research

November 2018

Researchers from the Pop Lab, with help from UC Davis researchers, published an article about electrochemically-driven nanoscale thermal regulators.

The paper's abstract states, "the ability to actively regulate heat flow at the nanoscale could be a game changer for applications in thermal management and energy harvesting. Such a breakthrough could also enable the control of heat flow using thermal circuits, in a manner analogous to electronic circuits. Here we demonstrate switchable thermal transistors with an order of magnitude thermal on/off ratio, based on reversible electrochemical lithium intercalation in MoS2 thin films."

In order to make this heat-conducting semiconductor into a transistor-like switch, the researchers bathed the material in a liquid with lots of lithium ions. When a small electrical current is applied to the system, the lithium atoms begin to infuse into the layers of the crystal, changing its heat-conducting characteristics. As the lithium concentration increases, the thermal transistor switches off. Working with Davide Donadio's group at the University of California, Davis, the researchers discovered that this happens because the lithium ions push apart the atoms of the crystal. This makes it harder for the heat to get through.

The researchers envision that thermal transistors connected to computer chips would switch on and off to help limit the heat damage in sensitive electronic devices.

Besides enabling dynamic heat control, the team's results provide new insights into what causes lithium ion batteries to fail. As the porous materials in a battery are infused with lithium, they impede the flow of heat and can cause temperatures to shoot up. Thinking about this process is crucial to designing safer batteries.

In a more distant future the researchers imagine that thermal transistors could be arranged in circuits to compute using heat logic, much as semiconductor transistors compute using electricity. But while excited by the potential to control heat at the nanoscale, the researchers say this technology is comparable to where the first electronic transistors were some 70 years ago, when even the inventors couldn't fully envision what they had made possible.

Excerpted from "How can we design electronic devices that don't overheat?" Nov 9, 2018.

 

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November 2018

The device is a solar harvester on top and radiative cooler on the bottom. Shanhui Fan says the goal is to figure out how to make solar cells more efficient so it's easier for the two technologies to share roof space. Fan states, "We think we can build a practical device that does both things."

The team's article, "Simultaneously and Synergistically Harvest Energy from the Sun and Outer Space", was published November 8, in Joule. It describes how their device is able to simultaneously harvest energy from the sun, and dispel heat from the building, addressing two of the most sought after energy needs.

The sun-facing layer of the device is nothing new. It's made of the same semiconductor materials that have long adorned rooftops to convert visible light into electricity. The novelty lies in the device's bottom layer, which is based on materials that can beam heat away from the roof and into space through a process known as radiative cooling.

In radiative cooling, objects – including our own bodies – shed heat by radiating infrared light. That's the invisible light night-vision goggles detect. Normally this form of cooling doesn't work well for something like a building because Earth's atmosphere acts like a thick blanket and traps the majority of the heat near the building rather allowing it to escape, ultimately into the vast coldness of space. Fan's cooling technology takes advantage of the fact that this thick atmospheric blanket essentially has holes in it that allow a particular wavelength of infrared light to pass directly into space. In previous work, Fan had developed materials that can convert heat radiating off a building into the particular infrared wavelength that can pass directly through the atmosphere. These materials release heat into space and could save energy that would have been needed to air-condition a building's interior. That same material is what Fan placed under the standard solar layer in his new device.

The researchers believe they can build a device that is able to both harvest solar and create The team is now designing solar cells that work without metal liners to couple with the radiative cooling layer.

...Stay tuned!


 

Read article from the theverge.com 

Excerpts from Stanford News, Stanford researchers develop a rooftop device that can make solar power and cool buildings, November 2018.

November 2018

Professor Dan Boneh is the Rajeev Motwani Professor in the School of Engineering and head of the Applied Cryptography Group. He and advisee, PhD candidate Henry Corrigan-Gibbs, developed a system called 'Prio.' Their data privacy system aims to allow data collection to be strictly device data, not personal data.

Many internet-enabled devices need to know how people use their products in order to make them better. But when faced with the request to send information about a computer error back to the developers, many of us are inclined to say "No," just in case that information is too personal.

The Applied Cryptography Group, has developed a new system for preserving privacy during data collection from the internet. Their technique emphasizes maintaining personal privacy.

"We have an increasing number of devices – in our lightbulbs, in our cars, in our toasters – that are collecting personal data and sending it back to the device's manufacturer. More of these devices means more sensitive data floating around, so the problem of privacy becomes more important," said Henry Corrigan-Gibbs, a graduate student in computer science who co-developed this system. "This type of system is a way to collect aggregate usage statistics without collecting individual user data in the clear."

Their system, called Prio, works by breaking up and obscuring individual information through a technique known as "secret sharing" and only allowing for the collection of aggregate reports. So, an individual's information is never reported in any decipherable form.

Prio is currently being tested by Mozilla in a version of Firefox called Nightly, which includes features Mozilla is still testing. On Nightly, Prio ran in parallel to the current remote data collection (telemetry) system for six weeks, gathering over 3 million data values. There was one glitch but once that was fixed, Prio's results exactly matched the results from the current system.

 

"This is rare example of a new privacy technology that is getting deployed in the real world," reports Dan, "It is really exciting to see this put to use."

 

Excerpted from Stanford News, "Stanford researchers develop new data privacy technique" November 1, 2018.

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October 2018

Professor Balaji Prabhakar researches traffic and routes and how a nudge can help us better manage our commute. Stanford Radio host Russ Altman speaks with Balaji on "The Future of Everything". 

While well-known mapping apps have transformed the daily commute through better information, Balaji Prabhakar is exploring ways to digitally incentivize people to improve their driving habits.

He calls it "nudging," and says that small shifts in commute times — just 20 minutes earlier or later — can make a considerable impact on the day's congestion in highly trafficked urban areas, like San Francisco.

A few years ago, Prabhakar made headlines with a Stanford-only study that used small monetary incentives backed by larger lottery-like rewards to reduce peak-hour commuting on campus. He later undertook a similar but much larger effort in Singapore to promote off-peak train travel. In four years, participation in Singapore grew from 20,000 to 400,000 users.

Listen to the Stanford Radio, "Nudging your Commute with guest Balaji Prabhakar"

Excerpted from the School of Engineering, Research & Ideas, "Balaji Prabhakar: Can digital incentives help alleviate traffic?" October 2018. 

Related News

"Research by EE PhD candidates Geng, Liu, and Yin featured in NYT Tech article", July 2018.

"Balaji Prabhakar has been named ACM Fellow", December 2017.

Yilong Geng (EE PhD candidate) presenting at NSDI '18
July 2018

Interdisciplinary research between professor Balaji Prabhakar, his team, and Google has produced a software clock synchronization system that can track time down to 100 billionths of a second.

The paper, presented at NSDI '18, describes a nanosecond-level clock synchronization that can be an enabler of a new spectrum of timing- and delay-critical applications in data centers.

The current, popular clock synchronization algorithm, NTP, can only achieve millisecond-level accuracy. Current solutions for achieving a synchronization accuracy of 10s-100s of nanoseconds require specially designed hardware throughout the network for combatting random network delays and component noise or to exploit clock synchronization inherent in Ethernet standards for the PHY.

The research team presents HUYGENS, named for the Dutch physicist Christiaan Huygens, who invented the pendulum clock in 1656. HUYGENS is a software clock synchronization system that uses a synchronization network and leverages three key ideas. First, coded probes identify and reject impure probe data—data captured by probes which suffer queuing delays, random jitter, and NIC timestamp noise. HUYGENS then processes the purified data with Support Vector Machines, a widely-used and powerful classifier, to accurately estimate one-way propagation times and achieve clock synchronization to within 100 nanoseconds. Finally, HUYGENS exploits a natural network effect—the idea that a group of pair-wise synchronized clocks must be transitively synchronized— to detect and correct synchronization errors even further.

The importance of technical advances in measuring time was underscored by European regulations that went into effect in January and that require financial institutions to synchronize time-stamped trades with microsecond accuracy.

Being able to trade at the nanosecond level is vital to Nasdaq. Two years ago, it debuted the Nasdaq Financial Framework, a software system that it has envisioned eventually trading everything from stocks and bonds to fish and car-sharing rides.

The new synchronization system will make it possible for Nasdaq to offer "pop-up" electronic markets on short notice anywhere in the world, Mr. Prabhakar said. He cited the World Cup as a hypothetical example of a short-term electronic marketplace.

"There are tickets needed, housing, people will need transportation," he said. "Think of an electronic market almost like a massive flea market hosted by Nasdaq software."

The HUYGENS team is Yilong Geng (EE PhD candidate), Shiyu Liu (EE PhD candidate), and Zi Yin (EE PhD candidate), Ashish Naik (Google Inc.) EE professors Balaji Prabhakar and Mendel Rosenblum, and Amin Vahdat (Google Inc.)

 

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July 2018

Congratulations to professors Jon Fan and Juan Rivas-Davila! Two of their researchers won the 2018 NASA iTech Forum. The event is a collaborative effort between NASA and the U.S. Department (DOE) of Energy's Advanced Research Projects Agency-Energy (ARPA-E) to find and foster innovative solutions for critical energy challenges on Earth and in space.

The winning project was presented by Grayson Zulauf and Thaibao (Peter) Phan. Both are PhD candidates. Their collaborative project is developing technology for wireless charging of electric vehicles on Earth, and eventually, Mars. The researchers received invaluable feedback from NASA and DOE's ARPA-E leaders, as well as experts in the field of advanced energy technology.

"NASA is proud to provide a platform for innovators that exposes them to a cadre of industry experts who will be instrumental in the development of their technologies," said Kira Blackwell, NASA iTech program executive for STMD. "NASA's chief technologists and the U.S. Department of Energy's leading subject matter experts provided the teams with a better understanding of requirements for potential infusion of their technologies within a space environment."

Judges selected the top three innovations based on criteria including technical viability, the likely impact on future space exploration, benefits to humanity and commercialization potential. The teams representing the top three entries selected at the end of the forum received a trophy during the recognition ceremony on June 14.

"Our mission at ARPA-E is to change what's possible. We've been delighted to collaborate with NASA for the iTech challenge, to highlight and empower the people driving energy innovation across our country," said Conner Prochaska, senior advisor and chief of staff for ARPA-E. "We look forward to future collaborative opportunities with NASA so, together, we can continue to cultivate the next generation of energy technologies for Americans on the ground and in space."

"It was an honor for Citi to host 'Energy-Tech' thought leaders -- policy makers, academics, scientists, investors and innovators -- for NASA iTech challenge," said Jay Collins, vice chairman of Corporate and Investment Banking at Citi. "We were proud to work with NASA on such an important effort to move energy technology out of the lab and into scalnble solutions for the Moon, Mars and the planet Earth. Congratulations to the winners, whose technological leadership and entrepreneurialism made us all proud."

The top three winners of NASA iTech's 2018 Energy Cycle are listed in alphabetical order:

  • iFeather, Boulder, Colorado. In-situ Fabrication of Extraterrestrial Aerogels for Transparency, Heat, and Energy Regulation (iFEATHER) for Habitat, Aeronautic and Space Vessel, and Space Suit Applications. Focus area: Innovative Power Management and Distribution
  • Stanford University - Department of Electrical Engineering, Stanford, California. Two C: Transportation Electrification through Ubiquitous Wireless Charging. Focus area: Innovative Power Management and Distribution
  • WBGlobalSemi, Inc., Lakewood Ranch, Florida. Commercializing High Power Silicon Carbide (SiC) Bipolar Junction Transistors (BJTs) and Power Modules for Power Management and Distributed Power Applications. Focus area: Innovative Power Management and Distribution

 

Grayson Zulauf (third from left) is an EE PhD candidate. He is a researcher in the SUPERLab, directed by Professor Juan Rivas-Davila. the Fan Lab is directed by professor Jonathan Fan.

 

 

Congratulations Jon, Juan, Grayson and Peter!

Nikhil Garg, EE PhD '20 interdisciplinary research using machine-learning
April 2018

Lead author Nikhil Garg (PhD candidate '20) demonstrates that word embeddings can be used as a powerful tool to quantify historical trends and social change. His research team developed metrics based on word embeddings to characterize how gender stereotypes and attitudes toward ethnic minorities in the United States evolved during the 20th and 21st centuries starting from 1910. Their framework opens up a fruitful intersection between machine learning and quantitative social science.

Nikhil co-authored the paper with history Professor Londa Schiebinger, linguistics and computer science Professor Dan Jurafsky and biomedical data science Professor James Zou.

Their research shows that, over the past century, linguistic changes in gender and ethnic stereotypes correlated with major social movements and demographic changes in the U.S. Census data.

The researchers used word embeddings – an algorithmic technique that can map relationships and associations between words – to measure changes in gender and ethnic stereotypes over the past century in the United States. They analyzed large databases of American books, newspapers and other texts and looked at how those linguistic changes correlated with actual U.S. Census demographic data and major social shifts such as the women's movement in the 1960s and the increase in Asian immigration, according to the research.

"Word embeddings can be used as a microscope to study historical changes in stereotypes in our society," said James Zou, a courtesy professor of electrical engineering. "Our prior research has shown that embeddings effectively capture existing stereotypes and that those biases can be systematically removed. But we think that, instead of removing those stereotypes, we can also use embeddings as a historical lens for quantitative, linguistic and sociological analyses of biases."

"This type of research opens all kinds of doors to us," Schiebinger said. "It provides a new level of evidence that allow humanities scholars to go after questions about the evolution of stereotypes and biases at a scale that has never been done before."

"The starkness of the change in stereotypes stood out to me," Garg said. "When you study history, you learn about propaganda campaigns and these outdated views of foreign groups. But how much the literature produced at the time reflected those stereotypes was hard to appreciate." 

The new research illuminates the value of interdisciplinary teamwork between humanities and the sciences, researchers said.

"This led to a very interesting and fruitful collaboration," Schiebinger said, adding that members of the group are working on further research together. "It underscores the importance of humanists and computer scientists working together. There is a power to these new machine-learning methods in humanities research that is just being understood." 


 

Proceedings of the National Academy of Sciences, "Word embeddings quantify 100 years of gender and ethnic stereotypes" April 3,2018.  

Excerpted from Stanford News, "Stanford researchers use machine-learning algorithm to measure changes in gender, ethnic bias in U.S." April 3, 2018.

 

 

 

Graduate student David Lindell and Matt O’Toole, a post-doctoral scholar, work in the lab. (Image credit: L.A. Cicero)
March 2018

A driverless car is making its way through a winding neighborhood street, about to make a sharp turn onto a road where a child’s ball has just rolled. Although no person in the car can see that ball, the car stops to avoid it. This is because the car is outfitted with extremely sensitive laser technology that reflects off nearby objects to see around corners.

“It sounds like magic but the idea of non-line-of-sight imaging is actually feasible,” said Gordon Wetzstein, assistant professor of electrical engineering and senior author of the paper describing this work, published March 5 in Nature.

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image credit: L. Cicero
February 2018


Krishna Shenoy and team have been researching the use of brain machine interfaces (BMI) to assist people with paralysis. Recently, one of the researchers changed the task, requiring physical movement from a change in thought. He realized that the BMI would allow study of the mental rehearsal that occurs before the physical expression.

Although there are some important caveats, the results could point the way toward a deeper understanding of what mental rehearsal is and, the researchers believe, to a future where brain-machine interfaces, usually thought of as prosthetics for people with paralysis, are also tools for understanding the brain.

"Mental rehearsal is tantalizing, but difficult to study," said Saurabh Vyas, a graduate student in bioengineering and the paper's lead author. That's because there's no easy way to peer into a person's brain as he imagines himself racing to a win or practicing a performance. "This is where we thought brain-machine interfaces could be that lens, because they give you the ability to see what the brain is doing even when they're not actually moving," he said.

"We can't prove the connection beyond a shadow of a doubt," Krishna said, but "this is a major step in understanding what mental rehearsal may well be in all of us." The next steps, he and Vyas said, are to figure out how mental rehearsal relates to practice with a brain-machine interface – and how mental preparation, the key ingredient in transferring that practice to physical movements, relates to movement.

Meanwhile, Krishna said, the results demonstrate the potential of an entirely new tool for studying the mind. "It's like building a new tool and using it for something," he said. "We used a brain-machine interface to probe and advance basic science, and that's just super exciting."

Additional Stanford authors are Nir Even-Chen, a graduate student in electrical engineering, Sergey Stavisky, a postdoctoral fellow in neurosurgery, Stephen Ryu, an adjunct professor of electrical engineering, and Paul Nuyujukian, an assistant professor of bioengineering and of neurosurgery and a member of Stanford Bio-X and the Stanford Neurosciences Institute.

Funding for the study came from the National Institutes of Health, the National Science Foundation, a Ric Weiland Stanford Graduate Fellowship, a Bio-X Bowes Fellowship, the ALS Association, the Defense Advanced Research Projects Agency, the Simons Foundation and the Howard Hughes Medical Institute.

Excerpted from Stanford News, "Mental rehearsal prepares our minds for real-world action, Stanford researchers find," February 16, 2018.

 

Related News:

Research by PhD candidate and team detects errors from Neural Activity, November 2017.

Krishna Shenoy's translation device; turning thought into movement, March 2017.

Brain-Sensing Tech Developed by Krishna Shenoy and Team, September 2016.

Krishna Shenoy receives Inaugural Professorship, February 2017.

 

February 2018

Angad Rekhi (PhD candidate) and Amin Arbabian have developed a wake-up receiver that turns on a device in response to incoming ultrasonic signals – signals outside the range that humans can hear. By working at a significantly smaller wavelength and switching from radio waves to ultrasound, this receiver is much smaller than similar wake-up receivers that respond to radio signals, while operating at extremely low power and with extended range.

This wake-up receiver has many potential applications, particularly in designing the next generation of networked devices, including so-called "smart" devices that can communicate directly with one another without human intervention.

"As technology advances, people use it for applications that you could never have thought of. The internet and the cellphone are two great examples of that," said Rekhi. "I'm excited to see how people will use wake-up receivers to enable the next generation of the Internet of Things."

Excerpted from Stanford News, "Stanford researchers develop new method for waking up small electronic devices", February 12, 2018

 

Related news:

Amin's Research Team Powers Tiny Implantable Devices, December 2017.

Stanford Team led by Amin Arbabian receives DOE ARPA-E Award, January 2017.

Amin Arbabian receives Tau Beta Pi Undergrad Teaching Award, June 2016.

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