Kinetic Mechanism Research Articles

Flame stabilization and pollutant emissions of turbulent ammonia and blended ammonia flames: A review of the recent experimental and numerical advances

Compared to traditional hydrocarbon fuels, ammonia presents significant challenges as a fuel, including high ignition energy, low reactivity, slow flame propagation, and high NOx emissions, which hinder its use as a renewable fuel. Blending ammonia with fossil fuels like natural gas improves its combustion reactivity and helps mitigate CO2 emissions. However, there is still much to understand about the complex dynamics of ammonia and its blends with hydrocarbons. Key areas such as reaction kinetics mechanisms, ignition properties, flame propagation behaviors, and methods for controlling combustion performance under various conditions require further elucidation. This paper reviews recent advancements in experiments and numerical simulations aimed at developing stable, low-emission combustors for ammonia-fired power generation. Recent burner and flame configurations, including non-swirling jets, single-stage swirl burners, two-stage burners, and newly developed double-swirl burners are analyzed for their flame stability and pollutant emission potential when firing ammonia and ammonia blends. Chemical kinetic modeling of ammonia and its blends plays a crucial role in understanding combustion behavior and pollutant emissions, particularly for NOx. However, there are challenges in predicting NOx emissions accurately, with significant disparities among different models. High-fidelity numerical simulations using detailed and skeletal mechanisms, direct numerical simulation, and large eddy simulation, have helped uncover crucial operational conditions affecting combustion and pollutant emissions, such as combustor pressure, air dilution, wall cooling, fuel/air mixing, and fuel blending. Nonetheless, the accuracy of chemical kinetic models and their integration into turbulent flow simulations remain critical limitations for numerical simulations of ammonia combustion.

Phase separation behavior and CO2 absorption kinetic analysis of DETA/DEA/DMAC biphasic absorbent

Lower regeneration energy and superior cyclic capacity have enabled biphasic absorbents great potential in the area of flue gas CO2capture. The liquid film mass transfer coefficient(kL) is a vital parameter in the development of absorbents with efficient CO2 absorption mass transfer performance, while the phase separation behavior of biphasic solutions could be an essential factor for the absorption mass transfer and the stability of absorber. However, systemic kinetic research towards biphasic absorbents, especially the impact of phase separation behavior, is limited. In this study, a typical amide-based biphasic absorbent diethylenetriamine(DETA)/diethanolamine(DEA)/N, N-dimethylacetamide(DMAC) which has achieved great reduction in regeneration energy, was selected as the subject of kinetic investigation in a wetted wall column. The CO2 overall mass transfer coefficient(KG) of DETA/DEA/DMAC exceeded other biphasic solvents, blended amine solution, and 40% K2CO3 solution, with 3 times that of 40% K2CO3 solution. Moreover, various operational conditions including absorption temperature, gas flow rate, and water content of solution were taken into account to build a multiple-condition kinetic mechanism to offer guidance for biphasic absorbents. Furthermore, phase separation behavior was revealed as the main blame for the deterioration in the liquid film chemical mass transfer process of biphasic solvents in the CO2 absorption process, resulting in the kL of DETA/DEA/DMAC before phase separation decreased by 75.3% at the phase separation stage. Therefore, it is crucial to ensure that the CO2 loading of the solution entering absorber is lower than the phase separation point in applications. After phase separation, DETA/DEA/DMAC split into the organic and aqueous phases, the kL of the aqueous phase gradually exceeded that of the organic phase as CO2 loading increased for its higher chemical enhancement factor(E).

What drives the heterogeneous interdiffusion in the Li-Si interfacial region of Si anodes: the Li flux or the Si flux?

The electrochemical reaction in silicon (Si) electrode, accompanying with tremendous volume expansion, causes rapid capacity fade of Li-ion batteries. The Li-ion concentration gradient and structural distribution uniformity influence the inhomogeneous expansion, and the kinetic mechanism of lithiation and interfacial morphology evolvement remains debated. The present study focuses on the dynamics of Li-Si interdiffusion at Si/Li interfaces with various Si-facet orientations and phases using a machine-learning potential. We find that the Si flux from bulk Si to Li-Si interface regions controls the length of Li-Si interdiffusion region. The lithiation length in different Si/Li interface systems exhibits the order of amorphous-Si > crystalline-Si(110) > crystalline-Si(100) > crystalline-Si(111), which agrees with the experimental trend. Our atomic simulations further reveal that the key factor determining the Li-Si interdiffusion is the difference of on-site Si atomic energies between the bulk Si and the Li-Si interface regions. We propose that the large interdiffusion extent is due to a low thermodynamics barrier. Our findings provide insights for the development of high-performance Si anode materials.

A comprehensive kinetic study on low-GHG hydrogen production from microwave-driven methane pyrolysis

The present study focuses on the cogeneration of hydrogen (H2) and solid carbon from microwave-driven methane pyrolysis in a fluidized bed of carbon pellets. Numerical simulations using a coupled gas-solid chemistry approach reveal that introducing microwave thermal effects improves methane conversion rate, H2 selectivity, and carbon deposition rate. The chemical pathways analysis divulges that once the leading reaction for decomposing CH4 into H2, i.e., CH4+H ↔ CH3+H2, is completed, the C2H2 deposition mechanism onto the carbon pellets is the dominant pathway for the solid carbon production, indicating almost no carbon black (i.e., nanoparticles) formation. Carbon pellets provide abundant surface area for the conversion of C2H2 to H2, enhancing H2 selectivity in the resulting products. More importantly, the importance of more complex molecules, such as polycyclic aromatic hydrocarbons, greatly diminishes when using carbon pellets in the pyrolysis process, implying that smaller kinetic mechanisms are equally effective and desirable.

Modeling the Initiation Phase of the Catalytic Cycle in the Glycyl-Radical Enzyme Benzylsuccinate Synthase.

The reaction of benzylsuccinate synthase, the radical-based addition of toluene to a fumarate cosubstrate, is initiated by hydrogen transfer from a conserved cysteine to the nearby glycyl radical in the active center of the enzyme. In this study, we analyze this step by comprehensive computer modeling, predicting (i) the influence of bound substrates or products, (ii) the energy profiles of forward- and backward hydrogen-transfer reactions, (iii) their kinetic constants and potential mechanisms, (iv) enantiospecificity differences, and (v) kinetic isotope effects. Moreover, we support several of the computational predictions experimentally, providing evidence for the predicted H/D-exchange reactions into the product and at the glycyl radical site. Our data indicate that the hydrogen transfer reactions between the active site glycyl and cysteine are principally reversible, but their rates differ strongly depending on their stereochemical orientation, transfer of protium or deuterium, and the presence or absence of substrates or products in the active site. This is particularly evident for the isotope exchange of the remaining protium atom of the glycyl radical to deuterium, which appears dependent on substrate or product binding, explaining why the exchange is observed in some, but not all, glycyl-radical enzymes.

Oxygen Release in Ni‐Rich Layered Cathode for Lithium‐Ion Batteries: Mechanisms and Mitigating Strategies

AbstractLiNixCoyAlzO2 (NCA) and LiNixCoyMnzO2 (NCM) have become extensively utilized as cathodes in lithium‐ion batteries for consumer electronics, electric vehicles, and energy storage applications that necessitate consistent power output over prolonged periods and under varying environmental conditions. A crucial structural degradation issue leading to cycling‐induced deterioration, rapid loss of cell capacity/voltage, and the onset of undesirable thermal runaway events involves the decay of cathode materials enriched in nickel. This contribution offers a comprehensive evaluation of cutting‐edge strategies in engineering and material design to enhance the structural stability of cathode materials and reduce detrimental oxygen evolution reactions. It also provides the most recent discoveries regarding oxygen release phenomena and associated mechanisms contributing to structural breakdown in high‐nickel cathodes. The primary source of oxygen depletion and the ensuing structural deterioration caused are thoroughly examined. Additionally, the kinetic mechanisms responsible for oxygen loss are scrutinized, and measures to mitigate resulting electrochemical degradation are elaborated. This overview can guide researchers in the development of oxygen‐containing cathode materials in the future, where oxygen leakage is of lesser concern compared to other forms of deterioration.

A Comparison of Sigma Phase Formation in Solubilized Hyper Duplex Stainless Steel and Super Duplex Stainless Steel Filler Metals

This study focuses on the kinetic analysis of sigma phase formation in filler metal wires on Super Duplex Stainless Steel (SDSS) and Hyper Duplex Stainless Steel (HDSS). Precipitation data reveal that in the solubilized microstructure, sigma phase kinetics are more prominent in SDSS. This increased susceptibility is attributed to the greater number of nucleation sites, which is facilitated by the larger interface area/volume and the higher chromium content in the ferrite. The difference in interface area/volume is significantly more influential in determining kinetics than the composition difference, with nucleation sites playing a central role. The sigma phase transformation in both materials was modeled using the JMAK kinetic law. The JMAK plots exhibit a transition in kinetic mechanisms, evolving from discontinuous precipitation to diffusion-controlled growth. In SDSS, the JMAK values indicate “grain boundary nucleation after saturation,” followed by “thickening of large plates.” In contrast, HDSS values point to “grain edge nucleation after saturation,” followed by “thickening of large needles.” The higher kinetics in SDSS are characterized by a smaller nucleation activation energy of 56.4 kJ/mol, in contrast to HDSS's 490.0 kJ/mol. CALPHAD-based data support the JMAK results, aligning with the maximum kinetics temperature of SDSS (875 °C to 925 °C) and HDSS (900 °C to 925 °C). Therefore, the JMAK sigma phase kinetics effectively describe the experimental data and its dual kinetics behavior, even though CALPHAD-based TTT calculations often overestimate sigma formation.

Research on the Mechanism and Propagation Characteristics of Combustion and Explosion of Natural Gas/Ammonia/Hydrogen Mixed Gas Fuel.

The addition of ammonia and hydrogen into natural gas fuel is an effective method to reduce carbon emissions. This study aims to investigate the effect of adding ammonia and hydrogen on the mechanism of natural gas combustion and emission characteristics. Based on a self-developed mixed gas deflagrate experimental platform, the deflagrate characteristics, emission characteristics, and chemical reaction kinetics mechanism of mixed gas fuels under different composition ratios (natural gas 0-100%, hydrogen 10-85%, and ammonia 0-100%) were studied. The results indicate that the propagation of the deflagration shock wave can be categorized into an initial stage (L < 3 m) and a development stage (L > 3 m) based on the observed trend of shock wave intensity variation with distance. The intensity of the deflagration shock wave for the mixed gases increases monotonically as the hydrogen content ratio rises. In contrast, the impact of the ammonia content ratio on the shock wave intensity exhibits a distinct pattern that varies with changes in the equivalence ratio and hydrogen content ratio. In terms of carbon emissions per unit of heat value produced by the fuel, adding hydrogen to natural gas proves to be more effective at reducing carbon emissions than adding ammonia. When the ammonia content ratio is 50% and the hydrogen content ratio is 40%, the combustion performance of the mixed gas fuel is similar to that of natural gas, but its carbon emissions are lower than 30% of natural gas, making it a new type of mixed fuel with potential application value; the interaction between reflected pressure waves and flames is the main reason for the fluctuation of deflagrate shock wave pressure; ammonia lowers the temperature of the reaction system by reducing the concentration of OH radicals.

Quantitative analysis of flame luminance and explosion pressure in liquefied petroleum gas explosion and inerting: Grey relation analysis and kinetic mechanisms

To evaluate the explosion intensity by flame luminance, a series of explosive and inerting tests on LPG in a 20-L spherical chamber were taken. A quantitative assessment of flame luminance was performed using the grey level theory, and the association between explosion pressure parameters and flame luminance parameters was examined through grey relation analysis. Furthermore, the intrinsic relationship and mechanism between these two variables were explored based on heat-chain reaction kinetics and energy conversion. The findings revealed a synchronous trend between flame luminance and explosion pressure during the LPG explosion process. Notably, a significant positive correlation between explosion pressure and flame luminance was established. Flame luminance emerged as a valuable indicator of explosion intensity, akin to explosion pressure. The grey relational grade between flame luminance and explosion pressure remained remarkably consistent under varying volume fractions of both LPG and CO2. The addition of CO2 exerted a comprehensive influence on factors such as reaction rate, heat release rate, and the concentration of key radicals. This collective impact resulted in reduced explosion pressure and flame luminance. This study offers a theoretical foundation for assessing explosion risks and enhancing energy safety management within the domains of chemical, petroleum, and natural gas industries.

Flame propagation dynamic characteristics and mechanisms of methane–syngas–air mixtures in a semi-enclosed duct

The composition of syngas is complex, often leading to the generation of methane, which impacts the explosive characteristics of syngas. The analysis focused on the kinetic characteristics and mechanisms of flame propagation in methane–syngas–air mixtures in a semi-enclosed duct under various equivalence ratios (φ = 0.8–1.4) and methane volume ratios (R = 0 %–70 %) under ambient temperature and pressure. The results indicated that the flame speed and pressure propagation of methane–syngas–air mixtures could be divided into three stages: a stable stage, an oscillatory increase stage, and an oscillatory decrease stage. In the stable stage, as the methane proportion in the premixed gas increased, the oscillations in the flame and pressure decreased. Turbulent flow of the mixed gas was observed due to restrictions and obstructions within the duct. This led to an increase in the peak pressure and flame speed of the mixed gas, thereby resulting in an oscillatory increase stage. Distorted tulip-shaped flames were also formed in the semi-enclosed duct. The flame of the pure syngas/air mixture exhibited a hemispherical shape and a finger-shaped and slope-shaped propagation structure. When 30 %, 50 %, or 70 % of the methane in the methane–syngas–air mixtures was added, the flame exhibited a propagation structure characterized by a hemispherical shape, finger shape, slope shape, flat shape, tulip shape, or distorted tulip shape. The flame front evolved with time from a linear growth stage to a nonlinear growth stage. The flame front speed of the methane–syngas–air mixtures was closely related to the pressure and flame structure. With the increase in the methane proportion in the methane–syngas–air mixtures, the concentration of key radicals and the rate of OH* generation and consumption gradually decreased. Sensitivity analysis revealed that with increasing methane proportion in the premixed gas, the most important reaction dominating OH* consumption changed from R15 (H + O2(+M) <=> HO2(+M)) to R138 (CH4 + OH <=> CH3 + H2O) and then to R112 (2CH3(+M) <=> C2H6(+M)); moreover, the most important reaction dominating OH* generation remained R1 (H + O2 <=> O + OH). The addition of methane interrupted the hydrogen–oxygen chain reaction of the methane–syngas–air explosion process.

Novel aerogel of aminated MXene composite orange peel biomass for ultra-high capacity of V(V) adsorption

Efficient and selective adsorption of V(V), pentavalent vanadium, from strategic polymetallic shale leaching solutions is crucial for resource utilization. However, the lack of a high-capacity adsorbent poses a significant challenge. Herein, we have successfully developed a novel composite adsorbent material by cross-linking orange peel biomass with aminated MXene, referred to as OPM. The incorporation of aminated MXene enhanced the availability of reactive groups within the material. The unique aerogel structure avoids the accumulation of MXene, thus improving the exposure of active sites. Furthermore, the positively charged surface of OPM enabled efficient adsorption of pentavalent vanadium ions. Experimental results showed that the adsorption of V(V) fitted well with the Langmuir adsorption isotherm model, and its adsorption rate was controlled by the pseudo-second-order kinetic mechanism. Remarkably, OPM exhibited a remarkable maximum adsorption capacity of 748.42 mg/g at pH=4. Even in the presence of interfering anions and cations, OPM maintains a high adsorption capacity for V(V).In the simulated wastewater adsorption experiment, the removal rate of V by the adsorbent exceeded 80 % After five cycles of adsorption, the material retains an adsorption capacity of more than 78 %. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy revealed that the adsorption mechanism of OPM on V(V) is attributed to the fact that OPM is protonated under acidic conditions and has strong electrostatic interactions with pentavalent vanadium anion, in which abundant hydroxyl and carboxyl groups can undergo ion-exchange reactions with vanadium anion. Meanwhile, the amino group reduces V(V) to V(IV) and forms a complex with the oxygen/nitrogen functional group. This study provides theoretical understanding and practical application for the synergistic adsorption of V(V) on aerogels prepared from MXene composite orange peel biomass.

Na-doped Li4SiO4 as an efficient sorbent for low-concentration CO2 capture at high temperature: Superior adsorption and rapid kinetics mechanism

Lithium silicate (Li4SiO4) sorbent has garnered attention in CO2 capture due to its high theoretical adsorption capacity and fast kinetics. However, its adsorption capacity and kinetics were hindered by low CO2 concentration. Improving adsorption performance of Li4SiO4 at low CO2 concentration has become the key to industrial application. In this work, high-activity Na-doped Li4SiO4 with controllable active substance Li3NaSiO4 was achieved. The influences of raw materials ratios on the CO2 adsorption performance were systematically investigated. When RLi/Si=4.05:1 and RNa/Si=0.15:1, the sample exhibited the highest adsorption capacity of 32.28 wt% with an equilibrium time of 29 min, and a superior stable capacity of 31.09 wt% in 15 cycles. Importantly, the double exponential fitting revealed that LiNaCO3 accelerated the ion diffusion rate and real-time adsorption processes showed Li3NaSiO4 expedited surface chemical reaction rate. Based on these, a novel Na2CO3 eutectic doping mechanism was proposed. The active substance Li3NaSiO4, generated through Na doping, along with its product formed from the reaction with CO2, molten LiNaCO3, acted synergistically to improve adsorption performance by accelerating surface chemical reaction rate and ion diffusion rate. Compared with other doped Li4SiO4, the sorbent prepared in this work demonstrated competitive adsorption performance, providing theoretical and technical support for the large-scale production of high-activity Li4SiO4.

The valorization of Prunus mahaleb shell through acid modification for the sorption of Pb2+ removal from aqueous solution

AbstractThis study aimed to investigate the biosorption performance of acid-modified waste Prunus mahaleb (PMA) shells in the removal of Pb2+ ions from aqueous solutions. Changes in the morphological properties and functional components of PMA biosorbent were characterized using SEM–EDX, FT-IR, BET, and PZC analyses. The effect of various parameters such as initial Pb2+ concentration, pH, PMA dosage, contact time, and temperature on biosorption was investigated using a batch biosorption procedure. The maximum biosorption capacity, determined using the Langmuir isotherm, was calculated to be 119 mg g−1. It was found that the biosorption kinetic mechanism followed pseudo-second-order kinetics and intraparticle diffusion model. According to the determined thermodynamic parameters, the biosorption mechanism was found to be endothermic (ΔH° &gt; 0), spontaneous (ΔS° &gt; 0), and entropy-increasing (ΔG° &lt; 0). The outcomes of the experiment were evaluated in comparison to other sorbents that have been previously commonly used in the literature. It was demonstrated that PMA could be a promising, environmentally friendly, cost-effective, and sustainable potential biosorbent for the removal of Pb2+ ions.

Exploring microfine magnesite based on thermal decomposition and sintering kinetics: A new direction in the one-step preparation of high-density sintered magnesia

The thermal decomposition and sintering kinetics of microfine magnesite were investigated to inaugurate a new One-step process for preparing high-density sintered magnesia. The optimal parameters for the discharging particle size of magnesite through ball milling were determined using an orthogonal experiment and Three-Way Measures ANOVA. The model for the thermal decomposition process of microfine magnesite was established through TGA-DSC and nonlinear regression analysis. Meanwhile, by describing the sintering process of microfine magnesite in detail through microstructure and CTE, the kinetic mechanisms of grain growth at different sintering stages were obtained. The results revealed that increasing the ratio of ball to powder can quickly obtain microfine magnesite which the bulk density reaches 3.45 g·cm−3 after One-step sintering. The thermal decomposition process required an activation energy of only 124.98 kJ·mol−1, which is much lower than existing technology and followed the Two-dimensional phase boundary reaction mechanism R2. Additionally, the densification process was dominated alternatively by grain boundary diffusion and volume diffusion. This paper provided a detailed theoretical basis and leads a new direction in the One-step preparation of high-density sintered magnesia.

Direct numerical simulation of shock wave/boundary layer interaction controlled by steady microjet in a compression ramp

Shock wave/boundary layer interaction in a 24° turning angle of the compression ramp at Mach number 2.9 controlled by steady microjet is investigated using direct numerical simulation. Three different jet spacings which are termed as sparse, moderate and dense are considered, and the induced vortex system and shock structures are compared. A moderate jet spacing configuration is found to generate counter-rotating vortex pairs that transport high-momentum fluid towards the vicinity of wall and strengthen the boundary layer to resist separation, reducing the separation region. The dense jet spacing configuration creates a larger momentum deficit region, reducing the friction downstream of the corner. Analysis of pressure and pressure gradient reveals that dense jet spacing configuration reduces the intensity of separation shock. The impact of varying jet spacings on the turbulent kinetic energy transport mechanism is also investigated by decomposing the budget terms in the transport equation. Furthermore, the spectral characteristics of the separation region are studied using power spectral density and dynamic mode decomposition methods, revealing that moderate jet spacing configuration suppresses low-frequency fluctuations in the separation region.

Evaporation rate and kinetic mechanism of noble antimony under vacuum

Herein, a novel mathematical and statistical method is applied to the kinetic study of vacuum gasification of noble-antimony alloys. The evaporation rates of pure and noble antimony in a unit time at 823–1023 K and 5–600 Pa are determined using a vacuum differential gravimetric furnace, and their respective evaporation mechanisms under vacuum are analyzed in detail in conjunction with their triple point. Results show that the actual evaporation rates of pure and noble antimony are consistent with those obtained using a nonlinear logistic model (ω=A2+(A1-A2)/[1+P/P0a); the goodness of fit (R2) is > 0.9965 at all temperatures. The critical pressure values of pure and noble antimony at 823–1023 K are obtained, which are linearly dependent on the temperature. According to the theoretical and actual maximum evaporation rates of pure and noble antimony, the evaporation coefficient is corrected and the relation between the actual evaporation rate and temperature (lgω=AT+B) is further obtained, which can be used to calculate and predict the evaporation rates of noble antimony at different temperatures. By studying the evaporation rate of pure and noble antimony, this study provides the kinetic parameters for vacuum gasification of noble antimony and simultaneously enriches the kinetic database, which develops and improves the theory and practice of vacuum gasification of noble-metal alloys.

Persulfide Transfer to SufE Activates the Half-Sites Reactivity of the E. coli Cysteine Desulfurase SufS.

The Escherichia coli cysteine desulfurase SufS (EcSufS) is a dimeric, PLP-dependent enzyme responsible for sulfur mobilization in the SUF Fe-S cluster bioassembly pathway. The enzyme uses cysteine as a sulfur source and generates alanine and a covalent persulfide located on an active site of cysteine. Optimal in vitro activity of EcSufS requires the presence of the transpersulfurase protein, EcSufE, and a strong reductant. Here, presteady-state and single-turnover kinetics are used to investigate the mechanism of EcSufS activation by EcSufE. In the absence of EcSufE, EcSufS exhibits a presteady-state burst of product production with an amplitude of ∼0.4 active site equivalents, consistent with a half-sites reactivity. KinTek Explorer was used to isolate the first turnover of alanine formation and fit the data with a simplified kinetic mechanism with steps for alanine formation (k3) and a net rate constant for the downstream steps (k5). Using this treatment, microscopic rate constants of 2.3 ± 0.5 s-1 and 0.10 ± 0.01 s-1 were determined for k3 and k5, respectively. The inclusion of EcSufE in the reaction results in a similar rate constant for k3 but induces a 10-fold enhancement of k5 to 1.1 ± 0.2 s-1, such that both steps are partially rate-determining. The most likely downstream step where EcSufE could exert influence on EcSufS activity is the removal of the persulfide intermediate. Importantly, this step appears to serve as a limiting feature in the half-sites activity such that activating persulfide transfer allows for rapid shifting between active sites. Single-turnover assays show that the presence of EcSufE slightly slowed the rates of alanine-forming steps, suggesting it does not activate steps in the desulfurase half reaction.

Microscopic structure of electromagnetic whistler wave damping by kinetic mechanisms in hot magnetized Vlasov plasmas

Electromagnetic transverse perturbations propagating parallel to the external magnetic field in a warm electron plasma, specifically the warm electron whistler-mode waves, are simulated in Maxwellian as well as κ distributed (with energetic tail) electrons. The Vlasov-Maxwell phase-space continuum simulations are applied to the stable and unstable (i.e. isotropic and anisotropic) VDFs. The variation of real frequency from both numerical solution of dispersion relation and simulations show limited sensitivity to electron temperature in low wave-number regime as compared to high wave number regime, however the opposite holds for the imaginary frequency or the decay rate. The analytically predicted reduction in the decay rate of the whistler-mode with increasing electron temperature is recovered by the Vlasov-Maxwell simulations. The phase-space portraits of the these cases show that after the linear damping phase of the evolution, the particles are trapped in the wave magnetic field leading to the wave amplitudes oscillating about a mean value which follow the theoretical analysis. Palmadesso and Schmidt (1971) Physics of Fluids 14, 1411.

Kinetics of programmed and spontaneous ribosome sliding along the mRNA.

The ribosome can slide along mRNA without establishing codon-anticodon interactions. This movement can be regulated (programmed) by the elements encoded in the mRNA, as observed in bypassing of non-coding gap in gene 60 of bacteriophage T4, or occur spontaneously, such as during traversal by the 70S ribosome of the 3'UTRs or upon re-initiation on bacterial polycistronic genes. In this study, we investigate the kinetic mechanism underlying the programmed and spontaneous ribosome sliding. We show that the translation rate of gene 60 mRNA decreases as the ribosome approaches the take-off site, especially when the KKYK regulatory sequence in the nascent peptide reaches the constriction site in the ribosome exit tunnel. However, efficiency of bypassing increases when the ribosome traverses the gap quickly. With the non-coding gap exceeding the natural 50 nt, the processivity of sliding remains high up to 56 nt, but drops sharply beyond that due to the loss of mRNA elements support. Sliding efficiency is temperature-dependent; while temperature regulates the number of ribosomes initiating programmed bypassing, traversing the long gaps becomes increasingly unfavorable at lower temperatures. This data offers novel insights into the kinetic determinants of programmed and spontaneous ribosome sliding along the mRNA.

A novel copper ion enhanced electrochemical DNA biosensor for the determination of epinephrine

A novel electrochemical biosensor was developed for the detection of epinephrine (EP) by immobilizing double-strand DNA (dsDNA) bound with copper ions on a gold electrode (Cu2+/dsDNA/MCH/AuE). The electrochemical behavior of EP at Cu2+/dsDNA/MCH/AuE was examined, and the results demonstrated a significant enhancement in the electrocatalytic oxidation peak current of EP due to the formation of a stable G-Cu(II)-G sandwich structure between Cu2+ and guanine at the modified electrode. The modification process of the electrode was characterized by scanning electron microscopy, infrared spectroscopy, electrochemical impedance spectroscopy, and differential pulse voltammetry. A study on the effect of pH in phosphate buffer solution on the electrochemical oxidation of EP indicated that the catalytic oxidation process was pH-dependent. A plot of catalytic current versus EP concentration exhibited a dual-linear relationship within two ranges: 1.0–12.5 μM and 12.5–1000.0 μM, with correlation coefficients of 0.995 and 0.997, respectively. The limit of detection was determined to be 47 nM (S/N = 3). According to the calculated Hill coefficient (0.99), it can be concluded that the electrocatalytic process followed the Michaelis-Menten kinetic mechanism. The maximum catalytic current Im was 25 μA, while the apparent Michaelis-Menten constant Km was 1.425 mM. These findings indicated excellent electrocatalytic activity of the modified electrode towards oxidation of EP. The developed biosensor successfully detected EP in spiked mouse serum as well as epinephrine hydrochloride injection with high selectivity, sensitivity, stability, and accuracy.