Resistive Transition and Upper Critical Field in Underdoped YBa_2Cu_3O_{6+x} Single Crystals

A superconducting transition in the temperature dependence of the ab-plane resistivity of underdoped YBa_2Cu_3O_{6+x} crystals in the range T_c<30 K has been investigated. Unlike the case of samples with the optimal level of doping, the transition width increased insignificantly with magnetic field, and in the range T_c<13 K it decreased with increasing magnetic field. The transition point T_c(B) was determined by analyzing the fluctuation conductivity. The curves of B_{c2}(T) measured in the region T/T_c>0.1 did not show a tendency to saturation and had a positive second derivative everywhere, including the immediate neighborhood of T_c. The only difference among the curves of B_{c2}(T) for different crystal states is the scales of T and B, so they can be described in terms of a universal function, which fairly closely follows Alexandrov's model of boson superconductivity.Comment: 10 Revtex pages, 6 figures, uses psfig.st

Anisotropic optical properties of single-crystal GdBa2Cu3O7-delta

The optical spectrum of reduced-T(c) GdBa2Cu3O7-delta has been measured for polarizations parallel and perpendicular to the ab plane. The sample was an oxygen-deficient single crystal with a large face containing the c axis. The polarized reflectance from this face was measured from 20-300 K in the spectral region from 30-3000 cm-1, with 300 K data to 30 000 cm-1. Kramers-Kronig analysis was used to determine the spectral dependence of the ab and the c components of the dielectric tensor. The optical properties are strongly anisotropic. The ab-plane response resembles that of other reduced-T(c) materials whereas the c axis, in contrast, shows only the presence of several phonons. There is a complete absence of charge carrier response along c above and below T(c). This observation allows us to set an upper limit to the free-carrier spectral weight for transport perpendicular to the CuO2 planes

Изменения в серотиповом составе Streptococcus pneumoniae, циркулирующих среди детей в Российской Федерации, после внедрения 13-валентной пневмококковой конъюгированной вакцины

During a prospective multicenter non-interventional observational study, a comparative assessment was made of the serotype structure of pneumococci circulating among healthy children under the age of 5 years and children of the same age group with signs of respiratory infections in the periods 2016-2018 and 2020-2022. Data on the serotype structure of pneumococci in the period from 2016-2018 were obtained from our previous works. In 2020-2022 the study included 2066 healthy children and 603 children with respiratory infections. Streptococcus pneumoniae and their DNA were detected in nasopharyngeal swabs by classical culture and molecular methods. Typing was carried out by molecular methods. On the territory of the Russian Federation, pneumococci belonging to the serotypes included in the 13-valent vaccine are being forced out of circulation and replaced by non-vaccine serotypes. Before the introduction of mass antipneumococcal vaccination (until 2015), the 13-valent conjugate vaccine covered from 66.2% to 92% of pneumococci, after the start of mass anti-pneumococcal vaccination in the period 2016-2018, coverage decreased to 57.3%. Between 2020 and 2022, coverage was less than 40%. The main “non-vaccine” serotypes/serogroups circulating in the Russian Federation are 15AF, 11AD, 23A, 9LN and 16F.В ходе проспективного многоцентрового не интервенционного обсервационного исследования была проведена сравнительная оценка серотиповой структуры пневмококков, циркулирующих среди здоровых детей в возрасте до 5 лет и детей этой же возрастной группы с признаками респираторных инфекций в периоды 2016–2018 гг. и 2020–2022 гг. Данные о серотиповой структуры пневмококков в период 2016–2018 гг. были получены из наших предыдущих работ. В 2020–2022 гг. в исследование было включено 2066 здоровых детей и 603 ребенка с респираторными инфекциями. Streptococcus pneumoniae и их ДНК детектировали в назофарингеальных мазках классическими культуральными и молекулярными методами. Типирование проводили молекулярными методами. На территории Российской Федерации происходят процесс вытеснения из циркуляции пневмококков, относящихся к серотипам, входящим в 13-валентную вакцину, и их замещение невакцинными серотипами. Перед внедрением массовой антипневмококковой вакцинации (до 2015 г.) конъюгированная 13-валентная вакцина обеспечивала на тот момент охват от 66,2% до 92% пневмококков, после начала массовой антипневмококковой вакцинации в период 2016–2018 гг. охват снизился до 57,3%. В период с 2020 по 2022 г. охват составил менее 40%. К основным «невакцинным» серотипам/серогруппам, циркулирующим на территории Российской Федерации, относятся 15AF, 11AD, 23A, 9LN, 16F