Basic Parameters Research Articles

Investigation of H-Bonding and pH on the Fluorescence Spectral Behavior of Valsartan.

The photophysical properties of valsartan (VAL), a potent phenyl tetrazole derivative sartan, were investigated. Valsartan has absorption bands at 230nm and 255nm and a fluorescence band at about [Formula: see text] = 346nm in butanol which is red shifted depending on the H-bonding capability of the solvent. The role of H-bonding in the excited state was approved through the linear correlation of the emission energy of VAL with Camlet-Taft acidity and basicity parameters, α and β, of polar protic solvents. The position and intensity of fluorescence emission bands of VAL are found to be pH dependent, shifting from 425nm at pH 2 to 375nm at pH 4 with enhancement of intermolecular H-bonding and fluorescence intensity depletion beyond pH 5 with formation of tetrazole anion. The results were supported by time-resolved fluorescence measurements which indicated the presence of different species with different lifetimes in the excited state depending on solution pH value. Computational results based on time dependent density functional methods (TDDFT) show that the tetrazole moiety is involved in the [Formula: see text] absorption transitions, while natural bond analysis (NBO) shows that VAL adopts a dimer conformation in water because of effective intermolecular H-bonding.

Solvent Acidity and Basicity Scales: Analysis of Catalan’s SB and SA Scales and Gutmann’s Acceptor Number and Comparison with Kamlet and Taft’s β and α Solvent Scales, Gutmann’s Donor Number and Abraham’s B and A Solute Scales

The use of experimental parameters to quantify solvent properties, for example in linear free energy relationships, is well established and several scales of solvent acidity, basicity and polarity/polarizability have been developed. The success of this approach raises questions of which molecular properties contribute to particular solvent parameters and whether these contributions are found in all parameters representing a particular solvent property. In the present study, Catalan’s hydrogen bond basicity and acidity parameters, SB and SA, and Gutmann’s acceptor number, AN, a measure of a solvent’s Lewis acidity, are correlated with molecular properties derived from computational chemistry. The results are compared with the results of similar correlations with Kamlet and Taft’s β and α Solvent Scales, Gutmann’s donor number DN) and Abraham’s B and A solute scales. The results show that measures of solvent basicity, SB, β and DN all correlate strongly with the partial charge on the most negative atom in the solvent molecule and the energy of the donor orbital and, in all cases, the parameter values for hydrogen-bonded solvents are anomalous. Abraham’s B, a measure of solute hydrogen basicity, depends only on the partial charge on the most negative atom and there is no anomaly in the values for solutes that, in the pure state, form hydrogen-bonded liquids. Similarly, all measures of solvent acidity, SA, α and AN, and Abraham’s A, a measure of solute hydrogen bond acidity, depend on the partial charge on the most positive hydrogen on the molecule.

Structural, Physical and Optical studies of Sc3+ doped Lithium Aluminum Borate glasses

Optically transparent lithium aluminum borate containing scandium glasses with composition 70B2O3 – 20Li2O – (10 – x) Al2O3 – xSc2O3 (where x= 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 and 0.7 in mol %) were fabricated by conventional melt quenching technique. The non-crystalline nature of the samples was monitored by X-ray diffraction and it confirms non-crystalline nature. Structure of the fabricated glasses are assessed using the Fourier transform infrared spectra. The absorption spectra of these glasses have been recorded in the wavelength range 200 nm – 1100 nm. Direct and indirect optical energy band gaps were calculated from Tauc’s plots. The physical parameters such as refractive index (RI), optical basicity and interaction parameters were determined using proper formulas to know the characteristics of fabricated glass matrix. The results obtained indicate that 0.3 mol% Sc2O3-containing BLASc glass is more suitable for w-LEDs and lasers applications.

Activation volume and quantum tunneling in the hydrogen transfer reaction between methyl radical and methane: A first computational study.

We present a theory of the effect of quantum tunneling on the basic parameter that characterizes the effect of pressure on the rate constant of chemical reactions in a dense phase, the activation volume. This theory results in combining, on the one hand, the extreme pressure polarizable continuum model, a quantum chemical method to describe the effect of pressure on the reaction energy profile in a dense medium, and, on the other hand, the semiclassical version of the transition state theory, which includes the effect of quantum tunneling through a transmission coefficient. The theory has been applied to the study of the activation volume of the model reaction of hydrogen transfer between methyl radical and methane, including the primary isotope substitution of hydrogen with deuterium (H/D). The analysis of the numerical results offers, for the first time, a clear insight into the effect of quantum tunneling on the activation volume for this hydrogen transfer reaction: this effect results from the different influences that pressure has on the competing thermal and tunneling reaction mechanisms. Furthermore, the computed kinetic isotope effect (H/D) on the activation volume for this model hydrogen transfer correlates well with the experimental data for more complex hydrogen transfer reactions.

The effect of different non-Saccharomyces strains on the flavour characteristics of mead

AbstractAs research advances, it is generally acknowledged that non-Saccharomyces yeast contribute to the addition of aromatic compounds during mead fermentation. In this experiment, eight different non-Saccharomyces strains and Saccharomyces cerevisiae co-fermentation, their aroma composition, and basic physicochemical parameters were investigated. More than 30 compounds with favourable impact were discovered using solid-phase microextraction (SPME) coupled to gas chromatography-mass spectrometry (GC-MS). Co-fermentation of non-Saccharomyces spp. and S. cerevisiae can affect the concentration of volatile compounds, so that the mead presents different aroma characteristics. Co-fermented meads of Wickerhamomyces anomalus strains and S. cerevisiae (Wa 27-Sc and Wa 5-Sc) had higher alcohol, acids, aldehyde, and ester concentrations than those fermented with S. cerevisiae alone. In terms of taste, Wa 27-Sc was superior to Wa 5-Sc. Overall, the Wa 27-Sc received the highest score for its strong secondary aroma and good mouthfeel. The results show that the W. anomalus Wa 27 strain has a good potential to produce high quality mead.

Low-cost microstrip sensor based on coupled step line (CSL) resonator for blood plasma glucose determination

In this paper, a microstrip sensor structure was designed and implemented to detect blood glucose levels (BGL) based on changes in resonant frequencies, achieved by creating couplings at sensitive regions. A coupled step line was used to create a sensitive region on the sensor suitable for BGL testing. Transmission matrix theory was employed for the mathematical analysis to obtain the resonant frequency. Received blood samples from 50 different patients were centrifuged, and their serums were extracted to study the performance of the microchip sensor. By placing individual serum samples (50 µl) at the sensitive region of the sensor, the scattering parameters of the sensor were measured to investigate the resonant frequency variation. In addition, the effects of basic blood parameters were analyzed based on the amount of frequency shift. High sensitivity, suitable quality (Q) factor, compact size, and acceptable reproducibility of the measured results are important features of the developed sensor.

Preliminary Insight into Ice Melting, Surface Subsidence, and Wellhead Instability during Oil and Gas Extraction in Permafrost Region

Oil and gas production in permafrost can effectively alleviate energy tensions. However, ice melting around wellbores and the accompanying wellhead instability affect the efficiency and safety of oil and gas development in permafrost. Moreover, the potential oil and gas leakage will damage the environment and the ecology of permafrost. Unfortunately, ice melting, formation subsidence, and wellhead behavior during this process have rarely been investigated in previous studies. In the present work, mechanical properties of permafrost were first experimentally investigated, which provided the basic parameter for subsequent numerical simulation. It was found that the ultimate strength gradually increased with the decreasing temperature, as well as the increasing confining pressure. Meanwhile, although the elastic modulus increased with decreasing temperature, it was less affected by confining pressure. Unlike other parameters, the Poisson’s ratio was hardly affected by temperature and confining pressure. Moreover, both the internal friction angle and the cohesion increased with decreasing temperature, but the influence degree varied within different temperature ranges. Then, ice melting, formation subsidence, and the instability behavior of the wellhead caused by the disturbance of the development operation were numerically explored. The investigation results show that the ice melting range in the reservoir section reached 8.06 m, which is much wider than that in other well sections. Moreover, failure of the cement–permafrost interface, caused by ice melting, resulted in a wellhead sinking of up to 1.350 m. Finally, the insulation effect of the vacuum-insulated casing showed that the temperature drop of the designed vacuum-insulated casing was much lower than that of the ordinary casing. When the fluid temperature within the wellbore was 70 °C, the temperature drop of the designed vacuum-insulated casing was 3.54 °C lower than that of the ordinary casing. This study provides support for maintaining wellhead stability during oil and gas extraction in permafrost for avoiding some environmental disasters (such as oil and gas leakage).

Design of a New Drip Irrigation Belt Recovery Machine with Anti Breakage Function

Drip irrigation technology is widely used in agricultural production in the Xinjiang region. However, there are still a series of problems in the mechanized recovery of field drip irrigation belts, such as easy breakage of drip irrigation belts, low recovery efficiency, and excessive doping of recycled drip irrigation belts. This study focused on the problems of mechanized recovery of drip irrigation belts in Xinjiang and designed a new type of drip irrigation belt recovery machine. The key mechanisms of the new drip irrigation belt recovery machine were designed and theoretically analyzed, and their basic parameters were determined. Then, the superiority of the new drip irrigation belt recovery machine’s operational performance was verified through experiments. The experimental results showed that the new drip irrigation belt recovery machine is superior to existing machines in terms of the drip irrigation belt recovery rate and operational efficiency. In addition, the drip irrigation belts recovered by the newly designed machine have low impurity content. During the recovery process, the new machine requires less labor input than that of the existing machine.

Establishment and Parameter Calibration of a Simulation Model of Coated Cotton Seeds and Soil

Precision seeding technology is an important component of agricultural mechanization production. The precise regulation of seed movement behavior is the core of precision sowing technology and the key to improving the quality of single seed precision sowing. To accurately obtain the interaction law between seeds and soil after touching the soil, it is necessary to conduct comprehensive physical experiments to determine the simulation parameters of the seed and soil. This article takes coated cotton seeds as the research object, and the basic physical parameters of coated cotton seeds are measured through biological experiments. Based on the Hertz–Mindlin with bonding V2 contact model, a simulation model of compression between coated cotton seeds and soil is established. Using peak compression force as the response value, a combination of physical experiments and simulation simulations was used to calibrate the simulation parameters of the simulation mode of coated cotton seeds and soil. Through PB testing, it was found that four factors have a significant impact on the peak compressive force, and the parameter range was obtained. The Poisson’s ratio of coated cotton seeds was 0.14–0.26. The static friction coefficient between coated cotton seeds and steel plate was 0.38–0.58. The static friction coefficient between soil and soil was 0.3–1.2. The rolling friction coefficient between soil and soil was 0.1–0.6. Through response surface experiments with four factors and three levels, regression models were established between various factors and response values, and the optimal combination of simulation parameters was determined: the Poisson’s ratio of coated cotton seeds was 0.21; the static friction coefficient between coated cotton seed and steel plate was 0.47; the static friction coefficient between soil and soil was 0.34; and the rolling friction coefficient between soil and soil was 0.59. Based on the optimal parameter combination, the simulation of compression between coated cotton seeds and soil was continued, and the variation law of soil particle bonding bonds at different positions of coated cotton seeds during the compression process was obtained. This study provides a basis for exploring the interaction mechanism between the trencher seed soil of precision seeders and optimizing the design of critical components of cotton precision seeders.

Вооруженные силы Латинской Америки: силовой потенциал, новые функции и фактор внерегиональных связей

Introduction. As a state institution, the Armed Forces of countries in Latin America maintain certain development dynamics in the 21st century. The analysis of those problems gives an opportunity to determine the armed force potential of the Latin American region. Methods and materials. The study is based on distinguishing between the quantitative and qualitative aspects of the transformation of the Armed Forces of the Latin American region. During the analysis of both aspects, the key methodic role belongs to the comparative method. The quantitative parameters are represented in two aspects: national and international. The dynamics of the basic quantitative parameter, the Armed Forces number, and also the positioning of the armies of that region on the global scale are compared. Analysis. Since the eve of the 21st century, practically all the countries of Latin America have demonstrated a tendency toward the growth of the active military staff, proving the increment of the militarization of the region. That process represents one of the macrotendencies characterizing the actual development of the region. Results. According to the criteria of the militarization degree, three groups of countries are singled out: the stable high dynamics group, the middle dynamics indications group, and the low indications group. In the transformation of regional armies in the 21st century, the qualitative change is the appearance of a spectrum of new non-traditional functions. The hypotheses formulated in the study are the following: “The broadening of the sociopolitical functions of the military is related to the changes in attitudes toward security in the countries of the region.” The scrutiny of the military-industrial complexes of the Latin American countries gives a reason to affirm that their potentiality is mainly restricted in its character. The dependent and peripheric character of the region determines its quality as a market for the NATO countries military-technical arsenal.

Hot subdwarf wind models with accurate abundances

Context. Helium-dominated subdwarfs are core helium burning stars stripped of their envelope. The nuclear evolution of these stars alters surface abundances. Modified abundances impact the strength of the stellar wind. Aims. We aim to understand the influence of modified surface abundances on the strength of the stellar wind in the helium-dominated subdwarfs CD–46 8926 and CD–51 11879. A modified wind strength could resolve the problem with the X-ray emission of these stars, as the expected X-ray luminosity of both stars is significantly higher than the upper limit determined from observations. Methods. We used our own optical spectroscopy combined with archival ultraviolet spectroscopy and photometry to derive basic parameters and surface abundances of selected subdwarfs. The resulting parameterst served as input for the METUJE stellar wind code, which predicts the wind structure of these stars. We compared the derived wind parameters with the predictions derived for solar abundances. Results. The optical analysis showed that both subdwarfs have effective temperatures in excess of 60 kK and a strong overabundance of carbon in the case of CD–46 8926 and nitrogen in the case of CD–51 11879. We interpret the abundance patterns as being a result of enrichment by the products of nuclear reactions. The modified abundances reduce the wind mass-loss rate by tens of percent. The reduction improves the predicted wind line profiles in comparison to observations. The change in helium abundance does not have a strong effect on the wind parameters. As a result of a lower estimated bolometric luminosity and mass-loss rate and a larger distance, the expected X-ray luminosities become lower and agree with observational upper limits. Conclusions. The nucleosynthesis does not significantly alter the strength of the wind of hot subdwarfs, but the inclusion of proper stellar parameters improves the agreement with observational wind characteristics. Our analysis indicates that subdwarfs overabundant in helium are typically able to launch wind. This conclusion is supported by data gathered for thousands of subdwarfs from the literature, which shows that subdwarfs overabundant in helium avoid the region in the Kiel diagram where the winds are predicted to be absent. This can be interpreted in terms of the gravitational settling of helium, which is suppressed by the winds.

A Rapid and Inexpensive Method for Finding the Basic Parameters of Involute Helical Gears

The paper proposes a rapid, straightforward, and inexpensive method for finding the basic parameters of helical gears with an involute profile. The basic parameters envisaged are the normal module, normal profile shift coefficient, and the helix angle. The proposed method uses balls introduced between the teeth and, thus, the contact with the measuring device surfaces is of the point type, and the centres of the balls are positioned symmetrically with respect to the measuring direction. The condition that the centre of the ball occupies an imposed position is mandatory. Additionally, there is the condition of the positions of the contact points between the balls and the flanks of the teeth. Two sets of balls of different sizes are necessary for a measurement. The conditions of the balls’ positioning lead to a system of five unknowns. The methodology of solving the system is detailed and the method is exemplified for an actual helical gear. The new proposed method is based on the distance over pins but, using balls, presents the following advantages: It can be applied equally to all gears, regardless of the odd or even number of teeth. Furthermore, the dimension to be measured is singular compared to the dimension over pins when a maximum value must be found from several measurements.

Screening for Sleep Disordered Breathing in Three Distinct Neurological Diseases in the Bulgarian Population

Sleep disordered breathing (SDB) is a common medical problem in the general population. Neurological disorders such as ischemic stroke (IS), myasthenia gravis (MG), or multiple sclerosis (MS) seem to be of higher risk of SDB. Nevertheless, the implementation of screening for SDB in such disorders has not been well studied. Therefore, the aim of this study was to explore screening parameters for SDB in IS, MG and MS, in our region. We included prospectively patients with diagnosed IS, MG and MS. Psychometric tools such as the Epworth Sleepiness Scale (ESS), the STOP-BANG, and the Berlin questionnaire were implemented. For the respiratory screening portable recording device was used. Seventy-two patients, 25 with IS (mean age 66.3 years), 24 with MG (mean age 47.9 years), and 23 with MS (mean age 40.1 years) were enrolled. Basic anthropometric parameters such as BMI, neck and waist circumference were higher in IS than in MG and MS ($$p<0.001$$). The ESS scores were 5.5±3.2 for IS, 5.6±3.3 for MG, and 5.9±4.5 for MS, but without significant difference between the groups. Contrariwise, STOP-BANG scores in IS were 4.8±1.3, significantly higher ($$p<0.0001$$) than both MG (2.1±1.4) and MS (1.2±0.9). A high risk for OSA in BQ was calculated in 68% of IS, much higher ($$p<0.0001$$) than in MG (33.3%) and in MS (13%). In the respiratory screening, the mean apnea-hypopnea index in the IS group (20±18.3) was statistically higher than in MG (8.1±12.7, $$p<0.005$$), and in MS patients (2.3±4.9, $$p<0.001$$). Oxygen desaturation index in IS (19.3±19) differed statistically from the one in MG (8.1±12.9, $$p<0.005$$), and in MS (2.6±5.5, $$p<0.001$$). The oxygen saturation (SO2) showed difference only between IS and MS in all three measured values – baseline SO2 ($$p<0.001$$), median SO2 ($$p<0.05$$) and lowest SO2 ($$p<0.05$$). IS, MG and MS, as distinct neurological entities, show different clinical profiles with respect to screening for SDB. These should be taken into consideration in the individual evaluation for sleep disordered breathing.

Friction Force Reduction Efficiency in Sliding Motion Under Tangential Vibrations of Elastic Support

Abstract The efficiency of reducing the friction force in sliding motion under the influence of forced vibrations of an elastic substrate significantly depends on the direction of these vibrations in relation to the sliding direction. This article presents a comparison of computational models developed by the authors to estimate the friction force in sliding motion under longitudinal and transverse tangential vibrations of the substrate. Fundamental differences between these models are discussed, and the results of comparative analyses of the impact of tangential vibrations on the friction force depending on their direction are presented. In the developed models describing the friction force, dynamic friction models of Dahl and Dupont and the so-called LuGre model were utilised. The analyses were performed as a function of the sliding velocity and two basic parameters of vibration, which are frequency f and amplitude u0. It has been shown that under longitudinal vibrations, the key parameter, which determines the occurrence of friction force reduction at a given driving velocity vd, is the amplitude va of vibration velocity. However, the level of this reduction cannot be determined unequivocally based on the value of this parameter alone since the identical value va can be obtained at different magnitudes of the frequency and amplitude of vibrations, and the reduction level is a nonlinear function of these parameters. The results of simulation analyses were verified experimentally.

Suitability of Lupinus albus L. Genotypes for Organic Farming in Central Northern Bulgaria

Cultivars suitable for organic production systems differ in many aspects from those adapted to a conventional one. The present study aimed to evaluate 23 white lupine genotypes for a range of traits: stability, biomass productivity and related parameters, tolerance to Fusarium oxysporum, and nutritional forage value. The goal was to identify white lupine genotypes suitable for organic production conditions in Central Northern Bulgaria. Among the genotypes, Solnechnii, Termis Mestnii, and Tel Keram exhibited the highest dry mass productivity, surpassing 14 t/ha. Solnechnii and Termis Mestnii showed no symptoms of F. oxysporum infection but were unstable in terms of forage yield. On the other hand, the genotypes Bezimenii 1, Barde, 17 Nahrquell, and WAT showed a satisfactory level of stability. Ranking according to basic parameters of biochemical composition, energy, and protein nutritional value determined ranks 1 and 2 for Pink Mutant and Kijewskij Mutant. A genotype with a good balance and complex suitability for organic conditions, considering stability, productivity, and tolerance to F. oxysporum, was identified as Bezimenii 1. This genotype exhibited both stability and productivity while demonstrating high resistance to F. oxysporum (infestation index of 7.18%).

Влияние гидроабразивного износа форсунок на производительность струйного насоса

A finite-elemental model of a jet pump was created. The pump consisted of a case, in which there were eight jets, situated in a circle, symmetrically relative to the circle axis, on the equal distance of each other around the outlet of a pipeline, along which the pulp was pumped. The basic element size of the net in creating the model amounts to 50 mm, whereas the net elements size was diminished in the region of jets. The numerical experiment was carried out in order to evaluate the influence of the jets hydroabrasive wear parameters on the pump output. In conducting the computations, the assumptions were as follows: the liquid columns in the suction and force-feed pipelines were neglected; there was pure water modelled in the suction pipeline instead of the pulp taking into account that the concentration of the sand in the pulp does not exceed 10% by volume. The computations were realized in the stationary formulation of the problem. As basic parameters of the hydroabrasive wear of the jets the following were chosen: the angle of the skew of the jet forward end; a jet shortening – the displacement of the jet forward end center along the jet axis. As a result of the numerical experiment the body of data was obtained. Using the least squares method to process the data, the second order model was created, describing the dependence of the pump output on the jets wear parameters. The analysis of the model showed that the change of the angle of the forward end skew of the jets has a weak influence on the output of the pump, whereas the shortening of the jets by each millimeter causes the decrease of 1% to the nominal value of the pump output.

Effects of Chemical Short-Range Order and Temperature on Basic Structure Parameters and Stacking Fault Energies in Multi-Principal Element Alloys

In the realm of advanced material science, multi-principal element alloys (MPEAs) have emerged as a focal point due to their exceptional mechanical properties and adaptability for high-performance applications. This study embarks on an extensive investigation of four MPEAs—CoCrNi, MoNbTa, HfNbTaTiZr, and HfMoNbTaTi—alongside key pure metals (Mo, Nb, Ta, Ni) to unveil their structural and mechanical characteristics. Utilizing a blend of molecular statics and hybrid molecular dynamics/Monte Carlo simulations, the research delves into the impact of chemical short-range order (CSRO) and thermal effects on the fundamental structural parameters and stacking fault energies in these alloys. The study systematically analyzes quantities such as lattice parameters, elastic constants (C11, C12, and C44), and generalized stacking fault energies (GSFEs) across two distinct structures: random and CSRO. These properties are then evaluated at diverse temperatures (0, 300, 600, 900, 1200 K), offering a comprehensive understanding of temperature’s influence on material behavior. For CSRO, CoCrNi was annealed at 350 K and MoNbTa at 300 K, while both HfMoNbTaTi and HfNbTaTiZr were annealed at 300 K, 600 K, and 900 K, respectively. The results indicate that the lattice parameter increases with temperature, reflecting typical thermal expansion behavior. In contrast, both elastic constants and GSFE decrease with rising temperature, suggesting a reduction in resistance to stability and dislocation motion as thermal agitation intensifies. Notably, MPEAs with CSRO structures exhibit higher stiffness and GSFEs compared to their randomly structured counterparts, demonstrating the significant role of atomic ordering in enhancing material strength.

Sensory attributes and quality perception of red natural wines: a comparative study in Spain and France

Although the definition of natural wine remains contested and still lacks official recognition, it can be broadly described as a wine made with organic or biodynamic grapes without oenological additives in the cellar and minimal intervention in all winemaking stages. Despite growing interest in natural wines, uncertainty prevails about their sensory and quality attributes among both consumers and experts. In light of this research gap, this study aims to determine, first, if there are specific sensory dimensions allowing to differentiate natural wine as a wine category from conventional wines; second, if this sensory dimension affects the perception of the quality; and third, to characterise the physicochemical differences in terms of basic oenological parameters between natural wines and their conventional counterparts. To do so, 24 red wines (12 self-defined as natural and 12 conventional wines) were sensory and chemically characterised. The sensory evaluation was first carried out by winemakers from Spain. It consisted of a descriptive task (labelled sorting task) followed by a quality evaluation under two conditions: with and without information regarding the production method. A second panel of French experts carried out the same quality assessment, also with and without information. The aim was to find out whether expectations existed linked to each type of wine and to explore potential cross-cultural effects. The results of the labelled sorting task showed that natural wines tended to be different from conventional wines, but the difference was not clear-cut. However, natural wines were perceived to be of lower quality than their conventional counterparts, both with and without the information provided, regardless of the origin of winemakers. Results of the chemical analysis showed that natural wines presented higher values for volatile and total acidity and turbidity, while they had lower values for total and free sulphur. The study points to the existence of sensory dimensions with an impact on overall quality associated with the production method.

Study on the evolution characteristics of molecular surface active sites of low-rank coal in low-temperature oxidation stage

Compared with other coal types of coal, low - metamorphic coal contains numerous active sites, making it susceptible to spontaneous combustion and posing significant risks during production, transportation, and storage. To further reveal the evolution characteristics and laws of low-rank coal's active sites during the process of low-temperature oxidation of coal (LTOC), X-ray photoelectron spectroscopy (XPS), 13C nuclear magnetic resonance (13C NMR), and Fourier transform infrared (FTIR) experiments were used to determine the basic structural parameters such as the valence state of non-carbon features, types of carbon elements in coal macromolecules, and structure and quantity of functional groups. Combined with molecular modelling software (GaussView 6.0) and macromolecular calculation software (Grimme-XTB), macromolecular models of coal at different temperature points were constructed, and the surface energy field distribution was calculated. The number and energy change information of chemical and physical adsorption sites of low-rank coal during heating were obtained. The results show that during the LTOC, the chemical adsorption sites such as aliphatic hydrocarbons (-CH3/-CH2) have higher reactivity and can be converted into oxygen-containing functional groups (-CHO, –OH, –COOH); the number of physical adsorption sites increased first and then decreased, and reached the maximum at 50 °C. Coal exhibited a higher affinity for O2 at this temperature. The peroxide (-C-O-O-H) undergoes thermal decomposition, leading to H2O and weight loss of coal. The –CO and –COO structures undergo decarboxylation to generate CO, CO2, and other gases. This study comprehensively revealed the evolution of active sites through two key coal oxygen processes, physical and chemical adsorption, based on the gradual temperature elevation of low-rank coal. This holds immense significance for improving and enriching the understanding of the mechanism of coal spontaneous combustion(CSC), preparing more targeted CSC inhibition, and formulating efficient fire prevention and extinguishing measures.

Mechanical properties of poplar (NL-3412) branches

ABSTRACT The mechanical properties of poplar (NL-3412) branches are the basis for designing and optimizing the working parameters of branch pruning and crushing machinery. In this study, the tensile, compression, bending and shear properties of poplar branches were investigated by utilizing a precision microcomputer-controlled electronic universal testing machine. The test results suggested that the elastic constitutive relationship of the stress–strain curves of poplar branches under longitudinal compression, transverse compression, and bending conformed to Hooke's law, and longitudinal tensile and shear exhibited plastic damage; the anti-failure strength, anti-failure elastic modulus, and external work of poplar branches under longitudinal compression were greater than those under transverse compression. The analysis results indicated that the correlation function between the anti-failure strength and the external force work of poplar branches is positively correlated, and the external force work required to destroy poplar branches can be estimated by the established regression mathematical model. The results of the study can provide important data support for the optimal design of poplar branch pruning and shredding machinery and related simulation experimental research. HIGHLIGHTS The basic parameters of mechanical properties of poplar branches were determined. The variation law of stress–strain curve of poplar branch mechanical test was proved. The mathematical model between the strength and external force work was established. Provide reference for the optimal design of branch pruning and crushing machinery. Provide data support for the simulation cutting test of poplar branch.