EES Division Highlights Archive - Oct.-Dec., 2007

Other Archived Highlights

December 17, 2007

Monitoring Progressive Bone Fatigue Damage for Osteoporosis

Progressive bone density loss and microcracking occurs in osteoporosis. It is a serious health issue striking approximately 40% of women and 20% of men over the age of 50. In addition, accumulated microdamage is also a concern in bone strength and health.

Using the present X-ray method to determine bone mineral density and follow the disease progression is relatively insensitive to increased bone microcracking. However, a solution could be found in 'nonlinear acoustics'. Nonlinear acoustic methods can measure damage very sensitively in a wide variety of materials.

Researchers TJ Ulrich and Paul Johnson of EES-11 and collaborators in France have examined nonlinear elastic wave spectroscopy (NEWS) to monitor both mechanical damage in bone and bone healing. This could allow physicians to monitor the onset and progression of degenerative bone diseases such as osteoporosis and to monitor the development or healing of fractures.

Nonlinear methods rely on inducing elastic wave distortion - either locally or volumetrically - in the regions that are elastically soft relative to the surrounding material. A wave that encounters a crack in a solid will distort as associated harmonics are formed. In the presence of two or more waves propagating with two different frequencies at the crack, the waves multiply creating sum and difference frequencies or 'sidebands'. The scientists investigated fatigue damage induced in a bone sample by cyclic uniaxial compression-compression loading and measurement of the elastic nonlinear response from the sideband amplitudes.

Sample of human cortical bone used in the measurements.

The results illustrate the sensitivity of this method and the great potential for in vitro measurements. The researchers are developing methods to make in vivo measurements as a medical diagnostic tool.

Although the dynamic strain amplitudes used in this experiment are not damaging to the bone (order 5 x 10^-6 to 10 x ^-5), it is not known if these are reasonable amplitudes for an in vivo application, given the increased attenuation of the complete biological system. A major issue to be addressed for both in vitro and in vivo applications is the quantitative relationship between the measured nonlinear response and the microdamage state as reflected by crack density, length, and orientation. However, bone density data obtained from x-rays, the current diagnostic method, does not convey any information at all about microcracking.

The research has been published and is downloadable from the EES-11 Nonlinear publications page. It also has been selected to appear in the Virtual Journal of Nanoscience and Technology in the "Statistical and Nonlinear Physics" category. The Virtual Journal, published by the American Physical Society and the American Institute of Physics, contains selected articles covering a focused area of frontier research. The research was also reported in an invited lecture at the International Congress on Acoustics in Madrid, Spain. LDRD supported the LANL research.

December 10, 2007

Los Alamos Convenes New Mexico Geological Society Field Conference

Jamie Gardner (EES-9) was a co-convener of the 58th annual New Mexico Geological Society field conference. With about 200 participants, the 3-day field Los Alamos-based conference focused on the geology of the Jemez Mountains and neighboring areas such as the Española Basin of the Rio Grande rift. The Jemez Mountains are one of the most intensively studied mountain ranges in North America and probably in the world. Best known for the early Pleistocene Valles Caldera (the world's best example of a resurgent caldera), the Jemez Mountains also include a wide variety of other volcanic features. The New Mexico Geological Society guidebook published as part of the conference is about 500 pages and features twenty-one papers with Los Alamos authors.

November 19, 2007

More Meteoroids Than Expected Produce Infrasound at Earth's Surface

Meteoroids falling though Earth's atmosphere produce infrasound - frequencies below the audibility range of the human ear. Infrasonic observations of meteoroids less than 10 centimeters in diameter remain rare; therefore, fundamental meteor infrasound theory (ReVelle 1974, 1976) and its predictions generally have remained untested and unconstrained by observation for more than 30 years.

D. O. ReVelle (EES-2) and Ph.D. students and faculty researchers W.N. Edwards, R. Weryk and P.G. Brown from the University of Western Ontario (UWO) have embarked on a long-term campaign to determine 1) the flux of infrasound producing meteoroids at the Earth's surface, 2) the altitudes at which these infrasonic waves are generated, 3) the fundamental physics of shock production during hypersonic flight of meteoroids, and 4) the relationship between a meteoroid's kinetic energy and surface observations of period and amplitude.

The researchers performed observational studies using meteor patrol radar, optical video all-sky cameras, as well as infrasonic, seismic and VLF (very low frequency radio-wave) sensors permanently installed at the Elgin Field Observatory at UWO and throughout southern lower Ontario.

Single infrasonic array element at the Elgin Field Observatory

Researchers have collected infrasonic recordings at the rate of more than one per month. Optical cameras, patrol radar, or both also have independently confirmed these. A number of the signals also have seismic arrivals as well. The current results are a lower limit because no daytime events or meteors occurring during bad weather were detected. The researchers reason that significant advances in computer technology and digital signal processing since the late 1970s and early 1980s, has likely made identification of these sometimes very weak signals far easier. The scientist's recent observations show that the flux is at least two orders of magnitude higher than earlier observations suggest. Comparisons to current meteor infrasound theory show excellent agreement with amplitude and period predictions for weakly non-linear shock waves using a realistic vertically inhomogeneous atmosphere. Their research, "Infrasonic Observations of Meteoroids: Preliminary Results from a Coordinated Optical-radar-infrasound Observing Campaign", has been published in Earth Moon Planet. The LANL work was supported by NA-22 through the Los Alamos, Ground-based Nuclear Explosion Monitoring (GNEM) Infrasound program.

November 5, 2006

Stardust Sample Return Shockwave

A paper titled "Calibrating Infrasonic to Seismic Coupling using the Stardust Sample Return Capsule Shockwave: Implications for Seismic Observations of Meteors" was published in the Journal of Geophysical Research. This work is a continuation and an expansion of previous work published in Meteoritics and Planetary Science on the infrasonic and seismic monitoring of the NASA Stardust space capsule during its reentry into the atmosphere in January 2006. The velocity of the space capsule was the highest ever for an artificial object and is on the low end of the range typical of meteoroids. This work, a collaboration between D.O. ReVelle (EES-2) and researchers at the University of Western Ontario (Canada), is the first calibrated measurement of acoustic-seismic coupling efficiency for a meteor analog.

This research focuses on the interpretation and modeling of the seismic data measured during the reentry and its relationship to the recorded infrasound data. The ensemble of infrasonic data consisted of about 1-2 minutes of rumbling which first began as a normal hypersonic boom from about 40 km altitude (which is also very near to the point of closest approach to the reentry trajectory) when the capsule was still moving at hyper/supersonic speeds. The delay time to the start of the hypersonic boom was totally normal and the "boom" was recorded well within the direct nominal "hypersonic sonic boom corridor". This degree of normalcy was previously expected because the scientists had also monitored the NASA Genesis space capsule reentry in September 2004 at the same location (Wendover, Nevada). However, some 10 sec after the onset of the initial boom, a second set of enigmatic infrasonic signals arrived that could not be interpreted as emanating directly from the entry trajectory. The subsequent detailed analysis and modeling shows that these signals indicate that acoustical energy from the reentry had penetrated directly into the ground and then subsequently reemerged into the air from below (referred to as higher order Airy phases). This set of observations is similar to the so-called earthquake sound phenomenon that has been known for many years. These observations also give new limiting values of the air-ground seismic coupling factor over desert playa regions. The Ground-Based Nuclear Explosion Monitoring program, the ISR RD Program Office, IGPP, and NASA supported the LANL work.

October 29, 2007

Feature Article on Clathrates Published in Physics Today

Wendy Mao, recent J.R. Oppenheimer Fellow co-sponsored by LANSCE-LC and EES-6 and currently an assistant professor at Stanford University, published a feature article on clathrates in the October 2007 issue of Physics Today. Clathrates are an ice-like framework of polyhedral cages around guest molecules formed when water comes into contact with simple gases and hydrocarbons at high pressure and low temperature. Mao and C. A. Koh and E. D. Sloan (both at Colorado School of the Mines) review the potential importance of gas-hydrate clathrates for energy security and for planetary science. The authors delineate the history of gas-hydrate clathrate research starting with initial discoveries by Davy and continuing through recent studies of clathrate-bearing planetary ices on Saturn's moon Enceladus and the high-pressure behavior of hydrogen clathrates and filled ices. They emphasize the widespread occurrence of methane hydrates on continental shelves and in permafrost regions, with estimates of the total mass of methane in such clathrates at twice the mass of all other terrestrial hydrocarbons. They refer to recent pilot-scale tests at the Mallik well in Canada to mine methane from clathrates in Arctic environments. The authors discuss recent high-pressure research (some of which was conducted at LANSCE) on hydrogen clathrates, filled ices, and other molecular hydrogen-bearing compounds. Such compounds show promise as H2 storage materials for a hydrogen economy - if appropriate stabilizer-compounds for the H2 phases to near-ambient pressure conditions can be developed.

October 15, 2007

Resurgent Doming in the Valles Caldera Published

Jamie Gardner (EES-9) and Fraser Goff (retired from EES-6) collaborated with students and faculty at New Mexico Tech, and staff of the New Mexico Bureau of Geology and Mineral Resources, on a project to establish the timing and rates of uplift of the caldera floor to form a central structural dome (resurgent doming) in the Valles caldera. Because of its young age (1.25 Ma) and location in a relatively dry climate, the caldera is well preserved and yields important details about the nature and timing of the resurgency. An understanding of the timing and rates of resurgence is of interest not only for the study of previously active calderas, such as the Valles caldera, but for volcanic centers that have experienced more recent uplift, such as Yellowstone. The Valles caldera exhibits a distinct geometry in which the resurgent dome (Redondo Peak) lies near what was once the center of the collapsed caldera. The researchers used the 40Ar/39Ar dating method because it has a high level of precision for dating volcanic rocks of this age. The study shows that resurgent doming happened very soon after caldera formation (within 27 +/- 27 ka) with a minimum upheaval rate of about 2 cm/yr. The results highlight the physicomagmatic differences between resurgence at the Valles Caldera and resurgence at Yellowstone, a caldera that erupted at 0.6 Ma and had an uplift about 600-700 ka after the last major eruption. Thus the uplift at Yellowstone may represent different processes than those that caused the resurgent uplift of the Valles caldera. Results of the project were published in the August issue of the Journal of Geophysical Research: Phillips, E. H., F. Goff, P. R. Kyle, W. C. McIntosh, N. W. Dunbar, and J. N. Gardner (2007), "The 40Ar /39Ar age constraints on the duration of resurgence at the Valles Caldera, New Mexico", Journal of Geophysical Research, 112, B08201, doi:10.1029/2006JB004511.

Panoramic view of the Valle Grande looking NW toward the resurgent dome of Redondo Peak.

Actinide Migration Conference

Don Reed and Jef Lucchini (both in EES-12) presented five papers (three posters and two talks) at the Migration 07 Conference, held in Munich, Germany. Migration 07 was the 11th International Conference on the Chemistry and Migration Behavior of Actinides and Fission products in the Geosphere. Over 350 scientists were in attendance, and all countries with active nuclear programs and nuclear environmental issues were well represented. This remains a key and important conference for actinide/nuclear environmental research, and there were several beneficial discussions and relevant presentations to LANL/EES interests.

The Waste Isolation Pilot Plant (WIPP) update at the Migration 07 Conference - Photo by Don Reed, EES-12.

The posters and presentations given corresponded to the two main emphases in the Actinide Chemistry and Repository Science Program (ACRSP) team research: Waste Isolation Pilot Plant (WIPP) actinide chemistry and plutonium biogeochemistry (ERSP program). The WIPP-related posters were: "Effect of Carbonate on Uranium (VI) Solubility in WIPP Brine" and "Actinide Speciation in the WIPP," which provided an overview of current results in the WIPP actinide research program. Don Reed gave an invited presentation update of the WIPP transuranic repository on behalf of Dave Moody, the Department of Energy Carlsbad Field Office (DOE/CBFO) manager. The remaining poster and talk were centered on recent progress in the plutonium biogeochemistry ERSP program area. The poster was entitled "Role of Fe (II) in the Abiotic and Biotic Reduction of High-valent Plutonium." The talk was entitled "Plutonium Reduction by Metal Reducing Bacteria" and presented an overview of recent results in the LANL ERSP plutonium biogeochemistry research program (our ACRSP results, but mostly those of Hakim Boukhalfa, EES-6).

October 1, 2007

Paper Published in International Journal of Wildland Fire

Wildfires are an extremely complex phenomenon that involve feedbacks between fuel loads and moisture levels, local and regional topography, wind speeds and weather, and combustion physics and small-scale turbulence. One of the major difficulties in constructing numerical models to study wildfire behavior is the enormous range of spatial scales that must be considered. A wildfire typically propagates on a kilometer scale, and geographical features are important to how they spread. Local terrain and fuel characteristics can change on a scale of meters, minimum flamelet size and fuel/oxygen spatial gradients are on the order of centimeters, and gradients of short-lived radical species within the flame sheet of a given flame operate on a sub-micrometer scale. A similar analysis applies to temporal scales.

HIGRAD/FIRETC is a coupled atmosphere/wildfire behavior model. It combines a three-dimensional transport model that uses a compressible gas fluid dynamics formulation with a physics-based wildfire model, to represent the coupled behavior of the local atmosphere and wildfire. Rodman Linn and Jonah Colman (EES-2) published a paper titled, "Separating Combustion from Pyrolysis in HIGRAD/FIRETEC", in the International Journal of Wildland Fire, 2007, 16, 493-502. The paper details efforts to extend the functionality of HIGRAD/FIRETEC by modifying the burning model to handle pyrolysis and combustion as separate processes. Some fire behaviors, such as flash events, crowning, and fire 'whirls', may depend on the ability of combustion to take place in a separate spatial location from the pyrolysis. The new burning model is referred to as 'non-local'. Pyrolysis is considered as an endothermic process that produces a mixture of inert and combustible gasses. The researchers introduced a transportable gas species to the model. Combustion of this gas produces all the heat necessary to drive fire spread. The basic premise of the HIGRAD/FIRETEC burning model is retained, i.e. that the rate of a reaction is limited by the rate at which the reactants can be brought together (mixing limited). In the non-local burning model, the reactants for pyrolysis can be thought of as heat and wood, for combustion: the reactive gas and oxygen. Linn and Colman performed a few simple idealized test cases with both burning models and compared the simulations to each other and to empirical data. The non-local burning model gave results comparable to the local burning model in terms of the fire-line shape and the spread rate. LDRD funded the initial development of the FIRETEC model, which has received a R&D100 Award. The U.S. Forest Service funded the work described in the paper.

The spread rate in meters per second is plotted versus the wind speed. The inlet wind speed is used and results from the Cheney et al. (1998) empirical model are also plotted.

Cross-section of the gas parameters from the u3 simulation (inlet wind speed of 3m/sec) along the mid-line of the fire near the leading edge of the fire after 60 sec of simulated time have passed. Spatial scales are approximately 10 m vertically, and 30 m horizontally. In (a) the gas reaction rate is depicted in units of kg/sec; in (b) the reactive gas concentration is depicted in units of kg/m3; and in (c) the gas temperature is depicted in units of K.

Research on Tectonic History of the Colorado Plateau Published in Tectonophysics

The Colorado Plateau, roughly centered on the Four Corners region of the SW United States, is one of the major tectonic plateaus in the world. The plateau is composed primarily of undeformed sedimentary rocks that are many tens of millions of years old. Originally, the rocks were created in an oceanic environment; however, they are now at an elevation several kilometers above sea level. The timing and mechanism of the uplift history of the Colorado Plateau continues to be a contentious issue.

David Coblentz and Aviva J. Sussman (both in EES-11) and collaborators J. C. Lobarkin (Michigan State University) and C. G. Chase (University of Arizona have published Paleolithospheric Structure Revealed by Continental Geoid Anomalies, Tectonophysics, 443, pp.106-120, 2007), which addresses this issue. Their analysis takes into account both the crust and mantle lithosphere, which enables a closer approximation of relative elevation changes and better constrains proposed mechanisms of deformation and uplift. Their research indicates that deformation involving both the crust and the mantle lithosphere is responsible for the modern elevation of the Colorado Plateau and the Basin Range Province. This research is a major step furthering the understanding of the tectonic history of the Colorado Plateau and the Western U.S and in understanding how and why continental topography is developed. The research provides a new approach for investigating other uplifted regions by combining geoid anomalies with whole-column isostasy. (Geoid is a surface to which the force of gravity is everywhere perpendicular. Isostasy is the state of gravitational equilibrium between the Earth's lithosphere and asthenosphere such that the tectonic plates 'float' at an elevation which depends on their thickness and density.)

Colorado Plateau of the Western U.S.

LANL Research in Time Reversal Acoustics and Invited Talk at the Center for Research, Advanced Studies and Development in Pula, Italy

Michele Griffa (Nonlinear Elasticity Team, EES-11), visited the Center for Research (CRS), Advanced Studies and Development in Sardinia (www.crs4.it) at the Polaris Technological Park, Pula (Cagliari), Italy, to present an invited talk entitled, 'Exploiting Time Reversal Acoustics for the Development of New Ultrasonic and Seismic Imaging Techniques in Complex Solid Media'. Ernesto Bonomi, Energy and Environment Division head, CRS hosted the visit. The goal of the visit was to present some of the ongoing EES-11 research activities regarding the applications of Time Reversal Acoustics in ultrasound and seismic imaging.

Time Reversal Acoustics (TRA) has been developing since the '90s as a new intriguing field of Research in Elastic Wave Propagation in complex fluid and solid media. Typical TRA experiments are performed with arrays called Time Reversal Mirrors (TRMs) and are composed of two steps. The first step is forward propagation, during which a source (or many) emits a pulse that travels throughout the specimen and is recovered by the TRM. The second step is backward propagation, where each detected signal is digitally time-reversed then re-injected at the detection point (the detector acts as both receiver and source). The invariance of the elastodynamics wave equation to time-reversal implies the retro-focusing of the backward waves on the location of the source(s), as in a movie played backward. Scatterers in the medium (cracks, voids, inhomogeneities), acting as secondary sources, can be preferentially focused on as well, by using additional signal processing techniques and iteration of the TRA procedure itself. Although complete Time Reversal (TR) invariance of (elastic) wave phenomena is limited to lossless media, it has been shown not only that Time Reversal Mirrors are robust enough to retro-focus elastic energy onto primary/secondary sources, but that they can take advantage of multiple (random) scattering in order to improve temporal and spatial resolution, also beyond the limits imposed by diffraction effects.

The talk focused on how new experimental techniques, new signal processing approaches, and numerical simulations can be used synergistically to exploit Time Reversal Acoustics techniques for the localization and characterization (in space and time) of both primary and secondary sources in complex solid media. Cross fertilization between Nonlinear Nonclassical Elasticity, Non-Destructive Evaluation techniques, High Performance Scientific Computing, and Seismology is the basis of the work under development by Paul A. Johnson, Brian E. Anderson, Carene Larmat, TJ Ulrich, R.A. Guyer, Pierre-Yves Le Bas, M. Griffa, Jim A. TenCate and Lianjie Huang (all in EES-11). Their research, supported by LDRD funding. The research is aimed at using such new techniques for solving long-standing problems as 'How to selectively localize in 3D distributions of micro-cracks embedded in composite structured solid specimens' and 'How to localize in space earthquake sources at faults with a complicated pattern of emission in time and space'.

Invited Talk Results in Potential Collaborations with Procter & Gamble

Michael W. Blair, an EES-2 postdoc, recently was a keynote speaker at the inaugural Procter & Gamble Colour Community in Practice symposium. Blair's talk was entitled, 'Combining Spectroscopic Techniques to Understand Color Change' and was part of a larger session entitled, "From Protons to Profits-Colour Science at Los Alamos National Laboratory," in which Steve Stringer of Tech Transfer also participated. As a result of the presentation and interactions with Procter & Gamble employees, up to 10 potential collaborations between Procter & Gamble and LANL have been identified.

Other Archived Highlights