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On the Motion of a Nearly Incompressible Viscous Fluid Containing a Small Rigid Body
No full textWe consider the motion of a compressible viscous fluid containing a moving rigid body
confined to a planar domain ⊂ R2. The main result states that the influence of the
body on the fluid is negligible if (i) the diameter of the body is small and (ii) the fluid
is nearly incompressible (the low Mach number regime). The specific shape of the
body as well as the boundary conditions on the fluid–body interface are irrelevant and
collisions with the boundary ∂ are allowed. The rigid body motion may be enforced
externally or governed solely by its interaction with the fluid
An integer programming model for obtaining cyclic quasi-difference matrices
Get PDFOrthogonal arrays are of great importance in mathematical sciences. This paper analyses a certain practical advantage of quasi-difference matrices over difference matrices to obtain orthogonal arrays with given parameters. We also study the existence of quasi-difference matrices over cyclic groups originating orthogonal arrays with t=2 and λ=1, proving their existence for some parameters sets. Moreover, we present an Integer Programming model to find such quasi-difference matrices and also a Bimodal Local Search algorithm to obtain them. We provide a conjecture related to the distributions of differences along rows and columns of arbitrary square matrices with entries in a cyclic group in positions outside the main diagonal which shows an intriguing symmetry, and we prove it when the matrix is a quasi-difference matrix.US21/27 (UPV/EHU and BCAM)
PID2019-104933GB-I00/AEI/10.13039/ 501100011033 (Spanish Ministry of Science and Innovation)
IT1494-22 (UPV/EHU)
GIU20/054 (UPV/EHU
Solving boundary value problems via the Nyström method using spline Gauss rules
Get PDFWe propose to use spline Gauss quadrature rules for solving boundary value problems (BVPs) using the Nyström method. When solving BVPs, one converts the corresponding partial differential equation inside a domain into the Fredholm integral equation of the second kind on the boundary in the sense of boundary integral equation (BIE). The Fredholm integral equation is then solved using the Nyström method, which involves the use of a particular quadrature rule, thus, converting the BIE problem to a linear system. We demonstrate this concept on the 2D Laplace problem over domains with smooth boundary as well as domains containing corners. We validate our approach on benchmark examples and the results indicate that, for a fixed number of quadrature points (i.e., the same computational effort), the spline Gauss quadratures return an approximation that is by one to two orders of magnitude more accurate compared to the solution obtained by traditional polynomial Gauss counterparts
Minimax Risk Classifiers with 0-1 Loss
Get PDFSupervised classification techniques use training samples to learn a classification rule with
small expected 0 -1 loss (error probability). Conventional methods enable tractable learning
and provide out-of-sample generalization by using surrogate losses instead of the 0 -1 loss
and considering specific families of rules (hypothesis classes). This paper presents minimax
risk classifiers (MRCs) that minimize the worst-case 0 -1 loss with respect to uncertainty
sets of distributions that can include the underlying distribution, with a tunable confidence.
We show that MRCs can provide tight performance guarantees at learning and are strongly
universally consistent using feature mappings given by characteristic kernels. The paper also
proposes efficient optimization techniques for MRC learning and shows that the methods
presented can provide accurate classification together with tight performance guarantees in
practice.PID2022-137063NB-I00,
CNS2022-13520
Large Eddy Simulations of Isolated and Installed Jet Noise using the High-Order Discontinuous Galerkin Method
Get PDFA recently developed computational framework for jet noise is used to compute the noise generated by an isolated and installed jet. The framework consists of two parts. In the first part, the spectral/hp element framework Nektar++ is used to compute the near-field flow. Nektar++ solves the unfiltered Navier-Stokes equations on unstructured grids using the high-order discontinuous Galerkin method. The discrete equations are integrated in time using an implicit scheme based on the matrix-free Newton-GMRES method. In the second part, the Antares library is used to compute the far-field noise. Antares solves the Ffowcs Williams - Hawkings equation for a permeable integration surface in the time domain using a source-time dominant algorithm. The simulations are validated against experimental data obtained in the Doak Laboratory Flight Jet Rig, located at the University of Southampton. For the isolated jet, good agreement is achieved, both in terms of the flow statistics and the far-field noise. The discrepancies observed for the isolated jet are believed to be caused by an under-resolved boundary layer in the simulations. For the installed jet, the flow statistics are also well predicted. In the far-field, very good agreement is achieved for downstream observers. For upstream observers, some discrepancies are observed for very high and very low frequencies
Fire-spotting modelling in operational wildfire simulators based on cellular automata: a comparison study
No full textOne crucial mechanism in the spread of wildfires is the so-called fire-spotting: a random phenomenon which occurs when embers are transported over large distances. Fire-spotting speeds up the Rate of Spread and starts new ignitions which constitute a menace for fire fighting operations. Unfortunately, operational fire-spread simulators may not account for spotting effects, thus overlooking the harmful consequences associated with this phenomenon. In this work, several fire spotting methods are integrated in the operational wildfire simulator PROPAGATOR based on Cellular Automata (CA). Ran- domFront, a physics-based parametrization of fire-spotting, is tested for the first time in the context of CA simulators. RandomFront is compared with other two parametrizations already adopted in CA based simulators, the ones of Alexandridis et al. and Perryman et al. A wildfire occurred in the summer of 2021 in the municipality of Campomarino (Molise, Italy), and where spotting effects were clearly reported, has been used as a study case. RandomFront parametrization produced a more complex burnt probability pattern than the other models. Moreover, it predicted higher burning proba- bility in the area of the domain affected by spotting effects in the real wildfire event.This research has been supported by the Basque Government through the BERC 2022–2025 programme; by the Spanish Ministry of Economy and Competitiveness (MINECO) through the BCAM Severo Ochoa excel- lence accreditation SEV-2017-0718 and CEX2021-001142-S / MICIN / AEI / 10.13039/501100011033 and through the national projects PID2019-107685RB- I00 and PDC2022-133115-I00; by the European Regional Development Fund (ERDF) and the Department of Education of the regional government, the Junta of Castilla y Le ́on, (Grant contract SA089P20); and by the Interreg IPA CBC Italy-Albania-Montenegro programme through the project The flOod and Big firE foREst, prediction, forecAst anD emergencY management (TO BE READY). This work has been partially supported by the Horizon 2020-funded project SAFERS “Structured Approaches for Forest Fire Emer- gencies in Resilient Societies” (H2020/Innovation Action), grant agreement No. 869353
Data-driven estimation of the instantaneous reproduction number and growth rates for the 2022 monkeypox outbreak in Europe
Get PDFObjective: To estimate the instantaneous reproduction number and the epidemic growth rates for the 2022 monkeypox outbreaks in the European region.
Methods: We gathered daily laboratory-confirmed monkeypox cases in the most affected European countries from the beginning of the outbreak to September 23, 2022. A data-driven estimation of the instantaneous reproduction number is obtained using a novel filtering type Bayesian inference. A phenomenological growth model coupled with a Bayesian sequential approach to update forecasts over time is used to obtain time-dependent growth rates in several countries.
Results: The instantaneous reproduction number for the laboratory-confirmed monkeypox cases in Spain, France, Germany, the UK, the Netherlands, Portugal, and Italy. At the early phase of the outbreak, our estimation for , which can be used as a proxy for the basic reproduction number , was ( CI ) for Spain, ( CI ) for France, ( CI ) for Germany, ( CI ) for the UK, ( CI ) for the Netherlands, ( CI ) for Portugal, ( CI ) for Italy. Cumulative cases for these countries present subexponential rather than exponential growth dynamics.
Conclusions: Our findings suggest that the current monkeypox outbreaks present limited transmission chains of human-to-human secondary infection so the possibility of a huge pandemic is very low. Confirmed monkeypox cases are decreasing significantly in the European region, the decline might be attributed to public health interventions and behavioral changes in the population due to increased risk perception. Nevertheless, further strategies toward elimination are essential to avoid the subsequent evolution of the monkeypox virus that can result in new outbreaks.Non
On the doubling condition in the infinite-dimensional setting
Get PDFWe present a systematic approach to the problem whether a topologically infinite-dimensional space can be made homogeneous in the Coifman–Weiss sense. The answer to the question is negative, as expected. Our leading representative of spaces with this property is with the natural product topology.Basque Government (BERC 2022-2025),
Spanish State Research Agency (CEX2021-001142-S and RYC2021-031981-I),
Foundation for Polish Science (START 032.2022)
Kernel-based Construction Operators for Boolean Sum and Ruled Geometry
Get PDFBoolean sum and ruling are two well-known construction operators for both parametric surfaces and
trivariates. In many cases, the input freeform curves in IR2
or surfaces in IR3
are complex, and as a result,
these construction operators might fail to build the parametric geometry so that it has a positive Jacobian
throughout the domain.
In this work, we focus on cases in which those constructors fail to build parametric geometries with a
positive Jacobian throughout while the freeform input has a kernel point. We show that in the limit, for
high enough degree raising or enough refinement, our construction scheme must succeed if a kernel exists. In
practice, our experiments, on quadratic, cubic and quartic B´ezier and B-spline curves and surfaces show that
for a reasonable degree raising and/or refinement, the vast majority of construction examples are successful
Indoor Localization System With NLOS Mitigation Based on Self-Training
Get PDFLocation-awareness has become a fundamental requirement for multiple emerging applications with the rapid development
of wireless technologies. The high-accuracy ranging enabled by ultra-wide bandwidth (UWB) signals is often deteriorated by clocks
imperfections and non-line-of-sight (NLOS) propagation. Existing supervised learning methods for NLOS identification and mitigation
are time-consuming, labor-intensive, and cost-inefficient due to the need for training data acquisition and label assignment. This paper
presents an indoor localization system that enables NLOS mitigation based on self-training. The system provides a general information
fusion framework that integrates map, inertial sensors, and UWB measurements, where the weak labels for UWB measurements are
produced and iteratively refined by multi-sensory information fusion for self-training. In addition, the system utilizes the maximum
likelihood ranging estimator that considers the impact of clock drift. The effectiveness of the proposed system is demonstrated via
extensive experimentation in multiple real-world environments, e.g., the proposed methods reduce the NLOS ranging error by 80% and
result in a 90th localization error percentile of 0.5 meters in a complex indoor environment