Search results for "Hierarchical"
showing 10 items of 260 documents
A fast 3D dual boundary element method based on hierarchical matrices
2008
AbstractIn this paper a fast solver for three-dimensional BEM and DBEM is developed. The technique is based on the use of hierarchical matrices for the representation of the collocation matrix and uses a preconditioned GMRES for the solution of the algebraic system of equations. The preconditioner is built exploiting the hierarchical arithmetic and taking full advantage of the hierarchical format. Special algorithms are developed to deal with crack problems within the context of DBEM. The structure of DBEM matrices has been efficiently exploited and it has been demonstrated that, since the cracks form only small parts of the whole structure, the use of hierarchical matrices can be particula…
Energy Efficient Consensus Over Complex Networks
2015
The need to extract large amounts of information from the environment to have precise situation awareness and then react appropriately to certain events has led to the emergence of complex and heterogeneous sensor networks. In this context, where the sensor nodes are usually powered by batteries, the design of new methods to make inference processes efficient in terms of energy consumption is necessary. One of these processes, which is present in many distributed tasks performed by these complex networks, is the consensus process. This is the basis for certain tracking algorithms in monitoring and control applications. To improve the energy efficiency of this process, in this paper we propo…
Mapping traditional cultural landscapes in the Mediterranean area using a combined multidisciplinary approach: Method and application to Mount Etna (…
2011
Traditional cultural landscapes (TCLs) are prominent in Mediterranean countries. The abundance of this landscape type, however, is not reflected by broad-scale inventories and mapping tools. The aim of this paper is to highlight the need for a multidisciplinary approach to landscape analysis, with special reference to the Mediterranean area. We propose an integrated method that combines deductive and inductive processes to define and map TCLs in a study area (Mount Etna, Sicily, Italy). We also develop a procedure to characterize the primary components of these landscapes as a reference to be used in cultural-landscape descriptions. For mapping purposes, three different scales of analysis w…
Emerging Evidences of Mesoscopic-Scale Complexity in Neat Ionic Liquids and Their Mixtures
2017
Ionic liquids (ILs) represent a blooming class of continuously developing advanced materials, with the aiming of a green chemical industry. Their appealing physical and chemical properties are largely influenced by their micro- and mesoscopic structure that is known to possess a high degree of hierarchical organization. High-impact application fields are largely affected by the complex morphology of neat ionic liquids and their mixtures. This Perspective highlights new arising research directions that point to an enhanced level of structural complexity in several IL-based systems, including mixtures. The latter represent a change in paradigm in the approach to formulate new, task-specific I…
Outlier detection to hierarchical and mixed effects models
2008
Hierarchical and mixed effects models are models where a varying number of coefficients may be random at different levels of the hierarchy. The purpose of outlier analysis for these models is to determine whether an outlying unit at higher level is entirely outlying, or outlying due to effect of one or a few aberrant lower level units. Most works on diagnostics for these complex models have focused on the mixed model rather than on the hierarchical models, obscuring some relevant aspects of the hierarchical model. In this paper we will present an approach to influence analysis and outlier detection for mixed and hierarchical model, focusing on the special structure of nested data that these…
On the Provisioning of Mobile Digital Terrestrial TV Services to Vehicles With DVB-T
2012
[EN] Most of the DVB-T (Digital Video Broadcasting -Terrestrial) networks deployments worldwide have been designed for fixed rooftop antennas and high transmission capacity, not providing good coverage level for vehicular mobile reception. This letter analyzes how to combine different technical solutions, so far studied individually, in order to increase the robustness of the transmission for vehicular reception to provide in-band mobile services. In particular, we consider: receive antenna diversity, hierarchical modulation, and Application Layer Forward Error Correction (AL-FEC). Performance evaluation results have been obtained by means of simulations, laboratory tests, and field measure…
Verification of scope-dependent hierarchical state machines
2008
AbstractA hierarchical state machine (Hsm) is a finite state machine where a vertex can either expand to another hierarchical state machine (box) or be a basic vertex (node). Each node is labeled with atomic propositions. We study an extension of such model which allows atomic propositions to label also boxes (Shsm). We show that Shsms can be exponentially more succinct than Shsms and verification is in general harder by an exponential factor. We carefully establish the computational complexity of reachability, cycle detection, and model checking against general Ltl and Ctl specifications. We also discuss some natural and interesting restrictions of the considered problems for which we can …
Synthesis and Structure Determination of the Hierarchical Meso-Microporous Zeolite ITQ-43
2011
[EN] The formation of mesopores in microporous zeolites is generally performed by postsynthesis acid, basic, and steam treatments. The hierarchical pore systems thus formed allow better adsorption, diffusion, and reactivity of these materials. By combining organic and inorganic structure-directing agents and high-throughput methodologies, we were able to synthesize a zeolite with a hierarchical system of micropores and mesopores, with channel openings delimited by 28 tetrahedral atoms. Its complex crystalline structure was solved with the use of automated diffraction tomography.
Non-Hierarchical Clustering as a method to analyse an open-ended questionnaire on algebraic thinking
2016
The problem of taking a data set and separating it into subgroups, where the members of each subgroup are more similar to each other than they are to members outside the subgroup, has been extensively studied in science and mathematics education research. Student responses to written questions and multiple-choice tests have been characterised and studied using several qualitative and/or quantitative analysis methods. However, there are inherent difficulties in the categorisation of student responses in the case of open-ended questionnaires. Very often, researcher bias means that the categories picked out tend to find the groups of students that the researcher is seeking out. In this paper, …
Visitor arrivals forecasts amid COVID-19: A perspective from the Africa team
2021
Abstract COVID-19 disrupted international tourism worldwide, subsequently presenting forecasters with a challenging conundrum. In this competition, we predict international arrivals for 20 destinations in two phases: (i) Ex post forecasts pre-COVID; (ii) Ex ante forecasts during and after the pandemic up to end 2021. Our results show that univariate combined with cross-sectional hierarchical forecasting techniques (THieF-ETS) outperform multivariate models pre-COVID. Scenarios were developed based on judgemental adjustment of the THieF-ETS baseline forecasts. Analysts provided a regional view on the most likely path to normal, based on country-specific regulations, macroeconomic conditions,…