9,183 research outputs found
New Variable Jet Models for HH 34
We consider newly derived proper motions of the HH 34 jet to reconstruct the evolution of this outflow. We first extrapolate ballistic trajectories for the knots (starting from their present-day positions and velocities) and find that at ~1000 yr in the future most of them will merge to form a larger-mass structure. This mass structure will be formed close to the present-day position of the HH 34S bow shock. We then carry out a fit to the ejection velocity versus time reconstructed from the observed proper motions (assuming that the past motion of the knots was ballistic) and use this fit to compute axisymmetric jet simulations. We find that the intensity maps predicted from these simulations do indeed match reasonably well the [S II] structure of HH 34 observed in Hubble Space Telescope images
Spitzer observations of the HH 1/2 system. The discovery of the counterjet
We present unpublished Spitzer IRAC observations of the HH 1/2 young stellar outow processed
with a high angular resolution deconvolution algorithm, that produces sub-arcsecond (~ 0.6 - 0.8”)
images. In the resulting mid-infrared images, the optically invisible counterjet is detected for the first
time. The counterjet is approximately half as bright as the jet at 4.5 µm (the IRAC band that best
traces young stellar outows) and has a length of ~ 10”. The NW optical jet itself can be followed back
in the mid-IR to the position of the exciting VLA 1 source. An analysis of the IRAC colors indicates
that the jet/counterjet emission is dominated by collisionally excited H_2 pure rotational lines arising
from a medium with a neutral Hydrogen gas density of ~ 1000-2000 cm^(-3) and a temperature ~ 1500
K. The observed jet/counterjet brightness asymmetry is consistent with an intrinsically symmetric
outow with extinction from a dense, circumstellar structure of ~ 6” size (along the outow axis),
and with a mean visual extinction, A_V ~ 11 mag
Modeling of the Sub-Tg Relaxation Spectrum of Pd42.5Ni7.5Cu30P20 Metallic Glass
In this work we study the mechanical relaxation spectrum of Pd42.5Ni7.5Cu30P20
metallic glass. The effect of aging on the relaxation behavior is analyzed by measuring the
internal friction during consecutive heating runs. The mechanical relaxation of the wellannealed
glass state is modeled by fitting susceptibility functions to the primary and
secondary relaxations of the system. The model is able to reproduce the mechanical
relaxation spectrum below the glass transition temperature (sub-Tg) in the frequency-
temperature ranges relevant for the high temperature physical properties and forming
ability of metallic glasses. The model reveals a relaxation spectrum composed by the
overlapping of primary and secondary processes covering a wide domain of times but with
a relatively narrow range of activation energies.Postprint (author's final draft
Strain mapping and nanocrystallite size determination by neutron diffraction in an aluminum alloy (AA5083) severely plastically deformed through equal channel angular pressing
Six specimens of an aluminum alloy (AA-5083) extruded by Equal Channel Angular Pressing following two different routes plus a blank sample were examined with a neutron radiation of 1.5448 Å. Macrostrain maps from the (311) reflection were obtained. A clear difference about accumulated macrostrain with the extrusion cycles between the two routes is shown. The diffraction data of annealed specimens did permit to estimate crystallite sizes that range between 89 nm and 115 nm depending on the routes
Dissipative vortex solitons in 2D-lattices
We report the existence of stable symmetric vortex-type solutions for
two-dimensional nonlinear discrete dissipative systems governed by a
cubic-quintic complex Ginzburg-Landau equation. We construct a whole family of
vortex solitons with a topological charge S = 1. Surprisingly, the dynamical
evolution of unstable solutions of this family does not alter significantly
their profile, instead their phase distribution completely changes. They
transform into two-charges swirl-vortex solitons. We dynamically excite this
novel structure showing its experimental feasibility.Comment: 4 pages, 20 figure
Local superconducting density of states of ErNi2B2C
We present local tunnelling microscopy and spectroscopy measurements at low
temperatures in single crystalline samples of the magnetic superconductor
ErNi2B2C. The electronic local density of states shows a striking departure
from s-wave BCS theory with a finite value at the Fermi level, which amounts to
half of the normal phase density of states.Comment: 9 pages, 3 figure
Evaluación cuantitativa de la influencia de los espacios de color para la detección automática de células
En este artĂculo proponemos el estudio de los espacios de color en el marco de la segmentaciĂłn automática de
estructuras celulares. En contraste con estudios neuro-fĂsicos orientados a describir la percepciĂłn humana del
color nosotros desarrollamos un análisis cuantitativo tomando como referencia el resultado de algoritmos de
segmentaciĂłn y plantillas generadas manualmente. Los resultados obtenidos demuestran que el color tiene una
influencia considerable sobre la capacidad de análisis de una imagen y que los espacios de color que además de
separar la cromaticidad y luminancia procuran la normalizaciĂłn de las distancias entre colores proveen una
mejor representaciĂłn de la informaciĂłn presente en la imagen a diferencia de los espacios de color tales como el
RGB y HSI que han dominado la literatura de procesamiento de imágenes biomédicas en el pasadoIn this paper we study color spaces in the framework of automatic segmentation of cellular structures. In contrast
to neuro-physical studies focused on human perception of color we resort to a quantitative evaluation of such
impact using as reference segmentation outputs and ground truth images. The results show that color
representation has a considerable influence in the capabilities of such algorithms and color spaces that separate
chromaticity and luminance components, and normalize color differences, provide a representation of image data
better than color spaces such as RGB and HSI used extensively in the field of biomedical image processing in the
past
- …