Induction probes differential

Examples of these curves are presented in Figs. 5.54 5.56. The main features of profiling curves such as differentiation, width of the intermediate zone, are similar to those in the second case. Although the vertical response of the probe becomes better with an increase of a frequency, a value of apparent conductivity essentially differs from that corresponding to a medium with conductivity even for large values of n2- For example, if 0 /g2 = 1/16, H/L — 0.5 and ri2 = 0.16 ratio Oa/G = 2.5. Determination of thickness of such beds is also difficult. If // < 1/4L and oi/a 1/8, distinguishing such a bed is practically impossible with a two coil induction probe. 

Arbitrarily, a multi-coil induction probe can be presented as a sum of two-coil induction probes. Currently, there are known symmetrical and non-symmetrical multi-coil induction probes, and their characteristics will be considered in detail in the next sections. As a rule in induction logging using one frequency the electromotive force, caused by the current in the transmitter coil or coils, is significantly greater than that generated by induced currents in the medium. For this reason an additional compensating coil to increase the accuracy of measurement is installed. Due to this the electromotive force caused by the primary field is practically equal to zero. It is also appropriate to notice that some differential probes do not require a compensation coil. 

Methods of choosing probe parameters are based on the use of differential and integral responses of two-coil induction probes. The differential radial response defines a signal from a thin cylindrical shell, expressed in units of the signal, caused by currents in a uniform conducting medium. In accord with Doll s theory, described above, we have ... 

It is obvious that the radial differential response of the multi-coil induction probe does not depend on the distribution of conductivity in the radial direction if within every cylindrical layer the resistivity remains constant. 

It is obvious that the number of equations can be taken either equal to the unknown parameters or greater. In the latter the least squares method can be applied if the system is linear or in a more general case gradient methods can be used. Function Gi La0) can be either the geometric factor or a very thin cylindrical shell (the differential response) or that of a relatively thin cylindrical layer. In such a case this function is expressed through the integral response of a two-coil induction probe Gi(La0)-... 

Thus, for efficiency of differential induction probes designed to measure a formation conductivity, two conditions have to be met, namely ... 

As is well known, coil induction probes used in induction logging have various arrangements of coils. It is appropriate to distinguish in every differential probe the basic (main) two-coil probe having a maximal product of transmitter (T) and receiver (R) coil moments. Other coils are considered to be focusing coils and, they form several additional coil probes which provide focusing features of the induction tool. 

Introducing a fifth compensating coil, coefficient K becomes equal to zero, and correspondingly the radial response somewhat improves at its initial part. From this consideration follows that with an increase of the length of two-coil induction probes, forming a differential four-coil probe, the cylinder radius, characterized by small values of geometric factor, increases, provided that the primary electromotive force is compensated. 

G is the differential response of a four-coil induction probe and defines the ratio of signals from a thin cylindrical shell to that from a uniform medium. 

Calibration curves for basic two-coil induction probes are also shown in Figs. 7.11-7.13. From comparison with calibration curves of corresponding differential probes it follows that a decrease of the signal with respect to that of the basic probe within the range of measured resistivities in average constitutes ... 

As was shown before, the better the focusing of a multi-coil induction probe the narrower the range of measured resistivities, and correspondingly the same effect is observed for other differential probes. We will characterize the range of measured resistivities by the... 

Any multi-coil induction probe, regardless of the amount of transmitter and receiver coils, by no means performs focusing of the field as it takes place, for example, in optics. In effect, every induction probe, except a two-coil one, is a differential system measuring such a difference of signals in receivers that the influence of induced currents in the borehole and in the invasion zone is significantly reduced. 

In fact, the integral response, as well as the differential one, defining a signal in receiver coils due to induced currents in an arbitrary cylindrical layer with a constant resistivity, present the basic element of these calculations. However, the presence of caverns, deviation from radial distribution of resistivity because of nonuniform penetration of a borehole filtrate into a formation, its finite thickness are factors which can influence the focusing features of multi-coil induction probes. In order to eliminate the influence of these factors and to increase the depth of investigation, regardless of the geoelectric section, we will consider in this chapter another approach, based on the use of a two-coil probe and a simultaneous measurement at two or more frequencies if the quadrature component is measured. 

The induction of PAL activity at the onset of vascular differentiation can be shown by the use of plant tissue cultures (37-39). Xylem cells with secondary and lignified walls are differentiated over a time course of 3-14 days by the application of the plant growth factors naphthylene acetic acid (NAA) and kinetin in the ratio 5 1 (1.0 mg/liter NAA, 0.2 mg/liter kinetin) to tissue cultures of bean cells (Phaseolus vulgaris) (37,40). The time for differentiation varies with the type of culture, solid or suspension, and with the frequency and duration of subculture, but for any one culture it is relatively constant (37,41,42). At the time of differentiation when the xylem vessels form, the activity of PAL rises to a maximum. The rising phase of the enzyme activity was inhibited by actinomycin D and by D-2,4-(4-methyl-2,6-dinitroanilino)-N-methylpropionamide (MDMP) applied under carefully controlled conditions (42). This indicated that both transcription and translation were necessary for the response to the hormones. Experiments using an antibody for PAL and a cDNA probe for the PAL-mRNA have also shown that there is an increase in the amount of transcript for PAL during the formation of lignin when Zinnia mesophyll cells are induced to form xylem elements in culture (Lin and Northcote, unpublished work). 

In spite of these problems, induction or disappearance of optical activity in products affords a sensitive measure of the degree to which cholestric liquid-crystalline or other chiral solvents Interact with reacting solutes. When absolute rotations are large, as they are for JBN (30) even small interactions can be detected. On a molecular level, these interactions can be considered dlastereoraeric and arising via differential solvation (52) of the R or form of BN by enantioraerically pure neighbors. The macro order Imposed by a cholesteric phase may result in more complex Interactions. It is these which we seek to probe. 

The determination of copper is also discussed under Multi-Metal Analysis of Soils in Sect. 2.55 (atomic absorption spectrometry), Sect. 2.55 (emission spectrometry), Sect. 2.55 (inductively coupled plasma atomic emission spectrometry), Sect. 2.55 (photon activation analysis), Sect. 2.55 (neutron activation analysis), Sect. 2.55 (electron probe microanalysis) and Sect. 2.55 (differential pulse anodic stripping voltammetry). 

H. Doll also introduced the differential multi-coil probes, which became very efficient logging tools and defined the path of development and application of induction logging over almost forty years. The use of these differential measurements in induction logging provides a result in which the effect of the borehole fluid, and in many cases also the invasion zone, on measurements is greatly reduced. Such devices are described in detail in this monograph. 

The use of differential multi-coil probes is the most conventional approach in application of induction logging. 

Interpretation of induction logging data measured by such differential probes is mainly based on measuring the quadrature component of the electromotive force, shifted by 90° with respect to the primary electromotive force. 

As is well known, an increase of the depth of investigation in induction logging is usually realized with the help of multi-coil differential probes that in many cases permit us to eliminate the influence of currents in the borehole and in the invasion zone. 

All these factors, which restrict to a certain degree the application of induction logging with differential probes, impel us to investigate the possibilities of the transient method, which is successfully applied in other areas of exploration geophysics. 

Fig. 3. The difTerent oxidative metabolic pathways of antipyrine. hydroxymephenytoin was not affected by either treatment, nor was the metabohc ratio of sparteine/dehydrosparteine in 8 hour urine [6, 27], The results of this study have clearly illustrated that the cocktail allows the assessment of the differential effects of dmg treatment on oxidative enzyme activity. This approach could also be usefiil in new dmg development in order to assess whether or not a new compoimd will give rise to potential risks of dmg-drag interactions through induction or inhibition of dmg metabolism. Rather than performing several different studies with different (probe) dmgs, the cocktail approach should allow sufficient pertinent information to be obtained in the context of one experimental protocol.

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