Variational principle for unsteady heat conduction equation

The semi-inverse method is used to establish a variational principle for an unsteady heat conduction equation

Ultrafast and Sensitive Self-Powered Photodetector Featuring Self-Limited Depletion Region and Fully Depleted Channel with van der Waals Contacts

Self-powered photodetectors with great potential for implanted medical diagnosis and smart communications have been severely hindered by the difficulty of simultaneously achieving high sensitivity and fast response speed. Here, we report an ultrafast and highly sensitive self-powered photodetector based on two-dimensional (2D) InSe, which is achieved by applying a device architecture design and generating ideal Schottky or ohmic contacts on 2D layered semiconductors, which are difficult to realize in the conventional semiconductors owing to their surface Fermi-level pinning. The as-fabricated InSe photodiode features a maximal lateral self-limited depletion region and a vertical fully depleted channel. It exhibits a high detectivity of 1.26 × 1013 Jones and an ultrafast response speed of ∼200 ns, which breaks the response speed limit of reported self-powered photodetectors based on 2D semiconductors. The high sensitivity is achieved by an ultralow dark current noise generated from the robust van der Waals (vdW) Schottky junction and a high photoresponsivity due to the formation of a maximal lateral self-limited depletion region. The ultrafast response time is dominated by the fast carrier drift driven by a strong built-in electric field in the vertical fully depleted channel. This device architecture can help us to design high-performance photodetectors utilizing vdW layered semiconductors

Exact Solutions for Nonlinear Wave Equations by the Exp-Function Method

This paper elucidates the main advantages of the exp-function method in finding exact solutions of nonlinear wave equations. By the aid of some mathematical software, the solution process becomes extremely simple and accessible

Process schemes for future energy-positive water resource recovery facilities

There are numerous successful studies on optimizing the performance of conventional activated sludge (CAS)-based wastewater treatment plants. However, recent studies have shown that a more significant improvement of the plant performance is achievable through integration of established technologies in novel process schemes. High-rate activated sludge system, chemically enhanced primary treatment, partial nitritation-anammox, partial nitrification-denitrification over nitrite and anaerobic digestion are integrated in two process schemes to determine to which extent energy savings and energy production can be achieved with these new process layouts compared to a CAS-based process scheme. The results presented in this paper show that there is potential for achieving future energy-positive water resource recovery facilities through novel integration of mature technologies for municipal wastewater treatment

Elucidating the competition between heterotrophic denitrification and DNRA using the resource-ratio theory

Heterotrophic denitrification and dissimilatory nitrate reduction to ammonium (DNRA) are two microbial processes competing for two shared resources, namely, nitrate and organic carbon (COD). Their competition has great implications for nitrogen loss, conservation, and greenhouse gas emissions. Nevertheless, a comprehensive and mechanistic understanding of the governing factors for this competition is still lacking. We applied the resource-ratio theory to study this competition and validated the theory with experimental data from continuous cultures reported in the literature. Based on this theory, we revealed that influent COD/N ratio alone was not sufficient to predict the competition outcome as the boundary values for different competition outcomes changed substantially with influent resource concentrations. The stoichiometry of the two processes was determinative for the boundaries, whereas the affinity for the shared resources (KS), maximum specific growth rate (μmax) of the two species, and the dilution rate had significant impacts as well but mainly at low influent resource concentrations (e.g., <100 μM nitrate). The presented approach allows for a more comprehensive understanding of the parameters controlling microbial competition. The computational comparison between continuous and batch cultures could explain seemingly conflicting experimental results as to the impact of the COD/N ratio. The results also include testable hypotheses and tools for understanding and managing the fate of nitrate in ecosystems, which could also be applied more widely to other species competing for two shared resources

Challenges and strategies of formulating low‐temperature electrolytes in lithium‐ion batteries

Abstract Lithium‐ion batteries (LIBs) have monopolized energy storage markets in modern society. The reliable operation of LIBs at cold condition (<0°C), nevertheless, is inevitably hampered by the sluggish kinetics and parasite reactions, which falls behind the increasing demands for portable electronics and electric vehicles. The electrolyte controls both Li+ transport and interfacial reaction, dictating the low‐temperature performance substantially. Therefore, the rational formulation of electrolytes is significant for realizing superior low‐temperature performance and broadening application niches of LIBs. Herein, we first discuss the kinetic limitations of low‐temperature LIBs, highlighting the importance of electrolyte structure and interfacial chemistry. Then, the advancements for formulating subzero‐temperature electrolyte are summarized with in‐depth discussions about electrolyte formulation, solvation structure, interfacial chemistry, and low‐temperature behaviors. Moreover, some opportunities for lithium metal batteries and the corresponding low‐temperature electrolyte are covered. Finally, the major challenges and future perspectives are outlined for low‐temperature LIBs