Improved short tau inversion recovery (iSTIR) for increased tumor conspicuity in the abdomen

Object

To develop an improved short tau inversion recovery (iSTIR) technique with simultaneous suppression of fat, blood vessels and fluid to increase tumor conspicuity in the abdomen for cancer screening.

Materials and methods

An adiabatic spectrally selective inversion pulse was used for fat suppression to overcome the reduced signal to noise ratio associated with chemically non-selective inversion pulse of STIR. A motion-sensitizing driven equilibrium was used for blood vessel suppression and a dual-echo single-shot fast spin echo acquisition was used for fluid suppression. The technique was optimized on four normal subjects and later tested on five patients referred for metastatic tumor evaluation.

Results

A velocity encoding of 2 cm/s achieved effective blood suppression even in small vessels. Subtraction of two images (one with 60 ms and the other with 280 ms echo time) acquired in the same echo train achieved excellent fluid suppression (>70 % reduction). Simultaneous suppression of fat, blood vessels and fluid improved the tumor conspicuity compared to corresponding fat-suppressed (STIR) image.

Conclusion

This technique generated two complementary images from a single scan: one that is equivalent to a STIR image and the other that qualitatively resembles a diffusion-weighted image and may have potential for magnetic resonance imaging cancer screening.

     

Development of high efficiency GaN-based multiquantum-welllight-emitting diodes and their applications

Highly efficient GaInN-GaN multiple quantum-well (MQW) light-emitting diodes (LEDs) were successfully developed by the low-temperature AlN buffer layer method for metal-organic vapor phase epitaxy (MOVPE). The light-emitting layer of the GaInN-GaN MQW drastically enhances the performance of GaN-based LEDs in terms of the efficiency and spectrums. Flip-chip (FC) type MQW LEDs have been newly developed to increase efficiency in extracting light from the GaN-based crystal to the outside. The luminous intensities of FC type blue and green LEDs are typically 6 and 14 cd, respectively, at 20 mA. The output power of the FC-type LEDs was 14 mW at 20 mA, which was approximately two times higher than that of the conventional face-up type blue LEDs. The external quantum efficiency of blue FC-type LEDs was as high as 20% at 20 mA. New multicolor package was developed using these high performance nitride-based LEDs and commercial AlGaInP-based red LEDs, the color range of which is the largest among other flat panel display devices     

Series and parallel operation of the emitter turn-off (ETO)thyristor

By dramatically decreasing the storage time, the emitter turn-off thyristor (ETO) has a very good match in storage time. Storage time dispersion of less than ±100 ns is normal for ETOs and can be further reduced through adjustment of the emitter switch gate resistance. Thus, the capacitance required for dynamic voltage balancing in the ETO series connection is significantly reduced. Uniform current sharing for parallel-connected ETOs is also guaranteed at the device level through the open-base p-n-p turn-off mechanism. The current-balancing inductance can be essentially removed. Theoretical analysis and experimental results of 53-mm ETOs are presented     

神经网络在自动调速中的应用(综述)

神经网络具有逼近非线性函数的能力，神经网络控制器的设计可以不依赖于被控对象的精确数学模型，具有这样的优点，使它在电机控制中具有很好的发展前途。     

Oxynitride/nitride phosphors for white light-emitting diodes (LEDs)

Oxynitride/nitride phosphors have attracted significant attention recently because they have promising luminescence properties and superior thermal and chemical stabilities which predestinates them for use in white LEDs to generate white light. This paper reports on luminescence spectra of Eu²⁺ or Ce³⁺-activated α-SiAlON, β-SiAlON, and alkaline earth silicon nitride (M₂Si₅N₈, M = Ca, Sr, Ba). A single broad emission band is observed for all samples, and the emission color depends on the type of activators and host lattice: α-SiAlON:Ce³⁺ (blue), α-SiAlON:Eu²⁺ (yellow), β-SiAlON:Eu²⁺ (green), and M₂Si₅N₈:Eu²⁺ (red). The excitation spectrum of these oxynitride/nitride phosphors covers a wide range from ultraviolet to visible light, enabling them to be used for white LEDs when an ultraviolet or blue LED chip is combined.     

透平式能量回收一体机水力特性数值分析

反渗透式海水淡化是目前工业化应用规模最大的海水淡化技术.反渗透式海水淡化装置工作时,反渗透膜的工作压力约为6 MPa,淡化过程持续供给高压原海水所需的能耗较大;淡化后的浓海水仍维持高压状态,蕴含大量余压能,透平式能量回收一体机将此余压能驱动泵侧加压供水侧,可大幅降低反渗透海水淡化装置的运行能耗.本文以三沙岛海水淡化装置...     

基于锁相环技术的直流机调速与调速系统模拟

介绍了锁相环技术用于直流电动机（动模发电机的原动机）调速与调速系统模拟的方法及其相关技术,即同步相位的选择方法以及转速的开环调节与闭环比例积分调节的无扰切换。并且给出了水轮机调速系统的阶跃响应和正弦响应实验结果。实验结果表明该系统结构简单、灵活,转速调节平稳,完善了动模水轮机或汽轮机调速系统的动态模拟,为在调速系统研究发电机的稳定控制方法奠定了良好的基础。     

Analytical calculation of the extraction efficiency of microcavitylight-emitting diodes for display and fiber coupling applications

This paper presents a simple analytical expression of the extraction efficiency for planar dielectric microcavity light-emitting diodes (MCLEDs) based on two distributed Bragg reflectors (DBRs). The calculations take into account the optical properties of the resonator (reflectivities and index contrast of the DBRs, cavity length, refractive index of the outside medium), as well as the spectral properties of the active material. The analytical results are compared to exact numerical calculations based on the plane wave expansion method and show good agreement. Simple design rules for optimizing the extraction efficiency of MCLEDs are proposed and discussed for display and fiber coupling applications. The limits of MCLEDs are finally investigated and compared to those of conventional light-emitting diodes     

基于MPPT算法的温差发电回收效率研究

针对目前汽车尾气温差发电效率低的问题,通过搭建温差发电实验平台获取温差发电模型,验证最大功率点追踪(MPPT)算法的可行性.分析热电片的开路电压与温差的工作特性,并绘制负载特性曲线,结合改进的二分梯度MPPT控制算法,以提高温差发电回收效率.通过Matlab/Simulink仿真结果表明:相比于传统开路电压法(OCV)...     

Integrated GaInAsP laser diodes with monitoring photodiodes throughsemiconductor/air Bragg reflector (SABAR)

A 1.3-μm GaInAsP laser diode (LD) is integrated with a monitoring photodiode (M-PD) through a semiconductor/air Bragg reflector (SABAR). Instead of conventional cleavage, the SABAR can provide not only Fabry-Perot resonance with high reflectivity, but also possibility of integration of laser with other functional devices. The design, fabrication, and some characteristics including threshold current, monitoring photocurrent, SABAR reflectivity as a function of the number of semiconductor/air pairs N are reported. The threshold current of ridge waveguide laser with SABAR (cavity length L=160 μm, ridge width W=7 μm, SABAR pairs N=3) is 20 mA. The threshold current is reduced by improving butt-coupled interface between active and passive waveguides employed in this laser and is expected 2 mA/μm. The monitoring photocurrent responds linearly with output power from the laser and 0.024 mA at laser output power of 5 mW. From the threshold characteristics, SABAR reflectivity is determined to >80%. The increase of photocurrent can be achieved by optimizing the number of SABAR pairs to N=1. We have obtained threshold current of 22 mA in the followed laser structure (L=270 μm, W=7 μm, N=1), and detector photocurrent of 1.13 mA (@5 mW). The experimental SABAR reflectivity is ~50%, which is estimated by threshold characteristics and efficiency of light output power. The laser has a mode field converter section, resulting in narrow beam divergence 11° along vertical axis. This integrated laser is very promising candidate for coming optical module in low-power consumption and low-cost access network systems     

提高降压变换器轻载效率的改进型恒定导通时间控制方法

本文提出一种数字化控制方法,用以提高恒定导通时间控制Buck变换器的轻载效率.不同于传统恒定导通时间控制方法,所提方法通过增大恒定导通时间控制Buck变换器轻载状态时的导通时间,以进一步降低变换器开关损耗、提高轻载效率.此外,所提方法无需增加外部传感检测电路,可直接根据开关频率变化来判断电感电流过零点,使变换器工作在电...     

MODIFIED SLIDING MODE (MSM) VERSUS PI SPEED CONTROL OF A CURRENT-CONTROLLED FIELD-ORIENTED INDUCTION MOTOR DRIVE

ABSTRACT

This paper describes the dynamic performance of a new, modified sliding mode (MSM), speed control system for an existing current-controlled field-oriented induction motor drive with rather robust rotor flux estimator.

Extensive digital simulations and some test results prove the superiority of IBM versus PI in terms of reduced speed overshooting, response quickness, and robustness to rotor resistance variation. The rotor flux estimator amplitude and phase error during severe transients has also been investigated through digital simulations.     

一种改进的RCM方法--精简型RCM(SRCM)

以可靠性为中心的维修(RCM)因其先进性和实用性正得到广泛的应用,但其复杂冗长的分析过程又妨碍了它的推广和取得更好的经济效益。为此,精简型RCM(SRCM)对RCM作了简化和改进,使之更适宜于电力系统。现介绍SRCM产生的背景和特点,描述SRCM的主要流程,并比较SRCM与经典RCM的联系与区别,从中可以看出SRCM的独特之处和价值所在。     

一种改进的直接转矩控制方案研究

针对异步电动机直接转矩控制系统低速性能差的问题,提出了两项改进措施。首先在磁通观测器中增加定子电阻压降补偿,以此来修正定子磁通模型;其次采用三点式转矩调节器来优化空间电压矢量的选择;最后采用TMS320C31评估板对上述方案进行了实验验证。     

改进GM(1,1)模型在电力负荷预测中的应用

灰色预测技术原理简单、样本量小、计算简便,适合用于负荷预测,但其存在很多局限性。从建模原理出发,利用最小二乘法和积分法,改进影响模型精度最重要的两个因素——初始值和背景值。以北京市1999—2005年的电力消费量数据加以计算,证明改进效果较为显著。     

Improvement in the volume efficiency of multilayered ceramic capacitors (MLCCs)

An attempt was made to improve the conventional lamination process in the multilayered ceramic capacitors (MLCCs) fabrication by adapting a solvent treatment on the BaTiO₃ green sheets. During the lamination process, additional particle rearrangement in the BaTiO₃ green block was stimulated by solvent treatment. This rearrangement resulted in a more compact structure of the BaTiO₃ green sheets compared to that obtained through the conventional lamination process. The overall thickness of BaTiO₃/Ni/BaTiO₃ laminates was also reduced after solvent treatment. It is suggested that miniaturization in the fabrication of MLCCs can be improved by adapting a solvent treatment during the lamination process.     

晶闸管换流阀反向恢复特性建模及阻容参数优化设计

晶闸管换流阀作为特高压直流输电的核心设备,其阻容参数设计关系到换流阀的性能乃至整个直流输电工程的安全可靠。基于晶闸管反向恢复电流的指数衰减模型,建立了换流阀关断时刻的数学模型,求解出晶闸管换流阀的反向恢复电压计算公式,总结出阻容参数对反向恢复电压过冲的影响规律。同时考虑关断时刻电压下降率、开通时刻电流上升率以及阻尼损耗等性能指标的限制,提出一种换流阀阻容参数的优化设计方法。在PSCAD/EMTDC中搭建12脉动换流器模型,对阻容参数的优化设计结果进行了仿真验证。     

N位取代聚苯并咪唑酰亚胺薄膜:改善的溶解性与透过率

试验合成了两种新型的N-苯基取代苯并咪唑二胺,区别在于N-苯基的邻位分别由甲基和氟原子取代.将新型二胺分别与二酐4,4′-(六氟异丙烯)二酞酸酐(6FDA)和4,4′-氧双邻苯二甲酸酐(ODPA)通过两步热亚胺法制备聚苯并咪唑酰亚胺(PBII)薄膜,并对新型二胺单体及PBII薄膜进行了性能测试与表征.结果表明:新型PBII薄膜表现出良好的耐热性(玻璃化转变温度Tg=341～381℃)和拉伸强度(σ=95～135 MPa).不同邻位取代的N-苯基破坏了分子的有效堆积,使得PBII薄膜的溶解性和光学透明性得到改善.     

Skills shortages threaten recovery (analysis) [Briefing in Depth]

The recession has hit job vacancies, but several reports show that we still need to nurture engineering skills.     

Investigation of the nonlinearity properties of the DC I-V characteristics of metal-insulator-metal (MIM) tunnel diodes with double-layer insulators

The DC I-V characteristics of metal-insulator-metal (MIM) tunnel diodes with double insulator layer is investigated by means of computer simulations. Simulation results on the properties of the diode characteristics such as resistance and quality factor are presented in various diagrams and the dependences on the different diode parameters are discussed. The simulations algorithm applied is also described in brief.