261 research outputs found
Traveling Wave Fronts and Localized Traveling Wave Convection in Binary Fluid Mixtures
Nonlinear fronts between spatially extended traveling wave convection (TW)
and quiescent fluid and spatially localized traveling waves (LTWs) are
investigated in quantitative detail in the bistable regime of binary fluid
mixtures heated from below. A finite-difference method is used to solve the
full hydrodynamic field equations in a vertical cross section of the layer
perpendicular to the convection roll axes. Results are presented for
ethanol-water parameters with several strongly negative separation ratios where
TW solutions bifurcate subcritically. Fronts and LTWs are compared with each
other and similarities and differences are elucidated. Phase propagation out of
the quiescent fluid into the convective structure entails a unique selection of
the latter while fronts and interfaces where the phase moves into the quiescent
state behave differently. Interpretations of various experimental observations
are suggested.Comment: 46 pages, 11 figures. Accepted for publication in Phys. Rev.
Friction Drag on a Particle Moving in a Nematic Liquid Crystal
The flow of a liquid crystal around a particle does not only depend on its
shape and the viscosity coefficients but also on the direction of the
molecules. We studied the resulting drag force on a sphere moving in a nematic
liquid crystal (MBBA) in a low Reynold's number approach for a fixed director
field (low Ericksen number regime) using the computational artificial
compressibility method. Taking the necessary disclination loop around the
sphere into account, the value of the drag force anisotropy
(F_\perp/F_\parallel=1.50) for an exactly computed field is in good agreement
with experiments (~1.5) done by conductivity diffusion measurements. We also
present data for weak anchoring of the molecules on the particle surface and of
trial fields, which show to be sufficiently good for most applications.
Furthermore, the behaviour of the friction close to the transition point
nematic isotropic and for a rod-like and a disc-like liquid crystal will be
given.Comment: 23 pages RevTeX, including 3 PS figures, 1 PS table and 1 PS-LaTeX
figure; Accepted for publication in Phys. Rev.
Intermittency of Height Fluctuations and Velocity Increment of The Kardar-Parisi-Zhang and Burgers Equations with infinitesimal surface tension and Viscosity in 1+1 Dimensions
The Kardar-Parisi-Zhang (KPZ) equation with infinitesimal surface tension,
dynamically develops sharply connected valley structures within which the
height derivative is not continuous. We discuss the intermittency issue in the
problem of stationary state forced KPZ equation in 1+1--dimensions. It is
proved that the moments of height increments behave as with for length scales . The length scale is the characteristic length of the
forcing term. We have checked the analytical results by direct numerical
simulation.Comment: 13 pages, 9 figure
Dependence of magnetic field generation by thermal convection on the rotation rate: a case study
Dependence of magnetic field generation on the rotation rate is explored by
direct numerical simulation of magnetohydrodynamic convective attractors in a
plane layer of conducting fluid with square periodicity cells for the Taylor
number varied from zero to 2000, for which the convective fluid motion halts
(other parameters of the system are fixed). We observe 5 types of hydrodynamic
(amagnetic) attractors: two families of two-dimensional (i.e. depending on two
spatial variables) rolls parallel to sides of periodicity boxes of different
widths and parallel to the diagonal, travelling waves and three-dimensional
"wavy" rolls. All types of attractors, except for one family of rolls, are
capable of kinematic magnetic field generation. We have found 21 distinct
nonlinear convective MHD attractors (13 steady states and 8 periodic regimes)
and identified bifurcations in which they emerge. In addition, we have observed
a family of periodic, two-frequency quasiperiodic and chaotic regimes, as well
as an incomplete Feigenbaum period doubling sequence of bifurcations of a torus
followed by a chaotic regime and subsequently by a torus with 1/3 of the
cascade frequency. The system is highly symmetric. We have found two novel
global bifurcations reminiscent of the SNIC bifurcation, which are only
possible in the presence of symmetries. The universally accepted paradigm,
whereby an increase of the rotation rate below a certain level is beneficial
for magnetic field generation, while a further increase inhibits it (and halts
the motion of fluid on continuing the increase) remains unaltered, but we
demonstrate that this "large-scale" picture lacks many significant details.Comment: 39 pp., 22 figures (some are low quality), 5 tables. Accepted in
Physica
Validation and data characteristics of methane and nitrous oxide profiles observed by MIPAS and processed with Version 4.61 algorithm
The ENVISAT validation programme for the atmospheric instruments MIPAS, SCIAMACHY and GOMOS is based on a number of balloon-borne, aircraft, satellite and ground-based correlative measurements. In particular the activities of validation scientists were coordinated by ESA within the ENVISAT Stratospheric Aircraft and Balloon Campaign or ESABC. As part of a series of similar papers on other species [this issue] and in parallel to the contribution of the individual validation teams, the present paper provides a synthesis of comparisons performed between MIPAS CH4 and N2O profiles produced by the current ESA operational software (Instrument Processing Facility version 4.61 or IPF v4.61, full resolution MIPAS data covering the period 9 July 2002 to 26 March 2004) and correlative measurements obtained from balloon and aircraft experiments as well as from satellite sensors or from ground-based instruments. In the middle stratosphere, no significant bias is observed between MIPAS and correlative measurements, and MIPAS is providing a very consistent and global picture of the distribution of CH4 and N2O in this region. In average, the MIPAS CH4 values show a small positive bias in the lower stratosphere of about 5%. A similar situation is observed for N2O with a positive bias of 4%. In the lower stratosphere/upper troposphere (UT/LS) the individual used MIPAS data version 4.61 still exhibits some unphysical oscillations in individual CH4 and N2O profiles caused by the processing algorithm (with almost no regularization). Taking these problems into account, the MIPAS CH4 and N2O profiles are behaving as expected from the internal error estimation of IPF v4.61 and the estimated errors of the correlative measurements
Nonequilibrium effects in DNA microarrays: a multiplatform study
It has recently been shown that in some DNA microarrays the time needed to
reach thermal equilibrium may largely exceed the typical experimental time,
which is about 15h in standard protocols (Hooyberghs et al. Phys. Rev. E 81,
012901 (2010)). In this paper we discuss how this breakdown of thermodynamic
equilibrium could be detected in microarray experiments without resorting to
real time hybridization data, which are difficult to implement in standard
experimental conditions. The method is based on the analysis of the
distribution of fluorescence intensities I from different spots for probes
carrying base mismatches. In thermal equilibrium and at sufficiently low
concentrations, log I is expected to be linearly related to the hybridization
free energy with a slope equal to , where is
the experimental temperature and R is the gas constant. The breakdown of
equilibrium results in the deviation from this law. A model for hybridization
kinetics explaining the observed experimental behavior is discussed, the
so-called 3-state model. It predicts that deviations from equilibrium yield a
proportionality of to . Here, is an
effective temperature, higher than the experimental one. This behavior is
indeed observed in some experiments on Agilent arrays. We analyze experimental
data from two other microarray platforms and discuss, on the basis of the
results, the attainment of equilibrium in these cases. Interestingly, the same
3-state model predicts a (dynamical) saturation of the signal at values below
the expected one at equilibrium.Comment: 27 pages, 9 figures, 1 tabl
Viscous-Inviscid Interactions in a Boundary-Layer Flow Induced by a Vortex Array
In this paper we investigate the asymptotic validity of boundary layer
theory. For a flow induced by a periodic row of point-vortices, we compare
Prandtl's solution to Navier-Stokes solutions at different numbers. We
show how Prandtl's solution develops a finite time separation singularity. On
the other hand Navier-Stokes solution is characterized by the presence of two
kinds of viscous-inviscid interactions between the boundary layer and the outer
flow. These interactions can be detected by the analysis of the enstrophy and
of the pressure gradient on the wall. Moreover we apply the complex singularity
tracking method to Prandtl and Navier-Stokes solutions and analyze the previous
interactions from a different perspective
Sedimentation and Flow Through Porous Media: Simulating Dynamically Coupled Discrete and Continuum Phases
We describe a method to address efficiently problems of two-phase flow in the
regime of low particle Reynolds number and negligible Brownian motion. One of
the phases is an incompressible continuous fluid and the other a discrete
particulate phase which we simulate by following the motion of single
particles. Interactions between the phases are taken into account using locally
defined drag forces. We apply our method to the problem of flow through random
media at high porosity where we find good agreement to theoretical expectations
for the functional dependence of the pressure drop on the solid volume
fraction. We undertake further validations on systems undergoing gravity
induced sedimentation.Comment: 22 pages REVTEX, figures separately in uudecoded, compressed
postscript format - alternatively e-mail '[email protected]' for
hardcopies
TIMASSS: The IRAS16293-2422 Millimeter And Submillimeter Spectral Survey. I. Observations, calibration and analysis of the line kinematics
While unbiased surveys observable from ground-based telescopes have
previously been obtained towards several high mass protostars, very little
exists on low mass protostars. To fill up this gap, we carried out a complete
spectral survey of the bands at 3, 2, 1 and 0.8 mm towards the solar type
protostar IRAS16293-2422. The observations covered about 200\,GHz and were
obtained with the IRAM-30m and JCMT-15m telescopes. Particular attention was
devoted to the inter-calibration of the obtained spectra with previous
observations. All the lines detected with more than 3 sigma and free from
obvious blending effects were fitted with Gaussians to estimate their basic
kinematic properties. More than 4000 lines were detected (with sigma \geq 3)
and identified, yielding a line density of approximatively 20 lines per GHz,
comparable to previous surveys in massive hot cores. The vast majority (~2/3)
of the lines are weak and due to complex organic molecules. The analysis of the
profiles of more than 1000 lines belonging 70 species firmly establishes the
presence of two distinct velocity components, associated with the two objects,
A and B, forming the IRAS16293-2422 binary system. In the source A, the line
widths of several species increase with the upper level energy of the
transition, a behavior compatible with gas infalling towards a ~1 Mo object.
The source B, which does not show this effect, might have a much lower central
mass of ~0.1 Mo. The difference in the rest velocities of both objects is
consistent with the hypothesis that the source B rotates around the source A.
This spectral survey, although obtained with single-dish telescope with a low
spatial resolution, allows to separate the emission from 2 different
components, thanks to the large number of lines detected. The data of the
survey are public and can be retrieved on the web site
http://www-laog.obs.ujf-grenoble.fr/heberges/timasss.Comment: 41 pages (26 pages of online Tables), 7 Tables and 6 Figure
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