Bayesian inference of nanoparticle-broadened x-ray line profiles

A single and self-contained method for determining the crystallite-size distribution and shape from experimental x-ray line profile data is presented. We have shown that the crystallite-size distribution can be determined without assuming a functional form for the size distribution, determining instead the size distribution with the least assumptions by applying the Bayesian/MaxEnt method. The Bayesian/MaxEnt method is tested using both simulated and experimental CeO$_{2}$ data. The results demonstrate that the proposed method can determine size distributions, while making the least number of assumptions. The comparison of the Bayesian/MaxEnt results from experimental CeO$_2$ with TEM results is favorableComment: 43 pages, 13 Figures, 5 Table

Student attitudes to learning business statistics: Comparison of online and traditional methods

Worldwide, electronic learning (E-learning) has become an important part of the education agenda in the last decade. The Suan Dusit Rajabhat University (SDRU), Thailand has made significant efforts recently to use Internet technologies to enhance learning opportunities. The results reported here are part of a pioneering study to determine the effectiveness of a new online learning course in the subject "Business Statistics". This paper compares two groups of students, one studying using a traditional lecture-based approach, and the other studying using e-learning. The comparison is based on students' attitudes towards statistics measured using a validated questionnaire, both before and after the 16-week course, and for each of the modes of study. Comparisons are also made with students studying by distance, although the numbers in these groups are too small for sensible statistical analysis. The questionnaire data are augmented by material from interviews and other student reports of their experience. The results showed highly significant differences in attitudes towards statistics between the students studying online and the students using a traditional approach

Effect of injection current on the repeatability of laser diode junction voltage-temperature measurements

The junction-voltage temperature relationship of a laser diode is used to determine the temperature of the device in the range -20 to 120 °C. We consider changes that occur to this relationship when the diode is driven at its nominal operating current and above. It is found that estimates of the parameters that appear in a function fitted to the voltage-temperature data are sensitive to driving currents at and above the nominal operating current. Changes in parameter estimates are attributed to degradation due to surface recombination at facets occurring when the laser diode is overdriven. An indication of this degradation is the change in the ideality factor that occurs as the current to the device is raised. This work indicates that the temperature of the junction can be determined over the range -20 to 120 °C with a standard uncertainty of ≈0.5 °C. © 2007 American Institute of Physics

System for measuring the junction temperature of a light emitting diode immersed in liquid nitrogen

A versatile system has been developed for the measurement under LABVIEW™ control of junction temperatures in a light emitting diode (LED). Measurements are reported on a commercially available high-intensity InGaAlP LED immersed in liquid nitrogen and driven by currents in the range of 18.5-204 mA. The measured junction temperature has an expanded uncertainty of ±2 K at the 95% level of confidence for temperatures from 70 to 298 K. Using the measured junction temperatures, the junction-to-case thermal resistance of the LED was established as 440 KW for devices with intact encapsulation and 307 KW for partial encapsulation. © 2006 American Institute of Physics

Cathodoluminescence microanalysis of diamond nanocrystals in fused silicon dioxide

MeV carbon ion implantation followed by thermal annealing in a hydrogen-containing atmosphere produces a layer of diamond nanocrystals within fused quartz (SiO2). Cathodoluminescence (CL) microanalysis in a scanning electron microscope has revealed at least three previously unreported low intensity CL emissions from carbon implanted and thermally annealed fused SiO2. The CL emissions are observed at 2.78 eV [full width at half maximum (FWHM) of 0.08 eV], ~3 eV (FWHM of 0.4 eV), and 3.18 eV (FWHM of 0.11 eV). The peak widths and energies of these emissions are incompatible with any known defects associated with the silicon dioxide host lattice. Nondestructive depth resolved CL microanalysis investigations confirm that these CL emissions originate from the near-surface region, consistent with their association with the layer of diamond nanocrystal

Bayesian analysis of ceria nanoparticles from line profile data

A Bayesian/Maximum entropy (MaxEnt) emthod is applied to quantify the broadening of X-ray line profiles in terms of the nanocrystallite size effects in ceria. The analysis is in general agreemetn with transmission electron microscopy results, while demonstrating the importance of appropriate a priori information needed in the method. The analysis also identifies other microstructural effects, such as the presence of dislocations and shape anisotropic effects which may be influencing the size distributions determined from the Bayesian/Max-Ent method

X-ray reflectivity study of radio frequency sputtered silicon oxide on silicon

An X-ray reflectivity study carried out on 45-450 Å films of radio frequency sputtered silicon oxide on silicon, with particular attention given to the interface between film and substrate. In order to model reflectivity data it was necessary to include an interface layer for all films. This interface layer had a density approaching that of the substrate but due to differing compositions of the deposited film and substrate it was subject to a variation in scattering and absorption properties. © 2005 Elsevier B.V. All rights reserved

A Bayesian/Maximum Entropy Method for Certification of a Nanocrystalline-Size NIST Reference Material

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