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Joris _

Cosmic Log - Volunteers find another prize pulsar - 2 views

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    http://einstein.phys.uwm.edu/
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    like the profiles ... "The clearest evidence for the pulsar's existence was provided by computers operated by two volunteers: Vitaly Shiryaev, a Russian researcher who has a Ph.D. in radio physics; and Stacey Eastham, who does vehicle testing for the British government in Darwen. In his profile, Eastham says he's studying astronomy and physics on the side. He got involved in the Einstein @ Home project because he's interested in "anything space-like, and being able to be part of something like this is right up my street."
LeopoldS

[0812.2633] Ghost imaging with a single detector - 2 views

shared by LeopoldS on 20 Sep 11 - No Cached
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    anything happening on this since 3 years?
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    yes it seems like. most of it seems however directed toward understanding this effect, and not toward applications. But i'm still convinced that we could find many very interesting applications !!! a few references from ADS: 1 2011PhRvA..83f3807B 1.000 06/2011 A E X R C U Brida, G.; Chekhova, M. V.; Fornaro, G. A.; Genovese, M.; Lopaeva, E. D.; Berchera, I. Ruo Systematic analysis of signal-to-noise ratio in bipartite ghost imaging with classical and quantum light 2 2011PhRvA..83e3808L 1.000 05/2011 A E R U Liu, Ying-Chuan; Kuang, Le-Man Theoretical scheme of thermal-light many-ghost imaging by Nth-order intensity correlation 3 2011PhRvA..83e1803D 1.000 05/2011 A E R C U Dixon, P. Ben; Howland, Gregory A.; Chan, Kam Wai Clifford; O'Sullivan-Hale, Colin; Rodenburg, Brandon; Hardy, Nicholas D.; Shapiro, Jeffrey H.; Simon, D. S.; Sergienko, A. V.; Boyd, R. W.; Howell, John C. Quantum ghost imaging through turbulence 4 2011SPIE.7961E.160O 1.000 03/2011 A E T Ohuchi, H.; Kondo, Y. Complete erasing of ghost images caused by deeply trapped electrons on computed radiography plates 5 2011ApPhL..98k1115M 1.000 03/2011 A E R U Meyers, Ronald E.; Deacon, Keith S.; Shih, Yanhua Turbulence-free ghost imaging 6 2011ApPhL..98k1102G 1.000 03/2011 A E R C U Gan, Shu; Zhang, Su-Heng; Zhao, Ting; Xiong, Jun; Zhang, Xiangdong; Wang, Kaige Cloaking of a phase object in ghost imaging 7 2011RScI...82b3110Y 1.000 02/2011 A E R U Yang, Hao; Zhao, Baosheng; Qiu
LeopoldS

Phys. Rev. Lett. 107, 126402 (2011): Anisotropic Dirac Fermions in a Bi Square Net of SrMnBi_{2} - 0 views

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    new wonder material ?
jmlloren

Scientists discover how to turn light into matter after 80-year quest - 5 views

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    Theoretized 80 years ago was Breit-Wheeler pair production in which two photons result in an electron-positron pair (via a virtual electron). It is a relatively simple Feynmann diagram, but the problem is/was how to produce in practice a high energy photon-photon collider... The collider experiment that the scientists have proposed involves two key steps. First, the scientists would use an extremely powerful high-intensity laser to speed up electrons to just below the speed of light. They would then fire these electrons into a slab of gold to create a beam of photons a billion times more energetic than visible light. The next stage of the experiment involves a tiny gold can called a hohlraum (German for 'empty room'). Scientists would fire a high-energy laser at the inner surface of this gold can, to create a thermal radiation field, generating light similar to the light emitted by stars. They would then direct the photon beam from the first stage of the experiment through the centre of the can, causing the photons from the two sources to collide and form electrons and positrons. It would then be possible to detect the formation of the electrons and positrons when they exited the can. Now this is a good experiment... :)
  • ...6 more comments...
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    The solution of thrusting in space.
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    Thrusting in space is solved already. Maybe you wanted to say something different?
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    Thrusting until your fuel runs out is solved, in this way one can produce mass from, among others, solar/star energy directly. What I like about this experiment is that we have the technology already to do it, many parts have been designed for inertial confinement fusion.
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    I am quite certain that it would be more efficient to use the photons directly for thrust instead of converting them into matter. Also, I am a bit puzzled at the asymmetric layout for photon creation. Typically, colliders use two beam of particle with equal but opposite momentum. Because the total momentum for two colliding particles is zero the reaction products are produced more efficiently as a minimum of collision energy is waisted on accelerating the products. I guess in this case the thermal radiation in the cavity is chosen instead of an opposing gamma ray beam to increase the photon density and increase the number of collisions (even if the efficiency decreases because of the asymmetry). However, a danger from using a high temperature cavity might be that a lot of thermionic emission creates lots of free electrons with the cavity. This could reduce the positron yield through recombination and would allow the high energetic photons to loose energy through Compton scattering instead of the Breit-Wheeler pair production.
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    Well, the main benefit from e-p pair creation might be that one can accelerate these subsequently to higher energies again. I think the photon-photon cross-section is extremely low, such that direct beam-beam interactions are basically not happening (below 1/20.. so basically 0 according to quantum probability :P), in this way, the central line of the hohlraum actually has a very high photon density and if timed correctly maximizes the reaction yield such that it could be measured.
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    I agree about the reason for the hohlraum - but I also keep my reservations about the drawbacks. About the pair production as fuel: I pretty sure that your energy would be used smarter in using photon (not necessarily high energy photons) for thrust directly instead of putting tons of energy in creating a rest-mass and then accelerating that. If you look at E² = (p c)²+(m0 c)² then putting energy into the mass term will always reduce your maximum value of p.
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    True, but isnt it E2=(pc)^2 + (m0c^2)^2 such that for photons E\propto{pc} and for mass E\propto{mc^2}. I agree it will take a lot of energy, but this assumes that that wont be the problem at least. The question therefore is whether the mass flow of the photon rocket (fuel consumed to create photons, eg fission/fusion) is higher/lower than the mass flow for e-p creation. You are probably right that the low e-p cross-section will favour direct use of photons to create low thrust for long periods of time, but with significant power available the ISP might be higher for e-p pair creation.
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    In essence the equation tells you that for photons with zero rest mass m0 all the energy will be converted to momentum of the particles. If you want to accelerate e-p then you first spend part of the energy on creating them (~511 keV each) and you can only use the remaining energy to accelerate them. In this case the equation gives you a lower particle momentum which leads to lower thrust (even when assuming 100% acceleration efficiency). ISP is a tricky concept in this case because there are different definitions which clash in the relativistic context (due to the concept of mass flow). R. Tinder gets to a I_SP = c (speed of light) for a photon rocket (using the relativistic mass of the photons) which is the maximum possible relativistic I_SP: http://goo.gl/Zz5gyC .
jcunha

Mystery of where Earth's water came from deepens: Comet water is different - 2 views

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    "Over the past few months, the European Space Agency's Rosetta space probe closely examined the type of comet that some scientists theorized could have brought water to our planet 4 billion years ago. It found water, but the wrong kind."
Paul N

Room temperature superconductors - 4 views

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    With the aid of short infrared laser pulses, researchers have succeeded for the first time in making a ceramic superconducting at room temperature - albeit for only a few millionths of a microsecond.
jcunha

Artifitial Intelligence to predict solar flares - 0 views

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    A team from Stanford showing possibility of solar flare prediction using AI techniques and data from the NASA SDO observatory.
jcunha

Missing link in metal physics explains Earth's magnetic field - 0 views

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    In a work published on Nature (http://www.nature.com/nature/journal/v517/n7536/full/nature14090.html#affil-auth) a new DFT based simulation of convection in Earth's Core iron shows that electron-electron scattering has a similar contribution to electron's thermal vibration. The outcome is that using the old dynamo theory the simulation matches the Earth magnetic field experimental results, solving an 80 years old puzzle.
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    Yay to science! I'm always intrigued by related experiments that try to measure material properties at the GPa range. Especially, the efforts of reaching 'metallic hydrogen' (http://en.wikipedia.org/wiki/Metallic_hydrogen), requiring pressures above 25GPa at which hydrogen becomes conductive. It is thought that gas giant planets could have such a core, but no-one has been able to produce/verify this theory as off yet.
johannessimon81

No Big Bang? Quantum equation predicts universe has no beginning - 3 views

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    Told you so...
jcunha

Quantum machine learning - 1 views

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    Quantum Computing and Machine Learning in the same sentence. The association started to be put forward by Google and NASA playing with D-WAVE computers. Meanwhile in the academic media, https://journals.aps.org/prx/pdf/10.1103/PhysRevX.4.031002
Thijs Versloot

Popper's experiment realized again-but what does it mean? - 1 views

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    Although it may seem like the above two experiments violate the uncertainty principle because the results show a smaller-than-required degree of uncertainty, Shih and his coauthors explain that no violation has occurred due to the fact that the experiments involve photon pairs rather than individual photons. The scientists argue that Popper's original thought experiment was based on a misunderstanding of the proper context of the uncertainty principle: it governs the behavior of single particles only, not the "correlation" of two particles.
jcunha

Metals used in high-tech products face future supply risks - 0 views

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    First peer review study about he criticality of rare-earth metals. It can be read "They found that supply limits for many metals critical in the emerging electronics sector (including gallium and selenium) are the result of supply risks. The environmental implications of mining and processing present the greatest challenges with platinum-group metals, gold, and mercury. For steel alloying elements (including chromium and niobium) and elements used in high-temperature alloys (tungsten and molybdenum), the greatest vulnerabilities are associated with supply restrictions" Questions about estimation apart, this can be a valuable market for asteroid mining.. (ot just more market for Infinium-like companies http://www.technologyreview.com/news/527526/a-cleaner-cheaper-way-to-make-metals/).
jcunha

Space data representation - 1 views

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    A common data hub that allows the representation and comparison of data from numerous space missions. "The IMPEx portal offers tools for the visualization and analysis of datasets from different space missions. Furthermore, several computational model databases are feeding into the environment." As they say, with its massive 3D-visualization capabilities it offers the possibility of displaying spacecraft trajectories, planetary ephemerides as well as scientific representations of observational and simulation datasets.
jcunha

Electron spins controlled using sound waves - 0 views

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    Cornell applied physicists have demonstrated an unprecedented method of control over electron spins using extremely high-frequency sound waves - new insights in the study of the spin of the electron. Crazy idea but, no further need for complicated quantum encryption techniques of sound signals?
jcunha

New angry birds type game with cats and quantum mechanics - 6 views

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    "A new Angry Birds-style game is set to help launch a new understanding of quantum science. Some find the concepts of quantum science confusing or unintuitive. Einstein even called quantum effects "spooky." To help people better understand some of the core concepts of quantum science, the Institute for Quantum Computing (IQC) at the University of Waterloo is launching a game - the Quantum Cats" Looking forward to see the ACT winning the Quantum Cats competition :)
jaihobah

Phys. Rev. Lett. 116, 031301 (2016) - Dark Matter Velocity Spectroscopy - 1 views

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    'Whether mysterious high-energy photon emissions from our Galaxy come from dark matter or a more mundane source might be resolved by detecting their Doppler shifts along different lines-of-sight.'
Nina Nadine Ridder

Material could harvest sunlight by day, release heat on demand hours or days later - 5 views

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    Imagine if your clothing could, on demand, release just enough heat to keep you warm and cozy, allowing you to dial back on your thermostat settings and stay comfortable in a cooler room. Or, picture a car windshield that stores the sun's energy and then releases it as a burst of heat to melt away a layer of ice.
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    interesting indeed: Such chemically-based storage materials, known as solar thermal fuels (STF), have been developed before, including in previous work by Grossman and his team. But those earlier efforts "had limited utility in solid-state applications" because they were designed to be used in liquid solutions and not capable of making durable solid-state films, Zhitomirsky says. The new approach is the first based on a solid-state material, in this case a polymer, and the first based on inexpensive materials and widespread manufacturing technology. Read more at: http://phys.org/news/2016-01-material-harvest-sunlight-day-demand.html#jCp
jcunha

Silicon chip with integrated laser: Light from a nanowire - 2 views

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    A nanolaser, a thousand times thinner than a human hair.
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