基于结构方程模型的宁波城市居民休闲满意度研究

休闲满意度研究对于提升城市居民美好生活质量具有重要意义。采用Beard等编制的休闲满意度量表,以问卷调查数据为基础,通过构建结构方程模型对浙江省宁波城市居民休闲满意度进行了研究。结果表明:①宁波城市居民对休闲带来的放松体验最满意,教育功能和审美体验次之,身体和心理满意度相对较低,而社会满意度最低。②审美满意度、身体满意度和心理满意度对宁波城市居民休闲总体满意度具有显著影响,其中,审美满意度的影响程度最大,其次为心理满意度和身体满意度,而放松、社交以及教育满意度对休闲总体满意度具有显著影响的研究假设未获支持。③构建的宁波城市居民休闲满意度结构方程模型具有跨样本稳定性特征。研究结果可为提升宁波城市居民休闲满意度提供理论依据。     

Effects of aluminum toxicity induced by acid deposition on pine forest ecosystem in Longli of Guizhou Province,Southwestern China

The effects of acid deposition on pine forest ecosystems in Longli of Guizhou Province, southwestern China are studied using indoor experiments and model simulations. Indoor experiments are designed to explore the aluminum toxicity on pine seedlings, and the long-term soil acidification model（LTSAM） and a terrestrial biogeochemistry model（CENTURY） are used to simulate the influences of acid deposition on pine forest ecosystems. The indoor experiment results of aluminum toxicity show that aluminum ions in solution limit plant growth and acid deposition enhances this effect by facilitating the release of aluminum ions from the soil. Pine seedling biomass and root elongation decrease as the aluminum concentration increases. The results of model simulations show that the soil chemistry varies significantly with different changes in acid deposition. When the acid deposition increases, the pH value in the soil solution decreases and the soil Al³⁺ concentration increases. The increased acid deposition also has negative impacts on the forest ecosystem, i.e., decreases plant biomass, net primary productivity（NPP） and net CO₂ uptake. As a result, the soil organic carbon（SOC） decreases because of the limited supply of decomposition material. Thus acid deposition need be reduced to help protect the forest ecosystems.     

Multifractal characteristics of the jet turbulent intensity depending on the outfall nozzle geometry

The multifractal measure enables an examination of the characteristics of a quantity distributed over a domain. This study examined the multifractal properties of turbulent intensities obtained from jet discharge experiments, where three types of nozzle geometries were examined in terms of the velocity fields and turbulent characteristics using particle image velocimetry. Depending on the nozzle geometry, the experimental results showed that the distribution of turbulent intensities and resulting dilution exhibited different behaviors. The experiment also showed that the transversal velocity profiles are similar to each other regardless of the outfall nozzle shapes and demonstrates the traditional similarity assumption at the same time. The multifractal exponents of the turbulent intensities were obtained with Box Count Method in a two-dimensional space. The results showed that the turbulent intensities obtained in two-dimensional space have a common multifractal spectrum, which was not the case for the velocity or shear stress observed in the same space. Although the transversal velocity profiles are similar, the multifractal exponent clearly shows a difference depending on the outfall geometries. In particular, the minimum value of the Lipschitz–Hölder exponent (α _min) and the entropy dimension (α ₁) tends to increase as turbulent intensity and dilution increase. These results suggest that the multifractal properties can be utilized potentially to categorize and evaluate the discharge outfall capabilities in terms of the resulting dilution.     

Effect of Wetland Reclamation on Soil Organic Carbon Stability in Peat Mire Soil Around Xingkai Lake in Northeast China

Content and density of soil organic carbon(SOC) and labile and stable SOC fractions in peat mire soil in wetland, soybean field and rice paddy field reclaimed from the wetland around Xingkai Lake in Northeast China were studied. Studies were designed to investigate the impact of reclamation of wetland for soybean and rice farming on stability of SOC. After reclamation, SOC content and density in the top 0–30 cm soil layer decreased, and SOC content and density in soybean field were higher than that in paddy field. Content and density of labile SOC fractions also decreased, and density of labile SOC fractions and their ratios with SOC in soybean field were lower than that observed in paddy field. In the 0–30 cm soil layer, densities of labile SOC fractions, namely, dissolved organic carbon(DOC), microbial biomass carbon(MBC), readily oxidized carbon(ROC) and readily mineralized carbon(RMC), in both soybean field and paddy field were all found to be lower than those in wetland by 34.00% and 13.83%, 51.74% and 35.13%, 62.24% and 59.00%, and 64.24% and 17.86%, respectively. After reclamation, SOC density of micro-aggregates( 0.25 mm) as a stable SOC fraction and its ratio with SOC in 0–5, 5–10, 10–20 and 20–30 cm soil layers increased. SOC density of micro-aggregates in the 0–30 cm soil layer in soybean field was 50.83% higher than that in paddy field. Due to reclamation, SOC density and labile SOC fraction density decreased, but after reclamation, most SOC was stored in a more complex and stable form. Soybean farming is more friendly for sustainable SOC residence in the soils than rice farming.     

Numerical Study on the Vertical Water Exit of A Cylinder with Cavity

When a high-speed body with cavity passes through water-air free surface and exits water, its mechanical environment and dynamic characteristics change significantly due to the great difference in density and viscosity between water and air. With focusing on this problem, the Computational Fluid Dynamics (CFD) method is applied to perform numerical calculation on the process of this vapor-liquid-gas flow during the water exit of a high-speed cylinder, with the Volume of Fraction (VOF) multiphase flow interface-capturing techniques and the overset grid technology. After the verification and validation of the CFD model through mesh convergence study and a water-entry experiment, cavity evolution and flow characteristics including pressure and velocity distribution during the water exit are analyzed. The effects of different initial velocities on the pressure distribution and drag characteristics of the cylinder are investigated. Calculated results show that the cavity collapse during water exit causes strong pressure fluctuation on the cylinder; when the cylinder exits water enveloped in a supercavity, the pressure distribution on its wall surface and surrounding water region is relatively uniform, and the drag changes gently, and thus the cylinder has good motion stability.

     

Study on Transient Gap Resonance with Consideration of the Motion of Floating Body

In this paper, the transient fluid resonance phenomenon inside a narrow gap between two adjacent boxes excited by the incident focused waves with various spectral peak periods and focused wave amplitudes is simulated by utilizing the open-sourced computational fluid dynamics software, OpenFOAM. The weather-side box is allowed to heave freely under the action of waves, and the lee-side box keeps fixed. This paper mainly focuses on how both the spectral peak period and the focused wave amplitude affect the free-surface amplification inside the gap, the motion of the weather-side box, and the wave loads (including the vertical and the horizontal wave forces) acting on both boxes. For comparison, another two-box system with both boxes fixed is also considered as a control group. It is found that the motion of the weather-side box significantly changes the characteristics of the transient gap resonance, and it would cause that the fluid resonant period becomes 1.4–1.6 times that of the two-box system with both boxes fixed. All the concerned physical quantities (i.e., the free-surface amplification in the gap, the motion of the weather-side box, the wave loads) are found to closely depend on both the spectral peak period and the focused wave amplitude.

     

南川黄泥垭隧道工程对水文地质条件的影响分析

隧道工程建设无疑对岩溶地区的水文地质环境地质带来巨大冲击。文章以重庆市南川区黄泥垭隧道工程为实例,采用地面调查、示踪试验、长观监测等方法进行综合研究,剖析隧道工程对隧址区水文地质环境的影响。研究结果表明:黄泥垭隧道工程改变了隧址区的地下水流场,疏干地表地下水、加剧干旱缺水程度,并随之出现新的人工水点——隧道涌水;同时隧道工程影响了水资源空间分配格局、降低了水资源利用率。      

Clay mineral assemblages of the oceanic red beds in the northern South China Sea and their responses to the Middle Miocene Climate Transition

Science China Earth Sciences - The Middle Miocene Climate Transition (MMCT, ～14 Ma) is the largest cooling event in the Cenozoic “Coolhouse”, which significantly impacts the...     

A glimpse into rapid freezing processes in clay with x-ray tomography

Acta Geotechnica - This short paper proposes time-series x-ray tomography as a valuable tool for quantifying freezing processes in a remoulded clay. As an example, three simple closed system...     

山东省绿色发展水平绩效评价与驱动机制——基于17地市面板数据

构建绿色发展评价指标体系,并利用熵值法、全局莫兰指数、GWR模型等多种计量方法对2005～2016年山东省17地级市绿色发展水平时空分异特征与驱动机制进行了综合研究,结果表明:①山东省绿色发展"自上而下"指令性特征比较突出,且依赖于物质消耗型规模增长,势必忽视经济要素横向转移反馈作用与产业集群效应;②山东省绿色发展水平逐年递增,俱乐部收敛特征较为突出,但其年均增长率仅为1.77%反映了产业轻型化与清型化进程缓慢,绿色发展质量提升之路漫长而艰巨;③山东省绿色发展经历了空间依存关系不明显到明显的过程,且绿色发展水平存在明显的空间分异态势,两极化发展特征较为明显;④加入空间效应的空间加权回归模型更具有解释力,人均GDP、万人R&D人员数、人均固定资产投资等对于绿色发展水平的优化提升起到正向促进作用,第二产业增加值/第三产业增加值对于绿色发展回归系数呈现负相关,实际利用外资对于绿色发展回归系数有正有负。