The effect of oxygen pickup during selective laser melting on the microstructure and mechanical properties of Ti-6Al-4V lattices.

Additive manufacturing techniques such as Selective Laser Melting (SLM) can produce complex shapes with relatively thin sections and fine detail. However, common materials for the process, such as Ti-6Al-4V, have microstructure and properties that are sensitive to the pickup of interstitial impurities, such as oxygen, which the material will be exposed to during the process. This problem would be especially severe for parts with thin sections, where surface effects can be more significant, and where poor properties may coincide with locally-elevated stress. Here we explore the effects of oxygen level in thin sections with the use of lattice materials (materials which can be considered to consist exclusively of near-surface material). Oxygen levels are artificially raised using repeated melting passes to result in more pickup, leading to significantly reduced ductility and hence reduced strength measured in compression. A ductile to brittle transition in strut failure mechanism is found with increasing number of melting passes, with significant modification in chemistry and crystallographic structure, despite the presence of a similar fine plate-like microstructure throughout.

Microbial Phosphite Oxidation and Its Potential Role in the Global Phosphorus and Carbon Cycles.

Phosphite [Formula: see text] is a highly soluble, reduced phosphorus compound that is often overlooked in biogeochemical analyses. Although the oxidation of phosphite to phosphate is a highly exergonic process (Eo'=-650mV), phosphite is kinetically stable and can account for 10-30% of the total dissolved P in various environments. There is also evidence that phosphite was more prevalent under the reducing conditions of the Archean period and may have been involved in the development of early life. Its role as a phosphorus source for a variety of extant microorganisms has been known since the 1950s, and the pathways involved in assimilatory phosphite oxidation have been well characterized. More recently, it was demonstrated that phosphite could also act as an electron donor for energy metabolism in a process known as dissimilatory phosphite oxidation (DPO). The bacterium described in this study, Desulfotignum phosphitoxidans strain FiPS-3, was isolated from brackish sediments and is capable of growing by coupling phosphite oxidation to the reduction of either sulfate or carbon dioxide. FiPS-3 remains the only isolated organism capable of DPO, and the prevalence of this metabolism in the environment is still unclear. Nonetheless, given the widespread presence of phosphite in the environment and the thermodynamic favorability of its oxidation, microbial phosphite oxidation may play an important and hitherto unrecognized role in the global phosphorus and carbon cycles.

[Family influence in the metabolic control of the type-2 diabetic]. / Influencia de la familia en el control metabólico del paciente diabético tipo II.

This paper presents the results of the identification and association of certain family characteristics of type II diabetes patients in relation with its metabolic control in 121 families of tw o health centers of Guadalajara, Jalisco, Mexico in 1989. The attitude an d information about of the sickness, and the complications and therapeutics were evaluated through psychosocial evaluations. The majority of the family members showed a negative attitude and a profound understanding of the disease process. Only a 16.5 per cent of the patients were under control, and found a strong association between lack of control and nuclear family involved in the last cycles of this type of unit: independence and retirement.