200 MW机组锅炉火焰图像检测系统

介绍了锅炉火焰图像检测系统硬件结构、系统功能和系统软件设计思想,根据火焰图像特征,提出了检测区域可变的火焰图像检测算法,不仅可以进行火焰检测,且具有故障诊断功能,提高了火焰检测的可靠性。系统进行了工业试验,取得了满意的结果。     

炉膛火焰检测与燃烧诊断

对炉膛火焰特征与火焰检测和诊断的关系进行了分析；对火焰检测的基本原理和方法以及燃烧诊断理论和技术进行了论述；并对目前火电厂燃煤锅炉应用的各种火焰检测器和燃烧诊断系统进行了分析比较，最后讨论了火焰检测和燃烧诊断技术的进一步研究方向。     

基于图像处理技术的火焰检测算法研究

针对传统火焰检测方法可靠性不高、准确性不够的问题。本文提出了一种基于图像处理的火焰检测算法,通过计算火焰图像相关区域像素的数值,来直接对火焰燃烧的＂有＂、＂无＂做出判别。根据火焰在正常燃烧下分为初燃烧区、完全燃烧区和燃尽区的特性,设计了相应区域的火焰检测算法,并给出了详细的检测流程。在实际环境下,对算法在燃烧器不同火焰燃烧状态下进行了验证。结果表明,所设计的的火检算法具有较高的可靠性和准确性,可以满足火焰检测的需要。     

锅炉火焰检测系统的改造

针对火焰检测装置故障率高,常发生"偷看""漏看",光线损坏频繁、更换难度大等问题,四平热电公司对350 MW机组的锅炉火焰检测系统进行改造,通过修改火焰检测探头的放大器放大倍数、门槛值等参数,使火焰检测灵敏度提高了将近5倍;优化安装在炉膛内部火焰检测器光纤套管的安装结构和连接方式,更有效地保护了光纤,并及时更换损坏的光纤,提高了火焰检测信号的可靠性和锅炉运行的经济安全性。     

电站锅炉火焰图像检测系统

为了有效、可靠地进行火焰检测,针对200MW机组锅炉设计了一套火焰图像检测系统.提出了一种火焰图像检测算法,由于算法的自适性和故障判断功能,解决了以往火焰检测装置的各种误报问题,提高了系统的可靠性.该系统同时还具有火焰监测和燃烧温度场偏移的初步诊断功能.在200MW机组锅炉进行了工业性试验,取得了满意的结果.     

单燃烧器火焰检测装置的开发

针对大型锅炉燃烧调整需要高灵敏度火焰检测装置的现象 ,根据煤粉燃烧特性和火焰的频谱分析原理 ,开发了单燃烧器火焰检测装置。通过在国产 410、670 t/ h锅炉上的试验 ,得到了单燃烧器火焰有别于背景火焰的频谱特性 ,经过对比分析认为该装置具有很高的检测灵敏度     

图像火焰检测系统特点及其应用

阐述了图像火焰检测系统的组成和特点,在性能上与常规火焰检测装置进行了对比分析,表明该图像火焰检测系统能够运用计算机数字图像处理技术对燃烧器火焰图像进行分析,监测锅炉内温度场和浓度场,判断火焰燃烧状态,使运行人员直接观察到火焰图像,掌握燃烧状况,及时对燃烧进行调整,提高燃烧稳定性和燃烧效率。     

图像火焰检测系统特点及其应用

阐述了图像火焰检测系统的组成和特点,在性能上与常规火焰检测装置进行了对比分析,表明该图像火焰检测系统能够运用计算机数字图像处理技术对燃烧器火焰图像进行分析,监测锅炉内温度场和浓度场,判断火焰燃烧状态,使运行人员直接观察到火焰图像,掌握燃烧状况,及时对燃烧进行调整,提高燃烧稳定性和燃烧效率.     

炉膛火焰与IDD -Ⅱ火检的原理、调试与维护

锅炉燃烧火焰的光学特性和火焰检测器件的原理特点决定了固体火焰检测器是按照火焰光强波动来区别煤／油火焰,判定着火区和火焰背景。     

基于火焰光能的炉膛火焰温度在线检测研究进展

炉膛火焰的温度场分布及燃烧状态对于窑炉安全经济运行具有极其重要的意义.近年来,以火焰光能为核心的火焰数字图像监测方法逐渐成为主流.本文从火焰的不同辐射光能入手,介绍了基于可见光能和红外光能两种不同的火焰温度检测方法,分析了误差来源,介绍了相关技术的最新进展,探讨了基于火焰光能的炉膛温度在线检测技术的发展方向.     

Clinical applications and techniques of echo-planar imaging

The ultrafast magnetic resonance imaging technique known as echo-planar imaging has undergone considerable technical improvements in recent years. It is currently being evaluated at only a few institutions worldwide. Although EPI, invented by P. Mansfield in 1977, is the oldest fast MRI technique, it is still not widely available on clinical scanners. Only 20–30 EPI scanners exist worldwide, compared to about 7000 conventional MRI scanners. The main reason why EPI has not emerged from the scientific prototype niche is its high demands on hardware and software. However, the time is now coming when EPI is entering the clinical stage. We describe the common EPI sequence types, show clinical results, and describe the contrast in the measured images.     

Fingerprinting for security

The authors describe how the biometric fingerprint scanning technology implemented in such scanners on the market today is adequate for the current tasks; but, for biometrics to become more widely accepted and implemented, improvement is necessary. They argue that fingerprint scanners need to be able to produce useful results under a wide range of situations. Scanning technology will remain a hot field for research until these problems are solved     

MEMS optical scanners for microscopes

Microelectromechanical systems (MEMS) optical scanners have been around for more than two decades. Various applications have been presented, but few of them have advanced to the commercial level to date due to the difficulties of combination of optics and MEMS devices. This paper presents our activities of investigating MEMS scanner applications related to microscopic imaging. First, we started with developing a millimeter-sized one-dimensional scanner for commercially available laser scanning microscope. This microscope with the MEMS scanner is now commercially available. In order to take advantage of the miniaturization capability of MEMS, the next step was to miniaturize the whole optics together with the scanners. Miniaturized confocal microscope with a two-dimensional (2-D) scanner has been developed, and its feasibility and key issues are clarified. Additionally, an alternative 2-D scanner capable of scanning wide angle has been prototyped and fundamental characterization showed a promising result. Throughout the study, feasibility of MEMS optical scanners for microscopes has been demonstrated.     

Diffraction grating scanners using polysilicon micromotors

This paper describes polysilicon micromotors with single and pyramidal diffraction grating elements fabricated on the polished surface of large-area rotors for optical scanning applications. While taking full advantage of planar processing, such scanners have high-quality scan profiles, good efficiency, meter working distances, and multiple out of plane beam diffraction orders. Chemical-mechanical polishing was used to reduce the 5-μm-thick polysilicon rotors' average surface roughness from 420 Å to below 17 Å, with less than 1500-Å film removal, improving the optical performance of the gratings as well as the definition, delineation, and side wall quality of the device features. Self-assembled monolayers (SAM) were found to improve the overall micromotor's dynamic performance. SAM-coated scanners could operate at voltages as low as 15 V and maximum operational speeds of 5200 rpm. The gratings were tested optically at 633-nm wavelength and were verified to have spatial periods of 1.80 and 3.86 μm, closely matching their design values. Stepping and continuous mode dynamic operation of the scanners was demonstrated with visible diffraction orders at meter distances away     

Subjective perception of safety in healthy individuals working with 7 T MRI scanners: a retrospective multicenter survey

Objective

To retrospectively assess perception of safety of healthy individuals working with human 7 Tesla (T) magnetic resonance imaging (MRI) scanners.

Materials and methods

A total of 66 healthy individuals with a mean age of 31 ± 7 years participated in this retrospective multicentre survey study. Nonparametric correlation analysis was conducted to evaluate the relation between self-reported perception of safety and prevalence of sensory effects while working with 7 T MRI scanners for an average 47 months.

Results

The results indicated that 98.5 % of the study participants had a neutral or positive feeling about safety aspects at 7 T MRI scanners. 45.5 % reported that they feel very safe and none of the participants stated that they feel moderately or very unsafe while working with 7 T MRI scanners. Perception of safety was not affected by the number of hours per week spent in the vicinity of the 7 T MRI scanner or the duration of experience with 7 T MRI. More than 50 % of individuals experienced vertigo and metallic taste while working with 7 T MRI scanners. However, participants’ perceptions of safety were not affected by the prevalence of MR-related symptoms.

Conclusions

The overall data indicated an average perception of a moderately safe work environment. To our knowledge, this study delineates the first attempt to assess the subjective safety perception among 7 T MRI workers and suggests further investigations are indicated.

     

A Large-Area High-Reflectivity Broadband Monolithic Single-Crystal-Silicon Photonic Crystal Mirror MEMS Scanner With Low Dependence on Incident Angle and Polarization

In this paper, we introduce a single-axis resonant combdrive microelectromechanical systems (MEMS) scanner with a large-area highly reflective broadband monolithic single-crystal-silicon (SCS) photonic crystal (PC) mirror. PC mirrors can be made from a single monolithic piece of silicon through alternate steps of etching and oxidation. This process allows the fabrication of a stress-free PC reflector in SCS with better optical flatness than deposited films such as polysilicon slabs on low-index oxide. PC mirrors can be made in IR transparent dielectric material and can achieve high reflectivity over a broad wavelength range. PC reflectors have several advantages over other mirror technologies. They can tolerate much higher processing temperatures and higher incident optical powers as well as operate in more corrosive environments than metals. Compared to multilayer dielectric stacks, PC mirrors allow for simpler process integration, thus making them highly compatible with CMOS and MEMS processing. In this paper, we fabricate a PC mirror MEMS scanner in SCS without any deposited films. Our PC mirrors show broadband high reflectivity in the wavelength range from 1550 to 1600 nm, and very low angular and polarization dependence over this same range. The single-axis MEMS scanners are fabricated on silicon-on-insulator (SOI) wafers with the PC mirrors also fabricated in the SOI device layer. The scanners are actuated by electrostatic comb drives on resonance. Dynamic deflection measurements show that the scanners achieve 22deg total scan angle with an input square wave of 67 V and have a resonance frequency of 2.13 kHz.     

Comparison between different implementations of the 3D FLASH sequence for knee cartilage quantification

Objective

To compare several sequence implementations of the 3D FLASH sequence in the context of quantitative cartilage imaging.

Materials and methods

Test–retest coronal fast low angle shot (FLASH) sequences with water excitation were acquired in knees of 12 healthy participants, using two 1.5?T scanners from the same manufacturer. On one of the scanners, the FLASH was additionally compared with a FLASH VIBE, 75% with 100% slice resolution, a non-selective with a conventional spatial pulse, and “asymmetric echo allowed” with “not allowed”.

Results

Implementations of the FLASH showed systematic differences of up to 3.3%, but these were not statistically significant. Precision errors were similar between protocols, but tended to be smallest for the FLASH VIBE with 100% slice resolution (0.6–6.7%). In the medial tibia cartilage volume and thickness differed significantly (P?Conclusion Using a validated FLASH sequence, one can reduce slice resolution to 75% and allow asymmetric echo without sacrificing precision, in order to reduce the total acquisition time. However, in longitudinal studies, the scanner and the specific sequence implementation should be kept constant between baseline and follow-up, in order to avoid systematic off-sets in the measurements.     

Introduction to the Issue on Nanophotonics and Optical MEMS

This is an introduction to the papers that were included in this special issue. The papers cover the topics in: optical scanners and mirrors; adaptive and tunable optics; nanoscale resources and emission; optical sensors and biochemical sensors; plasmonics; and optical MEMS.     

A comprehensive experimental study of micro-perforated panel acoustic absorbers in MRI scanners

Object  

A comprehensive experimental study has been conducted to investigate the possibilities of using micro-perforated panel (MPP) acoustic absorbers in magnetic resonance imaging (MRI) scanners.     

Advances in nuclear emission PET and SPECT imaging

Improvements in technology and methods have resulted in a field that is ready to unlock the body's secrets. The advancements reviewed in this article are remarkable. Just ten years ago, SPECT myocardial tomograms exhibited a spatial resolution of close to 2 cm and PET scanners were prohibitively expensive. The instrumentation reviewed can image down to a 1.8 mm spatial resolution, and high-performance PET scanners and PET/SPECT cameras are being routinely sold for one-third the cost of the high-end PET scanners of ten years ago. These gains, coupled with the relative ease of developing positron-emitting radiopharmaceuticals, opens a new chapter in physiologic imaging. Add to this that these modalities are inherently digital, facilitating their progress in totally automatic analysis; multidimensional, multimodality display; and computer-assisted image interpretation by the use of AI techniques. The result is a field poised to unlock the secrets of the body's functions, when the only limitation is one's own imagination and the number of scientists working to bring it to its full potential