Recent astronomical results from the infrared spatial interferometer and their implications for LOUISA

A new heterodyne interferometer for the atmospheric window from 9 to 12 microns was developed during the past five years. This instrument, called the Infrared Spatial Interferometer (ISI), was designed to use earth rotation aperture synthesis techniques developed in radio interferometry. It was moved to Mt. Wilson, California, in January 1988 and first fringes were obtained in June of that year. Systematic observations of some of the brighter late-type stars began shortly after the first fringes were obtained. We describe the basic principles and design of the ISI and give an overview of some of the initial results obtained from these observations. The implications of our work to the proposed Lunar Optical/UV/IR Synthesis Array (LOUISA) are discussed. We also analyze the conditions for the maximum signal-to-noise ratio of such an interferometer as a function of wavelength. The optimum wavelength is found to depend on the assumed scaling relation between telescope area and wavelength

Influence of the charge carrier tunneling processes on the recombination dynamics in single lateral quantum dot molecules

We report on the charge carrier dynamics in single lateral quantum dot molecules and the effect of an applied electric field on the molecular states. Controllable electron tunneling manifests itself in a deviation from the typical excitonic decay behavior which is strongly influenced by the tuning electric field and inter-molecular Coulomb energies. A rate equation model is developed to gain more insight into the charge transfer and tunneling mechanisms. Non-resonant (phonon-mediated) electron tunneling which changes the molecular exciton character from direct to indirect, and vice versa, is found to be the dominant tunable decay mechanism of excitons besides radiative recombination.Comment: 4 pages, 4 figure

Methodologies for the analysis of pesticides and pharmaceuticals in sediments and plant tissue

Eco-technologies that utilize natural processes involving wetland vegetation, soil and their associated microbial assemblages are increasingly used for the removal of contaminants of emerging concern (CECs) from polluted water. However, information on removal processes in these systems is not always available, possibly due to the lack of simple and robust methodologies for analysis of CECs in complex matrices such as sediment and plant tissue. The aim of the present study was to use a simple and fast procedure based on ultrasonic extraction (USE) and reduced clean-up procedures to analyse 8 pesticides and 9 pharmaceuticals by high-performance liquid chromatography (HPLC) coupled with diode array detector. The established methods demonstrated suitable sensitivity and reliability, and proved fit-for-purpose in quantifying multiple classes of pesticides and pharmaceuticals. For sediments, extraction with methanol/acetone (95:5, v/v) followed by a simple evaporation to dryness and redissolution (water:methanol 50:50) provided acceptable recovery (50 - 101%) and RSD 64%) with RSD < 22% determined using different types of wetland plants. The methodology has been successfully applied in different studies on the fate of emerging contaminants in water treatment eco-technology systems

Experimental imaging and atomistic modeling of electron and hole quasiparticle wave functions in InAs/GaAs quantum dots

We present experimental magnetotunneling results and atomistic pseudopotential calculations of quasiparticle electron and hole wave functions of self-assembled InAs/GaAs quantum dots. The combination of a predictive theory along with the experimental results allows us to gain direct insight into the quantum states. We monitor the effects of (i) correlations, (ii) atomistic symmetry and (iii) piezoelectricity on the confined carriers and (iv) observe a peculiar charging sequence of holes that violates the Aufbau principle.Comment: Submitted to Physical Review B. A version of this paper with figures can be found at http://www.sst.nrel.gov/nano_pub/mts_preprint.pd

Quality and location choices under price regulation

In a model of spatial competition, we analyze the equilibrium outcomes in markets where the product price is exogenous. Using an extended version of the Hotelling model, we assume that firms choose their locations and the quality of the product they supply. We derive the optimal price set by a welfarist regulator. If the regulator can commit to a price prior to the choice of locations, the optimal (second-best) price causes overinvestment in quality and an insufficient degree of horizontal differentiation (compared with the first-best solution) if the transportation cost of consumers is sufficiently high. Under partial commitment, where the regulator is not able to commit prior to location choices, the optimal price induces first-best quality, but horizontal differentiation is inefficiently high

Comparing the Job Satisfaction and Intention to Leave of Different Categories of Health Workers in Tanzania, Malawi, and South Africa.

Job satisfaction is an important determinant of health worker motivation, retention, and performance, all of which are critical to improving the functioning of health systems in low- and middle-income countries. A number of small-scale surveys have measured the job satisfaction and intention to leave of individual health worker cadres in different settings, but there are few multi-country and multi-cadre comparative studies. The objective of this study was to compare the job satisfaction and intention to leave of different categories of health workers in Tanzania, Malawi, and South Africa. We undertook a cross-sectional survey of a stratified cluster sample of 2,220 health workers, 564 from Tanzania, 939 from Malawi, and 717 from South Africa. Participants completed a self-administered questionnaire, which included demographic information, a 10-item job satisfaction scale, and one question on intention to leave. Multiple regression was used to identify significant predictors of job satisfaction and intention to leave. There were statistically significant differences in job satisfaction and intention to leave between the three countries. Approximately 52.1% of health workers in South Africa were satisfied with their jobs compared to 71% from Malawi and 82.6% from Tanzania (χ2=140.3, p<0.001). 18.8% of health workers in Tanzania and 26.5% in Malawi indicated that they were actively seeking employment elsewhere, compared to 41.4% in South Africa (χ2=83.5, p<0.001). The country differences were confirmed by multiple regression. The study also confirmed that job satisfaction is statistically related to intention to leave. We have shown differences in the levels of job satisfaction and intention to leave between different groups of health workers from Tanzania, Malawi, and South Africa. Our results caution against generalising about the effectiveness of interventions in different contexts and highlight the need for less standardised and more targeted HRH strategies than has been practised to date

Recent advances in exciton based quantum information processing in quantum dot nanostructures

Recent experimental developments in the field of semiconductor quantum dot spectroscopy will be discussed. First we report about single quantum dot exciton two-level systems and their coherent properties in terms of single qubit manipulations. In the second part we report on coherent quantum coupling in a prototype "two-qubit" system consisting of a vertically stacked pair of quantum dots. The interaction can be tuned in such quantum dot molecule devices using an applied voltage as external parameter.Comment: 37 pages, 15 figures, submitted to New Journal of Physics, focus issue on Solid State Quantum Information, added reference

A review of data on abundance, trends in abundance, habitat use and diet of ice-breeding seals in the Southern Ocean

The development of models of marine ecosystems in the Southern Ocean is becoming increasingly important as a means of understanding and managing impacts such as exploitation and climate change. Collating data from disparate sources, and understanding biases or uncertainties inherent in those data, are important first steps for improving ecosystem models. This review focuses on seals that breed in ice habitats of the Southern Ocean (i.e. crabeater seal, Lobodon carcinophaga; Ross seal, Ommatophoca rossii; leopard seal, Hydrurga leptonyx; and Weddell seal, Leptonychotes weddellii). Data on populations (abundance and trends in abundance), distribution and habitat use (movement, key habitat and environmental features) and foraging (diet) are summarised, and potential biases and uncertainties inherent in those data are identified and discussed. Spatial and temporal gaps in knowledge of the populations, habitats and diet of each species are also identified