In this paper, a series of uniaxial compression experiments were carried out on sandstone with varying water contents, and acoustic emission (AE) signals were synchronously collected in the ...experimental process. It reveals that water content has a significant effect on the mechanical behavior and AE signals of sandstone. As the water content increases, both the uniaxial compression strength and the elastic modulus decrease while the peak strain and energy dissipation increase. In the perspective of AE signals, both the peak and the cumulative AE energy drop with the water content, and an exponential empirical function was proposed to describe their relationships. Multi-fractal analyses of AE signals were also performed. The uniformity of signal distribution (∆a) and the difference between frequencies of largest and smallest signals (∆f) also decrease with the increase of water content. All these phenomena can be explained by the fact that more and more intergranular fractures occur at the higher water content condition. Moreover, a sudden increase of ∆a and a sudden decrease of ∆f in time series can be used as the precursor of rock destabilization and failure which have potential engineering application value.
•Water reduces the strength of sandstone, increases energy dissipation and weakens acoustic emission(AE).•The change of micro fracture mechanism of sandstone is an important reason.•The multifractal parameters ∆a and ∆f of AE have potential engineering application value.
To promote the accuracy of infrared monitoring of water-bearing rock stability, sandstone samples with varying moisture contents were subjected to infrared monitoring experiments under uniaxial ...compression. Additionally, the temporal-spatial variations of infrared radiation were analyzed. Furthermore, the infrared precursor information of water-bearing rock fracture was quantitatively discussed in light of the critical slowing down theory. The results reveal that the infrared radiation temperature of sandstone surface decreases as the moisture content rises. Variations of maximum infrared radiation temperature (MIRT) during loading on sandstone samples present distinct characteristics in different stages. As the moisture content rises, in the early stage, the trend of MIRT decrease weakens, and the effect of stress on MIRT variation is more obvious. In the plastic deformation stage, the MIRTs fluctuate earlier and more violently. When samples finally break, the MIRTs change suddenly in a reduced range. With the rise of moisture content, the variation trend of infrared image and MIRT gradually changes from falling-rising-abruptly changing to rising-being abnormal-abruptly changing. The MIRTs of sandstone samples with varying moisture contents present the characteristics of critical slowing down during loading; and the sample with a higher moisture content exhibits more notable precursor characteristics. In addition, the variance index is more sensitive to macro-fractures than the autocorrelation coefficient and can provide more accurate precursor information for the fracture and instability monitoring of water-bearing rock.
The applications in coal mine rock burst prevention using water jet cutting technology (WJCT) have progressed slowly. In this paper we analyzed the possibility and reasonableness of WJCT application ...to rock burst relief and prevention, used the ABAQUS software to simulate the distributive characteristics of stress and energy fields suffered by hard coal roadway wallrock and the internal relationships of the fields to the instability due to WJC on roadway wallrock, and conducted field WJCT tests using electromagnetic radiation (EMR) measurement technology. The results showed that WJCT can unload rock burst effectively by inducing stress release and energy dissipation in coal mass near its cut slots; its annular slots also can decrease rock burst risks through blocking or weakening stress and energy transfer in coal mass. The horizontal radial slots and annular vertical slots may cause “the beam structure” and “the small pillar skeleton”, and “the layered energy reservoir structure”, respectively, which lead to an increase in stress concentration and energy accumulation in coal element mass near the slots. The reasonable design and optimization of slots׳ positions and their combination not only can significantly reduce the scope of stress concentration and energy accumulation, but also can destroy coal mass structure on a larger scale to force stress to transfer deeper coal mass, eventually avoiding high intensity and large-scale rock bursts. The field tests of WJC for pressure relief using EMR verified the above conclusions.
•The mechanism of rockburst relief and prevention using WJCT is analyzed.•Horizontal radial slots will produce “beam structure” and “small pillar skeleton”.•Annular vertical slots will generate “layered energy reservoir structure”.•The slots׳ positions and their combination are reasonably designed and optimized.•Rockburst relief and prevention effect were verified using EMR method.
Aimed at exploring the influence of methane to coal and studying fractal characteristics and acoustic emission (AE) features in the damage evolution, the triaxial compression experiments of coal ...containing methane were conducted, and acoustic emission response was collected simultaneously in the loading process. Based on the method for calculating the correlation dimension, the fractal dimension was calculated with regard to time series of acoustic emission. Our experimental results indicate that AE response and fractal dimension can reflect the evolution and propagation of cracks in the loading process. Corresponding to the load–time, acoustic emission experiences active, linearly increasing, rapidly augmenting and decreasing stage. However, the fractal dimension of AE develops from chaos to orderly state. Late loading, a continued slowdown in fractal dimension, can be used as a precursory signal of coal sample destruction. In addition, the amount of gas in the coal sample will influence the evolution of pore and fracture, which causes a variation in the acoustic emission signals and fractal dimension. The maximum bearing load reduces 18.85% and 49.18% within pore pressure of 0.75 and 1.5MPa, compared with it (24.4kN) of the coal sample (without gas). What's more, the increase of pore pressure will cause the growth of AE count and energy, but the correlation dimension of AE parameters drops. This study is helpful for us to understand the effects of methane to coal and the evolution mechanism of cracks, and it can be applied to the research on occurrence mechanism and early warning of coal and gas outburst.
•Conducted experiments on coal containing methane under triaxial compression.•Analyzed load and acoustic emission changes with time in the failure process.•Studied fractal characteristics of AE.•Discussed the methane effects on the mechanical properties of coal, damage evolution, AE responses, fractal characteristics.
Fully understanding the influence of water on the rock materials' mechanical properties is of great significance to the safety design and evaluation in rock engineering. In this study, sandstone was ...pretreated with different wetting-drying cycles (0-15), and its pore characteristics were characterized by low-field nuclear magnetic resonance (LF-NMR) and scanning electron microscope (SEM) methods. Then, the split Hopkinson pressure bar (SHPB) tests with the same impact velocity were carried out in its dry and saturated states, respectively. The effects of water saturation on the dynamic behavior of sandstone under different porosity conditions and their mechanisms were emphasized. The results show that with the increase of cycle numbers, the porosity of sandstone increases, the dynamic strength and the total energy dissipation decreases. Moreover, the proportion of post-peak energy dissipation rises, and the degree of fragmentation intensifies. With the increase of porosity, the effect of water saturation on dynamic strength changes from enhancement to weakening. This may be related to the competition between the the Stefan effect and the contribution of pore water pressure. Finally, a dynamic damage constitutive model considering the coupling effect of the wetting-drying cycles and dynamic loads was established, and its effectiveness was verified.
•As the wetting-drying cycles increases, the porosity of the sandstone increases and its dynamic strength decreases.•The effect of water saturation on dynamic strength change from enhancement to weakening with increasing porosity.•A dynamic damage constitutive model considering porosity is established and its validity is verified.
In order to study the effect of water on the electromagnetic radiation (EMR) signals released during rock deformation and fracturing, uniaxial compression experiments were performed on sandstone ...samples with different water contents. During the experiments, the EMR signals were acquired. Furthermore, the time-frequency characteristics of the signals were analyzed, and their generation mechanism and the effect of water were discussed in depth. The results show that the EMR energy released decreases gradually with the increase of water content, and the EMR energy and water content can be linked by a binomial equation. For sandstone with higher water content, the precursor characteristics of EMR released in the fracturing process are more obvious. With the increase of water content, the proportion of signals in the low frequency band grows gradually, while that of signals in high frequency band falls gradually. Water reduces the macroscopic mechanical strength and fracture mechanical characteristics of sandstone, which weakens the EMR signals produced by piezoelectric effect and charge separation. Besides, with respect to the microscopic fracturing mode, the sandstone with higher water content is more likely to undergo inter-granular fracturing, which may be an important microscopic reason for the weakening of EMR of water-bearing sandstone. An EMR-based damage evolution model of water-bearing sandstone was preliminarily established, and the model helps to calculate the stress state of water-bearing rock.
•The time-frequency characteristics of EMR of sandstone with different water content during loading were studied.•The causes of EMR reduction of water-bearing sandstone were studied.•A damage evolution model of water-bearing sandstone based on EMR was established.
Abstract The NK cell is an important component of the tumor microenvironment of pancreatic ductal adenocarcinoma (PDAC), also plays a significant role in PDAC development. This study aimed to explore ...the relationship between NK cell marker genes and prognosis, immune response of PDAC patients. By scRNA-seq data, we found the proportion of NK cells were significantly downregulated in PDAC and 373 NK cell marker genes were screened out. By TCGA database, we enrolled 7 NK cell marker genes to construct the signature for predicting prognosis in PDAC patients. Cox analysis identified the signature as an independent factor for pancreatic cancer. Subsequently, the predictive power of signature was validated by 6 GEO datasets and had an excellent evaluation. Our analysis of relationship between the signature and patients’ immune status revealed that the signature has a strong correlation with immunocyte infiltration, inflammatory reaction, immune checkpoint inhibitors (ICIs) response. The NK cell marker genes are closely related to the prognosis and immune capacity of PDAC patients, and they have potential value as a therapeutic target.
Dynamic collapses of deeply mined coal rocks are severe threats to miners. To predict the collapses more accurately using electromagnetic radiation (EMR), we investigate the time-varying multifractal ...characteristics and formation mechanism of EMR induced by underground coal mining. A series of uniaxial compression and multi-stage loading experiments with coal samples of different mechanical properties were carried out. The EMR signals during their damage evolution were monitored in real-time; the inherent law of EMR time series was analyzed by fractal theory. The results show that the time-varying multifractal characteristics of EMR are determined by damage evolutions process, the dissipated energy caused by damage evolutions such as crack propagation, fractal sliding and shearing can be regard as the fingerprint of various EMR micro-mechanics. Based on the Irreversible thermodynamics and damage mechanics, we introduced the damage internal variable, constructed the dissipative potential function and established the coupled model of the EMR and the dissipative energy, which revealed the nature of dynamic nonlinear characteristics of EMR. Dynamic multifractal spectrum is the objective response of EMR signals, thus it can be used to evaluate the coal deformation and fracture process.
Undifferentiated carcinoma with osteoclast-like giant cells (OGCs) of pancreas (UCOGCP) is a rare subtype of pancreatic ductal adenocarcinoma (PDAC), which had poorly described histopathological and ...clinical features.
In this study, single-cell RNA sequencing (scRNA-seq) was used to profile the distinct tumor microenvironment of UCOGCP using samples obtained from one UCOGCP patient and three PDAC patients. Bioinformatic analysis was carried out and immunohistochemical (IHC) staining was used to support the findings of bioinformatic analysis. After quality control of the raw data, a total of 18,376 cells were obtained from these four samples for subsequent analysis. These cells were divided into ten main cell types following the Seurat analysis pipeline. Among them, the UCOGCP sample displayed distinct distribution patterns from the rest samples in the epithelial cell, myeloid cell, fibroblast, and endothelial cell clusters. Further analysis supported that the OGCs were generated from stem-cell-like mesenchymal epithelial cells (SMECs).
Functional analysis showed that the OGCs cluster was enriched in antigen presentation, immune response, and stem cell differentiation. Gene markers such as LOX, SPERINE1, CD44, and TGFBI were highly expressed in this SMECs cluster which signified poor prognosis. Interestingly, in myeloid cell, fibroblasts, and endothelial cell clusters, UCOGCP contained higher percentage of these cells and unique subclusters, compared with the rest of PDAC samples.
Analysis of cell communication depicted that CD74 plays important roles in the formation of the microenvironment of UCOGCP. Our findings illustrated the genesis and function of OGCs, and the tumor microenvironment (TME) of UCOGCP, providing insights for prognosis and treatment strategy for this rare type of pancreatic cancer.
A large number of electromagnetic radiation (EMR) signals are released during loading failure of rock mass, and these signals which contain complex and abundant fracture information can provides ...precursor of rock mass instability. In order to investigate the effect of water on the EMR characteristics of fractured sandstone, a uniaxial compression experiment was performed on the dried and saturated sandstone samples with prefabricated parallel double cracks. The EMR signals during loading failure of rock samples were acquired and their mechanical properties and EMR signal characteristics were analyzed. Besides, the precursor of rock sample instability was extracted based on the critical slowing down theory. The experimental results show that compared with the dried rock sample, the saturated rock sample has lower compressive strength, starts to crack earlier, and exhibits a more complicated failure mode. During the loading failure of rock samples, their EMR signals respond well to the fracturing and damage. The cumulative number of pulses of saturated rock sample grows uniformly, while that of dried rock sample show a “gentle-violent” rising mode. Moreover, the cumulative number of pulses of dried rock sample is greater than that of saturated rock sample. Water reduces the crack initiation stress level, and the saturated rock sample is the first to experience a sudden jump of EMR pulse. With the increase of the loading stress, the dominant frequency of EMR gradually transitions from low frequency to high frequency. Compared with dried rock samples, saturated rock samples have a lower proportion of high-frequency signals. Since the dominant mechanism of EMR varies with the change of failure stage, water first promotes the EMR signals of rock samples in the early stage of loading; then, it weakens the EMR signals in the middle and late stages of loading. Based on the critical slowing down theory, the EMR pulse signals were analyzed, which conduces to the extraction of potential precursor of rock sample failure and instability. Compared with dried rock samples, the precursory characteristic of saturated rock sample is more obvious. The research results provide some guidance for the stability of water-bearing fractured rock mass and the monitoring and early warning of related geological hazards.
