16,330 research outputs found
Dynamical density functional theory with hydrodynamic interactions and colloids in unstable traps
A density functional theory for colloidal dynamics is presented which
includes hydrodynamic interactions between the colloidal particles. The theory
is applied to the dynamics of colloidal particles in an optical trap which
switches periodically in time from a stable to unstable confining potential. In
the absence of hydrodynamic interactions, the resulting density breathing mode,
exhibits huge oscillations in the trap center which are almost completely
damped by hydrodynamic interactions. The predicted dynamical density fields are
in good agreement with Brownian dynamics computer simulations
Experimental investigation of cut-off phenomena in non-linear photonic crystal fibers
The modal cut-off is investigated experimentally in a series of high quality
non-linear photonic crystal fibers. We demonstrate a suitable measurement
technique to determine the cut-off wavelength and verify it by inspecting the
near field of the modes that may be excited below and above the cut-off. We
observe a double peak structure in the cut-off spectra, which is attributed to
a splitting of the higher order modes. The cut-off is measured for seven
different fiber geometries with different pitches and relative hole size, and a
very good agreement with recent theoretical work is found.Comment: 3 pages including 1 table and 4 figures. Accepted for Optics Letter
Symmetry of the CMB sky as a new test of its statistical isotropy. Non Cosmological Octupole?
In this article we propose a novel test for statistical anisotropy of the
CMB. The test is based on the fact, that the Galactic foregrounds have a
remarcably strong symmetry with respect to their antipodal points and with
respect to the Galactic plane, while the cosmological signal should not be
symmetric or asymmetric under these transitions. We have applied the test for
the octupole component of the WMAP ILC 7 map, by looking at a_3,1 and a_3,3,
and their ratio to a_3,2 both for real and imaginary values. We find abnormal
symmetry of the octupole component at the level of 0.58%, compared to Monte
Carlo simulations. By using the analysis of the phases of the octupole we found
remarkably strong cross-correlations between the phases of kinematic dipole and
ILC 7 octupole, in full agreement with previous results. We further test the
multipole range 2<l<100, by investigating the ratio between the l+m=even and
l+m=odd parts of power spectra. We compare the results to simulations of a
Gaussian random sky, and find significant departure from the statistically
isotropic and homogeneous case, for a very broad range of multipoles. We found
that for the most prominent peaks of our estimator, the phases of the
corresponding harmonics are coherent with phases of the octupole. We believe,
our test would be very useful for detections of various types of residuals of
the foreground and systematic effects at very a broad range of multipoles 2 < l
< 1500-3000 for the forthcoming PLANCK CMB map, before any conclusions about
primordial non-Gaussianity and statistical anisotropy of the CMB.Comment: Slight modifications, based on proofread version from JCAP. 17 pages,
9 figures, 3 table
Density profiles of a colloidal liquid at a wall under shear flow
Using a dynamical density functional theory we analyze the density profile of
a colloidal liquid near a wall under shear flow. Due to the symmetries of the
system considered, the naive application of dynamical density functional theory
does not lead to a shear induced modification of the equilibrium density
profile, which would be expected on physical grounds. By introducing a
physically motivated dynamic mean field correction we incorporate the missing
shear induced interparticle forces into the theory. We find that the shear flow
tends to enhance the oscillations in the density profile of hard-spheres at a
hard-wall and, at sufficiently high shear rates, induces a nonequilibrium
transition to a steady state characterized by planes of particles parallel to
the wall. Under gravity, we find that the center-of-mass of the density
distribution increases with shear rate, i.e., shear increases the potential
energy of the particles
Pearson's random walk in the space of the CMB phases: evidence for parity asymmetry
The temperature fluctuations of the Cosmic Microwave Background (CMB) are
supposed to be distributed randomly in both magnitude and phase, following to
the simplest model of inflation. In this paper, we look at the odd and even
multipoles of the spherical harmonic decomposition of the CMB, and the
different characteristics of these, giving rise to a parity asymmetry. We
compare the even and odd multipoles in the CMB power spectrum, and also the
even and odd mean angles. We find for the multipoles of the power spectrum,
that there is power excess in odd multipoles, compared to even ones, meaning
that we have a parity asymmetry. Further, for the phases, we present a random
walk for the mean angles, and find a significant separation for even/odd mean
angles, especially so for galactic coordinates. This is further tested and
confirmed with a directional parity test, comparing the parity asymmetry in
galactic and ecliptic coordinates.Comment: Accepted for publication in Phys. Rev. D, 10 pages, 10 figures, 1
table. Some typographical errors corrected, and further references adde
First-order virial expansion of short-time diffusion and sedimentation coefficients of permeable particles suspensions
For suspensions of permeable particles, the short-time translational and
rotational self-diffusion coefficients, and collective diffusion and
sedimentation coefficients are evaluated theoretically. An individual particle
is modeled as a uniformly permeable sphere of a given permeability, with the
internal solvent flow described by the Debye-Bueche-Brinkman equation. The
particles are assumed to interact non-hydrodynamically by their excluded
volumes. The virial expansion of the transport properties in powers of the
volume fraction is performed up to the two-particle level. The first-order
virial coefficients corresponding to two-body hydrodynamic interactions are
evaluated with very high accuracy by the series expansion in inverse powers of
the inter-particle distance. Results are obtained and discussed for a wide
range of the ratio, x, of the particle radius to the hydrodynamic screening
length inside a permeable sphere. It is shown that for x >= 10, the virial
coefficients of the transport properties are well-approximated by the
hydrodynamic radius (annulus) model developed by us earlier for the effective
viscosity of porous-particle suspensions
Morphology of High-Multiplicity Events in Heavy Ion Collisions
We discuss opportunities that may arise from subjecting high-multiplicity
events in relativistic heavy ion collisions to an analysis similar to the one
used in cosmology for the study of fluctuations of the Cosmic Microwave
Background (CMB). To this end, we discuss examples of how pertinent features of
heavy ion collisions including global characteristics, signatures of collective
flow and event-wise fluctuations are visually represented in a Mollweide
projection commonly used in CMB analysis, and how they are statistically
analyzed in an expansion over spherical harmonic functions. If applied to the
characterization of purely azimuthal dependent phenomena such as collective
flow, the expansion coefficients of spherical harmonics are seen to contain
redundancies compared to the set of harmonic flow coefficients commonly used in
heavy ion collisions. Our exploratory study indicates, however, that these
redundancies may offer novel opportunities for a detailed characterization of
those event-wise fluctuations that remain after subtraction of the dominant
collective flow signatures. By construction, the proposed approach allows also
for the characterization of more complex collective phenomena like higher-order
flow and other sources of fluctuations, and it may be extended to the
characterization of phenomena of non-collective origin such as jets.Comment: Matches version accepted for publication in Physical Review C. 13
pages, 9 figure
Statistically derived contributions of diverse human influences to twentieth-century temperature changes
The warming of the climate system is unequivocal as evidenced by an increase in global temperatures by 0.8 °C over the past century. However, the attribution of the observed warming to human activities remains less clear, particularly because of the apparent slow-down in warming since the late 1990s. Here we analyse radiative forcing and temperature time series with state-of-the-art statistical methods to address this question without climate model simulations. We show that long-term trends in total radiative forcing and temperatures have largely been determined by atmospheric greenhouse gas concentrations, and modulated by other radiative factors. We identify a pronounced increase in the growth rates of both temperatures and radiative forcing around 1960, which marks the onset of sustained global warming. Our analyses also reveal a contribution of human interventions to two periods when global warming slowed down. Our statistical analysis suggests that the reduction in the emissions of ozone-depleting substances under the Montreal Protocol, as well as a reduction in methane emissions, contributed to the lower rate of warming since the 1990s. Furthermore, we identify a contribution from the two world wars and the Great Depression to the documented cooling in the mid-twentieth century, through lower carbon dioxide emissions. We conclude that reductions in greenhouse gas emissions are effective in slowing the rate of warming in the short term.F.E. acknowledges financial support from the Consejo Nacional de Ciencia y Tecnologia (http://www.conacyt.gob.mx) under grant CONACYT-310026, as well as from PASPA DGAPA of the Universidad Nacional Autonoma de Mexico. (CONACYT-310026 - Consejo Nacional de Ciencia y Tecnologia; PASPA DGAPA of the Universidad Nacional Autonoma de Mexico
New constraints on Parity Symmetry from a re-analysis of the WMAP-7 low resolution power spectra
The Parity symmetry of the Cosmic Microwave Background (CMB) pattern as seen
by WMAP 7 is tested jointly in temperature and polarization at large angular
scale. A Quadratic Maximum Likelihood (QML) estimator is applied to the WMAP 7
year low resolution maps to compute all polarized CMB angular power spectra.
The analysis is supported by 10000 realistic Monte-Carlo realizations. We
confirm the previously reported Parity anomaly for TT in the range at C.L.. No anomalies have been detected in TT for a
wider range (up to ). No violations have been found for
EE, TE and BB which we test here for the first time. The cross-spectra TB and
EB are found to be consistent with zero. We also forecast {\sc Planck}
capabilities in probing Parity violations on low resolution maps.Comment: 8 pages, 6 figures, 4 tables. Accepted for publication in MNRA
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