Electrical Breakdown Behaviors in Microgaps

The study of electrical breakdown behaviors in microgaps has drawn intensive attention around the world due to the miniaturization of electronic devices that allows electronic circuits to be packaged more densely, making possible compact computers, advanced radar and navigation systems, and other devices that use very large numbers of components. Therefore, a clear understanding of the electrical breakdown behaviors in microgaps is required to avoid the dielectric breakdown or to trigger the breakdown at microscale. This chapter introduces the significance of understanding breakdown characterization and reliability assessment for electrostatically actuated devices, magnetic recording devices, photomasks, RF MEMS switches, and micromachines and points out the derivation of the classical Paschen’s law at microscale. Then it summarizes the state-of-the-art research work on the methodology, influencing factors, dynamics, and physical mechanisms of electrical breakdown in microgaps, which is expected to expand the general knowledge of electrical breakdown to the microscale regime or more and benefits the reliability assessment and ESD protection of microscale and nanoscale devices

Wave-Absorbing Properties of Multi-Walled Carbon Nanotubes Reinforced Cement-Based Composites

Multi-walled carbon nanotube (MWCNT)/Portland cement (PC) composites have been prepared to evaluate their electromagnetic wave absorbing properties. The effects of MWCNTs content and sample thickness were discussed in the frequency ranges of 2–18 GHz. Results show that the absorbing properties of cement-based composites are affected by the content of MWCNT and the thickness of the samples. When MWCNTs contents are 0, 0.25, 0.50, 0.75, and 1.00%, absorbing property of sample of 5 mm is unstable due to the resonance absorption. Samples of 10 mm and 15 mm thickness show stable microwave absorbing properties, and a sample of 15 mm thickness has better absorbing property than that of 10 mm. Optimum contents of carbon nanotube (CNT) of 0.75, 0.50, and 0.5% by mass are found in 5, 10, and 15 mm thick samples, respectively. A sample with thickness of 5 mm and 0.50% mass content of CNT has the best absorbing property and the peak is –15.3 dB

Corporate human rights accountability:contextualising the United Nations guiding principles on business and human rights in multinational corporation supply chains In China

This study sets out to examine the contextualisa2on of a par2cular United Na2ons (UN)human rights instrument, called the UN Guiding Principles on Business and Human Rights(UNGPs), in the supply chain of a mul2na2onal corpora2on (MNC, Alpha). In doing so,special aFen2on is given to the contextualisa2on of these principles in China, where someof the main suppliers of Alpha are located (such as a company which will be called Beta).The contextualisa2on is mainly approached from an accountability perspec2ve, which isconceived as expressions of the quality of human relatedness. Through the theore2callens of Edward Said’s concepts of authority and molesta-on, this research aims to addressthe ques2on of how the text of UNGPs with respect to human rights accountability isauthored and molested by several (inter)na2onal actors including the UN, the Chinesegovernment, Alpha and its supplier Beta, and finally by several important local actors:workers and managers who are employed by Beta. Data is collected in the form of Said’sno2on of “text” as both wri2ngs, uFerings and inscrip2ons through qualita2ve researchmethods. These include document analysis of UN interpre2ve reports, several Chinesegovernment documents, Alpha’s and Beta’s codes of conduct (CoC), and posters collectedwithin Beta’s factories rela2ng to human rights. Spoken texts are collected as well,through semi-structured interviews with workers and managers, as well as throughpar2cipant observa2on in one Beta factory. By analysing these texts, this researchsketches the process in which the text of UNGPs is cascaded down and made prac2cal (ornot) through molesta-on by the aforemen2oned actors. The examina2on of formalwriFen texts authored by UN, the Chinese government, Alpha and Beta suggests that thetext regarding human rights accountability in the UNGPs are interpreted in a par2cularway, which demonstrates both the enabling and constraining func2ons of molesta-on.That is to say, these interpre2ve texts will never be the faithful copy of the UNGPs, but areinten-onally (or some2mes uninten-onally) reconstruc2ng UNGPs in a way that deviatesifrom its original meanings by adding, dele2ng, selec2ng and re-shaping certain ideas. Inthis way, they constrain the text of UNGPs. However, the molesta-on is also enabling bygiving the text of UNGPs a reality check, thereby rendering them more prac2cal in theactors’ contexts. The informal texts uFered by local workers and managers display a largerextent of molesta-on. While it is understandable that the text of UNGPs will not be fullypresented on the ground level, this study revealed that the molested version of UNGPs—the corporate CoCs and onsite posters are further molested by workers as largely voidpromises or symbolic prac2ces, while they are oWen held in high regards by managers.This study also explores the cultural, social and economic sources that give rise to thesemolesta-ons. Such molesta-on can be enabling as it makes abstract human rightsprinciples ac2onable and brings them closer to the local actors’ context. However, it isalso constraining as it impedes the way that accountability works in the UNGPs

Fundamental issues, technology development and challenges of boiling heat transfer, critical heat flux and two-phase flow phenomena with nanofluids

This paper presents a comprehensive and critical review of studies on nucleate pool boiling heat transfer, flow boiling heat transfer, critical heat flux (CHF) and two-phase flow phenomena with nanofluids. First, general analysis of the available studies on the relevant topics is presented. Then, studies of physical properties of nanofluids are discussed. Next, boiling heat transfer, CHF phenomena and the relevant physical mechanisms are explored. Finally, future research needs have been identified according to the review and analysis. As the first priority, the physical properties of nanofluids have a significant effect on the boiling and CHF characteristics but the lack of the accurate knowledge of the physical properties has greatly limited the studies. Fundamentals of boiling heat transfer and CHF phenomena with Nanofluids have not yet been well understood. Flow regimes are important in understanding the boiling and CHF phenomena and should be focused on. Two phase pressure drops of nanofluids should also be studies. Furthermore, economic evaluation of the enhancement technology with nanofluid should be considered for the new heat transfer enhancement technology with nanofluids. Finally, applied research should be targeted to achieve an enabling practical heat transfer and CHF enhancement technology for engineering application with nanofluids

Flow patterns and flow pattern maps for adiabatic and diabatic gas liquid two phase flow in microchannels: fundamentals, mechanisms and applications

This paper mainly presents comprehensive review on the research regarding adiabatic and diabatic gas–liquid two-phase flow patterns, bubble growth, flow pattern transitions and flow pattern maps in microchannels over the past 15 years. First, criteria for distinction of macro- and micro-channels are discussed. Then, fundamentals of gas liquid two-phase flow patterns, flow pattern maps and techniques for two phase flow visualization and sensing are presented. Next, experimental studied of adiabatic and diabatic two phase flow patterns, bubble behaviour, flow pattern transitions and flow pattern maps in microchannels with plain and enhanced structures are reviewed. Finally, applications of flow patterns and flow pattern maps are discussed. Flow pattern based mechanistic heat transfer prediction methods are focused on and studies on unstable and transient two phase flow patterns and heat transfer in microscale channels are addressed. According to the review and analysis, recommendations on the future research needs have been given. Systematic and accurate experimental data on flow patterns, bubble growth, flow pattern transitions are still needed. In particular, there are lacks general flow pattern transition criteria. Therefore, effort should be made to develop generalized flow pattern transition criteria based on well documented experimental observation and data. Furthermore, studies of mechanistic and theoretical models for flow patterns, flow pattern transitions bubble growth in microchannels should be further conducted. As an important topic, unstable and transient gas liquid two phase flow patterns and heat transfer in microchannels should be systematically investigated as well in order to understand the flow pattern transition mechanisms in microchannels with plain and enhanced structures

Progress and Prospects for Research and Technology Development of Supercritical CO2 Thermal Conversion Systems for Power, Energy Storage, and Waste Heat Recovery

CO2 is an environmentally friendly heat transfer fluid and has many advantages in thermal energy and power systems due to its peculiar thermal transport and physical properties. Supercritical CO2 (S-CO2) thermal energy conversion systems are promising for innovative technology in domestic and industrial applications including heat pump, air-conditioning, power generation, renewable energy systems, energy storage, thermal management, waste heat recovery and others. Both S-CO2 and transcritical CO2 thermodynamic cycles have been extensively investigated in order to improve the efficiencies of thermal and power systems and achieve net zero carbon emissions. This paper focuses on the progress and prospects for current research and technology development of S-CO2 thermal energy conversion systems and their applications including power generation, energy storage and waste heat recovery. First, the CO2 thermal transport and physical properties and benefits using CO2 as a heat transfer fluid in thermal energy and power systems are discussed. Then, classification of CO2 thermodynamic systems is presented. Next, S-CO2 for power generation, energy storage and waste heat recovery systems are presented. Finally, research needs of subcritical and supercritical CO2 heat transfer, fluid flow and heat exchangers for the development of various thermal energy and power systems are discussed

Experimental study and modelling of average void fraction of gas-liquid two-phase flow in a helically coiled rectangular channel

Void fraction is an important parameter in designing and simulating the relevant gas-liquid two-phase flow equipment and systems. Although numerous experimental research and modelling of void fraction in straight circular channels have been conducted over the past decades, the experimental data and prediction methods for the average void fraction in helically coiled channels are limited and needed. Especially, there is no such information in helically coiled channels with rectangular cross section. Therefore, it is essential to advance the relevant knowledge through experiments and to develop the corresponding prediction methods in helically coiled rectangular channels. This paper presents experimental results of the average void fraction and new models for the void fraction in a horizontal helically coiled rectangular channel. First, experiments were conducted with air-water two-phase flow in the horizontal helically coiled rectangular channel at a wide range of test conditions: the liquid superficial velocity ranges from 0.11 to 2 m/s and the gas superficial velocity ranges from 0.18 to 16 m/s. The average void fractions were measured with a quick-closing valve (QCV) method. The measured void fraction ranges from 0.012 to 0.927 which cover four flow regimes including unsteady pulsating, bubbly, intermittent and annular flow observed with a high speed camera. Second, comparisons of the entire measured average void fraction data to 32 void fraction models and correlations were made. It shows a low accuracy of these models and correlations in predicting the experimental data for the void fraction smaller than 0.5 while the drift flux model of Dix (Woldesemayat and Ghajar, 2007) predicts 98.3% of the entire experimental data within ±10% for the void fraction larger than 0.5. Therefore, the Dix model is recommended for the void fraction larger than 0.5. Furthermore, the observed flow regimes in the coiled channels were compared to two mechanistic flow regime maps developed for horizontal straight circular tubes. The flow regime maps do not capture all flow regimes in the present study. Finally, the effects of the limiting affecting parameters on the void fraction models are analyzed according to the physical phenomena and mechanisms. Incorporating the main affecting parameters, new void fraction models have been proposed for the void fractions in the ranges of 0 < α ≤ 0.2 and 0.2 < α ≤ 0.5 respectively according to the slip flow model. Both models predict the experimental data reasonably well. Overall, the new proposed models and the recommended model predict 92.8% of the entire void fraction data within ±30%

Efficient Segmentation with Texture in Ore Images Based on Box-supervised Approach

Image segmentation methods have been utilized to determine the particle size distribution of crushed ores. Due to the complex working environment, high-powered computing equipment is difficult to deploy. At the same time, the ore distribution is stacked, and it is difficult to identify the complete features. To address this issue, an effective box-supervised technique with texture features is provided for ore image segmentation that can identify complete and independent ores. Firstly, a ghost feature pyramid network (Ghost-FPN) is proposed to process the features obtained from the backbone to reduce redundant semantic information and computation generated by complex networks. Then, an optimized detection head is proposed to obtain the feature to maintain accuracy. Finally, Lab color space (Lab) and local binary patterns (LBP) texture features are combined to form a fusion feature similarity-based loss function to improve accuracy while incurring no loss. Experiments on MS COCO have shown that the proposed fusion features are also worth studying on other types of datasets. Extensive experimental results demonstrate the effectiveness of the proposed method, which achieves over 50 frames per second with a small model size of 21.6 MB. Meanwhile, the method maintains a high level of accuracy compared with the state-of-the-art approaches on ore image dataset. The source code is available at \url{https://github.com/MVME-HBUT/OREINST}.Comment: 14 pages, 8 figure

The effects of short-term rainfall variability on leaf isotopic traits of desert plants in sand-binding ecosystems

Author's manuscript made available in accordance with the publisher's policy.Sand-binding vegetation is effective in stabilizing sand dunes and reducing soil erosion, thus helps minimize the detrimental effects of desertification. The aim of this study is to better understand the relationships between water and nutrient usage of sand-binding species, and the effects of succession and rainfall variability on plants’ water–nutrient interactions. We examined the effects of long-term succession (50 years), inter-annual rainfall variability (from 65% of the mean annual precipitation in 2004 to 42% in 2005) and seasonality on water–nutrient interactions of three major sand-binding species (Artemisia ordosica, Hedysarum scoparium and Caragana korshinskii) by measuring foliar δ13C, δ15N and [N]. Long-term succession in general did not significantly alter δ13C, δ15N and [N] of the three species. Short-term rainfall variability, however, significantly increased foliar δ13C levels of all three species by 1.0–1.8‰ during the severely dry year. No significant seasonal patterns were found in foliar δ13C and δ15N values of the three species, whereas foliar [N] varied by season. For the two leguminous shrubs, the correlations between δ13C and δ15N were positive in both sampling years, and the positive correlation between [N] and δ13C was only found in the severely dry year. The results indicate that these sand-binding plants have developed into a relatively stable stage and they are able to regulate their nitrogen and water use in responding to environmental conditions, which reinforces the effectiveness of plantation of native shrubs without irrigation in degraded areas. However, the results also indicate that short-term climate variability could have severe impact on the vegetation functions