Hyperbolic Covariant Coherent Structures in two dimensional flows

A new method to describe hyperbolic patterns in two dimensional flows is proposed. The method is based on the Covariant Lyapunov Vectors (CLVs), which have the properties to be covariant with the dynamics, and thus being mapped by the tangent linear operator into another CLVs basis, they are norm independent, invariant under time reversal and can be not orthonormal. CLVs can thus give a more detailed information on the expansion and contraction directions of the flow than the Lyapunov Vector bases, that are instead always orthogonal. We suggest a definition of Hyperbolic Covariant Coherent Structures (HCCSs), that can be defined on the scalar field representing the angle between the CLVs. HCCSs can be defined for every time instant and could be useful to understand the long term behaviour of particle tracers. We consider three examples: a simple autonomous Hamiltonian system, as well as the non-autonomous "double gyre" and Bickley jet, to see how well the angle is able to describe particular patterns and barriers. We compare the results from the HCCSs with other coherent patterns defined on finite time by the Finite Time Lyapunov Exponents (FTLEs), to see how the behaviour of these structures change asymptotically

Material for knitwear: a new contemporary design scenario

En el contexto globalizado actual en el que la fertilización cruzada entre disciplinas y diferentes campos de proyecto se mezcla generando formas, sistemas y procesos, el diseño de Tejidos de Punto puede marcar la diferencia en la producción y en el consumo de los productos. En realidad, son ideas reales sobre los diversos temas que caracterizan esta área. Actualmente el diseño en áreas muy específicas como diseño de tejido de punto italiano, realizado por artistas, diseñadores, hilanderos, empresas, continuamente entre la tradición y el producto manual industrial, hace de la investigación un desafío realmente complicado. En los escenarios contemporáneos el diseño de tejido de punto es un proceso complejo, que combina antiguas técnicas tradicionales de conocimiento con la experimentación y la innovación tecnológica. Es un desafío que alimenta la curiosidad y el deseo de buscar más.In the actual globalized context in which the cross-fertilization among disciplines and different fields of project mixes together forms, systems and processes, Knitwear Design can make the difference in the production and in the consumption of the products.  Actually they are real insights on the various issues that characterize this area; today designing in very specific areas such as Italian knitwear, made of artists, designers, spinners, companies, perpetually poised between tradition and manual industrial product, makes research a really complicated challenge.  In contemporary scenarios knitwear design is a complex process, combining ancient techniques of traditional knowledge with experimentation and technological innovation. It’s a challenge that feeds the curiosity and the desire to seek more.No contexto globalizado de hoje, em que a fertilização cruzada entre diferentes disciplinas e áreas de projeto é misturada gerando formas, sistemas e processos, Design de tecidos pode fazer a diferença na produção e consumo de produtos.  Na realidade, são ideias reais sobre várias questões que caracterizam esta área. Atualmente o projeto em áreas muito específicas, como ponto de design de tecido italiano por artistas, designers, spinners, empresas continuamente entre tradição e manual do produto industrial, torna a pesquisa um desafio realmente difícil.  Em cenários de design contemporâneo, tricô é um processo complexo que combina técnicas tradicionais antigos de conhecimento através da experimentação e inovação tecnoló- gica. É um desafio que alimenta a curiosidade e o desejo de procurar ainda mais

Human capital, employment protection and growth in Europe

Using data for 51 manufacturing and service sector for the period 1970-2005 in 14 countries, this paper show that employment protection legislation has a negative and significant effect on growth of value added and hours of work in more human capital intensive sectors. We argue that labour market regulation has a negative impact on the technology adoption mechanism through its heterogeneous impact on firms' workforce adjustment requirements. In fact, technology adoption depends both on the skill level of the workforce and the capacity of firms to optimally adjust their employment levels as technology changes. As a consequence, firing costs have a relatively stronger impact in sectors in which technology adoption is more important. Our empirical results are robust to various sensitivity checks such as interactions of human capital intensity with other country level variables, of employment protection with other sector level variables and endogeneity of firing restrictions. We also show that the negative effect of EPL is stronger the smaller the distance from the technology frontier and after the 1990s

Human Capital, Employment Protection and Growth in Europe

Using data for a large sample of manufacturing and service sectors in 14 EU countries, this paper shows that the value added and TFP growth rate differential between high and low human capital intensive industries is greater in countries with low than countries with high levels of employment protection legislation. We also find that such negative effect of EPL is slightly stronger for countries near the technology frontier, in the manufacturing sector and after the 1990s. We interpret these results suggesting that technology adoption depends on the skill level of the workforce and on the capacity of firms to adjust employment as technology changes: therefore, firing costs have a stronger impact in sectors where technical change is more skill-biased and technology adoption more important

Elasticity of an electron liquid

URL:http://link.aps.org/doi/10.1103/PhysRevB.60.7966 DOI:10.1103/PhysRevB.60.7966The zero-temperature response of an interacting electron liquid to a time-dependent vector potential of wave vector q and frequency ω, such that q≪qF, qvF≪ω≪EF/ħ (where qF, vF, and EF are the Fermi wave vector, velocity, and energy, respectively), is equivalent to that of a continuous elastic medium with nonvanishing shear modulus μ, bulk modulus K, and viscosity coefficients η and ζ. We establish the relationship between the viscoelastic coefficients and the long-wavelength limit of the “dynamical local-field factors” GL(T)(q,ω), which are widely used to describe exchange-correlation effects in electron liquids. We present several exact results for μ, including its expression in terms of Landau parameters, and practical approximate formulas for μ, η, and ζ as functions of density. These are used to discuss the possibility of a transverse collective mode in the electron liquid at sufficiently low density. Finally, we consider impurity scattering and/or quasiparticle collisions at nonzero temperature. Treating these effects in the relaxation-time (τ) approximation, explicit expressions are derived for μ and η as functions of frequency. These formulas exhibit a crossover from the collisional regime (ωτ≪1), where μ∼0 and η∼nEFτ, to the collisionless regime (ωτ≫1), where μ∼nEF and η∼0.This work was supported by NSF Grant No. DMR- 9706788. S.C. acknowledges a grant from the Max-Planck-Institute for Mathematics in the Sciences. G.V. was also supported in part by the Institute for Theoretical Physics at the University of California, Santa Barbara, under NSF Grant No. PHY94-07194

Collective modes and electronic spectral function in smooth edges of quantum hall systems

URL:http://link.aps.org/doi/10.1103/PhysRevB.54.R14309 DOI:10.1103/PhysRevB.54.R14309We present a microscopic theory of the collective modes of a ''smooth'' edge of a quantum Hall system, showing under what conditions these modes can be described as a set of independent bosons. We then calculate the electronic spectral function in an independent-boson model—a procedure that reduces to standard bosonization in the limit of ''sharp'' edge. The I-V tunneling characteristics deduced from this model exhibit, for low voltage, a power-law behavior, with exponents that differ significantly from those of the sharp edge model.We gratefully acknowledge support from NSF Grant No.DMR-9403908. One of us (S.C.) acknowledges travel support from Scuola Normale Superiore

Bosonization theory for tunneling spectra in smooth edges of Quantum Hall systems

We calculate the spectral function of a smooth edge of a quantum Hall system in the lowest Landau level by means of a bosonization technique. We obtain a general relationship between the one electron spectral function and the dynamical structure factor. The resulting I-V characteristics exhibit, at low voltage and temperature, power law scaling, generally different from the one predicted by the chiral Luttinger liquid theory, and in good agreement with recent experimental results.Comment: 3 pages, includes 2 figure

Employment protection, temporary contracts and firm-provided training: Evidence from Italy

In this study we leverage on Italy’s size-contingent firing restrictions in order to identify the causal effect of employment protection legislation (EPL) on firm-provided training using a regression discontinuity design. Our analysis demonstrates that higher levels of EPL reduce firms’ incentives to invest in workers’ training. The number of trained workers falls by about 1.5-1.9 units at the threshold: this is a non-negligible effect, corresponding to a 16-20 per cent reduction in the number of trained workers. The results are robust to several sensitivity checks and controls for potential confounding factors (e.g., worker councils). The EPL effect on training is not mediated by different levels of investment in physical capital or propensities to innovate, while it is mostly accounted for by larger workers’ turnover and use of temporary contracts, which entail lower training, in firms with higher firing costs. Our study points to potential adverse effects of EPL on workers’ training in dual labor markets, owing to larger firms seeking to avoid higher EPL costs by means of temporary contracts.JRC.I.1-Modelling, Indicators and Impact Evaluatio