4,617 research outputs found
Experimental designs for environmental valuation with choice-experiments: A Monte Carlo investigation
We review the practice of experimental design in the environmental economics literature concerned with choice experiments. We then contrast this with advances in the field of experimental design and present a comparison of statistical efficiency across four different experimental designs evaluated by Monte Carlo experiments. Two different situations are envisaged. First, a correct a priori knowledge of the multinomial logit specification used to derive the design and then an incorrect one. The data generating process is based on estimates from data of a real choice experiment with which preference for rural landscape attributes were studied. Results indicate the D-optimal designs are promising, especially those based on Bayesian algorithms with informative prior. However, if good a priori information is lacking, and if there is strong uncertainty about the real data generating process - conditions which are quite common in environmental valuation - then practitioners might be better off with conventional fractional designs from linear models. Under misspecification, a design of this type produces less biased estimates than its competitors
The oxygen abundance deficiency in irregular galaxies
The observed oxygen abundances in a number of irregular galaxies have been
compared with predictions of the closed-box model of chemical and photometric
evolution of galaxies. Oxygen is found to be deficient with respect to the
predicted abundances. This is an indicator in favor of loss of heavy elements
via galactic winds or/and of infall of low--abundance gas onto the galaxy.
The oxygen abundance deficiency observed within the optical edge of a galaxy
cannot be explained by mixing with the gas envelope observed outside the
optical limit. We confirm the widespread idea that a significant part of the
heavy elements is ejected by irregular galaxies in the intergalactic medium.Comment: 8 pages, 7 figures, accepted for publication in Astronomy and
Astrophysic
Bulges
We model the evolution of the galactic bulge and of the bulges of a selected
sample of external spiral galaxies, via the multiphase multizone evolution
model. We address a few questions concerning the role of the bulges within
galactic evolution schemes and the properties of bulge stellar populations. We
provide solutions to the problems of chemical abundances and spectral indices,
the two main observational constraints to bulge structure.Comment: 15 pages, 10 figures, to be published in MNRA
Polynomial approximation of non-Gaussian unitaries by counting one photon at a time
In quantum computation with continous-variable systems, quantum advantage can
only be achieved if some non-Gaussian resource is available. Yet, non-Gaussian
unitary evolutions and measurements suited for computation are challenging to
realize in the lab. We propose and analyze two methods to apply a polynomial
approximation of any unitary operator diagonal in the amplitude quadrature
representation, including non-Gaussian operators, to an unknown input state.
Our protocols use as a primary non-Gaussian resource a single-photon counter.
We use the fidelity of the transformation with the target one on Fock and
coherent states to assess the quality of the approximate gate.Comment: 11 pages, 7 figure
Evaluating Research Activity:Impact Factor vs. Research Factor
The Impact Factor (IF) âhas moved ... from an obscure bibliometric indicator to become the chief quantitative measure of the quality of a journal, its research papers, the researchers who wrote those papers, and even the institution they work inâ ([2], p. 1). However, the use of this index for evaluating individual scientists is dubious. The present work compares the ranking of research units generated by the Research Factor (RF) index with that associated with the popular IF. The former, originally introduced in [38], reflects article and book publications and a host of other activities categorized as coordination activities (e.g., conference organization, research group coordination), dissemination activities (e.g., conference and seminar presentations, participation in research group), editorial activities (e.g., journal editor, associate editor, referee) and functional activities (e.g., Head of Department). The main conclusion is that by replacing the IF with the RF in hiring, tenure decisions and awarding of grants would greatly increase the number of topics investigated and the number and quality of long run projects.scientific research assessment, Impact Factor, bibliometric indices, feasible Research Factor
A grid of chemical evolution models along the Hubble Sequence
We have computed a grid of multiphase chemical evolution models whose results
are valid for any spiral galaxy, using as input the maximum rotation velocity
and the morphological type or index T.Comment: 2 pag., contribution to the conference Cosmic Evolution (Paris, Nov.
2000
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