3,312 research outputs found
The effect of the environment on the Faber Jackson relation
We investigate the effect of the environment on the Faber Jackson (FJ)
relation, using a sample of 384 nearby elliptical galaxies and estimating
objectively their environment on the typical scale of galaxy clusters. We show
that the intrinsic scatter of the FJ is significantly reduced when ellipticals
in high density environments are compared to ellipticals in low density ones.
This result, which holds on a limited range of overdensities, is likely to
provide an important observational link between scaling relations and formation
mechanisms in galaxies.Comment: accepted by Ap
The T2K experiment
The T2K experiment is a long baseline neutrino oscillation experiment. Its main goal is to measure the last unknown lepton sector mixing angle theta(13) by observing nu(e) appearance in a nu(mu) beam. It also aims to make a precision measurement of the known oscillation parameters, Delta m(23)(2) and sin(2)2 theta(23), via nu(mu) disappearance studies. Other goals of the experiment include various neutrino cross-section measurements and sterile neutrino searches. The experiment uses an intense proton beam generated by the J-PARC accelerator in Tokai, Japan, and is composed of a neutrino beamline, a near detector complex (ND280), and a far detector (Super-Kamiokande) located 295 km away from J-PARC. This paper provides a comprehensive review of the instrumentation aspect of the T2K experiment and a summary of the vital information for each subsystem. (C) 2011 Elsevier B.V. All rights reserved
Photon Structure and Quantum Fluctuation
Photon structure derives from quantum fluctuation in quantum field theory to
fermion and anti-fermion, and has been an experimentally established feature of
electrodynamics since the discovery of the positron. In hadronic physics, the
observation of factorisable photon structure is similarly a fundamental test of
the quantum field theory Quantum Chromodynamics (QCD). An overview of
measurements of hadronic photon structure in e+e- and ep interactions is
presented, and comparison made with theoretical expectation, drawing on the
essential features of photon fluctuation into quark and anti-quark in QCD.Comment: 29 pages, 15 figures, to appear in Philosophical Transactions of the
Royal Society of London (Series A: Mathematical, Physical and Engineering
Sciences
The performance of thin NaI(Tl) scintillator plate for dark matter search
A thin (0.05cm) and wide area (5cmX5cm) NaI(Tl) scintillator was developed.
The performance of the thin NaI(Tl) plate, energy resolution, single
photoelectron energy and position sensitivity were tested. An excellent energy
resolution of 20% (FWHM) at 60keV was obtained. The single photoelectron energy
was calculated to be approximately 0.42 0.02keV. Position information in the
5cmx5cm area of the detector was also obtained by analyzing the ratio of the
number of photons collected at opposite ends of the detector. The position
resolution was obtained to be 1cm (FWHM) in the 5cmx5cm area.Comment: 10 pages. Accepted to Journal of Physical Society of Japa
Development of a dose distribution shifter to fit inside the collimator of a Boron Neutron Capture Therapy irradiation system to treat superficial tumours
The Kansai BNCT Medical Center has a cyclotron based epithermal neutron source for clinical Boron Neutron Capture Therapy. The system accelerates a proton to an energy of 30 MeV which strikes a beryllium target producing fast neutrons which are moderated down to epithermal neutrons for BNCT use. While clinical studies in the past have shown BNCT to be highly effective for malignant melanoma of the skin, to apply BNCT for superficial lesions using this system it is necessary to shift the thermal neutron distribution so that the maximum dose occurs near the surface. A dose distribution shifter was designed to fit inside the collimator to further moderate the neutrons to increase the surface dose and reduce the dose to the underlying normal tissue. Pure polyethylene was selected, and a Monte Carlo simulation was performed to determine the optimum thickness of the polyethylene slab. Compared with the original neutron beam, the shifter increased the thermal neutron flux at the skin by approximately 4 times. The measured and simulated central axis depth distribution and off axis distribution of the thermal neutron flux were found to be in good agreement. Compared with a 2 cm thick water equivalent bolus, a 26% increase in the thermal neutron flux at the surface was obtained, which would reduce the treatment time by approximately 29%. The DDS is a safe, simple and an effective tool for the treatment of superficial tumours for BNCT if an initially fast neutron beam requires moderation to maximise the thermal neutron flux at the tissue surface
Optical photometric GTC/OSIRIS observations of the young massive association Cygnus OB2
In order to fully understand the gravitational collapse of molecular clouds,
the star formation process and the evolution of circumstellar disks, these
phenomena must be studied in different Galactic environments with a range of
stellar contents and positions in the Galaxy. The young massive association
Cygnus OB2, in the Cygnus-X region, is an unique target to study how star
formation and the evolution of circumstellar disks proceed in the presence of a
large number of massive stars. We present a catalog obtained with recent
optical observations in r,i,z filters with OSIRIS, mounted on the GTC
telescope, which is the deepest optical catalog of Cyg OB2 to date.
The catalog consist of 64157 sources down to M=0.15 solar masses at the
adopted distance and age of Cyg OB2. A total of 38300 sources have good
photometry in all three bands. We combined the optical catalog with existing
X-ray data of this region, in order to define the cluster locus in the optical
diagrams. The cluster locus in the r-i vs. i-z diagram is compatible with an
extinction of the optically selected cluster members in the 2.64<AV<5.57 range.
We derive an extinction map of the region, finding a median value of AV=4.33 in
the center of the association, decreasing toward the north-west. In the
color-magnitude diagrams, the shape of the distribution of main sequence stars
is compatible with the presence of an obscuring cloud in the foreground at
about 850+/-25 pc from the Sun.Comment: Accepted for publication ApJS 201
Transformations between WISE, 2MASS, SDSS and BVRI photometric systems: I. Transformation equations for dwarfs
We present colour transformations for the conversion of the W1 and W2
magnitudes of WISE photometric system to the Johnson-Cousins' BVRI, SDSS (gri),
and 2MASS (JHK_s) photometric systems, for dwarfs. The W3 and W4 magnitudes
were not considered due to their insufficient signal to noise ratio (S/N). The
coordinates of 825 dwarfs along with their BVRI, gri, and JHK_s data, taken
from Bilir et al. (2008) were matched with the coordinates of stars in the
preliminary data release of WISE (Wright et al., 2010) and a homogeneous dwarf
sample with high S/N ratio have been obtained using the following constraints:
1) the data were dereddened, 2) giants were identified and excluded from the
sample, 3) sample stars were selected according to data quality, 4)
transformations were derived for sub samples of different metallicity range,
and 5) transformations are two colour dependent. These colour transformations,
coupled with known absolute magnitudes at shorter wavelenghts, can be used in
space density evaluation for the Galactic (thin and thick) discs, at distances
larger than the ones evaluated with JHK_s photometry.Comment: 16 pages, including 5 figures and 7 tables, accepted for publication
in MNRA
Scale Dependence of Halo Bispectrum from Non-Gaussian Initial Conditions in Cosmological N-body Simulations
We study the halo bispectrum from non-Gaussian initial conditions. Based on a
set of large -body simulations starting from initial density fields with
local type non-Gaussianity, we find that the halo bispectrum exhibits a strong
dependence on the shape and scale of Fourier space triangles near squeezed
configurations at large scales. The amplitude of the halo bispectrum roughly
scales as . The resultant scaling on the triangular shape is consistent
with that predicted by Jeong & Komatsu based on perturbation theory. We
systematically investigate this dependence with varying redshifts and halo mass
thresholds. It is shown that the dependence of the halo bispectrum is
stronger for more massive haloes at higher redshifts. This feature can be a
useful discriminator of inflation scenarios in future deep and wide galaxy
redshift surveys.Comment: 27 pages, 10 figures; revised argument in section 6, added appendix
C, JCAP accepted versio
Multiple hadron production in e+e- annihilation induced by heavy primary quarks. New analysis
In this paper we present an analysis of the multiple hadron production
induced by primary heavy quarks in e+e- annihilation with the account of most
complete and corrected experimental data. In the framework of perturbative QCD,
new theoretical bounds on the asymptotically constant differences of the
multiplicities in processes with light and heavy quarks are given.Comment: 26 pages, 7 figures, to be published in Particles & Nucle
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