39,012 research outputs found
Measuring the impact of international R&D cooperation: the case of Spanish firms participating in the EU Framework Programme
The objective of this paper is to analyse the effects of international R&D cooperation on firmsâ economic performance. Our empirical analysis, based on Spanish firmsâ participation in the Framework Programme (FP) between 1995 and 2005, has confirmed that: (1) cooperation within the FP has a positive impact on the technological capacity of firms, captured through intangible fixed assets and (2) the technological capacity of firms is positively related to their economic performance, measured by labour productivity.International R&D cooperation, Framework Programme, Impact assessment
Numerical modelling of non-ionic microgels: an overview
Microgels are complex macromolecules. These colloid-sized polymer networks
possess internal degrees of freedom and, depending on the polymer(s) they are
made of, can acquire a responsiveness to variations of the environment
(temperature, pH, salt concentration, etc.). Besides being valuable for many
practical applications, microgels are also extremely important to tackle
fundamental physics problems. As a result, these last years have seen a rapid
development of protocols for the synthesis of microgels, and more and more
research has been devoted to the investigation of their bulk properties.
However, from a numerical standpoint the picture is more fragmented, as the
inherently multi-scale nature of microgels, whose bulk behaviour crucially
depends on the microscopic details, cannot be handled at a single level of
coarse-graining. Here we present an overview of the methods and models that
have been proposed to describe non-ionic microgels at different length-scales,
from the atomistic to the single-particle level. We especially focus on
monomer-resolved models, as these have the right level of details to capture
the most important properties of microgels, responsiveness and softness. We
suggest that these microscopic descriptions, if realistic enough, can be
employed as starting points to develop the more coarse-grained representations
required to investigate the behaviour of bulk suspensions
Synchronization of networks with variable local properties
We study the synchronization transition of Kuramoto oscillators in scale-free
networks that are characterized by tunable local properties. Specifically, we
perform a detailed finite size scaling analysis and inspect how the critical
properties of the dynamics change when the clustering coefficient and the
average shortest path length are varied. The results show that the onset of
synchronization does depend on these properties, though the dependence is
smooth. On the contrary, the appearance of complete synchronization is
radically affected by the structure of the networks. Our study highlights the
need of exploring the whole phase diagram and not only the stability of the
fully synchronized state, where most studies have been done up to now.Comment: 5 pages and 3 figures. APS style. Paper to be published in IJBC
(special issue on Complex Networks' Structure and Dynamics
Weighted random--geometric and random--rectangular graphs: Spectral and eigenfunction properties of the adjacency matrix
Within a random-matrix-theory approach, we use the nearest-neighbor energy
level spacing distribution and the entropic eigenfunction localization
length to study spectral and eigenfunction properties (of adjacency
matrices) of weighted random--geometric and random--rectangular graphs. A
random--geometric graph (RGG) considers a set of vertices uniformly and
independently distributed on the unit square, while for a random--rectangular
graph (RRG) the embedding geometry is a rectangle. The RRG model depends on
three parameters: The rectangle side lengths and , the connection
radius , and the number of vertices . We then study in detail the case
which corresponds to weighted RGGs and explore weighted RRGs
characterized by , i.e.~two-dimensional geometries, but also approach
the limit of quasi-one-dimensional wires when . In general we look for
the scaling properties of and as a function of , and .
We find that the ratio , with , fixes the
properties of both RGGs and RRGs. Moreover, when we show that
spectral and eigenfunction properties of weighted RRGs are universal for the
fixed ratio , with .Comment: 8 pages, 6 figure
The power spectrum of solar convection flows from high-resolution observations and 3D simulations
We compare Fourier spectra of photospheric velocity fields from very high
resolution IMaX observations to those from recent 3D numerical
magnetoconvection models. We carry out a proper comparison by synthesizing
spectral lines from the numerical models and then applying to them the adequate
residual instrumental degradation that affects the observational data. Also,
the validity of the usual observational proxies is tested by obtaining
synthetic observations from the numerical boxes and comparing the velocity
proxies to the actual velocity values from the numerical grid.
For the observations, data from the SUNRISE/IMaX instrument with about 120 km
spatial resolution are used, thus allowing the calculation of observational
Fourier spectra well into the subgranular range. For the simulations, we use
four series of runs obtained with the STAGGER code and synthesize the IMaX
spectral line (FeI 5250.2 A) from them. Proxies for the velocity field are
obtained via Dopplergrams (vertical component) and local correlation tracking
(horizontal component).
A very good match between observational and simulated Fourier power spectra
is obtained for the vertical velocity data for scales between 200 km and 6 Mm.
Instead, a clear vertical shift is obtained when the synthetic observations are
not degraded. The match for the horizontal velocity data is much less
impressive because of the inaccuracies of the LCT procedure. Concerning the
internal comparison of the direct velocity values of the numerical boxes with
those from the synthetic observations, a high correlation (0.96) is obtained
for the vertical component when using the velocity values on the
log() = -1 surface in the box. The corresponding Fourier spectra are
near each other. A lower maximum correlation (0.5) is reached (at =
1) for the horizontal velocities as a result of the coarseness of the LCT
procedure.Comment: 12 pages, 9 figures, accepted in A&
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