Polarization effects in the reaction e++e−→ρ++ρ−e^++e^-\to \rho^+ +\rho^- and determination of the ρ−\rho - meson form factors in the time--like region

The electron positron annihilation reaction into four pion production has been studied, through the channel $e^++e^-\to \bar \rho+\rho$. The differential (and total) cross sections and various polarization observables for this reaction have been calculated in terms of the electromagnetic form factors of the corresponding $\gamma^*\rho\rho$ current. The elements of the spin--density matrix of the $\rho -$meson were also calculated. Numerical estimations have been done, with the help of phenomenological form factors obtained in the space--like region of the momentum transfer squared and analytically extended to the time-like region.Comment: 19 pages, 2 figures, to appear in Phys Rev

Suppressed absolute negative conductance and generation of high-frequency radiation in semiconductor superlattices

We show that space-charge instabilities (electric field domains) in semiconductor superlattices are the attribute of absolute negative conductance induced by small constant and large alternating electric fields. We propose the efficient method for suppression of this destructive phenomenon in order to obtain a generation at microwave and THz frequencies in devices operating at room temperature. We theoretically proved that an unbiased superlattice with a moderate doping subjected to a microwave pump field provides a strong gain at third, fifth, seventh, etc. harmonics of the pump frequency in the conditions of suppressed domains.Comment: 8 pages. Development of cond-mat/0503216 . Version 2: Final version, erratum is include

Subterahertz chaos generation by coupling a superlattice to a linear resonator

We investigate the effects of a linear resonator on the high-frequency dynamics of electrons in devices exhibiting negative differential conductance. We show that the resonator strongly affects both the dc and ac transport characteristics of the device, inducing quasiperiodic and high-frequency chaotic current oscillations. The theoretical findings are confirmed by experimental measurements of a GaAs=AlAs miniband semiconductor superlattice coupled to a linear microstrip resonator. Our results are applicable to other active solid state devices and provide a generic approach for developing modern chaos-based high-frequency technologies including broadband chaotic wireless communication and superfast random-number generation

Bloch gain in dc-ac-driven semiconductor superlattices in the absence of electric domains

We study theoretically the feasibility of amplification and generation of terahertz radiation in dc-ac-driven semiconductor superlattices in the absence of electric domains. We find that if in addition to dc bias a strong THz pump field is applied, Bloch gain profile for a small THz signal can be achieved under conditions of positive static differential conductivity. Here the positive differential conductivity arises, similarly to the case of large-signal amplification scheme [H. Kroemer, cond-mat/0009311)], due to modifications of dc current density caused by the application of high-frequency ac field [K. Unterrainer \textit{et al.}, Phys. Rev. Lett. \textbf{76}, 2973 (1996)]. Whereas the sign of absorption at low and zero frequencies is sensitive to the ac fields, the gain profile in the vicinity of gain maximum is robust. We suggest to use this ac-induced effect in a starter for THz Bloch oscillator. Our analysis demonstrates that the application of a short THz pulse to a superlattice allows to suppress the undesirable formation of electric domains and reach a sustained large-amplitude operation of the dc-biased Bloch scillator.Comment: 13 pages, 12 figure

Donor states in modulation-doped Si/SiGe heterostructures

We present a unified approach for calculating the properties of shallow donors inside or outside heterostructure quantum wells. The method allows us to obtain not only the binding energies of all localized states of any symmetry, but also the energy width of the resonant states which may appear when a localized state becomes degenerate with the continuous quantum well subbands. The approach is non-variational, and we are therefore also able to evaluate the wave functions. This is used to calculate the optical absorption spectrum, which is strongly non-isotropic due to the selection rules. The results obtained from calculations for Si/Si$_{1-x}$Ge$_x$ quantum wells allow us to present the general behavior of the impurity states, as the donor position is varied from the center of the well to deep inside the barrier. The influence on the donor ground state from both the central-cell effect and the strain arising from the lattice mismatch is carefully considered.Comment: 17 pages, 10 figure

Poloidal inhomogeneity of the particle fluctuation induced fluxes near of the LCFS at lower hybrid heating and improved confinement transition at the FT-2 tokamak

This paper deals with the new spectral and microturbulence experimental data and their analysis, which show, that the radial electric field Er generated at the LH heating (LHH) in the FT-2 is high enough to form the transport barriers. The ETB is formed when LHH is switched off. The radial fluctuation-induced EB drift flux densities near LCFS in SOL are measured at two different poloidal angles. For this purpose two Langmuir probes located at low and high field sides of the torus are used. Registration of the poloidal and radial components of the electric field and density fluctuations at the same time during one discharge permits to measure the poloidal asymmetry of the transport reduction mechanism of the radial and poloidal particle fluxes in the SOL. The absolute E(~) fluctuation levels show dependence on the sign of Er shear. The modification of the microscale turbulence by the poloidal Er x B rotation shear EB at the L - H transition near LCFS is also studied by X-mode fluctuation Reflectometry. The new data were obtained by spatial spectroscopic technique.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France

Circularly polarized electroluminescence from silicon nanostructures heavily doped with boron

The circularly polarized electroluminescence (CPEL) from silicon nanostructures which are the p-type ultra-narrow silicon quantum well (Si-QW) confined by {\delta}-barriers heavily doped with boron, 5 10^21 cm^-3, is under study as a function of temperature and excitation levels. The CPEL dependences on the forward current and temperature show the circularly polarized light emission which appears to be caused by the exciton recombination through the negative-U dipole boron centers at the Si-QW {\delta}-barriers interface

A MSFD complementary approach for the assessment of pressures, knowledge and data gaps in Southern European Seas : the PERSEUS experience

PERSEUS project aims to identify the most relevant pressures exerted on the ecosystems of the Southern European Seas (SES), highlighting knowledge and data gaps that endanger the achievement of SES Good Environmental Status (GES) as mandated by the Marine Strategy Framework Directive (MSFD). A complementary approach has been adopted, by a meta-analysis of existing literature on pressure/impact/knowledge gaps summarized in tables related to the MSFD descriptors, discriminating open waters from coastal areas. A comparative assessment of the Initial Assessments (IAs) for five SES countries has been also independently performed. The comparison between meta-analysis results and IAs shows similarities for coastal areas only. Major knowledge gaps have been detected for the biodiversity, marine food web, marine litter and underwater noise descriptors. The meta-analysis also allowed the identification of additional research themes targeting research topics that are requested to the achievement of GES. 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license.peer-reviewe

Сравнительный анализ кишечной микробиоты при болезни Паркинсона и других неврологических заболеваниях

Currently the role of microbiota in diseases pathogenesis, its therapeutic and diagnostic potential are of the utmost interest for scientists and medical doctors. Parkinson’s disease is neurodegenerative disorder for which microbiota’s dysbiosis was previously shown.The main goal of the study is to compare the colon microbiota composition in case of Parkinson’s disease and other neurological pathologies, including idiopathic familial dystonia, essential tremor, multiple sclerosis, multiple system atrophy in order to determine the intestinal flora landscape specific to Parkinson’s disease.Material and methods. One hundred twenty-six patients, 93 with Parkinson’s disease and 33 with other neurological pathology were examined. For all patients, physical examination and fecal samples collection were performed. Microbiota taxonomic composition was analyzed by sequencing of bacterial 16S rRNA genes followed by bioinformatic and statistical analysis.As a result of the study, significant differences between groups in microbiota composition were found. Gut microbiota of patients with Parkinson’s disease was characterized by increase of Desulfovibrio piger, Lactobacillus mucosae, Yokenella regensburgei, Alistipes indistinctus, Oscillospira capillosus, Clostridium bolteae, Soleaferrea massiliensis, Butyricimonas virosa, Dorea massiliensis, Victivallis vadensis abundances. Patients with other neurological diseases had increased levels of bacteria belonging to Blautia, Intestinibacter, Coprococcus genera and Anoxystipes fissicatena, Fusobacterium periodonticum, Gemmiger formicilis, Papillibacter cinnamivorans, Roseburia faecis, Lachnoclostridium indolis, Clostridium populeti, Clostridium tertium, Roseburia intestinalis, Eubacterium desmolans, Eubacterium cylindroides, Clostridium clariflavum, Eubacterium eligens, Coprococcus eutactus, Intestinibacter bartlettii species in their gut microbiota.Consequently, gut microbiota in case of Parkinson’s disease was different from the microbiota of patients with other neurological diseases, including neuroinflammatory and neurodegenerative disorders, in terms of taxonomic diversity and composition. В настоящее время большой интерес представляет роль микробиоты в патогенезе различных болезней, а также ее диагностический и терапевтический потенциал. Болезнь Паркинсона – нейродегенеративное заболевание, для которого было показано изменение состава кишечной микробиоты в сравнении со здоровым контролем.Цель данного исследования – сравнительная характеристика кишечной микробиоты лиц с болезнью Паркинсона и другими неврологическими заболеваниями, включая идиопатическую семейную дистонию, эссенциальный тремор, рассеянный склероз, множественную системную атрофию для определения микробиотического ландшафта, характерного именно для болезни Паркинсона.Материал и методы. В исследование были включены 93 пациента с диагнозом болезни Паркинсона и 33 пациента с иными неврологическими заболеваниями. Для каждого пациента проведено физикальное обследование и собраны образцы фекалий. Определение состава микробиоты проводилась секвенированием бактериальных генов 16S рРНК с последующим биоинформатическим и статистическим анализом.Результаты. При сравнительном анализе состава микробиоты были найдены значимые различия. Микробиота кишечника лиц с болезнью Паркинсона характеризовалась увеличением содержания бактерий видов Desulfovibrio piger, Lactobacillus mucosae, Yokenella regensburgei, Alistipes indistinctus, Oscillospira capillosus, Clostridium bolteae, Soleaferrea massiliensis, Butyricimonas virosa, Dorea massiliensis, Victivallis vadensis. У лиц с другими неврологическими заболеваниями преобладали бактерии родов Blautia, Intestinibacter, Coprococcus и видов Anoxystipes fissicatena, Fusobacterium periodonticum, Gemmiger formicilis, Papillibacter cinnamivorans, Roseburia faecis, Lachnoclostridium indolis, Clostridium populeti, Clostridium tertium, Roseburia intestinalis, Eubacterium desmolans, Eubacterium cylindroides, Clostridium clariflavum, Eubacterium eligens, Coprococcus eutactus, Intestinibacter bartlettii.Выводы. Микробиота кишечника при болезни Паркинсона отличается по таксономическому разнообразию и бактериальному составу от микробиоты пациентов с другими неврологическими заболеваниями, в том числе нейровоспалительными и нейродегенеративными.