Tensile Mechanical Behavior and Failure Mechanism of a Plain-Woven SiCf/SiC Composites at Room and Elevated Temperatures

Ceramic matrix composites (CMCs) are the preferred materials for solving advanced aerospace high-temperature structural components;it has the comprehensive advantages of higher temperature (~1500˚C) and low density. In service environments, CMCs exhibit complex damage mechanisms and failure modes, which are affected by constituent materials, meso-architecture and inhere defects. In this paper, the in-plane tensile mechanical behavior of a plain-woven SiCf/SiC composite at room and elevated temperatures was investigated, and the factors affecting the tensile strength of the material were discussed in depth. The results show that the tensile modulus and strength of SiCf/SiC composites at high temperature are lower, but the fracture strain increases and the toughness of the composites is enhanced;the stitching holes significantly weaken the tensile strength of the material, resulting in the material is easy to break at the cross-section with stitching holes.

火星无线电掩星探测进展

火星是地球的姊妹星,研究火星对了解火星、地球乃至太阳系的演化具有重要意义.自从1964年美国水手4号发射,首次成功地运用无线电掩星技术探知到火星的环境特征之后,国际上不少的火星任务都开展了掩星实验,取得了重要进展.本文依据采用了无线电掩星技术进行勘探的火星探测器发射时间顺序展开调研,针对具有开创性的水手系列、火星全球勘测者、火星快车、火星大气挥发演化探测器、天问一号等,梳理分析和总结了各任务的火星无线电掩星方式以及所获取的廓线数量、位置分布、获取方式等产品信息,以及部分相关的研究结果.本文还分析了当前火星无线电掩星探测方式存在的局限性,并探讨了可能的对策.火星无线电掩星后续可重点考虑多颗星-星掩星结合星-地掩星方式形成掩星星座;并通过选用适当的信号探测频率、改进反演算法等方式进一步提高掩星质量;火星掩星探测手段还可与火星顶部探测雷达、直接探测等手段相结合,发展火星多源数据融合技术.随着探测方式的不断改进,无线电掩星探测将是火星探测的重要手段.未来会有数量越来越多、时间与空间覆盖越来越全面、精度越来越高的掩星数据用于火星的整个空间环境研究,包括大、中尺度乃至小尺度结构的特征与演化规律都将被人类掌握.

IR-YOLO: Real-Time Infrared Vehicle and Pedestrian Detection

Road traffic safety can decrease when drivers drive in a low-visibility environment.The application of visual perception technology to detect vehicles and pedestrians in infrared images proves to be an effective means of reducing the risk of accidents.To tackle the challenges posed by the low recognition accuracy and the substan-tial computational burden associated with current infrared pedestrian-vehicle detection methods,an infrared pedestrian-vehicle detection method A proposal is presented,based on an enhanced version of You Only Look Once version 5(YOLOv5).First,A head specifically designed for detecting small targets has been integrated into the model to make full use of shallow feature information to enhance the accuracy in detecting small targets.Second,the Focal Generalized Intersection over Union(GIoU)is employed as an alternative to the original loss function to address issues related to target overlap and category imbalance.Third,the distribution shift convolution optimization feature extraction operator is used to alleviate the computational burden of the model without significantly compromising detection accuracy.The test results of the improved algorithm show that its average accuracy(mAP)reaches 90.1%.Specifically,the Giga Floating Point Operations Per second(GFLOPs)of the improved algorithm is only 9.1.In contrast,the improved algorithms outperformed the other algorithms on similar GFLOPs,such as YOLOv6n(11.9),YOLOv8n(8.7),YOLOv7t(13.2)and YOLOv5s(16.0).The mAPs that are 4.4%,3%,3.5%,and 1.7%greater than those of these algorithms show that the improved algorithm achieves higher accuracy in target detection tasks under similar computational resource overhead.On the other hand,compared with other algorithms such as YOLOv8l(91.1%),YOLOv6l(89.5%),YOLOv7(90.8%),and YOLOv3(90.1%),the improved algorithm needs only 5.5%,2.3%,8.6%,and 2.3%,respectively,of the GFLOPs.The improved algorithm has shown significant advancements in balancing accuracy and computational efficiency,making it promising for practical use in resource-limited scenarios.

Research on Quantitative Identification of Three-Dimensional Connectivity of Fractured-Vuggy Reservoirs

The fractured-vuggy carbonate oil resources in the western basin of China are extremely rich.The connectivity of carbonate reservoirs is complex,and there is still a lack of clear understanding of the development and topological structure of the pore space in fractured-vuggy reservoirs.Thus,effective prediction of fractured-vuggy reservoirs is difficult.In view of this,this work employs adaptive point cloud technology to reproduce the shape and capture the characteristics of a fractured-vuggy reservoir.To identify the complex connectivity among pores,fractures,and vugs,a simplified one-dimensional connectivity model is established by using the meshless connection element method(CEM).Considering that different types of connection units have different flow characteristics,a sequential coupling calculation method that can efficiently calculate reservoir pressure and saturation is developed.By automatic history matching,the dynamic production data is fitted in real-time,and the characteristic parameters of the connection unit are inverted.Simulation results show that the three-dimensional connectivity model of the fractured-vuggy reservoir built in this work is as close as 90%of the fine grid model,while the dynamic simulation efficiency is much higher with good accuracy.

沉积温度对甲基硅烷化学气相沉积SiC涂层显微组织和烧蚀性能的影响

以甲基硅烷(MS)为气源,采用化学气相沉积方法于不同温度下在石墨表面制备SiC涂层,并系统研究温度对SiC涂层的沉积速率、显微组织和抗烧蚀性能的影响规律。实验结果表明:当沉积温度为1000℃时,以MS为气源的SiC涂层的沉积速率为50~120μm/h,远高于以甲基三氯硅烷为气源的沉积速率(5~10μm/h)。当沉积温度较低(900~1000℃)时,以MS为气源所制备的SiC涂层整体光滑、平整,呈球形紧密堆积形貌;沉积温度较高(1100~1200℃)时,SiC涂层呈不规则菜花状颗粒堆积形貌,且微晶尺寸明显增大;当沉积温度为1000℃时,SiC涂层具有合适的致密性、粗糙度以及尺寸均匀的显微组织,同时,该涂层经2300℃等离子烧蚀80 s后,其质量烧蚀率和线性烧蚀率分别为0.0096 mg/s和0.3750μm/s,显示优异的抗烧蚀性能。本研究为以MS为气源的化学气相沉积法制备SiC涂层提供一定的理论基础和技术支撑。

Novel carbon-nitride based catalysts for enhanced CH_(4) reforming under visible light: From morphology to heterojunction design principles

The synthesis of high value-added chemical products using CO_(2)and CH_(4)is a promising CO_(2)conversion technology that can reduce greenhouse gas emissions while also alleviating the energy crisis.However,problems such as high energy consumption and strict reaction conditions in reforming process hinder the further development of the technology.In this work,carbon-nitrogen based composites were prepared for the first time according to the design principle from morphology to heterojunction,which is innovatively applied in the process of photocatalytic CH4reforming.Firstly,C_(3)N_(4)materials with different dimensions(D) are prepared and applied to a CO_(2)-CH_(4)photocatalytic system.Additionally,the 2D/2D TiO_(2)/g-C_(3)N_(4)heterostructure is constructed with the ultrasonic impregnation method to further improve charge generation,transfer,and separation efficiency.It is worth noting that the yield of CO reaches173.80 μmol g^(-1),and the catalytic performance is improved by 1546% compared to bulk C_(3)N_(4).Moreover,the physical and chemical properties of 2D/2D TiO_(2)/g-C_(3)N_(4)materials are studied using a variety of cha racterization methods.Furthermore,the work fu nction and adsorption energy of different C3N4/TiO_(2)models for CO_(2)adsorption are calculated by density functional theory(DFT).Then,a possible catalytic mechanism for photocatalytic CO_(2)and CH_(4) conversion is proposed based on DFT calculations and experimental results.This work provides a new technical route for the rapid conversion of CO_(2)and CH_(4) at room temperature,as well as a new research concept for achieving carbon neutrality.

A highly efficient La-modified ZnAl-LDO catalyst and its performance in the synthesis of dimethyl carbonate from methyl carbamate and methanol

In this paper,the highly efficient ZnAlLa layered double oxide(ZnAlLa-LDO)catalyst was evaluated and used in methyl carbamate(MC)alcoholysis synthesis of dimethyl carbonate.Under optimal conditions,the MC conversion was 33.5% and the dimethyl carbonate(DMC)selectivity was up to 92,4% at 443 K and in 9 h.The prepared catalysts were well characterized to investigate the effect on the catalytic performance and reaction catalysis mechanism.The experimental results show that the addition of La adjusted the structure and chemical properties of ZnAl composite oxide and that the synergistic effect among Zn,Al and La play a key role in adjusting the acid-base properties and stability of the catalyst,which definitely improved the DMC selectivity and catalytic stability.Based on the proposed reaction mechanism,two kinetic models of the catalytic reaction were established and modified:LangmuirHinshelwood and power-rate law kinetic model.The good agreement between kinetic models and experimental data showed that the power-rate law kinetic model based on the elementary reactions is a suitable model for providing a theoretical basis.The pre-exponential factor and activation energy of the main reaction are 5.77×10^(7)and 77.60 kJ·mol^(-1),respectively.

Malignant proliferative ependymoma of the neck with lymph node metastasis:A case report

BACKGROUND Malignant proliferating trichilemmal tumor(MPTT)is an infrequent malignant neoplasm originating from cutaneous appendages,with only a handful of documented cases.This report delineates a unique instance of MPTT situated in the neck,accompanied by lymph node metastasis.A comprehensive exposition of its clinical trajectory and imaging manifestation is presented,aiming to enhance comprehension and management of this atypical ailment.CASE SUMMARY Patient concerns:A 79-year-old male presented with a longstanding right neck mass persisting for over six decades,exhibiting recent enlargement over the past year.Diagnoses:Enhanced magnetic resonance imaging of the neck unveiled an elliptical mass on the right neck side,characterized by an ill-defined border and a heterogeneous signal pattern.The mass exhibited subdued signal intensity on T1-weighted imaging(T1WI)and a heterogeneous high signal on T2-weighted imaging(T2WI),interspersed with a lengthy T1 and T2 cystic signal motif.Close anatomical association with the submandibular gland joint was noted,and intravenous gadolinium diethylene triamine pentaacetic acid administration facilitated conspicuous enhancement.Substantial enhancement of the solid segment prompted an initial preoperative diagnosis of malignant nerve sheath tumor.However,post-surgery histopathological and immunohistochemical analysis conclusively confirmed the diagnosis as malignant hyperplastic external hair root sheath tumor.Intervention:Complete excision of the tumor was successfully executed.Outcomes:The patient experienced a favorable postoperative recovery.CONCLUSION Malignant proliferative trichilemmal tumor external hair root sheath tumor is a cystic-solid lesion,appearing as low signal on T1WI images or high signal on T2WI with enhancement of the solid component.Suspicions of malignancy are heightened when the tumor border is indistinct,tissue planes are breached,or when linear or patchy high signals are observed in the subcutaneous tissue on T1 liver acquisition with volume acceleration enhanced images along with intermediate signal on T2WI and restricted diffusion on diffusion-weighted imaging images.Strong consideration for malignancy should arise if there are signs of compromised adjacent tissue relationships or direct invasion evident on imaging.We have incorporated the above-mentioned content into the entire manuscript.

适应性生成——常德柳叶湖管理委员会行政中心

柳叶湖管理委员会行政中心毗邻柳叶湖度假区,具有重要的城市节点的功能。文章探讨大湘西地区传统的风雨桥和吊脚楼等建筑形式在城市建筑中的适应性生成,将场地的场所感、地域类型与行政中心的开放性、公共性结合,用线式空间的组织方式串联内部功能,进行了一次将传统空间形式应用于当代行政办公建筑的实践。

Preparation and Performance of the Hyperbranched Polyamine as an Effective Shale Inhibitor for Water-Based Drilling Fluid

Seeking effective solutions to control and mitigate the interaction between drilling fluids and clay formations has been a challenge for many years, and various shale inhibitors have shown excellent results in problematic shale formations around the world. Herein, the hyperbranched polyamine (HBPA) inhibitor with a higher ratio of amine groups and obvious tendentiousness in protonation was successfully synthesized from ethylenediamine, acryloyl chloride and aziridine by five steps, in which the metal-organic framework (MOF) was employed as a catalyst for ring-open polycondensation (ROP). The structure and purity were confirmed by nuclear magnetic resonance hydrogen spectroscopy and high-performance liquid chromatography (HPLC) respectively. The HBPA displays more excellent performance than EDA and KCl widely applied in the oil field. After aging at 80°C and 180°C, the YP of a slurry system containing 25 wt.% bentonite and 2 wt.% HBPA are just 8.5 Pa and 5.5 Pa (wt.%: percentage of mass), respectively. The swelling lengths of 2 wt.% HBPA are estimated to be 1.78 mm, which falls by 70% compared with that of freshwater. Under a hot rolling aging temperature of 180°C, the HBPA system demonstrates a significant inhibition with more than 85% shale cuttings recovery rate and is superior to conventional EDA and KCl. Mechanism analysis further validates that the HBPA can help to increase the zeta potential.

微悬浮聚合法制备丙烯酸-丙烯酸正丁酯-丙烯酸甲酯共聚物纳米破乳剂

以丙烯酸(AA)、丙烯酸甲酯(MA)和丙烯酸正丁酯(BA)为单体,N,N-亚甲基双丙烯酰胺(MBA)为交联剂,偶氮二异丁腈(AIBN)为引发剂,利用微悬浮聚合法制备了丙烯酸-丙烯酸正丁酯-丙烯酸甲酯共聚物(P(AA-BA-MA))。采用红外光谱和核磁共振对聚合物的结构进行了表征,分析了聚合物的粒径及其分布,测试了不同温度下聚合物在甲苯中的表面张力,探讨了丙烯酸丁酯含量对破乳性能影响,并综合考察了聚合物在原油乳液中的破乳性能。研究结果表明,P(AA-BA-MA)的平均粒径为83.81 nm,在甲苯溶液中能有效降低表面张力;随着丙烯酸丁酯含量增加,对原油乳液具有良好的破乳性能;当单体质量比m(AA)∶m(MA)∶m(BA)=3∶1∶6、破乳温度70℃和破乳剂浓度为100 mg/L以上时,破乳效率可达到85.91%以上,能快速高效地实现油水分离,且水相清亮,油水界面整齐。

我国中小学课后服务经费的供给模式研究

完善的课后服务经费供给模式是推进中小学课后服务的有力保障。基于56份课后服务政策文本分析,发现我国中小学课后服务经费的供给模式主要有单一主体供给型、多主体供给型、复合供给型三种。单一主体供给型是指课后服务经费由政府全部承担或者由学校自筹,并严禁向学生收费。多主体供给型包括:政府补助、学校支持、家长合理分担型;政府补助、学校支持、家长分担、社会资助型。复合供给型包括:从经济条件看,有经济条件的地区由政府单一供给,无经济条件的地区由多主体分担;从城乡差别来看,城市地区采用多主体供给,农村地区采取政府单一供给;从课后服务基本类型来看,基本托管服务费用由政府单一供给,个性化服务费用由多主体供给。研究还发现课后服务经费供给模式的确定主要受政府对课后服务基本属性的认知、政府财政状况、城乡地域差别、课后服务的基本类型、学生家庭经济状况等因素的影响。为此,应实事求是,从本省实际财政状况出发制定课后服务经费供给模式;求同存异,始终确保课后服务的公益属性和民生属性;多元配合,确保课后服务经费供给的稳定性和充沛性;追求公平,加大对贫困家庭学生的课后服务费用减免力度。

Development and application of a multi-physics and multi-scale coupling program for lead-cooled fast reactor

In this study,a multi-physics and multi-scale coupling program,Fluent/KMC-sub/NDK,was developed based on the user-defined functions(UDF)of Fluent,in which the KMC-sub-code is a sub-channel thermal-hydraulic code and the NDK code is a neutron diffusion code.The coupling program framework adopts the"master-slave"mode,in which Fluent is the master program while NDK and KMC-sub are coupled internally and compiled into the dynamic link library(DLL)as slave codes.The domain decomposition method was adopted,in which the reactor core was simulated by NDK and KMC-sub,while the rest of the primary loop was simulated using Fluent.A simulation of the reactor shutdown process of M2LFR-1000 was carried out using the coupling program,and the code-to-code verification was performed with ATHLET,demonstrating a good agreement,with absolute deviation was smaller than 0.2%.The results show an obvious thermal stratification phenomenon during the shutdown process,which occurs 10 s after shutdown,and the change in thermal stratification phenomena is also captured by the coupling program.At the same time,the change in the neutron flux density distribution of the reactor was also obtained.

Startup scheme optimization and flow instability of natural circulation lead-cooled fast reactor SNCLFR-100

Owing to the inherent instability of the natural circulation system,flow instability can easily occur during the operation of a natural circulation lead-cooled fast reactor,especially during the startup phase.A comprehensive startup scheme for SNCLFR-100,including primary and secondary circuits,is proposed in this paper.It references existing more mature startup schemes in various reactor types.It additionally considers the restriction conditions on the power increase in other schemes and the characteristics of lead-based coolant.On this basis,the multi-scale coupling code ATHLET-OpenFOAM was used to study the flow instability in the startup phase under different power-step amplitudes and power duration times.The results showed that obvious flow instability phenomena were found in the different startup schemes,such as the short-term backflow phenomenon of the core at the initial time of the startup.Moreover,an obvious increase in the flow rate and temperature to the peak value at the later stage of a continuous power rise was observed,as well as continuous oscillations before reaching a steady state.It was determined that the scheme with smaller power-step amplitude and a longer power duration time requires more time to start the reactor.Nevertheless,it will be more conducive to the safe and stable startup of the reactor.

替吉奥治疗进展期胃癌的临床疗效分析

目的探讨替吉奥治疗进展期胃癌的临床效果。方法选取我院收治的进展期胃癌患者140例,随机分为两组,研究组应用替吉奥治疗,对照组应用奥沙利铂治疗。比较两组患者的临床疗效、不良反应发生率、生活质量。结果研究组临床疗效优于对照组,差异有统计学意义(P<0.05);研究组不良反应发生率低于对照组,差异有统计学意义(P<0.05);研究组生活质量高于对照组,差异有统计学意义(P<0.05)。结论替吉奥对进展期胃癌患者的治疗效果较好,值得临床推广使用。

Photoreduction of CO_(2) in the presence of CH_(4) over g-C_(3)N_(4) modified with TiO_(2) nanoparticles at room temperature

CO_(2)reduction under simulated sunlight over photocatalysts has become an attractive researcher area recently.In this work,carbon nitride compounds modified by TiO_(2)nanoparticles(TNPs)have been used for the photoreduction of CO_(2)in the presence of CH_(4)at room temperature.Briefly,a series of noble-metal-free TNP-graphitic-carbon nitride(g-C_(3)N_(4),also abbreviated CN)photocatalysts with different TNPs loadings and calcination temperatures have been synthesized by a wet-chemical method.The characterization results of XRD,FTIR,SEM,TEM,BET,XPS,CO_(2)Adsorption,UV-vis,and PL demonstrate that the BET surface area and CO_(2)adsorption capacity have been improved after the calcination.Besides,the g-C_(3)N_(4)has been successfully coupled with the TNPs and a heterojunction has formed at their interface.These characters contribute to increase the photocatalytic activity of TNPs-CN toward reducing CO_(2)in the presence of CH_(4),and its'performance is better than bare g-C_(3)N_(4),Titania(P_(25))-CN,MgO-CN,or Cu_(2)O-CN.Orthogonal experiments are then carried out to investigate the sensitivity factors and optimum conditions.The sensitivity results show that the reaction pressure makes little difference on the photocatalysis results,which verifies the photoinduced CO_(2)-CH_(4)reaction has a tiny change in gas volume.In addition,under the optimum conditions,the turnover frequency(TOF)of CO after 4 h reaction can reach 9.98μmol g-cat.^(-1)h^(-1),and traces of ethane and ethylene have been detected during the reactions.In addition,surface acetate and carbonaceous deposit are found on the(20)TNPs-CN/450 surface after continuous 24 h irradiation under the optimum conditions,which resulting in the inactivation of the catalyst.Finally,possible reaction mechanisms have been proposed based on the results.

Development of a subchannel code for blockage accidents of LMFRs based on the 3D fuel rod model

To predict the thermal-hydraulic(T/H)parameters of the reactor core for liquid-metal-cooled fast reactors(LMFRs),especially under flow blockage accidents,we developed a subchannel code called KMC-FB.This code uses a time-dependent,four-equation,singlephase flow model together with a 3D heat conduction model for the fuel rods,which is solved by numerical methods based on the finite difference method with a staggered mesh.Owing to the local effect of the blockage on the flow field,low axial flow,increased forced crossflow,and backflow occur.To more accurately simulate this problem,we implemented a robust and novel solution method.We verified the code with a low-flow(~0.01 m/s)and large-scale blockage case.For the preliminary validation,we compared our results with the experimental data of the NACIE-UP BFPS blockage test and the KIT19ROD blockage test.The results revealed that KMC-FB has sufficient solution accuracy and can be used in future flow blockage analyses for LMFRs.

Imaging changes in neural circuits in patients with depression using 1 H-magnetic resonance spectroscopy and diffusion tensor imaging

1 H-magnetic resonance spectroscopy imaging and diffusion tensor imaging were performed in 19 patients with mild depression and in 13 controls.The mean age of the patients was 31 years.The mean Hamilton depression score of the patients was 22.5±13.2.N-acetylaspartate,choline and creatine concentrations and the average diffusion coefficient and fractional anisotropy values were measured in the bilateral hippocampus,striatum,thalamus and prefrontal deep white matter. Compared with the control group,the mild depressed patients had：（1）a higher choline/creatine ratio and a negative correlation between the choline/creatine ratio and the average diffusion coefficient in the hippocampus;（2）a lower choline/creatine ratio and a higher fractional anisotropy in the striatum;（3）a lower fractional anisotropy and a positive correlation between the fractional anisotropy and the choline/creatine ratio in the prefrontal deep white matter;and（4）a higher average diffusion coefficient and a positive correlation between the choline/creatine ratio and the N-acetylaspartate/creatine ratio in the thalamus,as well as positive correlation between the choline/creatine ratio and Hamilton depression scores.These data suggest evidence of abnormal connectivity in neurofibrotic microstructures and abnormal metabolic alterations in the limbic-cortical-striatal-pallidal-thalamic neural circuit in patients with mild depression.

An improved CFD model of gas flow and particle interception in a fiber material

An improved CFD model of gas flow and particle interception in a fiber material which fiber size is Y-shape was developed in this work. The porous medium model was used to build the model of the whole size of fiber filter medium. Mixture model was adopted. The algorithm of particle interception in the whole size of fiber filter medium was derived and UDF(User Defined Function) that described kinds of particle filtering mechanisms in filter fibrous media was added to the Fluent default conservation equation as source term for simulation. The inertial resistance of the filter was taken into consideration, which provided a more precise measurement of the smoke flow and the particle interception in the filter under higher smoke speed conditions. The commercial software, Fluent 6.3, was used to simulate the smoke flow and particle interception in the filter in a single suction. The velocity and pressure profiles of smoke or nicotine particle in the filter, as well as nicotine particle volume fraction profile were well simulated. Finally, the comparisons of nicotine particle filtration efficiency between Fluent simulation results in this work and experimental results, as well as the model prediction in the literature were made to validate the simulation model. The comparisons showed that the particle entrapment model from simulation results was in good agreement with that from the experimental results. In addition, the Fluent simulation results are closer to reality both at the beginning and the end of the smoke process comparing with the model predicted results in the literature.

Synthesis of Bio-Plasticizer from Soybean Oil and Its Application in Poly(Vinyl Chloride) Films

Herein,epoxidized soybean oil methyl ester(ESOM)plasticizer was synthesized for the preparation of plasticized poly(vinyl chloride)(PVC)films by the alcoholysis and epoxidation.The chemical structure of ESOM was investigated by infrared spectrum and 1 H nuclear magnetic resonance.The effect of content of ESOM and petroleum based plasticizer di-2-ethylhexyl phthalate(DEHP)on the performance of plasticized PVC films was studied.The result showed that substituting DEHP with ESOM can improve the thermal stability of plasticized PVC films.When the weight ratio of ESOM and PVC is fixed at 1:2,plasticized PVC film presents higher elongation at break(350.8%vs.345.1%)and lower tensile strength(14.21 MPa vs.15.8 MPa)compared with PVC plasticized with DEHP.ESOM showed less weight loss than DEHP in all solvents.The excellent migration resistance of ESOM is helpful to improve stability of plasticized PVC films.In all,the obtained bio-based plasticizer will be potential to replace petroleum based plasticizer DEHP in flexible PVC materials.