2,395 research outputs found
A general solution in the Newtonian limit of f(R)- gravity
We show that any analytic -gravity model, in the metric approach,
presents a weak field limit where the standard Newtonian potential is corrected
by a Yukawa-like term. This general result has never been pointed out but often
derived for some particular theories. This means that only allows to
recover the standard Newton potential while this is not the case for other
relativistic theories of gravity. Some considerations on the physical
consequences of such a general solution are addressed.Comment: 5 page
Axially symmetric solutions in f(R)-gravity
Axially symmetric solutions for f (R)-gravity can be derived starting from
exact spherically sym- metric solutions achieved by Noether symmetries. The
method takes advantage of a complex coordi- nate transformation previously
developed by Newman and Janis in General Relativity. An example is worked out
to show the general validity of the approach. The physical properties of the
solution are also considered.Comment: 13 pages, 1 figure, to appear in Classical and Quantum Gravity 201
Spherically symmetric solutions in f(R)-gravity via Noether Symmetry Approach
We search for spherically symmetric solutions of f(R) theories of gravity via
the Noether Symmetry Approach. A general formalism in the metric framework is
developed considering a point-like f(R)-Lagrangian where spherical symmetry is
required. Examples of exact solutions are given.Comment: 17 pages, to appear in Class. Quant. Gra
Geological and geophysical characterization of the southeastern side of the High Agri Valley (southern Apennines, Italy)
Abstract. In the frame of a national project funded by Eni S.p.A. and developed by three institutes of the National Research Council (the Institute of Methodologies for Environmental Analysis, the Institute of Research for Hydrogeological Protection and the Institute for Electromagnetic Sensing of the Environment), a multidisciplinary approach based on the integration of satellite, aero-photogrammetric and in situ geophysical techniques was applied to investigate an area located in the Montemurro territory in the southeastern sector of the High Agri Valley (Basilicata Region, southern Italy). This paper reports the results obtained by the joint analysis of in situ geophysical surveys, aerial photos interpretation, morphotectonic investigation, geological field survey and borehole data. The joint analysis of different data allowed us (1) to show the shallow geological and structural setting, (2) to detect the geometry of the different lithological units and their mechanical and dynamical properties, (3) to image a previously unmapped fault beneath suspected scarps/warps and (4) to characterize the geometry of an active landslide affecting the study area
Corrigendum to "Geological and geophysical characterization of the southeastern side of the High Agri Valley (southern Apennines, Italy)" published in Nat. Hazards Earth Syst. Sci., 15, 315–323, 2015
No abstract available
The Cauchy problem of f(R) gravity
The initial value problem of metric and Palatini f(R)gravity is studied by
using the dynamical equivalence between these theories and Brans-Dicke gravity.
The Cauchy problem is well-formulated for metric f(R)gravity in the presence of
matter and well-posed in vacuo. For Palatini f(R)gravity, instead, the Cauchy
problem is not well-formulated.Comment: 16 latex pages, to appear in Class. Quantum Grav; typographical
errors corrected, new references adde
Modified-Source Gravity and Cosmological Structure Formation
One way to account for the acceleration of the universe is to modify general
relativity, rather than introducing dark energy. Typically, such modifications
introduce new degrees of freedom. It is interesting to consider models with no
new degrees of freedom, but with a modified dependence on the conventional
energy-momentum tensor; the Palatini formulation of theories is one
example. Such theories offer an interesting testing ground for investigations
of cosmological modified gravity. In this paper we study the evolution of
structure in these ``modified-source gravity'' theories. In the linear regime,
density perturbations exhibit scale dependent runaway growth at late times and,
in particular, a mode of a given wavenumber goes nonlinear at a higher redshift
than in the standard CDM model. We discuss the implications of this
behavior and why there are reasons to expect that the growth will be cut off in
the nonlinear regime. Assuming that this holds in a full nonlinear analysis, we
briefly describe how upcoming measurements may probe the differences between
the modified theory and the standard CDM model.Comment: 22 pages, 6 figures, uses iopart styl
Spherical symmetry in -gravity
Spherical symmetry in gravity is discussed in details considering also
the relations with the weak field limit. Exact solutions are obtained for
constant Ricci curvature scalar and for Ricci scalar depending on the radial
coordinate. In particular, we discuss how to obtain results which can be
consistently compared with General Relativity giving the well known
post-Newtonian and post-Minkowskian limits. Furthermore, we implement a
perturbation approach to obtain solutions up to the first order starting from
spherically symmetric backgrounds. Exact solutions are given for several
classes of theories in both constant and .Comment: 13 page
The Effort of Increasing Reynolds Number in Projection-Based Reduced Order Methods: From Laminar to Turbulent Flows
We present in this double contribution two different reduced order strategies for incompressible parameterized Navier-Stokes equations characterized by varying Reynolds numbers. The first strategy deals with low Reynolds number (laminar flow) and is based on a stabilized finite element method during the offline stage followed by a Galerkin projection on reduced basis spaces generated by a greedy algorithm. The second methodology is based on a full order finite volume discretization. The latter methodology will be used for flows with moderate to high Reynolds number characterized by turbulent patterns. For the treatment of the mentioned turbulent flows at the reduced order level, a new POD-Galerkin approach is proposed. The new approach takes into consideration the contribution of the eddy viscosity also during the online stage and is based on the use of interpolation. The two methodologies are tested on classic benchmark test cases
Geological and geophysical characterization of the southeastern side of the High Agri Valley (southern Apennines, Italy)
In the frame of a national project funded by Eni S.p.A. and developed by
three institutes of the National Research Council (the Institute of
Methodologies for Environmental Analysis, the Institute of Research for
Hydrogeological Protection and the Institute for Electromagnetic Sensing of
the Environment), a multidisciplinary approach based on the integration of
satellite, aero-photogrammetric and in situ geophysical techniques was
applied to investigate an area located in the Montemurro territory in the
southeastern sector of the High Agri Valley (Basilicata Region, southern
Italy).
This paper reports the results obtained by the joint analysis of in situ
geophysical surveys, aerial photos interpretation, morphotectonic
investigation, geological field survey and borehole data. The joint analysis
of different data allowed us (1) to show the shallow geological and
structural setting, (2) to detect the geometry of the different lithological
units and their mechanical and dynamical properties, (3) to image a previously
unmapped fault beneath suspected scarps/warps and (4) to characterize the
geometry of an active landslide affecting the study area
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