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535 results on '"Garzon, Fernando"'

6. Massively enhanced ionic transport in irradiated crystalline pyrochlore

Author

Kreller, Cortney R, Valdez, James A, Holesinger, Terry G, Morgan, Jonathan, Wang, Yongqiang, Tang, Ming, Garzon, Fernando H, Mukundan, Rangachary, Brosha, Eric L, and Uberuaga, Blas P

Subjects
Macromolecular and Materials Chemistry, Materials Engineering, Interdisciplinary Engineering
Abstract

The conductivity of Gd2Ti2O7 with irradiation-induced structural disorder increased with disorder as the material transformed from ordered pyrochlore to defect-fluorite.

Published
2019

36. Additive manufacturing and characterization of AgI and AgI–Al2O3 composite electrolytes for resistive switching devices.

Author

Brownlee, Benjamin J., Tsui, Lok-kun, Vempati, Karthik, Plumley, John B., Iverson, Brian D., Peng, Thomas L., and Garzon, Fernando H.

Subjects
ELECTROLYTES, ELECTRIC conductivity, SUPERIONIC conductors, NEGATIVE electrode, ELECTRICAL resistivity, PLATINUM electrodes, IONIC conductivity
Abstract

This work investigates the electrochemical dynamics and performance of additively manufactured composite electrolytes for resistive switching. Devices are comprised of a Ag/AgI–Al2O3/Pt stack, where the solid state electrolyte is additively manufactured using extrusion techniques. AgI–Al2O3 composite electrolytes are characterized by x-ray diffraction and electrochemical impedance spectroscopy. The ionic conductivities of the electrolytes were measured for different concentrations of Al2O3, observing a maximum conductivity of 4.5 times the conductivity of pure AgI for composites with 20 mol. % Al2O3. There was little change in activation energy with the addition of Al2O3. Setting the Ag layer as the positive electrode and the Pt layer as the negative electrode, a high conductivity state was achieved by applying a voltage to electrochemically establish an electrically conducting Ag filament within the solid state AgI–Al2O3 electrolyte. The low conductivity state was restored by reversing this applied voltage to electrochemically etch the newly grown Ag filament. Pure AgI devices switch between specific electrical resistivity states that are separated by five orders of magnitude in electrical conductivity. Endurance tests find that the AgI resistive switches can transition between a low and high electrical conductivity state over 8500 times. Composite AgI–Al2O3 resistive switches formed initial Ag filaments significantly faster and also demonstrated two orders of magnitude separation in resistivity when cycling for 1600 cycles. [ABSTRACT FROM AUTHOR]

Published
2020
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37. Machine learning prediction of self-diffusion in Lennard-Jones fluids.

Author

Allers, Joshua P., Harvey, Jacob A., Garzon, Fernando H., and Alam, Todd M.

Subjects
FORECASTING, EMPIRICAL research, REGRESSION analysis, FLUIDS, MOLECULAR dynamics
Abstract

Different machine learning (ML) methods were explored for the prediction of self-diffusion in Lennard-Jones (LJ) fluids. Using a database of diffusion constants obtained from the molecular dynamics simulation literature, multiple Random Forest (RF) and Artificial Neural Net (ANN) regression models were developed and characterized. The role and improved performance of feature engineering coupled to the RF model development was also addressed. The performance of these different ML models was evaluated by comparing the prediction error to an existing empirical relationship used to describe LJ fluid diffusion. It was found that the ANN regression models provided superior prediction of diffusion in comparison to the existing empirical relationships. [ABSTRACT FROM AUTHOR]

Published
2020
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38. Bismuth Oxychloride Nanoflakes Enabled High Sensitivity Colorimetric UV Dosimetry.

Author

Troche, Kyle, Ramaiyan, Kannan, Boyle, Timothy J., and Garzon, Fernando H.

Abstract

Excessive exposure to sunlight's ultraviolet (UV) radiation causes adverse effects such as premature aging, sunburn, and skin cancers. Monitoring daily exposure to sunlight is essential to avoid developing health risks. Colorimetric UV sensors change color as a function of UV exposure, provide onsite information about the level of exposure, and can act as a personal wearable device to assist in making informed decisions on sunlight exposure. These sensors utilize radiation-induced reactions on a dye to produce a color change. Here, BiOCl based UV sensor is reported for monitoring UV exposure where a white-to-black color transformation is induced due to the creation of oxygen vacancies in BiOCl. This color transformation is not quantifiable in bulk BiOCl; hence BiOCl was purposely dispersed on filter paper to form petal-like nanostructures that help quantify the color change. Four different dye molecules, 6-carboxyfluorescein, 5-carboxyfluorescein, rhodamine-B, and Prussian blue were evaluated, where 6-carboxyfluorescein gave the best color contrast. The sensor responds to UVA, UVB, and UVC and with proper UV filters can be made selective for specific UV radiations. This unique colorimetric UV sensor can help manage personal UV exposure and reduce the risk of sun exposure ailments. [ABSTRACT FROM AUTHOR]

Published
2023
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41. Landscape disturbances in the Sumapaz páramo area during and after the Colombian armed conflict

Author

Mendez Garzon, Fernando Arturo and Valanszki, Istvan

Abstract

The Sumapaz páramo has been widely studied for its high supply of goods and ecosystem services provided to Bogotá, the central Colombian region and for its role as an ecological network linking the foothills rainforest of the Orinoquia and Amazonas with the montane forest of the Andean highlands. Sumapaz is the largest páramo in the world, with 333.420 ha; it is in Colombia's eastern Andean mountain range between 3,250 to 4,230 m.a.s.l. The landscape comprises a wide range of ecosystems, from the páramo and sub-páramo with montane forests, shrubs forests, and peatlands until the super-páramo of alpine tundra landscape with open vegetation of small bushes, frailejones (Espeletia sp) and grasslands. During the Colombian internal armed conflict and due to the strategic location of Sumapaz, the guerrillas found refuge in páramos and high mountains, generating a series of problems that strongly affected the landscape. They developed activities such as the construction of camps, collection and burning of firewood, deforestation and earthworks to build trenches, roads, guard posts, canalization and damming of water. Currently, the landscape disturbances are primarily due to fires, crops or pastures for livestock. This study presents a qualitative and quantitative assessment linking how disturbance rates are related directly to the conflict intensity data and the geographic location. We identified landscape disturbances, such as degradation and deforestation generated by direct causes such as military confrontations, antipersonnel mines, and trenches, or indirect causes such as crops, mining, livestock, or forced migration. We used Google Engine to perform the Hansen and Coded algorithm to identify these disturbances from 2001 to 2020 using Landsat TM 4-5, Landsat ETM+ 7, and Landsat 8 OLI satellite imagery. We found a noticeable pattern of higher landscape disturbance during the high-intensity conflict period (2001-2012) compared with a decrease in deforestation rates since the peace talks (2012-2016) and post-agreement period (2016-2020). Studies like the ones presented here can become a tool to understand the reasons behind the conflict and its consequences in highly vulnerable landscape networks and ecosystems, such as the páramo.

Published
2022
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