Magnetic resonance spectroscopy data analysis: time or frequency domain?

Comparisons of time and frequency domain methods are presented forin vitro ¹H andin vivo ³¹P magnetic resonance spectroscopy (MRS) data. Many distortions in the MR spectrum, introduced by applying the Fourier transform to a nonideal free-induction decay (FID), can be handled more elegantly in the time domain, where operations are carried out directly on the measured signal. It was found that if the measured signal is well conditioned—high signal-to-noise ratio (S/N), no truncation, no baseline problems—then both time and frequency domain methods give the same results within the error limits. However, distortions in the measured signal make analysis by time domain methods preferable over frequency domain methods. In all applications, the use of prior knowledge appeared to play an important role.     

Lp norm approaches for estimating voltage flicker

It is important to accurately estimate instantaneous voltage flicker magnitudes and frequencies in order to correctly evaluate voltage fluctuations. Voltage flicker is a problem in electric power quality. Different approaches used to determine the magnitude of the voltage flicker have been presented: measurement methods generally use a flickermeter device. Simulation methods require a computer model of the disturbing load and the flickermeter. Calculation methods necessitate a simplified empirical formula. Estimation algorithms are based on the estimation of the voltage flicker components. In this paper, two models of voltage flicker are discussed: L_p estimation algorithms utilizing L₁, L₂ and L_∞ norms are used to estimate the voltage magnitudes of the flicker signals as well as the fundamental voltage magnitude. The main result is that it is possible to design an L_p estimator to identify flicker frequency and amplitude from time series measurements.     

Frequency domain discussions on PD signal propagation characteristics in GIS

The frequency dependency of PD signal propagation in GIS was investigated at an underground substation. Injecting dummy pulses into a GIS through its internal electrode, frequency spectra were measured by a spectrum analyzer at various points of the GIS. It is shown that this measurement is very reproducible and the signal propagation phenomena are independent of its direction. It is also clarified that the PD signal reduction phenomena are closely related with mode transfer from TEM to TE or TM. The major higher mode seems to be TE₁₁. Pulse waveforms were also measured with 65‐MHz bandpass filter. Their magnitudes are compared with the gain of the 65‐MHz component of the frequency spectra and good agreement is obtained. This implies the possibility of PD location by observing a frequency pattern with several bandpass filters. © 2000 Scripta Technica, Electr Eng Jpn 133(3): 9–17, 2000     

Transient analysis of printed lines using finite‐difference time‐domain method

Comprehensive studies of ultra‐wideband pulses and electromagnetic coupling on printed coupled lines have been performed using full‐wave 3D finite‐difference time‐domain analysis. Effects of unequal phase velocities of coupled modes, coupling between line traces, and the frequency dispersion on the waveform fidelity and crosstalk have been investigated in detail. To discriminate the contributions of different mechanisms into pulse evolution, single and coupled microstrip lines without (ϵ_r = 1) and with (ϵ_r > 1) dielectric substrates have been examined. To consistently compare the performance of the coupled lines with substrates of different permittivities and transients of different characteristic times, a generic metric similar to the electrical wavelength has been introduced. The features of pulse propagation on coupled lines with layered and pedestal substrates and on the irregular traces have been explored. Physical interpretations of the simulation results are discussed in the paper. Copyright © 2012 John Wiley & Sons, Ltd.     

A transmission line transformer having frequency independent matching properties

In this paper, we present a new transmission line transformer which is capable of matching a load resistance R_L to a given source of internal resistance R_g in a frequency independent manner. This matching can be made perfect at all frequencies if R_L/R_g = 4; for R_L/R_g ≠ 4, the matching can still be made frequency independent but the power transferred to the load becomes less than the maximum available power.     

Harmonic distortion degradation and filter optimization based on sensitivity studies with considering resonance issue

Voltage distortions are characterized by the harmonic spectrum of the nonlinear load (NLL) and harmonic impedance of the whole system. On one hand, the harmonic impedance is at the peak value when the frequency is at the resonance point, which leads to serious voltage distortions. On the other hand, harmonic distortions will be excited from excessive harmonic emission without resonance. In order to address the above causes, shifting the resonance frequency sensitivity (RFS) and the critical individual harmonic voltage distortion (IHD_V) sensitivity (IHDS) indices are presented here to control the critical IHD_V and total harmonic voltage distortion (THD_V). The main idea is to find and adjust the most sensitive network parameter against these sensitivity indices until the harmonic distortion reaches the required value. A three‐bus test system and the IEEE 14‐bus system are used to verify the proposed method. Comparison of the results shows that these indices complement each other for solving the harmonics problems with or without harmonic resonance. The sensitivity‐based methods can be effective for system optimization and filter design by considering harmonic resonance. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Enhancement of thermoelectric performance in rare earth-doped Sr<Subscript>3</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript> by symmetry restoration of TiO<Subscript>6</Subscript> octahedra

Aiming at the realization of the enhancement of thermoelectric performance through structural modification, the present work has clarified the significant effects of rare earth (RE=Gd, Sm, Nd, and La) doping at Sr-sites in Sr₃Ti₂O₇, both on the structural restoration of distorted TiO₆ octahedra and on the Seebeck coefficient, especially at high temperatures. The preferential substitution of RE ³⁺ at the nine-coordinate Sr-sites can facilitate the degeneration of the conduction band (Ti 3d-t _2g ) orbital, owing to its special capability in restoring TiO₆ octahedra to a higher state of symmetry and thus enhance the density of states (DOS) effective mass of the carriers, which gives rise to a rather large increase in the Seebeck coefficient. The present findings have affirmed the effectiveness of structural restoration in enhancing the Seebeck coefficient by Sr-site-doping, which will help establish a useful solution for Ti-based thermoelectric oxides with inherently distorted TiO₆ octahedra to achieve high thermoelectric performance.     

Estimating power-frequency characteristics in power systems by means of spectral analysis techniques

This paper shows that normal power system operating data may be used to determine the power-frequency characteristics in power systems. Data are processed as random signals using spectral analysis techniques, and the results estimate the generator and load power-frequency characteristics as transfer functions. The generator characteristics K_g are determined as a transfer function of the system in which input signals are frequency fluctuation ΔF and generator power setting signal ΔP_g, and output signal is generator power output ΔP_e, To estimate the load characteristics K_l, a difficulty arises. There is a relation ΔP_/ = ΔL_o + K_lΔF between actual load ΔP_l, ideal load under the state of nominal frequency ΔL_o, and fluctuation of system frequency ΔF. Because it is impossible to measure ΔL_o directly, ΔL_o and K_lΔF cannot be separated. With regard to a partial system, when its capacity is small enough compared with the total system capacity, the contribution of ΔL_o in a partial system to ΔF of the total system may be ignored, that is, ΔF and ΔL_o are considered as independent phenomena. Thus the cross spectrum of ΔF and ΔL_o decreases to zero according to the increase of data in number, and K_l of the partial system can be estimated.     

混合十三电平逆变器调制策略及功率均衡方法

混合多电平逆变器因其能输出更多电平数且使用的开关器件较少而得到广泛应用,但对电压比为3:1:1:1混合级联H桥十三电平逆变器使用传统的载波移幅调制(phase disposition pulse width modulation,PD-PWM)策略,各单元的功率并不均衡。为了达到功率均衡的目的,文中针对混合十三电平拓扑提出了一种改进的混合调制方法,并在此基础上,进一步重构PD调制下的三角载波和调节高压单元的输出脉冲,在实验室条件下,以调制度0.9为例,3个低压单元L₁、L₂、L₃的开关损耗分别为4.6、4.4、4.2 W,开关损耗基本相等。L₁、L₂、L₃输出功率基本一致,高压单元H₁输出功率为51.7 W,3个低压单元功率均为17.2 W,高低压单元输出功率比接近3:1。仿真得到3个低压H桥单元的开关损耗相同,4个单元的功率均衡,高压和低压部分的功率开关分别工作在基频和高频状态,谐波特性良好。     

锥形绕组特快速暂态过电压分布研究

为了研究在陡波前、高重复频率的电压冲击下,脉冲变压器(PT)锥形绕组中的特快速暂态过电压(VFTO)分布特性,建立了基于多导体传输线(MTL)理论的PT二次绕组分布参数模型;利用锥形绕组结构上的特性,提出一种有限元法(FEM)和插值公式相结合的方法以快速计算锥形绕组的感应系数矩阵K;通过求解频域下的电报方程可得到绕组的对地电压分布以及匝间电压分布;进行了绕组暂态电压的测量,从实验结果可以看出电压分布的一定规律,并分析了造成计算与实验结果间误差的原因;结合实验提出一种改善电压分布的措施,对大功率PT二次绕组的绝缘设计有一定的参考意义。     

Inner Intrinsically Safe Criterion and Design Considerations of Buck Converter Based on Equivalent Inductance

To obtain the intrinsic safety criterion of the Inner-intrinsic-Safety-Buck-Converter (ISBC) based on equivalent-inductance to guide its optimal design, the Inductor Disconnected Discharge (IDD) behavior of ISBC is researched, and the Equivalent-Simple-Inductive-Circuit (ESIC) based on the equivalent inductance is defined. According to ESIC based on the equivalent-current and the energy equivalence, the expression of the equivalent inductance L_ei is derived. The effect of the inductance L, the capacitance C, the input voltage V_i and the load resistance R_L on L_ei is deeply studied, and it’s pointed out that L_ei increases with the increase of V_i, L, C, and R_L, respectively. According to the minimal ignition current curve of the Simple-Inductive-Circuit (SIC), the nonexplosive intrinsically safe criterion based on L_ei is proposed. Combining the proposed criterion, the output ripple voltage and the expression of L_ei, the design region of the capacitance and inductance of the Buck converter meeting the demands of both inner intrinsic safety and electric performance is obtained. The feasibility of the design method and the proposed criterion is proved by the simulation and experimental results.     

Complex permeability of polycrystalline Mn-Zn and Ni-Zn ferrites

The complex permeability of ferrites is frequency dependent. The real part of the complex permeability deteriorates in a high frequency range and the imaginary part has a peak after starting the deterioration. This paper examines the possibility that the frequency characteristics for some ferrites can be approximately derived from a first-order linear differential equation for the magnetic field intensity and magnetic flux density. The first-order differential equation is expressed by the reciprocal of the complex permeability and provides first-order magnetic and electric circuits for ferrite cores. In contrast with the commonly used series R_s-L_s, circuit for the cores, obtained from B = (μ′ − jμ′)H, the first-order electric circuit derived consists of an inductance (L) and resistance connected in parallel. In this paper, it is demonstrated that the inductance L remains constant, whereas Ls decrease with the increase in frequency. In other words, the real part of the reciprocal of the complex permeability remains constant for an increase in frequency. In addition, it is found that the imaginary part of the reciprocal of the complex permeability is approximately proportional to the frequency. © 1998 Scripta Technica, Electr Eng Jpn, 123(2): 1–7, 1998     

Symmetric dual-mode filter based on substrate integrated waveguide (SIW)

A planar four-pole dual-mode filter with symmetric transmission response based on substrate integrated waveguide (SIW) is proposed. The filter centered at 10 GHz, consisting of two TE₁₀₂–TE₂₀₁ dual-mode SIW cavities, is implemented in a single layer substrate by PCB process. A linear microstrip taper is used to implement the transition between 50 Ω microstrip and SIW. The measured results are in agreement with simulated results.     

Current-Mode Pulse Train Controlled Quadratic Boost Converter Operating in Discontinuous Conduction Mode

Unlike the conventional pulse width modulation control, a unique current-mode pulse train (CMPT) control technique presents a different nonlinear dynamics associated with the power electronics system. The quadratic boost converter in discontinuous conduction mode (DCM) is examined under CMPT control. The control performance of the system is studied by analyzing the combination of high-power control pulse P_H and low-power control pulse P_L of a control pulse repetition cycle in regulating the output voltage. The computer simulation is accomplished to capture the gist of the system dynamics revealing the periodic transition manifested due to border collision bifurcation under the influence of the variation in input voltage and load resistance. The stability of the system is assessed with the evidence of loci of eigenvalues from two-dimensional discrete-time model and maximal Lyapunov exponents obtained using QR decomposition algorithm. An experimental setup is also developed to verify the simulated and analytical dynamics witnessed.     

锥形转子永磁电机的结构对性能参数的影响

锥形转子永磁电机具有与普通永磁电机不同的结构特点,电机的分析计算有其特殊性,以简化方法计算容易得出误差较大的结果.以三维有限元法分析了不同结构参数下锥形转子永磁电机的磁场分布,结果表明其磁场沿轴向分布比较均匀,并且气隙磁场随着转子轴向位移的增大线性降低.在此基础上,分析了锥角,转子轴向位移,永磁体形状等结构参数对交直轴电感、转矩等的影响,结果表明交直轴电感参数在不同的永磁体形状下随着转子轴向位移有着不同的变化趋势,锥角影响着交直轴电感的变化幅度,转矩随着转子轴向位移的增大而减小.同时计算分析的正确性通过样机实测值得到了验证.     

Nonlinear distortion cancellation in class a junction transistor amplifier stages

Various sources of distortion in class A junction transistor amplifier stages are investigated using a unified method of analysis. Expressions for simultaneous cancellation of second and third harmonic distortions at low frequencies are derived giving the design relations between the source and load resistances together with the transistor operating parameters. High frequency effects are considered and a simple compensating method is devised to extend the gain-bandwidth product to the order of (1/2°C_TCr_b′b).     

Two organic–inorganic hybrid Schiff base copper materials: synthesis and their catalytic properties for constructing C–N bonds

Abstract

Two Schiff base copper complexes: [Cu(H₂O)₂(HL¹)]·2H₂O (1) (H₃L¹ =2-((2,4-dihydroxybenzylidene)amino)acetic acid) and [Cu(L²) (CH₃OH)]₄ (2) (H₂L² = 3-phenyl-2-(2-hydroxy-5-chlorobenzylideneamino)propane-1-ol), have been simply synthesized and fully characterized. Single crystal X-ray diffraction (SXRD) revealed that 1 consists of one five-coordinated copper atom and one deprotonated Schiff base ligand HL¹. The copper atom in 1 showed the distorted tetragonal pyramid geometry, whereas, four copper atoms in 2 were six-coordinated and exhibited the distorted octahedron geometry. Importantly, two Schiff base complexes were further used as catalysts in Chan–Lam coupling reaction and 2 demonstrated excellent catalytic performance in construction of C–N bonds (yields up to 87%).     

An accurate rational 2-port model of a class of tapered lossless and RC lines

A rational 2-port model of a class of tapered LC and RC lines which includes the exponential, hyperbolic, trigonometric and square, or Bessel, lines is presented. The model for the exponential RC line (ERC ), considered as an example, accurately describes the actual frequency and transient response for various values of taper factor over wide ranges of frequency and time. In an ERC notch network configuration, application of this model predicts the results very closely for various values of taper factor.     

Numerically optimized hard pulse sequences for fast frequency selective excitation and inversion

Numerically optimized hard pulse sequences were developed providing a frequency selective response of the transverse and longitudinal magnetization for several applicationsin vivo. The sequences are based on pulse trains with binomial ratios of the pulse angles and constant time intervals between the pulses. These pulse trains were systematically optimized to obtain broad Larmor frequency ranges in which the magnetization is not markedly influenced by the pulse sequence. In addition, the sequences had to provide maximum transverse magnetization or complete inversion of the magnetization beside the suppression range. Such behaviour is needed for chemical shift selective imaging, pulsed magnetization transfer, and frequency selective spectroscopyin vivo. The phase of the magnetization response is shown and adequate rephasing conditions are discussed as well as the actual phase duration. Short optimized hard pulse sequences for water and fat-selective imaging provide lowT ₂-sensitivity of the resulting magnetization. The new optimized hard pulse sequences are suitable, if optimum suppression of signals at one single point in the Larmor frequency spectrum is less important than good suppression in a larger frequency range.     

Coupling and conversion characteristics of spot-size-converterintegrated laser diodes

The coupling and conversion characteristics of four types of spot-size converter integrated laser diodes (SS-LDs) to a single-mode fiber (SMF) in the 1.3-μm-wavelength region are numerically clarified. The SS-LDs are categorized into types with vertical tapers and types with a combination of a lateral taper and a thin-film core. The eigenmodes are obtained by the finite-element method (FEM). The semivectorial 3-D finite-difference (FD) beam propagation method (BPM) is used to calculate the propagating beams