Condensed Matter
244. An efficient local method for community detection in large networks
This is a guest blog post by Symeon Papadopoulos (MKLab, Informatics and Telematics Institute, Greece) who is going to determine whether effective community exist in the complex network of NEQNET readers 
Dmitry.
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228. Book review: D. Yoshioka. The quantum Hall effect
About a week ago we have briefly discussed the physics of the quantum Hall effect. Let me remind you the conclusions we came to.
We discriminate between the integer and fractional quantum Hall effects according to the value of the filling factor 
. The latter characterizes the many-particle wave function describing behaviour of electrons in the sample. effectively depends only on which Landau levels are filled and which – aren’t, i.e., on 
and ultimately on Landau levels themselves (that is, the value of magnetic field we apply to the sample).
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226. Top ten open problems in physics
What is the ultimate purpose of my work as theoretical physicist and, if you want, my existence itself? Is it serving the community of other physicists like organizing and participating in conferences? Nop. Then, maybe teaching future physicists in the University, encourage young people to enter the exciting field of physics? Not quite. Writing good papers? Ei. Maybe blogging? Sorry but nein. I think… the ultimate purpose of my work is solving unsolved mysteries in physics. I am afraid, this and only this makes my work enjoyable for me, makes it fun. For the sake of future reference, let me enlist here the most important (from my point of view), hard and interesting unsolved problems in physics.
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205. Multifractality and metal-insulator transition
This is a guest blog post by Matthew Foster from Rutgers about his recent paper arXiv:0901.0284v1 [cond-mat.dis-nn]. Dmitry.
In most electronic materials, impurities and other defects (“quenched disorder”) play a dominant role in shaping transport phenomena. Of particular interest has been the interplay between multiple impurity scattering and quantum interference effects. The scaling theory of localization, developed nearly 30 years ago by Abrahams, Anderson, Licciardello, and Ramakrishnan, predicts that sufficiently strong impurity scattering can exponentially localize electronic wavefunctions; when all states at the Fermi energy become localized, the material is an insulator, incapable of conducting electric current at zero temperature. This effect is especially pronounced in low dimensions, where the scaling theory in fact predicts that all wavefunctions localize for arbitrarily weak disorder (in the conventional symmetry classes of disordered metals). By contrast, in three and higher dimensions, a continuous metal-insulator transition (MIT) is predicted to occur at a critical value of the sample conductance.
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203. Quantum Hall effect. One open question
I cannot finish discussing quantum Hall effect without explaining why, after all those years of study, Laughlin wavefunction and composite fermions, it still remains interesting for a condensed matter theorist.
The reason is existence of the state with 
, the only state with even denominator of the filling factor
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198. Fractional quantum Hall effect – a few words about theory
Finally, after going through the integer quantum Hall effect, we are a kind of ready to discuss one of the biggest puzzles in condensed matter theory: the fractional quantum Hall effect.
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195. Integer quantum Hall effect – plateaus in Hall resistivity
This post is my attempt to give an answer to tg’s question: Ok, we a kind of proved that the Hall resistivity is quantized in the integer quantum Hall effect, but how to explain plateaus in the Hall resistivity 
and deep minima in diagonal resistivity 
as shown on the Fig.
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191. Integer quantum Hall effect – theory
I guess, my reader, you are either a) an undergrad, b) a graduate student, c) a postdoc (or even professor? Cheers, Joe) or d) you are just interested in science and theoretical physics in particular (maybe, you even had a couple of courses related to physics in college). If b) or c) holds, you will probably fail to find anything interesting in this post, but if I am lucky, then a) or d) holds
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188. Integer and fractional quantum Hall effect – what is it?
Fractional quantum Hall effect was and remains one of the biggest mysteries in condensed matter theory. To be as arrogant as usual, I will claim that theorist’s brain work necessary to explain fractional quantum Hall effect is roughly equal to the work necessary to explain confinement in QCD, although the former problem is much younger than the latter – the fractional Hall effect was first observed in 1982 by Tsui, Stormer and Gossard.
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148. On surface growth
As Barabasi and Stanley state in the book “Fractal concepts of surface growth“,
most of our life takes place on the surface of something.
Indeed, authors of several thousands of paper citing the Randall-Sundrum seminal work take seriously the idea that our 4-dimensional world is localized on the surface of a membrane located in turn in a warped 5-dimensional universe. Many processes important for our biology are realized on the surface of cellular membranes. Phases in a first order phase transition are separated in space by an interface, with its dynamics in time being very non-trivial.
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141. On information loss paradox, statistical and quantum mechanics
Recently, I got into the discussion of information loss paradox in spacetimes with timelike and spacelike horizons (that is, black holes, de Sitter and staff like them). Let me remind you what is the issue (see for example Susskind’s recent book for details).
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140. First two weeks of December at NEQNET
Dear friends
Before I proceed to the (becoming usual already) list of posts published at NEQNET during the last two weeks, let me say a couple of words about the blog itself, which is currently the source of my pride 
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123. AdS/CFT and condensed matter applications
This post is going to be, I think, somewhat controversial but… if you feel that I greatly miss some important point regarding the subject, then please feel free to explain that to me in the comments. And the subject is… ta-da-da-daam…
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97. Second week of November on NEQNET
Physics
* Quintessence on the string theory landscape?
I discuss the recent paper by Kaloper and Sorbo explaining how quintessence can be realized on the string theory landscape, as follows from the title. The post also contains small introduction explaining what is quintessence field and why we want so hard to find it on the landscape
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95. One second order phase transition: video
Discussion of the Shaposhnikov-Tkachev paper has somewhat inspired me as you might expect, and I decided to browse the net for a bit That’s what I have found -
what you see below is a phase transition of the second kind, the one where correct degrees of freedom are decribed by CFT at 
. Can you guess what is the phase transition and what is the medium it happens in?
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