极低频磁场天线运动感应噪声研究

通过对极低频拖曳磁场天线运动感应噪声产生原理的研究,得出了潜艇磁场天线的运动感应噪声功率谱的表达式,探讨了减小运动感应噪声的方法,并与实验测得的噪声电压进行比较证实上述理论。     

超低频拖曳磁场天线磁致伸缩噪声分析

研究了海水中超低频拖曳磁场接收天线机械振动在地磁场中产生磁致伸缩噪声的机理,导出了计算磁场拖曳天线磁致伸缩噪声功率谱的理论公式,分析了天线灵敏度、电缆特性、地磁场等因素对磁致伸缩噪声的影响,并总结了降低磁场天线磁致伸缩噪声的四种有效方法.     

基于罚函数算法的感应式磁力仪优化设计

低等效磁场噪声、轻小型感应式磁力仪是空间、深地磁测等应用的必然要求。本文提出了一种在感应式磁力仪参数及等效磁场噪声、轻小化约束下，求解最优感应线圈匝数、线径参数配置的方法。文中首先建立了感应式磁力仪等效磁场噪声、重量指标数学模型，然后基于罚函数算法求解其数值解，从而得到感应线圈匝数、线径参数最优值。为验证理论分析结果，根据优化参数制作感应式磁力仪并进行指标测试，测试结果与理论设计相吻合，验证了基于罚函数算法求解感应式磁力仪最优参数的准确性。     

自制业余电台定向谐振天线

用于业余无线电的接收——发射天线,较多地采用大型的双极天线,其效果好。但架设天线占地大且不能随意移动。鞭状天线简单、轻便,但接收效果不好。单方面加长天线,尽管可以增大接收信号电平,但噪声同时也增大,因此,信噪比并未得到明显改善。众所周知,通常接收到的业余电台信号场强只有短波广播电台的千分之一甚至更弱。有时反而因加长天线感应了较多的噪波而淹没了有用的业余电台信号。用定向的     

125kHz赛鸽电子脚环感应踏板设计

使用交替扫描方式,以微控制器ATMEGA64为核心控制电子脚环感应踏板接收电路,实现了6格感应踏板错时接收电子脚环信息的设计方案。系统采用6片专用集成电路芯片HTRC11O驱动天线线圈产生磁场,利用HTRC110的接收通道接收电子脚环发射的编码信号。该编码信号经AT-MEGA64解码后得到电子脚环识别信息,识别信息最后通过串口输出到鸽钟。     

激励磁场对逆磁致伸缩索力传感器影响仿真

基于钢缆索索力传感理论模型和环式结构的索力传感器,对索力测量原理做了详细推导,传感器输出感应电压与激励磁场变化、加载外力变化、某一激励磁场下的材料磁导率及空气间隙尺寸等有关.重点分析了激励磁场变化对传感器输出的影响,分别在激励磁场为稳恒直流磁场、交流磁场、按矩形波规律变化磁场三种情况下对传感器输出进行了讨论和仿真分析.仿真结果表明,在稳恒磁场激励下,可通过感应积分电压求缓变外力,通过感应电压求得非缓变外力.在交流激励下.激励磁场频率对传感器输出有明显影响,频率越高,由激励磁场变化所引起的感应电压幅值越大.     

低噪声宽频带感应式磁传感器

感应式磁传感器是频率域电磁（FEM）法中使用最广泛的磁传感器,通常由感应线圈和前置放大器组成,其中前置放大电路是影响磁感应式磁传感器性能指标的核心因素。为了增加感应式磁传感器探测深度和微弱磁场信号的能力,要求前置放大电路具有宽频带、低噪声等性能。基于磁通负反馈的原理,设计并研制了斩波前置放大器,有效抑制了感应线圈的输出噪声,使感应线圈谐振频率两侧具有平坦的幅频特性曲线,拓宽了感应式传感器的响应频带。在屏蔽室内对感应式磁传感器的性能指标进行了测试,其频带范围为0.001Hz～10kHz,输入噪声为3.75nVHz（1/2）,为感应式磁传感器在实际中的应用提供了性能保障。     

多线圈磁电感应的逆压电式FBG磁场传感器

将光纤Bragg光栅(FBG)的传感检测技术、直流发电机内部结构的磁电感应原理及压电陶瓷的逆压电效应相结合,研制了一种多线圈磁电感应的逆压电式FBG磁场传感器.设计中采用多线圈磁电感应,输出电流的变化变小,测量均匀磁场的多线圈磁电感应的逆压电式FBG传感器的灵敏度和准确率都能显著提高.对设计的磁场传感器进行了正反行程的重复性测试,并进行对比分析.测试结果表明:该磁场传感器的灵敏度为0.1128 pm/Gs,迟滞为6.61％FS,重复性误差为6.29 ％FS.     

基于模糊卡尔曼滤波的四旋翼姿态估计方法

针对四旋翼在飞行中因运动加速度及磁场干扰等影响引起的姿态估计误差，提出一种基于动态估计的模糊扩展卡尔曼滤波姿态估计算法。该算法利用传感器数据对运动频率、运动加速度及磁场干扰的大小进行估计，对估计值模糊推理后，使用输出值调整卡尔曼滤波测量噪声方差和梯度下降步长，增加姿态估计算法的动态适应性。为验证所设计算法的估计效果，使用四旋翼仿真模型进行验证。实验结果表明，该算法能够有效地提高四旋翼在高机动、强干扰情况下姿态估计的姿态跟踪精度、动态性能、抗干扰能力。     

具有感应反馈环的超高频RFID标签天线设计

针对标签天线在RFID系统中的重要性,基于微带天线设计和电磁场散射理论,设计和分析了一种具有感应反馈环的超高频段RFID标签天线。天线的谐振频率为915 MHz,尺寸为78 mm×23 mm,天线显示近线性相位特性,在电压驻波比小于2的条件下,天线的阻抗带宽为100 MHz。可以通过调整感应反馈环的长度来调整天线的谐振频率,天线的增益为2.5 dBi左右。通过仿真和测量可知,这种天线能较好地满足RFID超高频段标签的要求。     

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).