985 research outputs found
Effect of heat treatment temperature on microstructure and mechanical and tribological properties of cold sprayed Ti-6Al-4V coatings
No full textIn this study, Ti-6Al-4V (Ti-64) coatings were prepared on commercial Ti-64 substrates via a high-pressure cold spray process. The coatings were heat treated at different temperatures of 400–1000°C to investigate the effect of heat treatment temperature on their microstructure and mechanical and tribological properties. The increased heat treatment temperature from 400 to 600°C promoted diffusion between sprayed Ti-64 particles. Recrystallization of the sprayed particles was found at the heat treatment temperature of 800°C and grain growth was found in the microstructure of the coating heat treated at 1000°C. The highest and lowest hardnesses of the heat-treated coatings were found at heat treatment temperatures of 400 and 800°C, respectively. Therefore, the lowest and highest specific wear rates of the coatings were consistently found at 400 and 800°C due to their highest and lowest abrasive wear resistances associated with their highest and lowest surface hardnesses, respectively. The coating heat treated at 400°C showed the highest surface hardness of 470.1 Hv and lowest specific wear rate of 69.6 × 10−14 m3/Nm. It could be concluded that the microstructure and mechanical and tribological properties of the Ti-64 coatings were significantly influenced by heat treatment temperature
Beyond Lesson Studies and Design Experiments: Using theoretical tools in practice and finding out how they work
No full textThis paper aims to illustrate how fruitful insights into the link between school teaching practice and student learning outcomes can be theoretically grounded by the variation theory from the field of phenomenography; and from this framework demonstrate how a 'pedagogy of awareness' can be implemented in the classroom. In this study, five teachers and 162 students at Primary Four level of school education in Hong Kong participated and the practice of the 'learning study' was adopted. By comparing the results of pre- and posttests, a significant gain was observed in the students learning outcomes.
Investigation on Fault-ride Through Methods for VSC-HVDC Connected Offshore Wind Farms
No full textRecently, there has been a fast development and deployment of wind energy to meet the increasing electrical power demand and to limit the use of fossil fuels. More and more wind farms are planned far from shore because of good wind condition and less visual impact. This is so called offshore wind farm (OWF). In such a situation, high voltage direct current (HVDC) transmission is a favorable option for integrating these OWFs to the onshore grid, because HVDC, compared with high voltage alternating current (HVAC), has lower losses and higher transmission efficiency. For HVDC transmission, voltage source converter (VSC) has some advantages over current source converter (CSC), e.g. independent control of active power and reactive power, bidirectional power transfer for fixed voltage polarity. When a fault occurs at the onshore ac grid which connects OWFs via VSC-HVDC, the active power cannot be fully transmitted to onshore grid, while OWFs still produce active power. The imbalanced power will increase the HVDC-link voltage. This increased dc voltage will lead to high electrical stress for the insulated gate bipolar transistor (IGBT) modules, capacitors as well as cables, and even damage them. There have been different proposed methods to deal with this problem, e.g. chopper controlled resistor, wind turbine generator power setpoint adjustment, wind turbine grid side converter active current reduction, offshore voltage reduction. Chopper resistor method limits dc-link voltage by dissipating the imbalanced power . The second and third method reduce the power output from each wind turbine to limit the dc-link voltage increase. These two methods need communication between HVDC converter and each wind turbine. Offshore voltage reduction method initiates a controlled voltage drop by offshore converter to achieve a fast power reduction. All these four fault ride through (FRT) methods will be implemented in a test system and the effectiveness of these methods are evaluated with simulations made in PSCAD environment. Finally, based on the proposed methods, an enhanced FRT method is developed and its effectiveness is tested with the system. The advantages and disadvantages of different FRT methods are compared and summarized.Electrical Sustainable EnergyElectrical Engineering, Mathematics and Computer Scienc
Logit-based transit assignment: approach-based formulation and paradox revisit
No full textCASPT 2018 Extended Abstract S. Sun The University of Hong Kong Shenzhen Institute of Research and Innovation, Shenzhen, P. R. China Department of Civil Engineering, The University of Hong Kong, Hong Kong, P. R. China Email: [email protected] W.Y. Szeto The University of Hong Kong Shenzhen Institute of Research and Innovation, Shenzhen, P. R. China Department of Civil Engineering, The University of Hong Kong, Hong Kong, P. R. China Email: [email protected] Sin C. Ho Department of Systems Engineering and Engineering Management, The Chinese University of Hong Kong, Hong Kong, P. R. China Email: [email protected] Logit-based transit assignment: Approach-based formulation and paradox revisit S. Sun · W.Y. Szeto · Sin C. Ho Abstract This paper proposes an approach-based transit assignment model, under the assumption of logit-based stochastic user equilibrium (SUE) with fixed demand. This model is proven to have a unique solution. A cost-averaging version of the self-regulated averaging method (SRAM) is developed to solve the proposed problem. It is proven that the algorithm converges to the model solution. Numerical examples with discussions are presented to investigate the model properties, a paradoxical phenomenon due to the stochastic nature of the model, capacity paradox, and the performance of the proposed algorithm. The proposed methodology is demonstrated to be able to solve the Winnipeg transit networklink_to_OA_fulltex
Optical Investigation of a Sun Simulator for Concentrator PV Applications
No full textS.A1270-A1279In photovoltaics (PV), sun simulators are used to reproduce outdoor conditions in a lab environment such as irradiance level, light uniformity and spectral distribution. Concentrator (C)PV applications additionally require the sun simulators to provide rays with an angular distribution similar to that of the sun rays. However, different factors in CPV sun simulator setups make it difficult to achieve the perfect sun like angular distribution. This is mainly caused by the unavailability of appropriate light sources. Therefore it is investigated, to which deviations such a non-ideal light source can lead and which impact is expected at the measurement of a CPV module. Therefore, two ray tracing models are presented – one for the simulation of natural sunrays, another one for the simulation of sun simulator conditions. The models are validated based on measurements and subsequently used to simulate the impact on a typical CPV module with silicone-on-glass Fresnel lenses. Here, significant deviations to outdoor conditions are found.23Nr.1
Is traditional Chinese medicine recommended in Western medicine clinical practice guidelines in China? A systematic analysis
No full textBackgroundEvidence-based medicine promotes and relies on the use of evidence in developing clinical practice guidelines (CPGs). The Chinese healthcare system includes both traditional Chinese medicine (TCM) and Western medicine, which are expected to be equally reflected in Chinese CPGs.ObjectiveTo evaluate the inclusion of TCM-related information in Western medicine CPGs developed in China and the adoption of high level evidence.MethodsAll CPGs were identified from the China Guideline Clearinghouse (CGC), which is the main Chinese organisation maintaining the guidelines issued by the Ministry of Health of China, the Chinese Medical Association and the Chinese Medical Doctors’ Association.TCM-related contents were extracted from all the CPGs identified. Extracted information comprised the institution issuing the guideline, date of issue, disease, recommendations relating to TCM, evidence level of the recommended content and references supporting the recommendations.ResultsA total of 604 CPGs were identified, only a small number of which (74/604; 12%) recommended TCM therapy and only five guidelines (7%) had applied evidence grading. The 74 CPGs involved 13 disease systems according to the International Classification of Diseases 10th edition. TCM was mainly recommended in the treatment part of the guidelines (73/74, 99%), and more than half of the recommendations (43/74, 58%) were related to Chinese herbal medicine (single herbs or herbal treatment based on syndrome differentiation).ConclusionsFew Chinese Western medicine CPGs recommend TCM therapies and very few provide evidence grading for the TCM recommendation. We suggest that future guideline development should be based on systematic searches for evidence to support CPG recommendations and involve a multidisciplinary approach including TCM expertise
Effects of Nd: YAG laser surface treatment on tribological properties of cold-sprayed Ti-6Al-4V coatings tested against 100Cr6 Steel under dry condition
No full textThe surfaces of cold-sprayed Ti-6Al-4V (Ti64) coatings were laser irradiated with different laser powers of 50–200 W to study the effects of Nd:YAG laser surface treatment on their tribological properties. The hardness of the laser-treated Ti64 coatings became higher with higher laser power due to the more rapid cooling caused by a larger temperature difference between the coating temperature and room temperature. The wear of the laser-treated Ti64 coatings tested against 6-mm 100Cr6 steel balls under dry condition at room temperature decreased with increased laser power as a result of their increased surface wear resistance associated with their increased surface hardness. It could be concluded that the laser surface treatment of the cold-sprayed Ti64 coatings improved their surface wear resistance compared to that of the untreated Ti64 coatings
Wear and Corrosion Resistance of Thick Ti-6Al-4V Coating Deposited on Ti-6Al-4V Substrate via High-Pressure Cold Spray
No full textTi-6Al-4V (Ti64) coating with a thickness of about 9 mm was deposited on commercial Ti64 substrate via a high-pressure cold spray process. The microstructure, hardness, and wear and corrosion resistance of the Ti64 coating were systematically investigated. The hardness of the Ti64 coating was higher than that of the Ti64 substrate due to the cold-worked microstructure of the coating. The tribological results showed that there was no significant difference in the surface wear rates of the Ti64 coating measured on its different layers while the surface wear resistance of the Ti64 coating was lower than its cross-sectional wear resistance. The corrosion results showed that the Ti64 coating did not effectively prevent its underlying Ti64 substrate from corrosion due to the occurrence of pores in the coating microstructure. It could be concluded that the hardness and wear resistance of the Ti64 coating were comparable to those of the commercial Ti64 substrate.Published versio
Metadevice of three dimensional split ring resonators
No full textSplit-ring resonator (SRR), a kind of building block for metamaterial unit cell, has attracted wide attentions due to the resonance excitation of electric and magnetic dipolar response. Here, different from prior published lectures, fundamental plasmon properties and potential applications in novel three dimensional vertical split-ring resonators (VSRRs ) are designed and investigated. The resonant properties arose from the electric and magnetic interactions between the VSRR s and light are firstly theoretically and experimentally studied (Fig. 1(a)). Tuning the configuration of VSRR unit cells is able to generate various novel coupling phenomena in VSRRs, such as plasmon hybridization and Fano resonance, as shown in Figs. 1(b) and 1(c) . Subsequently, the VSRR-based refractive-index sensor will be demonstrated. Due to the unique structural configuration, the enhanced plasmon fields localized in VSRR gaps can be lifted off from the dielectric substrate, allowing for the increase of sensing volume and enhancing the sensitivity (Fig. 1(d)) . We further perform a VSRR based metasurface for light manipulation in optical communication frequency, as shown in Fig. 1(e). Moreover, isotropic VSRRs are approached by optimizing the structural arrangement within a unit cell (Fig. 1(f)). Figure 1(g) shows the schematic for isotropic VSRR-based perfect absorber. By incorporating a metallic mirror with isotropic VSRRs, a stronger field confinement happens to enhance the absorption ability, benefitting the development of refractive index sensor. Finally, a transverse toroidal moment generated by normal incident optical wave at gold dumbbell-shaped aperture and a VSRR is designed and experimentally demonstrated , as shown in Fig. 1(h)
Monitoring the Bifurcated Recurrent Laryngeal Nerve
No full textAnatomical anomalies of the recurrent laryngeal nerve (RLN) can not only mean an operational challenge in thyroid operations for the endocrine surgeon, but also an increased risk of postoperative vocal cord paralysis (VCP). Atypical courses of the RLN are frequent and observed in about a quarter of the thyroid gland operations. Anatomical RLN variations are represented by an atypical RLN pattern as anterior or lateral to the thyroid gland, an anteriorly RLN to a Zuckerkandl tuberculum nodule, a fixed, splayed, or entrapped RLN with capsular association through fascial bands, an invaded RLN, a nerve posterior to ligament of Berry, a thin <1 mm nerve, or antevascular RLN, a non-RLN, a ramificated RLN. Anatomical variations of RLN rarely can be identified preoperatively. The bifurcated RLN represent
a significant anatomical variation because prevention of VCP requires preservation of all branches of the RLN. An awareness of the surgical anatomy and the possible dispositions and ramifications of the RLN is very helpful in avoiding its injury during thyroidectomy.
The current report derives from a review of the literature and personal experience on identification, confirmation, and monitoring the bifurcated RLN
- …
