半悬挂扭曲舵水动力及空化性能研究

In this study,we designed a new,semi-balanced,twisted rudder to reduce the surface cavitation problem of medium-high-speed surface warships.Based on the detached eddy simulation(DES)with the Spalart-Allmaras(SA)model(SA-DES)and the volume of fluid(VOF)method,the hydrodynamic and cavitation performances of an ordinary semi-balanced rudder and semi-balanced twisted rudder at different rudder angles were numerically calculated and compared using the commercial computational fluid dynamics(CFD)software STAR-CCM+with the whole-domain structured grid.The calculation results showed that,under the same working conditions,the maneuverability of the semi-balanced twisted rudder basically remained unchanged compared with that of the ordinary semi-balanced rudder.Furthermore,the surface cavitation range of the semi-balanced twisted rudder was much smaller,and the inception rudder angle of the rudder surface cavitation increased by at least 5°at the maximum speed.In conclusion,the semi-balanced twisted rudder effectively reduced the cavitation of the rudder surface without reducing the rudder effect and exhibited excellent anti-cavitation performance.

项目式翻转学习在表界面现象教学中的尝试

根据物理化学教学现状及教学活动中存在问题,展开了全面分析,并提出了项目驱动式翻转学习的教学模式,对课程项目进行了优化设计,有效展开创新型教学活动,结合表界面现象一章的教学内容,用具体教学案例说明这种新型教学模式的具体实施策略。该模式有助于培养学生思维的独立性和学习的自主性,激发学生的学习积极性,使课堂教学的质量和效果得到明显提高。

An Analysis of the Benfit on Green Risk in Construction Projects

The Construction project green risks (CPGRs) refer to those threats to environment, energy sources and material re-sources during the entire life-cycle of a construction project. The emergent green risks in exploiting these resources are of varying concern to all. In this paper, evolutionary game is introduced to make about impacts of strategy choices from interactions among the choices developers, and between the choices developers and EPDs on project green risk. The results show that CPGRs will occur if either developers find that not managing CPGRs has a better payoff than opting for CPGR management, or if monitors impose only mild fines even when they find CPGRs within construction projects of developer’s firms. The study also shows that there is a prohibitively expensive cost incurred by EPDs in monitoring CPGRs. Finally, some strategies are given for EPDs to help them make policies to regulate the strategies of developers.

椭圆截面弹体贯穿有限厚金属靶特性研究

本文结合弹性衰减-塑性衰减-开裂三阶段贯穿模型及椭圆截面弹体形状函数,建立了椭圆截面弹体贯穿有限厚金属靶侵彻模型.随后,开展了两种椭圆截面弹体及一种圆截面弹体以230~570 m/s的撞击速度对铝合金靶板的贯穿试验,且试验覆盖了弹道极限速度.在此基础上,采用本文及文献中的试验数据对模型进行了验证,模型的计算结果与试验结果吻合较好.此外,对比分析了椭圆截面弹体与圆截面弹体对有限厚金属靶的贯穿特性.结果表明,当椭圆截面弹体与圆截面弹体的质量、弹体头部长度、任意弹体截面面积及弹体长度相等时,二者可视为等效弹体.其次,确定了无量纲靶体临界厚度与弹体撞击因子间的关系.计算结果表明,无量纲靶体临界厚度与弹体撞击因子呈线性关系,同时,进一步分析了椭圆截面弹体头部形状因子对其贯穿特性的影响规律.

Frequency-constrained Unit Commitments with Linear Rules Extracted from Simulation Results Considering Regulations from Battery Storage

Heavy renewable penetrations and high-voltage cross-regional transmission systems reduce the inertia and critical frequency stability of power systems after disturbances.Therefore,the power system operators should ensure the frequency nadirs after possible disturbances are within the set restriction,e.g.,0.20 Hz.Traditional methods utilize linearized and simplified control models to quantify the frequency nadirs and achieve frequency-constrained unit commitments(FCUCs).However,the simplified models are hard to depict the frequency responses of practical units after disturbances.Also,they usually neglect the regulations from battery storage.This paper achieves FCUCs with linear rules extracted from massive simulation results.We simulate the frequency responses on typical thermal-hydro-storage systems under diverse unit online conditions.Then,we extract the rules of frequency nadirs after disturbances merely with linear support vector machine to evaluate the frequency stability of power systems.The algorithm holds a high accuracy in a wide range of frequency restrictions.Finally,we apply the rules to three typical cases to show the influences of frequency constraints on unit commitments.

HyperRefiner:a refined hyperspectral pansharpening network based on the autoencoder and self-attention

Deep learning has been developed to generate promising super resolution hyperspectral imagery by fusing hyperspectral imagery with the panchromatic band.However,it is still challenging to maintain edge spectral information in the necessary upsampling processes of these approaches,and diffcult to guarantee effective feature extraction.This study proposes a pansharpening network denoted as HyperRefiner that consists of,(1)a well performing upsampling network SRNet,in which the dual attention block and refined attention block are cascaded to accomplish the extraction and fusion of features;(2)a spectral autoencoder that is embedded to perform dimensionality reduction under constrained feature extraction;and(3)the optimization module which performs self-attention at the pixel and feature levels.A comparisonwithseveral state-of-the-art models reveals that HyperRefiner can improve the quality of the fused image.Specifically,compared to the single-head HyperTransformer and with the Chikusei dataset,our network improved the Peak Signal-to-Noise Ratio,Erreur Relative Globale Adimensionnelle de Synthese and Spectral Angle Mapper by 0.86%,3.62%,and 2.09%,and reduce the total memory,floating point operations,model parameters and computation time by 41%,75%,86%and 46%,respectively.The experimental results show that HyperRefiner outperforms several networks and demonstrates its usefulness in hyperspectral image fusion.The code is publicly available athttps://github.com/zsspo/Fusion_HyperRefiner.

降雨年型变化及竞争对反枝苋和大豆生长的影响

为探索不同降雨年型及栽培方式下外来杂草与本地作物的竞争机制, 为未来全球变化背景下控制外来杂草提供理论依据, 本研究以广泛入侵东北农田生态系统的外来杂草反枝苋(Amaranthus retroflexus)和本地作物大豆(Glycine max)为研究对象, 在遮雨棚内人工模拟正常、欠缺、丰沛三种降雨年型, 采用盆栽实验的方法, 研究两种植物在单种和混种条件下的生长季节动态。结果表明, 降雨丰沛年两种植物的株高和总生物量均大于降雨正常年, 降雨欠缺年则均小于降雨正常年。生长季初期两种植物的根冠比均在降雨欠缺年最高, 说明两种植物均可通过增大根系的生物量分配, 减少地上生物量的分配来适应干旱环境。在三种降雨年型下, 混种时大豆的株高、相对生长速率及总生物量均显著小于单种大豆, 而反枝苋则相反, 尽管有时不显著, 说明种间竞争抑制大豆生长而促进反枝苋的生长, 两种植物之间的竞争是不对称竞争。总的来看, 降雨增加有利于提高大豆的竞争能力, 降雨减少有利于提高反枝苋的竞争能力, 随着生长发育的推移, 这种现象更明显。反枝苋可以在较广的降雨变化范围内保持较高的株高、相对生长速率及生物量, 这很可能是其成为全球范围成功入侵的外来杂草的重要原因之一; 干旱更有利于反枝苋入侵大豆田。

A seven-gene-deleted African swine fever virus is safe and effective as a live attenuated vaccine in pigs

African swine fever(ASF)is a devastating infectious disease in swine that is severely threatening the global pig industry.An efficacious vaccine is urgently required.Here,we used the Chinese ASFV HLJ/18 as a backbone and generated a series of genedeleted viruses.The virulence,immunogenicity,safety,and protective efficacy evaluation in specific-pathogen-free pigs,commercial pigs,and pregnant sows indicated that one virus,namely HLJ/18-7GD,which has seven genes deleted,is fully attenuated in pigs,cannot convert to the virulent strain,and provides complete protection of pigs against lethal ASFV challenge.Our study shows that HLJ/-18-7GD is a safe and effective vaccine against ASFV,and as such is expected to play an important role in controlling the spread of ASFV.

Emergence and prevalence of naturally occurring lower virulent African swine fever viruses in domestic pigs in China in 2020

African swine fever virus(ASFV)has been circulating in China for more than two years,and it is not clear whether the biological properties of the virus have changed.Here,we report on our surveillance of ASFVs in seven provinces of China,from June to December,2020.A total of 22 viruses were isolated and characterized as genotype II ASFVs,with mutations,deletions,insertions,or short-fragment replacement occurring in all isolates compared with Pig/HLJ/2018(HLJ/18),the earliest isolate in China.Eleven isolates had four different types of natural mutations or deletion in the EP402R gene and displayed a nonhemadsorbing(non-HAD)phenotype.Four isolates were tested for virulence in pigs;two were found to be as highly lethal as HLJ/18.However,two non-HAD isolates showed lower virulence but were highly transmissible;infection with 106 TCID50 dose was partially lethal and caused acute or sub-acute disease,whereas 103 TCID50 dose caused non-lethal,sub-acute or chronic disease,and persistent infection.The emergence of lower virulent natural mutants brings greater difficulty to the early diagnosis of ASF and creates new challenges for ASFV control.

Exploiting oleic acid to prepare two-dimensional assembly of Si@graphitic carbon yolk-shell nanoparticles for lithium-ion battery anodes

Carbon coati ng has bee n a routi ne strategy for improvi ng the performa nee of Si-based anode materials for lithium-ion batteries. The ability to tailor the thick ness, homoge neity and graph itizati on degree of carb on-coati ng layers is esse ntial for addressi ng issues that hamper the real applicatio ns of Si anodes. Herein, we report the con structio n of two-dime nsional (2D) assemblies of intercon nected Si @ graphitic carb on yolk-shell nano particles (2D-Si@gC) from commercial Si powders by exploiting oleic acid (OA). The OA molecules act as both the surface-coati ng liga nds for facilitating 2D nano particle assembly and the precursor for forming uniform and conformal graphitic shells as thin as 4 nm. The as-prepared 2D-Si@gC with rationally designed void space exhibits excellent rate capability and cycling stability when used as anode materials for lithium-ion batteries, delivering a capacity of 1,150 mAh·g^-1 at an ultrahigh current density of 10 A·g^-1 and maintaining a stabilized capacity of 1,275 mAh·g^-1 after 200 cycles at 4 A·g^-1 The formatio n of yolk-shell nano particles 8nfines the depositi on of solid electrolyte in terphase (SEI) onto the outer carb on shell, while simulta neously providing sufficie nt space for volumetric expa nsion of Si nano particles. These attributes effectively mitigate the thickness variations of the entire electrode during repeated lithiation and delithiation, which combined with the unique 2D architecture and interc onn ected graphitic carbon shells of 2D-Si@gC contributes to its superior rate capability and cycling performa nee.

High stearic acid diet modulates gut microbiota and aggravates acute graft-versus-host disease

Dear Editor,Acute graft-versus-host disease(aGVHD)is the leading cause of transplantation-related mortality,and limits therapeutic benefits of allogeneic bone marrow transplantation(allo-BMT).New insight is needed into the development of aGVHD.Most nutritional metabolites contribute to host health and immune homeostasis.

Basic requirements of dunk tank settings and verification of the disinfection effect in high-level biosafety laboratories

This study presents the structure and application of dunk tanks in high-level biosafety laboratories.The test methods and sterilization effects of dunk tanks were evaluated by using Bacillus subtilis as indicator.Results showed that sterilization effects of dunk tanks could be achieved by immersing the goods in 0.5%sodium hypochlorite disinfectant solution for 30 min at room temperature.Neutralizer sodium thiosulfate had no effect on the growth of Bacillus subtilis,and thus would not affect the disinfection results of sodium hypochlorite.Furthermore,suggestions for safe operation of dunk tanks are also provided in this study.

Theoretical analysis for self-sharpening penetration of tungsten high-entropy alloy into steel target with elevated impact velocities

The“self-sharpening”effect has been observed experimentally in the penetration of tungsten high-entropy alloy(WHEA)into steel targets in previous study.From the microscopic observation of the residual WHEA long-rod projectile(LRP),the multiphase structure at micro-scale of WHEA is the key effects on self-sharpening penetration process.In order to describe the distinctive penetration behavior,the interaction between micro phases is introduced to modify the hydrodynamic penetration model.The yield strengths of WHEA phases are determined based on the solid solution strengthening methods.Combined with the elbow-streamline model,the self-sharpening mechanism is revealed in view of the multi-phase flow dynamics and the flow field in the deformation area of the LRP nose is characterized to depict the shear layer evolution and the shape of the LRP’s nose as well as the determination of the penetration channel.The self-sharpening coefficient considering the reduction of nose radius is proposed and introduced into the penetration model to calculate the depth of penetration and the penetration channel.Results show that the multi-phase interaction at the microscopic level contributes to the inhomogeneous distribution of the WHEA phases.The shear layer evolution separates part of the LRP material from the nose and makes the nose radius decrease more quickly.It is also the reason that WHEA LRPs have a pointed nose compared with the mushroom nose of WHA heavy alloy(WHA)LRPs.The calculated results agree well with the corresponding experimental data of WHA and WHEA LRPs penetrating into semi-infinite medium carbon steel targets with elevated impact velocities.

Carbon Nanotube-Textured Sand for Controlling Bioavailability of Contaminated Sediments

Sand particles textured with multi-walled carbon nanotubes (MWCNTs) can efficiently control the mobility and bioavailability of contaminants found in aquatic sediments. Adsorption measurements for a wide variety of aquatic contaminants (chlorinated hydrocarbons) on MWCNT-textured sand showed orders of magnitude increase in their sorption coefficients compared to traditional materials (sand) when used for physically separating contaminated sediments from overlying water. Molecular dynamics simulations performed on model experimental systems emphasize that the hydrophobic interactions of the MWCNT surfaces play a crucial role in driving the water molecules away, promoting such enhanced contaminant uptake. The MWCNT-textured sand significantly reduced the migration of contaminants from sediments to overlying water and possesses suitable parameters needed for contaminant sequestration and sediment remediation technologies. The single step and scalable procedure described here for synthesizing robust MWCNT-textured sand surfaces will provide important improvements in the field of remediation/aquatic environment restoration technologies.