A densification mechanism to model the mechanical effect of methane hydrates in sandy sediments

Recent pore-scale observations and geomechanical investigations suggest the lack of true cohesion in methane hydrate-bearing sediments (MHBSs) and propose that their mechanical behavior is governed by kinematic constrictions at pore-scale. This paper presents a constitutive model for MHBS, which does not rely on physical bonding between hydrate crystals and sediment grains but on the densification effect that pore invasion with hydrate has on the sediment mechanical properties. The Hydrate-CASM extends the critical state model Clay and Sand Model (CASM) by implementing the subloading surface model and introducing the densification mechanism. The model suggests that the decrease of the sediment available void volume during hydrate formation stiffens its structure and has a similar mechanical effect as the increase of sediment density. In particular, the model attributes stress-strain changes observed in MHBS to the variations in sediment available void volume with hydrate saturation and its consequent effect on isotropic yield stress and swelling line slope. The model performance is examined against published experimental data from drained triaxial tests performed at different confining stress and with distinct hydrate saturation and morphology. Overall, the simulations capture the influence of hydrate saturation in both the magnitude and trend of the stiffness, shear strength, and volumetric response of synthetic MHBS. The results are validated against those obtained from previous mechanical models for MHBS that examine the same experimental data. The Hydrate-CASM performs similarly to previous models, but its formulation only requires one hydrate-related empirical parameter to express changes in the sediment elastic stiffness with hydrate saturation.     

基于复杂网络的城市公交网络研究综述

近年来,基于复杂网络理论的城市公交网络研究得到了人们的广泛关注,相关的研究成果有助于深入理解城市公交网络的运行机理,并为这类网络的设计、优化与控制提供帮助.首先介绍了城市公交网络的研究背景、城市公交系统的网络描述和相关的网络概念.然后从网络的静态特性分析、演化生成建模、行为研究和应用研究等方面对国内外的研究现状进行了总结和分析.最后,总结并讨论了当前基于复杂网络的城市公交网络的研究状况与发展机遇.     

Public Participation in Rural Environmental Governance around the Water Source of Xiqin Water Works in Fujian

Public participation is an important way to improve the overall effect and social recognition of rural environmental governance in water source areas. Public participation makes environmental governance measures more targeted and effective, contributes to protecting the basic environmental rights of the public, and makes it easier to meet the livelihood needs of rural people. Public participation in rural environmental governance in water source areas is characterized by complex behavior and is dependent on public willingness to participate. Amongst other factors, it is subject to the combined influences of both internal (psychological cognition) and external (environmental regulation) conditions. This paper builds a theoretical framework for understanding public participation behavior in rural environmental governance, and uses it to analyze a case in the rural area surrounding the Xiqin Water Works in Fujian Province. In the case study, the public shows high willingness to participate, but low actual rates of participation. At the same time, the willingness of villagers to pay for the control of pollution from livestock and poultry breeding varies greatly from village to village, and there are also noticeable individual differences in public participation in the use of public collection points for rural household waste. We found that gender, understandings of environmental protection and perception of environmental regulation, play a key role in influencing the willingness of farmers to pay for the control of pollution from livestock and poultry breeding. Individual awareness of environmental protection, environmental protection facility conditions, and environmental service quality had a significant influence on public participation in the use of public collection points for rural household waste.     

Thermodynamic mixing behavior of synthetic Ca-Tschermak–diopside pyroxene solid solutions: III. An analysis of IR line broadening and heat of mixing behavior

A series of synthetic Ca-Tschermak–diopside (CaAlAlSiO₆–CaMgSi₂O₆) clinopyroxenes were investigated by powder infrared spectroscopy at room temperature in the wavenumber range 80–2,000 cm⁻¹. Measurable local structural heterogeneities in the crystals are suggested by the line broadening parameter, Δcorr that are observed for intermediate solid-solution compositions. The broadening is most pronounced in the high wavenumber region of the IR spectra that contains stretching modes involving the TO₄ polyhedra. The effective line widths for three selected wavenumber regions deviate positively from linear behavior. This is also observed for the enthalpy of mixing of this solid solution. The relationship between “excess Δcorr”, δΔcorr, and heat of mixing, ΔH _mix, behavior was investigated for this clinopyroxene series and for several other binary silicate solid solutions. The ΔH _mix versus δΔcorr slope values show a linear relationship with respect to the integrated excess volume of the various solid solutions.     

中立型随机发展系统的适定性

针对中立型随机发展系统的温和解与轨道温和解,给出了其存在唯一性与渐近估计的充分条件,推广了经典的Pazy定理与一些近期文献的主要工作.     

Choosing the Right Policy Tools to Encourage Watershed Stewardship through the Study of Attitude

Recently, a number of “Payment for Watershed Services” programs have aimed to engage private landowners in watershed stewardship initiatives by offering financial incentives for adopting watershed best management practices. However, a growing field of research suggests that financial incentives alone may be of limited utility to encourage widespread and long-standing behavior change, and other policy tools may be required. This research examines how attitudes may influence enrollment in watershed stewardship programs to shed light the application of incentive, capacity building, and symbolic policy tools. We distributed a questionnaire to rural landowners in the Clackamas River watershed, OR, and received 281 valid responses (29% response rate). We found that attitudes associated with trust, ecological understanding, and technical capacity played more fundamental roles compared with financial considerations. We interpret these findings by evaluating the likely efficacy of various policy tools, and stress the importance of engaging landowners by building capacity and trust.     

Environmental Policies Can Buttress Conservation Norms

In an attempt to solve large-scale environmental problems, government agencies often resort to formal sanctioning systems: market-based incentives or command-and-control regulations, to promote cooperation. The purpose of this study was to investigate how the presence of these formal sanctioning systems impacts informal sanctioning systems for environmental protection. Study 1 used an experimental game to explore the influence of market-based and regulatory programs on informal sanctioning in a laboratory setting. Study 2 was a quasi-experimental field survey that compared informal sanctioning among Massachusetts residents living in towns with voluntary, mandatory, and pay-as-you-throw recycling programs. Results showed that in the presence of a formal sanctioning system, individuals felt guiltier for not engaging in the cooperative behavior and expressed more disapproval for non-cooperators. Combined, these results show that environmental policies can buttress conservation norms.     

A context-sensitive correlated random walk: a new simulation model for movement

Computational Movement Analysis focuses on the characterization of the trajectory of individuals across space and time. Various analytic techniques, including but not limited to random walks, Brownian motion models, and step selection functions have been used for modeling movement. These fall under the rubric of signal models which are divided into deterministic and stochastic models. The difficulty of applying these models to the movement of dynamic objects (e.g. animals, humans, vehicles) is that the spatiotemporal signal produced by their trajectories a complex composite that is influenced by the Geography through which they move (i.e. the network or the physiography of the terrain), their behavioral state (i.e. hungry, going to work, shopping, tourism, etc.), and their interactions with other individuals. This signal reflects multiple scales of behavior from the local choices to the global objectives that drive movement. In this research, we propose a stochastic simulation model that incorporates contextual factors (i.e. environmental conditions) that affect local choices along its movement trajectory. We show how actual global positioning systems observations can be used to parameterize movement and validate movement models and argue that incorporating context is essential in modeling movement.     

空心砖保温夹心开洞墙体的抗震试验研究

本文通过6片不同拉接筋间距的空心砖复合夹心开洞墙及2片空心砖实体开洞墙的低周期反复荷载试验。研究其破坏形态、抗震性能及变形能力。试验结果表明：空心砖夹心空洞墙的抗剪承载力要低于空心砖实体开洞墙，拉接筋对墙体的内外叶墙的协调变形及整体稳定都起着较好的作用。