scholarly journals Radiation impedance of torsionally vibrating seismic sources

Geophysics ◽  
1983 ◽  
Vol 48 (11) ◽  
pp. 1453-1467
Author(s):  
Geoffrey A. Dorn
Keyword(s):  
Surface Layer ◽  
Half Space ◽  
Circular Disk ◽  
Shear Velocity ◽  
Low Frequencies ◽  
Radiation Impedance ◽  
Impedance Measurements ◽  
Impedance Contrast ◽  
Resonant Effect ◽  
Impedance Curve

The thickness and shear‐wave velocity of a surface layer can theoretically be determined from seismic radiation impedance measurements using a torsional vibrator. These studies also provide physical insight into vibrator‐earth interaction. The radiation impedance of a circular disk vibrating torsionally on an anelastic half‐space has resonance peaks with a spacing that is a function of the ratio between baseplate radius and seismic wavelength. At low frequencies the shape of the impedance function is nearly independent of the baseplate flexure, although the magnitude is affected. At high frequencies the impedance depends strongly on the flexibility of the baseplate. The mass of the baseplate introduces an additional resonant effect, the frequency of which is a function of the baseplate mass. The presence of a surface layer produces an impedance curve which oscillates around the half‐space response. The amplitude of the oscillations is a function of the acoustic impedance contrast and depends upon the radiation pattern of the source. The oscillations are resonances caused by reflections within the surface layer, and both the period and amplitude of the oscillations are inversely proportional to the layer thickness. The amplitude of the layer resonance decreases rapidly as material damping increases. With impedance measurements over a sufficiently broad frequency range (up to about 500 Hz), it may be feasible to use half‐space oscillations and the layer resonances to determine the shear velocity and thickness of the layer of material beneath the baseplate.

Dispersive characteristics of the first three Rayleigh modes for a single surface layer

1966 ◽  
Vol 56 (1) ◽  
pp. 43-67 ◽  
Author(s):  
Harold M. Mooney ◽  
Bruce A. Bolt
Keyword(s):  
Surface Layer ◽  
Half Space ◽  
Poisson’S Ratio ◽  
Velocity Ratio ◽  
Surface Displacement ◽  
Shear Velocity ◽  
Poisson's Ratio ◽  
Wave Number ◽  
Model Parameters ◽  
Higher Modes

abstract The dispersive characteristics of a single elastic layer overlying an elastic half-space are examined in detail for the fundamental and the first and second higher modes of Rayleigh waves. Phase velocity, group velocity, and the ratio of horizontal to vertical surface displacement are computed as functions of dimensionless quantities proportional to period and wave number. The significant range for the independent variable, B1T/H, proves to be largely independent of the parameters of the structure. The range is 1 to 20 for the fundamental, 0.3 to cutoff for the first higher mode, and 0.2 to cutoff for the second higher mode. The most important parameter of the structure for Rayleigh wave dispersion is the shear velocity ratio. Variations in the Poisson's ratio in the surface layer and the density contrast may produce substantial effects. Poisson's ratio in the half-space is of least significance. The dependence on model parameters of the long-period cutoff for the higher modes is determined. Specific results are given for the following geophysical examples: continental crust, continental ice cap, sedimentary basin, alluvial overburden, and laboratory seismic models.

scholarly journals The Sources of Moisture in the Sand Dunes – The Example of the Western Sahara Dune Field

2014 ◽  
Vol 33 (3) ◽  
pp. 199-204 ◽  
Author(s):  
Elwira Żmudzka ◽  
Dariusz Woronko ◽  
Maciej Dłużewski
Keyword(s):  
Surface Layer ◽  
Moisture Content ◽  
Wind Velocity ◽  
Sand Dune ◽  
Sand Dunes ◽  
Shear Velocity ◽  
Meteorological Conditions ◽  
Aeolian Transport ◽  
Western Sahara ◽  
Dune Field

Abstract Climatic and meteorological conditions may limit the aeolian transport within barchans. An explanation of that issue was the main goal of the investigation held in Western Sahara dune fields located around Tarfaya and Laâyoune. Particular attention was paid to the factors causing the moisture content rising of the sand dune surface layer, which could influence the wind threshold shear velocity in the aeolian transport. The wetted surface layer of sand, when receiving moisture from precipitation or suspensions, reduces the aeolian transport, even in case of wind velocity above 4-5 m s-1. Fog and dew condensation does not affect the moisture of deeper sand layers, what occurs after rainfall.

Electrical Impedance Measurements of PZT Nanofiber Sensors

2016 ◽  
Author(s):  
Richard Galos ◽  
Xin Li
Keyword(s):  
Dielectric Constant ◽  
Material Properties ◽  
Electrical Impedance ◽  
Impedance Measurement ◽  
Low Frequencies ◽  
Impedance Measurements ◽  
Conductive Afm ◽  
Electrical Impedance Measurement ◽  
Microfabrication Techniques

Electrical Impedance Measurement of PZT Nanofiber sensors are performed and material properties including resistivity and dielectric constant are derived from the measurements. Nanofibers formed by electro-spinning with diameters ranging from 10 to 150 nm were collected and integrated into sensors using microfabrication techniques. The nanosensor impedance was extremely high at low frequencies and special matching circuitry was fabricated to detect output. The resulting impedance measurements are also compared with those of individual nanofibers that were tested using Scanning Conductive Microscopy (SCM) and Conductive AFM.

MONITORED DEFORMATION BY POTENTIAL-INDUCED DEFECTS IN CH3(CH2)n−1SH SELF-ASSEMBLED MONOLAYERS ON GOLD: EIS STUDY OF CHAIN LENGTH EFFECT ON SUBDIFFUSION AND SAMs’ HETEROGENEITY

2019 ◽  
Vol 26 (10) ◽  
pp. 1950067 ◽  
Author(s):  
AHMED MOUGARI ◽  
MOKHTAR ZABAT ◽  
SMAIL BOUDJADAR
Keyword(s):  
Charge Transfer ◽  
Electrochemical Impedance ◽  
Defect Density ◽  
Charge Transfer Resistance ◽  
Electrical Circuit ◽  
Transfer Resistance ◽  
Low Frequencies ◽  
Interface Evolution ◽  
Impedance Measurements ◽  
Self Assembled

From the defects-free self-assembled organic layers (SAMs) of CH3([Formula: see text]SH molecules with short chain lengths ([Formula: see text]) electrodeposited on the (111) surface of monocrystalline gold previously prepared, monitored defects (pinholes) were potential-induced from cyclic partial reduction of SAMs at an appropriate potential. Electrochemical impedance measurements were in-situ conducted and [Fe(CN)6][Formula: see text] ions were used as probes for mass and charge transfer. Interface evolution was modeled with an equivalent electrical circuit containing two distinct constant-phase elements (CPEs). One is a generalized semi-infinite Warburg element in series with a charge transfer resistance attributed to subdiffusion phenomenon through leaky sublayers at low frequencies; the other CPE is used for characterizing the interface heterogeneity at medium and high frequencies. At low frequencies, electrochemical impedance measurements show subdiffusion phenomenon, which depends on the remaining sublayer and its thickness. When the defect density increases, diffusion tends to be ordinary, obeying the Fick’s law.

Abnormal Structural Strength of Topocomposites

2012 ◽  
Vol 560-561 ◽  
pp. 338-343 ◽  
Author(s):  
Nikolay A. Voronin
Keyword(s):  
Surface Layer ◽  
Bearing Capacity ◽  
Half Space ◽  
Contact Interaction ◽  
Solid Body ◽  
Mechanical Characteristics ◽  
Structural Strength ◽  
Layered Material ◽  
Thin Surface Layer ◽  
Layer Coating

The mechanics of contact interaction of rigid spherical indenter with two-layer elastic - plastic half-space, simulating a surface of a solid body with a thin surface layer is considered. Analytical dependences of critical indentation and bearing capacity on mechanical characteristics of materials of a base and a coating, and as well as that for thickness of top layer (coating) in all region of possible thickness are received and analyzed. Existence of regions of the abnormal structural strength allowing the surface layered material to identify unequivocally as a topocomposite is shown. Theoretical dependences were verified by a final elements method.

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