417 research outputs found
Approximate solutions in space mission design
In this paper, we address multi-objective space mission design problems. From a practical point of view, it is often the case that,during the preliminary phase of the design of a space mission, the solutions that are actually considered are not 'optimal' (in the Pareto sense)but belong to the basin of attraction of optimal ones (i.e. they are nearly
optimal). This choice is motivated either by additional requirements that the decision maker has to take into account or, more often, by robustness considerations. For this, we suggest a novel MOEA which is a modification of the well-known NSGA-II algorithm equipped with a recently
proposed archiving strategy which aims at storing the set of approximate solutions of a given MOP. Using this algorithm we will examine some space trajectory design problems and demonstrate the benefit of the novel approach
The Quantum Mechanics of Hyperion
This paper is motivated by the suggestion [W. Zurek, Physica Scripta, T76,
186 (1998)] that the chaotic tumbling of the satellite Hyperion would become
non-classical within 20 years, but for the effects of environmental
decoherence. The dynamics of quantum and classical probability distributions
are compared for a satellite rotating perpendicular to its orbital plane,
driven by the gravitational gradient. The model is studied with and without
environmental decoherence. Without decoherence, the maximum quantum-classical
(QC) differences in its average angular momentum scale as hbar^{2/3} for
chaotic states, and as hbar^2 for non-chaotic states, leading to negligible QC
differences for a macroscopic object like Hyperion. The quantum probability
distributions do not approach their classical limit smoothly, having an
extremely fine oscillatory structure superimposed on the smooth classical
background. For a macroscopic object, this oscillatory structure is too fine to
be resolved by any realistic measurement. Either a small amount of smoothing
(due to the finite resolution of the apparatus) or a very small amount of
environmental decoherence is sufficient ensure the classical limit. Under
decoherence, the QC differences in the probability distributions scale as
(hbar^2/D)^{1/6}, where D is the momentum diffusion parameter. We conclude that
decoherence is not essential to explain the classical behavior of macroscopic
bodies.Comment: 17 pages, 24 figure
A review of research into business coaching supervision
A systematic search of the coaching literature for original peer-reviewed studies into business coaching supervision yielded seven research reports. Evaluation of these studies showed them to be low in the reporting of methodological rigour. However, as an emerging area of research with great importance for the development of the profession of business coaching these studies provide valuable insights into the functions of supervision and its benefits. Gaps in knowledge and directions for future research are identified. There is a need for future research to be more rigorous in its reporting of methods and analytic procedures, small scale qualitative research that can provide insight into the issues and challenges of coaching supervision in specific contexts, and large scale quantitative research which can provide broader and generalizable understandings into the uses and benefits of supervision
Celestial mechanics in Kerr spacetime
The dynamical parameters conventionally used to specify the orbit of a test
particle in Kerr spacetime are the energy , the axial component of the
angular momentum, , and Carter's constant . These parameters are
obtained by solving the Hamilton-Jacobi equation for the dynamical problem of
geodesic motion. Employing the action-angle variable formalism, on the other
hand, yields a different set of constants of motion, namely, the fundamental
frequencies , and associated with
the radial, polar and azimuthal components of orbital motion. These
frequencies, naturally, determine the time scales of orbital motion and,
furthermore, the instantaneous gravitational wave spectrum in the adiabatic
approximation. In this article, it is shown that the fundamental frequencies
are geometric invariants and explicit formulas in terms of quadratures are
derived. The numerical evaluation of these formulas in the case of a rapidly
rotating black hole illustrates the behaviour of the fundamental frequencies as
orbital parameters such as the semi-latus rectum , the eccentricity or
the inclination parameter are varied. The limiting cases of
circular, equatorial and Keplerian motion are investigated as well and it is
shown that known results are recovered from the general formulas.Comment: 25 pages (LaTeX), 5 figures, submitted to Class. Quantum Gra
SU(N) Antiferromagnets and Strongly Coupled QED: Effective Field Theory for Josephson Junctions Arrays
We review our analysis of the strong coupling of compact QED on a lattice
with staggered Fermions. We show that, for infinite coupling, compact QED is
exactly mapped in a quantum antiferromagnet. We discuss some aspects of this
correspondence relevant for effective field theories of Josephson junctions
arrays.Comment: 33 pages,latex,Proceedings of "Common Trends in Condensed Matter and
High Energy Physics",DFUPG 1/9
SU(N) Quantum Antiferromagnets and the Phase Structure of QED in the Strong Coupling Limit
We examine the strong coupling limit of both compact and non compact QED on a
lattice with staggered fermions. We show that every SU(N) antiferromagnet with
spins in a particular fundamental representation of the SU(N) Lie Algebra and
with nearest neighbor couplings on a bipartite lattice is exactly equivalent to
the infinite coupling limit of lattice QED with the numbers of flavors of
electrons related to N and the dimension of spacetime D+1. We find that,for
both compact and noncompact QED,when N is odd the ground state of the strong
coupling limit breaks chiral symmetry in any dimensions and for any N and the
condensate is an isoscalar mass operator. When N is even,chiral symmetry is
broken if D is bigger or equal to 2 and N is small enough and the order
parameter is an isovector mass operator. We also find the exact ground state of
the lattice Coulomb gas as well as a variety of related lattice statistical
systems with long ranged interactions.Comment: latex, 45 pages, DFUPG 69/9
Color Transparency Effects in Electron Deuteron Interactions at Intermediate Q^2
High momentum transfer electrodisintegration of polarized and unpolarized
deuterium targets, is studied. We show that the importance of final
state interactions-FSI, occuring when a knocked out nucleon interacts with the
other nucleon, depends strongly on the momentum of the spectator nucleon. In
particular, these FSI occur when the essential contributions to the scattering
amplitude arise from internucleon distances . But the absorption
of the high momentum may produce a point like configuration, which
evolves with time. In this case, the final state interactions probe the point
like configuration at the early stage of its evolution. The result is that
significant color transparency effects, which can either enhance or suppress
computed cross sections, are predicted to occur for .Comment: 37 pages LaTex, 12 uuencoded PostScript Figures as separate file, to
be published in Z.Phys.
The Abnormally Weighting Energy Hypothesis: the Missing Link between Dark Matter and Dark Energy
We generalize tensor-scalar theories of gravitation by the introduction of an
abnormally weighting type of energy. This theory of tensor-scalar anomalous
gravity is based on a relaxation of the weak equivalence principle that is now
restricted to ordinary visible matter only. As a consequence, the convergence
mechanism toward general relativity is modified and produces naturally cosmic
acceleration as an inescapable gravitational feedback induced by the
mass-variation of some invisible sector. The cosmological implications of this
new theoretical framework are studied. From the Hubble diagram cosmological
test \textit{alone}, this theory provides an estimation of the amount of
baryons and dark matter in the Universe that is consistent with the independent
cosmological tests of Cosmic Microwave Background (CMB) and Big Bang
Nucleosynthesis (BBN). Cosmic coincidence is naturally achieved from a equally
natural assumption on the amplitude of the scalar coupling strength. Finally,
from the adequacy to supernovae data, we derive a new intriguing relation
between the space-time dependences of the gravitational coupling and the dark
matter mass, providing an example of crucial constraint on microphysics from
cosmology. This glimpses at an enticing new symmetry between the visible and
invisible sectors, namely that the scalar charges of visible and invisible
matter are exactly opposite.Comment: 24 pages, 6 figures, new version with extended discussions and added
references. Accepted for publication in JCAP (sept. 2008
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
Inflationary attractor in Gauss-Bonnet brane cosmology
The inflationary attractor properties of the canonical scalar field and
Born-Infeld field are investigated in the Randall-Sundrum II scenario with a
Gauss-Bonnet term in the bulk action. We find that the inflationary attractor
property will always hold for both the canonical and Born-Infeld fields for any
allowed non-negative Gauss-Bonnet coupling. We also briefly discuss the
possibility of explaining the suppressed lower multiples and running scalar
spectral index simultaneously in the scenario of Gauss-Bonnet brane inflation.Comment: 7 pages, no figures. An error in the discussion of BI field
corrected, conclusion correcte
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