We present petrological investigations and mineral chemistry of several Tethyan ophiolites to reveal the occurrence, origin, and fate of water in podiform chromitites. The results show that ...clinopyroxene and olivine in chromitites have H2O contents of 801-366 and 53-17 ppm, respectively. The highest water contents of olivine occur in massive chromitite and the lowest always in the clinopyroxene-bearing ores because much of the available hydrous fluids was taken up by the clinopyroxene during crystallization. The major and trace elemental and Li isotopic compositions of clinopyroxene associated with chromite and olivine in podiform chromitites indicate formation from a mixture of surface hydrous fluids on chromite grains and evolved melts from which olivine crystallized. The hydrous fluids initially originated from dehydration of a subducting slab as revealed by Li isotopic compositions of clinopyroxene and olivine in the chromitites. High fluid/rock ratios facilitated concentration of chromite to form chromitite, suppressing crystallization of olivine. The hydrous fluids that were collected on the chromite grain surface during crystallization allowed chromite grains to rise via decreasing density in the form of bubbles, thus promoting their gathering and concentration. The fate of these hydrous fluids depends on ambient physical and chemical conditions. Mostly they hydrate adjacent olivine grains in the chromitite or penetrate the surrounding dunite envelope. In some cases, the fluids dissolve into silicate melts to produce water-bearing clinopyroxene and/or hydrous minerals, such as amphibole, or infiltrate silicate and chromite grains to form inclusions, which may exsolve later in the form of mineral lamellae. Our investigations provide direct natural evidence for the presence and importance of water in the formation and evolution of chromite deposits, as inferred by earlier experimental studies.
Spectral features of hydrogen defects in natural mantle minerals derive from physico-chemical conditions of the lithosphere. Although hydrogen defects in synthetic orthopyroxene have been well ...investigated, their complex spectral features in natural orthopyroxenes are still difficult to decipher. To clarify this issue, it is indispensable to reveal what happens to hydrogen defects during high-temperature processes, thereby fingerprinting the origins of hydrogen defects observed in natural orthopyroxene. Here, we carry out Fourier transform infrared spectroscopic studies on hydrogen defects of three natural orthopyroxenes at elevated temperatures to 1000 °C. Hydrogen defects display reversible disordering at temperatures above 700 °C, which is different from those at ambient conditions. Moreover, hydrogen diffusivities are significantly different between the orthopyroxene samples from different tectonic settings despite their similar iron contents. Even for the same crystal, different hydrogen defects display different diffusion behaviors. Hydrogen defects corresponding to the 3420 cm-1 band have the fastest diffusivity relative to the other hydrogen defects. Most importantly, hydrogen defects can redistribute in the crystal, with new hydrogen defects produced at the cost of the initial hydrogen defects rather than involving a reaction with an external hydrogen source. Combining these findings with previously reported hydrogen defects in natural olivine and clinopyroxene at high temperatures, we propose that: (1) to correctly relate hydrogen defects features to geological processes, it is imperative to understand their behavior and origin, and (2) hydrogen disordering should be taken into account when predicting and extrapolating data on physical properties of the mantle from room-temperature measurements.
By laser cladding, FeCoNi2CrMnV0.5Nbx high-entropy alloy (HEA) coatings with different content of Nb were fabricated on the ZG25MnNi cast steel in the current study. The microstructure evolution, ...microhardness, corrosion resistance and wear resistance of FeCoNi2CrMnV0.5Nbx HEA coatings were studied systematically. The results indicated that the HEA alloy coatings transformed into dendrite (DR) structure after adding the Nb element. The dendrite was FCC phase and the interdendritic (IR) eutectic structure was composed of the FCC phase and Laves phase. The wear resistance and microhardness of the HEA coatings increased gradually with the increase of Nb content. When the Nb content x was 1.2, the microhardness of the upper part of the coatings reached 631.1 HV, which was 4 times higher than that of the base metal, and the wear resistance was improved to about 14.2 times the substrate. With the increase of Nb content, the corrosion resistance of coatings first increased and then weakened. When the Nb content x was 0.8, FeCoNi2CrMnV0.5Nbx HEA coatings had the best corrosion resistance.
Ovarian cancer is a predominant gynecologic malignancy and correlated with high mortality and severe morbidity. Exosomal microRNAs (miRNAs) play crucial roles in various processes during the ...progression of ovarian cancer, such as cell proliferation, apoptosis, and invasion. However, the function of exosomal miR-21-5p in ovarian cancer is still unknown. Here, we found that miR-21-5p was upregulated in ovarian cancer tissues, plasma exosomes of ovarian cancer patients, and exosomes from ovarian cancer cells. MiR-21-5p was incorporated in the exosomes from the ovarian cancer cells. In addition, 5-ethynyl-2′-deoxyuridine (Edu), a marker of cancer cell proliferation, was enhanced by miR-21-5p mimic while reduced by miR-21-5p inhibitor in ovarian cancer cells. MiR-21-5p mimic could increase, but miR-21-5p inhibitor could decrease the migration and invasion of cancer cells. Ovarian cancer cell apoptosis was induced by miR-21-5p inhibitor. Moreover, miR-21-5p inhibitor could up-regulate the expression of pro-apoptotic cleaved caspase3 and Bax while downregulate the expression of anti-apoptotic Bcl2 in the cells. Exosomal miR-21-5p inhibited the expression of cyclin-dependent kinase 6 (CDK6) by targeting its 3′-untranslated region (3′-UTR) at both the mRNA and protein levels. Tumorigenicity analysis in nude mice revealed that exosomal miR-21-5p could increase tumor volume, size, and weight of ovarian cancer in vivo. Besides, miR-21-5p targeted CDK6 in tumor tissues of nude mice. In conclusion, exosomal miR-21-5p contributes to the progression of ovarian cancer by regulating CDK6. Our findings will provide novel insights into the mechanism of exosomal miR-21-5p in the development of ovarian cancer. Exosomal miR-21-5p may serve as a potential target for the therapy of ovarian cancer.
This study aims to explore the relationship between social capital and the innovation performance of digital firms. In addition, we examine the mediation effect of cross-border knowledge search on ...this relationship and investigate the serial mediation effect of cross-border knowledge search and absorptive capacity between social capital and innovation performance. Using data collected from 217 Chinese digital companies, we tested the proposed hypotheses by constructing structural equation models through SPSS 22.0 and AMOS 24.0. Based on the results of theoretical deductions and empirical tests, some conclusions can be drawn. First, for digital firms, social capital remains significantly and positively associated with innovation performance during the COVID-19 pandemic. Meanwhile, digital firms with higher social capital are likely to generate higher innovation performance even if they experience a more severe impact of the COVID-19 pandemic. Second, cross-border knowledge search effectively mediates the relationship between social structural capital, social relational capital, and innovation performance, whereas this mediation effect is not significant between social cognitive capital and innovation performance. Finally, the serial mediation effect of cross-border knowledge search and absorptive capacity on the relationship between social capital and innovation performance is confirmed. Some managerial implications are summarized based on our findings. On the one hand, digital firms should still actively build social capital to enhance innovation performance during the pandemic. On the other hand, social capital can help digital firms implement cross-border knowledge search and develop absorptive capacity. Thus, digital firms can effectively utilize heterogeneous knowledge to enhance their innovation performance.
Mg/Al dissimilar metals were joined together utilizing ultrasonic spot welding (USW) with a Zn interlayer. The interfacial layer forming, microstructure, mechanical properties and fracture mechanisms ...of the Mg/Zn/Al ultrasonic spot welded (USWed) joints were studied systematically. Results showed that four typical regions with different forming morphologies emerged in the interface owing to the uneven distribution of stress and temperature. These four regions were the vortex-like plastic deformation region on the outside of the sonotrode tip teeth, the thinner flat region directly under the sonotrode tip teeth, the network-like diffusion region inside of the sonotrode tip teeth, and the thicker flat region between the two sonotrode tip teeth. The interfacial layer of Mg/Zn/Al USWed joints was mainly composed of a Mg-Zn liquid phase layer of α-Mg + (α-Mg + MgZn) + MgZn2 + (Mg2Zn11 + β-Zn), a residual Zn interlayer, and a η-Zn + α-Al solid solution layer. The addition of Zn interlayer blocked the inter-diffusion of Mg and Al atoms successfully and avoided the generation of Mg-Al IMCs effectively. The formed Mg-Zn system structure and Zn-Al solid solution have relatively good performances and lower brittleness. In comparison, Mg/Al joints welded with a Zn interlayer in-between displayed the maximum shearing strength about 89.6% greater than those of joints without a Zn interlayer.
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•The key innovation points of the paper lay in the following aspects:(1) Existing studies focused on the microstructure and mechanical properties of joints, but there were few reports on the interfacial stress and temperature distribution during welding process in the field of Mg/Al ultrasonic spot welding (USW).•(2) In this paper, the evolutionary model was used to explain the microstructure characteristics of the Mg/Zn/Al USW joint interface and the microstructural transformation process of each region was described in terms of mechanism, which has been little studied in the related literatures so far.
Ni-based filler metal and Ni-Cu-based filler metal were used to obtain copper/stainless steel (Cu/SS) joints through wire-feeding laser welding. Along the SS/weld interface, there exist different ...grain sizes (from coarse columnar grains to fine equiaxed grains). The heat affected zone (HAZ) on the copper side consisted of two areas with different grain sizes and the size of the grain in the Cu-HAZ of the Ni-Cu-based filled joint was much smaller than that of the Ni-based filled joint. Our results showed that grain refinement at the copper/weld (Cu/weld) interface of the Ni-Cu-based filled joint was observed through high-resolution electron backscattered diffraction (EBSD). There was a hardness elevation at the Cu/weld interface of the Ni-Cu-based filled joint due to the grain refinement on the weld of the copper side. The maximum tensile strength of the Ni-Cu-based filled joint was obtained and reached 91.2% of the tensile strength of the copper base metal (Cu-BM). Joints in this study were observed to fracture in a ductile mode. Furthermore, the Ni-Cu-based filled joint exhibited a higher plastic deformation, which was primarily caused by the large deformation of the weld zone and the large deformation of the Cu-BM due to the high plasticity of the weld, which alleviated the stress concentration, as indicated by 2D-digital image correlation (DIC) test results.
Hybrid laser–double-arc welding (HLDAW) is a perspective welding technology with high-deposition quantity, deep penetration, superior gap-bridging ability, and is simply equipped and flexibly ...adjusted. Either double-power supply system or single-power supply system can be used in this welding system. In the single-power supply mode, there is a particular phenomenon called “alternative burning” presented under certain welding conditions. The frequency of alternative burning is the key to the welding stability. However, the mechanism of this phenomenon and its change rules are not clear. This research mainly aims at the change laws of alternative burning and its essential mechanism. It was found that the alternating period is inversely proportional to laser power and wire-feeding speed, and is proportional to wire spacing and arc voltage. The essence of alternative burning is the regularly repetitive transfer of arc from one wire tip to the other in the condition of relatively low electron density in arc zone which is hard to maintain two arcs burning simultaneously. This phenomenon will disappear when the electron density is greater than 5.54 × 10
16
cm
−1
. Results are meaningful for understanding the interaction mechanism of heat source and its influence on welding stability of HLDAW process in this kind of power supply.
Foliar nitrogen (N) fertilizer application at later stages of wheat (
) growth is an effective method of attenuating drought stress and improving grain filling. The influences or modes of action of ...foliar application of various nitrogen forms on wheat growth and grain filling need further research. The objective of this study was to examine the regulatory effects of various forms of foliar nitrogen NO
, NH
, and CO(NH
)
on wheat grain filling under drought stress and to elucidate their underlying mechanisms. The relative effects of each nitrogen source differed in promoting grain filling. Foliar NH
-N application notably prolonged the grain filling period. In contrast, foliar application of CO(NH
)
and NO
-N accelerated the grain filling rate and regulated levels of abscisic acid (ABA), z-riboside (ZR), and ethylene (ETH) in wheat grains. Analysis of gene expression revealed that CO(NH
)
and NO
-N upregulated the genes involved in the sucrose-starch conversion pathway, promoting the remobilization of carbohydrates and starch synthesis in the grains. Besides, activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were increased, whereas the content of malondialdehyde (MDA) declined under foliar nitrogen application (especially NH
-N). Under drought stress, enhancement of carbohydrate remobilization and sink strength became key factors in grain filling, and the relative differences in the effects of three N forms became more evident. In conclusion, NH
-N application improved the antioxidant enzyme system and delayed photoassimilate transportation. On the other hand, foliar applications of NO
-N and CO(NH
)
enhanced sink capacity and alleviated drought stress injury in wheat.
Most deep-learning-based object detection algorithms exhibit low speeds and accuracy in gear surface defect detection due to their high computational costs and complex structures. To solve this ...problem, a lightweight model for gear surface defect detection, namely STMS-YOLOv5, is proposed in this paper. Firstly, the ShuffleNetv2 module is employed as the backbone to reduce the giga floating-point operations per second and the number of parameters. Secondly, transposed convolution upsampling is used to enhance the learning capability of the network. Thirdly, the max efficient channel attention mechanism is embedded in the neck to compensate for the accuracy loss caused by the lightweight backbone. Finally, the SIOU_Loss is adopted as the bounding box regression loss function in the prediction part to speed up the model convergence. Experiments show that STMS-YOLOv5 achieves frames per second of 130.4 and 133.5 on the gear and NEU-DET steel surface defect datasets, respectively. The number of parameters and GFLOPs are reduced by 44.4% and 50.31%, respectively, while the mAP@0.5 reaches 98.6% and 73.5%, respectively. Extensive ablation and comparative experiments validate the effectiveness and generalization capability of the model in industrial defect detection.
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