11,494 research outputs found
Dynamical coupled-channels: the key to understanding resonances
Recent developments on a dynamical coupled-channels model of hadronic and
electromagnetic production of nucleon resonances are summarized.Comment: Invited Plenary talk at the 20th European Conference on Few-Body
Problems in Physics (EFB20), September 10-14 2007, Pisa, Italy. To appear in
the proceedings in Few-Body System
Enhanced Parallel Generation of Tree Structures for the Recognition of 3D Images
Segmentations of a digital object based on a connectivity
criterion at n-xel or sub-n-xel level are useful tools in image topological
analysis and recognition. Working with cell complex analogous of digital
objects, an example of this kind of segmentation is that obtained from
the combinatorial representation so called Homological Spanning Forest
(HSF, for short) which, informally, classifies the cells of the complex as
belonging to regions containing the maximal number of cells sharing the
same homological (algebraic homology with coefficient in a field) information.
We design here a parallel method for computing a HSF (using
homology with coefficients in Z/2Z) of a 3D digital object. If this object
is included in a 3D image of m1 × m2 × m3 voxels, its theoretical time
complexity order is near O(log(m1 + m2 + m3)), under the assumption
that a processing element is available for each voxel. A prototype implementation
validating our results has been written and several synthetic,
random and medical tridimensional images have been used for testing.
The experiments allow us to assert that the number of iterations in which
the homological information is found varies only to a small extent from
the theoretical computational time.Ministerio de Economía y Competitividad MTM2016-81030-
Haro15: Is it actually a low metallicity galaxy?
We present a detailed study of the physical properties of the nebular
material in multiple knots of the blue compact dwarf galaxy Haro 15. Using long
slit and echelle spectroscopy, obtained at Las Campanas Observatory, we study
the physical conditions (electron density and temperature), ionic and total
chemical abundances of several atoms, reddening and ionization structure. The
latter was derived by comparing the oxygen and sulphur ionic ratios to their
corresponding observed emission line ratios (the eta and eta' plots) in
different regions of the galaxy. Applying direct and empirical methods for
abundance determination, we perform a comparative analysis between these
regions.Comment: (Poster paper) 2 pages, 2 figure
Environment effects on the electric conductivity of the DNA
We present a theoretical analysis of the environment effects on charge
transport in double-stranded synthetic poly(G)-poly(C) DNA molecules attached
to two ideal leads. Coupling of the DNA to the environment results in two
effects: (i) localization of carrier functions due to the static disorder and
(ii) phonon-induced scattering of the carrier between these localized states,
resulting in hopping conductivity. A nonlinear Pauli master equation for
populations of localized states is used to describe the hopping transport and
calculate the electric current as a function of the applied bias. We
demonstrate that, although the electronic gap in the density of states shrinks
as the disorder increases, the voltage gap in the characteristics becomes
wider. Simple physical explanation of this effect is provided.Comment: 8 pages, 2 figures, to appear in J. Phys.: Condens. Matte
Kinematics of gas and stars in circumnuclear star-forming regions of early type spirals
(Abbr.) We present high resolution (R~20000) spectra in the blue and the far
red of cicumnuclear star-forming regions (CNSFRs) in three early type spirals
(NGC3351, NGC2903 and NGC3310) which have allowed the study of the kinematics
of stars and ionized gas in these structures and, for the first time, the
derivation of their dynamical masses for the first two. In some cases these
regions, about 100 to 150 pc in size, are seen to be composed of several
individual star clusters with sizes between 1.5 and 4.9 pc estimated from
Hubble Space Telescope (HST) images. The stellar dispersions have been obtained
from the Calcium triplet (CaT) lines at 8494,8542,8662 \AA,
while the gas velocity dispersions have been measured by Gaussian fits to the
H and [OIII] 5007 \AA lines on the high dispersion
spectra. Values of the stellar velocity dispersions are between 30 and 68 km/s.
We apply the virial theorem to estimate dynamical masses of the clusters,
assuming that systems are gravitationally bounded and spherically symmetric,
and using previously measured sizes. The measured values of the stellar
velocity dispersions yield dynamical masses of the order of 10 to 10
solar masses for the whole CNSFRs. Stellar and gas velocity dispersions are
found to differ by about 20 to 30 km/s with the H emission lines being
narrower than both the stellar lines and the [OIII] 5007 \AA
lines. The twice ionized oxygen, on the other hand, shows velocity dispersions
comparable to those shown by stars, in some cases, even larger. We have found
indications of the presence of two different kinematical components in the
ionized gas of the regions...Comment: 4 pages, proceeding of the meeting "Young massive star clusters -
Initial conditions and environments", Granada, Spain, 200
Speeding up antidynamical Casimir effect with nonstationary qutrits
The antidynamical Casimir effect (ADCE) is a term coined to designate the
coherent annihilation of excitations due to resonant external perturbation of
system parameters, allowing for extraction of quantum work from nonvacuum
states of some field. Originally proposed for a two-level atom (qubit) coupled
to a single cavity mode in the context of nonstationary quantum Rabi model, it
suffered from very low transition rate and correspondingly narrow resonance
linewidth. In this paper we show analytically and numerically that the ADCE
rate can be increased by at least one order of magnitude by replacing the qubit
by an artificial three-level atom (qutrit) in a properly chosen configuration.
For the cavity thermal state we demonstrate that the dynamics of the average
photon number and atomic excitation is completely different from the qubit's
case, while the behavior of the total number of excitations is qualitatively
similar yet significantly faster.Comment: 9 pages, 4 figure
Slope failure in Caracas, Venezuela: The influence of squatter settlement
In Caracas, Venezuela, landslides have become an increasing problem frequently associated with the rainy season and the creation of more vulnerable areas by the urbanization process. Their effects have been particularly evident in the squatter settlements or barrios in the hillsides surrounding Caracas. The purpose of this research is to examine the incidence of slope failure in the barrios. An account of the urban growth of Caracas is given in order to illustrate how population has been progressively occupying the valley and its hillsides. A data set of 205 slope failures which occurred over a six year period is set up. The slope failures in the Metropolitan Area are analyzed both spatially and over time in order to elucidate some of the factors responsible for their incidence. Besides location and date of occurrence, the data set incorporates rainfall seasonality and cumulative totals, lithology, slope angle, type of mass movement, and location within the urban context. The role of the rainfall as a triggering factor for the slope failures is examined. Cumulative rainfall values are considered for 10, 30 days and seasonally. With the help of a sequence of aerial photographs, the evolution of slope failure in barrio El Cipres is used to examine the links between the settlement process and the evolution of the local geomorphology. A Landslide Susceptibility Map is then produced.
The research shows that rainfall plays an important role in the incidence of slope failures, but its influence in barrios is also compounded by other factors such as enhanced infiltration and the changes in slope produced by the settlements process. In this connection improvements in services and the consolidation of the barrio may add to the problem if they are not carefully planned
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