Enhancing electromagnetic wave absorption with core‐shell structured SiO_(2)@MXene@MoS_(2) nanospheres

Material composition and structural design are important factors influencing the electromagnetic wave(EMW)absorption performance of materials.To alleviate the impedance mismatch attributed to the high dielectric constant of Ti_(3)C_(2)T_(x)MXene,we have successfully synthesized core‐shell structured SiO_(2)@MXene@MoS_(2)nanospheres.This architecture,comprising SiO_(2) as the core,MXene as the intermediate layer,and MoS_(2) as the outer shell,is achieved through an electrostatic self‐assembly method combined with a hydrothermal process.This complex core‐shell structure not only provides a variety of loss mechanisms that effectively dissipate electromagnetic energy but also prevents self‐aggregation of MXene and MoS_(2) nanosheets.Notably,the synergistic combination of SiO_(2) and MoS_(2) with highly conductive MXene enables the suitable dielectric constant of the composites,ensuring optimal impedance matching.Therefore,the core‐shell structured SiO_(2)@MXene@MoS_(2) nanospheres exhibit excellent EMW absorption performance,featuring a remarkable minimum reflection loss(RL_(min))of−52.11 dB(2.4 mm).It is noteworthy that these nanospheres achieve an ultra‐wide effective absorption bandwidth(EAB)of 6.72 GHz.This work provides a novel approach for designing and synthesizing high‐performance EMW absorbers characterized by“wide bandwidth and strong reflection loss.”

Preparation of a p-n heterojunction BiFeO_3@TiO_2 photocatalyst with a core–shell structure for visible-light photocatalytic degradation

Magnetically separable bismuth ferrite(BiFeO3)nanoparticles were fabricated by a citrate self‐combustion method and coated with titanium dioxide(TiO2)by hydrolysis of titanium butoxide(Ti(OBu)4)to form BiFeO3@TiO2core-shell nanocomposites with different mass ratios of TiO2to BiFeO3.The photocatalytic performance of the catalysts was comprehensively investigated via photocatalytic oxidation of methyl violet(MV)under both ultraviolet and visible‐light irradiation.The BiFeO3@TiO2samples exhibited better photocatalytic performance than either BiFeO3or TiO2alone,and a BiFeO3@TiO2sample with a mass ratio of1:1and TiO2shell thickness of50-100nm showed the highest photo‐oxidation activity of the catalysts.The enhanced photocatalytic activity was ascribed to the formation of a p‐n junction of BiFeO3and TiO2with high charge separation efficiency as well as strong light absorption ability.Photoelectrochemical Mott-Schottky(MS)measurements revealed that both the charge carrier transportation and donor density of BiFeO3were markedly enhanced after introduction of TiO2.The mechanism of MV degradation is mainly attributed to hydroxyl radicals and photogenerated electrons based on energy band theory and the formation of an internal electrostatic field.In addition,the unique core-shell structure of BiFeO3@TiO2also promotes charge transfer at the BiFeO3/TiO2interface by increasing the contact area between BiFeO3and TiO2.Finally,the photocatalytic activity of BiFeO3@TiO2was further confirmed by degradation of other industrial dyes under visible‐light irradiation.

Plate/shell structure topology optimization of orthotropic material for buckling problem based on independent continuous topological variables

The purpose of the present work is to study the buckling problem with plate/shell topology optimization of orthotropic material. A model of buckling topology optimization is established based on the independent, continuous, and mapping method, which considers structural mass as objective and buckling critical loads as constraints. Firstly, composite exponential function (CEF) and power function (PF) as filter functions are introduced to recognize the element mass, the element stiffness matrix, and the element geometric stiffness matrix. The filter functions of the orthotropic material stiffness are deduced. Then these filter functions are put into buckling topology optimization of a differential equation to analyze the design sensitivity. Furthermore, the buckling constraints are approximately expressed as explicit functions with respect to the design variables based on the first-order Taylor expansion. The objective function is standardized based on the second-order Taylor expansion. Therefore, the optimization model is translated into a quadratic program. Finally, the dual sequence quadratic programming (DSQP) algorithm and the global convergence method of moving asymptotes algorithm with two different filter functions (CEF and PF) are applied to solve the optimal model. Three numerical results show that DSQP&CEF has the best performance in the view of structural mass and discretion.

Design and Synthesis of Cu@CuS Yolk–Shell Structures with Enhanced Photocatalytic Activity

Non-spherical Cu@Cu S yolk–shell structures are successfully obtained using Cu_2 O cube templates in a process combining rapid surface sulfidation followed by disproportionation of the Cu_2 O core upon treatment with a hydrochloric acid solution. By employing the above method,Cu@Cu S yolk–shell structures with different morphologies,including octahedral, truncated octahedral, and cuboctahedral shapes, can be synthesized. The void space within the hollow structures provides a unique confined space, where the metallic copper present in the core of a shell can be protected from agglomeration and oxidation. Furthermore,the presence of metal copper in these hollow structurescontributes to improvement in the photocatalytic properties of these materials. The application of these Cu@Cu S structures indeed shows clearly improved photocatalytic performance.

Research on mode localization of reticulated shell structures

Reticulated shell structures （RSSs） are characterized as cyclically periodic structures. Mistuning of RSSs will induce structural mode localization. Mode localization has the following two features： some modal vectors of the structure change remarkably when the values of its physical parameters （mass or stiffness） have a slight change; and the vibration of some modes is mainly restricted in some local areas of the structure. In this paper, two quantitative assessment indexes are introduced that correspond to these two features. The first feature is studied through a numerical example of a RSS, and its induced causes are analyzed by using the perturbation theory. The analysis showed that internally, mode localization is closely related to structural frequencies and externally, slight changes of the physical parameters of the structure cause instability to the RSS. A scaled model experiment to examine mode localization was carried out on a Kiewit single-layer spherical RSS, and both features of mode localization are studied. Eight tests that measured the changes of the physical parameters were carried out in the experiment. Since many modes make their contribution in structural dynamic response, six strong vibration modes were tested at random in the experimental analysis. The change and localization of the six modes are analyzed for each test. The results show that slight changes to the physical parameters are likely to induce remarkable changes and localization of some modal vectors in the RSSs.

A Review: Enhanced Anodes of Li/Na-Ion Batteries Based on Yolk–Shell Structured Nanomaterials

Lithium-ion batteries(LIBs) and sodium-ion batteries(SIBs) have received much attention in energy storage system. In particular, among the great efforts on enhancing the performance of LIBs and SIBs, yolk–shell(YS) structured materials have emerged as a promising strategy toward improving lithium and sodium storage. YS structures possess unique interior void space, large surface area and short diffusion distance, which can solve the problems of volume expansion and aggregation of anode materials, thus enhancing the performance of LIBs and SIBs. In this review, we present a brief overview of recent advances in the novel YS structures of spheres, polyhedrons and rods with controllable morphology and compositions. Enhanced electrochemical performance of LIBs and SIBs based on these novel YS structured anode materials was discussed in detail.

Low stress no distortion welding for aerospace shell structures

To fit in with the strict geometrical integrity and ensure dimensionally consistent fabrication of the welded aerospace structures. the low stress no distortion(LSND)welding, a technique for thin materials, was poineered and developed to provide an ininprocess active control of welding distortion. Satisfactory distortion free results were achieved in both welding of jet engine cases of heat-resistance alloys and rocket fuel tanks of aluminuim alloys, and there need no. reworking operations for post-weld distortion correction. Based on the 'static' method a newly developed method for dvnamic in-process control is also discussed in this paper. Both methods provide quanutiative in-process control of incompatible strains in weld zone and low stress no distortion welding results.

Reduced-temperature ordering of FePt nanoparticle assembled films by Fe30Pt70/Fe3O4 core/shell structure

In this paper, Fe30Pt70/Fe3O4 core/shell nanoparticles were synthesized by chemical routine and the layered polyethylenimine （PEI）-Fe30Pt70/Fe3O4 structure was constructed by molecule-mediated self-assembly technique. The dimension of core/shell structured nanoparticles was that of 4nm core and 2 nm shell. After annealing under a flow of forming gas （50%Ar2＋30%H2） for 1 h at or above 400℃, the iron oxide shell was reduced to Fe and diffused to Pt-rieh core, which leaded to the formation of L1. phase FePt at low temperature. The x-ray diffraction results and magnetic properties measurement showed that the chemical ordering temperature of Fe30Pt70/Fe3O4 core/shell nanoparticles assembly can be reduced to as low as 400℃. The sample annealed at 400℃ showed the eoereivity of 4KOe with the applied field of 1.5T. The core/shell structure was suggested to be an effective way to reduce the ordering temperature obviously.

The Coupling Effect of Spatial Reticulated Shell Structure with Cables

The spatial reticulated shell structure with cables (RSC) is a kind of coupling working system, which consists of flexible cables, reticulated shell structure (RS) and tower columns. The dynamic analysis of RSC based on the coupling model was carried out. Three kinds of elements such as the spatial bar element, cable element and beam element were introduced to analyze the reticulated shell, cable and tower column respectively. Furthermore, such parameter influences as structural boundary conditions, grid configuration, the span-to-depth ratio and the arrangement of cable system upon structural dynamics were analyzed. The structural vibration modes can be divided into four groups based on some numerical examples. And the frequencies in the same group are very close while the frequencies in different groups are different from each other obviously. It is clear that the sequence of the appearance of the each mode group heavily depends on the comparative stiffness of the tower column system, RS and cables.

Research on numerical welding experiment of a thick spherical shell structure

In this paper, in order to predict the residual deformation of thick spherical structure, a welding program is compiled in APDL language based on Ansys and a numerical welding experiment of a welding example is carried out. The temperature field of welding was simulated firstly, then a thermal-structure coupling analysis was carried out, and at last the residual stress and deformation after welding were got. After that, the numerical experiment result was compared with physical experiment one. The comparative analysis shows that the numerical simulation fits well with physical experiment. On the basis of that, a three-dimensional numerical experiment of a thick spherical shell structure was carried out to get the changing rule of stress and deformation of a thick spherical shell structure during welding. The research is of great value to the prediction of residual deformation and high precision machining.

Wind-induced vibration of single-layer reticulated shell structures

Aiming at the dynamic response of reticulated shell structures under wind load,systematic parameter analyses on wind-induced responses of Kiewitt6-6 type single-layer spherical reticulated shell structures and three-way grid single-layer cylindrical reticulated shell structures were performed with the random simulation method in time domain,including geometric parameters,structural parameters and aerodynamic parameters.Moreover,a wind-induced vibration coefficient was obtained,which can be a reference to the wind-resistance design of reticulated shell structures.The results indicate that the geometric parameters are the most important factor influencing wind-induced responses of the reticulated shell structures;the wind-induced vibration coeffi-cient is 3.0-3.2 for the spherical reticulated shell structures and that is 2.8-3.0 for the cylindrical reticula-ted shell structures,which shows that the wind-induced vibration coefficients of these two kinds of space frames are well-proportioned.

Preparation and upconversion luminescence properties of LaF_3:Yb^(3 +),Er^(3 +) /SiO_2 nanocomposites with core /shell structure

LaF^3＋ Yb^3＋ , Er^3＋ nanoparticles were successfully synthesized using solvothermal treatment, and LaF^3＋ Yb^3＋ , Er^3＋/SiO2 core/shell nanoparticles were also prepared with reverse microemulsion technique. The crystal structure, morphology and photoluminescence properties of as-prepared core/shell nanoparticles were in- vestigated by X-ray diffraction, transmission electron microscopy and fluorescence spectrophotometer. The re- sults showed thatLaF^3＋ Yb^3＋ , Er^3＋ nanoparticles are of hexagonal structure and SiO2 shell is amorphous. The size ofLaF^3＋ Yb^3＋ , Er^3＋. nanoparticles is 13 nm and the LaF^3＋ Yb^3＋ , Er^3＋/SiO2 nanoparticles present clearly a core/shell structure with 12 nm shell thickness. The solubility of LaF^3＋ Yb^3＋ , Er^3＋ nanocrystals in water and the biocompatibility are both improved by the SiO2 shell. The upconversion luminescence spectra suggested that the SiO~ shell has small effect on the upconversion luminescence properties of the LaF^3＋ Yb^3＋ , Er^3＋ nanocrys- tals. The core/shell structure LaF^3＋ Yb^3＋ , Er^3＋ /SiO2. nanopartlcles are expected to be used in biological appli- cations.

THE RATIONALISM THEORY AND ITS FINITE ELEMENT ANALYSIS METHOD OF SHELL STRUCTURES

In this paper, a kind of rationalism theory of shell is established which is of different mechanic characters in tension and in compression, and the finite element numerical analysis method is also described.

SHAKEDOWN ANALYSIS OF SHELL STRUCTURES OF KINEMATIC HARDENING MATERIALS

It is of great practical importance to analyze the shakedown of shell structures under cyclic loading, especially of those made of strain hardening materials.In this paper, same further understanding of the shakedown theorem for kinematic hardening materials has been made, and it is applied to analyze the shakedown of shell structures Though the residual stress of a real stale is related to plastic strain, the time-independent residual stress field as we will show in the theorem may be unrelated to the time-independent kinematically admissible plastic strain field For the engineering application, it will lie much more convenient to point this out clearly and definitely, otherwise it will be very difficult. Also, we have proposed a new method of proving this theorem.The above theorem is applied to the shakedown analysis of a cylindrical shell with hemispherical ends. According to the elastic solution, various possible residual sfcss and plastic strain Jlelds, the shakedown analysis of the structure can be reduced to a mathematical programming problem.The results of calculation show that the shakedown load oj strain hardening materials is about 30-40% higher than that of ideal plastic materials. So it is very important to consider the hardening of materials in the shakedown analysis,for it can greatly increase the structure design capacity, and meanwhile provide ascicntific basis to improve the design of shell structures.

A universal performance-enhancing method for Li-S batteries:the cathode material of Li_(2)S@Li_(2)S_(2)@Li_(2)S_(6) double-shell structure

Lithium sulfide(Li_(2)S)as a cathode material for lithium-sulfur(Li-S)batteries,one of the most promising advanced batteries in the future,has received tremendous attention in the past decades.However,developing the practical Li_(2)S cathode confronts challenges of low conductivity for Li-ions and electrons,high sensitivity to environmental moisture,big overpotential barrier to electrochemical activation,and poor cyclability due to the shuttle effect of intermediate species.This article herein reports a simple and effective strategy for making Li_(2)S@Li_(2)S_(2)@Li_(2)S_(6) double-shelled microparticles,which can significantly mitigate these problems.They are synthesized by dissolving Li2S together with S in dimethoxyethane,then drying off the solvent,and finally calcining the collected solid.Compared with pure Li_(2)S,such a double-shell material presents a 26.7% improvement in cycling capacity,0.5 V lower in activation overpotential,and prolonged tolerance in the ambient environment.The density functional theory calculation shows that the performance enhancement lies in the higher stability of Li2S6in contact with moisture and some autocatalytic effect of Li_(2)S_(2)@Li_(2)S_(6).Such a double-shell structure becomes a universal performanceenhancing approach when being combined with other means,such as cathodes composited with catalytic MoS_(2),separators modified with selenium-doped sulfurized-polyacrylonitrile/montmorillonite,electrolytes containing fluorenone additive,and Li anodes coated with a layer of Li_(3)N.The corresponding capacity retention shows up to 80%improvement compared with pure Li_(2)S.

Structural optimization of four designed roof modules:Inspired by Voronax grid shell structures

Architects have been following nature in their constructions for a long time.Observations of nature reveal that it has many highly developed structures that provide scientists and engineers with a lot of useful clues for creating more efficient structures and building forms.Therefore,revealing systematic thinking about natural species is a crucial requirement for today’s buildings.A software analysis method was used to design four modules in the roof structure of the Iranian University of Science and Technology’s exhibition.The roof structure is based on the Voronax structure,which is a relaxed form of Voronoi,which is seen in the structures of many natural creatures.They were analyzed in terms of optimization and structural simulation using Grasshopper plugins and tools by taking into account Von Mises stress in the structural design.The results indicated that by increasing the density of Voronax cells in the areas with high Von Mises stress concentration,a more efficient structure could be achieved in terms of load-bearing and designing predefined free-form roof structures.By analyzing predefined roof structures in an optimum way,the study took a step toward optimizing these kinds of structures.

Decellularized Extracellular Matrix Containing Electrospun Fibers for Nerve Regeneration:A Comparison Between Core–Shell Structured and Preblended Composites

Advanced biomaterial-based strategies for treatment of peripheral nerve injury require precise control over both topological and biological cues for facilitating rapid and directed nerve regeneration.As a highly bioactive and tissue-specifc natural material,decellularized extracellular matrix(dECM)derived from peripheral nerves(decellularized nerve matrix,DNM)has drawn increasing attention in the feld of regenerative medicine,due to its outstanding capabilities in facilitating neurite outgrowth and remyelination.To induce and maintain sufcient topological guidance,electrospinning was conducted for fabrication of axially aligned nanofbers consisting of DNM and poly(ε-caprolactone)(PCL).Core–shell structured fbers were prepared by coaxial electrospinning using DNM as the shell and PCL as the core.Compared to the aligned electrospun fbers using preblended DNM/PCL,the core–shell structured fbers exhibited lower tensile strength,faster degradation,but considerable toughness for nerve guidance conduit preparation and relatively intact fbrous structure after long-term degradation.More importantly,the full DNM surface coverage of the aligned core–shell fbers efectively promoted axonal extension and Schwann cells migration.The DNM contents further triggered neurite bundling and myelin formation toward nerve fber maturation and functionalization.Herein,we not only pursue a multi-functional scafold design for nerve regeneration,a detailed comparison between core–shell structured and preblended electrospinning of DNM/PCL composites was also provided as an applicable paradigm for advanced tissue-engineered strategies using dECM-based biomaterials.

Microwave-assisted synthesis of Cr_(3)C_(2)@C core shell structure anchored on hierarchical porous carbon foam for enhanced polysulfide adsorption in Li-S batteries

In this paper,we use microwave reduction strategy to synthesize a new bi-functional sulfur host material at the service of cathode substrate for lithium-sulfur batteries(LSBs),the composite is made of hierarchical porous carbon foam supported carbon-encapsulated chromium carbide nano-particles(Cr_(3)C_(2)@C/HPCF),in which the well-distributed conductive Cr_(3)C_(2) nano-particles can act as powerful chemical adsorbent and are effective in restraining the shuttle effect of lithium polysulfides(LiPSs).Test results show that the Cr_(3)C_(2)@C/HPCF based sulfur electrodes with 75 wt.%of sulfur exhibit a high initial discharging capacity of 1,321.1 mAh·g^(−1) at 0.1 C(3.5 mg·cm^(−2)),and a reversible capacity can still maintain stability at 1,002.1 mAh·g^(−1) after 150 cycles.Even increasing the areal sulfur loading to 4 mg·cm^(−2),the electrodes can still deliver an initial discharging capacity of 948.0 mAh·g^(−1) at 0.5 C with ultra-slow capacity decay rate of 0.075%per cycle during 500 cycles.Furthermore,the adsorption energy between the Cr_(3)C_(2) surface and LiPSs as well as theoretic analysis based on first-principles is also investigated.

Transcriptome Analysis of Mantle Tissues Reveals Potential Shell-Matrix-Protein Genes in Gigantidas haimaensis

Haima cold seep ecosystem is on the northwestern slope of the South China Sea,which is characterised by high pressure,low temperature,hypoxia,and low pH value.The deep-sea mussel Gigantidas haimaensis is distributed in this ecosystem.Previous studies have focused on its adaptation to abiotic stress,biogeography,ecotoxicology,genomes,immunity and symbiosis,but knowledge on biomineralisation remains lacking.Herein,we generated a comprehensive transcript dataset from G.haimaensis mantle tissue,and 30255 unigenes were assembled.The top 20 most highly expressed genes are related to energy supply,such as mitochondrial genes,suggesting they may mediate the adaptability of this deep-sea mussel to the high pressure and hypoxia environment.Eleven shell matrix protein(SMP)-related genes were identified from the transcriptome data.Quantitative PCR analyses showed that five of ten acidic SMPs and nacreous-layer-matrix-protein genes(nacrein,perlucin,perlwapin,pif and mantle protein)were highly expressed in mantle tissue,while the expressions of other five genes(chitinase,SPARC,TRY,papilin and calmodulin)were low.Scanning electron microscopy showed that the shell was composed of a prismatic layer and a nacreous layer,and every nacreous layer was made of the whole pieces of aragonite that stacked on top of each other.These results indicated the conservation of the structure and functions of nacreous matrix genes in G.haimaensis.Moreover,the nacreous layer was made of whole pieces of aragonite that were not quadrilateral or polygonal pieces.Studying these genes will likely reveal the molecular mechanisms of biomineralisation in G.haimaensis and other deep-sea mussels.

The crystal structure of pearls and related shellfish's shells

In this article we explored the crystal structure of a few pearls and shellfish's shell of fresh water and sea water, and found that pearls and nacreous layer (perhaps and prismatic layer) of shells are all the same: CaCO3, orthorhombic system, aragonite structure and the value of lattice spacings are almost identical. This shows that the pearls of fresh water and sea water are all the same in nature.