867 research outputs found
Radio morphology and spectral analysis of cD galaxies in rich and poor galaxy clusters
We present a radio morphological study and spectral analysis for a sample of
13 cD galaxies in rich and poor clusters of galaxies.} Our study is based on
new high sensitivity Giant Metrewave Radio Telescope (GMRT) observations at
1.28 GHz, 610 MHz and 235 MHz, and on archival data. From a statistical sample
of cluster cD galaxies we selected those sources with little information
available in the literature and promising for the detection of aged radio
emission. Beyond the high sensitivity images for all 13 radio galaxies, we
present also a detailed spectral analysis for 7 of them. We found a variety of
morphologies and linear sizes, as typical for radio galaxies in the radio power
range sampled here (low to intermediate power radio galaxies). The spectral
analysis shows that 10/13 radio galaxies have steep radio spectrum, with
spectral index . In general, the radiative ages and growth
velocities are consistent with previous findings that the evolution of radio
galaxies at the cluster centres is affected by the dense external medium (i.e.
low growth velocities and old ages. We suggest that the dominant galaxies in A
2622 and MKW 03s are dying radio sources, which at present are not fed by
nuclear activity. On the other hand, the spectacular source at the centre of A
2372 might be a very interesting example of restarted radio galaxy. For this
source we estimated a life cycle of the order of 10 yr.Comment: Accepted by A&A, 25 pages, 28 figures, 6 tables and appendix Full
version including high quality images available at
http://www.ira.inaf.it/~tventuri/pap/Venturi.pd
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Photoneutron effects on pulse reactor kinetics for the Annular Core Research Reactor (ACRR).
The Annular Core Research Reactor (ACRR) is a swimming-pool type pulsed reactor that maintains an epithermal neutron flux and a nine-inch diameter central dry cavity. One of its uses is neutron and gamma-ray irradiation damage studies on electronic components under transient reactor power conditions. In analyzing the experimental results, careful attention must be paid to the kinetics associated with the reactor to ensure that the transient behavior of the electronic device is understood. Since the ACRR fuel maintains a substantial amount of beryllium, copious quantities of photoneutrons are produced that can significantly alter the expected behavior of the reactor power, especially following a reactor pulse. In order to understand these photoneutron effects on the reactor kinetics, the KIFLE transient reactor-analysis code was modified to include the photoneutron groups associated with the beryllium. The time-dependent behavior of the reactor power was analyzed for small and large pulses, assuming several initial conditions including following several pulses during the day, and following a long steady-state power run. The results indicate that, for these types of initial conditions, the photoneutron contribution to the reactor pulse energy can have a few to tens of percent effect
La bicicleta como transporte sostenible en México
De acuerdo a los datos publicados por el Banco Mundial (actualización 31 de octubre del 2012), México presentó una tendencia hacia la baja a pesar de esto, aún sigue siendo considerable sus emisiones de CO2 actualmente es de 3.98 ton per cápita. Esto contribuye al efecto invernadero y a su vez desequilibrios en nuestros ecosistemas. Siendo así uno de los eventos que aportan efectos al cambio climático. A partir de este planteamiento se busca llevar a cabo propuestas viables y que motiven a la creación de un sistema que sea respetuoso con el medio ambiente con un desarrollo económico local y eficientizar la infraestructura existente además de mejorar la imagen urbana así como promover la salud a través del uso de la bicicleta, así mismo tener una ciudad más competitiva con reducciones de emisiones de carbono que abone a la reducción del cambio climático. Para contribuir en su mitigación, se impulsa la realización del Plan de Movilidad Ciclista de Ensenada, con el fin de mejorar la calidad de vida de la población y mejorar las condiciones actuales de los problemas medioambientales al participar en la reducción de CO2 y promover el uso de la bicicleta como medio de transporte no motorizado. El proyecto, en su primera fase, consiste en retirar 166 aparcamientos dispuestos a lo largo del Boulevard Costero de la zona turística en aparcamientos públicos, y así usar este espacio para desarrollar una ruta de la ciclovía. Comprobamos que uno de los medios de transporte más vendidos en México (no así en el 2012) es el Nissan Tsuru 2008, por ser un auto económico y de bajo mantenimiento. Analizamos la emisión del CO2, considerándolo como un vehículo de rango medio en la eficiencia de emisión de gases contaminantes, y si consideramos que el 34.14% (como valor representativo) de los autos que ya no estarían estacionados en esa vialidad se sustituyen por uso de bicicleta, obtenemos que la reducción de emisiones de CO2 durante un año al implementar la primera fase del Plan de Movilidad Ciclista, es de 71,76 tonelada
X-ray-emitting Atmospheres of B2 Radio Galaxies
We report ROSAT PSPC spatial and spectral analysis of the eight B2 radio
galaxies NGC 315, NGC 326, 4C 35.03, B2 0326+39, NGC 2484, B2 1040+31, B2
1855+37, and 3C 449, expected to be representative of the class of low-power
radio galaxies. Multiple X-ray components are present in each, and the gas
components have a wide range of linear sizes and follow an extrapolation of the
cluster X-ray luminosity/temperature correlation, implying that there is no
relationship between the presence of a radio galaxy and the gas fraction of the
environment. No large-scale cooling flows are found. There is no correlation of
radio-galaxy size with the scale or density of the X-ray atmosphere. This
suggests that it is processes on scales less than those of the overall gaseous
environments which are the major influence on radio-source dynamics. The
intergalactic medium is usually sufficient to confine the outer parts of the
radio structures, in some cases even to within 5 kpc of the core. In the case
of NGC 315, an extrapolation suggests that the pressure of the atmosphere may
match the minimum pressure in the radio source over a factor of about 40 in
linear size (a factor of about 1600 in pressure).Comment: 34 pages, including 10 figures, using aasms4.sty To appear in the Ap
Spin Flips and Precession in Black-Hole-Binary Mergers
We use the `moving puncture' approach to perform fully non-linear evolutions
of spinning quasi-circular black-hole binaries with individual spins not
aligned with the orbital angular momentum. We evolve configurations with the
individual spins (parallel and equal in magnitude) pointing in the orbital
plane and 45-degrees above the orbital plane. We introduce a technique to
measure the spin direction and track the precession of the spin during the
merger, as well as measure the spin flip in the remnant horizon. The former
configuration completes 1.75 orbits before merging, with the spin precessing by
98-degrees and the final remnant horizon spin flipped by ~72-degrees with
respect to the component spins. The latter configuration completes 2.25 orbits,
with the spins precessing by 151-degrees and the final remnant horizon spin
flipped ~34-degrees with respect to the component spins. These simulations show
for the first time how the spins are reoriented during the final stage of
binary black hole mergers verifying the hypothesis of the spin-flip phenomenon.
We also compute the track of the holes before merger and observe a precession
of the orbital plane with frequency similar to the orbital frequency and
amplitude increasing with time.Comment: Revtex4, 17 figures, 14 pages. Accepted for publication in PR
Status report on a natural laminar-flow nacelle flight experiment
The natural laminar flow (NLF) nacelle experiment is part of a drag reduction production program, and has the dual objectives of studying the extent of NLF on full scale nacelles in a flight environment and the effect of acoustic disturbance on the location of transition on the nacelle surface. The experiment is being conducted in two phases: (1) an NLF fairing was flown on a full scale Citation nacelle to develop the experiment technique and establish feasibility; (2) full scale, flow through, NLF nacelles located below the right wing of an experimental NASA OV-1 aircraft are evaluated. The measurements of most interest are the static pressure distribution and transition location on the nacelle surface, and the fluctuating pressure levels associated with the noise sources. Data are collected in combinations of acoustic frequencies and sound pressure levels. The results of phase 2 tests to date indicate that on shape GE2, natural laminar flow was maintained as far aft as the afterbody joint at 50 percent of the nacelle length. An aft facing step at this joint caused premature transition at this station. No change was observed in the transition pattern when the noise sources were operated
Kiloparsec-Scale Jets in FR I Radio Galaxies and the Gamma-Ray Background
We discuss the contribution of kiloparsec-scale jets in FR I radio galaxies
to the diffuse gamma-ray background radiation. The analyzed gamma-ray emission
comes from inverse-Compton scattering of starlight photon fields by the
ultrarelativistic electrons whose synchrotron radiation is detected from such
sources at radio, optical and X-ray energies. We find that these objects, under
the minimum-power hypothesis (corresponding to a magnetic field of 300 muG in
the brightest knots of these jets), can contribute about one percent to the
extragalactic gamma-ray background measured by EGRET. We point out that this
result already indicates that the magnetic fields in kpc-scale jets of
low-power radio galaxies are not likely to be smaller than 10 muG on average,
as otherwise the extragalactic gamma-ray background would be overproduced.Comment: 18 pages, 3 figures included. ApJ accepte
Thermal Performance of the LHC Short Straight Section Cryostat
The LHC Short Straight Section (SSS) cryostat houses and thermally protects in vacuum the cold mass which contains a twin-aperture superconducting quadrupole magnet and superconducting corrector magnets operating at 1.9 K in superfluid helium. In addition to mechanical requirements, the cryostat is designed to minimize the heat in-leak from the ambient temperature to the cold mass. Mechanical components linking the cold mass to the vacuum vessel such as support posts and an insulation vacuum barrier are designed to have minimum heat conductivity with efficient thermalisations for heat interception. Heat in-leak by radiation is reduced by employing multilayer insulation wrapped around the cold mass and an actively cooled aluminium thermal shield. The recent commissioning and operation of two SSS prototypes in the LHC Test String 2 have given a first experimental validation of the thermal performance of the SSS cryostat in nominal operating conditions. Temperature sensors mounted in critical locations provide a temperature mapping which allows a crosscheck with the calculated temperature values and thermal performance. Moreover the measurements allowed a validation of the efficiency of the employed thermalisations. This paper presents the experimental results for the thermal performance of cryostat components and gives a first comparison with the design values
Coaxial Jets and Sheaths in Wide-Angle-Tail Radio Galaxies
We add 20, 6 and 3.6 cm wavelength VLA observations of two WATs, 1231+674 and
1433+553, to existing VLA data at 6 and 20 cm, in order to study the variations
of spectral index as a function of position. We apply the spectral tomography
process that we introduced in our analysis of 3C67, 3C190 and 3C449. Both
spectral tomography and polarization maps indicate that there are two distinct
extended components in each source. As in the case of 3C449, we find that each
source has a flat spectrum jet surrounded by a steeper spectrum sheath. The
steep components tend to be more highly polarized than the flat components. We
discuss a number of possibilities for the dynamics of the jet/sheath systems,
and the evolution of their relativistic electron populations. While the exact
nature of these two coaxial components is still uncertain, their existence
requires new models of jets in FR I sources and may also have implications for
the dichotomy between FR Is and FR IIs.Comment: 29 text pages plus 13 figures. Scheduled for publication in May 10,
1999 Ap
Multifrequency VLA observations of the FR I radio galaxy 3C 31: morphology, spectrum and magnetic field
We present high-quality VLA images of the FR I radio galaxy 3C 31 in the
frequency range 1365 to 8440 MHz with angular resolutions from 0.25 to 40
arcsec. Our new images reveal complex, well resolved filamentary substructure
in the radio jets and tails. We also use these images to explore the spectral
structure of 3C 31 on large and small scales. We infer the apparent magnetic
field structure by correcting for Faraday rotation. Some of the intensity
substructure in the jets is clearly related to structure in their apparent
magnetic field: there are arcs of emission where the degree of linear
polarization increases, with the apparent magnetic field parallel to the ridges
of the arcs. The spectral indices are significantly steeper (0.62) within 7
arcsec of the nucleus than between 7 and 50 arcsec (0.52 - 0.57). The spectra
of the jet edges are also slightly flatter than the average for their
surroundings. At larger distances, the jets are clearly delimited from
surrounding larger-scale emission both by their flatter radio spectra and by
sharp brightness gradients. The spectral index of 0.62 in the first 7 arcsec of
3C 31's jets is very close to that found in other FR I galaxies where their
jets first brighten in the radio and where X-ray synchrotron emission is most
prominent. Farther from the nucleus, where the spectra flatten, X-ray emission
is fainter relative to the radio. The brightest X-ray emission from FR I jets
is therefore not associated with the flattest radio spectra, but with a
particle-acceleration process whose characteristic energy index is 2.24. The
spectral flattening with distance from the nucleus occurs where our
relativistic jet models require deceleration, and the flatter-spectra at the
jet edges may be associated with transverse velocity shear. (Slightly abridged)Comment: 17 pages, 13 figures, accepted for publication in MNRA
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