Tuesday, January 19, 2010

IN ALL THE GALAXY, JUST 15 PERCENT OF SOLAR SYSTEMS ARE LIKE OURS

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In their quest to find solar systems analogous to ours, astronomers have determined how common our solar system is.

They’ve concluded that about 15 percent of stars in the galaxy host systems of planets like our own, with several gas giant planets in the outer part of the solar system.

“Now we know our place in the universe,” said Ohio State University astronomer Scott Gaudi. “Solar systems like our own are not rare, but we’re not in the majority, either.”

The find comes from a worldwide collaboration headquartered at Ohio State called the Microlensing Follow-Up Network (MicroFUN), which searches the sky for extrasolar planets.

MicroFUN astronomers use a method called gravitational microlensing, which occurs when one star happens to cross in front of another as seen from Earth. The nearer star magnifies the light from the more distant star like a lens. If planets are orbiting the lens star, they boost the magnification briefly as they pass by.

This method is especially good at detecting giant planets in the outer reaches of solar systems -- planets analogous to our own Jupiter.

This latest MicroFUN result is the culmination of 10 years’ work -- and one sudden epiphany, explained Gaudi and Andrew Gould, professor of astronomy at Ohio State.

Ten years ago, Gaudi wrote his doctoral thesis on a method for calculating the likelihood that extrasolar planets exist. At the time, he concluded that less than 45 percent of stars could harbor a configuration similar to our own solar system.

Then, in December of 2009, Gould was examining a newly discovered planet with Cheongho Han of the Institute for Astrophysics at Chungbuk National University in Korea. The two were reviewing the range of properties among extrasolar planets discovered so far, when Gould saw a pattern.

“Basically, I realized that the answer was in Scott’s thesis from 10 years ago,” Gould said. “Using the last four years of MicroFUN data, we could add a few robust assumptions to his calculations, and we could now say how common planet systems are in our galaxy.”

The find boils down to a statistical analysis: in the last four years, the MicroFUN survey has discovered only one solar system like our own -- a system with two gas giants resembling Jupiter and Saturn, which astronomers discovered in 2006 and reported in the journal Science in 2008.

“We’ve only found this one system, and we should have found about six by now -- if every star had a solar system like Earth’s,” Gaudi said.

The slow rate of discovery makes sense if only a small number of systems -- around 15 percent -- are like ours, they determined.

“While it is true that this initial determination is based on just one solar system and our final number could change a lot, this study shows that we can begin to make this measurement with the experiments we are doing today,” Gaudi added.

As to the possibility of life as we know it existing elsewhere in the galaxy, scientists will now be able to make a rough guess based on how many solar systems are like our own.

Our solar system may be a minority, but Gould said that the outcome of the study is actually positive.

“With billions of stars out there, even narrowing the odds to 15 percent leaves a few hundred million systems that might be like ours,” he said.

(Photo: OSU)

Ohio State University

PENN STUDY SHOWS ANTIDEPRESSANTS WORK BEST FOR SEVERE DEPRESSION, PROVIDE LITTLE TO NO BENEFIT OTHERWISE

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A study of 30 years of antidepressant-drug treatment data published today in the Journal of the American Medical Association shows that the benefit of antidepressant medication compared with placebo may be minimal or nonexistent in patients with mild or moderate symptoms. University of Pennsylvania researchers say, however, the benefit of medications is substantial for patients with very severe depression.

Ultimately, according to the study, the majority of patients who were prescribed antidepressants did not suffer from a severity of depression that would be improved by the medications.

The research team, led by psychologists at Penn, analyzed data from studies that spanned a 30-year period to gauge the benefit of antidepressant medication compared to placebo pills across a range of patients with varying degrees of depression. The team collected data from placebo-controlled trials of antidepressants approved by the U.S. Food and Drug Administration for the treatment of Major or Minor Depressive Disorder. Studies comprised adult outpatients and included a medication vs. placebo comparison for at least six weeks. Researchers calculated depression severity scores before and after treatment using the standard Hamilton Rating Scale for Depression.

The scientists learned that medication vs. placebo differences varied substantially, relative to the severity of depression suffered by patients. Those patients shown to have less severe depression experienced little to no greater improvement in their symptoms from antidepressant medication as compared to a placebo sugar pill.

The results imply that doctors who are advising treatment for patients with mild or moderate cases of depression should consider the lack of evidence for specific benefits of the medications and compare the expected costs and benefits of the medications against alternatives such as self-help, exercise or psychological therapy.

“Antidepressant medications represent the best established treatment for Major Depressive Disorder, but there is little evidence that they have a specific pharmacological effect relative to pill-placebo for patients with less severe depression,” said Robert DeRubeis, principal investigator and professor in the Department of Psychology in Penn’s School of Arts and Sciences.

Researchers concluded that the ability of antidepressant medications to reduce depressive symptoms varied considerably. For people whose depression was considered to be mild, moderate or even severe, little evidence showed that the medications yield specific benefit beyond what is provided by engagement in treatment and the resulting boost in the patient’s expectation for improvement.

“For very severe depressions, the benefits of medications are clear and substantial,” said Jay Fournier, lead author and a doctoral candidate in Penn’s Department of Psychology. “But for others, the results of this study demonstrate how important it is for persons who are suffering from depression to take an active role in their care, regardless of the severity of their symptoms. Even placebo treatments help most people, and, although we do not fully understand how placebos work, part of the benefit comes from patients taking their depressive symptoms seriously and acting on their concern about their own mental health.”

University of Pennsylvania

ENGINEERED TOBACCO PLANTS HAVE MORE POTENTIAL AS A BIOFUEL

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Researchers from the Biotechnology Foundation Laboratories at Thomas Jefferson University have identified a way to increase the oil in tobacco plant leaves, which may be the next step in using the plants for biofuel. Their paper was published online in Plant Biotechnology Journal.

According to Vyacheslav Andrianov, Ph.D., assistant professor of Cancer Biology at Jefferson Medical College of Thomas Jefferson University, tobacco can generate biofuel more efficiently than other agricultural crops. However, most of the oil is typically found in the seeds – tobacco seeds are composed of about 40 percent oil per dry weight.

Although the seed oil has been tested for use as fuel for diesel engines, tobacco plants yield a modest amount of seeds, at only about 600 kg of seeds per acre. Dr. Andrianov and his colleagues sought to find ways to engineer tobacco plants, so that their leaves expressed the oil.

“Tobacco is very attractive as a biofuel because the idea is to use plants that aren’t used in food production,” Dr. Andrianov said. “We have found ways to genetically engineer the plants so that their leaves express more oil. In some instances, the modified plants produced 20-fold more oil in the leaves.”

Typical tobacco plant leaves contain 1.7 percent to 4 percent of oil per dry weight. The plants were engineered to overexpress one of two genes: the diacyglycerol acytransferase (DGAT) gene or the LEAFY COTYLEDON 2 (LEC2) gene. The DGAT gene modification led to about 5.8 percent of oil per dry weight in the leaves, which about two-fold the amount of oil produced normally. The LEC2 gene modification led to 6.8 percent of oil per dry weight.

“Based on these data, tobacco represents an attractive and promising ‘energy plant’ platform, and could also serve as a model for the utilization of other high-biomass plants for biofuel production,” Dr. Andrianov said.

The paper was co-authored by Dr. Andrianov and Nikolai Borisjuk, Ph.D., also from the Jefferson Biotechnology Foundation Laboratories. Hilary Koprowski, M.D., is the director of the Jefferson Biotechnology Foundation Laboratories, and also participated in the research.

Thomas Jefferson University

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