Transmission electron microscopy characterization of microstructural features of Al-Li-Cu alloys

A transmission electron microscopy (TEM) examination of aluminum-lithium-copper alloys was conducted. The principal purpose is to characterize the nature, size, and distribution of stringer particles which result from the powder metallurgy (P/M) processing of these alloys. Microstructural features associated with the stringer particles are reported that help explain the stress corrosion susceptibility of the powder metallurgy-processed Al-Li-Cu alloys. In addition, matrix precipitation events are documented for a variety of heat treatments and process variations. Hot rolling is observed to significant alter the nature of matrix precipitation, and the observations are correlated with concomitant mechanical property variations

Mesoscopic non-equilibrium thermodynamics approach to the dynamics of polymers

We present a general formalism able to derive the kinetic equations of polymer dynamics. It is based on the application of nonequilibrium thermodynamics to analyze the irreversible processes taking place in the conformational space of the macromolecules. The Smoluchowski equation results from the analysis of the underlying diffusion process in that space within the scheme of nonequilibrium thermodynamics. We apply the method to different situations, concerning flexible, semiflexible and rod-like polymers and to the case of more concentrated solutions in which interactions become important.Comment: 13 pages (RevTex). To be published in Physica

Design of bias circuit for charge pump in 130nm BiCMOS technology

El presente trabajo muestra el diseño de un circuito de polarización en la tecnología de 130nm BiCMOS con las herramientas de diseño de Cadence. El circuito de polarización es parte de un circuito Charge Pump (CP), el cual a su vez es parte de un circuito PLL (Phased Locked Loop) que se utilizará en una implementación de señal mixta de un Recuperador de Datos (CDR). Al inicio del trabajo se presenta una descripción general de los módulos analógicos y digitales que conforman el proyecto. La topología de diseño propuesta refleja la enorme dependencia del circuito de polarización con el circuito CP. Un circuito replica permite “seguir” las variaciones de carga y descarga de corriente del circuito CP para compensar mediante un OTA (Operational Transconductance Amplifier) el nivel de voltaje requerido en los transistores del circuito diferencial del CP. El proceso de diseño, la generación de esquemáticos y bancos de pruebas son mostrados durante los primeros capítulos del trabajo. La verificación del diseño pre-layout a través del proceso de esquinas, así como el uso el uso de las herramientas de verificación de reglas de diseño post-layout son mostradas durante los capítulos finales.The present work shows the design of a Bias circuit in 130 nm of BiCMOS process using Cadence tools. The Bias circuit is part of a Charge Pump (CP) circuit, which in turn is one block of a PLL (Phased Locked Loop) that will be used in a mixed-signal implementation of a Clock and Data Recovery (CDR) circuit. This PLL-based CDR is the project of the generation 2018 of the Specialty in System on a Chip at ITESO. A general description of the analog and digital modules that make up this project is shown at the beginning of this work. As it is described in detail in this work, the proposed design topology reveals the enormous dependence of the polarization circuit to the CP circuit. The replica method used in the Bias circuit allows to "follow" the current variations of CP charge/discharge process to compensate through an OTA (Operational Transconductance Amplifier) the level of voltage required by the tail transistors of CP circuit. The design procedure, the generation of schematics and test benches are shown during the first chapters of this work. The verification of the pre-layout design through the corners process, as well as the use of the post-layout design rules verification tools, are shown during the final chapters of this work.Consejo Nacional de Ciencia y Tecnologí

Realisation of Bullard's disc dynamo

We report experimental results from three successful runs of a Bullard-type homopolar disc dynamo. The set-up consisted of a copper disc with a radius of 30 cm and thickness of 3 cm which was placed co-axially beneath a flat, multi-arm spiral coil of the same size and connected to it electrically at the centre and along the circumference by sliding liquid-metal contacts. The magnetic field was measured using Hall probes which were fixed on the top face of the coil. We measured also the radial voltage drop across the coil. When the disc rotation rate reached $\Omega\approx 7$ Hz, the magnetic field increased steeply approaching $B_{0}\approx 40$ mT in the central part of the coil. This field was more than two orders of magnitude stronger than the background magnetic field. In the first two runs, the electromagnetic torque braking the disc in the dynamo regime exceeded the breakdown torque of the electric motor driving the disc. As a result, the motor stalled and the dynamo was interrupted. Stalling did not occur in the third run when the driving frequency was set higher and increased faster. We also propose an extended disc dynamo model which qualitatively reproduces the experimental results.Comment: 21 page, 11 figure

Inteligencia competitiva y definición de una estrategia para la comercialización del cacao de la variedad arriba

Esta tesis está basada en el diseño de una estrategia de comercialización del cacao variedad "arriba o nacional", el cual es identificado como un cacao fino y de aroma. En este estudio, hacemos un análisis de la oferta de cacao fino y de aroma descubriendo a Indonesia y Ecuador como uno de los mayores productores de cacao fino y de aroma. También hemos estudiado la demanda, que está compuesta por algunos países especialmente europeos, ya que éstos son los mayores productores de chocolate fino del mundo. Así hemos identificado el mercado al cual nos dirigimos a través del análisis de la demanda mundial. El Ecuador se encuentra ante una serie de ventajas agroclimáticas, de trayectoria y, de posicionamiento muy buenas que permitirían al país incrementar los niveles de exportaciones de este tipo de cacao. Así mismo, se encuentra ante una serie de desventajas culturales, tecnológicas y de infraestructura que no permiten desarrollar el sector cacaotero interno lo cual se convierte en una amenaza que nos perjudicaría en el comercio internacional del cacao Dadas estas condiciones, se propone una estrategia formada de tres fases, la primera, es la renovación de un cuarto de las plantaciones actuales. La segunda fase, está dirigida a los compradores del cacao fino y de aroma y la tercera está dirigida al consumidor de chocolate que será quien exija cacao del Ecuador para el chocolate que consuma

Uv-visible characterization of gold exchanged in beta zeolite

info:eu-repo/semantics/publishe

Aprendizaje basado en problemas en Biología Vegetal

El aprendizaje basado en problemas (ABP) es un método de enseñanzaaprendizaje que usa el problema como punto de partida para la adquisición e integración de nuevos conocimientos. En el desarrollo del ABP el problema es el camino para que los estudiantes alcancen los objetivos de conocimientos, destrezas y habilidades. El ABP y el estudio de casos se centran en el estudiante lo cual implica necesariamente un cambio de función en el profesor que deja de ser protagonista para convertirse en una guía o en tutor. El tutor plantea problemas y cuestiones que contribuyen al entendimiento y a la resolución de problemas promoviendo de esta forma un aprendizaje significativo. Por otra parte, las nuevas tecnologías de la información y la comunicación introducen cambios importantes en el proceso de enseñanza-aprendizaje en base a lo siguiente: a) el acceso a la información y el modo de adquirir información, b) las nuevas formas de relación profesor-alumno. Este trabajo muestra algunas experiencias para el desarrollo de ABP, el estudio de casos y la elaboración de mapas conceptuales e infografías, experiencias realizadas en el aula con estudiantes de Biología de la Universidad Complutense de Madrid y en relación con dos campos de la Biología: la Fisiología Vegetal y la Biología Evolutiva.The problem-based learning (PBL) is a teaching-learning method that uses the problem as a starting point for the acquisition and integration of new knowledge. In the development of PBL the problem is the way to achieve the knowledge, skills and abilities. Problem-based learning and case study focuses on the student and therefore imply a change in the teacher role: from protagonist to tutor or guide. A tutor offers questions that contribute to understanding and managing the problem promoting meaningful learning. On the other hand, information and communication technologies introduces important changes in teaching and learning on the basis of two issues: a) access and how to acquire information, b) new forms of teacher-student relationship. This work shows some experiences for the development of PBL, case studies and concept mapping as classroom experiences for Biological Sciences students at the Complutense University of Madrid. Two biological sciences fields were considered: plant physiology and evolutionary plant biology

A homopolar disc dynamo experiment with liquid metal contacts

We present experimental results of a homopolar disc dynamo constructed at CICATA-Quer\'etaro in Mexico. The device consists of a flat, multi-arm spiral coil which is placed above a fast-spinning metal disc and connected to the latter by sliding liquid-metal electrical contacts. Theoretically, self-excitation of the magnetic field is expected at the critical magnetic Reynolds number Rm~45, which corresponds to a critical rotation rate of about 10 Hz. We measured the magnetic field above the disc and the voltage drop on the coil for the rotation rate up to 14 Hz, at which the liquid metal started to leak from the outer sliding contact. Instead of the steady magnetic field predicted by the theory we detected a strongly fluctuating magnetic field with a strength comparable to that of Earth's magnetic field which was accompanied by similar voltage fluctuations in the coil. These fluctuations seem to be caused by the intermittent electrical contact through the liquid metal. The experimental results suggest that the dynamo with the actual electrical resistance of liquid metal contacts could be excited at the rotation rate of around 21 Hz provided that the leakage of liquid metal is prevented.Comment: 6 pages, 5 figures (to appear in Magnetohydrodynamics

ESCUELA DE PRODUCCIÓN ORGÁNICA DE CACAO CRIOLLO (Theobroma cacao L. var. Carmelo), EN TABASCO, MÉXICO

With the objective of innovating and evaluating qualitatively and quantitatively the production of Creole cacao (Theobroma cacao L.) with organic management, a school was established in 2006 at the El Carmelo ranch, Ranchería Río Seco, Cunduacan Tabasco, México, in order to train in an organic management plan, taking into consideration: local inputs and technology; innovation in the management of Creole cacao Carmelo variety; use of nitrogen-fixing species for shade; plant coverage for soil fertilizing; planting timber-yielding trees on the perimeters; manual weed control; use of compost and vermicompost; leaf fertilization with earthworm leaching; moderate use of Bordeaux mixture to control bud-rot (Phytophthora palmivora) and moniliasis (Moniliophthora roreri). Out of eight years of yield records, it was calculated that by year ten (2017) the yield will be 1.3 t ha-1. From year seven to eight, the yield varied from 0.923 t ha-1 to 1 t ha-1, resulting in a higher yield compared to traditional cacao. Concerning the value of the sale, the price was $11 USD per kg, while that of organic origin ranged between$2 and $3 USD kg of dry cacao.Con el objetivo de innovar y evaluar cualitativamente y cuantitativamente la producción de cacao criollo (Theobroma cacao L.) con manejo orgánico, se estableció en el 2006, una escuela en el rancho el Carmelo, Ranchería Río Seco, Cunduacan Tabasco, México, para capacitar en un plan de manejo orgánico, considerando: insumos y tecnología local: innovación del manejo del cacao criollo variedad Carmelo, empleo de especies fijadoras de nitrógeno para sombra, coberteras vegetales para abonado del suelo, siembra de árboles maderables en perímetros, control manual de malezas, empleo de composta y vermicomposta; fertilización foliar con lixiviado de lombrices, uso moderado de caldo bordelés para control de mancha negra (Phytophthora palmivora) y moniliasis (Moniliophthora roreri). Durante ocho años de registro de rendimientos, se calculó que para el año diez (2017) el rendimiento será de 1.3 t ha-1. Del año siete al ocho, el rendimiento varió de 0.923 t ha-1 a 1 t ha-1, resultando superior en el rendimiento respecto al cacao tradicional. Respecto al valor de venta, el precio fue de$11 USD por kg, mientras que el de origen orgánico oscilo entre $2 y$3 USD kg de cacao seco

Histogram Reweighting Method for Dynamic Properties

The histogram reweighting technique, widely used to analyze Monte Carlo data, is shown to be applicable to dynamic properties obtained from Molecular Dynamics simulations. The theory presented here is based on the fact that the correlation functions in systems in thermodynamic equilibrium are averages over initial conditions of functions of the trajectory of the system in phase-space, the latter depending on the volume, the total number of particles and the classical Hamiltonian. Thus, the well-known histogram reweighting method can almost straightforwardly be applied to reconstruct the probability distribution of initial states at different thermodynamic conditions, without extra computational effort. Correlation functions and transport coefficients are obtained with this method from few simulation data sets.Comment: 4 pages, 3 figure