1 

Critical Dynamics : The Expansion of the Master Equation Including a Critical Point
In this thesis it is shown how to solve the master equation for a Markov process including a critical point by means of successive approximations in terms of a small parameter. A critical point occurs if, by adjusting an externally controlled quantity, the system shows a transition from normal monostable to bistable behaviour. Examples of the external quantity (the pump parameter) are temperature, electric discharge current, chemical concentrations and mechanical force. The appropriate small parameter may be either the diffusion coefficient or the inverse size of the system. The latter is usually given by the volume or by the total number of constituents such as spins, photons or molecules. The fundamental idea of the theory is to separate the master equation into its proper irreducible part and a corrective remainder. The irreducibleor zeroth order stochastic approximation will be a relatively simple FokkerPlanck equation that contains the essential features of the process. Once the solution of this irreducible equation is known, the higher order corrections in the original master equation can be incorporated in a systematic manner. In part I of this thesis we consider the problem of diffusion in an externally applied potential showing a monostable to bistable transition. The appendix of part I presents a discussion of the irreducible solutions. In part II we examine the general Markov process. The appendix of part II is devoted to an example, namely the magnetic mean field Ising model.

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2 

Spectra and pseudospectra of neutral delay differential equations with application to realtime substructuring
This paper deals with the computation of pseudospectra of neutral delay differential equations (NDDEs) with fixed finite delays. This method provides information on the sensitivity of eigenvalues of the system under perturbations of a given size, allowing one to analyse uncertainties in, for example, structural dynamical systems. Furthermore, pseudospectra computations are a fast and efficient method by which to identify the spectra of NDDEs in any chosen part of the complex plane. This is of particular advantage as the spectra of NDDEs consists of infinitely many eigenvalues. We illustrate these methods by considering a scalar secondorder NDDE with one or more fixed delays. Such systems are used to model realtime substructuring experiments, where the delay arises from the response time of actuator(s) forming a coupling between a numerical model and the substructure being tested. We identify changes in the stability and sensitivity to perturbation of this system both as the delay time and as the mass of the substructure are varied. In particular, the latter reveals an essential instability in which infinitely many eigenvalues move to the righthalf plane. Finally, we investigate the relationship between pseudospectra and the effect of periodic forcing on the substructured system. Copyright Â© 2009 Springer Science+Business Media B.V.

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3 

Salinization effects on the water sorption of porous building materials
The interaction of salt transport and moisture transport plays a crucial role in some deterioration mechanisms of porous building materials. For this reason it has been an important research subject for mant' years. Yet most research was still complicated by the lack of experimental techniques capable of measuring., salt content. Therefore TNO initiated some research projects. in which the development and 'practical use' of such experimental techniques are central issues. Part of the research focuses on the hygroscopic response of salinized porous materials. For a typical firedclay brick and a calcium silicate brick, both salted with sodium chloride. the sorption isotherm was measured continuously by means of Microcalorimetry. The firedclay brick contained no micropores and consequently the sorption isotherm was determined by sodium chloride only. The calcium silicate brick. however contained a reasonable amount of micropores so that the sorption isotherm was determined both by sodium chloride and by capillary condensation in the micropores. This paper shows that the measured adsorption isotherms can be predicted by a modified Kelvin equation accounting for capillary condensation at a solutionvapour interface

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4 

Path control in limit handling and drifting conditions using State Dependent Riccati Equation technique
Tyres operated at or close to their friction limits show a highly nonlinear motion to force response. This state is called limit handling. The objective of this research is to minimize lateral path tracking error while the tyres operate in limit handling. The State Dependent Riccati Equation technique is employed to develop a feedbackfeedforward steering controller. It gives a systematic approach to take into account model nonlinearities such as combined slip tyre characteristics. Furthermore, the controller is implemented in a test vehicle and tested on a low friction skid pad. The controller shows robust path tracking performance even when the rear wheels are operated beyond their friction limits, and large body sideslip prevails.

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5 

Environment dependent transition frequencies for RAM and Bellhop
Passivesonarperformance modelling requires the accurate estimation of the acoustic field for a broad range of frequencies in various environments. In this paper, we assess the suitability of a Gaussian Beam (Bellhop) and Parabolic Equation model (RAM), whereby we focus primarily on computational efficiency. For Parabolic Equation (PE) models the computation time increases with the number of gridpoints required to provide accurate results. Since the gridsize scales to the wavelength, the computation time generally increases with frequency. The computation time of Gaussian Beam models increases primarily with longer maximum range. Since lower frequencies result in relevant acoustic intensities at larger distances, this results in a computation time increase in case of lower frequencies. Our aim is to estimate a singlerun ‘transition frequency’ that determines which model is optimal in terms of computational costs, while ensuring that each model is subjected to a convergence criterion we set at 1 dB. We only consider singlefrequency runs in this paper. The transition frequencies are estimated for three different scenarios that vary in depth and sound speed profile (SSP). We find that RAM is the computationally efficient choice up to a transition frequency of about 11 kHz and 12 kHz in the case of the shallow water scenarios: Weston Case 1 and 4, respectively. For the deep water scenario, a Munk profile truncated at 1 km depth, RAM is found to be the most efficient choice up to about 4.5 kHz.

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6 

An integral quadratic constraint approach to the robust performance estimation problem of guidance loops
The problem of evaluating the performance of an uncertain guidance loop system is considered, when the uncertainty is described in terms of an integral quadratic constraint. The idea of the approach proposed in this paper is to determine the set of all possible state vector values at the end of the flight that are compatible with the model uncertainty and determine the upper and lower bound for the miss distance by solving two optimization problems on this set. The main theoretical result of the paper shows that this is a quadric that can be determined by the solving a differential Riccati equation and a set of coupled linear differential equations. Unfortunately, numerical experiments showed that the method is practically unusable for realistic models of guidance loops. A single integral quadratic constraint is a poor representation of the usual model uncertainties, meaning that the results are certainly too conservative. In addition, the optimization problem turns out to be badly conditioned in all cases of interest for homing guidance loop analysis. This is illustrated using a contrived numerical example based on a relatively wellbehaved linear timeinvariant system. Although in its present form, the approach taken in this paper did not achieve the results that were hoped for, the ideas advanced here, and some of the technical results are interesting in themselves and may be useful in future research on this theme.

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7 

Solving Algebraic Riccati Equation Real Time for Integrated Vehicle Dynamics Control
In this paper we present a comparison study of different computational methods to implement State Dependent Riccati Equation (SDRE) based control in real time for a vehicle dynamics control application. Vehicles are mechatronic systems with nonlinear dynamics. One of the promising nonlinear control methods to control vehicle dynamics is based on SDRE. In this method, an Algebraic Riccati Equation (ARE) is solved at each sample to generate the control signal. However solving ARE is computationally complex. In this work, Extended Kalman Filter (EKF) iterative, Schur, Eigenvector, and Hamiltonian methods to solve ARE real time are implemented and studied for their timing, accuracy, and feasibility. Three methods, Schur, Eigenvector, and Hamiltonian are found to have an average calculation time of 3.9, 2.5, and 1.6 milliseconds on a dSPACE real time processor. This timing is acceptable as the controller sampling time is 10 milliseconds. In addition to the least processing time, the Hamiltonian based approach yields the lowest quadratic cost for SDRE based Integrated Vehicle Dynamics Control (IVDC).

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8 

Modeling of thickness for semisolid foods
We investigated the relationship between orally perceived thickness and calculated shear stress on the tongue for mayonnaise and custard. To this end, the applicability of the models of Kokini et al. (1977), describing the mechanical breakdown in the mouth, have been tested. Within a limited range of shear stresses (mayonnaise < 150 Pa; custard < 30 Pa), there was a linear relationship between shear stress and thickness, in accordance with the work of Kokini et al. (1977). Beyond this range, the linear relationship breaks down and the thickness levels off with shear stress for both mayonnaise and custard. The relationship over the entire range of shear stresses used in this paper can be satisfactorily described by a semilogarithmic (Fechner) relation. For both types of products, the quality of the thickness prediction by the decreasingheight model and the constantheight model of Kokini et al. (1977) is similar. For most mayonnaises, the contribution of the lateral movement of the tongue to the shear stress in the decreasingheight model of Kokini et al. (1977) is orders of magnitude larger than the contribution of the squeezing or compression movement of the tongue towards the palate. This difference in magnitude is affected by the low value measured for the compression force and by the high values for material consistency K. The values for K are high because yieldstress behavior has been neglected when the flow curves were analyzed. For custard, the models of Kokini et al. (1977) are found to be less adequate. It is proposed that this is because the models ignore interactions with saliva. Several routes to improve the modeling by incorporating viscoelastic behavior were unsuccessful. Elongational stress and yield stress were neglected in all tested models. © Copyright 2005, Blackwell Publishing.

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9 

Stochastic Theory of Turbulence Mixing by Finite Eddies in the Turbulent Boundary Layer
Turbulence mixing is treated by means of a novel formulation of nonlocal Ktheory, involving sample paths and a stochastic hypothesis. The theory simplifies for mixing by exchange (strongeddies) and is then applied to the boundary layer (involving scaling). This maps boundary layer turbulence onto a nondiffusive (KuboAnderson or kangaroo) type stochastic process. The theory involves an exponent epsilon (with the significance of a Cantor set dimension if epsilon is less than 1). With expsilon approximately equal to 0.58 (epsilon approaches infinity in the diffusion limit) the ensuing mean velocity profile Ubar+ = f(y+) is in perfect agreement with experimental data. The nearwall (y approaches 0) velocity fluctuations agree with recent direct numerical simulations

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10 

Adaptive regenerative braking for electric vehicles with an electric motor at the front axle using the state dependent Riccati equation control technique
In this paper a novel adaptive regenerative braking control concept for electric vehicles with an electric motor at the front axle is presented. It is well known that the "phased" type regenerative braking systems of category B maximize the amount of regenerative energy during braking. However, there is an increased risk of maneuvering capability loss especially during cornering. An integrated braking controller which determines  in a single step  the desired yaw moment and allocates the braking demand between hydraulic brakes and electric motor during cornering is designed using the State Dependent Riccati Equation (SDRE) method. A unique method for deriving the State Dependent Coefficient (SDC) formulation of the system dynamics is proposed. Soft constraints are included in the state dynamics while an augmented penalty approach is followed to handle hard constraints. The performance of the controller has been evaluated for different combined corneringbraking scenarios using simulations in a Matlab/Simulink environment. For this an eight degrees of freedom (DOF) nonlinear vehicle model has been utilized. The numerical results show that the controller is able to optimize (locally) the amount of regenerative braking energy while respecting system's constraints such as tire force saturation, vehicle yaw rate and slip angle errors.

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11 

Additive diffusion from LDPE slabs into contacting solvents as a function of solvent absorption
This article describes the simultaneous diffusion of a migrant and a solvent in low density polyethylene (LDPE). The migrant (Irganox 1076) moves out of the slab, while the solvent (isooctane, nheptane or cyclohexane) moves inwards. Solvent absorption was measured separately by following the increase of the mass of the slab in time. It can be described by the Fick diffusion equation with a diffusivity depending on the solvent concentration, and an interface concentration depending on time. The final absorptions were 12% for isooctane, 14% for nheptane, and 29% for cyclohexane. Additive concentrations in the slab were determined at different positions by microtoming. Experiments were done for several contacting times. The concentration profiles were strongly affected by the solvent. A larger local solvent concentration increases the diffusivity of the migrant. The Fick equation with a migrant diffusivity depending on the solvent concentration gives a good description for the results with isooctane and nheptane. The description is less good for the measurements with cyclohexane (when the polymer swells strongly).

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12 

Modelling community, family, and individual determinants of childhood dental caries
This crosssectional study empirically tested a theoretical model of pathways and interrelationships among community, family, and individual determinants of childhood dental caries in a sample of 630, 6yearold children from the Netherlands. Children's decayed, missing, and filled teeth (dmft) scores were extracted from dental records. A validated parental questionnaire was used to collect data on sociodemographic characteristics, psychosocial factors, and oral hygiene behaviours. Data on neighbourhood quality were obtained from the Dutch Central Bureau of Statistics. Structural equation modelling indicated that the model was valid after applying a few modifications. In the revised model, lower maternal education level was related to poorer family organization, lower levels of social support, lower dental selfefficacy, and an external dental health locus of control. These, in turn, were associated with poorer oral hygiene behaviours, which were linked to higher levels of childhood dental caries. In addition, lower maternal education level and poorer neighbourhood quality were directly associated with higher caries levels in children. This model advances our understanding of determinants of childhood dental caries and the pathways in which they operate. Conception of these pathways is essential for guiding the development of cariespreventive programmes for children. Clues for further development of the model are suggested. © 2014 Eur J Oral Sci.

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13 

Employer attitudes towards peak hour avoidance
Peak Hour Avoidance is a relatively new Dutch mobility management measure. To reduce congestion frequent car drivers are given a financial reward for reducing the proportion of trips that they make during peak hours on a specific motorway section. Although previous studies show that employers are not eager to support mobility management measures, employers are nevertheless an important stakeholder. They can provide their employees with alternatives such as other travel times, work locations or travel modes and encourage their use. This paper investigates the attitudes of Dutch employers towards Peak Hour Avoidance. Exploring the factors that influence these attitudes may help to fully utilise employer support. The data from 103 employers were collected through a web questionnaire. A structural equation model on the employer support for Peak Hour Avoidance was estimated. The results demonstrate that the size of the organisation and sector only have an indirect effect on the support for Peak Hour Avoidance. Results reveal that most support for Peak Hour Avoidance can be expected from organisations who feel responsible for influencing the commuting behaviour of employees, that have human resource managers with a positive attitude towards Peak Hour Avoidance, with flexible working times and that have already implemented mobility management measures. The largest contribution to PHA that can be expected from employers is providing employees with flexible working times and encouraging employees to fully utilise this option as an alternative for driving in peak hours. This would not only be beneficial for PHA but for a wide range of mobility management initiatives as well.

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14 

Control allocation for for regenerative braking of electric vehicles with an electric motor at the front axle using the statedependent Riccati equation control technique
In this paper the systematic development of an integrated braking controller for a vehicle driven by an electric motor on the front axle is presented. The objective is to engage the electric motor only during braking, up to the point at which the vehicle reaches its manoeuvrability and stability limit. The control challenges are to distribute the braking effort correctly between the hydraulic brakes at the four tyres and the electric motor, to handle the tyre saturation and motor constraints effectively and to adapt the control allocation based on the vehicle’s states. The controller is designed using the statedependent Riccati equation control technique, the vehicle state estimation and the ‘magic formula’ tyre model. The statedependent Riccati equation control technique is a suboptimal control design technique for nonlinear systems. A novel method for constructing the statedependent coefficient formulation of the system dynamics is proposed. Soft constraints in the state dynamics are described, while an augmented penalty approach is suggested for handling the system’s hard constraints. The performance of the controller was evaluated for different braking scenarios using simulations in a MATLAB/Simulink environment. An eightdegreeoffreedom nonlinear vehicle model was utilized. The numerical results show that the controller suboptimizes the regenerative braking effort while considering the tyre force saturation, the motor torque limits, the vehicle yaw rate and the slip angle error. A comparison with a constrained linear quadratic regulator shows the advantages of the proposed controller.

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15 

Prediction of noise radiation from basic configurations of landing gears by means of computational aeroacoustics
Noise radiation from aircraft during the takeoff and landing has become a major issue for inhabitants living in the vicinity of airports and thus for regulation authorities and aircraft developers. However the numerical simulation of aeroacoustic noise, especially for complex geometries like a landing gear, remains one of the most difficult challenges in aeroacoustics. The present study, aiming at predicting noise radiation from basic geometries as well as the noise radiation of a simplified landing gear, employs a hybrid approach that combines a CFD simulation with the decoupled computational aeroacoustics (CAA) simulation. Flowinduced noise is assumed to originate from turbulence. Reynoldsaveraged NavierStokes equations with different closure approaches can be employed to gain the required turbulent quantities. Subsequently, quantities as the mean flow velocities, pressure, density, turbulent kinetic energy and dissipation rate of the CFD simulation are the starting point for the generation of the transient acoustic sources by the stochastic noise generation and radiation (SNGR) method. It is assumed that the acoustic phenomena do not provide feedback to the mean flow field and turbulence and thus a recalculation of the flow field is not required. Since the propagation of sound is insignificantly influenced by turbulent and viscous effects, it can be described by the Euler equations in the near field. The CAA simulation is extended with a Ffowcs Williams Hawkings (FWH) module that calculates the noise levels in the far field upon integrating the surface source terms on a porous FWH surface within the CAA domain. The results of the simulations are compared with experimental data, obtained by measurements in an acoustic wind tunnel.

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16 

Residual load carrying capacity of timber joints
Timber joints that have been preloaded for 2 to 8 years have been short term tested in accordance with EN 26891. The applied load levels varied between 30% and 50% of the average short term strength. The study comprised nailed, toothedplate and splitring joints. All joints were made of spruce and loaded in tension. The test results indicated no strength loss during this period. The strength of the preloaded joints was at least equal to the average short term strength of joints with no preloading prior to testing. Actually, the results indicate a slight increase in strength. The development of the strength of the joints in time is modelled with an exponential damage equation. The parameters of the damage equations have been determined on the basis of time to failure tests on the same types of joints.

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17 

Steadystate hydrazinium nitroformate (HNF) combustion modeling
Two simplified modeling approaches are used to model the combustion of hydrazinium nitroformate (HNF), N2H5·C(NO2)3. The condensed phase is treated by highactivationenergy asymptotics. The gas phase is treated by two limit cases: the classical highactivationenergy approximation and the recently introduced lowactivationenergy approach. This results in simplification of the gasphase energy equation, making an (approximate) analytical solution possible. The results of both models are compared with experimental results of HNF combustion. It is shown that the lowactivationenergy approach yields better agreement with experimental observations, for example, regression rate and temperature sensitivity, than the highactivationenergy approach.

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18 

Calculating traffic noise reduction at long distance using diffracting elements
A series of resonators alongside a road or railway can be used to diffract noise upwards to create a zone of noise reduction behind the elements. The company 4Silence developed the socalled Whisstone, a concrete block with 18 resonators of different depths designed to operate in a broad frequency range. Several measurements at short distance, up to 15 meters, have proven that a noise reduction up to 4 dB(A) can be achieved. To determine the noise reduction at long distances calculations are necessary, due to the uncertainties of ground and meteorological effects. In this paper a comparison between measurements and numerical results (FEM) at short distance is presented. The positive results of this comparison allow the numerical method to be applied at larger ranges, up to 600 meters, taking a downwind condition into account. To this end the FEM method is coupled to a Green's function parabolic equation method (GFPE). The calculations for long distances show noise reductions up to 5 dB in octave bands and 3 dB(A) for the broadband level. These results can be used to account for the diffracting elements in standard noise calculation models used in practice, such as the Dutch national standard model or Cnossos. © INTERNOISE 2018  47th International Congress and Exposition on Noise Control Engineering: Impact of Noise Control Engineering. All rights reserved.

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19 

Solution of surface water flow equations using Clebsch variables.
Conventionally, the flow equations for surface waters are obtained by integrating vertically the basic continuum conservation equations governing three‐dimensional motion, thus reducing the problem to two dimensions. However, when vertical transport is important, this model fails, and the basic equations for three‐dimensional motion must be solved directly. With the advent of super computers and attached array processors this has become feasible. In this paper a formulation based on so‐called Clebsch variables is presented. This formulation is basically equivalent to a formulation based on the vorticity. However, the formulation based on Clebsch variables does not exhibit the disadvantages of the formulation based on the vorticity. Since in the Clebsch representation an explicit expression for the pressure is available (generalized Bernoulli equation), this formulation may be considered as an extension of the well‐known potential theory for irrotational flow. A groundwater reservoir simulator solving for the pressure, temperature, and concentration can, in principle, be applied to determine the Clebsch variables describing flow in surface water, thus unifying the mathematical description of surface and subsurface hydrology. The conclusion is that a computer program based on a formulation with Clebsch variables is quite competitive, especially for three‐dimensional calculations where it should lead to a more economical use of the computer.

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20 

The relationships between work characteristics and mental health: Examining normal, reversed and reciprocal relationships in a 4wave study
This longitudinal study examined the causal relationships between job demands, job control and supervisor support on the one hand and mental health on the other. Whereas we assumed that work characteristics affect mental health, we also examined reversed causal relationships (mental health influences work characteristics). Further, the topic of the appropriate time lag for testing causal relationships was addressed. Our hypotheses were tested in a 4wave study among a heterogeneous sample of 668 Dutch employees using structural equation modelling. The results provide evidence for reciprocal causal relationships between the work characteristics and mental health, although the effects of work characteristics on wellbeing were causally predominant. The best model fit was found for a 1year time lag. Compared to earlierpredominantly crosssectionalresults, the present study presents a stronger case for the effects of work characteristics on the development of strain. The results also emphasize the need for a dynamic view of the relationship between work and health; the onedirectional viewpoint in many work stress models does not seem to fully capture the relations between work characteristics and wellbeing.

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