Suppression of dislocations by Sb spray in the vicinity of InAs/GaAs quantum dots

The effect of Sb spray prior to the capping of a GaAs layer on the structure and properties of InAs/GaAs quantum dots (QDs) grown by molecular beam epitaxy (MBE) is studied by cross-sectional high-resolution transmission electron microscopy (HRTEM). Compared to the typical GaAs-capped InAs/GaAs QDs, Sb-sprayed QDs display a more uniform lens shape with a thickness of about 3 ~ 4 nm rather than the pyramidal shape of the non-Sb-sprayed QDs. Particularly, the dislocations were observed to be passivated in the InAs/GaAs interface region and even be suppressed to a large extent. There are almost no extended dislocations in the immediate vicinity of the QDs. This result is most likely related to the formation of graded GaAsSb immediately adjacent to the InAs QDs that provides strain relief for the dot/capping layer lattice mismatch.

PACS

81.05.Ea; 81.07.-b; 81.07.Ta     

Network Model for Rural Roadway Tolling with Pavement Deterioration and Repair

The objective of roadway tolling in rural areas is often tied to revenue generation for roadway maintenance. Thus, rural pricing models should directly incorporate a pavement deterioration and maintenance model. However, the interactions between these models are not simple, because tolls cause traffic diversion, which in turn affects deterioration rates and forecasted revenue. This article describes a rural pricing model which calculates diversion endogenously with a network assignment model. This model captures deterioration rates and pavement condition in the toll‐setter's objective function, maximizing long‐run net present value of the highway infrastructure. A novel deterioration model is used which is particularly suitable for computational efficiency. The resulting model is discontinuous and nondifferentiable, and involves solving a combinatorial knapsack problem as a subproblem. Thus, a simulated annealing‐based algorithm is presented to solve it, in the framework of a new solution method built upon partitioning the feasible region. A demonstration is made using a network representing the state of Wyoming (28 zones, 60 nodes, and 188 links). Sensitivity analyses reveal that although the locations for optimal tolling are relatively stable as demand changes, the revenue collected can vary substantially. Relatively simple models are used throughout for computational reasons, and future research should investigate strategies for incorporating more advanced pavement and network models.     

Energy and urban built form: an empirical and statistical approach

The geometrical forms of buildings have important effects on their use of energy. These relationships are explored at the scale of the entire non-domestic building stock of London. A three-dimensional digital model of the city is used to make a series of geometrical measures: building volume, exposed surface area (walls plus roof) and plan depth. These are compared with figures for the consumption of gas and electricity published by the UK Department of Energy and Climate Change (DECC). The comparisons are made at different levels of spatial aggregation, from boroughs to census districts. Strong correlations are demonstrated between exposed surface area and both gas and electricity use. The analysis also provides some evidence of a sharp increase in electricity use in districts with buildings whose depth in plan exceeds 14 m (in which air-conditioning and permanent artificial lighting are typically required). A multiple regression model is used to measure the contribution of these effects to total energy use, as compared with floor area, activities and number of employees.     

Design and Expected Performance of GISMO-2, a Two Color Millimeter Camera for the IRAM 30 m Telescope

We present the main design features for the GISMO-2 bolometer camera, which we build for background-limited operation at the IRAM 30 m telescope on Pico Veleta, Spain. GISMO-2 will operate simultaneously in the 1 and 2 mm atmospherical windows. The 1 mm channel uses a \(32 \times 40\) TES-based backshort under grid (BUG) bolometer array, the 2 mm channel operates with a \(16 \times 16\) BUG array. The camera utilizes almost the entire full field of view provided by the telescope. The optical design of GISMO-2 was strongly influenced by our experience with the GISMO 2 mm bolometer camera, which is successfully operating at the 30 m telescope. GISMO is accessible to the astronomical community through the regular IRAM call for proposals.