Mechanical Character Research Articles

Numerical Simulation of Mechanical Characteristics and Safety Performance for Pre-Cracked Tunnel Lining with the Extended Finite Element Method

The service performance of tunnel lining is affected by crack properties and development states. In this paper, numerical simulation models were established to investigate the mechanics characteristics and safety performance for lining structures under different cracks based on the extended finite element method (XFEM). Analyze multiple quantitative factors in simulation, including changes in crack location, crack length, and crack distribution range in the lining structure. The axial force and bending moment of the preset cracks in the lining structures were first studied. The maximum safety factor attenuation rate (Dkmax) was proposed to analyze the impact of longitudinal and annular cracks on the safety performance. The axial force at the vault of the lining arch is the most significantly affected by the combined longitudinal cracks at multiple locations. When the length of a longitudinal crack increases from 1 m to 6 m, the axial force value at the crack point decreases by 33.77%, 36.15%, and 11.32%. However, the bending moment value increases by 4.47 times, 2.50 times, and 1.69 times. Under the influence of longitudinal cracks in an “arch crown + arch shoulder”, “arch crown + arch waist”, and “arch crown + arch shoulder + arch waist”, the axial force in the arch vault increased by 21.55%, decreased by 17.52%, and decreased by 13.45%. The distribution pattern of the bending moment under the influence of circumferential cracks shows convexity at the arch shoulder and arch foot, and concavity at the arch waist and side walls. The safety factor scatter curve with longitudinal cracks shows a gradual transition from a “W” shape to a “U” shape. The safety factor curve with circumferential cracks presents an approximately symmetrical wave-shaped distribution.

Optimal entropic properties of SARS-CoV-2 RNA sequences.

The reaction of the scientific community against the COVID-19 pandemic has generated a huge (approx. 106 entries) dataset of genome sequences collected worldwide and spanning a relatively short time window. These unprecedented conditions together with the certain identification of the reference viral genome sequence allow for an original statistical study of mutations in the virus genome. In this paper, we compute the Shannon entropy of every sequence in the dataset as well as the relative entropy and the mutual information between the reference sequence and the mutated ones. These functions, originally developed in information theory, measure the information content of a sequence and allows us to study the random character of mutation mechanism in terms of its entropy and information gain or loss. We show that this approach allows us to set in new format known features of the SARS-CoV-2 mutation mechanism like the CT bias, but also to discover new optimal entropic properties of the mutation process in the sense that the virus mutation mechanism track closely theoretically computable lower bounds for the entropy decrease and the information transfer.

Respiratory mechanics characteristics at the time of barotrauma presentation in patients with critical COVID-19 infection.

To evaluate how ventilatory support, the duration of invasive ventilatory support use and lung mechanics are related to barotrauma development in patients who are severely infected with COVID-19 and who are admitted to the intensive care unit and develop pulmonary barotrauma. Retrospective cohort study of patients who were severely infected with COVID-19 and who developed pulmonary barotrauma secondary to mechanical ventilation. This study included 60 patients with lung barotrauma who were divided into two groups: 37 with early barotrauma and 23 with late barotrauma. The early barotrauma group included more individuals who needed noninvasive ventilation (62.2% versus 26.1%, p = 0.01). The tidal volume/kg of predicted body weight on the day of barotrauma was measured, and 24 hours later, it was significantly greater in the late barotrauma group than in the early barotrauma group. During the day, barotrauma was accompanied by plateau pressure and driving pressure accompanied by tidal volume, which significantly increased in the late barotrauma group. According to the SAPS 3, patients in the early barotrauma group had more pulmonary thromboembolism and more severe illness. However, the intensive care unit mortality rates did not significantly differ between the two groups (66.7% for early barotrauma versus 76.9% for late barotrauma). We investigated the effect of respiratory mechanics on barotrauma in patients with severe COVID-19 and found that 25% of patients were on nonprotective ventilation parameters when they developed barotrauma. However, 50% of patients were on protective ventilation parameters, suggesting that other nonventilatory factors may contribute to barotrauma.

Respiratory mechanics characteristics at the time of barotrauma presentation in patients with critical COVID-19 infection

RESUMO Objetivo: Avaliar como o suporte ventilatório, o tempo de uso do suporte ventilatório invasivo e a mecânica pulmonar estão relacionados ao desenvolvimento de barotrauma em pacientes com infecção grave pela COVID-19 admitidos na unidade de terapia intensiva. Métodos: Trata-se de estudo de coorte retrospectivo de pacientes com infecção grave pela COVID-19 que desenvolveram barotrauma pulmonar secundário à ventilação mecânica. Resultados: Este estudo incluiu 60 pacientes com barotrauma pulmonar divididos em dois grupos: 37 com barotrauma precoce e 23 com barotrauma tardio. O grupo com barotrauma precoce incluiu mais indivíduos que precisaram de ventilação não invasiva (62,2% versus 26,1%, p = 0,01). O volume corrente/kg de peso corporal previsto no dia do barotrauma foi medido e, 24 horas depois, foi significativamente maior no grupo com barotrauma tardio do que no grupo com barotrauma precoce. Durante o dia, o barotrauma foi acompanhado pela pressão de platô e pela pressão de distensão acompanhada do volume corrente, o qual aumentou significativamente no grupo com barotrauma tardio. De acordo com o SAPS 3, os pacientes do grupo com barotrauma precoce apresentaram mais tromboembolia pulmonar e doença mais grave. Entretanto, as taxas de mortalidade na unidade de terapia intensiva não diferiram significativamente entre os dois grupos (66,7% para barotrauma precoce versus 76,9% para barotrauma tardio). Conclusão: Investigamos o efeito da mecânica respiratória no barotrauma em pacientes com COVID-19 graves e descobrimos que um quarto dos pacientes estava em parâmetros de ventilação não protetores quando desenvolveram barotrauma. No entanto, 50% dos pacientes estavam em parâmetros de ventilação protetora, sugerindo que outros fatores não ventilatórios podem contribuir para o barotrauma.

A Retrospective Histological Study on Palatal and Gingival Mucosa Changes during a Rapid Palatal Expansion Procedure.

The most common inflammatory reactions in the oral mucosa are found at the gingival level. The treatment of these inflammations requires, first of all, the removal of the causative factor; often, this maneuver is sufficient. The aim of this retrospective study was to evaluate clinical and histopathological changes that occur in terms of gingival and palatal mucosa enlargement during palatal expansion treatment and their evolution during treatment. Twenty-five (n = 25) research participants, aged between thirteen and twenty-six years old, were examined in this retrospective study. At the end of the treatment, fragments of tissue from the affected level were obtained via incisional biopsy and sent to the histopathology laboratory for a specialized examination. The changes identified were specific to mechanical traumatic injuries, thus excluding hyperplasia from other etiologies (infectious, tumoral, or non-mechanical traumatic). The examined fragments showed hyperplasia. The histopathological examination revealed the mechanical character of the lesion, strengthening the causal relationship between the insertion of the expander and the occurrence of hyperplasia of the palatal mucosa. The type of palatal expander influenced the degree of inflammation, with the severity of hyperplasia being more pronounced in the case of mini-implant-anchored rapid palatal expander (MARPE) usage than in the case of tooth-borne rapid palatal expander (RPE) usage. The analysis of the distance between the expander and the palatal mucosa did not provide conclusive results; the incidence and severity of the reaction were variable in patients with the same distance between the expander and the palatal or gingival mucosa.

Aging and Homogenized Mechanical Character of Quasi-Statically Charged Gr-Si and NMC Based Electrodes Using Damage Material Modeling

Aging and Homogenized Mechanical Character of Quasi-Statically Charged Gr-Si and NMC Based Electrodes Using Damage Material Modeling

Study on the mechanical properties of sandstone-shale composite continental shale gas based on the discrete element method

China has abundant continental shale oil resources, and multiple shale oil exploration and development demonstration zones have been established, making it a key field for oil and gas exploration and development. However, drilling and fracturing treatment often encounter vertically interlaced and superimposed sandstone and shale reservoirs, which significantly affect the stability of the reservoir and the propagation of fractures. Therefore, it is of great significance to study the rock mechanics characteristics of sandstone-shale composite. Using the orthogonal experimental method for microscale parameter calibration, this study established the relationship between the macroscopic and microscopic parameters of sandstone-shale in the parallel bond model. The results of the orthogonal experimental scheme were analyzed using multi-factor variance analysis and linear regression analysis to determine the influence and ranking of each microscale parameter on the macroscopic parameters. Based on the results of uniaxial and triaxial compression experiments, the particle flow simulation of sandstone-shale composite rock samples was studied using the discrete element method. The study investigated the influence of the thickness ratio, combination form, and confining pressure of sandstone-shale on the mechanical properties of composite rock samples. The results showed that: (1) Under uniaxial loading conditions, for the combination form of sandstone on top and shale on the bottom (M-S type), the peak stress of the composite rock sample increased first and then decreased and then increased again with the increase of the thickness of sandstone; for the combination form of shale on top and sandstone on the bottom (S-M type), the peak stress of the composite sample decreased first and then increased and then decreased again with the increase of the thickness of shale. (2) After applying confining pressure, the compressive strength of the M-S type composite sample decreased with the increase of the thickness ratio of sandstone, while the compressive strength of the S-M type composite sample increased with the increase of the thickness ratio of shale as well as the compressive strength of the composite sample was lower than that of any complete rock sample. (3) Under uniaxial loading, the fracture mode of the composite sample was related to the combination form and the thickness ratio of different lithologies. For the M-S type sample, when the thickness ratio of sandstone was <30%, the sample was mainly fractured by tension, and when the thickness ratio of sandstone was >30%, it was mainly fractured by shear mode. For the S-M type sample, when the thickness ratio of shale was <70%, the sample had the most internal shear cracks, and when the thickness ratio of shale was >70%, it had the most tension cracks.

Fabrication, characterization and optimal selection of aluminium alloy 8011 composites reinforced with B 4 C-aloe vera ash

The aim of this study is to determine the use of B 4 C along with AVA as economical reinforcements to improve the mechanical properties of aluminium alloy 8011. The purpose of this investigation is the development of cost-effective hybrid metal matrix composites. The present investigation assessed the mechanical characteristics of Al-8011 alloy, Al-8011/3AVA, Al-8011/4B 4 C, Al-8011/2.5B 4 C/2.5AVA, and Al-8011/3B 4 C/3AVA composites, which were manufactured through stir-casting techniques. Scanning electron microscope (SEM) imaging with an energy-dispersive spectroscope (EDS) was performed on the fabricated composites to confirm the presence of reinforcements, and the images revealed a uniform distribution of reinforcements in the matrix. The density of the composite decreased with an increase in weight % of AVA-B 4 C in comparison with that of matrix aluminum alloy 8011. Results obtained for tensile strength and hardness exhibit the optimal results from adding 3 wt.% B 4 C with 3 wt.% AVA. The present paper also investigates the application of three multiple criteria decision-making (MCDM) methodological approaches to select the best option.

Few-Shot Fault Diagnosis Method of Rotating Machinery Using Novel MCGM Based CNN

The existing fault diagnosis methods can achieve good results when various status fault data are available. However, the construction of the diagnosis model is often unachievable in the actual application because only normal data are available, which is actually a few-shot fault diagnosis problem. Therefore, a novel intelligent few-shot fault diagnosis method of rotating machinery based on the convolutional neural network (CNN) using virtual samples generated by the mechanism character generative model (MCGM) integrating the generative adversarial network (GAN) is proposed. The distribution pattern of common parameters that reflect the fault category is learned using the GAN and source domain fault data. Then, the normal state data of the target domain is combined with the distribution common parameters to generate virtual samples in target domain based on the MCGM. Moreover, the fault diagnosis model is trained by virtual samples based on the CNN. Finally, the proposed fault diagnosis method is validated using the laboratory bearing data, the industrial data and the public data of the rotating machinery, respectively. The results show that the proposed method achieves an average accuracy of 93.38% in the diagnostic task, exhibiting at least 4.56% better performance than other comparison methods.

Exploring structural, thermodynamic, elastic, electro-optic, and thermoelectric characteristics of double perovskites Rb2XInBr6 (X = Na, K) for photovoltaic applications: A DFT approach

The structural, thermodynamic, elastic, electro-optic, and thermoelectric properties of the emerging double perovskites Rb2XInBr6 (X = Na, K) were investigated. The cubic phase of Rb2KInBr6 and Rb2NaInBr6 wasverified by tolerance factor (τ) values of 0.89 and 0.83, respectively. The negative formation energies and Gibbs free energies of both perovskites demonstrated their thermodynamic stability. The elastic parameters suggested the mechanical stability, brittle character, and anisotropic behavior of both materials. The electronic band gap and density of states calculations confirmed the presence of a direct band gap (Eg) for Rb2KInBr6 and Rb2NaInBr6, having an Eg of 3.2 eV and2.6 eV, respectively. The present research focuses on the investigation of light energy absorption, polarization, refractive index, and optical loss throughout the energyspectrum ranging from zero to 10 eV. The optical parameters were appropriate for photovoltaic systems since the absorption occurs in the ultraviolet range. The thermoelectric characteristics, as measured by the use of the BoltzTraP code, revealed that the maximum ZT values were determined to be 0.73and 0.72, respectively, for both materials. Despite the presence of moderate optical absorption and a ZT value in these materials, it is necessary to investigate efficient techniques for adjusting the electronic band gapto enhance the material's optical and thermoelectric response, therefore making it more suitable for practical applications in energy generation.

Experimental and Numerical Investigation on Pile Foundation Underpinning Structure System in Urban Overpass.

In view of the complexity of the pile foundation underpinning structure system and the stringent requirements of the construction process, this paper briefly describes the necessity of introducing epoxy resin reinforcing adhesive of planting rebar in the design of pile foundation underpinning beam structure to improve the mechanical properties of the reinforced beam new and old concrete joint surfaces and proposes a new type of pile foundation replacement beam system construction method by "chiseling + prestressed reinforcement + epoxy resin reinforcing adhesive". This paper uses an actual pile foundation underpinning project of an urban overpass as a prototype, designs and creates a model structure with a similarity ratio of 1/6, and performs repeated progressive static loading tests to study the load carrying capacity, displacement change, and other properties of the strengthened replacement structure, as well as analyses and distorts the overall working performance and failure mode of them. On this basis, the prototype structure's finite element analysis model was built, and the finite element analysis results were compared with the test results to obtain the mechanical properties and deformation characters of the actual pile foundation underpinning structure system corresponding to the actual underpinning beam load. This paper's study can lay the theoretical and experimental foundation for the smooth development of similar projects.

A New Method for Evaluating Fracability Based on Cluster Analysis and Well Logging Petrophysical Facies Division

The fracability of rock is a crucial parameter in determining the efficiency of fracturing in tight reservoirs. However, current methods for evaluating fracability have significant limitations. This paper proposes a new method for evaluating reservoir fracability based on cluster analysis of logging petrophysical facies. This method considers rock mechanics characteristics, petrophysical response characteristics, and reservoir physical parameters, among other factors. The Well X of the block was used as the research subject. Using the brittleness index and permeability evaluation index, the reservoir fracability of the target block is classified into five categories: high brittleness and low permeability rock, high brittleness and super low permeability rock, low brittleness and low permeability rock, low brittleness and super low permeability rock, and clay/shale. Geolog software is used to generate fracability prediction profiles for representative wells based on petrophysical facies. To further validate this evaluation method, the fracture construction data and microseismic monitoring interpretation results of Well Y in a tight block of an oil field were synthesized and analyzed to predict its fracability. The overall prediction accuracy reached 81.8%, indicating that the new fracability evaluation method has good application effect.

Response of the mechanical and chiral character of ethane to ultra-fast laser pulses.

A pair of simulated left and right circularly polarized ultra-fast laser pulses of duration 20 femtoseconds that induce a mixture of excited states are applied to ethane. The response of the electron dynamics is investigated within the next generation quantum theory of atoms in molecules (NG-QTAIM) using third-generation eigenvector-trajectories which are introduced in this work. This enables an analysis of the mechanical and chiral properties of the electron dynamics of ethane without needing to subject the C-C bond to external torsions as was the case for second-generation eigenvector-trajectories. The mechanical properties, in particular, the bond-flexing and bond-torsion were found to increase depending on the plane of the applied laser pulses. The bond-flexing and bond-torsion, depending on the plane of polarization, increases or decreases after the laser pulses are switched off. This is explainable in terms of directionally-dependent effects of the long-lasting superpositions of excited states. The chiral properties correspond to the ethane molecule being classified as formally achiral consistent with previous NG-QTAIM investigations. Future planned investigations using ultra-fast circularly polarized lasers are briefly discussed.

Modelling and mechanical characteristics of PDC cutter-rock interaction by combining mixed fragmentation modes with dynamic rock strength

Polycrystalline diamond compact (PDC) bit is one of the most widely used drill bits for improving the rate of penetration in deep oil and gas well and geothermal well. However, the dynamic rock fragmentation mechanics characteristics of PDC bits are still unclearly. A coupled fragmentation mechanics model of PDC cutter-rock interaction is established by combining the mixed fragmentation modes with dynamic strength. The coupling influence laws of cutter angle, cutting depth, dynamic strength ratio, breaking modes on the horizontal force coefficient (HFC), vertical force coefficient (VFC) and specific energy are analyzed. The model of this paper can optimize cutter inclination angle, cutting depth and minimum specific energy. With the increase of the cutter inclination angle, the dynamic VFC changes into two modes. The definition of the dynamic modes depends on the dynamic strength ratio. As the cutting angle increases, the cutting force increases. The cutting force increases nonlinearly with increasing cutting depth. The specific energy of rock fragmentation increases nonlinearly with increasing cutting depth. With the increase of dynamic strength, the specific energy of rock fragmentation increases nonlinearly. When the input-energy increases, the rate of penetration response is divided into three stages. The results have important guiding significance for the PDC bit design and drilling parameters optimization to increase the rate of penetration and the efficiency of exploration and development.

First principles investigations of the electronic, elastic, mechanical, anisotropic, optical, and thermoelectric performance of monoclinic SiGe semiconductors

Since crystal structure dictates the resultant physical properties of materials, titled physical features of the P21 monoclinic SiGe semiconductors, which are still unclear, have been revealed by density functional theory (DFT). The electronic band gap value with 0.49[Formula: see text]eV was found to be in the order of previously published cubic and hexagonal closed-packed SiGe semiconductors. Surprisingly, P21 monoclinic SiGe has a room temperature Seebeck coefficient of 1500[Formula: see text][Formula: see text]V/K which is higher than the reported data of both cubic and hexagonal SiGe alloys. Further, the mechanically stable P21 monoclinic phase of the SiGe displays a brittle mechanical character with clear elastic anisotropy has also been deduced. The P21 monoclinic phase of the SiGe can be also considered a good high-dielectric material and beneficial for practical applications of IR or UV goals due to its high refractive index.

Effect of Electroless Nickel Coating on Wear Rate of EN8 Steel

Electroless Nickel coating has emerged as a major breakthrough in the development of novel materials with excellent tribological properties. In the present work Ni-P coating has been performed over EN8 steel specimens for an hour. Mechanical and tribological character was determined for the coated samples. Tribological tests were performed for various loads and the wear behavior of coated steel has been analyzed. The coated samples were found to be harder with improved frictional characteristics like lesser wear under similar working conditions.

Burden of disease and impact on quality of life in chronic back pain - a comparative cross-sectional study of 150 axial spondyloarthritis and 150 orthopedic back pain patients.

Chronic back pain (CBP) constitutes one of the most common complaints in primary care and a leading cause of disability worldwide. CBP may be of mechanical or inflammatory character and may lead to functional impairment and reduced quality of life. In this study, we aimed to assess and compare burden of disease, functional capacity, quality of life and depressive symptoms in axial spondyloarthritis (axSpA) patients with orthopedic chronic back pain patients (OBP). We further aimed to identify factors associated with quality of life. Cross-sectional survey of a cohort of 300 CBP patients including 150 patients from a University Hospital Orthopedic Back Pain Outpatient Clinic with OBP and 150 patients with confirmed axSpA from a University Hospital Rheumatology Outpatient Clinic. Questionnaire-based assessment of pain character (Inflammatory Back Pain, MAIL-Scale), functional status (FFbH, BASFI), quality of life (WHOQOL-Bref) and depressive symptoms (Phq9) and retrospective medical chart analysis. Both, OBP and axSpA patients reported on average intermediate pain levels of mostly mixed pain character. Both groups demonstrated a reduced health-related quality of life and the presence of depressive symptoms. However, axSpA patients reported a significantly better subjective quality of life, more satisfaction with their health status and better functional capacity compared to OBP patients (all p < 0.001). In a multivariate regression model, depressive symptoms, mechanical back pain, pain level and age were negative predictors of subjective quality of life, whereas functional capacity was a positive predictor. Chronic back pain was associated with a high morbidity and reduced quality of life regardless of pain character. We identified multiple factors associated with reduced quality of life. Awareness and addressing of these factors may help to overcome unmet needs and improve quality of life for these patients.

Mechanical characteristics and fracture mechanisms of fissured rock mass samples with various opening sizes

To obtain the effect of fracture failure mechanics characteristics and behavior of brittle rock masses on the compound factors of fissure openings and inclination, uniaxial loading tests were performed on single-fissured rock-mass specimens with different openings using a rock mechanics test machine. The test results show that with the increase in fissure openings, the fissured rock-mass peak strength variation behavior with the increase in fissure inclination angle changes from first decreasing and then increasing to gradually increasing, and the angle at the minimum value of peak strength shifts from 45° to 0°. At the same fissure angle, the peak strength of the fissured rock mass decreases with the increase in the fissure opening size. The greater the opening size of the prefabricated fissure, the smaller the peak strength of the fissured rock mass and the greater the influence of changes in the fissure inclination angle. The elastic modulus of the fissured rock-mass specimen shows a positive correlation with the fissure inclination angle and a negative correlation with the fissure opening size. Combined with the neighborhood stress field analysis of the open fissure tip, the criterion of composite fracture under tension failure is established, and the linear relationship between the stress intensity factors KI and KII is verified. The criterion of composite fracture of open fissures under shear failure is also identified, which is based on the linear relationship between the stress intensity factors.

Liquid–Solid Triboelectric Probes for Real‐Time Monitoring of Sucrose Fluid Status

AbstractTriboelectric probes have rapidly developed as an efficient tool for understanding contact electrification at liquid–solid interfaces. However, the liquid–solid electrification process is susceptible to interference from chemical components in mixed solutions, severely limiting the potential applications of triboelectric probes in various liquid environments. This study for the first time reports a triboelectric probe capable of sucrose solution concentration sensing, finding that the dissolution of sucrose destroys the hydrogen bond network between water molecules and forms sucrose–water hydrogen bonds, which alters the fluid mechanics characteristics of the solution and enhances its conductivity, thereby reducing the droplet size and causing an ion charge shielding effect that significantly affects the electron transfer in liquid–solid contact electrification. Owing to the feedback of the triboelectric probe on the sucrose concentration gradient‐type sensing electrical signals, efficient sensing of sucrose solution was achieved (sensitivity of −0.0038%−1, response time of 90 ms). The triboelectric probe is also used as a wireless smart terminal to enable real‐time detection of sucrose solution. This work contributes to the understanding of the structure–function relationship between micro hydrogen bonding and macro performance, and provides a promising solution for building sustainable intelligent sensors.

The osteogenic effects of sponges synthesized with biomaterials and nano-hydroxyapatite

Artificial bone substitutes have been developed using various biomaterials for use in medicine. Silk fibroin (SF) displays excellent mechanical properties and cell compatibility. Nonetheless, the mechanical properties of silk fibroin scaffolds used in artificial bone substitutes are weaker than those of natural bone, and silk fibroin is deficient as an osteogenic agent. This limits their effectiveness in bone tissue engineering. We added nano-hydroxyapatite (nHAp) particles to an existing cell-based artificial bone substitute with a silk fibroin scaffold, which will improve its mechanical properties and osteogenic efficacy, leading to significant bone regeneration. The mechanical characters of silk fibroin modifying with nHAp were measured by Atomic Force Microscopy Analysis, dispersive x-ray spectroscopy, Porosity measurement, and Microcomputed Tomography. The proliferation and toxicity of a fibroin/dextran/collagen sponge (FDS) containing nHAp were evaluated in vitro, and its osteogenic efficacy was evaluated using nude mouse and rabbit radius defect models. The defect area was repaired and showed callus formation of new bone in the rabbit radius defect models of the nHAp-FDS-treated group, whereas the defect area was unchanged in the FDS-treated group. The nHAp-FDS manufactured in this study showed significant bone regeneration owing to the synergistic effects of the components, such as those due to the broad range of pore sizes in the sponge and protein adsorbability of the nHAp, which could be suggested as a better supportive material for bone tissue engineering.