Mechanical Perspective Research Articles

Extrusion bioprinting from a fluid mechanics perspective

Bioprinting is an emerging technology for fabricating intricate and diverse structures that closely mimic natural tissues and organs for such applications as tissue engineering, drug delivery, and cancer research as well. Among the various bioprinting techniques, extrusion-based bioprinting stands out due to its capability to apply a wide range of biomaterials and living cells and its controllability over printed structures. In bioprinting, the bioink stored in a syringe is forced to flow through the nozzle connected to the syringe, and then to exit and deposit onto the printing stage to form three-dimensional (3D) structures. The bioprinting process involves the flow of bioink in both syringe and nozzle and then its flow or spreading on a printing stage. As a result, fluid mechanics plays a crucial role in extrusion bioprinting. Notably, the biomaterials used in bioprinting are typically non-Newtonian fluids, which have complex viscoelastic and thixotropic behaviors; and the influence of these behaviors on the bioprinting process has been drawn considerable attention by employing various methods, including the numerical simulations via computational fluid dynamics (CFD). This paper reviews the latest development in the fluid mechanics aspects of extrusion-based bioprinting to shed light on the challenges and key considerations involved. It covers the topics of extrusion bioprinting (including driving mechanisms, printability, cell viability), biomaterial rheology and its effect on bioprinting, multi-material bioprinting and numerical simulation of bioprinting. Key issues and challenges are also discussed along with the recommendations for future research.

How industrial robots affect labor income share in task model: Evidence from Chinese A-share listed companies

This paper analyses the impact of the use of industrial robots on labor income shares at both the theoretical and empirical levels. On the theoretical side, the role of induced technological progress, the creation of new tasks, and the penetration of industrial robots on labor income shares are systematically explored by incorporating industrial robots into task models and endogenizing the task induced technological progress. Empirically, industrial robot penetration at the regional level in China is constructed from the industrial robots data released by the International Federation of Robotics (IFR), which is matched with Chinese A-share listed companies in 2011–2019, and the causal strategy of Bartik-style instrumental variables is used to analyze the impact of the penetration of industrial robots and task induced technological progress on the share of labor income. The study shows that the penetration of industrial robots significantly increases the share of labor income, but the task induced technological progress reduces the share of labor income, and that the impact of the penetration of industrial robots varies significantly external financing dependence, ownership, and regions. From the perspective of the impact mechanism, robot penetration increase the levels of inputs complementarity and hence reduce the elasticity of substitution between robots and labor. Meanwhile, robots can effectively increase the wage level of the labor force, thus increasing the labor income share. The findings of this paper provide a decision-making reference for how industrial robots can better serve human beings in the new era so that workers can share the fruits of economic development.

Phase-field investigation of dendrite suppression strategies for all-solid-state lithium metal batteries

All-solid-state Li metal batteries are widely considered as the most promising technologies to realize the increasing safety and capacity requirements for the next generation of Li batteries. However, it is experimentally demonstrated that the penetration of stiff solid electrolytes by Li dendrites seems even more severe than that of liquid electrolytes and the abnormal failure behavior of soft Li metal penetrating hard SEs is quite elusive. In the present work, a multi-coupling phase field model of Li electrodeposition is further developed to incorporate the elasto-plastic mechanical behavior and the significant size effect of Li metal. Then, the established approach is utilized to specifically evaluate the different mechanisms of Li electrodeposition and stripping in liquid electrolytes and hard solid electrolytes with various governing factors including applied voltage, external stress, ionic conductivity, SEI inhomogeneity and interfacial porosity. Especially, we summarize the accurate quantification of the regularity of external stress mechanisms which determine whether the external stress can either promote or demote the nonuniformity of Li/ solid electrolytes interface. This research provides a theoretical perspective of mechanical mechanism to reveal the conflict of experimental optimization strategies and may be instructive for the Li/ solid electrolytes interface design of all-solid-state Li metal batteries.

Analysis of the effect of digital financial inclusion on agricultural carbon emissions in China

<p style="text-align:justify"><font _mstmutation="1">In the context of China's "dual carbon" goal, digital financial inclusion plays an important role in agricultural carbon reduction. Based on the provincial panel data of 31 provinces in China from 2012 to 2022, this paper analyzes the impact of digital financial inclusion on agricultural carbon emissions and its transmission mechanism. The results show that digital financial inclusion has a significant inhibitory effect on agricultural carbon emissions. From the perspective of mechanism, inclusive digital finance can reduce agricultural carbon emissions through the upgrading of agricultural industrial structure. In addition, in the mechanism of digital inclusive finance affecting agricultural carbon emissions, there is a threshold effect, and only when rural human capital is higher than a certain threshold, digital inclusive finance can show an inhibitory effect on agricultural carbon emissions. Therefore, it is necessary to strengthen the multi-dimensional development of digital technology facilities, the development of digital inclusive finance and the upgrading of agricultural industrial structure, promote the green and low-carbon transformation of agriculture, comprehensively reduce agricultural carbon emissions, and realize the low-carbon and sustainable development of China's agriculture.</font></p>

Overnight return reversal in the Chinese stock market

ABSTRACT This article shows that the overnight return reversal is strong at a firm level in the Chinese stock market: the overnight return negatively predicts the first half-hour return of individual stocks. We explain this phenomenon from the perspective of the pre-open auction mechanism. Taking a step further, we find that the Chinese stock market shows a pattern with average negative overnight return and positive first half-hour return. Additionally, the predictability is stronger on negative overnight returns and negative informational shocks compared with positive overnight returns and positive informational shocks. Both phenomena may be led by the combined effects of the pre-open auction mechanism and T + 1 trading rule.

The yielding of granular matter is marginally stable and critical

Amorphous materials undergo a transition from liquid-like to solid-like states through processes like rapid quenching or densification. Under external loads, they exhibit yielding, with minimal structural changes compared to crystals. However, these universal characteristics are rarely explored comprehensively in a single granular experiment due to the added complexity of inherent friction. The discernible differences between static configurations before and after yielding are largely unaddressed, and a comprehensive examination from both statistical physics and mechanical perspectives is lacking. To address these gaps, we conducted experiments using photoelastic disks, simultaneously tracking particles and measuring forces. Our findings reveal that the yielding transition demonstrates critical behavior from a statistical physics standpoint and marginal stability from a mechanical perspective, akin to the isotropic jamming transition. This criticality differs significantly from spinodal criticality in frictionless amorphous solids, highlighting unique characteristics of granular yielding. Furthermore, our analysis confirms the marginal stability of granular yielding by assessing the contact number and evaluating the balance between weak forces and small gaps. These factors serve as structural indicators for configurations before and after yielding. Our results not only contribute to advancing our understanding of the fundamental physics of granular materials but also bear significant implications for practical applications in various fields.

Numerical Investigation of Bedding Rock Slope Potential Failure Modes and Triggering Factors: A Case Study of a Bridge Anchorage Excavated Foundation Pit Slope

The analysis of slope failure modes is essential for understanding slope stability. This study investigated the failure modes and triggering factors of a rock slope using the limit equilibrium method, finite differences method, and exploratory factor analysis. First, the limit equilibrium method was used to identify potential sliding surfaces. Then, the finite differences method was employed to study deformation and failure features in a slope. Stability factors were calculated considering specific conditions such as rainfall, prestressing loss, and earthquakes using the strength reduction method. Finally, exploratory factor analysis was utilized to identify the triggering factors of each failure mode. The results revealed that failure modes were categorized into two types based on the positions of the sliding surface. The main triggering factors for Failure Mode 1 were rainfall and prestress loss, while for Failure Mode 2 they were earthquake loading and prestress loss. This study offers a comprehensive exploration of potential failure modes and their triggering factors from mechanical and statistical perspectives, enriching our understanding of potential failure modes in rock slopes.

Leader Developmental Feedback and Team Adaptation: An Integrative Mechanism Perspective

Leader Developmental Feedback and Team Adaptation: An Integrative Mechanism Perspective

Towards the circular economy from the perspective of new institutional theory: a systematic analysis of the literature with InOrdinatio protocol

Purpose This study aims to analyse the publication stage on the transition to a circular economy (CE) from the perspective of the isomorphic mechanisms of the new institutional theory (NIT). Design/methodology/approach The authors conducted a systematic literature review using the Methodi Ordinatio protocol across four databases, resulting in the analysis of 17 articles. Findings The authors identified a network of CE studies among universities in different countries. As a main result, this study contributed to demonstrating the diversity of approaches available to investigate CE, the importance of stakeholders in the process of transition from linear economy to CE and the means for the transition to CE, as well as the need for future studies covering the detailed analysis of the transition process and the comparison of the evolution of the states/regions of the same country in this process. Originality/value The study analyses and summarises the existing literature on CE through the lens of the NIT, analysing the stage of publication based on the phases of implementation of CE (micro, meso and macro). With a research agenda, it presents the current gaps, providing a possible direction for future studies.

Tailoring Interfacial Structures to Regulate Carrier Transport in Solid-State Batteries.

Solid-state lithium-ion batteries (SSLIBs) have been considered as the priority candidate for next-generation energy storage system, due to their advantages in safety and energy density compare with conventional liquid electrolyte systems. However, the introduction of numerous solid-solid interfaces results in a series of issues, hindering the further development of SSLIBs. Therefore, a thorough understanding on the interfacial issues is essential to promote the practical applications for SSLIBs. In this review, the interface issues are discussed from the perspective of transportation mechanism of electrons and lithium ions, including internal interfaces within cathode/anode composites and solid electrolytes (SEs), as well as the apparent electrode/SEs interfaces. The corresponding interface modification strategies, such as passivation layer design, conductive binders, and thermal sintering methods, are comprehensively summarized. Through establishing the correlation between carrier transport network and corresponding battery electrochemical performance, the design principles for achieving a selective carrier transport network are systematically elucidated. Additionally, the future challenges are speculated and research directions in tailoring interfacial structure for SSLIBs. By providing the insightful review and outlook on interfacial charge transfer, the industrialization of SSLIBs are aimed to promoted.

Can green finance policies accurately promote corporate environmental investment?—a comprehensive evaluation from multiple aspects

The 28th United Nations Climate Change Conference, held in the United Arab Emirates at the end of November 2023, stated that climate action cannot be delayed and the financing and investment situation for adapting to climate change needs a qualitative leap. Vigorously developing green finance is one of the important ways to achieve this goal. The core question of this paper is: Can green finance policies promote enterprises’ environmental investment? This article uses the formal implementation of the “Green Credit Guidelines” in 2012 as a quasi-natural experiment, bases on the micro data of A-share listed companies from 2004 to 2020, and adopts the difference-indifferences propensity score matching method (PSM-DID) to explore the role of green credit policy in guiding corporate environmental protection investment from multiple dimensions. The research shows that the implementation of the “Green Credit Guidelines” has promoted corporate environmental protection investment to a certain extent, and the conclusion still holds after a series of robustness tests. Heterogeneity tests found that the impact of green credit policy on corporate environmental protection investment varies significantly among different ownership enterprises and enterprises in different regions. Further research shows that the Green Credit Guidelines are regulated by macro and meso factors. From the perspective of mechanism, this paper finds out the mechanism of promoting enterprises’ environmental protection investment at the micro level. At the macro level, economic policy uncertainty and monetary policy tightening affect the degree of corporate environmental protection investment. At the meso level, the government’s attention to environmental protection determines the behavior of local enterprises, which in turn affects the attitude of enterprises towards environmental protection investment activities. At the micro level, the implementation of green credit on the one hand exacerbates the problem of corporate financing constraints, making companies have incentives to invest in environmental protection to alleviate this problem. On the other hand, it will also promote changes in innovation and capital factors in enterprises, directly increasing corporate environmental protection investment. This paper is helpful for the theoretical circle and management departments, so as to provide reference for the government to issue relevant policies.

Exploration on the synergistic effect of antioxidants for coal-to-liquid base oil: From the perspective of oxidation resistance and thermal stability

Coal-to-liquid (CTL) base oil is a high-quality lubricant base oil made from coal. However, its poor oxidation stability and short service life limit its application. Pressurized differential scanning calorimetry and Rotary bomb oxidation test are utilized for the evaluation of oxidation stability. Thermogravimetric analysis is performed for the thermal stability assessment. The results showed the reasonable combination of commercial antioxidants can significantly improve the oxidative and thermal stability of two typical CTL base oils, CTL3 and CTL6. The synergistic mechanism of antioxidants in CTL base oil was studied from the perspective of pyrolysis kinetics and pyrolysis mechanism. For CTL3, adding the compound antioxidant 2,6-di-tert-butyl-4-methylphenol (T501) and n-phenyl-1-naphthylamine (T531) results in an almost eightfold increase in oxidation induction time (OIT) and a 33.4 % increase in activation energy compared to pure CTL3. For CTL6, adding the compound antioxidant dialkyl dithiophosphate (T203) and diphenylamine (L57) results in an almost tenfold increase in OIT and a 10.9 % increase in activation energy compared to pure CTL6. The designed commercial antioxidant compound systems had excellent synergistic effects and the synergistic mechanisms were illustrated.

Review on Artificial Interphases for Lithium Metal Anodes: From a Mechanical Perspective

AbstractLithium (Li) metal is a promising candidate for next‐generation high‐energy‐density rechargeable batteries. However, the solid electrolyte interphase (SEI) inevitably suffers from mechanical fracture owing to the large morphological change during Li cycling, leading to the uncontrollable growth of Li dendrites, low Coulombic efficiency, and short cycle life. The fabrication of an artificial interphase is an effective strategy for improving the performances of Li metal anodes. The ideal artificial interphase should provide sufficient mechanical robustness to suppress dendritic Li growth and accommodate large volume changes during Li deposition‐dissolution cycles. In this review, we focus on the fabrication of mechanically robust artificial interphases for stabilizing Li‐metal anodes, including the underlying mechanism of SEI fracture, quantitative requirements for mechanical properties, measurements of mechanical properties, and recent progress in the fabrication of mechanically stable artificial interphases.

Optimum moment to heal cracks in asphalt pavement by means of waste carbon fiber-enhanced electromagnetic induction heating during multiple damage-healing cycles

This study investigated the optimal timing for healing asphalt pavement cracks using waste carbon fibers (WCFs) reinforced electromagnetic induction (EMI) technology through multiple "damage-healing" cycles, focusing on mechanical and fatigue performance. Initially, an extensive research project was carried out to evaluate the rate of induction heating, surface temperature decline rate, and effective heating depth of the asphalt mixture. Subsequently, from a mechanical performance perspective, semi-circular bending (SCB) tests were employed. By setting four different load termination conditions, the extent of cracking in the specimens was quantitatively controlled, followed by multiple "damage-healing" tests to analyze the impact of healing timing on the mechanical properties and healing efficiency of the asphalt mixture. Lastly, from the perspective of fatigue performance, using the four-point bending fatigue test (4 PB), the fatigue damage extent of specimens was quantitatively controlled through the attenuation rate of stiffness modulus. Multiple "damage-healing" tests were carried out at four different healing timings to study the effect of healing timing on the fatigue performance and healing efficiency of the asphalt mixture. The results indicated that WCFs improved the heating performance of asphalt mixture, enabling 5 cm-thick specimens to be fully heated within 6 min. Both SCB and 4 PB tests yielded similar conclusions: in the process of multiple "damage-healing" cycles, earlier healing interventions were beneficial for the recovery and maintenance of the mechanical properties of asphalt mixtures and effectively extended their service life. However, the fatigue tests also revealed that overly early self-healing interventions, where cracks were insufficiently formed, did not fully exploit the potential of the healing process. Conversely, healing interventions conducted too late were extremely detrimental to the restoration of mechanical characteristics and the prolongation of the asphalt mixture's lifespan.

Structural implementation of recycled lump prepared from waste concrete after elevated temperatures: Mechanical and environmental performances

To find a sustainable treatment for construction and demolition waste, the utilization of recycled lump (RL) prepared from waste concrete after elevated temperatures as coarse aggregate in concrete was investigated. The mechanical and environmental properties of recycled lump concrete (RLC) and reinforced recycled lump concrete (RRLC) were discussed with three RL replacement ratios and five treatment temperatures. The results show that increasing the RL replacement ratio would reduce the slump, and axial compressive performance of RLC, resulting from the presence of old adhered mortar on RL. The treatment of elevated temperature for RLC would improve the adverse effect of increasing the RL replacement ratio, resulting from the decreasing amount of old adhered mortar and interfacial transition zone on RL. The prediction formulas for the mechanical model of RLC were proposed while the design method for the axial compressive strength for RRLC was modified against the existing standard to conduct the full-range parametric analysis. The environment assessment indicates that the sustainable utilization of RL as coarse aggregate could reduce the environmental impact and global warming from concrete production whilst the RL prepared from waste concrete after 400 °C treatment is an appreciated option for the production of RLC and RRLC products from a mechanical and environmental perspective. In addition, the increase in external diameter would remarkably dwindle the environmental impact caused by the utilization of RL in structural members.

Contributing factors to preterm pre-labor rupture of the fetal membrane: Biomechanical analysis of the membrane under different physiological conditions

The fetal membranes are a complex biological structure essential for pregnancy, comprising two main layers: the amnion and the chorion. Characterizing each layer from a mechanical perspective is extremely important to understand the rupture process of the membrane at term or preterm. It is still unclear what factors lead to preterm pre-labor rupture of the membrane (PPROM) due to ethical and technical factors associated with in-vivo experimental tests. Numerical simulations may offer some answers, clarifying the biomechanics of the fetal membrane during gestation.This work uses a validated multilayer fetal membrane model to evaluate whether certain physiological conditions occurring during pregnancy contribute to PPROM. The following factors are evaluated: (i) contact conditions between the amnion and the chorion, (ii) normal and abnormal intrauterine pressures, (iii) amnion and chorion thicknesses, and (iv) orientation of the collagen fibers within the amnion layer. Our results show that PPROM might be potentiated under certain physiological circumstances: (i) the existence of interconnection (friction or tied contact) between the two main layers of the fetal membrane increases the stress in the mechanical dominant amnion, (ii) larger intrauterine pressures and (iii) smaller amnion and chorion thicknesses lead to the same increase in stress, and (iv) different off-plane angles of the collagen fibers tend to modify the stress distribution and thickness variation in both layers.

Ecuadorian Woods: Building Material Selection Using an Entropy-COPRAS Comparative Analysis Based on the Characterization of Ecuadorian Oak and Guayacan Timber.

Considering that global awareness for sustainable development has risen to face environmental damages, different building materials have been considered from a mechanical perspective. In this sense, considering the richness of South America regarding its woods, the Guayacan and the Ecuadorian oak timbers have not been previously characterized. The present research has performed mechanical, thermal, and moisture content characterizations to acknowledge the benefits of considering these materials for the building industries. In this sense, Guayacan has been shown to have lower thermal conductivity, making it ideal for thermal insulation; the oak from Manabi showed the best compressive strength; while the oak from El Oro stands with the best tensile strength; and the oak from Loja showed the best modulus of elasticity. On the other hand, all the materials were compared by multicriteria decision methods to select the best, by using the COPRAS method driven by the objective entropy-weighted method, showing that the oak from Loja is the best choice considering the advantage that presents with the modulus of elasticity. In this sense, it is concluded that regarding the mechanical properties, there is not much difference for the compression, bending, and tensile strength; nevertheless, for the modulus of elasticity the oak from Loja stands out, making it a factor to be considered in the selection of a wood for building applications that is corroborated through multicriteria decision methods.

The balance issue of the proportion between new energy and traditional thermal power: An important issue under today's low-carbon goal in developing countries

The stability of the new power system depends on the balance between controllable flexible resources and uncontrollable uncertain resources. For many developing countries and regions lacking advanced flexible resources, thermal power is the main force in solving the problem of new energy consumption. Finding the balance between new energy and traditional thermal power is the key for today's low-carbon goal. To solve this problem, this paper calculates the power range and climbing rate range of thermal power based on physical principles and actual data, and characterizes the characteristics of wind power, photovoltaic power, load and net load based on the five proposed volatility indicators. Then, a logically clear method for determining the required number of thermal power units based on the volatility indicators of new energy from the mechanism and principle perspective is proposed. Finally, under the premise of meeting the power balance and flexibility balance of the power system, the reasonable ratios between the installed capacity of new energy and the number of thermal power units are calculated in four seasons. The results indicate that the judgment system can provide guidance for the energy structure of developing regions.

[formula omitted] symmetry in hydrogen-atom-like model with spin

As the simplest atom in nature, the hydrogen atom has been explored thoroughly from the perspective of non-relativistic quantum mechanics to relativistic quantum mechanics. Among the research on hydrogen atom, its energy level is the most basic, which can be obtained more conveniently predicated on the SO(4) symmetry than the wave-equation resolution. Moreover, “spin” is another indispensable topic in quantum mechanics, appearing as an intrinsic degree of freedom. In this work, we generalize the quantum Runge-Lenz vector to a spin-dependent one, and then extract a novel Hamiltonian of hydrogen-atom-like model with spin based on the requirement of SO(4) symmetry. Furthermore, the energy spectrum of hydrogen-atom-like model with spin potentials is also determined by the remarkable approach of SO(4) symmetry. Our findings extend the ground of hydrogen atom, and may contribute to other complicated models based on hydrogen atom.

Study on the Repair Effect of Self-Healing Cementitious Material with Urea-Formaldehyde Resin/Epoxy Resin Microcapsule

Recent studies on microencapsulated self-healing cementitious materials have primarily focused on the particle size and preparation methods of the microcapsules. However, there has been limited attention paid to the microscopic aspects, such as the selection of curing agents and the curing duration of these materials. In this study, urea-formaldehyde resin/epoxy resin E-51 microcapsules were synthesized through in situ polymerization. This research investigates the feasibility of self-healing from a molecular mechanism perspective and evaluates the repair performance of microencapsulated self-healing cement mortar with varying microcapsule concentrations, curing agent types, and curing ages. The findings demonstrate that the microcapsule shells bond effectively with the cementitious matrix, with radial distribution function peaks all located within 3.5 Å. The incorporation of microcapsules enhanced the tensile strength of the modified cement mortar by 116.83% and increased the failure strain by 110%, indicating improved adhesion and mechanical properties. The restorative agent released from the microcapsule core provided greater strength after curing compared to the uncured state. Although the overall strength of the microencapsulated self-healing cement mortar decreased with higher microcapsule concentrations, the repair efficiency improved. The strength recovery rate of 28-day aged modified cement mortar had a significant improvement with the addition of X and Y curing agents, respectively.