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Background Circulating tumor DNA (ctDNA) enables rapid and repeat testing of actionable mutations with fewer side effects compared to tissue biopsy. And the use of next-generation sequencing (NGS) based on ctDNA as a diagnostic tool in clinical settings is growing. We developed a hybridization capture massively parallel NGS assay using ctDNA, USCI-CT, across 20 cancer relevant genes of non-small cell lung cancer (NSCLC). Clinical validations of this assay across 17 mutations were presented.Methods Clinical NSCLC samples and simulated negative and positive cell-free DNA (cfDNA) samples were applied to validate the technical performance of this assay. First, 40 simulated negative control cfDNA samples were used to evaluate the systemic error levels to delimit the limit of detection of variant allele frequency (VAF). And, 92 clinical NSCLC samples were genotyped by USCI-CT and ddPCR to decide the proper limit of VAF, depth of coverage, and the average depth of target regions for confidently detecting mutations for USCI-CT. Second, one simulated negative cfDNA sample and two simulated positive cfDNA samples in seven replicates were used to assess the precision of the assay. Finally, 518 clinical NSCLC samples were recruited to evaluate the analytical sensitivity and specificity of USCI-CT.Results The assay-specific systemic error rate was below 0.20% by sequencing sixty-seven simulated negative control cfDNA samples. The proper cutoff of detection of VAF, coverage of depth of mutation loci, and average depth of target regions were decided at 0.20%, 1000×, and 1400×. The analytical sensitivity and specificity achieved a satisfactory level with 98.32% and 99.85% for single nucleotide variant (SNV) detection and 97.30% and 96.86% for EGFR exon 19 deletions, respectively.Conclusions The results indicated that the USCI-CT assay can reliably detect NSCLC related mutations at 0.20% variant frequency level and provided insights into the incorporation of hybridization captured NGS-based ctDNA assay into oncology clinical settings.

Purpose: Cell-free circulating tumor DNA (ctDNA) in plasma enables rapid and repeat testing of actionable mutations. Next-generation sequencing (NGS) is an attractive platform for multiplex sequencing capabilities compared to traditional methods such as PCR. The purpose of this study is to evaluate the value of the NGS-based ctDNA assay and to identify the genomic alteration profile of ctDNA in real-world Chinese non-small cell lung (NSCLC) patients. Methods: In total, 294 Chinese patients with pathological diagnosis of Phase III-IV NSCLC were enrolled. 3-4mL peripheral blood was collected and NGS-based analysis was carried out using a 20-gene panel. The analytical sensitivity and specificity of ctDNA NGS-based assay was validated using droplet digital PCR (ddPCR). Results: We have tested 570 sites from 286 samples using ddPCR, which included 108 positive sites and 462 negative sites from NGS results, and the concordance rate was 99.8% (418/419) for single-nucleotide variants (SNVs) and 96.7% (146/151) for insertions and deletions (InDels). The most frequent genes were TP53 (32%), EGFR (31.97%), KRAS (6.46%), PIK3CA (4.76%), and MET (4.08%). Exon 19 deletion (19del) was the most common alteration in EGFRand G12C was the most common alteration in KRAS. Furthermore, the detection rate of TP53was higher in the male and patients with squamous cell carcinoma. We also found the prevalence of TP53 in L858R was higher than in 19del (61.29% vs. 40%; p=0.1115). Conclusion: The results indicate that the results of NGS-based ctDNA assay are highly consistent with ddPCR. In Chinese NSCLC patients, TP53 mutation was more frequently associated with male and squamous cell carcinoma. The prevalence of concomitant mutations in L858R may be different from that in 19del.

Owing to the corrosive sulphides in the mineral insulating oil such as dibenzyl disulphide (DBDS), copper windings in oil‐immersed transformers may suffer sulphur corrosion. This study investigates the influence of different contact conditions on the corrosion of copper conductors in transformers. Oil‐immersed accelerated corrosion experiment was conducted on copper conductors with various contact materials and different layers of insulating paper. The surface micromorphology, deposition component and the potentiodynamic polarization characteristics of copper conductors were explored. The results show that copper with different contact materials suffer sulphur corrosion; conversely, bare copper rarely does. It was also verified that the existence of a particular gap between copper and contact layer is a significant factor in sulphur corrosion by the formation of a concentration cell on the copper surface. The insulating paper wrapped around copper conductors does not increase the corrosion tendency of copper; however, it contributes to the formation of a region concentrated with DBDS, Cu2+, H+ by adsorption and impediment, which plays a key role in facilitating the sulphur corrosion of copper conductors. Moreover, sulphur corrosion can also occur on other metal parts in transformers when there is a particular gap on surfaces other than copper.

Hypothesis Due to the complex hydrodynamics of droplet impact on ridged superhydrophobic surfaces, quantitative droplet spreading characteristics are unrevealed, limiting the practical applications of ridged superhydrophobic surfaces. During droplet impacting, the size ratio (the ratio of the ridge diameter to the droplet diameter) is an important factor that affects droplet spreading dynamics. Experiments We fabricated ridged superhydrophobic surfaces with size ratios ranging from zero to one, and conduct water droplet impact experiments on these surfaces at varied Weber numbers. Aided by the numerical simulations and theoretical analysis, we illustrate the droplet spreading dynamics and reveal the law on the maximum axial spreading coefficient. Finds The results show that the droplet spreading and retraction dynamics on ridged superhydrophobic surfaces are significantly asymmetric in the axial and spanwise directions. Focusing on the maximum axial spreading coefficient, we find it decreases first and then increases with increasing size ratios, indicating the existence of the critical size ratio. The maximum axial spreading coefficient can be reduced by 25-40% at the critical size ratio compared with that on flat surfaces. To predict the maximum axial spreading coefficient, two theoretical models are proposed respectively for size ratios smaller and larger than the critical size ratio.

Sulfur corrosion has been proven to significantly decrease the insulation performance of oil-immersed transformer and the addition of benzotriazole passivator (BTA) to insulating oil has been widely used to control the sulfur corrosion. However, the relevant studies indicate that the addition of metal passivator to oil can cause abnormal generation of dissolved gases in oil. Thus, this study further explores the effects of metal passivator degradation on the dissolved gas characteristics of oil in oil-immersed transformers. Several accelerated aging experiments on oil-paper insulations with and without BTA are conducted. The results indicate that the addition of BTA lead to the generation of abnormal dissolved gases in the oil along with an increase of stray gases, especially the increase of H 2 , CO and CO 2 . Moreover, an abnormal production of the total hydrocarbon fraction is found, which may interfere with the DGA results. Finally, the degradation of BTA related to abnormal production of stray gases in the insulating oil was preliminarily analyzed and discussed.

Coalescence-induced droplet jumping could promote self-removal of droplets, which has broad potential in related fields such as heat-transfer enhancement, self-cleaning, energy harvesting, electricity generation, radiative cooling, and antifrosting/icing. In practical applications, droplets often have initial velocity under external forces. In this work, the coalescence-induced jumping of centripetal moving droplets on a superhydrophobic plane is experimentally observed using a high-speed photography platform, and the effects of the initial velocity of the moving droplet on jumping velocity, energy conversion, and droplet morphology are numerically investigated. Results show that the jumping velocity decreases and then increases as the

This study extensively investigated the ageing characteristics and lifetime model of oil–paper insulation for oil‐immersed paper condenser bushing. The accelerated thermal and electrothermal ageing experiments of oil‐immersed paper condenser bushing were conducted respectively. The properties of oil–paper insulation during the ageing process were investigated. Results showed that descending speed of degree of polymerization of the innermost and the outermost layer paper was higher than that of middle layer paper, the difference in water content on different paper layers caused varying deterioration speeds. The aluminium foil contributed to a surge in aluminium dissolution in oil, further accelerating the ageing of insulation. Based on the obtained degree of polymerization data under thermal ageing at 90°C, 100°C and 130°C, the lifetime model of oil–paper insulation for condenser bushing model was established. In addition, the surface breakdown of the scale model of bushing occurred after 133 days ageing, the properties of bushing decreased gradually during the ageing process and sharply after the breakdown. Degree of polymerization deviation of different paper layers in bushing between calculated value according to the above lifetime model and actual value of bushing after the breakdown was less than 6%, further verifying the validity of lifetime model.

Land Surface Temperature (LST) derived from space-borne Thermal-infrared (TIR) sensors is a key parameter of urban climate studies. Current studies are inefficient to capture the spatial and temporal variations of LST for only one snapshot adopted at one time. Focusing on the characterization of the spatial and temporal of LST variations at local scales, the latent patterns, and morphological characteristics are extracted in this study. Technically, sixteen MODerate-resolution Imaging Spectroradiometer (MODIS) eight-day synthesized LST products (MYD11A2) in 2002, 2007, 2012, and 2017 are employed. First, the non-parametric Multi-Task Gaussian Process Model (MTGP) is used to extract the smooth and continuous Latent LST (LLST) patterns using one LST subset and its temporally adjacent images. Second, the Multi-Scale Shape Index (MSSI) is then applied to quantify the morphological characteristics at the optimal scale. Then, the LLST patterns and MSSI maps are clustered into multiple spatial categories. The specific clusters with the highest LLST and MSSI values are considered as local LLST hotspots. The Hotspots Weighted Mean Center (HSWMC) and standard deviation ellipse are adopted to further investigate the spatiotemporal change of hotspots orientation, direction, and trajectories. Results revealed that Impervious Surfaces (IS) composition is the most significant external forcing of local LST anomalies. The configuration factors (e.g., shape index, aggregation index) also have a noticeable local warming effect. This study represents a latent pattern and morphology-based framework for LST hotspots spatial and temporal variations characterization, catering to the zoning and grading strategies in urban planning.

There has been a growing interest in finding mitigation measures for urban heat islands and urban pollution islands that focus mainly on urban landscape mechanisms. However, relatively little research has considered spatial non-stationarity and temporal non-stationarity, which are both intrinsic properties of the environmental system, simultaneously. At the same time, the relevance of and differences between the thermal environment and air pollution has also been rarely discussed, and both issues are of great importance to urban planning. In this study, which is aimed at improving urban ventilation to reduce the urban heat island and urban pollution island effects, an urban ventilation potential evaluation, land surface temperature time-series clustering and air pollution source identification are comprehensively applied to identify the operational areas, compensation areas and ventilation corridors in Xiangyang, China, thus bridging the gap between academic research and urban planning. The specific research areas include: (1) defining the operational areas for urban ventilation corridor planning through an urban ventilation potential evaluation featuring urban morphology indicators, land surface temperature time-series clustering with k-means and an urban air pollution source diffusion analysis via the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) and geographically weighted regression (GWR) methods; (2) identifying urban cold islands through land surface temperatures and delimiting the compensation areas in urban ventilation corridor planning; (3) designating urban ventilation corridors through an urban ventilation potential evaluation and computational fluid dynamics (CFD); and (4) improving urban ventilation corridor planning through defining operational areas, compensation areas and ventilation corridors as well as proposing corresponding control measures.

The life of transformer oil-paper insulation is determined by the insulation property of transformer cellulosic insulation. Existing studies have shown that sulfur corrosion poses a serious threat to the properties of transformer oil-immersed cellulosic insulation due to the reaction of corrosive sulfur dissolved in oil with copper winding. This paper investigated the effect of sulfur corrosion on the characteristics of transformer cellulosic insulation, cellulosic insulation winding samples with different degrees of sulfur corrosion were obtained through an accelerated thermal aging experiment. Then, short-/long-term withstand voltage tests for the cellulosic insulation winding were conducted. Experimental results showed that the contamination of sulfur corrosion had a minimal effect on the power–frequency breakdown voltage of the cellulosic insulation winding but considerably decreased its long-term electrical life. Combined with the analysis of the electrical/physical and chemical parameters of oil-immersed cellulosic insulation, the failure mechanism of transformer oil-immersed cellulosic insulation induced by sulfur corrosion was synthetically discussed and analyzed.

Enhancing the horizontal mobility of coalesced droplets on a plane could promote droplet jumping. Here, we achieve enhanced horizontal mobility of a coalesced jumping droplet on superhydrophobic surfaces with an asymmetric ridge and investigate the underlying mechanism through experiment and simulation. Results indicate that the coalesced droplet accelerates during the coalescence-induced jumping stage and gains horizontal velocity during the rebound stage. The nondimensional horizontal velocity can reach 0.47, which is about 2.3 times the jumping velocity on the plane. Depending on the height-to-width ratio of the asymmetric ridge, the ratio of the horizontal velocity to the fallen velocity when the fallen droplet makes contact with the ridge is 0.55–0.75. Furthermore, the coalesced droplet can still obtain considerable horizontal velocity on superhydrophobic surfaces with an asymmetric ridge when the initial droplet radius is unequal. This work provides new insights for improving droplet jumping by surface structure in related fields.

The essential characteristic of the self-propelled jumping droplet is the jumping velocity, which determines its application value in heat transfer enhancement, antifrosting, self-cleaning, and so on. The jumping velocity is directly related to the energy conversion efficiency (i.e., the ratio of jumping kinetic energy surface energy released by coalescence to surface energy released by coalescence) and it is affected by the initial state of droplets but there is no unified theory to describe the relationship between the initial state of droplets and the energy conversion efficiency. In this paper, the projection of the initial chemical potential and the final chemical potential difference of droplets in the direction of jumping is defined as jumping potential by theoretical analysis of the chemical potential evolution. The effects of droplet number, distribution, and radius ratio on energy conversion efficiency can be synthetically characterized by jumping potential. The larger the jumping potential is, the higher the energy conversion efficiency is. Finally, the rationality and universality of the jumping potential are verified by numerical simulations and comparison with previous studies. The jumping potential can explain phenomena that cannot be explained in previous studies and can provide a synthesis critical value of droplet jumping.

As a corrosive sulfur, dibenzyl disulfide (DBDS) is an efficient antioxidant in oil-immersed insulation. This study explored the reaction mechanism of corrosive sulfur with copper through heating experiments stipulated by IEC 62535. Thermal aging experiments were further conducted at 130 °C under nitrogen to investigate the comprehensive effect of the oxidation resistance and corrosivity of DBDS on the properties of oil-paper insulation. Experimental results showed that DBDS can decompose into corrosive benzyl mercaptan at a high temperature. Dibenzyl sulfide cannot corrode copper to form copper sulfide at 150 °C. Furthermore, the oxidation resistance and corrosivity of DBDS depend on the dynamic change in DBDS concentrations. This study suggests that 25 mg/kg should be used as the maximum additive content of DBDS in oil. With this additive content, the oxidation resistance of oil can be improved, and the corrosion damage of insulation winding can be controlled to a certain extent.

This paper investigated the influence of paper-wrapped on the deposition of sulfur corrosion on the insulation winding (paper-wrapped copper conductor) in oil-immersed insulation containing dibenzyl disulfide (DBDS). The distribution of sulfur corrosion deposit on a 500-kV electric reactor was investigated and analyzed, and the properties of oil were analyzed. Aging experiments were also conducted for oil-paper insulation with 500-mg/kg DBDS under IEC 62535 corrosion test condition. The corrosion degree of insulation winding was evaluated, and the properties of oil were also discussed. Results showed that the enwinding pattern of the insulating paper on the copper conductor affected the deposition distribution of copper sulfide to be an alternate appearance of a non-corroded crevice and a strip-shaped corrosion deposit on the copper conductor according to the results of field and laboratory. Furthermore, for the insulation winding, the increased number of paper layers on the copper conductor led to the aggravation of sulfur corrosion, prevented the diffusion of copper ions in the oil, and accelerated the formation of acids, which co-affected the properties of the oil. The enwinding of insulating paper on the copper conductor led to the appearance of a tiny crevice on the insulation winding, which is an important occurrence precondition of crevice corrosion. Finally, the mechanism underlying crevice corrosion for insulation winding was theorized as electrochemical corrosion leading to copper sulfide formation.

Local warming induced by rapid urbanization has been threatening residents&rsquo, health, raising significant concerns among urban planners. Local climate zone (LCZ), a widely accepted approach to reclassify the urban area, which is helpful to propose planning strategies for mitigating local warming, has been well documented in recent years. Based on the LCZ framework, many scholars have carried out diversified extensions in urban zoning research in recent years, in which urban functional zone (UFZ) is a typical perspective because it directly takes into account the impacts of human activities. UFZs, widely used in urban planning and management, were chosen as the basic unit of this study to explore the spatial heterogeneity in the relationship between landscape composition, urban morphology, urban functions, and land surface temperature (LST). Global regression including ordinary least square regression (OLS) and random forest regression (RF) were used to model the landscape-LST correlations to screen indicators to participate in following spatial regression. The spatial regression including semi-parametric geographically weighted regression (SGWR) and multiscale geographically weighted regression (MGWR) were applied to investigate the spatial heterogeneity in landscape-LST among different types of UFZ and within each UFZ. Urban two-dimensional (2D) morphology indicators including building density (BD), three-dimensional (3D) morphology indicators including building height (BH), building volume density (BVD), and sky view factor (SVF), and other indicators including albedo and normalized difference vegetation index (NDVI) and impervious surface fraction (ISF) were used as potential landscape drivers for LST. The results show significant spatial heterogeneity in the Landscape-LST relationship across UFZs, but the spatial heterogeneity is not obvious within specific UFZs. The significant impact of urban morphology on LST was observed in six types of UFZs representing urban built up areas including Residential (R), Urban village (UV), Administration and Public Services (APS), Commercial and Business Facilities (CBF), Industrial and Manufacturing (IM), and Logistics and Warehouse (LW). Specifically, a significant correlation between urban 3D morphology indicators and LST in CBF was discovered. Based on the results, we propose different planning strategies to settle the local warming problems for each UFZ. In general, this research reveals UFZs to be an appropriate operational scale for analyzing LST on an urban scale.

Urban development has significantly modified the surface thermal environment in urban areas. This study provides the first attempt to characterize the urban development imprint on surface thermal environment for 323 cities across the entire country of China, using an intra-urban perspective. Specifically, it investigates the variation of surface thermal environment in terms of land surface temperature (LST) difference triggered by significant urban evolution of intra-urban division containing two primary classes: old urban areas developed by 1992 and new ones expanded in the 1992–2015 period. Under this “old-new” dichotomy, the relationship between urban development and the LST difference is explored through Multi-scale Geographically Weighted Regression (MGWR). Results reveal that urban development is closely related to the difference in LST between old and new urban areas in 2015, which varies from −2.66 °C to 2.46 °C, up to −6.27 °C in western China. 264 cities manifest relatively “cooler” urban environments in the generally larger-sized new urban areas. The seven selected urban development indicators can explain 75% of the variance in the LST difference through MGWR. Among them, the old-new elevation difference, the normalized difference vegetation index (NDVI) difference, and Gini coefficient are found to influence the LST difference in various spatially varying manners. The elevation difference, a generally underestimated nature-driven indicator, is found dominant in explaining the LST difference for 252 cities, among which 216 cities demonstrate higher LSTs in the urban areas with lower elevations. Overall, this study provides valuable information of human-environment interaction across many cities in a generalized way, which complements similar studies at local level, and helps to depict a complete picture of environmental impacts of urban development. The integrated workflow can also be promoted to other periods or other countries to examine the corresponding urbanization imprint on intra-urban surface warming.

Sulfur corrosion induced by active sulfur has been proved to significantly decrease the insulation performance of oil-immersed equipment. In order to protect the oil-paper insulation from sulfur corrosion, active sulfur is cleared in the refining process of crude oil. Some inactive sulfur with high-efficiency antioxidant is still retained in the mineral oil to improve the oxidation stability of oil, such as thiophenic compounds. However, the corrosive effect of inactive sulfur on the oil-paper insulation has not yet clear. Therefore, thiophene that is the largest content of sulfide in the insulating oil was selected as the research object, a series of accelerated thermal ageing experiments of oil-paper without and with thiophene under the different high temperature were conducted, scanning electron microscope equipped with an energy-dispersive X-ray spectrometer (SEM/EDX) and inductively coupled plasma atomic emission spectrometry (ICP-AES) were used to characterize the corrosion degree of oil-paper insulation. The results show that no corrosive deposit was observed on the surface of oilpaper insulation without thiophene even at very high temperature, while a few corrosive deposit was accumulated on the surface of oil-paper insulation with 500 mg/kg thiophene. The corrosion degree of oil-paper insulation with thiophene had an uptrend as the increase of temperature (130°C-180°C), preliminarily indicating that thiophene may be activated in the oil-paper system under the action of overheating fault of oil-immersed transformer and posed a corrosion threat to oil-paper insulation.

Insulation failures of oil-immersed power transformer induced by sulfur corrosion can be controlled by adding the metal passivator into insulating oil. However, it has been reported that the addition of benzotriazole and its derivative passivators into insulating oil would cause abnormal generation of dissolved gases in the oil during the operation of oil-immersed transformer. Therefore, this paper investigated on the effect of passivator on the characteristics of dissolved gas in the oil under the action of thermal field. Benzotriazole (BTA) that widely used in the oil-immersed transformer was selected as the research object, the thermogravimetric analysis of BTA was conducted, and a series of accelerate thermal ageing experiments of oil-paper insulation with and without BTA were also conducted, the composition and content of dissolved gases in oil were measured and analyzed. The results show that BTA was pyrolyzed continuously as the temperature increase. The addition of BTA in oil accelerated the contents of H2, CO and CO2 and decelerated the content of hydrocarbon gases, which lead to abnormal generation of dissolved gases in oil. All of these may interfere the operation condition evaluation of oil-immersed transformer based on DGA technology.

The accelerated thermal aging test is an effective method to simulate insulation material degradation in oil-immersed transformers. Traditionally, cellulose paper and mineral oil are heated up together at the same temperature when a thermal aging test is conducted. However, variation occurs between laboratory results and field conditions. Temperature gradients exist in real transformers, and each part of the winding is aged under various conditions. In order to rebuild temperature gradients and conduct a thermal aging test under this condition. First, 3D models with designed U-shape wingding which can guarantee different parts aged simultaneously under different temperatures are calculated for temperature field analysis. Then a thermal aging platform with a large current generator is proposed to construct temperature gradients in a thermal aging test. The large current generator helps to heat up the copper winding. Temperature sensors are installed in the aging tank to monitoring winding and oil temperature and control temperature. The aging temperature is selected according to the standard IEC 60076-7 for the over-load condition. The degree of polymerisation of the insulation paper is measured and properties of each layer of the insulation paper are analysed. Other aging products under both traditional test and method in this study are compared.

Meticulously understanding the local processes of particulate pollution can help evaluate and mitigate its impact on residents. However, this issue is not sufficiently addressed on intra-community scales, as the characterization and comparison of short-term variations in urban environment is challenged by dynamic misalignment. Our study integrates discrete wavelet transforms (DWT) and dynamic time warping (DTW) to tackle this problem, and formulate practical pollution process indicators from a time-domain perspective. Specifically, original PM2.5 series are decomposed into multi-scale wavelet approximates, which are temporally realigned using DTW. Then, background variation series is estimated by seeking commonality among the majority of stations on time and frequency domains. Indicators are calculated by comparing local PM2.5 variation and estimated background variation, thus describing the local processes of background pollution episodes and discovering possible local pollution incidents. On this basis, empirical analysis in a campus network identified distinct information conveyed on different temporal scales. Case study discovered four phases within a 3-day period based on changes in dominating temporal scale of the background series, which is consistent with known pollution processes. Respective investigations of each phase show good capability in reflecting the influence of terrain, meteorology and dominant emission sources. Inter-station comparisons suggest significant influence from micro-scale spatial environment even when subject to exterior emissions. In general, the method can provide pertinent indicators for evaluation, prediction and optimization efforts in local pollution mitigation. The empirical results imply potentials of urban design measures for such mitigation, on which our future studies will focus.

There is a growing demand for urban form optimization to mitigate urban heat island (UHI) effect. Nevertheless, how UHI responds to various urban morphological patterns is still limitedly understood, especially for cities in developing countries. Here, based on 1288 urban clusters identified automatically across China, we created a consistent analytical environment to recognize both homogeneity and heterogeneity of the relationship. Specifically, urban form was characterized from aspects of size, shape, and centrality, respectively measured using metrics of urban size, area-weighted mean shape index (AWMSI) and dispersion index (DI), entropy and Moran’s I. Then, relationships between the metrics and surface UHI (SUHI) were modelled using the ordinary least squares (OLS). Results reveal that in nighttime when stronger relationships were observed than in daytime, centrality, a feature of intra-urban development structure largely neglected by previous studies, dominated as the most influential aspect. The relationships also varied across climate zones. A two-step OLS regression further reveals them to be size-dependent. As city expanded, the rising shape irregularity created a cooling impact, while the rising centrality leaded to urban warming. Overall, this study suggests that, in addition to controlling urban expansion, the optimal urban form for SUHI mitigation is moderately dispersed, polycentric, and decentralized.

The failures of high-voltage transformers and reactors can result from the deposition of copper sulfide on the oil-impregnated paper insulation. This study explored the influence of electric fields on copper sulfide deposition and the properties of insulating oils as a result of the reaction of dibenzyl disulfide (DBDS) with copper in oil-immersed transformers. Accelerated aging experiments were conducted for pig-tail windings under two sets of conditions, namely, thermal aging only at 140 °C and AC/DC electrical and thermal aging at 5 kV/140 °C under low oxygen condition. This was combined with oil containing dibenzyl disulfide (DBDS) added to the non-corrosive oil to a concentration of 200 mg/kg. The corrosive sulfur deposits were examined by observing the surface morphology of the windings and measuring the copper and sulfur contents on the windings via inductively coupled plasma-atomic emission spectrometry and a precipitation method. The properties of the insulating oils were measured and analyzed at intervals. The results indicate that electric fields increased the amount of deposited copper sulfide on the windings. The higher the electric field strength, the higher the amount of deposited copper sulfide on the insulating paper surface. Subjecting the oil-paper insulation to electric field and elevated temperature generates dissolved copper in the insulating oil. The electric field can promote the dissolution of copper in oil. The ageing oil under thermal and electrical stresses promote copper dissolution and increase corrosion rate.

Numerous failures of high-voltage transformers and reactors are caused by copper sulfide formation in oil-immersed insulations. This study explored the effect of electrical fields on copper sulfide formation. Accelerated aging experiments were conducted for mineral oil that contains dibenzyl disulfide, which was aged along with insulation windings under different conditions, including single thermal aging and electrical–thermal aging. The corrosive sulfur deposits were quantified using SEM/EDX and ICP-AES. The properties of the insulation oils were also measured and analyzed. Corrosion mechanisms for electrical fields leading to the acceleration of copper sulfide deposition on the oil-immersed insulation were proposed.

Numerous failures of high-voltage transformers occur because of sulfur corrosion in oil-impregnated paper insulation containing dibenzyl disulfide (DBDS). This study determines the effects of DBDS, the copper-insulating paper contact, the insulating paper and the atmosphere on copper sulfide formation. Accelerated thermal aging experiments were conducted for mineral oil that contained DBDS and insulation windings under atmospheric (nitrogen/air) conditions. The corrosive sulfur deposits were quantified using SEM/EDX, ICP-AES and precipitation methods. Oil acidity was measured and analyzed. The study proposes a corrosion mechanism for local enrichment of acids and copper ions in copper-insulating paper contacts leading to the acceleration of sulfur corrosion.

Conspicuous expansion and intensification of impervious surfaces accompanied by rapid urbanization are widely recognized to have exerted evident impacts on the urban thermal environment. Investigating the spatially and temporally varying relationships between Land Surface Temperature (LST) and impervious surfaces (IS) at multiple scales is of great significance for steering IS expansion and intensification. This study proposes an analytical framework to investigate the spatiotemporal variations of LST and its responses to IS in Wuhan, China at both city scale and sub-region scale. The summer LST patterns in 2002&ndash, 2017 are extracted by Multi-Task Gaussian Process (MTGP) model from raw 8-day synthesized MODerate-resolution Imaging Spectroradiometer (MODIS) LST data. At the city scale, the weighted center of LST (LSTWC) and impervious surface fraction (ISFWC), multi-temporal trajectories and coupling indicators are utilized to comprehensively examine the spatial and temporal dynamics of LST and IS within Wuhan. At the sub-region scale, urban heat island ratio index (URI), impervious surfaces contribution index (ISCI) and sprawl rate are introduced for further quantifying the relationships of LST and IS. The results reveal that IS and hot thermal landscapes expanded by 407.43 km2 and 255.82 km2 in Wuhan in 2002&ndash, 2017 at city scale. The trajectories of LSTWCs and ISFWCs are visually coherent and both heading to southeast direction in general. At the sub-region scale, the specific cardinal directions with the highest ISCI variations are examined to be the exact directions of ISFWC trajectories in 2002&ndash, 2017. The results reveal that the spatiotemporal variations of LST and IS are highly correlated at both city and sub-region scales within Wuhan, thus testifying the significance of steering IS expansion and renewal for controlling urban thermal environment deterioration.

Coalescence-induced droplet jumping on superhydrophobic surfaces has good application potential in the fields of heat transfer enhancement, self-cleaning, water collection, and microfluidics. However, the direction of droplets jumping on the plane is uncontrollable and the energy conversion rate is low, which limits the application of droplets jumping. In this work, we report a flexible approach to efficiently regulate the direction and velocity of droplet jumping on superhydrophobic surfaces using superhydrophobic string. By changing the inclination angle of the string, the jumping direction of the coalescent droplet shows a maximum deviation of 68.1° from the surface normal. The maximum energy conversion rate is 32.1%, which is about 5.4 times higher than that of jumping on the plane. We analyzed the mechanism of the efficient regulation and found that the string affected the hydrodynamic characteristics of the jumping process, thus changing the jumping direction and the speed of the coalescent droplet.

This paper investigated the influence of 2, 6-di-tert-butyl-p-cresol (DBPC) on the long-term ageing characteristics of oil–paper insulation and the deposition and migration of copper sulphide induced by the reaction of copper and dibenzyl disulphide (DBDS) in oil-immersed transformers. A thermal ageing experiment at 130°C were designed and conducted by adding different concentrations of DBPC to the naphthenic mineral oil and after the experiments a set of characteristic parameters were tested. The result indicates that the excessive concentration (≥0.6%) of DBPC will slightly increase the ageing of insulating oil and increase the carboxyl group in the mineral oil, affecting the reaction of DBDS and copper, and the insulating paper wrapped on the copper strip was also aged seriously accordingly. Meanwhile, the deposition of copper sulphide on the insulating paper is found to be slightly increased with the increase of the concentration of DBPC. When insulating oil contains DBPC and DBDS, due to migration of DBDS–Cu and DBPC–Cu in oil, the copper ions in the oil would be fluctuating at a certain period of time. Although the addition of a small concentration of DBPC can improve the antioxygenic property of the insulting oil to some extent, the transformers that contain excessive concentration of DBPC may be more harmful than beneficial.

This study investigated the inhibitory effects of adsorption treatment on the degradation of oil–paper insulation and corrosive sulphur in oil. A thermal ageing experiment at 130°C was conducted using five different adsorbents to adsorb some impurities in oil on the 15th day of a 30 day ageing test, the related characteristics of oil–paper insulation before and after the adsorption treatment were measured and analysed. Meanwhile, a thermal ageing experiment at 150°C was also conducted before using five different adsorbents to adsorb dibenzyl disulphide (DBDS) in oil, energy dispersive X-ray was used to evaluate the degree of the corrosion of windings. The result indicates that adsorption treatment is an effective method to inhibit the degradation of oil–paper insulation. A molecular sieve, silica gel and activated alumina can effectively improve the performance of oil–paper insulation. By contrast, the antioxidant (2, 6-di-tert-butyl-p-cresol) can be also adsorbed by adsorbents, which accelerate the ageing degradation of the insulating oil. On the other hand, the adsorbents can adsorb DBDS in oil, but cannot remove all DBDS. The effect achieved from silica gel is especially significant, which not only effectively improves the performance of oil–paper insulation but also adsorbs DBDS in oil.

As, a kind of sulfur antioxidant, dibenzyl disulfide (DBDS) generally exist in the mineral insulating oil, which can improve the oxidation stability of oil. However, DBDS can also lead to corrosion problems of transformer oil. To investigate the effect of the corrosive action and the antioxidant action of DBDS on the oil-paper insulation, oil samples with different DBDS concentration (0–200mg/kg) were made and conducted to perform thermal aging experiments together with insulation windings at 130Ό under the condition of nitrogen. After the aging experiment, the copper strip and insulating paper surface were observed, the properties of insulating oil were also measured and analyzed. Experimental results showed that when the insulating oil contained less than 25mg/kg DBDS, the antioxidant effect of DBDS would be dominant, the oxidation stability of insulating oil was improved, the performance of oil was better than that of excluding DBDS samples. When the insulating oil contained more than 25mg/kg DBDS, the corrosive effect of DBDS will be greater than its antioxidant effect, copper ions and acid will be accelerated, it will lead to more serious of aging oil.