Inferring possible magnetic field strength of accreting inflows in EXor-type objects from scaled laboratory experiments

Aims. EXor-type objects are protostars that display powerful UV-optical outbursts caused by intermittent and powerful events of magnetospheric accretion. These objects are not yet well investigated and are quite difficult to characterize. Several parameters, such as plasma stream velocities, characteristic densities, and temperatures, can be retrieved from present observations. As of yet, however, there is no information about the magnetic field values and the exact underlying accretion scenario is also under discussion. Methods. We use laboratory plasmas, created by a high power laser impacting a solid target or by a plasma gun injector, and make these plasmas propagate perpendicularly to a strong external magnetic field. The propagating plasmas are found to be well scaled to the presently inferred parameters of EXor-type accretion event, thus allowing us to study the behaviour of such episodic accretion processes in scaled conditions. Results. We propose a scenario of additional matter accretion in the equatorial plane, which claims to explain the increased accretion rates of the EXor objects, supported by the experimental demonstration of effective plasma propagation across the magnetic field. In particular, our laboratory investigation allows us to determine that the field strength in the accretion stream of EXor objects, in a position intermediate between the truncation radius and the stellar surface, should be of the order of 100 G. This, in turn, suggests a field strength of a few kilogausses on the stellar surface, which is similar to values inferred from observations of classical T Tauri stars

Ультрафиолетовое излучение импульсно–периодических разрядов высокого давления в ксеноне

Pulsed quartz-jacketed high-pressure xenon lamps, operating in the periodic pulse repetition modes, despite the appearing UV radiation sources of other types, remain a critical component of the processing equipment used in photochemistry, photo-medicine, nanoelectronics, biology, etc. Their main advantages, namely high power and radiation energy are slightly devalued by a relatively low efficiency of the shortwave radiation. Available literature data concerning the influence of various factors on the energy level of short-wave radiation in xenon need to be systematised and generalised because they have been obtained under conditions of uncontrolled quartz-jacketed transmission. The transmission of quartz can degrade after a while and, in addition, undergo great changes during the pulse. Besides, as a rule, in the literature, there is no detailed description of a complete kit of experimental setting. As a result, to analyse the factors affecting the efficiency of studying in the UV range is difficult, and there arises a relevant problem to optimise this type of discharge parameters to increase the efficiency in the range of 220-400 nm. A mathematical model of the radiation source, realistically describing the processes in the xenon plasma and in the stabilising envelope, can be a reliable ground for such a study. The paper shows an impact of the discharge channel diameter and length, the filling pressure of xenon, the pulse duration, the parameters of discharge circuit, and the current of pilot arc on the radiation yield. Based on the simulation-found relationship of internal plasma parameters (temperature distributions, fields of particle concentration and radiation, dynamics of electrical resistance of discharge channel, and plasma emission spectra) with radiation characteristics of discharge, are determined conditions to ensure the greatest radiation yield in the UV region.  The experimental data prove the computational results. A material obtained gives practice-critical guidelines for development and correct selection of the short-wave radiation source.Импульсные ксеноновые лампы высокого давления в кварцевой оболочке, работающие в режимах периодического следования импульсов, несмотря на появление источников УФ- излучения других типов остаются важнейшим компонентом технологического оборудования, применяемого в фотохимии, фотомедицине, наноэлектронике, биологии и т.д. Главные их достоинства -  высокая мощность и энергия излучения - несколько обесценивает относительно низкая эффективность излучения в коротковолновой области. Имеющиеся литературные данные о влиянии различных факторов на уровень энергии коротковолнового излучения разрядов в ксеноне нуждаются в систематизации и обобщении, т.к. они получены в условиях неконтролируемого значения пропускания кварцевой оболочки. Пропускание кварца может деградировать со временем и, кроме того,  сильно меняться в течение импульса. Кроме того,  в литературе отсутствует, как правило, детальное описание полного набора условий проведения эксперимента. В итоге анализ факторов, влияющих на  эффективность изучения в УФ- области затруднен, и возникает актуальная задача оптимизации параметров разрядов указанного типа с целью увеличения КПД в области 220-400 нм. Надежной основой для проведения такой работы может служить расчетно- теоретическое исследование с помощью  математической модели источника излучения, реалистично описывающей процессы в плазме ксенона и стабилизирующей оболочке. В работе  показано влияние на  выход излучения диаметра и длины разрядного канала, давления наполнения ксенона, длительности импульса, параметров разрядного контура, тока дежурной дуги. На основе устанавливаемой при моделировании связи внутренних параметров плазмы (температурных распределений, полей концентрации частиц и радиации, динамики электрического сопротивления канала разряда и спектров излучения плазмы) с радиационными характеристиками разряда определены условия, обеспечивающие наибольший выход излучения в УФ- области. Результаты вычислений  подтверждены экспериментальными данными. Полученныйматериал дает важные для практики ориентиры для разработки и правильного выбора источника излучения коротковолнового диапазона

Новые комбинации и названия сосудистых растений Азиатской России.

In this paper, we present nomenclatural novelties required in the course of the preparation of the second, revised version of the checklist of vascular plants of Asian Russia. The first version was published in 2012 (Baikov 2012). At the family level, we accepted the modern classification systems (APG IV for flowering plants, PPG I for lycophytes and ferns, and GPG for gymnosperms). At the genus level, we follow the generic concepts applied for particular taxonomic groups according to the Catalogue of Life (COL; https://www.catalogueoflife.org/), version COL23.5. At the species level, we consistently apply the monotypic species concept (also known in Russia as Komarov’s concept). In total, this paper presents one new nothogenus name (× Sibirotrisetokoeleria Chepinoga nom. nov., Poaceae) and 156 new names in the rank of species, in 28 families: Amaranthaceae Juss. (1 name), Amaryllidaceae J. St.-Hil. (1), Apiaceae Lindl. (2), Asteraceae Bercht. & J.Presl (12), Boraginaceae Juss. (4), Caryophyllaceae Juss. (11), Crassulaceae J. St.-Hill. (3), Cyperaceae Juss. (8), Ericaceae Juss. (2), Fabaceae Lindl. (16), Gentianaceae Juss. (1), Geraniaceae Juss. (1), Juncaceae Juss. (1), Lamiaceae Martinov (1), Menyanthaceae Dumort. (1), Orchidaceae Juss. (1), Orobanchaceae Vent. (1), Papaveraceae Juss. (4), Plantaginaceae Juss. (1), Poaceae Barnhart (49), Polygonaceae Juss. (4), Primulaceae Batsch. ex Borkh. (6), Ranunculaceae Juss. (4), Rosaceae Juss. (5), Salicaceae Mirb. (2), Saxifragaceae Juss. (11), Vitaceae Juss. (1), Zygophyllaceae R. Br. (2 names)

DETERMINATION OF THE MOLAR RATIO AlCl3/KCl IN THE MELT ZrCl4 – KCl – AlCl3

A method for determining the molar ratio of AlCl3/KCl in the melt ZrCl4-KCl – AlCl3 has been developed. The developed technique was tested on the working melt of the rectification plant of JSC ChMZ. Frozen alloy samples were analyzed by X-ray diffractometry

Orbital effects of a monochromatic plane gravitational wave with ultra-low frequency incident on a gravitationally bound two-body system

We analytically compute the long-term orbital variations of a test particle orbiting a central body acted upon by an incident monochromatic plane gravitational wave. We assume that the characteristic size of the perturbed two-body system is much smaller than the wavelength of the wave. Moreover, we also suppose that the wave's frequency is much smaller than the particle's orbital one. We make neither a priori assumptions about the direction of the wavevector nor on the orbital geometry of the planet. We find that, while the semi-major axis is left unaffected, the eccentricity, the inclination, the longitude of the ascending node, the longitude of pericenter and the mean anomaly undergo non-vanishing long-term changes. They are not secular trends because of the slow modulation introduced by the tidal matrix coefficients and by the orbital elements themselves. They could be useful to indepenedently constrain the ultra-low frequency waves which may have been indirectly detected in the BICEP2 experiment. Our calculation holds, in general, for any gravitationally bound two-body system whose characteristic frequency is much larger than the frequency of the external wave. It is also valid for a generic perturbation of tidal type with constant coefficients over timescales of the order of the orbital period of the perturbed particle.Comment: LaTex2e, 24 pages, no figures, no tables. Changes suggested by the referees include

Molecular and electronic structure of terminal and alkali metal-capped uranium(V) nitride complexes

Determining the electronic structure of actinide complexes is intrinsically challenging because inter-electronic repulsion, crystal field, and spin–orbit coupling effects can be of similar magnitude. Moreover, such efforts have been hampered by the lack of structurally analogous families of complexes to study. Here we report an improved method to U≡N triple bonds, and assemble a family of uranium(V) nitrides. Along with an isoelectronic oxo, we quantify the electronic structure of this 5f1 family by magnetometry, optical and electron paramagnetic resonance (EPR) spectroscopies and modelling. Thus, we define the relative importance of the spin–orbit and crystal field interactions, and explain the experimentally observed different ground states. We find optical absorption linewidths give a potential tool to identify spin–orbit coupled states, and show measurement of UV···UV super-exchange coupling in dimers by EPR. We show that observed slow magnetic relaxation occurs via two-phonon processes, with no obvious correlation to the crystal field

Strongly coupled binuclear uranium-oxo complexes from uranyl oxo rearrangement and reductive silylation

The most common motif in uranium chemistry is the d0f0 uranyl ion [UO2]21 in which the oxo groups are rigorously linear and inert. Alternative geometries, such as the cis-uranyl, have been identified theoretically and implicated in oxo-atom transfer reactions that are relevant to environmental speciation and nuclear waste remediation. Single electron reduction is now known to impart greater oxo-group reactivity, but with retention of the linear OUO motif, and reactions of the oxo groups to form new covalent bonds remain rare. Here, we describe the synthesis, structure, reactivity and magnetic properties of a binuclear uranium–oxo complex. Formed through a combination of reduction and oxo-silylation and migration from a trans to a cis position, the new butterfly-shaped Si–OUO2UO–Si molecule shows remarkably strong UV–UV coupling and chemical inertness, suggesting that this rearranged uranium oxo motif might exist for other actinide species in the environment, and have relevance to the aggregation of actinide oxide clusters.JRC.E.6-Actinides researc

Small Molecule Activation by Uranium Tris(aryloxides): Experimental and Computational Studies of Binding of N-2, Coupling of CO, and Deoxygenation Insertion of CO2 under Ambient Conditions

Previously unanticipated dinitrogen activation is exhibited by the well-known uranium tris(aryloxide) U(ODtbp)(3), U(OC6H3-Bu-2(t)-2,6)(3), and the tri-tert-butyl analogue U(OTtbp)(3), U(OC6H2-Bu-3(t)-2,4,6)(3), in the form of bridging, side-on dinitrogen complexes [U(OAr)(3)](2)(mu-eta(2):eta(2)-N-2), for which the tri-tert-butyl N-2 complex is the most robust U-2(N-2) complex isolated to date. Attempted reduction of the tris(aryloxide) complex under N-2 gave only the potassium salt of the uranium(III) tetra(aryloxide) anion, K[U(OAr)(4)], as a result of ligand redistribution. The solid-state structure is a polymeric chain formed by each potassium cation bridging two arenes of adjacent anions in an eta(6) fashion. The same uranium tris(aryloxides) were also found to couple carbon monoxide under ambient conditions to give exclusively the ynediolate [OCCO](2-) dianion in [U(OAr)(3)](2)(mu-eta(1):eta(1)-C2O2), in direct analogy with the reductive coupling recently shown to afford [U{N(SiMe3)(2)}(3)](2)(mu-eta(1):eta(1)-C2O2). The related U-III complexes U{N(SiPhMe2)(2)}(3) and U{CH(SiMe3)(2)}(3) however do not show CO coupling chemistry in our hands. Of the aryloxide complexes, only the U(OC6H2-Bu-3(t)-2,4,6)(3) reacts with CO2 to give an insertion product containing bridging oxo and aryl carbonate moieties, U-2(OTtbp)(4)(mu-O)(mu-eta(1):eta(1)-O2COC6H2-Bu-3(t)-2,4,6)(2), which has been structurally characterized. The presence of coordinated N-2 in [U(OTtbp)(3)](2)(N-2) prevents the occurrence of any reaction with CO2, underscoring the remarkable stability of the N-2 complex. The di-tert-butyl aryloxide does not insert CO2, and only U(ODtbp)(4) was isolated. The silylamide also reacts with carbon dioxide to afford U(OSiMe3)(4) as the only uranium-containing material. GGA and hybrid DFT calculations, in conjunction with topological analysis of the electron density, suggest that the U-N-2 bond is strongly polar, and that the only covalent U -> N-2 interaction is pi backbonding, leading to a formal (U-IV)(2)(N-2)(2-) description of the electronic structure. The N-N stretching wavenumber is preferred as a metric of N-2 reduction to the N-N bond length, as there is excellent agreement between theory and experiment for the former but poorer agreement for the latter due to X-ray crystallographic underestimation of r(N-N). Possible intermediates on the CO coupling pathway to [U(OAr)(3)](2)(mu-C2O2) are identified, and potential energy surface scans indicate that the ynediolate fragment is more weakly bound than the ancillary ligands, which may have implications in the development of low-temperature and pressure catalytic CO chemistry