Closed Abrikosov Vortices in a Superconducting Cylinder

The new type of solutions of the London equation for type-II superconductors is obtained to describe the ring-shaped (toroidal) Abrikosov vortices. The specific feature of these solutions is the self-consistent localization of both the supercurrent and the magnetic field, enabling one to construct compact magnetic structures inside a superconductor. The torus vortex contraction caused by the vortex instability leads to the destruction of the Cooper pairing and the formation of a normal electron stream in the vicinity of the torus axis. The thermodynamic condition for the excitation of a small closed vortex by a bunch of charged particles contains the fine-structure constant as a determining parameter.Comment: LaTex using revtex, 12 pages. 5 Figures available upon request from [email protected] Accepted for publication in Physica

Critical flux pinning and enhanced upper-critical-field in magnesium diboride films

We have conducted pulsed transport measurements on c-axis oriented magnesium diboride films over the entire relevant ranges of magnetic field 0 \alt H \alt H_{c2} (where \hcu is the upper critical field) and current density 0 \alt j \alt j_{d} (where $j_{d}$ is the depairing current density). The intrinsic disorder of the films combined with the large coherence length and three-dimensionality, compared to cuprate superconductors, results in a six-fold enhancement of $H_{c2}$ and raises the depinning current density $j_{c}$ to within an order of magnitude of $j_{d}$. The current-voltage response is highly non-linear at all fields, resulting from a combination of depinning and pair-breaking, and has no trace of an Ohmic free-flux-flow regime. Keywords: pair, breaking, depairing, superconductor, superconductivity, flux, fluxon, vortex, mgb

Grain Surface Models and Data for Astrochemistry

AbstractThe cross-disciplinary field of astrochemistry exists to understand the formation, destruction, and survival of molecules in astrophysical environments. Molecules in space are synthesized via a large variety of gas-phase reactions, and reactions on dust-grain surfaces, where the surface acts as a catalyst. A broad consensus has been reached in the astrochemistry community on how to suitably treat gas-phase processes in models, and also on how to present the necessary reaction data in databases; however, no such consensus has yet been reached for grain-surface processes. A team of ∼25 experts covering observational, laboratory and theoretical (astro)chemistry met in summer of 2014 at the Lorentz Center in Leiden with the aim to provide solutions for this problem and to review the current state-of-the-art of grain surface models, both in terms of technical implementation into models as well as the most up-to-date information available from experiments and chemical computations. This review builds on the results of this workshop and gives an outlook for future directions

БЫСТРЫЙ ЯМР-СКРИНИНГ СОДЕРЖАНИЯ ФЛАВОНОИДОВ В РАСТИТЕЛЬНОМ СЫРЬЕ

Evaluation of the prospects of various plant biomass for the extraction of biologically active substances from it requires the development of simple and rapid methods for measuring their content in extractive substances. Study of various groups of natural polyphenolic compounds by 1H NMR spectroscopy in DMSO-d6 solvent allowed us to establish for them the characteristic positions of hydroxyl group proton signals forming intramolecular hydrogen bonds. An attractive feature of these signals for the identification of individual flavonoids and their groups is the fact that in DMSO-d6 solvent they are observed in the 1H NMR spectral region free of all other signals. Since the quantitative content of the components of complex mixtures can be determined by the integral intensities of the signals of individual protons in the quantitative 1H NMR spectra, these signals are most convenient for such assessments. By the example of several groups of flavonoids of great interest as effective natural antioxidants contained in a significant amount of biomass of plant raw materials (taxifolin in Larix sibirica, flavolignans in Silybum marianum, flavonoglycosides in Ginkgo biloba) its possibilities for rapid assessment of resource potential of raw materials are shown.Оценка перспективности различных видов биомассы растительного сырья для извлечения из него биологически активных веществ требует разработки простых и быстрых методов измерения их содержания в экстрактивных веществах. Исследования различных групп природных полифенольных соединений методом спектроскопии ЯМР 1Н в растворителе ДМСО позволили нам установить для них характеристичность положений сигналов протонов гидроксильных групп, образующих внутримолекулярные водородные связи. Привлекательной особенностью этих сигналов для идентификации по ним отдельных флавоноидов и их групп является то обстоятельство, что в растворителе ДМСО они наблюдаются в области спектра ЯМР 1Н, свободной от всех других сигналов. Поскольку количественное содержание компонентов сложных смесей может быть определено по интегральным интенсивностям сигналов отдельных протонов в количественных спектрах ЯМР 1Н, указанные сигналы наиболее удобны для таких оценок. На примере нескольких групп флавоноидов, представляющих большой интерес как эффективные природные антиоксиданты, содержащиеся в значительном количестве биомассе растительного сырья (таксифолин в Lаrix sibirica, флаволигнаны в Sílybum mariánum, флавоногликозиды в Ginkgo biloba) показаны его возможности для быстрой оценки ресурсных возможностей сырья

Modern Methods for Identification and Quantitative Analysis of Undeclared Phosphodiesterase-5 Inhibitors as Pharmaceutically Active Substances in Dietary Supplements (Review)

This review is devoted to consideration of physicochemical methods for detection of pharmaceutically active substances, in particular, phosphodiesterase-5 (PDE-5) inhibitors, present in dietary supplements. The necessity of using the most informative approaches for the identification of PDE-5 inhibitors registered as drugs and their structurally modified analogs with unknown safety and efficacy in the composition of dietary supplements is emphasized. © 2022, Springer Science+Business Media, LLC, part of Springer Nature

Bioavailability and Safety of Dihydroquercetin (Review)

Dihydroquercetin (DHQ) is a bioflavonoid with high antioxidant, capillary-protective, and anti-inflammatory activity. DHQ has previously been used for treating Middle East respiratory syndrome coronavirus (MERS-CoV) infection and is currently considered a potential regulator of oxidative stress as part of COVID-19 multipurpose therapy. DHQ has a high safety profile but low bioavailability that limits its use. Innovative techniques (liposomization, crystal engineering, etc.) can be used to increase its bioavailability. © 2022, Springer Science+Business Media, LLC, part of Springer Nature