Thermal Transport in Layer-by-Layer Assembled Polycrystalline Graphene Films

New technologies are emerging which allow us to manipulate and assemble 2-dimensional (2D) building blocks, such as graphene, into synthetic van der Waals (vdW) solids. Assembly of such vdW solids has enabled novel electronic devices and could lead to control over anisotropic thermal properties through tuning of inter-layer coupling and phonon scattering. Here we report the systematic control of heat flow in graphene-based vdW solids assembled in a layer-by-layer (LBL) fashion. In-plane thermal measurements (between 100 K and 400 K) reveal substrate and grain boundary scattering limit thermal transport in vdW solids composed of one to four transferred layers of graphene grown by chemical vapor deposition (CVD). Such films have room temperature in-plane thermal conductivity of ~400Wm−1 K−1. Cross-plane thermal conductance approaches 15MWm−2 K−1 for graphene-based vdW solids composed of seven layers of graphene films grown by CVD, likely limited by rotational mismatch between layers and trapped particulates remnant from graphene transfer processes. Our results provide fundamental insight into the in-plane and cross-plane heat carrying properties of substrate-supported synthetic vdW solids, with important implications for emerging devices made from artificially stacked 2D materials

Experimental test for interpreting the increase in sensibility of doped CR-39

In recent years the sensibility of CR-39 to nuclear tracks has been increased by doping the corresponding monomer with dioctyl phtalate. At this regard, two theoretical approaches are current managed to explain this phenomenon: either the doping react with the active radicals in the chain blocking them, stopping crosslinking between chains, or alternatively that the doping gets between them giving wider space between the crosslinkined chains

Coenzyme q10 microparticles formation with supercritical carbon dioxide

Coenzyme Q10 is a powerful antioxidant used on cardiovascular, neurodegenerative and cancer diseases. Its hydrophobic nature do limit its applications, because human body absorbs it with dfculty, that is why it was proposed to increase its bioavailability by diminishing the particle size using supercritical carbon dioxide. It was determined experimentally the phase behavior of the coenzyme in a supercritical system. The equilibrium data and a factorial 2k experimental design were utilized to find how the shape and size of the microparticles are affected by temperature, coQ10 concentration and nozzle diameter. Microparticles were characterized using infrared spectrometry and chromatography. For verify the fundamental chemical structure, the size and the shape of the microparticles was used scanning electronic microscopy. It was found a significant decrease in particle size and a modification of physical structure. The antioxidant power of coQ10 after micronization was measured, showing an increase of this property. Finally, in order to evaluate the bioavailability, the kinetic of solubility was determined in ethanol, having a substantial increase on solubilization speed of micronized coQ10 compared with the commercial one

Clamp Fixture for Computer Navigated Total Hip Arthroplasty

During total hip arthroplasty, surgeons insert a prosthetic femur head onto the femur bone, as well as inserting a prosthetic acetabular cup so both prosthetic components can cope with one other. Surgeons also insert pins onto the hip and femur bones to track the movement of those bones via infrared arrays, using computer navigated software, in order to mitigate surgical error. In the US there is more than 310,000 total hip replacement surgeries conducted per year, most of which are over the age of 45. Hip replacement surgery is needed for individuals who have osteoarthritis, avascular necrosis, and/or trauma. The average stay after total hip replacement for patients aged 45 and over is 4 days. The average cost of the surgery is about $31,000. Decreasing recovery time in the hospital by just one day can decrease the cost between 10-20%. The greatest risks of this procedure would be misalignment of the hip bones or impairment of the femur bones. The objective is to design a surgical clamp fixture which will replace the current pins being used. Instead of penetrating a hole of 10 mm in diameter onto the hip, the design will clamp onto the iliac crest horizontally, along with the attached infrared arrays and provide proper fixation with no more than 0.5 mm of deviation from the clamping axis. By performing specific testing protocols the resulting outcome will be more beneficial than the current pins. The clamp fixture will be applied to synthetic material and then subjected to surgical forces, including application of excess forces along all axis’, torsional forces and rotational forces to ensure stability and rigidity. The surgical clamp will be used to improve the clinical outcomes of the procedure by introducing a less invasive attachment for the infrared detection without compromising the current rigidity and effectiveness

Recorrido de la madera como material sostenible del proyecto: sabemos dónde va, pero no de dónde viene

Hablar de un proyecto en madera tiene como base realizar una pausa, una mirada en todo lo que ello conlleva. El bosque, el transporte y el proceso industrial. Visibilizar el proceso de un material sostenible y natural por si mimo, radica en observar si somos capaces, como proyectistas, de mantener esa sostenibilidad y cuidado del medioambiente. De esta misma forma, ver si somos capaces de utilizar las diferentes innovaciones tecnológicas de las que disponemos para la renovación de la materia prima, pudiendo crear así un proceso cerrado e infinito en su utilización. Devolver a la madera aquello que nos proporciona, un equilibro medioambiental y una construcción sostenible

Mining in Mexico: forms of accumulation and environmental effects

A la acumulación originaria fue la primera negación de la propiedad individual basada en el trabajo, dando paso a la propiedad privada de los medios de producción y la posibilidad de apropiarse del trabajo de los campesinos que fueron despojados de sus bienes. A partir de la disolución de la propiedad colectiva de la tierra, y de otros bienes comunes.La actividad minera en México ha sido muy importante, por el valor de los recursos minerales. Se emplean formas de acumulación que se han instrumentado para la generación de riqueza a costa de la segregación como efecto ambiental. Este artículo aborda los modelos de acumulación para poder comprender cómo se maneja la actividad minera en México, implementando un modelo extractivo exportador que admite la imposición de una lógica de saqueo, contaminación y recolonización sobre los recursos naturales y las formas de vida. En los estudios de minería, la acumulación de capital es respaldado por estrategias como el despojo que permiten la implementación de diferentes procesos de extracción, lo que ha provocado a lo largo de la historia efectos ambientales. Esta última etapa denominada por desposesión, abordada por David Harvey, genera efectos sociales. El objetivo es abordar los modelos de acumulación, las características, los mecanismos de despojo, las leyes y los reglamentos que facilitan la inversión minera en el país. La metodología empleada para esta investigación es a través del materialismo histórico donde algunas de las categorías teóricas centrales son las relaciones y fuerzas de producción, la explotación y la lucha de clases que trae como resultado una forma de vida.Universidad autónoma del Estado de México Consejo Nacional de Ciencia y Tecnología (Beca Nacional

Experimental Two-Phase Flow Characterization of Subcooled Boiling in a Rectangular Channel

On the efforts to provide a reliable source of experimental information on turbulent subcooled boiling ow, time resolved Particle Tracking Velocimetry (PTV) experiments were carried out using HFE-301 refrigerant ow through a vertical rectangular channel with one heated wall. Measurements were performed at liquid Reynolds numbers of 3309, 9929 and 16549 over a wall heat flux range of 0.0 to 64.0 kW=m2. From the PTV measurements, liquid two dimensional turbulence statistics are available, such as: instantaneous 2-D velocity fields, time-averaged axial and normal velocities, axial and normal turbulence intensities, and Reynolds stresses. The present results agree with previous works and provide new information due to the 2-D nature of the technique, for instance, this work shows that by increasing heat ux, the boiling bubbles influence on the liquid phase is portrayed as a persistent increase of axial velocity on regions close to the heater wall. This persistent increase on the axial velocity reaches a maximum value attributed to the terminal bubble velocity. These new observed phenomena must be considered for the development and improvement of two-phase ow turbulence models. To this end, an extensive error analysis was also performed with emphasis on the applicability of the PTV measurement technique on optically inhomogeneous flows. The error quantification exhibited negligible optically induced errors for the current conditions, making the data acquired in this work a vast and reliable source

Implicancia del pensamiento crítico en la comprensión lectora en estudiantes en una institución educativa pública, Abancay 2022

El problema que ha motivado se realice la investigación fue el bajo nivel presentado por los estudiantes en la comprensión lectora por lo que se ha implementado un plan de intervención orientado al desarrollo del pensamiento crítico con el propósito de mejorar esta capacidad. El diseño utilizado ha sido el cuasi experimental con grupo control y experimental con pre y pos prueba. La muestra de estudio lo conformaron 29 alumnos matriculados en el VI ciclo (grupo experimental) y 27 alumnos matriculados en el VII ciclo (grupo control). El recojo de la información ha sido posible a través de la aplicación de una prueba de desempeño que ha medida el nivel literal, inferencial y crítico de la comprensión lectora, la misma que fue administrada antes y después de la intervención. El procesamiento de la información demandó la elaboración de tablas y figuras estadísticas y para los resultados inferenciales se ha calculado los Rangos de Wilcoxon (para muestras relacionadas) y la de Mann Whitney (para muestras independientes). Las conclusiones registran que el pensamiento crítico influye significativamente sobre el desarrollo de la comprensión lectora (W+=-4,771; U+=236,500; p_valor=0,00; α=0,05

Multi-Scale Experiments in Turbulent Subcooled Boiling Flow Through a Square Channel with a Single Heated Wall

In this work, visualization experimental techniques that provide whole-field and multi-scale measurements of the liquid turbulence parameters, liquid and heater wall temperatures, and gas phase local parameters, were used to study subcooled boiling flow through a square channel. The explored visualization techniques were: 1) Particle tracking velocimetry (PTV), which provides velocity measurements of the liquid phase, 2) High-speed shadowgraphy (HSS) which is used to study the dispersed phase dynamics. 3) Laser induced fluorescence thermometry (LIF) to measure whole-field liquid temperature fields. 4) High-speed infrared thermometry (IR-T), to study the impact of the boiling level on the heated wall temperature. A series of sensitivity studies were performed with which, knowledge for the optimal implementation of each technique was gained. Identification and quantification of uncertainties allowed to optimize the experimental conditions to achieve reliable and accurate liquid velocity measurements with the PTV technique. New procedures were designed to measure the average bubble velocity, bubble size, and void fractions. The single-nucleation site experiments provided optimal characteristics for the study of the bubble and liquid dynamics by means of PTV-shadowgraphy technique. This experiment simplified the quantification of the relationship that exist between the vapor and liquid parameters. From these results, new relationships and correlations are proposed to describe the near-wall liquid velocity behavior depending on local two-phase flow parameters. For the LIF thermometry, sensitivity studies were performed to evaluate the effects of excitation wavelength, dyes concentration ratios, solution pH, and selected emission bands on the temperature sensitivity of the two-color two-dye LIF thermometry technique. Temperature sensitivities of about 4% per °C were obtained, which is better than the traditionally used RhB-Rh60 solution which provides sensitivities of about 2% per °C. The present study is intended to lay down the experimental and data analysis foundations required to improve the understanding of subcooled flow boiling. This study also provides reliable and accurate experimental information for development and validation of two-phase flow computational models

Analysis, comparison and modification of various Particle Image Velocimetry (PIV) algorithms

A program based on particle tracking velocimetry (PTV) was developed in this work. The program was successfully validated by means of artificial images where parameters such as radius, concentration, and noise were varied in order to test their influence on the results. This program uses the mask cross correlation technique for particle centroid location. The sub-pixel accuracy is achieved using two different methods, the three point Gaussian interpolation method and the center of gravity method. The second method is only used if the first method fails. The object matching algorithm between frames uses cross correlation with a non binarized image. A performance comparison between different particle image velocimetry (PIV) and PTV algorithms was done using the international standard PIV challenge artificial images. The best performance was obtained by the program developed in this work. It showed the best accuracy, and the best spatial resolution by finding the larger number of correct vectors of all algorithm tested. A procedure is proposed to obtain error estimates for real images based on errors calculated with experimental ones. Using this procedure a real PIV image with 20% noise has an estimated average error of 0.1 pixel. Results of the analysis of 200 experimental images are shown for the two best PTV algorithms