Recent advances in study of high-temperature behavior of non-stoichiometric TaCX, HfCXand ZrCX in the domain of their congruent melting point

Melting behavior of nonstoichiometric carbides of tantalum and hafnium remains one of the most challenging tasks in the high-temperature materials science despite the fact that the first studies of melting of these compounds are dated back to the beginning of 60’s. However, the data on melting points of tantalum and hafnium carbides in the vicinity of their homogeneity domain are still very contradictory. Zirconium carbide is a more studied compound, which makes him a sort of the reference material for testing the method of investigation, since its melting point is substantially lower. But even for this material, the data on its solidus and liquidus parameters look very incomplete and need to be clarified. In present study the parameters of the solidus and liquidus line for TaCx, HfCx and ZrCx are studied using laser heating technique similar to what described in [1]. A special emphasis is given on the accurate measurement of temperature and determination of spectral emissivity in course of the experiment using advanced multichannel pyrometry. The phase transitions corresponding to solidus and liquidus are determined by means of the laser-probe reflectometry, peculiarities in spectral emissivity behavior in the vicinity of the phase transitions and by high-speed video recording of the melt formation and freezing. New data on solidus and liquidus parameters for the Zr-C system in the homogeneity domain are presented. The temperatures of congruent melting of super-refractory carbides TaC and HfC are determined along with the data on their solidus and liquidus lines close to the congruent composition. The measured melting point of HfC was found to be close to the value given in a recent paper [2], whereas the melting point of TaC, according to the data of the present study, exceeds the value given in [2] by more than 150 K. The second part of the study concerns evaporation of UHTC carbides and focused at significant extension of the temperature domain limited earlier to ca. 3000 K. In the present study the method and apparatus used for determination of the composition of carbon vapor presented in [3] were significantly improved in order to make a further considerable extension towards extremely high temperatures. Due to some major improvements in the design of the TOF mass spectrometer, time-shape of the laser pulse and pyrometer time resolution the vapor composition at laser-induced evaporation of zirconium carbide samples of various starting composition within the homogeneity domain ranging from ZrC0.65 to ZrC1.0 were investigated up to 4500 K. Thus, molecular composition in vapor during evaporation of liquid ZrCx was obtained for the first time. The conditions of congruent evaporation of liquid zirconium carbide are estimated using the experimental data. References 1. Manara, D., Sheindlin, M., Heinz, W. & Ronchi, C. New techniques for high-temperature melting measurements in volatile refractory materials via laser surface heating. The Review of scientific instruments 79, 113901, (2008). 2. Cedillos-Barraza, O. et al. Investigating the highest melting temperature materials: A laser melting study of the TaC-HfC system. Sci. Rep. 6, 37962, (2016). 3. Pflieger R., Sheindlin M., Colle J.-Y. Advances in the mass spectrometric study of the laser vaporization of Graphite. J. Appl. Phys. 104, 054902 (2008). This work was supported by Russian Science Foundation under Grant No. 14-50-0012

Chronicles of nature calendar, a long-term and large-scale multitaxon database on phenology

We present an extensive, large-scale, long-term and multitaxon database on phenological and climatic variation, involving 506,186 observation dates acquired in 471 localities in Russian Federation, Ukraine, Uzbekistan, Belarus and Kyrgyzstan. The data cover the period 1890-2018, with 96% of the data being from 1960 onwards. The database is rich in plants, birds and climatic events, but also includes insects, amphibians, reptiles and fungi. The database includes multiple events per species, such as the onset days of leaf unfolding and leaf fall for plants, and the days for first spring and last autumn occurrences for birds. The data were acquired using standardized methods by permanent staff of national parks and nature reserves (87% of the data) and members of a phenological observation network (13% of the data). The database is valuable for exploring how species respond in their phenology to climate change. Large-scale analyses of spatial variation in phenological response can help to better predict the consequences of species and community responses to climate change.Peer reviewe

Phenological shifts of abiotic events, producers and consumers across a continent

Ongoing climate change can shift organism phenology in ways that vary depending on species, habitats and climate factors studied. To probe for large-scale patterns in associated phenological change, we use 70,709 observations from six decades of systematic monitoring across the former Union of Soviet Socialist Republics. Among 110 phenological events related to plants, birds, insects, amphibians and fungi, we find a mosaic of change, defying simple predictions of earlier springs, later autumns and stronger changes at higher latitudes and elevations. Site mean temperature emerged as a strong predictor of local phenology, but the magnitude and direction of change varied with trophic level and the relative timing of an event. Beyond temperature-associated variation, we uncover high variation among both sites and years, with some sites being characterized by disproportionately long seasons and others by short ones. Our findings emphasize concerns regarding ecosystem integrity and highlight the difficulty of predicting climate change outcomes. The authors use systematic monitoring across the former USSR to investigate phenological changes across taxa. The long-term mean temperature of a site emerged as a strong predictor of phenological change, with further imprints of trophic level, event timing, site, year and biotic interactions.Peer reviewe

Extracellular Vesicles in Viral Pathogenesis: A Case of Dr. Jekyll and Mr. Hyde

Secretion of extracellular vesicles (EVs) is a fundamental property of living cells. EVs are known to transfer biological signals between cells and thus regulate the functional state of recipient cells. Such vesicles mediate the intercellular transport of many biologically active molecules (proteins, nucleic acids, specific lipids) and participate in regulation of key physiological processes. In addition, EVs are involved in the pathogenesis of multiple diseases: infectious, neurodegenerative, and oncological. The current EV classification into microvesicles, apoptotic bodies, and exosomes is based on their size, pathways of cellular biogenesis, and molecular composition. This review is focused on analysis of the role of EVs (mainly exosomes) in the pathogenesis of viral infection. We briefly characterize the biogenesis and molecular composition of various EV types. Then, we consider EV-mediated pro- and anti-viral mechanisms. EV secretion by infected cells can be an important factor of virus spread in target cell populations, or a protective factor limiting viral invasion. The data discussed in this review, on the effect of EV secretion by infected cells on processes in neighboring cells and on immune cells, are of high significance in the search for new therapeutic approaches and for design of new generations of vaccines

Exosomes as Natural Nanocarriers for RNA-Based Therapy and Prophylaxis

Exosomes are natural nanocontainers actively secreted by the body’s cells and transmitting molecular signals of various types to recipient cells. Cellular mechanisms of exosomes’ biogenesis involve specific sorting of RNA for incorporation into them. As a result, the molecular composition of exosomes is closely related to the donor cell’s functional state, and this makes exosomes an important diagnostic and prognostic marker in a number of diseases (primarily oncological). The ability of exosomes to transport biologically active molecules and to protect the cargo from degradation makes them nearly ideal candidates as delivery carriers of RNA in therapeutic or prophylactic regimes. Potential of exosomal surface functionalization enables improved targeting to specific organs, tissues and cells. However, the development of an effective technology for RNA’s loading into exosomes cannot be considered resolved. This review is focused on experimental data on the use of exosomes as vehicles for the delivery of therapeutic and prophylactic RNAs. We briefly consider the biogenesis and functions of exosomes, focusing on those biological properties that make them formidable candidates in the race to develop effective delivery carriers. Furthermore, we describe various techniques of cargo loading into exosomes. Prospects of exosomes application as therapeutic delivery system for siRNAs, miRNAs, and long RNAs are considered

Fluorescence Imaging of Cell Membrane Potential: From Relative Changes to Absolute Values

Membrane potential is a fundamental property of biological cells. Changes in membrane potential characterize a vast number of vital biological processes, such as the activity of neurons and cardiomyocytes, tumorogenesis, cell-cycle progression, etc. A common strategy to record membrane potential changes that occur in the process of interest is to utilize organic dyes or genetically-encoded voltage indicators with voltage-dependent fluorescence. Sensors are introduced into target cells, and alterations of fluorescence intensity are recorded with optical methods. Techniques that allow recording relative changes of membrane potential and do not take into account fluorescence alterations due to factors other than membrane voltage are already widely used in modern biological and biomedical studies. Such techniques have been reviewed previously in many works. However, in order to investigate a number of processes, especially long-term processes, the measured signal must be corrected to exclude the contribution from voltage-independent factors or even absolute values of cell membrane potential have to be evaluated. Techniques that enable such measurements are the subject of this review