Uniqueness of limit cycles for quadratic vector fields

Producción CientíficaThis article deals with the study of the number of limit cycles surrounding a critical point of a quadratic planar vector field, which, in normal form, can be written as x ′ = a1x − y − a3x 2 + (2a2 + a5)xy+a6y 2 , y ′ = x+a1y+a2x 2+(2a3+a4)xy−a2y 2 . In particular, we study the semi-varieties defined in terms of the parameters a1, a2, . . . , a6 where some classical criteria for the associated Abel equation apply. The proofs will combine classical ideas with tools from computational algebraic geometry.Agencia Estatal de Investigación - Fondo Europeo de Desarrollo Regional (grant MTM 2011-22751)Junta de Extremadura (grant GR15055)Ministerio de Economía, Industria y Competitividad - Fondo Europeo de Desarrollo Regional (grant MTM2015-65764-C3-1-P

Vanishing Abelian integrals on zero-dimensional cycles

In this paper we study conditions for the vanishing of Abelian integrals on families of zero-dimensional cycles. That is, for any rational function $f(z)$, characterize all rational functions $g(z)$ and zero-sum integers $\{n_i\}$ such that the function $t\mapsto\sum n_ig(z_i(t))$ vanishes identically. Here $z_i(t)$ are continuously depending roots of $f(z)-t$. We introduce a notion of (un)balanced cycles. Our main result is an inductive solution of the problem of vanishing of Abelian integrals when $f,g$ are polynomials on a family of zero-dimensional cycles under the assumption that the family of cycles we consider is unbalanced as well as all the cycles encountered in the inductive process. We also solve the problem on some balanced cycles. The main motivation for our study is the problem of vanishing of Abelian integrals on single families of one-dimensional cycles. We show that our problem and our main result are sufficiently rich to include some related problems, as hyper-elliptic integrals on one-cycles, some applications to slow-fast planar systems, and the polynomial (and trigonometric) moment problem for Abel equation. This last problem was recently solved by Pakovich and Muzychuk (\cite{PM} and \cite{P}). Our approach is largely inspired by their work, thought we provide examples of vanishing Abelian integrals on zero-cycles which are not given as a sum of composition terms contrary to the situation in the solution of the polynomial moment problem.Comment: 35 pages, 1 figure; one reference added; abstract, introduction and structure change

High Vapor Transport Deposition: A Novel Process to Develop Cu2ZnSn(SxSe1–x)4 Thin Film Solar Cells

Kesterite thin film solar cells are known to be a promising cost-effective solution because they are based on earth-abundant and environmental compounds. However, it is known that their best efficiency (12.6%) has not been improved since 2013, meanwhile other thin-film solar cells have demonstrated that their performance has been enhanced continuously. The main drawbacks to explain this situation is the narrow process window of this compound and simultaneously, the high composition and thermal control needed to avoid intrinsic defects in the p-type layer. The high vapor transport deposition process has not been explored yet by kesterite thin film solar cell developers. Herein, we present the results obtained using a design of a new vacuum deposition method similar to close space sublimation, which reported excellent results in CdTe. The main advantages of this novel process are: 1) to achieve a high deposition rate; 2) to be able to deposit precursor materials and to carry out the sulfur-selenization in the same process chamber, avoiding the two steps used in the sequential process; 3) to provide a high accuracy in the chemical composition control; and 4) simple design using commercial components to facilitate its scalability for large production

Influence of Degradation Processes in Lead–Acid Batteries on the Technoeconomic Analysis of Photovoltaic Systems

Most technoeconomic feasibility studies of photovoltaic (PV) systems with batteries are mainly focused on the load demand, PV system profiles, total system costs, electricity price, and the remuneration rate. Nevertheless, most do not emphasise the influence degradation process such as corrosion, sulphation, stratification, active material seeding, and gassing on battery lifetime, efficiency, and capacity. In this paper, it is analysed the influence of the degradation processes in lead–acid batteries on the technoeconomic analysis of PV systems with and without battery. Results show that Net Present Value (NPV), Payback Period (PBP), and Discounted PayBack Period (DPBP) have a heavy dependence on the assumptions about the value of the battery performance parameters according to its degradation processes. Results show NPV differences in the range from −307% to 740%, PBP differences in the range from 9% to 188%, and DPBP differences in the range from 0% to 211%

Angular Dependence of Photonic Crystal Coupled to Photovoltaic Solar Cell

Photonic crystals have the advantage of minimizing thermal losses from solar cells, reflecting the solar radiation that is not absorbed by the photovoltaic device. To optimize this optical response, photonic crystals are designed considering the relative position of the Bragg peak and the bandgap of the solar cell, under normal incident irradiation conditions. The aim of this research article was to determine experimentally the optical limits of a solar cell coupled to a photonic crystal acting as beam splitter. For that purpose, the photovoltaic system was characterized under indoor and outdoor conditions; angular dependence of the irradiation source was determined in each case, and both results were compared with good agreement. Moreover, other parameters such as irradiation spectrum and polarization of the light were investigated. The main conclusion is that photovoltaic performance is highly affected by the Bragg peak shifting and the profile is distorted, due to the angular dependence with the sun. These experimental limits must be considered at the early design stage to avoid performance losses

Una breve descripción del programa FSIT

"El lenguaje utilizado para realizar este proyecto es Python 3, que suele" "tener mucha aceptación en Informática Forense (“Digital Forensic”) gracias a la cantidad de librerías existentes y su gran portabilidad: puede correr en diferentes sistemas operativos. Para no restringir el ámbito del programa se decidió usar la librería PyQt4 en el diseño de la interfaz gráfica. Otras de las razones que nos llevó a elegir este paquete, es que sus componentes son de un alto nivel y también gozan de una gran aceptación en la comunidad."Como esto es solo el inicio y aspiramos a ampliar la herramienta a otros sistemas de archivos el código ha sido escrito basa´ndose en la programacio´n orientada a objetos. Y para que el programa sea más fácil de reutilizar se ha seguido el patrón MVC. Todo este esfuerzo ha permitido mejorar la "usabilidad de la aplicación."Departamento de Informática (Arquitectura y Tecnología de Computadores, Ciencias de la Computación e Inteligencia Artificial, Lenguajes y Sistemas Informáticos

Calidad de sentencias de primera y segunda instancia sobre obligación de dar suma de dinero, expediente N° 00028- 2015-0-1703-jp-ci-02, del distrito judicial de Lambayeque-Jaén

La investigación tuvo como problema: ¿Cuál es la calidad de las sentencias de primera y segunda instancia sobre, Obligación de Dar Suma de Dinero, según los parámetros normativos, doctrinarios y jurisprudenciales pertinentes, en el expediente N° 00028- 2015- 0-1703-JP-CI-02, del Distrito Judicial De Lambayeque – Jaén. 2020; el objetivo fue: determinar la calidad de las sentencias en estudio. Es de tipo, cuantitativo cualitativo, nivel exploratorio descriptivo y diseño no experimental, retrospectivo y transversal. La unidad de análisis fue un expediente judicial, seleccionado mediante muestreo por conveniencia; para recolectar los datos se utilizó las técnicas de la observación y el análisis de contenido; y como instrumento una lista de cotejo, validado mediante juicio de expertos. Los resultados revelaron que la calidad de la parte expositiva, considerativa y resolutiva, pertenecientes a: la sentencia de primera instancia fueron de rango: muy alta, muy alta y muy alta; mientras que la sentencia de segunda instancia fueron: muy alta, muy alta y muy alta. En conclusión, la calidad de las sentencias de primera y segunda instancia, fueron de rango muy altas, muy altas y muy altas, respectivamente.Tesi