Pub Date : 1999-10-17DOI: 10.1109/ULTSYM.1999.849389
H. Engan, A. Rønnekleiv
Many different types of the SAW laser probe have been used for several years to characterize SAW devices as well as inherent properties of particular materials. Our laser probe is of a modified knife-edge type. Operating with a linear response, it has a high dynamic range. The probe provides full phasor information of the detected signal, and directional properties of the detection process makes it possible to determine the surface tilt components in two spatially orthogonal directions. We first sum up the basic characteristics of the probe. We show several examples where we take advantage of these features combined with signal processing techniques such as the fast Fourier transform. This enables us to concentrate on distinct properties of the devices under test. We thus exploit the spatial frequency domain and, in the basic detection process, the directions of the wavecrests, to enhance measurements of particular properties. Examples include results obtained from measurements on a selection of components containing various structures.
{"title":"Enhancement of SAW laser probe measurements by signal processing","authors":"H. Engan, A. Rønnekleiv","doi":"10.1109/ULTSYM.1999.849389","DOIUrl":"https://doi.org/10.1109/ULTSYM.1999.849389","url":null,"abstract":"Many different types of the SAW laser probe have been used for several years to characterize SAW devices as well as inherent properties of particular materials. Our laser probe is of a modified knife-edge type. Operating with a linear response, it has a high dynamic range. The probe provides full phasor information of the detected signal, and directional properties of the detection process makes it possible to determine the surface tilt components in two spatially orthogonal directions. We first sum up the basic characteristics of the probe. We show several examples where we take advantage of these features combined with signal processing techniques such as the fast Fourier transform. This enables us to concentrate on distinct properties of the devices under test. We thus exploit the spatial frequency domain and, in the basic detection process, the directions of the wavecrests, to enhance measurements of particular properties. Examples include results obtained from measurements on a selection of components containing various structures.","PeriodicalId":339424,"journal":{"name":"1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027)","volume":"97 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132912619","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1999-10-17DOI: 10.1109/ULTSYM.1999.849470
S. Sathish, R. Martin
A high precision scanning acoustic microscope system to generate C-scan type velocity images of Rayleigh, surface skimming longitudinal (SSLW) and surface skimming shear waves (SSSW), has been developed. The acoustic microscope utilizes impulse excitation to separate in the time domain the direct reflected signal from the surface acoustic wave signals. Differences in the arrival times of these signals at two defocuses are used to compute the velocity and display a 2D x/y velocity in real time during the scan. A map of the Young's modulus of the material is generated using the velocity images. Examples of measurement on standard samples and Ti-6Al-4V alloys are presented.
{"title":"Development of a scan system for Rayleigh, shear and longitudinal wave velocity mapping","authors":"S. Sathish, R. Martin","doi":"10.1109/ULTSYM.1999.849470","DOIUrl":"https://doi.org/10.1109/ULTSYM.1999.849470","url":null,"abstract":"A high precision scanning acoustic microscope system to generate C-scan type velocity images of Rayleigh, surface skimming longitudinal (SSLW) and surface skimming shear waves (SSSW), has been developed. The acoustic microscope utilizes impulse excitation to separate in the time domain the direct reflected signal from the surface acoustic wave signals. Differences in the arrival times of these signals at two defocuses are used to compute the velocity and display a 2D x/y velocity in real time during the scan. A map of the Young's modulus of the material is generated using the velocity images. Examples of measurement on standard samples and Ti-6Al-4V alloys are presented.","PeriodicalId":339424,"journal":{"name":"1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027)","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133674932","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1999-10-17DOI: 10.1109/ULTSYM.1999.849473
V. V. Proklov, O. Byshevski-Konopko, V. N. Kurskii
The presentation considers properties of the acoustooptic (AO) digital matrix multipliers based on the algorithm of digital multiplication via an analog convolution (DMAC) in the spectrum domain. The calculations, of main working regimes of the planar Bragg cell on base of Ti-diffused waveguides on YX-LiNbO3 with so called collinear waves interaction have been performed. The possibility of very high bit rate capabilities in AO digital matrix-vector multiplications up to 1.5×1010 mult.-adds/sec with 16-bit accuracy, is theoretically predicted . There are firstly discovered facility of the spectral DMAC for operation in the floating point regime as well as advantages of the AO digital multiplier implementation for a some prospective telecommunication systems. The most significant features of the proposed AO multipliers have been verified experimentally.
{"title":"Advances in acoustooptic digital computations via analog convolution in spectrum domain","authors":"V. V. Proklov, O. Byshevski-Konopko, V. N. Kurskii","doi":"10.1109/ULTSYM.1999.849473","DOIUrl":"https://doi.org/10.1109/ULTSYM.1999.849473","url":null,"abstract":"The presentation considers properties of the acoustooptic (AO) digital matrix multipliers based on the algorithm of digital multiplication via an analog convolution (DMAC) in the spectrum domain. The calculations, of main working regimes of the planar Bragg cell on base of Ti-diffused waveguides on YX-LiNbO3 with so called collinear waves interaction have been performed. The possibility of very high bit rate capabilities in AO digital matrix-vector multiplications up to 1.5×1010 mult.-adds/sec with 16-bit accuracy, is theoretically predicted . There are firstly discovered facility of the spectral DMAC for operation in the floating point regime as well as advantages of the AO digital multiplier implementation for a some prospective telecommunication systems. The most significant features of the proposed AO multipliers have been verified experimentally.","PeriodicalId":339424,"journal":{"name":"1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027)","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132652630","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1999-10-17DOI: 10.1109/ULTSYM.1999.849399
S. Tomabechi, K. Wada, S. Saigusa, H. Matsuhashi, H. Nakase, K. Masu, K. Tsubouchi
We have developed aluminum nitride (AlN) epitaxial growth technology using Knudsen pressure MOCVD method. The thickness uniformity was ±1%. However groove-like cracks were formed on the surface of the AlN epitaxial film. AlN deposition on off-angle substrates and the AlN deposition at high temperature have been investigated for eliminating the cracks on the surface. AlN deposition on an Al2O3 surface which is -4 degree off-angle from c'-axis has resulted in elimination of the cracks from the SEM (Scanning Electron Microscope) observations. The cracks in an AlN film deposited at a higher temperature of 1140°C/40mTorr are found to be completely eliminated on the whole 2"-φ wafer from SEM and laser-scan microscope observations. The propagation loss has been evaluated from the characteristics of time domain impulse response of 2.4 GHz matched filters fabricated on 2"-φ wafers. The propagation loss of crackless AlN films is drastically improved by one order compared with that of cracked AlN films.
{"title":"Development of high quality AlN epitaxial film for 2.4 GHz front-end SAW matched filter","authors":"S. Tomabechi, K. Wada, S. Saigusa, H. Matsuhashi, H. Nakase, K. Masu, K. Tsubouchi","doi":"10.1109/ULTSYM.1999.849399","DOIUrl":"https://doi.org/10.1109/ULTSYM.1999.849399","url":null,"abstract":"We have developed aluminum nitride (AlN) epitaxial growth technology using Knudsen pressure MOCVD method. The thickness uniformity was ±1%. However groove-like cracks were formed on the surface of the AlN epitaxial film. AlN deposition on off-angle substrates and the AlN deposition at high temperature have been investigated for eliminating the cracks on the surface. AlN deposition on an Al2O3 surface which is -4 degree off-angle from c'-axis has resulted in elimination of the cracks from the SEM (Scanning Electron Microscope) observations. The cracks in an AlN film deposited at a higher temperature of 1140°C/40mTorr are found to be completely eliminated on the whole 2\"-φ wafer from SEM and laser-scan microscope observations. The propagation loss has been evaluated from the characteristics of time domain impulse response of 2.4 GHz matched filters fabricated on 2\"-φ wafers. The propagation loss of crackless AlN films is drastically improved by one order compared with that of cracked AlN films.","PeriodicalId":339424,"journal":{"name":"1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027)","volume":"23 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115454698","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1999-10-17DOI: 10.1109/ULTSYM.1999.849390
K. Hirota, K. Nakamura
Conventional SAW grating waveguide analyses based on the scalar potential theory regard the phase velocity in the grating region as a constant. The velocity at the center frequency of the stop band was often used as a constant in those analyses. In reality, velocity dispersion is caused by the reflectivity of finger electrodes, and the velocity changes near the stop band. In this paper, a new approximate analytical model of SAW grating waveguides is proposed. This model includes the effect of the velocity dispersion, by placing a longitudinal component of wave number in such a way that it becomes a solution of the coupling-of-modes equations. To verify the adequacy of the model, 2-port resonators on 36.5°Y-X quartz and 45°X-Z Li2B4O7 are measured and compared with the computational results.
{"title":"Analysis of SAW grating waveguides considering velocity dispersion caused by reflectivity","authors":"K. Hirota, K. Nakamura","doi":"10.1109/ULTSYM.1999.849390","DOIUrl":"https://doi.org/10.1109/ULTSYM.1999.849390","url":null,"abstract":"Conventional SAW grating waveguide analyses based on the scalar potential theory regard the phase velocity in the grating region as a constant. The velocity at the center frequency of the stop band was often used as a constant in those analyses. In reality, velocity dispersion is caused by the reflectivity of finger electrodes, and the velocity changes near the stop band. In this paper, a new approximate analytical model of SAW grating waveguides is proposed. This model includes the effect of the velocity dispersion, by placing a longitudinal component of wave number in such a way that it becomes a solution of the coupling-of-modes equations. To verify the adequacy of the model, 2-port resonators on 36.5°Y-X quartz and 45°X-Z Li2B4O7 are measured and compared with the computational results.","PeriodicalId":339424,"journal":{"name":"1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027)","volume":"373 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115784867","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1999-10-17DOI: 10.1109/ULTSYM.1999.849213
T. Ritter, K. Shung, R. Tutwiler, T. Shrout
A fabrication method has been developed for composite linear arrays operating at a frequency of 30 MHz. The design features dual matching layers, a lens for focusing in the elevation direction, a 2-2 composite with 28 /spl mu/m wide ceramics and 5.3 /spl mu/m polymer widths, and coaxial cable for electrical impedance matching. Bandwidths exceeding 65% and crosstalk values less than -30 dB were measured on prototype arrays. A non-composite 35 MHz design has also been investigated. An interconnect method using a flex circuit and sputtered metal has been tested. Properties were then measured by fitting experimental impedance data to a model using a non-linear regression technique. A k/sub 33/' of 0.63 and an /spl epsiv//sub 33//sup S///spl epsiv//sub 0/ of 1310 were measured for array elements operating at 35 MHz.
{"title":"Medical imaging arrays for frequencies above 25 MHz","authors":"T. Ritter, K. Shung, R. Tutwiler, T. Shrout","doi":"10.1109/ULTSYM.1999.849213","DOIUrl":"https://doi.org/10.1109/ULTSYM.1999.849213","url":null,"abstract":"A fabrication method has been developed for composite linear arrays operating at a frequency of 30 MHz. The design features dual matching layers, a lens for focusing in the elevation direction, a 2-2 composite with 28 /spl mu/m wide ceramics and 5.3 /spl mu/m polymer widths, and coaxial cable for electrical impedance matching. Bandwidths exceeding 65% and crosstalk values less than -30 dB were measured on prototype arrays. A non-composite 35 MHz design has also been investigated. An interconnect method using a flex circuit and sputtered metal has been tested. Properties were then measured by fitting experimental impedance data to a model using a non-linear regression technique. A k/sub 33/' of 0.63 and an /spl epsiv//sub 33//sup S///spl epsiv//sub 0/ of 1310 were measured for array elements operating at 35 MHz.","PeriodicalId":339424,"journal":{"name":"1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027)","volume":"36 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124202188","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1999-10-17DOI: 10.1109/ULTSYM.1999.849288
P. Delachartre, E. Brusseau, F. Guérault, G. Finet, C. Cachard, D. Vray
A model has been developed for correcting geometric artifacts observed in intravascular ultrasound imaging during coronary artery stent implantation. Geometric artifacts occur when the position of the transducer inside the stent is off-centered and inclined. In coronary applications, the position of the catheter changes a lot due to the curved nature of the arteries. This gives images that do not correspond to the expected cross section of the stent and lead to ambiguous interpretation by physicians. The authors' work consists of estimating and correcting artifacts in all stent images where the catheter is positioned off-centered and not parallel with the vessel axis. Estimation is made using the analytical model of geometric artifacts which predicts positioning of the ultrasound catheter inside the stent (tilt angle, off centering in both directions x and y, azimuth angle). Correction consists in using the predicted values of artifacts to calculate the equivalent stent image seen by a centered and non-inclined catheter. The "corrected" image is then used to compute clinical parameters for quantitative analysis of stent implantation.
{"title":"Correction of geometric artifacts in intravascular ultrasound imaging during stent implantation","authors":"P. Delachartre, E. Brusseau, F. Guérault, G. Finet, C. Cachard, D. Vray","doi":"10.1109/ULTSYM.1999.849288","DOIUrl":"https://doi.org/10.1109/ULTSYM.1999.849288","url":null,"abstract":"A model has been developed for correcting geometric artifacts observed in intravascular ultrasound imaging during coronary artery stent implantation. Geometric artifacts occur when the position of the transducer inside the stent is off-centered and inclined. In coronary applications, the position of the catheter changes a lot due to the curved nature of the arteries. This gives images that do not correspond to the expected cross section of the stent and lead to ambiguous interpretation by physicians. The authors' work consists of estimating and correcting artifacts in all stent images where the catheter is positioned off-centered and not parallel with the vessel axis. Estimation is made using the analytical model of geometric artifacts which predicts positioning of the ultrasound catheter inside the stent (tilt angle, off centering in both directions x and y, azimuth angle). Correction consists in using the predicted values of artifacts to calculate the equivalent stent image seen by a centered and non-inclined catheter. The \"corrected\" image is then used to compute clinical parameters for quantitative analysis of stent implantation.","PeriodicalId":339424,"journal":{"name":"1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027)","volume":"268 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114476137","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1999-10-17DOI: 10.1109/ULTSYM.1999.849424
Dai Enguang, Wu Deming, Xu Anshi
A WDM/CDMA optical fiber communication system with asynchronous despreading technology employing surface acoustic wave MSK match filter is reported. Key devices were designed and fabricated. The system can be used as a signaling network to manage other networks and can be evolved into a multi-stage multiplexing system.
{"title":"A novel WDM-CDMA optical fiber communication system with asynchronous despreading technology","authors":"Dai Enguang, Wu Deming, Xu Anshi","doi":"10.1109/ULTSYM.1999.849424","DOIUrl":"https://doi.org/10.1109/ULTSYM.1999.849424","url":null,"abstract":"A WDM/CDMA optical fiber communication system with asynchronous despreading technology employing surface acoustic wave MSK match filter is reported. Key devices were designed and fabricated. The system can be used as a signaling network to manage other networks and can be evolved into a multi-stage multiplexing system.","PeriodicalId":339424,"journal":{"name":"1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027)","volume":"7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114896871","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1999-10-17DOI: 10.1109/ULTSYM.1999.849509
T. Pfeifer, M. Benz
The integration of metrology into the manufacturing process is becoming more and more important for production technology. The measurement directly on machine tools is especially improving manufacturing strategies. So far optical or tactile measuring systems are the state-of-the-art for dimensional measurements in process metrology. However, the wall thickness of structures with inner cavities can not be measured with these systems. Due to these deficits, an ultrasonic system has been integrated into the periphery of a machine tool. Both the extensive, multi-level signal processing of the acoustic echoes and the developed software tool “μ-sonic” are discussed in the paper. The aim of this presentation is to illustrate the potential of the ultrasonic in-line measurement. Finally, the practical realization for a lathe and initial results are presented.
{"title":"Multi-level signal processing for very precise ultrasonic measurement on machine tools","authors":"T. Pfeifer, M. Benz","doi":"10.1109/ULTSYM.1999.849509","DOIUrl":"https://doi.org/10.1109/ULTSYM.1999.849509","url":null,"abstract":"The integration of metrology into the manufacturing process is becoming more and more important for production technology. The measurement directly on machine tools is especially improving manufacturing strategies. So far optical or tactile measuring systems are the state-of-the-art for dimensional measurements in process metrology. However, the wall thickness of structures with inner cavities can not be measured with these systems. Due to these deficits, an ultrasonic system has been integrated into the periphery of a machine tool. Both the extensive, multi-level signal processing of the acoustic echoes and the developed software tool “μ-sonic” are discussed in the paper. The aim of this presentation is to illustrate the potential of the ultrasonic in-line measurement. Finally, the practical realization for a lathe and initial results are presented.","PeriodicalId":339424,"journal":{"name":"1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027)","volume":"30 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117040041","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1999-10-17DOI: 10.1109/ULTSYM.1999.849405
V. B. Chvets, P. G. Ivanov, V. M. Makarov, V. S. Orlov
Due to good temperature stability and moderately high electromechanical coupling coefficient langasite (Li3Ga5SiO4 or LGS) is known as a promising material for SAW devices. The characteristics of the Rayleigh wave propagation on LGS have been studied fairly well. However, no design of SAW devices on LGS suitable for modern communication systems has been reported as yet. In this paper, transversal filters on LGS based on bidirectional interdigital transducers, and low-loss filters on LGS based on natural single phase unidirectional transducers (NSPUDT), are described. The filters on LGS have exhibited better electrical parameters than their analogues on quartz and lithium tantalate.
{"title":"Design of SAW filters on langasite","authors":"V. B. Chvets, P. G. Ivanov, V. M. Makarov, V. S. Orlov","doi":"10.1109/ULTSYM.1999.849405","DOIUrl":"https://doi.org/10.1109/ULTSYM.1999.849405","url":null,"abstract":"Due to good temperature stability and moderately high electromechanical coupling coefficient langasite (Li3Ga5SiO4 or LGS) is known as a promising material for SAW devices. The characteristics of the Rayleigh wave propagation on LGS have been studied fairly well. However, no design of SAW devices on LGS suitable for modern communication systems has been reported as yet. In this paper, transversal filters on LGS based on bidirectional interdigital transducers, and low-loss filters on LGS based on natural single phase unidirectional transducers (NSPUDT), are described. The filters on LGS have exhibited better electrical parameters than their analogues on quartz and lithium tantalate.","PeriodicalId":339424,"journal":{"name":"1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027)","volume":"123 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117158410","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：