Application of a new screening model to thermonuclear reactions of the rp process

A new screening model for astrophysical thermonuclear reactions was derived recently which improved Salpeter's weak-screening one. In the present work we prove that the new model can also give very reliable screening enhancement factors (SEFs) when applied to the rp process. According to the results of the new model, which agree well with Mitler's SEFs, the screened rp reaction rates can be, at most, twice as fast as the unscreened ones.Comment: 8 RevTex pages + 7 ps figures. (Revised version). Accepted for publication in Journal of Physics

Screened alpha decay in dense astrophysical plasmas and magnetars

This paper shows that ultrastrong magnetic fields (such as those of magnetars) and dense astrophysical plasmas can reduce the half life of alpha decaying nuclei by many orders of magnitude. In such environments the conventional Geiger-Nuttall law is modifed so that all half lives are shifted to dramatically lower values. Those effects, which have never been investigated before, may have significant implications on the universal abundances of heavy radioactive elements and the cosmochronological methods that rely on them.Comment: 15 RevTex pages, 3 ps figures (minor revision). This work was presented during the conference ''Supernova, 10 years of SN1993J'', April 2003, Valencia, Spain. Accepted for publication in Phys.Rev.

Astrophysical factors:Zero energy vs. Most effective energy

Effective astrophysical factors for non-resonant astrophysical nuclear reaction are invariably calculated with respect to a zero energy limit. In the present work that limit is shown to be very disadvantageous compared to the more natural effective energy limit. The latter is used in order to modify the thermonuclear reaction rate formula so that it takes into account both plasma and laboratory screening effects.Comment: 7 RevTex pages. Accepted for publication in Phys.Rev.

A stochastic approach for dynamic soil-pile interaction under enviromental effects.

The paper deals with a computational stochastic approach for the unilateral contact problem of dynamic soil-pile interaction. Unilateral contact effects due to tensionless soil capacity, soil elastoplastic-fracturing behaviour and gapping are strictly taken into account, as well as environmental effects under uncertainty decreasing the soil resistance. The proposed methodology concerns the treatment of both, the deterministic and the probabilistic problem. The numerical approach concerning the deterministic problem is based on a double discretization, in space by the Finite Element Method combined with Boundary Element Method, and in time, and on nonconvex optimization. Uncertainties concerning the input parameter values are treated by the Monte Carlo method in the probabilistic problem section. Finally, the proposed methodology is applied for a practical case of dynamic soil-pile interaction

Atomic effects in astrophysical nuclear reactions

Two models are presented for the description of the electron screening effects that appear in laboratory nuclear reactions at astrophysical energies. The two-electron screening energy of the first model agrees very well with the recent LUNA experimental result for the break-up reaction $He3(He3,2p)He^{4}$, which so far defies all available theoretical models. Moreover, multi-electron effects that enhance laboratory reactions of the CNO cycle and other advanced nuclear burning stages, are also studied by means of the Thomas-Fermi model, deriving analytical formulae that establish a lower and upper limit for the associated screening energy. The results of the second model, which show a very satisfactory compatibility with the adiabatic approximation ones, are expected to be particularly useful in future experiments for a more accurate determination of the CNO astrophysical factors.Comment: 14 RevTex pages + 2 ps (revised) figures. Phys.Rev.C (in production

Progressive Collapse of Existing RС Structures due to Environmental Effects: A Numerical Approach for Strengthening by Ties

Existing old reinforced concrete (RC) buildings are sometimes subjected to obligatory removal of some structural element‐members, e.g. columns, and so to the risk of a progressive collapse. This happens due to various reasons, which can concern changes of serviceability and requirements, or environmental effects which cause strength degradation etc. In order to avoid such a progressive collapse, a modification of the structural response and a redistribution of internal actions can result to a requirement for strengthening the remaining structure after the removal of the degraded elements. The present study deals with such a case, which concerns the computational analysis of framed RC structures under the removal of some columns and the so‐induced requirement of a strengthening by ties (tension only elements). The unilateral behaviour of these cable‐ties, which can undertake only tension, is strictly considered, and the response of the remaining historic structure strengthened by ties is computed. Finally, in a practical case of a framed RC structure, the effectiveness of the proposed methodology is shown.ABSTRACTS ХІХ МЕЖДУНАРОДНА НАУЧНА КОНФЕРЕНЦИЯ ПО СТРОИТЕЛСТВО И АРХИТЕКТУРА ВСУ'2019 се организира със съдействието на Фонд "Научни изследвания" с договор за съфинансиране № КП‐06‐МНФ/34. Editors: Vanyo Georgiev, Assoc. Prof. PhD Aleksandra Ivanova, Assoc. Prof. PhD artist Ventsislav Stoyanov, Assoc. Prof. PhD Eng. Yulia Ilieva, Assoc. Prof. PhD Architec

Screened thermonuclear reactions and predictive stellar evolution of detached double-lined eclipsing binaries

The low energy fusion cross sections of charged-particle nuclear reactions (and the respective reaction rates) in stellar plasmas are enhanced due to plasma screening effects. We study the impact of those effects on predictive stellar evolution simulations for detached double-lined eclipsing binaries. We follow the evolution of binary systems (pre-main sequence or main sequence stars) with precisely determined radii and masses from 1.1Mo to 23Mo (from their birth until their present state). The results indicate that all the discrepancies between the screened and unscreened models (in terms of luminosity, stellar radius, and effective temperature) are within the observational uncertainties. Moreover, no nucleosynthetic or compositional variation was found due to screening corrections. Therefore all thermonuclear screening effects on the charged-particle nuclear reactions that occur in the binary stars considered in this work (from their birth until their present state) can be totally disregarded. In other words, all relevant charged-particle nuclear reactions can be safely assumed to take place in a vacuum, thus simplifying and accelerating the simulation processes.Comment: 5 RevTex pages,no figures. Accepted for publication in Phys.Rev.

Screening enhancement factors for laboratory CNO and rp astrophysical reactions

Cross sections of laboratory CNO and rp astrophysical reactions are enhanced due to the presence of the multi-electron cloud that surrounds the target nuclei. As a result the relevant astrophysical factors are overestimated unless corrected appropriately. This study gives both an estimate of the error committed if screening effects are not taken into account and a rough profile of the laboratory energy thresholds at which the screening effect appears. The results indicate that, for most practical purposes, screening corrections to past relevant experiments can be disregarded. Regarding future experiments, however, screening corrections to the CNO reactions will certainly be of importance as they are closely related to the solar neutrino fluxes and the rp process. Moreover, according to the present results, screening effects will have to be taken into account particularly by the current and future LUNA experiments, where screened astrophysical factors will be enhanced to a significant degree.Comment: 6 RevTex pages + 2 ps figures. (Revised version). Accepted for publication in Journal of Physics