Літературне редагування у системі фахової підготовки філологів

Bischofite exits in the upper crust with its related minerals carnallite, sylvite and halite, and is known as the most ductile material within the halide family of minerals. It is normally extracted from the subsurface by solution mining in underground caverns. Abandonment of the caverns causes the wall rock to creep towards the inside due to overburden stress, which in turn results in subsidence at the surface. In order to allow reliable prediction of the creep of Bischofite at cavern walls, a well-defined flow law is required that can be applied at strain rates at least as low as 10-9 s-1. Such rates are difficult to achieve in the laboratory. We have conducted new, conventional axi-symmetric compression tests on as-received polycrystalline Bischofite samples from natural cores. The experiments have been carried out at near real in situ conditions of temperature and pressure (70oC and 40 MPa, respectively), using a range of strain rates from 10-5 to 10-8 s-1. All experiments were strain rate stepping experiments including stress relaxation after every step down to strain rates of 3×10-9 s-1. In the relaxation part of the experiments, the deformation piston was arrested at fixed position and the stored elastic energy in the sample and in the machine was allowed to relax through plastic deformation of the sample. The measured mechanical data were used to obtain the stress exponent (n) as included in a conventional (Dorn-type) power law. We observed that during the stress relaxation, the n-value gradually changed from n>5 at 10-5 to n~1 at 10-9 s-1. The absolute strength of the samples remained higher if the relaxation started at a higher stress, i.e. at a faster rate within the range tested. We interpret this as indicating a difference in microstructure at the initiation of the relaxation, notably a smaller grain size related to dynamical recrystallization during the constant strain rate part of the test just before relaxation. The data thus suggest that there is gradual change in mechanism with decreasing strain rate, from grain size insensitive (GSI) dislocation creep to grain size sensitive (GSS) pressure solution creep. We propose that a hybrid flow law in which strain rate is equal to A’σnexp(σ/B) should best be applied to describe the flow of Bischofite at in situ conditions of 70oC, 40 MPa and slow strain rate. Best fit analysis resulted in values n=3.4, A’= 10(-8.519) and B = 2.26

Using a composite flow law to model deformation in the NEEM deep ice core, Greenland — Part 2: The role of grain size and premelting on ice deformation at high homologous temperature

The ice microstructure in the lower part of the North Greenland Eemian Ice Drilling (NEEM) ice core consists of relatively fine-grained ice with a single maximum crystallographic preferred orientation (CPO) alternated by much coarser-grained ice with a partial (great circle) girdle or multi-maxima CPO. In this study, the grain-size-sensitive (GSS) composite flow law of Goldsby and Kohlstedt (2001) was used to study the effects of grain size and premelting (liquid-like layer along the grain boundaries) on strain rate in the lower part of the NEEM ice core. The results show that the strain rates predicted in the fine-grained layers are about an order of magnitude higher than in the much coarser-grained layers. The dominant deformation mechanisms, based on the flow relation of Goldsby and Kohlstedt (2001), between the layers is also different, with basal slip rate limited by grain boundary sliding (GBS-limited creep) being the dominant deformation mechanism in the finer-grained layers, while GBS-limited creep and dislocation creep (basal slip rate limited by non-basal slip) contribute both roughly equally to bulk strain in the coarse-grained layers. Due to the large difference in microstructure between finer-grained ice and the coarse-grained ice at premelting temperatures (T>262 K), it is expected that the fine-grained layers deform at high strain rates, while the coarse-grained layers are relatively stagnant. The difference in microstructure, and consequently in viscosity, between impurity-rich and low-impurity ice can have important consequences for ice dynamics close to the bedrock

Rationale and design of the PRAETORIAN-COVID trial:A double-blind, placebo-controlled randomized clinical trial with valsartan for PRevention of Acute rEspiraTORy dIstress syndrome in hospitAlized patieNts with SARS-COV-2 Infection Disease

There is much debate on the use of angiotensin receptor blockers (ARBs) in severe acute respiratory syndrome–coronavirus-2 (SARS-CoV-2)–infected patients. Although it has been suggested that ARBs might lead to a higher susceptibility and severity of SARS-CoV-2 infection, experimental data suggest that ARBs may reduce acute lung injury via blocking angiotensin-II–mediated pulmonary permeability, inflammation, and fibrosis. However, despite these hypotheses, specific studies on ARBs in SARS-CoV-2 patients are lacking. Methods: The PRAETORIAN-COVID trial is a multicenter, double-blind, placebo-controlled 1:1 randomized clinical trial in adult hospitalized SARS-CoV-2–infected patients (n = 651). The primary aim is to investigate the effect of the ARB valsartan compared to placebo on the composite end point of admission to an intensive care unit, mechanical ventilation, or death within 14 days of randomization. The active-treatment arm will receive valsartan in a dosage titrated to blood pressure up to a maximum of 160 mg bid, and the placebo arm will receive matching placebo. Treatment duration will be 14 days, or until the occurrence of the primary end point or until hospital discharge, if either of these occurs within 14 days. The trial is registered at clinicaltrials.gov (NCT04335786, 2020). The PRAETORIAN-COVID trial is a double-blind, placebo-controlled 1:1 randomized trial to assess the effect of valsartan compared to placebo on the occurrence of ICU admission, mechanical ventilation, and death in hospitalized SARS-CoV-2–infected patients. The results of this study might impact the treatment of SARS-CoV-2 patients globally

Coordination of policies and governance: regime requirements in Dutch freshwater management

Sustainable development presents public authorities with many challenges. Increasing steering capacity, legitimising current actions to address intergenerational benefits, and developing capacity to incorporate learning while dealing with complexities and uncertainties are needed to address upcoming dilemmas (Bressers and Rosenbaum, 2003). Consequently, the coordination of policies across policy domains and governance scales is essential. &nbsp

Application of composite flow laws to grain size distributions derived from polar ice cores

Apart from evaluating the crystallographic orientation, focus of microstructural analysis of natural ice during the last decades has been to create depth-profiles of mean grain size. Several ice flow models incorporated mean grain size as a variable. Although such a mean value may coincide well with the size of a large proportion of the grains, smaller/larger grains are effectively ignored. These smaller/larger grains, however, may affect the ice flow modeling. Variability in grain size is observed on centimeter, meter and kilometer scale along deep polar ice cores. Composite flow laws allow considering the effect of this variability on rheology, by weighing the contribution of grain-size-sensitive (GSS, diffusion/grain boundary sliding) and grain-size-insensitive (GSI, dislocation) creep mechanisms taking the full grain size distribution into account [Herwegh et al., 2005, J. Struct. Geol., 27, 503-521]. Extraction of hundreds of grain size distributions for different depths along an ice core has become relatively easy by automatic image processing techniques [T. Binder et al., 2013, J. Microsc., 250, 130-141]. The shallow ice approximation is widely adopted in ice sheet modeling and approaches the full-Stokes solution for small ratios of vertical to horizontal characteristic dimensions. In this approximation shear stress in the vertical plain dominates the strain. This assumption is not applicable at ice divides or dome structures, where most deep ice core drilling sites are located. Within the upper two thirds of the ice column longitudinal stresses are not negligible and ice deformation is dominated by vertical strain. The Dansgaard-Johnsen model [W. Dansgaard & S.J. Johnsen, 1969, J. Glaciol., 8, 215-223] predicts a dominating, constant vertical strain rate for the upper two thirds of the ice sheet, whereas in the lower ice column vertical shear becomes the main driver for ice deformation. We derived vertical strain rates from the upper NEEM ice core (North-West Greenland) and compared them to classical estimates of strain rates at the NEEM site. Assuming intervals of constant accumulation rates, we found a variation of vertical strain rates by a factor 2-3 in the upper ice column. We discuss the current applicability of composite flow laws to grain size distributions extracted from ice cores drilled at sites where the flow direction rotates by 90 degrees with depth (i.e. ice divide). An interesting finding is that a transition to a glacial period in future would be associated with a decrease in vertical strain rate (due to a reduced accumulation rate) and an increase of the frequency of small grains (due to an enhanced impurity content). Composite flow laws assign an enhanced contribution of GSS creep to this transition. It is currently unclear which factor would have a greater influence

Introduction to Journal of Structural Geology special issue on “Deformation of the lithosphere. How small structures tell a big story”

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