Caltech Boasts Silver Medal Winners at the 34th International Physics Olympiad

PASADENA, Calif.—The California Institute of Technology adds two silver medals to its list of distinguished honors, won by freshmen Emily Russell and Yernur Rysmagambetov, at the 34th International Physics Olympiad in Taiwan.

In addition to her silver medal, Russell was named "Best Female Participant" in the physics competition.

Russell, who is from Yorktown Heights, New York, is majoring in physics at Caltech. She is the recent recipient of both a Lingle and an Axline scholarship.

Caltech freshman Rysmagambetov, who also earned a silver medal in the competition, is originally from Kazakhstan and plans to major in computer science while at Caltech.

Day one of the rigorous two-day competition was devoted to solving complex theoretical physics problems including "A Swing of a Falling Weight," "A Piezoelectric Crystal Resonator under an Alternating Voltage," and "Neutrino Mass and Neutron Decay." After a day of rest, the next competition day consisted of solving five-hour experimental problems utilizing laser beams or diodes, photodetectors, multimeters, and nematic liquid crystal.

At this year's International Physics Olympiad, 238 students from 54 countries participated. Originating in 1967 in Warsaw, this is the major international physics competition for secondary school students. Every year the competition is held in a different country around the world. Next year's 2004 competition will be held in July in Pohang, South Korea.

Contact: Deborah Williams-Hedges (626) 395-3227 debwms@caltech.edu

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A Detailed Map of Dark Matter in a Galactic Cluster Reveals How Giant Cosmic Structures Formed

Astrophysicists have had an exceedingly difficult time charting the mysterious stuff called dark matter that permeates the universe because it's--well--dark. Now, a unique "mass map" of a cluster of galaxies shows in unprecedented detail how dark matter is distributed with respect to the shining galaxies. The new comparison gives a convincing indication of how dark matter figures into the grand scheme of the cosmos.

Using a technique based on Einstein's theory of general relativity, an international group of astronomers led by Jean-Paul Kneib, Richard Ellis, and Tommaso Treu of the California Institute of Technology mapped the mass distribution of a gigantic cluster of galaxies about 4.5 billion light-years from Earth. They did this by studying the way the cluster bends the light from other galaxies behind it. This technique, known as gravitational lensing, allowed the researchers to infer the mass contribution of the dark matter, even though it is otherwise invisible.

Clusters of galaxies are the largest stable systems in the universe and ideal "laboratories" for studying the relationship between the distributions of dark and visible matter. Caltech's Fritz Zwicky realized in 1937 from studies of the motions of galaxies in the nearby Coma cluster that the visible component of a cluster--the stars in galaxies--represents only a tiny fraction of the total mass. About 80 to 85 percent of the matter is invisible.

In a campaign of over 120 hours of observations using the Hubble Space Telescope, the researchers surveyed a patch of sky almost as large as the full moon, which contained the cluster and thousands of more distant galaxies behind it. The distorted shapes of these distant systems were used to map the dark matter in the foreground cluster. The study achieved a new level of precision, not only for the center of the cluster, as has been done before for many systems, but also for the previously uncharted outlying regions.

The result is the most comprehensive study to date of the distribution of dark matter and its relationship to the shining galaxies. Signals were traced as far out as 15 million light-years from the cluster center, a much larger range than in previous investigations.

Many researchers have tried to perform these types of measurements with ground-based telescopes, but the technique relies heavily on measuring the exact shapes of distant galaxies behind the cluster, and for this the "surgeon's eye" of the Hubble Space Telescope is far superior.

The study, to be published soon in the Astrophysical Journal, reveals that the density of dark matter falls fairly sharply with distance from the cluster center, defining a limit to its distribution and hence the total mass of the cluster. The falloff in density with radius confirms a picture that has emerged from detailed computer simulations over the past years.

Team member Richard Ellis said, "Although theorists have predicted the distribution of dark matter in clusters from numerical simulations based on the effects of gravity, this is the first time we have convincing observations on large scales to back them up.

"Some astronomers had speculated clusters might contain large reservoirs of dark matter in their outermost regions," Ellis added. "Assuming our cluster is representative, this is not the case."

In finer detail, the team noticed that some structure emerged from their map of the dark matter. For example they found localized concentrations of dark matter associated with galaxies known to be slowly falling into the system. Overall there is a striking correspondence between features in the dark matter map and that delineated by the cluster galaxies, which is an important result in the new study.

"The close association of dark matter with structure in the galaxy distribution is convincing evidence that clusters like the one studied built up from the merging of smaller groups of galaxies, which were prevented from flying away by the gravitational pull of their dark matter," says Jean-Paul Kneib, who is the lead author in the publication.

Future investigations will extend this work using Hubble's new camera, the Advanced Camera for Surveys (ACS), which will be trained on a second cluster later this year. ACS is 10 times more efficient than the Wide Field and Planetary Camera 2, which was used for this investigation. With the new instrument, it will be possible to study clumps of finer mass in galaxy clusters in order to investigate how the clusters originally were assembled.

By tracing the distribution of dark matter in the most massive structure in the universe using the powerful trick of gravitational lensing, astronomers are making great progress towards a better understanding of how such systems were assembled, as well as toward defining the key role of dark matter.

In addition to Kneib, Ellis, and Treu, the other team members are Patrick Hudelot of the Observatoire Midi-Pyrénées in France, Graham P. Smith of Caltech, Phil Marshall of the Mullard Radio Observatory in England, Oliver Czoske of the Institut für Astrophysik und Extraterrestrische Forschung in Germany, Ian Smail of the University of Durham in England, and Priya Natarajan of Yale University.

For more information, please contact:

Jean-Paul Kneib Caltech/Observatoire Midi-Pyrénées (currently in Hawaii) Phone: (808) 881-3865 E-mail: jean-paul.kneib@ast.obs-mip.fr

Richard Ellis Caltech Phone: (626) 395-4970 (secretary) (Australia: Cellular: 011-44-7768-923277) E-mail: rse@astro.caltech.edu

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International Teams Set New Long-range Speed Record with Next-generation Internet Protocol

Scientists at the California Institute of Technology (Caltech) and the European Organization for Nuclear Research (CERN) have set a new Internet2 land speed record using the next-generation Internet protocol IPv6. The team sustained a single stream TCP rate of 983 megabits per second for more than one hour between the CERN facility in Geneva and Chicago, a distance of more than 7,000 kilometers. This is equivalent to transferring a full CD in 5.6 seconds.

The performance is remarkable because it overcomes two important challenges:

· IPv6 forwarding at Gigabit-per-second speeds · High-speed TCP performance across high bandwidth/latency networks.

This major step towards demonstrating how effectively IPv6 can be used should encourage scientists and engineers in many sectors of society to deploy the next-generation Internet protocol, the Caltech researchers say.

This latest record by Caltech and CERN is a further step in an ongoing research-and-development program to develop high-speed global networks as the foundation of next generation data-intensive grids. Caltech and CERN also hold the current Internet2 land speed record in the IPv4 class, where IPv4 is the traditional Internet protocol that carries 90 percent of the world's network traffic today. In collaboration with the Stanford Linear Accelerator Center (SLAC), Los Alamos National Laboratory, and the companies Cisco Systems, Level 3, and Intel, the team transferred one terabyte of data across 10,037 kilometers in less than one hour, from Sunnyvale, California, to Geneva, Switzerland. This corresponds to a sustained TCP rate of 2.38 gigabits per second for more than one hour.

Multi-gigabit-per-second IPv4 and IPv6 end-to-end network performance will lead to new research and business models. People will be able to form "virtual organizations" of planetary scale, sharing in a flexible way their collective computing and data resources. In particular, this is vital for projects on the frontiers of science and engineering, projects such as particle physics, astronomy, bioinformatics, global climate modeling, and seismology.

Harvey Newman, professor of physics at Caltech, said, "This is a major milestone towards our dynamic vision of globally distributed analysis in data-intensive, next-generation high-energy physics (HEP) experiments. Terabyte-scale data transfers on demand, by hundreds of small groups and thousands of scientists and students spread around the world, is a basic element of this vision; one that our recent records show is realistic. IPv6, with its increased address space and security features is vital for the future of global networks, and especially for organizations such as ours, where scientists from all world regions are building computing clusters on an increasing scale, and where we use computers including wireless laptop and mobile devices in all aspects of our daily work.

"In the future, the use of IPv6 will allow us to avoid network address translations (NAT) that tend to impede the use of video-advanced technologies for real-time collaboration," Newman added. "These developments also will empower the broader research community to use peer-to-peer and other advanced grid architectures in support of their computationally intensive scientific goals."

Olivier Martin, head of external networking at CERN and manager of the DataTAG project said, "These new records clearly demonstrate the maturity of IPv6 protocols and the availability of suitable off-the-shelf commercial products. They also establish the feasibility of transferring very large amounts of data using a single TCP/IP stream rather than multiple streams as has been customarily done until now by most researchers as a quick fix to TCP/IP's congestion avoidance algorithms. I am optimistic that the various research groups working on this issue will now quickly release new TCP/IP stacks having much better resilience to packet losses on long-distance multi-gigabit-per-second paths, thus allowing similar or even better records to be established across shared Internet backbones."

The team used the optical networking capabilities of the LHCnet, DataTAG, and StarLight and gratefully acknowledges support from the DataTAG project sponsored by the European Commission (EU Grant IST-2001-32459), the DOE Office of Science, High Energy and Nuclear Physics Division (DOE Grants DE-FG03-92-ER40701 and DE-FC02-01ER25459), and the National Science Foundation (Grants ANI 9730202, ANI-0230967, and PHY-0122557).

About the California Institute of Technology (Caltech):

With an outstanding faculty, including four Nobel laureates, and such off-campus facilities as Palomar Observatory, and the W. M. Keck Observatory, the California Institute of Technology is one of the world's major research centers. The Institute also conducts instruction in science and engineering for a student body of approximately 900 undergraduates and 1,000 graduate students who maintain a high level of scholarship and intellectual achievement. Caltech's 124-acre campus is situated in Pasadena, California, a city of 135,000 at the foot of the San Gabriel Mountains, approximately 30 miles inland from the Pacific Ocean and 10 miles northeast of the Los Angeles Civic Center. Caltech is an independent, privately supported university, and is not affiliated with either the University of California system or the California State Polytechnic universities. More information is available at http://www.caltech.edu.

About CERN:

CERN, the European Organization for Nuclear Research, has its headquarters in Geneva, Switzerland. At present, its member states are Austria, Belgium, Bulgaria, Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Italy, the Netherlands, Norway, Poland, Portugal, Slovakia, Spain, Sweden, Switzerland, and the United Kingdom. Israel, Japan, the Russian Federation, the United States of America, Turkey, the European Commission, and UNESCO have observer status. For more information, see http://www.cern.ch.

About the European Union DataTAG project:

The DataTAG is a project co-funded by the European Union, the U.S. Department of Energy, and the National Science Foundation. It is led by CERN together with four other partners. The project brings together the following European leading research agencies: Italy's Istituto Nazionale di Fisica Nucleare (INFN), France's Institut National de Recherche en Informatique et en Automatique (INRIA), the UK's Particle Physics and Astronomy Research Council (PPARC), and Holland's University of Amsterdam (UvA). The DataTAG project is very closely associated with the European Union DataGrid project, the largest grid project in Europe also led by CERN. For more information, see http://www.datatag.org.

 

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Astronomers "weigh" pulsar's planets

For the first time, the planets orbiting a pulsar have been "weighed" by measuring precisely variations in the time it takes them to complete an orbit, according to a team of astronomers from the California Institute of Technology and Pennsylvania State University.

Reporting at the summer meeting of the American Astronomical Society, Caltech postdoctoral researcher Maciej Konacki and Penn State astronomy professor Alex Wolszczan announced today that masses of two of the three known planets orbiting a rapidly spinning pulsar 1,500 light-years away in the constellation Virgo have been successfully measured. The planets are 4.3 and 3.0 times the mass of Earth, with an error of 5 percent.

The two measured planets are nearly in the same orbital plane. If the third planet is co-planar with the other two, it is about twice the mass of the moon. These results provide compelling evidence that the planets must have evolved from a disk of matter surrounding the pulsar, in a manner similar to that envisioned for planets around sun-like stars, the researchers say.

The three pulsar planets, with their orbits spaced in an almost exact proportion to the spacings between Mercury, Venus, and Earth, comprise a planetary system that is astonishingly similar in appearance to the inner solar system. They are clearly the precursors to any Earth-like planets that might be discovered around nearby sun-like stars by the future space interferometers such as the Space Interferometry Mission or the Terrestrial Planet Finder.

"Surprisingly, the planetary system around the pulsar 1257+12 resembles our own solar system more than any extrasolar planetary system discovered around a sun-like star," Konacki said. "This suggests that planet formation is more universal than anticipated."

The first planets orbiting a star other than the sun were discovered by Wolszczan and Frail around an old, rapidly spinning neutron star, PSR B1257+12, during a large search for pulsars conducted in 1990 with the giant, 305-meter Arecibo radio telescope. Neutron stars are often observable as radio pulsars, because they reveal themselves as sources of highly periodic, pulse-like bursts of radio emission. They are extremely compact and dense leftovers from supernova explosions that mark the deaths of massive, normal stars.

The exquisite precision of millisecond pulsars offers a unique opportunity to search for planets and even large asteroids orbiting the pulsar. This "pulsar timing" approach is analogous to the well-known Doppler effect so successfully used by optical astronomers to identify planets around nearby stars. Essentially, the orbiting object induces reflex motion to the pulsar which result in perturbing the arrival times of the pulses. However, just like the Doppler method, the pulsar timing method is sensitive to stellar motions along the line-of-sight, the pulsar timing can only detect pulse arrival time variations caused by a pulsar wobble along the same line. The consequence of this limitation is that one can only measure a projection of the planetary motion onto the line-of-sight and cannot determine the true size of the orbit.

Soon after the discovery of the planets around PSR 1257+12, astronomers realized that the heavier two must interact gravitationally in a measurable way, because of a near 3:2 commensurability of their 66.5- and 98.2-day orbital periods. As the magnitude and the exact pattern of perturbations resulting from this near-resonance condition depend on a mutual orientation of planetary orbits and on planet masses, one can, in principle, extract this information from precise timing observations.

Wolszczan showed the feasibility of this approach in 1994 by demonstrating the presence of the predicted perturbation effect in the timing of the planet pulsar. In fact, it was the first observation of such an effect beyond the solar system, in which resonances between planets and planetary satellites are commonly observed. In recent years, astronomers have also detected examples of gravitational interactions between giant planets around normal stars.

Konacki and Wolszczan applied the resonance-interaction technique to the microsecond-precision timing observations of PSR B1257+12 made between 1990 and 2003 with the giant Arecibo radio telescope. In a paper to appear in the Astrophysical Journal Letters, they demonstrate that the planetary perturbation signature detectable in the timing data is large enough to obtain surprisingly accurate estimates of the masses of the two planets orbiting the pulsar.

The measurements accomplished by Konacki and Wolszczan remove a possibility that the pulsar planets are much more massive, which would be the case if their orbits were oriented more "face-on" with respect to the sky. In fact, these results represent the first unambiguous identification of Earth-sized planets created from a protoplanetary disk beyond the solar system.

Wolszczan said, "This finding and the striking similarity of the appearance of the pulsar system to the inner solar system provide an important guideline for planning the future searches for Earth-like planets around nearby stars."

Contact: Robert Tindol (626) 395-3631

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Caltech Faculty Member Named Scientist of the Year

PASADENA, Calif. — The California Science Center has announced the joint selection of Andrew Lange and Saul Perlmutter as 2003 California Scientist of the Year.

Lange is Marvin L. Goldberger Professor of Physics at the California Institute of Technology in Pasadena, and Perlmutter is senior scientist and group leader at the Lawrence Berkeley National Laboratory in Berkeley. Using two very different techniques, Lange and Perlmutter's experimental efforts have confirmed a remarkable theory of how the universe expanded and evolved after the "big bang."

Lange and Perlmutter will be recognized during the annual presentation of the California Scientist of the Year and the Amgen Award for Science Teaching Excellence, a special event to honor excellence in scientific achievement and education, on May 8 at the California Science Center in Exposition Park, Los Angeles.

Lange is the 14th Caltech faculty member to be named Scientist of the Year.

The California Science Center established the California Scientist of the Year Award in recognition of the prominent role California plays in the areas of scientific and technological development. A blue-ribbon panel selects a nominee whose work is current and advances the boundaries of any field of science. Of those selected for California Scientist of the Year honors, 11 later became Nobel laureates. The panel concluded that Lange and Perlmutter's discoveries complement each other so well in revealing the nature of the universe that both scientists should be recognized this year.

According to the most widely held theory of cosmic evolution, the universe went though an inflationary phase during which its size rapidly increased and the universe's geometrical structure took on a very specific form: parallel lines never meet, and the sum of the angles inside an astronomically sized triangle add up to 180 degrees. Scientists refer to this particular form of geometry as being mathematically "flat." According to the general theory of relativity, a mathematically flat universe places constraints on the amount of mass and energy in the universe. Unfortunately, astronomers could not account for the requisite mass and energy. Therefore, either the standard cosmological or—"big bang"—theory was incorrect and the universe's geometrical structure was not that of Euclid, or the astronomers were missing something important.

Lange studies fluctuations in the cosmic microwave background (CMB) radiation, a relic of the primeval "fireball" that filled the early universe. These signals, which are visible today at microwave frequencies, provide a clear "snapshot" of the embryonic universe at an epoch long before the first stars or galaxies had formed. In general, this radiation reaches the earth uniformly from all directions in the sky. However, at the level of 0.003 percent there is an intricate pattern of fluctuations in the CMB. Using novel detectors developed at the Jet Propulsion Laboratory and flown on a balloon-borne telescope high above Antarctica, Lange's group was able to make the first resolved images of these very faint patterns. The images demonstrate that the radiation fluctuates on an angular scale of one degree, which is exactly what scientists expected from a mathematically flat universe. Since the 1930s, scientists have known that galaxies are moving away from one another, and there has been a concerted effort to study the rate of this expansion. Prior to Perlmutter's efforts, almost all astronomers expected that the expansion of the universe was slowing, due to the gravitational attraction of galaxies and other matter. However, Perlmutter's group found that the universe is actually expanding at an accelerating rate, as if a "negative pressure" were pushing everything apart. This negative pressure may be what scientists call the cosmological constant, first hypothesized by Albert Einstein in an attempt to prescribe a stable universe but later rejected by him. Perlmutter's estimates of the cosmological constant's magnitude are consistent with Lange's observations of a flat universe.

Lange's work demonstrates that the universe is mathematically flat, and that the standard cosmological theory is correct, while Perlmutter's work indicates that the source of astronomical energy giving rise to a flat universe comes from a type of negative gravitational pressure or dark energy permeating the universe. The nature of this dark energy remains a mystery.

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MEDIA CONTACT: Jill Perry, Media Relations Director (626) 395-3226 jperry@caltech.edu

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Caltech astrophysicist Shrinivas Kulkarni electedto National Academy of Sciences

Shrinivas Kulkarni, who is the MacArthur Professor of Astronomy and Planetary Science at the California Institute of Technology, has been elected to the National Academy of Sciences.

Kulkarni is a leading authority on exotic astrophysical phenomena such as gamma-ray bursts, brown dwarfs, and millisecond pulsars, and has been associated with many of the major advances in understanding the universe that have been made over the last decade.

In 1982, along with Don Backer of UC Berkeley, Kulkarni discovered the first millisecond pulsar. These pulsars have turned out to be very precise natural clocks with many applications. In 1995, Kulkarni led a group that discovered the first "brown dwarf." Hypothesized since the sixties, a brown dwarf is a "failed star," with a mass too low to shine brightly like our own sun but too high for it to be classified as a planet. Brown dwarfs are now considered to be quite abundant. In 1997, he and his colleagues demonstrated that gamma-ray bursts were extragalactic in origin, and Kulkarni has led many investigations since then that have further uncovered the nature of the phenomenon.

Kulkarni has been a prime mover in the quest to improve the resolution of optical instruments with a technique known as "interferometry," which exploits the wave nature of light in such a way that light from two or more mirrors can be combined for a superior image. Working in collaboration with Jet Propulsion Laboratory engineers, his research team used the testbed interferometer at Caltech's Palomar Observatory in 2000 to obtain the most precise distance to date for a Cepheid variable, a type of regularly pulsating star that has long been a standard of reference in the "cosmic yardstick" used to gauge astronomical distances.

Kulkarni is heavily involved in the Keck Interferometer and is the interdisciplinary scientist for NASA's ambitious Space Interferometry Mission (SIM), which is expected to be launched in 2009. With SIM, astronomers hope to measure and catalog planets around nearby stars.

A Pasadena resident, Kulkarni earned his master's degree in 1978 from the Indian Institute of Technology and his doctorate from UC Berkeley in 1983. He came to Caltech in 1985 as a research fellow, and received a faculty appointment in 1987. He is also a former Presidential Young Investigator and Sloan Research Fellow, and winner of the Waterman Prize.

Kulkarni joins 71 other prominent scientists this year as new members, bringing the total active membership to 1,922. Caltech currently has 67 other faculty members and three trustees who are members of the academy.

Contact: Robert Tindol (626) 395-3631

 

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Astronomers find new evidence aboutuniverse's heaviest phase of star formation

New distance measurements from faraway galaxies further strengthen the view that the strongest burst of star formation in the universe occurred about two billion years after the Big Bang.

Reporting in the April 17 issue of the journal Nature, California Institute of Technology astronomers Scott Chapman and Andrew Blain, along with their United Kingdom colleagues Ian Smail and Rob Ivison, provide the redshifts of 10 extremely distant galaxies which strongly suggest that the most luminous galaxies ever detected were produced over a rather short period of time. Astronomers have long known that certain galaxies can be seen about a billion years after the Big Bang, but a relatively recent discovery of a type of extremely luminous galaxy -- one that is very faint in visible light, but much brighter at longer wavelengths -- is the key to the new results.

This type of galaxy was first found in 1997 using a new and much more sensitive camera for observing at submillimeter wavelengths (longer than the wavelengths of visible light that allows us to see, but somewhat shorter than radio waves). The camera was attached to the James Clerk Maxwell Telescope (JCMT), on Mauna Kea in Hawaii.

Submillimeter radiation is produced by warm galactic "dust" -- micron-sized solid particles similar to diesel soot that are interspersed between the stars in galaxies. Based on their unusual spectra, experts have thought it possible that these "submillimeter galaxies" could be found even closer in time to the Big Bang.

Because the JCMT cannot see details of the sky that are as fine as details seen by telescopes operating at visible and radio wavelengths, and because the submillimeter galaxies are very faint, researchers have had a hard time determining the precise locations of the submillimeter galaxies and measuring their distances. Without an accurate distance, it is difficult to tell how much energy such galaxies produce; and with no idea of how powerful they are, it is uncertain how important such galaxies are in the universe.

The new results combine the work of several instruments, including the Very Large Array in New Mexico (the world's most sensitive radio telescope), and one of the 10-meter telescopes at the W. M. Keck Observatory on Mauna Kea, which are the world's largest optical telescopes. These instruments first pinpointed the position of the submillimeter galaxies, and then measured their distances. Today's article in Nature reports the first 10 distances obtained.

The Keck telescope found the faint spectral signature of radiation that is emitted, at a single ultraviolet wavelength of 0.1215 micrometers, by hydrogen gas excited by either a large number of hot, young stars or by the energy released as matter spirals into a black hole at the core of a galaxy. The radiation is detected at a longer, redder wavelength, having been Doppler shifted by the rapid expansion of the universe while the light has been traveling to Earth.

All 10 of the submillimeter galaxies that were detected emitted the light that we see today when the universe was less than half its present age. The most distant produced its light only two billion years after the Big Bang (12 billion years ago). Thus, the submillimeter galaxies are now confirmed to be the most luminous type of galaxies in the universe, several hundred times more luminous than our Milky Way, and 10 trillion times more luminous than the sun.

It is likely that the formation of such extreme objects had to wait for a certain size of a galaxy to grow from an initially almost uniform universe and to become enriched with carbon, silicon, and oxygen from the first stars. The time when the submillimeter galaxies shone brightly can also provide information about how the sizes and makeup of galaxies developed at earlier times.

By detecting these galaxies, the Caltech astronomers have provided an accurate census of the most extreme galaxies in the universe at the peak of their activity and witnessed the most dramatic period of star buildup yet seen in the Milky Way and nearby galaxies. Now that their distances are known accurately, other measurements can be made to investigate the details of their power source, and to find out what galaxies will result when their intense bursts of activity come to an end.

James Clerk Maxwell Telescope is at http://www.jach.hawaii.edu/JACpublic/JCMT The Very Large Array is at http://www.aoc.nrao.edu/vla/html. Keck Observatory is at http:/www.astro.caltech.edu/mirror/keck/index.html

Contact: Robert Tindol (626) 395-3631

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Discovery of giant planar Hall effect could herald a generation of "spintronics" devices

A basic discovery in magnetic semiconductors could result in a new generation of devices for sensors and memory applications -- and perhaps, ultimately, quantum computation -- physicists from the California Institute of Technology and the University of California at Santa Barbara have announced.

The new phenomenon, called the giant planar Hall effect, has to do with what happens when the spins of current-carrying electrons are manipulated. For several years scientists have been engaged in exploiting electron spin for the creation of a new generation of electronic devices --hence the term "spintronics" -- and the Caltech-UCSB breakthrough offers a new route to realizing such devices.

The term "spintronics" is used instead of "electronics" because the technology is based on a new paradigm, says Caltech physics professor Michael Roukes. Rather than merely using an electric current to make them work, spintronic devices will also rely on the magnetic orientation (or spin) of the electrons themselves. "In regular semiconductors, the spin freedom of the electrical current carriers does not play a role," says Roukes. "But in the magnetic semiconductors we've studied, the spin polarization -- that is, the magnetism -- of electrical current carriers is highly ordered. Consequently, it can act as an important factor in determining the current flow in the electrical devices."

In the naturally unpolarized state, there is no particular order between one electron's spin and its neighbor's. If the spins are aligned, the result can be a change in resistance to current flow.

Such changes in resistance have long been known for metals, but the current research is the first time that semiconductor material has been constructed in such a way that spin-charge interaction is manifested as a very dramatic change in resistivity. The Caltech-UCSB team managed to accomplish this by carefully preparing a ferromagnetic semiconductor material made of gallium manganese arsenide (GaMnAs). The widely-used current technology employs sandwiched magnetic metal structures used for magnetic storage.

"You have much more freedom with semiconductors than metals for two reasons," Roukes explains. "First, semiconductor material can be made compatible with the mainstream of semiconductor electronics; and second, there are certain phenomena in semiconductors that have no analogies in metals."

Practical applications of spintronics will likely include new paradigms in information storage, due to the superiority of such semiconductor materials to the currently available dynamic random access memory (or DRAM) chips. This is because the semiconductor spintronics would be "nonvolatile," meaning that once the spins were aligned, the system would be as robust as a metal bar that has been permanently magnetized.

The spintronics semiconductors could also conceivably be used in magnetic logic to replace transistors as switches in certain applications. In other words, spin alignment would be used as a logic gate for faster circuits with lower energy usage.

Finally, the technology could possibly be improved so that the quantum states of the spins themselves might be used for logic gates in future quantum computers. Several research teams have quantum logic gates, but the setup is the size of an entire laboratory, rather than at chip scale, and therefore still unsuitable for device integration. By contrast, a spintronics-based device might be constructed as a solid-state system that could be integrated into microchips.

A full description of the Caltech-UCSB team's work appeared in the March 14 issue of Physical Review Letters [Tang et al, Vol 90, 107201 (2003)]. The article is available by subscription, but the main site can be accessed at http://prl.aps.org/. This discovery is also featured in the "News and Views" section of the forthcoming issue of Nature Materials.

Contact: Robert Tindol (626) 395-3631

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Six Caltech Professors Awarded Sloan Research Fellowships

PASADENA, Calif.— Six Caltech professors recently received Alfred P. Sloan Research Fellowships for 2003.

The Caltech recipients in the field of chemistry are Paul David Asimow, assistant professor of geology and geochemistry, Linda C. Hsieh-Wilson, Jonas C. Peters, and Brian M. Stoltz, assistant professors of chemistry. In mathematics, a Sloan Fellowship was awarded to Danny Calegari, associate professor of mathematics, and in neuroscience, to Athanassios G. Siapas, assistant professor of computation and neural systems.

Each Sloan Fellow receives a grant of $40,000 for a two-year period. The grants of unrestricted funds are awarded to young researchers in the fields of physics, chemistry, computer science, mathematics, neuroscience, computational and evolutionary molecular biology, and economics. The grants are given to pursue diverse fields of inquiry and research, and to allow young scientists the freedom to establish their own independent research projects at a pivotal stage in their careers. The Sloan Fellows are selected on the basis of "their exceptional promise to contribute to the advancement of knowledge."

From over 500 nominees, a total of 117 young scientists and economists from 50 different colleges and universities in the United States and Canada, including Caltech's six, were selected to receive a Sloan Research Fellowship.

Twenty-eight former Sloan Fellows have received Nobel prizes.

"It is a terrific honor to receive this award and to be a part of such a tremendous tradition of excellence within the Sloan Foundation," said Stoltz. Asimow commented that he will use his Sloan Fellowship to "support further investigation into the presence of trace concentrations of water in the deep earth... I'm pleased because funds that are unattached to any particular grant are enormously useful for seeding new and high-risk projects that are not quite ready to turn into proposals." On his research, Peters said, "The Sloan award will provide invaluable seed money for work we've initiated in the past few months regarding nitrogen reduction using molecular iron systems."

The Alfred P. Sloan Research Fellowship program was established in 1955 by Alfred P. Sloan, Jr., who was the chief executive officer of General Motors for 23 years. Its objective is to encourage research by young scholars at a time in their careers when other support may be difficult to obtain. It is the oldest program of the Alfred P. Sloan Foundation and one of the oldest fellowship programs in the country.

Contact: Deborah Williams-Hedges (626) 395-3227 debwms@caltech.edu

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Quick action by astronomers worldwide leadsto new insights on mysterious gamma-ray bursts

Scientists "arriving quickly on the scene" of an October 4 gamma-ray burst have announced that their rapid accumulation of data has provided new insights about this exotic astrophysical phenomenon. The researchers have seen, for the first time, ongoing energizing of the burst afterglow for more than half an hour after the initial explosion.

The findings support the "collapsar" model, in which the core of a star 15 times more massive than the sun collapses into a black hole. The black hole's spin, or magnetic fields, may be acting like a slingshot, flinging material into the surrounding debris.

The prompt observation—and by far the most detailed to date—was made possible by several ground- and space-based observatories operating in tandem. The blast was initially detected by NASA's High-Energy Transient Explorer (HETE) satellite, and follow-up observations were quickly undertaken using ground-based robotic telescopes and fast-thinking researchers around the globe. The results are reported in the March 20 issue of the journal Nature.

"If a gamma-ray burst is the birth cry of a black hole, then the HETE satellite has just allowed us into the delivery room," said Derek Fox, a postdoctoral researcher at the California Institute of Technology and lead author of the Nature paper. Fox discovered the afterglow, or glowing embers of the burst, using the Oschin 48-inch telescope located at Caltech's Palomar Observatory.

Gamma-ray bursts shine hundreds of times brighter than a supernova, or as bright as a million trillion suns. The mysterious bursts are common, yet random and fleeting. The gamma-ray portion of a burst typically lasts from a few milliseconds to a couple of minutes. An afterglow, caused by shock waves from the explosion sweeping up matter and ramming it into the region around the burst, can linger for much longer, releasing energy in X rays, visible light, and radio waves. It is from the studies of such afterglows that astronomers can hope to learn more about the origins and nature of these extreme cosmic explosions.

This gamma-ray burst, called GRB021004, appeared on October 4, 2002, at 8:06 a.m. EDT. Seconds after HETE detected the burst, an e-mail providing accurate coordinates was sent to observatories around the world, including Caltech's Palomar Observatory. Fox pinpointed the afterglow shortly afterward from images captured by the Oschin Telescope within minutes of the burst, and notified the astronomical community through a rapid e-mail system operated by NASA for the follow-up studies of gamma-ray bursts. Then the race was on, as scientists in California, across the Pacific, Australia, Asia, and Europe employed more than 50 telescopes to zoom in on the afterglow before the approaching sunrise.

At about the same time, the afterglow was detected by the Automated Response Telescope (ART) in Japan, a 20-centimeter instrument located in Wako, a Tokyo suburb, and operated by the Japanese research institute RIKEN. The ART started observing the region a mere 193 seconds after the burst, but it took a few days for these essential observations to be properly analyzed and distributed to the astronomical community.

Analysis of these rapid observations produced a surprise: fluctuations in brightness, which scientists interpreted as the evidence for a continued injection of energy into the afterglow, well after the burst occurred. According to Shri Kulkarni, who is the McArthur Professor of Astronomy and Planetary Science at Caltech, the newly observed energizing of the burst afterglow indicates that the power must have been provided by whatever object produced the gamma-ray burst itself.

"This ongoing energy shows that the explosion is not a simple, one-time event, but that the central source lives for a longer time," said Kulkarni, a co-author of the Nature paper. "This is bringing us closer to a full understanding of these remarkable cosmic flashes."

Added Fox, "In the past we used to be impressed by the energy release in gamma-rays alone. These explosions appear to be more energetic than meets the eye."

Later radio observations undertaken at the Very Large Array in New Mexico and other radio telescopes, including Caltech's Owens Valley Radio Observatory and the IRAM millimeter telescope in France, lend further support to the idea that the explosions continued increasing in energy. "Whatever monster created this burst just refused to die quietly," said D. A. Frail, co-author and a staff astronomer at the Very Large Array.

Fox and his colleagues relied on data from the RIKEN telescope, in Japan, and from the Palomar Oschin Telescope and its Near Earth Asteroid Tracking (NEAT) camera, an instrument that has been roboticized and is currently managed by a team of astronomers at JPL led by Steven Pravdo. The collaboration of the Caltech astronomers and the NEAT team has proven extremely fruitful for the global astronomical community, helping to identify fully 25 percent of the afterglows discovered worldwide since Fox retrofitted the telescope software for this new task in the autumn of 2001.

HETE is the first satellite to provide and distribute accurate burst locations within seconds. The principal investigator for the HETE satellite is George Ricker of the Massachussetts Institute of Technology. HETE was built as a "mission of opportunity" under the NASA Explorer Program, a collaboration among U.S. universities, Los Alamos National Laboratory, and scientists and organizations in Brazil, France, India, Italy, and Japan.

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Contact: Robert Tindol (626) 395-3631

Writer: 
RT

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