Influence of Embankments with Parapets on the Cross-Wind Turbulence Intensity at the Contact Wire of Railway Overheads

Winds as an environmental factor can cause significant difficulties for the railway system operation. The railway overhead has been particularly vulnerable to cross-winds related problems, such as development of undamped oscillations due to galloping phenomenon. The installation of windbreaks to decrease the aerodynamic loads on the train can affect the loads on railway overheads triggering cable galloping. One essential parameter to indicate the influence of the parapet wake on the catenary contact wire is the turbulence intensity. In this paper the results of an experimental analysis of the turbulence intensity due to the presence of parapets carried out in a wind tunnel are reported. Embankments equipped with different parapets have been tested and turbulence intensity has been measured at both contact wire locations, windward and leeward. The relative influence of the parapets is measured through a reduced turbulence intensity, defined as the ratio between the turbulence intensity measured with parapet and the turbulence intensity in the case without any parapet on the embankment. In general the reduced turbulence intensity increases as the height of the parapet increases

Business demography in Spain : determinants of firm survival

The impact of entry upon market performance depends not only on the number of entries and their size, but also on how long do the firms last. Consequently, there are an increasing number of papers, most of them focused on the United States and restricted to the manufacturing sector, aimed at analysing the post-entry performance of firms. Unfortunately, there is not much about this important topic in Spain due to the lack of appropriate longitudinal micro data on firms. The current paper aims to fill this gap by means of a new database covering all sectors of the business economy constructed at the Bank of Spain. We study the determinants of new firm survival using non-parametric and parametric procedures especially designed to analyse duration phenomena. We find that larger start-ups survive longer and that the probability of exit is larger in sectors with high entry rates and low concentration. One of the contributions of the paper is the inclusion of the initial firm’s financial structure among the determinants of survival. Our results suggest that holding debt, instead of equity, has positive and important effects on survival up to some point. Beyond this point, further debt increments have a negative impact on survival, and this effect is more important the higher is the corresponding debt ratio or indebtness of the firm. [resumen de autor

What makes a high-growth firm? : a probit analysis using Spanish firm-level data

Many studies have established that a small number of firms, known as fast-growth firms or Gazelles, create most of the new jobs. In spite of the importance of this topic from a policy-point of view, most of those studies are descriptive and limited to a comparison of the characteristics of the high-growth group with respect to a control group of firms. This paper, on the other hand, performs a multivariate analysis of the determinants of the fast growth of Spanish firms controlling for the possible endogeneity of some variables. We use for that purpose a firm-level database with information for about 200,000 Spanish firms per year between 1996 and 2003. We find that being a start-up increases the probability of fast growth by more than 30 percentage points, conditioned on having survived over the period. Firms with initial higher relative wages and debt ratio, up to a certain point, also experience higher chances of fast growth. Hence, as it was established elsewhere, better access to finance and to human capital are key to increase the number and growth of Gazelles. We also find that high-growth firm sustain their expansion with relatively more debt and fixed-term contracts than the rest of the firms in the sampl