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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 .... ??
LeopoldS

Physicists twist water into knots : Nature News & Comment - 3 views

www.nature.com/...twist-water-into-knots-1.12534

mathematics

shared by LeopoldS on 01 Apr 13 - No Cached
  • LeopoldS on 01 Apr 13
     
    More than a century after the idea was first floated, physicists have finally figured out how to tie water in knots in the laboratory. The gnarly feat, described today in Nature Physics1, paves the way for scientists to experimentally study twists and turns in a range of phenomena - ionized gases like that of the Sun's outer atmosphere, superconductive materials, liquid crystals and quantum fields that describe elementary particles.

    Lord Kelvin proposed that atoms were knotted "vortex rings" - which are essentially like tornado bent into closed loops and knotted around themselves, as Daniel Lathrop and Barbara Brawn-Cinani write in an accompanying commentary. In Kelvin's vision, the fluid was the theoretical 'aether' then thought to pervade all of space. Each type of atom would be represented by a different knot.

    Related stories
    Solar magnetism twists braids of superheated gas
    Electron microscopy gets twisted
    Topological insulators: Star material
    More related stories
    Kelvin's interpretation of the periodic table never went anywhere, but his ideas led to the blossoming of the mathematical theory of knots, part of the field of topology. Meanwhile, scientists also have come to realize that knots have a key role in a host of physical processes.
jcunha

Synthetic Landau levels for photons - 1 views

www.nature.com/...nature17943.html

PHY quantum hall effect topology experiment photons

shared by jcunha on 09 Jun 16 - No Cached
  • jcunha on 09 Jun 16
     
    Very nice experiment on the verge of Condensed matter Physics! The presence of Landau levels is a necessary condition to obtain a Quantum Hall state. Quantum Hall states have first appeared in 2D electronic gases when applied a perpendicular magnetic field that induces a new topological state of the "electronic gas". This new topological state is believed to "protect" some parameters of the system, such as conductance making it possible to measure fundamental constants with very high precision even in imperfect experimental conditions. In this fundamental experiment, a synthetic magnetic field was created that acts in continuum photons, producing "an integer quantum Hall system in curved space, a long-standing challenge in condensed matter physics".
santecarloni

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

arxiv.org/1101.6015

radio light antennas technology

shared by santecarloni on 20 Oct 11 - No Cached
  • 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.
  • santecarloni on 20 Oct 11
     
    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.
  • LeopoldS on 20 Oct 11
     
    and how can we use this?
annaheffernan

Acoustic topological insulator could hide submarines - 2 views

physicsworld.com/...nsulator-could-hide-submarines

technology science PHY

shared by annaheffernan on 30 Mar 15 - No Cached
  • annaheffernan on 30 Mar 15
     
    Researchers have proposed a new "acoustic topological insulator" that could help alleviate sound scattering problems by transmitting sound in certain directions without any backscattering.
  • Athanasia Nikolaou on 30 Mar 15
     
    If I understood correctly the triangular structure would channel the incident sound wave to a unique direction between two options, according to the rotation direction of the cylinders included in its mesh. So, one (possibly two) directions left to detect the hypothetical submarines? Very interesting though, I hope no oceanographers take measurements simultaneously to the signals as climate models will get even more wrong...!
jaihobah

Topological insulator laser - 2 views

science.sciencemag.org/...science.aar4003.full

PHY Lasers

shared by jaihobah on 05 Feb 18 - No Cached
jcunha liked it
  • jaihobah on 05 Feb 18
     
    These are lasers whose lasing mode exhibits topologically-protected transport without magnetic fields. The underlying topological properties lead to a highly efficient laser, robust to defects and disorder, with single mode lasing even at very high gain values.
duncan barker

Phys. Rev. Lett. 89, 210401 (2002): Locality and Topology in the Molecular Aharonov-Boh... - 2 views

prl.aps.org/...e210401

shared by duncan barker on 01 Nov 10 - No Cached
  • Luzi Bergamin on 01 Nov 10
     
    If it's neither topological nor nonlocal, why on Earth is it then called Aharonov-Bohm effect?
Ma Ru

IEEE Trans. Evolutionary Computation - Special Issue on Differential Evolution - 3 views

ieeexplore.ieee.org/...tocresult.jsp

inf optimisation differential evolution evolutionary computation

shared by Ma Ru on 03 Mar 11 - No Cached
  • Ma Ru on 03 Mar 11
     
    Dario - perhaps worth giving a look to be up-to-date... There's even an article "Improving Classical and Decentralized Differential Evolution with New Mutation Operator and Population Topologies". They quote our CEC paper, but not the ParCo.
  • ...1 more comment...
  • Ma Ru on 03 Mar 11
     
    Don't know if you have full text access, so here goes the quote: "Recently, Izzo et al. designed in [27] a heterogeneous asynchronous island model for DE. They considered five islands and five DE strategies (DE/best/1/exp, DE/rand/1/exp, DE/rand-to-best/1/exp, DE/best/2/exp, and DE/rand/2/exp), and studied five distributed DEs using the same DE strategy in all the islands, and a heterogeneous model with one different DE strategy in every island. As a result, the heterogeneous model is not outstanding, but performs as well as the others."
  • Joris _ on 03 Mar 11
     
    Isn't it a bit a paper-killing quote?
  • Ma Ru on 03 Mar 11
     
    :) It's in the context of a review of the work that's been done about DE with island model in general, they don't evaluate. Pity they didn't refer to the ParCo article on topologies, as it was a bit more extensive and more focused on the method (as they do in the article) rather than on the problem (as was our CEC paper, if I recall well).
johannessimon81

Exotic Quantum Effects Could Follow from Compound Now Confirmed to Conduct Only at Surface - 1 views

www.scientificamerican.com/article.cfm

science quantum

shared by johannessimon81 on 13 Dec 12 - No Cached
  • johannessimon81 on 13 Dec 12
     
    Samarium hexaboride seems to be a topological insulator as a bulk material. It conducts electricity only at its surface, i.e., in a 2D layer (like graphene). This might allow all kinds of exotic (quantum) effects...
johannessimon81

Data visualization through algebraic topology - 3 views

www.wired.com/...data-viz-ayasdi-iris

AI

shared by johannessimon81 on 21 Jan 13 - No Cached
  • johannessimon81 on 21 Jan 13
     
    Data-Visualization Firm's New Software Autonomously Finds Abstract Connections --> Annalisa?
  • Annalisa Riccardi on 21 Jan 13
     
    I had a nice introduction about Ordinal Regression via Manifold Learning by Francisco last week. It is doubtless a very actual research branch!
  • Dario Izzo on 22 Jan 13
     
    I doubt :) The original paper from Liu is from 2011 and has .... wait for it .... 1 quotation (and a self-one)!!! http://scholar.google.it/scholar?hl=it&q=Ordinal+Regression+via+Manifold+Learning&btnG=&lr=
santecarloni

[1203.6902] Gods as Topological Invariants - 1 views

arxiv.org/1203.6902

gods phy science

shared by santecarloni on 02 Apr 12 - No Cached
  • santecarloni on 02 Apr 12
     
    Truth has been revealed!!!
Beniamino Abis

The Wisdom of (Little) Crowds - 1 views

phenomena.nationalgeographic.com/...the-wisdom-of-little-crowds

BIO science math groups

shared by Beniamino Abis on 30 Apr 14 - No Cached
Dario Izzo liked it
  • Beniamino Abis on 30 Apr 14
     
    What is the best (wisest) size for a group of individuals? Couzin and Kao put together a series of mathematical models that included correlation and several cues. In one model, for example, a group of animals had to choose between two options-think of two places to find food. But the cues for each choice were not equally reliable, nor were they equally correlated. The scientists found that in these models, a group was more likely to choose the superior option than an individual. Common experience will make us expect that the bigger the group got, the wiser it would become. But they found something very different. Small groups did better than individuals. But bigger groups did not do better than small groups. In fact, they did worse. A group of 5 to 20 individuals made better decisions than an infinitely large crowd. The problem with big groups is this: a faction of the group will follow correlated cues-in other words, the cues that look the same to many individuals. If a correlated cue is misleading, it may cause the whole faction to cast the wrong vote. Couzin and Kao found that this faction can drown out the diversity of information coming from the uncorrelated cue. And this problem only gets worse as the group gets bigger.
  • Dario Izzo on 02 May 14
     
    Couzin research was the starting point that co-inspired PaGMO from the very beginning. We invited him (and he came) at a formation flying conference for a plenary here in ESTEC. You can see PaGMO as a collective problem solving simulation. In that respect, we learned already that the size of the group and its internal structure (topology) counts and cannot be too large or too random. One of the project the ACT is running (and currently seeking for new ideas/actors) is briefly described here (http://esa.github.io/pygmo/examples/example2.html) and attempts answering the question :"How is collective decision making influenced by the information flow through the group?" by looking at complex simulations of large 'archipelagos'.
santecarloni

[1010.3437] Dynamical mass generation via space compactification in graphene - 0 views

arxiv.org/1010.3437

technology science PHY

shared by santecarloni on 27 Oct 10 - No Cached
  • santecarloni on 27 Oct 10
     
    Is it really possible?
  • ...2 more comments...
  • Luzi Bergamin on 27 Oct 10
     
    The affiliation is Saudi Arabia and Marocco, not countries famous for their contributions to physics... But nonetheless, yes this is possible, to me it even looks very plausible! But you should know that the term "mass" in this context just means a certain parameter in the dynamical equations and only has a loose relation to what we usually call "mass" in the macroscopic world.
  • LeopoldS on 27 Oct 10
     
    ok - admit that I only read the abstract but to me the seems to be a little bit of magic happening ... even if "mass is only a certain parameter in the dynamical equations" ... I assume it still bears some "heavy" consequences in terms of their speed, interactions etc, no? and assuming that you gradually bend such a structure from a 2D to a 1D one ... does it "gain" mass gradually? all very strange to me ...
  • santecarloni on 28 Oct 10
     
    I think the problem is in the boundary conditions... the issue is that if you use and infinite sheet or a cylinder in the equations you always take cyclic boundary condition. If this guys are right then the mass of the quasi-particles in a crystal depends on its topology... this is a major thing...
  • Luzi Bergamin on 28 Oct 10
     
    BINGO!! It's almost like good ol' Kaluza-Klein...
Tobias Seidl

Photosynthesis: Quantum design for a light trap : Article : Nature - 0 views

www.nature.com/...463614a.html

BIO PHY quantum photosynthesis

shared by Tobias Seidl on 04 Feb 10 - Cached
  • Tobias Seidl on 04 Feb 10
     
    Quantum-stuff in bio-stuff. Finally! Anyone wants to work on biomimetic quantum theory?
  • Luzi Bergamin on 04 Feb 10
     
    I'll start once we have the "Topological Metabiostring".
  • pacome delva on 05 Feb 10
     
    ooh yeah! do you have some time on sunday...? well this falls i think in the "Can we use it for space?" category... but I would like to read a bit more about it (just had the time to read the sciencenow news few post below...)
pacome delva

Condensation transition in networks and other complex systems - 4 views

nuweb.neu.edu/...Condensation.html

phy bio complex_networks

shared by pacome delva on 15 Jan 10 - Cached
  • pacome delva on 15 Jan 10
     
    I like this work... it mixes physics, networks and biology ! Anyone heard about her ? Here's an interesting paper found on this website: http://nuweb.neu.edu/gbianconi/condensation.pdf
  • ...3 more comments...
  • Francesco Biscani on 15 Jan 10
     
    Eh... Barabasi is really milking the golden cow :) It seems interesting, even if I don't remember enough from my statistical mechanics classes to truly understand it without a major effort. Maybe you could make a layman's science coffee about it?
  • pacome delva on 15 Jan 10
     
    yeah i could if there's enough interest...? do u know Barabasi ?
  • Francesco Biscani on 15 Jan 10
     
    He's quite well known for his work on scale-free networks: http://en.wikipedia.org/wiki/Albert-L%C3%A1szl%C3%B3_Barab%C3%A1si He's applying them for everything and the kitchen sink :) We have a Barabasi-Albert network topology implemented in PaGMO...
  • Dario Izzo on 16 Jan 10
     
    We worked on this with Luzi a few years back ... while the analogy is original and interesting it fails to capture the dynamics of a network, e.g. if a network has hubs that grow and shrink .... Luzi worked on an extended model to solve this issue, but, if I remember correctly, he got stuck in a computationally very hard problem .... We intended to develop and use the extended model to define relevant characteristic of the ESA network formed by mail exchanges.....
  • nikolas smyrlakis on 18 Jan 10
     
    ...but then the CMS YGT didn't really like the project
Ma Ru

Ten Simple Rules for Providing a Scientific Web Resource - 0 views

www.ploscompbiol.org/...10.1371%2Fjournal.pcbi.1001126

INF science publication web

shared by Ma Ru on 27 May 11 - No Cached
  • Ma Ru on 27 May 11
     
    May be an interesting reading for those who add auxiliary on-line materials to their publications. This reminds me... results of my topology study aren't on-line yet :-)
Ma Ru

IEEE Xplore - Diversity Through Multiculturality: Assessing Migrant Choice Policies in ... - 0 views

ieeexplore.ieee.org/...abs_all.jsp

INF island model migration PaGMO

shared by Ma Ru on 02 Sep 11 - No Cached
  • Ma Ru on 02 Sep 11
     
    Article on migration policies in the island model. Focus on so-called "multikulti" approach which fosters diversification. Interesting quote: "Other possible avenues of research will be to investigate the influence of the topology on the performance, in relation with the average path length from one node to another and in the sense of the general connectivity." Would be indeed...
ESA ACT

Interaction ruling animal collective behavior depends on topological rather than metric... - 0 views

www.pnas.org/...1232

paper swarm

shared by ESA ACT on 24 Apr 09 - Cached
  • ESA ACT on 24 Apr 09
     
    Some rules of swarming.
LeopoldS

Microsoft's Strange Quest for the Topological Qubit | MIT Technology Review - 2 views

www.technologyreview.com/...microsofts-quantum-mechanics

quantum computing

shared by LeopoldS on 13 Oct 14 - No Cached
  • LeopoldS on 13 Oct 14
     
    loads of nice passwords - should we have a closer look at it? anybody volunteering? e.g. Anna and Daniel?
  • jcunha on 16 Oct 14
     
    Just to add to this possible discussion, two important breakthroughs in Quantum Computing using Silicon were published last week (October 12th). Check it here: http://phys.org/news/2014-10-physicists-silicon-quantum.html
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