Bulgarian Academy of Sciences

About: Bulgarian Academy of Sciences is a government organization based out in Sofia, Bulgaria. It is known for research contribution in the topics: Catalysis & Coupling constant. The organization has 17989 authors who have published 36276 publications receiving 642820 citations. The organization is also known as: Bulgarian Academy of Sciences，簡稱：BAS & Balgarska Akademiya na Naukite.

Numerical modelling of finite-amplitude electro-thermo-convection in a dielectric liquid layer subjected to both unipolar injection and temperature gradient

Abstract: In this paper, we solve numerically the entire set of equations associated with the electro-thermo-convective phenomena that take place in a planar layer of dielectric liquid heated from below and subjected to unipolar injection. For the first time the whole set of coupled equations is solved: Navier–Stokes equations, electrohydrodynamic (EHD) equations and the energy equation. We first validate the numerical simulation by comparing the electro-convection stability criteria with ones obtained with a stability approach. The numerical solution of the electro-thermo-convection problem is then presented entirely with a detailed analysis of stability parameters. In particular, the relation between fluid velocity, non-dimensional electrical parameter T, Rayleigh number Ra and Prandtl number Pr is given. An analytical model is presented in order to understand the flow behaviour at some critical conditions. The way that the onset of motion passes from purely electrical convection to purely thermal convection is, in particular, investigated and explained in detail. Finally, a result on the heat transfer enhancement due to electro-convection is exhibited and compared with data from experimental works available in this field.

Precision neutrino oscillation physics with an intermediate baseline reactor neutrino experiment

Abstract: We discuss the physics potential of intermediate $L\ensuremath{\sim}20--30\mathrm{km}$ baseline experiments at reactor facilities. Assuming that the solar neutrino oscillation parameters $\ensuremath{\Delta}{m}_{\ensuremath{\bigodot}}^{2}$ and ${\ensuremath{\theta}}_{\ensuremath{\bigodot}}$ lie in the high LMA solution region, we show that such an intermediate baseline reactor experiment can determine both $\ensuremath{\Delta}{m}_{\ensuremath{\bigodot}}^{2}$ and ${\ensuremath{\theta}}_{\ensuremath{\bigodot}}$ with a remarkably high precision. We perform also a detailed study of the sensitivity of the indicated experiment to $\ensuremath{\Delta}{m}_{\mathrm{atm}}^{2},$ which drives the dominant atmospheric ${\ensuremath{ u}}_{\ensuremath{\mu}}$ $({\overline{\ensuremath{ u}}}_{\ensuremath{\mu}})$ oscillations, and to \ensuremath{\theta}---the neutrino mixing angle limited by the data from the CHOOZ and Palo Verde experiments. Irrespective of the actual values of $\ensuremath{\Delta}{m}_{\ensuremath{\bigodot}}^{2},$ we find that this experiment can improve the bounds on ${\mathrm{sin}}^{2}\ensuremath{\theta},$ and, if the value of ${\mathrm{sin}}^{2}\ensuremath{\theta}$ is large enough, ${\mathrm{sin}}^{2}\ensuremath{\theta}\ensuremath{\gtrsim}0.02,$ the energy resolution of the detector is sufficiently good and if the statistics is relatively high, it can determine with extremely high precision the value of $\ensuremath{\Delta}{m}_{\mathrm{atm}}^{2}.$ We also explore the potential of the intermediate baseline reactor neutrino experiment for determining the type of the neutrino mass spectrum, which can be with normal or inverted hierarchy, assuming $\ensuremath{\Delta}{m}_{\ensuremath{\bigodot}}^{2}$ to lie in the high LMA solution region. We show that the conditions under which the type of neutrino mass hierarchy can be determined are quite challenging, but are within the reach of the experiment under discussion.

A new activity phase of the blazar 3C 454.3. Multifrequency observations by the WEBT and XMM-Newton in 2007-2008

Abstract: We present and analyse the WEBT multifrequency observations of 3C 454.3 in the 2007-2008 observing season, including XMM-Newton observations and near-IR spectroscopic monitoring, and compare the recent emission behaviour with the past one. In the optical band we observed a multi-peak outburst in July-August 2007, and other faster events in November 2007 - February 2008. During these outburst phases, several episodes of intranight variability were detected. A mm outburst was observed starting from mid 2007, whose rising phase was contemporaneous to the optical brightening. A slower flux increase also affected the higher radio frequencies, the flux enhancement disappearing below 8 GHz. The analysis of the optical-radio correlation and time delays, as well as the behaviour of the mm light curve, confirm our previous predictions, suggesting that changes in the jet orientation likely occurred in the last few years. The historical multiwavelength behaviour indicates that a significant variation in the viewing angle may have happened around year 2000. Colour analysis reveals a complex spectral behaviour, which is due to the interplay of different emission components. All the near-IR spectra show a prominent Halpha emission line, whose flux appears nearly constant. The analysis of the XMM-Newton data indicates a correlation between the UV excess and the soft-X-ray excess, which may represent the head and the tail of the big blue bump, respectively. The X-ray flux correlates with the optical flux, suggesting that in the inverse-Compton process either the seed photons are synchrotron photons at IR-optical frequencies or the relativistic electrons are those that produce the optical synchrotron emission. The X-ray radiation would thus be produced in the jet region from where the IR-optical emission comes.