Models of Transportation and Land Use Change: A Guide to the Territory

Modern urban regions are highly complex entities. Despite the difficulty of modeling every relevant aspect of an urban region, researchers have produced a rich variety models dealing with inter-related processes of urban change. The most popular types of models have been those dealing with the relationship between transportation network growth and changes in land use and the location of economic activity, embodied in the concept of accessibility. This paper reviews some of the more common frameworks for modeling transportation and land use change, illustrating each with some examples of operational models that have been applied to real-world settings.Transport, land use, models, review network growth, induced demand, induced supply

Markov chain aggregation and its application to rule-based modelling

Rule-based modelling allows to represent molecular interactions in a compact and natural way. The underlying molecular dynamics, by the laws of stochastic chemical kinetics, behaves as a continuous-time Markov chain. However, this Markov chain enumerates all possible reaction mixtures, rendering the analysis of the chain computationally demanding and often prohibitive in practice. We here describe how it is possible to efficiently find a smaller, aggregate chain, which preserves certain properties of the original one. Formal methods and lumpability notions are used to define algorithms for automated and efficient construction of such smaller chains (without ever constructing the original ones). We here illustrate the method on an example and we discuss the applicability of the method in the context of modelling large signalling pathways

Formal analysis techniques for gossiping protocols

We give a survey of formal verification techniques that can be used to corroborate existing experimental results for gossiping protocols in a rigorous manner. We present properties of interest for gossiping protocols and discuss how various formal evaluation techniques can be employed to predict them

Integrated models of transport and energy demand: A literature review and framework

Energy and transport demand can both be considered as being derived from an individual’s activity participation. As such, both energy and transport demand are inherently linked: completing activities inside the home generates residential energy demand, where completing activities outside the home generates transportation and non-residential energy demand. Whilst there are several works in the literature that focus on either energy or transportation demand, there remain very few studies which explicitly investigate their interaction. To address this need, in this paper we conduct in-depth literature review of transportation and energy demand modeling. The review analyses the methodologies employed within each domain in order to (a) establish the state-of-research for energy demand modeling and (b) identify the suitable opportunities for joining these two domains. Drawing on a review of the current papers, we identify four key areas of practice: (i) activity scheduling, (ii) building energy demand, (iii) transportation energy demand, and (iv) the integration of components. Finally, based on the findings from the review, we propose a new framework for joint building and transportation energy demand modeling at an urban scale

Epidemic Thresholds with External Agents

We study the effect of external infection sources on phase transitions in epidemic processes. In particular, we consider an epidemic spreading on a network via the SIS/SIR dynamics, which in addition is aided by external agents - sources unconstrained by the graph, but possessing a limited infection rate or virulence. Such a model captures many existing models of externally aided epidemics, and finds use in many settings - epidemiology, marketing and advertising, network robustness, etc. We provide a detailed characterization of the impact of external agents on epidemic thresholds. In particular, for the SIS model, we show that any external infection strategy with constant virulence either fails to significantly affect the lifetime of an epidemic, or at best, sustains the epidemic for a lifetime which is polynomial in the number of nodes. On the other hand, a random external-infection strategy, with rate increasing linearly in the number of infected nodes, succeeds under some conditions to sustain an exponential epidemic lifetime. We obtain similar sharp thresholds for the SIR model, and discuss the relevance of our results in a variety of settings.Comment: 12 pages, 2 figures (to appear in INFOCOM 2014

Empirical analysis of farm structural change at EU-level

The drastic changes of the European farm structure have led to plenty of research on farm structural change with recent studies focusing more and more on regional differences and spatial interaction of farmers. The thesis adds to this literature by providing a large-scale analysis of farm structural change across EU15 regions. For this purpose, farm structural change is defined as the change of the number of farms in different farm types over time. The agricultural economics literature is reviewed in order to find a methodological approach suitable to model and to analyse farm structural change at such a large regional scale and adhering to a multi-dimensional farm typology. A Markov chain estimation framework is identified to be the best suitable approach for the task at hand. In both empirical parts of the thesis, Markov chain transition probabilities are estimated representing the likelihood of a farm to change from one farm type to another in a given period of time. For the estimation of the transition probabilities, a generalised cross-entropy estimator is applied. The estimator allows, for the first time, the combination of two different data types in one estimation step, thereby significantly improving the empirical base for estimating transition probabilities compared to previous studies. Aggregate data giving the distribution of farms across farm types in the population is used in establishing the Markov chain and micro data on the specific movements of sample farms across farm types is used as a priori information in the estimation framework. Transition probabilities are estimated for each of about 100 EU15 regions based on FADN (Farm Accountancy Data Network) data from 1990/1995 to 2005. The thesis categorises theoretical determinants of farm structural change into the concepts technology/economies of scale, farm household theory, path dependency, land immobility, policy, and market conditions. Functions of the (in part time-varying) transition probabilities are cross-sectionally regressed against explanatory variables picked from these concepts. Two empirical applications, one analysing structural change encompassing all production specialisations and the other one focused on dairy farms are conducted. In both studies significant regional difference in farm structural change are observed. Whereas the expected impact of the technology/economies of scale concept is generally confirmed, the effect of the variables from the other concepts on farm structural change remains often ambiguous. Overall, the thesis confirms the widely acknowledged complexity of farm structural change.Empirische Analyse des Agrarstrukturwandels auf EU-Ebene Die drastischen Veränderungen der landwirtschaftlichen Betriebsstruktur in Europa haben zu einer Vielzahl wissenschaftlicher Studien in diesem Bereich geführt. Die neuesten dieser Studien konzentrieren sich dabei zunehmend auf regionale Unterschiede des Strukturwandels und die räumliche Interaktion der Betriebe. Die vorliegende Dissertation analysiert den EU15-Agrarstrukturwandel auf regionaler Ebene. Agrarstrukturwandel ist hier definiert als die Veränderung der Anzahl der landwirtschaftlichen Betriebe in verschiedenen Betriebsklassen über die Zeit. Die agrarökonomische Literatur wird mit dem Ziel der Identifikation eines methodischen Ansatzes besprochen, der es erlaubt den agrarstrukturellen Wandel in einem derart großen Umfang und gebunden an eine multidimensionale Betriebstypologie zu erklären und zu modellieren. Als geeignetster methodischer Ansatz stellt sich eine Markowketten-Analyse heraus. In den beiden empirischen Teilen der Arbeit werden Markowketten-Übergangswahrscheinlichkeiten geschätzt, die jeweils die Wahrscheinlichkeit eines Betriebes repräsentieren, von einem Betriebstypen zum nächsten in einer bestimmten Zeitperiode zu wechseln. Die Übergangswahrscheinlichkeiten werden mit Hilfe eines Generalised Cross-Entropy-Schätzers bestimmt, welcher - erstmalig in der Literatur - die Kombination zweier verschiedener Datenarten in einer Schätzung erlaubt. Verglichen mit vorhergegangenen Studien führt die Kombination der Datenarten zu einer deutlichen Vergrößerung der empirischen Basis für die Schätzung der Übergangswahrscheinlichkeiten. Die Markowkette konstituiert sich aus aggregierten Daten, die die Verteilung der Betriebe auf die Betriebstypen in der Population wiedergeben. Spezifische Wechsel von Testbetrieben zwischen den Betriebstypen, sogenannte Mikrodaten, werden als a priori-Information in den Schätzansatz eingebunden. Für jede von etwa 100 EU15-Regionen werden Übergangswahrscheinlichkeiten basierend auf FADN (Farm Accountancy Data Network) Daten von 1990/1995 bis 2005 geschätzt. Die Arbeit unterteilt theoretisch relevante Determinanten des Strukturwandels in die Konzepte technischer Fortschritt/economies of scale, Theorie des landwirtschaftlichen Haushalts, Pfadabhängigkeit, Immobilität des Bodens, Politik und Marktbedingungen. Funktionen der (teilweise zeitvariierenden) Übergangswahrscheinlichkeiten werden erklärenden Variablen aus diesen Konzepten in Querschnittsanalysen gegenübergestellt. In zwei empirischen Anwendungen wird der Agrarstrukturwandel einmal allgemein über alle Betriebsspezialisierungen hinweg und einmal mit Fokus auf Milchviehbetriebe analysiert. Beide Anwendungen offenbaren große regionale Unterschiede des agrarstrukturellen Wandels. Während der erwartete Einfluss der Determinanten aus dem Konzept technischer Fortschritt/economies of scale größtenteils bestätigt wird, weicht der Effekt der Einflussgrößen aus den anderen Konzepten auf die Übergangswahrscheinlichkeiten zum Teil von den Hypothesen ab. Insgesamt ist die Identifikation der zugrundeliegenden Prozesse über Regionen hinweg nur bedingt möglich. Die Dissertation bestätigt somit die weithin propagierte Komplexität des agrarstrukturellen Wandels

Scalable Population Synthesis with Deep Generative Modeling

Population synthesis is concerned with the generation of synthetic yet realistic representations of populations. It is a fundamental problem in the modeling of transport where the synthetic populations of micro-agents represent a key input to most agent-based models. In this paper, a new methodological framework for how to 'grow' pools of micro-agents is presented. The model framework adopts a deep generative modeling approach from machine learning based on a Variational Autoencoder (VAE). Compared to the previous population synthesis approaches, including Iterative Proportional Fitting (IPF), Gibbs sampling and traditional generative models such as Bayesian Networks or Hidden Markov Models, the proposed method allows fitting the full joint distribution for high dimensions. The proposed methodology is compared with a conventional Gibbs sampler and a Bayesian Network by using a large-scale Danish trip diary. It is shown that, while these two methods outperform the VAE in the low-dimensional case, they both suffer from scalability issues when the number of modeled attributes increases. It is also shown that the Gibbs sampler essentially replicates the agents from the original sample when the required conditional distributions are estimated as frequency tables. In contrast, the VAE allows addressing the problem of sampling zeros by generating agents that are virtually different from those in the original data but have similar statistical properties. The presented approach can support agent-based modeling at all levels by enabling richer synthetic populations with smaller zones and more detailed individual characteristics.Comment: 27 pages, 15 figures, 4 table