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

Boekbespreking

No abstract available

Boekbespreking

No abstract available

Boekbespreking

No abstract available

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 $L(t)/L(s)$, where $L$ is the time-dependent correlation length, whereas $s$ is the waiting time and $t$ 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

Boekbespreking

No abstract available

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 J/ψJ/\psi in QCD sum rules

Within the Standard Model, we investigate the semi-leptonic weak decays of $J/\psi$. The various form factors of $J/\psi$ transiting to a single charmed meson ($D^{(*)}_{(d,s)}$) are studied in the framework of the QCD sum rules. These form factors fully determine the rates of the weak semi-leptonic decays of $J/\psi$ and provide valuable information about the non-perturbative QCD effects. Our results indicate that the decay rate of the semi-leptonic weak decay mode $J/\psi \to D^{(*)-}_{s}+e^{+}+\nu_{e}$ is at order of $10^{-10}$.Comment: 28 pages, 6 figures, revised version to be published in Eur.Phys.J.