1,721,065 research outputs found
The HST view of FR I radio galaxies: evidence for non--thermal sources
No full textUnresolved nuclear sources are detected by the Hubble Space Telescope in the great majority of a complete sample of 33 FR I radio galaxies belonging to the 3CR catalogue.
The optical flux of these Central Compact Cores (CCC) shows a striking linear correlation with the radio core one over four decades, arguing for a non-thermal synchrotron origin of the CCC radiation. We also find evidence that this emission is anisotropic, which leads us to identify CCCs with the misoriented relativistic jet component which dominates in BL Lac objects. This interpretation is also supported by the similarity in the radio-to-optical and optical spectral indices.
The high rate of CCC detection (85%) suggests that a "standard" pc scale, geometrically thick torus is not present in low luminosity radio-galaxies. Thus the lack of broad lines in FR I cannot be attributed to obscuration.
CCC fluxes also represent upper limits to any thermal/disc emission. For a 10(9)M(.) black hole, typical of FR I sources, these limits translate into a fraction as small as less than or similar to 10(-7) - 10(-5) of the Eddington luminosity
Analyzing relationship between maize height and spectral indices derived from remotely sensed multispectral imagery
No full textFor maize crop, biophysical parameters such as canopy height and above ground biomass are the crucial agro-ecological indicator that can be used to describe the crop growth, photosynthetic efficiency and carbon stock. Remote sensing is widely used approach and most appropriate source in terms of area coverage that can be used to monitor vegetative conditions over the large area. In this study, sentinel-2 multispectral imagery is used to calculate spectral vegetation indices over the different maize growth period using some visible bands including near infrared spectrum. The relationship has been established and analyzed between maize biophysical variables (height of the canopy and above ground biomass) collected during the field measurements and derived spectral vegetation indices using simple linear regression and pearson correlation to exploit the possibility of using satellite imagery for estimation of crop biophysical parameters
The HST view of the FR I FR II dichotomy
No full textIn order to explore how the FR I/FR II dichotomy is related to the nuclear properties of radio galaxies, we studied a complete sample of 26 nearby FR II radio galaxies using Hubble Space Telescope (HST) images and compared them with a sample of FR I previously analyzed. FR I nuclei lie in the radio-optical luminosity plane along a tight linear correlation, which argues for a common synchrotron origin. FR II show a more complex behavior, which is however clearly related to their optical spectral classification.
Broad line FR II radio galaxies (BLRG) are located overall well above the FR I correlation, suggesting that a contribution from thermal (disc) emission is present. Three narrow line (NLRG) and one weak line radio galaxy (WLRG), in which no nuclear source is seen, can be interpreted as the obscured counter-parts of BLRG, in agreement with the current unification schemes.
Conversely, in 5 sources of the sample, all of them NLRG or WLRG, optical cores are located on the same correlation defined by FR I and with similar radio and optical luminosities. This suggests that, in analogy to FR I, the emission is dominated by synchrotron radiation and represents the optical counter-part of the non-thermal radio cores. Interestingly, all these galaxies are located in clusters, an environment typical of FR I.
These results imply that, at least at low redshifts, the FR II population is not homogeneous. Furthermore, the traditional dichotomy between edge darkened and brightened radio morphology is not unequivocally connected with the innermost nuclear structure, as we find FR II with FR I-like nuclei and this has interesting bearings from the point of view of the AGN unified model
The BL Lac heart of Centaurus A
No full textEmission from the nucleus of the closest radio galaxy, Centaurus A, is observed from the radio to the gamma ray band. We build, for the first time, its overall Spectral Energy Distribution (SED) that appears to be intriguingly similar to those of blazars, showing two broad peaks located in the far-infrared band and at ~0.1 MeV respectively. The whole nuclear emission of Centaurus A is successfully reproduced with a synchrotron self-Compton model. The estimated physical parameters of the emitting source are similar to those of BL Lacs, except for a much smaller beaming factor, as qualitatively expected when a relativistic jet is orientated at a large angle to the line of sight. These results represent strong evidence that Centaurus A is indeed a misoriented BL Lac and provide strong support in favour of the unification scheme for low luminosity radio-loud AGNs. Modeling of the SED of Centaurus A also provides further and independent indications of the presence of velocity structures in sub-pc scale jets
Understanding effects of atmospheric variables on spectral vegetation indices derived from satellite based time series of multispectral images
No full textIn agricultural practices, it is very essential to monitor crops phenological pattern over the time to manage agronomic activities such as irrigation, weed control, pest control, fertilization, drainage system etc. From the past decade, due to free availability of data and large coverage area, satellite based remote sensing has been most popular and widely used among other techniques such as physical ground surveys, ground based sensors and aerial based remote sensing. Sentinel-2 is European based satellite equipped with the state of the art multispectral imager which offers high spectral resolution (13- spectral bands), high spatial resolution (up to 10m pixel -1 ) and good temporal resolution (6 to 10days). Considering these features, time series of multispectral images of sentinel-2 has been used to establish temporal pattern of spectral vegetation indices (i.e. NDVI, SAVI, EVI, RVI) of crops to monitor the phenological behavior over time. In addition, the influence of various atmospheric variables (such as temperature in the air and precipitation ) on the derived spectral vegetation indices has also been investigated in this work. Land use and coverage area frame survey (LUCAS-2015) has been used as ground reference data for this study. This study shows that by using sentinel-2, understanding relation between atmospheric conditions and crops phenological behavior can be useful to manage agricultural activities
Robust Control Architecture for Waste Heat Harvesting with Non-Inverting Buck-Boost Converter
Full text linkThermoelectric generators (TEG) can be used to harvest wasted heat. TEGs are characterized by a wide output voltage range and a considerable output resistance leading to a maximum power point dependent on the working temperature. Non-Inverting Buck-Boost converter is used to manage, from one side, the wide voltage range, and from the other a battery. This article investigates a robust control architecture to recover the maximum energy from the exhaust's heat avoiding instability issues and maximizing converter efficiency
Understanding the nature of FR II optical nuclei: a new diagnostic plane of radio galaxies
No full textWe extend our study of the nuclei of 3CR FR II radio galaxies through HST optical images up to z=0.3. In the majority of them an unresolved nucleus (central compact core, CCC) is found. We analyze their position in the plane formed by the radio and optical nuclear luminosities in relation to their optical spectral properties. The broad-lined objects (BLO) have the brightest nuclei: they are present only at optical luminosities nu L_nu > 4 X 10^42 erg s^-1 which we suggest might represent a threshold in the radiative efficiency combined to a small range of black hole masses. About 40 % of the high and low excitation galaxies (HEG and LEG) show CCC which resemble those previously detected in FR I galaxies, in apparent contrast to the unification model. The equivalent width of the [OIII] emission line (with respect to the nuclear luminosity) reveals the nature of these nuclei, indicating that the nuclei of HEG are obscured to our line of sight and only scattered radiation is observed. This implies that the population of FR II is composed by objects with different nuclear properties, and only a fraction of them can be unified with quasars
Does the unification of BL Lac and FR I radio galaxies require jet velocity structures?
No full textWe explore the viability of the unification of BL Lacs and FR 1 radio galaxies by comparing the core emission of radio galaxies with those of BL Lacs of similar extended radio power, taking advantage of the newly measured optical nuclear luminosity of FR I sources. The spectral properties of complete samples are also studied in the radio-optical luminosity plane: starting from the Spectral Energy Distribution (SED) of BL Lacs, we calculate the predicted luminosity of FR I nuclei in the frame of a simple one-zone model, by properly taking into account the relativistic transformations. We find that the bulk Lorentz factors required by the spread in the observed luminosities in all bands are significantly smaller than those implied by other, both observational and theoretical, considerations. This discrepancy is also reflected in the fact that FR I nuclei are overluminous by a factor of 10-10(4), with respect to the predictions, both in the radio and in the optical band
Modular/Scalable approach for energy storage and peak shaving applications
No full textThis paper shows a novel design and implementation of a multi-purpose power module used to manage the energy produced by renewable energy sources and at the same time compensate the discontinuous power absorption from loads, with the final goals to increase power distribution efficiency and grid stability
- …
