Researchers from Lawrence Livermore, the University of Vermont, Boston College, and Imperial College London analyzed marine sediment cores containing isotopes of aluminum (Al) and beryllium (Be), which are like a time capsule preserving records of glacial processes, and discovered that East Greenland experienced deep, ongoing glacial erosion over the past 7.5 million years. Appearing in the December 8, 2016, issue of Nature, their research reconstructed ice sheet erosion dynamics in the region over this timeframe.
Cosmic rays continually bombard Earth and produce Al and Be isotopes in mineral lattices. The concentrations of these cosmogenic nuclides in rock, sand, and soil reveal the exposure history of the surface. Production rates and nuclide concentrations decrease exponentially within a few meters of the surface, so a covering of ice stops cosmogenic nuclide production in the underlying rock. Coauthor and Livermore scientist Susan Zimmerman used the Laboratory’s Center for Accelerator Mass Spectrometry to analyze the isotopes found in the quartz sand from ice-rafted debris in sediment cores.
Analyzing these isotopes in sediment shed from the land and stored at the bottom of the ocean as marine sediment gave scientists insight into how Greenland responded to climate change in the past and how, in turn, it may respond in the future. “The East Greenland Ice Sheet has been dynamic over the last 7.5 million years,” says lead author and University of Vermont scientist Paul Bierman. “Greenland was mostly ice-covered during the mid- to late Pleistocene. At major climate transitions, the ice sheet expanded into previously ice-free terrain, confirming that the East Greenland Ice Sheet has consistently responded to global climate change.”
Contact: Susan Zimmerman (925) 422-8462 (zimmerman17@llnl.gov).
Lawrence Livermore materials scientist Juergen Biener and collaborators from Harvard University and Lawrence Berkeley and Brookhaven national laboratories found a way to make nanoporous gold alloys more efficient catalysts through restructuring. Such nanostructured materials hold promise for improving catalyst activity and selectivity, but until now little has been known about the dynamic compositional and structural changes that the system undergoes during pretreatment leading to efficient catalyst function.
Nanoporous gold can be used in electrochemical sensors, catalytic platforms, fundamental structure property studies at the nanoscale, and tunable drug release. The material also features high effective surface area, tunable pore size, well-defined conjugate chemistry, high electrical conductivity, and compatibility with traditional fabrication techniques. Ozone-activated silver–gold alloys in the form of nanoporous gold were used to demonstrate the dynamic behavior of bimetallic systems during activation to produce a functioning catalyst. In a reactant stream of methanol and oxygen, advanced in situ transmission electron microscopy and ambient pressure x-ray photoelectron spectroscopy revealed that major restructuring and compositional changes occurred along the path to catalytic function.
Researchers found an increased concentration of silver at the surface plays a key role in facilitating the catalytic function of the nanoporous gold, whereby the oxygen is more efficiently dissociated and made available for methanol oxidation. Biener, a coauthor of the research published in the December 19, 2016, online edition of Nature Materials, says, “Our results demonstrate that characterization of these dynamic changes is necessary to unlock the full potential of bimetallic catalytic materials.”
Contact: Juergen Biener (925) 422-9081 (biener2@llnl.gov).
The Perseus cluster is a group of galaxies in the constellation Perseus (see image at left) and is one of the most massive objects in the known universe, containing thousands of galaxies immersed in a vast cloud of multimillion-degree gas. The Hitomi collaboration, in which Lawrence Livermore scientist Greg Brown is a member, found that the turbulent motion of the intracluster gas in the Perseus cluster is only a small fraction of the mechanism responsible for heating the gas to 50 million kelvins.
This finding, published in the July 6, 2016, edition of Nature, demonstrates that an accurate mass of a cluster can be inferred almost exclusively from its thermal hydrostatic pressure without having to rely on low-accuracy measurements and estimates of the turbulent pressure of the system. Accurate cluster masses provide strong constraints on cluster cosmology and dark matter.
This recent discovery is the result of measurements taken with the Soft X-ray Spectrometer (SXS), which was flown on the Hitomi X-ray Observatory and designed and built at NASA’s Goddard Space Flight Center. The high-energy resolution of the SXS made it possible, for the first time, to measure a high-resolution, high-throughput spectrum of a cluster of galaxies. Brown says, “The high-resolution of the SXS has revolutionized our view of some of the largest, most energetic objects in the universe.”
Contact: Greg Brown (925) 422-6879 (brown86@llnl.gov).
A team of Lawrence Livermore researchers developed a semiempirical, particle-based computer model for electrophoretic deposition (EPD) that will provide scientists and engineers with unprecedented insights into this widely used coating technique. The process uses an electric field to drive colloidal particles—that is, particles suspended in a liquid—from a solution onto a conductive substrate. Commonly used to apply paint to cars, EPD can be used to coat ceramics, metals, and polymers. New applications of EPD used with additive manufacturing are also being developed.
The team, led by principal investigator Todd Weisgraber, developed the model and ran different mesoscale simulations, changing the strength of the electrical field and the electrolyte concentration. Using a particle dynamics framework and run on the Laboratory’s Vulcan supercomputing system, the model tracks every single particle—each about 200 nanometers wide—throughout the entire EPD process. The team’s research is published in the December 20, 2016, issue of the journal Langmuir.
“This framework gives us more information than any model before and fresh insights that were previously inaccessible,” says Brian Giera, the study’s coauthor. “Within this particle dynamics framework, we were able to get really detailed information.” The model can be used to better understand deposition kinetics and can be augmented to allow for virtually any type of material, extending the science to a broad range of applications. Giera adds, “The model is poised to take on a lot of questions. It gives us more predictive information to optimize the system.”
Contact: Todd Weisgraber (925) 423-6349 (weisgraber2@llnl.gov).