50 research outputs found
Current State of Research on the Viscosity of Molten Fluorides
No full textReceived: 16 February 2024. Accepted: 18 March 2024. Published online: 22 March 2024.The development of new high-precision equipment for the experimental study of the physical-chemical properties of molten salts has led to the emergence of new data. This review examines recent experimental results on the viscosity of molten salt mixtures based on alkali fluorides, which are currently used in modern technologies for the production of metals and alloys and are also promising media for application in molten salt nuclear reactors. Various approaches to the analysis of experimental data are discussed. A different mechanism of viscous flow in the series LiF – NaF – KF and KF – RbF – CsF is well explained from the position of the theory of the autocomplex structure of molten salts. An anomalous decrease in the viscosity of fluorides from lithium to cesium, in comparison with other alkali metal halides, the viscosity of which increases with increasing the cation radius, is confirmed by calculations of the formation energy of the autocomplex and the binding energy between the complex-forming ion and the free ion of the second coordination sphere. To study the mechanism of liquid flow, the temperature dependence of dynamic viscosity is analyzed using the fluidity parameter. Additional information regarding the mechanism of viscous flow can be obtained from the relationship between the viscosity and electrical conductivity of melts. It was assumed that the most promising approach to studying the kinematic properties and the structure of molten salts is the use of both high-precision experiment and mathematical modeling based on first principles.This work was supported by the Ministry of Science and Higher Education of the RF under the program of scientific research "Fundamental studies of thermodynamics and kinetics of processes in molten salts", registration number: 122020100205-5.The author expresses deep gratitude to Alexey Rudenko and Alexander Kataev for providing unpublished experimental data on the viscosity of KCl
Viscosity of fluoride melts promising for molten salt nuclear reactors
No full textThe viscosity of molten salt, as an important hydrodynamic property, should be taken into account when creating and operating molten salt nuclear reactors (MSRs). An eutectic FLiNaK is considered to be one of the most suitable for use in MSR designed for the minor actinides transmutation. The dynamic viscosity of the molten mixtures FLiNaK + NdF3, FLiNaK + CeF3 and FLiNaK + LaF3 was measured in a temperature range of 600–700 °C using the high-temperature rotary rheometer FRS-1600. Lanthanide fluorides were considered as analogues of actinide fluorides. It was revealed that the additions of rare earth fluorides (REM)F3 in amount of 15 mol. % significantly impact the viscosity of the system FLiNaK + (REM)F3,but the effect of NdF3, CeF3 and LaF3 was found to be almost the same. In order to calculate the kinematic viscosity of the molten mixture FLiNaK + NdF3, a regression equation depending on several parameters was derived. This model equation can be used for predicting the kinematic viscosity of molten mixtures of FLiNaK with other rare earth fluorides
Mouse models for preeclampsia: disruption of redox-regulated signaling
No full textThe concept that oxidative stress contributes to the development of human preeclampsia has never been tested in genetically-defined animal models. Homozygous deletion of catechol-Omethyl transferase (Comt-/-) in pregnant mice leads to human preeclampsia-like symptoms (high
blood pressure, albuminurea and preterm birth) resulting from extensive vasculo-endothelial pathology, primarily at the utero-fetal interface where maternal cardiac output is dramatically increased during pregnancy. Comt converts estradiol to 2-methoxyestradiol 2 (2ME2) which
counters angiogenesis by depleting hypoxia inducible factor-1 alpha (HIF-1 alpha) at late pregnancy. We propose that in wild type (Comt++) pregnant mice, 2ME2 destabilizes HIF-1 alpha by inhibiting mitochondrial superoxide dismutase (MnSOD). Thus, 2ME2 acts as a pro-oxidant, disrupting
redox-regulated signaling which blocks angiogenesis in wild type (WT) animals in physiological pregnancy. Further, we suggest that a lack of this inhibition under normoxic conditions in mutant animals (Comt-/-) stabilises HIF-1 alpha by inactivating prolyl hydroxlases (PHD). We predict that a lack of inhibition of MnSOD, leading to persistent accumulation of HIF-1 alpha, would trigger
inflammatory infiltration and endothelial damage in mutant animals. Critical tests of this hypothesis would be to recreate preeclampsia symptoms by inducing oxidative stress in WT animals or to ameliorate by treating mutant mice with Mn-SOD-catalase mimetics or activators of PHD
Horizontal convection driven by nonuniform radiative heating in liquids with different surface behavior
No full textReconstruction of turbulent flow from temperature field measured using Background Oriented Schlieren
No full textNew data assimilation technique for turbulent flows is proposed, which allows determination of the turbulent viscosity, velocity and pressure distributions from the experimentally measured temperature fields. Measurements are performed for a round jet of hot air using nonintrusive Background Oriented Schlieren technique. Thus, seedless velocity and pressure measurement is realized, as well as measurement of the turbulent viscosity field without usage of any particular turbulence model. Data assimilation results are shown to be in good agreement with the conventional RANS simulations using the Spalart–Allmaras and k-ɛ turbulence models, if adequate smoothing of the input temperature field is performed and sufficient regularization of the energy equation in regions with uniform temperature is provided
Color-encoded M-array Background Oriented Schlieren for measurements of strongly refracting objects
No full textNew variant of Background Oriented Schlieren (BOS) technique is proposed for the measurements of strongly refracting objects. The employed pattern presents a rectangular grid of color dots. Special color encoding makes every dot unique provided its nearest neighbors can be identified. This allows robust matching of the dot images for schlieren objects with arbitrary large apparent displacements. Also, possible formation of multiple images of the same dot due to strongly nonlinear variations of the refractive index can be used to improve the accuracy of the refractive index field measurement. Multi-frame approach is employed to improve the spatial resolution. Potential of the proposed technique is demonstrated by measurements of the diffusion layers in aqueous solutions of sodium chloride and ethanol
Нелокальная дисперсия и ультразвуковое туннелирование в материалах с градиентной структурой
No full textThe non-local dispersion of longitudinal ultrasonic waves is shown to appear in the heterogeneous solids due to continuous spatial distributions of their density and/or elasticity (gradient solids). This dispersion gives rise to the diversity of ultrasonic transmittance spectra, including the broadband total reflectance plateau, total transmission and tunneling spectral ranges. The ultrasonic wave fields in gradient solids, formed by interference of forward and backward travelling waves as well as by evanescent and antievanescent modes are examined in the framework of exactly solvable models of media with continuously distributed density and elasticity. Examples of transmittance spectra for both metal and semiconductor gradient structures are presented, and the generality of concept of artificial non-local dispersion for gradient composite materials is considered. It should also be noted that the wave equation for acoustic waves in gradient media with a constant elasticity modulus and a certain predetermined density distribution reduces to an equation describing the electromagnetic wave propagation in transparent dielectric media. This formal similarity shows that the concept of nonlocal dispersion is common for both optical and acoustic phenomena, which opens the way to the direct use of physical concepts and exact mathematical solutions, developed for gradient optics, to solve the corresponding acoustic problems.Показано, что в материалах с пространственным распределением (градиентом) плотности и/или упругости имеет место нелокальная дисперсия продольных ультразвуковых волн. Эта дисперсия приводит к возникновению ультразвуковых спектров, таких как широкодиапазонное плато полного отражения, туннельные спектральные области и области полного пропускания. В рамках точно решаемых моделей сред с непрерывно распределенными плотностью и упругостью исследованы ультразвуковые волны в градиентных материалах, сформированные интерференцией прямых и обратных волн, а также затухающими и незатухающими модами. Приведены примеры спектров пропускания как для металлических, так и для полупроводниковых градиентных структур, а также рассмотрена общая концепция искусственной нелокальной дисперсии для градиентных композитных материалов. Необходимо заметить, что волновое уравнение для акустических волн в градиентных средах с постоянным модулем упругости и определенным заданным распределением плотности сводится к уравнению, описывающему распространение электромагнитных волн в прозрачных диэлектрических средах. Это формальное сходство свидетельствует о том, что концепция нелокальной дисперсии является общей как для оптических, так и для акустических явлений, что позволяет напрямую использовать разработанные для градиентной оптики физические принципы и точные математические решения при реализации соответствующих акустических задач
zFP538, a Yellow Fluorescent Protein from Coral, Belongs to the DsRed Subfamily of GFP-Like Proteins but Possesses the Unexpected Site of Fragmentation<sup>†</sup>
No full textThe yellow fluorescent protein (zFP538) from coral Zoanthus sp. belongs to a family of green
fluorescent protein (GFP). Absorption and emission spectra of zFP538 show an intermediate bathochromic
shift as compared with a number of recently cloned GFP-like red fluorescent and nonfluorescent
chromoproteins of the DsRed subfamily. Here we report that the zFP538 chromophore is very close, if
not identical, in chemical structure to that of DsRed. To gain insight into the mechanism of zFP538
fluorescence and chromophore structure and chemistry, we studied three chromophore-containing peptides
isolated from enzymatic digests of zFP538. Like GFP and DsRed chromophores, these contain a
p-hydroxybenzylideneimidazolinone moiety formed by Lys-66, Tyr-67, and Gly-68 of zFP538. One of
the peptides studied, the hexapeptide FKYGDR derivative, is a proteolysis product of the zFP538 full-length polypeptide containing a GFP-type chromophore already formed and arrested at an earlier stage of
maturation. The two other peptides are the derivatives of the pentapeptide KYGDR resulted from the
protein in which the chromophore maturation process had been completed. One of these has an oxogroup
at Lys-66 Cα and is a hydrolysis product of another one, with the imino group at Lys-66 Cα. The
N-unsubstituted imino moiety of the latter is generated by spontaneous polypeptide chain fragmentation
at a very unexpected site, the former peptide bond between Phe-65 C‘ and Lys-66 Nα. Also observed in
the entire protein under mild denaturing conditions, this fragmentation is likely the feature of native zFP538
chromophore that distinguishes it chemically from the DsRed chromophore
Traditional GFP-Type Cyclization and Unexpected Fragmentation Site in a Purple Chromoprotein from <i>Anemonia sulcata</i>, asFP595<sup>†</sup>
No full textThe purple chromoprotein (asFP595) from Anemonia sulcata belongs to the family of green
fluorescent protein (GFP). Absorption and emission spectra of asFP595 are similar to those of a number
of recently cloned GFP-like red proteins of the DsRed subfamily. The earlier proposed asFP595
chromophore structure [Martynov, V. I.; et al. (2001) J. Biol. Chem. 276, 21012−21016] was postulated
to result from an “alternative cyclization” giving rise to a pyrazine-type six-membered heterocycle. Here
we report that the asFP595 chromophore is actually very close in chemical structure to that of zFP538,
a yellow fluorescent protein [Zagranichny, V. E.; et al. (2004) Biochemistry 43, 4764−4772]. NMR
spectroscopic studies of four chromophore-containing peptides (chromopeptides) isolated under mild
conditions from enzymatic digests of asFP595 and one chromopeptide obtained from DsRed revealed
that all of them contain a p-hydroxybenzylideneimidazolinone moiety formed by Met-65/Gln-66, Tyr-66/67, and Gly-67/68 of asFP595/DsRed, respectively. Two asFP595 chromopeptides are proteolysis
products of an isolated full-length polypeptide containing a GFP-type chromophore already formed and
arrested at an earlier stage of maturation. The two other asFP595 chromopeptides were isolated as proteolysis
products of the purified chromophore-containing C-terminal fragment. One of these has an oxo group at
Met-65 Cα and is a hydrolysis product of another one, with the imino group at Met-65 Cα. The
N-unsubstituted imino moiety of the latter is generated by spontaneous polypeptide chain cleavage at a
very unexpected site, the former peptide bond between Cys-64 C‘ and Met-65 Nα. Our data strongly
suggest that both zFP538 and asFP595 could be attributed to the DsRed subfamily of GFP-like proteins
