Lawrence Livermore National Laboratory



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Predatory Bacteria Impact Microbial Food Web

The word “predator” may conjure images of leopards killing and eating impala on the African savannah or great white sharks attacking elephant seals off the coast of California. Some microorganisms are also predators that kill and eat other bacteria. Just like their macrobiology counterparts, bacteria belong to intricate food chains but until recently, it has been challenging for scientists to document their ecological significance.

A Lawrence Livermore–led research team discovered that predatory bacteria grow faster and consume more resources than nonpredatory bacteria. The team quantified the growth of predatory and nonpredatory bacteria in soils (and one stream) by tracking isotopically labeled substrates into newly synthesized DNA. Their findings were published in the April 27, 2021, issue of the journal mBio, published by the American Society for Microbiology.

The scientists studied three types of bacteria in soil—nonpredators, obligate predators, and facultative predators—and found that obligate-predatory bacteria grew 36 percent faster and assimilated carbon at rates 211 percent higher than nonpredatory bacteria. Livermore scientist Jennifer Pett-Ridge, a co-author of the paper, says, “These unique, quantitative measures of predator activity suggest that predatory bacteria—along with protists, nematodes, and phages—are active and important in microbial food webs.”
Contact: Jennifer Pett-Ridge (925) 424-2882 (pettridge2@llnl.gov).


Theoretical Laser-Driven Semiconductor

Engineers at Lawrence Livermore in collaboration with the University of Illinois Urbana-Champaign have designed and simulated a theoretical, laser-driven photo-conductive semiconductor switch (PCSS) that could support communication systems faster and more powerful than fifth-generation wireless technology. If realized, the device could achieve faster speeds at higher voltages than existing photoconductive devices and transfer more data over longer distances. The research, funded by the Laboratory Directed Research and Development Program, appeared in the May 5, 2021, issue of IEEE Journal of the Electron Devices Society.

Using experimental data and simulations, the team proposed that under extreme electric fields, the new, unique device could generate an electron-charged cloud in the base semiconductor material, gallium nitride (GaN). Unlike normal semiconductors, whose electrons move faster as the applied electrical field increases, gallium nitride, a wide bandgap material, generates a phenomenon called negative differential mobility (NDM), where an electron cloud slows down, allowing the device to create extremely fast pulses and high-voltage signals at frequencies approaching one terahertz (1012 hertz) when exposed to electromagnetic radiation. This work represents the first attempt to use NDM to push the power-frequency bounds of a GaN PCSS toward the sub-terahertz regime—the frequency range of 500 to 1,000 gigahertz.

“The goal was to build a device significantly more powerful than existing technology but also capable of operating at very high frequencies,” says Livermore engineer Lars Voss. “The output pulse is shorter than the laser’s input pulse and acts like a compression device. You can compress an optical input into an electrical output, potentially generating extremely high-speed, high-power radio frequency waves.”
Contact: Lars Voss (925) 423-0069 (voss5@llnl.gov).


Livermore Device Records Neuroscience Breakthrough

Brain activity in the hippocampus, a region responsible for memory and other cognitive functions, was previously thought to travel in one direction. A newfound phenomenon discovered using film-like electrodes developed at Lawrence Livermore suggests, however, that brain waves travel up and down the hippocampus, like a two-way street. The electrodes that recorded this never-before-seen brain activity were funded by the Defense Advanced Research Projects Agency’s Systems-Based Neurotechnology for Emerging Therapies Program, which aims to improve treatments for neuropsychiatric illnesses in military service members. The team’s findings were published in the May 12, 2021, issue of Nature Communications.

The device, smaller than a dime and consisting of a 32-channel, multielectrode array, was used by surgeons at the University of California at San Francisco to record electrical signals of conscious patients undergoing epilepsy-related surgery. When patients were given a cognitive test, their brain waves traveled toward the front of their hippocampus, and when they waited for the next test question, the waves reversed. This potentially indicates that brain wave direction may reflect distinctive cognitive processes.

Livermore’s Implantable Microsystems group leader Razi Haque says, “This research required the creation of novel, conformable, and higher density electrodes that could wrap around specific regions deep in the brain.” The team also used machine learning to reveal that certain areas of the hippocampal surface activated depending on the direction of the waves. Leveraging years of microfabrication capabilities and infrastructure, the research group is working toward obtaining accreditation from the U.S. Food and Drug Administration to build human-grade devices and exploring development of sub-chronic implants that could remain in the brain for up to 30 days.
Contact: Razi Haque (925) 422-1172 (haque3@llnl.gov).