Pub Date : 2010-04-12DOI: 10.17764/JIET.53.1.167M8136U6514056
M. Paulus, K. Doughty
Many vibration screening programs have implemented the use of repetitive shock (RS) machines. Examination of the RS power spectral density (PSD) shows there are many high and low points throughout the frequency band. The effect of these sharp peaks and valleys on the time to failure of a test item was unknown. A simple cantilevered beam was subjected to several vibration profiles with peaks and valleys. It was determined that the peaks and valleys had a significant effect on the time to failure due to resonant shifting of the beam during crack propagation.
{"title":"Effect of Resonant Frequency Shifting on Time to Failure of a Cantilevered Beam under Vibration","authors":"M. Paulus, K. Doughty","doi":"10.17764/JIET.53.1.167M8136U6514056","DOIUrl":"https://doi.org/10.17764/JIET.53.1.167M8136U6514056","url":null,"abstract":"Many vibration screening programs have implemented the use of repetitive shock (RS) machines. Examination of the RS power spectral density (PSD) shows there are many high and low points throughout the frequency band. The effect of these sharp peaks and valleys on the time to failure of a test item was unknown. A simple cantilevered beam was subjected to several vibration profiles with peaks and valleys. It was determined that the peaks and valleys had a significant effect on the time to failure due to resonant shifting of the beam during crack propagation.","PeriodicalId":35935,"journal":{"name":"Journal of the IEST","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2010-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67804655","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 : 2010-04-12DOI: 10.17764/JIET.53.1.1469P84588023508
Charles E. Wright
Valid test data from explosively or ordnance-initiated pyrotechnic shock tests are difficult to acquire. Measurement of these frequency-rich acceleration time histories, a prerequisite to calculation of a valid shock response spectrum, drives the measurement system to its performance limits. Successful acquisition of demonstrably valid acceleration time histories requires a series of performance compromises that must be made with a depth of measurements expertise. Such expertise may not be available from vendors of the various data acquisition systems sold for these tests. All measurement system performance characteristics (transducer mount dynamics, gain, frequency response, phase response, linearity, lead wire effects, sampling rate, etc.) require compromise. It takes professional-level knowledge and experience to make the proper compromises to assure data validity for the measured wave shape. These measurements should never be taken for granted, as often and unfortunately happens.Data validation method...
{"title":"Effective Data Validation Methodology for Pyrotechnic Shock Testing","authors":"Charles E. Wright","doi":"10.17764/JIET.53.1.1469P84588023508","DOIUrl":"https://doi.org/10.17764/JIET.53.1.1469P84588023508","url":null,"abstract":"Valid test data from explosively or ordnance-initiated pyrotechnic shock tests are difficult to acquire. Measurement of these frequency-rich acceleration time histories, a prerequisite to calculation of a valid shock response spectrum, drives the measurement system to its performance limits. Successful acquisition of demonstrably valid acceleration time histories requires a series of performance compromises that must be made with a depth of measurements expertise. Such expertise may not be available from vendors of the various data acquisition systems sold for these tests. All measurement system performance characteristics (transducer mount dynamics, gain, frequency response, phase response, linearity, lead wire effects, sampling rate, etc.) require compromise. It takes professional-level knowledge and experience to make the proper compromises to assure data validity for the measured wave shape. These measurements should never be taken for granted, as often and unfortunately happens.Data validation method...","PeriodicalId":35935,"journal":{"name":"Journal of the IEST","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2010-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67804278","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 : 2010-04-12DOI: 10.17764/JIET.53.1.1TP80T7P057487N2
M. Hale, N. Fitz-Coy
This paper provides results of a laboratory experiment designed to illustrate the theoretical control considerations for an over-actuated excitation system. The experiment is based on control of a beam pinned at one end providing a single rotational degree of freedom and excited by two electrodynamic actuators. Control is achieved through implementation of two different control reference techniques: (1) reference based on linear acceleration autospectral densities (ASD) and cross-spectral densities (CSD) using linear accelerometer feedback and (2) reference based on an angular acceleration ASD using estimates of angular acceleration as feedback. Correlations to the theoretical based predictions were conducted based on common measurements of both linear acceleration and estimates of angular acceleration acquired during each trial.
{"title":"Control of an Over-Actuated Single-Degree-of-Freedom Excitation System","authors":"M. Hale, N. Fitz-Coy","doi":"10.17764/JIET.53.1.1TP80T7P057487N2","DOIUrl":"https://doi.org/10.17764/JIET.53.1.1TP80T7P057487N2","url":null,"abstract":"This paper provides results of a laboratory experiment designed to illustrate the theoretical control considerations for an over-actuated excitation system. The experiment is based on control of a beam pinned at one end providing a single rotational degree of freedom and excited by two electrodynamic actuators. Control is achieved through implementation of two different control reference techniques: (1) reference based on linear acceleration autospectral densities (ASD) and cross-spectral densities (CSD) using linear accelerometer feedback and (2) reference based on an angular acceleration ASD using estimates of angular acceleration as feedback. Correlations to the theoretical based predictions were conducted based on common measurements of both linear acceleration and estimates of angular acceleration acquired during each trial.","PeriodicalId":35935,"journal":{"name":"Journal of the IEST","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2010-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67805313","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 : 2009-10-24DOI: 10.17764/JIET.52.2.GH0444564N8765K1
D. Smallwood
Three methods are introduced for generating realizations of time histories with a specified auto-spectral density while controlling the kurtosis. One of the methods also allows the skewness to be specified. A second method allows large excursions (that produce large kurtosis) to be randomly distributed or almost periodic. In addition, the second method allows the average number of large excursions per unit of time to be specified. All the methods are variations of the inverse Welch method. The shape of the discrete Fourier magnitude is specified for a frame of data, thus controlling the shape of the auto-spectral density. The phase of the frame of data or the magnitude of the amplitude spectrum is modified to control the kurtosis or the skewness. The frames of data are multiplied by a window and overlapped and added to produce the realization.
{"title":"Vibration with Non-Gaussian Noise","authors":"D. Smallwood","doi":"10.17764/JIET.52.2.GH0444564N8765K1","DOIUrl":"https://doi.org/10.17764/JIET.52.2.GH0444564N8765K1","url":null,"abstract":"Three methods are introduced for generating realizations of time histories with a specified auto-spectral density while controlling the kurtosis. One of the methods also allows the skewness to be specified. A second method allows large excursions (that produce large kurtosis) to be randomly distributed or almost periodic. In addition, the second method allows the average number of large excursions per unit of time to be specified. All the methods are variations of the inverse Welch method. The shape of the discrete Fourier magnitude is specified for a frame of data, thus controlling the shape of the auto-spectral density. The phase of the frame of data or the magnitude of the amplitude spectrum is modified to control the kurtosis or the skewness. The frames of data are multiplied by a window and overlapped and added to produce the realization.","PeriodicalId":35935,"journal":{"name":"Journal of the IEST","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2009-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67804559","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 : 2009-10-24DOI: 10.17764/JIET.52.2.GT556421M5N65LTP
A. Mayne
There is a significant and continuing worldwide interest in large Reverberant Acoustic Test Facilities (RATFs) that subject spacecraft to the simulated acoustic field of a rocket launch. Established companies continue to upgrade their existing RATFs or build new ones. Companies and countries that are just entering the field of spacecraft development must eventually build new integration and test facilities, including RATFs. Acoustic test facilities are rarer than vibration test systems and less well understood in general. Even experienced users typically require assistance during the development of specifications for an upgrade or for a new RATF. This paper provides an overview of some important topics that should be included in the specification of a large RATF, based on the many facilities the author has worked with over the past 23 years. Specific recommendations for certain aspects of an RATF are also included.
{"title":"The Specification of Large Reverberant Acoustic Test Facilities","authors":"A. Mayne","doi":"10.17764/JIET.52.2.GT556421M5N65LTP","DOIUrl":"https://doi.org/10.17764/JIET.52.2.GT556421M5N65LTP","url":null,"abstract":"There is a significant and continuing worldwide interest in large Reverberant Acoustic Test Facilities (RATFs) that subject spacecraft to the simulated acoustic field of a rocket launch. Established companies continue to upgrade their existing RATFs or build new ones. Companies and countries that are just entering the field of spacecraft development must eventually build new integration and test facilities, including RATFs. Acoustic test facilities are rarer than vibration test systems and less well understood in general. Even experienced users typically require assistance during the development of specifications for an upgrade or for a new RATF. This paper provides an overview of some important topics that should be included in the specification of a large RATF, based on the many facilities the author has worked with over the past 23 years. Specific recommendations for certain aspects of an RATF are also included.","PeriodicalId":35935,"journal":{"name":"Journal of the IEST","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2009-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67804583","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 : 2009-10-24DOI: 10.17764/JIET.52.2.G43282648562475Q
J. Weaver, M. Voorhis, R. Reifenberger
New buildings focused on the practice of nanotechnology reflect a pressing need to develop advanced techniques to enable reliable work at the nanoscale. Often when planning a nanotechnology building, a decision must be made to include high-accuracy nanometrology rooms. The purpose of these rooms is to provide high-quality space that can be utilized on a daily basis to facilitate experiments requiring nanoscale precision, to develop new instrumentation, and to develop new techniques capable of probing the nanoscale. Typically, these rooms reduce vibration (including acoustic noise) and electromagnetic interference to very low levels while maintaining a high level of temperature stability. This study describes the characterization and performance of the Kevin G. Hall Nanometrology Laboratory located in the Birck Nanotechnology Center at Purdue University.
以纳米技术实践为重点的新建筑反映了发展先进技术以实现纳米尺度上可靠工作的迫切需要。通常在规划纳米技术建筑时，必须决定包括高精度的纳米计量室。这些房间的目的是提供高质量的空间，可以在日常基础上利用，以促进需要纳米级精度的实验，开发新的仪器，并开发能够探测纳米级的新技术。通常，这些房间将振动(包括噪音)和电磁干扰降低到非常低的水平，同时保持高度的温度稳定性。本研究描述了位于普渡大学Birck纳米技术中心的Kevin G. Hall纳米计量实验室的表征和性能。
{"title":"Nanometrology Room Design: The Performance and Characterization of the Kevin G. Hall High-Accuracy Laboratory","authors":"J. Weaver, M. Voorhis, R. Reifenberger","doi":"10.17764/JIET.52.2.G43282648562475Q","DOIUrl":"https://doi.org/10.17764/JIET.52.2.G43282648562475Q","url":null,"abstract":"New buildings focused on the practice of nanotechnology reflect a pressing need to develop advanced techniques to enable reliable work at the nanoscale. Often when planning a nanotechnology building, a decision must be made to include high-accuracy nanometrology rooms. The purpose of these rooms is to provide high-quality space that can be utilized on a daily basis to facilitate experiments requiring nanoscale precision, to develop new instrumentation, and to develop new techniques capable of probing the nanoscale. Typically, these rooms reduce vibration (including acoustic noise) and electromagnetic interference to very low levels while maintaining a high level of temperature stability. This study describes the characterization and performance of the Kevin G. Hall Nanometrology Laboratory located in the Birck Nanotechnology Center at Purdue University.","PeriodicalId":35935,"journal":{"name":"Journal of the IEST","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2009-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67804434","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 : 2009-10-01DOI: 10.17764/JIET.52.2.G40W588835068522
Richard Heine, D. Barker
Use of a health and usage monitoring system (HUMS) is one method the Department of Defense is investigating to meet conflicting cost and performance goals for Army wheeled vehicles. One area where a HUMS would be of great benefit is monitoring critical components vulnerable to terrain-induced fatigue. While strain is typically the desired input to a fatigue model, acceleration sensors are less susceptible to damage from the military ground vehicle environment and provide more reliable data over long periods of usage. The feasibility of using vibratory inputs from an accelerometer to make component fatigue predictions for a military wheeled vehicle system is explored in this study, and the use of limited subsets of data for algorithm training are evaluated. An example component is used to demonstrate that the proposed HUMS algorithms are appropriate and provide suitably accurate fatigue predictions.
{"title":"Acceleration-Based Remaining Life Prognostics for Terrain-Loaded Components on an Army Ground Vehicle System","authors":"Richard Heine, D. Barker","doi":"10.17764/JIET.52.2.G40W588835068522","DOIUrl":"https://doi.org/10.17764/JIET.52.2.G40W588835068522","url":null,"abstract":"Use of a health and usage monitoring system (HUMS) is one method the Department of Defense is investigating to meet conflicting cost and performance goals for Army wheeled vehicles. One area where a HUMS would be of great benefit is monitoring critical components vulnerable to terrain-induced fatigue. While strain is typically the desired input to a fatigue model, acceleration sensors are less susceptible to damage from the military ground vehicle environment and provide more reliable data over long periods of usage. The feasibility of using vibratory inputs from an accelerometer to make component fatigue predictions for a military wheeled vehicle system is explored in this study, and the use of limited subsets of data for algorithm training are evaluated. An example component is used to demonstrate that the proposed HUMS algorithms are appropriate and provide suitably accurate fatigue predictions.","PeriodicalId":35935,"journal":{"name":"Journal of the IEST","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2009-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67804249","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 : 2009-04-07DOI: 10.17764/JIET.52.1.980053067640204J
Y. Zhou, G. Plaza, A. Dasgupta, M. Osterman
In this study, the durability of lead (Pb)-free tin(Sn3.0)silver(Ag0.5)copper(Cu) (SAC305) printed wiring assemblies (PWAs) is investigated under constant amplitude, narrow-band (harmonic) excitation and under step-stress broad-band (random) excitation, and compared to the durability of Pb-based Sn37Pb PWAs. The results show that Sn37Pb assemblies last longer than SAC305 assemblies at similar excitation levels, for both harmonic and random excitations used in this study. The test specimens are identical for all tests, consisting of a PWA with plastic ball grid array components, quad flat pack components, leadless ceramic chip carriers, and leadless chip resistors. The test matrix includes test boards with different kinds of finishes and different aging conditions. Both the harmonic and random vibration tests are conducted on single-axis electrodynamic shakers. The harmonic vibration excitation is applied to a single specimen at a time, while the random vibration excitation is applied simultaneously to 20 ...
{"title":"Vibration Durability of Sn3.0Ag0.5Cu (SAC305) Solder Interconnects: Harmonic and Random Excitation","authors":"Y. Zhou, G. Plaza, A. Dasgupta, M. Osterman","doi":"10.17764/JIET.52.1.980053067640204J","DOIUrl":"https://doi.org/10.17764/JIET.52.1.980053067640204J","url":null,"abstract":"In this study, the durability of lead (Pb)-free tin(Sn3.0)silver(Ag0.5)copper(Cu) (SAC305) printed wiring assemblies (PWAs) is investigated under constant amplitude, narrow-band (harmonic) excitation and under step-stress broad-band (random) excitation, and compared to the durability of Pb-based Sn37Pb PWAs. The results show that Sn37Pb assemblies last longer than SAC305 assemblies at similar excitation levels, for both harmonic and random excitations used in this study. The test specimens are identical for all tests, consisting of a PWA with plastic ball grid array components, quad flat pack components, leadless ceramic chip carriers, and leadless chip resistors. The test matrix includes test boards with different kinds of finishes and different aging conditions. Both the harmonic and random vibration tests are conducted on single-axis electrodynamic shakers. The harmonic vibration excitation is applied to a single specimen at a time, while the random vibration excitation is applied simultaneously to 20 ...","PeriodicalId":35935,"journal":{"name":"Journal of the IEST","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2009-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67803581","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 : 2009-04-07DOI: 10.17764/JIET.52.1.R38467496M5674P3
G. Wei
The most critical manufacturing processes for integrated circuits and thin-film transistors, mainstays of the semiconductor industry, take place in cleanrooms. The strictly controlled temperature and humidity in cleanrooms enable electrostatic charges to be generated and maintained on the surface of objects for an extended time. Electrostatic charge and discharge cause particle contamination, damage to products, and electromagnetic interference, which can lead to production tool lockup. With the development of new manufacturing technologies, products are becoming more sensitive to electrostatic discharge. How to control electrostatic charge and eliminate associated problems has become a challenge in the high-tech semiconductor industry.
{"title":"Electrostatic Control and Air Ionization in Cleanrooms for Semiconductor and TFT Production","authors":"G. Wei","doi":"10.17764/JIET.52.1.R38467496M5674P3","DOIUrl":"https://doi.org/10.17764/JIET.52.1.R38467496M5674P3","url":null,"abstract":"The most critical manufacturing processes for integrated circuits and thin-film transistors, mainstays of the semiconductor industry, take place in cleanrooms. The strictly controlled temperature and humidity in cleanrooms enable electrostatic charges to be generated and maintained on the surface of objects for an extended time. Electrostatic charge and discharge cause particle contamination, damage to products, and electromagnetic interference, which can lead to production tool lockup. With the development of new manufacturing technologies, products are becoming more sensitive to electrostatic discharge. How to control electrostatic charge and eliminate associated problems has become a challenge in the high-tech semiconductor industry.","PeriodicalId":35935,"journal":{"name":"Journal of the IEST","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2009-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67803207","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 : 2009-04-07DOI: 10.17764/JIET.52.1.T033663J86224006
J. A. Parian, A. Cozzani, M. Appolloni, G. Casarosa
In the frame of the development of a videogrammetric system to be used in thermal/vacuum chambers at the ESA-ESTEC and other sites across Europe, the design of a network using micro-cameras was specified by ESA-ESTEC. The selected test set-up is the photogrammetric test of the Herschel Spacecraft Flight Model in the ESTEC Large Space Simulator. The videogrammetric system will be used to verify the Herschel Telescope alignment and Telescope positioning with respect to the Local Oscillator Unit inside the Large Space Simulator during thermal/vacuum/balance test phases. We designed a close-range photogrammetric network by heuristic simulation with a global accuracy of 1:100,000. A thermal/vacuum qualified videogrammetric system, which is able to work in vacuum and at cryo-temperatures in order to acquire images according to the designed network, was constructed by ESA-ESTEC Test Centre Division. In this paper we will present the videogrammetric system, the photogrammetric considerations, accuracy aspects, th...
{"title":"Validation of a Strategy for Deformation Monitoring of the Herschel Spacecraft Under Ambient Conditions by Photogrammetry","authors":"J. A. Parian, A. Cozzani, M. Appolloni, G. Casarosa","doi":"10.17764/JIET.52.1.T033663J86224006","DOIUrl":"https://doi.org/10.17764/JIET.52.1.T033663J86224006","url":null,"abstract":"In the frame of the development of a videogrammetric system to be used in thermal/vacuum chambers at the ESA-ESTEC and other sites across Europe, the design of a network using micro-cameras was specified by ESA-ESTEC. The selected test set-up is the photogrammetric test of the Herschel Spacecraft Flight Model in the ESTEC Large Space Simulator. The videogrammetric system will be used to verify the Herschel Telescope alignment and Telescope positioning with respect to the Local Oscillator Unit inside the Large Space Simulator during thermal/vacuum/balance test phases. We designed a close-range photogrammetric network by heuristic simulation with a global accuracy of 1:100,000. A thermal/vacuum qualified videogrammetric system, which is able to work in vacuum and at cryo-temperatures in order to acquire images according to the designed network, was constructed by ESA-ESTEC Test Centre Division. In this paper we will present the videogrammetric system, the photogrammetric considerations, accuracy aspects, th...","PeriodicalId":35935,"journal":{"name":"Journal of the IEST","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2009-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67803390","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}
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