356 research outputs found
Mirror development for the Cherenkov Telescope Array
No full textThe Cherenkov Telescope Array (CTA) is a planned observatory for very-high energy gamma-ray astronomy. It will consist of several tens of telescopes of different sizes, with a total mirror area of up to 10,000 square meters. Most mirrors of current installations are either polished glass mirrors or diamond-turned aluminium mirrors, both labour intensive technologies. For CTA, several new technologies for a fast and cost-efficient production of light-weight and reliable mirror substrates have been developed and industrial pre-production has started for most of them. In addition, new or improved aluminium-based and dielectric surface coatings have been developed to increase the reflectance over the lifetime of the mirrors compared to those of current Cherenkov telescope instruments.Fil: Forster, A.. Max-Planck-Institut fur Kernphysik; AlemaniaFil: Armstrong, T.. Durham University; Reino UnidoFil: Baba, H.. Ibaraki University; JapónFil: Bähr, J.. No especifíca;Fil: Bonardi, A.. Universitat Tübingen; AlemaniaFil: Bonnoli, G.. Osservatorio Astronomico di Brera; ItaliaFil: Brun, P.. No especifíca;Fil: Canestrari, R.. Osservatorio Astronomico di Brera; ItaliaFil: Chadwick, P.. Durham University; Reino UnidoFil: Chikawa, M.. University of Tokyo; JapónFil: Carton, P.-H.. Centre de Saclay; FranciaFil: De Souza, V.. Universidade de Sao Paulo; BrasilFil: Dipold, J.. Universidade de Sao Paulo; BrasilFil: Doro, M.. Università di Padova; ItaliaFil: Durand, D.. No especifíca;Fil: Dyrda, M.. Polish Academy of Sciences; ArgentinaFil: Giro, E.. Osservatorio Astronomico di Padova; ItaliaFil: Glicenstein, J.-F.. No especifíca;Fil: Hanabata, Y.. Kinki University; JapónFil: Hayashida, M.. University of Tokyo; JapónFil: Hrabovski, M.. No especifíca;Fil: Jeanney, C.. Centre de Saclay; FranciaFil: Kagaya, M.. Ibaraki University; JapónFil: Katagiri, H.. Ibaraki University; JapónFil: Lessio, L.. Osservatorio Astronomico di Padova; ItaliaFil: Mandat, D.. Institute of Physics of the Academy of Sciences of the Czech Republic; República ChecaFil: Mariotti, M.. Università di Padova; ItaliaFil: Medina, Maria Clementina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Yoshida, T.. Ibaraki University; Japón33rd International Cosmic Ray ConferenceRío de JaneiroBrasilBrazilian Physical Societ
High resolution double crystal X-ray diffractometry and topography of III-V semiconductor compounds
No full textDouble crystal diffractometry and topography are now routinely used in many laboratories for the inspection of epitaxially grown devices. However the trend towards thinner layers and more complex structures requires the continued development of novel approaches using these techniques. This thesis is concerned with the development of these approaches to study the structural uniformity of semiconductor materials. The uniformity of large single crystals of lithium niobate has been studied using synchrotron radiation and double crystal X-ray topography. This study has shown a variety of contrast features including low angle grain boundaries and non-uniform dislocation densities. The abruptness of an interface between a layer and the underlying substrate has been studied using glancing incidence asymmetric reflections. Comparisons to simulated structures revealed that a closer match was achieved by the inclusion of a highly mismatched interfacial layer. This study illustrates the need for careful comparison between experimental and simulated rocking curves as different structures may produce very similar rocking curves. A double crystal topographic study of a AlGaAs laser structure revealed X-ray interference fringes. These are shown to be produced from the interaction of two simultaneously diffracting layers separated by a thin layer. Possible formation mechanisms have been discussed showing that these fringes are capable of revealing changes in the active layer at the atomic level. A novel approach has also been developed using synchrotron radiation to study the non-stoichiometry of GaAs. This approach uses the quasi-forbidden reflections which are present in III-V semiconductors due to the differences in the atomic scattering factors. This study has also discussed the behaviour of strong and weak reflections in the region of absorption edges and modelled their behaviour using the anomalous dispersion corrections of Cromer and Liberman
New air fluorescence detectors employed in the Telescope Array experiment
No full textSince 2007, the Telescope Array (TA) experiment, based in Utah, USA, has been observing ultra high energy cosmic rays to understand their origins. The experiment includes a surface detector (SD) array and three fluorescence detector (FD) stations. The FD stations, installed surrounding the SD array, measure the air fluorescence light emitted from extensive air showers (EASs) for precise determination of their energies and species. The detectors employed at one of the three FD stations were relocated from the High Resolution Fly's Eye (HiRes) experiment. At the other two stations, newly designed detectors were constructed for the TA experiment. An FD consists of a primary mirror and a camera equipped with photomultiplier tube pixels. To obtain the EAS parameters with high accuracy, understanding the FD optical characteristics is important. In this paper, we report the characteristics and installation of the new FDs and the performances of the FD components. The results of the monitored mirror reflectance during the observation time are also described in this report. © 2012 Elsevier B.V. All rights reserved.0SCOPUS: ar.jinfo:eu-repo/semantics/publishe
Concentration-Independent Solute Segregation in Laser Annealing of Semiconductor Crystals
No full textABSTRACTAtomic processes at the interface in regrowth following laser induced melting were investigated by observing behavior of impurity segregation. The interfacial segregation coefficient k* was obtained from depth profiles of solute atoms redistributed by laser irradiation of uniformly doped Si, Ge, and GayAl1−yAs crystals. It was found that k*=k0 for B in Si, Ga in Ge ih the growth rate range of 1 m/s. It is concluded that rapid growth freezes a state of liquid monolayer adjacent to the interface which has the character of ideal solution from dilute to eutectic composition for dopant-silicon systems and in the entire range of composition for the mixed crystal.</jats:p
Statistical Tests as Spherical Data for Angular Distributions of Neutrinos Burst from SN 1987A
No full textAn electron microscope study of liver cell in carbon tetrachloride intoxication, significance of "opaque area"
No full textElectron microscope study on the rat liver cells of carbon tetrachloride poisoning has been reported. Observations have been made on the osmic fixed tissue sections obtained from the liver at early stages of poisoning, 5 to 22 hours after carbon tetrachloride oral administration, 0.25ml. per 100g. body weight. Special attention is paid on the appearance of electron dense area,
opaque area, in cytoplasm, which is compased of fibrous components, probably originated from endoplasmic reticulum. This will be an important sign of cell degeneration. Toluidine blue, PAS and methyl green-pyronin stainings of the thicker sections from the same samples as used for electron microscopy revealed that the opaque area is stained by toluidine blue and pyronin but not by PAS.
The opaque areas appear already five hours after the carbon tetrachloride administration and show some continuity with elongated filaments of endoplasmic
reticulum. At an advanced stage of paisoning the opaque area increases in its number and size, but some of them are shrunk as a mass, being separated from the surrounding cytoplasm with scanty area. Often they form denser masses in the center and loak like the lipid deposition. The picture suggests formation of lipid droplets in the case of fatty degeneration of the liver cell.</p
Look Who's Visiting Supporting Visitor Awareness in the Web
No full textIndividuals, groups and organizations host places in the World Wide Web to attract visitors, but once they have established a web presence they usually maintain little or no awareness of visiting activity. However, the standard web infrastructure supports the capture of detailed activity-related information. In the first part of this paper, we contribute a preliminary study conducted with expert web hosts in different domains, investigating the use of information on visiting activity as feedback for web operation. From this study, we infer general requirements for web awareness support, based on which we have designed two systems aimed to promote more awareness of web activity and visitors. The first is a system supporting ambient notification of web events, end-user configurability, and ambient display for overview and comparison of activity in a web place. The second system moves beyond awareness of web activity to provide glances into the visitors' sites, introducing reciprocity to the host-visitor relationship. Both systems have been prototyped and deployed in work environments for an evaluation in everyday use
Look Who's Visiting: Supporting Awareness for Visitors in the Web
No full textIndividuals, groups and organizations host places in the World Wide Web to attract visitors, but once they have established a web presence they usually maintain little or no awareness of visiting activity. However, the standard web infrastructure supports the capture of detailed activity-related information. In the first part of this paper, we contribute a preliminary study conducted with expert web hosts in different domains, investigating the use of information on visiting activity as feedback for web operation. From this study, we infer general requirements for web awareness support, based on which we have designed two systems aimed to promote more awareness of web activity and visitors. The first is a system supporting ambient notification of web events, end-user configurability, and ambient display for overview and comparison of activity in a web place. The second system moves beyond awareness of web activity to provide glances into the visitors’ sites, introducing reciprocity to the host–visitor relationship. Both systems have been prototyped and deployed in work environments for an evaluation in everyday use
Status of the technologies for the production of the Cherenkov Telescope Array (CTA) mirrors
No full textThe Cherenkov Telescope Array (CTA) is the next generation very high-energy gamma-ray observatory, with at least 10 times higher sensitivity than current instruments. CTA will comprise several tens of Imaging Atmospheric Cherenkov Telescopes (IACTs) operated in array-mode and divided into three size classes: large, medium and small telescopes. The total reflective surface could be up to 10,000 m2 requiring unprecedented technological efforts. The properties of the reflector directly influence the telescope performance and thus constitute a fundamental ingredient to improve and maintain the sensitivity. The R&D status of lightweight, reliable and cost-effective mirror facets for the CTA telescope reflectors for the different classes of telescopes is reviewed in this paper
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