On: “Ionospheric induced very low frequency electric field wavetilt changes” by D. V. Thiel and I. J. Chant (GEOPHYSICS, Jan., 1982, p. 60–62)

Geophysics ◽  
1984 ◽  
Vol 49 (8) ◽  
pp. 1388-1388
Author(s):  
James R. Wait
Keyword(s):  
Electric Field ◽  
Surface Impedance ◽  
Low Frequency ◽  
Impedance Measurement ◽  
Minor Role ◽  
Elliptical Polarization ◽  
Vertical Electric Field ◽  
A Minor ◽  
Ground Wave ◽  
Measuring Scheme

With all due respect to Singh and Rankin (1983), I believe that their criticism of the paper by Thiel and Chant (cited above) needs clarification. Contrary to the assertion by Singh and Rankin, the quoted formula for the function [Formula: see text] (incorrectly called a wavetilt) can indeed depend upon the mode of propagation. The factor sin θ, appearing in the quoted expressions, is the sine of the complex angle of the incident wave whether it be a ground wave or a downgoing ionospherically reflected wave. This point is central to the long‐standing dispute between the “Cagniard school” of magnetotelluric sounding and those who believe that source field characteristics can play a role. Thiel and Chant correctly pointed out that the elliptical polarization of the downgoing wave can mess up the results. But possibly they overlooked that this effect, in a surface impedance measurement, is minimized compared with a true wavetilt measurement. The latter senses the vertical electric field with a vertical (i.e., whip) antenna, whereas in a true surface impedance measuring scheme both horizontal E and horizontal H fields are sensed. Actually Thiel and Chant measured surface impedance, so the elliptical polarization of the downgoing wave probably plays a minor role.

On modeling airborne very low‐frequency measurements

Geophysics ◽  
1989 ◽  
Vol 54 (12) ◽  
pp. 1596-1606 ◽  
Author(s):  
Ari Poikonen ◽  
Ilkka Suppala
Keyword(s):  
Plane Wave ◽  
Electric Field ◽  
Numerical Models ◽  
Vertical Component ◽  
Low Frequency ◽  
Primary Field ◽  
Vertical Electric Field ◽  
Inhomogeneous Plane ◽  
Inhomogeneous Plane Wave ◽  
Attenuation Characteristics

Numerical models employed in ground VLF modeling use a normally incident (homogeneous) plane wave as a primary field. We show that these models are not directly applicable to modeling the impedance and wavetilt in the air, quantities needed in the interpretation of airborne VLF resistivity measurements. Instead, the primary field must be replaced by an inhomogeneous plane wave incident on the ground at an angle close to 90 degrees in order to provide the correct behavior of the apparent resistivities in the air. VLF magnetic polarization parameters, however, can be modeled in the air using the normally incident plane wave as a primary field. We also show that the plane‐wave analysis provides the same attenuation characteristics for the wavetilt in the air that is predicted by the Norton’s surface wave obtained by using the vertical electric dipole as a source. Use of the inhomogeneous plane wave introduces the vertical component of the electric field in the model. A 2‐D modeling technique based on the network solution is used to demonstrate the effects of the vertical electric field in the H‐polarization case. The vertical electric field generates charge distributions on the horizontal boundaries of conductors. In the case of a vertical sheet‐like conductor, these charges cause a slight asymmetry in apparent‐resistivity anomalies. Attenuation characteristics of various VLF anomalies with altitude are also presented. The H‐polarization anomalies attenuate much more rapidly in the air than those for E‐polarization due to the difference in the dominating source of EM fields in each polarization.

Electric Field Strength Dependent Electric Conductivity in Highly Insulating Materials

2006 ◽  
Vol 514-516 ◽  
pp. 920-924
Author(s):  
Eugen R. Neagu ◽  
José N. Marat-Mendes
Keyword(s):  
Electric Field ◽  
Electric Conductivity ◽  
Ambient Air ◽  
Minor Role ◽  
Insulating Materials ◽  
Excess Electrons ◽  
The Mean ◽  
A Minor ◽  
Field Strengths ◽  
Trapped Charge

The electric conductivity σ in highly insulating materials is determined by the equilibrium thermally generated carriers and by the injected carriers. The injected excess electrons will dominate the thermally generated electrons when the total number of injected electrons substantially exceeds the total number of initially empty electron traps existing in the material. Under these circumstances the electrical charge transport mechanism is no longer ohmic. In order to analyze the dependence of σ upon injected/trapped charge, isothermal and non-isothermal currents in Teflon FEP have been investigated at various temperatures, field strengths, in a vacuum or in ambient air conditions. At temperatures below 413 K, for charging times longer than about 10 s but shorter than about 600 s, the electric conductivity is almost electrical field strengths independent proving that the injected charge plays a minor role. For these conditions the charge is mostly trapped in superficial traps. At higher temperatures σ is field dependent. The final thermally stimulate discharge current has a peak around 500 K with a mean apparent activation energy around 1.35 eV. For a well conditioned sample the peak current is strongly dependent on the charging electric field and on the mean trapping depth of the injected charge. The relaxation time of the trapped charge is around 106 s at 523 K, proving that the injected charge is very stable, a fact of significant importance for applications.

scholarly journals Variations of strong earthquake ground shaking in the Los Angeles area

1974 ◽  
Vol 64 (5) ◽  
pp. 1429-1454
Author(s):  
M. D. Trifunac ◽  
F. E. Udwadia
Keyword(s):  
Los Angeles ◽  
Ground Motion ◽  
Spectral Characteristics ◽  
Low Frequency ◽  
Soil Conditions ◽  
Minor Role ◽  
Ground Shaking ◽  
Local Soil ◽  
Recording Station ◽  
A Minor

Abstract Accelerograms recorded at six stations in the metropolitan Los Angeles area during the Borrego Mountain, 1968, the Lytle Creek, 1970, and the San Fernando, 1971, earthquakes in southern California have been studied. In comparing the ground motions recorded during different earthquakes at each of the six stations and in correlations of these motions recorded at different stations during the same earthquake, those aspects of the analysis which emerge from this study and are relevant for seismic zoning have been emphasized. It has been found that the patterns of strong ground shaking in this area depend predominantly on the mechanism and the distance of an earthquake source from a recording station and that the local soil conditions played only a minor role in modifying the ground motion at this particular area. It has been shown that gross spectral characteristics of ground motion recorded at various stations can be approximately related by the seismic moment at the low-frequency end and by the stress drop at the high-frequency end.

Comparison of the low-frequency variations of the vertical and horizontal components of the electric background field at the sea bottom

Geophysics ◽  
2012 ◽  
Vol 77 (6) ◽  
pp. E391-E396 ◽  
Author(s):  
Eirik G. Flekkøy ◽  
Endre Håland ◽  
Knut Jørgen Måløy
Keyword(s):  
Electric Field ◽  
Power Spectra ◽  
Low Frequency ◽  
Background Field ◽  
Sea Bottom ◽  
Vertical Electric Field ◽  
The Difference ◽  
Natural Electric Field ◽  
Frequency Variations ◽  
Averaging Techniques

Natural electric field variations are measured at the sea bottom over long periods of time by means of stationary, vertical, and horizontal galvanic antennas. We compare the power spectra of the vertical and horizontal field components and the extent to which they may be reduced by standard averaging techniques. Although the raw spectra of the vertical and horizontal components do not differ greatly, the difference in the spectra after averaging is significantly greater. Most significantly, in the frequency range between 0.0005 and 0.03 Hz, this averaging scheme suppresses the vertical electric field component more strongly than the horizontal component.

Reply by the authors (D. V. Thiel and I. J. Chant) to J. R. Wait

Geophysics ◽  
1984 ◽  
Vol 49 (8) ◽  
pp. 1389-1389
Author(s):  
D. V. Thiel ◽  
I. J. Chant
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Electric Field ◽  
Surface Impedance ◽  
Radiation Source ◽  
Horizontal Magnetic Field ◽  
Impedance Measurements ◽  
Vertical Electric Field ◽  
Elliptically Polarized ◽  
Polarized Radiation

In his discussion of our paper Wait refers to the effect of an elliptically polarized radiation source on both electric field wavetilt and surface impedance measurements. If such measurements are made at the surface of a uniform isotropic half‐space, then both the horizontal electric and horizontal magnetic field strengths measured will depend upon the characteristics of the polarization ellipse and the orientation of the antennas whereas the vertical electric field strength is independent.

scholarly journals Selection of Cytochrome b Mutants Is Rare among Plasmodium falciparum Patients Failing Treatment with Atovaquone-Proguanil in Cambodia

2020 ◽  
Vol 65 (3) ◽  
Author(s):  
Jessica T. Lin ◽  
Andreea Waltmann ◽  
Kara A. Moser ◽  
Zackary Park ◽  
Yu Bin Na ◽  
...  
Keyword(s):  
Clinical Trial ◽  
Plasmodium Falciparum ◽  
De Novo ◽  
Single Point ◽  
Low Frequency ◽  
Multidrug Resistant ◽  
Minor Role ◽  
Single Point Mutation ◽  
Content Type ◽  
A Minor

ABSTRACT Atovaquone-proguanil remains effective against multidrug-resistant Plasmodium falciparum in Southeast Asia, but resistance is mediated by a single point mutation in cytochrome b (cytb) that can arise during treatment. Among 14 atovaquone-proguanil treatment failures in a clinical trial in Cambodia, only one recrudescence harbored the cytb mutation Y268C. Deep sequencing did not detect the mutation at baseline or in the first 3 days of treatment, suggesting that it arose de novo. Further sequencing across cytb similarly found no low-frequency cytb mutations that were up-selected from baseline to recrudescence. Copy number amplification in dihydroorotate dehydrogenase (DHODH) and cytb as markers of atovaquone tolerance was also absent. Cytb mutation played a minor role in atovaquone-proguanil treatment failures in an active comparator clinical trial.

The Effect of Path Length and Display Size on Memory for Spatial Information

2012 ◽  
Vol 59 (3) ◽  
pp. 147-152 ◽  
Author(s):  
Katherine Guérard ◽  
Sébastien Tremblay
Keyword(s):  
Path Length ◽  
Potential Role ◽  
Spatial Information ◽  
Recall Performance ◽  
Minor Role ◽  
Length Effect ◽  
Serial Memory ◽  
Fixed Reference ◽  
A Minor

In serial memory for spatial information, some studies showed that recall performance suffers when the distance between successive locations increases relatively to the size of the display in which they are presented (the path length effect; e.g., Parmentier et al., 2005) but not when distance is increased by enlarging the size of the display (e.g., Smyth & Scholey, 1994). In the present study, we examined the effect of varying the absolute and relative distance between to-be-remembered items on memory for spatial information. We manipulated path length using small (15″) and large (64″) screens within the same design. In two experiments, we showed that distance was disruptive mainly when it is varied relatively to a fixed reference frame, though increasing the size of the display also had a small deleterious effect on recall. The insertion of a retention interval did not influence these effects, suggesting that rehearsal plays a minor role in mediating the effects of distance on serial spatial memory. We discuss the potential role of perceptual organization in light of the pattern of results.

Use of Different Tissue Thromboplastins in the Control of Anticoagulant-Therapy

1958 ◽  
Vol 02 (05/06) ◽  
pp. 462-480 ◽  
Author(s):  
Marc Verstraete ◽  
Patricia A. Clark ◽  
Irving S. Wright
Keyword(s):  
Prothrombin Time ◽  
Anticoagulant Therapy ◽  
Factor Vii ◽  
Rabbit Brain ◽  
Minor Role ◽  
Rabbit Lung ◽  
Coagulation Mechanism ◽  
Time Test ◽  
The One ◽  
A Minor

SummaryAn analysis of the results of prothrombin time tests with different types of thromboplastins sheds some light on the problem why the administration of coumarin is difficult to standardize in different centers. Our present ideas on the subject, based on experimental data may be summarized as follows.Several factors of the clotting mechanism are influenced by coumarin derivatives. The action of some of these factors is by-passed in the 1-stage prothrombin time test. The decrease of the prothrombin and factor VII levels may be evaluated in the 1-stage prothrombin time determination (Quick-test). The prolongation of the prothrombin times are, however, predominantly due to the decrease of factor VII activity, the prothrombin content remaining around 50 per cent of normal during an adequate anticoagulant therapy. It is unlikely that this degree of depression of prothrombin is of major significance in interfering with the coagulation mechanism in the protection against thromboembolism. It may, however, play a minor role, which has yet to be evaluated quantitatively. An exact evaluation of factor VII is, therefore, important for the guidance of anticoagulant therapy and the method of choice is the one which is most sensitive to changes in factor VII concentration. The 1-stage prothrombin time test with a rabbit lung thromboplastin seems the most suitable method because rabbit brain preparations exhibit a factor VII-like activity that is not present in rabbit lung preparations.

Sign in / Sign up

Export Citation Format

Share Document