Study on the critical stress threshold of weakly cemented sandstone damage based on the renormalization group method

During the microstructural analysis of weakly cemented sandstone,the granule components and ductile structural parts of the sandstone are typically generalized.Considering the contact between granules in the microstructure of weakly cemented sandstone,three basic units can be determined:regular tetrahedra,regular hexahedra,and regular octahedra.Renormalization group models with granule-and pore-centered weakly cemented sandstone were established,and,according to the renormalization group transformation rule,the critical stress threshold of damage was calculated.The results show that the renormalization model using regular octahedra as the basic units has the highest critical stress threshold.The threshold obtained by iterative calculations of the granule-centered model is smaller than that obtained by the pore-centered model.The granule-centered calculation provides the lower limit(18.12%),and the pore-centered model provides the upper limit(36.36%).Within this range,the weakly cemented sandstone is in a phase-like critical state.That is,the state of granule aggregation transforms from continuous to discrete.In the relative stress range of 18.12%-36.36%,the weakly cemented sandstone exhibits an increased proportion of high-frequency signals(by 83.3%)and a decreased proportion of low-frequency signals(by 23.6%).The renormalization calculation results for weakly cemented sandstone explain the high-low frequency conversion of acoustic emission signals during loading.The research reported in this paper has important significance for elucidating the damage mechanism of weakly cemented sandstone.

Investigation on the Changing Characteristics of Flow-Induced Noise in a Centrifugal Pump

Centrifugal pumps are widely used in engineering for a variety of applications.A known drawback of these devices is the high-level noise generated during operations,which can affect their stability and adversely influence the entire working environment.By combining the Powell vortex sound theory,numerical simulations and experimental measurements,this research explores the trends of variation and the corresponding underlying mechanisms for the flow-induced noise at various locations and under different operating conditions.It is shown that the total sound source intensity(TSSI)and total sound pressure level(TSPL)in the impeller,in the region between the inlet to the outlet and along the circumferential extension of the volute,are much higher than those at pump inlet and outlet.Additionally,under various rotational speeds with the design flow rate(Condition 1),the TSSI and TSPL at pump inlet and outlet are higher than those obtained with the opening of the valve kept unchanged(Condition 2);vice versa when these two parameters are evaluated at various locations in the impeller and the volute under the Condition 2,they exceed the equivalent values obtained for the other Condition 1.

Quality Analysis and Evaluation of Scylla paramamosain from Three Different Areas

[Objectives]The quality of Scylla paramammosain produced in Fujian,Sanmen and Shanghai were analyzed and evaluated.[Methods]Adult Scylla paramammosain from Fujian,Sanmen and Shanghai were separated for their muscles and gonads,which were analyzed for nutritional components.[Results]The muscle moisture content of S.paramammosain from Sanmen was significantly higher than those in S.paramammosain from Fujian and Shanghai.The muscle protein contents of S.paramammosain from the three regions ranked as Shanghai>Fujian>Sanmen(P<0.05).The muscles of S.paramammosain from Shanghai had the highest crude fat and crude ash contents.The moisture contents of the gonads of the S.paramammosain from the three regions had no significant differences.The protein contents of the gonads of S.paramammosain from the three regions ranked as Shanghai>Sanmen>Fujian(P<0.05).The S.paramammosain from Sanmen had the highest crude fat and crude ash contents in gonads.The contents of 17 amino acids detected in the muscles and gonads of S.paramammosain from the three different regions were different.The total amounts of total amino acids(TAA),essential amino acids(EAA)and flavor amino acids(FAA)in the muscles of S.paramammosain from Sanmen were significantly lower than those produced in Fujian and Shanghai(P<0.05),but the proportions of essential amino acids(EAA)and flavor amino acids were not significantly different.The proportion of EAA and FAA in the gonads of S.paramammosain produced in the three areas were significantly different(P<0.05).There were also differences in the fatty acid composition of the muscles and gonads of S.paramammosain from the three different regions.The proportion of EPA in the muscles of S.paramammosain from Fujian was higher than those of other two groups,but the differences were not significant;the proportion of DHA was significantly higher than those of other two groups,and the differences were significant(P<0.05);and the proportions of n3 PUFA in muscles of S.paramammosain produced in Fujian and Sanmen were significantly higher than that of S.paramammosain produced in Shanghai(P<0.05).The proportions of EPA,DHA and n6 PUFA in the gonads of S.paramammosain produced in Sanmen were significantly higher than those produced in Fujian and Shanghai(P<0.05),while the n3 PUFA was the highest in S.paramammosain produced in Fujian.The proportions of n6/n3 PUFA in S.paramammosain produced in the three different regions were significantly different(P<0.05).In summary,it could be seen that the nutritional composition of S.paramammosain produced in different regions has its own characteristics.[Conclusions]This study provides basic data for the establishment of quality evaluation standards for S.paramammosain,and provides a new perspective for the evaluation of breeding models.

教育技术服务教育强国建设:溯源、要义与路径

强国必先强教,教育技术在数智化赋能教育高质量发展过程中肩负服务强国建设的历史使命。追本溯源,教育技术发展史均与各国“教育强国”的发展路径耦合相连。教育技术服务教育强国建设的内涵在于构建中国教育技术学自主知识体系,在教育技术学科自身强大的基础上,充分利用数智化技术推动教育数字化转型,发挥教育技术作为教育“方法论”对教育学科的全面支撑作用,进而在多学科领域中应用教育技术服务强国建设,最终推动教育技术在为党育人、为国育才上的强国作用,培养服务强国建设的马克思主义人学理论上全面而自由发展的人。教育技术服务教育强国建设的行动路径在于坚持马克思主义中国实践化的创新理论成果指导学科建设,立足中华民族现代文明推动教育技术学科本土化纵深发展,发挥教育技术的方法论作用支撑高质量教育体系全面变革,讲好教育技术中国故事为世界教育创新发展提供智慧范本,完善教育技术服务教育学科发展与创新人才培育的顶层设计。

Optimizing protein and lipid levels in practical diet for juvenile northern snakehead fish(Channa argus)

A 3×3 factorial feeding trial was conducted to evaluate the production response of juvenile northern snakehead fish(Channa argus). Nine diets containing 3 protein levels(45%, 48% and 51%) and 3 lipid levels(9%,12% and 15%) were formulated and fed to triplicate groups of juvenile northern snakehead(15.78 ± 0.09 g/fish) for 8 weeks. The formulated diets were named as P45 L9, P45 L12, P45 L15, P48 L9,P48 L12, P48 L15, P51 L9, P51 L12 and P51 L15(P-Protein, L-Lipid), respectively. Fish fed diets with the lowest protein and lipid combination(P45 L9) had the lowest growth performance. Weight gains(WG) of fish fed the 4 diets P48 L12, P48 L15, P51 L9, and P51 L12 were not significantly different(P> 0.05), but significantly higher(P < 0.05) than those of fish fed the other diets. Fish fed diets P48 L12 and P48 L15 had significantly lower(P < 0.05) feed conversion ratios(FCR) than the rest of the treatments. Protein retentions(PR) among fish fed the diets P45 L12, P45 L15, P48 L12, P48 L15, P51 L9, and P51 L12 were similar and significantly higher(P < 0.05) than those of fish fed the remaining diets. Protein sparing effect was observed in the treatments when fish was fed diets containing 45% or 48% dietary protein levels with dietary lipid increased from 9% to12%. Fish fed diets with 9% lipid tended to have lower viscerosomatic index(VSI), hepatosomatic index(HSI),and whole-body lipid. Increasing dietary protein level significantly increased(P < 0.05) liver moisture and lipid while dietary lipid level increased liver lipid. Intestinal lipase activity increased significantly(P < 0.05)with increasing dietary lipid and protein levels while intestinal a-amylase and protease activities were not significantly influenced(P > 0.05) by dietary treatments. Based on these results, the diet containing 48%protein with either 12% or 15% lipid is the optimal for supporting growth and feed utilization of juvenile northern snakehead under the current testing conditions.

人工智能在消化内镜中应用的临床进展

随着人工智能(AI)的不断发展,其在临床医学中的应用已成为研究热点。消化内镜是消化系统疾病中较为常用且重要的辅助诊疗设备,辅助临床医生进行疾病的诊断及治疗。但由于病变性质、范围以及临床医生经验等不同,导致误诊、漏诊的出现。AI与内镜结合,培训及规范临床医师标准化操作流程,辅助临床医生进行病变的识别,提高检查质量,减少漏诊。本文就AI在消化内镜诊疗过程中的应用进展作一综述。