Fabrication of complex ceramic parts with sacrificial material using freeze-form extrusion fabrication

An additive manufacturing process called Freeze-form Extrusion Fabrication (FEF) was developed in this study to fabricate complex ceramic parts that require the use of sacrificial materials. The aqueous paste of alumina (Al₂O₃) was used as the main material, with solids loadings as high as 50 vol. % and water as the main liquid medium. Methyl cellulose, with a 10 vol. % solids loading and 90 vol. % water content, was used as the sacrificial material. The freeze-form extrusion machine has multiple extruders (extrusion devices) capable of fabricating parts from multiple materials without mixing them. The dynamic process of extruding alumina and methyl cellulose was characterized using an empirical first-order model with the ram velocity as the input and the extrusion force as the output for alumina and methyl cellulose pastes. After modeling the dynamics of extruding alumina and methyl cellulose pastes, a General Tracking Controller (GTC) was applied in order to achieve a consistent paste deposition with a constant extrusion rate for extrusion of both the part and sacrificial materials. This controller also performs Extrusion on Demand (EOD), which starts and stops the paste extrusion on demand and facilitates the switching process between different materials while fabricating complex parts. Freeze-drying was used to remove the water content after building parts from alumina and methyl cellulose pastes. Finally, the parts were debinded to burn out the methyl cellulose binder and sintered to densify the ceramic part --Abstract, page iii

Geometrical constraints on dark energy models

This contribution intends to give a pedagogical introduction to the topic of dark energy (the mysterious agent supposed to drive the observed late time acceleration of the Universe) and to various observational tests which require only assumptions on the geometry of the Universe. Those tests are the supernovae luminosity, the CMB shift, the direct Hubble data, and the baryon acoustic oscillations test. An historical overview of Cosmology is followed by some generalities on FRW spacetimes (the best large-scale description of the Universe), and then the test themselves are discussed. A convenient section on statistical inference is included as well.Comment: 28 pages, 15 pages, lecture notes prepared for the ``Advanced Summer School in Physics 2007" organized by Cinvestav (Mexico DF

Toward large-scale access-transistor-free memristive crossbars

Abstract — Memristive crossbars have been shown to be excel-lent candidates for building an ultra-dense memory system be-cause a per-cell access-transistor may no longer be necessary. However, the elimination of the access-transistor introduces sev-eral parasitic effects due to the existence of partially-selected de-vices during memory accesses, which could limit the scalability of access-transistor-free (ATF) memristive crossbars. In this paper we discuss these challenges in detail and describe some solutions addressing these challenges at multiple levels of design abstrac-tion. I

Monitoreo y control del proceso de germinación de plantones usando patrones de reconocimiento de imagen

Las empresas dedicadas a la germinación de plantones en la región Lambayeque-Perú, realizan el monitoreo y control de la germinación de plantones de forma manual, generando un retraso en la información, así como también cansancio visual a las personas que realizan este proceso durante tres días consecutivos, analizando cada bandeja de 200 plantas en filas de 200 bandejas ubicadas en sectores de 20 filas. El presente proyecto pretende disminuir los tiempos de control y monitorio manual en el proceso de germinación de plantones por medio del reconocimiento de imágenes capturadas por una cámara digital, que permite reconocer si en una celda de una bandeja, una semilla ha germinado. Un plantón es el producto de una siembra especial realizada en viveros bajo el cuidado y manejo de ingenieros especialistas que controlan su correcto crecimiento y nutrición. Los cuidados que se le brindan al plantón, permiten obtener características sobresalientes como precocidad, uniformidad de crecimiento, vigor de tallos y raíces, excelente sanidad y una aclimatación especial que reduce el estrés propio del cambio de ambiente, cuando la plántula es trasplantada a campo definitivo

A Primer on Resonances in Quantum Mechanics

After a pedagogical introduction to the concept of resonance in classical and quantum mechanics, some interesting applications are discussed. The subject includes resonances occurring as one of the effects of radiative reaction, the resonances involved in the refraction of electromagnetic waves by a medium with a complex refractive index, and quantum decaying systems described in terms of resonant states of the energy. Some useful mathematical approaches like the Fourier transform, the complex scaling method and the Darboux transformation are also reviewed.Comment: 28 pages, 9 figures, lectures presented at the Advanced Summer School in Physics 2008, Cinvestav, Mexic

Sentido y significado en las ocupaciones de las mujeres: una experiencia desde el municipio de Inzá, Cauca

Las transformaciones asumidas por la mujer, le han permitido trascender en distintas ocupaciones y suplir sus necesidades a partir del contexto histórico-cultural en el que participa. El objetivo de la investigación fue identificar el Sentido y el Significado que tienen las ocupaciones para las mujeres del municipio de Inzá, Cauca. Para ello se usó la metodología de Investigación Acción Participativa como alternativa que favorece la construcción colectiva de conocimiento. El proceso permitió encontrar conclusiones alrededor de la dinámica necesaria entre los determinantes y los componentes planteados. A partir de esto se dan recomendaciones encaminadas al conocimiento de diversos usos del tiempo libre. Se rescata la participación como ocupación importante para las mujeres, ya que genera sentido de pertenencia y autovaloración, convirtiéndose en un escenario que favorece la re-significación de la vida

Coherent psi (2S) photo-production in ultra-peripheral Pb-Pb collisions at root s(NN)=2.76TeV

We have performed the first measurement of the coherent psi(2S) photo-production cross section in ultraperipheral Pb-Pb collisions at the LHC. This charmonium excited state is reconstructed via the psi(2S) -> l(+)l(-) and ->(2S) -> J/psi pi(+)pi(-) decays, where the J/psi decays into two leptons. The analysis is based on an event sample corresponding to an integrated luminosity of about 22 mu b(-1). The cross section for coherent psi(2S) production in the rapidity interval -0.9 <y <0.9is d sigma(coh)(psi(2S))/dy = 0.83 +/- 0.19 (stat+syst) mb. The psi(2S) to J/psi coherent cross section ratio is 0.34(-0.07)(+0.08)(stat+syst). The obtained results are compared to predictions from theoretical models. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V.Peer reviewe