An inelastic Timoshenko beam element with axial–shear–flexural interaction

An enhanced beam element is proposed for the nonlinear dynamic analysis of skeletal structures. The formulation extends the displacement based elastic Timoshenko beam element. Shear-locking effects are eliminated using exact shape functions. A variant of the Bouc–Wen model is implemented to incorporate plasticity due to combined axial, shear and bending deformation components. Interaction is introduced through the implementation of yield functions, expressed in the stress resultant space. Three additional hysteretic degrees of freedom are introduced to account for the hysteretic part of the deformation components. Numerical results are presented that demonstrate the advantages of the proposed element in simulating cyclic phenomena, in which shear deformations are significant.     

Nanocrystalline Si3N4 with Si–C–N shell structure

Nanocrystalline Si₃N₄ with an amorphous Si–C–N shell structure was synthesized by mechanically activating Si₃N₄ and graphite powder in argon atmosphere at room temperature. Twenty hours of mechanical activation resulted in occurrence of CN bond, which can be identified using Fourier transform infrared spectrometry (FT-IR). When the mechanical activation period was extended to 67 h and then to 90 h, the CN bond was further established. The formation of CN bond under the mechanical activation for 90 h was further confirmed using X-ray photoelectron spectroscopy (XPS). The thickness of Si–C–N shell is 5–7 nm as observed using high-resolution transmission electron microscope.     

pH-responsive polymeric micelles with core–shell–corona architectures as intracellular anti-cancer drug carriers

Abstract

Polymeric micelles with core–shell–corona nanoarchitecture were designed for intracellular therapeutic anti-cancer drug carriers. Poly(styrene-b-acrylic acid-b-ethylene glycol) (PS-b-PAA-b-PEG) asymmetric triblock copolymer underwent self-assembly in aqueous solution to form spherical micelles with hydrophobic PS core, anionic PAA shell and hydrophilic PEG corona. The anti-cancer drug (doxorubicin, DOX) was successfully incorporated into the polymeric micelles. The in vitro release experiment confirmed that the release of DOX from the micelles was inhibited at pH 7.4. In contrast, an accelerated release of DOX was observed at mildly acidic conditions such as pH 4.5. The excellent biocompatibility of our PS-b-PAA-b-PEG-based micelles made the synthesized nano-carrier best suited for the delivery of anti-cancer drugs.     

Fabrication and characterization of microcapsules with polyamide–polyurea as hybrid shell

Well-defined microcapsules with polyamide–polyurea as a hybrid shell have been described for biomedical applications. Interfacial polymerization method with surfactant and cosurfactant was developed for the preparation of the hybrid microcapsules. After reaction, centrifugation, and freeze drying processes, the polyamide–polyurea hybrid microcapsules with porous membranes were successfully fabricated. Compared with previous researches of the single polyamide or polyurea microcapsules, experimental data showed that the hybrid microcapsules have a thicker shell and excellent mechanical property. Various diameters and morphologies for the hybrid microcapsules can be obtained by changing the stirring rate, drying method, and surfactant content.     

Formation of core–shell network structural titanium–nitrogen alloys with different nitrogen contents

High-dense titanium alloys with a 3D network core–shell structure of different N contents were synthesized successfully by means of spark plasma sintering of the nitrided titanium particles. The microstructure investigation shows that the core–shell structure with an obvious boundary within a grain is constructed in light of different solid solution levels of nitrogen in grain boundary and grain inner. The mechanical behaviors have been experimentally assessed through compressive testing. The compacts exhibit a much enhanced strength while retaining a reasonable ductility, which can be attributed to their novel core–shell structure. With an increasing N content as well as shell thickness, the strength increases and the ductility decreases, in accordance with the morphology observations.     

Meshless local Petrov–Galerkin (MLPG) method in combination with finite element and boundary element approaches

The meshless local Petrov–Galerkin (MLPG) method is an effective truly meshless method for solving partial differential equations using moving least squares (MLS) interpolants. It is, however, computationally expensive for some problems. A coupled MLPG/finite element (FE) method and a coupled MLPG/boundary element (BE) method are proposed in this paper to improve the solution efficiency. A procedure is developed for the coupled MLPG/FE method and the coupled MLPG/BE method so that the continuity and compatibility are preserved on the interface of the two domains where the MLPG and FE or BE methods are applied. The validity and efficiency of the MLPG/FE and MLPG/BE methods are demonstrated through a number of examples. Received 6 June 2000     

Experimental and finite element analysis of ultrasonic vibration−assisted continuous-wave laser surface drilling

In pulsed laser drilling with co-axial assisted gas, material removal mechanism (surface vaporization and melt expulsion) determines the machining/drilling rate and quality of the drilled holes. Incomplete melt expulsion is one of the major causes of laser drilling defects. To improve the drilling efficiency and quality of holes, a novel ultrasonic vibration?assisted continuous-wave laser drilling (UVLD) approach is proposed. The application of ultrasonic vibrations (of frequency of 20?kHz and vibration displacement of 23?µm) during laser surface melting facilitates the melt expulsion in the form of sideways melt flow and droplet ejection from the drilling front. A systematic experimental study on the ultrasonic vibration-assisted laser drilling of AISI 316 stainless steel is performed to investigate the effect of working distance on the geometric features and surface quality of the holes. The experimental results based on high-speed photography indicate that the melt expulsion under the influence of ultrasonic vibrations initiates after the laser melted pool reaches a critical size/volume. Based on this underlying mechanism, a simplified finite element analysis is performed for the UVLD process to predict the hole volumes for the investigated working distances.     

Transient liquid phase bonding of Cu@Sn core–shell particles with added Sn–3.0Cu–0.5Ag

Journal of Materials Science - A 3–5 μm Cu@Sn core–shell powder was prepared by chemical plating. Based on the mixture of this Cu@Sn and SAC305 powder, a solder material...     

Microstructure and mechanical properties of Sn–Bi solder joints reinforced with Zn@Sn core–shell particles

We proposed Zn@Sn particles to improve the mechanical properties of the Sn–58 wt% Bi (Sn58Bi) solder. The effects of 3, 6, and 9 wt% Zn@Sn particles on the microstructure and mechanical properties of Sn58Bi were investigated. The addition of Zn@Sn to Sn58Bi solder inhibited microstructural coarsening, which mitigated the brittleness of Sn58Bi solder joints during aging. The zinc-rich phases dispersively distributed in the solder joints effectively inhibited the coarsening of the Bi-riched phase. At the same time, Cu₅Zn₈ instead of Cu₆Sn₅ formed at the composite solder/Cu interface. After 21 days of aging, the shear strengths of solder joints doped with 6 wt% Zn@Sn decreased from 54.06 to 36.41 MPa. Compared with the undoped solder joints before and after aging, the shear strengths increased by 34% and 173.1%, respectively. Thus, the composite solder paste has great potential to be used as a low-temperature lead-free solder in the electronic packaging industry.

     

Room temperature single electron transistor with two-dimensional array of Au–SiO2 core–shell nanoparticles

The composite nanoparticles of gold core coated with SiO₂ shell have been fabricated into 2-dimensional array on a silicon surface by a simple self-assembly method combined with the technique of AFM (atomic force microscopy) nanolithography. The double-barrier-tunneling junction with AFM tip was also fabricated for the room-temperature single-electron tunneling study, by which the AFM tip was orientated on the surface of the SiO₂ coated gold composite nanoparticles. The 2D array shows well-pronounced Coulomb staircases with a period of 200 mV at room temperature, demonstrating single electron transistor behavior.     

Space–time SUPG finite element computation of shallow-water flows with moving shorelines

We show that combination of the Deforming-Spatial-Domain/Stabilized Space–Time and the Streamline-Upwind/Petrov–Galerkin formulations can be used quite effectively for computation of shallow-water flows with moving shorelines. The combined formulation is supplemented with a stabilization parameter that was originally introduced for compressible flows, a compressible-flow shock-capturing parameter adapted for shallow-water flows, and remeshing based on using a background mesh. We present a number of test computations and provide comparisons to theoretical results, experimental data and results computed with nonmoving meshes.     

A continuum eight‐parameter shell finite element for large deformation analysis

Abstract

In this paper, a finite element formulation, using eight independent parameters and high‐order spectral/hp functions, for nonlinear analysis is presented. This formulation allows the use of a third‐order thickness stretch kinematics, which also avoids Poisson's locking. Full nonlinear terms up to quadratic in the Green–Lagrange strain tensorare retained. Several nontrivial problems are solved using the presented formulation. A comparison between this formulation and others found in the literature,and with shell and solid elements in commercial codes ABAQUS and ANSYS are presented and the differences are brought out.     

Tunable photonic nanojet achieved using a core–shell microcylinder with nematic liquid crystal

A tunable photonic nanojet achieved using a core–shell microcylinder with nematic liquid crystal is reported. The core–shell microcylinder can be obtained by the infiltration of liquid crystal into the air core of a microcylinder. The refractive indices of the liquid crystals can be changed by rotating the directors of the liquid crystals. Therefore, we were able to control the flow direction of the photonic nanojet in two-dimensional core–shell microcylinder structures. Using high resolution finite-difference time-domain simulation, we demonstrate that the photonic nanojet can be continuously tuned in the core–shell microcylinder. The horizontal and vertical shifts of photonic nanojet depend strongly on the director of the liquid crystals. Such a mechanism of nanojet adjustment should open up a new application for using visible light to detect nanoparticles, optical gratings, and single molecules with subwavelength spatial resolution.     

The multifunctional wound dressing with core–shell structured fibers prepared by coaxial electrospinning

The non-woven wound dressing with core–shell structured fibers was prepared by coaxial electrospinning. The polycaprolactone (PCL) was electrospun as the fiber’s core to provide mechanical strength whereas collagen was fabricated into the shell in order to utilize its good biocompatibility. Simultaneously, the silver nanoparticles (Ag-NPs) as anti-bacterial agent were loaded in the shell whereas the vitamin A palmitate (VA) as healing-promoting drug was encapsulated in the core. Resulting from the fiber’s core–shell structure, the VA released from the core and Ag-NPs present in the shell can endow the dressing both heal-promoting and anti-bacteria ability simultaneously, which can greatly enhance the dressing’s clinical therapeutic effect. The dressing can maintain high swelling ratio of 190% for 3 d indicating its potential application as wet dressing. Furthermore, the dressing’s anti-bacteria ability against Staphylococcus aureus was proved by in vitro anti-bacteria test. The in vitro drug release test showed the sustainable release of VA within 72 h, while the cell attachment showed L929 cells can well attach on the dressing indicating its good biocompatibility. In conclusion, the fabricated nanofibrous dressing possesses multiple functions to benefit wound healing and shows promising potential for clinical application.     

In situ fabricated metal-carbide with core–shell structure for high impact-toughness iron-matrix composite

A series of metal-carbide (Ta–TaC, Nb–NbC and W–WC) with core–shell structure for iron-matrix composites are fabricated by in situ solid-phase diffusion. Results show that the formation of metal-carbide with a rod-shaped core–shell structure, in which the metal-rod surface was covered with a carbide shell layer, in the iron- matrix after in situ solid-phase diffusion. The TaC, NbC, and WC shell layers are in situ synthesised by the diffusion of carbon atoms from the iron-matrix onto the surface of the Ta, Nb, and W rods, respectively. Metallurgical integration occurs between metal-carbide and iron-matrix. The metal-carbide-reinforced iron-matrix composites show excellent impact resistance, and the shell-layer hardness is extremely high.     

Ultra-stable silica-coated chiral Au-nanorod assemblies: Core–shell nanostructures with enhanced chiroptical properties

Chiral nano-assemblies with amplified optical activity have attracted particular interest for their potential application in photonics, sensing and catalysis. Yet it still remains a great challenge to realize their real applications because of the instability of these assembled nanostructures. Herein, we demonstrate a facile and efficient method to fabricate ultra-stable chiral nanostructures with strong chiroptical properties. In these novel chiral nanostructures, side-by-side assembly of chiral cysteine-modified gold nanorods serves as the core while mesoporous silica acts as the shell. The chiral core–shell nanostructures exhibit an evident plasmonic circular dichroism (CD) response originating from the chiral core. Impressively, such plasmonic CD signals can be easily manipulated by changing the number as well as the aspect ratio of Au nanorods in the assemblies located at the core. In addition, because of the stabilization effect of silica shells, the chiroptical performance of these core–shell nanostructures is significantly improved in different chemical environments.

Open image in new window

     

Facile method to synthesise polystyrene/silver composite nanoparticles with core–shell structures

We report a facile method for the fabrication of polystyrene/silver composite nanoparticles with core–shell nanostructures. First, polystyrene (PS) nanoparticles with carboxyl acid groups on their surfaces were prepared via the dispersion polymerisation of styrene in water with the assistance of acrylic acid. Second, with the addition of [Ag(NH₃)₂]⁺ to the PS dispersion, [Ag(NH₃)₂]⁺ was absorbed onto the surfaces of the modified PS nanoparticles. Finally, the [Ag(NH₃)₂]⁺ complex ions were reduced to Ag to form the PS/Ag nanocomposites upon heating. The resulting PS/Ag composite nanoparticles were characterized via scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, and dynamic light scattering.     

Coupling of membrane element with material point method for fluid–membrane interaction problems

This paper proposes a coupled particle–finite element method for fluid–membrane structure interaction problems. The material point method (MPM) is employed to model the fluid flow and the membrane element is used to model the membrane structure. The interaction between the fluid and the membrane structure is handled by a contact method, which is implemented on an Eulerian background grid. Several numerical examples, including membrane sphere interaction, water sphere impact and gas expansion problems, are studied to validate the proposed method. The numerical results show that the proposed method offers advantages of both MPM and finite element method, and it can be used to simulate fluid–membrane interaction problems.