Browsing by Subject "Laws and legislation"

Now showing 1 - 3 of 3

Open Access
Financial earthquakes, aftershocks and scaling in emerging stock markets
(Elsevier BV, 2004) Selçuk, F.
This paper provides evidence for scaling laws in emerging stock markets. Estimated parameters using different definitions of volatility show that the empirical scaling law in every stock market is a power law. This power law holds from 2 to 240 business days (almost 1 year). The scaling parameter in these economies changes after a change in the definition of volatility. This finding indicates that the stock returns may have a multifractal nature. Another scaling property of stock returns is examined by relating the time after a main shock to the number of aftershocks per unit time. The empirical findings show that after a major fall in the stock returns, the stock market volatility above a certain threshold shows a power law decay, described by Omori's law. © 2003 Elsevier B.V. All rights reserved.
Open Access
Ionospheric total electron content estimation using IONOLAB method
(IEEE, 2007) Nayir, H.; Arıkan, F.; Erol, C. B.; Arıkan, Orhan
Ionosphere which is an important atmospheric layer for HF and satellite communications, can be investigated through Total Electron Content (TEC). Global Positioning System provides cost-effective means for TEC estimation. Regularized TEC estimation method (D-TEI) is developed to estimate high resolution, robust TEC values. The method combines measurements of GPS satellites above 10° elevation limit and estimates can be obtained with 30 s time resolution. In this paper, parameters that are used in D-TEI method such as ionospheric height, weighting function, and satellite receiver biases are studied. It is found that TEC estimation results of D-TEI method is almost independent of ionospheric height. Different weighting functions are tried and the weighting function that minimizes non-ionospheric effects is selected. By using satellite and receiver biases in the correct form consistent TEC estimation results are obtained with IGS analysis centers. In this paper, the method is improved to include phase measurements. Taking either pseudorange or phase measurements as input, high resolution, robust TEC estimates are obtained using D-TEI method.
Open Access
Optimal timing of project control points
(Elsevier, 2000) Raz, T.; Erel, E.
The project control cycle consists of measuring the status of the project, comparing to the plan, analysis of the deviations, and implementing any appropriate corrective actions. We present an analytical framework for determining the optimal timing of project control points throughout the life cycle of the project. Our approach is based on maximizing the amount of information generated by the control points, which depends on the intensity of the activities carried out since the last control point and on the time elapsed since their execution. The optimization problem is solved with a dynamic programming approach. We report the results of numerical experimentation with the model involving different types of activity intensity profiles and several levels of information loss. For each combination, we compared the optimal amount of information to the amount of information obtained with two simpler policies: control at equal time intervals, and control at equal activity contents intervals. We also investigated the effect of adding more control points on the amount of information generated.