Sofia University

About: Sofia University is a education organization based out in Sofia, Bulgaria. It is known for research contribution in the topics: Large Hadron Collider & Standard Model. The organization has 8533 authors who have published 15730 publications receiving 306320 citations. The organization is also known as: University of Sofia & BFUS.

Searches for invisible decays of the Higgs boson in pp collisions at √s = 7, 8, and 13 TeV

Abstract: Searches for invisible decays of the Higgs boson are presented. The data collected with the CMS detector at the LHC correspond to integrated luminosities of 5.1, 19.7, and 2.3 fb−1 at centre-of-mass energies of 7, 8, and 13 TeV, respectively. The search channels target Higgs boson production via gluon fusion, vector boson fusion, and in association with a vector boson. Upper limits are placed on the branching fraction of the Higgs boson decay to invisible particles, as a function of the assumed production cross sections. The combination of all channels, assuming standard model production, yields an observed (expected) upper limit on the invisible branching fraction of 0.24 (0.23) at the 95% confidence level. The results are also interpreted in the context of Higgs-portal dark matter models.

Variable chlorophyll fluorescence and its use for assessing physiological condition of plant photosynthetic apparatus

Abstract: Analysis of plant behavior under diverse environmental conditions would be impossible without the methods for adequate assessment of the processes occurring in plants. The photosynthetic apparatus and its reaction to stress factors provide a reliable source of information on plant condition. One of the most informative methods based on monitoring the plant biophysical characteristics consists in detection and analysis of chlorophyll a fluorescence. Fluorescence is mainly emitted by chlorophyll a from the antenna complexes of photosystem II (PSII). However, fluorescence depends not only on the processes in the pigment matrix or PSII reaction centers but also on the redox reactions at the PSII donor and acceptor sides and even in the entire electron transport chain. Presently, a large variety of fluorometers from various manufacturers are available. Although application of such fluorometers does not require specialized training, the correct interpretation of the results would need sufficient knowledge for converting the instrumental data into the information on the condition of analyzed plants. This review is intended for a wide range of specialists employing fluorescence techniques for monitoring the physiological plant condition. It describes in a comprehensible way the theoretical basis of light emission by chlorophyll molecules, the origin of variable fluorescence, as well as relations between the fluorescence parameters, the redox state of electron carriers, and the light reactions of photosynthesis. Approaches to processing and analyzing the fluorescence induction curves are considered in detail on the basis of energy flux theory in the photosynthetic apparatus developed by Prof. Reto J. Strasser and known as a “JIP-test.” The physical meaning and relation of each calculated parameter to certain photosynthetic characteristics are presented, and examples of using these parameters for the assessment of plant physiological condition are outlined.

Foaming and foam stability for mixed polymer-surfactant solutions: effects of surfactant type and polymer charge.

Abstract: Solutions of surfactant–polymer mixtures often exhibit different foaming properties, compared to the solutions of the individual components, due to the strong tendency for formation of polymer–surfactant complexes in the bulk and on the surface of the mixed solutions. A generally shared view in the literature is that electrostatic interactions govern the formation of these complexes, for example between anionic surfactants and cationic polymers. In this study we combine foam tests with model experiments to evaluate and explain the effect of several polymer–surfactant mixtures on the foaminess and foam stability of the respective solutions. Anionic, cationic, and nonionic surfactants (SDS, C12TAB, and C12EO23) were studied to clarify the role of surfactant charge. Highly hydrophilic cationic and nonionic polymers (polyvinylamine and polyvinylformamide, respectivey) were chosen to eliminate the (more trivial) effect of direct hydrophobic interactions between the surfactant tails and the hydrophobic regions ...