The electric field on the borehole axis in the presence of a casing can be divided into three zones: the near, intermediate, and far zones. Within the intermediate zone, determination of the second derivative of the potential allows me to define the formation resistivity. Outside the casing, the electric field, at large distances from the borehole, has a radial direction that provides a sufficient depth of investigation in this direction. The measurement requires knowledge of the casing conductance. Application of transmission line theory is based on the fact that the electric field in the formation is radial within the intermediate zone, resulting in the conclusion that the vertical resolution of such a measurement would depend only upon the spacing of the electrodes required to estimate the second derivative of the potential.

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Electrical logging in cased holes is a subject of strong current interest. In this paper we develop the conventional theory of physical responses of electrical logging through casing where the formation resistivity changes vertically and where the conductance of the casing varies. The theory is developed for a four‐electrode sonde with one current electrode, and three receiver electrodes that measure current leakage into the formation. All the theoretical developments in the paper are derived using approximate transmission‐line theory. An expression for the array coefficient is first derived and then used to obtain an expression for the apparent conductivity of the formation. Then a relation is established between the array coefficient, geometrical factor and conductance of the casing. This step led to a method of measuring casing conductance. Knowing casing conductance, the response of the array to vertical changes in formation conductivity is measurable. It was established, that when the array length is less than the thickness of the formation layer, the measured apparent conductivity is equivalent to the true conductivity of the formation, unlike the case of normal and induction logs. It was also established that measurement of apparent conductivity can be made accurately inside a casing of finite length when it essentially exceeds the length of the electrode array. The results contained in this paper show that electrical logging through casing is possible in wells with conventional casing strings that penetrate layered sedimentary formations.

The purpose of this study is to review the published literature for the range of radiographic findings present in patients suffering from coronavirus disease 2019 infection. This novel corona virus is currently the cause of a worldwide pandemic. Pulmonary symptoms and signs dominate the clinical picture and radiologists are called upon to evaluate chest radiographs (CXR) and computed tomography (CT) images to assess for infiltrates and to define their extent, distribution and progression. Multiple studies attempt to characterize the disease course by looking at the timing of imaging relative to the onset of symptoms. In general, plain CXR show bilateral disease with a tendency toward the lung periphery and have an appearance most consistent with viral pneumonia. Chest CT images are most notable for showing bilateral and peripheral ground glass and consolidated opacities and are marked by an absence of concomitant pulmonary nodules, cavitation, adenopathy and pleural effusions. Published literature mentioning organ systems aside from pulmonary manifestations are relatively less common, yet present and are addressed in this review. Similarly, publications focusing on imaging modalities aside from CXR and chest CT are sparse in this evolving crisis and are likewise addressed in this review. The role of imaging is examined as it is currently being debated in the medical community, which is not at all surprising considering the highly infectious nature of Severe Acute Respiratory Syndrome coronavirus 2.

This paper considers the behavior of the frequency and the distribution of the spectrum poles differ for and transient responses of the magnetic field created conductors having finite and infinite dimensions. by currents in conducting bodies. It is assumed that The dependence of various components of the field on the surrounding medium is an insulator. The relation-conductivity differs, which is important for under2 ship between the low-frequency part of the frequency standing the resolvjing capabilities of the inductive spectrum and the late stage of the transient response metinrds depends on the type of conductor. These responses CONDUCTORS OF FINITE DIMENSIONS Let us assume that there is a source of primary field in free space, for example, a loop through which an alternating current is flowing. When the primary magnetic field changes in time a primary eddy electrical field E,,(a) appears at every point u. This field is given by .&(a) = iwpu,H,,G(a)Zo, (1) where i=cl, o=Zirf 643 HO G eo and is the angular frequency (radianisec), is the permeability of free space, p0 = 4n x 10-7H/M, is the amplitude of the primary magnetic field (A/M), is a function of the geometrical parameters only (M-a), is a unit vector defining the direction of E,(a)> of the primary electrical field, currents arise in the conductor. When the electrical field E. intersects the surface, electrical charges appear instantly (quasistationary approximation), due to which the normal component of the electrical field I;' at the internal side of the surface is equal to zero. Hence, at every point inside the conductor the current density J is given by 7 = YE = r(Eo + fP),where y is the conductivity (mhosim). and E. is the primary electrical field.E is the electrical field connected with the change in time of the inductive currents as well as with the electrical field of the surface charges. It is reasonable to consider these two components together.Thus, in the common case, there are two kinds of field sources: (1) electrical charges. and (2) vortex currents. Obviously, the total electrical charge on the surface is equal to zero. Correspondingly, outside E,(a) is in units of V/M. the conductor, the magnetic field is defined by the Suppose a conductor of finite dimensions is eneddy currents, while the electrical field has two types veloped by an insulator and is subjected to a primary of sources: (I) currents and (2) charges. field.