A novel method of supporting gold nanoparticles on MWCNTs： Synchrotron X-ray reduction

Gold nanoparticles decorating the surface of multiwalled carbon nanotubes （MWCNTs） are prepared by photochemical reduction. The gold clusters form different interesting geometrical faceted shapes in accordance to time duration of synchrotron X-ray irradiation. The shape of nanogold could be spherical, rod-like, or triangular. Carbon nanotubes serve as optimal templates for the heterogeneous nucleation of gold nanocrystals. These nanocrystal structures are characterized by transmission electron microscope （TEM） and element analysis by energy dispersive spectroscopy （EDS）. 2007 Chinese Society of Particuology and Institute of Process Engineering,Chinese Academy of Sciences. Published by Elsevier B.V.     

The influence of mechanical strain on the optical properties of spherical gold nanoparticles

We utilize classical Mie scattering theory to investigate the effects of tensile and compressive mechanical strain on both the far field (absorption, scattering and extinction efficiencies) and near field (surface enhanced Raman scattering) optical properties of spherical gold nanoparticles with diameters ranging from 10 to 100 nm. By accounting for the strain effects on both the ionic core (bound) and conduction (free) electrons through appropriate modifications of the bulk dielectric functions, we find that gold nanoparticles are relatively sensitive to the effects of mechanical strain due to the fact that the plasmon resonance wavelength for spherical gold particles, which occurs around , is nearly coincident with the interband transitions of the core electrons. Specifically, we find that tensile strain leads to significant enhancements ranging from 60% to 120% in the far field optical efficiencies, while compressive strain leads to similar decreases, and that the plasmon resonance wavelength can be red or blueshifted up to 100 nm due to the applied strain. Finally, we find that tensile strain also strongly enhances the local electric (E)-field at the surface of the nanoparticles, which is of considerable interest for surface-enhanced Raman scattering applications; 5% tensile strain is found to enhance the |E|⁴ intensity by 63%. The present results demonstrate the potential of mechanical strain, and specifically that of tensile mechanical strain in enhancing and tailoring the optical properties of gold nanoparticles.     

爆轰法合成碳包覆纳米铜颗粒

以硝酸铜和柠檬酸制成的干凝胶为主要反应物,加入油酸有机碳源和黑索今炸药,在氮气保护气氛下在爆炸容器中引爆,成功地合成了碳包覆纳米铜颗粒。分别采用X射线衍射、透射电镜对产物形貌特征进行表征。结果表明,在爆轰产物中富含碳包覆纳米铜颗粒,产物呈圆球体,具有完好的核壳结构形貌,颗粒粒径在10~40nm 之间,外层碳壳结构主要由无定型碳和石墨构成。并对爆轰法合成碳包覆纳米铜颗粒的形成机理进行了分析。     

Green synthesis,characterization and physiological stability of gold nanoparticles from Stachys lavandulifolia Vahl extract

The synthesis of nontoxic stable gold nanoparticles is important for medical applications. An aqueous extract of the plant Stachys lavandulifolia Vahl was used to synthesize gold nanoparticles. This green method involved the S. lavandulifolia Vahl extract acting as a reducing and stabilizing agent. The nanoparticles were characterized by transmission electron microscopy, dynamic light scattering analysis and UV–vis absorption and Fourier transform-infrared spectroscopies. Stability under physiological conditions is important for medical applications. The stability of the nanoparticles was compared with that of conventional citrate-capped nanoparticles, under both synthetic and physiological conditions. The nanoparticles synthesized from the S. lavandulifolia Vahl extract were stable under physiological conditions, in contrast with conventional citrate-capped nanoparticles.     

A novel method for fast and continuous preparation of superfine titanium dioxide nanoparticles in microfluidic system

Previously we had developed a microfluidic system that can be easily fabricated by bending a stainless-steel tube into large circular loops. In this study, a fast and continuous preparation method for superfine TiO₂ nanoparticles (TiO₂-NPs) was developed for the aforementioned microfluidic system. The proposed method can yield anatase TiO₂ in 3.5 min, in contrast to the traditional hydrothermal reaction method, which requires hours or even days. Different reaction conditions, such as reaction temperature (120–200 °C), urea concentration (20–100 g/L), and tube length (5–20 m) were investigated. X-ray diffraction and Brunauer–Emmett–Teller analysis indicate that the as-prepared TiO₂-NPs have crystalline sizes of 4.1–5.8 nm and specific surface areas of 250.7–330.7 m²/g. Transmission electron microscopy images show that these TiO₂-NPs have an even diameter of approximately 5 nm. Moreover, because of their small crystalline sizes and large specific surface areas, most of these as-prepared TiO₂-NPs exhibit considerably better absorption and photocatalytic performance with methylene blue than commercial P5 TiO₂ does.     

A novel method for fast and continuous preparation of superfine titanium dioxide nanoparticles in microfluidic system

Previously we had developed a microfluidic system that can be easily fabricated by bending a stainless-steel tube into large circular loops.In this study,a fast...     

Key synthesis of magnetic Janus nanoparticles using a modified facile method

Inorganic/organic poly（methylmethacrylate-acrylic acid-divinylbenzene） iron oxide Janus magnetic nanoparticles（P（MMA-AA-DVB）/Fe3O4） with strong magnetic domains and unique surface functionalities were prepared using a solvothermal process.The P（MMA-AA-DVB） nanoparticles were prepared via soapfree emulsion polymerization and used as a precursor for preparing Janus nanoparticles.The morphology and magnetic properties of the magnetic Janus nanoparticles formed were characterized using a laser particle size analyzer,transmission electron microscopy,Fourier transform infrared spectroscopy,vibrating sample magnetometry,and thermogravimetric analysis.The synthesized P（MMA-AA-DVB）/Fe3O4 magnetic Janus nanoparticles were characterized by a Janus structure and possessed a stable asymmetric morphology after being dually functionalized.The particle size,magnetic content,and magnetic domain of the P（MMA-AA-DVB）/Fe3O4 magnetic Janus nanoparticles were 200 nm,40%,and 25 emu/g,respectively.The formation mechanism of the Janus nanoparticles was also investigated,and the results revealed that the reduction of Fe3＋ ions and growth of Fe3O4 took place on the surface of the P（MMA-AA-DVB） polymeric precursor particles.The size of the Janus particles could be controlled by narrowing the size distribution of the P（MMA-AA-DVB） precursor nanoparticles.     

A hybrid detailed level and configuration accounting model for investigating the radiative opacity of gold plasmas with open 4d and 4f shells

A hybrid model combining the detailed level accounting (DLA) and detailed relativistic configuration accounting (DCA) methods is developed to investigate the radiative opacity of gold plasmas with open 4d and 4f shells. Due to the collapse of 4f shells, the configurations with multi-electron excited from 4d and 4f shells are bound and can form a huge number of fine-structure levels and detailed transition lines. A full DLA calculation is time-consuming and intractable and thus a hybrid DLA and DCA method is needed. To obtain accurate radiative opacity, the transitions within the collapsed orbitals and transitions to the relatively lowly excited orbitals are treated by a DLA method, while the transitions to the higher excited orbitals are treated by a DCA method. As an illustrative example, the spectrally resolved, Rosseland and Planck mean opacity of gold plasmas at 100 eV and 0.001 g/cm³ are calculated by using the hybrid model. The present results are compared with those obtained by pure DCA and average atom models, where large discrepancies in the line intensities and positions are found for the strongest 4d–4f transitions due to the collapse of 4f shells indicating the importance of detailed treatment to obtain the accurate opacity.     

Ultrapermeable membranes based on connected cluster of hollow polydimethylsiloxane nanoparticles for gas separation

Mixed matrix membranes (MMMs) with the performance between the matrix and the filler is a promising strategy for membranes with excellent gas permeability-selectivity. In this study, the hollow polydimethylsiloxane nanoparticles were synthesized and then incorporated with the poly(oxide ethylene) monomer and tri-functional cross-linker to form mixed matrix membranes by in situ polymerization. The hollow nanoparticles formed the independent closed nanocavities in membranes, which enhanced the gas permeability contributed by both the improved diffusivity and solubility. At high loading, the hollow polydimethylsiloxane nanoparticle was converted into the continuous phase with the cross-linked poly(oxide ethylene) as the dispersed phase. Gases preferred to permeate through the connected cluster of hollow polydimethylsiloxane nanoparticles, finally leading to ultrahigh gas permeabilities far going beyond the instinct values of polydimethylsiloxane and the cross-linked poly(oxide ethylene). The optimized membrane with 34 wt% hollow nanoparticles loadings exhibited ultrahigh permeabilities with the values of 44186 Barrer for CO₂ and 11506 Barrer for O₂, accompanied with a CO₂/N₂ selectivity of 9.9 and an O₂/N₂ selectivity of 2.6, which exceeded the 2008 Robeson upper bound for O₂/N₂ and located at the 2008 Robeson upper bound for CO₂/N₂.     

A multigrid method for recirculating flows

The use of multigrid methods in complex fluid flow problems is recent and still under development. In this paper we present a multigrid method for the incompressible Navier-Stokes equations. The distinctive features of the method are the use of a pressure-correction method as a smoother and a novel continuity-preserving manner of grid coarsening. The shear-driven cavity problem is used as a test case to demonstrate the efficiency of the method.     

A wavelet multiscale method for inversion of Maxwell equations

This paper is concerned with estimation of electrical conductivity in Maxwell equations. The primary difficulty lies in the presence of numerous local minima in the objective functional. A wavelet multiscale method is introduced and applied to the inversion of Maxwell equations. The inverse problem is decomposed into multiple scales with wavelet transform, and hence the original problem is reformulated to a set of sub-inverse problems corresponding to different scales, which can be solved successively according to the size of scale from the shortest to the longest. The stable and fast regularized Gauss-Newton method is applied to each scale. Numerical results show that the proposed method is effective, especially in terms of wide convergence, computational efficiency and precision.     

Conductive hydrogels incorporating carbon nanoparticles: A review of synthesis,performance and applications

As one of the most rapidly expanding materials, hydrogels have gained increasing attention in a variety of fields due to their biocompatibility, degradability and hydrophilic properties, as well as their remarkable adhesion and stretchability to adapt to different surfaces. Hydrogels combined with carbon-based materials possess enhanced properties and new functionalities, in particular, conductive hydrogels have become a new area of research in the field of materials science. This review aims to provide a comprehensive overview and up-to-date examination of recent developments in the synthesis, properties and applications of conductive hydrogels incorporating several typical carbon nanoparticles such as carbon nanotubes, graphene, carbon dots and carbon nanofibers. We summarize key techniques and mechanisms for synthesizing various composite hydrogels with exceptional properties, and represented applications such as wearable sensors, temperature sensors, supercapacitors and human-computer interaction reported recently. The mechanical, electrical and sensing properties of carbon nanoparticles conductive hydrogels are thoroughly analyzed to disclose the role of carbon nanoparticles in these hydrogels and key factors in the microstructure. Finally, future development of conductive hydrogels based on carbon nanoparticles is discussed including the challenges and possible solutions in terms of microstructure optimization, mechanical and other properties, and promising applications in wearable electronics and multifunctional materials.     

一种新的减基法中的采样方法及误差估计

针对减基法中求解精度受减基空间完备性影响的问题,提出了一种基于向量空间逼近原理的采样方法及相应的误差估计。该方法使每一步采样得到的特征向量与之前已得到的特征向量所张成的向量空间角度最大,从而保证了每步采样所对应的特征向量都具有最弱相关性,进而使最终得到的特征向量基空间更具完备性。并且由该方法产生了一种先验特征值误差界,...     

New expression for collision efficiency of spherical nanoparticles in Brownian coagulation

The collision efficiency of dioctyl phthalate nanoparticles in Brownian coag- ulation has been studied. A set of collision equations is solved numerically to find the relationship between the collision efficiency and the particle radius varying in the range of 50 nm to 500 nm in the presence of Stokes resistance, lubrication force, van der Waals force, and elastic deformation force. The calculated results are in agreement with the experimental data qualitatively. The results show that the collision efficiency decreases with the increase of the particle radii from 50 nm to 500 nm. Based on the numerical data, a new expression for collision efficiency is presented.     

弹性力学的复变量无网格流形方法

为克服无网格流形方法配点过多、计算速度慢、容易形成病态方程组等缺点,将复变量移动最小二乘法与无网格流形方法相结合,提出了弹性力学的复变量无网格流形方法。分别采用线性基本与二次基进行计算,并与无网格流形方法相比。研究表明该方法计算量小、精度高。     

A boundary element method for anisotropic coupled thermoelasticity

Summary A boundary element formulation is presented for the solution of the equations of fully coupled thermoelasticity for materials of arbitrary degree of anisotropy. By employing the fundamental solutions of anisotropic elastostatics and stationary heat conduction, a system of equations with time-independent matrices is obtained. Since the fundamental solutions are uncoupled and time-independent, a domain integral remains in the representation formula which contains the time-dependence as well as the thermoelastic coupling. This domain integral is transformed to the boundary by means of the dual reciprocity method. By taking this approach, the use of dynamic fundamental solutions is avoided, which enables an efficient calculation of system matrices. In addition, the solution of transient processes as well as, free and forced vibration analysis becomes straightforward and can be carried out with standard time-stepping schemes and eigensystem solvers. Another important advantage of the present formulation is its versatility, since it includes a number of simplified thermoelastic theories, viz. the theory of thermal stresses, coupled and uncoupled quasi-static thermoelasticity, and stationary thermoelasticity. The accuracy of the new thermoelastic boundary element method is demonstrated by a number of example problems. Support by the Deutsche Forschungsgemeinschaft (DFG) of the Graduate Collegium Modelling and discretization methods for continua and fluids (GKKS) at the University of Stuttgart is gratefully acknowledged.     

非齐次动力学方程的一种精细积分单步方法

针对非齐次动力学方程■,结合精细积分法和微分求积法,利用同阶的显式龙格-库塔法对计算过程中待求的v_(k+i/s)(i=1,2,…,s)进行预估,提出了一种避免状态矩阵求逆的高效精细积分单步方法。该方法采用精细积分法计算e~(Ht),而Duhamel积分项采用s级s阶的时域微分求积法,计算格式统一且易于编程,可灵活实现变阶变步长。仿真结果表明,与其他单步法及预估校正-辛时间子域法进行数值比较,该方法具有高精度、高效率及良好的稳定性,在求解大规模动力系统时间响应问题中具有较大的优势。     

A modified method of averaging for solving a class of nonlinear equations

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A novel virtual node method for polygonal elements

A novel polygonal finite element method （PFEM） based on partition of unity is proposed, termed the virtual node method （VNM）. To test the performance of the present method, numerical examples are given for solid mechanics problems. With a polynomial form, the VNM achieves better results than those of traditional PFEMs, including the Wachspress method and the mean value method in standard patch tests. Compared with the standard triangular FEM, the VNM can achieve better accuracy. With the ability to construct shape functions on polygonal elements, the VNM provides greater flexibility in mesh generation. Therefore, several fracture problems are studied to demonstrate the potential implementation. With the advantage of the VNM, the convenient refinement and remeshing strategy are applied.     

一种处理弹性动力边界元法中奇异积分的方法

利用边界元法求解瞬态弹性动力学问题时,时域基本解函数的分段连续性和奇异性为该问题的求解带来很大的困难。为了解决时域基本解中的奇异性问题,本文依据柯西主值的定义,对经过时间解析积分之后的时域基本解进行奇异值分解,将其分成奇异和正则积分两部分;其中正则部分可通过采用常规高斯积分方法来计算,而奇异部分具有简单的形式,可以利用解析积分计算。经过上述操作之后,就可以达到直接消除时域基本解中奇异积分的目的。和传统方法相比,本文方法并不依赖静力学基本解来消除奇异性,是一种直接求解方法。最后给定两个数值算例来验证本文提出方法的正确性和可行性,结果表明使用本文算法可以解决弹性动力学边界积分方程中的奇异性问题。