Attractive interactions, molecular complexes, and polarons in coupled dipolar exciton fluids

Dipolar (or spatially indirect) excitons (IXs) in semiconductor double quantum well (DQW) subjected to an electric field are neutral species with a dipole moment oriented perpendicular to the DQW plane. Here, we theoretically study interactions between IXs in stacked DQW bilayers, where the dipolar coupling can be either attractive or repulsive depending on the relative positions of the particles. By using microscopic band structure calculations to determine the electronic states forming the excitons, we show that the attractive dipolar interaction between stacked IXs deforms their electronic wave function, thereby increasing the inter-DQW interaction energy and making the IX electrically polarizable. Many-particle effects interaction are addressed by considering the coupling between a single IX in one of the DQWs to a cloud of IXs in the other DQW, which is modeled either as a closed-packed lattice or as a continuum IX fluid. We find that the lattice model yields IX interlayer binding energies decreasing with increasing lattice density. This behavior is due to the dominating role of the intra-DQW dipolar repulsion, which prevents more than one exciton from entering the attractive region of the inter-DQW coupling. Finally, both models shows that the single IX distorts the distribution of IXs in the adjacent DQW, thus inducing the formation of an IX polaron. While the interlayer binding energy reduces with IX density for lattice polarons, the continuous polaron model predicts a non-monotonous dependence on density in semi-quantitative agreement with a recent experimental study [cf. Hubert {\it et al.}, Phys. Rev. {\bf X}9, 021026 (2019)].Comment: 12 figures, 12 page

Solution of the Dirac equation with non-minimal coupling to noncentral three-vector potential

We introduce non-minimal coupling to three-vector potential in the 3+1 dimensional Dirac equation. The potential is noncentral (angular-dependent) such that the Dirac equation separates completely in spherical coordinates. The relativistic energy spectrum and spinor wavefunctions are obtained for the case where the radial component of the vector potential is proportional to 1/r. The non-minimal coupling presented in this work is a generalization of that which was introduced by Moshinsky and Szczepaniak in the Dirac-Oscillator problem.Comment: 8 page

Meso-substituted cationic 3- and 4-N-Pyridylporphyrins and their Zn(II) derivatives for antibacterial photodynamic therapy

Photodynamic inactivation of microorganisms known as antibacterial photodynamic therapy (APDT) is one of the most promising and innovative approaches for the destruction of pathogenic microorganisms. Among the photosensitizers (PSs), compounds based on cationic porphyrins/ metalloporphyrins are most successfully used to inactivate microorganisms. Series of meso-substituted cationic pyridylporphyrins and metalloporphyrins with various peripheral groups in the third and fourth positions of the pyrrole ring have been synthesized in Armenia. The aim of this work was to determine and test the most effective cationic porphyrins and metalloporphyrins with high photoactivity against Gram negative and Gram positive microorganisms. It was shown that the synthesized cationic pyridylporphyrins/metalloporphyrins exhibit a high degree of phototoxicity towards both types of bacteria, including the methicillin-resistant S. aureus strain. Zinc complexes of porphyrins are more phototoxic than metal-free porphyrin analogs. The effectiveness of these Zn-metalloporphyrins on bacteria is consistent with the level of singlet oxygen generation. It was found that the high antibacterial activity of the studied cationic porphyrins/metalloporphyrins depends on four factors: The presence in the porphyrin macrocycle of a positive charge (+4), a central metal atom (Zn2+) and hydrophobic peripheral functional groups as well as high values of quantum yields of singlet oxygen. The results indicate that meso-substituted cationic pyridylporphyrins/metalloporphyrins can find wider application in photoinactivation of bacteria than anionic or neutral PSs usually used in APD

Фауна нематод рыб Армении

The purpose of the research is to study the species composition of nematodes dwelling in fish in natural reservoirs and on artificial pond fish farms in Armenia.Materials and methods. The studies were performed at the Research Center for Veterinary Medicine and Veterinary and Sanitary Expertise of the Armenian National Agrarian University and at the Laboratory of Molecular Parasitology of the Scientific Center of Zoology and Hydroecology from March 2020 to December 2022. Traditional ichthyo-parasitological methods were used to study 246 fish of 10 species from fish farms in the Ararat and Armavir Regions, from Lake Sevan and the Sevjur, Hrazdan, Marmarik, Akhuryan and Debed Rivers, as well as the Yerevan, Aparan and Akhuryan reservoirs. The study results were statistically processed (descriptive statistics) using the BioStat software.Results and discussion. The fish were found to have four types of nematodes: Contracaecum microcephalum Rudolphi, 1819, Philometroides sanguineus Rudolphi, 1819, Rhabdochona fortunatowi Dinnik, 1933 and Cystidicola farionis Fischer, 1798. Parasites were found in the body, on the serosa, in the air bladder walls, the intestinal lumen and the caudal fin thickness. The total nematode infection rate in fish was 9.76%. The nematode infection rate in fish was characterized by low values of prevalence and intensity other than the infection by the species Rh. fortunatowi (up to 24 specimens per fish). Among the found nematodes, the species C. microcephalum posed a potential threat to human health.Цель исследований – изучить видовой состав нематод, паразитирующих у рыб естественных водоёмов и искусственных прудовых хозяйств Армении.Материалы и методы. Исследования проводили с марта 2020 по декабрь 2022 гг. в Исследовательском центре ветеринарии и ветеринарно-санитарной экспертизы Национального аграрного университета Армении и в лаборатории молекулярной паразитологии Научного центра зоологии и гидроэкологии. Традиционными ихтиопаразитологическими методами исследовано 246 рыб 10 видов из рыбоводческих хозяйств Араратского и Армавирского марзов, озера Севан, рек Севджур, Раздан, Мармарик, Ахурян и Дебед, а также из Ереванского, Апаранского и Ахурянского водохранилищ. Результаты исследования подвергли статистической обработке (описательная статистика) с помощью компьютерной программы BioStat.Результаты и обсуждение. У рыб было обнаружено 4 вида нематод: Contracaecum microcephalum Rudolphi, 1819, Philometroides sanguineus Rudolphi, 1819, Rhabdochona fortunatowi Dinnik, 1933 и Cystidicola farionis Fischer, 1798. Паразиты были найдены в полости тела, на серозных покровах, в стенках плавательного пузыря, просвете кишечника и в толще хвостового плавника. Общая зараженность рыб нематодами составила 9,76%. Зараженность рыб нематодами характеризовалась низкими показателями экстенсивности и интенсивности, за исключением инвазии видом Rh. fortunatowi (до 24 экз. у одной рыбы). Среди обнаруженных нематод вид C. microcephalum представляет потенциальную угрозу здоровью человека

Measurements of Transverse Energy Flow in Deep-Inelastic Scattering at HERA

Measurements of transverse energy flow are presented for neutral current deep-inelastic scattering events produced in positron-proton collisions at HERA. The kinematic range covers squared momentum transfers Q^2 from 3.2 to 2,200 GeV^2, the Bjorken scaling variable x from 8.10^{-5} to 0.11 and the hadronic mass W from 66 to 233 GeV. The transverse energy flow is measured in the hadronic centre of mass frame and is studied as a function of Q^2, x, W and pseudorapidity. A comparison is made with QCD based models. The behaviour of the mean transverse energy in the central pseudorapidity region and an interval corresponding to the photon fragmentation region are analysed as a function of Q^2 and W.Comment: 26 pages, 8 figures, submitted to Eur. Phys.

Forward pi^0 Production and Associated Transverse Energy Flow in Deep-Inelastic Scattering at HERA

Deep-inelastic positron-proton interactions at low values of Bjorken-x down to x \approx 4.10^-5 which give rise to high transverse momentum pi^0 mesons are studied with the H1 experiment at HERA. The inclusive cross section for pi^0 mesons produced at small angles with respect to the proton remnant (the forward region) is presented as a function of the transverse momentum and energy of the pi^0 and of the four-momentum transfer Q^2 and Bjorken-x. Measurements are also presented of the transverse energy flow in events containing a forward pi^0 meson. Hadronic final state calculations based on QCD models implementing different parton evolution schemes are confronted with the data.Comment: 27 pages, 8 figures and 3 table