Lab Report

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The Lab Report is a weekly compendium of media reports on science and technology achievements at Lawrence Livermore National Laboratory. Though the Laboratory reviews items for overall accuracy, the reporting organizations are responsible for the content in the links below.

May. 08, 2015

Lawrence Livermore researchers have made graphene aerogel microlattices with an engineered architecture via a 3D printing technique known as direct ink writing. Illustratiion by Ryan Chen/LLNL

Inking a new class of aerogels

Researchers have printed inks containing nanoscopic graphene flakes to build macroscopic, three-dimensional objects that they say could benefit numerous fields, including energy storage and bioengineering.

A team at Lawrence Livermore has 3-D printed porous, highly compressible aerogels using a graphene oxide ink. This is not the first example of graphene inks. However, scientists are still searching for formulations that fully capitalize on the atomically thin material’s remarkable properties. For example, some existing inks sacrifice mechanical properties for high electrical conductivity.

“We were really trying to avoid making compromises,” said Marcus Worsley, who, along with his colleague, Cheng Zhu, led the Livermore researchers. Their goal was to devise a 3-D printing process that allowed conductive flakes to controllably coalesce and ultimately form aerogels: spongelike materials that are about as light as air yet mechanically robust.

An artist's portrayal of the Messenger spacecraft after its arrival at Mercury. Credit: NASA / JHU-APL / Carnegie Institution.

Messages from Mercury

NASA’s Mercury Messenger pulled the plug on itself when, as planned, it ran low on fuel, got pulled by the planet’s gravity and the sun and crashed onto Mercury on the afternoon of Friday, May 1.

But researchers learned a lot during the spacecraft’s 11-year voyage. One of the mission's most unexpected results was finding out why is Mercury so dark. The rocks and dust on Mercury's surface contain very little iron even though the planet has a huge, iron-dominated core that takes up three-fourths of the planet's diameter and half its volume. Geochemists expected that the planet's surface would contain an abundance of iron-rich minerals.

The planet's surface is very dark, reflecting only about 7 percent of the sunlight striking it. That's even darker than the moon. Earlier this year, a trio of researchers led by Megan Bruck Syal of Lawrence Livermore offered a reasonable alternative: "One thing that hadn’t been considered was that Mercury gets dumped on by a lot of material derived from comets.”

Rugby hohlraums resemble a cylinder, with the corners of the can rounded off to minimize surface area. The major sink of energy in a hohlraum is through the wall surface area, and the rugby shape helps to appreciably reduce this energy loss. Half of the hohlraum is shown here.

Going for the drive

For several years, the National Ignition Facility at Lawrence Livermore has pursued an indirect drive approach to ignition, using cylindrically shaped gold cans known as hohlraums. In this configuration, all of NIF’s 192 laser beams enter the hohlraum through a pair of laser entrance holes and deposit their energy on the gold (or depleted uranium) interior surface. The gold heats up and efficiently creates soft X-rays that bathe a centrally located plastic or high-density carbon capsule containing hydrogen fuel. The capsule compresses the fuel to conditions that approximate those at the center of the sun for realizing energy gain from nuclear fusion.

Due to the challenges of achieving energy break-even and net gain, other hohlraum platforms have been sought to achieve a balance of efficient and symmetric hohlraum drive. One of the candidates is a rugby football-like hohlraum shape, which resembles a cylinder with the corners of the can rounded off to minimize surface area. The major sink of energy in a hohlraum is through the wall surface area, and the rugby shape helps to appreciably reduce this energy loss.

Visible-light image of the Eagle Nebula pillars. The largest pillar is one parsec (about 19 trillion miles) high.

A star is born

Twenty-five years ago, the Hubble Space Telescope captured the famous images of the "Pillars of Creation" in the Eagle Nebula. Twenty years later to the day, the National Ignition team conducted the first experiment in a new discovery science campaign aimed at finding clues to the mystery of how stars are born in these spectacular cosmic formations.

"This project underlines the idea," said LLNL physicist Jave Kane, "that the human intellect can use mathematical equations, computer codes and millimeter-size objects that last nanoseconds in a laboratory to study parsec (trillions of miles)-scale objects thousands of light years distant that last for hundreds of thousands of years — yet evolve by the same physical laws as those on Earth."

The NIF experiment will investigate the origin and dynamics of pillar formation at the boundaries of HII regions (star-forming molecular hydrogen clouds) in the presence of a process called ablative stabilization. The laser will be fired at a novel configuration nicknamed "TriStar"— three hollow tubes (hohlraums) joined together — which mimics the cluster of bright massive stars illuminating the Eagle Nebula.

Lawrence Livermore Engineer Sat Pannu and his team are developing wireless electronic packages for HAPTIX called smart packages. These packages would contain electronics that record and stimulate the peripheral nervous system to control movement and sensation in a patient’s prosthetic hand. Photo by Julie Russell/LLNL

This time with feeling

The dream of replacing a lost or missing limb with a fully functional limb has been around for centuries. Historically, a prosthetic could assist the user in achieving basic tasks, but remained a far cry from what most users would consider fully functional. Though advances have been made in the prosthetic world, most lack the feeling — or more accurately, they aren’t connected with the nervous system, so they don’t actually work like a real limb, nor are they capable of sensory feedback.

This is exactly what Lawrence Livermore researchers are trying to change.

While several companies have developed advanced prosthetic limbs, Lawrence Livermore is working on bridging the gap between advanced prostheses, and a user’s own nervous system, so the limb may once again be used much more naturally. The program is referred to as HAPTIX.

The image depicts a neuronal network growing on a novel nanotextured gold electrode coating. Image by Ryan Chen/LLNL

Good as gold

A team of researchers from Lawrence Livermore  and University of California, Davis have found that covering an implantable neural electrode with nanoporous gold could eliminate the risk of scar tissue forming over the electrode’s surface.

The findings are featured in the journal Applied Materials & Interfaces.

Neural interfaces (for example, implantable electrodes or multiple-electrode arrays) have emerged as transformative tools to monitor and modify neural electrophysiology, both for fundamental studies of the nervous system, and to diagnose and treat neurological disorders. These interfaces require low electrical impedance to reduce background noise and close electrode-neuron coupling for enhanced recording fidelity.