The influence of interface temperature on the damage characteristics of C–Cu contacts’ interface plays a critical role in the current-carrying friction process which occurs between the contact pairs. ...In this paper, a method is proposed to adjust the interface temperature via settling an external heat source. The damage morphology and material transfer of C–Cu contacts are focused on when the range of interface temperature varies from the room temperature (25 °C) to 300 °C. Based on the experimental results, it can be found that high interface temperature can inhibit the surficial erosion of carbon materials, which tends to be obvious, especially along with the increment of current. Moreover, both the delamination wear of carbon surface and the copper-to-carbon transfer behavior decrease with the thermal surge of interface. This beneficial effect of interface temperature results in the reduction in friction coefficient by 14.3%, whereas the negative impacts brought from the high interface temperature are the surface cracking and the rapid recovery of wear rate of carbon materials, under high-current condition.
Graphical abstract
Carbon material, because of its high thermal conductivity, ablation resistance and friction resistance, has been widely used in the field of electrical engineering. When confronted strong thermal ...shock, the interface structure of carbon material would cause thermal shock damage by the rapid temperature difference. In order to systematically and quantificationally study the thermal shock damage of carbon materials, an experimental system that can provide rapid temperature difference was built. The experimental results showed that undergoing a temperature difference of 485 °C, more micro-cracks and holes arose in the pure carbon material, resulting in an increase of porosity by 26.39%, an increase friction coefficient by 48.65%, and a decrease of compressive strength by 23.96%. It was also found the ultrasonic velocity linearly decreased with the increase of porosity and the decrease of the compressive strength caused by thermal shock, which meant the non-destructive ultrasonic testing can be used to conveniently and accurately quantify the thermal shock damage. This conclusion also applies when testing copper-impregnated carbon material, making it a potential method to be used in the maintenance of pantograph which can effectively avoid in rail transit accidents.
Graphical abstract
The relationship between executive functions (EF) and bilingualism has dominated debate in the field. This debate was characterised by optimism for a bilingual advantage until the last decade, when a ...steady stream of articles reported failure to find a consistently positive effect for bilingualism. In addition to addressing concerns about study quality, this turn of events has spurred research into other variables that may explain the conflicting findings. While recent studies have focused on sociodemographic variables and interactional contexts such as age, code-switching frequency, and socioeconomic class to account for various group and individual differences, the impact of culture is seldom scrutinised. This paper examines the possible effect of culture among bilingual studies on EF by first contextualising how bilingual EF are studied and outlining the absence of culture as a macro variable, followed by a discussion on how culture and language are often conflated. This paper directs attention to the small but emerging research that tracks the importance of culture as a separate variable from language. This review discusses why macro culture and individual monoculturalism or biculturalism need to be carefully elucidated as a factor that can interact with the bilingual experience in shaping EF.
Although there is evidence of long-term effects of particulate matter (PM) on cardiovascular diseases (CVD), researches about long-term effects of PM1 on CVD are limited. We aimed to examine the ...long-term effects and magnitude of PM, especially PM1, on incident CVD in China.
We included 6016 participants aged ≥ 45 years without CVD at baseline in 2011 from the China Health and Retirement Longitudinal Study. Personal PM (PM1, PM2.5, and PM10) concentrations were estimated using geocoded residential address. Generalized linear mixed models and SHapley Additive exPlanation were utilized to calculate the impacts and contributions of PM on CVD. Sensitivity analyses were used to check the robustness.
After a follow up of 4-year, 481 (7.99 %) participants developed CVD. Per 10 μg/m3 uptick in 1-year average concentrations of PM1, PM2.5 and PM10 was associated with a 1.20 95 % confidence interval (CI): 1.05–1.37, 1.13 (95 % CI: 1.11–1.15), and 1.10 (95 % CI: 1.06–1.13) fold risk of incident CVD, respectively. The 2-year average concentrations of PM1, PM2.5 and PM10 were associated with incident CVD, corresponding to a 1.03 (95 % CI: 0.96–1.10), 1.11 (95 % CI: 1.02–1.21), and 1.09 (95 % CI: 1.03–1.15) fold risk, respectively. The SHapley Additive exPlanation values of PM1, PM2.5, and PM10 were 0.170, 0.153, and 0.053, respectively, corresponding to the first, second, and fifth among all air pollutants. Effects of PM1, PM2.5 and PM10 on CVD remained statistically significant in two-pollutant models. The elderly, males, smokers and alcohol drinkers tended to have slightly higher effects, while the differences were not statistically significant (all P-values > 0.05) between subgroups.
Long-term exposure to PM1, PM2.5, and PM10 was associated with an increased incidence of CVD. The smaller the particle size, the more important it was for incident CVD indicating that emphasis should be placed on small size of PM.
•Long-term exposure to PM1 was associated with an increased incidence of CVD.•The smaller the particle size, the more important it was for incident CVD.•Elderly, male, smoker and alcohol drinker tended to have slightly higher effects.
To find the phase change microcapsule material (MEPCM) with suitable temperature and high heat storage energy. The phase change microcapsules with sodium sulfate decahydrate (Na2SO4·10H2O) as core ...material and polystyrene (PS) as wall material were prepared by emulsion polymerization. The microcapsule is fixed on the cloth of the overalls by coating method, and the thermoregulation fabric is obtained. The microcapsules were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and infrared spectroscopy (FTIR). Fabrics are tested for durability, air permeability and temperature control. The DSC results show that the Tc and Tm of Na2SO4·10H2O/PS microcapsules are 26.0 °C and 58.0 °C, respectively, and the ΔHc and ΔHm are 64.0 J g−1 and 121.1 J g−1, respectively. The TG results show that the first weight loss temperature range is 104.1 ∼136.7 °C, and the second weight loss temperature range is 395.5 ∼434.6 °C. The infrared spectral characteristic peaks of microcapsules include all the characteristic peaks of Na2SO4·10H2O and PS. In the range of microcapsule phase transition temperature, the cloth treated with 0.5 g MEPCM and 1.5 g MEPCM delayed the temperature change by 16.0 ∼23.0 °C and 10.0 ∼18.0 °C, respectively, compared with the blank cloth. The fabric treated with 0.5 g microcapsules was subjected to 100 and 300 heating/cooling cycles. Compared with before and after the cycles, the fabric after thermal shock cycles showed a 4.15% and 3.56% reduction in delayed temperature changes rate in a rising and falling temperature environment. Therefore, Na2SO4·10H2O/PS microcapsule material can achieve the goal of heat storage and energy storage, and can be used as a low-temperature operation protection material.
Pantograph‐catenary arc fault is the primary factor threatening the stability of the power transmission for high‐speed railway. The motion characteristics of the pantograph‐catenary arc under low air ...pressure and strong airflow is significantly different from the case under atmospheric pressure. In this paper, an experimental platform of pantograph‐catenary arc was built to investigate arc root position‐time and arc column longitudinal drift height‐time characteristic curves under different air pressures and airflow velocites. Via analysing the corresponding results, it can be found that there are different arc root–arc column traction mechanisms at different stages of arc development. The arcing time and arc root stagnation time under low air pressure are significantly longer than the case under atmospheric pressure, resulting in more serious electrode ablation. The arc column longitudinal drift velocity and height are greater with the increase of airflow velocity. Two typical irregular arc motion phenomena—arc root jumping and arc reignition are observed. To clarify the internal mechanism of the above phenomenon, a magnetohydrodynamics (MHD) model of the pantograph‐catenary arc was lauched, the influence mechanism of the pantograph‐catenary arc temperature and voltage are studied, and the physical process of arc temperature oscillation is analysed. The research results provide theoretical support for arc protection in high‐altitude areas.
As common electric contact materials, copper‐carbon electrode pairs are widely used in the field of electric contact such as in high‐speed railways, motor collector rings and grounding brushes. They ...play a key role in energy transmission in the above‐mentioned systems. Arc erosion has become a key issue threatening system safety. In this work, a dedicated arc erosion platform was built to study the polarity effect of copper‐carbon electrode pairs. It was found that arc dynamics and electrodes erosion behaviours were significantly different under different polarities, which could be understood from the mechanism of heat transfer, cooling and electron emission of the electrode. Then, when the carbon material was used as an anode, the arc caused carbon transfer: the carbon material sublimated quickly due to electron condensation and thermal conduction and quickly condensed on the low‐temperature metal electrode, while the carbon material transfer could partly inhibit the oxidation of the cathode metal electrode. In addition, the rapid sublimation of the carbon material produced high‐temperature airflow, which would make the arc impedance fluctuate and cause the arc voltage to jump. Finally, the anode heat transfer and cathode cooling mechanism directly affected the material state, and the erosion of the anode material was more serious.
Orthoimage Creation of Extremely High Buildings Zhou, Guoqing; Xie, Wenhan; Cheng, Penggen
IEEE transactions on geoscience and remote sensing,
12/2008, Letnik:
46, Številka:
12
Journal Article
Recenzirano
This paper presents a method for creating orthoimage in the urban area of extremely high buildings. The proposed method in this paper is different from the traditional methods, which improved the ...accuracy by increasing the number and/or improved the geometric distribution of ground control points. This proposed method first established a mathematical model of constraint condition on the building edges, such as perpendicularity, and then the established constraint conditions are merged into the orthorectification model. A test field located in downtown of Denver, CO, has been used to evaluate our methods. The experiments of comparing the accuracy achieved by our method and other methods are conducted. The experimental results demonstrated that the proposed method can improve the accuracy of 2-5 ft for those buildings of over 100 m high and even 5-7 ft for those buildings over 100 m high in the margin of imagery.
This paper proposes a novel rigorous transformation model for 2D-3D registration to address the difficult problem of obtaining a sufficient number of well-distributed ground control points (GCPs) in ...urban areas with tall buildings. The proposed model applies two types of geometric constraints, co-planarity and perpendicularity, to the conventional photogrammetric collinearity model. Both types of geometric information are directly obtained from geometric building structures, with which the geometric constraints are automatically created and combined into the conventional transformation model. A test field located in downtown Denver, Colorado, is used to evaluate the accuracy and reliability of the proposed method. The comparison analysis of the accuracy achieved by the proposed method and the conventional method is conducted. Experimental results demonstrated that: (1) the theoretical accuracy of the solved registration parameters can reach 0.47 pixels, whereas the other methods reach only 1.23 and 1.09 pixels; (2) the RMS values of 2D-3D registration achieved by the proposed model are only two pixels along the x and y directions, much smaller than the RMS values of the conventional model, which are approximately 10 pixels along the x and y directions. These results demonstrate that the proposed method is able to significantly improve the accuracy of 2D-3D registration with much fewer GCPs in urban areas with tall buildings.
In most Mobile Laser Scanning (MLS) applications, filtering is a necessary step. In this paper, a segmentation-based filtering method is proposed for MLS point cloud, where a segment rather than an ...individual point is the basic processing unit. In particular, the MLS point clouds in some blocks are clustered into segments by a surface growing algorithm, and then the object segments are detected and removed. A segment-based filtering method is employed to detect the ground segments. The experiment in this paper uses two MLS point cloud datasets to evaluate the proposed method. Experiments indicate that, compared with the classic progressive TIN (Triangulated Irregular Network) densification algorithm, the proposed method is capable of reducing the omission error, the commission error and total error by 3.62%, 7.87% and 5.54% on average, respectively.
PDF
