We study by computer simulations the dynamics of a droplet of passive, isotropic fluid, embedded in a polar active gel. The latter represents a fluid of active force dipoles, which exert either contractile or extensile stresses on their surroundings, modelling for instance a suspension of cytoskeletal filaments and molecular motors. When the polarisation of the active gel is anchored normal to the droplet at its surface, the nematic elasticity of the active gel drives the formation of a hedgehog defect; this defect then drives an active flow which propels the droplet forward. In an extensile gel, motility can occur even with tangential anchoring, which is compatible with a defect-free polarisation pattern. In this case, upon increasing activity the droplet first rotates uniformly, and then undergoes a discontinuous nonequilibrium transition into a translationally motile state, powered by bending deformations in the surrounding active medium.

We discuss some basic properties of the eigenfunctions of a class of nonlocal operators whose model is the fractional p-Laplacian

We focus on three different convexity principles for local and nonlocal variational integrals. We prove various generalizations of them, as well as their equivalences. Some applications to nonlinear eigenvalue problems and Hardy-type inequalities are given. We also prove a measure-theoretic minimum principle for nonlocal and non- linear positive eigenfunctions.

In this paper, we survey emerging and established wireless ad-hoc technologies and we highlight their security/privacy features and deficiencies. We also identify open research issues and technology challenges for each surveyed technology. (c) 2014 Elsevier B.V. All rights reserved. Pervasive mobile and low-end wireless technologies, such as radio-frequency identification (RFID), wireless sensor networks and the impending vehicular ad-hoc networks (VANETs), make the wireless scenario exciting and in full transformation. For all the above (and similar) technologies to fully unleash their potential in the industry and society, there are two pillars that cannot be overlooked: security and privacy. Both properties are especially relevant if we focus on ad-hoc wireless networks, where devices are required to cooperate - e.g. from routing to the application layer - to attain their goals.

In this article, we face the problem of ensuring reliability of a wireless sensor network which is monitoring a given set of points of interest while maximizing its lifetime (i.e., the amount of time over which the monitoring activity can be performed). The two objectives are contrasting. Indeed, the traditional approach to achieve reliability involves providing redundant coverage, which, however, drastically reduces the network lifetime. We propose an alternative strategy where sensors adapt their sensing radii in response to failures to restore feasibility only when needed. We provide Column Generation exact algorithms for both the traditional approach and our variant, as well as a heuristic procedure for the coverage restoration phase. The advantages of our approach are shown by means of computational tests on a set of instances and failure simulations.

In this paper we take into account three different spanning tree problems with degree-dependent objective functions. The main application of these problems is in the field of optical network design. In particular, we propose the classical Minimum Leaves Spanning Tree problem as a relevant problem in this field and show its relations with the Minimum Branch Vertices and the Minimum Degree Sum Problems. We present a unified memetic algorithm for the three problems and show its effectiveness on a wide range of test instances. © 2013 Elsevier B.V. All rights reserved.

In the k-labeled Spanning Forest Problem (kLSF), given a graph G with a label (color) assigned to each edge, and an integer positive value kmax we look for the minimum number of connected components that can be obtained by using at most kmax different labels. The problem is strictly related to the Minimum Labelling Spanning Tree Problem (MLST), since a spanning tree of the graph (i.e. a single connected component) would obviously be an optimal solution for the kLSF, if it can be obtained without violating the bound on kmax. In this work we present heuristic and exact approaches to solve this new problem.

The authors regret that there was a mistake in the statement of Theorem 3.4. The correction follows.

We consider several possibilities on how to select a Filippov sliding vector field on a codimension 2 singularity surface Σ, intersection of two codimension 1 surfaces. We discuss and compare several, old and new, approaches, under the assumption that Σ is nodally attractive. Of specific interest is the selection of a smoothly varying Filippov sliding vector field. As a result of our analysis and experiments, the best candidates of the many possibilities explored are those based on the so-called barycentric coordinates. In the present context, one of these possibilities appear to be new. © 2013 Elsevier B.V. All rights reserved.

Fever plays a role in activating innate immunity while its relevance in activating adaptive immunity is less clear. Even brief exposure to elevated temperatures significantly impacts on the immunostimulatory capacity of dendritic cells (DCs), but the consequences on immune response remain unclear. To address this issue, we analyzed the gene expression profiles of normal human monocyte-derived DCs from nine healthy adults subjected either to fever-like thermal conditions (39°C) or to normal temperature (37°C) for 180 minutes. Exposure of DCs to 39°C caused upregulation of 43 genes and downregulation of 24 genes. Functionally, the up/ downregulated genes are involved in post-translational modification, protein folding, cell death and survival, and cellular movement. Notably, when compared to monocytes, DCs differentially upregulated transcription of the secreted protein IGFBP-6, not previously known to be specifically linked to hyperthermia. Exposure of DCs to 39°C induced apoptosis/necrosis and resulted in accumulation of IGFBP-6 in the conditioned medium at 48 h. IGFBP-6 may have a functional role in the hyperthermic response as it induced chemotaxis of monocytes and T lymphocytes, but not of B lymphocytes. Thus, temperature regulates complex biological DC functions that most likely contribute to their ability to induce an efficient adaptive immune response.

We developed an approach that integrates different network-based methods to analyze the correlation network arising from large-scale gene expression data. By studying grapevine (Vitis vinifera) and tomato (Solanum lycopersicum) gene expression atlases and a grapevine berry transcriptomic data set during the transition from immature to mature growth, we identified a category named “fight-club hubs” characterized by a marked negative correlation with the expression profiles of neighboring genes in the network. A special subset named “switch genes” was identified, with the additional property of many significant negative correlations outside their own group in the network. Switch genes are involved in multiple processes and include transcription factors that may be considered master regulators of the previously reported transcriptome remodeling that marks the developmental shift from immature to mature growth. All switch genes, expressed at low levels in vegetative/green tissues, showed a significant increase in mature/woody organs, suggesting a potential regulatory role during the developmental transition. Finally, our analysis of tomato gene expression data sets showed that wild-type switch genes are downregulated in ripening-deficient mutants. The identification of known master regulators of tomato fruit maturation suggests our method is suitable for the detection of key regulators of organ development in different fleshy fruit crops.

Aircraft measurements were used to estimate the CO2 emission rates of the city of Rome, assessed against high-resolution inventorial data. Three experimental flights were made, composed of vertical soundings to measure Planetary Boundary Layer (PBL) properties, and circular horizontal transects at various altitudes around the city area. City level emissions and associated uncertainties were computed by means of mass budgeting techniques, obtaining a positive net CO2 flux of 14.7±4.5, 2.5±1.2, and 10.3±1.2 ?mol m-2 s-1 for the three flights. Inventorial CO2 fluxes at the time of flights were computed by means of spatial and temporal disaggregation of the gross emission inventory, at 10.9±2.5, 9.6±1.3, and 17.4±9.6 ?mol m-2 s-1. The largest differences between the two dataset are associated with a greater variability of wind speed and direction in the boundary layer during measurements. Uncertainty partitioned into components related to horizontal boundary flows and top surface flow, revealed that the latter dominates total uncertainty in the presence of a wide variability of CO2 concentration in the free troposphere (up to 7 ppm), while it is a minor term with uniform tropospheric concentrations in the study area (within 2 ppm). Overall, we demonstrate how small aircraft may provide city level emission measurements that may integrate and validate emission inventories. Optimal atmospheric conditions and measurement strategies for the deployment of aircraft experimental flights are finally discussed.

Methods coming from statistics and pattern recognition to estimate the cloud mask from radiance measured by visible and infrared sensors on board satellites are gaining greater consideration for their ability to properly exploit the increasing number of channels available with current and next-generation sensors. Endowed with physical arguments, they give rise to robust methods for accurately estimating the cloud mask. Application of such classification methods to Moderate Resolution Imaging Spectroradiometer (MODIS) data is discussed in this paper. Three different types of MODIS datasets are considered: synthetic (radiance is simulated by proper radiative transfer models); annotated (real MODIS data labeled by a meteorologist as clear or cloudy); and real MODIS data, whose truth is obtained from the official MODIS cloud mask product. A full assessment of the MODIS spectral bands is performed, aimed at understanding the role of the spectral bands in detecting clouds and at achieving top performance with very few properly chosen spectral channels. Local methods that use spatial correlation of images to improve classification, reducing the pseudonuisance of nonlocal methods, have also been tested on real data.

We consider the estimation of a density function on the basis of a random sample from a weighted distribution. We propose linear and nonlinear wavelet density estimators, and provide their asymptotic formulae for mean integrated squared error. In particular, we derive an analogue of the asymptotic formula of the mean integrated square error in the context of kernel density estimators for weighted data, admitting an expansion with distinct squared bias and variance components. For nonlinear wavelet density estimators, unlike the analogous situation for kernel or linear wavelet density estimators, this asymptotic formula of the mean integrated square error is relatively unaffected by assumptions of continuity, and it is available for densities which are smooth only in a piecewise sense. We illustrate the behavior of the proposed linear and nonlinear wavelet density estimators in finite sample situations both in simulations and on a real-life dataset. Comparisons with a kernel density estimator are also given. © 2013 Elsevier B.V. All rights reserved.

In this paper the Acoustic Analogy is used to predict the underwater noise from a complete scaled ship model in a steady course. The numerical investigation is performed by coupling an incompressible RANS code, equipped with a level-set approach to account for the fundamental time evolution of the free surface, to a FWHbased hydroacoustic solver, here suitably designed to manage the huge set of data coming from a full-unsteady hydrodynamic simulation. The results reveal the overall limited contribution from the propeller thickness and loading noise components and the fundamental one from the nonlinear quadrupole sources. The comparison between the hydrodynamic and hydroacoustic solutions point out the noticeable scattering effects due to the hull surface, the possible influence of sound refractions at the free surface and, above all, the leading role played by the turbulent fluctuating component of the velocity field. Finally, by computing the pressure time histories at a prescribed set of virtual hydrophones and turning them into the frequency domain, the ship noise footprint in dB is traced out, thus showing how the Acoustic Analogy can be effectively used to analyze the ship hydroacoustic behavior, both in terms of amplitude and directivity.

The acoustic analogy represents a powerful and versatile approach, able to numerically predict the noise generated by a body moving in a fluid. It is widely used to provide essential indications about the aeroacoustic behavior of aircraft and helicopters (even at a design stage) and, eventually, to pursue effective strategies aimed at desirable reduction and/or control of noise. Nevertheless, applications in the area of hydroacoustics and in the prediction of ship underwater noise are very rare. In this paper, the potential of the acoustic analogy is directly tested on a large ferry, for which a measurement campaign at sea was performed. In spite of the complexity of the tested configuration [the ship mounts two contracted and loaded tip (CLT) propellers located ahead of two rudders, and its hull is characterized by a rather elongated skeg] and the many variables not taken into account in the numerical simulation (such as the contribution from machinery noise and the probable occurrence of tip vortex cavitation), the agreement between the measured and computed noise spectra is quite satisfactory. The analysis suggests many interesting features of the ship hydroacoustic field: the dominant role played by nonlinear sources far from the body and the relevance of scattering effects from the hull surface. Furthermore, the scattered pressure seems to contribute to alter the frequency content of the resulting signatures with respect to the blade passage frequencies. Finally, an overview of future developments and applications of this numerical approach for marine/maritime problems is presented

A system modeling fluid motions in horizontal porous layers, uniformly heated from below and salted from above by one salt is analyzed. The definitively boundedness of solutions (existence of absorbing sets in the phase space) is proved. Necessary and sufficient conditions ensuring the linear stability of a constant vertical throughflow have been obtained, via a new approach. Moreover, conditions guaranteeing the global nonlinear asymptotic stability are determined.

This book reviews the basic ideas of the Law of Large Numbers with its consequences to the deterministic world and the issue of ergodicity. Applications of Large Deviations and their outcomes to Physics are surveyed. The book covers topics encompassing ergodicity and its breaking and the modern applications of Large deviations to equilibrium and non-equilibrium statistical physics, disordered and chaotic systems, and turbulence.