Showing papers by "Worcester Polytechnic Institute published in 1968"

Radiometry and coherence

Abstract: The basic laws of photometry are derived from the theory of partial coherence by considering a generalized form of the Van Cittert–Zernike theorem.

Parameters of Microstrip Transmission Lines and of Coupled Pairs of Microstrip Lines

Abstract: A theoretical analysis is presented of microwave propagation on microstrip, with particular reference to the case of coupled pairs of microstrip lines. Data on this type of transmission line are needed for the design of directional couplers, filters, and other components in microwave integrated circuits. The inhomogeneous medium, consisting of the dielectric substrate and the vacuum above it, is treated in a rigorous manner through the use of a "dielectric Green's function" which expresses the discontinuity of the fields at the dielectric-vacuum interface. Results are presented in graphical form for substrate dielectric constants of 1, 9, and 16, and a range of values of width and spacing of the strips. Numerical tables for these and other cases are also available. The tables present capacitance, characteristic impedance, and velocity of propagation of the even and odd normal modes. The method lends itself to the treatment of other geometries which are of practical interest, such as "thick" strips, presence of an unsymmetrically located upper ground plane, etc.

Quantum-Mechanical Description of Two Coupled Harmonic Oscillators

Abstract: Systems of interacting harmonic oscillators have recently received considerable attention as models for describing a variety of physical problems. We have investigated the validity of the rotating-wave approximation which constitutes the traditional approach to the solution of the dynamical problem by comparing it with the exact solution. A numerical comparison has been made and the limits of validity of the rotating-wave approximation has been established in terms of the strength of oscillator interaction.In particular, the time development of dynamical operators and certain transition probabilities have been compared. In the region where the rotating-wave approximation is valid, the time evolution of the quasiprobability distribution $P(\ensuremath{\alpha}, t)$ of one oscillator is given for several initial conditions. A counting scheme similar to the argument given by Feynman for the driven harmonic oscillator, is proposed for the interpretation of the time-dependent transition amplitudes between number states.

A model for the prediction of velocity and void fraction profiles in two‐phase flow

Abstract: An experimental study of velocity and void-fraction profiles has been carried out for the cocurrent two-phase flow of both air and water, and air and glycerine-water systems. The investigation was restricted to flow in a horizontal, 1 in. diam. tube with primary emphasis on the bubble flow regime. The assumptions which must be made to reduce the general equations of continuity, momentum, and energy to the forms appropriate for two-phase flow are presented and the equations simplified for the case of no local slip. A model is proposed which allows the determination, by trial, of the two-phase velocity and void-fraction profiles. The profiles generated by the use of the model in conjunction with experimental sampling data are presented, the profile shapes are discussed, and their variations with Reynolds and Froude numbers and gas volumetric flow fraction are shown to be self-consistent. The horizontal profiles are found to be in fair agreement with those predicted from Levy's mixing length theory. A correlation scheme is outlined which, supplemented by data over wider ranges of operating conditions, would serve as a method for estimating pressure drops in two-phase flow.