Predicting tire/pavement noise impact reduction using numerical simulation and experimental data for open graded asphalt mixture

The environmental impact of noise from roads and highways traffic is relevant in urban and rural areas. The use of open-graded asphalt pavements reduces significantly the noise, entrapping the acoustic waves inside the porous structure of the material. In this paper we propose a simulation approach in order to predict the acoustic properties of the asphalt mixture from geometrical and topological indicators. In detail we have generated, using a Random Sequential Adsorption model, synthetic samples starting from the same grading and bitumen contents of real samples manufactured in laboratory. We have measured the acoustic adsorption coefficient of the real samples and we have investigated the correlation between this coefficient and some numerical indicators extracted from the simulated samples. Dimension and content of voids seem to be the most significant indicators for predicting acoustic properties of HMA. These correlations, that seem to be very promising, are useful in order to optimize the design of HMA in the perspective of minimizing noise impact

Observability of a 2-branch Double-Layer-Capacitor

n/

The Radio Corona of AR Lacertae

We present multifrequency VLA and VLBA observations at 8.4 GHz of the RS CVn system AR Lac, that were performed in autumn 1997 simultaneously with X-ray observations obtained from Rodono` et al. (1999). Our VLBA data indicate a resolved source with dimension close to the system separation, while the study of the flux density curve evidences a small amplitude outside of the eclipse variability. The derived five-frequencies spectra, combined with the size information from VLBA data, are compared with gyrosynchrotron emission from a two component structured source. A comparison with the results of the X-ray observations allow us to exclude the possibility that thermal gyrosynchrotron is responsible for the radio emission, but it is compatible with the hypothesis of co-spatial X-ray and radio emitting sources.Comment: 9 pages, 7 figures. Accepted for publication in A&

The REM Telescope: A robotic multiwavelength facility to promptly follow up GRB afterglows

The REM (Rapid Eye Mount) Telescope, located in la Silla Observatory Chile, is the first moderate (60 cm) aperture robotic telescope able to cover simultaneously both the visible and near-infrared (0.45–2.3 μm) wavelength range. The high-throughput Infrared Camera (REMIR) and the optical imaging spectrograph (ROSS), both equipping the REM telescope, are simultaneously fed by a dichroic and they allow to collect high-S/N data in an unprecedented large spectral range on a telescope of this size. The wide band covered, the very fast pointing capability (60 degrees in 5 seconds) and its full robotization make REM the ideal experiment for fast transients observation. The REM observatory is an example of a versatile and agile facility necessary to complement large telescopes in fields in which rapid response and/or target pre-screening are necessary. This paper describes the main characteristics and operation modes of the REM observatory and gives an overview of preliminary results obtained during the Science Verification Phase

Spots, plages, and flares on lambda Andromedae and II Pegasi

We present the results of a contemporaneous photometric and spectroscopic monitoring of lambda And and II Peg aimed at investigating the behavior of surface inhomogeneities in the atmospheres of these active stars which have nearly the same temperature but different gravity. The light curves and the modulation of the surface temperature, as recovered from LDRs, are used to map the photospheric spots, while the H-alpha emission has been used as an indicator of chromospheric inhomogeneities. The spot temperatures and sizes were derived from a spot model applied to the contemporaneous light and temperature curves. We find larger and cooler spots on II Peg (T_sp ~ 3600 K) compared to lambda And (T_sp ~ 3900 K); this could be the result of both the different gravity and the higher activity level of the former. Moreover, we find a clear anti-correlation between the H-alpha emission and the photospheric diagnostics. We have also detected a modulation of the intensity of the HeI D_3 line with the star rotation. A rough reconstruction of the 3D structure of their atmospheres has been also performed by applying a spot/plage model to the light and temperature curves and to the H-alpha flux modulation. A close spatial association of photospheric and chromospheric active regions has been found in both stars. Larger and cooler spots have been found on II Peg, the system with the active component of higher gravity and higher activity level. The area ratio of plages to spots seems to decrease when the spots get bigger. Moreover, with the present and literature data, a correlation between the temperature difference Delta_T = T_ph - T_sp and the surface gravity has been also suggested. In addition, a strong flare affecting the H-alpha, the HeI D_3, and the cores of NaI D_1,2 lines has been observed on II Peg.Comment: Accepted for publication in A&A (7 November 2007) 12 Pages, 7 Figure

REMIR: The REM infrared camera to follow up the early phases of GRBs afterglows

REMIR is a near-infrared camera, covering the 0.95–2.3 μm range with 5 filters (z,J,H,Ks and H2), mounted at one of the Nasmyth foci of the REM (Rapid Eye Mount) telescope. REM is a fully robotic fast-slewing 60 cm telescope, primarily designed to follow-up the early phases of the afterglow of GRBs detected by dedicated instruments onboard satellites (like SWIFT, a satellite entirely dedicated to GRBs science launched the 12 November 2004). Moreover REM hosts a slitless spectrograph covering the range 0.45–0.95 μm, with 30 sample points and with the possibility to perform broad-band V,R,I photometry (ROSS, REM Optical Slitless Spectrograph). The main task of REMIR is to perform realtime NIR observations of GRBs detected by gamma-ray monitors onboard satellites, looking for any possible infrared transient source. As soon as a transient source is detected in the IR images, larger telescopes are promptly alerted to perform early spectroscopy of the afterglow. All the above operations are performed in a fully automatic way and without any human supervision. We present the results of on-site tests that have been done to characterize the REMIR camera and the performances of the dedicated reduction pipeline AQuA (Automatic Quick Analysis), suited for fast transients detection

X-Ray Spectroscopy of Stars

(abridged) Non-degenerate stars of essentially all spectral classes are soft X-ray sources. Low-mass stars on the cooler part of the main sequence and their pre-main sequence predecessors define the dominant stellar population in the galaxy by number. Their X-ray spectra are reminiscent, in the broadest sense, of X-ray spectra from the solar corona. X-ray emission from cool stars is indeed ascribed to magnetically trapped hot gas analogous to the solar coronal plasma. Coronal structure, its thermal stratification and geometric extent can be interpreted based on various spectral diagnostics. New features have been identified in pre-main sequence stars; some of these may be related to accretion shocks on the stellar surface, fluorescence on circumstellar disks due to X-ray irradiation, or shock heating in stellar outflows. Massive, hot stars clearly dominate the interaction with the galactic interstellar medium: they are the main sources of ionizing radiation, mechanical energy and chemical enrichment in galaxies. High-energy emission permits to probe some of the most important processes at work in these stars, and put constraints on their most peculiar feature: the stellar wind. Here, we review recent advances in our understanding of cool and hot stars through the study of X-ray spectra, in particular high-resolution spectra now available from XMM-Newton and Chandra. We address issues related to coronal structure, flares, the composition of coronal plasma, X-ray production in accretion streams and outflows, X-rays from single OB-type stars, massive binaries, magnetic hot objects and evolved WR stars.Comment: accepted for Astron. Astrophys. Rev., 98 journal pages, 30 figures (partly multiple); some corrections made after proof stag

Doppler images of the RS CVn binary HR 1099 (V711 Tau) from the MUSICOS 1998 campaign

Peer reviewe

Long-term monitoring of active stars

As a part of an extensive program focused on the global properties and evolution of active stars, high-precision $UBV(RI)_{\rm c}$ and UBV photometry of 31 selected stars is presented. The $UBV(RI)_{\rm c}$ observations were collected at the European Southern Observatory over the 31 December 1992-18 January 1993 and the 20 November-3 December 1993 intervals. Additional UBV photometry obtained by the "Phoenix" and by the Catania Astrophysical Observatory Automatic Photoelectric Telescopes from 1990 to 1993 is also presented for some of the program stars. Significant evolution of the light curves, period variations and evidence for long-term variability of the global degree of spottedness are found. Some spectral classifications are revised and the inferred photometric parallaxes are compared, whenever possible, with the values measured by the Hipparcos satellite. These observations are finalized to the construction of an extended photometric database, which can give important clues on topics such as the stability of spotted areas, differential rotation, solar-like cycles and the correlation between inhomogeneities at different atmospheric levels