Classtalk: A Classroom Communication System for Active Learning

This pdf file is an article describing the advantages of using Classtalk technology in the classroom to enhance classroom communication. Classtalk technology cab facilitate the presentation of questions for small group work, collec the student answers and then display histograms showing how the class answered. This new communication technology can help instructors create a more interactive, student centered classroom, especially when teaching large courses. The article describes Classtalk as a very useful tool not only for engaging students in active learning, but also for enhancing the overall communication within the classroom. This article is a selection from the electronic Journal for Computing in Higher Education. Educational levels: Graduate or professional

Time-resolved photoluminescence system with subnanosecond resolution at wavelengths up to 1.65 mu m

A system for measuring carrier lifetimes as short as 100 ps at luminescence wavelengths up to 1.65 mu m has been developed. This uses the photoluminescence phase shift technique and is based around a guided-wave lithium niobate modulator with a high (5 GHz) bandwidth. Measurements have been performed on an MBE grown sample consisting of 25 AA thick quantum wells of Ga/sub 0.47/In/sub 0.53/As with 100 AA thick barriers of InP, and the lifetime was found to be 3 ns

Photoluminescence from In0.53Ga0.47As/InP quantum wells grown by molecular beam epitaxy

Room‐temperature and low‐temperature photoluminescence from quantum well In0.53Ga0.47As/InP structures grown by molecular beam epitaxy is reported for the first time. A range of well thicknesses from 240 down to 10 Å was studied. Emission as short as 1.16 μm (1.07 eV) at 3.8 K and 1.22 μm (1.02 eV) at 300 K was observed from a well ∼10 Å, and the overall luminescence efficiency of the structure was ∼50 times greater than that of a quaternary sample of similar carrier concentration grown by liquid phase epitaxy. The full width half‐maximum of the photoluminescence peak from a 20‐Å well was 11.6 meV at 3.8 K. These results indicate the cladding InP as well as the interfaces are of very high quality

Improved molecular beam epitaxial growth of InP using solid sources

Molecular beam epitaxy (MBE) has been used to grow high-purity InP layers using solid sources and a graphite cracking zone to generate P2. Close control of slice temperature was achieved by mounting the substrate on a 3 in (75.6 mm) silicon wafer with indium solder. In addition, two differently packed phosphorus sources were investigated to assess the effect of oxides/water on InP purity. Several InP layers with a 77 K mobility of ~50000 cm2V¿1s¿1 were grown using a phosphorus source vacuum-packed at manufacture

Time domain analysis of oxygen uptake kinetics in elite runners by pseudo random binary sequence (PRBS) exercise

Oxygen uptake kinetics assessed in the frequency domain are known to be differentially faster in elite endurance runners than in elite sprinters. Breath-by-breath data from PRBS testing have routinely been analysed by application of Fourier methods, however, it is possible to analyse the data in the time domain in the form of a Total Lag Time (TLT). In this study, correlational techniques were applied to yield an output response to a work rate input. An autocorrelation function was performed on the input work rate (WR) and a cross correlation function was performed on input (WR) and output (vO₂). The cross correlation function was analysed by fitting a linear summation of the ramp form of a two-component exponential function to a triangular pulse. Twelve elite male sprinters and 12 elite male endurance runners completed 3 identical PRBS cycles of 300 s with 20 s work rate changes between 25 and 85 W on an electrically braked cycle ergometer at a pedal cadence of 1 Hz. Oxygen uptake was measured on a breath-by-breath basis using a respiratory mass spectrometer. Statistical analysis using the analysis of variance revealed significantly faster oxygen uptake kinetics (TLT) in the elite endurance runners compared with the elite sprinters (33.3 s 3.39SD and 39.91 s 7.14SD respectively) (p < 0.01). The results of this study show that time domain analysis represents a possible alternative to frequency analysis in the study of oxygen uptake kinetics described by PRBS exercise

The test-retest reliability of gas exchange kinetics in humans using a pseudo random binary sequence exercise test

The purpose of this study was to compare the test-retest reliability of oxygen uptake (VO2) kinetics with carbon dioxide output (VCO2) kinetics using a pseudo random binary sequence (PRBS) exercise test. A reliable test of gas exchange kinetics would have the potential of being applied as a sports fitness test. Ten healthy male subjects agreed to participate in the study and all subjects completed two identical PRBS exercise tests (test 1 and test 2), separated by a 30 min period of inactivity. Three consecutive 300 s PRBS cycles were completed in each test with 20 s exercise intensity changes between 25 and 85 W using an electrically braked cycle ergometer. Fourier analysis was computed for frequencies 3.3, 6.7 and 10 mHz. Statistical analysis by two-way ANOVA with repeated measures did not reveal significant differences between test 1 and test 2 for either VO2 kinetics or VCO2 kinetics. Static gain of VO2 for test 1 [9.11 (SD 0.59) ml.min-1.W-1] and test 2 [9.23 (SD 0.64) ml.min-1.W-1] did not differ significantly between tests. The 95% limits of agreement for VCO2 kinetics displayed increased variability in comparison to VO2 kinetics at each frequency of amplitude ratio and phase shift. Systematic bias ranged between 0% and 4%, except at frequency 10 mHz of VCO2 kinetics phase shift which showed a 10% bias for slower VO2 kinetics in test 2. It is possible that the increased variability of VCO2 kinetics compared to VO2 kinetics might be attributable to a lower signal to noise ratio in VCO2 kinetics, variations in ventilation or the storage mechanisms of CO2. The lower variability of VO2 kinetics compared with VCO2 kinetics suggests that the PRBS test of VO2 kinetics has the greater potential for further development as an indicator of aerobic fitness