Modelling dynamic stochastic user equilibrium for urban road networks

In this study a dynamic assignment model is developed which estimates travellers' route and departure time choices and the resulting time varying traffic patterns during the morning peak. The distinctive feature of the model is that it does not restrict the geometry of the network to specific forms. The proposed framework of analysis consists of a travel time model, a demand model and a demand adjustment mechanism. Two travel time models are proposed. The first is based on elementary relationships from traffic flow theory and provides the framework for a macroscopic simulation model which calculates the time varying flow patterns and link travel times given the time dependent departure rate distributions; the second is based on queueing theory and models roads as bottlenecks through which traffic flow is either uncongested or fixed at a capacity independent of traffic density. The demand model is based on the utility maximisation decision rule and defines the time dependent departure rates associated with each reasonable route connecting, the O-D pairs of the network, given the total utility associated with each combination of departure time and route. Travellers' choices are assumed to result from the trade-off between travel time and schedule delay and each individual is assumed to first choose a departure time t, and then select a reasonable route, conditional on the choice of t. The demand model has therefore the form of a nested logit. The demand adjustment mechanism is derived from a Markovian model, and describes the day-to-day evolution of the departure rate distributions. Travellers are assumed to modify their trip choice decisions based on the information they acquire from recent trips. The demand adjustment mechanism is used in order to find the equilibrium state of the system, defined as the state at which travellers believe that they cannot increase their utility of travel by unilaterally changing route or departure time. The model outputs exhibit the characteristics of real world traffic patterns observed during the peak, i. e., time varying flow patterns and travel times which result from time varying departure rates from the origins. It is shown that increasing the work start time flexibility results in a spread of the departure rate distributions over a longer period and therefore reduces the level of congestion in the network. Furthermore, it was shown that increasing the total demand using the road network results in higher levels of congestion and that travellers tend to depart earlier in an attempt to compensate for the increase in travel times. Moreover, experiments using the queueing theory based travel time model have shown that increasing the capacity of a bottleneck may cause congestion to develop downstream, which in turn may result in an increase of the average travel time for certain O-D pairs. The dynamic assignment model is also applied to estimate the effects that different road pricing policies may have on trip choices and the level of congestion; the model is used to demonstrate the development of the shifting peak phenomenon. Furthermore, the effect of information availability on the traffic patterns is investigated through a number of experiments using the developed dynamic assignment model and assuming that guided drivers form a class of users characterised by lower variability of preferences with respect to route choice

Τα συστήματα λειτουργικής ενίσχυσης των ΑΠΕ και οι επιβαλλόμενες επιβαρύνσεις για τη χρηματοδότησή τους

Στο πρώτο μέρος, εξετάζεται η εξέλιξη των καθεστώτων στήριξης για την παραγωγή ενέργειας από ανανεώσιμες πηγές (ΑΠΕ). Παρατηρείται μια τάση από τον προστατευτισμό προς ένα "αγορακεντρικό μοντέλο". Ο προστατευτισμός εκδηλώνεται με την χορήγηση ενισχύσεων αποκλειστικά στην εγχώρια παραγωγή πράσινης ενέργειας, η οποία δικαιολογείται για λόγους προστασίας του περιβάλλοντος. Υπό το "αγορακεντρικό μοντέλο", οι ενισχύσεις χορηγούνται υπό την προϋπόθεση επιτυχούς συμμετοχής σε ανταγωνιστική διαδικασία. Στο δεύτερο μέρος, παρουσιάζεται η χρηματοδότηση των ΑΠΕ, η οποία βασίζεται στο ΕΤΜΕΑΡ, το οποίο επιβάλλεται στους καταναλωτές. Εξετάζεται η νομιμότητα της επιβάρυνσης υπό το συνταγματικό και το ενωσιακό δίκαιο. Με την κατάργηση των καθεστώτων στήριξης, η κρατική χρηματοδότηση των ΑΠΕ πρόκειται να αντικασταθεί από την ιδιωτική χρηματοδότηση μέσω της σύναψης εμπορικών συμβάσεων αγοράς ηλεκτρικής ενέργειας.In the first part of the essay, I examine the evolution of the support schemes for the generation of energy from renewable sources (RES). I observed a trend from a "protectionist approach" to a "market-based approach". Under the "protectionist approach", granting aid solely to the domestic producers of RES could be justified for the purpose of environmental protection. Under the "market-based approach", aid to RES is subject to a competitive procedure. In the second part of the essay, I consider the funding of the Greek support scheme for RES, which was based on levies imposed on energy consumers. I examine the legality of such measures with respect to constitutional and EU law. In tandem with the abolition of the support schemes for RES, public funding will be replaced by private funding through the conclusion of corporate power purchase agreements

DECAY PARAMETERS OF AFTERSHOCK SEQUENCES GLOBALLY DISTRIBUTED

The evaluation of the parameters c and k of the decay law of the aftershocks in an earthquake sequence has been carried out in this study. For this reason 170 seismic sequences globally distributed, during the time period 1964-1986, were performed. All of them modelled well by Omori’s law. We estimated that the mean global values of and parameters , are 0.660+0.181 and - 0.341+0.090, respectively. The values of these parameters are also estimated for different regions of the world, west and east part of circum-Pacific rim, as well as for the Eurasia belt.The parameters c and k calculated for the various regions of the world found to be spread around the global average, although admittedly few exceptions to this generalization are also observed to exist

User equilibrium traffic network assignment with stochastic travel times and late arrival penalty

The classical Wardrop user equilibrium (UE) assignment model assumes traveller choices are based on fixed, known travel times, yet these times are known to be rather variable between trips, both within and between days; typically, then, only mean travel times are represented. Classical stochastic user equilibrium (SUE) methods allow the mean travel times to be differentially perceived across the population, yet in a conventional application neither the UE or SUE approach recognises the travel times to be inherently variable. That is to say, there is no recognition that drivers risk arriving late at their destinations, and that this risk may vary across different paths of the network and according to the arrival time flexibility of the traveller. Recent work on incorporating risky elements into the choice process is seen either to neglect the link to the arrival constraints of the traveller, or to apply only to restricted problems with parallel alternatives and inflexible travel time distributions. In the paper, an alternative approach is described based on the ‘schedule delay’ paradigm, penalising late arrival under fixed departure times. The approach allows flexible travel time densities, which can be fitted to actual surveillance data, to be incorporated. A generalised formulation of UE is proposed, termed a Late Arrival Penalised UE (LAPUE). Conditions for the existence and uniqueness of LAPUE solutions are considered, as well as methods for their computation. Two specific travel time models are then considered, one based on multivariate Normal arc travel times, and an extended model to represent arc incidents, based on mixture distributions of multivariate Normals. Several illustrative examples are used to examine the sensitivity of LAPUE solutions to various input parameters, and in particular its comparison with UE predictions. Finally, paths for further research are discussed, including the extension of the model to include elements such as distributed arrival time constraints and penalties

Microsimulation models incorporating both demand and supply dynamics

There has been rapid growth in interest in real-time transport strategies over the last decade, ranging from automated highway systems and responsive traffic signal control to incident management and driver information systems. The complexity of these strategies, in terms of the spatial and temporal interactions within the transport system, has led to a parallel growth in the application of traffic microsimulation models for the evaluation and design of such measures, as a remedy to the limitations faced by conventional static, macroscopic approaches. However, while this naturally addresses the immediate impacts of the measure, a difficulty that remains is the question of how the secondary impacts, specifically the effect on route and departure time choice of subsequent trips, may be handled in a consistent manner within a microsimulation framework. The paper describes a modelling approach to road network traffic, in which the emphasis is on the integrated microsimulation of individual trip-makers’ decisions and individual vehicle movements across the network. To achieve this it represents directly individual drivers’ choices and experiences as they evolve from day-to-day, combined with a detailed within-day traffic simulation model of the space–time trajectories of individual vehicles according to car-following and lane-changing rules and intersection regulations. It therefore models both day-to-day and within-day variability in both demand and supply conditions, and so, we believe, is particularly suited for the realistic modelling of real-time strategies such as those listed above. The full model specification is given, along with details of its algorithmic implementation. A number of representative numerical applications are presented, including: sensitivity studies of the impact of day-to-day variability; an application to the evaluation of alternative signal control policies; and the evaluation of the introduction of bus-only lanes in a sub-network of Leeds. Our experience demonstrates that this modelling framework is computationally feasible as a method for providing a fully internally consistent, microscopic, dynamic assignment, incorporating both within- and between-day demand and supply dynamic

Σχολική επιτυχία/αποτυχία των Τσιγγάνων (Ρομά) μαθητών. Η μελέτη περίπτωσης ενός Γυμνασίου της Αγίας Βαρβάρας

Με την παρούσα διπλωματική εργασία μελετάται η σχολική επίδοση με όρους επιτυχίας/αποτυχίας των Ρομά μαθητών συγκριτικά με τους μη Ρομά μαθητές, ως προς την Γλώσσα, τα Μαθηματικά και τον Γενικό Μέσο Όρο (ΓΜΟ). Η έρευνα αποτελεί μελέτη περίπτωσης ενός Γυμνασίου του Δήμου Αγίας Βαρβάρας στον οποίο η ένταξη του Ρομά πληθυσμού θεωρείται πρότυπη σε πολλά επίπεδα και σε αυτό της σχολικής φοίτησης. Διερευνώνται πρώτα οι παράγοντες που συνέβαλαν στην συγκρότηση της ιδιαίτερης ταυτότητας των Ρομά της περιοχής και ειδικότερα οι παράγοντες που ενθαρρύνουν την φοίτηση των μαθητών και την μείωση της σχολικής διαρροής. Στο μελετώμενο δείγμα παρακολουθούνται οι επιδόσεις όλων των μαθητών σε βάθος τριετίας και διαφαίνεται μία απόκλιση στις υψηλότερες βαθμολογίες υπέρ των μη Ρομά μαθητών και σε βάρος των Ρομά. Η απόκλιση ερμηνεύεται με βάση τη θεωρία του «πολιτισμικού κεφαλαίου» και ως τρόπος άρσης της διαφοροποίησης προτείνεται η εφαρμογή στο ελληνικό εκπαιδευτικό σύστημα των αρχών της διαπολιτισμικής εκπαίδευσης.This dissertation examines Roma pupil performance by comparing their success/failure rates in Modern Greek, Mathematics and Cumulative Grade Average (CGA) to the performance of non-Roma peers. It relies on a case study of a lower secondary school located in Agia Varvara, a municipality of metropolitan Athens where Roma integration is considered exemplary in school attendance among other facets. It begins by probing for factors leading to the specific local Roma identity, especially for those favouring pupil attendance and reducing non-attendance. In the sample under study, pupil performance is monitored over a three-year span. Results indicate a tendency for higher grades among non-Roma versus Roma pupils. The divergence is accounted for on the basis of cultural capital theory. What is proposed for eliminating the variation is institutionalizing intercultural education principles in Greece’s educational apparatus

Torsades de Pointes due to multihormonal deficiency induced long QT syndrome

A 70-year-old patient suffering from multihormonal insufficiency presented several episodes of polymorphic ventricular tachycardia Torsades de pointes. A long QT interval was diagnosed which was due to hypoparathyroidism-induced hypocalcaemia refractory to the replacement therapy. Although several antiarrythmic drugs were used, only the administration with magnesium sulfate provided electrical stability. The multihormonal deficiency was due to ‘empty sella turcica syndrome’. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved