Transfer Hydrogenation in Mesoporous Palladium: Polar Hydrogen Engineering to Realize High Selectivity of Alkyne Semi-Hydrogenation

Semi-hydrogenation of alkynes to industrially important alkenes is earnestly desirable in the fine chemical industry but energetically unfavorable. Herein, it is reported that mesoporous palladium (meso-Pd) catalyst changes the hydrogenation pathways in ethanol with ammonium borane as the hydrogen source, realizing the high catalytic selectivity of ≈99% in semi-hydrogenation of alkynes. Mechanism studies reveal that the active polar hydrogen can be produced and reserved well in the electron-rich mesoporous channels of meso-Pd catalyst, resulting in a transfer hydrogenation pathway, which selectively semi-hydrogenates alkynes into alkenes without over-hydrogenating alkenes into alkanes. Moreover, it is demonstrated that the polar hydrogen engineering of meso-Pd catalyst is highly efficient in various alkyne semi-hydrogenation and chemoselective hydrogenation reactions. The results thus establish metal catalyst mesostructuring as an alternative route for engineering polar hydrogen in the transfer hydrogenation reactions, thus realizing the high catalytic selectivity in various selective catalysis.     

用户电路板中的抗干扰问题分析

用户电路板具有数字／模拟信号混合,电源种类多,地线种类多,元器件多密度大等特点,因而会带来一 系列干扰问题,正确合理的布局布线,对抑制其干扰起着重要作用。本文通过几个典型实例,分析其干扰现象和干扰原因,并给出了抑制其干扰的有效措施。最后提出了用户电路板中印制板电源,地线布线设计时应注意的问题。     

InGaAs-GaAs脊波导DBR激光器双模运行特性研究

对一种新型InGaAs-GaAs脊波导分布式Bragg反射(DBR)半导体激光器双模运行特性进行了研究.该激光器由1个普通增益区和2个DBR区组成,两DBR区采用均匀蚀刻的Bragg光栅,中间加入50～100 μm的分隔区,以减小两DBR区间的热作用影响.实验发现,在增益区偏置电流强度满足双模(双波长)运行条件的情况下,在分隔区施加一电流Ispace,会对双模调谐特性产生非常大的影响.结果表明:施加适当的Ispace可使双波长的可调谐间隔显著增加,并同时提高2个激射模的边模抑制比;在一定的范围内,较大的Ispace对应较好的双模运行参数.测量了3种几何尺寸样品在多种偏置电流下的双模运行特性,对分隔区长度、Ispace以及两者组合对双模调谐特性的影响作了深入研究.研究结果对改善双波长DBR半导体激光器双模运行特性给出了有用的信息.     

Energetics of Donor‐Doping,Metal Vacancies,and Oxygen‐Loss in A‐Site Rare‐Earth‐Doped BaTiO3

The energetics of La‐doping in BaTiO₃ are reported for both (electronic) donor‐doping with the creation of Ti³⁺ cations and ionic doping with the creation of Ti vacancies. The experiments (for samples prepared in air) and simulations demonstrate that ionic doping is the preferred mechanism for all concentrations of La‐doping. The apparent disagreement with electrical conduction of these ionic doped samples is explained by subsequent oxygen‐loss, which leads to the creation of Ti³⁺ cations. Simulations show that oxygen‐loss is much more favorable in the ionic‐doped system than undoped BaTiO₃ due to the unique local structure created around the defect site. These findings resolve the so‐called “donor‐doping” anomaly in BaTiO₃ and explain the source of semiconductivity in positive temperature coefficient of resistance (PTCR) BaTiO₃ thermistors.     

高性能计算资源管理平台设计

地震资料处理是典型的高性能计算,随着采集数据量越来越大,对计算机资源的快速调度和配置提出了要求。为达到高效管理的目的,需要从技术选择、生产实际情况、业务特点等方面综合考虑,建立智能化的资源管理调度平台,使资源的提供与回收等管理具备云计算特征。     

双绞传输线电磁兼容特性的FDTD分析

将曲线坐标系中的时域有限差分法（FDTD）拓展到空间为任意媒质情形，然后针对双绞传输线的特殊结构综合运用曲线坐标系、圆柱坐标系、旋转坐标系和子域连接法进行空间网格划分、FDTD建模，并通过求解双绞传输线和平行传输线的特性阻抗对该建模的准确度进行了验证，最后在空间线源激励下对双绞线和平行线的电磁兼容特性进行了比较，可以看出双绞线对空间电磁场的耦合能力远远低于平行线。     

Efficient recursive least squares parameter estimation algorithm for accurate nanoCMOS variable gain amplifier performances

ABSTRACT

With the aggressive scaling of integrated circuit technology, parametric estimation is a critical task for designers who looked for solutions to the challenges of some Nanoscale CMOS parameters. This paper presented the prediction of primary parameters of CMOS transistor for 16 nm to 10 nm process nodes using both of Bisquare Weights (BW) method and a novel recursive least squares (RLS) parameter estimation algorithm. The proposed RLS algorithm consists of the minimisation of a quadratic criterion relating to the prediction error in order to attain the best estimated parameters of the developed mathematical model. The obtained results thanks to the proposed RLS algorithm were better than those reached using the BW method. Comparisons between Predictive Technology Model (PTM) data and parameters estimated with RLS algorithm were made to check the validity and the consistency of the proposed algorithm. These predicted primary parameters were helpful to estimate and to optimise the performances of the Variable Gain Amplifier (VGA) which was a basic circuit element with a key role in the design of new upcoming receivers.     

A novel spectrum sensing scheme with sensing time optimization for energy-efficient CRSNs

Wireless Networks - The cognitive radio technology enables secondary users (SUs) to occupy licensed bands when primary users (PUs) are not occupy them. Spectrum sensing is a key technology for SUs...     

Interference analysis for asynchrounous OFDM/FBMC based cognitive radio networks over Rayleigh fading channel

In the future fifth generation networked society, devices will suffer from the asynchronous multi-carrier effect which impacts the user’s quality of experience. This paper investigates the timing misalignment effect on interference level in the context of a cognitive radio (CR) network. Our study considers both multicarrier techniques orthogonal frequency division multiplexing (OFDM) and filter bank multicarrier (FBMC). The originality of our paper consists in proposing a simple but accurate analytical model to evaluate our system’s performance in terms of interference level, signal-to-interference-plus-noise ratio and bit error rate. Specifically, two case studies are considered, a single-user case (one primary user and one secondary user) and a multi-user case with exact theoretical expressions of interference level. We had also made a comparison between OFDM and FBMC techniques. The most striking observation to emerge from our results is that the asynchronous interference is inversely propositional to timing offset even for the multi-user case, and that differences in the normalized interference level between the single/multi-user cases is barely perceived for the FBMC technique, proving its efficiency. Our simulations’ results had further strengthened our confidence in the suggested model. It shows that FBMC is best suited for CR networks since it provides BER improvements compared to OFDM.

     

Spectral properties of signal fading and Doppler spectra distribution in urban mobile communication links

In this work, we continue the analysis of a probabilistic approach and the corresponding stochastic multi‐parametric model of wave propagation, in built‐up areas with randomly distributed buildings. We have concentrated on the spectral properties of signal strength spatial variations and on Doppler spread spectrum distribution of signal power. The analysis is based on a unified stochastic approach of radio wave propagation above the built‐up terrain with applications to mobile communications. We analyze the signal power spectrum of spatial frequencies and the signal power distribution in the Doppler domain for moving vehicles, taking into account a Doppler shift proportional to the vehicle antenna speed relative to the base station. The comparison between the theoretical prediction and experimental data was motivated by the proposed stochastic model and other existing statistical models to verify the signal power distribution in the Doppler domain for various urban environments and terminal heights with respect to building rooftops. New effects of terrain features on signal spectrum are obtained, examined and compared with existing models. Copyright © 2006 John Wiley & Sons, Ltd.