Effect of casting procedures in the structure and flow behaviour of semisolid A356 alloy

Evaluation of different casting methods to produce raw material for thixoforming, aiming costs reduction in the production of thixoformable alloys. Reduction of costs may stimulate the commercial use of the semisolid processing technology (SSM). Design/methodology/approach: It is analysed the effect of different casting routes in the microstructure features in semisolid A356 alloy, and in its rheological behaviour. Different casting procedures were investigated: a) pouring in water cooled Cu mould; b) same as „a)” adding electromagnetic stirring; c) same as „a)” adding mechanical vibration; d) same as „b)” with addition of grain refiner; e) same as „c)” with addition of grain refiner. Cast materials were reheated to the semisolid sate and the effect of different holding times upon the globularization of the primary phase was analysed for each cast structure. The semisolid material in each condition was evaluated concerning rheological behaviour. Mechanical properties of thixoformed products were evaluated using flexion tests. Findings: Despite the several methods currently in use to produce raw material for thixoforming, this work shows that the best combination of quality of thixoformable material/ production cost /process operationality can be achieved using casting in permanent mould, under water cooling and mechanical vibration. Resulting cast material under this condition presents grain size smaller than 100 μm, ideal for SSM. Lower the grain size, lower the primary globule size and higher the roundness of the primary phase particle and lower the apparent viscosity of the semisolid. In the best condition achieved, apparent viscosity measured was circa 105 Pa.s (similar to the working range for glass), leading to a probable homogeneous die filling during thixoforming in high pressure die casting machines (HPDC). Research limitations/implications: Regardless the best microstructure for SSM resulting from casting under mechanical vibration, it is still necessary to reach the optimum casting condition in terms of vibration in order to improve, even more, refinement of the microstructure. Practical implications: The suggested process is a simple technique to reduce costs in the production of raw material for thixoforming. The technology is easily implementable in industries. Originality/value: The development of a simple, original, low cost method to produce raw material for SSM technology7328293CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP505859/2013-02013/09961-

Farfield Tracing of a Point Source Discharge Plume in the Coastal Ocean Using Sulfur Hexafluoride

Pathways and dilution of a point source ocean discharge in the farfield (≈10−66 km) were measured using the deliberate tracer sulfur hexafluoride (SF6). The injection of SF6 was performed by bubbling the gas over a period of 6 days into an ocean outfall pipe discharging into the southeast Florida coastal ocean. The surface SF6 concentrations show that the discharged water flowed northward parallel to the coast with a broadening of the width of the plume to about 3 km at the farthest point sampled, 66 km from the outfall. The discharge was fully mixed throughout the water column within 13 km of the outfall terminus. In the first 20 km from the outfall, SF6surface concentrations were highly variable, while beyond this the SF6 concentrations decreased monotonically going northward. The currents were measured during the study with a bottom-mounted acoustic Doppler current profiler (ADCP) located 5.5 km from the outfall. Velocities were variable in magnitude and direction but showed a net northward flow during the 6-day study. Maximum concentrations decreased by about 200-fold per kilometer from the outfall to the northern end of the study area. The study shows that SF6 is an effective method to trace point source releases far from their origin

Capacidade de resistência a altas e baixas temperaturas em operárias de Scaptotrigona postica (Latreille) (Hymenoptera, Apidae) durante os períodos de verão e inverno Capacity of resistance to high and low temperatures in workers of Scaptotrigona postica Latreille (Hymenoptera, Apidae) during periods of summer and winter

As abelhas sem ferrão são consideradas por muitos autores de grande importância para o ecossistema devido a sua eficiência como polinizadoras. O presente trabalho estudou a tolerância de operárias de Scaptotrigona postica (Latreille, 1807) à mudanças de temperatura, com o objetivo de determinar os limites térmicos letais (TL - temperatura letal) para altas e baixas temperaturas durante o verão e inverno. Os resultados mostraram um intervalo de tolerância entre -3,5ºC e 40ºC no verão e de -4,0 até 39,5ºC no inverno a 50% de sobrevivência de uma população (LT50). Os limites a 100% de mortalidade (LT100) foram entre -5ºC e 41ºC no verão e -5ºC e 40,5ºC no inverno.<br>Stingless bees are considered of great importance for the ecosystem by many authors because of their efficiency as pollinators. The present work studied the tolerance of workers of Scaptotrigona postica (Latreille, 1807) to temperature changes in order to determine the lethal thermal limits for high and low temperatures (LT - lethal temperature) during summer and winter. The results showed a tolerance interval between -3,5ºC and 40ºC in summer and of 4ºC up to 39,5ºC in winter for 50% of mortality (LT50). The thermal limits at 100% of mortality (LT100) was between 5ºC and 41ºC in summer and between 5ºC and 40,5ºC in winter