•The general energy product converges with the reduction in linear size at shear.•The fracture criterion includes the stress tensor hydrostatic component and the external boundary.•The influence of ...shear on the CRLD specimen is part of the general variational problem statement.•The linear size determining GEP convergence was taken for the characteristic size of the pre-fracture zone.
This article considers the influence of shear on a specimen with a crack-like defect (CRLD) as part of the general variational statement of the problem with a distinguished interactive layer. The delta-element fracture criterion is formulated as a generalized energy product (GEP), accounting for the influence of hydrostatic stress and the existence of an external boundary. The GEP convergence with a reduction of the layer thickness in the layers element is shown both in the simplified analytical solution and in the numerical solution by the finite elements method (FEM). The linear size determining the GEP convergence in the layers element is taken for the characteristic size of the finite element conjugate to the physical excision and its continuation. It is shown that, unlike the simplified analytical solution, the solution by FEM allows finding the maximum GEP outside the layer.
On the basis of the general variational formulation of the problem of the deformation of two bodies connected by a thin layer, a system of differential equations of equilibrium of the ...double-cantilever beam is obtained, taking into account the shear deformations of the cantilevers, both in the interface section and in the free section, taking into account also the elastoplastic properties of the layer. In this work, we use the connection representation of the
J
-integral in terms of the energy product and the energy product of dissipation. For purely elastic deformation, on the basis of the analytical solution of the system, an expression is obtained for the stress state of an extremely thin layer connecting the cantilevers, which is dependent on the material properties of both the layer and the cantilevers. The obtained expression for the elastic energy flux is compared with the known ones. The energy product at the top of the layer is found, the value of which depends only on the material properties of the consoles. With the elastoplastic behavior of the layer, the energy product of dissipation was found, which turned out to be dependent on the yield stress of the adhesive. The energy product in this case is proportional to the layer thickness. For adhesives with pronounced plastic properties, taking into account the dissipative mechanism of energy release leads to fundamental differences in the
J
-integral in comparison with the elastic calculation. The dependences of the DCB sample compliance with subcritical growth of the plastic deformation region in the adhesive are plotted.
Wetlands are the world's largest natural source of methane, a powerful greenhouse gas. The strong sensitivity of methane emissions to environmental factors such as soil temperature and moisture has ...led to concerns about potential positive feedbacks to climate change. This risk is particularly relevant at high latitudes, which have experienced pronounced warming and where thawing permafrost could potentially liberate large amounts of labile carbon over the next 100 years. However, global models disagree as to the magnitude and spatial distribution of emissions, due to uncertainties in wetland area and emissions per unit area and a scarcity of in situ observations. Recent intensive field campaigns across the West Siberian Lowland (WSL) make this an ideal region over which to assess the performance of large-scale process-based wetland models in a high-latitude environment. Here we present the results of a follow-up to the Wetland and Wetland CH4 Intercomparison of Models Project (WETCHIMP), focused on the West Siberian Lowland (WETCHIMP-WSL). We assessed 21 models and 5 inversions over this domain in terms of total CH4 emissions, simulated wetland areas, and CH4 fluxes per unit wetland area and compared these results to an intensive in situ CH4 flux data set, several wetland maps, and two satellite surface water products. We found that (a) despite the large scatter of individual estimates, 12-year mean estimates of annual total emissions over the WSL from forward models (5.34 ± 0.54 Tg CH4 yr-1), inversions (6.06 ± 1.22 Tg CH4 yr-1), and in situ observations (3.91 ± 1.29 Tg CH4 yr-1) largely agreed; (b) forward models using surface water products alone to estimate wetland areas suffered from severe biases in CH4 emissions; (c) the interannual time series of models that lacked either soil thermal physics appropriate to the high latitudes or realistic emissions from unsaturated peatlands tended to be dominated by a single environmental driver (inundation or air temperature), unlike those of inversions and more sophisticated forward models; (d) differences in biogeochemical schemes across models had relatively smaller influence over performance; and (e) multiyear or multidecade observational records are crucial for evaluating models' responses to long-term climate change.
The Mukhrino field station has participated in the national project on the inventory of carbon fluxes and pools in the terrestrial ecosystems of Russia since 2022. The development of a network of ...measurements of CO2 fluxes and phytomass covered six types of bog ecosystems typical to Western Siberia. The gross ecosystem exchange (GEE) of the field-layer vegetation (medians for the period from the end of May to the end of July, mgC m−2 h−1; see errors in Results section) decreased in series: Sphagnum bog with sparse low pine trees (“Open bog”), ridges in ridge-hollow patterned bogs (“Ridge”), pine-dwarf shrub-Sphagnum bog (“Tall ryam”), hollows in patterned bogs (“S.hollow”, “E.hollow”) and pine-dwarf shrub-Sphagnum bog (“Ryam”): −220, −200, −125, −120, −109 and −86, respectively. Ecosystem respiration (Reco) here was 106, 106, 182, 55, 97 and 136. The aboveground and belowground phytomass of mosses in this series varied between 368 ± 106–472 ± 184 and 2484 ± 517–6041 ± 2079 g/m2, respectively: the aboveground phytomass of vascular plants and plant litter—15 ± 7–128 ± 95 and 10 ± 6–128 ± 43, respectively. According to the results of mathematical modeling, the best proxy for GEE, in addition to photosynthetically active radiation and soil surface temperature, was the aboveground phytomass of vascular plants (PhV), and for Reco—PhV and the mass of the plant litter of vascular plants.
•A universal representation of the specific surface energy was found.•A fracture criterion containing a LP is proposed.•The existence of a threshold value of the LP was established.
The authors of ...the article considered a fracture model with a linear parameter (LP) associated with the thickness of the physical cut and the interaction layer (IL) on its continuation. With a zero value of the LP, the fracture model takes a form of a mathematical cut. The initial state of the body corresponds to the initial free binding energy, which is assumed to be negative. By the means of thermomechanical analysis of the fracturing processes, the authors established universal representation of the surface energy, which is valid for both physical and mathematical cuts. In the case of a physical cut, the surface energy is expressed as a product of multiplication of the LP value by the change in the specific free binding energy of the IL. It is called the energy product (EP). Using the proposed formulation, the authors considered the effect of decreasing LP on the critical state of samples of finite dimensions.
This paper describes a study of deformation of an ideal elastoplastic adhesive layer of a sample in the form of an elastic double-cantilever beam. The
integral values are determined for a number of ...adhesives with account for all diagonal stress tensor components in the layer. It is shown that the
integral value is significantly affected by the plane problem type in the case where an elastic-plastic model of layer deformation is applied. As demonstrated in the study, compressive stresses may be present during normal fracture in the irreversible deformation region of the adhesive in a plane stressed state.
A physical cut model is used to describe the changes in the stress-strain state (SSS) in elastoplastic bodies weakened by cracks. The distance between the crack edges is considered to be finite in ...contrast to the mathematical cut. The interactive layer with a thickness limited by the possibility of using the hypothesis of continuity is distinguished on the physical cut extension. Distribution of stresses and strains over the layer thickness is constant and does not depend on the geometry of the boundary between the cut and the interactive layer. The relationship between stresses and strains is determined by the deformation plasticity theory. The problem of plane strain or plane stress state of an arbitrary finite body weakened by a physical cut is reduced to solving a system of two variational equations for displacement fields in the body parts adjacent to the interactive layer. The proposed approach eliminates the singularity in stress distribution in contrast to the mathematical cut model. Use of local strength criteria allows us to determine the time, point and direction of the fracture initiation. Possibilities of the proposed model are illustrated by solving the problems of determining the SSS of a rectangular body weakened by a physical cut under symmetric and antisymmetric loadings.
Technology of creation effective photocathode based on the InP/InGaAs heterostructures is given. The results of an experimental study of pin-diode, which was used as the receiver of photoelectrons, ...are presented. Arrangement of the vacuum photoelectronic device with InP/InGaAs photocathode is proposed.
The expansive plains of West Siberia contain globally significant carbon stocks, with Earth's most extensive peatland complex overlying the world's largest‐known hydrocarbon basin. Numerous ...terrestrial methane seeps have recently been discovered on this landscape, located along the floodplains of the Ob and Irtysh Rivers in hotspots covering more than 2500 km2. We articulated three hypotheses to explain the origin and migration pathways of methane within these seeps: (H1) uplift of Cretaceous‐aged methane from deep petroleum reservoirs along faults and fractures, (H2) release of Oligocene‐aged methane capped or trapped by degrading permafrost, and (H3) horizontal migration of Holocene‐aged methane from surrounding peatlands. We tested these hypotheses using a range of geochemical tools on gas and water samples extracted from seeps, peatlands, and aquifers across the 120,000 km2 study area. Seep‐gas composition, radiocarbon age, and stable isotope fingerprints favor the peatland hypothesis of seep‐methane origin (H3). Organic matter in raised bogs is the primary source of seep methane, but observed variability in stable isotope composition and concentration suggest production in two divergent biogeochemical settings that support distinct metabolic pathways of methanogenesis. Comparison of these parameters in raised bogs and seeps indicates that the first is bogs, via CO2 reduction methanogenesis. The second setting is likely groundwater, where dissolved organic carbon from bogs is degraded via chemolithotrophic acetogenesis followed by acetate fermentation methanogenesis. Our findings highlight the importance of methane lateral migration in West Siberia's bog‐dominated landscapes via intimate groundwater connections. The same phenomenon could occur in similar landscapes across the boreal‐taiga biome, thereby making groundwater‐fed rivers and springs potent methane sources.
Аннотация
На территории Западно‐Сибирской равнины сосредоточены запасы углерода глобального значения, включая наибольшую по площади систему болот в мире и наибольший по величине разведанных ресурсов углеводородный бассейн в мире. Недавно в регионе были найдены многочисленные локальные выходы метана (сипы), покрывающие 2,500 квадратных километров в поймах Оби, Иртыша и их притоков. Мы рассматриваем три гипотезы, объясняющие происхождение метана в сипах и пути их миграции: (H1) вертикальная миграция метана из меловых нефтегазоносных отложений по трещинам и разрывам в земной коре, (H2) высвобождение метана в процессе деградации реликтовой мерзлоты, расположенной в отложениях олигоценового возраста, (H3) горизонтальная миграция метана голоценового возраста из окружающих болот. Мы протестировали предложенные гипотезы, определив значения различных геохимических показателей в образцах газа и воды, взятых из сипов, болот и грунтовых вод региона на территории площадью 120,000 квадратных километров. Компонентный состав газа, радиоуглеродный возраст метана, а также состав стабильных изотопов свидетельствовали в пользу болотной гипотезы происхождения метана в сипах. Органика верховых болот оказалась основным субстратом для продукции метана, выходящего через сипы, однако высокая вариабельность значений его концентрации и состава стабильных изотопов указывала на то, что этот метан был продуцирован по разным метаболическим путям в двух геохимически отличающихся источниках. Сравнение значений этих параметров между сипами и верховыми болотами показало, что один из этих источников ‐ сами верховые болота, в которых метан, выходящий через сипы, был продуцирован по гидрогенотрофному пути. Второй из этих источников ‐ это, вероятно, грунтовые воды, в которых финальными стадиями разложения растворённого органического углерода, поступившего из верховых болот, являются хемолитоавтотрофный ацетогенез, сопряжённый с ацетотрофным метаногенезом. Проведённые исследования иллюстрируют важность горизонтальной миграции между типичными бореальными биогеоценозами посредством грунтовых вод, раскрывая механизмы связей между ними. Такая же горизонтальная миграция метана может происходить и в других регионах мира, в которых болота покрывают значительные площади, что может приводить к высокой эмиссии метана из рек и ручьёв, питаемых грунтовыми водами.
We articulated three hypotheses to explain the origin and migration pathways of methane within seeps in the floodplains of West Siberian rivers: (H1) uplift of Cretaceous‐aged methane from deep petroleum reservoirs along faults and fractures, (H2) release of Oligocene‐aged methane capped or trapped by degrading permafrost, and (H3) horizontal migration of Holocene‐aged methane from surrounding peatlands. Seep‐gas composition, radiocarbon age, and stable isotope fingerprints favor the peatland hypothesis of seep‐methane origin (H3).
Bio-based semicrystalline polylactide (PLA) has a growing value as a substitute for fossil-based polyesters in technical applications and as a biocompatible material in medicine. The complexity of ...the behavior of PLA, determined by the presence of different stereoisomers, the role of electrostatic interactions, and its slow crystallization rate, makes computer simulations an important tool to discover new approaches to control the properties of PLA-based materials. The goal of this review is to summarize the efforts to simulate PLA materials with different levels of detail, including the quantum mechanical approach, all-atom modeling, and coarse-grained particle models. We focus on the validation of the models and the ways to cross-check the results with other simulation and experimental data. Special attention is devoted to the simulations of PLA in the presence of water, which provide insights into molecular mechanisms of hydrolytic degradation of PLA, especially at the initial stage, when the structural changes can not yet be detected by experimental methods. Ultimately, the selection of the appropriate simulation methods can facilitate material design, by combining the throughput and level of detail necessary for the job.
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