Institutional Repository | North-West University | NWU
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The NWU-IR digital repository system captures, stores, indexes, preserves, and distributes digital research material.2018-08-16T07:00:51ZStrategies to reduce traffic accident rates in developing countries: lessons learned for assessment and management
http://hdl.handle.net/10394/30711
Strategies to reduce traffic accident rates in developing countries: lessons learned for assessment and management
Schoeman, I.M.
Strategy formulation and approaches in assessment and management of traffic engineering challenges related to the impact of traffic accidents on road networks in developing countries is problematic. The core focus of this paper consists of research output derived from traffic accident data available in South Africa. The availability of traffic accident data will be assessed to formulate applicable intervention traffic management strategies. Furthermore, the paper will include a statistical analysis and projection of such road traffic accident data in order to derive at certain tendencies from existing realities.
From the outcome of the research lessons learned for improved traffic planning, management and formulation of intervention strategies in developing countries will be deduced. Improved traffic and transportation planning practices is a priority in developing countries and economies and will guide resilient and sustainable traffic planning in developing countries
2018-01-01T00:00:00ZStandard versus strict bounded real lemma with infinite-dimensional state space. I. The state-space-similarity approach
http://hdl.handle.net/10394/30710
Standard versus strict bounded real lemma with infinite-dimensional state space. I. The state-space-similarity approach
Ball, Joseph A.; Groenewald, Gilbert J.; Ter Horst, Sanne
The bounded real lemma, i.e., the state-space linear matrix inequality characterization (referred to as Kalman--Yakubovich--Popov or KYP-inequality) of when an input/state/output linear system satisfies a dissipation inequality, has recently been studied for infinite-dimensional discrete-time systems in a number of different settings: with or without stability assumptions, with or without controllability/observability assumptions, with or without strict inequalities. In these various settings, sometimes unbounded solutions of the KYP-inequality are required while in other instances bounded solutions suffice. In a series of reports we show how these diverse results can be reconciled and unified. This first instalment focusses on the state-space-similarity approach to the bounded real lemma. We shall show how these results can be seen as corollaries of a new state-space-similarity theorem for infinite-dimensional linear systems
2018-01-01T00:00:00ZA study of the stability properties of Sagdeev solutions in the ion-acoustic regime using kinetic simulations
http://hdl.handle.net/10394/30709
A study of the stability properties of Sagdeev solutions in the ion-acoustic regime using kinetic simulations
Hosseini-Jenab, S.M.; Spanier, F.; Brodin, G.
The Sagdeev pseudo-potential approach has been employed extensively in theoretical studies to determine large-amplitude (fully) nonlinear solutions in a variety of multi-species plasmas. Although these solutions are repeatedly considered as solitary waves (and even solitons), their temporal stability has never been proven. In this paper, a numerical study of the Vlasov-Poisson system is made to follow their temporal evolution in the presence of numerical noise and thereby test their long-time propagation stability. Considering the ion-acoustic regime, both constituents of the plasma, i.e., electrons and ions are treated following their distribution functions in these sets of fully-kinetic simulations. The findings reveal that the stability of the Sagdeev solution depends on a combination of two parameters, i.e., velocity and trapping parameter. It is shown that there exists a critical value of trapping parameter for both fast and slow solutions which separates stable from unstable solutions. In the case of stable solutions, it is shown that these nonlinear structures can propagate for long periods, which confirms their status as solitary waves. Stable solutions are reported for both Maxwellian and Kappa distribution functions. For unstable solutions, it is demonstrated that the instability causes the Sagdeev solution to decay by emitting ion-acoustic wave-packets on its propagation trail. The instability is shown to take place in a large range of velocities and even for Sagdeev solutions with a velocity much higher than the ion-sound speed. Besides, in order to validate our simulation code, two precautionary measures are taken. First, the well-known effect of the ion dynamics on a stationary electron hole solution is presented as a benchmarking test of the approach. Second, In order to verify the numerical accuracy of the simulations, the conservation of energy and entropy is presented
2018-01-01T00:00:00ZOptimizing tracking error-constrained portfolios
http://hdl.handle.net/10394/30708
Optimizing tracking error-constrained portfolios
Maxwell, Michael; Daly, Michael; Thomson, Daniel; Van Vuuren, Gary
Active portfolios subject to tracking error (TE) constraints are the typical setup for active
managers tasked with outperforming a benchmark. The risk and return relationship of such
constrained portfolios is described by an ellipse in traditional mean-variance space and the
ellipse
’
s flat shape suggests an additional constraint which improves the performance of the
active portfolio. Although subsequent work isolated and explored different portfolios subject to
these constraints, absolute portfolio risk has been consistently ignored. A different restriction
–
maximization of the traditional Sharpe ratio on the constant TE frontier in absolute risk/return
space
–
is added here to the existing constraint set, and a method to generate this portfolio is
explained. The resultant portfolio has a lower volatility and higher return than the benchmark, it
satisfies the TE constraint
and
the ratio of excess absolute return to risk is maximized (i.e.
maximum Sharpe ratio in absolute space)
2018-01-01T00:00:00Z