氧化铋掺杂制备SnO2棒状晶粒气敏材料的研究

探讨了氧化铋掺杂的SnO2纳米棒状晶粒气敏材料的制备,并测试了材料的气敏特性。氧化铋在高温形成液相,促进SnO2棒状晶粒的形成,同时氧化铋作为气敏材料的添加剂提高了对乙醇等气体的灵敏度。结果表明,采用液相沉淀法制备纳米粉体,在Bi添加量为10mol%,850℃保温2h的烧结条件下,得到的SnO2棒状晶粒直径约50nm,线径比为5,且较为均一。粉体经过稀硝酸溶液浸泡,其晶粒形貌及相结构不变,酸洗处理后的棒晶粉体制备的气敏元件,电阻值适中,对气体灵敏度提高。对乙醇、丙酮、汽油、苯和氨气的测试说明,氧化铋掺杂的SnO2棒状晶粒作为气敏材料,在不同温区对乙醇和丙酮的灵敏度较高,而且工作温度较低,对汽油、苯和氨气等气体有较好的选择性。     

半导体气敏元件在水果保鲜中的应用研究

以溶胶-凝胶法制备SnO_2和In_2O_3纳米晶粉体,以沉淀法制备WO_3粉体材料.经过掺杂及表面修饰技术研制出对低浓度乙烯、乙醇、H_2S有较高灵敏度、较好选择性和较快响应恢复特性的旁热式管式元件.用制得的三种元件对草莓和香蕉的存储过程进行测试,发现在水果存储过程中,各种气体在不同阶段释放的量是不同的,为水果的成熟度测试仪器的研究创造了条件.     

Y沸石改善SnO2气体传感器性能的研究

为了改善气体传感器的敏感性能,分别采用SnO2外涂Y沸石的涂覆法和Y沸石与SnO2混合法,用Y沸石对SnO2气体传感器进行改性.用X-射线衍射(XRD)、电子扫描显微镜(SEM)对混合法制备的Y沸石/SnO2复合材料的结构和表面进行了表征与分析.将这两类敏感元件进行了VOC气体的气敏测试.结果表明,与纯SnO2相比,Y沸石与SnO2直接混合的复合材料提高了对丙酮的响应值,而对其他气体响应值基本不变;涂覆法制备的气敏元件不仅提高对丙酮的响应值,而且减小了对乙醇的响应值,对乙醇起到一定抑制作用.初步分析了Y沸石对SnO2气敏特性改善的机理.     

水溶性聚苯胺/Sm0.5Ba0.5Cu0.8Cr0.2O3+δ材料的制备与氨敏性能研究

采用化学氧化法制备了水溶性聚苯胺(PANI),用溶胶凝胶法制备了Sm0.5Ba0.5Cu1-yCryO3+δ(y=0,0.1,0.2,0.3,0.4,0.5, 0.6)(SBCC)粉体,用微粒填充法制备了PANI/SBCC复合材料.利用XRD、EDS、FT-IR、TEM多种手段对产物进行表征,研究其在较低工作温度下(60℃)对氨气的敏感性.结果表明,在同等条件下,在PANI元件、SBCC元件及PANI/SBCC元件中,PANI/Sm0.5Ba0.5Cu0.8Cr0.2O3+δ(PANI/SBC80C20)元件对NH3的气敏性能最优,对体积分数为100×10-6 NH3的灵敏度在60℃条件下达到最大值为3.79,且响应恢复时间短,还具有较好的选择性.     

氨气检测的聚苯胺碳纳米管复合敏感膜的研究与应用

本文介绍了基于聚苯胺及多壁碳纳米管复合材料的氨气传感器的制备与测试,使用原位聚合法使苯胺单体以碳纳米管为核心进行聚合反应,运用介电泳法制备得聚苯胺/多壁碳纳米管气敏复合膜传感器。该传感器对10×10-6氨气的响应灵敏度为3.4,响应时间15 s,而对比实验中聚苯胺膜传感器的灵敏度为1.9。实验结果表明,由于碳纳米管在介电泳过程中构建的大比表面积纳米三维结构和优良的导电率,纳米复合材料的微观结构和导电性能都得到大幅改善,从而使得复合物具有相对于纯聚苯胺膜更好的气敏特性。     

发明与专利

一种基于二维MXene/SnO异质结的氨气气体传感器、制备工艺及应用【摘要】本发明提供了一种基于二维MXene/SnO2异质结的氨气气体传感器、制备工艺及应用,属于纳米材料技术领域。该氨气气体传感器主要由气敏材料和加热基板组成,工作温度为室温。     

一种新型石英晶振微天平水果气体传感器研究

为监测水果在仓储、运输等过程中的新鲜程度,研制了一种石英晶振微天平（QCM）气体传感器。以基频6 MHz的石英晶体为基片,运用一步原位聚合法在其上沉积了对甲苯磺酸（TSA）掺杂聚苯胺气敏薄膜,制作出QCM水果气体传感器。搭建了测试平台,设计了相应的起振、整形、差频、频压转换及数据采集电路。在室温下,测试了该传感器对放置不同天数的苹果释放气体的敏感特性。实验结果表明,在一定范围内,TSA掺杂浓度增加会改善传感器的气敏性能。传感器对放置不同天数的苹果释放气具有不同的响应特性,且具有灵敏度高、线性度好、响应速度快、重复性好等优点,有望在水果仓储运输方面得以应用。     

磁控溅射纳米SnO_2薄膜的气敏特性

采用磁控溅射制备SnO2薄膜气敏元件,测试了气敏元件的性能,研究了SnO2薄膜气敏元件薄膜厚度、元件加热功率和环境温度和湿度对元件的影响,气敏元件具有很好的灵敏度和选择性特性,对其敏感机理进行了探讨。     

基于SnO2/石墨烯异质结NO2气敏传感器

采用滴涂法和真空退火将纳米二氧化锡负载在单层石墨烯上,制备了SnO2/石墨烯异质结材料,进行拉曼光谱材料表征,研究了SnO2/石墨烯异质结对NO2的气敏特性。结果表明,SnO2/石墨烯异质结相对本征石墨烯在低NO2气体体积分数下灵敏度提升,解吸附时间短,NO2气体体积分数为10×10-6时,0.3mg/mlSnO2纳米溶液/石墨烯异质结传感器比单层石墨烯灵敏度提升近4倍,解吸附时间缩短近9倍。     

立方锡酸镁/氧化锡复合氧化物的合成及其气敏性能

采用水热法制备MgSn(OH)6前驱体,经过高温煅烧得到了Mg2SnO4/SnO2复合氧化物立方纳米颗粒。采用XRD、SEM、EDS对煅烧前后样品的物相、形貌、组分进行了表征。在不同温度下测试了Mg2SnO4/SnO2复合氧化物气敏元件对甲醇气体的敏感性能。结果表明,该复合氧化物对甲醇气体具有良好的灵敏度和选择性。在最佳工作温度为300℃时对50×10-6~5 000×10-6浓度范围内的甲醇气体具有良好的线性关系,2 000×10-6时气敏元件的响应、恢复时间分别为12 s和8 s。     

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).