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

Early-type objects in NGC6611 and Eagle Nebula

An important question about Be stars is whether Be stars are born as Be stars or not. It is necessary to observe young clusters to answer this question. Observations of stars in NGC6611 and the star-formation region of Eagle Nebula have been carried out with the ESO-WFI in slitless spectroscopic mode and at the VLT-GIRAFFE. The targets for the GIRAFFE observations were pre-selected from the literature and our catalogue of emission-line stars (ELS) based on the WFI study. GIRAFFE observations allowed us to study accurately the population of the early-type stars with and without emission lines. For this study, we determined the fundamental parameters of OBA stars. We also studied the status of the objects (main sequence or pre-main sequence stars) by using IR data, membership probabilities, and location in HR diagrams. The nature of the early-type ELS in M16 is derived. The slitless observations with the WFI clearly indicate a small number of ELS in M16. We observed with GIRAFFE 101 OBA stars, among them 9 are ELS with circumstellar emission in Halpha. We found that: W080 could be a new He-strong star, like W601. W301 is a possible classical Be star, W503 is a mass-transfer eclipsing binary with an accretion disk, and the other ones are possible Herbig Ae/Be stars. We also found that the rotational velocities of main sequence B stars are 18% lower than those of pre-main sequence B stars, in good agreement with theory about the evolution of rotational velocities. Combining different indications and technics, we found that 27% of the B-type stars are binaries. We also redetermined the age of NGC6611 found equal to 1.2--1.8 Myears in good agreement with the most recent determinations.Comment: Accepted by A&A, english not yet correcte

Assembly of a Three-Dimensional Multitype Bronchiole Coculture Model Using Magnetic Levitation

A longstanding goal in biomedical research has been to create organotypic cocultures that faithfully represent native tissue environments. There is presently great interest in representative culture models of the lung, which is a particularly challenging tissue to recreate in vitro. This study used magnetic levitation in conjunction with magnetic nanoparticles as a means of creating an organized three-dimensional (3D) coculture of the bronchiole that sequentially layers cells in a manner similar to native tissue architecture. The 3D coculture model was assembled from four human cell types in the bronchiole: endothelial cells, smooth muscle cells (SMCs), fibroblasts, and epithelial cells (EpiCs). This study represents the first effort to combine these particular cell types into an organized bronchiole coculture. These cell layers were first cultured in 3D by magnetic levitation, and then manipulated into contact with a custom-made magnetic pen, and again cultured for 48 h. Hematoxylin and eosin staining of the resulting coculture showed four distinct layers within the 3D coculture. Immunohistochemistry confirmed the phenotype of each of the four cell types and showed organized extracellular matrix formation, particularly, with collagen type I. Positive stains for CD31, von Willebrand factor, smooth muscle a-actin, vimentin, and fibronectin demonstrate the maintenance of the phenotype for endothelial cells, SMCs, and fibroblasts. Positive stains for mucin-5AC, cytokeratin, and E-cadherin after 7 days with and without 1% fetal bovine serum showed that EpiCs maintained the phenotype and function. This study validates magnetic levitation as a method for the rapid creation of organized 3D cocultures that maintain the phenotype and induce extracellular matrix formation

Fabrication and Mechanical Evaluation of Anatomically-Inspired Quasilaminate Hydrogel Structures with Layer-Specific Formulations

A major tissue engineering challenge is the creation of multilaminate scaffolds with layer-specific mechanical properties representative of native tissues, such as heart valve leaflets, blood vessels, and cartilage. For this purpose, poly(ethylene glycol) diacrylate (PEGDA) hydrogels are attractive materials due to their tunable mechanical and biological properties. This study explored the fabrication of trilayer hydrogel quasilaminates. A novel sandwich method was devised to create quasilaminates with layers of varying stiffnesses. The trilayer structure was comprised of two ‘‘stiff’’ outer layers and one ‘‘soft’’ inner layer. Tensile testing of bilayer quasilaminates demonstrated that these scaffolds do not fail at the interface. Flexural testing showed that the bending modulus of acellular quasilaminates fell between the bending moduli of the ‘‘stiff’’ and ‘‘soft’’ hydrogel layers. The bending modulus and swelling of trilayer scaffolds with the same formulations were not significantly different than single layer gels of the same formulation. The encapsulation of cells and the addition of phenol red within the hydrogel layers decreased bending modulus of the trilayer scaffolds. The data presented demonstrates that this fabrication method can make quasilaminates with robust interfaces, integrating layers of different mechanical properties and biofunctionalization, and thus forming the foundation for a multilaminate scaffold that more accurately represents native tissue

Spitzer/IRAC view of Sh 2-284: Searching for evidence of triggered star formation in an isolated region in the outer Milky Way

Using Spitzer/IRAC observations of a region to be observed by the CoRoT satellite, we have unraveled a new complex star-forming region at low metallicity in the outer Galaxy. We perform a study of S284 in order to outline the chain of events in this star-forming region. We used four-band Spitzer/IRAC photometry as well as Halpha imaging obtained with INT/WFC. Combining these data with the optical photometry obtained in the frame of CoRoTs preparation and the 2MASS catalog we analysed the properties and distribution of young stellar objects (YSOs) associated with point-like sources. We also studied the SEDs of regions of extended emission, complementing our dataset with IRAS and MSX data. We find that S284 is unique in several ways: it is very isolated at the end of a spiral arm and both the diffuse dust and ionized emission are remarkably symmetric. We have partially resolved the central clusters of the three bubbles present in this region. Despite the different scales present in its multiple-bubble morphology, our study points to a very narrow spread of ages among the powering high-mass clusters. In contrast, the particular sawtooth structure of the extended emission at the rim of each ionized bubble harbours either small lower-mass clusters with a younger stellar population or individual young reddened protostars. In particular, triggered star formation is considered to be at work in these regions.Comment: Accepted by A&A. 13 pages, 10 figures, 2 Table

Faraday rotation spectra of bismuth-substituted ferrite garnet films with in-plane magnetization

Single crystalline films of bismuth-substituted ferrite garnets have been synthesized by the liquid phase epitaxy method where GGG substrates are dipped into the flux. The growth parameters are controlled to obtain films with in-plane magnetization and virtually no domain activity, which makes them excellently suited for magnetooptic imaging. The Faraday rotation spectra were measured across the visible range of wavelengths. To interprete the spectra we present a simple model based on the existence of two optical transitions of diamagnetic character, one tetrahedral and one octahedral. We find excellent agreement between the model and our experimental results for photon energies between 1.77 and 2.53 eV, corresponding to wavelengths between 700 and 490 nm. It is shown that the Faraday rotation changes significantly with the amount of substituted gallium and bismuth. Furthermore, the experimental results suggest that the magnetooptic response changes linearly with the bismuth substitution.Comment: 15 pages, 6 figures, published in Phys. Rev.

The Efficacy of Biliary Diversion for Benign Disease: Long-Term Follow-up

Retrospective analysis of 70 patients who underwent biliary bypass operations for benign disease over an eight-year period was undertaken to evaluate long-term complications. Operative procedures included choledochoduodenostomy in 60 patients, choledochojejunostomy in four, and cholecystoduodenostomy, cholecystojejunostomy and hepaticojejunostomy in two patients each. The most common indication for surgery was choledocholithiasis, with or without hepatic stones, viscid bile, and ampullary stenosis (61 to 70 patients). Other indications included chronic pancreatitis, choledochal cyst, and sclerosing cholangitis. One patient died postoperatively from hemorrhage, and two others died from causes unrelated to surgery. Two patients developed cholangitis without reflux and demonstrated anastomotic stenosis at re-operation. Sixty-four patients in the series had reflux but remained asymptomatic. Our study supports the concept that cholangitis results from relative obstruction of the anastomosis rather than from reflux

Hybrid event beds dominated by transitional-flow facies: character, distribution and significance in the Maastrichtian Springar Formation, north-west Vøring Basin, Norwegian Sea

Hybrid event beds comprising clay-poor and clay-rich sandstone are abundant in Maastrichtian-aged sandstones of the Springar Formation in the north-west Vøring Basin, Norwegian Sea. This study focuses on an interval, informally referred to as the Lower Sandstone, which has been penetrated in five wells that are distributed along a 140 km downstream transect. Systematic variations in bed style within this stratigraphic interval are used to infer variation in flow behaviour in relatively proximal and distal settings, although individual beds were not correlated. The Lower Sandstone shows an overall reduction in total thickness, bed amalgamation, sand to mud ratio and grain size in distal wells. Turbidites dominated by clay-poor sandstone are at their most common in relatively proximal wells, whereas hybrid event beds are at their most common in distal wells. Hybrid event beds typically comprise a basal clay-poor sandstone (non-stratified or stratified) overlain by banded sandstone, with clay-rich non-stratified sandstone at the bed top. The dominant type of clay-poor sandstone at the base of these beds varies spatially; non-stratified sandstone is thickest and most common proximally, whereas stratified sandstone becomes dominant in distal wells. Stratified and banded sandstone record progressive deposition of the hybrid event bed. Thus, the facies succession within hybrid event beds records the longitudinal heterogeneity of flow behaviour within the depositional boundary layer; this layer changed from non-cohesive at the front, through a region of transitional behaviour (fluctuating non-cohesive and cohesive flow), to cohesive behaviour at the rear. Spatial variation in the dominant type of clay-poor sandstone at the bed base suggests that the front of the flow remained non-cohesive, and evolved from high-concentration and turbulence-suppressed to increasingly turbulent flow; this is thought to occur in response to deposition and declining sediment fallout. This research may be applicable to other hybrid event bed prone systems, and emphasizes the dynamic nature of hybrid flows