| 1. |
- Acharya, B. S., et al.
(författare)
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Introducing the CTA concept
- 2013
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Ingår i: Astroparticle physics. - : Elsevier BV. - 0927-6505 .- 1873-2852. ; 43, s. 3-18
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The Cherenkov Telescope Array (CTA) is a new observatory for very high-energy (VHE) gamma rays. CTA has ambitions science goals, for which it is necessary to achieve full-sky coverage, to improve the sensitivity by about an order of magnitude, to span about four decades of energy, from a few tens of GeV to above 100 TeV with enhanced angular and energy resolutions over existing VHE gamma-ray observatories. An international collaboration has formed with more than 1000 members from 27 countries in Europe, Asia, Africa and North and South America. In 2010 the CTA Consortium completed a Design Study and started a three-year Preparatory Phase which leads to production readiness of CTA in 2014. In this paper we introduce the science goals and the concept of CTA, and provide an overview of the project. (C) 2013 Elsevier B.V. All rights reserved.
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| 2. |
- Actis, M., et al.
(författare)
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Design concepts for the Cherenkov Telescope Array CTA : an advanced facility for ground-based high-energy gamma-ray astronomy
- 2011
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Ingår i: Experimental astronomy. - : Springer. - 0922-6435 .- 1572-9508. ; 32:3, s. 193-316
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Tidskriftsartikel (refereegranskat)abstract
- Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA.
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| 3. |
- Glicenstein, J-F, et al.
(författare)
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Status of the NectarCAM camera project
- 2014
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Ingår i: High Energy, Optical, and Infrared Detectors for Astronomy VI. - : SPIE - International Society for Optical Engineering. - 9780819496225
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Konferensbidrag (refereegranskat)abstract
- NectarCAM is a camera designed for the medium-sized telescopes of the Cherenkov Telescope Array (CTA) covering the central energy range 100 GeV to 30 TeV. It has a modular design based on the NECTAr chip, at the heart of which is a GHz sampling Switched Capacitor Array and 12-bit Analog to Digital converter. The camera will be equipped with 265 7-photomultiplier modules, covering a field of view of 7 to 8 degrees. Each module includes the photomultiplier bases, High Voltage supply, pre-amplifier, trigger, readout and Thernet transceiver. Events recorded last between a few nanoseconds and tens of nanoseconds. A flexible trigger scheme allows to read out very long events. NectarCAM can sustain a data rate of 10 kHz. The camera concept, the design and tests of the various subcomponents and results of thermal and electrical prototypes are presented. The design includes the mechanical structure, the cooling of electronics, read-out, clock distribution, slow control, data-acquisition, trigger, monitoring and services. A 133-pixel prototype with full scale mechanics, cooling, data acquisition and slow control will be built at the end of 2014.
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| 4. |
- Andreazza, A, et al.
(författare)
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The DELPHI very forward tracker for LEP200
- 1995
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Ingår i: NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT. ; 367:1-3
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Annan publikation (övrigt vetenskapligt/konstnärligt)
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| 5. |
- Boutonnet-Kizling, M, et al.
(författare)
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Surface oxidation of silicon carbide: quantitative measurement and Rh effect
- 1992
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Ingår i: Materials Chemistry and Physics. - 0254-0584 .- 1879-3312. ; 30, s. 273-277
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation degree of a commercial silicon carbide (SiC) powder was studied by means of Fourier transform infrared spectroscopy, using the intensity of the (SiO2) band at 450 cm-1 for measurements. Results are related to data obtained by LECO and gravimetric measurements. The influence of water in oxygen on the rate of the oxidation process was particularly examined. It was found that water alone had an oxidizing efficiency and that its mixture with oxygen increased the effect of the latter. The presence of Rh particles on SiC promoted the formation of SiO2. However, as shown by the IR study of CO adsorption, this formation embedded the metal particles. This effect can be avoided by loading Rh on a precalcined SiC sample.
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| 6. |
- Lögdberg, Sara, et al.
(författare)
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Effect of water on the space-time yield of different supported cobalt catalysts during Fischer-Tropsch synthesis
- 2011
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Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 393:1-2, s. 109-121
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Tidskriftsartikel (refereegranskat)abstract
- The effect of partial pressure of water on the Fischer-Tropsch (FT) rate of six cobalt-based catalysts supported on three different carrier materials (gamma-Al2O3, alpha-Al2O3, TiO2) with varying Co particle sizes was investigated in a fixed-bed reactor by changing space velocity and by external water vapour addition. A typical catalyst pellet size (<100 mu m) for industrial slurry-bed FT reactors was used. Water was found to have a positive kinetic effect, at least up to moderate amounts, on the FT rate of all catalysts in the present study, including the gamma-Al2O3-supported catalyst with pores smaller than similar to 10 nm. The reason for the apparent negative effect on the space-time yield at a direct exposure of Co supported on narrowpore gamma-Al2O3 to high partial pressures of water is due to a rapid and extensive deactivation. This could be ascribed to formation of hard-to-reduce oxidized cobalt species. The choice of support material was found to have a major effect on the response to changes in partial pressure of water, both with respect to deactivation behaviour and kinetics. However, there is a minor Co-particle size effect on the magnitude of the kinetic effect of water, larger Co particles showing a more positive response. Different extents of mass transfer limitations and/or differences in fugacities of H-2, CO and water among the six catalysts could be ruled out as causes for the observed differences.
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| 7. |
- Lögdberg, Sara, et al.
(författare)
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Further insights into methane and higher hydrocarbons formation over cobalt-based catalysts with γ-Al2O3, α-Al2O3 and TiO2 as support materials
- 2017
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Ingår i: Journal of Catalysis. - : Academic Press. - 0021-9517 .- 1090-2694. ; 352, s. 515-531
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Tidskriftsartikel (refereegranskat)abstract
- A range of cobalt-based catalysts varying in Co loading and prepared by incipient wetness impregnation of traditional support materials (γ-Al2O3, α-Al2O3 and TiO2), have been studied in the Fischer-Tropsch reaction at industrially relevant process conditions (483 K, 20 bar, H2/CO = 2.1). A high selectivity to C5+ hydrocarbons (SC5+) is to a great extent connected with a high site activity, but not exclusively. We propose that the ratio of monomer-production rate to C–C coupling rate of a catalyst determines chain-growth probability by means of governing the coverage of the monomer on the cobalt surface. We speculate that this ratio depends on e.g. shape, strain and size of the Co crystallites and, therefore, is highly dependent on the choice of support material. No general relationship between Co particle size and SC5+ is found, but individual correlations exist for each support material. Within each support material, there are indications of negative correlations between the chain-growth probability of the C1 ∗ surface intermediate (αC1) and the higher αCn values. This can be rationalized by assuming that the majority of methane is formed by a different mechanism, separate from chain growth, but connected with chain growth through a common carbon pool. We propose that the monomers and the majority of methane are produced at sites different from the ones involved in chain growth. There is no general correlation between αC1 and SC5+ for catalysts with different support materials, possibly due to small differences in cobalt surface coverage of hydrogen. For the TiO2-supported catalysts, a dramatically increased αC1 value observed for catalysts with Co particles smaller than approx. 15 nm, is probably associated with strong metal-support interactions (SMSI). This phenomenon apparently limits the effect (reduction) on the SC5+ when moving toward smaller Co particles.
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| 8. |
- Montes, V., et al.
(författare)
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Synthesis of different ZnO-supported metal systems through microemulsion technique and application to catalytic transformation of glycerol to acetol and 1,2-propanediol
- 2014
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 223, s. 129-137
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Tidskriftsartikel (refereegranskat)abstract
- Different systems consisting of diverse metals (Au, Pt, Pd, Rh) supported on ZnO (5% by weight) were synthesized through the microemulsion technique (ME) and tested for glycerol hydrogenolysis, the main products being hydroxyacetone (acetol) and 1,2-propanediol (1,2-PDO). The solids synthesized using sodium borohydride as the reducing agent (B series) had smaller particle sizes as compared to the use of hydrazine (H series) which, in turn, resulted in a better catalytic performance. This synthetic method allowed us to obtain similar metal particle sizes (2-4 nm) for Pt, Pd and Rh solids in B series, whereas average gold metal particle was higher (> 8 nm) which probably accounts for Au-containing systems being inactive under our experimental conditions. Reactivity order followed the sequence Rh > Pt > Pd. A comparison of the systems synthesized in the present paper through ME technique with those obtained in a previous work through the deposition-precipitation process revealed a higher activity and selectivity to acetol for the former solids which could be related to the presence of surfactant. Moreover, results suggested that metal sites could participate not only in hydrogenation of acetol to 1,2-propanediol but also in the previous dehydration step of glycerol to acetol.
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| 9. |
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| 10. |
- Sanchez-Dominguez, M., et al.
(författare)
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Synthesis of Pt Nanoparticles in oil-in-water microemulsions : Phase Behavior and Effect of Formulation Parameters on Nanoparticle Characteristics
- 2011
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Ingår i: Journal of Dispersion Science and Technology. - : Informa UK Limited. - 0193-2691 .- 1532-2351. ; 32:12, s. 1765-1770
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Tidskriftsartikel (refereegranskat)abstract
- Pt nanoparticles were synthesized in oil-in-water (o/w) microemulsions, in contrast to the typically used water-in-oil microemulsion method. The new strategy implies the use of a Pt organometallic precursor (1,5-cyclooctadiene dimethyl platinum (II)), dissolved in nanometre-scale oil droplets, stabilized by surfactant, and dispersed in a continuous aqueous phase. Three different nonionic microemulsion systems were used. Characterization studies demonstrate that small, nanocrystalline Pt nanoparticles were obtained. The particle size and agglomeration was dependant on the microemulsion system used and its composition. The obtained results demonstrate the feasibility of this approach for the controlled synthesis of Pt nanoparticles with potential for catalytic purposes.
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| 11. |
- Tiseanu, C., et al.
(författare)
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In situ Raman and time-resolved luminescence investigation of the local structure of ZrO 2 in the amorphous to crystalline phase transition
- 2012
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:31, s. 16776-16783
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Tidskriftsartikel (refereegranskat)abstract
- The local structure of europium doped and impregnated ZrO 2 in the amorphous state and during crystallization is investigated by in situ X-ray diffraction and in situ Raman, high-resolution transmission electron microscopy (HRTEM) and time-resolved photoluminescence spectroscopy. From Raman spectra excited at three different wavelengths (λ ex= 488, 514, and 633 nm), both phonon modes of ZrO 2 and photoluminescence (PL) corresponding to europium electronic transitions were investigated. In the as-synthetized state, samples were X-ray and Raman amorphous with few tetragonal (also monoclinic) crystallites being observed under HRTEM microscopy. In situ XRD patterns show that all samples crystallize in the tetragonal phase around 450 °C. The time-resolved PL spectra of europium doped and impregnated ZrO 2 show spectral dynamics with time delay after lamp/laser pulse which is assigned to the coexistence of the different amorphous and crystalline components or unreacted europium precursor. From in situ Raman spectra, crystallization was detected at 300-350 °C, monitoring for the characteristic tetragonal-like 5D 0- 7F 2 emission of europium at 606 nm. The ratio of tetragonal to amorphous emission increased abruptly from ca. 2-4% at 300-400 °C to almost 25% at 400-450 °C, whereas at 500 °C the emission is mostly tetragonal. A similar trend was found with the ex situ calcined samples, but relative strong tetragonal emission was observed at lower temperature in the range of 350 to 400 °C.
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| 12. |
- Tiseanu, C., et al.
(författare)
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Order and disorder effects in nano-ZrO 2 investigated by micro-Raman and spectrally and temporarily resolved photoluminescence
- 2012
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 14:37, s. 12970-12981
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Tidskriftsartikel (refereegranskat)abstract
- Pure and europium (Eu 3+) doped ZrO 2 synthesized by an oil-in-water microemulsion reaction method were investigated by in situ and ex situ X-ray diffraction (XRD), ex situ Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM), steady state and time-resolved photoluminescence (PL) spectroscopies. Based on the Raman spectra excited at three different wavelengths i.e. 488, 514 and 633 nm and measured in the spectral range of 150-4000 cm -1 the correlation between the phonon spectra of ZrO 2 and luminescence of europium is clearly evidenced. The PL investigations span a variety of steady-state and time resolved measurements recorded either after direct excitation of the Eu 3+ f-f transitions or indirect excitation into UV charge-transfer bands. After annealing at 500°C, the overall Eu 3+ emission is dominated by Eu 3+ located in tetragonal symmetry lattice sites with a crystal-field splitting of the 5D 0- 7F 1 emission of 20 cm -1. Annealing of ZrO 2 at 1000°C leads to a superposition of Eu 3+ emissions from tetragonal and monoclinic lattice sites with monoclinic crystal-field splitting of 200 cm -1 for the 5D 0- 7F 1 transition. At all temperatures, a non-negligible amorphous/disordered content is also measured and determined to be of monoclinic nature. It was found that the evolutions with calcination temperature of the average PL lifetimes corresponding to europium emission in the tetragonal and monoclinic sites and the monoclinic phase content of the Eu 3+ doped ZrO 2 samples follow a similar trend. By use of specific excitation conditions, the distribution of europium on the amorphous/disordered surface or ordered/crystalline sites can be identified and related to the phase content of zirconia. The role of zirconia host as a sensitizer for the europium PL is also discussed in both tetragonal and monoclinic phases.
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| 13. |
- Tiseanu, C., et al.
(författare)
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Temperature induced conversion from surface to bulk sites in Eu 3-impregnated CeO 2 nanocrystals
- 2012
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 112:1, s. 013521-
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Tidskriftsartikel (refereegranskat)abstract
- Evolution with calcination temperature of Eu 3 sites in CeO 2 nanocrystals is investigated by time-resolved photoluminescence spectroscopy. In the as-synthesized Eu 3 impregnated CeO 2, most of Eu 3 ions reside on surface (S) sites. The Eu 3emission in S sites is broad and short-lived (τ 240 Όs) being dominated by the electric dipole (ED) 5D 0- 7F 2 emission with little evidence for clustering. After calcination (between 500 and 1300 °C), Eu 3 is distributed on surface, cubic and up to three additional crystalline sites. Surface type emission could be detected until 1100 °C. In cubic sites, Eu 3 substitute for the lattice Ce 4 with O h symmetry (O sites). The emission of Eu 3 in O sites is characterized by relative long-lived (τ 1.8-2 ms) and ultra-narrow (FWHM 7 cm -1) magnetic dipole (MD) 5D 0- 7F 1 emission centered at ∌591 nm. Three more crystalline sites are attributed to the oxygen vacancy charge-compensated defects: trigonal with C 3v symmetry (C1 sites) and C2 and C3 sites with C 2v or lower symmetry. Eu 3 in C1 sites exhibits predominant ED 5D 0- 7F 2 emission centered at ∌610 and 632 nm with lifetime of 0.85-1 ms. The C1 sites are assigned to Eu 3-(oxygen vacancy)-associated cubic sites. The O 2- to Ce 4 electronic charge-transfer band sensitizes preferentially the Eu 3 emission in O and, to a less extent, C1 sites but not the S sites. Overall, the results show that the oxygen vacancies are distributed around both Eu 3 and Ce 4 and the Eu 3-oxygen vacancy interaction mode as nearest-neighbour or next-nearest-neighbour depends on the calcination temperature.
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