Tuesday, January 25, 2011
1/25/2011 07:02:00 AM Publicado por Alquimia
Sophisticated tools allow scientists to subject the basic elements of matter to conditions drastic enough to modify their behavior. By doing this, they can expand our understanding of matter. A research team including three Carnegie scientists was able to demonstrate surprising properties of the element lithium under intense pressure and low temperatures. Their results were published Jan. 9 on the Nature Physics website.
Lithium is the first metal in the periodic table and is the least dense solid element at room temperature. It is most commonly known for its use in batteries for consumer electronics, such as cell phones and laptop computers. And, with only three electrons per atom, lithium should behave like a model, simple metal.
However, this research has shown that under pressure ranging between about 395,000 atmospheres (40 GPa) and about 592,000 atmospheres (60 GPa), lithium behaves in a manner that’s anything but simple. Not only does it become a liquid at room temperature, but it then refuses to freeze until the temperature reaches a chilly -115o F. At pressures above about 592,000 atmospheres (60 GPa), when lithium does eventually solidify, it is into a range of highly complex, crystalline states. The highest pressure reached in the study was about 1.3 million atmospheres (130 GPa).
The research team, including Malcolm Guthrie, Stanislav Sinogeikin and Ho-kwang (Dave) Mao, of Carnegie’s Geophysical Laboratory, believe that this exotic behavior is directly due to the exceptionally low mass of the lithium atom. An elementary result of quantum physics is that atoms continue to move, even when cooled to the lowest possible temperature. As the mass of an atom decreases, the importance of this residual, so called ‘zero-point,’ energy increases. The researchers speculate that, in the case of lithium, the zero-point energy increases with pressure to the point that melting occurs. This work raises the possibility of uncovering a material that never freezes. The prospect of a metallic liquid at even the lowest temperatures raises the intriguing possibility of an entirely novel material, a superconducting liquid, as proposed previously by theorists for hydrogen at very high pressure.
(Photo: ©iStockphoto.com/David Freund)
1/25/2011 07:02:00 AM Publicado por Alquimia
Emil Kozarov and a team of researchers at the Columbia University College of Dental Medicine have identified specific bacteria that may have a key role in atherosclerosis, or what is commonly referred to as “hardening of the arteries,” caused by plaque build-up, which can lead to heart attack and stroke.
Fully understanding the role of bacterial infections in cardiovascular diseases has been challenging because researchers have previously been unable to isolate live bacteria from plaque tissue removed from the arteries. Using specimens from the Department of Surgery and the Herbert Irving Comprehensive Cancer Center at Columbia University, Kozarov and his team, however, were able to isolate bacteria from a 78-year-old male who had previously suffered a heart attack. Their findings are explained in the latest Journal of Atherosclerosis and Thrombosis.
In the paper, researchers describe using cell cultures to study the genetic make-up of the tissue and to look for the presence of bacteria that could be cultured and grown for analysis. In addition, they looked at five pairs of both diseased and healthy arteries. Culturing the cells aided in the isolation of the bacillus Enterobacter hormaechei from the patient’s tissue. Implicated in bloodstream infections such as sepsis and other life-threatening conditions, the isolated bacteria were resistant to multiple antibiotics. Surprisingly, this microbe was further identified in very high numbers in diseased but not in healthy arterial tissues.
The data suggest that a chronic infection may underlie the process of atherosclerosis, an infection that can be initiated by the spread of bacteria though different “gates” in the vascular wall—as in the case of someone with an intestinal infection. The data support Kozarov’s previous studies, where his team identified bacteria normally found in a person’s mouth and in the carotid artery, thus pointing to tissue-destructing periodontal, or tooth and gum, infections as one possible gate to the circulation.
Bacteria can gain access to blood vessels through different avenues, and then penetrate their vascular walls where they can create secondary infections that have been shown to lead to plaque formation, the researchers continued. “In order to test the idea that bacteria are involved, we must be able not only to detect bacterial DNA, but first of all to isolate the bacterial strains from the vascular wall from the patient,” Kozarov said.
One specific avenue of infection the researchers studied involved bacteria getting access to the circulatory system via white blood cells (phagocytes) designed to ingest harmful foreign particles. The model that Kozarov’s team was able to demonstrate showed an intermediate step where Enterobacter hormaechei is internalized by the phagocytic cells, but a step wherein bacteria are able to avoid immediate death in phagocytes. Once in circulation, Kozarov said, bacteria using this “Trojan horse” approach can persist in the organism for extended periods of time while traveling to and colonizing distant sites such as the carotid, femoral artery or the aorta. This can lead to failure of antibiotic treatment and initiation of an inflammatory process, or atherosclerosis.
“Our findings warrant further studies of bacterial infections as a contributing factor to cardiovascular disease,” said Kozarov, an associate professor of oral biology at the College of Dental Medicine. Jingyue Ju, co-author and director of the Columbia Center for Genome Technology & Biomolecular Engineering, also contributed to this research, which was supported in part by a grant from the National Heart, Lung, and Blood Institute of the National Institutes of Health and by the Columbia University Section of Oral and Diagnostic Sciences. “The concept that bacteria might not face an immediate death after being ingested by white blood cells likely contributes to the spread of potentially plaque-forming bacteria to sites where they might not normally be present.”
1/25/2011 07:01:00 AM Publicado por Alquimia
If the house seems dustier than it used to be, it may not be a reflection on your housekeeping skills. The amount of dust in the Earth's atmosphere has doubled over the last century, according to a new study; and the dramatic increase is influencing climate and ecology around the world.
The study, led by Natalie Mahowald, associate professor of earth and atmospheric sciences, used available data and computer modeling to estimate the amount of desert dust, or soil particles in the atmosphere, throughout the 20th century. It's the first study to trace the fluctuation of a natural (not human-caused) aerosol around the globe over the course of a century.
Mahowald presented the research at the fall meeting of the American Geophysical Union in San Francisco Dec. 13.
Desert dust and climate influence each other directly and indirectly through a host of intertwined systems. Dust limits the amount of solar radiation that reaches the Earth, for example, a factor that could mask the warming effects of increasing atmospheric carbon dioxide. It also can influence clouds and precipitation, leading to droughts; which, in turn, leads to desertification and more dust.
Ocean chemistry is also intricately involved. Dust is a major source of iron, which is vital for plankton and other organisms that draw carbon out of the atmosphere.
To measure fluctuations in desert dust over the century, the researchers gathered existing data from ice cores, lake sediment and coral, each of which contain information about past concentrations of desert dust in the region. They then linked each sample with its likely source region and calculated the rate of dust deposition over time. Applying components of a computer modeling system known as the Community Climate System Model, the researchers reconstructed the influence of desert dust on temperature, precipitation, ocean iron deposition and terrestrial carbon uptake over time.
Among their results, the researchers found that regional changes in temperature and precipitation caused a global reduction in terrestrial carbon uptake of 6 parts per million (ppm) over the 20th century. The model also showed that dust deposited in oceans increased carbon uptake from the atmosphere by 6 percent, or 4 ppm, over the same time period.
While the majority of research related to aerosol impacts on climate is focused on anthropogenic aerosols (those directly emitted by humans through combustion), Mahowald said, the study highlights the important role of natural aerosols as well.
"Now we finally have some information on how the desert dust is fluctuating. This has a really big impact for the understanding of climate sensitivity," she said.
It also underscores the importance of gathering more data and refining the estimates. "Some of what we're doing with this study is highlighting the best available data. We really need to look at this more carefully. And we really need more paleodata records," she said.
Meanwhile, the study is also notable for the variety of fields represented by its contributors, she said, which ranged from marine geochemistry to computational modeling. "It was a fun study to do because it was so interdisciplinary. We're pushing people to look at climate impacts in a more integrative fashion."
(Photo: Cornell U.)