Showing papers by "Leibniz University of Hanover published in 1994"
TL;DR: This paper applied various unit root tests to a panel of wage data and found that firm and industry wages both possess a unit root in the autoregressive representation of the distribution of hourly wages.
Abstract: Theoritical considerations suggest that spillover forces equalize wages for similar jobs Thus, it is expected that firm wages are cointegrated with the corresponding wage rates on an industrial level In this paper we apply various unit root tests to a panel of wage data We show that the familiar techniques can be adopted to this type of data allowing for unobserved heterogeneity and common time effects Our results suggest that firm and industry wages both possess a unit root in the autoregressive representation However, ther is only weak evidence for a cointegration realtionship
247 citations
TL;DR: The results suggest that the present design approaches cannot explain most of the failure modes reported, and that the stability of vertical breakwaters is an integrated and complex problem which can satisfactorily be solved only by dynamic analysis and probabilistic design approaches.
224 citations
TL;DR: It is suggested that temporary caval umbrellas are indicated in medically treated patients with shock and massive pulmonary embolism and thrombolysis may provide a life-saving option and a randomised trial is warranted.
190 citations
TL;DR: In this article, a two-dimensional computational fluid dynamics study of the two-phase gas-liquid flow in bubble columns is presented, where the flow is modelled by a Navier-Stokes system of equations in an Eulerian representation, whereas the motion of the gas is modeled on a smaller scale by tracking individual bubbles or bubble clusters through the liquid in a Lagrangian way.
187 citations
TL;DR: In this paper, a 2-year field study conducted on a high-fertilized Gleyic Luvisol in Stuttgart-Hohenheim significant differences among 10 maize cultivars were observed in soil nitrate depletion.
Abstract: In a 2-year field study conducted on a high fertilized Gleyic Luvisol in Stuttgart-Hohenheim significant differences among 10 maize cultivars were observed in soil nitrate depletion. The different capability of the cultivars to utilize nitrate particularly from the subsoil was positively correlated with (a) shoot N uptake at maturity, and (b) root length density (Lv) in the subsoil layers at silking. “Critical root length densities” for nitrate uptake were estimated by (a) calculating uptake rates per unit root length (U), (b) subsequent calculation of needed nitrate concentration in soil solution (C1) to sustain calculated U according to the Baldwin formula, and (c) reducing measured Lv and proportionate increase of U until needed concentration equaled measured concentration. Uptake rate generally increased with soil depth. “Critical root length densities” for cultivar Brummi (high measured root length densities and soil nitrate depletion) at 60–90 cm depth ranged from 7 % (generative growth) to 28 % (vegetative growth) of measured Lv Measured root length density of each other cultivar was higher than “critical root length density” for Brummi indicating that the root system of each cultivar examined would have been able to ensure N uptake of Brummi. Positive relationships between root length density and nitrate utilization as indicated by correlation analysis therefore could not be explained by model calculations. This might be due to simplifying assumptions made in the model, which are in contrast to non-ideal uptake conditions in the field, namely irregular distribution of roots and nitrate in the soil, limited root/soil contact, and differences between root zones in uptake activity. It is concluded from the field experiment that growing of cultivars selected for high N uptake-capacity of the shoots combined with “high” root length densities in the subsoil may improve the utilization of a high soil nitrate supply.
183 citations
TL;DR: In this article, a geometrically exact theory of finite deformation and finite rotation micropolar elastoplasticity is formulated to obtain a generalized nonlinear continuum framework.
171 citations
TL;DR: An improved technique of hybrid modelling biochemical production processes is described, composed of a set of dynamical differential equations, an artificial neural network and a fuzzy expert system, demonstrating the applicability of a hybrid model for state estimation, prediction, feed rate optimization, and process control.
161 citations
TL;DR: The new developments in drilling technology are shown in the following paper as mentioned in this paper, where new drilling tool materials like carbides, cermets, ceramics and hard coatings have been developed in the last years with an dramatically increase of tool life and cutting parameters.
120 citations
TL;DR: In this paper, both highly and slightly humified peat moss (ground to less than 63 μm) were incorporated into a silt loam and a clay soil in proportions of 0, 1, 3, 5 and 8 g (100 g)−1.
Abstract: The aim of this study was to examine the effects of incorporation of organic matter (peat moss) on the mechanical properties of soil aggregates. Both highly and slightly humified peat moss (ground to less than 63 μm) were incorporated into a silt loam and a clay soil in proportions of 0, 1, 3, 5 and 8 g (100 g)−1. The mixtures were wetted and stored for several months to simulate field conditions. Afterwards the Atterberg limits were determined. The mixtures were then crushed to less than 2 mm, kneaded at the liquid and plastic limits and at intermediate water contents, and left to dry. After drying, they were recrushed to form aggregates of less than 8 mm. Aggregate porosity increased whereas aggregate tensile strength decreased with increasing organic matter content. The less humifies the organic matter, the greater was its effect in increasing aggregate porosity and hence the greater the decrease in aggregate tensile strength. Mean weight diameter of aggregates obtained by dry-sieving decreased with increasing organic matter content, whereas in the case of wet-sieving it was not significantly affected by the organic matter incorporation. Moisture retention of beds of aggregates of less than 8 mm was increased with increasing organic matter content, and this increase was greater where slightly humified organic matter had been added than with highly humified material.
108 citations
TL;DR: In this article, a new isolation method has been developed for the determination of pesticides in environmental water samples using solid-phase microextraction (SPME), which can be used to identify even unknown compounds in environmental samples.
88 citations
TL;DR: In this paper, the authors formulate two wellknown isotropic elastoplastic damage concepts for ductile materials in the framework of geometrically exact finite multiplicative elastasticity.
Abstract: The new contribution of this study is to formulate two wellknown isotropic elastoplastic damage concepts for ductile materials in the framework of ‘geometrically exact’ finite multiplicative elastoplasticity. For the model originally proposed by Lemaitre the damage evolution follows from a dissipation potential and the hypothesis of general associativity. In contrast, the Gurson model takes into account the balance of mass separately to formulate damage evolution. In this contribution both formulations are based on logarithmic Hencky strains leading to a simple application of the so called ‘exponential map’ stress integrator which is the algorithmic counterpart of the multiplicative elastoplastic formulation adopted. Special emphasis is directed towards the numerical implementation of these models within the framework of finite element analysis of inelastic boundary value problems. To compare the results of numerical computations several standard examples within finite elastoplasticity are analysed with both damage models and the results are contrasted to the outcome of an analysis with the classical v. Mises model. thereby, the dramatic influence of damage on the behaviour within necking and localization computations is highlighted. The different behaviour of the two models considered within compression dominated problems is appreciated.
TL;DR: In this paper, the vertical two-phase crossflow on the shell side of a horizontal tube bundle was studied and flow patterns were established and visual observation together with photographic data and a video-film were used.
TL;DR: The results indicate that yield decline in maize monocropping might be due to allelopathic effects.
Abstract: In the northern Guinea Savanna of Ghana (1984–1987) a field experiment was conducted to study the reasons for beneficial effects of rotating maize (Zea mays) and cowpea (Vigna unguiculata) on yield and N and P use of maize. The treatments included two cropping systems, maize monocropping and maize/cowpea rotation, two levels of nitrogen (0 and 80 kg N ha-1 as urea) and two levels of phosphorus application (0 and 60 kg ha-1 P as Volta phosphate rock). Yields and nutrient accumulation of maize were larger in rotation than in monocropping, independent of the N and P level. Fertilizer application (N and P) increased yields of maize in both cropping systems to the same extent. Nitrate contents of the soil after cowpea and after maize monoculture were comparable at the beginning of the cropping period. Also, potential nitrogen mineralization was only slightly larger after cowpea in the unfertilized plots. However, soil nitrate of fertilized plots was similar or even higher under monocropping than under crop rotation, especially in deeper soil layers and at the end of the cropping period. This indicates that in addition to the availability of mineral N, its use by the plants was limiting for the productivity of maize. Root length densities of maize were significant lower in monocropped maize than in maize grown in rotation. Soil physical parameters (infiltration, bulk density, aggregate stability and water capacity) showed a significant deterioration compared to a bush fallow plot, but differed only slightly between the cropping systems. Also in a pot experiment maize growth was much better in the soil from the crop rotation than from the monocropping plots, provided P was eliminated as the main growth-limiting factor. Since this effect persisted in spite of N application and optimization of soil physical properties by mixing the soil with polystyrol it is concluded that the results indicate that yield decline in maize monocropping might be due to allelopathic effects.
TL;DR: In this paper, a sensitivity analysis of the relevant parameters affecting the dynamic response of a caisson breakwater subject to breaking wave loads is performed by using a numerical model validated by large-scale model tests.
TL;DR: A linkage map of rye (Secale cereale L.) is presented which comprises 60 loci including RFLPs, RAPDs, isozyme, morphological and physiological markers, which are unequally distributed over the seven chromosomes of rye.
Abstract: A linkage map of rye (Secale cereale L.) is presented which comprises 60 loci including RFLPs, RAPDs, isozyme, morphological and physiological markers. The genetics and linkage relationships of these markers were investigated in several inbred lines of rye. For the RFLP mapping a genomic library of PstI-digested DNA was constructed from which 50 size-selected clones were analysed. The portion of single-copy and multi-copy DNA and the frequency of polymorphic DNA was determined. The markers are unequally distributed over the seven chromosomes of rye. Many of them exhibit a distorted segregation. The main region of deviating segregation ratios could be localized near the self-incompatibility loci.
TL;DR: The essential oil of Indian Acorus calamus shows potential for stored-product pest control and β-asarone, its active ingredient, has toxic and sterilizing effects, is tested as possible control agents.
TL;DR: Novel immobilized metal affinity membrane adsorbers (IMA-MA) were studied for potential use as stationary phases for protein separation and the binding of proteins similar in terms of hydrophobicity, isoelectric point, size and mass-to-charge ratio but differing in their number of surface histidine residues was investigated.
TL;DR: A simple way of combining all the available knowledge relating to a given process is presented, including a hybrid model for state estimation and prediction on the example of a yeast production process.
Abstract: Process models are used to formulate knowledge about process behaviour. They are applied, e.g., to predict the process' future behaviour and for state estimation when reliable on-line measuring techniques to monitor the key variables of the process are not available. There are different sources of information available for modelling, which provide process knowledge in different representations. Some elements or aspects may be described by physically based mathematical models and others by heuristically obtained rules of thumb, while some information may still be hidden in the process data recorded during previous runs of the process. Heuristic rules are conveniently processed with fuzzy expert systems, while artificial neural networks present themselves as a powerful tool for uncovering the information within the process data without the need to transform the information into one of the other representations. Artificial neural networks and fuzzy technology are increasingly being employed for modelling biotechnological processes, thus extending the traditional way of process modelling by mathematical equations. However, a sufficiently comprehensive combination of all these techniques has not yet been put forward. Here, we present a simple way of combining all the available knowledge relating to a given process. In a case study, we demonstrate the development of a hybrid model for state estimation and prediction on the example of a yeast production process. The model was validated during a cultivation performed in a standard pilot-scale fermenter.
TL;DR: In this article, an LC separation in combination with postcolumn addition of a volatile salt solution was developed, which permits the analysis of 95 pesticides with a single LC-MS method using reversed phase gradient caution.
TL;DR: In this article, a comparison between anionic and group transfer polymerization (GTP) based poly-N,N-N-diethylacrylamide was made.
Abstract: Several batches of poly-N,N-diethylacrylamide were synthesized by anionic and by group transfer polymerization (GTP). A radical poly-N,N-diethylacrylamide prepared from the same monomer was also included in the comparison. According to matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) both types of living polymerization resulted in narrow molecular weight distributions with Mw/Mn values below 1.5. Average molecular weights (Mn) between 888 and 4678 g/mol were calculated in these cases. The radical polymer had an average molecular weight (Mn) of approximately 130,000 g/mol. The dry anionic and GTP polymers were investigated by differential scanning calorimetry (DSC) and x-ray diffraction spectrometry. Evidence for partial crystallinity in the solid state was found. The conformation of all polymers was examined by high resolution (600 MHz) NMR. According to these measurements, 75% of the CHR groups of the anionic poly-N,N-diethylacrylamide were located in an isotactic triade. The remaining 25% had heterotactic structure, while no indication for the presence of syndiotactic protons was found. Poly-N,N-diethylacrylamide prepared by GTP, on the other hand, had mainly syndiotactic structure. The aqueous solutions of the polymers showed phase separation upon heating. Whereas the lower critical solution temperature (LCST) was approximately 30°C in the case of the poly-N,N-diethylacrylamide prepared by GTP and by radical polymerization, uncommonly high LCSTs of more than 40°C were observed for the anionic poly-N,N-diethylacrylamide. © 1994 John Wiley & Sons, Inc.
TL;DR: In this article, a new biosensors were developed by immobilizing enzymes on simple EIS (Electrolyte Insulator Semiconductor) layer structures and measurements were made by using a C/V-measuring instrument in a constant charge mode.
17 Jun 1994
TL;DR: This paper demonstrates an approach to derive bottom-up query-evaluation algorithms from abstract properties of the underlying negation semantics for the disjunctive stable model semantics, and proposes an appropriate completion of the residual program, which syntactically characterizes the intended models.
Abstract: Our goal is to derive bottom-up query-evaluation algorithms from abstract properties of the underlying negation semantics. In this paper, we demonstrate our approach for the disjunctive stable model semantics, but the ideas are applicable to many other semantics as well. Our framework also helps to understand and compare other proposed query evaluation algorithms. It is based on the notion of conditional facts, developed by Bry and Dung/Kanchansut. We start by computing a “residual program” and show that it is equivalent to the original program under very general conditions on the semantics (which are satisfied, e.g., by the well-founded, stable, stationary, and static semantics). Many queries can already be answered on the basis of the residual program. For the remaining literals, we propose to use an appropriate completion of the residual program, which syntactically characterizes the intended models. In the case of the stable model semantics, we utilize an interesting connection to Clark's completion.
TL;DR: In this article, an empirical study of inter-industry and inter-temporal variations in entry of new firms using longitudinal data covering all manufacturing establishments in Lower Saxony between 1979 and 1989 is presented.
Abstract: This paper is an empirical study of inter-industry and inter-temporal variations in entry of new firms using longitudinal data covering all manufacturing establishments in Lower Saxony between 1979 and 1989. Patterns of entry are reported for 29 industries based on numbers of new firms, gross rates of entry, and entry intensities (shares of employees) in different types and size classes of new firms. Entry varies considerably between firm types, industries, and over time. Focussing on entry by small single firms an empirical model is applied to search for industry characteristics that are highly correlated with entry. Pooling of cross-section and time-series data allows to control for influences of varying macroeconomic conditions and unobserved industry characteristics. A highly robust estimation method is applied for the first time in a study of entry rates, and it turns out that extreme observations often have large effect on the results. Entry intensity tends to be positively related to industry growth, concentration, and high unemployment, but negatively to high interest rates, profits, and (insignificantly) to intensive use of capital and R&D. I plead for further research vialearning by asking those who are doing.
TL;DR: In this paper, an empirical study of inter-regional and inter-temporal variations in entry of new firms using longitudinal data covering all manufacturing establishments in Lower Saxony between 1979 and 1991 is presented.
Abstract: This paper is an empirical study of inter-regional and inter-temporal variations in entry of new firms using longitudinal data covering all manufacturing establishments in Lower Saxony between 1979 and 1991. Patterns of entry are reported for sixteen regions based on gross rates of entry (number of new firms) and entry intensities (shares of employees). An empirical model is applied to detect regional characteristics that are highly correlated with entry. Pooling of cross-section and time-series data allows for control of influences of varying macroeconomic conditions and unobserved regional characteristics that turned out to be important. Small firm entry tends to be positively related to high overall economic growth, and to be higher in regions where both the small firm employment share and the level of wealth are high while the wage rate is low. We find no evidence for a negative impact of the business tax rate or for a positive effect of regional subsidies.
TL;DR: Various toxicological symptoms were observed in Aiolopus thalassinus (Fabr.) adults which resulted from either contaminated soil or from being fed HgCl2, CdCl2-, and PbCl2-treated diet, and no long-term effect was found.
TL;DR: The effect of reforms during the first year of Germany's health reform legislation is examined and lessons for reform of the U.S. system are offered.
Abstract: Prologue: Germany's century-old universal health insurance plan represents a middle ground in the spectrum of approaches Western countries have adopted to protect their populations against the financial consequences of illness. Among industrialized countries, West Germany's health insurance plan came closest during the 1980s to limiting increases in spending to a rate equal to growth of its national income; the disparity between the two measures was greatest in the United States. Nevertheless, Germany has remained concerned about the continued rise in health care expenditures, particularly because of the increased pressure that unification of East and West Germany has placed on public spending. Here Klaus Henke, Margaret Murray, and Claudia Ade discuss the latest efforts by the German government to moderate the growth of health care spending. One of the striking features of the 1993 health care reform act in Germany, compared with the meandering pace of the U.S. reform effort, was the speed with which it ...
TL;DR: In this article, the authors present some aspects of the formulation and numerical implementation of localization phenomena in elastoplastic solids at small strains, and investigate two general constitutive approaches to the modelling of the displacement discontinuity and develop a finite-element formulation for its numerical implementation.
Abstract: The paper presents some aspects of the formulation and numerical implementation of localization phenomena in elastoplastic solids at small strains. At first we point out the theoretical foundation and algorithmic implementation of a localpre-critical localization analysis for the detection of critical zones which may cause a loss of global structural stability, e.g. shear-bands. The second part proposes a particular approach to thepost-critical localization analysis in order to trace post-critical localized equilibrium branches of solids with a global displacement-discontinuity surface. Within this context we investigate two general constitutive approaches to the modelling of the displacement discontinuity and develop a finite-element formulation for its numerical implementation.
TL;DR: In this paper, two different types of non-crystalline mullite precursor with identical bulk composition were prepared from tetraethoxysilane and silicon chloride, respectively, and aluminium sec-butozide by using different methods of hydrolysis.
Abstract: Two different types of non-crystalline mullite precursor with identical bulk composition (72 wt% Al 2 O 3 , 28 wt% SiO 2 ) were prepared from tetraethoxysilane and silicon chloride, respectively, and aluminium sec-butozide, by using different methods of hydrolysis. The precursors, designated as type I and III, display different crystallization processes above ≈ 900°C: type I precursors directly form mullite, while type III precursors yield crystallization of transient γ-alumina. Infrared (IR) spectroscopy, large angle X-ray scattering (LAXS) and 27 Al nuclear magnetic resonance spectroscopic studies, and 29 Si nuclear magnetic resonance (NMR) literature data give evidence for a high degree of structural mixing in type I precursors and for a beginning of segregation into Al 2 O 3 -rich domains in type III precursors prior to crystallization (⩽ 900°C). Both precursors are composed of (SiO) tetrahedra and of (AlO) octahedra, tetrahedra and pentahedra although pentahedra are dominant in type I while octahedra occur more frequently in type III precursors. The driving force for mullitization (type I) and γ-alumina formation (type III) taking place at the same temperature is believed to be the instability of pentahedrally coordinated Al above ≈ 900°C. The sudden disappearance of Al pentahedra probably depends on the formation of reactive network centers during dehydroxylation. This hypothesis is derived from the observation that dehydroxylation and condensation strongly take place in a similar temperature range prior to crystallization.
TL;DR: This article reviews methods that aim to make better use of empirical data, or of process knowledge derived from such data, in order to develop and improve the models.
01 Jan 1994
TL;DR: A new semantics for disjunctive logic programs in an abstract way is defined as the weakest semantics with certain properties, the most important being the unfolding-property (GPPE).
Abstract: We define a new semantics for disjunctive logic programs in an abstract way as the weakest semantics with certain properties, the most important being the unfolding-property (GPPE). Our semantics is similar to the strong well-founded semantics proposed by Ross, but seems to be more regularly behaved. It is an extension of both the well-founded semantics WFS and the generalized closed world semantics GCWA. We then present a bottom-up query-evaluation method for this semantics. An important feature of our approach is that we directly derive the algorithm from the given abstract properties of the logic programming semantics. The idea of the method is to compute derived rule instances with purely negative bodies (corresponding to Bry’s conditional facts and Chen/Warren’S residual program), and then to apply reduction steps in order to eliminate the conditions where possible.