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Analytical and computational methods for modeling mechanical filters against bloch wave propagation
No full textThe free propagation of elastic waves through periodic microstructured materials
can be studied by the analytical formulation of beam lattice models for the elementary cell, in
combination with the Floquet-Bloch theory. Within this framework, the present paper deals
with periodic tetrachiral materials characterized by a monoatomic cell. Alternative analytical
formulations can be developed by continualization-homogenization techniques in micropolar
equivalent continua, characterized by overall elastic and inertial tensors. Valid approaches
for the solution of the wave propagation problems are offered by perturbation methods, numerical
continuation techniques, and – finally – computational analyses, suited to account for
some mechanical updates or improvements that can hardly be included in synthetic formulations.
Based on these considerations, the dispersion curves achievable by different formulations
are compared and discussed. The major interest is focused on the spectral effects
determined by changes in the geometry, inertia, elasticity of the microstructural elements and,
finally, by variations in the cellular symmetry. Some attention is paid to the parameter combinations,
which might open band gaps in the low-frequency range, useful to filter undesired
dynamic signals for vibration shielding purposes
Tax morale, aversion to ethnic diversity, and decentralization
Full text linkThis paper analyzes theoretically and empirically the relationship between individuals' aversion to ethnic diversity, the degree of fiscal and political decentralization, and tax morale. We present a model showing how higher degrees of individuals' aversion to ethnic diversity may reduce tax morale and why this effects may be smaller in decentralized political and fiscal systems. We test these results by using individual data from the World Value Survey and several measures of decentralization. Our estimates robustly confirm that higher degrees of individuals' aversion to ethnic diversity are associated to lower tax morale and that this correlation is smaller or null in decentralized systems
Polymer Nanoparticles as Smart Carriers for the Enhanced Release of Therapeutic Agents to the CNS
No full textBackground: The brain is the most protected organ in the human body; its protective shield, relying on a complex system of cells, proteins and transporters, prevents potentially harmful substances from entering the brain from the bloodstream but, on the other hand, it also stops drugs administered via the systemic route. To improve the efficacy of pharmacological treatments, targeted drug delivery by means of polymer nanoparticles is a challenging but, at the same time, efficient strategy.
Methods: Thanks to a highly multidisciplinary approach, several ways to overcome the brain protection have provided effective solutions to treat a large number of diseases. Important advances in polymer science, together with the development of novel techniques for nanocarrier preparation, and the discovery of novel targeting ligands and molecules, allow a fine-tuning of size, shape, chemicophysical properties and surface chemistry of functional particulate systems; it enables the improvement of the therapeutic performances for several drugs, also toward districts that are difficult to be treated, such as the brain.
Conclusion: This review focuses on the great strides made from scientists and doctors in the development of polymer nano-sized drug delivery systems for brain diseases. Even though the optimal nanocarrier was not yet discovered, important advances were made to strive for safer, performant and successful systems, with the expectation to find soon better solutions to cure some still untreatable pathologies
The scientific impact of nations on scientific and technological development
No full textDetermining how scientific achievements influence the subsequent process of knowledge creation is a fundamental step in order to build a unified ecosystem for studying the dynamics of innovation and competitiveness. Yet, relying separately on data about scientific production on one side, through bibliometric indicators, and about technological advancements on the other side, through patents statistics, gives only a limited insight on the key interplay between science and technology which, as a matter of fact, move forward together within the innovation space. In this paper, using citation data of both scientific papers and patents, we quantify the direct impact of the scientific outputs of nations on further advancements in science and on the introduction of new technologies. Our analysis highlights the presence of geo-cultural clusters of nations with similar innovation system features, and unveils the heterogeneous coupled dynamics of scientific and technological success. This study represents a first step in the buildup of a comprehensive framework for knowledge creation and innovation
Partitioned coupling of advection–diffusion–reaction systems and Brinkman flows
No full textWe present a partitioned algorithm aimed at extending the capabilities of existing solvers for the simulation of coupled advection–diffusion–reaction systems and incompressible, viscous flow. The space discretisation of the governing equations is based on mixed finite element methods defined on unstructured meshes, whereas the time integration hinges on an operator splitting strategy that exploits the differences in scales between the reaction, advection, and diffusion processes, considering the global system as a number of sequentially linked sets of partial differential, and algebraic equations. The flow solver presents the advantage that all unknowns in the system (here vorticity, velocity, and pressure) can be fully decoupled and thus turn the overall scheme very attractive from the computational perspective. The robustness of the proposed method is illustrated with a series of numerical tests in 2D and 3D, relevant in the modelling of bacterial bioconvection and Boussinesq systems
Reconnecting statistical physics and combinatorics beyond ensemble equivalence
Full text linkIn statistical physics, the challenging combinatorial enumeration of the configurations of a system subject to hard constraints (microcanonical ensemble) is mapped to a mathematically easier calculation where the constraints are softened (canonical ensemble). However, the mapping is exact only when the size of the system is infinite and if the property of ensemble equivalence (EE), i.e. the asymptotic identity of canonical and microcanonical large deviations, holds. For finite systems, or when EE breaks down, statistical physics is currently believed to provide no answer to the combinatorial problem. In contrast with this expectation, here we establish exact relationships connecting conjugate ensembles in full generality, even for finite system size and when EE does not hold. We also show that in the thermodynamic limit the ensembles are directly related through the matrix of canonical (co)variances of the constraints, plus a correction term that survives only if this matrix has an infinite number of finite eigenvalues. These new relationships restore the possibility of enumerating microcanonical configurations via canonical probabilities, thus reconnecting statistical physics and combinatorics in realms where they were believed to be no longer in mutual correspondence
Enhanced Gravity Model of trade: reconciling macroeconomic and network models
Full text linkThe structure of the International Trade Network (ITN), whose nodes and links represent world countries and their trade relations respectively, affects key economic processes worldwide, including globalization, economic integration, industrial production, and the propagation of shocks and instabilities. Characterizing the ITN via a simple yet accurate model is an open problem. The traditional Gravity Model successfully reproduces the volume of trade between connected countries, using macroeconomic properties such as GDP, geographic distance, and possibly other factors. However, it predicts a network with complete or homogeneous topology, thus failing to reproduce the highly heterogeneous structure of the ITN. On the other hand, recent maximum-entropy network models successfully reproduce the complex topology of the ITN, but provide no information about trade volumes. Here we integrate these two currently incompatible approaches via the introduction of an Enhanced Gravity Model (EGM) of trade. The EGM is the simplest model combining the Gravity Model with the network approach within a maximum-entropy framework. Via a unified and principled mechanism that is transparent enough to be generalized to any economic network, the EGM provides a new econometric framework wherein trade probabilities and trade volumes can be separately controlled by any combination of dyadic and country-specific macroeconomic variables. The model successfully reproduces both the global topology and the local link weights of the ITN, parsimoniously reconciling the conflicting approaches. It also indicates that the probability that any two countries trade a certain volume should follow a geometric or exponential distribution with an additional point mass at zero volume
Foreground Enhancement and Background Suppression in Human Early Visual System During Passive Perception of Natural Images
No full textOne of the major challenges in visual neuroscience is represented by foreground-background segmentation, a process that is supposed to rely on computations in cortical modules, as information progresses from V1 to V4. Data from nonhuman primates (Poort et al., 2016) showed that segmentation leads to two distinct, but associated processes: the enhancement of cortical activity associated to figure processing (i.e., foreground enhancement) and the suppression of ground-related cortical activity (i.e., background suppression). To characterize foreground-background segmentation of natural stimuli in humans, we parametrically modulated low-level properties of 334 images and their behaviorally segmented counterparts. A model based on simple visual features was then adopted to describe the filtered and intact images, and to evaluate their resemblance with fMRI activity in different visual cortices (V1, V2, V3, V3A, V3B, V4, LOC). Results from representational similarity analysis (Kriegeskorte et al., 2008) showed that the correspondence between behaviorally segmented natural images and brain activity increases throughout the visual processing stream. We found evidence of foreground enhancement for all the tested visual regions, while background suppression occurs in V3B, V4 and LOC. Our results suggest that foreground-background segmentation is an automatic process that occurs during natural viewing, and cannot be merely ascribed to differences in objects size or location. Finally, neural images reconstructed from V4 and LOC fMRI activity revealed a preserved spatial resolution of foreground textures, indicating a richer representation of the salient part of natural images, rather than a simplistic model of objects shape
Inside the Echo Chamber
No full textDespite optimistic talk about “collective intelligence,” the Web has helped create an echo chamber where misinformation thrives. Indeed, the viral spread of hoaxes, conspiracy theories, and other false or baseless information online is one of the most disturbing social trends of the early 21st century.
Social scientists are studying this echo chamber by applying computational methods to the traces people leave on Facebook, Twitter and other such outlets. Through this work, they have established that users happily embrace false information as long as it reinforces their preexisting beliefs.
Faced with complex global issues, people of all educational levels choose to believe compact—but false—explanations that clearly identify an object of blame. Unfortunately, attempts to debunk false beliefs seem only to reinforce them. Stopping the spread of misinformation is thus a problem with no apparent simple solutions