Congestion-aware traffic routing for large-scale mobile agent systems

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 191-201).Traffic congestion is a serious world-wide problem. Drivers have little knowledge of historical and real-time traffic congestion for the paths they take and often tend to drive suboptimal routes. Congestion phenomena are sure to be influenced by the coming of autonomous cars. This thesis presents route planning algorithms and a system for either autonomous or human-driven cars in road networks dealing with travel time uncertainty and congestion. First, a stochastic route planning algorithm is presented that finds the best path for a group of multiple agents. Our algorithm provides mobile agents with optimized routes to achieve time-critical goals. Optimal selections of agent and visit locations are determined to guarantee the highest probability of task achievement while dealing with uncertainty of travel time. Furthermore, we present an efficient approximation algorithm for stochastic route planning based on pre-computed data for stochastic networks. Second, we develop a distributed congestion-aware multi-agent path planning algorithm that achieves the social optimum, minimizing aggregate travel time of all the agents in the system. As the number of agents grows, congestion created by agents' path choices should be considered. Using a data-driven congestion model that describes the travel time as a function of the number of agents on a road segment, we develop a practical method for determining the optimal paths for all the agents in the system to achieve the social optimum. Our algorithm uses localized information and computes the paths in a distributed manner. We implement the algorithm in multi-core computers and demonstrate that the algorithm has a good scalability. Third, a path planning system using traffic sensor data is then implemented. We predict the traffic speed and flow for each location from a large set of sensor data collected from roving taxis and inductive loop detectors. Our system uses a data-driven traffic model that captures important traffic patterns and conditions using the two sources of data. We evaluate the system using a rich set of GPS traces from 16,000 taxis in Singapore and show that the city-scale congestion can be mitigated by planning drivers' routes, while incorporating the congestion effects generated by their route choices.by Sejoon Lim.Ph.D

곤충의 보호색 및 방어행동의 기능, 지각 메커니즘 및 진화

학위논문 (박사)-- 서울대학교 대학원 : 생명과학부, 2014. 2. Piotr G. Jablonski.Cryptic color patterns in prey are classical examples of adaptations to avoid predation, but we still know little about behaviors that reinforce the match between animal body and the background. From observations of geometrid moths, Hypomecis roboraria and Jankowskia fuscaria, I determined that the positioning behavior, which consists of walking and turning the body while repeatedly lifting and lowering the wings, resulted in new resting spots and body orientations in J. fuscaria, and in new resting spots in H. roboraria. The body positioning behavior of the two species significantly decreased the probability of visual detection by humans, who viewed photos of the moths taken before and after the positioning behavior. This implies that body positioning significantly increases the camouflage effect provided by moths cryptic color pattern regardless of whether the behavior involves a new body orientation or not. However, this positioning behavior is not always performed: some moths stay put on the initial landing position. We hypothesized that the moths decision of whether or not to re-position itself is related to its crypticity at the landing spot. We determined the crypticity from a detection task experiment, in which human foragers searched for the moths in photos of moths at their landing spots. Moths that landed on the less cryptic positions were more likely to reposition themselves to the more cryptic positions. In contrast, moths that already landed on substantially cryptic positions were less likely to reposition themselves. Next I explored how a moth finds an appropriate resting position and orientation. Here, I used a geometrid moth Jankowskia fuscaria to examine i) whether a choice of resting orientation by moths depends on the properties of natural background, and ii) what sensory cues moths use. We studied moths behavior on natural (a tree log) and artificial backgrounds, each of which was designed to mimic one of the hypothetical cues that moths may perceive on a tree trunk (visual pattern, directional furrow structure, and curvature). We found that moths mainly used structural cues from the background when choosing their resting position and orientation. Then I tested through which sensory organs (which are directly related to sensory information types) moths perceive bark structures to find adaptive resting orientations. We amputated (or blocked) one of the hypothetical sensory organs from moths (antennae, forelegs, wings, and eyes) and tested whether they were still able to perceive bark structures properly. We found that moths use visual information from eyes and tactile information from wings to perceive bark structure and to adopt cryptic resting orientations. These studies collectively show how behavior mediates the camouflage of moths in nature and how moths perceive background information to find a cryptic spot. Next. I tackled the questions about a new strategy of chemically defended prey to show warning coloration to predators. Aposematic coloration in prey promotes its survival by conspicuously advertising unpalatability to predators. Although classical examples of aposematic signals involve constant presentation of a signal at a distance, some animals suddenly display warning colors only when they are attacked. Characteristics of body parts suddenly displayed, such as conspicuous coloration or eyespot pattern, may increase the survival of the prey by startling the predator, and/or by signaling unpalatability to the predators at the moment of attack. The adaptive value of such color patterns suddenly displayed by unpalatable prey has not been studied. We experimentally blackened the red patch in the conspicuous red-white-black hindwing pattern displayed by an unpalatable insect Lycorma delicatula (Hemiptera: Fulgoridae) in response to predators attack. There was no evidence that the presence of the red patch increased prey survival over several weeks. Next I asked the adaptive significance of this hidden-warning coloration and explored the mechanistic question how it provides survival benefits to the bearer. The main advantage of aposematism is that it enhances learning by predators to avoid the prey. Using wild birds (Parus minor) and novel prey models, I tested whether hidden conspicuous display of defended prey accelerates the avoidance learning rate of predators and how does it compare with the typical conspicuous/non-conspicuous signal. We found the evidence that hidden aposematic signal indeed accelerates the avoidance learning rate of predators by two stages: i) enhancing the learning rate of the association between non-conspicuous (normal) state of the prey and prey defense, ii) promoting rejection after an attack has occurred by showing hidden conspicuous coloration. We show here the unique defensive coloration of prey which may provide dual benefits of crypsis and aposematism and highlight the specific mechanisms that hidden-aposematic signal provide the prey with survival benefits.List of figures 3 List of Tables 5 Chapter 1. Camouflage through an active choice of a resting spot and body orientation in moths 9 ABSTRACT 10 INTRODUCTION 11 MATERIALS AND METHODS 13 RESULTS 17 DISCUSSION 22 SUPPORTING INFORMATION 26 Chapter 2. Moths on tree trunks seek out more cryptic positions when their current crypticity is low 27 ABSTRACT 28 INTRODUCTION 29 MATERIALS AND METHODS 31 RESULTS 37 DISCUSSION 41 SUPPORTING INFORMATION 45 Chapter 3. Cryptically patterned moths perceive bark structure when choosing body orientations that match wing color pattern to the bark pattern 51 ABSTRACT 52 INTRODUCTION 53 MATERIALS AND METHODS 55 RESULTS 66 DISCUSSION 70 SUPPORTING INFORMATION 74 Chapter 4. Multimodal information use to adopt adaptive resting orientations in moths 81 ABSTRACT 82 INTRODUCTION 83 MATERIALS AND METHODS 84 RESULTS 88 DISCUSSION 91 SUPPORTING INFORMATION 93 Chapter 5. Effect of sex and bright coloration on survival and wing damage in an aposematic lantern fly with startle display 95 ABSTRACT 96 INTRODUCTION 97 MATERIALS AND METHODS 99 RESULTS 106 DISCUSSION 111 Chapter 6. Hidden conspicuous signals augment predators learning to avoid non-conspicuously colored defended prey 116 ABSTRACT 117 INTRODUCTION 118 MATERIALS AND METHODS 123 RESULTS 130 DISCUSSION 135 General Conclusion 140 References 142 List of published chapters (2014. 02) 157 국문초록 158 Acknowledgements 162Docto