3499 research outputs found
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Anatomy of news consumption on Facebook
No full textThe advent of social media and microblogging platforms has radically changed the way we consume information and form opinions. In this paper, we explore the anatomy of the information space on Facebook by characterizing on a global scale the news consumption patterns of 376 million users over a time span of 6 y (January 2010 to December 2015). We find that users tend to focus on a limited set of pages, producing a sharp community structure among news outlets. We also find that the preferences of users and news providers differ. By tracking how Facebook pages “like” each other and examining their geolocation, we find that news providers are more geographically confined than users. We devise a simple model of selective exposure that reproduces the observed connectivity patterns
Modeling networks with a growing feature-structure
No full textWe present a new network model accounting for multidimensional assortativity. Each node is characterized by a number of features and the probability of a link between two nodes depends on common features. We do not fix a priori the total number of possible features. The bipartite network of the nodes and the features evolves according to a stochastic dynamics that depends on
three parameters that respectively regulate the preferential attachment in the transmission of the features to the nodes, the number of new features per node, and the power-law behavior of the total number of observed features.
Our model also takes into account a mechanism of triadic closure. We provide theoretical results and statistical estimators for the parameters of the model.
We validate our approach by means of simulations and an empirical analysis of a network of scientific collaborations
Global ownership and corporate control networks
No full textIn this contribution, at first, we introduce a basic network framework to study pyramidal structures and wedges between ownership and control of companies. Then, we apply it to a dataset of
53.5 million of companies operating in 208 countries. Among others, we detect a strong concentra-
tion of corporate power, as less than 1% of parent companies collect more than 100 subsidiaries, but
they are responsible for more than 50% of global sales. Therefore, we show that the role of indirect
control, i.e., through middlemen subsidiaries, is relevant in 15% of domestic and 54% of foreign
subsidiaries. Among foreign companies, cases emerge of blurring nationality, when control paths
cross more than one national border, in the presence of multiple passports (19.1%), indirectly for-
eign (24.5%), and round-tripping subsidiaries (1.33%). Finally, we relate indirect control strategies
to country indicators of the institutional environment. We find that pyramidal structures arise less
likely in the presence of good financial and contractual institutions in the parent's country, as these
foster more transparent forms of corporate governance. Instead, parent companies choose indirect
control through countries of subsidiaries that have better financial institutions, possibly because it
is easier to coordinate decisions from remote. Finally, we find that offshore financial centers are
preferred jurisdictions for middlemen subsidiaries, probably due to a lower taxation and a lack of
financial disclosure
Simulated hail impacts on flexible photovoltaic laminates: testing and modelling
No full textThe problem of simulated low-velocity
hail impacts on flexible photovoltaic (PV) modules
resting on a substrate with variable stiffness is investigated.
For this type of PV module it is shown that the
prescriptions of the IEC 61215 International Standard
for quality control used for rigid (glass-covered) PV
modules should be augmented by taking into account
their real mounting condition and the stiffness of the
substrate in the simulated hail impact tests. Moreover,
electroluminescence inspection of the crack pattern
should be made in addition to electric power output
measurements.An implicit finite element simulation of
the contact problem in dynamics is also proposed, with
two different degrees of accuracy, to interpret the
experimentally observed extension of cracking.
Results pinpoint the important role of stress wave
propagation and reflection in the case of soft substrates
Revisiting the problem of a crack impinging on an interface: a modeling framework for the interaction between the phase field approach for brittle fracture and the interface cohesive zone model
No full textThe problem of a crack impinging on an interface has been thoroughly investigated in the last three decades due to its important role in the mechanics and physics of solids. In the current investigation, this problem is revisited in view of the recent progresses on the phase field approach of brittle fracture. In this concern, a novel formulation combining the phase field approach for modeling
brittle fracture in the bulk and a cohesive zone model for pre-existing adhesive interfaces is herein proposed to investigate the competition between crack penetration and deflection at an interface. The model, implemented within the finite element method framework using a monolithic fully implicit solution strategy, is applied to provide a further insight into the understanding of the role of model parameters on the above competition. In particular, in this study, the role of the fracture toughness ratio between the interface and the adjoining bulks and of the characteristic fracture-length scales of the dissipative models is analyzed. In the case of a brittle interface, the asymptotic predictions based on linear elastic fracture mechanics criteria for crack penetration, single
deflection or double deflection are fully captured by the present method. Moreover, by increasing the size of the process zone along the interface, or by varying the internal length scale of the phase field model, new complex phenomena are emerging, such as simultaneous crack penetration and deflection and the transition from single crack penetration to deflection and penetration with
subsequent branching into the bulk. The obtained computational trends are in very good agreement with previous experimental observations and the theoretical considerations on the competition and interplay between both fracture mechanics models open new research perspectives for the simulation and understanding of complex fracture patterns
A nonlocal adaptive discrete empirical interpolation method combined with modified hp-refinement for order reduction of molecular dynamics systems
No full textModel order reduction is an emerging technique to tackle the computational complexities of molecular
dynamics (MD) simulations. Different strategies are required to adequately obtain the reduced solutions
of different classes of molecular dynamics systems. In this work, a proper orthogonal decomposition
(POD) is combined with the discrete empirical interpolation method (DEIM) to study atomic systems.
Due to the limitations of the DEIM in capturing the nonlocal response of the nonlinear force field of
MD systems, a nonlocal adaptive discrete empirical interpolation method (ADEIM) is proposed.
Furthermore, a modified hp-refinement algorithm is introduced to extend the application of the PODDEIM
approach to order reduction of multi-dimensional MD systems. In the DEIM, the distance between
atoms and hence the reduced internal force vector is estimated based on a local interpolation of the state
variables. The internal forces of a multi-dimensional MD system depend on the distance between the
atoms, represented in space by more than one coordinate. Therefore, the ADEIM approach seeks to obtain
a nonlocal interpolation of the state variables to accurately predict the distance between the interpolated
atoms and hence the reduced force vector. Simulation of MD systems with frequently changing neighbour
atoms leads to change in the system dynamics, which further leads to change of properties of the
snapshots. Therefore, the temporal domain is adaptively subdivided into smaller sub-domains using
the adopted hp-refinement procedure. The reduced system parameters are effectively derived over the
sub-domains. Considering the computational cost, a modified hp-refinement algorithm is developed in
this study, which is further coupled with the POD-ADEIM approach to obtain the reduced-order solution
of the MD systems. The results of the proposed approach demonstrate the efficiency and accuracy of the
reduced solutions
Strength prediction of notched thin ply laminates using finite fracture mechanics and the phase field approach
No full textThin ply laminates are a new class of composite materials with great potential for application in the design of thinner and highly optimized components, resulting in potential weight savings and improved mechanical performance. These new composites can stir the development of lighter structures, overcoming current design limitations as well as notably reducing the onset and development of matrix cracking and delamination events. This paper presents the application of two recent modeling methods for the failure analysis and strength prediction of open-hole thin ply laminates under tensile loading,
which exhibit a brittle response upon failure: (i) the analytical coupled energy-stress Finite Fracture Mechanics (FFMs) technique, and (ii) the FE-based Phase Field (PF) approach for fracture that is incorporated into an enhanced assumed solid shell element. The predictions obtained using both strategies are compared with experimental data. These correlations exhibit a very satisfactory level of agreement, proving the robustness and reliability of both methods under consideration
A new analytical critical thrust force model for delamination analysis of laminated composites during drilling operation
No full textFibre reinforced polymer (FRP) composite laminates are employed in many industrial applications due to
their attractive mechanical and structural properties. Machining operation, such as drilling of FRP
laminates, plays a significant role in the assembly of parts in aircraft and spacecraft production. Among
other production bottlenecks, drilling-induced delamination remains a major defect which adversely
affects the quality of assembly parts. An efficient strategy in preventing this problem is the calculation of
the critical thrust force above which delamination is initiated. Therefore, in this study, a new analytical
model is proposed to predict the critical thrust force for delamination. Unlike the general models in the
literature which derived only mode I strain energy release rate based on the assumption of classical
laminate plate theory (CLPT) combined with linear elastic fracture mechanics (LEFM) mode I considerations
in the elliptic delamination zone, the proposed analytical model is derived based on first-order
shear deformation theory (FSDT) and accounts for mode I and mode II strain energy release rates in
the delamination zone. This strategy allows to activate mixed mode criteria for delamination initiation
which is a valid assumption for laminates with layers of different orientations. The present model is
partly derived for general laminates subject to distributed loading and further extended to cross-ply
laminate sequence subject to a mixed load condition. The results show that the effect of shear deformation
in the prediction of the critical thrust force is influential with increasing ply thickness and the
effect of chisel edge on shear deformation is more profound in the distributed load regime
P3445Correlation between vascular age and surrogate markers of atherosclerosis and vascular aging
No full textBackground: The evaluation of Vascular Age, according to the definition given using the cardiovascular risk score tables, is a method of estimating individual cardiovascular risk, which may represent a new therapeutic target for physicians. However, the association of Vascular Age with surrogate markers of atherosclerosis and vascular aging, able to identify vascular alterations at the sub-clinical, asymptomatic stages, has not been determined yet
