Volume 2, Issue 13
Seeing Space
Most of us are enchanted by the twinkle of the stars in the night sky. For astronomers though, that twinkle represents a problem that has plagued stargazers since the days of Galileo. The twinkle of stars is caused by atmospheric distortion, air turbulence that warps the light waves as they travel to the Earth's surface. UC Berkeley astronomer James Graham is focused on fighting that distortion. Someday, his work could enable scientists to directly photograph planets orbiting distant stars.
A simulated image from the Gemini Extreme Adaptive Optics Coronagraph depicting a Jupiter-mass extrasolar planet in orbit around a solar-type star. The star is located behind an occulting spot. In hour-long exposures, the system will be 13 times more sensitive.
"For hundreds of years, terrestrial telescopes have been completely limited by the Earth's atmosphere," Graham says. "We're trying to overcome those limitations using modern technology to measure and correct the distortion of the atmosphere. That would allow the most grandiose telescopes to achieve their true potential."
For nearly a decade, Graham has aided several of the world's largest telescopes in adopting a technology called adaptive optics to boost their performance and limit atmospheric interference. The method works by measuring the distortion caused by the atmosphere and rapidly correcting for it by physically changing the shape of a deformable, or "rubber," mirror hundreds of times each second via an array of actuators. When used to its fullest potential, adaptive optics can dramatically improve the angular resolution, the minimum distance between distinguishable objects in the sky before they completely blur together. For example, the 10-meter Keck Observatory in Hawaii, fitted with adaptive optics in 1999, achieves angular resolution exceeding that of the Hubble Space Telescope at infrared wavelengths, Graham says.
At left, a star cluster in a nearby galaxy observed with the Hubble Space Telescope. At right is the same field imaged with adaptive optics at the Keck Observatory. The Keck provides far superior angular resolution. (Keck Observatory/James Graham & and Nate McCrady)
Already, Graham and his colleagues have used the tools they helped pioneer to do valuable science. Last year, Graham and graduate student Marshall D. Perrin employed the adaptive optics system of UC Berkeley's Lick Observatory and a camera Graham built to collect sharp images of faint stars thousands of miles away in the Milky Way. The adaptive optics system was augmented with an "artificial star" generated by a laser mounted on the telescope. The light from the artificial star aids the adaptive optics system in measuring the atmospheric turbulence so the rubber mirror can adjust accordingly. Those results were published in the journal Science.
There's always room for improvement though. According to Graham, today's adaptive optics systems make "modestly good" measurements of atmospheric distortion but still, something gets lost in the translation when the shape of the mirror is shifted in response.
"The corrections are somewhat crude," he says.
A sodium dye laser beam pierces the sky over Mt. Hamilton's Lick Observatory on July 22, 2003. The laser is the final piece of the laser guide star adaptive optics system that allows twinkle-free viewing of the entire nighttime sky. The beam, which reaches 60 miles into the upper atmosphere, is visible in scattered light for several kilometers. The yellowish cast of the dome is due to the street lights of nearby San Jose, Calif. (Marshall Perrin/UC Berkeley)
With increased speed and better resolution though, the telescopes should offer higher contrast. High contrast is key for astronomers to discern objects that may be near one another — planets orbiting stars, for example. Indeed, a star is often a billion times brighter and millions of times larger than the planet orbiting it. As a result, exosolar planets are far too small and faint to be seen against the star's glare. That's why planet hunters, like UC Berkeley's Geoff Marcy, make their discoveries indirectly, by detecting the wobble of the star caused by the planet's gravitational pull and then measuring the change in the wavelength of light coming from the star as the planet completes an orbit.
While a Jupiter-like planet might take a dozen years to orbit its parent star, a Neptune "clone" would have an orbital period of 160 years. According to Graham, advanced adaptive optics could enable astronomers to image and study extrasolar planets directly without waiting for the completion of an orbit.
To that end, Graham and Lawrence Livermore National Laboratory (LLNL) astrophysicist Bruce Macintosh are leading a large effort to build the Gemini Extreme Adaptive Optics Coronagraph, an adaptive optics system that would directly image distant planetary systems and help scientists understand the formation of stars and planets. The project is under the umbrella of the National Science Foundation-supported Center for Adaptive Optics, with members from UC Berkeley, LLNL, UC Santa Cruz, and the Jet Propulsion Laboratory, in collaboration with the Herzberg Institute of Astrophysics, the American Museum of Natural History, Université de Montréal, and UCLA. The planet-finder adaptive optics system is designed for the international Gemini Observatory consisting of two eight-meter telescopes, one on Mauna Kea in Hawaii and the other on Cerro Pachon, Chile.
An image of the star LkHalpha 198 taken at Lick Observatory in 2004 by Graham and his colleagues with the aid of a laser guide star system. At left, the star is seen through the adaptive optics system alone, and at right, through adaptive optics plus a polarimeter the researchers developed to separate unpolarized starlight from polarized scattered light cause by dust around the star. By viewing only the polarized component of the light, the polarimeter makes the dust envelope around the star more easily visible. (Marshall Perrin, James Graham/UC Berkeley)
The new system involves a novel method to control the deformable mirror. Current deformable mirrors are handmade, with each costing around $1,000 each. The Lick Observatory has just 127 actuators while Keck II is outfitted with 349. It takes several thousand actuators to achieve the fine-grain control necessary to see planets, Graham says. The Extreme Adaptive Optics system makes use of tiny micro-electromechanical systems (MEMS) actuatos. Fabricated inexpensively in bulk using processes similar to the way integrated circuits are manufactured, more than 4,000 of the MEMS actuators could be built right on the back of a deformable mirror. The technology is not unlike that found in modern desktop video projectors.
"Rather than starting off with a multi-million dollar price tag to build a telescope, MEMS enable you to do adaptive optics orders of magnitude more cheaply," Graham says.
Along with the MEMS actuators, the Extreme Adaptive Optics system will feature a state-of-the-art optical metrology system to measure the atmospheric interference and wave-front of the light with unprecedented accuracy. Meanwhile, a complex system of masks will limit the diffraction errors caused by reflecting the starlight.
The researchers have conducted multiple design studies and are expecting funding approval to begin building the device. The goal, Graham says, is to complete construction within four years and image the first planets shortly after the system is first switched on.
"The option is either to go into space and avoid the atmospheric distortion problem completely, or develop advanced adaptive optics like this so you can observe more from Earth," he says.
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Sweet Bioscience
UC Berkeley professor Carolyn Bertozzi keeps a close watch on carbohydrates, but it's not because she's on a trendy diet. In her chemistry laboratory, Bertozzi pays close attention to the carbohydrates that dot the surface of cells. These sugars decorating the cellular landscape are implicated in myriad biological processes, from intracellular communication to the growth of tumors. Bertozzi, a professor of chemistry and of biochemistry and molecular biology, and her graduate students have devised new chemical tools to uncover how the sugar structures change based on various factors. Someday, their research could aid doctors in diagnosing cancer and other diseases.
Carolyn Bertozzi, a researcher with the California Institute for Quantitative Biomedical Research (QB3), also studies tuberculosis to identify potential targets for drugs that would combat the disease. Bertozzi is also a professor of Molecular and Cellular Pharmacology at UC San Francisco. (LBNL photo)
"We work at the interface of chemistry and biology," says Bertozzi, a faculty scientist with Lawrence Berkeley National Laboratory (LBNL) and investigator with the Howard Hughes Medical Institute. "The chemical tools we develop allow us to probe these sugars to look at changes in their expression in different types of cells, both healthy and diseased."
A variety of sugars and sugar polymers (oligosaccharides and carbohydrates) are attached to the proteins and fats lodged in the cell wall. These sugars, collectively known as glycans, are involved in cell-cell interactions and infection by viruses, bacteria, and other diseases. As a result, their structure contains clues about the state of the cell itself. For example, glycans change during embryonic development and perhaps, Bertozzi says, even when stem cells differentiate.
While Bertozzi and her students have looked at the latter, they've made the most progress correlating certain glycan structures with cancer and other diseases. It's long been known that glycans harboring unnaturally high levels of sialic acid could indicate that the cell is cancerous. The trick though is observing the sugar structure and the glycosylation process, the addition of sugar molecules to proteins and other molecules. Only then, Bertozzi says, could physicians "look for signs in the sugar that something's wrong."
Last year, Bertozzi and her colleagues demonstrated a novel chemical reaction to "tag" the sugars on cells with tracer molecules called phosphines. The researchers used a live mouse "as a reaction vessel" without affecting the biology of the animal. By attaching a contrast agent or fluorescent dye to the phosphines, the surface sugars could then be seen using traditional medical imaging technology.
All cells decorate their surfaces with a variety of sugars and sugar polymers, called oligosaccharides. Carolyn Bertozzi attaches unnatural chemicals to simple sugars and feeds them to cells in order to get these chemicals onto the cell surface as part of the sugary landscape. (Bertozzi lab/UC Berkeley)
Bertozzi believes the highly-selective sugar tagging may result in fewer false-positives than current techniques to mark cells based on their metabolic activity. The researchers are currently developing tags that can be detected through positron emission spectroscopy (PET), single photon emission computed tomography (SPECT), and magnetic resonance imaging (MRI).
"Our hope is that we can use the reaction to target imaging probes to cells as a function of the cells' sugar patterns," Bertozzi says. "Visualizing glycosylation may be another way to look at a tumor."
As director of the Biological Nanostructures Facility of the Molecular Foundry at LBNL, Bertozzi is also exploring nanoscale materials with potential as biological probes. For example, the electrical properties of carbon nanotubes — tiny rolled-up crystalline sheets of carbon atoms — are highly sensitive to their environment. Someday, nanotubes might be introduced into the body to monitor the local conditions around a cell and whether it's responding to a particular analyte.
"When used in conjunction with existing imaging techniques, these tools may give us more reliable diagnostic capabilities," Bertozzi says. "It's always good to have options in your arsenal."
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Signaling Brain Cells
UC Berkeley neurobiologist Lu Chen believes that one of the best ways to learn about the brain is to build one of its key components. She and her colleagues are exploring how synapses form between neurons to make the circuits of the nervous system. Their approach is to identify the fewest ingredients necessary to create a synapse, mix them together in a "test tube" of non-neuronal cells, and let biology do the rest.
In 2004, Lu Chen was awarded a prestigious Packard Fellowship for Science and Engineering from the David and Lucile Packard Foundation.
"Our goal is to understand the molecular and cellular mechanisms of synaptogenesis, the formation of synapses," says Chen, associate professor in the Department of Molecular & Cell Biology, as well as a member of the Helen Wills Neuroscience Institute.
The basic unit of the nervous system is a neuron. The brain contains 100 billion of these nerve cells that are connected by 100 trillion synapses, junctions where the signal from one neuron is transmitted to its neighbor. The first neuron releases a chemical neurotransmitter that's converted into an electrical signal for propagation to the second neuron. The structure that releases the neurotransmitter across the synapse is known as a presynaptic cell while the receiving cell is postsynaptic.
The signals and proteins involved in the formation of the postsynaptic structure remain a mystery though. Historically, scientists have attempted to suss out the essential proteins for synapse formation by studying "knock out mice," rodents genetically engineered so that suspect proteins are not produced. The problem with that approach, Chen says, is that there's often redundancy in the system. If one protein isn't available, another may pick up the slack.
"Sometimes you can't identify a protein's function just by removing it," she says.
The left image shows a non-neuronal cell expressing neronal proteins (tagged to fluoresce green) forming a synapse with neuronal axons (stained red). The right panel shows synaptic responses recorded from a non-neuronal cell that expresses four neuronal proteins and receives input from neurons in the same culture. (courtesy the researchers)
That's why Chen takes the opposite approach. She essentially starts with nothing and builds a synapse from the bottom up.
"Rather than study a complicated system containing both pre- and postsynaptic structures, we replace one of the structures with a non-neuronal cell," she explains. "Then we can selectively add specific neuronal proteins into these 'clean' test-tubes and see how far we can get."
A synapse may contain hundreds of proteins, but only a few categories of them are involved in the postsynaptic assembly, Chen says. These include receptors for the neurotransmitters, scaffolding proteins--molecular links to connect receptors, signaling molecules, and the cell's structural support — and adhesion molecules that glue the pre- and postsynaptic structures together. The "glues" also serve to recruit the other proteins that combine together to form the synapse. The researchers added the proteins to non-neuronal cells and cultured them with neurons that are still actively seeking to form synapses. Axons extending from each neuron recognized the proteins in the non-neuronal cells and began to instruct the formation of a postsynaptic structure.
"We've shown that you can reproduce a synaptic response in non-neuronal cells," Chen says. "We're also looking at adding other proteins that can boost the process, increase the response, and stabilize the structure."
An image demonstrating that beta-neurexin, a "glue" protein (red), induces the accumulation of postsynaptic proteins (green) in contacting neuronal cells while other adhesion molecules (blue) do not have the same effect. (courtesy the researchers)
In recent months, Chen and graduate student Christine Nam removed the presynaptic axon from the stew. The aim was to identify the minimal signal an axon must send to induce the formation of a postsynaptic component.
"We knew that once the axon recognizes the proteins of a postsynaptic partner, something magical happens and the postsynaptic site starts to accumulate the necessary proteins to result in a fully-functional synapse," she says.
After plenty of informed trial-and-error, Chen and Nam determined that a single glue molecule and a chemical neurotransmitter are enough to get the postsynaptic assembly started. They published their results in the Proceedings of the National Academy of Sciences.
"In the next five to ten years we hope to test our knowledge of synapse function by building a rudimentary model system that actually works," Chen says.
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Berkeley's Scientific Legacy
Charles Townes and the Amazing Light
Charles Townes was married in 1941 to the former Frances H. Brown of Berlin, New Hampshire. They have four daughters--Linda, Ellen, Carla, and Holly. (BAP photos)
When UC Berkeley professor Charles H. Townes took his first physics course as an undergraduate in the early 1930s, he was fascinated by the "beautifully logical structure" of the discipline. That enchantment would lead Townes on a lifelong investigation into the very nature of reality and develop new tools to aid in the quest. In 1964, Townes shared the Nobel Prize in Physics for his role in the invention of the laser. On October 6-8, Townes's 90th birthday year will be celebrated with Amazing Light: Visions for Discovery, an international symposium at UC Berkeley where some of the greatest minds in physics and cosmology, including 18 Nobel Laureates, will explore the awe-inspiring challenges in twenty-first century science. A lifelong believer in the commonalities between science and religion, Townes received this year's $1.5 million Templeton Prize for Progress Toward Research or Discoveries About Spiritual Realities.
Townes was born in Greenville, South Carolina in 1915 and completed a B.S. in physics and B.A. in modern languages from Furman University. After earning his M.A. in physics from Duke University and his Ph.D. from the California Institute of Technology, Townes worked at Bell Telephone Laboratories during World War II designing radar bombing systems. Later, he began to apply what he had learned about microwaves during the wartime effort to spectroscopy, analyzing the composition of materials by looking at the light emitted.
In 1953 while on the faculty at Columbia University, he conceived of the MASER (Microwave Amplification by Stimulated Emission of Radiation), a device that produces a focused beam of energy in the microwave portion of the electromagnetic spectrum. Townes says the notion came to him in the form of a "revelation" while sitting on a park bench. Then, in 1958, Townes and his brother-in-law A. L. Schawlow, theoretically demonstrated the LASER (Light Amplification by Stimulated Emission of Radiation), essentially an optical MASER that produces an incredibly focused beam of light at a specific wavelength. The laser would quickly revolutionize a myriad of fields, from medicine to industry to telecommunications.
After several years as vice president and director of research at the Institute for Defense Analyses in Washington, DC, Townes joined the faculty at the Massachusetts Institute of Technology. He was awarded the Nobel Prize, with Nicolay Gennadiyevich Basov and Aleksandr Mikhailovich Prokhorov of the Lebedev Institute for Physics, Moscow, "for fundamental work in quantum electronics which has led to the construction of oscillators and amplifiers based on the maser-laser principle."
In 1967, Townes was appointed University Professor at the University of California. Based at UC Berkeley, his research continues, now focused on astrophysics. He is the recipient of dozens of prestigious awards, most recently the 2005 Templeton Prize, honoring the advancement of knowledge in spiritual matters.
"My own view is that, while science and religion may seem different, they have many similarities, and should interact and enlighten each other," Townes wrote in a statement accepting the prize. "Science tries to understand what our universe is like and how it works, including us humans. Religion is aimed at understanding the purpose and meaning of our universe, including our own lives. If the universe has a purpose or meaning, this must be reflected in its structure and functioning, and hence in science."
Honoring Townes's vision as a scientist, the upcoming symposium, Amazing Light: Visions for Discovery, will illuminate the creative edges of the experimental (observational) aspects of physics and cosmology on the path to new discoveries and the development of instruments that may transform human life.