Toward Decentralised Sanitary Sewage Collection Systems: A Multiobjective Approach for Cost-Effective and Resilient Designs

In recent years, the concept of a centralized drainage system that connect an entire city to one single treatment plant is increasingly being questioned in terms of the costs, reliability, and environmental impacts. This study introduces an optimization approach based on decentralization in order to develop a cost-effective and sustainable sewage collection system. For this purpose, a new algorithm based on the growing spanning tree algorithm is developed for decentralized layout generation and treatment plant allocation. The trade-off between construction and operation costs, resilience, and the degree of centralization is a multiobjective problem that consists of two subproblems: the layout of the networks and the hydraulic design. The innovative characteristics of the proposed framework are that layout and hydraulic designs are solved simultaneously, three objectives are optimized together, and the entire problem solving process is self-adaptive. The model is then applied to a real case study. The results show that finding an optimum degree of centralization could reduce not only the network’s costs by 17.3%, but could also increase its structural resilience significantly compared to fully centralized networks.

Herbivore Population Dynamics in Response to Plant Allocation Strategies

When herbivores feed, plants may respond by altering the quantity of edible biomass available to future feeders through mechanisms such as compensatory regrowth of edible structures or allocation of biomass to inedible reserves. Previous work showed that some forms of compensatory regrowth can drive insect outbreaks, but this work assumed regrowth occurred without any energetic cost to the plant. While this is a useful simplifying assumption for gaining preliminary insights, plants face an inherent trade-off between allocating energy to regrowth versus storage. Therefore, we cannot truly understand the role of compensatory regrowth in driving insect outbreaks without continuing on to more realistic scenarios. In this paper, we model the interaction between insect herbivores and plants that have a trade-off between compensatory regrowth and allocation to inedible reserves in response to herbivory. We found that the plant's allocation strategy, described in our model by parameters representing the strength of the overcompensatory response and the rates at which energy is stored and mobilized for growth, strongly affect whether herbivore outbreaks occur. Additional factors, such as the strength of food limitation and herbivore interference while feeding, influence the frequency of the outbreaks. Overall, we found a possible new role of overcompensation to promote herbivore fluctuations when it co-occurs with allocation to inedible reserves. We highlight the importance of considering trade-offs between tolerance mechanisms that plants use in response to herbivory by showing that new dynamics arise when different plant allocation strategies occur simultaneously.

Asynchronous nitrogen supply and demand produce nonlinear plant allocation responses to warming and elevated CO2

Terrestrial ecosystem responses to climate change are mediated by complex plant–soil feedbacks that are poorly understood, but often driven by the balance of nutrient supply and demand. We actively increased aboveground plant-surface temperature, belowground soil temperature, and atmospheric CO2 in a brackish marsh and found nonlinear and nonadditive feedbacks in plant responses. Changes in root-to-shoot allocation by sedges were nonlinear, with peak belowground allocation occurring at +1.7 °C in both years. Above 1.7 °C, allocation to root versus shoot production decreased with increasing warming such that there were no differences in root biomass between ambient and +5.1 °C plots in either year. Elevated CO2 altered this response when crossed with +5.1 °C, increasing root-to-shoot allocation due to increased plant nitrogen demand and, consequently, root production. We suggest these nonlinear responses to warming are caused by asynchrony between the thresholds that trigger increased plant nitrogen (N) demand versus increased N mineralization rates. The resulting shifts in biomass allocation between roots and shoots have important consequences for forecasting terrestrial ecosystem responses to climate change and understanding global trends.

Industrial proximity and vertical integration of multinational firms

Purpose With the rise of foreign direct investment and global value chain, firms organize their plant allocation across countries to take advantage of production cost reduction opportunities and market access. The purpose of this paper is to investigate the production-supply strategies of Korean firms over foreign and domestic affiliates, using industrial proximity between Korean parent firms and their affiliates. Design/methodology/approach In this paper first, using the Survey of Business Activities provided by Statistics Korea, the authors build a matching data set between a parent firm and each affiliate both in domestic and foreign countries. Second, the authors define their vertical relationship based on the input requirement coefficients of the Input-Output table (IO table). Furthermore, using the same IO table, the authors define the proximity for the pairs of the parent firm and the affiliates in domestic and foreign markets. Then, the authors test the relationship between the parent firm’s choice for foreign affiliate and their proximity index. Findings The main result shows that the stronger the industrial proximity between a final good producing firm and its input supplying affiliate is, the more likely the cross-border vertical integration is to be observed than the domestic vertical integration. Also, the authors find that the firms whose production structure accords the main result outperform and conduct more self-R&D and less R&D on trust than the other firms. Originality/value The finding is novel and original in a sense that the authors showed for the first time at firm-level microdata evidence that there is an optimal pattern of organizing supply chains within a multinational firm.