3499 research outputs found
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Experimental and computational study of mechanical and transport properties of a polymer coating for drug-eluting stents
No full textBackground: Experimental and computational characterizations in the preclinical development of biomedical devices are complementary and can significantly help in a thorough analysis of the performances before clinical evaluation. Methodology: Here mechanical and drug delivery properties of a polymer platform, ad hoc prepared to obtain coatings for drug-eluting stents, is reported; polymer formulation and starting drug loading were varied to study the behavior of the platform; a finite element model was constructed starting from experimental data. Results: Different platform formulations affected mechanical and drug transport properties; these properties can be fine tuned by varying the starting platform formulation. Finite element analysis allowed visualizing drug distribution maps over time in biological tissues for different commercial stents and polymer platform formulations
Quantitative analysis of myelin and axonal remodeling in the uninjured motor network after stroke
No full textObjectives: Contralesional brain connectivity plasticity was previously reported after stroke. This study aims at disentangling the biological mechanisms underlying connectivity plasticity in the uninjured motor network after an ischemic lesion. In particular, we measured generalized fractional anisotropy (GFA) and magnetization transfer ratio (MTR) to assess whether post-stroke connectivity remodeling depend on axonal and/or myelin changes. Materials and Methods: Diffusion Spectrum Imaging (DSI) and Magnetization Transfer MRI at 3T were performed in 10 patients in acute phase, at one and six months after stroke, which was affecting motor cortical and/or subcortical areas. Ten age- and gender- matched healthy volunteers were scanned one month apart for longitudinal comparison. Clinical assessment was also performed in patients prior to MRI. In the contra-lesional hemisphere, average measures and tract-based quantitative analysis of GFA and MTR was performed to assess axonal integrity and myelination along motor connections as well as their variations in time. Results and Conclusions: Mean and tract-based measures of MTR and GFA showed significant changes in a number of contralesional motor connections, confirming both axonal and myelin plasticity in our cohort of patients. Moreover, density-derived features (peak height, standard deviation-SD and skewness) of GFA and MTR along the tracts showed additional correlation with clinical scores than mean values. These findings reveal the interplay between contralateral myelin and axonal remodeling after stroke
Model order reduction applied to heat conduction in photovoltaic modules
No full textModeling of physical systems may be a challenging task when it requires solving large sets of numerical equations. This is the case of photovoltaic (PV) systems which contain many PV modules, each module containing several silicon cells. The determination of the temperature field in the modules leads to large scale systems, which may be computationally expensive to solve. In this context, Model Order Reduction (MOR) techniques can be used to approximate the full system dynamics with a compact model, that is much faster to solve. Among the several available MOR approaches, in this work we consider the Discrete Empirical Interpolation Method (DEIM), which we apply with a suitably modified formulation that is specifically designed for handling the nonlinear terms that are present in the equations governing the thermal behavior of PV modules. The results show that the proposed DEIM technique is able to reduce significantly the system size, by retaining a full control on the accuracy of the solution
Uncertainty and the politics of employment protection
No full textThis paper investigates social preferences over employment protection regulation in a general equilibrium model of dynamic labor demand and sheds some light on the comparative dynamics of Eurosclerosis. When firing costs are low, a transition to a rigid labor market is favored by all the employed workers with idiosyncratic productivity below some threshold; when their status quo level is high, preserving a rigid labor market is favored only by the employed with intermediate productivity. A more volatile environment and a lower rate of productivity growth increase the political support for labor market rigidity only in high-rents economies
Central Limit Theorems for an Indian Buffet Model with Random Weights
No full textThe three-parameter Indian buffet process is generalized. The possibly different role played by customers is taken into account by suitable (random) weights. Various limit theorems are also proved for such generalized Indian buffet process. Let L_n be the number of dishes experimented by the first n customers, and let
{\bar K}_n=(1/n)\sum_{i=1}^n K_i
where K_i is the number of dishes tried by customer i. The asymptotic distributions of L_n and {\bar K}_n, suitably
centered and scaled, are obtained. The convergence turns out to be stable (and not only in distribution). As a particular case, the results apply to the standard (i.e., non generalized) Indian buffet process
L’importanza sistemica delle banche: da una prospettiva globale a una locale? (Systemic Importance of Financial Institutions: from a Global to a Local Perspective? A Network Theory Approach)
No full textNonostante la vasta letteratura che si è occupata di rischio sistemico, non si è ancora giunti a definire misure e approcci metodologici standard volti a gestire questa tipologia di rischio. Questo lavoro illustra alcune questioni aperte e delinea possibili linee di ricerca future. In particolare, una eventuale declinazione su scala locale della nozione di rischio sistemico, di specifico interesse nel contesto italiano.
(English version:
After the systemic effects of bank defaults during the recent financial crisis, and despite a huge amount of literature on systemic risk, no standard methodologies have been set up until now. We aim to build a concise but comprehensive picture of the state of the art, illustrating the open issues and outlining pathways for future research. In particular, we propose the analysis of some examples of local systems that attract the attention of the financial sector.
A multiparametric quadratic programming algorithm with polyhedral computations based on nonnegative least squares
No full textModel Predictive Control (MPC) is one of the most successful techniques adopted in industry to control multivariable systems under constraints on input and output variables. To circumvent the main drawback of MPC, i.e., the need to solve a Quadratic Program (QP) on line to compute the control action, explicit MPC was proposed in the past to precompute the control law off line using multiparametric QP (mpQP). The resulting form of the MPC law is piecewise affine, which is extremely easy to code, can be computed online by simple arithmetic operations, and requires a maximum number of iterations that can be exactly determined a priori. On the other hand, the offline computations to solve the mpQP problem require detecting emptiness, full-dimensionality, and minimal hyperplane representations of polyhedra, and other computational geometric operations. While most of the existing methods solve such operations via linear programming, the approach proposed in this paper relies on a nonnegative least squares (NNLS) solver that is very simple to code, fast to execute, and provides solutions up to machine precision. In addition, the new approach exploits QP duality to identify and construct critical regions and to handle degeneracy issues
Homophily and Triadic Closure in Evolving Social Networks
No full textWe present a new network model accounting for homophily and triadic closure in the evolution of social networks. In particular, in our model, each node is characterized by a number of features and the probability of a link between
two nodes depends on common features. The bipartite network of the actors and features evolves according to a 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. 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 scientifc collaborations
Global Value Trees
No full textThe fragmentation of production across countries has become an important feature of the
globalization in recent decades and is often conceptualized by the term “global value chains” (GVCs). When empirically investigating the GVCs, previous studies are mainly in-
terested in knowing how global the GVCs are rather than how the GVCs look like. From a
complex networks perspective, we use the World Input-Output Database (WIOD) to study
the evolution of the global production system. We find that the industry-level GVCs are in-
deed not chain-like but are better characterized by the tree topology. Hence, we compute
the global value trees (GVTs) for all the industries available in the WIOD. Moreover, we
compute an industry importance measure based on the GVTs and compare it with other net-
work centrality measures. Finally, we discuss some future applications of the GVTs
