Search Results (3,287)

In this article, thermophysical modeling of boiling flows in the motive nozzle is carried out for a liquid–vapor jet apparatus (LVJA). Existing thermophysical models make it possible to calculate nozzles, which, in their shape, are close to Laval nozzles. They also allow for determining the position of the outlet cross-sectional area of the nozzle, where the flow separation from the channel walls occurs. However, these models do not allow for profiling the nozzle’s supersonic part, which does not make it possible to ensure the maximum efficiency of the vaporization process. Therefore, in the presented article, the available thermophysical model was improved significantly, which made it possible to obtain the profile of the supersonic part of the nozzle. As a result, a geometric shape that ensures the highest efficiency of the outflow process can be chosen for the primary flow at specified initial and final thermodynamic parameters. According to the calculation results and the proposed methodology, parameters were distributed along the nozzle for the primary flow. Also, efficiency indicators of the outflow of the boiling liquid underheated to saturation were achieved for the different geometric shapes. Mathematical modeling of the operating process in the motive nozzle using ANSYS CFX 2004 R1 (ANSYS, Inc., Canonsburg, PA, USA) was performed to prove the reliability of the results. Also, a comparative analysis of the obtained calculation and simulation results for nozzles with a profiled supersonic part and straight walls was carried out. To assess the expediency of profiling the supersonic part of the nozzle for the primary flow at the LVJA, a comparison of analytical modeling and numerical simulation results with the experimental studies was carried out for nozzles with straight walls. Finally, the velocity ratios of nozzles with profiled supersonic parts and straight walls were obtained. This allowed for rational choosing of the nozzle shape to ensure the highest vaporization efficiency. Full article

We analyze the communication link of an LEO satellite considering interference sources moving along various parabola-curved paths. In this situation, the location of the ground station, airborne interference source paths, and the satellite’s trajectory were expressed in the East-North-Up (ENU) coordinate system. The airborne interference source path is designed using a parabola equation with a directrix parallel to the satellite’s trajectory to analyze the interference situation for more diverse interference source paths, rather than using a straight path. To investigate critical interference situations where the J/S ratio is maintained above −20 dB with a small deviation during the communication time, we investigate interference situations by changing the parameters of the interference source path. The genetic algorithm (GA) is used to easily find an airborne interference source path that maintains the J/S ratio above −20 dB with a small deviation. A cost function for the GA is then defined as the average difference between the J/S ratio and the reference value (−10 dB and −20 dB) during the communication time. The optimum parameters of the interference source path are determined at a minimum cost in the GA. These results demonstrate that more significant interference situations for the communication link can be easily found by using parabola-curved paths and the GA. As a result, previous studies investigated the basic tendency of the J/S ratio using straight paths. However, this study provides a database for operating an anti-jamming system based on the obtained optimized path. Full article

This study evaluates the performance of biofuels created from triple blends of fossil diesel, sunflower or castor oil (SVOs), and 2-Ethylhexyl Nitrate (EHN), a low-viscosity, high-cetane (LVHC) solvent. EHN reduces the viscosity of SVOs to enable their use in conventional diesel engines without compromising fuel properties. The results show that the power output from these blends is similar to or greater than that of fossil diesel, with comparable fuel consumption. Furthermore, the blends significantly reduce emissions of carbon monoxide (CO) and soot, though NOx emissions are slightly higher due to the nitrogen content in EHN. However, NOx levels remain within permissible limits. The substitution of fossil diesel could be further enhanced if EHN were produced using green hydrogen and lignocellulosic biomass, making it a renewable and sustainable biofuel component. These findings support the potential of EHN/SVO biofuel blends to replace a significant portion of fossil diesel in conventional diesel engines while maintaining performance and reducing harmful emissions, except for a slight increase in NOx. Full article

This paper is devoted to the study of stationary trajectories of free particles. From a classical point of view, this appears to be an almost trivial problem: Free particles should follow straight lines as predicted by Newton’s first law, and straight lines are indeed the stationary trajectories of the standard action integrals in the classical theory. In the following, however, a general relativistic approach is studied, and in this situation it is much less evident what action integral should be used. As it turns out, using the traditional Einstein–Hilbert principle gives us stationary states very much in line with the classical theory. But it is suggested that a different action principle, and in fact one which is closer to quantum mechanics, gives stationary states with a much richer structure: Even if these states in a sense can represent particles which obey the first law, they are also inherently rotating. Although we may still be far from understanding how general relativity and quantum mechanics should be united, this may give an interesting clue to why rotation (or rather spin, which is a different but related concept) seems to be the natural state of motion for elementary particles. Full article

The static aeroelastic characteristics of the distributed propulsion wing (DPW) were studied using the CFD/CSD loose coupling method in this study. The momentum source method of the Reynolds-averaged Navier–Stokes equation based on the k-ω SST turbulence model solution was used as the CFD solution module. The upper and lower surfaces of the DPW were established using the cubic B-spline basis function method, and the surfaces of the inlet and outlet were established using the fourth-order Bezier curve. Finally, a three-dimensional parametric model of the DPW was established. A structural finite-element model of the DPW was established, a multipoint array method program based on the three-dimensional radial basis function (RBF) was written as a data exchange module to realize the aerodynamic and structural data exchange of the DPW’s static aeroelastic analysis process, and, finally, an aeroelastic analysis of the DPW was achieved. The results show that the convergence rate of the CFD/CSD loosely coupled method is fast, and the structural static aeroelastic deformation is mainly manifested as bending deformation and positive torsion deformation, which are typical static aeroelastic phenomena of the straight wing. Under the influence of static aeroelastic deformation, the increase in the lift characteristics of the DPW is mainly caused by the slipstream region of the lower surface and the non-slipstream region of the upper and lower surface. Meanwhile, the increase in its nose-up moment and the increase in the longitudinal static stability margin may have an impact on the longitudinal stability of the UAV. To meet the requirements of engineering applications, a rapid simulation method of equivalent airfoil, which can be applied to commercial software for analysis, was developed, and the effectiveness of the method was verified via comparison with the CFD/CSD loose coupling method. On this basis, the static aeroelastic characteristics of the UAV with DPWs were studied. The research results reveal the static aeroelastic characteristics of the DPW, which hold some significance for engineering guidance for this kind of aircraft. Full article

A graphical clustering approach was used to objectively identify prevalent surface circulation patterns in the East/Japan Sea (EJS). By applying a spectral clustering algorithm, three distinct patterns in the East Korea Warm Current (EKWC) and its extension were identified from daily maps of reanalyzed sea surface heights spanning the past 30 years. The results are consistent with previous studies that used manual classification of the EKWC’s Lagrangian trajectories, highlighting the effectiveness of spectral clustering in accurately characterizing the surface circulation states in the EJS. Notably, the recent dominance of northern paths, as opposed to routes along Japan’s coastline or those departing from Korea’s east coast further south, has prompted focused re-clustering of the northern paths according to their waviness. This re-clustering, with additional emphasis on path length, distinctly categorized two patterns: straight paths (SPs) and large meanders (LMs). Notably, SPs have become more prevalent in the most recent years, while LMs have diminished. An autoregression analysis reveals that seasonal anomalies in the cluster frequency in spring tend to persist through to the following autumn. The frequency anomalies in the SPs correlate strongly with the development of pronounced anomalies in the gradient of meridional sea surface height and negative anomalies in the surface wind stress curl in the preceding cold seasons. This relationship explains the observed correlation between a negative Arctic Oscillation during the preceding winter and the increased frequency of SPs in the subsequent spring. The rapid increase in the occurrence of SPs indicates that a reduction in LMs limits the mixing of cold, fresh, northern waters with warm, saline, southern waters, thereby reinforcing the presence of SPs due to a strengthened gradient of meridional surface height and contributing to a slowdown in the regional overturning circulation. Full article

Gear modification, which involves the removal of material from the theoretical surface to improve the contact characteristics of the gear face, is widely applied in gear vibration reduction and noise optimization design. This paper establishes a dynamic model of the straight bevel gear (SBG) transmission system to accurately and efficiently evaluate the effects of different modification strategies on the vibrational characteristics of SBGs. Initially, the time-varying meshing stiffness (TVMS) of standard SBGs was calculated, and methods such as the slicing method and deformation coordination equations were used to calculate the TVMS under tooth profile modification (TPM), Lead crown relief (LCR), and comprehensive modification (CM), which were then validated against finite element method (FEM) calculations. Subsequently, taking into account the impact of time-varying meshing point vectors and the degree of contact overlap, a finite element node dynamic model of the SBG transmission system was established. Finally, by comparing the dynamic characteristics under different modification conditions, the study further elucidates that selecting the appropriate modification method and amount according to different service scenarios is an effective means to suppress gear transmission vibration. This research provides a theoretical basis for the design of gear modification and vibration control for SBGs. Full article

The microstructure and impact toughness of a steel material subjected to multi-layer and multi-pass welding with varying secondary peak temperatures were investigated using welding thermal simulation. The detailed microstructures and fracture morphologies were examined by SEM, TEM, and EBSD. When the secondary peak temperature reaches 650 °C, the microstructure resembles that of a primary thermal cycle at 1300 °C, characterized by coarse grains and straight grain boundaries. As the temperature increases to 750 °C, chain-like structures of bulky M/A (martensite/austenite) constituents form at grain boundaries, widening them significantly. At 850 °C, grain boundaries become discontinuous, and large bulky M/A constituents disappear. At 1000 °C, smaller austenitic grains form granular bainite during cooling. However, at 1200 °C, grain coarsening occurs due to the significant increase in peak temperature, accompanied by a lath martensite structure at higher cooling rates. In terms of toughness, the steel exhibits better toughness at 850 °C and 1000 °C, with ductile fracture characteristics. Conversely, at 650 °C, 750 °C, and 1200 °C, the steel shows brittle fracture features. Microscopically, the fracture surfaces at these temperatures exhibit quasi-cleavage fracture characteristics. Notably, chain-like M/A constituents at grain boundaries significantly affect impact toughness and are the primary cause of toughness deterioration in the intercritical coarse-grained heat-affected zone. Full article

Path following is one of the key technologies for unmanned surface vehicles (USVs). This paper proposes a path-tracking control method for a single-outboard-motor USV based on a Deep Deterministic Policy Gradient (DDPG) algorithm and model predictive control (MPC) algorithm. Initially, the motion model and outboard motor model of the USV are analyzed. Subsequently, simulation and real ship experiments provide a comprehensive performance comparison between the proposed DDPG-MPC method and the traditional ALOS-PID method. The results indicate that for straight path tracking, the DDPG-MPC algorithm achieves 37% and 21% reductions in the average cross error and heading angle error, respectively, compared to the ALOS-PID algorithm. The real ship experiments further validate the DDPG-MPC algorithm’s advantages in real-world environments. Specifically, under disturbances like wind, waves, and currents, the maximum cross error of the DDPG-MPC algorithm is one-third of the ALOS-PID algorithm. Additionally, the DDPG-MPC algorithm sustains a higher and more stable longitudinal velocity over extended periods, while the ALOS-PID algorithm shows greater instability and variability. Overall, the findings confirm the feasibility and effectiveness of the proposed approach, highlighting its potential for enhancing path-tracking control performance in single-outboard-motor USVs. Full article

The kidney plays an essential role in the proper homeostasis of glucose. In the kidney, glucose transport is carried out across cell membranes by two families of glucose transporters—facilitated diffusion glucose transporters (GLUTs) and Na(+)-dependent glucose co-transporters (SGLT family). Among the transporters, sodium-dependent glucose co-transporters play a major role in the kidney‘s ability to reabsorb glucose. Although the localization of glucose transporters has been extensively studied in mammals, there are still knowledge gaps regarding the localization of SGLTs in birds. The aim of this research was to conduct a comparative study of the immunolocalization of the sodium-dependent glucose co-transporters SGLT1 and SGLT2 in the kidneys of healthy and T-2-mycotoxicated chickens. Immunohistochemical staining was carried out using the polyclonal primary antibodies SGLT1 and SGLT2 (Abcam, UK) in kidney tissue derived from seven healthy and seven T-2-mycotoxicated 7-day-old female layer-type Ross chickens (Gallus gallus domesticus). The sections were stained using an immunohistochemistry kit (Abcam, UK). In the kidneys of the healthy birds, strong staining of SGLT1 and SGLT2 was observed in the cytoplasm of the epithelial cells of the proximal straight and convoluted tubules. In the kidneys of the birds of the T-2 toxin group, weak expression of SGLT1 and SGLT2 with morphological changes occurred, indicating reduced glucose transport in the urinary system during T-2 mycotoxicosis. Full article

Background/Objectives: The active straight leg raise requires intricate coordination between the hip, knee, pelvis, and spine. Despite its complexity, limited research has explored the relationship between lower limb raising velocity and trunk muscle motor control during an active straight leg raise in healthy individuals. This study aimed to explore the potential effects of increased lower limb raising velocity on core muscle contractions during active straight leg raises. Methods: Six healthy adult men (mean age: 24.5 ± 2.5 years) participated in this study. Electromyography signals were recorded using surface electrodes placed on the rectus abdominis, external oblique, and internal oblique/transverse abdominis muscles. The participants performed active straight leg raises at three different velocities: 3 s, 2 s, and as fast as possible (max). The electromyography data were analyzed from 250 ms before to 1000 ms after movement initiation, with muscle activity expressed as a percentage of the maximal voluntary isometric contraction. Statistical analyses were conducted using non-parametric tests, including the Friedman test for overall differences, followed by pairwise Wilcoxon signed-rank tests with Bonferroni correction for multiple comparisons (p < 0.05). Results: During the 250 ms before movement initiation, the internal oblique/transverse abdominis, external oblique, and rectus abdominis muscles showed greater activity in the max condition compared to the 3 s and 2 s conditions (Friedman test, p < 0.05), but no significant differences were found in pairwise comparisons (Wilcoxon test, p > 0.05). Similarly, during the 500 ms after movement initiation, internal oblique/transverse abdominis activity was higher in the max condition, with no significant pairwise differences observed. Conclusions: Faster lower limb raising velocities during active straight leg raise may enhance core stability by activating anticipatory and sustained internal oblique/transverse abdominis, external oblique, and rectus abdominis activity on the raised limb side. Training to promote this activation could improve dynamic stability in rapid or asymmetric movements. Full article

Background/Objectives: Many social and environmental factors contribute to the disproportionate burden of COVID-19 mortality. Access to healthcare services has not been thoroughly examined as a factor contributing to COVID-19 mortality. This study examines distance to ERs and ICUs, uninsurance rates, and county-level COVID-19 mortality rates. Methods: Using data from the American Hospital Association survey, we identified hospitals providing emergency and intensive care services. Hospital locations were geocoded, and straight-line distance was calculated from the population-weighted county centroid. The county proportion of uninsured residents came from the American Community Survey. Generalized linear regression models with a log-link were used to examine study factors and county COVID-19 mortality rates. Results: A total of 2640 (84.0%) U.S. counties or county-equivalents were included in this analysis. The median COVID-19 mortality rate was 240 deaths per 100,000. In adjusted models, increasing distance to ERs (IRR: 0.95; 95% CI: 0.92, 0.98) or ICUs (IRR: 0.61; 95% CI: 0.57, 0.65) was not significantly associated with increased COVID-19 mortality. The proportion of residents (IRR: 3.81; CI: 2.58, 5.62) uninsured was significantly associated with increased COVID-19 mortality rates. Conclusions: Being in close proximity to hospital-based healthcare services may not provide any significant benefit for COVID-19 mortality outcomes, considering that hospitals are largely located in more densely populated areas conducive to COVID-19 spread. Financial barriers may largely contribute to persons avoiding necessary COVID-19 care. To continue to combat COVID-19 and future pandemics, greater attention should be focused on eliminating financial barriers to receiving medically necessary care. Full article

Towed streamer positioning is a vital and essential stage in marine seismic exploration, and accurate hydrophone coordinates exert a direct and significant influence on the quality and reliability of seismic imaging. Current methods predominantly rely on analytical polynomial models for towed streamer positioning; however, these models often produce significant errors when fitting to streamers with high curvature, particularly during turning scenarios. To address this limitation, this study introduces a novel multi-streamer analytical positioning method that uses a hybrid harmonic function to model the three-dimensional coordinates of streamers. This approach mitigates the substantial modeling errors associated with polynomial models in high-curvature conditions and better captures the dynamic characteristics of streamer fluctuations. Firstly, the mathematical model for the hybrid harmonic function is constructed. Then, the algorithmic implementation of the model is detailed, along with the derivation of the error equation and the multi-sensor fusion solution process. Finally, the validity of the model is verified using both simulated and field data. The results demonstrate that, in the turning scenario without added error, the proposed harmonic model improves simulation accuracy by 35.5% compared to the analytical polynomial model, and by 27.2% when error is introduced. For field data, accuracy improves by 18.1%, underscoring the model’s effectiveness in significantly reducing errors associated with polynomial models in turning scenarios. The performance of the harmonic function model is generally comparable to that of the polynomial model in straight scenarios. Full article

In order to address the issue of limited excavation footage in the drilling and blasting of a water diversion tunnel with a cross-section of approximately 10 m², which is unable to meet the demands of rapid construction, a blasting method combining long and short straight-hole cutting was proposed based on the theories of elastic mechanics, blasting craters, explosive gas and stress waves. A mechanical model was established to elucidate the parameter design method and cavity formation principle of the combined cutting. Numerical simulation and field tests were employed to analyze the rock-breaking process of combined cutting, with a view to comparing the blasting effect differences between the traditional inclined cutting method and the combined cutting method. The research results indicate that during the blasting process with combined long and short straight-hole cutting, the uncharged portion of the deep hole can serve as an empty hole during the subsequent blasting of the shallow hole. The concentration of stress at the wall of the empty hole and the superposition of reflected and incident waves serve to enhance the rock-breaking effect of the shallow hole, with the enhancement being influenced by the diameter of the hole and the distance between it and the empty hole. The preferential detonation of the shallow hole can provide a smaller resistance line and free surface distance for deep hole detonation, creating favorable conditions for rock fragmentation in deep hole blasting, making it easier for the rock in the cutting area to be thrown out and increasing the utilization rate of the blast holes. The shape of the formed cavity is a long strip-shaped cube, with its volume being influenced by the spacing between each group of deep and shallow holes. The rock mass damage is most severe in the vertical direction, while the rock mass damage at the center of the upper and lower edges is relatively weaker. In order to optimize the utilization of blasting energy, it is essential to select an appropriate spacing between each group of blast holes. In comparison to the utilization of traditional inclined cuts, the implementation of combined long and short holes has been observed to result in a greater extent of blasting footage and relatively lower explosive consumption. These research findings provide a reference point for the rapid and efficient construction of small-section tunnel engineering, as well as the design of straight-hole cut blasting with reduced consumption. Full article

Microstructure and deformation properties of both unaged and aged cladding material were studied at 400 °C for 10,000 h. The results indicated that carbide formation occurred in the cladding material, while thermal aging treatment resulted in spinodal decomposition and G-phase formation in the aged ferrite phase. Furthermore, intensive straight slip bands formed in both unaged and aged austenite phases. Continual straight slip bands formed in the unaged ferrite phase, while curvilinear slip bands formed in the aged ferrite phase during the plastic deformation process. Microcracks preferred to nucleate at the points of interaction between phase boundaries and carbides, while the aged ferrite phase experienced lowered microcrack formation along the carbide/ferrite phase boundary. Microcracks propagated along the straight slip bands in the unaged ferrite phases and curvilinear slip bands in the aged ferrite phases. Full article