3,844 research outputs found
Maintaining the Regular Ultra Passum Law in data envelopment analysis
The variable returns to scale data envelopment analysis (DEA) model is developed with a maintained hypothesis of convexity in input-output space. This hypothesis is not consistent with standard microeconomic production theory that posits an S-shape for the production frontier, i.e. for production technologies that obey the Regular Ultra Passum Law. Consequently, measures of technical efficiency assuming convexity are biased downward. In this paper, we provide a more general DEA model that allows the S-shape.Data envelopment analysis; homothetic production; S-shaped production function; non-convex production set
Free-floating molecular clumps and gas mixing: hydrodynamic aftermaths of the intraclusterinterstellar medium interaction
The interaction of gas-rich galaxies with the intra-cluster medium (ICM) of
galaxy clusters has a remarkable impact on their evolution, mainly due to the
gas loss associated with this process. In this work, we use an idealised,
high-resolution simulation of a Virgo-like cluster, run with RAMSES and with
dynamics reproducing that of a zoom cosmological simulation, to investigate the
interaction of infalling galaxies with the ICM. We find that the tails of ram
pressure stripped galaxies give rise to a population of up to more than a
hundred clumps of molecular gas lurking in the cluster. The number count of
those clumps varies a lot over time -- they are preferably generated when a
large galaxy crosses the cluster (M M), and their
lifetime ( Myr) is small compared to the age of the cluster. We
compute the intracluster luminosity associated with the star formation which
takes place within those clumps, finding that the stars formed in all of the
galaxy tails combined amount to an irrelevant contribution to the intracluster
light. Surprisingly, we also find in our simulation that the ICM gas
significantly changes the composition of the gaseous disks of the galaxies:
after crossing the cluster once, typically 20% of the cold gas still in those
disks comes from the ICM.Comment: 9 pages, 6 figures. Accepted for publication in MNRA
Gravitomagnetic time-varying effects on the motion of a test particle
We study the effects of a time-varying gravitomagnetic field on the motion of
test particles. Starting from recent results, we consider the gravitomagnetic
field of a source whose spin angular momentum has a linearly time-varying
magnitude. The acceleration due to such a time-varying gravitomagnetic field is
considered as a perturbation of the Newtonian motion, and we explicitly
evaluate the effects of this perturbation on the Keplerian elements of a closed
orbit. The theoretical predictions are compared with actual astronomical and
astrophysical scenarios, both in the solar system and in binary pulsars
systems, in order to evaluate the impact of these effects on real systems.Comment: 8 pages, RevTeX; revised to match the version accepted for
publication in General Relativity and Gravitatio
Light-cone fluctuations and the renormalized stress tensor of a massless scalar field
We investigate the effects of light-cone fluctuations over the renormalized
vacuum expectation value of the stress-energy tensor of a real massless
minimally coupled scalar field defined in a ()-dimensional flat space-time
with topology . For modeling the influence of
light-cone fluctuations over the quantum field, we consider a random
Klein-Gordon equation. We study the case of centered Gaussian processes. After
taking into account all the realizations of the random processes, we present
the correction caused by random fluctuations. The averaged renormalized vacuum
expectation value of the stress-energy associated with the scalar field is
presented
A post-Keplerian parameter to test gravito-magnetic effects in binary pulsar systems
We study the pulsar timing, focusing on the time delay induced by the
gravitational field of the binary systems. In particular, we study the
gravito-magnetic correction to the Shapiro time delay in terms of Keplerian and
post-Keplerian parameters, and we introduce a new post-Keplerian parameter
which is related to the intrinsic angular momentum of the stars. Furthermore,
we evaluate the magnitude of these effects for the binary pulsar systems known
so far. The expected magnitude is indeed small, but the effect is important per
se.Comment: 6 pages, RevTeX, 1 eps figure, accepted for publication in Physical
Review D; references adde
Gravito-electromagnetism versus electromagnetism
The paper contains a discussion of the properties of the gravito-magnetic
interaction in non stationary conditions. A direct deduction of the equivalent
of Faraday-Henry law is given. A comparison is made between the
gravito-magnetic and the electro-magnetic induction, and it is shown that there
is no Meissner-like effect for superfluids in the field of massive spinning
bodies. The impossibility of stationary motions in directions not along the
lines of the gravito-magnetic field is found. Finally the results are discussed
in relation with the behavior of superconductors.Comment: 13 Pages, LaTeX, 1 EPS figure, to appear in European Journal of
Physic
Doppler Effects from Bending of Light Rays in Curved Space-Times
We study Doppler effects in curved space-time, i.e. the frequency shifts
induced on electromagnetic signals propagating in the gravitational field. In
particular, we focus on the frequency shift due to the bending of light rays in
weak gravitational fields. We consider, using the PPN formalism, the
gravitational field of an axially symmetric distribution of mass. The zeroth
order, i.e. the sphere, is studied then passing to the contribution of the
quadrupole moment, and finally to the case of a rotating source. We give
numerical estimates for situations of physical interest, and by a very
preliminary analysis, we argue that analyzing the Doppler effect could lead, in
principle, in the foreseeable future, to the measurement of the quadrupole
moment of the giant planets of the Solar System.Comment: 16 pages, 2 EPS figures; to appear in the International Journal of
Modern Physics
On the possibility of measuring the Earth's gravitomagnetic force in a new laboratory experiment
In this paper we propose, in a preliminary way, a new Earth-based laboratory
experiment aimed to the detection of the gravitomagnetic field of the Earth. It
consists of the measurement of the difference of the circular frequencies of
two rotators moving along identical circular paths, but in opposite directions,
on a horizontal friction-free plane in a vacuum chamber placed at South Pole.
The accuracy of our knowledge of the Earth's rotation from VLBI and the
possibility of measuring the rotators'periods over many revolutions should
allow for the feasibility of the proposed experiment.Comment: Latex2e, 8 pages, no figures, no tables, accepted for publication by
Classical and Quantum Gravity. Typo corrected in the formula of the error in
the difference of the orbital period
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