74 research outputs found
3D Cadastres Best Practices, Chapter 5: Visualization and New Opportunities
This paper proposes a discussion on opportunities offered by 3D visualization to improve the understanding and the analysis of cadastre data. It first introduce the rationale of having 3D visualization functionalities in the context of cadastre applications. Second the publication outline some basic concepts in 3D visualization. This section specially addresses the visualization pipeline as a driven classification schema to understand the steps leading to 3D visualization. In this section is also presented a brief review of current 3D standards and technologies. Next is proposed a summary of progress made in the last years in 3D cadastral visualization. For instance, user’s requirement, data and semiotics, and platforms are highlighted as main actions performed in the development of 3D cadastre visualization. This review could be perceived as an attempt to structure and emphasise the best practices in the domain of 3D cadastre visualization and as an inventory of issues that still need to be tackled. Finally, by providing a review on advances and trends in 3D visualization, the paper initiates a discussion and a critical analysis on the benefit of applying these new developments to cadastre domain. This final section discusses about enhancing 3D techniques as dynamic transparency and cutaway, 3D generalization, 3D visibility model, 3D annotation, 3D data and web platform, augmented reality, immersive virtual environment, 3D gaming, interaction techniques and time
Morphology, ecology and biogeography of Stauroneis pachycephala P.T. Cleve (Bacillariophyta) and its transfer to the genusEnvekadea
Stauroneis pachycephala was described in 1881 from the Baakens River, Port Elizabeth, South Africa. Recently, it was found during surveys of the MacKenzie River (Victoria, Australia), the Florida Everglades (USA) and coastal marshes of Louisiana (USA). The morphology, ecology and geographic distribution of this species are described in this article. This naviculoid species is characterised by lanceolate valves with a gibbous centre, a sigmoid raphe, an axial area narrowing toward the valve ends, and capitate valve apices. The central area is a distinct stauros that is slightly widened near the valve margin. The raphe is straight and filiform, and the terminal raphe fissures are strongly deflected in opposite directions. Striae are fine and radiate in the middle of the valve, becoming parallel and eventually convergent toward the valve ends. The external surface of the valves and copulae is smooth and lacks ornamentation. We also examined the type material of S. pachycephala. Our observations show this species has morphological characteristics that fit within the genus Envekadea. Therefore, the transfer of S. pachycephala to Envekadea is proposed and a lectotype is designated
Naked Singularity Formation In f(R) Gravity
We study the gravitational collapse of a star with barotropic equation of
state in the context of theories of gravity.
Utilizing the metric formalism, we rewrite the field equations as those of
Brans-Dicke theory with vanishing coupling parameter. By choosing the
functionality of Ricci scalar as , we
show that for an appropriate initial value of the energy density, if
and satisfy certain conditions, the resulting singularity would be naked,
violating the cosmic censorship conjecture. These conditions are the ratio of
the mass function to the area radius of the collapsing ball, negativity of the
effective pressure, and the time behavior of the Kretschmann scalar. Also, as
long as parameter obeys certain conditions, the satisfaction of the
weak energy condition is guaranteed by the collapsing configuration.Comment: 15 pages, 4 figures, to appear in GR
Some exact solutions of F(R) gravity with charged (a)dS black hole interpretation
In this paper we obtain topological static solutions of some kind of pure
gravity. The present solutions are two kind: first type is uncharged
solution which corresponds with the topological (a)dS Schwarzschild solution
and second type has electric charge and is equivalent to the
Einstein--conformally invariant Maxwell solution. In other word,
starting from pure gravity leads to (charged) Einstein- solutions
which we interpreted them as (charged) (a)dS black hole solutions of pure
gravity. Calculating the Ricci and Kreschmann scalars show that there is
a curvature singularity at . We should note that the Kreschmann scalar of
charged solutions goes to infinity as , but with a rate slower
than that of uncharged solutions.Comment: 21 pages, 4 figures, generalization to higher dimensions, references
adde
Modified gravity and its reconstruction from the universe expansion history
We develop the reconstruction program for the number of modified gravities:
scalar-tensor theory, , and string-inspired, scalar-Gauss-Bonnet
gravity. The known (classical) universe expansion history is used for the
explicit and successful reconstruction of some versions (of special form or
with specific potentials) from all above modified gravities. It is demonstrated
that cosmological sequence of matter dominance, decceleration-acceleration
transition and acceleration era may always emerge as cosmological solutions of
such theory. Moreover, the late-time dark energy FRW universe may have the
approximate or exact CDM form consistent with three years WMAP data.
The principal possibility to extend this reconstruction scheme to include the
radiation dominated era and inflation is briefly mentioned. Finally, it is
indicated how even modified gravity which does not describe the
matter-dominated epoch may have such a solution before acceleration era at the
price of the introduction of compensating dark energy.Comment: LaTeX file, 24 pages, no figure, prepared for the proceedings of ERE
2006, minor correction
Crossing the Phantom Divide Line in a DGP-Inspired -Gravity
We study possible crossing of the phantom divide line in a DGP-inspired
braneworld scenario where scalar field and curvature quintessence
are treated in a unified framework. With some specific form of and
by adopting a suitable ansatz, we show that there are appropriate regions of
the parameters space which account for late-time acceleration and admit
crossing of the phantom divide line.Comment: 23 Pages, 10 figs, Submitted to JCA
Non linear equation of state and effective phantom divide in brane models
Here, DGP model of brane-gravity is analyzed and compared with the standard
general relativity and Randall-Sundrum cases using non-linear equation of
state. Phantom fluid is known to violate the weak energy condition. In this
paper, it is found that this characteristic of phantom energy is affected
drastically by the negative brane-tension of the RS-II model. It is
found that in DGP model strong energy condition(SEC) is always violated and the
universe accelerates only where as in RS-II model even SEC is not violated for
and the universe decelerates
Energy Conditions in Modified Gravity with Non-minimal Coupling to Matter
In this paper we study a model of modified gravity with non-minimal coupling
between a general function of the Gauss-Bonnet invariant, , and matter
Lagrangian from the point of view of the energy conditions. Such model has been
introduced in Ref. [21] for description of early inflation and late-time cosmic
acceleration. We present the suitable energy conditions for the above mentioned
model and then, we use the estimated values of the Hubble, deceleration and
jerk parameters to apply the obtained energy conditions to the specific class
of modified Gauss-Bonnet models.Comment: 12 pages, no figur, Accepted for publication in Astrophysics and
Space Scienc
CDM, DGP and extended phantom-like cosmologies
In this paper we compare outcomes of some extended phantom-like cosmologies
with each other and also with CDM\, and DGP. We focus on the
variation of the luminosity distances, the age of the universe and the
deceleration parameter versus the redshift in these scenarios. In a dynamical
system approach, we show that the accelerating phase of the universe in the
-DGP scenario is stable if one consider the \emph{curvature fluid} as a
phantom scalar field in the equivalent scalar-tensor theory, otherwise it is a
transient and unstable phenomenon. Up to the parameters values adopted in this
paper, the extended -DGP scenario is closer to the CDM
scenario than other proposed models. All of these scenarios explain the
late-time cosmic speed-up in their normal DGP branches, but the redshift at
which transition to the accelerating phase occurs are different: while the
DGP model transits to the accelerating phase much earlier, the
-DGP model transits to this phase much later than other scenarios.
Also, within the parameter spaces adopted in this paper, the age of the
universe in the -DGP model is larger than CDM, but this age in
-DGP is smaller than CDM.Comment: 37 pages, 6 figures, accepted for publication in Astrophyics and
Space Scienc
f(R) theories
Over the past decade, f(R) theories have been extensively studied as one of
the simplest modifications to General Relativity. In this article we review
various applications of f(R) theories to cosmology and gravity - such as
inflation, dark energy, local gravity constraints, cosmological perturbations,
and spherically symmetric solutions in weak and strong gravitational
backgrounds. We present a number of ways to distinguish those theories from
General Relativity observationally and experimentally. We also discuss the
extension to other modified gravity theories such as Brans-Dicke theory and
Gauss-Bonnet gravity, and address models that can satisfy both cosmological and
local gravity constraints.Comment: 156 pages, 14 figures, Invited review article in Living Reviews in
Relativity, Published version, Comments are welcom
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