News Article | May 9, 2017
Numerical simulations of tipping points provide a better understanding of the characteristics of the point of no return and what happens to a system after a occurrence A tipping point is a critical threshold at which a dynamical system undergoes an irreversible transformation, typically owing to a small change in inputs or parameters. This concept is very broad and can refer to the extinction of an animal or a plant species, the depletion of a water source, or the financial collapse of an institution, among many other natural and social phenomena. Numerical simulations of tipping points by Everton Santos Medeiros, a researcher at the University of São Paulo's Physics Institute (IF-USP) in Brazil, provide a better understanding of the characteristics of this point of no return and what happens to a system after its occurrence. The study is published in Scientific Reports in February 2017. "Oceanic, atmospheric, ecological, economic and other systems can undergo transitions of this kind," Medeiros told Agência FAPESP. "The system's parameters change gradually until a limit is reached at which one small change causes an abrupt and irreversible transition. The concept of a tipping point is well known in the literature. Our study set out to investigate what happens shortly after this critical transition." Medeiros designed a generic cyclical dynamical system to model this type of transition. He chose a cyclical system because most natural phenomena are cyclical in response to periodic forcings, such as differences in insolation (sunlight) associated with the seasons of the year. "Hence our preference for a generic cyclical dynamical system that could be described by a simple differential equation," Medeiros explained. "Our numerical simulations varied the parameters of the equation until they reached a tipping point defined by elimination of the behavior they described." Professor Iberê Luiz Caldas, co-author of the article, made an important distinction: "Our study focuses not on complex dynamical systems, but on simple dynamical systems that can display complex behavior, i.e., dynamical systems described by non-linear differential equations that have complex solutions." These systems were well studied by the great French physicist, mathematician and philosopher Henri Poincaré (1854-1912). Hysteresis is a key feature of the transitions that are classified as tipping points: once the critical threshold is reached and the dynamical regime is abruptly destroyed, the regime cannot be restored by simply reversing the trend that caused the collapse. The extinction of an animal species, the drying up of a water reservoir and the thawing of a glacier all follow this type of hysteretic pattern in which irreversible damage is done when the tipping point is reached. "But what our study showed, and this is its main contribution, is that for certain cyclical phenomena, the dynamics of the system last for a certain time after the tipping point, and this persistence may mask the transition itself," Medeiros said. "Take an endangered species, for example. It may have passed the point of no return and become irreversibly doomed. Nevertheless, individual members of the species continue to exist and reproduce in the wild. This transient effect conceals the fact that in the long run, the species is already extinct. In our study, through numerical simulation, we succeeded in observing this transient effect following the singularity that configures a tipping point." Thus, the fundamentals of a phenomenon change irreversibly at the tipping point, but owing to a kind of "residual effect" the process appears to retain its original characteristics for a time, masking the transformation that has occurred. "Because of the transient effect, hysteretic change is mistaken for gradual change that can easily be corrected. The transition may appear smooth but may actually be critical. In this case, eliminating the cause isn't sufficient to reverse the system's collapse," Medeiros said. "It's hard to know in real-life situations whether a tipping point has been reached or not," Caldas said. "For example, can the Atlantic Rainforest between São Paulo and Santos be rehabilitated, or is it irremediably lost? There's still a lot of vegetation in the area, so people get the impression that it can be restored by initiatives capable of remedying the damage done. But is that the case? Isn't the remaining vegetation just a transient effect, so that the collapse of the forest in that region can't be reversed? One lesson to be drawn from our study is that a great deal of care has to be taken when symptoms of deterioration appear. Not every deterioration can be reversed someday."
News Article | May 3, 2017
A recent study suggests that doxycycline can be prescribed at lower doses for the treatment of Parkinson's disease A study published in February in the journal Scientific Reports suggests that doxycycline, an antibiotic used for over half a century against bacterial infections, can be prescribed at lower doses for the treatment of Parkinson's disease. According to the authors, the substance reduces the toxicity of α-synuclein, a protein that, under certain conditions, forms abnormal accumulations of aggregates in central nervous system cells, which are damaged as a result. The death of dopaminergic neurons (which produce the neurotransmitter dopamine) is the main event relating to the development of such symptoms as tremor, slow voluntary movements and stiffness, among others. There are currently no drugs capable of halting the progress of this degenerative process. Three Brazilian scientists participated in the study, which was supported by FAPESP: Elaine Del-Bel, affiliated with the University of São Paulo's Ribeirão Preto Dental School (FORP-USP), and Leandro R. S. Barbosa and Rosangela Itri, at the same university's Physics Institute (IF-USP) in the city of São Paulo. "We have exciting data from experiments with mice and great expectations that the neuroprotective effect will also be observed in human patients," Del-Bel told. "This treatment could stop Parkinson's from progressing, and we therefore plan to start a clinical trial shortly." The discovery happened fortuitously some five years ago when Marcio Lazzarini, a former student of Del-Bel, was pursuing postdoctoral studies at the Max Planck Institute of Experimental Medicine in Germany. While looking for possible alternative treatments for Parkinson's in experiments with mice, the group used a well-known model for inducing a condition similar to the human disease. The model consists of administering 6-hydroxydopamine (6-OHDA), a neurotoxin that causes the death of dopaminergic neurons. "To our surprise, only two of the 40 mice given 6-OHDA developed symptoms of Parkinsonism, while the rest remained healthy," Del-Bel said. "A lab technician realized the mice had mistakenly been fed chow containing doxycycline, so we decided to investigate the hypothesis that it might have protected the neurons." The group repeated the experiment, adding a second group of animals that were given doxycycline in low doses by peritoneal injection instead of receiving it in their feed. Both cases were successful. Understanding the mechanisms behind the neuroprotective effect of doxycycline has been the focus for the most recent studies, conducted in collaboration with the group led by Rosana Chehin, a researcher at the University of Tucumán in Argentina, as well as Rita Raisman-Vozari and Julia Sepulveda-Diaz, researchers at the Brain & Bone Marrow Institute (ICM) in Paris, France. In these new trials, which involved structural and spectroscopic characterization methods, the focus was the protein α-synuclein, considered one of the leading causes of dopaminergic neuron death. "α-Synuclein is a small unstructured protein that, in the presence of the cellular membrane, aggregates to form fibrils with multiple regularly ordered layers of beta- sheets along the axis. We call these amyloid fibrils. It's been proven that large amyloid fibrils of this protein aren't toxic to cells; what damages cells is the so-called oligomeric stage formed by small amounts of aggregated α-synuclein. These oligomers can damage neuron membranes," Itri said. The researchers synthesized small oligomers of α-synuclein and conducted in vitro trials to find out whether doxycycline interfered in the process of aggregation and fibril formation. With a combination of three different techniques - nuclear magnetic resonance, X-ray scattering and infrared spectroscopy - they were able to observe two distinct situations. In medium without doxycycline, α-synuclein aggregated and began forming amyloid fibrils. In medium containing the antibiotic, α-synuclein formed another type of aggregate with a different shape and size. "In the tests with cultured cells and model membranes, we observed that they caused no damage to the cell membrane," Itri said. The tests in culture were performed in immortalized human neuroblastoma cells. Using transmission electron microscopy, the group observed that the presence of doxycycline in the culture medium reduced α-synuclein aggregation by more than 80%. "As a result, cell viability increased by more than 80%," Del-Bel said. Del-Bel has more deeply investigated the effects of treatment with doxycycline on mice. "We haven't published any data yet, but I can say right away that doxycycline improves the symptoms of the disease in the animal model," Del-Bel added. "Preliminary results suggest that besides its anti-inflammatory action via a reduction in the release of some cytokines, doxycycline also alters the expression of key genes for the development of Parkinson's." According to Del-Bel, evidence in the scientific literature shows that α-synuclein aggregates on and causes damage to not just neurons but also astrocytes and other glial cells. Besides Parkinson's, therefore, the process is associated with the development of other neurodegenerative diseases, such as Lewy body dementia (LBD), the second most common neurodegenerative disease after Alzheimer's. Future studies will investigate whether doxycycline can also have a beneficial effect in these other situations.
News Article | December 16, 2016
Whether water freezes to ice, iron is demagnetized or a material becomes superconducting - for physicists there is always a phase transition behind it. They endeavour to understand these different phenomena by searching for universal properties. Researchers at Goethe University Frankfurt and Technische Universität Dresden have now made a pioneering discovery during their study of a phase transition from an electrical conductor to an insulator (Mott metal-insulator transition). According to Sir Nevill Francis Mott's prediction in 1937, the mutual repulsion of charged electrons, which are responsible for carrying electrical current, can cause a metal-insulator transition. Yet, contrary to common textbook opinion, according to which the phase transition is determined solely by the electrons, it is the interaction of the electrons with the atomic lattice of the solid which is the determinant factor. The researchers have reported this in the latest issue of the Science Advances journal. The research group, led by Professor Michael Lang of the Physics Institute at Goethe University Frankfurt, succeeded in making the discovery with the help of a homemade apparatus which is unique worldwide. It allows the measurement of length changes at low temperatures under variable external pressure with extremely high resolution. In this way, it was possible to prove experimentally for the first time that it is not just the electrons which play a significant role in the phase transition but also the atomic lattice - the solid's scaffold. "These experimental results will herald in a paradigm shift in our understanding of one of the key phenomena of current condensed matter research", says Professor Lang. The Mott metal-insulator transition is namely linked to unusual phenomena, such as high-temperature superconductivity in copper oxide-based materials. These offer tremendous potential for future technical applications. The theoretical analysis of the experimental findings is based on the fundamental notion that the many particles in a system close to a phase transition not only interact with their immediate neighbours but also "communicate" over long distances with all other particles. As a consequence, only overarching aspects are important, such as the system's symmetry. The identification of such universal properties is thus the key to understanding phase transitions. "These new insights open up a whole new perspective on the Mott metal-insulator transition and permit more sophisticated theoretical modelling of the phase transition", explains Dr. Markus Garst, Senior Lecturer at the Institute of Theoretical Physics of Technische Universität Dresden. The research work was funded by the German Research Foundation in the framework of the Collaborative Research Centre/Transregio "Condensed Matter Systems with Variable Many-Body Interactions" led by Professor Michael Lang.
News Article | April 27, 2016
Kodari is a ghost town on an empty Nepalese highway that cuts through some of the steepest slopes of the Himalayas. One year after the magnitude-7.8 Gorkha earthquake killed nearly 9,000 people, the once-buzzing trade centre looks like a battlefield where armies of giants once waged war. The road is littered with rusting cars and trucks smashed into bizarre shapes. Massive boulders rest on the wreckage of homes. “It’s a good example of building a town in the wrong place,” says Kristen Cook, a geologist at the German Research Centre for Geosciences (GFZ) in Potsdam, as she climbs over the rubble from one of the landslides that crushed the town. The Arniko Highway, which runs through Kodari, is no stranger to such calamities, especially in the monsoon season. “It was in frequent repair and closure even before the earthquake,” says Shanmukesh Amatya, landslide-division chief at Nepal’s Department of Water Induced Disaster Prevention in Kathmandu. “The problem now is overwhelming.” The highway is not the only thing that keeps Amatya awake at night. The earthquake unleashed more than 10,000 landslides that blocked rivers and damaged houses, roads and other key pieces of infrastructure across the country. And the destruction didn’t stop with the shaking (see ‘Deadly impact’). The hilly terrain, severely weakened by the quake, is now more likely to slip after strong rains and aftershocks — a legacy that is likely to endure for years. During the most recent monsoon, the area affected by landslides was about ten times greater than usual. “It’s a real problem for reconstruction,” says Tara Nidhi Bhattarai, a geologist at Tribhuvan University in Kathmandu and chief scientist of Nepal’s National Reconstruction Authority — an agency established last year to manage the recovery efforts. “What are the safe places to rebuild, in a landscape that is evolving?” To answer that, geoscientists are wiring up the mountains in Nepal and other seismically active countries. By monitoring how hillsides evolve, researchers are learning why strong shaking weakens a slope and makes it more prone to give way during aftershocks or rainstorms. The lessons from such studies could help to pinpoint when and where the side of a mountain will collapse. The significance goes beyond quake recovery. Himalayan nations are facing increasing risks from landslides because of deforestation, road construction, population growth and other changes that have pushed people to live in hazardous locations. Climate change may exacerbate the problem by melting glaciers and triggering increasingly extreme rainfall. “There is a pressing need to monitor the risks in the long run,” says Amatya. “A nationwide early-warning system is long overdue.” A crowd eagerly looks on as Cook flies a drone through the skies near Listi, a small village perched on a mountainside above the Arniko Highway. With its four propellers, the little robot zips over landslide scars that run down from the ridge like gigantic frozen waterfalls. A camera and other sensors on the drone provide data that let Cook build a 3D reconstruction of the landscape. She started the work last October and will take measurements every few months over the next few years. By scanning as many landslide-inflicted areas as possible, she says, “we will be able trace how they change over time and what’s the effect of monsoons”. Such measurements of the surface will complement studies that track what’s happening underground. Not far from Cook is her colleague Christoff Andermann, another GFZ geologist, who is performing maintenance on a broadband seismometer, a device that measures shaking across a wide range of frequencies. Last June, the GFZ team installed a dozen such instruments, along with weather stations and river-flow sensors, across 50 square kilometres of landslide-riddled terrain. Seismometers are a relatively new addition to landslide studies by the GFZ researchers and their colleagues. They started using the sensors only after an accidental discovery. In 2003, a set of seismic stations installed in Nepal to study deep structures in Earth’s crust picked up high-frequency noise from nearby rivers and shifting slopes. Arnaud Burtin, a seismologist now at the Earth Physics Institute in Paris, noticed a series of peaks in that noise before a debris flow in central Nepal that killed 45 people. He and his colleagues went on to identify1 46 debris flows from seismograms taken during that monsoon season. By comparing the data with information from weather stations, the team also determined how much rainfall was required to trigger slides. Researchers have typically used satellite imagery or aerial photography to track landscape changes on a large scale, but these methods have relatively poor temporal resolution because images are taken days or months apart. Seismometers take snapshots hundreds of times per second, so they are ideal for monitoring slopes for instability, says Colin Stark, a geologist at the Lamont–Doherty Earth Observatory in Palisades, New York, who studies monster landslides using global seismic networks. When seismometers are placed strategically, he says, it’s also possible to precisely locate the source of seismic signals in a large area. “Until recently, we had little idea why landslides are more likely to happen after an earthquake or how the slopes recover over time,” says Stark. But work over the past decade has revealed that cracks produced by an earthquake can boost the shaking in future shocks. Unpublished results from seismic stations, for example, show that on fractured slopes, ground motion can be up to 30 times what is measured in neighbouring, undamaged areas, says Jeffrey Moore, a geophysicist at the University of Utah in Salt Lake City. This means that minor aftershocks could trigger unexpected levels of landslides in damaged slopes that did not fail in the main shock, he says. In some cases, the increased sensitivity can last for decades. A study2 of a magnitude-7.4 earthquake in New Zealand in 1968 found that the quake triggered more landslides than expected in places that had been affected by a magnitude-7.8 shock 21 kilometres away and nearly 4 decades before. Quake-stricken hills also have an increased sensitivity to rainfall, says Niels Hovius, a GFZ geologist who is leading the Nepal study. He and his colleagues have found3 that after the magnitude-7.6 ChiChi earthquake that hit Taiwan in 1999, the rate of rainfall-triggered landslides in the affected area jumped by a factor of 22. “The government cleared up the mess and rebuilt, but the same happened again a couple of years later,” he says. If scientists can develop greater insight into the mechanisms that control slope behaviour after an earthquake, that could help authorities to make better decisions about rebuilding. By analysing records after the ChiChi quake and three others with similar depths and slip mechanisms, Hovius and his colleagues also found3 that it took up to four years for landslide rates to return to pre-quake levels at those sites. In follow-up work, the team mined data from seismometers installed before ChiChi hit. The instruments were near roads, which made it possible to study subsurface properties by measuring how traffic vibrations travel through the ground. They found that the speed of seismic waves dropped markedly immediately after the quake. The velocities then recovered gradually, following roughly the same trajectory as the decline in landslide rates, says Odin Marc, a geologist at the GFZ, who presented the results last week at a meeting of the European Geosciences Union in Vienna. Over the same period, there were frequent, small surface displacements — presumably caused by the slow, creeping movement of Earth’s crust after an earthquake, a process known as post-seismic deformation. The researchers suspect that subsurface materials are packed together tightly before the earthquake, like beads in a box. Strong ground-shaking causes the granular mass to expand, opening up holes and cracks that make the ground less dense. “This is why seismic waves travel at reduced speeds,” says Hovius. Post-seismic deformation causes the openings to fill in and the subsurface sediments to become compact once more. “It’s an internal healing process of the landscape,” he says. Data collected after the Gorkha earthquake support that. Preliminary results show that seismic-wave velocities close to the surface declined sharply after the shock — and the volume of water flowing through rivers increased by 50%. That backs up the idea that the quake opened holes and fractures in the subsurface, which then allowed groundwater to leak more freely through the cracks, says Andermann, who has been monitoring river flows and sediment transport in the region for the past decade. Such findings suggest a way to predict landslides. Looking back over their data, the researchers were able to identify peaks of seismic signals in the run-up to a major landslide last July. “These precursors represent a sequence of processes that culminated in the failure,” says Hovius. “There was a systematic increase in the rate at which these precursor activities occurred, until the whole topography collapsed.” The GFZ team also found that seismic waves travel through the subsurface more quickly when the slope is drenched and pore spaces are filled with water. “We can see how quickly the effects of rainfall propagate into and through the subsurface” using seismic sensors, says Hovius.This effectively maps groundwater flow, a key factor in the strength of hillsides. With the seismic data, researchers can model the physics of slope stability and monitor changes in ground properties that might precipitate a landslide. In the village of Langtang in northern Nepal, a pile of rubble 60 metres deep provides ample incentive to improve landslide forecasts. During the earthquake last year, a mixture of ice and rock crashed down several kilo-metres onto the valley floor — landing with an impact that released half as much energy as the Hiroshima atomic bomb4. The slide buried Langtang and nearby villages, leaving nearly 400 people dead or missing. Research groups have been racing to understand where the avalanche began and whether the area is still at risk. One study5 found 5 initiation sites between altitudes of 6,800 and 7,200 metres, along a 3-kilometre ridge where the earthquake shook up snow and glaciers. These swept down the slope, picking up rocks as they went. Roughly 7 million cubic metres of debris filled the bottom of the valley, and another 10 million cubic metres still rest precariously on slopes more than 5,000 metres above sea level. A year after the quake, the sounds of falling rocks and shifting slopes frequently echo through the valley — a reminder of the remaining hazard. The Langtang case shares features with increasingly common rock avalanches in high mountains in Alaska and the Alps, says Marten Geertsema, a glaciologist with the British Columbia Ministry of Forests and Range in Prince George, Canada. In all these places, glaciers are quickly retreating, leaving rocky hillsides exposed and prone to failure. And warming at high elevations may cause frozen bedrock to thaw, he says, making it more permeable to melt water and weakening the rocks. “Climate change might have primed the landscape for the devastation.” At high-risk sites in Nepal, researchers are combining seismological and other techniques to watch for signs that mountainsides are growing restless. On the steep slope facing Listi, the earthquake caused the lower part of the ridge to subside, resulting in a 5-metre opening that skirts the mountain for about 2 kilometres. This gigantic crack and many smaller ones nearby pose a serious threat to downslope settlements, says Amod Dixit, executive director of Nepal’s National Society for Earthquake Technology (NEST) in Kathmandu. “They must be closely monitored.” Last August, Nick Rosser, a geologist at Durham University, UK, and his colleagues installed a series of instruments at ten locations across the slope — including strain meters to monitor changes in the cracks, accelerometers to measure ground vibration, and rain gauges. The data are relayed to a server at NEST, letting researchers track in real time whether the cracks are opening or contracting and how they respond to rainfall. Although it is not yet a fully fledged early-warning system, the set-up can identify signs of major deformation that could cause the slope to fail. Thankfully, says Rosser, “the cracks are not growing at the moment”. Settlements will be alerted to any impending danger, he adds. The researchers are using information from the field and from lab experiments on slope materials to try to determine what kind of ground deformation and rainfall would cause landslides. “This is crucial for setting the criteria for triggering an alert,” he says. The Durham sensors are within the area covered by the GFZ seismic array, so the teams will pool their field data. Together with satellite imagery and other measurements, this information will provide unprecedented insight into how the mountains are changing and what kind of danger this might pose to communities there, they say. At Listi, Cook is worried about a massive pile of debris that the drone has located high above the valley. The earthquake loosened a huge amount of rock and soil, but most did not make it all the way to the bottom. “They are just sitting there on the hillside,” says Cook, pointing to a mass on her remote-control screen. The materials could all come down in heavy rain — as some did during the last monsoon. “They are time bombs waiting to explode.”
News Article | November 2, 2016
GOAmazon researchers describe in Nature the role of clouds as transporters of particles between the ground and the upper atmosphere. New knowledge will enhance climate models A study published in the journal Nature solves a mystery that has puzzled scientists for over a decade: the origin of the atmospheric aerosols that contribute to cloud formation above the Amazon rainforest in the absence of local sources of pollution. Aerosols are microscopic particles suspended in the atmosphere. They play several essential roles in the climate system. For example, most clouds owe their existence to aerosols, because the water vapor in the atmosphere condenses on them to form cloud droplets that eventually precipitate as rain. These seed-like aerosol particles are called cloud condensation nuclei, the authors explain. According to the latest findings of the research project, conducted with FAPESP's support as part of the Green Ocean Amazon Experiment (GOAmazon), particles that serve as precursors of cloud condensation nuclei form in the upper atmosphere and are carried down toward the ground by clouds and rain. "We tried for at least 15 years to measure the formation of new aerosol particles in the Amazon at ground level and the result was always zero. The new nanometric particles simply didn't turn up there. Measurements were made on the surface or in aircraft flying no higher than 3,000 m. We only found the answer when we looked much higher up," said Paulo Artaxo, a professor at the University of São Paulo's Physics Institute (IF-USP) and a co-author of the article. According to Artaxo, the Amazon rainforest naturally emits gases known as volatile organic compounds (VOCs), including terpene and isoprene. They are swept into the upper atmosphere by cloud convection and can soar as high as 15,000 m, where the temperature is about minus 55 degrees Celsius. "At these very low temperatures, the VOCs condense and form tiny particles measuring 1-5 nm," Artaxo explained. "These nanoparticles absorb gases and collide with each other, rapidly agglomerating and growing to a size large enough to make them cloud condensation nuclei, typically more than 50-70 nm." At high altitudes, he added, particle agglomeration is facilitated by low atmospheric pressure, low temperature, and the vast numbers of particles in circulation there. "Eventually one of these giant convective clouds generates a strong downdraft of air and precipitates as rain, so that the particles plunge down toward the ground," Artaxo said. Some of the measurements presented in the article were made in March 2014 during the Amazon's rainy season by a Grumman Gulfstream-1, a research aircraft capable of flying at 6,000 m, or nearly 20,000 ft, and owned by Pacific Northwest National Laboratory (PNNL) in the US. Another dataset was obtained between March and May 2014 at the Amazon Tall Tower Observatory (ATTO), which is operated by Brazil's National Institute of Amazon Research (INPA). The ATTO is 320 m high and located in the heart of the rainforest on the Uatumã Biological Reserve, some 160 km northeast of Manaus - beyond the reach of urban pollution. Supplementary measurements of aerosols were made at the ZF2 towers around 55 km north of Manaus, and in Manacapuru some 100km west of Manaus at the Atmospheric Radiation Measurement (ARM) mobile facility comprising a number of ground-based and airborne devices developed for climate studies and owned by the US Department of Energy. "Much to our surprise, we found that the amount of particulate matter in the atmosphere increased with altitude. We would have expected higher concentrations nearer to the ground. We found very large amounts of aerosols at around 6,000 m, the highest the Gulfstream-1 can fly," said Luiz Augusto Toledo Machado, a researcher at the National Space Research Institute (INPE) and also a co-author of the article. The initial observation was confirmed by new measurements captured by the German High Altitude & Long Range Research Aircraft (HALO), which can fly at 16,000 m and is operated by a research consortium that includes the German Aerospace Center (DLR), Max Planck Institute (MPI) and German Research Foundation (DFG). "We found that in polluted areas there was an extremely high concentration of particulate matter near ground level, which wasn't the case in pollution-free areas. At high altitudes, however, we found large amounts of particles even in the absence of local pollution sources," Machado said. "This latest study shows how these nanoparticles are swept down toward the ground by rain to form new populations of particulate matter that act as cloud condensation nuclei at low altitudes." According to Artaxo, the observation was surprising because above the planetary boundary layer at 2,500 m there is a temperature inversion that usually inhibits the vertical movement of particules. "But we hadn't taken into account the role of convective clouds as transporters of the gases emitted by the forest," he said. The studies performed under the aegis of GOAmazon are proving that VOCs from plants are part of a fundamental mechanism for the production of aerosols in continental areas, he went on. "The combination of forest-emitted VOCs and clouds makes a very specific dynamic that produces huge amounts of particles at high altitudes, where there weren't thought to be any. It's the biology of the forest interacting with clouds to keep the Amazon's ecosystem functioning," Artaxo said. The VOCs soar into the upper atmosphere where wind speeds are very high, and are redistributed around the planet very efficiently. In the Amazon's case, part goes to the Andes and part to southern Brazil, while some remains in the tropical forest region itself. "At the moment we're modeling all our data to work out more precisely which regions are affected by VOCs from the Amazon that are transported by atmospheric circulation," Artaxo said. Because it was unknown until now, this aerosol production mechanism is not considered by any of the climate models currently in use. "The knowledge will have to be included," Machado said. "It will help make rainfall simulations more precise."
News Article | December 16, 2016
Electrons embedded in the atomic lattice – the components of a solid. The mutual repulsion of the electrons prevents them from coming into close contact. This impedes the electron flow and the system can become an insulator. Credit: Dr. Ulrich Tutsch Whether water freezes to ice, iron is demagnetized or a material becomes superconducting – for physicists there is always a phase transition behind it. They endeavour to understand these different phenomena by searching for universal properties. Researchers at Goethe University Frankfurt and Technische Universität Dresden have now made a pioneering discovery during their study of a phase transition from an electrical conductor to an insulator (Mott metal-insulator transition). According to Sir Nevill Francis Mott's prediction in 1937, the mutual repulsion of charged electrons, which are responsible for carrying electrical current, can cause a metal-insulator transition. Yet, contrary to common textbook opinion, according to which the phase transition is determined solely by the electrons, it is the interaction of the electrons with the atomic lattice of the solid which is the determinant factor. The researchers have reported this in the latest issue of the Science Advances journal. The research group, led by Professor Michael Lang of the Physics Institute at Goethe University Frankfurt, succeeded in making the discovery with the help of a homemade apparatus which is unique worldwide. It allows the measurement of length changes at low temperatures under variable external pressure with extremely high resolution. In this way, it was possible to prove experimentally for the first time that it is not just the electrons which play a significant role in the phase transition but also the atomic lattice—the solid's scaffold. "These experimental results will herald in a paradigm shift in our understanding of one of the key phenomena of current condensed matter research," says Professor Lang. The Mott metal-insulator transition is namely linked to unusual phenomena, such as high-temperature superconductivity in copper oxide-based materials. These offer tremendous potential for future technical applications. The theoretical analysis of the experimental findings is based on the fundamental notion that the many particles in a system close to a phase transition not only interact with their immediate neighbours but also "communicate" over long distances with all other particles. As a consequence, only overarching aspects are important, such as the system's symmetry. The identification of such universal properties is thus the key to understanding phase transitions. "These new insights open up a whole new perspective on the Mott metal-insulator transition and permit more sophisticated theoretical modelling of the phase transition," explains Dr. Markus Garst, Senior Lecturer at the Institute of Theoretical Physics of Technische Universität Dresden. Explore further: The metal-insulator transition depends on the mass of the Dirac electrons More information: E. Gati et al. Breakdown of Hookes law of elasticity at the Mott critical endpoint in an organic conductor, Science Advances (2016). DOI: 10.1126/sciadv.1601646
Sun T.,Wuhan University of Technology |
Sun T.,Physics Institute |
Qing G.,Wuhan University of Technology |
Qing G.,Physics Institute
Advanced Materials | Year: 2011
Controlling the surface chemical and physical properties of materials and modulating the interfacial behaviors of biological entities, e.g., cells and biomolecules, are central tasks in the study of biomaterials. In this context, smart polymer interface materials have recently attracted much interest in biorelated applications and have broad prospects due to the excellent controllability of their surface properties by external stimuli. Among such materials, poly(N-isopropylacrylamide) and its copolymer films are especially attractive due to their reversible hydrogen-bonding-mediated reversible phase transition, which mimics natural biological processes. This platform is promising for tuning surface properties or to introduce novel biofunctionalities via copolymerization with various functional units and/or combination with other materials. Important progress in this field in recent years is highlighted. A promising platform to realize special biofunctionalities and excellent controllability over the surface properties of smart biointerface materials is provided by the hydrogen-bonding-mediated reversible coil/globule transition of a poly(N-isopropylacrylamide) film. Copolymerization with other functional units and/or combination with other materials provide tools for a wide variety of attractive biological and biomedical applications (see graphic). Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Gerber S.,Princeton University |
Gerber S.,University of Florida |
Hedin L.O.,Princeton University |
Keel S.G.,Princeton University |
And 3 more authors.
Geophysical Research Letters | Year: 2013
Our understanding of Earth's carbon climate system depends critically upon interactions between rising atmospheric CO2, changing land use, and nitrogen limitation on vegetation growth. Using a global land model, we show how these factors interact locally to generate the global land carbon sink over the past 200 years. Nitrogen constraints were alleviated by N2 fixation in the tropics and by atmospheric nitrogen deposition in extratropical regions. Nonlinear interactions between land use change and land carbon and nitrogen cycling originated from three major mechanisms: (i) a sink foregone that would have occurred without land use conversion; (ii) an accelerated response of secondary vegetation to CO2 and nitrogen, and (iii) a compounded clearance loss from deforestation. Over time, these nonlinear effects have become increasingly important and reduce the present-day net carbon sink by ∼40% or 0.4 PgC yr-1. Key Points Interactions between land-use and CO2 response curtail the land carbon uptake Successional dynamics of land-use recovery affect nitrogen supply and CO2 sink ©2013. American Geophysical Union. All Rights Reserved.
Ritz S.P.,Physics Institute |
Stocker T.F.,Physics Institute |
Joos F.,Physics Institute
Journal of Climate | Year: 2011
The Bern3D coupled three-dimensional dynamical ocean-energy balance atmosphere model is introduced and the atmospheric component is discussed in detail. The model is of reduced complexity, developed to perform extensive sensitivity studies and ensemble simulations extending over several glacial-interglacial cycles. On large space scales, the modern steady state of the model compares well with observations. In a first application, several 800 000-yr simulations with prescribed orbital, greenhouse gas, and ice sheet forcings are performed. The model shows an increase of Atlantic meridional overturning circulation strength at glacial inceptions followed by a decrease throughout the glaciation and ending in a circulation at glacial maxima that isweaker than at present. The sensitivity of ocean temperature to atmospheric temperature,Atlanticmeridional overturning circulation (AMOC), and Antarctic bottomwater (AABW) strength is analyzed at 23 locations. In a second application the climate sensitivities of the modern and of the Last GlacialMaximum (LGM) state are compared. The temperature rise for a doubling of theCO2 concentration fromLGMconditions is 4.3°Cand thus notably larger than in themodern case (3°C). The relaxation time scale is strongly dependent on the response of AABW to the CO2 change, since it determines the ventilation of the deep Pacific and Indian Ocean. © 2011 American Meteorological Society.
Schicker R.,Physics Institute
EPJ Web of Conferences | Year: 2014
The interest in the study of diffractive meson production is discussed. The description of diffraction within Regge phenomenology is presented, and the QCD-based understanding of diffractive processes is given. Central production is reviewed, and the corresponding main results from the COMPASS experiment and from the experiments at the ISR, RHIC, TEVATRON and LHC collider are summarised. © Owned by the authors, published by EDP Sciences, 2014.