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Recent EES Division HighlightsMarch 10, 2008 Detecting Accumulated Damage in Human Bone Bone micro-damage is commonly accepted as a relevant parameter for fracture risk assessment in osteoporosis, but there is no available technique for its non-invasive characterization. Currently the x-ray bone density scan is used, but it offers very little information about bone damage. Paul Johnson (EES-11) and colleagues at the University of Paris Medical School and the Ecole Normal Superier in Paris are developing new methods for diagnosis and following the evolution of osteoporosis. The researchers' objective is to examine the potential of nonlinear ultrasound for damage detection in human bone. Ultrasound is particularly desirable due to its non-invasive and non-ionizing characteristics. The researchers' experiments explored progressive fatigue damage in human bone samples and methods to measure the damage. The team correlated the progressive fatigue of human bone samples to their nonlinear dynamical response. As damage accumulates during cycling, the measured nonlinear parameter was much more sensitive to damage than were standard measures. Using nonlinear parameter measurement techniques that were developed at LANL, this study represents the first application of the concept of nonlinear dynamic elasticity to human bone. The results are promising, suggesting the value of further work on this topic. Ultimately, the approach may have merit for in vivo bone damage characterization, especially for applications related to osteoporosis. The research, "Nonlinear Ultrasound Can Detect Accumulated Damage in Human Bone," by M. Muller, D. Mitton, M. Talmant, P. Johnson, and P. Laugier was published in the March issue of the Journal of Biomechanics. Marie Muller, the first author, was a student at LANL in 2006. LDRD supported the LANL research.
March 3, 2008 First 3-D In vivo Ultrasound Tomography Image of Breast Cancer Obtained High-quality, high-resolution images are critically important for early breast cancer detection and diagnosis. However, most breast cancers in women with dense breasts are undetectable by mammography, currently the only routine-screening tool for breast cancers. Lianjie Huang (EES-11), Kenneth M. Hanson (T-16), and collaborators from Stanford University, Karmanos Cancer Institute, Wayne State University, and Imperial College of London have developed a novel ultrasound-tomography technique which vastly enhances the capability to detect and diagnose breast cancer at its earliest stage. The difference between the new technique and conventional ultrasound tomography is the ability to produce high-resolution 3-dimensional (3-D) images. Figure 1, obtained using their novel clinical prototype of an ultrasound scanner with a ring transducer array, shows the high-resolution 3D ultrasound tomography in vivo image of a breast with a cancer, the bright "star" region at top. This cut-away view shows a cross section of the breast near the chest wall (top of image) and a vertical cut through the remainder of the breast. The voxels that make up this 3-D image measure 1mm x 1 mm x 1mm. The spatial resolution is 2mm x 2mm x 4mm (X x Y x Z, as shown).  Figure 1 This is the first time that a 3D in vivo ultrasound tomography image of the breast has been obtained. Clinical studies, already underway, show that ultrasound imaging has tremendous potential to detect small, early-stage breast cancers that cannot be detected by X-ray mammography. In addition, ultrasound breast imaging is one of the most promising screening tools as an alternative to X-ray mammography. The team gave five presentations of various aspects of this research at the SPIE Medical Imaging 2008 Meeting. They won the Honorable Mention Poster Award at the conference for the paper, "Frequency Diversity in Breast Ultrasound Tomography". The conference is the premier annual meeting on the scientific and technical aspects of medical imaging. LDRD supported the LANL research.
February 19, 2008 Times Marches Backwards - Time Reversal in Acoustics Today An article entitled "Time Reversal", written by Brian E. Anderson, Michele Griffa, Carene Larmat, and Paul A. Johnson of EES-11, was featured as the cover article in the January 2008 issue of Acoustics Today, a publication of the Acoustical Society of America. The article describes the basic physics of time reversal (TR) acoustics, its advantages and limitations, and reviews the main application areas of this exciting field of research. The article states, "Reversing time has been a compelling idea for ages. Today we can perform time reversal, leading not to the fountain of youth, but to very interesting physics and applications."  Potential applications include underwater acoustics, biomedical ultrasound imaging and therapy, nondestructive evaluation, and seismology. LANL researchers and collaborators are developing applications to a variety of geophysical problems from the field scale to the global scale. For example, scientists are investigating approaches for land mine detection using time reversal and nondestructive evaluation of solids for crack imaging. At a global scale, time reversal mirror (TRM) has been used to find earthquake source locations by taking the recorded seismograms, time-reversing them, and back propagating them through a numerical velocity model. In Figure 3, seismograms were recorded worldwide from the 2004 Parkfield Earthquake in California. The figure shows progressive snapshots of the back propagation of the velocity wavefield. The accuracy of reconstructing an earthquake source using TR relies upon the accuracy of the numerical modeling. With the development of efficient wave-propagation methods that can handle complex geologic models, the TR method is now an alternative to other source location methods. LDRD-DR supports the LANL research.  Images displaying the Time Reversal reconstruction of the 2004 Parkfield, CA earthquake. From top to bottom the images show the progressive reconstruction of the earthquake as the back propagated wave fronts coalesce at the original source location. This figure was made with the help of GMT software.
February 11, 2008 EES-11 Staff Edit Journal of Communications in Computational Physics  Lianjie Huang of EES-11 and former LANL EES Division Leader, Michael Fehler, served as guest editors on the recently published special issue on computation geophysics in the Journal of Communications in Computational Physics. The special issue contains 13 papers and encompasses several different and important computation geophysical problems including seismic-wave modeling, electromagnetic modeling and inversion, seismoelectric conversion, geomagnetic data assimilation, and tsunami simulation. Communications in Computational Physics, No. 1, 3 (2008)
February 4, 2008 EES-11 Staff Host & Speak at Seismo-Conference The world's leading seismologists will gather in Santa Fe for The Seismological Society of America's 2008 annual meeting April 16-18. The meeting will be hosted by LANL in cooperation with other Rio Grande institutions including New Mexico Tech, Sandia National Laboratory, and University of Texas El Paso. Meeting Chair Charlotte Rowe is also heading up the Program Committee. Researchers will present their work and participate in stimulating exchanges of the latest research on earthquakes, volcanoes, nuclear explosion monitoring, and more. Many EES-11 scientists will be in attendance. The EES Division scientists who are co-convening special sessions include the following scientists, all from EES-11...
In addition to the technical meetings and oral and poster presentations, there will be post-conference field trips including the Jemez Volcanics led by Scott Baldridge, Rio Grande Tectonics, and a trip to the Trinity Test Site led by Terry Wallace. Abstracts for the ~450 research papers that will be presented at the meeting as well as the detailed meeting schedule will appear in the March/April 2008 issue of Seismological Research Letters, and will be posted online after February 22. For more information on this meeting, see the SSA website.  The southerly flowing Rio Grande (shown near Pilar, New Mexico, 60 km north of Santa Fe) roughly bisects New Mexico. Its course is controlled by the Cenozoic mid-continental Rio Grande rift where the North American lithosphere thins exhibiting crustal extension and associated magmatism. Near Pilar, the river follows an active transfer fault connecting the San Luis and Española structural basins which form part of the southeastern boundary of the Colorado Plateau. In the background are rocks of Proterozoic age bounding the volcanic Taos Plateau. Blocks of Pliocene Servilleta basalt (seen on the left) have tumbled from the plateau surface to the river. Most earthquakes in New Mexico occur within the rift near Socorro (200 km southwest of Santa Fe), where an inflating mid-crustal magma body generates swarms of microearthquakes. Photo courtesy of Geraint Smith, Taos, NM.
January 21, 2008 Upscaling Pore Scale Reactive Transport Modeling to the Continuum Scale Multiphase flow and reaction in porous media are among the most complex and challenging problems in water resources research. Although pore-scale interfacial phenomena govern the key processes of fluid mobility, chemical transport, adsorption, and reaction, spatial heterogeneity at the pore scale cannot be resolved at the continuum scale where averaging typically occurs over length scales larger than typical pore sizes. An open question is how important spatial heterogeneity at the pore scale is on the observed behavior at the larger scale. Resolving pore-scale heterogeneity may explain some of the discrepancy between lab-measured and field-derived rate constants, as well as other issues leading to failure of macroscale models. To quantitatively investigate the effects of pore scale heterogeneity on the emergent behavior at the field scale, it is necessary to understand multiphase flow, transport, and reaction processes at the pore scale and subsequently upscale the results to the continuum scale. Researchers Qinjun Kang (EES-6), Peter Lichtner (EES-6), and Dongxiao Zhang (USC) recently improved the lattice Boltzmann pore-scale model for multicomponent reactive transport in porous media pioneered by them. In the improved model, solute mass is strictly conserved by heterogeneous reactions. The new model was published in Water Resources Research (WRR) in November 2007. In another paper published in WRR in December 2007, Lichtner and Kang presented ground-breaking work on upscaling pore-scale reactive transport equations to the continuum scale using a multiscale continuum formulation. In general a multiscale continuum formulation is required to fit the upscaled pore-scale results. The scientists suggest that a multiscale continuum approach may help explain the observed discrepancy between laboratory and field-derived reaction rates by explicitly representing distinct transport domains through separate interacting continua. DOE, Biological and Environmental Research and LDRD/DR supported the research.  Leaching of a tracer initially emplaced at time t = 0 in a two-dimensional structured porous medium (x axis horizontal and y axis vertical) with primary and secondary porosity for a domain size of 0.04 m x 0.012 m. The initial concentration in the primary continuum and matrix fluids is set to 0.1 mol/L.A fluid containing zero tracer is injected at the entrance on the left. The figure corresponds to an elapsed time of 2.6 x 104 s. The black spirals have zero porosity. Concentration units are mol/L.
January 14, 2008 Numerical Modeling of Seismic Phases in a Spherical Earth Model Seismic phases Pn and Sn are refracted waves that traverse the Earth's uppermost mantle and are typically the first compressional- and shear-wave arrivals at distances from ~200 to 1500 km. These phases are commonly characterized as being conical headwaves based on considerations of wave interactions with planar constant-velocity layered structures. However, the propagation of Pn and Sn in the actual spherical Earth is much more complex. As epicentral distance increases, Pn and Sn behavior is strongly influenced by the Earth's sphericity, and formal mapping between plane-layered structures and spherical velocity structures is needed. Researchers Xiaoning (David) Yang (EES-11) and collaborators at the University of California - Santa Cruz and the University of Alaska - Fairbanks have developed new geometric-spreading models for seismic phases Pn and Sn, taking into account effects of the Earth's sphericity. The new models provide better representations of Pn and Sn spreading in the real, spherical Earth than the commonly used standard power-law models (Figure 3). This conclusion is supported by synthetic simulations and by the successful application of the model on observed Pn data spanning wide distance ranges in Eurasia to yield reasonable attenuation estimates. The new Pn and Sn geometric-spreading models are useful in common situations where only simple velocity models with uppermost-mantle structure represented as constant velocity half-space are available. The use of these models should result in a smaller error in different applications compared with power-law models. Publication: "Geometric Spreading of Pn and Sn in a Spherical Earth Model", Bulletin of Seismological Society of America, Vol. 97, 2053-2065 (2007). NNSA funded the work.  Above - Comparison between synthetic amplitudes calculated for a spherical Earth model, the new Pn geometric-spreading model, and a power-law spreading model. The meshed surface is synthetic Pn amplitudes. The white, semitransparent surface bounded by the thick line is the new model. The surface outlined by dashed lines is the power-law model.
January 7, 2008 Dynamic Earthquake Triggering Earthquakes happen when Earth's crust slips along cracks called faults. Major faults are found at the junction of independently moving masses of crust and mantle or tectonic plates. Each earthquake releases seismic waves -- vibrations at the cusp or below the range of human hearing -- that travel through the earth. These waves can trigger aftershocks in a zone several to tens of miles away from the radiating main earthquake ("mainshock"). Most aftershocks usually occur within hours to days following the mainshock. The mechanism behind this phenomenon of dynamic earthquake triggering is unknown. Paul Johnson (EES-11), H. Savage (U. C. Santa Cruz), M. Knuth (U. Wisconsin), J. Gomberg (USGS) and C. Marone (Penn State) conducted laboratory granular friction studies to better understand the physics of dynamic triggering and the influence of dynamic stressing on earthquake recurrence. The researchers used a novel device to examine stick-slip in granular media (glass beads) and applied acoustic waves to simulate earthquake triggering. The experiments demonstrated how wave energy is stored in certain types of granular materials, similar to that found along certain fault lines across the Earth. This stored energy can suddenly be released as an earthquake when hit by relatively small seismic waves far beyond the traditional "aftershock zone" of a main quake. Vibrations also cause large slip events to be disrupted in time relative to those without wave perturbation, suggesting that dynamic stressing of tectonic faults may play a role in determining the complexity of earthquake recurrence. LDRD and the DOE Office of Basic Energy Research supported the LANL work. The research is published in Nature, "Effects of Acoustic Waves on Stick-slip in Granular Media and Implications for Earthquakes" doi:10.1038/nature06440 and in the Nature editor's summary. 
Image from Bob Behringer (Duke University) illustrates studies of stress and strain on granular media, similar to what was used in the Penn State University earthquake machine. Stresses on the photoelastic granules in the photo show up as brighter colors, with red showing the regions of highest stress. When forces are applied to granules beneath a plate in the earthquake machine, stresses propagate through the granules, creating "force chains", like the tracks of red visible in the image. Paul Johnson and colleagues showed that force chains break and reform during "earthquakes" induced in the Penn State machine, providing researchers with insight into the periodic behavior of quakes.
Research on Acoustic-Gravity Waves from Bolide Sources Published Douglas ReVelle (EES-2) constructed a model for the generation and propagation of acoustic-gravity waves (AGW) from bolide sources (exceptionally bright meteors). The overall goal is to predict the AGW waveform and the properties of the bolide sources. The model is linked at the source to satellite optical luminosity data to generate a reliable line source and blast wave relaxation radius. Beyond about 10 blast wave radii (near-field region), the model is linked to the well-known weak shock solutions for the amplitude and the wave period of the AGW radiated by the bolide in the continuum flow regime. Infrasound is the high frequency part of the full AGW spectrum of atmospheric waves. Beyond this limit the far-field wave pulse is linked to three well-known analytic solutions depending on factors related to the source properties (e.g., line source, blast radius, and altitude of the source) and upon how far away from the source the wave system is being observed. The combination of these separate analytic solutions under numerous differing propagation conditions leads to the final result and was compared with AGW observations. The amplitude of the waveform and its overall pressure wave signature are in good agreement. ReVelle applied this modeling technique to bolides, including Tunguska (the Great Siberian meteor of 1908 over Siberia and the Stony-Tunguska River), the Revelstoke meteorite fall of 1965 over British Columbia, Canada; the 2002 Mediterranean bolide; and the 2004 Antarctic bolide. This technique has an immediate application for modeling the infrasound generation from supersonic/hypersonic rocket sources in the atmosphere. The paper, "Acoustic-gravity Waves from Bolide Sources," is published in Earth Moon Planet.
EPA Tour of Yucca Mountain Project Brian Dozier and Richad Kovach (EES-7) gave a tour of Yucca Mountain to EPA Region 2 officials Alan Steinberg (Regional Administrator), Paul Giardina (Chief, Radiation and Indoor Air Branch), and Cosmo Sevidido (Chief of Staff to Region 2 Administrator). The visitors came to be educated about Yucca Mountain. "Tours" at Yucca Mountain consist of a general briefing of the tunnel/repository layout and experiments. The briefings are conducted in an underground excavation off the main tunnel, an "alcove", which has been customized for tours, including maps/displays. The information included an overview of geology, results of testing activities, and repository layout. The tour also included a stop at the Drift Scale Test about 1.75 miles into the tunnel where a test on the effects of long term heating of the repository rock is being conducted.  Left - Tunnel boring machine. Right - Alcove within Yucca Mountain.
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