Concept Of Equivalent Impedance Research Articles

Modelling travellers’ route choice behaviours with the concept of equivalent impedance

A novel concept is presented to capture route choice behaviours and to account for the correlation of routes in the logit model. The issue that route choice models are easily affected when irrelevant alternatives are included in the choice set is tackled. The concept of equivalent impedance is presented to simplify and aggregate a set of links based on the idea that people tend to remember and process road network information at an abstract level. Then, the equivalent impedance is utilized to derive a correction term for the utility of a multinomial logit model in which the advantages of a closed-form structure and easy computation remain unchanged. The results from the numerical examples suggest that the proposed model obtains reasonable results and provides more stable predictions than comparable models when the composition of the choice set changes. An application in a real urban network with GPS data is presented, and estimation results suggest that the new model is practical due to its robustness.

Travelling-wave Phototube Theory†

ABSTRACT The travelling-wave phototube (TWP) is a microwave detector of amplitudes modulation at optical frequencies. This paper gives an account of the theory of the TWP in terms of modified travelling-wave tube (TWT) coupled mode theory. The characteristics of the TWP are discussed and a comparison made between it and the TWT. The concept of equivalent impedance used to evaluate the performance of the TWP is introduced and its dependence on various parameters shown. Finally, the noise output is calculated and figures given for the performance of a practical device.

The Determination of Reverberant Sound Absorption Coefficients from Acoustic Impedance Measurements

A procedure is outlined whereby acoustic impedance measurements may be utilized to predict reverberant sound absorption coefficients. The average of coefficients for the six standard frequencies so determined agrees closely with the average reverberant coefficient, for cases where the material may be said to obey the normal impedance assumption. A method of utilizing acoustic impedance tube measurements in the field, for acceptance testing, is indicated which should be applicable even in cases where the normal impedance assumption is violated. On the theoretical side, best agreement with experiment was obtained by utilizing a new kind of statistics which associates, with each wave packet in a random field, a scalar quantity equal to the square of the absolute value of the sound pressure in each packet, instead of the customary energy flow treatment. On the other hand, it was found necessary to utilize a semi-empirical concept of equivalent impedance as distinguished from the usual complex impedance treatment.