7,550 research outputs found
Contact line stability of ridges and drops
Within the framework of a semi-microscopic interface displacement model we
analyze the linear stability of sessile ridges and drops of a non-volatile
liquid on a homogeneous, partially wet substrate, for both signs and arbitrary
amplitudes of the three-phase contact line tension. Focusing on perturbations
which correspond to deformations of the three-phase contact line, we find that
drops are generally stable while ridges are subject only to the long-wavelength
Rayleigh-Plateau instability leading to a breakup into droplets, in contrast to
the predictions of capillary models which take line tension into account. We
argue that the short-wavelength instabilities predicted within the framework of
the latter macroscopic capillary theory occur outside its range of validity and
thus are spurious.Comment: 6 pages, 1 figur
The Generation of Fullerenes
We describe an efficient new algorithm for the generation of fullerenes. Our
implementation of this algorithm is more than 3.5 times faster than the
previously fastest generator for fullerenes -- fullgen -- and the first program
since fullgen to be useful for more than 100 vertices. We also note a
programming error in fullgen that caused problems for 136 or more vertices. We
tabulate the numbers of fullerenes and IPR fullerenes up to 400 vertices. We
also check up to 316 vertices a conjecture of Barnette that cubic planar graphs
with maximum face size 6 are hamiltonian and verify that the smallest
counterexample to the spiral conjecture has 380 vertices.Comment: 21 pages; added a not
Arrest stress of uniformly sheared wet granular matter
We conduct extensive independent numerical experiments considering
frictionless disks without internal degrees of freedom (rotation etc.) in two
dimensions. We report here that for a large range of the packing fractions
below random-close packing, all components of the stress tensor of wet granular
materials remain finite in the limit of zero shear rate. This is direct
evidence for a fluid-to-solid arrest transition. The offset value of the shear
stress characterizes plastic deformation of the arrested state {which
corresponds to {\em dynamic yield stress} of the system}. {Based on an
analytical line of argument, we propose that the mean number of capillary
bridges per particle, , follows a non-trivial dependence on the packing
fraction, , and the capillary energy, \vareps. Most noticeably, we show
that is a generic and universal quantity which does not depend on the
driving protocol.} Using this universal quantity, we calculate the arrest
stress, , analytically based on a balance of the energy injection
rate due to the external force driving the flow and the dissipation rate
accounting for the rupture of capillary bridges. The resulting prediction of
is a non-linear function of the packing fraction , and the
capillary energy \vareps. This formula provides an excellent, parameter-free
prediction of the numerical data. Corrections to the theory for small and large
packing fractions are connected to the emergence of shear bands and of
contributions to the stress from repulsive particle interactions, respectively.Comment: 7 pages, g figure
Halos around edge-on disk galaxies in the SDSS
We present a statistical analysis of halo emission for a sample of 1047
edge-on disk galaxies imaged in five bands by the Sloan Digital Sky Survey
(SDSS). Stacking the homogeneously rescaled images of the galaxies, we can
measure surface brightnesses as deep as mu_r~31 mag/arcsec^2. The results
strongly support the almost ubiquitous presence of stellar halos around disk
galaxies, whose spatial distribution is well described by a power-law
, in a moderately flattened spheroid (c/a~0.6). The colour
estimates in g-r and r-i, although uncertain, give a clear indication for
extremely red stellar populations, hinting at old ages and/or non-negligible
metal enrichment. These results support the idea of halos being assembled via
early merging of satellite galaxies.Comment: 15 pages, 9 figures. Accepted for publication on MNRAS. Version with
full resolution images available at
http://www.mpa-garching.mpg.de/~zibetti/papers/halos_edgeon.pd
Detection of large scale intrinsic ellipticity-density correlation from the Sloan Digital Sky Survey and implications for weak lensing surveys
The power spectrum of weak lensing shear caused by large-scale structure is
an emerging tool for precision cosmology, in particular for measuring the
effects of dark energy on the growth of structure at low redshift. One
potential source of systematic error is intrinsic alignments of ellipticities
of neighbouring galaxies (II correlation) that could mimic the correlations due
to lensing. A related possibility pointed out by Hirata and Seljak (2004) is
correlation between the intrinsic ellipticities of galaxies and the density
field responsible for gravitational lensing shear (GI correlation). We present
constraints on both the II and GI correlations using 265 908 spectroscopic
galaxies from the SDSS, and using galaxies as tracers of the mass in the case
of the GI analysis. The availability of redshifts in the SDSS allows us to
select galaxies at small radial separations, which both reduces noise in the
intrinsic alignment measurement and suppresses galaxy- galaxy lensing (which
otherwise swamps the GI correlation). While we find no detection of the II
correlation, our results are nonetheless statistically consistent with recent
detections found using the SuperCOSMOS survey. In contrast, we have a clear
detection of GI correlation in galaxies brighter than L* that persists to the
largest scales probed (60 Mpc/h) and with a sign predicted by theoretical
models. This correlation could cause the existing lensing surveys at z~1 to
underestimate the linear amplitude of fluctuations by as much as 20% depending
on the source sample used, while for surveys at z~0.5 the underestimation may
reach 30%. (Abridged.)Comment: 16 pages, matches version published in MNRAS (only minor changes in
presentation from original version
How Saturated are Absorption Lines in the Broad Absorption Line Quasar PG 1411+442 ?
Recently, convincing evidence was found for extremely large X-ray absorption
by column densities in broad absorption line quasars. One
consequence of this is that any soft X-ray emission from these QSOs would be
the scattered light or leaked light from partially covering absorbing material.
A detection of the unabsorbed soft X-ray and absorbed hard X-ray compo nent
will allow to determine the total column density as well as the effective
covering factor of the absorbing material, which can be hardly obtained from
the UV absorption lines. Brinkmann et al. (1999) showed that both the
unabsorbed and absorbed components are detected in the nearby very bright broad
absorption line quasar PG 1411+442. In this letter, we make a further analysis
of the broad band X-ray spectrum and the UV spectrum from HST, and demonstrate
that broad absorption lines are completely saturated at the bottom of
absorption troughs.Comment: 6 pages, 3 postscript figures. to appear in Astrophy. J. Letter
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