Stress Difference Research Articles

Criterion for hydraulic fracture propagation behaviour at coal measure composite reservoir interface based on energy release rate theory

In this study, a discriminative model of fracture expansion through a composite reservoir interface was established. During fracture transformation, the model, based on the theory of energy release rate at the fracture tip, helps clarify the critical conditions and assess the law of hydraulic fracture expansion through coal composite reservoir interfaces. This model considers shear and tensile processes during fracturing at the coal–rock interface and the effects of interface material property differences on fracture extension. In addition, fracture extension pattern differentiation is achieved by comparing the hydraulic fracture tip penetration and bending energy release rates (Gp/Gd) with the ratio of reservoir fracture and interface fracture energies (ΓR/ΓF). The accuracy of this discriminant criterion was verified by comparing the predicted results of the discriminant model with fracturing test results under identical conditions. The effects of various factors on Gp/Gd and hydraulic fracture penetration extension were investigated by using the sand-mudstone composite reservoir of the Shibox Formation in the Linxing Block, China, as the geological background. The results indicate that for certain values of ΓR/ΓF, Gp/Gd increases logarithmically with an increase in water pressure in the wellbore. Moreover, the difference in ground stress and elastic modulus between the layers exponentially increases with increasing Poisson’s ratio difference and the angle between fracture and interface and decreases logarithmically with increasing fracture height. These results indicate that hydraulic fractures are likely to penetrate from reservoirs with a high elastic modulus and Poisson’s ratio into reservoirs with a low elastic modulus and Poisson’s ratio. Furthermore, hydraulic fractures are likely to penetrate formations with large differences in pinch angle and ground stress. Under specific geological conditions, high water pressure in the wellbore and small seam height are favourable for fracture penetration.

Prolonged Grief, Posttraumatic Stress and Depression Symptoms Before and After COVID-19 in Brazil.

This study aims to explore the differences in prolonged grief (PDG), posttraumatic stress (PTSD), and depression symptoms (MDD) following the loss of a loved one before and after the COVID-19 pandemic. Using a cross-sectional design, 888 bereaved individuals were classified on different groups according to the cause of death. Results indicate that participants who experienced a loss during the pandemic, regardless of the cause, presented higher levels of prolonged grief, posttraumatic stress and depression when compared to those who lost a loved one before the pandemic. This study sheds light on the environmental influences (ex: the COVID-19 pandemic) on the grieving process, emphasizing the need to take the context into account when tailoring interventions in bereavement and mental health care.

Extensional rheology of elastoviscous aqueous PEO/PEG or DMS Boger fluids and weakly elastic alternatives for investigating viscoelastic flows and instabilities

Boger fluids that exhibit a rate-independent shear viscosity (typically ∼ 1 Pa∙s = 1000x water viscosity) and elasticity measurable using torsional rheometers (modulus, relaxation time, or first normal stress difference) are considered as the realization of viscoelastic fluids described by the Oldroyd-B model. However, Boger fluids, conventionally formulated as dilute solutions of high molecular weight (Mw) polymers in relatively high viscosity solvents (or solutions of oligomers or lower Mw polymer), are unsuitable for emulating polymeric fluids used in coating formulations that are lower in viscosity, appear inelastic in torsional shear rheometry, and yet appear prone to viscoelastic instabilities. Therefore, Dontula, Macosko, and Scriven (DMS) (AIChE J, 1998) chose to create an alternative model of elastic fluids by dissolving ultrahigh molecular weight (UHMw) poly(ethylene oxide) (PEO) in an aqueous solution of its lower Mw analog, often referred to as poly(ethylene glycol) or PEG. Even though numerous studies of printing and coating flow instabilities use this aqueous PEO/PEG or DMS Boger fluids as model viscoelastic fluids, only a few explicitly measured elastic properties, especially using relaxation time, and hardly any characterized extensional rheology. In this contribution, we recreate the DMS Boger fluids to examine their elasticity and extensional rheology response using dripping-onto-substrate (DoS) rheometry that relies on an analysis of capillarity-driven pinching dynamics. Though the aqueous PEG solution is often treated as a viscous and Newtonian solvent, we discover that in DoS rheometry, both the PEG solution and the DMS Boger fluid display power law response followed by elastocapillary, in contradiction with the assumptions and the response expected of the Oldroyd-B model. Furthermore, the solution of entangled PEG chains influences specific viscosity, pinching dynamics, and measured extensional rheology response in striking contrast with Newtonian solvents of the same viscosity. Lastly, we describe the possibility of using dilute, aqueous solutions of UHMw PEO as model viscoelastic fluids for coating flows, for both elasticity and extensional viscosity can be determined using DoS rheometry. Due to their water-like viscosity, the aqueous PEO solutions appeal as model fluids that have elasticity, emulate Newtonian fluids in the early stages of pinching, and have a relaxation time tunable by changing polymer Mw or concentration.

Numerical simulation study of fracture propagation by internal plugging hydraulic fracturing

Internal temporary plugging fracturing technology improves the stimulated volume by forming a more complex fracture network, significantly enhancing the reservoir stimulation effect and effectively developing unconventional oil and gas resources. However, the current understanding of the fracture propagation mechanism on internal temporary plugging fracturing is still unclear, making it difficult to determine the main controlling factors that affect the shape of the fractures. In addition, the lack of practical numerical simulation methods for temporary plugging fracturing makes it challenging to provide guidance for field scheme design. Utilizing the finite element cohesive zone method, which incorporates globally embedded cohesive elements, this study constructs a comprehensive numerical model to investigate the propagation behavior of temporarily plugging fracturing fractures. The model delves into the impact of various geological and construction parameters on the opening conditions of branch fractures during the temporary plugging fracturing process, as well as the propagation patterns of fractures within naturally fractured reservoirs. The research findings indicate that the construction factors have the following impacts: When the pumping rate and viscosity of the fracturing fluid are comparatively high, the resulting fluid pressure within the fracture escalates, resulting in the creation of numerous branch fractures within the naturally fractured reservoir. This, in turn, augments the fracture’s complexity. However, these two factors have little influence on the maximum deflection distance of the deflected fracture. As for the geological factors, an increase in the horizontal stress difference will decrease the maximum deflection distance of the deflected fracture, reducing the number of natural fractures intersected and shortening the length of the deflected fracture. Conversely, an increase in the approach angle will increase the maximum deflection distance of the deflected fracture, thereby expanding the affected area. Additionally, the influence of Young’s modulus and Poisson’s ratio on fracture propagation is very slight. A decrease in the tensile strength of natural fractures leads to more natural fractures being intersected during the process, resulting in increasing the length of the fracture and an improvement in the complexity of the fracture grid.

Relationships between Anxiety, Repetitive Behavior and Parenting Stress: A Comparative Study between Individuals with Autism from Spain and Colombia.

The present study analyzed the association between anxiety, repetitive behavior and parental stress in individuals with autism from Spain (n = 60, mean age = 8.52, SD = 4.41) and Colombia (n = 58, mean age = 10.29, SD = 4.98). Similarly, differences in anxiety, repetitive behavior and parental stress between both countries were analyzed. Outcomes revealed a strong relationship between anxiety and repetitive behavior in both populations. Furthermore, moderate positive associations were observed between anxiety, repetitive behavior and parental stress in the Spanish sample. However, parental stress was found to be moderately and negatively related with anxiety and repetitive behavior in the Colombian sample. Finally, no differences were found in anxiety and repetitive behavior between countries, but differences did emerge for parental stress which was found to be higher in the Colombian sample. In conclusion, differences in parental stress may be due to regional differences in socio-health resources, socio-economics, parenting styles, etc.

Impacts of paternal latitudinal origin on herbivore response strategies in Lythrum salicaria

Plants have evolved different strategies to withstand and respond to herbivore stress. The two main strategies plants employ under herbivore stress are known as tolerance and induced resistance. Tolerance is the ability to maintain high fitness despite experiencing high levels of herbivore damage. While induced resistance typically involves changing the concentrations of internal secondary metabolites as a response to initial herbivory and to prevent further damage. These strategies can lead to fitness differences between populations that vary by latitudinal origin. Previous studies have focused on the occurrence of herbivore response in general, whereas this study will make a direct comparison between response types and their fitness implications. Our study investigates whether eastern North American populations of Lythrum salicaria respond differently to herbivore stress. F1 crosses between L. salicaria individuals with different parental latitudinal ranges were grown in a common garden under two experimental herbivory treatments (pesticide sprayed vs. no pesticide) at the Queen’s University Biological Station. To identify differences in herbivore tolerance, we measured plant growth and development over 13 weeks and quantified herbivore damage, caused by the biocontrol beetle Galerucella calmariensis. A 48-hour feeding assay was then conducted to identify differences in herbivore resistance between populations. This assay provided beetles with a choice between young and old L. salicaria leaves from each experimental treatment. Our preliminary analysis of the feeding assay showed differences in leaf damage between parental lines. The initial analysis also showed that older leaves generally experienced more damage than younger leaves over the course of the 48-hour period. These results indicate population differences in herbivory stress response and differences in stress response effectiveness that varies with plant age. This experiment showed that L. salicaria individuals have varying degrees of herbivore stress response and effectiveness. However, further analysis that includes reproductive outputs and developmental differences will be completed to clearly identify the type of strategies L. salicaria populations with different parental latitudinal origins employ in response to herbivore damage.

Data-driven multiscale geomechanical modeling of unconventional shale gas reservoirs: a case study of Duvernay Formation, Alberta, West Canadian Basin

The Duvernay Formation in Canada is one of the major oil and gas source formations in the Western Canadian Sedimentary Basin, located at its deepest point. While it demonstrates promising development potential, challenges arise in the urgent need for integration of geology and engineering models, as well as in optimizing sweet spots, particularly as infill wells and pads become central operational objectives for the shale gas field. A lack of the geomechanical understanding of shale gas reservoirs presents a significant obstacle in addressing these challenges. To overcome this, we implemented data acquisition and prepared historical models and profiles, resulting in an extended high-resolution geological and reservoir property model with a fine grid system. Subsequently, a 3D full-field multi-scale geomechanical model was constructed for the main district by integrating seismic data (100 m), geological structures (km), routine logs (m), core data (cm), and borehole imaging (0.25 m), following a well-designed workflow. The predicted fracturability index (brittleness) ranges from 0.6 to 0.78, and a lower horizontal stress difference (STDIFF) is anticipated in the target formation, Upper Duvernay_D, making it a favorable candidate for hydraulic fracturing treatment. Post-analysis of the multi-disciplinary models and various data types provides guidelines for establishing a specific big database, which serves as the foundation for production performance analysis and aggregate sweet spot analysis. Fourteen geological and geomechanical candidate parameters are selected for the subsequent sweet spot analysis. This study highlights the effectiveness of multi-scale geomechanical modeling as a tool for the integration of multi-disciplinary data sources, providing a bridge between geological understanding and future field development decisions. The workflows also offer a data-driven framework for selecting parameters for sweet spot analysis and production dynamic analysis.

Effect of bedding planes and property contrast between layers on the propagation mechanism of hydraulic fracture height in shale reservoirs

Bedding planes and property contrast between layers plays an important role in preventing hydraulic fracture height extension in shale reservoirs. However, the intrinsic causes of fracture containment have not been elucidated, and few studies have considered the effects of mixed factors on fracture height extension. Based on the continuum-discontinuum element method, a 3D hydraulic-mechanical coupling model was established to explore the influence mechanism of bedding planes, stress and modulus difference between layers, and mixing factors on fracture height extension in a transversely isotropic shale reservoir. Shear failure usually occurs preferentially when the fracture approaches the bedding plane, and the essential reason for fracture containment is that the shear slip on the bedding plane blunts the fracture tip. The stronger stress barrier formed by the higher minimum principal stress in adjacent formation effectively enables the fracture to terminate at the interlayer interface. The lower modulus in adjacent formation is more prone to rock initiation, but the larger elastic deformation absorbs the fracture tip stress and impedes height propagation. The comprehensive effect of bedding planes and property contrast between layers on fracture propagation is more complex than that of a single factor. When different factors have positive effects on fracture containment, the fracture is easier to terminate at the bedding plane. Otherwise, the dominant factor determines whether the fracture can be captured. No matter what the conditions, the pressure relief in the bedding plane can slow down the propagation rate. The findings can offer theoretical support for predicting fracture height during field fracturing in shale reservoirs.

Effect of stress unloading rate on fine-scale deformation mechanism of rock under high osmotic pressure

To explore the influence of the working face excavation rate on the rock deformation mechanism and seepage characteristics, deformation and seepage tests of sandstone under different loading and unloading stress paths, such as constant axial pressure unloading confining pressure and loading axial pressure unloading confining pressure, were carried out. Particle Flow Code in 3 Dimensions (PFC3D) and Python were used to realize fluid-solid coupling, and numerical simulation calculations were performed along the test path to analyze the influence of the unloading rate on the fine-scale deformation mechanism and permeability characteristics of sandstone, and the relationship between crack type and permeability was obtained. A sandstone fracture mechanics model is established to analyze the stress concentration degree at the end of the branch crack of the test path. The results show that the rate of confining pressure unloading is inversely proportional to the strain. Additionally, permeability correlates with the principal stress difference in an exponential manner. Interestingly, the sensitivity of permeability to stress shows an inverse trend with the unloading rate of confining pressure. Furthermore, there exists a linear relationship between permeability and the number of cracks. During the unloading process, tensile cracks predominate, and the propagation of shear cracks lags behind that of tensile cracks. The proportion of tensile cracks decreases with the increase of the unloading rate when the axial pressure is unchanged but increases when axial pressure is added, resulting in axial compression deformation and expansion deformation along the unloading direction. These research outcomes offer theoretical insights for the prudent selection of mining rates, and they hold significant implications for mitigating water inrush disasters in deep mining operations.

Analysis of near-well hydraulic fracture propagation behavior in inhomogeneous deep-sea hydrate-bearing-sediments

The hydrate reservoirs exhibit significant inhomogeneity due to the presence of various hydrate types, potentially impacting the effectiveness of hydraulic fracturing. The investigation of the relationship between hydraulic fracture extension patterns and pure hydrate blocks for varying conditions is highly valuable. The extended finite element method (XFEM) is applied to reveal the influence mechanism of hydrate heterogeneity on fracture propagation law. First, compared with the results of the fracturing experiments in hydrate-bearing clayey silt sediments, the accuracy of the method is verified. Subsequently, a model for fracturing near-well in deep-sea inhomogeneous hydrate-bearing-sediments is established, containing sedimentary matrix and pure hydrate blocks. The effects of disseminated hydrate saturation, injection rate, horizontal stress difference and the distribution location of pure hydrate blocks on the fracture extension path are investigated. Due to the pure hydrate is much more brittle, most hydraulic fractures, once encountered with it, choose to bypass. If the fracture is unable to bypass the pure hydrate block, the fracture appears to arrest and penetrate. The seafloor sediment matrix is characterized by its loose nature, and a continuous increase in the injection rate may result in the competing development of the fractures in both length and width directions.

Differences in syncytiotrophoblast shear stress and mechanosensing protein expression in fetal growth restriction.

Differences in syncytiotrophoblast shear stress and mechanosensing protein expression in fetal growth restriction.

Hydride induced embrittlement and fracture of non-hardening metals under hydrogen chemical equilibrium

The stress field in the hydride precipitation zone is examined, under conditions of hydrogen chemical equilibrium and constant temperature, in the case of non-hardening metals, by applying slip-line theory. It is proven that the hydride precipitation zone, in any geometry, is a constant stress area. In this area, the principal stresses are equal to the respective principal stresses, before hydride precipitation, minus the difference of hydrostatic stress before and after hydride precipitation. The general relations are applied to the case of a stationary sharp mode-I plane-strain crack and the deviations from Prandtl-field are derived, in the [-π/4, +π/4] sector ahead of the tip, where hydrides precipitate. In this case, the hydride precipitation sector is characterized by a constant hydride volume fraction. In addition, hydride precipitation is associated with the development of elastic sectors along the crack faces and the reduction of the centered fan sectors; the relation between hydride precipitation zone stress trace and the extent of the centered fan sector is presented. The mode-I plane-strain blunted crack is also considered and the deviations from the logarithmic spiral slip-lines is discussed together with the reduction of hydride volume fraction as the blunted crack-tip is approached. A general fracture criterion, based on the strength of hydride platelets, is derived, which indicates that fracture occurs, when a critical hydride precipitation zone stress trace dominates. The criterion is applied, under the condition of a dominant K-field annulus, surrounding the plastic zone, and the estimated threshold stress intensity factor of delayed hydride cracking correlates favorably with experimental measurements.

A damage rock model considering shear failure by modified logistic growth theory

Localized rock failures, like cracks or shear bands, demand specific attention in modeling for solids and structures. This is due to the uncertainty of conventional continuum-based mechanical models when localized inelastic deformation has emerged. In such scenarios, as macroscopic inelastic reactions are primarily influenced by deformation and microstructural alterations within the localized area, internal variables that signify these microstructural changes should be established within this zone. Thus, localized deformation characteristics of rocks are studied here by the preset angle shear experiment. A method based on shear displacement and shear stress differences is proposed to identify the compaction, yielding, and residual points for enhancing the model's effectiveness and minimizing subjective influences. Next, a mechanical model for the localized shear band is depicted as an elasto-plastic model outlining the stress-displacement relation across both sides of the shear band. Incorporating damage theory and an elasto-plastic model, a proposed damage model is introduced to replicate shear stress-displacement responses and localized damage evolution in intact rocks experiencing shear failure. Subsequently, a novel nonlinear mathematical model based on modified logistic growth theory is proposed for depicting the shear band's damage evolution pattern. Thereafter, an innovative damage model is proposed to effectively encompass diverse rock material behaviors, including elasticity, plasticity, and softening behaviors. Ultimately, the effects of the preset angles, temperature, normal stresses and the residual shear strength are carefully discussed. This discovery enhances rock research in the proposed damage model, particularly regarding shear failure mode.

Analysis of Deformation Characteristics and Failure Mechanism of Interbedded Surrounding Rock Tunnels Based on Principal Stress Difference

Analysis of Deformation Characteristics and Failure Mechanism of Interbedded Surrounding Rock Tunnels Based on Principal Stress Difference

Types and Predictors of Acculturative Stress Among Multicultural Adolescents in Middle School

Objectives: This study examines how acculturative stress in multicultural adolescents changes during their middle school years and categorizes groups with similar patterns of change. Additionally, the study explores predictive variables influencing these distinct acculturative stress trajectories and verifies how depression and life satisfaction vary according to different patterns of change.Methods: Leveraging data from the Multicultural Adolescent Panel (MAPS 1) conducted by the Korea Institute for Health and Social Affairs across the fourth to sixth waves, the researchers analyzed a cohort of 1,316 participants, including multicultural adolescents and their parents. Logistic regression analysis and ANOVA were employed to investigate potential disparities in growth mixture modeling and acculturative stress latent classes based on predictive factors.Results: Three latent groups of multicultural adolescents’ acculturative stress were identified: low-retention group, persistent increasing group, persistent decrease group. The logistic regression analysis revealed that gender, bicultural acceptance attitude, Korean-language proficiency, foreign parent’s native-language proficiency, parental acculturative stress, and peer support were significantly associated with latent groups. Additionally, significant differences in depression and life satisfaction during the third grade of middle school were observed according to the types of acculturative stress changes.Conclusion: Our study results indicate the need for various support programs aimed at promoting the psychosocial adaptation of multicultural adolescents. These programs should take into account the characteristics and individual differences in acculturative stress and should be implemented at the family level to facilitate social adaptation.

Traumatic Stress, Psychological Well-being, and Sociodemographic Correlates in High-stress Environments among Healthcare Professionals

Background Healthcare staff provide crucial services to their patients; hence, their well-being is essential to ensure they offer the best services with minimal harm to their health. Aim This study aimed to identify associations of traumatic stress, psychological well-being, and sociodemographic variables to provide insight into the experiences and feelings of healthcare personnel in high-stress settings. Furthermore, we will examine how sociodemographic factors and traumatic stress impact the psychological well-being of high-stress environment healthcare professionals. Objective This research investigated the relationship between traumatic stress, psychological well-being, and sociodemographic factors in high-stress environments among healthcare personnel in different medical units. It was hypothesized that sociodemographic variables and traumatic stress will predict psychological well-being among healthcare workers who work in high-stress environments. Furthermore, there will be differences in traumatic stress and psychological well-being based on sociodemographic variables among healthcare workers working in high-stress environments. will experience high l Methods To accomplish this goal, an online survey including sociodemographic information, standardized questionnaires of Secondary Traumatic Stress Scale, and a Brief Inventory of Thriving were administered to healthcare personnel (N=290) to collect data for sociodemographic characteristics, traumatic stress levels, and psychological well-being. The results were processed by using SPSS. The descriptive statistics measured participants' characteristics, traumatic stress levels, and psychological well-being. The pearson product-moment correlation, regression analysis, and ANOVA were used to measure the relationship and impact of sociodemographic factors, traumatic stress, and psychological well-being. Results A significant inverse relationship between traumatic stress and psychological well-being (r= -0.518, p < 0.05) was reported. Furthermore, multiple regression analysis provided the predictive association of traumatic stress and negative well-being (p<0.05). Additionally, ANOVA was conducted to measure the differences in socio- demographic variables of traumatic stress and the psychological well-being level of healthcare professionals. Conclusion The results of this research could help inform policy decisions and interventions that may improve the psychological well-being of healthcare personnel in high-stress environments. Ethical considerations such as participant privacy protection and addressing potential psychological distress are also discussed.

Attributes of multiple concurrent functional gastrointestinal disorders in female university students in South Korea

ABSTRACT Functional gastrointestinal disorders (FGIDs) are common in young adults, particularly women, who tend to develop multiple FGIDs over time. This study aimed to investigate the prevalence of multiple concurrent FGIDs among female university students and identify differences in dietary habits, academic stress, and quality of life (QOL) based on the number of concurrent FGIDs. This secondary analysis included data from 406 female participants, originally collected through an online survey from two universities in one city in Korea. The online survey was accessible only after participants were verified as students through their online community. Concurrent FGID was present in 25.8 percent (n = 16) of the participants with FGIDs (n = 62), with the most common being irritable bowel syndrome + functional dyspepsia overlap (43.8 percent, 7/16). Participants with multiple concurrent FGIDs consumed fewer grains and vegetables, while significantly more of them consumed instant food, fast food, milk, and tea/coffee. They experienced significantly higher academic stress and lower QOL than those without the disease. Female university students with concurrent FGIDs tend to have unhealthy dietary habits, and concurrent FGIDs negatively affect academic stress and QOL. Therefore, female university students should undergo early-stage screening for FGIDs, and a comprehensive program should address their dietary habits and stress-coping skills.

Differences in human thermal and physiological responses under corridor and greenway in summer in guangzhou

As urbanization and the heat island effect intensify, comfortable and healthy outdoor micro-environments are particularly important for sustainable urban development, encouraging more outdoor activities. Fewer studies have focused on differences in thermal comfort and thermal physiology of users in potential outdoor open spaces. Therefore, this study aims to examine the differences in thermal comfort and thermal stress among users of common outdoor open shady spaces, contributing towards a better thermal experience and mitigating heat stress. In this study, a field investigation of corridors and greenways was conducted on a campus in Guangzhou in the summer based on subjective questionnaires and objective measurements of thermal environment, and thermal physiological parameters. The results found that people were more likely to experience good thermal comfort and weaker intensity of thermal stress in corridors with significant differences in physiological responses. Furthermore, the upper limit comfort temperatures of the corridor and greenway were 34.0 and 33.4 °C, respectively. In addition, it can be concluded that the corridor was a more optimal space for outdoor shade before evening, whereas the greenway was more optimal in the evening in summer. The findings determine the thermal benchmarks for typical outdoor shady spaces in hot and humid regions in summer, which can help designers create comfortable outdoor public spaces that improve thermal comfort and people's health.

The Exponential Shapeshifting Response of N-Vinylcaprolactam Hydrogel Bilayers Due to Temperature Change for Potential Minimally Invasive Surgery.

Poly (N-vinylcaprolactam) (PNVCL) and poly (N-isopropylacrylamide) (PNIPAm) are two popular negatively temperature-responsive hydrogels, due to their biocompatibility, softness, hydrophilicity, superabsorbency, viscoelasticity, and near-physiological lower critical solution temperature (LCST). These characteristics make them ideal for biomedical applications. When combined with other materials, hydrogel expansion induces the morphing of the assembly due to internal stress differences. Our recent developments in NVCL hydrogel, enhanced by nanoclay incorporation, have driven us to the creation of a bilayer structure to study its shapeshifting response across various temperatures. This study focused on the bending behaviour of bilayer samples composed of an active hydrogel layer and a passive non-swellable layer. Using photopolymerisation, circular discs and rectangular bilayer samples of varying sizes were fabricated. Homogeneous circular samples demonstrated that hydrogel density increased proportionally with temperature, with the swelling ratio exhibiting two distinct rates of change below and above its LCST. In bilayer samples, the volume of the passive layer influenced bending, and its optimal volume was identified. The investigation revealed that geometry affected the overall bending effect due to changes in the passive layer stiffness. Lastly, a temperature-responsive gripper capable of picking up objects several times its own weight was demonstrated, highlighting the potential of NVCL hydrogels as bioactuators for minimally invasive surgery.

Rapid particle generation from an STL file and related issues in the application of material point methods to complex objects

In this paper, we focus on three issues related to applications of material point methods (MPMs) to objects with complex geometries. They are material point generation, compatibility of material points with a mesh, and sensitivity to mesh orientation. An efficient method of generating material points from a stereolithography (STL) file is introduced. This material point generation method is independent of the mesh used in MPM calculations. The compatibility between the material points and the mesh is then studied. We also show that the original MPM and the dual domain material point (DDMP) method are sensitive to mesh orientation. These issues are related to the calculation of the internal force and are concerns of the MPMs. They become more prominent when MPMs are applied to complex geometries. Our numerical results show that the recently developed local stress difference (LSD) algorithm (Perez et al. in J Comp Phys 498:112681, 2024) can be used to effectively address them.