导线阵列产生的微电磁力操纵磁粒子

当磁粒子包裹相应的外层物质时,可以与细胞产生选择性黏附,该特性可用于细胞分离、分选、药物运输等.在硅片上制做导线阵列,通过对相应导线阵列的通断电控制,可以控制微磁粒子运动,也就控制了与其相联的细胞运动.细胞运动到指定位置,借助工具对细胞进行操作,研究细胞特性.讨论导线阵列的MEMS工艺,对通电导线产生的磁场、温度场进行了仿真,了解电磁力大小的影响因素.     

T形接头冷丝填充双热源协同焊接数值模拟

为提高T形接头的焊接效率、降低其焊接变形,本文提出了冷丝填充双热源协同焊接的工艺方法,主要利用有限元模拟技术研究了厚度6 mm的5083铝镁合金T形接头双热源协同焊接温度场、应力场及变形特征.模拟结果显示,双热源热输入相同的情况下,T形接头焊接温度场在立板两侧呈对称椭圆形分布,椭圆长轴与焊接方向一致,热源后方区域的温度梯度小于前方,主要是同时受到电弧与凝固焊道热量的叠加作用所致,热量分布范围拓宽;底板x方向的纵向残余应力呈"多峰"状对称分布,近缝区以拉应力为主,应力峰值为111.6 MPa;远缝区以压应力为主,应力值随着远离焊缝而变大,原因是距离热源越远,焊接热应力越小,压应力峰值为73.4 MPa;立板y方向从底部到顶部呈从"拉"到"压"的演变趋势,纵向残余应力先减小后微增,近缝区应力峰值为183 MPa,远缝区应力峰值为33.5 MPa;T形接头的横向收缩变形最大,变形量峰值为1.727 mm,主要与熔池金属冷却凝固时横向剧烈收缩、"拉拽"热影响区和母材有关.     

Fabrication of precisely controlled silicon wire and cone arrays by electrochemical etching

There is an exponentially growing need for well-oriented, vertical silicon nano/micro-structure arrays, particularly in high-density integrated electronic devices. Here, we demonstrate that precisely controlled vertical arrays of silicon wires and cones can be fabricated by a combined treatment strategy of electrochemical and chemical etchings. First, a periodically ordered array of silicon wires was readily fabricated at microscale by simple electrochemical etching in which the current density played a critical role in determining the wire diameter and interspacing. The microstructures fabricated by electrochemical etching were more precisely tuned by further chemical etching, thereby transforming into cone arrays with extremely sharp tips where the cone height was controlled by the etching time. This approach could have broad utility in many electronics requiring miniaturization and high-density integration such as field emitters, photovoltaic and thermoelectric devices.     

Convergence acceleration of the doubly periodic Green?s function for the analysis of thin wire arrays

A method is proposed to accelerate the evaluation of the Green's function of an infinite double periodic array of thin wire antennas. The method is based on the expansion of the Green's function into series corresponding to the propagating and evanescent waves and the use of Poisson and Kummer transformations enhanced with the analytic summation of the slowly convergent asymptotic terms. Unlike existing techniques the procedure reported here provides uniform convergence regardless of the geometrical parameters of the problem or plane wave excitation wavelength. In addition, it is numerically stable and does not require numerical integration or internal tuning parameters, since all necessary series are directly calculated in terms of analytical functions. This means that for nonlinear problem scenarios that the algorithm can be deployed without run time intervention or recursive adjustment within a harmonic balance engine. Numerical examples are provided to illustrate the efficiency and accuracy of the developed approach as compared with the Ewald method for which these classes of problems requires run time splitting parameter adaptation.     

Fringe pattern of the field diffracted by axicons

The far-field intensity pattern of laser beams diffracted by axicons is extensively characterized both theoretically and experimentally. The regular structure of the pattern, consisting of high-contrast fringes, is explained. The experimental results have been interpreted by representing the diffracted field as generated by an extended virtual source shaped as a circle centered on the optical axis of the incident laser beam. The simulations include modifications to the diffraction pattern arising from the laser radiation diffraction limit at the axicon tip, and they reproduce well the measured intensity profile at different distances from the axicon.     

Enhancing the spectral response of filled bolometer arrays for submillimeter astronomy

Future missions for astrophysical studies in the submillimeter region will need detectors with very high sensitivity and large fields of view. Bolometer arrays can fulfill these requirements over a very broad band. We describe a technique that enables bolometer arrays that use quarter-wave cavities to have a high spectral response over most of the submillimeter band. This technique is based on the addition on the front of the array of an antireflecting dielectric layer. The optimum parameters (layer thickness and distance to the array) are determined by a 2D analytic code. This general principle is applied to the case of Herschel PACS bolometers (optimized for the 60 to 210 μm band). As an example, we demonstrate experimentally that a PACS array covered by a 138 μm thick silicon layer can improve the spectral response by a factor of 1.7 in the 450 μm band.     

Calculating the pulsed response of linear arrays: accuracy versuscomputational efficiency

The accuracy and computational efficiency of different methods for calculating the field profile from linear arrays are examined. Specifically, various approximations used for time and frequency domain solutions are studied and compared to the exact time domain impulse response method, which is taken to be the “gold standard”. The accuracy is measured in terms of the error in the 6 dB spatial resolution, whereas the efficiency is represented by the normalized computation time. The results demonstrate that in the frequency domain the Fresnel approximation yields accurate results (errors <1%) for the unsteered array, but that the accuracy degrades with increasing steering angles (>10°). It is also shown that, in general, this method is computationally more efficient as compared with the exact method since the efficiency of the latter depends highly on the field point location and array geometry     

Dynamic bending response of double cylindrical tubes filled with aluminum foam

The dynamic three-point bending behavior of double cylindrical tubes filled with closed-cell aluminum foam core was studied experimentally and numerically. It is found that the deformation mode of this new structure under impact loading is different to that under quasi-static loading. The load carrying capacity of the structure subjected to impact remains at the level of that in the quasi-static situation. Compared with traditional foam-filled single tubes, the specific energy absorption efficiency of this new structure is much higher, and that of both foam-filled structures in the dynamic situation are higher than that in static situation. A preliminary experimental study on the effect of profiles and span of the structure were performed, and the result shows that these parameters affect the structure together. Numerical simulation of the bending behavior was also executed with the explicit finite element method. The mechanism of the dynamic response is revealed by comparison of the maximum strain history in the simulation.     

Nonlinear optical response from arrays of Au bowtie nanoantennas

We demonstrate that the optical response of a single Au bowtie nanoantenna can be favorably modified to increase the local intensity by a factor of 10(3) in the feed gap region when a periodic array of antennas are used. We find that the array periodicity can be used to modulate and shape the spectral emission. An analysis of the emission confirms the presence of second-harmonic generation and two-photon photoluminescence, typical of gold nanostructures, but also reveals a portion of the emitted spectrum that cannot be attributed to a single multiphoton process. Our investigations have important implications for understanding the role of resonant nanostructures in designing optical antennas for next-generation photonic technologies.     

A complication of double lumen hemocatheter guide wire entrapment in a hemodialysis patient

Double lumen hemocatheter is commonly used for temporary hemodialysis patient and various complications have been documented but few reports of guide wire‐related complications. We report a complication of double lumen hemocatheter guide wire entrapment in a 43‐year‐old female of type 1 diabetes mellitus and hemodialysis patient. She was admitted for left arteriovenous shunt dysfunction and right internal jugular vein hemocatheter chamber clotting was found while on hemodialysis, so a new hemocatheter was changed over guide wire. Guide wire was introduced without any resistance and the clotting hemocatheter was removed. During the procedure, the J‐tipped guide wire could not be withdrawn and portable chest radiography revealed the J‐tip of the guide wire was in the right ventricle near the region of tricuspid valve. Fluoroscopy was arranged and it also confirmed the J‐tip was lying in the ventricle near the tricuspid valve where it was stuck. Snare catheter kit was inserted through the 10 Fr sheath and the cardiologist untied the knot by endovascular snare and removed the guide wire smoothly. This report emphasizes the importance of awareness on guide wire entrapment while inserting double lumen hemocatheter. When a guide wire became hard to withdraw, extracting an entrapped guide wire with fluoroscopy guide and snare catheter is a preferable and minimal invasive approach.     

Time domain modelling of thin wire arrays in the presence of a two media configuration using the boundary element analysis

Transient response of a multiple wire configuration in the presence of a two-media configuration excited by a voltage source (antenna mode) or illuminated by an incident field is analysed using the boundary element method (BEM). The analysis is based on the solution of the corresponding set of the coupled space-time Hallen integral equation and it is carried out directly in the time domain. The influence of a two media configuration is taken into account via the space time reflection coefficient. The corresponding integral equation set is handled via the time domain variant of the Galerkin–Bubnov indirect boundary element method (GB-IBEM). Some illustrative numerical results for both antenna and scattering mode are presented in the paper.     

A finite element model for independent wire rope core with double helical geometry subjected to axial loads

Due to the complex geometry of wires within a wire rope, it is difficult to model and analyse independent wire rope core accurately (IWRC). In this paper, a more realistic three-dimensional modelling approach and finite element analysis of wire ropes are explained. Single helical geometry is enough to model simple straight strand while IWRC has a more complex geometry by inclusion of double helical wires in outer strands. Taking the advantage of the double helical wires, three-dimensional IWRCs modelling is applied for both right regular lay and lang lay IWRCs. Wire-by-wire based results are gathered by using the proposed modelling and analysis method under various loading conditions. Illustrative examples are given for those show the accuracy and the robustness of the present FE analysis scheme with considering frictional properties and contact interactions between wires. FE analysis results are compared with the analytical and available test results and show reasonable agreement with a simpler and more practical approach.     

Analysis of diffracted fields with the extended theory of the boundary diffraction wave for impedance surfaces

Uniform diffracted fields from impedance surfaces are investigated by the extended theory of boundary diffraction wave (ETBDW). The new vector potential of the ETBDW is constructed by considering the pseudoimpedance boundary condition. The method is applied to the diffraction problem from an impedance half-plane. It is shown that the total fields from an impedance half-plane reduce to the case of a perfectly electric or magnetic conducting and opaque half-plane for special values of surface impedance. The total and diffracted fields are compared numerically with the exact solution for the impedance half-plane and modified theory of physical optics (MTPO) solution for an impedance wedge. The numerical results show that the field expressions are in very good agreement with the exact and MTPO solutions.     

Electrical-contact-free readout of the response of superconductive bolometer arrays using thermal cross talk

We utilized and investigated the unique dependence of the magnitude and phase of the response on thermal cross talk between bolometer pixels in an array to measure the response of the devices through fewer monitoring devices. We show the feasibility of the proposed readout technique by use of two source pixels in an array, as the image-mapping devices, and one optically shielded pixel as the readout device. While the sensing pixels were electrical-contact free, the readout device was current biased in 4-probe current-bias configuration. Both the phase and the magnitude of the response due to the cross talk in the array were found to be strongly dependent on the modulation frequency and the distance between the sensing and the readout pixels. A series of measurements were designed to extract the response of each single-sensing pixel. By combining the measured data, the response of individual pixels could be extracted through the interpolation of the mapped responses.     

基于可控波束响应的球形传声器阵列定位方法研究

球形传声器阵列因其完全对称的结构,可在三维空间内实现有效的声源定位。文章重点关注基于球谐函数展开的可控波束响应算法,推导了算法的实现流程,并通过仿真验证了可控波束响应算法的性能。建立了包含8个传声器单元的实验系统,其中球形结构在8个单元的条件下可以视为立方结构,通过低阶球谐展开实验验证了可控波束算法的性能。在视听室的实验结果充分验证了定位算法的有效性,定位误差小于10°。     

双链式悬索桥地震反应特征研究

双链式悬索桥采用钢加劲梁和钢筋混凝上索塔,使得阻尼在全桥中呈非经典阻尼耗能特性,导致主坐标系中的运动方程耦联。基于复阻尼理论求解等效粘滞阻尼比,以近似描述非经典阻尼体系的阻尼耗能特性。考虑几何非线性及非经典阻尼因素,对一座双链式悬索桥进行了地震反应谱和时程反应分析。引入主缆形状系数,将单链式悬索桥作为双链式悬索桥的特例,就同跨度同矢高的双链式悬索桥和单链式（普通式）悬索桥地震反应进行对比分析,揭示双链式悬索桥地震反应特征。双链式悬索桥地震反应特征的研究对该类桥设计选型、动力性能评估及抗震加固设计都有重要的工程意义     

Study of incident angle dependence for dual-band double negative-index material using elliptical nanohole arrays

This work demonstrates the angular dependence of dual-band negative-index materials implemented by elliptical nanohole arrays (ENAs) consisting of an Al2O3 dielectric layer between two Au films. This article, it is believed for the first time, analyzes the scattering coefficients and displacement current of the ENA at different angles of plane-wave incidence to show that the ENA is double negative (showing both a negative effective permeability μ(eff) and a negative effective permittivity ε(eff) at multiple wavelengths (1095 and 1680 nm) for p polarization over a broad range of incident angles.     

单缝衍射暗条纹中心距的精确测量

由于较高次衍射条纹的光强很微弱,以及激光的漫反射和CCD器件本身存在的暗电流噪声等原因,使得暗条纹中心距难以精确测量,这是单缝衍射法测量几何量中影响测量精度的主要原因。为此,提出了分步滤波法和暗条纹中心判定条件。对衍射条纹原始采集数据先进行过滤波,再进行欠滤波,尽量消除干扰信号的影响,获得有用信号;利用最小二乘法对衍射条纹曲线进行拟合,并利用二分搜索法对拟合曲线的波谷进行精确定位,就可较精确地得到暗条纹的中心位置。实验表明,暗条纹中心距的测量精度达到优于5μm的水平。