Environmental changes in the western Black Sea related to anthropogenic and natural conditions

The Black Sea northwestern shelf (NWS) ecosystem has been subjected to the strongest anthropogenic pressure of the entire Black Sea as about 80% of the freshwater runoff is discharged there.This paper presents a review of the global environmental changes related mainly to increased eutrophication in the western Black Sea basin.A case study (CoMSBlack 92a cruise) attempts to highlight the interaction of some natural and anthropogenic factors responsible for specific chemical and biological features in the western Black Sea environment. The significance of processes located near the Danube river mouth, which, due to their relatively small space scale, have not been recognized before, is clarified. Hydrological processess of specific importance to the distribution and transformation of antropogenic inputs are river plume dynamics, coastal upwelling and mixing and downwelling over the shelf break and slope in this part of the basin. A layer of low hydrological variability (“conservative layer”) appears to be a natural feature of the area, hypothesized to precondition specific biological and chemical processes there.The results suggest that the interplay between the Danube anthropogenic nutrient load with the natural hydrological fronts and gradients provides opportunities for enhanced biological activity thus contributing to the global environmental changes in the Black Sea NWS.     

Aspects of the stability of jack-up spud-can foundations

A three-level procedure for assessing jack-up foundation stability for more or less homogenous soils is described. The objective is to provide a rational framework for these assessments that ensures their safe operation in extended year-round operations and enables their use in deeper waters than at present.

The three levels of the procedure have to be entered successively as long as foundation stability cannot be proven. The first level is a screening exercise and essentially replaces the well-known preload check. The second level compares factored foundation loads resulting from a structural analysis with foundation capacities obtained with ultimate bearing capacity formulae. The most refined third level assesses whether the displacements associated with these loads lead to an acceptable situation, i.e. capacity increase and/or load redistribution that does not result in collapse of the jack-up unit.

Since, for maximum benefit, this third-stage analysis requires a non-linear foundation model to be linked with the structural package used: such a tool is provided in the paper. Examples are given to demonstrate the impact of the assessment procedure.

This procedure forms part of the overall in-house approach to the assessment of jack-ups and has already been offered to the jack-up industry as part of the continuing efforts towards establishing common and accepted standards for jack-up assessments. Further developments have been identified and will be pursued.     

Non-linear utility functions in models of travel choice behavior

Models of individual choice behavior have been extensively developed and used in travel prediction during the last ten years. These models are generally formulated with utility functions that are linear in parameters. Theories of economics and psychology suggest that the true relationship between service variables and utility is non-linear. In this paper we demonstrate that non-linear transformations of time and cost variables produce statistically significant improvements in the model estimated, have a theoretically appealing interpretation, and lead to managerially important differences in policy evaluations. These results support the need to refine the specification of choice utility functions based on theoretical considerations and empirical research.     

Spatial price equilibrium sensitivity analysis

A direct approach to performing sensitivity analysis for a spatial price equilibrium problem with nonlinear transportation cost, commodity supply and commodity demand functions is presented. The first order derivatives of all decision variables with respect to parameter perturbations are shown to be expressable in a simple from which requires inversion of a matrix whose rank is the number of regions considered. A typical network usually involves several hundred regions and several thousand links; thus, by working with a matrix whose rank depends only on the number of regions rather than the number of links, computer storage is minimized and the necessary matrix inversion is made feasible, enabling us to perform the sensitivity analyses of very large nonlinear equilibrium problems. An example is presented to demonstrate application of the method. The approach taken here is also adaptable to the sensitivity analysis of Wardropian equilibrium problems.     

An analysis of seasonality of non-OPEC supply

The purpose of this study is first to find out whether quarterly averages of non-OPEC (Organization of the Petroleum Exporting Countries) supply follow a seasonal pattern. If that is mathematically established, then, second, it is attempted to estimate the best seasonal factors to decompose the forecast yearly average into quarterly averages. A set of historical data consisting of quarterly supply averages of individual countries, regional subtotals and the aggregate non-OPEC supply for the period 1973-2002 forms the basis of the analysis. The study applies Fourier analysis to quarterly supply series to test for seasonality, and provides estimates of seasonal factors for the years 2000-2002 by applying the so-called X-11 decomposition method to the historical annual averages. The accuracy of the results of the application of X-11 is then tested. It is demonstrated that the combination of the Fourier and X-11 methods provides mostly acceptable and in some cases, such as that of China, impressively accurate forecast quarterly supply averages.     

Discrete Adaptive Active Suspension for Hardware Implementation

This paper presents a discrete adaptive control approach for an active suspension. The study involves formulation of an active suspension as a digital controller problem involving the time delays. A nonlinear time varying (NTV), single input single output (SISO) suspension model is considered for the analysis. A discrete model reference adaptive control (DMRAC) approach with recursive least square (RLS) estimation is used to form the controller. The controller is designed to maintain the static equilibrium irrespective of dynamic load variations as a disturbance force on the model. Simulation results for deterministic and stochastic inputs are presented to substantiate the approach. Results indicate good performance of adaptive controller even for large dynamic variations of the model and has the potential for a successful hardware implementation.     

The legal framework

The major and minor ports in India operate within different legal frameworks. Both allow privatization, but impose different conditions. Administrative culture has acted as a constraint on privatization in the major ports; private development at the minor ports has been very responsive to the amount of assistance offered by individual States.     

Application of Sensitivity Methods to Analysis and Synthesis of Vehicle Dynamic Systems

The development and application of sensitivity methods for determining the effects of parameter changes on the response of vehicle dynamic systems is presented. The procedures shown can be used to enhance the analysis and synthesis processes of virtually any road or rail vehicle system regardless of its complexity. The parametric sensitivity of vehicle models in time domain, steady state models and vehicle models in frequency domain can be investigated using different types of sensitivity functions, both dimensional and dimensionless including first order standard, percentage, logarithmic, second order standard, and logarithmic and percentage sensitivity measures. These sensitivity functions and measures are determined as functions of partial derivatives of system variables taken with respect to system parameters. In the case of sensitivity functions in the frequency domain the variable values are computed as either the magnitude or phase angle of a complex element of the transfer function matrix. The methods presented enable to determine the influence of all system primary (constant) and secondary (non-constant) parameters on system primary and secondary variables. The primary variables are state variables or elements of the transfer function matrix and the secondary variables may be any functions of primary variables and system parameters. Typical secondary system parameters which can be examined include initial conditions, time variant coefficients, natural frequencies, loads, and typical secondary variables are forces, weight transfers, stability factors and energy components. The analysis of sensitivity results obtained for three vehicle handling models in both linear and nonlinear regimes of vehicle performance and utilizing various types of sensitivity functions is also presented.     

Urban travel demand: The impact of Box-Cox transformations with nonspherical residual errors

We develop an algorithm for solving regression models with Box-Cox transformations on both the dependent and independent variables, while simultaneously taking into account corrections for serial correlation of several orders and for heteroscedasticity. The latter correction is of a general form which contains as special cases most specifications of heteroscedasticity found in practice. We apply the procedure to three urban travel demand functions, two of which are currently used in their linear form by the Montreal Transit Authority, and analyze more than 100 specifications. Our results show that taking into account nonsphericalness of the residuals has a major impact on model parameter estimates, notably on those which determine the functional form of the model, and that, conversely, modifications of the functional form have strong implications for both the structure of autocorrelation and the importance of heteroscedasticity; moreover, we find interactions between autocorrelation and heteroscedasticity structures. We introduce a special measure of elasticity for variables which contain zero observations, particularly dummy variables. Moreover, we find that elasticities of demand and implicit values of time depend to a large extent on the stochastic specification of the model.