284 research outputs found
Recent progress in silica aerogel Cherenkov radiator
In this paper, we present recent progress in the development of hydrophobic
silica aerogel as a Cherenkov radiator. In addition to the conventional method,
the recently developed pin-drying method for producing high-refractive-index
aerogels with high transparency was studied in detail. Optical qualities and
large tile handling for crack-free aerogels were investigated. Sufficient
photons were detected from high-performance aerogels in a beam test.Comment: Proceedings of 2nd International Conference on Technology and
Instrumentation in Particle Physics (TIPP 2011), to be published in Physics
Procedia, 8 pages, 7 figure
Hydrophobic silica aerogel production at KEK
We present herein a characterization of a standard method used at the High
Energy Accelerator Research Organization (KEK) to produce hydrophobic silica
aerogels and expand this method to obtain a wide range of refractive index (n =
1.006-1.14). We describe in detail the entire production process and explain
the methods used to measure the characteristic parameters of aerogels, namely
the refractive index, transmittance, and density. We use a small-angle X-ray
scattering (SAXS) technique to relate the transparency to the fine structure of
aerogels.Comment: To be published in Nucl. Instr. and Meth. A, 9 pages, 10 figures, 1
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Control technique for planetary rover
Beginning next century, several schemes for sending a planetary rover to the moon or Mars are being planned. As part of the development program, autonomous navigation technology is being studied to allow the rover the ability to move autonomously over a long range of unknown planetary surface. In the previous study, we ran the autonomous navigation experiment on an outdoor test terrain by using a rover test-bed that was controlled by a conventional sense-plan-act method. In some cases during the experiment, a problem occurred with the rover moving into untraversable areas. To improve this situation, a new control technique has been developed that gives the rover the ability of reacting to the outputs of the proximity sensors, a reaction behavior if you will. We have developed a new rover test-bed system on which an autonomous navigation experiment was performed using the newly developed control technique. In this outdoor experiment, the new control technique effectively produced the control command for the rover to avoid obstacles and be guided to the goal point safely
Optical and radiographical characterization of silica aerogel for Cherenkov radiator
We present optical and X-ray radiographical characterization of silica
aerogels with refractive index from 1.05 to 1.07 for a Cherenkov radiator. A
novel pin-drying method enables us to produce highly transparent hydrophobic
aerogels with high refractive index by shrinking wet-gels. In order to
investigate the uniformity in the density (i.e., refractive index) of an
individual aerogel monolith, we use the laser Fraunhofer method, an X-ray
absorption technique, and Cherenkov imaging by a ring imaging Cherenkov
detector in a beam test. We observed an increase in density at the edge of the
aerogel tiles, produced by pin-drying.Comment: To be published in IEEE Trans. Nucl. Sci., 7 pages, 9 figures, 1
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Comparative study of hybrid functionals applied to structural and electronic properties of semiconductors and insulators
We present a systematic study that clarifies validity and limitation of
current hybrid functionals in density functional theory for structural and
electronic properties of various semiconductors and insulators. The three
hybrid functionals, PBE0 by Perdew, Ernzerhof, and Becke, HSE by Heyd,
Sucseria, and Ernzerhof, and a long-range corrected (LC) functional, are
implemented in a well-established plane-wave-basis-set scheme combined with
norm-conserving pseudopotentials, thus enabling us to assess applicability of
each functional on equal footing to the properties of the materials. The
materials we have examined in this paper range from covalent to ionic materials
as well as a rare-gas solid whose energy gaps determined by experiments are in
the range of 0.6 eV - 14.2 eV: i.e., Ge, Si, BaTiO, -GaN, diamond,
MgO, NaCl, LiCl, Kr, and LiF. We find that the calculated bulk moduli by the
hybrid functionals show better agreement with the experiments than the
generalized gradient approximation (GGA) provides, whereas the calculated
lattice constants by the hybrid functionals and GGA show comparable accuracy.
The calculated energy band gaps and the valence-band widths for the ten
prototype materials show substantial improvement using the hybrid functional
compared with GGA. In particular, it is found that the band gaps of the ionic
materials as well as the rare-gas solid are well reproduced by the LC-hybrid
functional, whereas those of covalent materials are well described by the HSE
functional. We also examine exchange effects due to short-range and long-range
components of the Coulomb interaction and propose an optimum recipe to the
short-range and long-range separation in treating the exchange energy.Comment: 13pages, 4 figures, 4 table
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