2,257 research outputs found
Gauge Field Strength Tensor from the Overlap Dirac Operator
We derive the classical continuum limit of the operator tr with being the overlap Dirac operator and show that it
corresponds to the gauge field strength tensor .Comment: 17 page
Instanton dominance of topological charge fluctuations in QCD?
We consider the local chirality of near-zero eigenvectors from Wilson-Dirac
and clover improved Wilson-Dirac lattice operators as proposed recently by
Horv\'ath et al. We studied finer lattices and repaired for the loss of
orthogonality due to the non-normality of the Wilson-Dirac matrix. As a result
we do see a clear double peak structure on lattices with resolutions higher
than 0.1 fm. We found that the lattice artifacts can be considerably reduced by
exploiting the biorthogonal system of left and right eigenvectors. We conclude
that the dominance of instantons on topological charge fluctuations is not
ruled out by local chirality measurements.Comment: 10 pages, 6 figure
Further Study of the Gamma-Ray Bursts Duration Distribution
Two classes of gamma-ray bursts have been identified so far, characterized by
durations shorter and longer than approximately 2 seconds. In 1998 two
independent papers indicated the existence of the third class of the bursts
roughly duration between 2 and 10 seconds. In this paper, using the full BATSE
Catalog, the maximum likelihood estimation is presented, which gives a 0.5%
probability to having only two subclasses. The Monte-Carlo simulation confirms
this probability, too.Comment: submitted to A&
Low-Dimensional Long-Range Topological Charge Structure in the QCD Vacuum
While sign-coherent 4-dimensional structures cannot dominate topological
charge fluctuations in the QCD vacuum at all scales due to reflection
positivity, it is possible that enhanced coherence exists over extended
space-time regions of lower dimension. Using the overlap Dirac operator to
calculate topological charge density, we present evidence for such structure in
pure-glue SU(3) lattice gauge theory. It is found that a typical equilibrium
configuration is dominated by two oppositely-charged sign-coherent connected
structures (``sheets'') covering about 80% of space-time. Each sheet is built
from elementary 3-d cubes connected through 2-d faces, and approximates a
low-dimensional curved manifold (or possibly a fractal structure) embedded in
the 4-d space. At the heart of the sheet is a ``skeleton'' formed by about 18%
of the most intense space-time points organized into a global long-range
structure, involving connected parts spreading over maximal possible distances.
We find that the skeleton is locally 1-dimensional and propose that its
geometrical properties might be relevant for understanding the possible role of
topological charge fluctuations in the physics of chiral symmetry breaking.Comment: 4 pages RevTeX, 4 figures; v2: 6 pages, 5 figures, more explanations
provided, figure and references added, published versio
Topological Charge Fluctuations and Low-Lying Dirac Eigenmodes
We discuss the utility of low-lying Dirac eigenmodes for studying the nature
of topological charge fluctuations in QCD. The implications of previous results
using the local chirality histogram method are discussed, and the new results
using the overlap Dirac operator in Wilson gauge backgrounds at lattice
spacings ranging from a~0.04 fm to a~0.12 fm are reported. While the degree of
local chirality does not change appreciably closer to the continuum limit, we
find that the size and density of local structures responsible for chiral
peaking do change significantly. The resulting values are in disagreement with
the assumptions of the Instanton Liquid Model. We conclude that the
fluctuations of topological charge in the QCD vacuum are not locally quantized.Comment: 3 pages, 4 figures, Lattice2001(confinement
A new approach of analyzing GRB light curves
We estimated the Txx quantiles of the cumulative GRB light curves using our
recalculated background. The basic information of the light curves was
extracted by multivariate statistical methods. The possible classes of the
light curves are also briefly discussed.Comment: 4 pages, 8 figure
Surface modes and parity violation in Schwinger model on the lattice
The phase diagram of the Schwinger model on the lattice with Wilson fermions
is investigated in the Hartree-Fock approximation. In case of single flavour
(not directly amenable to simulations), the calculation indicates the existence
of the parity violating phase at both weak and intermediate-to-strong
couplings. Hartree-Fock vacuum sustains a nonzero electric field in this broken
phase. The phase structure of the model with two flavours is also discussed.Comment: 4 pages, uuencoded compressed PostScript (using uufiles),
contribution to LATTICE 9
Different sensing mechanisms in single wire and mat carbon nanotubes chemical sensors
Chemical sensing properties of single wire and mat form sensor structures
fabricated from the same carbon nanotube (CNT) materials have been compared.
Sensing properties of CNT sensors were evaluated upon electrical response in
the presence of five vapours as acetone, acetic acid, ethanol, toluene, and
water. Diverse behaviour of single wire CNT sensors was found, while the mat
structures showed similar response for all the applied vapours. This indicates
that the sensing mechanism of random CNT networks cannot be interpreted as a
simple summation of the constituting individual CNT effects, but is associated
to another robust phenomenon, localized presumably at CNT-CNT junctions, must
be supposed.Comment: 12 pages, 5 figures,Applied Physics A: Materials Science and
Processing 201
Understanding the Order of Engineering Design Research
Engineering design research manifests as a platform for exploration, description, arrangement, rationalization, and application of design knowledge. What we can see when we are looking at the research into engineering design is an almost chaotically fragmented picture. Is it possible to have a holistic view on the contents and internal relationships of engineering design research? This paper considers teleology, a reflection of a branch of philosophical speculations, as the doctrine of ordering knowledge of engineering design and structuring engineering design research accordingly. Teleology explains that the ultimate reason behind design is to sustain human existence and well being by virtual creation of artifacts and services for society. To this end, knowledge of engineering research is supposed to be transferred from the platform of scientific/theoretical exploration and comprehension to the platform of technical/pragmatic application. This implies a natural streaming of knowledge of engineering design. In order to make the teleological explanation operational, a framework of reasoning has been constructed by adopting the analogy of the source, channel and sink of a stream. To represent the source, channel and sink categories of engineering design knowledge, the author inaugurated nine categories in the framework. It has been hypothesized that the introduced categories are equally valid for research in engineering design as well as for the knowledge of engineering design. Within each category, research domains and trajectories have been defined. The proposed teleology-based framework lends itself to a better understanding of the disciplinary articulation and intrinsic relationships of engineering design research. It is hoped, among other things, to form a basis for a shared understanding, to make the influence of decisions on research programs more transparent, as well as to facilitate organizing subject materials for various design courses
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