Dongwon Lee

Antecedents and consequences of mobile phone usability

We propose simplicity and interactivity as key determinants of usability.We examine the effects of usability on user satisfaction, trust, and brand loyalty.Increasing simplicity will increase interactivity and usability experience.Usability is a distal determinant of brand loyalty.Satisfaction and trust mediate the effects usability on brand loyalty. Usability is a central issue for mobile phone design and service because users need to access various functionalities via limited user interfaces (UI) often while they are on the road. In this paper, we propose simplicity and interactivity as the key determinants of mobile phone usability and assess their significance in an empirical setting. Furthermore, we examine the effects of mobile phone usability on user satisfaction, trust, and brand loyalty and provide a holistic view of the causal relationships between the proposed UI features and important organizational variables for building and maintaining long-term customer relationships. The study was conducted using survey questionnaire data collected from 310 mobile phone users in South Korea. The findings of the study confirm that simplicity and interactivity are two significant determinants of mobile phone usability and that interface simplicity is an important precondition for positive interactivity and usability experience. Our findings also show that usability is a distal determinant of brand loyalty, exerting its influence indirectly through the mediators of satisfaction and trust. We discuss the implications of the study findings for usability research and UI design.

Understanding music sharing behaviour on social network services

Purpose – The purpose of this paper is to understand music sharing behaviour on social networking services (SNS). This study suggests and examines a research model which focuses on the influences of user motivations, such as self‐expression, ingratiation, altruism, and interactivity, on music sharing behaviour in SNS through social motivation factors.Design/methodology/approach – Data were collected from 153 Korean SNS (i.e. Cyworld, Naver Blog, Daum Blog, and Tistory) users, who have experience in purchasing music and legally sharing it on SNS. The partial least squares method was used to analyse the measurement and structural models.Findings – The study shows that interactivity, perceived ease of use, self‐expression, social presence, and social identity are significant positive predictors of music sharing intention on SNS.Research limitations/implications – This research is significant in light of recent interest in user activities in SNS. Better understanding of the music sharing behaviour on SNS can ...

Watermarking two dimensional data object identifier for authenticated distribution of digital multimedia contents

A digital object identifier refers to diverse technologies associated with assigning an identifier to a digital resource and managing the identification system. One type of implementation of a digital object identifier developed by the Korean Government is termed the Universal Content Identifier (UCI) system. It circulates and utilizes identifiable resources efficiently by connecting various online and offline identifying schemes. UCI tags can contain not only identifiers but also abundant additional information regarding contents. So, researchers and practitioners have shown great interest in methods that utilize the two-dimensional barcode (2D barcode) to attach UCI tags to digital contents. However, attaching a 2D barcode directly to a digital content raises two problems. First, quality of the content may deteriorate due to the insertion of the barcode; second, a malicious user can invalidate the identifying tag, simply by removing the tag from the original content. We believe that these concerns can be mitigated by inserting an invisible digital tag containing information about an identifier and digital copyrights into the entire area of the digital content. In this study, to protect copyrights of digital contents securely without quality degradation, we attempt to discover a sequence of process for generating a 2D barcode from a UCI tag and watermarking the barcode into a digital content. Such a UCI system can be widely applied to areas such as e-learning, distribution tracking, transaction certification, and reference linking services when the system is equipped with 2D barcode technology and secure watermarking algorithms. The latter part of this paper analyzes intensive experiments conducted to evaluate the robustness of traditional digital watermarking algorithms against external attacks.

Factors affecting the perceived usability of the mobile web portal services: comparing simplicity with consistency

Korean IT industry has noticed innovative changes emerging along with the increased popularity of smartphones. Increase of smartphone user has extended the smartphone business arena from simple and personal applications and content to professional software for the purpose of working in- and out of the office. In this regard, developing their services to be mobile-friendly would be important business strategies for Web business companies. The mobile data traffic in Korea had been 11.2 times increased from January 2010 to January 2011 and the average traffic per user in Korea is much higher than other countries. Usage of smartphones also has been steadily increased with the diffusion of smartphones. This may indicate that the dependency level on mobile portal service in Korea would be higher and more important than in other countries. This study analyzes the influences of UI simplicity and UI consistency on user perceptions of mobile portal services using PLS methodology. Simplicity shows a greater effect on usability and credibility than does consistency although consistency also shows a significant effect. In this regard, developing mobile Web services to be simple by following the selection and concentration strategy can be an effective strategic approach. Credibility shows a greater and direct effect on user satisfaction in this study than simplicity. But it does not mean that the perceived credibility should be treated simply as more important to user satisfaction than usability. Credibility of mobile Web services would be concreted more when the perceived usability would be developed with proper UI simplicity and consistency following the suggestion of Mann and Sahni. Also satisfaction significantly turns out to mediate the effect of credibility on loyalty. This study contributes as an earlier study on how and what the mobile Web service providers should design and provide their services.

Cerebellar Shank2 Regulates Excitatory Synapse Density, Motor Coordination, and Specific Repetitive and Anxiety-Like Behaviors

Shank2 is a multidomain scaffolding protein implicated in the structural and functional coordination of multiprotein complexes at excitatory postsynaptic sites as well as in psychiatric disorders, including autism spectrum disorders. While Shank2 is strongly expressed in the cerebellum, whether Shank2 regulates cerebellar excitatory synapses, or contributes to the behavioral abnormalities observed in Shank2−/− mice, remains unexplored. Here we show that Shank2−/− mice show reduced excitatory synapse density in cerebellar Purkinje cells in association with reduced levels of excitatory postsynaptic proteins, including GluD2 and PSD-93, and impaired motor coordination in the Erasmus test. Shank2 deletion restricted to Purkinje cells (Pcp2-Cre;Shank2fl/fl mice) leads to similar reductions in excitatory synapse density, synaptic protein levels, and motor coordination. Pcp2-Cre;Shank2fl/fl mice do not recapitulate autistic-like behaviors observed in Shank2−/− mice, such as social interaction deficits, altered ultrasonic vocalizations, repetitive behaviors, and hyperactivity. However, Pcp2-Cre;Shank2fl/fl mice display enhanced repetitive behavior in the hole-board test and anxiety-like behavior in the light-dark test, which are not observed in Shank2−/− mice. These results implicate Shank2 in the regulation of cerebellar excitatory synapse density, motor coordination, and specific repetitive and anxiety-like behaviors. SIGNIFICANCE STATEMENT The postsynaptic side of excitatory synapses contains multiprotein complexes, termed the postsynaptic density, which contains receptors, scaffolding/adaptor proteins, and signaling molecules. Shank2 is an excitatory postsynaptic scaffolding protein implicated in the formation and functional coordination of the postsynaptic density and has been linked to autism spectrum disorders. Using Shank2-null mice and Shank2-conditional knock-out mice with a gene deletion restricted to cerebellar Purkinje cells, we explored functions of Shank2 in the cerebellum. We found that Shank2 regulates excitatory synapse density, motor coordination, and specific repetitive and anxiety-like behaviors, but is not associated with autistic-like social deficits or repetitive behaviors.

Functional and Physical Interaction of Diacylglycerol Kinase ζ with Protein Kinase Cα Is Required for Cerebellar Long-Term Depression

The balance between positive and negative regulators required for synaptic plasticity must be well organized at synapses. Protein kinase Cα (PKCα) is a major mediator that triggers long-term depression (LTD) at synapses between parallel fibers and Purkinje cells in the cerebellum. However, the precise mechanisms involved in PKCα regulation are not clearly understood. Here, we analyzed the role of diacylglycerol kinase ζ (DGKζ), a kinase that physically interacts with PKCα as well as postsynaptic density protein 95 (PSD-95) family proteins and functionally suppresses PKCα by metabolizing diacylglycerol (DAG), in the regulation of cerebellar LTD. In Purkinje cells of DGKζ-deficient mice, LTD was impaired and PKCα was less localized in dendrites and synapses. This impaired LTD was rescued by virus-driven expression of wild-type DGKζ, but not by a kinase-dead mutant DGKζ or a mutant lacking the ability to localize at synapses, indicating that both the kinase activity and synaptic anchoring functions of DGKζ are necessary for LTD. In addition, experiments using another DGKζ mutant and immunoprecipitation analysis revealed an inverse regulatory mechanism, in which PKCα phosphorylates, inactivates, and then is released from DGKζ, is required for LTD. These results indicate that DGKζ is localized to synapses, through its interaction with PSD-95 family proteins, to promote synaptic localization of PKCα, but maintains PKCα in a minimally activated state by suppressing local DAG until its activation and release from DGKζ during LTD. Such local and reciprocal regulation of positive and negative regulators may contribute to the fine-tuning of synaptic signaling. SIGNIFICANCE STATEMENT Many studies have identified signaling molecules that mediate long-term synaptic plasticity. In the basal state, the activities and concentrations of these signaling molecules must be maintained at low levels, yet be ready to be boosted, so that synapses can undergo synaptic plasticity only when they are stimulated. However, the mechanisms involved in creating such conditions are not well understood. Here, we show that diacylglycerol kinase ζ (DGKζ) creates optimal conditions for the induction of cerebellar long-term depression (LTD). DGKζ works by regulating localization and activity of protein kinase Cα (PKCα), an important mediator of LTD, so that PKCα effectively responds to the stimulation that triggers LTD.

Ontology based information distribution in the pervasive display environment

Displays providing different information at many different locations are exponentially increasing. Under this pervasive display environment, users may be provided with customized information in real-time at each point of interest (POI). However what type of information to be provided is not easy to define. In this paper, architecture for information distribution based on the “environment ontology” is proposed. Display system embedded with the environment ontology relates the location with available services/information with the user profile. We implemented information push and pull system SAS (Shopping Agent Service) integrated with environment ontology to support human decision in the process of purchasing a product within a shopping mall. SAS demonstrates how the information is distributed harnessing ontology and user profile at each different location.

Reducing repair-bandwidth using codes based on factor graphs

Distributed storage systems suffer from significant repair traffic generated due to frequent storage node failures. This paper shows that properly designed low-density parity-check (LDPC) codes can substantially reduce the amount of required block downloads for repair thanks to the sparse nature of their factor graph representation. In particular, with a careful construction of the factor graph, both low repair-bandwidth and high reliability can be achieved for a given code rate. First, a formula for the average repair bandwidth of LDPC codes is developed. This formula is then used to establish that the minimum repair bandwidth can be achieved by forcing a regular check node degree in the factor graph. It is also shown that for a given repair-bandwidth overhead, LDPC codes can have substantially higher reliability than currently utilized Reed-Solomon (RS) codes. Our reliability analysis is based on a formulation of the general equation for the mean-time-to-data-loss (MTTDL) associated with LDPC codes. The formulation reveals that the stopping number is highly related to MTTDL. For code rates 1/2, 2/3, and 3/4, our results show that quasi-cyclic (QC) progressive-edge-growth (PEG) LDPC codes with variable node degree 2 allow 25% ~ 50% reduction in the repair bandwidth while maintaining higher MTTDL compared to currently employed RS codes.

Diacylglycerol Kinases in the Coordination of Synaptic Plasticity

Synaptic plasticity is activity-dependent modification of the efficacy of synaptic transmission. Although, detailed mechanisms underlying synaptic plasticity are diverse and vary at different types of synapses, diacylglycerol (DAG)-associated signaling has been considered as an important regulator of many forms of synaptic plasticity, including long-term potentiation (LTP) and long-term depression (LTD). Recent evidences indicate that DAG kinases (DGKs), which phosphorylate DAG to phosphatidic acid to terminate DAG signaling, are important regulators of LTP and LTD, as supported by the results from mice lacking specific DGK isoforms. This review will summarize these studies and discuss how specific DGK isoforms distinctly regulate different forms of synaptic plasticity at pre- and postsynaptic sites. In addition, we propose a general role of DGKs as coordinators of synaptic plasticity that make local synaptic environments more permissive for synaptic plasticity by regulating DAG concentration and interacting with other synaptic proteins.

Collective intelligence based Collaborative Learning platform

Networked computers provide an environment for students to work, learn, explore and think in small groups of peers connected globally. However, previous CSCL (Computer Supported Collaborative Learning) studies consider primitive level of knowledge sharing and knowledge building on Web 2.0 environment. In this study we propose the architecture of collective intelligence based collaborative learning platform consisting following four modules: 1) knowledge gathering module, 2) knowledge stratification/structuring module, 3) knowledge visualization module, and 4) knowledge evaluation module. Moreover this study analyzes how each module is related with the collaborative knowledge building model and collective mental map.