748 research outputs found
Development of a Large-Area Aerogel Cherenkov Counter Onboard BESS
This paper describes the development of a threshold type aerogel Cherenkov
counter with a large sensitive area of 0.6 m to be carried onboard the BESS
rigidity spectrometer to detect cosmic-ray antiprotons. The design incorporates
a large diffusion box containing 46 finemesh photomultipliers, with special
attention being paid to achieving good performance under a magnetic field and
providing sufficient endurance while minimizing material usage. The refractive
index of the aerogel was chosen to be 1.03. By utilizing the muons and protons
accumulated during the cosmic-ray measurements at sea level, a rejection factor
of 10 was obtained against muons with , while keeping 97%
efficiency for protons below the threshold.Comment: 13 pages, LaTex, 9 eps figures included, submitted to NIM
Measurements of Atmospheric Antiprotons
We measured atmospheric antiproton spectra in the energy range 0.2 to 3.4
GeV, at sea level and at balloon altitude in the atmospheric depth range 4.5 to
26 g/cm^2. The observed energy spectra, including our previous measurements at
mountain altitude, were compared with estimated spectra calculated on various
assumptions regarding the energy distribution of antiprotons that interacted
with air nuclei.Comment: Accepted for publication in PL
Measurements of 0.2 to 20 GeV/n cosmic-ray proton and helium spectra from 1997 through 2002 with the BESS spectrometer
We measured low energy cosmic-ray proton and helium spectra in the kinetic
energy range 0.215 - 21.5 GeV/n at different solar activities during a period
from 1997 to 2002. The observations were carried out with the BESS spectrometer
launched on a balloon at Lynn Lake, Canada. A calculation for the correction of
secondary particle backgrounds from the overlying atmosphere was improved by
using the measured spectra at small atmospheric depths ranging from 5 through
37 g/cm^2. The uncertainties including statistical and systematic errors of the
obtained spectra at the top of atmosphere are 5-7 % for protons and 6-9 % for
helium nuclei in the energy range 0.5 - 5 GeV/n.Comment: 27 pages, 7 Tables, 9 figures, Submitted to Astroparticle Physic
Measurements of Proton, Helium and Muon Spectra at Small Atmospheric Depths with the BESS Spectrometer
The cosmic-ray proton, helium, and muon spectra at small atmospheric depths
of 4.5 -- 28 g/cm^2 were precisely measured during the slow descending period
of the BESS-2001 balloon flight. The variation of atmospheric secondary
particle fluxes as a function of atmospheric depth provides fundamental
information to study hadronic interactions of the primary cosmic rays with the
atmosphere.Comment: 21 pages, 11 figures, 4 table
On the Doppler effect for light from orbiting sources in Kerr-type metrics
A formula is derived for the combined motional and gravitational Doppler
effect in general stationary axisymmetric metrics for a photon emitted parallel
or antiparallel to the assumed circular orbital motion of its source. The same
formula is derived from eikonal approximation and Killing vector approaches to
elucidate connections between observational astronomy and modern Relativity.
The formula yields expected results in the limits of a moving or stationary
source in the exterior Kerr and Schwarzschild metrics and a moving source in
flat space.Comment: Accepted for publication in in Monthly Notices of the Royal
Astronomical Society Main Journal 1.23.15. This version has substantially
shortened and clarified derivations and added content regarding applicability
of the derivation
Asymmetric Patterns of Visual Field Defect in Primary Open-Angle and Primary Angle-Closure Glaucoma
Purpose: To compare the hemifield asymmetry of visual field (VF) loss in primary open-angle glaucoma (POAG) and primary angle-closure glaucoma (PACG) across all severity levels.
Methods: A total of 522 eyes of 327 patients with POAG (mean age ± SD, 54.1 ± 12.4 years) and 375 eyes of 204 patients with PACG (67.3 ± 8.9 years) were included. Subjects meeting the definitions of POAG or PACG were included. Means of the total deviation (TD) values (Humphrey 24-2 VF) in the Glaucoma Hemifield Test (GHT) regions were calculated in early (â„ â6 dB), moderate (< â6 dB and â„ â12 dB), and advanced (< â12 dB) stages of POAG and PACG eyes. Then the differences of the TD values between superior and inferior hemifield GHT regions of POAG and PACG eyes were calculated. Also, the relationship between the values of pattern SD (PSD) and mean TD (mTD) was compared between POAG and PACG.
Results: In POAG eyes in the early stage, three regions (central, paracentral, and peripheral) in the superior hemifield had greater loss than their inferior counterparts; in moderate and advanced stages, all GHT regions in the superior hemifield had greater loss than their inferior counterparts. In PACG eyes, siginificantly fewer regions in the superior hemifield were significantly worse than their inferior counterpart, compared with POAG: one region (central) in early stage, two regions (central and peripheral) in moderate stage, and one region (central) in advanced stage. POAG eyes had greater PSD values than PACG eyes for given mean of TD values.
Conclusions: In both POAG and PACG eyes, VF damage was more pronounced in superior hemifield than inferior hemifield; however, this tendency was more obvious in POAG eyes than in PACG eyes
ASCA Observations of the Supernova Remnant IC 443: Thermal Structure and Detection of Overionized Plasma
We present the results of X-ray spatial and spectral studies of the
``mixed-morphology'' supernova remnant IC 443 using ASCA. IC 443 has a
center-filled image in X-ray band, contrasting with the shell-like appearance
in radio and optical bands. The overall X-ray emission is thermal, not from a
synchrotron nebula. ASCA observed IC 443 three times, covering the whole
remnant. From the image analysis, we found that the softness-ratio map reveals
a shell-like structure. At the same time, its spectra require two (1.0 keV and
0.2 keV) plasma components; the emission of the 0.2 keV plasma is stronger in
the region near the shell than the center. These results can be explained by a
simple model that IC 443 has a hot (1.0 keV) interior surrounded by a cool (0.2
keV) outer shell. From the emission measures, we infer that the 0.2 keV plasma
is denser than the 1.0 keV plasma, suggesting pressure equilibrium between the
two. In addition, we found that the ionization temperature of sulfur, obtained
from H-like K to He-like K intensity ratio, is 1.5 keV,
significantly higher than the gas temperature of 1.0 keV suggested from the
continuum spectrum. The same can be concluded for silicon. Neither an
additional, hotter plasma component nor a multi-temperature plasma successfully
accounts for this ratio, and we conclude that the 1.0 keV plasma is
overionized. This is the first time that overionized gas has been detected in a
SNR. For the gas to become overionized in the absence of a photoionizing flux,
it must cool faster than the ions recombine. Thermal conduction from the 1.0
keV plasma to the 0.2 keV one could cause the 1.0 keV plasma to become
overionized, which is plausible within an old (3 yr) SNR.Comment: 11 pages, 15 figures, 2 tables, accepted for publication in The
Astrophysical Journa
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