Three‐dimensional Printing for Catalytic Applications: Current Status and Perspectives

Three‐dimensional (3D) printing, also known as additive manufacturing, is a fabrication method that has recently received worldwide attention. It provides a convenient and economical way to prepare 3D structures in designable ways. As the technology has developed and the operational costs have decreased, the applications of 3D printing have greatly expanded. Catalyst fabrication is a promising area for 3D printing. Printing processes result in better control of catalyst structures and catalyst distribution. In this perspective, a general overview of the commonly available 3D printing methods that are feasible for the preparation of heterogeneous catalysts is given. Additionally, recent works on printing strategies and new materials for catalysts are discussed. Future development is also addressed.     

Building Three‐Dimensional Graphene Frameworks for Energy Storage and Catalysis

Due to their unique architectures and outstanding electrical properties, three dimensional graphene‐based frameworks (3DGFs) have attracted extensive attention in wide fields. However, recently reported techniques always require complex processes and high cost, which severely limit their large‐scale application. In this study, the massive preparation of macroscopically porous 3DGFs from the inherently inexpensive graphite paper is for the first time realized by simply combining the modified Hummer's method with freezing technique. The as‐prepared 3DGFs that consist of well exfoliated, high‐quality reduced graphene oxide (RGO) exhibit a mesoporous structure and superior conductivity. Such unique features enable the 3DGFs to be directly used as a supercapacitor electrode and as ideal 3D scaffolds to create PANI@3DGFs, Pd@3DGFs, and Pt@3DGFs composites, which hold great potential applications in supercapacitors and catalysts.     

悬停回转试飞方法在直升机超短波天线方向图测试中的应用

借鉴飞机天线方向图地面自由空间测试场测试方法,利用直升机空中悬停特性进行天线方向图测试,以达到节省试飞架次的目的.分析了如何进行直升机悬停位置的选择以及直升机到测试点的距离和垂直高度的计算,总结了直升机超短波天线方向图测试中的定点悬停试飞驾驶技术.该试验方法在飞行试验中得到了验证,与传统试飞方法进行对比,工作效率提高2倍.     

Three‐Dimensional Heteroatom‐Doped Carbon Nanofiber Networks Derived from Bacterial Cellulose for Supercapacitors

Recently, heteroatom‐doped three‐dimensional (3D) nanostructured carbon materials have attracted immense interest because of their great potential in various applications. Hence, it is highly desirable to exploit a simple, renewable, scalable, multifunctional, and general strategy to engineer 3D heteroatom‐doped carbon nanomaterials. Herein, a simple, eco‐friendly, general, and effective way to fabricate 3D heteroatom‐doped carbon nanofiber networks on a large scale is reported. Using this method, 3D P‐doped, N,P‐co‐doped, and B,P‐co‐doped carbon nanofiber networks are successfully fabricated by the pyrolysis of bacterial cellulose immersed in H₃PO₄, NH₄H₂PO₄, and H₃BO₃/H₃PO₄ aqueous solution, respectively. Moreover, the as‐prepared N,P‐co‐doped carbon nanofibers exhibit good supercapacitive performance.     

A Review of Three‐Dimensional Resistive Switching Cross‐Bar Array Memories from the Integration and Materials Property Points of View

Issues in the circuitry, integration, and material properties of the two‐dimensional (2D) and three‐dimensional (3D) crossbar array (CBA)‐type resistance switching memories are described. Two important quantitative guidelines for the memory integration are provided with respect to the required numbers of signal wires and sneak current paths. The advantage of 3D CBAs over 2D CBAs (i.e., the decrease in effect memory cell size) can be exploited only under certain limited conditions due to the increased area and layout complexity of the periphery circuits. The sneak current problem can be mitigated by the adoption of different voltage application schemes and various selection devices. These have critical correlations, however, and depend on the involved types of resistance switching memory. The problem is quantitatively dealt with using the generalized equation for the overall resistance of the parasitic current paths. Atomic layer deposition is discussed in detail as the most feasible fabrication process of 3D CBAs because it can provide the device with the necessary conformality and atomic‐level accuracy in thickness control. Other subsidiary issues related to the line resistance, maximum available current, and fabrication technologies are also reviewed. Finally, a summary and outlook on various other applications of 3D CBAs are provided.     

High‐Density Hotspots Engineered by Naturally Piled‐Up Subwavelength Structures in Three‐Dimensional Copper Butterfly Wing Scales for Surface‐Enhanced Raman Scattering Detection

Very recently, wing scales of natural Lepidopterans (butterflies and moths) manifested themselves in providing excellent three dimensional (3D) hierarchical structures for surface‐enhanced Raman scattering (SERS) detection. But the origin of the observed enormous Raman enhancement of the analytes on 3D metallic replicas of butterfly wing scales has not been clarified yet, hindering a full utilization of this huge natural wealth with more than 175 000 3D morphologies. Herein, the 3D sub‐micrometer Cu structures replicated from butterfly wing scales are successfully tuned by modifying the Cu deposition time. An optimized Cu plating process (10 min in Cu deposition) yields replicas with the best conformal morphologies of original wing scales and in turn the best SERS performance. Simulation results show that the so‐called “rib‐structures” in Cu butterfly wing scales present naturally piled‐up hotspots where electromagnetic fields are substantially amplified, giving rise to a much higher hotspot density than in plain 2D Cu structures. Such a mechanism is further verified in several Cu replicas of scales from various butterfly species. This finding paves the way to the optimal scale candidates out of ca. 175 000 Lepidopteran species as bio‐templates to replicate for SERS applications, and thus helps bring affordable SERS substrates as consumables with high sensitivity, high reproducibility, and low cost to ordinary laboratories across the world.     

Nanoparticle Direct Doping: Novel Method for Manufacturing Three‐Dimensional Bulk Plasmonic Nanocomposites

Metallodielectric materials with plasmonic resonances at optical and infrared wavelengths are attracting increasing interest, due to their potential novel applications in the fields of photonics, plasmonics and photovoltaics. However, simple and fast fabrication methods for three‐dimensional bulk plasmonic nanocomposites that offer control over the size, shape and chemical composition of the plasmonic elements have been missing. Here, such a manufacturing method and examples of experimental realizations of volumetric isotropic nanocomposites doped with plasmonic nanoparticles that exhibit resonances at visible and infrared wavelengths are presented. This method is based on doping a low‐melting dielectric material with plasmonic nanoparticles, using a directional glass‐solidification process. Transmission‐spectroscopy experiments confirm a homogenous distribution of the nanoparticles, isotropy of the material and resonant behavior. The phenomenon of localized surface plasmon resonance is also observed visually. This approach may enable rapid and cost‐efficient manufacturing of bulk nanoplasmonic composites with single or multiple resonances at various wavelength ranges. These composites could be isotropic or anisotropic, and potentially co‐doped with other chemical agents, in order to enhance different optical processes.     

Service‐based high‐speed railway base station arrangement

To provide stable and high data rate wireless access for passengers in the train, it is necessary to properly deploy base stations along the railway. We consider this issue from the perspective of service, which is defined as the integral of the time‐varying instantaneous channel capacity. With large‐scale fading assumption, it will be shown that the total service of each base station is inversely proportional to the velocity of the train. Besides, we find that if the ratio of the service provided by a base station in its service region to its total service is given, the base station interval (i.e., the distance between two adjacent base stations) is a constant regardless of the velocity of the train. On the other hand, if a certain amount of service is required, the interval will increase with the velocity of the train. The aforementioned results apply not only to simple curve rails, like line rail and arc rail, but also to any irregular curve rail, provided that the train is traveling at a constant velocity. Furthermore, the new developed results are applied to analyze the on–off transmission strategy of base stations. Copyright © 2013 John Wiley & Sons, Ltd.     

Adaptive antennas for MIMO OFDM‐CDMA communication systems

In this paper, we propose symbol‐based receivers for orthogonal frequency division multiplexing (OFDM) code‐division multiple‐access (CDMA) multiple‐input‐multiple‐output (MIMO) communications in multipath fading channels. For multiuser and multipath fading environments, both intersymbol interference and multiple‐access interference must be considered. We propose narrowband and wideband antennas and Wiener code filter for MIMO OFDM‐CDMA systems. The proposed receivers are updated symbol‐by‐symbol to achieve low computational complexity. Simulation results show that the proposed Wiener code filter can improve the system performance for the proposed adaptive antennas. The wideband antenna can achieve better error‐rate performance than that of the narrowband antenna when multipath effect exists. The convergence rate of the recursive least squares antennas is faster than that of the least mean square antennas. Copyright © 2013 John Wiley & Sons, Ltd.     

Direct Transcription of Two‐Dimensional Colloidal Crystal Arrays into Three‐Dimensional Photonic Crystals

A simple protocol for the fabrication of three‐dimensional (3D) photonic crystals in silicon is presented. Surface structuring by nanosphere lithography is merged with a novel silicon etching method to fabricate ordered 3D architectures. The SPRIE method, sequential passivation reactive ion etching, is a one‐step processing protocol relying on sequential passivation and reactive ion etching reactions using C₄F₈ and SF₆ plasma chemistries. The diffusion of fresh reactants and etch product species inside the etched channels is found to play an important role affecting the structural uniformity of the designed structures and the etch rate drift is corrected by adjusting the reaction times. High quality photonic crystals are thus obtained by adding the third dimension to the two‐dimensional (2D) colloidal crystal assemblies through SPRIE. Careful adjustments of both mask design and lateral etch extent balance allow the implementation of even more complex functionalities including photonic crystal slabs and precise defect engineering. 3D photonic crystal lattices exhibiting optical stop‐bands in the infrared spectral region are demonstrated, proving the potential of SPRIE for fast, simple, and large‐scale fabrication of photonic structures.     

Controlled Fabrication of Multitiered Three‐Dimensional Nanostructures in Porous Alumina

We present the fabrication of multitiered branched porous anodic alumina (PAA) substrates consisting of an array of pores branching into smaller pores in succeeding tiers. The tiered three‐dimensional structure is realized by sequentially stepping down the anodization potential while etching of the barrier layer is performed after each step. We establish the key processing parameters that define the tiered porous structure through systematically designed experiments. The characterization of the branched PAA structures reveals that, owing to constriction, the ratio of interpore distance to the anodization potential is smaller than that for pristine films. This ratio varies from 1.8 to 1.3 nm V^?1 depending on the size of the preceding pores and the succeeding tier anodization potential. Contact angle measurements show that the multitiered branched PAA structures exhibit a marked increased in hydrophilicity over two‐dimensional PAA films.     

Three‐Dimensional Co3O4@MnO2 Hierarchical Nanoneedle Arrays: Morphology Control and Electrochemical Energy Storage

In this paper, a highly ordered three‐dimensional Co₃O₄@MnO₂ hierarchical porous nanoneedle array on nickel foam is fabricated by a facile, stepwise hydrothermal approach. The morphologies evolution of Co₃O₄ and Co₃O₄@MnO₂ nanostructures upon reaction times and growth temperature are investigated in detail. Moreover, the as‐prepared Co₃O₄@MnO₂ hierarchical structures are investigated as anodes for both supercapacitors and Li‐ion batteries. When used for supercapacitors, excellent electrochemical performances such as high specific capacitances of 932.8 F g^?1 at a scan rate of 10 mV s^?1 and 1693.2 F g^?1 at a current density of 1 A g^?1 as well as long‐term cycling stability and high energy density (66.2 W h kg^?1 at a power density of 0.25 kW kg^?1), which are better than that of the individual component of Co₃O₄ nanoneedles and MnO₂ nanosheets, are obtained. The Co₃O₄@MnO₂ NAs are also tested as anode material for LIBs for the first time, which presents an improved performance with high reversible capacity of 1060 mA h g^?1 at a rate of 120 mA g^?1, good cycling stability, and rate capability.     

Differential Dual‐Frequency Antenna for Wireless Communication

A novel differential dual‐frequency antenna using proximity coupling is proposed. Dual bands are realized by a slot in the ground plane. The lower resonant frequency is controlled by the slot in the ground plane, and the upper resonant frequency is mainly determined by the dimensions of the radiating patch. Measured results show that the proposed antenna can operate at 2.51 GHz and 5.38 GHz.     

Hybrid Planar Inverted‐F Antenna with a T‐Shaped Slot on the Ground Plane

In this letter, a novel hybrid planar inverted‐F antenna (PIFA) with a T‐shaped slot on the ground plane is proposed. The loop structure formed by the feed line and shorting pin can be operated as a series and shunt inductance for the PIFA and the T‐shaped slot antenna, respectively. The PIFA operates at a frequency of 1.75 GHz, while the T‐shaped slot on the ground plane operates at 2.4 GHz by the same voltage feeding source. The height of the PIFA is 6.5 mm, and the size of an upper patch is designed to be 30 mm…16 mm. The measured relative impedance bandwidth of the PIFA and the T‐shaped slot are about 12% and 21%, respectively. In addition, good antenna performance was achieved.     

遥感卫星"夸父A"星地通信接收站布局建模与分析

面向实时接收遥感卫星"夸父A"连续对日观测数据的应用需求,提出"夸父A"卫星与地面单个固定接收站相对位置模型,在此基础上定量评估现有国内及海外站的接收效率,并进一步提出地面接收站全球布局的基本原则及其可行的优化方案.研究成果将为"夸父"计划星地数据通信系统的实施提供重要的技术参考.     

用于扩展SPM检测范围的精密定位系统

本文介绍了所研制的二维微定位柔性系统和一维精密转动系统,进行了相关技术的研究并给出了设计参数,使SPM能够满足高精度下的大尺寸平面样品以及球形被测样品的全范围检测,扩大了扫描探针显微镜（SPM）在超精密工程中的应用范围。     

Design for a Dual‐Frequency Antenna‐in‐Package

For an antenna‐in‐package (AiP), via holes are used to connect the antenna ground and system ground. In this letter, a dual‐frequency AiP with a U‐slot embedded in the patch is proposed. By properly arranging three via holes under the non‐radiating edge, an AiP with two resonant frequencies is realized. Then a U‐slot is embedded in the patch to further improve the bandwidth of the AiP. To validate the proposed design, an AiP with the bandwidth of 4.49% at 2.45 GHz and 6.02% at 5.32 GHz is achieved and fabricated. The measured results agree with the simulated results.     

A study on one‐dimensional k‐coverage problem in wireless sensor networks

In this paper, we study the one‐dimensional coverage problem in a wireless sensor network (WSN) and consider a network deployed along a one‐dimensional line according to a Poisson distribution. We analyze three important parameters that are related to the problem, i.e., expected k‐coverage proportion, full k‐coverage probability, and partial k‐coverage probability, and derive mathematical models that describe the relationships between the node density in the network and these parameters. The purpose is to calculate or estimate the node density required for achieving a given coverage probability, which is useful in the deployment of a one‐dimensional network for many applications. We first analyze the expected k‐coverage proportion, then analyze the full k‐coverage probability for k = 1 and the lower bound to the full k‐coverage probability for k > 1, and finally analyze the partial k‐coverage probability for k = 1 and give a brief discussion of the partial k‐coverage probability for k > 1. The mathematical models are validated through simulation. Copyright © 2011 John Wiley & Sons, Ltd.     

Mobile‐to‐mobile MIMO transmit–receive diversity systems: analysis and performance in three‐dimensional double‐correlated channels

Mobile‐to‐mobile (M‐to‐M) communications are expected to play a crucial role in future wireless systems and networks. In this paper, we consider M‐to‐M multiple‐input multiple‐output (MIMO) maximal ratio combining system and assess its performance in spatially correlated channels. The analysis assumes double‐correlated Rayleigh‐and‐Lognormal fading channels and is performed in terms of average symbol error probability, outage probability, and ergodic capacity. To obtain the receive and transmit spatial correlation functions needed for the performance analysis, we used a three‐dimensional (3D) M‐to‐M MIMO channel model, which takes into account the effects of fast fading and shadowing. The expressions for the considered metrics are derived as a function of the average signal‐to‐noise ratio per receive antenna in closed‐form and are further approximated using the recursive adaptive Simpson quadrature method. Numerical results are provided to show the effects of system parameters, such as distance between antenna elements, maximum elevation angle of scatterers, orientation angle of antenna array in the x–y plane, angle between the x–y plane and the antenna array orientation, and degree of scattering in the x–y plane, on the system performance. Copyright © 2011 John Wiley & Sons, Ltd.