Algorithmic Magic: Behind the Scenes of Modern Computer Science

Computer science permeates many aspects of our lives, from games on a smartphone to global online banking systems. It is crucial for scientists and programmers within the field to have a theoretical and robust understanding of its limits.

On Wednesday, January 20, at 8 p.m. in Beckman Auditorium, Professor of Computer Science Chris Umans will discuss how computer scientists identify and conceptualize computational problems, what sorts of ideas are used to solve them, and how they encapsulate deep questions about the nature of computation itself. Admission is free.

What do you do?

I am a theoretical computer scientist in the Division of Engineering and Applied Science, which means I am interested in understanding the possibilities and limitations of computation, in a provable, mathematical sense. Computational complexity attempts to answer the question, what is computationally feasible given limited computational resources? It studies general techniques for trading off resources such as running time, storage space, randomness, and parallelism; it devises methods for transforming whole classes of problems into simple "complete" problems that capture the difficulty of the whole class; and it establishes results about the limits of efficient computation, in a rigorous way. It encompasses some of the deepest and most fundamental open—or unsolved—problems in computer science and mathematics.

Computational complexity also excels at exposing computational problems that we regard as "fundamental" because they lie at the heart of many applications.

I also work on a variety of problems concerning the power of randomness in computation, algorithms for some fundamental algebraic problems, and some questions in quantum computation. Much of my work has an algebraic component to it.

Why is this important?

Theoretical computer science is the "science" behind computer science. It develops the ideas and the mathematics to be able to solve key problems in fast and clever ways and these problems in turn lie at the heart of the technologies that permeate our everyday lives.

Understanding what's possible algorithmically and what's computationally impossible is a fundamental scientific and mathematical question. One major implication is for computer security. We base cryptography and online security on the believed difficulty of problems which seem intractable—problems that can theoretically be solved but not in practice—but we don't know how to prove that these problems don't have an unexpected, fast solution. If we're wrong about their assumed intractability, most of the cryptography currently in use can be broken.

How did you get into this line of work?

As a kid, I enjoyed programming and mathematics. When I took my first course on algorithms I realized I enjoyed figuring out clever ways to solve problems more than coding the solutions themselves. When I learned about the P versus NP problem and the other deep unsolved problems of computational complexity, I was hooked. I feel very fortunate to have the freedom to think deeply about the difficult problems that fascinate me.

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Wednesday, February 3, 2016
Beckman Institute Auditorium – Beckman Institute

"Words Are Obsolete": Explaining and Understanding in the Dynamic Medium

Microscopic Materials: An Interview with Marco Bernardi

All materials, including the screen on which you are currently reading this text, are composed of a tiny universe of particles. These particles are not only the physical ones, like electrons and atomic nuclei, but also excited states (or so-called quasiparticles) that constantly collide and bounce, gaining and losing energy. Marco Bernardi, a newly appointed assistant professor of applied physics and materials science in the Division of Engineering and Applied Science, is fascinated by these interactions and how they give rise to the world around us. We spoke with Bernardi about his research on energy in materials and also about his new life in the California sun.

You study materials on a tiny, atomic scale. What does that look like?

At the microscopic scale, all materials are made up of numerous interacting particles, trading energy with one another through various collisions that we call scattering processes. For example, if you excite a material with light, electrons inside will undergo scattering processes to release this excess energy. They can emit light as a photon, emit vibrations as a phonon, or trade energy with other electrons. Surprisingly, these processes occur even in the dark, as all materials maintain an equilibrium with the environment by exchanging energy. Materials hide an intangible universe.

What are you trying to discover about these excited states?

We study the collision processes between these excited states, both to understand the fundamental science and because they are essential for applications. These processes take place on a femtosecond timescale—a femtosecond is a millionth of a billionth of a second—so they are very challenging to study experimentally. One thing we examine is how long it takes for a material to go back to its normal state of equilibrium after it has been excited. For example: if you excite a piece of gallium arsenide by shining light on it, then it will reemit light as it returns back to its equilibrium state. This emission fades out in time. We want to characterize the timescale for this emission decay, which is called the photoluminescence lifetime. Other examples are the scattering of an electron by a crystalline defect in a material, or the time for the spin of an electron to reorient. If we can understand the timescale for the interactions among electrons, phonons, light, defects, spin, and other excited states, we can predict how materials transport electricity and heat, emit and absorb light, and convert energy into different forms. Applications in electronics, optoelectronics, ultrafast science, and renewable energy abound.

In some cases, the questions we ask have already been examined experimentally. Experimentally, it has been determined that an excited electron in silicon loses energy on a femtosecond timescale, and the conductivity of a simple material like gold has been found. But my group aims to look at materials theoretically. We use the atomic structure of materials—the way their atoms are positioned—as the only input, and solve the equations of quantum mechanics in a computer, without any information from experiment. With this approach, we can understand microscopic details out of reach for experiments and can investigate materials that have not yet been fabricated, besides being able to obtain known experimental results. Some problems, like calculating the conductivity of gold, may sound trivial—but nobody has ever computationally calculated the correct conductivity of gold without any information from experiment, and in particular without knowledge of the timescale for electron scattering. There are also a lot of new experiments studying materials at extremely short timescales, some of them requiring multimillion-dollar lasers, but few theories that can explain them. We are working on computational tools that can understand and microscopically interpret both traditional and less traditional experimental scenarios.

We have a fair understanding of most of the different types of scattering processes, and we have ambitious plans to combine all of these computational approaches for different microscopic phenomena into one big code that can calculate everything that's going on in an excited material. Employing massively parallel algorithms and running them on our computer cluster at Caltech or at national supercomputing facilities, this code would open new avenues for our research.

What are some applications of this work?

In any application where current or light is involved, scattering processes between electrons or other excited states control the behavior of the device. This includes solar panels, circuits, transistors, displays, and other electrically conductive materials. Understanding the timescale and the microscopic details of these scattering processes could allow one to create more efficient solar energy conversion devices, light emitters, and circuits, among other applications; or even "just" understand the behavior of matter at the shortest possible timescale.

What excites you most about being at Caltech?

I'm most excited about the emphasis on fundamental science here. People can be really tempted by "flashy" science or experiments on hot topics. But to compute what I'm trying to look at, we have to first build our understanding on simple experiments and materials—boring things—before we are able to tackle materials at the frontier of condensed matter research. Nobody really wants to do basic measurements on pieces of silicon or gold. But fundamentally we don't know how to compute in detail basic excitations in materials. Caltech supports this kind of science. And no matter what you're working on, you can talk to somebody who will give you some unique perspective or insight.

What is your background? How did you get interested in this field?

I grew up in Italy. In high school, I really enjoyed math and physics. I read an article about carbon nanotubes and nanotechnology, and during my undergraduate education in Italy I became very interested in the physics of materials. Carbon nanotubes can be either metallic or semiconducting—a material where you can control how much current can flow through—so you should be able to create all kinds of parts of a device just made out of these tubes. During my PhD work at MIT, my advisor and I predicted that it would be possible to create a solar cell entirely out of carbon nanotubes. We worked together with a colleague who synthesized the device from our design, and now we have the world record for making a solar cell entirely out of carbon. In the two years that I spent at Berkeley, I discovered that I wanted to understand the dynamics of how particles and excited states exchange energy in materials. Now I'm deeply settled and focused on this problem.

What's your favorite thing about being in Southern California?

It's always sunny. I love swimming, and the outdoor swimming pools are great—at MIT, it was generally too cold to go swim outside. So I'm taking full advantage of how warm it is here.

What do you like to do outside of work?

I love traveling and planning trips. I like to pick a country, go online and find all kinds of options for routes and itineraries, and go explore for two weeks. If I weren't doing science I would probably be traveling and learning languages and talking to people. I've been to Japan and Chile recently, and I would really like to see more of Asia but it's getting more complicated—my wife and I are expecting a baby! My maps tell me that I currently have seen 20 percent of the whole world—on land, that is. My ambition is to get to 80 percent one day.

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Friday, January 22, 2016
Cahill, Hameetman Auditorium – Cahill Center for Astronomy and Astrophysics

Innovation in Aerospace - An Idea 2 Innovation Event

National Academy of Inventors Names Three Caltech Fellows

Caltech professors Harry Atwater, Mark Davis, and Ali Hajimiri have been named as fellows of the National Academy of Inventors (NAI). According to the NAI press release, fellows are "academic inventors who have demonstrated a prolific spirit of innovation in creating or facilitating outstanding inventions that have made a tangible impact on quality of life, economic development, and the welfare of society."

Harry Atwater is the Howard Hughes Professor of Applied Physics and Materials Science as well as the director of the Department of Energy Joint Center for Artificial Photosynthesis (JCAP). His research focuses on photovoltaics and solar energy—he helped develop an artificial leaf as part of his work with JCAP—as well as plasmonics (oscillations of electrons on the surface of materials) and optical metamaterials (materials comprised of nanostructures). Atwater joined the Caltech faculty in 1988 and is a fellow of the Materials Research Society and member of U.S. National Academy of Engineering.

Mark Davis is the Warren and Katharine Schlinger Professor of Chemical Engineering and a member of the City of Hope Comprehensive Cancer Center and the UCLA Jonsson Comprehensive Cancer Center. Davis's research aims to synthesize catalytic materials called zeolites—crystalline solids made of silicon, aluminum, and oxygen and containing "micropores"—and biocompatible materials for the delivery of macromolecular therapeutics. Davis arrived at Caltech in 1991 and is a member of the National Academy of Sciences, the National Academy of Medicine and the National Academy of Engineering. In 2014, he received the Prince of Asturias Award for Technical and Scientific Research. Davis is the holder of more than 50 U.S. patents.

Ali Hajimiri is the Thomas G. Myers Professor of Electrical Engineering, the executive officer for Electrical Engineering, and director of Information Science and Technology. Hajimiri's research covers broad areas within high-speed and high-frequency electronics- and photonics-integrated circuits. This year, the Hajimiri group synthesized a 3-D camera—called a nanophotonic coherent imager—that provides the highest depth-measurement accuracy (similar to resolution) of any such nanophotonic 3-D imaging device. He joined the Caltech faculty in 1998 and holds 78 issued U.S. patents. Hajimiri is also a fellow of the Institute of Electrical and Electronics Engineers.

The 2015 fellows account for more than 5,300 issued U.S. patents. This year's fellows will be inducted on April 15, 2016, as part of the Fifth Annual Conference of the National Academy of Inventors at the United States Patent and Trademark Office in Virginia.

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15 for 2015: The Year in Research News at Caltech

The year 2015 proved to be another groundbreaking year for research at Caltech. From seeing quantum motion, to reconfiguring jellyfish limbs, to measuring stellar magnetic fields, researchers continued to ask and answer the deepest scientific questions.

In case you missed any of them, here are 15 stories highlighting a few of the discoveries, methods, and technologies that came to life at Caltech in 2015.

 

 

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15 for 2015: The Year in Research News at Caltech
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Here are 15 stories highlighting a few of the discoveries, methods, and technologies that came to life at Caltech in 2015.

Two Caltech Faculty Win ASME Medals

Kaushik Bhattacharya, Caltech's Howell N. Tyson, Sr., Professor of Mechanics and professor of materials science, has received the Warner T. Koiter Medal from the American Society of Mechanical Engineers (ASME), and Michael Ortiz, Frank and Ora Lee Marble Professor of Aeronautics and Mechanical Engineering, has received the society's Timoshenko Medal.

Established in 1996, the Warner T. Koiter Medal recognizes distinguished contributions to the field of solid mechanics. The award honors the late Warner T. Koiter, professor of applied mechanics at Delft University of Technology, for his fundamental work in nonlinear stability of structures, diligence in the effective application of these theories, international leadership in mechanics, and effectiveness as a teacher and researcher. This year, Bhattacharya, who is also the executive officer for mechanical and civil engineering in the Division of Engineering and Applied Science, received the medal "for the development of novel, rigorous, and predictive methods for the multi-scale behavior of modern engineering materials at scales ranging from the sub-atomic to the polycrystal, with special focus on multi-functional materials." Bhattacharya's research group studies the mechanical behavior of solids and uses theory to guide the development of new materials.

"Our challenge is not to shape the material to get the function we want, but how we create a specific material that already possesses the function we want. We are in fact merging both material and machine—and that is absolutely exciting!" says Bhattacharya.

The Timoshenko Medal, established in 1957, is given to recognize contributions to the field of applied mechanics. This award commemorates the late Stephen P. Timoshenko's contributions to applied mechanics as an author and a teacher. Timoshenko is often revered as the "father of mechanical applied mechanics" and worked at the Kiev Polytechnic Institute, St. Petersburg Polytechnic Institute, Ways of Communication Institute, University of Michigan, and Stanford University. Ortiz was honored "for his seminal, groundbreaking and remarkably creative contributions" that resulted in the creation of new methods and models for the field of solid mechanics.

Ortiz views his research as a "bridge between fundamental science and industry," focusing on real-world applications. His research group is interested in "understanding and modeling the behavior of materials and structures across length and time scales" and in "understanding the limits of usability of materials," according to his website.

"The recognition of one's peers is the sweetest thing of all in our line of business, and it is one of the main things that keep us going in our careers. To say that I am deeply moved and honored by this award is an understatement, I am actually tickled pink," says Ortiz.

Bhattacharya and Ortiz received the medals during the 2015 International Mechanical Engineering Congress and Exposition, held in Houston, Texas, in November.

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15 for 2015: The Year in Research News at Caltech

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Credit: K.Batygin/Caltech

New Research Suggests Solar System May Have Once Harbored Super-Earths

Thanks to recent surveys of exoplanets—planets in solar systems other than our own—we know that most planetary systems typically have one or more super-Earths (planets that are substantially more massive than Earth but less massive than Neptune) orbiting closer to their suns than Mercury does. In March, researchers showed that our own solar system may have once had these super-Earths, but they were destroyed by Jupiter's inward and outward migration through the solar system. This migration would have gravitationally flung small planetesimals through the solar system, setting off chains of collisions that would push any interior planets into the sun.
Credit: Lance Hayashida/Caltech and the Hoelz Laboratory/Caltech

Caltech Biochemists Shed Light on Cellular Mystery

The nuclear pore complex (NPC) is an intricate portal linking the cytoplasm of a cell to its nucleus. It is made up of many copies of about 34 different proteins. Around 2,000 NPCs are embedded in the nuclear envelope of a single human cell and each NPC shuttles hundreds of macromolecules of different shapes and sizes between the cytoplasm and nucleus. In February, Caltech biochemists determined the structure of a significant portion of the NPC called the outer rings; in August, the same group solved the structure of the pore's inner ring. Understanding the structure of the NPC could lead to new classes of cancer drugs as well as antiviral medicines.
Credit: iStockphoto

Research Suggests Brain's Melatonin May Trigger Sleep

For decades, supplemental melatonin has been sold over the counter as a sleep aid despite the absence of scientific evidence proving its effectiveness. Few studies have investigated melatonin produced naturally in the human body. This March, Caltech researchers studying zebrafish—animals that, like humans, are awake during the day and asleep at night—determined that the melatonin hormone does help the body fall asleep and stay asleep. Specifically, they found that zebrafish larvae that could not produce melatonin slept for only half as long as normal larvae.
Credit: Gregg Hallinan/Caltech

Advances in Radio Astronomy

In May, a new radio telescope array called the Owens Valley Long Wavelength Array (OV-LWA) saw its first light. Developed by a consortium led by Caltech, the OV-LWA has the ability to image simultaneously the entire sky at radio wavelengths with unmatched speed, helping astronomers to search for objects and phenomena that pulse, flicker, flare, or explode.

In July, Caltech researchers used both radio and optical telescopes to observe a brown dwarf located 20 light-years away and found that these so-called failed stars host powerful auroras near their magnetic poles.
Credit: Michael Abrams and Ty Basinger

Injured Jellyfish Seek to Regain Symmetry

Some kinds of animals can regrow lost limbs and body parts, but moon jellyfish have a different strategy. In June, Caltech researchers reported that the star-shaped eight-armed moon jellyfish rearranges itself when injured to maintain symmetry. It is hypothesized that the rearrangement helps to preserve the jellyfish's propulsion mechanism.
Credit: NASA/JPL-Caltech

Geologists Characterize Nepal Earthquake

In April, a magnitude 7.8 earthquake rocked Nepal. While the damage was extensive, it was not as severe as many geologists predicted. This year, a Caltech team of geologists used satellite radar imaging data and measurements from seismic instruments in Nepal to create models of fault rupture and ground movement. They found that the quake ruptured only a small fraction of the "locked" tectonic plate and that there is still the potential for the locked portion to produce a large earthquake.
Credit: Caltech/JPL

New Polymer Creates Safer Fuels

Plane crashes cause devastating damage, but this damage is often exacerbated by the highly explosive nature of jet fuel. This October, researchers at Caltech and JPL discovered a polymeric fuel additive that can reduce the intensity of postimpact explosions that occur during accidents and crashes. Preliminary results show that the additive can provide this benefit without adversely affecting fuel performance. The polymer works by inhibiting "misting"—the process that causes fuel to rapidly disperse and easily catch fire—under crash conditions.
Credit: Spencer Kellis/Caltech

Controlling a Robotic Arm with a Patient's Intentions

When you reach for a glass of water, you do not consciously think about moving your arm muscles or grasping with your fingers—you think about the goal of the movement. This May, by implanting neural prosthetic devices into the posterior parietal cortex (PCC)—the region of the brain that governs intentions for movement—rather than the motor cortex, which controls movement, Caltech researchers enabled a paralyzed patient to more smoothly and naturally control a prosthetic limb. In November, the researchers showed that there are individual neurons in the PPC that encode for entire hand shapes, such as those used for grasping or gesturing.

 

Caltech Scientists Develop Cool Process to Make Better Graphene

Graphene is an ultrastrong and conductive material made of a single layer of carbon atoms. While it is a promising material for scientific and engineering advances, manufacturing it on an industrially relevant scale has proven to be impractical, requiring temperatures of around 1,800 degrees Fahrenheit and long periods of time. A new technique invented at Caltech allows the speedy production of graphene—in just a few minutes—at room temperatures. The technique also produces graphene that is stronger, smoother, and more electrically conductive than normally produced synthetic graphene.
Credit: Rafael A. García (SAp CEA), Kyle Augustson (HAO), Jim Fuller (Caltech) & Gabriel Pérez (SMM, IAC), Photograph from AIA/SDO

Astronomers Peer Inside Stars, Finding Giant Magnets

Before this October, astronomers have only been able to study the magnetic fields of stars on the stellar surfaces. Now, using a technique called asteroseismology, scientists were able to probe the fusion-powered hearts of dozens of red giants (stars that are evolved versions of our sun) to calculate the magnetic field strengths inside those stars. They found that the internal magnetic fields of the red giants were as much as 10 million times stronger than Earth's magnetic field. Magnetic fields play a key role in the interior rotation rate of stars, which has a dramatic effect on how the stars evolve.
Credit: Chan Lei and Keith Schwab/Caltech

Seeing Quantum Motion

To the casual observer, an object at rest is just that—at rest, motionless. But on the subatomic scale, the object is most certainly in motion—quantum mechanical motion. Quantum motion, or noise, is ever-present in nature, and in August, Caltech researchers discovered how to observe and manipulate that motion in a small device. By creating what they called a "quantum squeezed state," they were able to periodically reduce the quantum fluctuations of the device. The ability to control quantum noise could one day be used to improve the precision of very sensitive measurements.
Credit: Ali Hajimiri/Caltech

New Camera Chip Provides Superfine 3-D Resolution

3-D printing can produce a wide array of objects in relatively little time, but first the printer needs to have a blueprint of what to print. The blueprints are provided by 3-D cameras, which scan objects and create models for the printer. Caltech researchers have now developed a 3-D camera that produces the highest depth-measurement accuracy of any similar device, allowing it to deliver replicas of an object to be 3-D printed within microns of similarity to the original object. In addition, the camera, known as a nanophotonic coherent imager, is inexpensive and small.
Credit: Image provided courtesy of Joint Center for Artificial Photosynthesis; artwork by Darius Siwek.

One Step Closer to Artificial Photosynthesis and 'Solar Fuels'

Plants are masters of photosynthesis—the process of turning carbon dioxide, sunlight, and water into oxygen and sugar. Inspired by this natural and energy-efficient process, Caltech researchers have created an "artificial leaf" that takes in CO2, sunlight, and water to produce hydrogen fuels. This solar-powered system, one researcher says, shatters all of the combined safety, performance, and stability records for artificial leaf technology by factors of 5 to 10 or more.
Credit: Santiago Lombeyda and Robin Betz

Potassium Salt Outperforms Precious Metals As a Catalyst

Rare precious metals have been the standard catalyst for the formation of carbon-silicon bonds, a process crucial to the synthesis of a host of products from new medicines to advanced materials. However, they are expensive, inefficient, and produce toxic waste byproducts. This February, Caltech researchers discovered a much more sustainable catalyst in the form of a simple potassium salt that is one of the most abundant metals on Earth and thousands of times less expensive than other commonly used catalysts. In addition, the potassium salt is much more effective at running challenging chemical reactions than state-of-the-art precious metal complexes.
Credit: Qi Zhao/National University of Singapore

Probing the Mysterious Perceptual World of Autism

The way in which people with autism spectrum disorder (ASD) perceive the world is unique. It has been a long-standing belief that people with ASD often miss facial cues, contributing to impaired social interaction. In a study published in October, Caltech researchers showed 700 images to 39 subjects and found that people with ASD pay closer attention to simple edges and patterns in images than to the faces of people. The study also found that subjects were strongly attracted to the center of images—regardless of what was placed there—and to differences in color and contrast rather than facial features. These findings may help doctors diagnose and more effectively treat the different forms of autism.
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The year 2015 proved to be another groundbreaking year for research at Caltech. From seeing quantum motion, to reconfiguring jellyfish limbs, to measuring stellar magnetic fields, researchers continued to ask and answer the deepest scientific questions.

In case you missed any of them, here are 15 stories highlighting a few of the discoveries, methods, and technologies that came to life at Caltech in 2015.

Written by Lori Dajose

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Popping Microbubbles Help Focus Light Inside the Body

A new technique developed at Caltech that uses gas-filled microbubbles for focusing light inside tissue could one day provide doctors with a minimally invasive way of destroying tumors with lasers, and lead to improved diagnostic medical imaging.

The primary challenge with focusing light inside the body is that biological tissue is optically opaque. Unlike transparent glass, the cells and proteins that make up tissue scatter and absorb light. "Our tissues behave very much like dense fog as far as light is concerned," says Changhuei Yang, professor of electrical engineering, bioengineering, and medical engineering. "Just like we cannot focus a car's headlight through fog, scientists have always had difficulty focusing light through tissues."

To get around this problem, Yang and his team turned to microbubbles, commonly used in medicine to enhance contrast in ultrasound imaging.

The gas-filled microbubbles are encapsulated by thin protein shells and have an acoustic refractive index—a property that affects how sound waves propagate through a medium—different from that of living tissue. As a result, they respond differently to sound waves. "You can use ultrasound to make microbubbles rapidly contract and expand, and this vibration helps distinguish them from surrounding tissue because it causes them to reflect sound waves more effectively than biological tissue," says Haowen Ruan, a postdoctoral scholar in Yang's lab.

In addition, the optical refractive index of microbubbles is not the same as that of biological tissue. The optical refractive index is a measure of how much light rays bend when transitioning from one medium (a liquid, for example) to another (a gas).

Yang, Ruan, and graduate student Mooseok Jang developed a novel technique called time-reversed ultrasound microbubble encoded (TRUME) optical focusing that utilizes the mismatch between the acoustic and optical refractive indexes of microbubbles and tissue to focus light inside the body. First, microbubbles injected into tissue are ruptured with ultrasound waves. By measuring the difference in light transmission before and after such an event, the Caltech researchers can modify the wavefront of a laser beam so that it is focuses on the original locations of the microbubbles. The result, Yang explains, "is as if you're searching for someone in a dark field, and suddenly the person lets off a flare. For a brief moment, the person is illuminated and you can home in on their location."

In a new study, published online November 24, 2015, in the journal Nature Communications, the team showed that their TRUME technique could be used as an effective "guidestar" to focus laser beams on specific locations in a biological tissue. A single, well-placed microbubble was enough to successfully focus the laser; multiple popping bubbles located within the general vicinity of a target functioned as a map for the light.

"Each popping event serves as a road map for the twisting light trajectories through the tissue," Yang says. "We can use that road map to shape light in such a way that it will converge where the bubbles burst."

If TRUME is shown to work effectively inside living tissue—without, for example, any negative effects from the bursting microbubbles—it could enable a range of research and medical applications. For example, by combining the microbubbles with an antibody probe engineered to seek out biomarkers associated with cancer, doctors could target and then destroy tumors deep inside the body or detect malignant growths much sooner.

"Ultrasound and X-ray techniques can only detect cancer after it forms a mass," Yang says. "But with optical focusing, you could catch cancerous cells while they are undergoing biochemical changes but before they undergo morphological changes."

The technique could take the place of other of diagnostic screening methods. For instance, it could be used to measure the concentrations of a protein called bilirubin in infants to determine their risk for jaundice. "Currently, this procedure requires a blood draw, but with TRUME, we could shine a light into an infant's body and look for the unique absorption signature of the bilirubin molecule," Ruan says.

In combination with existing techniques that allow scientists to activate individual neurons in lab animals using light, TRUME could help neuroscientists better understand how the brain works. "Currently, neuroscientists are confined to superficial layers of the brain," Yang says. "But our method of optical focusing could allow for a minimally invasive way of probing deeper regions of the brain."

The paper is entitled "Optical focusing inside scattering media with time-reversed ultrasound microbubble encoded (TRUME) light." Support for the research was provided by the National Institutes of Health, the National Institutes of Health BRAIN Initiative, and a GIST-Caltech Collaborative Research Proposal.

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A new technique could one day provide doctors with a minimally invasive way of destroying tumors with lasers, and lead to improved diagnostic medical imaging.

Two Caltech Faculty Inducted into the AAAS

Erik Winfree (PhD '98) and Jay R. Winkler (PhD '84) have been elected as Fellows of the American Association for the Advancement of Science (AAAS). Winfree, a professor of computer science, computation and neural systems, and bioengineering, was recognized by the AAAS for his "foundational contributions to biomolecular computing and molecular programming." Winkler is a faculty associate and lecturer in chemistry in the Division of Chemistry and Chemical Engineering, as well as the director of the Beckman Institute Laser Resource Center. He was elected for "distinguished contributions to the field of electron transfer chemistry and the development of its applications in biology, materials science, and solar energy."

Winfree's research with biological computing aims to "coax DNA into performing algorithmic tricks," he says. An algorithm is a collection of mechanistic rules—information—that directs the creation and organization of structure and behavior. In biology, information in DNA can be likened to an algorithm: it encodes instructions for biochemical networks, body plans, and brain architectures, and thus produces complex life. The Winfree group is developing molecular engineering methods that exploit the same principles as those used by biology: they study theoretical models of computation based on realistic molecular biochemistry, write software for molecular system design and analysis, and experimentally synthesize promising systems in the laboratory using DNA nanotechnology.

"We are seeking to create a kind of molecular programming language: a set of elementary components and methods for combining them into complex systems that involve self-assembled structures and dynamical behaviors," Winfree says. "DNA is capable of and can be rationally designed to perform a wide variety of tasks. We want to know if DNA is a sufficient building block for constructing arbitrarily complex and sophisticated molecular machines."

Winfree became an assistant professor at Caltech in 2000, an associate professor in 2006, and was named full professor in 2010. He was also named a MacArthur Fellow in 2000.

Winkler works on developing new methods for using laser spectroscopy to study chemical kinetics and the intermediate molecules that form during chemical reactions. In particular, his work involves experimental investigations of the factors that affect the rates of long-range electron-tunneling processes—the processes by which electrons are transported between atoms and molecules.

"Electron transfer reactions are fundamental processes in many chemical transformations, including electrochemical catalysis, solar energy conversion, and biological energy transduction," Winkler says. "In the Beckman Institute Laser Center, we have spent the past 25 years studying electron transfer reactions in small inorganic molecules and in metalloproteins"—proteins that contain metal atoms. "Our studies are aimed at experimentally elucidating the molecular factors that regulate the speed and efficiency of electron flow.

"I have been fortunate to work on these projects with many dedicated and talented students and postdoctoral scholars at Caltech. It is extremely gratifying to have this work recognized by the AAAS," he adds.

Following postdoctoral work at the Brookhaven National Laboratory, Winkler returned to Caltech as a Member of the Beckman Institute in 1990. He was first appointed as a lecturer in chemistry in 2002, and later a faculty associate in chemistry in 2008.

In addition to Winkler and Winfree, eight other Caltech alumni were named as AAAS Fellows: Edmund W. Bertschinger (BS '79), J. Edward Russo (BS '63), Mitchell Kronenberg (PhD '83), Donald P. Gaver III (BS '82), James W. Demmel II (BS '75), Jacqueline E. Dixon (PhD '92), Brian K. Lamb (PhD '78), and Shelly Sakiyama-Elbert (MS '98, PhD '00).

The AAAS is the world's largest general scientific society. This year, the AAAS awarded the distinction of Fellow to 347 of its members. New Fellows will be honored during the 2016 AAAS Annual Meeting in February.

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