Browsing by Author "Aguilar, Claudio "
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- ItemA SIMULATION MODEL OF MESOPHYTIC PERENNIAL GRASSLANDS(INST INVESTIGACIONES AGROPECUARIAS, 2012) Castellaro, Giorgio; Aguilar, Claudio; Vera, Raul; Morales, LuisGrasslands are complex ecosystems and their processes are affected by soil, meteorological, and management variables. In this context, dynamic simulation models are useful to understand these processes and to design grassland use strategies. The aim of this study was to develop and validate a simulation model of perennial pasture growth based on soil and climate variables. A first approach considered that soil fertility levels were adequate; therefore, soil water availability and phytomass level were the main variables affecting pasture growth. The subroutines considered were water balance, pasture growth, and root biomass dynamics. The hypotheses regarding the functioning of the system were formulated as a group of equations which were solved numerically with a program written in Visual Basic (R). Model validation was performed by statistical comparison between simulated DM and DM obtained from experiments conducted in Valdivia (39 degrees 47' S., 73 degrees 15' W; 9 m a.s.l.). In these experiments we measured DM accumulation on naturalized grassland and ryegrass (Lolium perenne L.)-white clover (Trifolium repens L.) pastures under frequent defoliation. Soil data, temperature, solar radiation, and rainfall were obtained from a meteorological station located in Valdivia. The coefficient of determination between simulated values and those measured in the experiments were higher in the DM accumulation (R-2 = 98%) simulations. When pasture was subjected to frequent defoliation, the degree of fit of the model was lower (R-2 = 60%); however, the model was able to predict the trend in the data.
- ItemA Tribological and Ion Released Research of Ti-Materials for Medical Devices(2021) Silva, Daniela ; Montero, M. Cecilia ; Guerra, Carolina ; Martinez Ugalde, Carola ; Li, Xuejie ; Ringuedé, Armelle ; Cassir, Michel ; Ogle, Kevin ; Guzman, Danny ; Aguilar, Claudio ; Paez, Maritza ; Sancy, MamiéThe increase in longevity worldwide has intensified the use of different types of prostheses for the human body, such as those used in dental work as well as in hip and knee replacements. Currently, Ti-6Al-4V is widely used as a joint implant due to its good mechanical properties and durability. However, studies have revealed that this alloy can release metal ions or particles harmful to human health. The mechanisms are not well understood yet and may involve wear and/or corrosion. Therefore, in this work, commercial pure titanium and a Ti-6Al-4V alloy were investigated before and after being exposed to a simulated biological fluid through tribological tests, surface analysis, and ionic dissolution characterization by ICP-AES. Before exposure, X-ray diffraction and optical microscopy revealed equiaxed alpha-Ti in both materials and beta-Ti in Ti-6Al-4V. Scratch tests exhibited a lower coefficient of friction for Ti-6Al-4V alloy than commercially pure titanium. After exposure, X-ray photoelectron spectroscopy and surface-enhanced Raman spectroscopy results showed an oxide film formed by TiO2, both in commercially pure titanium and in Ti-6Al-4V, and by TiO and Al2O3 associated with the presence of the alloys. Furthermore, inductively coupled plasma atomic emission spectroscopy revealed that aluminum was the main ion released for Ti-6Al-4V, giving negligible values for the other metal ions.
- ItemEffect of hot pressing and hot isostatic pressing on the microstructure, hardness, and wear behavior of nickel(2020) Martinez, Carola; Briones, Francisco; Aguilar, Claudio; Araya, Nicolas; Iturriza, Inigo; Machado, Izabel; Rojas, PaulaNanocrystalline Ni (Ni-nc) obtained by mechanical milling may present improved mechanical properties paired with high abrasion resistance. Different sintering processes were used to consolidate Nanocrystaline Ni: hot pressed (HP) and hot-isostatic pressed (HIP). The microstructure, mechanical properties, and tribological were evaluated to compare the processes. X-ray diffraction patterns showed that HIP-consolidated specimens had larger crystallite sizes and 37% less microstrain when compared to the HP specimens. The nanohardness of the HIP specimens was also carried out and it was 50% lower than that of HP specimens, whereas its coefficient of friction found was 25% higher. These results show the advantages of the HP process over the HIP since the high pressure. The low sintering temperature of HP inhibited the grain growth, which leads excellent mechanical and tribological properties of Ni. (C) 2020 Elsevier B.V. All rights reserved.
- ItemFEEDING DRY OLIVE CAKE MODIFIES SUBCUTANEOUS FAT COMPOSITION IN LAMBS, NOTING CAKE RESISTANCE TO DEGRADATION AND PEROXIDATION(INST INVESTIGACIONES AGROPECUARIAS, 2009) Vera, Raul; Aguilar, Claudio; Lira, Rodrigo; Toro, Paula; Barrales, Luis; Pena, Ivan; Squella, Fernando; Perez, Patricio; Quenaya, Javiera; Yutronic, Hanja; Briones, IgnacioThe purpose of this experiment was to determine the extent to which lamb carcass quality and fat composition could be altered by applying a dry olive cake-based ration instead of a conventional ration or pasture feeding. Three treatments were compared in a completely randomized experiment using 36 single male Suffolk Down lambs with an initial age and live weight of 80 d and 25 kg, respectively. The three treatments were: (a) suckling lambs kept with their mothers on annual Mediterranean grassland (GRAZE); (b) weaned stall-fed lambs on a control ration (CONC); and (c) weaned stall-fed lambs on an olive cake-based ration (CAKE). At the end of the 28-d experimental period, lambs were slaughtered, carcass quality evaluated, and samples of subcutaneous fat analyzed for fatty acids. Treatments did not differ in weight gain or carcass weight and quality, but highly significant differences were found in several fatty acid contents. CAKE animals had reduced palmitic acid as well as increased oleic and stearic acid contents. Atherogenic and thrombogenic indices improved with cake feeding. Principal component and discriminant analyses clearly differentiated treatments suggesting they could be applicable for traceability purposes. A laboratory experiment demonstrated that with or without added vitamin E, the dry olive cake did not alter its lipid properties with increased storage time.
- ItemMODELLING SUPPLEMENTATION STRATEGIES FOR BEEF STEER REARING AND FATTENING SYSTEMS IN SOUTHERN CHILE(INST INVESTIGACIONES AGROPECUARIAS, 2009) Toro, Paula; Catrileo, Adrian; Aguilar, Claudio; Vera, RaulA mathematical model was developed to analyze beef production systems in Southern Chile. The study considered the identification of the main components of systems under different beef steer management strategies, using pasture with or without supplementation and back grounding cattle on pasture followed by a winter period of confined feeding with pasture silage and concentrates. Validation of model outputs using 200 kg LW Hereford steers against real experimental data showed no significant differences (P >= 0.01) between simulated and observed final weights. In order to analyze the interaction between the stocking rate (SR) and supplementation, three SR of 2, 2.5 and 3 steers ha(-1) with and without pasture silage supplementation at the rate of 5 kg DMd(-1) steer(-1) for the length of the entire period were simulated. Means were compared by the least significant difference (LSD, P <= 0.05). Significant differences were found in terms of final weights, which decreased with increasing SR regardless of the supplementation level, although silage supplementation tended to reduce differences between SR. A second set of simulation runs was carried out to simulate on-farm finishing of the steers through a final phase of confined feeding based on a ration of silage and concentrates. Final weights differed between SR and systems and results showed that the optimum corresponded to 2.5 steers ha(-1), since at this SR the largest income corresponded to the smallest mean cost. It is concluded that a stocking rate of 2.5 steers ha(-1) is feasible if winter supplementation is available, independently of a finishing period in feedlot.
- ItemSimulation of the Influence of the Radial Graded Porosity Distribution on Elastic Modulus of γ/β Phase Ti-Based Alloy Foams for Bone Implant(2023) Aguilar, Claudio; Alfonso, Ismeli; Gonzalez, Daniel; Pio, Edgar; Neves, Guilherme Oliveira; De Barbieri, Flavio; Sancy, Mamie; Munoz, LisaThis research aims to examine how a radial graded porosity distribution affects the elastic modulus by conducting simulations on Ti-based alloy foams with face-centered cubic and body-centered cubic crystal structures. Four types of foams were analyzed; commercially pure-Ti, Ti-13Ta-6Mn (TTM), Ti-13Ta-(TT) and Ti-13Ta-6Sn (TTS), (all in at.%). Four radial graded porosity distribution configurations were modeled and simulated using the finite element analysis (FEA). The radial graded porosity distribution configurations were generated using a Material Designer (Ansys) with a pore range of 200 to 600 mu m. These radial graded porosity distributions had average porosity values of 0, 20, 30 and 40%. The consolidated samples that were obtained through a powder metallurgy technique in two step samples were synthesized using a powder metallurgy technique, with the elastic moduli values of the aforementioned Ti based alloys being measured by ultrasound using similar to 110, similar to 69, similar to 61 and similar to 65 GPa, respectively. The results showed that the modulus decreased as a function of porosity level in all simulated materials. The TTM, TT and TTS foams, with average porosities of 20, 30 and 40%, exhibited an modulus smaller than 30 GPa, which is a requirement to be used as a biomaterial in human bones. The TT foams showed the lowest modulus when compared to the other foams. Finally, certain theoretical models were used to obtain the modulus, the best being; the Gibson-Ashby model (alpha = 1 and n = 2.5) for the cp-Ti foams and Knudsen-Spriggs model (b = 3.06) for the TTM, TT and TTS foams.