623 research outputs found
Credit Constraints and the Cyclicality of R&D Investment: Evidence from France.
We use a French firm-level panel data set over the period 1993-2004 to analyze the relationship between credit constraints and firms' R&D behavior over the business cycle. Our main results can be summarized as follows: (i) the share of R&D investment over total investment is countercyclical without credit constraints, but it becomes more procyclical as firms face tighter credit constraints; (ii) the result is magnified for firms in sectors that depend more heavily upon external finance; (iii) in more credit constrained firms, R&D investment share plummets during recessions but does not increase proportionally during upturns; (iv) average R&D investment and productivity growth are more negatively correlated with sales volatility in more credit constrained firms.Business cycles ; R&D ; Credit constraints ; Volatility.
A finite volume scheme for nonlinear degenerate parabolic equations
We propose a second order finite volume scheme for nonlinear degenerate
parabolic equations. For some of these models (porous media equation,
drift-diffusion system for semiconductors, ...) it has been proved that the
transient solution converges to a steady-state when time goes to infinity. The
present scheme preserves steady-states and provides a satisfying long-time
behavior. Moreover, it remains valid and second-order accurate in space even in
the degenerate case. After describing the numerical scheme, we present several
numerical results which confirm the high-order accuracy in various regime
degenerate and non degenerate cases and underline the efficiency to preserve
the large-time asymptotic
How much larger quantum correlations are than classical ones
Considering as distance between two two-party correlations the minimum number
of half local results one party must toggle in order to turn one correlation
into the other, we show that the volume of the set of physically obtainable
correlations in the Einstein-Podolsky-Rosen-Bell scenario is (3 pi/8)^2 = 1.388
larger than the volume of the set of correlations obtainable in local
deterministic or probabilistic hidden-variable theories, but is only 3 pi^2/32
= 0.925 of the volume allowed by arbitrary causal (i.e., no-signaling)
theories.Comment: REVTeX4, 6 page
Probabilistic analysis of the upwind scheme for transport
We provide a probabilistic analysis of the upwind scheme for
multi-dimensional transport equations. We associate a Markov chain with the
numerical scheme and then obtain a backward representation formula of
Kolmogorov type for the numerical solution. We then understand that the error
induced by the scheme is governed by the fluctuations of the Markov chain
around the characteristics of the flow. We show, in various situations, that
the fluctuations are of diffusive type. As a by-product, we prove that the
scheme is of order 1/2 for an initial datum in BV and of order 1/2-a, for all
a>0, for a Lipschitz continuous initial datum. Our analysis provides a new
interpretation of the numerical diffusion phenomenon
On the bounded cohomology of semi-simple groups, S-arithmetic groups and products
We prove vanishing results for Lie groups and algebraic groups (over any
local field) in bounded cohomology. The main result is a vanishing below twice
the rank for semi-simple groups. Related rigidity results are established for
S-arithmetic groups and groups over global fields. We also establish vanishing
and cohomological rigidity results for products of general locally compact
groups and their lattices
Finite volume scheme based on cell-vertex reconstructions for anisotropic diffusion problems with discontinuous coefficients
We propose a new second-order finite volume scheme for non-homogeneous and anisotropic diffusion problems based on cell to vertex reconstructions involving minimization of functionals to provide the coefficients of the cell to vertex mapping.
The method handles complex situations such as large preconditioning number diffusion matrices and very distorted meshes.
Numerical examples are provided to show the effectiveness of the method
A global method for coupling transport with chemistry in heterogeneous porous media
Modeling reactive transport in porous media, using a local chemical
equilibrium assumption, leads to a system of advection-diffusion PDE's coupled
with algebraic equations. When solving this coupled system, the algebraic
equations have to be solved at each grid point for each chemical species and at
each time step. This leads to a coupled non-linear system. In this paper a
global solution approach that enables to keep the software codes for transport
and chemistry distinct is proposed. The method applies the Newton-Krylov
framework to the formulation for reactive transport used in operator splitting.
The method is formulated in terms of total mobile and total fixed
concentrations and uses the chemical solver as a black box, as it only requires
that on be able to solve chemical equilibrium problems (and compute
derivatives), without having to know the solution method. An additional
advantage of the Newton-Krylov method is that the Jacobian is only needed as an
operator in a Jacobian matrix times vector product. The proposed method is
tested on the MoMaS reactive transport benchmark.Comment: Computational Geosciences (2009)
http://www.springerlink.com/content/933p55085742m203/?p=db14bb8c399b49979ba8389a3cae1b0f&pi=1
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