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Science Highlights, July 27, 2018

Awards and Recognition

Jaqueline Kiplinger elected Fellow of the American Chemical Society

Jaqueline Kiplinger

Jaqueline Kiplinger

The American Chemical Society (ACS) has named Jaqueline L. Kiplinger (Inorganic, Isotope and Actinide Chemistry, C-IIAC) as a Fellow. The ACS cited her “pioneering contributions in the synthetic chemistry of uranium and thorium, for significantly expanding the understanding of fundamental actinide and lanthanide chemistry, and for outstanding mentoring at every level,” and “leadership at ACS, including Division of Inorganic Chemistry, Committee on Ethics, and National Awards Selection Committees, and for many contributions to the ACS community, especially with regards to mentoring.”

Kiplinger received a Ph.D. in Chemistry from the University of Utah, and then joined the Laboratory as the first Frederick Reines Postdoctoral Fellow in 1999. She has accomplished pioneering work to establish synthetic routes to novel uranium and thorium compounds that have opened new frontiers in understanding the nature of bonding and reactivity in actinides. In addition to discovering new actinide reactivity patterns and bonding motifs, Kiplinger developed inexpensive, simple, and safe techniques to make thorium and uranium halide starting materials. The methods have been critical to advancing the synthetic and mechanistic chemistry of these important elements and for understanding their behavior in a variety of applications. Her novel synthetic approaches have led to the systematic isolation of entirely new classes of molecular uranium and thorium complexes. In other work, she pioneered the use of copper and gold reagents as one-electron oxidants for actinide compounds and designed a photochemical synthesis that established the first-ever evidence for the formation of a uranium complex that contains a terminal uranium-nitrogen triple bond. Her research provides scientific underpinning that supports the Laboratory’s national security mission and advances the fundamental understanding of actinide chemistry. Kiplinger’s mentoring in the chemical community and service to the ACS promote the development of the next generation of chemists.

With more than 161,000 members, the ACS is the world’s largest scientific society and the premier professional home for chemists, chemical engineers, and related professions worldwide. The ACS Fellows Program recognizes members of ACS for their outstanding achievements in and contributions to science, the profession and the Society. The lifelong designation recognizes ACS members for their excellence in scientific leadership and for their exceptional volunteer service to the ACS community. Kiplinger is among 51 new fellows in the ACS, and is one of only seven Los Alamos chemists honored in this way in the 75-year history of the Laboratory. Technical contact: Jaqueline Kiplinger

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Cesar Da Silva, Stefano Gandolfi, Alex Zylstra win DOE Early Career Awards

The DOE Office of Science has selected 84 scientists from across the nation – including three researchers from Los Alamos – to receive funding as part of DOE’s 2018 Early Career Research Program. The program supports the development of individual research programs of outstanding scientists early in their careers and stimulates research careers in the disciplines supported by the DOE Office of Science.

Cesar Da Silva

Photo credit: Furhana Ebner, Los Alamos National Laboratory

Cesar Da Silva (Subatomic Physics, P-25) was honored for his work in the Nuclear Physics program area on “Gluon saturation search in the deep small Bjorken-x region using the Large Hadron Collider Beauty Experiment.” Da Silva received a Ph.D. in Nuclear Physics from the University of Sao Paulo, Brazil. He joined the Lab as a Director’s Postdoctoral Fellow in 2010. Da Silva leads P-25’s High Energy Nuclear Physics team. He has won a RHIC/AGS User’s Executive Committee merit award, has organized multiple RHIC/AGS Annual Users’ Meeting workshops on heavy-quark physics, has served as the heavy-quark convener for PHENIX, and has played a key role in leading the upgrade of the Forward Silicon Vertex detector. Da Silva has also introduced a new technique that made B meson measurements possible with PHENIX.

Stefano Gandolfi

Photo credit: Furhana Ebner, Los Alamos National Laboratory

Stefano Gandolfi (Nuclear and Particle Physics, Astrophysics and Cosmology, T-2) was recognized for his work in the Nuclear Physics program area on “Weak interactions in nuclei and nuclear matter.” Gandolfi obtained a Ph.D. in Physics from the University of Trento, Italy. His thesis received an award for the best Ph.D. thesis of the year. He became a postdoctoral fellow at the International School for Advanced Studies (SISSA) in Trieste, Italy, before moving to Los Alamos in 2009. Gandolfi received the Young Scientist Prize from the International Union of Pure and Applied Physics (IUPAP) in 2013. His research at the Lab focuses on nuclear interactions, nuclear structure, electroweak interactions in nuclei and dense matter, physics of neutron stars, and strongly correlated ultracold Fermi gases.

Alex Zylstra

Photo credit: Furhana Ebner, Los Alamos National Laboratory

Alex Zylstra (Plasma Physics, P-24) was recognized in the Fusion Energy Sciences program area for “Studying nuclear astrophysics with inertial fusion implosions.” He received a Ph.D. in Physics from the Massachusetts Institute of Technology and joined the Lab as a Reines Distinguished Postdoctoral Fellow in 2015. Zylstra studies inertial confinement fusion, high-energy-density physics, and plasma physics at the National Ignition Facility (NIF). He is a campaign leader in the national program to increase NIF’s fusion performance . Zylstra has received a Los Alamos Postdoctoral Distinguished Performance Award for his work developing a new experimental platform at NIF, a National Science Foundation Graduate Research Fellowship, and a DOE NNSA Stewardship Science Graduate Fellowship.

To be eligible for the DOE award, a researcher must have received a Ph.D. within the past 10 years and be an untenured, tenure-track assistant, or associate professor at a U.S. academic institution or a full-time employee at a DOE national laboratory. Research topics must be within one of the Office of Science’s six major program offices.

Awardees were selected from a large pool of university- and national laboratory-based applicants. Selection was based on peer review by outside scientific experts. A list of all 84 awardees, their institutions, and titles of research projects is available on the Early Career Research Program webpage http://science.energy.gov/early-career/. Technical contact: Don Rej

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New Distinguished Postdoctoral Fellows Copp, Girolami, Goodwin, Popov, and Trugman arrive

The Lab selected new Distinguished Postdoctoral Fellows during the December quarterly review. Candidates must display extraordinary ability in scientific research, potential to impact Laboratory programs and/or ability to establish new capabilities, and show clear promise of becoming outstanding leaders. These fellowships provide the opportunity to collaborate with Los Alamos scientists and engineers on staff-initiated research. Initial appointments are three years in length. Technical contact: Mary Anne With

Darleane Christian Hoffman Distinguished Postdoctoral Fellow - Named after the distinguished Los Alamos nuclear scientist and recipient of the U.S. National Medal of Science, this fellowship recognizes, encourages, and rewards outstanding scientific and engineering contributions by women.

Stacy Copp

Stacy Copp

Stacy Copp (Center for Integrated Nanotechnologies, MPA-CINT) received a Ph.D. in Physics from the University of California – Santa Barbara. She joined the Lab as a Director’s Postdoc Fellow and then a University of California President’s Fellow before becoming a Hoffman Distinguished Postdoc Fellow.

Inspired by the elegant and complex systems that biology has evolved to manipulate light, she studies how soft materials can organize and enhance the function of photonic nanomaterials. Her work focuses on the ways that biomimetic polymer membranes arrange light-active nanoparticles and molecules. Copp examines self-assembly in composite mixtures of polymers, nanoparticles, and molecules to understand how individual components can be programmed to drive the assembly of novel photonic materials. She uses tools from machine learning and data mining to “learn” the underlying scientific principles that govern self-assembly and to design new materials with exciting photonic applications. Sergei Ivanov, Jennifer Hollingsworth, and Millicent Firestone (MPA-CINT) mentor her.

J. Robert Oppenheimer Distinguished Postdoctoral Fellow - Named after the Laboratory’s first Dir­ector, this fellowship recognizes individuals whose research aligns with the Laboratory’s mission.

Davide Girolami

Davide Girolami

Davide Girolami (Physics of Condensed Matter Complex Systems, T-4 and Applied Modern Physics, P-21) received a Ph.D. in Mathematics from The University of Nottingham. He joined the Lab as a Director’s Postdoctoral Fellow before becoming an Oppenheimer Distinguished Postdoctoral Fellow.

Girolami works in quantum information theory to develop new methods to control complex quantum networks, the architecture of future quantum technologies. Although macroscopic objects are relatively easy to control, atoms and photons demand exquisite techniques. A controller acquires information about a system of interest via measurements. Then, it drives the system into a target configuration by exerting an appropriate force or field. Such interactions usually destroy the fragile properties of a quantum system. By employing correlated quantum controllers, Girolami seeks to develop protocols to control quantum systems that outperform classical strategies, reducing the cost of quantum information processing. Wojciech Zurek and Lukasz Cincio (T-4) and Malcolm Boshier (P-21) co-mentor him.

Conrad Goodwin

Conrad Goodwin

Conrad Goodwin (Inorganic, Isotope and Actinide Chemistry, C-IIAC) received a Ph.D. in Chemistry from the University of Manchester.

Goodwin works in the area of f-element chemistry, focusing on electronic structure, new oxidation states, and oxidation state/structure/bonding interrelations. He explores structure/oxidation state relationships in metal-ligand covalency, and how these factors perturb f-element properties such as magnetic response and optical phenomena. Goodwin has received the Dalton Emerging Researcher award from the Royal Society of Chemistry, as well as a School of Chemistry Outstanding Achievement Award from the University of Manchester. Andrew Gaunt (C-IIAC) mentors him.

Ivan Popov

Ivan Popov

Ivan Popov (Physics and Chemistry of Materials, T-1 and Center for Non-linear Studies, T-CNLS) received a Ph.D. in Chemistry from Utah State University. He joined the Lab as a Director’s Postdoctoral Fellow before becoming an Oppenheimer Distinguished Postdoctoral Fellow.

Popov’s research involves accurate quantum mechanical calculations of electronic properties, chemical bonding interactions, and spectroscopic signatures of actinide and transition-metal containing compounds. He performs computational predictions of novel redox flow cells for large-scale energy storage, which are critical for the deployment of power grids with significant renewable energy. Popov develops the design principles needed for the discovery of novel electrolytes with higher energy density storage characteristics. Experimental groups in the Materials Physics and Applications (MPA) and Chemistry (C) Divisions at the Lab will chemically and spectroscopically verify the proposed complexes and their electrochemical properties. Ping Yang (T-1) and Enrique Batista (T-CNLS) co-mentor him.

Richard P. Feynman Distinguished Postdoc Fellow - Named after the famed theoretical physicist and winner of the 1965 Nobel Prize in Physics, this fellowship recognizes individuals whose research is in theory or computing.

Daniel Trugman

Daniel Trugman

Daniel Trugman (Geophysics, EES-17 and Physics and Chemistry of Materials, T-1) received a Ph.D. in Geophysics at the University of California – San Diego.

Trugman applies machine learning techniques to tackle challenging problems in the solid earth sciences, with a particular emphasis on understanding earthquake source processes and quantifying seismic hazard. His research includes data-driven analyses of the waveform features radiated during the initial rupture process of large earthquakes and imaging of failure stresses and stress transfer from human-triggered earthquakes induced during industrial mining operations. Paul Johnson (EES-17), Andrew Delorey (EES-17), and Kipton Barros (T-1) co-mentor him.

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Bioscience

Carbon use efficiency diagnostics developed in Nannochloropsis salina

Algae, as feedstocks for biofuels and bioproducts, can enhance energy security and spur the advancement of the bioeconomy. Improvements in algal biomass productivity are key to realizing algae’s potential. Carbon dioxide (CO2) use efficiency is an important key metric in algal biomass productivity. Methods to measure CO2 efficiency are needed to optimize growth conditions in industry and characterize improvements. In a publication in Algal Research, Lab researchers describe the measurement of carbon isotope fractionation as a key diagnostic tool for characterizing carbon use efficiency in Nannochloropsis salina CCMP 1776, a benchmark strain in algal biofuels research due to its high oil content.

Photo. Bioreactors growing algae

Photo. Bioreactors growing algae.

During CO2 fixation by the enzyme ribulose bisphosphate carboxylase oxygenase (RuBisCO), fractionation of carbon isotopes occurs. The preferential fixation of 12CO2 leads to depletion of the heavier isotope, 13C. In algae grown in controlled photobioreactors, photosynthetic discrimination of carbon isotopes can be calculated as the difference in isotopic signatures between the media and the algae. By measuring photosynthetic discrimination under different conditions, the scientists found the optimal conditions under which RuBisCO saturation can be achieved to maximize biomass productivity (non-limiting CO2 supply with efficient sparging, characteristic of photobioreactor systems).

Figure. Conceptual model for carbon uptake in algae showing possible fractionation steps (modified from Sharkey and Berry, 1985), where k = uptake of inorganic carbon from the external pool of dissolved inorganic carbon, k−1 = back diffusion of inorganic carbon, k2 = incorporation of intracellular carbon into algae (carbon fixation by RuBisCO), k3 = dark respiration, POC (particulate organic carbon) represents the carbon in the organisms. N. salina has been suggested to activate a bicarbonate pump under low CO2.

Figure. Conceptual model for carbon uptake in algae showing possible fractionation steps (modified from Sharkey and Berry, 1985), where k = uptake of inorganic carbon from the external pool of dissolved inorganic carbon, k−1 = back diffusion of inorganic carbon, k2 = incorporation of intracellular carbon into algae (carbon fixation by RuBisCO), k3 = dark respiration, POC (particulate organic carbon) represents the carbon in the organisms. N. salina has been suggested to activate a bicarbonate pump under low CO2.

The team used a conceptually simple model to examine carbon uptake in algae. The Figure depicts the possible fractionation steps. The experimentally determined value of photosynthetic discrimination of carbon isotopes at saturating conditions (37–40%) matched the value predicted by the team’s model of carbon uptake and fractionation in algae, taking into account RuBisCO fractionation and fractionation associated with equilibrium between CO2 and bicarbonate. This is the first report where a theoretical maximum of photosynthetic discrimination has been measured in a strain of algae used for biofuel production. The results demonstrate that measurement of photosynthetic discrimination can be a useful tool to provide feedback on engineering and growth improvements that can impact carbon use efficiency and biomass productivity during algal cultivation for fuels and other products.

Reference: “Carbon Use Efficiency Diagnostics in Nannochloropsis salina,” Algal Research 31, 40 (2018); https://doi.org/10.1016/j.algal.2018.01.011. Authors: Tawanda Zidenga, Munehiro Teshima, and Scott Twary (Bioenergy and Biome Sciences, B-11); George Perkins, Thom Rahn, and Jeffrey Heikoop (Earth System Observations, EES-14).

Laboratory Research and Development (LDRD) funded the work, which supports the Lab’s Energy Security mission area and the Science of Signatures mission area through the development of more efficient biofuel production. Technical contact: Scott Twary

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Chemistry

New neptunium (III) compound isolated

Figure. Journal cover depicts a route to a well-defined Np(III) starting material without the need to employ scarce Np metal. Credit: Josh Smith (Chemistry Division, C-DO)

Figure. Journal cover depicts a route to a well-defined Np(III) starting material without the need to employ scarce Np metal. Credit: Josh Smith (Chemistry Division, C-DO)

Los Alamos and Purdue University researchers have isolated and structurally characterized a new, rare, easily prepared, neptunium (III) [Np3+] starting material to provide access to non-aqueous studies. Their work helps solve the problem of a scarcity of Np metal by converting readily accessible Np oxide/aqueous solutions to a non-aqueous Np(III) molecule. This development enables comparison to uranium (III) and plutonium (III) chemistry. The journal Chemical Communications reported the findings and featured them on the cover.

Most neptunium (III) is formed in nuclear reactors. Its presence contributes to the radiotoxicity of nuclear waste. A lack of practical forms of neptunium has limited the ability of scientists to study its chemical behavior under nuclear fuel processing and environmental conditions. The team aimed to create a new, facile, synthetic access route into air-sensitive non-aqueous neptunium chemistry in the +3 oxidation state.

The Figure describes the chemical reactions that the researchers developed. Commercially available Np oxide dissolved in acid generates the Np(IV) parent, NpCl4(DME)2. Addition of CsC8 in tetrahydrofuran (THF) produces ‘NpCl3(THF)xin situ. Addition of pyridine (py) allowed isolation and structural characterization of the Np(III) molecule NpCl3(py)4.

Figure. Synthetic route and crystallization conditions that lead to NpCl4(THF)3 and NpCl3(py)4 .

Figure. Synthetic route and crystallization conditions that lead to NpCl4(THF)3 and NpCl3(py)4 .

The work helps elucidate new understanding of redox chemistry, new bonding motifs, and electronic structure trends across the actinide series. In order to compare and contrast to the recent advances in uranium chemistry, the field requires a widely accessible route to prepare non-aqueous Np(III) complexes. Uranium species are often achieved by oxidizing uranium metal. Neptunium metal is very scarce and not commercially available, but aqueous acidic stock solutions of neptunium can be prepared from dissolution of commercially available neptunium oxide. The non-aqueous Np(IV) molecule NpCl4(DME)2 is easily made from aqueous stocks. The authors demonstrated that Np(IV) can be reduced to Np(III) to afford a structurally characterized starting material of known molecular formula that can be isolated. This is an advantaged compared with previous in situ methods, in which the exact nature of the starting material is not known.

This new method provides a widely accessible entry point to Np(III) chemistry for any approved radiological laboratory. The synthesis of UI3(THF)4 from uranium (U) metal by Zwick, Sattelberger, and Clark, reported in 1994, greatly facilitated the study of low valent uranium chemistry. The Np(IV) reduction method may find similar utility in neptunium synthetic chemistry. The current paper also notes some key differences in redox stability in tetrahydrofuran between neptunium and plutonium (Pu) – notably that while Np(IV) is stable in tetrahydrofuran, Pu(IV) is not and forms a mixed valent Pu(III)/Pu(IV) complex salt.

Reference: “Non-aqueous Neptunium and Plutonium Redox Behaviour in THF – Access to a Rare Np(III) Synthetic Precursor,” Chemical Communications 54, 6113 (2018);  doi: 10.1039/c8cc02611d. Authors: Andrew Gaunt and Nickolas Anderson (Inorganic, Isotope and Actinide Chemistry, C-IIAC), Brian Scott (Materials Synthesis and Integrated Devices, MPA-11), Suzanne Bart (Purdue University), and Scott A. Pattenaude (Purdue University and C-IIAC).

An article in CHEMISTRYWORLD reported the work:  https://www.chemistryworld.com/news/new-route-to-3-oxidation-state-of-neptunium/3009107.article

The DOE Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division, Heavy Element Program funded the Los Alamos work. Scott Pattenaude received a Seaborg Summer Fellowship at the Laboratory, and a Laboratory Director’s Postdoctoral Fellowship sponsored Nikolas Anderson. The work supports the Lab’s Global and Energy Security Mission areas and the Materials for the Future science pillar through the development and understanding of actinide chemistry. Technical contact: Andrew Gaunt

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Earth and Environmental Sciences

Studies examine climate processes affecting critical watersheds

The impacts of climate-driven disturbance could lead to massive ecosystem changes. Such impacts might affect water catchment areas such as the Colorado River Basin (CRB), which is essential to energy, agriculture, and urban development. Lab researchers and collaborators on the Critical Watersheds project examined multi-scale processes, some at the plot scale (tens of square meters), and some encompassing the entire CRB (approximately 600,000 square kilometers). Results showed that climate-driven disturbances could be more severe than previously predicted. The following paragraphs summarize the research.

This work supports the Lab’s Energy Security mission area and the Science of Signatures science pillar through studies of the impact of climate on water availability and ecosystem. A Laboratory Directed Research & Development (LDRD) project to Principal Investigator Richard Middleton (Computational Earth Science, EES-16) primarily funded the Los Alamos work. Kurt Solander received a NASA Earth and Space Science Fellowship, and Katrina Bennett received a Director’s Postdoctoral Fellowship.

Figure.  2003-2015 annual water use to water availability ratio (%) for 18 major U.S. watersheds. The Lower CRB was the least sustainable.

Figure. 2003-2015 annual water use to water availability ratio (%) for 18 major U.S. watersheds. The Lower CRB was the least sustainable.

Satellite data shows unsustainable water resource management in the Southwest U.S.

Remotely sensed data can provide crucial insights, especially in regions lacking spatially continuous and high-resolution information, or where population growth and temperatures project water shortages. The team used data from the Gravity Recovery and Climate Experiment (GRACE) satellite mission and in-situ records to assess groundwater resources and surface water for 18 major U.S. watersheds. Satellite data revealed that annual water consumption twice exceeded natural supplies during 2003-2015 in the lower CRB (Figure). An increasing water-use-to-availability ratio in five of the six basins indicates regional sustainability declines. Increased warming and population growth make future water use uncertain.

 Reference: “GRACE Satellite Observations Reveal the Severity of Recent Water Consumption in the United States,” Scientific Reports 7, 8273 (2017); https://www.nature.com/articles/s41598-017-07450-y. Authors: Kurt Solander and Richard Middleton (EES-16), John Reager and James Famiglietti (Jet Propulsion Laboratory, California Institute of Technology), and Yoshihide Wada (International Institute for Applied Systems Analysis, Austria). Technical contact: Kurt Solander

Figure. Average future streamflow (m3s-1, 2070–2099) compared to historical (1970–1999) for the San Juan River basin.

Figure. Average future streamflow (m3s-1, 2070–2099) compared to historical (1970–1999) for the San Juan River basin.

Forest disturbance exacerbates Colorado River declines

Researchers used a hydrologic model to analyze the coupled impacts of climate and forest disturbance on Colorado River headwaters. Results indicate that future forest disturbances would greatly impact water resources. This contradicts the conventional thinking that forest disturbances increase streamflow by reducing evaporation and transpiration. Instead, the coupled scenarios show that the annual average regional streamflow is at least 6–11% lower than when only modeling climate variation. Within forested zones of the San Juan River basin, streamflow is 15–21% lower (Figure). A 10% flow reduction would impact water management in a water-limited basin like the Colorado. These findings indicate that models must accurately represent land cover change when considering the effects of climate change on water resources.

Reference: “Climate-driven Disturbances in the San Juan River Sub-basin of the Colorado River,” Hydrology & Earth System Sciences 22, 709 (2018);  https://doi.org/10.5194/hess-22-709-2018. Authors: Katrina Bennett, Kurt Solander, and Richard Middleton (EES-16); Chonggang Xu (Earth System Observations, EES-14); Theodore Bohn and Enrique Vivoni (Arizona State University); and Nate McDowell (Pacific Northwest National Laboratory). Technical contact: Katrina Bennett

Changes in Colorado River flow indicate altered snowmelt patterns

Warming temperatures across the CRB also alter streamflow seasonality and impact water management. The team studied these changes using gauges in the CRB and spanning 60 years. Findings indicate increases in high and low streamflows during March-April, and declines of up to 41% during June-July. Shifts indicate a greater percentage of early snowpack melting. Long-term changes of runoff timing could affect: 1) a greater risk of winter flooding, 2) altered fish habitat, and 3) less water for irrigation, municipal supplies and power generation. Research identified where severe changes could affect CRB watersheds. The insight could help resource managers prepare for changes due to anticipated future temperature increases.

Reference: “Shifts in Historical Streamflow Extremes in the Colorado River Basin,” Journal of Hydrology: Regional Studies 12, 363 (2017); https://doi.org/10.1016/j.ejrh.2017.05.004 . Authors: Kurt Solander, Katrina Bennett, and Richard Middleton (EES-16). Technical contact: Kurt Solander

Figure. Graphical depiction of the combined effects of ecosystem temperature change and drought stress through the 21st century via: A) temperature increases, B) chronically high drought stress and mortality, and C) chronically low biomass.

Figure. Graphical depiction of the combined effects of ecosystem temperature change and drought stress through the 21st century via: A) temperature increases, B) chronically high drought stress and mortality, and C) chronically low biomass.

Predicting and planning for chronic climate-driven disturbances

Increasing climate-driven disturbances could strain environmental resources simultaneously with increasing societal demands. Researchers outlined the concepts underlying chronic decline in ecosystem services due to climate-driven disturbances (the chronic disequilibrium hypothesis) and discussed opportunities to better predict disturbances using Earth System Models (ESMs). Chronic disequilibrium describes systems that cannot return to their prior structure and function due to increasing frequency/severity of extreme events associated with chronic warming. Each disturbance reduces forest stand biomass, and increasing disturbances accelerate the decline. Because climate-driven plant mortality is usually size dependent, this biomass reduction alters the size distribution of plants within the disturbed area, influencing ecosystem stocks and fluxes.

The team developed a novel mechanistic theory that combines models for disturbance mortality and metabolic scaling to link size-dependent plant mortality to changes in ecosystems stocks and fluxes. The findings indicate that strong dependence of carbon and water fluxes on biomass combined with progressive biomass decline would result in decreasing overall fluxes. Fortunately, ESMs provide a way forward. Experiments could represent disturbance processes. Next-generation ESM development would allow researchers to test how critical resources are sensitive to future change, and mitigation techniques could be evaluated without relying on historical data that fails to account for anticipated changes.

Reference: “Predicting Chronic Climate-Driven Disturbances and Their Mitigation,” Trends in Ecology & Evolution 33, 15 (2018); https://doi.org/10.1016/j.tree.2017.10.002. Authors: Nate McDowell (Pacific Northwest National Laboratory), Sean Michaletz (University of Arizona), Katrina Bennett, Kurt Solander, and Richard Middleton (EES-16); Chonggang Xu (EES-14); and R. M. Maxwell (Colorado School of Mines). Technical contact: Chonggang Xu

Narrowed uncertainty improves decision-making tools for water management   

Streamflow estimates use modeling tools that rely on uncertain parameters. Sensitivity analysis can help determine which parameters impact model results. Although simulated flows respond to changing climate and vegetation, simulation sensitivity has rarely been considered. The team evaluated the parameters’ sensitivity in the Variable Infiltration Capacity (VIC) hydrologic model to changes in runoff, evapotranspiration, snow water equivalent, and soil moistures in the Colorado Basin. Results indicated that snow-dominated regions are much more sensitive to uncertainties in the model’s parameters. The team discovered that changes in runoff and evapotranspiration are sensitive to the Earth’s surface reflectivity, while changes in snow water equivalent are sensitive to vegetation canopy size. Projections anticipate that parameters will change. Narrowing uncertainty is critical for improved modeling and decision-making, particularly in the water-stressed Southwest.

Reference: “Global Sensitivity of Simulated Water Balance Indicators under Future Climate Change in the Colorado Basin,” Water Resources Research 54, 132 (2017); https://doi.org/10.1002/2017WR020471 . Authors: Katrina Bennett, Alex Jonko, Adam Atchley, and Richard Middleton (EES-16); Jorge Blanco and Nathan Urban (Computational Physics and Methods, CCS-2); and Theodore Bohn (Arizona State University). Technical contact: Katrina Bennett

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Explosive Science and Shock Physics

Melt-cast explosive material developed as a potential TNT replacement

David Chavez (High Explosive Science and Technology, M-7) and collaborators with the U.S. Army Research Laboratory in Aberdeen, MD have developed a novel “melt-cast” explosive material that could be a suitable replacement for Trinitrotoluene, more commonly known as TNT. The Army and the Lab, through the Joint Munitions Program, have sought a TNT replacement due to toxicity and environmental concerns with TNT. The scientists aimed to create a material with the appropriate melting point to enable melting and casting for use in a variety of munitions. The journal Organic Process Research & Development has published the synthesis and characterization of the nitrogen-containing compound, called bis-oxadiazole, that the researchers developed.

Photo. Explosives chemist David Chavez pours a melt-castable explosive into a copper mold at the Laboratory’s Technical Area 9.

Photo. Explosives chemist David Chavez pours a melt-castable explosive into a copper mold at the Laboratory’s Technical Area 9.

TNT has been in use as a munitions explosive since 1902, and it is considered the benchmark for melt-castable explosives. However, TNT has some drawbacks. The Environmental Protection Agency has listed TNT as a possible carcinogen, and exposure to the material has been linked to disorders of the blood, such as anemia, and abnormal liver function, according to the Centers for Disease Control. Red water and pink water, two types of wastewater that are generated from the TNT manufacturing process, can find their way into the waste stream. The Environmental Protection Agency has declared TNT a pollutant and has pushed for its removal from military munitions.

Researchers seek melt-cast explosives because they allow for scalable and efficient manufacturing processes. However, these materials must also possess specific unique properties, which significantly narrows the range of new target materials that can be pursued. For example, although a melt-cast material can have a melting point between 70 and 120 ° C, a melting point below 100 ° C is ideal. This allows steam heating to be used at ambient pressure in casting operations, which can dramatically reduce costs in manufacturing. Other important properties of a melt-castable explosive include low vapor pressure, a significant difference between the melting temperature and the decomposition temperature, high density, low sensitivity, and “green” and affordable synthesis.

Photo. Photograph of the bis(1,2,4-oxadiazole)bis(methylene)dinitrate explosive. The molecular structure is overlaid on the photo.

Photo. Photograph of the bis(1,2,4-oxadiazole)bis(methylene)dinitrate explosive. The molecular structure is overlaid on the photo.

Chavez has been developing high-nitrogen explosive compounds for decades at the Lab. He has focused on low explosive sensitivity and good environmental properties. Chavez collaborated with Jesse Sabatini and colleagues at Aberdeen to develop a 24-atom molecule that is packed with nitrogen. It has increased performance 1.5 times greater than TNT, and the melting point is in the desired range. The dinitrate compound exhibits a relatively high decomposition temperature and lower sensitivities to impact and friction compared with the commonly used explosive RDX. The authors suggest that intramolecular hydrogen bonding observed in the crystal lattice assists in the relatively high thermal stability and relatively low sensitivity of the material.

One of the team’s biggest technical challenges was obtaining a high enough yield of the material from the synthesis process. An early procedure produced only a 4 percent yield, far too low to be practical and affordable. After several iterations of the process, the scientists boosted the yield to 44 percent. 

The characteristics and performance properties of the new molecule indicate that it might serve as a powerful stand-alone melt-castable explosive material. This work may enable the preparation of munitions with enhanced performance compared with the TNT-based formulation. This advance could allow for smaller designs or more effective energy delivery. In addition, the material might serve as an energetic plasticizing ingredient for nitrocellulose-based propellant formulations, potentially reducing volatility and migration during thermal and mechanical shock events. The team plans to continue research with production of the material on a kilogram scale, explosive testing, and toxicity studies. 

Reference: “Bis(1,2,4-oxadiazole)bis(methylene) Dinitrate: A High-Energy Melt- Castable Explosive and Energetic Propellant Plasticizing Ingredient,” Organic Process Research & Development  22, 736 (2018); doi: 10.1021/acs.oprd.8b00076. Authors: Eric C. Johnson, Jesse J. Sabatini, Rosario C. Sausa, Edward F. C. Byrd, Leah A. Wingard, and Pablo E. Guzmàn (U.S. Army Research Laboratory, Aberdeen Proving Ground); and David E. Chavez (High Explosive Science and Technology, M-7).

The DoD/DOE Joint Munitions Program funded the work, which supports the Lab’s Nuclear Deterrence and Global Security mission areas and Materials for the Future science pillar. The research benefits new material development and additive manufacturing areas of the program. Technical contact: David Chavez

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Intelligence and Space Research

Multipoint satellite observations provide insight into the origins of substorms

The nature of substorms in the magnetosphere, the magnetic-field region that surrounds the Earth, has long been a topic of research. A substorm results from the interaction between the Sun and Earth. The sun’s outer atmosphere is constantly expanding into space producing the solar wind. When the solar wind interacts with the Earth’s magnetic field, it couples energy into the magnetosphere through magnetic reconnection. A research team, including Geoffrey Reeves (Intelligence & Space Research, ISR-DO) has investigated observations from multiple satellites to develop a more comprehensive picture of substorm interactions with the Earth’s magnetosphere. The Journal of Geophysical Research: Space Physics published their findings.

Figure. Artist’s conception of the reconnection of the magnetic field lines. Credit: NASA

Figure. Artist’s conception of the reconnection of the magnetic field lines. Credit: NASA

Magnetic reconnection happens between the Sun’s magnetic field (carried by the solar wind) and the Earth’s. The reconnection happens on the sunward side (the day side) of the Earth where the two systems interact. After dayside reconnection, one end of the field line remains connected to the Earth while the solar wind carries the other end to the night side of the Earth. This action stretches and compresses the magnetic field on the night side forming a magnetotail. When sufficient magnetic energy builds up, reconnection starts between the field lines attached to Earth in the northern and southern hemispheres. Reconnection in the magnetotail has two effects. It produces a magnetic “bubble” that pops off back into the solar wind and it creates a slingshot of magnetic field lines that return toward Earth. The result is a substorm, a type of space weather. Learn more about NASA animation detailing a magnetospheric substorm

Substorms drive huge electrical currents and energize the protons and electrons in the magnetotail. One of the signatures of substorm activity is the sudden Earthward transport of tens to hundreds of keV electrons and/or ions throughout the near-Earth plasma sheet and into the inner magnetosphere, a phenomenon called energetic particle injection. Often the energetic particles appear near geosynchronous orbit, the area where most large satellites operate including some that carry Los Alamos-developed sensors used to monitor the Nuclear Test Ban Treaty. With satellite use becoming increasingly pervasive for missions including expanded communications and Internet access, Earth imaging, and more, scientists seek to understand how and why substorms occur. These space weather effects can disrupt satellites via the buildup of electrical charge on the surface of a satellite damaging its electronics. Researchers aim to predict when substorms are likely and how severe their effects might be. Better data about space weather could enable satellites design to better address the specific radiation conditions they will encounter. Watch Reeves discussing the potential catastrophic effects of space weather on satellites. 

Los Alamos has been studying substorms and substorm injections since the 1970s. Lab researchers have flown energetic particle instruments on over a dozen different satellites in geosynchronous orbit (35,786 km above Earth’s equator). As a result, most of what the scientific community knew about substorm injections until recently was based on geosynchronous measurements. The Laboratory’s work continues today with the Space and Atmospheric Burst Reporting System (SABRS) payload, part of the United States Nuclear Detonation Detection System (USNDS) program.

In this new study, the team capitalized on recent observations during a conjunction between NASA’s Magnetospheric Multiscale Mission (primarily measures the region outside geosynchronous orbit) and Van Allen Radiation Belt Storm Probes mission (measures inside geosynchronous) that occurred on 7 April 2016. With complementary data from Time History of Events and Macroscale Interactions during Substorms, Geotail, and Los Alamos National Laboratory spacecraft in geosynchronous orbit (16 spacecraft in total), this is the first research to use data from all of these satellite systems to examine the complex dynamics of charged particles in substorm injections.  The event occurred during generally quiet magnetospheric activity under steady, below-average solar wind conditions. The investigators aimed to develop a more comprehensive global picture of injections and the injection region and to gain insight on the nature of substorms and reconnection in Earth’s magnetotail.

The data resulted in a more comprehensive picture of substorm injections. Previous studies could only look at two points: geosynchronous orbit+inward or geosynchronous orbit+outward but not both simultaneously. In this study the team analyzed the three regions (outside, inside, and at geosynchronous) and confirmed that the observed injections moved Earthward. The analysis revealed that at least five electron injections, which were localized in magnetic local time, preceded a larger injection of both electrons and ions across nearly the entire nightside of the magnetosphere near geosynchronous orbit. The discrepancy between the number, penetration depth, and complexity of electron versus ion injections presents challenges to the current conceptual models of energetic particle injections.

The Los Alamos team and their collaborators now have two years of overlapping data from the collection of satellites. They will continue looking at similar events and collecting new data to produce a more comprehensive and complete analysis of these space weather events.

Reference: “Multipoint Observations of Energetic Particle Injections and Substorm Activity during a Conjunction between Magnetospheric Multiscale (MMS) and Van Allen Probes,” Journal of Geophysical Research: Space Physics 122, 11,481 (2017);  https://doi.org/10.1002/2017JA024554 . Authors: D. L. Turner, J. F. Fennell, J. B. Blake, S. G. Claudepierre, and J. H. Clemmons (The Aerospace Corporation); A. N. Jaynes, T. Leonard, and D. N. Baker (University of Colorado – Boulder); I. J. Cohen, M. Gkioulidou, A. Y. Ukhorskiy, and B. H. Mauk (Johns Hopkins University); C. Gabrielse, V. Angelopoulos, and R. J. Strangeway (University of California – Los Angeles); C. A. Kletzing (University of Iowa); O. Le Contel (CNRS/Ecole Polytechnique/UPMC Université Paris Université Paris-Sud/Observatoire de Paris); H. E. Spence and R. B. Torbert (University of New Hampshire); R. B. Torbert and J. L. Burch (Southwest Research Institute); and G. D. Reeves (Intelligence & Space Research, ISR-DO).

The NASA Magnetospheric Multiscale mission (MMS) Spacecraft Program funds the current work. DOE sponsors current work in space weather and development of Los Alamos instruments that measure the space environment. The research supports the Laboratory’s Global Security mission area and the Information Science and Technology and Science of Signatures pillars through research and development of remote sensing for situational awareness in space. Technical contact: Geoffrey Reeves  

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Materials Physics and Applications

Novel exciton interactions observed in compositionally-defined bundles of carbon nanotubes

Photo. Steve Doorn works on an instrument used for spectroscopic characterization of carbon nanotubes.

Photo. Steve Doorn works on an instrument used for spectroscopic characterization of carbon nanotubes.

Laboratory researchers in collaboration with the National Institute of Standards and Technology (NIST) have discovered an optical signature of novel exciton interactions in small bundles of carbon nanotubes (CNTs). The quantum tunneling action could impact energy distribution in carbon nanotube networks and enable potential use in light-harvesting films and other applications. The journal Nature Communications has published their findings.

Carbon nanotubes are cylinders of graphene with their atoms arranged in hexagons. CNTs have potential as near-infrared light emitters and nanoscale semiconductor materials for electronics and optoelectronics applications. Excitons effectively carry energy in CNTs as tightly bound and highly correlated pairs of negative and positive charge (electrons and holes) and are created when light is absorbed by the material. This discovery provides clear evidence that in small bundles of CNTs, in which each nanotube has an identical structure, typical excitons that are bound to a single nanotube (intratube excitons) are now accompanied by excitons that instead tunnel across closely interacting nanotubes (intertube excitons).

Interactions between individual elements of nanomaterials can give rise to new emergent behaviors. Intertube excitons are a one-dimensional analogue to a broader class of interlayer excitons found in two-dimensional materials like transition metal dichalcogenides that are also of growing interest for their optical and electronic properties. Exotic behaviors such as exciton condensation may result. Intertube excitons of CNTs could add to the range of observed exciton behaviors and potentially impact how energy moves around in CNT networks of interest as light-emitting films or for light harvesting applications. While intertube excitons had previously been suggested based on observations of light absorption and emission in CNT bundles, limitations of these optical probes have restricted further study.

Figure. Plot of exciton energy resonances determined by resonance Raman spectroscopy for a carbon nanotube bundle limited solely to (6,5) nanotubes. The red-circled feature highlights the new resonance behavior introduced by intertube interactions in bundles, depicted in the upper right inset. The lower left inset depicts the interaction between cross-polarized intertube (blue) and intratube (red) excitons.

Figure. Plot of exciton energy resonances determined by resonance Raman spectroscopy for a carbon nanotube bundle limited solely to (6,5) nanotubes. The red-circled feature highlights the new resonance behavior introduced by intertube interactions in bundles, depicted in the upper right inset. The lower left inset depicts the interaction between cross-polarized intertube (blue) and intratube (red) excitons.

The Los Alamos/NIST team showed that Raman spectroscopy (a form of light scattering) can provide more extensive characterization of intertube excitons. The team used chemical separations to isolate a sample of a single type of CNT structure. The nanotubes in these samples were then bundled to force interactions between individual nanotubes. The researchers measured the intensity of Raman scattered light as the wavelength of light was varied to provide a profile or map of the CNT exciton energies. The team found a previously unobserved sharp feature in the Raman profile of the bundled CNTs (red-circled region in the Figure). The investigators did not find this unexpected feature for non-interacting individual CNTs.

Theoretical analysis showed that the unique packing geometry produced in bundles comprised of a single CNT structure results in chains of closely interacting carbon atoms that promote the formation of intertube excitons (Figure inset, upper right). Further analysis showed that the intertube excitons by themselves cannot interact with light in a way that generates the sharp feature. Instead, an interaction (depicted in lower left inset, Figure) between the intertube excitons and intratube excitons leads to an exciton scattering process that is accompanied by a quantum interference. The Raman spectral signature of such an interference, known as a Fano resonance, is exactly the sharp asymmetric feature observed experimentally.

The Fano interference has been well known in atomic and condensed matter physics. It is becoming increasingly important as a means for creating new optical behaviors in nanoscale composite materials such as plasmonic assemblies and metamaterials, as routes to manipulate light. The team’s findings reveal this behavior as a new class of exciton response in CNT assemblies, suggesting such Fano resonances may be found in a broader class of 2D quantum composite materials, for which expanded optical functionality of interest for optoelectronic and photonic applications may result. 

Reference: “Resonance Raman Signature of Intertube Excitons in Compositionally-Defined Carbon Nanotube Bundles,” Nature Communications 9, 637 (2018); doi: 10.1038/s41467-018-03057-7). https://www.nature.com/articles/s41467-018-03057-7 Authors: Stephen Doorn, Erik Haroz, and Hagen Telg (Center for Integrated Nanotechnologies, MPA-CINT); Andrei Piryatinski (Physics of Condensed Matter and Complex Systems, T-4); Oleksiy Roslyak (Fordham University, CINT user); Jared Crochet and Juan Duque (Physical Chemistry and Applied Spectroscopy, C-PCS); Jeffrey Simpson (Towson University and NIST); and Angela Hight Walker (NIST).

This work was supported in part by the Laboratory Directed Research and Development (LDRD) program and was performed in part at both the Center for Integrated Nanotechnologies (a DOE Office of Science user facility jointly operated by Sandia and Los Alamos National Laboratories) and the National Institute of Science and Technology in Gaithersburg, MD.

The work supports the Laboratory’s Energy Security mission area and its Materials for the Future and Science of Signatures science pillars by developing new methods to define, probe, and model novel materials interactions with the aim of developing technologically useful quantum materials. Such understanding aids efforts to develop materials with predictable performance and controlled functionality, such as for photovoltaic and optoelectronic devices. Technical contacts: Stephen Doorn and Andrei Piryatinski

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Materials Science and Technology

Chemical vapor deposition methods improve molybdenum-based nuclear fuel cladding

Although current nuclear reactor designs and components are already considered to be accident tolerant, the 2011 Fukushima disaster spurred efforts to develop enhanced accident tolerant materials for the nuclear energy industry. The DOE Fuel Cycle Research & Development Program has placed priority on the search for durable fuel and cladding materials as the most important component for both safety and energy production. Los Alamos researchers have investigated molybdenum (Mo) for nuclear fuel cladding applications due to its high melting temperature, high strength, and high creep resistance at elevated temperatures. Such properties are extremely important under accident conditions when the flow of cooling medium is interrupted. The journal Surface and Coatings Technology published the research.

The desirable mechanical and radiation tolerance properties of molybdenum for fuel cladding applications are highly dependent upon purity and microstructure. Conventional metallurgical methods do not allow fabrication of Mo tubing with the very fine (submicron scale) and randomly oriented grains needed for nuclear fuel cladding applications. Therefore, the team investigated chemical vapor deposition (CVD) techniques to produce tubes with the desired properties. The method produced free-standing molybdenum tubes with lengths and wall thickness up to 9.5 inches and exceeding 250 μm, respectively. The work demonstrated a method to produce sufficient film thickness, high purity, and sub-micro randomly oriented grains. Characterization of these tubes revealed that the properties of the tubes varied along the length. For example, the wall thickness of the resulting tubes decreased with distance from one end to the other, and the microstructure varied greatly as shown in the Figure.

Figure. SEM (scanning electron microscope) images of molybdenum tube wall cross sections from various locations along the tube. The scale given by the ruler is in inches.

Figure. SEM (scanning electron microscope) images of molybdenum tube wall cross sections from various locations along the tube. The scale given by the ruler is in inches.

The process produced microstructure suitable for the needs of a molybdenum-based cladding locally with the tubes. The researchers suggest that reconfiguring the deposition system with a translating mechanism (as has been demonstrated for silicon carbide tubes) could achieve a Mo tube with the desired microstructure along its entire length.

Reference: “Chemical Vapor Deposition of Mo Tubes for Fuel Cladding Applications,” Surface and Coatings Technology 337, 510 (2018). https://doi.org/10.1016/j.surfcoat.2018.01.063     Authors: Miles F. Beaux II, Douglas R. Vodnik, Reuben J. Peterson, Bryan L. Bennett, David J. Devlin, and Igor O. Usov (Engineered Materials, MST-7); Graham King and Stuart A. Maloy (Materials Science in Radiation and Dynamic Extremes, MST-8), Jesse J. Salazar and Terry G. Holesinger (Nuclear Materials Science, MST-16).

The DOE Nuclear Energy Office Fuel Cycle R&D Program (Laboratory Project Lead, Stuart Maloy, MST-8) funded this work, which supports the Laboratory’s Energy Security mission area and the Materials for the Future science pillar through the development of materials for nuclear energy applications. Technical contact: Miles Beaux

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Mesoscale Materials Science on the Roadmap to MaRIE

Synergistic methods improve materials fatigue life predictions

Microstructurally small crack propagation accounts for most of the fatigue life of engineering structures subject to high-cycle fatigue. Determining the crack path and growth rate of small cracks propagating in engineering alloys is a critical step towards improving fatigue life predictions. This information would lower cost and increase safety. A team of researchers from Purdue University, Ecole de Mines de Paris, Los Alamos National Laboratory, and the European Synchrotron Research Facility (ESRF) used a combination of 3D in situ synchrotron x-ray experiments performed at ESRF, the Lab’s fast Fourier transform (FFT)-based micromechanical modeling, and Bayesian network analysis for these studies. Bayesian network analysis enabled machine learning from a fusion of experimental and simulated data of a new material-specific indicator to predict the propagation path and growth-rate of a fatigue crack in a polycrystalline engineering alloy. The Journal of the Mechanics and Physics of Solids published the research.

In this study, cycle-by-cycle measurements of a small crack propagating in a beta metastable Ti (b-Ti) alloy using phase (PCT) and diffraction contrast tomography (DCT) measured at ESRF (Figure panel a) provided input to the Lab’s micromechanical FFT-based simulations (panel b) to supplement the experimental data, by including the micromechanical fields ahead of the crack tip. Supervised Bayesian network analysis (panel c) demonstrated that existing fatigue indicator parameters, proposed in the literature for other materials and loading conditions, were not predictive (i.e., correct less than 50% of the time). When unsupervised Bayesian network analysis, driven by the PCT/DCT/FFT multimodal dataset, was used for machine-learning of a newly postulated crack propagation driving force, the spatial correlation of the identified driving force showed much better agreement (correct 60-80% of the time) with the experimentally determined crack path.

Figure. (a) In-situ synchrotron x-ray experiments used to characterize polycrystalline microstructure (by DCT) and fatigue crack path (by PCT) in beta-Ti notched samples. (b) FFT-based polycrystal plasticity model operating directly on DCT images, used to obtain micromechanical fields. c) Supervised Bayesian network analysis, used to assess existing fatigue indicator parameters (FIPs) (poor correlation), and unsupervised BN analysis, used to learn from multimodal data a new material-specific driving-force for fatigue crack propagation, which was highly correlated with measured crack path.

Figure. (a) In-situ synchrotron x-ray experiments used to characterize polycrystalline microstructure (by DCT) and fatigue crack path (by PCT) in beta-Ti notched samples. (b) FFT-based polycrystal plasticity model operating directly on DCT images, used to obtain micromechanical fields. c) Supervised Bayesian network analysis, used to assess existing fatigue indicator parameters (FIPs) (poor correlation), and unsupervised BN analysis, used to learn from multimodal data a new material-specific driving-force for fatigue crack propagation, which was highly correlated with measured crack path.

This synergistic combination of state-of-the-art experimental, modeling, and machine-learning capabilities has contributed to the discovery of material-specific correlations between microstructure and fatigue life. The research illustrates the Lab’s progress in developing new techniques to model materials at the mesoscale. Future light sources such as the Lab’s proposed MaRIE facility would enable in-situ 3D characterization as materials are processed and/or dynamically deformed, and the use of such data to inform and refine predictive models. The research presents a path towards this goal.

Reference: “Predicting the 3-D Fatigue Crack Growth Rate of Short Cracks using Multimodal Data via Bayesian Network: in-situ experiments and crystal plasticity simulations”, Journal of the Mechanics and Physics of Solids 115, 208 (2018). https://doi.org/10.1016/j.jmps.2018.03.007 Authors: A. Rovinelli and M.D. Sangid (Purdue University), H. Proudhon (Ecole de Mines de Paris), Y. Guilhem (ENS/CNRS/ Université Paris, R.A. Lebensohn and W. Ludwig (University of Lyon).

The Laboratory Directed Research and Development (LDRD) funded the work, which supports the Lab’s Energy Security mission area and its Materials for the Future science pillar. This research developed capabilities for the creation of new materials with controlled functionality, specifically structural materials with superior fatigue resistance by means of microstructure co-design. Technical contact: Ricardo Lebensohn

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Physics

Muon radiography verifies spent nuclear fuel in sealed casks

International nuclear safeguard inspectors are tasked with monitoring the heavily shielded waste casks that store used plutonium produced as a byproduct of the nuclear fuel cycle. However, these inspectors have no immediate way to determine the amount of reactor fuel in a sealed cask if tamper-indicating seals on those casks are damaged. Compromised casks are typically sent elsewhere to be opened and reverified – a costly, time-consuming process. Los Alamos researchers and collaborators have investigated a method to “see” inside of these casks using naturally occurring cosmic-ray muons. In research featured as an Editor’s Choice in Physical Review Applied, the team showed that this method is sensitive enough to measure an entire storage cask and detect multiple missing fuel bundles. The results mean that muon radiography could be a solution to the longstanding problem of certifying that casks – and by extension, all fissionable material – comply with international nuclear safeguards and nonproliferation requirements.

Photo. Measurement of the cask using two muon trackers. One tracker is elevated by 1.2 m relate to the other to sample the muon flux at smaller zenith angles.

Photo. Measurement of the cask using two muon trackers. One tracker is elevated by 1.2 m relate to the other to sample the muon flux at smaller zenith angles.

Researchers used a cask housed at the Idaho National Laboratory to test the method. The team measured the scattering angles of cosmic-ray muons that travel through a cask to verify the contents in situ. The investigators chose this particular cask as a test object because it is only partially loaded with 18 out of 24 possible fuel positions filled. Two identical muon-tracking detectors placed on opposite sides of the cask measured the trajectories of muons before and after passing through the cask. As muons pass through the cask, the amount of scattering they undergo is dependent on the path lengths of the cask shielding material and fuel encountered along their trajectory.

Figure. A diagram showing the cask loading configuration and the detector positions during the measurements.

Figure. A diagram showing the cask loading configuration and the detector positions during the measurements.

Muon radiography revealed multiple fuel bundles missing from the dry storage cask. The technique also demonstrated potential sensitivity to detect the removal of a single bundle of fuel. The team is now testing the sensitivity of muon radiography in more complicated scenarios, such as the removal of part of a single assembly or the replacement of a spent fuel assembly with a dummy.

The research indicates that measurements of cosmic-ray muon scattering could be used as a stand-alone method to independently determine if fuel assemblies are missing from a sealed dry storage cask. Unlike more conventional radiographic probes, muons can penetrate the cask shielding and emerge with useful information about the contents of the cask. Moreover, muons are not subject to backgrounds from other casks and do not require any previous knowledge of the fuel history. Measurement times on the order of weeks to several months could provide sufficient data to draw conclusions about cask content and satisfy the requirements of the International Atomic Agency (IAEA).

Reference: “Verification of Spent Nuclear Fuel in Sealed Dry Storage Casks via Measurements of Cosmic-Ray Muon Scattering,” Physical Review Applied 9, 044013 (2018); doi.org/10.1103/PhysRevApplied.9.044013. https://journals.aps.org/prapplied/pdf/10.1103/PhysRevApplied.9.044013 Authors: J. M. Durham, J. Bacon, E. Guardincerri, and C. L. Morris (Subatomic Physics, P-25); D. Poulson (P-25 and University of New Mexico –Albuquerque); K. Plaud-Ramos (formerly P-25, now with Aerotek); D. L. Chichester, W. Schwendiman, J. D. Tolman, and P. Winston (Idaho National Laboratory).

The National Nuclear Security Administration’s Office of Defense Nuclear Nonproliferation Research and Development (Lab Program Manager Bob Shirey) funded the work, which supports the Laboratory’s Global Security mission area and the Science of Signatures and Nuclear and Particle Futures science pillars by applying technology and methods used in high-energy particle physics to solve a challenge in international nuclear safeguards. Los Alamos built the detectors and invented the muon scattering radiography technique used for this measurement. Technical contact: Matt Durham

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Sigma

Uric acid crystal study reveals the effect of water on mechanical properties

A large percentage of molecular compounds – materials ranging from explosives to pharmaceuticals – can crystallize in different hydration states. This makes understanding how water affects their physical properties such as solubility, thermal stability, and an important research focus.

The uric acid crystals that make up kidney stones can exist in both hydrated and anhydrous (water-free) forms. Both forms share a similar two-dimensional layer structure, making uric acid a particularly useful crystal system for examining the contribution of water molecules to overall mechanical properties.

A team from Georgetown University, Finishing Manufacturing Science (Sigma-2), and the Center for Integrated Nanotechnologies (MPA-CINT) used nanoindentation and atomic force microscopy (AFM) to assess how these two crystal forms responded to localized surface stresses. The presence or absence of water between the layers imparts these crystal forms with dramatically different mechanical properties. Their results showed that uric acid is substantially harder and more brittle than hydrated uric acid. The journal Chemistry of Materials published their findings.

The study relied on the Laboratory’s expertise in atomic force microscopy (AFM) and in nanoindentation, which involves indentation hardness tests applied to small volumes. Post-indent imaging revealed slip planes in preferred crystallographic directions and oriented crack formation at higher load forces. By contrast, the hydrated forms were much softer and had substantial creep in response to indentation. Time-lapsed images of hydrated crystal indents revealed that some amount of “self-healing” on the surface may be possible at shallow indentation depths of ∼100 nm.

Figure. Postindent images of anhydrous uric acid (100) resulting from cono-spherical indents at loads of (A) 2000 micronewtons and (B) 5000 micronewtons.

Figure. Postindent images of anhydrous uric acid (100) resulting from cono-spherical indents at loads of (A) 2000 micronewtons and (B) 5000 micronewtons.

These findings have significance to understanding fundamental materials science and treating kidney stones. Mechanical perturbation is a current method of treating kidney stones. Therefore, determining and controlling the mechanical properties of these surrogate stones could provide insight into the development of better treatments.

Reference: “Mechanical Properties of Anhydrous and Hydrated Uric Acid Crystals,” Chemistry of Materials 30, 3798 (2018); doi: 10.1021/acs.chemmater.8b00939. https://pubs.acs.org/doi/10.1021/acs.chemmater.8b00939 Authors: Fan Liu and Jennifer A. Swift (Georgetown University), Daniel E. Hooks (Finishing Manufacturing Science, Sigma-2), Nan Li and Nathan A. Mara (Center for Integrated Nanotechnologies, MPA-CINT).

The work supports the Laboratory’s Nuclear Deterrence and Global Security mission areas and its Materials for the Future science pillar by expanding the understanding of defects and interfaces and improving controlled functionality. NNSA funded the Los Alamos portion of the research, which was performed, in part, at the Center for Integrated Nanotechnologies (CINT), a DOE Office of Science Basic Energy Sciences user facility jointly operated by Sandia National Laboratories and Los Alamos National Laboratory. Technical contact: Daniel Hooks

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Theoretical

Software predicts complex multi-species multi-phase turbulent reactive flows in engines

Reduced dependence on petroleum products could lead to greater energy security. Some vehicles are now achieving 42–50 mpg. With continued investment and research into new technical innovations, the potential exists to save more than 4 million barrels of oil per day. This could lead to a significant decrease in emissions because the use of petroleum in vehicles accounts for approximately 20% of greenhouse gas emissions. Moreover, it would be a large stimulus to the U.S. economy because it would represent a savings of $200 to $400 million per day.

David Carrington and Jiajia Waters (Fluid Dynamics and Solid Mechanics, T-3) have developed a new software toolkit, FEARCE (Fast, Easy, Accurate and Robust Continuum Engineering), that predicts complex multi-species, multi-phase, turbulent, reactive flows in combustion engines. FEARCE uses the Finite Element Method (FEM) in computational fluid dynamics. Earlier Los Alamos codes for this type of modeling in engines used a finite volume method, known as KIVA.  Previous versions of KIVA have added significant modeling capabilities to the previously licensed version.  However, FEARCE changes the numerical method and provides a new solution method for all flow regimes. This provides a state-of-the-art capability for accurately simulating turbulent reactive multi-phase flow with sprays and robust moving immersed parts (valves and pistons or any moving part), and addition of true multi-phase flow simulation of liquid fuel jets injected into gases and its subsequent break-up into ligaments and droplets. These advances mean that engine combustion processes are becoming more predictive, which provides researchers with tools to address national goals on emissions and engine efficiencies.

Figure. Dynamic multiphase flow of liquid fuel jet injected to quiescent domain showing jet break-up into ligaments where lower density regions represent the dispersed spray droplets.

Figure. Dynamic multiphase flow of liquid fuel jet injected to quiescent domain showing jet break-up into ligaments where lower density regions represent the dispersed spray droplets.

The researchers model a predictive jet break-up using a Volume of Fluids (VOF) method with turbulence models. Large-Eddy Simulation (LES) is extremely important in engines because the flow is highly unsteady, changing continuously from near quiescent to highly turbulent thousands of times per minute.  FEARCE incorporates dispersed spray modeling and Kelvin Helmholtz-Rayleigh Taylor (KH-RT) instability growth for more robust and accurate dispersed spray modeling from larger ligaments to droplets. 

FEARCE simulation

Figure. Engine Modeling System in FEARCE simulating a modern 4-valve combustion engine: Gridded system.

Figure. Fuel species mixing with air during intake stroke.

Figure. Fuel species mixing with air during intake stroke.

FEARCE employs parallelism for the rapid solution of complex and resolved engine physics problems. FEARCE is faster and more accurate than the KIVA-4mpi code, the Laboratory’s previous unstructured grid finite volume code for engines.

A code module in the Engine Modeling System (EMS) provides for automatic grid refinement. The top portion of the Figure depicts the system using overset surface grids for the moving parts of a modern four-valve combustion engine. This allows for easy and automatic hexahedral grid generation of the engine without concern for the moving parts. The bottom portion of the Figure and linked video show fuel mixing (red is high fuel content, blue is least) during the intake stroke. Modeling mixing properly is critical for combustion simulations. FEARCE models the mixing with a high order of accuracy.

Click here to see a FEARCE (Fast, Easy, Accurate and Robust Continuum Engineering) simulation of a 4-valve engine.

Selection of recent references:

 “Three-Dimensional ALE-FEM method for fluid flow in domains containing moving boundaries part I: algorithm description” Progress in Computational Fluid Dynamics, An International Journal 18, no 4, 199 (2018); http://dx.doi.org/10.1504/PCFD.2016.10001470. Authors: D. B. Carrington (T-3), M. Mazumder, and J. C. Heinrich (UNM).  

“Three-dimensional ALE-FEM method for fluid flow in domains containing moving boundaries part II: accuracy and convergence” Progress in Computational Fluid Dynamics, An International Journal 18, no 4, 215 (2018); http://dx.doi.org/10.1504/PCFD.2018.10014680. Authors: V. D. Hatamipour (Utah State University), D. B. Carrington (Fluid Dynamics and Solid Mechanics, T-3), and J. C. Heinrich (University of New Mexico, UNM). 

 “A Dynamic LES Model for Turbulent Reactive Flow with Parallel Adaptive Finite Elements,” Energy for Propulsion, Chapter 3: Turbulent Combustion Modeling and Simulations, Springer, Singapore, pp. 217-235, 2018. https://doi.org/10.1007/978-981-10-7473-8. Authors: J. Waters and D. B. Carrington (T-3), X. Wang (Purdue University – Northwest), and D. W. Pepper (University of Nevada – Las Vegas).

The DOE Energy Efficiency and Renewable Energy (EERE) Vehicle Technology Office funded the work, which supports the Laboratory’s Energy Security mission area and the Information, Science and Technology science pillar. The software to predict reactive flow in engines could be used as a tool in engine design to enhance fuel efficiency and reduce emissions. Technical contacts: David Carrington and Jiajia Waters

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