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

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

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

Heat transfer characteristics and flow visualization during flow boiling of acetone in semi-open multi-microchannels

Experimental results of flow boiling characteristics and flow patterns with acetone in two different microchannel heat sinks are presented in this paper. A semi-open microchannel heat sink and a straight microchannel heat sink with 19 parallel microchannels each were designed and tested. The semi-open microchannels have a channel width of 0.8 mm, fin width of 0.4 mm, and pedestal height of 0.2 mm and the straight microchannels have a rectangular cross section of 0.8 mm × 1 mm. The experimental heat fluxes ranged from 0 to 90 kW/m2, vapor quality ranged from 0.05 to 0.5, mass fluxes ranged from 4.34 to 15.62 kg/m2·s and the inlet temperatures were 20 and 30°C, respectively. Compared to those in the straight microchannels, flow boiling heat transfer coefficients can be improved by up to 36.2%. Furthermore, flow patterns were observed with a speed video camera. The flow boiling heat transfer mechanisms are analyzed according to the observed flow pattern

Simulating cold regions hydrological processes using a modular model in the west of China

SummaryThe Cold Regions Hydrological Model platform (CRHM), a flexible object-oriented modeling system, was devised to simulate cold regions hydrological processes and predict streamflow by its capability to compile cold regions process modules into purpose-built models. In this study, the cold regions hydrological processes of two basins in western China were evaluated using CRHM models: Binggou basin, a high alpine basin where runoff is mainly caused by snowmelt, and Zuomaokong basin, a steppe basin where the runoff is strongly affected by soil freezing/thawing. The flexibility and modular structure of CRHM permitted model structural intercomparison and process falsification within the same model framework to evaluate the importance of snow energy balance, blowing snow and frozen soil infiltration processes to successful modeling in the cold regions of western China. Snow accumulation and ablation processes were evaluated at Binggou basin by testing and comparing similar models that contained different levels of complexity of snow redistribution and ablation modules. The comparison of simulated snow water equivalent with observations shows that the snow accumulation/ablation processes were simulated much better using an uncalibrated, physically based energy balance snowmelt model rather than with a calibrated temperature index snowmelt model. Simulated seasonal snow sublimation loss was 138mm water equivalent in the alpine region of Binggou basin, which accounts for 47 % of 291mm water equivalent of snowfall, and half of this sublimation loss is attributed to 70mm water equivalent of sublimation from blowing snow particles. Further comparison of simulated results through falsification of different snow processes reveals that estimating blowing snow transport processes and sublimation loss is vital for accurate snowmelt runoff calculations in this region. The model structure with the energy balance snowmelt and blowing snow components performed well in reproducing the measured streamflow using minimal calibration, with R2 of 0.83 and NSE of 0.76. The influence of frozen soil and its thaw on runoff generation was investigated at Zuomaokong basin by comparing streamflow simulated by similar CRHM models with and without an infiltration to frozen soil algorithm. The comparison of simulated streamflow with observation shows that the model which included an algorithm describing frozen soil infiltration simulated the main runoff events for the spring thawing period better than that which used an unfrozen infiltration routine, with R2 of 0.87 and NSE of 0.79. Overall, the test results for the two basins show that hydrological models that use appropriate cold regions algorithms and a flexible spatial structure can predict cold regions hydrological processes and streamflow with minimal calibration and can even perform better than more heavily calibrated models in this region. Given that CRHM and most of its algorithms were developed in western Canada, this is encouraging for predicting hydrology in ungauged cold region basins around the world