Design and development of a digital farmer field school. Experiences with a digital learning environment for cocoa production and certification in Sierra Leone

This article reports on the design and development of the Digital Farmer Field School (DFFS). The DFFS offers a tablet-based digital learning environment for farmers and extension agents for knowledge sharing and knowledge co-creation. It provides an alternative to conventional agricultural extension training and monitoring. The prototype DFFS applies Farmer Field School (FFS) learning principles and is designed and developed following user experience (UX) design principles and user interface (UI) design principles from a responsible innovation perspective, using existing FFS material and tailored films which support and enrich the content. The prototype DFFS has been tested in Sierra Leone to assess its success in providing a substitute for face-to-face voluntary sustainability standard certification training for cocoa farmers. Results show that the DFFS as an off-line, telephonically connected and regular on-line updated learning platform offers an appropriate environment in which collective and individual learning is stimulated and facilitated. The DFFS prototype was socio-culturally and technologically appropriate and fitted the operational and strategic communication skills of cocoa farmers and other value chain stakeholders. Films capturing the testing are available as additional learning media.     

Erosion wear and mechanical properties of plasma-sprayed nickel- and iron-based coatings subjected to service conditions in boilers

The erosion wear and mechanical properties after exposure to simulated industrial service conditions in boilers of nickel-based, iron-based and chromium–nickel plasma-sprayed coatings on carbon steel and stainless steel have been obtained. These types of coatings are used as heat transfer and structural elements in boilers. Different tests simulating boiler service conditions under standard and extreme situations were carried out at 400, 600 and 800°C in a laboratory combustion unit. The influence of high temperature oxidation processes on the adherence, microhardness, microstructure, and wear erosion behaviour of both base materials and coatings have been evaluated.     

Effect of the O2/CO2 ratio and welding current on the geometry of square groove weld joints in low carbon steels obtained with GMAW

Welding with fusible electrode and shielding gas (GMAW) using a shielding mixture based on CO₂ + O₂ is a procedure with high potential for joining low-carbon and low-alloy steels compared with traditional mixtures based on argon. One of the reasons for this is related to the possibility of achieving a high penetration level without the need to increase the heat supply of the electric arc, by employing the shielding mixture of CO₂ + O₂, and the consequent decrease in the consumption of energy carriers. For that reason, the present paper presents a study on the influence of the shielding atmosphere characteristics (O₂/CO₂ ratio) and the welding current in the geometry of square groove weld joints on plates. For this purpose, a factorial experimental design was applied to obtaining regression equations, which would map such a behaviour. The equations were obtained using the O₂/CO₂ ratio and the welding current as independent variables. Nomograms were also plotted in order to make it easier to apply the results of this paper.     

Active correlation technology applied to maintenance program based on voltage sags control

This paper presents an Active Correlation Technology (ACT) for voltage sag detection and control. ACT is a conceptual architecture developed by IBM and can be successfully implemented to manage maintenance activities of distribution networks. As an instrument, maintenance clearly impacts on system reliability and quality of supply, i.e., very limited maintenance will result in an excessive number of costly failures and poor system performance, and therefore, reliability and quality of supply are degraded; done often, both reliability and quality of supply may improve but the cost of maintenance will sharply increase. Efficient maintenance schemes consider condition monitoring and maintenance activities are performed when a threshold pattern is violated. In this paper, a correlation engine is proposed to set voltage sag threshold patterns to detect abnormal sag incidence on MV feeders and trigger alarms to indicate the need for maintenance activities. The central ideas are validated with records obtained from a medium voltage circuit operated by one of the distribution divisions of the Mexican utility.     

Phase diagram of different epoxy-amine precursors modified with a thermoplastic: Effect of structure of epoxy-amine system on miscibility

The miscibility of a thermoplastic with the precursors of different epoxy-amine systems was analyzed thermodynamically in which the dependence of interaction parameter on temperature and composition χ (T, ?) and the polydispersity of components were considered. The epoxy-amine precursors were different only in the nature of amino groups, which were provided by a monoamine and a diamine in different proportions. Cloud-point curves were measured for five unreacted modified systems resulting that miscibility of the system increased with the proportion of monoamine. The thermodynamic analysis was realized in two steps: first, the model was applied to each system individually and secondly, a general equation for χ (T, ?) depending on the monoamine-diamine proportion was searched and used to analyze all systems together. Theoretical calculations of cloud-point curves, shadow curves, spinodal curves, critical points, vitrification curves and species distributions were realized and discussed for those systems.     

Strain rate and loading modes in DMTA experiments on ethylene/propylene block copolymers

A broad experimental programme using Dynamical–Mechanical Thermal Analysis (DMTA) was carried out on ethylene/propylene block copolymers (EPBC). The samples were subjected to frequency scans to evaluate the dependence of stored modulus on frequency. Tests were conducted on similar samples using different loading modes such as single cantilever, dual cantilever and tension configurations. If the stored modulus is plotted versus the test frequency, a different trend corresponding to each loading mode is obtained. Similar conclusions can be drawn regarding the glass transition temperature. In this work, strain rate, instead of frequency, is used to compare results provided by different loading modes. If the strain rate is used as the reference variable, a unique trend is observed despite the loading modes used to perform the experiment.     

Analysis of linear time-varying systems via Hartley series

A method for finding approximated solutions of linear time-varying systems via Hartley series is proposed. The most relevant properties of the Hartley series are presented first. The operational matrix of integration together with the product and coefficient matrices are developed. They are used to transform dynamical equations of linear, time varying systems to a set of linear algebraic equations. Practical applications relating to the operation of electric networks are given.     

The Stratosphere platform for big data analytics

We present Stratosphere, an open-source software stack for parallel data analysis. Stratosphere brings together a unique set of features that allow the expressive, easy, and efficient programming of analytical applications at very large scale. Stratosphere’s features include “in situ” data processing, a declarative query language, treatment of user-defined functions as first-class citizens, automatic program parallelization and optimization, support for iterative programs, and a scalable and efficient execution engine. Stratosphere covers a variety of “Big Data” use cases, such as data warehousing, information extraction and integration, data cleansing, graph analysis, and statistical analysis applications. In this paper, we present the overall system architecture design decisions, introduce Stratosphere through example queries, and then dive into the internal workings of the system’s components that relate to extensibility, programming model, optimization, and query execution. We experimentally compare Stratosphere against popular open-source alternatives, and we conclude with a research outlook for the next years.     

Parameter Estimation Using An Orthogonal Series Expansion

This paper presents an innovative alternative to estimate parameters of a system for which a dynamic model is known. The focus of this paper is the estimation of the armature circuit parameters of large utility generators using real time operating data. Other applications are possible. The alternatives considered are the use of orthogonal series expansions, in general, and the Hartley series, in particular. The main idea considers the use of orthogonal series expansions for fitting operating data (e.g., voltage and currents measurements). This allows writing a set of linear algebraic equations that can be “ solved” in the least squares sense for the unknown parameters. The method shown utilizes the pseudoinverse in the solution. The essence of the approach is linear state estimation. Several alternative types of orthogonal expansions are briefly discussed. Although solutions are the same in all domains, one wishes to employ the expansion that gives the most efficient computation. The approach may be used for static as well as dynamic problems. The approach is tested for noise corruption likely to be found in measurements. The method is found to be suitable for the processing of digital fault recorder data to identify synchronous machine parameters.