Effect Of Gradient Research Articles

More is not always better: revealing the impact of cumulative risk on health-promoting behaviors among miners and the mediating role of health beliefs

Objective Health-promoting behaviors carry substantial significance for miners’ overall health and well-being. This study aimed to examine the association between cumulative risk (CR) and miners’ health-promoting behaviors and test the mediating role of health beliefs in this relationship. Methods Data were collected from a sequential survey conducted among 712 frontline miners (M age=41.7 ± 10.1 years) in China. The survey entailed online questionnaire measurements at three distinct time points, each spaced two weeks apart. This study utilized the conceptual model of health-promoting behaviors, the CR model, and structural equation modeling in the analysis of relationships. Results CR was negatively related to health-promoting behaviors, with a negative acceleration effect. CR was positively associated with perceived threat in a gradient effect, while negatively associated with perceived benefits in a gradient effect. Furthermore, CR was negatively related to self-efficacy, following a negative acceleration effect. Perceived threat, perceived benefits, and self-efficacy emerged as significant mediators in the relationship between CR and health-promoting behaviors. Conclusion This study highlights the critical role of considering both CR and health beliefs in shaping miners’ health-promoting behaviors. Understanding these dynamics is pivotal for developing interventions to enhance miners’ health and well-being.

Predicting fatigue failure in five‐axis machined ball‐end milled components through FKM local stress approach

AbstractComponents created with five‐axis machining show a multi‐scale surface character due to cusps created on the surface and feed and tool marks within the cusps. Therefore, it becomes difficult to incorporate the effects of surface character on fatigue life for such components. In this work, an Forschungskuratorium Maschinenbau (FKM) guideline is adapted to develop a fatigue prediction model which considers cusps as notches and marks within the cusps as surface roughness (characterized by parameter R10z). The assessment uses stresses obtained from an finite element analysis model to predict the fatigue life of components whilst considering stress concentration, stress gradient, mean stress, and surface roughness effects. When cusps are regarded as surface roughness within the conventional FKM approach, fatigue life is considerably underestimated. In comparison, fatigue life predictions that take into consideration the roughness within cusps and treat cusps as stress‐raising notches are closer to experimental life.

Fluid-Solid Interaction Analysis for Developing In-Situ Strain and Flow Sensors for Prosthetic Valve Monitoring.

Transcatheter aortic valve implantation (TAVI) was initially developed for adult patients, but there is a growing interest to expand this procedure to younger individuals with longer life expectancies. However, the gradual degradation of biological valve leaflets in transcatheter heart valves (THV) presents significant challenges for this extension. This study aimed to establish a multiphysics computational framework to analyze structural and flow measurements of TAVI and evaluate the integration of optical fiber and photoplethysmography (PPG) sensors for monitoring valve function. A two-way fluid-solid interaction (FSI) analysis was performed on an idealized aortic vessel before and after the virtual deployment of the SAPIEN 3 Ultra (S3) THV. Subsequently, an analytical analysis was conducted to estimate the PPG signal using computational flow predictions and to analyze the effect of different pressure gradients and distances between PPG sensors. Circumferential strain estimates from the embedded optical fiber in the FSI model were highest in the sinus of Valsalva; however, the optimal fiber positioning was found to be distal to the sino-tubular junction to minimize bending effects. The findings also demonstrated that positioning PPG sensors both upstream and downstream of the bioprosthesis can be used to effectively assess the pressure gradient across the valve. We concluded that computational modeling allows sensor design to quantify vessel wall strain and pressure gradients across valve leaflets, with the ultimate goal of developing low-cost monitoring systems for detecting valve deterioration.

Scale Differences and Gradient Effects of Local Climate Zone Spatial Pattern on Urban Heat Island Impact—A Case in Guangzhou’s Core Area

With the continuous development of cities, the surface urban heat island intensity (SUHII) is increasing, leading to the deterioration of the urban thermal environment, increasing energy consumption, and endangering the health of urban residents. Understanding the spatio-temporal scale difference and gradient effect of urban spatial patterns on the impact of SUHII is crucial for improving the climate resilience of cities and promoting sustainable urban development. This paper investigated the characteristics of SUHII changes at different time periods based on local climate zones (LCZs) and downscaled land surface temperature (LST) data. Meanwhile, landscape pattern indicators and the multiscale geographically weighted regression (MGWR) model were utilized to analyze the impacts of urban spatial patterns on SUHII at multiple spatial–temporal scales. The results indicated that the SUHII of each LCZ type exhibited diverse patterns in different time periods. High SUHII occurred in summer daytime and autumn nighttime. Compact and high-rise buildings (LCZ1/2/4) showed markedly higher SUHII during the daytime or nighttime, except for heavy industry. The extent of influence and the dominant factors of LCZ spatial patterns on SUHII exhibit obvious scale differences and gradient effects. At the regional scale, highly regular and compacted built-up areas tended to increase SUHII, while single and continuously distributed built-up areas had a greater impact on increasing SUHII. At the local scale, the impact of the PLAND (1/2/4/5/10) on SUHII exhibited a trend of diminishing from urban to suburban areas. In urban areas, the PLAND of LCZ 1, LCZ 2, and LCZ4 was the major factor affecting the increase in SUHII, whereas, in suburban areas, the PLAND of LCZ 2 and LCZ 10 was the major influencing factor on SUHII. The results can provide a scientific reference for mitigating urban heat island effects and constructing an ecologically ‘designed’ city.

WITHDRAWN: Examining the Effects of Land Use, Salinity Gradient, and Water Pollution on Greenhouse Gas Emissions in Urbanized Estuaries

Estuaries are significant contributors to greenhouse gases (GHGs) in waterways. However, the effects of human activities and ecological variables on GHG emissions in estuaries remain poorly understood. This study examines the patterns and causes of GHG emissions in the Scheldt Estuary, focusing on the roles of salinity, water contamination, and land use. The findings indicate that salinity negatively impacts the release of carbon dioxide (CO2) and nitrous oxide (N2O), likely due to reduced salt levels and cleaner water upstream. Water contamination's influence on GHG emissions was more pronounced in cleaner, upriver sites compared to saltier downstream locations. Specifically, CO2 emissions quadrupled, and N2O emissions tripled as water conditions worsened from healthy (near the mouth, bordered by agricultural land) to polluted (farther downstream, bordered by urban areas). Methane (CH4) emissions were significantly higher in aquatic locations than in salty sites. The reduced impact of contamination from downstream to the river mouth may be due to increasing population density. Urban sites emitted about twice as much CO2 and N2O as those in natural and industrial areas. Machine learning analysis also showed that fertilizers and organic enrichment, along with salinity, significantly increased GHG emissions. These results highlight the importance of understanding the interplay of salinity, water contamination, and land use in influencing GHG emissions in coastal ecosystems.

Reconstructing Prospective Intergenerational Educational Mobility in 12 Countries

In this article, we reconstruct prospective intergenerational educational mobility and explore fertility's role in this process for women born between 1925 and 1950 in 12 European countries. We do so by combining high-quality retrospective data (Generations and Gender Survey) and low-requirement prospective datasets using an inferential method developed and advanced in prior research. Our analysis shows that the negative educational fertility gradient partly compensates for the inequality in prospective mobility rates between lower and higher educated women and is most pronounced in high-inequality contexts. However, fertility's role is small and declining and thus does not account for much of the differences in mobility rates between countries. We also explore the relative importance of sibship size effects in mediating the effect of fertility gradient, finding it negligible. Finally, we explore the correspondence between prospective and retrospective estimates in the reconstruction of prospective mobility rates and suggest why the former, when available, must be preferred.

Assessment of selected ionospheric mapping functions using SF-PPP on different solar activities

In single-frequency precise point positioning (SF-PPP), the ionospheric delays provided by global ionosphere maps (GIMs) are in the vertical direction. Therefore, an ionospheric mapping function is applied to convert the vertical direction to the slant one. However, the performance of mapping functions (MF) applied in SF-PPP under different solar activities is unknown. Meanwhile, understanding their performance can help us better improve the accuracy of the ionospheric mapping function. For this purpose, three traditional ionospheric mapping functions, such as the standard single-layer model mapping function (SLM MF), the modified single-layer model mapping function (MSLM MF), and the Klobuchar MF, are evaluated. Additionally, the mapping function named SGG MF, which considers the effect of ionospheric gradients, is also assessed. The positioning results indicate that the SGG MF has an improvement of (50.3 %, 37.3 %), (31.7 %, 23.4 %), and (16.8 %, 13.3 %) compared with Klobuchar MF, SLM MF, and MSLM MF during the year (2014, 2021), respectively. The mean positioning errors of SLM MF, MSLM MF, and SGG MF are about (0.20 m, 0.05 m), (0.25 m, 0.10 m), and (0.30 m, 0.10 m) smaller than that of Klobuchar MF over high-/mid- latitude during the year (2014, 2021), while the values are (0.25 m, 0.20 m), (0.40 m, 0.35 m), and (0.55 m, 0.50 m) over low-latitude region. Furthermore, the correlation coefficients between positioning results and solar activities are (0.114, 0.354), (0.058, 0.324), (0.098, 0.295), and (0.235, 0.271) for Klobucahr MF, SLM MF, MSLM MF, and SGG MF during corresponding year.

Improved Design Method for Hypersonic Intakes Using Pressure-Corrected Osculating Axisymmetric Flows Method

The efficient design of air intake is crucial for high-speed airbreathing propulsion systems. This paper presents a novel design method that integrates the recently introduced internal conical flow M (ICFM) basic flowfield (Musa et al., “New Parent Flowfield for Streamline-Traced Intakes,” AIAA Journal, Vol. 61, No. 7, 2023, pp. 2906–2921) with the pressure-corrected osculating axisymmetric flows and streamline tracing techniques. The new design method takes into account the effects of lateral pressure gradients by incorporating pressure corrections into the original design method using crossflow velocity information from the ICFM flowfield. Additionally, new entrance and throat profiles are introduced for designing two hypersonic internal waverider intakes with shape transition. One intake is designed using the new method, and the other using the original method. Viscous simulations have been performed at design (i.e., Mach 6.0) and off-design (i.e., Mach 4.0 and 3.5) conditions. The results indicate that the pressure-corrected intake exhibits superior performance in terms of total pressure recovery and reduced flow distortion. This reveals that the new design method can achieve a smooth shape and efficient aerodynamic transitions between the intake entrance and throat. The new entrance and throat profiles realized better performance than the typical ones. The startability analysis reveals that the Van Wie curve controls the considered intakes. Thus, combining the pressure-corrected osculating axisymmetric flows with the ICFM flowfield enhances the performance of hypersonic intakes, making this approach a promising avenue for future hypersonic vehicles.

Improving the energy efficiency and riding comfort of high-speed trains across slopes by the optimized suspension control

As the link between cities, the high-speed train (HST) not only effectively enhances national and regional accessibility, but also induces much energy consumption. On the other hand, passengers have a higher requirement for riding comfort of HST than before. Considering the impacts of slope gradient on energy consumption and vertical carbody acceleration, this paper optimizes the scale factor of the damper controller depending on the running condition to juggle the energy efficiency and riding comfort when HST is across slopes. Firstly, the multibody dynamics simulation model of HST is established to evaluate the energy consumed by motion resistances and carbody vibrations. Then the Skyhook control strategy is applied to the secondary vertical damper of the vehicle model. The effects of vehicle speed, slope gradient, and scale factor of the Skyhook controller on energy saving and vertical carbody acceleration of HST are investigated. Based on the simulation results, the Gaussian process regression model is established to predict the vehicle performance and describe the bi-objective optimization problem. It is demonstrated that the optimized Skyhook control system can at most save energy consumed by motion resistances by 8.52 % or reduce vertical carbody acceleration by 37.14 % without sacrificing the other target. Finally, a comprehensive feasibility and economic analysis of the proposed control system is carried out to promote its practical implementation.

On the Cauchy problem of 2D compressible fluid model with the horizontal thermal gradient effect

This article mainly investigates the existence of local strong solution to the Cauchy problem of the 2D compressible fluid model with the horizontal thermal gradient effect. By using delicate weighted energy estimates, the existence of a local strong solution is obtained with the initial density and the initial temperature decay not too slowly at infinity.

Exploring the spatial and temporal evolution of landscape ecological risks under tourism disturbance: A case study of the Min River Basin, China

Numerous ecological issues will arise from the expansion of tourism-related infrastructure and activities, potentially having a major effect on the ecosystem. However, its impact on landscape ecological risk (LER) is still poorly understood. Taking the Min River Basin as an example, an improved LER evaluation method was adopted in this study, which uses landscape disturbance based on landscape pattern and incorporates ecosystem services (ESs) represent landscape vulnerability. On this basis, the impacts of tourism-related infrastructure and activities on ecology environment were comprehensively considered, and buffer zone analysis, scenario analysis, response index (RI), and the bivariate Moran’s I approaches were applied to identify the spatio-temporal evolution characteristics of LER under tourism interference. The results show that: (1) The Min River Basin’s LER from 2000 to 2020 demonstrates a trend of gradually decreased, primarily in the middle and low risk areas. Most of the areas where scenic spots and roads are located are high risk areas, suggesting that tourism disturbances negatively affect LER. (2) There is a spatial gradient effect associated with the influence of tourism infrastructure on LER, and the impact degree varies throughout different tourism infrastructure. (3) The difference of scenic spots causes diverse degrees of LER. Through comparison, it is found that the LER of high-grade and cultural scenic spots is larger than that of low-grade and natural scenic spots. The quantitative results of the RI show that the values inside the influence zones of scenic spots and roads are 5 times and 9 times more than the values outside, respectively. This suggests that tourism infrastructure increases LER. (4)There is a spatial correlation between LER and tourism activities intensity. In order to offer a scientific reference for balancing local tourism development and ecological environmental conservation, this study develops a more thorough and rigorous research framework of the impact of tourism on LER.

Lower-order mechanism-based strain gradient plastic model considering stress gradient effect

Lower-order mechanism-based strain gradient plastic model considering stress gradient effect

Investigation of temperature gradient effects and effective thermal inertia during adiabatic decomposition of substances with varying exothermic characteristics

To further study adiabatic parameters distortion, the adiabatic decomposition of 2,4-DNT, 20%DTBP, and 45%Glucose was systematically analyzed using thermal analysis calorimetry and numerical simulation methods. The study revealed the variation laws and influence mechanisms of the temperature gradient effects and thermal inertia in adiabatic systems. A numerical model for decomposition in a closed adiabatic system was developed by integrating the apparent kinetics into the CFD code. The results show that the temperature gradient effects during adiabatic decomposition initially increase and then decrease until reaching zero. The temperature gradient effects become more pronounced as the exothermic characteristics of substances increase. They are the most significant at the peak self-heating rate, with gradients of 182.4 °C·cm−1, 21.6 °C·cm−1, and 0.78 °C·cm−1, respectively. Specific data segments for adiabatic analysis should maintain α values below 0.138 for 2,4-DNT, 0.484 for 20%DTBP, and should utilize complete 100 % adiabatic data for 45%Glucose, aiming to mitigate potential distortion in adiabatic parameters. Furthermore, Фeff varies with the reaction, initially increasing and then decreasing in deviation from the theoretical value, with peak deviations of 60 %, 20 %, and 0.3 % for three substances, respectively. These findings lay the foundation for further optimizing the temperature gradient effects and establishing a dynamic Фeff correction model.

Selective impacts of subsistence hunting on mammal communities in Manu National Park, Peru

AbstractResearch on impacts of subsistence hunting on habitat use and species communities of forest wildlife is limited. Subsistence hunting of mammals in one of the world's most biodiverse region, Manu National Park, Peru, is considered sustainable, but this is based on sparse evidence. We analyzed change in species relative abundance and functional composition of mammal communities, including non‐hunted species along a hunting pressure gradient. We used camera trap data and tested for confounding effects of environmental and disturbance gradients (distances to rivers, lakes, settlements, and trails; NDVI at survey point). We found that sites with no hunting or at further distances from settlements harbor relatively more species with a larger body mass, long generation lengths, and small litters (primarily carnivores: 36% at non‐hunted site vs. 13%–29% at hunted sites), indicating selective impacts of hunting pressure on mammal communities. However, all carnivore species still occurred at all sites. Species with a smaller body mass, short generation lengths, and large litters were more prevalent at the hunted sites (mostly rodents: 23%–31% at hunted sites vs. 20% at non‐hunted site). Surprisingly, large herbivores appeared unaffected by hunting despite being one of the most hunted mammals in Manu (25% at non‐hunted site vs. 23%–27% at hunted sites). Our findings suggest that current hunting pressure is largely sustainable with only local depletion of a few sensitive species. Habitat is more important for some species than hunting pressure (e.g., distance to lake), further emphasizing the importance of local forest management.

Simulation Study on Quasi-Static Compressive Mechanical Properties of Honeycomb Structures with Negative Poisson’s Ratio

Negative Poisson’s ratio structures are widely used in military, aerospace, vehicles, air-dropped packages, and medical devices due to their high strength, stiffness, energy absorption, and impact resistance, but their mechanical properties are significantly affected by geometric parameters. In this paper, for the compression energy-absorbing mechanism of the re-entrant hexagonal honeycomb structure, numerical simulations are used to study the effects of wall thickness and angular gradient on its compression failure mode and energy-absorbing performance. The results show that the wall thickness has little impact on the compression failure mode, while the angular gradient has a significant impact on the compression failure mode. The wall thickness has a significant effect on the energy-absorbing performance, and the larger the wall thickness is, the better the energy-absorbing property is; the energy-absorbing performance of the symmetric negative gradient structure is significantly better than that of the other three angular gradients, and all the four kinds of angular gradient structures have better energy-absorbing performance than that of the conventional re-entrant honeycomb. The results obtained provide a reference for improving the energy absorption performance of negative Poisson’s ratio honeycomb structures under quasi-static compression.

Land use function changes and trade-offs/synergies across topographic gradients in the Three Gorges Reservoir Area, China

Driven by the natural environment and socio-economic development, land use functions (LUFs) experience dynamics and trade-offs/synergies across topographic gradients. This global pattern has a significant impact to the United Nations Sustainable Development Goals. However, there is no direct study investigated the effects of topographical gradients on LUFs trade-offs. Thus, the present study applied an object-based topographical gradient analysis, multi-criteria evaluation, and correlation analysis to evaluate the topographic gradient differentiation in the spatial patterns and characteristic changes in LUFs and their trade-offs/synergies in the Middle Reaches of the Three Gorges Reserve Area (MRTGRA) in China. The findings revealed that: (1) Ecological function (EF) was dominant in the high topographic gradients, whereas production function (PF) and living function (LF) were widely distributed in the low topographic gradients. (2) The changes in LUFs across the topographic gradients experienced a transformation process. Between 1990 and 2000, PF remarkably intensified whereas EF consistently declined across all gradient levels, exhibiting a homogenous LUF change trend across the topographic gradient. Conversely, from 2000 to 2020, PF and LF showed a notable increase at lower topographic gradients, while EF significantly increased at higher gradients, indicating a heterogeneous LUF change trend across the topographic gradient. (3) Trade-offs dominated the relationships between PF and LF, and LF and EF, with decreasing trade-offs between PF and LF as the topographic gradient increases, and weak trade-offs between LF and EF on medium topographic gradients. Similarly, synergies predominantly observed between PF and LF, with a prominent trade-off between PF and EF in high topographic gradients. The findings of present study developed critical considerations for territorial spatial planning, management, and ecological restoration efforts in the MRTGRA and similar hilly and mountainous areas globally.

Exact solutions for thermally induced electromechanical fields of PN junctions in centrosymmetric semiconductors

PN junctions play important roles in semiconductor devices. Flexoelectricity, an electromechanical coupling between strain gradient and electric polarization, has non-negligible contributions in nano-devices. The thermoflexoelectric effect is a phenomenon in which temperature gradients generate inhomogeneous strains and further induce flexoelectric polarizations. Therefore, temperature gradients can affect carrier transport in PN junctions through the thermoflexoelectric effect. In this paper, a one-dimensional model of the PN junction under a uniform temperature change is established. Exact solutions for the electromechanical fields in the PN junction are obtained for the first time. The effects of the temperature gradient, doping level, and flexoelectric coefficient on the electromechanical behaviors of the PN junction are numerically analyzed. The results indicate that carrier concentrations in the p and n regions are sensitive to temperature gradients because of the screening effect of the mobile charge on the flexoelectric polarization induced by the temperature gradient. Meanwhile, the flexoelectric field and the initial built-in electric field in the depletion region jointly determine the magnitude of the potential barrier, and thus, the temperature-gradient-induced flexoelectric field can tune the switching characteristics of the PN junction. This study provides a theoretical basis for the tuning of the electromechanical behavior of the PN junction by thermally induced flexoelectric fields.

The effect of stress gradient on the formation of topologically close packed phases in a Ni-based single crystal superalloy at 1050 °C

The formation of topologically close packed (TCP) phases is detrimental to the mechanical properties of Ni-based single crystal (SX) superalloys, which are used in harsh environments with high temperature and gradient stress caused by centrifugal force during service. In order to study the precipitation behavior of TCP phases in coupling with temperature and stress gradient, a third generation Ni-based SX superalloy is selected to conduct force holding experiments at 1050 °C for 8 hours. Stress gradient can be realized under constant load by designing tensile samples with cross-sectional area continuously changed. The results indicate that the area fraction of TCP phases varies at different positions of the sample, where the effective tensile stress is different. The area fraction of TCP phases decreases at the thinner region of the sample, which means that the amount of TCP phases decreases as applied stress increases. At the thinnest position, where the stress is estimated to be 400 MPa, almost no TCP was observed. The inhibition of stress on the formation of TCP phase may be due to the reduction of Re concentration in the γ matrix, because of the segregation of Re at γ/γ′ phase interfacial dislocation cores and the dissolving of γ′ phase.

Stress–diffusion coupling. Application to interstitial diffusion

A numerical study of the stress–diffusion coupling theory based on the Cahn–Larché method is presented in the case of interstitial diffusion. Indeed, the interaction between diffusion and stress fields has been widely studied in the past. Most of the studies focused on the effect of chemical stress due to mass transport on diffusion. The majority of the studies have been focusing on the coupling between external mechanical and chemical stresses with diffusion. In this study, the effect of stress/strain on mobility and stress gradient mobility and driving forces are presented, based on the model of Voorhees and Larché. The analytical solutions are detailed, from general equations (interstitial diffusion, elastic material) to a macroscopic model (interstitial diffusion, isotropic elastic material, infinite dilute solution, 2D axisymmetric). Numerical simulations for different samples thickness and β parameter helped to better understand and then experimentally identify the prevailing effect of stress on mobility or diffusion driving forces. These studies demonstrated the impact of constant compressive and tensile stress on diffusion kinetics through the mobility term of the equation, as well as the effects of negative and positive stress gradients via the Nernstian term. The results show that constant compressive stress and negative stress gradient hinder the diffusion. On the contrary, tensile stress and positive stress gradient promote the diffusion. This work also demonstrates the importance of coupling between mobility and Nernstian effect on the diffusion promotion.

Effect of temperature gradient on the chemical structure and physical morphology of polyacrylonitrile fibers during thermal stabilization process

The thermal stabilization process is a crucial stage for microstructure transformation and quality of carbon fibers, which is determined by the stabilization temperature gradient. In this work, the effect of the temperature gradient on the evolution of both chemical structures and physical morphology of polyacrylonitrile (PAN) fibers at multistage of thermal stabilization process was investigated. Combined with functional groups, oxygen element content, and aromatization index, increasing temperature reasonably shifted oxidation and cyclization reaction into early stage and the corresponding samples possessed relatively large degree of cyclization. It was worth noting that high stabilization temperature gradient could accelerate the formation of the conjugated structures at early stage and facilitate the cyclization reaction in the stabilized fibers. As for morphologies, there were aligned microfibrils and transvers lamellae in stabilized fibers. Their radial structure difference increased firstly and then decreased in the later stage. The tensile strength and tensile modulus decreased during the thermal stabilization process. Moreover, increasing temperature resulted in reduction of tensile strength and tensile modulus, which was mainly resulted by the high degree of cyclization instead of structural defects. These results guide the design and optimization of temperature program and adjusting the processing parameters for all commercially PAN fibers without any additional conditions.