But lasers also show promise to do quite the opposite — to cool materials. Lasers that can cool materials could revolutionize fields ranging from bio-imaging to quantum communication.

In 2015, University of Washington researchers announced that they can use a laser to cool water and other liquids below room temperature. Now that same team has used a similar approach to refrigerate something quite different: a solid semiconductor. As the team shows in a paper published June 23 in Nature Communications, they could use an infrared laser to cool the solid semiconductor by at least 20 degrees C, or 36 F, below room temperature.

The device is a cantilever — similar to a diving board. Like a diving board after a swimmer jumps off into the water, the cantilever can vibrate at a specific frequency. But this cantilever doesn’t need a diver to vibrate. It can oscillate in response to thermal energy, or heat energy, at room temperature. Devices like these could make ideal optomechanical sensors, where their vibrations can be detected by a laser. But that laser also heats the cantilever, which dampens its performance.

“Historically, the laser heating of nanoscale devices was a major problem that was swept under the rug,” said senior author Peter Pauzauskie, a UW professor of materials science and engineering and a senior scientist at the Pacific Northwest National Laboratory. “We are using infrared light to cool the resonator, which reduces interference or ‘noise’ in the system. This method of solid-state refrigeration could significantly improve the sensitivity of optomechanical resonators, broaden their applications in consumer electronics, lasers and scientific instruments, and pave the way for new applications, such as photonic circuits.”

The team is the first to demonstrate “solid-state laser refrigeration of nanoscale sensors,” added Pauzauskie, who is also a faculty member at the UW Molecular Engineering & Sciences Institute and the UW Institute for Nano-engineered Systems.

The results have wide potential applications due to both the improved performance of the resonator and the method used to cool it. The vibrations of semiconductor resonators have made them useful as mechanical sensors to detect acceleration, mass, temperature and other properties in a variety of electronics — such as accelerometers to detect the direction a smartphone is facing. Reduced interference could improve performance of these sensors. In addition, using a laser to cool the resonator is a much more targeted approach to improve sensor performance compared to trying to cool an entire sensor.

In their experimental setup, a tiny ribbon, or nanoribbon, of cadmium sulfide extended from a block of silicon — and would naturally undergo thermal oscillation at room temperature.

At the end of this diving board, the team placed a tiny ceramic crystal containing a specific type of impurity, ytterbium ions. When the team focused an infrared laser beam at the crystal, the impurities absorbed a small amount of energy from the crystal, causing it to glow in light that is shorter in wavelength than the laser color that excited it. This “blueshift glow” effect cooled the ceramic crystal and the semiconductor nanoribbon it was attached to.

“These crystals were carefully synthesized with a specific concentration of ytterbium to maximize the cooling efficiency,” said co-author Xiaojing Xia, a UW doctoral student in molecular engineering.

The researchers used two methods to measure how much the laser cooled the semiconductor. First, they observed changes to the oscillation frequency of the nanoribbon.

“The nanoribbon becomes more stiff and brittle after cooling — more resistant to bending and compression. As a result, it oscillates at a higher frequency, which verified that the laser had cooled the resonator,” said Pauzauskie.

The team also observed that the light emitted by the crystal shifted on average to longer wavelengths as they increased laser power, which also indicated cooling.

Using these two methods, the researchers calculated that the resonator’s temperature had dropped by as much as 20 degrees C below room temperature. The refrigeration effect took less than 1 millisecond and lasted as long as the excitation laser was on.

“In the coming years, I will eagerly look to see our laser cooling technology adapted by scientists from various fields to enhance the performance of quantum sensors,” said lead author Anupum Pant, a UW doctoral student in materials science and engineering.

Researchers say the method has other potential applications. It could form the heart of highly precise scientific instruments, using changes in oscillations of the resonator to accurately measure an object’s mass, such as a single virus particle. Lasers that cool solid components could also be used to develop cooling systems that keep key components in electronic systems from overheating.

The researchers created a mutant rotavirus that unexpectedly replicated much slower than the original virus, allowing them to observe the first steps of viral assembly. The findings, published in the Journal of Virology, open new possibilities for treating and preventing this viral disease and for understanding how similar factories of other viruses work.

“The formation of viroplasms is indispensable for a successful rotavirus infection. They form quickly inside infected cells and are made of both viral and cellular proteins that interact with lipid droplets, but the details of how the parts are put together are still not clear,” said first author Dr. Jeanette M. Criglar, a former postdoctoral trainee and now staff scientist in the Department of Molecular Virology and Microbiology at Baylor in Dr. Mary Estes’s lab.

To get new insights into the formation of viroplasms, Criglar and her colleagues studied NSP2, one of the viral proteins that is required for the virus to replicate. Without it, neither viroplasms nor new viruses would form.

Like all proteins, NSP2 is made of amino acids strung together like beads on a necklace. ‘Bead’ 313 is the amino acid serine. Importantly, serine 313 is phosphorylated — it has a phosphate chemical group attached to it. Protein phosphorylation is a mechanism cells use to regulate protein activity. It works like an on-and-off switch, activating or deactivating a protein. Here, the researchers evaluated the role NSP2’s phosphorylation of serine 313 plays on viroplasm formation.

A serendipitous finding

Using a recently developed reverse genetics system, Criglar and her colleagues generated a rotavirus carrying an NSP2 protein with a mutation in amino acid 313, called a phosphomimetic mutation, by changing serine to aspartic acid. The name phosphomimetic indicates that the mutant protein mimics the phosphorylated protein in the original rotavirus. Reverse genetics starts with a protein and works backward to make the mutant gene, which then is made part of the virus to study the function of the protein on viral behavior.

“In laboratory experiments, our phosphomimetic mutant protein crystalized faster than the original, within hours as opposed to days,” Criglar said. “But surprisingly, when compared to non-mutant rotavirus, the phosphomimetic virus was slow to make viroplasms and to replicate.”

“This is not what we expected. We thought that rotavirus with the mutant protein also would replicate faster,” said Estes, Cullen Foundation Endowed Chair and Distinguished Service Professor of molecular virology and microbiology at Baylor. “We took advantage of the delay in viroplasm formation to observe very early events that have been difficult to study.”

Early steps: NSP2 and lipid droplets come together

The researchers discovered that one of the first steps in viroplasm formation is the association of NSP2 with lipid droplets, indicating that NSP2 phosphorylated on position 313 alone can interact with the droplets, without interacting with other components of the viroplasm.

Lipid droplets are an essential part of viroplasms. It is known that rotavirus coaxes infected cells to produce the droplets, but how it does it is unknown. The new findings suggest that rotavirus may be using phosphorylated NSP2 to trigger lipid droplet formation.

“It was very exciting to see that just changing a single amino acid in the NSP2 protein affected the replication of the whole virus,” Criglar said. “The phosphomimetic change altered the dynamics of viral replication without killing the virus. We can use this mutant rotavirus to continue investigating the sequence of events leading to viroplasm formation, including a long-standing question in cell biology about how lipid droplets form.”

“This is the first study in our lab that has used the reverse genetics system developed for rotavirus by Kanai and colleagues in Japan, and that’s very exciting for me,” Estes said. “There have been very few papers that use the system to ask a biological question, and ours is one of them.”

Story Source:

Materials provided by Baylor College of Medicine. Original written by Ana María Rodríguez, Ph.D.. Note: Content may be edited for style and length.

Dr. Kanad Basu, assistant professor of electrical and computer engineering in the Erik Jonsson School of Engineering and Computer Science and lead author of the study, along with colleagues elsewhere, developed a tool that can determine whether an Android game or other mobile app complies with the federal Children’s Online Privacy Protection Act (COPPA).

The researchers introduced and tested their “COPPA Tracking by Checking Hardware-Level Activity,” or COPPTCHA, tool in a study published in the March edition of IEEE Transactions on Information Forensics and Security. The tool was 99% accurate. Researchers continue to improve the technology, which they plan to make available for download at no cost.Basu said games and other apps that violate COPPA pose privacy risks that could make it possible for someone to determine a child’s identity and location. He said the risk is heightened as more people are accessing apps from home, rather than public places, due to the COVID-19 pandemic.

“Suppose the app collects information showing that there is a child on Preston Road in Plano, Texas, downloading the app. A trafficker could potentially get the user’s email ID and geographic location and try to kidnap the child. It’s really, really scary,” Basu said.

Apps can access personal identifiable information, including names, email addresses, phone numbers, location, audio and visual recordings, and unique identifiers for devices such as an international mobile equipment identity (IMEI), media access control (MAC) addresses, Android ID and Android advertising ID. The advertising ID, for example, allows app developers to collect information on users’ interests, which they can then sell to advertisers.

“When you download an app, it can access a lot of information on your cellphone,” Basu said. “You have to keep in mind that all this info can be collected by these apps and sent to third parties. What do they do with it? They can pretty much do anything. We should be careful about this.”

The researchers’ technique accesses a device’s special-purpose register, a type of temporary data-storage location within a microprocessor that monitors various aspects of the microprocessor’s function. Whenever an app transmits data, the activity leaves footprints that can be detected by the special-purpose register.

COPPA requires that websites and online services directed to children obtain parental consent before collecting personal information from anyone younger than 13; however, as Basu’s research found, many popular apps do not comply. He found that many popular games designed specifically for young children revealed users’ Android IDs, Android advertising IDs and device descriptions.

Basu recommends that parents use caution when downloading or allowing children to download apps.

“If your kid asks you to download a popular game app, you’re likely to download it,” Basu said. “A problem with our society is that many people are not aware of — or don’t care about — the threats in terms of privacy.”

Basu advises keeping downloads to a minimum.

“I try to limit my downloading of apps as much as possible,” Basu said. “I don’t download apps unless I need to.”

Researchers from the Georgia Institute of Technology, Intel Corp. and New York University also contributed to the work.

Story Source:

Materials provided by University of Texas at Dallas. Original written by Kim Horner. Note: Content may be edited for style and length.