Real Physical Model Research Articles

Efficient reduction of fault current through the grounding grid of a substation supplied by an overhead line

AbstractThe paper presents a directly applicable and reasonably accurate method for the evaluation of the effects of the counterpoise, the measure for the reduction of the fault current through the substation grounding grid. Under practical conditions the magnitude of the current diverted from a substation grounding grid by the counterpoise conductor is a very complex function of the self and mutual impedances of overhead and underground conductors, substation grounding impedance, transmission line towers resistance, proximity effect between the grounding grid and the counterpoise conductor, as well as on many other factors of lower order. Therefore certain idealizations and simplification of the real physical model were indispensable to develop the mathematical model presented here. The obtained expressions are mostly based on the general equations of a line represented by its lumped parameters and the general equations of uniform ladder circuits. Copyright © 2006 John Wiley & Sons, Ltd.

Numerical Simulation Techniques to Study the Structural Response of the Human Chest Following Median Sternotomy

The optimal closure technique of median sternotomy remains controversial. The objective of this study was to analyze the structural response of the separated sternum using computer-based numerical discretization techniques, such as finite element methods. Thoracic computer tomographic scans (2.5-mm slices) were segmented, analyzed by image processing techniques, and transferred into a three-dimensional finite element model. In a first approach a linear elastic material model was used; neglecting nonlinear and damage effects of the bones. The influence of muscles and tendons was disregarded. Nonlinear contact conditions were applied between the two sternal parts and between fixation wires and sternum. The structural response of this model was investigated under normal breathing and asymmetric leaning on one side of the chest. Displacement and stress response of the segmented sternum were compared regarding two different closure techniques (single loop, figure-of-eight). The obtained results revealed that for the normal breathing load case the single loop technique is capable of clamping the sternum sufficiently, assuming that the wires are prestressed. For asymmetric loading conditions, such as leaning on one side of the chest, the figure-of-eight loop can substantially reduce the relative longitudinal displacement between the two parts compared with the single loop. The application of numerical simulation techniques using complex computer models enabled the determination of structural behavior of the chest regarding the influence of different closure techniques. They allowed easy and fast modifications and therefore, in contrast to a real physical model, in-depth parameter studies.

Polarization effects in the radiation of magnetized envelopes and extended accretion structures

We have calculated the degree and position angle of the polarization of radiation scattered in a magnetized, optically thin or optically thick envelope around a central source, taking into account Faraday rotation of the plane of polarization during the propagation of the scattered radiation and the finite size of the radiation source. The wavelength dependence of the degree of polarization can be used to estimate the magnetic field of the source (a star, the region around a neutron star, or a black hole), and we have used our calculations to estimate the magnetic fields in a number of individual objects: several hot O and Wolf-Rayet stars, compact objects in X-ray close binaries with black holes (SS 433, Cyg X-1), and supernovae. The spectrum of the linear polarization can be used to determine the magnetic field in the vicinity of a central supermassive black hole, where the polarized optical radiation is generated. In a real physical model, this value can be extrapolated to the region of the last stable orbit. In the future, the proposed technique will make it possible to directly estimate the magnetic field in the region of the last stable orbit of a supermassive black hole using X-ray polarimetry.

Evaluation of Physical versus Virtual Surgical Training Simulators

With the recent attention on patient safety, there is an increased interest in standardized training for laparoscopic surgeons. Studies have shown that laparoscopic simulators can be used to train surgical skills. A comparison of two popular systems (a real physical model and a virtual model) was conducted to determine the relative effectiveness of the systems for training purposes. Twenty-two medical students and surgical residents were tested on both simulators. Time to task completion and errors committed were recorded and compared. Our results showed that the physical training system was more sensitive to the experience levels of the subjects than the virtual system, and may be more effective as a tool for standardized training. However, as virtual reality technology becomes better developed, and surgeons become more familiar with the technology, we may see a change.

Does Touching a Projection Augmented Model and Interacting with it using a Spatially-Coincident Device, Affect a User's Perception of its Size?

A Projection Augmented model (PA model) is a novel type of display. It consists of a real physical model, onto which a computer image is projected to create a realistic looking object. PA models provide their users with whole-hand haptic feedback and support spatially-coincident haptic interaction devices. This paper reports on an experiment that investigated the effect these factors have on a user’s perception of the size a PA model. Results showed that touching a PA model increased the accuracy of size estimates; however using a spatially-coincident haptic interaction device had no effect.

Intelligent modeling of materials

Intelligent modeling of materials

Numerical inversion of two-dimensional geoelectric conductivity distributions from magnetotelluric data

In this paper, a new inversion technique, called the minimum first-order entropy (MinEnt-1) method, is proposed for the reconstruction of two-dimensional geoelectric conductivity distributions from magnetotelluric (MT) data. The method combines an iterative search with a regularization technique based on the minimization of the entropy measure of the vector of first-differences of the unknown conductivities. Numerical simulations, using synthetic data corrupted with gaussian noise, show that the MinEnt-1 algorithm converges to excellent conductivity reconstructions, yielding in many cases results that are superior to those obtained by the maximum entropy formalism. Unlike other classical regularization schemes, which maximize smoothness for a given data, the proposed method constrains the class of possible solutions into a restricted set of low entropy models, constituted by locally smooth regions separated by sharp discontinuities. This may be an effective approach for the incorporation of prior information about the local smoothness of the real physical model.

Derivation of inertial forces from the Einstein-de Broglie-Bohm (E.d.B.B.) causal stochastic interpretation of quantum mechanics

The physical origin of inertial forces is shown to be a consequence of the local interaction of Dirac's real covariant ether model(1) with accelerated microobjects, considered as real extended particlelike solitons, piloted by surrounding subluminal real wave fields packets.(2) Their explicit form results from the application of local inertial Lorentz transformations to the particles submitted to noninertial velocitydependent accelerations, i.e., constitute a natural extension of Lorentz's interpretation of restricted relativity.(3) Indeed Dirac's real physical covariant ether model implies inertial forces if one considers the real accelerated noninertial motions of general relativity, defined within the absolute local inertial frames associated with the observed local isotropy of the 2.7° K background microwave radiation.(4) Inertia thus appears as a necessary consequence of the real particle motions described by the E.d.B.B. formalism of quantum mechanics.

Wave propagation in a qualitative model of combustion under equilibrium conditions

We study various aspects of wave motion within the context of the Fickett-Majda qualitative model of combustion, under the assumption that the waves are propagating into an equilibrium state of a material governed by a two-way, model chemical reaction. In particular, we examine the hydrodynamic stability of an equilibrium state and the properties of a wavefront propagating into the state. We also investigate the signalling problem and use asymptotic methods and steepest descent to determine the long time behavior of the solution. Comparisons are made to the real physical model.

SIMPLIFIED TRANSFER FUNCTION MODEL FOR GENERATORS

ABSTRACT The mathematical equations which are commonly used to represent generators are cumbersome to handle and when applied in transient studies of electrical power systems take up much computer storage and waste a lot of computer time. A simplified model representation of a generator would be more convenient. A first order transfer function model of a generator has been obtained by the model adjustment, method. It is shown how the model adjustment techniqjes was used to obtain the parameters of this simplified model from input-output data of the real physical model representation.

On solitary waves in liquid crystals

The problem of solitary waves in nematic liquid crystals is discussed in connection with an experiment reported by Zhu. This discussion, which is different from that of Lin Lei et al., is based on the well-known nonlinear diffusion equation. We present a real physical model, which can be described by a nonlinear diffusion equation.