112 research outputs found
Gravitational Redshift of Emission Lines in the AGN Spectra
The detection of gravitationally redshifted optical emission lines has been
reported just for a few active galaxies. In this paper we give a short overview
of studies that analyzed or exploited the detection of the gravitational
redshift in optical AGN spectra. In addition, we tested the consistency of
gravitational redshift as the physical origin of the redward shifts observed in
their spectra using a sample of 50 Hamburg-ESO intermediate to high
redshift quasars that are among the most luminous quasars known ( erg/s), and are expected to host very massive
black holes. To this aim we modeled the line profile with accretion disk models
around a black hole.Comment: 10 pages, 2 figures, 3 table
AGN Broad Line Region variability in the context of Eigenvector 1: case of NGC 5548
Many active galactic nuclei (AGN) show strong variability of the optical
continuum. Since the line flux, profile shapes and intensity ratios are
changing, we analyze the variability patterns and possible periodicity of Type
1 AGN NGC 5548, using the Eigenvector 1 (EV1) diagram in different variability
states, taking advantage of very long term monitoring campaign data. The
preliminary results suggest that NGC 5548 - a highly variable object that over
several decades has shown large amplitude continuum fluctuations and flaring
behavior - remains Pop B. This means that the range in Eddington ratio, even
when the source is in a bright state, remains consistent with the value of the
low accreting Pop B. We inspected EV 1 parameters of a single object though
long term monitoring, assuming an inclination and black hole mass to be
constant during the observational time. Our results imply that the main driver
for the variations along the EV 1 diagram could be dimensionless accretion
rate. If so, then it appears that the source never crossed the boundary for
structural changes, indicatively placed at 0.2.Comment: 14 pages, 7 figures, accepted for publication in Frontiers in
Astronomy and Space Scienc
Periodic optical variability of AGN
Here we present the evidence for periodicity of an optical emission detected in several AGN. Significant periodicity is found in light curves and radial velocity curves. We discuss possible mechanisms that could produce such periodic variability and their implications. The results are consistent with possible detection of the orbital motion in proximity of the AGN central supermassive black holes
Reflections on the future of research, development and innovation in Colombia
Colombia is going through a moment of historical change. After four years of formal peace negotiations and the signing of a peace agreement with the FARC in November 2016, the country is set to enter an era of increased stability. In this perspective, the Colombian government should concentrate its effort to respond to societal challenges by improving infrastructure, promoting social inclusion and a sustainable use of natural resources. However, while it is acknowledged that greater investments in science and technology could foster economic growth and development and respond to societal needs, Colombia is still lagging behind. Greater investment in science and technology with a long-term perspective should support the country’s efforts for growth and development. Furthermore, considering Colombia´s great diversity in terms of population, topography and societal needs, it appears reductive to apply a ‘one size fits all’ solution. This article presents some reflections on how strengthening the capacity of higher education institutions (HEIs) for research and internationalization and strengthening the link between knowledge, practice and policy would contribute to more and better research, development and innovation in Colombia
A Main Sequence for Quasars
AD and MM-A acknowledge financial support from the Spanish Ministry for Economy and Competitiveness through grants AYA2013-42227-P and AYA2016-76682-C3-1-P. DD and CN acknowledge support from grants PAPIIT108716, UNAM, and CONACyT221398. EB and NB acknowledge grants 176003 Gravitation and the large scale structure of the Universe and 176001 Astrophysical spectroscopy of extragalactic objects supported by the Ministry of Education and Science of the Republic of Serbia
Ski Boot Soles Based on a Glass Fiber/Rubber Composite with Improved Grip on Icy Surfaces
Abstract A study on the effect of glass fibers/rubber composites on the grip on ice has been conducted in order to develop new materials for ski boot soles with increased grip in winter environments. The study has been conducted analyzing the friction of a composite material and of a ski boot sole containing an insert made of the composite material and comparing the results with those obtained using rubber and a thermoplastic elastomer. The analysis of the morphology of the composite surface, by Scanning Electron Microscopy, shows a homogenous distribution of glass fibers of approximately 10 μm of diameter in the rubber matrix. Moreover, the measure of the contact angle shows that the composite material has a higher water repellency compared to the rubber matrix. The measure of the coefficient of friction indicates a significant effect of the glass fibers on the grip on icy surfaces. The increased grip can be ascribed to the stiffness of the glass fibers that are able to have a mechanical grip on the ice surface and to the increased contact angle and water repellency of the composite that decrease the formation of a water layer below the sole
Analysis of HIV-1 drug resistant mutations by line probe assay and direct sequencing in a cohort of therapy naive HIV-1 infected Italian patients
BACKGROUND: The routine determination of drug resistance in newly HIV-1 infected individuals documents a potential increase in the transmission of drug-resistant variants. Plasma samples from twenty seven therapy naive HIV-1 infected Italian patients were analyzed by the line probe assay (LIPA) and the TruGene HIV-1 assay for the detection of mutations conferring resistance to HIV-1. RESULTS: Both tests disclosed amino-acid substitutions associated with resistance in a variable number of patients. In particular, two mutations (K70R and V118I), detectable by LIPA and by sequencing analysis respectively, revealed resistance to NRTIs in two plasma samples. At least three mutations conferring resistance to NNRTIs, not detectable by commercial LIPA, able to reveal mutations associated only with nucleoside reverse transcriptase analogues, were disclosed by viral sequence analysis. Moreover, most samples showed mutations correlated with resistance to protease inhibitors. Remarkably, a key mutation, like V82A (found as a mixture), and some "indeterminate" results (9 samples), due the absence of signal on the lines corresponding to a specific probe, was revealed only by LIPA, while a variable number of secondary mutations was detectable only by TruGene HIV-1 assay. CONCLUSION: Even if further studies are necessary to establish the impact of different tests on the evaluation of drug-resistant strains transmission, LIPA might be useful in a wide population analysis, where bulk results are needed in a short time, while sequencing analysis, able to detect mutations conferring resistance to both NRTIs and NNRTIs, might be considered a more complete assay, albeit more expensive and more technically complex
Optical Singly-Ionized Iron Emission in Radio-Quiet and Relativistically Jetted Active Galactic Nuclei
The issue of the difference between optical and UV properties of radio-quiet and radio-loud (relativistically "jetted ") active galactic nuclei (AGN) is a long standing one, related to the fundamental question of why a minority of powerful AGN possess strong radio emission due to relativistic ejections. This paper examines a particular aspect: the singly-ionized iron emission in the spectral range 4400-5600 & ANGS;, where the prominent HI H beta and [Oiii]lambda lambda 4959,5007 lines are also observed. We present a detailed comparison of the relative intensity of Feii multiplets in the spectral types of the quasar main sequence where most jetted sources are found, and afterwards discuss radio-loud narrow-line Seyfert 1 (NLSy1) nuclei with gamma-ray detection and with prominent Feii emission. An Feii template based on I Zw 1 provides an accurate representation of the optical Feii emission for RQ and, with some caveats, also for RL sources. CLOUDY photoionization simulations indicate that the observed spectral energy distribution can account for the modest Feii emission observed in composite radio-loud spectra. However, spectral energy differences alone cannot account for the stronger Feii emission observed in radio-quiet sources, for similar physical parameters. As for RL NLSy1s, they do not seem to behave like other RL sources, likely because of their different physical properties, that could be ultimately associated with a higher Eddington ratio
Optical variability patterns of radio-quiet and radio-loud quasars
We analyzed the light curves (LCs) of several radio-quiet and radio-loud quasars belonging to the same parameter space volume in the 4D Eigenvector 1 (4DE1) quasar sequence, using data from the Catalina Real-time Transient Survey (CRTS). We report preliminary results on detected variability pattern, and discuss possible cases of periodic variability
Il professionista riflessivo: apprendere dalla pratica professionale
Il professionista pu\uf2 arrivare a comprendere che la realizzazione di s\ue9 passa attraverso l\u2019esercizio e l\u2019interpretazione della propria professione. Il riconoscimento del legame tra lavoro e vita reale pu\uf2 spiegare da dove pu\uf2 scaturire la forza per dare una motivazione di senso a favore di ci\uf2 che fa, delle persone per cui lavora e dell\u2019ambiente che vuole contribuire a trasformare
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