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Mechanical characteristics, instability precursors, and fatigue life prediction of rocks under fatigue loading are significant for the prediction and prevention of mining disasters. Taking the porous siltstone widely distributed in the mining area of western China as the research object, a characteristic stress determination method based on the evolution characteristics of the multiphase volumetric strain of porous rocks was established. Referring to the characteristic stress interval, bivariate fatigue damage-controlled tests with different upper limit loads and different numbers of cycles were conducted. The results indicate that the strengthening and the weakening of the macroscopic strength of siltstone under fatigue loading are caused by the competition of two mesostructure effects, namely the "weak structure failure effect" and the "compaction embedment effect". The dominant effect varies with different upper limit loads and different numbers of cycles. Importantly, the transition of the bulk compliance from positive to negative is an early precursor of fatigue failure, while the simultaneous sudden increase in cumulative acoustic emission count, acoustic emission bk value, and energy dissipation ratio is an imminent precursor of fatigue failure. The evolution characteristics of the strain, acoustic emission, and energy dissipation indicate that the crack damage stress of siltstone is a reliable indicator of its fatigue strength. Furthermore, a nonlinear viscoplastic damage element was introduced to construct a nonlinear fatigue rheological damage model, and model validation and quantitative analysis of parameter effects were conducted. Finally, by determining the accelerated rheological start threshold and the accelerated rheological failure threshold, a rapid prediction method for the fatigue life was established. Highlights: A characteristic stress determination method suitable for porous rock. Mesoscopic mechanism of strength strengthening and weakening. Early and imminent precursors of fatigue rheological failure. A nonlinear fatigue rheological damage model. [ABSTRACT FROM AUTHOR]

During underground engineering projects, siltstone—a porous, weakly cemented rock—commonly undergoes cyclical states of creep and fatigue, raising questions about its mechanical stability under such conditions. To investigate, this study employed laboratory experiments, featuring a creep-fatigue alternation action test and uniaxial reloading test, with the absolute expansion stress serving as the upper load limit. Results reveal a counterintuitive synergy between creep and fatigue actions. Fatigue processes reduced the viscoplastic deformation capacity of siltstone, prolonging its creep rupture life. Besides, creep actions amplified the fatigue life of siltstone by over 168%, attributable to the filling and embedding of rock debris particles in the rock matrix. Additionally, siltstone’s elastic modulus and Poisson’s ratio displayed a periodic “rise-drop” oscillatory pattern under the creep-fatigue regime. Plastic strain values emerged as a robust metric for quantifying damage. Intriguingly, creep-fatigue alternation increased the absolute expansion stress by 11.7%, bolstering the rock’s damage resistance. However, this cyclical regime exacerbated the postpeak fracture behavior of siltstone, underscoring the complexity of its mechanical response. [ABSTRACT FROM AUTHOR]

In order to understand the structure of asphaltene after its disaggregating by chemical processing, a comprehensive study for exploring the structural changes of asphaltene after acylation as a case of chemical processing was conducted. Functional groups, crystal parameters, hydrogen types, and micromorphology of acylated asphaltenes were analyzed by FT-IR, XPS, XRD, 1H NMR, SEM and IFM (inverted fluorescence microscope) methods. Additionally, fluorescence spectroscopy methods were performed to analyze the effect of acylation on the aggregation ability of asphaltene. Experimental results indicated that the C=O double bond was enhanced and the content of O–C=O was increased on the surface of acylated asphaltene. The number of stacking layers and the aggregate size of asphaltene decreased obviously after acylation. Fluorescence spectral analysis showed that the critical aggregation concentration of acylated asphaltenes increased compared to the raw asphaltenes. These results indicate that acylation reaction can disaggregate asphaltenes and hinder their re-aggregation in a solution. The disaggregation effect of asphaltene acylation can be attributed to the weakening of a hydrogen bonding and enhancement of a steric hindrance in the asphaltene molecule. This study provided the further understanding of the structural changes of asphaltene after the chemical treatment. [ABSTRACT FROM AUTHOR]

Micro-mesoporous zeolite shows great potential in the field of fuel denitrogenation. However, the current preparation method of zeolite with composite pores still has the problems of high cost and low denitrification rate. Herein, we prepared a low-cost phosphorus doped zeolite by directly impregnated Y zeolite in phosphoric acid and calcinated at 400 °C firstly. Experimental results showed that phosphorus doped 10 wt.% PA/MY provided optimum denitrogenation performance with denitrogenation rate as high as 97% compared to unmodified MY zeolite (21.11%) and ion exchanged 1.0 MHY zeolite (91.38%). What's more, it was found that the introduction of phosphorus led to the formation of P–O tetrahedra and Al–O–P bonds in zeolite, which increased the amount of mesopore and the Lewis acid in zeolite. Meanwhile, the comparative study found that ion exchanged MHY zeolite depended on the limited pore matching effect of micropores and nitrogen-containing molecules and the chemisorption reaction of non-regenerable Brøsted acid to achieve denitrogenation performance. However, phosphorus doped zeolite PA/MY not only had a better size matching effect between the mesopore and the size of nitrogen-containing molecules, but also had more Lewis acid to play a major role in denitrogenation. The Lewis acid on PA/MY zeolite also had the advantage of being easy to regenerate by desorption of the nitrogen-containing molecules absorbed. This study showed good prospects for the industrial application of the doped zeolite. [ABSTRACT FROM AUTHOR]

Detecting a pipeline's abnormal status, which is typically a blockage and leakage accident, is important for the continuity and safety of mine backfill. The pipeline system for gravity-transport high-density backfill (GHB) is complex. Specifically designed, efficient, and accurate abnormal pipeline detection methods for GHB are rare. This work presents a long short-term memory-based deep learning (LSTM-DL) model for GHB pipeline blockage and leakage diagnosis. First, an industrial pipeline monitoring system was introduced using pressure and flow sensors. Second, blockage and leakage field experiments were designed to solve the problem of negative sample deficiency. The pipeline's statistical characteristics with different working statuses were analyzed to show their complexity. Third, the architecture of the LSTM-DL model was elaborated on and evaluated. Finally, the LSTM-DL model was compared with state-of-the-art (SOTA) learning algorithms. The results show that the backfilling cycle comprises multiple working phases and is intermittent. Although pressure and flow signals fluctuate stably in a normal cycle, their values are diverse in different cycles. Plugging causes a sudden change in interval signal features; leakage results in long variation duration and a wide fluctuation range. Among the SOTA models, the LSTM-DL model has the highest detection accuracy of 98.31% for all states and the lowest misjudgment or false positive rate of 3.21% for blockage and leakage states. The proposed model can accurately recognize various pipeline statuses of complex GHB systems. [ABSTRACT FROM AUTHOR]

It is urgent to reduce NOX emissions during motor fuel combustion nowadays. Among all the denitrogenation technologies for motor fuel, adsorption is the most energy saving and environmentally friendly. Herein, a new method was used to prepare nickel-doped micro-mesoporous zeolite with good denitrogenation. Researches demonstrated that by the one-step microwave ion exchange method, a Ni-MHY zeolite with composites of micro-mesopores was obtained. The denitrogenation rate of Ni-MHY reached to 96.58%, which was higher than that of the undoped MY (21.11%) zeolite. More importantly, the influence of nickel doping on the structure of zeolite was found that the Lewis acid was improved on the surface of the zeolite and the proportion of mesopores increased greatly. In the process of adsorption of nitrogen-containing compounds by Ni-MHY, the chemical adsorption effect of acid sites and the size matching effect of pores worked together. The nickel-doped micro-mesoporous zeolite showed potential application prospects. [ABSTRACT FROM AUTHOR]

Novel B-doped NiP/Hβ (Hβ is the hydrogen proton exchanged β molecular sieve) catalysts were prepared and the catalytic performance for n-C6 (n-hexane) isomerization was studied firstly. It was found that the mole ratio of Ni, P and B in preparing B-doped NiP had important influence on the crystalline structure and catalytic activity of NiPB. When the mole ratio of Ni, P and B was 1:1:1, the prepared NiPB was amorphous and NiPB/Hβ had the best catalytic activity with the conversion rate of n-C6, the yield and selectivity of isoparaffins being 79.93%, 78.34% and 98.01% respectively. It was also showed that the preparation conditions of catalyst including NiPB loading on carrier and calcination temperatures were the key factors for the catalytic performance of NiPB/Hβ. In controlled experiments, ammonia poisoned acid sites on the catalyst led to the markedly reducing of catalytic performance and metal sites were essentially for the dehydrogenation-hydrogenation reaction. The isomerization of n-C6 catalyzed by NiPB/Hβ is a continuous alternating process of acid catalysis and metal catalysis, and the matching of acid sites and metal sites is of importance. [ABSTRACT FROM AUTHOR]

A graded cyclic loading test was designed and conducted. The mechanical characteristics, acoustic emission (AE), and energy evolution law of granite under cyclic loading were demonstrated. Meanwhile, a multifactor damage model of granite under graded cyclic loading was constructed. Results indicated that hysteresis evidently existed in the stress–strain curve of granite. The envelope curve consisted of compaction, elastic, yield, failure, and residual strength stages. The Poisson's ratio of granite was minimally affected by cyclic loading and confining pressure. Conversely, the elastic modulus of granite was highly sensitive to cyclic loading and confining pressure. Considerable AE phenomena occurred in the yield and failure stages. After entering the residual strength stage, the AE intensity of granite decreased until it disappeared. In the cycle process, the proportion of elastic energy is higher than that of dissipated energy. As the number of cycles increased, the elastic energy proportion and dissipated energy proportion increased and decreased, respectively; finally, both tended to be stable. The damage state of granite during the cyclic loading test was quantitatively described by the newly established multifactor damage model. The damage degree of granite under graded cyclic loading was mainly determined by loading stress level. [ABSTRACT FROM AUTHOR]

Fast and accurate prediction for rock strength of intact rock in underground engineerings is the key to ensure the construction safety. Hence, a test method combing ultrasonic wave and rebound for rock strength is established through the test of rock surface hardness and internal defect. Meanwhile, the ultrasonic-rebound-strength model is built by combining traditional mechanical rebound value and new energy rebound value with rock longitudinal wave velocity test value with the methods of bivariate regression analysis, BP neural network and support vector machine (SVM). It applies the models established in the prediction of gneiss strength prediction and determines the optimal model for ultrasonic-rebound strength prediction after analyzing correlation coefficient and relative standard strength deviation. From the prediction results of five test samples, the rock strength prediction model of ultrasonic-rebound method obtained from the SVM method reveals the highest accuracy. At the same time, according to the strength test results of the test samples, the use of new energy resiliometer can greatly improve the prediction accuracy of rock strength. [ABSTRACT FROM AUTHOR]

A novel bimetallic bifunctional Pt–NiP/Hβ isomerization catalyst was successfully prepared by introducing a small amount of noble metal Pt into the NiP on the Hβ carrier. The catalyst demonstrated superior catalytic activity to Pt/Hβ and NiP/Hβ catalysts for n-hexane isomerization, due to the good surface property, the synergistic effect of the two metals, the suitable match between acid site and metal site, as well as good reduction stability. The effects of Pt loading and NiP addition amount on the surface property were studied comprehensively through a series of characterization, and the correlation among surface property with catalytic behavior was also analyzed. The results indicated that the Pt (0.1 mol%)–NiP (10 mol%)/Hβ catalyst had good structural characters, surface acid property and an uniform distribution of NiP and Pt active components on surface, which is helpful to obtain a highly efficient catalytic performance. Additionally, the influence of reduction/reaction conditions on the catalytic activity, as well as the catalyst tolerance to water and thiophene sulfur, was investigated furtherly. [ABSTRACT FROM AUTHOR]

In constructing cracked surrounding rock tunnels, installing systematic bolts is difficult, and construction cost is high. To solve these problems, feet-lock bolts have become a new potential substitute. Therefore, the safety and support effect of feet-lock bolts must be studied. A programme in which feet-lock bolts replace systematic bolts is adopted in the Fulushan Tunnel. A numerical simulation and a field test for preliminary support structure and surrounding rock have been conducted in this research. Results show that, (1) in the numerical simulation, the deformation and stress errors of the preliminary support structure are relatively minimal when systematic bolts are replaced by feet-lock bolts. (2) In the field test, the deformation and stress of the preliminary support structure satisfy the specification requirement after systematic bolts are replaced by feet-lock bolts. Therefore, installing feet-lock bolts, rather than systematic bolts, is reasonable and feasible in constructing cracked surrounding rock tunnels. [ABSTRACT FROM AUTHOR]

Intermediate principal stress is a significant factor when calculate to determine the surrounding rock loose circles. Based on it, this paper is trying to modify the Hoek-Brown strength criterion, and put forwards a theoretical formula of the loose circle radius. The theoretical formula is applied to Shimen Tunnel, and a comparative analysis between theoretical calculations and field test results is conducted. Here are the results as follows: 1) With an increase of intermediate principal stress, the strength of the rock mass increases and the surrounding rock becomes more difficult to break. Consequently, loose circle thickness is gradually reduced and forms a significant negative linear relationship with the Lode parameter. 2) The results indicate that with a decrease of surrounding rock level in a three-lane hard rock tunnel, the radius of the loose circle increases continuously. 3) The results of the field acoustic wave test show that the theoretical calculation values are consistent with the field measurement results. According to above analysis, the deduced formula is feasible. [ABSTRACT FROM AUTHOR]

MCM-41 was selectively functionalized with CuO on the external surface and Cu coordinated by organosilanes on the internal surface. The production of CuO and removal of template were achieved in one step, which is convenient and a save of energy. Results of transmission electron microscopy indicate the presence of CuO on outer surface of MCM-41. The successful grafting of organosilanes was confirmed by C and Si nuclear magnetic resonance. The prepared M(CuO)N(Cu) shows more comprehensive desulfurization performance due to the simultaneous and independent incorporation of CuO and copper ions. Dimethyl sulfide and dimethyl disulfide are selectively adsorbed on external surface of M(CuO)N(Cu), while tert-butyl mercaptan can be adsorbed on both external and internal surface of M(CuO)N(Cu). [ABSTRACT FROM AUTHOR]

Cu-incorporated MCM-41 was prepared by the direct synthesis method. The Cu-incorporated MCM-41 was then organically functionalized by grafting of organosilanes followed by the complexation of copper ions. The results of powder X-ray diffraction, Fourier transform infrared, and temperature-programmed reduction suggest the incorporation of Cu into the framework of MCM-41 during the direct synthesis process. The mesostructure of prepared samples is preserved after functionalization. The sulfur capacities for tert-butyl mercaptan, dimethyl sulfide, and dimethyl disulfide decrease in the same order (40)Cu-M > (40)Cu-M-N-Cu. The (40)Cu-M synthesized through the direct synthesis method also shows better desulfurization performance than M-Cu prepared by the incipient wetness impregnation method. This is attributed to the incorporated Cu species in the framework and well-dispersed CuO species of (40)Cu-M. [ABSTRACT FROM AUTHOR]

Hydrogels resulting from the self-assembly of small peptides are smart nanobiomaterials as their nanostructuring can be readily tuned by environmental stimuli such as pH, ionic strength and temperature, thereby favoring their practical applications. This work reports experimental observations of formation of peptide hydrogels in response to the redox environment. Ac-IK-NH is a short peptide amphiphile that readily self-assembles into long nanofibers and its gel formation occurs at concentrations of about 10 mmol/L. Introduction of a Cys residue into the hydrophilic region leads to a new molecule, Ac-ICGK-NH, that enables the formation of disulfide bonds between self-assembled nanofibers, thus favoring cross-linking and promoting hydrogel formation. Under oxidative environment, Ac-ICGK-NH formed hydrogels at much lower concentrations (even at 0.5 mmol/L). Furthermore, the strength of the hydrogels could be easily tuned by switching between oxidative and reductive conditions and time. However, AFM, TEM, and CD measurements revealed little morphological and structural changes at molecular and nano dimensions, showing no apparent influence arising from the disulfide bond formation. [ABSTRACT FROM AUTHOR]