Temperature rise in shear bands in a simulated metallic glass

Temperature rise ($\Delta T$) associated with shear-banding of metallic glasses is of great importance for their performance. However, experimental measurement of $\Delta T$ is difficult due to temporal and spatial localization of shear bands and, as a result, our understanding of the mechanism of $\Delta T$ is limited. Here, based on molecular dynamics simulations we observe a spectrum of $\Delta T$, which depends on both sample size and strain rate, in the shear bands of CuZr metallic glass under tension. More importantly, we find that the maximum sliding velocity of the shear bands correlates linearly with the corresponding $\Delta T$, ranging from $\sim$25 K up to near the melting point for the samples studied. Taking heat diffusion into account, we expect $\Delta T$ to be lower than 25 K for the lower end of sliding velocity. At high temperature, shear band bifurcation and/or multiplication can occur as a negative feedback mechanism that prevents temperature rising well above the melting point

The effect of seawater layer on cable-stayed bridge under tri-direction spatial varying ground motions

In recently years, many sea-crossing bridges were built in some countries. For the complexity of seafloor condition and the stochastic characteristics of earthquakes, it is necessary to research the seismic responses of these sea-crossing bridges located on seawater layer and irregular bottom conditions. In this paper, a theory of the spatial varying ground motions was derived considering the wave propagation in soil and water. The effects of sea water layer, wave passage, coherence, local site and soil saturation on the seismic responses of a cable-stayed bridge were researched. The transfer function was used to calculate the local site effect and soil saturation effect. The seawater layer effect was studied via a simple medal from Crouse and Quilter. Multi-support and tri-direction excitations were utilized with large mass method. The seismic responses of a long span cable-stay bridge in the site conditions with and without seawater were compared. The results present that the seawater layer affects the earthquake response of bridge greatly, and the soil types have different effects on the different component of bridge. The research will help reasonably evaluate the security of sea-crossing bridge under earthquake excitation

The "Rights Awakening" of Chinese Migrant Workers: Beyond the Generational Perspective

In the spring of 2010, the strike of the Honda workers in Nanhai instigated an on-going discourse on the rights awakening of the new generation of migrant workers. Since then, much has been written about these young workers, generally described as more pro-active and ready to stand up against their employers than the older and more subservient generation. Drawing from statistical findings from two factory-gate surveys in the metal mechanics and garment sectors in Shenzhen, this paper tests two hypotheses: (a) that workers of the younger generation are more cognizant of their legal rights than older workers; (b) that the younger generation wants to work fewer hours and to enjoy life more. We argue that this popular image of the younger generation of migrant workers is one-dimensional and reductive, as it focuses only on generational differences as an explanatory factor for worker activism, while ignoring other issues such as types of industries and payment systems. In this paper, we purport that these elements play important roles in shaping the attitude of this younger generation toward their work and rights

Quantum mechanical computations of collision-induced absorption in the second overtone band of hydrogen

The second overtone band of hydrogen is important for studies of both planetary and stellar atmospheres. Until recently, only one experimental measurement existed, taken at 85 K (McKellar, Welsh. Proc Roy Soc London Ser A 1971;322:421). In this paper we present the first quantum mechanical computations of the collision-induced rotovibrational absorption spectra of H2 pairs in the second (3-0) overtone band of hydrogen. We compare our computations with the data by McKellar and Welsh. The second overtone band is very weak and thus it is extremely difficult to measure it in the laboratory, as well as to compute it based on the first principles. As it appears, the collision-induced dipoles of H2 pairs, which give rise to this CIA band spectra are so weak, that the numerical results, at some particular mutual orientations, are almost at the level of numerical uncertainty. Our computations are based on an extension of a database of H2-H2 collision-induced dipoles which already exists (Meyer et al. Phys Rev A 1989;39:2434-48) but which is inadequate for computing CIA bands of hydrogen at overtones higher than the first overtone. © 2000 Elsevier Science Ltd. All rights reserved

Research on Low-Voltage AC Series Arc-Fault Detection Method Based on Electromagnetic Radiation Characteristics

Arc fault is an important cause of electrical fire. At present, the arc-fault detection method based on current and voltage is vulnerable to the influence of a nonlinear load and switching operation in the line, resulting in misjudgment and omission. Therefore, an arc-fault detection method based on the characteristics of electromagnetic radiation is proposed. A low-voltage AC series arc-fault simulation platform is built, and a simple annular antenna is designed to receive an electromagnetic radiation signal. It is proved by experiments that electromagnetic radiation signals have similar characteristic frequencies (13.6–14.2 MHz) under different currents, loads, arc positions and arc occurrence times. At the same time, the electromagnetic radiation signal of a low-voltage AC series arc and normal switching operations are compared. The pulse oscillation time of the radiation signals of the operating arc (2 μs) is far shorter than that of the faulty arc (4 μs), and the characteristic frequency of the radiation signal generated by the switching operation (9.35 MHz) is significantly lower than that of the series arc radiation signal (14 MHz). Compared with the existing methods, this method does not need to consider the influence of current, nonlinear load and other factors in the line, and can accurately distinguish the operating arc and faulty arc

Research on Low-Voltage AC Series Arc-Fault Detection Method Based on Electromagnetic Radiation Characteristics

Arc fault is an important cause of electrical fire. At present, the arc-fault detection method based on current and voltage is vulnerable to the influence of a nonlinear load and switching operation in the line, resulting in misjudgment and omission. Therefore, an arc-fault detection method based on the characteristics of electromagnetic radiation is proposed. A low-voltage AC series arc-fault simulation platform is built, and a simple annular antenna is designed to receive an electromagnetic radiation signal. It is proved by experiments that electromagnetic radiation signals have similar characteristic frequencies (13.6–14.2 MHz) under different currents, loads, arc positions and arc occurrence times. At the same time, the electromagnetic radiation signal of a low-voltage AC series arc and normal switching operations are compared. The pulse oscillation time of the radiation signals of the operating arc (2 μs) is far shorter than that of the faulty arc (4 μs), and the characteristic frequency of the radiation signal generated by the switching operation (9.35 MHz) is significantly lower than that of the series arc radiation signal (14 MHz). Compared with the existing methods, this method does not need to consider the influence of current, nonlinear load and other factors in the line, and can accurately distinguish the operating arc and faulty arc

Preparation and properties of MDA-BAPP-BTDA copolyimide/18-crown ether-6 supramolecular films with inclusion structure and ultralow dielectric constants

In order to obtain polyimide composites with ultra-low dielectric constant, a series of MDA-BAPP-BTDA copolyimides/18-crown ether-6 (CPI/18-CE) supramolecular films with inclusion structure were prepared. The effects of 18-CE on CPI’s thermal, mechanical, dielectric and water absorption properties were investigated. The inclusion rate of 18-CE to CPI backbone was ∼50%. The introduction of 18-CE slightly reduced the thermal properties of CPI/18-CE supramolecular films, but greatly improved their mechanical, dielectric and hydrophobic properties. The tensile strength, young’s modulus and elongation at break of CPI/18-CE supramolecular films were maximally increased by 21.8%, 34.1% and 92.9% respectively. Meanwhile their dielectric constant, dielectric loss and water absorption were as low as 2.10, 0.007 and 0.63%, respectively. In summary, CPI/18-CE supramolecular films possess excellent dielectric properties and broad application prospect in the field of microelectronics

Hydrometeor Budget of the Meiyu Frontal Rainstorms Associated With Two Different Atmospheric Circulation Patterns

Characteristics of hydrometeor budget and the microphysical processes responsible for heavy precipitation are studied based on the WRF model simulations of two representative Meiyu frontal rainstorms that are associated with two distinct atmospheric circulation patterns. Case 1 is characterized by the coupling of the Eastward Propagating Mesoscale Vortex (EPMV) and Meiyu front, while Case 2 is dominated by the interaction between the Low-Level Wind Shear (LLWS) and Meiyu front. The temporal and spatial characteristics of the hydrometeor budget are validated against observations and assimilation products including those obtained during the 2018 Integrative Monsoon Frontal Rainfall Experiment (IMFRE) campaign and discussed in the context of contrasting the precipitation intensification and dissipation stage. Specifically, the ice-dependent cloud processes, rather than the liquid-dependent cloud processes, are predominantly responsible for the variation of precipitation. These terms include the deposition from water vapor to the ice phase hydrometeors, the accretion from cloud liquid water to the ice phase hydrometeors in the upper troposphere, and the melting of the ice phase hydrometeors into raindrops in the mid-lower troposphere. Then three major ice cloud conversion pathways and two minor warm cloud conversion pathways for the formation of raindrops are extracted from the overall microphysical processes active in both Case 1 and Case 2. One of the key findings is that ice-dependent cloud processes are significantly more active in the case characterized by the coupling of EPMV and Meiyu front, and this difference is at least partly explained by the differences in dynamical and thermodynamic conditions dominated by the circulation patterns.6 month embargo; first published online 29 July 2020This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Contrasting Pre-Mei-Yu and Mei-Yu Extreme Precipitation in the Yangtze River Valley: Influencing Systems and Precipitation Mechanisms

The mei-yu season over the Yangtze-Huai Rivers basin, typically occurring from mid-June to mid-July, is one of three heavy-rainfall periods over China and can contribute 50% of the annual precipitation. In this study, the first and second heaviest daily precipitation events at the Wuhan station have been selected to represent typical mei-yu and pre-mei-yu precipitation events where the differences in the atmospheric thermodynamic characteristics, precipitation nature, influencing systems, and mechanisms are investigated. During the mei-yu case, moist air mainly came from the South China Sea. Precipitation occurred south of the mei-yu front where abundant moisture and favorable thermodynamic conditions were present. The main influencing systems include a stable blocking pattern and strong and stable western Pacific subtropical high in the midtroposphere, and a small yet intense mesoscale cyclonic vortex in the low troposphere. Rainfall in Wuhan was continuous, caused by a well-organized convective line. A heavy rainband was located along the narrow band between the elongated upper-level jet (ULJ) and the low-level jet (LLJ) where the symmetric instability was found in the midtroposphere near Wuhan. Quite differently, for the pre-mei-yu precipitation case, moist air primarily came from the Beibu Gulf and the Bay of Bengal. Precipitation happened in the low-level convective instability region, where a short-wave trough in the midtroposphere and a mesoscale cyclonic vortex in the low-troposphere were found. Precipitation in Wuhan showed multiple peaks associated with independent meso-beta-scale convective systems. A rainstorm occurred at the exit of the LLJ and the right entrance of the ULJ, where convective instability exited in the mid- to low troposphere.National Natural Science Foundation of ChinaNational Natural Science Foundation of China [41705019, 41620104009, 91637211]; IHR; U.S. National Science FoundationNational Science Foundation (NSF) [AGS-1354402, AGS-1445956]6 month embargo; published online: 16 November 2019This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Vertical Structures of Typical Meiyu Precipitation Events Retrieved From GPM‐DPR

This work for the first time analyzed the vertical structures of the different stages of Meiyu precipitation systems over the Yangtze-Huai River Valley in central China using measurements and retrievals from the Global Precipitation Measurement Mission Dual-Frequency Precipitation Radar (GPM-DPR) and Feng Yun satellites. GPM-DPR-retrieved near-surface rain and drop size distributions were first validated against the surface disdrometer measurements and showed good agreement. Then we analyzed three cases from the Integrative Monsoon Frontal Rainfall Experiment to demonstrate the different characteristics of convective precipitation and stratiform precipitation (SP) in the developing, mature, and dissipating stages of the Meiyu precipitation systems, respectively. For statistical analysis, all Meiyu cases during the period 2016-2018 detected by GPM-DPR were collected and classified into different types and stages. In the stratiform regions of Meiyu precipitation systems, coalescence slightly overwhelms breakup and/or evaporation processes, but it was dominant in the convective regions when raindrops fall. There were large numbers of large ice particles during the developing stage due to strong updrafts and abundant moisture, whereas there were both large ice and liquid particles in the mature stage. The vertical structures of the SP examined in this study were similar to those over the ocean regions due to high relative humidity but different to the mountainous west regions of the USA. The findings of the stage-dependent SP vertical structures provide better understanding of the evolution of monsoon frontal precipitation, as well as the associated microphysical properties, and provide insights to improve microphysical parameterization in future models.6 month embargo; published online: 18 December 2019This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]