Radio frequency self-interference from a data processing centre at a radio telescope site     

Roberto Ambrosini  Pietro Bolli  Claudio Bortolotti  Francesco Gaudiomonte  Filippo Messina  Mauro Roma 《Experimental Astronomy》2010,27(3):121-130

Apart from externally generated Radio Frequency Interference (RFI), the occurrence of self-interference is a major concern at any modern radio telescope site. Antenna servo motor controllers, data acquisition processors, and fast computing capabilities operate very close to extremely sensitive and wideband radio astronomical receivers. In this paper, we present a set of measurements of the RFI level generated by a cluster of computers that will be installed at the site of the Sardinia Radio Telescope (SRT). The measured levels are compared to Recommendation ITU-R RA.769-2, which gives the threshold levels for interference detrimental to radio astronomy observations. Our analysis shows that, with proper shielding of the noisiest devices, it will be possible to preserve the present excellent RFI conditions of the SRT site.  相似文献   

The JCMT Legacy Survey of the Gould Belt: a first look at Orion B with HARP     

J. V. Buckle  E. I. Curtis  J. F. Roberts  G. J. White  J. Hatchell  C. Brunt  H. M. Butner  B. Cavanagh  A. Chrysostomou  C. J. Davis  A. Duarte-Cabral  M. Etxaluze  J. Di Francesco  P. Friberg  R. Friesen  G. A. Fuller  S. Graves  J. S. Greaves  M. R. Hogerheijde  D. Johnstone  B. Matthews  H. Matthews  D. Nutter  J. M. C. Rawlings  J. S. Richer  S. Sadavoy  R. J. Simpson  N. F. H. Tothill  Y. G. Tsamis  S. Viti  D. Ward-Thompson  J. G. A. Wouterloot  J. Yates 《Monthly notices of the Royal Astronomical Society》2010,401(1):204-222

The Gould Belt Legacy Survey will survey nearby star-forming regions (within 500 pc), using Heterodyne Array Receiver Programme (HARP), Submillimetre Common-User Bolometer Array 2 and Polarimeter 2 on the James Clerk Maxwell Telescope. This paper describes the initial data obtained using HARP to observe ¹²CO, ¹³CO and C¹⁸O   J = 3 → 2  towards two regions in Orion B, NGC 2024 and NGC 2071. We describe the physical characteristics of the two clouds, calculating temperatures and opacities utilizing all the three isotopologues. We find good agreement between temperatures calculated from CO and from dust emission in the dense, energetic regions. We determine the mass and energetics of the clouds, and of the high-velocity material seen in ¹²CO emission, and compare the relative energetics of the high- and low-velocity material in the two clouds. We present a clumpfind analysis of the ¹³CO condensations. The slope of the condensation mass functions, at the high-mass ends, is similar to the slope of the initial mass function.  相似文献   

Supernova remnants, planetary nebulae and the distance to NGC 4214     

Michael A. Dopita  Daniela Calzetti  Jesús Maíz Apellániz  William P. Blair  Knox S. Long  Max Mutchler  Bradley C. Whitmore  Howard E. Bond  John MacKenty  Bruce Balick  Marcella Carollo  Michael Disney  Jay A. Frogel  Robert O’Connell  Donald Hall  Jon A. Holtzman  Randy A. Kimble  Patrick McCarthy  Francesco Paresce  Abhijit Saha  Alistair R. Walker  Joe Silk  Marco Sirianni  John Trauger  Rogier Windhorst  Erick Young 《Astrophysics and Space Science》2010,330(1):123-131

We present narrow band, continuum subtracted Hα, [S ii], Hβ, [O iii] and [O ii] data taken with the Wide Field Camera 3 on the Hubble Space Telescope in the nearby dwarf starburst galaxy NGC 4214. From these images, we identify seventeen new planetary nebula candidates, and seven supernova remnant candidates. We use the observed emission line luminosity function of the planetary nebulae to establish a new velocity-independent distance to NGC 4214. We conclude that the PNLF technique gives a reddening independent distance to NGC 4214 of 3.19±0.36 Mpc, and that our current best-estimate of the distance to this galaxy ids 2.98±0.13 Mpc.  相似文献   

Hydrogeochemistry of Roccamonfina volcano (Southern Italy)   总被引：1，自引：1，他引：0  

Emilio Cuoco  Giuseppe Verrengia  Stefano De Francesco  Dario Tedesco 《Environmental Earth Sciences》2010,61(3):525-538

This is the first hydro-geochemical investigation carried out on the Roccamonfina Volcanic Complex groundwaters. The chemistry of Roccamonfina waters is defined by water–rock and water–rock–gas interactions. In fact, interactions between rocks of the first eruptive high-K formations and circulating groundwaters are recognized by high K concentrations. On the other hand, inverse concentration of calcium versus alkali metals is related to two different rock interactions occurring in different areas of the volcano: (a) within the caldera where groundwaters flow within latite and pyroclastic formations releasing calcium, and (b) similarly at the base of the volcano where groundwaters flowing from surrounding carbonates got strongly enriched in Ca. These geochemical processes are also associated with K (SE of caldera) and Mg/Ca (in sites located at the NE base of the volcano) decrease. Completely different dynamics occurs at Riardo groundwaters (SE). Here waters are the result of a mix between the Roccamonfina deep aquifer and the carbonate aquifer of the Riardo plain. Rich-CO₂ emissions make these waters strongly mineralized. Minor elements show a similar geochemical behavior of major ions and are crucial defining interactions processes. The evolution of Roccamonfina groundwaters is also evident along the simultaneous enrichment of Ba, Sr, and Ca. Ba increase is the result of deep local carbonate alteration enhanced by CO₂ emissions and, the lower Sr/Ca ratio, from 10 to 2 (ppb/ppm), is also due to the same process. In the light of our results the Roccamonfina aquifer can be schematically divided into two main reservoirs: (a) a superficial aquifer which basically follows the volcanic structure morphology and tectonics and (b) a deeper reservoir, originating within the oldest Roccamonfina volcano ultra potassic lavas and then flowing into the carbonate aquifers of the neighboring plain. Eventually, the chemistry of the Roccamonfina aquifer does not show any specific and visible pollution, contrary to what happens in the volcano surrounding plains. In fact, only 14% of the samples we collected (206) show a NO₃ content >30 mg/l. These sites are all located at the base of the volcano, near the plain.  相似文献   

First-principles calculation of H/D isotopic fractionation between hydrous minerals and water     

Merlin Méheut  Michele Lazzeri  Etienne Balan  Francesco Mauri 《Geochimica et cosmochimica acta》2010,74(14):3874-3882

Hydrogen fractionation laws between selected hydrous minerals (brucite, kaolinite, lizardite, and gibbsite) and perfect water gas have been computed from first-principles quantum-mechanical calculations. The β-factor of each phase was calculated using the harmonic phonon dispersion curves obtained within density functional theory. All the fractionation laws show the same shape, with a minimum between 200 °C (brucite) and 500 °C (gibbsite). At low temperatures, the mineral/liquid water fractionation laws have been obtained using the experimental gas/liquid water fractionation laws. The resulting fractionation laws systematically overestimate measurements by 15‰ at low temperatures to 8‰ at ≈400 °C. Based on this general agreement, all calculated laws were empirically corrected with reference to brucite/water data. These considerations suggest that the experimental or natural calibrations by Xu and Zheng (1999) and Horita et al. (2002) (brucite/water), Gilg and Sheppard (1996) (kaolinite/water), Wenner and Taylor (1973) (lizardite/water), and in some extents Vitali et al. (2001) (gibbsite/water) are representative of equilibrium fractionations. Besides, internal isotopic fractionation of hydrogen between inner-surface and inner hydroxyl groups has been computed for kaolinite and lizardite. The obtained fractionation is large, of opposite sign for the two systems (respectively, −23‰ and +63‰ at 25 °C) and is linear in T^-2. Internal fractionation of hydrogen in TO phyllosilicates might thus be used in geothermometry.  相似文献   

Contrasting physical and chemical conditions of two rock glacier springs     

Stefano Brighenti  Michael Engel  Monica Tolotti  Maria Cristina Bruno  Geraldene Wharton  Francesco Comiti  Werner Tirler  Leonardo Cerasino  Walter Bertoldi 《水文研究》2021,35(4):e14159

  相似文献   

Economic impacts of climate change in Europe: sea-level rise     

Francesco?BoselloEmail author  Robert?J.?Nicholls  Julie?Richards  Roberto?Roson  Richard?S.?J.?Tol 《Climatic change》2012,112(1):63-81

This paper uses two models to examine the direct and indirect costs of sea-level rise for Europe for a range of sea-level rise scenarios for the 2020s and 2080s: (1) the DIVA model to estimate the physical impacts of sea-level rise and the direct economic cost, including adaptation, and (2) the GTAP-EF model to assess the indirect economic implications. Without adaptation, impacts are quite significant with a large land loss and increase in the incidence of coastal flooding. By the end of the century Malta has the largest relative land loss at 12% of its total surface area, followed by Greece at 3.5% land loss. Economic losses are however larger in Poland and Germany (483 and483 and 391 million, respectively). Coastal protection is very effective in reducing these impacts and optimally undertaken leads to protection levels that are higher than 85% in the majority of European states. While the direct economic impact of sea-level rise is always negative, the final impact on countries’ economic performances estimated with the GTAP-EF model may be positive or negative. This is because factor substitution, international trade, and changes in investment patterns interact with possible positive implications. The policy insights are (1) while sea-level rise has negative and huge direct economic effects, overall effects on GDP are quite small (max −0.046% in Poland); (2) the impact of sea-level rise is not confined to the coastal zone and sea-level rise indirectly affects landlocked countries as well (Austria for instance loses −0.003% of its GDP); and (3) adaptation is crucial to keep the negative impacts of sea-level rise at an acceptable level.  相似文献   

“Galileo Galilei” (GG) a small satellite to test the equivalence principle of Galileo, Newton and Einstein     

Anna M. Nobili  Gian Luca Comandi  Suresh Doravari  Donato Bramanti  Rajeev Kumar  Francesco Maccarrone  Erseo Polacco  Slava G. Turyshev  Michael Shao  John Lipa  Hansjoerg Dittus  Claus Laemmerzhal  Achim Peters  Jurgen Mueller  C. S. Unnikrishnan  Ian W. Roxburgh  Alain Brillet  Christian Marchal  Jun Luo  Jozef van der Ha  Vadim Milyukov  Valerio Iafolla  David Lucchesi  Paolo Tortora  Paolo De Bernardis  Federico Palmonari  Sergio Focardi  Dino Zanello  Salvatore Monaco  Giovanni Mengali  Luciano Anselmo  Lorenzo Iorio  Zoran Knezevic 《Experimental Astronomy》2009,23(2):689-710

“Galileo Galilei” (GG) is a small satellite designed to fly in low Earth orbit with the goal of testing the Equivalence Principle—which is at the basis of the General Theory of Relativity—to 1 part in 10¹⁷. If successful, it would improve current laboratory results by 4 orders of magnitude. A confirmation would strongly constrain theories; proof of violation is believed to lead to a scientific revolution. The experiment design allows it to be carried out at ambient temperature inside a small 1-axis stabilized satellite (250 kg total mass). GG is under investigation at Phase A-2 level by ASI (Agenzia Spaziale Italiana) at Thales Alenia Space in Torino, while a laboratory prototype (known as GGG) is operational at INFN laboratories in Pisa, supported by INFN (Istituto Nazionale di fisica Nucleare) and ASI. A final study report will be published in 2009.  相似文献   

Nebular shock waves generated by planetesimals passing through Jovian resonances: Possible sites for chondrule formation     

Lon L. HOOD  Fred J. CIESLA  Natalia A. ARTEMIEVA  Francesco MARZARI  Stuart J. WEIDENSCHILLING 《Meteoritics & planetary science》2009,44(3):327-342

Abstract— The primordial asteroid belt contained at least several hundred and possibly as many as 10,000 bodies with diameters of 1000 km or larger. Following the formation of Jupiter, nebular gas drag combined with passage of such bodies through Jovian resonances produced high eccentricities (e = 0.3‐0.5), low inclinations (i < 0.5°), and, therefore, high velocities (3–10 km/s) for “resonant” bodies relative to both nebular gas and non‐resonant planetesimals. These high velocities would have produced shock waves in the nebular gas through two mechanisms. First, bow shocks would be produced by supersonic motion of resonant bodies relative to the nebula. Second, high‐velocity collisions of resonant bodies with non‐resonant bodies would have generated impact vapor plume shocks near the collision sites. Both types of shocks would be sufficient to melt chondrule precursors in the nebula, and both are consistent with isotopic evidence for a time delay of ?1‐1.5 Myr between the formation of CAIs and most chondrules. Here, initial simulations are first reported of impact shock wave generation in the nebula and of the local nebular volumes that would be processed by these shocks as a function of impactor size and relative velocity. Second, the approximate maximum chondrule mass production is estimated for both bow shocks and impact‐generated shocks assuming a simplified planetesimal population and a rate of inward migration into resonances consistent with previous simulations. Based on these initial first‐order calculations, impact‐generated shocks can explain only a small fraction of the minimum likely mass of chondrules in the primordial asteroid belt (?10²⁴‐10²⁵g). However, bow shocks are potentially a more efficient source of chondrule production and can explain up to 10–100 times the estimated minimum chondrule mass.  相似文献   

The hypsometric curve of Mars     

Marcello Coradini  Marcello Fulchignoni  Francesco Visicchio 《Earth, Moon, and Planets》1980,22(2):201-210

For the construction of the hypsometric curve of Mars the topographic map of the planet produced by the U.S.G.S. has been utilized. All the areas delimited by isolines and geographic grid have been measured, then summing all the contributions given by the areas included between the same isolines. Such measurements have been effected by means of a solid-state optical image analyzer.A comparative study of the hypsometric curves of the Earth and the Moon shows that, on Mars, several processes of vertical differentiation of the crust started, but did not develop completely owing to the exhaustion of the endogenic forces which determine the surficial dynamics of a planet.A model of the evolution of the Martian crust is discussed in order to justify the shape of the hypsometric curve.Paper presented at the European Workshop on Planetary Sciences, organised by the Laboratorio di Astrofisica Spaziale di Frascati, and held between April 23–27, 1979, at the Accademia Nazionale del Lincei in Rome, Italy.  相似文献