Self-assembled nanoholes, lateral quantum-dot molecules, and rolled-up nanotubes

We present a detailed investigation of novel strain-driven semiconductor nanostructures. Our examinations include self-assembled nanoholes, lateral quantum-dot (QD) molecules, and rolled-up nanotubes. We overgrow InAs QDs with GaAs and apply atomically precise in situ etching to fabricate homogeneous arrays of nanometer-sized holes with diameters of 40 to 60 nm and depths up to 6.2 nm. The structural properties of the nanoholes can be precisely tuned by changing the QD capping thickness and the in situ etching time. We show that strain fields surrounding the buried quantum dots drive the nanohole formation process. We overgrow the nanoholes with 0.2- to 2.5-ML InAs and observe the formation of compact lateral InAs QD molecules. The number of QDs involved in a lateral QD molecule can be tuned from two to six by changing the growth temperature. Our systematic photoluminescence study documents the QD molecule formation process step by step and helps to interpret our structural results. We also present the fabrication of laterally aligned lateral QD bimolecules by growing InGaAs on a GaAs [001] substrate patterned with a square array of nanometer sized holes. Charge carriers in such bimolecules might serve as quantum gates in a future semiconductor based quantum computer. Furthermore, we release strained semiconductor bilayers from their surface to fabricate individual rolled-up semiconductor micro- and nanotubes. We control the diameter of strain-driven In(Ga)As-GaAs tubes from the nanometer to micrometer range by simply changing the layer thicknesses and built-in strain. We propose to roll in metal strip lines to fabricate nanocoils and nanotransformers. To support our proposition, we fabricate homogeneous single and twin GaInP tubes. We present a straight GaInP microtube of more than 2 mm in length and a length-to-diameter ratio of about 2000, thus, elucidating the great potential of this technology.     

The Well Mannered Wearable Computer

In this paper we describe continuing work being carried out as part of the Bristol Wearable Computing Initiative. We are interested in the use of context sensors to improve the usefulness of wearable computers. A CyberJacket incorporating a Tourist Guide application has been built, and we have experimented with location and movement sensing devices to improve its performance. In particular, we have researched processing techniques for data from accelerometers which enable the wearable computer to determine the user’s activity. We have experimented with, and review, techniques already employed by others; and then propose new methods for analysing the data delivered by these devices. We try to minimise the number of devices needed, and use a single X-Y accelerometer device. Using our techniques we have adapted our CyberJacket and Tourist Guide to include a multimedia presentation which gives the user information using different media depending on the user’s activity as well as location.     

Blood speed imaging with an intraluminal array

In applications in which Doppler processing is not possible, such as side-looking intravascular imaging systems, decorrelation methods can be used to estimate blood speed. Here, a method is presented measuring relative blood speed using an FIR filter bank to estimate temporal decorrelation rates. It can be implemented in a modern commercially available ultrasound imaging system with no additional hardware. Both simulations and experiments using an intraluminal scanner appropriate for coronary artery applications have tested the system. In this study, the FIR filter bank is contrasted with previous methods, and its utility is further demonstrated with real-time color flow images from a pig model.     

Mechatronical considerations in modern motorcar generators

The generator in use today is the air-cooled claw pole generator. It is highly optimized and has nearly reached its technical limits. However, despite this optimization, the efficiency is not very high. Therefore new kinds of electrical power supplies must be researched. For this, a mechatronic power supply system-consisting of the electric generator with its mechanically accelerated masses and its electronic parts for control-is under development. The various aspects to be considered in the design are discussed, the different kinds of generator losses are summarised and analysed, and the PM excited generator is described. Results for a 3 kW rated generator are discussed     

Selective doping of silicon by rapid thermal and laser assisted processes

The selective doping technique, made by the combination of spin-on dopant (SOD) source deposition, rapid thermal annealing (RTA) and laser treatments is proposed as an innovative process for large area devices, like silicon solar cells.Rapid thermal diffusion (RTD) is first carried out from phosphorus SOD layers to form a lightly doped junction followed by pulsed laser irradiation to induce overdoping in selectively chosen regions.Here we present extensive study on the dependence of selective doping efficiency through different working variables, such as dopant source dilution, diffusion temperature and time for RTPs, and power and translation velocity for lasers. Electrical and structural characterizations have been performed by using several techniques: SIMS, stripping-Hall, four-point probe resistivity, SEM and TEM analysis.The combined use of these processes has been applied to the realization of selective emitter structures for silicon solar cells.     

Vaccination protects beta 2 microglobulin deficient mice from immune mediated mortality but not from persisting viral infection

Intracranial (i.c.) infection of immunocompetent mice with lymphocytic choriomeningitis virus (LCMV) results in immunopathological lethal meningitis mediated by CD8+ cytotoxic T lymphocytes (CTL). Vaccination of immunocompetent mice elicits a CD8+ CTL response that can protect the mice from lethal meningitis. beta 2 microglobulin-deficient (beta 2m-/-) mice are deficient in CD8+ CTL, exhibit CD4+ CTL, and, after i.c. LCMV infection, undergo a less severe meningitis with decreased mortality and additionally develop a wasting disease. Both wasting disease and mortality in beta 2m-/- mice are mediated by CD4+ T cells. We studied the effects of vaccination and challenge dose on weight loss, mortality and viral clearance after i.c. LCMV infection in beta 2m-/- mice. Unvaccinated beta 2m-/- mice had significant weight loss and mortality at doses of 200 and 10(3) p.f.u. LCMV, while a dose of 10(6) p.f.u. LCMV elicited significant mortality but less weight loss. Vaccination with u.v.-inactivated LCMV in complete Freund's adjuvant or with vaccinia virus expressing the LCMV glycoprotein or nucleoprotein genes protected beta 2m-/- mice from mortality but not weight loss after 200 p.f.u. LCMV challenge. Although protected from mortality, beta 2m-/- mice were unable to clear LCMV from their brains or spleens. Therefore, we show that vaccination can protect against lethal immune-meningitis in the face of persistent infection.     

Reciprocal regulation of neu tyrosine kinase activity and caveolin-1 protein expression in vitro and in vivo. Implications for human breast cancer

Neu (c-erbB2) is a proto-oncogene product that encodes an epidermal growth factor-like receptor tyrosine kinase. Amplification of wild-type c-Neu and mutational activation of Neu (Neu T) have been implicated in oncogenic transformation of cultured fibroblasts and mammary tumorigenesis in vivo. Here, we examine the relationship between Neu tyrosine kinase activity and caveolin-1 protein expression in vitro and in vivo. Recent studies have suggested that caveolins may function as negative regulators of signal transduction. Our current results show that mutational activation of c-Neu down-regulates caveolin-1 protein expression, but not caveolin-2, in cultured NIH 3T3 and Rat 1 cells. Conversely, recombinant overexpression of caveolin-1 blocks Neu-mediated signal transduction in vivo. These results suggest a reciprocal relationship between c-Neu tyrosine kinase activity and caveolin-1 protein expression. We next analyzed a variety of caveolin-1 deletion mutants to map this caveolin-1-dependent inhibitory activity to a given region of the caveolin-1 molecule. Results from this mutational analysis show that this functional in vivo inhibitory activity is contained within caveolin-1 residues 32-95. In accordance with these in vivo studies, a 20-amino acid peptide derived from this region (the caveolin-1 scaffolding domain) was sufficient to inhibit Neu autophosphorylation in an in vitro kinase assay. To further confirm or refute the relevance of our findings in vivo, we next examined the expression levels of caveolin-1 in mammary tumors derived from c-Neu transgenic mice. Our results indicate that dramatic reduction of caveolin-1 expression occurs in mammary tumors derived from c-Neu-expressing transgenic mice and other transgenic mice expressing downstream effectors of Neu-mediated signal transduction, such as Src and Ras. Taken together, our data suggest that a novel form of reciprocal negative regulation exists between c-Neu and caveolin-1.     

Effects of neuromuscular blocking agents on excitatory transmission and gamma-aminobutyric acidA-mediated inhibition in the rat hippocampal slice

BACKGROUND: Although neuromuscular blocking agents do not cross the blood-brain barrier, they may penetrate the central nervous system under particular circumstances and eventually cause neurotoxic consequences. METHODS: The effects of neuromuscular blocking agents on excitatory and inhibitory transmission in area CA1 of rat hippocampal slices were investigated using extracellular and intracellular recording techniques. RESULTS: Application of atracurium in the perfusion medium resulted in a dose-dependent enhancement of excitatory synaptic responses averaging 48.7 +/- 4.3% at a concentration of 10 nM. This effect was correlated with an increase in the size of the presynaptic fiber volley. Laudanosine, but not pancuronium bromide or vecuronium bromide, produced similar changes. In addition, atracurium and laudanosine blocked inhibitory transmission and reduced intracellularly recorded gamma-aminobutyric acidA receptor-mediated potentials. These effects were observed only at concentrations >1 microM and were not reproduced by pancuronium bromide and vecuronium bromide. CONCLUSIONS: Atracurium and its metabolite, laudanosine, contrary to pancuronium bromide and vecuronium bromide, produce two distinct effects on hippocampal slices. They enhance excitatory transmission and neuronal excitability and they block inhibitory gamma-aminobutyric acidA-mediated synaptic responses.