中国科学院机构知识库网格系统: 检索

A Review on Vibration Control of Multiple Cylinders Subjected to Flow-Induced Vibrations 期刊论文 OAI收割
CHINA OCEAN ENGINEERING, 2024, 卷号: 38, 期号: 2, 页码: 183-197
作者: Xu, Wanhai; Ma YX(马烨璇)

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flow-induced vibration vibration control multiple cylinders tandem side-by-side staggered

Influence of high temperature annealing in nitrogen on upconversion luminescence of -NaYF4: Yb3+, Er3+ hexagonal sub-microplates (EI CONFERENCE) 会议论文 OAI收割
2012 International conference on Function Materials and Nanotechnology, FMN 2012, May 19, 2012 - May 20, 2012, Zhengzhou, China
作者: Zhao J.

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The pure -NaYF4: Yb3+ Er3+ hexagonal sub-microplates were successfully prepared by the combination of coprecipitation and hydrothermal methods using sodium citrate as chelator. The size of them is about 600 nm 400 nm (side length thickness). The obtained sample was divided into two parts and one of them was annealed in nitrogen at 300 C for 2 hours. The crystal structure of the -NaYF4: Yb3+ Er3+ hexagonal sub-microplates before and after annealing treatment is hexagonal phase. Under the excitation of 980 nm diode laser the upconversion luminescence intensity the sample after annealing is much stronger than that of the sample without annealing treatment. High temperature annealing process improved the crystallization of the sample resulting in the decrease of the nonradiative relaxation and the enhancement of the upconversion luminescence. (2012) Trans Tech Publications Switzerland.

A brushless DC motor controller with current-loop control (EI CONFERENCE) 会议论文 OAI收割
2nd Annual Conference on Electrical and Control Engineering, ICECE 2011, September 16, 2011 - September 18, 2011, Yichang, China
Gao S.

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This paper presents a brushless DC motor controller with current loop control. The controller applies a complementary PWM modulation scheme to the power MOSFET. The current processor employed by the controller could detect the current flow through the motor windings accurately and convert the current to a voltage input to the error amplifier. The controller has 100% duty cycle high side conduction capability and real four quadrant torque control capability. It is able to implement a tight torque control for a DC brushless motor to satisfy the need of some servo system which calls for high bandwidth and raid dynamic response. 2011 IEEE.

Computer simulation research on cognitive mechanism of human vision (EI CONFERENCE) 会议论文 OAI收割
International Conference on Measuring Technology and Mechatronics Automation, ICMTMA 2010, March 13, 2010 - March 14, 2010, Changsha, China
Ke H.; You W.

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The development of intelligent system which accorded with human cognitive mechanism will exert a profound influence on national defense economy education culture and etc. A computer simulation method according with cognitive mechanism of human vision was proposed on the basis of Structural Decomposition Theory. Many basic shape feature information tables of similar object from different side can determine a kind of object uniquely. System weighted basic shape features in two different information tables by membership degree and then calculated similarity. The identifying object which had the maximum similarity with it in system was what we needed. The system used 83 pictures of 6 kinds of objects with different side for training and testing. The experiment results demonstrated task of basic shape extraction object recognition and others can be completed effectively with the method in paper. The method in paper can be a new attempt on computer simulation method according with cognitive mechanism of human vision from cognitive field. 2010 Crown Copyright.

Theoretical analysis of emission characteristics of second-order distributed feedback semiconductor lasers (EI CONFERENCE) 会议论文 OAI收割
Semiconductor Lasers and Applications IV, October 18, 2010 - October 19, 2010, Beijing, China
作者: Liu Y.; Liu Y.; Qin L.; Liu Y.; Wang L.

收藏 | 浏览/下载：31/0 | 提交时间：2013/03/25

Based on the modified coupled-wave theory the emission characteristics including threshold gain photon density distribution in the cavity and external differential quantum efficiency for second-order DFB lasers are investigated. Numerical simulation results show that for given device structure with wavelength of 1.55 m the feedback coupling coefficient and the surface radiation coupling coefficient of the second-order grating have great influence on the emission characteristics of the device. By choosing different duty cycles of the grating we can change the two coupling coefficients which affect the emission characteristics. For an overall consideration an optimal duty cycle of 0.43 is chosen. The optimized results show that the device works without degeneracy modes and spatial burning hole. Besides the side-mode suppress ratio (SMSR) and external differential quantum efficiency reach as high as 42 dB and 47% respectively. 2010 SPIE.

Modulation transfer function in seeker camera limits resulting from missile flutter caused by aerodynamic force (EI CONFERENCE) 会议论文 OAI收割
2010 2nd International Conference on Industrial Mechatronics and Automation, ICIMA 2010, May 30, 2010 - May 31, 2010, Wuhan, China
作者: Zhang X.; Zhang X.; Zhang X.

收藏 | 浏览/下载：29/0 | 提交时间：2013/03/25

The imaging quality of seeker in flight mode has been evaluated through analyzing the effects of missile flutter on optical modulation transfer function (MTF) of the optical system. Firstly the data of transverse vibration has been processed to eliminate the trend term caused by the trajectory then obtained the displacement with two times trapezoidal integration. For the side rotation the high frequency noise interference in the data has been filtered by using five-point moving average method. Took this model as the quivering rule between the object and the image and then analyzed the effects of the transverse vibration and the side rotation on imaging quality through MTF. By calculation the r.m.s value of the image motion caused by missile transverse vibration is 0.026mm and the side rotation angle is 0.0044 . Through the establishment of two modulation transfer functions (MTF) of image random vibration and linear vibration the results show that the image quality had declined and the effect of transverse vibration on image quality is obvious. Through improving the rigidity of the missile and selection of small focal length optical system and shorten the time of exposure can improve the imaging quality of the seeker. 2010 IEEE.

A high-accuracy parameter estimation algorithm for jointless Frequency-shift track circuit (EI CONFERENCE) 会议论文 OAI收割
ISECS International Colloquium on Computing, Communication, Control, and Management, CCCM 2008, August 3, 2008 - August 4, 2008, Guangzhou, China
作者: Zheng X.

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FSK (Frequency Shift keying) signal which has advantages of narrow-bandwidth strong anti-interference ability long transmission distance and so on is used in jointless Frequency-shift track circuit to send different kinds of control signals. However as FSK is non-linearly modulated parameter estimation with high accuracy is hard to realize. Based on the spectrum analysis complement with time-frequency distribution a highaccuracy FSK signal parameter estimation algorithm is put forward in this paper. According to the signal characteristics under-sampling and ZFFT are used to improve the accuracy of spectrum analysis and the base frequency resolution meets system requirement of 0.02Hz. Wigner-Ville distribution has an excellent time-frequency concentration while serious cross-term interference at the same time. Through the design of kernel function the cross-terms are almost suppressed and the upper/down side frequency resolution meets the system requirement of 0.2Hz. The effectivities of all the methods mentioned above have been proved by MATLAB simulation which pave a solid way for the development of high-accuracy FSK signal parameter estimation devices. 2008 IEEE.

Data preprocessing of the exterior field of vision assembling photogrammetric camera (EI CONFERENCE) 会议论文 OAI收割
3rd International Symposium on Advanced Optical Manufacturing and Testing Technologies: Optical Test and Measurement Technology and Equipment, July 8, 2007 - July 12, 2007, Chengdu, China
作者: Li J.; Li J.; Li J.; Liu J.; Liu J.

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Transmit array photogrammetric camera can obtain image which is high geometric fidelity and high photogrammetric quality. However the single chip array CCD image sensor camera can't meet the need of measuring precision and photogrammetric covering area. In order to obtain large numbers of information and extensive photogrammetric covering area we must increase field of vision angle and improve photogrammetric covering area. And all these objects can be realized by exterior field of vision assembling photogrammetric camera. Two side work must be done before images which obtained by exterior field of vision assembling photogrammetric camera be used in photogrammetry. First all assembling camera focal plane need be converted to a benchmark coordinate focal plane to realize camera digital assembling. Second images must be re-sampled and processing. Because of coordinate conversion two images from different assembling cameras can be established function relation which a pixel of image from a camera is corresponding to a pixel of another image from different camera. But through this conversion some pixels maybe extrusion together and other pixels separate on an image area. So interpolation direction finding(IDF) is used to obtain these pixels and realize image re-sampling. In this paper the structure of exterior field of vision assembling photogrammetric camera is analyzed and the coordinate conversion method of exterior field of vision assembling photogrammetric camera and image gray re-sampling method also can be discussed. All the works are based to data pretreatment of exterior vision assembling photogrammetric camera.

Excitonic properties of vertically aligned ZnO nanotubes under high-density excitation (EI CONFERENCE) 会议论文 OAI收割
Lu Y. M.; Liang H. W.; Shen D. Z.; Zhang Z. Z.; Zhang J. Y.; Zhao D. X.; Liu Y. C.; Fan X. W.

收藏 | 浏览/下载：16/0 | 提交时间：2013/03/25

In this paper highly oriented and vertically arranged ZnO nanotubes are prepared on Al2O3 (0 0 0 1) substrate without employing any metal catalysts by plasma-assisted molecular beam epitaxy. The photoluminescence (PL) spectra at room temperature are studied under high excitation densities. Under lower excitation density (60 kW/cm2) PL spectrum shows that one strong free exciton emission (FE) locates at 3.306 eV. As the excitation density increases up to 200 kW/cm2 a new emission peak (Pn) located at low-energy side of FE is attributed to the spontaneous emission due to an exciton-exciton (Ex-E x) scattering process from two ground state excitons where one exciton is recombined by emitting a photon and the other is scattered into the excited states of n=2 3 4.... Under excitation density of 300 kW/cm 2 the stimulated emission originating from Ex-E x scattering is obtained. When the excitation density is above 580 kW/cm2 the emission from electron-hole plasma is observed in low-energy side of the P band and indicates a typical superradiation recombination processes with increasing excitation density. 2006 Elsevier B.V. All rights reserved.

The full hemisphere integrating measurement of the reflectance of black cavity (EI CONFERENCE) 会议论文 OAI收割
ICO20: Illumination, Radiation, and Color Technologies, August 21, 2005 - August 26, 2005, Changchun, China
作者: Wang Y.; Yu B.; Wang Y.; Wang Y.; Wang Y.

收藏 | 浏览/下载：21/0 | 提交时间：2013/03/25

The conical black cavities are used in the Solar Irradiance Absolute Radiometers (SIARs) of the solar constant monitor aboard on the SZ spaceship and of the Solar Total Irradiance Monitor (STIM) aboard on sun-synchronous polar orbit weather satellites. A low reflectance measurement instrument which is used for making the integrating measurement on the reflectance of the conical black cavity in a high precision within the full hemisphere (include the entrance of the Ulbrichtsphere) has been constructed. The characteristic of the instrument is the employment of a semi-transparent mirror which is mounted in an inclination angle of 45 degrees in front of the entrance of the Ulbrichtsphere. The incident beam is reflected to the black cavity or white board by the semi-transparent mirror. A portion of those which is made diffused reflection through the black cavity or white board is measured by the detector located in the side face of the Ulbrichtsphere and the other portion which is reflected to the entrance is measured by the other detector after passing through the semi-transparent mirror and then being focused on by an ellipsoidal mirror. The two measurement data are added up to get the integrating reflectance within full hemisphere. The presentation and verification on the measurement result of the reflectance of the black cavity and its precision are described in this article. The absolute accuracy can reach 0.012%.