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Los Alamos National Laboratory

Los Alamos National Laboratory

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Science Highlights, March 16, 2016

Awards and Recognition

Alexandrov and Van Buren win Postdoctoral Distinguished Performance Awards

The Laboratory’s annual Postdoctoral Distinguished Performance Awards recognize outstanding and unique contributions by postdocs, which result in a positive and significant impact on the Lab’s scientific efforts and status in the scientific community. These awards also honor outstanding creativity, innovation, and /or dedication and level of performance substantially beyond that which would normally be expected. Ludmil Alexandrov (Theoretical Biology and Biophysics, T-6/Center for Nonlinear Studies, T-CNLS) and Kendra Van Buren (Verification and Analysis, XCP-8) have won the 2015 awards.  Technical contact: Mary Anne With

Ludmil Alexandrov

Ludmil Alexandrov

Ludmil Alexandrov is a J. Robert Oppenheimer Distinguished Postdoctoral Fellow. The award recognized him for his outstanding research and leadership in genomics and data-intensive computing. Through computational analysis of normal and tumor genome sequences from more than 10,000 cancer patients, he discovered two clock-like mutational processes that independently generate somatic mutations in proportion to the chronological age of an individual. One of these processes can be linked to cell division. This explains why mutations accumulate at different rates in different tissues of the body, which can have widely divergent rates of cell division and turnover.

Alexandrov’s work, reported in Nature Genetics, provides new insights into how cells change with age. He also discovered a potential new treatment marker, which could identify cancer patients who would benefit from treatment with DNA-damaging agents. This research, published in Nature Communications, led the Laboratory to file two US patent applications and provides strong motivation for a clinical trial to assess the predictive value of the biomarker, a pattern of mutations that can be detected through individual genome sequencing. Bill Hlavacek and Nick Hengartner (T-6) nominated Alexandrov.

Kendra Van Buren

Kendra Van Buren

Kendra Van Buren was formerly a Postdoctoral Research Associate in the Lab’s National Security Education Center (NSEC). The award recognized her for exceptional research in the Verification, Validation and Uncertainty Quantification (VV&UQ) of computational simulations. Van Buren focused on improving the quality and usefulness of models and numerical simulations with applications to structural dynamics (wind turbines), shock physics (nuclear weapons performance), and non-proliferation (technical intelligence analysis). She conducted a comprehensive VV&UQ study to develop a validated finite element model of a 9-meter, all-composite wind turbine blade as part of a Laboratory Directed Research and Development (LDRD) project on Intelligent Wind Turbines. Van Buren made significant contributions to the state-of-the-art in modeling and simulation of wind turbines. She demonstrated to the wind energy community, which was not accustomed to these practices, that computational models could be thoroughly validated to improve their predictive credibility.

Van Buren also developed a novel approach to sensitivity analysis guaranteeing that the influence exercised by design parameters on the performance of an engineered system is robust to environmental variability. This method handles large-dimensional problems in computational physics and engineering that would otherwise be impossible to tackle. Van Buren also led a cross-laboratory project entitled “Answering the Multi-Intelligence Challenge through Robust Decision-Making,” which is a vital component of the Global Security Directorate’s fiscal year 2015 focus on Multi-Intelligence Analysis. The project’s success has led LANL to focus on developing a program around this concept. Her many contributions helped position the Lab with a unique capability to couple data analytics and decision theory with domain-specific knowledge of stockpile stewardship, non-proliferation, and emerging threats. Scott Doebling (XCP-8) and François Hemez (Integrated Design and Assessment, XTD-IDA) nominated her.

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Hemez, Korber, and Ronning receive Postdoctoral Distinguished Mentor Awards

François Hemez

François Hemez

François Hemez was nominated for his genuine interest in the development and success of the postdocs with whom he interacts, both internally to LANL and externally to the greater academic community. He has a keen understanding of how to build confidence in postdocs, which ultimately helps them transition to the next phase of their career. Hemez introduces them to new research topics to help expand their research portfolio, and as they pursue new ideas he encourages them to disseminate their research in quality peer-reviewed journal publications and conference proceedings. He allows postdocs to take leadership roles where they can be recognized for their work (e.g., by giving internal seminars or leading proposal efforts). His mentoring style has enabled all of his postdocs to have successful careers. Hemez’s dedication to postdocs is made obvious by the time that he is willing to spend with them, especially when he works with un-cleared students and must make it a priority to stop by their offices because they are unable to go to his. He always gives credit to the students and postdocs. Those who have had the pleasure of working with him understand his value as a mentor and as a representative of the Lab. Kendra Van Buren (XCP-8) nominated Hemez.
Bette Korber

Bette Korber

Bette Korber was nominated for being an exceptionally thoughtful and nurturing mentor. Her mentoring has helped her postdocs address key outstanding scientific problems, gain recognition in the field, and become successful independent researchers at LANL and universities. Her clear, innovative thinking and dedication to understand complex biological problems continue to inspire her postdocs in their scientific pursuits. Korber is a world-renowned expert in the field of HIV who guides her postdocs in identifying the right important problems to channel their skills and interests. She is very patient and generous with her time, providing a comfortable research environment where postdocs can engage in fruitful, two-way scientific discussions to develop their research ideas. Korber contributes her insights as needed and gives constructive critiques to stimulate intellectual growth. She shows appreciation of her postdocs’ work, praising it in front of leading experts. This contributes to their recognition in the field. Korber gives helps advance her postdocs’ careers by advising about career options, proactively seeking funding and other opportunities, and encouraging them to present their work at conferences. Seven of her former postdocs have converted to scientists at LANL, and two have found faculty positions in prestigious universities. Current postdoc Kshitij Wagh (T-6), and former postdocs (now staff at LANL) Elena Giorgi, Will Fischer, Peter Hraber, and Karina Yusim (T-6) nominated Korber.  

Filip Ronning

Filip Ronning

Filip Ronning was nominated for his unwavering dedication to the academic and personal well being of his postdocs. He is an extremely successful and knowledgeable scientist, and leads projects that consistently allow postdocs to produce high quality publications. Ronning is very generous with his knowledge and expertise, making himself available to discuss scientific ideas, and helping postdocs with writing presentations or papers. His kind and open manner encourages the free discussion of ideas, enabling the postdocs’ growth in understanding and confidence. Ronning’s genuine interest in the career development of his postdocs goes well beyond what might normally be expected. He encourages the postdocs to pursue their own interests and develop skills that will help them in their future careers. Ronning provides career guidance, planning, and networking. Moreover, he helps new postdocs settle into life in Los Alamos, particularly helping foreign nationals find their footing in a new country. All the postdocs who have had the pleasure of working with Ronning are delighted to see him rewarded for the outstanding contribution he has made to their time at LANL. Nicholas Wakeham (MPA-CMMS) nominated Ronning.

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Bioscience

Building international genomics collaborations for global health security

The Lab’s Genome Science Program is leveraging its expertise in genomics research to assist nations in advancing their genomics and bioinformatics capabilities. Reducing global health security risks from the spread of dangerous infectious diseases, whether natural or manmade, is a shared priority among the international public health communities. It has also become an overarching objective for cooperative biothreat reduction and scientific engagement efforts on a global scale. In an article in the Frontiers in Public Health journal, the Los Alamos researchers describe their work to establish genome centers with public health and research institutions, as well as broader collaborations in genomics applications with research institutions in many other countries.

Genomics is a relatively new scientific discipline, which is fundamental to many approaches to health security. Aided by highly automated Next-Generation DNA Sequencing (NGS) technologies, the field has advanced dramatically over the last decade, both in the depth of understanding genome structure and function of living organisms, and in the breadth of applications in areas, such as medicine (disease mechanisms, diagnostics, and therapeutics) and agriculture. Los Alamos has been a leader in genomics since the early 1980s, and is now leveraging its capabilities to provide support to a growing number of partner countries in developing molecular genomic-based capabilities. The team’s focus of international scientific engagement delivers molecular genomics-based scientific approaches for pathogen detection, characterization, and biosurveillance applications. Their general strategy includes introduction of basic principles in genomics technologies, training on laboratory methodologies and bioinformatic analysis of resulting data, procurement and installation of next-generation sequencing instruments, establishing bioinformatics software capabilities, and exploring collaborative applications of the genomics capabilities in public health.

LANL staff member Cheryl Gleasner demonstrates sample preparation and quality control techniques

Photo. LANL staff member Cheryl Gleasner demonstrates sample preparation and quality control techniques at the newly established Jordan University of Science and Technology Genomics Training Center.

LANL project leader Helen Cui (back row, left), scientist Armand Dichosa (back row, right), and Department of State program officers

Photo. LANL project leader Helen Cui (back row, left), scientist Armand Dichosa (back row, right), and Department of State program officers (back row, third from the left, and front row second from the left) hosted a collaboration- planning workshop with Iraqi public health, veterinary health, and high education officials in Istanbul, Turkey.

The team has established genome centers with four partner institutions in the Republic of Georgia, Kingdom of Jordan, Uganda, and Gabon. These genome centers are provided with a standardized sequencing platform, standard operation and good laboratory practice protocols, and bioinformatics analysis tools and associated computational hardware. The Laboratory investigators travel to each site and assist with setup and configuration for laboratory equipment and computational resources. They also provide on-site training for both laboratory and bioinformatics during these visits. The team guides the partners to perform sequencing runs on the newly provided equipment while they are on-site.

In addition to establishing the genome centers, the Laboratory team provides training and engages in collaborative research with other institutions that have Next-Generation DNA Sequencing capabilities or are on the path to acquire it. This type of collaboration has occurred in nine countries. It enables the partners to broaden international collaboration networks and to exercise and enhance local capabilities. These collaborations bring together complementary skill sets and resources, benefiting participating parties and promoting improved global health.

By engaging with and empowering infectious disease detection and surveillance capabilities in the partner countries, the Los Alamos team aims to enable a global network to reduce risk and enhance compliance with international guidelines, such as the International Health Regulations (from the World Health Organization in 2005) and the World Organization for Animal Health (OIE). A scientific approach using next-generation sequencing-enabled genomics research has the potential to positively impact global health security applications. Development of genome centers in many countries around the world will help the local public health authorities identify and monitor disease outbreaks, and also enable true global biosurveillance at a high temporal, geographic, and information resolution. Due to the potential for the rapid spread of the known pandemic pathogens and future emerging ones, a network of genome centers that can rapidly provide high-resolution genomic data would help improve the speed and accuracy of outbreak detection and monitoring, and reduce the global threat from these pathogens. The speed and efficacy of mitigation would be increased by the ability to test the samples locally, without having to ship the sample long distances.

Distribution of genome centers and collaborations.

Figure 1. Distribution of genome centers and collaborations. Red marks indicate genome centers established by the program. Yellow marks countries that are in collaborations focusing on training and research.

Reference: “Building International Genomics Collaboration for Global Health Security,” Frontiers in Public Health 3, Article 264 (2015); doi: 10.3389/fpubh.2015.00264. Authors: Helen H. Cui, Tracy Erkkila, Patrick S. G. Chain, and Momchilo Vuyisich (Bioenergy and Biome Sciences, B-11).

The U.S. Defense Threat Reduction Agency Cooperative Biological Engagement Program, U.S. Department of State Biosecurity Engagement Program, United Kingdom Global Partnership Programme, and Foreign Affairs, Trade and Development Canada Global Partnership Program funded the activities. The work supports the Lab’s Global Security mission area and the Science of Signatures science pillar through the development of scientific partnerships and sustainable technical capacity to address complex global health security challenges. Technical contact: Helen Cui

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Earth and Environmental Sciences

New fossil results of early primates

Team analysis of fossil teeth of 8-million-year-old Chororapithecus abyssinicus

Team analysis of fossil teeth of 8-million-year-old Chororapithecus abyssinicus, an extinct gorilla-like species, provided insights into the human-gorilla evolutionary split. Photo credit: Gen Suwa

A large, international collaboration has revealed the first known 8 million-year-old ape and other fossils south of the Sahara. In the work, Giday WoldeGabriel (Earth System Observations, EES-14), one of the researchers on this collaboration, used the types of analytical methods that he applies to programmatic work at the Lab. His studies of glass shards enabled the team to determine the age of volcanic rocks and sediments that encased the fossils. The new dates and fossils strengthen the view that the human and modern ape lines emerged in Africa between 10 and 7 million years ago. The journal Nature published the research.

The time period between 10 and 7 million years ago is when the human and African ape lines are thought to have split, but no mammalian fossils south of the Sahara have been confidently dated to 8 to 9 million years ago. The work presented in this publication is the first of such fossils, which are crucial for unraveling the history of human origins and emergence. Based on the new fossil evidence and analysis, the team suggests that the human branch of the tree (shared with chimpanzees) split away from gorillas about 10 million years ago – at least 2 million years earlier than previously claimed.

WoldeGabriel used glass shard chemistry and morphology to characterize volcanic ashes across the rugged terrain of the study area. The glass shards were found in volcanic rocks that surround the fossils. An electron microprobe at the New Mexico Institute of Technology (NM Tech) enabled the glass shard chemistry investigation. Tephra chemical correlation was aided by back-scattered secondary images of the glass morphology from individual tephra samples also generated at NM Tech (Figure 2). WoldeGabriel prepared thin sections of the tephra samples, analyzed the petrographic properties of the tephra samples, and obtained the chemistry and glass morphology data on each of the samples at NM Tech. Integrating the results from argon isotope (40Ar/39Ar) dating, electron microprobe chemistry, and glass shard morphology allowed the geology team to establish detailed correlations of the stratigraphic units across the densely faulted and rugged terrain along the rift margin of the transition zone between the Afar and the Main Ethiopian Rifts. This information enabled the researchers to determine the age of the fossils.

Back-scattered secondary of three tephra samples

Figure 2. Back-scattered secondary of three tephra samples. The distinct glass morphology of each sample is a product of the intensity of eruption and eruption mechanism. Discrete glass chemistry was collected on about 30 individual glass shards and pumice fragments shown in the image.

Reference: “New Geological and Palaeontological Age Constraint for the Gorilla–human Lineage Split,” Nature 530, 215 (2016); doi: 10.1038/nature16510. Authors: S. Katoh (Hyogo Museum of Nature and Human Activities, Japan), Y. Beyene (Association for Conservation of Culture Awassa, Ethiopia and French Ministry for Foreign Affairs, Ethiopia), T. Itaya and H. Hyodo (Okayama University of Science, Japan), M. Hyodo (Kobe University, Kobe 657-8501, Japan), K. Yagi and C. Gouzu (Hiruzen Institute for Geology and Chronology, Japan), G. WoldeGabriel (EES-14), W. K. Hart (Miami University), S. H. Ambrose (University of Illinois – Urbana), H. Nakaya (Kagoshima University, Japan), R. L. Bernor (Howard University), J.-R. Boisserie (French Ministry for Foreign Affairs, Ethiopia and Université de Poitiers, France), F. Bibi (Leibniz Institute for Evolution and Biodiversity Science, Germany), H. Saegusa (University of Hyogo, Japan), T. Sasaki, K. Sano, and G. Suwa (The University of Tokyo, Japan);  and Berhane Asfaw (Rift Valley Research Service, Ethiopia).

WoldeGabriel has applied the types of analytical techniques used in this research to study the complex volcanic structure and evolution of the Pajarito Plateau. This is important as it relates to the safety of Laboratory structures and facilities. The analytical capability supports the Lab’s Science of Signatures science pillar. Technical contact: Giday WoldeGabriel

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Materials Physics and Applications

Measurements in high magnetic fields aid understanding of 2-D materials

In 2010, a new family of atomically thin semiconductors was discovered: the monolayer transition-metal dichalcogenides (TMDs), which include materials such as molybdenum disulfide (MoS2) and tungsten diselenide (WSe2). These materials have a similar two-dimensional honeycomb structure to graphene, but with an important and technologically relevant difference. Unlike graphene, monolayer TMDs possesses a sizable semiconductor bandgap, which makes them potentially useful for future applications in electronics and electro-optics. The study of these new TMD semiconductors is an active area of research in materials science and condensed matter physics. Los Alamos researchers and collaborators have performed optical studies of TMDs in high pulsed magnetic fields. The journal Nature Communications published their research findings.

The elementary excitation in any semiconductor is the exciton, an electron in the conduction band that is electrostatically bound to a hole in the valence band. Excitons are created by absorption of light, and their radiative recombination gives rise to optical emission (luminescence). The fundamental properties of excitons in many new TMD semiconductors–i.e., their size, mass, binding energy, and magnetic moment–are largely unknown and have not been directly observed experimentally.
A depiction of the fundamental electron-hole excitation (exciton) in monolayer

Figure 3. A depiction of the fundamental electron-hole excitation (exciton) in monolayer WS2. Its size and magnetic moment are measured via magneto-reflection in high magnetic fields to 65 T

Researchers at the National High Magnetic Field Laboratory (NHMFL) in Los Alamos used large-area monolayer TMD films, grown by collaborators at the U.S. Naval Research Laboratory, for optical reflection spectroscopy studies of atomically thin tungsten disulfide (WS2) and MoS2 crystals in very high pulsed magnetic fields to 65 tesla (T). These measurements revealed the magnetic moment of the fundamental excitons and also, for the first time, their physical size. The parameters can be used to constrain estimates of the exciton binding energy itself, which is crucial for future applications in lasing and solar energy harvesting.

Figure 4. (a) The measured energy shift of the fundamental exciton peak at  ± 65 T in monolayer WS2 (from reflection spectroscopy). In addition to the splitting (which reveals magnetic moment), the average peak position reveals (b), the quadratic diamagnetic exciton shift, from which the exciton radius is directly inferred (1.53 nm for the “A” exciton).

Figure 4. (a) The measured energy shift of the fundamental exciton peak at ± 65 T in monolayer WS2 (from reflection spectroscopy). In addition to the splitting (which reveals magnetic moment), the average peak position reveals (b), the quadratic diamagnetic exciton shift, from which the exciton radius is directly inferred (1.53 nm for the “A” exciton).

Historically, magneto-optical measurements have played an essential role in determining the fundamental parameters of electronic excitations in bulk and quantum-confined semiconductors. In conventional semiconductors, such as gallium arsenide, electron/hole masses and exciton binding energies are small; consequently, magnetic fields only of order 10 T are sufficient to reveal the small quadratic spectral shift of the exciton’s optical transition (the exciton diamagnetic shift), from which the exciton size and binding energy can be directly inferred. However, excitons in the new family of monolayer TMD semiconductors are very strongly bound (and consequently they are very small), such that very large magnetic fields exceeding approximately 40 T are necessary to reveal these fundamental parameters. The new paper reported observation of the quadratic shift of both the “A” and “B” exciton in monolayer WS2 at low temperatures and in 65 T magnetic fields.

Reference: “Exciton Diamagnetic Shifts and Valley Zeeman Effects in Monolayer WS2 and MoS2 to 65 T,” Nature Communications 7, 10643 (2016); doi: 10.1038/ncomms10643. Authors: Andreas V. Stier and Scott A. Crooker (Condensed Matter and Magnet Science, MPA-CMMS), Kathleen M. McCreary and Berend T. Jonker (Naval Research Laboratory, Junichiro Kono (Rice University).

The team performed the optical studies at the National High Magnetic Field Laboratory, which the National Science Foundation and the State of Florida fund. The research supports the Lab’s Energy Security mission area and Materials for the Future science pillar by revealing the physical parameters for this new family of atomically thin semiconductors. Technical contact: Scott Crooker

 

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Materials Science and Technology

Los Alamos a member of DOE’s new lightweight manufacturing consortium

Los Alamos National Laboratory is one of nine members of the new Lightweight Materials Consortium (LightMAT), which is designed to streamline the process for connecting industry with expertise and equipment found only at the DOE national labs. By providing access to national labs’ materials capabilities, LightMAT aims to give U.S. manufacturing a competitive edge through materials that can be developed and deployed at considerable savings in cost and time.

DOE established LightMat as part of the Clean Energy Manufacturing Initiative in the Energy Materials Network. Accelerating advanced materials development, from discovery through deployment, could revolutionize whole industries and is critical for the U.S. to compete globally in manufacturing in the 21st century. However, today only a small fraction of materials innovations make it to widespread commercialization. The DOE Energy Manufacturing Network aims to dramatically decrease the time-to-market for advanced materials that are critical to manufacturing many clean energy technologies, enabling manufacturers to develop and deliver innovative, made-in-America products to the world market. DOE’s Vehicle Technologies Office, part of the Office of Energy Efficiency and Renewable Energy, sponsors LightMat. Pacific Northwest National Laboratory manages the consortium.

Ellen Cerreta [Materials Science in Radiation and Dynamics Extremes (MST-8) group leader] is a member of the LightMAT Steering Committee. The resource network includes Ames Laboratory, Argonne National Laboratory, Idaho National Laboratory, LANL, Lawrence Livermore National Laboratory, National Renewable Energy Laboratory, Oak Ridge National Laboratory, Pacific Northwest National Laboratory, and Sandia National Laboratories. It is composed of member teams who are experts in technical capabilities, technology transfer/agreements, and data.

As one of its first endeavors, the consortium has created the website https://lightmat.org/, where industrial researchers can search for capabilities in processing and manufacturing, computational tools, and materials characterization relevant to lightweight materials development and use—by category or national lab.
Web page for the LightMAT Consortium

Figure 5. Web page for the LightMAT Consortium

The LightMAT website provides detailed descriptions and experts to contact for the following Los Alamos capabilities:

  • Bulk fabrication of damage-tolerant layered nanocomposites (Nate Mara, Center for Integrated Nanotechnologies, MPA-CINT, and Metallurgy, MST-6)
  • Microstructure-based forming simulation tools for face-centered cubic and hexagonal close-packed metals and alloys (Ricardo Lebensohn and Carlos Tomé, MST-8; Irene Beyerlein, Fluid Dynamics and Solid Mechanics, T-3)
  • Multiscale process modeling of bulk nanolaminates (Irene Beyerlein)
  • Nanoscale in situ mechanical testing stage (Nan Li and Nate Mara, MPA-CINT)
  • Multiscale experiments and modeling of metal alloy solidification dynamics (Amy Clarke, MST-6)
  • Constitutive strength modeling (Rusty Gray, MST-8)
  • Advanced high strength steel development (Kester Clarke, MST-6)
  • In situ characterization of processing (Amy Clarke)
  • Dynamic performance (Rusty Gray)

The work supports the Laboratory’s mission areas through LANL’s Materials for the Future science pillar. Technical contact: Ellen Cerreta

 

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Physics

DANCE measures cross sections to probe conditions of element formation in stars

Neutron capture cross section measurements on a radioactive isotope of nickel with the Detector for Advanced Neutron Capture Experiments (DANCE) at the Laboratory’s Lujan Center have provided insight on how copper and zinc are made in stars. The journal Physical Review C published the work of an international team of scientists, including Lab investigators.

The elements heavier than iron are primarily produced through neutron capture processes in late stellar evolution of stars more massive than the sun. Both a slow and rapid neutron capture process can contribute to their production. The specific slow, or s-process, path depends on temperatures and neutron densities in stars, neutron capture cross sections, and half-lives of unstable isotopes. The s-process evolves along the line of beta stability, with neutrons being sequentially captured until an unstable isotope is created. If it is short-lived (less than 1 year), it will decay before another neutron capture can take place. If it is long-lived (greater 1000 years), it will capture another neutron. Isotopes with lifetimes between these extremes are called “branch-point” isotopes, as they split the reaction flow, including both neutron capture and beta decay. Nickel-63 (63Ni) is one such isotope. The mass flow can either proceed from 63Ni to 64Ni via neutron capture or via beta decay to copper-63 (63Cu). Precise knowledge of the neutron capture cross section on branch points allows researchers to determine stellar conditions at the s-process site. Before this work, there was only one measurement of the neutron capture cross section on 63Ni, which differed from theoretical estimates by almost a factor of two.
A schematic model of part of the DANCE array

Figure 6. A schematic model of part of the DANCE array. Different crystal shapes are indicated in different colors. Gamma rays are shown coming from the sample position. The sphere at the center represents the lithium-6 hydride (6LiH) sphere placed at the center of DANCE to absorb scattered neutrons.

The researchers used DANCE, which is located at the Laboratory’s Lujan Center, for the cross section studies. The DANCE instrument is a 160-element barium fluoride scintillator array designed to perform measurements on small samples of rare isotopes. The high segmentation combined with the high efficiency of the instrument have enabled measurements on a wide range of isotopes for programs ranging across national security, nuclear forensics, nuclear energy, nuclear structure, and nuclear astrophysics.

Nickel-63 is a radioisotope with a 101-year half-life, decaying via emission of a 67-keV electron. DANCE measured the 63Ni neutron cross section in the energy range from 40 eV to 500 keV. The team identified 13 resonances of the 63Ni(neutron, gamma) reaction. A Maxwellian-Averaged cross-section (MACS) is needed at 8, 25, and 90 keV for stellar nucleosynthesis calculations. Figure 7 depicts the measured MACS, together with the previous evaluation and the measurement from CERN neutron time of flight (n_TOF).

Figure 7. Comparison of MACS from DANCE and n_TOF measurements, which are in excellent agreement.

Figure 7. Comparison of MACS from DANCE and n_TOF measurements, which are in excellent agreement.

The excellent agreement between the DANCE and n_TOF results lends confidence to adopting the increased cross section relative to the theoretical estimate. This is particularly important because the 63Ni branching controls the production of both copper-63 (63Cu), which is primarily made in the s process, and zinc-64 (64Zn), which is exclusively made in the s process. Because 63Ni will capture more neutrons than previously expected, the reaction flow will bypass the production of both copper-63 and zinc-64 in these environments, leading to a roughly 30% reduction in the expected yield of these isotopes in massive stars.

Reference: “63Ni (n,g) Cross Sections Measured with DANCE,” Physical Review C 92, 045810 (2015); doi: 10.1103/PhysRevC.92.045810. Authors: M. Weigand, K. Göbel, T. Heftrich, C. Lederer, J. Ostermöller, R. Plag, and R. Reifarth, (Goethe University Frankfurt); T. A. Bredeweg and M. Jandel (Nuclear and Radiochemistry, C-NR); A. Couture, J. M. O’Donnell, and J. L. Ullmann (LANSCE Weapons Physics, P-27); F. Käppeler (Karlsruhe Institute of Technology); N. Kivel and D. Schumann (Paul Scherrer Institut); G. Korschinek (Technical University of Munich); M. Krtička (Charles University in Prague); and A. Wallner (Australian National University). This research was part of the Ph.D. thesis of Mario Weigand, an experimental nuclear physicist from the Goethe University of Frankfurt.

The DOE Office of Science/Nuclear Physics and the Laboratory Directed Research and Development (LDRD) program funded different aspects of the LANL work. This research supports the Lab’s Nuclear and Particle Futures science pillar, with particular impact on the goals of Cosmic Explosions: Origins to Ashes and the Origin, Evolution, and Properties of Atomic Nuclei. This work answered questions of the nucleosynthesis of copper and zinc. Technical contact: A. Couture

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Science on the Roadmap to MaRIE

New tools reveal hidden roots of material’s post-shock strength

Recent advances in synchrotron diagnostics coupled with dynamic compression platforms have enabled new opportunities for in situ investigations of extreme states of matter on nanosecond timescales. Examining the evolution of material properties at extreme conditions advances the understanding of numerous high-pressure phenomena – from natural events like meteorite impacts –to general solid mechanics and fluid flow behavior. Los Alamos researchers and collaborators used the IMPULSE (IMPact system for ULtrafast Synchrotron Experiments) gas-gun system at Argonne National Laboratory’s Advanced Photon Source (APS) to observe the evolution of jets formed from a Richtmyer-Meshkov instability in cerium metal initially shocked into a transient, high-pressure phase, and then released to a low-pressure, higher-temperature state. The Journal of Applied Physics published their findings.

The team used the jet formation technique to study how a shock-induced phase transition (g to a phase) affects material strength. The researchers investigated cerium metal because it has a rich phase diagram. Cerium has at least four phases at zero pressure, additional phases at higher pressure, and an anomalous liquid boundary. These features make cerium an ideal test-bed to study dynamic phase transitions within a pressure range easily accessible using their impact/loading facilities. The shock loaded the cerium into a new phase, just below the melt boundary, to examine strength following the g to a transition as the pressure increased toward melt. Past work on jet formation has used copper, which exhibits only elastic-plastic deformation – no phase transition. Due to the large body of dynamic data available on cerium, investigators have developed a physically reasonable and validated equation-of-state to analyze the data.

The IMPULSE gas-gun system launched projectiles at targets placed in the path of the APS x-ray beam. Projectiles with copper impactors struck the cerium, creating shock waves inside that transformed it from the ambient γ phase into a higher pressure, higher temperature α state. Then, the shock waves from the back of the cerium sample interacted with machined grooves in cerium. As the shocked cerium returned to its γ phase at a high temperature, protrusions (jets) formed and grew at the groove locations (Figure 8). Because cerium is opaque to x-rays at the x-ray energies used, the researchers could obtain images of the jets with micrometer spatial resolution as they formed. Photonic Doppler Velocimetry (PDV) probes simultaneously measured jet-growth velocities. By measuring the jet velocity, using the x-ray images to observe the jets as they evolved, and developing computer simulations to compare the experimental data to calculations, the researchers estimated the yield stress in tension for cerium. The researchers found good agreement found between the calculations and the data, illustrating the sensitivity of jet formation to yield stress values.

Schematic of the experimental configuration for shock wave experiments using x-ray imaging to observe jet formation in cerium (Ce).

Figure 8. Schematic of the experimental configuration for shock wave experiments using x-ray imaging to observe jet formation in cerium (Ce). A copper (Cu) plate impacted the Ce sample located in an evacuated target chamber generating a shock wave that interacted with the machined perturbations at the back surface. The x-ray beam passed through multiple slits and shutters, interacted with the sample and evolving jets, and was incident upon a scintillator. The scintillator light was imaged onto four optically multiplexed intensified detectors that were synchronized to the impact event and the x-rays. (Inset): Schematic showing the process of jet formation as the shock wave interacted with the groove in the sample. Richtmyer-Meshkov instabilities (RMI) are formed when a shock wave interacts with a perturbation at an interface, and have shown a sensitivity to strength in the post-shock state. RMI experiments can provide a unique data set to inform constitutive models intended to predict material behavior over a wide range of loading conditions.

The jets formed after shock waves passed through cerium metal provided insight into the yield stress of cerium in its post-shock state (Figure 9). Yield stress is the stress level at which a materials ceases to behave elastically and becomes permanently damaged.

The data and analysis provide insight into material strength during dynamic loading, which should aid in developing strength-aware multi-phase equation of state (EOS) required to predict the response of matter at extreme conditions. The work is relevant to meteorite impacts, the performance of explosives and detonators, and the development of new materials with tailored properties whose applications include automotive and airplane components, lighter and more impact-resistant armor, and debris shields in space.

This work complements other experiments underway at the APS Dynamic Compression Sector, the Z Machine at Sandia National Laboratories, and explosives loading facilities at Los Alamos. The researchers plan to combine x-ray imaging with x-ray diffraction to correlate microscopic and macroscopic material deformation under extreme conditions.

The work is an example of research that would be further advanced at MaRIE (Matter-Radiation Interactions in Extremes), the Laboratory’s proposed facility for time-dependent materials science at the mesoscale. With MaRIE’s combination of the world’s highest energy (42-keV) x-ray free-electron laser and in situ probes, researchers could observe materials deformation in real time at the mesoscale, the region between the atomic and macroscale. Understanding material properties at the mesoscale is key to predicting and controlling the performance of the material.

(A) Example x-ray images showing jet formation. (B) Corresponding velocimetry data (black curves) obtained using photon Doppler velocimetry showing the jet and free surface velocities. (C) A summary of x-ray images for five experiments

Figure 9. (A) Example x-ray images showing jet formation. (B) Corresponding velocimetry data (black curves) obtained using photon Doppler velocimetry showing the jet and free surface velocities. (C) A summary of x-ray images for five experiments reveal the effect of increasing the impact stress and groove depth on the jet formation. For the deepest grooves, the jet does not saturate and outruns the free surface.

References:

“Jet Formation in Cerium Metal to Examine Material Strength,” Journal of Applied Physics 118, 195903 (2015); doi: 10.1063/1.4935879. Authors: B. J. Jensen, F. J. Cherne, J. D. Yeager, and K. J. Ramos, (Shock and Detonation Physics, M-9); M. B. Prime (Advanced Engineering Analysis, W-13); K. Fezzaa (Argonne National Laboratory) A. J. Iverson and C. A. Carlson (National Security Technologies LLC); D. E. Hooks (Explosive Science and Shock Physics, M-DO); J. C. Cooley (Metallurgy, MST-6); and G. Dimonte (Materials and Physical Data, XCP-5). Charles Owens and Tim Pierce (M-9) assisted with target and projectile fabrication, gun setup, and shot execution.

“Imaged ‘Jets’ Reveal Cerium’s Post-shock Inner Strength,” Phys.org, January 29, 2016 (phys.org/news/2016-01-imaged-jets-reveal-cerium-post-shock.html)

The Laboratory’s MaRIE concept (LANL Capture Manager, Cris Barnes) and NNSA Science Campaign 2 (LANL Program Manager, Dana Dattelbaum) funded the Los Alamos researchers. The work supports the Lab’s Nuclear Deterrence mission area and the Science of Signatures and Materials for the Future science pillar. A LANL Agnew National Security Postdoctoral Fellowship sponsored Yeager. Technical contact: Brian Jensen

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Theoretical

Uncovering who-infected-whom from pathogen genetic data

Phylogenetic inference (creation of an organism’s genetic tree and evolutionary relationships) of pathogen transmission chains, outbreaks, and epidemics is a popular method to gain insight into the epidemiologic dynamics of transmission. Viruses, such as HIV-1, evolve faster than transmissions typically occur, making phylogenetic reconstruction an ideal tool for reconstruction of transmission events. Until now, however, there has not been a systematic evaluation of which phylogeny to expect from different transmission histories. A team of LANL Theoretical Biology and Biophysics (T-6) researchers developed computational methods to help determine who infected whom based on genetic data from the pathogen (HIV) that was transmitted. The Proceedings of the National Academy of Sciences published their findings. Previous critiques of phylogenetic reconstruction have claimed that direction of transmission is difficult to infer and that the existence of unsampled intermediary links or common sources can never be excluded. According to Thomas Leitner (T-6) there are three different types of transmission histories possible between two persons who might have infected each other. Using phylogenetic inference in the epidemiological investigations of HIV transmission, the Laboratory team determined that between two sampled, potentially epidemiologically linked persons, they could evaluate the possibility that an unsampled intermediary or common source existed - even without a sample from that individual.

The research team used a novel HIV-1 within-host coalescent model to evaluate probabilistically the transmission histories of two epidemiologically linked hosts. The scientists compared their computational phylogenetic analysis with case studies. They found that the direction of transmission and whether unsampled intermediary links or common sources existed make very different predictions about the expected phylogenetic relationships.

A typical phylogeny that is expected from direct transmission, indirect transmission, and transmission from a common source

Figure 10. A typical phylogeny that is expected from direct transmission, indirect transmission, and transmission from a common source with samples from two epidemiologically linked individuals. Donor is red, recipient is blue and an unsampled intermediate or common source is in grey outline. The exact phylogenetic expectation, however, depends on the number of transmitted lineages, the sample size, times between transmissions and the time of the sample relative to transmission, and how fast the diversity of the pathogen increases after infection.

Their findings validated the use of viral phylogenies to investigate the existence of a transmission event as well as its direction and directness. Because different transmission histories (direct, indirect, and common source transmissions) impose very different population size dynamics, mainly determined by the transmission bottleneck(s), the phylogeny in each case has a different expected distribution of topologies. This result may enable exclusion of possible intermediary links or identify cases where a common source was likely but not sampled. Leitner suggests that the systematic classification and evaluation of expected topologies should make future interpretation of phylogenetic results in epidemiological investigations more objective and informative. This technique could have a large impact on future epidemiological investigations, including forensics and outbreak investigations.

Reference: “Phylogenetically Resolving Epidemiologic Linkage,” Proceedings of the National Academy of Sciences 113, 2690 (2016); doi: 10.1073/pnas.1522930113. Authors: Ethan O. Romero-Severson, Ingo Bulla, and Thomas Leitner (T-6).

The National Institutes of Health funded the research, which supported the Laboratory’s Global Security mission area and the Information, Science, and Technology and the Science of Signatures science pillars. Technical contact: Thomas Leitner

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