research

November 2016

A team led by Jim Harris and Thomas Jaramillo, an associate professor of chemical engineering and of photon science, has made a significant improvement to the efficiency of solar energy. In work published in Nature Communications, they were able to capture and store 30 percent of the energy captured from sunlight into stored hydrogen, beating the prior record of 24.4 percent.

Solar energy has the potential to provide abundant power, but only if scientists solve two key issues: storing the energy for use at all hours, particularly at night, and making the technology more cost effective. The interdisciplinary team has made significant strides toward solving the storage issue, demonstrating the most efficient means yet of storing electricity captured from sunlight in the form of chemical bonds. If the team can find a way of lowering the cost of their technology, they say it would be a huge step toward making solar power a viable alternative to current, more polluting energy sources.

The basic science behind the team's approach is well understood: Use the electricity captured from sunlight to split water molecules into hydrogen and oxygen gas. That stored energy can be recovered later in different ways: by recombining the hydrogen and oxygen into water to release electricity again, or by burning the hydrogen gas in an internal combustion engine, similar to those running on petroleum products today.

"It took specialists in different fields to do what none of us could have done alone," Harris said. "That's one of the lessons of this result: There is no single fix. How everything links together is the key."

 

Jim Harris is the James and Elenor Chesebrough Professor in the School of Engineering, professor, by courtesy, of applied physics and of materials science and engineering, a member of Stanford Bio-X and of the Stanford Neurosciences Institute, and an affiliate of the Precourt Institute for Energy and the Stanford Woods Institute for the Environment. Jamarillo is also an affiliate of the Precourt Institute for Energy.

 

This article is adapted from the Stanford Report. Read full article

September 2016

For years, the net neutrality debate has been at an impasse: either the internet is open or preferences are allowed. But professors Nick McKeown and Sachin Katti, and EE PhD Yiannis Yiakoumis ­– say their new technology, called Network Cookies, makes it possible to have preferential delivery and an open internet. Network Cookies allow users to choose which home or mobile traffic should get favored delivery, while putting network operators and content providers on a level playing field in catering to such user-signaled preferences.

"So far, net neutrality has been promoted as the best possible defense for users," Katti said. "But treating all traffic the same isn't necessarily the best way to protect users. It often restricts their options and this is why so-called exceptions from neutrality often come up. We think the best way to ensure that ISPs and content providers don't make decisions that conflict with the interests of users is to let users decide how to configure their own traffic."

McKeown said Network Cookies implement user-directed preferences in ways that are consistent with the principles of net neutrality.

"First, they're simple to use and powerful," McKeown said. "They enable you to fast-lane or zero-rate traffic from any application or website you want, not just the few, very popular applications. This is particularly important for smaller content providers – and their users – who can't afford to establish relationships with ISPs. Second, they're practical to deploy. They don't overwhelm the user or bog down user devices and network operators and they function with a variety of protocols. Finally, they can be a very practical tool for regulators, as they can help them design simple and clear policies and then audit how well different parties adhere to them."

 


This article is adapted from Stanford Engineering News. Read full article.

September 2016

Technology developed by Stanford Bio-X scientists Krishna Shenoy (EE) and postdoctoral fellow Paul Nuyujukian, directly reads brain signals to drive a cursor moving over a keyboard. In an experiment conducted with monkeys, the animals were able to transcribe passages from the New York Times and Hamlet at a rate of up to 12 words per minute.

Earlier versions of the technology have already been tested successfully in people with paralysis, but the typing was slow and imprecise. This latest work tests improvements to the speed and accuracy of the technology that interprets brain signals and drives the cursor.

"Our results demonstrate that this interface may have great promise for use in people," said Nuyujukian, who will join Stanford faculty as an assistant professor of bioengineering in 2017. "It enables a typing rate sufficient for a meaningful conversation."

The technology developed by the Stanford team involves a multi-electrode array implanted in the brain to directly read signals from a region that ordinarily directs hand and arm movements used to move a computer mouse.

It's the algorithms for translating those signals and making letter selections that the team members have been improving. They had tested individual components of the updated technology in prior monkey studies but had never demonstrated the combined improvements in typing speed and accuracy.

"The interface we tested is exactly what a human would use," Nuyujukian said. "What we had never quantified before was the typing rate that could be achieved." Using these high-performing algorithms developed by Nuyujukian and his colleagues, the animals could type more than three times faster than with earlier approaches.

 

This article is adapted from the Stanford Report. Read full article.

 

Related News:

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

Krishna Shenoy receives Inaugural Professorship, February 2017.


 

September 2016

As the breathalyzer does for alcohol, this experimental 'potalyzer' could provide a practical field test for determining whether a driver might be impaired from smoking marijuana.

This November, several states will vote whether to legalize marijuana use, joining more than 20 states that already allow some form of cannabis use. This has prompted a need for effective tools for police to determine on the spot whether people are driving under the influence.

Shan Wang and team have devised a potential solution, applying magnetic nanotechnology (GMR), previously used as a cancer screen, to create what could be the first practical roadside test for marijuana intoxication.

"To the best of our knowledge, this is the first demonstration that GMR biosensors are capable of detecting small molecules," Wang wrote in a paper describing the device, published in Analytical Chemistry.

Professor Shan Wang and team created a mobile device that uses magnetic biosensors to detect tiny THC molecules in saliva. Officers could collect a spit sample with a cotton swab and read the results on a smartphone or laptop in as little as three minutes.

Wang's device can detect concentrations of THC in the range of 0 to 50 nanograms per milliliter of saliva. While there's still no consensus on how much THC in a driver's system is too much, previous studies have suggested a cutoff between 2 and 25 ng/mL, well within the capability of Wang's device.

 

The co-authors of the Analytical Chemistry paper are Jung-Rok Lee (ME PhD'15), Joohong Choi (EE PhD'15), and Tyler O. Shultz (Biology BS'13).

 

This article is adapted from the Stanford Report.

September 2016

Shanhui Fan and research team are developing a material that cools by letting perspiration evaporate through the material – something ordinary fabrics already do. But the Stanford material provides a second, revolutionary cooling mechanism: allowing heat that the body emits as infrared radiation to pass through the plastic textile.

"Forty to 60 percent of our body heat is dissipated as infrared radiation when we are sitting in an office," states Shanhui Fan, who specializes in photonics. "But until now there has been little or no research on designing the thermal radiation characteristics of textiles."

To develop their cooling textile, the Stanford researchers blended nanotechnology, photonics and chemistry to give polyethylene – the clear, clingy plastic we use as kitchen wrap – a number of characteristics desirable in clothing material: It allows thermal radiation, air and water vapor to pass right through, and it is opaque to visible light.

Eventually, the research culminated in a single-sheet material that met their three basic criteria for a cooling fabric. To make this thin material more fabric-like, they created a three-ply version: two sheets of treated polyethylene separated by a cotton mesh for strength and thickness.

"Wearing anything traps some heat and makes the skin warmer," Fan said. "If dissipating thermal radiation were our only concern, then it would be best to wear nothing."

Comparing the new fabric with cotton fabric, showed cotton making the skin surface 3.6 F warmer than their cooling textile. The researchers said this difference means that a person dressed in their new material might feel less inclined to turn on a fan or air conditioner.

Fan believes that this research opens up new avenues of inquiry to cool or heat things, passively, without the use of outside energy, by tuning materials to dissipate or trap infrared radiation.

 

 

This article is adapted from the Stanford Report.
Read full article

May 2016

Early results show that the quality of optical materials grown from diamondoid seeds is consistently high, says Stanford's Jelena Vuckovic, a professor of electrical engineering who is leading this part of the research with Steven Chu, professor of physics and of molecular and cellular physiology.

"Developing a reliable way of growing the nanodiamonds is critical," says Vuckovic, who is also a member of Stanford Bio-X and SystemX. "And it's really great to have that source and the grower right here at Stanford. Our collaborators grow the material, we characterize it and we give them feedback right away. They can change whatever we want them to change."

 

Excerpted from Stanford News. Read full article.

May 2016

Recently published in Lab on a Chip, a journal of the Royal Society of Chemistry, Professor Audrey Bowden and Gennifer Smith, a PhD student in electrical engineering, detail their new low-cost, portable device that would allow patients to get consistently accurate urine test results at home, easing the workload on primary care physicians.

Other do-it-yourself systems are emerging, but Bowden and Smith's approach is inexpensive and reliable, in part because they base their system on the same tried and trusted dipstick used in medical offices.

Their approach uses an easy-to-assemble black box that allows a smartphone camera to capture video that accurately analyzes color changes in a standard paper dipstick.

 

Excerpts from Stanford News, May 16, 2016.

Read full Stanford News article

December 2015

Collaborative efforts of researchers at Stanford, University of California Berkeley, University of Michigan, and Carnegie Mellon University are working toward creating a faster and more efficient computing architecture.

The team describes their approach as 'N3XT, Nano-Engineered Computing Systems Technology.' N3XT will eliminate bottlenecks by integrating processors and memory like floors in a skyscraper and by connecting these components with millions of "vias," which play the role of tiny electronic elevators.

The key is the use of non-silicon materials that can be fabricated at much lower temperatures than silicon, so that processors can be built on top of memory without the new layer damaging the layer below.

N3XT high-rise chips are based on carbon nanotube transistors (CNTs). Transistors are fundamental units of a computer processor, the tiny on-off switches that create digital zeroes and ones. CNTs are faster and more energy-efficient than silicon processors. Moreover, in the N3XT architecture, they can be fabricated and placed over and below other layers of memory.

Mitra and Wong have already demonstrated a working prototype of a high-rise chip. At the International Electron Devices Meeting in December 2014 they unveiled a four-layered chip made up of two layers of RRAM memory sandwiched between two layers of CNTs.

In their N3XT paper they ran simulations showing how their high-rise approach was a thousand times more efficient in carrying out many important and highly demanding industrial software applications.

"When you combine higher speed with lower energy use, N3XT systems outperform conventional approaches by a factor of a thousand," Wong said.

 

Excerpts from the Stanford Report.

November 2015

Professor Arbabian and research professo Khuri-Yakub's research was spurred by a challenge posed by the Defense Advanced Research Projects Agency (DARPA), best known for sponsoring the studies that led to the Internet. DARPA sought to develop a system to detect plastic explosives buried underground – improvised explosive devices (IEDs) – that are currently invisible to metal detectors. The task included one important caveat: The detection device could not touch the surface in question, so as not to trigger an explosion.

Professor Arbabian and research professor Khuri-Yakub detail their latest step toward developing such a device through experiments, which are detailed in Applied Physics Letters and presented at the International Ultrasonics Symposium in Taipei, Taiwan.

The work grows out of research designed to detect buried plastic explosives, but the researchers said the technology could also provide a new way to detect early stage cancers.

"We've been working on this for a little over two years," Khuri-Yakub said. "We're still at an early stage but we're confident that in five to ten to fifteen years, this will become practical and widely available."

 

The research team includes graduate students Hao Nan, Kevin Boyle, Nikhil Apte, Miaad Aliroteh, Anshuman Bhuyan and senior research associate Amin Nikoozadeh.

 

Excerpts from Stanford Report.

October 2015

Recent articles published by EE Professors Eric Pop and H.S. Philip Wong describe advances in memory and data storage using graphene. The three experiments demonstrate post-silicon materials and technologies that store more data per square inch and use a fraction of the energy of today's memory chips.

The unifying thread in all three experiments is graphene, an extraordinary material isolated a decade ago but which had, until now, relatively few practical applications in electronics.

"Graphene is the star of this research," said Eric Pop, associate professor of electrical engineering and a contributor to two of the three memory projects. "With these new storage technologies, it would be conceivable to design a smartphone that could store 10 times as much data, using less battery power, than the memory we use today."

Professor H.-S. Philip Wong and Pop led an international group of collaborators who describe the graphene-centric memory technologies in separate articles in Nature Communications, Nano Letters, and Applied Physics Letters.

"Data storage has become a significant, large-scale consumer of electricity, and new solid-state memory technologies such as these could also transform cloud computing," Wong said.

Pop and Wong agree that these studies show that graphene is far from a laboratory curiosity. The material's unique electrical, thermal and atomically thin properties can be utilized to create more energy-efficient data storage. Such properties do not exist in the silicon world, yet could potentially transform the way we store and access our digital data in the future.

 

Excerpts from the Stanford Report

Pages

Subscribe to RSS - research