Constant Stress Conditions Research Articles

Viscoelastic study of cement and emulsified asphalt mortar under temperature variations based on a novel variable-order fractional Maxwell model

Cement and emulsified asphalt (CA) mortar is a critical viscoelastic component of ballastless track systems, exhibiting pronounced temperature sensitivity. However, accurately predicting the mechanical responses of CA mortar due to temperature fluctuations remains a challenge. This work proposes a novel variable-order fractional Maxwell (VOFM) model to investigate the viscoelastic properties of CA mortar under temperature variations. The VOFM model is numerically solved using a time-varying coefficient ladder (TVL) model. The VOFM model is validated by comparing with both numerical integration methods and experimental data. The basic properties of the VOFM model, the viscoelastic responses of CA mortar under varying temperatures and alternating stress are systematically investigated. The results show that the mechanical properties of VOFM model agree with the FM model when time-dependent parameters of the VOFM model correspond to that of the FM model. Moreover, high temperatures have a promoting effect on the deformation of CA mortar under both alternating and constant stress conditions. The peak amplitude of CA mortar strain under practical varying temperature and stress loading correlates with the trend of temperature changes.

Surface water dynamics of Africa: Analysing continental trends and identifying drivers for major lakes and reservoirs

ABSTRACT Africa has the most dynamic demographic development worldwide. Current projections predict a population of > 3 billion people by the end of the century. Sub-Saharan Africa alone will likely see a 40% increase in population between 2020 and 2050. Although it is well known that large parts of Africa are in a constant state of water stress, its surface water resources remain understudied. This study analyses long-term trends of surface water in Africa. It identifies causal impacts on major lakes and reservoirs for the timeframe 2003–2020, as well as dynamic and causal similarities between the various lakes. For this, a set of daily time series based on Earth observation is employed. Global WaterPack data is used for a daily uninterrupted time series of the continent’s surface water area. Additionally, an array of relevant independent variables, namely precipitation, total evapotranspiration, groundwater, soil moisture, and gross primary productivity (GPP) in different land use areas is analysed. For causal identification, the Peter and Clark Momentary Conditional Independence algorithm is used. Findings show that > 42% of African countries and > 34% of African ecoregions experience shrinking surface water area. Over 80% of investigated surface water bodies are driven by the surface water in their upstream subbasins and GPP in agriculturally used areas. About 85% of investigated lakes are significantly driven by agricultural usage, often in the form of water abstraction, as referenced regional studies confirm. Our analysis demonstrates the feasibility of conducting causal analyses of surface water dynamics using Earth observation data. Dynamically similar lakes are often impacted by the same drivers, forming regional lake clusters. Considering the causes identified may greatly help adapt strategies for sustainable development. A causality analysis to identify drivers of surface water dynamics has, to our knowledge, never been performed before on this scale and at such high temporal resolution.

Behaviour of sand under the constant shear drained stress path: the role of fines

This paper presents a specifically designed experimental study aimed at exploring the role of fines in altering the behaviour of sand under the constant shear drained (CSD) stress path. The novelty of this study includes that the interplay of several key factors (fines shape, fines content, void ratio) was investigated systematically and the true constant shear stress condition was fulfilled by means of an advanced servo system which allowed the entire loading response to be captured. One of the marked findings is that the presence of fines not only alters the onset of instability of loose sand but also affects the deformation development thereafter. Drained instability can be triggered more easily in loose sand mixed with silica fines compared with the sand on its own. At the same quantity of fines, instability can be triggered more easily for sand mixed with rounded fines. However, the effect of fines appears to be marginal for sand at dense state. For all tested specimens, values of the axial strain rate at instability fall in a narrow range (0.008%/min–0.016%/min), meaning that the axial strain rate can be potentially a useful guide for quantitatively determining the inception of instability under the CSD conditions. The stress ratio q/p′ at onset of instability under the CSD conditions is also state dependent as under the undrained conditions.

The influence of internal personal conflicts on the formation of personality in adolescent age

The article examines and analyzes modern and foreign research on the influence of intrapersonal conflicts on personality formation in adolescence. The factors that contribute to the emergence of intrapersonal conflicts, including physiological changes, social pressure and the search for self-identity, are analyzed. The positive and negative effects of intrapersonal conflicts on the formation of a teenager's personality are determined. Insufficient understanding of the nature and consequences of intrapersonal conflicts in adolescence makes it difficult to develop effective strategies to support young people. Internal conflicts in adolescence are usually associated with contradictions between the desire for independence and the need for support, the search for one's own identity and pressure from peers and society, as well as with changes in physiological development. These conflicts can lead to emotional stress, increased anxiety, depression and other mental disorders. Effective overcoming of such conflicts contributes to the formation of a healthy, mature and stable personality. Russia's full-scale invasion of Ukraine and hostilities have a profound effect on the psychological state of teenagers. War creates a constant state of danger, uncertainty, and stress that exacerbates intrapersonal conflicts. Adolescents who live in a war zone or have lost loved ones face additional emotional and mental challenges. Intrapersonal conflicts in adolescence are an inevitable part of the growing up process and have a significant impact on personality formation. This emphasizes the need to conduct a comprehensive study aimed at studying specific aspects of the influence of these conflicts on the formation of the personality of teenagers in the conditions of modern Ukraine. The results of such a study can become the basis for the development of recommendations for psychologists, teachers and parents on supporting adolescents in overcoming internal contradictions and promoting their positive development.

Cyclic cumulative strain of coarse-grained soil under large cyclic stress amplitude

The deformation behavior of coarse-grained soil under large cyclic stresses, such as those induced by strong earthquakes, has received limited attention. This study aims to investigate the cyclic accumulation behaviors and hysteresis loops of coarse-grained soil during drained cyclic triaxial tests, spanning a range from small to large cyclic stresses. The cyclic triaxial tests were primarily conducted under anisotropic consolidation conditions, with an axial-to-radial stress ratio of 2.0, confining pressures ranging from 100 to 500 kPa, and cyclic stresses varying from 0.01 to 1.85 times the confining pressure. Additionally, cyclic triaxial tests under isotropic consolidation conditions and constant mean stress conditions were performed for comparison and validation. The test results reveal that the properties of the hysteresis loops exhibit significant nonlinear behavior as cyclic stress increases, particularly concerning their shape, symmetry, degree of closure, and initial tangent modulus of elasticity. The cumulative axial strain displays three stages: strain increases slightly and gently at small cyclic stress, increases rapidly and substantially at medium cyclic stress, and decreases at large cyclic stress. The delineation of these phases is largely governed by the behaviors observed during the first cycle. Moreover, the cumulative volumetric strain increases monotonically with the increase of cyclic stress, with a more rapid increase at large cyclic stress. This study provides valuable insights into the cyclic deformation and constitutive modeling of coarse-grained soil under significant cyclic stress.

A unique time-dependent deformation behavior of coral reef limestone

Catastrophic failure in engineering structures of island reefs would occur when the tertiary creep initiates in coral reef limestone with a transition from short-to long-term load. Due to the complexity of biological structures, the underlying micro-behaviors involving time-dependent deformation are poorly understood. For this, an abnormal phenomenon was observed where the axial and lateral creep deformations were mutually independent by a series of triaxial tests under constant stress and strain rate conditions. The significantly large lateral creep deformation implies that the creep process cannot be described in continuum mechanics regime. Herein, it is hypothesized that sliding mechanism of crystal cleavages dominates the lateral creep deformation in coral reef limestone. Then, approaches of polarizing microscope (PM) and scanning electronic microscope (SEM) are utilized to validate the hypothesis. It shows that the sliding behavior of crystal cleavages combats with conventional creep micro-mechanisms at certain condition. The former is sensitive to time and strain rate, and is merely activated in the creep regime.

Granular behaviour under bi-directional shear with constant vertical stress and constant volume

This paper aims to investigate the role of bi-directional shear in the mechanical behaviour of granular materials and macro-micro relations by conducting experiments and discrete element method (DEM) modelling. The bi-directional shear consists of a static shear consolidation and subsequent shear under constant vertical stress and constant volume conditions. A side wall node loading method is used to exert bi-directional shear of various angles. The results show that bi-directional shear can significantly influence the mechanical behaviour of granular materials. However, the relationship between bi-directional shear and mechanical responses relies on loading conditions, i.e. constant vertical stress or constant volume conditions. The stress states induced by static shear consolidation are affected by loading angles, which are enlarged by subsequent shear, consistent with the relationship between bi-directional shear and principal stresses. It provides evidence for the dissipation of stresses accompanying static liquefaction of granular materials. The presence of bi-directional principal stress rotation (PSR) is demonstrated, which evidences why the bi-directional shear of loading angles with components in two directions results in faster dissipations of stresses with static liquefaction. Contant volume shearing leads to cross-anisotropic stress and fabric at micro-contacts, but constant vertical stress shearing leads to complete anisotropic stress and fabric at micro-contacts. It explains the differentiating relationship between stress-strain responses and fabric anisotropy under these two conditions. Micromechanical signatures such as the slip state of micro-contacts and coordination number are also examined, providing further insights into understanding granular behaviour under bi-directional shear.

Effects of microbially induced calcite precipitation on static liquefaction behavior of a gold tailings sand

Loose tailings are susceptible to static liquefaction during which they lose a substantial amount of their strength. This study examines a sustainable technique known as Microbially-Induced Calcite Precipitation (MICP) to improve the static liquefaction resistance of gold mine silty sand tailings. These materials were enriched with Sporosarcina pasteurii, consolidated in a direct simple shearing apparatus, and subjected to several injections of a cementation solution. Calcified tailings were then sheared under constant-volume and constant vertical stress conditions to evaluate their undrained and drained shearing behaviors. Results showed that bio-mineralization can prevent the occurrence of static liquefaction in tailings by reducing their contraction tendency. This is demonstrated by the strong strain-hardening behaviors of the treated tailings specimens compared to the strain-softening and undrained strength loss in specimens of the untreated tailings. Substantial increases in the tailings undrained and drained shear strengths (by up to 30 - 50 kPa), improvements (by up to 5 MPa) in their tangent moduli, and more than 5° rise in their friction angles are observed in the direct simple shear tests following MICP-treatment. The critical state line of tailings is also found to be steeper and shifted to denser void ratios following MICP treatment. These changes reduce liquefaction susceptibility of tailings and enhance their resistance against static liquefaction. Post-treatment acid dissolution further indicates that CaCO3 contents of about 4% to 11% precipitated in the treated specimens. This amount decreases with increasing specimens void ratio. Changes in the microstructural fabric of the cemented tailings particles are also characterized using scanning electron microscopic (SEM) images and X-ray diffraction (XRD) analyses.

Cyclic shear behavior of dredged soil under constant normal stress conditions

Cyclic shear behavior of dredged soil under constant normal stress conditions

RelA-mediated signaling connects adaptation to chronic cardiomyocyte stress with myocardial and systemic inflammation in the ADCY8 model of accelerated aging.

Mice with cardiac-specific overexpression of adenylyl cyclase (AC) type 8 (TGAC8) are under a constant state of severe myocardial stress. They have a remarkable ability to adapt to this stress, but they eventually develop accelerated cardiac aging and experience reduced longevity. We have previously demonstrated through bioinformatics that constitutive adenylyl cyclase activation in TGAC8 mice is associated with the activation of inflammation-related signaling pathways. However, the immune response associated with chronic myocardial stress in the TGAC8 mouse remains unexplored. Here we demonstrate that chronic activation of adenylyl cyclase in cardiomyocytes of TGAC8 mice results inactivation of cell-autonomous RelA-mediated NF-κB signaling. This is associated with non-cell-autonomous activation of proinflammatory and age-associated signaling in myocardial endothelial cells and myocardial smooth muscle cells, expansion of myocardial immune cells, increase in serum levels of inflammatory cytokines, and changes in the size or composition of lymphoid organs. All these changes precede the appearance of cardiac fibrosis. We provide evidence indicating that RelA activation in cardiomyocytes with chronic activation of adenylyl cyclase is mediated by calcium-protein Kinase A (PKA) signaling. Using a model of chronic cardiomyocyte stress and accelerated aging, we highlight a novel, calcium/PKA/RelA-dependent connection between cardiomyocyte stress, myocardial inflammation, and systemic inflammation. These findings suggest that RelA-mediated signaling in cardiomyocytes might be an adaptive response to stress that, when chronically activated, ultimately contributes to bothcardiac and systemic aging.

An apparatus to measure thermal conductivity of ceramic pebble beds under uniaxial compressive stress

Pebble beds have various applications in many industrial and research sectors. Lithium ceramic pebble beds have specific application in fusion reactors as one of the most promising candidates for tritium breeding material. During the operation of the fusion reactor, these pebble beds will have to sustain various thermal and mechanical stresses. Therefore, it is necessary to do thermal characterisation of these pebble beds under different stress conditions and generate sufficient data on their thermal properties, which is essential for designing breeder units of fusion reactors. In this work, an apparatus has been designed to evaluate the thermal conductivity of ceramic pebble beds under compressive stress. It can be mounted to any standard universal testing machine with the necessary adjustments. The apparatus is based on the transient hot-wire method, widely used to evaluate the thermal conductivity of porous materials. A platinum wire with a diameter of 0.5 mm was used as a hot-wire. Instead of utilising a thermocouple, the 4-wire approach was used to obtain the temperature. The transient temperature response of the hot-wire was obtained by applying a 7A constant current to it and monitoring the voltage drop along its 40 mm length. The thermal conductivity of the water gel was measured to assess the accuracy of the apparatus; the results showed a less than 1.5 % variation from the reference value. In this study, the thermal conductivity of Li2TiO3 pebbles was measured in an air and helium environment in different stress conditions. In an air environment, measurements were done at atmospheric pressure, whereas in a helium gas environment, they were performed at gauge pressures of 0.05 bar, 0.5 bar, and 1 bar. The measurements were conducted in two scenarios: (i) constant stress condition at 0, 3, and 6 MPa, and (ii) Cyclic loading-unloading of 0.037–3 MPa and 0.037–6 MPa. It was found that the pebble bed's thermal conductivity rose in tandem with increased compressive stress in both the helium and air environments. Pebble bed’s thermal conductivity was found to be higher in a helium gas environment than in air. The thermal conductivity of the pebble bed increased slightly with rising helium gas gauge pressure from 0.05 bar to 1 bar. This work provides a design to incorporate 4-wire temperature measurement in the hot-wire method for thermal conductivity measurement of compressed pebble beds. It also contributes to the thermal conductivity data of Li2TiO3 pebbles in cyclic stress conditions in helium and air environments.

On the b-value dependency of injection-induced seismicity on geomechanical parameters

Variability in the b-value, which describes the frequency distribution of earthquake magnitudes, is usually attributed to variations in differential stress in the setting of natural and laboratory earthquakes. However, differential stress is unlikely to explain b-value variations on the reservoir scale of injection-induced seismicity cases where significant differential stress variability can hardly be expected. We investigate the responsible geomechanical parameters for the b-value reduction observed in injection-induced seismicity at the Basel EGS field in Switzerland, for which a measured in-situ stress model and fault orientations of numerous microseismic events are available. We estimate the shear and normal stresses along faults, differential stress, pore pressure increase at failure, and the Coulomb failure stress, for each event. Event magnitude and shear stress display the most systematic and clear correlation between each other, while other parameters do not show a clear correlation with event magnitude. We further examine the relationship between the b-value and these geomechanical parameters. We discover that the b-value systematically decreases with increasing shear stress. Again, other geomechanical parameters do not show a clear correlation with the b-value. We conclude that b-value variability is explained by variations in shear stress in the injection-induced seismicity setting, where near constant differential stress conditions are expected. Furthermore, we observe that b-value reduction with time also correlates with an increasing number of events along faults having high shear stress, which strongly supports our conclusions. Thus, we discovered a profound physical mechanism behind b-value variation in injection-induced seismicity beyond general understanding of b-value variation.

Психологічні підходи і техніки розвитку резильєнтності педагогів: зарубіжний досвід

This article explores the building of teacher resilience, a critical factor in sustaining educators' well-being and effectiveness in the face of various professional challenges. Resilience is understood as a person's ability to correctly allocate and use their own resources in difficult life circumstances, maintain psychological well-being and increase the level of functioning after experiencing stress. Based on the generalization of the results of the analysis of psychological sources, a number of approaches and psychological techniques for developing the resilience of teachers substantiated in foreign psychology have been singled out: cognitive-behavioral approach; an approach based on the principles of positive psychology; the concept of identifying and using the strengths and individual merits of teachers; creation and use of external resilience resources; application of psychological techniques of self-awareness; ensuring a healthy lifestyle and psychological well-being of teachers; building of teachers' resilience in the process of professional development and training. Foreign programs for the development of teacher resilience are aimed at strengthening psychological health with the help of such psychotechniques as reflection, meditation, stress management, mastering constructive strategies of coping behavior, maintaining a balance between work and personal life. Studying and using these strategies and techniques can help Ukrainian teachers maintain their psychological health in conditions of constant stress. Acquaintance with approaches to the development of teachers' resilience substantiated in foreign psychology can contribute to the development by Ukrainian scientists of psychological tools aimed at overcoming stressful situations, increasing professional and personal well-being, and building a more sustainable educational system.

PECULIARITIES OF THE COURSE OF PREGNANCY IN WOMEN OF DIFFERENT POPULATION GROUPS BURDENED WITH ANEMIA AND HELICOBACTERIOSIS

Peculiarities of the course of pregnancy in women of different ethnic groups are burdened with anemia and helicobacteriosis in modern living conditions after the pandemic of coronavirus infection, the state of constant stress of the war in Ukraine. The purpose of the study was to determine the characteristics of the course of pregnancy in women of different population groups burdened with anemia and helicobacteriosis
 Materials and Methods. 30 pregnant women of reproductive age, burdened with anemia, residents of the city of Odesa (group I) and countries of Southeast Asia (group II) were under our observation. All women were registered at the women’s clinic. The monitoring algorithm included clinical and laboratory studies of Helicobacter pylori infection (total antibodies (IgG, IgM, IgA) to Helicobacter pylori antigens).
 Results. The presence of infectious processes in the body of women is one of the etiological factors of gestational complications, including the progression of the severity of anemia in pregnant women. The clinical severity of anemia in pregnant women was consistent with a high coefficient of positivity of total antibodies (IgG, IgM, IgA) to Helicobacter pylori antigens and a low level of hemoglobin, the level of ferritin, folic acid, cyanocobalamin, the vital trace element iron. Indicators of the clinical course of pregnancy in group I and group II had a significant difference (p<0.05), respectively: early toxicosis (mild, moderate, severe) – 20.0 %, 0 %, 0 % and 26.7 %, 20.0 %, 0 %; syndrome of the threat of early miscarriage - 13.3 % and 33.3 %; late miscarriage threat syndrome – 6.7 % and 20.0 %; secondary placental dysfunction – 0 % and 20.0 %; fetal growth retardation syndrome (FGRS) – 0 % and 6.7 %; intranatal fetal distress – 0 % and 6.7 %. The postpartum period in 13.3 % of women in the 2nd group had a lochiometer.
 Conclusions. Peculiarities of the course of pregnancy in women of different population groups burdened with anemia and helicobacteriosis consisted in the progression of the severity of the clinical and laboratory course of anemia and gestational complications during the trimesters. The clinical severity of anemia in pregnant women was consistent with a high ratio of total antibodies (IgG, IgM, IgA) to Helicobacter pylori antigens and a low level of hemoglobin, the level of ferritin, folic acid, cyanocobalamin, the vital trace element iron. It is recommended to determine the ratio of total antibodies (IgG, IgM, IgA) to Helicobacter pylori antigens in the blood of pregnant women with anemia and at the stage of pregnancy planning. Positive results are an indication for examination of all family members.

Cavity expansions in two silty tailings with high degrees of saturation and a comparison to CPT results

Tailings, being mixtures of water and soil-sized particles, and sometimes air, are waste products generated by mining. They are stored on sites, often contained by embankments, forming what are known as tailings storage facilities (TSFs). Assessments of the state and strength of tailings inside a TSF may involve in situ tests, especially the cone penetration test (CPT) and occasionally the pressuremeter test (PMT). Cavity expansion theory may assist the interpretation of these tests. The coexistence of air and water in the pore space means the tailings is unsaturated and gives rise to a suction. The suction, and the extent to which air and/or water can drain through the pores, affects the cavity expansion results as well as CPT and PMT results. The cavity expansion problem is solved here considering four possible drainage conditions, constant suction, constant water mass, constant contribution of suction to the effective stress, and a constant air and water mass (closed system). It is reasoned that solutions for a closed system are relevant to the interpretations of CPTs and PMTs when < 15 % of the tailings volume is occupied by air, and that the constant effective stress condition (which is a close approximation to a constant water mass condition) is relevant when larger air volumes are present. By considering CPT data it is observed that linear proportionalities exist between effective cone penetration resistances and cavity wall pressures. The cavity expansion results are then converted to equivalent CPT results and used to construct charts which relate the normalised cone penetration resistance to the initial state parameter. The charts have use for unsaturated conditions and a variety of air volume fractions, as well as saturated conditions when the cone penetration rate is slow enough so drained conditions prevail or fast enough so that undrained conditions prevail.

Developing an artificial neural network controller for accelerating the hot deformation of the titanium aluminide TNM-B1 using reinforcement learning and finite element simulations

This work presents a framework for interfacing a reinforcement learning algorithm with a finite element model in order to develop an artificial neural network controller. The goal of the controller is accelerating the hot compression process of the titanium aluminide TNM-B1. The reinforcement learning algorithm interacts with the finite element model by exploring different die velocities and receiving input measurements (the velocity, displacement and force of the die) while collecting rewards if a constant stress state in the workpiece is achieved. Synthetic stochastic material behavior was used to simulate the observed variations in deformation behavior of TNM-B1. The same reinforcement learning setup and reward function was able to adapt to two example finite element environments; the compression of a simple cylinder workpiece between flat dies and the compression of a more complex bone workpiece between flat dies. The performance of the controller for the bone compression environment was comparatively reduced and less consistent. In addition, training times and training instability were significantly increased. Furthermore, the results suggest that the framework can be used as a tool to find process optimizations or alternative process routes. This work demonstrates the concept and provides the groundwork and fundamentals for transferring the method to a physical setup.

Study on Cyclic Shear Properties of Siliceous Sand–Steel Interface under Different Normal Loading Conditions

It is of great significance to deeply understand the stress damage mechanism of the pile–soil interface under cyclic loading for the safety control of engineering entities. Large-scale self-developed shear equipment was used to conduct cyclic shear tests of the interface between steel and siliceous sand, and the macroscopic shear characteristics and particle crushing characteristics were analyzed. Finally, the interface micro characteristics were analyzed through numerical simulation. The results indicate that the interface peak shear stress under constant stress conditions mainly exhibits strengthening characteristics, while under constant stiffness conditions it exhibits weakening characteristics. The position of the relationship curve between shear stress and normal stress gradually moves towards the direction of low normal stress as the experiment progresses, and the distance between the curves gradually decreases. The degree of particle breakage increases with the number of cycles but is mainly concentrated in the first few cycles. The principal stress is proportional to the normal stress, and its rotation degree gradually weakens with the normal stress. The contact number of particles at any angle increases with the normal stress.

Tertiary creep behavior for various rate- and state-dependent friction laws

Forecasting the acceleration of slow landslides to the point of catastrophic failure is crucial. It follows the Voight power-law model with the power exponent α, which is typically close to 2 but can be significantly smaller. Understanding the underlying mechanisms may improve landslide warnings. A previous study applied a rate- and state-dependent friction (RSF) law in the form of the aging law to the creep behavior of an underlying shear zone of landslides, and showed an α value of 2. The aging law is one of the conventional forms of RSF law, and we extended the analysis to other representative laws: the slip law, Perrin-Rice-Zheng (PRZ) law, composite law, and Nagata law. We showed that the acceleration is expressed in terms of the slip rate using the state-evolution equation. As the slip rate increases, α decays to 2, regardless of the frictional parameters, following a power law for the aging and Nagata laws and logarithmically for the slip and the composite laws. For the PRZ law, the asymptotic value of α is between 2 and 3 and depends on frictional parameters. In typical RSF laws, the logarithm of the slip rate is proportional to the friction coefficient or normalized shear stress f minus frictional strength Θ. The logarithmic direct effect and a linear increase with slip in f−Θ independent of the slip rate, which is a characteristic of aging and Nagata laws under constant stress conditions, leads to α=2. By contrast, a purely time-dependent increase in f−Θ would lead to α=1. If these two effects coexist, α increases from 1 to 2 with acceleration. In laboratory experiments of investigation of RSF law, constant-load creep tests in the tertiary-creep stage have been rarely conducted, but they could provide new insights on the form of the state-evolution equation and deserve future study.

Machine learning of twin/matrix interfaces from local stress field

Twinning is an important deformation mode in plastically deformed hexagonal close-packed materials. The extremely high twin growth rates at the nanoscale make atomistic simulations an attractive method for investigating the role of individual twin/matrix interfaces such as twin boundaries and basal-prismatic interfaces in twin growth kinetics. Unfortunately, there is no single framework that allows researchers to differentiate such interfaces automatically, neither in experimental in-situ transmission electron microscopy analysis images nor in atomistic simulations. Moreover, the presence of alloying elements introduces substantial noise to local atomic environments, making it nearly impossible to identify which atoms belong to which interface. Here, with the help of advanced machine learning methods, we provide a proof-of-concept way of using the local stress field distribution as an indicator for the presence of interfaces and for determining their types. We apply such an analysis to the growth of twin embryos in Mg-10 at.% Al alloys under constant stress and constant strain conditions, corresponding to two extremes of high and low strain rates, respectively. We discover that the kinetics of such growth is driven by high-energy basal-prismatic interfaces, in line with our experimental observations for pure Mg.

Warmer waters make sturgeon think they're sick

In the lakes and rivers of Manitoba lives the lake sturgeon (Acipenser fulvescens), a large truly prehistoric fish. In years past, this bottom-dwelling fish has been overfished for its meat and eggs, but recent efforts have helped to restore their populations. However, the warming of their waters due to global climate change is causing these sturgeon to face new challenges. Once reaching adulthood, lake sturgeon are hardy and incredibly long lived (the oldest fish caught was estimated to be 125 years old!), but the hatchlings aren't so robust. William Bugg and colleagues from the University of Manitoba, Canada, are trying to determine what happens to the little developing fish when their waters get warmer. Are they in a constant state of stress? And will the warmer waters affect other aspects of their well-being?After obtaining fertilized eggs, the researchers hatched the sturgeon and began the process of getting some of them used to 20°C water. This temperature is within the range that the sturgeon experience in the lakes and rivers early in their development, but these higher temperatures are expected to last longer and get even hotter as the climate changes. The team then measured the expression levels of genes related to stress, including those that are important in fighting off infections. When the fish were raised at 20°C, they had higher levels of mRNA for genes involved in detecting pathogens (bacteria and viruses), the immune system response (to attack the bacteria and viruses) and the stress response. This suggests that being raised in warmer water causes the fish to be stressed and their immune system to respond similarly to the way it does when the fish are sick.So, if the sturgeon were already responding as if they were stressed and sick, what would happen if they really were under attack by bacteria? To answer this, Bugg and colleagues measured the mRNA levels of these same genes after the sturgeon were given doses of bacteria. The sturgeon raised at 20°C couldn't generate as big of a response to these bacterial invaders as sturgeon that were raised at 16°C. This means that sturgeon from warmer waters couldn't fight off bacterial infections as well as those raised in cooler waters. In fact, when given the higher dose of bacteria, 100% of the sturgeon raised in 20°C succumbed to the infection, while only 1.3% of the fish raised at 16°C were unable to fight off the same dose of bacteria.This surprising result led the team to question whether there were other aspects of the sturgeon's stress response or development that were affected by being raised at 20°C. The increased temperature also caused an increase in the levels of the stress hormone cortisol, and a decrease in liver size, which is an indication of the amount of energy stores the fish have. Interestingly, the fish raised at 20°C were bigger, suggesting the sturgeon were putting most of their energy towards growth without reserving as much for energy stores. In this case, having additional energy stores may have helped fish fight off bacterial infections.However, being raised at 20°C did have one potential benefit; it increased the temperature at which fish could function. As the researchers slowly increased the water temperature, they tested the ability of the sturgeon to withstand rising temperatures in the future. Sturgeon raised in warmer waters were able to tolerate hotter water temperatures than those raised at 16°C. So, while our efforts at conserving this important fish species have shown some success, global climate change will present a new and unexpected challenge to these potentially long-lived fish.