Cable Of Length Research Articles

The effect of cellular discontinuities on the transient subthreshold response of a one-dimensional cardiac model

Previous studies have examined the influence of the gap-junction discontinuity on the steady-state response of a cardiac cable to electrical defibrillation. It is important to understand when steady-state conditions may be assumed. For this reason, the transient, subthreshold behavior of a discontinuous cardiac cable is examined in this study. The behavior of the cable reflects two characteristics: 1) the continuous nature of the entire cable and 2) the isolated behavior of individual cells imposed by the junction discontinuity. The results show two effective time constants of activation: a large time constant corresponding to the time constant of a continuous cable of equivalent length, and a small time constant reflecting the rapid activation of an isolated cell. The rapid activation establishes a voltage gradient across each cell of the cable with one end of the cell hyperpolarized and the opposite end depolarized. This pattern of hyperpolarization and depolarization reaches a maximum value in approximately 3 microseconds and may play an important role in the mechanism of defibrillation.

Experience with AC hipot and partial discharge tests for commissioning generating station cables and switchgear

Test equipment is described which is suitable for AC hipot and partial discharge testing of 5 and 15 kV shielded cables of lengths up to about 600 m. The equipment can be used to test 5 and 15 kV metal-clad switchgear. Ontario Hydro's experience at two nuclear generating stations using this AC test equipment is presented. The equipment can be used to assure the integrity of cable systems (less than 600 m long) already in service. The reasons for switching to AC testing of cable systems are outlined. Practical experience shows that the partial-discharge test is very effective in identifying installation problems in cables and switchgear. A number of problems are identified with the AC tests that a DC test would have missed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A simple and versatile phase comparison method can accurately measure long term instability

Accurate long-term phase noise measurements are performed by a mixer, a personal computer, and a general-purpose interface. When absolute noise has to be characterized, it is possible to have measuring sessions virtually infinite in time, utilizing a simple discrete phase shifter realized by switching three coaxial cables of different lengths. Accurate phase retrievement is accomplished by antitransforming the ideal sinusoidal transfer function of the mixer, while its higher spurious responses are minimized by a careful optimization of its operating parameters. This configuration has been successfully used to estimate the Allan variances from 1 s up to 100000 s of the phase comparison of two H-maser atomic standards, for almost nine days, without the need of any frequency offset between the two sources, which were used at the same time as timekeepers. A computer simulation is also presented to predict a priori the level of inaccuracy determined by the higher-order mixer nonlinearities and the final effect of each experimental parameter.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Practical modelling of monopolar axonal stimulation

Three models describing monopolar electrical stimulation of unmyelinated axons in large, uniformly conducting volumes are presented. The first is a representation of the axon as a continuous and straight electric cable of finite length with sealed ends. It has a power-series solution for the steady state which after truncation beyond the fifth term provides an accurate reflection of the imposed membrane potential for all parts of the axon except, under certain conditions, near terminals and directly opposite a closely apposed electrode. At these points, the inclusion of higher-order terms improves the accuracy quite slowly — II terms are sometimes still unsatisfactory. The second is a steady-state solution, in terms of higher transcendental functions, for the point opposite the stimulating electrode in a similar but infinitely long cable. This turns out to be practical for estimating the membrane potential at the site of cathodal excitation under the majority of realistic geometrical and electrical parameters, and consequently complements the first method. It may be calculated with ease from mathematical tables. The third, a simulation of the cable by means of discrete electrical components (compartments), can give the complete distribution of membrane potential as a function of time with potentially unlimited accuracy. However, it takes special computer programs to set up and solve either the steady-state determinant or, if transients are desired, the time-dependent differential equation. Calculation of the voltage distribution with one of the analytical methods will often be faster for a reasonable level of accuracy, since their algorithms are independent of the total number of points introduced.

Elimination of coupling between cylindrical transmit coils and surface-receive coils for in vivo NMR.

Coupling between large transmit and surface-receive coils is eliminated using a lambda/4 cable, terminated with crossed diodes to ground, inserted between the receive coil and ground, and by using a cable of length a little less than lambda/2 inserted between the transmit match capacitance and the normal crossed diodes in the transmit input line.

A Broadband Local Area Network

The IEEE 802 standard for local area network based on Carrier Sense Multiple-Access with Collision Detection (CSMA/CD) operates at a peak rate of 10 Mb/s on a cable of maximum length 2.5 km using baseband signaling. In many situations, larger channel rates are required over a much larger area. However, the efficiency of the CSMA/CD access method decreases rapidly if either the length of the cable is increased for a fixed bit rate or if the bit rate is increased for a fixed cable length. In this paper, we propose a broadband network for computer communications containing several CSMA/CD-type systems, each operating in a different frequency band. In addition, in order to have a wide area access, while minimizing the loss of performance associated with large collision delays, terminals in a small given geographical area are given one of the frequency bands for transmission. Two access protocols are developed. Using these schemes, it is possible to increase the channel throughput and the access area and to reduce the collision delay. We present a simplified analysis to quantify the improvement in performance using our schemes.

Electromagnetic surface fields of an inclined buried cable of finite length

The magnetic fields on the surface produced by a buried current-carrying cable of finite length are considered. A homogeneous half-space model of the earth and quasistatic conditions are assumed. The cable is grounded at its end points and oriented at an arbitrary angle to the interface. While, in general, numerical integration is required, the low-frequency limit may be treated analytically. Small cable tilts are shown to modify the direction of the surface field but not the magnitude. The results have possible application to uplink communication and radio location of trapped miners.

Subsurface electric fields of a grounded cable of finite length for both frequency and time domain

The subsurface electric fields of a current-carrying cable are examined for both steady-state and transient situations. Closed form expressions are obtained for two of the electric field components, and a numerical integration is used to obtain the third component. Waveforms for a stepfunction current excitation are displayed. The results have possible application to pulsed downlink communication in mine rescue operations.

End Effect Bending Stresses in Cables

An analysis of bending stresses in flexible cables has been carried out. It has been found that stresses which arise due to fixity at the boundaries or other points of discontinuity, decay in an exponential manner from such boundaries, similar to the edge effect solutions of shell theory. Such a phenomenon makes it possible to analyze a finite cable of sufficient length using solutions which are applicable only to infinite or very long cables. In this way the cumbersome but otherwise exact solutions of the elastica are replaced by much simpler ones of sufficient engineering accuracy. The term “sufficient length” is defined as part of the analysis.

Problems with Measurement of Void Discharge in High Voltage Cable of Full Reel Length.

Problems with Measurement of Void Discharge in High Voltage Cable of Full Reel Length.

A probe type direct reading dosage-rate meter.

A direct-reading probe type dosage-rate meter suitable for radium or X-ray measurements inside the human body is described. The instrument utilises an “air-walled” chamber of 0·07 c.c. volume together with a miniature thermionic electrometer system, the whole comprising a probe which may be shaped to specific requirement and be readily capable of insertion into the major body cavities. The electrometer output is conveyed by a flexible multicored cable of any desired length to the amplifying and indicating system which may be housed at any convenient distance. The most sensitive range of the instrument gives full scale deflection for five r/min., but the sensitivity is easily adjustable from this figure up to several hundred r/min. if required. Standard components are used throughout, the electrometer system being comprised of miniature radio valves. Some clinical uses to which the instrument has already been put in this hospital are described.

Societies and Academies

PARIS. Academy of Sciences, September 26.—M. Bouchard in the chair.—The president announced the death of Mme. Pasteur.—M. Darboux presented vol. xiv. of the Travaux et Mémoires du Bureau international, containing a full account of the measurements of the exact volume of the kilogram of water. Three different methods have been employed, and the mean of the closely concordant results gives 1.000027 cubic decimetres as the volume of the kilogram of water at 4° C. and under normal atmospheric pressure.—A. Laveran: The treatment of different trypanosomiases by arsenic and antimony emetic. The compound used was obtained in large crystals by crystallising together under certain conditions aniline-arsenyl-tartrate and aniline-antimonyl-tartrate. Details of the methods and dosage are given. Fifteen guinea-pigs infected with T. evansi, T. gambiense, T. dimorphon, or by T. congolense were cured. In four of these cases there was a relapse, which was cured by a second treatment. The possibilities of application to the human subject are discussed.—R. Bourgeois: The comparison of two astronomical pendulums with the aid of electrical signals transmitted by a submarine cable of great length. A Thomson siphon recorder was modified in a manner to suit this work. The method will be used to determine the difference of time between Brest and Dakar, a distance of about 4500 kilometres.—A. Demoulin: Ihe families of Lamé composed of surfaces possessing singular points.—Gaston Darboux: Remarks en the preceding communication.—Carl Störmer: The canonical forms of the general equations of motion of a particle in a magnetic field and an electric field superposed. —H. True and C. Flcig: Experimental ocular action of the dust on tarred roads. Dust from tarred roads is shown experimentally to be capable of provoking much more serious eye troubles than dust from untreated roads, and the smaller the lapse of time since the road has been tarred the more serious are the lesions produced. —H. Guillemard and G. Regnier: Observations on animal calorimetry made on Mt. Blanc. Increase of altitude has no sensible effect on the body temperature, but there is a marked increase in the amount of heat evolved by the body as the altitude increases, amounting to more than 30 per cent, between Chamonix and the summit of Mt. Blanc. A discussion of the results leads to the conclusion that protection against the cold is the best way of combating mountain sickness.—Charles Nicolle and E. Conseil: Properties of the serum of convalescents and animals cured of exanthematic typhus. Serum collected from the ninth to the fourteenth day of convalescence has well-marked preventive and curative properties against the disease. The curative effects disappear if the serum is collected later.—Joseph Roussel: The mode of formation of tricalcium phosphate in Algeria and Tunis.

XXVII. On the relative speed of the electric wave through submarine cables of different lengths, and a unit of speed for comparing electric cables by bisecting the electric wave

The present paper gives the results of some experiments which were undertaken to determine, first, the relative speed of the electric wave through cables of various lengths; secondly, the retarding effect of the iron covering of the cable; and thirdly, methods for the increase of the speed of the electric wave. When a long submarine cable or subterranean wire is connected at one end through a galvanometer to the earth, and the other end is connected with a battery, a current flows through it, deflecting the galvanometer-needle.