Short channel effects in graphene-based field effect transistors targeting radio-frequency applications

Channel length scaling in graphene field effect transistors (GFETs) is key in the pursuit of higher performance in radio frequency electronics for both rigid and flexible substrates. Although two-dimensional (2D) materials provide a superior immunity to Short Channel Effects (SCEs) than bulk materials, they could dominate in scaled GFETs. In this work, we have developed a model that calculates electron and hole transport along the graphene channel in a drift-diffusion basis, while considering the 2D electrostatics. Our model obtains the self-consistent solution of the 2D Poisson's equation coupled to the current continuity equation, the latter embedding an appropriate model for drift velocity saturation. We have studied the role played by the electrostatics and the velocity saturation in GFETs with short channel lengths L. Severe scaling results in a high degradation of GFET output conductance. The extrinsic cutoff frequency follows a 1/L^n scaling trend, where the index n fulfills n < 2. The case n = 2 corresponds to long-channel GFETs with low source/drain series resistance, that is, devices where the channel resistance is controlling the drain current. For high series resistance, n decreases down to n= 1, and it degrades to values of n < 1 because of the SCEs, especially at high drain bias. The model predicts high maximum oscillation frequencies above 1 THz for channel lengths below 100 nm, but, in order to obtain these frequencies, it is very important to minimize the gate series resistance. The model shows very good agreement with experimental current voltage curves obtained from short channel GFETs and also reproduces negative differential resistance, which is due to a reduction of diffusion current.Comment: 27-pages manuscript (10 figures) plus 6 pages of supplementary information. European Union Action H2020 (696656) / Department d'Universitats, Recerca i Societat de la Informaci\'o of the Generalitat de Catalunya (2014 SGR 384) / Ministerio de Econom\'ia y Competitividad of Spain (TEC2012-31330 and TEC2015-67462-C2-1-R) / MINECO FEDE

Activation of mammalian Chk1 during DNA replication arrest: a role for Chk1 in the intra-S phase checkpoint monitoring replication origin firing

Checkpoints maintain order and fidelity in the cell cycle by blocking late-occurring events when earlier events are improperly executed. Here we describe evidence for the participation of Chk1 in an intra-S phase checkpoint in mammalian cells. We show that both Chk1 and Chk2 are phosphorylated and activated in a caffeine-sensitive signaling pathway during S phase, but only in response to replication blocks, not during normal S phase progression. Replication block–induced activation of Chk1 and Chk2 occurs normally in ataxia telangiectasia (AT) cells, which are deficient in the S phase response to ionizing radiation (IR). Resumption of synthesis after removal of replication blocks correlates with the inactivation of Chk1 but not Chk2. Using a selective small molecule inhibitor, cells lacking Chk1 function show a progressive change in the global pattern of replication origin firing in the absence of any DNA replication. Thus, Chk1 is apparently necessary for an intra-S phase checkpoint, ensuring that activation of late replication origins is blocked and arrested replication fork integrity is maintained when DNA synthesis is inhibited

Evaluación de la gestión de la calidad educativa del Colegio de Bachillerato “Ciudad de Cuenca”

This research contextualizes the application of Educational Evaluation as a line of scientific research in the Colegio de Bachillerato "Ciudad de Cuenca" based on a case study, with a mixed approach. The findings of the problematization of the research were based on the use of the participatory action research (PAR) method; Information collection was carried out through documentary review and institutional focus groups in the 2017-2018 and 2021-2022 school periods. The results of the Final Report of the Regular General Audit (ARG) have determined a situational status of 61.04% which is equivalent to a yellow alert. There are 33 quality standards that do not meet the educational quality indicators, so the Educational Evaluation was developed on the basis of the complement between a Follow-up Audit process to the General Regular Audit (A-SARG) and the application of the Stufflebeam CIPP evaluation model related to the Manual for the implementation and evaluation of educational quality standards belonging to the Ministry of Education. According to the results, in the School Management component, compliance has been achieved of 9.09%, in Professional Managerial Performance it has been fulfilled 7.69% and in Professional Teaching Performance, the institution has reached 22.22%; the level of student learning has presented an improvement of 1% between the school years 2017-2018 and 2021-2022, consequently, the educational institution obtained a situational status of 47.27% of compliance with the recommendations of the ARG.&nbsp;La presente investigación contextualiza la aplicación de la Evaluación Educativa como línea de la investigación científica en el Colegio de Bachillerato “Ciudad de Cuenca” basado en un estudio de caso, con un enfoque es mixto. Los hallazgos de la problematización de la investigación se basaron en el uso del método investigación acción participativa (IAP); la recolección de información se realizó por medio de revisión documental y grupos focales institucionales en los períodos lectivos 2017-2018 y 2021-2022.&nbsp; Los resultados del Informe Final de Auditoría Regular General (ARG) han determinado un estado situacional del 61,04% el cual equivale a un alerta color amarillo. Existen 33 estándares de calidad que no cumplen los indicadores de calidad educativa, por lo cual la Evaluación Educativa se desarrolló sobre la base del complemento entre un proceso de Auditoría de Seguimiento a la Auditoría Regular General (A-SARG) y la aplicación del modelo de evaluación CIPP de Stufflebeam relacionado con el Manual para la implementación y evaluación de los estándares de calidad educativa perteneciente al Ministerio de Educación. De acuerdo con los resultados, en el componente de Gestión Escolar se ha alcanzado un cumplimiento de un 9,09%, en Desempeño Profesional Directivo se ha cumplido un 7.69% y en Desempeño Profesional Docente, la institución ha alcanzado un 22.22%; el nivel de aprendizaje de los estudiantes ha presentado una mejora del 1% entre los años lectivos 2017-2018 y 2021-2022, en consecuencia, la institución educativa obtuvo un estado situacional de 47.27% del cumplimiento de las recomendaciones de la ARG

Diseño y simulación de un filtro activo para redes eléctricas monofásicas residenciales mediante un controlador P.I.

Ante la expansión de Tecnologías de la Información y Comunicación (TIC) en el siglo XXI, dispositivos como computadoras, teléfonos móviles, convertidores de señal, variadores de velocidad de motores eléctricos entre otros, son parte de cargas de tipo no lineal, han puesto de manifiesto perturbaciones en la onda de corriente eléctrica distorsionándola respecto a la señal a frecuencia fundamental, lo cual ha generado efectos negativos en la vida útil de elementos del circuito eléctrico y consecuentemente reduciendo la calidad de energía eléctrica de la red. El presente trabajo de titulación promueve el aporte a la investigación en el contexto de control de sistemas eléctricos, el diseño y simulación del filtro activo tiene el fin de mitigar distorsiones armónicas de corriente (THDi, por sus siglas en inglés) y compensar potencia reactiva. El controlador es del tipo proporcional integral (PI) y la extracción armónica se realiza en el marco de referencia síncrono (DQ) y las pruebas de dinamismo se basan en simulaciones en diferentes contextos de carga y comparaciones con otras técnicas de control. El objetivo radica que el filtro activo cumpla con las recomendaciones establecidas en el estándar IEEE 519-2014, referente a los rangos máximos admisibles de distorsión total armónica (THD, por sus siglas en inglés) de señales de intensidad de la corriente eléctrica. Para el efecto, el trabajo de titulación se realizó con base en la metodología investigación-acción (IA) con un enfoque es comparativo y su alcance es construccionista. En los 7 escenarios de prueba del filtro activo, frente a diversas cargas no lineales y variación de la distancia entre la red secundaria y el cliente del servicio eléctrico, el filtro activo reduce un 89.92% la THDi en condiciones nominales de carga en el punto de acople común (PCC, por sus siglas en inglés) cuyos valores se encuentran en el rango admisible del estándar IEEE 519- 2014.Faced with the expansion of Information and Communication Technologies in the 21st century, devices such as computers, mobile phones, signal converters, speed variators of electric motors, among others, are part of non-linear loads, they have revealed disturbances in the wave of electric current distorting it with respect to the signal at fundamental frequency, which has generated negative effects on the useful life of elements of the electric circuit and consequently reducing the quality of electric power in the network. The present degree work promotes the contribution to research in the context of control of electrical systems, the design and simulation of the active filter has the purpose of mitigating harmonic current distortions (THDi) and compensating reactive power. The controller is of the proportional-integral (PI) type and the harmonic extraction is carried out in the synchronous reference frame (DQ) and the dynamics tests are based on simulations in different load contexts and comparisons with other control techniques. The objective is that the active filter complies with the recommendations established in the IEEE 519-2014 standard, referring to the maximum admissible ranges of total harmonic distortion (THD) of electrical current intensity signals. For this purpose, the degree work was carried out based on the action research methodology (IA) with a comparative approach and its scope is constructionist. In the 7 test scenarios of the active filter, in the face of various non-linear loads and variation in the distance between the secondary network and the electric service customer, the active filter reduces the THDi by 89.92% under nominal load conditions at the point of Common Coupling (PCC) whose values are within the allowable range of the IEEE 519-2014 standard.Magíster en Electricidad mención Redes Eléctricas InteligentesCuenc

2D pn junctions driven out-of-equilibrium

The pn junction is a fundamental electrical component in modern electronics and optoelectronics. Currently, there is a great deal of interest in the two-dimensional (2D) pn junction. Although many experiments have demonstrated the working principle, there is a lack of fundamental understanding of its basic properties and expected performances, in particular when the device is driven out-of-equilibrium. To fill the current gap in understanding, we investigate the electrostatics and electronic transport of 2D lateral pn junctions. To do so we implement a physics-based simulator that self-consistently solves the 2D Poisson's equation coupled to the drift-diffusion and continuity equations. Notably, the simulator takes into account the strong influence of the out-of-plane electric field through the surrounding dielectric, capturing the weak screening of charge carriers. Supported by simulations, we propose a Shockley-like equation for the ideal current-voltage (J-V) characteristics, in full analogy to the bulk junction after defining an effective depletion layer (EDL). We also discuss the impact of recombination-generation processes inside the EDL, which actually produce a significant deviation with respect to the ideal behavior, consistently with experimental data. Moreover, we analyze the capacitances and conductance of the 2D lateral pn junction. Based on its equivalent circuit we investigate its cut-off frequency targeting RF applications. To gain deeper insight into the role played by material dimensionality, we benchmark the performances of single-layer MoS2 (2D) lateral pn junctions against those of the Si (3D) junction. Finally, a practical discussion on the short length 2D junction case together with the expected impact of interface states has been provided. Given the available list of 2D materials, this work opens the door to a wider exploration of material-dependent performances