ALLELOPATHIC CHANGES OF FAGUS ORIENTALIS L. UNDER INFLUENCE OF RECREATION

Проводится оценка изменений аллелопатической составляющей фитогенного поля бука восточного под воздействием рекреационной нагрузки. Методом биотестов определено, что воздействие разовой предельно допустимой рекреационной нагрузки отражается на пространственном изменении величины аллелопатического влияния в зонах фитогенного поля. Changes in the allelopathic component of the phytogenic field of the beech eastern under the influence of recreational load were estimated. Using the biotest method, it was found that the influence of a single maximum permissible recreational load affects the spatial change in the magnitude of the allelopathic effect in the zones of the phytogenic field.

Influence of initial preferred orientations on strain localisation and fold patterns in non-linear viscous anisotropic materials

<p>Deformation localisation in rocks can lead to a variety of structures, such as shear zones and shear bands that can range from grain to crustal scale, from discrete and isolated zones to anastomosing networks. The heterogeneous strain field can furthermore result in a wide range of highly diverse fold geometries.</p><p>We present a series of numerical simulations of the simple-shear deformation of an intrinsically anisotropic non-linear viscous material with a single maximum crystal preferred orientation (CPO) in dextral simple shear. We use the Viscoplastic Full-Field Transform (VPFFT) crystal plasticity code (e.g. Lebensohn & Rollett, 2020) coupled with the modelling platform ELLE (http://elle.ws) to achieve very high strains. The VPFFT-approach simulates viscoplastic deformation by dislocation glide, taking into account the different available slip systems and their critical resolved shear stresses. The approach is well suited for strongly non-linear anisotropic materials (de Riese et al., 2019). We vary the anisotropic behaviour of the material from isotropic to highly anisotropic (according to the relative critical resolved shear stress required to activate the different slip systems), as well as the orientation of the initial single maximum orientation, which we vary from parallel to perpendicular to the shear plane. To visualize deformation structures, we use passive markers, for which we also systematically vary the initial orientation.</p><p>At relatively low strains the amount of strain rate localisation and resulting deformation structures highly depend on the initial single maximum orientation in the material in all anisotropic models. Three regimes can be recognised: distributed shear localisation, synthetic shear bands and antithetic shear bands. However, at very high strains localisation behaviour always tends to converge to a similar state, independent of the initial orientation of the anisotropy.</p><p>In rocks, shear localisation is often detected by the deflection and/or folding of layers, which may be parallel to the anisotropy (e.g. cleavage formed by aligned mica), or by deflection/deformation of passive layering, such as original sedimentary layers. The resulting fold patterns vary strongly, depending on the original orientation of layering relative to the deformation field. This can even result in misleading structures that seem to indicate the opposite sense of shear. Most distinct deformation structures tend to form when the layering is originally parallel to the shear plane.</p><p> </p><p>de Riese, T., Evans, L., Gomez-Rivas, E., Griera, A., Lebensohn, R.A., Llorens, M.-G., Ran, H., Sachau, T., Weikusat, I., Bons, P.D. 2019. Shear localisation in anisotropic, non-linear viscous materials that develop a CPO: A numerical study. J. Struct. Geol. 124, 81-90.</p><p>Lebensohn, R.A., Rollett, A.D. 2020. Spectral methods for full-field micromechanical modelling of polycrystalline materials. Computational Mat. Sci. 173, 109336.</p>

Brief communication: Sampling c-axes distributions from the eigenvalues of ice fabric orientation tensors

For simulation purposes involving different realizations of ice fabrics, it can be necessary to generate arbitrarily large samples of c-axes based on the second-order orientation tensor, a commonly used descriptive statistics provided in publications of ice core measurements. This paper describes a sampling technique based on the combination of a vertical girdle and a single maximum Watson distributions.

Development of Regional Maximum Permissible Concentrations of Oil in the Soils of Arid Ecosystems in the South of Russia

Objective difficulties and incorrect use of a single maximum permissible concentration of oil for all soils of Russia are considered. It is more expedient to use regional maximum permissible concentrations (RMPC) of oil in different soils of Russia, taking into account their regional ecological-genetic and ecological-geographical features. RMPC of oil in arid soils of the South of Russia was developed on the basis of violation of their ecosystem functions. Regional MPC of oil in dark chestnut soils (haplic kastanozems) is 0.40 % of oil in soil, chestnut (haplic kastanozems) and light chestnut (haplic kastanozems) – 0.30 %, brown semi-desert (haplic calcisols) – 0.24 %, sandy brown semi-desert (calcaric arenosols) – 0.20 %. The developed RPMCs can be used not only for arid soils in southern Russia, but also for similar arid soils in other regions.

Physical analysis of an Antarctic ice core—towards an integration of micro- and macrodynamics of polar ice

Microstructures from deep ice cores reflect the dynamic conditions of the drill location as well as the thermodynamic history of the drill site and catchment area in great detail. Ice core parameters (crystal lattice-preferred orientation (LPO), grain size, grain shape), mesostructures (visual stratigraphy) as well as borehole deformation were measured in a deep ice core drilled at Kohnen Station, Dronning Maud Land (DML), Antarctica. These observations are used to characterize the local dynamic setting and its rheological as well as microstructural effects at the EDML ice core drilling site (European Project for Ice Coring in Antarctica in DML). The results suggest a division of the core into five distinct sections, interpreted as the effects of changing deformation boundary conditions from triaxial deformation with horizontal extension to bedrock-parallel shear. Region 1 (uppermost approx. 450 m depth) with still small macroscopic strain is dominated by compression of bubbles and strong strain and recrystallization localization. Region 2 (approx. 450–1700 m depth) shows a girdle-type LPO with the girdle plane being perpendicular to grain elongations, which indicates triaxial deformation with dominating horizontal extension. In this region (approx. 1000 m depth), the first subtle traces of shear deformation are observed in the shape-preferred orientation (SPO) by inclination of the grain elongation. Region 3 (approx. 1700–2030 m depth) represents a transitional regime between triaxial deformation and dominance of shear, which becomes apparent in the progression of the girdle to a single maximum LPO and increasing obliqueness of grain elongations. The fully developed single maximum LPO in region 4 (approx. 2030–2385 m depth) is an indicator of shear dominance. Region 5 (below approx. 2385 m depth) is marked by signs of strong shear, such as strong SPO values of grain elongation and strong kink folding of visual layers. The details of structural observations are compared with results from a numerical ice sheet model (PISM, isotropic) for comparison of strain rate trends predicted from the large-scale geometry of the ice sheet and borehole logging data. This comparison confirms the segmentation into these depth regions and in turn provides a wider view of the ice sheet. This article is part of the themed issue ‘Microdynamics of ice’.

Fluctuation enhancement of ion diffusivity in liquids

The diffusivity of ions in liquid solutions is known either to decrease with an increase in the ion size or to have a single maximum depending on the ion size. This article presents evidence for the appearance of multiple maxima and thus multiple ion sizes with enhanced diffusivity.

Small-scale disturbances in the stratigraphy of the NEEM ice core: observations and numerical model simulations

Disturbances on the centimetre scale in the stratigraphy of the North Greenland Eemian Ice Drilling (NEEM) ice core (North Greenland) can be mapped by an optical line scanner as long as the ice has visual layering, such as, for example, cloudy bands. Different focal depths allow, to a certain extent, a three-dimensional view of the structures. In this study we present a detailed analysis of the visible folds, discuss their characteristics and frequency, and present examples of typical fold structures. We also analyse the structures with regard to the deformation boundary conditions under which they formed. The structures evolve from gentle waves at about 1500 m to overturned z folds with increasing depth. Occasionally, the folding causes significant thickening of layers. Their similar fold shape indicates that they are passive features and are probably not initiated by rheology differences between alternating layers. Layering is heavily disturbed and tracing of single layers is no longer possible below a depth of 2160 m. C axes orientation distributions for the corresponding core sections were analysed, where available, in addition to visual stratigraphy. The data show axial-plane parallel strings of grains with c axis orientations that deviate from that of the matrix, which shows a single maximum fabric at the depth where the folding occurs. Numerical modelling of crystal viscoplastic deformation and dynamic recrystallisation was used to improve the understanding of the formation of the observed structures during deformation. The modelling reproduces the development of bands of grains with a tilted-lattice orientation relative to the single maximum fabric of the matrix, and also the associated local deformation. We conclude from these results that the observed folding can be explained by formation of these tilted-lattice bands.

Small-scale disturbances in the stratigraphy of the NEEM ice core: observations and numerical model simulations

Disturbances on the centimetre scale in the stratigraphy of the NEEM ice core (North Greenland) can be mapped by an optical line scanner as long as the ice does have a visual layering, such as, for example, cloudy bands. Different focal depths allow, to a certain extent, a three dimensional view of the structures. In this study we present a detailed analysis of the visible folds, discuss their characteristics and frequency and present examples of typical fold structures. We also analyse the structures with regard to the deformation boundary conditions under which they formed. The structures evolve from gentle waves at about 1500 m to overturned z-folds with increasing depth. Occasionally, the folding causes significant thickening of layers. Their similar-fold shape indicates that they are passive features and are probably not initiated by rheology differences between alternating layers. Layering is heavily disturbed and tracing of single layers is no longer possible below a depth of 2160 m. c-axes orientation distributions for the corresponding core sections were analysed where available in addition to visual stratigraphy. The data show axial-plane parallel strings of grains with c-axis orientations that deviate from that of the matrix, which shows a single-maximum fabric at the depth where the folding occurs. Numerical modelling of crystal viscoplasticity deformation and dynamic recrystallisation was used to improve the understanding of the formation of the observed structures during deformation. The modelling reproduces the development of bands of grains with a tilted orientation relative to the single maximum fabric of the matrix, and also the associated local deformation. We conclude from these results that the observed folding is a consequence of localized deformation at the boundaries of kink bands.

Qualification of Temper Bead Welding by an Alternative Hardness Testing Approach

In 2004, ASME Section IX added maximum hardness essential variables for temper bead procedure qualification when impact testing is not specified or required by the applicable book section. The assumption with specifying a maximum hardness criterion is that high hardness after temper bead welding indicates inadequate tempering. As discussed in PVP2013-97793 [2], imposing a maximum hardness criterion for temper bead qualification can actually lead to acceptance of a heat affected zone (HAZ) microstructure with less than optimum impact properties. In fact, depending on the weld HAZ microstructure the impact properties can vary widely from very low to very high at the same hardness. This paper describes an alternative hardness test protocol for temper bead procedure qualification. Rather than using a single maximum hardness acceptance threshold, this new test protocol characterizes the base material response to temper bead welding by determining the maximum achievable hardness with a bead-on-plate test and with a hardness calculation. Research shows that a high hardness in the HAZ prior to depositing the tempering weld layers provides the optimum microstructure for achieving desired HAZ impact properties. With proper tempering the HAZ hardness is reduced below the maximum achievable hardness. Temper bead procedure acceptance is thus determined by the drop in HAZ hardness after depositing the temper bead weld layers. Application of this new hardness test protocol for temper bead qualification is proposed as an alternative to a single maximum hardness acceptance criterion.

Fabric measurement along the NEEM ice core, Greenland, and comparison with GRIP and NGRIP ice cores

Fabric (distribution of crystallographic orientations) profile along the full NEEM ice core, Greenland, is presented in this work. Data were measured in the field by an Automatic Ice Texture Analyzer every 10 m, from 33 m down to 2461 m depth. The fabric evolves from a slightly anisotropic fabric at the top, toward a strong single maximum at about 2300 m, which is typical of a deformation pattern mostly driven by uniaxial compression and simple shearing. A sharp increase in the fabric strengthening is observed at the Holocene to Wisconsin climatic transition. A similar strengthening, toward an anisotropic single maximum-type fabric, has been observed in several ice cores from Greenland and Antarctica, and can be attributed to a positive feedback between changes in ice viscosity at the climatic transition, and the impact of a shear component of stress. Centimeter scale abrupt texture (fabric and microstructure) variations are observed in the bottom part of the core. Their positions are in good agreement with the folding hypothesis used for a climatic reconstruction by Dahl-Jensen et al. (2013). Comparison is made to two others ice cores drilled along the same ridge; the GRIP ice core drilled at the summit of the ice sheet, and the NorthGRIP ice core, drilled 325 km to the NNW of the summit along the ridge, and 365 km upstream from NEEM. The fabric profile clearly reflects the increase in shear deformation when moving NW along the ridge from GRIP to NorthGRIP and NEEM. The difference in fabric profiles between NEEM and NorthGRIP also evidences a stronger lateral extension associated with a sharper ridge at NorthGRIP.