Search Results (1,892)

Background/Objectives: Advancements in DNA profiling have made it possible to retrieve intact DNA profiles from increasingly minute biological samples. This increased sensitivity in DNA detection has highlighted crucial considerations to be made when handling and packing items from the crime scene to minimize potential contamination from either direct or indirect transfer of DNA. To investigate potential DNA transfer between items stored within the same evidence package, we conducted a simulation study with items commonly encountered during forensic casework. Methods: Participants were grouped in pairs, each of them handling the same type of item to simulate the activity conducted at the crime scene. The items were then collected from each pair of participants and stored in the same evidence package for 4 to 5 days. To evaluate the basal DNA transfer between items within the same package, the packed items were not subjected to friction, force, or long-distance movement in this study. Results: We have observed the occurrence of DNA transfer on 39% of the studied items inside the package, which changed the source attribution of the DNA profiles for 10% of the recovered samples. Our results showed that the types of items were associated with the number of transferred alleles and the amount of DNA recovered, while no association was found between the number of transferred alleles and the amount of DNA on the studied items. Conclusions: Taken together, the results from this study reiterate the importance of packing each item from the crime scene separately, especially when packing items together may impact the interpretation of source attribution. Full article

This study aimed to investigate the dynamic characteristics of shafts joined by friction welding and to update their finite element models. The first five bending mode resonance frequencies, damping ratios, and mode shapes of SAE 304 steel beams, friction-welded at three different rotational speeds (1200, 1500, and 1800 rpm), were determined using the Experimental Modal Analysis method. This approach allowed for an examination of how the dynamic properties of friction-welded beams change at varying rotational speeds. A slight decrease in resonance frequency values was observed with the transition from lower to higher rotational speeds. The largest difference of 3.28% was observed in the first mode, and the smallest difference of 0.19% was observed in the second mode. Different trends in damping ratios were observed for different modes. In the first, second, and fourth modes, damping ratios tended to increase with increasing rotational speeds, while they tended to decrease in the third and fifth modes. The largest difference was calculated as 52.83% in the third vibration mode. However, no significant change in mode shapes was observed for different rotational speeds. Based on the examined Modal Assurance Criterion (MAC) results, cross-comparisons of the mode shapes obtained for all three different speeds yielded a minimum similarity of 93.8%, reaching up to 99.9%. For model updating, a Frequency Response Assurance Criterion (FRAC)-based method utilizing frequency response functions (FRFs) was employed. Initially, a numerical model of the welded shaft was created using MATLAB-R2015a, based on the Euler–Bernoulli beam theory. Since rotational coordinates were not used in the EMA analyses, static model reduction was performed on the numerical model to reduce the effect of rotational coordinates to translational coordinates. For model updating, experimentally obtained FRFs from EMA and FRFs from the numerical model were used. The equivalent modulus of elasticity and equivalent density of the friction weld region were used as updating parameters. Successful results were achieved by developing an algorithm that ensured the convergence of the numerical model’s FRFs and natural frequencies. Full article

The present study was motivated by the need to enhance indoor air quality and reduce airborne disease transmission in dense urban environments where high-rise residential buildings face challenges in achieving effective natural ventilation. The problem lies in the lack of scalable and convenient tools to optimize natural ventilation rate, particularly in urban settings with varying building heights. To address this, the scientific technique developed with an innovative metric, the urbanized natural ventilation effectiveness factor (uNVeF), integrates regression analysis of wind direction, velocity, air change rate per hour (ACH), window configurations, and building height to quantify ventilation efficiency. By employing a field measurement methodology, the measurements were conducted across 25 window-opening scenarios in a 13.9 m² residential unit on the 35/F of a Hong Kong public housing building, supplemented by the Hellman Exponential Law with a site-specific friction coefficient (0.2907, R² = 0.9232) to estimate the lower floor natural ventilation rate. The results confirm compliance with Hong Kong’s statutory 1.5 ACH requirement (Practice Note for Authorized Persons, Registered Structural Engineers, and Registered Geotechnical Engineers) and achieving a peak ACH at a uNVeF of 0.953 with 75% window opening. The results also revealed that lower floors can maintain 1.5 ACH with adjusted window configurations. Using the Wells–Riley model, the estimation results indicated significant airborne disease infection risk reductions of 96.1% at 35/F and 93.4% at 1/F compared to the 1.5 ACH baseline which demonstrates a strong correlation between ACH, uNVeF and infection risks. The uNVeF framework offers a practical approach to optimize natural ventilation and provides actionable guidelines, together with future research on the scope of validity to refine this technique for residents and developers. The implications in the building industry include setting up sustainable design standards, enhancing public health resilience, supporting policy frameworks for energy-efficient urban planning, and potentially driving innovation in high-rise residential construction and retrofitting globally. Full article

Basketball requires intense movements like jumping and sudden changes in direction, increasing the risk of slips and falls due to poor shoe–court traction. Therefore, a significant demand is for good traction performance in basketball shoes, particularly in the heel region on different court surfaces, to prevent slipping. This study examined the traction performance of fifteen common basketball shoe designs that were considered and developed using thermoplastic polyurethane to assess the available coefficient of friction (ACOF) on popular floorings (hardwood, synthetic, and polyurethane) under dry and wet conditions using a robotic slip tester. Results indicate that the hardwood flooring provided better traction, followed by the synthetic flooring, while the polyurethane flooring showed reduced friction. The study also examined the traction with apparent contact areas. Shoes with herringbone and circular tread patterns demonstrated the highest traction on all flooring in dry conditions. This research is anticipated to help basketball shoemakers choose safer shoes for player safety and performance, providing a foundation for future research on shoe flooring interaction in basketball. Full article

Surfactants can be utilized to improve oil recovery by changing the performance of reservoirs in rock pores. Kerogen is the primary organic matter in shale; however, high temperatures will affect the overall performance of this surfactant, resulting in a decrease in its activity or even failure. The effect of surfactants on kerogen pyrolysis has rarely been researched. Therefore, this study synthesized a polymeric surfactant (PS) with high temperature resistance and investigated its effect on kerogen pyrolysis under the friction of drill bits or pipes via molecular dynamics. The infrared spectra and thermogravimetric and molecular weight curves of the PS were researched, along with its surface tension, contact angle, and oil saturation measurements. The results showed that PS had a low molecular weight, with an MW value of 124,634, and good thermal stability, with a main degradation temperature of more than 300 °C. It could drop the surface tension of water to less than 25 mN·m⁻¹ at 25–150 °C, and the use of slats enhanced its surface activity. The PS also changed the contact angles from 127.96° to 57.59° on the surface of shale cores and reversed to a water-wet state. Additionally, PS reduced the saturated oil content of the shale core by half and promoted oil desorption, indicating a good cleaning effect on the shale oil reservoir. The kerogen molecules gradually broke down into smaller molecules and produced the final products, including methane and shale oil. The main reaction area in the system was the interface between kerogen and the surfactant, and the small molecules produced on the interface diffused to both ends. The kinetics of the reaction were controlled by two processes, namely, the step-by-step cleavage process of macromolecules and the side chain cleavage to produce smaller molecules in advance. PS could not only desorb oil in the core but also promote the pyrolysis of kerogen, suggesting that it has good potential for application in shale oil exploration and development. Full article

Atmospheric climate science lacks the capacity to integrate thermodynamics with the gravitational potential of air in a classical quantum theory. To what extent can we identify Carnot’s ideal heat engine cycle in reversible isothermal and isentropic phases between dual temperatures partitioning heat flow with coupled work processes in the atmosphere? Using statistical action mechanics to describe Carnot’s cycle, the maximum rate of work possible can be integrated for the working gases as equal to variations in the absolute Gibbs energy, estimated as sustaining field quanta consistent with Carnot’s definition of heat as caloric. His treatise of 1824 even gave equations expressing work potential as a function of differences in temperature and the logarithm of the change in density and volume. Second, Carnot’s mechanical principle of cooling caused by gas dilation or warming by compression can be applied to tropospheric heat–work cycles in anticyclones and cyclones. Third, the virial theorem of Lagrange and Clausius based on least action predicts a more accurate temperature gradient with altitude near 6.5–6.9 °C per km, requiring that the Gibbs rotational quantum energies of gas molecules exchange reversibly with gravitational potential. This predicts a diminished role for the radiative transfer of energy from the atmosphere to the surface, in contrast to the Trenberth global radiative budget of ≈330 watts per square metre as downwelling radiation. The spectral absorptivity of greenhouse gas for surface radiation into the troposphere enables thermal recycling, sustaining air masses in Lagrangian action. This obviates the current paradigm of cooling with altitude by adiabatic expansion. The virial-action theorem must also control non-reversible heat–work Carnot cycles, with turbulent friction raising the surface temperature. Dissipative surface warming raises the surface pressure by heating, sustaining the weight of the atmosphere to varying altitudes according to latitude and seasonal angles of insolation. New predictions for experimental testing are now emerging from this virial-action hypothesis for climate, linking vortical energy potential with convective and turbulent exchanges of work and heat, proposed as the efficient cause setting the thermal temperature of surface materials. Full article

To address the engineering challenges associated with Guilin red clay, such as its potentially low strength and unfavorable mechanical behavior, this study investigated the effectiveness of lignin and lime as modifiers. Consolidation undrained triaxial tests and scanning electron microscopy (SEM) were employed to evaluate the strength characteristics and microstructural changes in modified clay specimens with varying dosages. The results demonstrate distinct strengthening mechanisms: Lignin exhibits an optimal dosage (6%), significantly increasing cohesion and internal friction angle through physical reinforcement (“soil fiber” formation), but higher dosages (8%) lead to particle separation and strength reduction. In contrast, lime provides continuous and substantial strength enhancement with increasing dosage (up to 8%), primarily through chemical reactions producing cementitious compounds (e.g., C-S-H, C-A-H) that densify the structure. Consequently, lime-modified clay shows significantly higher cohesion and internal friction angle compared to lignin-modified clay at equivalent or higher dosages, with corresponding stress–strain curves shifting from enhanced (strain-hardening) to softening behavior. These findings provide practical insights into red clay improvement in geotechnical engineering applications. Full article

This study investigated the effect of adding superhard ReB₂ to atmospheric plasma sprayed (APS) coatings based on 60 wt% Al₂O₃ and 40 wt% ZrO₂. The amorphous phases commonly present in such coatings are known to impair their performance. ReB₂ was introduced as a crystallization nucleus due to its high melting point. ReB₂ decomposes in the presence of moisture and oxygen into H₃BO₃, ReO₃, HBO₂, and HReO₄. ReB₂ was encapsulated with Al₂O₃ via metallothermic synthesis to improve moisture stability, yielding a powder with d₉₀ = 15.1 μm. After milling, it was added at 20 wt% to the Al₂O₃-ZrO₂ feedstock. Agglomeration parameters were optimized, and coatings were deposited under varying APS conditions onto 316L steel substrates with a NiAl bond coat. In the coating with the highest ReB₂ content, the identified phases included ReB₂ (2.6 wt%), Re (0.8 wt%), α-Al₂O₃ (30.9 wt%), η-Al₂O₃ (32.4 wt%), and monoclinic and tetragonal ZrO₂. The nanohardness of the coating, measured using a Vickers indenter at 96 mN and calculated via the Oliver–Pharr method, was 9.2 ± 1.0 GPa. High abrasion resistance was obtained for the coating with a higher content of η-Al₂O₃ (48.7 wt%). The coefficient of friction, determined using a ball-on-disc test with a corundum ball, was 0.798 ± 0.03. After 15 months, the formation of (H₃O)(ReO₄) was observed, suggesting initial moisture-induced changes. The results confirm that Al₂O₃-encapsulated ReB₂ can enhance phase stability and crystallinity in APS coatings. Full article

To explore the influence of mine roof on the damage and failure of sandstone surrounding rock under different pressure rates, mechanical experiments with different strain rates were carried out on sandstone rock samples. The strength, deformation, failure, energy and damage characteristics of rock samples with different strain rates were also discussed. The research results show that with the increases in the strain rate, peak stress, and elastic modulus show a monotonically increasing trend, while the peak strain decreases in the reverse direction. At a low strain rate, the proportion of the mass fraction of complete rock blocks in the rock sample is relatively high, and the shape integrity is good, while rock samples with a high strain rate retain more small-sized fragmented rock blocks. This indicates that under high-rate loading, the bifurcation phenomenon of secondary cracks is obvious. The rock samples undergo a failure form dominated by small-sized fragments, with severe damage to the rock samples and significant fractal characteristics of the fragments. At the initial stage of loading, the primary fractures close, and the rock samples mainly dissipate energy in the forms of frictional slip and mineral fragmentation. In the middle stage of loading, the residual fractures are compacted, and the dissipative strain energy keeps increasing continuously. In the later stage of loading, secondary cracks accelerate their expansion, and elastic strain energy is released sharply, eventually leading to brittle failure of the rock sample. Under a low strain rate, secondary cracks slowly expand along the clay–quartz interface and cause intergranular failure of the rock sample. However, a high strain rate inhibits the stress relaxation of the clay, forces the energy to transfer to the quartz crystal, promotes the penetration of secondary cracks through the quartz crystal, and triggers transgranular failure. A constitutive model based on energy damage was further constructed, which can accurately characterize the nonlinear hardening characteristics and strength-deformation laws of rock samples with different strain rates. The evolution process of its energy damage can be divided into the unchanged stage, the slow growth stage, and the accelerated growth stage. The characteristics of this stage reveal the sudden change mechanism from the dissipation of elastic strain energy of rock samples to the unstable propagation of secondary cracks, clarify the cumulative influence of strain rate on damage, and provide a theoretical basis for the dynamic assessment of surrounding rock damage and disaster early warning when the mine roof comes under pressure. Full article

The control of lubricity induced by electric potential is appealing for numerous applications. On the other hand, the high polarity of ionic liquids facilitates the adsorption of equally charged molecules onto polar surfaces. This phenomenon and its consequences are well understood at the nanoscale; however, they have recently garnered significant attention at the macroscale. This study investigates the lubricity of trihexyltetradecylphosphonium dicyanamide, a phosphonium ionic liquid, when used as a neat lubricant in reciprocating sliding under electrically charged conditions. Two different polarities with the same potential were applied to the friction pair of bearing steel against bearing steel while monitoring electrical contact resistance. The lubricity was evaluated through measurements of friction, wear, surface morphology, and composition. It was found that the application of electric potential significantly alters the lubricity of the investigated ionic liquid where a positive potential applied to the ball resulted in the least damaging situation. The recorded electrical contact resistance enabled the monitoring of tribofilm formation during reciprocation. It was found that there was minimal to no separation between interacting surfaces when the ball was changing direction. Full article

Frictional conditions at the workpiece–die interface are critical in metal forming, as significant plastic deformation generates heat that affects lubricant performance. Understanding lubricant behavior, especially its influence on friction under elevated temperatures, is essential for optimizing forming processes and meeting ecological demands. While the conventional ring compression test evaluates friction through inner diameter changes, it becomes unreliable when friction is transient. In this study, a warm ring compression test incorporating an in situ measurement system is proposed to evaluate the transient frictional behavior of lubricants under temperature rise due to plastic deformation. Results show that at T = 50 °C and 150 °C, the friction coefficient increases notably with the compression ratio, whereas at T = 100 °C, it remains relatively stable. This stability is likely due to the optimal performance of the chlorinated base lubricant at 100 °C, where boundary lubrication is most effective. At T = 50 °C, the additive activation is insufficient, and at T = 150 °C, thermal degradation may reduce its effectiveness. Finite element simulations using the transient friction coefficient reproduce the deformed ring cross-section with high accuracy, while those using constant friction values show less agreement. Full article

Both biosystems and engineering fields demand advanced friction-reducing and lubricating materials. Due to their hydrophilicity and tissue-mimicking properties, hydrogels are ideal candidates for use as lubricants in water-based environments. They are particularly well-suited for applications involving biocompatibility or interactions with intelligent devices such as soft robots. However, external environments, whether within the human body or in engineering applications, often present a wide range of dynamic conditions, including variations in shear stress, temperature, light, pH, and electric fields. Additionally, hydrogels inherently possess low mechanical strength, and their dimensional stability can be compromised by changes during hydration. This review focuses on recent advancements in using environmentally responsive hydrogels as lubricants. It explores strategies involving physical or structural modifications, as well as the incorporation of smart chemical functional groups into hydrogel polymer chains, which enable diverse responsive mechanisms. Drawing on both the existing literature and our own research, we also examine how composite friction materials where hydrogels serve as water-based lubricants offer promising solutions for demanding engineering environments, such as bearing systems in marine vessels. Full article

Due to their self-adaptability, low friction, low loss, and high-speed stability, bump foil aerodynamic journal bearings are widely used in high-speed rotating equipment such as turbomachinery and flywheel energy storage. In the process of high-speed operation, the heat generated leads to changes in air parameters (such as viscosity, density, etc.), thus affecting the overall performance of air bearings. In this paper, combined with the compressible Reynolds equation, a fluid–solid coupling model was established to analyze the steady-state characteristics and key influencing factors of bearings. Through the energy equation, the air viscosity–temperature effect was considered, and different boundary conditions were set. The internal temperature distribution of the air bearing and the influence of the temperature on the bearing characteristics were systematically analyzed. It was found that the bearing capacity increased when the temperature was considered. In a certain range, with the increase in ambient temperature, the increase in bearing capacity is reduced. This paper provides a theoretical design basis for the design of high-stability bearings and promotes the design of next-generation air bearings with higher speed, lower loss, and stronger adaptability, which has very important theoretical and engineering significance. Full article

Jacking-pipe construction has the advantages of high mechanization, low environmental impact and fast construction speed. It is widely used in the project of underground pipeline under river. However, jacking-pipe grouting under shallow burial conditions is prone to cause surface bubbling problems. Based on the jacking-pipe project of Meichong Lake in Changfeng County, Hefei, this paper discussed the mechanism of grouting surface leakage, and defined the relationship between the critical pressure of jacking-pipe grouting and the ultimate pressure of shear damage of mud jacket. Mechanical model of surface leakage from shallow buried jacking-pipe grouting was established. A general mathematical expression for the grouting critical pressure was derived and a sensitivity analysis was performed. A numerical model was established based on the background engineering, and multiple sets of grouting pressure conditions for simulation and analysis were set up. The results showed that the cohesive force $c$, the angle of internal friction $\phi$, and the overburden thickness $h_s$ were all approximately linearly and positively correlated with the critical pressure of grouting. When the grouting pressure was less than 197.54 kPa the surface settlement increased. When this value was exceeded the surface displacement changed from settlement to uplift and the risk of slurry bubbling increased significantly. The theoretical calculation matched the value of grouting critical pressure from numerical simulation. The actual grouting pressure in the project was lower than the theoretical grouting critical pressure value and no slurry bubbling occurred during construction, which had verified the reliability of the theoretical model. This study can provide theoretical basis and investigation ideas for the setting of reasonable grouting pressure in similar projects. Full article

One of the important parameters of the sheet metal forming process is the coefficient of friction (CoF). Therefore, monitoring the friction coefficient value is essential to ensure product quality, increase productivity, reduce environmental impact, and avoid product defects. Conventional CoF monitoring techniques pose a number of problems, including the difficulty in identifying the features of force signals that are sensitive to the variation in the coefficient of friction. To overcome these difficulties, this paper proposes a new approach to apply unsupervised artificial intelligence techniques with unbalanced data to classify the CoF of DP780 (HCT780X acc. to EN 10346:2015 standard) steel sheets in strip-drawing tests. During sheet metal forming (SMF), the CoF changes owing to the evolution of the contact conditions at the tool–sheet metal interface. The surface topography, the contact loads, and the material behaviour affect the phenomena in the contact zone. Therefore, classification is required to identify possible disturbances in the friction process causing the change in the CoF, based on the analysis of the friction process parameters and the change in the sheet metal’s surface roughness. The Kohonen self-organising map (SOM) was created based on the surface topography parameters collected and used for CoF classification. The CoF determinations were performed in the strip-drawing test under different lubrication conditions, contact pressures, and sliding speeds. The results showed that it is possible to classify the CoF using an SOM for unbalanced data, using only the surface roughness parameter Sq and selected friction test parameters, with a classification accuracy of up to 98%. Full article