Spatial and observational homogeneities of the galaxy distribution in standard cosmologies

This work discusses the possible empirical verification of the geometrical concept of homogeneity of the standard relativistic cosmology considering its various definitions of distance. We study the physical consequences of the distinction between the usual concept of spatial homogeneity (SH), as defined by the Cosmological Principle, and the concept of observational homogeneity (OH), arguing that OH is in principle falsifiable by means of astronomical observations, whereas verifying SH is only possible indirectly. Simulated counts of cosmological sources are produced by means of a generalized number-distance expression that can be specialized to produce either the counts of the Einstein-de Sitter (EdS) cosmology, which has SH by construction, or other types of counts, which do, or do not, have OH by construction. Expressions for observational volumes and differential densities are derived with the various cosmological distance definitions in the EdS model. Simulated counts that have OH by construction do not always exhibit SH features. The reverse situation is also true. Besides, simulated counts with no OH features at low redshift start showing OH characteristics at high redshift. The comoving distance seems to be the only distance definition where both SH and OH appear simultaneously. The results show that observations indicating possible lack of OH do not necessarily falsify the standard Friedmannian cosmology, meaning that this cosmology will not necessarily always produce observable homogeneous densities. The general conclusion is that the use of different cosmological distances in the characterization of the galaxy distribution lead to significant ambiguities in reaching conclusions about the behavior of the large-scale galaxy distribution in the Universe.Comment: 12 pages, 12 figures, LaTeX. Matches the final version sent to the journal. Accepted for publication in "Astronomy and Astrophysics

ATP as a presynaptic modulator

© 2000 Elsevier Science Inc.There is considerable evidence that ATP acts as a fast transmitter or co-transmitter in autonomic and sensory nerves mostly through activation of ionotropic P2X receptors but also through metabotropic P2Y receptors. By analogy, the observations that ATP is released from stimulated central nervous system (CNS) nerve terminals and that responses to exogenously added ATP can be recorded in central neurons, lead to the proposal that ATP might also be a fast transmitter in the CNS. However, in spite of the robust expression of P2 receptor mRNA and binding to P2 receptors in the CNS, the demonstration of central purinergic transmission has mostly remained elusive. We now review evidence to suggest that ATP may also act presynaptically rather than solely postsynaptically in the nervous system.Fundação Ciência e Tecnologia and European nio

The Electronic States of Two Oppositely doped Mott Insulators Bilayers

We study the effect of Coulomb interaction between two oppositely doped low-dimensional tJ model systems. We exactly show that, in the one-dimensional case, an arbitrarily weak interaction leads to the formation of charge neutral electron-hole pairs. We then use two different mean-field theories to address the two-dimensional case, where inter-layer excitons also form and condense. We propose that this results in new features which have no analog in single layers, such as the emergence of an insulating spin liquid phase. Our simple bilayer model might have relevance to the physics of doped Mott insulator interfaces and of the new four layer Ba2CaCu4O8 compound.Comment: 4 pages, 1 figur

Product Attribute Saliency and Region of Origin: Some Empirical Evidence from Portugal

This paper empirically investigates the extent to which consumer preferences may act as promoters of regional products. Three products are studied in terms of the importance consumers attach to various product attributes with particular emphasis on region of origin information. The estimation of a hedonic price function, which relates the price of Portuguese regional products to its various attributes, provided empirical support to the hypothesis that region of origin matters to consumers. The study shows that wine, olive oil and cheese from some regions of origin have a significant impact on price. Particularly, some regions of origin are expected to have price premiums, while others are expected to have discounts.regional products, hedonic approach, wine, olive oil, cheese, Food Consumption/Nutrition/Food Safety, C21, D83, Q18,

Foreign firms in Portuguese manufacturing and retail sectors: a similar or different location

Foreign Directo Investment (FDI) is increasingly important in the portuguese economy since it integration in the European Union (1986), although from 1997 onwards it has considerably decreased. In 1995 and 1996, the share of the FDI in the GDP reached it peak obtaining a value of 4,29 and 4,34 respectively. The manufacturing and retailing sectors represent a good part of the total FDI. In this paper we investigate the industrial and retail services location factors. Two surveys have been carried out allowing for the identification of the most preferable factors by the foreign investors. In the manufacturing sector the selection of Portugal to invest depended upon the labour costs and the importance of domestic market. In the retailing sector the government regulations, market size, cultural and geographic proximity to the host country are the most relevent factors.