Toroidal PCA via density ridges

Principal Component Analysis (PCA) is a well-known linear dimension-reduction technique designed for Euclidean data. In a wide spectrum of applied fields, however, it is common to observe multivariate circular data (also known as toroidal data), rendering spurious the use of PCA on it due to the periodicity of its support. This paper introduces Toroidal Ridge PCA (TR-PCA), a novel construction of PCA for bivariate circular data that leverages the concept of density ridges as a flexible first principal component analog. Two reference bivariate circular distributions, the bivariate sine von Mises and the bivariate wrapped Cauchy, are employed as the parametric distributional basis of TR-PCA. Efficient algorithms are presented to compute density ridges for these two distribution models. A complete PCA methodology adapted to toroidal data (including scores, variance decomposition, and resolution of edge cases) is introduced and implemented in the companion R package ridgetorus. The usefulness of TR-PCA is showcased with a novel case study involving the analysis of ocean currents on the coast of Santa Barbara.Comment: 20 pages, 8 figures, 1 tabl

Short Videos to Communicate Effectively to Engineering Students

[EN] The use of multimedia in education has become a basic tool for educators. As Millennials and Generation Z use technology in their everyday life, the educational model has been shifting towards the use of multimedia and technology to enhance the active learning process. The objective of this project was to design, produce and implement short educational or instructional videos to present content with a more active approach and measure the impact on their understanding and preference. A video with the content of graduation requirements was produced, shared with 240 seniors of Engineering Academic Programs. The results show that 97% of the students liked the video and the way the content was shared and 91.6% of the students find the video format useful. The results show that the learning process was active and effective. The exit poll also shows that 97% of the students think that there should be more educational videos on some other processes. This project included the design, production and implementation of 18 videos. This research describes the approach and impact of using short videos in engineering and transition from a traditional method of sharing content to students to a more active learning environment.The authors would like to acknowledge the financial support of Writing Lab, Institute for the Future of Education, Tecnologico de Monterrey, Mexico, in the production of this work.Arrambide-Leal, E.; Lara-Prieto, V.; García-García, R. (2021). Short Videos to Communicate Effectively to Engineering Students. En 7th International Conference on Higher Education Advances (HEAd'21). Editorial Universitat Politècnica de València. 509-517. https://doi.org/10.4995/HEAd21.2021.13002OCS50951

Impedance modelling and parametric sensitivity of a VSC-HVDC system: New insights on resonances and interactions

Pervasiveness of power converters in the electric power system is expected in the future. Such large penetration will change the current power system dynamics leading to uncertain, unexpected, and potentially critical responses. This paper investigates the stability and resonance of a VSC-HVDC (Voltage Source Converter High Voltage Direct Current) link within an AC grid, whilst providing insights into resonances having a role on the grid. This is studied through the impedance-based modelling of the entire system (AC and DC grids), including controls of converters. Additionally, the impact of the different parameters of the hybrid AC-DC power system such as control systems and grid components on the system dynamics and stability is investigated. From this study, the impact of the system components and the controls of the converter on overall resonance response and stability is shown, including potential undesired sub-synchronous and harmonic resonances due to AC-DC system interactions. The analytical impedance-based models developed and obtained is validated through time-domain simulations, the physical model of the whole system is built in Simscape™ Power Systems™ and control systems in MATLAB/Simulink® (R2017b). This has demonstrated the validity of the model to deal with and detect such dynamics. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.Peer ReviewedPostprint (published version

Impact of converter losses on the optimal power flow solution of hybrid networks based on VSC-MTDC

This paper studies the impact of voltage source converter (VSC) losses on the solution of the optimal power flow (OPF) of hybrid AC/DC systems with a multi-terminal configuration. The motivation of this analysis is that the expected development of high voltage direct current (HVDC) systems will entail an increase of the number of converter stations, and consequently, converter losses might not be negligible when compared with conventional transmission losses of AC and DC lines. Towards this end, an extended OPF model is proposed considering a combination of VSC based multi-terminal HVDC grids (VSC-MTDC) and AC systems. The OPF model represents converter losses according to the state-of-the art modeling where different expressions are used when the converter functions as an inverter or as a rectifier. Three simpler alternative approaches are also implemented and the obtained OPF solutions are assessed. In order to compare the OPF solutions, a comparison metric is proposed. Obtained results show that modeling the converter losses in a simplified way could lead to very different power flow solutions, especially for the DC branches.Postprint (author's final draft

Flow Prediction in Ungauged Catchments Using Probabilistic Random Forests Regionalization and New Statistical Adequacy Tests

Flow prediction in ungauged catchments is a major unresolved challenge in scientific and engineering hydrology. This study attacks the prediction in ungauged catchment problem by exploiting advances in flow index selection and regionalization in Bayesian inference and by developing new statistical tests of model performance in ungauged catchments. First, an extensive set of available flow indices is reduced using principal component (PC) analysis to a compact orthogonal set of ?flow index PCs.? These flow index PCs are regionalized under minimal assumptions using random forests regression augmented with a residual error model and used to condition hydrological model parameters using a Bayesian scheme. Second, ?adequacy? tests are proposed to evaluate a priori the hydrological and regionalization model performance in the space of flow index PCs. The proposed regionalization approach is applied to 92 northern Spain catchments, with 16 catchments treated as ungauged. It is shown that (1) a small number of PCs capture approximately 87% of variability in the flow indices and (2) adequacy tests with respect to regionalized information are indicative of (but do not guarantee) the ability of a hydrological model to predict flow time series and are hence proposed as a prerequisite for flow prediction in ungauged catchments. The adequacy tests identify the regionalization of flow index PCs as adequate in 12 of 16 catchments but the hydrological model as adequate in only 1 of 16 catchments. Hence, a focus on improving hydrological model structure and input data (the effects of which are not disaggregated in this work) is recommended

Optimal power flow operation of an interline current flow controller in an hybrid AC/DC meshed grid

This paper is meant to show that an interline Current Flow Controller (CFC) is able to reduce the operating costs of hybrid AC/DC meshed grids by alleviating the congestion within the DC lines. The work considers a unidirectional DC/DC CFC with a simple structure and its average model is introduced into the mathematical formulation of the Optimal Power Flow (OPF) problem of an hybrid AC/DC meshed grid, which also considers the losses of the Voltage Source Converters (VSC). The CFC restrictions and the different connection arrangements of the device into the AC/DC grid are also included in the model and show an important effect on the OPF solution. The case studies are conducted in a 5-terminal AC/DC meshed grid and point out that the CFC has a reduced capability to reduce the operating costs of the system if there are no overloads in the DC lines. However, when the power limit of one of the lines is reached, the CFC can redirect part of the DC current and, therefore, reduce the operating costs compared to the case without CFC.Postprint (author's final draft

SWIMM 2.0: Enhanced Smith–Waterman on Intel’s Multicore and Manycore Architectures Based on AVX-512 Vector Extensions

The well-known Smith–Waterman (SW) algorithm is the most commonly used method for local sequence alignments, but its acceptance is limited by the computational requirements for large protein databases. Although the acceleration of SW has already been studied on many parallel platforms, there are hardly any studies which take advantage of the latest Intel architectures based on AVX-512 vector extensions. This SIMD set is currently supported by Intel’s Knights Landing (KNL) accelerator and Intel’s Skylake (SKL) general purpose processors. In this paper, we present an SW version that is optimized for both architectures: the renowned SWIMM 2.0. The novelty of this vector instruction set requires the revision of previous programming and optimization techniques. SWIMM 2.0 is based on a massive multi-threading and SIMD exploitation. It is competitive in terms of performance compared with other state-of-the-art implementations, reaching 511 GCUPS on a single KNL node and 734 GCUPS on a server equipped with a dual SKL processor. Moreover, these successful performance rates make SWIMM 2.0 the most efficient energy footprint implementation in this study achieving 2.94 GCUPS/Watts on the SKL processor.Facultad de Informátic

Accelerating Smith-Waterman Alignment of Long DNA Sequences with OpenCL on FPGA

With the greater importance of parallel architectures such as GPUs or Xeon Phi accelerators, the scientific community has developed efficient solutions in the bioinformatics field. In this context, FPGAs begin to stand out as high performance devices with moderate power consumption. This paper presents and evaluates a parallel strategy of the well-known Smith-Waterman algorithm using OpenCL on Intel/Altera’s FPGA for long DNA sequences. We efficiently exploit data and pipeline parallelism on a Intel/Altera Stratix V FPGA reaching upto 114 GCUPS in less than 25 watt power requirements.Publicado en Lecture Notes in Computer Science book series (LNCS, vol. 10209).Facultad de Informátic

Development of an empirical wall-friction model for 2D simulations of pseudo-2D bubbling fluidized beds

Pseudo-2D fluidized beds have been crucial for the understanding of the dynamics of gas-particle systems. In these systems the distance between the front and back walls is narrow, which restricts and creates a resistance to the solids motion, leading to a different flow behaviour compared to fully 3D systems. This interaction of the particle motion with the walls can be significant and should not be neglected in numerical simulations. The present work develops a new model to easily account for the friction effect between the walls and the particles in a pseudo-2D bed. The model is based on experimental results combined with simplifications of the shear force on a wall provided by the kinetic theory of granular flows. The dependence on the particle diameter and bed thickness is directly introduced in the model through the use of a straightforward expression that is easy to code and does not lead to numerical divergence. To test the model two beds of different thickness were simulated, and the resulting time-averaged solids concentration and velocity as well as bubble properties were compared with experiments. It is shown that the numerical results with the new wall-friction model improve the prediction of the standard 2D-simulations