386. Saturday’s photoguess
Save This Post as PDFThe questions related to this photoguess: a) what is the physical phenomenon on the photo? b) who made it? (where it was made?)
Seek and thou shalt find!
Update: kudos to hukrepus 
, according to him/her this is
larger than average (>5m) lumps of material in Saturn’s rings with the Sun shining almost edge on casting a shadow. The Cassini probe/CICLOPS team.
Way too easy 
I’ll try to dig something more tricky next time.
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385. NEQNET: Last two weeks of April
The last month of the spring 2009 has started. Like all crazies, who usually get a bit more active during spring, I want (need) to become more active – my spirit requires some change. In this respect, I would like to ask you – what do you want to see new on NEQNET? New design? New guest bloggers? Are you unhappy about anything, that is, do you think that something has to be improved on the blog? Do you want to discuss some particular topic?
In the mean time here is what happened on NEQNET during last two weeks…
1. String theory, field theory, quantum gravity
1.1. M2 branes and Chern-Simons theories by John Davey, graduate student at Imperial College, London. John discusses some basics behind quiver Chern-Simons theories and their relation to membrane mini-revolution in string theory.
2. Nuclear physics
Somehow, I decided to study the physics of thermonuclear fusion a bit to get some understanding of the problem that I assigned N7 in my list to…
2.1. Introduction into thermonuclear reactors, where I introduce classification of thermonuclear reactors based on how plasma is confined in the reactor.
2.2. Thermonuclear reactors. Inertial confinement, where I calculate reaction rate in this type of reactors.
2.3. Thermonuclear reactors. More on inertial confinement, where I discuss several important parameters characterizing nuclear reactors with inertial confinement of plasma.
2.4. Inertial confinement – using lasers for compression, where it is explained why laser is such a great thing.
2.5. Inertial confinement: more on interaction of laser emission with matter, where I list different mechanisms of laser/matter interaction.
2.6. Inertial confinement: concluding part on lasers, where I describe what exactly happens with ablator and fuel in the capsule after the laser impulse.
3. Quantum mechanics and quantum computations
3.1. Temporal and spatial dependence of quantum entanglement by Shih-Yuin Lin, professor at National Center for Theoretical Sciences, Taiwan. Shih-Yuin discusses his recent exciting work done in collaboration with Bei-Lok Hu.
4. Cosmology, astrophysics, space research
4.1. Cosmological parameters in the context of time varying w by Rahul Biswas, graduate student of Benjamin Wandelt. Rahul explains how robust are bounds on cosmological parameters of 
CDM, if we allow effective equation of state for the dark energy to vary with time.
4.2. Kepler sees first light. Kepler is a new NASA space telescope, its particular mission being the estimation of number of planets per cubic kPc in our Galaxy.
4.3. Vector inflation by Alexey Golovnev (U. of Munich). Alex explains the core physics behind his recent work with Slava Mukhanov and Vitaly Vanchurin.
4.4. Some musings about Unruh effect, where I duscuss recent paper by Ugo Moschella and Richard Schaeffer.
4.5. A GRB detected at z=8.3 – the most distant object in the Universe so far!
4.6. Lester Lyles is not to be the next NASA administrator, and it seems that Steve Isakowitz is the favorite N1 in the run now.
5. Hydrodynamics, turbulence
5.1. Vortex line representation. Coulomb interaction of vortex lines, where I prove that energy should be dissipated inhomogeneously in the flow with very large Reynolds numbers. No more, no less.
5. Fun and things
5.1. The future of science blogs, where I ask you, my good readers, whether NEQNET should join some blog portal or not. Your answer is unclear to me
5.2. On science (in Russia), where I discuss some rather interesting statistics showing that science in Russia is in a decline after the decay of USSR. As if you wouldn’t now
6. Videos posted
6.1. ISS Tour.
6.2. ATLAS/CERN 2009 multimedia contest.
6.3. Steven Hawking’s “Black holes and beyond”.
6.5. Sounds of Jupiter.
Cheers and have a good weekend!
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384. More news from NASA
First, it seems that Orion will generally (that is, not just on missions to the Moon) carry 4 astronauts instead of 6, as was initially planned. This is fantastic news for the Russian Space Agency, since NASA will have to use Soyuz spacecrafts as an escape module for ISS – the number of crew members is going back to 6 starting next year.
The explanation that Jeff Hanley gave sounds also somewhat surprising to me – does NASA really save the budget that much by cancelling 6-crew option?
Second, it seems that NASA is going to abandon plans for permanent base on the Moon altogether. This option is costly indeed, but WTF is the physical meaning to have another flyby/short landing of the Moon 40 years after the last one??
And according to New Scientist, Scolese’s
… comments also hinted that the agency is open to putting more emphasis on human missions to destinations like Mars or a near-Earth asteroid.
Yeah, sure, I’ll tell you this: if they cancelled lunar base, they will cancel lunar missions as well, and the only thing that will be eventually done (hopefully, before 2020) is designing and launching 4-crew Orions. Let me kindly remind you that ISS will have to go out of the orbit on 2015. Taking into account how much was the ISS budget overextended, one would seriously doubt that the agreement on the next generation space station will be ever achieved.
What is really going on with Constellation, I wonder?
Mood: severely disappointed.
Update: Here is a related episode from spacevidcast –
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383. Puzzling kinetics of Bose-Enstein condensation
Just finished reading a really review “Magnon BEC and spin superfluidity” by Yu. Bunkov and G. Volovik, which left me with quite a bit of material to think about… Probably the thing that stroke me most after digesting the review is how poorly I (or in truth – it’s better to say “we”) actually understand the kinetics of Bose-Einstein condensation. But before I’ll try to explain why I think so, let me briefly describe the setup discussed by the authors.
1. Bose-Einstein condensation of magnons
They talk about Bose-Einstein condensation (BEC) in 
, but their BEC is not the one that leads to superfluidity of . The story is actually much funnier: are fermions carrying spin 1/2. As a result of spin-spin and spin-orbital interactions, spin waves can be excited in . The ground state of the system (at T=0) corresponds to all spins of all nuclei oriented in the same direction. An excitation above the ground state corresponds to one or several spins oriented downwards. There are of course quasi-particles associated with these excitations called magnons, that carry spin 1 (since the difference between 
of nuclei with spins oriented upwards and downwards is 1). Since these quasi-particles are bosons, it is natural to expect that Bose-Einstein condensation is possible for them.
Magnon BEC corresponds to a situation when spins of all nuclei in the superfluid precess coherently. Such state was indeed observed in experimentally not so long ago (you can find references to original papers in the bibliography section of the review). More over, it was even possible experimentally to observe vortices – topological excitations in the corresponding Bose-Einstein condensate.
What surprised me the most is the time scale at which Bose-Einstein magnon condensate gets established after the system’s cooling.
Formation of magnon BEC. From Bunkov, Volovik, 09.
First of all, note that magnons are quasi-particles. The true ground state does not contain any spin excitations – in other words, all magnons decay before the ground state is reached. As seen from the plot on the left, the characteristic time scale of their decay is rather short – about 0.5-1 sec. On the other hand, as follows from the plot on the right, true BEC (that is, off-diagonal long range order) is formed at time scales 10 times shorter – at 0.05 sec after cooling. So, why am I excited so much about it?
2. How kinetics of BEC formation is understood at present time
The main reason is that according to our present understanding of BEC kinetics, formation of the condensate peak in a weakly interacting Boise gas requires infinite time (in the system with infinite time, see Nozieres, Levich-Yakhot), although formation of Bose distribution with chemical potential close to zero is of the order of mean free time for particles forming the condensate. By the condensate peak I mean as usual a delta-function contribution into the distribution function of elementary excitations at 
.
Condensation proceeds in several steps. First of all, particles start to condense in the energy interval
,
where 
is equilibrium density of condensate, 
is effective interaction vertex for elementary excitations. It is said that precondensate or short range order is formed. The state of the liquid is then described by the non-linear Schrodinger (or better say Gross-Pitaevskii) equation
,
where 
is the wavefunction of the precondensate.
The modulus and the phase of this wave function still fluctuate strongly after formation of precondensate.
Short range order is formed at time scales
,
a relatively short time scale.
The order is called short since the correlation length exists in the system that is of the order
–
inside domains of the size 
the phase of the wave function is correlated, and it remains uncorrelated between different domains.
But what we ultimately want to see is not a precondensate in the sense above but the formation of the delta-function in the distribution function 
at . The latter does not happen even at 
.
The reason is that the phase is rapid variable, and while the absolute value of the wave function achieves its equilibrium value at time scale of the order 
, the phase of the wavefunction continues to fluctuate strongly. In a sense, the system of magnons can be described in terms of vortices (topological excitations associated to fluctuations of the phase) and “phonons” – spin waves.
In order for off-diagonal long range order to appear, both vortex field and spin waves should relax.
Characteristic time scale for the appearance of the topological LR order (in other words, the time scale for decay of vortices) depends on the size of the system 
(this is a kind of apparent, since long vortices may be present with characteristic size of the same order of magnitude as ) can be estimated as follows:
,
where 
and 
is the quantum of circulation. As you see, this is rather long time scale that depends on the size of the system.
Finally, for the long range order spin waves should also relax, and their relaxation time is the longest one in the system and is given by
where 
is the scattering length for spin waves (related to the parameter above in the known way). This time scale is also proportional to the size of the system…
So, why the time scale of magnon BEC formation is so short? Probably, something goes wrong with considerations above, but I am not sure what exactly…
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382. Lester Lyles is not to be the next NASA administrator
Lester Lyles, retired air force general, has confirmed yesterday that he has taken his name out of consideration for the NASA administrator post. He was clearly a favorite in the run started on Jan 20, to the point that Obama administration pushed him to take the post. I think it would be fair to say – thank you, Mr. Lyles.
In the mean time, it is rather unclear again who is going to be the next NASA administrator (is it true that Isakowitz is the candidate N1 right now, after Gration is appointed special envoy to Sudan?). Man, how are they supposed to manage to go to the Moon, if they are unable to make a single administrative decision for months?
Isakowitz bio from the DoE website:
Steve Isakowitz was sworn in June 1, 2007 as Chief Financial Officer of the Department of Energy after being unanimously confirmed by the United States Senate. As CFO, Mr. Isakowitz plays a vital role in the Department’s $24 billion budget that supports important energy, scientific, and national security investments. He has overall responsibility for the Department’s financial management, budget formulation and execution, program analysis and evaluation, corporate information systems, and loan guarantee program.
Prior to DOE, Mr. Isakowitz held important positions in policy, finance, program management, and engineering. Since 1991, he has led key efforts for the US Government in support of major national goals in research and development, space exploration, and national security. At the Office of Management and Budget, he supported the White House in overseeing $50 billion in Federal science and technology programs across multiple Federal agencies and led development of major interagency initiatives. At the National Aeronautics and Space Administration, he was the Deputy Chief Financial Officer and Comptroller responsible for directing the agency’s $16 billion annual budget, and Deputy Associate Administrator in charge of major space exploration programs. At the Central Intelligence Agency, he was a senior manager with the Science & Technology Directorate responsible for devising innovative technical projects and addressing high priority issues within the intelligence community.
Previously, Mr. Isakowitz was a corporate manager and senior engineer at Lockheed Martin Corporation and a senior consultant at Booz, Allen & Hamilton. He is also the recipient of the Presidential Distinguished Rank Award, a top award for executive performance, and an author of a technical book on space launch vehicles.
A native of Cleveland, Ohio, Mr. Isakowitz graduated from the Massachusetts Institute of Technology with a bachelor’s and master’s degree in aerospace engineering. He and his wife, Monica, live in Virginia and have four children.
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