| 1. |
- Aamodt, K., et al.
(författare)
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The ALICE experiment at the CERN LHC
- 2008
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 3:S08002
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Forskningsöversikt (refereegranskat)abstract
- ALICE (A Large Ion Collider Experiment) is a general-purpose, heavy-ion detector at the CERN LHC which focuses on QCD, the strong-interaction sector of the Standard Model. It is designed to address the physics of strongly interacting matter and the quark-gluon plasma at extreme values of energy density and temperature in nucleus-nucleus collisions. Besides running with Pb ions, the physics programme includes collisions with lighter ions, lower energy running and dedicated proton-nucleus runs. ALICE will also take data with proton beams at the top LHC energy to collect reference data for the heavy-ion programme and to address several QCD topics for which ALICE is complementary to the other LHC detectors. The ALICE detector has been built by a collaboration including currently over 1000 physicists and engineers from 105 Institutes in 30 countries, Its overall dimensions are 16 x 16 x 26 m(3) with a total weight of approximately 10 000 t. The experiment consists of 18 different detector systems each with its own specific technology choice and design constraints, driven both by the physics requirements and the experimental conditions expected at LHC. The most stringent design constraint is to cope with the extreme particle multiplicity anticipated in central Pb-Pb collisions. The different subsystems were optimized to provide high-momentum resolution as well as excellent Particle Identification (PID) over a broad range in momentum, up to the highest multiplicities predicted for LHC. This will allow for comprehensive studies of hadrons, electrons, muons, and photons produced in the collision of heavy nuclei. Most detector systems are scheduled to be installed and ready for data taking by mid-2008 when the LHC is scheduled to start operation, with the exception of parts of the Photon Spectrometer (PHOS), Transition Radiation Detector (TRD) and Electro Magnetic Calorimeter (EMCal). These detectors will be completed for the high-luminosity ion run expected in 2010. This paper describes in detail the detector components as installed for the first data taking in the summer of 2008.
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| 2. |
- Berseth, P. A., et al.
(författare)
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Carbon Nanomaterials as Catalysts for Hydrogen Uptake and Release in NaAlH4
- 2009
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Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 9:4, s. 1501-1505
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Tidskriftsartikel (refereegranskat)abstract
- A synergistic approach involving experiment and first-principles theory not only shows that carbon nanostructures can be used as catalysts for hydrogen uptake and release in complex metal hydrides such as sodium alanate, NaAlH4, but also provides an unambiguous understanding of how the catalysts work. Here we show that the stability of NaAlH4 originates with the charge transfer from Na to the AlH4 moiety, resulting in an ionic bond between Na+ and AlH4- and a covalent bond between Al and H. Interaction of NaAlH4 with an electronegative substrate such as carbon fullerene or nanotube affects the ability of Na to donate its charge to AlH4, consequently weakening the Al-H bond and causing hydrogen to desorb at lower temperatures as well as facilitating the absorption of H-2 to reverse the dehydrogenation reaction. In addition, based on our experimental observations and theoretical calculations it appears the curvature of the carbon nanostructure plays a role in the catalytic process. Ab initio molecular dynamics simulation further reveals the time evolution of the charge transfer process.
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| 3. |
- Araujo, Carlos Moyses, et al.
(författare)
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Role of titanium in hydrogen desorption in crystalline sodium alanate
- 2005
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 86:25
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Tidskriftsartikel (refereegranskat)abstract
- The role of Ti in improving the thermodynamics of hydrogen desorption in crystalline sodium alanate (NaAlH4) has been investigated by using the density functional theory. The total energy calculations reveal that Ti prefers to occupy the Na site over that of the Al site when the atomic energies are used as the reference. However, the use of the cohesive energies of Al, Na, and Ti leads to the Al site being the least unfavourable site. Irrespective of whether Ti occupies the Na or the Al site, the energy necessary to remove a hydrogen atom from Ti substituted sodium alanate is significantly lowered from that of the pure alanate. The understanding gained here may help in designing hydrogen storage materials suitable for industrial applications.
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| 4. |
- Blomqvist, Andreas, et al.
(författare)
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Dehydrogenation from 3d-transition-metal-doped NaAlH4 : Prediction of catalysts
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90:14
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Tidskriftsartikel (refereegranskat)abstract
- A fundamental understanding of the role of catalysts in improving the kinetics and thermodynamics of hydrogen sorption in NaAlH4 is the key for using this material in hydrogen storage. The authors present a systematic theoretical study of energies needed to desorb hydrogen in 3d transition metal (Sc-Cu)-doped NaAlH4. They show that Cr and Fe atoms can be far more effective catalysts than Ti in desorbing hydrogen. The role of the 3d metal atoms in improving the thermodynamics of dehydrogenation is attributed to a significant shortening of the bond length with neighboring Al atoms.
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| 5. |
- Li, S., et al.
(författare)
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Dehydrogenation Mechanism in Catalyst-activated MgH2
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 74:13, s. 132106-
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Tidskriftsartikel (refereegranskat)abstract
- A small amount of Nb2O5 catalyst is known to substantially improve the desorption thermodynamics and kinetics of MgH2. Using density functional theory in combination with ab initio molecular dynamics simulation, we provide theoretical understanding of the mechanism of dehydrogenation in Nb doped MgH2. We show that the substitution of Nb at the Mg site followed by the clustering of H around Nb is a likely pathway for hydrogen desorption. We also find that dehydrogenation from the vicinity of Mg vacancies is exothermic. However, the vacancies are not likely to play a significant role in hydrogen desorption due to their high formation energy (3.87 eV).
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| 6. |
- Li, S., et al.
(författare)
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Effect of Ti and metal vacancies on the electronic structure, stability, and dehydrogenation of Na3AlH6 : Supercell band-structure formalism and gradient-corrected density-functional theory
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - Virginia Commonwealth Univ, Dept Phys, Richmond, VA 23284 USA. Uppsala Univ, Dept Phys, Condensed Matter Theory Grp, SE-75121 Uppsala, Sweden.. - 1098-0121 .- 1550-235X. ; 73:21
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Tidskriftsartikel (refereegranskat)abstract
- Electronic and structural properties of sodium-aluminum hexahydride (Na3AlH6) formed during the decomposition reaction of sodium alanate (NaAlH4) and the effects of Ti catalyst are studied using supercell approach and density-functional theory. The preferred site of Ti has been determined by substituting it at both the Na and Al sites and comparing the respective formation energies. The least unfavorable site for Ti is found to be the Al site. To examine the role of Ti substitution on the desorption of hydrogen, the energy cost to remove a H atom from the vicinity of Ti was calculated and compared with that from the pure Na3AlH6 The improvement in dehydrogenation of Na3AlH6 was found to be due to the weakening the Al-H bond caused by Ti substitution. We also studied the role of metal vacancies on hydrogen desorption. Although this desorption was exothermic, the energies to create these vacancies are high.
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| 7. |
- Li, S., et al.
(författare)
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Optical properties of Ti3SiC2 and Ti4AlN3
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92:22
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Tidskriftsartikel (refereegranskat)abstract
- The dielectric functions of the MAX phases, Ti3SiC2 and Ti4AlN3, have been determined from first principles calculations. We compared the dielectric functions and the reflectivity spectra of Ti3SiC2 and Ti4AlN3 with those of TiC and TiN. The optical spectra were analyzed by means of the electronic structure, which provides theoretical understanding of the conduction mechanism of these two phases. We found that Ti4AlN3 can be used to avoid solar heating and also increase the radiative cooling due to the increased thermal emittance as compared to TiN. Ti4AlN3 can therefore be a candidate coating material for temperature control of space vehicles.
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