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Lionel Jacques

Quirky solar cell sets new efficiency record - physicsworld.com - 1 views

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    Researchers in the US have built a new type of solar cell that emits light as well as absorbs it, making it the most efficient solar cell ever developed. The efficiency of their prototype cell allows it to convert 28.6% of the Sun's energy into electricity.
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    well, the text is at best misleading ... the most efficient solar cells are well over 35% and approach the 40s with concentration! what they have done is to increase the limit of a single junction cell it seems to me ... still, nteresting though from text most details on how this was done are missing ... paper is not yet published, correct?
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    I learn of it in a workshop few weaks ago. It's on GaAs and I think that the key theoretical aspects are explained here: http://arxiv.org/abs/1106.1603
johannessimon81

Google combines skycrane, VTOL and lifting wing to make drone deliveries - 6 views

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    Nice video featuring the technology. Plus it comes with a good soundtrack! Google's project wing uses a lifting wing concept (more fuel efficient than normal airplane layouts and MUCH more efficient than quadrocopters) but it equips the plane with engines strong enough to hover in a nose up position, allowing vertical landing and takeoff. For the delivery of packages the drone does not even need to land - it can lower them on a wire - much like the skycrane concept used to deliver the Curiosity rover on Mars. Not sure if the skycrane is really necessary but it is certainly cool. Anyways, the video is great for its soundtrack alone! ;-P
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    could we just use genetic algorithms to evolve these shapes and layouts? :P
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    > Not sure if the skycrane is really necessary but it is certainly cool. I think apart from coolness using a skycrane helps keep the rotating knives away from the recipient...
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    Honest question, are we ever going to see this in practice? I mean besides some niche application somewhere, isn't it fundamentally flawed or do I need to keep my window opened on the 3rd floor without a balcony when I ordered something from DX? Its pretty cool yes, but practical?
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    Package delivery is indeed more complicated than it may seem at first sight, although solutions are possible for instance by restricting delivery to distribution centers. What we really need of course is some really efficient and robust AI to navigate without any problems in urban areas : ) The hybrid is interesting since it combines the advantage of a Vertical Takeoff and Landing (and hover), and a wing for more efficient forward flight. Challenges lie in the control of the vehicle under any angle and all that this entails also for higher levels of control. Our lab has first used this concept a few years ago for the DARPA UAVforge challenge, and we had two hybrids in our entry last year for the IMAV 2013 (for some shaky images: https://www.youtube.com/watch?v=Z7XgRK7pMoU ).
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    Fair enough, but even if you consider advanced/robust/efficient AI, why would you use a drone? Do we envision hundreds of drones above our heads in the street instead of UPS vans, or postmen, considering delivers letters might be more easily achievable. I am not so sure if personal delivery will take this route. On the other hand, if the system would work smoothly, I can image that I'm send a mail with the question whether I'm home (or they might know already from my personal GPS tracker) and then notify me that they are launching my DVD and it will come crashing into my door in 5min.
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    I'm more curios how they're planning to keep people from stealing the drones. I could do with a drone army myself and having cheap amazon or google drones flying about sounds like a decent source.
santecarloni

Coated quantum dots make superior solar cells - physicsworld.com - 0 views

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    Researchers at the University of Toronto in Canada and KAUST in Saudi Arabia have made a solar cell out of colloidal quantum dot (CQD) films that has a record-breaking efficiency of 7%. This is almost 40% more efficient than the best previous devices based on CQDs.
johannessimon81

High efficiency solid state heat engine - 0 views

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    We discussed this today during coffee. The inventor claims that he claims that a pressure differential can push hydrogen through a proton conductive membrane (thereby stripping off the electrons) which flow through an electric circuit and provide electric power. The type of membrane is fairly similar to that found in a hydrogen fuel cell. If the pressure differential is cause by selective heating this is in essence a heat engine that directly produces electricity. The inventor claims that this could be a high efficiency alternative to thermoelectric devices and could even outperform PV and Sterling engines with an efficiency close to that of fuel cells (e.g., ~60% @ dT=600K). I could not find any scientific publications as the inventor is not affiliated to any University - he has however an impressive number of patents from a very wide field (e.g., the "Super Soaker" squirt gun) and has worked on several NASA and US military projects. His current research seams to be funded by the latter as well. Here are some more links that I found: http://www.theatlantic.com/magazine/archive/2010/11/shooting-for-the-sun/308268/ http://www.johnsonems.com/?q=node/13 http://scholar.google.nl/scholar?q=%22lonnie+g+johnson%22+&btnG=&hl=nl&as_sdt=0%2C5
Chritos Vezyri

New fabrication technique could provide breakthrough for solar energy systems - 3 views

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    The principle behind that is Nantenna.
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    this is fantastic!!!! waiting of somebody to make this happen since years The size of the gap is critical because it creates an ultra-fast tunnel junction between the rectenna's two electrodes, allowing a maximum transfer of electricity. The nanosized gap gives energized electrons on the rectenna just enough time to tunnel to the opposite electrode before their electrical current reverses and they try to go back. The triangular tip of the rectenna makes it hard for the electrons to reverse direction, thus capturing the energy and rectifying it to a unidirectional current. Impressively, the rectennas, because of their extremely small and fast tunnel diodes, are capable of converting solar radiation in the infrared region through the extremely fast and short wavelengths of visible light - something that has never been accomplished before. Silicon solar panels, by comparison, have a single band gap which, loosely speaking, allows the panel to convert electromagnetic radiation efficiently at only one small portion of the solar spectrum. The rectenna devices don't rely on a band gap and may be tuned to harvest light over the whole solar spectrum, creating maximum efficiency. Through atomic layer deposition, Willis has shown he is able to precisely coat the tip of the rectenna with layers of individual copper atoms until a gap of about 1.5 nanometers is achieved. The process is self-limiting and stops at 1.5 nanometer separation The size of the gap is critical because it creates an ultra-fast tunnel junction between the rectenna's two electrodes, allowing a maximum transfer of electricity. The nanosized gap gives energized electrons on the rectenna just enough time to tunnel to the opposite electrode before their electrical current reverses and they try to go back. The triangular tip of the rectenna makes it hard for the electrons to reverse direction, thus capturing the energy and rectifying it to a unidirectional current. Impressively, the rectennas, because of th
LeopoldS

Ministry of Science and Technology of the People's Republic of China - 0 views

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    University Alliance for Low Carbon Energy   Three universities, including Tsinghua University, University of Cambridge, and the Massachusetts Institute of Technology, have fostered up an alliance on November 15, 2009 to advocate low carbon energy and climate change adaptation The alliance will mainly work on 6 major areas: clean coal technology and CCS, homebuilding energy efficiency, industrial energy efficiency and sustainable transport, biomass energy and other renewable energy, advanced nuclear energy, intelligent power grid, and energy policies/planning. A steering panel made up of the senior experts from the three universities (two from each) will be established to review, evaluate, and endorse the goals, projects, fund raising activities, and collaborations under the alliance. With the Headquarters at the campus of Tsinghua University and branch offices at other two universities, the alliance will be chaired by a scientist selected from Tsinghua University.   According to a briefing, the alliance will need a budget of USD 3-5 million, mainly from the donations of government, industry, and all walks of life. In this context, the R&D findings derived from the alliance will find its applications in improving people's life.
Tobias Seidl

Cognitive fitness of cost-efficient brain functional networks - 0 views

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    The information processing performance of a network can be enhanced by a sparse or low-cost configuration with disproportionately high efficiency. --> any ideas?
LeopoldS

Google-Ergebnis für http://www.umerc.umd.edu/research/images/efficiency06.png - 0 views

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    electric grid modelling .... Nikolaos could you have a look at this?
ESA ACT

Hairy Solar Cells Could Mean Higher Efficiency - 0 views

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    A new manufacturing process could mean improved efficiency for solar cells. The technique, which is being pioneered by researchers at the University of California, San Diego, results in "hairy" solar cells.
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... :)
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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

The thermodynamics of learning - 3 views

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    It is typically considered that brain's process of learning is highly energy efficient. While investigating how efficiently the brain can learn new information, physicists have found that, at the neuronal level, learning efficiency is ultimately limited by the laws of thermodynamics.
LeopoldS

Phys. Rev. Lett. 108, 097403 (2012): Thermoelectrically Pumped Light-Emitting Diodes Op... - 0 views

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    Does not seem to be in any way of any use for space but more than 100% efficiency always sounds ...(cool/stupid/ridiculous/ignorant/headline catching...)
Thijs Versloot

Solar singlet fission bends the laws of physics to boost solar power efficiency by 30% ... - 2 views

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    Chemists at UCR have found a way of turning a single photon into two excitons, by a process known as singlet fission. By doubling the yield of excitons in a solar cell, you theoretically double the number of electrons produced and could lead to having a max theoretical efficiency of 60% or more in an (organic) solar cell See also DOI: 10.1021/jz500676c - "Singlet Fission: From Coherences to Kinetics"
Nicholas Lan

Energy Efficient Hardware Investigated - 2 views

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    sorry, geek central. in case anyone is interested in some new energy efficient pc components. they do energy use/time measurements under load. Unfortunately they don't seem to take idle consumption into account
ESA ACT

Printing Highly Efficient Organic Solar Cells - 0 views

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    We report a new record power conversion efficiency of 3.5% for inkjet printed
santecarloni

[1101.6015] Radio beam vorticity and orbital angular momentum - 1 views

  • It has been known for a century that electromagnetic fields can transport not only energy and linear momentum but also angular momentum. However, it was not until twenty years ago, with the discovery in laser optics of experimental techniques for the generation, detection and manipulation of photons in well-defined, pure orbital angular momentum (OAM) states, that twisted light and its pertinent optical vorticity and phase singularities began to come into widespread use in science and technology. We have now shown experimentally how OAM and vorticity can be readily imparted onto radio beams. Our results extend those of earlier experiments on angular momentum and vorticity in radio in that we used a single antenna and reflector to directly generate twisted radio beams and verified that their topological properties agree with theoretical predictions. This opens the possibility to work with photon OAM at frequencies low enough to allow the use of antennas and digital signal processing, thus enabling software controlled experimentation also with first-order quantities, and not only second (and higher) order quantities as in optics-type experiments. Since the OAM state space is infinite, our findings provide new tools for achieving high efficiency in radio communications and radar technology.
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    It has been known for a century that electromagnetic fields can transport not only energy and linear momentum but also angular momentum. However, it was not until twenty years ago, with the discovery in laser optics of experimental techniques for the generation, detection and manipulation of photons in well-defined, pure orbital angular momentum (OAM) states, that twisted light and its pertinent optical vorticity and phase singularities began to come into widespread use in science and technology. We have now shown experimentally how OAM and vorticity can be readily imparted onto radio beams. Our results extend those of earlier experiments on angular momentum and vorticity in radio in that we used a single antenna and reflector to directly generate twisted radio beams and verified that their topological properties agree with theoretical predictions. This opens the possibility to work with photon OAM at frequencies low enough to allow the use of antennas and digital signal processing, thus enabling software controlled experimentation also with first-order quantities, and not only second (and higher) order quantities as in optics-type experiments. Since the OAM state space is infinite, our findings provide new tools for achieving high efficiency in radio communications and radar technology.
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    and how can we use this?
santecarloni

Semiconductor funnel could boost solar cells - physicsworld.com - 1 views

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    Computer simulations by researchers in the US and China could lead to solar cells that work efficiently across a broad range of the solar spectrum.
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    doubt that this would work ...
Daniel Hennes

CubeSat Ambipolar Thruster - 2 views

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    "Cast your name into deep space in style!"
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    Interesting approach, but with 99.9% probability they will miserably fail (at least in terms of their time schedule) simply because the technology is untested. I haven't read the refs (which miss by the way important works of E. Ahedo et al. on magnetic nozzle acceleration by ambipolar effects), but 1. using water means that you produce oxygen radicals which will erode chamber walls (ionisation efficiency is not 100% and experimental tests haven't been performed yet). 2. Electronic excitation (and radiation), rotational excitation, vibrational excitation, and dissociation are all processes which consume energy and reduce ionisation efficiency drastically. 3. It is a miniaturised Helicon thruster. Theoretical analysis probably does not consider near field effects. Far field models are probably not applicable due to the size of the thruster. I expect some surprises during thruster testing. In any case - good luck!
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    Apparently, there is only one qualification constraint regarding CubeSat propulsion which is related to volatile propellant. Since they use water as propellant and are also the owner of the CubeSat it is actually up to them how they qualify their thruster. Given that it is also possible to qualify the thruster within 18 months - since they define what "qualification" means.
Wiktor Piotrowski

Ultra-efficient LED puts out more power than is pumped in - 4 views

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    Nice.
jmlloren

Cheap and easy-to-make perovskite films rival silicon for efficiency. - 11 views

I just wanted to put another paper in this context: http://science.sciencemag.org/content/324/5923/63.short Solar cells based on Oxides, in particular BiFeO3. The key point here, is that while hali...

solar cells technology

started by fichbio on 09 Mar 16 1 follow-up, last by jmlloren on 11 Mar 16
jcunha liked it
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