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jmlloren

Exotic matter : Insight : Nature - 5 views

www.nature.com/...index.html

nan phy

shared by jmlloren on 03 Aug 10 - Cached
LeopoldS liked it
  • jmlloren on 03 Aug 10
     
    Trends in materials and condensed matter. Check out the topological insulators. amazing field.
  • ...12 more comments...
  • Luzi Bergamin on 03 Aug 10
     
    Aparently very interesting, will it survive the short hype? Relevant work describing mirror charges of topological insulators and the classical boundary conditions were done by Ismo and Ari. But the two communities don't know each other and so they are never cited. Also a way to produce new things...
  • jmlloren on 04 Aug 10
     
    Thanks for noticing! Indeed, I had no idea that Ari (don't know Ismo) was involved in the field. Was it before Kane's proposal or more recently? What I mostly like is that semiconductors are good candidates for 3D TI, however I got lost in the quantum field jargon. Yesterday, I got a headache trying to follow the Majorana fermions, the merons, skyrnions, axions, and so on. Luzi, are all these things familiar to you?
  • Luzi Bergamin on 04 Aug 10
     
    Ismo Lindell described in the early 90's the mirror charge of what is now called topological insulator. He says that similar results were obtained already at the beginning of the 20th century... Ismo Lindell and Ari Sihvola in the recent years discussed engineering aspects of PEMCs (perfect electro-megnetic conductors,) which are more or less classical analogues of topological insulators. Fundamental aspects of PEMCs are well knwon in high-energy physics for a long time, recent works are mainly due to Friedrich Hehl and Yuri Obukhov. All these works are purely classical, so there is no charge quantisation, no considerations of electron spin etc. About Majorana fermions: yes, I spent several years of research on that topic. Axions: a topological state, of course, trivial :-) Also merons and skyrnions are topological states, but I'm less familiar with them.
  • LeopoldS on 04 Aug 10
     
    "Non-Abelian systems1, 2 contain composite particles that are neither fermions nor bosons and have a quantum statistics that is far richer than that offered by the fermion-boson dichotomy. The presence of such quasiparticles manifests itself in two remarkable ways. First, it leads to a degeneracy of the ground state that is not based on simple symmetry considerations and is robust against perturbations and interactions with the environment. Second, an interchange of two quasiparticles does not merely multiply the wavefunction by a sign, as is the case for fermions and bosons. Rather, it takes the system from one ground state to another. If a series of interchanges is made, the final state of the system will depend on the order in which these interchanges are being carried out, in sharp contrast to what happens when similar operations are performed on identical fermions or bosons." wow, this paper by Stern reads really weired ... any of you ever looked into this?
  • jmlloren on 04 Aug 10
     
    C'mon Leopold, it's as trivial as the topological states, AKA axions! Regarding the question, not me!
  • LeopoldS on 04 Aug 10
     
    just looked up the wikipedia entry on axions .... at least they have some creativity in names giving: "In supersymmetric theories the axion has both a scalar and a fermionic superpartner. The fermionic superpartner of the axion is called the axino, the scalar superpartner is called the saxion. In some models, the saxion is the dilaton. They are all bundled up in a chiral superfield. The axino has been predicted to be the lightest supersymmetric particle in such a model.[24] In part due to this property, it is considered a candidate for the composition of dark matter.[25]"
  • jmlloren on 04 Aug 10
     
    Thank's Leopold. Sorry Luzi for being ironic concerning the triviality of the axions. Now, Leo confirmed me that indeed is a trivial matter. I have problems with models where EVERYTHING is involved.
  • Luzi Bergamin on 04 Aug 10
     
    Well, that's the theory of everything, isn't it?? Seriously: I don't think that theoretically there is a lot of new stuff here. Topological aspects of (non-Abelian) theories became extremely popular in the context of string theory. The reason is very simple: topological theories are much simpler than "normal" and since string theory anyway is far too complicated to be solved, people just consider purely topological theories, then claiming that this has something to do with the real world, which of course is plainly wrong. So what I think is new about these topological insulators are the claims that one can actually fabricate a material which more or less accurately mimics a topological theory and that these materials are of practical use. Still, they are a little bit the poor man's version of the topological theories fundamental physicists like to look at since electrdynamics is an Abelian theory.
  • jmlloren on 04 Aug 10
     
    I have the feeling, not the knowledge, that you are right. However, I think that the implications of this light quantum field effects are great. The fact of being able to sustain two currents polarized in spin is a technological breakthrough.
  • LeopoldS on 04 Aug 10
     
    not sure how much I can contribute to your apparently educated debate here but if I remember well from my work for the master, these non-Abelian theories were all but "simple" as Luzi puts it ... and from a different perspective: to me the whole thing of being able to describe such non-Abelian systems nicely indicates that they should in one way or another also have some appearance in Nature (would be very surprised if not) - though this is of course no argument that makes string theory any better or closer to what Luzi called reality ....
  • Luzi Bergamin on 04 Aug 10
     
    Well, electrodynamics remains an Abelian theory. From the theoretical point of view this is less interesting than non-Abelian ones, since in 4D the fibre bundle of a U(1) theory is trivial (great buzz words, eh!) But in topological insulators the point of view is slightly different since one always has the insulator (topological theory), its surrounding (propagating theory) and most importantly the interface between the two. This is a new situation that people from field and string theory were not really interested in.
  • Dario Izzo on 04 Aug 10
     
    guys... how would you explain this to your gran mothers?
  • jmlloren on 05 Aug 10
  • LeopoldS on 07 Aug 10
     
    *you* tried *your* best .... ??
pandomilla

Not a scratch - 7 views

www.economist.com/21545971

BIO

shared by pandomilla on 12 Apr 12 - No Cached
LeopoldS liked it
  • pandomilla on 12 Apr 12
     
    I hate scorpions, but this could be a nice subject for a future Ariadna study! This north African desert scorpion, doesn't dig burrows to protect itself from the sand-laden wind (as the other scorpions do). When the sand whips by at speeds that would strip paint away from steel, the scorpion is able to scurry off without apparent damage.
  • LeopoldS on 13 Apr 12
     
    Nice research, though they have done almost all the work that we could do in an Ariadna, didnt they? "To check, they took further photographs. In particular, they used a laser scanning system to make a three-dimensional map of the armour and then plugged the result into a computer program that blasted the virtual armour with virtual sand grains at various angles of attack. This process revealed that the granules were disturbing the air flow near the skeleton's surface in ways that appeared to be reducing the erosion rate. Their model suggested that if scorpion exoskeletons were smooth, they would experience almost twice the erosion rate that they actually do. Having tried things out in a computer, the team then tried them for real. They placed samples of steel in a wind tunnel and fired grains of sand at them using compressed air. One piece of steel was smooth, but the others had grooves of different heights, widths and separations, inspired by scorpion exoskeleton, etched onto their surfaces. Each sample was exposed to the lab-generated sandstorm for five minutes and then weighed to find out how badly it had been eroded. The upshot was that the pattern most resembling scorpion armour-with grooves that were 2mm apart, 5mm wide and 4mm high-proved best able to withstand the assault. Though not as good as the computer model suggested real scorpion geometry is, such grooving nevertheless cut erosion by a fifth, compared with a smooth steel surface. The lesson for aircraft makers, Dr Han suggests, is that a little surface irregularity might help to prolong the active lives of planes and helicopters, as well as those of scorpions."
  • Ma Ru on 13 Apr 12
     
    What bugs me (pardon the pun) is that the dimensions of the pattern they used were scaled up by many orders of magnitude, while "grains of sand" with which the surface was bombarded apparently were not... Not being a specialist in the field, I would nevertheless expect that the size of the surface pattern *in relation to* to size of particles used for bombarding would be crucial.
Luzi Bergamin

[1107.0167] Nonlinear transformation optics and engineering of the Kerr effect - 9 views

arxiv.org/1107.0167

PHY nan optics metamaterials

shared by Luzi Bergamin on 04 Jul 11 - No Cached
LeopoldS liked it
  • Luzi Bergamin on 04 Jul 11
     
    The best paper on transformation optics written ever :-)
  • ...2 more comments...
  • jmlloren on 05 Jul 11
     
    Finally something worth to read in the MM field!. The idea is excellent, congratullations. However, I think there is a typo or mistake in the definition of l=3x10-13 m, the "waist" of the laser beam. Seems clear that 0.3 pm is too small for being a waist of any laser beam.
  • Luzi Bergamin on 05 Jul 11
     
    Thanks for your commendation. Of course, the problem with nonlinear transformation optics is the same as with linear: it's very easy to come up with theoretical descriptions of devices that have the most absurd properties, but it will be extremely hard to fabricate them. But if you have any good suggestion, please shoot! About the laser beam: Pekka made the simulations, since I am not a "Comsolist", but still I think the numbers are correct. You are right that we should not call this a laser beam. Our problem was the following: we need to have a very simple model that can be simulated exactly (full Maxwell equations) but naturally exhibits self focusing. The Gaussian beam was the simplest solution. Since our model is purely classical and moreover we do not take into account diffraction effects, the parameter "l" is of minor importance. Taking "l" much larger gives almost the same picture but requires much more computer power to simulate. I guess that's why Pekka chose an unnaturally small number.
  • jmlloren on 05 Jul 11
     
    Concerning the fabrication... as usual, no idea. I agree that this is the main drawback of MM, and certainly difficult to overcome. I would double check that number, because its value is related with the beam shape of Fig. 1 A. I believe that the simulations are correct, it's just a detail.
  • LeopoldS on 06 Jul 11
     
    wow ... still publishing despite babysitting and new job!!
Luís F. Simões

The Emerging Revolution in Game Theory - Technology Review - 2 views

www.technologyreview.com/...ging-revolution-in-game-theory

game theory evolution cooperation

shared by Luís F. Simões on 21 Aug 12 - No Cached
  • The world of game theory is currently on fire. In May, Freeman Dyson at Princeton University and William Press at the University of Texas announced that they had discovered a previously unknown strategy for the game of prisoner's dilemma which guarantees one player a better outcome than the other. That's a monumental surprise. Theorists have studied Prisoner's Dilemma for decades, using it as a model for the emergence of co-operation in nature. This work has had a profound impact on disciplines such as economics, evolutionary biology and, of course, game theory itself. The new result will have impact in all these areas and more.
  • Ref: arxiv.org/abs/1208.2666: Winning isn't everything: Evolutionary stability of Zero Determinant strategies
johannessimon81

Genetic mugshot recreates faces from nothing but DNA - 3 views

www.newscientist.com/...aces-from-nothing-but-dna.html

BIO science technology

shared by johannessimon81 on 23 Mar 14 - No Cached
  • johannessimon81 on 23 Mar 14
     
    By just getting a DNA footprint of a person scientists (and soon police) can produce an image of the person's face. Check out the pictures!
  • ...2 more comments...
  • Thijs Versloot on 23 Mar 14
     
    wow thats pretty amazing! Ok, the pictures are not great (mainly due to skin surface, baggy eyes, zits I guess) but considering its only from DNA it is pretty close already. That will help crime scene investigations greatly, whether positively or negatively.
  • johannessimon81 on 23 Mar 14
     
    Ouch! You're pretty harsh on that lady... :-o
  • Paul N on 24 Mar 14
     
    should try it the other way around, deduce the DNA from facial features. That would be even cooler.
  • Thijs Versloot on 25 Mar 14
     
    Well actually, they did something like that as they searched for common DNA patterns in people that had similar facial features. With a large enough dataset that could provide already 24 DNA tracers that could used reliably for prediction. Imagine if you had even more data available, who needs a model then... just let the NN do it :)
Luís F. Simões

Mars Code | Communications of the ACM - 1 views

cacm.acm.org/...fulltext

INF software redundancy fault detection model checking Curiosity Mars

shared by Luís F. Simões on 12 Mar 14 - No Cached
  • As can be expected, all functions on the rover, and on the spacecraft that brought it to its destination 350 million miles from Earth, are controlled by software. This article discusses some of the precautions the JPL flight software team took to improve its reliability.
  • Luís F. Simões on 12 Mar 14
     
    Interesting read if you're interested on the kind of coding that goes into something like the Curiosity rover. :) btw.. nice fill-packet being sent by Curiosity: "Elvis has Spirit. The answer is 42....END\r\n"
Athanasia Nikolaou

Nature Paper: Rivers and streams release more CO2 than previously believed - 6 views

www.klimacampus.de/631+M59214efc590.html

climate emissions

shared by Athanasia Nikolaou on 25 Nov 13 - No Cached
LeopoldS liked it
  • Athanasia Nikolaou on 25 Nov 13
     
    Another underestimated source of CO2, are turbulent waters. "The stronger the turbulences at the water's surface, the more CO2 is released into the atmosphere. The combination of maps and data revealed that, while the CO2 emissions from lakes and reservoirs are lower than assumed, those from rivers and streams are three times as high as previously believed." Alltogether the emitted CO2 equates to roughly one-fifth of the emissions caused by humans. Yet more stuff to model...
  • ...10 more comments...
  • Dario Izzo on 26 Nov 13
     
    This could also be a mechanism to counter human CO2 emission ... the more we emit, the less turbulent rivers and stream, the less CO2 is emitted there ... makes sense?
  • johannessimon81 on 27 Nov 13
     
    I guess there is a natural equilibrium there. Once the climate warms up enough for all rivers and streams to evaporate they will not contribute CO2 anymore - which stops their contribution to global warming. So the problem is also the solution (as always).
  • Athanasia Nikolaou on 27 Nov 13
     
    "The source of inland water CO2 is still not known with certainty and new studies are needed to research the mechanisms controlling CO2 evasion globally." It is another source of CO2 this one, and the turbulence in the rivers is independent of our emissions in CO2 and just facilitates the process of releasing CO2 waters. Dario, if I understood correct you have in mind a finite quantity of CO2 that the atmosphere can accomodate, and to my knowledge this does not happen, so I cannot find a relevant feedback there. Johannes, H2O is a powerful greenhouse gas :-)
  • Dario Izzo on 27 Nov 13
     
    Nasia I think you did not get my point (a joke, really, that Johannes continued) .... by emitting more CO2 we warm up the planet thus drying up rivers and lakes which will, in turn emit less CO2 :) No finite quantity of CO2 in the atmosphere is needed to close this loop ... ... as for the H2O it could just go into non turbulent waters rather than staying into the atmosphere ...
  • Athanasia Nikolaou on 03 Dec 13
     
    Really awkward joke explanation: I got the joke of Johannes, but maybe you did not get mine: by warming up the planet to get rid of the rivers and their problems, the water of the rivers will be accomodated in the atmosphere, therefore, the greenhouse gas of water.
  • Dario Izzo on 03 Dec 13
     
    from my previous post: "... as for the H2O it could just go into non turbulent waters rather than staying into the atmosphere ..."
  • johannessimon81 on 03 Dec 13
     
    I guess the emphasis is on "could"... ;-) Also, everybody knows that rain is cold - so more water in the atmosphere makes the climate colder.
  • LeopoldS on 03 Dec 13
     
    do you have the nature paper also? looks like very nice, meticulous typically german research lasting over 10 years with painstakingly many researchers from all over the world involved .... and while important the total is still only 20% of human emissions ... so a variation in it does not seem to change the overall picture
  • Athanasia Nikolaou on 04 Dec 13
     
    here is the nature paper : http://www.nature.com/nature/journal/v503/n7476/full/nature12760.html I appreciate Johannes' and Dario's jokes, since climate is the common ground that all of us can have an opinion, taking honours from experiencing weather. But, the same as if I am trying to make jokes for material science, or A.I. I take a high risk of failing(!) :-S Water is a greenhouse gas, rain rather releases latent heat to the environment in order to be formed, Johannes, nice trolling effort ;-) Between this and the next jokes to come, I would stop to take a look here, provided you have 10 minutes: how/where rain forms http://www.scribd.com/doc/58033704/Tephigrams-for-Dummies
  • Dario Izzo on 04 Dec 13
     
    omg
  • johannessimon81 on 09 Dec 13
     
    Nasia, I thought about your statement carefully - and I cannot agree with you. Water is not a greenhouse gas. It is instead a liquid. Also, I can't believe you keep feeding the troll! :-P But on a more topical note: I think it is an over-simplification to call water a greenhouse gas - water is one of the most important mechanisms in the way Earth handles heat input from the sun. The latent heat that you mention actually cools Earth: solar energy that would otherwise heat Earth's surface is ABSORBED as latent heat by water which consequently evaporates - the same water condenses into rain drops at high altitudes and releases this stored heat. In effect the water cycle is a mechanism of heat transport from low altitude to high altitude where the chance of infrared radiation escaping into space is much higher due to the much thinner layer of atmosphere above (including the smaller abundance of greenhouse gasses). Also, as I know you are well aware, the cloud cover that results from water condensation in the troposphere dramatically increases albedo which has a cooling effect on climate. Furthermore the heat capacity of wet air ("humid heat") is much larger than that of dry air - so any advective heat transfer due to air currents is more efficient in wet air - transporting heat from warm areas to a natural heat sink e.g. polar regions. Of course there are also climate heating effects of water like the absorption of IR radiation. But I stand by my statement (as defended in the above) that rain cools the atmosphere. Oh and also some nice reading material on the complexities related to climate feedback due to sea surface temperature: http://journals.ametsoc.org/doi/abs/10.1175/1520-0442(1993)006%3C2049%3ALSEOTR%3E2.0.CO%3B2
  • Athanasia Nikolaou on 10 Dec 13
     
    I enjoy trolling conversations when there is a gain for both sides at the end :-) . I had to check upon some of the facts in order to explain my self properly. The IPCC report states the greenhouse gases here, and water vapour is included: http://www.ipcc.ch/publications_and_data/ar4/wg1/en/faq-2-1.html Honestly, I read only the abstract of the article you posted, which is a very interesting hypothesis on the mechanism of regulating sea surface temperature, but it is very localized to the tropics (vivid convection, storms) a region of which I have very little expertise, and is difficult to study because it has non-hydrostatic dynamics. The only thing I can comment there is that the authors define constant relative humidity for the bottom layer, supplied by the oceanic surface, which limits the implementation of the concept on other earth regions. Also, we may confuse during the conversation the greenhouse gas with the Radiative Forcing of each greenhouse gas: I see your point of the latent heat trapped in the water vapour, and I agree, but the effect of the water is that it traps even as latent heat an amount of LR that would otherwise escape back to space. That is the greenhouse gas identity and an image to see the absorption bands in the atmosphere and how important the water is, without vain authority-based arguments that miss the explanation in the end: http://www.google.nl/imgres?imgurl=http://www.solarchords.com/uploaded/82/87-33833-450015_44absorbspec.gif&imgrefurl=http://www.solarchords.com/agw-science/4/greenhouse--1-radiation/33784/&h=468&w=458&sz=28&tbnid=x2NtfKh5OPM7lM:&tbnh=98&tbnw=96&zoom=1&usg=__KldteWbV19nVPbbsC4jsOgzCK6E=&docid=cMRZ9f22jbtYPM&sa=X&ei=SwynUq2TMqiS0QXVq4C4Aw&ved=0CDkQ9QEwAw
LeopoldS

Tox: A New Kind of Instant Messaging - 5 views

tox.im

shared by LeopoldS on 02 Sep 14 - No Cached
  • LeopoldS on 02 Sep 14
     
    skype alternative - open source, no central server, encryption built in ....
  • ...4 more comments...
  • dejanpetkow on 04 Sep 14
     
    It's free and w/o ads. What's the business model? Their page doesn't say anything about it.
  • Thijs Versloot on 04 Sep 14
     
    To help society...
  • Ma Ru on 05 Sep 14
     
    They plan to secretly capture all communications and then sell them to NSA...
  • Paul N on 08 Sep 14
     
    probably developed by the NSA directly
  • LeopoldS on 16 Sep 14
     
    its open source - go check it :-)
  • LeopoldS on 16 Sep 14
     
    my ID: 7C53B574D888EE0E2A97FCD62B144DD14730E45C1B7158D4ED3EBCCB920CB93A68C62E6C9385
nikolas smyrlakis

mentored by the Advanced Concepts Team for Google Summer of Code 2010 - 4 views

socghop.appspot.com/...advancedconceptsteam

pagmo google summerofcode

shared by nikolas smyrlakis on 19 Mar 10 - Cached
LeopoldS liked it
  • nikolas smyrlakis on 19 Mar 10
     
    you propably already know,I post it for the twitter account and for your comments
  • ...4 more comments...
  • LeopoldS on 20 Mar 10
     
    once again one of these initiatives that came up from a situation and that would never have been possible with a top-down approach .... fantastic! and as Dario said: we are apparently where NASA still has to go with this :-)
  • Joris _ on 20 Mar 10
     
    Actually, NASA Ames did that already within the NASA Open Source Agreement in 2008 for a V&V software!
  • Joris _ on 20 Mar 10
  • LeopoldS on 20 Mar 10
     
    indeed ... you are right .... interesting project btw - they started in 1999, were in 2005 the first NASA project on Sourceforge and won several awards .... then this entry why they did not participate last year: "05/01/09: Skipping this years Google Summer-of-Code - many of you have asked why we are not participating in this years Summer of Code. The answer is that both John and Peter were too busy with other assignments to set this up in time. We will be back in 2010. At least we were able to compensate with a limited number of NASA internships to continue some of last years projects." .... but I could not find them in this years selected list - any clue?
  • LeopoldS on 20 Mar 10
     
    but in any case, according to the apple guru, Java is a dying technology, so their project might as well ...
  • Joris _ on 21 Mar 10
     
    They participate under the name "The Java Pathfinder Team" (http://babelfish.arc.nasa.gov/trac/jpf/wiki/events/soc2010). It is actually a very useful project for both education and industry (Airbus created a consortium on model checking soft, and there is a lot of research on it) As far as I know, TAS had some plans of using Java onboard spacecrafts, 2 years ago. Not sure the industry is really sensible about Jobs' opinions ;) particularly if there is no better alternative!
pacome delva

Physicists study how moral behaviour evolved - 2 views

physicsworld.com/...42540

phy ia cooperation

shared by pacome delva on 07 May 10 - Cached
  • A statistical-physics-based model may shed light on the age-old question "how can morality take root in a world where everyone is out for themselves?" Computer simulations by an international team of scientists suggest that the answer lies in how people interact with their closest neighbours rather than with the population as a whole.
  • pacome delva on 07 May 10
     
    Reminds me something... :)
  • nikolas smyrlakis on 07 May 10
     
    I check diigo for the first time since I left and my spirit is still there yeah !
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