50 research outputs found
High performance wobbling subreflector for the MITO 2.6-m telescope
No full textThe Millimetre and Infrared Testa Grigia Observatory 2.6-m Cassegrain telescope has been designed to allow high-sensitivity observations in the millimeter spectral range. For this purpose, in order to reduce unwanted contributions from local foregrounds, we adopted a sky-chopping technique, by wobbling the telescope subreflector. We describe the design and performance of the wobbling system, which can endure external forced two and three fields square-wave modulation and includes features such as high frequency, high amplitude, high duty cycle, low microphonics, and high stability. © 1996 Optical Society of America
Power spectra and multifractal structure of the intensity fluctuations in the solar photosphere
No full textWe analyze the scaling properties of the intensity fluctuations in the solar photosphere. This analysis is based on monochromatic and white light images obtained at the THEMIS telescope with the Italian Panoramic Monochromator. We compute power spectra of the intensity fluctuations, showing that these spectra decrease with a power law with an exponent close to -17/3 in the range of scales smaller than 1.5 Mm. We also analyze the height dependence of the multifractal structure of the "dissipation" fields obtained from the intensity fields, in analogy with the dissipation of passive scalars in turbulent fluids. We show that in the higher photosphere the dissipation field become more intermittent and that it is characterized by more singular structures
The multiple jet impingement heat rejecter prototype for the GREGOR solar telescope
No full textHeat rejecter (HR) is a critical component of large aperture solar telescopes. It has the double task of acting as a Field Stop, to select the solar region to be studied, and as a heat rejecter to reduce the thermal load in the subsequent optics and keep the temperature of all internal surfaces within a few degrees of the ambient temperature. This last request is necessary to avoid the onset of internal convective air plumes and the subsequent generation of internal seeing. Since the thermal flux at the primary focus of a 4-m class telescope, as the European Solar Telescope (EST), is expected to be of the order of several MW=m2, even considering high HR reflectivity, the residual thermal load is conceivably high and a suitable Cooling Systems must be considered. Among the available cooling techniques, the most promising, and already applied in critical conditions such as for nuclear fusion reactor divertor, is the Multiple Jet Impingement (MJI) techniques. To fulfill the technological challenge of the HR for the next generation 4-m class European Solar Telescope (EST), a new prototype for the 1.5 meters GREGOR solar telescope has been developed as technological proof of concept. With the aim of testing this technique, a prototype of HR was realized to be mounted at the 1.5 meters GREGOR solar telescope at the at the Teide Observatory (Canary Islands, Spain). We present the HR thermal-hydraulic design based on the expected thermal load on the GREGOR primary focal plane (≃ 1500W) and the constraints on the HR temperature. The MJI technology consists in a series of nozzles impinging the liquid coolant on the backside of the field stop hot wall. The high cooling capabilities of MJI relies on the high Reynolds numbers achievable, even with modest velocity flow. In this work we describe our efforts to design, fabricate and test the prototype of an HR to characterize the MJI technology. More in detail, we show the results of the hydraulic and thermal tests carried out in the opto-electronics laboratory of the Physics Department of the University of Rome Tor Vergata
Preliminary results on solar photospheric MHD turbulence studied via signed measures. (Based on THEMIS/IPM observations.)
No full textIn the present paper the autors report about the occurrence of sign-singularity in the solar photospheric MHD turbulence, using Dopplergrams provided during the past August 1997 by the Italian Panoramic Monochromator (IPM) at the THEMIS telescope (Tenerife)
The Car Sharing experience in Rome: when less is more
No full textCar Sharing (CS) in Rome started to be operative in March 2005, as a trial within an EC-funded project; despite its initial, modest implementation, the measure soon proved to be popular and therefore worth to be progressively enlarged across the city. Nowadays, CS is available in the most central neighbourhoods of the city, but more vehicles are expected to be operative in other areas very soon. A co-operation between the local CS operator (Agenzia Roma Servizi della Mobilità) and the “Sapienza” Department of Civil Engineering was started to develop such an expansion plan, according to an in-depth analysis of the operations run so far. For this purpose, a series of performance indicators has been defined and elaborated in order to assess the efficiency of CS not only under the operational point of view, but also in terms of achievable environmental benefits. Hence, the general approach has been two-pronged: on the one hand, operational indicators have been meant to provide values which may constitute a kind of threshold for the feasibility of the planned expansion to other areas; on the other, calculations of emissions of the CS fleet have been aimed at proving how a niche measure, as sharing cars, may positively contribute to improve air quality levels. If the former goal is clearly aimed at providing the local CS operator with sound reasons to upscale operations and place new resources at a given place rather than another in sight of major incomes, the latter is, on the contrary, focused on increasing the awareness, among the traditional drivers, of the need to switch towards more sustainable mobility patterns, in a city as Rome, where one of the highest motorization rates in Europe is recorded: 978 vehicles, including two-wheelers, every 1,000 in-habitants.
To have car-dependent citizens renouncing to their own vehicles in favor of paratransit seems, therefore, to be a very challenging task whose positive outcomes can go far beyond the simple promotion of an alternative mode of transportation, being less pollution and increased livability more important premium values for the built environment
Dependence of the photospheric vertical flow characteristics on the granule dimension
No full textThe first high spectral resolution and white-light images obtained at the THEMIS telescope with the Italian Panoramic Monochromator (IPM), are analyzed to study intensity and velocity fluctuations in the photosphere of the sun. Monochromatic images, in two spectral ranges around 538.03 nm (C I line) and 557.61 nm (Fe I line), are used to characterize the vertical structure of the photosphere. Granulation cells and granules are obtained by segmentation of white-light images using suitable finding algorithms. We observe the height dependence of velocity vs. intensity fluctuations, and we found a dependence of velocity and intensity on granule dimension. Our results show that granules increase their intensity with dimension in the lower solar photosphere. In the higher photosphere, on the contrary, the intensity decreases with the dimension. Based on THEMIS/CNRS-INSU/CNR telescope observation
Scaling behavior of the vertical velocity field in the solar photosphere
No full textWe analyze, for the first time, the scaling behavior of the photospheric vertical velocity field. Our analysis is based on data collected by the Italian Panoramic Monocromator (IPM) mounted at the THEMIS telescope at the Spanish ``Observatorio del Teide'' (Tenerife) of the Instituto de Astrofisica de Canarias. We investigate the occurrence of scaling in the cancellations between downflow and upflow of the vertical velocity field, showing that the field possesses well pronunced sign-singularity in the range of scales from more than 10 Mm down to the granulation scale. Based on THEMIS/CNRS--INSU/CNR telescope observation
MITO: the 2.6-m millimetre telescope at Testa Grigia
No full textWe describe a new ground based telescope dedicated to millimetre cosmological research: MITO, Millimetre and Infrared Testagrigia Observatory. The site and all the instrumental subsystems of the telescope have been chosen to perform high sensitivity measurements for wavelengths ranging from 300 micron to 2 millimetre. The possibility of detecting fluctuations of the Cosmic Microwave Background has been explored for some observational strategies
A ground-based experiment for CMBR anisotropy observations: MITO
No full textGround-based observations at millimeter wavelengths are still competitive with space observatories if inevitable foreground contamination is considered at all stages of data acquisition and analysis. Technical solutions together with carefully chosen cosmological targets and observational strategies are the key points in the development of the MITO experiment. © 1999 Elsevier Science B.V. All rights reserved
