2,800 research outputs found
Multiscale Fractal Descriptors Applied to Nanoscale Images
This work proposes the application of fractal descriptors to the analysis of
nanoscale materials under different experimental conditions. We obtain
descriptors for images from the sample applying a multiscale transform to the
calculation of fractal dimension of a surface map of such image. Particularly,
we have used the}Bouligand-Minkowski fractal dimension. We applied these
descriptors to discriminate between two titanium oxide films prepared under
different experimental conditions. Results demonstrate the discrimination power
of proposed descriptors in such kind of application
Characterization of nanostructured material images using fractal descriptors
This work presents a methodology to the morphology analysis and
characterization of nanostructured material images acquired from FEG-SEM (Field
Emission Gun-Scanning Electron Microscopy) technique. The metrics were
extracted from the image texture (mathematical surface) by the volumetric
fractal descriptors, a methodology based on the Bouligand-Minkowski fractal
dimension, which considers the properties of the Minkowski dilation of the
surface points. An experiment with galvanostatic anodic titanium oxide samples
prepared in oxalyc acid solution using different conditions of applied current,
oxalyc acid concentration and solution temperature was performed. The results
demonstrate that the approach is capable of characterizing complex morphology
characteristics such as those present in the anodic titanium oxide.Comment: 8 pages, 5 figures, accepted for publication Physica
Lognormal variability in BL Lacertae
X-ray data from the blazar BL Lac are used to investigate the nature of its
variability, and more precisely the flux dependency of the variability and the
distribution of fluxes. The variations in the flux are found to have a
lognormal distribution and the average amplitude of variability is proportional
to the flux level. BL Lac is the first blazar in which lognormal X-ray
variability is clearly detected. Lognormal variability in X-ray light curves,
probably related to accretion disk activity, has been discovered in various
compact systems, such as Seyfert galaxies and X-ray binaries. The light curve
is orders of magnitude less variable than other blazars, with few bursting
episodes. If this defines a specific state of the source, then the lognormality
might be the imprint of the accretion disk on the jet, linking for the first
time accretion and jet properties in a blazar.Comment: Accepted for Astronomy & Astrophysic
Magnetic excitations in vanadium spinels
We study magnetic excitations in vanadium spinel oxides AVO (A=Zn,
Mg, Cd) using two models: first one is a superexchange model for vanadium S=1
spins, second one includes in addition spin-orbit coupling, and crystal
anisotropy. We show that the experimentally observed magnetic ordering can be
obtained in both models, however the orbital ordering is different with and
without spin-orbit coupling and crystal anisotropy. We demonstrate that this
difference strongly affects the spin-wave excitation spectrum above the
magnetically ordered state, and argue that the neutron measurement of such
dispersion is a way to distinguish between the two possible orbital orderings
in AVO.Comment: accepted in Phys. Rev.
QMA with subset state witnesses
The class QMA plays a fundamental role in quantum complexity theory and it
has found surprising connections to condensed matter physics and in particular
in the study of the minimum energy of quantum systems. In this paper, we
further investigate the class QMA and its related class QCMA by asking what
makes quantum witnesses potentially more powerful than classical ones. We
provide a definition of a new class, SQMA, where we restrict the possible
quantum witnesses to the "simpler" subset states, i.e. a uniform superposition
over the elements of a subset of n-bit strings. Surprisingly, we prove that
this class is equal to QMA, hence providing a new characterisation of the class
QMA. We also prove the analogous result for QMA(2) and describe a new complete
problem for QMA and a stronger lower bound for the class QMA
Extraction of the electron mass from factor measurements on light hydrogenlike ions
The determination of the electron mass from Penning-trap measurements with
C ions and from theoretical results for the bound-electron
factor is described in detail. Some recently calculated contributions slightly
shift the extracted mass value. Prospects of a further improvement of the
electron mass are discussed both from the experimental and from the theoretical
point of view. Measurements with He ions will enable a consistency
check of the electron mass value, and in future an improvement of the He
nuclear mass and a determination of the fine-structure constant
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