arXiv subjects

A. A. Radu

Publications and source records attributed to A. A. Radu.

6 recordsLinked to original sources

arXiv2017

Advanced Kelvin Probe Operational Methodology for Space Applications

We present a novel methodology for the operation of macroscopic Kelvin Probe instruments. The methodology is based on the use of a harmonic backing potential signal to drive the tip-sample variable capacitance and on a Fourier representation of the tip current, allows for the operation of the instrument under full control and improves its scanning performance by a factor of 60 or more over that of currently available commercial instruments.

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arXiv2011

An astroclimatological study of candidate sites to host an imaging atmospheric Cherenkov telescope in Romania

We come out in this paper with an astroclimatological study of meteorological data on relative humidity, dew point temperature, air temperature, wind speed, barometric air pressure, and sky cloudiness recorded at four Romanian locations (Baisoara, Rosia Montana, Semenic, Ceahlau) and Nordic Optical Telescope (NOT) located at Observatorio del Roque de Los Muchachos, in the Canary Islands. Long term trends of microclimates have been compared in order to identify the site-to-site variations. We have performed this analysis as part of a site testing campaign aimed at finding the best location for the establishment of a small Cherenkov telescope in Romania. The conditions at the Romanian sites have been compared to those of the Canary Islands considered as a reference. A statistical approach has been used for data analysis. Monthly and annual samples have been extracted from series of raw data for nighttime, daytime and entire day intervals. Percentage distributions of meteorological parameters, whose values exceed certain limits, have been derived. Significant differences have been found between the Romanian sites and the NOT site. The comparison of the Romanian locations indicates Baisoara to be the best site for the establishment of the telescope, closely followed by Rosia Montana. As these two sites are both located in the Apuseni Mountains, we consider this area as the optimal place for performing astronomical observations in Romania.

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arXiv2010

A Site Evaluation Campaign for a Ground Based Atmospheric Cherenkov Telescope in Romania

Around the world, several scientific projects share the interest of a global network of small Cherenkov telescopes for monitoring observations of the brightest blazars - the DWARF network. A small, ground based, imaging atmospheric Cherenkov telescope of last generation is intended to be installed and operated in Romania as a component of the DWARF network. To prepare the construction of the observatory, two support projects have been initiated. Within the framework of these projects, we have assessed a number of possible sites where to settle the observatory. In this paper we submit a brief report on the general characteristics of the best four sites selected after the local infrastructure, the nearby facilities and the social impact criteria have been applied.

astro-ph.IM↗

arXiv2009

Intermittency route to chaos for the nuclear billiard - a quantitative study

We extended a previous qualitative study of the intermittent behaviour of a chaotical nucleonic system, by adding a few quantitative analyses: of the configuration and kinetic energy spaces, power spectra, Shannon entropies, and Lyapunov exponents. The system is regarded as a classical "nuclear billiard" with an oscillating surface of a 2D Woods-Saxon potential well. For the monopole and dipole vibrational modes we bring new arguments in favour of the idea that the degree of chaoticity increases when shifting the oscillation frequency from the adiabatic to the resonance stage of the interaction. The order-chaos-order-chaos sequence is also thoroughly investigated and we find that, for the monopole deformation case, an intermittency pattern is again found. Moreover, coupling between one-nucleon and collective degrees of freedom is proved to be essential in obtaining chaotic states.

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arXiv2009

Intermittency route to chaos for the nuclear billiard - a qualitative study

We analyze on a simple classical billiard system the onset of chaotical behaviour in different dynamical states. A classical version of the "nuclear billiard" with a 2D deep Woods-Saxon potential is used. We take into account the coupling between the single-particle and the collective degrees of freedom in the presence of dissipation for several vibrational multipolarities. For the considered oscillation modes an increasing divergence of the nucleonic trajectories from the adiabatic to the resonance regime was observed. Also, a peculiar case of intermittency is reached in the vicinity of the resonance, for the monopole case. We examine the order-to-chaos transition by performing several types of qualitative analysis including sensitive dependence on the initial conditions, single-particle phase space maps, fractal dimensions of Poincare maps and autocorrelation functions.

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arXiv2008

Experimental Evidence for Optimal Resonances in Pion-Nucleus Scattering

Experimental data on the pion-nucleus total cross sections are analyzed in terms of the optimal resonances predictions (OR). The OR-predictions are found in a good agreement with the actual experimental data in the region corresponding to the Delta(1236) resonance in elementary pi-N scattering. The essential signatures of the optimal resonances are experimentally verified with high accuracy.

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