Results 1 - 10 of 195
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[en] Physical phenomena during biological freezing and thawing processes at the molecular, cellular, tissue, and organ levels are examined. The basics of cryosurgery and cryopreservation of cells and tissues are presented. Existing cryobiological models, including numerical ones, are reviewed. (reviews of topical problems)
[en] Wear and tear of concrete and reinforced concrete structures in harsh climatic conditions is analyzed as a fatigue process with various cumulative failures. For the criteria of their prediction, it is proposed to use dynamic models containing the kinetics of changes of informative and sensitive indicators of the constructive properties of concrete during cyclical freezing and thawing (CFT). An experimental-analytical generalization of the measurement of the following indicators is presented: strength, components of deformations, cracking, and the energy potential of concrete destruction during the exhaustion of its frost resistance. It is proposed, as a first approximation permissible under the conditions of the onset of fatigue parametric failures, to take the level of external temperature and humidity effects equivalent to (ultimately) 85 ÷ 90% of the frost resistance mark. (paper)
[en] The string inspired tachyon field can serve as a candidate of dark energy. Its equation of state parameter w varies from 0 to -1. In the case of tachyon field potential V(φ)→0 slower (faster) than 1/φ2 at infinity, dark energy (dark matter) is a late time attractor. We investigate the tachyon dark energy models under the assumption that w is close to -1. We find that all the models exhibit unique behavior around the present epoch which is exactly the same as that of the thawing quintessence.
[en] Objective: To explore the relationship between the blastocyst quality and biochemical pregnancy or early embryonic cessation of development during the freeze-thaw cycle of in vitro fertilisation embryo transfer (IVF-ET). Study Design: Descriptive study. Place and Duration of Study: Reproductive Centre of Baoding Maternal and Child Health Hospital, from January 2014 to August 2019. Methodology: Eight hundred and twenty-nine embryos, treated by frozen-thawed blastocyst transfer, were analysed, retrospectively. These included 232 embryos in inner cell mass (ICM) Grade C, 272 embryos with trophoderm (TE) Grade C, and 325 embryos with Grades excluding C; ICM Grade and TE Grade were A or B. The pregnancy rate, rate of early embryonic cessation of development, and biochemical pregnancy rate were compared among the three groups after transfer. Results: Compared with embryos with Grades excluding C in the score (with 55.7% in clinical pregnancy rate, 6.5% in biochemical pregnancy rate, and 5.2% in early embryonic development arrest rate), the embryos with ICM Grade C has lower clinical pregnancy rate (43.5%), higher biochemical pregnancy rate (15.1%), and rate of early embryonic cessation of development (19.8%), while the embryos with TE Grade C has lower pregnancy rate (41.2%) and higher biochemical pregnancy rate (14.3%). The differences were statistically significant (all p □0.05). There was no significant difference about the above indicators between the ICM Grade C and TE Grade C groups (p >0.05). Conclusion: Embryos with Grades excluding C in the score had better developmental potential and better prognosis. The rate of early embryonic development arrest in the ICM Grade C group was higher than that in the TE Grade C group. (author)
[en] We studied the effect of storage conditions on the safety of microvesicles produced by human multipotent umbilical cord mesenchymal stromal cells into the conditioned medium. It was found that microvesicles can be stored without serious degradation for up to 1 week at 4°С, but were almost completely destroyed during freezing and thawing cycles irrespective of the storage temperatures (-20°С, -70°С, or -196°С). Similar results were obtained for lyophilized medium conditioned by human multipotent umbilical cord mesenchymal stromal cells. Addition of a cryoprotectant (5-10% DMSO) followed by freezing and/or lyophilization preserved microvesicles at a nearly initial level. These findings indicate that during storage, microvesicles, being membrane structures, behave similar to living cells and require appropriate conditions for prolonged storage.
[en] Arctic surface temperature has increased at approximately twice the global rate over the past few decades and is also projected to warm most in the 21st century. However, the mechanism of Arctic vegetation response to this warming remains largely uncertain. Here, we analyse variations in the seasonal profiles of MODerate resolution Imaging Spectroradiometer Leaf Area Index (LAI) and ERA-interim cumulative near-Surface Air Temperature (SATΣ) over the northern Russia, north of 60° N for 2000–2019. We find that commonly used broad temporal interval (seasonal) trends cannot fully represent complex interannual variations of the LAI profile over the growing season. A sequence of narrow temporal interval (weekly) LAI trends form an inverted S-shape over the course of the growing season with enhanced green-up and senescence, but balanced during the growing season’s peak. Spatial patterns of weekly LAI trends match with those of weekly SATΣ trends during the green-up, while the drivers of the browning trends during senescence remain unclear. Geographically the area with the statistically significant temperature-driven enhanced green-up is restricted by a large patch carrying significant positive SATΣ trends, which includes North Siberian Lowland, Taimyr, Yamal and adjacent territories. The strength, duration and timing of the changes depend on vegetation type: enhanced green-up is most pronounced in tundra, while enhanced senescence is pronounced in forests. Continued release of the climatic constraints will likely increase the capacity both of the environment (i.e. permafrost thawing) and vegetation (i.e. appearance of more productive woody species), and transform LAI seasonal shifts to change of LAI seasonal amplitude. (letter)