Stepwise and Pulse Transient Methods of Thermophysical Parameters Measurement

Stepwise transient and pulse transient methods are experimental techniques for measuring the thermal diffusivity and conductivity of solid materials. Theoretical models and experimental apparatus are presented, and the influence of the heat source capacity and the heat transfer coefficient is investigated using the experiment simulation. The specimens from low-density polyethylene (LDPE) and polymethylmethacrylate (PMMA) were measured by both methods. Coefficients of variation were better than 0.9 % for LDPE and 2.8 % for PMMA measurements. The time dependence of the temperature response to the input heat flux showed a small drop, which was caused by thermoelastic wave generated by thermal expansions of the heat source.     

Openness and Technology Diffusion in Payment Systems: The Case of NAFTA

We study the relationship between openness and payment system development. In particular, we analyze how the existence of technology diffusion from a more developed country fosters a transformation of payment choice in a less developed country. We apply our analysis to Mexico. Economic growth in Mexico was not high enough to cause a transformation of payment choice observed in the data after 2001. We argue that the switch towards electronic payments can be attributed to openness and related payment technology spillovers from the US in the context of NAFTA.     

Model complexity reduction of chemical reaction networks using mixed-integer quadratic programming

The model complexity reduction problem of large chemical reaction networks under isobaric and isothermal conditions is considered. With a given detailed kinetic mechanism and measured data of the key species over a finite time horizon, the complexity reduction is formulated in the form of a mixed-integer quadratic optimization problem where the objective function is derived from the parametric sensitivity matrix. The proposed method sequentially eliminates reactions from the mechanism and simultaneously tunes the remaining parameters until the pre-specified tolerance limit in the species concentration space is reached. The computational efficiency and numerical stability of the optimization are improved by a pre-reduction step followed by suitable scaling and initial conditioning of the Hessian involved. The proposed complexity reduction method is illustrated using three well-known case studies taken from reaction kinetics literature.     

A numerical reconstruction method in inverse elastic scattering

In this paper a new numerical method for the shape reconstruction of obstacles in elastic scattering is proposed. Initially, the direct scattering problem for a rigid body and the mathematical setting for the corresponding inverse one are presented. Inverse uniqueness issues for the general case of mixed boundary conditions on the boundary of our obstacle, which are valid for a rigid body as well are established. The inversion algorithm based on the factorization method is presented into a suitable form and a new numerical scheme for the reconstruction of the shape of the scatterer, using far-field measurements, is given. In particular, an efficient Tikhonov parameter choice technique, called Improved Maximum Product Criterion (IMPC) and its linchpin within the framework of the factorization method is exploited. Our regularization parameter is computed via a fast iterative algorithm which requires no a priori knowledge of the noise level in the far-field data. Finally, the effectiveness of IMPC is illustrated with various numerical examples involving a kite, an acorn, and a peanut-shaped object.     

Cyanidation kinetics of silver telluride (Ag2Te)

The extraction of precious metals from tellurides by cyanidation is more difficult than when they are in their native form, nevertheless the reason for their refractory nature has not been adequately supported. In this study, the mechanism of the cyanidation kinetics of silver telluride (Ag₂Te) was investigated. For this purpose, cyanidation experiments were carried out to: (1) study the difference between the cyanidation kinetics of elemental silver and silver telluride; (2) study the effect of temperature (i.e. 20, 25, 27, 30, 35 and 40°C) on silver telluride dissolution; and (3) elucidate the kinetic mechanism of the silver telluride cyanidation. The results obtained showed that: (1) while 83.5% of elemental silver was dissolved in 8?h, only 13.2% of silver from silver telluride was dissolved in the same time; (2) temperature has an important effect on silver extraction from silver telluride, but a minor effect on tellurium dissolution; and (3) at temperatures between 20 and 27°C, the process was controlled by the chemical reaction with an apparent activation energy of 191.9?kJ?mol^?1, whereas at temperatures between 30 and 40°C, the process was controlled by diffusion through a Ag₅Te₃ layer of products with an apparent activation energy of 25.2?kJ?mol^?1.     

Comparison of arc stability and variability of geometry of welds obtained by MIG/MAG and FCAW processes

Despite their similarity, the MIG/MAG and Tubular Electrode processes display particular features with regard to arc stability and variability in the characteristics of the beads. Thus, selection of one of these processes for a specific application will have to consider how these particular features affect the quality of the welds. To support this choice, the present study aimed to investigate how changing the average current affects the stability and regularity of metal transfer in welds carried out with constant voltage and pulsed current and compare the variability in the geometry and dilution of these welds. To achieve these aims, automatic welding was carried out, with steel ABNT 1020 as base metal and wire AWS ER70S-6 and AWS E71T-1 as filler metals. Besides the welds with variation in the average current, the tests involved determination of the parameters for occurrence of stable short circuiting, drop and pulsed transfer. The results showed that the voltage that gives the highest stability in short circuiting transfer is independent of the welding speed and increases with the wire speed, and also showed that welds made with hollow wire displayed greater variability compared to solid wire.     

A review of manufacturing flexibility: systematising the concept

The present work is an attempt to contribute to the conceptual systematisation of the manufacturing flexibility types by synthesising the vast literature available after a systematic review. We classified the papers in two perspectives (hierarchical and strategic), and engaged in a systematic process of standardisation of the definitions and names of various flexibility types leading to a better understanding of them. This process allowed us to clearly show: (a) the existence of a broader consensus in the field than expected; (b) that problems are limited to concrete aspects related to the level of analysis or the scope of certain flexibility types; (c) the possibility of a theoretical integration between the two perspectives which would permit a standardisation of the names and definitions for the flexibility types which make up the manufacturing flexibility construct.     

The human role in the age of information

Age of automation entails freedom from most of the common working roles. Signs are changes in employment, unemployment, professional structures, relevance of services, entertainment industry, working hours, and the nature of social relations. Warnings are suggested against voluntaristic interventions, neglect of social, historical relations. New approaches are required in the fields of lifelong education and in the education of socially disadvantaged people. The changes in evolutionary inherited motivations and life styles are critical challenges to mankind. Open society and lessons of system control are recommended.