54,383 research outputs found
The revival of the Baldwin Effect
The idea that a genetically fixed behavior evolved from the once differential
learning ability of individuals that performed the behavior is known as the
Baldwin effect. A highly influential paper [Hinton G.E., Nowlan S.J., 1987. How
learning can guide evolution. Complex Syst. 1, 495-502] claimed that this
effect can be observed in silico, but here we argue that what was actually
shown is that the learning ability is easily selected for. Then we demonstrate
the Baldwin effect to happen in the in silico scenario by estimating the
probability and waiting times for the learned behavior to become innate.
Depending on parameter values, we find that learning can increase the chance of
fixation of the learned behavior by several orders of magnitude compared with
the non-learning situation
Region's reputation and the price of regional products: a hedonic analysis of Portuguese quality cheese
Resources (tangible and intangible) can be mobilized to increase region's reputation and image giving a competitive advantage to certain products with origin in that region. The returns of a region's resources depend upon the ability of local firms to appropriate the rents earned and whether the consumers value the characteristics of the region that are associated with the product, being disposed to pay a price premium. The estimation of a hedonic price function, which relates the price of Portuguese regional cheeses to its various attributes provided empirical support to test the importance of designation of origin on price. The study showsthat some designations of origin and milk types have a significant impact on price, while retailer format (hypermarket versus online store)and cheese characteristics (cured versus not cured)are nor significant. Specifically, while cheeses from regions of Minho e TrĂĄs os Montes and Alentejo are expected to have price premiums, cheeses from regions of Beiras and Ilhas are expected to have discounts. Also, cheeses made with mixed milk and goat's and ewe's milk all have positive effects on price regarding cow's milk (base category).
A biodiversity information system in an open data/metadatabase architecture
This thesis presents an overview of biological collections, their complexity and related bio-information management activities in the main institutes in the Amazon region
Retail Macro-location Factors: Empirical Evidence from the Portuguese Shopping Centres
Shopping Centres have appeared in Portugal in the beginning of the seventies and have consolidated their presence from the eighties onwards. This study aims to identify the retail macro-location factors that attracts or deters the location of shopping centres at regional (municipality) level. Using OLS regression, we tested some hypothesis as pointed out by the theory, namely the number of potential consumers, their purchasing power, the presence of competitiors, accessibility to the shopping centre and costs (e.g., land, installation). The results allow for the acceptance of the hypothesis which unveil that the promoters of shopping centres seems to value highly the size of the market, both in terms of potential consumers and purchasing power. On the other hand, due to lack of atatistical significance, we cannot infer about the other hypothesis formulated above.
Modelling spin waves in noncollinear antiferromagnets: spin-flop states, spin spirals, skyrmions and antiskyrmions
Spin waves in antiferromagnetic materials have great potential for
next-generation magnonic technologies. However, their properties and their
dependence on the type of ground-state antiferromagnetic structure are still
open questions. Here, we investigate theoretically spin waves in one- and
two-dimensional model systems with a focus on noncollinear antiferromagnetic
textures such as spin spirals and skyrmions of opposite topological charges. We
address in particular the nonreciprocal spin excitations recently measured in
bulk antiferromagnet -- utilizing
inelastic neutron scattering experiments [Phys.\ Rev.\ Lett.\ \textbf{119},
047201 (2017)], where we help to characterize the nature of the detected
spin-wave modes. Furthermore, we discuss how the Dzyaloshinskii-Moriya
interaction can lift the degeneracy of the spin-wave modes in antiferromagnets,
resembling the electronic Rashba splitting. We consider the spin-wave
excitations in antiferromagnetic spin-spiral and skyrmion systems and discuss
the features of their inelastic scattering spectra. We demonstrate that
antiskyrmions can be obtained with an isotropic Dzyaloshinskii-Moriya
interaction in certain antiferromagnets.Comment: 26 pages, 9 figure
First-principles investigation of spin wave dispersions in surface-reconstructed Co thin films on W(110)
We computed spin wave dispersions of surface-reconstructed Co films on the
W(110) surface in the adiabatic approximation. The magnetic exchange
interactions are obtained via first-principles electronic structure
calculations using the Korringa-Kohn-Rostoker Green function method. We analyze
the strength and oscillatory behavior of the intralayer and interlayer magnetic
interactions and investigate the resulting spin wave dispersions as a function
of the thickness of Co films. In particular, we highlight and explain the
strong impact of hybridization of the electronic states at the Co-W interface
on the magnetic exchange interactions and on the spin wave dispersions. We
compare our results to recent measurements based on electron energy loss
spectroscopy [E. Michel, H. Ibach, and C.M. Schneider, Phys. Rev. B 92, 024407
(2015)]. Good overall agreement with experimental findings can be obtained by
considering the possible overestimation of the spin splitting, stemming from
the local spin density approximation, and adopting an appropriate correction.Comment: 14 pages, 14 figure
Portuguese quality wine and the region-of-origin effect: consumers' and retailers' perceptions
This study investigates the relative importance of region of origin associated with extrinsic (price, brand, promotion) and intrinsic (grape, type of wine, colour, age, special references) cues in the decisions of final consumers and small retailers to buy Portuguese quality wine. In order to attain this goal we conducted a survey through face-to-face interviews in the Minho region. The results show that the dominant factor of influence in the acquisition of wine is the region of origin, both for final consumers and small retailers. Despite its importance, brand was not the principal variable to influence consumersâ wine choice, while price has been regarded as a less important extrinsic quality cue. One interesting result is the type of wine (âmaduroâ or âverdeâ) which seems to be the most preferred intrinsic cue for final consumers and small retailers. The findings also indicate that the regions of Alentejo, Douro and Verde are clearly the leaders in terms of customer acceptance.
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