826,954 research outputs found
Exports, sunk costs and financial restrictions in Argentina during the 1990s
This paper examines firms' export decisions in Argentina during the 1990s. Using a sample of 1600 Argentine industrial firms with information for the years 1992, 1996, 1998 and 2001, we test which factors affect the probability of entering foreign markets. We focus on the role of sunk costs and the access to financial markets as key determinants of firms' export decisions. The estimation of a non-linear binary variable model using export prior experience and explicit sunk costs variables confirms self-selection hypothesis on export markets participation. Results also suggest that firm-specific characteristics are significant to explain export decisions, particularly firm's access to the financial systemsunk costs ; firm's export decisions ; financial restrictions ; Argentina
Brownian motion from molecular dynamics
Brownian motion of single particles with various masses M and diameters D is
studied by molecular dynamics simulations. Besides the momentum
auto-correlation function of the Brownian particle the memory function and the
fluctuating force which enter the generalized Langevin equation of the Brownian
particle are determined and their dependence on mass and diameter are
investigated for two different fluid densities. Deviations of the fluctuating
force distribution from a Gaussian form are observed for small particle
diameters. For heavy particles the deviations of the fluctuating force from the
total force acting on the Brownian particle decrease linearly with the mass
ratio m/M where m denotes the mass of a fluid particle
Stochastic differential equations for non-linear hydrodynamics
We formulate the stochastic differential equations for non-linear
hydrodynamic fluctuations. The equations incorporate the random forces through
a random stress tensor and random heat flux as in the Landau and Lifshitz
theory. However, the equations are non-linear and the random forces are
non-Gaussian. We provide explicit expressions for these random quantities in
terms of the well-defined increments of the Wienner process.Comment: 11 pages, submitted to Phys. Rev.
How would you integrate the equations of motion in dissipative particle dynamics simulations?
In this work we assess the quality and performance of several novel
dissipative particle dynamics integration schemes that have not previously been
tested independently. Based on a thorough comparison we identify the respective
methods of Lowe and Shardlow as particularly promising candidates for future
studies of large-scale properties of soft matter systems
Modelling Shear Flows with SPH and Grid Based Methods
Given the importance of shear flows for astrophysical gas dynamics, we study
the evolution of the Kelvin-Helmholtz instability (KHI) analytically and
numerically. We derive the dispersion relation for the two-dimensional KHI
including viscous dissipation. The resulting expression for the growth rate is
then used to estimate the intrinsic viscosity of four numerical schemes
depending on code-specific as well as on physical parameters. Our set of
numerical schemes includes the Tree-SPH code VINE, an alternative SPH
formulation developed by Price (2008), and the finite-volume grid codes FLASH
and PLUTO. In the first part, we explicitly demonstrate the effect of
dissipation-inhibiting mechanisms such as the Balsara viscosity on the
evolution of the KHI. With VINE, increasing density contrasts lead to a
continuously increasing suppression of the KHI (with complete suppression from
a contrast of 6:1 or higher). The alternative SPH formulation including an
artificial thermal conductivity reproduces the analytically expected growth
rates up to a density contrast of 10:1. The second part addresses the shear
flow evolution with FLASH and PLUTO. Both codes result in a consistent
non-viscous evolution (in the equal as well as in the different density case)
in agreement with the analytical prediction. The viscous evolution studied with
FLASH shows minor deviations from the analytical prediction.Comment: 16 pages, 17 figure
On the diffusive propagation of warps in thin accretion discs
In this paper we revisit the issue of the propagation of warps in thin and
viscous accretion discs. In this regime warps are know to propagate
diffusively, with a diffusion coefficient approximately inversely proportional
to the disc viscosity. Previous numerical investigations of this problem
(Lodato & Pringle 2007) did not find a good agreement between the numerical
results and the predictions of the analytic theories of warp propagation, both
in the linear and in the non-linear case. Here, we take advantage of a new,
low-memory and highly efficient SPH code to run a large set of very high
resolution simulations (up to 20 million SPH particles) of warp propagation,
implementing an isotropic disc viscosity in different ways, to investigate the
origin of the discrepancy between the theory and the numerical results. Our new
and improved analysis now shows a remarkable agreement with the analytic theory
both in the linear and in the non-linear regime, in terms of warp diffusion
coefficient and precession rate. It is worth noting that the resulting
diffusion coefficient is inversely proportional to the disc viscosity only for
small amplitude warps and small values of the disc coefficient
(). For non-linear warps, the diffusion coefficient is a function
of both radius and time, and is significantly smaller than the standard value.
Warped accretion discs are present in many contexts, from protostellar discs to
accretion discs around supermassive black holes. In all such cases, the exact
value of the warp diffusion coefficient may strongly affect the evolution of
the system and therefore its careful evaluation is critical in order to
correctly estimate the system dynamics (abridged).Comment: 16 pages, 14 figures. Accepted to MNRAS. Movies and additional
figures can be found at
http://users.monash.edu.au/~dprice/pubs/warp/index.htm
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