Direct-writing organic three-dimensional nanofibrous structure

Direct-writing technology based on Near-Field Electrospinning (NFES) was used to fabricate an organic three-dimensional nanofibrous circle on the patterned silicon substrate. In NFES, straight jet without splitting and chaotic motion was utilized to direct-write orderly nanofiber. When the collector movement speed was lower than electrospinning rate, the relaxed nanofiber would be lead into the pendulum motion by the electrical field force and Coulomb repulsion force from the residual charges on the collector. When the relative air humidity is lower than 35%, individual nanofiber with larger elastic resistance would reveal a good self-assembly performance. Owing to the guidance of the electric field force at the edge of the micro-pattern, a nanofiber was deposited layer by layer to format a 3D nanofibrous circle on the top surface of the micro-pattern. The dimension scale of 3D nanofibrous circle was smaller than 30 μm. With the help of a microscope, a 3D nanofibrous circle can be deposited precisely on the strip micro-pattern with width of 4 μm. Furthermore, a 3D nanofibrous circle in different shapes can be obtained by using special micro-patterns. This organic three-dimensional nanofibrous circle has created a new aspect for the fabrication of organic micro/nanosystems.     

Structuring of micro line conductor using electro-hydrodynamic printing of a silver nanoparticle suspension

The generation of a fine pattern of metallic materials from suspensions is gaining significant interest because it is the key in the fabrications of displays and printed circuit boards. In our experiments, a silver nanoparticle suspension was first deposited onto a Kapton® polyimide film by using an electro-hydrodynamic printing system, including a guide ring and pin (nozzle)-to-pin (ground) electrodes. Then after thermal curing of the particles deposited, a conductor line as fine as 32 μm in width and 0.3 μm in thickness was obtained onto the film. The resistivity of the line was about 13 μΩ?cm. The pin type ground electrode was helpful in the deposit of the silver nanoparticle suspension along a specific direction. The guide ring repressed the chaotic motion of the jet and prevented the jet from digressing from the centerline. With the electro-hydrodynamic printing method, a nozzle (inner diameter: 140 μm, outer diameter: 320 μm) much larger than an ink jet nozzle could be used.     

Fabrication of size-controlled three-dimensional structures consisting of electrohydrodynamically produced polycaprolactone micro/nanofibers

In this paper, we report a facile method of fabricating size-controlled three-dimensional (3D) polycaprolactone (PCL) micro/nanofiber structure using a modified electrospinning supplemented with a specially designed solvent bath in which the flow rate of the solvent (EtOH) was controlled. By varying the flow rate of the EtOH into the grounded bath and the electrospinning parameters including a distance between the nozzle and target, the height, diameter, porosity, and micro/nanofiber size of the 3D structures were controlled. To show stable micro/nanofibrous structures under the fabricating conditions, we characterized a process diagram for various flow rates of EtOH and weight percents of PCL. We believe that this modified electrospinning process may be a new means of fabricating micro/nanofibrous 3D structures.     

An Experimental Investigation of Forced Convection Heat Transfer from a Coiled Heat Exchanger Embedded in a Packed Bed

Forced convection heat transfer from a helically coiled heat exchanger embedded in a packed bed of spherical glass particles was investigated experimentally. With dry air at ambient pressure and temperature as a flowing fluid, the effect of particle size, helically coiled heat exchanger diameter, and position was studied for a wide range of Reynolds numbers. It was found that the particle diameter, the helically coiled heat exchanger diameter and position, and the air velocity are of great influence on the convective heat transfer between the helically coiled heat exchanger and air. Results indicated that the heat transfer coefficient increased with increasing the air velocity, increasing helically coiled heat exchanger diameter, and decreasing the particle size. The highest heat transfer coefficients were obtained with the packed-bed particle size of 16 mm and heat exchanger coil diameter of 9.525 mm (1/4 inch) at a Reynolds number range of 1,536 to 4,134 for all used coil positions in the conducted tests. A dimensionless correlation was proposed for Nusselt number as a function of Reynolds number, particle size, coil size, and coil position.     

Time-resolved imaging of hydrogel printing via laser-induced forward transfer

In this work, the printing mechanism of an alginate-based hydrogel via laser-induced forward transfer (LIFT) is investigated by spatial and temporal high-resolved stroboscopic imaging. First, the generation of the liquid jet is studied at two different laser fluences in a process without collector slide. Furthermore, the impingement process onto the collector slide at the same fluence levels is observed. With the help of these images the development of the jet is explained. Besides the influences of the collector slide as well as the applied laser fluence on the transfer are demonstrated.     

Highly porous 3D nanofibrous scaffolds processed with an electrospinning/laser process

Electrospinning has been widely used to produce micro/nanosized fibres. Although the method is very simple, easy, and effective for obtaining nanosized material, the fabrication of three dimensional (3D) shapes comprised of micro/nanofibres has been a major obstacle for use in tissue engineering. In this study, a new electrospinning method to fabricate controllable 3D micro/nanofibrous structure (with thickness over 3 mm) is suggested. The fabricated 3D fibrous structure was fully porous and successfully consisted of submicron-sized fibres. However, the pores in the 3D fibrous structure were too small (5–10 μm), so we used a femtosecond laser process to achieve enough cell infiltration and proliferation in the thickness direction of the 3D structure. By controlling appropriate processing conditions, we can successfully fabricate a highly porous 3D micro/nanofibrous structure with various pore sizes ranging from 189 ± 28 μm to 380 ± 21 μm. The fabricated 3D fibrous scaffolds were assessed for in vitro biological capabilities by culturing osteoblast like cells (MG63). Compared with the rapid-prototyped PCL scaffold, the 3D fibrous scaffold exhibited significantly higher biological activities (initial cell attachment and cell proliferation) due to the topographical structure of micro/nanofibres.     

Controlling the fiber diameter during electrospinning

We present a simple analytical model for the forces that determine jet diameter during electrospinning as a function of surface tension, flow rate, and electric current in the jet. The model predicts the existence of a terminal jet diameter, beyond which further thinning of the jet due to growth of the whipping instability does not occur. Experimental data for various electrospun fibers attest to the accuracy of the model.     

Modifying wire-array Z-pinch ablation structure using coiled arrays

A new wire-array configuration has been used to control the modulation of ablated plasma flow for the first time. Cylindrical aluminum coiled arrays, in which each straight wire is replaced with a single helix, were driven by a 1 MA, 240 ns current pulse. Ablated plasma is directed away from the coiled wire cores in a manner that can be understood in terms of Lorentz forces that arise from a complex current path modeled by 3D magnetohydrodynamic simulations. Outside the diameter of the helix, the flow of ablated plasma is axially modulated at the wavelength of the coil.     

A review of 3D-printed sensors

Nowadays, sensors play an important role in human life. Among the many manufacturing methods used in the fabrication of sensors, three-dimensional (3D) printing has gradually shown its advantages, particularly with commercial products. Physical sensors, biosensors, and chemical sensors can all be fabricated via 3D printing technology, through either directly printing sensing components, printing molds for casting sensors, or printing platforms to be integrated with commercial sensors. In this article, the varieties of features and applications of 3D printing technologies used in the fabrication of sensors are reviewed. Several types of 3D printing technologies are compared for better understanding of the tools. With the development of new or hybrid manufacturing methods and materials used in the 3D printing technology, this technology will show its great advantages and potential in the fabrication of highly sensitive nanosensors or compound sensors with 3D intricate structures.     

一种基于3D打印技术的结构型宽频吸波超材料

设计了一种三层宽频吸波超材料,其表层和中间层为单元尺寸不同的周期阵列结构,底层为吸波平板结构,优化后的总厚度仅为4.7 mm,并采用三维(3D)打印技术成功制备了该吸波超材料.吸波体反射率测试结果表明,在电磁波垂直入射条件下,宽频吸收峰分别出现在5.3和14.1 GHz,两峰叠加使得其在4-18 GHz频率范围内反射损耗均小于-10 dB.采用S参数反演法计算了每一层的等效电磁参数,并利用多层结构反射率公式推导得出该模型的理论反射率,理论计算结果与实测结果基本一致.通过研究能量损耗、电场分布和磁场分布揭示了吸波机理,分析表明该吸波体的宽频吸收效果源于三层结构产生的吸收带宽叠加.本文提出的吸波超材料具有良好的宽频吸收效果,尤其在低频范围吸波性能较佳,结合3D打印快速成型技术,可获得结构精细的三层吸波超材料,具有重要的实际应用价值和广阔的应用前景.     

Atomized spraying of liquid metal droplets on desired substrate surfaces as a generalized way for ubiquitous printed electronics

A direct electronics printing technique through atomized spraying for patterning room-temperature liquid metal droplets on desired substrate surfaces is proposed and experimentally demonstrated for the first time. This method is highly flexible and capable of fabricating electronic components on various target objects, with either flat or rough surfaces, made of different materials, or having different orientations from 2D to 3D geometrical configurations. With a pre-designed mask, the liquid metal ink can be directly deposited on the substrate to form various specific patterns which lead to the rapid prototyping of electronic devices. Further, extended printing strategies were also suggested to illustrate the adaptability of the method. For example, it can be used for making transparent conductive film with an optical transmittance of 47 % and a sheet resistance of 5.167Ω/□ due to natural porous structure. Different from the former direct writing technology where large surface tension and poor adhesion between the liquid metal and the substrate often impede the flexible printing process, the liquid metal here no longer needs to be pre-oxidized to guarantee its applicability on target substrates. One critical mechanism was that the atomized liquid metal microdroplets can be quickly oxidized in the air due to its large specific surface area, resulting in a significant increase of the adhesion capacity and thus firm deposition of the ink to the substrate. This study paved a generalized way for pervasively and directly printing electronics on various substrates which are expected to be significant in a wide spectrum of electrical engineering areas.     

利用动态微纳结构调控颜色方法的仿真研究

随着微纳米技术的进步,利用人工制备的微纳米结构实现颜色的呈现成为了可能,开辟了无油墨印刷的新思路,“结构色”的研究迅速成为该领域的焦点。提出了一种基于动态周期性微纳结构阵列的颜色调控新方法。设计在周期性微结构阵列中,填充一定厚度的功能材料薄膜,通过实时控制功能材料的外部电压,精确调控微结构上下表面的高度差,以实现在同一器件表面不同预期颜色的呈现和切换。建立了微结构的物理模型,并用时域有限差分方法(finite difference time domain,FDTD)进行了仿真研究,光源采用垂直入射的线偏振光,对微纳结构阵列上下表面高度差及结构周期进行了参数扫描,获得了系列反射光谱,并用光谱功率积分的方法计算得到了相应的颜色系列,直观地标注在CIE1931颜色空间色品图上。仿真结果表明,当微纳结构阵列周期在100~300 nm范围内时,通过调节电压改变填充的功能材料的高度,可实现全光谱范围的颜色动态调控,且反射光谱的相对峰值强度在60%左右,效率可观。该方法原理新颖,为研制动态颜色调控微器件提供了理论基础,有望在无油墨印刷、显示技术等领域获得广泛应用。     

Fabrication of corner cube array retro-reflective structure with DLP-based 3D printing technology

In this article, the fabrication of a corner cube array retro-reflective structure is presented by using DLP-based 3D printing technology. In this additive manufacturing technology a pattern of a cube corner array is designed in a computer and sliced with specific software. The image of each slice is then projected from the bottom side of a reservoir, containing UV cure resin, utilizing a DLP video projector. The projected area is cured and attached to a base plate. This process is repeated until the entire part is made. The best orientation of the printing process and the effect of layer thicknesses on the surface finish of the cube has been investigated. The thermal reflow surface finishing and replication with soft molding has also been presented in this article.     

Two-dimensional nanopatterning by PDMS relief structures of polymeric colloidal crystals

A new constructive method of fabricating a nanoparticle self-assembly on the patterned surface of a poly(dimethylsiloxane) (PDMS) relief nanostructure was demonstrated. Patterned PDMS templates with close-packed microwells were fabricated by molding against a self-assembled monolayer of polystyrene spheres. Alkanethiol-functionalized gold nanoparticles with an average particle size of 2.5 nm were selectively deposited onto a hydrophobic self-assembled monolayer printed on the substrate by the micro-contact printing (μCP) of the prepared PDMS microwell, in which the patterned gold nanoparticles consisted of close-packed hexagons with an average diameter of 370 nm. In addition, two-dimensional colloidal crystals derived from PMMA microspheres with a diameter of 380 nm and a negative surface charge were successfully formed on the hemispherical microwells by electrostatic force using positively charged PAH-coated PDMS as a template to produce multidimensional nanostructures.     

中带电压法分离栅控横向pnp双极晶体管辐照感生缺

设计并制作了一种新型双极测试结构,即在常规横向pnp双极晶体管基区表面氧化层上淀积一栅电极,通过扫描栅极所加电压,获得漏极(集电极)电流随栅极电压的变化特性,利用中带电压法分离栅控横向pnp双极晶体管 在辐照过程中感生的氧化物陷阱电荷和界面陷阱电荷.本文对设计的晶体管测试结构和采用 的测试方法做了具体介绍.     

Simple design changes to wires to substantially reduce MRI-induced heating at 1.5 T: implications for implanted leads

Reductions in MRI-induced heating at 1.5 T resulting from a simple design change to coiled wires were investigated. MRI-induced heating was assessed for two different coiled wire forms (length, 26 cm): (1) multi-filar coiled wire form and (2) multi-filar coiled wire form having a different coiled pitch, providing an air gap spacing between adjacent five-filar coil loops. Each wire had an electrode and was insulated to create a lead, similar to that which would be used for a medical implant. The wire forms were placed in a gelled-saline-filled head/torso phantom and imaged at 1.5 T [whole-body average specific absorption rate (SAR), 1.79 W/kg]. Fluoroptic thermometry probes were used to measure temperatures at the distal ends of the wires. The experiments demonstrated a substantial reduction in MRI-induced heating for the modified wire compared to the unmodified wire (i.e., 10.5 degrees C difference observed in one experiment and 26 degrees C difference in another). These findings have important implications for MRI-induced heating of leads used for medical implants.     

空心微球结构Au/Ag合金泡沫块体的制备

将平均晶粒尺寸为4.6 nm的金粒子通过静电作用粘附于聚苯乙烯（PS）微球表面用于化学镀,化学镀金后PS表面的金沉积层几乎达到完全包覆,厚度70~90 nm;在Au/PS表面进行化学镀银,沉积的银颗粒堆积紧密,颗粒大小较先前沉积的金颗粒大,镀覆层厚度增厚至200~400 nm;模板去除后,获得了完全自支撑的Au40Ag60空心微球结构的圆柱状泡沫材料。制备的金银合金泡沫由直径约10 m的空心球壳组成,圆柱体直径约5 mm,密度约1.2 g/cm3。     

Electrospray deposit structure of nanoparticle suspensions

Electrospray atomization has unique capabilities for deploying colloidal suspensions to create nanoparticle films and coatings. This technique can deliver precise quantities of particles in a dry state to a target substrate and overcomes many limitations of other printing and coating technologies. Since the structure of a nanoparticle layer governs its functionalities, it is essential to understand the relationship between the key operating parameters and the macro- and microstructure of an electrospray deposit. We investigated the role of three key parameters on the deposit structure: electrospray time, the target substrate electrical properties, and the polydispersity of the colloidal suspension. The macrostructure of the nanoparticle deposits was similar for all spray times and substrates. In particular, the deposited particles segregate to the center and edge of a deposit, leaving a depletion region in between. We speculate that the mutual Coulombic forces due to the space charge inside the plume play a key role in governing the trajectory of the nanoparticles and the ensuing deposit morphology. Since particles emitted by electrospray are highly charged, the microstructure of a deposit was strongly influenced by the electrical conductivity of the target substrate. By maintaining a net charge, particles deposited on to a dielectric substrate could influence the deposition of subsequent in-flight particles, which opens new routes for exerting control over the deposit structure.     

Modification of the boundary layer theory for analysis of wave motions in a cylindrical jet of a viscous liquid

The existent concepts of the boundary layer near the free surface of a viscous liquid, which is related to its periodic motion, are modified with the aim of analyzing the finite-amplitude wave motion on the surface of a thick charged jet of a viscous conducting liquid. To describe the flow in the boundary layer, a model problem is proposed that is simpler in statement compared with the complete problem and the solution of which uses the governing properties of the exact solution obtained in the low-viscosity asymptotics: the form of the dispersion relation, wave profile, and rate of velocity field viscous damping with time. An estimate is made of the boundary layer thickness at which the discrepancy between the exact solution and solution to the model problem (stated in terms of the theory proposed) falls into a given interval in the low-viscosity asymptotics. The domain of applicability of the modified theory is determined.     

A study of jets in electron positron annihilation into hadrons in the energy range 3.1 to 9.5 GeV

From an analysis of data taken with the detector PLUTO and the DORIS storage rings we have obtained evidence for jet structure in e⁺e^? annihilation with hadrons. Results for mean sphericity, mean thrust, the angular dependence of the jet axis and for 〈p_t〉 and 〈p_∥〉 with respect to the jet axis are presented. At 9.4 GeV we also discuss the angular dependence of the charged and neutral deposited energy with respect to the jet axis.