Room-temperature optically-pumped InGaSb quantum well lasers monolithically grown on Si(100) substrate

Room-temperature optically-pumped In/sub 0.2/Ga/sub 0.8/Sb quantum well lasers on Si are reported. The defect-free monolithic epistructure growth on a Si(100) substrate is initiated by an AlSb quantum dot nucleation layer followed by an AlSb/GaSb superlattice. The 13% mismatch between the AlSb and Si lattice is accommodated by misfit dislocations and associated crystallographic undulations in the AlSb buffer. The nucleation layer and buffer are characterised by atomic force microscopy and transmission electron microscopy. The lasing spectrum is characterised as a function of pump power and polarisation analysis.     

Flow and pressure drop fluctuations in a vertical tube subject to low frequency oscillations

Heat transfer and other equipment mounted on off-shore platforms may be subjected to low frequency oscillations. The effect of these oscillations, typically in the frequency range of 0.1–1 Hz, on the flow rate and pressure drop in a vertical tube has been studied experimentally in the present work. A 1.75 m-long vertical tube of inner diameter 0.016 m was mounted on a plate and the whole plate was subjected to oscillations in the vertical plane using a mechanical simulator capable of providing low frequency oscillations in the range of 8–30 cycles/min at an amplitude of 0.125 m. The effect of the oscillations on the flow rate and the pressure drop has been measured systematically in the Reynolds number range 500–6500. The induced flow rate fluctuations were found to be dependent on the Reynolds number with stronger fluctuations at lower Reynolds numbers. The effective friction factor, based on the mean pressure drop and the mean flow rate, was also found to be higher than expected. Correlations have been developed to quantify this Reynolds number dependence.     

Post-CHF heat transfer during two-phase upflow boiling of R-407C in a vertical pipe

This paper reports a study of heat transfer in the post-critical heat flux (post-CHF) regime under forced convective upflow conditions in a uniformly heated vertical tube of 12.7 mm internal diameter and 3 m length. Experiments were conducted with non-azeotropic ternary refrigerant mixture R-407C for reduced pressures ranging from 0.37 to 0.75, mass flux values from 1200 to 2000 kg/m² s and heat flux from 50 to 80 kW/m². Data shows a considerable effect of system pressure on the post-CHF heat transfer coefficient for specified mass and heat fluxes. The post-CHF heat transfer coefficients for R-407C are compared with three existing correlations which are found to over predict the current data. A modified correlation to represent the experimental data for R-407C is presented.     

Intelligibility of speech in a virtual 3-D environment

In a simulated air traffic control task, improvement in the detection of auditory warnings when using virtual 3-D audio depended on the spatial configuration of the sounds. Performance improved substantially when two of four sources were placed to the left and the remaining two were placed to the right of the participant. Surprisingly, little or no benefits were observed for configurations involving the elevation or transverse (front/back) dimensions of virtual space, suggesting that position on the interaural (left/right) axis is the crucial factor to consider in auditory display design. The relative importance of interaural spacing effects was corroborated in a second, free-field (real space) experiment. Two additional experiments showed that (a) positioning signals to the side of the listener is superior to placing them in front even when two sounds are presented in the same location, and (b) the optimal distance on the interaural axis varies with the amplitude of the sounds. These results are well predicted by the behavior of an ideal observer under the different display conditions. This suggests that guidelines for auditory display design that allow for effective perception of speech information can be developed from an analysis of the physical sound patterns.     

Information tradeoffs in model building: A network routing application

An integral part of the model-building process is the modeler's choice of how much information to gather and encode in the decision model. Obtaining more detailed and accurate information enables a more precise problem representation which, in turn, leads to more effective decision making. However, acquiring extensive and accurate information entails higher costs and delays. This paper uses a network routing decision context to illustrate the tradeoff between model precision and decision effectiveness, and explores a formal decision-theoretic approach to determine an appropriate model specification that balances information gathering costs and decision quality. We propose optimal and heuristic methods for generating good information search strategies, and report computational results based on random test problems. Our results highlight the importance of simultaneously considering information costs and decision payoffs for constructing a decision model to support routing decisions. The issues raised in this paper are especially significant for modeling dynamic, real-time decision contexts where delays induced by information gathering activities could have significant economic impact.     

Minimizing Energy for Wireless Web Access with Bounded Slowdown

On many battery-powered mobile computing devices, the wireless network is a significant contributor to the total energy consumption. In this paper, we investigate the interaction between energy-saving protocols and TCP performance for Web-like transfers. We show that the popular IEEE 802.11 power-saving mode (PSM), a static protocol, can harm performance by increasing fast round trip times (RTTs) to 100 ms; and that under typical Web browsing workloads, current implementations will unnecessarily spend energy waking up during long idle periods. To overcome these problems, we present the Bounded-Slowdown (BSD) protocol, a PSM that dynamically adapts to network activity. BSD is an optimal solution to the problem of minimizing energy consumption while guaranteeing that a connections RTT does not increase by more than a factor p over its base RTT, where p is a protocol parameter that exposes the trade-off between minimizing energy and reducing latency. We present several trace-driven simulation results that show that, compared to a static PSM, the Bounded-Slowdown protocol reduces average Web page retrieval times by 5–64%, while simultaneously reducing energy consumption by 1–14% (and by 13× compared to no power management).     

Micellar catalyzed degradation of fenitrothion, an organophosphorus pesticide, in solution and soils

We report on a study of the decomposition of fenitrothion (an organophosphorus pesticide that is a persistent contaminant in soils and groundwater) as catalyzed by cetyltrimethylammonium (CTA+) micelles. The CTA micelles were associated with two types of counterions: (1) inert counterions (e.g. CTABr) and (2) reactive counterions (e.g. CTAOH). The reactive counterion surfactants used were hydroxide anion (HO-) as a normal nucleophile and hydroperoxide anion (HOO-) and the anion of pyruvaldehyde oxime (MINA-) as two alpha-nucleophiles. The reactivity order followed: CTABr < CTAOH < CTAMINA < CTAOOH. Treatment of the rate data using the Pseudo-Phase Ion Exchange (PPIE) model of micellar catalysis showed the ratio k2M/k2w to be less than unity for all the surfactants employed. Rather than arising from a "true catalysis", we attributed the observed rate enhancements to a "concentration effect", where both pesticide and nucleophile were incorporated into the small micellar phase volume. Furthermore, the CTAOOH/CTAOH pair gave an alpha-effect of 57, showing that the alpha-effect can play an important role in micellar systems. We further investigated the effectiveness of reactive counterion surfactants in decontaminating selected environmental solids that were spiked with 27 ppb fenitrothion. The solids were as follows: the clay mineral montmorillonite and SO-1 and S0-2 soils (obtained from the Canadian Certified Reference Materials Project). The reactive counterion surfactant solutions significantly enhanced the rate of fenitrothion degradation in the spiked solids over that obtained when the spiked solid was placed in contact with either 0.02 M KOH or water. The rate enhancements followed the order CTAOOH > CTAMINA approximately CTAOH > KOH > water. We conclude that reactive counterion surfactants, especially with alpha-nucleophiles, hold great potential in terms of remediating soils contaminated by toxic organophosphorus esters.     

3D tool wear measurement and visualisation using stereo imaging

Tool wear detection has traditionally restricted itself to 2D study and measurement. A new technique for the measurement and visualisation of tool wear pattern has been presented in this paper. This method provides visualisation of the tool wear geometry using a pair of stereo images and generates the volume of crater wear as a new parameter for inspection. The results demonstrate that the volume of crater wear can be effectively used to characterise the tool wear. The average depth of the tool wear and surface area of the crater are also obtained as parameters for measurement. The technique provides a fast and a possible on-line method of tool wear analysis and measurement.