behaviour indicator: EE (both habitual and acute), adherence and appeal (i.e., participation and enjoyment), opportunity cost (both time and financial considerations, and adverse events), adiposity, cardiometabolic health, energy intake, adaptation (effects of continued play), learning and rehabilitation, and video game evolution (i.e., sustainability of AVG technology). RESULTS: 51 unique studies, represented in 52 articles were included in the review. Data were available from 1992 participants, aged 3â17 years, from 8 countries, and published from 2006â2012. Overall, AVGs are associated with acute increases in EE, but effects on habitual physical activity are not clear. Further, AVGs show promise when used for learning and rehabilitation within special populations. Evidence related to other indicators was limited and inconclusive. CONCLUSIONS: Controlled studies show that AVGs acutely increase light- to moderate-intensity physical activity; however, the findings about if or how AVG lead to increases in habitual physical activity or decreases in sedentary behaviour are less clear. Although AVGs may elicit some health benefits in special populations, there is not sufficient evidence to recommend AVGs as a means of increasing daily physical activity
Distribution-based bisimulation for labelled Markov processes
In this paper we propose a (sub)distribution-based bisimulation for labelled
Markov processes and compare it with earlier definitions of state and event
bisimulation, which both only compare states. In contrast to those state-based
bisimulations, our distribution bisimulation is weaker, but corresponds more
closely to linear properties. We construct a logic and a metric to describe our
distribution bisimulation and discuss linearity, continuity and compositional
properties.Comment: Accepted by FORMATS 201
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