Closure Measurements Research Articles

Baseline Intraoperative Left Ventricular Diastolic Function Is Associated with Postoperative Atrial Fibrillation after Cardiac Surgery.

Detailed understanding of the association between intraoperative left atrial and left ventricular diastolic function and postoperative atrial fibrillation is lacking. In this post hoc analysis of the Posterior Left Pericardiotomy for the Prevention of Atrial Fibrillation after Cardiac Surgery (PALACS) trial, we aimed to evaluate the association of intraoperative left atrial and left ventricular diastolic function as assessed by transesophageal echocardiography (TEE) with postoperative atrial fibrillation. PALACS patients with available intraoperative TEE data (n = 402 of 420; 95.7%) were included in this cohort study. We tested the hypotheses that preoperative left atrial size and function, left ventricular diastolic function, and their intraoperative changes were associated with postoperative atrial fibrillation. Normal left ventricular diastolic function was graded as 0 and with lateral e' velocity 10 cm/s or greater. Diastolic dysfunction was defined as lateral e' less than 10 cm/s using E/e' cutoffs of grade 1, E/e' 8 or less; grade, 2 E/e' 9 to 12; and grade 3, E/e' 13 or greater, along with two criteria based on mitral inflow and pulmonary wave flow velocities. A total of 230 of 402 patients (57.2%) had intraoperative diastolic dysfunction. Posterior pericardiotomy intervention was not significantly different between the two groups. A total of 99 of 402 patients (24.6%) developed postoperative atrial fibrillation. Patients who developed postoperative atrial fibrillation more frequently had abnormal left ventricular diastolic function compared to patients who did not develop postoperative atrial fibrillation (75.0% [n = 161 of 303] vs. 57.5% [n = 69 of 99]; P = 0.004). Of the left atrial size and function parameters, only delta left atrial area, defined as presternotomy minus post-chest closure measurement, was significantly different in the no postoperative atrial fibrillation versus postoperative atrial fibrillation groups on univariate analysis (-2.1 cm2 [interquartile range, -5.1 to 1.0] vs. 0.1 [interquartile range, -4.0 to 4.8]; P = 0.028). At multivariable analysis, baseline abnormal left ventricular diastolic function (odds ratio, 2.02; 95% CI, 1.15 to 3.63; P = 0.016) and pericardiotomy intervention (odds ratio, 0.46; 95% CI, 0.27 to 0.78, P = 0.004) were the only covariates independently associated with postoperative atrial fibrillation. Baseline preoperative left ventricular diastolic dysfunction on TEE, not left atrial size or function, is independently associated with postoperative atrial fibrillation. Further studies are needed to test if interventions aimed at optimizing intraoperative left ventricular diastolic function during cardiac surgery may reduce the risk of postoperative atrial fibrillation.

Bi-layered nanofibers loaded with pomegranate flowers extract as a novel wound dressing: Fabrication, characterization, and in vivo healing promotion

Prolonged and impaired wound healing is a serious complication, and there is an emerging demand for strategies to overcome this problem. In this study, we developed electrospun bilayer nanofibers consisting of a chitosan/PVA active layer loaded with pomegranate flower extract (PFE) and a PCL inactive back layer. Structural, morphological, and physicochemical properties of nanofibers were characterized and wound healing effects of PFE-loaded nanofibers were assessed by in vitro and in vivo experiments, including antibacterial tests, wound closure measurements, and histological and immunohistochemical (IHC) analyses. Nanofibers with optimum formulation showed good hydrophilicity, a mean diameter of 404 nm, and an average roughness of 217 nm. TGA and FTIR studies exhibited typical absorption characteristics of PFE, PCL, and PVA and the compatibility of PFE with the components of bilayer nanofibers. The cumulative amount of PFE released from the monolayer and bilayer fibers after 6 h was measured to be 100% and 64%, respectively, indicating the more sustained release of PFE from bilayer scaffolds. Based on mechanical studies, a more ductile behavior was observed for bilayer fibers than monolayer fibers. The antibacterial assay for PFE-loaded nanofibers exhibited an inhibition zone with a diameter of 19.0 ± 0.5 mm and 15.8 ± 0.3 mm for S. aureus and P. aeruginosa, respectively. PFE-loaded nanofiber exposure contributed to faster wound closure (88% in 14 days) and a significant rise in the expression of α-SMA, CD31, collagen I, and vimentin, indicating a higher tissue regeneration rate for PFE-loaded nanofibers over other treatment groups. In conclusion, bilayer nanofibers containing PFE have a promising potential for wound healing acceleration.

Robust Loop Closure Selection Based on Inter-Robot and Intra-Robot Consistency for Multi-Robot Map Fusion

In multi-robot simultaneous localization and mapping (SLAM) systems, the system must create a consistent global map with multiple local maps and loop closures between robot poses. However, false-positive loop closures caused by perceptual aliasing can severely distort the global map, especially in GNSS-denied areas, where a good prior of relative poses between robots is unavailable. In addition, the performance of the consistency metric in existing map fusion methods relies on accurate odometry from each robot. However, in practice, cumulative noise is inevitably present in robot trajectories, which leads to poor map fusion with existing methods. Thus, in this paper, we propose a robust consistency-based inter-robot and intra-robot loop closure selection algorithm for map fusion. We consider both pairwise-loop consistency and loop-odometry consistency to improve robustness against false-positive loop closures and accumulative noise in the odometry. Specifically, we select a reliable inter-robot loop closure measurement with a consistency-based strategy to provide an initial prior of relative pose between two robot trajectories and update the pose variables of the robot trajectories. The loop closure selection problem is formulated as a maximum edge weight clique problem in graph theory. A performance evaluation of the proposed method was conducted on the ManhattanOlson3500, modified CSAIL and Bicocca datasets, and the experimental results demonstrate that the proposed method outperforms the pairwise consistency measurement set maximization method (PCM) under severe accumulative noise and can be integrated with M-estimation methods.

Tubomanometry in measurement of velopharyngeal closure: A pilot study.

To investigate the differences in velum closure pattern in people with and without a history of middle ear disease using intranasal pressure curves recorded with the tubomanometer, a Eustachian tube (ET) testing device. Case control study. Tertiary referral center. Tubomanometry nasopharyngeal pressure curves from 20 controls (Group 1) and 20 people with history of otitis media (OM) and possible ongoing ET dysfunction (ETD) (Group 2 or OM/ETD group) were compared. The variables included in the analysis were: (a) ratio of signal amplitude relative to the delivered nasal pressure (C2/delivered pressure x10); (b) time (s) to achieve maximal signal amplitude (C2-C1); (c) duration of velum closure (s) and (d) plateau decay during the isometric contraction of the velum (C3-C2) and (e) swallow duration (s) (C4-C1). Statistical analysis was conducted using mixed models for the normalized values of individual characteristics. Age, race and sex distribution in each group was as follows: 24 ± 8 years, 15 whites and 12 females in Group 1; 20 ± 10 years, 19 whites and 15 females in Group 2. Group 2 demonstrated a greater velopharyngeal pressure decay (p= .13), longer swallow duration (p= .10), and longer duration of velum closure (p= .14). This is the first study using tubomanometry to investigate differences in velopharyngeal closure between controls and individuals with OM/ETD. Although not statistically significant, our results showed that those with OM/ETD demonstrated a longer swallow and velum closure duration, and a higher degree of leakage during velum contraction compared to controls.

Cycle-by-cycle crack closure measurements and fatigue crack growth in CT specimen made of 7075-T7351 aluminium

In this study, an advanced piezoelectric strain sensor is applied to measure the crack opening loads of a compact tension specimen with a fatigue crack under variable amplitude block loading. The crack opening loads are subsequently utilised to modify the stress intensity factor range by taking into account the proportion of each load cycle for which the fatigue crack remained closed. This effective stress intensity factor is applied to collapse the growth rate curve, which initially displays a strong dependence on stress ratio, into a single master curve where the only variable governing crack extension is the effective stress intensity factor. The findings of this study provide strong evidence for the crack closure concept, which is important for the development of algorithms which can compress/truncate large spectrums. These algorithms rely on a detailed understanding of how much the crack is open or closed during each load cycle. Furthermore, the results indicate that the piezoelectric sensor could be used to study crack closure under realistic spectrum loading conditions, which will be the subject of future investigations.

Application of an advanced piezoelectric strain sensor for crack closure measurement

It is well known that fatigue crack growth in airframe structures is governed by sequence effects in aircraft load spectrums, which typically include millions of load cycles of varying amplitude. In predicting the fatigue life of airframe structures, one advanced method used to account for these effects considers the concept of crack closure. This concept requires the measurement or prediction of the load required to open the crack tip, otherwise known as the crack opening load. However, traditional methods used to directly measure the level of crack closure for each cycle tend to be prohibitive for large load sequences. This is mainly due to sensor limitations and large scatter using traditional measurement techniques. The current study proposes a new piezoelectric strain sensor for detection of the crack opening load to addresses these issues. In this work, a comparison is conducted using three sensors on a compact fatigue test specimen: an extensometer (clip gauge), a conventional back face strain gauge, and the piezoelectric strain sensor. It is shown that the piezoelectric strain sensor exhibits far superior performance in measuring the crack opening load relative to the back face strain gauge and the extensometer. At minimum, for all cases considered the piezoelectric strain sensor displayed 100% or better reduction in measurement scatter than the next best sensing method considered. In some cases where the stress ratio is high and the crack length is small, the improvement seen using the piezoelectric strain sensor approached 200%. Crack tip opening loads were detected in almost all cycles across a wide range of crack sizes and load ratios; while the efficiency of the traditional sensors reduced significantly for relatively short cracks and high load ratios. The outcomes of this work will help to better understand the load sequence effects on crack growth rates, improve fatigue life predictive methods and develop effective procedures of truncation/compression of load spectrums for accelerated testing of aircraft components.

Efficient Bayesian inference for mechanistic modelling with high-throughput data.

Bayesian methods are routinely used to combine experimental data with detailed mathematical models to obtain insights into physical phenomena. However, the computational cost of Bayesian computation with detailed models has been a notorious problem. Moreover, while high-throughput data presents opportunities to calibrate sophisticated models, comparing large amounts of data with model simulations quickly becomes computationally prohibitive. Inspired by the method of Stochastic Gradient Descent, we propose a minibatch approach to approximate Bayesian computation. Through a case study of a high-throughput imaging scratch assay experiment, we show that reliable inference can be performed at a fraction of the computational cost of a traditional Bayesian inference scheme. By applying a detailed mathematical model of single cell motility, proliferation and death to a data set of 118 gene knockdowns, we characterise functional subgroups of gene knockdowns, each displaying its own typical combination of local cell density-dependent and -independent motility and proliferation patterns. By comparing these patterns to experimental measurements of cell counts and wound closure, we find that density-dependent interactions play a crucial role in the process of wound healing.

Tunnel support practice in small hydropower tunnels in the Himalayas through observational approach

With the high mountains, steep terrain and fast flowing river, the Himalayan region has a great opportunity and potential for hydropower development. In Nepal, many hydropower projects have been constructed and many are under construction among which majority of the project are small to medium scale project. For such project, medium size tunnel provides an economic and safe route for water convergence. Squeezing and collapse have been observed in most of the hydropower tunnels, which have resulted in support failure, as the tunnel passes through weak rock mass under high in-situ stress during construction. Due to insufficient tunnel closure measurements, field-based observation has been conducted to study the installed support at different tunnels in the Himalayas. The observational approach is used for analysis and recommendations have been made for designing a stable and safe support system for tunnels. Through an analysis of a case study from Nepal, comparison has been made on the design and practiced support systems, and description of supports used in various case histories from Nepal have been provided.

A reinvestigation into Munson’s model for room closure in bedded rock salt

Accurate predictions of room closure are important for hazardous waste repositories in rock salt formations, such as the Waste Isolation Pilot Plant (WIPP). When Munson and co-workers simulated several room closure experiments conducted at the WIPP during the 1980’s and 1990’s, their simulated closure curves closely agreed with the closure measurements. A careful review of their work, however, raised concerns and prompted the reinvestigation in this paper. To begin the reinvestigation, Munson’s legacy Room D closure simulation was reasonably recreated in a current-day finite element code. Next, special care was taken to obtain numerically converged results, re-introduce the anhydrite strata intermittently ignored by Munson, and calibrate the Munson–Dawson (M–D) constitutive model for salt as much as possible from laboratory test measurements. When this new model was used to simulate Room D’s closure, it under-predicted the horizontal and vertical closure rates by 2 . 34 × and 3 . 10 × , respectively, at 5.7 years after room excavation. As a result, the M–D model was extended to capture the newly established creep behavior at low equivalent stresses ( < 8 MPa ) and replace the Tresca with the Hosford equivalent stress. Simulations using the new M–D model over-predicted the horizontal closure rate by 1 . 15 × and under-predicted the vertical closure rate by 1 . 08 × at 5.7 years, averaged over three room closure experiments. Although further improvements could be made, the new model has a stronger scientific foundation than Munson’s legacy model and appears ready for careful engineering use.

Measuring crack growth and related opening and closing stresses using continuous potential drop recording

To improve resolution of in-situ measurement of crack closure and opening in fatigue, potential drop (PD) measurement technique has been further developed to measure thousands of times through each load cycle with high precision. The results are interpreted with physical phenomena like strain, Poisson’s effect, piezo-resistivity, plasticity, and crack growth. Application of the technique to fatigue crack growth tests on aluminum 2024-T3 CCT specimens at different maximum stresses and stress ratios, demonstrate that indeed variations in PD can be associated to development of plasticity and crack opening and closure. Hence, the technique allows to measure timing and magnitude of crack opening and closure stresses in-situ in fatigue crack growth experiments.

Salivary VEGF and post-extraction wound healing in type 2 diabetic immediate denture wearers

Objective Oral wound healing in healthy could be promoted by VEGF in saliva, and immediate denture wearing, but data in type 2 diabetes are lacking. Aims were to investigate the timeline of extraction wound healing in diabetic participants wearing immediate dentures and its correlation to salivary VEGF, as well as to examine the impact of the palatal plate on tissue VEGF during palatal wound healing in rat diabetic model. Material and methods Healthy (42) and type 2 diabetic (36) denture wearers, candidates for teeth extractions were included. Extraction wound healing was followed via measurements of socket closure, gingival hyperaemia, pain and presence of necrosis on 3rd, 7th, 14th and on 21st-day post-extraction. Salivary VEGF was measured before and on the 3rd and 21st day after the extraction. In streptozotocin-induced diabetic (30) as well as non-diabetic rats (30), tissue VEGF was measured in palatal wounds healing under or without a palatal plate. Results Type 2 diabetic prosthetic patients exhibit delayed socket closure, with pronounced hyperaemia, pain and necrosis. Salivary VEGF is increased in diabetes and positively correlates to socket closure while negatively with pain on 21st day after the extraction. Palatal incision induced VEGF increase in non-diabetic and diabetic, but less pronounced in diabetic rats. Wound healing under the palatal plate exhibit higher tissue VEGF. Conclusion Type 2 diabetes-induced increase in salivary VEGF may mitigate diabetes-induced detrimental effects on extraction wound healing. Lack of adequate tissue VEGF response to injury may underly dysregulation of diabetic oral wound healing.

Effect of Underload Cycles on Oxide-Induced Crack Closure Development in Cr-Mo Low-Alloy Steel

Underload cycles with small load amplitudes below the fatigue crack growth threshold are dominantly considered as insignificant cycles without any influence on fatigue lifespan of engineering structural components. However, this paper shows that in some cases these underload cycles can retard the consequent crack propagation quite significantly. This phenomenon is a consequence of oxide-induced crack closure development during cyclic loading below the threshold. The experimentally described effect of fatigue crack growth retardation was supported by measurement of the width and the thickness of the oxide debris layer using the EDS technique and localized FIB cuts, respectively. Both the retardation effect and the amount of oxide debris were larger for higher number and larger amplitudes of the applied underload cycles. Crack closure measurement revealed a gradual increase of the closure level during underload cycling. Specimens tested in low air humidity, as well as specimens left with the crack open for the same time as that needed for application of the underload cycles, revealed no retardation effect. The results can improve our understanding of environmental effects on fatigue crack propagation and understanding the differences between the results of laboratory testing and the fatigue lives of components in service.

WNT signalling in the normal human adult testis and in male germ cell neoplasms.

Is WNT signalling functional in normal and/or neoplastic human male germ cells? Regulated WNT signalling component synthesis in human testes indicates that WNT pathway function changes during normal spermatogenesis and is active in testicular germ cell tumours (TGCTs), and that WNT pathway blockade may restrict seminoma growth and migration. Regulated WNT signalling governs many developmental processes, including those affecting male fertility during early germ cell development at embryonic and adult (spermatogonial) ages in mice. In addition, although many cancers arise from WNT signalling alterations, the functional relevance and WNT pathway components in TGCT, including germ cell neoplasia in situ (GCNIS), are unknown. The cellular distribution of transcripts and proteins in WNT signalling pathways was assessed in fixed human testis sections with normal spermatogenesis, GCNIS and seminoma (2-16 individuals per condition). Short-term (1-7 h) ligand activation and long-term (1-5 days) functional outcomes were examined using the well-characterised seminoma cell line, TCam-2. Pathway inhibition used siRNA or chemical exposures over 5 days to assess survival and migration. The cellular localisation of WNT signalling components was determined using in situ hybridisation and immunohistochemistry on Bouin's- and formalin-fixed human testis sections with complete spermatogenesis or germ cell neoplasia, and was also assessed in TCam-2 cells. Pathway function tests included exposure of TCam-2 cells to ligands, small molecules and siRNAs. Outcomes were measured by monitoring beta-catenin (CTNNB1) intracellular localisation, cell counting and gap closure measurements. Detection of nuclear-localised beta-catenin (CTNNB1), and key WNT signalling components (including WNT3A, AXIN2, TCF7L1 and TCF7L2) indicate dynamic and cell-specific pathway activity in the adult human testis. Their presence in germ cell neoplasia and functional analyses in TCam-2 cells indicate roles for active canonical WNT signalling in TGCT relating to viability and migration. All data were analysed to determine statistical significance. No large-scale datasets were generated in this study. As TGCTs are rare and morphologically heterogeneous, functional studies in primary cancer cells were not performed. Functional analysis was performed with the only well-characterised, widely accepted seminoma-derived cell line. This study demonstrated the potential sites and involvement of the WNT pathway in human spermatogenesis, revealing similarities with murine testis that suggest the potential for functional conservation during normal spermatogenesis. Evidence that inhibition of canonical WNT signalling leads to loss of viability and migratory activity in seminoma cells suggests that potential treatments using small molecule or siRNA inhibitors may be suitable for patients with metastatic TGCTs. This study was funded by National Health and Medical Research Council of Australia (Project ID 1011340 to K.L.L. and H.E.A., and Fellowship ID 1079646 to K.L.L.) and supported by the Victorian Government's Operational Infrastructure Support Program. None of the authors have any competing interests.

Carbon stock assessment using forest canopy density mapper in agroforestry land in Berau, East Kalimantan, Indonesia

Abstract. Hartoyo APP, Prasetyo LB, Siregar IZ, Supriyanto, Theilade I, Siregar UJ. 2019. Carbon stock assessment using forest canopy density mapper in agroforestry land in Berau, East Kalimantan, Indonesia. Biodiversitas 20: 2661-2676. In the Reducing Emissions from Deforestation and forest Degradation (REDD+) program, remote sensing is the most important tool for measuring forest cover and carbon dynamic, including the utilization of software Forest Canopy Density (FCD) mapper. However, there have been rarely untested the accuracy of FCD applied in agroforestry landscapes to support carbon stock assessment compared to conventional field measurement data. This research was aimed to investigate the correlation between: (i) the value of FCD (%) and tree stand density (N/ha), (ii) the value of FCD (%) and basal area (m2/ha), (iii) the value of FCD (%) and total carbon stock (Mg C/ha), and iv) total carbon stock and percentage of canopy closure (%). Tree stand density, basal area, carbon stock and canopy profile were conventionally measured by trained members of local communities. The results of this study showed that the R2 between FCD and tree density was 37.7% (r = 61.4%), while the R2 between FCD and the basal area was 3.33% (r = 18.3%). The result of normality and heteroscedasticity tests showed that FCD was more accurate and precise in estimating the tree stand density model than the basal area model. Total carbon stock differed significantly (p&lt;0.1) from tree density with R2 = 27.7% (r = 27.3%). Total carbon can be predicted using FCD with total carbon (Mg C/ha) = 13.005 + 0.826 FCD. Our findings suggest that FCD can be used as a new method to estimate tree density and total carbon stock cheaply, efficiently and accurately to support carbon stock assessment in agroforest practices. In carbon assessment, total carbon stock can also be estimated using canopy closure measurement.

Self-Calibration and Verification of Phase Angle Errors of Two Voltage Dividers at High Frequencies

A set of cascaded inductive voltage dividers (IVDs) with a ratio of $2^{n}$ :1 and resistive voltage dividers (RVDs) with serial–parallel connection structure is presented in this paper. The IVD with the ratio of $2^{n}$ :1 is built with a $2^{n-1}$ :1 IVD and a binary IVD connected in the cascade structure. The phase angle errors of the IVDs are calibrated in a step-up procedure by using the three BIVDs in cascade connection as the reference standard. The phase angle errors of the RVDs can also be self-calibrated. The self-calibration results and uncertainties of phase angle errors of the IVDs and RVDs have been both given at frequencies up to 100 kHz. A closure measurement between the IVD with the ratio of 256:1 and the RVD with the ratio of 257:1 has also been done at frequencies from 25 to 100 kHz. The closure results show good agreement within 15 $\mu $ rad compared to the self-calibration results.

Identification of Relationships between Heat Treatment and Fatigue Crack Growth of αβ Titanium Alloys

This study deals with the influence of microstructure on the fatigue crack growth resistance of αβ titanium alloys: Ti-6Al-4V ELI (Extra Low Interstitial) that may compete with the conventional Ti-6Al-4V alloy in the manufacture of high performance aircraft. Six different microstructures have been considered: the as-received bimodal microstructures and five distinct fully lamellar microstructures. The characteristic parameters of these microstructures were determined and crack growth tests were performed with crack closure measurements in order to evaluate the shielding effect induced by closure. A comparison of crack growth rates, fracture surfaces, and crack path was carried out for the different microstructures. The results outline a transition between two propagation regimes from a microstructure-sensitive to microstructure-insensitive propagation.

Analysis Quality Determines Value of Diagnostic Fracture Injection Tests

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 191458, “Good Tests Cost Money, Bad Tests Cost More: A Critical Review of DFIT and Analysis Gone Wrong,” by R.V. Hawkes, SPE, Trican Well Service; R. Bachman, SPE, CGG; K. Nicholson, Perpetual Energy; D.D. Cramer, SPE, ConocoPhillips; and S.T. Chipperfield, SPE, Santos, prepared for the 2018 SPE International Hydraulic Fracturing Technology Conference and Exhibition, Muscat, Oman, 16–18 October. The paper has not been peer reviewed. Diagnostic fracture injection tests (DFITs) incur direct and indirect costs resulting from the tests themselves and the extended time required for the pressure falloff, which delays the completion of the well. The benefits, therefore, must outweigh the costs if the test is to be justified. These tests are performed regularly around the world because a DFIT is one of only a few processes that can help quantify both geomechanical properties and reservoir-performance drivers within the same test. Introduction Operators and service providers commonly experience problems with DFIT execution and analysis despite efforts to reduce errors and inconsistencies. Before any field execution or analysis, the objectives of a DFIT must be considered. Historically, DFITs were performed predominantly for the purpose of designing better full-scale hydraulic-fracture treatments with early-time measurements of initial shut-in pressure, leakoff coefficient, and fracture closure having priority over reservoir parameters such as permeability and pore pressure. Increasingly, practitioners are using DFITs to measure reservoir parameters such as initial pressure and permeability. While, in many cases, these parameters may be obtained from a single successful test, other situations have time constraints or rock and reservoir properties that constrain operations to a point where priorities must be set. While leakoff and closure values are determined early in the DFIT shut-in period, reservoir pressure and permeability are derived from late-time measurements that may require longer falloff times. The complete paper presents cases encountered in which test procedures/operations or incorrect analysis misled engineers. Cases presented are Several Canadian Duvernay shale wells illustrating the importance of multiple tests and the use of gradients to understand fracture orientation and possible complexity. A well where the initial DFIT had an injection rate that was too low combined with operational issues. A second test on the same interval yielded better results. A Canadian Montney well where rock/fluid interactions led to a false radial-flow signature. Two subnormally pressured Canadian oil wells where surface falloff pressure dropped to a vacuum (i.e., falling liquid level), causing late-time effects that were not reservoir related. The authors present a work flow to determine reservoir pressure in this situation. An Australian naturally fractured gas well showing the importance of sufficient falloff time. A proper DFIT may be critical for assessing the geomechanical and reservoir properties of unconventional reservoirs. However, simple guidelines such as wellbore conditioning, the understanding of pressure anomalies resulting from wells going on vacuum, and the importance of flow-regime identification are often overlooked, leading to poor results. Having access to numerous high-quality data sets from various international oil and gas operators provides insight to establishing some useful guidelines that are applicable anywhere in the world.

Synthesis of mechanically strong waterborne poly(urethane-urea)s capable of self-healing at elevated temperatures

Although various chemistries have been introduced into polyurethanes in order to obtain self-healing abilities, implementing these materials in applications requiring high strength is challenging as strong materials imply a limited molecular motion, but without movement of polymer chains self-healing is not possible. Here, waterborne poly(urethane-urea)s (PU(U)s) based on aromatic disulfide compounds are developed which balance these contradictory requirements by presenting good mechanical properties at room temperature, while showing the mobility necessary for healing when moderately heated. The influence of hard monomers on the stability and mobility of the materials is investigated by scratch closure, cut healing and rheological measurements, so that the limits of the readily available aromatic disulfide compounds, bis(4-aminophenyl)- and bis(4-hydroxyphenyl)disulfide, can be determined. Subsequently, a modified aromatic disulfide compound, bis[4-(3′-hydroxypropoxy)phenyl]disulfide, with increased reactivity, solubility and flexibility is synthesized and incorporated into the PU backbone, so that materials with more attractive mechanical properties, reaching ultimate tensile strengths up to 23 MPa, and self-healing abilities at elevated temperatures could be obtained.

Comparison of closure measurements with finite element model results in an underground coal mine in central Utah

Quantitative analysis of mine-wide subsidence at the kilometer scale and details of stress distribution about an advancing longwall face are estimated using an adaptation of the finite element method. The method is well suited to the tasks at hand. For greater realism, variability of strata properties is taken into account as are the effects of joints and cleats on elastic moduli and strengths. Evolution of pillar stress and entry closure remote from the face is readily quantified in a series of analyses that simulate face advance. Computed results compare favorably with the evolution of closure measurements about an instrumented pillar in a two-entry headgate. The appropriateness of the finite element method is confirmed. This method is based on first principles that avoid empirical schemes of uncertain applicability and numerical models “calibrated” by fitting computer output to mine measurements.

A comparison of DIC-based techniques to measure crack closure in LCF

Crack closure is one of the most important phenomenon for the comprehension of fatigue behavior of metallic alloys. The effect of mean stress, overloads and variable amplitude loadings can be predicted modeling the crack closure in terms of opening and closing stress levels. Experimentally, the characterization of the crack closure in high and low cycle fatigue has gained large attention in the last fifty years. In fact, the proper detection of the opening and closing levels enhances the definition of a proper crack driving force and its modeling. This work primarily focuses on the measurement of the opening and closing stresses for cracks propagating in low cycle fatigue conditions. High-resolution full-field digital image correlation technique was adopted to track the crack profiles during cyclic loading and different approaches were adopted to analyze the displacement fields extracted with the virtual extensometers. The closure measurements were performed for three metallic alloys, different strain ranges (from elastic to dominant-plastic behaviors) and strain ratio to enlarge the field of applicability of the techniques presented.