无人水面艇在信息战中的应用

通过对无人水面艇历史和现状的介绍,以及对信息战概念的理解,提出了无人水面艇信息作战的思想。对无人水面艇在信息战中的应用做出了分析和展望,认为无人水面艇在信息战中将扮演重要角色。     

n-ZnO/p-Si异质结J-V特性的实验研究

本文首次报道n-ZnO/p-Si异质结J－V特性实验测量的初步结果－经退火处理的异质结反向饱和电流密度比未经退火的减少一个数量级,表明退火改善ZnO／Si晶格界面结构,提高了n-ZnO/p-Si异质结性能。     

Design and Optimization of the Extended True Single-Phase Clock-Based Prescaler

The power consumption and operating frequency of the extended true single-phase clock (E-TSPC)-based frequency divider is investigated. The short-circuit power and the switching power in the E-TSPC-based divider are calculated and simulated. A low-power divide-by-2/3 unit of a prescaler is proposed and implemented using a CMOS technology. Compared with the existing design, a 25% reduction of power consumption is achieved. A divide-by-8/9 dual-modulus prescaler implemented with this divide-by-2/3 unit using a 0.18-mum CMOS process is capable of operating up to 4 GHz with a low-power consumption. The prescaler is implemented in low-power high-resolution frequency dividers for wireless local area network applications     

Jamming sensor networks: attack and defense strategies

Wireless sensor networks are built upon a shared medium that makes it easy for adversaries to conduct radio interference, or jamming, attacks that effectively cause a denial of service of either transmission or reception functionalities. These attacks can easily be accomplished by an adversary by either bypassing MAC-layer protocols or emitting a radio signal targeted at jamming a particular channel. In this article we survey different jamming attacks that may be employed against a sensor network. In order to cope with the problem of jamming, we discuss a two-phase strategy involving the diagnosis of the attack, followed by a suitable defense strategy. We highlight the challenges associated with detecting jamming. To cope with jamming, we propose two different but complementary approaches. One approach is to simply retreat from the interferer which may be accomplished by either spectral evasion (channel surfing) or spatial evasion (spatial retreats). The second approach aims to compete more actively with the interferer by adjusting resources, such as power levels and communication coding, to achieve communication in the presence of the jammer.     

Performance of large-size superconducting coil in 0.21T MRI system

A high-temperature superconductor (HTS) was used on magnetic resonance imaging (MRI) receiver coils to improve image quality because of its intrinsic low electrical resistivity. Typical HTS coils are surface coils made of HTS thin-film wafers. Their applications are severely limited by the field of view (FOV) of the surface coil configuration, and the improvement in image quality by HTS coil is also reduced as the ratio of sample noise to coil noise increases. Therefore, previous HTS coils are usually used to image small in vitro samples, small animals, or peripheral human anatomies. We used large-size HTS coils (2.5-, 3.5-, and 5.5-in mean diameter) to enhance the FOV and we evaluated their performance through phantom and human MR images. Comparisons were made among HTS surface coils, copper surface coils, and cool copper surface coils in terms of the signal-to-noise ratio (SNR) and sensitivity profile of the images. A theoretical model prediction was also used to compare against the experimental result. We then selected several human body parts, including the wrist, feet, and head, to illustrate the advantage of HTS coil over copper coil when used in human imaging. The results show an SNR gain of 200% for 5.5-in HTS coil versus same size copper coils, while for 2.5- and 3.5-in coils it is 250%. We also address the various factors that affect the performance of large size HTS coils, including the coil-to-sample spacing due to cryogenic probe and the coil-loading effect.     

A new method to support UMTS/WLAN vertical handover using SCTP

This article proposes a new method to facilitate seamless vertical handover between wide area cellular data networks such as UMTS and WLANs using the stream control transmission protocol (SCTP). The multihoming capability and dynamic address configuration extension of SCTP are applied in UMTS/WLAN overlay architecture to decrease handover delay and improve throughput performance. Unlike techniques based on mobile IP or session initiation protocol, the SCTP-based vertical handover scheme does not require the addition of components such as home/foreign agents or a SIP server to existing networks. Therefore, the proposed scheme provides a network-independent solution preferred by service providers. Performance evaluations are presented to demonstrate the effectiveness of the proposed scheme.     

市场研究相关的大数据技术与资源介绍

在笔者前两篇讨论产品方法论和业务模式变化的文章中,可以发现,IT技术成为大数据业务生态下的重要竞争力。本文中笔者将结合自身工作,针对市场研究所需的大数据IT技术及可用资源进行简要介绍。内容主要面向非技术性的研究人员,不涉及技术细节。     

光栅投影相位测量轮廓术在SMT锡膏三维检测中的应用研究

该文研究采用光栅投影相位测量轮廓术实现锡膏三维测量,选择合适的硬件设备搭建了锡膏三维测量实验系统,采用四步相移法进行锡膏三维测量.实验结果表明,该文所设计的锡膏三维测量实验系统采用光栅投影相位测量轮廓术能够重建锡膏三维信息,可以达到锡膏三维检测精度的要求.     

Physical properties and electrical characteristics of H2O-based and O3-based HfO2 films deposited by ALD

Ozone (O₃) and H₂O are used as the oxidant to deposit hafnium oxide (HfO₂) thin films on p-type Si (1 0 0) wafers by atomic layer deposition (ALD). The physical properties and electrical characteristics of HfO₂ films change greatly for different oxidants and deposition temperature. Compared with O₃ as the oxidant, HfO₂ films grown with H₂O as the oxidant are more consistent in composition and growth rate. The O₃-based HfO₂ films have lower C impurity and higher concentration N impurity than the H₂O-based HfO₂ films. The impact of the annealing process on the electrical properties and stability of HfO₂ films are also investigated. A width step is observed in the O₃-based HfO₂ C–V curves, which disappears after annealing process. It is because the unstable Hf–O–N and Hf–N bonds in O₃-based HfO₂ films are re-bonded with the non-HfO₂ oxygen after annealing process, and the binding energy of N_1s shifts.     

A W-band Third Harmonic Gyrotron with an Iris Cavity

The design and experimental results of a W-band gyrotron operating at the third cyclotron harmonic are presented. The gyrotron is designed to operate at the TE₆₁ mode, which is significantly distinct from competing modes. An iris cavity is employed for the purpose of trapping the third harmonic mode more effectively and lowering its start current. In the experiment, the gyrotron is drived by a triode magnetron injection gun (MIG) which can produce a 45 kV, 3 A electron beam. When maximum axial magnetic field is 1.22 T, a single mode third harmonic gyrotron radiation is observed with the frequency of 94.86 GHz. The maximum output power is 5.5 kW, corresponding to an efficiency of 4%. Another third harmonic mode TE₀₂ is also detected at 88.8 GHz, with maximum output power of 1.5 kW.