From VIB‑to VB‑Group Transition Metal Disulfides:Structure Engineering Modulation for Superior Electromagnetic Wave Absorption

The laminated transition metal disulfides(TMDs),which are well known as typical two-dimensional(2D)semiconductive materials,possess a unique layered structure,leading to their wide-spread applications in various fields,such as catalysis,energy storage,sensing,etc.In recent years,a lot of research work on TMDs based functional materials in the fields of electromagnetic wave absorption(EMA)has been carried out.Therefore,it is of great significance to elaborate the influence of TMDs on EMA in time to speed up the application.In this review,recent advances in the development of electromagnetic wave(EMW)absorbers based on TMDs,ranging from the VIB group to the VB group are summarized.Their compositions,microstructures,electronic properties,and synthesis methods are presented in detail.Particularly,the modulation of structure engineering from the aspects of heterostructures,defects,morphologies and phases are systematically summarized,focusing on optimizing impedance matching and increasing dielectric and magnetic losses in the EMA materials with tunable EMW absorption performance.Milestones as well as the challenges are also identified to guide the design of new TMDs based dielectric EMA materials with high performance.

扭转双层石墨烯物理性质、制备方法及其应用的研究进展

石墨烯是一种准二维蜂窝网状结构新型纳米材料,石墨烯的层数和构型对其性能产生重要影响.固体中准粒子的量子状态由其本身的对称性质所决定,扭转双层石墨烯打破了对称性,引起了强烈的层间耦合作用,改变了扭转双层石墨烯的电子能带、声子色散、形成能垒等物性,产生了独特的性能,如可以连续调控带隙0-250 meV,光电效应的响应度相比于单层石墨烯提高了80倍,因此对扭转双层石墨烯功能化研究有重大意义.本文同时还论述了扭转双层石墨烯向类金刚石转变的理论与实验研究进展,发现扭转双层石墨烯呈现出具有类金刚石结构与性能特征.进一步阐述调控扭转双层石墨烯的扭转角度对其内在性能的影响,揭示这种新型纳米结构在原子层次的行为特征.最后介绍了如何调控制备扭转双层石墨,分析其调控机理,讨论了各种制备工艺的不足与发展趋势.因此本文从扭转双层石墨烯的输运性质、晶体结构转变、制备三个方面展开阐述,并对其在先进电子器件领域的潜在应用进行了展望.

激光3D打印80Ni20Cr合金的显微组织及力学性能

研究激光3D打印80Ni20Cr合金的层-层正交和层-层同向两种不同层激光加工路径打印的合金样件微结构和力学性能。结果表明:合金样件具有细小的等轴晶组织和柱状晶组织,柱状晶粒沿着激光加工路径生长。合金样件成分为Cr溶质溶于Ni溶剂的固溶体,打印样件密度与理论密度接近。层-层正交工艺打印合金样件的孔隙率要低于层-层同向工艺打印合金样件的,微观硬度和拉伸性能也要优于采用层-层同向工艺打印合金样件的,其抗拉强度可达410 MPa,硬度可达406 HV0.2。

SLM成形镍基高温合金及其数值模拟的研究进展

镍基高温合金在高温高压条件下具有较高的强度和良好的抗氧化、抗燃气腐蚀能力,广泛地用来制造航空喷气发动机、各种工业燃气轮机最热端部件。首先介绍了用选区激光熔化成形技术(SLM)3D打印镍基高温合金零件及其数值模拟的国内外研究现状,然后介绍了SLM技术成形的镍基高温合金的力学性能和微观组织结构以及后处理对其微观组织及性能的影响。其次介绍了通过有限元对增材制造过程的模拟,以及其对工艺过程指导意义。最后进一步介绍了SLM成形镍基高温合金领域的研究热点以及数值模拟在这一领域的应用。

石墨烯疏水性能研究

通过化学气相沉积(CVD)方法在蓝宝石衬底表面生长石墨烯,探究生长时间对石墨烯疏水性能和微结构的影响。利用接触角测量仪、傅里叶红外光谱仪、拉曼光谱仪、场发射扫描电镜研究石墨烯的疏水性能和微结构。发现生长时间是30min时,石墨烯的接触角最大,为129.96°,表现出疏水性,红外测试表明只有CC,拉曼分析发现在10~30 min的生长时间下,石墨烯都出现了3个特征峰。较大的接触角使石墨烯有望作为疏水材料,甚至可以通过对其疏水改性让它在超疏水领域存在潜在应用。

Numerical Study on Helical Fiber Fragmentation in Chiral Biological Materials

Chiral microstructures exist widely in natural biological materials such as wood, bone, and climbing tendrils. The helical shape of such microstructures plays an important role in stress transfer between fiber and matrix,and in the mechanical properties of biological materials. In this paper, helical fiber fragmentation behavior is studied numerically using the finite-element method(FEM), and then, the effects of helical shape on fiber deformation and fracture,and the corresponding mechanical mechanisms are investigated. The results demonstrate that, to a large degree, the initial microfibril angle(MFA) determines the elastic deformation and fracture behavior of fibers. For fibers with a large MFA, the interfacial area usually has large values, inducing a relatively low fragment density during fiber fragmentation. This work may be helpful in understanding the relationship between microstructure and mechanical property in biological materials, and in the design and fabrication of bio-inspired advanced functional materials.

Mode Ⅲ fracture analysis by Trefftz boundary element method

This paper presents a hybrid Trefftz （HT） boundary element method （BEM） by using two indirect techniques for mode III fracture problems. Two Trefftz complete functions of Laplace equation for normal elements and a special purpose Trefftz function for crack elements are proposed in deriving the Galerkin and the collocation techniques of HT BEM. Then two auxiliary functions are introduced to improve the accuracy of the displacement field near the crack tips, and stress intensity factor （SIF） is evaluated by local crack elements as well. Furthermore, numerical examples are given, including comparisons of the present results with the analytical solution and the other numerical methods, to demonstrate the efficiency for different boundary conditions and to illustrate the convergence influenced by several parameters. It shows that HT BEM by usingthe Galerkin and the collocation techniques is effective for mode III fracture problems.

Pullout of the Cylindrical Helicoidal Fiber

The multi-layer cylindrical helicoidal fiber structure(MCHFS)exists widely in biological materials such as bone and wood at the microscale.MCHFSs typically function as reinforcing elements to enhance the toughness of materials.In this study,we establish a shear lag-based pullout model of the cylindrical helicoidal fiber(CHF)for investigating interlayer stress transfer and debonding behaviors,with implications regarding the underlying toughening mechanism of MCHFS.Based on the shear lag assumptions,analytical solutions for the stress and displacement fields of the MCHFS during the pullout are derived by considering the CHF as a cylindrically monoclinic material and verified through the 3D finite element simulation.It is found that the helical winding of CHF results in both axial and hoop interlayer shear stresses.Both the helical winding angle and the elastic moduli of the fiber and matrix have significant influences on interlayer stress transfer.This work reveals a new interlayer stress transfer mechanism in the MCHFS existing widely in biological materials.

The stance and factors of international organizations towards countries from a Chinese perspective

The degree and scope of constraints imposed by International Organizations(IOs)on States are increasing,and identifying the factors affecting the IOs’stances on States is helpful to enhance the state's discourse power and influence in the international community.First,by coding the records of Regular Press Conferences of the Speaking Office of the Chinese Ministry of Foreign Affairs during the period of 20182022,we obtained a dataset of IOs’stances on China-related events.Second,we constructed political relation,economic relation,and humanistic relation indicators to complement the influence factors,adopted the Bayesian logit model,and applied the Monte Carlo Markov chain algorithm and Gibbs sampling to analyze the probability of IOs’positive stances towards China.The result shows that IOs’category,length of establishment,functional position,and relationship with China are all related to their tendency of making a statement about China.In terms of the heterogeneity of event types,forum-type IOs are significantly inclined to give positive assessment compared to service-type IOs on events focusing on China's own development.Further analysis reveals that the model for analyzing and predicting the attitudes of IOs is more effective when the international situation is in a stable period.

多层级手性结构生物丝束力学性能的理论模拟

高度有序的多层级手性结构赋予肌腱、韧带和植物卷须等生物丝束优异的力学性能.然而,多层级手性结构如何影响丝束的力学性能尚不清楚.本文建立了具有自相似多层级手性结构的生物丝束的理论模型.基于此模型,研究了丝束载荷传递机制、材料手性和手性组装形式及结构层级数对生物丝束的模量、刚度等力学性能的影响.结果表明,丝束的力学性能显著依赖于纤维的材料手性和多层级手性结构.材料手性可以使纤维更加柔软,多层级手性结构使丝束能够承受大的拉伸变形.此工作不仅加深了对生物丝束结构-性能关系的理解,还有助于人造肌肉和柔性致动器、传感器等的设计.

Association between IDEAL-IQ MRI fat fraction quantification and pelvic bone marrow reserve function in concurrent chemoradiotherapy for cervical cancer

Objective:To analyze the association between iterative decomposition of water and fat with echo asymmetry and least-squares estimation quantification sequence(IDEAL-IQ)magnetic resonance imaging(MRI)of bone marrow fat fraction and bone marrow reserve function during concurrent chemoradiotherapy for cervical cancer.Methods:The study retrospectively analyzed twenty-six patients with stage IB1 to IVA cervical cancer treated between February 2020 and November 2020.All patients received concurrent chemoradiotherapy that included platinum alone or combined paclitaxel and platinum.Pelvic IDEAL-IQ MRI(plain and enhanced)was performed before and after treatment.Regions of interest,including the fifth lumbar vertebra,sacrum,ilium,ischium,and femoral neck,were manually delineated,and the bone marrow fat fraction was measured.Peripheral blood cell counts were recorded during treatment,and the relationship between the fat fraction values and changes in the blood cell counts was explored.Results:IDEAL-IQ MRI bone marrow fat fraction was associated with platelet nadir and platelet decline during treatment.The average pelvic bone marrow fat fraction before chemoradiotherapy was moderately negatively correlated with platelet count nadir during concurrent chemoradiotherapy(r=-0.450,P?0.021).The change in average pelvic bone marrow fat fraction through chemoradiotherapy was moderately positively correlated with the degree of thrombocytopenia(r=0.399,P=0.044).Conclusion:Bone marrow fat content quantified by IDEAL-IQ was associated with platelet count nadir and the degree of thrombocytopenia in patients with cervical cancer undergoing concurrent chemoradiotherapy.

复杂载荷下双金属复合管的屈曲失效研究

论文采用有限元方法系统地研究了复杂载荷下双金属复合管的屈曲失效,三维有限元数值模型考虑了双金属复合管的准静态复合成型制造过程中产生的残余应力,分析了外基管直径、内衬管壁厚、内外管初始间隙、内衬管屈服强度、内压及内外管间摩擦力等因素对双金属复合管屈曲失效的影响.结果表明,加载路径、复合管的几何尺寸及内衬管的屈服强度对双金属复合管的屈曲性能均有较大影响,内充压力可以延缓内衬管的屈曲.该研究结果将为双金属复合管的设计和应用提供重要的技术支持.

ANALYTICAL SOLUTIONS FOR A ONE-DIMENSIONAL CHEMO-MECHANICAL COUPLING PROBLEM

Chemo-mechanical coupling exists in a lot of intelligent materials including hy- drogels, biological tissues and other soft materials. These materials are able to respond to ex- ternal stimulus, such as temperature, chemical concentration, and pH value. In this paper, a one-dimensional theoretical model for chemo-mechanical coupling is proposed for analyzing the uniaxial stress/strain state of coupling materials. Based on the chemo-mechanical coupled gov- erning equation, the displacement function and concentration function are derived and the stress and chemical potential are obtained. It is shown that the present chemo-mechanical theory can characterize the chemo-mechanical coupling behavior of intelligent materials.

Atomically thin optical lenses and gratings

Two-dimensional(2D)materials have emerged as promising candidates for miniaturized optoelectronic devices due to their strong inelastic interactions with light.On the other hand,a miniaturized optical system also requires strong elastic light–matter interactions to control the flow of light.Here we report that a single-layer molybdenum disulfide(MoS2)has a giant optical path length(OPL),around one order of magnitude larger than that from a single-layer of graphene.Using such giant OPL to engineer the phase front of optical beams we have demonstrated,to the best of our knowledge,the world’s thinnest optical lens consisting of a few layers of MoS2 less than 6.3 nm thick.By taking advantage of the giant elastic scattering efficiency in ultra-thin high-index 2D materials,we also demonstrated high-efficiency gratings based on a single-or few-layers of MoS2.The capability of manipulating the flow of light in 2D materials opens an exciting avenue towards unprecedented miniaturization of optical components and the integration of advanced optical functionalities.More importantly,the unique and large tunability of the refractive index by electric field in layered MoS2 will enable various applications in electrically tunable atomically thin optical components,such as micro-lenses with electrically tunable focal lengths,electrical tunable phase shifters with ultra-high accuracy,which cannot be realized by conventional bulk solids.

Ballistic Resistance of Novel Amorphous-Alloy-Reinforced Perforated Armor

A new concept of lightweight structure,namely amorphous-alloy-reinforced perforated armor(ARPA)consisting of the amorphous alloy coating and perforated metal substrate plate,is proposed.The ballistic performance of the ARPA is investigated numerically.The failure modes of ARPA and projectiles are identified,and the defeating mechanism of the ARPA is explored.It is shown that the amorphous alloy coating is helpful for enhancing the target’s ballistic performance by seriously eroding and fracturing the penetrators.The effects of coating thickness,initial impact velocity and impact angle are also discussed for the target’s ballistic performance.The optimal design of coating thickness may be necessary for enhancing the ballistic resistance of ARPAs.

Helical Fiber Pull-out in Biological Materials

Many biological materials, such as wood and bone, possess helicoid microstructures at microscale, which can serve as reinforcing elements to transfer stress between crack surfaces and improve the fracture toughness of their composites. Failure processes, such as fiber/matrix inter- face debonding and sliding associated with pull-out of helical fibers, are responsible mainly for the high energy dissipation needed for the fracture toughness enhancement. Here we present systemic analyses of the pull-out behavior of a helical fiber from an elastic matrix via the finite element method （FEM） simulation, with implications regarding the underlying toughening mechanism of helicoid microstructures. We find that, through their uniform curvature and torsion, helical fibers can provide high pull-out force and large interface areas, resulting in high energy dissipation that accounts, to a large extent, for the high toughness of biological materials. The helicity of fiber shape in terms of the helical angle has significant effects on the force-displacement relationships as well as the corresponding energy dissipation during fiber pull-out.

A novel oscillator based on heterogeneous carbon@ MoS2 nanotubes

Oscillatory behavior of novel heterogeneous oscillators composed of carbon and molybdenum disulfide nanotubes （CNT@MST） was investigated for the first time, by using the methods of classical molecular dynamics. In the proposed oscillators, a molybdenum disulfide nanotube （MST） was set as an outer tube, leading to better compatibility with the semiconductor industry standards. A smooth and stable oscillator with a frequency reaching 20 GHz was obtained based on a double-walled CNT@MST hetero-nanotube for a wide range of gap widths, indicating that the proposed oscillators perform much better than those built from double-walled carbon nanotubes （CNTs） that require a narrow range of gap widths. In addition, the oscillation characteristics of CNT@MST oscillators containing different inner and outer tube chirality were significantly better than those of CNT@MST oscillators containing two tubes with the same chirality.

Tensile behaviors of filaments with misfit of chirality

Slender chiral filaments are ubiquitous in both artificial and biological materials.Due to their chiral microstructures,chiral filaments usually exhibit favorable properties such as superior elasticity and unusual stretch-twist coupling deformation.However,how these chiral microstructures affect the elastic behavior of filaments remains unclear.In this paper,a refined Cosserat rod model with misfit or mismatching of chirality induced by inhomogeneous arrangement of chiral microstructures incorporated is developed.Using the refined rod model,the force-displacement relationships and variation of structural chirality during the tensile processes of two typical helical structures,i.e.,single-strand helix and double-strand helix,are investigated.The results show that the misfit of chirality can lead to a bend-twist deformation with a high coupling degree,which makes the rod much“soft”when stretched.The chiral filaments undergo an unusual twist when stretched,corresponding to an obviously nonlinear variation of structural chirality.The work suggests that the misfit of chirality can be used to tune the elastic behavior of chiral filaments,which is helpful in guiding the design of flexible actuators and soft devices.