Competitive Online Searching for a Ray in the Plane

We consider the problem of a searcher that looks, for example, for a lost flashlight in a dusty environment. The searcher finds the flashlight as soon as it crosses the ray emanating from the flashlight. In order to pick it up, the searcher moves to the origin of the light beam. We compare the length of the path of the searcher to the shortest path to the goal. First, we give a search strategy for a special case of the ray search---the window shopper problem---, where the ray we are looking for is perpendicular to a known ray. Our strategy achieves a competitive factor of $1.059ldots$, which is optimal. Then, we consider rays in arbitrary position in the plane. We present an online strategy that achieves a factor of $22.513ldots$, and give a lower bound of $2pi,e=17.079ldots$

Online exploration and search in graphs

There are three fundamental online problems in robotics: naviga-tion/search, localization, and exploration. Constructing a complete map of an unknown environment while using a short path is the task of autonomous robots when they have to explore a whole environ-ment. Besides the practical problems that arise when an autonomous robot needs to travel through real terrain there is the question of how well the robot will perform compared to an optimal strategy that has complete knowledge of the environment and can plan an exploration path in advance. The robot must always decide its further move-ments online and with only partial knowledge of the already explored environment. Different models of the environment lead to different algorithms that try to cope with the difficulties given by a particular modeling. The advantage of modeling environments as graphs lies in the fact that the geometric features are neglected and one can concentrate on the combinatorial aspects of the exploration problem. While we are fo-cusing on directed graphs in the case of exploration we consider both directed and undirected graphs for the search problem, in which the robot needs to find a specific goal. The thesis begins with a short explanation of the motivation behind online search and exploration. We survey existing algorithms, involv-ing a detailed discussion of some of those algorithms, which - or parts of which - are reused in some of our algorithms. The thesis continues with the study of the problem of exploring an unknown, strongly connected directed graph G. Starting at some ver-tex of the graph, we must visit every edge and every vertex at least once. The goal is to minimize the number of edge traversals. It is known that the competitive ratio of online algorithms for this prob-lem depends on the deficiency d of the graph, which is the minimum number of edges that must be added to make the graph Eulerian. We present the first deterministic online exploration algorithm whose competitive ratio is polynomial in the deficiency d of G (it is O(d7)). An extensive experimental study investigates all major online graph traversal algorithms. This includes many simple natural algorithms as well as more sophisticated strategies, and some variants of the original algorithms. Our work helps to provide a better insight into the practical perfor-mance of these algorithms on various graph families. It is to observe that all tested algorithms perform closely to the optimum offline al-gorithm in a huge family of random graphs. Only few very specific lower bound examples cause bad results. The remainder of the thesis is concerned with the questions of how efficiently we can search an unknown environment for a goal in an unknown position, and how much it would help if the environment were known. We answer these questions for general graphs and trees, by providing online search strategies that are as good as the best offline search algorithms, up to a constant factor. Furthermore, we show that for some more restricted environments no online search strategies with this performance guarantee exist

Phenotyping of effector T cells in Juvenile Idiopathic Arthritis (JIA)

Background: Juvenile Idiopathic Arthritis (JIA) is a heterogeneous disease with unknown etiology of arthritis for more than six weeks in patients aged under 16 years. Human Cytomegalovirus (HCMV) is a lymphotropic betaherpesvirus that persists in the human body and causes ongoing stimulation of the effector T-cell system. For both, JIA and HCMV, a premature immunosenescence is shown. Aim: To investigate the potential influence of HCMV on the prematurely altered immune system of JIA patients. Methods: T-cell phenotype, intracellular cytokine production and the expression of chemokine receptors were measured by flow cytometry (FACS). HCMV serostatus was measured by enzyme-linked immunosorbent assay (ELISA). Phenotype and cytokine production of lymphocytes derived from JIA patients and healthy donors were compared regarding their HCMV serostatus. Results: Both JIA patients and healthy donors showed an association between HCMV seropositivity and immunosenescence resulting in low proportions of naive T-cells and relatively higher proportions of differentiated T-cells. Within the JIA patients HCMV seropositivity was associated with higher intracellular IFNγ production. T-cells in JIA patients showed a higher CCR5 expression in association with HCMV seropositivity. This association was not seen in healthy donors. Conclusion: The T-cell phenotype was similarly associated with HCMV in JIA patients and healthy donors. In contrast, JIA patients showed evidence of TH1 predominance in association with HCMV seropositivity. Regarding CCR5 this effect is significantly stronger in JIA patients than in healthy donors. The present study suggests that HCMV associated changes of the T-cell differentiation may be corroborated in JIA patients.Hintergrund: Die Juvenile Idiopathische Arthritis (JIA) ist eine heterogene Erkrankung mit unbekannter Ätiologie der Arthritis bei Patientinnen und Patienten unter 16 Jahren für mehr als sechs Wochen. Das Humane Zytomegalievirus (HCMV) ist ein lymphotropes Betaherpesvirus, das im menschlichen Körper persistiert und eine anhaltende Stimulation des Effektor-T-Zell-Systems bewirkt. Sowohl für JIA als auch für HCMV zeigt sich eine vorzeitige Immunoseneszenz. Ziel: Untersuchung des potenziellen Einflusses von HCMV auf das vorzeitig gealterte Immunsystem von JIA-Patientinnen und Patienten. Methoden: T-Zell-Phänotyp, intrazelluläre Zytokinproduktion und die Expression von Chemokinrezeptoren wurden mittels Durchflusszytometrie (FACS) gemessen. Der HCMV-Serostatus wurde mittels Enzyme-Linked Immunosorbent Assay (ELISA) gemessen. Phänotyp und Zytokinproduktion von Lymphozyten von JIA-Patientinnen und Patienten und Gesundkontrollen wurden hinsichtlich ihres HCMV-Serostatus verglichen. Ergebnisse: Sowohl JIA-Patientinnen und Patienten als auch Gesundkontrollen zeigten einen Zusammenhang zwischen HCMV-Seropositivität und Immunseneszenz, nämlich geringere Anteile naiver T-Zellen und relativ höhere Anteile an differenzierten T-Zellen. Bei den JIA-Patientinnen und Patienten war die HCMV-Seropositivität mit einer höheren intrazellulären IFNγ-Produktion verbunden. T-Zellen bei JIA-Patientinnen und Patienten zeigten eine höhere CCR5-Expression in Verbindung mit HCMV-Seropositivität. Diese Assoziation wurde bei Gesundkontrollen nicht beobachtet. Schlussfolgerung: Der T-Zell-Phänotyp war bei JIA-Patientinnen und Patienten und Gesundkontrollen ähnlich mit HCMV assoziiert. Im Gegensatz dazu zeigten JIA-Patientinnen und Patienten Hinweise auf eine TH1-Dominanz in Verbindung mit HCMV-Seropositivität. Bei CCR5 ist dieser Effekt bei JIA-Patientinnen und Patienten signifikant stärker als bei Gesundkontrollen. Die vorliegende Studie legt nahe, dass HCMV-assoziierte Veränderungen der T-Zell-Differenzierung bei JIA-Patientinnen und Patienten bestätigt werden können

Algorithms and Computation

xvii, 935hal.; 22c

Optimal Robot Localization in Trees

This video shows the problem of localization. A robot has to find its position on a map, in our case a geometric tree of bounded degree. The strategy LPS (Localize-by-PlacementSeparation) is known to guarantee that the distance traveled by the robot is at most O( p n) times longer than the shortest possible route to localize the robot, where n is the number of nodes of the tree T with degree greater than two. We explain the algorithm by running it on a tree of n = 169 nodes

On the Effectiveness of Visualizations in a Theory of Computing Course

We report on two tests we performed in Hong Kong and Shanghai to verify the hypothesis that one can learn better when being given access to visualizations beyond the standard verbal explanations in a classroom. The outcome of the first test at HKUST was inconclusive, while the second test at Fudan University showed a clear advantage for those students who had access to visualizations

Managementperspektiven und Managementausbildung: Herrn Dr. Dr. h.c. Ludwig Trippen, anlaesslich des Ausscheidens aus der Geschaeftsfuehrung der Handelshochschule Leipzig (HHL) gewidmet

SIGLEAvailable from Bibliothek des Instituts fuer Weltwirtschaft, ZBW, D-21400 Kiel C 206462 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Optimal Robot Localization in Trees

The problem of localization, that is, of a robot finding its position on a map, is an important task for autonomous mobile robots. It has applications in numerous areas of robotics ranging from aerial photography to autonomous vehicle exploration. In this paper we present a new strategy LPS (Localize-by-PlacementSeparation) for a robot to find its position on a map, where the map is represented as a geometric tree of bounded degree. Our strategy exploits to a high degree the self-similarities that may occur in the environment