# Showing papers in "Bell System Technical Journal in 1950"

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TL;DR: The author was led to the study given in this paper from a consideration of large scale computing machines in which a large number of operations must be performed without a single error in the end result.

Abstract: The author was led to the study given in this paper from a consideration of large scale computing machines in which a large number of operations must be performed without a single error in the end result. This problem of “doing things right” on a large scale is not essentially new; in a telephone central office, for example, a very large number of operations are performed while the errors leading to wrong numbers are kept well under control, though they have not been completely eliminated. This has been achieved, in part, through the use of self-checking circuits. The occasional failure that escapes routine checking is still detected by the customer and will, if it persists, result in customer complaint, while if it is transient it will produce only occasional wrong numbers. At the same time the rest of the central office functions satisfactorily. In a digital computer, on the other hand, a single failure usually means the complete failure, in the sense that if it is detected no more computing can be done until the failure is located and corrected, while if it escapes detection then it invalidates all subsequent operations of the machine. Put in other words, in a telephone central office there are a number of parallel paths which are more or less independent of each other; in a digital machine there is usually a single long path which passes through the same piece of equipment many, many times before the answer is obtained.

5,408 citations

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TL;DR: In this article, a theoretical analysis of the flow of added current carriers in homogeneous semiconductors is given, and a general formulation of differential equations and boundary condition relationships in suitable reduced variables and parameters are derived from fundamental equations which take into account the phenomena of drift, diffusion, and recombination.

Abstract: A theoretical analysis of the flow of added current carriers in homogeneous semiconductors is given. The simplifying assumption is made at the outset that trapping effects may be neglected, and the subsequent treatment is intended particularly for application to germanium. In a general formulation, differential equations and boundary-condition relationships in suitable reduced variables and parameters are derived from fundamental equations which take into account the phenomena of drift, diffusion, and recombination. This formulation is specialized so as to apply to the steady state of constant total current in a single cartesian distance coordinate, and properties of solutions which give the electrostatic field and the concentrations and flow densities of the added carriers are discussed. The ratio of hole to electron concentration at thermal equilibrium occurs as parameter. General solutions are given analytically in closed form for the intrinsic semiconductor, for which the ratio is unity, and for some limiting cases as well. Families of numerically obtained solutions dependent on a parameter proportional to total current are given for n-type germanium for the ratio equal to zero. The solutions are utilized in a consideration of simple boundary-value problems concerning a single plane source in an infinite filament.

622 citations

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TL;DR: In this paper, the power output of a traveling-wave tube has been analyzed using a linearized theory only, and no attempt has been made to develop a non-linear theory.

Abstract: A Theoretical Evaluation of the power output of a traveling-wave tube requires a theory of the non-linear behavior of the tube. In this book we have dealt with a linearized theory only. No attempt will be made to develop a non-linear theory. Some results of non-linear theory will be quoted, and some conclusions drawn from experimental work will be presented.

552 citations

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TL;DR: In this paper, the preface and the historical introduction of the Hell System Technical Journal are published in its entirety. But they do not cover the introduction and chapter 6 in their full version.

Abstract: Under the above title, D. Van Nostrand Company, Inc. will shortly publish the book from which the following article is excerpted. Dr. Southworth is one of the leading authorities on waveguides and was one of the first to foresee the great usefulness that this form of transmission might offer. The editors of the Hell System Technical Journal are grateful for permission to publish here parts of the preface and the historical introduction and chapter 6 in its entirety.

97 citations

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TL;DR: Comparison of any proposed design with the minimum requirements obtained from the relations gives a measure of the efficiency in memory utilization of the design.

Abstract: A General telephone exchange with N subscribers is indicated schematically in Fig. 1. The basic function of an exchange is that of setting up a connection between any pair of subscribers. In operation the exchange must “remember,” in some form, which subscribers are connected together until the corresponding calls are completed. This requires a certain amount of internal memory, depending on the number of subscribers, the maximum calling rate, etc. A number of relations will be derived based on these considerations which give the minimum possible number of relays, crossbar switches or other elements necessary to perform this memory function. Comparison of any proposed design with the minimum requirements obtained from the relations gives a measure of the efficiency in memory utilization of the design.

79 citations

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TL;DR: This paper bears on the problem of splitting a signal into two parts of like amplitudes but different phases and shows how to compute the best approximation to a constant phase difference obtainable over a prescribed frequency range with a network of prescribed complexity.

Abstract: This paper bears on the problem of splitting a signal into two parts of like amplitudes but different phases. Constant phase differences are utilized in such circuits as Hartley single sideband modulators. The networks considered here are pairs of constant-resistance phase-shifting networks connected in parallel at one end. The first part of the paper shows how to compute the best approximation to a constant phase difference obtainable over a prescribed frequency range with a network of prescribed complexity. The latter part shows how to design networks producing the best approximation.

72 citations

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TL;DR: In this paper, the spectral density for the electrical resistance when it is linearly coupled to a diffusing medium (particles or heat) undergoing thermally excited fluctuations is calculated.

Abstract: The spectral density is calculated for the electrical resistance when it is linearly coupled to a diffusing medium (particles or heat) undergoing thermally excited fluctuations. Specific forms of the spectral density are given for several types of coupling which arc simple and physically reasonable. The principal objective is the understanding of the frequency dependence of the resistance fluctuations in contacts, rectifying crystals, thin films, etc.

70 citations

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TL;DR: Two encoding schemes are described in which the ideal rate is approached when the signal length is increased, an idea suggested by Shannon's observation that in an efficient encoding system the typical signal will resemble random noise.

Abstract: Recent work by C. E. Shannon and others has led to an expression for the maximum rate at which information can be transmitted in the presence of random noise. Here two encoding schemes are described in which the ideal rate is approached when the signal length is increased. Both schemes are based upon drawing random numbers from a normal universe, an idea suggested by Shannon's observation that in an efficient encoding system the typical signal will resemble random noise. In choosing these schemes two requirements were kept in mind: (1) the ideal rate must be approached, and (2) the problem of computing the probability of error must be tractable. Although both schemes meet both requirements, considerable work has been required to put the expression for the probability of error into manageable form.

46 citations

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TL;DR: In this paper, the relation between the low-voltage conductance of a metal-point contact to n-type germanium and the concentration of holes in the vicinity of the contact is discussed.

Abstract: The theory of the relation between the current-voltage characteristic of a metal-point contact to n-type germanium and the concentration of holes in the vicinity of the contact is discussed. It is supposed that the hole concentration has been changed from the value corresponding to thermal equilibrium by hole injection from a neighboring contact (as in the transistor), by absorption of light or by application of a magnetic field (Suhl effect). The method of calculation is based on treating separately the characteristics of the barrier layer of the contact and the flow of holes in the body of the germanium. A linear relation between the low-voltage conductance of the contact and the hole concentration is derived and compared with data of Pearson and Suhl. Under conditions of no current flow the contact floats at a potential which bears a simple relation, previously found empirically, with the conductance. When a large reverse voltage is applied the current flow is linearly related to the hole concentration, as has been shown empirically by Haynes. The intrinsic current multiplication factor, α, of the contact can be derived from a knowledge of this relation.

35 citations

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TL;DR: The electro-optic and photoelastic effects in crystals were first investigated by Pockels, who developed a phenomenological theory for these effects and measured the constants for a number of crystals as discussed by the authors.

Abstract: The electro-optic and photoelastic effects in crystals were first investigated by Pockels,1 who developed a phenomenological theory for these effects and measured the constants for a number of crystals. Since then not much work has been done on the subject till the very large electro-optic effects were discovered in two tetragonal crystals ammonium dihydrogen phosphate (ADP) and potassium dihydrogen phosphate (KDP). With these crystals light modulators can be obtained which work on voltages of 2000 volts or less. Their use has been suggested2 in such equipment as light valves for sound on film recording and in television systems. Furthermore, since the electro-optic effect depends on a change in the dielectric constant with voltage, and the dielectric constant is known to follow the field up to 1010 cycles, it is obvious that this effect can be used to produce very short light pulses which may be of interest for physical investigations and for stroboscope instruments of very high resolution. Hence these crystals renew an interest in the electro-optic effect.

33 citations

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TL;DR: In this paper, the microwave triode B.T.L. 1553 was developed for microwave relay systems for frequencies around 4000 megacycles, and both theoretical and experimental factors arc involved; illustration of these factors in some detail is the purpose of the present paper.

Abstract: In Developing microwave relay systems for frequencies around 4000 megacycles, one of the major problems is to provide an amplifier tube which will meet the requirements on gain, power output, and distortion over very wide bands. As the number of repeaters is increased to extend the relay to greater distances, the requirements on individual amplifiers for the system become increasingly severe. A tube developed for this service is the microwave triode B.T.L. 1553, the physical and electrical characteristics of which were briefly described in a previous article.1 In the development of such a tube, both theoretical and experimental factors arc involved; illustration of these factors in some detail is the purpose of the present paper.

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TL;DR: This chapter shall use this representation in justifying the circuit equation of Chapter II and in adding to it a term to take into account the local fields produced by a-c space charge to obtain a combined circuit and ballistical equation, which will be used in the following chapters in deducing various properties of traveling-wave tubes.

Abstract: In Chapter VI we have expressed the properties of a circuit in terms of its normal modes of propagation rather than its physical dimensions. In this chapter we shall use this representation in justifying the circuit equation of Chapter II and in adding to it a term to take into account the local fields produced by a-c space charge. Then, a combined circuit and ballistical equation will be obtained, which will be used in the following chapters in deducing various properties of traveling-wave tubes.

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TL;DR: In this article, a microwave circuit designed for use with the 1553-416A close-spaced triode at 4000 m.c. was described and the results obtained in a multistage amplifier having 90 db gain.

Abstract: This paper describes a microwave circuit designed for use with the 1553–416A close-spaced triode at 4000 m.c. It presents data on tubes used as amplifiers and modulators and concludes with the results obtained in a multistage amplifier having 90 db gain.

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TL;DR: The relativistic and wave mechanical properties of particles appear to be consistent with a picture in which particles are represented by localized oscillatory disturbances in a mechanical ether of the MacCullagh-Kelvin type as mentioned in this paper.

Abstract: Both the relativistic and wave mechanical properties of particles appear to be consistent with a picture in which particles are represented by localized oscillatory disturbances in a mechanical ether of the MacCullagh-Kelvin type. Gyrostatic forces impart to such a medium an elasticity to rotation, such that, for very small velocities, its approximate equations are identical with those of Maxwell for free space. The important results, however, follow from the inherent non-linearity of the complete equations and the time dependence of the elasticity associated with finite displacements. These lead to reflections which permit of a wave of finite energy remaining localized. Because of the non-linearity, the amplitude and energy of a stable mode, as well as the frequency, are determined by the constants of the medium. Such a stable mode is capable of translational motion and so is suitable to represent a particle. The mass assigned to it is derived from its energy by the relativity relation. While this mass is dimensionally the same as that of the medium it is differently related to the energy and so need not conform to the classical laws which the latter is assumed to obey.

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TL;DR: In the preparation of magnetic materials for practical use, it is important to know how to obtain products of the best quality and uniformity as discussed by the authors, and the principal factors which influence magnetic behavior.

Abstract: In the preparation of magnetic materials for practical use it is important to know how to obtain products of the best quality and uniformity. In the scientific study of magnetism the goal is to understand the relation between the structure and composition on the one hand and the magnetic properties on the other. From both standpoints it is necessary to know the principal factors which influence magnetic behavior. These are briefly reviewed here.

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TL;DR: In this article, it is shown that for a small constant angular displacement of an element, the restoring torque, instead of being constant, decreases progressively with time, due to the fact that the elastic forces are of gyrostatic origin.

Abstract: This paper furnishes the basis for a companion one, which discusses the possibility of describing material particles as localized oscillatory disturbances in a mechanical medium. If a medium is to support such disturbances it must reflect a part of the energy of a diverging spherical wave. It is here shown that this property is possessed by a medium, such as that proposed by Kelvin, in which the elastic forces are of gyrostatic origin. This is due to the fact that, for a small constant angular displacement of an element of this medium, the restoring torque, instead of being constant, decreases progressively with time.