167 research outputs found
Uniform electric field distribution in microwave heating applicators by means of genetic algorithms optimization of dielectric multilayer structures
In this paper, the design of a dielectric multilayer
around a clay sample is presented to achieve a uniform electric
field distribution over that sample. This structure is located within
a multimode microwave-heating oven and is designed by means
of genetic algorithms. The permittivity and geometric values for
the sample surrounding layers are the selected parameters to
be optimized in order to minimize the ratio between the typical
deviation and the absolute value of the electric field. The results
demonstrate the improvement of the electric field uniformity over
the sample using dielectric layers.This work was supported
in part by the Fundación Séneca under Project 00700/PPC/0
Polynomials of least deviation from zero in Sobolev p-Norm
The first part of this paper complements previous results on characterization of polynomials of least deviation from zero in Sobolev p-norm (1<p<∞) for the case p=1. Some relevant examples are indicated. The second part deals with the location of zeros of polynomials of least deviation in discrete Sobolev p-norm. The asymptotic distribution of zeros is established on general conditions. Under some order restriction in the discrete part, we prove that the n-th polynomial of least deviation has at least n−d∗ zeros on the convex hull of the support of the measure, where d∗ denotes the number of terms in the discrete part.The research of H. Pijeira-Cabrera was partially supported by Ministry of Science, Innovation and Universities of Spain, under grant PGC2018-096504-B-C33.
Funding Open Access funding provided by Universidad Carlos III de Madrid thanks to the CRUE-CSIC 2021 agreement with Springer Nature
Combined use of genetic algorithms and gradient descent optimization methods for accurate inverse permittivity measurement
A novel inverse transmission-line method for the
complex permittivity determination of arbitrary shaped materials
is presented. Complex permittivity is inferred by using an inverse
calculation procedure, which is based on a combined optimization
strategy of both genetic algorithms and the gradient descent
method. The optimization procedure matches the measured and
simulated complex scattering parameters’ frequency behavior
of materials within a WR340 waveguide. High accuracy and
practical suitability are validated through experimental tests.
The dielectric properties of PTFE and epoxy resin mixed with
iron–oxide-doped fiberglass have been measured for different
shapes and positions. Dielectric multilayer structures have been
used to demonstrate that this technique is able to measure the
individual permittivity of each element of the structure. Both twoand
three-dimensional approaches have been carried out and their
advantages and drawbacks discussed
Multimode cavity efficiency optimization by optimum load location-experimental approach
In this paper, a novel load-matching procedure for
microwave-heating applicators is presented and tested. In order to
accomplish the optimization procedure, an optimization method
based on the use of the Lebenverg–Marquardt technique has
been specifically developed and tested on two different microwave
ovens. The proposed procedure allows an efficient optimization of
three-dimensional microwave applicators by means of the dielectric
sample relocation as a function of its complex permittivity,
size, and operating frequency. Experimental measurements of
the reflection coefficient are presented and analyzed over several
samples and multimode cavities. Results indicate that high power
efficiencies can be obtained provided that operating frequency
is not just below TM-mode cutoff frequencies for the transverse
dimensions of the oven.This work
was supported in part by the Spanish Science and Technology Ministry under
Project TIC2001-2778-CO2-02
Microondas: lÃneas de transmisión, guÃas de onda y cavidades resonantes
Como su tÃtulo indica, este libro pretende servir de apoyo al estudio de la parte de la asignatura de Microondas relacionada con la teorÃa de lÃneas de transmisión y guÃas de onda, asà como de otros dispositivos creados a partir de éstas, como las cavidades resonantes. Aunque existen en el mercado excelentes publicaciones sobre esta materia, con esta obra se ha intentado ajustar los contenidos con el fin de que éstos puedan ser impartidos de un modo claro y sosegado en un total de ocho semanas con tres horas semanales de clase magistral y de resolución de problemas. Se pretende seguir una estructura clara y progresiva que facilite el aprendizaje por parte del alumno o lector, incorporando contenidos teóricos y prácticos para cada uno de los temas planteados. Se han incluido en el texto de un modo detallado todas las demostraciones de importantes expresiones matemáticas con el fin de que el propio alumno sea capaz de seguirlas sin necesidad de que el profesor las desarrolle en clase. A lo largo de cada capÃtulo se desarrollan ejemplos y se plantean ejercicios a realizar por el lector. Asimismo, al final de cada capÃtulo se han añadido cuestiones de repaso y problemas. El capÃtulo de introducción define el concepto de microondas, repasa los principales hitos históricos en esta rama de la ingenierÃa y presenta un breve resumen de las aplicaciones fundamentales de las microondas. El estudio de lÃneas de transmisión se desarrolla a lo largo de los capÃtulos 2, 3 y 4. En el segundo se presenta la lÃnea de transmisión ideal, estudiando su comportamiento tanto en el dominio del tiempo (análisis de transitorios) como en el dominio de la frecuencia, donde el análisis se centra en el uso del diagrama de Smith para adaptación de cargas. En el tercer capÃtulo se aborda el estudio de lÃneas de transmisión reales, presentando los conceptos de atenuación y dispersión y analizando las principales lÃneas con dos conductores. Para finalizar el estudio de lÃneas de transmisión, el capÃtulo 4 aborda el análisis de guÃas de onda, asà como de modos superiores del cable coaxial, cuya resolución electromagnética presenta una dificultad superior. Aquà se presentan los modos transversal eléctrico y transversal magnético y se analizan sus caracterÃsticas de propagación y de potencia. Este capÃtulo finaliza con el análisis de cavidades resonantes rectangulares y cilÃndricas a partir del estudio previamente realizado sobre guÃas de onda
Aplicación de algoritmos genéticos en el diseño de hornos microondas: eficiencia energética y calentamiento uniforme
En este artÃculo se describe la aplicación de algoritmos genéticos en el diseño de hornos microondas para procesos industriales de calentamiento. Los objetivos perseguidos en estos diseños son, fundamentalmente, la eficiencia energética mediante una adecuada adaptación entre la fuente de microondas y su carga, y la obtención de un campo eléctrico sobre la muestra lo más uniforme
posible, con el fin de generar un calentamiento homogéneo en todo el producto y aumentando asà la calidad del producto fina
Precise evaluation of coaxial to waveguide transitions by means of inverse techniques
In this paper, a new two-tier inverse characterization
technique for coaxial to waveguide transition evaluation is
presented and properly validated. The transition is characterized
by estimating its scattering parameters and a cascade procedure
is employed in order to compare simulations and measurements
during the unterminating procedure. In contrast to other unterminating
methods there are no restrictions concerning the
number and type of standards and two transitions are simultaneously
characterized. Additionally, genetic algorithms and the
gradient descent method are used for error minimization during
the unterminating stage. The accuracy of this two-tier inverse
technique is evaluated as a function of the employed standards and
the obtained results are compared to those provided by different
well-known calibration algorithms. Results show that it is possible
to properly characterize the coaxial to waveguide transition in a
very flexible and accurate way
Impacto en los resultados infecciosos durante la colecistectomÃa laparoscópica con el uso de una bolsa de extracción de vesÃcula biliar casera frente a una comercial: estudio comparativo retrospectivo en un centro de gran volumen
Antecedentes La colecistectomÃa laparoscópica (CL) es una de las intervenciones de urgencia más frecuentes, a la que se someten aproximadamente 600.000 pacientes al año en Estados Unidos. Aunque la CL se asocia a menos complicaciones en comparación con la colecistectomÃa abierta, el riesgo de complicaciones infecciosas, incluida la infección del sitio quirúrgico y el absceso intraabdominal, sigue siendo una fuente importante de morbilidad postoperatoria. El objetivo de este estudio es determinar si la técnica de extracción de la vesÃcula biliar durante la CL afecta al riesgo de complicaciones infecciosas. Métodos y procedimientos Se realizó un estudio comparativo retrospectivo en un centro de cirugÃa mÃnimamente invasiva de alto volumen en Bogotá, Colombia. Se identificaron los pacientes sometidos a LC entre 2018 y 2020. Los pacientes se dividieron en tres grupos. Un grupo de LC realizado con bolsa de recuperación de vesÃcula biliar casera (HMGRB), y otro grupo de LC realizado con bolsa de recuperación de vesÃcula biliar comercial (CGRB). Los resultados primarios fueron las complicaciones infecciosas de infección superficial y absceso intraabdominal. Resultados Un total de 68 (7,58%) pacientes se sometieron a CL utilizando una HMGRB, y 828 (92,41%) utilizando una CGRB. No hubo diferencias significativas en la sepsis preoperatoria, ni en la distribución por sexos entre los grupos de pacientes. Utilizando la prueba t, encontramos diferencias en la distribución de edad entre los grupos (p < 0,01), los tiempos quirúrgicos (p < 0,01) y la duración de la estancia (p = 0,01). Al utilizar Chi cuadrado, encontramos diferencias en la gravedad de la escala de graduación de Tokio y Parkland (p < 0,01), el uso de antibióticos postoperatorios (p < 0,01) y el uso de drenajes (p < 0,01). Sin embargo, no hubo diferencias en la tasa de infección superficial del sitio quirúrgico (p = 0,92). Conclusión Los HMGRB no se asocian a un mayor riesgo de absceso intraabdominal postoperatorio ni de infección superficial del sitio quirúrgico en comparación con los CGRB, pero implican tiempos quirúrgicos y estancias más prolongados. El uso de HMGRB es seguro, factible y tiene menor coste durante la LC.Background Laparoscopic cholecystectomy (LC) is one of the most commonly performed emergency procedures, with approximately 600,000 patients undergoing the procedure every year in the United States. Although LC is associated with fewer complications when compared with open cholecystectomy, the risk for infectious complications, including surgical site infection and intra-abdominal abscess, remains a significant source of postoperative morbidity. The goal of this study is to determine whether the gallbladder retrieval technique during LC affects risk of infectious complications. Methods and procedures We conducted a retrospective comparative study in a minimally invasive surgery high-volume center in Bogota, Colombia. Patients who underwent LC in 2018 to 2020 were identified. The patients were divided into three groups. One group of LC performed using home-made gallbladder retrieval bag (HMGRB), and another group of LC performed using commercial gallbladder retrieval bag (CGRB). The primary outcomes were infectious complications of superficial site infection and intra-abdominal abscess. Results A total of 68 (7.58%) patients underwent LC using an HMGRB, and 828 (92.41%) using a CGRB. There was no significant difference in preoperative sepsis, or sex distribution between patient groups. Using t test, we found differences on age distribution among groups (p < 0.01), surgical times (p < 0.01), and length of stay (p = 0.01). When using Chi square, we found differences in Tokyo and Parkland Grading Scale severity (p < 0.01), use of postoperative antibiotics (p < 0.01), and drain use (p < 0.01). Nonetheless, there was no difference in the rate of superficial surgical site infection (p = 0.92). Conclusion HMGRB are not associated with increased risk of postoperative intra-abdominal abscess or superficial surgical site infection in comparison with CGRB but imply longer surgical times and length of stay. The use of HMGRB is safe, feasible, and has lower cost during LC
Development of a prototype test system for certification of curved fuselage panels
Volume 1024, Issue 1
Article number 012081A prototype test system with capacity to reproduce combined loads representative of real loading cases of a curved fuselage panel has been developed. This prototype test system allows the structural validation of curved fuselage panels to be accomplished. The developed system is able to apply combined mechanical and pressurization loading states under quasi-static and dynamic loading conditions. It has been designed using CAD models and calculated with the aid of Finite Element models to ensure its integrity. A data acquisition system synchronized with a control system enables real time monitoring of test parameters.Horizonte 2020 (Unión Europea) CS2-AIR-GAM-2014-2015-0
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