Home  About us  Contact
 

Pressure Sensitivity (pressure + sensitivity)

Distribution by Scientific Domains
Earth and Environmental Science50%

Selected Abstracts

A laboratory study of seismic velocity and attenuation anisotropy in near-surface sedimentary rocks

GEOPHYSICAL PROSPECTING, Issue 5 2007
Angus I. Best
ABSTRACT The laboratory ultrasonic pulse-echo method was used to collect accurate P- and S-wave velocity (±0.3%) and attenuation (±10%) data at differential pressures of 5,50 MPa on water-saturated core samples of sandstone, limestone and siltstone that were cut parallel and perpendicular to the vertical borehole axis. The results, when expressed in terms of the P- and S-wave velocity and attenuation anisotropy parameters for weakly transversely isotropic media (,, ,, ,Q, ,Q) show complex variations with pressure and lithology. In general, attenuation anisotropy is stronger and more sensitive to pressure changes than velocity anisotropy, regardless of lithology. Anisotropy is greatest (over 20% for velocity, over 70% for attenuation) in rocks with visible clay/organic matter laminations in hand specimens. Pressure sensitivities are attributed to the opening of microcracks with decreasing pressure. Changes in magnitude of velocity and attenuation anisotropy with effective pressure show similar trends, although they can show different signs (positive or negative values of ,, ,Q, ,, ,Q). We conclude that attenuation anisotropy in particular could prove useful to seismic monitoring of reservoir pressure changes if frequency-dependent effects can be quantified and modelled. [source]

Morphometry and composition of aragonite and vaterite otoliths of deformed laboratory reared juvenile herring from two populations

JOURNAL OF FISH BIOLOGY, Issue 6 2003
J. Tomás
Vaterite otoliths were sampled from two reared populations (Celtic and Clyde Seas) of juvenile herring Clupea harengus. The crystallography, elemental composition and morphometry were analysed and compared with those of normal aragonite otoliths. The incidence of vaterite otoliths in the juveniles sampled (n = 601) ranged from 7·8% in the Clyde population to 13·9% in the Celtic Sea population, and was 5·5% in the small sample (n = 36) of wild adults examined. In all but one case fish had only one vaterite otolith; the corresponding otolith of the pair was completely aragonite. Although the majority of the juveniles sampled showed craniofacial deformities, there was no link between the skull or jaw malformation and the incidence of vaterite otoliths. All vaterite otoliths had an aragonite inner area, and vaterite deposition began sometime after the age of 90 days. The vaterite otoliths were larger and lighter than their corresponding aragonite partners, and were less dense as a consequence of the vaterite crystal structure. The vaterite areas of the otoliths were depleted in Sr, Na and K. Concentrations of Mn were higher in the vaterite areas. The transition between the aragonite inner areas and the vaterite areas was sharply delineated. Within a small spatial scale (20 ,m3) in the vaterite areas, however, there was co-precipitation of both vaterite and aragonite. The composition of the aragonite cores in the vaterite otoliths was the same as in the cores of the normal aragonite otoliths indicating that the composition of the aragonite cores did not seed the shift to vaterite. Vaterite is less dense than aragonite, yet the concentrations of Ca analysed with wavelength-dispersive spectrometry (WDS) were the same between the two polymorphs, indicating that Ca concentrations measured with WDS are not a good indicator of hypermineralized zones with high mineral density. The asymmetry in density and size of the otoliths may cause disruptions of hearing and pressure sensitivity for individual fish with one vaterite otolith, however, the presence of vaterite otoliths did not seem to affect the growth of these laboratory reared juvenile herring. [source]

Conduction band filling in In-rich InGaN and InN under hydrostatic pressure

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008
G. Franssen
Abstract We demonstrate the effect of conduction band shape evolution of InGaN with increasing In content and applying hydrostatic pressure. The influence of conduction band filling on the hydrostatic pressure dependence of photoluminescence in In0.7Ga0.3N and InN is investigated. It is found that the PL pressure coefficient dEPL/dp of InN changes from ,27 meV/GPa to ,21 meV/GPa when the electron concentration increases from 3.6×1017 cm,3 to 1.1×1019 cm,3. In contrast, no significant change of dEPL/dp with electron concentration was observed for In0.7Ga0.3N. We conclude that the pressure sensitivity of the Fermi level, which is responsible for the lowering of dEPL/dp with respect to dEG/dp in InN, is much less prominent in In0.7Ga0.3N than in InN. We attribute this difference to the larger band gap of In0.7Ga0.3N, which lowers the pressure sensitivity of m*. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Measurement of AC current using an optical fibre sensor

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2007
C. H. Cheng
Abstract In the power industry, current is measured for metering and protection purposes. For said measurement, we demonstrated an optical fibre sensor using a single Fibre Bragg Grating (FBG) for measuring AC current for this paper. The sensor head is based on an FBG encased in a polymer-half-field metal cylinder, embedded in a magnetic material at the measuring point with the characteristics of an all-optical high pressure sensitivity. The operating mechanism is that the sensor can be attracted by the induced magnetic force created by the solenoid along one radial direction only, and responds to an axial force on the magnetic rod attached to the round plate, creating an axial attraction on the FBG. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]