SPECTRAL STUDIES OF MARINE GEOPHYSICAL PROFILES

Geophysics ◽  
1966 ◽  
Vol 31 (1) ◽  
pp. 122-134 ◽  
Author(s):  
Norman S. Neidell
Keyword(s):  
Spectral Methods ◽  
Spectral Studies ◽  
Two Dimensional ◽  
Single Track ◽  
Structural Pattern ◽  
Sea Floor ◽  
Geophysical Exploration ◽  
Interpeak Interval ◽  
Echo Sounding

Gravity, magnetic, and echo‐sounding data profiles from widely separated single‐track surveys in the Atlantic and Indian Oceans were subjected to spectral studies. A two‐dimensional sea floor with a recurring structural pattern seemed a model able to explain the computed results. In testing the model, the most important quantity to be determined from the spectra was the “ripple frequency” or interpeak interval. During the course of this work, a number of practical problems connected with the computation of spectra were considered. In addition, the spectral methods were also shown to be tools capable of investigating more complex geophysical theories. The experience and techniques of this investigation can be of value in treating analogous problems which arise in geophysical exploration.

Structural characteristics of a developing turbulent planar jet

1986 ◽  
Vol 163 ◽  
pp. 227-256 ◽  
Author(s):  
F. O. Thomas ◽  
V. W. Goldschmidt
Keyword(s):  
Large Scale ◽  
Structural Characteristics ◽  
Energy Spectra ◽  
Two Dimensional ◽  
Structural Pattern ◽  
Potential Core ◽  
Planar Jet ◽  
Fluctuation Phase ◽  
Oriented Parallel ◽  
Phase Angles

An experimental study of the developing structural characteristics of a two-dimensional jet in an extremely quiet environment was performed. The jet, at an exit Reynolds number of 6000 and with fluctuation intensity under 0.2% at the mouth, was operated within a large anechoic room. Measurements of energy spectra, fluctuation phase angles and two-dimensionality led to the inference of structural patterns in the flow. These patterns are initially characterized by relatively strong symmetric modes exhibiting limited two-dimensionality and oriented parallel to the mouth of the jet. Subsequent downstream evolution led to the formation of an antisymmetric pattern beyond the jet potential core and the associated development of extended structures possessing a definite large lateral inclination. The results of this work suggest a developing large-scale structural pattern more complicated than previously supposed.

scholarly journals LOW- TO MID-FREQUENCY SCATTERING FROM ELASTIC OBJECTS ON A SAND SEA FLOOR: SIMULATION OF FREQUENCY AND ASPECT DEPENDENT STRUCTURAL ECHOES

2012 ◽  
Vol 20 (02) ◽  
pp. 1240007 ◽  
Author(s):  
MARIO ZAMPOLLI ◽  
AUBREY L. ESPANA ◽  
KEVIN L. WILLIAMS ◽  
STEVEN G. KARGL ◽  
ERIC I. THORSOS ◽  
...  
Keyword(s):  
Scattering Problem ◽  
Three Dimensional ◽  
Element Model ◽  
Propagation Model ◽  
Target Strength ◽  
Unexploded Ordnance ◽  
Two Dimensional ◽  
Axially Symmetric ◽  
Sea Floor ◽  
Spectral Integral

The scattering from roughly meter-sized targets, such as pipes, cylinders and unexploded ordnance shells in the 1–30 kHz frequency band is studied by numerical simulations and compared to experimental results. The numerical tool used to compute the frequency and aspect-dependent target strength is a hybrid model, consisting of a local finite-element model for the vicinity of the target, based on the decomposition of the three-dimensional scattering problem for axially symmetric objects into a series of independent two-dimensional problems, and a propagation model based on the wavenumber spectral integral representation of the Green's functions for layered media.

Survey of Two Drowned River Valleys in Devon

1955 ◽  
Vol 92 (5) ◽  
pp. 419-429 ◽  
Author(s):  
P. B. McFarlane
Keyword(s):  
Sea Level ◽  
Seismic Refraction ◽  
Sea Floor ◽  
Sea Bed ◽  
River Valleys ◽  
Echo Sounding

AbstractSeismic refraction surveys of the rock channels of the River Erme (S. Devon) and the Rivers Tawe and Torridge (N. Devon) suggest that at the time these were eroded the sea-level relative to land stood some 150 ft. lower than at present. Echo-sounding and sea-bed sampling off S. Devon have failed to reveal any trace of ancient channels in the sea floor at distances greater than one mile from shore.

Two-dimensional turbulence on the surface of a sphere

1978 ◽  
Vol 87 (2) ◽  
pp. 305-319 ◽  
Author(s):  
Cha-Mei Tang ◽  
Steven A. Orszag
Keyword(s):  
Energy Transfer ◽  
Spectral Methods ◽  
Large Scale ◽  
Spherical Geometry ◽  
Numerical Results ◽  
Two Dimensional ◽  
Atmospheric Flow ◽  
Constants Of Motion ◽  
Cartesian Geometry ◽  
Back Transfer

Large-scale atmospheric flow shares certain attributes with two-dimensional turbulence. In this paper, we study the effect of spherical geometry on two-dimensional turbulence.Energy transfer is multi-component in spherical geometry in contrast to energy transfer among triads of wave vectors in Cartesian geometry. It follows that energy transfer is more local in spherical than in Cartesian geometry. Enstrophy transfer to higher wavenumbers in spherical geometry is less than enstrophy transfer to higher wavenumbers in Cartesian geometry. Since both energy and enstrophy are inviscid constants of motion, the back transfer of energy is also less in spherical than in Cartesian geometry. Therefore, with a finite viscosity, enstrophy decays more slowly in spherical geometry than in Cartesian geometry. Here these conjectures are tested numerically by spectral methods. The numerical results agree well with the conjectures.

scholarly journals Advances in geophysical exploration of ice sheets and glaciers

1975 ◽  
Vol 15 (73) ◽  
pp. 113-135 ◽  
Author(s):  
Charles R. Bentley
Keyword(s):  
Seismic Wave ◽  
Seismic Refraction ◽  
Seismic Wave Propagation ◽  
Snow Accumulation ◽  
Geophysical Exploration ◽  
Special Cases ◽  
Radio Echo Sounding ◽  
Vlf Propagation ◽  
Echo Sounding

AbstractThe techniques of geophysical exploration can be used in a number of ways to investigate the internal characteristics of ice bodies. The application of radio-echo sounding is discussed elsewhere by Robin (1975[a]) so is not considered here except for a few special cases. Anisotropy resulting from non-random ordering of crystal axes produces effects on seismic wave propagation speeds measurable by both refraction and reflection techniques. The effects on shear waves are particularly strong, so the recent development of an effective shear-wave generator should prove very useful. Marked effects on radio-wave polarizations have also been noted, but are not readily interpretable because the anisotropic dielectric characteristics of single-crystal ice in the radio-echo frequency range are not yet known. Elastic internal friction can be determined by careful measurements of seismic-wave amplitudes. Dielectric properties of the ice can be found from VLF propagation experiments and electrical logging in drill holes as well as from the radio-echo sounding techniques discussed by Robin (1975[a]). An activation energy can be estimated from d.c. resistivity measurements where the temperature profile is known. Recent developments have led to much improved methods of determining density-depth variations and long-term mean annual snow accumulation rates from seismic refraction shooting. Internal discontinuities which can be studied include a probable morainal layer detected by seismic reflections, a brine-soaked zone in shelf ice observed from radio-echo. sounding and electrical resistivity surveying, and inverted crevasses penetrating upward from the base of shelf ice, detected by radio echoes. Secular changes in gravity offer a sensitive means of determining long-term changes in surface elevation.

scholarly journals Isolation and Identification of Neo-Clerodane Diterpenes from Ajuga Nipponensis Makino

2006 ◽  
Vol 1 (3) ◽  
pp. 1934578X0600100 ◽  
Author(s):  
Josep Coll ◽  
Yudelsy A. Tandrón
Keyword(s):  
Spodoptera Littoralis ◽  
Reversed Phase ◽  
Chromatographic Behavior ◽  
Spectral Studies ◽  
Two Dimensional ◽  
Reversed Phase Hplc ◽  
Antifeedant Activity ◽  
Isolation And Identification ◽  
Aerial Parts ◽  
Clerodane Diterpenes

An extract of the aerial parts of Ajuga nipponensis Makino was examined by HPLC for neo-clerodane diterpenes. The suitability of reversed-phase HPLC for the semi-preparative fractionation of this extract was explored, resulting in the isolation of two new neo-clerodane diterpenes, which we have named ajuganipponin A, (12S)-1β,6α,19-triacetoxy-4α,18-epoxy-12-tigloyl-neo-clerod-13-en-15,16-olide (AJNP A, 1), and ajuganipponin B, (12S)-6α,19-diacetoxy-4α,18-epoxy-12-tigloyl-neo-clerod-13-en-15,16-olide (AJNP B, 6). In addition, ajugamarins A2 and F4, ajugamacrin B, ajugacumbin A and ajugatakasin A, were newly isolated compounds from A. nipponensis, along with the previously reported ajugamarins A1, B2 and L2 (ajugacumbin B). The structures of all the isolated compounds were unambiguously elucidated based on extensive NMR spectral studies (one and two-dimensional experiments) and their reversed-phase chromatographic behavior was established. The antifeedant activity of the isolated diterpenes against Spodoptera littoralis is also reported here.

scholarly journals Analytical solutions for the neutron transport using the spectral methods

2006 ◽  
Vol 2006 ◽  
pp. 1-11 ◽  
Author(s):  
Abdelouahab Kadem
Keyword(s):  
Analytical Solutions ◽  
Spectral Methods ◽  
Chebyshev Polynomials ◽  
Neutron Transport ◽  
Two Dimensional ◽  
Dimensional Problem ◽  
One Dimensional ◽  
Multidimensional Problems ◽  
Dimensional Equation ◽  
Transport Problems

We present a method for solving the two-dimensional equation of transfer. The method can be extended easily to the general linear transport problem. The used technique allows us to reduce the two-dimensional equation to a system of one-dimensional equations. The idea of using the spectral method for searching for solutions to the multidimensional transport problems leads us to a solution for all values of the independant variables, the proposed method reduces the solution of the multidimensional problems into a set of one-dimensional ones that have well-established deterministic solutions. The procedure is based on the development of the angular flux in truncated series of Chebyshev polynomials which will permit us to transform the two-dimensional problem into a set of one-dimensional problems.

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