Diss., Naturwissenschaften, Eidgenössische Technische Hochschule ETH Zürich, Nr. 16831, 2006.

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We study the behavior of diffusive Lotka-Volterra systems in environments with spatially varying carrying capacities. In particular, we use numeric and analytic techniques to study two similar models for population growth, in order to determine their qualitative differences. Additionally, we investigate competition models in the presence of periodic disasters, in order to determine what factors affect competitive dominance. We found that under conditions of high spatial heterogeneity, the model for population growth was the main factor determining coexistence. Under low spatial heterogeneity, the effect of disturbance on the stronger competitor was the main factor determining coexistence.

This study investigated the impact of participation in the Seeds of Peace International Summer Camp program on attitudes toward perceived enemies and in-group members. Specifically, individuals’ social dominance orientation, stereotype attributions, closeness to own and out-group members, attitudes about peace, beliefs about ability to think independently and ideas about how to facilitate peace were examined. Three groups of adolescents were studied: Israeli, Palestinian and Non-Palestinian Arab campers who came from Jordan and Egypt. Two hundred and forty eight adolescents between the ages of 14 and 17 participated in Study 1, and a 62 participant sub-sample of the original group participated in the follow up study. The two studies together revealed several important findings. The results from Study 1 suggest that the experience of participating in the Seeds of Peace camp program is effective for fostering feelings of closeness to the out-group, and for evaluating the other side’s attitudes toward peacemaking more positively. Results also suggested that cognitively-oriented ratings, such as stereotypes of warmth and competence, were more resistant to change. The results of the follow up study conducted ten months after camp had ended were mixed. Generally, out-group evaluations became less positive, although there was some maintenance of effects. The present research supports previous findings that the use of coexistence programs as a means to improve intergroup relations is generally beneficial in the short term. The results also highlighted the importance of the experience of participating in the Seeds of Peace camp program to changing the beliefs held about perceived enemies. The significant contributions of the current research include underlining the importance of intergroup contact, the experience of living with perceived enemies, and becoming ready to listen to the other side, in order to change beliefs held about them.

This study investigated the impact of participation in the Seeds of Peace International Summer Camp program on attitudes toward perceived enemies and in-group members. Specifically, individuals’ social dominance orientation, stereotype attributions, closeness to own and out-group members, attitudes about peace, beliefs about ability to think independently and ideas about how to facilitate peace were examined. Three groups of adolescents were studied: Israeli, Palestinian and Non-Palestinian Arab campers who came from Jordan and Egypt. Two hundred and forty eight adolescents between the ages of 14 and 17 participated in Study 1, and a 62 participant sub-sample of the original group participated in the follow up study. The two studies together revealed several important findings. The results from Study 1 suggest that the experience of participating in the Seeds of Peace camp program is effective for fostering feelings of closeness to the out-group, and for evaluating the other side’s attitudes toward peacemaking more positively. Results also suggested that cognitively-oriented ratings, such as stereotypes of warmth and competence, were more resistant to change. The results of the follow up study conducted ten months after camp had ended were mixed. Generally, out-group evaluations became less positive, although there was some maintenance of effects. The present research supports previous findings that the use of coexistence programs as a means to improve intergroup relations is generally beneficial in the short term. The results also highlighted the importance of the experience of participating in the Seeds of Peace camp program to changing the beliefs held about perceived enemies. The significant contributions of the current research include underlining the importance of intergroup contact, the experience of living with perceived enemies, and becoming ready to listen to the other side, in order to change beliefs held about them.

Wireless network systems, such as IEEE 802.11 wireless local area networks (WLANs) and Bluetooth, are increasingly constructed in our surrounding environment. Although devices running these two wireless systems operate with different technologies, they both work in the 2.4 GHz ISM (Industrial, Scientific, and Medical) band, and therefore lead to interference. The problem of Bluetooth interfering with a WLAN is particularly serious with a Bluetooth device located in an area with more than one overlapping WLAN. Interference is not a significant problem if it only degrades data throughput. However, it is unacceptable if it causes disconnection of the Bluetooth SCO link (i.e., voice connection). This study presents mechanisms to sustain the quality of Bluetooth SCO link, under the interference, with only at a minor cost of WLAN¡¦s data throughput.

The doped perovskite manganite La1-xCaxMnO3 (0<x<1) has been extensively studied due to the interactions between the electronic, magnetic and crystal lattices, and the wide range of phases that can coexist. The region of greatest interest in the bulk material is around x~0.5, where there is often mesoscopic phase coexistence between a ferromagnetic metal (FM) and an antiferromagnetic insulator (AF). The first part of the dissertation describes a systematic study on a series of La1-xCaxMnO3 films deposited onto SrTiO3 (001) by pulsed laser deposition with compositions in the range 0.40<x<0.45. From electrical transport and magnetisation measurements, the limit of metallic behaviour was found to be x=0.41 whereas ferromagnetism was seen up to x=0.45. Although the transition temperatures of 150-200 K were comparable with the bulk material, the saturation moment at 20 K was about 40% of the fully spin-aligned value, which suggests the possibility of a phase separated mixture of FM and AF regions. The deviation from the bulk behaviour is thought to be due to substrate-induced strain altering the crystal symmetry and making the cubic ferromagnetic state less favourable. In the remainder of this work, the nature of phase separation in 60 nm La0.59Ca0.41MnO3 and La0.60Ca0.40MnO3 films is investigated. The effect of an external magnetic field is studied. A high-field magnetoresistance (Δρ/ρB=0) of 41% in fields of 400 mT was observed for a La0.60Ca0.40MnO3 film, which, while not as large as the values previously reported in the literature, is still significant. The magnetic history of the films was found to be very significant, with the zero-field resistivity depending on the highest field applied. The isothermal time dependence of the resistivity was found to be exponential, with a time constant in the range 100-1000 s. Possible mechanisms for the MR effect and the dependence on magnetic history are discussed.

ZigBee based Wireless Sensor Networks (WSN) and Wireless Local Area Networks (WLAN) utilize the same un-licensed 2.4GHz frequency band. In our research, it is noticed that ZigBee could suffer serious performance degradation due to the collocated WLAN interference. After going through the available literature and combining with a thorough statistical analysis of our experimental results, several important factors that severely impact the ZigBee packet transmission performance have been identified. Motivated by these findings, novel techniques are designed to improve the performance of ZigBee packet transmission under WLAN interference. ACK with Interference Detection (ACK-ID) technique is developed to improve the delivery rate of ACK packets, and consequently reduce the number of redundant retransmissions. In order to improve the energy efficiency, Adaptive Transmit Power Adjustment (ATPA) is proposed to adaptively adjust the optimal transmit power while maintaining the predefined Packet Loss Rate (PLR) requirement. Time Aware Backoff and Transmission (TABTx) technique controls the time spent on each packet transmission attempt so as to avoid the Transmit First In First Out Byte Register (TXFIFO) overflow. Adaptive Preamble Padding with Retransmission Control (APPRC) is proposed to improve the transmission efficiency while satisfying the PLR requirement by determining the appropriate number of protective preamble padding bytes and whether or not to adopt packet retransmission. All these novel techniques have been implemented in the Crossbow MICAz motes and evaluated through extensive experimental measurements in the testbed.

My project is about the growing problem of relations between humans and wildlife in cities. The more we built, the less space of habitat for wildlife to survive. I choose to work in Beijing, a megacity with a population of tens of millions, also home to many wildlife. I investigated the issue about coexistence of humans and wild animals in Beijing. I choose to design something for birds. Birds, along humans, are the most powerful biological force of globalization on the planet. I mainly studied one type of birds in Beijing called Beijing Swift. The purpose is to create a new mode in which people and birds could coexist in the city by exploring the concept of territory for birds. I use activeness and passiveness to define the concept of territory in terms of time, vertical space and horizontal space. Humans have dominance in the city where animals may be disturbed by people's behavior at any time or  any place. Therefore I want to improve birds’ active dominance in their territory by providing bird-specific architecture, restricting human’s behavior and hiding human’s behavior in birds’ habitat.

The global mobile data usage has grown nearly 70\% annually in recent years. The huge mobile data usage requirement drives the mobile industry to brace the formidable challenge and invent next-generation mobile technologies. LTE, as a successful cellular technology, has gained tremendous importance in recent years due to its high data-rates and improved data access method for mobile devices. Even though LTE still may not be able to meet the mobile data challenge due to current spectrum scarcity in licensed bands. Thus, cellular network faces serious challenges to provide high performance mobile service to end users in the near future. In order to sustain the possible increase in mobile capacity demand, utilizing the unlicensed band as a supplementary band for LTE is being considered as a promising solution to expand the capacity of mobile systems. Based on the innovation of carrier aggregation, 3GPP has approved a study item on LAA-LTE, which will assist LTE by offloading mobile data in unlicensed band. Thus, LAA-LTE will operate in the spectrum that overlaps with WiFi, which is another popular unlicensed band technology. The concern is that LAA-LTE and WiFi are unlikely to have mechanisms to directly coordinate with each other, considering different core networks, backhauls and deployment plans of LAA-LTE and WiFi networks. The overarching goal of my research is to investigate the following two aspects: 1) Investigate how LTE will impact on WiFi using experimental analysis when both of them share the same channel, 2) Develop a possible coexistence algorithm to trigger the coexistence between LAA-LTE and WiFi in unlicensed band.