Rodrigo Palma

Influence of Atmosphere on Sintering of T15 and M2 Steel Powders

The sintering behavior of T15 and M2 water-atomized high-speed steel powders under vacuum and N2-H2-CH4 atmosphere is analyzed. Sintering under the gas mixture allows high densities [99 to 100 pct total density (TD)] to be obtained at temperatures 45 to 50 K lower than for vacuum sintering for steel T15, but the high densities are reached at slightly higher temperatures (15K) than for vacuum sintering for steel M2. Chemical analysis of gas-sintered specimens has shown that a higher amount of nitrogen is absorbed during sintering of steel T15 (0.72 to 0.78 pct) than in the case of steel M2 (0.34 to 0.38 pct). Although MC and M6C primary particles are observed during vacuum sintering, in gas sintering, the MC carbides change to MX carbonitrides. These particles are very fine (1 μm) and are very resistant to coarsening during oversintering. Sintering in the gas atmosphere allows important oversinterings (up to 50 K above the minimum sintering temperature for achieving a density higher than 99 pct of theoretical density) to be reached in the case of steel T15 without the formation of eutectic films. In the case of M2 steel, for gas sintering, the eutectic films appear for oversinterings smaller or equal to those for vacuum sintering.

Evolving Visual Object Recognition for Legged Robots

Recognition of relevant game field objects, such as the ball and landmarks, is usually based upon the application of a set of decision rules over candidate image regions. Rule selection and parameters tuning are often arbitrarily done. We propose a method for evolving the selection of these rules as well as their parameters with basis on real game field images, and a supervised learning approach. The learning approach is implemented using genetic algorithms. Results of the application of our method are presented.

Comparative analysis of five case studies: commonalities and differences in approaches to mitigation actions in five developing countries

In light of the ongoing international discussions about the Nationally Appropriate Mitigation Action concept, this study takes instead a more ‘bottom-up’ approach through a comparative analysis of five studies of mitigation actions (MAs) in Brazil, Colombia, Chile, Peru and South Africa. The analysis shows that MAs are driven by both developmental and climate objectives. The character, scope, policy horizon and potential success of an action are closely linked to the developmental path of countries such that MAs that directly address poverty and development seem to have a better chance of being implemented since they address issues higher on the policy agenda of developing countries. Where international support is sought, all five countries have some existing measurement, reporting and verification (MRV) and technical competence capacity that can be built upon. The choice of MAs is evidently linked to institutional capacity (both for design and implementation of MAs and possible MRV), emissions profile and the relative resource endowments of countries. The policy environments – from highly planned to less coordinated – and time-horizons – from 4-year plans to 40-year scenarios – differ substantially between the countries. Thus, the comparative analysis underscores the diversity of possible MAs and capabilities and the concomitant need for flexibility in definition, design and implementation.

Prospects for photovoltaics in sunny and arid regions: A solar grand plan for Chile -Part I-investigation of PV and wind penetration

New markets for photovoltaics are being created in emerging economies where rich solar resources can produce solar electricity at affordable costs. A case in point is Chile, a country with great solar resources planning renewable energy deployment to address the needs of an expanding mining industry and a growing economy, while preserving the environment. The expansion of metal mining and smelting operations is constrained by the cost of electricity and the unavailability of water in northern Chile, offering an opportune synergy between photovoltaics and mining. Local estimates put the potential for solar electricity in the north interconnect at more than 200 GW, those of geothermal in the north and central interconnects from 3-16 GW, wind in the central interconnect from 5-40 GW, and small hydro and biomass in the south at 0.3 and 0.4 GW, correspondingly. These resources can supply not only the needs for sustainable development in Chile but can also produce electricity for neighboring countries. This paper examines the potential for immediate PV penetration in Chiles main electricity grids (SING and SIC) and options (i.e., curtailment, PV and wind combinations) that can increase such penetration.

The relation of hardness to toughness and retained austenite content in N2-H2-CH4 sintered T6, T15 and T42 high-speed steels

The increase of toughness, 10 to 35 MPam1/2, with decreasing hardness,VH 950 to 500, is reported for sintered T6, T15 and T42 high-speed steels. This range of properties resulted from combinations of sintering temperatures (in N2-H2-CH4), HIPping and tempering treatments of steels processed from water-atomized powders. Toughness is related to the properties of the matrix, but more specifically to the retained austenite content, varying between 5% (HV10 ≃950,Klc ≃ 10 MPam1/2) and 70% (HV10 ≃ 500,Klc ≃ 35 MPam1/2). Austenite retention is caused by the stabilizing affect of nitrogen (0.3 to 0.7%), picked up from the sintering atmosphere. Fractographic examination revealed that, although failure proceeded by complex modes that could be described mainly as quasi-cleavage, microplasticity was observed in the high austenite materials, as opposed to the flatter fracture surfaces, with much less plasticity apparent, for the lower retained austenite-containing materials.

Effect of photon flux density and temperature on the production of halogenated monoterpenes by Plocamium cartilagineum (Plocamiaceae, Rhodophyta).

Abstract The effect of different photon flux densities (PFD) and temperatures on the relative growth rate (RGR) and the concentration of three halogenated monoterpenes in samples of Plocamium cartilagineum L.( Dixon), a marine alga (Rhodophyceae), were studied. The highest RGR (22.8 ± 0.04 d-1) was obtained at 15 °C and 41 μmol m-2 s-1 of PFD and the lowest (18.0 ± 0.2 d-1) was obtained at 18 °C and 120 μmol m-2 s-1. The different temperatures and light used in assays did not affect significantly the production of organic compounds. The production of mertensene and violacene was not affected significantly. However, compound 1 reached the highest concentration at 15 °C and 65 μmol m-2 s-1. The relationship between growth and production of monoterpenes of P. cartilagineum and the effect of temperature and the PFD were analyzed.

Buckling of Cu–Zr-based metallic glasses nanowires: molecular dynamics study of surface effects

The phenomenon of buckling in Cu45Zr45Al10 metallic glass nanowires with different slenderness ratios was studied by means of molecular dynamics simulation. The values of critical stress versus slenderness ratio for two nanowire diameters were obtained. We analyzed the results within the framework of the modified Euler theory of buckling, obtaining values for the surface elastic modulus and the residual surface stress for the two different diameters. Our results show that the Cu45Zr45Al10 metallic glass in nanometric size become stiffer and exhibits a lower Young’s modulus than that of a bulk sample.

Metallographic changes in the sintering of grade T high speed steels in an industrial atmosphere and vacuum

The metallographic changes taking place in three T grade steels, T42, T15 and T1 in the range of optimum sintering temperature to oversintering in vacuum and in an industrial atmosphere — base nitrogen — have been investigated using SEM and EDS techniques. M6C and MC primary carbides have been observed for vacuum sintering and MX carbonitrides instead of MC carbides were found in the specimens sintered in the atmosphere. Small amounts of an eutectic carbide rich in Cr and Fe have been observed at the optimum sintering temperature. By oversintering in vacuum different type of eutectic carbides can be observed: MC, needle shape, M6C, but only M6C type eutectic carbide have been observed by oversintering the samples in the industrial atmosphere.

Tarificación de la Transmisión Eléctrica Usando Factores GGDF y GLDF: Una Estimacion de sus Efectos Distributivos

Los factores de distribucion GGDF y GLDF son un metodo atractivo para prorratear los peajes que deben pagar los usuarios de sistemas electricos de transmision. Sin embargo, se demuestra que el metodo no es suficiente para definir un unico prorrateo. Los g

Sequence Independent, Simultaneous and Multidimensional Lifting of Generalized Flow Covers for the Semi-Continuous Knapsack Problem with Generalized Upper Bounds Constraints

We consider the semi-continuous knapsack problem with generalized upper bound constraints on binary variables. We prove that generalized flow cover inequalities are valid in this setting. We also prove that, under mild assumptions, they are facet-defining inequalities for the full problem. We then focus on simultaneous lifting of pairs of variables. The associated lifting problem naturally induce multidimensional lifting functions, and we prove that a simple relaxation, in a restricted domain, is a superadditive function. We also prove that in many cases this approximation is actually the optimal lifting function. We then analyze the separation problem, which we separate in two phases: first, find a seed inequality, where we evaluate both exact and heuristic methods; secondly, since the lifting is simultaneous, our class of lifted inequalities might contain an exponential number of them. We choose a strategy of maximizing resulting violation. Finally, we test this class of inequalities on instances arising from electricity planning problems. Our test show that the proposed class of inequalities are strong in the sense that adding a few of these inequalities, they close, on average, 57.70% percent of the root integrality gap, and close 97.70% of the relative gap, while adding very few cuts.