Reducing the NMR sample volume using a single organic liquid: Increased sensitivity for mass-limited samples with standard NMR probes

A simple inexpensive protocol for confining an aqueous sample to the active region of a standard NMR probe is examined for high-resolution NMR. The aqueous sample is sandwiched between an inert perfluorinated organic liquid that has been exploited in the design of micro-coil NMR probes. The procedure is demonstrated with 3 mm NMR tubes at ambient and elevated temperatures but should be equally applicable to smaller diameter tubes. It is shown that confinement has minimal effects on line shape and provides at least a two fold increase in sensitivity over a conventional sample, for the same mass of solute.     

High Input Impedance Voltage-Mode Universal Biquadratic Filter with Three Inputs Using DDCCs

A new high input impedance voltage-mode universal biquadratic filter with three input terminals and five output terminals is presented. The proposed circuit uses three plus-type differential difference current conveyors, two grounded resistors and two grounded capacitors. The proposed circuit can realize all the standard filter functions: lowpass, bandpass, highpass, notch and allpass, without component matching conditions. The proposed circuit offers the features of high input impedance, low active and passive sensitivities and the use of only grounded resistors and capacitors.     

光纤通信系统中偏振模色散补偿的二种反馈控制信号的特性比较

为了说明当光纤通信系统中存在高阶偏振模色散时,采用DOP和电带宽作反馈信号PMD补偿效果均会受到高阶偏振模色散的影响,用数值模拟方法比较了二种常用的反馈控制信号与偏振模色散的性能,模拟结果表明,从性能上讲,二种反馈信号都随一阶PMD变化而具有线性变化,当系统中有高阶偏振模色散时,二者均不具有线性的变化。模拟结果对偏振模色散补偿具有一定的指导意义。     

Experiment-based identification of time delays in linear systems

This paper presents an identification approach to time delays in single-degree-of-freedom (SDOF) and multiple-degree-of-freedom (MDOF) systems. In an SDOF system, the impedance function of the delayed system is expressed by the system parameters, the feedback gain, and the time delay. The time delay can be treated as the "fre-quency"of the difference between the impedance function of the delayed system and that of the corresponding uncon-trolled system. Thus, it can be identified from the Fourier transform of the difference between the two impedance func-tions. In an MDOF system, the pseudo-impedance functions are defined. The relationships between the time delay and the pseudo-impedance functions of the delayed system and uncontrolled system are deduced. Similarly, the time delay can be identified from the Fourier transform of the difference between the two pseudo-impedance functions. The results of numerical examples and experimental tests show that the identification approach to keeps a relatively high accuracy.     

Enhancement of noise reduction efficiency based on compensation in the ANC headset using fixed-point DSP

In this paper, we have proposed a new algorithm considering commutation error and feedback effect to enhance the convergence rate and noise reduction efficiency of ANC controller. In order to improve noise reduction performance of the ANC headset with fixed-point DSP, we have proposed a new FxLMS algorithm, FxLMS CF, which considers the commutation error and feedback. Also, using a non-real-time simulation, we have decided the phase and amplitude compensation factors of anti-noise signal considering round-off and quantization error, nonlinear distortion and delay of analog device. We estimated the phase and amplitude compensation factors by simulation without using any special measuring devices or analysis devices, and reduced the broadband noise by 24 dB.     

Active manipulation of EM fields in open waveguides

The central question addressed in this paper is whether we can introduce an antenna array into a circular cylindrical waveguide to accurately control or determine the local field around the array with vanishingly small reflection from the boundary of the waveguide. We ask this question since we perceive the answer to be important to the applied community through its relevance for applications to electromagnetic shielding or slot antennas. We make use of the results presented in Onofrei (2014) for the scalar Helmholtz equation and show, by using the Debye representation in waveguides, how they apply to the current EM waveguide model. We prove the existence of a class of solutions and include a feasibility discussion for the antenna synthesis problem together with relevant simulations.     

Wave-based control of planar motion of beam-like mass–spring arrays

Wave-based control (WBC) is a simple and relatively new technique for motion control of under-actuated flexible systems. To date it has been mainly applied to rectilinear lumped flexible systems. The current work focuses on a development of WBC to control two-dimensional beam-like structures in which an actuator, attached to one end, acts to translate and rotate the structure through an arbitrary path in the plane. In this work, first a lumped model of a beam is developed using mass–spring arrays. The lumped beam model is of interest here as a benchmark control challenge. It can also be considered as a model of various lumped or distributed mass structures. To check the latter, the mode shapes and frequencies are first compared with those of classical beam theory. This involved a new technique to find mode shapes and frequencies for arrays. The control strategy is then presented and tested for a range of manoeuvres. As a system to be controlled, the mass–spring array presents many challenges. It has many degrees of freedom, many undamped vibration modes, is highly under-actuated, and sensing of system states is difficult. Despite these challenges, WBC performs well, combining a fairly rapid response with active vibration damping and zero steady-state error. The controller is simple to implement and of low order. It does not need or use any system model and is very robust to system changes.     

HL-2M装置反馈控制系统的设计

简要描述HL-2M控制系统的概念设计,主要对其中反馈控制部分作了介绍,重新编写了反馈控制程序。为了满足HL-2M装置对控制系统的进一步要求,重新设计了反馈控制系统程序。对其中一些功能的实现方法进行了设计改进,引入了由反射内存卡构建的实时通讯网络,并以此通讯网络为基础进行了反馈控制系统的架构布局。在Linux操作系统中,利用以前放电的实验数据,模拟测试了新的反馈控制系统。测试结果良好,满足预期要求。     

载体表面性质对Cu2O/AC催化剂结构和活性的影响

采用活性炭(AC)载体浸渍醋酸铜, 然后热分解制备甲醇气相氧化羰基化合成碳酸二甲酯的无氯Cu2O/AC催化剂. 用硝酸或氨水处理活性炭后, 其表面的化学性质发生了变化, 从而影响了Cu2O/AC催化剂的结构和催化活性. 实验结果表明, 硝酸或氨水改性后的活性炭表面不仅有新的含氮基团产生, 而且含氧基团C-O-C, C-O和CO-O增加, CO基团明显减少或消失. 其中, 含氮基团的供电子效应和富余的CO-O基团使负载在载体上的CuⅡ更容易被还原成CuⅠ, 有利于获得组分单一且分散较好的Cu2O负载型催化剂, 从而显著地提高了催化活性. 氨水改性的活性炭更加有利于活性物种Cu2O的分散, 能够进一步改善催化性能, 在n(CO)∶n(MeOH)∶n(O2)=4∶10∶1, SV=5600 h-1条件下, 甲醇转化率达到7.0%, DMC的时空收率为145.1 mg/(g·h), 基于甲醇的选择性为68.7%.     

大功率单相完全有源功率因数校正器的实现

首先基于现有的、典型的模拟PFC控制芯片,较为详细地描述了单级升压变换的单相AC—DC变换器领域几种基本的有源功率因数校正技术,其中包括传统有源PFC技术、跟随有源PFC技术和单周期有源PFG技术。最后基于PFC控制芯片L4981B详细地介绍了支持较大功率输出的有源PFC电路设计过程,并给出部分实验结果。