Rates of urbanisation and the resiliency of air and water quality

Global human population and urban development are increasing at unprecedented rates and creating tremendous stress on local, regional, and global air and water quality. However, little is known about how urban areas vary in their capacity to address effectively air and water quality impacts associated to urban development. There exists a need to better understanding the factors that mediate the interactions between urbanisation and variations of environmental quality. By synthesizing literatures on the relationship between urban development and air and water quality, we assess the amount of scholarship for each of these cities, characterize population growth rates in one hundred of the largest global cities, and link growth trends to changes in air and water quality. Our results suggest that, while there is a growing literature linking urbanisation and environmental quality, some regions of the globe are better represented than others, and that these trends are consistent with our characterization of population growth rates. In addition, the comparison between population growth rates and air and water quality suggest that multiple factors affect the environmental quality, and that approaching rates of urbanisation through the lens of ‘resiliency’ can be an effective integrative concept for studying the capacity of urban areas to respond to rapid rates of change. Based on these results we offer a framework for systematically assessing changes in air and water quality in megacities.     

Dynamic real‐time monitoring of chloroform in an indoor swimming pool air using open‐path Fourier transform infrared spectroscopy

This study used open‐path Fourier transform infrared (OP‐FTIR) spectroscopy to continuously assess the variation in chloroform concentrations in the air of an indoor swimming pool. Variables affecting the concentrations of chloroform in air were also monitored. The results showed that chloroform concentrations in air varied significantly during the time of operation of the swimming pool and that there were two peaks in chloroform concentration during the time of operation of the pool. The highest concentration was at 17:30, which is coincident with the time with the highest number of swimmers in the pool in a day. The swimmer load was one of the most important factors influencing the chloroform concentration in the air. When the number of swimmers surpassed 40, the concentrations of chloroform were on average 4.4 times higher than the concentration measured without swimmers in the pool. According to the results of this study, we suggest that those who swim regularly should avoid times with highest number of swimmers, in order to decrease the risk of exposure to high concentrations of chloroform. It is also recommended that an automatic mechanical ventilation system is installed to increase the ventilation rate during times of high swimmer load.     

Cu Substrates with Different Grain Sizes

Cu₆Sn₅ and Cu₃Sn are easily formed at the interface between Sn and Cu during reflow and aging processes. Thick Cu-Sn compounds at the interface become brittle, reducing the mechanical strength of solder joints and increasing the consumption of under bump metallization (UBM). It is noted that intermetallic compound (IMC) growth and substrate consumption are affected by factors such as substrate fabrication, substrate orientation, and substrate microstructure. In this study, to determine the effects of substrate grain size on IMC growth and substrate consumption, pure Sn solder was reflowed on annealed Cu substrates with different grain sizes at 250°C for 30 s to 600 s. It was revealed that Cu substrates with smaller grain sizes exhibited reduced IMC growth. In addition, the interdiffusion coefficients of Cu₆Sn₅ and Cu₃Sn were decreased for the Cu substrate with the smaller grain size. The influence of the Cu substrate grain size on IMC growth and substrate consumption is discussed.     

Oxidation resistance of nanocomposite CrAlSiN under long-time heat treatment

To investigate the oxidation behavior and structure stability, Si was doped into CrAlN films to deposit on silicon wafers by RF magnetron sputtering and annealed at 1000 °C for 10 to 100 h. The X-ray diffraction patterns revealed that the grain size of as-deposited CrAlSi_xN (x = 0–9.9 at.%) coatings became finer with silicon doping. According to SEM images, the growth of oxide layer was restrained with increasing silicon content after heat treatment in air. Additionally, the surface roughness of CrAlSiN using AFM analysis increased slightly even though annealed for a long time. TEM micrographs demonstrated that the CrAlSiN coatings could well retain the nanocomposites structure after heat treatment at elevated temperature, indicating that CrAlSiN exhibits good structure stability. To conclude, doping certain Si content could reduce the grain size and prolong the diffusion paths in CrAlN coatings, thereby effectively inhibiting nitrogen outward diffusion and oxygen penetration into the coatings. Furthermore, there was no significant variation in the microstructure of CrAlSiN after heat treatment, suggesting that the nanocomposites could preserve the oxidation resistance at elevated temperature.     

Nano‐to‐Microdesign of Marimo‐Like Carbon Nanotubes Supported Frameworks via In‐spaced Polymerization for High Performance Silicon Lithium Ion Battery Anodes

Silicon (Si) has been perceived as a promising anode material for lithium‐ion batteries for decades due to its superior theoretical capacity, environmental benignity, and earth abundance. To accommodate the drastic volume expansion during lithiation, which is the primary drawback leading to poor cycling life, a novel structural design via fabricating the Marimo‐like carbon nanotubes frameworks with silicon nanoparticle (SiNP) filling in internal space has been developed. This facile fabrication procedure involves an in‐spaced polymerization process through ex situ polymerization, using pyrrole monomers with a soft organic template in which well‐dispersed SiNPs are present. Carbonization post‐treatment is then performed to construct rigid conductive networks. The thus‐fabricated 3D Marimo‐like hybrid structure exhibits a remarkably improved electrochemical performance compared with that of the simple ball‐milling method, which mainly originates from their structural advantages, including the built‐in buffer spaces and the robust line‐to‐line contact mode between the components. The state‐of‐the‐art structure exhibits an optimal high‐rate capability (422 mAh g^?1 at a current rate of 2 A g^?1) and long cycling stability (916 mAh g^?1 for 200th cycles at a current rate of 0.2 A g^?1) and achieves the requirements for industrial production with the facile and cost‐effective synthetic approach.     

Magnetocaloric effect of La0.8Ce0.2Fe11.4−xMnxSi1.6 compounds

The effect of Mn addition on the magnetocaloric effect (MCE) of the La_0.8Ce_0.2Fe_11.4?xMn_xSi_1.6 (x = 0.0, 0.1, 0.2, 0.3) compounds was investigated. It was revealed that the transition temperatures of the compounds are sensitive to Mn composition. The temperatures are shifted from 177 to 121 K for Mn composition from 0.0 to 0.3. Moreover, thermal lag and magnetic hysteresis loss of the compounds are reduced largely due to Mn addition. A good MCE with a large and almost constant refrigerant capacity in a large temperature span over 50 K was achieved in the investigated compounds. The investigated compounds are promising magnetic entropy change materials.     

Interfacial morphology and concentration profile in the unleaded solder/Cu joint assembly

A joint assembly of lead-free solder/intermetallic layers/copper was prepared by hot-dipped solder coated on a copper substrate and then by thermal ageing at 100, 125, 150, and 170°C for 50, 100, 200, and 600 h, respectively. Results of interfacial morphologies and concentration profiles on the solder/copper joint were presented. Optical and scanning electron microscope (OM and SEM) were used to measure the thickness of intermetallic layers and then to illucidate the development of microstructure at the joint assembly. The phases of intermetallic compound were identified to be Cu₃Sn and Cu₆Sn₅ by both X-ray mapping in electron probe micro-analysis (EPMA), and X-ray diffraction. The intermetallic layers, subtracted from the initial thickness formed by hot dipping, showed a linear dependence on the square root of ageing time at various ageing temperatures. The diffusion coefficients of intermetallic compounds are estimated by an Arrhenius equation, and the pre-exponential terms of Cu₃Sn layer and Cu₆Sn₅ layer are 7.10×10^-7cm²s^-1 and 6.1×10^-3cm²s^-1, respectively. The associated activation energies of Cu₃Sn layer and Cu₆Sn₅ layer are 57.03kJmol^-1 and 83.76kJmol^-1, respectively. A model of a diffusion-controlled mechanism is used to fit the concentration profiles of the joint assembly, and exhibits a fairly good quantitative agreement with the measured data. The initial thickness formed as soldering proceeds is also taken into account to evaluate the apparent thickness by introducing a term of corrected ageing time. ©1999 Kluwer Academic Publishers     

The phase transformations and cycling performance of copper-tin alloy anode materials synthesized by sputtering

A sputtering technique was adopted to synthesize Sn-Cu thin film electrodes. Island Sn particles were obtained on the copper foil. Cu₆Sn₅ was spontaneously generated at the interface between Sn and Cu foil. To further improve the cycling stability, Cu source was introduced to increase the formation of Cu₆Sn₅ and to serve as a buffer during cycling. Moreover, the phase and elemental ratio of Sn and Cu varied in the synthesized electrode by alternately adjusting sputtering time for Sn and Cu. The cell synthesized by sputtering Sn for 5 min and Cu for 9 s alternately exhibited the best cycling stability. The 1st charge capacity of cell was 635 mA hg⁻¹, and the 1st efficiency was even higher than 97%. The capacity remained higher than 500 mA hg⁻¹ after 15 cycles. The phase transformation of cell was investigated through voltage profile, CV curve and in situ XRD analysis. The in situ XRD analysis confirmed that Cu₆Sn₅ could react with lithium directly without the presence of Li₂CuSn during cycling. The reaction mechanism of Cu₆Sn₅ with lithium during cycling was demonstrated to be an alloying process, and the structure of Cu₆Sn₅ was thus a low-temperature monoclinic phase.     

On-state breakdown in power HEMTs: measurements and modeling

We have carried out a systematic study of on-state breakdown in a sample set of InAlAs/InGaAs HEMT's using a new gate current extraction technique in conjunction with sidegate and temperature-dependent measurements. We find that as the device is turned on, the breakdown voltage limiting mechanism changes from a TFE-dominated process to a multiplication-dominated process. This physical understanding allows the creation of a phenomenological physical model for breakdown which agrees well with all our experimental results, and explains the relationship between BV_on and the sheet carrier concentration. Our results suggest that depending on device design, either on-state or off-state breakdown can limit maximum power