arXiv subjects

G. Lombardi

Publications and source records attributed to G. Lombardi.

21 records · Page 2Linked to original sources

arXiv2007

El Roque de Los Muchachos Site Characteristics. II. Analysis of Wind, Relative Humidity and Air Pressure

In this paper we present an analysis of wind speed, wind direction, relative humidity and air pressure taken at TNG, CAMC and NOT at Observatorio del Roque de Los Muchachos, in the Canary Islands. Data are compared in order to check local variations and both long term and short term trends of the microclimate. Furthermore, influence of wind speed on the astronomical seeing is estimated to the aim to better understand the influence of wide scale parameters on local meteorological data. The three telescopes show different prevailing wind direction, wind speed, relative humidity and air pressure confirming differences in local microclimate. We found that seeing deteriorates when wind speed is lower than 3.3 m/s. Comparison in terms of wind speed and high relative humidity (> 90%) shows that TNG seems to have optimal observational conditions with respect to CAMC and NOT. Air pressure analysis shows that ORM is dominated by high pressure. Short time variations of pressure anticipate temperature variations tipically by 2-3 hours, this property vanishes in time scales higher than some hours and disappear in longer time scales.

astro-ph↗

arXiv2006

El Roque de Los Muchachos site characteristics, I.Temperature analysis

In this paper we present an analysis of temperature taken at two telescopes located at the Observatorio del Roque de Los Muchachos in the Canary Islands. More than 20 years of measurements at CAMC are included. The analysis of the data from TNG and CAMC are compared in order to check local variations and long term trends. Furthermore, the temperatures at different heights are correlated to the quality of astronomical seeing. We considered the correlation of NAO Index and annual downtime with mean annual temperatures. The final aim of this work is to better understand the influence of wide scale parameters on local meteorological data. The analysis is done using a statistical approach. From each long series of data we compute the hourly averages and than the monthly averages in order to reduce the short time fluctuations due to the day/night cycle. A particular care is used to minimize any effect due to biases in case of lacking of data. Finally, we compute the annual average from the monthly ones. The two telescopes show similar trends. There is an increase of temperatures of about 1.0 deg/10yrs from the annual means and a more rapid increase of the annual minimums then the maximums. We found that positive NAO Index reduces the increase of temperatures, and accelerates the decrease. Moreover, there is no evidence that positive NAO Index corresponds to a lower number of non-observable nights. Finally, seeing deteriorates when the gradient of temperatures between 2 and 10 m above the ground is greater than -0.6 deg.

astro-ph↗

arXiv1997

Enhanced shot noise in resonant tunneling: theory and experiment

We show that shot noise in a resonant tunneling diode biased in the negative differential resistance regions of the I-V characteristic is enhanced with respect to ``full'' shot noise. We provide experimental results showing a Fano factor up to 6.6, and show that it is a dramatic effect caused by electron-electron interaction through Coulomb force, enhanced by the particular shape of the density of states in the well. We also present numerical results from the proposed theory, which are in agreement with the experiment, demonstrating that the model accounts for the relevant physics involved in the phenomenon.

cond-mat.str-el↗