Study of the properties of low-cost powder metallurgy titanium alloys by 430 stainless steel addition

Titanium is a lightweight metal with an outstanding combination of properties which make it the material of choice for many different applications. Nonetheless, its employment at industrial level is not widespread due to higher production costs with respect to competitor metals like steel and aluminium. In this work the production of low-cost titanium alloys is attempted by combining the utilisation of a powder metallurgy process and cheap alloying elements (i.e. commercial 430 stainless steel powder optimised for the powder metallurgy industry). Low-cost titanium alloys are fabricated by blending elemental titanium with stainless steel. The behaviour of the powders as well as that of the sintered materials are analysed and compared to that of a master alloy addition Ti6Al4V alloy. The produced low-cost titanium alloys show comparable properties to both wrought and powder metallurgy titanium alloys and, therefore, they are proposed as an alternative to obtain structural component made out of titanium alloys.The authors want to acknowledge the financial support from the Spanish Ministry of Science through the R&D Projects MAT2012-38650-C02-01, and from Regional Government of Madrid through the ESTRUMAT (S2009/MAT-1585) projec

Inductive hot-pressing of titanium and titanium alloy powders

Inductive hot-pressing is a field-assisted sintering process (FAST) in which an electrical current is used to enhance the densification of the powder. Inductive hot-pressing could be employed to enable titanium powder to reach a higher density in less time than the pressing and sintering process. In this study, titanium and titanium alloy powders with different features were processed by means of inductive hot-pressing. The influence of processing temperature on density, microstructure, quantity of interstitial elements and hardness was investigated. Generally, practically fully dense materials were obtained without any carbon pick-up, even if the materials were in contact with the graphite matrix during processing. Nevertheless, there was an increment of the nitrogen content and some oxygen pick-up, especially for the powders with smaller particle size. Hardness is not significantly affected by the pressing temperature, but it strongly depends on the amount of interstitials.The authors are thankful for the financial support from Comunidad de Madrid through the ESTRUMAT (S-2009/MAT-1585) project and from the Spanish Ministry of Education through the R&D MAT2009-14448 ProjectPublicad

Clonal interference and Muller's ratchet in spatial habitats

Competition between independently arising beneficial mutations is enhanced in spatial populations due to the linear rather than exponential growth of clones. Recent theoretical studies have pointed out that the resulting fitness dynamics is analogous to a surface growth process, where new layers nucleate and spread stochastically, leading to the build up of scale-invariant roughness. This scenario differs qualitatively from the standard view of adaptation in that the speed of adaptation becomes independent of population size while the fitness variance does not. Here we exploit recent progress in the understanding of surface growth processes to obtain precise predictions for the universal, non-Gaussian shape of the fitness distribution for one-dimensional habitats, which are verified by simulations. When the mutations are deleterious rather than beneficial the problem becomes a spatial version of Muller's ratchet. In contrast to the case of well-mixed populations, the rate of fitness decline remains finite even in the limit of an infinite habitat, provided the ratio $U_d/s^2$ between the deleterious mutation rate and the square of the (negative) selection coefficient is sufficiently large. Using again an analogy to surface growth models we show that the transition between the stationary and the moving state of the ratchet is governed by directed percolation

Testing machine learning algorithms for the prediction of depositional fluxes of the radionuclides 7Be, 210Pb and 40K

The monthly depositional fluxes of 7Be, 210Pb and 40K were measured at Malaga, (Southern Spain) from 2005 to 2018. In this work, the depositional fluxes of these radionuclides are investigated and their relations with several atmospheric variables have been studied by applying two popular machine learning methods: Random Forest and Neural Network algorithms. We extensively test different configurations of these algorithms and demonstrate their predictive ability for reproducing depositional fluxes. The models derived with Neural Networks achieve slightly better results, in average, although similar, having into account the uncertainties. The mean Pearson-R coefficients, evaluated with a k-fold cross-validation method, are around 0.85 for the three radionuclides using Neural Network models, while they go down to 0.83, 0.79 and 0.8 for 7Be, 210Pb and 40K, respectively, for the Random Forest models. Additionally, applying the Recursive Feature Elimination technique we determine the variables more correlated with the depositional fluxes of these radionuclides, which elucidates the main dependences of their temporal variability.This research was funded by Consejo de Seguridad Nuclear (Spain). Funding for open access charge: Universidad de Málaga / CBU

Study of Compaction and Ejection of Hydrided-Dehydrided Titanium Powder

Three similar varieties of pure Ti hydride-dehydried (HDH) powders were tested for the understanding of the variables that have an influence on the compaction process of Ti powders. The study shows that small differences in the characteristics of the powders lead to very different behaviours in the compaction stage. Compressibility curves, friction with the die walls and ejection forces are discussed in this study. The results are compared with a commercial iron powder as a reference to complete the discussion, as well as to show the enhancements and modifications that should be performed in Ti powders to design an optimized powder suitable for being pressed in an industrial process.The authors want to acknowledge the contribution and effort of Mr. Paul-Émile Mongeon from Industrial Materials Institute (IMI, Canada), as well as for his teaching and advises during the use of Powder Testing Center located at IMI. Shirley Mercier from IMI and Dr. Begoña Ferrari from Instituto de Cerámica y Vidrio (ICV, Spain), are also acknowledged for their contribution to the experimental work. Authors want to acknowledge Fundación Carlos III and Instituto Álvaro Alonso Barba for the funds supplied during the stay at IMI of P.G. Esteban, and the Spanish Ministry of Education for the funds provided for the research thought the I+D project MAT2006-02458.Publicad

Plankton biomass and larval fish abundance prior to and during the El Niño period of 1997–1998 along the central Pacific coast of México

The temporal and spatial distributions of zooplankton biomass and larval fish recorded during 27 months (December 1995–December 1998) off the Pacific coast of central México are analyzed. A total of 316 samples were obtained by surface (from 40–68 to 0 m) oblique hauls at 12 sampling sites using a Bongo net. Two well-defined periods were observed: a pre-ENSO period (December 1995–march 1997) and an ENSO event (July 1997–September 1998) characterized by impoverishment of the pelagic habitat. The highest biomass concentrations occurred at coastal stations during the pre-ENSO period. During the El Nin˜o period no spatial patterns were found in coastal waters. The months with highest biomass were those in which the lowest sea surface temperature (SST) occurred (January–May), and this pattern was also observed during the ENSO period. A typical, although attenuated, seasonal environmental pattern with enhanced phytoplankton (diatoms and dinoflagellates) was prevalent during the El Nin˜o event in nearshore waters. During the El Niño period the phytoplankton was mainly small diatoms (microphytoplankton), while dinoflagellates were practically absent. The most parsimonious generalized linear models explaining spatial and temporal distribution of larval fish species included the ENSO index (MEI), upwelling index (UI) and distance to the coast. The environmental variability defined on an interannual time-scale by the ENSO event and the seasonal hydroclimatic pattern defined by the UI (intra-annualscale) controlled the ecosystem productivity patterns. The small-scale distribution patterns (defined by a cross-shore gradient) of plankton were related to the hydroclimatic seasonality and modulated by interannual anomaliesUniversidad de Guadalajara, Méxic

Two modes of evolution shape bacterial strain diversity in the mammalian gut for thousands of generations

How and at what pace bacteria evolve when colonizing healthy hosts remains unclear. Here, by monitoring evolution for more than six thousand generations in the mouse gut, we show that the successful colonization of an invader Escherichia coli depends on the diversity of the existing microbiota and the presence of a closely related strain. Following colonization, two modes of evolution were observed: one in which diversifying selection leads to long-term coexistence of ecotypes and a second in which directional selection propels selective sweeps. These modes can be quantitatively distinguished by the statistics of mutation trajectories. In our experiments, diversifying selection was marked by the emergence of metabolic mutations, and directional selection by acquisition of prophages, which bring their own benefits and costs. In both modes, we observed parallel evolution, with mutation accumulation rates comparable to those typically observed in vitro on similar time scales. Our results show how rapid ecotype formation and phage domestication can be in the mammalian gut.info:eu-repo/semantics/publishedVersio

Sequenciamento do transcriptoma de Pimenta-do-reino (Piper nigrum) utilizando Plataforma de Sequenciadores de Nova Geração (NGS) - SOLiD System 3 Plus.

A pimenta-do-reino Piper nigrum é um dos principais produtos agrícolas do Pará gerando sustentabilidade para uma porcentagem considerável dos agricultores do estado. A Embrapa (PA) desenvolve trabalhos com a espécie como uma coleção de germoplasma. Com o objetivo de conhecer os potenciais recursos genéticos da espécie, foi sequenciado o transcriptoma de P. nigrum. Uma plataforma de sequenciamento de nova geração foi usada para gerar as sequencias dos genes e o trabalho foi analisado com recursos de bioinformática. Foram anotados automaticamente uma lista de transcritos da espécie

Design and evaluation of PM Ti surfaces modified by colloidal techniques and diffusion processes for biomedical applications

The aim of this work was the modification of the composition and surface microstructure of powder metallurgy titanium to improve the wear resistance and reduce the elastic modulus while maintaining the corrosion behavior, characteristics needed for biomedical applications. For this purpose, Mo and Nb coatings were produced by colloidal techniques. Stable aqueous suspensions were prepared from micro-sized powder of Mo and Nb particles, deposited onto the powder metallurgy titanium substrates (green or sintered). After a heat treatment to promote the diffusion and the consolidation of the layers, microstructural changes were obtained. In the case of green substrates, the co-sintering process provides a diffusion depth of 85-100 micron. In the as-sintered case, a uniform depth of 40-65 microns was reached. The surfaces were characterised by micro-hardness, corrosion and tribocorrosion testing, and the results showed that hardened surfaces presented lower tendency to corrosion both under static conditions and under sliding.Funds were provided by Spanish Government (programme MINECO, ref. MAT2012-38650-C02-01), Regional Government of Madrid (programme MULTIMAT-CHALLENGE, ref. S2013/MIT-2862) and Institute of Alvaro Alonso Barba (IAAB) for the research stay in CMEMS-UMINHO (University of Minho).info:eu-repo/semantics/publishedVersio

Characterization of novel W alloys produced by HIP

W and W alloys containing 0.5 Wt% Y(2)O(3), x wt% Ti and (x wt% Ti + 0.5 Wt% Y₂O₃) have been prepared, x 2 or 4. Elemental powders were blended or ball milled, canned, degassed and finally consolidated by a two-stage HIP process under a pressure of 195 MPa. It is found that Ti addition favours the densification attaining a fully dense material. XRD, SEM and EDX analyses of he material with Ti addition reveal the formation of a microstructure consisting of tungsten particles embedded in a W-Ti matrix. The microhardness of these materials increased noticeably with the titanium content