371. Saturday’s photoguess
Save This Post as PDFKindly take a look at photos below and try to guess what are these nice guys building and where exactly does it happen 
Hint: Photo 3 has all information you need to guess correctly what it is.
Answer: This is the launch pad for Soyuz rocket being built in Korou, French Guyana. Kudos to Gabriel 
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370. The future of science blogs
I’ve just finished a reading rather interesting article by Mark Penn on WSJ called “America’s newest profession: bloggers for hire“. Penn presents rather interesting stats there (based on analysis by Technorati):
The best studies we can find say we are a nation of over 20 million bloggers, with 1.7 million profiting from the work, and 452,000 of those using blogging as their primary source of income.
I guess, it is well explained in comments after the post how much these estimations are actually worthy, but the very point of the post remains solid as I think: blogging is a possibility to make full-time income, albeit maybe only hundreds of people in the world are able to make it their full-time income.
What I’ve also noticed is a general tendency for smaller blogs to be submerged into larger blogs/blog portals. The reason for that becomes very clear when you compare Alexa ranks of individual blogs (say, Lubos Motl’s Reference Frame – around 217000 right now) and portals (say, Science Blogs – around 8000 right now) and take into account that rank does scale with internet traffic. In other words, if a site has more content, it will have larger traffic, and individual blogs will always loose in this respect to blog portals.
As I said, this seems to be a general tendency. What about science blogs, close to our hearts? The same thing holds here as well: during last months many individual popular blogs “went corporate” including Cosmic Variance, ArXiv Blog and Quantum Diaries Survivor.
So, the statement of the problem I would like to solve is the following: blog portals have much more traffic than individual blogs since they produce much more content (let us say, a blog portal produces 50 updates per day, while an individual blog – 2-3 posts/day at maximum). How to make the individual blog competitive with a portal? I’ll be really happy to hear your thoughts…
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369. Stephen Hawking’s “Black holes and beyond”: video of the day
Black holes, wormholes, initial singularity in cosmology… as explained by Stephen Hawking. Rumor says he is in Addenbrooke’s hospital now fighting with chest infection. I wish you quick and full recovery, Prof. Hawking.
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368. Inertial confinement: more on interaction of laser emission with matter
Yeah… so, where did we stop last time? I’ve just said another triviality – that laser emission strongly interacts with material of the fuel capsule. There are several mechanisms of this interaction: deflection (ablator and fuel are almost transparent but not quite), absorption and scattering.
Wired Science visits LLNL and National Ignition Facility
As for absorption, the most important mechanisms that play role in the particular physics that we discuss are bremsstrahlung absorption, anomalous effects (like decay of photon into two plasmons) and resonant absorption. The later appears when the plasma density approaches the critical value
,
where 
is the wave length of laser emission.
Let us discuss absorption in a bit more details… Bremsstrahlung absorption is most important for short wavelength lasers (in what follows we suppose that the flux is of the order 
). For 
absorption factor is
.
Bremsstrahlung absorption becomes less important with increase of the flux, since 
and 
.
Resonant absorption is more important (and actually dominates in the interval of fluxes that is available for the present-day technology) for long wavelength lasers. It is called "resonant" since near 
the frequency of plasma oscillations coincides with frequency of the laser beam. This leads to resonant amplification of oscillations in plasma and generation of fast electrons. In practice, more than 50% of the beam energy can be absorbed by this mechanism (it is established experimentally that about 25%-90% of the total energy of the beam gets absorbed for beams with 
, 
and wavelengths 
). The distribution function of fast electrons is Maxwell-like, with effective temperature about 10 times higher than the temperature of "normal" electrons in plasma.
The most important mechanisms of scattering of laser emission on material of the capsule are Raman and Mandelstam-Brillouin scatterings.
Next time I’ll explain how energy of the beam is transferred at deeper, denser layers of the compressed fuel capsule.
Literature
1. J. Duderstadt, G. Moses, “Inertial confinement fusion”
2. S. Atzeni, J. Meyer-ter-Vehn, “The physics of inertial fusion”
3. For the Russian-speaking part of the audience, I would really recommend to read all articles on thermonuclear fusion in “Fizicheskaya Encyclopedia”, Moscow, 1990-98.
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367. ATLAS/CERN 2009 multimedia contest: video of the day
Are you a graduate student at physics department who is badly annoyed by the fact that your girlfriend calls you nerd? Do you want to be like Brian Cox instead? (oh God, my answer would be resounding No ) or at least to get an internship at CERN, to take a closer look on LHC and maybe even touch it?
In case you know how to deal with multimedia, here is one simple way to get it: make a short movie about ATLAS, register at http://www.atlas.ch/contest/ and enter the contest (deadline is June 15). The winner of the contest will spend three months of fall 2009 at ATLAS/CERN, Switzerland, covering the excitement of physicists as they witness the first collisions produced by the LHC.
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