The area code tree for approximate nearest neighbour search in dense point sets

Location based Services (LBSs) have become very popular due to the rapid development of wireless technology and mobile devices. A LBS provides results to a user of a mobile device (e.g.smart phone, tablet) based on their location, interests, and the type of query being performed. For example, a user may want to know the location of the closest restaurant to them. Sometimes the user may also be happy with another suggestion that may not be the closest but close enough to satisfy them. This is an example of an approximate nearest neighbour search. In this thesis, we propose a spatial data structure the Area Code Tree which is a trie-type structure. The Area Code Tree stores Points of Interest (POIs) that are represented in area code format. We also present the algorithms for mapping the area code of a POI, inserting and building an Area Code Tree, and approximate nearest neighbour search. Next we evaluate the Area Code Tree for accuracy, tree construction time, and compare its search performance with the Brute Force Method. We find that the average search time for Area Code Tree in locating nearest neighbour is very low and constant regardless of the number of POIs in the index. In addition, the Area Code Tree can achieve up to 60\% accuracy for locating the nearest neighbour in dense point sets. This makes the Area Code tree an excellent candidate for continuous approximate nearest neighbour search for location-based services

Continuous spatial query processing over clustered data set

There exists an increasing usage rate of location-based information from mobile devices, which requires new query processing strategies. One such strategy is a moving (continuous) region query in which a moving user continuously sends queries to a central server to obtain data or information. In this thesis, we introduce two strategies to process a spatial moving query over clustered data sets. Both strategies utilize a validity region approach on the client in order to minimize the number of queries that are sent to the server. We explore the use of a two-dimensional indexing strategy, as well as the use of Expectation Maximization (EM) and k-means clustering. Our experiments show that both strategies outperform a Baseline strategy where all queries are sent to the server, with respect to data transmission, response time, and workload costs

The significance of silence. Long gaps attenuate the preference for ‘yes’ responses in conversation.

In conversation, negative responses to invitations, requests, offers and the like more often occur with a delay – conversation analysts talk of them as dispreferred. Here we examine the contrastive cognitive load ‘yes’ and ‘no’ responses make, either when given relatively fast (300 ms) or delayed (1000 ms). Participants heard minidialogues, with turns extracted from a spoken corpus, while having their EEG recorded. We find that a fast ‘no’ evokes an N400-effect relative to a fast ‘yes’, however this contrast is not present for delayed responses. This shows that an immediate response is expected to be positive – but this expectation disappears as the response time lengthens because now in ordinary conversation the probability of a ‘no’ has increased. Additionally, however, 'No' responses elicit a late frontal positivity both when they are fast and when they are delayed. Thus, regardless of the latency of response, a ‘no’ response is associated with a late positivity, since a negative response is always dispreferred and may require an account. Together these results show that negative responses to social actions exact a higher cognitive load, but especially when least expected, as an immediate response

Third International Symposium on Space Mission Operations and Ground Data Systems, part 1

Under the theme of 'Opportunities in Ground Data Systems for High Efficiency Operations of Space Missions,' the SpaceOps '94 symposium included presentations of more than 150 technical papers spanning five topic areas: Mission Management, Operations, Data Management, System Development, and Systems Engineering. The papers focus on improvements in the efficiency, effectiveness, productivity, and quality of data acquisition, ground systems, and mission operations. New technology, techniques, methods, and human systems are discussed. Accomplishments are also reported in the application of information systems to improve data retrieval, reporting, and archiving; the management of human factors; the use of telescience and teleoperations; and the design and implementation of logistics support for mission operations