Resolution of Semantic Heterogeneity in Database Schema Integration Using Formal Ontologies

This paper addresses the problem of handling semantic heterogeneity during database schema integration. We focus on the semantics of terms used as identifiers in schema definitions. Our solution does not rely on the names of the schema elements or the structure of the schemas. Instead, we utilize formal ontologies consisting of intensional definitions of terms represented in a logical language. The approach is based on similarity relations between intensional definitions in different ontologies. We present the definitions of similarity relations based on intensional definitions in formal ontologies. The extensional consequences of intensional relations are addressed. The paper shows how similarity relations are discovered by a reasoning system using a higher-level ontology. These similarity relations are then used to derive an integrated schema in two steps. First, we show how to use similarity relations to generate the class hierarchy of the global schema. Second, we explain how to enhance the class definitions with attributes. This approach reduces the cost of generating or re-generating global schemas for tightly-coupled federated database

Productivity Differences in the European Union: National, Regional and Spatial Effects

Using panel data on European regions and applying Analysis of Covariance, our study provides an empirical assessment of the relative importance of national, regional and spatial factors for explaining variations of productivity. Our analysis shows that initial economic conditions or agglomeration and centrality are indeed relevant for differences in productivity levels. What is far more important, however, is which country a region belongs to. Productivity differences in the European Union are thus obviously dominated by national regimes. In light of the historically strong influence of the nation states, this result may come as no surprise. What is surprising is the fact that the role of countries has not decreased over time, despite intensive integration efforts (European Single Market, Economic and Monetary Union).Regional productivity, agglomeration and centrality, panel data econometrics

The DLR Complex Irradiation Facility (CIF)

The DLR Institute of Space Systems in Bremen has built a new facility to study the behavior of materials under complex irradiation and to estimate their degradation in a space environment. It is named Complex Irradiation Facility (CIF). CIF allows simultaneously irradiating samples with three light sources for the simulation of the spectrum of solar electromagnetic radiation. The light sources are a solar simulator with a Xe-lamp (wavelength range 300-1200nm), a deuterium-UV-source (112-200nm), and an Argon-gas-jet-VUV-simulator. The latter allows irradiating samples with shorter wavelengths below the limitation of any window material. The VUV-simulator has been validated at the PTB (Physikalisch Technische Bundesanstalt) in Berlin by calibration that uses synchrotron radiation in the wavelength range between 40 and 400nm. Beside the different light sources CIF provides also electron and proton sources. Electrons and protons are generated in a low energy range from 1 to 10 keV with currents from 1 to 100 nA and in a higher range from 10 to 100 keV with 0.1 to 100 µA. Both particle sources can be operated simultaneously. In order to model temperature variations as appear in free space, the sample can be cooled down to liquid Nitrogen and heated up to about 450 K during irradiation. The complete facility has been manufactured in UHV-technology with metal sealing. It is free of organic compounds to avoid self-contamination. The different pumping systems achieve a final pressure of 1*1010 mbar (empty sample chamber) Besides the installed radiation sensors that control the stability of the various radiation sources and an attached mass spectrometer for analyzing the outgassing processes in the chamber, the construction of CIF allows adding other in-situ measurement systems to measure parameters that are of the user’s interest. We are currently planning to develop an in-situ measurement system in order to determine changes in the optical properties of the samples caused by irradiation. Within this paper we will show the design of CIF in more detail and discuss the performance of the various radiation sources

Regional productivity differences in the European Union - Theoretical predictions and empirical evidence

The analysis of regional income and productivity differences in the European Union (EU) has some tradition. The theoretical framework of most empirical studies on these subjects is the neoclassical growth model. Thus, research has focussed on convergence of income and productivity among EU regions. While spatial clustering is an issue in a number of studies, geography is rarely taken into account. This paper takes an explicitly spatial perspective, so we are able to look at an alternative theoretical approach, the New Economic Geography (NEG). Our regional classification is a modified version of the NUTS2 level. We use the degree of agglomeration and the geographical location (core vs. periphery) as geographical indicators. This allows for the empirical evaluation of some of the ideas of NEG regarding the pattern and development of regional productivity differences of EU regions. The analysis covers the period from 1982 to 2000. We develop a two-stage estimation strategy. Using panel data analysis in the first stage we estimate region-specific effects on productivity and its dynamics in terms of production and employment growth. In the second stage we apply Analysis of Covariance in order to explain those region-specific effects through other time-invariant factors and to estimate the impact of these factors on productivity. Our results indicate a strong significance of region-specific factors for productivity differences in the EU. The geographical indicators are significant but their impact appears to be rather limited. While the estimated parameters of the categorial spatial variables are consistent with predictions of the NEG, unobserved heterogenity at the national level is much more important. State-specific effects can explain a major part of variation in regional productivity. This implies that the regional pattern of productivity in the EU still is largely determined by national "productivity regimes". Regarding the productivity dynamics in the EU, we find a tendency towards convergence. This is in line with most other empirical studies on this subject. However the decrease of regional productivity differences is the result of two opposite processes: There is convergence of production but divergence of employment. Again national factors appear to dominate. We find that the dynamics of regional development in terms of output and employment growth are strongly determined by state-specific effects and these effects are varying significantly over time. A tentative interpretation of our results is that the economic development of regions within the EU can not be easily explained by either neoclassical theory or NEG. The reduction in regional productivity differences appears to be formed to a large extent by factors at the national level. Examples are the downsizing of low productivity agriculture in southern european countries or the boost in part-time employment in the Netherlands during the eighties. Further empirical research will have to establish whether the national component in regional development is attenuating and a European pattern of productivty growth is emerging.

Regional Disparities in the European Union: Convergence and Agglomeration

Economic disparities between the regions of the European Union are of constant concern both for policy and economic research. In this paper we examine whether there are overlapping trends of regional development in the EU: overall convergence on the one hand and persistent or even increasing spatial concentration (agglomeration) on the other. Kernel density estimation, Markov chain analysis and cross-sectional regressions provide evidence that convergence of regional per-capita income in the EU15 has become considerably stronger in the 1990s. The reduction of income disparities, however, is a phenomenon between nations but not between regions within the EU countries. European integration (and possibly European regional policy) foster the catching-up of lagging countries but at the same time forces for agglomeration of economic activities tend to increase disparities within the EU member states. Obviously, the productive advantages of spatial proximity do not vanish in the knowledge economy.Regional growth; Agglomeration; Markov chains

Regional Disparities in the European Union: Convergence and Agglomeration

Economic disparities between the regions of the European Union are of constant concern both for policy and economic research. In this paper we examine whether there are overlapping trends of regional development in the EU: overall convergence on the one hand and persistent or even increasing spatial concentration (agglomeration) on the other. Kernel density estimation, Markov chain analysis and cross-sectional regressions provide evidence that convergence of regional per-capita income in the EU15 has become considerably stronger in the 1990s. The reduction of income disparities, however, is a phenomenon between nations but not between regions within the EU countries. European integration (and possibly European regional policy) foster the catching-up of lagging countries but at the same time forces for agglomeration of economic activities tend to increase disparities within the EU member states. Obviously, the productive advantages of spatial proximity do not vanish in the knowledge economy. --Regional growth,agglomeration,Markov chains

Regional disparities in the European Union: Convergence and Agglomeration

Economic disparities between the regions of the European Union are of constant concern both for policy and economic research. One of the “stylised facts” from the empirical literature is that the process of absolute convergence observed for decades has slowed down or even petered out during the 1980s. In this paper we analyse whether it has resumed and persisted in the 1990s when European integration made huge steps forward. We construct a typology of regions in order to examine whether there are overlapping trends of regional development, in particular, overall convergence on the one hand and persistent or even increasing spatial concentration (agglomeration) on the other. Both of our approaches, Marcov chain analysis and dynamic panel estimation, provide evidence that regional convergence in the EU15 has become stronger in the 1990s. At the same time there appears to exist a tendency towards further agglomeration of high income economic activities. Keywords: Regional growth, agglomeration, dynamic panel estimation

Regional Disparities in the European Union: Convergence and Agglomeration

Economic disparities between the regions of the European Union are of constant concern both for policy and economic research. In this paper we examine whether there are overlapping trends of regional development in the EU: overall convergence on the one hand and persistent or even increasing spatial concentration (agglomeration) on the other. Kernel density estimation, Markov chain analysis and cross-sectional regressions provide evidence that convergence of regional per-capita income in the EU15 has become considerably stronger in the 1990s. The reduction of income disparities, however, is a phenomenon between nations but not between regions within the EU countries. European integration (and possibly European regional policy) foster the catching-up of lagging countries but at the same time forces for agglomeration of economic activities tend to increase disparities within the EU member states. Obviously, the productive advantages of spatial proximity do not vanish in the knowledge economy

Design and performance of a vacuum-UV simulator for material testing under space conditions

This paper describes the construction and performance of a VUV-simulator that has been designed to study degradation of materials under space conditions. It is part of the Complex Irradiation Facility at DLR in Bremen, Germany, that has been built for testing of material under irradiation in the complete UV-range as well as under proton and electron irradiation. Presently available UV-sources used for material tests do not allow the irradiation with wavelengths smaller than about $115$ nm where common Deuterium lamps show an intensity cut-off. The VUV-simulator generates radiation by excitation of a gas-flow with an electron beam. The intensity of the radiation can be varied by manipulating the gas-flow and/or the electron beam. The VUV simulator has been calibrated at three different gas-flow settings in the range from $40$ nm to $410$ nm. The calibration has been made by the Physikalisch-Technische Bundesanstalt (PTB) in Berlin. The measured spectra show total irradiance intensities from $24$ to $58$ mW$\rm{m^{-2}}$ (see Table 4.2) in the VUV-range, i.e. for wavelengths smaller than $200$ nm. They exhibit a large number of spectral lines generated either by the gas-flow constituents or by metal atoms in the residual gas which come from metals used in the source construction. In the range from $40$ nm to $120$ nm where Deuterium lamps are not usable, acceleration factors of $3$ to $26.3$ Solar Constants are reached depending on the gas-flow setting. The VUV-simulator allows studies of general degradation effects caused by photoionization and photodissociation as well as accelerated degradation tests by use of intensities that are significantly higher compared to that of the Sun at $1$ AU