Hyungsoo Lee

A Critical Review of User Studies on Healthy Smart Homes

Considerable research has been conducted on smart services and technologies over the past decades, and the realization of smart environments has been one of the important research themes in housing studies. However, there is a lack of evaluation of the effects of those technologies on user experience from a cognitive perspective. This paper reviews the evaluation methods adopted in user studies of healthy smart homes. The review of user studies would enable the consolidation of knowledge to develop appropriate evaluation strategies for investigating user experience of smart services and technologies. Through an exhaustive search on contents pages of articles, different strategies for user studies were examined that span a range of experimental settings and analysis methods. These strategies can potentially work together in complementary ways to provide insights into user experience of healthy smart homes. The review highlighted research issues on user experience to be addressed for smart environments, giving valuable insights on cognitive paradigms to develop guide for smart services and technologies, which would ultimately encourage user satisfaction and foster sensibility.

Self-oriented Sb2Se3 nanoneedle photocathodes for water splitting obtained by a simple spin-coating method

Synthesis of one-dimensional nanostructured chalcogenide compounds using nontoxic and abundant constituents provides an important pathway to the development of commercially feasible photoelectrochemical water splitting. In this study, grass-like Sb2Se3 nanoneedle arrays are successfully fabricated on a substrate via a facile spin-coating method without any complicated processes such as templating, seed formation, or use of a vapor phase. Preferential [001] growth of the initial single-crystalline Sb2Se3 occurs during the first spin-coating, but interfacial defects are generated upon subsequent spin-coating iterations, resulting in annual-ring-like growth of Sb2Se3 nanoneedles. After sequential surface modification with TiO2 and Pt, the resistance to charge transfer from the photoelectrode to the electrolyte decreases significantly, yielding a remarkable record-high photocurrent of 2 mA cm−2 at 0 VRHE (4.5 mA cm−2 at −0.2 VRHE).

Patterns and predictors of non-use of family planning methods in Ethiopian women: a panel survey

PURPOSE Family planning (FP) is a key global health issue for achieving millennium development goals by 2015. The aim of this study was to identify predictors of changes in FP practice before and after interventions among Ethiopian women of reproductive age in a rural area. METHODS This study used a panel survey to identify predictors that placed women at greater risk for non-use of FP methods. The sample consisted of 407 women aged 19-49 years old living in a rural community of Ethiopia who completed both a baseline and follow-up survey. Trained local enumerators conducted face-to-face interviews during home visits. Patterns of FP practice were categorized into four groups: FP use at both baseline and follow-up; use at baseline but non-use at follow-up; non-use at baseline but use at follow-up; non-use at both baseline and follow-up. Logistic regression and classification and regression tree analyses were used. RESULTS In a binary logistic regression, women over 35 years old with a negative attitude towards FP and resided in the Sibu area were less likely to start FP practice. Women over 35 years who were in poor health and resided in Sibu were less likely to continue FP practice. For the decision tree, age was the primary node for FP non-users at baseline while area of residence was the primary node for FP users at baseline. CONCLUSION Age, health status, attitude towards FP, and area of residence are the primary considerations when developing FP interventions for Ethiopian women in a resource-limited rural area.

Detection of EEG Arousals in Patients with Respiratory Sleep Disorder

This paper describes the detection of arousals from sleep in patients with respiratory sleep disorder using a single channel EEG signal and support vector machine classifier. Determining the occurrence and the frequency of occurrence of arousals from sleep is very important because it is directly related to the quality of sleep. In this paper we used twenty polysomnographic recordings of patients with respiratory sleep disorder. Six recordings were used as training sets and fourteen recordings were used as test sets. We extracted three types of features, which are six indices relating to sleep states, the powers of each of four frequency bands and variations of power of EEG frequency, using time-frequency analysis. We detected arousals from sleep using the above features and SVM classifier. From the results, the sensitivity of 79.65% and the specificity of 89.52% were obtained. The error between the total arousal time detected by the proposed method and the annotated data was 15.09±10.76 min and it showed the possibility of application for the detection of arousal from sleep using a single channel EEG signal.

Photoelectrodes based on 2D opals assembled from Cu-delafossite double-shelled microspheres for an enhanced photoelectrochemical response

Although a unique light-harvesting property was recently demonstrated in a photocathode based on 2-dimensional (2D) opals of CuFeO2-shelled SiO2 microspheres, the performance of a monolayer of ultra-thin CuFeO2-shelled microspheres is limited by ineffective charge separation. Herein, we propose an innovative design rule, in which an inner CuFeO2/outer CuAlO2 double-shelled heterojunction is formed on each partially etched microsphere to obtain a hexagonally assembled 2D opal photoelectrode. Our Cu-delafossite double-shelled photocathode shows a dramatically improved charge separation capability, with a 9-fold increase in the photocurrent compared to that of the single-shelled counterpart. Electrochemical impedance spectroscopy clearly confirms the reduced charge transport/transfer resistance associated with the Cu-delafossite double-shelled photocathode, while surface photovoltage spectra reveal enhanced polarization of the photogenerated carrier, indicating improved charge separation capability with the aid of the heterojunction. Our finding sheds light on the importance of heterojunction interfaces in achieving optimal charge separation in opal architectures as well as the inner-shell/electrolyte interface to expedite charge separation/transport.

Controlled Electrodeposition of Photoelectrochemically Active Amorphous MoSx Cocatalyst on Sb2Se3 Photocathode

Amorphous molybdenum sulfide (a-MoS x) is a promising hydrogen evolution catalyst owing to its low cost and high activity. A simple electrodeposition method (cyclic voltammetry) allows uniform formation of a-MoS x films on conductive surfaces. However, the morphology of a-MoS x deposited on a TiO2/Sb2Se3 photocathode could be modulated by varying the starting potential. The cathodically initiated a-MoS x showed conformal filmlike morphology, whereas anodic initiation induced inhomogeneous particulate deposition. The filmlike morphology of a-MoS x was subjected to catalyst activation, which improved the photocurrent density and reduced the charge-transfer resistance at the semiconductor/electrolyte interface, as compared to that of its particulate counterpart. X-ray photoelectron spectroscopy confirmed that different chemical states of a-MoS x (photoelectrochemically active sites) were developed on the basis of the electrodeposited a-MoS x morphology. The research provides an effective approach for uniformly depositing cost-effective a-MoS x on nanostructured photoelectrodes, for photoelectrochemical water splitting.

Time-Resolved Observations of Photo-Generated Charge Carrier Dynamics in Sb2Se3 Photocathodes for Photoelectrochemical Water Splitting

Solar-energy conversion by photoelectrochemical (PEC) devices is driven by the separation and transfer of photogenerated charge carriers. Thus, understanding carrier dynamics in a PEC device is essential to realizing efficient solar-energy conversion. Here, we investigate time-resolved carrier dynamics in emerging low-cost Sb2Se3 nanostructure photocathodes for PEC water splitting. Using terahertz spectroscopy, we observed an initial mobility loss within tens of picoseconds due to carrier localization and attributed the origin of carrier localization to the rich surface of Sb2Se3 nanostructures. In addition, a possible recombination at the interface between Sb2Se3 and the back contact is elucidated by time-resolved photoluminescence analysis. We also demonstrated the dual role of the RuO x co-catalyst in reducing surface recombination and enhancing charge transfer in full devices using intensity-modulated spectroscopy. The relatively low onset potential of the Sb2Se3 photocathode is attributed to the sluggish charge transfer at a low applied bias rather than to fast surface recombination. We believe that our insights on carrier dynamics would be an important step toward achieving highly efficient Sb2Se3 photocathodes.