Displacements analysis of self-excited vibrations in turning

The actual research deals with determining by a new protocol the necessary parameters considering a three-dimensional model to simulate in a realistic way the turning process on machine tool. This paper is dedicated to the experimental displacements analysis of the block tool / block workpiece with self-excited vibrations. In connexion with turning process, the self-excited vibrations domain is obtained starting from spectra of two accelerometers. The existence of a displacements plane attached to the tool edge point is revealed. This plane proves to be inclined compared to the machines tool axes. We establish that the tool tip point describes an ellipse. This ellipse is very small and can be considered as a small straight line segment for the stable cutting process (without vibrations). In unstable mode (with vibrations) the ellipse of displacements is really more visible. A difference in phase occurs between the tool tip displacements on the radial direction and on the cutting one. The feed motion direction and the cutting one are almost in phase. The values of the long and small ellipse axes (and their ratio) shows that these sizes are increasing with the feed rate value. The axis that goes through the stiffness center and the tool tip represents the maximum stiffness direction. The maximum (resp. minimum) stiffness axis of the tool is perpendicular to the large (resp. small) ellipse displacements axis. FFT analysis of the accelerometers signals allows to reach several important parameters and establish coherent correlations between tool tip displacements and the static - elastic characteristics of the machine tool components tested

Modélisation du perçage vibratoire sur UPA

Les unités de perçage automatiques ont été récemment associées à des technologies permettant de percer en mode vibratoire pour favoriser l'évacuation des copeaux métalliques lors des perçages d'empilages multi-matériaux. Après une présentation de l'apport du vibratoire en perçage, un état de l'art des systèmes vibratoires utilisés sur UPA sera présenté. Dans un deuxième temps, une modélisation du système vibratoire à oscillations forcées sera exposée. Des résultats expérimentaux seront confrontés au modèle obtenu afin de vérifier sa robustesse et d'évaluer l'efficacité du perçage vibratoire

Análisis de la heurística en la contratación empresarial a través de una cartera de derivados reales

Departing from the notion that labour legislation should be founded in the generation of job stability a model for recruitment is presented in which the employer is likened to the holder of an investment portfolio containing two real derivatives – swap or the option of sale. This model allows us on one hand to analyze sensitivity to the variables that are at play in an employment contract and, on the other, look at the effects that the most recent reforms in Spanish labour laws have had on contracting decisions made by employers. The results are clear: social security benefits are shown to be the most sensitive variable on the work contract, and applying the changes proposed in the latest labour reforms, this effect is upheld. The study concludes that reducing the costs of dismissal does not increase the likelihood of employers’ taking on new staff.Dada la situación actual y partiendo del supuesto que como herramienta para una correcta política de empleo la legislación laboral debe sentar las bases sólidas para que en el momento de recuperación económica se generen puestos de trabajo estables, se presenta un modelo de simulación de contratación que nos va a permitir un análisis de sensibilidad de las distintas variables a tener en cuenta en una regulación del mercado laboral. El modelo consiste en asimilar el comportamiento del empresario al del propietario de una cartera de inversión compuesta por dos derivados reales, un swap y una opción de venta americana. Este modelo nos permite, por un lado, hacer un análisis de sensibilidad de las diferentes variables que intervienen en la contratación, y, por otro lado, analizar los efectos que la última reforma laboral española tiene sobre la decisión de contratar del empresario. Los resultados son claros, la variable que más sensibilidad presenta sobre la contratación es la cuota patronal de la seguridad social, y aplicando los cambios propuestos en esta última reforma laboral, se concretan estos efectos y también se concluye que la reducción de los costes de despido no acelera la decisión de contratar.Dada a situação atual e partindo do suposto que como ferramenta para uma correta política de emprego, a legislação laboral deve instituir as bases sólidas para que, no momento da recuperação econômica, se gerem postos de trabalho estáveis, se apresentem um modelo de simulação de contratação que nos permitirá uma análise de sensibilidade das diferentes variáveis a considerar em uma regulação do mercado laboral. O modelo consiste em assimilar o comportamento do empresário ao do proprietário de uma carteira de investimento composto por dois derivados reais, um swap e uma opção de venda americana. Esse modelo nos permite, por um lado, fazer uma análise de sensibilidade das diferentes variáveis que intervêm na contratação e, por outro lado, analisar os efeitos que a última reforma laboral espanhola tem sobre a decisão de contratar do empresário. Os resultados são claros, a variável que mais sensibilidade apresenta sobre a contratação é a cota patronal da previdência social e aplicando as mudanças propostas nesta última reforma laboral, concretizam-se esses efeitos e também se conclui que a redução dos custos de demissão não acelera a decisão de contrata

Firm heterogeneity and wages under different bargaining regimes : does a centralised union care for low-productivity firms?

This paper studies the relationship between wages and the degree of firm heterogeneity in a given industry under different wage setting structures. To derive testable hypotheses, we set up a theoretical model that analyses the sensitivity of wages to the variability in productivity conditions in a unionsised oligopoly framework. The model distinguishes centralised and decentralised wage determination. The theoretical results predict wages to be negatively associated with the degree of firm heterogeneity under centralised wage-setting, as unions internalise negative externalities of a wage increase for low-productivity firms. We test this prediction using a linked employeremployee panel data set from the German mining and manufacturing sector. Consistent with our hypotheses, the empirical results suggest that under industry-level bargaining workers in more heterogeneous sectors receive lower wages than workers in more homogeneous sectors. In contrast, the degree of firm heterogeneity is found to have no negative impact on wages in uncovered firms and under firm-level contracts

Market Work, Home Production, Consumer Demand and Unemployment among the Unskilled

We develop a general equilibrium model in which longer working time and higher labor force participation lead to a fall in unemployment. Longer working hours and higher labor force participation have two direct effects: People have higher incomes and less (leisure) time. This has implications for the composition of consumer demand, since people spend less time on home production. Instead, they outsource more domestic tasks to the market. Consumer demand shifts toward unskill-intensive goods. The relative demand for unskilled labor rises and unemployment falls. We provide empirical evidence for our theoretical predictions in several ways: We study the link between labor market participation, home production and the demand for household and similar services using the German time use survey conducted in 1991/92. In addition, we use panel data for 23 OECD countries between 1980 and 2003 to directly examine the link between labor force participation and the unemployment rate. The empirical results corroborate the predictions from the theoretical model

Labor Market Segmentation and Efficient Bargaining in a Macroeconomic Model

Claas O. Labor Market Segmentation and Efficient Bargaining in a Macroeconomic Model. Center for Mathematical Economics Working Papers. Vol 600. Bielefeld: Center for Mathematical Economics; 2018.This paper studies the implications of a segmented labor market with efficient wage– employment bargaining on the internal labor market and a competitive external labor market on the temporary equilibrium of a closed monetary macroeconomy of the AS– AD type with government activity, fiat money, and expectations. Workers have identical preferences, those on the internal labor market are represented by a labor union. There is no mobility between the labor markets. Union power measured by the share of the production surplus allotted to the union and union density measured by the fraction of workers who are union members impact the functional income distribution, but neither affect the individual employment levels nor the aggregate employment level and the aggregate supply function. The wage on the internal labor market is above the wage on the external labor market if and only if the profit share of total revenue is smaller than under a fully competitive labor market. Unique temporary equilibria exist for all combinations of union power and union density. The paper provides a complete comparative-statics analysis showing in particular a negative price effect of union power and a positive price effect of union density. In general, the effects of union power and union density on any equilibrium value are usually of opposite signs. Single-labor-market models with a fully competitive or a fully unionized labor market are special or limiting cases of the segmented-labor-market model

Trust and Quality of Growth: A Note

The transition from Millennium Development Goals (MDGs) to Sustainable Development Goals (SDGs) has substantially shifted the policy debate from growth to inclusive growth. In this short note, we revisit the trust-growth nexus by exploiting a dataset on quality of growth (QG), recently made available to the scientific community. The empirical evidence is based on interactive contemporary and non-contemporary quantile regressions. Inequality and human development modifying variables are used as additional controls. The findings broadly support the positive role of trust in QG. In addition, relatively high thresholds of inequality are needed to change this positive trust-QG nexus in some distributions.https://jpconley.wordpress.com/economics-bulletinhb2017Economic