Pub Date : 1997-04-20DOI: 10.1109/CITCON.1997.599342
H. Meyer, A. Wolter
Mechanical equipment, hydraulic components, its control as well as the process design, all play an important role in the reliability of the clinker cooling system. Only by optimizing all of them can the performance and the availability be optimized. In addition to new design features like the anti-riddling side plates or the aerated beams it is shown that a new solution for the cooler inlet section, called the cross motion grate (CMG), is applied. The aim is to widen-up the grate at increased throughput capacities of up to 15000 t clinker/day and to equalize the clinker distribution actively instead of randomly as in the case of fixed inlet grates. The CMG design reduces the frequency of strokes and the wear rate respectively. Furthermore more attention has to be paid to the movement characteristics generated by the hydraulic drive. Any sharp and discontinuous motion has to be eliminated for reducing the mechanical stress in all components and avoiding the wear-intensive slipping of clinker as far as possible. In the 'competition' of thermal efficiency, power consumption and availability the latter seems to be the most attractive one in the long term, because it combines low maintenance costs with steady product quality and attractive return on investment.
{"title":"To improve the availability of grate coolers","authors":"H. Meyer, A. Wolter","doi":"10.1109/CITCON.1997.599342","DOIUrl":"https://doi.org/10.1109/CITCON.1997.599342","url":null,"abstract":"Mechanical equipment, hydraulic components, its control as well as the process design, all play an important role in the reliability of the clinker cooling system. Only by optimizing all of them can the performance and the availability be optimized. In addition to new design features like the anti-riddling side plates or the aerated beams it is shown that a new solution for the cooler inlet section, called the cross motion grate (CMG), is applied. The aim is to widen-up the grate at increased throughput capacities of up to 15000 t clinker/day and to equalize the clinker distribution actively instead of randomly as in the case of fixed inlet grates. The CMG design reduces the frequency of strokes and the wear rate respectively. Furthermore more attention has to be paid to the movement characteristics generated by the hydraulic drive. Any sharp and discontinuous motion has to be eliminated for reducing the mechanical stress in all components and avoiding the wear-intensive slipping of clinker as far as possible. In the 'competition' of thermal efficiency, power consumption and availability the latter seems to be the most attractive one in the long term, because it combines low maintenance costs with steady product quality and attractive return on investment.","PeriodicalId":443254,"journal":{"name":"1997 IEEE/PCA Cement Industry Technical Conference. XXXIX Conference Record (Cat. No.97CH36076)","volume":"2422 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130784631","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 : 1997-04-20DOI: 10.1109/CITCON.1997.599284
J. Folsberg
The symmetrical air-swept ring roller mill heralds a new era in cement grinding. To really understand the advantages of the new mill concept compared to other mill systems, the basis of its development is thoroughly described. Furthermore, the working principles of the mill itself as well as the entire mill system are outlined. The operating data of the first air-swept ring roller mill in operation is presented and compared with data from other mill systems. Similarly, the laboratory results' of testing cement samples are discussed and compared with results obtained with ball mill systems. In addition to the higher power savings and the improved cement properties compared with other mill systems, the basis for improvement of the service life of mechanical elements such as grinding parts and mill internals is explained.
{"title":"The air-swept ring roller mill for clinker grinding","authors":"J. Folsberg","doi":"10.1109/CITCON.1997.599284","DOIUrl":"https://doi.org/10.1109/CITCON.1997.599284","url":null,"abstract":"The symmetrical air-swept ring roller mill heralds a new era in cement grinding. To really understand the advantages of the new mill concept compared to other mill systems, the basis of its development is thoroughly described. Furthermore, the working principles of the mill itself as well as the entire mill system are outlined. The operating data of the first air-swept ring roller mill in operation is presented and compared with data from other mill systems. Similarly, the laboratory results' of testing cement samples are discussed and compared with results obtained with ball mill systems. In addition to the higher power savings and the improved cement properties compared with other mill systems, the basis for improvement of the service life of mechanical elements such as grinding parts and mill internals is explained.","PeriodicalId":443254,"journal":{"name":"1997 IEEE/PCA Cement Industry Technical Conference. XXXIX Conference Record (Cat. No.97CH36076)","volume":"45 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125968324","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 : 1997-04-20DOI: 10.1109/CITCON.1997.599349
B. Klotz
The evolving design of the preheater in a modern cement plant has changed very little. Some of the design details, such as low pressure drop cyclones and designs with an eye toward easier and less maintenance are among some of the more significant changes. The preheater must achieve a transfer of heat from the pyroprocessing system exhaust gases to the incoming raw meal in preparation for the energy intensive decarbonation process to occur in the calciner. However, the optimum design is a series of compromises that attempts to balance a lower preheater tower pressure drop (fan electric power) with cyclone collection efficiency (fuel consumption) and cyclone vessel volume (capital cost). Today's preheater cyclones normally are dimensioned smaller, equipped with larger gas inlets and outlets for decreased pressure drop, and don't necessarily yield the highest possible particulate collection efficiency when compared to a decade ago. As a result, the volume occupied in the preheater tower is significantly less for a given capacity resulting in a smaller tower structure to house and support these vessels. With the dynamic environmental regulations constantly becoming more and more strict, equipment suppliers must develop combustion methods to keep pace with the newly imposed limits. Multi-staged combustion, at least for now, offers a relatively low cost approach to meeting the accepted emission levels.
{"title":"New developments in precalciners and preheaters","authors":"B. Klotz","doi":"10.1109/CITCON.1997.599349","DOIUrl":"https://doi.org/10.1109/CITCON.1997.599349","url":null,"abstract":"The evolving design of the preheater in a modern cement plant has changed very little. Some of the design details, such as low pressure drop cyclones and designs with an eye toward easier and less maintenance are among some of the more significant changes. The preheater must achieve a transfer of heat from the pyroprocessing system exhaust gases to the incoming raw meal in preparation for the energy intensive decarbonation process to occur in the calciner. However, the optimum design is a series of compromises that attempts to balance a lower preheater tower pressure drop (fan electric power) with cyclone collection efficiency (fuel consumption) and cyclone vessel volume (capital cost). Today's preheater cyclones normally are dimensioned smaller, equipped with larger gas inlets and outlets for decreased pressure drop, and don't necessarily yield the highest possible particulate collection efficiency when compared to a decade ago. As a result, the volume occupied in the preheater tower is significantly less for a given capacity resulting in a smaller tower structure to house and support these vessels. With the dynamic environmental regulations constantly becoming more and more strict, equipment suppliers must develop combustion methods to keep pace with the newly imposed limits. Multi-staged combustion, at least for now, offers a relatively low cost approach to meeting the accepted emission levels.","PeriodicalId":443254,"journal":{"name":"1997 IEEE/PCA Cement Industry Technical Conference. XXXIX Conference Record (Cat. No.97CH36076)","volume":"93 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134046420","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 : 1997-04-20DOI: 10.1109/CITCON.1997.599362
G. Conroy
In the authors' 1992 IEEE paper entitled "Low NO/sub x/ Pyro-systems", they outlined the design concept of a new calciner generation which allows for the reduction of nitric oxides generated in a rotary cement kiln. Since that time, five industrial installations have gone into operation and another 12 are in some phase of construction. After a brief description of the process and the specific factors governing equipment design, this paper presents the industrial experience gained at several installations operating with a Humboldt Wedag calciner. The present and future development of this technology is also discussed, concluding with comments concerning the important aspects to be considered when applying this new calciner technology.
{"title":"Industrial applications and results of low NO/sub x/ precalciner systems [cement industry]","authors":"G. Conroy","doi":"10.1109/CITCON.1997.599362","DOIUrl":"https://doi.org/10.1109/CITCON.1997.599362","url":null,"abstract":"In the authors' 1992 IEEE paper entitled \"Low NO/sub x/ Pyro-systems\", they outlined the design concept of a new calciner generation which allows for the reduction of nitric oxides generated in a rotary cement kiln. Since that time, five industrial installations have gone into operation and another 12 are in some phase of construction. After a brief description of the process and the specific factors governing equipment design, this paper presents the industrial experience gained at several installations operating with a Humboldt Wedag calciner. The present and future development of this technology is also discussed, concluding with comments concerning the important aspects to be considered when applying this new calciner technology.","PeriodicalId":443254,"journal":{"name":"1997 IEEE/PCA Cement Industry Technical Conference. XXXIX Conference Record (Cat. No.97CH36076)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130762523","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 : 1997-04-20DOI: 10.1109/CITCON.1997.599374
D. Stepien, D. Funk, I. M. Brown
Variation is present in all manufacturing processes and "control" is not a natural state. In fact, a lack of variation in a process which indicates "perfect" control, should make one suspicious. Using control charts will keep a process operating within specified limits most of the time and, more importantly, control charting can both alert an operator when a process goes out of control and suggest how to bring it back. Learning about a process never stops manufacturing is a grand experiment that goes on each and every day. A proactive approach to one's manufacturing process is vital if companies wish to gain process knowledge. Shewhart control charts, for example, have been in use since the 1950s, but going beyond this basic level of knowledge has been troublesome due to the excessive number of statistical calculations required. The onset of the information age and the geometric growth in the amount of data generated by online controllers had, until recently, complicated efforts to make more than a basic use of data. Here, the authors describe a new process analysis package which can enable management to come to grips with this problem and gain insight into its manufacturing processes.
{"title":"Refractory management using fact-based analysis for the cement kiln","authors":"D. Stepien, D. Funk, I. M. Brown","doi":"10.1109/CITCON.1997.599374","DOIUrl":"https://doi.org/10.1109/CITCON.1997.599374","url":null,"abstract":"Variation is present in all manufacturing processes and \"control\" is not a natural state. In fact, a lack of variation in a process which indicates \"perfect\" control, should make one suspicious. Using control charts will keep a process operating within specified limits most of the time and, more importantly, control charting can both alert an operator when a process goes out of control and suggest how to bring it back. Learning about a process never stops manufacturing is a grand experiment that goes on each and every day. A proactive approach to one's manufacturing process is vital if companies wish to gain process knowledge. Shewhart control charts, for example, have been in use since the 1950s, but going beyond this basic level of knowledge has been troublesome due to the excessive number of statistical calculations required. The onset of the information age and the geometric growth in the amount of data generated by online controllers had, until recently, complicated efforts to make more than a basic use of data. Here, the authors describe a new process analysis package which can enable management to come to grips with this problem and gain insight into its manufacturing processes.","PeriodicalId":443254,"journal":{"name":"1997 IEEE/PCA Cement Industry Technical Conference. XXXIX Conference Record (Cat. No.97CH36076)","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128304694","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 : 1997-04-20DOI: 10.1109/CITCON.1997.599277
G. Kliman, J.G. Mazereeuw, S. Patel
Loss of process, reduced productivity, equipment damage, safety issues and life extension have driven continuing research in the area of noninvasive online motor diagnostics to recognize incipient failures and avoid the catastrophic results. Breakthroughs have been made utilizing a variety of methods which can be applied on today's cost-effective microprocessor hardware platforms to accurately diagnose impending failures of motors. These include failure modes involving bearings, broken bar or shorted turns, and abnormal shaft torque conditions. This paper describes the research, methodology and application of this technology.
{"title":"Sensorless approach to on-line motor diagnostics","authors":"G. Kliman, J.G. Mazereeuw, S. Patel","doi":"10.1109/CITCON.1997.599277","DOIUrl":"https://doi.org/10.1109/CITCON.1997.599277","url":null,"abstract":"Loss of process, reduced productivity, equipment damage, safety issues and life extension have driven continuing research in the area of noninvasive online motor diagnostics to recognize incipient failures and avoid the catastrophic results. Breakthroughs have been made utilizing a variety of methods which can be applied on today's cost-effective microprocessor hardware platforms to accurately diagnose impending failures of motors. These include failure modes involving bearings, broken bar or shorted turns, and abnormal shaft torque conditions. This paper describes the research, methodology and application of this technology.","PeriodicalId":443254,"journal":{"name":"1997 IEEE/PCA Cement Industry Technical Conference. XXXIX Conference Record (Cat. No.97CH36076)","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121994460","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}
Combining the power of electric utility deregulation with in-plant energy upgrades can provide dramatic improvements in cement plant profitability. Often overlooked in the push for greater production, enlightened utility management now offers one of the cheapest, most cost effective ways to lower operating costs. This paper is a case study of the results of such a program in a major midwestern USA cement plant.
{"title":"Taking full advantage of utility deregulation","authors":"P. Cunningham","doi":"10.1109/2943.667910","DOIUrl":"https://doi.org/10.1109/2943.667910","url":null,"abstract":"Combining the power of electric utility deregulation with in-plant energy upgrades can provide dramatic improvements in cement plant profitability. Often overlooked in the push for greater production, enlightened utility management now offers one of the cheapest, most cost effective ways to lower operating costs. This paper is a case study of the results of such a program in a major midwestern USA cement plant.","PeriodicalId":443254,"journal":{"name":"1997 IEEE/PCA Cement Industry Technical Conference. XXXIX Conference Record (Cat. No.97CH36076)","volume":"24 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116665317","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 : 1997-04-20DOI: 10.1109/CITCON.1997.599357
O. L. Jepsen, S. W. Miller
Many countries-especially the USA, Canada, and European countries-have enacted stringent requirements for the emission of NO/sub x/ from new or upgraded cement plants. In many cases the NO/sub x/ emission must be lower than 500-800 mg NO/sub x//NM/sup 3/ of dry gas (corrected to 10% oxygen) which is equivalent to approximately 1.10-1.76 kgNO/sub x//MT clinker for a modern pyroprocessing system. Actual field data show that while some existing plants can meet this emission level, most plants cannot. Therefore, new plants must be capable of attaining NO/sub x/ emissions that are below most existing plants. To meet these emissions requirements, it is logical to consider redesign of the precalciner. With this in mind, studies were carried out to determine the best methods for reducing NO/sub x/ in the calciner area and to incorporate these findings into a new generation of low NO/sub x/ calciners.
{"title":"New generation of low NO/sub x/ calciners","authors":"O. L. Jepsen, S. W. Miller","doi":"10.1109/CITCON.1997.599357","DOIUrl":"https://doi.org/10.1109/CITCON.1997.599357","url":null,"abstract":"Many countries-especially the USA, Canada, and European countries-have enacted stringent requirements for the emission of NO/sub x/ from new or upgraded cement plants. In many cases the NO/sub x/ emission must be lower than 500-800 mg NO/sub x//NM/sup 3/ of dry gas (corrected to 10% oxygen) which is equivalent to approximately 1.10-1.76 kgNO/sub x//MT clinker for a modern pyroprocessing system. Actual field data show that while some existing plants can meet this emission level, most plants cannot. Therefore, new plants must be capable of attaining NO/sub x/ emissions that are below most existing plants. To meet these emissions requirements, it is logical to consider redesign of the precalciner. With this in mind, studies were carried out to determine the best methods for reducing NO/sub x/ in the calciner area and to incorporate these findings into a new generation of low NO/sub x/ calciners.","PeriodicalId":443254,"journal":{"name":"1997 IEEE/PCA Cement Industry Technical Conference. XXXIX Conference Record (Cat. No.97CH36076)","volume":"85 1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124523386","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 : 1997-04-20DOI: 10.1109/CITCON.1997.599414
X. Dupont-Wavrin, M. C. Mound
In the modern cement plant, there is the challenge to balance production efficiency and quality to meet internal and international requirements for standards. Focus is concentrated on the process, rather than the individual job units. Defined in this way, a process is a sequence of activities which provide value and quality to meet production goals. At most innovative companies, the drive to achieve this balance relies on state-of-the-art technology and maintaining a level of quality consistency from plant to plant. Productivity, which is the underpinning of consistent process operations, is effectively maximized by means of automation. A potentially complicating factor in meeting this objective is that there is usually a combination of existing, relatively new plants and a number of older plant operations which are in various stages of upgrading. The level of sophistication of equipment and integration of several generations of technology represents a rather formidable obstacle to achieving the objective of consistency of integration and production quality control. Nowhere is this more important than in the area of automation of the cement plant production laboratory.
{"title":"Commitment to the fully-automated cement laboratory concept: a cement industry trend whose time has come","authors":"X. Dupont-Wavrin, M. C. Mound","doi":"10.1109/CITCON.1997.599414","DOIUrl":"https://doi.org/10.1109/CITCON.1997.599414","url":null,"abstract":"In the modern cement plant, there is the challenge to balance production efficiency and quality to meet internal and international requirements for standards. Focus is concentrated on the process, rather than the individual job units. Defined in this way, a process is a sequence of activities which provide value and quality to meet production goals. At most innovative companies, the drive to achieve this balance relies on state-of-the-art technology and maintaining a level of quality consistency from plant to plant. Productivity, which is the underpinning of consistent process operations, is effectively maximized by means of automation. A potentially complicating factor in meeting this objective is that there is usually a combination of existing, relatively new plants and a number of older plant operations which are in various stages of upgrading. The level of sophistication of equipment and integration of several generations of technology represents a rather formidable obstacle to achieving the objective of consistency of integration and production quality control. Nowhere is this more important than in the area of automation of the cement plant production laboratory.","PeriodicalId":443254,"journal":{"name":"1997 IEEE/PCA Cement Industry Technical Conference. XXXIX Conference Record (Cat. No.97CH36076)","volume":"67 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123587298","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 : 1997-04-20DOI: 10.1109/CITCON.1997.599413
S. Regis
Arizona Portland Cement (APC), USA, has operated a prompt gamma neutron activation analyzer (PGNAA) on its 1000 TPH overland belt conveyor system since August of 1995. The belt conveyor passes through the analyzer enclosure where a neutron source under the belt causes gamma ray releases identified by the sodium iodide scintillation detector above the belt. Sophisticated analytical software operating on a personal computer decomposes the gamma ray spectrum into its constituent elements. The result is a real-time one minute update of the complete chemical composition of the crushed rock headed down the beltline. The Crossbelt Analyzer project was a 1995 Capital Budget project. APC ordered the equipment from GammaMetrics in February and completed the installation in August 1995. Training and acceptance testing were conducted in late 1995. This paper summarizes the project after one year of operation.
{"title":"Performance evaluation of an on-line PGNAA cross-belt analyzer [cement plant monitoring]","authors":"S. Regis","doi":"10.1109/CITCON.1997.599413","DOIUrl":"https://doi.org/10.1109/CITCON.1997.599413","url":null,"abstract":"Arizona Portland Cement (APC), USA, has operated a prompt gamma neutron activation analyzer (PGNAA) on its 1000 TPH overland belt conveyor system since August of 1995. The belt conveyor passes through the analyzer enclosure where a neutron source under the belt causes gamma ray releases identified by the sodium iodide scintillation detector above the belt. Sophisticated analytical software operating on a personal computer decomposes the gamma ray spectrum into its constituent elements. The result is a real-time one minute update of the complete chemical composition of the crushed rock headed down the beltline. The Crossbelt Analyzer project was a 1995 Capital Budget project. APC ordered the equipment from GammaMetrics in February and completed the installation in August 1995. Training and acceptance testing were conducted in late 1995. This paper summarizes the project after one year of operation.","PeriodicalId":443254,"journal":{"name":"1997 IEEE/PCA Cement Industry Technical Conference. XXXIX Conference Record (Cat. No.97CH36076)","volume":"36 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116146382","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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