8,765 research outputs found
Colloidal hard-rod fluids near geometrically structured substrates
Density functional theory is used to study colloidal hard-rod fluids near an
individual right-angled wedge or edge as well as near a hard wall which is
periodically patterned with rectangular barriers. The Zwanzig model, in which
the orientations of the rods are restricted to three orthogonal orientations
but their positions can vary continuously, is analyzed by numerical
minimization of the grand potential. Density and orientational order profiles,
excess adsorptions, as well as surface and line tensions are determined. The
calculations exhibit an enrichment [depletion] of rods lying parallel and close
to the corner of the wedge [edge]. For the fluid near the geometrically
patterned wall, complete wetting of the wall -- isotropic liquid interface by a
nematic film occurs as a two-stage process in which first the nematic phase
fills the space between the barriers until an almost planar isotropic --
nematic liquid interface has formed separating the higher-density nematic fluid
in the space between the barriers from the lower-density isotropic bulk fluid.
In the second stage a nematic film of diverging film thickness develops upon
approaching bulk isotropic -- nematic coexistence.Comment: 9 pages, 9 figure
High Redshift Quasars and Star Formation in the Early Universe
In order to derive information on the star formation history in the early
universe we observed 6 high-redshift (z=3.4) quasars in the near-infrared to
measure the relative iron and \mgii emission strengths. A detailed comparison
of the resulting spectra with those of low-redshift quasars show essentially
the same FeII/MgII emission ratios and very similar continuum and line spectral
properties, indicating a lack of evolution of the relative iron to magnesium
abundance of the gas since z=3.4 in bright quasars. On the basis of current
chemical evolution scenarios of galaxies, where magnesium is produced in
massive stars ending in type II SNe, while iron is formed predominantly in SNe
of type Ia with a delay of ~1 Gyr and assuming as cosmological parameters H_o =
72 km/s Mpc, Omega_M = 0.3, and Omega_Lambda = 0.7$, we conclude that major
star formation activity in the host galaxies of our z=3.4 quasars must have
started already at an epoch corresponding to z_f ~= 10, when the age of the
universe was less than 0.5 Gyrs.Comment: 29 pages, 5 figures, ApJ in pres
Magnetization and susceptibility of ferrofluids
A second-order Taylor series expansion of the free energy functional provides
analytical expressions for the magnetic field dependence of the free energy and
of the magnetization of ferrofluids, here modelled by dipolar Yukawa
interaction potentials. The corresponding hard core dipolar Yukawa reference
fluid is studied within the framework of the mean spherical approximation. Our
findings for the magnetic and phase equilibrium properties are in quantitative
agreement with previously published and new Monte Carlo simulation data.Comment: 8 pages including 4 figure
Tunability of Critical Casimir Interactions by Boundary Conditions
We experimentally demonstrate that critical Casimir forces in colloidal
systems can be continuously tuned by the choice of boundary conditions. The
interaction potential of a colloidal particle in a mixture of water and
2,6-lutidine has been measured above a substrate with a gradient in its
preferential adsorption properties for the mixture's components. We find that
the interaction potentials at constant temperature but different positions
relative to the gradient continuously change from attraction to repulsion. This
demonstrates that critical Casimir forces respond not only to minute
temperature changes but also to small changes in the surface properties.Comment: 4 figures;
http://www.iop.org/EJ/article/0295-5075/88/2/26001/epl_88_2_26001.htm
Strong interactions in air showers
We study the role new gauge interactions in extensions of the standard model
play in air showers initiated by ultrahigh-energy cosmic rays. Hadron-hadron
events remain dominated by quantum chromodynamics, while projectiles and/or
targets from beyond the standard model permit us to see qualitative differences
arising due to the new interactions.Comment: 35 pages, 12 figures. Accepted for publication in JCA
High-harmonic generation: taking control of polarization
The ability to control the polarization of short-wavelength radiation generated by high-harmonic generation is useful not only for applications but also for testing conservation laws in physics
Identifying and reducing model structure uncertainty based on analysis of parameter interaction
International audienceMulti-objective optimization algorithms are widely used for the calibration of conceptual hydrological models. Such algorithms yield a set of Pareto-optimal solutions, reflecting the model structure uncertainty. In this study, a multi-objective optimization strategy is suggested, which aims at reducing the model structure uncertainty by considering parameter interaction within Pareto-optimal solutions. The approach has been used to develop a nested setup of a rainfall-runoff model, which is integrated in a probabilistic meso-/macroscale flood forecasting system. The optimization strategy aided in determining the best combination of a lumped (computationally efficient in operational real time forecasting) and a semi-distributed parameterization of the hydrological model. First results are shown for two subbasins of the Mulde catchment in Germany. The different phenomena of parameter interaction were analysed in this case study to reduce the model structure uncertainties
Adsorption and thermal dehydrogenation of ammonia on Ru(11¯21)
Adsorption and thermal dehydrogenation of NH3, adsorbed at 80 K on the open Ru(11(2) over bar 1) surface, was studied using high-resolution electron energy-loss spectroscopy (HREELS) and thermal desorption spectroscopy (TDS). For the NH3 monolayer, a strong dipole-active mode is found at 15 meV which is newly assigned to T-z, the frustrated-translation mode perpendicular to the surface of NH3 bonding with the nitrogen atom to the Ru surface. Increasing the temperature. 70% of NH3 desorbs before a channel for dehydrogenation opens at about 280 K. The remaining 30% decomposes completely during further warming to 470 K. The dehydrogenation of NH3 gives rise to four peaks in the H-2 TDS which are assigned to desorption of coadsorbed hydrogen at 220 K and three dehydrogenation reaction steps at 320, 360. and 420 K in accordance with HREELS. The reaction intermediates NH2 and NH are identified through HREELS. In a new interpretation NH2 is characterized by intense modes at 163 meV (rocking) and at 189 meV (scissoring). Using a maximum entropy algorithm six frequencies for v(Ru-N) were resolved at 46, 50, 58, 61, 69, and 75 meV
Linear confinement without dilaton in bottom-up holography for walking technicolour
In PRD78(2008)055005 [arXiv:0805.1503 [hep-ph]] and PRD79(2009)075004
[arXiv:0809.1324 [hep-ph]], we constructed a holographic description of walking
technicolour theories using both a hard- and a soft-wall model. Here, we show
that the dilaton field becomes phenomenologically irrelevant for the spectrum
of spin-one resonances once a term is included in the Lagrangian that mixes the
Goldstone bosons and the longitudinal components of the axial vector mesons. We
show how this mixing affects our previous results and we make predictions about
how this description of technicolour can be tested.Comment: 7 pages, no figure
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