Growth and optical properties of strained GaAs-GaxIn 1-x P core-shell nanowires

We have synthesized GaAs-Ga(x)In(1-x)P (0.34 < x < 0.69) core-shell nanowires by metal-organic vapor phase epitaxy. The nanowire core was grown Au-catalyzed at a low temperature (450 degrees C) where only little growth takes place on the side facets. The shell was added by growth at a higher temperature (600 degrees C), where the kinetic hindrance of the side facet growth is overcome. Photoluminescence measurements on individual nanowires at 5 K showed that the emission efficiency increased by 2 to 3 orders of magnitude compared to uncapped samples. Strain effects on the band gap of lattice mismatched core-shell nanowires were studied and confirmed by calculations based on deformation potential theory.     

New Pathways for Modifying the Surface of High Density Polyethylene: Chemically Benign Adhesion Promotion and Subsequent Reactivity

Summary The surface of high density polyethylene (HDPE) was modified using a two-step chemical process. HDPE panels were initially immersed in a heated, aqueous hypochlorite solution containing a carboxylic acid promoter and quenched with deionized water at room temperature following a heterogeneous chemical reaction process patented by Beholz (U.S. Patents 6,077,913 and 6,100,343). 1-5 mole percent chlorine heteroatoms were identified on the resulting HDPE surface using ESCA techniques. The surface chlorine concentration was optimized as a function of reaction time, reaction stoichiometry and number of repeated chemical treatments. The chlorinated HDPE surface was subsequently exposed to ultra-violet (UV) light and surface alkene moieties were noted using ATR FT-IR methods along with a concomitant reduction in surface chlorine from ESCA measurements. The photochemically induced free radical surface dehydrochlorination mechanism was observed to follow first-order kinetics and potentially produce a focussed pattern for information storage. Facile subsequent reactivity of the isolated surface alkene groups was demonstrated using electrophilic addition of Br₂. Furthermore, poly(4-hydroxy styrene) architectures were covalently tethered to either the chlorinated or unsaturated HDPE surface in an effort to ultimately tailor surface polarity and adhesiveness as well as create laminate poly(-olefin) containing structures. This economical and benign surface chlorination/photochemical two-step treatment process produced relatively small disposal risks as well as no apparent polymer degradation.     

Microfocal X-ray computed tomography post-processing operations for optimizing reconstruction volumes of stented arteries during 3D computational fluid dynamics modeling

Restenosis caused by neointimal hyperplasia (NH) remains an important clinical problem after stent implantation. Restenosis varies with stent geometry, and idealized computational fluid dynamics (CFD) models have indicated that geometric properties of the implanted stent may differentially influence NH. However, 3D studies capturing the in vivo flow domain within stented vessels have not been conducted at a resolution sufficient to detect subtle alterations in vascular geometry caused by the stent and the subsequent temporal development of NH. We present the details and limitations of a series of post-processing operations used in conjunction with microfocal X-ray CT imaging and reconstruction to generate geometrically accurate flow domains within the localized region of a stent several weeks after implantation. Microfocal X-ray CT reconstruction volumes were subjected to an automated program to perform arterial thresholding, spatial orientation, and surface smoothing of stented and unstented rabbit iliac arteries several weeks after antegrade implantation. A transfer function was obtained for the current post-processing methodology containing reconstructed 16 mm stents implanted into rabbit iliac arteries for up to 21 days after implantation and resolved at circumferential and axial resolutions of 32 and 50 microm, respectively. The results indicate that the techniques presented are sufficient to resolve distributions of WSS with 80% accuracy in segments containing 16 surface perturbations over a 16 mm stented region. These methods will be used to test the hypothesis that reductions in normalized wall shear stress (WSS) and increases in the spatial disparity of WSS immediately after stent implantation may spatially correlate with the temporal development of NH within the stented region.     

Single-cell protein from methanol: Economic aspects of the norprotein® process

Norprotein is a subsidiary of the Norwegian chemical group Norsk Hydro A.S and the Swedish food company AB Marabou. Since 1974 the main activity of research has been to develop a process for single-cell protein production from methanol. At present, research activities are directed towards finding alternative applications for the developed technology within the field of biotechnology.     

Influence of heating rate on the pyrolysis of oil shale

The decomposition of oil shale from the Kvarntorp deposit in Sweden has been investigated using isothermal and non-isothermal methods. It was found that the heating rate during the initial non-isothermal period in the isothermal experiments had a considerable effect on the rate of devolatilization. At heating rates in the order of 10⁵°C/s the total weight loss exceeded the weight loss predicted from the volatile matter according to a proximate analysis.The effect of particle and sample size on the rate of decomposition (weight loss) was studied and found to have a significant influence at heating rates of the order of 10⁵°C/s while no effect was detected at heating rates around 200 °C/s (isothermal) or below 50°C/min (non-isothermal). The decomposition at low heating rates was completed at temperatures below 600°C and about 50 percent of the devolatilization could be described by first order kinetics with an apparent activation energy of 130 KJ/mole.At heating rates of 200°C/s (isothermal) the decomposition could also be described by simple first order kinetics but with an activation energy of 67 KJ/mole, thus indicating a different rate-determining mechanism.     

Naphtali-Sandholm distillation calculations for NGL mixtures near the critical region

Multicomponent distillation calcultions are carried out using a modification of the Naphtali-Sandholm column calcultaion procedure coupled with the Soave-Redlich-Kwong equation of state for generating K-values and enthalpies.

The modified Naphtali-Sandholm procedure is applicable when the individual stage efficiencies are unity and the K-values are not strongly dependent on the vapour-phase composition. For a column with M components and N stages, N(M + 2) relationships are set up.

The N(M + 2) equations are solved using Newton-Raphson iteration with imposed maximum allowable changes of the independent variables between iterations. Analytical derivatives of the K-values and enthalpies with respect to composition and temperature are employed in the Jacobian.

The method has been used for the process development and design of distillation columns associated with the separation of natural gas liquids (NGL). Fast and safe convergence is obtained even near the critical region.     

Creating robust high-throughput traffic sign detectors using centre-surround HOG statistics

In this paper, we detail a system for creating object detectors which meet the extreme demands of real-world traffic sign detection applications such as GPS map making and real-time in-car traffic sign detection. The resulting detectors are designed to detect and locate multiple traffic sign types in high-definition video (high throughput) from several cameras captured along thousands of kilometers of road with minimal false-positives and detection rates in excess of 99%. This allows for the accurate detection and location of traffic signs in geo-tagged video datasets of entire national road networks in reasonable time using only moderate computing infrastructure. A key to the success of the methods described in this paper is the use of extremely efficient classifier features. In this paper, we identify two obstacles to achieving the desired performance for all target traffic sign types, feature memory bandwidth requirements and feature discriminance. We introduce our use of centre-surround histogram of oriented gradient (HOG) statistics which greatly reduce the per-feature memory bandwidth requirements. Subsequently we extend our use of centre-surround HOG statistics to the color domain, raising the discriminant power of the final classifiers for more challenging sign types.     

Robuste multikriterielle Dienstkomposition in Informationssystemen

Service compositions are used to implement business processes in a variety of application domains. A quality of service (QoS)-aware selection of the service to be composed involves multiple, usually conflicting and possibly uncertain QoS attributes. A multi-criteria solution approach is desired to generate a set of alternative service selections. In addition, the uncertainty of QoS-attributes is neglected in existing solution approaches. Hence, the need for service reconfigurations is imposed to avoid the violation of QoS restrictions. The researched problem is NP-hard. This article presents a heuristic multi-criteria service selection approach that is designed to determine a Pareto frontier of alternative service selections in a reasonable amount of time. Taking into account the uncertainty of response times, the obtained service selections are robust with respect to the constrained execution time. The proposed solution approach is based on the Non-dominated Sorting Genetic Algorithm (NSGA)-II extended by heuristics that exploit problem specific characteristics of the QoS-aware service selection. The applicability of the solution approach is demonstrated by a simulation study.     

A survey of semiconductor supply chain models part I: semiconductor supply chains,strategic network design,and supply chain simulation

Supply chain management issues have become increasingly important to the semiconductor industry over the last two decades due to the global distribution of facilities and increasing numbers of firms specialising in particular stages. This series of three papers reviews the literature on modelling and analysis of the larger semiconductor supply chain. After describing the structure of semiconductor supply chains to provide context for the research efforts, we propose a classification scheme for the relevant literature. The remainder of this paper (Part I) then focuses on Strategic Network Design models for this industry, supply chain coordination through contracting and semiconductor supply chain simulation. Part II discusses Demand Planning, Inventory Management and Capacity Planning, while Part III addresses Master Planning, Production Planning and Demand Fulfilment.