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SUMMARY Peak delays of acoustic emission (AE) data from rock deformation laboratory experiments are sensitive to both sample heterogeneities and deformation-induced impedance contrasts inside the sample. However, the relative importance of stochastic heterogeneity and discontinuities is uncertain, as is the relationship between peak delays and applied stress and strain. In the companion paper, we presented and analysed peak delay data from AE recorded in a sandstone sample that was triaxially deformed to failure. Here, we simulate P–SV waveforms of dominant frequency 200 kHz in a 2-D isotropic, layered medium using realistic parameters derived from the laboratory experiments previously analysed. Our aim is to provide a physical interpretation of the laboratory findings and constrain the role of a proxy of the evolving fault zone on peak delays. We consider a 2-D fault zone embedded in a host material that simulates the fracture plane as a more compliant layer and allows us to numerically investigate variations in peak delay. Measurements of background parameters, including isotropic velocity and fault thickness were optimized using laboratory data via an evolutionary algorithm. Our simulations clarify that near-source peak delay observations are sensitive to the heterogeneity within zones of intense strain even when far-field approximations are not valid. This sensitivity manifests through the arrival of trapped waves within the layer that is coupled with multiple reflections from the sample boundaries. Substantial uncertainties remain on the possibility of inverting sample parameters with 2-D simulations and such complex physics. Our combined experimental and modelling study suggests that peak delays and coda parameters are sensitive to the heterogeneity caused by faulting and strain variations at different stages of fault-inducing slow deformation.

SUMMARY Seismic waves produced by stressed and deforming rocks lose coherence when they cross regions of high heterogeneity. The delay in the arrival of maximum seismic energy amplitude (peak delay), an essential attribute to model earthquake source characteristics, is increasingly used to map complex crustal geology, heterogeneous reservoirs and fault networks. However, no laboratory calibration for the sensitivity of this parameter to fractures is currently available due to both experimental challenges and the difficulty in modelling wavefields in the near field. In this study, peak delays have been measured and mapped in space in the frequency range 50 kHz to 1 MHz using acoustic emission data recorded during a triaxial deformation experiment of Darley Dale Sandstone. Peak delays can increase dramatically throughout the experiment, but their behaviour depends on frequency and, especially, anomalous azimuth-dependent scattering. The changes in frequency depend on strain. At low frequencies, peak delays are sensitive to surface waves generated at the sample boundaries, but they also mark the zones of shadow and intense/intermediate strains expected for an heterogeneous sample. At high frequencies, peak delays detect the zone of intense strain corresponding to the post-deformation shear zone. Temporal variations of peak delays show a frequency-dependent sensitivity to fracture nucleation, fault coalescence and sample failure. Scattering from these heterogeneities produces waves reverberating through seismic coda if the source–station path is close to an acoustic boundary, such as the fault zone or the sample boundaries. Our results confirm that peak delay has notable sensitivity to heterogeneity and can map and monitor structural- and deformation-induced changes in the near-field. The companion modelling paper tests this sensitivity and the corresponding imaging potential.

Hydraulic fracture in deep rock masses is used across a variety of disciplines, from unconventional oil and gas to geothermal exploration. The overall efficiency of this process requires not only knowledge of the fracture mechanics of the rocks, but also how the newly generated fractures influence macro-scale pore connectivity. We here use cylindrical samples of Crab Orchard sandstone (90 mm length and 36 mm diameter), drilled with a central conduit of 9.6 mm diameter, to simulate hydraulic fracture. Results show that the anisotropy (mm-scale crossbedding orientation) affects breakdown pressure, and subsequent fluid flow. In experiments with samples cored parallel to bedding, breakdown pressures of 11.3 MPa, 27.7 MPa and 40.5 MPa are recorded at initial confining pressures at injection of 5 MPa, 11 MPa and 16 MPa, respectively. For samples cored perpendicular to bedding, breakdown pressure of 15.4 MPa, 27.4 MPa and 34.2 MPa were recorded at initial confining pressure at injection of 5 MPa, 11 MPa and 16 MPa, respectively. An increase in confining pressure after the initial fracture event often results in a significant decrease in flow rate through the newly generated fracture. We note that fluid flow recovers during a confining pressure “re-set” and that the ability of flow to recover is strongly dependent on sample anisotropy and initial confining pressure at injection.

Parametric analysis of laboratory Acoustic Emission (AE) during rock deformation laboratory experiments has revealed periodic trends and precursory behaviour of the rupture source, as crack damage nucleates, it grows and coalesces into a fault zone. Due to the heterogeneity of rocks and the different effective pressures, finding a full prediction of rupture mechanisms is still an open goal.4x10cm cylindrical samples of Alzo granite were triaxially deformed at confining pressures of 5-40 MPa, while AE are recorded by an array of twelve 1MHz Piezo-Electric Transducers. AE are then post-processed to derive attributes and parameters. We aim to identify what are our most important parameters, and more interestingly, when they are most relevant for predicting when the rock will fail.Time Delay Neural Networks (TDNN) have shown promise in forecasting failure when using AE-derived parameters. We trained a TDNN with 5 key parameters: 1) AE event rate, i.e. the number of events obtained during the incremental deformation (strain); 2) AE amplitude, i.e. maximum amplitude of S-waves, 3) AE source mechanisms inferred by the source radiation patterns to categorize events and obtain source orientations of mixed-mode type mechanisms; 4) Seismic scattering, i.e. the ratio between the low frequency (LF, 50-500 kHz) and high frequency (HF, 500-1000 kHz) peak delay (PD) values for individual AE and 5) Bulk elastic S-wave velocity measured at intervals throughout the experiment along the ray-paths created by transmitters and receivers. As each parameter investigates a specific mechanical aspect, taken together they provide information on deformation, fracturing and the evolving state of the background medium as failure is approached. These timeseries are then classified by the TDNN as variations in stress and strain (target parameters).We are currently assessing the importance of individual parameters by omitting one at a time from the training routine. The more important the omitted parameter, the larger the misfit will be when comparing the network output and the target timeseries. The omission analysis determines what are the most important parameters to use when training a neural network to predict dynamic failure. Results are strongly dependent on the methods used to define the training parameters, but several trends are emerging. Event rate and amplitude differently influence predictions of stress and strain. Event rate appears relevant only in the early deformation phases, while amplitude seems much more significant during the coalescence/propagation phase. Seismic scattering and source mechanisms also show an early relevance, interpreted as due 1) to the breakup of low frequency surface waves as microcracks begin to coalesce and 2) bursts of tensile events in the enucleation phase and an increase at ~80% UCS, likely related to the crack propagation. Similarly, there is a clear pivot in the importance of seismic velocity during the early stage, but it emerges a progressive increase ~40% UCS whose origin is unclear. We are currently determining if these variations are directly related to the mechanics of the fault zone or are simply an artifact of the processing.

Clinical oncology heavily relies on formalin-fixed, paraffin-embedded (FFPE) tissue samples for histology and molecular characterization. The chemical and physical modifications of nucleic acids introduced during fixation, storage and purification negatively impact molecular profiling and vary from sample-to-sample. Conventional sonication and ligation-based library preparation is considered the gold-standard approach for FFPE samples, but it is time-consuming and expensive. Importantly, these processes introduce artifacts that impact downstream analysis and interpretation (Haile et al., 2019). We have developed a novel fragmentation chemistry that virtually eliminates hairpin artifacts, achieving levels on par with non-FFPE control samples. Our fragmentation method is highly scalable, exhibits minimal sequence bias, and reduces cost and workflow inefficiencies associated with mechanical shearing. In this study, we developed a unified method for library preparation from FFPE samples which produces similar insert sizes across variable input mass and quality of FFPE samples. We carefully evaluated the performance of this method relative to a sonication-based approach employing the KAPA HyperPrep kit. Libraries were constructed from 50 to 200 ng of FFPE DNA, inputs typically used for NGS, ranging from low-to high-quality as assessed using a qPCR-based method and DNA integrity (DIN). Targeted sequencing was performed using a 37 kb custom oncology hybridization capture panel to investigate molecular complexity. Our workflow virtually eliminated hairpin artifacts that were present in up to 4.5% of reads in sonication-based libraries. Soft-clipping was also 3- to 7-fold lower in libraries prepared with the Watchmaker kit relative to sonicated DNA libraries, improving overall sequencing economy. Furthermore, the mean target coverage achieved with the Watchmaker kit was comparable to or higher than sonication libraries using the same input mass. Because input masses were normalized post-shearing, which typically results in 20-40% sample loss, coverage with our approach is significantly higher relative to sonication, if normalizing to pre-sheared DNA input. Watchmaker DNA Library Preparation with Fragmentation enables high-quality DNA library preparation from damaged FFPE samples, producing high target coverage, uniform insert size, and minimizing sequencing artifacts to improve sensitivity and specificity. This approach is highly scalable and automatable, enabling various oncology applications. Citation Format: Giulia Corbet, Philip Benson, Kailee Reed, Skyler Mishkin, Thomas Harrison, Kristin Scott, Zane Jaafar, Kristina Giorda, Josh Haimes, Martin Ranik, Brian Kudlow. A novel enzymatic library preparation workflow that dramatically reduces artifacts associated with damaged FFPE samples [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 215.

Objective: To investigate young people’s experiences of retainers, the associated impact of retainers on their lives and their perceptions of what influences their own co-operation. Design: Qualitative, cross-sectional study. Setting: An orthodontic department in a UK dental hospital. Participants: Purposive sampling was used to recruit young people, aged 11–17 years, wearing a range of different types of retainers. Methods: Semi-structured interviews were conducted and transcribed. The resultant data were analysed using codebook thematic analysis. Results: Ten patients were recruited before thematic saturation was achieved. Four themes were identified: impact and experiences of wearing retainers; facilitators and barriers to retainer adherence; finding out about retainers; and, finally, involvement in decisions about retainers. Although some initial negative impacts were described, participants generally adapted quickly to retainers. Several factors were perceived to influence co-operation with removable retainers, including concerns about relapse and the associated waste of personal effort and wider resources. There were perceived deficiencies in the information provided by clinicians, which led participants to seek advice from other sources, including social media. Some young people wanted to be more involved in decisions about their retainers. Conclusion: While patients perceived retainers to be easier to wear than active appliances, some transient negative impacts occurred, largely related to initial periods of full-time wear. There were a range of factors which patients perceived to influence their adherence with removable retainers.

The ability to detect precursors of dynamic failure in brittle rocks has key implications for hazard forecasting at the field scale. In recent years, laboratory scale rock deformation experiments are providing a wealth of information on the physics of the fracture process ranging from fracture nucleation, crack growth and damage accumulation, to crack coalescence and strain localization. Parametric analysis of laboratory Acoustic Emission (AE) data has revealed periodic trends and precursory behaviour of the rupture source mechanisms as a fault zone enucleates and develops, suggesting these processes are somehow repeatable and forecastable. However, due to the inherent anisotropy of rock media and the range of environmental conditions in which deformation occurs, finding full consistency between AE datasets and a prediction of rupture mechanisms from AE analysis is still an open goal. Here we apply a Time Delay Neural Network (TDNN) to Acoustic Emission (AE) sets recorded during conventional triaxial rock deformation tests. We forecast the Time-to-Failure using the discrete, non-continuous timeseries of AE rate, amplitude, focal mechanism and forward scattering properties. 4x10 cm samples of Alzo granite, a homogeneous medium-grained plutonic rock from NW Italy with an initial porosity as low as 0.72%, were triaxially deformed at strain rates of 3.6mm/hr under dry conditions until dynamic failure at confining pressures of 5, 10, 20 and 40 MPa respectively. Each sample was positioned inside an engineered rubber jacket fitted with ports where an array of twelve 1 MHz single-component Piezo-Electric Transducers were embedded, allowing to record AE during the experimentation. Several parameters were considered for the TDNN training: AE rate, deformation stages prior failure (elasticity, inelasticity and coalescence), AE amplitude, source mechanisms and scattering. All these parameters are key indicators of the evolving damage in the medium. Our training input consists of simplified timeseries of the previously discussed AE parameters from the experiments carried out at the lowest confining pressure (5 MPa). The inputs are classified as the stress-until failure and strain-until-failure for each AE. Once trained we then simulate the model on the untrained datasets to test it as a forecasting tool at higher confinements. At each step the model is simulated on AE data from the previous 0.2% of strain. At 10 MPa we observe a reliable forecast of failure that starts with the anelastic phase and becomes more accurate during strain-softening. At higher confining pressure, an increased limit of forecasting the solution is observed and interpreted with more complexity in the coalescence process. Despite these limitations, the model shows that when trained even on a limited input it is able to forecast dynamic failure in unseen data with surprising accuracy. Future studies should investigate AE spatial distribution for the TDNN training.

A concomitant effect of a hydraulic fracturing experimenting is frequently fluid permeation into the rock matrix, with the injected fluid permeating through the porous rock matrix (leak-off) rather than contributing to the buildup of borehole pressure, thereby slowing down or impeding the hydro-fracturing process. Different parameters, such as low fluid viscosity, low injection rate and high rock permeability, contribute to fluid permeation. This effect is particularly prominent in highly permeable materials, therefore, making sleeve fracturing tests (where an internal jacket separates the injected fluid in the borehole from the porous rock matrix) necessary to generate hydraulic fractures. The side effect, however, is an increase in pressure breakdown, which results in higher volume of injected fluid and in higher seismic activity. To better understand this phenomenon, we report data from a new comparative study from a suite of micro-hydraulic fracturing experiments on highly permeable and on low-permeability rock samples. Experiments were conducted in both sleeve fracture and direct fluid fracture modes using two different injection rates. Consistent with previous studies, our results show that hydraulic fracturing occurred only with low permeation, either due to the intrinsic low permeability or due to the presence of an inner silicon rubber sleeve. In particular, due to the presence of quasi-impermeable inner sleeve or borehole skin in the sleeve fracturing experiment, fracturing occurs, with the breakdown pressure supporting the linear elastic approach considering poroelastic effects, therefore, with low stress drop and consequently low microseismicity. Rock matrix permeability also controls the presence of precursory Acoustic Emission activity, as this is linked to the infiltration of fluids and consequent expansion of the pore space. Finally, permeability is shown to mainly control fracturing speed, because the permeation of fluid into the newly created fracture via the highly permeable rock matrix slows down its full development. The application of these results to the field may help to reduce induced seismicity and to conduct well stimulation in a more efficient way.

Cells are exposed to a plethora of influences that can cause damage to DNA and alter the genome, often with detrimental consequences for health. Cells mitigate this damage through a variety of repair protein pathways, and accurate measurement of the accumulation, action, and dissipation timescales of these repair proteins is required to fully understand the DNA damage response. Recently, we described the Q-FADD (Quantitation of Fluorescence Accumulation after DNA Damage) method, which enhances the analytical power of the widely used laser microirradiation technique. In that study, Q-FADD and its preprocessing operations required licensed software and a significant amount of user overhead to find the model of best fit. Here, we present “qFADD.py”, an open-source implementation of the Q-FADD algorithm that is available as both a stand-alone software package and on a publicly accessible webserver (https://qfadd.colorado.edu/). Furthermore, we describe significant improvements to the fitting and preprocessing methods that include corrections for nuclear drift and an automated grid-search for the model of best fit. To improve statistical rigor, the grid-search algorithm also includes automated simulation of replicates. As an example, we discuss the recruitment dynamics of the signaling protein PARP1 to DNA damage sites, and we show how to compare different populations of qFADD.py models.Statement of SignificanceCells are constantly bombarded by factors that can alter or damage their genome, and they have evolved a variety of proteins that can identify and fix this damage. To fully understand how these proteins interact in repair pathways, we need robust methods to quantify the timescales between the initial identification of the DNA damage event and the subsequent protein-protein interactions that lead to repair. Laser microirradiation is a popular method for studying these repair protein cascades in vivo, and methods for quantifying the timescales of recruitment in these experiments have historically been simple to implement but lacking in physical interpretation. Here, we present qFADD.py, the next iteration of the Q-FADD method, which uses Monte Carlo diffusion models to interpret repair protein recruitment timescales to sites of DNA damage. By moving towards automated fitting procedures with minimal bias from the user, qFADD.py provides a statistically robust but low-effort means to analyze laser microirradiation experiments through a biophysical framework.

Identifying deformation and pre-failure mechanisms preceding faulting is key for fault mechanics and for interpreting precursors to fault rupture. This study presents the results of a new and robust derivation of first motion polarity focal mechanism solutions (FMS) applied to acoustic emission (AE). FMS are solved using a least squares minimization of the fit between projected polarity measurements and the deviatoric stress field induced by dilatational (T-type), shearing (S-type), and compressional (C-type) sources. 4 × 10 cm cylindrical samples of Alzo Granite (AG, porosity

Background The objectives of this study were to investigate relationships between change in the aesthetic appearance before and after orthodontic treatment and patient-reported change in oral health-related quality of life (OHRQoL), and to assess the responsiveness of two OHRQoL measures to any changes from orthodontic treatment. Methods Two hundred and ten participants in a multicentre (two teaching hospitals and four specialist orthodontic practices), single blinded, randomised clinical trial with 2 parallel groups, were administered one of two age-specific questionnaires, either the Child Perceptions Questionnaire (CPQ11-14-ISF-16) or the Psychosocial Impact of Dental Aesthetics Questionnaire (PIDAQ), before and after orthodontic treatment. Clinical photographs were assessed by two groups of laypeople and orthodontists using the Index of Orthodontic Treatment Need Aesthetic Component (IOTN-AC). Results Two hundred and ten participants were randomised, and 197 completed the trial. Before and after OHRQoL data were successfully obtained from 110 participants. There was a mean reduction in the total CPQ11-14-ISF-16 scores of 3.9 (SD = 8.0), and a mean reduction of 34.2 (SD = 18.5) in the total PIDAQ score. CPQ11-14-ISF-16 demonstrated poor longitudinal construct validity (p = 0.155). Correlations between the change in total CPQ11-14-ISF-16 scores and change in IOTN-AC assessments were small for both orthodontists (r=-0.084; p = 0.516) and laypeople (r=-0.140; p = 0.225). There were higher associations between the improvement in the Social well-being (SWB) subdomain and improvement in IOTN-AC. Correlations between the changes in total PIDAQ scores and the IOTN-AC assessments, were higher in comparison to the correlations with CPQ11-14-ISF-16 (orthodontists; r = 0.223, laypeople; r = 0.025). There were no adverse effects. Conclusion CPQ11-14-ISF-16 and IOTN-AC measure different attributes. This demonstrated the role of SWB on children OHRQoL. Condition-specific measures (PIDAQ) are more responsive to change in self-reported OHRQoL than generic measures (CPQ11-14-ISF-16) after treatment. Trial Registration: The trial was registered at ClinicalTrials.gov NCT01925924.

Background: The objectives of this study were to investigate relationships between change in the aesthetic appearance before and after orthodontic treatment and patient-reported change in oral health-related quality of life (OHRQoL), and to assess the responsiveness of two OHRQoL measures to any changes from orthodontic treatment.Methods: Two hundred and one participants in a randomized clinical trial, involving two teaching hospitals and four specialist practices, were administered one of two age-specific questionnaires, either the Child Perceptions Questionnaire (CPQ11-14-ISF-16) or the Psychosocial Impact of Dental Aesthetics Questionnaire (PIDAQ), before and after orthodontic treatment. Clinical photographs were assessed by two groups of laypeople and orthodontists using the Index of Orthodontic Treatment Need Aesthetic Component (IOTN-AC).Results: There was a mean reduction in the total CPQ11-14-ISF-16 scores of 3.9 (SD=8.0), and a mean reduction of 34.2 (SD=18.5) in the total PIDAQ score. CPQ11-14-ISF-16 demonstrated poor longitudinal construct validity (p=0.155). Correlations between the change in total CPQ11-14-ISF-16 scores and change in IOTN-AC assessments was small for both orthodontists (r=-0.084; p=0.516) and laypeople (r=-0.140; p=0.225). There were higher associations between the improvement in the Social well-being (SWB) subdomain and improvement in IOTN-AC. Correlations between the changes in total PIDAQ scores and the IOTN-AC assessments, were higher in comparison to the correlations with CPQ11-14 (orthodontists; r=0.223, laypeople; r=0.025).Conclusion: CPQ11-14-ISF-16 and IOTN-AC measure different attributes. This demonstrated the role of SWB on children OHRQoL. Condition-specific measures (PIDAQ) are more responsive to change in self-reported OHRQoL than generic measures (CPQ11-14-ISF-16) after treatment.

Fluid-driven fracturing is a key process in enhancing production in both the hydrocarbon and geothermal energy extraction industries. However, whilst a large number of studies have now developed laboratory methods to simulate the process in a range of settings, and across a number of different rock types, data relating the fundamental material parameters (such as fracture toughness) to the overall rock mechanics response as a function of parameters such as confining and pore pressure remain limited. Here we report a new analysis to recover fracture toughness across a range of effective pressures from hydraulic fracturing experiments that use a modified thick-walled cylinder sample mounted in a conventional triaxial deformation apparatus. We use samples that are 90mm in length and 40mm diameter, with a central, axially drilled borehole 12.6 mm in diameter. An array of 16 ports in the engineered, nitrile, sample jacket allows us to record radial strain (4 channels), acoustic emission output (11 channels) and borehole fluid pressure (1 channel) continuously throughout each test. The sample material was Nash Point shale (NPS) from the south coast of Wales, UK, with samples cored both normal and parallel to bedding in order to investigate the effect of anisotropy. Earlier, ambient pressure fracture toughness tests using the Semi-Circular Bend sample geometry had indicated significant anisotropy, values of 0.24 – 0.30 MPa.m1/2 in the Short-Transverse (ST) orientation, and 0.71 - 0.73 MPa.m1/2 in the Divider (DIV) orientation.Here, we present results from a suite of 9 experiments, 6 with samples cored parallel to bedding (ST fracture orientation) and 3 with samples cored normal to bedding (DIV fracture orientation). We find that the fluid injection pressure required to fracture our annular shell samples is significantly higher for DIV samples than for ST samples, and increases significantly with increasing confining pressure in both orientations; ranging from 10 to 36 MPa for ST samples and 30 to 58 MPa for DIV samples as confining pressure is increased from 2.2 to 20.5 MPa. We note that the fluid injection pressure undergoes a number of oscillations between fracture nucleation and the fracture reaching the sample boundary. Such oscillations are more common in ST samples than in DIV samples, and in experiments at lower confining pressures. We use the magnitude of each pressure oscillation to estimate the associated increment of fracture extension via the proportion of AE energy generated relative to the total energy accumulated when the fracture reaches the sample boundary. This analysis produces fracture toughness values ranging from 0.36 to 2.76 MPa.m1/2 (ST orientation) and 2.98 to 4.05 MPa.m1/2 (DIV orientation) as confining pressure was increased from 2.2 to 20.5 MPa. We further find that the increase in fracture toughness increases essentially linearly with increasing effective pressure, and this trend appears to be independent of orientation and the material anisotropy.

Acoustic Emissions (AE), the laboratory analogue to seismic events, recorded during conventional triaxial deformation tests allow for an unprecedented amount of information on the evolution of fractured media within a controlled environment. This study presents the results of a new and robust derivation of first motion polarity focal mechanism solutions (FMS). 4 x 10 cm cylindrical samples of Alzo Granite (AG) and Darley Dale Sandstone (DDS) underwent systematic triaxial deformation testing (5, 10, 20 and 40 MPa) in order to investigate the relationships between increasing confining pressure, deformation and failure mode and role of pre-existing microstructure. With an average of 11 of 12 waveforms picked using a neural network for each AE, high resolution datasets are obtained that can track the evolution of deformation structure through time. Focal mechanisms are solved using a least squares minimisation of the fit between projected polarity measurements and the deviatoric stress field induced by tensile, shearing and collapse/closing type sources. Results reveal a surprisingly limited dependency on the distribution of shear fracturing in the lead up to dynamic failure. Instead, deformation is driven by the competition between the opening and closure of fractures that is strongly related to the coupling of local stress fields with pre-existing damage.Spatio-temporal trends in mechanism type and AE amplitude allow for clear identification of: a) Fracture Enucleation. This phase is characterised by broadly distributed tensile fracturing that becomes preferentially aligned as confining pressure increases; b) Fracture Growth. The onset is characterized by a discrete increase in low amplitude shearing events and cyclic fracture development that evolves from a dominance of collapse to shearing followed by tensile fracturing which then returns to collapse type. Influences in mechanism dominance due to rock type are highlighted by increased tensile fracturing in AG, which is replaced by shearing in DDS. A reduction in low amplitude tensile events at 10 MPa in both rock types further reveals a switch from axial splitting to planar localisation as confinement increases; c) Crack Coalescence. The cyclic fracture growth prior to dynamic failure and the amount of strain of this phase share a positive log-linear relationship with confining pressure, allowing to identify the potential for real-time failure prediction; d) Dynamic Failure: High amplitude events characterize the propagation of fractures. Taken together results highlight that failure of the studied samples is the result of the complex interaction between distinct regions of dilatant and compactant deformation. Although planar localisation and preferentially aligned flaws play a more significant role at higher confining pressures, it is the initial heterogeneity or patchiness of the regions undergoing damage that control dynamic failure occurrence and the eventual fracture plane features.

A number of key processes, both natural and anthropogenic, involve the fracture of rocks subjected to tensile stress, including vein growth and mineralization, and the extraction of hydrocarbons through hydraulic fracturing. In each case, the fundamental material property of mode‐I fracture toughness must be overcome in order for a tensile fracture to propagate. Whilst measuring this parameter is relatively straightforward at ambient pressure, estimating fracture toughness of rocks at depth, where they experience confining pressure, is technically challenging. Here, we report a new analysis that combines results from thick‐walled cylinder burst tests with quantitative acoustic emission to estimate the mode‐I fracture toughness (KIc) of Nash Point Shale at confining pressure simulating in‐situ conditions to approximately 1km depth. In the most favorable orientation, the pressure required to fracture the rock shell (injection pressure, Pinj) increases from 6.1 MPa at 2.2 MPa confining pressure (Pc), to 34 MPa at 20 MPa confining pressure. When fractures are forced to cross the shale bedding, the required injection pressures are 30.3 MPa (at Pc = 4.5 MPa) and 58 MPa (Pc = 20 MPa), respectively. Applying the model of Abou‐Sayed (1978) to estimate the initial flaw size, we calculate that this pressure increase equates to an increase in KIc from 0.36 to 4.05 MPa.m1/2 as differential fluid pressure (Pinj ‐ Pc) increases from 3.2 to 22.0 MPa. We conclude that the increasing pressure due to depth in the Earth will have a significant influence on fracture toughness, which is also a function of the inherent anisotropy.

We report a new method using a time delay neural network to transform acoustic emission (AE) waveforms into a time series of instantaneous frequency content and permutation entropy. This permits periods of noise to be distinguished from signals. The model is trained in sequential batches, using an automated process that steadily improves signal recognition as new data are added. The model was validated using AE data from rock deformation experiments, using Darley Dale sandstone in fully drained conditions at a confining pressure of 20 MPa (approximately 800 m simulated depth). The model is initially trained by manual picking of five high-amplitude waveforms randomly selected from the dataset (experiment). This is followed by semisupervised training on a subset of 300 waveforms.

Volcanic edifices are commonly unstable, with magmatic and non‐magmatic fluid circulation, and elevated temperature gradients having influence on the mechanical strength of edifice and basement rocks. We present new mechanical characterization of the Comiso limestone of the Mount Etna Volcano (Italy) basement to constrain the effects of regional ambient conditions associated with the volcanic system: the effects of pore fluid on rock strength and the effects of distal magmatic heating (~20 °C to 600 °C) at a range of simulated depths (0.2 to 2.0 km). The presence of water promotes ductile behaviour at shallow depths and causes a significant reduction in brittle rock strength compared to dry conditions. Thermal stressing, in which specimens were heated and cooled before mechanical testing at room temperature, has a variable effect for dry and saturated cases. In dry conditions, thermal stressing up to 450 °C homogenizes the strength of the specimen such that the majority of the specimens exhibit the same peak stress; at 600 °C, the brittle failure is promoted at lower differential stress. The presence of water in thermally‐stressed specimens promotes ductile behaviour and reduces peak strength. Acoustic emission monitoring suggests that accumulated damage is associated with the heating–cooling sequence, particularly in the 300–450‐600°C. Based on conduction modeling, we estimate this temperature range could affect basement rocks up to 300 m away from minor sheet intrusions and much further with larger bodies. Considering the dyke spacing beneath Etna, these conditions may apply to a significant percentage of the basement, promoting ductile behaviour at relatively shallow depths.

The measurement of strain is a fundamental and widely studied parameter in engineering, rock mechanics, construction and materials testing. Contact sensors often used in these fields require contact with the target surface throughout the duration of a strain event. Non-contact methods typically require that that the measurement surface is prepared and often coated prior to testing. This paper considers the potential application of near infrared spectroscopy as a non-contact technique for the measurement of strain on natural surfaces. Excellent correlation was found between surface measurements of visible-NIR spectra and longitudinal strain taken during indirect Brazilian Disc Test for samples of sandstone, marble and basalt.

The challenges of gaining access to opportunities to use the target language in contexts of study abroad, international education and migration are well-documented. In this Sydney-based study, these are reconceptualized as challenges of access to English in an English-speaking, but increasingly multilingual, city. The notion of "context" in overseas study is also reconceptualized in spatial terms as the environmental circumstances of students’ everyday lives, which are partly fixed in advance of their arrival but also shaped by their agency. A narrative case study of a recently arrived international student’s daily activities and language use draws on online diary and stimulated recall interview data. The case study illustrates both the importance of the spatial dimensions of her everyday life to her use of languages and the how she manages these spatial dimensions to enhance her access to opportunities for English language use and learning.

Stromboli volcano has experienced four sector collapses over the past 13,000 years, resulting in the formation of the Sciara del Fuoco (SDF); a horseshoe-shaped flank collapse scarp where episodes of instability are continuously observed and recorded. A NE / SW striking rift zone across the SDF and the western sector of the island is inferred to be a potential weakness zone for further instability episodes. This study reports new data of fracture density using remote sensing imagery, across within and outside the rift zone, to identify areas of damage that could reduce the edifice strength and promote fracturing. Pleiades satellite data of 0.5 m resolution was processed to highlight 23635 distinct linear features, determine fracture density across the island, and identify key areas of macro-scale weakness on the volcano. These data suggest that the SW sector of the island, including the summit area and the slopes of SDF, have an average fracture density between 1.18 – 2.73 × 10−5m−2 in contrast to the rest of the volcano that has an average fracture density of 4.56 × 10−6m−2. Analysis was also conducted on the orientation of fracture strikes across the volcanic edifice by analysing fracture data specifically associated with areas of intrusions and fissures: the NW / SE rift zone and the SDF. Preliminary results show that the average fracture strike ranged from between 030 – 047 NE/SW and thus broadly parallel to the inferred rift axis.

Those who have advocated social approaches to applied linguistics have often been critical of the individualism of second language acquisition (SLA) research. This paper identifies the emergence of a more balanced view of the social and individual in recent work. Adopting Berger's (1972) metaphor of ‘ways of seeing’, it offers a history of applied linguistics based on three eras: the era of ‘the invisible learner’, the era of ‘learner-centredness’, and the era of ‘person-centredness’, which we may now be entering. It suggests dominant research methodologies have led to the particular ways of seeing language learners that are characteristic of each of the three eras. In spite of the critique of individualism, the preference for individual case studies in social approaches is leading to a new theoretical focus on the individual that may be best captured by the term ‘person-centredness’.

Permeability in tight crustal rocks is primarily controlled by the connected porosity, shape and orientation of microcracks, the preferred orientation of cross-bedding, and sedimentary features such as layering. This leads to a significant permeability anisotropy. Less well studied, however, are the effects of time and stress recovery on the evolution of the permeability hysteresis which is becoming increasingly important in areas ranging from fluid migration in ore-forming processes to enhanced resource extraction. Here, we report new data simulating spatio-temporal permeability changes induced using effective pressure, simulating burial depth, on a tight sandstone (Crab Orchard). We find an initially (measured at 5 MPa) anisotropy of 2.5% in P-wave velocity and 180% in permeability anisotropy is significantly affected by the direction of the effective pressure change and cyclicity; anisotropy values decrease to 1% and 10% respectively after 3 cycles to 90 MPa and back. Furthermore, we measure a steadily increasing recovery time (10–20 min) for flow parallel to cross-bedding, and a far slower recovery time (20–50 min) for flow normal to cross-bedding. These data are interpreted via strain anisotropy and accommodation models, similar to the “seasoning” process often used in dynamic reservoir extraction.

Based on narratives from Hong Kong students on one-semester programmes at universities in Australia, Britain and Canada, this study focused on the emotional charge of expectations and day-to-day realities of homestay. It showed how, for many of the students, this emotional charge was related to the adoption of imagined identities as family members within the homestay. It also showed how a corresponding sense of inclusion or exclusion could arise from recognition or non-recognition of these imagined identities. The students’ experiences of homestay were often shaped by an expectation that a degree of emotional intensity within a family environment would lead to a successful language learning experience. Paradoxically, emotionally disturbing experiences could also contribute to a positive overall experience from the student’s perspective, if they led to a stronger sense of emotional inclusion. The experience was least satisfying overall in homestays where students were unable to feel this sense of inclusion.

The generation mechanics of fluid-driven volcano seismic signals, and their evolution with time, remains poorly understood. We present a laboratory study aiming to better constrain the time evolution of such signals across temperature conditions 25 to 175 °C in order to simulate a “bubbly liquid”. Simulations used pressures equivalent to volcanic edifices up to 1.6 km in depth using a triaxial deformation apparatus equipped with an array of Acoustic Emission (AE) sensors. We investigate the origin of fluid driven seismic signals by rapidly venting the pore pressure through a characterized damage zone. During the release of water at 25 °C broadband signals were generated, with frequencies ranging from 50 to 160 kHz. However the decompression of a water/steam phase at 175 °C generated a bi-modal spectrum of different signals, in the range 100 kHz and 160 kHz. These new results are consistent with natural signals from active volcanoes, such as Mt. Etna, and highlight the role of fluid and gas phases (such as “bubbly liquids”) in generating different types of volcano-tectonic seismicity.

Unconventional 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.

The process of hydraulic fracture is well known in both natural (e.g. veining and mineralisation) and engineered environments (e.g. stimulating tight mudrocks and sandstones to boost their hydraulic properties). Here, we report a method and preliminary data that simulates both tensile fracture and fluid flow at elevated pressures. To achieve this we developed a sample assembly consisting of a cylindrical core drilled with an axial borehole encapsulated in a 3D printed jacket permitting fluid from the borehole to move through the freshly generated tensile fracture to a voluometer. The permeability of Nash Point Shale increases from a pre-fracture value of 10−18 to 10−20 m2 (1 microDarcy, μD to 0.01 μD) to 2 × 10−15 m2 (2 milliDarcy, mD) immediately after fracture (at 2.1 MPa confining pressure). Permeability is strongly dependent on confining pressure, decreasing to 0.25 × 10−15 m2 (0.25 mD) at 19 MPa confining pressure (approximately 800 m depth), and does not recover when confinement is removed. Using concomitant measurements of the radial strain as a proxy for fracture aperture, we conclude that the effective permeability is governed solely by the width of the developed cracks, revealed by post-test X-Ray Computed Tomography to be planar, extending radially from the central conduit.

Seismic based geophysical methods are seeing increased usage in evaluating geothermal resources in order to maximize resource potential. However, interpreting geophysical data (such as velocities and dynamic modulus and fracture density/alignment) generated from geothermal reservoirs remains difficult. Here we present the results of a new laboratory study measuring seismic attributes of fresh and hydrothermally altered rocks from a Philippine geothermal field (Southern Negros Geothermal Project - SNGP) during triaxial deformation. Two types of rocks were obtained by sub-coring samples of low porosity (~1%) andesite and higher porosity (~10%) volcaniclastic samples from the SNGP. Samples were prepared with two offset drill holes to allow a natural fracture to permit fluid flow along the fracture. An embedded array of Acoustic Emission (AE) sensors allows elastic wave and induced microseismic data to be collected. We measure a significant reduction in elastic wave velocities and moduli, with the exception of Poisson's ratio, after shear fracture development. An initially pre-fractured permeability of approximately 10−17 m2 is measured. We find that the permeability decreases from 2.0 × 10−14 m2 to lower than 7.4 × 10−15 m2 as the confining pressure is increased from 5 MPa to 30 MPa. A concomitant increase in P and S-wave velocities, dynamic bulk and Young's moduli are also measured. Finally, we simulate a geothermal ‘venting’ situation by intentionally releasing the high pore fluid (water) pressure from 10 to 50 MPa to ambient pressure, generating a swarm of AE that increases in duration with higher pore pressure. We postulate that this is due to fluid phase change (liquid to gas) and movement along the natural fracture plane and damage zone.

Fluid-induced seismicity has been observed and recorded for decades. Seismic energy necessarily requires a source, which is frequently related to rock fracture either in compression or tension. In both cases, such fracture may be promoted by crustal fluids. In this paper, we review some of the advances in the field of fluid-induced seismicity, with a particular focus on the use and application of new and innovative laboratory methods to better understand the complex, coupled, processes in shallow sub-surface energy extraction applications. We discuss the current state-of-the-art with specific reference to Thermal-Hydraulic-Coupling in volcanotectonic environments, which has a long history of fluid-driven seismic events linked to deep fluid movement. This ranges from local earthquakes to fluid-driven resonance, known as volcanic tremor. More recently so-called non-volcanic tremor has been identified in a range of scenarios where motion at an interface is primarily driven by fluids rather than significant stress release. Finally, we review rock fracture in the tensile regime which occurs naturally and in the engineered environment for developing fractures for the purpose of resource extraction, such as hydraulic fracturing in unconventional hydrocarbon industry or developing Hot-Dry-Rock geothermal reservoirs.

To reach the surface, dykes must overcome the inherent tensile strength of the country rock. As they do they generate swarms of seismic signals, frequently used for forecasting. In this study we pressurize and inject molten acrylic into an encapsulating host rocks of 1) Etna basalt and 2) Comiso limestone; at 30 MPa of confining pressure. Fracture was achieved at 12 MPa for Etna basalt, 7.2 MPa for Comiso limestone. The generation of radial fractures was accompanied by acoustic emissions (AE) at a dominant frequency of 600 kHz. During “magma” movement in the dykes, AE events of approximately 150 kHz dominant frequency were recorded. We interpret our data using AE location and dominant frequency analysis, concluding that the seismicity associated with magma transport in dykes peaks during initial dyke creation but remains significant as long as magma movement continues. These results have important implications for seismic monitoring of active volcanoes.

The styles and mechanisms of deformation associated with many variably dolomitized limestone shear systems are strongly controlled by strain partitioning between dolomite and calcite. Here, we present experimental results from the deformation of four composite materials designed to address the role of dolomite on the strength of limestone. Composites were synthesized by hot isostatic pressing mixtures of dolomite (Dm) and calcite powders (% Dm: 25%-Dm, 35%-Dm, 51%-Dm, and 75%-Dm). In all composites, calcite is finer grained than dolomite. The synthesized materials were deformed in torsion at constant strain rate (3 × 10−4 and 1 × 10−4 s−1), high effective pressure (262 MPa), and high temperature (750 °C) to variable finite shear strains. Mechanical data show an increase in yield strength with increasing dolomite content. Composites with 50%) dolomite content samples, the addition of 25% fine-grained calcite significantly weakens dolomite, such that strain can be partially localized along narrow ribbons of fine-grained calcite. Deformation of dolomite grains by shear fracture is observed; there is no intracrystalline deformation in dolomite irrespective of its relative abundance and finite shear strain.

Characterizing the interaction between fluids and microscopic defects is one of the long-standing challenges in understanding a broad range of cracking processes, in part because they are so difficult to study experimentally. We address this issue by reexamining records of emitted acoustic phonon events during rock mechanics experiments under wet and dry conditions. The frequency spectrum of these events provides direct information regarding the state of the system. Such events are typically subdivided into high frequency (HF) and low frequency (LF) events, whereas intermediate “Hybrid” events, have HF onsets followed by LF ringing. At a larger scale in volcanic terranes, hybrid events are used empirically to predict eruptions, but their ambiguous physical origin limits their diagnostic use. By studying acoustic phonon emissions from individual microcracking events we show that the onset of a secondary instability–related to the transition from HF to LF–occurs during the fast equilibration phase of the system, leading to sudden increase of fluid pressure in the process zone. As a result of this squeezing process, a secondary instability akin to the LF event occurs. This mechanism is consistent with observations of hybrid earthquakes.

Acoustic emissions exhibit complex correlations between space, time, and magnitude. As such, they present a unique example for a complex time series. We apply the recently introduced method of natural time analysis, which enables the detection of long-range temporal correlations even in the presence of heavy tails and find that the acoustic emissions exhibits features similar to that of other equilibrium or non-equilibrium critical systems such as worldwide seismicity as presented in the Centennial earthquake catalogue which includes global seismicity events with magnitude Mw>7.0. These results support the universal behaviour of the fracturing processes from the laboratory to the global scale.

Decoupling of paramagnetic and ferrimagnetic AMS development during the experimental chemical compaction of illite shale powder

The literature on non-native English-speaking teachers (NNESTs) and native English-speaking teachers (NESTs) tends to focus on their respective strengths, the main strengths of NNESTs being their experience of learning English as a second language and their familiarity with their students’ language and educational background. This article proposes a further distinction between NNESTs who are local to their teaching settings, and ‘non-local NNESTS’, who are at risk of falling between the cracks of the NNEST–NEST distinction if they do not share their students’ first language and educational background. It also argues that the strengths of NNESTs and NESTs (local or non-local) are not intrinsic to these categories, but instead serve as contexts of discourse in which teachers construct their ‘authority’ to teach English in particular settings. A case study of two non-local NNESTs in their final year of a pre-service teacher education degree in Hong Kong explores how they struggled to construct authoritative identities as English teachers in the context of discourses that primarily validate the status of NESTs and local NNESTs. It concludes by calling for a more nuanced view of the NNEST–NEST distinction and for further fine-grained studies of the experiences of local and non-local NNESTs elsewhere in the world.

During volcanic unrest, high magma pressure induces cracking and faulting of the country rock, providing conduits for the transport of magma and other fluids. These conduits, known as dykes, are fundamental structures for the transport of magma to the surface in volcanically active regions. The mechanics of dyke propagation is not yet fully understood but is crucial to better model dyke emplacement and eruption in volcanoes. Central to this need is a greater understanding of the mechanical properties of the magma/country rock interaction as a function of known magmatic pressure, temperature and stress. Here, we report data from a series of experiments in which we cyclically compress viscoelastic rhyolitic magma (at 828 °C, 892 °C and 918 °C) inside a cylindrical conduit-like shell of basalt (from Mt. Etna, Italy) until fracture occurs. The compression is performed under strain rates cyclically varying between 5×10−6 and 5×10−5 s−1. The resultant monitored (axial) loading and relaxation illustrates how the presence of a visco-elastic fluid (magma) controls the stress induced at the conduit margin boundary. This is achieved by analysing the viscoelastic relaxation (through time) to calculate an apparent modulus, which is found to decrease with both increasing temperature and time. In the 4 cycles before failure we find that the apparent modulus decreases from 180 to 40 GPa, 80 to 20 GPa and 8 to 1 GPa for imposed stress cycles at 828 °C, 892 °C and 918 °C, respectively. We theoretically estimate a tensile strength at failure of approximately 7–11 MPa, consistent with recent field data and in agreement with a model derived from the sample geometry and basic material parameters. Post-experimental neutron computed tomography and microscopic analyses further reveal the fragmentation of the melt and generation of tuffisite veins inside the conduit due to spontaneous crack nucleation associated with conduit wall fracture. The geometry of the rupture area inside the melt is akin to a Mach cone associated with supershear fractures. We discuss our findings in terms of magma-rock interaction leading to dykes, tuffisite veins and magma fragmentation.

Information relating to the fracture toughness of geomaterials is critical to our understanding of tensile fracturing, and in particular in geological and rock engineering projects that are subjected to elevated moisture levels. In this study, we conducted a comprehensive set of fracture toughness tests on a suite of key rock types in air under different relative humidities and at constant temperature in order to investigate the influence of relative humidity on fracture toughness. Three sandstones and two igneous rocks were chosen for this purpose. We show that the value of fracture toughness decreases with increasing relative humidity. In addition, we find that the decrease in fracture toughness was more significant when the expansive clay such as smectite was included in rock. Since smectite is prone to expanding in the presence of water, the strength and thus crack growth resistance decrease when relative humidity is high. Therefore, we interpret the decreasing fracture toughness upon the degradation of expansive clays with increasing water content. It was also shown that the decrease of the fracture toughness with increasing humidity is less significant than the concomitant decrease in the measured value of the subcritical stress intensity factor. This was likely as a result of stress corrosion having little influence on the fracture toughness. We conclude that crack growth in rock is affected by humidity, and that clay content is an important contributing factor to changes in fracture toughness and subcritical stress intensity factor.