271 research outputs found
Alternative method to find orbits in chaotic systems
We present here a new method which applies well ordered symbolic dynamics to
find unstable periodic and non-periodic orbits in a chaotic system. The method
is simple and efficient and has been successfully applied to a number of
different systems such as the H\'enon map, disk billiards, stadium billiard,
wedge billiard, diamagnetic Kepler problem, colinear Helium atom and systems
with attracting potentials. The method seems to be better than earlier applied
methods.Comment: 5 pages, uuencoded compressed tar PostScript fil
Bifurcations and Complete Chaos for the Diamagnetic Kepler Problem
We describe the structure of bifurcations in the unbounded classical
Diamagnetic Kepler problem. We conjecture that this system does not have any
stable orbits and that the non-wandering set is described by a complete trinary
symbolic dynamics for scaled energies larger then .Comment: 15 pages PostScript uuencoded with figure
Design and evaluation of neural classifiers application to skin lesion classification
We address design and evaluation of neural classifiers for the problem of skin lesion classification. By using Gauss Newton optimization for the entropic cost function in conjunction with pruning by Optimal Brain Damage and a new test error estimate, we show that this scheme is capable of optimizing the architecture of neural classifiers. Furthermore, error-reject tradeoff theory indicates, that the resulting neural classifiers for the skin lesion classification problem are near-optimal. 1 INTRODUCTION Melanoma is the most lethal of skin cancers. However, patients may be saved from this life threatening cancer if their lesion is detected at an early stage. Computer imaging may assist and improve the detection of such early lesions. The "State of the art" in this field was recently reviewed in an editorial in the journal "Computerized Medical Imaging and Graphics" [1]. Although applied to the problem of skin lesion classification, the main objective of this paper is to introduce and app..
The Cold Spot as a Large Void: Lensing Effect on CMB Two and Three Point Correlation Functions
The "Cold Spot" in the CMB sky could be due to the presence of an anomalous
huge spherical underdense region - a "Void" - of a few hundreds Mpc/h radius.
Such a structure would have an impact on the CMB two-point (power spectrum) and
three-point (bispectrum) correlation functions not only at low-l, but also at
high-l through Lensing, which is a unique signature of a Void. Modeling such an
underdensity with an LTB metric, we show that for the power spectrum the effect
should be visible already in the WMAP data only if the Void radius is at least
L \gtrsim 1 Gpc/h, while it will be visible by the Planck satellite if L
\gtrsim 500 Mpc/h. We also speculate that this could be linked to the high-l
detection of an hemispherical power asymmetry in the sky. Moreover, there
should be non-zero correlations in the non-diagonal two-point function. For the
bispectrum, the effect becomes important for squeezed triangles with two very
high l's: this signal can be detected by Planck if the Void radius is at least
L \gtrsim 300 Mpc/h, while higher resolution experiments should be able to
probe the entire parameter space. We have also estimated the contamination of
the primordial non-Gaussianity f_NL due to this signal, which turns out to be
negligible.Comment: v1: 18 pages, 12 figures; v2: 19 pages, 12 figures, calculation of
bispectrum improved, reference added, published version; v3: 19 pages, 12
figures, refined eq.(9) and related figures, conclusions strengthene
Combined CI+MBPT calculations of energy levels and transition amplitudes in Be, Mg, Ca, and Sr
Configuration interaction (CI) calculations in atoms with two valence
electrons, carried out in the V(N-2) Hartree-Fock potential of the core, are
corrected for core-valence interactions using many-body perturbation theory
(MBPT). Two variants of the mixed CI+MBPT theory are described and applied to
obtain energy levels and transition amplitudes for Be, Mg, Ca, and Sr
Light propagation in statistically homogeneous and isotropic universes with general matter content
We derive the relationship of the redshift and the angular diameter distance
to the average expansion rate for universes which are statistically homogeneous
and isotropic and where the distribution evolves slowly, but which have
otherwise arbitrary geometry and matter content. The relevant average expansion
rate is selected by the observable redshift and the assumed symmetry properties
of the spacetime. We show why light deflection and shear remain small. We write
down the evolution equations for the average expansion rate and discuss the
validity of the dust approximation.Comment: 42 pages, no figures. v2: Corrected one detail about the angular
diameter distance and two typos. No change in result
Evolution of deformation and recrystallization textures in high-purity Ni and the Ni-5 at. pct W alloy
An attempt has been made to study the evolution of texture in high-purity Ni and Ni-5 at. pct W alloy prepared by the powder metallurgy route followed by heavy cold rolling (∼95 pct deformation) and recrystallization. The deformation textures of the two materials are of typical pure metal or Cu-type texture. Cube-oriented ({001} {100}) regions are present in the deformed state as long thin bands, elongated in the rolling direction (RD). These bands are characterized by a high orientation gradient inside, which is a result of the rotation of the cube-oriented cells around the RD toward the RD-rotated cube ({013} {100}). Low-temperature annealing produces a weak cube texture along with the {013} {100} component, with the latter being much stronger in high-purity Ni than in the Ni-W alloy. At higher temperatures, the cube texture is strengthened considerably in the Ni-W alloy; however, the cube volume fraction in high-purity Ni is significantly lower because of the retention of the {013} {100} component. The difference in the relative strengths of the cube, and the {013} {100} components in the two materials is evident from the beginning of recrystallization in which more {013} {100} -oriented grains than near cube grains form in high-purity Ni. The preferential nucleation of the near cube and the {013} {100} grains in these materials seems to be a result of the high orientation gradients associated with the cube bands that offer a favorable environment for early nucleation
Characterisation of the muon beams for the Muon Ionisation Cooling Experiment
A novel single-particle technique to measure emittance has been developed and used to characterise seventeen different muon beams for the Muon Ionisation Cooling Experiment (MICE). The muon beams, whose mean momenta vary from 171 to 281 MeV/c, have emittances of approximately 1.2–2.3 π mm-rad horizontally and 0.6–1.0 π mm-rad vertically, a horizontal dispersion of 90–190 mm and momentum spreads of about 25 MeV/c. There is reasonable agreement between the measured parameters of the beams and the results of simulations. The beams are found to meet the requirements of MICE
Search for the Flavor-Changing Neutral Current Decay with the HERA-B Detector
We report on a search for the flavor-changing neutral current decay using events recorded with a dimuon trigger in
interactions of 920 GeV protons with nuclei by the HERA-B experiment. We find
no evidence for such decays and set a 90% confidence level upper limit on the
branching fraction .Comment: 17 pages, 4 figures (of which 1 double), paper to be submitted to
Physics Letters
Measurement of the J/Psi Production Cross Section in 920 GeV/c Fixed-Target Proton-Nucleus Interactions
The mid-rapidity (dsigma_(pN)/dy at y=0) and total sigma_(pN) production
cross sections of J/Psi mesons are measured in proton-nucleus interactions.
Data collected by the HERA-B experiment in interactions of 920 GeV/c protons
with carbon, titanium and tungsten targets are used for this analysis. The
J/Psi mesons are reconstructed by their decay into lepton pairs. The total
production cross section obtained is sigma_(pN)(J/Psi) = 663 +- 74 +- 46
nb/nucleon. In addition, our result is compared with previous measurements
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