Changyong Zhang

This book encompasses various approaches to electrochemical water treatment, emphasizing a well-structured framework within the nexus of electrochemistry, water, and energy. It addresses the urgent challenges of water scarcity and pollution and offers practical insights and operational guidance on removing pollutants and preserving water resources through water purification. Applications and real-life case studies support the innovative nature of electrochemical processes as a sustainable and efficient alternative. The user-friendly approach makes this book accessible to a broad audience, being a specialist seeking advanced techniques or a concerned citizen. Features Covers comprehensively the most recent and advanced electrochemical water treatment techniques. Presents practical operational guidelines and insights. Includes real-world examples and case studies. Focuses on environmental impacts and sustainability. Addresses innovative approaches in technology, theoretical computational analysis, and future development guidance for electrochemical water treatment. This book is for professionals, students, and researchers in water and environmental sciences interested in water treatment, management, and resource recovery. It is also a great resource for public and environmental health experts and readers who work in related disciplines and readers interested in water management, treatment, and the health of the environment.

Selective separation of ions in aqueous solutions is important for water purification and resource recovery. In the last decade, capacitive deionization (CDI) has been employed not only for desalination but also for recovering resources and selectively separating particular ions in solutions containing multiple types of ions. Due to its customizable electrode materials and interfaces as well as flexible operation, CDI has shown great advantages in modulating the ion electrosorption process, thus achieving considerable selective adsorption of target pollutants. In this chapter, we review the development of CDI, mainly summarize the mechanism of selective separation of ions from mixed salt solutions using various electrodes (capacitive and pseudocapacitive materials) and membranes (ion-exchange membranes and ion-exchange resin coatings), and discuss the effects of different factors (e.g., electrode pore characteristics, various physical and chemical properties of ions, and operating parameters) and different chemical modification methods on the performance of CDI. This chapter also provides an outlook on the future development of CDI and analyzes the challenges of its practical application in selective separation, with a view to providing a reference for future researchers to solve the problems of selective CDI system development and application.

With the aim of looking into a comparatively more efficient solution approach for the unique shortest path routing problem, an alternative problem formulation to a counterpart is first introduced. The model is mathematically equivalent to the counterpart concerning both the feasibility and optimality of the problem. By exploring the constraint structures and model sizes of the two formulations, the former is identified to be a more appropriate one for a decomposition algorithm to solve the problem. An enhanced Benders decomposition method, embedded with redundancy generation strategy, is then proposed, based on the study of problem properties of network flow problems.

Gold has been traditionally well recognized as a safe heaven for financial markets. Lately, Bitcoin has been gradually considered as a popular alternative. Since the outbreak of COVID-19 in early 2020, it has become even more necessary and critical to examine the diversification capability of them to hedge financial risks associated with an unexpected crisis comparable to the pandemic. This paper hence employs the wavelet analysis, complemented by the multivariate DCC-GARCH approach, to measure the coherence of the gold and Bitcoin prices with six representative stock market indices, three for developed economies and three for emerging economies, all of which are heavily affected by the pandemic. To have a more balanced and comprehensive analysis, two-year data are used, spanning from 12th April 2019 to 15th April 2021, which covers approximately one year before and one year after the announcement of the COVID-19 pandemic. The results suggest that the returns of both gold and Bitcoin are generally not strongly correlated with the market returns of all six indices, particularly for short-term investment horizons. That is, investors in all six indices can benefit through gold, as well as Bitcoin, in terms of hedging. Meanwhile, compared with Bitcoin, gold shows to be less correlated with the indices, particularly for long-term investment horizons. The findings hence suggest that gold and Bitcoin offer diversification benefits to investors in the market indices during a crisis such as the COVID-19 pandemic, especially for short-term investment horizons. The study also reminds policymakers thinking beyond the pandemic about the future of the earth, including air pollution and health, for sustainable development of the whole world.

To measure the diversification capability of Bitcoin, this study employs wavelet analysis to investigate the coherence of Bitcoin price with the equity markets of both the emerging and developed economies, considering the COVID-19 pandemic and the recent Russia-Ukraine war. The results based on the data from January 9, 2014 to May 31, 2022 reveal that compared with gold, Bitcoin consistently provides diversification opportunities with all six representative market indices examined, specifically under the normal market condition. In particular, for short-term horizons, Bitcoin shows favorably low correlation with each index for all years, whereas exception is observed for gold. In addition, diversification between Bitcoin and gold is demonstrated as well, mainly for short-term investments. However, the diversification benefit is conditional for both Bitcoin and gold under the recent pandemic and war crises. The findings remind investors and portfolio managers planning to incorporate Bitcoin into their portfolios as a diversification tool to be aware of the global geopolitical conditions and other uncertainty in considering their investment tools and durations.

This paper studies the weak Euler approximation for solutions to stochastic differential equations (SDEs) driven by point and martingale measures, with Hölder-continuous coefficients. The equation under consideration includes a nondegenerate main part whose jump intensity measure is absolutely continuous with respect to the Lévy measure of a spherically symmetric stable process. It encompasses a broad range of stochastic processes including the nondegenerate diffusions and SDEs driven by Lévy processes. To investigate the dependence of the convergence rate on the regularity of the coefficients and driving processes, the regularity of a solution to the associated backward Kolmogorov equation is considered. In particular, for the first time the Hölder norm of the subordinated part of the corresponding generator is rigorously estimated.