Some optical and mechanical properties of a number of langasite family crystals have been compared. It is shown that electron-density regions in the form of helices, twisted in the opposite directions for the right- and left-handed crystals, make a structural basis of the optical activity. The characteristic surfaces of Young’s modulus have been calculated for some langasite family crystals, and the difference between them is explained from the structural point of view. The fracture anisotropy under Berkovich indentation of the (0001) basal plane has been considered for five crystals. It is shown that crystallographic cracks (straight-line ones and those formed exactly at the indenter angles) are obtained at indenter rotations with a step of 60° from the position in which the indenter angles coincide with the 〈 $$\bar {1}$$ 010〉 directions. The structural basis of piezoelectricity of langasites is established, and a difference in the piezoelectric properties of the right- and left-handed crystals (which is important for manufacture of piezoelectric devices) are shown.

Bulk c-oriented CeF3 single crystals (sp. gr. P3¯c1) were grown successfully by the vertical Bridgman technique in a fluorinating atmosphere. A description of the crystal growth procedure and the solution of the difficulties during the growth process are presented in detail. The anisotropy of the mechanical, thermal and electrophysical properties were studied for the first time. The maximum values of the thermal conductivity coefficient (α = 2.51 ± 0.12 W·m−1·K−1) and the ionic conductivity (σdc = 2.7 × 10−6 S/cm) at room temperature are observed in the [0001] direction for the CeF3 crystals. The Vickers (HV) and Berkovich (HB) microhardnesses for the (0001), (101¯0) and (112¯0) crystallographic planes were investigated. The HB values were higher than the HV ones and decreased from 3.8 to 2.9 GPa with an increase in the load in the range of 0.5–0.98 N for the hardest (0001) plane. The {112¯0}, {101¯0} and {0001} cleavage planes were observed during the indentation process of the CeF3 crystals. The variability of Young’s, the shear modules and Poisson’s ratio were analyzed. A significant correlation between the shapes of the Vickers indentation patterns with Young’s modulus anisotropy was found. The relationship between the anisotropy of the studied properties and the features of the CeF3 trigonal crystal structure is discussed.

The anisotropy of microhardness and fracture of the (0001) basal plane of langasite crystal has been studied using Berkovich indentation under a load of 100 g at different indenter positions. The formation of “crystallographic” microcracks (straight-line and emerging exactly from the impression angles), which propagate in six directions, spaced by 60°, is observed. It is suggested that the observed specific features of microcrack formation are based structurally on the presence of a mixed cation site. As follows from the structural model of a multicell, fractures propagate along the direction of polyhedra with mixed cation occupancy, and the fracture line pushes apart unit cells of different chemical compositions. The Young’s modulus of langasite crystal has been calculated for different crystallographic planes.

The impact of modern climate change on lakes is one of the most relevant problems in the field of limnology. For Lake Baikal this impact is manifested in the change in abiotic characteristics of the lake ecosystem. It is shown that the pattern of modern climate change in the Baikal region includes both the “secular” warming trend and the intrasecular variations which exceed this trend in the scale and may be caused by atmospheric circulation. The effect of atmospheric circulation is associated with the physiographic characteristics of separate parts of the lake and its watershed. The influence of changes in atmospheric circulation on the ice and thermal regime of Lake Baikal is analyzed for the period of 1950–2017 for which objective analysis data on the large-scale atmospheric circulation in the Northern Hemisphere are available.

The anisotropy of the mechanical characteristics of CeF3 crystals (sp. gr. $$P\bar {3}c1$$) grown from the melt by the Bridgman technique has been studied for the first time. The variability of Young’s modulus, the shear modulus, and the Poisson’s ratio has been analyzed and the Vickers microhardness HV of the (0001) and $$(10\bar {1}0)$$ crystal planes at room temperature has been determined (2.9 and 2.3 GPa, respectively, under a load of P = 60 g). The $${{\{ 11\bar {2}0\} }}$$ primary cleavage surfaces (slip planes) and the $${\text{\{ }}10\bar {1}0{\text{\} }}$$ and {0001} secondary cleavage planes for the CеF3 crystals have been established. A correlation between the shape of Vickers indentations and the Young’s modulus anisotropy have been observed.

The crystal structure of potassium, rubidium, cesium, and ammonium hydrophthalates is analyzed based on the data in the literature. A relationship between their structure and elastic and mechanical properties has been established for the first time. Young’s moduli, shear moduli, and Poisson’s ratios in the (100), (010), and (001) planes of these crystals are calculated, and Knoop indentation of these planes is performed. Anisotropy of the elastic and mechanical properties of the crystals is revealed. Rubidium, cesium, and ammonium hydrophthalates are found to be partial auxetics. Ammonium hydrophthalate, whose structure contains additional (as compared with other hydrophthalates) hydrogen bonds, exhibits the highest anisotropy of properties.

TbF3 (sp. gr. Pnma) crystals up to 40 mm in diameter have been grown from melt by a Bridgman technique. The anisotropy of their mechanical properties is studied for the first time. the technical elasticity constants are calculated, and room-temperature values of Vickers microhardness for the (010) and (100) planes are measured. The shape of indentation impressions is found to correlate with Young's modulus anisotropy for TbF3 crystals.

The article presents a summary of the most important results obtained during the studies of the heat balance at Lake Baikal since the 1930s. The systematic regime measurements of water temperature initiated in Limnological Institute since 1970 indicated the features of the spatial structure and temporal changes in the elements of the Baikal heat balance. We have determined the magnitude of the annual evaporation from the surface of Lake Baikal by the independent method considering the data on temperature of the water column. We have investigated one of the main renewal processes of deep and near-bottom Baikal waters associated with thermobaric effect. As a result of this effect, the water renewal and aeration in the near-bottom layer annually occurs under certain hydrological conditions. We have determined the vertical flows of mass, heat and gas exchange of the upper and deep layers in Lake Baikal. We have studied the effect of changes in the characteristics (indices) of the atmospheric circulation in the Northern Hemisphere on the variability of the characteristics of climate and ice-thermal regime at Baikal, i.e. air temperature and water surface temperature, ice thickness, as well as dates of ice phenomena during the modern period. Anomalies of the atmospheric circulation are most obvious in the ice processes. We have found the relationship between the water temperature of the warm (May-September) period and the indicators of the zonal circulation (positive relationship), as well as indices of the formations blocking the western transfer (negative relationship). There is an obvious effect on the water surface temperature of the winter circulation indices. We have shown that these changes are associated with the fluctuations in the intensity of the zonal circulation and the baric formations blocking them. There is the effect of circulation on the moisture characteristics (precipitation and runoff), but it is complicated by large differences in climate within the Baikal catchment area.

The microhardness on the (010) and (001) planes in K2Co(SO4)2 · 6H2O crystal has been measured by the Vickers indentation method. Its values are, respectively, 11500 and 1300 MPa. No microhardness anisotropy of the first kind is revealed on either plane. The fracture geometry under indentation by a spherical indenter and Vickers and Knoop indenters is studied. The crystal has lower brittleness than the isomorphic Cs2Ni(SO4)2 · 6H2O crystal.

A study is made of the influence of the large-scale atmospheric circulation, described by the indices of Northern Hemisphere Teleconnection Patterns, on air temperature and ice-thermal characteristics of Lake Baikal for the time interval 1950–2010. Multiple linear regression equations have been obtained to account for 46–47% of the air temperature changes during the winter, spring and autumn seasons, and for 18% during the summer season. The main contribution to air temperature change for separate seasons (except in the summertime) and ice-thermal characteristics is made by the fluctuations of the AO and NAO indices characterizing the west-east transport of air masses, and of the SCAND and Sh indices of the mechanisms blocking this transport.

We examine the changes in water inflow into Baikal that are taking place due to global warming that enhanced beginning in the 1970s as well as due to the different responses of discharges of separate rivers within the Baikal watershed basin to climate change.

The microhardness of the (010), (100), and (001) planes in the Cs 2 Ni(SO 4 ) 2 · 6H 2 O crystal and the geometry of destruction of the (010) plane around impressions of different (spherical, Vickers, and Knoop) indenters has been studied using Vickers indentation. It is shown that the crystal under study is characterized by enhanced brittleness and that the cleavage along the (201) plane is highly imperfect. The maximum microhardness ( H = 1140 MPa) is characteristic of the (001) plane under a load of 20 g.

The correlation of the anisotropy of the Young’s modulus of organic single crystals of potassium, rubidium, cesium, and ammonium acid phthalates with strain and fracture patterns during Knoop indentation on the (010) cleavage plane in the [001] and [100] directions has been studied. The data on the maximum anisotropy of the strain and fracture patterns of the ammonium acid phthalate single crystal have been discussed in view of the published data on the structure, mechanical, elastic, and X-ray spectral properties of these crystals.

The optical (transmission and circular dichroism) spectra and mechanical (Vickers microhardness and fracture toughness K 1 c ) properties of langasite La 3 Ga 5 SiO 14 crystals have been studied after γ irradiation and exposure for a month. It is shown that, as a result of irradiation crystals become more transparent in the range 310–640 nm, nonstructural defects with the energies of excited states in the range 2.06–4.13 eV decay and new structural defects with the excited-state energies in the range 4.14–5.00 eV are formed. Irradiation does not lead to a change in microhardness, while the coefficient K 1 c increases from 0.32 to 0.36 MPa m 1/2 .