Size dependence of THz region dielectric properties for barium titanate fine particles

Barium titanate (BaTiO₃) crystallites with various particle sizes from 22 to 500 nm were prepared by the two-step thermal decomposition method of barium titanyl oxalate. Various characterizations revealed that these particles were impurity-free, defect-free, dense BaTiO₃ particles. The powder dielectric measurement clarified that the dielectric constant of BaTiO₃ particles with a size of around 58 nm exhibited a maximum of over 15,000. To explain this size dependence, the THz region dielectric properties of BaTiO₃ fine particles, especially Slater mode frequency, were measured using the far infrared (FIR) reflection method. As the result, the lowest Slater mode frequency was obtained at 58 nm. This tendency was completely consistent with particle size dependence of the dielectric constant.     

Self-starting 6.5-fs pulses from a Ti:sapphire laser using asemiconductor saturable absorber and double chirped mirrors

We demonstrate self-starting 6.5-fs pulses from a Kerr-lens-mode-locked Ti:sapphire laser with an average output power of 200 mW at a pulse repetition rate of 86 MHz. We have achieved a mode-locking buildup time of only 60 μs, using a broad-band semiconductor saturable absorber mirror to initiate the pulse formation. The dispersion has been compensated with a prism pair in combination with improved double-chirped mirrors. The prism pair allows for the flexible adjustment of both the duration and the center wavelength of the pulse. The double-chirped mirrors show a high reflectivity better than 99.8% over the full bandwidth of 300 nm and a controlled group delay over more than 250 nm. The choice of a proper output coupler turns out to be critical for ultrashort pulse generation directly from the laser     

Low-dropout regulator with dual cross-coupled current mirrors

A low-dropout regulator (LDO) based on dual cross-coupled current mirrors is reported in this paper. The proposed dual cross-coupled current mirrors boost output signal current such that the loop gain of LDO is significantly enhanced, and the error amplifier in LDO retains single-pole property within the loop bandwidth of LDO. Designed in a 65-nm CMOS process and operating at a minimum of 1-V supply, the proposed LDO provides a 0.8-V output and delivers a maximum of 50 mA. The figure-of-merit of the proposed LDO is 8.9 ps.     

New CMOS current mirrors with improved high-frequency response

A new CMOS current mirror is presented which has the static characteristic of the cascode current mirror and a high-frequency performance equivalent to or better than that of the simple current mirror. Moreover, the circuit proposed does not present the instability problem of the improved cascode utilized to increase the high-frequency response. The circuit is designed using CMOS 2 μm technology with various aspect ratios and simulated with the SPICE programme.     

火电厂复杂地形的烟气扩散风洞试验研究

通过风洞模拟试验，研究广西合山火力发电厂烟羽在复杂地形环境中的扩散特征，提出复杂地形条件下的烟气扩散预测模式。根据试验和预测结果，探讨选择火电厂环保设施经济合理运行参数的可能性，为考虑环保因素电网调度合理安排火电厂运行周期及运行时段提供依据。     

Nano-precision metrology of X-ray mirrors with laser speckle angular measurement

X-ray mirrors are widely used for synchrotron radiation, free-electron lasers, and astronomical telescopes. The short wavelength and grazing incidence impose st...     

碳纤维复合材料不同深度缺陷的太赫兹检测研究

太赫兹(THz)无损检测技术具有非破坏性、非电离和非接触的优点,在航空航天领域纤维增强复合材料无损检测中得到了较快的发展和应用。在碳纤维复合材料层合板的4个不同深度(0.225、0.450、0.675、0.900 mm)插入聚四氟乙烯作为人工缺陷,采用太赫兹时域光谱和成像系统对其进行成像和光谱分析,探讨太赫兹波辐射下缺陷的成像效果和光谱特性。研究结果发现,在0.25~2.0 THz频率范围内,太赫兹反射成像可以成功检测出碳纤维复合材料中不同深度缺陷:随着缺陷深度的增加,太赫兹频域成像信号和光谱信号随缺陷深度线性增大,吸收系数成像信号和光谱信号随缺陷深度线性减小;随着频率的增加,缺陷的功率谱密度先增大后减小,吸收系数缓慢增大。该结果可以为碳纤维复合材料缺陷深度的可视化和定量化分析提供参考依据。     

Graphene-based four-port circulator with an elliptical resonator for THz applications

Journal of Computational Electronics - We suggest a new graphene-based four-port circulator for THz applications that consists of two parallel graphene waveguides coupled to an elliptical graphene...     

采用150Hz交流发电机组进行YZ,YZR系列电机超速及升高电压试验

应用异步电机拖动绕线转子异步电机超速运行且其转子绕组加以工频交流励磁生高频交流电的原理，组成１５０Ｈｚ固定频率Ｍ－Ｇ交流发电机组，进行ＹＺ，ＹＺＲ系列电机超速及升高电压试验。     

Rate control for streaming media transmission over WLAN

In order to solve the problems of link layer retransmission and packet fragment strategies for IEEE 802.11, this paper proposes a variable packet TCPfriendly rate control (VPTFRC) scheme for streaming media transmission over wireless local area network (WLAN) by researching on the policy of packet size adjustment in transport layer based on the minimum retransmit-delay constraint. Unlike other proposals, this process considers the impact of wireless packet error ratio (PER) on the packet size adjustment and the performance of rate control. Simulation results demonstrate that our proposed process can simultaneously achieve higher throughput, better fairness, shorter transmission delay and less jitter than TFRC. Among them, the ratio of delay, jitter and packet loss rate can reach a maximum improvement ratio of 58%, 42% and 85% respectively. __________ Translated from Journal of Huazhong University of Science and Technology (Nature Science Edition), 2007, 35(1): 1–3 [译自: 华中科技大学学报(自然科学版)]     

All-optical synchronization and mode locking of solid-state lasers with nonlinear semiconductor Fabry-Perot mirrors

The dynamics of laser oscillators can be directly accessed by modulating the intracavity losses. The authors present a new approach of optically driven loss modulation by means of a nonlinear semiconductor mirror based on a Fabry-Pe/spl acute/rot structure [Fabry-Pe/spl acute/rot modulator (FPM)]. The modulation depth of this device can be several percent and the response time is dominated by the recombination time of the generated free carriers inside the semiconductor, which can be reduced by ion implantation. This paper reviews the design of the FPMs and their optical characterization via spectrally resolved two-color pump-probe spectroscopy. Applications of the FPM are the synchronization of the pulse trains of independent mode-locked laser oscillators. The authors demonstrate the synchronization of a ps-Nd:YVO/sub 4/ laser to a fs-Ti:sapphire laser in a master-slave configuration and show experiments on the carrier-envelope phase relationship between the two synchronized pulse trains. Finally, they show that it is possible to actively mode lock a solid-state laser by an optically driven FPM. The resulting pulsewidths of the actively mode-locked Nd:YVO/sub 4/ laser are as short as 6 ps, which is comparable to passively generated pulses.     

Change of dielectric property with water-treed region

By dividing a water-treed XLPE sheet sample into a non-degraded layer and a water-treed one, relative permittivity ε_r2' and dielectric loss factor ε_r2^" of the water-treed layer have been estimated using an equivalent circuit. The way of changes in ε_r2' and ε_r2^" with the water tree length r estimated by the pulsed electroacoustic method has been discussed based on a Maxwell-Wagner-Sillars (MWS) model. It has been concluded that the MWS model gives a reasonable fit to the experimental data providing that the water conductivity in voids lies between 1×10^-3 S/m and 8×10^-3 S/m, and the minor and major axis ratio of the ellipsoids, to which water-filled voids are compared, lies in the range of 1:20 to 1:50     

SINAMICS G150在HH300液压钻机电控系统中的应用

介绍了SINAMICS G150变频器的特点以及在HH300液压钻机电控系统中的应用情况.     

多模式无线视频码流的传输与控制

采用快速传送协议/用户数据报协议/IP方式实现了多模式无线网络（WLAN、GPRS、CDMA）的码流传输,并完成无线通信下的RTCP双向控制信息链路.针对无线IP网络的传输特性,选取了适当的QoS参数反馈控制传输质量.实验测试表明,多模式无线通信系统下的码流传输在接收端取得了较好的视频传输质量.     

A current‐mode automatic frequency tuning system for filters with current mirrors

A new current‐mode automatic frequency tuning system is proposed in this paper. The system is based on the master–slave technique and is suitable for integrated current‐mode filters based on current mirrors. Automatic control is accomplished by controlling the bias current of the current mirrors employed in the master and slave filters. The proposed scheme has been applied in the leapfrog and wave filters and the corresponding simulation results confirm its validity. Copyright © 2009 John Wiley & Sons, Ltd.     

Multifunctional control of the process variables in the thermal-electric facility for high-frequency dielectric heating

A method to control the characteristics of a dielectric heating process using the instantaneous parameters of a high-frequency generator is proposed. An example of practical use for the proposed method is presented on the basis of the proposed expression for the power of internal thermal sources, from which the dependences of the current temperature in a welded joint during the high-frequency welding of plastics is obtained.     

Broadband amplification of 800-nm pulses with a combination of negatively and positively chirped pulse amplification

It is experimentally proved that successive amplification of negatively and positively chirped laser pulses (NPCPA) counteracts the gain narrowing effect typical in chirped pulse amplification (CPA) lasers. The scheme is robust and easy to adopt to even petawatt (PW) level high power laser systems. As a demonstration, a multi-terawatt (TW) Ti:sapphire laser system was modified to the NPCPA. The bandwidth of the 150 mJ output pulses exceeds 50 nm without any additional spectral correction, which is 30% broader than those currently available from conventional CPA lasers. Moreover, the NPCPA scheme gives an opportunity to increase an intensity temporal contrast without any compromise in pulse energy.     

On studying methods for cleaning dielectric oil for impregnation of high-voltage pulse capacitors with film dielectric

Methods for cleaning commercial T-1500 dielectric oil with different adsorbents are studied. The oil is intended for impregnation of high-voltage pulse capacitors with film dielectric.     

直线电机的线性自抗扰控制

光刻机的工件台是高动态精密伺服运动平台,它要求在系统高速运动的同时,采用长行程直线电机宏动跟随音圈电机高精密微动的驱动方式,实现系统纳米级的精确定位及跟踪。为减小微动电机的运动范围和加速度,必须提高直线电机的跟踪精度。针对该系统的直线电机模型设计了一种线性自抗扰控制方法,该方法的控制器首先通过扩张状态观测器观测系统的动态变化,补偿系统中的各种扰动,再运用前馈对系统的跟踪误差进行补偿,减小系统的动态跟踪误差。在此复合控制方式下,控制器实现了自抗扰控制,前馈控制器很好的补偿了误差,从而提高了系统的抗干扰和跟踪性能。实验表明,该方法与传统的控制方法相比,改善了系统的动态性能和抗干扰能力。     

Dynamic control over optical solitons in a resonant photonic crystal

When a defect associated with a weak linear excitation or incoherent pump inside a resonant photonic crystal is created, dynamics of light propagation in a gap soliton regime undergo a considerable modification. We show that dynamic control of such a defect can be used to convert coherently a propagating optical pulse into a stationary excitation trapped inside the photonic crystal. This can also impose changes onto a pulse interaction with each other, thus facilitating possible applications in optical switching, signal processing, and quantum computing.