The effects of the marginal tax rate in a matching model with endogenous labor supply

This paper analyzes the effects of the marginal tax rate on unemployment and economic efficiency in a matching model with homogenous agents when wages and working hours are bargained over. I show that the theoretical impact of a higher marginal tax rate on unemployment is ambiguous whatever the instantaneous utility in unemployment i.e. for an utility in unemployment that is either fixed or perfectly indexed on net wages. These results are in sharp contrast with the literature. Numerical simulations applied to France suggest that a higher marginal tax rate generally reduces the unemployment rate but at the expense of lower economic efficiency. The simulations point also out that the relation between the optimal marginal tax rate and the elasticity of labor supply is not monotonic.Matching model; Marginal Tax Rate; Labor supply; Utility in unemployment

Research Diary Visual Mapping : a reflective methodological tool for process and strategy-as-practice studies

Balogun, Huff and Johnson (2003) highlight the growing paradox for researchers who must focus on context and details while favouring general lines of research. These authors focus their reflection around the collection of qualitative data, particularly those of discussion groups, collaborative research and of research journal redaction techniques. We propose, in the context of collaborative research, a new utilisation of the personal diary, fuelled by our doctoral experiences in collaborative research. While the personal diary in its usual form increases the level of reflectivity on an intervening process, it is nevertheless difficult to exploit for the work of interpreting and legitimizing research. We therefore propose personal diary mapping. In addition to the advantages of personal diary mapping as a methodological tool for viewing the phenomenon, it allows a process to be described by highlighting specifics that are not obvious in reading a text. Moreover, the process of personal diary mapping provides a contribution to the epistemic work in a constructivist reference because it helps make the relationship between knowledge and empirical information explicit (Martinet 2007). After a summary bringing process studies closer to SaP and a review of the modalities of action research and their implications in terms of ethics and researcher responsibility, we present the origins, principles and benefits of visual mapping as regards the researcher's responsibility. In a second step, we illustrate the normative elements of this approach through a case study on strategic competence development based on personal diary mapping.Research Diary ; Visual Mapping ; methodological tool ; process ; strategy-as-practice

Local-Density Driven Clustered Star Formation

A positive power-law trend between the local surface densities of molecular gas, $\Sigma_{gas}$, and young stellar objects, $\Sigma_{\star}$, in molecular clouds of the Solar Neighbourhood has been identified by Gutermuth et al. How it relates to the properties of embedded clusters, in particular to the recently established radius-density relation, has so far not been investigated. In this paper, we model the development of the stellar component of molecular clumps as a function of time and initial local volume density so as to provide a coherent framework able to explain both the molecular-cloud and embedded-cluster relations quoted above. To do so, we associate the observed volume density gradient of molecular clumps to a density-dependent free-fall time. The molecular clump star formation history is obtained by applying a constant SFE per free-fall time, \eff. For volume density profiles typical of observed molecular clumps (i.e. power-law slope $\simeq -1.7$), our model gives a star-gas surface-density relation $\Sigma_{\star} \propto \Sigma_{gas}^2$, in very good agreement with the Gutermuth et al relation. Taking the case of a molecular clump of mass $M_0 \simeq 10^4 Msun$ and radius $R \simeq 6 pc$ experiencing star formation during 2 Myr, we derive what SFE per free-fall time matches best the normalizations of the observed and predicted ($\Sigma_{\star}$, $\Sigma_{gas}$) relations. We find \eff \simeq 0.1. We show that the observed growth of embedded clusters, embodied by their radius-density relation, corresponds to a surface density threshold being applied to developing star-forming regions. The consequences of our model in terms of cluster survivability after residual star-forming gas expulsion are that due to the locally high SFE in the inner part of star-forming regions, global SFE as low as 10% can lead to the formation of bound gas-free star clusters.Comment: 16 pages, 15 figures, Astronomy & Astrophysics, in pres

The puzzle of the cluster-forming core mass-radius relation and why it matters

We highlight how the mass-radius relation of cluster-forming cores combined with an external tidal field can influence infant weight-loss and disruption likelihood of clusters after gas expulsion. Specifically, we study how the relation between the bound fraction of stars staying in clusters at the end of violent relaxation and the cluster-forming core mass is affected by the slope and normalization of the core mass-radius relation. Assuming mass-independent star formation efficiency and gas-expulsion time-scale $\tau_{GExp}/\tau_{cross}$ and a given external tidal field, it is found that constant surface density cores and constant radius cores have the potential to lead to the preferential removal of high- and low-mass clusters, respectively. In contrast, constant volume density cores result in mass-independent cluster infant weight-loss, as suggested by observations. Our modelling includes predictions about the evolution of high-mass cluster-forming cores, a regime not yet covered by the observations. An overview of various issues directly affected by the nature of the core mass-radius relation is presented (e.g. cluster mass function, galaxy star formation histories, globular cluster self-enrichment). Finally, we emphasize that observational mass-radius data-sets of dense gas regions must be handled with caution as they may be the imprint of the molecular tracer used to map them, rather than reflecting cluster formation conditions. [Abridged]Comment: 14 pages, 7 figures, accepted to MNRA

The mass function and dynamical mass of young star clusters: Why their initial crossing-time matters crucially

We highlight the impact of cluster-mass-dependent evolutionary rates upon the evolution of the cluster mass function during violent relaxation, that is, while clusters dynamically respond to the expulsion of their residual star-forming gas. Mass-dependent evolutionary rates arise when the mean volume density of cluster-forming regions is mass-dependent. In that case, even if the initial conditions are such that the cluster mass function at the end of violent relaxation has the same shape as the embedded-cluster mass function (i.e. infant weight-loss is mass-independent), the shape of the cluster mass function does change transiently {\it during} violent relaxation. In contrast, for cluster-forming regions of constant mean volume density, the cluster mass function shape is preserved all through violent relaxation since all clusters then evolve at the same mass-independent rate. On the scale of individual clusters, we model the evolution of the ratio between the dynamical mass and luminous mass of a cluster after gas expulsion. Specifically, we map the radial dependence of the time-scale for a star cluster to return to equilibrium. We stress that fields-of-view a few pc in size only, typical of compact clusters with rapid evolutionary rates, are likely to reveal cluster regions which have returned to equilibrium even if the cluster experienced a major gas expulsion episode a few Myr earlier. We provide models with the aperture and time expressed in units of the initial half-mass radius and initial crossing-time, respectively, so that our results can be applied to clusters with initial densities, sizes, and apertures different from ours.Comment: 14 pages, 10 figures, accepted for publication in MNRA

A dazzling number of beetles (Coleoptera) in a hibernating nest of red wood ants, Formica Rufa Linnaeus (Hymenoptera : Formicidae)

status: publishe

The width of fault zones in a brittle-viscous lithosphere: Strike-slip faults

A fault zone in an ideal brittle material overlying a very weak substrate could, in principle, consist of a single slip surface. Real fault zones have a finite width consisting of a number of nearly parallel slip surfaces on which deformation is distributed. The hypothesis that the finite width of fault zones reflects stresses due to quasistatic flow in the ductile substrate of a brittle surface layer is explored. Because of the simplicity of theory and observations, strike-slip faults are examined first, but the analysis can be extended to normal and thrust faulting