Ретроспективний огляд формування іхтіокомплексу р. Оріль

Dynamics of the ichthyofauna in theOrelRiverunder the intensification of transformational processes connected with the large-scaled hydro construction and reformation of the river’s flow. Modern basic indices of the river’s ichthyocomplex are ascertained. Changes in species composition and numbers of fish communities are disclosed for the total period of ichthyologic investigations (1948–2010). Main directions of the ichthyofauna changes and consequences of the introduction of nature protection status of the water area are ascertained. Measures on increasing the ichthyofauna sustainability of the Orel River, as a unique nature object of the central Dnieper region, are proposed.Прослежена динамика состояния ихтиофауны р. Орель в условиях усиления трансформационных процессов, связанных с масштабным гидростроительством и формированием стока. Установлены современные базовые показатели ихтиокомплекса реки. Выявлены изменения видового состава и численных показателей сообществ рыб за весь период ихтиологических исследований (1948–2010 гг.). Установлены основные направления изменения состава ихтиофауны и последствия введения природоохранного статуса на акватории реки. Предложены мероприятия по повышению устойчивости ихтиоценоза р. Орель – уникального природного объекта степного Приднепровья.Простежено динаміку стану іхтіофауни р. Оріль в умовах посилення трансформаційних процесів, пов’язаних із масштабним гідробудівництвом і формуванням стоку. Установлено сучасні базові показники іхтіокомплексу ріки. Виявлено зміни видового складу та числових показників угруповань риб за весь період іхтіологічних досліджень (1948–2010 рр.). Визначено основні напрями змін складу іхтіофауни та наслідки енняввед природоохоронного статусу на акваторії ріки. Запропоновано заходи з підвищення усталеності іхтіоценозу р. Оріль – унікального природного об’єкта степового Придніпров’я

Electrical and optical properties of a PtSn 4 single crystal

A topological semimetal PtSn4 single crystal was grown by method of crystallization from a solution in a melt. Then the electrical resistivity and galvanomagnetic properties (magnetoresistivity and the Hall effect) were studied in the temperature range from 4.2 to 80 K and in magnetic fields up to 100 kOe. The optical measurements were carried out at room temperature. The residual resistivity is shown to be low enough and amount to ∼ 0.5 μOhm•cm. The temperature dependence of the electrical resistivity has a metallic type, increasing monotonically with temperature. A sufficiently large magnetoresistance of 750% is observed. The majority carriers are supposed to be holes with a concentration of ∼ 6.8•10 21 cm -3 and mobility of ∼ 1950 cm 2 /Vs at T = 4.2 K as a result of the Hall effect studies. The optical properties of PtSn 4 have features characteristic of "bad" metals. © 2019 Published under licence by IOP Publishing Ltd.This work was partly supported by the state assignment of Russia (theme “Spin” No. АААА-А18-18020290104-2 and theme “Electron” No. АААА-А18-118020190098-5), by the RFBR (project No.17-52-52008) and by the Government of the Russian Federation (state contract No. 02.A03.21.0006)

Peculiarities of the electro- And magnetoresistivity of WTe2and MoTe2single crystals before and after quenching

WTe2 and MoTe2 single crystals were grown, some of them were quenched, and the following properties were studied: electroresistivity in the temperature range from 1.8 to 300 K, magnetoresistivity at temperatures from 1.8 to 300 K in magnetic fields of up to 9 T. On the one hand, quenching leads to dramatic changes in the behaviour and value of the electroresistivity of MoTe2; the type of the electroresistivity changes from "semiconductor"to "metallic", and the electroresistivity values of MoTe2 before and after quenching differ by 8 orders of magnitude (!) at low temperatures. On the other hand, quenching is shown not to lead to significant changes in the behaviour and value of the electroresistivity of WTe2. A relatively small increase in the electroresistivity of quenched WTe2 at low temperatures can be associated with the scattering of current carriers by structural defects. The magnetoresistivity of MoTe2 increases from 7 to 16% in a field of 9 T at a temperature of 12 K as a result of quenching. The magnetoresistivity of WTe2 is shown to reach ∼1700% in a field of 9 T at 2 K. The behaviour of the magnetoresistivity of non-quenched samples is typical for compensated conductors with a closed Fermi surface. © 2021 Author(s).The research was carried out within the state assignment of Ministry of Education and Science of the Russian Federation (theme “Spin”, No. AAAA-A18-118020290104-2), supported in part by RFBR (Project No. 20-32-90069) and the Government of the Russian Federation (Decree No. 211, Contract No. 02.A03.21.0006)

Electro- And magnetotransport properties of a WTe2 single crystal

A single crystal of a topological Weyl semimetal WTe2 was grown and its electrical resistivity and galvanomagnetic properties (magnetoresistivity and the Hall effect) were investigated in detail in the temperature range from 1.8 K to 300 K and in magnetic fields of up to 9 T. © Published under licence by IOP Publishing Ltd.The research was carried out within the state assignment of Ministry of Education and Science of the Russian Federation (theme “Spin”, No. АААА-А18-118020290104-2), supported in part by RFBR (Project No. 20-32-90069) and the Government of Russian Federation (Decree No. 211, Contract No. 02.A03.21.0006)

Features of the Resistivity of MnBi2Te4 Single Crystals and Polycrystals

Single crystals and polycrystals of an antiferromagnetic topological insulator MnBi2Te4 were grown. Their structure and temperature dependences of the resistivity were investigated. The presence of anisotropy in the electrical resistivity of the MnBi2Te4 single crystal was demonstrated.Работа выполнена в рамках государственного задания МИНОБРНАУКИ России (тема «Спин», № АААА-А18-118020290104-2) при частичной поддержке Правительства РФ (постановление № 211, контракт № 02.A03.21.0006) и стипендии Президента РФ молодым ученым и аспирантам (СП-2705.2022.1)