Terahertz and Microwave Detection Using Metallic Single Wall Carbon Nanotubes

Carbon nanotubes (CNTs) are promising nanomaterials for high frequency applications due to their unique physical characteristics. CNTs have a low heat capacity, low intrinsic capacitance, and incredibly fast thermal time constants. They can also exhibit ballistic transport at low bias, for both phonons and electrons, as evident by their fairly long mean free paths. However, despite the great potential they present, the RF behavior of these nanostructures is not completely understood. In order to explore this high frequency regime we studied the microwave (MW) and terahertz (THz) response of individual and bundled single wall nanotube based devices. This thesis is an experimental study which attempts to understand the high frequency characteristics of metallic single walled carbon nanotubes, and to develop an ultra-fast and sensitive direct THz detector. First, the appropriate high frequency detector background is introduced. CNTs previously measured behavior draws similarities to two types of detectors: diode and bolometer. Therefore, our CNT devices are geared towards those designs. Second the fabrication process of devices is reviewed. UV lithography is used to pattern THz coupling log periodic antennas, on top of which CNTs are deposited by using a dielectrophoretic process. Third, the fabricated devices are tested at DC, MW, and THz frequencies. All of these measurements are done as a function of temperature, power, and frequency. Finally, the physical processes that give rise to the diode and bolometric detections at MW and THz detection at different temperatures and under different bias regimes (i.e. low and high) are explained

Level shifts in a panel data based unit root test. An application to the rate of unemployment

Several unit root tests in panel data have recently been proposed. The test developed by Harris and Tzavalis (1999 JoE) performs particularly well when the time dimension is moderate in relation to the cross-section dimension. However, in common with the traditional tests designed for the unidimensional case, it was found to perform poorly when there is a structural break in the time series under the alternative. Here we derive the asymptotic distribution of the test allowing for a shift in the mean, and assess the small sample performance. We apply this new test to show how the hypothesis of (perfect) hysteresis in Spanish unemployment is rejected in favour of the alternative of the natural unemployment rate, when the possibility of a change in the latter is considered.structural breaks, unit roots, panel data, unemployment

Breaking the panels. An application to the GDP per capita

This paper proposes a test statistic for the null hypothesis of panel stationarity that allows for the presence of multiple structural breaks. Two different specications are considered depending on the structural breaks affecting the individual effects and/or the time trend. The model is exible enough to allow the number of breaks and their position to differ across individuals. The test is shown to have an exact limit distribution with a good nite sample performance. Its application to a typical panel data set of real per capita GDP gives support to the trend stationarity of these series.stationarity test, multiple structural changes, gdp per capita, panel data

Level shifts in a panel data based unit root test. An application to the rate of unemployment

Several unit root tests in panel data have recently been proposed. The test developed by Harris and Tzavalis (1999 JoE) performs particularly well when the time dimension is moderate in relation to the cross-section dimension. However, in common with the traditional tests designed for the unidimensional case, it was found to perform poorly when there is a structural break in the time series under the alternative. Here we derive the asymptotic distribution of the test allowing for a shift in the mean, and assess the small sample performance. We apply this new test to show how the hypothesis of (perfect) hysteresis in Spanish unemployment is rejected in favour of the alternative of the natural unemployment rate, when the possibility of a change in the latter is considered.

Reforzamiento de muros de mampostería con mallas poliméricas y electrosoldada para la reducción de la vulnerabilidad sísmica de viviendas informales en el distrito de Ate - Lima, 2022

Este trabajo de investigación fue impulsado por una necesidad en el Perú cuya razón es contribuir a la economía de las personas que edifican sus viviendas con mampostería de ladrillos, por el cual difiere económicamente de un muro de albañilería mixta, el propósito de este estudio es la de mejorar la resistencia de estos muros de mampostería con ayuda del refuerzo de mallas poliméricas para reducir la vulnerabilidad sísmica en este tipo de elemento. Adicionalmente, se evaluó y analizó el refuerzo estructural y la aplicación de la geo malla biaxial, triaxial y malla electro soldada en muros de mampostería, teniendo en cuenta las características del ladrillo según la Norma E.070 “Diseño y Construcción con Albañilería”. Obteniendo datos como, por ejemplo: fuerza de tracción, fuerza de corte y desplazamientos de los muros de ladrillo reforzados. Así mismo, se realizó una comparación entre el método tradicional de mampostería de ladrillos y el muro de ladrillos reforzado con mallas poliméricas y con mallas electro soldada, utilizando el software de estructuras Etabs y los datos obtenidos de la revisión sistemática. Finalmente, los datos obtenidos fueron analizados con los ensayos a compresión axial en pilas de ladrillos. El objetivo general de la misma es determinar la influencia mecánica del reforzamiento estructural y la aplicación de las mallas poliméricas biaxial, triaxial y malla electrosoldada en el comportamiento estructural de los muros de ladrillo para reducir la vulnerabilidad sísmica de viviendas informales con costos beneficiosos, por lo tanto, como conclusiones después de usar el software de estructuras Etabs, se ha tenido los datos de la comparación entre ambas edificaciones, la malla electrosoldada confiere grandes ventajas a las propiedades del muro de mampostería de ladrillo con respecto a la reducción de vulnerabilidad sísmica de viviendas informales en el año 2021.This research work was driven by a need in Peru whose reason is to contribute to the economy of the people who build their homes with brick masonry, for which it differs economically from a mixed masonry wall, the purpose of this study is to to improve the resistance of these masonry walls with the help of the reinforcement of polymeric meshes to reduce the seismic vulnerability in this type of element. Additionally, the structural reinforcement and the application of biaxial, triaxial and electro-welded mesh in masonry walls were evaluated and analyzed, taking into account the characteristics of the brick according to Standard E.070 “Design and Construction with Masonry”. Obtaining data such as, for example: traction force, shear force and displacements of the reinforced brick walls. Likewise, a comparison was made between the traditional brick masonry method and the brick wall reinforced with polymeric meshes and electro-welded meshes, using the Etabs structure software and the data obtained from the systematic review. Finally, the data obtained were analyzed with axial compression tests in brick piles. The general objective of the same is to determine the mechanical influence of structural reinforcement and the application of biaxial, triaxial polymeric meshes and electro-welded mesh in the structural behavior of brick walls to reduce the seismic vulnerability of informal homes with beneficial costs, for Therefore, as conclusions after using the Etabs structure software, the data of the comparison between both buildings has been obtained, the electro-welded mesh confers great advantages to the properties of the brick masonry wall with respect to the reduction of seismic vulnerability informal housing in 2021

Hysteresis-Free Nanosecond Pulsed Electrical Characterization of Top-Gated Graphene Transistors

We measure top-gated graphene field effect transistors (GFETs) with nanosecond-range pulsed gate and drain voltages. Due to high-k dielectric or graphene imperfections, the drain current decreases ~10% over time scales of ~10 us, consistent with charge trapping mechanisms. Pulsed operation leads to hysteresis-free I-V characteristics, which are studied with pulses as short as 75 ns and 150 ns at the drain and gate, respectively. The pulsed operation enables reliable extraction of GFET intrinsic transconductance and mobility values independent of sweep direction, which are up to a factor of two higher than those obtained from simple DC characterization. We also observe drain-bias-induced charge trapping effects at lateral fields greater than 0.1 V/um. In addition, using modeling and capacitance-voltage measurements we extract charge trap densities up to 10^12 1/cm^2 in the top gate dielectric (here Al2O3). Our study illustrates important time- and field-dependent imperfections of top-gated GFETs with high-k dielectrics, which must be carefully considered for future developments of this technologyComment: to appear in IEEE Transactions on Electron Devices (2014

Deviations of cup anemometer rotational speed measurements due to steady state harmonic accelerations of the rotor

The measurement deviations of cup anemometers are studied by analyzing the rotational speed of the rotor at steady state (constant wind speed). The differences of the measured rotational speed with respect to the averaged one based on complete turns of the rotor are produced by the harmonic terms of the rotational speed. Cup anemometer sampling periods include a certain number of complete turns of the rotor, plus one incomplete turn, the residuals from the harmonic terms integration within that incomplete turn (as part of the averaging process) being responsible for the mentioned deviations. The errors on the rotational speed due to the harmonic terms are studied analytically and then experimentally, with data from more than 500 calibrations performed on commercial anemometers

Anomaly detection on cup anemometers

The performances of two rotor-damaged commercial anemometers (Vector Instruments A100 LK) were studied. The calibration results (i.e. the transfer function) were very linear, the aerodynamic behavior being more efficient than the one shown by both anemometers equipped with undamaged rotors. No detection of the anomaly (the rotors'damage) was possible based on the calibration results. However, the Fourier analysis clearly revealed this anomaly

On the cup anemometer working condition monitoring

The analysis of the harmonic terms related to the rotational speed of a cup anemometer is a way to detect anomalies such as wear and tear, rotor non-symmetries (rotor damage) or problems at the output signal system. The research already done in this matter at the IDR/UPM Institute is now taken to cup anemometers working on the field. A 1-2 year testing campaign is being carried out in collaboration with Kintech Engineering. 2 Thies First Class Advanced installed at 58 m and 73 m height in a meteorology tower are constantly monitored. The results will be correlated to the anemometer performance evolution studied through several calibrations planned to be performed along the testing campaign