39,045 research outputs found
Central Schemes for Porous Media Flows
We are concerned with central differencing schemes for solving scalar
hyperbolic conservation laws arising in the simulation of multiphase flows in
heterogeneous porous media. We compare the Kurganov-Tadmor, 2000 semi-discrete
central scheme with the Nessyahu-Tadmor, 1990 central scheme. The KT scheme
uses more precise information about the local speeds of propagation together
with integration over nonuniform control volumes, which contain the Riemann
fans. These methods can accurately resolve sharp fronts in the fluid
saturations without introducing spurious oscillations or excessive numerical
diffusion. We first discuss the coupling of these methods with velocity fields
approximated by mixed finite elements. Then, numerical simulations are
presented for two-phase, two-dimensional flow problems in multi-scale
heterogeneous petroleum reservoirs. We find the KT scheme to be considerably
less diffusive, particularly in the presence of high permeability flow
channels, which lead to strong restrictions on the time step selection;
however, the KT scheme may produce incorrect boundary behavior
An unified cosmological evolution driven by a mass dimension one fermionic field
An unified cosmological model for an Universe filled with a mass dimension
one (MDO) fermionic field plus the standard matter fields is considered. After
a primordial quantum fluctuation the field slowly rolls down to the bottom of a
symmetry breaking potential, driving the Universe to an inflationary regime
that increases the scale factor for about 71 e-folds. After the end of
inflation, the field starts to oscillate and can transfer its energy to the
standard model particles through a reheating mechanism. Such a process is
briefly discussed in terms of the admissible couplings of the MDO field with
the electromagnetic and Higgs fields. We show that even if the field loses all
its kinetic energy during reheating, it can evolve as dark matter due a
gravitational coupling (of spinorial origin) with baryonic matter. Since the
field acquires a constant value at the bottom of the potential, a non-null,
although tiny, mass term acts as a dark energy component nowadays. Therefore,
we conclude that MDO fermionic field is a good candidate to drive the whole
evolution of the Universe, in such a way that the inflationary field, dark
matter and dark energy are described by different manifestations of a single
field.Comment: 22 pages, 5 figure
85% efficiency for cw frequency doubling from 1.08 to 0.54 μm
Conversion efficiency of 85% has been achieved in cw second-harmonic generation from 1.08 to 0.54 μm with a potassium titanyl phosphate crystal inside an external ring cavity. An absolute comparison between the experimental data and a simple theory is made and shows good agreement
A water level relationship between consecutive gauge stations along Solim\~oes/Amazonas main channel: a wavelet approach
Gauge stations are distributed along the Solim\~oes/Amazonas main channel to
monitor water level changes over time. Those measurements help quantify both
the water movement and its variability from one gauge station to the next
downstream. The objective of this study is to detect changes in the water level
relationship between consecutive gauge stations along the Solim\~oes/Amazonas
main channel, since 1980. To carry out the analyses, data spanning from 1980 to
2010 from three consecutive gauges (Tefe, Manaus and Obidos) were used to
compute standardized daily anomalies. In particular for infra-annual periods it
was possible to detect changes for the water level variability along the
Solim\~oes/Amazonas main channel, by applying the Morlet Wavelet Transformation
(WT) and Wavelet Cross Coherence (WCC) methods. It was possible to quantify the
waves amplitude for the WT infra-annual scaled-period and were quite similar to
the three gauge stations denoting that the water level variability are related
to the same hydrological forcing functions. Changes in the WCC was detected for
the Manaus-Obidos river stretch and this characteristic might be associated
with land cover changes in the floodplains. The next steps of this research,
will be to test this hypotheses by integrating land cover changes into the
floodplain with hydrological modelling simulations throughout the time-series
Phantom Accretion by Black Holes and the Generalized Second Law of Thermodynamics
The accretion of a phantom fluid with non-zero chemical potential by black
holes is discussed with basis on the Generalized Second Law of thermodynamics.
For phantom fluids with positive temperature and negative chemical potential we
demonstrate that the accretion process is possible, and that the condition
guaranteeing the positiveness of the phantom fluid entropy coincides with the
one required by Generalized Second Law. In particular, this result provides a
complementary confirmation that cosmological phantom fluids do not need to have
negative temperatures
A Random Multifractal Tilling
We develop a multifractal random tilling that fills the square. The
multifractal is formed by an arrangement of rectangular blocks of different
sizes, areas and number of neighbors. The overall feature of the tilling is an
heterogeneous and anisotropic random self-affine object. The multifractal is
constructed by an algorithm that makes successive sections of the square. At
each -step there is a random choice of a parameter related to the
section ratio. For the case of random choice between and we
find analytically the full spectrum of fractal dimensions
- …