This paper investigates the passive beamforming and information transfer (PBIT) technique for multiuser multiple-input multiple-output (Mu-MIMO) systems with the aid of reconfigurable intelligent ...surfaces (RISs), where the RISs enhance the primary communication via passive beamforming (P-BF) and at the same time deliver additional information by the on-off reflecting modulation (in which the RIS information is carried by the on/off state of each reflecting element). For the P-BF design, we propose to maximize the achievable user sum rate of the RIS-aided Mu-MIMO channel and formulate the problem as a two-step stochastic program. A sample average approximation (SAA) based iterative algorithm is developed for the efficient P-BF design of the considered scheme. To strike a balance between complexity and performance, we further propose a simplified P-BF algorithm by approximating the stochastic program as a deterministic alternating optimization problem. For the receiver design, the signal detection at the receiver is a bilinear estimation problem since the RIS information is multiplicatively modulated onto the reflected signals of the reflecting elements. To solve this bilinear estimation problem, we develop a turbo message passing (TMP) algorithm in which the factor graph associated with the problem is divided into two modules: one for the estimation of the user signals and the other for the estimation of the on-off state of each RIS element. The two modules are executed iteratively to yield a near-optimal low-complexity solution. Furthermore, we extend the design of the Mu-MIMO PBIT scheme from single-RIS to multi-RIS, by leveraging the similarity between the single-RIS and multi-RIS system models. Extensive simulation results are provided to demonstrate the advantages of our P-BF and receiver designs.
In this letter, we consider the problem of channel estimation for large intelligent metasurface (LIM) assisted massive multiple-input multiple-output (MIMO) systems. The main challenge of this ...problem is that the LIM integrated with a large number of low-cost metamaterial antennas can only passively reflect the incident signals by certain phase shifts, and does not have any signal processing capability. To deal with this, we introduce a general framework for the estimation of the transmitter-LIM and LIM-receiver cascaded channel, and propose a two-stage algorithm that includes a sparse matrix factorization stage and a matrix completion stage. Simulation results illustrate that the proposed method can achieve accurate channel estimation for LIM-assisted massive MIMO systems.
Aiming for increased nickel and lower cobalt content in layered transition metal oxide cathodes (NCM) is a feasible strategy for achieving increased energy density and cost competitiveness in ...commercial lithium‐ion batteries. However, the practical long‐term cycling of NCM cathodes suffers from severe capacity degradation due to irreversible interface phase transformation and unavoidable crack formation. Herein, an in situ modification strategy is used to form a uniform and conformal Li1.8Sc0.8Ti1.2(PO4)3 (LSTP) protective layer by interconnecting the single‐crystal‐layered LiNi0.6Co0.1Mn0.3O2 (SC‐NCM) particles. LSTP surface modification helps to construct a robust cathode‐electrolyte interphase thin film between the cathode and the electrolyte, which can prevent SC‐NCM corrosion by electrolyte, and the stability of the mechanics can improve the intergranular cracks caused by long cycles under harsh conditions. Moreover, the LSTP conductive modification layer facilitates the lithium‐ion transport among cathode particles, effectively enhancing the rate capability. Impressively, the LSTP modified SC‐NCM exhibits a high reversible capacity of 144.3 mAh g−1 at the high discharge rate of 5 C and maintains a capacity retention of 90.27% even at the ultrahigh charge voltage of 4.6 V operation after 500 cycles. Moreover, in a pouch‐type full battery, the graphite/LSTP modified SC‐NCM maintains a capacity retention of 89.6% after 1700 cycles.
An innovative surface modification is developed to improve the long‐term cyclability and rate capability of a single‐crystalline Ni‐rich cathode. The surface modification strategy improves the mechanical stability and lithium‐ion transport, which creates a strong CEI interface to prevent electrolyte corrosion and improve the intergranular cracks caused by long cycles under harsh conditions.
Electrochemical impedance spectroscopy (EIS) is a powerful nondestructive technique that can act as a beneficial addition to the current techniques for studying microbial fuel cells (MFCs). Its ...application in MFC research should be further explored in the analysis of the internal resistance of MFCs, electrode materials, catalyst coatings on electrodes, biofilm development and electrochemical reactions on the anodes and the cathodes of MFCs.
•Nutrients are key contaminants to be removed in bioelectrochemical systems (BES).•Nitrogen is removed by biological and bioelectrochemical reactions.•Nitrogen is recovered through ammonia migration ...and volatilization.•Phosphorus is removed and recovered in precipitates due to high electrolyte pH.•Effective and efficient nutrients removal/recovery will make BES more competitive.
Nutrient removal and recovery has received less attention during the development of bioelectrochemical systems (BES) for energy efficient wastewater treatment, but it is a critical issue for sustainable wastewater treatment. Both nitrogen and phosphorus can be removed and/or recovered in a BES through involving biological processes such as nitrification and bioelectrochemical denitrification, the NH4+/NH3 couple affected by the electrolyte pH, or precipitating phosphorus compounds in the high-pH zone adjacent a cathode electrode. This paper has reviewed the nutrients removal and recovery in various BES including microbial fuel cells and microbial electrolysis cells, discussed the influence factors and potential problems, and identified the key challenges for nitrogen and phosphorus removal/recovery in a BES. It expects to give an informative overview of the current development, and to encourage more thinking and investigation towards further development of efficient processes for nutrient removal and recovery in a BES.
The feasibility of using agricultural waste of rice husk to prepare highly reactive rice husk ash for sustainable cement-based material was explored through five sets of procedures: optimization of ...rice husk ash with an improved combustion technique, pozzolanic activity evaluation of the prepared rice husk ash, strength development of mortar with rice husk ash, sulfate attack experiment to investigate the potential durability, and environmental evaluation of rice husk ash utilization. From the results, the optimum rice husk ash using improved combustion technique had high pozzolanic activity, it presented the highest lime-ash compressive strength, a violent pozzolanic reaction heat flow as well as rapid Ca(OH)2 consumption ability among different mineral additives. Compressive strengths of mortars have been enhanced with the increase of rice husk ash contents. The results of sulfate attack indicated that paste with 15% rice husk ash improved sulfate resistance by stabilization of C–S–H and the refinement of pore structure. Sustainability analysis including embodied carbon dioxide emission and energy consumption confirmed the environmental friendliness of rice husk ash utilization. This study verified the feasibility of highly reactive rice husk ash from agricultural waste and the potential utilization of it as sustainable mineral admixture in cement-based materials.
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•An improved combustion technique for rice husk ash was proposed using the self-designed combustion system.•High pozzolanic activity of rice husk ash was verified through a series of methodology.•The feasibility of rice husk ash as a mineral admixture was explored, and the mechanism of it to improve sulfate resistance was uncovered.•Sustainability analysis including embodied carbon dioxide emission and energy consumption confirmed the environmental friendliness of rice husk ash utilization.
There is an increasing interest to integrate phototrophic microorganisms into microbial fuel cells (MFCs) to assist electricity generation. In general, this integration can be accomplished in three ...ways: (1) phototrophic microorganisms function as or provide a substrate for supplying electrons; (2) photoheterotrophic microorganisms catalyze the anode reaction; and (3) photoautotrophic microorganisms provide oxygen as an electron acceptor to the cathode reaction. Direct use of phototrophic microorganisms for electricity production in MFCs faces significant challenges, because of the complex composition of microbial cells and their resistance to hydrolysis, and low conversion efficiency to electric energy by MFCs. Proper pretreatment using chemical or biological methods may improve degradability of microbial cells. Some purple nonsulfur bacteria exhibit strong electrochemical catalysis of organic compounds in the anode of an MFC, and the effect of illumination on the catalytic performance needs further investigation. Electricity generation via syntrophic relationship between photosynthetic microorganisms (providing organic compounds) and heterotrophic bacteria (oxidizing organics) in the anode is generally low due to low concentration of the electron donors and adverse effect of oxygen as a result photosynthesis on anode activities. It is promising to apply photosynthetic microorganisms in the cathode with multiple functions of oxygen supply, nutrient removal and biomass production. To address some of the challenges, two paradigms are proposed to encourage further investigation and development of effective processes with strong synergy between phototrophic microorganisms and MFCs.
Cadmium contamination in soil, water and food has become a global problem since last century's industrial and agricultural revolution. It is a highly toxic metal with serious consequences on human ...and animal health. Different natural and anthropogenic sources are responsible for Cd release in the soil which ultimately leads to the food chain. Cd persists in soil for long durations due to its minimal microbial or chemical loss. There are various physical, chemical or biological techniques which are helpful to minimize Cd risk in food chain. Among them, in-situ immobilization with organic, inorganic or clay amendments is a cost-effective and an environment friendly strategy to remediate Cd polluted sites. Lime, biochar, organic wastes, phosphorus fertilizers, sepiolite, zeolite, hydroxyapatite and bentonite are commonly used amendments for amelioration of Cd contaminated soils. These amendments reduce Cd uptake and enhance immobilization by adsorption, complexation, and precipitation processes. This review is aimed to provide a comprehensive note on Cd toxicity in humans and environment, its immobilization by different agents through variety of processes, and comparison of technologies for Cd removal from contaminated sites.
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•This manuscript explores Cd phytoavailability and its immobilizing agents.•Inorganic, organic and mineral amendments can immobilize Cd in polluted sites.•A number of publications have confirmed Cd toxicity and stabilization.•Variation in moisture regime influences Cd phytoavailability and immobilization.
Forward osmosis (FO) has emerged as a potentially energy-efficient membrane treatment technology to yield high-quality reusable water from various wastewater/saline water sources. A key challenge ...remained to be solved for FO is reverse solute flux (RSF), which can cause issues like reduced concentration gradient and loss of draw solutes. Yet no universal parameters have been developed to compare RSF control performance among various studies, making it difficult to position us in this “battle” against RSF. In this paper, we have conducted a concise review of existing RSF reduction approaches, including operational strategies (e.g., pressure-, electrolysis-, and ultrasound-assisted osmosis) and advanced membrane development (e.g., new membrane fabrication and existing membrane modification). We have also analyzed the literature data to reveal the current status of RSF reduction. A new parameter, mitigation ratio (MR), was proposed and used together with specific RSF (SRSF) to evaluate RSF reduction performance. Potential research directions have been discussed to help with future RSF control. This review intends to shed more light on how to effectively tackle solute leakage towards a more cost-effective and environmental-friendly FO treatment process.
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•Reverse solute flux is a critical challenge to address for a healthy FO process.•Operational strategies can be employed to reduce reverse permeation of draw solutes.•Both membrane surface modification and new membranes can reduce RSF.•The RSF reduction can be quantified by using specific RSF and mitigation ratio.•Selection of appropriate draw solutes will also result in decreased RSF.
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