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Macroscopic Bilaterian Animals, 555 Million Years Ago
Posted: Monday, September 30, 2002
Source: University Of California - Riverside (http://www.ucr.edu/)
Dating Our Ancestors: Study Suggests Macroscopic Bilaterian Animals Did Not Appear Until 555 Million Years Ago
RIVERSIDE, Calif. -- The traces left behind by ancient animals may hold the key to determining when macroscopic bilaterians -- animals that are symmetric about a central axis, with a body divided into equivalent right and left halves, and with an anterior-posterior polarity (e.g., this includes worms, ants, and ranging up to humans) -- first appeared. A team led by Dr. Mary Droser, professor of geology at the University of California, Riverside, studied "trace" fossils, e.g., burrows, trails and tracks left behind by the earliest bilaterian animals. Results from their study suggest that bilaterian animals did not appear until approximately 555 million years ago.
The authors published their findings in a paper entitled "Trace fossils and substrates of the terminal Proterozoic-Cambrian transition: Implications for the record of early bilaterians and sediment mixing" in the Proceedings of the National Academy of Sciences (PNAS). They report that these trace fossils, found in many different locations around the world, were preserved very well in sediment beds from the Early Cambrian (544 to 510 million years ago), both in terms of quality of detail and in preserving traces made close to this sediment-water interface. Trace fossils can shed light on an organism's behavioral activity.
"The timing of the appearance of bilaterian animals, while clearly by 555 million years ago, is the subject of some debate," said Droser. "One of the most important pieces of evidence for early animals is the record of trace fossils. That is, animal burrows, tracks and trails preserved in the rock record. Based on evidence from functional morphology, many of the features that define bilaterians could only have originated in a relatively large animal that inhabited the seafloor and thus produced trace fossils. Early bilaterians, in particular, were soft-bodied and thus difficult to preserve."
The trace fossils examined in the study are from the transition between the Proterozoic Era (2.5 billion to 544 million years ago), where few animal body fossils are found, and the Cambrian (544 to 490 million years ago), where diverse animal body fossils such as trilobites are found. Proterozoic trace fossils, typically only a few millimeters wide, are found at the interface between water and sediment. The Cambrian trace fossils are more diverse in size, shape and depth of penetration into the sediment.
The researchers examined and did field work on thousands of meters of rock. "We collected samples from Australia, Newfoundland, the western United States, Scandinavia and Namibia," said Soren Jensen, co-author of the PNAS paper and a postdoctoral researcher in the department of earth sciences at UC Riverside. "These samples of ancient marine rocks were then carefully inspected, x-rayed, and thin-sectioned for microscopic examination to provide us with an even closer look."
The authors attribute the exceptional preservation of Early Cambrian trace fossils to the low levels of sediment mixing, which resulted in relatively firm substrates less prone to resuspension. Close inspection of these fossils could help determine exactly when bilaterian animals emerged, a topic of much controversy.
"There have been reports of trace fossils as old as 1 billion years old," said Droser. "But these records are scarce and, on critical examination, are not convincing. On examining the trace fossil record from 565 million years ago through until 535 million years ago, we found that the substrate conditions -- for example, the bottom of the ocean -- were such that if animals were burrowing or walking or crawling along the seafloor, their traces would have likely been preserved. We see a gradual increase in diversity and complexity of trace fossils from about 555 million years ago, known as the Cambrian Explosion and which likely reflects the appearance of bilaterians. We found no evidence for a long history of large animals before this time."
Editor's Note: The original news release can be found here
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Posted: Thursday, September 26, 2002
Source: Georgetown University Medical Center (http://gumc.georgetown.edu/)
Two new studies by faculty at Georgetown University Medical Center and colleagues shed new light on the brain mechanisms underlying conscious awareness. The studies are published in the current issue of the journal Neurology. "Despite many advances in our understanding of the brain, the mechanisms of conscious awareness are still poorly understood," said Kimford J. Meador, MD, professor and chair of neurology at Georgetown University Medical Center and the senior author of both articles. "As our understanding of the processes underlying conciousness advances, so will our ability to help patients suffering from a variety of neural impairments."
The first article, "Gamma coherence and conscious perception," adds to the growing body of knowledge about the role of brain waves, or electrical pulses in the brain. Gamma waves are fast electrical waves that have been hypothesized to be involved in conscious perception. However, scientists still do not fully understand their role.
In this study, researchers looked at electrical activity from a grid of electrodes implanted in the brains of six patients who were undergoing surgery to treat their epileptic seizures. The implantation was part of a medical procedure that is routinely conducted before brain surgery in some patients to determine the precise location in the brain causing the seizures.
While the electrodes were implanted, researchers used this opportunity to study how the patients' brains responded to a painless stimulus to one of their fingers. Although the patients were conscious each time they received the stimulus, they did not always notice it, even though the stimuli were identical. The initial electrical response of the brain was similar for both the perceived and non-perceived stimuli, but only the perceived stimuli were associated with synchronized gamma waves in the hand sensory region. The results suggest that synchronized fast neural activity in the sensory area may be necessary to perceive simple stimuli.
The second study, "Pathophysiology of altered consciousness during seizures," used single-photon computed tomography (SPECT) scans to show blood flow changes in the brain when patients with epilepsy lost consciousness during seizures. It involved 71 patients with epilepsy who received the SPECT scans while having seizures, or very shortly after the seizures, as part of a diagnostic evaluation, to determine the parts of their brains affected during seizures. The researchers looked particularly at the thalamus, a walnut-sized mass located deep within the brain, and the midbrain which is a region just below the thalamus. Previous studies have shown that the thalamus and midbrain play an important role in consciousness, but it was unclear how focal seizures impair consciousness.
Of the 49 patients who experienced complete loss of consciousness during seizures, 92% showed an increased blood flow to the thalamus or midbrain on their SPECT scans. Eight of the nine patients who experienced no loss of consciousness during their seizures also had no increased blood flow to the thalamus or midbrain.
"These findings are consistent with a role for the thalamus and upper brainstem in conscious mechanisms," the authors wrote. Impaired consciousness from seizures adversely impacts the quality of life of patients with epilepsy. It appears that distant effects or actual spread of the seizure to the thalamus or midbrain produces loss of awareness in patients with epilepsy. Techniques that block this effect on the thalamus/midbrain would likely benefit patients with epilepsy.
This research was funded by the Medical College of Georgia Research Foundation, and was conducted at the Medical College of Georgia, where the senior author was a faculty member before coming to Georgetown. Part of these findings were presented at the 2001 annual meeting of the American Academy of Neurology in Philadelphia.
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Mystery Object Orbits Earth Posted: Friday, September 20, 2002
science.nasa.gov
Something odd is circling our planet. It's small, perhaps only 60-ft long, and rotates once every minute or so. Bill Yeung, an amateur astronomer in California, first spotted the 16th magnitude speck of light on Sept. 3rd in the constellation Pisces. He named it J002E3.
Automated asteroid surveys scan the skies every few weeks, yet there was no sign of Yeung's object earlier this year. "It must have entered Earth orbit recently," says Paul Chodas of NASA's Near-Earth Object Program at JPL. "But it doesn't match any recently-launched spacecraft."
In other words, it's a mystery. MORE
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A Shocking Space Movie Posted: Thursday, September 19, 2002
Astronomers have captured extraordinary footage of a Manhattan-sized star rotating and spewing antimatter jets into space.
Just when it seemed the summer movie season had ended, two of NASA's Great Observatories have produced their own action movie. Multiple observations made over several months with the Chandra X-ray Observatory and the Hubble Space Telescope captured the spectacle of matter and antimatter propelled to nearly the speed of light by the Crab pulsar, a rapidly rotating neutron star the size of Manhattan. MORE
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"Runaway Universe" May Collapse In 10 Billion Years Posted: Tuesday, September 17, 2002
Source: Stanford University (http://www.stanford.edu/)
The recent discovery that the universe is expanding at an ever-increasing rate has led many astronomers to forecast a dark and lonely future for our galaxy. According to some predictions, the rapidly accelerating universe will cause all galaxies to run away from each other until they are no longer visible. In this widely accepted scenario, our own Milky Way will become an isolated island adrift in a sea of totally black space 150 billion years from now.
But two new studies by Stanford University cosmologists suggest that it may be time to rethink this popular view of a "runaway universe." Instead of expanding exponentially, our cosmos may be in danger of collapsing in a "mere" 10 to 20 billion years, according to the Stanford team.
"The standard vision at the moment is that the universe is speeding up," said physics Professor Andrei Linde, "so we were surprised to find that a collapse could happen within such a short amount of time."
Linde and his wife, Renata Kallosh – also a professor of physics at Stanford – have authored two companion studies that raise the possibility of a cosmic "big crunch." Both papers are available on the physics research website, www.arXiv.org. "We tried our best to come up with a good theory that explains the acceleration of the universe, but ours is just a model," Linde noted. "It's just part of the answer."
If the Linde-Kallosh model is correct, then the universe, which appears to accelerating now, will begin to slow down and contract. "The universe may be doomed to collapse and disappear," Linde said. "Everything we see now, and at a much larger distance that we cannot see, will collapse into a point smaller than a proton. Locally, it will be the same as if you were inside a black hole. You will just discontinue your existence."
Einstein's "blunder"
The fate of the cosmos has been hotly debated for decades.
In the early 20th century, Albert Einstein, along with most physicists, believed that the universe was static – even though the equations he developed for his general theory of relativity in 1917 suggested that space itself was either contracting or expanding. To ensure that his new theory was consistent with nature, Einstein invented the "cosmological constant": an arbitrary mathematical term he inserted into his equations to guarantee a static universe – at least on paper.
To Einstein, the cosmological constant may have represented some kind of invisible energy that exists in the vacuum of empty space – a force strong enough to repel the gravitational force exerted by matter. Without this mysterious vacuum energy opposing gravity, the universe eventually would crash in on itself, according to general relativity theory.
But observations by astronomer Edwin Hubble and others in the 1920s proved that distant galaxies are not stationary but are, in fact, moving away from one another. Since the universe was expanding, Einstein no longer needed an antigravity factor in his equations, so he rejected the cosmological constant as irrelevant.
"First Einstein introduced the cosmological constant in his equations, then he said that this was the biggest blunder of his life," Linde observed. "But I recently heard that, apparently, he still liked the idea and discussed it many years later – and continued writing equations that included it."
Dark energy
Fast-forward to 1998, when two independent teams of astronomers discovered that not only is the universe expanding, it is doing so at an ever-faster pace. Their findings were based on observations of supernovae – exploding stars that emit extraordinarily bright light. A supernova is a rare event, but new telescopes equipped with sophisticated electronic sensors allowed the research teams to track dozens of stellar explosions in the sky. What they saw astonished the world of astronomy: The supernovae, it turned out, actually were speeding up at a rate that outpaced the predicted gravitational pull of matter.
What force could be strong enough to overcome gravity and cause the universe to accelerate? Perhaps Einstein was right all along – maybe there is some kind of vacuum energy in space. Einstein called it the cosmological constant, and 80 years later, astronomers would give this invisible force a new name – dark energy.
"The supernova experiments four years ago confirmed a simple picture of the universe where approximately 30 percent of it is made of matter and 70 percent is made of dark energy – whatever it is," Linde observed.
Overnight, a concept that Einstein had rejected was now considered the dominant force in the universe. "The cosmological constant remains one of the biggest mysteries of modern physics," Linde pointed out.
Negative energy
Current predictions that dark energy will continue to overwhelm gravity and produce a runaway universe are based on the assumption that the total density of dark energy in the universe is greater than zero and will remain so forever.
This seems obvious at first glance, since logic dictates that the density of dark energy has to be a positive number. After all, how could the universe be filled with "negative energy"?
But in the strange world of quantum physics and elementary particle theory, everyday logic doesn't always apply.
"During the last year, physicists came to the realization that it is very difficult to understand the origin of positive dark energy in the most advanced versions of elementary particle theory – such as string theory and extended supergravity," Linde said.
"We have found that some of the best attempts to describe dark energy predict that it will gradually become negative, which will cause the universe to become unstable, then collapse," he added. "People who studied general relativity many years ago were aware of this, but to them, this was an academic possibility. It was weird to think about negative vacuum energy seriously. Now we have some reasons to believe it."
The Linde-Kallosh model produced another surprising result: The cosmos will collapse in 10 to 20 billion years – a timeframe comparable with the age of the universe, which is estimated to be about 14 billion years old.
"This was really strange," Linde recalled. "Physicists have known that dark energy could become negative and the universe could collapse sometime in the very distant future, perhaps in a trillion years, but now we see that we might be, not in the beginning, but in the middle of the life cycle of our universe."
The good news, wrote Linde and Kallosh, is that "we still have a lot of time to find out whether this is going to happen."
Cosmic bubbles
Linde is quick to acknowledge that the collapsing universe scenario is not the final word on the fate of the cosmos.
"Astronomy is a science once known for its continuous errors," he quipped."There was even a joke: 'Astrophysicists are always in error but never in doubt.' We are just in the very beginning of our investigation of this issue, and it would be incorrect to interpret our results as a reliable doomsday prediction. In any case, our model teaches us an interesting lesson: Even the most abstract theories of elementary particles may end up having great importance in helping us understand the fate of the universe and the fate of humanity."
Direct observation of space with state-of-the-art telescopes, satellites and other instruments will answer many unresolved questions, he added. "We're entering the era of precision cosmology, where we really can get a lot of data, and these data become more precise. Perhaps 10 years, 20 years, 30 years, I don't know, but this is the timescale in which we will get a map of the universe with all its observable parts. So things that were a matter of speculation will gradually become better and better established."
Linde helped pioneer inflationary cosmology – the theory that the universe began not with a fiery big bang but with an extraordinarily rapid expansion (inflation) of space in a vacuum-like state. According to inflationary theory, what we call the universe is just a minute fraction of a much larger cosmos.
"The universe actually looks, not like a bubble, but like a bubble producing new bubbles," Linde explained. "We live in a tiny part of one bubble, and we look around and say, 'This is our universe.'"
If our bubble collapses into a point, a new bubble is likely to inflate somewhere else – possibly giving rise to an entirely new form of life, Linde said.
"Our part of the universe may die, but the universe as a whole, in a sense, is immortal – it just changes its properties," he concluded. "People want to understand their place in the universe, how it was created and how it all will end – if at all. That is something that I would be happy to know the answer to and would pay my taxpayer money for. After all, it was never easy to look into the future, but it is possible to do so, and we should not miss our chance."
Graduate student Sergey Prokushkin and Marina Shmakova, a research associate at the Stanford Linear Accelerator Center, also contributed to the studies. Research was supported with grants from the National Science Foundation, the Templeton Foundation, the U.S. Department of Energy and the Stanford Graduate Fellowships program.
Relevant Web URLs:
http://snap.lbl.gov/brochure/index.html
http://www.biols.susx.ac.uk/home/John_Gribbin/
http://imagine.gsfc.nasa.gov/docs/science/know_l1/supernovae.html
Editor's Note: The original news release can be found at http://www.stanford.edu/dept/news/pr/02/universe925.html
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Water Molecules Star In Action Movies Posted: Tuesday, September 17, 2002
Source: Lawrence Berkeley National Laboratory (http://www.lbl.gov/)
Scientists at the Lawrence Berkeley National Laboratory (Berkeley Lab) have produced the first ever action movies starring individual water molecules on a metal surface. The ending was a surprise even to the producers.
Working with a unique scanning tunneling microscope (STM), a team led by Miquel Salmeron, a physicist with Berkeley Lab's Materials Sciences Division, cooled the surface of a single crystal of palladium, a good catalyst for reactions involving hydrogen and water, to a temperature of about 40 Kelvins(-233 degrees Celsius) in an ultrahigh vacuum. Water molecules were then introduced onto this surface and their motion was tracked with the STM. As expected from previous studies, single molecules migrated across the surface to aggregate into clusters of two (dimers), three (trimers), four (tetramers) five (pentamers) and six (hexamers). The surprise came when the scientists were able to watch the molecules as they moved.
"Isolated water molecules moved by hopping from one lattice point (on the substrate's crystal) to the nearest neighboring point whereupon if they collided with another water molecule they began to form clusters," says Salmeron. "The speed with which the molecules moved increased by four orders of magnitude when dimers were formed. The mobility of trimers and tetramers was also very high compared to the isolated molecules."
This ran contrary to the usual storyline in which single molecules diffuse or move across a surface more rapidly than clusters. Salmeron likens the situation to pulling either one skater across the ice or a group of skaters connected by a line.
"Since each skater rubs against the surface of the ice, to pull them all together means a lot of rubbing," he says. "The situation can be quite different, however, when the sliding takes place over a corrugated surface, like atoms sliding over the atomic landscape of a surface."
What he and his colleagues observed in their movies was that the hydrogen bonds which held two, three or four water molecules together in a cluster forced the cluster into a geometric configuration that was mismatched with the lattice of the palladium surface. The individual water molecules within these clusters could no longer be bound to the palladium's lattice points with the same strength as when they were isolated. This allowed dimers, trimers and tetramers to easily slide across the palladium's surface.
When clusters reached five water molecules in size, however, the combined strength of the water-substrate bonds prevailed and the movement of the pentamers slowed or stopped altogether. The addition of a sixth water molecule created highly stable hexamer rings, which spread out as a hexagonal honeycomb structure over the palladium substrate. This, too, brought a surprise.
Explains Salmeron, "The hexagonal honeycomb of water molecules does not exactly match palladium's lattice and as a result honeycombs grow to a certain size and then stop, forming islands across the substrate's surface. As additional water molecules are introduced, they pile up on top of these islands. Slight heating will break these islands up into holes that form beautiful patterns, like nanometer-scale snow flakes."
Working with Salmeron on this study were Toshi Mitsui and Frank Ogletree, both with Berkeley Lab's Materials Sciences Division, and Mark Rose and Evgueni Fomin, students with the Physics Department of the University of California at Berkeley. Their results were reported in the September 13 issue of the journal Science.
A lot of time, effort, and money goes into water-proofing materials so they don't stain, mildew, rust, or suffer any of the other damages that can happen when something gets wet. The interaction of water with surfaces drives a wide variety of important phenomena that include wetting, corrosion, ice-melting, electrochemistry, dissolution, and solvation. Such interactions are equally important to many biological processes as well. Despite the broad concern, the interactions of individual water molecules with surfaces have remained somewhat of a scientific enigma.
"Numerous fundamental questions regarding the adsorption of water on surfaces and its evolution from isolated molecules to clusters, complete layers, and beyond, remain unanswered," says Salmeron. "Structural probes that analyze cluster formation do not address the important issue of the movement of water on surfaces."
An STM is the ideal instrument for studying the diffusion of individual molecules or atoms along the surface of a material, Salmeron says. Working off a probe that tapers to a single atom at its point, the STM sweeps over a sample area barely a nanometer above the surface. An electrical current is generated by electrons that "tunnel" through the gap between the atoms on the sample surface and the STM tip. This current is extremely sensitive to changes in the gap distance and produces, through a feedback mechanism, displacements in the STM tip that can recorded and translated into topographic images of individual surface atoms. The Berkeley Lab STM is one of the few such instruments in the world that can be operated at the extremely low temperatures needed to slow the process of molecular diffusion down enough for it to be imaged.
"At 40 Kelvins, the diffusion of water on palladium proceeds slowly enough for us to make movies by acquiring sequences of images at 20 second intervals," says Salmeron. "By measuring jump distances and directions in our movie images, diffusion was observed to proceed by random hopping over to the nearest neighbor sites of the palladium substrate."
Diffusion was studied using an atom-tracking technique as well as the movie-making technique. The atom-tracking experiment confirmed the movie-based observations.
"Our findings allow for a deeper understanding of the physics and chemistry of water on surfaces," Salmeron says. "Nature is always full of surprises and all it takes is to look carefully to discover new things."
Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California.
Editor's Note: The original news release can be found at http://www.lbl.gov/Science-Articles/Archive/MSD-action-movies-Salmeron.html
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Overlapping Genetic and Archaeological Evidence Suggests Neolithic Migration Posted: Wednesday, September 11, 2002
Source: Stanford University Medical Center (http://www-med.stanford.edu/school/)
STANFORD, Calif. - For the first time, Stanford researchers have compared genetic patterns with archeological findings to discover that genetics can help predict with a high degree of accuracy the presence of certain artifacts. And they say the strength of this link adds credence to theories that prehistoric people migrated from the Middle East to Europe, taking both their ideas and their way of life with them. "The recovery of history is really a jigsaw puzzle," said Peter Underhill, PhD, senior research scientist in the department of genetics and one of the study's authors. "You have to look at genetics, material culture (archeological findings), linguistics and other areas to find different lines of evidence that reinforce each other."
The researchers' mathematical analysis showed that a pair of mutations on the Y chromosome, called Eu9, predicted the presence of certain figurines from the Neolithic period with 88 percent accuracy and the presence of painted pottery with 80 percent accuracy. The study is published in the September issue of Antiquity.
"The strength of the association is very surprising," said Roy King, MD, PhD, associate professor of psychiatry and behavioral sciences at Stanford who co-authored the study. "The genetic measures are very precise, and archaeology is pretty precise - either a figurine is there or it isn't. The strength of the correlation is driven by the strength of our measures."
It is known that agriculture spread from the Middle East to Europe during the Neolithic period about 12,000 years ago, but for many years archeologists have debated how this occurred. Was it due to the movement of people or to the movement of ideas? Previous genetic analysis of people living today suggests a migration - that the people moved - but critics have questioned this view. The latest study reinforces evidence of a migration in which people brought their ideas and lifestyle with them.
Genetics can answer the question in a roundabout way. Human DNA sequences today may shed light on our ancestors because some portions of the human genome change very slowly. One of these is the Y chromosome. Women carry two X chromosomes, while men have one X and one Y. The X and Y cannot exchange DNA like the 22 pairs of non-sex chromosomes in humans or the paired X chromosomes in women. As a result, a man should have a carbon copy of the Y chromosome of his father, grandfather and so on. But sometimes a harmless mutation, a misspelling in the genetic code, occurs. The mutation will be passed on to all the man's male descendants. If millions of men have the same mutation, then they all share a distant paternal ancestor.
Underhill studies pairs of mutations on the Y chromosome in current populations. He combines data about the geographic distribution of the mutations with information about when the mutations arose to trace historical migrations.
While reading a previous paper on Y-chromosome mutations in Science that Underhill co-authored, King thought the geographic distribution of some pairs of mutations paralleled that of Neolithic decorative ceramics. King, a psychiatrist with a PhD in mathematics and a deep interest in art history, called Underhill and suggested they compare the two sets of data.
Critics argue that the contemporary gene pool does not reflect what happened thousands of years ago because people have moved around too much since then. Many also see genetics as an entirely separate line of investigation from archaeological work. Researchers had compared genetic studies to language evolution, but no one had attempted to link genetics and material culture. Underhill agreed to undertake the analysis with King.
The Science paper Underhill co-authored described the Y chromosomes of more than 1,000 men in 25 different Middle Eastern and European geographic regions. They found that the frequency of four pairs of mutations was highest in the Middle East but also significant in eastern and southern Europe. While it is likely that all the mutations studied originated prior to the Neolithic period, the distribution suggested a westward migration.
The researchers took the distribution of the four pairs of Y-chromosome mutations found to originate in the Middle East and compared it to the regions where certain decorated ceramics have been found in Neolithic sites. They focused on figurines and pottery with painted geometric and abstract designs. Most of the figurines are female; researchers have speculated that they were used for magic or religious purposes, as amulets or charms, or even as dolls for children, King said.
The researchers found a strong correlation in their study between the Y-chromosome mutations and the presence of certain artifacts. Nonetheless, Underhill remains cautious. "No gene on the Y chromosome is going to program you to make pottery," he said. Instead, the Y-chromosome mutation pairs used in the study are simply population markers that in this case were compared to ceramics. The same mutations could be compared to many different types of artifacts.
King and Underhill hope that archaeologists will follow them in trying to blend these two lines of historical evidence. They are continuing to gather genetic data from areas in Greece near Neolithic archaeological sites and in western Turkey, which researchers believe to be the jumping-off point for Neolithic migration.
Stanford University Medical Center integrates research, medical education and patient care at its three institutions - Stanford University School of Medicine, Stanford Hospital & Clinics and Lucile Packard Children's Hospital at Stanford. For more information, please visit the Web site of the medical center's Office of Communication & Public Affairs at http://mednews.stanford.edu.
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