bluuebunny/crossref_metadata_2025 huggingface dataset:
Teacher and peer relationships and life satisfaction: Mediating the role of student resilience in south korean elementary schools
Authors: Lee Minyoung , Lee Sang Min
Published: November 2020

The purpose of this study was to examine the association between life satisfaction and positive student-teacher and peer relationships. Further, we aimed to test the mediating effects of student resilience in a multilevel model. The data were collected from elementary students in South Korea. To examine the mediating effects of student resilience, multilevel structural equation modelling was conducted. The results indicated that schools with positive student-teacher relationships correlated with higher life satisfaction for children. This relationship was fully mediated by student resilience. However, the mediating effects of student resilience in the relationship between peer relationships and life satisfaction was found to be at the individual level rather than by school climate. Practical implications on ways to improve students’ life satisfaction within the school and classroom settings are discussed.
On the Use of Two-Way Fixed Effects Regression Models for Causal Inference with Panel Data
Authors: Imai Kosuke , Kim In Song
Published: November 2020

The two-way linear fixed effects regression (2FE) has become a default method for estimating causal effects from panel data. Many applied researchers use the 2FE estimator to adjust for unobserved unit-specific and time-specific confounders at the same time. Unfortunately, we demonstrate that the ability of the 2FE model to simultaneously adjust for these two types of unobserved confounders critically relies upon the assumption of linear additive effects. Another common justification for the use of the 2FE estimator is based on its equivalence to the difference-in-differences estimator under the simplest setting with two groups and two time periods. We show that this equivalence does not hold under more general settings commonly encountered in applied research. Instead, we prove that the multi-period difference-in-differences estimator is equivalent to the weighted 2FE estimator with some observations having negative weights. These analytical results imply that in contrast to the popular belief, the 2FE estimator does not represent a design-based, nonparametric estimation strategy for causal inference. Instead, its validity fundamentally rests on the modeling assumptions.
The Forgotten Child of the Wider Corded Ware Family: Russian Fatyanovo Culture in Context
Authors: Nordqvist Kerkko , Heyd Volker
Published: November 2020

The Fatyanovo Culture, together with its eastern twin, the Balanovo Culture, forms part of the pan-European Corded Ware Complex. Within that complex, it represents its eastern expansion to the catchment of the Upper and Middle Volga River in the European part of Russia. Its immediate roots are to be found in the southern Baltic States, Belarus, and northern Ukraine (the Baltic and Middle-Dnepr Corded Ware Cultures), from where moving people spread the culture further east along the river valleys of the forested flatlands. By doing so, they introduced animal husbandry to these regions. Fatyanovo Culture is predominately recognised through its material culture imbedded in its mortuary practices. Most aspects of every-day life remain unknown. The lack of an adequate absolute chronological framework has thus far prevented the verification of its internal cultural dynamics while overall interaction proposed also on typo-stratigraphical grounds suggests a contemporaneity with other representations of the Corded Ware Complex in Europe. Fatyanovo Culture is formed by the reverse movement to the (north-)east of the Corded Ware Complex, itself established in the aftermath of the westbound spread of Yamnaya populations from the steppes. It thus represents an important link between west and east, pastoralists and last hunter-gatherers, and the 3rd and the 2nd millenniabc. Through its descendants (including Abashevo, Sintashta, and Andronovo Cultures) it becomes a key component in the development of the wider cultural landscape of Bronze Age Eurasia.
Longitudinal and Interhemispheric Ionospheric Response to 2009 and 2013 SSW Events in the African‐European and Indian‐East Asian Sectors
Authors: Kakoti Geetashree , Kalita Bitap Raj , Bhuyan P. K. , Baruah S. , Wang K.
Published: November 2020

The ionospheric response to two sudden stratospheric warming (SSW) events that occurred during low (2009) and moderate solar activity (2013) around 10°E (±10°) African‐European and 95°E (±10°) Indian‐East Asian sectors is investigated. The total electron content (TEC) obtained from a meridional chain of stations in the two sectors are used to understand the interlongitudinal and interhemispheric response to these SSW events. Significant depletion of daytime TEC was observed after the onset of 2009 SSW around the equatorial ionization anomaly (EIA) crest followed by an increase during the decaying phase of SSW. The formation of an early peak in the daytime TEC and semidiurnal variation in the response of TEC in the form of morning enhancement and afternoon depletion was observed at low latitudes. The morning enhancement is prominent at northern low latitudes while afternoon depletion is more at southern low latitudes. The conspicuous TEC perturbations characterized by semidiurnal variation in mid‐January of 2013 override the sudden increase in solar activity after the onset of the SSW. SSW impacted semidiurnal perturbations in F2 layer peak electron density (NmF2) and height (hmF2) noticed at Cocos Island, the southern hemisphere low latitude station. Longitudinal and interhemispheric differences in the magnitude and evolution of TEC perturbations were noticed. The longitudinal differences in SSW modulation of TEC might be attributed to the differential impact of the nonmigrating tides and differences in the geomagnetic field elements between the two sectors. The meridional wind in the mesosphere and lower thermosphere region contribute to the TEC enhancement.
Particles and Aeration at Mire‐Stream Interfaces Cause Selective Removal and Modification of Dissolved Organic Matter
Authors: Einarsdóttir Karólína , Attermeyer Katrin , Hawkes Jeffrey A. , Kothawala Dolly , Sponseller Ryan A. , Tranvik Lars J.
Published: November 2020

Peatlands are dominant sources of dissolved organic matter (DOM) to boreal inland waters and play important roles in the aquatic carbon cycle. Yet before peat‐derived DOM enters aquatic networks, it needs to pass through peat‐stream interfaces that are often characterized by transitions from anoxic or hypoxic to oxic conditions. Aeration at these interfaces may trigger processes that impact the DOM pool, and its fate downstream. Here we experimentally assessed how the aeration of iron‐ and organic‐rich mire‐waters influences biodegradation, particle‐formation, and modification of DOM. In addition, we investigated how suspended peat‐derived particles from mires may influence these processes. We found that within 5 days of aeration, 20% of the DOM transformed into particulate organic matter (POM). This removal was likely due to combination of mechanisms including coprecipitation with oxidized iron, aggregation, and DOM‐adsorption onto peat‐derived particles. Peat‐derived particles promoted microbial activity, but biodegradation was a minor loss mechanism of DOM removal. Interestingly, microbial respiration accounted for only half of the oxygen loss, suggesting substantial nonrespiratory oxygen consumption. The differences observed in DOM characteristics between anoxic and aerated treatments suggest that hydrophilic, aromatic DOM coprecipitated with iron oxides in aerated samples, and the corresponding C:N analysis of generated POM revealed that these organic species were nitrogen‐poor. Meanwhile, POM formed via adsorption onto peat‐derived particles generated from nonaromatic DOM and more nitrogen‐rich species. Hence, selective removal of DOM, dissolved iron, and thus oxygen may be important and overlooked processes in mire‐dominated headwater systems.
Neuronal cell life, death, and axonal degeneration as regulated by the BCL-2 family proteins
Authors: Pemberton James M. , Pogmore Justin P. , Andrews David W.
Published: November 2020

Axonal degeneration and neuronal cell death are fundamental processes in development and contribute to the pathology of neurological disease in adults. Both processes are regulated by BCL-2 family proteins which orchestrate the permeabilization of the mitochondrial outer membrane (MOM). MOM permeabilization (MOMP) results in the activation of pro-apoptotic molecules that commit neurons to either die or degenerate. With the success of small-molecule inhibitors targeting anti-apoptotic BCL-2 proteins for the treatment of lymphoma, we can now envision the use of inhibitors of apoptosis with exquisite selectivity for BCL-2 family protein regulation of neuronal apoptosis in the treatment of nervous system disease. Critical to this development is deciphering which subset of proteins is required for neuronal apoptosis and axon degeneration, and how these two different outcomes are separately regulated. Moreover, noncanonical BCL-2 family protein functions unrelated to the regulation of MOMP, including impacting necroptosis and other modes of cell death may reveal additional potential targets and/or confounders. This review highlights our current understanding of BCL-2 family mediated neuronal cell death and axon degeneration, while identifying future research questions to be resolved to enable regulating neuronal survival pharmacologically.
Microalgae-blend tilapia feed eliminates fishmeal and fish oil, improves growth, and is cost viable
Authors: Sarker Pallab K. , Kapuscinski Anne R. , McKuin Brandi , Fitzgerald Devin S. , Nash Hannah M. , Greenwood Connor
Published: November 2020

Aquafeed manufacturers have reduced, but not fully eliminated, fishmeal and fish oil and are seeking cost competitive replacements. We combined two commercially available microalgae, to produce a high-performing fish-free feed for Nile tilapia (Oreochromis niloticus)—the world’s second largest group of farmed fish. We substituted protein-rich defatted biomass of Nannochloropsis oculata (leftover after oil extraction for nutraceuticals) for fishmeal and whole cells of docosahexaenoic acid (DHA)-rich Schizochytrium sp. as substitute for fish oil. We found significantly better (p < 0.05) growth, weight gain, specific growth rate, and best (but not significantly different) feed conversion ratio using the fish-free feed compared with the reference diet. Fish-free feed also yielded higher (p < 0.05) fillet lipid, DHA, and protein content (but not significantly different). Furthermore, fish-free feed had the highest degree of in-vitro protein hydrolysis and protein digestibility. The median economic conversion ratio of the fish-free feed ($0.95/kg tilapia) was less than the reference diet ($1.03/kg tilapia), though the median feed cost ($0.68/kg feed) was slightly greater than that of the reference feed ($0.64/kg feed) (p < 0.05). Our work is a step toward eliminating reliance on fishmeal and fish oil with evidence of a cost-competitive microalgae-based tilapia feed that improves growth metrics and the nutritional quality of farmed fish.
Red-COLA1: a human fibroblast reporter cell line for type I collagen transcription
Authors: Wong Hui Hui , Seet Sze Hwee , Bascom Charles C. , Isfort Robert J. , Bard Frederic
Published: November 2020

Type I collagen is a key protein of most connective tissue and its up-regulation is required for wound healing but is also involved in fibrosis. Control of expression of this collagen remains poorly understood apart from Transforming Growth Factor beta (TGF-β1)-mediated induction. To generate a sensitive, practical, robust, image-based high-throughput-compatible reporter system, we genetically inserted a short-lived fluorescence reporter downstream of the endogenous type I collagen (COL1A1) promoter in skin fibroblasts. Using a variety of controls, we demonstrate that the cell line faithfully reports changes in type I collagen expression with at least threefold enhanced sensitivity compared to endogenous collagen monitoring. We use this assay to test the potency of anti-fibrotic compounds and screen siRNAs for regulators of TGF-β1-induced type I collagen expression. We propose our reporter cell line, Red-COLA1, as a new efficient tool to study type I collagen transcriptional regulation.
Metric basis and metric dimension of 1-pentagonal carbon nanocone networks
Authors: Hussain Zafar , Munir Mobeen , Ahmad Ashfaq , Chaudhary Maqbool , Alam Khan Junaid , Ahmed Imtiaz
Published: November 2020

Resolving set and metric basis has become an integral part in combinatorial chemistry and molecular topology. It has a lot of applications in computer, chemistry, pharmacy and mathematical disciplines. A subset S of the vertex set V of a connected graph G resolves G if all vertices of G have different representations with respect to S. A metric basis for G is a resolving set having minimum cardinal number and this cardinal number is called the metric dimension of G. In present work, we find a metric basis and also metric dimension of 1-pentagonal carbon nanocones. We conclude that only three vertices are minimal requirement for the unique identification of all vertices in this network.
A natriuretic peptide from Arabidopsis thaliana (AtPNP-A) can modulate catalase 2 activity
Authors: Turek Ilona , Wheeler Janet , Bartels Sebastian , Szczurek Jolanta , Wang Yu Hua , Taylor Phil , Gehring Chris , Irving Helen
Published: November 2020

Analogues of vertebrate natriuretic peptides (NPs) present in plants, termed plant natriuretic peptides (PNPs), comprise a novel class of hormones that systemically affect salt and water balance and responses to plant pathogens. Several lines of evidence indicate that Arabidopsis thaliana PNP (AtPNP-A) affects cellular redox homeostasis, which is also typical for the signaling of its vertebrate analogues, but the molecular mechanism(s) of this effect remains elusive. Here we report identification of catalase 2 (CAT2), an antioxidant enzyme, as an interactor of AtPNP-A. The full-length AtPNP-A recombinant protein and the biologically active fragment of AtPNP-A bind specifically to CAT2 in surface plasmon resonance (SPR) analyses, while a biologically inactive scrambled peptide does not. In vivo bimolecular fluorescence complementation (BiFC) showed that CAT2 interacts with AtPNP-A in chloroplasts. Furthermore, CAT2 activity is lower in homozygous atpnp-a knockdown compared with wild type plants, and atpnp-a knockdown plants phenocopy CAT2-deficient plants in their sensitivity to elevated H2O2, which is consistent with a direct modulatory effect of the PNP on the activity of CAT2 and hence H2O2 homeostasis. Our work underlines the critical role of AtPNP-A in modulating the activity of CAT2 and highlights a mechanism of fine-tuning plant responses to adverse conditions by PNPs.
Artificial whole genome duplication in paleopolyploid sturgeons yields highest documented chromosome number in vertebrates
Authors: Lebeda Ievgen , Ráb Petr , Majtánová Zuzana , Flajšhans Martin
Published: November 2020

Critically endangered sturgeons, having undergone three whole genome duplication events, represent an exceptional example of ploidy plasticity in vertebrates. Three extant ploidy groups, combined with autopolyploidization, interspecific hybridization and the fertility of hybrids are important issues in sturgeon conservation and aquaculture. Here we demonstrate that the sturgeon genome can undergo numerous alterations of ploidy without severe physiological consequences, producing progeny with a range of ploidy levels and extremely high chromosome numbers. Artificial suppression of the first mitotic division alone, or in combination with suppression of the second meiotic division of functionally tetraploid zygotes (4n, C-value = 4.15) of Siberian sturgeon Acipenser baerii and Russian sturgeon A. gueldenstaedtii resulted in progeny of various ploidy levels—diploid/hexaploid (2n/6n) mosaics, hexaploid, octoploid juveniles (8n), and dodecaploid (12n) larvae. Counts between 477 to 520 chromosomes in octoploid juveniles of both sturgeons confirmed the modal chromosome numbers of parental species had been doubled. This exceeds the highest previously documented chromosome count among vertebrates 2n ~ 446 in the cyprinid fish Ptychobarbus dipogon.
Better continuity of care improves the quality of end-of-life care among elderly patients with end-stage renal disease
Authors: Chen Annie Y. , Chen Bradley , Kuo Chin-Chi
Published: November 2020

Continuity of care (COC) has been emphasized in research on terminal cancer patients to increase the quality of end-of-life care; however, limited research has been conducted on end-stage renal disease patients. We applied a retrospective cohort design on 29,095 elderly patients with end-stage renal disease who died between 2005 and 2013. These patients were identified from the National Health Insurance Research Database of Taiwan. The provider Continuity of Care Index (COCI) and site COCI were calculated on the basis of outpatient visits during the 6–12 months before death. We discovered that increases in the provider COCI were significantly associated with reductions in health expenditures after adjusting for confounders, especially in inpatient and emergency departments, where the treatment intensity is high. Higher provider and site COC were also associated with lower utilization of acute care and invasive treatments in the last month before death. Provider COC had a greater effect on end-of-life care expenditures than site COC did, which indicated significant care coordination gaps within the same facility. Our findings support the recommendation of prioritizing the continuity of end-of-life care, especially provider continuity, for patients with end-stage renal disease.
Identifying potential biomarkers related to pre-term delivery by proteomic analysis of amniotic fluid
Authors: Hong Subeen , Lee Ji Eun , Kim Yu Mi , Park Yehyon , Choi Ji-Woong , Park Kyo Hoon
Published: November 2020

We sought to identify biomarkers in the amniotic fluid (AF) and specific signaling pathways related to spontaneous preterm delivery (SPTD, < 34 weeks) in women with preterm labor (PTL) without intra-uterine infection/inflammation (IUI). This was a retrospective cohort study of a total of 139 PTL women with singleton gestation (24 + 0 to 32 + 6 weeks) who underwent amniocentesis and who displayed no evidence of IUI. A nested case–control was conducted using pooled AF samples (n = 20) analyzed via label-free liquid chromatography-tandem mass spectrometry. In the total cohort, an ELISA validation study was performed for seven candidate proteins of interest. Proteomic analysis identified 77 differentially expressed proteins (DEPs, P < 0.05) in the AF from SPTD cases compared to term delivery controls. ELISA validation confirmed that women who had an SPTD before 34 weeks had significantly independently lower levels of VEGFR-1 and higher levels of lipocalin-2 and the Fc fragment of IgG binding protein in the AF. Five principle pathways associated with the 77 DEPs were identified, including glycolysis, gluconeogenesis, and iron homeostasis. The proteomic analysis data of AFs from women with PTL identified several novel biomarkers and specific protein pathways related to SPTD in the absence of IUI.
Pressure-driven switching of magnetism in layered CrCl3
Authors: Ahmad Azkar Saeed , Liang Yongcheng , Dong Mingdong , Zhou Xuefeng , Fang Leiming , Xia Yuanhua , Dai Jianhong , Yan Xiaozhi , Yu Xiaohui , Dai Junfeng , Zhang Guo-jun , Zhang Wenqing , Zhao Yusheng , Wang Shanmin
Published: November 2020

Pressure-induced switching of magnetism from FM to AFM phase has been observed in layered CrCl3. Concurrently, pressure-induced isostructural transition accompanied with an unusual semiconductor-to-semiconductor transition has been reported.
Correction: Functionalized fluorescent terephthalate monomers and their attempted polyester formation
Authors: Choo Yvonne S. L. , Giamberini Marta , Reina José Antonio , Waddell Paul G. , Benniston Andrew C.
Published: November 2020

Correction for ‘Functionalized fluorescent terephthalate monomers and their attempted polyester formation’ by Yvonne S. L. Choo et al., Org. Biomol. Chem., 2020, 18, 8735–8745, DOI: 10.1039/D0OB01533D.
Transitions from One Electronic Health Record to Another: Challenges, Pitfalls, and Recommendations
Authors: Huang Chunya , Koppel Ross , McGreevey John D. , Craven Catherine K. , Schreiber Richard
Published: November 2020

Objective We address the challenges of transitioning from one electronic health record (EHR) to another—a near ubiquitous phenomenon in health care. We offer mitigating strategies to reduce unintended consequences, maximize patient safety, and enhance health care delivery.

Methods We searched PubMed and other sources to identify articles describing EHR-to-EHR transitions. We combined these references with the authors' extensive experience to construct a conceptual schema and to offer recommendations to facilitate transitions.

Results Our PubMed query retrieved 1,351 citations: 43 were relevant for full paper review and 18 met the inclusion criterion of focus on EHR-to-EHR transitions. An additional PubMed search yielded 1,014 citations, for which we reviewed 74 full papers and included 5. We supplemented with additional citations for a total of 70 cited. We distinguished 10 domains in the literature that overlap yet present unique and salient opportunities for successful transitions and for problem mitigation.

Discussion There is scant literature concerning EHR-to-EHR transitions. Identified challenges include financial burdens, personnel resources, patient safety threats from limited access to legacy records, data integrity during migration, cybersecurity, and semantic interoperability. Transition teams must overcome inadequate human infrastructure, technical challenges, security gaps, unrealistic providers' expectations, workflow changes, and insufficient training and support—all factors affecting potential clinician burnout.

Conclusion EHR transitions are remarkably expensive, laborious, personnel devouring, and time consuming. The paucity of references in comparison to the topic's salience reinforces the necessity for this type of review and analysis. Prudent planning may streamline EHR transitions and reduce expenses. Mitigating strategies, such as preservation of legacy data, managing expectations, and hiring short-term specialty consultants can overcome some of the greatest hurdles. A new medical subject headings (MeSH) term for EHR transitions would facilitate further research on this topic.
Subcategorization frame identification for learner English
Authors: Huang Yan , Murakami Akira , Alexopoulou Theodora , Korhonen Anna
Published: November 2020

As large-scale learner corpora become increasingly available, it is vital that natural language processing (NLP)
technology is developed to provide rich linguistic annotations necessary for second language (L2) research. We present a system for
automatically analyzing subcategorization frames (SCFs) for learner English. SCFs link lexis with morphosyntax, shedding light on the
interplay between lexical and structural information in learner language. Meanwhile, SCFs are crucial to the study of a wide range of
phenomena including individual verbs, verb classes and varying syntactic structures. To illustrate the usefulness of our system for learner
corpus research and second language acquisition (SLA), we investigate how L2 learners diversify their use of SCFs in text and how this
diversity changes with L2 proficiency.
Optimizing the electric field strength in multiple targets for multichannel transcranial electric stimulation
Authors: Saturnino Guilherme B , Madsen Kristoffer H , Thielscher Axel
Published: November 2020

Objective. Most approaches to optimize the electric field pattern generated by multichannel transcranial electric stimulation (TES) require the definition of a preferred direction of the electric field in the target region(s). However, this requires knowledge about how the neural effects depend on the field direction, which is not always available. Thus, it can be preferential to optimize the field strength in the target(s), irrespective of the field direction. However, this results in a more complex optimization problem. Approach. We introduce and validate a novel optimization algorithm that maximizes focality while controlling the electric field strength in the target to maintain a defined value. It obeys the safety constraints, allows limiting the number of active electrodes and allows also for multi-target optimization. Main results. The optimization algorithm outperformed naïve search approaches in both quality of the solution and computational efficiency. Using the amygdala as test case, we show that it allows for reaching a reasonable trade-off between focality and field strength in the target. In contrast, simply maximizing the field strength in the target results in far more extended fields. In addition, by maintaining the pre-defined field strengths in the targets, the new algorithm allows for a balanced stimulation of two or more regions. Significance. The novel algorithm can be used to automatically obtain individualized, optimal montages for targeting regions without the need to define preferential directions. It will automatically select the field direction that achieves the desired field strength in the target(s) with the most focal stimulation pattern.
Sensitivity analysis of factors influencing pillar stability in the deep stope of underground salt mine
Authors: Qin X S , Cao H , Guo L J
Published: November 2020

The orebody and the surrounding rock of underground salt mine are generally divided into soft rock or extremely soft rock. In these mines, the strip room pillar method is primarily used. Continuous pillars with a certain width are left between every two mining strips. These pillars are used to provide support to the overlying surrounding rock. However, the stability of the pillars restricts the stope structural parameters of the mining method. Thus, it is important to first determine the main factors that affect pillar stability and analyze the influence level of these factors. Using a deep mining underground salt mine as an example, the characteristics of pillar instability and the pillar load are analyzed. The safety factor of the pillar refers to the ratio of pillar strength to pillar load, which can be used to quantitatively evaluate pillar stability. Based on the formula of pillar stress and the empirical formula of pillar strength, the formula of the pillar safety factor is deduced. Based on this formula, the primary factors affecting pillar stability are comprehensively analyzed. Moreover, the sensitivities of these factors are compared and analyzed based on the orthogonal range theory. According to the calculation results of the range, the factors influencing pillar stability in the underground salt mine are the mining depth and uniaxial compressive strength of ore, which are the most significant factors, followed by the height and width of pillars, and then the room width and unit weight of the overlying strata, which have relatively small influence. The safety factor of the pillar is positively correlated with the pillar width and uniaxial compressive strength but negatively correlated with the mining depth, pillar height, room width, and the unit weight of the overlying strata. The specific reasons of each factor affecting the safety coefficient are analyzed in detail. The changing trend of the pillar safety factor with various influencing factors can provide an important basis for the optimal design of stope structural parameters and the determination of support scheme.
Cause Analysis and Treatment Measures of Tunnel Diseases in Complex Geological Structure with Gypsum-bearing Rock Layers
Authors: Song Chaoye , He Weiguo , Wang Hanchen , Wu Weihao
Published: November 2020

The length of NL Tunnel in North China is 23.4 km. The ballast bed of the tunnel is a heavy-haul and double-block, ballast-less track. After being completed and opened to traffic, serious diseases such as concrete corrosion, cracking of the lining, deformation of the side wall, and uplift of the track bed were observed. The cumulative length of the disease-carrying tunnel, ~1.4 km, negatively affects the safety of motorists. On-site investigation, theoretical analysis, experimental testing, and numerical calculations, revealed that tunnel diseases result from various factors. That is, owing to the complex geological structure, changes in the volume and quality of groundwater in the gypsum-bearing rock layer were accompanied by special low-temperature sulfate corrosion, rare differential expansion, and significant water-sensitive softening with rheological characteristics. These phenomena eventually resulted in tunnel diseases. Through stability analysis and field practice, an effective set of measures was adopted. These measures included a support structure system combined with near-circular cross sections and buffer layers, a new type of drainage system with special rock layers from inside to outside, and lining structural materials with low-temperature sulfate resistance.
A rock self-supporting high conductivity acid fracturing technique in a deep carbonate reservoir
Authors: Baoping Lu , Zhou Jun , Jiang Tingxue , Ding Shidong , Zhou Linbo , Deng Dawei , Zhou Jian
Published: November 2020

As carbonate reservoirs in deeper strata continue to develop, reservoir closure stress has significantly increased, where conventional acid fracturing technology cannot maintain acid-etched fracture conductivity and single well production rates are decreasing more quickly. This study proposes a rock self-supporting, highly conductive acid fracturing technique, where the shielding materials cover a portion of the primary hydraulic fracture surface to block the acid rock reaction. After acid injection, the unetched part will be a bearing surface, which serves as a large area and self-supporting high strength rock. This technique fundamentally changes the existing point support pattern of acid-etched fractures. Experimental results demonstrate that when the closed stress is <50 MPa, the self-supporting conductivity is 42% higher than the conventionally acid etched fractures. At 90 MPa closed stress, it can still maintain high support strength, which is more than eight times that of a conventional acid etched fracture. The equilibrium relationship between the fracture conductivity and rock support strength was determined using finite element stress simulation and fluid mechanics simulation. The results demonstrate that using a small cylindrical area, dislocation support, and multi-point support is conducive to the dispersion of high closure stress; moreover, the concentrated stress intensity of supporting rock can be reduced by 3–12 MPa. With decrease in supporting area, the stress intensity of the supporting rock is higher. Considering the compressive strength of the rock, the supporting area is >25%. When the rock is in the form of a dislocation support, the fluid disperses in the larger void channels, thus effectively maintaining fracture conductivity. The self-supporting acid fracturing technique is useful for increasing the utility of acid fracturing stimulation in deep and ultra-deep wells.
Failure Mechanisms and Mitigation Measures of the G1006 Electricity Pylon Landslide in the Dam Area of the Jinping I Hydropower Station
Authors: Yang Y X , Luo G , Duan Y Y , Zhang C Z , Zhang Y G , Lei Q
Published: November 2020

On the 29th and 30th of August 2012, more than 100 geological disasters occurred near the dam area of Jinping I Hydropower Station, Xichang, China due to local intense rainstorm. The upper part of the left valley slope, which is 500 m upstream of the dam, failed and slid, exposing the C-pile of the G1006 electricity pylon and threatening the entire power transmission lines. Therefore, ensuring the stability of the residual rock masses in the rear of the main scarp and the safety of the G1006 electricity pylon became a primary emergency task. Field geological survey, topographic mapping, and the instability mechanism study of the G1006 electricity pylon landslide were conducted. Results revealed that the G1006 electricity pylon landslide (here after represented as the G1006 EPL) occurred in the middle block cut by two faults, and the rock masses had inferior mechanical properties. Intense unloading effects and frequent microseism events during the dam construction relaxed the rock mass structural planes and reduced the geotechnical parameters. Under the influence of intense rainfall, the failure mechanisms of the slope were a combination of slope surface effect from rainfall and lateral erosion and undercutting of the slope toe by high flooding. The residual rock masses and landslide deposits around the pylon foundation were unstable under natural conditions and during the rainstorm. To prevent the continuous damage and exposure of C-pile foundation and ensure the stability of pylon foundation, the mitigation measure of “retaining piles + platform + retaining wall” was arranged. Moreover, a check dam was added to stabilize the slope toe and prevent the landslide deposits, which are the starting material source of debris flow that threatens the safety of the arch dam.
Grouting Reinforcement Technology of Weak Fractured Rock Mass in Subway Open-cut Station
Authors: Liu Quanwei , Tian Jiawei , Liu Yankai , Jiang Qichen , Wang Meng , Liu Linsheng , Liu Rentai
Published: November 2020

In the process of subway open-cut station construction, excavation deformation seriously threatens the safety of municipal pipelines and buildings. To ensure the effectiveness of grouting reinforcement, drilling exploration and pressure water test were conducted on the basis of the grouting reinforcement project of the excavation of an open-pit station in Qingdao metro, the permeability coefficient and crack characteristics were studied, and the equivalent crack width was calculated on the basis of cubic law. To determine the injectability index of grout and realize the optimal selection of grouting materials, the statistical distribution law of the equivalent crack width was analyzed on the basis of the Pareto distribution, and an effective method of grout selection was proposed. The PQT curve in the grouting process was analyzed by flow dimension theory to realize the dynamic adjustment of the grouting process. Finally, the grouting reinforcement effect was evaluated on the basis of the core sample and borehole TV. Results show that if the permeability coefficient is subject to Pareto distribution with parameters tmin and k, then the distribution curve of the permeability coefficient in the logarithmic coordinate is a straight line; the equivalent crack width obtained on the basis of the cubic law is also subject to the Pareto distribution with parameters bmin and 3k. Therefore, the equivalent crack width distribution curve can be obtained to provide a basis for the grout selection.
Study on the Method of Constructing Engineering Geological Three-dimensional Model of Hydrate Area in South China Sea Based on ArcGIS
Authors: Yang J P , Shi Y H , Chen M , He J , Chen K H , Hou J M
Published: November 2020

The trial production of marine natural gas hydrates (NGH) in China is gradually increasing, attracting concerns on related environmental issues. The entire regional conditions of engineering geological environment must be investigated thoroughly before NGH production. These conditions should be defined, among others, in terms of seabed topography, stratigraphic structure, soil types, physical and mechanical characteristics, hazardous geological factors and distributions, and hydrodynamic characteristics, which provide a variety of geological spatial information and can be obtained from different sources. Due to the high cost and low efficiency of deep-sea engineering geological drilling, only few stations can be deployed. Hence, not enough data are available for the construction three-dimensional (3D) geological models. This study considered the data of only a few drilling stations and compared them with well logging and 3D seismic data. First, the engineering geological standard strata were established. Second, we interpreted and exported the stratigraphic (based on virtual boreholes) and spatial information (in terms of X, Y, and Z) of existent geological structures in GeoFrame. Finally, using several technical modules of ArcGIS (i.e., ArcMap, ArcScene, ArcCatalog), we constructed a spatial database and a comprehensively intuitive 3D visualization data management platform for engineering geological environmental surveys and evaluations in the hydrate area. By clicking any element included in the platform, the correspondent data or results can be looked over: this efficient and continuous systematic database can be used to support the future production of NGH in the area.
DEM simulation of the complete triaxial test of sandstone
Authors: Li Lei , Huang Jun Guang , Li Wei Ke , Jiang Ming Jing
Published: November 2020

Complete triaxial tests considering residual strength are of great significance in analyses of the mechanical properties of rock in deep-rock engineering. In this paper, the complete triaxial test of Berea sandstone was quantitatively simulated using the discrete element method. The macro- and micromechanical properties of Berea sandstone were analyzed, and the following conclusions were obtained: (1) As the confining pressure increases, the peak and residual strengths of the sample increases, the stress–strain curves gradually change from softening to hardening, and the volume curves gradually change from dilatancy to shrinkage. (2) When the confining pressure is low, bond failure between particles mainly occurs under the state of tensile stress. As the confining pressure increases, compressive state failure gradually exceeds tensile state failure. (3) Under different confining pressures, the energy dissipated by friction between particles is far greater than other forms of energy dissipation and the energy dissipated by rolling between particles is always greater than the energy dissipated by twisting.
Numerical Simulation and Analysis of Cave Penetration by Hydraulic Fractures
Authors: Kao Jiawei , Wang Wenzhi , Jin Yan , Liu Hailong
Published: November 2020

The cavernous carbonate reservoir in the Tahe oilfield in northwestern China has high development potential. Fluid is distributed in caves due to low matrix permeability, and recombination acid fracturing is a primary development method. The effects of fracturing depend on the number of caves connected by fractures. An estimate of whether a hydraulic fracture can penetrate a cave and continue propagation is therefore important for production safety and efficiency. We developed a numerical model using COMSOL Multiphysics to calculate the fluid-solid coupling stress distribution after fractures connect with caves and determine whether the fractures can continue to expand. We first developed an analysis group based on parameters from fracturing experiments in which caves were placed in man-made samples. A comparison of the calculation and experimental results verifies that the model is reasonable. The penetration ability of hydraulic fractures and influencing factors under different conditions were analyzed in combination with characteristics of the cavernous carbonate reservoir in the Tahe oilfield. The results show that when holding fixed certain working parameters, such as displacement and fluid viscosity during fracturing, the hydraulic fractures more easily penetrate smaller caves, the in-situ stress ratio increases, and the distance between the well and caves that would lead to a higher penetration ability decreases. If the fractures of a given cave are connected but not penetrated, several methods can be applied to effectively increase the hydraulic pressure in the cave, such as increased fracturing injection fluid displacement or replacing low-viscosity fracturing fluid. This can form new fractures in the wall that continue to expand and connect more caves. We calculated the fluid-solid coupling stress distribution after the fractures had connected caves to determine whether hydraulic fractures could also achieve penetration. The main influencing factors and optimization methods affecting the ability of fracture penetration are clarified, which provide an important reference for fracturing design in the Tahe cavernous carbonate reservoir.
Fluid solid coupling analysis of hard rock wall structure in over kilometer deep shaft
Authors: Li Cheng , Xingquan Liu , Mingde Zhu , Kuikui Hou
Published: November 2020

Taking the auxiliary shaft proposed by Ruihai Mining Co., Ltd. as the research object, in order to study the load law of shaft lining and ingate under high stress fluid solid coupling in deep bedrock and the influence of different permeability coefficient on the stability of shaft lining and ingate surrounding rock, Midas software was used for numerical simulation analysis, and the results show that:( 1) After the shaft excavation, the pore water pressure of surrounding rock around the shaft wall and ingate decreases gradually, which is the main permeable area. After the support, the pore water pressure is obviously raised, and the water isolation effect of the supporting layer is obvious. (2) After the shaft excavation, the area near the arc surface of shaft wall tangent to Y direction shows high compressive stress, and the maximum principal stress at - 1277.5m depth is more than 150MPa. When the polar angle increases from 0 to 180 °, the maximum principal stress increases first and then decreases. (3) After the excavation of ingate, the bottom corner and arch top are stress concentration areas before and after support. ( 4) Under the action of three different permeability coefficients, the influence of permeability coefficient on pore water pressure and maximum principal stress can be ignored after supporting measures are taken. The research results provide important theoretical basis for auxiliary shaft construction design.
Phase field modeling of hydraulic fracture propagation in spatially variable rock masses
Authors: Chen F Y , Zhou S W , Zhuang X Y , Zhang W G
Published: November 2020

Due to differences in mineral compositions, sedimentary conditions, stress history, and geological processes, the spatial variability of the mechanical properties of rock masses is usually considerable. Therefore, the influence of the spatial variability of rock mass parameters on the irregular propagation of hydraulic fractures should be studied. In this work, an efficient approach is proposed for studying the irregular propagation of hydraulic fractures considering the spatial variability of rock mass parameters; this approach is based on the phase field method and random field theory. Combined with random field theory, the phase field method is adopted to simulate the fracture propagation in a spatially variable rock mass. Random fields of the Young’s modulus are generated using the Cholesky decomposition method and then embedded into the phase field model. The influences of different scales of fluctuation of the rock mass parameters’ random fields on the fracture shape under fluid-driven conditions are investigated in this study. The results indicate that the spatial variability of the Young’s modulus has a significant influence on the propagation of hydraulic fractures.
Two-Dimensional Representation and Connectivity Analysis of Nature Fracture in Fractured Reservoir
Authors: Zhao Huan , Li Wei , Li Siqi
Published: November 2020

The mechanism of hydraulic fracturing in fractured reservoirs is complex. To understand the complex distribution characteristics of natural fractures and the mechanism of hydraulic fracture propagation in fractured reservoirs, the natural fracture characterization of a two-dimensional model was established based on the fractal method and topology principle. Furthermore, based on this model, the hydraulic fracture propagation dynamic fluid-structure interaction model was built using the global embedded cohesive element method. The influence of natural fracture connectivity on hydraulic fracture morphology was analyzed. The results show that multi-fracture development can effectively reduce the influence of stress anisotropy on the fracture propagation direction and improve the natural fracture connectivity of the reservoir. Moreover, the reservoir connectivity reached 35.87% after fracturing.
Spectral Correlation Between the Non-uniform Input Ground Motion and the Dynamic Response of the Surrounding Rocks of a Long Tunnel
Authors: Zhou Yongqiang , Sheng Qian , Li Nana , Fu Xiaodong
Published: November 2020

To generate several different time-history curves of ground motion, which have the ability to reflect local site effects, such as the traveling-wave effect and attenuation effect, for long circular tunnels, a random method for the synthesis of ground motion is employed. The dynamic response of the surrounding rocks of a long tunnel under the uniform and non-uniform input ground motions is analyzed using the vertical input method. Based on this, the spectral correlation between the input ground motion and the dynamic response of the surrounding rocks is investigated through the coherence function. Unlike the results under the uniform input ground motion, the transmission coefficient of the surrounding rock monitoring points of each section along the axial direction of the tunnel under the non-uniform input ground motion varies in the main frequency band. In addition, at the same frequency, the transmission coefficient of the monitoring points gradually increases along the tunnel’s axial direction, but the increasing magnitude is variable. The correlation function of each monitoring point along the tunnel axis under the non-uniform input ground motion generally decreases with frequency. Moreover, the further the distance from the tunnel entrance, the faster the attenuation of correlation. The maximum coherence coefficient and the axial distance of the tunnel are basically in conformity with the quadratic polynomial relationship. However, the maximum coherence coefficient of the non-uniform input ground motion is considerably greater than that of the uniform input ground motion. The gap increases with the distance, and the maximum gap is about 0.15.
Coupling DDA and 4D-LSM through contact theory for rock cutting
Authors: Zhao Gao-Feng , Li Yiming , Jiang Baoyuan
Published: November 2020

In this work, the rock cutting is modelled through coupling of 4D-LSM with DDA. The rock cutter and its 3D motion were simulated by using DDA with triangular surface mesh, and the rock is modelled by using 4D-LSM with multi-body failure criterion. The dynamic contact treatment between the cutter and the rock specimen was further handled by using Dr. Shi’s contact theory where the entrance block of the cutter between spherical particles was used to calculate the contact forces. Then, the 4D-LSM and DDA were coupled through an explicit-implicit mixed solving scheme. Finally, the coupled model is used to model rock cutting problems and compared with exist numerical approach to highlight its advantages.