Skip to main content

Home/ Advanced Concepts Team/ Group items tagged insulator

Rss Feed Group items tagged

Filter: All | Bookmarks | Topics Simple Middle
15More

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 .... ??
2More

Fur and feathers keep animals warm by scattering light - 1 views

www.sciencedaily.com/...140123125834.htm BIO science light fur
shared by Tom Gheysens on 24 Jan 14 - No Cached
  • Tom Gheysens on 24 Jan 14
     
    In work that has major implications for improving the performance of building insulation, scientists at the University of Namur in Belgium and the University of Hassan I in Morocco have calculated that hairs that reflect infrared light may contribute significant insulating power to the exceptionally warm winter coats of polar bears and other animals.
  • Paul N on 25 Jan 14
     
    That's quite interesting. Maybe the future of buildings and spacecraft is furry?
2More

Bacteria grow electric wire in their natural environment - 1 views

www.sciencedaily.com/...121024133358.htm bio technology science
shared by johannessimon81 on 29 Oct 12 - No Cached
LeopoldS liked it
  • johannessimon81 on 29 Oct 12
     
    Bacterial wires explain enigmatic electric currents in the seabed: Each one of these 'cable bacteria' contains a bundle of insulated wires that conduct an electric current from one end to the other. Cable bacteria explain electric currents in the seabed Electricity and seawater are usually a bad mix.
  • LeopoldS on 29 Oct 12
     
    WOW!!!! don't want to even imagine what we do to these with the trailing fishing boats that sweep through sea beds with large masses .... "Our experiments showed that the electric connections in the seabed must be solid structures built by bacteria," says PhD student Christian Pfeffer, Aarhus University. He could interrupt the electric currents by pulling a thin wire horizontally through the seafloor. Just as when an excavator cuts our electric cables. In microscopes, scientists found a hitherto unknown type of long, multi-cellular bacteria that was always present when scientists measured the electric currents. "The incredible idea that these bacteria should be electric cables really fell into place when, inside the bacteria, we saw wire-like strings enclosed by a membrane," says Nils Risgaard-Petersen, Aarhus University. Kilometers of living cables The bacterium is one hundred times thinner than a hair and the whole bacterium functions as an electric cable with a number of insulated wires within it. Quite similar to the electric cables we know from our daily lives. "Such unique insulated biological wires seem simple but with incredible complexity at nanoscale," says PhD student Jie Song, Aarhus University, who used nanotools to map the electrical properties of the cable bacteria. In an undisturbed seabed more than tens of thousands kilometers cable bacteria live under a single square meter seabed. The ability to conduct an electric current gives cable bacteria such large benefits that it conquers much of the energy from decomposition processes in the seabed. Unlike all other known forms of life, cable bacteria maintain an efficient combustion down in the oxygen-free part of the seabed. It only requires that one end of the individual reaches the oxygen which the seawater provides to the top millimeters of the seabed. The combustion is a transfer of the electrons of the food to oxygen which the bacterial inner wires manage over centimeter-long distances. However, s
2More

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...!
1More

Finding the Source of the Pioneer Anomaly - IEEE Spectrum - 0 views

spectrum.ieee.org/...-source-of-the-pioneer-anomaly NPS RPS RTG nuclear pioneer
shared by LeopoldS on 08 Dec 12 - No Cached
  • LeopoldS on 08 Dec 12
     
    The article came out some time ago of course and was posted here, though the story here is still well written. If you are lazy to read the rel long article, here the summary explanation: The team found that a good half of the force came from heat from the RTGs, which bounced off the back of the spacecraft antenna. The other half came from electrical heat from circuitry in the heart of the spacecraft. Most of that heat was radiated through louvers at the back of the probes, which weren't as well insulated as the rest of their bodies, further contributing to the deceleration.
1More

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.
4More

Personal Thermal Management by Metallic Nanowire-Coated Textile - 2 views

pubs.acs.org/...nl5036572 thermal management silver nanotechnology
shared by Thijs Versloot on 12 Jan 15 - No Cached
annaheffernan, Paul N, and jcunha liked it
  • Thijs Versloot on 12 Jan 15
     
    By wearing clothes that have been dip-coated in a silver nanowire (AgNW) solution that is highly radiation-insulating, a person may stay so warm in the winter that they can greatly reduce or even eliminate their need for heating their home. With as extra bonus: Besides providing high levels of passive insulation, AgNW-coated clothing can also provide Joule heating if connected to an electricity source, such as a battery. The researchers demonstrated that as little as 0.9 V can safely raise clothing temperature to 38 °C, which is 1 °C higher than the human body temperature of 37 °C. How about that for personal comfort during the cold winter months
  • ...1 more comment...
  • jcunha on 13 Jan 15
     
    These applications seem more and more promising. However I wonder about the toxicity aspects of wearing this stuff and apparently some research is starting to be developed to assess that, see http://www.particleandfibretoxicology.com/content/11/1/52 showing results of pulmonary toxicity of AgNW
  • LeopoldS on 17 Jan 15
     
    sounds almost like the asbestos story re-started :-)
  • jcunha on 09 Apr 15
     
    Found an European project that takes care of the environmental, health and safety aspects of nanomaterials http://phys.org/news/2015-04-unleash-full-potential-nanomaterials.html
1More

Photonic Thermos | Physical Review Focus - 0 views

focus.aps.org/st14 phy thermodynamics insulator
shared by pacome delva on 19 Oct 09 - Cached
  • The pure vacuum of a thermos is not the best possible insulator for keeping your soup warm. Last year a team found theoretically that a structure known as a photonic crystal could block heat flow even more effectively than vacuum.
1More

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...
1More

Maze-solving automatons can repair broken circuits - 1 views

scitation.aip.org/...1.4916513 technology PHY space
shared by jcunha on 09 Apr 15 - No Cached
  • jcunha on 09 Apr 15
     
    Researchers in Bangalore, India together with the Indian Space Research organization come up with an intelligent self-healing algorithm that can locate open-circuits faults and repair them in real-time. They used an insulating silicon oil containing conductive particles. Whenever a fault happens, an electric field develops there, causing the fluid to move in a 'thermodynamic automaton' way repairing the fault. The researchers make clear it could be one advantage for electronics in harsh environments, such as in space satellites.
1More

Solar power without solar cells - 2 views

physicsworld.com/...45787 phy solar_radiation insulator
shared by pacome delva on 27 Apr 11 - No Cached
  • pacome delva on 27 Apr 11
     
    not very advanced and maybe non practical but...
1More

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.
1 - 13 of 13
Showing 20▼ items per page