25,456 research outputs found
The return to firm investment in human capital
In this paper we estimate the rate of return to firm investments in human capital in
the form of formal job training. We use a panel of large firms with unusually detailed
information on the duration of training, the direct costs of training, and several firm
characteristics such as their output, workforce characteristics and capital stock. Our
estimates of the return to training vary substantially across firms. On average it is
-7% for firms not providing training and 24% for those providing training. Formal job
training is a good investment for many firms and the economy, possibly yielding higher
returns than either investments in physical capital or investments in schooling. In spite
of this, observed amounts of formal training are very small
Enforcement of regulation, informal labor and firm performance
This paper investigates how enforcement of labor regulation affects the firm’s use
of informal labor and firm performance. Using firm level data on informal employment
and firm performance, and administrative data on enforcement of regulation at
the city level, we show that in areas where law enforcement is stricter firms employ a
smaller amount of informal employment. Furthermore, by reducing the firm’s access
to unregulated labor, stricter enforcement is also associated with lower labor productivity.
We control for different regional and firm characteristics, and we instrument
enforcement with a measure of the access of labor inspectors to firms. Taken together,
our findings suggest that increased access to labor flexibility significantly improves firm
performance
Some Implications of the Cosmological Constant to Fundamental Physics
In the presence of a cosmological constant, ordinary Poincare' special
relativity is no longer valid and must be replaced by a de Sitter special
relativity, in which Minkowski space is replaced by a de Sitter spacetime. In
consequence, the ordinary notions of energy and momentum change, and will
satisfy a different kinematic relation. Such a theory is a different kind of a
doubly special relativity. Since the only difference between the Poincare' and
the de Sitter groups is the replacement of translations by certain linear
combinations of translations and proper conformal transformations, the net
result of this change is ultimately the breakdown of ordinary translational
invariance. From the experimental point of view, therefore, a de Sitter special
relativity might be probed by looking for possible violations of translational
invariance. If we assume the existence of a connection between the energy scale
of an experiment and the local value of the cosmological constant, there would
be changes in the kinematics of massive particles which could hopefully be
detected in high-energy experiments. Furthermore, due to the presence of a
horizon, the usual causal structure of spacetime would be significantly
modified at the Planck scale.Comment: 15 pages, lecture presented at the "XIIth Brazilian School of
Cosmology and Gravitation", Mangaratiba, Rio de Janeiro, September 10-23,
200
Living bacteria rheology: population growth, aggregation patterns and cooperative behaviour under different shear flows
The activity of growing living bacteria was investigated using real-time and
in situ rheology -- in stationary and oscillatory shear. Two different strains
of the human pathogen Staphylococcus aureus -- strain COL and its isogenic cell
wall autolysis mutant -- were considered in this work. For low bacteria
density, strain COL forms small clusters, while the mutant, presenting
deficient cell separation, forms irregular larger aggregates. In the early
stages of growth, when subjected to a stationary shear, the viscosity of both
strains increases with the population of cells. As the bacteria reach the
exponential phase of growth, the viscosity of the two strains follow different
and rich behaviours, with no counterpart in the optical density or in the
population's colony forming units measurements. While the viscosity of strain
COL keeps increasing during the exponential phase and returns close to its
initial value for the late phase of growth, where the population stabilizes,
the viscosity of the mutant strain decreases steeply, still in the exponential
phase, remains constant for some time and increases again, reaching a constant
plateau at a maximum value for the late phase of growth. These complex
viscoelastic behaviours, which were observed to be shear stress dependent, are
a consequence of two coupled effects: the cell density continuous increase and
its changing interacting properties. The viscous and elastic moduli of strain
COL, obtained with oscillatory shear, exhibit power-law behaviours whose
exponent are dependent on the bacteria growth stage. The viscous and elastic
moduli of the mutant have complex behaviours, emerging from the different
relaxation times that are associated with the large molecules of the medium and
the self-organized structures of bacteria. These behaviours reflect
nevertheless the bacteria growth stage.Comment: 9 pages, 10 figure
Cosmological Term and Fundamental Physics
A nonvanishing cosmological term in Einstein's equations implies a
nonvanishing spacetime curvature even in absence of any kind of matter. It
would, in consequence, affect many of the underlying kinematic tenets of
physical theory. The usual commutative spacetime translations of the Poincare'
group would be replaced by the mixed conformal translations of the de Sitter
group, leading to obvious alterations in elementary concepts such as time,
energy and momentum. Although negligible at small scales, such modifications
may come to have important consequences both in the large and for the
inflationary picture of the early Universe. A qualitative discussion is
presented which suggests deep changes in Hamiltonian, Quantum and Statistical
Mechanics. In the primeval universe as described by the standard cosmological
model, in particular, the equations of state of the matter sources could be
quite different from those usually introduced.Comment: RevTeX, 4 pages. Selected for Honorable Mention in the Annual Essay
Competition of the Gravity Research Foundation for the year 200
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