Magnetotelluric soundings across the Pemberton Volcanic Belt, British Columbia

1980 ◽  
Vol 17 (2) ◽  
pp. 161-167 ◽  
Author(s):  
H. Dragert ◽  
L. K. Law ◽  
P. O. Sule
Keyword(s):  
British Columbia ◽  
Transfer Functions ◽  
Three Dimensional ◽  
Volcanic Belt ◽  
Two Dimensional ◽  
Magnetotelluric Soundings ◽  
Western Cordillera ◽  
Profile Line ◽  
Conductivity Structure ◽  
Short Period

Magnetotelluric soundings were carried out at three sites about 30 km apart in a line crossing the Lillooet Valley near Pemberton, British Columbia, to determine the regional conductivity structure and its relationship to the Meager Creek geothermal area. Telluric data were limited to a period band of 10–500 s, while geomagnetic data were recorded in this band as well as a longer period band of 5 min–3 h.Single-station vertical transfer functions indicate that no simple, two-dimensional conductivity discontinuity crosses the profile line or its immediate extension. Thus, the Pemberton volcanic line of plutons does not have an associated two-dimensional continuous conductivity anomaly. Impedance tensors calculated from the short period data are dominated by three-dimensional effects and surface structure effects at the western and eastern sites respectively. The results from the central site indicate a macro-anisotropy in horizontal conductivities, possibly produced by local fracture zones. One-dimensional modelling suggests a vertical conductivity structure consisting of a highly resistive upper crust 15–25 km thick, underlain by a conductive region. Though this conductive layer beneath Pemberton is more resistive, a similar layer has been noted in previous studies in southern British Columbia and appears to be a feature of the western Cordillera.

Groundwater exploration using combined controlled-source and radiomagnetotelluric techniques

Geophysics ◽  
2005 ◽  
Vol 70 (1) ◽  
pp. G8-G15 ◽  
Author(s):  
Laust B. Pedersen ◽  
M. Bastani ◽  
L. Dynesius
Keyword(s):  
Transfer Functions ◽  
Three Dimensional ◽  
Groundwater Exploration ◽  
Impedance Tensor ◽  
Two Dimensional ◽  
Controlled Source ◽  
Reflection Seismic ◽  
Seismic Sections ◽  
Clay Layers ◽  
Clay Lenses

Radiomagnetotelluric (RMT) (14–250 kHz) combined with controlled-source magnetotelluric (CSMT) (1–12 kHz) measurements were applied to the exploration of groundwater located in sandy formations at depths as great as 20 m below thick clay lenses. A combination of approximately 30 radio frequencies and controlled-source frequencies is essential for penetrating the thick clay layers. The electromagnetic transfer functions of impedance tensor and tipper vectors point toward a structure that is largely two-dimensional, although clear three-dimensional effects can be observed where the sandy formation is close to the surface. The determinant of the impedance tensor was chosen for inversion using two-dimensional models. The final two-dimensional model fits the data to within twice the estimated standard errors, which is considered quite satisfactory, given that typical errors are on the level of 1% on the impedance elements. Comparison with bore-hole results and shallow-reflection seismic sections show that the information delivered by the electromagnetic data largely agrees with the former and provides useful information for interpreting the latter by identifying lithological boundaries between the clay and sand and between the sand and crystalline basement.

A Transfer Function Analysis of a Geomagnetic Depth Sounding-Profile across Central British Columbia

1973 ◽  
Vol 10 (7) ◽  
pp. 1089-1098 ◽  
Author(s):  
H. Dragert
Keyword(s):  
British Columbia ◽  
Transfer Functions ◽  
Function Analysis ◽  
Three Dimensional ◽  
Vertical Component ◽  
Rocky Mountain ◽  
Three Dimensional Model ◽  
Transfer Function Analysis ◽  
Single Station ◽  
Depth Sounding

Time variations of the geomagnetic field observed across British Columbia at a mean latitude of 54 °N are analyzed using 'single-station' and 'paired-station' optimum transfer functions. The frequency and spatial dependence of both coastal and inland geomagnetic anomalies are estimated with the following results. (1) The normal coast effect is strongly perturbed by lateral conductivity inhomogeneities both north and south of the profile. (2) A simple, single NW–SE striking conductivity contrast between the Cordillera and plains cannot account for the total geomagnetic anomaly in the area of the Rocky Mountain Trench; a three-dimensional model is required, incorporating (i) a lateral inhomogeneity striking east–west and located to the south of the profile, (ii) the effect of induction by the vertical component of source or secondary fields.

scholarly journals Exploring Effects in Tippers at Island Magnetic Observatories due to Realistic Depth- and Time-Varying Oceanic Electrical Conductivity

2020 ◽  
Author(s):  
Rafael Rigaud ◽  
Mikhail Kruglyakov ◽  
Alexey Kuvshinov ◽  
Katia Pinheiro ◽  
Johannes Petereit ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Electric Conductivity ◽  
Transfer Functions ◽  
Sea Water ◽  
Three Dimensional ◽  
Oceanic Lithosphere ◽  
Induction Effect ◽  
Period Range ◽  
Short Period ◽  
The World

Abstract Geomagnetic observatories around the world continuously measure time variations of the geomagnetic field. Long-period (> 3 hours) variations are traditionally used to constrain the electrical conductivity of the Earth’s mantle either in terms of one-dimensional (1-D) or three-dimensional (3-D) conductivity distributions. Recent studies have also shown that vertical transfer functions (tippers) estimated from short-period (< 3 hours) variations at island observatories can constrain the 1-D conductivity distribution of the oceanic lithosphere and upper mantle. This is feasible due to the bathymetry-dependent ocean induction effect (OIE), which originates from lateral conductivity contrasts between ocean and land and leads to non-zero tippers even for 1-D conductivity distributions below the ocean. Thus, proper analysis of island tippers requires accurate 3-D modeling of the OIE, for which so far was performed assuming constant sea water electric conductivity with depth. However, significant changes of electric conductivity with depth in the top hundreds of meters of the water column do occur. In this study we explore – using rigorous 3-D electromagnetic (EM) modeling – to what extent realistic, depth-dependent, oceanic conductivity affects island tippers. The modeling is performed for 10 island observatories around the world in the period range 10 −1 to 10 4 seconds, for which a perceptible OIE on tippers is expected. We then compare the predicted tippers with tippers estimated from the observatory data. We also investigate, again using 3-D EM modeling, the effect of seasonal variations of the oceanic conductivity and to which extent this could explain the observed systematic seasonal variation of tippers. We find good agreement between predicted and estimated tippers for all 10 island observatories. This confirms that tippers at island observatories are mainly influenced by the bathymetry-dependent OIE. Our model studies suggest that for most of the considered island observatories, the effect from depth-varying oceanic conductivity is tangible and exceeds the error floor of 0.025, which usually is assigned to tippers during their inversion. Contrarily, the effects from seasonally varying oceanic conductivity were found to be too small to be worth consideration.

High Resolution Microscopy of Multi-Layered Biological Crystals

1982 ◽  
Vol 40 ◽  
pp. 80-83
Author(s):  
H.A. Cohen ◽  
T.W. Jeng ◽  
W. Chiu
Keyword(s):  
High Resolution ◽  
Low Dose ◽  
Three Dimensional ◽  
Data Interpretation ◽  
Two Dimensional ◽  
Biological Objects ◽  
Density Maps ◽  
Density Map ◽  
Complex Crystal ◽  
High Resolution Microscopy

This tutorial will discuss the methodology of low dose electron diffraction and imaging of crystalline biological objects, the problems of data interpretation for two-dimensional projected density maps of glucose embedded protein crystals, the factors to be considered in combining tilt data from three-dimensional crystals, and finally, the prospects of achieving a high resolution three-dimensional density map of a biological crystal. This methodology will be illustrated using two proteins under investigation in our laboratory, the T4 DNA helix destabilizing protein gp32*I and the crotoxin complex crystal.

Instrumentation For Quantitative Microscopy

1977 ◽  
Vol 35 ◽  
pp. 206-209
Author(s):  
B. Ralph ◽  
A.R. Jones
Keyword(s):  
Volume Fraction ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Automatic Data ◽  
Phase Volume Fraction ◽  
Statistical Confidence ◽  
Resultant Data ◽  
Automatic Data Collection ◽  
Third Dimension ◽  
Evolution Of Microstructure

In all fields of microscopy there is an increasing interest in the quantification of microstructure. This interest may stem from a desire to establish quality control parameters or may have a more fundamental requirement involving the derivation of parameters which partially or completely define the three dimensional nature of the microstructure. This latter categorey of study may arise from an interest in the evolution of microstructure or from a desire to generate detailed property/microstructure relationships. In the more fundamental studies some convolution of two-dimensional data into the third dimension (stereological analysis) will be necessary.In some cases the two-dimensional data may be acquired relatively easily without recourse to automatic data collection and further, it may prove possible to perform the data reduction and analysis relatively easily. In such cases the only recourse to machines may well be in establishing the statistical confidence of the resultant data. Such relatively straightforward studies tend to result from acquiring data on the whole assemblage of features making up the microstructure. In this field data mode, when parameters such as phase volume fraction, mean size etc. are sought, the main case for resorting to automation is in order to perform repetitive analyses since each analysis is relatively easily performed.

A linearity test for thick specimens imaged by HVEM over a 180° angular range

1991 ◽  
Vol 49 ◽  
pp. 552-553
Author(s):  
Yu Liu
Keyword(s):  
Phase Contrast ◽  
Three Dimensional ◽  
Angular Range ◽  
Two Dimensional ◽  
Back Projection ◽  
Line Integral ◽  
Exponential Law ◽  
Transmission Electron ◽  
Absorption Law ◽  
Linearity Test

The image obtained in a transmission electron microscope is the two-dimensional projection of a three-dimensional (3D) object. The 3D reconstruction of the object can be calculated from a series of projections by back-projection, but this algorithm assumes that the image is linearly related to a line integral of the object function. However, there are two kinds of contrast in electron microscopy, scattering and phase contrast, of which only the latter is linear with the optical density (OD) in the micrograph. Therefore the OD can be used as a measure of the projection only for thin specimens where phase contrast dominates the image. For thick specimens, where scattering contrast predominates, an exponential absorption law holds, and a logarithm of OD must be used. However, for large thicknesses, the simple exponential law might break down due to multiple and inelastic scattering.

An Image Reconstruction System Applied to High Voltage Microscopy

1975 ◽  
Vol 33 ◽  
pp. 292-293
Author(s):  
D. E. Johnson
Keyword(s):  
High Voltage ◽  
Prior Information ◽  
Block Diagram ◽  
Three Dimensional ◽  
Real Space ◽  
Two Dimensional ◽  
Efficient Manner ◽  
Fourier Methods ◽  
Tilt Series ◽  
Methods Of Reconstruction

Increased specimen penetration; the principle advantage of high voltage microscopy, is accompanied by an increased need to utilize information on three dimensional specimen structure available in the form of two dimensional projections (i.e. micrographs). We are engaged in a program to develop methods which allow the maximum use of information contained in a through tilt series of micrographs to determine three dimensional speciman structure.In general, we are dealing with structures lacking in symmetry and with projections available from only a limited span of angles (±60°). For these reasons, we must make maximum use of any prior information available about the specimen. To do this in the most efficient manner, we have concentrated on iterative, real space methods rather than Fourier methods of reconstruction. The particular iterative algorithm we have developed is given in detail in ref. 3. A block diagram of the complete reconstruction system is shown in fig. 1.

Computer Assisted Image Reconstruction of Oligomer Structure

1976 ◽  
Vol 34 ◽  
pp. 472-473
Author(s):  
A.M. Jones ◽  
A. Max Fiskin
Keyword(s):  
Three Dimensional ◽  
Depth Of Field ◽  
Computer Assisted ◽  
Projection Data ◽  
Two Dimensional ◽  
Single Particles ◽  
Dimensional Reconstruction ◽  
Computer Assisted Image ◽  
The Fourier Transform ◽  
Space Approach

If the tilt of a specimen can be varied either by the strategy of observing identical particles orientated randomly or by use of a eucentric goniometer stage, three dimensional reconstruction procedures are available (l). If the specimens, such as small protein aggregates, lack periodicity, direct space methods compete favorably in ease of implementation with reconstruction by the Fourier (transform) space approach (2). Regardless of method, reconstruction is possible because useful specimen thicknesses are always much less than the depth of field in an electron microscope. Thus electron images record the amount of stain in columns of the object normal to the recording plates. For single particles, practical considerations dictate that the specimen be tilted precisely about a single axis. In so doing a reconstructed image is achieved serially from two-dimensional sections which in turn are generated by a series of back-to-front lines of projection data.

Polymorphic phase transition of a membrane protein - analysis of continuous diffuse electron diffraction intensity

1986 ◽  
Vol 44 ◽  
pp. 166-167
Author(s):  
Douglas L. Dorset ◽  
Andrew K. Massalski
Keyword(s):  
Molecular Sieve ◽  
Three Dimensional ◽  
Pore Geometry ◽  
Two Dimensional ◽  
Diffraction Intensity ◽  
Polymorphic Phase Transition ◽  
E Coli ◽  
Crystallographic Study ◽  
Hexagonal Form ◽  
Polymorphic Forms

Matrix porin, the ompF gene product of E. coli, has been the object of a electron crystallographic study of its pore geometry in an attempt to understand its function as a membrane molecular sieve. Three polymorphic forms have been found for two-dimensional crystals reconstituted in phospholipid, two hexagonal forms with different lipid content and an orthorhombic form coexisting with and similar to the hexagonal form found after lipid loss. In projection these have been shown to retain the same three-fold pore triplet geometry and analyses of three-dimensional data reveal that the small hexagonal and orthorhombic polymorphs have similar structure as well as unit cell spacings.

Two-Dimensional Crystallization of Tetanus Toxin

1985 ◽  
Vol 43 ◽  
pp. 528-529
Author(s):  
Jeffry A. Reidler ◽  
John P. Robinson
Keyword(s):  
Electron Microscopy ◽  
Tetanus Toxin ◽  
Structural Information ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Membrane Interface ◽  
3D Reconstructions ◽  
Cellular Receptors ◽  
Computer Reconstruction ◽  
2D Crystals

We have prepared two-dimensional (2D) crystals of tetanus toxin using procedures developed by Uzgiris and Kornberg for the directed production of 2D crystals of monoclonal antibodies at an antigen-phospholipid monolayer interface. The tetanus toxin crystals were formed using a small mole fraction of the natural receptor, GT1, incorporated into phosphatidyl choline monolayers. The crystals formed at low concentration overnight. Two dimensional crystals of this type are particularly useful for structure determination using electron microscopy and computer image refinement. Three dimensional (3D) structural information can be derived from these crystals by computer reconstruction of photographs of toxin crystals taken at different tilt angles. Such 3D reconstructions may help elucidate the mechanism of entry of the enzymatic subunit of toxins into cells, particularly since these crystals form directly on a membrane interface at similar concentrations of ganglioside GT1 to the natural cellular receptors.

Sign in / Sign up

Export Citation Format

Share Document