SEMCIÊNCIA

Power Laws, Weblogs, and Inequality First published February 8, 2003 on the "Networks, Economics, and Culture" mailing list. Subscribe to the mailing list. Version 1.1: Changed 02/10/03 to point to the updated "Blogging Ecosystem" project, and to Jason Kottke's work using Technorati.com data. Added addendum pointing to David Sifry's "Technorati Interesting Newcomers" list, which is in part a response to this article. A persistent theme among people writing about the social aspects of weblogging is to note (and usually lament ) the rise of an A-list, a small set of webloggers who account for a majority of the traffic in the weblog world. This complaint follows a common pattern we've seen with MUDs, BBSes, and online communities like Echo and the WELL. A new social system starts, and seems delightfully free of the elitism and cliquishness of the existing systems. Then, as the new system grows, problems of scale set in. Not everyone can partic...

The Death of Nemesis: The Sun's Distant, Dark Companion Posted:  11 Jul 2010 09:10 PM PDT The data that once suggested the Sun is orbited by a distant dark companion now raises even more questions Over the last 500 million years or so, life on Earth has been threatened on many occasions; the fossil record is littered with extinction events. What's curious about these events is that they seem to occur with alarming regularity. The periodicity is a matter of some controversy among paleobiologists but there is a growing consensus that something of enormous destructive power happens every 26 or 27 million years. The question is what? In this blog, we've looked at various ideas such as the Sun's passage through the various spiral arms of the Milky Way galaxy (it turns out that this can't explain the extinctions because the motion doesn't have had the right periodicity). But another idea first put forward in the 1980s is that the Sun has a distant dark companion calle...

Fig. 3. Nested θ- and β/γ-oscillations organize in the form of neuronal avalanches. ( A ) Definition of neuronal avalanches formed by the nested θ- and β/γ-oscillations. ( Top ) Threshold detection (broken line) of nLFPs (filled circles) at a single electrode. ( Middle ) Corresponding time–amplitude raster plot of nLFPs on the MEA (color: nLFP amplitude). ( Bottom ) Spatiotemporal nLFP clusters occupy successive bins of width Δ t avg (dotted rectangles). ( B ) Average cross-correlation function for nLFPs in vivo at P8 (red) and P13 (black; single experiments). ( C ) nLFP clusters from nested θ- and β/γ-oscillations organize in the form of neuronal avalanches, i.e., distribute in sizes according to a power law with slope close to α = −1.5 (broken line). Average cluster size distribution in vivo plotted in log–log coordinates for P8 (red open circles; n = 5) and P13 (black; n = 7). ( D ) Example of two simultaneous burst periods before (black) and after (red) phase-shuffling. ( E )...

How to Build a Dark Energy Detector Posted:  25 Jan 2010 09:10 PM PST All the evidence for dark energy comes from the observation of distant galaxies. Now physicists have worked out how to spot it in the lab The notion of dark energy is peculiar, even by cosmological standards. Cosmologists have foisted the idea upon us to explain the apparent accelerating expansion of the Universe. They say that this acceleration is caused by energy that fills space at a density of 10^-10 joules per cubic metre. What's strange about this idea is that as space expands, so too does the amount of energy. If you've spotted the flaw in this argument, you're not alone. Forgetting the law of conservation of energy is no small oversight. What we need is another way of studying dark energy, ideally in a lab on Earth. Today, Martin Perl at Stanford University and Holger Mueller down the road at the University of California, Berkeley, suggest just such an experiment The dark energy density might soun...