Image credit: David Tarpy. (Click to enlarge.)

“We wanted to determine whether a colony’s genetic diversity has an impact on its survival, and what that impact may be,” says Dr. David Tarpy, an associate professor of entomology at North Carolina State University and lead author of a paper describing the study. “We knew genetic diversity affected survival under controlled conditions, but wanted to see if it held true in the real world. And, if so, how much diversity is needed to significantly improve a colony’s odds of surviving.”

Tarpy took genetic samples from 80 commercial colonies of honey bees (Apis mellifera) in the eastern United States to assess each colony’s genetic diversity, which reflects the number of males a colony’s queen has mated with. The more mates a queen has had, the higher the genetic diversity in the colony. The researchers then tracked the health of the colonies on an almost monthly basis over the course of 10 months – which is a full working “season” for commercial bee colonies.

Bee colony survival is linked to the number of times a queen has mated. Image: David Tarpy. (Click to enlarge.)

The researchers found that colonies where the queen had mated at least seven times were 2.86 times more likely to survive the 10-month working season. Specifically, 48 percent of colonies with queens who had mated at least seven times were still alive at the end of the season. Only 17 percent of the less genetically diverse colonies survived. “48 percent survival is still an alarmingly low survival rate, but it’s far better than 17 percent,” Tarpy says.

“This study confirms that genetic diversity is enormously important in honey bee populations,” Tarpy says. “And it also offers some guidance to beekeepers about breeding strategies that will help their colonies survive.”

The paper, “Genetic diversity affects colony survivorship in commercial honey bee colonies,” was published online this month in the journal Naturwissenschaften. Co-authors of the study are Dr. Dennis vanEngelsdorp of the University of Maryland and Dr. Jeffery Pettis of USDA. The work was supported by the USDA Cooperative State Research, Education and
Extension Service, the USDA Agricultural Research Service, the North Carolina Department of Agriculture and Consumer Services and the National Honey Board.

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Note to Editors: The study abstract follows.

“Genetic diversity affects colony survivorship in commercial honey bee colonies”

Authors: David R. Tarpy, North Carolina State University; Dennis vanEnglesdorp, University of Maryland; and Jeffery S. Pettis, USDA-ARS Bee Research Laboratory

Published: June 2013, Naturwissenschaften

DOI: 10.1007/s00114-013-1065-y

Abstract: Honey bee (Apis mellifera) queens mate with unusually high numbers of males (average of approximately 12 drones), although there is much variation among queens. One main consequence of such extreme polyandry is an increased diversity of worker genotypes within a colony, which has been shown empirically to confer significant adaptive advantages that result in higher colony productivity and survival. Moreover, honey bees are the primary insect pollinators used in modern commercial production agriculture, and their populations have been in decline worldwide. Here, we compare the mating frequencies of queens, and therefore, intracolony genetic diversity, in three commercial beekeeping operations to determine how they correlate with various measures of colony health and productivity, particularly the likelihood of queen supersedure and colony survival in functional, intensively managed beehives. We found the average effective paternity frequency (me ) of this population of honey bee queens to be 13.6?±6.76, which was not significantly different between colonies that superseded their queen and those that did not. However, colonies that were less genetically diverse (headed by queens with me [less than or equal to]7.0) were 2.86 times more likely to die by the end of the study when compared to colonies that were more genetically diverse (headed by queens with me >7.0). The stark contrast in colony survival based on increased genetic diversity suggests that there are important tangible benefits of increased queen mating number in managed honey bees, although the exact mechanism(s) that govern these benefits have not been fully elucidated.

Cross-section of a nano-volcano carved using light. Click to enlarge. (Image credit: Chih-Hao Chang)

The researchers create the nano-volcanoes by placing spherical, transparent polymer nanoparticles directly onto the flat surface of a thin film. They then shine ultraviolet light through the transparent sphere, which scatters the light and creates a pattern on the thin film. The thin film is made of a photoreactive material that undergoes a chemical change wherever it has been struck by the light. The researchers then submerge the thin film in a liquid solution that washes away the parts of the film that were exposed to light. The material that remains is shaped like a nanoscale volcano.

“We can control the pattern of light by changing the diameter of the nanoparticle spheres, or by changing the wavelength – or color – of the light that we shine through the spheres,” says Xu Zhang, a doctoral student in mechanical and aerospace engineering at NC State and lead author of a paper describing the work. “That means we can control the shape and geometry of these structures, such as how big the cavity of the nano-volcano will be.”

The researchers developed a highly accurate computer model that predicts the shape and dimensions of the nano-volcanoes based on the diameter of the nanoscale sphere and the wavelength of light.

Because these structures have precisely measured hollow cores, and precisely measured openings at the “mouth” of the nano-volcanoes, they are good candidates for drug-delivery mechanisms. The size of the core would allow users to control the amount of the drug a nano-volcano would store, while the size of the opening at the top of the nano-volcano could be used to regulate the drug’s release.

“The materials used in this process are relatively inexpensive, and the process can be easily scaled up,” says Dr. Chih-Hao Chang, an assistant professor of mechanical and aerospace engineering at NC State and co-author of the paper. “In addition, we can produce the nano-volcanoes in a uniformly patterned array, which may also be useful for controlling drug delivery.”

Chang’s team is now working to improve its understanding of the release rate from the nano-volcanoes, such as how quickly nanoparticles of different sizes will “escape” from nano-volcanoes with different-sized mouths. “That’s essential information for drug-delivery applications,” Chang says.

“It’s exciting to take our understanding of how light scatters by particles and apply it to nanolithography in order to come up with something that could actually help people.”

The paper, “Three-Dimensional Nanolithography Using Light Scattering from Colloidal Particles,” was published online June 12 in ACS Nano. Lead author of the paper is NC State Ph.D. student Xu Zhang. Co-authors are Chang and NC State master’s student Jonathan Elek. The research was supported by a NASA Early Career Faculty Award and the National Science Foundation’s ASSIST Engineering Research Center at NC State.

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Note to Editors: The study abstract follows.

“Three-Dimensional Nanolithography Using Light Scattering from Colloidal Particles”

Authors:  Xu A. Zhang, Jonathan Elek and Chih-Hao Chang, North Carolina State University

Published: June 12, 2013, ACS Nano

DOI: 10.1021/nn402637a

Abstract: The interaction between light and colloidal elements can result in a wealth of interesting near-field optical patterns. By examining the optical and colloidal properties, the intensity distribution can be tailored and harnessed for three-dimensional nanolithography. Here, we examine the use of light scattering from colloidal particles to fabricate complex hollow nanostructures. In this approach, a single colloidal sphere is illuminated to create a scattering pattern, which is captured by photoresist in close proximity. No external optical elements are required, and the colloidal elements alone provide the modulation of the optical intensity pattern. The fabricated nanostructures can be designed to have multiple shells, confined volumes, and single top openings, resembling “nano-volcanoes.” The geometry of such structures is dependent on the scattered light distribution, and can be accurately modeled by examining the light-particle interaction. The hollow nanostructures can be used to trap nanomaterial, and we demonstrate their ability to trap 50 nm silica nanoparticles. These well-defined surface hollow structures can be further functionalized for applications in controlled drug delivery and bio-trapping. Colloidal elements with different geometries and material compositions can also be incorporated to examine other light-colloid interactions.

The research, published online in Proceedings of the National Academy of Sciences the week of June 10, describes how one strand of micro-RNA reduced by more than 20 percent the formation of lignin, which gives wood its strength. Understanding how to reduce lignin at the cellular level could lead to advances in paper and biofuels production, where harsh chemicals and costly treatments are used to remove lignin from wood.

“This is the first time that we have proof that a micro-RNA controls lignin biosynthesis,” said Dr. Vincent Chiang, who co-directs NC State’s Forest Biotechnology Group with Dr. Ron Sederoff, a member of the National Academy of Sciences.

Through five years of “very detailed analysis,” the team confirmed that micro-RNA acts as a master regulator in reducing formation of lignin in transgenic black cottonwood, Chiang said.

Researchers used mathematical analysis to map out a three-layered network of relationships among key transcription factors and the micro-RNA that controls expression of laccase genes as well as other peroxidase genes involved in wood formation.

The network illustrates the hierarchy of gene control and narrows the transcription factors of interest from approximately 2,000 to 20. “That’s still a career’s worth of research,” Chiang said.

Lead authors are Dr. Shanfa Lu, former NC State postdoctoral scientist and now professor with the Chinese Academy of Medical Sciences and Peking Union Medical College, and Dr. Quanzi Li, senior research associate with NC State’s Forest Biotechnology Group. Dr. Hairong Wei, professor of systems and computational biology at Michigan Technological University, created a unique algorithm for mapping the genetic regulatory network.

The research was funded with a National Science Foundation Plant Genome Research Program Grant (DBI-0922391).

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Note to editors: An abstract of the paper follows.

“Ptr-miR397a is a negative regulator of laccase genes affecting lignin content in Populus trichocarpa”

Published: Online the week of June 10 in Proceedings of the National Academy of Sciences

Authors: Shanfa Lu, Quanzi Li, Hairong Wei, Mao-Ju Chang, Sermsawat Tunlaya-Anukit, Hoon Kim, Jie Liu, Jingyuan Song, Ying-Hsuan Sun, Lichai Yuan, Ting-Feng Yeh, Ilona Peszlen, John Ralph, Ronald R. Sederoff and Vincent L. Chiang

Co-lead author Li, Tunlaya-Anukit, Liu, Sederoff and Chiang are members of the Forest Biotechnology Group at North Carolina State University. Co-lead author Lu, a former postdoctoral researcher at NC State, Song and Yuan are with the Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences and Peking Union Medical College. Wei is with Michigan Technological University. Chang and Yeh are with National Taiwan University. Sun is with National Chung Hsing University in Taiwan. Peszlen is with the Department of Forest Biomaterials, NC State. Kim and Ralph are with the University of Wisconsin, Madison.

Abstract: Laccases, as early as 1959, were proposed to catalyze the oxidative polymerization of monolignols. Genetic evidence in support of this hypothesis has been elusive due to functional redundancy of laccase genes. An Arabidopsis double mutant demonstrated the involvement of laccases in lignin biosynthesis. We previously identified a subset of laccase genes to be targets of a microRNA (miRNA) ptr-miR397a in Populus trichocarpa. To elucidate the roles of ptr-miR397a and its targets, we characterized the laccase gene family and identified 49 laccase gene models, of which 29 were predicted to be targets of ptr-miR397a. We overexpressed Ptr MIR397a in transgenic P. trichocarpa. In each of all nine transgenic lines tested, 17 PtrLACs were down-regulated as analyzed by RNA-seq. Transgenic lines with severe reduction in the expression of these laccase genes resulted in an ~40% decrease in the total laccase activity. Overexpression of Ptr-MIR397a in these transgenic lines also reduced lignin content, whereas levels of all monolignol biosynthetic gene transcripts remained unchanged. A hierarchical genetic regulatory network (GRN) built by a bottom-up graphic Gaussian model algorithm provides additional support for a role of ptr-mi397a as a negative regulator of laccases for lignin biosynthesis. Full transcriptome-based differential gene expression in the overexpressed transgenics and protein domain analyses implicate previously unidentified transcription factors and their targets in an extended hierarchical GRN including ptr-miR397a and laccases that coregulate lignin biosynthesis in wood formation. Ptr-miR397a, laccases, and other regulatory components of this network may provide additional strategies for genetic manipulation of lignin content.

“This study shows that providing mental health care is not only in the best interest of people with mental illness, but in the best interests of society,” says Dr. Sarah Desmarais, an assistant professor of psychology at NC State and co-author of a paper describing the research.

The researchers wanted to determine the extent to which treating mental illness can keep people with mental health problems out of trouble with the law. It is well established that people with mental health problems, such as schizophrenia or bipolar disorder, make up a disproportionate percentage of defendants, inmates and others who come into contact with the criminal justice system.

The researchers identified 4,056 people who had been hospitalized for mental illness in 2004 or 2005 and then tracked them from 2005 to 2012. The researchers were able to determine which individuals were receiving government-subsidized medication and which were receiving government-subsidized outpatient services, such as therapy. The researchers were also able to determine who was arrested during the seven-year study period.

“Our research shows that people receiving medication were significantly less likely to be arrested,” Desmarais says. “Outpatient services also resulted in a decreased likelihood of arrest.”

The researchers also compared criminal justice costs with mental health treatment costs. Individuals who were arrested received less treatment and each cost the government approximately $95,000 during the study period. Individuals who were not arrested received more treatment and each cost the government approximately $68,000 during the study period.

“It costs about $10 less per day to provide treatment and prevent crime. That’s a good investment,” Desmarais says.

The paper, “Effects of Outpatient Treatment on Risk of Arrest of Adults With Serious Mental Illness and Associated Costs,” was published online May 15 in the journal Psychiatric Services. Lead author of the paper is Dr. Richard Van Dorn of RTI. Co-authors include John Petrila, Diane Haynes and Dr. Jay Singh of the University of South Florida. The research was supported by the Florida Agency for Health Care Administration.

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Note to Editors: The study abstract follows.

“Effects of Outpatient Treatment on Risk of Arrest of Adults With Serious Mental Illness and Associated Costs”

Authors: Richard A. Van Dorn, Research Triangle Institute; Sarah L. Desmarais, North Carolina State University; John Petrila, Diane Haynes and Jay P. Singh, University of South Florida

Published: Online May 2013, Psychiatric Services

DOI: 10.1176/appi.ps.201200406

Abstract: Objective: This study examined whether possession of psychotropic medication and receipt of outpatient services reduce the likelihood of posthospitalization arrest among adults with serious mental illness. A secondary aim was to compare service system costs for individuals who were involved with the justice system and those who were not. Methods: Claims data for prescriptions and treatments were used to describe patterns and costs of outpatient services between 2005 and 2012 for 4,056 adult Florida Medicaid enrollees with schizophrenia or bipolar disorder after discharge from an index hospitalization. Multivariable time-series analysis tested the effects of medication and outpatient services on arrest (any, felony, or misdemeanor) in subsequent 30-day periods. Results: A total of 1,263 participants (31%) were arrested at least once during follow-up. Monthly medication possession and receipt of outpatient services reduced the likelihood of any arrests (misdemeanor or felony) and of misdemeanor arrests. Possession of medications for 90 days after hospital discharge also reduced the likelihood of arrest. Prior justice involvement, minority racial-ethnic status, and male sex increased the risk of arrest, whereas older age decreased it. Criminal justice and behavioral health system costs were significantly higher for the justice-involved group than for the group with no justice involvement. Conclusions: Routine outpatient treatment, including medication and outpatient services, may reduce the likelihood of arrest among adults with serious mental illness. Medication possession over a 90-day period after hospitalization appears to confer additional protection. Overall, costs were lower for those who were not arrested, even when they used more outpatient services.

Mycoplasma gallisepticum (MG) is a bacterium that emerged on the East Coast in 1994 as a cause of pink eye, or conjunctivitis, in house finches and has since spread across the U.S. David Ley, a professor of population health and pathobiology at North Carolina State University, has studied MG for decades, since in North Carolina it has also been found in poultry. When house finches first showed signs of the disease, Ley identified MG as the cause, collected samples of the pathogen from infected birds and preserved them for future study.

Ornithologist Dana Hawley and ecologist André Dhondt, from Virginia Tech and Cornell University, respectively, were interested in how MG had spread across the country’s house finch populations and wanted to understand its evolution. Using samples of the bacterium taken from the Eastern and Californian house finch populations that Ley had collected between 1994 and 2010, the team of researchers – which also included Cornell University’s Wesley Hochachka and Princeton’s Andrew Dobson – found that the virulence of MG had increased over time in both locations.

In both locations the disease was less virulent when it emerged and established itself in areas with high populations of susceptible finches. However, as the disease caused the populations to decrease and immunity within the remaining populations increased, the bacteria responded by becoming more virulent, with higher pathogen loads to overcome immunity and sustain transmissibility.

Ley believes that this study of house finch eye disease provided a unique opportunity to understand the evolution of virulence in emergent diseases. “We were able to identify a new MG disease in a free-ranging population early on, and study it over time, location and host species,” he says. “Now we can see if similar patterns occur across other infectious diseases, and what that may mean for our ability to understand factors that drive virulence evolution both naturally and perhaps even in response to treatments and vaccinations.”

The researchers’ results appear in PLOS Biology. Hawley is lead author. The research was funded by grants from the National Science Foundation, the National Institutes of Health and the U.S. Department of Agriculture.

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Note to editors: Abstract follows.

“Parallel Patterns of Increased Virulence in a Recently Emerged Wildlife Pathogen”

Published: PLOS Biology

Authors: Dana M. Hawley, Virginia Tech; André A. Dhondt, Andrew P. Dobson and Wesley M. Hochachka, Cornell Lab of Ornithology; Erik E. Osnas, Princeton University; David H. Ley, North Carolina State University

Abstract:
The evolution of higher virulence during disease emergence has been predicted by theoretical models, but empirical studies of short-term virulence evolution following pathogen emergence remain rare. Here we examine patterns of short term virulence evolution using archived isolates of the bacterium Mycoplasma gallisepticum collected during sequential emergence events in two geographically distinct populations of the host, the North American house finch (Haemorhous [formerly Carpodacus] mexicanus). We present results from two complementary experiments, one that examines the trend in pathogen virulence in eastern North American isolates over the course of the eastern epidemic (1994–2008), and the other a parallel experiment on Pacific coast isolates of the pathogen collected after M. gallisepticum established itself in western North American house finch populations (2006–2010). Consistent with theoretical expectations regarding short-term or dynamic evolution of virulence, we show rapid increases in pathogen virulence on both coasts following the pathogen’s establishment in each host population. We also find evidence for positive genetic covariation between virulence and pathogen load, a proxy for transmission potential, among isolates of M. gallisepticum. As predicted by theory, indirect selection for increased transmission likely drove the evolutionary increase in virulence in both geographic locations. Our results provide one of the first empirical examples of rapid changes in virulence following pathogen emergence, and boththe detected pattern and mechanism of positive genetic covariation between virulence and pathogen load are consistent with theoretical expectations. Our study provides unique empirical insight into the dynamics of short-term virulence evolution that are likely to operate in other emerging pathogens of wildlife and humans.

Researchers found that each sampled locations harbored its own unique collection of bacteria. (Click to enlarge.)

“We wanted to know what variables influence the microbial ecosystems in our homes, and the biggest difference we’ve found so far is whether you own a dog,” says Dr. Rob Dunn, an associate professor of biology at NC State and co-author of a paper describing the work. “We can tell whether you own a dog based on the bacteria we find on your television screen or pillow case. For example, there are bacteria normally found in soil that are 700 times more common in dog-owning households than in those without dogs.”

And these microbial differences may be important. For example, it’s known that women who have a dog in the home when pregnant are less likely to have children with allergies. This is a correlation – there’s no known causal link between the presence of a dog and the absence of allergies – but it has been hypothesized that the difference is related to the women’s exposure to a wider variety of microbes. However, to this point there were few data on what the differences in microbial populations might be. While this study doesn’t demonstrate a causal link, it sheds more light on the subject, showing that dogs have a major influence on which microbes are found in our homes.

Citizen scientists in 40 homes sampled nine common surfaces to help researchers determine what kinds of bacteria lived there, and in what relative numbers. The nine surfaces were wiped with sterile swabs from which researchers collected DNA to see which organisms were present. The nine surfaces were the television screen, kitchen counter, refrigerator, toilet seat, cutting board, pillow case, exterior door handle, the trim around an interior door and the trim around an exterior door.

The study found 7,726 phylotypes, or kinds, of bacteria in the homes. The study also found that each of the locations sampled harbored its own unique collection of bacteria. Researchers were able to group the sampled surfaces in the homes into one of three general habitats: places we touch, places our food touches and places that collect dust. For example, the types of bacteria found in refrigerators, on kitchen counters and on cutting boards tended to be similar – because they were primarily linked to our food. Meanwhile, the bacteria found on doorknobs, pillow cases and toilet seats were also fairly similar – and came from humans.

A citizen scientist swabs the surface of a cutting board for bacterial DNA. (Click to enlarge.)

“We leave a microbial ‘fingerprint’ on everything we touch,” Dunn says. “Sometimes those microbes come from our skin, sometimes they’re oral bacteria and – as often as not – they’re human fecal bacteria.”

The research also shows that the difference between habitats is greater than the difference between homes. For example, the bacteria on my pillow case are probably more similar to the bacteria on your pillow case than they are to the bacteria on my kitchen counter.

“This makes sense,” Dunn says. “Humans have been living in houses for thousands of years, which is sufficient time for organisms to adapt to living in particular parts of houses. We know, for example, that there is a species that only lives in hot-water heaters. We deposit these bacterial hitchhikers in different ways in different places, and they thrive or fail depending on their adaptations.”

The researchers are currently processing samples from another 40 homes, and are preparing to process samples from a national survey of 1,300 homes across the United States. The national survey sampled four sites in each home, representing the various habitats.

“The larger sample size will help us better understand the range of variables that influence these microbial ecosystems,” Dunn says. “Does it matter if you have kids or live in an apartment? We expect the microbial populations of homes in deserts to be different from the populations of homes in Manhattan, but no one knows if that’s true. We want to find out.”

The paper, “Home Life: Factors structuring the bacterial diversity found within and between homes,” was published in PLOS ONE May 22. The paper was co-authored by Dunn; Dr. Holly Menninger, director of public science for the Your Wild Life program at NC State; and Dr. Noah Fierer, Jessica Henley and Jonathan Leff of the University of Colorado. The research was supported by the Sloan Foundation and the Howard Hughes Medical Institute. The dataset used for the paper is also publicly available at figshare: http://dx.doi.org/10.6084/m9.figshare.674588.

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Note to Editors: The study abstract follows.

“Home Life: Factors structuring the bacterial diversity found within and between homes”

Authors: Robert R. Dunn and Holly L. Menninger, North Carolina State University; Noah Fierer, Jessica B. Henley and Jonathan W. Leff, University of Colorado

Published: May 22, PLOS ONE

DOI: 10.1371/journal.pone.0064133

Abstract: Most of our time is spent indoors where we are exposed to a wide array of different microorganisms living on surfaces and in the air of our homes. Despite their ubiquity and abundance, we have a limited understanding of the microbial diversity found within homes and how the composition and diversity of microbial communities change across different locations within the home. Here we examined the diversity of bacterial communities found in nine distinct locations within each of forty homes in the Raleigh-Durham area of North Carolina, USA, using high-throughput sequencing of the bacterial 16S rRNA gene. We found that each of the sampled locations harbored bacterial communities that were distinct from one another with surfaces that are regularly cleaned typically harboring lower levels of diversity than surfaces that are cleaned infrequently. These location-specific differences in bacterial communities could be directly related to usage patterns and differences in the likely sources of bacteria dispersed onto these locations. Finally, we examined whether the variability across homes in bacterial diversity could be attributed to outdoor environmental factors, indoor habitat structure, or the occupants of the home. We found that the presence of dogs had a significant effect on bacterial community composition in multiple locations within homes as the homes occupied by dogs harbored more diverse communities and higher relative abundances of dog-associated bacterial taxa. Furthermore, we found a significant correlation between the types of bacteria deposited on surfaces outside the home and those found inside the home, highlighting that microbes from outside the home can have a direct effect on the microbial communities living on surfaces within our homes. Together this work provides the first comprehensive analysis of the microbial communities found in the home and the factors that shape the structure of these communities both within and between homes.

“This could be used to scale current semiconductor technologies down to the atomic scale – lasers, light-emitting diodes (LEDs), computer chips, anything,” says Dr. Linyou Cao, an assistant professor of materials science and engineering at NC State and senior author of a paper on the work. “People have been talking about this concept for a long time, but it wasn’t possible. With this discovery, I think it’s possible.”

The researchers worked with molybdenum sulfide (MoS2), an inexpensive semiconductor material with electronic and optical properties similar to materials already used in the semiconductor industry. However, MoS2 is different from other semiconductor materials because it can be “grown” in layers only one atom thick without compromising its properties.

In the new technique, researchers place sulfur and molybdenum chloride powders in a furnace and gradually raise the temperature to 850 degrees Celsius, which vaporizes the powder. The two substances react at high temperatures to form MoS2. While still under high temperatures, the vapor is then deposited in a thin layer onto the substrate.

“The key to our success is the development of a new growth mechanism, a self-limiting growth,” Cao says. The researchers can precisely control the thickness of the MoS2 layer by controlling the partial pressure and vapor pressure in the furnace. Partial pressure is the tendency of atoms or molecules suspended in the air to condense into a solid and settle onto the substrate. Vapor pressure is the tendency of solid atoms or molecules on the substrate to vaporize and rise into the air.

To create a single layer of MoS2 on the substrate, the partial pressure must be higher than the vapor pressure. The higher the partial pressure, the more layers of MoS2 will settle to the bottom. If the partial pressure is higher than the vapor pressure of a single layer of atoms on the substrate, but not higher than the vapor pressure of two layers, the balance between the partial pressure and the vapor pressure can ensure that thin-film growth automatically stops once the monolayer is formed. Cao calls this “self-limiting” growth.

Partial pressure is controlled by adjusting the amount of molybdenum chloride in the furnace – the more molybdenum is in the furnace, the higher the partial pressure.

“Using this technique, we can create wafer-scale MoS2 monolayer thin films, one atom thick, every time,” Cao says. “We can also produce layers that are two, three or four atoms thick.”

Cao’s team is now trying to find ways to create similar thin films in which each atomic layer is made of a different material. Cao is also working to create field-effect transistors and LEDs using the technique. Cao has filed a patent on the new technique.

The paper, “Controlled Scalable Synthesis of Uniform, High-Quality Monolayer and Few-layer MoS2 Films,” was published online May 21 in Scientific Reports, a journal of the Nature Publishing Group. Lead author of the paper is NC State Ph.D. student Yifei Yu. Co-authors are Dr. Chun Li, a former postdoctoral researcher at NC State; Yi Liu, a laboratory manager at NC State; Liqin Su and Dr. Yong Zhang of the University of North Carolina at Charlotte. The research was funded by the U.S. Army Research Office.

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Note to Editors: The study abstract follows.

“Controlled Scalable Synthesis of Uniform, High-Quality Monolayer and Few-layer MoS2 Films”

Authors: Yifei Yu, Chun Li, Yi Liu, and Linyou Cao, North Carolina State University; Liqin Su and Yong Zhang, University of North Carolina at Charlotte

Published: May 21, Scientific Reports

DOI: 10.1038/srep01866

Abstract: Two dimensional (2D) materials with a monolayer of atoms represent an ultimate control of material dimension in the vertical direction. Molybdenum sulfide (MoS2) monolayers, with a direct bandgap of 1.8 eV, offer an unprecedented prospect of miniaturizing semiconductor science and technology down to a truly atomic scale. Recent studies have indeed demonstrated the promise of 2D MoS2 in fields including field effect transistors, low power switches, optoelectronics, and spintronics. However, device development with 2D MoS2 has been delayed by the lack of capabilities to produce large-area, uniform, and high quality MoS2 monolayers. Here we present a self-limiting approach that can grow high quality monolayer and few-layer MoS2 films over an area of centimeters with unprecedented uniformity and controllability. This approach is compatible with the standard fabrication process in the semiconductor industry. It paves the way for the development of practical devices with 2D MoS2 and opens up new avenues for fundamental research.

Thin-film interference occurs when a thin film of one substance lies on top of a second substance. For example, thin-film interference is what causes the rainbow sheen we see when there is gasoline in a puddle of water.

The nanostructures limit the amount of light reflected at the thin film interface. (Click to enlarge.)

Gasoline is transparent, but some light is still reflected off of its surface. Similarly, some of the light that passes through the gasoline is reflected off the underlying surface of the water where the two substances interface, or meet. Because the light reflected off the water has to pass back through the gasoline, it takes a slightly different optical path than the light that was reflected off the surface of the gasoline. The mismatch of these optical path “lengths” is what creates the rainbow sheen – and that phenomenon is thin-film interference.

Thin-film interference is a problem for devices that use multiple layers of thin films, like thin-film solar cells, because it means that some wavelengths of light are being reflected – or “lost” – at every film interface. The more thin films a device has, the more interfaces there are, and the more light is lost.

“We were inspired by the surface structure of a moth’s eye, which has evolved so that it doesn’t reflect light,” says Dr. Chih-Hao Chang, an assistant professor of mechanical and aerospace engineering at NC State and co-author of a paper on the research. “By mimicking that concept, we’ve developed a nanostructure that significantly minimizes thin-film interference.”

The nanostructures are built into thin films that will have a second thin film placed on top of them. The nanostructures are an extension of the thin film beneath them, and resemble a tightly-packed forest of thin cones. These nanostructures are “interfacial,” penetrating into whatever thin film is layered on top of them – and limiting the amount of light reflected at that interface. Chang’s team found that the an interface featuring the interfacial nanostructures reflects 100 times less light than an interface of thin films without the nanostructures.

“Our next steps are to design a solar device that takes advantage of this concept and to determine how we can scale it up for commercial applications,” Chang says.

The paper, “Antireflection Effects at Nanostructured Material Interfaces and the Suppression of Thin-Film Interference,” was published online May 15 in the journal Nanotechnology. Lead author of the paper is former NC State graduate student Qiaoyin Yang. Co-authors are Chang and NC State Ph.D. students Xu A. Zhang, Abhijeet Bagal and Wei Guo. The research was supported by a NASA Early Career Faculty Award and the National Science Foundation’s ASSIST Engineering Research Center at NC State.

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Note to Editors: The study abstract follows.

“Antireflection Effects at Nanostructured Material Interfaces and the Suppression of Thin-Film Interference”

Authors:  Qiaoyin Yang, Xu A. Zhang, Abhijeet Bagal, Wei Guo and Chih-Hao Chang, North Carolina State University

Published: May 16, Nanotechnology

DOI: 10.1088/0957-4484/24/23/235202

Abstract: Thin-film interference is a well-known effect, and it is commonly observed in the colored appearance of many natural phenomena. Caused by the interference of light reflections from the interfaces of thin material layers, such interference effects can lead to wavelength and angle-selective behavior in thin-film devices. In this work, we describe the use of interfacial nanostructures to eliminate interference effects in thin films. Using the same principle inspired by the moth-eye structures, this approach creates an effective medium where the index is gradually varying between the neighboring materials. We present the fabrication process for such nanostructures at a polymer-silicon interface, and experimentally demonstrate its effectiveness in suppressing thin-film interference. The principle demonstrated in this work can lead to enhanced efficiency and reduce wavelength/angle sensitivity in multilayer optoelectronic devices.

Networked control systems are essentially pathways that connect and coordinate activities between computers and physical devices. For example, the systems that connect temperature sensors, heating systems and user controls in modern buildings are networked control systems.

But, on a much larger scale, these systems are also becoming increasingly important to national infrastructure, such as transportation and power. And, because they often rely on wireless or Internet connections, these systems are vulnerable to cyber-attacks. “Flame” and “Stuxnet” are examples of costly, high-profile attacks on networked control systems in recent years.

As networked control systems have grown increasingly large and complex, system designers have moved away from having system devices – or “agents” – coordinate their activities through a single, centralized computer hub, or brain. Instead, designers have created “distributed network control systems” (D-NCSs) that allow all of the system agents to work together, like a bunch of mini-brains, to coordinate their activities. This allows the systems to operate more efficiently. And now these distributed systems can also operate more securely.

NC State researchers have developed a software algorithm that can detect when an individual agent in a D-NCS has been compromised by a cyber-attack. The algorithm then isolates the compromised agent, protecting the rest of the system and allowing it to continue functioning normally. This gives D-NCSs resilience and security advantages over systems that rely on a central computer hub, because the centralized design means the entire system would be compromised if the central computer is hacked.

“In addition, our security algorithm can be incorporated directly into the code used to operate existing distributed control systems, with minor modifications,” says Dr. Mo-Yuen Chow, a professor of electrical and computer engineering at NC State and co-author of a paper on the work. “It would not require a complete overhaul of existing systems.”

“We have demonstrated that the system works, and are now moving forward with additional testing under various cyber-attack scenarios to optimize the algorithm’s detection rate and system performance,” says Wente Zeng, a Ph.D. student at NC State and lead author of the paper.

The paper, “Convergence and Recovery Analysis of the Secure Distributed Control Methodology for D-NCS,” will be presented at the IEEE International Symposium on Industrial Electronics, May 28-31, in Taipei, Taiwan. The research was funded by the National Science Foundation.

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Note to Editors: The study abstract follows.

“Convergence and Recovery Analysis of the Secure Distributed Control Methodology for D-NCS”

Authors: Wente Zeng and Mo-Yuen Chow, North Carolina State University

Presented: May 28-31, IEEE International Symposium on Industrial Electronics, Taipei, Taiwan

Abstract: Distributed control algorithms (e.g., consensus algorithm) are vulnerable to the misbehaving agent compromised by the cyber-attacks in Distributed Networked Control Systems (D-NCS). In this paper we continue our work on the proposed secure distributed control methodology that is capable of performing a secure consensus computation in D-NCS in the presence of misbehaving agents. The methodology is introduced first and proved to be effective through the convergence analysis. We then extend our secure distributed control methodology to the leaderless consensus network by introducing and adding two recovery schemes into the current secure distributed control framework to guarantee the accurate convergence in the presence of misbehaving agents. All phases in our method are distributed in the sense that at each step of the detection, mitigation, identification, update and recovery, every agent only uses local and one-hop neighbors’ information.  The simulation results are presented to demonstrate the effectiveness of the proposed methods.

The face of an unfortunate Budgett's frog tadpole that is being digested inside the stomach of its larger sibling. (click to enlarge)

A carnivorous, cannibalistic tadpole may play a role in understanding the evolution and development of digestive organs, according to research from North Carolina State University. These findings may also shed light on universal rules of organ development that could lead to better diagnosis and prevention of intestinal birth defects.

NC State developmental biologist Nanette Nascone-Yoder, graduate student Stephanie Bloom and postdoc Cris Ledon-Rettig looked at Xenopus laevis (African clawed frog) and Lepidobatrachus laevis (Budgett’s frog) tadpoles. These frog species differ in diet and last shared a common ancestor about 110 million years ago. Like most tadpoles, Xenopus exist primarily on a diet of algae, and their long, simple digestive tracts are not able to process insects or proteins until they become adult frogs. Budgett’s is an aggressive species of frog which is carnivorous – and cannibalistic – in the tadpole stage.

Nascone-Yoder knew that Budgett’s tadpoles had evolved shorter, more complex guts to digest protein much earlier in their development. She and her team exposed Xenopus embryos to molecules that inactivated a variety of genes to see if any might coax Xenopus to develop a more carnivore-like digestive tract. Remarkably, five molecules caused Xenopus tadpoles to develop guts that were closer in appearance to those of the Budgett’s tadpoles. Taking it one step further, Nascone-Yoder exposed Budgett’s frog embryos to molecules with opposite effects, and got tadpole guts that were closer to those of Xenopus.

“Essentially, these molecules are allowing us to tease apart the processes that play a key role in gut development,” Nascone-Yoder says. “Understanding how and why the gut develops different shapes and lengths to adapt to different diets and environments during evolution gives us insight into what types of processes can be altered in the context of human birth defects, another scenario in which the gut also changes its shape and function.”

The researchers’ next steps include finding out whether the changes in these gut tubes were merely cosmetic, or if they also function (digest) differently.

The findings appear in Evolution and Development. James Hanken, Carlos Infante and Anne Everly from the Harvard Museum of Comparative Zoology contributed to the work. The research was funded in part by the National Science Foundation.

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Note to editors: Abstract follows.

“Developmental origins of a novel gut morphology in frogs”

Published: Evolution and Development

Authors: Nanette Nascone-Yoder, Stephanie Bloom and Cris Ledon-Rettig, North Carolina State University; Carlos Infante, Anne Everly, and James Hanken, Harvard University

Abstract:
Phenotypic variation is a prerequisite for evolution by natural selection, yet the processes that give rise to the novel morphologies upon which selection acts are poorly understood. We employed a chemical genetic screen to identify developmental changes capable of generating ecologically relevant morphological variation as observed among extant species. Specifically, we assayed for exogenously applied small molecules capable of transforming the ancestral larval foregut of the herbivorous Xenopus laevis to resemble the derived larval foregut of the carnivorous Lepidobatrachus laevis. Appropriately, the small molecules that demonstrate this capacity modulate conserved morphogenetic pathways involved in gut development, including downregulation of retinoic acid (RA) signaling. Identical manipulation of RA signaling in a species that is more closely related to Lepidobatrachus, Ceratophrys cranwelli, yielded even more similar transformations, corroborating the relevance of RA signaling variation in interspecific morphological change. Finally, we were able to recover the ancestral gut phenotype in Lepidobatrachus by performing a reverse chemical manipulation to upregulate RA signaling, providing strong evidence that modifications to this specific pathway promoted the emergence of a lineage-specific phenotypic novelty. Interestingly, our screen also revealed pathways that have not yet been implicated in early gut morphogenesis, such as thyroid hormone signaling. In general, the chemical genetic screen may be a valuable tool for identifying developmental mechanisms that underlie ecologically and evolutionarily relevant phenotypic variation.