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Atmospheric deposition of nitrogen (N) and sulfur (S) alter tree demographic processes via changes in nutrient pools, soil acidification, and biotic interactions. Previous work established tree growth and survival response to atmospheric N and S deposition in the conterminous United States (CONUS) data by species; however, it was not possible to evaluate regional variation in response using that approach. In this study, we develop species- and region-specific relationships for growth and survival responses to N and S deposition for roughly 140 species within spatially demarcated regions of the U.S. We calculated responses to N and S deposition separately for 11 United States Forest Service (USFS) Divisions resulting in a total of 241 and 268 species × Division combinations for growth and survival, respectively. We then assigned these relationships into broad categories of vulnerability and used ordinal logistic regressions to explore the covariates associated with vulnerability in growth and survival to N and S deposition. As with earlier studies, we found growth and survival responses to air pollution differed by species; but new to this study, we found 45%−70% of species responses also varied spatially across regions. The regional variation in species responses was not simply related to atmospheric N and S deposition, but was also associated with regional effects from precipitation, soil pH, mycorrhizal association, and deciduousness. A large amount of the variance remained unexplained (total variation explained ranged from 6.8%−13.8%), suggesting that these or additional factors may operate at finer spatial scales. Taken together, our results demonstrate that regional variation in tree species' response has significant implications for setting critical load targets, as critical loads can now be tailored for specific species at management-relevant scales. [ABSTRACT FROM AUTHOR]

AbstractIn this article, two analytical solutions, one semi-analytical solution, and one numerical solution are proposed to calculate the global critical buckling load of buildings employing a continuum model parallel coupling two Timoshenko beams. The parallel coupling of two Timoshenko beams represents the four types of building behavior: global bending, global shear, local bending, and local shear, the latter of which has been widely ignored in the literature. The model is associated with one translational kinematic field and two rotational fields. The equilibrium equations, constitutive laws, and boundary conditions are derived using a variational approach by applying Hamilton’s principle to the relevant Lagrangian function. Specifically, to solve the classical problem of buildings with uniform properties along their height, the first analytical solution proposes exact closed-form equations for a vertical load applied at the top and a closed-form analytical solution based on the decomposition of two subsystems for a polynomial vertical load uniformly applied along the height of the beam. Meanwhile, the semi-analytical solution exactly solves the differential equation associated with a polynomial vertical load profile and is based on coefficient iteration, converging with only two or three iterations. To address the challenge of buildings with variable properties along their height, the combined application of the continuous method and the transfer matrix method allows us to propose an efficient numerical method leading to a 6 × 6 transfer matrix, constant regardless of the number of discretizations and derived analytically, which results in a computational advantage by drastically reducing computational costs. The numerical results are encouraging and show good agreement with the results of the finite element method, suggesting that the proposed method can be used for engineering purposes in both the preliminary and final phases of the structural analysis of tall buildings. [ABSTRACT FROM AUTHOR]

In order to quantitatively calculate the critical depth and critical load of mines affected by rock burst, and to achieve effective prevention and control of rock burst in coal mines, this paper proposes a mechanical model for predicting the occurrence of rock burst in coal mine roadways based on catastrophe theory. Additionally, a theoretical calculation formula for initiating rock burst is derived. The first step was to establish a mechanical analysis model, which directly correlated with the in-situ stress, physical and mechanical characteristics of the coal-rock mass, and engineering structural parameters. Following this, a mechanical instability criterion was derived for the key load-bearing circle within the surrounding rock of the roadway. In the final step, the critical depth and load for rock burst initiation were verified for 25 distinct coal mines in China that were prone to rock burst hazards. The research results demonstrate that the discrepancy between the theoretically calculated critical depth and the actual measured statistical values was less than 35%. In addition, the difference between the theoretically determined critical depth and the value calculated by Pan Yishan was less than 32%. Notably, the ratio of the theoretically calculated critical load to the uniaxial compressive strength of the coal-rock mass ranged from 0.38 to 1.93. This aligns with empirical data on rock burst occurrences, as set out in the engineering classification standards for rock masses. These research outcomes substantiated the practical utility of the proposed theory, thereby laying a robust theoretical groundwork for the quantitative control of rock burst. [ABSTRACT FROM AUTHOR]

The structural stability of clamped-free beam-columns resting on a two-parameter foundation under a nonconservative force is investigated. The higher-order beam theory is developed by considering the warping of the cross-section, rotary inertia, and axial force's direction. The characteristic equation of dynamic stability of rectangular/circular cantilevers on a Winkler-Pasternak foundation is obtained for a generalized follower force. Critical loads for divergence instability and flutter instability are evaluated. The influences of foundation stiffness, cross-sectional warping shape, the tangency coefficient on the critical loads are analyzed. The load-frequency interaction-curves are given for different directions of the follower force. The normal/shear stiffness of foundation on divergence and flutter loads has different effects. The normal stiffness increases the first divergence load but decreases the flutter load, reducing to the Herrmann–Smith paradox for Euler columns. The rise of shear stiffness enlarges the first divergence load and lowers the flutter loads. The effects are more sensitive for short beam-columns. Different warping shapes slightly affect the critical loads and the natural frequencies. The exponential warping shape gives the smallest critical divergence loads and the fundamental frequencies. The results of Haringx hypothesis are larger than those of Engesser hypothesis. For shorter columns, the classical results are overestimated and the higher-order beam theory is necessary. [ABSTRACT FROM AUTHOR]

In this paper, the nonlinear post-buckling analysis of imperfect two-dimensional quasicrystal cylindrical shells is performed. The nonlinear governing equations are established by considering initial geometric imperfection, higher-order shear deformation theory and phonon-phason fields coupling effect. The load-shortening curves and buckling modes are obtained by the Galerkin's method. Numerical results are compared with the existing results and excellent agreements are obtained. Effects of geometrical parameters, initial imperfection and phonon-phason fields coupling effect on the critical load and imperfection sensitivity of two-dimensional quasicrystal cylindrical shells are discussed in detail. [ABSTRACT FROM AUTHOR]

Enhanced sulfur and nitrogen deposition has been observed in many transect regions worldwide, from urban/agricultural areas to mountains. The Sichuan Basin (SCB), with 18 prefectural cities, is the most economically-developed region in western China, while the rural Qinghai-Tibetan Plateau (QTP) lies west of the SCB. Previous regional and national atmospheric modeling studies have suggested that large areas in the SCB-to-QTP transect region experience excessive deposition of sulfur and nitrogen. In this study, we applied a passive monitoring method at 11 sites (one in urban Chengdu and 10 from fivenature reserves) in this transect region from September 2021 to October 2022 to confirm the high sulfur and nitrogen deposition fluxes and to understand the gaps between the modeling and observation results for this transect region. These observations suggest that the five reserves are under eutrophication risk, and only two reserves are partially under acidification risk. Owing to the complex topography and landscapes, both sulfur and nitrogen deposition and critical loads exhibit large spatial variations within a reserve, such as Mount Emei. Regional atmospheric modeling may not accurately capture the spatial variations in deposition fluxes within a reserve; however, it can capture general spatial patterns over the entire transect. This study demonstrates that a combination of state-of-the-art atmospheric chemical models and low-cost monitoring methods is helpful for ecological risk assessments at a regional scale. [ABSTRACT FROM AUTHOR]

Pine forests growing on psammozems, found on sandy Kama terraces above the floodplain within the territory of Perm, encompass roughly 2 thousand hectares. The study was conducted on psammozems under the influence of advancing pollution caused by heavy metals, highlighting the significance of soil’s buffering capacity in preserving the ecosystem’s stability. It is of great interest to investigate the morphogenetic properties of psammozems and evaluate the risks linked to the accumulation of Cu and Cd in these soils through the analysis of changes in soil enzyme activity (catalase, urease, and invertase) and the occurrence of phytotoxicity. The psammozems found in the Kama region originated from periglacial sandy alluvium, which was deposited during glacial melting in the Mesozoic era. The variety of humus psammozems includes typical, podzolized, illuvial-ferruginous, and pseudofibrous subtypes. These soils are highly acidic, have a very low absorption capacity, low base saturation, and reduced activity of soil enzymes. The contents of Cu, Cd, Zn, and Pb in psammozems are notably lower compared to the regional soil clarks; however, in the underdeveloped humus horizons, the concentrations of these metals are slightly higher than in soil-forming sands. The experiment was conducted to determine the ecotoxicological load, where mixed soil samples from a 0–20 cm layer of humus psammozems were treated with solutions containing copper acetate and cadmium acetate. The application of solutions was done individually, with Cu and Cd ranging from 2.5 to 250 mg/kg of soil. Upon introducing Cu and Cd into the soil at the rate of 2.5–10 mg/kg, a decrease in invertase activity, deterioration of the physiological and biochemical parameters of the test crop (Lepidium sativum L.), along with the inhibition of Cd catalase activity, were observed.

Translation abstract Buckling lengths in the digital age – a didactic‐technical toolThe critical load of a member in the case of stability failure is the basis for the design according to the equivalent member method of EN 1993‐1‐1. It has become established that the critical load is determined via the buckling length. In the simplest case, the buckling length corresponds to one of the Euler cases, which rarely occurs in typical steel structures. In more complex systems, the buckling length often depends on adjacent structures and their stiffnesses. Determining the buckling length is so important that it is usually taught in steel construction lessons, although it is a classic structural analysis problem. The same happens at the Innsbruck Chair of Steel Construction. A tool that is didactically and technically state‐of‐the‐art and intended to improve education has been developed as part of educational modernization. This tool can playfully convey access to the determination of buckling lengths on complex structures while modern numerical methods take over the actual calculation work in the background. The developed software buckL.ing (freeware) is available for download on the Unit of Steel Construction and Mixed Building Technology's homepage (www.uibk.ac.at/stahlbau/software). [ABSTRACT FROM AUTHOR]

The study concerns the comparative analysis of selected solutions of thin-walled structures subjected to constrained torsion, representing the simulation of wing areas weakened by large cutouts. The chosen variants of stiffening were based on the concept of so-called "Misztal torsion box", used in the wing of the PZL-37 aircraft. A series of numerical analyses were conducted, aiming to compare selected variants of structures with reinforcements and a reference structure based on a traditional design scheme. The calculations were performed using software based on the finite element method. An analysis of the stress and displacement distribution of the examined structure was conducted, and the results demonstrating the advantages of the proposed structural solution were presented. [ABSTRACT FROM AUTHOR]

The set of critical points of a simple mechanical device undergoing static or quasi-static evolution is investigated. When the system is fully elastic open bifurcation problems in the static case remain only for special structures or loadings. But the state of the art is different in the case of elastic-plasticity when addressing general solids or structures and general loadings where many difficult problems remain and where a relatively complete bifurcation diagram has been obtained only for a very simple mechanical system. The present paper focuses on the same simple system but in the case of damage which turns out to be very different since a part of the static equilibrium equations turns to be non-local. [ABSTRACT FROM AUTHOR]

The method of numerical-analytical modeling using Maple 18 of the strong buckling of a uniform console with a symmetrical cross-section is presented. The range of plastic deformations in a materials with conditional yield strength (CYS) is studied. Standard profiles and sections made of low-carbon steel, titanium, polyethylene etc. were investigated. Were found and compared with the proper Eulerian values the critical loads of Fcr, N, the shape of buckled console y(z). The quasi-identity of the latter is established for the same slope pf = dy/dz near the free console end. The method can be applied in robotics, structural mechanics, medical prosthetics, etc. where the materials been used with relatively high Young's modulus and low the CYS. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Computational Mechanics / Jisuan Lixue Xuebao is the property of Chinese Journal of Computational Mechanics Editorial Office, Dalian University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

For many decades, acid deposition used to pose a significant regional air pollution challenge in China. After substantial emission control of anthropogenically derived sulfur and nitrogen containing gasses, both sulfur and nitrogen deposition, as well as the acid rain-affected area, have significantly decreased compared to their peak levels. Forests, particularly in the humid subtropics, are sensitive to acid deposition, as evidenced by soil acidification, sulfate and nitrate leaching in stream water, and elevated soil nitrous oxide emission. Reduction in the total deposition of sulfur and nitrogen, caused a significant decline in sulfate and nitrate leaching from subtropical forest and subsequently in sulfate and nitrate concentrations in stream water, although there was about a 5-year delay. This delay may be attributed to the desorption of accumulated sulfate and continued elevated mineralization of accumulated nitrogen pools. Emissions of nitrous oxide, a potent greenhouse gas, also declined in nitrogen-saturated subtropical forest soils, as soil water nitrate concentration decreased. Therefore, subtropical forests in China suffering from elevated acid deposition have begun to recover. Yet, the current levels of sulfur and nitrogen deposition continue to exceed the critical loads, i.e., the assigned threshold levels in accordance with emission control policies, in more than 10% of the country’s land area, respectively, indicating remaining risks of acidification and eutrophication. Thus, further emission reductions are urgently needed, also because they will help achieving goals related to air quality and nitrous oxide emissions. [ABSTRACT FROM AUTHOR]

Atmospheric deposition of nitrogen (N) and sulfur (S) alter tree demographic processes via changes in nutrient pools, soil acidification, and biotic interactions. Previous work established tree growth and survival response to atmospheric N and S deposition in the conterminous United States (CONUS) data by species; however, it was not possible to evaluate regional variation in response using that approach. In this study, we develop species- and region-specific relationships for growth and survival responses to N and S deposition for roughly 140 species within spatially demarcated regions of the U.S. We calculated responses to N and S deposition separately for 11 United States Forest Service (USFS) Divisions resulting in a total of 241 and 268 species × Division combinations for growth and survival, respectively. We then assigned these relationships into broad categories of vulnerability and used ordinal logistic regressions to explore the covariates associated with vulnerability in growth and survival to N and S deposition. As with earlier studies, we found growth and survival responses to air pollution differed by species; but new to this study, we found 45%−70% of species responses also varied spatially across regions. The regional variation in species responses was not simply related to atmospheric N and S deposition, but was also associated with regional effects from precipitation, soil pH, mycorrhizal association, and deciduousness. A large amount of the variance remained unexplained (total variation explained ranged from 6.8%−13.8%), suggesting that these or additional factors may operate at finer spatial scales. Taken together, our results demonstrate that regional variation in tree species' response has significant implications for setting critical load targets, as critical loads can now be tailored for specific species at management-relevant scales.

Abstract In order to quantitatively calculate the critical depth and critical load of mines affected by rock burst, and to achieve effective prevention and control of rock burst in coal mines, this paper proposes a mechanical model for predicting the occurrence of rock burst in coal mine roadways based on catastrophe theory. Additionally, a theoretical calculation formula for initiating rock burst is derived. The first step was to establish a mechanical analysis model, which directly correlated with the in-situ stress, physical and mechanical characteristics of the coal-rock mass, and engineering structural parameters. Following this, a mechanical instability criterion was derived for the key load-bearing circle within the surrounding rock of the roadway. In the final step, the critical depth and load for rock burst initiation were verified for 25 distinct coal mines in China that were prone to rock burst hazards. The research results demonstrate that the discrepancy between the theoretically calculated critical depth and the actual measured statistical values was less than 35%. In addition, the difference between the theoretically determined critical depth and the value calculated by Pan Yishan was less than 32%. Notably, the ratio of the theoretically calculated critical load to the uniaxial compressive strength of the coal-rock mass ranged from 0.38 to 1.93. This aligns with empirical data on rock burst occurrences, as set out in the engineering classification standards for rock masses. These research outcomes substantiated the practical utility of the proposed theory, thereby laying a robust theoretical groundwork for the quantitative control of rock burst.

Mechanical metamaterials are valued for their diverse properties and potential applications. Due to the instability and large deformability of soft mechanical metamaterials (SMMs), geometric reorganization will occur and lead to some unusual properties. It is possible to change the properties of materials by varying the parameters. Conventional SMMs contain a periodic distribution of holes with the same size and shape, which can be changed to a lesser extent. Periodic dispersion of regular through-hole patterns of various sizes or shapes into elastomers, resulting in metamaterials with more mechanical functionality and deformation scenarios. In this paper, we investigated the influence of parameters on the buckling mechanical behavior of SMMs and the buckling mechanical behavior of structures with multiple sizes and geometric shapes. The parameters studied include geometric parameters (pore shape, porosity and area ratio) and physical parameters (Poisson's ratio and compression mode). Simulation of the buckling behavior of SMMs uses the finite element method. The finite element software ABAQUS is used, taking into account the almost incompressible characteristics of materials, the triangular quadratic plane strain hybrid element is selected (CPE6H). Numerical calculation gives the following results: Area ratio, pore shape and compression mode have obvious effects on buckling behavior, but Poisson's ratio has little effect; the influence of parameters on the buckling critical strains varied for SMMs with various pore shapes; very different buckling behaviors will result from swapping out the pattern of holes with the same size or shape for holes with two different sizes or shapes; the expression of buckling behavior is also varied when the mix of hole shapes is modified. These findings demonstrate that the design parameters may be used to achieve the desired buckling behaviors. This is a new method that can be used to control the deformation of structures; modify the properties of the SMMs without changing stiffness; simplify the structures without significantly changing the material properties. The design path of mechanical metamaterials is increased. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of an open hole on the stability of a compressed laminated composite plate. The study was carried out in two ways: using experimental tests and numerical analysis. As a result of the experiment, the buckling form and path of the plate were recorded. The form of buckling was determined using the ARAMIS non-contact measurement system. The critical load value was determined from the working path using the approximation method. The experimental results were verified by numerical analysis based on the finite element method. FEM investigations were carried out in terms of a linear eigenproblem analysis. This allowed the bifurcation load and the corresponding buckling form of the numerical model of the plate to be determined. Investigating the effect of the hole in the compressed plate at a critical state showed high agreement between the proposed test methods. No clear effect of the hole size on the buckling of the plate was observed. In contrast, a clear effect of the hole on the critical load value was determined. The maximum decrease in the critical load value was 14%. The same decrease was observed for the stiffness of the post-critical characteristics. It was shown that the [45|−45|90|0]s composite plate had more than three times lower strength compared to [0|−45|45|90]s and [0|90|0|90]s. The novelty of this article is the development of a research methodology based on new interdisciplinary research methods for describing the influence of the central hole on the stability of compressed composite plates. The ABAQUS system was used for the numerical analysis. [ABSTRACT FROM AUTHOR]

A family of locking-free Kriging-based Timoshenko beam elements with a new implementation of the discrete shear gap technique was recently developed (referred to as K-beam-DSG1 elements). Performance of the K-beam-DSG1 elements has been shown to be very satisfactory in the linear static analysis of beams for a wide variety of thicknesses. This paper presents further development of the K-beam-DSG1 elements to free vibration and bifurcation buckling analyses of prismatic and non-prismatic beams. Consistent Kriging-based mass matrices are used for free vibration analysis and similarly, consistent Krigingbased geometric stiffness matrices are used for buckling analysis. The results show that for most of the cases, the K-beam-DGS1 elements yield remarkably accurate natural frequencies and critical compressive loads using a reasonable number of elements to discretize the beam. For an axially functionally graded fixed-fixed supported beam, however, the elements fail to predict the critical load accurately. [ABSTRACT FROM AUTHOR]

This manuscript concerns the investigation of the influence of the open hole on stability of the compression plate made of carbon-epoxy composite. Experimental tests carried out on the real plate resulted in a postcritical path from which the critical load value was determined using appropriate approximation method. In parallel, an independent study was carried out based on a numerical analysis using the finite element method (FEM). Investigations were conducted in terms of a linear eigenproblem analysis, from which the value of the bifurcation load was determined for the FEM model of the plate. Its values resulting from the numerical analyses were validated against the experimental results, thus confirming the adequacy of the designed FEM model of the plate. The paper shows that the incremental increase of the hole in the plate monotonically influences the decrease in the critical load of the plate. The largest decrease was observed for the specimen with the largest hole analysed and was 13.5% compared to a plate without a hole. The newness of the paper is the application of interdisciplinary investigation methods to describe the influence of the open hole compression (OHC) on the stability of composite plates. ABAQUS® was used as the tool with which the numerical analyses were realised. [ABSTRACT FROM AUTHOR]

Copyright of Electric Machines & Control / Dianji Yu Kongzhi Xuebao is the property of Electric Machines & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The paper analyzes the influence of cutouts on the buckling of shallow shells with double curvature. Based on the Timoshenko-Reissner hypothesis, a mathematical model is presented that considers transverse shifts, material orthotropy, geometric nonlinearity and structural weakening by cutouts. Cutouts are specified discretely by single columnar functions. The computational algorithm is based on the Ritz method and the Newton method. The implementation of the algorithm is carried out in the Maple 2022 software package. To study the buckling, the Lyapunov criterion is adopted. Calculations of the buckling of flat shells of double curvature with square cuts, graphs of the dependence of deflections on loads and deflection fields are given. Accounting for the structural cutouts leads to a decrease in the critical load. At the same time, for the considered problems, it is found that the decrease in the critical load does not exceed 25 % for the cutout volume not exceeding 10 % of the shell volume.

An approach to the construction of equilibrium state diagrams is presented in order to reduce the sensitivity to initial imperfections for the problem of stability for reinforced plates (transfer of the bifurcation point corresponding to the wave formation of ribs and cladding). New ratios of geometric parameters for two variants of strengthened plates have been obtained, where the first critical load of the general form of stability loss is the first by value, and the next critical load corresponds to the local form of wave formation of ribs or cladding. The finite element complex MSC PATRAN - NASTRAN was used to solve the stated above problems. Flat four-node finite elements were applied for modeling. The calculations were performed with account of geometric nonlinearity. The material was considered to be absolutely elastic. Curves of critical load sensitivity to the amplitudes of the initial imperfections were generated. The results demonstrate that transposition of bifurcation points of wave formation in the plate or ribs enabled to obtain curves with less significant decrease of critical load as compared to the initial ones. Consequently, the presented algorithm for changing the geometric parameters of reinforced plates obtained in accordance with new equilibrium state diagrams implements the possibility of rational design of the specified thin-walled systems.

The paper analyzes the influence of cutouts on the buckling of shallow shells with double curvature. Based on the Timoshenko-Reissner hypothesis, a mathematical model is presented that considers transverse shifts, material orthotropy, geometric nonlinearity and structural weakening by cutouts. Cutouts are specified discretely by single columnar functions. The computational algorithm is based on the Ritz method and the Newton method. The implementation of the algorithm is carried out in the Maple 2022 software package. To study the buckling, the Lyapunov criterion is adopted. Calculations of the buckling of flat shells of double curvature with square cuts, graphs of the dependence of deflections on loads and deflection fields are given. Accounting for the structural cutouts leads to a decrease in the critical load. At the same time, for the considered problems, it is found that the decrease in the critical load does not exceed 25 % for the cutout volume not exceeding 10 % of the shell volume. [ABSTRACT FROM AUTHOR]

In order to identify the occurrence characteristics of old gob in abandoned iron mine accurately, evaluate its stability scientifically, prevent and control surface collapse disaster of gob effectively, Dunqiu iron mine in Jinan City was taken as an engineering background, occurrence characteristics and stability of old gob were studied. By the geophysical exploration and exploration drilling, the plane and horizon distribution of the goaf was obtained, furthermore, a three-dimensional geological model of old gob was built, which could realize the three-dimensional display of gob occurrence characteristics. Three methods of surface deformation monitoring, critical load depth calculation and ratio of burial depth to mining thickness were used to evaluate the stability of old gob. The results show that the plane area of gob formed by the mining of No. 2 orebody group is 4 992. 5 m² . The gob can be divided into pure gob and backfill gob, which is 2 ~ 4 floors, 38 ~ 152 m depth and 1. 6 ~ 45. 7 m thickness, the maximum thickness of pure gob is 10. 8 m. The stability of old gob is poor and has a risk of collapse. It is concluded that the research methods and results have certain guiding significance for the detection and treatment of old gob in iron mine. [ABSTRACT FROM AUTHOR]

The formation of a mixed-type (fracture modes I and II) internal crack in a pipe wall that is made of an ideal elastoplastic material under the action of combined tensile (compression) and bending loads is described. The fracture of such materials is illustrated using a modified Leonov–Panasyuk–Dugdale model, which additionally uses the parameter of fracture process zone diameter. Another case under consideration is complex loading during which the crack path becomes curved, so its bend angle is determined using a force integral criterion based on the stress field asymptotics in the vicinity of the crack tip. Critical fracture parameters are obtained using a two-parameter (dual) strength criterion in the case of a complex stress state. The parameters included in the resulting analytical model are analyzed. The dimensionless geometric parameters of the structure are obtained numerically using the finite element method. Quasibrittle fracture diagrams are constructed. [ABSTRACT FROM AUTHOR]

A study is performed of a single-channel queuing system with two classes of priority requests, a relative priority discipline, a Poisson incoming flow with random intensity, and an infinite number of waiting places. The intensity is selected at the moment the countdown begins until the next request arrives, and the intensity does not change with a predetermined probability. The limit distribution of the number of requests of the lowest priority class at a critical system load is found. [ABSTRACT FROM AUTHOR]

A family of locking-free Kriging-based Timoshenko beam elements with a new implementation of the discrete shear gap technique was recently developed (referred to as K-beam-DSG1 elements). Performance of the K-beam-DSG1 elements has been shown to be very satisfactory in the linear static analysis of beams for a wide variety of thicknesses. This paper presents further development of the K-beam-DSG1 elements to free vibration and bifurcation buckling analyses of prismatic and non-prismatic beams. Consistent Kriging-based mass matrices are used for free vibration analysis and similarly, consistent Kriging-based geometric stiffness matrices are used for buckling analysis. The results show that for most of the cases, the K-beam-DGS1 elements yield remarkably accurate natural frequencies and critical compressive loads using a reasonable number of elements to discretize the beam. For an axially functionally graded fixed-fixed supported beam, however, the elements fail to predict the critical load accurately.

This paper presents Transistor Clamped H-Bridge (TCHB) inverter-based Electric Spring (ES), a demand side management device that enhances the voltage stability of the critical load connected to the grid through Renewable Energy Sources (RES). This configuration of ES provides the solution to voltage sag/swell for reduced size, %THD and input power required. To validate the effectiveness of the system performance of TCHB-based ES, detailed simulation studies are performed using MATLAB/Simulink environment.

We explored patterns of benthic diatom composition across sixty-two high-elevation alpine lakes spanning a wide range of nitrogen (N) concentrations due to atmospheric deposition and background variation in lake and watershed characteristics. Our goals were to (1) assess the effect of lake water N concentration on benthic diatom composition during late summer or fall conditions and (2) identify policy-relevant response thresholds. The analyses were carried out on a large set of diatom and water chemistry data, integrated with new data. Multivariate and correlation analyses revealed associations between pH, N concentration, and benthic diatom composition, but the effects of pH and N were confounded. However, partial correlation analysis allowed us to identify “N-responsive diatoms”; that is, diatom taxa with nonspurious associations with N. Focusing on these taxa, we detected a decline in the abundance of taxa preferring low N concentrations and an increase in the abundance of taxa preferring high N concentrations starting at NO3 concentrations of approximately 5 µmol L−1. We interpreted this shift as an effect of watershed N saturation due to atmospheric deposition. Based on the results, we suggest a late-summer or fall concentration threshold of 5 µmol NO3 L−1 to prevent change in benthic diatoms in high-elevation alpine lakes.

After extreme natural disasters like storms, earthquakes, and floods, the connection of the distribution network with the main grid may lose. In this condition, the power of the main grid is unavailable, and the survived microgrids (MGs) are the only power sources. Since the outputs of MGs are limited, re-energizing of all out-of-service loads is impossible, and restoring critical loads (CLs) becomes the priority of the network operators. We propose a new multistage restoration strategy to improve the network's resiliency by critical loads restoration after fault occurrence and blackout. The considered objective functions include weighted restored energy and switching operations. The presented strategy offers the best restoration plan for each hour of outage duration with the help of the VIKOR method. The presented method is tested on an IEEE 123-bus distribution network. The simulation results confirm that the proposed multistage restoration strategy reaches better restoration plans compared to conventional methods. [ABSTRACT FROM AUTHOR]

The introduction of downhole safety valve performance envelope curves can effectively prevent the failure of the downhole safety valves during field operations. The method of drawing the performance envelope curve of high-temperature and pressure downhole safety value was proposed based on the mechanical properties of the downhole safety valve. The numerical simulation method was used for the mechanical performance of the downhole safety valve, and the stress change law of the overall structure of the downhole safety valve under the ultimate load was obtained. The ultimate bearing state and the failure threshold stress value of the key components of the downhole safety valve were further determined. The performance envelope curve of the downhole safety valve was finally completed. The results of the study show that the downhole safety value envelope curve can be obtained by studying the mechanical properties of the downhole safety valve, and each section of the envelope curve corresponded to the cause of failure of the downhole safety valve, giving the theoretical calculation idea of the downhole safety valve performance envelope curve. This study provides theoretical and methodological support for the study of the performance envelope curves of the downhole safety valves, packers, and other complex working conditions of downhole tools and their application in the field. [ABSTRACT FROM AUTHOR]

After extreme natural events like earthquakes, storms, and floods, the electrical distribution network may be isolated from the upstream grid. In such a situation, the electrical power of the upstream grid is lost and the available microgrids (MGs) are the only power sources. Since the power outputs of MGs are restricted, restoring all de-energized loads is impossible and restoring critical loads (CLs) becomes the most important concern of the distribution network operators. Therefore, in this paper, a new hour-by-hour restoration strategy for CLs restoration after a blackout is proposed. The desired objective functions include restored energy and switching operations. The proposed restoration strategy presents a restoration plan for each hour of the outage period. The efficiency of the proposed strategy is carried out on an IEEE 123-bus distribution network and the simulation results confirm the superiority of the proposed hour-by-hour restoration strategy over the other conventional restoration methods.

To identify the relationship between load and the number of repetitions performed to momentary failure in the pin press exercise, the present study compared different statistical model types and structures using a Bayesian approach. Thirty resistance-trained men and women were tested on two separate occasions. During the first visit, participants underwent assessment of their one-repetition maximum (1-RM) in the pin press exercise. On the second visit, they performed sets to momentary failure at 90%, 80% and 70% of their 1-RM in a fixed order during a single session. The relationship between relative load and repetitions performed to failure was fitted using linear regression, exponential regression and the critical load model. Each model was fitted according to the Bayesian framework in two ways: using an across-subjects pooled data structure and using a multilevel structure. Models were compared based on the variance explained (R2) and leave-one-out cross-validation information criterion (LOOIC). Multilevel models, which incorporate higher-level commonalities into individual relationships, demonstrated a substantially better fit (R2: 0.97–0.98) and better predictive accuracy compared to generalised pooled-data models (R2: 0.89–0.93). The multilevel 2-parameter exponential regression emerged as the best representation of data in terms of model fit, predictive accuracy and model simplicity. The relationship between load and repetitions performed to failure follows an individually expressed exponential trend in the pin press exercise. To accurately predict the load that is associated with a certain repetition maximum, the relationship should therefore be modelled on a subject-specific level. [ABSTRACT FROM AUTHOR]

In this work, titanium oxide nanotubes (TNTs) were formed by anodic oxidation on the surface of a Ti–6Al–4V alloy. An electrolyte based on ethylene glycol (EG) and ammonium fluoride (NH4F) was used. Different anodizing periods (10, 20, 30, 40, 50, and 60 min) with a constant potential of 60 V were established. The morphology of the TNT array was observed by scanning electron microscopy (SEM). The adhesion strength of the TNTs to the Ti–6Al–4V surface was evaluated using nanoscratch tests. The critical load of the different TNT layers was determined from the analysis of the groove of the nanoindenter path. It ranged from 0 mN for the samples exposed to 10 min of anodization to 47.0 ± 3.0 mN for samples exposed to 50 min. These results indicate the TNT layers formed at 50 min presented the best substrate adhesion among the specimen tested. [ABSTRACT FROM AUTHOR]

In the present study, implant material Ti-6Al-4V has been coated with eudragit (EU) and chitosan (CH) polymers to enhance surface properties. The deposition of polymer coating has covered the surface cracks to a significant level and the fact has been confirmed by FE-SEM coupled with EDAX wherein the atomic percentage of Ti (99.90%) in non-coated surface has been decreased markedly to 0.42% after coating. Scratch resistance and adhesion power of bilayer coating has been increased as indicated by the higher critical loads Lc1 (16.71 N), Lc2 (17.56 N), Lc3 (17.96 N) when a progressive load of 1 N to 20 N is applied over the coated surface. Further, Electrochemical impedance spectroscopy (EIS) and potentiodynamic-polarization studies have shown that the value of polarization resistance is inversely proportional to the corrosion rate. Thus decrease in the corrosion rate from 107.5×10-2 (mm year-1) for the non-coated alloy to 2.88×10-2 (mm year-1) for CH/EU coating demonstrated that coating enhanced the corrosion resistance of the alloy in the physiological condition. The in vitro antibacterial test conducted against S. aureus, B. subtilis, P. vulgaris and P. auregenosa has shown a significant inhibition zone of 9 mm, 6 mm, 7 mm and 10 mm, respectively, thus indicating the possible application of the polymeric coating material on the dental implants. [ABSTRACT FROM AUTHOR]

Critical loads (CLs) of atmospheric deposition have been used for multiple decades to assess the impacts of air pollutants on terrestrial and aquatic ecosystems. However, these CLs have been developed by different researchers, at different times, using different methods, and are named in different ways with varying levels of information and levels of specificity. In this study, we identified the elements that describe CLs and used them to develop and test a standardized CL naming convention and a complementary CL classification system applicable to all CLs. The CL naming convention consists of: the form of deposition; the biological receptor, response, and threshold; and chemical criterion and threshold, thereby clearly communicating what the CL is and what it protects. The CL classification system contains all the elements that define and describe a CL, but the CL classes are not fixed and are therefore, defined by the user. The application of the CL naming convention and classification system to an existing US CL database and national forest was successful, demonstrating not only the utility of the naming convention and classification system, but how both can also be used to guide future CL science. [ABSTRACT FROM AUTHOR]

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Copyright of Chinese Journal of Applied Mechanics is the property of Chinese Journal of Applied Mechanics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Chronic elevated nitrogen (N) deposition can have adverse effects on terrestrial ecosystems. For large areas of northern Canada distant from emissions sources, long-range atmospheric transport of N may impact plant species diversity, even at low deposition levels. The objective of this study was to establish plant species community thresholds for N deposition under multiple environmental gradients using gradient forest analysis. Plant species abundance data for 297 Jack pine (Pinus banksiana Lamb.)-dominant forest plots across Alberta and Saskatchewan, Canada, were evaluated against 43 bioclimatic and deposition variables. Bioclimatic variables were overwhelmingly the most important drivers of community thresholds. Nonetheless, dry N oxide (DNO) and dry N dioxide deposition inferred a total deposited N (TDN) community threshold of 1.4–2.1 kg N ha−1 yr−1. This range was predominantly associated with changes in several lichen species, including Cladina mitis, Vulpicida pinastri, Evernia mesomorpha and Lecanora circumborealis, some of which are known bioindicators of N deposition. A secondary DNO threshold appeared to be driving changes in several vascular species and was equivalent to 2.45–3.15 kg N ha−1 yr−1 on the TDN gradient. These results suggest that in low deposition ‘background’ regions a biodiversity-based empirical critical load of 1.4–3.15 kg N ha−1 yr−1 will protect lichen communities and other N-sensitive species in Jack pine forests across Northwestern Canada. Nitrogen deposition above the critical load may lead to adverse effects on plant species biodiversity within these forests.

It is our main objective to find the critical load for three beams with cross sectional heterogeneity. Each beam has three supports, of which the intermediate one is a spring support. Determination of the critical load for these beams leads to three point boundary value problems (BVPs) associated with homogeneous boundary conditions—the mentioned BVPs constitute three eigenvalue problems. They are solved by using a novel solution strategy based on the Green functions that belong to these BVPs: the eigenvalue problems established for the critical load are transformed into eigenvalue problems governed by homogeneous Fredholm integral equations with kernels that can be given in closed forms provided that the Green function of each BVP is known. Then the eigenvalue problems governed by the Fredholm integral equations can be manipulated into algebraic eigenvalue problems solved numerically by using effective algorithms. It is an advantage of the way we attack these problems that the formalism established and the results obtained remain valid for homogeneous beams as well. The numerical results for the critical forces can be applied to solve some stability problems in the engineering practice.

Introduction. Large-span structures are designed as entertainment and mass-use buildings, sports facilities, etc. A steel arched structure can be used as a covering for large-span structures. The issue of the rational design of large-span steelarches, as well as the proper choice of the structural design and the analysis of its bearing capacity is relevant.Materials and methods. The covering of a tennis sports facility with the span of 108 m, that represents a double-hinged steel arch without tightening, arches with prestressed tightening and several lattice options are considered. The cross-section of structural elements was selected; the effect of prestressing on forces and displacements in the arch, as well as the amount of metal per structure were analyzed. The general stability of these arched structures was analyzed. Calculations were performed in the geometrically nonlinear formulation using the LIRA-SAPR software package.Results. It is determined that the weight of the arch, including the tightening and the lattice is smaller than the weight of the arch without the tightening. The amount of metal, used to make columns, can be reduced to simplify structural units due to the absence of gusset transfer from the arch with tightening to columns. The required prestressing value is set for the tightening to ensure the required rigidity of the arch. Several methods were used to determine the critical load at which the arch loses its stability in its plane: the analytical method, geometrically nonlinear calculation results, and the Stability mode implemented in LIRA-SAPR software package were employed. The critical load turned out to be higher for the arch with tightening.Conclusions. Following the above computations, a decision was made to use a double-hinged arch with prestressed tightening and a lattice as the covering of the sports facility. The values of the critical load that triggers the arch stability loss, obtained using the geometrical nonlinear finite-element analysis and the Stability mode, were quite close. Application of the analytical method resulted in an overestimated value of the critical load, which prevents it from being recommended for use.

The authors deal with the structures of buildings in the form of shallow shells with some damage. The derivation of equations is given taking into account the geometric nonlinearity of the work of a thin-walled structure. A technique for solving systems of equations using the Bubnov - Galyorkin method is given. The work of the structure with various ways of fixing the edges is simulated. Damage is specified by changing the modulus of elasticity in an arbitrary section of the structure. The influence of the shape and location of the defect on the value of the critical load is investigated. The results of the studies carried out are given in a dimensionless form and illustrated by graphs, which makes it convenient to use them in engineering calculations. Recommendations are given for correcting the shape and thickness of coating structures in the form of shallow shells in order to maintain their bearing capacity in the event of defects. The proposed method can be used to determine and investigate the stress-strain state of structures in the form of shallow shells, taking into account the geometric nonlinearity of work in the presence of defects in them. The constructed graphs of the dependence of the critical load on various parameters make it possible to evaluate the operation of structures, taking into account changes in various factors at various stages of the structure's operation. The use of varying characteristics of the reduction in the modulus of elasticity, which appears because of the occurrence of a defect, shows results that are close to real conditions.