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Search Results: 1 - 10 of 715815 matches for " M. A. Prieto "
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Radio structures of the nuclei of nearby Seyfert galaxies and the nature of the missing diffuse emission
M. Orienti,M. A. Prieto
Physics , 2009, DOI: 10.1111/j.1365-2966.2009.15837.x
Abstract: We present archival high spatial resolution VLA and VLBA data of the nuclei of seven of the nearest and brightest Seyfert galaxies in the Southern Hemisphere. At VLA resolution (~0.1 arcsec), the nucleus of the Seyfert galaxies is unresolved, with the exception of MCG-5-23-16 and NGC 7469 showing a core-jet structure. Three Seyfert nuclei are surrounded by diffuse radio emission related to star-forming regions. VLBA observations with parsec-scale resolution pointed out that in MRK 1239 the nucleus is clearly resolved into two components separated by ~30 pc, while the nucleus of NGC 3783 is unresolved. Further comparison between VLA and VLBA data of these two sources shows that the flux density at parsec scales is only 20% of that measured by the VLA. This suggests that the radio emission is not concentrated in a single central component, as in elliptical radio galaxies, and an additional low-surface brightness component must be present. A comparison of Seyfert nuclei with different radio spectra points out that the ``presence'' of undetected flux on milli-arcsecond scale is common in steep-spectrum objects, while in flat-spectrum objects essentially all the radio emission is recovered. In the steep-spectrum objects, the nature of this ``missing'' flux is likely due to non-thermal AGN-related radiation, perhaps from a jet that gets disrupted in Seyfert galaxies because of the denser environment of their spiral hosts.
Evidence of parsec-scale jets in Low-luminosity Active Galactic Nuclei
M. Mezcua,M. A. Prieto
Physics , 2014, DOI: 10.1088/0004-637X/787/1/62
Abstract: The nuclear radio emission of low-luminosity active galactic nuclei (LLAGN) is often associated with unresolved cores. In this paper we show that most LLAGN present extended jet radio emission when observed with sufficient angular resolution and sensitivity. They are thus able to power, at least, parsec-scale radio jets. To increase the detection rate of jets in LLAGN, we analyze subarcsecond resolution data of three low-ionization nuclear emission regions. This yields the detection of extended jet-like radio structures in NGC\,1097 and NGC\,2911 and the first resolved parsec-scale jet of NGC\,4594 (Sombrero). The three sources belong to a sample of nearby LLAGN for which high-spatial-resolution spectral energy distribution of their core emission is available. This allows us to study their accretion rate and jet power ($Q_\mathrm{jet}$) without drawing on (most) of the ad hoc assumptions usually considered in large statistical surveys. We find that those LLAGN with large-scale radio jets ($>$100 pc) have $Q_\mathrm{jet} > 10^{42}$ erg s$^{-1}$, while the lowest $Q_\mathrm{jet}$ correspond to those LLAGN with parsec-scale ($\leq$100 pc) jets. The $Q_\mathrm{jet}$ is at least as large as the radiated bolometric luminosity for all LLAGN, in agreement with previous statistical studies. Our detection of parsec-scale jets in individual objects further shows that the kinematic jet contribution is equally important in large- or parsec-scale objects. We also find that the Eddington-scaled accretion rate is still highly sub-Eddington ($<10^{-4}$) when adding the $Q_\mathrm{jet}$ to the total emitted luminosity (radiated plus kinetic). This indicates that LLAGN are not only inefficient radiators but that they also accrete inefficiently or are very efficient advectors.
Study on the structure and composition of aortic valve calcific deposits. etiological aspects  [PDF]
R. M. Prieto, I. Gomila, O. S?hnel, A. Costa-Bauza, O. Bonnin, F. Grases
Journal of Biophysical Chemistry (JBPC) , 2011, DOI: 10.4236/jbpc.2011.21003
Abstract: The structures and chemical compositions of valve calcific deposits were investigated. The deposits was chosen arbitrarily and subjected to chemical analysis, observation with scanning microscope, semi-quantitative determination of Ca, Mg, Na, K, P and C elements by energy dispersive X-ray, X-ray diffraction and Fourier transform infrared spectroscopy carried out. These deposits were found to have non-uniform internal structures composed of layers of a structureless aspidinic inorganic material, substantial amounts of voluminous organic material and in a few samples small spheres were also present. Two groups of deposits with distinctly different chemical compositions were identified: one group with a low Ca/P molar ratio (1.59) and the other group with a high (1.82) Ca/P molar ratio. The deposits belonging to the group with a low Ca/P molar ratio contain higher concentration of magnesium and consist of increased amount of amorphous calcium phosphate. The deposits with a high Ca/P molar ratio contain low concentration of magnesium and consist predominantly of carbonated hydroxyapatite. The inorganic material was identified as a poorly crystalline carbonate hydroxyapatite containing molecular water of the average formula Ca9.1Mg0.4(Na,K)(PO4)5.8(CO3)0.3(OH)2. The actual chemical composition of the apatitic solid phase varies not only from deposit to deposit but also within the same deposit. The non-uniform internal structure of the deposits, the occasional presence of spherical particles and the variable point composition of the individual deposits indicate that their formation did not proceed under more or less constant conditions.
VLT diffraction-limited imaging at 11 and 18 micron of the nearest active galactic nuclei
J. Reunanen,M. A. Prieto,R. Siebenmorgen
Physics , 2009, DOI: 10.1111/j.1365-2966.2009.15997.x
Abstract: Mid-infrared imaging at resolutions of 300 mas of the central kpc region of 13 nearby, well-known active galaxies is presented. The bulk of the mid-IR emission is concentrated on an unresolved central source within a size of less than 5 to 130 pc, depending on the object distance. Further resolved emission is detected in 70% of the sample in the form of circumnuclear star-forming rings or diffuse nuclear extended emission. In the three cases with circumnuclear star formation, the stellar contribution is at least as important as that of the AGN. In those with extended nuclear emission -- a third of the sample -- this emission represents a few per cent of the total measured; however, this contribution may be underestimated because of the chopped nature of these observations. This extended emission is generally collimated in a preferential direction often coinciding with that of the extended ionized gas or the jet. In all cases, the nuclear fluxes measured at 11.8 and 18.7 micron represent a minor contribution of the flux levels measured by large aperture IRAS data at the nearest energy bands of 12 and 25 micron. This contribution ranges from 30% to less than 10%. In only three cases do the AGN fluxes agree with IRAS to within a factor of 2. In the AGNs with strong circumnuclear star formation, this component can well account for most of the IRAS flux measured in these objects. But in all other cases, either a low surface brightness component extending over galactic scales or strong extra-nuclear IR sources -- e.g. HII regions in spiral arms -- have to be the main source of the IRAS emission. In either case, the contribution of these components dwarfs that of the AGN at mid-IR wavelengths.
Near-infrared spectroscopy of nearby Seyfert galaxies - II. Molecular content and coronal emission
J. Reunanen,J. Kotilainen,M. A. Prieto
Physics , 2003, DOI: 10.1046/j.1365-8711.2003.06771.x
Abstract: We present sub-arcsec near-infrared 1.5 - 2.5 micron moderate resolution long-slit spectra of eight nearby Seyfert galaxies (z<0.01), both parallel to the ionization cone and perpendicular to it. These spectra complement similar data on six Seyferts, presented in Reunanen, Kotilainen & Prieto (2002). Large concentrations of molecular gas (H2) are present in the nucleus regardless of the Seyfert type. The spatial extent of the H2 emission is larger perpendicular to the cone than parallel to it in 6/8 (75 %) galaxies, in agreement with the unified models of Active Galactic Nuclei. Broad BrGamma was detected in nearly half of the optically classified Seyfert 2 galaxies, including two objects with no evidence for hidden polarized Broad Line Region. Nuclear [FeII] emission is generally blueshifted which together with high BrGamma/[FeII] ratios suggests shocks as the dominant excitation mechanism in Seyfert galaxies. Bright coronal emission lines [SiVI] and [SiVII] are common in Seyferts, as they are detected in ~60 % of the galaxies. In three galaxies the coronal lines are extended only in the direction parallel to the cone. This could be explained by shock excitation due to the jet or superwind interacting with the interstellar medium.
Contraste experimental de un modelo probalístico para el dimensionamiento de elementos de vidrio plano con consideraciones de modo mixto de carga
García Prieto, M. A.,Miranda Prieto, A.,Bernardo Sánchez, A.,Lamela Rey, M. J.
Boletín de la Sociedad Espa?ola de Cerámica y Vidrio , 1999,
Abstract: A characteristic of the glass is its fragility and the scatter of the experimental mechanical strength due to the presence of defects that appear in the process of manufacturing or handling. Accordingly, investigations on this material were priorly conducted to improve the processes of manufacturing and to establish design methodologies based on probabilistic approaches. The influence of mode II of loading was traditionally ignored or considered as ratio of mode II. Recent studies have shown that when a shear-loaded crack becomes unstable a new compressive stress concentration field builds up in the notch formed between the original crack and the branch crack. This stress field affects the energy balance and also the beginning of crack extension. A procedure to design glass elements was developed jointly with CIDA of Cristalería Espa ola, S.A. The aim of this work is to improve the model by the consideration of a mixed mode loading and its experimental contrast. Una de las características del vidrio es su fragilidad y la gran dispersión de sus valores de resistencia mecánica, motivado fundamentalmente por la presencia de defectos procedentes de su fabricación o de su manipulación. Como consecuencia, las investigaciones en este material se han dirigido preferentemente a la mejora de los procesos de fabricación y al establecimiento de metodologías de dise o basadas en modelos probabilísticos. Tradicionalmente, en el análisis de la rotura se ha despreciado la influencia del modo II o se ha representado como un porcentaje del modo I. Recientes estudios demuestran la aparición de un nuevo campo de tensiones de compresión cuando una fisura crece bajo una carga en modo II puro situado en el codo que se forma entre la fisura original y su ramificación. Este campo de compresión influye en el equilibrio energético y, en consecuencia, en la predicción de la rotura. En colaboración con el CIDA de Cristalería Espa ola, S.A. se ha desarrollado un procedimiento para el dimensionamiento probabilista de elementos de vidrio plano para edificación. En este artículo se propone ahora una mejora del modelo, considerando la existencia de un modo mixto de carga y procediendo posteriormente a su contraste experimental.
Gas and Dust Emission from the Nuclear Region of the Circinus Galaxy
M. Contini,M. A. Prieto,S. M. Viegas
Physics , 1998, DOI: 10.1086/306196
Abstract: Simultaneous modeling of the line and continuum emission from the nuclear region of the Circinus galaxy is presented. Composite models which include the combined effect of shocks and photoionization from the active center and from the circumnuclear star forming region are considered. The effects of dust reradiation, bremsstrahlung from the gas and synchrotron radiation are treated consistently. The proposed model accounts for two important observational features. First, the high obscuration of Circinus central source is produced by high velocity and dense clouds with characteristic high dust-to-gas ratios. Their large velocities, up to 1500 km\s, place them very close to the active center. Second, the derived size of the line emitting region is well in agreement with the observed limits for the coronal and narrow line region of Circinus.
The signature of high velocity gas in the spectra of NGC 4151
M. Contini,S. M. Viegas,M. A. Prieto
Physics , 2002, DOI: 10.1051/0004-6361:20020245
Abstract: The multiwavelength emission spectrum and associated velocity field of the Seyfert prototype NGC 4151 is modeled. HST data has impressively revealed the existence of a large range of velocities (100 - 1500 \kms) dominating the emitting clouds in the extended emission line region of the galaxy. Following this observational result, a revision of the photoionization modeling approach applied to NGC 4151 is presented. It is concluded that a mixture of radiation dominated clouds and shock dominated clouds are required to explain the multiwavelength line and continuum spectra of the galaxy.
Nonthermal plasma reactors for the production of light hydrocarbon olefins from heavy oil
Prieto, G.;Okumoto, M.;Takashima, K.;Katsura, S.;Mizuno, A.;Prieto, O.;Gay, C.R.;
Brazilian Journal of Chemical Engineering , 2003, DOI: 10.1590/S0104-66322003000100011
Abstract: during the last decade, nonthermal plasma technology was applied in many different fields, focusing attention on the destruction of harmful compounds in the air. this paper deals with nonthermal plasma reactors for the conversion of heavy oil into light hydrocarbon olefins, to be employed as gasoline components or to be added in small amounts for the catalytic reduction of nitrogen oxide compounds in the treatment of exhaust gas at power plants. for the process, the plate-plate nonthermal plasma reactor driven by ac high voltage was selected. the reactor was modeled as a function of parameter characteristics, using the methodology provided by the statistical experimental design. the parameters studied were gap distance between electrodes, carrier gas flow and applied power. results indicate that the reactions occurring in the process of heavy oil conversion have an important selective behavior. the products obtained were c1-c4 hydrocarbons with ethylene as the main compound. operating the parameters of the reactor within the established operative window of the system and close to the optimum conditions, efficiencies as high as 70 (ml/joule) were obtained. these values validate the process as an in-situ method to produce light olefins for the treatment of nitrogen oxides in the exhaust gas from diesel engines.
Anti-inflammatory activity of β-sitosterol in a model of oxazoloneinduced contact-delayed-type hypersensitivity
José M. Prieto,María C. Recio,Rosa M. Giner
Boletín Latinoamericano y del Caribe de Plantas Medicinales y Aromáticas , 2006,
Abstract: Hemos comprobado el efecto in vivo del β-sitosterol en un modelo de dermatitis de contacto por hipersensibilidad retardada (DTH). Este compuesto fue igualmente ensayado en modelos de liberación de eicosanoides en leucocitos polimorfonucleares de rata y plaquetas humanas estimuladas con ionóforo A23817 en incubaciones de 15 min. El compuesto reduce de manera significativa el edema inducido por oxazolona a las 24 horas, sin mostrar efecto alguno sobre las enzimas de la cascada del acido araquidónico implicadas en la iniciación del fenómeno inflamatorio, en las condiciones descritas. Los resultados indican que este compuesto puede modular el edema mediado por respuesta celular sin ningún efecto a corto plazo en la cascada del acido araquidónico. La ubicuidad del β-sitosterol puede explicar, y predecir, el efecto de muchos extractos vegetales en este modelo in vivo, y por tanto estoe dato puede ser de ayuda en procesos de de-replicación .
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