This issue of The Caltech Effect features scientists and engineers whose research helps us better understand how we sense and make sense of the world.
The year was 2012. A small NASA telescope named NuSTAR launched on a rocket. When it reached space, its tightly folded mast stretched out to 33 feet, and two very new eyes started to record the light that reached them.
Caltech’s Zhongwen Zhan has a vision for the next generation of earthquake-monitoring networks: the use of lasers to assemble the most detailed picture yet of how the earth vibrates.
Multisensory perceptual illusions are surprising and fun, and they also provide insight into neural processing in the brain. The AV Rabbit, Caltech’s most-viewed video of 2018, reveals that an auditory stimulus can retroactively affect your visual perception.
Noelle Stiles (PhD ’15), then a visitor in biology and biological engineering, led the design of this illusion, with contributions from Shinsuke Shimojo, the Gertrude Baltimore Professor of Experimental Psychology and an affiliated faculty member of the Tianqiao and Chrissy Chen Institute for Neuroscience at Caltech, along with former Caltech postdoc Yukiyasu Kamitani (PhD ’01), Carmel Levitan of Occidental College, Monica Li (BS ’16), Ishani Ganguly (class of 2020), and Armand Tanguay (BS ’71) of USC.
Read the story that accompanied the video’s original release in 2018.
Like any scientist, Noelle Davis has an eye for detail. But this rising senior from Fort Worth, Texas, brings unusual focus to the visual world.
“The goal in all photography,” Davis says, “is to highlight the beauty in an interaction, person, or situation.” Credit: Mike Wong (PhD ’18)
“I take my best shots while cheering my lungs out,” Davis says.
During her first year at Caltech, Davis practiced and played with the men’s soccer team. Credit: Caltech Athletics
“Lovely blue swimming pools, but the water’s 175° and pH 1,” Davis says about Hot Creek Geological Site.
Davis asks: “Why does the cafeteria provide such an extraordinary array of fruit? Is this just a California thing? I don’t know, but I love it.”
Davis captured this image of cobalt oxide crystals in APh 109, Introduction to the Micro/Nanofabrication Laboratory.
“The nightmarish part of homework is supposed to be what’s in the problem set, not what’s literally on it,” Davis says.
On her first visit to Caltech, Davis fell in love with the plants on campus.
Annelise Thompson was among the performers Davis photographed at the Caltech Dance Show in April 2019.
Davis originally programmed this simulation for ACM 95b, Introductory Methods of Applied Mathematics.
Davis built this light sensor for EE/ME 7, Introduction to Mechatronics.
We asked members of the Caltech community to explain how sensing and sensors inspire their research.
The Sensory Passageway for Nicotine Addiction
In Dennis Dougherty’s lab, we study receptors in the brain that are drug targets for treating a variety of health conditions and disorders. A receptor functions as a means for two neurons to communicate when it is activated by specific chemicals that nature designed it to detect. I create amino acids that are not found in nature and use them to subtly change the nicotinic receptor nAChr, and I also make tiny changes to a chemical that it detects. My objective is to learn how cytisine, a smoking cessation drug, activates this receptor. To use an analogy, I make precise alterations to a key (cytisine) and a lock (nAChr), all to better understand nicotine addiction.
— Annet Blom (PhD ’19), former llene and Howard Marshall Fellow
The Sensitivity of Pectin
My adviser, Chiara Daraio, was combining plant cells with carbon nanotubes to create synthetic wood when she noticed the new material was responsive to temperature changes. Her curiosity led her to discover that pectin, an organic polymer found in wood and other plant cell walls, when dehydrated, outperforms the best thermal sensors on the market. Today, we continue to improve the stability and sensitivity of pectin. We aim to create inexpensive, flexible, temperature-sensing films that could be used, for example, in health-monitoring devices, car batteries, and electronics. Also, from our many experiments, I am developing computational and theoretical models to systematically explain pectin’s electrical properties.
— Linghui Wang, graduate student in applied physics
How a Drone "Sees"
As a SURF student in Soon-Jo Chung’s aerospace robotics lab, I helped test a sensor that could be used on an autonomous flying ambulance drone. The sensor, an IMU (inertial measurement unit), measures linear acceleration and angular velocity. Now, on a team led by Joel Burdick, I am building on what I learned to help design a tunnel-traversing drone for the DARPA Subterranean Challenge. The drone computes its position and plans its path using IMUs in combination with other instruments, including LIDAR (light detection and ranging), which measures the distance between the drone and obstacles, and a visualization system with high-definition cameras that feed into a flight controller. Sensors plus robust algorithms: Together, these are how we enable a drone to navigate and “see.”
— Anuj Chadha, Robert J. Kieckhefer, Jr. Memorial Scholarship recipient
Making Sense of Survival
We simulate naturalistic conditions for mice and observe responses necessary for survival. For example, predator avoidance: A dark expanding disk shown on an overhead monitor elicits fleeing or freezing because mice sense an approaching aerial predator. Or prey capture: Despite differences in the time each mouse requires to learn how to capture an insect, it always takes just one successful hunt for a mouse to become an efficient hunter. With two faculty advisers, Markus Meister and David Anderson (both from the Tianqiao and Chrissy Chen Institute for Neuroscience at Caltech), I study these behaviors and the involvement of evolutionarily conserved, relatively ancient subcortical structures of the brain. We want to understand these instinctive reactions and where that information is transformed into a successful motor output.
— Zeynep Turan, graduate student in neurobiology
What Creates Our Moral Sense?
Philosophers have long suspected that humans possess a unique faculty of perception dubbed “the moral sense,” which you can think of as an evolved capacity to perceive and react to morally significant events. In the Caltech Brain Imaging Center (part of the Tianqiao and Chrissy Chen Institute for Neuroscience at Caltech), my laboratory studies how this sense arises by peering inside the brains of people making difficult moral decisions, such as how to distribute scarce food resources among orphans. We find that how fairly people distribute these resources depends on how emotionally averse they are to inequity, and this is reflected in differences in brain activity. Our sense of fairness, viewed by philosophers as humans’ most complex capacity, is deeply rooted in the brain’s machinery.
— Steven Quartz, Professor of Philosophy
For NuSTAR’s initial target, Professor Fiona Harrison and her students chose a black hole that shines brightly in X-rays. They wondered: Was the telescope correctly aligned to see it? Would this novel telescope be able to capture an image?
“There were questions in my mind about whether we were going to succeed, and how long it was going to take,” Harrison says. “So when we saw the pictures of the black hole, we were all very relieved. It was just a point source, a very bright dot, but we could tell from its constituent colors that it was the right source.”
NuSTAR maps black holes, collapsed stars, and the remnants of exploded stars. It images them in high-energy X-rays, which no other telescope has been able to focus before. It can do this because Harrison’s research group worked for two decades to develop new detectors, electronics, and optics, and special coatings for the optics.
“You have to pull from a lot of different sources when you’re trying to do something new,” Harrison says. A Danish collaborator on a country drive saw barns with curved glass windows that inspired an affordable method to shape the 266 glass cones in NuSTAR’s optics. Then, Harrison, her students, and a collaborator took a road trip to see how U.S. national labs and manufacturers produce certain coatings. “We stayed in a lot of Motel 6s,” she says. Upon their return, the researchers invented atom-thick layers that make NuSTAR’s optics more reflective than mirrors.
On NuSTAR, two sets of four crystal-shielded semiconductors detect when, where, and how hard each X-ray hits them. Chips bonded to these detectors record and transmit the information. For the electronics, Harrison’s group customized techniques developed by Caltech microelectronics innovator Carver Mead (BS ’56, MS ’57, PhD ’60).
As its data pours in, NuSTAR is helping astronomers learn how stellar explosions created and spread the elements that Earth is made of, what energy sources power extremely active galaxies, and which objects are which in the cosmos.
“I think my favorite discovery,” Harrison says, “is when we found completely unexpected pulses coming from one of these very, very bright sources that people had long assumed were massive black holes.” Turns out they were neutron stars.
Each breakthrough validates efforts by generations of young scholars in Harrison’s research group, who worked without a guarantee of NuSTAR’s success.
Harrison now holds the Kent and Joyce Kresa Leadership Chair in Caltech’s Division of Physics, Mathematics and Astronomy. As chair, she sees that graduate students across the division will gain exploratory latitude because of the financial support provided by new endowed fellowships, including those created by Anneila Sargent (MS ’67, PhD ’78), Tom (BS ’68) and Mary Anna Soifer, and a group of donors who gave in honor of Robbie Vogt.
“These fellowships help launch future generations of researchers,” Harrison says, adding that fellowships help students and their mentors try unproven, divergent approaches.
Now that they have flung open the high-energy X-ray window, Harrison’s research group is starting to explore ultraviolet wavelengths. She and her students have plans for a new space mission that will scan the sky and follow up on gravitational wave detections, bringing home another new view of the cosmos.
Illustrations by Jeremy Leung
Zhan (PhD ’13), an assistant professor of geophysics, has repurposed a tool from industry to send a laser through an underground fiber optic cable and detect vibrations using the light that reflects back.
In partnership with the City of Pasadena, Zhan and his team are taking unused strands of optical fiber in the city’s telecommunication cables and turning those strands into the equivalent of 5,000 sensors. With so many data points grouped so closely together, scientists can watch a quake propagate in a way that is impossible with current networks, where sensors are kilometers apart. The map above shows the full extent of the Pasadena Array planned for October 2019. With success, Zhan hopes to set up similar networks in other cities.
“We can provide better earthquake hazard assessment for the future at no cost to the city,” he says. “This is an important public service because it could save lives, and it’s good for fundamental research, too.”
This image includes a snapshot of data captured by the nascent Pasadena Array on the morning of May 8, 2018. Zhan and his colleagues detected shaking from a 4.5-magnitude quake centered in Cabazon, California, about 90 miles away. (The “P” marks the primary wave, which is faster but weaker; the “S” is the secondary wave that is slower but causes most of the damage from a quake.)
The new seismic network also picked up shaking from a heavy vehicle as it traveled on the streets above. The researchers are able to tell the difference between natural and human-made vibrations because of the network’s high resolution. With more detectors, it is easier to distinguish a faraway quake from a big rig rumbling down the road.
On the roof of Caltech’s Millikan Library, there is a vibration generator that simulates quakes. The instrument was built during the 1970s to help scientists study how the building responds to shaking. Now, Zhan and his team use the shaker to reveal the geological characteristics of land in Pasadena. On occasion, late in the night, the researchers create miniature, artificial quakes—approximately 1.3 in magnitude—and detect the results with the Pasadena Array. Their findings ultimately could help the city identify the neighborhoods most at risk and prioritize which buildings to retrofit to protect against quakes.
Discretionary funds donated by Caltech trustee Li Lu will support Zhan’s fiber-optic cable seismology research and provide a much-needed upgrade to the Millikan shaker. Across the Institute, philanthropy gives Caltech a competitive edge in projects such as this one. “It’s great to have the flexibility to try exciting new things quickly,” Zhan says. “This is only possible because of our donors.”
In July 2019, after a series of earthquakes centered in Ridgecrest, California, Zhan and his colleagues received access to the fiber optic network in Ridgecrest and the surrounding area to monitor aftershocks. To watch a video that provides more information about Zhan, the Pasadena Array, and Caltech’s Seismological Laboratory, click here.
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