784 research outputs found
Wetting of crossed fibers: multiple steady states and symmetry breaking
We investigate the wetting properties of the simplest element of an array of
random fibers: two rigid fibers crossing with an inclination angle and in
contact with a droplet of a perfectly wetting liquid. We show experimentally
that the liquid adopts different morphologies when the inclination angle is
increased: a column shape, a mixed morphology state where a drop lies at the
end of a column, or a drop centered at the node. An analytical model is
provided that predicts the wetting length as well as the presence of a
non-symmetric state in the mixed morphology regime. The model also highlights a
symmetry breaking at the transition between the column state and the mixed
morphology. The possibility to tune the morphology of the liquid could have
important implications for drying processes
Dynamics of elastocapillary rise
We present the results of a combined experimental and theoretical
investigation of the surface-tension-driven coalescence of flexible structures.
Specifically, we consider the dynamics of the rise of a wetting liquid between
flexible sheets that are clamped at their upper ends. As the elasticity of the
sheets is progressively increased, we observe a systematic deviation from the
classical diffusive-like behaviour: the time to reach equilibrium increases
dramatically and the departure from classical rise occurs sooner, trends that
we elucidate via scaling analyses. Three distinct temporal regimes are
identified and subsequently explored by developing a theoretical model based on
lubrication theory and the linear theory of plates. The resulting free-boundary
problem is solved numerically and good agreement is obtained with experiments
Variational description of the dimensional cross-over in the array of coupled one-dimensional conductors
Variational wave function is proposed to describe electronic properties of an
array of one-dimensional conductors coupled by transverse hopping and
interaction. For weak or intermediate in-chain interaction the wave function
has the following structure: Tomonaga-Luttinger bosons with momentum higher
then some variational quantity \tilde\Lambda are in their ground state while
other bosons (with |k|<\tilde\Lambda) form kinks -- fermion-like excitations of
the Tomonaga-Luttinger boson field. Nature of the ground state for this
quasiparticles can be determined by solving three dimensional effective
hamiltonian. Since the anisotropy of the effective hamiltonian is small the use
of the mean field theory is justified. For repulsive interaction possible
phases are density wave and p-wave superconductivity. Our method allows us to
calculate the low-energy part of different electronic Green's functions. In
order to do that it is enough to apply standard perturbation theory technique
to the effective hamiltonian. When the in-chain interaction is strong
\tilde\Lambda vanishes and no fermionic excitation is present in the system. In
this regime the dynamics is described by transversally coupled
Tomonaga-Luttinger bosons
Análise da comercialização e consumo de cogumelos comestĂveis no mercado do Distrito Federal e entorno.
bitstream/CENARGEN/24692/1/bp048.pd
Contrasting intrainterstadial climatic evolution between high and middle North Atlantic latitudes: A close-up of Greenland Interstadials 8 and 12
Three highly resolved pollen and sea surface temperature records from the Iberian margin (36â "42°N) reveal the local evolution of vegetation and climate associated with the rapid climatic variability of marine isotope stage 3. The comparison of the climate at these midlatitudes with δD and d excess from Greenland ice cores shows that the northâ south climatic gradient underwent strong variations during the long Greenland Interstadials (GIs) 8 and 12. After the Northern Hemispheric rapid warming at the Greenland Stadial (GS)â GI transition, the trend during the first part of the GI is a Greenland cooling and an Iberian warming. This increase of the North Atlantic climatic gradient led to moisture transportation to Greenland from midlatitudes (lightest d excess) and to a drying episode in Iberia. The subsequent temperature decrease in Greenland and Iberia associated with the precipitation increase in the latter region occurred when the major source of Greenland precipitation shifted to lower latitudes (d excess increase)
Nuclear break-up of 11Be
The break-up of 11Be was studied at 41AMeV using a secondary beam of 11Be
from the GANIL facility on a 48Ti target by measuring correlations between the
10Be core, the emitted neutrons and gamma rays. The nuclear break-up leading to
the emission of a neutron at large angle in the laboratory frame is identified
with the towing mode through its characteristic n-fragment correlation. The
experimental spectra are compared with a model where the time dependent
Schrodinger equation (TDSE) is solved for the neutron initially in the 11 Be. A
good agreement is found between experiment and theory for the shapes of neutron
experimental energies and angular distributions. The spectroscopic factor of
the 2s orbital is tentatively extracted to be 0.46+-0.15. The neutron emission
from the 1p and 1d orbitals is also studied
Mechanical tuning of the evaporation rate of liquid on crossed fibers
We investigate experimentally the drying of a small volume of perfectly
wetting liquid on two crossed fibers. We characterize the drying dynamics for
the three liquid morphologies that are encountered in this geometry: drop,
column and a mixed morphology, in which a drop and a column coexist. For each
morphology, we rationalize our findings with theoretical models that capture
the drying kinetics. We find that the evaporation rate depends significantly on
the liquid morphology and that the drying of liquid column is faster than the
evaporation of the drop and the mixed morphology for a given liquid volume.
Finally, we illustrate that shearing a network of fibers reduces the angle
between them, changes the morphology towards the column state, and so enhances
the drying rate of a volatile liquid deposited on it
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