Monomolecular layers and thin films of silane coupling agents by vapor-phase adsorption on oxidized aluminum

Thin films of tetraethoxysilane [TEOS], (3-bromopropyl)trimethoxysilane [BPS], trimethoxyvinylsilane [VS], and 3-(tri-methoxysily1)propyl methacrylate [TPM] on oxidized aluminum surfaces have been investigated by reflection-absorption FTIR spectroscopy, ellipsometry, contact angle, and quartz crystal microbalance (QCM) measurements. Gravimetric measurements with the QCM can reveal quantitative aspects of adsorption and film formation, even for films as thin as monolayers. Adsorption of these silane coupling agents from solution typically produces multilayer films. Vapor-phase adsorption of TEOS and TPM at room temperature results in monomolecular layers. The coupling agents VS and BPS require additional heating after the vapor-phase adsorption to initiate the hydrolysis and condensation reactions necessary for the surface attachment, which produces one to three layers. For vapor adsorbed films a packing density of 4-7 molecules/nm2 was found. The data strongly suggest that the organic moieties in several of these films have a preferential orientation on the surface; they can be viewed as two-dimensional, oligomeric siloxane networks with oriented organic chains. Subsequent heating of TPM films results in structural rearrangements; heating of TEOS results in complete condensation to Si02 films

Regional Path-Dependence in Start-up Activity

This paper studies the impact of an existing industrial structure in a region on the number of start-ups in this region. The aim is to detect path-dependencies in the regional industry structure. To this end we study empirically the regional factors that influence start-up rates. The approach deviates from the huge literature on start-up rates by studying each 2-digit industry separately, including the employment in other industries into the analysis and distinguishing between factors that provide founders and factors that influence their likelihood to start a firm.industrial dynamics, regional industry structure, start-ups, entrepreneurship, path-dependence

Consolidation and Market Power of Energy Utilities - The case of US-American and German Utility Takeovers

Between 1990 and 2002 a wave of takeovers was observed in the North American and European energy utilities market. We analyze the impact of these takeovers on market power, studying 70 takeovers of US-American and 69 takeovers of German energy utilities by applying event study methodology. Stock price reactions of acquiring and target firms as well as of their competitors are used as an indicator for market power. While we do not find any significant results pointing in this direction for transactions in the US, our findings clearly indicate that the potential to increase market power is indeed an important motive for takeovers within the German energy utilities market.acquisitions, energy utilities, market power, oligopoly, regulation

Influence of surface tension on the conical miniscus of a magnetic fluid in the field of a current-carrying wire

We study the influence of surface tension on the shape of the conical miniscus built up by a magnetic fluid surrounding a current-carrying wire. Minimization of the total energy of the system leads to a singular second order boundary value problem for the function $\zeta(r)$ describing the axially symmetric shape of the free surface. An appropriate transformation regularizes the problem and allows a straightforward numerical solution. We also study the effects a superimposed second liquid, a nonlinear magnetization law of the magnetic fluid, and the influence of the diameter of the wire on the free surface profile

Network-Induced Oscillatory Behavior in Material Flow Networks

Network theory is rapidly changing our understanding of complex systems, but the relevance of topological features for the dynamic behavior of metabolic networks, food webs, production systems, information networks, or cascade failures of power grids remains to be explored. Based on a simple model of supply networks, we offer an interpretation of instabilities and oscillations observed in biological, ecological, economic, and engineering systems. We find that most supply networks display damped oscillations, even when their units - and linear chains of these units - behave in a non-oscillatory way. Moreover, networks of damped oscillators tend to produce growing oscillations. This surprising behavior offers, for example, a new interpretation of business cycles and of oscillating or pulsating processes. The network structure of material flows itself turns out to be a source of instability, and cyclical variations are an inherent feature of decentralized adjustments.Comment: For related work see http://www.helbing.or

Polarization and Rising Wage Inequality: Comparing the U.S. and Germany

This paper compares trends in wage inequality in the U.S. and Germany using an approach developed by MaCurdy and Mroz (1995) to separate age, time, and cohort effects. Between 1979 and 2004, wage inequality increased strongly in both the U.S. and Germany but there were various country specific aspects of this increase. For the U.S., we find faster wage growth since the 1990s at the top (80% quantile) and the bottom (20% quantile) compared to the median of the wage distribution, which is evidence for polarization in the U.S. labor market. In contrast, we find little evidence for wage polarization in Germany. Moreover, we see a large role played by cohort effects in Germany, while we find only small cohort effects in the U.S. Employment trends in both countries are consistent with polarization since the 1990s. We conclude that although there is evidence in both the U.S. and Germany which is consistent with a technology-driven polarization of the labor market, the patterns of trends in wage inequality differ strongly enough that technology effects alone cannot explain the empirical findings.wage inequality, polarization, international comparison, cohort study, quantile regression