Decentralised control of material or traffic flows in networks using phase-synchronisation

We present a self-organising, decentralised control method for material flows in networks. The concept applies to networks where time sharing mechanisms between conflicting flows in nodes are required and where a coordination of these local switches on a system-wide level can improve the performance. We show that, under certain assumptions, the control of nodes can be mapped to a network of phase-oscillators. By synchronising these oscillators, the desired global coordination is achieved. We illustrate the method in the example of traffic signal control for road networks. The proposed concept is flexible, adaptive, robust and decentralised. It can be transferred to other queuing networks such as production systems. Our control approach makes use of simple synchronisation principles found in various biological systems in order to obtain collective behaviour from local interactions

Traffic flow on realistic road networks with adaptive traffic lights

We present a model of traffic flow on generic urban road networks based on cellular automata. We apply this model to an existing road network in the Australian city of Melbourne, using empirical data as input. For comparison, we also apply this model to a square-grid network using hypothetical input data. On both networks we compare the effects of non-adaptive vs adaptive traffic lights, in which instantaneous traffic state information feeds back into the traffic signal schedule. We observe that not only do adaptive traffic lights result in better averages of network observables, they also lead to significantly smaller fluctuations in these observables. We furthermore compare two different systems of adaptive traffic signals, one which is informed by the traffic state on both upstream and downstream links, and one which is informed by upstream links only. We find that, in general, both the mean and the fluctuation of the travel time are smallest when using the joint upstream-downstream control strategy.Comment: 41 pages, pdflate

Optimal control of a deterministic multiclass queuing system by serving several queues simultaneously

In this report we consider the optimal control problem of emptying a deterministic single server multiclass queuing system without arrivals. We assume that the server is able to serve several queues simultaneously, each at its own rate, independent of the number of queues being served. We showed that the optimal sequence of modes is ordered by rate of cost decrease. However, queues are not necessarily emptied. We propose a dynamic programming approach for solving the problem, which reduces the multiparametric QP (mpQP) to a series of problems that can be solved readily

Impact of aldehyde Dehydrogenase isotypes on xenograft and syngeneic mouse models of human primary glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most common malignant primary brain tumour in adults with a median survival, despite of multimodal aggressive therapy, of only 15 months. Relapse occurs inevitably because of the infiltrative nature of GBM. To date, only the MGMT promoter methylation is a reliable marker for therapy sensitivity. Survival-associated prognostic factors as well as novel therapy targets are urgently needed. Multiple genetic and metabolic pathway alterations contribute to tumour progression and therapy resistance. Recently proposed CSC markers for solid cancers include the aldehyde dehydrogenase (ALDH) superfamily. This cytoplasmic enzyme family consists of 19 different isoforms. The ALDH enzymes act upon oxidative stress and participate in proliferation, differentiation, and cell cycle arrest. The evolutionary conservation of the protein family enables comparative considerations of different species. In the presented study, isotype specific expression of ALDH is analysed in human GBM tumours and in two commonly used mouse GBM models. Expression of ALDH in the mouse models is then compared with the human GBM to find a suitable model for further research. The presented results indicate that there is, though challenging, a necessity for isotype specific analysis of ALDH expression. ALDH1A1 immunohistochemical expression in human PGBM was found primarily in the tumour adjacent region, whereas ALDH1A3 positive cells were more frequently found among tumour cells. Prognostic relevance for PGBM patients’ outcome was found for the ALDH1 immunohistochemical expression. Moreover, female PGBM patients were shown to have prolonged survival if neither ALDH1A1 nor ALDH1A3 expression is present. For male PGBM patients, ALDH1A1 and ALDH1A3 immunohistochemical expression could not be correlated to the medium overall survival. The reasons for this gender difference remain yet undetermined. Both the murine and the human GBM cells analysed in this thesis did not show ALDH1A1 immunohistochemical expression in cell culture or after implantation. The expression of ALDH1A3 is inhomogeneous in the analysed groups, raising further questions, which will be investigated in the future.The investigative approach of this thesis showed that the analysed canine GBM samples express ALDH1A3 but not ALDH1A1. This difference to human PGBM tumours in ALDH expression can help to understand more about the metabolic processes in tumour cells and the reactions to the tumour cells in the surrounding tissue. Finally, there are two particularly promising research subjects for future investigations: the gender specific prognostic power of ALDH expression in PGBM patients and the reason for the change in ALDH1A3 expression between in vitro and in vivo conditions. This knowledge can contribute to finding new targets for PGBM therapy and to prolonging patient survival.Das Glioblastoma multiforme (GBM) ist der häufigste maligne hirneigene Tumor des erwachsenen Menschen, mit einem mittleren Überleben, trotz aggressiver multimodaler Therapie, von nur 15 Monaten. Aufgrund der infiltrativen Natur des GBM treten Rezidive unvermeindlich auf. Zur Zeit gibt es nur einen zuverlässigen Marker für das Ansprechen der Therapie, die MGMT Promoter Methylierung. Mit dem Überleben assoziierte Marker und neue Therapieziele werden dringend benötigt. Viele genetische und metabolische Veränderungen führen zu Tumorwachstum und Therapieresistenz. Zu den vorgeschlagenen neuen Markern für CSC der soliden Tumoren gehört die Aldehyddehydrogenase-Superfamilie (ALDH-Superfamilie). Diese Enzymfamilie besteht aus 19 verschiedenen, im Zytoplasma lokalisierten Isoformen. Die ALDH-Enzyme sind beteiligt an der Reaktion auf oxidativen Stress, an Proliferation, Differenzierung, und Zellzyklus-Arrest. Die evolutionäre Konserviertheit der Proteinfamilie lässt eine vergleichende Betrachtung zwischen verschiedenen Spezies zu. Diese Arbeit vergleicht isotypenspezifisch die ALDH Expression von menschlichen GBM Tumoren mit zwei weitverbreiteten Tierversuchssmodellen. Die ALDH Expression der Maustumoren wird verglichen mit der der menschlichen GBM, um für zukünftige Untersuchungen ein geeignetes Modell zu finden. Die vorliegenden Resultate deuten darauf hin, dass die isotypenspezifische Analyse der ALDH notwendig, jedoch herausfordernd ist. Die immunhistochemische Expression von ALDH1A1 in humanen GBM Tumoren wurde hauptsächlich in der an den Tumor angrenzenden Region detektiert, während ALDH1A3 positive Zellen häufiger unter den Tumorzellen gefunden wurden. Eine prognostische Relevanz für das Überleben der PGBM Patienten konnte für die ALDH1 Expression nachgewiesen werden. Darüber hinaus zeigte sich, dass weibliche PGBM Patienten einen Überlebensvorteil haben, falls weder ALDH1A1 noch ALDH1A3 Expression vorliegt. Für männliche PGBM Patienten konnte keine Korrelation der ALDH1A1 und ALDH1A3 Expression mit der mittleren Überlebenszeit gefunden werden. Die Gründe für die geschlechtsspezifischen Unterschiede sind unbekannt und bedürfen weiterer Forschung. Die in der vorliegenden Arbeit untersuchten murinen und humanen GBM Zellen zeigten in der Zellkultur und nach Implantation keine ALDH1A1 Expression. Die Expression von ALDH1A3 ist uneinheitlich in den untersuchten Gruppen, welches neue Fragen aufwirft, die in späteren Studien untersucht werden sollen. Die hier durchgeführte investigative Untersuchung von caninen GBM Tumoren zeigte, dass nur ALDH1A3, nicht jedoch ALDH1A1 exprimiert wird. Dieser Unterschied in der ALDH Expression zum menschlichen PGBM kann in weiteren Studien helfen, die metabolischen Prozesse im Tumor und die Reaktion des umliegenden Gewebes auf die Tumorzellen besser zu verstehen. Abschließend sind im Hinblick auf weitere Untersuchungen vor allem zwei vielversprechende Ansatzpunkte zu nennen: die geschlechtsspezifisch unterschiedliche Eignung der ALDH Expression in PGBM als prognostischer Marker sowie die Ursache für die Veränderung der ALDH1A3 Expression zwischen in vitro und in vivo Bedingungen. Das gewonnene Verständnis kann in der Zukunft benutzt werden, um Angriffsziele für neue PGBM Therapien zu finden und zu einer Verlängerung des Lebens von Patienten beizutragen

Scaling laws in the spatial structure of urban road networks

The urban road networks of the 20 largest German cities have been analysed, based on a detailed database providing the geographical positions as well as the travel-times for network sizes up to 37,000 nodes and 87,000 links. As the human driver recognises travel-times rather than distances, faster roads appear to be 'shorter' than slower ones. The resulting metric space has an effective dimension d>2, which is a significant measure of the heterogeneity of road speeds. We found that traffic strongly concentrates on only a small fraction of the roads. The distribution of vehicular flows over the roads obeys a power law, indicating a clear hierarchical order of the roads. Studying the cellular structure of the areas enclosed by the roads, the distribution of cell sizes is scale invariant as well

Physics, Stability and Dynamics of Supply Networks

We show how to treat supply networks as physical transport problems governed by balance equations and equations for the adaptation of production speeds. Although the non-linear behaviour is different, the linearized set of coupled differential equations is formally related to those of mechanical or electrical oscillator networks. Supply networks possess interesting new features due to their complex topology and directed links. We derive analytical conditions for absolute and convective instabilities. The empirically observed "bull-whip effect" in supply chains is explained as a form of convective instability based on resonance effects. Moreover, it is generalized to arbitrary supply networks. Their related eigenvalues are usually complex, depending on the network structure (even without loops). Therefore, their generic behavior is characterized by oscillations. We also show that regular distribution networks possess two negative eigenvalues only, but perturbations generate a spectrum of complex eigenvalues.Comment: For related work see http://www.helbing.or