Effect of Carbon-Doping on Microstructure and Nanomechanical/Tribological Behavior of Ti–B–C Coatings onto H13 Steel

E. Contreras,D. Grisales,W. Tillmann,A. Hurtado‑Macias,M. A. Gómez‑Botero 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.8

Due to its high hardness, chemical and thermal resistance, TiB2has become a great candidate to be used as a protective coating. However, high residual stresses after the deposition and brittleness have become the main obstacles for implementation atindustrial levels. In the present work, the incorporation of graphite was studied as an alternative to improve the performanceof the TiB2coatings and study the influence in the microstructure, Nano mechanical and tribological properties. Ti–B–Ccoatings were deposited with different carbon contents of 10, 20, 28 and 38 at%. XRD results showed that the carbon atomsenter within the crystal lattice of the TiB2forming a solid solution, and consequently, deforming crystal and modifying itslattice parameter of 3.2237–3.3414 Å. HRTEM images and selected area electron diffraction patterns analysis display thelow crystallite or degree of amorphosity due to the carbon concentration (C1.9 mol). Compressive residual stresses decreasein the coatings containing the higher amounts of carbon. The formation of a TiB2-C solid solution contributed to the incrementof nanohardness (H = 25 GPa) and improvement of the resistance to plastic deformation (H3/E2) of coatings. Regardingthe tribological behaviour of the coatings, higher friction coefficient than those obtained on the uncoated substrate wereobserved. However, a reduction of the wear rate was also evident. The presence of a high amount of debris and severe wearof the counterpart material indicates a highly aggressive tribological contact. Roll-like debris with a shape of needles wasfound within the tribological tracks perpendicular to the sliding direction.

Infall Signatures in a Prestellar Core Embedded in the High-mass 70 <i>μ</i>m Dark IRDC G331.372-00.116

Contreras, Yanett,Sanhueza, Patricio,Jackson, James M.,Guzmá,n, André,s E.,Longmore, Steven,Garay, Guido,Zhang, Qizhou,Nguyê,̃,n-Lu’o’, Quang,Tatematsu, Ken’ichi,Nakamura, Fumita American Astronomical Society 2018 The Astrophysical journal Vol.861 No.1

<P>Using Galactic Plane surveys, we have selected a massive (1200M circle dot), cold (14 K) 3.6-70 mu m dark IRDC, G331.372-00.116. This infrared dark cloud (IRDC) has the potential to form high-mass stars, and given the absence of current star formation signatures, it seems to represent the earliest stages of high-mass star formation. We have mapped the whole IRDC with the Atacama Large Millimeter/submillimeter Array (ALMA) at 1.1 and 1.3 mm in dust continuum and line emission. The dust continuum reveals 22 cores distributed across the IRDC. In this work, we analyze the physical properties of the most massive core, ALMA1, which has no molecular outflows detected in the CO (2-1), SiO (5-4), and H2CO (3-2) lines. This core is relatively massive (M = 17.6M circle dot), subvirialized (virial parameter alpha(vir) = M-vir/M = 0.14), and is barely affected by turbulence (transonic Mach number of 1.2). Using the HCO+ (3-2) line, we find the first detection of infall signatures in a relatively massive, prestellar core (ALMA1) with the potential to form a high-mass star. We estimate an infall speed of 1.54 km s(-1) and a high accretion rate of 1.96. x. 10(-3) M circle dot yr(-1). ALMA1 is rapidly collapsing, out of virial equilibrium, which is more consistent with competitive accretion scenarios rather than the turbulent core accretion model. On the other hand, ALMA1 has a mass similar to 6 times larger than the clumps Jeans mass, as it is in an intermediate mass regime (M-J = 2.7 < M less than or similar to 30 M circle dot), contrary to what both the competitive accretion and turbulent core accretion theories predict.</P>

Adaptive length SMA pendulum smart tuned mass damper performance in the presence of real time primary system stiffness change

Contreras, Michael T.,Pasala, Dharma Theja Reddy,Nagarajaiah, Satish Techno-Press 2014 Smart Structures and Systems, An International Jou Vol.13 No.2

In a companion paper, Pasala and Nagarajaiah analytically and experimentally validate the Adaptive Length Pendulum Smart Tuned Mass Damper (ALP-STMD) on a primary structure (2 story steel structure) whose frequencies are time invariant (Pasala and Nagarajaiah 2012). In this paper, the ALP-STMD effectiveness on a primary structure whose frequencies are time varying is studied experimentally. This study experimentally validates the ability of an ALP-STMD to adequately control a structural system in the presence of real time changes in primary stiffness that are detected by a real time observer based system identification. The experiments implement the newly developed Adaptive Length Pendulum Smart Tuned Mass Damper (ALP-STMD) which was first introduced and developed by Nagarajaiah (2009), Nagarajaiah and Pasala (2010) and Nagarajaiah et al. (2010). The ALP-STMD employs a mass pendulum of variable length which can be tuned in real time to the parameters of the system using sensor feedback. The tuning action is made possible by applying a current to a shape memory alloy wire changing the effective length that supports the damper mass assembly in real time. Once a stiffness change in the structural system is detected by an open loop observer, the ALP-STMD is re-tuned to the modified system parameters which successfully reduce the response of the primary system. Significant performance improvement is illustrated for the stiffness modified system, which undergoes the re-tuning adaptation, when compared to the stiffness modified system without adaptive re-tuning.

The phytohormone abscisic acid increases triacylglycerol content in the green microalga Chlorella saccharophila (Chlorophyta)

Contreras-Pool, Patricia Yolanda,Peraza-Echeverria, Santy,Ku-Gonzalez, Angela Francisca,Herrera-Valencia, Virginia Aurora The Korean Society of Phycology 2016 ALGAE Vol.31 No.3

Microalgae are currently a very promising source of biomass and triacylglycerol (TAG) for biofuels. In a previous study, we identified Chlorella saccharophila as a suitable source of oil for biodiesel production because it showed high biomass and lipid content with an appropriate fatty acid methyl esters profile. To improve the TAG accumulation in C. saccharophila, in this study we evaluated the effect of abscisic acid (ABA) addition on cell concentration, lipid content and TAG production in this microalga. First, we evaluated the effects of four ABA concentrations (1, 4, 10, and 20 μM) added at the beginning of a single-stage cultivation strategy, and found that all concentrations tested significantly increased cell concentration and TAG content in C. saccharophila. We then evaluated the addition of 1 μM ABA during the second stage of a two-stage cultivation strategy and compared it with a nitrogen deficiency treatment (ND) and a combination of ND and ABA (ND + ABA). Although ABA alone significantly increased lipid and TAG contents compared with the control, ND showed significantly higher TAG content, and ND + ABA showed the highest TAG content. When comparing the results of both strategies, we found a superior response in terms of TAG accumulation with the addition of 1 μM ABA at the beginning of a single-stage cultivation system. This strategy is a simple and effective way to improve the TAG content in C. saccharophila and probably other microalgae as a feedstock for biodiesel production.

Influence of the Morphology and the Particle Size on the Processing of Bronze 90/10 Powders by Metal Injection Moulding (MIM)

Contreras Jose M.,Jimenez-Morales Antonia,Torralba Jose M. 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1

The MIM technology is an alternative process for fabricating near net shape components that usually uses gas atomised powders with small size (< 20 μm) and spherical shape. In this work, the possibility of changing partially or totally spherical powder by an irregular and/or coarse one that is cheaper than the former was investigated. In this way, different bronze 90/10 components were fabricated by mixing three different types of powder, gas and water atomised with different particle sizes, in order to evaluate how the particle shape and size affect the MIM process.

Pectin from Passion Fruit Fiber and Its Modification by Pectinmethylesterase

Contreras-Esquivel, Juan Carlos,Aguilar, Cristobal N.,Montanez, Julio C.,Brandelli, Adriano,Espinoza-Perez, Judith D.,Renard, Catherine M.G.C. The Korean Society of Food Science and Nutrition 2010 Preventive Nutrition and Food Science Vol.15 No.1

Passion fruit fiber pectin gels represent a new alternative pectin source with potential for food and non-food applications on a commercial scale. Pectic polysaccharides were extracted from passion fruit (Passiflora edulis) fiber using citric acid as a clean catalyst and autoclaved for 20 to 60 min at $121^{\circ}C$. The best condition of pectin yield with the highest molecular weight was obtained with 1.0% of citric acid (250 mg/g dry passion fruit fiber pectin) for 20 min of autoclaving. Spectroscopic analyses by Fourier transform infrared, enzymatic degradation reactions, and ion-exchange chromatography assays showed that passion fruit pectin extracted for 20 min was homogeneous high methoxylated pectin (70%). Gel permeation analysis confirmed that the pectin extract obtained by autoclaving by 20 min showed higher molecular weights than those autoclaved for 40 and 60 min. Passion fruit pectin extracted for 20 min was enzymatically modified with fungal pectinmethylesterase to create restructured gels. Short autoclave treatment (20 min) with citric acid as extractant resulted in a significant increase of gel strength, improving pectin extraction in terms of functionality. The treatment of solubilized material (pectic polysaccharides) in the presence of insoluble material (cellulose and hemicellulose) with pectinmethylesterase and calcium led to the creation of a stiffer passion fruit fiber pectin gel, while syneresis was not observed.

Gulf of Urabá (Caribbean Colombia), a Tropical Estuary: A Review with Some General Lessons About How it Works

Sebastián Contreras-Fernández,Lennin Florez-Leiva,María Camila Bernal-Sánchez,Wilberto Pacheco-Paternina,Shalenys Bedoya-Valestt,Lorenzo Portillo-Cogollo 한국해양과학기술원 2022 Ocean science journal Vol.57 No.4

Estuaries are highly diverse ecosystems that occur at the interface between land and sea and thus possess a high degree of environmental variation over short spatial and temporal scales. The Gulf of Urabá (1800 km 2; mean depth ~ 40 m) is a semiclosed estuarine area located in the southwestern part of the Caribbean Sea (South America). This large coastal–estuarine ecosystem operates as a biogeochemical reactor due to it featuring examples of high nutrient concentrations on the surface (NO 3- = 1619 μM; NO 2- = 0.505 μM; NH 4+  = 2.938 μM; PO 4 3- = 7.603 μM), high Chl α (max = 30.17; min = 0.02; mean = 9 mg m−3), as well as blooms of toxic algae, mostly Pseudo-nitzschia pseudodelicatissima. An outbreak of Tripos fusus causes bioluminescence and about 20 events of hypoxia (< 2–4 mg O 2 L−1) within a time series of 10 years. Despite this, information regarding the biological and biogeochemical oceanography (chlorophyll α, biomass, planktonic composition, nutrient cycling, mass balance of elements, and interannual variability) remains non-existent. Therefore, elucidating an ecosystem’s thresholds for various features is necessary for managing marine ecosystems, and especially for climate change projections. We here present a review of the functioning of this estuary, evaluating and reviewing each aspect of oceanographic variability.

IoET enabled classrooms to foster Education 4.0 in Mexican elementary schools

Juan Contreras-Castillo,Pedro C. Santana-Mancilla,Norma Barón-Ramírez,Elba Abigail Morales Vanegas APEC국제교육협력원 2020 Asia-Pacific Cybereducation Journal Vol.16 No.1

The changes of the Fourth Industrial Revolution (Industry 4.0) are inevitable in all areas of daily life, from government to healthcare and commerce, including the educational field. Education 4.0 brings potential challenges to schools around the globe, such as digital technology, personalized data, and a connected world. Thus, this paper presents a Mexican case study about a classroom enhanced with digital technology to study the challenges that both students and teachers face to acquire and transmit the skills and competencies that Industry 4.0 requires. As a preliminary result, we found that the probability of students accepting this technology for learning is very high.

Effects of Day Length during Seed Development in Lettuce (Lactuca sativa L.)

Samuel Contreras,David Tay,Mark A. Bennett 한국원예학회 2006 한국원예학회 기타간행물 Vol.- No.-

Parental Quality Investment, Child Effort, and Human Capital Accumulation

Salvador Contreras 한국국제경제학회 2011 International Economic Journal Vol.25 No.3

This paper develops a theoretical model that explores the effects of child investment on human capital accumulation. Household investment effects are measured as a function of quality of investment choices, time allocation, child effort, and spillover effects. The theory dynamics are derived by employing a two-period OLG model. The model dynamics reveal the existence of multiple steady states of quality investment and child human capital accumulation under two stages of development. These dynamics show why poor households are often unable to escape poverty. Empirically, the theory and dynamics are tested with United States data. The data suggest that for poor households, income and parental human capital have no significant effect on child performance at school. Child effort and parental quality investment are shown to be significant determinants of child performance at school across household types.