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LAWRENCE -- In 2016, researchers published "slam dunk" evidence, based on iron-60 isotopes in ancient seabed, that supernovae buffeted the Earth -- one of them about 2.6 million years ago. University of Kansas researcher Adrian Melott, professor of physics and astronomy, supported those findings in Nature with an associated letter, titled "Supernovae in the neighborhood." Melott has followed up since those findings with an examination of the effects of the supernovae on Earth's biology. In new research to appear in Astrophysical Journal, the KU researcher and colleagues argue the estimated distance of the supernova thought to have occurred roughly 2.6 million years ago should be cut in half. "There's even more evidence of that supernova now," he said. "The timing estimates are still not exact, but the thing that changed to cause us to write this paper is the distance. We did this computation because other people did work that made a revised distance estimate, which cut the distance in half. But now, our distance estimate is more like 150 light years." A supernova exploding at such a range probably wouldn't touch off mass extinctions on Earth, Melott said. "People estimated the 'kill zone' for a supernova in a paper in 2003, and they came up with about 25 light years from Earth," he said. "Now we think maybe it's a bit greater than that. They left some effects out or didn't have good numbers, so now we think it may be a bit larger distance. We don't know precisely, and of course it wouldn't be a hard-cutoff distance. It would be a gradual change. But we think something more like 40 or 50 light years. So, an event at 150 light years should have some effects here but not set off a mass extinction." In addition to its distance, interstellar conditions at the time of a supernova would influence its lethality to biology on Earth. "Cosmic rays like to travel along magnetic field lines," Melott said. "They don't like to cut across magnetic field lines as they experience forces to stop them from doing that. If there's a magnetic field, we don't know its orientation, so it can either create a superhighway for cosmic ray, or it could block them. The main interesting case did not assume the superhighway. It assumed that much of the magnetic field was blasted out by a series of supernovae, which made the Local Bubble -- and we and the most recent supernovae were inside. This is a weak, disordered magnetic field. The best analogy I can think of is more like off-road driving." In such a case, the authors think cosmic rays from the supernova at 150 light years would have penetrated to Earth's lower atmosphere. "This is a much stronger thing," he said. "The cosmic rays from the supernova would be getting down into the lower atmosphere -- having an effect on the troposphere. All kinds of elementary particles are penetrating from altitudes of 45-10 miles, and many muons get to the ground. The effect of the muons is greater -- it's not overwhelming, but imagine every organism on Earth gets the equivalent of several CT scans per year. CT scans have some danger associated with them. Your doctor wouldn't recommend a CT scan unless you really needed it." Melott said cancer and mutations would be the most obvious consequences for Earth's biology of a supernova's cosmic rays. With his co-authors -- B.C. Thomas of Washburn University (2005 KU physics doctoral graduate and recent winner of the A. Roy Myers Excellence in Research Award), M. Kachelrieß of Institutt for fysikk in Norway, D.V. Semikoz of the Observatoire de Paris, Sorbonne Paris Cite in France and the National Research Nuclear University in Moscow, and A.C. Overholt (2013 KU physics doctoral graduate) of MidAmerica Nazarene University -- Melott looked at the fossil record in Africa, the most geographically stable continent on earth during the Pleistocene, when a supernova was likely to have occurred. "There isn't a mass extinction, but there is kind of a lot of extinction going on at that time and species turnover," he said. "It's not quite severe enough to call it a mass extinction. There is some effect possibly connected to the supernova. That's more difficult to say because there are many competing effects. Even in Africa you have climate change, and you don't know if climate change is causing the effects you see or if a supernova has something to do with the climate change." In addition to cosmic rays, the team found a supernova would have caused blue light to shine in the sky at night for about a month. "That's been shown to be a fairly bad thing for almost all living organisms," Melott said. "It throws off sleep and messes up your melatonin production. I would never want a blue LED alarm clock in my bedroom, for example. Blue LED streetlights have been shown to have bad effects in animals, causing behavioral changes. But this effect would only last a month or so. I think you would never see evidence in the fossil record." Atmospheric ionization would have been a more serious effect from a supernova, according to the KU researcher. "Atmospheric ionization can help lightning get started," Melott said. "When a cosmic ray comes down, it makes a path through the atmosphere, where it knocks electrons out of atoms, and that makes a pathway for lightning to get started. We'd expect to see a big increase with cloud-to-ground lightning. That would be good for some organisms and bad for others. Lightning is the number one cause of wildfires other than humans. So, we'd expect a whole lot more wildfires, and that could change the ecology of different regions, such as a loss of tree cover in northeast Africa, which could even have something to do with human evolution. The Great Plains has recently been largely kept grass-covered by a bunch of wildfires. A big increase in lightning would also mean a big increase in nitrate coming out of the rain, and that would act like fertilizer." Indeed, Melott said 2.6 million years ago there was in Africa a loss of tree cover and increase in grassland, possibly attributable to lightning-driven wildfires. "We think it's possible that the cosmic rays may have had something to do with that," he said. Melott added he's often asked by people if they should fear a supernova exploding close to Earth today. "I tell them they should worry about global warming and nuclear war, not this stuff," he said. "There's nothing close enough to cause this kind of event in the very near future." The closest potential supernova is Betelgeuse, about 600 light years away, according to Melott. "It's much further away than this one we've been talking about," he said. "It's close enough to be spectacular in the sense that it would be bright and you'd see it in daytime, but there'd be no harmful effects."


News Article | May 12, 2017
Site: astrobiology.com

In 2016, researchers published "slam dunk" evidence, based on iron-60 isotopes in ancient seabed, that supernovae buffeted the Earth One of these supernovae was about 2.6 million years ago. University of Kansas researcher Adrian Melott, professor of physics and astronomy, supported those findings in Nature with an associated letter, titled "Supernovae in the Neighborhood" [http://www.nature.com/nature/journal/v532/n7597/full/532040a.html]. Melott has followed up since those findings with an examination of the effects of the supernovae on Earth's biology. In new research to appear in Astrophysical Journal, the KU researcher and colleagues argue the estimated distance of the supernova thought to have occurred roughly 2.6 million years ago should be cut in half. "There's even more evidence of that supernova now," he said. "The timing estimates are still not exact, but the thing that changed to cause us to write this paper is the distance. We did this computation because other people did work that made a revised distance estimate, which cut the distance in half. But now, our distance estimate is more like 150 light-years." A supernova exploding at such a range probably wouldn't touch off mass extinctions on Earth, Melott said. "People estimated the 'kill zone' for a supernova in a paper in 2003, and they came up with about 25 light-years from Earth," he said. "Now we think maybe it's a bit greater than that. They left some effects out or didn't have good numbers, so now we think it may be a bit larger distance. We don't know precisely, and of course it wouldn't be a hard-cutoff distance. It would be a gradual change. But we think something more like 40 or 50 light-years. So, an event at 150 light-years should have some effects here but not set off a mass extinction." In addition to its distance, interstellar conditions at the time of a supernova would influence its lethality to biology on Earth. "Cosmic rays like to travel along magnetic field lines," Melott said. "They don't like to cut across magnetic field lines as they experience forces to stop them from doing that. If there's a magnetic field, we don't know its orientation, so it can either create a superhighway for cosmic ray, or it could block them. The main interesting case did not assume the superhighway. It assumed that much of the magnetic field was blasted out by a series of supernovae, which made the Local Bubble -- and we and the most recent supernovae were inside. This is a weak, disordered magnetic field. The best analogy I can think of is more like off-road driving." In such a case, the authors think cosmic rays from the supernova at 150 light-years would have penetrated to Earth's lower atmosphere. "This is a much stronger thing," he said. "The cosmic rays from the supernova would be getting down into the lower atmosphere -- having an effect on the troposphere. All kinds of elementary particles are penetrating from altitudes of 45-10 miles, and many muons get to the ground. The effect of the muons is greater -- it's not overwhelming, but imagine every organism on Earth gets the equivalent of several CT scans per year. CT scans have some danger associated with them. Your doctor wouldn't recommend a CT scan unless you really needed it." Melott said cancer and mutations would be the most obvious consequences for Earth's biology of a supernova's cosmic rays. With his co-authors -- B.C. Thomas of Washburn University (2005 KU physics doctoral graduate and recent winner of the A. Roy Myers Excellence in Research Award), M. Kachelrieß of Institutt for fysikk in Norway, D.V. Semikoz of the Observatoire de Paris, Sorbonne Paris Cite in France and the National Research Nuclear University in Moscow, and A.C. Overholt (2013 KU physics doctoral graduate) of MidAmerica Nazarene University -- Melott looked at the fossil record in Africa, the most geographically stable continent on Earth during the Pleistocene, when a supernova was likely to have occurred. "There isn't a mass extinction, but there is kind of a lot of extinction going on at that time and species turnover," he said. "It's not quite severe enough to call it a mass extinction. There is some effect possibly connected to the supernova. That's more difficult to say because there are many competing effects. Even in Africa you have climate change, and you don't know if climate change is causing the effects you see or if a supernova has something to do with the climate change." In addition to cosmic rays, the team found a supernova would have caused blue light to shine in the sky at night for about a month. "That's been shown to be a fairly bad thing for almost all living organisms," Melott said. "It throws off sleep and messes up your melatonin production. I would never want a blue LED alarm clock in my bedroom, for example. Blue LED streetlights have been shown to have bad effects in animals, causing behavioral changes. But this effect would only last a month or so. I think you would never see evidence in the fossil record." Atmospheric ionization would have been a more serious effect from a supernova, according to the KU researcher. "Atmospheric ionization can help lightning get started," Melott said. "When a cosmic ray comes down, it makes a path through the atmosphere, where it knocks electrons out of atoms, and that makes a pathway for lightning to get started. We'd expect to see a big increase with cloud-to-ground lightning. That would be good for some organisms and bad for others. Lightning is the number one cause of wildfires other than humans. So, we'd expect a whole lot more wildfires, and that could change the ecology of different regions, such as a loss of tree cover in northeast Africa, which could even have something to do with human evolution. The Great Plains has recently been largely kept grass-covered by a bunch of wildfires. A big increase in lightning would also mean a big increase in nitrate coming out of the rain, and that would act like fertilizer." Indeed, Melott said 2.6 million years ago there was in Africa a loss of tree cover and increase in grassland, possibly attributable to lightning-driven wildfires. "We think it's possible that the cosmic rays may have had something to do with that," he said. Melott added he's often asked by people if they should fear a supernova exploding close to Earth today. "I tell them they should worry about global warming and nuclear war, not this stuff," he said. "There's nothing close enough to cause this kind of event in the very near future." The closest potential supernova is Betelgeuse, about 600 light-years away, according to Melott. "It's much further away than this one we've been talking about," he said. "It's close enough to be spectacular in the sense that it would be bright and you'd see it in daytime, but there'd be no harmful effects." Reference: "A Supernova at 50 pc: Effects on the Earth's Atmosphere and Biota," A. L. Melott et al., 2017, to appear in the Astrophysical Journal [http://apj.aas.org, preprint: https://arxiv.org/abs/1702.04365].


Melott has followed up since those findings with an examination of the effects of the supernovae on Earth's biology. In new research to appear in Astrophysical Journal, the KU researcher and colleagues argue the estimated distance of the supernova thought to have occurred roughly 2.6 million years ago should be cut in half. "There's even more evidence of that supernova now," he said. "The timing estimates are still not exact, but the thing that changed to cause us to write this paper is the distance. We did this computation because other people did work that made a revised distance estimate, which cut the distance in half. But now, our distance estimate is more like 150 light years." A supernova exploding at such a range probably wouldn't touch off mass extinctions on Earth, Melott said. "People estimated the 'kill zone' for a supernova in a paper in 2003, and they came up with about 25 light years from Earth," he said. "Now we think maybe it's a bit greater than that. They left some effects out or didn't have good numbers, so now we think it may be a bit larger distance. We don't know precisely, and of course it wouldn't be a hard-cutoff distance. It would be a gradual change. But we think something more like 40 or 50 light years. So, an event at 150 light years should have some effects here but not set off a mass extinction." In addition to its distance, interstellar conditions at the time of a supernova would influence its lethality to biology on Earth. "Cosmic rays like to travel along magnetic field lines," Melott said. "They don't like to cut across magnetic field lines as they experience forces to stop them from doing that. If there's a magnetic field, we don't know its orientation, so it can either create a superhighway for cosmic ray, or it could block them. The main interesting case did not assume the superhighway. It assumed that much of the magnetic field was blasted out by a series of supernovae, which made the Local Bubble—and we and the most recent supernovae were inside. This is a weak, disordered magnetic field. The best analogy I can think of is more like off-road driving." In such a case, the authors think cosmic rays from the supernova at 150 light years would have penetrated to Earth's lower atmosphere. "This is a much stronger thing," he said. "The cosmic rays from the supernova would be getting down into the lower atmosphere—having an effect on the troposphere. All kinds of elementary particles are penetrating from altitudes of 45-10 miles, and many muons get to the ground. The effect of the muons is greater—it's not overwhelming, but imagine every organism on Earth gets the equivalent of several CT scans per year. CT scans have some danger associated with them. Your doctor wouldn't recommend a CT scan unless you really needed it." Melott said cancer and mutations would be the most obvious consequences for Earth's biology of a supernova's cosmic rays. With his co-authors— B.C. Thomas of Washburn University (2005 KU physics doctoral graduate and recent winner of the A. Roy Myers Excellence in Research Award), M. Kachelrieß of Institutt for fysikk in Norway, D.V. Semikoz of the Observatoire de Paris, Sorbonne Paris Cite in France and the National Research Nuclear University in Moscow, and A.C. Overholt (2013 KU physics doctoral graduate) of MidAmerica Nazarene University—Melott looked at the fossil record in Africa, the most geographically stable continent on earth during the Pleistocene, when a supernova was likely to have occurred. "There isn't a mass extinction, but there is kind of a lot of extinction going on at that time and species turnover," he said. "It's not quite severe enough to call it a mass extinction. There is some effect possibly connected to the supernova. That's more difficult to say because there are many competing effects. Even in Africa you have climate change, and you don't know if climate change is causing the effects you see or if a supernova has something to do with the climate change." In addition to cosmic rays, the team found a supernova would have caused blue light to shine in the sky at night for about a month. "That's been shown to be a fairly bad thing for almost all living organisms," Melott said. "It throws off sleep and messes up your melatonin production. I would never want a blue LED alarm clock in my bedroom, for example. Blue LED streetlights have been shown to have bad effects in animals, causing behavioral changes. But this effect would only last a month or so. I think you would never see evidence in the fossil record." Atmospheric ionization would have been a more serious effect from a supernova, according to the KU researcher. "Atmospheric ionization can help lightning get started," Melott said. "When a cosmic ray comes down, it makes a path through the atmosphere, where it knocks electrons out of atoms, and that makes a pathway for lightning to get started. We'd expect to see a big increase with cloud-to-ground lightning. That would be good for some organisms and bad for others. Lightning is the number one cause of wildfires other than humans. So, we'd expect a whole lot more wildfires, and that could change the ecology of different regions, such as a loss of tree cover in northeast Africa, which could even have something to do with human evolution. The Great Plains has recently been largely kept grass-covered by a bunch of wildfires. A big increase in lightning would also mean a big increase in nitrate coming out of the rain, and that would act like fertilizer." Indeed, Melott said 2.6 million years ago there was in Africa a loss of tree cover and increase in grassland, possibly attributable to lightning-driven wildfires. "We think it's possible that the cosmic rays may have had something to do with that," he said. Melott added he's often asked by people if they should fear a supernova exploding close to Earth today. "I tell them they should worry about global warming and nuclear war, not this stuff," he said. "There's nothing close enough to cause this kind of event in the very near future." The closest potential supernova is Betelgeuse, about 600 light years away, according to Melott. "It's much further away than this one we've been talking about," he said. "It's close enough to be spectacular in the sense that it would be bright and you'd see it in daytime, but there'd be no harmful effects." Explore further: Ancient supernovae buffeted Earth's biology with radiation dose, researcher says More information: "A Supernova at 50 pc: Effects on the Earth's Atmosphere and Biota," A. L. Melott et al., 2017, to appear in the Astrophysical Journal: arxiv.org/abs/1702.04365


Lozovik Y.E.,Moscow Institute of Physics and Technology | Ogarkov S.L.,National Research Nuclear University | Sokolik A.A.,Russian Academy of Sciences
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

Condensation of pairs formed by spatially separated electrons and holes in a system of two isolated graphene layers is studied beyond the mean-field approximation. Suppression of the screening of the pairing interaction at large distances, caused by the appearance of the gap, is considered self-consistently. A mutual positive feedback between the appearance of the gap and the enlargement of the interaction leads to a sharp transition to a correlated state with a greatly increased gap above some critical value of the coupling strength. At a coupling strength below the critical value, this correlation effect increases the gap approximately by a factor of 2. The maximal coupling strength achievable in experiments is close to the critical value. This indicates the importance of correlation effects in closely spaced graphene bilayers at weak substrate dielectric screening. Another effect beyond the mean-field approximation considered is the influence of vertex corrections on the pairing, which is shown to be very weak. © 2012 American Physical Society.


Ivanov Y.B.,National Research Nuclear University | Soldatov A.A.,National Research Nuclear University MEPhI
Physical Review C - Nuclear Physics | Year: 2015

The transverse-momentum-integrated elliptic flow of charged particles at midrapidity, v2(charged), and that of identified hadrons from Au+Au collisions are computed in a wide range of incident energies 2.7 ≤sNN≤39 GeV. The simulations are performed within a three-fluid model by employing three different equations of state (EoSs): a purely hadronic EoS and two versions of the EoS involving the deconfinement transition - a first-order phase transition and a smooth crossover one. The present simulations demonstrate low sensitivity of v2(charged) to the EoS. All considered scenarios equally well reproduce recent STAR data on v2(charged) for mid-central Au+Au collisions and properly describe its change of sign at the incident energy decrease below sNN≈3.5 GeV. The predicted integrated elliptic flow of various species exhibits a stronger dependence on the EoS. A noticeable sensitivity to the EoS is found for antibaryons and, to a lesser extent, for K- mesons. In particular, the v2 excitation functions of antibaryons exhibit a nonmonotonicity within the deconfinement scenarios that was predicted by Kolb, Sollfrank, and Heinz. However, low multiplicities of antibaryons at sNN≤10 GeV result in large fluctuations of their v2, which may wash out this nonmonotonicity. © 2015 American Physical Society.


Skorobogatov P.K.,National Research Nuclear University
Russian Microelectronics | Year: 2013

The adequacy of the laser simulation of volume ionization effects (dose rate) in microcircuits is violated due to the influence of surface metallization. It is shown that the optical diffraction of the laser emission restricts possible applications of this method by 0.18-μm design rules and higher. © 2013 Pleiades Publishing, Ltd.


Ivanov Y.B.,National Research Nuclear University
Journal of Physics: Conference Series | Year: 2016

It is argued that an irregularity in the baryon stopping is a natural consequence of onset of deconfinement occurring in the compression stage of a nuclear collision. It is an effect of the softest point inherent in an equation of state (EoS) with a deconfinement transition. In order to illustrate this effect, calculations within the three-fluid model were performed with three different EoS's: a purely hadronic EoS, an EoS with a first-order phase transition and that with a smooth crossover transition.


The results of experimental studies and simulations of transient radiation effects in microwave monolithic integrated circuits, based on heterostructure field-effect transistors, affected by the pulse ionizing radiation, are presented. The physical model, which adequately describes transient radiation effects in field-effect transistors in dose rate range up to 1012 rad/s, is proposed. Based on the physical model, the equivalent electric circuit, taking into account the dominating ionization effects, intended for using in the computer-aided design (CAD), is constructed. The simulated ionizing responses of the microwave low-noise amplifier (LNA) MIC are in accordance with the experimental data. © 2014 Pleiades Publishing, Ltd.


News Article | December 13, 2016
Site: www.cemag.us

National Research Nuclear University (MEPhI) scientists have figured out how the change of nanostructure of materials for energy reactors of the future will affect their plasticity, heat resistance, and other important properties. Currently, one of the most promising areas in nuclear power are the development of new fast reactors and the creation of a workable fusion reactor. The first will allow close the nuclear fuel cycle and make nuclear energy more environmentally friendly. If the second becomes possible, then in the future there will be a chance to produce energy in a brand new way. The most famous project is designed to bring the appearance of an energy fusion reactor — ITER (International Thermonuclear Experimental Reactor). One difficulty in creating new energy devices is that they all suggest the presence of extreme conditions of use in the energy zone. Therefore, the materials to be used in the active areas of new reactors must meet extremely high demands. Being exposed to high temperatures and the flow of high-energy radiation, modern materials are rapidly degraded. Most of them can withstand strong irradiation dose, at which each atom in the material moves 80 to 90 times. For the energy of thermonuclear installations this parameter should be twice as much. This resistance of the materials in the area of ​​use of energy determines the effectiveness and safety of a nuclear reactor. MEPhI scientists consider it possible to solve this problem with the help of nanotechnology. Ferritic-martensitic steels based on Fe-Cr alloys and dispersion-hardened steel oxides are considered to be promising for future power plants. In their works, scientists managed to experimentally demonstrate the mechanisms of atomic-scale restructuring of these materials, as well as to show how redistribution of atoms happens, resulting in a significant increase in their fragility and loss of plasticity. The results of these studies have been published in the Journal of Nuclear Materials and Journal of Nuclear Materials and Energy. It is known that the change of the nanostructure can fundamentally change the properties of the structural material. And, as a result, significantly reduce the time of operation of settings’ active zones, made of it. In some cases, scientists, on the contrary, succeed in picking up such nanostructured changes that significantly extend the capabilities of the products and provide them with unique properties, such as large heat resistance. In their experiments, experts influenced in a different way the model alloys Fe-Cr and steels, dispersion-reinforced by oxides, and then recorded arising changes in the properties of materials on the nanoscale, using the atomic-probe tomography. "In our studies, we have analyzed the state of nanoscale materials and adjustment under different impacts. We carried out the thermal aging, and then, using beams of metal ions, found that their effects might lead to the reducing of nanostructures," says Deputy Head of MEPhI department of physics of extreme states of matter of the Institute of nuclear physics and technologies Sergey Rogozhkin. According to Rogozhkin, research results can be used both when creating materials for ITER, and for the future energy systems. "The aim of the ITER is to demonstrate the efficiency of the concept of fusion reactor. Requirements to the materials at this stage are severe, but a fusion plant of the next generation will create even more extreme conditions, for work in which, in fact, fundamentally new materials have been developed, including those that we are now investigating, " says Rogozhkin.


Researchers from the National Research Nuclear University, working as part of an IAEA project, have created the most accurate method to date of obtaining the data needed to reliably operate a thermonuclear reactor. The results were published in the Journal of Nuclear Materials.

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