Thermal analysis of mid-infrared quantum-cascade lasers

We present a theoretical thermal analysis of mid-infrared quantum-cascade lasers (QCLs) using a two-dimensional anisotropic heat diffusion model. Several InP-based devices are simulated over a range of operating conditions in order to extract temperature-dependent thermal resistances. These thermal resistances are used to compare the effectiveness of various heat management techniques. Finally, heat flow analysis is performed in order to understand the internal thermal dynamics of these devices

Thermal effects in InGaAs/AlAsSb quantum-cascade lasers

A quantum-cascade laser (QCL) thermal model is presented. On the basis of a finite-difference approach, the model is used in conjunction with a self-consistent carrier transport model to calculate the temperature distribution in a near-infrared InGaAs/AlAsSb QCL. The presented model is used to investigate the effects of driving conditions and device geometries on the active-region temperature, which has a major influence on the device performance. A buried heterostructure combined with epilayer-down mounting is found to offer the best performance compared with alternative structures and has thermal time constants up to eight times smaller. The presented model provides a valuable tool for understanding the thermal dynamics inside a QCL and will help to improve operating temperatures

Substrate orientation and alloy composition effects in n-type SiGe quantum cascade structures

We show using a theoretical self-consistent effective mass/rate equation approach that n-type SiGe-based quantum cascade lasers are potentially made viable by either using the (111) orientation or a Ge-rich substrate

Investigation of thermal effects in quantum-cascade lasers

The development of a thermal model for quantum cascade lasers (QCLs) is presented. The model is used in conjunction with a self-consistent scattering rate calculation of the electron dynamics of an InGaAs-AlAsSb QCL to calculate the temperature distribution throughout the device which can be a limiting factor for high temperature operation. The model is used to investigate the effects of various driving conditions and device geometries, such as epilayer down bonding and buried heterostructures, on the active region temperature. It is found that buried heterostructures have a factor of eight decrease in thermal time constants compared to standard ridge waveguide structures in pulsed mode and allow a /spl sim/78% increase in heat sink temperature compared to epilayer down mounted devices in continuous-wave mode. The model presented provides a valuable tool for understanding the thermal dynamics inside a quantum cascade laser and will help to improve their operating temperatures

Thermal modeling of terahertz quantum-cascade lasers: comparison of optical waveguides

We compare a set of experimental lattice temperature profiles measured in a surface-emitting terahertz (THz) quantum-cascade laser (QCL) with the results of a 2-D anisotropic heat diffusion model. We evaluate the temperature dependence of the cross-plane thermal conductivity (kappaperp) of the active region which is known to be strongly anisotropic due to its superlattice-like nature. Knowledge of kappaperp and its temperature dependence is crucial in order to improve the temperature performance of THz QCLs and this has been used to investigate the longitudinal lattice temperature distribution of the active region and to compare the thermal properties of metal-metal and semi-insulating surface-plasmon THz optical waveguides using a 3-D anisotropic heat diffusion model

Land

Pressure on land resources has increased during recent years despite international goals to improve their management. The fourth Global Environment Outlook (UNEP 2007) highlighted the unprecedented land-use changes created by a burgeoning population, economic development and global markets. The outcome of those drivers continues to cause resource depletion and ecosystem degradation

Perceptions of final-year UKZN medical students about anaesthesia as a specialty choice

Background: South Africa suffers from a drastic shortage of anaesthesiologists. This shortage has a major impact on the provision of safe, timeous and appropriate surgery for the population. One factor implicated in this shortage may be the difficulty in appropriate recruitment of trainees.Methods: A questionnaire-based cross-sectional study was conducted among the final-year medical students at the University of KwaZulu-Natal (UKZN), for the year 2013.Results: At total of 112 final-year medical students participated in the study. The majority (93%) of the medical students would like to specialise in the future. Anaesthesiology ranked fourth in popularity among the specialties presented to the students. The students’ opinion of the key positive attributes of anaesthesiology was that it was interesting (26.8%), mentally challenging (22.3%) and afforded good working hours (18.8%). The key negative attributes of anaesthesiology highlighted by the students were that it was boring (21.4%), stressful (20.5%) and frightening (15.2%). The biggest influence on the medical students’ perceptions of anaesthesiology was the medical school rotation, with the need for longer duration of exposure, highlighted by 24 (21.4%) of the students.Conclusion: The perceptions of medical students concerning anaesthesia are multi-faceted, with the undergraduate anaesthetic rotation viewed as the biggest influence on their perceptions regarding anaesthesia. All anaesthetists should strive to improve the discipline profile, change the misconceptions and enhance the attractiveness of the specialty amongst medical students from foundation level upwards.Keywords: anaesthesia, education, medical students, perceptions, workforce shortag

Evaluating Socioeconomic Influences on Pinterest Consumer Behavior

Given the increasing popularity of social media channels for influential consumption mechanisms, this research aims to evaluate socioeconomic factors with Pinterest behaviors, underpinned by consumer behavior characteristics. Strategic recommendations are also proposed for marketing managers to optimize their usage of Pinterest. An online questionnaire was completed by a sample of 50 Pinterest users, while 4 face-to-face interviews were conducted with the aim of providing a framework for enhanced use of Pinterest. Findings indicated that virtual exploration is seen as a key Pinterest motivator, supported by the top pinboard rankings of Food, DIY, and Home. Secondly, occupation and family status were the two most significant socioeconomic factors that influences behavioral uses of Pinterest. A concentrated population between ages 25–34, representing higher income households and occupations consisting of Teachers and Business Professionals, exemplified the highest usage and self-efficacy of Pinterest. Low frequency of actual consumption through Pinterest, resulting in high visual consumption, curation of pins, and pinning behaviors were apparent throughout all socioeconomic factors, however the minimal actual consumption can be improved upon, as ease-of-use features are enhanced to embedded e-commerce and online blogs

A multi-isotope investigation of diet and subsistence amongst island and mainland populations from early medieval western Britain

Objectives: This is the first investigation of dietary practices amongst multiple early medieval populations (AD 500–1000) from Wales and the Isle of Man using carbon, nitrogen, and sulphur isotope analysis. The analysis will illuminate similarities or differences between the diets and subsistence strategies of populations occupying different geographical regions, specifically those living in marginal coastal regions in comparison to inland populations well-connected to ecclesiastical centres and high-status settlements. Materials and Methods: One hundred and two human skeletons were sampled for carbon and nitrogen isotope analysis, and 69 human skeletons were sampled for sulphur isotope analysis from nine cemetery sites from western Britain (Isle of Man = 3, southwest Wales = 4, southeast Wales = 2). Thirteen faunal skeletons from St Patrick's Chapel (southwest Wales) were sampled for carbon, nitrogen, and sulphur isotope analysis. Results: Human δ13C values range from −19.4‰ to −21.2‰ (δ13C mean=−20.4 ±0.4‰, 1σ, n = 86), and δ15N values range from 9.1‰ to 13.8‰ (δ15N mean = 10.8 ± 0.9‰, 1σ, n = 86). δ34S values range from 1.2‰ to 18.4‰ (δ34S mean = 11.6 ± 4.5‰, 1σ, n = 66). Significant differences were noted between the mean δ13C, δ15N and δ34S values according to geographic region: Isle of Man (δ13C = −20.7 ± 0.4‰, δ15N = 11.4 ±0.6‰, n = 13/86; δ34S mean = 17.1 ±0.6, n = 4/66), southwest Wales (δ13C = −20.5 ± 0.4‰, δ15N = 11.0 ±1‰, n = 32/86; δ34S = 16.1 ± 2.1, n = 21/66), and southeast Wales (δ13C =−20.3 ±0.4‰, δ15N = 10.4 ±0.7‰, n = 41/86; δ34S= 8.8 ±3‰, n = 41/66). Faunal δ13C values range from −23.1‰ to −21.2‰ (δ13C mean= −22.1 ±0.5‰, 1σ, n = 13), and δ15N values range from 6.3‰ to 9.8‰ (δ15N mean = 7.3 ± 1.1‰, 1σ, n = 13). δ34S values range from 4.7‰ to 18.4‰ (δ34S mean= 16.3 ± 3.6‰, 1σ, n = 13). Conclusions: The data reveal a reliance on terrestrial protein, however differences are observed between the resource consumption of populations from southwest Wales and the Isle of Man in comparison to the populations from southeast Wales. Populations from the west coast have a marine sulphur signature that reflects their coastal proximity and may also include a reliance on seaweed as a fertiliser/food source. Populations in the southeast were connected to ecclesiastical centres and high-status settlements and had access to inland-grown produce. The data add support to the suggestion that δ34S can be used as a mobility indicator