Fluctuations of the Casimir potential above a disordered medium

We study the statistical fluctuations of the Casimir potential felt by an atom approaching a dielectric disordered medium. Starting from a microscopic model for the disorder, we calculate the variance of potential fluctuations in the limit of a weak density of heterogeneities. We show that fluctuations are essentially governed by scattering of the radiation on a single heterogeneity, and discuss in which limits they become larger than the average value predicted by effective medium theory. Finally, for denser disorder we show that multiple scattering processes become relevant.Comment: 9 pages, 5 figure

Statistical approach to Casimir-Polder potentials in heterogeneous media

We explore the statistical properties of the Casimir-Polder potential between a dielectric sphere and a three-dimensional heterogeneous medium, by means of extensive numerical simulations based on the scattering theory of Casimir forces. The simulations allow us to confirm recent predictions for the mean and standard deviation of the Casimir potential, and give us access to its full distribution function in the limit of a dilute distribution of heterogeneities. These predictions are compared with a simple statistical model based on a pairwise summation of the individual contributions of the constituting elements of the medium.Comment: 8 pages, 8 figure

The Determinants of Venture Capital: Additional Evidence

This paper attempts to identify and evaluate the main determinants of venture capital (VC). We develop a theoretical model where macroeconomic conditions, technological opportunity, and the entrepreneurial environment affect the demand and supply of VC. The quantitative results, based on a panel dataset of 16 OECD countries from 1990 to 2000, show that VC intensity is pro-cyclical. Interest rates affect more the demand side of VC (entrepreneurs) than the supply side. Indicators of technological opportunity, such as the stock of knowledge and the number of triadic patents affect positively and significantly the relative level of VC. Labour market rigidities reduce the impact of the GDP growth rate and of the stock of knowledge, whereas a minimum level of entrepreneurship is required in order to have a positive effect of the available stock of knowledge on VC intensity. --Venture Capital,Technological Opportuniy,Entrepreneurship,Labour Market Regidities

The Economic Impact of Venture Capital

The objective of this paper is to perform a first evaluation of the macroeconomic impact of venture capital (VC). The main assumption is that VC can be considered as being similar to business R&D performed by large firms. It can therefore contribute to economic growth through two main channels. The first one is innovation, characterized by the introduction of new products, processes or services on the market that directly contribute to improve economic performances. The second one is the development of an absorptive capability. These hypotheses are tested quantitatively with a production function model. The estimates are run over a panel data set of 16 OECD countries from 1990 to 1998. The results show that the accumulation of VC is a significant factor contributing directly to Multi-Factor Productivity (MFP) growth. The social rate of return to VC is twice as high as the social rate of return to business or public R&D. VC has also an indirect impact on MFP in the sense that it improves the output elasticity of R&D. An increased VC intensity makes it easier to absorb the knowledge generated by the universities and firms, and therefore improves aggregate economic performance.Venture Capital, Innovation, Productivity Growth, Absorptive Capability

The Determinants of Venture Capital: A Panel Data Analysis of 16 OECD Countries

The objective of this paper is to identify the main determinants of venture capital (VC). We develop a theoretical model where three main types of factors affect the demand and supply of VC. These factors are related to macroeconomic conditions, research efforts and technological opportunity, and the entrepreneurial environment. The model is evaluated econometrically with a panel dataset of 16 major OECD countries over the period 1990-1998. The estimates confirm that VC intensity is highly pro-cyclical - it reacts positively and significantly to GDP growth. Short-term (one-year) interest rates have a positive impact on VC intensity, which means that they affect more the demand side of VC (entrepreneurs) than the supply side. Indicators of technological opportunity, such as the growth rate of R&D investment, the stock of knowledge and the number of triadic patents affect positively and significantly the relative level of VC. The factors associated with the entrepreneurial environment also explain a substantial part of cross-country variations in VC intensity. An increase in corporate income tax rate has a negative effect on VC intensity. Labour market rigidities reduce the impact of the GDP growth rate and of the stock of knowledge, whereas a minimum level of entrepreneurship is required in order to have a positive effect of the available stock of knowledge on VC intensity. One important policy implication emerges from these results. It is not by providing money for VC that public decision makers will stimulate VC, but by providing knowledge and improving the entrepreneurial environment.Venture Capital, Technological Opportunity, Entrepreneurship, Labour Market Rigidities

The Economic Impact of Venture Capital

This paper attempts to evaluate the macroeconomic impact of venture capital (VC). We test the assumption that VC is similar in several respects to business R&D performed by large firms and therefore contributes to economic growth through two main channels: innovation and absorptive capacity. The quantitative results, based on a panel of 16 OECD countries from 1990 to 2001, show that the social return of VC is significantly higher than the social return of business or public R&D. An increased VC intensity also makes it easier to absorb the knowledge generated by universities and firms. --Venture Capital,Productivity Growth,Innovation,Absorptive Capacity

Surveying Technology-Based Small Firms: A Perspective From Belgium

This paper details a survey methodology on technology-based small firms (TBSF) in Belgium. The survey's objective is to better understand the factors underlying the creation and development of firms with high growth potentials. In this respect it focuses on the socio-economic factors associated with the entrepreneurs, on the national framework conditions affecting entrepreneurship and on the financial architecture of the firms. The survey data of 103 TBSFs shows that 82 percent of entrepreneurs finance their firms with their own personal savings at seed stage. The debt-financing funds mostly in the form of government subsidies of all kind and commercial bank loans are the secondary source of finance and together constitute the biggest portion of total external finance. 26 percent of these firms had at start-up stage been recipient of venture capital funds and 20 percent of "angel" funds. There is also evidence that as firms get older the proportion of internal finance decreases while external finance first increases at start-up, peaks at early growth, and gradually decreases at later stages of development. Several strengths and weaknesses of the Belgian framework conditions for entrepreneurship are identified. The results also allow to better understand the key socio-cultural determinants of entrepreneurs themselves. 97 percent of technology-based small firm entrepreneurs are male. Over 80 percent of entrepreneurs in the survey have a university degree and 42 percent hold post-graduate degrees. We briefly discuss these findings in light of existing literature.technology-based small firms, entrepreneurship, start-up financing, survey data