Potential methods for the fabrication ofhigh-Tc superconductors for wires and cables

Studies of practical properties, such as upper critical field (H_C2) and critical-current density, of high-T _c oxide superconductors of Y-Ba-Cu-O Bi-Sr-Ca-Cu-O, and Tl-Ba-Ca-Cu-O systems are reviewed. The H_c2 of these materials is much higher than that of conventional metallic superconductors, indicating a high potential for practical applications, even when they are used in liquid nitrogen. However, the H_C2 of these materials is also highly anisotropic, as can be expected from an examination of their crystal structure. In addition to this anisotropy, the presence of weak links and a weak pinning force in this material limit the transport current density J₃ to much lower levels than that required for practical applications. Recent fabrication processes that have good potential for producing wire or tape conductors or high-T_c oxide are reviewed. Some details are presented of the powder method and other fabrication processes using diffusion, solidification, and deposition techniques. For the Ag-sheathed oxide tapes, J_c values exceeding 10000 A/cm² at 77 K and 0 T have been reported for both Bi and Tl oxide materials     

On electron transport across interfaces connecting materials withdifferent effective masses

We reconsider the problem of electronic transport across a heterojunction interface connecting two materials with different effective masses. Thermionic current does not remain invariant when the position X_int of the interface is shifted relative to that of the potential energy maximum, X_max, even if the shift is smaller than the carrier mean free path. We analyze every situation that arises when X_max=X_int, as well as the limiting case X_max→X_int. Besides the effective mass discontinuity at the interface, we allow for a band-edge discontinuity within a potential barrier of arbitrary shape. In most practical situations, the effective Richardson constant governing thermionic emission over a heterointerface barrier is determined by the effective mass in the material that contains X_max. This statement is rigorously true when the effective mass at X_max is lower than that in the other material, otherwise it is an approximation dependent on the value of the interface potential. The issue clarified in this work has relevance to theoretical constructs involving model boundary conditions at heterojunction interfaces     

A practical technique for controlling field profile in thin layers of n-GaAs

A practical technique has been developed for controlling the field profile in a thin epitaxial layer of n-GaAs biased above the transferred-electron threshold. This employs a special cathode composed of an electron-injecting n⁺contact complemented by an electron-blocking (reverse-biased Schottky barrier) contact, which extends a selected distance past the n⁺contact. The situation is characterized theoretically, and potential profile measurements confirm that the desired profile can be obtained in this manner.     

Edge Diffraction Suppression in Rectangular Dielectric Resonators for Quality Factor Enhancement Using Artificial Plasma

The concept of quality factor enhancement in a two dimensional rectangular dielectric resonator (RDR), based on the phenomenon of edge diffraction suppression by a plasma, is presented. This phenomenon occurs when the plasma exhibits the specific negative permittivity, which makes the RDR separable, i.e., analytically solvable by means of the separation of variables. The Rotman plasma, constituted of metal thin wires is proposed as a practical implementation of this ideal plasma, and the diffraction suppression concept is demonstrated with this plasma by an SIE/MoM approach verified by using a finite element method solver, HFSS. It is shown that a relatively small number of wires (4 $,times,$4) in the plasma is sufficient to mimic a close-to-ideal plasma medium, which suggests a potential for practical applications. This study reveals that the utilization of this plasma allows a strong (high-$Q$ ) resonance even for low-permittivity dielectrics otherwise improper to act as resonators.      

Examination of electrostatic potential distribution across an implanted p-n junction by electron holography

In the manufacture of semiconductor microelectronic devices, a p-n junction is formed usually by implanting a high concentration of impurity into a less heavily doped region and then heat annealing. A Si/Si p-n junction test sample has been made following the above practical process and thinned for electron holographic observation by using argon ion-milling. From the reconstructed phase image, the phase shift induced by potential drop across p-n junction can be seen clearly. To characterize quantitatively this potential drop, the mean inner potential V0 of silicon was measured precisely by electron holographic method. By measuring 25 different crystalline silicon spheres with diameter ranging from 40 to 170 nm, an average result of V0 = 12.16 +/- 0.83 V was obtained. By using this V0 value, a quantitative measurement yields the potential drop approximately 0.70 V, which is reasonably consistent with expected Si/Si junction parameter. The thickness of electric dead layer in depletion region produced from this measuring is approximately 20 nm on each sample surface.     

Capacity of MIMO systems with closely spaced antennas

Wide-band radio channel measurements at 5.2 GHz with four transmit and four receive antennas at variable element spacing are reported, aiming to evaluate the potential of compact antenna arrays at mobile terminals. We show that, for an element spacing d<0.5/spl middot//spl lambda/ (down to 0.2/spl middot//spl lambda/), the link capacity is not smaller than that for much larger d. This is explained by the observation that mutual coupling changes the radiation patterns of closely spaced antenna elements, individually. Compact multi-antenna terminals may thus become practical.     

1/f, g–r and burst noise used as a screening threshold for reliability estimation of optoelectronic coupled devices

In this paper the theoretical analysis of noise sources in Optoelectronic Coupled Devices (OCDs) is given and the relation between typical defects and 1/f, g–r and burst noise is described. According to statistical and experimental results, a threshold to screen potential devices with excess noise is derived, which has been proved theoretically that the screening criterion is reasonable. Moreover, the experimental results show that the method is of practical value.     

快速傅里叶变换在OFDM系统中的应用

本文简要分析了未来OFDM数字通信系统的基本模型和可能采用的信号调制与解调的方法,在此基础上详细地解析了数据序列经过快速傅里叶逆变换 /快速傅里叶变换 (IFFT/FFT)后的输出结果与M进制数字调制解调之间的联系,并给出了能够实现OFDM调制解调的合适的IFFT/FFT算法,实际仿真结果表明快速傅里叶变换及反变换在未来OFDM技术中具有一定的实用价值。     

机载无线电罗盘垂直天线电参数及测量方法

从机载无线电罗盘垂直天线的基本工作原理出发,结合天线使用过程中的实际情况,以及当今测试技术的发展状态,总结出了一套较为完整的测试方法,并对测试数据的准确性提出了相关建议。工程应用证明,该测试方法合理可行,避免了潜在问题的发生。     

冷链物流监控系统设计

系统针对冷链物流需求设计,包括终端设备与服务器。终端设备采用单片机低功耗、传感器、远程无线监控、数据管理与压缩、GPRS基站定位技术,使得终端设备能够良好地服务于冷链物流。服务器采用B/S服务器网络技术,用户可以登陆网页配置终端设备工作参数,并可以查看终端设备过程状态。系统在冷链物流的实际应用过程中,表现出良好的实际应用价值,对冷链监控有一定的意义,在市场中具有广泛的发展前景。     

Engineering of the Crystalline Lattice of Hard Carbon Anodes Toward Practical Potassium-Ion Batteries

Hard carbons have attracted increased interest as an alternative of graphite for the anodes of potassium-ion batteries (PIBs). However, the practical applications of hard carbon anodes are hampered by their low capacities, high potential platforms, and large potential hysteresis. Hard carbons coupled with graphitic nanodomains can achieve stable potassium-ion storage behaviors with low potential platforms and low potential hysteresis. Herein, the crystalline lattice in hard carbon anodes is tuned by incorporating graphene oxide in renewable lignin precursors. The modified hard carbon (i.e., QLGC) anodes show graphitized nanodomains in the carbon matrix with an expanded interlayer spacing (0.42 nm) in the amorphous regions, which results in a stable potassium-ion (de)intercalation behavior. Thus, the QLGC anodes exhibit a high capacity of 164 mAh g⁻¹ with low potential hysteresis in the low potential platform region. Moreover, the QLGC anode delivered a highly stabilized capacity of 283 mAh g⁻¹ at 50 mA g⁻¹, a high-rate capability, and stable cycling performance. Furthermore, the charge storage mechanisms of QLGC anode are elucidated by electro-kinetic analysis and ex/in situ physicochemical characterizations. This study opens a new avenue for designing hard carbon anodes with engineered crystalline lattices toward practical PIBs.     

Real-time morphology processing using highly parallel 2-D cellular automata CAM/sup 2/

Mathematical morphology is a promising computer paradigm based on set theory and has many applications in image processing. Although some architectures have been proposed, there are as yet no compact, practical computers that can handle a variety of morphological operations with large, complex structuring elements at video rates. This has prevented the great potential of morphology from being fully realized. This paper describes a morphology processing method that uses a highly parallel two-dimensional (2-D) cellular automaton architecture called it CAM/sup 2/ (Cellular AutoMata on Content Addressable Memory). New mapping methods achieve high-throughput complex morphology processing. Evaluation results show that CAM/sup 2/ performs one morphological operation for basic structuring elements within 30 /spl mu/s. Furthermore, CAM/sup 2/ can also handle an extremely large and complex structuring element of 100/spl times/100 at video rates. CAM2 will increase the potential use of morphology and make a significant contribution to the development of various real-time image processing systems.     

逸出功的某些特性

在实用热阴极中,测量得的发射常数值经常小于120A/cm2T2。这是由于逸出功有一分布所致,而不是由于电子遇到表面势垒时的反射。用单晶面测量时,理论和实验值便相符了。事实上发射来源于已穿透进势垒的表面电子。这些电子既不能进入真空,也不能在金属导带中自由运动,否则不同晶面便不可能有不同的逸出功。异族元素的吸附增加表面电子的数目和能量,因而使逸出功下降。     

An optical holographic backplane interconnect system

An optical holographic backplane interconnect system capable of high-speed information transmission between optoelectronic transmitter/receiver boards is described. Using conjugate pairs of transmission gratings in a folded reflection geometry, a practical method of insulating the interconnect system from wavelength variations due to temperature or power fluctuations can be achieved. The final demonstration unit was developed in a fully packaged form and has the potential for reconfigurable interconnects and may serve as a testbed for a variety of interconnect networks and hardware protocols     

复杂静电场问题中电势零点选取的合理性

对一个复杂静电场问题分解为两个甚至多个子问题利用叠加原理进行电势求解时,如何合理地选取各个子问题的电势零点的问题进行了研究和讨论。首先讨论了电势参考点选取的任意性和相对性,然后通过一个实际的静电场问题引出了电势参考点选取的合理性。最后,从做功与能量和唯一性定理两个方面对电势参考点选取的合理性进行了分析与讨论。     

Hierarchical Ni/N/C Single-Site Catalyst Achieving Industrial-Level Current Density and Ultra-Wide Potential Plateau of High CO Faradic Efficiency for CO2 Electroreduction

The practical applications of CO₂ electroreduction to CO driven by renewable electricity should simultaneously meet the requests of industrial-level CO partial current density (J_CO) at least 100 mA cm⁻², wide potential window of high CO faradic efficiency (FE_CO), and low cost. Herein, a new strategy is reported to construct porous hierarchical Ni/N/C single-site catalyst with excellent catalytic activity via coating Ni-containing ZIF-8 on mesostructured basic magnesium carbonate template followed by pyrolysis. The abundant micropores facilitate the formation of numerous edge-hosted Ni-N₄ sites with high intrinsic activity, and the interconnected macro/mesopores much promote CO₂ delivery and CO release for the full expression of intrinsic activity. Consequently, the catalyst exhibits the industrial-level J_CO of 105–462 mA cm⁻² at the potential range of −0.6∼−1.3 V with ultra-wide high FE_CO plateau (>90%@−0.4∼−1.3 V), showing great promise for practical application. This study provides a general synthetic strategy to explore high-performance hierarchical M/N/C electrocatalysts.     

Signature verification revisited: promoting practical exploitationof biometric technology

Despite research over a long period, biometric approaches to authenticating personal identity have not met with the degree of success in practical applications originally predicted. This paper discusses approaches to biometric testing, focusing particularly on automatic signature verification, and addresses some of the important issues which might help to promote the introduction of practical systems in the future. Examples associated with the adoption of an explicitly flexible approach to signature verification are used to illustrate the discussion, and it is argued that there is still considerable potential for practical exploitation of this type of technology     

GIS在国内广播电视设施管理中的应用探讨

从国内广电网络状况出发,回顾了当前广电GIS应用的相关研究,探讨了广电GIS在应用中遇到的普遍问题.并用实例分析了广电设施管理系统在应用中遇到的一些问题,针对以上研究对GIS设施管理应用系统的需求分析和应用进行了探讨.最后作者对当前广电GIS的应用提出了几点建议.     

Backbone Network Design and Performance Analysis: A Methodology for Packet Switching Networks

This paper describes a packet network design and analysis (PANDA) model which captures the important features of different packet technologies. This model evolved from many iterations with technology developers and network planners over several years. The main contribution is a methodology for designing low-cost backbone packet networks with satisfactory performance which is both practical and useful. This methodology is useful for investigating cost/performance tradeoffs of various network capabilities and components, thus providing a means for identifying potential cost and performance bottlenecks for different packet technologies and to guide capability requirements for new technologies.     

High-gain series fed printed dipole arrays made of high-Tc superconductors

High-gain arrays are designed from closely spaced printed dipoles, alternately crossed by an integrated series feed. Both the array elements and the feeding and matching network are made of thick film YBa ₂Cu₃O_7-x material for increased efficiency. The optimization of directive gain in terms of spacing and dipole length, under constraints in array size, is performed by combining the space domain method of moments (MM) with transmission line theory. A practical design is experimentally demonstrated, and its performance is compared to simulated data. The superconducting array presents gain higher than that of similar cryogenically cooled Cu and Ag arrays tested. Supergain potential is discussed