Showing papers by "National Taiwan University of Science and Technology published in 2013"

Current status, opportunities and challenges of augmented reality in education

Abstract: Although augmented reality (AR) has gained much research attention in recent years, the term AR was given different meanings by varying researchers. In this article, we first provide an overview of definitions, taxonomies, and technologies of AR. We argue that viewing AR as a concept rather than a type of technology would be more productive for educators, researchers, and designers. Then we identify certain features and affordances of AR systems and applications. Yet, these compelling features may not be unique to AR applications and can be found in other technological systems or learning environments (e.g., ubiquitous and mobile learning environments). The instructional approach adopted by an AR system and the alignment among technology design, instructional approach, and learning experiences may be more important. Thus, we classify three categories of instructional approaches that emphasize the ''roles,'' ''tasks,'' and ''locations,'' and discuss what and how different categories of AR approaches may help students learn. While AR offers new learning opportunities, it also creates new challenges for educators. We outline technological, pedagogical, learning issues related to the implementation of AR in education. For example, students in AR environments may be cognitively overloaded by the large amount of information they encounter, the multiple technological devices they are required to use, and the complex tasks they have to complete. This article provides possible solutions for some of the challenges and suggests topics and issues for future research.

A survey of DEA applications

Abstract: The literature of data envelopment analysis (DEA) encompasses many surveys, yet all either emphasize methodologies or do not make a distinction between methodological and application papers. This study is the first literature survey that focuses on DEA applications, covering DEA papers published in journals indexed by the Web of Science database from 1978 through August 2010. The results show that on the whole around two-thirds (63.6%) of DEA papers embed empirical data, while the remaining one-third are purely-methodological. Purely-methodological articles dominated the first 20 years of DEA development, but the accumulated number of application-embedded papers caught up to purely-methodological papers in 1999. Among the multifaceted applications, the top-five industries addressed are: banking, health care, agriculture and farm, transportation, and education. The applications that have the highest growth momentum recently are energy and environment as well as finance. In addition to the basic statistics, we uncover the development trajectory in each application area through the main path analysis. An observation from these works suggests that the two-step contextual analysis and network DEA are the recent trends across applications and that the two-step contextual analysis is the prevailing approach.

Affordances of Augmented Reality in Science Learning: Suggestions for Future Research

Abstract: Augmented reality (AR) is currently considered as having potential for pedagogical applications. However, in science education, research regarding AR-aided learning is in its infancy. To understand how AR could help science learning, this review paper firstly has identified two major approaches of utilizing AR technology in science education, which are named as image-based AR and location-based AR. These approaches may result in different affordances for science learning. It is then found that students’ spatial ability, practical skills, and conceptual understanding are often afforded by image-based AR and location-based AR usually supports inquiry-based scientific activities. After examining what has been done in science learning with AR supports, several suggestions for future research are proposed. For example, more research is required to explore learning experience (e.g., motivation or cognitive load) and learner characteristics (e.g., spatial ability or perceived presence) involved in AR. Mixed methods of investigating learning process (e.g., a content analysis and a sequential analysis) and in-depth examination of user experience beyond usability (e.g., affective variables of esthetic pleasure or emotional fulfillment) should be considered. Combining image-based and location-based AR technology may bring new possibility for supporting science learning. Theories including mental models, spatial cognition, situated cognition, and social constructivist learning are suggested for the profitable uses of future AR research in science education.

Tunable Band Gap Photoluminescence from Atomically Thin Transition-Metal Dichalcogenide Alloys

Abstract: Band gap engineering of atomically thin two-dimensional (2D) materials is the key to their applications in nanoelectronics, optoelectronics, and photonics. Here, for the first time, we demonstrate that in the 2D system, by alloying two materials with different band gaps (MoS2 and WS2), tunable band gap can be obtained in the 2D alloys (Mo1–xWxS2 monolayers, x = 0–1). Atomic-resolution scanning transmission electron microscopy has revealed random arrangement of Mo and W atoms in the Mo1–xWxS2 monolayer alloys. Photoluminescence characterization has shown tunable band gap emission continuously tuned from 1.82 eV (reached at x = 0.20) to 1.99 eV (reached at x = 1). Further, density functional theory calculations have been carried out to understand the composition-dependent electronic structures of Mo1–xWxS2 monolayer alloys.

Data envelopment analysis 1978-2010: A citation-based literature survey

Abstract: This study surveys the data envelopment analysis (DEA) literature by applying a citation-based approach. The main goals are to find a set of papers playing the central role in DEA development and to discover the latest active DEA subareas. A directional network is constructed based on citation relationships among academic papers. After assigning an importance index to each link in the citation network, main DEA development paths emerge. We examine various types of main paths, including local main path, global main path, and multiple main paths. The analysis result suggests, as expected, that Charnes et al. (1978) [Charnes A, Cooper WW, Rhodes E. Measuring the efficiency of decision making units. European Journal of Operational Research 1978; 2(6): 429–444] is the most influential DEA paper. The five most active DEA subareas in recent years are identified; among them the “two-stage contextual factor evaluation framework” is relatively more active. Aside from the main path analysis, we summarize basic statistics on DEA journals and researchers. A growth curve analysis hints that the DEA literature’s size will eventually grow to at least double the size of the existing literature.

A collaborative game-based learning approach to improving students' learning performance in science courses

Abstract: In this study, a collaborative game-based learning environment is developed by integrating a grid-based Mindtool to facilitate the students to share and organize what they have learned during the game-playing process. To evaluate the effectiveness of the proposed approach, an experiment has been conducted in an elementary school natural science course to examine the students' performance in terms of their learning attitudes, learning motivation, self-efficacy and learning achievements. From the experimental results, it is found that the Mindtool-integrated collaborative educational game not only benefits the students in promoting their learning attitudes and learning motivation, but also improves their learning achievement and self-efficacy owing to the provision of the knowledge organizing and sharing facility embedded in the collaborative gaming environment.

A review of technological pedagogical content knowledge

Abstract: This paper reviews 74 journal papers that investigate ICT integration from the framework of technological pedagogical content knowledge (TPACK). The TPACK framework is an extension of the pedagogical content knowledge (Shulman, 1986). TPACK is the type of integrative and transformative knowledge teachers need for effective use of ICT in classrooms. As a framework for the design of teacher education programs, the TPACK framework addresses the problem arising from overemphasis on technological knowledge in many ICT courses that are conducted in isolation from teachers' subject matter learning and pedagogical training. The present review we have conducted indicates that TPACK is a burgeoning area of research with more application in the North American region. Studies conducted to date employed varied and sophisticated research methods and they have yielded positive results in enhancing teachers' capability to integrate ICT for instructional practice. However, there are still many potential gaps that the TPACK framework could be employed to facilitate deeper change in education. In particular, we suggest more development and research of technological environments base on TPACK; study of students' learning conception with technology; and cross fertilization of TPACK with other theoretical frameworks related to the study of technology integration.

Graphene oxide as a promising photocatalyst for CO2 to methanol conversion

Abstract: Photocatalytic conversion of carbon dioxide (CO2) to hydrocarbons such as methanol makes possible simultaneous solar energy harvesting and CO2 reduction, two birds with one stone for the energy and environmental issues. This work describes a high photocatalytic conversion of CO2 to methanol using graphene oxides (GOs) as a promising photocatalyst. The modified Hummer's method has been applied to synthesize the GO based photocatalyst for the enhanced catalytic activity. The photocatalytic CO2 to methanol conversion rate on modified graphene oxide (GO-3) is 0.172 μmol g cat−1 h−1 under visible light, which is six-fold higher than the pure TiO2.

One-Pot Synthesis of Fluorescent Carbon Dots from Orange Waste Peels

Abstract: A simple and facile one-pot synthesis of fluorescent carbon dots from orange waste peels was performed using the hydrothermal carbonization method at a mild temperature (180 °C). The chemical composition and morphological feature of the obtained carbon dots (C-dots) were characterized using various spectroscopies and a transmission electron microscopy. The prepared hydrothermal carbons were amorphous in nature, and clusters of polyaromatic hydrocarbons included a large quantity of oxygen functional groups. A composite of C-dot with ZnO was used as a photocatalyst for degradation of naphthol blue-black azo dye under UV irradiation, and the superior photocatalytic activity was demonstrated. Overall, the present preparation method of C-dots takes on meaning in the area of green synthesis in aqueous solutions, and the product has great potential as a component material in the development of a remarkably efficient catalytic system.

A concept map-embedded educational computer game for improving students' learning performance in natural science courses

Abstract: Many recent studies have reported the benefits of educational computer games in promoting students' learning motivations. On the other hand, however, the effect of digital game-based learning in improving students' learning performance has been questioned. Several previous studies have reported that without properly integrating learning strategies into gaming scenarios, the effectiveness of educational computer games could be limited, or may be even worse than that of the conventional technology-enhanced learning approach. In this study, a concept map-embedded gaming approach is proposed for developing educational computer games by integrating concept mapping as part of the gaming scenarios to help students organize what they have learned during the game-based learning process. Moreover, a role-playing game has been developed for an elementary school natural science course based on the proposed approach. From the experimental results, it is found that the concept map-embedded gaming approach can significantly improve the students' learning achievement and decrease their cognitive load. Moreover, the students who learned with the proposed approach revealed a significantly higher degree of perceived usefulness than those who learned with the conventional game-based learning approach.

Application-Oriented License Plate Recognition

Abstract: We split the applications of vehicle license plate recognition (LPR) into three major categories and propose a solution with parameter settings that are adjustable for different applications. The three categories are access control (AC), law enforcement (LE), and road patrol (RP). Each application is characterized by variables of different variation scopes and thus requires different settings on the solution with which to deal. The proposed solution consists of three modules for plate detection, character segmentation, and recognition. Edge clustering is formulated for solving plate detection for the first time. It is also a novel application of the maximally stable extreme region (MSER) detector to character segmentation. A bilayer classifier, which is improved with an additional null class, is experimentally proven to be better than previous methods for character recognition. To assess the performance of the proposed solution, the application-oriented license plate (AOLP) database is composed and made available to the research community. Experiments show that the proposed solution outperforms many previous solutions, and LPR can be better solved by solutions with settings oriented for different applications.

Game-Based Learning in Science Education: A Review of Relevant Research

Abstract: The purpose of this study is to review empirical research articles regarding game-based science learning (GBSL) published from 2000 to 2011. Thirty-one articles were identified through the Web of Science and SCOPUS databases. A qualitative content analysis technique was adopted to analyze the research purposes and designs, game design and implementation, theoretical backgrounds and learning foci of these reviewed studies. The theories and models employed by these studies were classified into four theoretical foundations including cognitivism, constructivism, the socio-cultural perspective, and enactivism. The results indicate that cognitivism and constructivism were the major theoretical foundations employed by the GBSL researchers and that the socio-cultural perspective and enactivism are two emerging theoretical paradigms that have started to draw attention from GBSL researchers in recent years. The analysis of the learning foci showed that most of the digital games were utilized to promote scientific knowledge/concept learning, while less than one-third were implemented to facilitate the students’ problem-solving skills. Only a few studies explored the GBSL outcomes from the aspects of scientific processes, affect, engagement, and socio-contextual learning. Suggestions are made to extend the current GBSL research to address the affective and socio-contextual aspects of science learning. The roles of digital games as tutor, tool, and tutee for science education are discussed, while the potentials of digital games to bridge science learning between real and virtual worlds, to promote collaborative problem-solving, to provide affective learning environments, and to facilitate science learning for younger students are also addressed.

An investigation of learners' collaborative knowledge construction performances and behavior patterns in an augmented reality simulation system

Abstract: The purpose of this study was to investigate how a mobile collaborative augmented reality (AR) simulation system affects learners' knowledge construction behaviors and learning performances. In this study, 40 undergraduate students were recruited and divided into dyads to discuss a given task either with the assistance of a mobile collaborative AR system or traditional 2D simulation system. The participants' knowledge acquisition regarding elastic collision was evaluated through a pre-test and a post-test comparison. Learners' knowledge construction behaviors were qualitatively identified according to an adapted three-category coding scheme including construction of problem space (PS), construction of conceptual space (CS), and construction of relations between conceptual and problem space (CPS), and were then analyzed by adopting lag sequential analysis. The results indicated that the learners who learned with the AR system showed significant better learning achievements than those who learned with the traditional 2D simulation system. Furthermore, the sequential patterns of the learners' behaviors were identified, including three sustained loops (PS->PS, CS->CS, CPS->CPS), a bi-directional path between the PS and CPS activities (PS@?CPS), and a one way path from the PS activity to the CS activity (PS->CS). The revealed behavior patterns suggest that the AR Physics system may serve as a supportive tool and enable dyad learners to respond quickly to the displayed results and support their knowledge construction processes to produce a positive outcome. Based on the behavioral patterns found in this study, suggestions for future studies and further modifications to the system are proposed.

Band Gap Engineering of Chemical Vapor Deposited Graphene by in Situ BN Doping

Abstract: Band gap opening and engineering is one of the high priority goals in the development of graphene electronics. Here, we report on the opening and scaling of band gap in BN doped graphene (BNG) films grown by low-pressure chemical vapor deposition method. High resolution transmission electron microscopy is employed to resolve the graphene and h-BN domain formation in great detail. X-ray photoelectron, micro-Raman, and UV–vis spectroscopy studies revealed a distinct structural and phase evolution in BNG films at low BN concentration. Synchrotron radiation based XAS-XES measurements concluded a gap opening in BNG films, which is also confirmed by field effect transistor measurements. For the first time, a significant band gap as high as 600 meV is observed for low BN concentrations and is attributed to the opening of the π–π* band gap of graphene due to isoelectronic BN doping. As-grown films exhibit structural evolution from homogeneously dispersed small BN clusters to large sized BN domains with embedded d...

Glutaraldehyde Vapor Cross-linked Nanofibrous PVA Mat with in Situ Formed Silver Nanoparticles

Abstract: Polyvinyl alcohol (PVA) nanofibrous mat can be easily prepared via electrospinning its aqueous solution. However, the obtained nanofibrous mat is instantaneously dissolved in water. Therefore, rendering the environmentally friendly nanofibrous mat water insoluble by cross-linking mechanism is of great interest. The electrospun PVA nanofibrous mat with an average fiber diameter of ca. 400 nm could be effectively cross-linked by glutaraldehyde vapor at room temperature. The cross-linking not only resulted in a water-insoluble nanofibrous mat but also generated an excess amount of unreacted aldehyde functional groups that could reduce silver salts into silver nanoparticles. The in situ formed silver nanoparticles along the fibrous surface showed excellent antimicrobial activity against Escherichia coli. The vapor cross-linked nanofibrous mat shows a high potential to be used for efficiently capturing and killing pathogenic bacteria.

A personalized recommendation-based mobile learning approach to improving the reading performance of EFL students

Abstract: In this paper, a personalized recommendation-based mobile language learning approach is proposed. A mobile learning system has been developed based on the approach by providing a reading material recommendation mechanism for guiding EFL (English as Foreign Language) students to read articles that match their preferences and knowledge levels, and a reading annotation module that enables students to take notes of English vocabulary translations for the reading content in individual or shared annotation mode. To evaluate the effectiveness of the proposed approach, an experiment was conducted on a senior high school English course by assigning three classes of students to two experimental groups and a control group. One experimental group learned with the recommendation system with the individual annotation function, the other experimental group learned with the recommendation system with the shared annotation function, while the students in the control group learned with the individual annotation function, but without the recommendation system. The experimental results show that both experimental groups outperformed the control group, but there was no difference in learning outcome between the two experimental groups in terms of learning achievements.

FeS2 Nanocrystal Ink as a Catalytic Electrode for Dye‐Sensitized Solar Cells

Abstract: In the last decade, dye-sensitized solar cells (DSSCs) have attracted great interest for the fabrication of low-cost largearea photovoltaic devices as an alternative to conventional inorganic counterparts. The counter electrode (CE) is a critical component in DSSCs, where electrons are injected into the electrolyte to catalyze iodine reductions (I3 to I ). The most commonly used CE is based on indium-doped tin oxide (ITO)-coated glass loaded with platinum by sputtering. Platinum has a high catalytic activity for triiodide reduction and presents sufficient corrosion resistance. However, Pt is expensive because of its scarcity, and thus, the development of so-called Pt-free CEs for DSSCs using cheaper and abundant materials becomes technologically desirable. Recently, carbon-based materials, such as graphite, graphene, carbon nanotubes, and conducting polymers, have been used to replace Pt as electrocatalysts for triiodide reduction in DSSCs, although these devices still suffer from poor thermal stability and weak corrosion resistance. Extensive research has been performed on using inorganic compounds such as transitional metal carbides, nitrides, oxides, and sulfides as a new class of alternative catalytic materials for Pt in DSSC systems. Therefore, pursuing low-cost and stable CE materials as alternatives to expensive Pt is crucial to make DSSC systems more competitive for future commercial applications. Pyrite iron disulfide (FeS2, so-called fool s gold) is an interesting next-generation photovoltaic material candidate that is abundant in nature and is nontoxic. It is ranked as having the highest material availability among 23 existing semiconducing photovoltaic systems that could potentially lead to lower costs compared to conventional silicon solar cells. Colloidal pyrite nanocrystals (NCs) were recently synthesized and characterized, providing great potential for developing low-cost fabrications of FeS2-based photovoltaic devices using solution processes. We first demonstrated pyrite NC-based photodiode devices with a spectral response extended to near infrared (NIR) wavelengths because of its large optical absorption coefficient (> 10 cm ) and narrow band gap of 0.95 eV, which provided a crucial step toward success in producing colloidal pyrite NCs thin films as photovoltaic absorption layers. This study demonstrates an important photovoltaic application using FeS2 nanocrystal pyrite ink to fabricate a cost-effective CE in DSSCs, which has the unique advantages of earth abundance and of being solution-processable. The DSSC device with the CE using the FeS2 NC ink exhibits a promising power conversion efficiency of 7.31% comparable to that of the cell using the precious metal of Pt deposited by sputtering (7.52 %), as well as remarkable electrochemical stability of greater than 500 consecutive cycle scans. Solution-processable and semi-transparent FeS2 NC-based CEs also enable the fabrication of flexible and bifacial DSSCs. The results indicate that FeS2 NC ink is an extremely promising candidate for replacing Pt to substantially reduce the cost of DSSCs in future commercial applications and have also shed light on employing the low-cost FeS2 NC catalyst in other electrochemical cells. The FeS2 NCs were prepared using wet solution-phase chemical syntheses with a number of modifications according to our previous reports. 25] Figure 1a shows a highresolution transmission electron microscopy (HR-TEM) image of an FeS2 NC with a diameter of 15 3 nm. The clear lattice fringes of the FeS2 NCs with a lattice spacing of 0.31 nm matched the (111) plane of pyrite. The fast Fourier transform (FFT) patterns shown in Figure 1b exhibited various index facets, including {210}, {211}, and {311} on the NC, showing typical signatures of a pyrite-phased crystal structure.Figure 1 c shows a photograph of the FeS2 NCs ink. For fabricating the FeS2 NC CE, FeS2 NC ink of concentration 30 mg mL 1 was spin-coated onto an ITO glass substrate at 4000 rpm for 20 s, as shown in Figure 1d. Because as[*] Y.-C. Wang, Dr. D.-Y. Wang, H.-A. Chen, Prof. C.-W. Chen Department of Materials Science and Engineering National Taiwan University No. 1, Sec. 4, Roosevelt Rd., Taipei, 10617 (Taiwan) E-mail: chunwei@ntu.edu.tw

b-SPECS+: Batch Verification for Secure Pseudonymous Authentication in VANET

Abstract: The security and privacy preservation issues are prerequisites for vehicular ad hoc networks. Recently, secure and privacy enhancing communication schemes (SPECS) was proposed and focused on intervehicle communications. SPECS provided a software-based solution to satisfy the privacy requirement and gave lower message overhead and higher successful rate than previous solutions in the message verification phase. SPECS also presented the first group communication protocol to allow vehicles to authenticate and securely communicate with others in a group of known vehicles. Unfortunately, we find out that SPECS is vulnerable to impersonation attack. SPECS has a flow such that a malicious vehicle can force arbitrary vehicles to broadcast fake messages to other vehicles or even a malicious vehicle in the group can counterfeit another group member to send fake messages securely among themselves. In this paper, we provide a secure scheme that can achieve the security and privacy requirements, and overcome the weaknesses of SPECS. Moreover, we show the efficiency merits of our scheme through performance evaluations in terms of verification delay and transmission overhead.

Properties of Individual Dopant Atoms in Single-Layer MoS2: Atomic Structure, Migration, and Enhanced Reactivity

Abstract: The differences in the behavior of Re (n-type) and Au (p-type) dopant atoms in single-layered MoS2 were investigated by in situ scanning transmission electron microscopy. Re atoms tend to occupy Mo sites, while Au atoms exist as adatoms and show larger mobility under the electron beam. Re substituted to Mo site showed enhanced chemical affinity, evidenced by agglomeration of Re adatoms around these sites. This may explain the difficulties in achieving a high compositional rate of homogeneous Re doping in MoS2. In addition, an in situ coverage experiment together with density functional theory calculations discovered a high surface reactivity and agglomeration of other impurity atoms such as carbon at the Re doped sites.

Photovoltaic Power-Increment-Aided Incremental-Conductance MPPT With Two-Phased Tracking

Abstract: This paper presents a two-phased tracking that forms a photovoltaic (PV) power-increment-aided incremental-conductance (PI-INC) maximum power point tracking (MPPT) to improve the tracking behavior of the conventional INC MPPT. The PI-INC MPPT performs, using either variable-frequency constant-duty control (VFCD) or constant-frequency variable-duty control (CFVD), with reference to a collectively called threshold-tracking zone (TTZ), beyond which a power-increment (PI) tracking along the Ppv -Vpv curve executes and within which an INC tracking along the Ipv-Vpv curve toward maximum power point (MPP) does. Delay tracking due to ambiguous conductance-increment detection in the flat portion of the left-hand side of the MPP along the Ipv -Vpv curve will not appear in the PI-INC MPPT by using the PI tracking with clear and correct power-increment detection along the Ppv- Vpv curve. In addition, the merit of INC MPPT to accurately track against the random solar insolation change still retains in the PI-INC MPPT that uses INC tracking toward MPP along the Ipv -Vpv curve when tracking in the TTZ. Modeling and analysis of two typical PV power converters with VFCD and CFVD controls are addressed for implementing the tracking of the PI-INC MPPT in design and experiment. The tracking behavior of PI-INC MPPT and the conventional INC MPPT is assessed and compared through elaborate experimental tests.

Visualization and quantification of transition metal atomic mixing in Mo 1− x W x S 2 single layers

Abstract: Understanding the influence of disorder on the properties of two-dimensional materials is of increasing importance, given the interest in these compounds for electronic applications. Using a scanning transmission electron microscope, Dumcenco et al. quantify the atomic mixing in two-dimensional films of Mo1–xWxS2.

On Secrecy Rate of the Generalized Artificial-Noise Assisted Secure Beamforming for Wiretap Channels

Abstract: In this paper we consider the secure transmission with multiple-input, single-output, single-antenna eavesdropper (MISOSE) in fast fading channels where the transmitter knows perfect legitimate channel state information but only the statistics of the eavesdropper's channel. For the MISOSE channels, the artificial noise assisted beamforming proposed by Goel and Negi is a promising technique, where the artificial noise is imposed on the null space of the legitimate channel to disrupt the eavesdropper's reception. Here we propose a generalized artificial noise scheme which allows the injection of the artificial noise to the legitimate channel. Although the generalized artificial noise may cause the leakage of artificial noise at the legitimate receiver, the secrecy rate can still be improved since the covariance matrix of it is more flexible than the heuristic one selected by Goel and Negi. To fully characterize the proposed scheme, we investigate the optimization of its secrecy rate. We first derive the conditions under which the beamformers of the message bearing signal and the generalized artificial noise being the same is optimal. Based on this choice, the complicated secrecy rate optimization problem over the covariance matrices of the message-bearing signal and the generalized artificial noise can be reduced to a much simpler power allocation problem. We also develop an efficient algorithm to solve this non-convex power allocation problem. Numerical results show that our generalized artificial noise scheme outperforms Goel and Negi's heuristic selection, especially in the near eavesdropper settings. In particular, with the aid of the proposed scheme, the regime with non-zero secrecy rate is enlarged, which can significantly improve the connectivity of the network.

Cascade Cockcroft–Walton Voltage Multiplier Applied to Transformerless High Step-Up DC–DC Converter

Abstract: This paper proposes a high step-up dc-dc converter based on the Cockcroft-Walton (CW) voltage multiplier without a step-up transformer. Providing continuous input current with low ripple, high voltage ratio, and low voltage stress on the switches, diodes, and capacitors, the proposed converter is quite suitable for applying to low-input-level dc generation systems. Moreover, based on the n-stage CW voltage multiplier, the proposed converter can provide a suitable dc source for an n + 1-level multilevel inverter. In this paper, the proposed control strategy employs two independent frequencies, one of which operates at high frequency to minimize the size of the inductor while the other one operates at relatively low frequency according to the desired output voltage ripple. A 200-W laboratory prototype is built for test, and both simulation and experimental results demonstrate the validity of the proposed converter.

Identifying Science Teachers’ Perceptions of Technological Pedagogical and Content Knowledge (TPACK)

Abstract: The application of information and communication technology in instruction is highly emphasized in the contemporary education of science teachers. This paper hence aims to explore science teachers’ perceptions of technological pedagogical content knowledge (TPACK) addressing teachers’ perceptions of the affordances of technology application in instruction. A total of 222 pre- and in-service science teachers in Singapore were surveyed. Structural equation models analysis was utilized to examine the model of TPACK involving the seven factors of technological knowledge (TK), pedagogical knowledge (PK), content knowledge (CK), technological content knowledge (TCK), technological pedagogical knowledge (TPK), pedagogical content knowledge (PCK), as well as synthesized knowledge of technology, pedagogy, and content (TPC). The results confirm the seven-factor model and indicate that the science teachers’ perceived TPC significantly and positively correlated with all the other TPACK factors. This paper further reveals the relationships between the science teachers’ perceptions of TPACK and their demographic characteristics such as teaching experience, gender, and age. The findings indicate that female science teachers perceive higher self-confidence in pedagogical knowledge but lower self-confidence in technological knowledge than males. Further, female in-service science teachers’ perceptions of TK, TPK, TCK, and TPC significantly and negatively correlate with their age.