225 research outputs found
Morphology of rain water channelization in systematically varied model sandy soils
We visualize the formation of fingered flow in dry model sandy soils under
different raining conditions using a quasi-2d experimental set-up, and
systematically determine the impact of soil grain diameter and surface wetting
property on water channelization phenomenon. The model sandy soils we use are
random closely-packed glass beads with varied diameters and surface treatments.
For hydrophilic sandy soils, our experiments show that rain water infiltrates
into a shallow top layer of soil and creates a horizontal water wetting front
that grows downward homogeneously until instabilities occur to form fingered
flows. For hydrophobic sandy soils, in contrast, we observe that rain water
ponds on the top of soil surface until the hydraulic pressure is strong enough
to overcome the capillary repellency of soil and create narrow water channels
that penetrate the soil packing. Varying the raindrop impinging speed has
little influence on water channel formation. However, varying the rain rate
causes significant changes in water infiltration depth, water channel width,
and water channel separation. At a fixed raining condition, we combine the
effects of grain diameter and surface hydrophobicity into a single parameter
and determine its influence on water infiltration depth, water channel width,
and water channel separation. We also demonstrate the efficiency of several
soil water improvement methods that relate to rain water channelization
phenomenon, including pre-wetting sandy soils at different level before
rainfall, modifying soil surface flatness, and applying superabsorbent hydrogel
particles as soil modifiers
Kinetics of Gravity-Driven Water Channels Under Steady Rainfall
We investigate the formation of fingered flow in dry granular media under
simulated rainfall using a quasi-2D experimental set-up composed of a random
close packing of mono-disperse glass beads. Using controlled experiments, we
analyze the finger instabilities that develop from the wetting front as a
function of fundamental granular (particle size) and fluid properties
(rainfall, viscosity).These finger instabilities act as precursors for water
channels, which serve as outlets for water drainage. We look into the
characteristics of the homogeneous wetting front and channel size as well as
estimate relevant time scales involved in the instability formation and the
velocity of the channel finger tip. We compare our experimental results with
that of the well-known prediction developed by Parlange and Hill [1976]. This
model is based on linear stability analysis of the growth of perturbations
arising at the interface between two immiscible fluids. Results show that in
terms of morphology, experiments agree with the proposed model. However, in
terms of kinetics we nevertheless account for another term that describes the
homogenization of the wetting front. This result shows that the manner we
introduce the fluid to a porous medium can also influence the formation of
finger instabilities.Comment: 13 pages, 7 figure
Gapless Color Superconductivity
We present the dispersion relations for quasiparticle excitations about the
color-flavor locked ground state of QCD at high baryon density. In the presence
of condensates which pair light and strange quarks there need not be an energy
gap in the quasiparticle spectrum. This raises the possibility of gapless color
superconductivity, with a Meissner effect but no minimum excitation energy.
Analysis within a toy model suggests that gapless color superconductivity may
occur only as a metastable phase.Comment: 4 pages, Revtex, eps figures include
Effective gluon interactions in the Colour Superconductive Phase of two flavor QCD
The gluon self-energies and dispersion laws in the color superconducting
phase of QCD with two massless flavors are calculated using the effective
theory near the Fermi surface. These quantities are calculated at zero
temperature for all the eight gluons, those of the remaining SU(2) color group
and those corresponding to the broken generators. The construction of the
effective interaction is completed with the one loop calculation of the three-
and four-point gluon interactions.Comment: LaTeX, p 17, 4 figures. Final version to be published in Phys. Lett.
B. Several corrections have been done and some point clarifie
Superconductivity from perturbative one-gluon exchange in high density quark matter
We study color superconductivity in QCD at asymptotically large chemical
potential. In this limit, pairing is dominated by perturbative one-gluon
exchange. We derive the Eliashberg equation for the pairing gap and solve this
equation numerically. Taking into account both magnetic and electric gluon
exchanges, we find with ,
verifying a recent result by Son. For chemical potentials that are of physical
interest, GeV, the calculation ceases to be reliable quantitatively,
but our results suggest that the gap can be as large as 100 MeV.Comment: 19 pages, 6 figures. I accidentally replaced the paper with an
outdated version. This version has typos corrected and will appear in PR
Quark description of nuclear matter
We discuss the role of an adjoint chiral condensate for color superconducting
quark matter. Its presence leads to color-flavor locking in two-flavor quark
matter. Color is broken completely as well as chiral symmetry in the two-flavor
theory with coexisting adjoint quark-antiquark and antitriplet quark-quark
condensates. The qualitative properties of this phase match the properties of
ordinary nuclear matter without strange baryons. This complements earlier
proposals by Schafer and Wilczek for a quark description of hadronic phases. We
show for a class of models with effective four-fermion interactions that
adjoint chiral and diquark condensates do not compete, in the sense that
simultaneous condensation occurs for sufficiently strong interactions in the
adjoint chiral channel.Comment: 15 pages, 3 figure
Effective Field Theory for the Crystalline Colour Superconductive Phase of QCD
We present an effective field theory for high density, low temperature QCD in
the crystalline colour superconductive phase (LOFF phase). This interesting
phase of QCD is characterized by a gap parameter with a crystalline pattern,
breaking traslational and rotational invariance, and could have astrophysical
applications. In the effective theory the fermions have a Majorana mass, which,
besides colour, breaks translation and rotation symmetries. Fermions couple to
the three phonons arising from the breaking of rotation and translation
invariance. Integrating out the fermions leads eventually to an effective
lagrangian in terms of the phonon fields only, which satisfies an anisotropic
dispersion relation.Comment: Latex, 17 pages, Modifications in the effective goldstone boson
descriptio
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