1,128 research outputs found
Parity Effects in Stacked Nanoscopic Quantum Rings
The ground state and the dielectric response of stacked quantum rings are
investigated in the presence of an applied magnetic field along the ring axis.
For odd number of rings and an electric field perpendicular to the axis, a
linear Stark effect occurs at distinct values of the magnetic field. At those
fields energy levels cross in the absence of electric field. For even values of
a quadratic Stark effect is expected in all cases, but the induced electric
polarization is discontinuous at those special magnetic fields. Experimental
consequences for related nanostructures are discussed.Comment: typos corrected, to appear Phys. Rev. B (Rapid Communication) 15 Au
Interfaces with a single growth inhomogeneity and anchored boundaries
The dynamics of a one dimensional growth model involving attachment and
detachment of particles is studied in the presence of a localized growth
inhomogeneity along with anchored boundary conditions. At large times, the
latter enforce an equilibrium stationary regime which allows for an exact
calculation of roughening exponents. The stochastic evolution is related to a
spin Hamiltonian whose spectrum gap embodies the dynamic scaling exponent of
late stages. For vanishing gaps the interface can exhibit a slow morphological
transition followed by a change of scaling regimes which are studied
numerically. Instead, a faceting dynamics arises for gapful situations.Comment: REVTeX, 11 pages, 9 Postscript figure
A Bayesian view of the current status of dark matter direct searches
Bayesian statistical methods offer a simple and consistent framework for
incorporating uncertainties into a multi-parameter inference problem. In this
work we apply these methods to a selection of current direct dark matter
searches. We consider the simplest scenario of spin-independent elastic WIMP
scattering, and infer the WIMP mass and cross-section from the experimental
data with the essential systematic uncertainties folded into the analysis. We
find that when uncertainties in the scintillation efficiency of Xenon100 have
been accounted for, the resulting exclusion limit is not sufficiently
constraining to rule out the CoGeNT preferred parameter region, contrary to
previous claims. In the same vein, we also investigate the impact of
astrophysical uncertainties on the preferred WIMP parameters. We find that
within the class of smooth and isotropic WIMP velocity distributions, it is
difficult to reconcile the DAMA and the CoGeNT preferred regions by tweaking
the astrophysics parameters alone. If we demand compatibility between these
experiments, then the inference process naturally concludes that a high value
for the sodium quenching factor for DAMA is preferred.Comment: 37 pages, 14 figures and 7 tables. Replacement for matching the
version accepted for publicatio
SRAO CO Observation of 11 Supernova Remnants in l = 70 to 190 deg
We present the results of 12CO J = 1-0 line observations of eleven Galactic
supernova remnants (SNRs) obtained using the Seoul Radio Astronomy Observatory
(SRAO) 6-m radio telescope. The observation was made as a part of the SRAO CO
survey of SNRs between l = 70 and 190 deg, which is intended to identify SNRs
interacting with molecular clouds. The mapping areas for the individual SNRs
are determined to cover their full extent in the radio continuum. We used
halfbeam grid spacing (60") for 9 SNRs and full-beam grid spacing (120") for
the rest. We detected CO emission towards most of the remnants. In six SNRs,
molecular clouds showed a good spatial relation with their radio morphology,
although no direct evidence for the interaction was detected. Two SNRs are
particularly interesting: G85.4+0.7, where there is a filamentary molecular
cloud along the radio shell, and 3C434.1, where a large molecular cloud appears
to block the western half of the remnant. We briefly summarize the results
obtained for individual SNRs.Comment: Accepted for publication in Astrophysics & Space Science. 12 pages,
12 figures, and 3 table
A cognitive framework for the categorisation of auditory objects in urban soundscapes
Categorisation is a fundamental cognitive process that plays a central role in
everyday behaviour and action. Whereas previous studies have investigated the
categorisation of isolated everyday sounds, this paper presents an experiment to
investigate the cognitive categorisation of everyday sounds within their original
context. A group of eighteen expert and non-expert listeners took part in a free
sorting task using 110 sounds identified within ambisonic reproductions of urban
soundscapes. The participants were asked to sort the objects into groups of
sounds that served a similar purpose in the overall perception of the soundscape.
Following this, the participants were asked to provide descriptive labels for the
groups they had formed. The results were analysed using hierarchical agglomerative
clustering and non-metric multidimensional scaling (MDS) to explore
both the structure and dimensionality of the data. The resulting hierarchical
clustering of objects show three top level categories relating to transient sounds,
continuous sounds, and speech and vocalisations. Sub-categories were identified
in each of the top level categories which included harmonic and non-harmonic
continuous sounds, clear speech, unintelligible speech, vocalisations, transient
sounds that indicate actions, and non-salient transient sounds. The first two
dimensions revealed by the MDS analysis relate to temporal extent and intelligibility
respectively. Interpretation of the third dimension is less clear, but may be related to harmonic content
The effects of sample position and gas flow pattern on the sintering of a 7xxx aluminum alloy
The effects of sample position and gas flow pattern on the sintering of a 7xxx aluminum alloy Al-7Zn-2.5Mg-1Cu in flowing nitrogen have been investigated both experimentally and numerically. The near-surface pore distribution and sintered density of the samples show a strong dependency on the sample separation distance over the range from 2 mm to 40 mm. The open porosity in each sample increases with increasing separation distance while the closed porosity remains essentially unchanged. A two-dimensional computational fluid dynamics (CFD) model has been developed to analyze the gas flow behavior near the sample surfaces during isothermal sintering. The streamlines, velocity profile, and volume flow rate in the cavity between each two samples are presented as a function of the sample separation distance at a fixed nitrogen flow rate of 6 L/min. The CFD modeling results provide essential details for understanding the near-surface pore distribution and density of the sintered samples. It is proposed that the different gas flow patterns near the sample surfaces result in variations of the oxygen content from the incoming nitrogen flow in the local sintering atmosphere, which affects the self-gettering process of the aluminum compacts during sintering. This leads to the development of different near-surface pore distributions and sintered densities
A Measurement of the Branching Fraction for the Inclusive B --> X(s) gamma Decays with the Belle Detector
We have measured the branching fraction of the inclusive radiative B meson
decay B --> X(s) gamma to be Br(B->X(s)gamma)=(3.36 +/- 0.53(stat) +/-
0.42(sys) +0.50-0.54(th)) x 10^{-4}.
The result is based on a sample of 6.07 x 10^6 BBbar events collected at the
Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric e^+e^-
storage ring.Comment: 14 pages, 6 Postsript figures, uses elsart.cl
Longitudinal double-spin asymmetry and cross section for inclusive neutral pion production at midrapidity in polarized proton collisions at sqrt(s) = 200 GeV
We report a measurement of the longitudinal double-spin asymmetry A_LL and
the differential cross section for inclusive Pi0 production at midrapidity in
polarized proton collisions at sqrt(s) = 200 GeV. The cross section was
measured over a transverse momentum range of 1 < p_T < 17 GeV/c and found to be
in good agreement with a next-to-leading order perturbative QCD calculation.
The longitudinal double-spin asymmetry was measured in the range of 3.7 < p_T <
11 GeV/c and excludes a maximal positive gluon polarization in the proton. The
mean transverse momentum fraction of Pi0's in their parent jets was found to be
around 0.7 for electromagnetically triggered events.Comment: 6 pages, 3 figures, submitted to Phys. Rev. D (RC
Azimuthal anisotropy and correlations in p+p, d+Au and Au+Au collisions at 200 GeV
We present the first measurement of directed flow () at RHIC. is
found to be consistent with zero at pseudorapidities from -1.2 to 1.2,
then rises to the level of a couple of percent over the range . The latter observation is similar to data from NA49 if the SPS rapidities
are shifted by the difference in beam rapidity between RHIC and SPS.
Back-to-back jets emitted out-of-plane are found to be suppressed more if
compared to those emitted in-plane, which is consistent with {\it jet
quenching}. Using the scalar product method, we systematically compared
azimuthal correlations from p+p, d+Au and Au+Au collisions. Flow and non-flow
from these three different collision systems are discussed.Comment: Quark Matter 2004 proceeding, 4 pages, 3 figure
Azimuthal anisotropy: the higher harmonics
We report the first observations of the fourth harmonic (v_4) in the
azimuthal distribution of particles at RHIC. The measurement was done taking
advantage of the large elliptic flow generated at RHIC. The integrated v_4 is
about a factor of 10 smaller than v_2. For the sixth (v_6) and eighth (v_8)
harmonics upper limits on the magnitudes are reported.Comment: 4 pages, 6 figures, contribution to the Quark Matter 2004 proceeding
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