EMERSON推出高精度液体超声波流量计

艾默生过程控制于近日正式发布最新产品DanielTM3812液体超声波流量计。其具有计量可靠、维护简便、易于操作等特点,可广泛应用于石化、油品和水处理等行业。革命性的电子单元整合高级数字信号手段,使得DanielTM3812液体超声波流量计     

煤气计量仪表的分析

针对大管径、低流速、低压力煤气计量，在分析涡轮流量计、阿牛巴流量计、超声波流量计的测量原理、优缺点及运行情况基础上，说明了超声波流量计在煤气计量方面优势。结合工作实践，对超声波流量计在使用和调校过程中出现的问题提供了解决方法，超声波流量计在煤气计量方面得到成功应用。     

超声波流量计在高酸气田的应用

针对高含硫气田气相流量计应用现状,以及高级孔板阀存在计量偏差较大、五阀组解堵频繁、孔板清洗危险大及维护维修不便等缺点,介绍外夹式超声波流量计的优点及应用效果.     

DanielTM3818型高精度液体超声波流量计 艾默生过程控制有限公司

艾默生推出用于液化天然气高精度流量计量的DanielTM3818型液体超声波流量计。该流量计专为降低液化天然气流量计量的不确定度而设计,是海运及近海应用场合的理想选择,可用于贸易交接和财务结算计量、管线平衡、计量比对、分配计量以及轮船装卸等场合。利用DanielTM3818型液体超声波流量计对液化天然气进行动态流量计量可实现更高的精度,并且真正     

不理想条件下的水流量计量

采用以超声波液位计为核心的自动集、排气系统克服水气二相介质的影响；利用超声波流量计进行水中含有大量铁锈情况下的水流量计量；用插入式流量计进行不间断供水情况下的水流量计量。增加管衬克服管道锈蚀对计量的影响。     

超声波流量计在热工试验中的应用研究

超声波流量计因为其准确度高、维护成本低等优势在流量测量中广泛应用。但在使用过程中,由于管道条件和安装过程的不确定性,以及测量介质的温度压力等状态参数发生变化,都增大了流量测量误差。基于热工水力试验应用需求,提出了一种提高超声波流量计测量准确度的方法,并阐述了超声波流量计时差法的工作原理、现场校准方法和结果,最后进行了不确定评定。     

超声波流量计与孔板流量计的比较

本文通过大量详实的理论推导、可信的应用实例，经过技术性能、现场安装使用、长期使用、经济性几个方面的比较详细论述了超声波流量计与孔板流量计的优劣。提出高压、大流量计量优先选用超声波流量计的建议。     

提高超声波流量计量精度的方法

时差法超声波流量计通过检测换能器发射和接收的超声波信号的传播时间信号,实现流量的计量。超声波换能器的谐振频率及超声波信号传播过程中相位和幅值的变化等因素,会影响对超声波信号到达时间的准确计量,从而影响流量测量的精度。准确计量超声波信号的到达时刻是提升时差法超生波流量计的计量精度的关键之一。针对换能器发射和接收超声波信号的处理和获取电路进行了设计和分析,得出了实验结果和实验数据,对实验结果给出了实验分析和结论,并通过软件算法给出了进一步提高测量精度的方法。     

超声波流量计在能源数据采集上的应用

济钢在能源中心(EMCC)中采用了超声波流量计作为水计量仪表,对全厂的水资源进行测量采集,实现水的有效利用和实时监控、平衡,减少能源浪费.该流量计采用超声波时差法测量介质流量,具有精度高、可靠性高、智能化等特点,另外,价格低及不停产在线安装是其最大的优势.详细介绍了EMCC系统中流量计的选用原则、超声波流量计的工作特点、安装调试中遇到的问题和解决方法、超声波流量计与能源中心监控平台的数据通信等情况.     

液体超声波流量计在海上原油贸易计量中的应用

介绍超声波流量计的测量原理,以及FPSO贸易交接计量仪表选型过程。     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。     

How do children do mathematics with LOGO?

Abstract  This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development.     

Editorial: Special issue on recent advances in hybrid control theory and applications

正The demands of a rapidly advancing technology for faster and more accurate controllers have always had a strong influence on the progress of automatic control theory.In recent years control problems have been arising with increasing frequency in widely different areas,which cannot be addressed using conventional control techniques.The principal reason for this is the fact that a highly competitive economy is forcing systems to operate in regimes where     

Information for Authors

正Aim The Journals of Zhejiang University-SCIENCE(A/B/C)areedited by the international board of distinguished Chinese andforeign scientists,and are aimed to present the latest devel-opments and achievements in scientific research in China andoverseas to the world’s scientific circles,especially to stimulateand promote academic exchange between Chinese and for-eign scientists everywhere.     

Enhancing a leaf radiative transfer model to estimate concentrations and in vivo specific absorption coefficients of total carotenoids and chlorophylls a and b from single-needle reflectance and transmittance

The relative concentrations of different pigments within a leaf have significant physiological and spectral consequences. Photosynthesis, light use efficiency, mass and energy exchange, and stress response are dependent on relationships among an ensemble of pigments. This ensemble also determines the visible characteristics of a leaf, which can be measured remotely and used to quantify leaf biochemistry and structure. But current remote sensing approaches are limited in their ability to resolve individual pigments. This paper focuses on the incorporation of three pigments—chlorophyll a, chlorophyll b, and total carotenoids—into the LIBERTY leaf radiative transfer model to better understand relationships between leaf biochemical, biophysical, and spectral properties.Pinus ponderosa and Pinus jeffreyi needles were collected from three sites in the California Sierra Nevada. Hemispheric single-leaf visible reflectance and transmittance and concentrations of chlorophylls a and b and total carotenoids of fresh needles were measured. These data were input to the enhanced LIBERTY model to estimate optical and biochemical properties of pine needles. The enhanced model successfully estimated reflectance (RMSE = 0.0255, BIAS = 0.00477, RMS%E = 16.7%), had variable success estimating transmittance (RMSE = 0.0442, BIAS = 0.0294, RMS%E = 181%), and generated very good estimates of carotenoid concentrations (RMSE = 2.48 µg/cm², BIAS = 0.143 µg/cm², RMS%E = 20.4%), good estimates of chlorophyll a concentrations (RMSE = 10.7 µg/cm², BIAS = − 0.992 µg/cm², RMS%E = 21.1%), and fair estimates of chlorophyll b concentrations (RMSE = 7.49 µg/cm², BIAS = − 2.12 µg/cm², RMS%E = 43.7%). Overall root mean squared errors of reflectance, transmittance, and pigment concentration estimates were lower for the three-pigment model than for the single-pigment model. The algorithm to estimate three in vivo specific absorption coefficients is robust, although estimated values are distorted by inconsistencies in model biophysics. The capacity to invert the model from single-leaf reflectance and transmittance was added to the model so it could be coupled with vegetation canopy models to estimate canopy biochemistry from remotely sensed data.     

Mr. Twinn’s bombes

This article discusses the history and design of the special versions of the bombe key-finding machines used by Britain’s Government Code & Cypher School (GC&CS) during World War II to attack the Enigma traffic of the Abwehr (the German military intelligence service). These special bombes were based on the design of their more numerous counterparts used against the traffic of the German armed services, but differed from them in important ways that highlight the adaptability of the British bombe design, and the power and flexibility of the diagonal board. Also discussed are the changes in the Abwehr indicating system that drove the development of these machines, the ingenious ways in which they were used, and some related developments involving the bombes used by the U.S. Navy’s cryptanalytic unit (OP-20-G).