Browsing by Subject "Estimates"

Now showing 1 - 2 of 2
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    Accurate Recovery of H i Velocity Dispersion from Radio Interferometers
    (2017) Ianjamasimanana, R; Blok, W J G de; Heald, George H
    Gas velocity dispersion measures the amount of disordered motion of a rotating disk. Accurate estimates of this parameter are of the utmost importance because the parameter is directly linked to disk stability and star formation. A global measure of the gas velocity dispersion can be inferred from the width of the atomic hydrogen (H I) 21 cm line. We explore how several systematic effects involved in the production of H I cubes affect the estimate of H I velocity dispersion. We do so by comparing the H I velocity dispersion derived from different types of data cubes provided by The H I Nearby Galaxy Survey. We find that residual-scaled cubes best recover the H I velocity dispersion, independent of the weighting scheme used and for a large range of signal-to-noise ratio. For H I observations, where the dirty beam is substantially different from a Gaussian, the velocity dispersion values are overestimated unless the cubes are cleaned close to (e.g., ˜1.5 times) the noise level.
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    Factors affecting the accuracy of quantity surveyors pre-tender price forecasts in South Africa
    (1992) Pearl, Robert Gilfillan; Stevens, A.J.
    The primary purpose of this dissertation is to identify the factors which affect the accuracy of South African quantity surveyors' pre-tender price forecasts. Prices submitted by bidders at the tender submission stage of project development are utilised as the best practical measure for establishing the degree of accuracy achieved. A large number of design price forecasting techniques are available to estimators. Many of the techniques used in the early stages of design are applicable for providing budget amounts for design control purposes, whilst others are more· appropriate for forecasting anticipated tender sums. Features of price forecasting requiring attention at all stages of design development are identified as: (i) the influence of uncertainty inherent in the process, (ii) data / information availability and management, and (iii) the utilization of tendering data by means of 'feedback' systems. The factors affecting the accuracy of price forecasts are examined by means of a literature study, opinion surveys of estimators and empirical research on the results of estimate /tender comparisons. The relevance of the question of pre-tender price forecasts is demonstrated by the results of the study which indicates that the accuracy and reliability of South African quantity surveyors' estimates produced at the tender stage is inferior to that generally found overseas and do not meet the expectations of architects and clients. The conclusions drawn from this study indicate a distinct potential for improvement in early design stage price management.