Gas tungsten arc welding of NiTi shape memory alloy

Shape memory alloys are characterized by the ability of recovering their initial shape after being deformed and by superelasticity. Since the discovery of these alloys, a new field of interest emerged not only for the scientific community but also to many industries. However, these alloys present poor machinability which constitute a constrain in the design of complex components for new applications. Thus, the demand for joining techniques able to join these alloys without compromising their properties became of great importance to enlarge the complexity of existing applications. Literature shows that these alloys are joined mainly using laser welding. In the present study, similar NiTi butt joints, were produced using TIG welding. The welds were performed in 1.5 mm thick plates across the rolling direction. A special fixture and gas assist device was designed and manufactured. Also a robot arm was adapted to accommodate the welding torch to assure the repeatability of the welding parameters. Welds were successfully achieved without macroscopic defects, such as pores and distortions. Very superficial oxidation was seen on the top surface due to insufficient shielding gas flow on the weld face. The welded joints were mechanically tested and structurally characterized. Testing methods were used to evaluate macro and microstructure, as well as the phase transformation temperatures, the mechanical single and cyclic behaviour and the shape recovery ability. Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), microhardness measurements were techniques also used to evaluate the welded joints. A depletion in Ni in the fusion zone was seen, as well as a shift in Ms temperature. For strain values of 4% the accumulated irrecoverable strain was of about 30% and increased with the strain imposed during cycling. Nevertheless, a complete recovery of initial shape was observed when testing the shape memory effect on a dedicated device that introduces a deformation of 6.7%. That is, the welding procedure does not remove the ability of the specimens to recover their initial shape.

40 K Liquid Neon Energy Storage Unit

A thermal Energy Storage Unit (ESU) could be used to attenuate inherent temperature fluctuations of a cold finger, either from a cryocooler working or due to sudden income heat bursts. An ESU directly coupled to the cold source acts as a thermal buffer temporarily increasing its cooling capacity and providing a better thermal stability of the cold finger (“Power Booster mode”). The energy storage units presented here use an enthalpy reservoir based on the high latent heat of the liquid-vapour transition of neon in the temperature range 38 - 44 K to store up to 900 J, and that uses a 6 liters expansion volume at RT in order to work as a closed system. Experimental results in the power booster mode will be described: in this case, the liquid neon cell was directly coupled to the cold finger of the working cryocooler, its volume (12 cm3) allowing it to store 450 J at around 40 K. 10 W heat bursts were applied, leading to liquid evaporation, with quite reduced temperature changes. The liquid neon reservoir can also work as a temporary cold source to be used after stopping the cryocooler, allowing for a vibration-free environment. In this case the enthalpy reservoir implemented (24 cm3) was linked to the cryocooler cold finger through a gas gap heat switch for thermal coupling/decoupling of the cold finger. We will show that, by controlling the enthalpy reservoir’s pressure, 900 J can be stored at a constant temperature of 40 K as in a triple-point ESU.

Building a thinner gap in a gas-gap heat switch

25th International Cryogenic Engineering Conference and the International Cryogenic Materials Conference in 2014, ICEC 25–ICMC 2014

Young adults' preferences and satisfaction levels in Duty-free shopping in airports

This study aims to explore and understand what young adults’ duty free shoppers (18-26 years old) want and are getting from travel retail shopping on airport environments and to evaluate their satisfaction levels with the service. It has important managerial contributions since it is an important target in a fast growing market. An online survey was conducted with 188 young adults and its results show that young adults’ are somewhat satisfied with the overall service on duty free stores mainly in what concerns quality of the products and physical evidence of the stores. Results also show that the majority of buyers within this segment are price driven and strongly influenced by promotions associated with price reductions, and do not seem very satisfied with respect to that. Keywords: Young

Galp Energia Oil & Gas

Equity research report

Sol-gel entrapped biosystems: enzyme(s) and whole cells

In this work two different procedures to utilize the sol-gel technology were applied to immobilize/encapsulate enzymes and living cells. CO2 has reached levels in the atmosphere that make it a pollutant. New methods to utilize this gas to obtain products of added value can be very important, both from an environmentally point of view and from an economic standpoint. The first goal of this work was to study the first reaction of a sequential, three-step, enzymatic process that carries out the conversion of CO2 to methanol. Of the three oxidoreductases involved, our focus was on formate dehydrogenase (FateDH) that converts CO2 to formate. This reaction requires the presence of the cofactor β-nicotinamide adenine dinucleotide in reduced form (NADH). The cofactor is expensive and unstable. Our experiments were directed towards generating NADH from its oxidized form (NAD+), using glutamate dehydrogenase (GDH). The formation of NADH from NAD+ in aqueous medium was studied with both free and sol-gel entrapped GDH. This reaction was then followed by the conversion of CO2 to formate, catalysed by free or sol-gel entrapped FateDH. The quantification of NADH/NAD+ was made using UV/Vis spectroscopy. Our results showed that it was possible to couple the GDH-catalyzed generation of the cofactor NADH with the FateDH-catalyzed conversion of CO2, as confirmed by the detection of formate in the medium, using High Performance Liquid Chromatography (HPLC). The immobilization of living cells can be advantageous from the standpoint of ease of recovery, reutilization and physical separation from the medium. Also dead cells may not always exhibit enzymatic activities found with living cells. In this work cell encapsulation was performed using Escherichia coli bacteria. To reduce toxicity for living organisms, the sol-gel method was different than for enzymes, and involved the use of aqueous-based precursors. Initial encapsulation experiments and viability tests were carried out with E. coli K12. Our results showed that sol-gel entrapment of the cells was achieved, and that cell viability could be increased with additives, namely betaine that led to greater viability improvement and was selected for further studies. For an approach to “in-cell” Nuclear Magnetic Resonance (NMR) experiments, the expression of the protein ctCBM11 was performed in E. coli BL21. It was possible to obtain an NMR signal from the entrapped cells, a considerable proportion of which remained alive after the NMR experiments. However, it was not possible to obtain a distinctive NMR signal from the target protein to distinguish it from the other proteins in the cell.

Noble energy oil & Gas

Equity research report