2,321 research outputs found
Power spectrum of mass and activity fluctuations in a sandpile
We consider a directed abelian sandpile on a strip of size ,
driven by adding a grain randomly at the left boundary after every
time-steps. We establish the exact equivalence of the problem of mass
fluctuations in the steady state and the number of zeroes in the ternary-base
representation of the position of a random walker on a ring of size . We
find that while the fluctuations of mass have a power spectrum that varies as
for frequencies in the range , the activity
fluctuations in the same frequency range have a power spectrum that is linear
in .Comment: 8 pages, 10 figure
Stability of Coalescence Hidden variable Fractal Interpolation Surfaces
In the present paper, the stability of Coalescence Hidden variable Fractal
Interpolation Surfaces(CHFIS) is established. The estimates on error in
approximation of the data generating function by CHFIS are found when there is
a perturbation in independent, dependent and hidden variables. It is proved
that any small perturbation in any of the variables of generalized
interpolation data results in only small perturbation of CHFIS. Our results are
likely to be useful in investigations of texture of surfaces arising from the
simulation of surfaces of rocks, sea surfaces, clouds and similar natural
objects wherein the generating function depends on more than one variable
Limits on the time variation of the electromagnetic fine-structure constant in the low energy limit from absorption lines in the spectra of distant quasars
Most of the successful physical theories rely on the constancy of few
fundamental quantities (such as the speed of light, , the fine-structure
constant, \alpha, the proton to electron mass ratio, \mu, etc), and
constraining the possible time variations of these fundamental quantities is an
important step toward a complete physical theory. Time variation of \alpha can
be accurately probed using absorption lines seen in the spectra of distant
quasars. Here, we present the results of a detailed many-multiplet analysis
performed on a new sample of Mg II systems observed in high quality quasar
spectra obtained using the Very Large Telescope. The weighted mean value of the
variation in \alpha derived from our analysis over the redshift range 0.4<z<2.3
is \Delta\alpha/\alpha = (-0.06+/-0.06) x 10^{-5}. The median redshift of our
sample (z=1.55) corresponds to a look-back time of 9.7 Gyr in the most favored
cosmological model today. This gives a 3\sigma limit, -2.5 x 10^{-16} yr^-1
<(\Delta\alpha/\alpha\Delta t) <+1.2x10^{-16} yr^-1, for the time variation of
\alpha, that forms the strongest constraint obtained based on high redshift
quasar absorption line systems.Comment: uses revtex, 4 pages 3 figures. Accepted for publication in Physical
Review Letter
Kinesin Light Chains Are Essential for Axonal Transport in Drosophila
Kinesin is a heterotetramer composed of two 115-kD heavy chains and two 58-kD light chains. The microtubule motor activity of kinesin is performed by the heavy chains, but the functions of the light chains are poorly understood. Mutations were generated in the Drosophila gene Kinesin light chain (Klc), and the phenotypic consequences of loss of Klc function were analyzed at the behavioral and cellular levels. Loss of Klc function results in progressive lethargy, crawling defects, and paralysis followed by death at the end of the second larval instar. Klc mutant axons contain large aggregates of membranous organelles in segmental nerve axons. These aggregates, or organelle jams (Hurd, D.D., and W.M. Saxton. 1996. Genetics. 144: 1075-1085), contain synaptic vesicle precursors as well as organelles that may be transported by kinesin, kinesin-like protein 68D, and cytoplasmic dynein, thus providing evidence that the loss of Klc function blocks multiple pathways of axonal transport. The similarity of the Klc and Khc ((Saxton et al. Cell 64:1093-1102; Hurd, D.D., and W.M. Saxton. 1996. Genetics 144: 1075-1085) mutant phenotypes indicates that KLC is essential for kinesin function, perhaps by tethering KHC to intracellular cargos or by activating the kinesin motor
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