Tuesday, January 18, 2011
1/18/2011 04:50:00 PM Publicado por Alquimia
Turning fossil fuel into energy is easy: You just burn it. And live with the carbon dioxide byproduct.
What if we could reverse the process and turn carbon dioxide back into fuel? A dream solution, but it may seem like trying to put the genie back in the bottle.
Not for University of Minnesota researchers Jane Davidson, Wojciech Lipinski, however. They and their colleagues are using concentrated light energy equal to 3,000 suns to find the most efficient way to convert carbon dioxide and water into synthetic gas, or "syngas," with solar power.
Syngas is easy to transport via pipelines and is readily converted to high-energy-density liquid hydrocarbon fuels, or "synfuels," with properties equivalent to what we derive from petroleum. An analysis by researchers from the University and Sandia National Laboratory indicates that an entire sunlight-to-synfuels process could be done with 9 percent efficiency and no input of fossil fuels.
"With 9 percent efficiency—which would be many times more efficient than using biofuels—we could replace all the petroleum consumed today in the United States with solar collectors covering 15 million acres," says Davidson, a mechanical engineering professor. "That's the size of West Virginia, and half of what we use for highways."
Davidson, Lipinski, and their colleagues are working on other approaches to conversion of concentrated sunlight. They're researching the production of syngas from biomass and aiming to generate electricity using solar heat.
"With 9 percent efficiency—which would be many times more efficient than using biofuels—we could replace all the petroleum in the United States with solar collectors covering 15 million acres," says Davidson, a mechanical engineering professor. "That's the size of West Virginia, and half of what we use for highways."
At the University's Solar Energy Laboratory, the process begins with a solar simulator in the form of seven mirrored, 6,500-watt lamps that concentrate the light on a 10-centimeter spot with an irradiance of 3,000 suns. (One "sun" equals 1,000 watts of solar energy falling per square meter of surface.) With this concentrated radiant energy, one can generate temperatures of more than 3,600 F in a chemical reactor. There, carbon dioxide and water are split to form carbon monoxide and hydrogen, the two components of syngas.
If the technology works in the laboratory, it could be scaled up to take advantage of the world's abundant solar energy. Deploying these technologies in the Earth's sunbelt could yield enough renewable energy to significantly exceed the world's current needs, the researchers say.
"More sun falls on Earth in one hour than is consumed globally in a year," Davidson notes. "Harvesting the sun to meet our energy needs is a challenge with a huge payoff."
Of course, it's a little more complicated than focusing concentrated sunlight into a reactor filled with carbon dioxide and water. The key to the technology rests with oxides of two metals: zinc and cerium.
"Metal oxides allow you to split water and carbon dioxide at temperatures achievable with modern solar concentrating devices," Davidson explains.
In the reactor, the metal oxides go through cycles in which they strip oxygen alternately from carbon dioxide or water--forming carbon monoxide or hydrogen, respectively--then release the oxygen as a byproduct. The syngas formed from the carbon monoxide and hydrogen can be converted into gasoline, diesel, jet fuel, methane (natural gas), or other products.
Davidson and her colleagues have produced syngas this way in their laboratory. They are now moving from laboratory demonstration to development of prototype reactors. While Davidson and Lipinski concentrate on making the next generation of reactors, University chemistry professor Andreas Stein and colleagues at Caltech and UCLA are researching new materials that could increase the efficiency and ease of operation.
If adopted, a "sunlight to synfuels" process would be an energy supply system in which the same amount of carbon dioxide that is removed from the atmosphere and locked into the fuels is released when the fuels are burned. Thus, it would be carbon neutral.
"And because synfuels can be the same as the conventional fuels, they won't require a new infrastructure," notes Lipinski.
(Photo: U. Minnesota)
University of Minnesota
1/18/2011 04:49:00 PM Publicado por Alquimia
A cat regularly vomiting hairballs or refusing to eat probably isn’t being finicky or otherwise “cat-like,” despite what conventional wisdom might say. There is a good chance that the cat is acting sick because of the stress caused by changes in its environment, new research suggests.
Healthy cats were just as likely as chronically ill cats to refuse food, vomit frequently and leave waste outside their litter box in response to changes in their routine, according to the Ohio State University study. Veterinary clinicians refer to these acts as sickness behaviors.
The researchers documented sickness behaviors in healthy cats and in cats with feline interstitial cystitis, a chronic illness characterized by recurring discomfort or pain in the bladder and often both an urgent and frequent need to urinate.
When the cats experienced what were called “unusual external events,” such as a change in feeding schedule or caretaker, the healthy cats were just as likely to exhibit sickness behaviors as were the chronically ill cats. The two groups had the same number of sickness behaviors in response to unusual events, and both groups were at more than three times the risk of acting sick when their routines were disrupted.
Previous research has indicated that a diagnosis of interstitial cystitis, known as IC, in cats is strongly associated with a number of other health problems. The fact that healthy cats exhibit some of those same problems in the face of stress suggests that veterinary clinicians should consider cats’ environmental conditions during assessments for health problems, researchers say.
“For veterinary clinicians, when you have a cat that’s not eating, is not using the litter box or has stuff coming up out of its mouth, the quality of the environment is another cause that needs to be addressed in coming up with a diagnosis,” said Tony Buffington, professor of veterinary clinical sciences at Ohio State and senior author of the study.
“We are cautious about extrapolating these findings to the average home, but we will say that anyone who has a pet accepts the responsibility of understanding their pet’s needs and providing them,” he added. “And what we’ve learned is that all cats need to have some consideration of environmental enrichment.”
The study is published in the Jan. 1, 2011, issue of the Journal of the American Veterinary Medical Association.
This research project didn’t begin as a study of cats’ tendency to exhibit sickness behaviors. Ohio State’s Veterinary Medical Center was housing 12 healthy cats and 20 cats with IC, including those at risk of euthanasia because their previous owners were unable to tolerate their sickness behaviors, for a variety of other research efforts, many related to better understanding the chronic disease.
Judi Stella, a doctoral candidate in veterinary preventive medicine, was the primary caretaker of this colony of cats. Based on previous work by Buffington about the benefits of environmental enrichment for cats that stay indoors, Stella spent months setting up a standardized feeding, play and cleaning schedule that seemed the least stressful for all of the cats.
And then she noticed that the cats with the chronic illness looked better: Their coats were shinier, their eyes were clearer and, perhaps most surprising of all, none of these cats missed the litter box or vomited for two weeks.
“At the time, we assumed the IC cats were always going to have these problems. When I started looking at the data, it was the lack of sickness behaviors that tipped me off. It was not expected,” said Stella, lead author of the study.
“This became a study of enrichment as an approach to therapy for these syndromes because there is no good drug therapy in cats, or in people, for that matter, with this disorder. What we found, in other clinical studies and with this study, is that by enriching the environment, you can reduce IC cats’ symptom burden by about 75 or 80 percent,” Buffington said.
Another important finding: “A healthy cat – or any healthy mammal – can feel the stress of environmental disruption and exhibit sickness behaviors as a result,” he said.
After the environment was stable for all of the cats, Stella observed them for another 77 weeks. The nature of the research changed again over the course of the observation. When Stella took a vacation and was replaced by substitute caretakers, or when she changed the feeding schedule for the cats as part of yet another project, it became clear that these changes had an influence on the cats’ sickness behaviors. So she tracked those changes.
During the period of observation, these changes – called unusual external events – included a discontinuation of contact with Stella, the longtime primary caretaker; a combination of husbandry schedule changes, food removal, restraint stress and withdrawal of playtime and music; a three-hour delay in feeding time; and a dramatic change in caretaker personnel.
During control weeks, when the routine was unaltered, the healthy cats, on average, exhibited 0.4 sickness behaviors and the cats with IC exhibited 0.7 sickness behaviors – virtually no difference. Similarly, during weeks containing unusual external events, those numbers increased to 1.9 sickness behaviors for healthy cats and 2.0 sickness behaviors for cats with interstitial cystitis. Overall, this translated to a 3.2-fold increase in the risk for sickness behaviors by all cats when their routines were disrupted.
The three most common sickness behaviors – vomiting, urination or defecation outside the litter box and decreased food intake – accounted for 88 percent of all sickness behaviors in healthy cats and 78 percent of sickness behaviors in the cats with IC.
Buffington noted that these three signs of illness are among those that often lead pet owners to take their cats to a veterinarian for evaluation. And interestingly, these sickness behaviors also are seen in other captive housing environments, such as zoos, kennels and shelters.
So how does a cat owner enrich the animal’s environment? In this study, this included routine care and feeding at the same time every morning, keeping food and litter boxes in consistent locations, daily cleaning of cages, provision of a clean litter box, regularly washed bedding, hiding boxes, numerous commercial cat toys and classical music for one to two hours each day. Stella also released all cats from their cages for 60 to 90 minutes each afternoon to allow them to interact and play with toys or use climbing and scratching posts.
“I think a huge part of this is giving cats resources they can interact with and control. Litter boxes and food bowls go without saying, but I also think that equally important are predictable schedules and some semblance of control so they don’t feel trapped. And their humans can focus on quality interaction rather than the quantity of interaction. Understanding how they live in the world can allow humans to interact with them more effectively,” Stella said.
There is also a need to recognize that what might be common isn’t necessarily normal.
“There is not another mammal on the planet that wouldn’t be hospitalized for throwing up once a week,” Buffington said. “Vomiting hairballs is not normal. What we think happens is that stress changes motility in their stomach and that leads to vomiting. Pet owners have to recognize that vomiting is not normal in cats.”
The researchers noted a few other findings of interest: Older cats had a higher risk for an increase in the total number of sickness behaviors and for an increase in upper gastrointestinal symptoms and avoidance behavior. The oldest cat in the study was 8 years old.
In addition, the sickness behaviors of cats with interstitial cystitis were reduced even though they were not treated with any drugs and were eating commercially available dry food, which suggests these cats do not require drugs or special diets as part of their therapy.
“You get the environment right and they’ll recover,” Buffington said. “It’s like having lactose intolerance – you can’t put the corrective gene into the intestinal tract, but you can teach people to avoid milk sugar and that’s just as good. That’s what we’re doing – teaching these cats how to avoid threats that cause stress.”
Ohio State University
1/18/2011 04:49:00 PM Publicado por Alquimia
Researchers are creating a new type of solar cell designed to self-repair like natural photosynthetic systems in plants by using carbon nanotubes and DNA, an approach aimed at increasing service life and reducing cost.
"We've created artificial photosystems using optical nanomaterials to harvest solar energy that is converted to electrical power," said Jong Hyun Choi, an assistant professor of mechanical engineering at Purdue University.
The design exploits the unusual electrical properties of structures called single-wall carbon nanotubes, using them as "molecular wires in light harvesting cells," said Choi, whose research group is based at the Birck Nanotechnology and Bindley Bioscience centers at Purdue's Discovery Park.
"I think our approach offers promise for industrialization, but we're still in the basic research stage," he said.
Photoelectrochemical cells convert sunlight into electricity and use an electrolyte - a liquid that conducts electricity - to transport electrons and create the current. The cells contain light-absorbing dyes called chromophores, chlorophyll-like molecules that degrade due to exposure to sunlight.
"The critical disadvantage of conventional photoelectrochemical cells is this degradation," Choi said.
The new technology overcomes this problem just as nature does: by continuously replacing the photo-damaged dyes with new ones.
"This sort of self-regeneration is done in plants every hour," Choi said.
The new concept could make possible an innovative type of photoelectrochemical cell that continues operating at full capacity indefinitely, as long as new chromophores are added.
Findings were detailed in a November presentation during the International Mechanical Engineering Congress and Exhibition in Vancouver. The concept also was unveiled in an online article (http://spie.org/x41475.xml?ArticleID=x41475) featured on the Web site for SPIE, an international society for optics and photonics.
The talk and article were written by Choi, doctoral students Benjamin A. Baker and Tae-Gon Cha, and undergraduate students M. Dane Sauffer and Yujun Wu.
The carbon nanotubes work as a platform to anchor strands of DNA. The DNA is engineered to have specific sequences of building blocks called nucleotides, enabling them to recognize and attach to the chromophores.
"The DNA recognizes the dye molecules, and then the system spontaneously self-assembles," Choi said
When the chromophores are ready to be replaced, they might be removed by using chemical processes or by adding new DNA strands with different nucleotide sequences, kicking off the damaged dye molecules. New chromophores would then be added.
Two elements are critical for the technology to mimic nature's self-repair mechanism: molecular recognition and thermodynamic metastability, or the ability of the system to continuously be dissolved and reassembled.
The research is an extension of work that Choi collaborated on with researchers at the Massachusetts Institute of Technology and the University of Illinois. The earlier work used biological chromophores taken from bacteria, and findings were detailed in a research paper published in November in the journal Nature Chemistry (http://www.nature.com/nchem/journal/v2/n11/abs/nchem.822.html).
However, using natural chromophores is difficult, and they must be harvested and isolated from bacteria, a process that would be expensive to reproduce on an industrial scale, Choi said.
"So instead of using biological chromophores, we want to use synthetic ones made of dyes called porphyrins," he said.
(Photo: Purdue University/Mark Simons)