1,124 research outputs found
Understanding and profiling user requirements to support the conceptual design of an integrated land monitoring system
Acquiring and organizing knowledge and information elements can be essential not only to understand, but also to eliminate, reduce and control complexity and uncertainty. An integration of tools from different disciplines could systematically help in the construction of an agreed framework for problem formulation, above all when the situation is "new". An application was de-veloped in relation to an industrial project, in order to propose profiles of the potential users of an innovative system and of their requirements, and to for-mally develop models that can orient analysis, decision and action. Some ele-ments and results of this integrated application of "soft" and "hard" decision aid tools are here proposed as steps of an organizational learning cycle, which is a basic element of each innovation proces
The mass of the graviton and the cosmological constant
We show that the graviton acquires a mass in a de Sitter background given by
This is precisely the fine-tuning value required for
the perturbed gravitational field to mantain its two degrees of freedom.Comment: Title changed and few details added, without any changes in the
conclusio
A Spinor Theory of Gravity and the Cosmological Framework
Recently we have presented a new formulation of the theory of gravity based
on an implementation of the Einstein Equivalence Principle distinct from
General Relativity. The kinetic part of the theory - that describes how matter
is affected by the modified geometry due to the gravitational field - is the
same as in General Relativity. However, we do not consider the metric as an
independent field. Instead, it is an effective one, constructed in terms of two
fundamental spinor fields and and thus the metric does not
have a dynamics of its own, but inherits its evolution through its relation
with the fundamental spinors. In the first paper it was shown that the metric
that describes the gravitational field generated by a compact static and
spherically symmetric configuration is very similar to the Schwarzschild
metric. In the present paper we describe the cosmological framework in the
realm of the Spinor Theory of Gravity
Effective geometry in Astrophysics
The effective metric is introduced by means of two examples (non-linear
electromagnetism and hydrodynamics),along with applications in Astrophysics. A
sketch of the generality of the effect is also given.Comment: 9 pages, contributions for the proceedings of the First International
Workshop on Astronomy and Relativistic Astrophysics (IWARA 2003), Olinda
(Brazil
A Note on the Local Cosmological Constant and the Dark Energy Coincidence Problem
It has been suggested that the Dark Energy Coincidence Problem could be
interpreted as a possible link between the cosmological constant and a massive
graviton. We show that by using that link and models for the graviton mass a
dark energy density can be obtained that is indeed very close to measurements
by WMAP. As a consequence of the models, the cosmological constant was found to
depend on the density of matter. A brief outline of the cosmological
consequences such as the effect on the black hole solution is given
Understanding and profiling user requirements to support the conceptual design of an integrated land monitoring system
Acquiring and organizing knowledge and information elements can be essential not only to understand, but also to eliminate, reduce and control complexity and uncertainty. An integration of tools from different disciplines could systematically help in the construction of an agreed framework for problem formulation, above all when the situation is ânewâ. An application was de-veloped in relation to an industrial project, in order to propose profiles of the potential users of an innovative system and of their requirements, and to for-mally develop models that can orient analysis, decision and action. Some ele-ments and results of this integrated application of âsoftâ and âhardâ decision aid tools are here proposed as steps of an organizational learning cycle, which is a basic element of each innovation process
Quantum vacuum fluctuations and dark energy
It is shown that the curvature of space-time induced by vacuum fluctuations
of quantum fields should be proportional to the square of Newton's constant
. This offers a possible explanation for the success of the approximation for the dark energy density, with being a typical mass of
elementary particles.Comment: Changed conten
Integrated use of mathematical programming and multiple criteria methods in engineering design processes
A decision aiding methodology was required by a company of the aeronautical sector to support their engineering design processes. An integrated use of mathematical programming and multiple criteria methods was proposed to orient the conceptual design of functional and physical solutions.
As a first step, linear programming was used in relation to some case studies to generate design alternatives that satisfy the initial requirements. Subsequently multiple criteria methods were proposed to interact transparently with the client in relation to some aspects that were not included in the linear programming model. Design alternatives were evaluated and compared, in order to identify and formalize expectations that the first design solutions were not able to meet.
An iterative use of the two approaches, in a cyclic procedure of mutual learning, can allow the requirements to be defined more clearly and a final satisfying solution to be reached
Cosmological Effects of Nonlinear Electrodynamics
It will be shown that a given realization of nonlinear electrodynamics, used
as source of Einstein's equations, generates a cosmological model with
interesting features, namely a phase of current cosmic acceleration, and the
absence of an initial singularity, thus pointing to a way to solve two
important problems in cosmology
Doping nature of native defects in 1T-TiSe2
The transition metal dichalcogenide 1T-TiSe2 is a quasi two-dimensional
layered material with a charge density wave (CDW) transition temperature of
TCDW 200 K. Self-doping effects for crystals grown at different temperatures
introduce structural defects, modify the temperature dependent resistivity and
strongly perturbate the CDW phase. Here we study the structural and doping
nature of such native defects combining scanning tunneling
microscopy/spectroscopy and ab initio calculations. The dominant native single
atom dopants we identify in our single crystals are intercalated Ti atoms, Se
vacancies and Se substitutions by residual iodine and oxygen.Comment: 5 pages, 3 figure
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