439 research outputs found
Fluxes of atmospheric muons underwater depending on the small-x gluon density
The prompt muon contribution to the deep-sea atmospheric muon flux can serve
as a tool for probing into the small-x feature of the gluon density inside of a
nucleon, if the muon energy threshold could be lifted to 100 TeV. The prompt
muon flux underwater is calculated taking into consideration predictions of
recent charm production models in which the small-x behaviour of the gluon
distribution is probed. We discuss the possibility of distinguishing the PQCD
models of the charm production differing in the small-x exponent of the gluon
distribution, in measurements of the muon flux at energies 10-100 TeV with
neutrino telescopes.Comment: 9 pages, 4 eps figures, uses iopart.st
Extracting Electron-Ion Differential Scattering Cross Sections for Partially Aligned Molecules by Laser-Induced Rescattering Photoelectron Spectroscopy
Bremsstrahlung Suppression due to the LPM and Dielectric Effects in a Variety of Materials
The cross section for bremsstrahlung from highly relativistic particles is
suppressed due to interference caused by multiple scattering in dense media,
and due to photon interactions with the electrons in all materials. We present
here a detailed study of bremsstrahlung production of 200 keV to 500 MeV
photons from 8 and 25 GeV electrons traversing a variety of target materials.
For most targets, we observe the expected suppressions to a good accuracy. We
observe that finite thickness effects are important for thin targets.Comment: 52 pages, 13 figures (incorporated in the revtex LaTeX file
Detection of an iron K Emission Line from the LINER NGC 4579
We present the results of an ASCA observation of the LINER NGC 4579. A
point-like X-ray source is detected at the nucleus with a 2-10 keV luminosity
of 1.5x10^41 ergs/s assuming a distance of 16.8 Mpc. The X-ray spectrum is
represented by a combination of a power-law with a photon index of ~1.7 and
soft thermal component with kT~0.9 keV. An iron K emission line is detected at
6.73+/-0.13 keV (rest frame) with an equivalent width of 490 +180/-190 eV and
is statistically significant at more than 99.9 % confidence. The line center
energy is consistent with Helium-like iron and is significantly higher than 6.4
keV which is expected from fluorescence by "cold" (or a lower ionization state
of) iron. The iron line profile shows no significant red tail in contrast to
Seyfert 1 galaxies although the statistics are limited. The line center energy,
equivalent width, and profile are consistent with an origin in an ionized
accretion disk. However the large mass accretion rate necessary to ionize the
accretion disk is not consistent with the observed luminosity and normal
accretion models.Comment: 15 pages, 5 figures, to appear in The Astrophysical Journa
Development of Hydrophones for Detecting High-Energy Reactions in Water(III. Accelerator, Synchrotron Radiation, and Instrumentation)
Acoustic detectors were developed using a piezo ceramic compound PZT. A shape of the PZT detector was essential to obtain a high sensitivity. A detector of a spherically shaped shell structure, whose size was 50 mm in diameter and 2 mm thick, was fabricated. Its sensitivity was calibrated to be about 40 mV/Pa at 54 kHz. Using the hydrophone, acoustic signals generated by an electron-induced cascade shower in water were detected. Experimental results were compared with simulation data and confirmed a consistency in between
Iron K line Variability in the Low-Luminosity AGN NGC 4579
We present results of new ASCA observations of the low-luminosity AGN (LLAGN)
NGC 4579 obtained on 1998 December 18 and 28, and we report on detection of
variability of an iron K emission line. The X-ray luminosities in the 2--10 keV
band for the two observations are nearly identical (LX
2 ergs/s), but they are 35% larger than that measured in
1995 July by Terashima et al. An Fe K emission line is detected at
keV (source rest frame) which is lower than the line energy
keV in the 1995 observation. If we fit the Fe lines with
a blend of two Gaussians centered at 6.39 keV and 6.73 keV, the intensity of
the 6.7 keV line decreases, while the intensity of the 6.4 keV line increases,
within an interval of 3.5 yr. This variability rules out thermal plasmas in the
host galaxy as the origin of the ionized Fe line in this LLAGN. The detection
and variability of the 6.4 keV line indicates that cold matter subtends a large
solid angle viewed from the nucleus and that it is located within pc
from the nucleus. It could be identified with an optically thick standard
accretion disk. If this is the case, a standard accretion disk is present at
the Eddington ratio of . A
broad disk-line profile is not clearly seen and the structure of the innermost
part of accretion disk remains unclear.Comment: 9 pages, 3 figures, To appear in the Astrophyscal Jounal Letter
Atmospheric muon flux at PeV energies
In the near future the energy region above few hundreds of TeV may really be
accessible for measurements of the atmospheric muon spectrum by the IceCube
array. Therefore one expects that muon flux uncertainties above 50 TeV, related
to a poor knowledge of charm production cross sections and insufficiently
examined primary spectra and composition, will be diminished. We give
predictions for the very high-energy muon spectrum at sea level, obtained with
the three hadronic interaction models, taking into account also the muon
contribution due to decays of the charmed hadrons.Comment: 8 pages, 3 figures. The version published in Int. J. Mod. Phys.
Assembly of α-Glucan by GlgE and GlgB in Mycobacteria and Streptomycetes
Actinomycetes, such as mycobacteria and streptomycetes, synthesize α-glucan with α-1,4 linkages and α-1,6 branching to help evade immune responses and to store carbon. α-Glucan is thought to resemble glycogen except for having shorter constituent linear chains. However, the fine structure of α-glucan and how it can be defined by the maltosyl transferase GlgE and branching enzyme GlgB were not known. Using a combination of enzymolysis and mass spectrometry, we compared the properties of α-glucan isolated from actinomycetes with polymer synthesized in vitro by GlgE and GlgB. We now propose the following assembly mechanism. Polymer synthesis starts with GlgE and its donor substrate, α-maltose 1-phosphate, yielding a linear oligomer with a degree of polymerization (âŒ16) sufficient for GlgB to introduce a branch. Branching involves strictly intrachain transfer to generate a C chain (the only constituent chain to retain its reducing end), which now bears an A chain (a nonreducing end terminal branch that does not itself bear a branch). GlgE preferentially extends A chains allowing GlgB to act iteratively to generate new A chains emanating from B chains (nonterminal branches that themselves bear a branch). Although extension and branching occur primarily with A chains, the other chain types are sometimes extended and branched such that some B chains (and possibly C chains) bear more than one branch. This occurs less frequently in α-glucans than in classical glycogens. The very similar properties of cytosolic and capsular α-glucans from Mycobacterium tuberculosis imply GlgE and GlgB are sufficient to synthesize them both
Atmospheric Muon Flux at Sea Level, Underground, and Underwater
The vertical sea-level muon spectrum at energies above 1 GeV and the
underground/underwater muon intensities at depths up to 18 km w.e. are
calculated. The results are particularly collated with a great body of the
ground-level, underground, and underwater muon data. In the hadron-cascade
calculations, the growth with energy of inelastic cross sections and pion,
kaon, and nucleon generation in pion-nucleus collisions are taken into account.
For evaluating the prompt muon contribution to the muon flux, we apply two
phenomenological approaches to the charm production problem: the recombination
quark-parton model and the quark-gluon string model. To solve the muon
transport equation at large depths of homogeneous medium, a semi-analytical
method is used. The simple fitting formulas describing our numerical results
are given. Our analysis shows that, at depths up to 6-7 km w. e., essentially
all underground data on the muon intensity correlate with each other and with
predicted depth-intensity relation for conventional muons to within 10%.
However, the high-energy sea-level data as well as the data at large depths are
contradictory and cannot be quantitatively decribed by a single nuclear-cascade
model.Comment: 47 pages, REVTeX, 15 EPS figures included; recent experimental data
and references added, typos correcte
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