1,104 research outputs found
The STAR MAPS-based PiXeL detector
The PiXeL detector (PXL) for the Heavy Flavor Tracker (HFT) of the STAR
experiment at RHIC is the first application of the state-of-the-art thin
Monolithic Active Pixel Sensors (MAPS) technology in a collider environment.
Custom built pixel sensors, their readout electronics and the detector
mechanical structure are described in detail. Selected detector design aspects
and production steps are presented. The detector operations during the three
years of data taking (2014-2016) and the overall performance exceeding the
design specifications are discussed in the conclusive sections of this paper
Evaluation of the BCS Approximation for the Attractive Hubbard Model in One Dimension
The ground state energy and energy gap to the first excited state are
calculated for the attractive Hubbard model in one dimension using both the
Bethe Ansatz equations and the variational BCS wavefunction. Comparisons are
provided as a function of coupling strength and electron density. While the
ground state energies are always in very good agreement, the BCS energy gap is
sometimes incorrect by an order of magnitude, particularly at half-filling.
Finite size effects are also briefly discussed for cases where an exact
solution in the thermodynamic limit is not possible. In general, the BCS result
for the energy gap is poor compared to the exact result.Comment: 25 pages, 5 Postscript figure
The TANAMI Program
TANAMI (Tracking Active Galactic Nuclei with Austral Milliarcsecond
Interferometry) is a monitoring program to study the parsec-scale structures
and dynamics of relativistic jets in active galactic nuclei (AGN) of the
Southern Hemisphere with the Long Baseline Array and associated telescopes.
Extragalactic jets south of -30 degrees declination are observed at 8.4 GHz and
22 GHz every two months at milliarcsecond resolution. The initial TANAMI sample
is a hybrid radio and gamma-ray selected sample since the combination of VLBI
and gamma-ray observations is crucial to understand the broadband emission
characteristics of AGN.Comment: Confernce Proceedings for "X-ray Astronomy 2009" (Bologna), 3 pages,
3 figures, needs cls-fil
TANAMI - Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry
We present a summary of the observation strategy of TANAMI (Tracking Active
Galactic Nuclei with Austral Milliarcsecond Interferometry), a monitoring
program to study the parsec-scale structure and dynamics of relativistic jets
in active galactic nuclei (AGN) of the Southern Hemisphere with the Australian
Long Baseline Array (LBA) and the trans-oceanic antennas Hartebeesthoek, TIGO,
and O'Higgins. TANAMI is focusing on extragalactic sources south of -30 degrees
declination with observations at 8.4 GHz and 22 GHz every ~2 months at
milliarcsecond resolution. The initial TANAMI sample of 43 sources has been
defined before the launch of the Fermi Gamma Ray Space Telescope to include the
most promising candidates for bright gamma-ray emission to be detected with its
Large Area Telescope (LAT). Since November 2008, we have been adding new
sources to the sample, which now includes all known radio- and gamma-ray bright
AGN of the Southern Hemisphere. The combination of VLBI and gamma-ray
observations is crucial to understand the broadband emission characteristics of
AGN and the nature of relativistic jets.Comment: Conference proceedings "2009 Fermi Symposium" eConf Proceedings
C09112
Size of the Vela Pulsar's Emission Region at 18 cm Wavelength
We present measurements of the linear diameter of the emission region of the
Vela pulsar at observing wavelength lambda=18 cm. We infer the diameter as a
function of pulse phase from the distribution of visibility on the
Mopra-Tidbinbilla baseline. As we demonstrate, in the presence of strong
scintillation, finite size of the emission region produces a characteristic
W-shaped signature in the projection of the visibility distribution onto the
real axis. This modification involves heightened probability density near the
mean amplitude, decreased probability to either side, and a return to the
zero-size distribution beyond. We observe this signature with high statistical
significance, as compared with the best-fitting zero-size model, in many
regions of pulse phase. We find that the equivalent full width at half maximum
of the pulsar's emission region decreases from more than 400 km early in the
pulse to near zero at the peak of the pulse, and then increases again to
approximately 800 km near the trailing edge. We discuss possible systematic
effects, and compare our work with previous results
Gamma-ray emission in radio galaxies under the VLBI scope -- II. The relationship between gamma-ray emission and parsec-scale jets in radio galaxies
Following our study of the radio and high-energy properties of
-ray-emitting radio galaxies, here we investigate the kinematic and
spectral properties of the parsec-scale jets of radio galaxies that have not
yet been detected by Fermi-LAT. We take advantage of the regular VLBI
observations provided by the TANAMI monitoring program, and explore the
kinematic properties of six -ray-faint radio galaxies. We include
publicly available VLBI kinematics of -ray-quiet radio galaxies
monitored by the MOJAVE program and perform a Fermi-LAT analysis, deriving
upper limits. We combine these results with those from our previous paper to
construct the largest sample of radio galaxies with combined VLBI and
-ray measurements to date. We find superluminal motion up to
in the jet of PKS 215369. We find a clear trend of
higher apparent speed as a function of distance from the jet core on scales of
, corresponding to the end of the collimation and acceleration
zone in nearby radio galaxies. We find evidence of subluminal apparent motion
in the jets of PKS 1258321 and IC 4296, and no measurable motion for PKS
154979, PKS 1733565 and PKS 2027308. We compare the VLBI properties of
-ray-detected and undetected radio galaxies, and find significantly
different distributions of median core flux density, and, possibly, of median
core brightness temperature. We find a significant correlation between median
core flux density and -ray flux, but no correlation with typical
Doppler boosting indicators such as median core brightness temperature and core
dominance. Our study suggests that high-energy emission from radio galaxies is
related to parsec-scale radio emission from the inner jet, but is not driven by
Doppler boosting effects, in contrast to the situation in their blazar
counterparts.Comment: Main text: 15 pages, 12 figures, 6 tables. Appendix: 14 pages, 20
figures, 13 tables. Accepted for publication in Astronomy and Astrophysic
Finite Temperature Time-Dependent Effective Theory for the Phase Field in two-dimensional d-wave Neutral Superconductor
We derive finite temperature time-dependent effective actions for the phase
of the pairing field, which are appropriate for a 2D electron system with both
non-retarded d- and s-wave attraction. As for s-wave pairing the d-wave
effective action contains terms with Landau damping, but their structure
appears to be different from the s-wave case due to the fact that the Landau
damping is determined by the quasiparticle group velocity v_{g}, which for
d-wave pairing does not have the same direction as the non-interacting Fermi
velocity v_{F}. We show that for d-wave pairing the Landau term has a linear
low temperature dependence and in contrast to the s-wave case are important for
all finite temperatures. A possible experimental observation of the phase
excitations is discussed.Comment: 23 pages, RevTeX4, 10 EPS figures; final version to appear in PR
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