External Stress Conditions Research Articles

Resistance to H2O2-induced oxidative stress in human cells of different phenotypes

Application of genetically encoded biosensors of redox-active compounds promotes the elaboration of new methods for investigation of intracellular redox activities. Previously, we have developed a method to measure quantitatively the intracellular concentration of hydrogen peroxide (H2O2) in living cells using genetically encoded biosensor HyPer. In the present study, we refined the method and applied it for comparing the antioxidant system potency in human cells of different phenotypes by measuring the gradient between the extracellular and cytoplasmic H2O2 concentrations under conditions of H2O2-induced external oxidative stress. The measurements were performed using cancer cell lines (K-562 and HeLa), as well as normal human cells – all expressing HyPer in the cell cytoplasm. As normal cells, we used three isogenic lines of different phenotypes – mesenchymal stem/stromal cells (MSCs), induced pluripotent stem cells (iPSCs) derived from MSCs by reprogramming, and differentiated iPSC progenies with the phenotype resembling precursory MSCs. When exposing cells to exogenous H2O2, we showed that at low oxidative loads (<50 μM of H2O2) the gradient depended on extracellular H2O2 concentration. At high loads (>50 μM of H2O2), which caused the exhaustion of thioredoxin activity in the cell cytoplasm, the gradient stabilized, pointing out that it is the functional status of the thioredoxin-depended enzymatic system that drives the dependence of the H2O2 gradient on the oxidative load in human cells. At high H2O2 concentrations, the cytoplasmic H2O2 level in cancer cells was found to be several hundred times lower than the extracellular one. At the same time, in normal cells, extracellular-to-intracellular gradient amounted to thousands of times. Upon reprogramming, the potency of cellular antioxidant defense increased. In contrast, differentiation of iPSCs did not result in the changes in antioxidant system activity in the cell cytoplasm, assuming that intensification of the H2O2-detoxification processes is inherent to a period of early human development.

Three-dimensional lamellar orientation and stress condition induced sudden fracture of directional solidified γ-TiAl alloys produced by electromagnetic confinement

Ф 16.5 mm directional solidified Ti-45Al-5Nb alloys with full-lamellar microstructure were successfully obtained through electromagnetic confinement and seed crystal methods. Tensile experiments at ambient temperature were performed to evaluate the industrial processability of the alloy. Although the angle between the full-lamellar structure and the applied stress is approximately 0°, the elongation is still extremely low. The fracture morphology and internal microstructure were observed from multiple directions. Combined with external mechanical stress condition, the reason for sudden fracture was discovered and the lamella orientation control plan is proposed based on different specimen conditions. The cognition of the relationship between the lamellar orientation and mechanical performance was supplemented and expanded on the three-dimensional scale.

A Bio-Based Render for Insulating Agglomerated Cork Panels

Natural and bio-based thermal insulation materials play an important role in the lifecycle impact of buildings due to their influence on the amount of energy used in indoor temperature control and the environmental impact of building debris. Among bio-based materials, cork is widespread in the Mediterranean region and is one of the bio-based materials that is most frequently used as thermal insulation for buildings. A particular problem is the protection of the cork-agglomerated panels from external stress and adverse weather conditions; in fact, cork granulates are soft and, consequently, cork panels could be damaged by being hit or by excessive sun radiation. In this study, an innovative external coat for cork-agglomerated panels made of a blending composite of beeswax and rosin (colophony) is proposed. The performance of this composite, using different amounts of elements, was analysed to discover which mix led to the best performance. The mix of 50% beeswax and 50% rosin exhibited the best performance out of all the mixes. This blend demonstrated the best elongation and the lowest fracture density, characteristics that determine the durability of the coating. A performance comparison was carried out between cork panel samples coated with lime render and beeswax–rosin coating. The coating of beeswax and resin highlighted a detachment value about 3.5 times higher than the lime plaster applied on the side of the cork.

Maturation of UTR-Derived sRNAs Is Modulated during Adaptation to Different Growth Conditions.

Small regulatory RNAs play a major role in bacterial gene regulation by binding their target mRNAs, which mostly influences the stability or translation of the target. Expression levels of sRNAs are often regulated by their own promoters, but recent reports have highlighted the presence and importance of sRNAs that are derived from mRNA 3′ untranslated regions (UTRs). In this study, we investigated the maturation of 5′ and 3′ UTR-derived sRNAs on a global scale in the facultative phototrophic alphaproteobacterium Rhodobacter sphaeroides. Including some already known UTR-derived sRNAs like UpsM or CcsR1-4, 14 sRNAs are predicted to be located in 5 UTRs and 16 in 3′ UTRs. The involvement of different ribonucleases during maturation was predicted by a differential RNA 5′/3′ end analysis based on RNA next generation sequencing (NGS) data from the respective deletion strains. The results were validated in vivo and underline the importance of polynucleotide phosphorylase (PNPase) and ribonuclease E (RNase E) during processing and maturation. The abundances of some UTR-derived sRNAs changed when cultures were exposed to external stress conditions, such as oxidative stress and also during different growth phases. Promoter fusions revealed that this effect cannot be solely attributed to an altered transcription rate. Moreover, the RNase E dependent cleavage of several UTR-derived sRNAs varied significantly during the early stationary phase and under iron depletion conditions. We conclude that an alteration of ribonucleolytic processing influences the levels of UTR-derived sRNAs, and may thus indirectly affect their mRNA targets.

Child physical abuse and COVID-19: Trends from nine pediatric trauma centers

BackgroundEconomic, social, and psychologic stressors are associated with an increased risk for abusive injuries in children. Prolonged physical proximity between adults and children under conditions of severe external stress, such as witnessed during the COVID-19 pandemic with “shelter-in-place orders”, may be associated with additional increased risk for child physical abuse. We hypothesized that child physical abuse rates and associated severity of injury would increase during the early months of the pandemic as compared to the prior benchmark period. MethodsWe conducted a nine-center retrospective review of suspected child physical abuse admissions across the Western Pediatric Surgery Research Consortium. Cases were identified for the period of April 1-June 30, 2020 (COVID-19) and compared to the identical period in 2019. We collected patient demographics, injury characteristics, and outcome data. ResultsThere were no significant differences in child physical abuse cases between the time periods in the consortium as a whole or at individual hospitals. There were no differences between the study periods with regard to patient characteristics, injury types or severity, resource utilization, disposition, or mortality. ConclusionsApparent rates of new injuries related to child physical abuse did not increase early in the COVID-19 pandemic. While this may suggest that pediatric physical abuse was not impacted by pandemic restrictions and stresses, it is possible that under-reporting, under-detection, or delays in presentation of abusive injuries increased during the pandemic. Long-term follow-up of subsequent rates and severity of child abuse is needed to assess for unrecognized injuries that may have occurred.

Impact of Sorption-Induced Strain and Effective Stress on the Evolution of Coal Permeability under Different Boundary Conditions

Coalbed methane (CBM) is a relatively common unconventional natural gas, which has great exploitation value. Coal permeability is an important parameter that affects the production and production efficiency of CBM, which is mainly controlled by the sorption expansion/contraction strain and effective stress. To study the seepage characteristics of coal in the process of CBM production, we have used CH4 and CO2 as test gases separately and conducted comparative seepage tests of different gases under constant pore pressure conditions. At the same time, the elastic modulus reduction coefficient Rm has been introduced to characterize the sorption strain of coal, following which the permeability models suitable for different boundary conditions were derived according to the stress–strain relationship. Under the two gases, the new model could not only better reflect the law of coal sorption strain but also better reflect the relationship among effective stress, pore pressure, and coal permeability. Under the conditions of constant pore pressure, coal permeability was mainly controlled by effective stress; with the increase of effective stress, permeability decreased sharply initially and then gradually. Under the conditions of uniaxial strain and constant external stress, with an increase of pore pressure and Rm, the matrix sorption expansion strain increased, resulting in a narrowing of the seepage channel, and Rm indirectly inhibited permeability. At this point, coal permeability was mainly controlled by sorption expansion/contraction strain and effective stress. In addition, compared with other permeability models, the new permeability model possesses higher applicability both in theoretical mechanism and in data matching. The general change trend concerning coal permeability, determined by rebound pressure prb, was consistent with the test results, which further verified the applicability of the model. It is believed that the results of this study could provide a basis for subsequent research on the stress–strain–permeability relationship and for the study of efficient development of CBM.

Identification of cassava alternative splicing-related genes and functional characterization of MeSCL30 involvement in drought stress

Alternative splicing (AS) is an important post-transcriptional regulation strategy that can increase the proteome diversity and regulate mRNA level in eukaryote. Multi-exon genes can be alternative spliced to generate two or more transcripts, thereby increasing the adaptation to the external stress conditions in planta. However, AS-related proteins were less explored in cassava which is an important staple crop in the tropical area. A total of 365 genes encoding AS-related proteins were identified and renamed in the cassava genome, and the transcriptional and splicing changes of 15 randomly selected genes were systematically investigated in the tissues under diverse abiotic stress conditions. 13 out of 15 genes undergo AS in the tissues and under diverse environmental stress condition. Importantly, the greatest changes of splicing patterns were found in the leaf or in response to temperature stress, indicating that AS-related proteins had their tissue-specific regulation patterns and might be participated in the plant adaptation to temperature stress. We then found that overexpression of MeSCL30 in Arabidopsis enhanced the tolerance to drought stress through maintaining reactive oxygen species (ROS) homeostasis and increasing the expression of drought-responsive genes. Therefore, these findings refined the AS-related protein-coding genes and provided novel insights for manipulation of AS-related genes in order to enhance the resistance to environmental stress in plant.

Nanoscale Coal Deformation and Alteration of Porosity and Pore Orientation Under Uniaxial Compression: An In Situ SANS Study

Nanoscale coal deformation affects the geomechanics response of coal structure under external stress conditions. In this study, in situ small-angle neutron scattering (SANS) is used to characterize the evolution of nanopore structures under uniaxial compression on an Illinois coal specimen. Porod invariant mapping is used to estimate apparent porosities at different azimuthal angles. Structure-free orientation factors, including the alignment factor and Hermans’ orientation factor, are used to characterize orientation degree in nanopores quantitatively. The nanoscale pore deformation and evolution with stress have not been directly measured before, and the in situ SANS technique offers the unique capability to probe the nanoscale rock deformation. From the results, higher values of apparent porosities are shown near the coal bedding direction. At different azimuthal angles, the apparent porosities increase with increasing uniaxial stress in the elastic deformation range (54–575 bar) for the measured coal. The pore-scale degree of orientation is a size-dependent parameter, and pore orientation along the coal bedding generally increases as pore size increases. The degree of orientation in nanopores on average (in a size range between ~ 2 × 103 A and ~ 15 A) tends to increase first and then decreases with increasing stress loading, although different from that of macropores, indicating higher stresses on the nanopore edges along the bedding direction and then on the nanopore body along the normal direction. There is no distinct permanent change of porosity within the measured stress range (0–575 bar) after the stress relief.

Overexpression of SCL30A from cassava (Manihot esculenta) negatively regulates salt tolerance in Arabidopsis.

Soil salinity is a significant threat to sustainable agricultural production. Plants must adjust their developmental and physiological processes to deal with environmental salt conditions. We previously identified 18 serine-arginine-rich (SR) proteins from cassava (Manihot esculenta Crantz) that play pivotal roles in alternative splicing when encountering the external stress condition. However, functional characterisation of SR proteins is less reported in cassava, which is an important staple crop in the world. In the current study, we found that the expression of cassava spliceosomal component 35-like 30A (MeSCL30A) was significantly induced in response to drought and salt stress. The MeSCL30A overexpressing lines were also obtained in Arabidopsis thaliana L., which flowered earlier when compared with Col-0. Moreover, the MeSCL30A overexpressing lines were hypersensitive to salt and drought stress with lower germination and greening rate in comparison to Col-0. Importantly, soil-grown overexpression lines exhibited salt sensitivity through modulating the reactive oxygen species homeostasis and negatively regulating the gene expression that involved in ionic stress pathway. Therefore, these findings refined the SR protein-coding genes and provided novel insights for enhancing the resistance to environmental stress in plant.

Reliability Modeling for Metallized Film Capacitors Based on Time-Varying Stress Mission Profile and Aging of ESR

Metallized film capacitor (MFC) is one of the key components in power electronic converters, accounting for a large proportion of failures. However, the time-varying external stress in long-term mission profile and time-varying internal stress due to the degradation of MFC are not well described by the conventional reliability evaluation method, which leads to a large deviation between the evaluation results and the engineering practices. Therefore, an improved reliability evaluation method considering time-varying stress mission profile and aging process for MFC is proposed. First, this article analyzes the influence of harmonics and provides a more accurate lifetime model under constant stress condition, compared with the conventional method. Second, the subsection integral accumulated damage model is proposed to transform the long-term time-varying stress mission profile to the short-term ideal constant stress condition, solving the reliability evaluation under time-varying external stress condition. And then, an improved aging model is proposed to describe the nonlinear variation of equivalent series resistance (ESR) and internal temperature rise due to the degradation process of MFC. Furthermore, Monte Carlo simulation is applied to analyze the difference of individual capacitor, obtaining lifetime distribution. Finally, a practical application example of modular multilevel converter (MMC) system is implemented to verify the superiority of the improved method.

The Helicobacter pylori HspR-Modulator CbpA Is a Multifunctional Heat-Shock Protein.

The medically important human pathogen Helicobacter pylori relies on a collection of highly conserved heat-shock and chaperone proteins to preserve the integrity of cellular polypeptides and to control their homeostasis in response to external stress and changing environmental conditions. Among this set of chaperones, the CbpA protein has been shown to play a regulatory role in heat-shock gene regulation by directly interacting with the master stress-responsive repressor HspR. Apart from this regulatory role, little is known so far about CbpA functional activities. Using biochemistry and molecular biology approaches, we have started the in vitro functional characterization of H. pylori CbpA. Specifically, we show that CbpA is a multifunctional protein, being able to bind DNA and to stimulate the ATPase activity of the major chaperone DnaK. In addition, we report a preliminary observation suggesting that CbpA DNA-binding activity can be affected by the direct interaction with the heat-shock master repressor HspR, supporting the hypothesis of a reciprocal crosstalk between these two proteins. Thus, our work defines novel functions for H. pylori CbpA and stimulates further studies aimed at the comprehension of the complex regulatory interplay among chaperones and heat-shock transcriptional regulators.

Stability of the chaperonin system GroEL-GroES under extreme environmental conditions.

The chaperonin system GroEL-GroES is present in all kingdoms of life and rescues proteins from improper folding and aggregation upon internal and external stress conditions, including high temperatures and pressures. Here, we set out to explore the thermo- and piezostability of GroEL, GroES and the GroEL-GroES complex in the presence of cosolvents, nucleotides and salts employing quantitative FTIR spectroscopy and small-angle X-ray scattering. Owing to its high biological relevance and lack of data, our focus was especially on the effect of pressure on the chaperonin system. The experimental results reveal that the GroEL-GroES complex is remarkably temperature stable with an unfolding temperature beyond 70 °C, which can still be slightly increased by compatible cosolutes like TMAO. Conversely, the pressure stability of GroEL and hence the GroEL-GroES complex is rather limited and much less than that of monomeric proteins. Whereas GroES is pressure stable up to ∼5 kbar, GroEl and the GroEl-GroES complex undergo minor structural changes already beyond 1 kbar, which can be attributed to a dissociation-induced conformational drift. Quite unexpectedly, no significant unfolding of GroEL is observed even up to 10 kbar, however, i.e., the subunits themselves are very pressure stable. As for the physiological relevance, the structural integrity of the chaperonin system is retained in a relatively narrow pressure range, from about 1 to 1000 bar, which is just the pressure range encountered by life on Earth.

Understanding the pathogenesis of peripartum heart failure in northern Nigeria based on interactions of external heat stress conditions with coenzyme Q10, selenium and magnesium - shared biochemical similarities with the pathogenesis of thyroid disease

Understanding the pathogenesis of peripartum heart failure in northern Nigeria based on interactions of external heat stress conditions with coenzyme Q10, selenium and magnesium - shared biochemical similarities with the pathogenesis of thyroid disease

Coal Permeability Evolution Under Different Water-Bearing Conditions

The seepage problem of coal-bed methane (CBM) has attracted increasing attention from the research and industry communities. Coal permeability, which is a key parameter for CBM production, has been extensively studied through both laboratory and field tests, mathematical modeling, and numerical simulations. However, relatively little work has been done to investigate the effect of matrix water content on coal permeability evolution. Because most coal seams contain water, it may have direct impact on the CBM seepage capacity. Therefore, in this paper, CBM seepage at different matrix water contents was investigated experimentally. Results demonstrate that coal permeability decreases with the increase in water content. It was also found that both pore pressure and water content can greatly affect CBM migration characteristics and that the sorption strain and permeability were mostly controlled by pore pressure. In addition, water can have an impact on gas adsorption and sorption-induced deformation, which can further affect seepage channel width, leading to change in coal permeability. In general, coal permeability was observed to decrease exponentially with the increase in water content and pore pressure. Moreover, a coal adsorption model and an adsorption-permeability model were established, considering water content and excess adsorption under constant external stress and triaxial strain conditions. The proposed permeability model showed good agreement with the experimental results. The present study provides for better understanding of coal permeability evolution in a water-bearing condition and for developing an improved model to simulate the CBM migration process under such condition more accurately.

Genome-Wide Identification of Cassava Serine/Arginine-Rich Proteins: Insights into Alternative Splicing of Pre-mRNAs and Response to Abiotic Stress.

Serine/arginine-rich (SR) proteins have an essential role in the splicing of pre-messenger RNA (pre-mRNA) in eukaryote. Pre-mRNA with introns can be alternatively spliced to generate multiple transcripts, thereby increasing adaptation to the external stress conditions in planta. However, pre-mRNA of SR proteins can also be alternatively spliced in different plant tissues and in response to diverse stress treatments, indicating that SR proteins might be involved in regulating plant development and adaptation to environmental changes. We identified and named 18 SR proteins in cassava and systematically studied their splicing and transcriptional changes under tissue-specific and abiotic stress conditions. Fifteen out of 18 SR genes showed alternative splicing in the tissues. 45 transcripts were found from 18 SR genes under normal conditions, whereas 55 transcripts were identified, and 21 transcripts were alternate spliced in some SR genes under salt stress, suggesting that SR proteins might participate in the plant adaptation to salt stress. We then found that overexpression of MeSR34 in Arabidopsis enhanced the tolerance to salt stress through maintaining reactive oxygen species homeostasis and increasing the expression of calcineurin B-like proteins (CBL)-CBL-interacting protein kinases and osmotic stress-related genes. Therefore, our findings highlight the critical role of cassava SR proteins as regulators of RNA splicing and salt tolerance in planta.

CaMKII Activity in the Inflammatory Response of Cardiac Diseases.

Inflammation is a physiological process by which the body responds to external insults and stress conditions, and it is characterized by the production of pro-inflammatory mediators such as cytokines. The acute inflammatory response is solved by removing the threat. Conversely, a chronic inflammatory state is established due to a prolonged inflammatory response and may lead to tissue damage. Based on the evidence of a reciprocal regulation between inflammation process and calcium unbalance, here we described the involvement of a calcium sensor in cardiac diseases with inflammatory drift. Indeed, the Ca2+/calmodulin-dependent protein kinase II (CaMKII) is activated in several diseases with an inflammatory component, such as myocardial infarction, ischemia/reperfusion injury, pressure overload/hypertrophy, and arrhythmic syndromes, in which it actively regulates pro-inflammatory signaling, among which includes nuclear factor kappa-B (NF-κB), thus contributing to pathological cardiac remodeling. Thus, CaMKII may represent a key target to modulate the severity of the inflammatory-driven degeneration.

Seismo‐Mechanical Response of Anisotropic Rocks Under Hydraulic Fracture Conditions: New Experimental Insights

AbstractUnconventional hydrocarbon resources found across the world are driving a renewed interest in mudrock hydraulic fracturing methods. However, given the difficulty in safely measuring the various controlling factors in a natural environment, considerable challenges remain in understanding the fracture process. To investigate, we report a new laboratory study that simulates hydraulic fracturing using a conventional triaxial apparatus. We show that fracture orientation is primarily controlled by external stress conditions and the inherent rock anisotropy and fabric are critical in governing fracture initiation, propagation, and geometry. We use anisotropic Nash Point Shale (NPS) from the early Jurassic with high elastic P wave anisotropy (56%) and mechanical tensile anisotropy (60%), and highly anisotropic (cemented) Crab Orchard Sandstone with P wave/tensile anisotropies of 12% and 14%, respectively. Initiation of tensile fracture requires 36 MPa for NPS at 1‐km simulated depth and 32 MPa for Crab Orchard Sandstone, in both cases with cross‐bedding favorable orientated. When unfavorably orientated, this increases to 58 MPa for NPS at 800‐m simulated depth, far higher as fractures must now traverse cross‐bedding. We record a swarm of acoustic emission activity, which exhibits spectral power peaks at 600 and 100 kHz suggesting primary fracture and fluid‐rock resonance, respectively. The onset of the acoustic emission data precedes the dynamic instability of the fracture by 0.02 s, which scales to ~20 s for ~100‐m size fractures. We conclude that a monitoring system could become not only a forecasting tool but also a means to control the fracking process to prevent avoidable seismic events.

Defect‐Driven Structural Distortions at the Surface of Relaxor Ferroelectrics

AbstractRelaxor‐ferroelectric materials find application in a broad range of technological devices, including ultrasonic imaging transducers, nanopositioning, and high‐performance capacitors. They generally exhibit occupationally disordered structures creating local polar fluctuations that are highly sensitive to applied electric or stress fields. The sensitivity of the material structure to external field and stress conditions also makes them likely to develop skin or surface phases that are unique from the bulk. Surface layers can adjust the material response and also lead to ambiguity in structural characterization. Here, using a combination of X‐ray diffraction methods, it is shown that a ≈20 µm skin structure commonly exists in the lead‐free relaxor‐ferroelectric ceramic (Na1/2Bi1/2)TiO3–BaTiO3. Using experiments and density functional theory calculations, it is shown that the combined action of oxygen vacancies providing internal chemical pressure and the surface plane stress state dictates the stability and structure of the skin layer. This work can be extended to all perovskite relaxor ferroelectrics and provides new insights into the origin of skin layers in these materials. The opportunity exists to further enhance the functionality of these materials through engineering of surface structures using the methods outlined here.

Selection and validation of appropriate reference genes for real-time quantitative PCR analysis in Momordica charantia

Real time quantitative reverse transcription PCR (RT-qPCR) has been attracting more attention for its high sensitivity in gene expression analysis. Given the widely use of RT-qPCR in normalization, it is playing a pivotal role for seeking suitable reference genes in different species. In current work, 12 candidate reference genes including Actin 2 (ACT2), Cyclophilin 2 (CYP2), Glyceraldehyde-3-phosphate dehydrogenase C2 (GAPC2), Elongation factor 1-α (EF1-α), Nuclear cap binding protein 20 (NCBP20), Serine/threonine-protein phosphatase PP2A (PP2A), Polypyrimidine tract-binding protein 1 (PTBP1), SAND family protein (SNAD), TIP41-like protein (TIP41), Tubulin beta-6 (TUB6), Ubiquitin-conjugating enzyme 9 (UBC9) and Glyceraldehyde-3-phosphatedehydrogenase (GAPDH) were screened from the transcriptome datasets of M. charantia. Afterwards, GeNorm, NormFinder and BestKeeper algorithms were applied to assess the expression stability of these 12 genes under different abiotic stresses including drought, cold, high-salt, hormone, UV, oxidative and metal stress. The results indicated that 12 selected genes exhibited various stability across the samples under different external stress conditions, but TIP41, PTBP1 and PP2A presented high stability among all the reference genes. To validate the suitability of the identified reference genes, the results of hormone subset were compared with RNA sequencing (RNA-seq) data, and the relative abundance of Ascorbate peroxidase 1（APX1）was used to confirm the reliability of the results. This work assesses the stability of reference genes in M. charantia under different abiotic stress conditions, which will be beneficent for accurate normalization of target genes in M. charantia.

Laboratory hydraulic fracturing of granite: Acoustic emission observations and interpretation

Hydraulic fracturing is routinely used, but the fracturing processes that occur when rocks are hydraulically-fractured are not entirely understood and require further investigation. This study presents the acquisition, analysis and interpretation of acoustic emissions data from a series of laboratory hydraulic fracturing experiments on granite. Specimens with different orientations of two pre-cut flaws were tested under both 0 MPa and 5 MPa of vertical uniaxial stress to understand the effect of the external stress conditions. Acoustic emissions data are related to corresponding visual observations made using high-resolution and high-speed imaging. We find that in general, (1) the AE begin to occur at approximately 80% of peak pressure, (2) the focal mechanisms suggest that 55–60% of the radiation pattern could be explained by a double couple mechanism and is well-explained by simulation results, (3) hypocenter locations tended to agree well with visually observed white patching (process zone) and crack patterns, (4) spatio-temporal analysis revealed points in time at which microcrack coalescence were detected by AE, (5) that the AE could be used to make a non-unique prediction of crack initiation, and lastly (6) that exponential AE energy accumulation in the last 5–10 s prior to crack initiation can be modelled by time-to-failure methods.