检索结果-内蒙古大学图书馆

Ab initio investigation of barium-scandium-oxygen coatings on tungsten for electron emitting cathodes

Physical Review B 2010年第5期81卷 054207-054207页

作者： Vasilios Vlahos John H. Booske Dane Morgan Interdisciplinary Materials Science Program University of Wisconsin–Madison 1509 University Avenue Madison Wisconsin 53706 USA Department of Electrical and Computer Engineering University of Wisconsin–Madison 1415 Engineering Drive Madison Wisconsin 53706 USA Department of Materials Science and Engineering University of Wisconsin–Madison 1509 University Avenue Madison Wisconsin 53706 USA

Microwave, x-ray, and radio-frequency radiation sources require a cathode emitting electrons into vacuum. Thermionic B-type dispenser cathodes consist of BaxOz coatings on tungsten (W), where the surface coatings lower the W work function and enhance electron emission. The new and promising class of scandate cathodes modifies the B-type surface through inclusion of Sc, and their superior emissive properties are also believed to stem from the formation of a low work function surface alloy. In order to better understand these cathode systems, density-functional theory (DFT)-based ab initio modeling is used to explore the stability and work function of BaxScyOz on W(001) monolayer-type surface structures. It is demonstrated how surface depolarization effects can be calculated easily using ab initio calculations and fitted to an analytic depolarization equation. This approach enables the rapid extraction of the complete depolarization curve (work function versus coverage relation) from relatively few DFT calculations, useful for understanding and characterizing the emitting properties of novel cathode materials. It is generally believed that the B-type cathode has some concentration of Ba-O dimers on the W surface, although their structure is not known. Calculations suggest that tilted Ba-O dimers are the stable dimer surface configuration and can explain the observed work function reduction corresponding to various dimer coverages. Tilted Ba-O dimers represent a new surface coating structure not previously proposed for the activated B-type cathode. The thermodynamically stable phase of Ba and O on the W surface was identified to be the Ba0.25O configuration, possessing a significantly lower Φ value than any of the Ba-O dimer configurations investigated. The identification of a more stable Ba0.25O phase implies that if Ba-O dimers cover the surface of emitting B-type cathodes, then a nonequilibrium steady state must dominate the emitting surface. The identification of a

关键词：

来源：评论

学校读者我要写书评

暂无评论

Carbon nanostructures as thermal field emitters for waste heat recovery

引用

Diamond and Related Materials 2009年第2-3期18卷 563-566页

作者： Wong, Y.M. Kang, W.P. Davidson, J.L. Raina, S. Huang, J.H. Department of Electrical Engineering and Computer Science Vanderbilt University Nashville TN 37235 United States Interdisciplinary Program in Material Science Vanderbilt University Nashville TN 37235 United States Department of Materials Science and Engineering National Tsing Hua University Hsinchu 300 Taiwan

Traditional vacuum-based thermal energy conversion (VTEC) devices with "flat" metal emitters have been compromised by high working temperature mainly due to high work function and electron space charge effect. However, a VTEC system is inherently efficient due to unimpeded flow of electrons through vacuum and reduction of heat conduction by the vacuum medium. Consequently, VTEC devices are attractive in terms of space, weight and energy efficiency for waste heat recovery in a TEC system. Carbon nanostructured emitters including multiwalled carbon nanotubes (CNTs) and "ridge" nanodiamond thin films have shown relatively low threshold fields for electron field emission mainly due to their nanoscaled, high aspect ratio, emitting surfaces. In this study, the field-enhancing features of carbon nanostructures were investigated as thermal-field emitters for waste heat recovery. The turn-on field of CNTs was found to decrease from ~ 1.9V/μm at room temperature to ~ 0.9V/μm at 400°C. A high emission current of ~ 26μA was achieved at relatively low field of ~ 1.5V/μm and low temperature of 400°C. The maximum efficiency of the VTEC device is estimated to be ~ 15% at 300°C with a current density of 54mA/cm2. © 2008 Elsevier B.V.

关键词： Temperature

来源：评论

学校读者我要写书评

暂无评论

Effect of nitrogen concentration on nanodiamond film characteristics for electrode application

Effect of nitrogen concentration on nanodiamond film charact...

引用

作者： Raina, Supil LeQuan, X.C. Kang, W.P. Davidson, J.L. Interdisciplinary Program in Materials Science Vanderbilt University Nashville TN 37235 United States Department of Electrical Engineering and Computer Science Vanderbilt University Nashville TN 37235 United States

ISBN: (纸本)9781607681137

Microwave plasma chemical vapor deposition was used to fabricate nanodiamond films. Nitrogen incorporation was achieved by the introduction of N2 gas along with H2 and CH4 gases in the plasma. SEM studies revealed a change in the microstructure with increase in the N2 flow rate, transitioning from a 'ridge'-like surface morphology to a more 'cauliflower'-like structure. X-ray photoelectron spectroscopy (XPS) analysis showed a general decrease in the sp3 hybridized carbon content while the sp hybridized carbon content increased with N2 flow rate (up to 28.7%) after which it declines. Deconvolution of the C1s XPS spectra indicates incorporation of nitrogen and existence of carbon-nitrogen bonding. Raman spectroscopy shows diamond peak at 1332 cm-1 and the graphite peak, which increases in intensity and shifts towards lower wave number with increase in the N2 flow rate. A diffuse band at 1140 cm -1 indicates presence of a nanocrystalline phase in the films. ©The Electrochemical Society.

关键词： Nitrogen

来源：评论

学校读者我要写书评

暂无评论

Registration of finger vein image using skin surface information for authentication

Registration of finger vein image using skin surface informa...

引用

Image Processing: Machine Vision Applications II

作者： Noh, SeungWoo Kong, Hyoun-Joong Park, SangYun Kim, JiMan Lee, Seung-Rae Kim, Taejeong Kim, Hee Chan Interdisciplinary Program Bioengineering Major Graduate School Seoul National University Seoul Korea Republic of Interdisciplinary Program Biomedical Engineering Major Graduate School Seoul National University Seoul Korea Republic of Institute of Medical and Biological Engineering Medical Research Center Seoul National University Seoul Korea Republic of Department of Electrical Engineering and Computer Sciences Seoul National University Seoul Korea Republic of Department of Biomedical Engineering College of Medicine Seoul National University Seoul Korea Republic of

ISBN: (纸本)9780819475015

The finger vein image acquired with an acquisition system should be properly aligned to proceed with comparing algorithm. However it is not easy to find control the points since the images are naturally blurred with an inherent scattering property. To overcome this problem, we propose a novel finger vein registration method utilizing skin surface information (i.e. wrinkles and outlines). We assumed that finger crooking was insignificant. Images were sampled with intended translation and rotation. Each time, two images were acquired successively by switching the light source;one with infrared light and the other with white light. Degree of rotation and translation of sampled image were calculated using outline features in the white light image and then the infrared image was transformed according to the calculated data. To validate our method, correlation values were computed between identical subjects and different subjects. High correlation values were shown between identical subjects whereas low values were shown between different subjects. © 2009 SPIE.

关键词： Authentication

来源：评论

学校读者我要写书评

暂无评论

Indirect ophthalmoscopic stereo video system using three-dimensional LCD

Indirect ophthalmoscopic stereo video system using three-dim...

引用

Stereoscopic Displays and Applications XX

作者： Kong, Hyoun-Joong Seo, Jong Mo Hwang, Jeong Min Kim, Hee Chan Interdisciplinary Program Biomedical Engineering Major Graduate School Seoul National University Seoul Korea Republic of Department of Electrical Engineering and Computer Sciences Seoul National University Seoul Korea Republic of Department Ophthalmology College of Medicine Seoul National University Seoul Korea Republic of Department of Biomedical Engineering College of Medicine Seoul National University Seoul Korea Republic of

Binocular indirect ophthalmoscope (BIO) provides a wider view of fundus with stereopsis contrary to the direct one. Proposed system is composed of portable BIO and 3D viewing unit. The illumination unit of BIO utilized high flux LED as a light source, LED condensing lens cap for beam focusing, color filters and small lithium ion battery. In optics unit of BIO, beam splitter was used to distribute an examinee's fundus image both to examiner's eye and to CMOS camera module attached to device. Captured retinal video stream data from stereo camera modules were sent to PC through USB 2.0 connectivity. For 3D viewing, two video streams having parallax between them were aligned vertically and horizontally and made into side-by-side video stream for cross-eyed stereoscopy. And the data were converted into autostereoscopic video stream using vertical interlacing for stereoscopic LCD which has glass 3D filter attached to the front side of it. Our newly devised system presented the real-time 3-D view of fundus to assistants with less dizziness than cross-eyed stereoscopy. And the BIO showed good performance compared to conventional portable BIO (Spectra Plus, Keeler Limited, Windsor, UK). © 2009 SPIE-IS&T.

关键词： Stereo image processing

来源：评论

学校读者我要写书评

暂无评论

Non-contact finger vein acquisition system using NIR laser

Non-contact finger vein acquisition system using NIR laser

引用

Sensors, Cameras, and Systems for Industrial/Scientific Applications X

作者： Kim, Jiman Kong, Hyoun-Joong Park, Sangyun Noh, SeungWoo Lee, Seung-Rae Kim, Taejeong Kim, Hee Chan Interdisciplinary Program Graduate School Seoul National University Seoul Korea Republic of Department of Electrical Engineering and Computer Sciences Seoul National University Seoul Korea Republic of Department of Biomedical Engineering College of Medicine Seoul National University Seoul Korea Republic of Institute of Medical and Biological Engineering Medical Research Center Seoul National University Seoul Korea Republic of

Authentication using finger vein pattern has substantial advantage than other biometrics. Because human vein patterns are hidden inside the skin and tissue, it is hard to forge vein structure. But conventional system using NIR LED array has two drawbacks. First, direct contact with LED array raise sanitary problem. Second, because of discreteness of LEDs, non-uniform illumination exists. We propose non-contact finger vein acquisition system using NIR laser and Laser line generator lens. Laser line generator lens makes evenly distributed line laser from focused laser light. Line laser is aimed on the finger longitudinally. NIR camera was used for image acquisition. 200 index finger vein images from 20 candidates are collected. Same finger vein pattern extraction algorithm was used to evaluate two sets of images. Acquired images from proposed non-contact system do not show any non-uniform illumination in contrary with conventional system. Also results of matching are comparable to conventional system. We developed Non-contact finger vein acquisition system. It can prevent potential cross contamination of skin diseases. Also the system can produce uniformly illuminated images unlike conventional system. With the benefit of non-contact, proposed system shows almost equivalent performance compared with conventional system. © 2009 SPIE-IS&T.

关键词： Biometrics

来源：评论

学校读者我要写书评

暂无评论

Gratings on porous silicon structures for sensing applications

Gratings on porous silicon structures for sensing applicatio...

引用

Conference on Lasers and Electro-Optics, CLEO 2009

作者： Liscidini, M. Wei, X. Kang, C. Rong, G. Retterer, S.T. Patrini, M. Sipe, J.E. Weiss, S.M. Department of Physics University of Toronto 60 St. George St Toronto M5S 1A7 ON Canada Department of Electrical Engineering and Computer Science Vanderbilt University Nashville TN 37235 United States Interdisciplinary Graduate Program in Materials Science Vanderbilt University Nashville TN 37235 United States Center for Nanophase Materials Sciences Oak Ridge National Laboratory Oak Ridge TN 37831 United States CNISM and Dipartimento di Fisica 'A. Volta' Università degli Studi di Pavia via Bassi 6 27100 Pavia Italy

We investigate the use of gratings on porous silicon structures for sensing applications. Examples of two classes of systems are studied: grating-coupled waveguide biosensors, and diffraction-based biosensors. © ... 详细信息

ISBN: (纸本)9781557528698

关键词： Biosensors

来源：评论

学校读者我要写书评

暂无评论

Models for analyzing cognitive radio interference to wireless microphones in TV bands

Models for analyzing cognitive radio interference to wireles...

引用

2008 3rd IEEE Symposium on New Frontiers in Dynamic Spectrum Access Networks, DySPAN 2008

作者： Dhillon, Ramandeep S. Brown, Timothy X. Interdisciplinary Telecommunication Program Electrical and Computer Engineering Department University of Colorado Boulder CO 80309-0530 United States

ISBN: (纸本)9781424420179

TV bands are candidates for unlicensed spectrum access based on cognitive radio (CR) devices. However, for a successful dynamic spectrum access regime in TV bands, any new unlicensed devices need to ensure that they do not interfere with the incumbent devices such as TV receivers and wireless microphones in these bands. This paper presents models for carrying out interference analysis of CR devices to wireless microphones. The wireless microphone systems are more susceptible to interference by CR devices compared to TV receivers due to their lower power and use of randomly selected idle TV bands at a given location. We present two models for interference, a single interferer model that determines the unlicensed device characteristics needed to protect a wireless microphone system from interference, and a multiple interferers model that provides a measure of the maximum density of unlicensed devices that can operate in a given region without affecting wireless microphone systems. We further analyze the benefits of cooperative sensing among CR devices using the multiple interferers model. Lastly, we provide recommendations for reducing interference based on the two interference models. ©2008 IEEE.

关键词： Cognitive radio

来源：评论

学校读者我要写书评

暂无评论

Models for Analyzing Cognitive Radio Interference to Wireless Microphones in TV Bands

Models for Analyzing Cognitive Radio Interference to Wireles...

引用

IEEE International Symposium on New Frontiers in Dynamic Spectrum Access Networks, DySPAN

作者： Ramandeeep S. Dhillon Timothy X. Brown Interdisciplinary Telecommunication Program Electrical and Computer Engineering Department University of Colorado Boulder USA

TV bands are candidates for unlicensed spectrum access based on cognitive radio (CR) devices. However, for a successful dynamic spectrum access regime in TV bands, any new unlicensed devices need to ensure that they do not interfere with the incumbent devices such as TV receivers and wireless micro phones in these bands. This paper presents models for carrying out interference analysis of CR devices to wireless microphones. The wireless microphone systems are more susceptible to interference by CR devices compared to TV receivers due to their lower power and use of randomly selected idle TV bands at a given location. We present two models for interference, a single interferer model that determines the unlicensed device characteristics needed to protect a wireless microphone system from interference, and a multiple interferers model that provides a measure of the maximum density of unlicensed devices that can operate in a given region without affecting wireless microphone systems. We further analyze the benefits of cooperative sensing among CR devices using the multiple interferers model. Lastly, we provide recommendations for reducing interference based on the two interference models.

关键词： Wireless communication Microphones Chromium Interference Wireless sensor networks Receivers TV

来源：评论

学校读者我要写书评

暂无评论

Light scattering by white-emitting CdSe nanocrystals and traditional YAG:Ce3+ phosphor particles

Light scattering by white-emitting CdSe nanocrystals and tra...

引用

2008 MRS Fall Meeting

作者： Gosnell, Jonathan D. Weiss, Sharon M. Interdisciplinary Graduate Program in Materials Science Vanderbilt University Station B 350106 Nashville TN 37235 United States Department of Electrical Engineering and Computer Science Vanderbilt University Station B 351824 Nashville TN 37235 United States

ISBN: (纸本)9781615677740

In order for solid state lighting technology to become a mainstream technology, one of the major challenges to overcome is increasing the efficiency of these devices while maintaining a proper color balance. A significant source of efficiency loss in commercial phosphor-based white light-emitting diodes (LEDs) is light scattering off large, micron-sized phosphor particles. The use of recently reported single-size CdSe white-light nanocrystals in place of traditional phosphors, such as YAG:Ce3+, could lead to lower scattering losses and higher device efficiencies as a result of the extremely small CdSe core diameter of approximately 1.5 nm. This work theoretically and experimentally investigates the absorption, scattering, and extinction coefficients and cross sections of CdSe white-light nanocrystals in comparison to YAG:Ce3+ phosphor particles. Calculations were performed based on the Rayleigh approximation and Mie theory of scattering. Experiments were carried out using thin films of encapsulated nanocrystals. By measuring the absorbance and thickness of the films, in addition to the concentration of the nanocrystals, extinction coefficients and cross sections were determined using the Beer-Lambert law. A reasonable agreement was obtained between theoretical and experimental data showing that the size of the particle has a significant impact on the extinction, absorption, and scattering properties of thin films. The considerably reduced scattering from the nanocrystals compared to traditional phosphors, along with their inherent high quality white light emission, makes them a promising candidate for future solid state lighting applications. © 2009 Materials Research Society.

关键词： Cadmium compounds

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：