Dark Energy: fiction or reality?

Is Dark Energy justified as an alternative to the cosmological constant $\Lambda$ in order to explain the acceleration of the cosmic expansion ? It turns out that a straightforward dimensional analysis of Einstein equation provides us with clear evidences that the geometrical nature of $\Lambda$ is the only viable source to this phenomenon, in addition of the application of Ockham's razor principle. This contribution is primarily a review of the main stream in the interpretation of $\Lambda$ because it is at the origin of such a research program.Comment: 9 pages, Invited talk at Tenth International Symposium Frontiers of Fundamental and Computational Physics (FFP10) Perth, Western Australia, November 24-26, 200

An Issue to the Cosmological Constant Problem

According to general relativity, the present analysis shows on geometrical grounds that the cosmological constant problem is an artifact due to the unfounded link of this fundamental constant to vacuum energy density of quantum fluctuations.Comment: 7 page

A Solution to the Cosmological Constant Problem

According to general relativity, the present analysis shows on geometrical grounds that the cosmological constant problem is an artifact due to the unfounded link of this fundamental constant to vacuum energy density of quantum fluctuations.Comment: 7 pages. to appear in IJMP

Voids in the distribution of galaxies and the Cosmological constant

With the motivation in mind to evaluate the contribution of the cosmological constant $\Lambda$ on the foam like patterns formation process in the distribution of galaxies, we investigate the Newtonian dynamics of a spherical void embedded in an uniform medium which undergoes a Hubble expansion. We use a covariant approach for deriving the evolution with time of the shell (S) acting as a boundaries condition for the inside and outside media. As a result, with the usual values for the cosmological parameters, S expands with a huge initial burst that freezes up to matching Hubble flow. With respect to Friedmann comoving frame, its magnification increases nonlinearly with $\Lambda$, with a maximal growth rate at redshift $z\sim 1.7$. The velocity field inside S shows an interesting feature which enables us to disentangle a spatially closed from open universe. Namely, the void region are swept out in the first case, what can be interpreted as a stability criterion.Comment: 4 pages, 1 figur

Entrepreneurship, organization and economic performance among Spanish firms, 1930-1975. The case of the motor industry

Before the Civil War (1936-1939), Spain had seen the emergence of firms of complex organizational forms. However, the conflict and the postwar years changed this pattern. The argument put forward in this paper is based on historical experience, the efforts will be addressed to explain the development of Spanish entrepreneurship during the second half of the twentieth century. To illustrate the change in entrepreneurship and organizational patterns among the Spanish firms during the Francoist regime we will turn to the case of the motor vehicle industry.Entrepreneurship, motor industry, multinational entreprises, organizational capabilities, state intervention

The Spanish motor industry in the first third of the 20th Century: A lost opportunity

The Spanish automobile industry had a late start. Although the country proved capable of short production runs of high- quality vehicles during the first third of the century it never managed to build up its own industry, unlike Great Britain, France, or Italy. What then, were the critical shortcomings that prevented the establishment of large Spanish motor manufacturers? Put another way, why did all of the companies set up during the first half-century fail to survive? This paper attempts to shed some light on these questions, employing a wide-ranging analysis of both internal and external factors affecting the industry. A feeble internal market, lack of resources and production factors are usually adduced as reasons, as are Spain's general economic backwardness and the role played by the public authorities. However, this paper mainly focuses on the internal factors concerning company strategy and organisation. A comparison with the Italian case helps put the traditional arguments in proper perspective and highlights those covering business strategies. Finally, we argue that a broad range of factors needs to be analysed to fully understand why Spain failed to establish a motor industry.Automobile industry, firm organization and behavior, government policy, Spain

Semi-classical limit of large fermionic systems at positive temperature

We study a system of $N$ interacting fermions at positive temperature in a confining potential. In the regime where the intensity of the interaction scales as $1/N$ and with an effective semi-classical parameter $\hbar=N^{-1/d}$ where $d$ is the space dimension, we prove the convergence to the corresponding Thomas-Fermi model at positive temperature.Comment: Convergence of states rewritten. Some references adde

The Tully-Fisher relation : Correspondence between the Inverse and Direct approaches

In a previous paper, we have demonstrated the importance to define a statistical model describing the observed linear correlation between the absolute magnitude $M$ and the log line width distance indicator $p$ of galaxies (the Tully-Fisher relation). As long as the same statistical model is used during the calibration step of the relation and the step of the determination of the distances of galaxies, standard statistical methods such as the maximum likelihood technic permits us to derive bias free estimators of the distances of galaxies. However in practice, it is convenient to use a different statistical model for calibrating the Tully-Fisher relation (because of its robustness, the Inverse Tully-Fisher relation is prefered during this step) and for determining the distances of galaxies (the Direct Tully-Fisher relation is more accurate and robust in this case). Herein, we establish a correspondence between the Inverse and the Direct Tully-Fisher approaches. Assuming a gaussian luminosity function, we prove that the ITF and DTF models are in fact mathematically equivalent (i.e. they describe the same physical data distribution in the TF diagram). It thus turns out that as long as the calibration parameters are obtained for a given model, we can deduce the corresponding parameters of the other model. We present these formulae of correspondence and discuss their validitity for non-gaussian luminosity functions.Comment: 10 pages, uuencoded en compressed Postscript file, figures avaible under requests. To be published in A\&