Artículos (Física Aplicada I)

URI permanente para esta colecciónhttps://hdl.handle.net/11441/10849

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Design of Broadband Aperture-Coupled Microstrip Antenna Arrays With Differential Feeding
(Institute of Electrical and Electronics Engineers Inc., 2024) Delgado Lozano, Ignacio María; Fernández Prieto, Armando; Losada Torres, Vicente; Boix, R. R.; Medina Mena, Francisco; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Universidad de Sevilla. Departamento de Física Aplicada I; Ministerio de Ciencia, Innovación y Universidades (MICIU). España
This paper proposes the design of broadband microstrip antennas fed by differential microstrip lines. The designed broadband antennas are composed of two capacitively coupled rectangular stacked patches excited through a dog-bone shaped aperture by short-circuited differential microstrip lines. The short-circuited lines are symmetrically located with respect to the apertures so that their differential-mode (DM) naturally excites the aperture, while their common-mode (CM) is intrinsically rejected. The DM design of the antennas is based on an equivalent second-order filter circuit consisting of two capacitively coupled parallel LC resonators, which helps to ensure the DM broadband impedance matching of the antenna. Two different 2 × 2 arrays using the proposed antennas have been designed, fabricated and measured, one involving four 180° hybrids and three power dividers in the feeding network, the other involving one 180° hybrid and six power dividers. Bandwidths larger than 25%, gains around 12 dBi and cross-polarization below -25 dB have been achieved by the two arrays at a center frequency of 5.5 GHz.
Multidimensional nanoarchitectures for improved indoor light harvesting in dye-sensitized solar cells
(Elsevier, 2025-04) Castillo Seoane, Javier; Contreras Bernal, Lidia; Riquelme Expósito, Antonio Jesús; Fauvel, Samuel; Kervella, Yann; Gil Rostra, Jorge; Lozano Barbero, Gabriel Sebastián; Barranco Quero, Ángel; Demadrille, Renaud; Sánchez Valencia, Juan Ramón; Borrás Martos, Ana Isabel; Universidad de Sevilla. Departamento de Física Aplicada I; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; Consejo Superior de Investigaciones Científicas (CSIC); European Union (UE). H2020; Universidad de Sevilla. TEP123: Metalurgia e Ingeniería de los Materiales
Dye Sensitized Solar Cells (DSSCs) have recently gained renewed interest for their potential in indoor light harvesting and powering wireless devices. However, to fully exploit their potential, crucial aspects require further attention, in particular, the improvement of spectral compatibility and low-light harvesting mechanisms, as well as the development of efficient photoanodes through high-yield scalable methods. In this article, we propose the use of nanocomposite photoanodes integrating mesoporous TiO2 nanoparticles, ITO nanotubes (NT), and anatase TiO2 shells (ITO@TiO2 NT) prepared by step-by-step method relying on mild temperature conditions and avoiding toxic precursors. These photoanodes outperform previous attempts to implement low-dimensional ITO and ITO@TiO2 nanowires and nanotubes for outdoor light conversion, demonstrating a power conversion efficiency under low artificial light intensity of 24 % for at 0.014 mW cm−2, a 166 % increase compared to the conventional architectures. Advanced microstructural, optical, and electrochemical characterizations have revealed that the strong scattering effect of the light in the visible range coupled with enhanced charge collection at low-intensity illumination are the essential mechanisms responsible for such enhanced energy conversion. Remarkably, our devices retain up to 90 % of the normal incidence efficiency even under glancing illumination, while conventional reference devices retain only 30 %.
Triboelectric pixels as building blocks for microscale and large-area integration of drop energy harvesters
(Cell Press, 2024-10-03) Ghaffarinejad, Ali; García Casas, Xabier; Núñez-Gálvez, Fernando; Budagosky Marcilla, Jorge Alejandro; Fortio Godinho, Vanda Cristina; López Santos, Carmen; Sánchez Valencia, Juan Ramón; Barranco Quero, Ángel; Borrás, Ana; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Universidad de Sevilla. Departamento de Física Aplicada I; Ministerio de Ciencia e Innovación (MICIN). España; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Universidad de Sevilla; Ministerio de Ciencia, Innovación y Universidades (MICIU). España; European Union (UE). H2020
Triboelectric nanogenerators (TENGs) are the most promising technology for harvesting energy from low-frequency liquid flows and impacts such as rain droplets. However, current drop energy harvester technologies suffer from low output power due to limitations in triboelectric materials, suboptimal device designs, and the inability to fully capture the kinetic energy of falling drops. This article introduces a microscale TENG capable of efficiently converting drop impact energy into electrical power in a single, rapid step. The device features a capacitive structure that enhances energy conversion through instantaneous capacitance changes when the drops contact the submillimetric top electrodes. This compact design establishes a path toward the development of dense arrays and rain panels and is adaptable to various liquids, scales, triboelectric surfaces, and thin-film configurations, including flexible and transparent materials.
Compositional and microstructural study of joining methods in archaeological gold objects
(John Wiley and Sons Ltd, 2017-03) Scrivano, Simona; Gómez-Tubio, Blanca María; Ortega-Feliú, Inés; Ager Vázquez, Francisco José; Paúl Escolano, Antonio; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; Universidad de Sevilla. Departamento de Física Aplicada III; Universidad de Sevilla. Departamento de Física Aplicada I; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; Ministerio de Economía y Competitividad (MINECO). España
This work arises in response to the need to understand the production techniques of pre-roman gold jewels, starting from the systematic characterization of the different methods of metal joining used in antiquity to produce these objects. To meet this requirement, different procedures used in antiquity were reproduced by means of experimental archaeology. These models correspond to three metal-joining methods reported by ancient recipes: solid-state diffusion with copper salt, brazing and autogenous welding. These techniques were studied by different analytical methods in order to characterize them at both compositional and microstructural level (SEM-EDS, metallography, μ-XRF and μ-PIXE). The results obtained show that the solid-state diffusion bonding with copper salt presents a crystal hexagonal structure without phase changes in the joining point, where only a variation in the grain size is observed. At the compositional level, this soldering method is characterized by a local increase in copper concentration and a small decrease in gold content. In contrast, brazing shows a dendritic-porous structure due to the superposition of the soldering alloy and the crystal structure of the original foils. Besides, the compositional analysis revealed an increment of silver and copper concentrations and a simultaneous reduction of gold concentration. Finally, in the autogenous welding, no changes at the microstructural and compositional levels were observed. The results obtained have also demonstrated the usefulness of a portable μ-XRF system for the in-situ characterization of ancient jewels.
Combining XRF and GRT for the analysis of ancient silver coins
(Elsevier, 2016-05) Ager Vázquez, Francisco José; Gómez-Tubio, Blanca María; Paúl Escolano, Antonio; Gómez-Morón, A.; Scrivano, Simona; Ortega-Feliú, Inés; Respaldiza Galisteo, Miguel Ángel; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; Universidad de Sevilla. Departamento de Física Aplicada I; Universidad de Sevilla. Departamento de Física Aplicada III; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; Ministerio de Economía y Competitividad (MINECO). España
Archaeological silver-copper alloys are usually affected by silver enrichment of the near surface layers, either intentional or fortuitous. In previous studies we have shown that surface composition of archaeological bronzes and leaded copper coins obtained by XRF can be corrected by means of gamma-ray transmission (GRT) to obtain the bulk composition. In the present work, we have studied the applicability of this method to silver-copper alloys and established the most suitable conditions for the GRT correction calculation. The analysis of the microstructure of the core and the corrosion layers of a set of silver roman coins shows that copper could be leached from the surface during corrosion and cleaning treatments, resulting in an apparent silver surface enrichment. After the correction calculations by GRT method, the concentrations of the major elements, Ag and Cu, were found to be in good agreement with the bulk composition obtained by direct analysis of the cut cross-sections of the coins. The GRT method shows to be a useful tool to study metal artefacts having a surface composition modified by corrosion or cleaning treatments.
The complete solution of the Schrödinger equation with the Rosen–Morse type potential via the Nikiforov–Uvarov method
(Elsevier, 2024-02) Gordillo Núñez, Guillermo; Álvarez Nodarse, Renato; Quintero, Niurka R.; Universidad de Sevilla. Departamento de Física Aplicada I; Ministerio de Ciencia e Innovación (MICIN). España; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Junta de Andalucía; Universidad de Granada; Andalusian research group; Universidad de Sevilla. FQM415: Modelado Físico-Matemático de Sistemas no Lineales
We determine exact solutions of the time-independent Schrödinger equation for the Rosen–Morse type potential by using the Nikiforov–Uvarov method. This method allows us to write the eigenfunctions of the Schrödinger equation as the product of two simpler functions in a constructive way. The resolution of this problem is used to show that the kinks of the non-linear Klein–Gordon equation with 𝜑2𝑝+2 type potentials are stable. We also derive the orthogonality and completeness relations satisfied by the set of eigenfunctions, which are useful in the description of the dynamics of kinks under perturbations or interacting with antikinks.
Picosecond lifetimes of hydrogen bonds in the halide perovskite CH₃NH₃PbBr₃
(American Chemical Society, 2024-11-26) Garrote Márquez, Alejandro; Lodeiro Moraga, Lucas; Cruz Hernández, Norge; Liang, Xia; Walsh, Aron; Menéndez-Proupin, Eduardo; Universidad de Sevilla. Departamento de Física Aplicada I; Universidad de Sevilla. FQM401: Simulación y Aplicación de Materiales
The structures and properties of organic–inorganic perovskites are influenced by the hydrogen bonding between the organic cations and the inorganic octahedral networks. This study explores the dynamics of hydrogen bonds in CH3NH3PbBr3 across a temperature range from 70 to 350 K, using molecular dynamics simulations with machine-learning force fields. The results indicate that the lifetime of hydrogen bonds decreases with increasing temperature from 7.6 ps (70 K) to 0.16 ps (350 K), exhibiting Arrhenius-type behavior. The geometric conditions for hydrogen bonding, which include bond lengths and angles, maintain consistency across the full temperature range. The relevance of hydrogen bonds for the vibrational states of the material is also evidenced through a detailed analysis of the vibrational power spectra, demonstrating their significant effect on the physical properties for this class of perovskites.
Investigación multidisciplinar basada en el uso de aceleradores de partículas: el Centro Nacional de Aceleradores
(Fundación General de la Universidad Autónoma de Madrid, 2024-09) López Gutiérrez, José María; García-Tenorio García-Balmaseda, Rafael; Universidad de Sevilla. Departamento de Física Aplicada I; Universidad de Sevilla. RNM138: Física Nuclear Aplicada
En este artículo se lleva a cabo un análisis descriptivo a distintos niveles del Centro Nacional de Aceleradores, dedicado fundamentalmente a la realización de investigaciones multidisciplinares basadas en el uso de aceleradores de partículas y equipos asociados. En el artículo se hace así referencia a las seis instalaciones principales que posee este centro y a las distintas líneas de investigación asociadas a ellas. Igualmente se describe la estructura de recursos personales que posee, y que integra un conjunto de sesenta personas, mencionándose igualmente las características orientadas a los usuarios externos del centro a través de las actividades de carácter transversal que desarrolla y a las colaboraciones estratégicas con empresas e instituciones que viene poniendo en práctica en los últimos años.
Metal-only additive manufacturing of V-band lightweight waveguide and horn components
(Institute of Electrical and Electronics Engineers, 2024-09) Chen, Mingzheng; Rico Fernández, José; Mesa Ledesma, Francisco Luis; Quevedo Teruel, Óscar; Universidad de Sevilla. Departamento de Física Aplicada I; Ministerio de Ciencia, Innovación y Universidades (MICIU). España; Universidad de Sevilla. TIC112: Microondas
Additive manufacturing (AM) is growing as a key technology for the miniaturization and integration of microwave components. Among several AM processes, laser powder-bed fusion (LPBF) is especially convenient for waveguides and horns because it allows for 3-D printing of metal-only parts with high accuracy and low surface roughness. During the 3-D printing process, metallic powder materials are selectively consolidated by melting layer by layer together using a heat source, that is, a laser, allowing for adaptation to complex and shaped structures. The present study investigates the feasibility of using LPBF-AM to fabricate waveguides and geodesic H-plane horns in V-band. Geodesic H-plane horns comprise two parallel curved metallic plates to reduce phase errors and achieve high gain and aperture efficiency, and are particularly suited to be fabricated using LPBF. The monolithic waveguides demonstrate significantly better performance than their two-piece counterparts, achieving an average attenuation coefficient of 5.3 dB/m for the straight waveguide and 8 dB/m for the 90° E-plane waveguide bend at 50–70 GHz. Similarly, the monolithic geodesic H-plane horn has higher realized gains and radiation efficiencies with only a sixth of the weight compared to the two-piece version at 52–68 GHz. The results demonstrate that the LPBF-AM technique is a promising candidate to produce monolithic metal-only microwave components in V-band.
Theory and design of waveguide dual polarization-plane rotators based on rotational corrugations
(Institute of Electrical and Electronics Engineers, 2024-11) García Contreras, Ginés; Mesa Ledesma, Francisco Luis; Córcoles Ortega, Juan; Ruiz Cruz, Jorge Alfonso; Quevedo Teruel, Óscar; Universidad de Sevilla. Departamento de Física Aplicada I; Ministerio de Ciencia, Innovación y Universidades (MICIU). España; Universidad de Sevilla. TIC112: Microondas
This work presents a framework for the introduction of reciprocal dual polarization-plane rotators in waveguide technology. This concept is presented using rotational and longitudinal unit cells (rotational corrugations), stating rigorously the geometrical constraints required for its implementation. The devices have been studied from both a linear and a circular polarization modal perspective, using a mode-matching technique for rotationally symmetric modes and dispersion diagrams. Furthermore, various devices that use the proposed scheme have been designed to show the operation principle. A prototype has been built using additive manufacturing as a proof of concept. It has been measured using dedicated ortho-mode transducers (OMTs) for extracting the different involved signals and fully characterizing their performance.
Numerical modelling of higher-symmetric periodic structures with hexagonal lattice
(Institute of Electrical and Electronics Engineers, 2024-11) Petek, Martin; Rico Fernández, José; Tobón Vásquez, Jorge Alberto; Valerio, Guido; Mesa Ledesma, Francisco Luis; Quevedo Teruel, Óscar; Vipiana, Francesca; Universidad de Sevilla. Departamento de Física Aplicada I; European Cooperation in Science and Technology (COST); Ministerio de Ciencia e Innovación (MICIN). España; Universidad de Sevilla. TIC112: Microondas
This paper presents the development of the multi-modal transfer matrix method (MMTMM) to deal with periodic structures with hexagonal unit cells and higher symmetries. The method is able to calculate complex modal solutions, including the attenuation in the stopband. A key feature is the reformulation of the MMTMM into an eigenvalue problem whose eigensolutions in the complex plane can be systematically obtained for the boundaries of the irreducible Brillouin zone, where the phase-shift conditions are linearly dependent. The obtained phase-shift dispersion diagrams are verified against a commercial software, while the attenuation constant is validated with a developed method of moments. A glide-symmetric structure and a mirror half-turn structure are investigated. The latter is found to possess a highly isotropic stopband with a fractional bandwidth of 94.9%, wider than previously reported for holey structures. Finally, the operation of the unit cell is demonstrated with a practical implementation for preventing leakage in a waveguide flange.
Mechanisms of de-icing by surface rayleigh and plate lamb acoustic waves
(Wiley, 2024-12) Pandey, Shilpi; Moral Jalón, Jaime del; Jacob, Stefan; Montes Montañez, Laura; Gil Rostra, Jorge; Frechilla Zabal, Alejandro; Karimzadeh, Atefeh; Rico Gavira, Victor J.; Kanter, Raul; Kandelin, Niklas; López Santos, Carmen; Koivuluoto, Heli; Angurel Lambán, Luis Alberto; Winkler, Andreas; Borrás Martos, Ana Isabel; Rodríguez González-Elipe, Agustín; Universidad de Sevilla. Departamento de Física Aplicada I; Agencia Estatal de Investigación. España; European Union (UE). H2020
Acoustic waves (AW) have recently emerged as an energy-efficient ice-removal procedure compatible with functional and industrial-relevant substrates. However, critical aspects at fundamental and experimental levels have yet to be disclosed to optimize their operational conditions. Identifying the processes and mechanisms by which different types of AWs induce de-icing are some of these issues. Herein, using model LiNbO3 systems and two types of interdigitated transducers, the e-icing and anti-icing efficiencies and mechanisms driven by Rayleigh surface acoustic waves (R-SAW) and Lamb waves with 120 and 510 μm wavelengths, respectively, are analyzed. Through the experimental analysis of de-icing and active anti-icing processes and the finite element simulation of the AW generation, propagation, and interaction with small ice aggregates, it is disclosed that Lamb waves are more favorable than R-SAWs to induce de-icing and/or prevent the freezing of small ice droplets. Prospects for applications of this study are supported by proof of concept experiments, including de-icing in an icing wind tunnel, demonstrating that Lamb waves can efficiently remove ice layers covering large LN substrates. Results indicate that the de-icing mechanism may differ for Lamb waves or R-SAWs and that the wavelength must be considered as an important parameter for controlling the efficiency.
Improving the scanning coverage of array antennas with multilayer lenses designed with a ray tracing
(Institute of Electrical and Electronics Engineers, 2024-11) Castillo Tapia, Pilar; Flores Espinosa, Núria; Mesa Ledesma, Francisco Luis; Viganó, María Carolina; Quevedo Teruel, Óscar; Universidad de Sevilla. Departamento de Física Aplicada I; Ministerio de Ciencia, Innovación y Universidades (MICIU). España; Universidad de Sevilla. TIC112: Microondas
Integrating dielectric lenses with phased array antennas can be beneficial in numerous applications, yet the design procedure typically requires significant computational effort. In this work, we employ a streamlined in-house two-dimensional ray-tracing model to design dielectric lenses, with the goal of enhancing the gain of an array antenna at large scanning angles. The ray-tracing model also accounts for losses from material absorption and reflections. The interfaces between the dielectric layers of these lenses devised in this study are defined using splines to allow a large flexibility of their shape. First, dielectric lenses consisting of a core layer supplemented by two matching layers are investigated. The results show better performance compared to the lens constructed using the conic equation. In addition, multilayer dielectric lenses also provide more flexibility, as proved by the proposed configuration with five layers which also minimizes reflections in the optimized direction. Finally, a nonuniform multilayer lens, featuring two layers on the sides and a single layer near to broadside can improve gain at 60° while maintaining efficiency at smaller angles.
The dissipative effect of Caputo–time-fractional derivatives and its implications for the solutions of nonlinear wave equations
(Elsevier, 2024-09) Bountis, Tassos; Cantisán Gómez, Julia; Cuevas-Maraver, Jesús; Macías Díaz, Jorge Eduardo; Kevrekidis, Panayotis G.; Universidad de Sevilla. Departamento de Física Aplicada I; Agencia Estatal de Investigación. España; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Universidad de Sevilla. FQM280: Física no Lineal
In honor of the great Russian mathematician A. N. Kolmogorov, we would like to draw attention in the present paper to a curious mathematical observation concerning fractional differential equations describing physical systems, whose time evolution for integer derivatives has a time-honored conservative form. This observation, although known to the general mathematical community, (Achar et al., 2001; Stanislavsky, 2004; Diethelm and Ford, 2010; Chung and Jung, 2014; Olivar-Romero and Rosas-Ortiz, 2017; Baleanu et al., 2020) has not, in our view, been satisfactorily addressed. More specifically, we follow the recent exploration of Caputo–Riesz time–space-fractional nonlinear wave equation of Macias Diaz (2022), in which two of the present authors introduced an energy-type functional and proposed a finite-difference scheme to approximate the solutions of the continuous model. The relevant Klein–Gordon equation considered here has the form: 𝜕𝛽𝜙(𝑥, 𝑡) - 𝜕𝑡𝛽 − 𝛥 𝛼𝜙(𝑥, 𝑡) + 𝐹′(𝜙(𝑥, 𝑡)) = 0, ∀(𝑥, 𝑡) ∈ (−∞, ∞) (0.1) where we explore the sine-Gordon nonlinearity 𝐹(𝜙) = 1 − cos(𝜙) with smooth initial data. For 𝛼 = 𝛽 = 2, we naturally retrieve the exact, analytical form of breather waves expected from the literature. Focusing on the Caputo temporal derivative variation within 1 < 𝛽 < 2 values for 𝛼 = 2, however, we observe artificial dissipative effects, which lead to complete breather disappearance, over a time scale depending on the value of 𝛽. We compare such findings to single degree-of-freedom linear and nonlinear oscillators in the presence of Caputo temporal derivatives and also consider anti-damping mechanisms to counter the relevant effect. These findings also motivate some interesting directions for further study, e.g., regarding the consideration of topological solitary waves, such as kinks/antikinks and their dynamical evolution in this model.
Evaluation of losses in 3D-printed geodesic lenses using a ray-tracing model
(Institute of Electrical and Electronics Engineers, 2024-01) Castillo Tapia, Pilar; Rico Fernández, José; Clendinning, Sarah; Mesa Ledesma, Francisco Luis; Quevedo Teruel, Óscar; Universidad de Sevilla. Departamento de Física Aplicada I; Universidad de Sevilla. TIC112: Microondas
This article applies an in-house generalized ray-tracing (RT) model to efficiently compute both the radiation pattern and the efficiency of geodesic lenses with nonrotationally symmetric shapes. Losses due to ohmic effects and surface roughness are included in the model. These losses are very relevant for monolithic geodesic lens antennas as postprocessing techniques cannot be applied to reduce the surface roughness of internal part of the metallic plates. The model is validated by comparison with full-wave simulations for three different lenses: a circular flat parallel-plate waveguide (PPW), an elliptically compressed geodesic lens, and a water-drop lens. These results show a reduction in computational time by a factor of 600 using the RT model. A non-rotationally symmetric water drop lens has been manufactured in a monolithic piece using the laser powder-bed fusion (LPBF) technique with successful experimental results.
The validity of physical optics for microwave analysis: accuracy through simplicity
(2025) Mesa Ledesma, Francisco Luis; Quevedo Teruel, Óscar; Universidad de Sevilla. Departamento de Física Aplicada I; Universidad de Sevilla. TIC112: Microondas
Traditionally, the optics and microwave communities have been separated not only by the THz band but also by differences in technical knowledge, analytical and computational approaches, design processes, and measurement methodologies. In this contribution, we aim to bridge this divide by leveraging a computational asymptotic technique from optics, known as physical optics, which holds significant potential for the microwave/antenna community. This technique allows for precise microwave calculations for radiation patterns, reflection coefficients, material losses, and mutual coupling between antennas.
On the fractional dynamics of kinks in sine-Gordon models
(MDPI, 2025-01-10) Bountis, Tassos; Cantisán Gómez, Julia; Cuevas-Maraver, Jesús; Macías Díaz, Jorge Eduardo; Kevrekidis, Panayotis G.; Universidad de Sevilla. Departamento de Física Aplicada I; National Science Foundation (NSF). United States; European Union (UE); Agencia Estatal de Investigación. España; Universidad de Sevilla. FQM280: Física no Lineal
I the present work, we explored the dynamics of single kinks, kink–anti-kink pairs and bound states in the prototypical fractional Klein–Gordon example of the sine-Gordon equation. In particular, we modified the order 𝛽 of the temporal derivative to that of a Caputo fractional type and found that, for 1<𝛽<2, this imposes a dissipative dynamical behavior on the coherent structures. We also examined the variation of a fractional Riesz order 𝛼 on the spatial derivative. Here, depending on whether this order was below or above the harmonic value 𝛼=2, we found, respectively, monotonically attracting kinks, or non-monotonic and potentially attracting or repelling kinks, with a saddle equilibrium separating the two. Finally, we also explored the interplay of the two derivatives, when both Caputo temporal and Riesz spatial derivatives are involved.
Thermal lifetime of breathers
(Elsevier, 2025-03) Archilla, Juan F. R.; Bajārs, Jānis; Flach, Sergej; Universidad de Sevilla. Departamento de Física Aplicada I; Archilla, Juan F. R.; Ministerio de Ciencia, Innovación y Universidades (MICIU). España; Universidad de Sevilla; Faculty of Science and Technology of the University of Latvia; Institute for Basic Science (IBS) in the Republic of Korea; Universidad de Sevilla. FQM280: Física No Lineal
In this article, we explore the lifetime of localized excitations in nonlinear lattices, called breathers, when a thermalized lattice is perturbed with localized energy delivered to a single site. We develop a method to measure the time it takes for the system to approach equilibrium based on a single scalar quantity, the participation number, and deduce the value corresponding to thermal equilibrium. We observe the time to achieve thermalization as a function of the energy of the excited site. We explore a variety of different physical system models. The result is that the lifetime of breathers increases exponentially with the breather energy for all the systems. This increase becomes observable when this energy is larger than approximately ten times the local average thermal energy. These results may provide a method to detect the existence of breathers in real systems.
Discrete derivative nonlinear Schrödinger equations
(MDPI, 2024-12-30) Hennig, Dirk; Cuevas-Maraver, Jesús; Universidad de Sevilla. Departamento de Física Aplicada I; Universidad de Sevilla. FQM280: Física no Lineal
We consider novel discrete derivative nonlinear Schrödinger equations (ddNLSs). Taking the continuum derivative nonlinear Schrödinger equation (dNLS), we use for the discretisation of the derivative the forward, backward, and central difference schemes, respectively, and term the corresponding equations forward, backward, and central ddNLSs. We show that in contrast to the dNLS, which is completely integrable and supports soliton solutions, the forward and backward ddNLSs can be either dissipative or expansive. As a consequence, solutions of the forward and backward ddNLSs behave drastically differently compared to those of the (integrable) dNLS. For the dissipative forward ddNLS, all solutions decay asymptotically to zero, whereas for the expansive forward ddNLS all solutions grow exponentially in time, features that are not present in the dynamics of the (integrable) dNLS. In comparison, the central ddNLS is characterized by conservative dynamics. Remarkably, for the central ddNLS the total momentum is conserved, allowing the existence of solitary travelling wave (TW) solutions. In fact, we prove the existence of solitary TWs, facilitating Schauder’s fixed-point theorem. For the damped forward expansive ddNLS we demonstrate that there exists such a balance of dissipation so that solitary stationary modes exist.
Nitrogen plasma functionalization of low density polyethylene
(Elsevier, 2011-02-25) López Santos, Carmen; Yubero Valencia, Francisco; González-Elipe, Agustín R.; Universidad de Sevilla. Departamento de Física Aplicada I; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; Ministerio de Ciencia y Educación. España; Junta de Andalucía; Universidad de Sevilla. FQM196: Nanotecnología en Superficies y Plasma
Low density polyethylene (LDPE) films have been treated with different nitrogen containing plasmas with the purpose of incorporating nitrogen functional groups on its surface and analyzing the changes experienced in their surface tension. Effects of a dielectric barrier discharge (DBD) at atmospheric pressure and a microwave discharge (MW) at reduced pressure are compared with those obtained by using an atom source supplied with N₂ and mixtures Ar + NH₃ as plasma gas. X-ray photoelectron spectroscopy (XPS) analysis has provided information about the chemical surface changes whereas the surface topography of the treated samples has been examined by atomic force microscopy (AFM). Non-destructive depth profiles of oxygen and carbon have been obtained for the treated and one month aged samples by means of the non-destructive Tougaard's method of XPS background analysis. Generally, an oxygen enrichment of the deeper region of treated LDPE surfaces has been observed. Chemical derivatization of the treated samples has shown that a DBD plasma with a mixture of Ar + NH₃ was the most efficient treatment for nitrogen and amine group functionalization. It is argued that the high concentration of NH* species in this plasma is the most important factor in enhancing the nitrogen functionalization of this polymer. It has been also found that the observed increase in hydrophilicity and surface tension cannot be attributed to the anchored nitrogen functional groups formed on plasma treated LDPE. Differences in the plasma activation behaviour of LDPE and that of other polymers subjected to similar treatments are stressed.

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