220 research outputs found
Boundary data reconstruction for open channel networks using modal decomposition
This article presents a method to estimate flow variables for an open channel network governed by first-order, linear hyperbolic partial differential equations and subject to periodic forcing. The selected external boundary conditions of the system are defined as the model input; the flow properties at internal locations, as well as the other external boundary conditions, are defined as the output. A spatially-dependent transfer matrix in the frequency domain is constructed to relate the model input and output. A data reconciliation technique efficiently eliminates the error in the measured data and results in a reconciliated external boundary conditions; subsequently, the flow properties at any location in the system can be accurately evaluated. The applicability and effectiveness of the method is substantiated with a case study of the river flow subject to tidal forcing in the Sacramento-San Joaquin Delta, California. It is shown that the proposed method gives an accurate estimation of the flow properties at any intermediate location within the channel network
Flatness-based control of open-channel flow in an irrigation canal using SCADA
Open channels are used to distribute water to large irrigated areas. In these systems, ensuring timely water delivery is essential to reduce operational water losses. This article derives a method for open-loop control of open channel flow, based on the Hayami model, a parabolic partial differential equation resulting from a simplification of the Saint-Venant equations. The open-loop control is represented as infinite series using differential flatness. Experimental results show the effectiveness of the approach by applying the open-loop controller to a real irrigation canal located in South of France
On Metric Dimension of Functigraphs
The \emph{metric dimension} of a graph , denoted by , is the
minimum number of vertices such that each vertex is uniquely determined by its
distances to the chosen vertices. Let and be disjoint copies of a
graph and let be a function. Then a
\emph{functigraph} has the vertex set
and the edge set . We study how
metric dimension behaves in passing from to by first showing that
, if is a connected graph of order
and is any function. We further investigate the metric dimension of
functigraphs on complete graphs and on cycles.Comment: 10 pages, 7 figure
Effective gravitational equations for f(R) braneworld models
The viability of achieving gravitational consistent braneworld models in the
framework of a f(R) theory of gravity is investigated. After a careful
generalization of the usual junction conditions encompassing the embedding of
the 3-brane into a f(R) bulk, we provide a prescription giving the necessary
constraints in order to implement the projected second order effective field
equations on the brane.Comment: 15 pages, no figures. Accepted for publication in the Physical Review
The inflationary bispectrum with curved field-space
We compute the covariant three-point function near horizon-crossing for a
system of slowly-rolling scalar fields during an inflationary epoch, allowing
for an arbitrary field-space metric. We show explicitly how to compute its
subsequent evolution using a covariantized version of the separate universe or
"delta-N" expansion, which must be augmented by terms measuring curvature of
the field-space manifold, and give the nonlinear gauge transformation to the
comoving curvature perturbation. Nonlinearities induced by the field-space
curvature terms are a new and potentially significant source of
non-Gaussianity. We show how inflationary models with non-minimal coupling to
the spacetime Ricci scalar can be accommodated within this framework. This
yields a simple toolkit allowing the bispectrum to be computed in models with
non-negligible field-space curvature.Comment: 22 pages, plus appendix and reference
Curvature singularities, tidal forces and the viability of Palatini f(R) gravity
In a previous paper we showed that static spherically symmetric objects
which, in the vicinity of their surface, are well-described by a polytropic
equation of state with 3/2<Gamma<2 exhibit a curvature singularity in Palatini
f(R) gravity. We argued that this casts serious doubt on the validity of
Palatini f(R) gravity as a viable alternative to General Relativity. In the
present paper we further investigate this characteristic of Palatini f(R)
gravity in order to clarify its physical interpretation and consequences.Comment: 15 pages. CQG in press. Part of the material moved to an appendix,
discussion on the meV scale predictions of Palatini f(R) gravity adde
Simulation of merging binary neutron stars in full general relativity: case
We have performed 3D numerical simulations for merger of equal mass binary
neutron stars in full general relativity. We adopt a -law equation of
state in the form where P, , \varep and
are the pressure, rest mass density, specific internal energy, and the
adiabatic constant with . As initial conditions, we adopt models of
corotational and irrotational binary neutron stars in a quasi-equilibrium state
which are obtained using the conformal flatness approximation for the three
geometry as well as an assumption that a helicoidal Killing vector exists. In
this paper, we pay particular attention to the final product of the
coalescence. We find that the final product depends sensitively on the initial
compactness parameter of the neutron stars : In a merger between sufficiently
compact neutron stars, a black hole is formed in a dynamical timescale. As the
compactness is decreased, the formation timescale becomes longer and longer. It
is also found that a differentially rotating massive neutron star is formed
instead of a black hole for less compact binary cases, in which the rest mass
of each star is less than 70-80% of the maximum allowed mass of a spherical
star. In the case of black hole formation, we roughly evaluate the mass of the
disk around the black hole. For the merger of corotational binaries, a disk of
mass may be formed, where M_* is the total rest mass of the
system. On the other hand, for the merger of irrotational binaries, the disk
mass appears to be very small : < 0.01M_*.Comment: 27 pages, to appear in Phys. Rev.
Evolution and Flare Activity of Delta-Sunspots in Cycle 23
The emergence and magnetic evolution of solar active regions (ARs) of
beta-gamma-delta type, which are known to be highly flare-productive, were
studied with the SOHO/MDI data in Cycle 23. We selected 31 ARs that can be
observed from their birth phase, as unbiased samples for our study. From the
analysis of the magnetic topology (twist and writhe), we obtained the following
results. i) Emerging beta-gamma-delta ARs can be classified into three
topological types as "quasi-beta", "writhed" and "top-to-top". ii) Among them,
the "writhed" and "top-to-top" types tend to show high flare activity. iii) As
the signs of twist and writhe agree with each other in most cases of the
"writhed" type (12 cases out of 13), we propose a magnetic model in which the
emerging flux regions in a beta-gamma-delta AR are not separated but united as
a single structure below the solar surface. iv) Almost all the "writhed"-type
ARs have downward knotted structures in the mid portion of the magnetic flux
tube. This, we believe, is the essential property of beta-gamma-delta ARs. v)
The flare activity of beta-gamma-delta ARs is highly correlated not only with
the sunspot area but also with the magnetic complexity. vi) We suggest that
there is a possible scaling-law between the flare index and the maximum umbral
area
Morris-Thorne wormholes with a cosmological constant
First, the ideas introduced in the wormhole research field since the work of
Morris and Thorne are briefly reviewed, namely, the issues of energy
conditions, wormhole construction, stability, time machines and astrophysical
signatures. Then, spherically symmetric and static traversable Morris-Thorne
wormholes in the presence of a generic cosmological constant are analyzed. A
matching of an interior solution to the unique exterior vacuum solution is done
using directly the Einstein equations. The structure as well as several
physical properties and characteristics of traversable wormholes due to the
effects of the cosmological term are studied. Interesting equations appear in
the process of matching. For instance, one finds that for asymptotically flat
and anti-de Sitter spacetimes the surface tangential pressure of the
thin-shell, at the boundary of the interior and exterior solutions, is always
strictly positive, whereas for de Sitter spacetime it can take either sign as
one could expect, being negative (tension) for relatively high cosmological
constant and high wormhole radius, positive for relatively high mass and small
wormhole radius, and zero in-between. Finally, some specific solutions with
generic cosmological constant, based on the Morris-Thorne solutions, are
provided.Comment: latex, 49 pages, 8 figures. Expanded version of the paper published
in Physical Review
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