Quantitative measurement of channel temperature of GaAs devices for reliable life-time prediction

The channel temperature of Gallium Arsenide (GaAs) devices was quantitatively measured using scanning thermal microscopy (SThM), which is a variation of atomic force microscopy (AFM). The temperature of the devices was also characterized by infrared (IR) imaging and thermal modeling. The measured SThM temperature values were close to the calculated values from the model, and were higher than those found by IR, as predicted. In contrast to most published AFM results which have reported only qualitative and indirect semi-quantitative thermal information about the sample, the results presented here can be used directly to determine accurately the device-temperature. These results are useful to the reliability community in that they help to predict a more accurate semiconductor device lifetime. By careful calibration of an AFM thermistor probe tip, a quantitative temperature measurement of the channel temperature of the GaAs PHEMTs and MESFETs can be made. The result of the measurement can be substantiated by applying a suitable thermal calculation, such as the Cooke model. A secondary measurement technique, such as IR microscopy, can also be useful in providing further information about the thermal response of the device. Published results using AFM techniques have been unable to determine the channel temperature quantitatively. The method in this paper applies to other types of electronic devices for which the channel (or junction) temperature can be probed from the top surface of the device.     

Designing appliances for mobile commerce and retailtainment

In the emerging world of the new consumer and the `anytime, anywhere' mobile commerce, appliances are located at the collision point of the retailer and consumer agendas. The consequence of this is twofold: on the one hand appliances that were previously considered plain and utilitarian become entertainment devices and on the other, for the effective design of consumer appliances it becomes paramount to employ multidisciplinary expertise. In this paper, we discuss consumer perceptions of a retailtainment commerce system developed in collaboration between interactivity designers, information systems engineers, hardware and application developers, marketing strategists, product development teams, social scientists and retail professionals. We discuss the approached employed for the design of the consumer experience and its implications for appliance design.     

Stochastic production phase design for an open pit mining complex with multiple processing streams

In a mining complex, the mine is a source of supply of valuable material (ore) to a number of processes that convert the raw ore to a saleable product or a metal concentrate for production of the refined metal. In this context, expected variation in metal content throughout the extent of the orebody defines the inherent uncertainty in the supply of ore, which impacts the subsequent ore and metal production targets. Traditional optimization methods for designing production phases and ultimate pit limit of an open pit mine not only ignore the uncertainty in metal content, but, in addition, commonly assume that the mine delivers ore to a single processing facility. A stochastic network flow approach is proposed that jointly integrates uncertainty in supply of ore and multiple ore destinations into the development of production phase design and ultimate pit limit. An application at a copper mine demonstrates the intricacies of the new approach. The case study shows a 14% higher discounted cash flow when compared to the traditional approach.     

Schedule-based pushback design within the stochastic optimisation framework

The traditional mine planning framework employs a flawed approach in the design of ultimate pit limits and phases. Conventional methods arbitrarily confine the mine’s extraction schedule during the initial stages, detracting from its optimality before it is created. This work aims to provide a method by which a mine’s phase design is created from an optimal extraction schedule. The schedule-based approach to phase design yields implementable mining phases that mimic the initial raw optimal schedule from which it is based. An attempt to minimise the trade-off between mineability and value is inherent to the approach.     

The Greek computer attitudes scale: construction and assessment of psychometric properties

The purpose of this paper was to develop and test the psychometric properties of a computer attitudes scale for the Greek population. Through both adapting items from other scales and writing new items, this study developed a Greek Computer Attitudes Scale of 30 items, with three subscales: confidence, affection, and cognitive. This study also explored sex differences on the GCAS, and the relationship between age, computer experience, and confidence with computers and participants’ responses on the scale. Questionnaire data from four Greek samples, which included participants from the general population (185 and 354 individuals, respectively), 222 teachers and 99 undergraduate students, were analyzed. Results indicated that: (1) both the reliability (internal consistency and test–retest) and validity (concurrent) of the GCAS were adequate; (2) the relationship between age and GCAS was not significant, whereas sex did not have a significant effect on GCAS scores; and (3) perceived computer experience and confidence with computers were strongly related to favorable attitudes toward computers.     

Simultaneous stochastic optimisation of an open-pit gold mining complex with waste management

ABSTRACT

Simultaneous stochastic optimisation manages risk and capitalises on the unique interactions that occur in a mining complex, where materials are transferred between mines, processors, stockpiles, and waste facilities to achieve a marketable product. Typically, when optimising the production schedule, the primary focus is to deliver valuable products to the market. However, this tends to ignore the environmental and economic impact of simplifying waste management requirements, including the storage and disposal of waste material. Stricter regulations and engineering requirements are transforming past mining practices to develop more sustainable operations. These transformations increase the financial cost of waste management and identify the requirement to integrate waste management into the production schedule. Additionally, misrepresenting the material uncertainty and variability associated with the amount of waste produced can impact, both, the stakeholders and the profitability of a mining complex. In this case study, a simultaneous stochastic optimisation approach is applied in a gold mining complex that integrates waste management into the long-term production schedule. The resulting schedule leads to a 6% increase in the net present value when compared to a conventional approach, while minimising the likelihood of deviating from production targets and ensuring permit constraints are satisfied.     

Multi-fractal conditional simulation of fault populations in coal seams using analogues: Method and application

The modelling of fault populations and quantification of fault risk is a challenge for earth science and engineering applications, including minerals and coal mining, tunnel construction, forecasting of petroleum reservoir production, and selection of subterranean repositories for the disposal of toxic waste. This paper discusses a new advance in the use of stochastic fault simulation methods for the quantification of the risk of fault presence. The multi-fractal properties of a fully known fault population are used as an analogue of the properties of an undiscovered fault population. The approach is elucidated through the quantification of fault risk in a prospective coalfield at Wyong, New South Wales, Australia, and incorporates spatial patterns of available ‘hard’ and ‘soft’ geological data. The method does not find faults unequivocally; rather, the output is a map of fault probability. Simulations are found to be consistent with the available information and are statistically and spatially reasonable in geological terms. Significantly, the analogue approach provides a robust, quantified assessment of fault risk using limited exploration information.     

A conditional fractal (fBm) simulation approach for orebody modelling

Abstract

Fractal methods provide scale-invariant approaches to modelling the in-situ variability of orebody attributes. Fractional Brownian motion (fBm) models are a specific class of random fractals that offer a fast and efficient way to generate simulations of pertinent orebody characteristics. fBm models are constructed using the Weierstrass-Mandelbrodt equation and a fractal co-dimension inferred from the available data. Unconditional fBm simulations can be further constrained to existing data to generate conditional simulations reproducing the (i) available data, (ii) data statistics, and (iii) power law variogram and fractal co-dimension. The computational efficiency of the conditioning process is improved based on dual kriging. Testing conditional fBm simulation in a controlled environment indicates that it is an efficient approach to generating multiple realisations, when the available conditioning data is in the order of several hundred. The efficiency and performance of the approach suggest that it may be particularly suitable for delineating ore/waste boundaries and grade control.     

Effect of two azadirachtin formulations against adults of Sitophilus oryzae and Tribolium confusum on different grain commodities

The insecticidal effect of two azadirachtin-based insecticides, NeemAzal-T/S and Oikos 32 EC, was examined against adults of the grain beetles Sitophilus oryzae and Tribolium confusum on wheat and maize under different temperature and humidity regimes. The insecticides were applied at three dosages, equivalent to 50, 100, and 200 mg of active ingredient per kg of grain. Adults of the above species were exposed to the treated grains at 20, 25, and 30 degrees C and two relative humidity levels (55 and 75%), and mortality was assessed after 14 days of exposure. All adults were then removed, and the treated substrate remained under the same conditions for 45 more days. After this period, the grains were checked for progeny production. In both species and both commodities, mortality increased with insecticide dosage. For many dosage-formulation combinations, mortality increased with temperature at 55% relative humidity but the reverse was observed at 75% relative humidity. Comparing the two formulations, NeemAzal-T/S was more effective than Oikos 32 EC at all the combinations tested. NeemAzal-T/S was more effective at high relative humidity, but the efficacy of Oikos 32 EC was not much affected by the relative humidity. Survival was high, even at the higher dosages, in some of the temperature-humidity combinations. Progeny production of S. oryzae in the treated grains was considerably higher than that of T. confusum. The results of the present study indicate that further dosage increases and longer exposure times are needed to obtain a complete (100%) adult mortality in all combinations tested. However, the feasibility of using higher azadirachtin dosages (>200 mg/kg grain) is questionable for cost reasons. Consequently, the use of these substances is not comparable to the use of traditional grain protectants, which are usually used at dosages of <5 mg/kg grain. Although azadirachtin-based insecticides can be used with success for protection of stored grain, our study demonstrated that under certain circumstances such an application may not be effective. Abiotic factors (formulation, temperature, and relative humidity) had a more serious impact on the efficacy of these insecticides than did biotic factors (target species and commodity).