The image shows a neuron with a tree trunk-like dendrite. Each triangular shape touching the dendrite represents a synapse, where inputs from other neurons, called spikes, arrive (the squiggly shapes). Synapses that are further away on the dendritic tree from the cell body require a higher spike frequency (spikes that come closer together in time) and spikes that arrive with perfect timing to generate maximal learning.(Credit: Image courtesy of University of California – Los Angeles)
Contrary to what was previously assumed, Mehta and Kumar found that when it comes to stimulating synapses with naturally occurring spike patterns, stimulating the neurons at the highest frequencies was not the best way to increase synaptic strength.
When, for example, a synapse was stimulated with just 10 spikes at a frequency of 30 spikes per second, it induced a far greater increase in strength than stimulating that synapse with 10 spikes at 100 times per second.
“The expectation, based on previous studies, was that if you drove the synapse at a higher frequency, the effect on synaptic strengthening, or learning, would be at least as good as, if not better than, the naturally occurring lower frequency,” Mehta said. “To our surprise, we found that beyond the optimal frequency, synaptic strengthening actually declined as the frequencies got higher.”
The knowledge that a synapse has a preferred frequency for maximal learning led the researchers to compare optimal frequencies based on the location of the synapse on a neuron. Neurons are shaped like trees, with the nucleus being the base of the tree, the dendrites resembling the extensive branches and the synapses resembling the leaves on those branches.
When Mehta and Kumar compared synaptic learning based on where synapses were located on the dendritic branches, what they found was significant: The optimal frequency for inducing synaptic learning changed depending on where the synapse was located. The farther the synapse was from the neuron’s cell body, the higher its optimal frequency.
“Incredibly, when it comes to learning, the neuron behaves like a giant antenna, with different branches of dendrites tuned to different frequencies for maximal learning,” Mehta said.
The researchers found that not only does each synapse have a preferred frequency for achieving optimal learning, but for the best effect, the frequency needs to be perfectly rhythmic — timed at exact intervals. Even at the optimal frequency, if the rhythm was thrown off, synaptic learning was substantially diminished.
Their research also showed that once a synapse learns, its optimal frequency changes. In other words, if the optimal frequency for a naïve synapse — one that has not learned anything yet — was, say, 30 spikes per second, after learning, that very same synapse would learn optimally at a lower frequency, say 24 spikes per second. Thus, learning itself changes the optimal frequency for a synapse.
This learning-induced “detuning” process has important implications for treating disorders related to forgetting, such as post-traumatic stress disorder, the researchers said.
Although much more research is needed, the findings raise the possibility that drugs could be developed to “retune” the brain rhythms of people with learning or memory disorders, or that many more of us could become Einstein or Mozart if the optimal brain rhythm was delivered to each synapse.
“We already know there are drugs and electrical stimuli that can alter brain rhythms,” Mehta said. “Our findings suggest that we can use these tools to deliver the optimal brain rhythm to targeted connections to enhance learning.”
Funding for the study was provided by the National Science Foundation, the National Institutes of Health, the Whitehall Foundation, and the W.M. Keck Foundation.
Each day, many students cross the Fifth Street Bridge not thinking much of the downtown connector that exhales exhaust below; but a few are working to electrify the cars that pass beneath.
In a competition hosted by the City of Atlanta and Emory University’s Goizueta Business School, a team of Georgia Tech students earned first prize and a monetary award for proposing a system for electric vehicle adoption in Atlanta.
Undergraduate students Corbin Klett, Matt Jacobson, Logan Marett, Kevin Miron and Andrew Vaziri earned $5,000 for their proposal of how to drive demand for 50,000 electric cars on Atlanta’s roads during a two-year period. The students represent both Solar Jackets, Georgia Tech’s student group dedicated to the design, creation and expansion of solar technology, and the College of Management’s Technology and Management Program.
“Our approach was to devise creative and unique solutions to electric vehicle adoption, emphasizing ways of reducing the cost to the city government,” said Jacobson. “We stressed branding and education, creating a new ‘EV Brand’ we dubbed ChargeATL, and a website mockup to go along with it.”
The City will use funding received from the Department of Energy to implement ideas generated from the competition, with the goal of the Atlanta area being the first region in the country to have 50,000 electric vehicles on its roads. The Mayor’s office wanted to utilize the creativity of Georgia students to find ways to make the state competitive in this market.
“The Solar Jackets were incredible, coming up with as much as they did on their own,” said Jules Toraya, program manager in the City of Atlanta Mayor’s Office of Sustainability. “They stood out over the rest because they had answers — answers to tough questions, how to get budgets — and you could tell they had scoped out their ideas and had conviction about them.” Execution of these ideas will begin with an effort to pass electric vehicle-related legislation in the fall.
Four other teams presented at the competition on Sept. 13, including three from Tech and one from Emory. The groups were chosen from a pool of nearly 30 team applications spanning many Georgia universities, including Tech, Emory and the University of Georgia.
“It was an exciting opportunity to be able to tackle a problem the City of Atlanta is facing and feel like we could have an impact,” said Melissa McCoy, who participated on another Georgia Tech team. “The Solar Jackets team did a truly amazing job.”
Researchers have shown they can reverse the aging process for human adult stem cells, which are responsible for helping old or damaged tissues regenerate. The findings could lead to medical treatments that may repair a host of ailments that occur because of tissue damage as people age. A research group led by the Buck Institute for Research on Aging and the Georgia Institute of Technology conducted the study in cell culture, which appears in the September 1, 2011 edition of the journal Cell Cycle
The regenerative power of tissues and organs declines as we age. The modern day stem cell hypothesis of aging suggests that living organisms are as old as are its tissue specific or adult stem cells. Therefore, an understanding of the molecules and processes that enable human adult stem cells to initiate self-renewal and to divide, proliferate and then differentiate in order to rejuvenate damaged tissue might be the key to regenerative medicine and an eventual cure for many age-related diseases. A research group led by the Buck Institute for Research on Aging in collaboration with the Georgia Institute of Technology, conducted the study that pinpoints what is going wrong with the biological clock underlying the limited division of human adult stem cells as they age.
“We demonstrated that we were able to reverse the process of aging for human adult stem cells by intervening with the activity of non-protein coding RNAs originated from genomic regions once dismissed as non-functional ‘genomic junk’,” said Victoria Lunyak, associate professor at the Buck Institute for Research on Aging.
Adult stem cells are important because they help keep human tissues healthy by replacing cells that have gotten old or damaged. They’re also multipotent, which means that an adult stem cell can grow and replace any number of body cells in the tissue or organ they belong to. However, just as the cells in the liver, or any other organ, can get damaged over time, adult stem cells undergo age-related damage. And when this happens, the body can’t replace damaged tissue as well as it once could, leading to a host of diseases and conditions. But if scientists can find a way to keep these adult stem cells young, they could possibly use these cells to repair damaged heart tissue after a heart attack; heal wounds; correct metabolic syndromes; produce insulin for patients with type 1 diabetes; cure arthritis and osteoporosis and regenerate bone.
The team began by hypothesizing that DNA damage in the genome of adult stem cells would look very different from age-related damage occurring in regular body cells. They thought so because body cells are known to experience a shortening of the caps found at the ends of chromosomes, known as telomeres. But adult stem cells are known to maintain their telomeres. Much of the damage in aging is widely thought to be a result of losing telomeres. So there must be different mechanisms at play that are key to explaining how aging occurs in these adult stem cells, they thought.
Researchers used adult stem cells from humans and combined experimental techniques with computational approaches to study the changes in the genome associated with aging. They compared freshly isolated human adult stem cells from young individuals, which can self-renew, to cells from the same individuals that were subjected to prolonged passaging in culture. This accelerated model of adult stem cell aging exhausts the regenerative capacity of the adult stem cells. Researchers looked at the changes in genomic sites that accumulate DNA damage in both groups.
“We found the majority of DNA damage and associated chromatin changes that occurred with adult stem cell aging were due to parts of the genome known as retrotransposons,” said King Jordan, associate professor in the School of Biology at Georgia Tech.
“Retroransposons were previously thought to be non-functional and were even labeled as ‘junk DNA’, but accumulating evidence indicates these elements play an important role in genome regulation,” he added.
While the young adult stem cells were able to suppress transcriptional activity of these genomic elements and deal with the damage to the DNA, older adult stem cells were not able to scavenge this transcription. New discovery suggests that this event is deleterious for the regenerative ability of stem cells and triggers a process known as cellular senescence.
“By suppressing the accumulation of toxic transcripts from retrotransposons, we were able to reverse the process of human adult stem cell aging in culture,” said Lunyak.
“Furthermore, by rewinding the cellular clock in this way, we were not only able to rejuvenate ’aged’ human stem cells, but to our surprise we were able to reset them to an earlier developmental stage, by up-regulating the “pluripotency factors” – the proteins that are critically involved in the self-renewal of undifferentiated embryonic stem cells.” she said.
Next the team plans to use further analysis to validate the extent to which the rejuvenated stem cells may be suitable for clinical tissue regenerative applications.
The study was conducted by a team with members from the Buck Institute for Research on Aging, the Georgia Institute of Technology, the University of California, San Diego, Howard Hughes Medical Institute, Memorial Sloan-Kettering Cancer Center, International Computer Science Institute, Applied Biosystems and Tel-Aviv University.
Civil engineering professor Ernest “Chip” R. Blatchley III inspects a parabolic reflector for a prototype water-disinfection system he built as part of an effort to help provide safe drinking water to a large segment of the world’s population in developing nations. The system uses ultraviolet radiation from the sun to kill waterborne pathogens. Sunlight is captured by the reflector and focused onto a UV-transparent pipe though which water flows continuously. (Purdue University photo/Andrew Hancock)
A team of Purdue University researchers has invented a prototype water-disinfection system that could help the world’s 800 million people who lack safe drinking water.
The system uses the sun’s ultraviolet radiation to inactivate waterborne pathogens. Sunlight is captured by a parabolic reflector and focused onto a UV-transparent pipe though which water flows continuously.
“We’ve been working on UV disinfection for about 20 years,” said Ernest “Chip” R. Blatchley III, a professor of civil engineering. “All of our work up until a couple years ago dealt with UV systems based on an artificial UV source. What we are working on more recently is using ultraviolet radiation from the sun.”
Motivating the research is the need to develop practical, inexpensive water-treatment technologies for a large segment of the world’s population in developing nations.
“More than 800 million people lack access to what we consider to be ‘improved’ water,” Blatchley said. “The water available for people to drink in many developing countries hasn’t been treated to remove contaminants, including pathogenic microorganisms. As a result, thousands of children die daily from diarrhea and its consequences, including dehydration. Half of the world’s hospital beds are occupied by people who are sickened by the water they drink.”
Blatchley built the parabolic reflector in his garage. The team, including an undergraduate student supported by a National Science Foundation program, finished the prototype in the lab, lining it with aluminum foil. The system was then tested on the roof of Purdue’s Civil Engineering Building.
“It turns out that the solar radiation we receive in Indiana at some times of year is intense enough to inactivate some waterborne microorganisms with this type of system,” he said. “We demonstrated that we can disinfect water using sunlight. The reactor was very inexpensive to build, less than $100 for the materials.”
The natural UV system inactivated E. coli bacteria. However, the system must be able to kill dangerous pathogens such as Vibrio cholerae, which causes cholera, and Salmonella typhi, which causes typhoid, and Cryptosporidium parvum, which causes cryptosporidiosis, a parasitic disease that causes diarrhea.
“In the future we want to prove that our solar-UV system is going work against these other pathogens,” said Blatchley, who has worked on the project with doctoral student Eric Gentil Mbonimpa, who is from Rwanda, and Bryan Vadheim, an undergraduate from Montana State University. “We also want to automate it and build sensors for it so that we know how fast the water should be pumped through the system, depending on how sunny it is at any particular time.”
The NSF funded Vadheim’s work through its Research Experiences for Undergraduates program.
The parabolic reflector is made out of a wood called paulownia.
“That material was selected because the tree grows very rapidly in regions near the equator, where many people lack safe drinking water,” Blatchley said. “It is very light, strong and stable, so it’s not going to twist or warp or bend or crack in a climate that’s alternating between humid and dry.”
Natural UV has a longer wavelength than most artificial UV sources, which means it has less energy. Blatchley’s hypothesis, however, is that UV from sunlight will inactivate pathogens via the same mechanism as artificial UV: The radiation damages the genetic material of microbes, preventing them from reproducing.
“We are looking at other inexpensive reflecting materials, for example metalized plastic,” Blatchley said. “It’s similar to the material that’s used to make potato chip bags. We’ve done measurements, and some of these materials are about twice as reflective as aluminum foil.”
Improving water quality in developing countries is one of 14 “grand challenges” established by the National Academy of Engineering and also has been named a “millennium development goal” by the United Nations.
Blatchley also is working on an inexpensive filtration system that uses layers of sand and gravel to clean water. The filters were developed by Aqua Clara International, a Michigan-based non-profit corporation. Purdue and Aqua Clara are teaming up with Moi University in Kenya on that project. Purdue students tested the behavior of the filters in a Global Design Team project in Africa through Purdue’s Global Engineering Program.
Water flows slowly through the filter, allowing a bacterial film to establish near the top of the filter to remove organic contaminants while certain pathogens also are removed by attachment to the sand.
Findings by UT Southwestern Medical Center researchers may suggest new strategies for successful donor adult stem cell transplants in patients with blood cancers such as leukemia, lymphoma and myeloma.
The study, published Aug. 5 in Cell Stem Cell, showed for the first time that adult blood stem cells can be regulated to overcome an immune response that leads to transplant rejection. It also opens up further studies in stem cell immunology, said Dr. Chengcheng “Alec” Zhang, assistant professor of physiology and developmental biology at UT Southwestern and senior author of the study.
“We speculate that a common mechanism exists to regulate immune inhibitors in different types of stem cells,” he said.
Nearly 1 million people in the U.S. are living with or in remission from blood cancers; more than 135,000 are expected to be diagnosed this year. Blood and bone marrow stem cell transplants are needed when a patient’s body stops making enough healthy blood cells.
In this current study, UT researchers developed a culture “cocktail” that successfully supported adult blood stem cells from humans and from mice, and found that they express immune inhibitors on their surfaces that protect them from immune attack. Using the increased number of cultured blood stem cells, the scientists were able to overcome the protein barrier that alerts the immune system to foreign material and significantly repopulated healthy cells in the rodent transplantation recipients.
“We revealed that the expansion of adult blood stem cells through culture and an increase in cell surface expression of an immune molecule are the keys for this to happen,” Dr. Zhang said.
In new research that could have implications for improving fertilization in humans and other mammals, life scientists studied interactions between individual sperm and eggs in red abalone, an ocean-dwelling snail, and made precise chemical measurements and physical models of these interactions. They are the first scientists to do so.
By simulating the natural habitat of the abalone in the laboratory, the scientists were able to determine the conditions under which sperm–egg encounters and fertilization were most likely to occur.
“If we can understand the basic physics, chemistry and biology of reproduction, then moving from one species to the next is like dotting I’s and crossing T’s,” said the study’s lead author, Richard Zimmer, a UCLA distinguished professor of ecology and evolutionary biology.
Red abalone live in ocean crevices and spawn year-round, with females releasing several million eggs and males releasing up to 10 billion sperm directly into the ocean, Zimmer said.
In 2002, Zimmer’s research team identified a molecule called tryptophan that is released by female abalone eggs to attract sperm. Now Zimmer and Jeffrey Riffell, an assistant professor of biology at the University of Washington, report that the released tryptophan creates a plume around the egg, greatly enlarging the target area for sperm, in much the same way using a larger tennis racket increases the chances of hitting the ball. The plume increases the egg size by a factor of five, the researchers said.
In addition, the egg has to release very little tryptophan to increase its target area, Zimmer and Riffell report in the journal Proceedings of the National Academy of Sciences. The research is currently online and will be in published an upcoming print edition of the journal.
“We established that less than 1 percent of an egg’s tryptophan reserves are used by eggs to communicate with sperm,” Zimmer said. “The egg does not want to give up tryptophan. The egg sequesters tryptophan and releases just a whiff — just enough to attract a sperm. It’s an effective, evolved trick to enhance the likelihood of an encounter between sperm and egg. There is essentially no cost to the egg for this very effective communication system.”
An abalone egg also uses tryptophan for constructing an embryonic nervous system and building neurotransmitters, as well as for other purposes, Zimmer said.
But the success of the egg’s plume in attracting sperm, as well as sperm motility and other elements of the fertilization process, are greatly influenced by ocean flow conditions. Therefore, the biologists analyzed the physics of fluid motion in mediating sperm–egg interactions.
“The effect is huge, and was previously unsuspected,” said Zimmer, who is a member of UCLA’s neuroscience program. “The physics of fluid motion has a profound consequence on the ability of sperm to navigate and find an egg, and therefore on fertilization. We have identified the principal mechanisms by which eggs and sperm communicate and interact within an environment that has fluid motion. The method by which sperm in humans search for and find an egg seems to be the same process as in abalone. Similar fluid dynamics operate whether in the turbulent ocean environment or within a mammalian reproductive tract.
“It appears the forces imposed by fluid motion have acted as selective forces in the evolution of the communication system between sperm and egg within abalone. I expect that we will be able to describe the specific environmental conditions within the human reproductive system that will maximize the likelihood of contact between sperm and egg. The physical and chemical environments are actually quite similar.”
Zimmer and Riffell, who was formerly a graduate student in Zimmer’s lab, conducted fieldwork at San Diego’s Point Loma. They employed tiny sensors in a novel way, using Doppler acoustic technology to measure fluctuations of fluid motion in the environment where abalone naturally reproduce.
The biologists also devised an experimental technique by which they could generate the type of water flow and physical forces found in those habitats in a specialized tank. They used a computer and laser-based imaging system to study and quantify individual interactions between single sperm cells and single eggs, at long distances, away from any walls or boundaries. They are the first scientists to conduct such research.
“We now know properties of fluid motion that relate to the forces imposed at a microscopic scale on individual sperm and individual eggs as they interact,” Zimmer said.
As part of the study, Zimmer and Riffell also developed mathematical models that describe the plumes of tryptophan that come off of eggs under a variety of physical conditions.
“We have theoretical models of what the plumes should look like, and images of eggs with sperm swimming around them,” Zimmer said. “We mapped the empirical data on top of the theoretically predicted plumes. The question was whether sperm’s attraction to eggs could be predicted from our theoretical models of the physics of what the plume looks like. The two mapped onto each other beautifully. The interaction could be predicted.”
Because aspects of fluid flow in coastal ocean environments are remarkably similar to those in the human reproductive tract, the research could lead to methods to identify which human donors’ sperm are the “most vigorous,” with the highest probability of fertilizing an egg, Zimmer said. It may also suggest how to add fluid motion to maximize the probability of sperm fusing with an egg.
The study was funded by the National Science Foundation, the National Institutes of Health, the National Oceanic and Atmospheric Administration, and UCLA’s Council on Research.
Scientists have been trying to describe interactions between microorganisms in oceans and chemical plumes for years. Zimmer and Riffell are the first to achieve the chemical measurements and develop the physical models.
Zimmer has received a new three-year federal award from the National Science Foundation for further studies in humans, abalone and sea urchins, working with Riffell and Roman Stocker, an associate professor of in civil and environmental engineering at the Massachusetts Institute of Technology. Stocker is building microscopic devices that will allow the researchers to study a wide variety of chemical and physical environmental conditions.
Zimmer, Riffell and former UCLA postdoctoral scholar Patrick Krug isolated tryptophan and determined its function.
“Sexual reproduction and fertilization are controlled to a significant degree by chemical communication,” Zimmer said. “We are learning how chemical communication occurs.”
Got lots of fast food restaurants and other outlets that sell junk food in your neighborhood? Then your teen is more likely to nosh regularly on burgers and fries and wash them down with a soda.
That is the unpalatable finding of a new study from the UCLA Center for Health Policy Research that examined the effect of higher concentrations of less healthy food outlets on adolescent junk food consumption.
The upshot? Nearly three-quarters of California teenagers live or go to school in neighborhoods that are crowded with fast food restaurants and other outlets that sell unhealthy food — convenience stores, liquor stores, dollar stores and pharmacies — relative to the number of healthier food outlets, such as grocery stores, produce vendors and farmers markets. And unsurprisingly, teens who live or go to school in such neighborhoods are more likely to drink soda and eat fast food.
Research has shown that the consumption of fast food and soda has been linked to taking in excess calories and can contribute to diabetes and obesity.
“You are what you eat. You are, also, where you live,” said Susan Babey, a study co-author and a senior research scientist at the center. “And if you live in a place where there’s a fast food restaurant or convenience store on every block, with few healthier alternatives, you are likely to eat more junk.”
Many more unhealthy outlets
Using both the 2007 California Health Interview Survey and InfoUSA, a 2007 database of U.S. businesses, the study’s authors calculated a Home and School Retail Food Environment Index, which measured the number of less healthy food outlets relative to the number of healthier outlets surrounding the homes and schools of California teens, and compared that measurement to teen junk food consumption.
They found that the average California teen has more than seven times as many junk food outlets near home and school as healthier food outlets.
And teens in more unhealthy neighborhoods were 17 percent more likely to drink soda every day and 18 percent more likely to eat fast food at least twice a week than their peers in healthier neighborhoods.
“It is a travesty that our kids have better access to liquor stores and other unhealthy food outlets than a grocery store,” said Robert K. Ross, M.D., president and CEO of the California Endowment, which funded the study. “We have put our children and youth in harm’s way, and they are paying the price for our carelessness. If nothing is done, this will be the first generation to live shorter lives than their parents.”
Few counties immune
The research showed that few counties, whether rural or urban, were immune from the unhealthy effects of junk-food outlet density. In San Benito, Sutter, Merced and Fresno counties, more than 70 percent of teens consume at least one soda per day. In Tulare, Riverside, Ventura and Kern counties, more than 55 percent of teens eat fast food at least twice a week. In total, 13 counties across California had Home and School Retail Food Environment Index scores of more than 8 points — an indication of a relatively unhealthy food environment.
The authors recommended a number of policy options to improve the food environments where teens live and go to school, including better zoning, especially around schools, and farm-to-school programs that bring fresh produce into school cafeterias. They also noted that better incentives were needed to bring healthy food outlets, such as farmers markets and grocery stores, into underserved neighborhoods.
“The research shows that how we plan and zone our communities has a real impact on our health and quality of life,” Babey said. “Policymakers need to take this into account when deciding whether to zone a new grocery store or a fast food restaurant. Hopefully, they will make the healthy choice.”
Charles Stanish at excavation site in Taraco (Credit: Image courtesy of University of California – Los Angeles)
Warfare, triggered by political conflict between the fifth century B.C. and the first century A.D., likely shaped the development of the first settlement that would classify as a civilization in the Titicaca basin of southern Peru, a new UCLA study suggests.
Charles Stanish, director of UCLA’s Cotsen Institute of Archaeology, and Abigail Levine, a UCLA graduate student in anthropology, used archaeological evidence from the basin, home to a number of thriving and complex early societies during the first millennium B.C., to trace the evolution of two larger, dominant states in the region: Taraco, along the Ramis River, and Pukara, in the grassland pampas.
“This study is part of a larger, worldwide comparative research effort to define the factors that gave rise to the first societies that developed public buildings, widespread religions and regional political systems — or basically characteristics associated with ancient states or what is colloquially known as ‘civilization,'” said Stanish, who is also a professor of anthropology at UCLA. “War, regional trade and specialized labor are the three factors that keep coming up as predecessors to civilization.”
The findings appear online in the latest edition of Proceedings of the National Academy of Sciences.
Conducted between 2004 and 2006, the authors’ excavations in Taraco unearthed signs of a massive fire that raged sometime during the first century A.D., reducing much of the state to ash and architectural rubble. The authors compared artifacts dating from before and after the fire and concluded that agriculture, pottery and the obsidian industry, all of which had flourished in the state, greatly declined after the fire.
Based on the range and extent of the destruction and the lack of evidence supporting reconstruction efforts, the authors suggest that the fire was a result of war, not of an accident or a ritual.
Iconographic evidence of conflict in regional stone-work, textiles and pottery suggests that the destruction of Taraco had been preceded by several centuries of raids. This includes depictions of trophy heads and people dressed in feline pelts cutting off heads, among other evidence.
Because the downfall of Taraco, which was home to roughly 5,000 people, coincided with the rise of neighboring Pukara as a dominant political force in the region, the authors suggest that warfare between the states may have led to the raids, shaping the early political landscape of the northern Titicaca basin.
Inhabited between 500 B.C. and 200 A.D., Pukara was the first regional population center in the Andes highlands. During its peak, it covered more than 2 square kilometer and housed approximately 10,000 residents, including bureaucrats, priests, artisans, farmers, herders and possibly warriors.
The civilization’s ruins include impressive monolithic sculptures with a variety of geometric, zoomorphic and anthropomorphic images, plus intricate, multi-colored pottery in a variety of ritual and domestic forms.
War appears to have played a similar civilizing role in Mesoamerica, as well as Mesopotamia, Stanish said. To further test his theories on the origins of civilization, Stanish will begin a new project next year at a Neolithic site in Armenia.
An array of piezoelectrically modulated resistive memory (PRM) cells is shown being studied in an optical microscope. (Georgia Tech Photo: Gary Meek)
The piezotronic memory devices developed by Wang and graduate student Wenzhuo Wu take advantage of the fact that piezoelectric materials like zinc oxide produce a charge potential when they are mechanically deformed or otherwise put under strain. These PRM devices use the piezoelectric charge created by the deformation to control the current flowing through the zinc oxide nanowires that are at the heart of the devices — the basic principle of piezotronics. The charge creates polarity in the nanowires — and increases the electrical resistance much like gate voltage in a conventional transistor.
“We are replacing the application of an external voltage with the production of an internal voltage,” Wang explained. “Because zinc oxide is both piezoelectric and semiconducting, when you strain the material with a mechanical action, you create a piezopotential. This piezopotential tunes the charge transport across the interface — instead of controlling channel width as in conventional field effect transistors.”
The mechanical strain could come from mechanical activities as diverse as signing a name with a pen, the motion of an actuator on a nanorobot, or biological activities of the human body such as a heart beating.
“We control the charge flow across the interface using strain,” Wang explained. “If you have no strain, the charge flows normally. But if you apply a strain, the resulting voltage builds a barrier that controls the flow.”
The piezotronic switching affects current flowing in just one direction, depending on whether the strain is tensile or compressive. That means the memory stored in the piezotronic devices has both a sign and a magnitude. The information in this memory can be read, processed and stored through conventional electronic means.
Taking advantage of large-scale fabrication techniques for zinc oxide nanowire arrays, the Georgia Tech researchers have built non-volatile resistive switching memories for use as a storage medium. They have shown that these piezotronic devices can be written, that information can be read from them, and that they can be erased for re-use. About 20 of the arrays have been built so far for testing.
The zinc oxide nanowires, which are about 500 nanometers in diameter and about 50 microns long, are produced with a physical vapor deposition process that uses a high-temperature furnace. The resulting structures are then treated with oxygen plasma to reduce the number of crystalline defects — which helps to control their conductivity. The arrays are then transferred to a flexible substrate.
“The switching voltage is tunable, depending on the number of oxygen vacancies in the structure,” Wang said. “The more defects you quench away with the oxygen plasma, the larger the voltage that will be required to drive current flow.”
The piezotronic memory cells operate at low frequencies, which are appropriate for the kind of biologically-generated signals they will record, Wang said.
These piezotronic memory elements provide another component needed for fabricating complete self-powered nanoelectromechanical systems (NEMS) on a single chip. Wang’s research team has already demonstrated other key elements such as nanogenerators, sensors and wireless transmitters.
“We are taking another step toward the goal of self-powered complete systems,” Wang said. “The challenge now is to make them small enough to be integrated onto a single chip. We believe these systems will solve important problems in people’s lives.”
Wang believes this new memory will become increasingly important as devices become more closely connected to individual human activities. The ability to build these devices on flexible substrates means they can be used in the body — and with other electronic devices now being built on materials that are not traditional silicon.
“As computers and other electronic devices become more personalized and human-like, we will need to develop new types of signals, interfacing mechanical actions to electronics,” he said. “Piezoelectric materials provide the most sensitive way to translate these gentle mechanical actions into electronic signals that can be used by electronic devices.”
Preschool children consumed nearly twice as many vegetables and 11 percent fewer calories over the course of a day when researchers from Penn State added pureed vegetables to the children’s favorite foods.
“Childhood obesity rates are on the rise, and at the same time children are not eating the recommended amount of vegetables,” said Barbara Rolls, professor of nutritional sciences and holder of the Helen A. Guthrie chair in nutritional sciences in Penn State’s College of Health and Human Development. “Vegetables have been shown to help lower calorie intake. The problem is getting kids to eat enough vegetables.”
In their study, the researchers served vegetable-enhanced entrées to 39 children between the ages of 3 and 6 on three separate days. They tested three familiar foods — zucchini bread for breakfast, pasta with a tomato-based sauce for lunch and chicken noodle casserole for dinner. The team modified the standard recipes for these foods by adding a variety of puréed vegetables to reduce the calories in the entrées by 15 percent and 25 percent.
“We incorporated several vegetables into the dishes, including broccoli, cauliflower, zucchini, tomatoes and squash,” said Maureen Spill, a post-doctoral fellow in nutritional sciences and the study’s lead author. “We were pleased to find that the children found the vegetable-enhanced versions to be equally acceptable to the standard recipes.”
According to Spill, the children ate the same weight of food regardless of the vegetable content of the entrées. And when they ate the vegetable-enhanced entrées as opposed to the standard-recipe entrées, their daily vegetable intake nearly doubled while their calorie intake decreased by 11 percent. The team’s findings are online in the American Journal of Clinical Nutrition.
Rolls and Penn State colleagues Alexandria Blatt, a recent doctoral degree recipient and Liane Roe, a researcher, both in nutritional sciences, found similar results when they served vegetable-enhanced entrées to adults. That work appeared in the April 2011 issue of the American Journal of Clinical Nutrition.
“Regarding children, some people argue that hiding vegetables in foods is deceptive and that doing so suggests that whole vegetables are not acceptable,” said Rolls. “But I don’t agree. Parents modify recipes all the time. For example, it is well-accepted that applesauce can be used to replace oil in cake batter.”
Spill noted that serving vegetables both within entrées and as side dishes is a great way to increase daily vegetable intake even more. “Preparing vegetable-enhanced entrées is a technique that should be used with other strategies, such as providing vegetables as snacks and side dishes. Together these strategies can substantially increase children’s vegetable intake while also teaching them to like vegetables.”
The National Institute of Diabetes and Digestive and Kidney Diseases funded this research. Other authors on the paper include Leann Birch, distinguished professor of human development and family studies, and Liane Roe, researcher in nutritional sciences.
