The Effects of Sparging on P- and SH- Vertical Seismic Profiles

While the introduction of pressurized air into an unconsolidated, coarse-grained fluvial aquifer might well be expected to affect the P-wave velocity profile below the water table, we have found that S-waves are also sensitive to changes induced by air sparging. In a study spanning over a year of sparging, observations of both P- and S-waves were conducted by Vertical Seismic Profiling (VSP). While the primary objective was to characterize the aquifer, we have found that air sparging has significantly affected both P- and S-wave propagation. Below the water table we have observed as much as a 54% decrease in P-wave velocity, and as much as a 31% increase in S-wave velocity after continued sparging. Above the water table, we observe only small changes in both P- and S-wave velocities. This pattern of velocity change (decreasing P, increasing S) may be due to an increase in the amount of trapped air below the water table. Published laboratory studies in the small strain regime have shown P-wave velocities to be sensitive to void ratio, fluid content, and confining stress. On the other hand, most similar studies of S-waves have only been conducted on either dry or saturated samples. However, one recent laboratory study suggests that shear modulus and shear velocity may increase significantly at partial water saturations (due to capillary forces). Data from our in-situ survey supports this more recent lab work. We have observed that S-wave propagation may be significantly altered by fluid content when soils are partially saturated with water (where trapped air may exist, producing a 3-phase fluid-frame system). In addition, we have observed changes in the propagating wavelet. This may be an indication that viscous damping is also affected by partial water saturation. We conclude by observing that S-waves may prove to be an attractive alternative for mapping the effects of air sparging

The Anomalous Behavior of SH‐Waves Across the Water Table

Most theoretical studies of seismic wave propagation in a porous medium do not predict a significant increase in SH-wave velocity with increasing water saturation. Although that type of behavior is commonly predicted for P-waves (and confirmed by countless observations), the expectation for SH-waves is a slight decrease in propagation velocity with increasing water saturations. While published measurements of SH-wave velocity in laboratory studies have been supportive of such a slight decrease in velocity, the data have been biased towards high pressures (typical of oil reservoirs at large depths of burial). On the other hand, the few published low pressure laboratory measurements have revealed significantly different results. The authors’ in-situ measurements of seismic wave velocities in a shallow, coarse grained, unconfined alluvial aquifer document a significant SH-wave velocity increase in the transition from the vadose zone to the water table. In one vertical seismic profile (VSP), the P-wave velocity increases by a factor of 4.2 and the SHwave velocity increases by a factor of 2.6. What is not clear at this point is the true nature of the increase. Is the velocity increase an expression of the presence of water in the pores, or does water alter the rigidity of the soil matrix? In addition to the broad-band velocity increase, we have also observed changes in the attenuation of SHwaves across the water table. After correcting for geometric spreading, the amplitude decay observed in the vadose zone has been found to be larger than that observed below the water table. However, the variation in amplitude decay as a function of frequency and the measurements of body wave dispersion were found to be larger below the water table than above. That is, the water saturated soil behavior is consistent with a Voigt solid, but the dry material appears to follow a different model. The authors will discuss these observations in the context of the current debate on Poisson’s ratio and the Vp/Vs ratio

Design, development and prototype fabrication of an area hydrogen detector summary report, 5 apr. 1963 - 4 apr. 1964

Area hydrogen detector for unpressurized environments - palladium film sensor elemen

Engineering Electromagnetic Properties of Periodic Nanostructures Using Electrostatic Resonances

Electromagnetic properties of periodic two-dimensional sub-wavelength structures consisting of closely-packed inclusions of materials with negative dielectric permittivity $\epsilon$ in a dielectric host with positive $\epsilon_h$ can be engineered using the concept of multiple electrostatic resonances. Fully electromagnetic solutions of Maxwell's equations reveal multiple wave propagation bands, with the wavelengths much longer than the nanostructure period. It is shown that some of these bands are described using the quasi-static theory of the effective dielectric permittivity $\epsilon_{qs}$, and are independent of the nanostructure period. Those bands exhibit multiple cutoffs and resonances which are found to be related to each other through a duality condition. An additional propagation band characterized by a negative magnetic permeability develops when a magnetic moment is induced in a given nano-particle by its neighbors. Imaging with sub-wavelength resolution in that band is demonstrated

Chemical Raman Enhancement of Organic Adsorbates on Metal Surfaces

Using a combination of first-principles theory and experiments, we provide a quantitative explanation for chemical contributions to surface-enhanced Raman spectroscopy for a well-studied organic molecule, benzene thiol, chemisorbed on planar Au(111) surfaces. With density functional theory calculations of the static Raman tensor, we demonstrate and quantify a strong mode-dependent modification of benzene thiol Raman spectra by Au substrates. Raman active modes with the largest enhancements result from stronger contributions from Au to their electron-vibron coupling, as quantified through a deformation potential, a well-defined property of each vibrational mode. A straightforward and general analysis is introduced that allows extraction of chemical enhancement from experiments for specific vibrational modes; measured values are in excellent agreement with our calculations.Comment: 5 pages, 4 figures and Supplementary material included as ancillary fil

Synthetic Mudscapes: Human Interventions in Deltaic Land Building

In order to defend infrastructure, economy, and settlement in Southeast Louisiana, we must construct new land to mitigate increasing risk. Links between urban environments and economic drivers have constrained the dynamic delta landscape for generations, now threatening to undermine the ecological fitness of the entire region. Static methods of measuring, controlling, and valuing land fail in an environment that is constantly in flux; change and indeterminacy are denied by traditional inhabitation. Multiple land building practices reintroduce deltaic fluctuation and strategic deposition of fertile material to form the foundations of a multi-layered defence strategy. Manufactured marshlands reduce exposure to storm surge further inland. Virtual monitoring and communication networks inform design decisions and land use becomes determined by its ecological health. Mudscapes at the threshold of land and water place new value on former wastelands. The social, economic, and ecological evolution of the region are defended by an expanded web of growing land

Do we understand the incompressibility of neutron-rich matter?

The ``breathing mode'' of neutron-rich nuclei is our window into the incompressibility of neutron-rich matter. After much confusion on the interpretation of the experimental data, consistency was finally reached between different models that predicted both the distribution of isoscalar monopole strength in finite nuclei and the compression modulus of infinite matter. However, a very recent experiment on the Tin isotopes at the Research Center for Nuclear Physics(RCNP) in Japan has again muddled the waters. Self-consistent models that were successful in reproducing the energy of the giant monopole resonance (GMR) in nuclei with various nucleon asymmetries (such as 90Zr, 144Sm, and 208Pb) overestimate the GMR energies in the Tin isotopes. As important, the discrepancy between theory and experiment appears to grow with neutron excess. This is particularly problematic as models artificially tuned to reproduce the rapid softening of the GMR in the Tin isotopes become inconsistent with the behavior of dilute neutron matter. Thus, we regard the question of ``why is Tin so soft?'' as an important open problem in nuclear structure.Comment: 12 pages, 3 figures, and 1 table. Submitted to the "Focus issue on Open Problems in Nuclear Structure", Journal of Physics