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Conforming and nonconforming virtual element methods for elliptic problemsJul 13 2015We present in a unified framework new conforming and nonconforming Virtual Element Methods (VEM) for general second order elliptic problems in two and three dimensions. The differential operator is split into its symmetric and non-symmetric parts and ... More

The non-conforming virtual element method for the Stokes equationsAug 03 2016Sep 06 2016We present the non-conforming Virtual Element Method (VEM) for the numerical approximation of velocity and pressure in the steady Stokes problem. The pressure is approximated using discontinuous piecewise polynomials, while each component of the velocity ... More

The nonconforming virtual element method for eigenvalue problemsFeb 08 2018We analyse the nonconforming Virtual Element Method (VEM) for the approximation of elliptic eigenvalue problems. The nonconforming VEM allow to treat in the same formulation the two- and three-dimensional case.We present two possible formulations of the ... More

Discretization of mixed formulations of elliptic problems on polyhedral meshesOct 19 2016We review basic design principles underpinning the construction of mimetic finite difference and a few finite volume and finite element schemes for mixed formulations of elliptic problems. For a class of low-order mixed-hybrid schemes, we show connections ... More

From H&M to Gap for Lightweight BWT MergingSep 15 2016Recently, Holt and McMillan [Bionformatics 2014, ACM-BCB 2014] have proposed a simple and elegant algorithm to merge the Burrows-Wheeler transforms of a family of strings. In this paper we show that the H&M algorithm can be improved so that, in addition ... More

On geodesic envelopes and causticsNov 19 2004Dec 09 2005We give a global description of envelopes of geodesic tangents of regular curves in (not necessarily convex) Riemannian surfaces. We prove that such an envelope is the union of the curve itself, its inflectional geodesics and its tangential caustics (formed ... More

Hecke algebra with respect to the pro-$p$-radical of a maximal compact open subgroup for $GL(n,F)$ and its inner formsMay 25 2016Let $G$ be a direct product of inner forms of general linear groups over non-archimedean locally compact fields of residue characteristic $p$ and let $K^1$ be the pro-$p$-radical of a maximal compact open subgroup of $G$. In this paper we describe the ... More

Cusp singularities of plane envelopesNov 21 2005We consider smooth 1-parameter families of plane curves tangent to a semicubic parabola, when the curvature radius of their curves at the tangency point vanishes at the cusp point. We find the $\A$-normal form of these families, their envelopes and local ... More

Simple tangential families and perestroikas of their envelopesSep 06 2004Tangential families are 1-parameter families of rays emanating tangentially from smooth curves. We classify tangential family germs up to Left-Right equivalence: we prove that there are two infinite series and four sporadic simple singularities of tangential ... More

Generic singularities of minimax solutions to Hamilton--Jacobi equationsJul 05 2004Minimax solutions are weak solutions to Cauchy problems involving Hamilton--Jacobi equations, constructed from generating families quadratic at infinity of their geometric solutions. We give a complete description of minimax solutions and we classify ... More

Legendrian graphs generated by Tangential FamiliesSep 29 2004We construct a Legendrian version of Envelope theory. A tangential family is a 1-parameter family of rays emanating tangentially from a smooth plane curve. The Legendrian graph of the family is the union of the Legendrian lifts of the family curves in ... More

Toward a Succinct Index for Order-Preserving Pattern MatchingOct 10 2016Although introduced only a few years ago, the problem of order-preserving pattern matching has already attracted significant attention. In this paper we introduce the first index for this problem that uses sublinear space in addition to the data, which ... More

Compressing and Indexing Stock Market DataJun 18 2016Sep 13 2016We show how to build a compressed index for the offline Order Preserving Pattern Matching problem. Our solution is based on the new approach of decomposing the sequence to be indexed into an order component, containing ordering information, and a delta ... More

Density and structural anomalies in soft-repulsive dimeric fluidsMar 07 2016We report Monte Carlo results for the fluid structure of a system of dimeric particles interacting via a core-softened potential. More specifically, dimers interact through a repulsive pair potential of inverse-power form, modified in such a way that ... More

Perestroikas of vertex sets at umbilic pointsMar 14 2006Aug 14 2007Mark all vertices on a curve evolving under a family of curves obtained by intersecting a smooth surface M with the 1-parameter family of planes parallel to the tangent plane to M at a point p. Those vertices trace out a set, called the vertex set of ... More

Minimum-Variance Importance-Sampling Bernoulli Estimator for Fast Simulation of Linear Block Codes over Binary Symmetric ChannelsNov 06 2013In this paper the choice of the Bernoulli distribution as biased distribution for importance sampling (IS) Monte-Carlo (MC) simulation of linear block codes over binary symmetric channels (BSCs) is studied. Based on the analytical derivation of the optimal ... More

Weil representations and metaplectic groups over an integral domainSep 20 2013Given F a locally compact, non-discrete, non-archimedean field of characteristic different from 2 and R an integral domain such that a non-trivial smooth F-character with values in the multiplicative group of R exists, we construct the (reduced) metaplectic ... More

Compressed Spaced Suffix ArraysDec 12 2013Mar 09 2014Spaced seeds are important tools for similarity search in bioinformatics, and using several seeds together often significantly improves their performance. With existing approaches, however, for each seed we keep a separate linear-size data structure, ... More

The Wigner-Poisson-Fokker-Planck system: global-in-time solution and dispersive estimatesMay 18 2005This paper is concerned with the Wigner-Poisson-Fokker-Planck system, a kinetic evolution equation for an open quantum system with a non-linear Hartree potential. Existence, uniqueness and regularity of global solutions to the Cauchy problem in 3 dimensions ... More

Online wheel speed filtering for periodic disturbance reduction: a strategy for an advanced bicycle applicationOct 04 2016Oct 05 2016Due to geometrical errors and possible misalignment of the sensors, wheel speed measurements provided by incremental encoders in road vehicles are usually affected by significant periodic noises. This paper presents an online wheel speed filtering procedure, ... More

Orthogonality and Cooperation in Collaborative Spectrum Sensing through MIMO Decision FusionAug 14 2013This paper deals with spectrum sensing for cognitive radio scenarios where the decision fusion center (DFC) exploits array processing. More specifically, we explore the impact of user cooperation and orthogonal transmissions among secondary users (SUs) ... More

Lightweight Data Indexing and Compression in External MemorySep 24 2009In this paper we describe algorithms for computing the BWT and for building (compressed) indexes in external memory. The innovative feature of our algorithms is that they are lightweight in the sense that, for an input of size $n$, they use only ${n}$ ... More

The fully nonconforming virtual element method for biharmonic problemsNov 26 2016In this paper we address the numerical approximation of linear fourth-order elliptic problems on polygonal meshes. In particular, we present a novel nonconforming virtual element discretization of arbitrary order of accuracy for biharmonic problems. The ... More

Streaming Similarity Self-JoinJan 19 2016Mar 08 2016We introduce and study the problem of computing the similarity self-join in a streaming context (SSSJ), where the input is an unbounded stream of items arriving continuously. The goal is to find all pairs of items in the stream whose similarity is greater ... More

Relative SelectJun 10 2015Motivated by the problem of storing coloured de Bruijn graphs, we show how, if we can already support fast select queries on one string, then we can store a little extra information and support fairly fast select queries on a similar string.

Reusing an FM-indexApr 18 2014May 09 2014Intuitively, if two strings $S_1$ and $S_2$ are sufficiently similar and we already have an FM-index for $S_1$ then, by storing a little extra information, we should be able to reuse parts of that index in an FM-index for $S_2$. We formalize this intuition ... More

A random telegraph signal of Mittag-Leffler typeAug 19 2008A general method is presented to explicitly compute autocovariance functions for non-Poisson dichotomous noise based on renewal theory. The method is specialized to a random telegraph signal of Mittag-Leffler type. Analytical predictions are compared ... More

Efficient and Compact Representations of Some Non-Canonical Prefix-Free CodesMay 21 2016For many kinds of prefix-free codes there are efficient and compact alternatives to the traditional tree-based representation. Since these put the codes into canonical form, however, they can only be used when we can choose the order in which codewords ... More

Balancing Opposing Views to Reduce ControversyNov 01 2016Society is often polarized by controversial issues, that split the population into groups of opposing views. When such issues emerge on social media, we often observe the creation of 'echo chambers', i.e., situations where like-minded people reinforce ... More

Structure and phase behavior of colloidal dumbbells with tunable attractive interactionsOct 16 2013We investigate thermodynamic and structural properties of colloidal dumbbells in the framework provided by the Reference Interaction Site Model (RISM) theory of molecular fluids and Monte Carlo simulations. We consider two different models: in the first ... More

Exploring Controversy in TwitterDec 17 2015Among the topics discussed on social media, some spark more heated debate than others. For example, experience suggests that major political events, such as a vote for healthcare law in the US, would spark more debate between opposing sides than other ... More

Tube filling technique influence on superconductivity in MgB2-based conductors prepared using laboratory made boronJun 12 2014Here we report a systematic study of superconductive properties of mono-filamentary MgB2-based wires, manufactured with different filling technique. A detailed comparison of the influence of filling technique and final heat treatment on superconducting ... More

Social content matching in MapReduceMay 21 2011Matching problems are ubiquitous. They occur in economic markets, labor markets, internet advertising, and elsewhere. In this paper we focus on an application of matching for social media. Our goal is to distribute content from information suppliers to ... More

A note on the birefringence angle estimation in CMB data analysisApr 18 2016Apr 26 2016Parity violating physics beyond the standard model of particle physics induces a rotation of the linear polarization of photons. This effect, also known as cosmological birefringence (CB), can be tested with the observations of the cosmic microwave background ... More

Scalable Facility Location for Massive Graphs on Pregel-like SystemsMar 12 2015We propose a new scalable algorithm for facility location. Facility location is a classic problem, where the goal is to select a subset of facilities to open, from a set of candidate facilities F , in order to serve a set of clients C. The objective is ... More

Quantifying Controversy in Social MediaJul 18 2015Jun 07 2016Which topics spark the most heated debates on social media? Identifying those topics is not only interesting from a societal point of view, but also allows the filtering and aggregation of social media content for disseminating news stories. In this paper, ... More

Scalable Online Betweenness Centrality in Evolving GraphsJan 27 2014Apr 28 2015Betweenness centrality is a classic measure that quantifies the importance of a graph element (vertex or edge) according to the fraction of shortest paths passing through it. This measure is notoriously expensive to compute, and the best known algorithm ... More

Stable tangential families and singularities of their envelopesJun 28 2004We study tangential families, i.e. systems of rays emanating tangentially from given curves. We classify, up to Left-Right equivalence, stable singularities of tangential family germs (under deformations among tangential families) and we study their envelopes. ... More

The nonconforming virtual element methodMay 15 2014May 16 2014We introduce the nonconforming Virtual Element Method (VEM) for the approximation of second order elliptic problems. We present the construction of the new element in two and three dimensions, highlighting the main differences with the conforming VEM ... More

A Legendre-Fourier spectral method with exact conservation laws for the Vlasov-Poisson systemSep 30 2016We present the design and implementation of an L2-stable spectral method for the discretization of the Vlasov- Poisson model of a collisionless plasma in one space and velocity dimension. The velocity and space dependence of the Vlasov equation are resolved ... More

Convergence analysis of the mimetic finite difference method for elliptic problems with staggered discretization of the diffusion coefficientsDec 06 2016We study the convergence of the new family of mimetic finite difference schemes for linear diffusion problems recently proposed in [38]. In contrast to the conventional approach, the diffusion coefficient enters both the primary mimetic operator, i.e., ... More

Says who? Automatic Text-Based Content Analysis of Television NewsJul 18 2013Aug 29 2013We perform an automatic analysis of television news programs, based on the closed captions that accompany them. Specifically, we collect all the news broadcasted in over 140 television channels in the US during a period of six months. We start by segmenting, ... More

Balancing Opposing Views to Reduce ControversyNov 01 2016Nov 07 2016Society is often polarized by controversial issues, that split the population into groups of opposing views. When such issues emerge on social media, we often observe the creation of 'echo chambers', i.e., situations where like-minded people reinforce ... More

VHT: Vertical Hoeffding TreeJul 28 2016IoT Big Data requires new machine learning methods able to scale to large size of data arriving at high speed. Decision trees are popular machine learning models since they are very effective, yet easy to interpret and visualize. In the literature, we ... More

Low-complexity dominance-based Sphere Decoder for MIMO SystemsMar 04 2013The sphere decoder (SD) is an attractive low-complexity alternative to maximum likelihood (ML) detection in a variety of communication systems. It is also employed in multiple-input multiple-output (MIMO) systems where the computational complexity of ... More

Heavy-traffic analysis through uniform acceleration of queues with diminishing populationsDec 17 2014Nov 30 2015We consider a single server queue that serves a finite population of $n$ customers that will enter the queue (require service) only once, also known as the $\Delta_{(i)}/G/1$ queue. This paper presents a method for analyzing heavy-traffic behavior by ... More

Road Network Fusion for Incremental Map UpdatesFeb 07 2018In the recent years a number of novel, automatic map-inference techniques have been proposed, which derive road-network from a cohort of GPS traces collected by a fleet of vehicles. In spite of considerable attention, these maps are imperfect in many ... More

The Power of Both Choices: Practical Load Balancing for Distributed Stream Processing EnginesApr 03 2015We study the problem of load balancing in distributed stream processing engines, which is exacerbated in the presence of skew. We introduce Partial Key Grouping (PKG), a new stream partitioning scheme that adapts the classical "power of two choices" to ... More

Reference Interaction Site Model and Optimized Perturbation theories of colloidal dumbbells with increasing anisotropyMay 26 2015We investigate thermodynamic properties of anisotropic colloidal dumbbells in the frameworks provided by the Reference Interaction Site Model (RISM) theory and an Optimized Perturbation Theory (OPT), this latter based on a fourth-order high-temperature ... More

Partial Key Grouping: Load-Balanced Partitioning of Distributed StreamsOct 26 2015We study the problem of load balancing in distributed stream processing engines, which is exacerbated in the presence of skew. We introduce Partial Key Grouping (PKG), a new stream partitioning scheme that adapts the classical "power of two choices" to ... More

When Two Choices Are not Enough: Balancing at Scale in Distributed Stream ProcessingOct 19 2015Jan 27 2016Carefully balancing load in distributed stream processing systems has a fundamental impact on execution latency and throughput. Load balancing is challenging because real-world workloads are skewed: some tuples in the stream are associated to keys which ... More

Comet McNaught (260P/2012 K2): spin axis orientation and rotation periodMar 22 2014Extensive observations of comet 260P (McNaught) were carried out between August 2012 and January 2013. The images obtained were used to analyze the inner coma morphology of the comet at resolutions ranging from 250 to about 1000 km/pixel. A deep investigation ... More

High temperature heat treatment of B precursor and P.I.T. process optimization to increase Jc performances of MgB2-based conductorMay 16 2014Promising results reported in our previous works led us to think that production of B powder plays a crucial role in MgB2 synthesis. A new method for boron preparation has been developed in our laboratory. This particular process is based on magnesiothermic ... More

Finite-pool queues with heavy-tailed servicesMay 20 2016We consider the $\Delta_{(i)}/G/1$ queue, in which a a total of $n$ customers independently demand service after an exponential time. We focus on the case of heavy-tailed service times, and assume that the tail of the service time distribution decays ... More

Top-k densest subgraphs in sliding-window graph streamsOct 19 2016Given a large graph, the densest-subgraph problem asks to find a subgraph with maximum average degree. When considering the top-k version of this problem, a naive solution is to iteratively find the densest subgraph and remove it in each iteration. However, ... More

Grain size determination of superconducting MgB2 powders from magnetization curve, image analysis and surface area measurementMay 19 2014The present article reports a method for the average grain size evaluation of superconducting nano-particles through their magnetic properties. The use of SQUID magnetometry to determine the average MgB2 particle size was investigated and the results ... More

Comet Machholz (C/2004 Q2): morphological structures in the inner coma and rotation parametersSep 19 2011Extensive observations of comet C/2004 Q2 (Machholz) were carried out between August 2004 and May 2005. The images obtained were used to investigate the comet's inner coma features at resolutions between 350 and 1500 km/pixel. A photometric analysis of ... More

HD 17156b: A Transiting Planet with a 21.2 Day Period and an Eccentric OrbitOct 03 2007Oct 20 2007We report the detection of transits by the 3.1 M_Jup companion to the V=8.17 G0V star HD 17156. The transit was observed by three independant observers on Sept. 9/10, 2007 (two in central Italy and one in the Canary Islands), who obtained detections at ... More

Cluster formation and phase separation in heteronuclear Janus dumbbellsDec 04 2014We have recently investigated the phase behaviour of model colloidal dumbbells constituted by two identical tangent hard spheres, with the first one being surrounded by an attractive square-well interaction (Janus dumbbells, Muna\`o G et al 2014 Soft ... More

New insights on the binary asteroid 121 HermioneApr 13 2009We report on the results of a six-month photometric study of the main-belt binary C-type asteroid 121 Hermione, performed during its 2007 opposition. We took advantage of the rare observational opportunity afforded by one of the annual equinoxes of Hermione ... More

The African Very Long Baseline Interferometry Network:The Ghana Antenna ConversionAug 07 2016The African Very Long Baseline Interferometry Network (AVN) is a pan-African project that will develop Very Long Baseline Interferometry (VLBI) observing capability in several countries across the African continent, either by conversion of existing telecommunications ... More

The non-convex shape of (234) Barbara, the first BarbarianFeb 02 2015Asteroid (234) Barbara is the prototype of a category of asteroids that has been shown to be extremely rich in refractory inclusions, the oldest material ever found in the Solar System. It exhibits several peculiar features, most notably its polarimetric ... More

Asteroids' physical models from combined dense and sparse photometry and scaling of the YORP effect by the observed obliquity distributionJan 29 2013The larger number of models of asteroid shapes and their rotational states derived by the lightcurve inversion give us better insight into both the nature of individual objects and the whole asteroid population. With a larger statistical sample we can ... More

New and updated convex shape models of asteroids based on optical data from a large collaboration networkOct 26 2015Asteroid modeling efforts in the last decade resulted in a comprehensive dataset of almost 400 convex shape models and their rotation states. This amount already provided a deep insight into physical properties of main-belt asteroids or large collisional ... More