Specific Decay Rate Research Articles

Constructing heterojunction on N-doped porous carbon nanofibers for Li-S batteries: Effect of built-in electric field on efficient catalytic transformation kinetics

In this study, the CoP-Co2P heterojunction nanoparticles embedded in N-doping porous carbon nanofibers (CoP-Co2P/NPCNFs) are designed and prepared. The highly conductive grid of NPCNFs can physically confining lithium polysulfide (LiPS) and provide facilitated channels for Li+ transport. Furthermore, due to the spontaneous built-in electric field (BIEF) based on at the formed heterogeneous interfaces of CoP-Co2P, the heterojunction can significantly catalyze bi-directional conversion of LiPS and chemically adsorb LiPS which confirmed by the DFT calculations, suppressing the “shuttle effect” of LiPS. Thus, the Li-S batteries with the CoP-Co2P/NPCNFs modified separators exhibit a high initial specific capacity of 1322.86 mAh g−1 at 1 mA cm−2 and stable 695 cycles with a low decay rate (0.069 %). More importantly, the assembled pouch cell also can run with ultra-low specific capacity decay rate. Additionally, the pouch battery can also be applied to the operation of fans, temperature and humidity meters, mobile phone charging, etc.

Modelling of high-rate activated sludge process: Assessment of model parameters by sensitivity and uncertainty analyses

The objective of this study is to develop a mechanistic model to predict the long-term dynamic performance of High-Rate Activated Sludge (HRAS) process, including the removal of carbon (COD), nitrogen (N), and phosphorus (P). The model was formulated with inspiration from Activated Sludge Models No. 1 and 3 (ASM1 and ASM3) to incorporate essential mechanisms, such as adsorption and storage substrate, specific to HRAS systems. A stepwise protocol was followed for calibration with dynamic data from a pilot-scale HRAS plant. Sensitivity analysis identified influential model parameters, including maximum specific growth rate (μ), growth yield (YH), storage yield (YSTO), storage rate (kSTO), decay rate (b), and half saturation of the readily biodegradable substrate for growth (KS1). The calibrated model achieved prediction efficiencies above the normalized Mean Absolute Error (MAE) of 70 % for mixed liquor suspended solids (MLSS), total chemical oxygen demand (TCOD), soluble COD (SCOD), particulate COD (XCOD), total nitrogen (TN), ammonia nitrogen (SNH), total phosphorus (TP), soluble TP (STP), and particulate TP (XTP). Uncertainty analysis revealed that SCOD was underestimated. Based on the dynamic profiles of uncertainty bands and observed data, there is potential for improving the estimation of dynamic behavior in STP. The observed discrepancies may be attributed to variations in wastewater characteristics during the monitoring period, particularly concerning the phosphorus (P) fractions of the readily biodegradable substrate (SS) and soluble inerts (SI), which were not considered as dynamically changing parameters in the model.

Design of Delay-based Proportional Integral Controllers (δ-PI) for Second-order LTI Systems

This note focuses on the design of a delay-based proportional integral (PI) control scheme, proposed as an alternative to the classical PI controller. By adopting a geometric approach, we establish tuning rules to achieve closed-loop stability, ensure a specific decay rate, and assess its fragility. Specifically, through the appropriate design of the delay parameter, the proposed controller facilitates improvement in settling time and reduction of overshoot, while maintaining control efforts lower than its classical counterpart. We present several numerical examples to illustrate the effectiveness of the proposed scheme.

Boosting lithium polysulfide conversion via TiO2-supported niobium catalyst for lithium sulfur battery

Lithium sulfur (Li–S) batteries demonstrate enormous promise as a high-performance high-capacity energy storage solution but are severely limited by a low cycle life which stems from rapid capacity decay due to the low conductivity of lithium polysulfides and the poor kinetics of the lithium sulfur reduction reaction, which combined lead to the loss of active cathodic material. In this work, titanium oxide (TiO2) nanostructures are used as a host for a niobium catalyst which accelerates the conversion of polysulfides. Cells containing the TiO2-supported niobium catalyst demonstrated a very high level of stability, with a specific capacity decay rate of 0.045 % per cycle over 350 cycles. Li–S cells using this cathode host material also demonstrated high initial specific capacities, with initial capacities as high as 961 mAh g−1 at 0.2 C and 629 mAh g−1 at 3.0 C.

Multiple heterostructures of Co and derivatives decorated high N-doped biochar host accelerating polysulfide redox kinetics for lithium sulfur batteries

Simultaneously improving the anchoring of polysulfides and the interconversion of polysulfides is an urgent problem to be solved to improve the redox kinetics of lithium-sulfur batteries. In this work, a multiple heterostructures of Co and derivatives decorated high N-doped biochar are fabricated. With the special synergistic effect, the anchoring of polysulfide compounds is enhanced through chemical adsorption (Co, O, N), and the excellent catalytic ability of Co and derivatives particles can speed up the electrochemical reaction process. After the injection of sulfur, The Co-N@PC@S electrode achieves a stable reversible capacity of 416.02 mAh g−1 after 1000 cycles at 0.5 C. And it also gets a reversible capacity of 334.10 mAh g−1 after 500 cycles at 5.0 C, with a specific capacity decay rate for a single turn of only 0.043%. When the sulfur loading reaches 3.2 mg cm−1, the reversible specific capacity can still reach 600.87 mAh g−1 at 0.2 C after 400 cycles and maintain a reversible specific capacity of 429.50 mAh g−1 after 400 cycles 0.5 C. This work provides a fresh idea to facilitate the process of commercialization of lithium-sulfur batteries in the industry.

A Hybrid Ultrasonic Membrane Anaerobic System (UMAS) Development for Palm Oil Mill Effluent (POME) Treatment

The high chemical oxygen demand (COD) and biochemical oxygen demand (BOD) levels in palm oil mill effluent (POME) wastewater make it an environmental contaminant. Moreover, conventional POME wastewater treatment approaches pose economic and environmental risks. The present study employed an ultrasonic membrane anaerobic system (UMAS) to treat POME. Resultantly, six steady states were procured when a kinetic assessment involving 11,800–21,700 mg·L−1 of mixed liquor suspended solids (MLSS) and 9800–16,800 mg·L−1 of mixed liquor volatile suspended solids (MLVSS) was conducted. The POME treatment kinetics were explained with kinetic equations derived by Monod, Contois and Chen and Hashimoto for organic at loading rates within the 1–11 kg·COD·m−3·d−1 range. The UMAS proposed successfully removed 96.6–98.4% COD with a 7.5 day hydraulic retention time. The Y value was 0.67 g·VSS/g·COD, while the specific micro-organism decay rate, b was 0.24 day−1. Methane (CH4) gas production ranged from 0.24 to 0.59 litres per gram of COD daily. Once the initial steady state was achieved, the incoming COD concentrations increased to 88,100 mg·L−1. The three kinetic models recorded a minimum calculated solids retention time of 12.1 days with maximum substrate utilization rate, K values ranging from 0.340 to 0.527 COD·g−1·VSS·d−1 and maximum specific growth rate, µmax from 0.248 to 0.474 d−1. Furthermore, the solids retention time (SRT) was reduced from 500 to 12.1 days, resulting in a 98.4% COD level reduction to 1400 mg·L−1.

Efficiency assessment of underground biomethanation with hydrogen and carbon dioxide in depleted gas reservoirs: A biogeochemical simulation

Underground biomethanation, which converts hydrogen and carbon dioxide to methane with the catalysis of methanogens in geological formations, has great potential for carbon dioxide utilization and sequestration, renewable natural gas production, and large-scale energy storage. However, the efficient conversion of hydrogen and carbon dioxide in a complex reservoir environment has not been explored. To address this issue, a novel biogeochemical model is developed for underground biomethanation that considers reservoir environment factors (e.g. pH, temperature, and salinity) and integrated into PHREEQC software. The biogeochemical model is validated with a laboratory experiment and utilized to investigate the effects of reservoir parameters and injection parameters on biomethanation efficiency in depleted gas reservoirs. Results show that the biomethanation efficiency is 94.2% after 360 days in both sandstone and carbonate reservoirs. Underground biomethanation can be completed in 30 days if initial biomass and optimum specific growth rate increase and decay rate decreases. Additionally, the optimal ratio of injected hydrogen and carbon dioxide for biomethanation is greater than 4:1 and increases with total pressure if it is above 70 atm. To improve the biomethanation efficiency, this study suggests utilizing geothermal energy and pre-injecting highly active methanogens cultured on the ground before mixed gas injection.

Landfill Codisposal of On-Site Vegetation and Coal Combustion Residuals: Implications for Gas Management

Historically, ash from coal combustion has been disposed of in ponds that were not designed with engineered containment systems. As a result of regulatory changes, it is estimated that coal combustion residuals (CCRs) from hundreds of unlined ponds will have to be excavated and disposed of in new lined landfills or the existing CCR ponds will have to been closed in-place with an engineered final cover system. The excavated or in-place CCR may contain vegetative matter that has the potential to decompose to CH4 and CO2. The objective of this study was to demonstrate a framework to assess the need for a gas collection system to accommodate the disposal of a mixture of CCR and vegetation in a lined landfill. Methane generation rates and yields for vegetative matter mixed with CCR were measured in biochemical methane potential and specific methane activity tests at 15, 20, and 37 °C. The data were then used to parameterize a methane generation model to estimate the gas flux at the landfill surface for a series of hypothetical disposal scenarios. Results showed that the specific decay rate constant (k) ranged from 0.00037 to 0.00872 yr–1, while the methane yield (L0) ranged from 84 to 120 mL CH4/dry g. Temperature was the most important determinant of the decomposition behavior. Simulations of gas flux for several disposal scenarios showed that the modeled flux from the decomposition of vegetation was below the CH4 and CO2 transmission rates reported for a geomembrane liner final cover system, suggesting that an active gas collection will not be necessary under the modeled disposal conditions.

Evaluation of Biological Pretreatment of Wormwood Rod Reies with White Rot Fungi for Preparation of Porous Carbon.

In this work, the wormwood rod residues are pretreated with white rot fungi as the precursor to preparing porous carbon following a simple carbonization and activation process (denoted herein as FWRA sample). The FWRA sample possesses abundant hierarchical pores structure with high specific surface area (1165.7 m2 g-1) and large pore volume (1.02 cm3 g-1). As an electrode for supercapacitors, the FWRA sample offers a high specific capacitance of 443.2 F g-1 at 0.5 A g-1 and superb rate ability holding a specific capacitance of 270 F g-1 at 100 A g-1 in 6 M KOH electrolyte. The corresponding symmetrical capacitor has a superb cyclic stability with a low specific capacitance decay rate of 0.4% after 20,000 cycles at 5 A g-1 in 1 M Na2SO4 electrolyte. Moreover, measurements revealed that when used as adsorbent, the FWRA sample is ideal for removing methyl orange (MO) from water, exhibiting a superior adsorption ability of 260.8 mg g-1. Therefore, this study is expected to provide a simple and environmentally friendly technique for the generation of value-added and functional porous carbon materials from Chinese medicinal herbal residues, thus offering promising candidates for broad application areas.

Effect of CeO2-x-CNT/S cathode on the electrochemical performance of lithium-sulfur batteries

Despite extensive research into cerium oxide as a cathode for lithium-sulfur batteries, there are still problems with low specific capacity and high decay rate. This paper used a simple gas reduction method to prepare CeO2-x nanoparticles with more oxygen vacancies. It has been demonstrated experimentally that the presence of oxygen defects increases the electrochemical reaction rate. Using CeO2-x-CNT/S as cathode for lithium-sulfur battery not only improves the conductivity of cathode, but also restricts the movement of polysulfide. The CeO2-x-CNT/S cathode exhibits good electrochemical properties. The first discharge specific capacity of CeO2-x-CNT/S cathode is 1556.8 mAh g -1 at 0.1C. The initial discharge specific capacity is 1233.9 mAh g -1 at 0.5C, and has a small capacity decay rate after 600 cycles. It provides a new answer to the problems in lithium-sulfur batteries.

The Multiple States of Environmental DNA and What Is Known about Their Persistence in Aquatic Environments.

Increased use of environmental DNA (eDNA) analysis for indirect species detection has spurred the need to understand eDNA persistence in the environment. Understanding the persistence of eDNA is complex because it exists in a mixture of different states (e.g., dissolved, particle adsorbed, intracellular, and intraorganellar), and each state is expected to have a specific decay rate that depends on environmental parameters. Thus, improving knowledge about eDNA conversion rates between states and the reactions that degrade eDNA in different states is needed. Here, we focus on eukaryotic extraorganismal eDNA, outline how water chemistry and suspended mineral particles likely affect conversion among each eDNA state, and indicate how environmental parameters affect persistence of states in the water column. On the basis of deducing these controlling parameters, we synthesized the eDNA literature to assess whether we could already derive a general understanding of eDNA states persisting in the environment. However, we found that these parameters are often not being measured or reported when measured, and in many cases very few experimental data exist from which to draw conclusions. Therefore, further study of how environmental parameters affect eDNA state conversion and eDNA decay in aquatic environments is needed. We recommend analytic controls that can be used during the processing of water to assess potential losses of different eDNA states if all were present in a water sample, and we outline future experimental work that would help determine the dominant eDNA states in water.

Instant preheating in a scale invariant two measures theory

The instant preheating mechanism in the framework of a scale invariant two measures theory is studied. We introduce this mechanism into a non oscillating inflationary model as another possible solution to the reheating of the universe in this theory. In this framework, we consider that the model includes two scalar matter fields, the first a dilaton field, that transforms under scale transformations and it will be considered also as the field that drives inflation and the second, a scalar field which will interact with the inflaton through an effective potential. By assuming this interaction term, we obtain a scenario of instant radiation or decay of particles according to the domain the effective mass of the field that interacts with the inflaton. Also, we consider a scale invariant Yukawa interaction and then after performing the transition to the physical Einstein frame we obtain an expression for the decay rate from our scalar field going into two fermions. Besides, from specific decay rates, different constraints and bounds for the coupling parameters associated with our model are found.

One-dimensional wave equation with set-valued boundary damping: well-posedness, asymptotic stability, and decay rates

This paper is concerned with the analysis of a one dimensional wave equation ztt − zxx = 0 on [0, 1] with a Dirichlet condition at x = 0 and a damping acting at x = 1 which takes the form (zt(t, 1), −zx(t, 1)) ∈ Σ for every t ≥ 0, where Σ is a given subset of ℝ2. The study is performed within an Lp functional framework, p ∈ [1, +∞]. We aim at determining conditions on Σ ensuring existence and uniqueness of solutions of that wave equation as well as strong stability and uniform global asymptotic stability of its solutions. In the latter case, we also study the decay rates of the solutions and their optimality. We first establish a one-to-one correspondence between the solutions of that wave equation and the iterated sequences of a discrete-time dynamical system in terms of which we investigate the above mentioned issues. This enables us to provide a simple necessary and sufficient condition on Σ ensuring existence and uniqueness of solutions of the wave equation as well as an efficient strategy for determining optimal decay rates when Σ verifies a generalized sector condition. As an application, we solve two conjectures stated in the literature, the first one seeking a specific optimal decay rate and the second one associated with a saturation type of damping. In case the boundary damping is subject to perturbations, we derive sharp results regarding asymptotic perturbation rejection and input-to-state issues.

Effects of low pH conditions on decay of methanogenic biomass

Acidic failure is relatively common in anaerobic digesters that receive readily biodegradable food wastes at high loading. Under low pH conditions, the activity of methanogenic biomass decreases resulting in complete failure of the digestion process. In this experimental study, we demonstrated that one of the causes for the digester failure under low pH conditions is due to accelerated decay of methanogenic biomass. When enriched acetate degrading methanogens were exposed to a low pH environment (pH = 5.1 with phosphoric acid) in a batch experiment without external substrate, the specific decay rate was observed to increase as much as 10 times of that at pH 7.0. The specific decay rate for formate degrader was also found to increase under low pH conditions whilst the fermentative microorganisms in the cultures appeared to be tolerant to low pH conditions. A Propidium Mono-Azide-quantitative Polymerase Chain Reaction (PMA-qPCR) analysis revealed that the archaeal biomass dominated by methanogens dropped by 71–79% from the initial concentration after 6 days of the acidic batch experiment whilst the bacterial biomass dominating acidogens decreased by only 25%. The decrease in the number of living cells in the batch experiments at different pH was monitored with time to determine a correlation between decay rate and incubation pH.

Output Regulation of Linearized Column Froth Flotation Process

This article explores the output regulation problem of the linearized column froth flotation process consisting of collection and froth regions that are modeled by a set of linear coupled heterodirectional hyperbolic partial differential equations (PDEs) and ordinary differential equations (ODEs) with time delay. Collection and froth regions are combined through PDE boundary conditions and time-delay models the interconnections between PDE boundary and ODEs representing well-stirred reactor dynamics. The linearization of the original nonlinear system is carried out to obtain a linearized PDE-ODE system. To complete the output regulation of resulting PDE-ODE systems, one challenge is the design of an observer and stabilization controller. We proposed to obtain the stabilization feedback gains and the observer injection gains by solving operator Riccati equations; in particular, these gains can also assign a specific exponential decay rate. Another challenge is the solvability of regulator equations that arise during the regulator design for the linearized PDE-ODE systems. In particular, we consider the tracking control of more general reference signals, including step, ramp, harmonic, and arbitrary polynomial signals, and novelty lies in the necessity to investigate the solvability of the corresponding regulator equations. In this article, the development of state feedback and error feedback regulators are designed and the regulator performance is demonstrated by simulation studies.

MOFs-derived porous Mo2C–C nano-octahedrons enable high-performance lithium–sulfur batteries

The shuttle effect causing by the dissolution of lithium polysulfides (LiPSs) and sluggish redox reaction kinetics during the charge/discharge processes significantly reduce the cycle life and sulfur utilization in lithium-sulfur (Li–S) batteries. Herein, Mo2C–C nano-octahedrons (Mo2C–C NOs) with Mo2C nanoparticles embedded in a three-dimensional porous carbon matrix have been prepared via a metal-organic frameworks (MOFs) assisted strategy, and used as the sulfur host for Li–S batteries. The Mo2C–C NOs@S cathode demonstrates a high initial specific capacity of 1396 and 1050 mAh g−1 at 0.1 C and 1 C, respectively, with an ultra-low average specific capacity decay rate of 0.0457% per cycle within 600 cycles at 1 C. Moreover, Mo2C–C NOs@S cathode with high areal sulfur loading of 4.2 mgS cm−2 can deliver a high initial discharge specific capacity of 807 mAh g−1, and a capacity of 623 mAh g−1 after 100 cycles at 0.5 C. The existence of Mo2C nanoparticles can not only immobilize LiPSs via the formation of Mo–S bond, but also electrocatalytically accelerate the redox kinetics towards LiPSs conversion. Meanwhile, the interconnected porous carbon matrices contributes to effective sulfur/electrolyte infiltration, fast electron/Li+ ion transportation and sufficient buffer for volume change.

New insights into the kinetics of bacterial growth and decay in pig manure-wheat straw aerobic composting based on an optimized PMA-qPCR method.

SummaryAerobic composting is a bacteria‐driven process to degrade and recycle wastes. This study quantified the kinetics of bacterial growth and decay during pig manure–wheat straw composting, which may provide insights into microbial reaction mechanisms and composting operations. First, a propidium monoazide–quantitative polymerase chain reaction (PMA–qPCR) method was developed to quantify the viable bacteria concentration of composting samples. The optimal PMA concentration and light exposure time were 100 μM and 8 min respectively. Subsequently, the concentrations of total and decayed bacteria were quantified. Viable and decayed bacteria coexisted during the entire composting period (experiments A and B), and the proportion of viable bacteria finally fell to only 35.1%. At the beginning, bacteria grew logarithmically and decayed rapidly. Later, the bacterial growth in experiment A remained stable, while that of experiment B was stable at first and then decomposed. The duration of the stable stage was positively related to the soluble sugar content of composting materials. The logarithmic growth and rapid decay of bacteria followed Monod equations with a specific growth (0.0317 ± 0.0033 h−1) and decay rate (0.0019 ± 0.0000 h−1). The findings better identified the bacterial growth stages and might enable better prediction of composting temperatures and the degree of maturation.

Hierarchical VS2 Nano-Flowers as Sulfur Host for Lithium Sulfur Battery Cathodes

Lithium sulfur batteries (LSB) are considered to be one of the most promising energy storage technologies due to their high energy density, low cost and environmental friendliness. However, there are still many defects such as the shuttle effect of polysulfide, the non-conductivity of sulfur and the large volume change of sulfur cathode leading to cyclic decay and instability. To overcome these challenges, in this study, we synthesized the VS2 nano-flowers (NFs) through the hydrothermal method, and then took them as the sulfur host. The VS2 NFs possess unique hierarchical structure and excellent electrical conductivity, which can promote Li+ and charge transmission, thus improving the reaction kinetics. Besides, the VS2 has excellent chemical interaction with polysulfides, which can efficiently suppress the migration of polysulfides and inhibit the shuttle effect. It possessed better cyclic stability compared with the pure sulfur counterparts. Impressively, the lithium sulfur batteries (LSBs) with VS2/S (1:5) cathodes whose specific capacity decay rate over 200 cycles at 0.2 C was ∼0.16% per cycle. It also greatly improved the sulfur utilization and the rate capability of LSBs. The above results demonstrate that the VS2 can enhance the cycling performance and has potential application in LSBs.

N-doped carbon-coated hollow carbon nanofibers with interspersed TiO2 for integrated separator of Li-S batteries

Li-ion batteries have held a dominant position in the energy storage area for decades. However, due to the limitation of its chemistry, the energy density of Li-ion batteries is limited to ∼300 W h kg−1. In recent years, more attention has been paid to the Li-S batteries that are environmentally friendly, cost-effective and high energy density (theoretical value of cathode: ∼2600 W h kg−1). In this study, carbonized polydopamine (C-PDA)-coated hollow carbon nanofibers (CNFs) with TiO2 nanoparticles interspersed in the void space between the CNF skeleton and carbon coating layer were subtly designed. The C-PDA/TiO2/CNF composite (CTC) was integrated with the commercial separator as a polysulfide filter to achieve high-performance Li-S batteries. It is reveals that the CTC coating layer could effectively filter and reactivate the dissolved polysulfides to achieve a stabilized sulfur-based cathode. The Li-S battery assembled by this integrated separator and the regular cathode (sulfur/Ketjen black) with 72.7 wt% of sulfur achieved a high specific capacity and low decay rate (632.5 mAh g−1 at the first cycle and 0.06% per cycle) at 2.0C for 500 cycles. These good results indicate that the C-PDA/TiO2/CNF-modified separator could be a promising separator candidate for high performance Li-S batteries.

Liquid state bioconversion continuous bioreactor of sewage sludge treatment: Determination and evaluation of mixed fungi growth kinetics

Abstract Liquid state bioconversion (LSB), a bioremediation and biodewatering process was applied for sewage sludge treatment in this study. The LSB process is a non-hazardous, safer and environmentally friendlier method for ultimate sludge management and disposal compared to the other available technologies. The system presented in this study was developed by using mixed fungi of Aspergillus niger and Penicillium corylophilum to treat sewage sludge in a LSB bioreactor. This research was conducted in order to study the LSB process on continuous system in terms of kinetic coefficients determination. For the continuous LSB process, a mathematical model was developed from the basic principles of material balance based on Monod equation. By investigating the kinetics of substrate utilisation and biomass growth, the kinetic coefficients of growth yield coefficient (Y), specific microorganism decay rate (Kd), half saturation constant (Ks) and maximum specific growth rate (μmax) were found to be 0.79 g VSS g COD−1, 0.012 day−1, 1.78 g COD L−1 and 0.357 day−1, respectively.