Search Results (21)

Underground pumped storage hydropower stations (UPSH) are of great significance for energy structure adjustment, and coal mine underground reservoirs are an integral part of UPSH. This study investigates the fracture mechanics behavior of coal in mine water immersion environments with varying loading rates and layer direction. Three types of samples were analyzed: Crack-arrester, Crack-splitter, and Crack-divider types. The immersion duration extended up to 120 days. The results indicate that, after immersion in mine water for 120 days, the fracture toughness (K_IC), fracture modulus (E_S), and absorbed energy (U_T) of coal decreased by 60.87%, 53.38%, and 63.21%, respectively, compared to the unsaturated coal samples. An immersion period of 30 days significantly weakens the mechanical properties of coal fractures. The K_IC, E_S, and U_T of coal demonstrate a positive correlation with loading rate, primarily influenced by the duration of coal damage. At the same loading rate, the order of fracture toughness among the three coal types is as follows: Crack-divider > Crack-arrester > Crack-splitter. This hierarchy is determined by the properties of the coal matrix and bedding planes, as well as the mechanical structures composed of them. This study holds significant implications for the safe construction and operational design of underground water reservoirs in coal mines. Full article

Hydraulic fracturing was the primary technology for shale oil and gas development. Creating a huge stimulated reservoir volume was essential to improving shale oil and gas production. Based on the CDEM, a 3D hydraulic fracturing numerical model was proposed to simulate the interaction between hydraulic fracture and natural fracture. The simulation indicated that net pressure decrease was the main factor affecting fracture propagation in the vertical direction. Under a high stress difference, when the stress difference is over 9.0 MPa, the propagation resistance of rock matrix is higher than that of the bedding plane, thus the bedding plane has a huge opening, and the hydraulic fracture was arrested by the bedding plane. For high formation permeability, increasing the viscosity of the fracturing fluid can effectively improve the fracture height, which can accelerate the hydraulic fracture across the bedding plane. Improving the injection rate also benefitted crossing the bedding plane. This research has great significance in improving the stimulated reservoir volume. Full article

The anisotropic fracture characteristics of oil shale are crucial in determining reservoir modification parameters and pyrolysis efficiency during in situ oil shale pyrolysis. Therefore, understanding the mechanisms through which temperature and bedding planes influence the fracture behavior of oil shale is vital for advancing the industrialization of in situ pyrolysis technology. In this study, scanning electron microscopy (SEM), CT scanning, and a real-time high-temperature rock fracture toughness testing system were utilized to investigate the spatiotemporal evolution of pores and fractures in oil shale across a temperature range of 20–600 °C, as well as the corresponding evolution of fracture behavior. The results revealed the following: (1) At ambient temperature, oil shale primarily contains inorganic pores and fractures, with sizes ranging from 50 to 140 nm. In the low-temperature range (20–200 °C), heating primarily causes the inward closure of inorganic pores and the expansion of inorganic fractures along bedding planes. In the medium-temperature range (200–400 °C), organic pores and fractures begin to form at around 300 °C, and after 400 °C, the number of organic fractures increases significantly, predominantly along bedding planes. In the high-temperature range (400–600 °C), the number, size, and connectivity of matrix pores and fractures increase markedly with rising temperature, and clay minerals exhibit adhesion, forming vesicle-like structures. (2) At room temperature, fracture toughness is highest in the Arrester direction (K_IC-Arr), followed by the Divider direction (K_IC-Div), and lowest in the Short-Transverse direction (K_IC-Shor). As the temperature increases from 20 °C to 600 °C, both K_IC-Arr and K_IC-Div initially decrease before increasing, reaching their minimum values at 400 °C and 500 °C, respectively, while K_IC-Shor decreases continuously as the temperature increases. (3) The energy required for prefabricated cracks to propagate to failure in all three directions reaches a minimum at 100 °C. Beyond 100 °C, the absorbed energy for crack propagation along the Divider and Short-Transverse directions continues to increase, whereas for cracks propagating in the Arrester direction, the absorbed energy exhibits a ‘W-shaped’ pattern, with troughs at 100 °C and 400 °C. These findings provide essential data for reservoir modification during in situ oil shale pyrolysis. Full article

This study employs the discrete element method to investigate the influence of particle size on the load-bearing characteristics of aggregates, with a specific emphasis on the aggregates used in escape ramp arrester beds. This study utilises the log edge detection algorithm to introduce an innovative approach for modelling irregularly shaped pebbles, integrating their physical properties into a comprehensive discrete element model to enhance the accuracy and applicability of simulations involving such pebbles. Meticulous validation and parameter calibration (friction coefficient: 0.37, maximum RMSE: 3.43) confirm the accuracy of the simulations and facilitate an in-depth examination of the mechanical interactions between aggregate particles at macroscopic and microscopic scales. The findings reveal a significant relationship between the particle size and load-bearing capacity of aggregates. Smaller pebbles, which are more flexible under pressure, can be packed more densely, thereby improving the distribution of vertical forces and increasing the concentration of local stress. This enhancement substantially increases the overall load-bearing capacity of aggregates. These discoveries hold significant implications for engineering practices, particularly in the optimisation of safety for truck escape ramps and in identifying the ideal sizes of pebbles with irregular shapes. Full article

The load-bearing capacity of pebble aggregates plays a pivotal role in influencing the operational performance of uncontrolled trucks on arrester beds. The complexity of this phenomenon stems from the nonuniformity in the shapes of the pebbles and their stochastic arrangement within the beds, presenting notable challenges for traditional mathematical modelling techniques in precisely evaluating the contact dynamics of these aggregates. This study leverages the discrete element method (DEM) to extensively analyse the arrester bed aggregate of a standard truck escape ramp. The aforementioned mechanism entails the gathering of morphological parameters of irregularly shaped aggregate particles and introduces a novel method for constructing random shapes that adhere to the observed distribution characteristics. A discrete element model, grounded in the physical properties of these aggregates, is formulated. This study focuses on the aggregate’s load-bearing capabilities, scrutinising the mechanical behaviour of the aggregate particles at the macroscopic and microscopic scales. These insights offer substantial scientific contributions and practical implications for assessing the safety of escape ramps and determining essential parameters for the brake bed design. Full article

We investigated independent factors predicting neurological outcome and death, comparing in-hospital (IHCA) and out-of-hospital cardiac arrest (OHCA) patients. The study was conducted in the mixed 34-bed Intensive Care Department at the Hôpital Universitaire de Bruxelles (HUB), Belgium. All adult consecutive cardiac arrest (CA) survivors were included between 2004 and 2022. For all patients, demographic data, medical comorbidities, CA baseline characteristics, treatments received during Intensive Care Unit stay, in-hospital major complications, and neurological outcome at three months after CA, using the Cerebral Performance Category (CPC) scale, were collected. In the multivariable analysis, in the IHCA group (n = 540), time to return of spontaneous circulation (ROSC), older age, unwitnessed CA, higher lactate on admission, asystole as initial rhythm, a non-cardiac cause of CA, the occurrence of shock, the occurrence of acute kidney injury (AKI), and the presence of previous neurological disease and of liver cirrhosis were independent predictors of an unfavorable neurological outcome. Among patients with OHCA (n = 567), time to ROSC, older age, higher lactate level on admission, unwitnessed CA, asystole or pulseless electrical activity (PEA) as initial rhythm, the occurrence of shock, a non-cardiac cause of CA, and a previous neurological disease were independent predictors of an unfavorable neurological outcome. To conclude, in our large cohort of mixed IHCA and OHCA patients, we observed numerous factors independently associated with a poor neurological outcome, with minimal differences between the two groups, reflecting the greater vulnerability of hospitalized patients. Full article

Cardiac arrest is a sudden loss of heart function with serious consequences. In developing countries, healthcare professionals use clinical documentation to track patient information. These data are used to predict the development of cardiac arrest. We published a dataset through open access to advance the research domain. While using this dataset, our work revolved around generating and utilizing synthetic data by harnessing the potential of synthetic data vaults. We conducted a series of experiments by employing state-of-the-art machine-learning techniques. These experiments aimed to assess the performance of our developed predictive model in identifying the likelihood of developing cardiac arrest. This approach was effective in identifying the risk of cardiac arrest in in-patients, even in the absence of electronic medical recording systems. The study evaluated 112 patients who had been transferred from the emergency treatment unit to the cardiac medical ward. The developed model achieved 96% accuracy in predicting the risk of developing cardiac arrest. In conclusion, our study showcased the potential of leveraging clinical documentation and synthetic data to create robust predictive models for cardiac arrest. The outcome of this effort could provide valuable insights and tools for healthcare professionals to preemptively address this critical medical condition. Full article

The fracture toughness of shale is a key parameter guiding hydraulic fracturing design and optimization. The hollow double-wing slotted (HDWS) specimen is a typical specimen configuration for measuring the mode I fracture toughness of rock. The calibration of the shape factor (f) is the basis for accurately obtaining the fracture toughness of rocks. In this study, the influences of crack length, hole size, and the anisotropy of elastic parameters on f for specimens with three typical bedding orientations—arrester (A), divider (D), and short-transverse (ST) orientations—are systematically investigated using finite element software. The numerical simulation results support the following findings. The mode I f increases monotonically with an increase in hole size. The influence of crack length on f varies depending on hole sizes. Under different bedding orientations, significant anisotropy in f was observed. In addition, the degree of anisotropy in Young’s modulus has a major impact on f, which is related to the bedding orientation of the specimen. The apparent shear modulus ratio has relatively little influence on f. As the hole size and crack length increase, the influence of the anisotropy of elastic parameters on f increases. Based on numerical calculations, hydraulic fracturing experiments were conducted on HDWS specimens of Longmaxi shale with three bedding orientations, and the results showed that the peak pressure and fracture toughness of the samples in the ST direction were the lowest, while those in the A direction were the highest. Full article

The microscopic anisotropy of shale has an important impact on its mechanical properties and crack behavior, so it is essential to understand the microscopic origin of anisotropic growth with a more effective laboratory work scheme. Uniaxial compression test and three-point bending test are considered to be efficient means to study the elastic properties and crack behavior of rocks. In this paper, uniaxial compression experiments and three-point bending experiments were conducted on shale outcrops in the Changqing area using field emission scanning electron microscopy (SEM) and in situ tensile testing, and the microscopic deformation and crack processes were quantitatively characterized by the digital image correlation (DIC) method. For the compression experiments, the observation of the first principal strain fields indicated that the microscopic anisotropy of shale was related to the bedding planes, and the microscopic deformations were mainly concentrated in the clay mineral accumulation area and at the microcracks. Elastic moduli and compressive strengths of specimens with different bedding angles were affected by the strong shear stress effects. The specimens with a bedding angle of 30° showed lower peak loads and compressive strengths, and the specimens with a bedding angle of 60° had lower elastic moduli. Three-point bending experiments were conducted for studying the effects of crack-bedding orientation relationships on cracking processes, and four critical fracturing mechanical properties were calculated. The short transverse-type cases were prone to break and had a lower peak load, tensile strength, fracture toughness and elastic-bending modulus. The divider-type cases were more difficult to break, formed a more tortuous crack and had a higher tensile strength, fracture toughness and elastic-bending modulus. The arrester-type cases had a middle range of mechanical parameters but developed the longest cracks. This study provides a feasible experimental and analysis method for understanding the microscopic anisotropy of shale samples. The small specimen size also makes the requirements of core samples easier to be satisfied considering the field application. Furthermore, the anisotropy of cracking processes can be understood better by building the connections between microstructural characteristics and mechanical performances. Full article

Heart failure exacerbations impart significant morbidity and mortality, however, large- scale studies assessing outcomes in the setting of concurrent coronavirus disease-19 (COVID-19) are limited. We utilized National Inpatient Sample (NIS) database to compare clinical outcomes in patients admitted with acute congestive heart failure exacerbation (CHF) with and without COVID-19 infection. A total of 2,101,980 patients (Acute CHF without COVID-19 (n = 2,026,765 (96.4%) and acute CHF with COVID-19 (n = 75,215, 3.6%)) were identified. Multivariate logistic regression analysis was utilized to compared outcomes and were adjusted for age, sex, race, income level, insurance status, discharge quarter, Elixhauser co-morbidities, hospital location, teaching status and bed size. Patients with acute CHF and COVID-19 had higher in-hospital mortality compared to patients with acute CHF alone (25.78% vs. 5.47%, adjust OR (aOR) 6.3 (95% CI 6.05–6.62, p < 0.001)) and higher rates of vasopressor use (4.87% vs. 2.54%, aOR 2.06 (95% CI 1.86–2.27, p < 0.001), mechanical ventilation (31.26% vs. 17.14%, aOR 2.3 (95% CI 2.25–2.44, p < 0.001)), sudden cardiac arrest (5.73% vs. 2.88%, aOR 1.95 (95% CI 1.79–2.12, p < 0.001)), and acute kidney injury requiring hemodialysis (5.56% vs. 2.94%, aOR 1.92 (95% CI 1.77–2.09, p < 0.001)). Moreover, patients with heart failure with reduced ejection fraction had higher rates of in-hospital mortality (26.87% vs. 24.5%, adjusted OR 1.26 (95% CI 1.16–1.36, p < 0.001)) with increased incidence of vasopressor use, sudden cardiac arrest, and cardiogenic shock as compared to patients with heart failure with preserved ejection fraction. Furthermore, elderly patients and patients with African-American and Hispanic descents had higher in-hospital mortality. Acute CHF with COVID-19 is associated with higher in-hospital mortality, vasopressor use, mechanical ventilation, and end organ dysfunction such as kidney failure and cardiac arrest. Full article

In order to accurately test the K_IC of the vertical stratification direction of shale, a semi-circular bending specimen with a linear chevron notch ligament (LCNSCB) was designed. The minimum dimensionless stress intensity factor (Y^*_min) of the LCNSCB specimen was calculated by the finite element method and the slice synthesis method, respectively. Two sets of prefabricated samples of the LCNSCB specimen under arrester and divider mode were used to conduct three-point bending loading experiments. The dispersion of the measured K_IC value of the specimens was analyzed by standard deviation and coefficient of variation, and the reason that the K_IC dispersion of specimens in divider mode was larger than in arrester mode was discussed. Compared with the experimental data of the existing literature, the data of this experiment shows that the LCNSCB specimen can avoid the disadvantage of lower measured K_IC values due to a larger fracture processing zone featured in the CSTSCB and CCNBD specimens, combined with the merits of a shorter fracture processing zone of the SR or CR specimens, and the render measured the K_IC value to be closer to the material’s true fracture toughness value. The narrow ligament of the LCNSCB specimen has a favorable crack propagation guiding effect, can generate consistent K_IC values, and could be used to accurately test the fracture toughness of rock material in vertical bedding direction. Full article

Migration of fine materials such as soil from the roadbed and the ground will gradually pollute the aggregate in the arrester bed of truck escape ramps. However, there are few studies on the impact of aggregate pollution of the arrester bed on the stopping distance of runaway vehicles. This paper uses the discrete element method to study the influence of aggregates with different degrees of pollution on stopping distance by taking silty cohesive soil as a typical pollutant. In this paper, the stopping process of the uncontrolled vehicle on the arrester bed with different pollution levels was numerically simulated. The simulation results show that the uncontrolled vehicle’s stopping distance increases with the contaminated aggregate’s soil content. The simulation results show that when the soil content in the contaminated aggregate is less than 15%, the increase in the stopping distance of the uncontrol vehicle is less than 5%; when the soil content is 20–25%, the stopping distance of the uncontrolled vehicle increases by more than 20%; and when the soil content is 30–35%, the stopping distance of uncontrol vehicle increases by more than 50%. Different maintenance measures should be taken according to the increase in stopping distance. Full article

The conventional fracture in shale hydraulic fracturing belongs to the type-I fracture, and the size of the fracture process zone (FPZ) is an important index to measure the fracability of rock mass. This index is also one of the feasible entry points to study the complexity of the fracture network. In order to visually observe the type-I FPZ at the tip of shale fractures, and to study the relationship between the mechanical properties, the shape and size of the FPZ, and the bedding structure, Notched Semi-Circular Bend (NSCB) tests were conducted with three typical fracture direction-bedding orientations (splitter, arrester, divider). The digital image correlation (DIC) method was used to realize the intuitive observation of the real fracture process and the FPZ near the fracture tip. The test found that the FPZ of shale is narrow and long as a whole and is “flame-like”. The height-to-length ratio of the FPZ at the fracture tip determines whether bending and deflection happen between the new fracture and the prefabricated cracks when the fracture occurs. Most of the specimens often appear in the FPZ with a beaded high shear strain zone before the fracture, which is caused by the oblique communication of micro-cracks in the FPZ before the fracture. The appearance of a beaded zone of high shear strain indicates that macroscopic fracture is imminent. The research results can be used for the design of disaster early warning and prevention programs. Full article

The need to arrest the continued environmental contamination and degradation associated with the consumption of fossil-based fuels has continued to serve as an impetus for the increased utilization of renewable fuels. The demand for biodiesel has continued to escalate in the past few decades due to urbanization, industrialization, and stringent government policies in favor of renewable fuels for diverse applications. One of the strategies for ensuring the intensification, commercialization, and increased utilization of biodiesel is the adaptation of reactor technologies, especially tubular reactors. The current study reviewed the deployment of different types and configurations of tubular reactors for the acceleration of biodiesel production. The feedstocks, catalysts, conversion techniques, and modes of biodiesel conversion by reactor technologies are highlighted. The peculiarities, applications, merits, drawbacks, and instances of biodiesel synthesis through a packed bed, fluidized bed, trickle bed, oscillatory flow, and micro-channel tubular reactor technologies are discussed to facilitate a better comprehension of the mechanisms behind the technology. Indeed, the deployment of the transesterification technique in tubular reactor technologies will ensure the ecofriendly, low-cost, and large-scale production of biodiesel, a high product yield, and will generate high-quality biodiesel. The outcome of this study will enrich scholarship and stimulate a renewed interest in the application of tubular reactors for large-scale biodiesel production among biodiesel refiners and other stakeholders. Going forward, the use of innovative technologies such as robotics, machine learning, smart metering, artificial intelligent, and other modeling tools should be deployed to monitor reactor technologies for biodiesel production. Full article

As the world’s population ages, technology-based support for the elderly is becoming increasingly important. This study analyzes the relationship between natural standing behavior measured in a living space of elderly people and the classes of standing aids, as well as the physical and cognitive abilities contributing to household fall injury prevention. In total, 24 elderly standing behaviors from chairs, sofas, and nursing beds recorded in an RGB-D elderly behavior library were analyzed. The differences in standing behavior were analyzed by focusing on intrinsic and common standing aid characteristics among various seat types, including armrests of chairs or sofas and nursing bed handrails. The standing behaviors were categorized into two types: behaviors while leaning the trunk forward without using an armrest as a standing aid and those without leaning the trunk forward by using an arrest or handrail as a standing aid. The standing behavior clusters were distributed in a two-dimensional map based on the seat type rather than the physical or cognitive abilities. Therefore, to reduce the risk of falling, it would be necessary to implement a seat type that the elderly can unconsciously and naturally use as a standing aid even with impaired physical and cognitive abilities. Full article