2,208 research outputs found
condensate for light quarks beyond the chiral limit
We determine the condensate for quark masses from zero up to
that of the strange quark within a phenomenologically successful modelling of
continuum QCD by solving the quark Schwinger-Dyson equation. The existence of
multiple solutions to this equation is the key to an accurate and reliable
extraction of this condensate using the operator product expansion. We explain
why alternative definitions fail to give the physical condensate.Comment: 13 pages, 8 figure
Graph Treewidth and Geometric Thickness Parameters
Consider a drawing of a graph in the plane such that crossing edges are
coloured differently. The minimum number of colours, taken over all drawings of
, is the classical graph parameter "thickness". By restricting the edges to
be straight, we obtain the "geometric thickness". By further restricting the
vertices to be in convex position, we obtain the "book thickness". This paper
studies the relationship between these parameters and treewidth.
Our first main result states that for graphs of treewidth , the maximum
thickness and the maximum geometric thickness both equal .
This says that the lower bound for thickness can be matched by an upper bound,
even in the more restrictive geometric setting. Our second main result states
that for graphs of treewidth , the maximum book thickness equals if and equals if . This refutes a conjecture of Ganley and
Heath [Discrete Appl. Math. 109(3):215-221, 2001]. Analogous results are proved
for outerthickness, arboricity, and star-arboricity.Comment: A preliminary version of this paper appeared in the "Proceedings of
the 13th International Symposium on Graph Drawing" (GD '05), Lecture Notes in
Computer Science 3843:129-140, Springer, 2006. The full version was published
in Discrete & Computational Geometry 37(4):641-670, 2007. That version
contained a false conjecture, which is corrected on page 26 of this versio
Novel deep learning approach to model and predict the spread of COVID-19
SARS-CoV2, which causes coronavirus disease (COVID-19) is continuing to spread globally, producing new variants and has become a pandemic. People have lost their lives not only due to the virus but also because of the lack of counter measures in place. Given the increasing caseload and uncertainty of spread, there is an urgent need to develop robust artificial intelligence techniques to predict the spread of COVID-19. In this paper, we propose a deep learning technique, called Deep Sequential Prediction Model (DSPM) and machine learning based Non-parametric Regression Model (NRM) to predict the spread of COVID-19. Our proposed models are trained and tested on publicly available novel coronavirus dataset. The proposed models are evaluated by using Mean Absolute Error and compared with the existing methods for the prediction of the spread of COVID-19. Our experimental results demonstrate the superior prediction performance of the proposed models. The proposed DSPM and NRM achieve MAEs of 388.43 (error rate 1.6%) and 142.23 (0.6%), respectively compared to 6508.22 (27%) achieved by baseline SVM, 891.13 (9.2%) by Time-Series Model (TSM), 615.25 (7.4%) by LSTM-based Data-Driven Estimation Method (DDEM) and 929.72 (8.1%) by Maximum-Hasting Estimation Method (MHEM)
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Analysis of differential protein expression in normal and neoplastic human breast epithelial cell lines
High resolution two dimensional get electrophoresis (2DE) and database analysis was used to establish protein expression patterns for cultured normal human mammary epithelial cells and thirteen breast cancer cell lines. The Human Breast Epithelial Cell database contains the 2DE protein patterns, including relative protein abundances, for each cell line, plus a composite pattern that contains all the common and specifically expressed proteins from all the cell lines. Significant differences in protein expression, both qualitative and quantitative, were observed not only between normal cells and tumor cells, but also among the tumor cell lines. Eight percent of the consistently detected proteins were found in significantly (P < 0.001) variable levels among the cell lines. Using a combination of immunostaining, comigration with purified protein, subcellular fractionation, and amino-terminal protein sequencing, we identified a subset of the differentially expressed proteins. These identified proteins include the cytoskeletal proteins actin, tubulin, vimentin, and cytokeratins. The cell lines can be classified into four distinct groups based on their intermediate filament protein profile. We also identified heat shock proteins; hsp27, hsp60, and hsp70 varied in abundance and in some cases in the relative phosphorylation levels among the cell lines. Finally, we identified IMP dehydrogenase in each of the cell lines, and found the levels of this enzyme in the tumor cell lines elevated 2- to 20-fold relative to the levels in normal cells
The second and third Sonine coefficients of a freely cooling granular gas revisited
In its simplest statistical-mechanical description, a granular fluid can be
modeled as composed of smooth inelastic hard spheres (with a constant
coefficient of normal restitution ) whose velocity distribution
function obeys the Enskog-Boltzmann equation. The basic state of a granular
fluid is the homogeneous cooling state, characterized by a homogeneous,
isotropic, and stationary distribution of scaled velocities, .
The behavior of in the domain of thermal velocities ()
can be characterized by the two first non-trivial coefficients ( and
) of an expansion in Sonine polynomials. The main goals of this paper are
to review some of the previous efforts made to estimate (and measure in
computer simulations) the -dependence of and , to report new
computer simulations results of and for two-dimensional systems,
and to investigate the possibility of proposing theoretical estimates of
and with an optimal compromise between simplicity and accuracy.Comment: 12 pages, 5 figures; v2: minor change
Nonperturbative structure of the quark-gluon vertex
The complete tensor structure of the quark--gluon vertex in Landau gauge is
determined at two kinematical points (`asymmetric' and `symmetric') from
lattice QCD in the quenched approximation. The simulations are carried out at
beta=6.0, using a mean-field improved Sheikholeslami-Wohlert fermion action,
with two quark masses ~ 60 and 115 MeV. We find substantial deviations from the
abelian form at the asymmetric point. The mass dependence is found to be
negligible. At the symmetric point, the form factor related to the
chromomagnetic moment is determined and found to contribute significantly to
the infrared interaction strength.Comment: 16 pages, 11 figures, JHEP3.cl
Diffuse light and galaxy interactions in the core of nearby clusters
The kinematics of the diffuse light in the densest regions of the nearby
clusters can be unmasked using the planetary nebulae (PNs) as probes of the
stellar motions. The position-velocity diagrams around the brightest cluster
galaxies (BCGs) identify the relative contributions from the outer halos and
the intracluster light (ICL), defined as the light radiated by the stars
floating in the cluster potential. The kinematics of the ICL can then be used
to asses the dynamical status of the nearby cluster cores and to infer their
formation histories. The cores of the Virgo and Coma are observed to be far
from equilibrium, with mergers currently on-going, while the ICL properties in
the Fornax and Hydra clusters show the presence of sub-components being
accreted in their cores, but superposed to an otherwise relaxed population of
stars. Finally the comparison of the observed ICL properties with those
predicted from Lambda-CDM simulations indicates a qualitative agreement and
provides insights on the ICL formation. Both observations and simulations
indicate that BCG halos and ICL are physically distinct components, with the
``hotter" ICL dominating at large radial distances from the BCGs halos as the
latter become progressively fainter.Comment: 14 pages, 5 figures. Invited review to appear in the proceedings of
"Galaxies and their masks" eds. Block, D.L., Freeman, K.C. and Puerari, I.,
2010, Springer (New York
Atom gratings produced by large angle atom beam splitters
An asymptotic theory of atom scattering by large amplitude periodic
potentials is developed in the Raman-Nath approximation. The atom grating
profile arising after scattering is evaluated in the Fresnel zone for
triangular, sinusoidal, magneto-optical, and bichromatic field potentials. It
is shown that, owing to the scattering in these potentials, two
\QTR{em}{groups} of momentum states are produced rather than two distinct
momentum components. The corresponding spatial density profile is calculated
and found to differ significantly from a pure sinusoid.Comment: 16 pages, 7 figure
Novae Ejecta as Colliding Shells
Following on our initial absorption-line analysis of fifteen novae spectra we
present additional evidence for the existence of two distinct components of
novae ejecta having different origins. As argued in Paper I one component is
the rapidly expanding gas ejected from the outer layers of the white dwarf by
the outburst. The second component is pre-existing outer, more slowly expanding
circumbinary gas that represents ejecta from the secondary star or accretion
disk. We present measurements of the emission-line widths that show them to be
significantly narrower than the broad P Cygni profiles that immediately precede
them. The emission profiles of novae in the nebular phase are distinctly
rectangular, i.e., strongly suggestive of emission from a relatively thin,
roughly spherical shell. We thus interpret novae spectral evolution in terms of
the collision between the two components of ejecta, which converts the early
absorption spectrum to an emission-line spectrum within weeks of the outburst.
The narrow emission widths require the outer circumbinary gas to be much more
massive than the white dwarf ejecta, thereby slowing the latter's expansion
upon collision. The presence of a large reservoir of circumbinary gas at the
time of outburst is suggestive that novae outbursts may sometime be triggered
by collapse of gas onto the white dwarf, as occurs for dwarf novae, rather than
steady mass transfer through the inner Lagrangian point.Comment: 12 pages, 3 figures; Revised manuscript; Accepted for publication in
Astrophysics & Space Scienc
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