Lawrence Livermore researchers have developed a method to fabricate graphene-based bulk materials from polymer-derived carbon foams. Carbon atoms are selectively removed from a network composed of both unstructured carbon and graphite nanoplatelets. “The new technique is inexpensive, scalable, and yields mechanically robust, centimeter-size monolithic samples composed almost entirely of interconnected networks of single-layer graphene nanoplatelets,” says Ted Baumann, who developed the synthetic approach.
The graphene bulk materials have an ultrahigh surface area and may thus be used for energy storage systems such as supercapacitors, where energy is stored by polarization of the graphene electrode–electrolyte interface. Graphene bulk material could also be used as an electrically conductive network to support the active material in battery applications. An emerging field in which the bulk material could be applied is capacitive deionization, a desalination method in which ions are removed from electrolytes to create a clean water source.(See A Better Method for Desalinating Water).
The advantage of using bulk materials rather than composite materials is their superior stability, which allows for longer lifetimes, higher conductivity (less loss during charging and discharging), and the ability to tune the pore structure. “This concept is potentially game-changing in the area of materials science,” says Juergen Biener, lead Livermore author of the cover article in the September 25, 2012, issue of Advanced Materials. Other institutions contributing to this effort include the Karlsruhe Institute of Technology, Technische Universität Darmstadt, and Technische Universität Hamburg–Harburg.
Contact: Ted Baumann (925) 423-5543 (baumann2@llnl.gov).Livermore scientist Bruce Buchholz and a team of international collaborators have found a multidisciplinary approach to identifying the remains of missing persons. Using “bomb pulse” radiocarbon analysis developed at the Laboratory (see S&TR, April/May 2010, An Improved Tool for Nuclear Forensics), combined with recently developed anthropological analytic and forensic DNA techniques, the researchers were able to identify the remains of a missing child four decades after discovery of the body.
In 1968, a child’s cranium was recovered from the banks of a northern Canadian river. Initial analyses using the technology at the time concluded that the cranium came from the body of a seven- to nine-year-old child, but no identity could be determined. At the Laboratory’s Center for Accelerator Mass Spectrometry (shown center), researchers recently conducted radiocarbon analysis of enamel from two of the child’s teeth and determined a more precise birth date—within one to two years. Forensic DNA analysis, conducted at Simon Fraser University in Canada, indicated the child was a male, and the obtained mitochondrial profile matched a living maternal relative to the presumed missing child. The multidisciplinary analyses indicated an age at death of approximately four and one-half years and resulted in a legal identification 41 years after the discovery of the remains. The effort highlights the potential of combining radiocarbon analysis with anthropological and mitochondrial DNA analyses to produce confident personal identifications in forensic cold cases dating to within the last 60 years.
“Thousands of John and Jane Doe cold cases exist in the United States,” says Buchholz, who conducted the radiocarbon analysis in the case. “We could provide birth and death dates for many of these cases.” Other institutions participating in the research are the Karolinska Institutet in Sweden and the British Columbia Institute of Technology. The research appeared in the September 2012 issue of the Journal of Forensic Sciences.
Contact: Bruce Buchholz (925) 422-1739 (buchholz2@llnl.gov).In an experiment led by the Laboratory’s Yuan Ping using the Titan laser at the Jupiter Laser Facility, researchers performed the first time-resolved measurements on the hole-boring process in the relativistic regime with a novel diagnostic called Specular FROG (frequency-resolved optical gating). The data show an unexpected slowing down of hole boring even when the laser intensity is still increasing over time.
When a laser beam is reflected from a mirror, a finite amount of momentum—carried by light—is transferred to the mirror so that the mirror is slightly pushed. At high laser intensities into the relativistic regime, the light pressure is intense enough to push a high-density plasma and create a channel along the light path. The channel helps to guide the laser beam and deliver energetic electrons to ignite the core of fuel.
Previous models on hole boring only take into account the ion momentum. Electron momentum has been ignored because electrons have much less mass. In the relativistic regime, however, electrons become so energetic that their momentum is no longer negligible. According to Livermore’s Andreas Kemp, these electrons quickly leave the laser–plasma interaction region. A return current flows to compensate the charge but not the loss of momentum. As a result, the hole boring becomes slower than previous predictions.
The results provide a new understanding of relativistic laser–plasma interaction, in particular how the energy and momentum are partitioned among different groups of particles. The research team includes scientists from Lawrence Livermore, General Atomics, University of California at San Diego, Ohio State University, and Princeton University. The team’s research appeared in the October 5, 2012, edition of Physical Review Letters.
Contact: Yuan Ping (925) 422-7052 (ping2@llnl.gov).