Anisotropic etching mechanisms of 4H-SiC:Experimental and first-principles insights

Molten-alkali etching has been widely used to reveal dislocations in 4H silicon carbide(4H-SiC),which has promoted the identification and statistics of dislocation density in 4H-SiC single crystals.However,the etching mechanism of 4H-SiC is limited misunderstood.In this letter,we reveal the anisotropic etching mechanism of the Si face and C face of 4H-SiC by combining molten-KOH etching,X-ray photoelectron spectroscopy(XPS)and first-principles investigations.The activation energies for the molten-KOH etching of the C face and Si face of 4H-SiC are calculated to be 25.09 and 35.75 kcal/mol,respectively.The molten-KOH etching rate of the C face is higher than the Si face.Combining XPS analysis and first-principles calculations,we find that the molten-KOH etching of 4H-SiC is proceeded by the cycling of the oxidation of 4H-SiC by the dissolved oxygen and the removal of oxides by molten KOH.The faster etching rate of the C face is caused by the fact that the oxides on the C face are unstable,and easier to be removed with molten alkali,rather than the C face being easier to be oxidized.

Design Principles and Mechanistic Understandings of Non-Noble-Metal Bifunctional Electrocatalysts for Zinc-Air Batteries

Zinc-air batteries(ZABs)are promising energy storage systems because of high theoretical energy density,safety,low cost,and abundance of zinc.However,the slow multi-step reaction of oxygen and heavy reliance on noble-metal catalysts hinder the practical applications of ZABs.Therefore,feasible and advanced non-noble-metal elec-trocatalysts for air cathodes need to be identified to promote the oxygen catalytic reaction.In this review,we initially introduced the advancement of ZABs in the past two decades and provided an overview of key developments in this field.Then,we discussed the work-ing mechanism and the design of bifunctional electrocatalysts from the perspective of morphology design,crystal structure tuning,interface strategy,and atomic engineering.We also included theoretical studies,machine learning,and advanced characterization technologies to provide a comprehensive understanding of the structure-performance relationship of electrocatalysts and the reaction pathways of the oxygen redox reactions.Finally,we discussed the challenges and prospects related to designing advanced non-noble-metal bifunctional electrocatalysts for ZABs.

International law obligations for the disposal of Fukushima nuclear-contaminated water under the principles of nuclear safety

The disposal of contaminated water from Japan’s Fukushima nuclear power plant is a significant international nuclear safety issue with considerable cross-border implications.This matter requires compliance not only with the law of the sea but also with the principles of nuclear safety under international law.These principles serve as the overarching tenet of international and China’s domestic nuclear laws,applicable to nuclear facilities and activities.The principle of safety in nuclear activities is fully recognized in international and domestic laws,carrying broad legal binding force.Japan’s discharge of nuclear-contaminated water into the sea violates its obligations under the principle of safety in nuclear activities,including commitments to optimum protection,as low as reasonably practicable,and prevention.The Japanese government and the International Atomic Energy Agency(IAEA)have breached the obligation of optimum protection by restricting the scope of assessments,substituting core concepts,and shielding dissenting views.In the absence of clear radiation standards,they have acted unilaterally without fulfilling the obligation as low as reasonably practicable principle.The discharge of Fukushima nuclear-contaminated water poses an imminent and unpredictable risk to all countries worldwide,including Japanese residents.Japan and the IAEA should fulfill their obligations under international law regarding disposal,adhering to the principles of nuclear safety,including optimum protection,the obligation as low as reasonably practicable,and prevention through multilateral cooperation.Specifically,the obligation to provide optimum protection should be implemented by re-evaluating the most reliable disposal technologies and methods currently available and comprehensively assessing various options.The standard of the obligation as low as reasonably practicable requires that the minimization of negative impacts on human health,livelihoods,and the environment should not be subordinated to considerations of cutting costs and expenses.Multilateral cooperation should be promoted through the establishment of sound multilateral long-term monitoring mechanisms for the discharge of nuclear-contaminated water,notification and consultation obligations,and periodic assessments.These obligations under international law were fulfilled after the accidents at the Three Mile Island and Chernobyl nuclear power plants.The implications of the principles of nuclear safety align with the concept of building a community of shared future for nuclear safety advocated by China.In cases of violations of international law regarding the disposal of nuclear-contaminated water that jeopardize the concept of a community of a shared future for nuclear safety,China can also rely on its own strength to promote the implementation of due obligations through self-help.

First-Principles Investigation of Charge Transfer Mechanism of B-Doped 3C-SiC Semiconductor Material

This study delves into the charge transfer mechanism of boron (B)-doped 3C-SiC through first-principles investigations. We explore the effects of B doping on the electronic properties of 3C-SiC, focusing on a 12.5% impurity concentration. Our comprehensive analysis encompasses structural properties, electronic band structures, and charge density distributions. The optimized lattice constant and band gap energy of 3C-SiC were found to be 4.373 Å and 1.36 eV respectively, which is in agreement with previous research (Bui, 2012;Muchiri et al., 2018). Our results show that B doping narrows the band gap, enhances electrical conductivity, and influences charge transfer interactions. The charge density analysis reveals substantial interactions between B dopants and surrounding carbon atoms. This work not only enhances our understanding of the material’s electronic properties, but also highlights the importance of charge density analysis for characterizing charge transfer mechanisms and their implications in the 3C-SiC semiconductors.

Stochastic Maximum Principle for Optimal Advertising Models with Delay and Non-Convex Control Spaces

In this paper we study optimal advertising problems that model the introduction of a new product into the market in the presence of carryover effects of the advertisement and with memory effects in the level of goodwill. In particular, we let the dynamics of the product goodwill to depend on the past, and also on past advertising efforts. We treat the problem by means of the stochastic Pontryagin maximum principle, that here is considered for a class of problems where in the state equation either the state or the control depend on the past. Moreover the control acts on the martingale term and the space of controls U can be chosen to be non-convex but now the space of controls U can be chosen to be non-convex. The maximum principle is thus formulated using a first-order adjoint Backward Stochastic Differential Equations (BSDEs), which can be explicitly computed due to the specific characteristics of the model, and a second-order adjoint relation.

Principles of Shiology——Revealing the Basic Rules of Human Shiance

The objective principles of shiology are mainly reflected in three fields as food acquisition, eaters' health and shiance order. Most of the objective principles in the field of food acquisition have been revealed by agronomy and foodstuff science. This research mainly focuses on 10 principles in the field of eaters' health and shiance order and in addition, there are also five lemmas that extend from the above principles. The 10 principles are the core theory of the shiology knowledge system, which play an important role in the objective principles revealed by human beings and constitute one of the basic principles of human civilization. Compared with the scientific principles of mathematics, physics, chemistry and economics, the principles of shiology have three characteristics as popularity, practicability and survivability. The principles of shiology in the field of eaters' health are all around us, and everyone can understand and master them. Using the principles of shiology can improve the healthy life span of 8 billion people. The principles of shiology in the field of shiance order is an important tool of social governance, which can reduce human social conflicts, reduce social involution, improve overall efficiency of social operation, and maintain the sustainable development of human beings.

An 8-Node Plane Hybrid Element for StructuralMechanics Problems Based on the Hellinger-Reissner Variational Principle

The finite element method (FEM) plays a valuable role in computer modeling and is beneficial to the mechanicaldesign of various structural parts. However, the elements produced by conventional FEM are easily inaccurate andunstable when applied. Therefore, developing new elements within the framework of the generalized variationalprinciple is of great significance. In this paper, an 8-node plane hybrid finite element with 15 parameters (PHQ8-15β) is developed for structural mechanics problems based on the Hellinger-Reissner variational principle.According to the design principle of Pian, 15 unknown parameters are adopted in the selection of stress modes toavoid the zero energy modes.Meanwhile, the stress functions within each element satisfy both the equilibrium andthe compatibility relations of plane stress problems. Subsequently, numerical examples are presented to illustrate theeffectiveness and robustness of the proposed finite element. Numerical results show that various common lockingbehaviors of plane elements can be overcome. The PH-Q8-15β element has excellent performance in all benchmarkproblems, especially for structures with varying cross sections. Furthermore, in bending problems, the reasonablemesh shape of the new element for curved edge structures is analyzed in detail, which can be a useful means toimprove numerical accuracy.

Lithium nitrate regulated carbonate electrolytes for practical Li-metal batteries: Mechanisms, principles and strategies

Li-metal batteries(LMBs)regain research prominence owing to the ever-increasing high-energy requirements.Commercially available carbonate electrolytes exhibit unfavourable parasitic reactions with Limetal anode(LMA),leading to the formation of unstable solid electrolyte interphase(SEI)and the breed of Li dendrites/dead Li.Significantly,lithium nitrate(LiNO_(3)),an excellent film-forming additive,proves crucial to construct a robust Li_(3)N/Li_(2)O/Li_(x)NO_(y)-rich SEI after combining with ether-based electrolytes.Thus,the given challenge leads to natural ideas which suggest the incorporation of LiNO_(3) into commercial carbonate for practical LMBs.Regrettably,LiNO_(3) demonstrates limited solubility(~800 ppm)in commercial carbonate electrolytes.Thence,developing stable SEI and dendrite-free LMA with the incorporation of LiNO_(3) into carbonate electrolytes is an efficacious strategy to realize robust LMBs via a scalable and cost-effective route.Therefore,this review unravels the grievances between LMA,LiNO_(3)and carbonate electrolytes,and enables a comprehensive analysis of LMA stabilizing mechanism with LiNO_(3),dissolution principle of LiNO_(3) in carbonate electrolytes,and LiNO_(3) introduction strategies.This review converges attention on a point that the LiNO_(3)-introduction into commercial carbonate electrolytes is an imperious choice to realize practical LMBs with commercial 4 V layered cathode.

Adaptive Optimal Discrete-Time Output-Feedback Using an Internal Model Principle and Adaptive Dynamic Programming

In order to address the output feedback issue for linear discrete-time systems, this work suggests a brand-new adaptive dynamic programming(ADP) technique based on the internal model principle(IMP). The proposed method, termed as IMP-ADP, does not require complete state feedback-merely the measurement of input and output data. More specifically, based on the IMP, the output control problem can first be converted into a stabilization problem. We then design an observer to reproduce the full state of the system by measuring the inputs and outputs. Moreover, this technique includes both a policy iteration algorithm and a value iteration algorithm to determine the optimal feedback gain without using a dynamic system model. It is important that with this concept one does not need to solve the regulator equation. Finally, this control method was tested on an inverter system of grid-connected LCLs to demonstrate that the proposed method provides the desired performance in terms of both tracking and disturbance rejection.

Four Dimensions of Integrating Chinese Culture Into College English Teaching From the Perspective of Tyler’s Basic Principles

Integrating Chinese culture into college English can not only enhance students’humanities literacy and cultivate their cultural confidence,but also facilitate the inheritance and international dissemination of Chinese culture.Taking Tyler’s curriculum framework as the starting point,this paper analyzes some factors that affect the integration of Chinese culture into the college English teaching and proposes some strategies for the integration of Chinese culture into college English teaching by innovating teaching objectives,enriching teaching contents,transforming modes of course delivery,and reconstructing the assessment system.

“Three Beauties”Principle in the English Versions of“Jing Ye Si”--Translations by Xu and Fletcher as Examples

“Jing Ye Si”is a classical poem with international influence by the Chinese poet Li Bai in the Tang Dynasty,which expresses the poet’s deep nostalgia.This paper compares and analyzes its two English versions translated by the Chinese translator Xu Yuanchong and the British translator W.J.B.Fletcher based on the“three beauties”principle(beauty in sense,beauty in sound,and beauty in form),and discovers that the English version of Xu basically achieves the unity of the“three beauties”,while the English version of Fletcher realizes the“beauty in sound and form”,but deviates from the“beauty in sense”mainly owing to the inaccurate comprehension of the moon as an image and other factors.This analysis may afford us with certain reference in poetry translation.

Research on Teaching Methods of Flight Control Principles

With the rapid development of China’s civil aviation industry,the teaching method of operating knowledge of flight principles has changed greatly,which creates a good implementation environment to improve the safety of civil aviation in our country.At present,the main training content of air route transport pilots in China is basic aviation theory,initial flight training,airline modification,etc.The principles of flight control are an important part of basic aviation theoretical knowledge training,which will involve a large number of flight technology training content,instructors will also be based on the pilot type.Teaching flight control theory and practical knowledge requires relatively high theoretical learning ability of students,and the learning effect of this part of theoretical knowledge will directly affect the quality of subsequent learning,but also directly affect the effectiveness of flight training.This paper focuses on the analysis of the basic concepts of flight control,studies the existing problems in the teaching of flight control principles,summarizes the teaching measures of flight control principles,aiming to provide a reference to teaching personnel.

Research on the Course of Principles of Concrete Structure Design

Nowadays,education and teaching have become a hot topic,and teaching in colleges and universities is facing a brand-new development direction.Principles of Concrete Structure Design,as one of the main courses,transmits professional knowledge for students,enhances the students’professional ability,and further carries out in-depth research on the course to bring a better teaching effect for students.The article mainly focuses on the research of the principles of concrete structure design course,conducts an analysis of the teaching characteristics of the principles of concrete structure design course,and reasonably sets the teaching content from the optimization of the course teaching objectives;innovative course teaching methods can deepen the effect of knowledge understanding;reform of experimental practice teaching can lay down the effect of the internalization of knowledge,etc.The in-depth description and discussion of the relevant aspects of the research aim to provide guidelines for related research.

Probability Distribution of SARS-Cov-2 (COVID) Infectivity Following Onset of Symptoms: Analysis from First Principles

The phasing out of protective measures by governments and public health agencies, despite continued seriousness of the coronavirus pandemic, leaves individuals who are concerned for their health with two basic options over which they have control: 1) minimize risk of infection by being vaccinated and by wearing a face mask when appropriate, and 2) minimize risk of transmission upon infection by self-isolating. For the latter to be effective, it is essential to have an accurate sense of the probability of infectivity as a function of time following the onset of symptoms. Epidemiological considerations suggest that the period of infectivity follows a lognormal distribution. This proposition is tested empirically by construction of the lognormal probability density function and cumulative distribution function based on quantiles of infectivity reported by several independent investigations. A comprehensive examination of a prototypical ideal clinical study, based on general statistical principles (the Principle of Maximum Entropy and the Central Limit Theorem) reveals that the probability of infectivity is a lognormal random variable. Subsequent evolution of new variants may change the parameters of the distribution, which can be updated by the methods in this paper, but the form of the probability function is expected to remain lognormal as this is the most probable distribution consistent with mathematical requirements and available information.

二氧化碳-水-岩作用机理及微观模拟方法研究进展

系统综述CO_(2)-水-岩复杂作用机理、多孔介质反应输运(溶解、沉淀及沉淀运移)微观模拟、CO_(2)-水-岩系统微观模拟3个方面的研究进展,指出目前研究存在的主要问题并提出了关于未来研究方向的建议。CO_(2)注入储集层后,不仅存在常规渗流体系的流动和传质作用,还会产生溶解、沉淀及沉淀运移等特殊物理化学现象,其耦合作用导致多孔介质的孔渗参数变化规律复杂。孔隙尺度的微观渗流模拟,可以得到孔喉三维空间内的详细信息,且能显性观察到多孔介质流-固界面随反应的变化。目前研究主要在复杂作用机理解耦合、多矿物差异性反应表征、沉淀生成机理及表征(晶体成核和矿物脱落)、沉淀-流体相互作用模拟方法、多物理化学过程耦合渗流机制等方面存在局限。未来研究中,需要创新实验方法对“溶解—沉淀—沉淀运移”解耦合,提高矿物地球化学反应相关参数实验测试的准确度,在不同沉淀机理可靠表征的基础上,建立沉淀-流体相互作用模拟方法,并有机耦合各个物理化学过程,最终实现对CO_(2)-水-岩系统中“溶解—沉淀—沉淀运移”的耦合渗流模拟。

老年急性脑梗死患者血清Del-1和IL-17水平变化及与梗死面积和预后的关系

目的 探究老年急性脑梗死(ACI)患者血清内皮发育调节基因-1(Del-1)、白细胞介素-17(IL-17)水平与脑梗死面积、病情严重程度及预后的关系。方法 回顾性收集2019-01-2021-12厦门大学附属东南医院收治的126例老年ACI患者(病例组)及105名健康体检者(对照组)的临床资料,根据脑梗死面积将病例组患者分为大面积梗死组(梗死最大直径>5 cm,n=14)、中面积梗死组(梗死最大直径3~5 cm,n=53)和小面积梗死组(梗死最大直径<3 cm,n=59);根据NIHSS评分分为重症组(NIHSS评分≥16分,n=13)、中症组(5分<NIHSS评分<15分,n=58)和轻症组(NIHSS评分≤5分,n=55);根据m RS评分分为预后良好组(mRS评分≤2分,n=81)和预后不良组(mRS评分>2分,n=45)。采用荧光免疫法检测血清Del-1、IL-17水平,受试者工作特征(ROC)曲线评估血清Del-1、IL-17水平预测老年ACI患者预后的价值。结果 病例组吸烟史比例、收缩压、舒张压、糖化血红蛋白、血清IL-17水平均高于对照组,血清Del-1水平低于对照组(P<0.05)。不同脑梗死面积患者血清Del-1水平比较,小面积梗死组>中面积梗死组>大面积梗死组;血清IL-17水平比较,小面积梗死组<中面积梗死组<大面积梗死组(P<0.05)。轻症组血清Del-1水平高于中症组、重症组(P<0.05),不同病情严重程度患者血清IL-17水平比较,重症组>中症组>轻症组(P<0.05)。预后良好组患者血清Del-1水平高于预后不良组,血清IL-17水平低于预后不良组(P<0.05)。ROC曲线分析显示,血清Del-1、IL-17预测ACI患者预后的AUC值分别为0.763、0.747(P<0.05)。结论 老年ACI患者血清Del-1水平较低,IL-17水平较高,二者与患者脑梗死面积、病情严重程度和预后关系密切,可作为预测老年ACI患者预后的可靠指标。

基于混合式教学的“教-学-评”一体化实验教学体系探索

实验能力是医学专业研究生的重要科研能力,实验能力的培养与实验教学的方法与质量密切相关。文章针对传统实验教学受到时间和空间限制且评价指标较为单一的现状,提出构建基于线上自主学习和现场实践相结合的“教-学-评”一体化实验教学体系,建立覆盖课前线上自主学习、课堂现场实践、课后作业提交与考核教学全过程的评价体系,以评促学,以评促教,通过评价反馈激发学生的学习热情,改进教学内容和方法,不断探索与完善实验教学体系,提高实验教学质量,以期为培养具有实践能力与创新精神的医学科研人才发挥积极作用。

小流域生态-岩土协同减灾原理与方法初探

随着全球变暖,极端降雨事件增多,导致山区小流域灾害频发,严重威胁人民生命财产安全。小流域防灾减灾形式多样,其中生态工程措施与岩土工程措施相结合协同减灾的方式,不仅能够充分发挥两种措施在不同时间段的减灾作用,而且能够增加整体减灾功效。目前,受限于生态工程措施与岩土工程措施协同减灾原理不明,评估方法缺乏,导致二者无法有机结合并开展综合减灾效益评估。本文在基于自然解决方案的基础上,提出了山区小流域生态-岩土措施协同减灾的原理,即利用生态工程与岩土工程协作,通过坡面防护和沟道调控,形成稳定阶梯-深潭结构的生态工程-岩土工程措施协同减灾原理。在此基础上,结合地理信息系统和最优化原理,给出基于能量消减的小流域生态工程-岩土工程协同减灾功效的定量化评价方法,为规划、设计、物种选择以及生态工程与岩土工程对策的结合提供依据。

基于“马赛克战”的水下有人-无人作战使用探讨

通过对“马赛克战”概念的背景和特点进行分析,提出基于马赛克的水下攻防作战运用构想,构建基于马赛克的水下有人-无人作战网络,分析多域背景下水下OODA作战网络的构成,利用OODA作战环理论对水下马赛克作战网络作战能力进行分析,并提出水下马赛克作战网络对抗单个平台和对抗作战网络的使用方法。最后,从通信组网、集群使用、人工智能、察打一体等4个方面对“马赛克战”概念下水下无人航行器装备使用提出建议。

基于CFD-DEM的流-固耦合数值建模方法研究进展

随着土体渗流侵蚀研究的逐渐深入,对土颗粒流失和变形破坏机理的研究方法呈现出多尺度的特点。其中,计算流体力学-离散元耦合方法(CFD-DEM)为在细观尺度上研究流-固耦合相互作用对土体宏观力学特性的影响提供了一种行之有效的方法。针对CFD-DEM耦合方法在岩土工程领域应用现状,本文系统总结现有流-固耦合计算方法的优缺点,重点论述CFD-DEM耦合方法的建模策略,包括固相颗粒形状建模与粒间接触模型、流体相控制方程及参数计算方法,以及CFD-DEM耦合计算,并就相关问题进行深入探讨,最后提出了CFD-DEM耦合方法未来的发展方向。