Mechanical Theory Research Articles

Perceptography unveils the causal contribution of inferior temporal cortex to visual perception

Neurons in the inferotemporal (IT) cortex respond selectively to complex visual features, implying their role in object perception. However, perception is subjective and cannot be read out from neural responses; thus, bridging the causal gap between neural activity and perception demands independent characterization of perception. Historically, though, the complexity of the perceptual alterations induced by artificial stimulation of IT cortex has rendered them impossible to quantify. To address this old problem, we tasked male macaque monkeys to detect and report optical impulses delivered to their IT cortex. Combining machine learning with high-throughput behavioral optogenetics, we generated complex and highly specific images that were hard for the animal to distinguish from the state of being cortically stimulated. These images, named “perceptograms” for the first time, reveal and depict the contents of the complex hallucinatory percepts induced by local neural perturbation in IT cortex. Furthermore, we found that the nature and magnitude of these hallucinations highly depend on concurrent visual input, stimulation location, and intensity. Objective characterization of stimulation-induced perceptual events opens the door to developing a mechanistic theory of visual perception. Further, it enables us to make better visual prosthetic devices and gain a greater understanding of visual hallucinations in mental disorders.

Research on the effect of water-cooling steel pipe on preventing spontaneous combustion of coal pile and its thermal migration behavior

During the storage and transportation process after mining, coal piles are placed in open environments, making them prone to self-heating and spontaneous combustion due to the nature of coal and factors like natural wind flow. In recent years, there have been frequent spontaneous combustion incidents involving coal piles, posing significant safety risks. To effectively prevent and control spontaneous combustion disasters in open-air coal storage piles, we propose a method involving the arrangement of water-cooling steel pipes within the coal piles. This method applies theories of coal spontaneous combustion mechanisms, porous media heat transfer, and non-isothermal pipeline heat transfer. The multi-physics coupling model of COMSOL numerical simulation software is used to analyze the spontaneous ignition process and prevention effect of open pit coal pile. In the model, the thin material transfer of porous media is taken as the oxygen concentration field, the heat transfer of porous media is taken as the temperature field, and the free and porous media flow is taken as the air seepage velocity field. The simulation results of the spontaneous combustion process in the coal pile indicate that the high-temperature zone of spontaneous combustion is situated within the range of 0.5 ~ 1.5 m inside the wind-facing surface and extends 0.5 m above the ground level. These findings serve as a basis for determining the optimal placement of water-cooling steel pipes within the coal pile. The simulation results of a single water-cooling steel pipe demonstrate a positive correlation between the cooling effect on the coal pile and the water cool flow, and a negative correlation with the water cool temperature. Additionally, the cooling radius of the water-cooling steel pipe is determined by the circumference of the pipe and remains unaffected by the water cool flow. Finally, simulations were conducted to evaluate the cooling effect of multiple rows of steel pipes, and optimal arrangement parameters were determined: a center distance between steel pipes of 1 m and a water cool flow rate of 1500 L/min. As a result, the onset of the self-heating period in the coal pile was delayed by 11 days, and the spontaneous combustion period was extended by 56 days. The arrangement of water-cooling steel pipes in the coal pile has demonstrated significant efficacy in preventing and controlling spontaneous combustion.

Study on the shape prediction of doubly curved shallow shell in flexible rolling process

Flexible rolling (FR) is a novel process for manufacturing doubly curved shallow shells with various shapes based on a pair of small-diameter bendable rolls. In this paper, the fundamental reason for bi-directional bending of the sheet metal in FR is explained. For the purpose of predicting the forming radii in the transverse and longitudinal directions more effectively, the exit velocity is divided into linear velocity and interference velocity, with the latter so small as to be considered to cause only elastic deformation of the sheet. The theoretical calculation model of the pre-curvature radius resulted from linear velocity is established. Using the mechanical theory of the doubly curved shallow shell, the transverse and longitudinal curvature changes caused by the interference velocity are derived and solved by the analytical approach, which are added to the transverse and longitudinal pre-curvatures respectively so that the actual curvature radii are obtained. In order to verify the reliability of the proposed shape prediction method of FR, numerical simulations and forming experiments for convex and saddle-shaped parts are carried out. Through measurement and comparison, it is found that the simulated and experimental results are extremely consistent with the theoretical data. Besides, the effect of important parameters on elastic deformation is investigated by means of the deduced formulas.

Asymptotically consistent and computationally efficient modeling of short-ranged molecular interactions between curved slender fibers undergoing large 3D deformations

This article proposes a novel computational modeling approach for short-ranged molecular interactions between curved slender fibers undergoing large 3D deformations, and gives a detailed overview how it fits into the framework of existing fiber or beam interaction models, either considering microscale molecular or macroscale contact effects. The direct evaluation of a molecular interaction potential between two general bodies in 3D space would require to integrate molecule densities over two 3D volumes, leading to a sixfold integral to be solved numerically. By exploiting the short-range nature of the considered class of interaction potentials as well as the fundamental kinematic assumption of undeformable fiber cross-sections, as typically applied in mechanical beam theories, a recently derived, closed-form analytical solution is applied for the interaction potential between a given section of the first fiber (slave beam) and the entire second fiber (master beam), whose geometry is linearly expanded at the point with smallest distance to the given slave beam section. This novel approach based on a pre-defined section–beam interaction potential (SBIP) requires only one single integration step along the slave beam length to be performed numerically. In addition to significant gains in computational efficiency, the total beam–beam interaction potential resulting from this approach is shown to exhibit an asymptotically consistent angular and distance scaling behavior. Critically for the numerical solution scheme, a regularization of the interaction potential in the zero-separation limit as well as the finite element discretization of the interacting fibers, modeled by the geometrically exact beam theory, are presented. In addition to elementary two-fiber systems, carefully chosen to verify accuracy and asymptotic consistence of the proposed SBIP approach, a potential practical application in form of adhesive nanofiber-grafted surfaces is studied. Involving a large number of helicoidal fibers undergoing large 3D deformations, arbitrary mutual fiber orientations as well as frequent local fiber pull-off and snap-into-contact events, this example demonstrates the robustness and computational efficiency of the new approach.

Theoretical Foundations for the Formation of Regional Economic Policy in Domestic and Foreign Practice

Relevance. This article examines the theoretical foundations of the formation and development, as an independent discipline, of regional economic policy in the works of domestic and foreign practitioners who studied such aspects as economic geography, theories of interregional development and regulatory mechanisms. The author analyzes the ongoing regional economic policy during the Soviet period and identifies its positive and negative aspects. The theoretical basis of economic policies implemented in the regions turns out to be an indispensable source of information for researchers and politicians who not only seek to understand the characteristics of the economic situation in certain regions, but also to develop effective measures for their comprehensive development.The purpose is to analyze domestic and foreign works in the field of regional economics, determine their significance for modern research, as well as identify factors influencing the development of economic indicators of the regions. Objectives: to reveal the essence of regional economic policy, to determine the degree of knowledge of regional economic policy in the works of domestic and foreign practitioners at the present stage and in past centuries.Methodology. This work uses the method of theoretical analysis of the sources of the problem under study, the method of historical and logical analysis and assessment of the current situation. Results: the main goals of regional economic policy are formulated; the theoretical foundations of regional economic policy have been identified; the contribution of domestic and foreign scientists to the development of the regional economy was considered; an analysis of the periods in which research took place in the field of territorial and economic processes in Soviet practice was carried out; the key issues on which research in the field of regional economics in the USSR focused were identified; the author's positive aspects of regional economic policy during the Soviet period are presented; It has been determined that the concept of industrial policy is the theoretical basis of the regional economy.Conclusions. Regional economics as a scientific discipline has made a huge contribution to the economic policy pursued in the regions, which has made it possible to increase the socio-economic indicators of the development of these territories.

A damage constitutive model of layered slate under the action of triaxial compression and water environment erosion

Based on the macroscopic structure control theory, The slate with a significant bedding plane is a composite rock mass composed of rock blocks containing microscopic defects, joint surface closure elements, and shear deformation elements. Considering the coupling damage effect of water erosion and triaxial compressive load on bedding structure plane, the transversely isotropic damage constitutive model of slate under triaxial compressive load is derived with the dip angle of bedding and confining pressure as the variable. Firstly, based on the statistical theory of continuous damage mechanics and the maximum tensile strain criterion, the transversely isotropic deformation constitutive model of rock block with micro-defects is given; Secondly, based on the phenomenological theory of closed deformation and shear-slip deformation mechanism of layered structural plane under the coupling action of water erosion and triaxial compression load, the calculation formula of axial deformation of layered structural plane under the coupling action is given; Finally, to verify the accuracy of the established constitutive model, triaxial compression tests are carried out to study the influence of dip angle and confining pressure on the macroscopic mechanical properties and mechanism of slate. The results show that: the established triaxial compression damage constitutive model of bedding slate can accurately describe the stress–strain relationship of bedding slate after water environment erosion. With the increase of bedding dip angle, the strength and deformation capacity of the bedding slate first decreases and then increases, showing a U-shaped distribution as a whole. There are three main types of failure: tension shear composite failure, shear slip failure, and splitting tension failure.

Copper Ion-Inspired Dual Controllable Drug Release Hydrogels for Wound Management: Driven by Hydrogen Bonds.

Bacterial infections and inflammation progression yield huge trouble for the management of serious skin wounds and burns. However, some hydrogel dressing exhibit poor wound-healing capabilities. Additionally, little information is given on the molecular theory of hydrogel gelation mechanisms and drug release performance from drug-polymer network in the water environment. Herein, cationic guar gum (CG) is first mixed with dipotassium glycyrrhizinate (DG), and then crosslinked Cu2+ to strengthen the mechanical strength followed by encapsulating mussel adhesive protein (MAP) as composite dressings. Intriguingly, CG-Cu2+ 0.5-DG10 possessed proper rheological properties and mechanical strength predominantly driven by strong CG-H2O-Cu2+ and Cu2+-CG hydrogen bonding interaction. Weak DG-CG hydrogen bonding only controlled DG release in the initial 4 h, while strong hydrogen bonding is the main force regulating the sustained release of Cu2+ within 48 h. The incorporation of MAP further loosened the tight crosslinking of CG-Cu2+ 0.5-DG10. The screened CG-Cu2+ 0.5-DG10/MAP possessed excellent self-healing, injectability, antibacterial, anti-inflammatory, cell proliferation-promotion activities with high biocompatibility. Therefore, CG-Cu2+ 0.5-DG10/MAP hydrogel expedited wound closure on S. aureus-infected full-thickness skin wound model and lowered necrosis progression to the unburned interspaces on a rat burn model. The results highlight the promising translational potential of Cu2+-inspired hydrogels for the management of burns and infected wounds.

System Identification Using Self-Adaptive Filtering Applied to Second-Order Gradient Materials

For many engineering applications, it is sufficient to use the concept of simple materials. However, higher gradients of the kinematic variables are taken into account to model materials with internal length scales as well as to describe localization effects using gradient theories in finite plasticity or fluid mechanics. In many approaches, length scale parameters have been introduced that are related to a specific micro structure. An alternative approach is possible, if a thermodynamically consistent framework is used for material modeling, as shown in the present contribution. However, even if sophisticated and thermodynamically consistent material models can be established, there are still not yet standard experiments to determine higher order material constants. In order to contribute to this ongoing discussion, system identification based on the method of self-adaptive filtering is proposed in this paper. To evaluate the effectiveness of this approach, it has been applied to second-order gradient materials considering longitudinal vibrations. Based on thermodynamically consistent models that have been solved numerically, it has been possible to prove that system identification based on self-adaptive filtering can be used effectively for both narrow-band and broadband signals in the field of second-order gradient materials. It has also been found that the differences identified for simple materials and gradient materials allow for condition monitoring and detection of gradient effects in the material behavior.

DESIGN OF AUTOMATIC VIBRATING CHAIR WITH ECCENTRIC-AND-PITMAN FOR PROLONGED SEDENTARY ACTIVITIES

Sedentary behavior has become one of main inducted cause of physical decline. The pressure of modern life has further increased more working or studying time at home or office, contributing to the growing population of sedentary people furthermore. Prolonged sitting will affect people’s physical health, injuring our muscles, and causing physical discomfort. Seriously, it will lead to death. The purpose of this paper is to design a small convenient automatic vibrative chair for sedentary groups, which are driven by eccentric-and-pitman drive system, producing vibration and body movement to relieve physical problems. Double diamond design thinking method was used to find out the health problems including sedentariness and isolation. As a solution, design of the vibrative automatic chair was set as the theme of this study. The automatic vibrative chair was designed with biomimetic method, combining with industrial design principles and mechanical theories throughout structural design. The vibrating performance of the chair was verified using simulation method by adopting SolidWorks software.

Mechanics of blood flow through narrow artery using Prandtl viscoelastic model

BackgroundThe mechanics of blood flow via converging diverging conduits is an intriguing phenomenon that involves multiple fundamental principles of fluid dynamics. Blood arteries can diverge, which means they expand, or converge, which means they contract down. This specific structure is essential for controlling blood flow and preserving adequate circulation across the body. The theory of fluid mechanics is significant concept related to blood flow along converging/divergent channels. Elevated shear strains near the narrower artery throat can stimulate platelets, causing thrombosis that can completely or partially stop blood supply to the human brain or heart. This communication addresses the blood flow in convergent and diverging artery using fundamental concept of fluid mechanics. The Prandtl fluid model is considered as a blood, because of its viscoelastic nature. The influence of heat source, frictional dissipations and a chemical reaction are included. MethodsThe Jaffrey-Hamel flow in a converging and diverging conduits is generalized to Prandtl fluid model considering the purely radial flow through cylindrical pipe like artery with an arbitrary cross section. The governing equations are solved computationally using the Runge–Kutta-Fehlberg (RKF-4) method. Significant findingThe rheological parameters ε and δ of blood show opposite tendencies for blood circulation. The Brownian and thermophoresis parameters has a significant effect on heat and mass transport rate. The presence of slip (semi blockage) produces flow reversal and higher drag forces at the arterial wall. Significant flow dynamics and heat-mass transport was reveled for diverging (wider) artery β > 0. The non-uniform heat source show similar trends for thermal profile and heat transfer rate.

Managers of complex change? How United Nations treaty secretariats jointly govern institutional interplay in global environmental governance

AbstractResearch on international bureaucracies, such as treaty secretariats, has predominantly focused on broadening our understanding of their role, function, and influence within their respective regulatory domains. However, the potential for treaty secretariats to manage situations of institutional overlap by coordinating with other agencies across policy areas has remained understudied. This article offers new empirical and theoretical insights for studying collective agency and coordination mechanisms in instances of institutional interaction within hybrid regime complexes. Specifically, it investigates how the treaty secretariats of the Rio Conventions under the United Nations employ joint interplay management as a means to improve institutional coherence within the climate change, biodiversity loss, and desertification nexus. Collectively, the public agencies aim to advance knowledge and discourse, influence norm‐building processes and regulation, or build capacity and support the joint implementation of policy objectives addressing the interlinked environmental problems. They do this by interacting with various actors across governance levels, including national governments, transnational initiatives, private actors, or civil society. By tracing the process linking joint activities with effects of such interactions, this qualitative case study makes a conceptual contribution by extrapolating a mechanistic theory for joint interplay management. The article demonstrates that treaty secretariats have to contend with challenges of resource allocation, diverging mandates, leadership priorities, and the degree of politicization and timing which frequently intervene stages of strategizing and executing joint activities. The results highlight that joint interplay management can be most impactful when secretariats employ orchestration practices through joint outreach and advocacy to advance coherent institutional responses to interdependent environmental problems.

Structural and Electrical Properties of Li Substituted Mg Nano Ferrites: Prepared by Citrate-gel Auto Combustion Method

LixMg1−xFe2O4 where x=0.0to0.5with0.1 nano ferrites were synthesized by citrate gel auto combustion. Using a field-emission scanning electron microscope (FE-SEM) and the X-ray diffraction technique, their structural and topographical studies were examined. The prepared nano ferrites’ single-phase cubic spinel along the Fd3m space group is confirmed by the structural investigation. The synthesized samples were found to have a crystalline size of 20–26 nm, as determined by the Debye–Scherrer formula. Lattice parameter variation observed for the samples indicates dopant atoms into a crystal lattice can also lead to changes in the lattice constant. FE-SEM images revealed the clear grain and grain boundaries with agglomerated structure and it varied between 33.6 nm-24.4 nm. Two bands observed in Fourier transform infrared spectroscopy illustrates the M-O band in tetrahedral and octahedral sites. Dielectric parameters of the sample observed by LCR meter. Single semicircle behavior observed in impedance spectra. Dielectric constant and dielectric loss decreased as increasing frequency explained by Koop’s theory of mechanism. AC conductivity increasing trend observed with frequency, mobility of charge carrier active at high frequency domain.

Structure evolution analysis of asphalt mixtures during compaction based on particle tracking and granular properties

Pavement compaction is a process of structure evolution of materials accompanied by energy dissipation, which is closely related to the inherent granular properties of asphalt mixture. This research achieved dynamic characterization of particle migration energy and contact force development through particle tracking technique and discrete element simulation. Analytical theories for multi-stage structure evolution and compaction mechanisms were proposed based on granular properties. Results indicate that kinetic, dissipative, and potential energies dynamically represent stages of structure evolution, determined by particle collisions, self-organization into arches, and interlocking reinforcement. The initial density state is established after interparticle collisions, while self-organization occurs as particles adaptively rearrange spatially by rotation in response to unbalanced forces, accompanied by a cyclical strengthening trend of arch formation and collapse. Arches facilitate stress redistribution toward isotropy, with strong contact forces exhibiting a top-down and side-center trend, progressively supported by particles larger than 4.75 mm. Theoretical measures for compaction control were proposed, including pre-calculation of IC, selection of compaction temperature corresponding to the optimum energy efficiency, and control of principal stress deflection within the friction cone. This research aims to provide insight into granular properties and compaction dynamics, thereby contributing to intelligent compaction.

A damage model for matrix cracks in composite laminates under fatigue loading based on continuum damage mechanics

A damage model for transverse matrix cracks in composite laminates under fatigue loading was presented in this paper. The model was prosed based on the theory of continuum damage mechanics (CDM) at macro level and could capture the ‘edge effect’ of matrix cracks in composite laminate under fatigue loading. To obtain the constitutive equation of UD lamina containing transverse matrix cracks, a polynomial Gibbs free energy function was derived, and a macro damage parameter was introduced to characterize the influence of matrix cracks on multidirectional stiffness properties of UD composite. To predict the initiation and evolution of matrix cracks, a previously deduced initial crack initiation life function and a Paris-like equation in terms of damage driving force were employed, respectively. Prediction results of two cross-ply laminates under fatigue loading with different stress levels were compared to the experimental results and prediction results obtained from previously proposed model. The comparison results indicate the presented model is more effective and reliable in predicting the initiation and evolution of matrix cracks and the corresponding stiffness degradation in composite laminates under fatigue loading.

Theoretical analysis and numerical simulation analysis of energy distribution characteristics of surrounding rocks of roadways

Energy is the driving force for the failure of rock materials, and the deformation and failure of the surrounding rock of the roadway is the result of energy accumulation, dissipation and release. Based on the theory of elastic-plastic mechanics and the law of energy conservation, the total energy, elastic strain energy, dissipation energy and release energy of the surrounding rock of the roadway are deduced and analyzed, and the relationship between the energy of all the components is revealed. The energy model is developed based on the Fish language embedded in FLAC3D, and the rationality and accuracy of the energy model are verified through elastic and elastic-plastic theoretical analysis; Through the practical engineering application of the energy model, the similarities and differences in the energy calculation results of the surrounding rock of the roadway through the Mohr Coulomb and Mohr-Coulomb strain softening constitutive models are revealed, and it is pointed out that it is more in line with engineering practices to consider the post-peak deterioration of the mechanical parameters of rock. The energy evolution model of the roadway is established, revealing the space-time effect of energy distribution of the surrounding rock of the roadway under different excavation speeds and conditions, and proposing the time lag of energy evolution and the peak circle effect of the elastic strain energy related to rock burst disaster. The research results can provide references for the research of disasters such as impact ground pressure and large deformation of soft rock, and provide some theoretical guidance for the supporting design of the roadway with large deformation of the surrounding rock and impact danger.

Computational fluid dynamics method for determining the rotational diffusion coefficient of cells

This work presents a straightforward computational method to estimate the rotational diffusion coefficient (Dr) of cells and particles of various sizes using the continuum fluid mechanics theory. We calculate the torque (Γ) for cells and particles immersed in fluids to find the mobility coefficient μ and then obtain the Dr by substituting Γ in the Einstein relation. Geometries are constructed using triangular mesh, and the model is solved with computational fluid dynamics techniques. This method is less intensive and more efficient than the widely used models. We simulate eight different particle geometries and compare the results with previous literature.

Mechanical integrity of tubular elements based on strength and fracture criteria during transient CO2 injection

Geological carbon sequestration (GCS) is an essential technology for reducing carbon emissions. Wellbore integrity is crucial to ensure the safety of GCS. During low-temperature carbon dioxide (CO2) injection, the wellbore temperature decreases, causing the tubing and casing to contract, resulting in considerable axial tensile stresses, and making mechanical failure likely. This paper establishes a transient flow model for CO2 injection to predict the temperature and pressure distribution in the wellbore. Then, the strength safety factor of the tubing and casing is calculated using the material strength criteria. Fracture mechanics theory is employed to analyze the risk of crack propagation in defective tubing or casing during CO2 injection. The study indicates that the wellbore temperature near the wellhead is lower as CO2 is injected. Under typical injection conditions, the tubing and casing have high strength safety factors but small crack propagation factors. The stress intensity factor of cracks on the tubing and casing's outer surface is more significant than inner surface defects, posing a higher risk of crack propagation. When the tubing or casing exits a penetrating crack, its propagation safety factor is less than 1, necessitating the avoidance of through-wall cracks. The results guide maintaining wellbore integrity in carbon dioxide geological sequestration engineering.

Resorption of lumbar disc herniations: a non-systematic literature review

Objective. To analyze the information on spontaneous resorption of lumbar disc herniation.Material and Methods. A non-systematic review of 37 publications on resorption of disc herniation was conducted. The data on the timing, mechanisms and predictors of regression of lumbar disc herniation were summarized. A clinical case is presented illustrating the resorption of a herniated L4–L5 intervertebral disc over 8 months.Results. The frequency and timing of resorption of lumbar disc herniation vary depending on the number of patients, follow-up period, the type and nature of the hernial bulging, and other characteristics of patients. The results of meta-analyses indicate that the average period of spontaneous resorption of lumbar disc herniation is more than 6 months. The main theories of spontaneous resorption of lumbar disc herniation are the dehydration theory, the mechanical theory, and mechanisms associated with inflammatory processes and neovascularization. Currently, predictors of disc herniation resorption include the type and size of the hernia, follow-up period, Modic changes, etc. Existing data on the timing, mechanisms and predictors of resorption of lumbar disc herniation are insufficient to improve treatment tactics for this category of patients.Conclusion. Herniated lumbar intervertebral discs tend to undergo spontaneous regression which, however, is not observed in all patients. The mechanisms of resorption can be different, and the fact of resorption itself can occur in different types of hernia with different frequencies. An analysis of large data sets is necessary to more accurately determine the timing and predictors of resorption of lumbar disc hernias.

Measurement and Influencing Factors of Export Resilience: From Material Mechanics to International Trade

The concept of resilience comes from the field of physics and refers to the ability of an object to resist damage under external forces. Nowadays, resilience is widely applied in engineering, ecology, psychology, and economics, especially in the field of international trade. Export resilience has become a hot research topic. However, how to measure export resilience and find the influencing factors of export resilience has become an urgent problem for relevant scholars to solve. This article first combines the theoretical knowledge of materials mechanics and economics in the field of international trade, and constructs the inherent connection between the two; In addition, this article proposes measurement methods and principles for three dimensions of export resilience; Finally, this study combines the theories of material mechanics and international trade to analyze the three major factors that affect export resilience, providing a basis and analytical approach for other studies.

Perturbation theory and canonical coordinates in celestial mechanics

Perturbation theory and canonical coordinates in celestial mechanics