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To further elucidate the mechanism of acoustic emission (AE) response when a fractured rock is compressed, a new method for calculating the AE characteristics from the perspective of relative particle motion based on the moment tensor theory in seismology was proposed in discrete element simulation. The crack expansion process and mechanical-deformation characteristics were simulated by the particle flow code (PFC). Based on the new AE response simulation method, the spatial evolution of AE events, magnitude distribution and the orientation of the moment tensor were calculated. The results showed that the stress of the pre-cracked rock under uniaxial compressive conditions drops dramatically after the peak, the cracks expanded rapidly into a macroscopic crack, the acoustic emission events surge, and the brittle damage characteristics after the peak are obvious. The number of tensile and shear cracks obtained from PFC showed a similar growth trend temporally, while the number of tensile cracks was more than that of shear cracks. The acoustic emission magnitudes obtained based on seismology principally concentrated in the range of [−6.9, −5.9], and the slope of the G-R statistical relationship (b value) was 1.81. The spatial orientation of the AE moment tensor coincided with the tensile-shear cracks: the moment tensor is mainly transverse in the wing crack region, with more tensile cracks than shear cracks; while in the main crack region, the moment tensor was heterogeneous, and the percentage of tensile and shear cracks is close to each other. The tensile and shear properties of microcracks were determined based on the T-k diagram and R-value theory of moment tensor. The trends of the percentage of tensile and shear cracks were basically consistent with those obtained by PFC, while the comparison revealed that using [−20, 20] as the interval of tensile-shear crack was more reasonable than that suggested by Feignier et al. The findings provide beneficial reference for accurate analysis of the characteristics of rock cracking seismic sources and the identification of tensile shear properties.

Fish skin is a multipurpose tissue with important functions—protection, perception, and hormone metabolism—in the fish body. As a byproduct of fish processing, it can be used as a material for extracting collagen, making leather, and related pathological research. However, there have been few reports on the tissue structure of fish skin. This study aimed to analyze the structural characteristics of Thamnaconus septentrionalis fish skin in order to provide a reference for the utilization of its resources. Six T. septentrionalis samples were selected and their skins were observed using frozen sectioning, skeletal, hematoxylin & eosin (H & E), Periodic acid-Schiff (PAS), Masson, Van Gieson (VG) staining, and scanning electron microscopy. The images obtained by slice scanning were analyzed using SlideViewer (3DHISTECH), ImageJ, and Photoshop software. The SEM images were analyzed using ImageJ and Photoshop software. SPSS25.0 software was used to analyze the data of epidermal and squamous layers, conical bone bulge, basal layer, and dermis thicknesses. The results showed that the histological structure of the skin comprised four parts: epidermis, scale layer, dermis, and subcutaneous tissue. The thickness of the epidermal layer was (26.81±7.48) μm. This layer was mainly composed of epithelial and basal cells but also contained a large number of mucus cells. The scale layer consisted of the spine of conical bone and a substrate. The thickness of this layer was (22.49±5.19) μm, and there were two to four rows of the spine of conical bone with different diameters, different bending degrees at the top, and a height of (257.13±10.41) μm unevenly distributed on the base plate. The average thickness of the dermis was (176.97±21.11) μm, and the dermis thickness of the head was lower than that of the middle part of the body, but higher than that of the tail, mainly composed of collagen fiber. The subcutaneous tissue layer was mainly comprised of collagen fibers and non-fibrous stroma. In this study, the histological pattern of the skin of T. septentrionalis was mapped according to its characteristics, providing valuable information for fish skin resource usage.

The acute toxicity of cadmium (Cd2+) to juvenile Thamnaconus septentrionalis was determined using a hydrostatic biological assay. According to the pre-experiment results, four Cd2+ concentration gradient test groups (8.19, 9.18, 10.30, and 11.56 mg/L) and one blank control group were selected for the acute toxicity test using the equilogarithmic spacing method. The mortality, LC50, and safe concentration of Cd2+ in juvenile fish at 24 h, 48 h, 72 h, and 96 h were calculated. Based on the experimental results of acute toxicity of Cd2+ to juvenile Thamnaconus septentrionalis, the Cd2+ concentration gradients were set as 1.84 mg/L, 2.76 mg/L, 3.68 mg/L and 4.60 mg/L at the safe concentration multiple. The activities of superoxide dismutase (SOD), catalase (CAT), glutathione antioxidant enzyme (GSH-PX), and the content of malondialdehyde (MDA) in liver and gill tissues were observed at 6 h, 12 h, 24 h, 48 h, 72 h and 96 h. The results showed that as Cd2+ concentration increased, the acute toxicity gradually increased, the LC50 at 24 h, 48 h, 72 h and 96 h was 11.47 mg/L, 10.82 mg/L, 9.84 mg/L, and 9.19 mg/L, respectively, and the safe concentration of Cd2+ on juvenile filefish was 0.92 mg/L at 96 h. Within 6 h, SOD activity in each concentration group was significantly higher than that in the control group (P < 0.01); SOD activity first decreased and then increased within 6–24 h; however, from 24 h to 96 h, SOD activity of all concentration groups showed a downward trend. SOD activity in the 1.84 mg/L and 2.76 mg/L groups was always higher than that in the control group within 96 h. The enzyme activities of the 3.68 mg/L and 4.60 mg/L groups decreased to below that of the control group from 6 h to 12 h, and increased at 24 h, after which it showed a constant downward trend and remained lower than that of the control group. From 6–12 h, MDA content first decreased and then increased. At 24 h, the enzyme content in each treatment group decreased, but was still higher than that in the control group, and the difference was significant (P < 0.05). From 12 h to 48 h, the 1.84 mg/L and 2.76 mg/L groups showed a trend of first decreasing and then increasing, whereas within the 24 h to 96 h period, the MDA content in the 3.68 mg/L and 4.60 mg/L groups kept increasing, and was significantly higher than in the control group (P < 0.01). At 6 h, CAT activity in all treatment groups was significantly increased when compared to that of the control group; however, CAT activity in the 3.68 mg/L and 4.60 mg/L groups was significantly inhibited at 48–96 h. Overall, the activity of GSH-PX in each treatment group showed a decreasing, increasing, and then decreasing trend within 6–96 h. The activity of GSH-PX in the 1.84 mg/L group was higher than that in the control group within 96 h. When compared with the control group, the activity of the 2.76 mg/L and 3.68 mg/L groups decreased from 24 h to 96 h, and the longer the stress time, the lower the activity. In the highest concentration group (4.60 mg/L), the enzyme activity first increased and then decreased, and the GSH-PX activity decreased to 300.12 U/mg prot at 96 h, which was significantly different from that in the control group (P < 0.01). In the 1.84 mg/L group, there was no significant change in liver tissue within 72 h, but in the 1.84 mg/L group at 96 h and the 2.76 mg/L group at 24 h, the cell volume was slightly increased, cells had an irregular shape, and some cell membrane boundaries were blurred. At 48–96 h in the 2.76 mg/L group, and 24–48 h in the 3.68 mg/L and 4.60 mg/L groups, the liver cells were disordered and scattered, and the structure of liver cells was mostly incomplete. After 72–96 h in the 3.68 mg/L group and 72 h in the 4.60 mg/L group, the abnormality of liver cells was significantly aggravated, including cell hypertrophy, large area disintegration, cytoplasm overflow, and cell cavitation. At 96 h in the 4.60 mg/L group, the nucleus shrank, intracellular material gathered, and a large irregular blank appeared. For 72 h in the 1.84 mg/L group and 24 h in the 2.76 mg/L group, there was no significant change in gill tissue structure, whereas after 96 h in the 1.84 mg/L group, 48 h in the 2.76 mg/L group, and 24 h in the 4.60 mg/L group, the gill microplates were curved and club-like with mucus secreted around them, and the epithelial cells were enlarged, showed edema and partial hyperplasia, and the distance between the adjacent lamella became smaller. At 72 h in the 2.76 mg/L group, and at 24–48 h in the 3.68 mg/L and 4.60 mg/L groups, a small number of adjacent gill lamellae would fuse and form a small epithelial cell plate, with a large amount of mucus around them, and the length of gill lamellae was significantly shortened. In the 2.76 mg/L group at 96 h and the 3.68 mg/L group at 72 h, most of the basal lamellae had fused together, the epithelial cells of the gill lamellae were swollen and showed hyperplasia, and exfoliated epithelial cells were scattered around. At 96 h in the 3.68 mg/L group and 72–96 h in the 4.60 mg/L group, adjacent gill lamellae had adhered and fused with each other without a free end, and a large number of cells were necrotic and exfoliated.

Electrical impedance tomography (EIT) is an emerging imaging technology developed at the end of the last century, which has outstanding advantages such as non-invasiveness, non-radiation, smart, low cost and easy operation. This article reviews the development, principles and clinical application of electrical impedance tomography in diagnosis, decision-making of clinical management of acute respiratory distress syndrome. The article also provides suggestions for the future development of EIT in terms of more clinical research, improving technical accuracy, cost/effectiveness and training of staff.

Background Hyperthyroidism is a common endocrine psychosomatic disease, which is often accompanied by negative emotions, seriously affecting the prognosis of patients. Moreover, it is associated with more than 5 times more higher risk of committing suicide. Therefore, it has certain clinical and social significance to explore the neuroimaging characteristics of brain damage in patients with hyperthyroidism. Objective To analyze the abnormal patterns of spontaneous brain activity measured by resting-state functional magnetic resonance imaging (rs-fMRI) , and the neuroimaging characteristics of brain damage in patients with hyperthyroidism. Methods Participants were recruited from December 2014 to June 2016, including 25 hyperthyroidism outpatients with 131I therapy from Xinxiang Central Hospital, and 28 sex-, age-, and education level-matched healthy volunteers from the same hospital and the community near the hospital. Symptom Checklist-90 (SCL-90) was used to assess the mental health. rs-fMRI was performed to measure the fractional fractional amplitude of low-frequency fluctuation (fALFF) to reflect local spontaneous brain activity. Correlations of the mean fALFF (mfALFF) and with clinical variables and psychological symptoms were analyzed. Results Hyperthyroidism patients had higher mean scores of anxiety and anger-hostility than controls (P