Computation of TM and TE modes in waveguides based on a surfaceintegral formulation

The surface integral formulation is used for the computation of TM and TE modes propagating in dielectric loaded waveguides. This formulation makes use of the surface equivalence principle whereby the field at any point internal or external to the waveguide can be expressed in terms of equivalent surface currents. This procedure reduces the original problem into a set of integro-differential equations which is then reduced to a matrix equation using the method of moments. The solution of this matrix equation provides the propagation characteristics of the waveguide and the equivalent surface currents existing on the waveguide walls. The equivalent surface currents can be used to compute the fields at all points, both inside and outside the waveguide. The surface integral method has been used to compute the propagation characteristics of waves propagating in dielectric loaded waveguides. The computed results agree very well with analytical and published data. A method that can be used to remove spurious modes is illustrated     

Transient electromagnetic scattering from dielectric objects using the electric field Integral equation with Laguerre polynomials as temporal basis functions

In this paper, we propose a time-domain electric field integral equation (TD-EFIE) formulation for analyzing the transient electromagnetic response from three-dimensional (3-D) dielectric bodies. The solution method in this paper is based on the Galerkin's method that involves separate spatial and temporal testing procedures. Triangular patch basis functions are used for spatial expansion and testing functions for arbitrarily shaped 3-D dielectric structures. The time-domain unknown coefficients of the equivalent electric and magnetic currents are approximated using a set of orthonormal basis function that is derived from the Laguerre functions. These basis functions are also used as the temporal testing functions. Use of the Laguerre polynomials as expansion functions for the transient portion of response enables one not only to handle the time derivative terms in the integral equation in an analytic fashion but also completely separates the space and the time variables. Thus, the time variable along with the Courant condition can be eliminated in a Galerkin formulation using this procedure. We also propose an alternative formulation using a different expansion of the magnetic current. The total computational cost for this new method is similar to that of an implicit marching-on in time (MOT)-EFIE scheme, even though at each step this procedure requires more computations. Numerical results involving equivalent currents and far fields computed by the two proposed methods are presented and compared.     

Finite element analysis of the three-dimensional transient temperature field in steam turbine casings

One of the important considerations going into the process of optimization of start-up schedules for steam turbines is the estimation of thermal stresses during the transients. This in turn requires prediction of the transient temperature fields. In the case of the turbine casing, the procedures are complex in view of the irregular geometrical shape. Finite element analysis offers better scope in this regard and has been employed in the present work to compute the 3-D transient temperature distribution in the casing metal. The results obtained by a code developed for a specific type of turbine casing have been compared with the values measured by experiment and have been found to validate the code. Time-temperature histories for two typical locations inside the casing metals are presented. Isotherm surfaces across the metal at a given instant are shown.     

An adaptive multipath routing scheme for connectionless traffic in an ATM network

This paper addresses the problem of routing connectionless traffic through an ATM network. A solution is proposed based on a per-packet adaptive multipath routing scheme which is added to the routing algorithm implemented at the Inter-Working Units. A scheme is presented that distributes packets among multiple Virtual Paths (VPs) according to the utilization of the links on these VPs. The utilization of the VPs is determined by a periodic feedback mechanism. Simulation studies show the effectiveness of the proposed adaptive multipath routing scheme.The work by J. Sole-Pareta was supported in part by a CIRIT (Generalitat de Catalunya) grant (expedient number EE92/2-338), and in part by the National Science Foundation under Grant No. INT-94033646. The work by I. Akyildiz was supported in part by the National Science Foundation under Grant No. INT-94033646.     

Deconvolution and total least squares in finding the impulseresponse of an electromagnetic system from measured data

Total least squares (TLS) is a method of solving over-determined sets of linear equations AX≈b when there are errors both in the observation vector b(m×1) and in the data matrix A(m×n). This method is particularly useful when the data matrix A is singular or highly ill conditioned. We present the method of finding the TLS by applying the singular value decomposition to the discrete deconvolution problem. Numerical results are presented for finding the impulse response of a transmission line from experimental data. The advantage of this approach is that this method can be automated based on the signal to noise ratio of the measured data     

KINETICS STUDIES OF THE DEVOLATILIZATION OF INDIAN COALS IN ISOTHERMAL AND NONISOTHERMAL CONDITIONS IN THERMOBALANCE AND IN A BATCH REACTOR

Kinetics studies of devolati1ization of Indian coals in inert gas atmosphere have been carried out under isothermal and nonisothermal conditions. Heating rates had negligible effects on the kinetic parameters under nonisothermal conditions. The devolati1ization reaction was found to be of the first order. The overall activation energy was found to be around 30 Kcal/mole. Isothermal data obtained from the batch reactor were also found to fit in the rate expression for a homogeneous first order, reversible reaction within temperature range of 380-445°C. The reaction was found to be kinetically controlled within the coal particles.     

Volume/surface formulation for analyzing scattering from coatedperiodic strips

A surface/surface formulation was used by Perte et al. (see IEEE Trans. Antennas. Propagat.) to analyze the scattering from periodic planar coated strips. This paper is an extension of that work where a combined volume/surface formulation has been used to solve the same problem. This formulation can be applied to problems which involve an inhomogeneous dielectric medium or/and a thick dielectric which requires the inclusion of the edge currents which were neglected as a simplification. Results obtained using the volume/surface formulation have been compared with the results published in the paper written by Petre et al. which were obtained using a surface/surface formulation     

The variation in optical gap of amorphous In33Se33Sb33 thin films with temperatures of heat treatment

Amorphous thin films of the ternary compound In₃₃Se₃₃Sb₃₃ have been produced by a vacuum evaporation technique. The optical gap Eg^opt of In₃₃Se₃₃Sb₃₃ thin films is measured as a function of temperature of heat treatment. It was found that the optical gap has a higher value than that of the binary compound In₅₀Se₅₀ at the initial stages of heat treatment, but after a particular temperature (423 K) of heat treatment, the value of optical gap decreases appreciably in the case of In₃₃Se₃₃Sb₃₃ thin films, while it increased in the case of In₅₀Se₅₀ thin films.     

The modal performance measure for parameter optimization of powersystem stabilizers

This paper develops an optimization approach using the modal performance measure for the selection of power system stabilizer (PSS) parameters in multimachine power systems. The goal of the optimization problem is to damp out the sustained low frequency oscillations in the outputs of a linearized power system. Thus, the modal performance measure optimization problem is to select a set of PSS parameters so that the area under the envelop of the oscillatory output response will be minimum. This paper also considers bounded and unbounded PSS parameters and compares the effects of bounds on the end results. Furthermore, this work also shows that the performance measure is not a convex function in the PSS parameters. That is, there exist many local minima and possibly a global minimum. Single-machine infinite-bus and two-machine three-bus power systems are used to show the effectiveness of the proposed work