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A wireless dimmable lighting system using variable-power variable-frequency control
No full textThis article proposes and implements a wireless dimmable lighting system using variable-power variable-frequency (VPVF) control, which can eliminate the use of secondary converters via wireless power transfer (WPT). The proposed scheme integrates the secondary T-LCL circuit into a sealed antiparallel light-emitting diode (LED) lamp, which takes the key merits of safety, flexibility, maintenance free, and convenience for manufacturing. Moreover, it can effectively widen the LED dimming range and reduce the starting voltage requirements, which inherently improve the output fluctuation insensitivity and voltage deviation tolerance. In contrast to phase shift control, a WPT-inherent VPVF control is proposed to realize effective reductions in both the switching frequency and switching losses, while maintaining the regulation accuracy and output fluctuation suppression by up to 48.45% as compared with burst firing control. The system electrical efficiency can reach 88.08% with 20-cm transfer distance and it is improved by 3.35% during power control. Both theoretical analysis and practical experimentation are given to verify the feasibility of proposed VPVF-modulated wireless dimmable lighting system
Design and Analysis of Wireless Direct-Drive High-Intensity Discharge Lamp
No full textThe wireless power transfer (WPT) for directly driving the high-intensity discharge (HID) lamp is proposed and implemented. In this article, the HID lamp is ignited and operated solely on the resonator without using any ignitor, ballast, or additional LC tank. Meanwhile, the key characteristics in the ignition and running phases are generally analyzed with the consideration of compensation schemes and number of coils. The even-coil series-series (SS) and odd-coil series-parallel (SP) WPT are identified to be more competent for wireless lighting with short and long transfer distances, respectively. In addition, the resonant frequency of 400 kHz is chosen to improve the luminous efficacy up to 150 lm/W. For exemplification, two-coil SS, three-coil SP, four-coil SS, and five-coil SP wireless HID lamps have been built and developed with the overall distances of 20, 40, 68, and 100 cm, and the transfer efficiencies are 94.1%, 89.6%, 83.1%, and 69.2%, respectively. Both the theoretical and experimental results are given to validate the feasibility and flexibility of the proposed system
Evaluating resilience in urban transportation systems for sustainability: A systems-based Bayesian network model
No full textThis paper proposes a hierarchical Bayesian network model (BNM) to quantitatively evaluate the resilience of urban transportation systems. Based on systemic thinking and taking a sustainability perspective, we investigate the long-term resilience of the road transportation systems in four cities in China from 1998 to 2017, namely Beijing, Tianjin, Shanghai, and Chongqing, respectively. The model takes into account various factors collected from multi-source data platforms involved in stages of design, construction, operation, management, and innovation in road transportation systems. We test the model with the forward inference, sensitivity analysis, and backward inference. The result shows that the overall resilience scores of all four cities’ transportation systems are within a moderate range with values between 49% to 59%. Although they all have an ever-increasing economic level, the levels of transportation resilience in Beijing and Tianjin decrease first and then gradually increase in a long run, which indicates a strong multi-dimensional, dynamic, and non-linear characteristic in resilience-economic coupling effect. Additionally, the results obtained from the sensitivity analysis and backward inference suggest that decision makers should pay more attention to the capabilities of quickly rebuilding and making changes to cope with future disturbances. As an exploratory study, this study clarifies the concepts of long-term multi-dimensional resilience and specific hazard-related resilience and provides an effective decision-support tool for stakeholders when building resilient infrastructure
A Design Engineering Approach for Quantitatively Exploring Context-Aware Sentence Retrieval for Nonspeaking Individuals with Motor Disabilities
No full textNonspeaking individuals with motor disabilities typically have very low communication rates. This paper proposes a design engineering approach for quantitatively exploring context-aware sentence retrieval as a promising complementary input interface, working in tandem with a word-prediction keyboard. We motivate the need for complementary design engineering methodology in the design of augmentative and alternative communication and explain how such methods can be used to gain additional design insights. We then study the theoretical performance envelopes of a context-aware sentence retrieval system, identifying potential keystroke savings as a function of the parameters of the subsystems, such as the accuracy of the underlying auto-complete word prediction algorithm and the accuracy of sensed context information under varying assumptions. We find that context-aware sentence retrieval has the potential to provide users with considerable improvements in keystroke savings under reasonable parameter assumptions of the underlying subsystems. This highlights how complementary design engineering methods can reveal additional insights into design for augmentative and alternative communication
Plasmonic Effects of Dual-Metal Nanoparticle Layers for High-Performance Quantum Dot Solar Cells
No full textTo improve quantum dot solar cell performance, it is crucial to make efficient use of the available incident sunlight to ensure that the absorption is maximized. The ability of metal nanoparticles to concentrate incident sunlight via plasmon resonance can enhance the overall absorption of photovoltaic cells due to the strong confinement that results from near-field coupling or far-field scattering plasmonic effects. Therefore, to simultaneously and synergistically utilize both plasmonic effects, the placement of different plasmonic nanostructures at the appropriate locations in the device structure is also critical. Here, we introduce two different plasmonic nanoparticles, Au and Ag, to a colloidal PbS quantum dot heterojunction at the top and bottom interface of the electrodes for further improvement of the absorption in the visible and near-infrared spectral regions. The Ag nanoparticles exhibit strong scattering whereas the Au nanoparticles exhibit an intense optical effect in the wavelength region where the absorption of light of the PbS quantum dot is strongest. It is found that these dual-plasmon layers provide significantly improved short-circuit current and power conversion efficiency without any form of trade-off in terms of the fill factor and open-circuit voltage, which may result from the indirect contact between the plasmonic nanoparticles and colloidal quantum dot films
Hybrid Smart Fiber with Spontaneous Self-Charging Mechanism for Sustainable Wearable Electronics
No full textSmart wearable electronics that are fabricated on light-weight fabrics or flexible substrates are considered to be of next-generation and portable electronic device systems. Ideal wearable and portable applications not only require the device to be integrated into various fiber form factors, but also desire self-powered system in such a way that the devices can be continuously supplied with power as well as simultaneously save the acquired energy for their portability and sustainability. Nevertheless, most of all self-powered wearable electronics requiring both the generation of the electricity and storing of the harvested energy, which have been developed so far, have employed externally connected individual energy generation and storage fiber devices using external circuits. In this work, for the first time, a hybrid smart fiber that exhibits a spontaneous energy generation and storage process within a single fiber device that does not need any external electric circuit/connection is introduced. This is achieved through the employment of asymmetry coaxial structure in an electrolyte system of the supercapacitor that creates potential difference upon the creation of the triboelectric charges. This development in the self-charging technology provides great opportunities to establish a new device platform in fiber/textile-based electronics
The global variation of medical student engagement in teaching: Implications for medical electives
No full textIntroduction: International medical electives, whereby undergraduates visit an institution in a country other than their own, are a common part of medical training. Visiting students are often asked to provide local teaching, which may be acceptable where the visitor is acting within the bounds of their own competency and the normal practices of both their home and host institutions. However, the extent to which teaching is an accepted student activity globally has not previously been described. This study aims to address this using an international survey approach. Methods: A voluntary electronic survey, created using the Checklist for Reporting Results of Internet E-Surveys (CHERRIES) framework, was distributed across established international medical student networks. This assessed the involvement of medical students in teaching and the educator training they receive, with the intention of comparing experiences between high-income countries (HICs) and low/middle-income countries (LMICs) to gauge the engagement of both "host" and "visiting" students. Results: 443 students from 61 countries completed the survey, with an equal proportion of respondents from LMICs (49.4%, 219/443) and HICs (50.6%, 224/443). Around two thirds of students reported providing teaching whilst at medical school, with most reporting teaching numerous times a year, mainly to more junior medical students. There was with no significant difference between LMICs and HICs. Around 30 per cent of all medical students reported having received no teacher training, including 40 per cent of those already providing teaching. Conclusion: This study suggests that students are engaged in teaching globally, with no difference between HIC and LMIC contexts. However, students are underprepared to act as educators in both settings. Providing teaching as part of an elective experience may be ethically acceptable to both host and home institutions, but needs to be supported by formal training in delivering teaching
Simulation of mechanical stresses in reinforced REBaCuO ring bulks during pulsed-field magnetization
No full textWe have performed numerical simulations of the electromagnetic, thermal and mechanical properties of a REBaCuO ring-shaped bulk with various reinforcement structures during pulsed-field magnetization (PFM). Compressive and tensile electromagnetic stresses, IMG ALIGN="MIDDLE" ALT="" SRC="JPCS-1559-1-012027-ieqn1.gif"/are developed in the ring-shaped bulk during the ascending and descending stages of PFM, respectively. These stresses increase at lower operating temperatures and for higher applied pulsed fields. In order to reduce these stresses, the ring-shaped bulk was fully encapsulated by outer and inner ring with upper and lower plates made by Al alloy. In particular, this reinforcement structure can achieve the lowest electromagnetic compressive stress, which corresponds to about 54% of that for a conventional ring reinforcement structure, and the electromagnetic tensile stress was also reduced. We also compared the simulation results of the electromagnetic stresses for the ring-shaped bulk to those for a disk-shaped bulk
Hardware implementations of computer-generated holography: a review
No full textComputer-generated holography (CGH) is a technique to generate holographic interference patterns. One of the major issues related to computer hologram generation is the massive computational power required. Hardware accelerators are used to accelerate this process. Previous publications targeting hardware platforms lack performance comparisons between different architectures and do not provide enough information for the evaluation of the suitability of recent hardware platforms for CGH algorithms. We aim to address these limitations and present a comprehensive review of CGH-related hardware implementations