A new cadmium-organic framework fluorescent sensor for Al3 + and Ca2 + ions in aqueous medium

A new metal-organic framework (MOF), [Cd₂(bptc)(HCOO)]·NH₂(CH₃)₂·3H₂O (1), where H₄bptc = 3,3′,5,5′-biphenyltetracarboxylic acid, was obtained by solvothermal reaction. The topology of MOF 1 is a (5,8)-connected net with {4¹⁶ · 5⁸ · 6⁴}{4⁴ · 5⁶}₂ point symbol. MOF 1 shows high stability in aqueous solution. Luminescence study indicates that MOF 1 possesses selective turn-on luminescent sensing functions towards Al^3 + and Ca^2 + ions in aqueous solutions.     

Partisan amplification of risk: American perceptions of nuclear energy risk in the wake of the Fukushima Daiichi disaster

AimThis study examines risk perceptions toward nuclear power before and after the Fukushima Daiichi disaster using nationally representative survey samples of American adults.ScopeOn March 11, 2011, a magnitude 8.4 earthquake, the largest in the nation's history, occurred off the coast of Japan. The earthquake produced a devastating tsunami that flooded areas of the Fukushima Daiichi nuclear plant and resulted in a loss of power to the plant's cooling system. In the weeks that followed, the world watched as Japanese and international nuclear power safety experts scrambled to contain the damage and prevent a full meltdown. Although the Fukushima Daiichi disaster was heavily covered in media, there is little empirical research on how this coverage impacted audience risk perceptions. Our analysis goes beyond examining aggregate risk perceptions, instead focusing on how specific sub-populations responded to the disaster.ConclusionWe found that ideological groups responded differently to the events in Japan. In particular, risk perceptions among conservatives decreased following the incident. Moreover, we found that media use exacerbated these effects. We discuss possible explanations for these findings.     

Trends and periodicities in observed temperature,precipitation and runoff in a desert catchment: case study for the Shiyang River Basin in Northwestern China

The Mann–Kendall test, wavelet analysis was used to analyse the long‐term trends and periodicities in temperature, precipitation and streamflow in China's Shiyang River Basin since 1950. The Principal components analysis (PCA) was used to quantify the impacts of climate change and human activities on water resources. The annual mean air temperature has increased, consistent with increasing global temperatures. The annual precipitation fluctuated but has generally increased since the 1990s. The air temperature and precipitation showed changes on periods ranging from 2 to 28 years. The correlation between annual runoff and precipitation variation was 0.61 (P < 0.05), indicating precipitation is the main source of the runoff. Human activities played the dominant role in the lower reaches, accounting for 58.5% of the total effect. The results have important implications for water resources management to support harmonisation of the relationship between humans and nature to combat the effect of climate.     

Effect of Nd-doping on structural,thermal and electrochemical properties of LaFe0.5Cr0.5O3 perovskites

The structural, thermal and electrochemical properties of the perovskite-type compound La_1−xNd_xFe_0.5Cr_0.5O₃ (x=0.10, 0.15, 0.20) are investigated by X-ray diffraction, thermal expansion, thermal diffusion, thermal conductivity and impedance spectroscopy measurements. Rietveld refinement shows that the compounds crystallize with orthorhombic symmetry in the space group Pbnm. The average thermal expansion coefficient decreases as the content of Nd increases. The average coefficient of thermal expansion in the temperature range of 30–850 °C is 10.12×10⁻⁶, 9.48×10⁻⁶ and 7.51×10⁻⁶ °C⁻¹ for samples with x=0.1, 0.15 and 0.2, respectively. Thermogravimetric analyses show small weight gain at high temperatures which correspond to filling up of oxygen vacancies as well as the valence change of the transition metals. The electrical conductivity measured by four-probe method shows that the conductivity increases with the content of Nd; the electrical conductivity at 520 °C is about 4.71×10⁻³, 6.59×10⁻³ and 9.62×10⁻³ S cm⁻¹ for samples with x=0.10, 0.15 and 0.20, respectively. The thermal diffusivity of the samples decreases monotonically as temperature increases. At 600 °C, the thermal diffusivity is 0.00425, 0.00455 and 0.00485 cm² s⁻¹ for samples with x=0.10, 0.15 and 0.20, respectively. Impedance measurements in symmetrical cell arrangement in air reveal that the polarization resistance decreases from 55 Ω cm⁻² to 22.5 Ω cm⁻² for increasing temperature from 800 °C to 900 °C, respectively.     

Preparation of hardened tiles from waste phosphogypsum by a new intermittent pressing hydration

The solid waste phosphogypsum (PG), as the sole-raw material, was processed into hardened tiles with favorable mechanical strength by a novel intermittent pressing hydration process. First, the raw PG with dihydrate gypsum was dehydrated into semi-hydrate gypsum. The dehydrated PG was granulated with water, press-formed, and then immersed in water under intermittent pressing. Using the optimal granulation humidity of 35%, pressing pressure of 20 MPa, pressing frequency of once per 2 min and total times of 24, PG hardened tiles with bending strength of 18.9 MPa was obtained. It was revealed that the dehydrated PG was hydrated into the dense dihydrate gypsum crystals under the action of intermittent pressing, which contributed to the high mechanical strength of the tiles. The hardened tile has the potential to be a new-type wall material and its application may help to solve PG׳s environmental risk.     

Clarifying the hydrological mechanisms and thresholds for rainfall-induced landslide: in situ monitoring of big data to unsaturated slope stability analysis

The development of early warning systems for landslide hazards has long been a challenge because the accuracy of such systems is limited by both the complicated underlying mechanisms of landslides and the lack of in situ data. In this study, we implemented a multivariate threshold criterion that integrates in situ monitoring data and data from unsaturated hydro-mechanical analyses as an early warning system for rainfall-induced landslides in the Wenchuan earthquake region of China. The results indicate that rainfall intensity is closely correlated with the probability of landslide occurrence. Variations in matric suction and suction stress were obtained from in situ measurements and used to quantify the soil water retention curve, which presented clear hysteresis characteristics. The impacts of rainfall infiltration on slope failure in post-earthquake landslide areas under transient rainfall conditions were quantified by hydro-mechanical modelling theories. Variations in the suction stress of unsaturated soil were used to calculate the safety factor. The influence of hydrological hysteresis processes on the slope failure mechanism was analysed. Multivariate threshold criteria that include the intensity–probability (I-P) threshold, soil moisture and matric suction based on in situ big data and unsaturated slope stability analysis benchmarks are proposed for use in an early warning system for rainfall-induced landslides.

     

挥发性有机污染场地原位评价的膜界面探测器MIP研究综述

膜界面探测器(Menmberane Interface Probe, MIP)是应用与土壤和地下水挥发性有机污染场地原位勘测的技术设备。近年来被广泛应用于VOCs污染场地勘测中。对MIP的结构、测试原理以及与其相匹配的气相色谱检测器进行了介绍,综述了MIP在国内外污染场地勘测的应用案例,总结了国外学者针对MIP测试精度进行的研究结果。分析表明,MIP原位测试能全面地、真实地反应污染场地挥发性有机物分布状况,减少污染场地勘查成本,提高污染场地勘查效率。通过与其它原位测试探头的结合,可同时对污染场地岩土工程特性进行评价,进而为后续污染场地治理方案的制定提供依据。     

纤维加筋微生物固化砂土的力学特性

微生物固化能有效提高砂土的强度,但同样会导致土体破坏时呈现明显的脆性。为了平衡微生物固化砂土脆性破坏的不利影响,提出纤维加筋与微生物固化相结合的改性方法,即将质量分数为0%,0.05%,0.15%,0.25%和0.30%的聚丙烯纤维与石英砂均匀混合,然后基于微生物诱导碳酸钙沉积(MICP)技术对土样进行固化,并开展了一系列无侧限抗压试验,同时采用酸洗法测定了各组试样中的碳酸钙含量,进一步分析了试样的微观结构及纤维–土颗粒之间的界面作用特征。结果表明:①在微生物固化砂土中掺入纤维,能极大提高土样的无侧限抗压强度和残余强度,并能显著改善土样破坏时的韧性;②纤维掺量对微生物固化砂土的力学特性有重要影响,无侧限抗压强度随纤维掺量总体上呈先增加后减小的趋势,最优纤维掺量为0.15%,峰后残余强度与纤维掺量呈单调正相关关系;③纤维加筋使微生物固化砂土的峰后应力–应变曲线呈阶梯式下降模式,局部存在波浪式起伏特征;④纤维加筋能够提高微生物诱导碳酸钙的沉积效率和产量,与此同时,碳酸钙的胶结作用对纤维加筋效果具有促进作用。纤维加筋技术与MICP技术相结合能够实现优势互补,对提高工程结构的安全性与稳定性具有积极意义。     

Spatial pattern of population mobility among cities in China: Case study of the National Day plus Mid-Autumn Festival based on Tencent migration data

Population migration, social check-in, vehicle navigation, and other spatial behavior big data have become vital carriers characterizing users' spatial behavior. “Tencent Migration” big data can real-timely, dynamically, completely and systematically record population flow routs using LBS device. Through gathering residents daily mobility among 299 cities in China during the period of “National Day–Mid-Autumn Festival” (NDMAF) vacation (from September 30 to October 8) in 2017 in “Tencent Migration” and defining three periods with “travel period, journey period, return period”, this paper is designed to analyze and explore the characteristics and spatial patterns of daily flow mobility cities from the perspective of population daily mobility distribution levels, flow distribution layers network aggregation, spatial patterns and characteristics of the complex structure of the flow network. Results show that “Tencent migration” big data clearly discovers the temporal-spatial pattern of population mobility in China during the period of NDMAF. The net inflow of population showed a diamond shaped with cross frame support in each period, the four nodes of the diamond contain Beijing, Shanghai, Guangzhou and Xi'an. Main mobility assembling centers are distributed in the urban agglomerations of Beijing-Tianjin-Hebei, Yangtze River Delta, Pearl River Delta and Chengdu-Chongqing, and those centers have strong coherence with those urban hierarchies. Most cities are in a state of “relative equilibrium” in the population flow, and clear hierarchical structure and level distinction can be identified. Spatial patterns of population mobility present obvious core-periphery structures. The Dali-Hegang line exhibits a significant network of spatial differences in terms of boundary divisions. In this context, the spatial distribution of urban network could be summarized as “dense in the East and sparse in the West”, and the core linkages of urban network could be characterized as “parallel in the East and series in the West”. The whole network exhibits a typical “small world” network characteristic, which shows that China's urban population flow network has high connectivity and accessibility during the period of NDMAF. The network has a distinct “community” structure in the local area, including 2 national communities, 2 regional communities and 3 local-level communities.