541 research outputs found
Energy Losses (Gains) of Massive Coloured Particles in Stochastic Colour Medium
The propagation of massive coloured particles in stochastic background
chromoelectric field is studied using the semiclassical equations of motion.
Depending on the nature of the stochastic background we obtain the formulae for
the energy losses of heavy coloured projectile in nonperturbative hadronic
medium and for the energy gains in the stochastic field present, e.g., in the
turbulent plasma. The result appears to be significantly dependent on the form
of the correlation function of stochastic external fieldComment: 9 pages, BI-TP 94/15, plain LaTe
Measuring medical students' professional competencies in a problem-based curriculum: A reliability study
Background: Identification and assessment of professional competencies for medical students is challenging. We
have recently developed an instrument for assessing the essential professional competencies for medical students
in Problem-Based Learning (PBL) programs by PBL tutors. This study aims to evaluate the reliability and validity of
professional competency scores of medical students using this instrument in PBL tutorials.
Methods: Each group of seven to eight students in PBL tutorials (Year 2, n = 46) were assessed independently by
two faculty members. Each tutor assessed students in his/her group every five weeks on four occasions. The
instrument consists of ten items, which measure three main competency domains: interpersonal, cognitive and
professional behavior. Each item is scored using a five-point Likert scale (1 = poor, 5 = exceptional). Reliability of
professional competencies scores was calculated using G-theory with raters nested in occasions. Furthermore,
criterion-related validity was measured by testing the correlations with students’ scores in written examination.
Results: The overall generalizability coefficient (G) of the professional competency scores was 0.80. Students’
professional competencies scores (universe scores) accounted for 27% of the total variance across all score
comparisons. The variance due to occasions accounted for 10%, while the student-occasion interaction was zero.
The variance due to raters to occasions represented 8% of the total variance, and the remaining 55% of the
variance was due to unexplained sources of error. The highest reliability measured was the interpersonal domain
(G = 0.84) and the lowest reliability was the professional behavior domain (G = 0.76). Results from the decision (D)
study suggested that an adequate dependability (G = 0.71) can be achieved by using one rater for five occasions.
Furthermore, there was a positive correlation between the written examination scores and cognitive competencies
scores (r = 0.46, P < 0.01), but not with the other two competency domains (interpersonal and professionalism).
Conclusions: This study demonstrates that professional competency assessment scores of medical students in PBL
tutorials have an acceptable reliability. Further studies for validating the instrument are required before using it for
summative evaluation of students by PBL tutors
Domain growth and aging scaling in coarsening disordered systems
Using extensive Monte Carlo simulations we study aging properties of two
disordered systems quenched below their critical point, namely the
two-dimensional random-bond Ising model and the three-dimensional
Edwards-Anderson Ising spin glass with a bimodal distribution of the coupling
constants. We study the two-times autocorrelation and space-time correlation
functions and show that in both systems a simple aging scenario prevails in
terms of the scaling variable , where is the time-dependent
correlation length, whereas is the waiting time and is the observation
time. The investigation of the space-time correlation function for the
random-bond Ising model allows us to address some issues related to
superuniversality.Comment: 8 pages, 9 figures, to appear in European Physical Journal
Particle Emissions from Domestic Gas Cookers
The authors experimentally studied the formation of submicron particles from a domestic gas cooker in a compartment free from external particle sources. The effects of fuel (methane, natural gas, odorant-free natural gas), primary aeration, flow rate, and fuel sulphur content on particle emissions were investigated. The experiments confirmed reports from literature that blue burning flames of domestic gas cookers emit submicron particles. The particle number concentrations varied in the range 103-106 particles/cm3, depending on the fuel, flow rate, and primary air addition. The diameters of the emitted particles were found to have a mean value of about 7 nm for partially premixed flames, increasing to ∼10 nm for nonpremixed flames. The quantity of primary air had a strong impact on the particle emissions, showing a minimum at a primary aeration level of 60-65%. Presence of sulphur in small quantities may enhance particle formation under some conditions, but results were not conclusive
The transition form factors for semi-leptonic weak decays of in QCD sum rules
Within the Standard Model, we investigate the semi-leptonic weak decays of
. The various form factors of transiting to a single charmed
meson () are studied in the framework of the QCD sum rules.
These form factors fully determine the rates of the weak semi-leptonic decays
of and provide valuable information about the non-perturbative QCD
effects. Our results indicate that the decay rate of the semi-leptonic weak
decay mode is at order of .Comment: 28 pages, 6 figures, revised version to be published in Eur.Phys.J.
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