Karen Fiuza
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Keeping an eye in the next challenge.
Keeping an eye in the next challenge.
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Coleção de imagens desde o micro até o macro-cosmos. Iniciado ontem, pelo meu perfil Fé-na-Física.
ORION NEBULA NGC1976 - Nebulosa de Orion: situada na constelação de Orion. Esta foto de domínio público, tirada pelo telescópio espacial Hubble em 2006, é uma das imagens astronômicas mais detalhadas que existem. É uma região de formação estelar. Está a 1300 anos-luz da Terra, com aproximadamente 30-40 anos-luz de diâmetro, dando luz a milhares de estrelas. Em 2012 um grupo internacional de astrofísicos anunciou resultados de simulações computacionais que sugeriram que existe um buraco negro no coração da Nebulosa, cuja massa seria de 200 sóis.
FONTES: https://www.uq.edu.au/news/article/2012/10/international-study-suggests-massive-black-hole-exists-sword-of-orion
https://en.wikipedia.org/wiki/Orion_Nebula
FONTES: https://www.uq.edu.au/news/article/2012/10/international-study-suggests-massive-black-hole-exists-sword-of-orion
https://en.wikipedia.org/wiki/Orion_Nebula
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Cenote Ik Kil, Yucatán, Mexico
Ik Kil is a well known cenote outside Pisté in the Municipality of Tinúm, Yucatán, Mexico. It is located in the northern center of the Yucatán Peninsula and is part of the Ik Kil Archeological Park near Chichen Itza.
Follow ► +Amazing Places to See For More
#TravelPhotography #NaturePhotography #BeautifulPlaces #HDRPhotography #BlackandWhite #Sunset #StreetPhotography #HDR #BlackandWhitePhotography #Sunrise #Sunsetphotography #Photographer #NightPhotography #Beach #TravelPhotography #Nature #Landscape #NaturePhotography #HDRphoto #MilkyWay #MilkyWayPhotography #waterfall #AmazingPlacesToSee #AmazingPlacesToVisit #Landscape
Copyright : Maxlight
Source : http://goo.gl/yDQaWl
Ik Kil is a well known cenote outside Pisté in the Municipality of Tinúm, Yucatán, Mexico. It is located in the northern center of the Yucatán Peninsula and is part of the Ik Kil Archeological Park near Chichen Itza.
Follow ► +Amazing Places to See For More
#TravelPhotography #NaturePhotography #BeautifulPlaces #HDRPhotography #BlackandWhite #Sunset #StreetPhotography #HDR #BlackandWhitePhotography #Sunrise #Sunsetphotography #Photographer #NightPhotography #Beach #TravelPhotography #Nature #Landscape #NaturePhotography #HDRphoto #MilkyWay #MilkyWayPhotography #waterfall #AmazingPlacesToSee #AmazingPlacesToVisit #Landscape
Copyright : Maxlight
Source : http://goo.gl/yDQaWl
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Hoje é o centenário deo escritor argentino Júlio Cortázar!
Cortázar é um dos grandes autores que também escreveram para crianças! É dele a obra "Discurso do Urso". Veja outras obras infantis escritas por grandes nomes da literatura --> http://abr.ai/1p6WSLs
Cortázar é um dos grandes autores que também escreveram para crianças! É dele a obra "Discurso do Urso". Veja outras obras infantis escritas por grandes nomes da literatura --> http://abr.ai/1p6WSLs
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The Isaac Newton Medal for “outstanding contributions to physics” went to Deborah Jin for “pioneering the field of quantum-degenerate Fermi gases”. http://goo.gl/UX9M06 #quantumphysics
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Produtores inovadores começam a cultivar a própria água no Mato Grosso http://abr.ai/1KAAdnl
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Problems with Perovskite Solar Cells
If you have read about solar cells you have probably read about the recent advances in the use of perovskite type materials to increase the efficiency of solar cells. The efficiency of solar cells is a measurement of how much the energy of the sun is converted into electricity.
Solar cell efficiency is the ratio of the electrical output of a solar cell to the incident energy in the form of sunlight. The energy conversion efficiency (η) of a solar cell is the percentage of the solar energy to which the cell is exposed that is converted into electrical energy. This is calculated by dividing a cell's power output (in watts) at its maximum power point (Pm) by the input light (E, in W/m2) and the surface area of the solar cell (Ac in m2). Wiki [solar cell efficiency]
Now what are perovskites? They are a type of mineral that was discovered in the Ural Mountains of Russia and is named after Russian mineralogist Lev Perovski. The name has now been used to describe an entire class of compounds that have the same basic crystal lattice structure as the original perovskites.
Perovskites have a cubic structure with general formula of ABO3. In this structure, an A-site ion, on the corners of the lattice, is usually an alkaline earth or rare earth element. B site ions, on the center of the lattice, could be 3d, 4d, and 5d transition metal elements. A large number of metallic elements are stable in the perovskite structure… Wiki [Perovskites]
What makes perovskite structures so promising for solar cells is that the band gap (or charge diffusion length) can be adjusted to absorb different wavelengths of sunlight and they can be made in a liquid solution for very low cost production.
NREL Research Fellow David Ginley, who is a world-renowned materials scientist and winner of several R&D 100 Awards, said what makes perovskite device structures so remarkable is that when processed in a liquid solution, they have unusual abilities to diffuse photons a long distance through the cell. That makes it far less likely that the electrons will recombine with their hole pairs and be lost to useful electricity. And that indicates a potential for low-cost, high-efficiency devices. ⓐ
NREL Senior Scientist Daniel Friedman notes that the light-absorbing perovskite cells have "a diffusion length 10 times longer than their absorption length," not only an unusual phenomenon, but a very useful one, too. ⓐ
The new cells are made from a relative of the perovskite mineral found in the Ural Mountains. Small but vital changes to the material allow it to absorb sunlight very efficiently. The material is also easy to fabricate using liquids that could be printed on substrates like ink in a printing press, or made from simple evaporation. These properties suggest an easy, affordable route to solar cells. ⓐ
By playing with the elemental composition, it is also possible to tune the perovskite material to access different parts of the sun's spectrum. That flexibility can be crucial, because it means that the material can be changed by deliberately introducing impurities, and in such a way that it can be used in multijunction solar cells that have ultra-high efficiencies. Multijunction solar cells are an NREL invention from 1991, but because of high material costs, standard multijunctions are used mostly in outer space applications such as satellites and the Mars rovers. Cheaper multijunction cells based on perovskites could radically change this. ⓐ
Perovskites sound very promising and have in only a few years reached efficiencies of almost 20%, but they have some major problems that have not been discussed much. These problems are the method of testing perovskite solar cells which do not account for hysteresis effects, and that perovskites solar cells are not stable in outdoor conditions.
But how realistic are these efficiency values? This question is now being asked by national laboratories, with a cluster of research groups finding that the very nature of efficiency testing, as well as the questionable stability of perovskites themselves, is only serving to exaggerate device performance. ⓑ
‘All the exciting efficiencies and any energy claims that are associated with [perovskite solar cells] should be taken with a grain of salt,’ according to Keith Emery, the manager of the National Renewable Energy Laboratory’s (NREL) photovoltaic cell and module performance characterization group in the US. ⓑ
Emery states that there is a simple reason for this distinction: ‘I felt [perovskites] were unstable to the point where I felt it would be misleading to even think of them as being on the same level as any of those entries in that table.’ ⓑ
This instability to which Emery refers concerns these cells’ rapid degradation as soon as they are tested. ‘[The efficiency calculations] are based on the assumption that they will not degrade any faster than silicon and yet [perovskites] are degrading spontaneously in light and air,’ says Emery. He also notes that the majority of the efficiency values ascribed to perovskite cells have not been independently verified. ⓑ
Martin Green, director of the Centre for Advanced Photovoltaics in Australia, agrees with Emery’s sentiment on perovskites’ stability. ‘Measurement is complicated by the fact that devices are not stable,’ says Green. ‘They display hysteresis in their output.’ ⓑ
Hysteresis, where a material’s performance relies upon its history – like the weakening of the rubber in a car tyre due to repeated use – is also a sticking point for Eva Unger, a postdoc at Lund University, Sweden. ‘Solar cells based on [perovskites] are afflicted by preconditioning prior to current– voltage measurements, as well as the scan conditions,’ Unger tells Chemistry World. ⓑ
Her recent research on this issue, 1 as well as work carried out by Wolfgang Tress and colleagues at the Swiss Federal Institute of Technology in Lausanne, 2 shows the way in which a current–voltage measurement is carried out will dictate the efficiency value you obtain. Both the rate at which you scan through the voltages, for example, or how long you ‘light soak’ the cell prior to testing can decrease its efficiency. Unger concludes: ‘They can lead to a coarse over or underestimation of the power conversion efficiency.’ ⓑ
For Emery, not discussing these issues whilst still claiming perovskites are as economical as silicon is ‘wishful thinking’. But, like Unger, he is confident the community will resolve the efficiency problem. ‘I believe the perovskites’ groups want to do this – where they are trying to address these issues as a community,’ he says. ‘They really all want to be on the same page.’ ⓑ
ⓐ National Renewable Energy Laboratory, April 2014
NREL Unlocking Secrets of New Solar Material
http://www.nrel.gov/news/features/feature_detail.cfm/feature_id=10333
ⓑ Royal Society of Chemistry, Chemistry World
Meteoritic rise of perovskite solar cells under scrutiny over efficiencies
http://www.rsc.org/chemistryworld/2015/02/meteoritic-rise-perovskite-solar-cells-under-scrutiny-over-efficiencies
Papers on this subject (paywalls)
Energy and Environmental Science, Issue 3, 2015
Understanding the rate-dependent J–V hysteresis, slow time component, and aging in CH3NH3PbI3 perovskite solar cells: the role of a compensated electric field
http://pubs.rsc.org/en/Content/ArticleLanding/2015/EE/C4EE03664F#!divAbstract
Journal of Materials Chemistry A
Review of recent progress in chemical stability of perovskite solar cells
http://pubs.rsc.org/en/content/articlelanding/2015/ta/c4ta04994b#!divAbstract
Energy and Environmental Science, Issue 11, 2014
Hysteresis and transient behavior in current–voltage measurements of hybrid-perovskite absorber solar cells
http://pubs.rsc.org/en/Content/ArticleLanding/2014/EE/C4EE02465F#!divAbstract
Image: NREL, Credit: Dennis Schroeder
If you have read about solar cells you have probably read about the recent advances in the use of perovskite type materials to increase the efficiency of solar cells. The efficiency of solar cells is a measurement of how much the energy of the sun is converted into electricity.
Solar cell efficiency is the ratio of the electrical output of a solar cell to the incident energy in the form of sunlight. The energy conversion efficiency (η) of a solar cell is the percentage of the solar energy to which the cell is exposed that is converted into electrical energy. This is calculated by dividing a cell's power output (in watts) at its maximum power point (Pm) by the input light (E, in W/m2) and the surface area of the solar cell (Ac in m2). Wiki [solar cell efficiency]
Now what are perovskites? They are a type of mineral that was discovered in the Ural Mountains of Russia and is named after Russian mineralogist Lev Perovski. The name has now been used to describe an entire class of compounds that have the same basic crystal lattice structure as the original perovskites.
Perovskites have a cubic structure with general formula of ABO3. In this structure, an A-site ion, on the corners of the lattice, is usually an alkaline earth or rare earth element. B site ions, on the center of the lattice, could be 3d, 4d, and 5d transition metal elements. A large number of metallic elements are stable in the perovskite structure… Wiki [Perovskites]
What makes perovskite structures so promising for solar cells is that the band gap (or charge diffusion length) can be adjusted to absorb different wavelengths of sunlight and they can be made in a liquid solution for very low cost production.
NREL Research Fellow David Ginley, who is a world-renowned materials scientist and winner of several R&D 100 Awards, said what makes perovskite device structures so remarkable is that when processed in a liquid solution, they have unusual abilities to diffuse photons a long distance through the cell. That makes it far less likely that the electrons will recombine with their hole pairs and be lost to useful electricity. And that indicates a potential for low-cost, high-efficiency devices. ⓐ
NREL Senior Scientist Daniel Friedman notes that the light-absorbing perovskite cells have "a diffusion length 10 times longer than their absorption length," not only an unusual phenomenon, but a very useful one, too. ⓐ
The new cells are made from a relative of the perovskite mineral found in the Ural Mountains. Small but vital changes to the material allow it to absorb sunlight very efficiently. The material is also easy to fabricate using liquids that could be printed on substrates like ink in a printing press, or made from simple evaporation. These properties suggest an easy, affordable route to solar cells. ⓐ
By playing with the elemental composition, it is also possible to tune the perovskite material to access different parts of the sun's spectrum. That flexibility can be crucial, because it means that the material can be changed by deliberately introducing impurities, and in such a way that it can be used in multijunction solar cells that have ultra-high efficiencies. Multijunction solar cells are an NREL invention from 1991, but because of high material costs, standard multijunctions are used mostly in outer space applications such as satellites and the Mars rovers. Cheaper multijunction cells based on perovskites could radically change this. ⓐ
Perovskites sound very promising and have in only a few years reached efficiencies of almost 20%, but they have some major problems that have not been discussed much. These problems are the method of testing perovskite solar cells which do not account for hysteresis effects, and that perovskites solar cells are not stable in outdoor conditions.
But how realistic are these efficiency values? This question is now being asked by national laboratories, with a cluster of research groups finding that the very nature of efficiency testing, as well as the questionable stability of perovskites themselves, is only serving to exaggerate device performance. ⓑ
‘All the exciting efficiencies and any energy claims that are associated with [perovskite solar cells] should be taken with a grain of salt,’ according to Keith Emery, the manager of the National Renewable Energy Laboratory’s (NREL) photovoltaic cell and module performance characterization group in the US. ⓑ
Emery states that there is a simple reason for this distinction: ‘I felt [perovskites] were unstable to the point where I felt it would be misleading to even think of them as being on the same level as any of those entries in that table.’ ⓑ
This instability to which Emery refers concerns these cells’ rapid degradation as soon as they are tested. ‘[The efficiency calculations] are based on the assumption that they will not degrade any faster than silicon and yet [perovskites] are degrading spontaneously in light and air,’ says Emery. He also notes that the majority of the efficiency values ascribed to perovskite cells have not been independently verified. ⓑ
Martin Green, director of the Centre for Advanced Photovoltaics in Australia, agrees with Emery’s sentiment on perovskites’ stability. ‘Measurement is complicated by the fact that devices are not stable,’ says Green. ‘They display hysteresis in their output.’ ⓑ
Hysteresis, where a material’s performance relies upon its history – like the weakening of the rubber in a car tyre due to repeated use – is also a sticking point for Eva Unger, a postdoc at Lund University, Sweden. ‘Solar cells based on [perovskites] are afflicted by preconditioning prior to current– voltage measurements, as well as the scan conditions,’ Unger tells Chemistry World. ⓑ
Her recent research on this issue, 1 as well as work carried out by Wolfgang Tress and colleagues at the Swiss Federal Institute of Technology in Lausanne, 2 shows the way in which a current–voltage measurement is carried out will dictate the efficiency value you obtain. Both the rate at which you scan through the voltages, for example, or how long you ‘light soak’ the cell prior to testing can decrease its efficiency. Unger concludes: ‘They can lead to a coarse over or underestimation of the power conversion efficiency.’ ⓑ
For Emery, not discussing these issues whilst still claiming perovskites are as economical as silicon is ‘wishful thinking’. But, like Unger, he is confident the community will resolve the efficiency problem. ‘I believe the perovskites’ groups want to do this – where they are trying to address these issues as a community,’ he says. ‘They really all want to be on the same page.’ ⓑ
ⓐ National Renewable Energy Laboratory, April 2014
NREL Unlocking Secrets of New Solar Material
http://www.nrel.gov/news/features/feature_detail.cfm/feature_id=10333
ⓑ Royal Society of Chemistry, Chemistry World
Meteoritic rise of perovskite solar cells under scrutiny over efficiencies
http://www.rsc.org/chemistryworld/2015/02/meteoritic-rise-perovskite-solar-cells-under-scrutiny-over-efficiencies
Papers on this subject (paywalls)
Energy and Environmental Science, Issue 3, 2015
Understanding the rate-dependent J–V hysteresis, slow time component, and aging in CH3NH3PbI3 perovskite solar cells: the role of a compensated electric field
http://pubs.rsc.org/en/Content/ArticleLanding/2015/EE/C4EE03664F#!divAbstract
Journal of Materials Chemistry A
Review of recent progress in chemical stability of perovskite solar cells
http://pubs.rsc.org/en/content/articlelanding/2015/ta/c4ta04994b#!divAbstract
Energy and Environmental Science, Issue 11, 2014
Hysteresis and transient behavior in current–voltage measurements of hybrid-perovskite absorber solar cells
http://pubs.rsc.org/en/Content/ArticleLanding/2014/EE/C4EE02465F#!divAbstract
Image: NREL, Credit: Dennis Schroeder
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These aren't your grandma's wallpaper! Breath-taking #Earth images for desktop wallpaper use: http://climate.nasa.gov/images_video/earth_wallpaper/
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It has been a decade since a robotic traveler from Earth first soared over rings of ice and fired its engine to fall forever into the embrace of Saturn. Today the Cassini mission celebrates 10 years of exploring the planet, its rings and moons.
The Cassini spacecraft, carrying the European Space Agency's Huygens probe, arrived in the Saturn system on June 30, 2004, for a four-year primary mission. Since 2008, NASA has granted the mission three extensions, allowing scientists an unprecedented opportunity to observe seasonal changes as the planet and its retinue completed one-third of their nearly 30-year-long trek around the sun.
After 10 years at Saturn, the stalwart spacecraft has beamed back to Earth hundreds of gigabytes of scientific data, enabling the publication of more than 3,000 scientific reports. Representing just a sampling, 10 of Cassini’s top accomplishments and discoveries are:
-- The Huygens probe makes first landing on a moon in the outer solar system (Titan)
-- Discovery of active, icy plumes on the Saturnian moon Enceladus
-- Saturn’s rings revealed as active and dynamic -- a laboratory for how planets form
-- Titan revealed as an Earth-like world with rain, rivers, lakes and seas
-- Studies of Saturn's great northern storm of 2010-2011 -- Studies reveal radio-wave patterns are not tied to Saturn’s interior rotation, as previously thought
-- Vertical structures in the rings imaged for the first time
-- Study of prebiotic chemistry on Titan
-- Mystery of the dual, bright-dark surface of the moon Iapetus solved
-- First complete view of the north polar hexagon and discovery of giant hurricanes at both of Saturn's poles
Further details about each of these top-10 discoveries are available at: http://1.usa.gov/1r8bTD7
In celebration of the 10th anniversary, members of the Cassini team selected some of their favorite images for a gallery, describing in their own words what makes the images special to them. The gallery is available at: http://1.usa.gov/1vpuisY
While Cassini was originally approved for a four-year study of the Saturn system, the project's engineers and scientists had high hopes that the mission might carry on longer, and designed the system for endurance. The spacecraft has been remarkably trouble-free, and from an engineering standpoint, the main limiting factor for Cassini's lifetime now is how much propellant is left in its tanks. The mission owes a great deal of its longevity to skillful and efficient piloting by the mission's navigation and operations teams.
Learn more: http://1.usa.gov/aAJMT3
#Cassini10
The Cassini spacecraft, carrying the European Space Agency's Huygens probe, arrived in the Saturn system on June 30, 2004, for a four-year primary mission. Since 2008, NASA has granted the mission three extensions, allowing scientists an unprecedented opportunity to observe seasonal changes as the planet and its retinue completed one-third of their nearly 30-year-long trek around the sun.
After 10 years at Saturn, the stalwart spacecraft has beamed back to Earth hundreds of gigabytes of scientific data, enabling the publication of more than 3,000 scientific reports. Representing just a sampling, 10 of Cassini’s top accomplishments and discoveries are:
-- The Huygens probe makes first landing on a moon in the outer solar system (Titan)
-- Discovery of active, icy plumes on the Saturnian moon Enceladus
-- Saturn’s rings revealed as active and dynamic -- a laboratory for how planets form
-- Titan revealed as an Earth-like world with rain, rivers, lakes and seas
-- Studies of Saturn's great northern storm of 2010-2011 -- Studies reveal radio-wave patterns are not tied to Saturn’s interior rotation, as previously thought
-- Vertical structures in the rings imaged for the first time
-- Study of prebiotic chemistry on Titan
-- Mystery of the dual, bright-dark surface of the moon Iapetus solved
-- First complete view of the north polar hexagon and discovery of giant hurricanes at both of Saturn's poles
Further details about each of these top-10 discoveries are available at: http://1.usa.gov/1r8bTD7
In celebration of the 10th anniversary, members of the Cassini team selected some of their favorite images for a gallery, describing in their own words what makes the images special to them. The gallery is available at: http://1.usa.gov/1vpuisY
While Cassini was originally approved for a four-year study of the Saturn system, the project's engineers and scientists had high hopes that the mission might carry on longer, and designed the system for endurance. The spacecraft has been remarkably trouble-free, and from an engineering standpoint, the main limiting factor for Cassini's lifetime now is how much propellant is left in its tanks. The mission owes a great deal of its longevity to skillful and efficient piloting by the mission's navigation and operations teams.
Learn more: http://1.usa.gov/aAJMT3
#Cassini10
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