Modeling of the Thermomechanical Process Effects on Machine Tool Structures

AbstractThermally induced deviations are a key issue in the development of machine tools, especially when considering the actual trends of high performance and dry cutting. The interactions between the cutting process and the machine tool structure are significant boundary conditions for the numerical prediction of the thermomechanical machine behavior. Within this paper an approach for the holistic modeling of process effects is presented, including process heat, cutting forces and increased load on feed and main drives. The modeling approach is supported by experimental investigations on a lathe to provide empiric data for the link between cutting forces and active drive power

Do employment subsidies reduce early apprenticeship dropout?

We evaluate the effect of the Apprenticeship Bonus, an employment subsidy programme, on early dropout of apprenticeship. Eligibility to the programme is restricted to school leavers who have actively searched for apprenticeship training to start immediately after leaving school, but were unsuccessful in finding a position. Our analysis is based on rich survey data that has been collected specifically for this study. Using this data, we describe the characteristics of school leavers who have searched for apprenticeship positions unsuccessfully directly leaving school and analyse the effect of the subsidy on the risk of apprenticeship dropout. Even though the subsidy provides strong incentives to prevent dropout, we do not find significant effects of the programme. Our finding suggests that financial incentives are not effective in increasing the probability to finish vocational in-firm training successfully

Risk attitudes, job mobility and subsequent wage growth during the early career

Job change is a decision under uncertainty: It is associated with costs whereas the decision is made without full knowledge about future benefits. In order to investigate the relationship between willingness to take risks and job mobility, we first extend a model for on-the-job search with nonwage job characteristics by including heterogeneity in risk attitudes. Second, we empirically test the model's implications showing that individuals who are more risk-averse choose to change their jobs less often than more risk-tolerant individuals. This difference in the job changing behaviour leads to only moderate differences wage growth during early career: Risk-averse individuals tend to have on average higher wage gains from each job change and have obtained higher overall wage growth at the end of the early career phase

Does it pay to move? Returns to regional mobility at the start of the career for tertiary education graduates

Decisions taken at the start of one’s career have long-term consequences and one important decision graduates have to make is whether to be regionally mobile when looking for the first job. We investigate whether being regionally mobile for the first job following graduation rather than to stay in the place of graduation pays off. Existing research on regional mobility mostly focuses on job-to-job mobility. We analyse the determinants of early career mobility and estimate a bivariate probit model to account for the dependency between the migration decisions for tertiary education and for the first job. In order to account for self-selection with respect to migration decisions, we exploit variation in the availability of university places at the regional level. Our results show that there is significant dependency between migration decisions made before and after tertiary education. Secondly, using an IV estimation strategy, we find significantly positive wage returns to regional mobility for the first job

Selbstständige Erwerbstätigkeit in Deutschland

Die Zahl der Selbstständigen in Deutschland beläuft sich derzeit auf über vier Millionen und ist das Ergebnis eines über die Jahre zunehmenden Trends, der vor allem von den heute zahlenmäßig dominierenden Solo-Selbstständigen getragen war. Für einen Überblick über die selbstständige Erwerbstätigkeit in Deutschland trägt der Bericht empirische Evidenz aus unterschiedlichen Datenquellen zusammen. Die Gruppe der Selbstständigen wird zunächst anhand soziodemographischer Merkmale näher beschrieben. Neben dem Bestand wird auch die Dynamik der selbstständigen Erwerbsarbeit anhand der Zugänge sowie dem Verbleib in Selbstständigkeit untersucht. Die Einkommenssituation von Selbstständigen ist auch unter dem Aspekt zu sehen, dass derzeit ein Großteil der Selbstständigen nicht obligatorisch für das Alter abgesichert ist. Der Bericht beschreibt zunächst das Arbeitsangebot von Selbstständigen und gibt dann anhand verschiedener Maße Auskunft über die Einkommensstruktur von Selbstständigen. Zur Beschreibung der Einkommenssituation werden auch die Haushaltssituation und der Vermögensbesitz berücksichtigt. Wie hoch schließlich die Zahl der Selbstständigen ist, die nicht obligatorisch für das Alter abgesichert sind, wird näherungsweise anhand verschiedener öffentlich zugänglicher Datenquellen ermittelt.The number of self-employed and entrepreneurs in Germany currently amounts to more than four million and is the result of an increasing trend over the years mainly supported by today's dominant group of self-employed which do not employ dependent workers. The report compiles empirical evidence from various data sources providing an overview of self-employment and entrepreneurship in Germany. Self-employed and entrepreneurs are first described in more detail on the basis of socio-demographic characteristics. In addition to the stock description, the dynamics of self-employment and entrepreneurship are also examined regarding additions and the stability of self-employment or businesses. The income situation of the self-employed and entrepreneurs must also be seen in the light of the fact that the majority is currently not covered by mandatory old age insurance plans. The report first describes the labour supply of the self-employed and entrepreneurs, followed by information on the income structure on the basis of various measures. In describing the income situation, the household situation and wealth measures are also taken into account. Finally, the number of self-employed and entrepreneurs persons who are not covered by mandatory old age insurance plans is estimated on the basis of various publicly available data sources

Confining dyon gas with finite-volume effects under control

As an approach to describe the long-range properties of non-Abelian gauge theories at non-zero temperature T < T_c, we consider a non-interacting ensemble of dyons (magnetic monopoles) with non-trivial holonomy. We show analytically, that the quark-antiquark free energy from the Polyakov loop correlator grows linearly with the distance, and how the string tension scales with the dyon density. In numerical treatments, the long-range tails of the dyon fields cause severe finite-volume effects. Therefore, we demonstrate the application of Ewald's summation method to this system. Finite-volume effects are shown to be under control, which is a crucial requirement for numerical studies of interacting dyon ensembles.Comment: 23 pages, 4 figures; minor modification

Plattformbasierte Erwerbsarbeit: Stand der empirischen Forschung

This study summarizes the current state of empirical research in economics and social sciences on contract work mediated or provided by online platforms (online contract work). Based on a systematic literature review, this study discusses results on the diffusion of online platforms, the characteristics of workers as well as the motives for labor supply and the working conditions. The study considers services which can be provided from anywhere via the internet (online labor markets), as well as services which are mediated by online platforms but are provided at a predefined location (mobile labor markets). Besides a summary of existing research findings on the topic, this study also evaluates the quality of the empirical methods. The focus lies on the applied methods for data collection as well as the statistical analyses of the data. As a result, the current state of knowledge on online contract work can be regarded as fragmented. While for the United States several studies already exist on the diffusion of online contract work, there is a paucity of corresponding studies in Europe. A considerably higher number of studies deals with other aspects of online contract work, out of which, however, only a few focus on mobile labor markets. Administrative statistics and largescale representative surveys do not yet contain information on online contract work. Existing research on the topic is therefore based on a variety of data sources and methodological approaches, which makes it difficult to compare empirical findings

Phytochemical characterization of Tabernanthe iboga root bark and its effects on dysfunctional metabolism and cognitive performance in high-fat-fed C57BL/6J mice

Preparations of the root bark of Tabernanthe iboga have long been used in Central and West African traditional medicine to combat fatigue, as a neuro-stimulant in rituals, and for treatment of diabetes. The principal alkaloid of T. iboga, ibogaine, has attracted attention in many countries around the world for providing relief for opioid craving in drug addicts. Using a plant metabolomics approach, we detected five phenolic compounds, including 3- O-caffeoylquinic acid, and 30 alkaloids, seven of which were previously reported from T. iboga root bark. Following a report that iboga extracts contain insulinotropic agents, we aimed to determine the potential alleviating effects of the water extract of iboga root bark on high-fat diet (HFD)-induced hyperglycemia as well as its effects on cognitive function in male C57BL/6J mice. Feeding a HFD to mice for 10 weeks produced manifestations of metabolic syndrome such as increased body weight and increased plasma levels of glucose, triacylglycerols, total cholesterol, LDL-cholesterol, insulin, leptin, and pro-inflammatory mediators (IL-6, MCP-1, ICAM-1), as compared to mice fed a low-fat diet (LFD). Supplementation of HFD with iboga extract at ibogaine doses of 0.83 (low) and 2.07 (high) mg/kg/day did not improve these HFD-induced metabolic effects except for a reduction of plasma MCP-1 in the low dose group, indicative of an anti-inflammatory effect. When the HFD mice were tested in the water maze, the high-dose iboga extract caused hippocampus-dependent impairments in spatial learning and memory, as compared to mice receiving only a HFD.Peer reviewedFinal Published versio