Slow Stage Research Articles

Study on the thermal release characteristics and the correlation transformation mechanism of microscopic active groups of oxidized coal combustion in a deep mined-out area

With the normalization of deep mining, the risk of residual coal spontaneous combustion (CSC) in deeply mined areas has gradually increased. To investigate the thermal characteristics and microgroup transformation mechanisms during the secondary oxidation of deep-well oxidized coal, a deep-well oxidation process was simulated in a synchronous thermal analyzer, and the thermal parameters of the oxidized coal were tested. The correlated transformation pathways of microscopic active groups was studied by electron paramagnetic resonance (EPR) and in situ diffuse reflectance (in situ FTIR) experiments during the reoxidation of oxidized coal. The results showed that with increasing deep-well ambient temperature and oxidation temperature, the characteristic temperature of coal gradually decreased, exothermic heat release gradually increased, and active aliphatic structures and -OH, -CHO and other active functional groups gradually accumulated and became distributed more uniformly. When the thermal conditions and oxidation temperature were very high (> 160 °C), the active free radicals in the oxidized coal were rapidly consumed, resulting in a gradual decrease in the characteristic temperature and heat release during the secondary oxidation process, while the contents of peroxy and carboxyl groups continued to increase. In the slow oxidation stage of oxidized coal, methyl groups were mainly transformed with hydroxyl and peroxide groups (r > 0.96), and the associated oxidative consumption of -CHO and -COOH mainly occurred in the rapid oxidation stage (r > 0.99). Geminal diols and peroxy groups are important intermediates in the coal–oxygen composite reaction process. With an increase in the deep-well temperature and initial oxidation temperature, the reoxidation tendency and heat release capacity of residual coal in the goaf gradually increased, and the risk of CSC intensified. The research results provide a theoretical reference for the prevention and control of coal fires in deep mines and play an important role in guiding environmental management and gas emissions reduction measures in mining areas.

Generation features and kinetics of gas products in bio-tar catalytic cracking by char for biomass gasification

This research focused on the reaction features and kinetics of tar catalytic conversion by char based on the generation and evolution of gas products. To probe the roles of heat and catalysis in tar conversion, a micro fluidized bed reaction analyzer (MFBRA) was used to assess tar thermal cracking (TC) and catalytic cracking (CC) by char at 1073, 1123, 1173, and 1223 K. The tar cracking behavior of the individual gas components (H2, CO, CO2, and CH4), generation rates, and reaction kinetics were thoroughly investigated. The results show that TC and CC included a fast (Stage-1) and slow (Stage-2) conversion stage, in which Stage-1 contributed more than 80% of the total conversion. Compared to TC, tar CC required a longer reaction time but obtained higher conversions to individual gas components and the total gas products. The final conversion ratios (XCC/TC) of H2, CO, CO2, and CH4 were kept above 1 at the tested temperature. The char catalytic action was very remarkable, especially at low temperatures. In tar CC, the generation rate of individual gas components slowly declined after quickly reaching the peak, forming a relatively stable zone. The volume reaction model (VRM) well described the tar conversion behavior with and without char. Compared to TC, char lowered the activation energy (Ea) of gas generation. For individual gas components (H2, CO, CO2, CH4) and the total gas products, the corresponding reduction degree of Ea was 25.56%, 24.18%, 22.14%, 4.75%, and 21.71%, respectively, further displaying the promoting impact of char. The evaluated generation features and kinetics of individual components in the gas products will benefit the in-situ tar removal in the biomass gasification process.

Two-photon absorption in La0.05Gd0.95VO4 crystal at 523 nm under irradiation with picosecond pulses

Two-photon absorption (TPA) in La0.05Gd0.95VO4 crystal under irradiation with picosecond laser pulses with the duration of 25 ps at the wavelength of 523.5 nm has been investigated. The TPA coefficient was measured to be 0.074 cm/GW. We found that the two-photon inter-band excitation led to the creation of optical centers, which were characterized by a wide absorption band in the visible spectral region. The decay of the induced absorption is characterized by two temporal stages. The first rapid stage has the decay time of about 70 μs. However, the slow stage is characterized by a decay time ranging from 270 to 520 ms depending on the initial concentration of the induced optical centers. Induced absorption should be taken into account when developing vanadate lasers with intra-cavity second harmonic converters.

Insight into the behavior regulation of drug transfer of nimodipine loaded PLGA microspheres by emulsion evaporation method

In the process of preparing microspheres by evaporation of emulsion, drug transfer in the system makes it difficult to control the drug loading and encapsulation efficiency of the product. In this study, Nimodipine loaded microspheres were prepared using poly(lactic-co-glycolic acid) (PLGA) as the matrix materials. The transfer process of drug molecules and solvent molecules in the preparation process were observed by online imaging. Combined with weighing experiments and molecular simulation, three stages of dichloromethane (DCM) diffusion in oil phase were proposed. At 20 °C,15 % and 46 % of DCM content were taken as the critical point, and between the content was slow volatilization stage, which dominated the occurrence of drug reflux and crystallization. The oil phase diffusion and emulsion mass transfer equations of DCM were proposed to judge the influence of each single factor on drug molecular transfer. Low temperature, oil-water ratio and stirring speed could slow down the volatilization of DCM and increase the drug loading and encapsulation efficiency. Low stirring speed could increase the drug loading while avoiding crystallization and reflux, which was the best control factor.

Experimental investigation on dynamic compressive properties of SHCC after freeze-thaw cycles

In this paper, the split Hopkinson pressure bar (SHPB) test was used to investigate the variation of dynamic compressive properties of SHCC with various freeze-thaw (FT) cycles and strain rates. The full-field strain distribution and cracking characteristics of FT-damaged SHCC after the SHPB test were quantitatively and characterized by the high-speed digital image correlation (DIC) technique. The internal damage was analyzed using an X-ray CT imaging technique and SEM (Scanning electron microscope). Results show that dynamic compressive strength, energy absorption ability and dynamic increase factor (DIF) increase as the increase of strain rate, and these increase trends are weakened by the FT damage. The DIF model is established considering the number of FT cycles and strain rates. Variation of crack width in SHCC obtained through the high-speed DIC technique can be divided into three stages: linear increase stage, plateau stage and slow increase stage.

Mechanism of elastic energy storage of honey bee abdominal muscles under stress relaxation

Energy storage of passive muscles plays an important part in frequent activities of honey bee abdomens due to the muscle distribution and open circulatory system. However, the elastic energy and mechanical properties of structure in passive muscles remain unclear. In this article, stress relaxation tests on passive muscles from the terga of the honey bee abdomens were performed under different concentrations of blebbistatin and motion parameters. In stress relaxation, the load drop with the rapid and slow stages depending on stretching velocity and stretching length reflects the features of myosin-titin series structure and cross-bridge-actin cyclic connections in muscles. Then a model with 2 parallel modules based on the 2 feature structures in muscles was thus developed. The model described the stress relaxation and stretching of passive muscles from honey bee abdomen well for a good fitting in stress relaxation and verification in loading process. In addition, the stiffness change of cross-bridge under different concentrations of blebbistatin is obtained from the model. We derived the elastic deformation of cross-bridge and the partial derivatives of energy expressions on motion parameters from this model, which accorded the experimental results. This model reveals the mechanism of passive muscles from honey bee abdomens suggesting that the temporary energy storage of cross-bridge in terga muscles under abdomen bending provides potential energy for springback during the periodic abdomen bending of honey bee or other arthropod insects. The finding also provides an experimental and theoretical basis for the novel microstructure and material design of bionic muscle.

Bending-damaged fracture criterion and numerical implementation of limestone beam under three-point bending test

To study the characteristics of tensile cracking by rock-bending damage, the bending stress–strain curves and the cumulative ringing counts were obtained by a three-point bending test and acoustic emission (AE) monitoring of limestone beams. Based on the Lemaitre strain equivalent principle and the continuous damage theory, the bending damage variable D was defined by the AE cumulative ringing counts, and the bending crack damage evolution equation was established according to the Weibull distribution of the rock element strength. To realize the numerical test of the bending deformation, the damage variable D was used as the intermediate variable, and the specific process of damage bending stress transformation and the realization of the tensile crack criterion were secondary developed by FISH language in FLAC3D. According to the results, the central part of rock beam deforms downward under the action of bending stress, and both ends tilt up. Therefore, the bending failure begins with the tensile crack at the bottom of the rock beam and gradually extends to the compression zone. The maximum damage value is about 0.402 before the peak stress. The compressive stress in the x direction increases from the neutral layer to the top of the rock beam, and the tensile stress in the x direction increases from the neutral layer to the bottom of the rock beam. The maximum tensile stress is distributed in the center of the bottom of the specimen, where the bending effect is obvious. The stress–time curve was divided into the (Ⅰ) compaction stage, (Ⅱ) expansion stage, and (Ⅲ) penetration stage, accordingly, and the evolution of damage equation was divided into three stages: initial damage stage, slow damage stage, and accelerated damage stage. The curves of the experimental result, theoretical model prediction result, and numerical simulation result were in good agreement with each other, which indicates that the numerical simulation based on the criterion of rock damaged fracture can better reflect the bending process of rock beams under three-point bending stress.

Effects of Different Delivery Methods on The Functional Status of The Postpartum Pelvic Floor and Guidance on Pelvic Floor Rehabilitation Training

Objective: This study is to investigate the effects of normal and cesarean delivery on the pelvic floor function of pregnant women in the early postpartum period. Methods: 277 pregnant women who delivered in our hospital were divided into two groups: normal delivery and cesarean delivery, and pelvic floor muscle function testing was performed at 42 d after delivery to compare the functional status of the pelvic floor in the two groups. Results: The overall score of the cesarean delivery group was higher than that of the normal delivery group; among the indicators, the incidence of abnormal pelvic floor muscles in the pre and post resting stages was higher in the cesarean delivery group than in the normal delivery group, and the incidence of abnormalities in the fast and slow muscle stages and the endurance test stage was lower than that in the normal delivery group, and the differences were statistically significant (p<0.05). Conclusion: Although cesarean delivery could reduce the incidence of early pelvic floor muscle abnormalities, postoperative pelvic floor muscle function and life would still be affected to a certain extent, and early instruction of pelvic floor rehabilitation training for pregnant women was beneficial to the recovery of pelvic floor function.

Topics and trends in fresh tea (Camellia sinensis) leaf research: A comprehensive bibliometric study.

Tea plant (Camellia sinensis) is a widely cultivated cash crop and tea is a favorite functional food in the world. Fresh tea leaves (FTLs) play a critical role in bridging the two fields closely related to tea cultivation and tea processing, those are, tea plant biology and tea biochemistry. To provide a comprehensive overview of the development stages, authorship collaboration, research topics, and hotspots and their temporal evolution trends in the field of FTLs research, we conducted a bibliometric analysis, based on 971 publications on FTLs-related research published during 2001-2021 from Web of Science Core Collection. CiteSpace, R package Bibliometrix, and VOSviewer were employed in this research. The results revealed that the development history can be roughly divided into three stages, namely initial stage, slow development stage and rapid development stage. Journal of Agricultural & Food Chemistry published most articles in this field, while Frontiers in Plant Science held the highest total citations and h-index. The most influential country, institution, and author in this field was identified as China, the Chinese Academy of Agricultural Sciences, and Xiaochun Wan, respectively. FTLs-related research can be categorized into three main topics: the regulation mechanism of key genes, the metabolism and features of essential compounds, and tea plants' growth and stress responses. The most concerning hotspots are the application of advanced technologies, essential metabolites, leaf color variants, and effective cultivation treatments. There has been a shift from basic biochemical and enzymatic studies to studies of molecular mechanisms that depend on multi-omics technologies. We also discussed the future development in this field. This study provides a comprehensive summary of the research field, making it easier for researchers to be informed about its development history, status, and trends.

SOME CHARACTERISTICS OF FISH SCALE COLLAGEN/ALLOPURINOL BIOCOMPOSITE

In this work, collagen extracted from fresh-water fish scales has been used as a matrix in the drug delivery polymeric system. Allopurinol has been applied to reduce the concentration of uric acid in blood and used as a model drug in collagen drug delivery system. The functional groups in collagen/allopurinol biocomposite as well as the morphology of this material were assessed by infrared (IR) spectroscopy and scanning electron microscopy (SEM). Allopurinol content released from collagen/allopurinol biocomposite in simulated body fluids was determined based on the optical absorbance of solutions containing drug by ultraviolet – visible (UV-Vis) spectra and allopurinol calibration equations. The analysis results of IR spectra of biocomposite samples indicated that the collagen/allopurinol biocomposite contains N–H, C–H, O–H linkages in collagen and C=O, C=N, N-H linkages in allopurinol. The SEM images showed that the morphology of collagen/allopurinol biocomposites differs to that of allopurinol. The allopurinol could release from the biocomposites in simulated body fluids (pH 2 and pH 7.4) according to two stages: fast release stage for 1 first hour and slow release stage in following hours. At the same time of testing, the content of allopurinol released from collagen/allopurinol biocomposite is higher than that from allopurinol free (allopurinol unloaded by collagen).

Functioning of a tripartite lignocellulolytic microbial consortium cultivated under two shaking conditions: a metatranscriptomic study

BackgroundIn a previous study, shaking speed was found to be an important factor affecting the population dynamics and lignocellulose-degrading activities of a synthetic lignocellulolytic microbial consortium composed of the bacteria Sphingobacterium paramultivorum w15, Citrobacter freundii so4, and the fungus Coniochaeta sp. 2T2.1. Here, the gene expression profiles of each strain in this consortium were examined after growth at two shaking speeds (180 and 60 rpm) at three time points (1, 5 and 13 days).ResultsThe results indicated that, at 60 rpm, C. freundii so4 switched, to a large extent, from aerobic to flexible (aerobic/microaerophilic/anaerobic) metabolism, resulting in continued slow growth till late stage. In addition, Coniochaeta sp. 2T2.1 tended to occur to a larger extent in the hyphal form, with genes encoding adhesion proteins being highly expressed. Much like at 180 rpm, at 60 rpm, S. paramultivorum w15 and Coniochaeta sp. 2T2.1 were key players in hemicellulose degradation processes, as evidenced from the respective CAZy-specific transcripts. Coniochaeta sp. 2T2.1 exhibited expression of genes encoding arabinoxylan-degrading enzymes (i.e., of CAZy groups GH10, GH11, CE1, CE5 and GH43), whereas, at 180 rpm, some of these genes were suppressed at early stages of growth. Moreover, C. freundii so4 stably expressed genes that were predicted to encode proteins with (1) β-xylosidase/β-glucosidase and (2) peptidoglycan/chitinase activities, (3) stress response- and detoxification-related proteins. Finally, S. paramultivorum w15 showed involvement in vitamin B2 generation in the early stages across the two shaking speeds, while this role was taken over by C. freundii so4 at late stage at 60 rpm.ConclusionsWe provide evidence that S. paramultivorum w15 is involved in the degradation of mainly hemicellulose and in vitamin B2 production, and C. freundii so4 in the degradation of oligosaccharides or sugar dimers, next to detoxification processes. Coniochaeta sp. 2T2.1 was held to be strongly involved in cellulose and xylan (at early stages), next to lignin modification processes (at later stages). The synergism and alternative functional roles presented in this study enhance the eco-enzymological understanding of the degradation of lignocellulose in this tripartite microbial consortium.

Estimation of the unfrozen water content of saturated sandstones by ultrasonic velocity

The unfrozen water content (UWC) of rocks at low temperature is an important index for evaluating the stability of the rock engineering in cold regions and artificial freezing engineering. This study addresses a new method to estimate the UWC of saturated sandstones at low temperature by using the ultrasonic velocity. Ultrasonic velocity variations can be divided into the normal temperature stage (20 to 0 ℃), quick phase transition stage (0 to −5 ℃) and slow phase transition stage (−5 to −25 ℃). Most increment of ultrasonic velocity is completed in the quick phase transition stage and then turns to be almost a constant in the slow phase transition stage. In addition, the UWC is also measured by using nuclear magnetic resonance (NMR) technology. It is validated that the ultrasonic velocity and UWC have a similar change law against freezing and thawing temperatures. The WE (weighted equation) model is appropriate to estimate the UWC of saturated sandstones, in which the parameters have been accurately determined rather than by data fitting. In addition, a linear relationship between UWC and ultrasonic velocity is built based on pore ice crystallization theory. It is evidenced that this linear function can be adopted to estimate the UWC at any freezing temperature by using P-wave velocity, which is simple, practical, and accurate enough compared with the WE model.

Impacts of controlled microwave field irradiation on o-cresol and p-cresol adsorption capability of activated carbon

ABSTRACT To access the feasibility of microwave in promoting adsorbability of carbonaceous adsorbents, microwave irradiation on activated carbon (AC) was conducted at powers of 400–800 W and duration of 10 min. Accordingly, the temperature rising of AC under microwave field were studied. Moreover, the alterations in physicochemical properties of AC and impacts on cresol isomer adsorption were investigated. Results indicated that the heating curve of AC displays the initial fast temperature rising stage and the final slow stage. Additionally, the bulk temperature at irradiation terminal increases with microwave power. The temperature rising further increases the pores with a diameter range of 1.00–6.00 nm of AC; it also increases the oxygenic functional groups of AC after irradiation at 400 W and 800 W, but decreases that of AC after irradiation at 640 W. The saturation adsorption capacity of o-cresol and p-cresol on the irradiated AC rises with elevated temperature. Additionally, the cresol isomer adsorption kinetics on the irradiated AC follows the Elovich model. The above-mentioned equilibrium and kinetics suggest that the cresol isomer adsorption on the irradiated AC is dominant by chemisorption. Finally, the optimum irradiation power for o-cresol and p-cresol adsorption is 800 W and 400 W, respectively, thereby fabricating AC with developed pores and abundant oxygenic functional groups. Accordingly, the saturation adsorption capacity of o-cresol and p-cresol reaches up to 111.11 mg·g−1 and 95.97 mg·g−1, respectively. Overall, microwave irradiation is a viable option to promote cresol isomer adsorption on AC.

Microstructure-based modelling of chloride diffusivity in non-saturated cement paste accounting for capillary and gel pores

Accurate prediction of chloride diffusivity in non-saturated cement paste is crucial for durability design of concrete. This paper presents an integrated framework for modelling chloride diffusivity in non-saturated cement paste considering 3D microstructure, water-gas distribution in pore network and electrical double layer effect. Results indicate that the chloride diffusivity in C-S-H pore solution is dominantly influenced by surface electric potential regardless of water saturation level, porosity of C-S-H and chloride concentration of bulk solution. With the decrease of water saturation level, the relative chloride diffusivity in cement paste experiences sharp, slow and slight decrease stages, followed by a non-diffusive stage, corresponding to connected capillary water, combination of capillary water and saturated C-S-H network and non-saturated C-S-H network as the main diffusion channel, and pore depercolation. The relative chloride diffusivity in cement paste at a given water content decreases with increasing water-to-cement ratio. The simulation results show good agreement with experimental data.

Study on the influence of key active groups on gas products in spontaneous combustion of coal

In order to reveal the internal relationship between the active groups and gas products in spontaneous combustion of coal, the correlation between the content of active functional groups and the production of gas products was studied by temperature programmed experiment and in situ infrared spectroscopy analysis experiment. The results show that there are three characteristic temperature points in the gas release curve of Jurassic coal spontaneous combustion in northern Shaanxi, which can be divided into slow oxidation stage, critical temperature stage, rapid oxidation reaction stage and combustion stage. CH3, CH2, C–H and OH are actively consumed in the spontaneous combustion of coal. CO gradually increased, which is an important oxidation product during Jurassic coal oxidation in northern Shaanxi. The chain length CH2/CH3 is attacked and the fracture shortened, while the oxygen enrichment degree of CO/CC in coal increases gradually. The correlation values of key active groups of CH3, CH2, C–H, OH, CO, CH2/CH3, and CO/CC with oxygen, carbon and oxygen gases and alkane and olefin gases in the process of coal oxidation heating in different coal seams in northern Shaanxi during Jurassic period are obtained. The results show that CH3, CH2 and CH2/CH3, are the main parts of oxygen molecules attacking and binding in the Jurassic coal oxidation process in northern Shaanxi, and the oxygen-rich products of coal decompose into carbon oxygen gas and alkane alkene gas. Due to the different activation energies of various active groups, the spontaneous combustion of coal shows different reaction degrees in each stage. The research results can be used to understand the occurrence and development degree of spontaneous coal combustion, and have important guiding significance for the monitoring and warning of spontaneous coal combustion and the targeted prevention and control of spontaneous coal combustion disasters.

Seed-mediated strategy for synthesis of enzyme-encapsulated metal-organic frameworks with enhanced enzyme activity

Encapsulation of enzymes into metal-organic frameworks (enzyme@MOF) can improve the stability of enzymes. Most present synthesis methods of enzyme@MOF rely on the complex modification of enzymes or the natural negative surface charge of enzymes to promote the synthesis of enzyme@MOF. Despite extensive efforts, it remains challenging to develop a surface charge-independent and convenient strategy to encapsulate various enzymes into MOF efficiently. In this study, we proposed a convenient seed-mediated strategy for efficient synthesis of enzyme@MOF from the perspective of MOF formation. The seed, acting as nuclei, makes the slow nucleation stage skipped, leading to the efficient synthesis of enzyme@MOF. The successful encapsulation of several proteins demonstrated the feasibility and advantages of the seed-mediated strategy. Moreover, the resulting composite, cytochrome (Cyt c) encapsulated in ZIF-8, exhibited a 5.6-fold increase in bioactivity compared to free Cyt c. The seed-mediated strategy provides an efficient, enzyme surface charge-independent, and non-modified method for the synthesis of enzyme@MOF biomaterials, which warrants further exploration and application in diverse fields.

The Two Stage Moisture Diffusion Model for Non-Fickian Behaviors of 3D Woven Composite Exposed Based on Time Fractional Diffusion Equation

The moisture diffusion behaviors of 3D woven composites exhibit non-Fickian properties when they are exposed to a hydrothermal environment. Although some experimental works have been undertaken to investigate this phenomenon, very few mathematical works on non-Fickian moisture diffusion predictions of 3D woven composites are available in the literature. To capture the non-Fickian behavior of moisture diffusion in 3D woven composites, this study first utilized a time fractional diffusion equation to derive the percentage of moisture content of a homogeneous material under hydrothermal conditions. A two-stage moisture diffusion model was subsequently developed based on the moisture diffusion mechanics of both neat resin and 3D woven composites, which describes the initial fast diffusion and the long-term slow diffusion stages. Notably, the model incorporated fractional order parameters to account for the nonlinear property of moisture diffusion in composites. Finally, the weight gain curves of neat resin and the 3D woven composite were calculated to verify the fractional diffusion model, and the predicted moisture uptake curves were all in good agreement with the experimental results. It is important to note that when the fractional order parameter α &lt; 1, the initial moisture uptake will become larger with a later slow down process. This phenomenon can better describe non-Fickian behavior caused by initial voids or complicated structures.

A-luminescence in CsI:Tl crystal excited by pulsed electron beam

The amplitude-time parameters of the A-luminescence at 3.12 eV are studied for CsI:Tl irradiated by a pulsed electron beam at temperatures 77–295 K. It has been established that the 3.12 eV band kinetics varies differently with temperature in two temperature ranges of 77–170 K and 170–295 K. The increase in temperature from 77 K to 170 K causes the decrease in the exponential decay time constant, while at temperatures above 170 K, there appeared the post-radiation rise stage followed by the slow exponential decay stage. The temperature behavior of the A-luminescence kinetics is interpreted in term of the model, according to which (i) the A band is due to the allowed electron transition 61P1 → 61S0 of Tl+ ions and (ii) the main excitation mechanism across the entire cathodoluminescence spectrum of CsI:Tl at temperatures near room temperature is the spontaneous disintegration of donor–acceptor dipoles [Tl0Vk].

Experimental Study on Neck Cutoff in Meandering River under Variable Discharges

Neck cutoff is a sudden phenomenon that occurs during the evolution of meandering rivers, but its process and mechanism remain unclear. In this investigation, the neck-narrowing process before cutoff, the formation of a new river, and the appropriate conditions for cutoff under constant and variable discharges were studied using experimental methods in a laboratory flume. The results indicated that bank erosion upstream and downstream of the neck was the main factor that triggered cutoff, regardless of whether the discharge changed. The sinuosity of the model river was approximately 7, the ratio of the neck width to the average river width reached approximately 0.43, and the experimental material was nonuniform natural sand. Under the conditions that the unit width discharge ranged from 0.0039 to 0.0069 m2/s and the longitudinal gradient was 1‰, neck cutoff could occur after sufficient bank erosion. When neck cutoff was imminent, the sinuosity of the channel increased and the channel rotated downstream. After neck cutoff, the formation of a new river experienced three stages, namely, the short-term longitudinal scouring stage, the long-term horizontal widening stage, and the long-term transverse widening and normal slow development stage. The discharge resulting in neck scouring was the effective discharge contributing to the cutoff, and this discharge directly affected the cutoff time and position. We attempted to explain the factors leading to neck cutoff from an energy consumption perspective. Neck cutoff was a sudden phenomenon that occurred when the energy consumption of a meandering river increased to its maximum value upon entry to the recession stage from the relative equilibrium stage. To a certain extent, this study is significant in understanding river evolution and neck cutoff.

Study on evolution characteristics of thermal contribution functional groups in low temperature oxidation process of bituminous coal

In order to study the key functional groups that play a major role in heat during the low-temperature oxidation of bituminous coal, this paper takes three kinds of bituminous coals with different degrees of metamorphism as the research objects, analyzes the variation law of thermal effect parameters during low-temperature oxidation of coal by C80 microcalorimetry experiment, and calculates and analyzes the activation energy of different oxidation stages by oxidation kinetics method. The change rule of functional groups during low temperature oxidation was analyzed by Fourier transform infrared experiment. The correlation between heat and functional groups was comparatively analyzed by using the grey correlation degree and frequency ratio model method, and the key functional groups of bituminous coal that play a major role in heat at different oxidation stages were identified. The results showed that with the deepening of metamorphism degree, the heat flow curve and exotherm gradually decrease, while the characteristic temperature and activation energy gradually increase. Among them, from Caojiatan's long-flame coal to Dongtan's gas coal, the exotherm decreased by 35.5 %, and the maximum endothermic rate temperature and heat balance temperature increased by 3.43 °C and 13.32 °C respectively. With the deepening of metamorphism degree, the content of hydroxyl groups keeps increasing, the content of aliphatic hydrocarbons, aromatic functional groups and fatty ethers first decreases and then increases, and the content of carboxyl groups first increases and then decreases. The correlation analysis between the gray correlation method and the frequency ratio model method shows that as the degree of metamorphic deepened, the key functional groups that play a major role in heat change from COOH to OH in the rapid endothermic stage, from-CH2- to COC in the slow endothermic stage, and from OH to COOH in the rapid exothermic stage. The key functional groups of bituminous coal, which play a major role in heat, follow the evolution of OH → CH2, COC → COOH as the oxidation stage advances.