Palomar Observes Broken Comet

PALOMAR MOUNTAIN, Calif.—Astronomers have recently been enjoying front-row seats to a spectacular cometary show. Comet 73P/Schwassmann-Wachmann 3 is in the act of splitting apart as it passes close to Earth. The breakup is providing a firsthand look at the death of a comet.

Eran Ofek of the California Institute of Technology and Bidushi Bhattacharya of Caltech's Spitzer Science Center have been observing the comet's tragic tale with the Palomar Observatory's 200-inch Hale Telescope. Their view is helping them and other scientists learn the secrets of comets and why they break up.

The comet was discovered by Arnold Schwassmann and Arno Arthur Wachmann 76 years ago and it broke into four fragments just a decade ago. It has since further split into dozens, if not hundreds, of pieces.

"We've learned that Schwassmann-Wachmann 3 presents a very dynamic system, with many smaller fragments than previously thought," says Bhattacharya. In all, 16 new fragments were discovered as a part of the Palomar observations.

A sequence of images showing the piece of the comet known as fragment R has been assembled into a movie. The movie shows the comet in the foreground against distant stars and galaxies, which appear to streak across the images. Because the comet was moving at a different rate across the sky than the stellar background, the telescope was tracking the comet's motion and not that of the stars. Fragment R and many smaller fragments of the comet are visible as nearly stationary objects in the movie.

"Seeing the many fragments was both an amazing and sobering experience," says a sleepy Eran Ofek, who has been working non-stop to produce these images and a movie of the comet's fragments.

The images used to produce the movie were taken over a period of about an hour and a half when the comet was approximately 17 million kilometers (10.6 million miles) from Earth. Astronomically speaking the comet is making a close approach to Earth this month giving astronomers their front-row seat to the comet's break up. Closest approach for any fragment of the comet occurs on May 12, when a fragment will be just 5.5 million miles from Earth. This is more than 20 times the distance to the moon. There is no chance that the comet will hit Earth.

"It is very impressive that a telescope built more than 50 years ago continues to contribute to forefront astrophysics, often working in tandem with the latest space missions and biggest ground-based facilities," remarks Shri Kulkarni, MacArthur Professor of Astronomy and Planetary Science and director of the Caltech Optical Observatories.

The Palomar observations were coordinated with observations acquired through the Spitzer Space Telescope, which imaged the comet's fragments in the infrared. The infrared images, combined with the visible-light images obtained using the Hale Telescope, will give astronomers a more complete understanding of the comet's break up.

Additional support for the observations and data analysis came from Caltech postdoc Arne Rau and grad student Alicia Soderberg.

Images of the comet and a time-lapse movie can be found at:

http://www.astro.caltech.edu/palomar/images/73p/

Contact:

Scott Kardel Palomar Public Affairs Director (760) 742-2111 wsk@astro.caltech.edu

Writer: 
RT

Biologists Uncover New Details of How Neural Crest Forms in the Early Embryonic Stages

PASADENA, Calif.—There's a time soon after conception when the stem cells in a tiny area of the embryo called the neural crest are working overtime to build such structures as the dorsal root ganglia, various neurons of the nervous system, and the bones and cartilage of the skull. If things go wrong at this stage, deformities such as cleft palates can occur.

In an article in this week's issue of Nature, a team of biologists from the California Institute of Technology announce that they have determined that neural crest precursors can be identified at surprisingly early stages of development. The work could lead to better understanding of molecular mechanisms in embryonic development that could, in turn, lead to therapeutic interventions when prenatal development goes wrong.

According to Marianne Bronner-Fraser, the Ruddock Professor of Biology at Caltech, the findings provide new information about how stem cells eventually form many and diverse cell types in humans and other vertebrates.

"We've always assumed that the precursor cells that form the neural crest arise at a time when the presumptive brain and spinal cord are first visible," she says. "But our work shows that these cells arise much earlier in development than previously thought, and well before overt signs of the other neural structures.

"We also show that a DNA binding protein called Pax7 is essential for formation of the neural crest, since removal of this protein results in absence of neural crest cells."

The work involves chicken embryos, which are especially amenable to the advanced imaging techniques utilized at Caltech's Biological Imaging Center. The results showed that interfering with the Pax7 protein also interfered with normal neural crest development.

"Because neural crest cells are a type of stem cell able to form cell types as diverse as neurons and pigment cells, understanding the molecular mechanisms underlying their formation may lead to therapeutic means of generating these precursors," Bronner-Fraser explains. "It may also help treat diseases of neural crest derivatives, like melanocytes, that can become cancerous in the form of melanoma."

The work was funded by the NIH and performed at Caltech by Martin Garcia-Castro, a former postdoctoral researcher who is currently an assistant professor at Yale University, and Martin Basch, a former Caltech graduate student who is currently a postdoctoral fellow at the House Ear Institute.

The paper appears in the May 11 issue of Nature. The title of the article is "Specification of the neural crest occurs during gastrulation and requires Pax7."

Writer: 
Robert Tindol
Writer: 

Aerospace Engineers and Biologists Solve Long-Standing Heart Development Mystery

PASADENA, Calif.—An engineer comparing the human adult heart and the embryo heart might never guess that the former developed from the latter. While the adult heart is a fist-shaped organ with chambers and valves, the embryo heart looks more like tube attached to smaller tubes. Physicians and researchers have assumed for years, in fact, that the embryonic heart pumps through peristaltic movements, much as material flows through the digestive system.

But new results in this week's issue of Science from an international team of biologists and engineers show that the embryonic vertebrate heart tube is indeed a dynamic suction pump. In other words, blood flows by a dynamic suction action (similar to the action of the mature left ventricle) that arises from wave motions in the tube. The findings could lead to new treatments of certain heart diseases that arise from congenital defects.

According to Mory Gharib, the Liepmann Professor of Aeronautics and Bioengineering at the California Institute of Technology, the new results show once and for all that "the embryonic heart doesn't work the way we were taught.

"The morphologies of embryonic and adult hearts look like two different engineers designed them separately," says Gharib, who has worked for years on the mechanical and dynamical nature of the heart. "This study allows you to think about the continuity of the pumping mechanism."

Scott Fraser, the Rosen Professor at Caltech and director of the MRI Center, adds that the study shows the promise of advanced biological imaging techniques for the future of medicine. "The reason this mechanism of pumping has not been noticed in the heart tube is because of the limitations of imaging," he says. "But now we have a device that is 100 times faster than the old microscopes, allowing us to see things that previously would have been a blur. Now we can see the motion of blood and the motions of vascular walls at very high resolutions."

The lead author of the paper is Gharib's graduate student Arian Forouhar. He and the other researchers used confocal microscopes in the Beckman Institute's biological imaging center on campus to do time-lapse photography of embryonic zebrafish. According to Fraser, embryonic zebrafish were chosen because they are essentially transparent, thus allowing for easy viewing, and since they develop completely in only a few days.

The time-lapse photography showed that peristalsis, an action similar to squeezing a tube of toothpaste, was not the pumping mechanism, but rather that valveless pumping known as "hydroelastic impedance pumping" takes place. In this model fewer active cells are required to sustain circulation.

Contraction of a small collection of myocytes, usually situated near the entrance of the heart tube, initiates a series of forward-traveling elastic waves that eventually reflect back after impinging on the end of the heart tube. At a specific range of contraction frequencies, these waves can constructively interact with the preceding reflected waves to generate an efficient dynamic-suction region at the outflow tract of the heart tube.

"Now there is a new paradigm that allows us to reconsider how embryonic cardiac mechanics may lead to anomalies in the adult heart, since impairment of diastolic suction is common in congestive heart-failure patients," says Gharib.

"The heart is one of the only things that makes itself while it's working," Fraser adds. "We often think of the heart as a thing the size of a fist, but it likely began forming its structures when it was a tiny tube with the diameter of a human hair."

"One of the most intriguing features of this model is that only a few contractile cells are necessary to provide mechanical stimuli that may guide later stages of heart development," says Forouhar. According to Gharib, this simplicity in construction will allow us to think of potential biomimicked mechanical counterparts for use in applications where delicate transport of blood, drugs, or other biological fluids are desired.

In addition to Forouhar, Gharib, and Fraser, the authors are Michael Liebling, a postdoctoral scholar in the Beckman Institute's biological imaging center; Anna Hickerson (BS '00; PhD '05) and Abbas Nasiraei Moghaddam, graduate students in bioengineering at Caltech; Huai-Jen Tsai of National Taiwan University's Institute of Molecular and Cellular Biology; Jay Hove of the University of Cincinnati's Genome Research Institute; and Mary Dickinson of the Baylor College of Medicine.

The article is titled "The Embryonic Vertebrate Heart Tube is a Dynamic Suction Pump," and appears in the May 5 issue of Science.

Writer: 
Robert Tindol
Writer: 

Letters and Symbols Originated Across Cultures to Mimic Natural Scenes, Study Says

PASADENA, Calif.—If a tree falls in the forest and a caveman sees it lying next to a standing tree, what does he do? New evidence suggests that he may proceed to invent the letter "L."

According to a new study in The American Naturalist, the shapes of letters and symbols used throughout history by the world's many cultures may have arisen to take advantage of the way human vision has evolved to see common structures and shapes in nature. Mark Changizi, a theoretical neurobiologist at the California Institute of Technology, says the evidence suggests that letters and symbols have their particular shapes because "these are what we are good at seeing."

In essence, this means that the letters of all writing systems-Chinese, Latin, Persian, as well as 97 other systems that have been used through the years-are visual repetitions of common sights, just as onomatopoeias such as 'bow wow" are aural repetitions of common sounds.

"Evolution has shaped our visual system to be good at seeing the structures we commonly encounter in nature, and culture has apparently selected our writing systems and visual signs to have these same shapes," says Changizi, the lead author of the paper.

Changizi says he got the initial insight for the hypothesis after reviewing the history of computer vision. Engineers have known for some time that the best way to create a system to allow for object recognition is to focus on the junctions of objects. In other words, a robot navigating a room sees the conglomeration of contours in a corner by its "Y" shape, and sees a wall because of its "L" junction with the floor.

"It struck me that these junctions are typically named with letters, such as 'L,' 'T,' 'Y,' 'K,' and 'X,' and that it may not be a coincidence that the shapes of these letters look like the things they really are in nature."

Changizi then proceeded to an ecological hypothesis of why the letters have their shapes, and decided to apply the basic contours of letters in various writing systems and symbols in symbolic systems to their basic topological contours. By this he means that a basic shape like an "L" can be turned into a "V," for example, and any other form that can be bent around so long as you don't cut the object.

He ended up with a catalog of 36 shapes employing two or three contours, and then ranked them according to how frequently they occur in the objects that primitive people would have seen millions of years ago, in pictures across many cultures that he took from National Geographic, and in computer-generated architectural forms.

It turns out that the common contours conglomerations are precisely those forms that frequently show up in the letters of various writing systems, as well as in company logos and in symbolic systems such as musical notations and the like. The forms not found as frequently in nature, by contrast, do not show up so often in writing systems or symbolic representations.

"We tested the hypothesis of whether cultures have selected visual signs and letter shapes to possess the shapes occurring in nature, and the answer is yes," Changizi says. "It's also striking that the systems that are intended to be seen have high correlations to natural forms. Company logos, for example, are meant to be recognized, and we found that logos have a high correlation. Shorthand systems, which are meant to give a note-taker speed at the expense of a commonly recognizable system of symbols, do not.

"So the figures we use in symbolic systems and writing systems seem to be selected because they are easy to see rather than easy to write," he concludes. "They're for the eye."

In addition to Changizi, the authors are Shinsuke Shimojo, a professor of biology at Caltech who specializes in psychobiology; and Qiong Zhang and Hao Ye, both undergraduate students at Caltech.

The title of the paper is "Structures of Letters and Symbols Throughout Human History Are Selected to Match Those Found in Objects in Natural Scenes." The paper is downloadable on the journal's webpage at http://www.journals.uchicago.edu/AN/journal/issues/v167n5/41010/41010.html.

Writer: 
Robert Tindol
Writer: 

Caltech Researchers Create New Proteins by Recombining the Pieces of Existing Proteins

PASADENA, Calif.—An ongoing challenge in biochemistry is getting a handle on protein folding-that is, the way that DNA sequences determine the unique structure and functions of proteins, which then act as "biology's workhorses." Gaining mastery over the construction of proteins will someday lead to breakthroughs in medicine and pharmaceuticals.

One method for studying the determinants of a protein's structure and function is to analyze numerous proteins with similar structure and function-a protein family-as a group. By studying families of natural proteins, researchers can tease out many of the fundamental interactions responsible for a given property.

A team of chemical engineers, chemists, and biochemists at the California Institute of Technology have now managed to create a large number of proteins that are very different in sequence yet retain similar structures. The scientists use computational tools to analyze protein structures and pinpoint locations at which they can break them apart and then reassemble them, like Lego pieces. Each new construction is a protein with new functions and new potential enzyme actions.

Reporting in the April 10 issue of the Public Library of Science Biology, Caltech graduate student Christopher Otey and his colleagues show that they have successfully taken three proteins from nature, broken them each into eight pieces, and successfully reconstructed the pieces to form many new proteins. According to Otey, the potential number of new proteins from just three proteins is three raised to the eighth power, or 6,561, assuming that each protein is divided into eight segments. "The result is an artificial protein family," Otey explains. "In this single experiment, we've been able to make about 3,000 new proteins."

About half of the 6,561 proteins are viable, having an average of about 72 sequence changes. "The benefit is that you can use the new proteins and new sequence information to learn new things about the original proteins," Otey adds. "For example, if a certain protein function depends on one amino acid that never changes, then the protein apparently must have that particular amino acid."

The proteins the team has been using are called cytochromes P450, which play critical roles in drug metabolism, hormone synthesis, and the biodegradation of many chemicals. Using computational techniques, the researchers predict how to break up this roughly 460-amino-acid protein into individual blocks of about 60 to 70 amino acids.

Otey says that this is an important result when considering the old-fashioned way of obtaining protein sequences. Whereas, over the past 40 years, researchers have fully determined 4,500 natural P450 sequences, the Caltech team required only a few months to create 3,000 additional new sequences.

"Our goal in the lab is to be able to create a bunch of proteins very quickly," Otey says, "but the overall benefit is an understanding of what makes a protein do what it does and potentially the production of new pharmaceuticals, new antibiotics, and such.

"During evolution, nature conserves protein structure, which we do with the computational tools, while changing protein sequence which can lead to proteins with new functions," he says. "And new functions can ultimately result in new treatments."

In addition to Otey, the other authors of the paper are Frances Arnold (the corresponding author), who is Dickinson Professor of Chemical Engineering and Biochemistry at Caltech, and Otey's supervising professor; Marco Landwehr, a postdoctoral scholar in biochemistry; Jeffrey B. Endelman, a recently graduated Caltech graduate student in bioengineering; Jesse Bloom, a graduate student in chemistry; and Kaori Hiraga, a Caltech postdoctoral scholar who is now at the New York State Department of Health.

The title of the article is "Structure-Guided Recombination Creates an Artificial Family of Cytochromes P450."

 

Writer: 
Robert Tindol
Writer: 
Exclude from News Hub: 
No

Fluid Mechanics Experts Come Up with New Test for Heart Disease

PASADENA, Calif.—Building on years of research on the way that blood flows through the heart valves, researchers from the California Institute of Technology and Oregon Health Science University have devised a new index for cardiac health based on a simple ultrasound test. The index is now ready for use, and provides a new diagnostic tool for cardiologists in searching for the very early signs of certain heart diseases.

In the April 18 issue of the journal Proceedings of the National Academy of Sciences (PNAS), the researchers show how ultrasound imaging can be used to create an extremely detailed picture of the jet of blood as it squirts through the cardiac left ventricle. Previous work by the Caltech team members has shown that there is an ideal length-to-diameter ratio for jets of fluid passing through valves, which means that any variation from this ratio is indicative of a heart that pumping in an abnormal manner.

According to Mory Gharib, Liepmann Professor of Aeronautics and Bioengineering at Caltech, the ideal stroke ratio for cardiac function is four. This means that the length of a jet of fluid is ideal in power efficiency if it is four times the diameter of the valve it is traveling through. Since pioneering the study of vortices in biological fluid transport, Gharib has worked at applying it to biomedical applications. The PNAS article presents the latest breakthrough.

"Vortex formation defines the optimal output of the heart," says Gharib. "The size and shape of the vortex is a diagnostic tool because the information can reveal whether a patient's heart is healthy or if there are problems that will lead to enlargement."

In vivo and in vitro images taken by the Caltech team and Oregon collaborators show that a healthy heart tends to form vortex rings in the blood as it passes through the left ventricle. If the valve is too large in diameter, the blood tends not to form strong vortices, and if it is too narrow, the heart has much less energy efficiency and must work harder in order to produce the effect of a healthy heart. In either case, the result of a non-optimal vortex formation is indicative of a malfunctioning heart.

The index that the researchers have created is a guide for cardiologists, who will be able to use a noninvasive ultrasound machine to image the heart, just as obstetricians use ultrasound devices to image developing fetuses. Thus, the technique can be used when the patient is at rest, unlike treadmill tests that can themselves pose a certain danger because they require patients to exert themselves.

"We're not saying that this technique replaces traditional diagnostic tools, but that it is another way of confirming if something is wrong," Gharib adds.

"We want to give people an earlier warning of disease with a new method that is non-invasive and relatively inexpensive," says John Dabiri, an assistant professor of aeronautics and bioengineering at Caltech and coauthor of the paper.

Continuing in vitro studies led by Arash Kheradvar, a medical doctor and graduate student in bioengineering at Caltech, are focused on correlating the new diagnostic index with specific symptoms of heart failure.

In addition to Gharib, the lead author, and Dabiri and Kheradvar, the authors are Edmond Rambod, a former postdoctoral researcher at Caltech, and David J. Sahn, a cardiologist at Oregon Health Science University.

The title of the PNAS paper is "Optimal vortex formation as an index of cardiac health."

 

Writer: 
Robert Tindol
Writer: 

Caltech Physicists and International MINOS Team Discover New Details of Why Neutrinos Disappear

PASADENA, Calif.—Physicists from the California Institute of Technology and an international collaboration of scientists at the Department of Energy's Fermi National Accelerator Laboratory have observed the disappearance of muon neutrinos traveling from the lab's site in Illinois to a particle detector in Minnesota. The observation is consistent with an effect known as neutrino oscillation, in which neutrinos change from one kind to another.

The Main Injector Neutrino Oscillation Search (MINOS) experiment at Fermilab's site in Batavia, Illinois, revealed a value of delta m^2 = 0.0031 eV^2, a quantity that plays a crucial role in neutrino oscillations and hence the role of neutrinos in the evolution of the universe.

The MINOS detector concept and design was originated by Caltech physicist Doug Michael. Caltech physicists also built half of the massive set of scintillator planes for the five-kiloton far detector. Michael led the formulation and pushed forward the program to increase the intensity of the proton beams that are the source of the neutrinos used by MINOS, leading to the present results.

"Only a year ago we launched the MINOS experiment," said Fermilab director Pier Oddone. "It is great to see that the experiment is already producing important results, shedding new light on the mysteries of the neutrino."

Nature provides for three types of neutrinos, yet scientists know very little about these "ghost particles," which can traverse the entire Earth without interacting with matter. But the abundance of neutrinos in the universe, produced by stars and nuclear processes, may explain how galaxies formed and why antimatter has disappeared. Ultimately, these elusive particles may explain the origin of the neutrons, protons and electrons that make up all the matter in the world around us.

"Using a man-made beam of neutrinos, MINOS is a great tool to study the properties of neutrinos in a laboratory-controlled environment," said Stanford University professor Stan Wojcicki, spokesperson of the experiment. "Our first result corroborates earlier observations of muon neutrino disappearance, made by the Japanese Super-Kamiokande and K2K experiments. Over the next few years, we will collect about 15 times more data, yielding more results with higher precision, paving the way to better understanding this phenomenon. Our current results already rival the Super-Kamiokande and K2K results in precision."

Neutrinos are hard to detect, and most of the neutrinos traveling the 450 miles from Fermilab to Soudan, Minnesota-straight through the earth, no tunnel needed-leave no signal in the MINOS detector. If neutrinos had no mass, the particles would not change as they traverse the earth and the MINOS detector in Soudan would have recorded 177 +/- 11 muon neutrinos. Instead, the MINOS collaboration found only 92 muon neutrino events-a clear observation of muon neutrino disappearance and hence neutrino mass.

The deficit as a function of energy is consistent with the hypothesis of neutrino oscillations, and yields a value of delta m^2, the square of the mass difference between two different types of neutrinos, equal to 0.0031 eV^2 +/- 0.0006 eV^2 (statistical uncertainty) +/- 0.0001 eV^2 (systematic uncertainty). In this scenario, muon neutrinos can transform into electron neutrinos or tau neutrinos, but alternative models-such as neutrino decay and extra dimensions-are not yet excluded. It will take the recording of much more data by the MINOS collaboration to test more precisely the exact nature of the disappearance process. Details of the current MINOS results were presented by David Petyt of the University of Minnesota at a special seminar at Fermilab on March 30. On Friday, March 31, the MINOS collaboration commemorated Michael, who was the MINOS co-spokesperson, at a memorial service at Fermilab. Michael died on December 25, 2005, at the age of 45 after a yearlong battle with cancer.

The MINOS experiment includes about 150 scientists, engineers, technical specialists, and students from 32 institutions in six countries, including Brazil, France, Greece, Russia, the United Kingdom, and the United States. The institutions include universities as well as national laboratories. The U.S. Department of Energy provides the major share of the funding, with additional funding from the U.S. National Science Foundation and from the United Kingdom's Particle Physics and Astronomy Research Council (PPARC).

"The MINOS experiment is a hugely important step in our quest to understand neutrinos-we have created neutrinos in the controlled environment of an accelerator and watched how they behave over very long distances," said Professor Keith Mason, CEO of PPARC. "This has told us that they are not totally massless as was once thought, and opens the way for a detailed study of their properties. U.K. scientists have taken key roles in developing the experiment and in exploiting the data from it, the results of which will shape the future of this branch of physics." The Fermilab side of the MINOS experiment consists of a beam line in a 4,000-foot-long tunnel pointing from Fermilab to Soudan. The tunnel holds the carbon target and beam focusing elements that generate the neutrinos from protons accelerated by Fermilab's main injector accelerator. A neutrino detector, the MINOS "near detector" located 350 feet below the surface of the Fermilab site, measures the composition and intensity of the neutrino beam as it leaves the lab. The Soudan side of the experiment features a huge 6,000-ton particle detector that measures the properties of the neutrinos after their 450-mile trip to northern Minnesota. The cavern housing the detector is located half a mile underground in a former iron mine.

The MINOS neutrino experiment follows a long tradition of studying neutrino properties originated at Caltech by physics professor (and former LIGO laboratory director) Barry Barish. Earlier measurements by the Monopole Astrophysics and Cosmic Ray Observatory (MACRO) experiment at the Gran Sasso laboratory in Italy, led by Barish, also showed evidence for the oscillation of neutrinos produced by the interactions of cosmic rays in the atmosphere.

The MINOS result also complemets results from the K2K long-baseline neutrino experiment in Japan. In 1999-2001 and 2003-2004, the K2K experiment in Japan sent neutrinos from an accelerator at the KEK laboratory in Tsukuba to a particle detector in Kamioka, a distance of about 150 miles. Compared to K2K, the MINOS experiment uses a three times longer distance, and the intensity and the energy of the MINOS neutrino beam are higher than those of the K2K beam. These advantages have enabled the MINOS experiment to observe in less than one year about three times more neutrinos than the K2K experiment did in about four years.

"It is a great gift for me to hear this news," said Yoji Totsuka, former spokesperson of the Super-Kamiokande experiment and now director general of KEK. "Neutrino oscillation was first established in 1998, with cosmic-ray data taken by Super-Kamiokande. The phenomenon was then corroborated by the K2K experiment with a neutrino beam from KEK. Now MINOS gives firm results in a totally independent experiment. I really congratulate their great effort to obtain the first result in such a short timescale."

According to Harvey Newman, a professor of physics at Caltech who now leads the MINOS group, the campus group has also had a key role in the research and development of the MINOS scintillators and optical fibers.

"Our Caltech group, then led by Michael, also had a key role in the research and development of the scintillators and optical fibers that led to MINOS having enough light to measure the muons that signal neutrino events.

"We are also working on the analysis of electron-neutrino events that could lead to a determination of the subdominant mixing between the first and third neutrino flavors, which is one of the next major steps in understanding the mysterious nature of neutrinos and their flavor-mixings. We are also leading the analysis of antineutrinos in the data, and the prospects for MINOS to determine the mixing of antineutrinos, where comparison of neutrinos and antineutrinos will test one of the most fundamental symmetries of nature (known as CPT).

"We are leading much of the R&D for the next generation, 25-kiloton detector called NOvA. Building on our experience in MINOS, we have designed the basic 50-foot-long liquid scintillator cell which contains a single 0.8 mm optical fiber to collect the light (there will be approximately 600,000 cells). We will measure and optimize the design this year in Lauritsen [a physics building on the Caltech campus], in time for the start of NOvA construction that will be completed by approximately 2010. We've also started prototype work on a future generation of megaton-scale detectors for neutrino and ultrahigh-energy cosmic rays. This has generated a lot of interest among Caltech undergraduates, who are now starting to contribute to these developments in the lab."

###

 

More information on the MINOS experiment: http://www-numi.fnal.gov/>http://www-numi.fnal.gov/

List of institutions collaborating on MINOS: http://www-numi.fnal.gov/collab/institut.html

The members of the Caltech MINOS group: Caius Howcroft, Harvey Newman, Juan "Pedro" Ochoa, Charles Peck, Jason Trevor, and Hai Zheng.

Writer: 
Robert Tindol
Writer: 

Researchers Determine How Plants Decide Where to Position Their Leaves and Flowers

PASADENA, Calif.—One of the quests of modern biologists is to understand how cells talk to each other in order to determine where to form major organs. An international team of biologists has solved a part of this puzzle by combining state-of-the-art imaging and mathematical modeling to reveal how plants go about positioning their leaves and flowers.

In the January 31 issue of the Proceedings of the National Academy of Sciences (PNAS), researchers from the California Institute of Technology, the University of California at Irvine, and Lund University in Sweden reported their success in determining how a plant hormone known as auxin affects plant organ positioning. Experts already knew that auxin played some role in the development of plant organs, but the new study employs imaging techniques and computer modeling to propose a new theory about how the mechanism works.

The research involves the growing tip of the shoot of the plant Arabidopsis thaliana, a relative of the mustard plant that has been studied intensely by modern biologists. With its simple and very well understood genome, Arabidopsis lends itself to a wide variety of experiments.

The achievement of the researchers is their demonstration of how plant cells, with purely local information about their nearest neighbors' internal concentration of auxin, can communicate to determine the position of new flowers or leaves, which form in a regular pattern, with many cells separating the newly formed primordia (the first traces of an organ or structure). The authors theorize that the template the plant uses to make the larger parts comes from two mechanisms: a polarized transport of auxin into a feedback loop and a dynamic geometry arising from the growth and division of cells.

To capture the development, Beadle Professor of Biology Elliot Meyerowitz, division chair of the biology division at Caltech, and his team used green fluorescent proteins to mark specific cell types in the plant's meristem, the plant tissue in which regulated cell division, pattern formation, and differentiation give rise to plant parts like leaves and flowers.

The marked proteins allowed the group to image the cell's lineages through meristem development and differentiation leading to specific arrangement of leaves and reproductive growth, and also to follow changes in the concentration and movement of auxin.

Although the study applies specifically to the Arabidopsis plant, Meyerowitz says the mechanism is probably similar for other plants and even other biological systems in which patterning occurs in the course of development.

In addition to Meyerowitz, the paper's authors are Henrik Jönsson of Lund University, Marcus G. Heisler of Caltech's Division of Biology, Bruce E. Shapiro of Caltech's Biological Network Modeling Center, and Eric Mjolsness of UC Irvine's Institute of Genomics and Bioinformatics and department of computer science.

 

Writer: 
Robert Tindol
Writer: 

Fault That Produced Largest Aftershock Ever Recorded Still Poses Threat to Sumatra

PASADENA, Calif.—A mere three months after the giant Sumatra-Andaman earthquake and tsunami of December 2004, tragedy struck again when another great earthquake shook the area just to the south, killing over 2,000 Indonesians. Although technically an aftershock of the 2004 event, the 8.7-magnitude Nias-Simeulue earthquake just over a year ago was itself one of the most powerful earthquakes ever recorded. Only six others have had greater magnitudes.

In the March 31 issue of the journal Science, a team of researchers led by Richard Briggs and Kerry Sieh of the California Institute of Technology reconstruct the fault rupture that caused the March 28, 2005, event from detailed measurements of ground displacements. Their analysis shows that the fault broke along a 400-kilometer length, and that the length of the break was limited by unstrained sections of the fault on either end.

The researchers continue to express concern that another section of the great fault, south of the 2005 rupture, is likely to cause a third great earthquake in the not-too-distant future. The surface deformation they observed in the 2005 rupture area may well be similar to what will occur when the section to the south ruptures.

Briggs, a postdoctoral scholar in Caltech's new Tectonics Observatory, and his colleagues determined the vertical displacements of the Sumatran islands that are directly over the deeply buried fault whose rupture generated the 2005 earthquake. The main technique they used was the examination of coral heads growing near the shore. The tops of these heads stay just at the waterline, so if they move higher or lower, it indicates that there has been uplift or subsidence.

The researchers also obtained data on ground displacements from GPS stations that they had rushed into place after the 2004 earthquake. "We were fortunate to have installed the geodetic instruments right above the part that broke," says Kerry Sieh, who leads the Sumatran project of Caltech's Tectonics Observatory. "This is the closest we've ever gotten to such a large earthquake with continuously recording GPS instruments."

From the coral and GPS measurements, the researchers found that the 2005 earthquake was associated with uplift of up to three meters over a 400-kilometer stretch of the Sunda megathrust, the giant fault where Southeast Asia is overriding the Indian and Australian plates. This stretch lies to the south of the 1600-kilometer section of the fault that ruptured in 2004.

Actual slippage on the megathrust surface (about 25 kilometers below the islands) was over 11 meters. The data permitted calculation of the earthquake's magnitude at 8.6, nearly the same as estimates based on seismological recordings.

Most of the deaths in the 2005 earthquake were the direct result of shaking and the collapse of buildings. The earthquake did not trigger a disastrous tsunami comparable to the one that followed the 2004 event. In part, this was because the 2005 rupture was smaller-about one-quarter the length and one-half the slip.

In addition, the largest uplift lay under offshore islands, where there was no water to be displaced. Finally, by rising during the earthquake, the islands gained some instant, extra protection for when the tsunami reached them tens of minutes later.

The scientists were surprised to find that the southern end of the 2004 rupture and the northern end of the 2005 rupture did not quite abut each other, but were separated by a short segment under the island of Simeulue on which the amount of slip was nearly zero. They infer that this segment had not accumulated enough strain to rupture during either event-perhaps, they speculate, because it slips frequently and therefore relieves strain without generating large earthquakes.

Thus, this segment might act as a barrier to rupture propagation. A similar 170-kilometer "creeping" section of the San Andreas fault, between San Francisco and Los Angeles, separates the long section that produced Northern California's great 1906 earthquake from the long section that ruptured during Southern California's great 1857 earthquake.

The southern end of the 2005 rupture was at another short "creeping" segment or weak patch. "Both ends of the 2005 rupture seem to have been at the edges of a weak patch," Sieh explains. The 2005 event therefore probably represents a "characteristic earthquake" that has recurred often over geological time. In fact, old historical records suggest that a very similar earthquake was caused by a rupture of this segment in 1861.

Sieh suggests that installation of GPS instruments along the world's other subduction megathrusts could help more clearly to define those sections that creep stably versus the segments that are locked and thus more likely to break in infrequent, but potentially devastating, ruptures.

Previous work by the Caltech group and their Indonesian colleagues has shown that south of the southern creeping segment lies another locked segment, about 600 kilometers long, which has not broken since a magnitude 9.0 earthquake in 1833. Corals and coastlines along the southern segment record decades of continual, pronounced subsidence, similar to the behavior of the northern region prior to its abrupt uplift during the 2005 fault rupture.

"This southern part is very likely about ready to go again," Sieh says. "It could devastate the coastal communities of southwestern Sumatra, including the cities of Padang and Bengkulu, with a combined population of well over a million people. It could happen tomorrow, or it could happen 30 years from now, but I'd be surprised if it were delayed much beyond that."

Sieh and his colleagues are engaged in efforts to increase public awareness and preparedness for future great earthquakes and tsunamis in Sumatra.

The Science paper is titled "Deformation and slip along the Sunda megathrust in the great 2005 Nias-Simeulue earthquake." The other authors are Aron Meltzner, John Galetzka, Ya-ju Hsu, Mark Simons, and Jean-Philippe Avouac, all at Caltech's Tectonics Observatory; Danny Natawidjaja, Bambang Suwargadi, Nugroho Hananto, and Dudi Prayudi, all at the Indonesian Institute of Sciences; Imam Suprihanto of Jakarta; and Linette Prawirodirdjo and Yehuda Bock at the Scripps Institution of Oceanography.

The research was funded by the Gordon and Betty Moore Foundation, the National Science Foundation, and NASA.

Writer: 
Robert Tindol
Writer: 

Neuroscientists Discover the Neurons That Act As Novelty Detectors in the Human Brain

PASADENA, Calif.—By studying epileptic patients awaiting brain surgery, neuroscientists for the first time have located single neurons that are involved in recognizing whether a stimulus is new or old. The discovery demonstrates that the human brain not only has neurons for processing new information never seen before, but also neurons to recognize old information that has been seen just once.

In the March 16 issue of the journal Neuron, researchers from the California Institute of Technology, the Howard Hughes Medical Institute, and the Huntington Memorial Hospital report their success in distinguishing single-trial learning events from novel stimuli in six patients awaiting surgery for drug-resistant epileptic seizures. As part of the preparation for surgery, the patients have had electrodes implanted in their medial temporal lobes. Inserting small additional wires inside the clinical electrodes provides a way for researchers to observe the firing of individual human brain cells.

According to lead author Ueli Rutishauser, a graduate student in the computation and neural systems program at Caltech, the neurons are located in the hippocampus and amygdala, two limbic brain structures located deeply in the brain. Both regions are known to be important for learning and memory, but neuroscientists had never been able to establish the role of individual brain cells during single-trial learning until now.

"This is an unprecedented look at single-trial learning," explains Rutishauser, who works in the lab of Erin Schuman, a Caltech professor of biology and senior author of the paper. "It shows that single-trial learning is observable at the single-cell level. We've suspected it for a long time, but it has proven difficult to conduct these experiments with laboratory animals because you can't ask the animal whether it has seen something only once—500 times, yes, but not once."

With the patients volunteering to do perceptual studies while their brain activity is being recorded, however, such experiments are entirely possible. For the study, the researchers showed the six volunteers 12 different visual images, each presented once and randomly in one of four quadrants on a computer screen. Each subject was instructed to remember both the identity and position of the image or images presented.

After a 30-minute or 24-hour delay, each subject was shown previously viewed images or new images presented at the center of the screen, and asked whether each image was new or old. For each image identified as familiar, the subject was also asked to identify the quadrant in which the stimulus was originally presented.

The six subjects correctly recognized nearly 90 percent of the images they had already seen, but were less able to correctly recall the quadrant location in which the images had originally appeared. The researchers identified individual neurons that increased their firing rate either for novel stimuli or for familiar stimuli, but not both. These neurons thus responded differently to the same stimulus, depending on whether it was seen the first or the second time.

The fact that certain individual neurons of patients can be shown to fire only for recognition of something seen before, in fact, demonstrates that there is a "familiarity detector" neuron that explains why a person can have a feeling he or she has seen a face sometime in the past. Further, these neurons continue to fire and signal the familiarity of a stimulus, even when the subject mistakenly reports that the stimulus is new.

This type of neuron can account for subconscious recollections. "Even if the patients think they haven't seen the stimulus, their neurons still indicate that they have," Rutishauser says.

The third author of the paper is Adam Mamelak, who is a neurosurgeon at the Huntington Memorial Hospital and the Maxine Dunitz Neurosurgical Institute at Cedars-Sinai Medical Center.

Schuman is professor of biology and executive officer for neurobiology at Caltech and an investigator with the Howard Hughes Medical Institute.

 

Writer: 
Robert Tindol
Writer: 

Pages