Chung-Pyo Hong

WidmanstÄtten Type Solidification in Squeeze Casting of Mg-Li-Al Alloys

The addition of 4--16 wt% Li to Mg lowers the density from 1.7 g/cm{sup 3} to 1.3--1.6 g/cm{sup 3}. Further this results in the h.c.p. {alpha} phase being replaced by the b.c.c. {beta} phase, leading to considerable low temperature formability. Detailed examination of the Mg-Li binary phase diagram shows that the {alpha} phase can precipitate in the {beta} phase matrix due to the decrease of Mg solubility in the {beta} phase as the temperature decreases. The addition of Al to Mg-Li alloys can improve strength by forming a uniform distribution of second phase particles. From the results of the previous study, Mg-8--10 wt% Li-3 {approximately} 5 wt% Al alloys consist of a mixture of {alpha} and {beta} grains, and fine second phase particles, showing the optimum combination of mechanical properties. Main emphasis in the present study was placed on investigating the effects of Widmanstaetten type solidification on the strengthening behavior in squeeze cast Mg-8 wt% Li-3 wt% Al and Mg-10 wt%-3 wt% Al alloys.

An effective vertical handoff scheme supporting multiple applications in ubiquitous computing environment

An intelligent network management should be designed to satisfy all the requirements of applications designed for ubiquitous computing environment. Recently there may be several heterogeneous network interfaces in the same location, where a mobile terminal needs switching from one wireless interface to another. However, most of vertical handoff mechanisms are based on the network information or requirements of any single application. Thus, they cannot perform vertical handoff (VHO) at the right time and do not satisfy all the applications running on any mobile terminal. To overcome this problem, we propose an efficient scheme to solve multi-application situation by designing application manager and VHO decision manager. The proposed scheme performs VHO after checking the quality of service (QoS) in factor by factor. Factors of the abstracted profile are used to verify the QoS of networks. By performing VHO in this way, we can design an effective handoff decision algorithm and consequently this algorithm provides a multi-application oriented and QoS enhanced VHO scheme.

An effective vertical handoff scheme based on service management for ubiquitous computing

When a ubiquitous computing environment is based on seamless connectivity, intelligent network management among heterogeneous network interfaces, called vertical handoff (VHO), is required. However, conventional VHO schemes are based only on network information, and do not address service management for seamless service execution. This paper thus proposes a middleware architecture supporting efficient seamless connectivity with service management. In this architecture, we define core modules to perform VHOs in accordance with the context of services and user intention, in addition to network information. We also define profiles that express the contexts associated with the VHO process and service management. With the proposed scheme, we show that the number of unnecessary VHOs and application failures is significantly reduced, leading to an enhancement of around 34% in data throughput. The approach also reduces application failures by 50% and the number of VHOs by 32%.

A profile based vertical handoff scheme for ubiquitous computing environment

Specifically ubiquitous computing paradigm is based on seamless connectivity. And also to guarantee the seamless connectivity, an intelligent network management between heterogeneous network interfaces, called vertical handoff (VHO), should be designed. Besides, conventional VHO schemes are based on network information only, and do not provide any service manage-ment scheme for seamless service. For this reason, this paper proposes a middleware architecture supporting efficient seamless connectivity with service management. In this architecture, we define modules to perform VHOs in accordance with contexts of services, user intention as well as network information. And also we define profiles used to express the contexts related to the process of VHOs and service management. With the proposed scheme, we can reduce the number of unnecessary VHOs and application failures significantly. This leads to around 130% of enhancement in data throughput, and also 85% of application failures can be reduced.

A seamless service management with context-aware handoff scheme in ubiquitous computing environment

Despite the importance of seamless connectivity in ubiquitous computing, research for seamless connectivity has not been considered properly. To provide seamless connectivity, this paper proposes an application execution model for seamless services with an intelligent context-aware handoff scheme based on context information, such as user intentions and application requirements as well as issues of network layer. In this paper, we define several profiles reflecting various context informations and design basic modules organizing middleware architecture for seamless service management and efficient vertical handoff (VHO) management. Consequently, the proposed seamless service management with context-aware handoff scheme provides service continuity in ubiquitous computing environment by preventing unnecessary handoffs, changing application service modes adaptively, and eventually maintaining optimal network configuration. And also simulation results show about 38% enhanced performance in the processing rate, about 13% enhanced performance from service continuity, and about 29% enhanced performance in the processing time, compared with conventional schemes.

A Profile-Based Multimedia Sharing Scheme With Virtual Community, Based on Personal Space in a Ubiquitous Computing Environment

For ubiquitous computing environments, an important parameter is whether all the components in the specific environment can connect with one another. Given this capability, we can share various kinds of content across mobile terminals. This paper introduces an effective scheme to manage multimedia sharing based on specially designed profiles and a virtual community. A virtual community is defined as any specific group of users connected for a common interest. Specifically the proposed scheme consists of two layers, i.e., a community construction layer and a multimedia sharing layer, based on personal spaces, which are responsible for constructing and managing the multimedia sharing community. The community construction layer, which is designed to be run on the mobile terminals, provides an effective way to find community members simultaneously, based on specially designed profiles, such as a user profile and an abstract profile. The multimedia sharing layer is responsible for sharing multimedia content, and is constructed as a specially designed scheme based on locality. The proposed scheme provides an effective multimedia sharing mechanism within a community. Simulation results show that the number of messages and the time required for community member discovery is reduced by 32% and 73%, respectively, in comparison with the conventional DHT-based scheme. The approach also reduces the time to exchange content by 50% with respect to the same baseline.

Improving performance on object recognition for real-time on mobile devices

Augmented reality has been on the rise due to the proliferation of mobile devices. At the same time, object recognition has also come to the fore. In particular, many studies have focused on object recognition based on markerless matching. However, most of these studies have focused on desktop systems, which can have high performance in terms of CPU and memory, rather than investigating the use of mobile systems, which have been previously unable to provide high-performance object recognition based on markerless matching. In this paper, we propose a method that uses the OpenCV mobile library to improve real-time object recognition performance on mobile systems. First, we investigate the original object recognition algorithm to identify performance bottlenecks. Second, we optimize the algorithm by analyzing each module and applying appropriate code enhancements. Last, we change the operational structure of the algorithm to improve its performance, changing the execution frequency of the object recognition task from every frame to every four frames for real-time operation. During the three frames in which the original method is not executed, the object is instead recognized using the mobile devices accelerometer. We carry out experiments to reveal how much each aspect of our method improves the overall object recognition performance; overall, experimental performance improves by approximately 800 %, with a corresponding reduction of approximately 1 % in object recognition accuracy. Therefore, the proposed technique can be used to significantly improve the performance of object recognition based on markerless matching on mobile systems for real-time operation.

Performance optimization of 3D applications by OpenGL ES library hooking in mobile devices

The mobile GPU (Graphic Processing Unit) market has grown steadily due to expansion of the mobile game industry. Despite the rapid computation capability of mobile devices, handling a large amount of high-quality graphics in real-time is difficult. Therefore, effective technologies for improving mobile GPU in smartphones are required. In this thesis, we examine the trade-off between quality and performance, and address the benefits of graphic performance improvement by degrading quality. To implement this idea, we propose performance optimization methodologies for 3D applications using an OpenGL ES library hooking method. Our methodologies do not require any source code from 3D applications, and can be applied to any Android phones that use OpenGL ES in real-time. To demonstrate the benefits of our methodology, we conducted performance verifications of five well-known benchmarks using a smartphone, and measured the quality in accordance with each methodology. In addition, we showed the optimal trade-offs between quality and performance. By using the proposed technique, the performance of mobile GPU can be significantly improved to achieve a better trade-off between quality and performance.

An Efficient Scheme to Construct Virtual Community for Multimedia Content Sharing Based on Profile in a Ubiquitous Computing Environment

For ubiquitous computing environments, an important assumption is that all the components in any specific environment are connected with each other. With this assumption, we can share various kinds of content across mobile terminals. This paper introduces an effective scheme to manage multimedia sharing based on specially designed profiles and a virtual community. A virtual community is defined as any specific group of users connected for a common interest. The proposed scheme consists of two layers, i.e., a community construction layer and a multimedia sharing layer, which are responsible for constructing and managing the multimedia sharing community. The community construction layer, which is designed to be run on the mobile terminals, provides an effective way to find community members simultaneously, based on specially designed profiles, such as a user profile and an abstracted profile. The multimedia sharing layer is responsible for sharing multimedia contents, and is constructed as a specially designed scheme based on locality. Specifically this paper focuses on an effective community construction scheme performed by community construction layer. The proposed scheme provides an effective community construction mechanism. Simulation results show that the number of messages and the time required for community member discovery is reduced by 32% and 73%, respectively, in comparison with the conventional DHT-based scheme.

Rotated Object Recognition Based on Corner Feature Points for Mobile Augmented Reality Applications

Object recognition technology has been a major issue in mobile environments. However, it is difficult to recognize any object on mobile devices, because mobile devices do not have enough performance on CPU and memory components. Thus, a new fast handling algorithm optimized for mobile devices is required to recognize objects. In this research, we propose new methods to recognize any object, especially rotated objects. Our method is designed to recognize any rotated object through corner point data. Corner data can be replaced by grouping those points having similar features as a representative one. And, corner data that are nearest from edge points are chosen to minimize any change of pixel information when rotating any given object. Also any specific pattern of the selected corner data and pixel information around the selected corner data need to be collected and stored for later matching operation. Experiment result shows that the proposed method can provide 96% accuracy. And, our algorithm shows highest performance. Therefore, our methods can be adapted to recognize any rotated object for performance and accuracy.