Formation of misfit dislocations in strained-layer GaAs/In_xGa_1–xAs/GaAs heterostructures during postfabrication thermal processing

It is demonstrated that relaxation of GaAs/InxGa1–xAs/GaAs strained-layer heterostructures can be brought about by postfabrication thermal processing. Misfit dislocations are introduced into the structure during thermal processing, even though the thickness of the strained layer is well below the critical value predicted by the Matthews–Blakeslee model. The misfit dislocations are observed to be of both 60° mixed type and 90° pure edge type. As no relaxation occurs at the lower temperatures encountered during fabrication by molecular-beam epitaxy, it can be inferred that the critical condition for the formation of misfit dislocations is not only a function of strained-layer thickness and composition, but also of temperature. This observation cannot be accounted for by differential thermal expansion or diffusion across the strained-layer interfaces, but the temperature-dependent Peierls force may offer an explanation. The high temperature required to produce relaxation of these structures suggests that they are sufficiently thermally stable for most practical applications

Does diet mediate associations of volume and bouts of sedentary time with cardiometabolic health indicators in adolescents?

Objective: Examine the mediating role of diet in the relationship between volume and duration of sedentary time with cardiometabolic health in adolescents. Methods: Adolescents (12-19 years) participating in the 2003/04 and 2005/06 U.S. National Health and Nutrition Examination Survey (NHANES) were examined. Cardiometabolic health indicators were body mass index z-scores (zBMI) (n 5 1,797) and metabolic syndrome (MetS) (n 5 812). An ActiGraph hip-worn accelerometer was used to derive total sedentary time and usual sedentary bout duration. Dietary intake was assessed using two 24-hour dietary recalls. Mediation analyses were conducted to examine five dietary mediators [total energy intake, discretionary foods, sugar-sweetened beverages (SSB), fruits and vegetables, and dietary quality] of the relationship between total sedentary time and usual sedentary bout duration with zBMI and MetS. Results: Total sedentary time was inversely associated with zBMI (b 5 21.33; 95% CI 22.53 to 20.13) but attenuated after adjusting for moderate-to-vigorous physical activity. No significant associations were observed between usual sedentary bout duration with zBMI or either sedentary measure with MetS. None of the five dietary variables mediated any of the relationships examined. Conclusions: Further studies are needed to explore associations of specific time periods (e.g., after school) and bout durations with both cardiometabolic health indicators and dietary behaviors

Factors determining the magnitude of grain-size strengthening in polycrystalline metals

Grain-size strengthening of polycrystalline metals, the Hall-Petch effect, has been described for the past sixty years as a dependence of the strength of polycrystalline metals on the inverse square-root of grain size, d. The value of the coefficient of the dependence has been the subject of discussion throughout. Here, we find what known factors in the experiments may determine its value, by meta-analysis using maximum-likelihood methods of the literature values of the coefficient in sixty-one datasets. No dependence of the coefficient is found on plastic strain, and a strong dependence is found on the average grain size of each study. Combining these and other factors accounts for the reported values of about 80% of the sixty-one coefficients. The grain-size dependence of the Hall-Petch coefficient is an artefact arising from fitting the data to an incorrect expression. An alternative grain-size effect described by a lnd/d function is consistent with the theory of dislocations dynamics and generation. The corresponding analysis of the coefficients of fits based on this theory shows that none of the factors investigated are statistically significant, confirming the correctness of this approach

Aviation spirit - past, present, and future

The volatile fuel of the high-speed internal combustion engine has, in the past, consisted almost exclusively of the lighter distillates from crude petroleum. Alternative and supplementary fuels are discussed such as: tetraline, dekalin, alcohol, cyclo-hexenes

Learn by doing: Modelling the effect of training and job interruptions on tree cutting time for chainsaw operators in plantation forests, Tanzania

Timber harvesting in Tanzania uses semi-mechanized and labour – intensive logging systems. Manual or semi-mechanized logging operations by using hand tools are more favoured due to cheap labour availability. For example, tree cutting is done manually using two-man crosscut saws, axes or chainsaws. This study was conducted at Sokoine University of Agriculture Training Forest to assess the effect of training and job interruptions for chainsaw operators during tree cutting operations in softwood plantation forests in Tanzania. Tree cutting operations using experienced and inexperienced chainsaw operators were studied in three experiments; before training, after training and after the break. Time study and work sampling techniques were used for data collection. Descriptive statistics and modeling was performed for each crews’ performance. Results show that generally, experienced crew spends lesser time in cutting as compared to inexperienced crews. However, start up chainsaw crew spent 32% higher time for preparation before tree felling. However, the crew showed significant improvement after training unlike the experienced one. The analysis of the delay times start up crew was had a significant proportion of the delay times during the first engagement which decreased substantially in the other two experiments. Generally, there was an improvement of the cutting time after training for all crew categories with decrease after the break. This observation signifies that job interruptions impact the productivity of the crews. Therefore, on job training on resumption of the operations may significantly improve crews’ productivity, safety as well as ensuring product quality. Key words: Tree cutting, training, chainsaws, time studies, Tanzania

Raman excitation spectroscopy of carbon nanotubes: effects of pressure medium and pressure

Raman excitation and emission spectra for the radial breathing mode (RBM) are reported, together with a preliminary analysis. From the position of the peaks on the two-dimensional plot of excitation resonance energy against Raman shift, the chiral indices (m, n) for each peak are identified. Peaks shift from their positions in air when different pressure media are added - water, hexane, sulphuric acid - and when the nanotubes are unbundled in water with surfactant and sonication. The shift is about 2 - 3 cm-1 in RBM frequency, but unexpectedly large in resonance energy, being spread over up to 100meV for a given peak. This contrasts with the effect of pressure. The shift of the peaks of semiconducting nanotubes in water under pressure is orthogonal to the shift from air to water. This permits the separation of the effects of the pressure medium and the pressure, and will enable the true pressure coefficients of the RBM and the other Raman peaks for each (m, n) to be established unambiguously.Comment: 6 pages, 3 Figures, Proceedings of EHPRG 2011 (Paris

77-4 Hydrographic and Biological Observations at an Anchor Station Off St. Augustine, Florida (Eastward Cruise E-1G-75)

The intrusion of deep, nutrient-rich Gulf Stream water into the shelf waters off the southeastern United States is probably the major source of nutrients in the shelf waters and consequently intrusions have a major impact on the biota. This particular cruise was one of the first to be designed to find the front that represents the interface between intruding Gulf Stream waters and normal shelf water. Once the front was delineated an anchor station was occupied to observe the time change at a particular location as the front moved back and forth past the station. The methods used and resultant data from that cruise are presented to aid others in the analyses of intrusions and related phenomena

Impacts of Policy on Electric Vehicle Diffusion

Selection and design of appropriate government policies to support electric vehicle (EV) adoption can be aided by modelling the future impact of policy instruments relative to a given baseline estimate. This paper highlights the innovative application of a diffusion model to analyse complex impacts of EV policy instruments on future incremental EV uptake. Several versions of four key policy instruments are tested in the model: linking electric vehicle sales to Renewable Electricity Purchases (RE-EV), financial subsidies, smart charging incentives and a common cost metric to educate consumers about the lifetime costs of EVs. Market share between battery electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), hybrid electric vehicles (HEVs) and internal combustion engine vehicles (ICEVs) were forecasted out to the year 2034 across all 1.5 million households in the state of Victoria, Australia. The RE-EV scenario had the strongest performance in terms of economic and societal indicators. Non-subsidy policy instruments can also support uptake of EVs, especially in the case of encouraging BEV adoption. We found feebate scenarios were more effective policies than rebates. Rebate and feebate scenarios applied within the 2014-2019 timeframe compared better than those with longer timeframes. Our analyses showed how combined policy scenarios not only further improved EV uptake but also allowed government to fund rebates through feebate income