Effects of High-Pressure High-Temperature Sintering on the Band Gap and Thermoelectric Properties of PbSe

In this study, PbSe bulk samples were prepared by a high-pressure high-temperature (HPHT) sintering technique, and the phase compositions, band gaps and thermoelectric properties of the samples were systematically investigated. The sintering pressure exerts a significant influence on the preferential orientation, band gap and thermoelectric properties of PbSe. With increasing pressure, the preferential orientation decreases, mainly due to the decreased crystallinity, while the band gap first decreases and then increases. The electrical conductivity and power factor decrease gradually with increasing pressure, mainly attributed to the decreased carrier concentration and mobility. Consequently, the sample prepared by 2 GPa shows the highest thermoelectric figure-of-merit, ZT, of 0.55 at ～ 475 K. The ZT of the HPHT-sintered PbSe could be further improved by properly doping or optimizing the HPHT parameters. This study further demonstrates that the sintering pressure could be another degree of freedom to manipulate the band structure and thermoelectric properties of materials.     

Optimized TQ-MAP: An Adaptive Mapping Mechanism to Guarantee the Coherence of QoS Support from IP to OBS

Because of its scalability, the idea of coarse packet classification can be utilized to OBS networks. However, due to the limited number of priorities supported by OBS networks, we usually adopt a many-to-one composite class burst (CCB) assembly technique, e.g., N:1-CCB. In this kind of technique, there are two aspects related to scalable QoS support, i.e., mapping relationship and assembly resource allocation. This paper simultaneously takes the two aspects into consideration, and proposes a novel assembly mapping mechanism, called Optimized TQ-MAP, in which the most important feature is adaptivity. Based on nonlinear programming and differential calculus, it allocates the burst assembling capacity between classes fairly, efficiently and differentially, and matches IP QoS requirement with OBS QoS capacity as possible as it can. The simulation results show that Optimized TQ-MAP is more adaptive, and can efficiently guarantee the coherence of QoS support from IP to OBS.     

Robust Digital Terrestrial TV Broadcasting System with Error-Resilient Schemes

In this paper, error-resilient schemes are proposed to support robust video transmission for digital terrestrial TV broadcasting (DTTB). In particular, a temporal error concealment incorporated with a low-complexity block-matching is developed, achieving an effective reception of predictive pictures in harsh terrestrial environment. Special algorithms are also designed for isolated I-pictures. Moreover, combined with an intra/inter case prediction, an adaptive error concealment scheme is further contrived to fit for different error conditions. Extensive simulations have been conducted under various DTTB channel conditions, even with a very high packet error rate, to verify the effectiveness of the proposed schemes.     

Light emission of heavily doped AlGaN structures under optical pumping

Spectral,temporal and polarization characteristics of spontaneous and stimulated luminescence of Al0.5Ga0.5N/AlN structures grown by molecular beam epitaxy were studied at the optical pulsed pumping with λ =266 nm.Samples with a high degree of silicon doping were investigated.The vast majority of radiation falls on transitions within the band gap between the levels of defects.As a result,the radiation band embracing the whole visible range of more than 300 THz is observed in both spontaneous radiation and induced luminescence.In spontaneous radiation the band has a smooth spectral intensity distribution over the wavelengths,whereas induced radiation has its sharp peaks corresponding to the mode structure of the planar waveguide.The measured gain of the active medium is g ≈ 70 cm-1 for a weak signal.     

“通信系统综合实验”教学平台建设

“通信系统综合实验”是我院一门综合性、实践性课程,在多年的教学实践中积累了大量的实验成果.在原有实验开设项目的基础上引入基于USRP和LabVIEW的通信系统实验平台,将真实的通信信道考虑到无线通信系统设计当中,使无线通信系统软件仿真和硬件实现真正统一,并为无线通信新技术的扩展学习和研究提供了可能.     

A Bubble‐Derived Strategy to Prepare Multiple Graphene‐Based Porous Materials

Graphene‐based porous structures have triggered tremendous attention due to their promising application in many fields. Recent progress has yielded structures with stochastic porous networks, which limit their controllability and potential performance. It still remains a big challenge for the scalable production to integrate the 2D building block into engineered porous architectures in multidimensions. Here, a versatile technique based on soft bubble templating and fixation by freezing is described to fabricate 3D bubble‐derived graphene foams (BGFs) and 2D bubble‐derived graphene porous membranes (BGPMs). These light‐weight novel structures are carefully tuned. The BGFs show high adsorption capabilities for organic solvents and good recovery in structural deformation. Furthermore, applications of BGFs and BGPMs in strain sensors for wearable devices are discussed, working as a combined system which can both detect the compressive and tensile deformation. This technique can be extended to assemble other nanomaterials as building blocks into macroscopic configurations.     

Differential space-time-frequency modulation over frequency-selective fading channels

We present a differential space-time-frequency (DSTF) modulation scheme for systems with two transmit antennas over frequency-selective fading channels. The proposed DSTF scheme employs a concatenation of a spectral encoder and a differential encoder/mapper, which are designed to yield the maximum spatio-spectral diversity and significant coding gain. To reduce the decoding complexity, the differential encoder is designed with a unitary structure that decouples the maximum likelihood (ML) detection in space and time; meanwhile, the spectral encoder utilizes a linear constellation decimation (LCD) coding scheme that encodes across a minimally required set of subchannels for full diversity and, hence, incurs the least decoding complexity among all full-diversity codes.     

Remarks on unknown key-share attack on authenticated multiple-key agreement protocol

Recently Shim gave an attack on Harn's modified authenticated multiple-key agreement protocol. The authors point out Shim's attack is not workable. However, Harn's modified protocol is still insecure and the authors give another attack on it. Finally, the authors propose an efficient protocol that can prevent this attack.     

2D DOA estimation for noncircular sources using L-shaped sparse array

We present an algorithm for two-dimensional (2D) direction-of-arrival (DOA) estimation of noncircular sources using an L-shaped sparse array. An L-shaped sparse array consisting of two co-prime arrays is firstly introduced. Then, the fourth-order-cumulants (FOCs) of received data are used to construct a FOC matrix (FOCM), by which we can get the estimations of elevation angles. With the estimated elevation angles, the azimuth angles can be estimated by a low-complexity signal separation algorithm. During the procedure used for estimating azimuth angles, no any eigenvalue decomposition (EVD), peak search and pair-matching procedure need to be implemented. Although the aperture is extended significantly, the computation complexity of proposed algorithm still is acceptable. Compared with some analogous algorithms, our approach shows more attractive estimation performance. A lot of simulation results prove the advantages of proposed DOA estimation technology.