Pub Date : 1938-05-01DOI: 10.1109/JRPROC.1938.228132
C. Bachman, C. W. Carnahan
The cathode-ray beams of electrostatically focused cathode-ray tubes were studied by mass spectrographic methods. The negative-ion components focused on the fluorescent screens were made evident by their ability to change the fluorescent qualities of the screen material. Persistent appearance of m/e values of 16, 26, 35, and 37 in the tubes studied were due to oxygen, some organic molecule, as C2H2or CN, and chlorine, respectively. Many other components were found in tubes with various preparation histories. Direct evidence of negatively charged molecules of the cathode material were found which may be of some aid in the theory of sputtering. An explanation of screen discolorations appearing under different conditions of bombardment and life is given in terms of the effects of negative ions, positive ions, and electrons of different energy. The presence on the bombarded screen of a latent image which may be rendered visible by chemical means is discussed.
{"title":"Negative-Ion Components in the Cathode-Ray Beam","authors":"C. Bachman, C. W. Carnahan","doi":"10.1109/JRPROC.1938.228132","DOIUrl":"https://doi.org/10.1109/JRPROC.1938.228132","url":null,"abstract":"The cathode-ray beams of electrostatically focused cathode-ray tubes were studied by mass spectrographic methods. The negative-ion components focused on the fluorescent screens were made evident by their ability to change the fluorescent qualities of the screen material. Persistent appearance of m/e values of 16, 26, 35, and 37 in the tubes studied were due to oxygen, some organic molecule, as C2H2or CN, and chlorine, respectively. Many other components were found in tubes with various preparation histories. Direct evidence of negatively charged molecules of the cathode material were found which may be of some aid in the theory of sputtering. An explanation of screen discolorations appearing under different conditions of bombardment and life is given in terms of the effects of negative ions, positive ions, and electrons of different energy. The presence on the bombarded screen of a latent image which may be rendered visible by chemical means is discussed.","PeriodicalId":54574,"journal":{"name":"Proceedings of the Institute of Radio Engineers","volume":"26 1","pages":"529-539"},"PeriodicalIF":0.0,"publicationDate":"1938-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1109/JRPROC.1938.228132","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"62307336","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 : 1938-05-01DOI: 10.1109/JRPROC.1938.228198
H. Roder
The theory of the frequency-discriminator circuit which is used in radio receivers equipped with automatic frequency control is worked out. Formulas for computing gain, frequency-control sensitivity, adjacent-channel attentuation, pull-in range, etc., are developed. These formulas apply to any value of primary or secondary inductance and to any value of coil quality factor. The loading represented by the plate impedance of the driver tube and by the diodes is also taken into account. After slight modification, the resulting formulas can be used for various different circuit arrangements. Nonlinear audio-frequency, distortion is found to exist in the case where the channels for signal and automatic frequency control are common; these distortions, however, are small. It is found that the loading effect of the diodes is responsible for the poor selectivity resulting for most automatic-frequency-control transformers. A circuit in which the automatic frequency control and the signal channel are separated is preferable if better selectivity is desired.
{"title":"Theory of the Discriminator Circuit for Automatic Frequency Control","authors":"H. Roder","doi":"10.1109/JRPROC.1938.228198","DOIUrl":"https://doi.org/10.1109/JRPROC.1938.228198","url":null,"abstract":"The theory of the frequency-discriminator circuit which is used in radio receivers equipped with automatic frequency control is worked out. Formulas for computing gain, frequency-control sensitivity, adjacent-channel attentuation, pull-in range, etc., are developed. These formulas apply to any value of primary or secondary inductance and to any value of coil quality factor. The loading represented by the plate impedance of the driver tube and by the diodes is also taken into account. After slight modification, the resulting formulas can be used for various different circuit arrangements. Nonlinear audio-frequency, distortion is found to exist in the case where the channels for signal and automatic frequency control are common; these distortions, however, are small. It is found that the loading effect of the diodes is responsible for the poor selectivity resulting for most automatic-frequency-control transformers. A circuit in which the automatic frequency control and the signal channel are separated is preferable if better selectivity is desired.","PeriodicalId":54574,"journal":{"name":"Proceedings of the Institute of Radio Engineers","volume":"6 1","pages":"590-611"},"PeriodicalIF":0.0,"publicationDate":"1938-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1109/JRPROC.1938.228198","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"62307692","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 : 1938-05-01DOI: 10.1109/JRPROC.1938.228326
C. Burrows, A. Decino, L. E. Hunt
The continuous records of the field strength received over a 60-kilometer path on a frequency of 150 megacycles for the year 1936 are analyzed. Preliminary comparison with other paths of the same length indicate that the magnitude of the recorded variations of the signals may be typical of paths of this length. A reduction in the path length by a factor of two reduced the fading range in decibels by a factor of five. The results are found to be in agreement with an earlier formula. Fading reduced the field 7 decibels below the average value 1 per cent of the time.
{"title":"Stability of Two-Meter Waves","authors":"C. Burrows, A. Decino, L. E. Hunt","doi":"10.1109/JRPROC.1938.228326","DOIUrl":"https://doi.org/10.1109/JRPROC.1938.228326","url":null,"abstract":"The continuous records of the field strength received over a 60-kilometer path on a frequency of 150 megacycles for the year 1936 are analyzed. Preliminary comparison with other paths of the same length indicate that the magnitude of the recorded variations of the signals may be typical of paths of this length. A reduction in the path length by a factor of two reduced the fading range in decibels by a factor of five. The results are found to be in agreement with an earlier formula. Fading reduced the field 7 decibels below the average value 1 per cent of the time.","PeriodicalId":54574,"journal":{"name":"Proceedings of the Institute of Radio Engineers","volume":"26 1","pages":"516-528"},"PeriodicalIF":0.0,"publicationDate":"1938-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1109/JRPROC.1938.228326","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"62307973","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 : 1938-05-01DOI: 10.1109/JRPROC.1938.228134
L. Leeds
A type of wave filter employing a concentric transmission line is described. Filters of this type are especially applicable to ultra-high-frequency operation where their physical size becomes reasonable and where the conventional lumped-constant filters become practically unrealizable. It is shown that the addition of a simple lumped-reactance element will result in a sharp cutoff characteristic analogous to that exhibited by a conventional m-derived lumped-constant filter but over a limited frequency band. This latter filter has allowed simultaneous transmission and reception using the same antenna, in the 30- to 42-megacycle band, transmitter pouer 150 watts, receiver sensitivity 5 microvolts, with a frequency difference of only 0.9 megacycle. It is shown that a 14 per cent increase in driving-point impedance of the filter can be obtained if the filter line is shortened 0.065 wavelength and tuned to resonance with a shunt capacitance. This result is applicable directly to the use of transmission lines as tank circuits when very high driving point impedance is required.
{"title":"Concentric Narrow-Band-Elimination Filter","authors":"L. Leeds","doi":"10.1109/JRPROC.1938.228134","DOIUrl":"https://doi.org/10.1109/JRPROC.1938.228134","url":null,"abstract":"A type of wave filter employing a concentric transmission line is described. Filters of this type are especially applicable to ultra-high-frequency operation where their physical size becomes reasonable and where the conventional lumped-constant filters become practically unrealizable. It is shown that the addition of a simple lumped-reactance element will result in a sharp cutoff characteristic analogous to that exhibited by a conventional m-derived lumped-constant filter but over a limited frequency band. This latter filter has allowed simultaneous transmission and reception using the same antenna, in the 30- to 42-megacycle band, transmitter pouer 150 watts, receiver sensitivity 5 microvolts, with a frequency difference of only 0.9 megacycle. It is shown that a 14 per cent increase in driving-point impedance of the filter can be obtained if the filter line is shortened 0.065 wavelength and tuned to resonance with a shunt capacitance. This result is applicable directly to the use of transmission lines as tank circuits when very high driving point impedance is required.","PeriodicalId":54574,"journal":{"name":"Proceedings of the Institute of Radio Engineers","volume":"26 1","pages":"576-589"},"PeriodicalIF":0.0,"publicationDate":"1938-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1109/JRPROC.1938.228134","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"62307387","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 : 1938-05-01DOI: 10.1109/JRPROC.1938.228199
W. Everitt, K. Spangenberg
In the design of class C amplifiers analytical methods have been proposed which give good results from the standpoint of plate-circuit operating condition. Similar methods have not been available for the determination of grid-circuit conditions. It is the purpose of this paper to describe a method by which this result can be obtained. An analytical determination of grid-circuit operating conditions requires a knowledge of grid current as a function of the grid and plate voltages. Since good approximations for the space current in a triode are available, an expression for grid current can be had if the ratio of plate-to-grid current as a function of plate and grid voltage can be determined. Theoretical considerations show that the ratio of plate current to grid current should be a function of the ratio of plate voltage to grid voltage. The nature of this functional relation is determined experimentally and a comparatively simple and accurate expression for grid current in cases in which there is only a small amount of secondary emission is thus obtained. The design procedure for class C amplifiers is based upon the allowable grid and plate dissipation. The method of determining optimum operating conditions on the basis of plate-circuit analysis alone is modified to include the analytical determination of the corresponding grid-driving power and grid loss. This procedure results in the determination of the operating conditions which will give the highest output which can be obtained without exceeding the allowable grid or plate dissipation.
{"title":"Grid-Current Flow as a Factor in the Design of Vacuum-Tube Power Amplifiers","authors":"W. Everitt, K. Spangenberg","doi":"10.1109/JRPROC.1938.228199","DOIUrl":"https://doi.org/10.1109/JRPROC.1938.228199","url":null,"abstract":"In the design of class C amplifiers analytical methods have been proposed which give good results from the standpoint of plate-circuit operating condition. Similar methods have not been available for the determination of grid-circuit conditions. It is the purpose of this paper to describe a method by which this result can be obtained. An analytical determination of grid-circuit operating conditions requires a knowledge of grid current as a function of the grid and plate voltages. Since good approximations for the space current in a triode are available, an expression for grid current can be had if the ratio of plate-to-grid current as a function of plate and grid voltage can be determined. Theoretical considerations show that the ratio of plate current to grid current should be a function of the ratio of plate voltage to grid voltage. The nature of this functional relation is determined experimentally and a comparatively simple and accurate expression for grid current in cases in which there is only a small amount of secondary emission is thus obtained. The design procedure for class C amplifiers is based upon the allowable grid and plate dissipation. The method of determining optimum operating conditions on the basis of plate-circuit analysis alone is modified to include the analytical determination of the corresponding grid-driving power and grid loss. This procedure results in the determination of the operating conditions which will give the highest output which can be obtained without exceeding the allowable grid or plate dissipation.","PeriodicalId":54574,"journal":{"name":"Proceedings of the Institute of Radio Engineers","volume":"26 1","pages":"612-639"},"PeriodicalIF":0.0,"publicationDate":"1938-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1109/JRPROC.1938.228199","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"62307251","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}
T. R. Gilliland, S. S. Kirby, N. Smith, S. E. Reymer
Graphs are presented to indicate the maximum usable frequencies for sky-wave transmission from June, 1933, to December, 1937. The graphs are given for March, June, and December to show equinoctial, summer, and winter conditions for each year. The factors which must be considered in deriving these graphs from vertical-incidence ionosphere measurements are outlined briefly. The principal factors are Snell's law, variation of virtual height of the ionosphere with frequency, the curvature of the ionosphere, and the effect of the earth's magnetic field. The method of applying these graphs to simple and complex transmission paths is indicated. The effect of sporadic E reflections, absorption, and scattered reflections are discussed briefly. In conclusion it is pointed out that the graphs and the ionosphere data, from which they were derived, may be used to estimate future diurnal, seasonal, and longtime variations of maximum usable frequencies.
{"title":"Maximum Usable Frequencies for Radio Sky-Wave Transmission, 1933 to 1937","authors":"T. R. Gilliland, S. S. Kirby, N. Smith, S. E. Reymer","doi":"10.6028/JRES.020.010","DOIUrl":"https://doi.org/10.6028/JRES.020.010","url":null,"abstract":"Graphs are presented to indicate the maximum usable frequencies for sky-wave transmission from June, 1933, to December, 1937. The graphs are given for March, June, and December to show equinoctial, summer, and winter conditions for each year. The factors which must be considered in deriving these graphs from vertical-incidence ionosphere measurements are outlined briefly. The principal factors are Snell's law, variation of virtual height of the ionosphere with frequency, the curvature of the ionosphere, and the effect of the earth's magnetic field. The method of applying these graphs to simple and complex transmission paths is indicated. The effect of sporadic E reflections, absorption, and scattered reflections are discussed briefly. In conclusion it is pointed out that the graphs and the ionosphere data, from which they were derived, may be used to estimate future diurnal, seasonal, and longtime variations of maximum usable frequencies.","PeriodicalId":54574,"journal":{"name":"Proceedings of the Institute of Radio Engineers","volume":"26 1","pages":"1347-1359"},"PeriodicalIF":0.0,"publicationDate":"1938-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71346248","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 : 1938-05-01DOI: 10.1109/JRPROC.1938.228200
T. R. Gilliland, S. S. Kirby, N. Smith
Data on the ordinary-wave critical frequencies and virtual heights of the ionospheric layers are presented for the period indicated in the title. The monthly average values of the maximum usable frequencies for undisturbed days, for radio transmission by way of the regular layers is also provided.
{"title":"Characteristics of the Ionosphere at Washington, D.C., March, 1938","authors":"T. R. Gilliland, S. S. Kirby, N. Smith","doi":"10.1109/JRPROC.1938.228200","DOIUrl":"https://doi.org/10.1109/JRPROC.1938.228200","url":null,"abstract":"Data on the ordinary-wave critical frequencies and virtual heights of the ionospheric layers are presented for the period indicated in the title. The monthly average values of the maximum usable frequencies for undisturbed days, for radio transmission by way of the regular layers is also provided.","PeriodicalId":54574,"journal":{"name":"Proceedings of the Institute of Radio Engineers","volume":"26 1","pages":"640-643"},"PeriodicalIF":0.0,"publicationDate":"1938-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1109/JRPROC.1938.228200","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"62307269","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 : 1938-05-01DOI: 10.1109/JRPROC.1938.228133
H. A. Wheeler, A. V. Loughren
There are described the necessary or preferred relations in the fine structure of television scanning, so chosen as to yield a system which is both theoretically ideal and practically optimum. The relations involve the width and spacing of the lines and the intensity distribution of circular scanning spots in both transmitter and receiver, which are correlated with the filter characteristics and the required width of the frequency band. A "flat" field of scanning, as distinguished from a "half-tone" field, is required at both ends, especially in the transmitter to suppress spurious large patterns otherwise generated in the scanning process. For equal horizontal and vertical "width of confusion," the nominal cutoff frequency of the system is found to be f. = fpN.' R/ V2N2 in which fp= frame frequency Ns= number of scanning lines, and R = aspect ratio. The over-all electrical characteristics require distortionless reproduction up to fcand permit a gradual cutoff between fcand 2fc. The "quadratic-sum rule" is derived for a special case and is offered as a generally approximate expression of the image width of confusion w in terms of the width of confusion of the respective individual components (object, optical, scanning, electrical): W = VWi2 + Wo2 + ± wn2. Based on the proposed television system of 30 frames per second, the full utilization of 441 lines requires a separation of 5.5 megacycles between picture and sound carriers. A separation of 4.
{"title":"The Fine Structure of Television Images","authors":"H. A. Wheeler, A. V. Loughren","doi":"10.1109/JRPROC.1938.228133","DOIUrl":"https://doi.org/10.1109/JRPROC.1938.228133","url":null,"abstract":"There are described the necessary or preferred relations in the fine structure of television scanning, so chosen as to yield a system which is both theoretically ideal and practically optimum. The relations involve the width and spacing of the lines and the intensity distribution of circular scanning spots in both transmitter and receiver, which are correlated with the filter characteristics and the required width of the frequency band. A \"flat\" field of scanning, as distinguished from a \"half-tone\" field, is required at both ends, especially in the transmitter to suppress spurious large patterns otherwise generated in the scanning process. For equal horizontal and vertical \"width of confusion,\" the nominal cutoff frequency of the system is found to be f. = fpN.' R/ V2N2 in which fp= frame frequency Ns= number of scanning lines, and R = aspect ratio. The over-all electrical characteristics require distortionless reproduction up to fcand permit a gradual cutoff between fcand 2fc. The \"quadratic-sum rule\" is derived for a special case and is offered as a generally approximate expression of the image width of confusion w in terms of the width of confusion of the respective individual components (object, optical, scanning, electrical): W = VWi2 + Wo2 + ± wn2. Based on the proposed television system of 30 frames per second, the full utilization of 441 lines requires a separation of 5.5 megacycles between picture and sound carriers. A separation of 4.","PeriodicalId":54574,"journal":{"name":"Proceedings of the Institute of Radio Engineers","volume":"26 1","pages":"540-575"},"PeriodicalIF":0.0,"publicationDate":"1938-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1109/JRPROC.1938.228133","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"62307344","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 : 1938-04-01DOI: 10.1109/JRPROC.1938.228129
J. Webb
The variation of the high-frequency resistance of ferromagnetic conductors as a function of a superimposed magnetic field is discussed. It is shown that very large changes in high-frequency resistance are obtainable in ferromagnetic conductors having high initial permeabilities. Some important applications of this effect are given. The application of high-frequency incremental permeability to remote tuning of radio circuits is briefly outlined.
{"title":"The Variation in the High-Frequency Resistance and Permeability of Ferromagnetic Materials due to a Superimposed Magnetic Field","authors":"J. Webb","doi":"10.1109/JRPROC.1938.228129","DOIUrl":"https://doi.org/10.1109/JRPROC.1938.228129","url":null,"abstract":"The variation of the high-frequency resistance of ferromagnetic conductors as a function of a superimposed magnetic field is discussed. It is shown that very large changes in high-frequency resistance are obtainable in ferromagnetic conductors having high initial permeabilities. Some important applications of this effect are given. The application of high-frequency incremental permeability to remote tuning of radio circuits is briefly outlined.","PeriodicalId":54574,"journal":{"name":"Proceedings of the Institute of Radio Engineers","volume":"26 1","pages":"433-441"},"PeriodicalIF":0.0,"publicationDate":"1938-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1109/JRPROC.1938.228129","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"62307290","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 : 1938-04-01DOI: 10.1109/JRPROC.1938.228196
D. L. Jaffe
When the side bands of an amplitude-modulated signal are shifted 90 degrees and then recombined with the carrier, a frequency-modulated carrier results. In this paper the order and magnitudes of the distortion components of such a frequency-modulated carrier are quantitatively determined assuming an idealized receiver. It is found that this type of distortion will be negligibly small after frequency multiplication to obtain the desired carrier frequency.
{"title":"Armstrong's Frequency Modulator","authors":"D. L. Jaffe","doi":"10.1109/JRPROC.1938.228196","DOIUrl":"https://doi.org/10.1109/JRPROC.1938.228196","url":null,"abstract":"When the side bands of an amplitude-modulated signal are shifted 90 degrees and then recombined with the carrier, a frequency-modulated carrier results. In this paper the order and magnitudes of the distortion components of such a frequency-modulated carrier are quantitatively determined assuming an idealized receiver. It is found that this type of distortion will be negligibly small after frequency multiplication to obtain the desired carrier frequency.","PeriodicalId":54574,"journal":{"name":"Proceedings of the Institute of Radio Engineers","volume":"26 1","pages":"475-481"},"PeriodicalIF":0.0,"publicationDate":"1938-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1109/JRPROC.1938.228196","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"62307610","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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