Departamento de Física
http://hdl.handle.net/10396/106
2024-03-28T09:16:13ZOn the impact of wavelength dependency on supercontinuum generation in photonic crystal fibers
http://hdl.handle.net/10396/27452
On the impact of wavelength dependency on supercontinuum generation in photonic crystal fibers
Díaz Soriano, Antonio Manuel; Ortiz Mora, Antonio; Martínez-Muñoz, David; Rodríguez, Pedro
It is common practice when simulating propagation through an optical fiber to assume that its characteristic parameters are constant and determined solely by the central wavelength of the input pulse. In this paper, we propose a study of the impact that the actual wavelength dependence of these parameters has on the propagation results. To this end, simulations were carried out considering both the constant model and the wavelength-dependent model, applying them to the case of the especially sensitive effect of supercontinuous generation in a photonic crystal fiber. The results showed differences of up to 20% of the spectrum and, hence, the importance of taking into account the wavelength dependence of the dispersion fiber parameters to obtain more-realistic results in the simulations.
2024-01-01T00:00:00ZDesign of multivariable PID control using iterative linear programming and decoupling
http://hdl.handle.net/10396/27451
Design of multivariable PID control using iterative linear programming and decoupling
Garrido, J.; Garrido-Jurado, Sergio; Vázquez, Francisco; Arrieta, Orlando
The design of multivariable process control systems is specially complicated when there are strong interactions between the different control loops, and even more with multiple time delays. This paper proposes an iterative design method of centralized proportional-integral-derivative (PID) controllers for stable linear systems. The methodology is based on the linear parameterization of equivalent loop transfer functions (ELTFs) for centralized control. These functions capture the dynamics of the other loops and, from a prior design, allow solving the design problem at each iteration with linear programming that shapes the Nyquist plot of the ELTFs in the frequency domain, which also avoids the need for approximations. Two optimizations are proposed: (I) maximizing integral gains by fulfilling linear robustness margins in each ELTF and (II) maximizing linear robustness margins by fulfilling minimum bandwidths in each loop. In both optimizations, static decoupling and decoupling at a frequency close to the bandwidth of each loop are included as constraints, which improves the decoupling performance and the procedure convergence. The effectiveness of the method is verified in three simulation examples (square and non-square) and a lab experimental process. The proposed designs achieve a similar or better response when compared to that achieved by other authors.
2024-01-01T00:00:00ZQuantitative comparison of impurity transport in turbulence reduced and enhanced scenarios at Wendelstein 7-X
http://hdl.handle.net/10396/26184
Quantitative comparison of impurity transport in turbulence reduced and enhanced scenarios at Wendelstein 7-X
Alcusón, J.A.; Wegner, Th.; Dinklage, A.; Langenberg, A.; Bähner, J.P.; Buttenschön, B.; Edlund, E.M.; Fuchert, G.; García-Regaña, J.M.; Grulke, O.; Huang, Z.; Porkolab, M.; Stechow, A.V.; Zocco, A.
We assess the turbulent particle transport being responsible for the limitation of the confinement and, thus, the overall performance of the neoclassically optimized stellarator Wendelstein 7-X. The radial particle transport is experimentally inferred from the evaluation of impurity injection into turbulence reduced and enhanced plasma scenarios revealing a completely different confinement behavior. The impact of the density gradient on the turbulent ion transport is theoretically estimated using large-scale non-linear gyro-kinetic simulations enabling, for the first time in Wendelstein 7-X, a quantitative comparison to the experimentally assessed impurity transport properties. We demonstrate that impurity transport in most of the Wendelstein 7-X discharges, up to now impossible to cover only with neoclassical estimations, is dominated by turbulence and can be modelled via gyro-kinetic simulations.
2023-01-01T00:00:00ZOptimizing high-quality graphene nanoflakes production through organic (bio)-precursor plasma decomposition
http://hdl.handle.net/10396/26180
Optimizing high-quality graphene nanoflakes production through organic (bio)-precursor plasma decomposition
Casanova, Ana; Rincón, Rocío; Muñoz, José; Ania, Conchi O.; Calzada Canalejo, María Dolores
Atmospheric pressure plasma-based technique for the decomposition of biofuels allows obtaining high-quality graphene powder in one step, without the use of neither metal catalysts nor specific substrates. Despite the numerous advantages of this technology as compared to others, it is necessary to optimize the process to produce high-quality graphene at industrial scale. In this research, the influence of the ethanol flows in the 2.00 to 4.00 g h−1 range on the production rate and the quality of graphene has been thoroughly assessed, through a deep characterization of the synthetized material by various techniques. The graphene production rate steadily increased for ethanol flows increasing from 2.00 to 3.40 g h−1, presenting a maximum rate of 1.45 and 1.55 mg min−1 for 2.90 and 3.40 g h−1, respectively. Higher ethanol flows lead to a decrease in the production rate, favouring the formation of other carbon-based by-products such as methane and ethylene. High-quality graphene is formed in all plasma conditions, with the lowest number of defects being obtained for an ethanol flow of 2.90 g h−1 together with hydrogen and carbon monoxide as main gaseous by-products.
2021-01-01T00:00:00Z