9,670 research outputs found
Simulation and analysis of solenoidal ion sources
We present a detailed analysis and simulation of solenoidal, magnetically confined electron bombardment ion sources, aimed at molecular beam detection. The aim is to achieve high efficiency for singly ionized species while minimizing multiple ionization. Electron space charge plays a major role and we apply combined ray tracing and finite element simulations to determine the properties of a realistic geometry. The factors controlling electron injection and ion extraction are discussed. The results from simulations are benchmarked against experimental measurements on a prototype source
Development of YAG:Dy Thermographic Phosphor Coatings for Turbine Engine Applications
The selection and development of thermographic phosphor coatings were pursued to meet the objective of demonstrating luminescence-decay-based temperature measurements up to 1300C on the surface of a vane in an operating demonstrator turbine engine. To meet this objective, YAG:Dy was selected based on the desirable luminescence performance observed for YAG:Dy powder: (1) excellent temperature sensitivity and intensity at operating turbine engine temperatures, (2) an emission peak at the relatively short wavelength of 456 nm, where the interference from background blackbody radiation is fairly low, and (3) its nearly single exponential decay which makes for a simple, reliable temperature calibration. However, implementation of YAG:Dy for surface temperature measurements required application of YAG:Dy as a coating onto the surface of a superalloy component with a preexisting yttria-stabilized zirconia (YSZ) thermal barrier coating (TBC). An inherent dilemma in producing a YAG:Dy coating is that coating processing is constrained to be performed at temperatures below (less than 1200C) what is considered safe for the superalloy component, much lower than temperatures used to produce the high quality crystalline powder. Therefore, YAG:Dy coatings tend to exhibit lower luminescence performance compared to well prepared YAG:Dy powder, and the luminescence performance of the coating will depend on the method of coating deposition. In this presentation, the luminescence performance of YAG:Dy coatings prepared by the different methods of (1) application of a binder-based YAG:Dy-containing paint, (2) solution precursor plasma spray (SPPS), and (3) electron-beam physical vapor deposition (EB-PVD) and the effect of post-deposition heat treatments will be discussed
High-velocity OH megamasers in IRAS 20100-4156: Evidence for a Supermassive Black Hole
We report the discovery of new, high-velocity narrow-line components of the
OH megamaser in IRAS 20100-4156. Results from the Australian Square Kilometre
Array Pathfinder (ASKAP)'s Boolardy Engineering Test Array (BETA) and the
Australia Telescope Compact Array (ATCA) provide two independent measurements
of the OH megamaser spectrum. We found evidence for OH megamaser clumps at
409 and 562 km/s (blue-shifted) from the systemic velocity of the galaxy,
in addition to the lines previously known. The presence of such high velocities
in the molecular emission from IRAS 201004156 could be explained by a ~50 pc
molecular ring enclosing an approximately 3.8 billion solar mass black hole. We
also discuss two alternatives, i.e. that the narrow-line masers are dynamically
coupled to the wind driven by the active galactic nucleus or they are
associated with two separate galactic nuclei. The comparison between the BETA
and ATCA spectra provides another scientific verification of ASKAP's BETA. Our
data, combined with previous measurements of the source enabled us to study the
variability of the source over a twenty-six year period. The flux density of
the brightest OH maser components has reduced by more than a factor of two
between 1988 and 2015, whereas a secondary narrow-line component has more than
doubled in the same time. Plans for high-resolution VLBI follow-up of this
source are discussed, as are prospects for discovering new OH megamasers during
the ASKAP early science program.Comment: Accepted to MNRAS. Seven pages, three figure
Muon counting using silicon photomultipliers in the AMIGA detector of the Pierre Auger observatory
AMIGA (Auger Muons and Infill for the Ground Array) is an upgrade of the Pierre Auger Observatory designed to extend its energy range of detection and to directly measure the muon content of the cosmic ray primary particle showers. The array will be formed by an infill of surface water-Cherenkov detectors associated with buried scintillation counters employed for muon counting. Each counter is composed of three scintillation modules, with a 10m(2) detection area per module. In this paper, a new generation of detectors, replacing the current multi-pixel photomultiplier tube (PMT) with silicon photo sensors (aka. SiPMs), is proposed. The selection of the new device and its front-end electronics is explained. A method to calibrate the counting system that ensures the performance of the detector is detailed. This method has the advantage of being able to be carried out in a remote place such as the one where the detectors are deployed. High efficiency results, i.e. 98% efficiency for the highest tested overvoltage, combined with a low probability of accidental counting (similar to 2 %), show a promising performance for this new system
Operation of a 1-Liter-Volume Gaseous Argon Scintillation Counter
We have built a gas-phase argon ionization detector to measure small nuclear
recoil energies (< 10 keVee). In this paper, we describe the detector response
to X-ray and gamma calibration sources, including analysis of pulse shapes,
software triggers, optimization of gas content, and energy- and
position-dependence of the signal. We compare our experimental results against
simulation using a 5.9-keV X-ray source, as well as higher-energy gamma sources
up to 1332 keV. We conclude with a description of the detector, DAQ, and
software settings optimized for a measurement of the low-energy nuclear
quenching factor in gaseous argon. This work was performed under the auspices
of the U.S. Department of Energy by Lawrence Livermore National Laboratory in
part under Contract W-7405-Eng-48 and in part under Contract DE-AC52-07NA27344.
Funded by Lab-wide LDRD. LLNL-JRNL-415990-DRAFT.Comment: 29 pages, single-column, double-spaced, 21 figure
Methods for the Assessment of Cell Wall Composition in \u3ci\u3eMiscanthus\u3c/i\u3e and Other \u27Energy Grasses\u27
Diagnosis of vertebral fractures in children: is a simplified algorithm-based qualitative technique reliable?
Background Identification of osteoporotic vertebral fractures
allows treatment opportunity reducing future risk. There is no
agreed standardised method for diagnosing paediatric vertebral
fractures.
Objective To evaluate the precision of a modified adult
algorithm-based qualitative (ABQ) technique, applicable to
children with primary or secondary osteoporosis.
Materials and methods Three radiologists independently
assessed lateral spine radiographs of 50 children with
suspected reduction in bone mineral density using a modified
ABQ scoring system and following simplification to include
only clinically relevant parameters, a simplified ABQ score. A
final consensus of all observers using simplified ABQ was
performed as a reference standard for fracture characterisation.
Kappa was calculated for interobserver agreement of the
components of both scoring systems and intraobserver agreement
of simplified ABQ based on a second read of 29 randomly
selected images.
Results Interobserver Kappa for modified ABQ scoring for
fracture detection, severity and shape ranged from 0.34 to
0.49 Kappa for abnormal endplate and position assessment
was 0.27 to 0.38. Inter- and intraobserver Kappa for simplified
ABQ scoring for fracture detection and grade ranged from
0.37 to 0.46 and 0.45 to 0.56, respectively. Inter- and
intraobserver Kappa for affected endplate ranged from 0.31
to 0.41 and 0.45 to 0.51, respectively. Subjectively, observers’
felt simplified ABQ was easier and less time-consuming.
Conclusion Observer reliability of modified and simplified
ABQ was similar, with slight to moderate agreement for fracture
detection and grade/severity. Due to subjective preference
for simplified ABQ, we suggest its use as a semi-objective
measure of diagnosing paediatric vertebral fracture
Neutrino mass matrix with U(2) flavor symmetry and neutrino oscillations
The three neutrino mass matrices in the model are studied
focusing on the neutrino oscillation experiments. The atmospheric neutrino
anomaly could be explained by the large oscillation.
The long baseline experiments are expected to detect signatures of the neutrino
oscillation even if the atmospheric neutrino anomaly is not due to the neutrino
oscillation. However, the model cannot solve the solar neutrino deficit while
it could be reconciled with the LSND data.Comment: 12 pages, LaTex file, to be published in PR
A Catalog of the Highest-energy Cosmic Rays Recorded during Phase I of Operation of the Pierre Auger Observatory
A catalog containing details of the highest-energy cosmic rays recorded through the detection of extensive air showers at the Pierre Auger Observatory is presented with the aim of opening the data to detailed examination. Descriptions of the 100 showers created by the highest-energy particles recorded between 2004 January 1 and 2020 December 31 are given for cosmic rays that have energies in the range 78-166 EeV. Details are also given on a further nine very energetic events that have been used in the calibration procedure adopted to determine the energy of each primary. A sky plot of the arrival directions of the most energetic particles is shown. No interpretations of the data are offered
- …