March 18, 2014
Cognitive scientists may have produced the strongest evidence yet that humans have separate and distinct cognitive systems with which they can categorize, classify, and conceptualize their worlds.
“Our finding that there are distinct, discrete systems has implications for the fields of child development and cognitive aging,” says lead researcher, cognitive psychologist J. David Smith, PhD, of the University at Buffalo.
“These distinct systems may have different developmental courses as the cortex matures,” he says, “meaning that children may categorize differently than adults, using different systems at different ages. This would have educational and training implications in cases of developmental disability.”
He says the systems also may have different courses of decline in cognitive aging, which would have ramifications for remediation and compensation in dementia.
The study “Deferred Feedback Sharply Dissociates Implicit and Explicit Category Learning,” was conducted by Smith and colleagues at UB and at the University of California at Santa Barbara. It was published in the Feb. 7 edition of the journal Psychological Science.
The age-old question of whether humans have discrete cognitive systems operating on different levels that are more or less conscious, more or less available to introspection, and so forth, has been debated for years.
“This issue of whether there are separate cognitive systems famously arose regarding humans’ declarative and procedural memory and in the field of categorization,” Smith says.
“Cognitive neuroscientists have hypothesized that humans have distinguishable systems for categorizing the objects in their world – one more explicit (i.e., conscious and available to introspection), one less so, or more implicit,” says Smith.
To grasp the differences between these two types of learning, Smith recommends that we remember certain distinctions in our performance of the tasks of daily life.
“For instance, when you select a cereal named ‘Chocoholic’ from the store shelf,” he says, “consider why you are doing so. Is it a deliberate, explicit choice, or is it possibly an implicit-procedural chocolate reaction, one triggered by processes, memories and so on, of which you are generally unaware?”
“Because of the considerable controversy surrounding the question of whether we have more than one cognitive system, researchers have continued to seek models that distinguish the processes of explicit and implicit category learning,” Smith says, “and this study presents the clearest distinction yet found between these systems.
“To make this discovery,” he says, “we borrowed an influential model from our studies of macaque monkeys, which illustrates the valuable synergies that exist between primate and human research.”
Their technique was to ask humans to work for blocks of trials without any corrective feedback, and then deliver feedback when they were finished. Smith likens this process to an undergraduate testing situation in which the student taking a test does not get item-by-item feedback, but receives a summary score once the test is completed.
Because this manipulation, he says, prevents the formation of automatic (implicit) stimulus-response associations, Smith and his colleagues hypothesized that it would undermine the processes of conditioning and eliminate the possibility of implicit category learning.
“Implicit category learning,” he says, “is a system that depends on trial-by-trial feedback of response correctness and incorrectness to establish the stimulus-response associations that allow implicit learning and responding.
“In fact,” Smith says, “the blocked-feedback technique made implicit category learning impossible. We then used extensive trial-strategy analyses and formal-mathematical modeling to demonstrate this conclusively.
“So we were able to selectively unplug one category-learning system – the implicit system – but leave the explicit-conscious system functioning and intact,” he says.
Smith et al. even found that, facing a task that could only be learned implicitly, participants with blocked feedback turned futilely to conscious strategies that were inadequate, because this was all they could do when implicit category learning was defeated.
“In the area of categorization research,” Smith says, “the issue of single vs. multiple systems is nearly closed. The evidence is now very strong that there are multiple category-learning systems – in particular, the explicit-conscious and the implicit-procedural system.”
Smith says it is fascinating to consider where in cognitive evolution the roots of the explicit-declarative categorization system lie. He and his colleagues have found the beginnings of this system in non-human primates like rhesus macaques and capuchin monkeys. Interestingly, though, thus far pigeons have shown no evidence of having distinguishable explicit and implicit systems.
Smith’s co-authors were Joseph Boomer and Alexandria C. Zakrzewski, graduate students, andBarbara Church PhD, senior research scientist, all in the UB Department of Psychology, and graduate student Jessica Roeder and F. Gregory Ashby, PhD, both in the Department of Psychological and Brain Sciences, University of California, Santa Barbara.
March 17, 2014
Shale, the source of the United States’ current natural gas boom, could help solve another energy problem: what to do with radioactive waste from nuclear power plants. The unique properties of the sedimentary rock and related clay-rich rocks make it ideal for storing the potentially dangerous spent fuel for millennia, according to a geologist studying possible storage sites who made a presentation here today.
The talk was one of more than 10,000 presentations at the 247th National Meeting & Exposition of the American Chemical Society (ACS), the world’s largest scientific society, taking place here through Thursday.
About 77,000 tons of spent nuclear fuel currently sit in temporary above-ground storage facilities, said Chris Neuzil, Ph.D., who led the research, and it will remain dangerous for tens or hundreds of thousands of years or longer.
“Surface storage for that length of time requires maintenance and security,” he said. “Hoping for stable societies that can continue to provide those things for millennia is not a good idea.” He also pointed out that natural disasters can threaten surface facilities, as in 2011 when a tsunami knocked cooling pumps in storage pools offline at the Fukushima Daiichi nuclear power plant in Japan.
Since the U.S. government abandoned plans to develop a long-term nuclear-waste storage site at Yucca Mountain in Nevada in 2009, Neuzil said finding new long-term storage sites must be a priority. It is crucial because nuclear fuel continues to produce heat and harmful radiation after its useful lifetime. In a nuclear power plant, the heat generated by uranium, plutonium and other radioactive elements as they decay is used to make steam and generate electricity by spinning turbines. In temporary pool storage, water absorbs heat and radiation. After spent fuel has been cooled in a pool for several years, it can be moved to dry storage in a sealed metal cask, where steel and concrete block radiation. This also is a temporary measure.
But shale deep under the Earth’s surface could be a solution. France, Switzerland and Belgium already have plans to use shale repositories to store nuclear waste long-term. Neuzil proposes that the U.S. also explore the possibility of storing spent nuclear fuel hundreds of yards underground in layers of shale and other clay-rich rock. He is with the U.S. Geological Survey and is currently investigating a site in Ontario with the Canadian Nuclear Waste Management Organization.
Neuzil explained that these rock formations may be uniquely suited for nuclear waste storage because they are nearly impermeable – barely any water flows through them. Experts consider water contamination by nuclear waste one of the biggest risks of long-term storage. Unlike shale that one might see where a road cuts into a hillside, the rocks where Neuzil is looking are much more watertight. “Years ago, I probably would have told you shales below the surface were also fractured,” he said. “But we’re seeing that that’s not necessarily true.” Experiments show that water moves extremely slowly through these rocks, if at all.
Various circumstances have conspired to create unusual pressure systems in these formations that result from minimal water flow. In one well-known example, retreating glaciers in Wellenberg, Switzerland, squeezed the water from subsurface shale. When they retreated, the shale sprung back to its original shape faster than water could seep back in, creating a low-pressure pocket. That means that groundwater now only flows extremely slowly into the formation rather than through it. Similar examples are also found in North America, Neuzil said.
Neuzil added that future glaciation probably doesn’t pose a serious threat to storage sites, as most of the shale formations he’s looking at have gone through several glaciations unchanged. “Damage to waste containers, which will be surrounded by a filler material, is also not seen as a concern,” he said.
He noted that one critical criterion for a good site must be a lack of oil or natural gas that could attract future interest.
Emerging role of shales as hosts for nuclear waste
Research findings from underground laboratories and instrumented boreholes in shales (here including claystones, argillites and other clay-rich rocks) is showing that such formations might effectively isolate spent nuclear fuel (SNF) and high-level waste (HLW). These results have led a number of nations to consider or actively plan repositories for SNF and HLW in shales and other clay-rich rocks. The investigations have made it increasingly clear that many shales effectively restrict pore fluid flow over extremely long spans of time. The fact that shales are also widespread, voluminous, and often in tectonically stable settings, has made them increasingly attractive candidates for repositories. Before the 1990s few reliable data existed on fluid transport properties and pore fluid movement in shales, but it is now apparent that many have extremely low permeability at spatial scales large enough to accommodate repositories. This is possible because shales frequently host natural pore fluid pressure anomalies and patterns of pore water constituents that can be analyzed as if they are large-scale, long-term permeability and tracer tests. This permits estimation of transport properties over areas of several km2 and million year time spans. In many clay-rich formations there is essentially no transport of dissolved constituents by advection, and even diffusion is slowed because they are more or less efficient membranes. A potential difficulty with shale host rocks is effects of thermal loading by the waste. Other concerns, namely limiting excavation damage to the formation and effectively sealing the repository, are common to all types of subsurface disposal.
March 6, 2014
A new dinosaur species found in Portugal may be the largest land predator discovered in Europe, as well as one of the largest carnivorous dinosaurs from the Jurassic, according to a paper published in PLOS ONE on March 5, 2014 by co-authors Christophe Hendrickx and Octavio Mateus from Universidade Nova de Lisboa and Museu da Lourinhã.
Scientists discovered bones belonging to this dinosaur north of Lisbon. They were originally believed to be Torvosaurus tanneri, a dinosaur species from North America. Closer comparison of the shin bone, upper jawbone, teeth, and partial tail vertebrae suggest to the authors that it may warrant a new species name, Torvosaurus gurneyi.
T. gurneyi had blade-shaped teeth up to 10 cm long, which indicates it may have been at the top of the food chain in the Iberian Peninsula roughly 150 million years ago. The scientists estimate that the dinosaur could reach 10 meters long and weigh around 4 to 5 tons. The number of teeth, as well as size and shape of the mouth, may differentiate the European and the AmericanTorvosaurus. The fossil of the upper jaw of T. tanneri has 11 or more teeth, while T. gurneyi has fewer than 11. Additionally, the mouth bones have a different shape and structure. The new dinosaur is the second species of Torvosaurus to be named.
“This is not the largest predatory dinosaur we know. Tyrannosaurus, Carcharodontosaurus, andGiganotosaurus from the Cretaceous were bigger animals,” said Christophe Hendrickx. “With a skull of 115 cm, Torvosaurus gurneyi was however one of the largest terrestrial carnivores at this epoch, and an active predator that hunted other large dinosaurs, as evidenced by blade shape teeth up to 10 cm.” Fossil evidences of closely related dinosaurs suggest that this large predator may have already been covered with proto-feathers. Recently described dinosaur embryos from Portugal are also ascribed to the new species of Torvosaurus.
Citation: Hendrickx C, Mateus O (2014) Torvosaurus gurneyi n. sp., the Largest Terrestrial Predator from Europe, and a Proposed Terminology of the Maxilla Anatomy in Nonavian Theropods. PLoS ONE 9(3): e88905. doi:10.1371/journal.pone.0088905
Financial Disclosure: This research was supported by the Fundação para a Ciência e a Tecnologia (FCT) scholarship SFRH/BD/62979/2009 (Ministério da Ciência, Tecnologia e Ensino superior, Portugal) and the Dinoeggs Project (PTDC/BIA-EVF/113222/2009) financed by FCT/MEC (PIDDAC). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interest Statement: The authors have declared that no competing interests exist.
February 12, 2014
Journalists and psychologists are quick to describe someone as being a porn “addict,” yet there’s no strong scientific research that shows such addictions actually exists. Slapping such labels onto the habit of frequently viewing images of a sexual nature only describes it as a form of pathology. These labels ignore the positive benefits it holds. So says David Ley, PhD, a clinical psychologist in practice in Albuquerque, NM, and Executive Director of New Mexico Solutions, a large behavioral health program. Dr. Ley is the author of a review article about the so-called “pornography addiction model,” which is published in Springer’s journal Current Sexual Health Reports.
“Pornography addiction” was not included in the recently revised Diagnostic and Statistical Manual because of a lack of scientific data. Fewer than two in every five research articles (37 percent) about high frequency sexual behavior describe it as being an addiction. Only 27 percent (13 of 49) of articles on the subject contained actual data, while only one related psychophysiological study appeared in 2013. Ley’s review article highlights the poor experimental designs, methodological rigor and lack of model specification of most studies surrounding it.
The research actually found very little evidence – if any at all – to support some of the purported negative side effects of porn “addiction.” There was no sign that use of pornography is connected to erectile dysfunction, or that it causes any changes to the brains of users. Also, despite great furor over the effects of childhood exposure to pornography, the use of sexually explicit material explains very little of the variance in adolescents’ behaviors. These are better explained and predicted by other individual and family variables.
Instead, Ley and his team believe that the positive benefits attached to viewing such images do not make it problematic de facto. It can improve attitudes towards sexuality, increase the quality of life and variety of sexual behaviors and increase pleasure in long-term relationships. It provides a legal outlet for illegal sexual behaviors or desires, and its consumption or availability has been associated with a decrease in sex offenses, especially child molestation.
Clinicians should be aware that people reporting “addiction” are likely to be male, have a non-heterosexual orientation, have a high libido, tend towards sensation seeking and have religious values that conflict with their sexual behavior and desires. They may be using visually stimulating images to cope with negative emotional states or decreased life satisfaction.
“We need better methods to help people who struggle with the high frequency use of visual sexual stimuli, without pathologizing them or their use thereof,” writes Ley, who is critical about the pseudoscientific yet lucrative practices surrounding the treatment of so-called porn addiction. “Rather than helping patients who may struggle to control viewing images of a sexual nature, the ‘porn addiction’ concept instead seems to feed an industry with secondary gain from the acceptance of the idea.”
Reference: Ley, D. et al. (2014). The Emperor Has No Clothes: A Review of the “Pornography Addiction” Model, Current Sexual Health Reports. DOI 10.1007/s11930-014-0016-8.
Springer Science+Business Media
February 2, 2014
In many people with autism and other neurodevelopmental disorders, different parts of the brain don’t talk to each other very well. Scientists have now identified, for the first time, a way in which this decreased functional connectivity can come about. In a study published online today in Nature Neuroscience, scientists at the European Molecular Biology Laboratory (EMBL) in Monterotondo, Italy, and collaborators at the Istituto Italiano di Tecnologia (IIT), in Rovereto, and La Sapienza University in Rome, demonstrate that it can be caused by cells called microglia failing to trim connections between neurons.
“We show that a deficit in microglia during development can have widespread and long-lasting effects on brain wiring and behaviour,” says Cornelius Gross, who led the study. “It leads to weak brain connectivity, decreased social behaviour, and increased repetitive behaviour, all hallmarks of autism.”
The findings indicate that, by trimming surplus connections in the developing brain, microglia allow the remaining links to grow stronger, like high-speed fibre-optic cables carrying strong signals between brain regions. But if these cells fail to do their job at that crucial stage of development, those brain regions are left with a weaker communication network, which in turn has lifelong effects on behaviour.
Yang Zhan, a postdoctoral fellow in Gross’ lab at EMBL, analysed the strength of connections between different areas of brain in mice that were genetically engineered to have fewer microglia during development. Working with Alessandro Gozzi’s lab at IIT and Davide Ragozzino at La Sapienza University, the EMBL scientists combined this approach with high-resolution fMRI (functional Magnetic Resonance Imaging) scans of the mice’s brains, taking full advantage of a novel technique developed at IIT, which enables scientists to obtain detailed, three-dimensional maps of the brain’s functional connections. The team found that mice with fewer microglia had weaker connections between neurons, and less cross-talk between different brain regions. When Rosa Paolicelli, a PhD student in Gross’ lab, studied the mice’s behaviour, she discovered that mice with fewer microglia and decreased connectivity displayed behaviours commonly associated with autism spectrum disorders. These mice spent more time repeatedly grooming themselves, and avoided social interactions.
“This is an exciting time to be studying microglia,” Gross concludes: “they’re turning out to be major players in how our brain gets wired up.”
January 31, 2014
Are they bomb craters from World War II? Are they landing marks for aliens? Since the first images of the mysterious ocean circles off the Baltic coast of Denmark were taken in 2008, people have tried to find an explanation. Now researchers from the University of Southern Denmark and University of Copenhagen finally present a scientific explanation.
The first pictures appeared in 2008, taken by a tourist and showing some strange circular formations in the shallow waters off the famous white cliffs of chalk on the island Møn in Denmark. In 2011, the circles came back, and this time there were so many that they made it to the media.
Investigating biologists then concluded that the circles consisted of eelgrass plants growing on the bottom of the shallow water. But only now scientists can explain why the eelgrass grows in circles here – eelgrass usually grows as continuous meadows on the seabed.
“It has nothing to do with either bomb craters or landing marks for aliens. Nor with fairies, who in the old days got the blame for similar phenomena on land, the fairy rings in lawns being a well known example”, say biologists Marianne Holmer from University of Southern Denmark and Jens Borum from University of Copenhagen.
The circles of eelgrass can be up to 15 meters in diameter and their rim consists of lush green eelgrass plants. Inside the circle there can be seen only very weak or no eelgrass plants.
“We have studied the mud that accumulates among the eelgrass plants and we can see that the mud contains a substance that is toxic to eelgrass”, explain Holmer and Borum.
The poison is sulfide, a substance that accumulates in the seabed off the island of Møn, because it is very calcareous and iron-deficient.
“Most mud gets washed away from the barren, chalky seabed, but like trees trap soil on an exposed hillside, eelgrass plants trap the mud. And therefore there will be a high concentrations of sulfide-rich mud among the eelgrass plants,” explain the researchers.
Sulfide is toxic enough to weaken the old and new eelgrass plants but not toxic enough to harm adult and strong plants. And since eelgrass spreads radially from the inside out the oldest and weakest plants are located in the center of the growth circle.
Jens Borum and Marianne Holmer say:
“Eelgrass populations grow vegetatively by stolons which spread radially in all directions and therefore each plant creates a circular growth pattern. When the sulfide begins to work, it starts with the oldest and thus the inner part of the population because here is an increased release of toxic sulfide and uptake by plants due to accumulation of mud. The result is an exceptional circular shape, where only the rim of the circle survives – like fairy rings in a lawn”.
The waters off Møn’s chalk cliffs are not the only place where sulfide destroys eelgrass. Sulfide poisoning of eelgrass is a major problem worldwide. Sulfide is often created where oxygen disappears from the seabed. This can happen when the seabed is fed nutrients from agriculture.
Underwater meadows of eelgrass and other seagrasses grow in many parts of the world where they serve as home to a variety of small animals, filter the water and trap carbon and nutrients. But the meadows are threatened in almost all regions of the world, and in several places, including Denmark, researchers and authorities work to prevent seagrasses from disappearing.
Facts about seagrass:
Seagrass is not seaweed, but a plant with flowers, leaves and roots just like plants on land. Seagrass also produces seeds that can be sown in the seabed and grow to new plants. There are approx. 60 seagrass species in the world with eelgrass (Zostera marina) in temperate areas and Halophila ovalis in tropical and subtropical areas as common species. Seagrass needs light and only grows where at least 10% of the sun’s light can reach the plants.
The University of Southern Denmark is a partner and coordinator of NOVA GRASS, an international five-year research project focused on the restoration of eelgrass meadows.
January 30, 2014
Remnants of Neanderthal DNA in modern humans are associated with genes affecting type 2 diabetes, Crohn’s disease, lupus, biliary cirrhosis and smoking behavior. They also concentrate in genes that influence skin and hair characteristics. At the same time, Neanderthal DNA is conspicuously low in regions of the X chromosome and testes-specific genes.
The research, led by Harvard Medical School geneticists and published Jan. 29 in Nature, suggests ways in which genetic material inherited from Neanderthals has proven both adaptive and maladaptive for modern humans. (A related paper by a separate team was published concurrently in Science.)
“Now that we can estimate the probability that a particular genetic variant arose from Neanderthals, we can begin to understand how that inherited DNA affects us,” said David Reich, professor of genetics at HMS and senior author of the paper. “We may also learn more about what Neanderthals themselves were like.”
In the past few years, studies by groups including Reich’s have revealed that present-day people of non-African ancestry trace an average of about 2 percent of their genomes to Neanderthals – a legacy of interbreeding between humans and Neanderthals that the team previously showed occurred between 40,000 to 80,000 years ago. (Indigenous Africans have little or no Neanderthal DNA because their ancestors did not breed with Neanderthals, who lived in Europe and Asia.)
Several teams have since been able to flag Neanderthal DNA at certain locations in the non-African human genome, but until now, there was no survey of Neanderthal ancestry across the genome and little understanding of the biological significance of that genetic heritage.
“The story of early human evolution is captivating in itself, yet it also has far-reaching implications for understanding the organization of the modern human genome,” said Irene A. Eckstrand of the National Institutes of Health’s National Institute of General Medical Sciences, which partially funded the research. “Every piece of this story that we uncover tells us more about our ancestors’ genetic contributions to modern human health and disease.”
Deserts and Oases
Reich and colleagues – including Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Germany – analyzed genetic variants in 846 people of non-African heritage, 176 people from sub-Saharan Africa, and a 50,000-year-old Neanderthal whose high-quality genome sequence the team published in 2013.
The most powerful information the researchers used to determine whether a gene variant came from a Neanderthal was if the variant appeared in some non-Africans and the Neanderthal but not in the sub-Saharan Africans.
Using this and other types of information, the team found that some areas of the modern non-African human genome were rich in Neanderthal DNA, which may have been helpful for human survival, while other areas were more like “deserts” with far less Neanderthal ancestry than average.
The barren areas were the “most exciting” finding, said first author Sriram Sankararaman of HMS and the Broad Institute. “It suggests the introduction of some of these Neanderthal mutations was harmful to the ancestors of non-Africans and that these mutations were later removed by the action of natural selection.”
The team showed that the areas with reduced Neanderthal ancestry tend to cluster in two parts of our genomes: genes that are most active in the male germline (the testes) and genes on the X chromosome. This pattern has been linked in many animals to a phenomenon known as hybrid infertility, where the offspring of a male from one subspecies and a female from another have low or no fertility.
“This suggests that when ancient humans met and mixed with Neanderthals, the two species were at the edge of biological incompatibility,” said Reich, who is also a senior associate member of the Broad Institute and an investigator at the Howard Hughes Medical Institute. Present-day human populations, which can be separated from one another by as much as 100,000 years (such as West Africans and Europeans), are fully compatible with no evidence of increased male infertility. In contrast, ancient human and Neanderthal populations apparently faced interbreeding challenges after 500,000 years of evolutionary separation.
“It is fascinating that these types of problems could arise over that short a time scale,” Reich said.
A Lasting Heritage
The team also measured how Neanderthal DNA present in human genomes today affects keratin production and disease risk.
Neanderthal ancestry is increased in genes affecting keratin filaments. This fibrous protein lends toughness to skin, hair and nails and can be beneficial in colder environments by providing thicker insulation, said Reich. “It’s tempting to think that Neanderthals were already adapted to the non-African environment and provided this genetic benefit to humans,” he speculated.
The researchers also showed that nine previously identified human genetic variants known to be associated with specific traits likely came from Neanderthals. These variants affect diseases related to immune function and also some behaviors, such as the ability to stop smoking. The team expects that more variants will be found to have Neanderthal origins.
The team has already begun trying to improve their human genome ancestry results by analyzing multiple Neanderthals instead of one. Together with colleagues in Britain, they also have developed a test that can detect most of the approximately 100,000 mutations of Neanderthal origin they discovered in people of European ancestry; they are conducting an analysis in a biobank containing genetic data from half a million Britons.
“I expect that this study will result in a better and more systematic understanding of how Neanderthal ancestry affects variation in human traits today,” said Sankararaman.
As another next step, the team is studying genome sequences from people from Papua New Guinea to build a database of genetic variants that can be compared to those of Denisovans, a third population of ancient humans that left most of its genetic traces in Oceania but little in mainland Eurasia.
This research was supported by the Presidential Innovation Fund of the Max Planck Society, NSF HOMINID grant 1032255, NIH grant GM100233 and the Howard Hughes Medical Institute.
Written by Stephanie Dutchen
January 27, 2014
New types of solotronic structures, including the world’s first quantum dots containing single cobalt ions, have been created and studied at the Faculty of Physics at the University of Warsaw. The materials and elements used to form these structures allow us forecast new trends in solotronics – a field of experimental electronics and spintronics of the future, based on operations occurring on a single-atom level.
Electronic systems operating on the level of individual atoms would seem to be the natural consequence of efforts to achieve ever-greater miniaturization. Already now, we are able to control the behavior of individual atoms by situating them within special semiconductor structures – this is the method used to form quantum dots that contain single magnetic ions. Until recently, only two variants of such structures were known. However, physicists from the Institute of Experimental Physics at the Faculty of Physics at the University of Warsaw (FUW) have successfully created and studied two completely new types of the structures. The materials and elements used in the process make it wholly likely that solotronic devices may come into widespread use in the future.
The results, the Warsaw physicists have just published in Nature Communications, pave the way for developing the field of solotronics.
“Quantum dots are semiconductor crystals on a nanometer scale. They are so tiny that the electrons within them exist only in states with specific energies. As such, quantum dots exhibit similar characteristics to atoms, and – just like atoms – they can be stimulated with light to reach higher energy levels. Conversely, this means they emit light as they return to states with lower energy levels,” says Prof. Piotr Kossacki (FUW).
The University laboratory creates quantum dots using molecular beam epitaxy. The process involves precision-heating crucibles containing elements placed in a vacuum chamber. Beams of elements are deposited on the sample. By carefully selecting materials and experimental conditions, the atoms assemble into tiny islands, known as quantum dots. The process is similar to how water vapor condenses on a hydrophobic surface.
While the dots settle, a small quantity of other atoms (for example magnetic ones) can be introduced into the vacuum chamber, with some becoming a part of the emerging dots. Once the sample is removed, it can be examined under a microscope to detect quantum dots containing a single magnetic atom at the center.
“Atoms with magnetic properties disrupt the energy levels of electrons in a quantum dot, which affects how they interact with light. As a result, the quantum dot becomes a detector of such an atom’s state. The relationship also works the other way: by changing energy states of electrons in quantum dots, we can affect the respective magnetic atoms,” explains Michał Papaj, a student at the UW Faculty of Physics, awarded the Gold Medal in Chemistry during last year’s national competition for the best B.Sc. thesis held by the Institute of Physical Chemistry of the Polish Academy of Sciences for his work on quantum dots containing single cobalt ions.
The most powerful magnetic properties are observed in manganese atoms stripped of two electrons (Mn2+). In experiments conducted thus far, the ions have been mounted in quantum dots made of cadmium telluride (CdTe) or indium arsenide (InAs). Using CdTe dots prepared by Dr. Piotr Wojnar at the PAS Institute of Physics, in 2009 Mateusz Goryca from the University of Warsaw demonstrated the first magnetic memory operating on a single magnetic ion.
“It was commonly believed that other magnetic ions, such as cobalt (Co2+), cannot be used in quantum dots. We decided to verify this, and nature gave us a pleasant surprise: the presence of a new magnetic ion turned out not to destroy the properties of the quantum dot,” says Jakub Kobak, doctoral student at the University of Warsaw.
Researchers from the University of Warsaw have presented two new systems with single magnetic ions: CdTe quantum dots with a cobalt atom, and cadmium selenide (CdSe) dots with a manganese atom.
As already stated, manganese atoms exhibit the most powerful magnetic properties. Unfortunately, they are caused by the atomic nucleus as well as the electrons, which means that quantum dots containing manganese ions are complex quantum systems. The discovery made by physicists at the University of Warsaw demonstrates that other magnetic elements – such as chromium, iron and nickel – can be used in place of manganese. These elements do not have nuclear spin, which should make quantum dots that contain them easier to manipulate.
In quantum dots where tellurium is replaced by the lighter selenium, researchers observed that the duration for which information was remembered increased by an order of magnitude. This finding suggests that using lighter elements should prolong the time quantum dots containing single magnetic ions store information, perhaps even by several orders of magnitude.
“We have demonstrated that two quantum systems that were believed not to be viable in fact worked very effectively. This opens up a broad field in our search for other, previously rejected combinations of materials for quantum dots and magnetic ions,” concludes Dr. Wojciech Pacuski (FUW).
The research into quantum dots containing single magnetic ions was funded with grants from the Polish National Science Centre and the Polish National Centre for Research and Development, as well as project funds from the Centre for Preclinical Research and Technology.
Physics and Astronomy were first taught at the University of Warsaw (UW) in 1816, at what was then the Faculty of Philosophy. The UW Astronomical Observatory was founded in 1825. Currently, the UW Faculty of Physics consists of the Institute of Experimental Physics, the Institute of Theoretical Physics, the Institute of Geophysics, the Faculty of Mathematical Methods, and the Astronomical Observatory. Research is conducted into most fields of modern physics, on scales ranging from the quantum to the cosmological. The UW Faculty of Physics has over 200 research and teaching staff, including 80 with the title of professor. The Faculty is attended by approx. 1,000 undergraduates and more than 140 doctoral students.
“Designing quantum dots for solotronics”; J. Kobak, T. Smoleński, M. Goryca, M. Papaj, K. Gietka, A. Bogucki, M. Koperski, J.-G. Rousset, J. Suffczyński, E. Janik, M. Nawrocki, A. Golnik, P. Kossacki & W. Pacuski; Nature Communications 5:3191, 27 January 2014; DOI: 10.1038/ncomms4191
January 21, 2014
A viral pathogen that typically infects plants has been found in honeybees and could help explain their decline. Researchers working in the U.S. and Beijing, China report their findings in mBio, the online open-access journal of the American Society for Microbiology.
The routine screening of bees for frequent and rare viruses “resulted in the serendipitous detection of Tobacco Ringspot Virus, or TRSV, and prompted an investigation into whether this plant-infecting virus could also cause systemic infection in the bees,” says Yan Ping Chen from the U.S. Department of Agriculture’s Agricultural Research Service (ARS) laboratory in Beltsville, Maryland, an author on the study.
“The results of our study provide the first evidence that honeybees exposed to virus-contaminated pollen can also be infected and that the infection becomes widespread in their bodies,” says lead author Ji Lian Li, at the Chinese Academy of Agricultural Science in Beijing.
“We already know that honeybees, Apis melllifera, can transmit TRSV when they move from flower to flower, likely spreading the virus from one plant to another,” Chen adds.
Notably, about 5% of known plant viruses are pollen-transmitted and thus potential sources of host-jumping viruses. RNA viruses tend to be particularly dangerous because they lack the 3′-5′ proofreading function which edits out errors in replicated genomes. As a result, viruses such as TRSV generate a flood of variant copies with differing infective properties.
One consequence of such high replication rates are populations of RNA viruses thought to exist as “quasispecies,” clouds of genetically related variants that appear to work together to determine the pathology of their hosts. These sources of genetic diversity, coupled with large population sizes, further facilitate the adaption of RNA viruses to new selective conditions such as those imposed by novel hosts. “Thus, RNA viruses are a likely source of emerging and reemerging infectious diseases,” explain these researchers.
Toxic viral cocktails appear to have a strong link with honey bee Colony Collapse Disorder (CCD), a mysterious malady that abruptly wiped out entire hives across the United States and was first reported in 2006. Israel Acute Paralysis Virus (IAPV), Acute Bee Paralysis Virus (ABPV), Chronic Paralysis Virus (CPV), Kashmir Bee Virus (KBV), Deformed Wing Bee Virus (DWV), Black Queen Cell Virus (BQCV) and Sacbrood Virus (SBV) are other known causes of honeybee viral disease.
When these researchers investigated bee colonies classified as “strong” or “weak,” TRSV and other viruses were more common in the weak colonies than they were in the strong ones. Bee populations with high levels of multiple viral infections began failing in late fall and perished before February, these researchers report. In contrast, those in colonies with fewer viral assaults survived the entire cold winter months.
TRSV was also detected inside the bodies of Varroa mites, a “vampire” parasite that transmits viruses between bees while feeding on their blood. However, unlike honeybees, the mite-associated TRSV was restricted to their gastric cecum indicating that the mites likely facilitate the horizontal spread of TRSV within the hive without becoming diseased themselves. The fact that infected queens lay infected eggs convinced these scientists that TRSV could also be transmitted vertically from the queen mother to her offspring.
“The increasing prevalence of TRSV in conjunction with other bee viruses is associated with a gradual decline of host populations and supports the view that viral infections have a significant negative impact on colony survival,” these researchers conclude. Thus, they call for increased surveillance of potential host-jumping events as an integrated part of insect pollinator management programs.
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January 6, 2014
The international team, which includes UBC astronomer Ingrid Stairs, reports their findings in the journal Nature on January 5.
Originally uncovered by an American graduate student using the National Science Foundation’s Green Bank Telescope, the pulsar – 4,200 light-years from Earth, spinning nearly 366 times per second – was found to be in close orbit with a white dwarf star and the pair is in orbit with another, more distant white dwarf.
The three-body system is scientists’ best opportunity yet to discover a violation of a key concept in Albert Einstein’s theory of General Relativity: the strong equivalence principle, which states that the effect of gravity on a body does not depend on the nature or internal structure of that body.
“By doing very high-precision timing of the pulses coming from the pulsar, we can test for such a deviation from the strong equivalence principle at a sensitivity several orders of magnitude greater than ever before available,” says Stairs, with UBC’s Department of Physics and Astronomy. “Finding a deviation from the strong equivalence principle would indicate a breakdown of General Relativity and would point us toward a new, revised theory of gravity.”
“This is the first millisecond pulsar found in such a system, and we immediately recognized that it provides us a tremendous opportunity to study the effects and nature of gravity,” says Scott Ransom of the National Radio Astronomy Observatory (NRAO), who led the study. “This triple system gives us a natural cosmic laboratory far better than anything found before for learning exactly how such three-body systems work and potentially for detecting problems with General Relativity that physicists expect to see under extreme conditions.”
When a massive star explodes as a supernova and its remains collapse into a superdense neutron star, some of its mass is converted into gravitational binding energy that holds the dense star together. The strong equivalence principle says that this binding energy will still react gravitationally as if it were mass. Virtually all alternatives to General Relativity hold that it will not.
Under the strong equivalence principle, the gravitational effect of the outer white dwarf would be identical for both the inner white dwarf and the neutron star. If the strong equivalence principle is invalid under the conditions in this system, the outer star’s gravitational effect on the inner white dwarf and the neutron star would be slightly different and the high-precision pulsar timing observations could easily show that.
“We have made some of the most accurate measurements of masses in astrophysics,” says Anne Archibald of the Netherlands Institute for Radio Astronomy and one of the authors of the study. “Some of our measurements of the relative positions of the stars in the system are accurate to hundreds of meters.” Archibald led the effort to use the measurements to build a computer simulation of the system that can predict its motions.
The NRAO’s Scott Ransom adds: “This is a fascinating system in many ways, including what must have been a completely crazy formation history, and we have much work to do to fully understand it.”
The scientists’ observational program used the National Science Foundation’s Green Bank Telescope, the Arecibo radio telescope in Puerto Rico, and the Westerbork Synthesis Radio Telescope in the Netherlands. They also studied the system using data from the Sloan Digital Sky Survey, the GALEX satellite, the WIYN telescope on Kitt Peak, Arizona, and the Spitzer Space Telescope.