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Welcome to the NWU Repository, the open access Institutional Repository of the North-West University (NWU-IR). This is a digital archive that collects, preserves and distributes research material created by members of NWU. The aim of the NWU-IR is to increase the visibility, availability and impact of the research output of the North-West University through Open Access, search engine indexing and harvesting by several initiatives.

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Now showing 1 - 5 of 18

Recent Submissions

Grain Price Discovery and Location Differentials in South Africa
(Universitatea Danubius Galati, 2024) Daniel Mokatsanyane; Mariette Geyser
This paper investigates the price discovery process between white and yellow maize spot prices and their respective futures prices in South Africa's SAFEX market, aiming to understand how futures prices inform spot markets. Building on previous South African studies, it employs the Toda and Yamamoto VAR Granger Causality method to analyze daily time series data for white and yellow maize from July 15, 2009, to March 23, 2023, revealing causal relationships between spot and futures prices. Results show white maize spot prices are Granger-caused by white maize futures prices, suggesting short-run causality and demonstrating price discovery in the spot market. A similar pattern is observed for yellow maize. However, mixed results emerge when futures prices are tested as the dependent variable, showing both bidirectional and unidirectional relationships between spot and futures prices. These findings emphasize the importance of futures prices in shaping spot prices for both maize types; while spot prices reflect fundamentals like supply and demand, futures prices capture market sentiment and external influences, valuable for traders and policymakers. This study adds insights into price discovery dynamics in the South African maize market, with implications for agricultural commodity traders and market analysts through its robust econometric approach.
Power law slip boundary condition for Navier-Stokes equations: Discontinuous Galerkin schemes
(Springer Nature, 2024) J.K. Djoko; V.S. Konlack; T. Sayah
This study deals with the numerical analysis of several discontinuous Galerkin (DG) methods for the resolution of the Navier-Stokes equations with power law slip boundary condition. The physical context corresponding to this problem is the description of a flow when a position and the direction slip boundary condition is taken into consideration. The main goal in this work is to examine the solvability, convergence of several DG methods, and to discuss their practical resolution by means of fixed point iterative algorithm. Theoretical findings are backed up by solid computational results.
Discontinuous Galerkin methods for Stokes equations under power law slip boundary condition: a priori analysis
(Springer Nature, 2024) Djoko Kamdem Jules; Gidey Hagos; Koko Jonas; Sayah Toni
In this work, three discontinuous Galerkin (DG) methods are formulated and analysed to solve Stokes equations with power law slip boundary condition. Numerical examples exhibited confirm the theoretical findings, moreover we also test the methods on the lid Driven cavity and compare the three DG methods
Energy estimate for Oldroyd-B model under Tresca boundary condition: scheme preserving properties
(Springer Nature, 2024) J. K. Djoko; J. Koko; T. Sayah
This paper is concerned with the design of a numerical scheme that preserves; the symmetry, positive definiteness, and a priori estimate for the Oldroyd-B model with Tresca boundary condition. Such a scheme is important for its numerical stability, and for investigation of long time behaviour of macro-macro models. The theoretical findings are validated with simulations for lid driven cavity
Stokes flow with Tresca boundary condition: a posteriori error analysis
(Springer-Verlag Italia s.r.l., 2024) R. Agroum; J. K. Djoko; J. Koko; T. Sayah
In this article, a reliable a posteriori error estimate of residual type is derived for a variational inequality of second kind modeling Stokes equations with Tresca’s boundary condition. Two sources of the error are considered here; the discretization error and the linearization error. Balancing these two errors is crucial to design an adaptive strategy for mesh refinement. Numerical results are reported to illustrate the good performance of the estimator constructed