Skip to main content

Home/ Advanced Concepts Team/ Group items tagged your

Rss Feed Group items tagged

Juxi Leitner

Send To Dropbox - Email files to your Dropbox! - 2 views

  •  
    for the dropbox users.. in case you e.g. would like to add things behind restrictive firewalls to your dropbox shared drives
  •  
    are they going to see the content of all my dropbox after the authorisation process this requires?
  •  
    I dunno but it would be nice if you could give permission to specific folders ... dunno how the API handles it...
jmlloren

Exotic matter : Insight : Nature - 5 views

shared by jmlloren on 03 Aug 10 - Cached
LeopoldS liked it
  •  
    Trends in materials and condensed matter. Check out the topological insulators. amazing field.
  • ...12 more comments...
  •  
    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...
  •  
    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?
  •  
    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.
  •  
    "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?
  •  
    C'mon Leopold, it's as trivial as the topological states, AKA axions! Regarding the question, not me!
  •  
    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]"
  •  
    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.
  •  
    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.
  •  
    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.
  •  
    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 ....
  •  
    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.
  •  
    guys... how would you explain this to your gran mothers?
  •  
    *you* tried *your* best .... ??
Kevin de Groote

WordItOut - Transform your text into word clouds! - 4 views

  •  
    Transform your text into word clouds! Word clouds are a fun way to show words, where the most important ones are bigger than the others. Make and share word clouds from any text with WordItOut!
  • ...1 more comment...
  •  
    WOW!!!!
  •  
    Impressive. Really nice work!!!
  •  
Francesco Biscani

STLport: An Interview with A. Stepanov - 2 views

  • Generic programming is a programming method that is based in finding the most abstract representations of efficient algorithms.
  • I spent several months programming in Java.
  • for the first time in my life programming in a new language did not bring me new insights
  • ...2 more annotations...
  • it has no intellectual value whatsoever
  • Java is clearly an example of a money oriented programming (MOP).
  •  
    One of the authors of the STL (C++'s Standard Template Library) explains generic programming and slams Java.
  • ...6 more comments...
  •  
    "Java is clearly an example of a money oriented programming (MOP)." Exactly. And for the industry it's the money that matters. Whatever mathematicians think about it.
  •  
    It is actually a good thing that it is "MOP" (even though I do not agree with this term): that is what makes it inter-operable, light and easy to learn. There is no point in writing fancy codes, if it does not bring anything to the end-user, but only for geeks to discuss incomprehensible things in forums. Anyway, I am pretty sure we can find a Java guy slamming C++ ;)
  •  
    Personally, I never understood what the point of Java is, given that: 1) I do not know of any developer (maybe Marek?) that uses it for intellectual pleasure/curiosity/fun whatever, given the possibility of choice - this to me speaks loudly on the objective qualities of the language more than any industrial-corporate marketing bullshit (for the record, I argue that Python is more interoperable, lighter and easier to learn than Java - which is why, e.g., Google is using it heavily); 2) I have used a software developed in Java maybe a total of 5 times on any computer/laptop I owned over 15 years. I cannot name of one single Java project that I find necessary or even useful; for my usage of computers, Java could disappear overnight without even noticing. Then of course one can argue as much as one wants about the "industry choosing Java", to which I would counterargue with examples of industry doing stupid things and making absurd choices. But I suppose it would be a kind of pointless discussion, so I'll just stop here :)
  •  
    "At Google, python is one of the 3 "official languages" alongside with C++ and Java". Java runs everywhere (the byte code itself) that is I think the only reason it became famous. Python, I guess, is more heavy if it were to run on your web browser! I think every language has its pros and cons, but I agree Java is not the answer to everything... Java is used in MATLAB, some web applications, mobile phones apps, ... I would be a bit in trouble if it were to disappear today :(
  •  
    I personally do not believe in interoperability :)
  •  
    Well, I bet you'd notice an overnight disappearance of java, because half of the internet would vanish... J2EE technologies are just omnipresent there... I'd rather not even *think* about developing a web application/webservice/web-whatever in standard C++... is it actually possible?? Perhaps with some weird Microsoft solutions... I bet your bank online services are written in Java. Certainly not in PHP+MySQL :) Industry has chosen Java not because of industrial-corporate marketing bullshit, but because of economics... it enables you develop robustly, reliably, error-prone, modular, well integrated etc... software. And the costs? Well, using java technologies you can set-up enterprise-quality web application servers, get a fully featured development environment (which is better than ANY C/C++/whatever development environment I've EVER seen) at the cost of exactly 0 (zero!) USD/GBP/EUR... Since many years now, the central issue in software development is not implementing algorithms, it's building applications. And that's where Java outperforms many other technologies. The final remark, because I may be mistakenly taken for an apostle of Java or something... I love the idea of generic programming, C++ is my favourite programming language (and I used to read Stroustroup before sleep), at leisure time I write programs in Python... But if I were to start a software development company, then, apart from some very niche applications like computer games, it most probably would use Java as main technology.
  •  
    "I'd rather not even *think* about developing a web application/webservice/web-whatever in standard C++... is it actually possible?? Perhaps with some weird Microsoft solutions... I bet your bank online services are written in Java. Certainly not in PHP+MySQL :)" Doing in C++ would be awesomely crazy, I agree :) But as I see it there are lots of huge websites that operate on PHP, see for instance Facebook. For the banks and the enterprise market, as a general rule I tend to take with a grain of salt whatever spin comes out from them; in the end behind every corporate IT decision there is a little smurf just trying to survive and have the back covered :) As they used to say in the old times, "No one ever got fired for buying IBM". "Industry has chosen Java not because of industrial-corporate marketing bullshit, but because of economics... it enables you develop robustly, reliably, error-prone, modular, well integrated etc... software. And the costs? Well, using java technologies you can set-up enterprise-quality web application servers, get a fully featured development environment (which is better than ANY C/C++/whatever development environment I've EVER seen) at the cost of exactly 0 (zero!) USD/GBP/EUR... Since many years now, the central issue in software development is not implementing algorithms, it's building applications. And that's where Java outperforms many other technologies." Apart from the IDE considerations (on which I cannot comment, since I'm not a IDE user myself), I do not see how Java beats the competition in this regard (again, Python and the huge software ecosystem surrounding it). My impression is that Java's success is mostly due to Sun pushing it like there is no tomorrow and bundling it with their hardware business.
  •  
    OK, I think there is a bit of everything, wrong and right, but you have to acknowledge that Python is not always the simplest. For info, Facebook uses Java (if you upload picture for instance), and PHP is very limited. So definitely, in company, engineers like you and me select the language, it is not a marketing or political thing. And in the case of fb, they come up with the conclusion that PHP, and Java don't do everything but complement each other. As you say Python as many things around, but it might be too much for simple applications. Otherwise, I would seriously be interested by a study of how to implement a Python-like system on-board spacecrafts and what are the advantages over mixing C, Ada and Java.
ESA ACT

CiteULike: A free online service to organise your academic papers - 0 views

  •  
    Personal (or maybe group) relevant page to manage your literature. Currently I check it out - ask me later. Tobias
ESA ACT

Power.com - All your friends in just one place. - 0 views

  •  
    Centralise all your networks / messaging in one place. One of the best I've seen available. Havent tested yet... (KdG)
jmlloren

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

  •  
    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...
  •  
    The solution of thrusting in space.
  •  
    Thrusting in space is solved already. Maybe you wanted to say something different?
  •  
    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.
  •  
    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.
  •  
    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.
  •  
    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.
  •  
    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.
  •  
    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 .
Alexander Wittig

Calling Bullshit - 2 views

  •  
    A college course at University of Washington on "Calling Bullshit". We should invite them to give a lunch lecture at ESA... Our aim in this course is to teach you how to think critically about the data and models that constitute evidence in the social and natural sciences. While bullshit may reach its apogee in the political domain, this is not a course on political bullshit. Instead, we will focus on bullshit that comes clad in the trappings of scholarly discourse. Our learning objectives are straightforward. After taking the course, you should be able to: * Remain vigilant for bullshit contaminating your information diet. * Recognize said bullshit whenever and wherever you encounter it. * Figure out for yourself precisely why a particular bit of bullshit is bullshit. * Provide a statistician or fellow scientist with a technical explanation of why a claim is bullshit. * Provide your crystals-and-homeopathy aunt or casually racist uncle with an accessible and persuasive explanation of why a claim is bullshit. We will be astonished if these skills do not turn out to be among the most useful and most broadly applicable of those that you acquire during the course of your college education.
  •  
    love it: "Politicians are unconstrained by facts. Science is conducted by press release. Higher education rewards bullshit over analytic thought. Startup culture elevates bullshit to high art. Advertisers wink conspiratorially and invite us to join them in seeing through all the bullshit - and take advantage of our lowered guard to bombard us with bullshit of the second order. The majority of administrative activity, whether in private business or the public sphere, seems to be little more than a sophisticated exercise in the combinatorial reassembly of bullshit. We're sick of it. It's time to do something, and as educators, one constructive thing we know how to do is to teach people. So, the aim of this course is to help students navigate the bullshit-rich modern environment by identifying bullshit, seeing through it, and combating it with effective analysis and argument."
LeopoldS

Inspiration Mars - 2 views

  •  
    married in a stable relationship? here comes your ticket for a swing-bye of Mars
Marcus Maertens

Everything You Wanted to Know about Space Tourism but Were Afraid to Ask | Space Safety... - 3 views

  •  
    "chances are that if 700 passengers are flown annually, up to 10 of them might not survive the flight in the first years of the operations." most remarkable also the question who is to blame if a dead and burned space tourist corps comes crashing down from the sky into your car.
  • ...3 more comments...
  •  
    How sure is the information that a human body would not completely burn / ablate during atmospheric re-entry? I am not aware of any material ground tests in a plasma wind tunnel confirming that human tissue would survive re-entry from LEO.
  •  
    Since a steak would not even be cooked by dropping it from very high altitudes (http://what-if.xkcd.com/28/) I would doubt that a space tourists body would desintegrate by atmospheric re-entry.
  •  
    Funny link, however, some things are not clear enough: 1. Ablation rate is unknown 2. What are the entry conditions? The link suggests that the steak is just dropped (no initial velocity). 3. What about the ballistic coefficient? 4. How would the entry body orientation? It would be a quite non-steady state configuration I guess with heavy accelerations. 5. How would vacuum exposure impact on the water in the body/steak and what would be the consequence for ablation behaviour? 6. Does surface chemistry play a role (not ablation, but catalysis)? My conclusion: the example with the steak is a funny and not so bad exercise, not more.
  •  
    This calls for some we serious simulations by the Petkow code it seems to me ...
  •  
    I still would need some serious input data...
Wiktor Piotrowski

How To Build Your Own Cockroach Cyborg | Popular Science - 1 views

  •  
    bio-robotics anybody?
  •  
    WIRING Poke the left silver wire about one millimeter into the roach's thorax, under a wing just behind its head, and secure it with superglue. Cut each antenna to expose a neuron-lined tube. Insert the middle wire one millimeter into the left tube, and the right wire into the right tube. Superglue both wires into place. CONNECT AND COMMAND Hot-glue the circuit board onto the roach's back and plug it into the head connector. After the roach wakes up, press the remote's left button to urge it right, and the right button to move it left. The cyborg will ignore commands after a few minutes. Peel off the circuit board and clip all wires to ensure a long retirement.
LeopoldS

Samsung's smart TVs 'wide open' to exploits * The Register - 0 views

  •  
    Your TV might be watching you :-) ... If you have one
Alexander Wittig

Why a Chip That's Bad at Math Can Help Computers Tackle Harder Problems - 1 views

  •  
    DARPA funded the development of a new computer chip that's hardwired to make simple mistakes but can help computers understand the world. Your math teacher lied to you. Sometimes getting your sums wrong is a good thing. So says Joseph Bates, cofounder and CEO of Singular Computing, a company whose computer chips are hardwired to be incapable of performing mathematical calculations correctly.
  •  
    The whole concept boils down to approximate computing it seems to me. In a presentation I attended once I prospected if the same kind of philosophy could be used as a radiation hardness design approach, the short conclusion being that surely will depend on the functionality intended.
LeopoldS

Two weeks of smartphone charging in your pocket | Cutting Edge - CNET News - 0 views

  •  
    finally a consumer fuel cell which looks promising to actually see the markets ...
Dario Izzo

ArduSat - Your Arduino Experiment in Space by ppl4world - Kickstarter - 1 views

  •  
    They made it :) fund raised and project kicked. + they aaplied to SOCIS
Luís F. Simões

Higgs Boson Particles being sold on eBay ! - 0 views

  •  
    "Higgs Boson partices - guaranteed to satisfy! Need mass in your objects? Get some Higg Bosons!" "The Higgs Boson particles are SOLD WITH THE JAR! You may not be able to SEE the Higgs Boson particles unless you use a large hadron collider." "Q: Since it is, after all, the god particle; can you observe closely and tell use what religion it is?"
Ma Ru

Memory and the Cybermind - 0 views

  •  
    or "your phone vs. your wife"...
santecarloni

Special Relativity And The Curious Physics of Chronology - Technology Review - 0 views

  •  
    Einstein showed that two unrelated events can appear in any order depending on your point of view. Now physicists have discovered the chronologies of three events, and more
LeopoldS

http://envisioningtech.com/envisioningtech.pdf - 3 views

  •  
    and what is your take?
  •  
    As William Gibson famously said "The future is already here - it's just not very evenly distributed." Many of the listed technologies are already here, in one way or another, the authors are just putting dates on when they think they'll achieve greater consumer impact. I have issues with many of those dates. I think there are a lot of under- and overestimations. Also, what a bleak future for AI it that's all it'll give the world in the next 30 years!
‹ Previous 21 - 40 of 308 Next › Last »
Showing 20 items per page