Engineering Surface Atomic Architecture of NiTe Nanocrystals Toward Efficient Electrochemical N2 Fixation

Efficient N₂ fixation at ambient condition through electrochemical processes has been regarded as a promising alternative to traditional Haber–Bosch technology. Engineering surface atomic architecture of the catalysts to generate desirable active sites is important to facilitate electrochemical nitrogen reduction reaction (NRR) while suppressing the competitive hydrogen evolution reaction. Herein, nickel telluride nanocrystals with selectively exposed {001} and {010} facets are synthesized by a simple process, realizing the manipulation of surface chemistry at the atomic level. It is found that the catalysts expose the {001} facets coupled with desirable Ni sites, which possess high Faraday efficiency of 17.38 ± 0.36% and NH₃ yield rate of 33.34 ± 0.70 μg h^?1 mg^?1 at ‐0.1 V vs RHE, outperforming other samples enclosed by {010} facets (8.56 ± 0.22%, 12.78 ± 0.43 μg h^?1 mg^?1). Both experimental results and computational simulations reveal that {001} facets, with selectively exposed Ni sites, guarantee the adsorption and activation of N₂ and weaken the binding for *H species. Moreover, the enhanced reduction capacity and accelerated charge transfer kinetics also contribute the superior NRR performance of {001} facets. This work presents a novel strategy in designing nonprecious NRR electrocatalyst with exposed favorable active sites.     

一种适应高多普勒频偏的突发传输高效导频图案

导频符号辅助调制技术广泛应用于数字通信系统的突发传输。在频偏范围较大和信噪比较低时,现有的前后式导频方案的频偏估计误差会远高于理论下界。该文研究了频偏估计最大似然检测量的主瓣和旁瓣分布,分析了对称分布导频图案在频偏估计时的模糊问题。在此基础上提出了一种新的混合对称式导频图案,并给出了相应的参数选取原则。新导频图案能够在较低的信噪比下具有大的频偏估计范围和较高的估计精度。仿真结果验证了新导频图案的良好性能。     

Terahertz Wave Polarization Beam Splitter Using Asymmetrical Coupler

This study has proposed and numerically demonstrated a compact terahertz wave polarization beam splitter. The splitter is built by using a asymmetrical directional coupler consisting of a bend waveguide and a slot bend waveguides and achieves a high extinction ratio of 24.88 dB and 16.55 dB for cross and through ports. The optimal coupling region length is found to be 26 μm. By using such a polarization beam splitter, the size of the terahertz wave system could be reduced significantly. The simulation results show that the designed polarization beam splitter can split TEand TM-polarized terahertz wave into different propagation directions with high efficiency over the terahertz wave frequency range from 9.40 THz to 9.65 THz. The device obtained is readily used for a polarization diversity terahertz wave integrated circuit field, particularly for platforms with slot waveguide.     

BER of OFDM in Rayleigh fading environments with selective diversity

This paper derives the analytical bit error rate (BER) of orthogonal frequency division multiplexing (OFDM) systems employing selective diversity in Rayleigh fading environments. First, the probability density function (pdf) of inter‐carrier interference (ICI) power in Rayleigh fading environments is derived. Second, the pdf of the signal‐to‐interference ratio (SIR) is then derived. The cumulative distribution function (cdf) and hence pdf of the SIR with selective diversity are then given in the third and fourth steps. Using the BER expressions of binary phase shift keying (BPSK) and differential BPSK (DBPSK) modulation in an added white Gaussian noise (AWGN), the corresponding BER expressions of OFDM systems can then be derived. Detailed discussions are given. Possible future work is also outlined. Copyright © 2009 John Wiley & Sons, Ltd.     

Evaluating the Performance of Cooperative NOMA with Energy Harvesting Under Physical Layer Security

Wireless Personal Communications - In this paper, we consider a non-orthogonal multiple access system with imperfect successive interference cancellation and physical layer security where the...     

一种无人机载超视距通信系统

针对中、高空长航时无人机超视距通信系统普遍采用Ku频段卫星中继存在信号可用带宽有限、干扰源众多、机载端设备较大的现状,提出了一种基于Ka频段卫星的无人机超视距通信系统总体与分系统工程实现方案,并给出了关键设计要素。在详细推导链路计算公式基础上,以前向速率为51.2 kb/s、返向速率为8 Mb/s为例进行了链路余量预算与数值仿真分析,并与传统Ku频段方案在传输速率、抗干扰能力、天线口径等方面进行了分析比较。结果表明,在同等条件下所设计的系统性能可提高20%左右。飞行试验结果验证了该方案的合理性、可行性、有效性和工程可实现性,为无人机超视距通信系统总体设计和工程实现提供了思路与参考。     

No-reference image quality assessment using structural activity

Presuming that human visual perception is highly sensitive to the structural information in a scene, we propose the concept of structural activity (SA) together with a model of SA indicator in a new framework for no-reference (NR) image quality assessment (QA) in this study. The proposed framework estimates image quality based on the quantification of the SA information of different visual significance. We propose some alternative implementations of SA indicator in this paper as examples to demonstrate the effectiveness of the SA-motivated framework. Comprehensive testing demonstrates that the model of SA indicator exhibits satisfactory performance in comparison with subjective quality scores as well as representative full-reference (FR) image quality measures.     

Gate-induced drain leakage in FD-SOI devices: What the TFET teaches us about the MOSFET

This paper compares the gate-induced drain leakage (GIDL) in fully-depleted (FD) silicon-on-insulator (SOI) tunneling field effect transistor (TFET) and in standard metal-oxide-semiconductor FET (MOSFET) fabricated in the same process. The measurements show that the MOSFET GIDL current is lower than the GIDL in a TFET with the same junction doping, especially for devices with thick gate oxide and under low drain bias. A model describing lateral band-to-band tunneling (BTBT) is developed for GIDL in the FD-SOI TFET. By combining the model of gate-controllable tunneling diode in series with a field effect diode, we achieve an accurate picture of GIDL in FD-SOI MOSFETs.     

New optical microwave up-conversion solution in radio-over-fiber networks for 60-GHz wireless applications

A new method for generating optical microwave mixing based on the optical phase modulation and the fiber chromatic dispersion is further investigated. A theoretical approach based on the analysis of the optical field spectrum has lead to the evaluation of the mixing power and optimal fiber lengths of 60-GHz radio-over-fiber (RoF) networks. Results have shown adaptable fiber lengths to match the network specifications.