105 research outputs found
Approximate Fitting of a Circular Arc When Two Points Are Known
The task of approximating points with circular arcs is performed in many
applications, such as polyline compression, noise filtering, and feature
recognition. However, the development of algorithms that perform a significant
amount of circular arcs fitting requires an efficient way of fitting circular
arcs with complexity O(1). The elegant solution to this task based on an
eigenvector problem for a square nonsymmetrical matrix is described in [1]. For
the compression algorithm described in [2], it is necessary to solve this task
when two points on the arc are known. This paper describes a different approach
to efficiently fitting the arcs and solves the task when one or two points are
known.Comment: 15 pages, 4 figures, extended abstract published at the conferenc
Holographic Pomeron: Saturation and DIS
We briefly review the approach to dipole-dipole scattering in holographic QCD
developed in ARXIV:1202.0831. The Pomeron is modeled by exchanging closed
strings between the dipoles and yields Regge behavior for the elastic
amplitude. We calculate curvature corrections to this amplitude in both a
conformal and confining background, identifying the holographic direction with
the virtuality of the dipoles. The it wee-dipole density is related to the
string tachyon diffusion in both virtuality and the transverse directions. We
give an explicit derivation of the dipole saturation momentum both in the
conformal and confining metric. Our holographic result for the dipole-dipole
cross section and the it wee-dipole density in the conformal limit are shown to
be identical in form to the BFKL pomeron result when the non-critical string
transverse dimension is . The total dipole-dipole cross section is
compared to DIS data from HERA
Coherence Phenomena in Charmonium Production off Nuclei at the Energies of RHIC and LHC
In the energy range of RHIC and LHC the mechanisms of nuclear suppression of
charmonia are expected to be strikingly different from what is known for the
energy of the SPS. One cannot think any more of charmonium produced on a bound
nucleon which then attenuates as it passes through the rest of the nucleus. The
coherence length of charmonium production substantially exceeds the nuclear
radius in the new energy range. Therefore the production amplitudes on
different nucleons, rather than the cross sections, add up and interfere, i.e.
shadowing is at work. So far no theoretical tool has been available to
calculate nuclear effects for charmonium production in this energy regime. We
develop a light-cone Green function formalism which incorporates the effects of
the coherence of the production amplitudes and of charmonium wave function
formation, and is the central result of this paper. We found a substantial
deviation from QCD factorization, namely, gluon shadowing is much stronger for
charmonium production than it is in DIS. We predict for nuclear effects
scaling which is violated at lower energies by initial state energy loss which
must be also included in order to compare with available data. In this paper
only the indirect J/Psi originating from decay of P-wave charmonia are
considered. The calculated x_F-dependence of J/Psi nuclear suppression is in a
good accord with data. We predict a dramatic variation of nuclear suppression
with x_F in pA and a peculiar peak at x_F=0 in AA collisions at RHIC.Comment: 51 pages including 12 figures. Two references and comments are added
at the en
Independent components in spectroscopic analysis of complex mixtures
We applied two methods of "blind" spectral decomposition (MILCA and SNICA) to
quantitative and qualitative analysis of UV absorption spectra of several
non-trivial mixture types. Both methods use the concept of statistical
independence and aim at the reconstruction of minimally dependent components
from a linear mixture. We examined mixtures of major ecotoxicants (aromatic and
polyaromatic hydrocarbons), amino acids and complex mixtures of vitamins in a
veterinary drug. Both MICLA and SNICA were able to recover concentrations and
individual spectra with minimal errors comparable with instrumental noise. In
most cases their performance was similar to or better than that of other
chemometric methods such as MCR-ALS, SIMPLISMA, RADICAL, JADE and FastICA.
These results suggest that the ICA methods used in this study are suitable for
real life applications. Data used in this paper along with simple matlab codes
to reproduce paper figures can be found at
http://www.klab.caltech.edu/~kraskov/MILCA/spectraComment: 22 pages, 4 tables, 6 figure
Effect of Zero Modes on the Bound-State Spectrum in Light-Cone Quantisation
We study the role of bosonic zero modes in light-cone quantisation on the
invariant mass spectrum for the simplified setting of two-dimensional SU(2)
Yang-Mills theory coupled to massive scalar adjoint matter. Specifically, we
use discretised light-cone quantisation where the momentum modes become
discrete. Two types of zero momentum mode appear -- constrained and dynamical
zero modes. In fact only the latter type of modes turn out to mix with the Fock
vacuum. Omission of the constrained modes leads to the dynamical zero modes
being controlled by an infinite square-well potential. We find that taking into
account the wavefunctions for these modes in the computation of the full bound
state spectrum of the two dimensional theory leads to 21% shifts in the masses
of the lowest lying states.Comment: LaTeX with 5 postscript file
Topological Aspects of Gauge Fixing Yang-Mills Theory on S4
For an space-time manifold global aspects of gauge-fixing are
investigated using the relation to Topological Quantum Field Theory on the
gauge group. The partition function of this TQFT is shown to compute the
regularized Euler character of a suitably defined space of gauge
transformations. Topological properties of the space of solutions to a
covariant gauge conditon on the orbit of a particular instanton are found using
the isometry group of the base manifold. We obtain that the Euler
character of this space differs from that of an orbit in the topologically
trivial sector. This result implies that an orbit with Pontryagin number
\k=\pm1 in covariant gauges on contributes to physical correlation
functions with a different multiplicity factor due to the Gribov copies, than
an orbit in the trivial \k=0 sector. Similar topological arguments show that
there is no contribution from the topologically trivial sector to physical
correlation functions in gauges defined by a nondegenerate background
connection. We discuss possible physical implications of the global gauge
dependence of Yang-Mills theory.Comment: 13 pages, uuencoded and compressed LaTeX file, no figure
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