989 research outputs found
Macroscopic amplification of electroweak effects in molecular Bose-Einstein condensates
We investigate the possible use of Bose-Einstein condensates of diatomic
molecules to measure nuclear spin-dependent parity violation effects, outlining
a detection method based on the internal Josephson effect between molecular
states of opposite parity. When applied to molecular condensates, the fine
experimental control achieved in atomic bosonic Josephson junctions could
provide data on anapole moments and neutral weak couplings.Comment: 5 pages. To be published Phys. Rev. A (Rapid Communication) (2012
Where are the Walls?
The reported spatial variation in the fine-structure constant at high
redshift, if physical, could be due to the presence of dilatonic domains, and
one or more domain walls inside our horizon. An absorption spectrum of an
object in a different domain from our own would be characterized by a different
value of alpha. We show that while a single wall solution is statically
comparable to a dipole fit, and is a big improvement over a weighted mean
(despite adding 3 parameters), a two-wall solution is a far better fit (despite
adding 3 parameters over the single wall solution). We derive a simple model
accounting for the two-domain wall solution. The goodness of these fits is
however dependent on the extra random error which was argued to account for the
large scatter in most of the data. When this error is omitted, all the above
solutions are poor fits to the data. When included, the solutions that exhibit
a spatial dependence agree with the data much more significantly than the
Standard Model; however, the Standard Model itself is not a terrible fit to the
data, having a p-value of ~ 20 %
Nonlinear dynamos at infinite magnetic Prandtl number
The dynamo instability is investigated in the limit of infinite magnetic
Prandtl number. In this limit the fluid is assumed to be very viscous so that
the inertial terms can be neglected and the flow is slaved to the forcing. The
forcing consist of an external forcing function that drives the dynamo flow and
the resulting Lorentz force caused by the back reaction of the magnetic field.
The flows under investigation are the Archontis flow, and the ABC flow forced
at two different scales. The investigation covers roughly three orders of
magnitude of the magnetic Reynolds number above onset. All flows show a weak
increase of the averaged magnetic energy as the magnetic Reynolds number is
increased. Most of the magnetic energy is concentrated in flat elongated
structures that produce a Lorentz force with small solenoidal projection so
that the resulting magnetic field configuration was almost force-free. Although
the examined system has zero kinetic Reynolds number at sufficiently large
magnetic Reynolds number the structures are unstable to small scale
fluctuations that result in a chaotic temporal behavior
Protein and DNA sequence determinants of thermophilic adaptation
Prokaryotes living at extreme environmental temperatures exhibit pronounced
signatures in the amino acid composition of their proteins and nucleotide
compositions of their genomes reflective of adaptation to their thermal
environments. However, despite significant efforts, the definitive answer of
what are the genomic and proteomic compositional determinants of Optimal Growth
Temperature of prokaryotic organisms remained elusive. Here the authors
performed a comprehensive analysis of amino acid and nucleotide compositional
signatures of thermophylic adaptation by exhaustively evaluating all
combinations of amino acids and nucleotides as possible determinants of Optimal
Growth Temperature for all prokaryotic organisms with fully sequences genomes..
The authors discovered that total concentration of seven amino acids in
proteomes, IVYWREL, serves as a universal proteomic predictor of Optimal Growth
Temperature in prokaryotes. Resolving the old-standing controversy the authors
determined that the variation in nucleotide composition (increase of purine
load, or A+G content with temperature) is largely a consequence of thermal
adaptation of proteins. However, the frequency with which A and G nucleotides
appear as nearest neighbors in genome sequences is strongly and independently
correlated with Optimal Growth Temperature. as a result of codon bias in
corresponding genomes. Together these results provide a complete picture of
proteomic and genomic determinants of thermophilic adaptation.Comment: in press PLoS Computational Biology; revised versio
Compact Waves in Microscopic Nonlinear Diffusion
We analyze the spread of a localized peak of energy into vacuum for nonlinear
diffusive processes. In contrast with standard diffusion, the nonlinearity
results in a compact wave with a sharp front separating the perturbed region
from vacuum. In spatial dimensions, the front advances as
according to hydrodynamics, with the nonlinearity exponent. We show that
fluctuations in the front position grow as , where
is a new exponent that we measure and is a random
variable whose distribution we characterize. Fluctuating corrections to
hydrodynamic profiles give rise to an excess penetration into vacuum, revealing
scaling behaviors and robust features. We also examine the discharge of a
nonlinear rarefaction wave into vacuum. Our results suggest the existence of
universal scaling behaviors at the fluctuating level in nonlinear diffusion.Comment: 5 pages, 4 figure
Formation of the First Supermassive Black Holes
We consider the physical conditions under which supermassive black holes
could have formed inside the first galaxies. Our SPH simulations indicate that
metal-free galaxies with a virial temperature ~10^4 K and with suppressed H2
formation (due to an intergalactic UV background) tend to form a binary black
hole system which contains a substantial fraction (>10%) of the total baryonic
mass of the host galaxy. Fragmentation into stars is suppressed without
substantial H2 cooling. Our simulations follow the condensation of ~5x10^6
M_sun around the two centers of the binary down to a scale of < 0.1pc. Low-spin
galaxies form a single black hole instead. These early black holes lead to
quasar activity before the epoch of reionization. Primordial black hole
binaries lead to the emission of gravitational radiation at redshifts z>10 that
would be detectable by LISA.Comment: 11 pages, 9 figures, revised version, ApJ in press (October 10, 2003
- …