Sungyong Park

Discovery of Hidden Similarity on Collaborative Filtering to Overcome Sparsity Problem

This paper presents a method for overcoming sparsity problem of collaborative filtering system. The proposed method is based on an intuition on a network of human (such as a friendship network with friends of a friend). This method increases the density of similarity matrix and the coverage of predictions. We use sparse training data to test the sparsity of real-world situation. Consequently, experimental results show that this method increases coverage and f-measure especially for sparse training data.

Does background parenchymal enhancement on MRI affect the rate of positive resection margin in breast cancer patients

OBJECTIVE The purpose of our study was to evaluate whether strong background parenchymal enhancement (BPE) would be a significant independent factor associated with positive resection margin in patients treated initially with breast-conserving surgery (BCS). METHODS Retrospective evaluation of breast MRI examinations of 314 patients with breast cancer was carried out. Breast cancer was histologically confirmed in all patients who underwent BCS from January 2008 to December 2010. BPE was dichotomized into weak (minimal or mild) and strong (moderate or marked) enhancement for statistical analysis. Histopathological features of attained specimens were evaluated by an experienced pathologist and were also dichotomized for statistical analysis. RESULTS On univariate analysis, positive extensive intraductal component (p < 0.001), strong BPE (p = 0.001) and human epidermal growth factor receptor 2 (HER2) positivity (p = 0.08) had significant association with positive surgical margin. Tumour size, axillary lymph node metastasis, nuclear grade, histological grade, lymphovascular invasion, oestrogen receptor and progesterone receptor did not show significant correlation with positive surgical margin. On multivariate analysis, the significant independent predictors were extensive intraductal component [odds ratio, 5.68; 95% confidence interval (CI), 2.72-11.82] and strong BPE (odds ratio, 2.39; 95% CI, 1.20-4.78). CONCLUSION Strong BPE is a significant independent factor for positive resection margin along with positive extensive intraductal component, and performing MRI during the period of lower parenchymal enhancement is needed in patients with strong BPE. ADVANCES IN KNOWLEDGE As far as we know, this is the first study to reveal that BPE is a significant independent factor associated with positive resection margin.

A Performance Evaluation Methodology in Virtual Environments

System virtualization come into the spotlight again with the emerging virtual machine (VM) technologies (e.g., Parallels, VMware and Xen). With these market trends toward virtual environments, many research groups are developing evaluation tools to check the performance of virtual systems and their overheads. However, the performance characterization in virtual environments has not been established yet for many challenging issues. In this paper, we categorize four virtualization models for characterizing the performance of virtual environments and present an efficient evolution methodology to compare the performance of virtualized versus non-virtualized systems.

MPICH-GP: a Private-IP-Enabled MPI over grid environments

This paper presents an overview of MPICH-GP, which extends the MPICH-G2 functionality to support private IP clusters. To support the communication among private IP clusters, the MPICH-GP uses a communication relay scheme combining the NAT and a user-level proxy. The benchmarking results show that MPICH-GP outperforms the user-level two-proxy scheme used in PACX-MPI and Firewall-enabled MPICH-G, and also show comparable application performance to that of original MPICH-G2, especially in large message (or problem) size.

Wapee: a fault-tolerant semantic middleware in ubiquitous computing environments

A middleware in ubiquitous computing environment (UbiComp) is required to support seamless on-demand services over diverse resource situations in order to meet various user requirements [11]. Since UbiComp applications need situation-aware middleware services in this environment. In this paper, we propose a semantic middleware architecture to detect errors, analyze causes of errors, and plan semantically meaningful strategies to deal with a problem with associating fault and service ontology in UbiComp environment. We implemented a referenced prototype, Web-service based Application Execution Environment (Wapee), as a proof-of-concept, and showed the efficiency in runtime recovery.

A QoS Assured Network Service Chaining Algorithm in Network Function Virtualization Architecture

In the Network Function Virtualization (NFV) architecture, Network Service Chaining (NSC) is consisted in a certain order of network elements so that it can provide flexible network services to users. Due to the complexity of network infrastructure, creating a service chain requires high operation cost especially in carrier-grade network service providers and supporting stringent QoS requirements is also a challenge. Although several vendors provide various solutions for the NSC, there is only few information and the detailed algorithm or implementation logic is hidden. This paper presents an NSC algorithm in NFV that assures QoS from the perspective of service providers. In order to formulate NSC path selection problem, we apply the NP complete genetic algorithm. The evaluation results show that the proposed algorithm minimizes the operation cost of service providers by approximately 10.6% while the requested QoS targets is not violated.

A video streaming system for mobile phones: practice and experience

This paper presents a case of video streaming system for mobile phone which has actually been implemented and deployed for commercial services in CDMA2000 1X cellular phone networks. As the computing environment and the network connection of cellular phones are significantly different from the wired desktop environment, the traditional desktop streaming method is not applicable. Therefore, a new architecture is required to suit the successfully streaming in the mobile phone environment. We have developed a very lightweight video player for use in mobile phone and the related authoring tool for the player. The streaming server has carefully been designed to provide high efficiency, reliability and scalability. Based on a specifically-designed suite of streaming protocol, the server employs an adaptive rate control mechanism which transmits the media packets appropriately into the network according to the change in network bandwidth.

An efficient collective communication method for grid scale networks

This research is to design a collection of effective collective operations for the Grid scale network environment. In the Grid, several network features should be specified and adapted into the algorithmic design of collective operations. For this, we characterize the Grid and design hierarchical latency optimal tree algorithm for the MPI (message passing interface) library. The experimental results show that performance gain in performing collective operations can be achieved by around 160% compared with MPICH-G2 which is based on the flat algorithm.

Energy Efficient Online Routing Algorithm for QoS-Sensitive Sensor Networks

In this letter, we propose a new energy efficient online routing algorithm for QoS-sensitive sensor networks. An important design principle underlying our algorithm is online decision making based on real time network estimation. This on-line approach gives adaptability and flexibility to solve a wide range of control tasks for efficient network performance. In addition, our distributed control paradigm is practical for real sensor network management. Simulation results indicate the superior performance of our algorithm between energy efficiency and QoS provisioning.

Dynamic Topology Selection for High Performance MPI in the Grid Environments

MPI (Message Passing Interface) is getting more popular and important even in the Grid, but its performance still remains a problem, which is caused by the communication bottleneck on wide area links. To overcome such performance wall problem, we propose a dynamic topology selection which provides an effective resource selection service based on the principles of wide area message passing. It attempts to match the communication pattern of application with the topology of resources. Consequently, the proposed method provides an optimized set of resources and improves overall application performance by reducing the communication delay. To demonstrate the proposed method, we executed parallel benchmark programs and measured each execution time in five geometrically distributed clusters by changing resource selection method. When using topology selection method, experimental results show that performance gain can be achieved by up to 200%.