706 research outputs found
Effective interactions and equilibrium configurations of colloidal particles on a sessile droplet
We study the free energy landscapes of a pair of submicron spherical
particles floating at the surface of a sessile droplet. The particles are
subjected to radial external forces resulting in a deformation of the droplet
shape relative to the reference shape of a spherical cap. This deformation
leads to tangential forces on the particles. For small deformations and for the
contact angle at the substrate being equal to , the
corresponding linearized Young-Laplace equation is solved analytically. The
solution is constructed by employing the method of images from electrostatics,
where each of the particles plays the role of a capillary monopole and the
substrate is replaced by a virtual drop with image charges and by imposing the
conditions of fixed droplet volume and vanishing total force on the droplet.
The substrate boundary conditions determine the signs of the image capillary
charges and therefore also the strength of the tangential forces on the
particles. In the cases of an arbitrary contact angle these forces
are calculated numerically by employing a finite element method to find the
equilibrium shape of the droplet for those configurations in which the
particles are close to the local free energy minima.Comment: 23 pages, 8 figure
The short-time self-diffusion coefficient of a sphere in a suspension of rigid rods
The short--time self diffusion coefficient of a sphere in a suspension of
rigid rods is calculated in first order in the rod volume fraction. For low rod
concentrations the correction to the Einstein diffusion constant of the sphere
is a linear function of the rod volume fraction with the slope proportional to
the equilibrium averaged mobility diminution trace of the sphere interacting
with a single freely translating and rotating rod. The two--body hydrodynamic
interactions are calculated using the so--called bead model in which the rod is
replaced by a stiff linear chain of touching spheres. The interactions between
spheres are calculated numerically using the multipole method. Also an
analytical expression for the diffusion coefficient as a function of the rod
aspect ratio is derived in the limit of very long rods. We show that in this
limit the correction to the Einstein diffusion constant does not depend on the
size of the tracer sphere. The higher order corrections depending on the
applied model are computed numerically. An approximate expression is provided,
valid for a wide range of aspect ratios.Comment: 11 pages, 6 figure
Capillary interactions in Pickering emulsions
The effective capillary interaction potentials for small colloidal particles
trapped at the surface of liquid droplets are calculated analytically. Pair
potentials between capillary monopoles and dipoles, corresponding to particles
floating on a droplet with a fixed center of mass and subjected to external
forces and torques, respectively, exhibit a repulsion at large angular
separations and an attraction at smaller separations, with the latter
resembling the typical behavior for flat interfaces. This change of character
is not observed for quadrupoles, corresponding to free particles on a
mechanically isolated droplet. The analytical results for quadrupoles are
compared with the numerical minimization of the surface free energy of the
droplet in the presence of ellipsoidal particles.Comment: twocolumn, 8 pages, 3 figures, submitted to Phys. Rev.
Direct comparison of sterile neutrino constraints from cosmological data, <i>ν</i><sub><i>e</i></sub> disappearance data and <i>ν</i><sub><i>μ</i></sub>→ <i>ν</i><sub><i>e</i></sub> appearance data in a 3+1 model
Direct comparison of sterile neutrino constraints from cosmological data, disappearance data and appearance data in a model
We present a quantitative, direct comparison of constraints on sterile
neutrinos derived from neutrino oscillation experiments and from Planck data,
interpreted assuming standard cosmological evolution. We extend a model,
which is used to compare exclusions contours at the 95% CL derived from Planck
data to those from -disappearance measurements, to a model. This
allows us to compare the Planck constraints with those obtained through
appearance searches, which are sensitive to more
than one active-sterile mixing angle. We find that the cosmological data fully
exclude the allowed regions published by the LSND, MiniBooNE and Neutrino-4
collaborations, and those from the gallium and rector anomalies, at the 95% CL.
Compared to the exclusion regions from the Daya Bay -disappearance
search, the Planck data are more strongly excluding above and
, with the Daya Bay
exclusion being stronger below these values. Compared to the combined Daya
Bay/Bugey/MINOS exclusion region on appearance,
the Planck data is more strongly excluding above , with the exclusion strengths of the Planck
data and the Daya Bay/Bugey/MINOS combination becoming comparable below this
value.Comment: 9 pages, 4 figures, accepted by Eur. Phys. J.
Free energy of colloidal particles at the surface of sessile drops
The influence of finite system size on the free energy of a spherical
particle floating at the surface of a sessile droplet is studied both
analytically and numerically. In the special case that the contact angle at the
substrate equals a capillary analogue of the method of images is
applied in order to calculate small deformations of the droplet shape if an
external force is applied to the particle. The type of boundary conditions for
the droplet shape at the substrate determines the sign of the capillary
monopole associated with the image particle. Therefore, the free energy of the
particle, which is proportional to the interaction energy of the original
particle with its image, can be of either sign, too. The analytic solutions,
given by the Green's function of the capillary equation, are constructed such
that the condition of the forces acting on the droplet being balanced and of
the volume constraint are fulfilled. Besides the known phenomena of attraction
of a particle to a free contact line and repulsion from a pinned one, we
observe a local free energy minimum for the particle being located at the drop
apex or at an intermediate angle, respectively. This peculiarity can be traced
back to a non-monotonic behavior of the Green's function, which reflects the
interplay between the deformations of the droplet shape and the volume
constraint.Comment: 24 pages, 19 figure
Measurement of inclusive charged current interactions on carbon in a few-GeV neutrino beam
The SciBooNE Collaboration reports a measurement of inclusive charged current
interactions of muon neutrinos on carbon with an average energy of 0.8 GeV
using the Fermilab Booster Neutrino Beam. We compare our measurement with two
neutrino interaction simulations: NEUT and NUANCE. The charged current
interaction rates (product of flux and cross section) are extracted by fitting
the muon kinematics, with a precision of 6-15% for the energy dependent and 3%
for the energy integrated analyses. We also extract CC inclusive interaction
cross sections from the observed rates, with a precision of 10-30% for the
energy dependent and 8% for the energy integrated analyses. This is the first
measurement of the CC inclusive cross section on carbon around 1 GeV. These
results can be used to convert previous SciBooNE cross section ratio
measurements to absolute cross section values.Comment: 21 pages, 16 figures. Accepted by Phys. Rev. D. Minor revisions to
match the accepted versio
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