Inversion of guided-wave dispersion data with application to borehole acoustics

The problem of inferring unknown geometry and material parameters of a waveguide model from noisy samples of the associated modal dispersion curves is considered. In a significant reduction of the complexity of a common inversion methodology, the inner of two nested iterations is eliminated: The approach described does not employ explicit fitting of the data to computed dispersion curves. Instead, the unknown parameters are adjusted to minimize a cost function derived directly from the determinant of the boundary condition system matrix. This results in an efficient inversion scheme that, in the case of noise-free data, yields exact results. Multimode data can be simultaneously processed without extra complications. Furthermore, the inversion scheme can accommodate an arbitrary number of unknown parameters, provided that the data have sufficient sensitivity to these parameters. As an important application, we consider the sonic guidance condition for a fluid-filled borehole in an elastic, homogeneous, and isotropic rock formation for numerical forward and inverse dispersion analysis. We investigate numerically the parametric inversion with errors in the model parameters and the influence of bandwidth and noise, and examine the cases of multifrequency and multimode data, using simulated flexural and Stoneley dispersion data.     

Solution of pressure diffusion in radially composite reservoirs

This paper presents a new general method for solving the pressure-diffusion equation in cylindrically radial composite reservoirs, where the rock and fluid properties may change radially as a function ofr. Composite systems, such as formations with wellbore filtrate invasion and reservoirs with peripheral water encroachment, can be encountered as a result of drilling, secondary oil recovery, and water influx.The new solution method utilizes the reflection and transmission concept of electromagnetics to solve fluid flow problems in three-dimensional cylindrically radial reservoirs, where heterogeneity is in only one direction. The Green's function for a point source in a three-dimensional radially composite system is developed by using the reflection and transmission method. The method as well as the point source solution are sufficiently general that they may be applied to similar fluid flow and well testing problems involving single-phase flow.     

The electrical impedance,AC conductivity and dielectric properties of phenol red compound investigated and modeled by an artificial neural network

The impedance spectroscopy, electrical conductivity and electric modulus of bulk phenol red were measured, as a function of both frequency and temperature. Artificial neural networks (ANNs) were used for modeling its electrical properties. The two parts (real and imaginary) of its complex impedance (Z*) were analyzed and the activation energy related to the electrical relaxation process was evaluated. Nyquist curves were plotted showing semicircles for the different temperatures. The AC electrical conductivity follows a power law σ_ac(ω) α ω^η. The maximum barrier height B_m was derived for specific temperatures. A plausible mechanism for the AC conduction of bulk phenol red was deduced from the temperature reliance of the frequency exponent. The dielectric data was analyzed using electric modulus as a tool. In addition, ANNs were used to model the impedance parts and the total electrical conductivity. Numerous runs were tried, to obtain the best performance. The training and prediction results were compared to the equivalent experimental results, with a good match obtained. An equation describing the experimental results was obtained mathematically, based on the use of ANNs. The outputs demonstrated that ANNs are an admirable tool for modeling experimental results.     

Polarographic microdetermination of halogens in organic compounds after oxygen flask combustion

A method for the microdetermination of organic compounds containing halogens, by a polarographic finish, is reported. After the combustion of the organic sample in the oxygen flask, the products are absorbed in a suitable absorbent and chemically treated to produce Cl(-), Br(-), BrO(3)(-) or IO(3)(-) ions in solution before the polarography. The method is applicable to partially, highly, and fully halogenated aromatic and aliphatic compounds, whether solid or liquid. The results are generally within the acceptable limits of error.     

On multidimensional ultrasonic scattering in an inhomogeneous elastic background.

This work is concerned with the modeling of elastic wave scattering by solid or fluid-filled objects embedded in an inhomogeneous elastic background. The medium is probed by a monochromatic force and the scattered field is computed (forward problem) or observed (inverse problem) at some known receiver locations. Based on vector integral equations for elastic scattering, a general framework is developed, independent of both the problem geometry and the transmitter-receiver characteristics. This framework encompasses both forward and inverse modeling. In the forward model, a Born approximation for an inhomogeneous background is applied to obtain a closed form expression for the scattered field. In the inverse model, this approximation is also invoked to linearize for the multiparameter characteristic of the object. Finally, an iterative inversion scheme alternating forward and inverse modeling is proposed to improve the resolution and accuracy of the reconstruction algorithm.     

Electron spin density distribution in the polymer phase of CsC60: assignment of the NMR spectrum

We present high resolution 133Cs-13C double resonance NMR data and 13C-13C NMR correlation spectra of 13C enriched samples of the polymeric phase of CsC60. These data lead to a partial assignment of the lines in the 13C NMR spectrum of CsC60 to the carbon positions on the C60 molecule. A plausible completion of the assignment can be made on the basis of an ab initio calculation. The data support the view that the conduction electron density is concentrated at the C60 "equator," away from the interfullerene bonds.     

Polarography as a tool in organic analysis

Summary A polarographic micromethod has been developed for the analysis of mono-, di-, tri- and polynitro compounds, standard titanium(III) sulphate solution being used as a reducing agent. The cathodic part of the Kalousek cell has been modified to serve as a reaction vessel. The results agree favourably with those obtained by visual back-titration of excess of titanium(III) with iron(III), thiocyanate being used as indicator, and the relative error is ± 0.5%. This polarographic finish proved to be of general applicability particularly with nitro compounds that give rise to coloured reduction products.

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Zusammenfassung Eine polarographische Mikromethode zur Analyse von Mono-, Di-, Tri- und Polynitroverbindungen mit Titan(III)-sulfatlösung als Reduktionsmittel wurde ausgearbeitet. Der Kathodenteil der Kalousek-Zelle wurde als Reaktionsgefäß umgestaltet. Die Analysenresultate stimmen sehr gut mit jenen überein, die man durch visuelle Rücktitration des überschüssigen Titan(III) mit Eisen(III) gegen Thiocyanat als Indikator erhält. Der relative Fehler beträgt ± 0,5%. Dieses polarographische Verfahren dürfte allgemein für Nitroverbindungen anwendbar sein, aus denen sich gefärbte Reduktions-produkte bilden können.