171 research outputs found
Modelling and motion control of a liquid metal droplet in a fluidic channel
No full textAs an emerging multifunctional material, Gallium-based room temperature liquid metal has attracted a lot of attention for a variety of applications due to its mobility and deformability. However, controlling the motion of a liquid metal droplet accurately still remains unrevealed, which restricts its application in many fields. In this article, we propose a hybrid framework that would control the motion of a liquid metal droplet in a one-dimensional (1-D) fluidic channel. A dynamic model of a liquid metal droplet immersed in the electrolyte when an electrical field is applied to each end of the channel is discussed first, followed by a setpoint controller designed to calculate the current input needed to drive the liquid metal droplet to its destination with vision feedback. To obtain the desired high-resolution current output, a fast and high-resolution current output power supply will be established by integrating a fast PID controller and a simple programmable dc power supply. The effectiveness of this proposed approach will be verified by controlling a liquid metal droplet so that it reaches its destination inside the polymethyl methacrylate channel. In this article, the proposed approach may lead to the development of tiny soft robots, or microfluidic systems that can be driven accurately by the liquid metal droplets.</p
Enhancement of laminar convective heat transfer using microparticle suspensions
No full textThis paper investigates the enhancement of convective heat transfer within a sub-millimetre diameter copper tube using Al2O3, Co3O4 and CuO microparticle suspensions. Experiments are conducted at different particle concentrations of 1.0, 2.0 and 5.0 wt% and at various flow rates ranging from 250 to 1000 µl/min. Both experimental measurements and numerical analyses are employed to obtain the convective heat transfer coefficient. The results indicate a significant enhancement in convective heat transfer coefficient due to the implementation of microparticle suspensions. For the case of Al2O3 microparticle suspension with 5.0 wt% concentration, a 20.3 % enhancement in convective heat transfer coefficient is obtained over deionised water. This is comparable to the case of Al2O3 nanofluid at the same concentration. Hence, there is a potential for the microparticle suspensions to be used for cooling of compact integrated systems.</p
X-Band Reconfigurable Phase Shifters Based on SIW and Liquid Metal Technologies
No full textThis paper presents three reconfigurable phase shifters operate at X-band and designed utilizing liquid metal (LM). The phase shifters operate at 10 GHz and they have very low insertion loss performance and able to handle high levels of radio frequency (RF) power. Besides, the proposed phase shifters able to achieve a total of 360° phase shift and they are compact in size as they are designed using substrate integrated waveguides (SIW). This enable the proposed phase shifters to be integrated within SIW based feeding structures to realize complete phased array antenna systems. The phase shift is realized by inserting a series of liquid metal vias in the SIW. When a single or multiple via connection is needed, the via hole is filled with liquid metal and conversely, the liquid metal is withdrawn from the via when the connection is no longer required.</p
10 GHz Low Loss Liquid Metal SIW Phase Shifter for Phased Array Antennas
Get PDFThis article presents a proof of concept demonstrator for a pair of novel phase shifters based on substrate integrated waveguide (SIW) technology. Gallium-based liquid metal (LM) is used to reconfigure each phase shifter. This article presents LM phase shifters that, for the first time, have a phase shifting range of 360°. The phase shifters have a small electrical size, and they are intended for use within phased array antenna applications. This article also presents a design procedure for the phase shifters. The procedure has been used to design two phase shifters operating at 10 GHz. The design process can be readily scaled for operation at other frequencies. The proposed phase shifters are reciprocal and bidirectional, and they have very low insertion loss (IL). A series of reconfigurable LM vias are used to achieve the phase shift. Each of LM via is activated once a drill hole is filled with LM and it is deactivated once LM is removed. Using this method, it is possible to achieve a phase shift step ranging from 1° to 100° using a single LM via. Moreover, the overall phase shift can be extended to 360° by employing several LM vias in series inside the SIW. The proposed phase shifters have an IL lower than 3 dB and provide a total phase shifting range of approximately 360° in eight steps of approximately 45° each. This enables the proposed two phase shifters to have an extraordinary figure of merit (FoM) of 131.3°/dB and 122.4°/dB
Dean-flow-coupled elasto-inertial particle and cell focusing in symmetric serpentine microchannels
No full textThis work investigates particle focusing under Dean-flow-coupled elasto-inertial effects in symmetric serpentine microchannels. A small amount of polymers were added to the sample solution to tune the fluid elasticity, and allow particles to migrate laterally and reach their equilibriums at the centerline of a symmetric serpentine channel under the synthesis effect of elastic, inertial and Dean-flow forces. First, the effects of the flow rates on particle focusing in viscoelastic fluid in serpentine channels were investigated. Then, comparisons with particle focusing in the Newtonian fluid in the serpentine channel and in the viscoelastic fluid in the straight channel were conducted. The elastic effect and the serpentine channel structure could accelerate the particle focusing as well as reduce the channel length. This focusing technique has the potential as a pre-ordering unit in flow cytometry for cell counting, sorting, and analysis. Moreover, focusing behaviour of Jurkat cells in the viscoelastic fluid in this serpentine channel was studied. Finally, the cell viability in the culture medium containing a dissolved polymer and after processing through the serpentine channel was tested. The polymer within this viscoelastic fluid has a negligible effect on cell viability.Full Tex
From Residents to ‘New Citizens’: Aspirations, Identities and Decision-Making of Internal Migrants in China
No full textNitrene-mediated intermolecular N–N coupling for efficient synthesis of hydrazides
No full text© 2021, The Author(s), under exclusive licence to Springer Nature Limited.N–N linkages are found in many natural compounds and endow fascinating structural and functional properties. In comparison to the myriad methods for the construction of C–N bonds, chemistry for N–N coupling, especially in an intermolecular fashion, remains underdeveloped. Here, we report a nitrene-mediated intermolecular N–N coupling of dioxazolones and arylamines under iridium or iron catalysis. These reactions offer a simple and efficient method for the synthesis of various hydrazides from readily available carboxylic acid and amine precursors. Although the Ir-catalysed conditions usually give higher N–N coupling yield than the Fe-catalysed conditions, the reactions of sterically more demanding dioxazolones derived from α-substituted carboxylic acids work much better under the Fe-catalysed conditions. Mechanistic studies revealed that the nitrogen atom of Ir acyl nitrene intermediates has strong electrophilicity and can undergo nucleophilic attack with arylamines with the assistance of Cl···HN hydrogen bonding to form the N–N bond with high efficiency and chemoselectivity. [Figure not available: see fulltext.]11Nsciescopu
A portable, hand-powered microfluidic device for sorting of biological particles
No full textManually hand-powered portable microfluidic devices are cheap alternatives for point-of-care diagnostics. Currently, on-field tests are limited by the use of bulky syringe pumps, pressure controller and equipment. In this work, we present a manually operated microfluidic device incorporated with a groove-based channel. We show that the device is capable to effectively sort particles/cells by manual hand powering. First, the grooved-based channel with differently sized polystyrene particles was characterized using syringe pumps to study their distributions under various flow rate conditions. Afterward, the particle mixtures were sorted manually using hand power to verify the capability of this device. Finally, the manually operated device was used to sort platelets from peripheral blood mononuclear cells (PBMCs). The platelets were collected with a purity of ~ 100%. The purity of PBMCs was enhanced from 0.8 to 10.4% after multiple processes which results in an enrichment ratio of 13.8. During the process of manual hand pumping, the flow fluctuation caused by unstable injection will not influence the sorting performance. Due to its simplicity, this manually operated microfluidic chip is suitable for outfield settings.No Full Tex
Sponge Design: A Study on Comprehensive Sponge City Design Approach
No full textWater is cherished as treasure in traditional Chinese culture and expected to stay in harmony with human. However, the disharmony between water and urban life is looming especially after over thirty-year rapid urbanization in China with notable global climate change. Faced with water-related issues, e.g. flooding, water pollution, water shortage, etc., Government of China initiated a so-called Sponge City Program (SCP) in 2014 for constructing ‘sponge-like’ water-resilient cities. Nevertheless, challenges and gaps lie in practice of SCP, one of which is that an operationalizable design approach of a sponge city to realise its multiple objectives is neither available in current guidelines, nor thoroughly studied or proposed in recent literatures.The aim of this master thesis was to formulate an improved approach, as well as to improve planning & design framework for supporting integrated sponge design process and enhancing the involvement of various stakeholders. Literature study, the study of current guidelines and sponge plans of Nanjing, and interviews with sponge city practitioners were performed to evaluate current Sponge City (SC) concept and assess SC planning & design practice. Analysis of SC concept development showed that SC has been evolving from a term mainly describing measures with ecological benefits towards a more inclusive urban development paradigm, considering not only water ecology, but also water safety, water environment and water resource. Analysis on SC practice identified the gaps in current SC water management contents, including a lack of design method for calculating storage capacity against pluvial flooding, ignorance of extreme drought assessment, missing groundwater management, etc. Challenges that might impede comprehensive sponge city planning & design process were also enumerated, including data availability and accessibility, the bond between SC and other sector plans, etc. Based on the identified challenges and gaps, improvements on current planning & design practices were given and a new design approach was proposed, including changing collaboration method, introducing a co-design workshop and using a sponge design toolbox to facilitate planning & design process. The approach provided a method to calculate the required sponge capacity for not only preventing flood damage but also mitigating water shortage in dry spells, as well as quantifying other co-benefits. The improved design approach was tested by a case study in Nanjing, in the Qinhuai District sponge city planning project. Case study results showed that most steps in the proposed design process were successfully taken in Qinhuai project, and the toolbox was able to facilitate planning and design of sponge measures to have functions not only for pluvial flooding prevention and control, but also for water shortage mitigation, ecological benefits and other day-to-day values. The design process also demonstrated the collaborative contribution to a sponge city plan from water managers, water engineers and landscape architects. Therefore, the new design approach can contribute to a more integrated SC planning and design.Water Managemen
Flood prevention on the lower reaches of the Rellow River
No full textProceedings of a congerence in Zhenzhou, China, 1990: Gong Shiyan, Wu Zhiyao: Introduction. Bao Zicheng, Zhang Mingde, Wang Rudiu: Strenghtening of dykes by Warping. Cheng Zidao, Liu Yuli: To remedy hidden defects in dykes by probing with pointed steed rods and subsequent grouting. Hu Yisan: River training works on the lower reaches of the Yellow River. Shen Hongxin, Xu Fuling: Engineering structures for river correction on the lower reaches of the Yellow River. Bao Xicheng, Zho Guangming, Wang Hongxiang: Ice dam on the lower reaches of the Yellow River. Liu7 Ruyun, Tong Linlang: Organizing for flood protection on the lower reaches fo the Yellow river. A brief account of Dongpinghu detention reservoir
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