Pub Date : 1973-10-01DOI: 10.1002/J.1538-7305.1973.TB02026.X
D. Marcuse
The coupling coefficients of the modes of a parabolic index fiber with randomly curved axis are derived and are used to compute its excess losses and impulse response. It is found that bends with a period comparable to the natural ray oscillation period in the parabolic index medium are catastrophic. The average radius of curvature R c of a guide composed of circular sections with an average length of 1 cm must not decrease below approximately R c = 1 m. Mode coupling by random bends has the tendency to reduce the width of the impulse response function. However, this improvement is accompanied by losses. Reducing the width of the impulse response for coupled mode operation to half its uncoupled width causes 0.7 dB additional loss, a ten-fold reduction of the pulse width costs 18 dB.
{"title":"Losses and impulse response of a parabolic index fiber with random bends","authors":"D. Marcuse","doi":"10.1002/J.1538-7305.1973.TB02026.X","DOIUrl":"https://doi.org/10.1002/J.1538-7305.1973.TB02026.X","url":null,"abstract":"The coupling coefficients of the modes of a parabolic index fiber with randomly curved axis are derived and are used to compute its excess losses and impulse response. It is found that bends with a period comparable to the natural ray oscillation period in the parabolic index medium are catastrophic. The average radius of curvature R c of a guide composed of circular sections with an average length of 1 cm must not decrease below approximately R c = 1 m. Mode coupling by random bends has the tendency to reduce the width of the impulse response function. However, this improvement is accompanied by losses. Reducing the width of the impulse response for coupled mode operation to half its uncoupled width causes 0.7 dB additional loss, a ten-fold reduction of the pulse width costs 18 dB.","PeriodicalId":55391,"journal":{"name":"Bell System Technical Journal","volume":"21 1","pages":"1423-1437"},"PeriodicalIF":0.0,"publicationDate":"1973-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84338033","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 : 1973-10-01DOI: 10.1002/J.1538-7305.1973.TB02025.X
R. D. Coleman
We consider an N-server queuing system with Poisson arrivals and exponential service, in which arriving customers must pass through a gate into a waiting room before becoming eligible for service. Customers who find the gate closed wait outside until the gate opens; customers inside the waiting room are served at random. When the last customer inside acquires a server, the gate admits all those outside and then closes again. If no customer is waiting outside when the gate opens, the gate remains open until there is a queue of k waiting customers. Service offered by this system is intermediary between random service and order-of-arrival service. As long as the gate is open and fewer than N + k customers are in the system, service is purely random. The parameter k can be regarded as a threshold at which the queue is judged too long to permit random service to continue. Our main results are (i) the Laplace-Stieltjes transform of the equilibrium distribution of the waiting time of an arbitrary customer and (ii) a comparison of the second moments of the waiting time for different values of k with those of the waiting time under random service and order-of-arrival service. The service is shown to be “nearly random” at low loads and “not quite order-of-arrival” at high loads; for higher values of k this transition occurs at higher traffic intensities.
{"title":"Use of a gate to reduce the variance of delays in queues with random service","authors":"R. D. Coleman","doi":"10.1002/J.1538-7305.1973.TB02025.X","DOIUrl":"https://doi.org/10.1002/J.1538-7305.1973.TB02025.X","url":null,"abstract":"We consider an N-server queuing system with Poisson arrivals and exponential service, in which arriving customers must pass through a gate into a waiting room before becoming eligible for service. Customers who find the gate closed wait outside until the gate opens; customers inside the waiting room are served at random. When the last customer inside acquires a server, the gate admits all those outside and then closes again. If no customer is waiting outside when the gate opens, the gate remains open until there is a queue of k waiting customers. Service offered by this system is intermediary between random service and order-of-arrival service. As long as the gate is open and fewer than N + k customers are in the system, service is purely random. The parameter k can be regarded as a threshold at which the queue is judged too long to permit random service to continue. Our main results are (i) the Laplace-Stieltjes transform of the equilibrium distribution of the waiting time of an arbitrary customer and (ii) a comparison of the second moments of the waiting time for different values of k with those of the waiting time under random service and order-of-arrival service. The service is shown to be “nearly random” at low loads and “not quite order-of-arrival” at high loads; for higher values of k this transition occurs at higher traffic intensities.","PeriodicalId":55391,"journal":{"name":"Bell System Technical Journal","volume":"41 1","pages":"1403-1422"},"PeriodicalIF":0.0,"publicationDate":"1973-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82698761","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 : 1973-10-01DOI: 10.1002/J.1538-7305.1973.TB02019.X
S. Rice
Consider a nonlinear system, with memory, which has two input ports and one output port. It is assumed that the system can be represented by a double Volterra series. Two results for such a system are stated in Part I. The first is a general expression for the sinusoidal components of the output y (t) when the two inputs x u (t) and x v (t) are sums of sinusoidal terms. The second result is an expression for the power spectrum of y (t) when x u (t) is a stationary Gaussian process and x v (t) = P cos pt. Part II is concerned with using results from the theory of Volterra series for multi-input systems to calculate the third-order distortion in an idealized frequency converter.
考虑一个有内存的非线性系统，它有两个输入端口和一个输出端口。假设系统可以用双Volterra级数表示。第一部分给出了这样一个系统的两个结果。第一个是当两个输入x u (t)和x v (t)是正弦项的和时，输出y (t)的正弦分量的一般表达式。第二个结果是当x u (t)是平稳高斯过程且x v (t) = pcos pt时y (t)的功率谱的表达式。第二部分涉及使用多输入系统Volterra级数理论的结果来计算理想变频器中的三阶失真。
{"title":"Volterra systems with more than one input port — distortion in a frequency converter","authors":"S. Rice","doi":"10.1002/J.1538-7305.1973.TB02019.X","DOIUrl":"https://doi.org/10.1002/J.1538-7305.1973.TB02019.X","url":null,"abstract":"Consider a nonlinear system, with memory, which has two input ports and one output port. It is assumed that the system can be represented by a double Volterra series. Two results for such a system are stated in Part I. The first is a general expression for the sinusoidal components of the output y (t) when the two inputs x u (t) and x v (t) are sums of sinusoidal terms. The second result is an expression for the power spectrum of y (t) when x u (t) is a stationary Gaussian process and x v (t) = P cos pt. Part II is concerned with using results from the theory of Volterra series for multi-input systems to calculate the third-order distortion in an idealized frequency converter.","PeriodicalId":55391,"journal":{"name":"Bell System Technical Journal","volume":"59 1","pages":"1255-1270"},"PeriodicalIF":0.0,"publicationDate":"1973-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86475273","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 : 1973-10-01DOI: 10.1002/J.1538-7305.1973.TB02022.X
M. Pinnel, J. Bennett
A recent development effort in telecommunications switching apparatus has been directed toward the production of a remanent reed, dry, sealed contact (remreed). Remendur, a medium-hard magnetic alloy nominally composed of equal parts iron and cobalt and 2.7-wt. percent vanadium, was chosen as the reed material in this contact. However, the application required the alloy to possess rather specific magnetic and mechanical properties and considerable difficulty was experienced in consistently processing Remendur into wire with these specified properties. To ascertain the sensitivity of these properties to variations in processing times and temperatures, and vanadium content, two melts of Remendur (2.5-percent V and 3.0-percent V) were processed with selected alterations in annealing temperatures at several stages. Microstructures were characterized following each step by light microscopy and were correlated with the appropriate ternary equilibrium diagram. Results demonstrate that microstructures developed by anneals between 900°C and 950°C are extremely sensitive to the precise temperature of the anneal and composition of the alloy. The microstructure, which strongly influences magnetic and mechanical properties, can be varied over the limits of the two-phase α 1 + γ region by variations in vanadium content of only 0.5 wt. percent and by the small 50°C temperature range.
{"title":"The metallurgy of remendur: Effects of processing variations","authors":"M. Pinnel, J. Bennett","doi":"10.1002/J.1538-7305.1973.TB02022.X","DOIUrl":"https://doi.org/10.1002/J.1538-7305.1973.TB02022.X","url":null,"abstract":"A recent development effort in telecommunications switching apparatus has been directed toward the production of a remanent reed, dry, sealed contact (remreed). Remendur, a medium-hard magnetic alloy nominally composed of equal parts iron and cobalt and 2.7-wt. percent vanadium, was chosen as the reed material in this contact. However, the application required the alloy to possess rather specific magnetic and mechanical properties and considerable difficulty was experienced in consistently processing Remendur into wire with these specified properties. To ascertain the sensitivity of these properties to variations in processing times and temperatures, and vanadium content, two melts of Remendur (2.5-percent V and 3.0-percent V) were processed with selected alterations in annealing temperatures at several stages. Microstructures were characterized following each step by light microscopy and were correlated with the appropriate ternary equilibrium diagram. Results demonstrate that microstructures developed by anneals between 900°C and 950°C are extremely sensitive to the precise temperature of the anneal and composition of the alloy. The microstructure, which strongly influences magnetic and mechanical properties, can be varied over the limits of the two-phase α 1 + γ region by variations in vanadium content of only 0.5 wt. percent and by the small 50°C temperature range.","PeriodicalId":55391,"journal":{"name":"Bell System Technical Journal","volume":"57 1","pages":"1325-1340"},"PeriodicalIF":0.0,"publicationDate":"1973-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86741695","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 : 1973-10-01DOI: 10.1002/J.1538-7305.1973.TB02027.X
J. Cook, W. Mammel, R. Grow
Analysis and computations made here, corroborated by experiment, determine the effects of axial displacement and angular misalignment on the power coupled between butt-joined, single-mode optical fibers. The absolute accuracy with which fibers must be joined on-centers is reduced for fibers with relatively smaller core; the angular accuracy is increased.
{"title":"Effect of misalignments on coupling efficiency of single-mode optical fiber butt joints","authors":"J. Cook, W. Mammel, R. Grow","doi":"10.1002/J.1538-7305.1973.TB02027.X","DOIUrl":"https://doi.org/10.1002/J.1538-7305.1973.TB02027.X","url":null,"abstract":"Analysis and computations made here, corroborated by experiment, determine the effects of axial displacement and angular misalignment on the power coupled between butt-joined, single-mode optical fibers. The absolute accuracy with which fibers must be joined on-centers is reduced for fibers with relatively smaller core; the angular accuracy is increased.","PeriodicalId":55391,"journal":{"name":"Bell System Technical Journal","volume":"11 1","pages":"1439-1448"},"PeriodicalIF":0.0,"publicationDate":"1973-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75760422","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 : 1973-10-01DOI: 10.1002/J.1538-7305.1973.TB02020.X
J. Limb
A method is suggested for inserting viewer criteria directly into coding algorithms; any complex visual model may be used. The technique is applied to a DPCM-type coder, and a number of variations are compared on the basis of entropy, quality, and complexity. It is found that, using a simple one-dimensional filter model, the first-order entropy of the DPCM signal can be reduced by 30 percent for a high-detail picture with only a small reduction in picture quality. Furthermore, by means of a single threshold control, one can efficiently trade off bit-rate and picture quality over a large range for use in adaptive strategies.
{"title":"Picture coding: The use of a viewer model in source encoding","authors":"J. Limb","doi":"10.1002/J.1538-7305.1973.TB02020.X","DOIUrl":"https://doi.org/10.1002/J.1538-7305.1973.TB02020.X","url":null,"abstract":"A method is suggested for inserting viewer criteria directly into coding algorithms; any complex visual model may be used. The technique is applied to a DPCM-type coder, and a number of variations are compared on the basis of entropy, quality, and complexity. It is found that, using a simple one-dimensional filter model, the first-order entropy of the DPCM signal can be reduced by 30 percent for a high-detail picture with only a small reduction in picture quality. Furthermore, by means of a single threshold control, one can efficiently trade off bit-rate and picture quality over a large range for use in adaptive strategies.","PeriodicalId":55391,"journal":{"name":"Bell System Technical Journal","volume":"1 1","pages":"1271-1302"},"PeriodicalIF":0.0,"publicationDate":"1973-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75774915","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 : 1973-10-01DOI: 10.1002/J.1538-7305.1973.TB02021.X
M. Chao
Simple statistical procedures for analyzing error data, e.g., in digital data transmission systems, are usually based on the assumption of independence. This paper studies the performance and potential utility of such simple statistical procedures in the case of nonindependent error occurrences. The burst noise model is selected for this purpose because of its neatness, its mathematical tractability, its built-in structure of dependence, and its importance in communication theory. We show that statistical procedures designed under the assumption of independence tend to be conservative for the burst noise model. For example, the usual binomial test will reject, on the average, more channels with small error rates than it would if the errors were independent. The case that the sample size n and the error rate ρ converge in such a way that nρ→ µ 0 is also studied. It is shown that the error process can be approximated by a compound Poisson process in continuous time t. The statistical implications of this fact are also discussed.
{"title":"Statistical properties of gilbert's burst noise model","authors":"M. Chao","doi":"10.1002/J.1538-7305.1973.TB02021.X","DOIUrl":"https://doi.org/10.1002/J.1538-7305.1973.TB02021.X","url":null,"abstract":"Simple statistical procedures for analyzing error data, e.g., in digital data transmission systems, are usually based on the assumption of independence. This paper studies the performance and potential utility of such simple statistical procedures in the case of nonindependent error occurrences. The burst noise model is selected for this purpose because of its neatness, its mathematical tractability, its built-in structure of dependence, and its importance in communication theory. We show that statistical procedures designed under the assumption of independence tend to be conservative for the burst noise model. For example, the usual binomial test will reject, on the average, more channels with small error rates than it would if the errors were independent. The case that the sample size n and the error rate ρ converge in such a way that nρ→ µ 0 is also studied. It is shown that the error process can be approximated by a compound Poisson process in continuous time t. The statistical implications of this fact are also discussed.","PeriodicalId":55391,"journal":{"name":"Bell System Technical Journal","volume":"119 1","pages":"1303-1324"},"PeriodicalIF":0.0,"publicationDate":"1973-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76983420","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 : 1973-10-01DOI: 10.1002/J.1538-7305.1973.TB02023.X
J. Salz
In this work we report new results relating to decision feedback equalization. The equalizer and the transmitting filter are optimized in a PAM data communication system operating over a linear noisy channel. We use a mean-square error criterion and impose an average power constraint at the transmitter. Assuming correct past decisions, an explicit formula for the minimum attainable mean-square error is given. The possible advantages of signaling faster than the Nyquist rate while decreasing the number of levels to maintain the same information rate are investigated. It is shown that, in all cases of practical interest, signaling faster than the Nyquist rate, while keeping fixed the information rate, increases the mean-square error. Finally, to illustrate the use of the results, application is made to a cable channel where the loss in dB varies as the square root of frequency. Various asymptotic formulas and curves are provided to exhibit the relationships between the quantities of interest.
{"title":"Optimum mean-square decision feedback equalization","authors":"J. Salz","doi":"10.1002/J.1538-7305.1973.TB02023.X","DOIUrl":"https://doi.org/10.1002/J.1538-7305.1973.TB02023.X","url":null,"abstract":"In this work we report new results relating to decision feedback equalization. The equalizer and the transmitting filter are optimized in a PAM data communication system operating over a linear noisy channel. We use a mean-square error criterion and impose an average power constraint at the transmitter. Assuming correct past decisions, an explicit formula for the minimum attainable mean-square error is given. The possible advantages of signaling faster than the Nyquist rate while decreasing the number of levels to maintain the same information rate are investigated. It is shown that, in all cases of practical interest, signaling faster than the Nyquist rate, while keeping fixed the information rate, increases the mean-square error. Finally, to illustrate the use of the results, application is made to a cable channel where the loss in dB varies as the square root of frequency. Various asymptotic formulas and curves are provided to exhibit the relationships between the quantities of interest.","PeriodicalId":55391,"journal":{"name":"Bell System Technical Journal","volume":"43 1","pages":"1341-1373"},"PeriodicalIF":0.0,"publicationDate":"1973-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76887071","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 : 1973-10-01DOI: 10.1002/J.1538-7305.1973.TB02024.X
A. Descloux
Under equilibrium conditions, the sample average of the delays encountered by all the calls submitted during a given time interval is an unbiased estimate of the mean of the delay distribution. If some of the delays are not observed, the resulting sample average need no longer be an unbiased estimator of the corresponding population mean. This is the case when, for instance, only a limited number of delays can be timed simultaneously. The purpose of this paper is to investigate these biases for queuing systems when only one clock is available and thus one delay only can be measured at a time. It is shown that, regardless of the order of service, the expected value of the observed average delays is always smaller than the mean waiting time for all calls. Although the average delay on all calls is independent of the order of service, the measurement biases resulting when only one delay can be measured at once depend on the queue discipline. In particular, we shall show that the average delay for all calls is always larger than the average delay of the observed calls even if these calls are always served last (observed-call served-last).
{"title":"Traffic measurement biases induced by partial sampling","authors":"A. Descloux","doi":"10.1002/J.1538-7305.1973.TB02024.X","DOIUrl":"https://doi.org/10.1002/J.1538-7305.1973.TB02024.X","url":null,"abstract":"Under equilibrium conditions, the sample average of the delays encountered by all the calls submitted during a given time interval is an unbiased estimate of the mean of the delay distribution. If some of the delays are not observed, the resulting sample average need no longer be an unbiased estimator of the corresponding population mean. This is the case when, for instance, only a limited number of delays can be timed simultaneously. The purpose of this paper is to investigate these biases for queuing systems when only one clock is available and thus one delay only can be measured at a time. It is shown that, regardless of the order of service, the expected value of the observed average delays is always smaller than the mean waiting time for all calls. Although the average delay on all calls is independent of the order of service, the measurement biases resulting when only one delay can be measured at once depend on the queue discipline. In particular, we shall show that the average delay for all calls is always larger than the average delay of the observed calls even if these calls are always served last (observed-call served-last).","PeriodicalId":55391,"journal":{"name":"Bell System Technical Journal","volume":"49 1","pages":"1375-1402"},"PeriodicalIF":0.0,"publicationDate":"1973-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90580612","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 : 1973-09-01DOI: 10.1002/J.1538-7305.1973.TB02009.X
B. Kernighan, S. Lin
This paper discusses a heuristic solution procedure for a combinatorial optimization problem that originates in designing signal constellations for modems. The design problem is to place m signals in a two-dimensional space to minimize the average error rate under specified noise conditions, using a maximum-likelihood decoding scheme. Intuitively, it amounts (roughly) to spreading the signal points as far apart as possible, according to the distance measurement implied by the noise function. We show how this problem can be reduced to a discrete one: Given an l by n matrix P, and m 1 , …, i m } of the rows of P that maximizes and then describe an efficient procedure for finding this maximizing set. Experiments indicate that the procedure is a useful tool, both for analysis of existing and proposed signal constellations and for finding new, near-optimum ones.
{"title":"Heuristic solution of a signal design optimization problem","authors":"B. Kernighan, S. Lin","doi":"10.1002/J.1538-7305.1973.TB02009.X","DOIUrl":"https://doi.org/10.1002/J.1538-7305.1973.TB02009.X","url":null,"abstract":"This paper discusses a heuristic solution procedure for a combinatorial optimization problem that originates in designing signal constellations for modems. The design problem is to place m signals in a two-dimensional space to minimize the average error rate under specified noise conditions, using a maximum-likelihood decoding scheme. Intuitively, it amounts (roughly) to spreading the signal points as far apart as possible, according to the distance measurement implied by the noise function. We show how this problem can be reduced to a discrete one: Given an l by n matrix P, and m 1 , …, i m } of the rows of P that maximizes and then describe an efficient procedure for finding this maximizing set. Experiments indicate that the procedure is a useful tool, both for analysis of existing and proposed signal constellations and for finding new, near-optimum ones.","PeriodicalId":55391,"journal":{"name":"Bell System Technical Journal","volume":"3 1","pages":"1145-1159"},"PeriodicalIF":0.0,"publicationDate":"1973-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87120694","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：