Browsing by Author "Kayaaslan, Enver"

Now showing 1 - 4 of 4

Open Access
Combinatorial reductions between graph partitioning by vertex separator and hypergraph partitioning problems for parallel and scientific computing applications
(2009) Kayaaslan, Enver
Colour as an effective design tool influences people’s emotions in interior spaces. Depending on the assumption that colour has an impact on human psychology, this study stresses the need for further studies that comprise colour and emotion association in interior space in order to provide healthier spaces for inhabitants. Emotional reactions to colour in a living room were investigated by using self report measure. Pure red, green and blue were chosen to be investigated as chromatic colours, whereas gray was the achromatic colour used as a control variable. The study was conducted at Bilkent University in Ankara, Turkey. Hundred and eighty people from various ages and academic departments participated in the study. Participants first watched a short video showing an overlook of a 3D model of a living room. Next, they were asked to match the distinct coloured living rooms with facial expressions of six basic emotions that covers anger, disgust, surprise, happiness, fear, sadness and in addition with neutral. The results of the study indicated that the most stated emotions associated for the room with red walls were disgust and happiness, while the least stated emotions were sadness, fear, anger, and surprise. Neutral and happiness were the most stated emotions for the room with green walls and anger, surprise, fear and sadness were the least stated ones. The most stated emotion associated for the room with blue walls was neutral, while the least stated emotions were anger and surprise. Neutral, disgust and sadness were the most stated emotions for the room with gray walls. Gender differences were not found in human emotional reactions to living rooms with different wall colours.
Open Access
Energy-price-driven query processing in multi-center web search engines
(IEEE, 2011-07) Kayaaslan, Enver; Cambazoglu, B. B.; Blanco, R.; Junqueira, F. P.; Aykanat, Cevdet
Concurrently processing thousands of web queries, each with a response time under a fraction of a second, necessitates maintaining and operating massive data centers. For large-scale web search engines, this translates into high energy consumption and a huge electric bill. This work takes the challenge to reduce the electric bill of commercial web search engines operating on data centers that are geographically far apart. Based on the observation that energy prices and query workloads show high spatio-temporal variation, we propose a technique that dynamically shifts the query workload of a search engine between its data centers to reduce the electric bill. Experiments on real-life query workloads obtained from a commercial search engine show that significant financial savings can be achieved by this technique.
Open Access
Hypergraph-based data partitioning
(2013) Kayaaslan, Enver
A hypergraph is a general version of graph where the edges may connect any number of vertices. By this flexibility, hypergraphs has a larger modeling power that may allow accurate formulaion of many problems of combinatorial scientific computing. This thesis discusses the use of hypergraph-based approaches to solve problems that require data partitioning. The thesis is composed of three parts. In the first part, we show how to implement hypergraph partitioning efficiently using recursive graph bipartitioning. The remaining two parts show how to formulate two important data partitioning problems in parallel computing as hypergraph partitioning. The first problem is global inverted index partitioning for parallel query processing and the second one is row-columnwise sparse matrix partitioning for parallel matrix vector multiplication, where both multiplication and sparse matrix partitioning schemes has novelty. In this thesis, we show that hypergraph models achieve partitions with better quality.
Open Access
Query forwarding in geographically distributed search engines
(ACM, 2010) Cambazoglu, B.B.; Varol, Emre; Kayaaslan, Enver; Aykanat, Cevdet; Baeza-Yates, R.
Query forwarding is an important technique for preserving the result quality in distributed search engines where the index is geographically partitioned over multiple search sites. The key component in query forwarding is the thresholding algorithm by which the forwarding decisions are given. In this paper, we propose a linear-programming-based thresholding algorithm that significantly outperforms the current state-of-the-art in terms of achieved search efficiency values. Moreover, we evaluate a greedy heuristic for partial index replication and investigate the impact of result cache freshness on query forwarding performance. Finally, we present some optimizations that improve the performance further, under certain conditions. We evaluate the proposed techniques by simulations over a real-life setting, using a large query log and a document collection obtained from Yahoo!. © 2010 ACM.