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The potential of young, green finger-jointed Eucalyptus grandis lumber for roof truss manufacturing
Item type: Journal Article • Journal: Southern Forests: a Journal of Forest Science • Authors: Philip L Crafford --- Department of Forest and Wood Science, South Africa C Brand Wessels --- Department of Forest and Wood Science, South AfricaSouth Africa is a timber-scarce country that will most probably experience a shortage of structural softwood lumber in the near future. In this study the concept of using young, green finger-jointed Eucalyptus grandis lumber was evaluated for possible application in... -
Putting the squeeze on the sample covariance matrix for portfolio construction
Item type: Journal Article • Journal: Investment Analysts Journal • Authors: Brian Munro --- Cadiz Asset Management, The Terraces, South Africa David Bradfield --- Department of Statistical Sciences, South AfricaPortfolio construction plays a critical role in adding performance to a fund. Central to portfolio construction are the two primary inputs: the vector of forecast returns and the covariance matrix. Our focus is on the covariance matrix. With guidance from... -
Variation in selected solid wood properties of young Pinus patula from diverse sites in the Mpumalanga escarpment area in South Africa
Item type: Journal Article • Journal: Southern Forests: a Journal of Forest Science • Authors: Barry G Muller --- Nelson Mandela Metropolitan University, South Africa Josua H Louw --- Nelson Mandela Metropolitan University, South Africa Francois S Malan --- Research Centre, South Africa (retired)Regression analyses identified ‘Growth Days’ (an index expressing site moisture availability) as the only site variable contributing significantly to the prediction to wood density (R2 = 0.57), whereas the model predicting grain angle included only ‘Altitude’ (R2 = 0.60). These... -
A new approach for the mix design of (patch) repair mortars
Item type: Journal Article • Journal: African Journal of Science, Technology, Innovation and Development • Authors: Inès L. Tchetgnia Ngassam --- Department of Civil Engineering, South Africa Philemon Arito --- Department of Civil Engineering, South Africa Hans Beushausen --- Department of Civil Engineering, South AfricaThe failure of most repairs in concrete structures is mainly manifested in the form of cracking and/or debonding of the repair layer. These two repair mechanisms could lead to the continuous corrosion of reinforcing steel in concrete. Cracking and debonding... -
Effect of cassava starch on shrinkage characteristics of concrete
Item type: Journal Article • Journal: African Journal of Science, Technology, Innovation and Development • Authors: Akindehinde Ayotunde Akindahunsi --- Department of Civil Engineering, Nigeria Wolfram Schmidt --- BAM Federal Institute for Materials Research and Testing, GermanyThe use of starch and its derivatives in concrete as an admixture to modify relevant properties of concrete has been on the increase in recent times. It is known to modify the rheology, affect the hydration kinetics of cement, and... -
Risk-based portfolio sensitivity to covariance estimation
Item type: Journal Article • Journal: Investment Analysts Journal • Authors: Hannes du Plessis --- , Paul van Rensburg --- ,Risk-based portfolio construction methods focus on optimally extracting information from the covariance matrix of asset returns, as opposed to utilising forecasts of expected returns, in determining the portfolio allocation. This improves their robustness to estimation error in means, but this... -
Which shrinkage is better? Portfolio selection with a cleaned random matrix
Item type: Journal Article • Journal: Investment Analysts Journal • Authors: Young C. Joo --- Shanghai University, China Sung Y. Park --- Chung-Ang University, KoreaCovariance matrix estimation is of great importance in formulating a portfolio. The sample covariance matrix, the most frequently used estimator, is well known to be unstable due to the estimation error, when the sample size is small. A shrinkage approach... -
Adaptive Beta Shrinkage estimation of covariance matrices
Item type: Journal Article • Journal: Investment Analysts Journal • Authors: Henri Staal --- Department of Statistics and Actuarial Science, Stellenbosch University, South Africa Emlyn Flint --- Peresec, South AfricaAccurate estimation of the covariance matrix is essential for mean-variance portfolio optimisation, yet the sample covariance matrix is a notoriously noisy estimate, especially in high dimensions. Contemporary shrinkage methods attempt to mitigate this noise but often retain significant estimation error...