Reduction In Force Research Articles

Reduced-Order Model of a Time-Trial Cyclist Helmet for Aerodynamic Optimization Through Mesh Morphing and Enhanced with Real-Time Interactive Visualization

Aerodynamics is a key factor in time-trial cycling. Over the years, various aspects have been investigated, including positioning, clothing, bicycle design, and helmet shape. The present study focuses on the development of a methodology for the aerodynamic optimization of a time-trial helmet through the implementation of a reduced-order model, alongside advanced simulation techniques, such as computational fluid dynamics, radial basis functions, mesh morphing, and response surface methodology. The implementation of a reduced-order model enhances the understanding of aerodynamic interactions compared to traditional optimization workflows reported in sports-related research, facilitating the identification of an optimal helmet shape during the design phase. The study offers practical insights for refining helmet design. Starting with a baseline teardrop profile, several morphing configurations are systematically tested, resulting in a 10% reduction in the drag force acting on the helmet. The reduced-order model also facilitates the analysis of turbulent flow patterns on the cyclist’s body, providing a detailed understanding of aerodynamic interactions. By leveraging reduced-order models and advanced simulation techniques, this study contributes to ongoing efforts to reduce the aerodynamic resistance of time-trial helmets, ultimately supporting the goal of improved athlete performance.

Holographic drag force with translational symmetry breaking

In order to investigate how the drag force is affected by translational symmetry breaking (TSB), we utilize a holographic model in which the background metric remains translational symmetric while a graviton mass or other fields in the theory break this symmetry. We calculate analytically the drag force, considering an asymptotic AdS5 in which parameter α arises from TSB. This parameter can be intuitively understood as a measure of TSB strength and we anticipate that non-zero values of it will affect the drag force. In this asymptotic AdS5 background, we will demonstrate that a decrease in α results in a reduction of the drag force. Moreover, we study the diffusion constant, which falls with increasing α. It will eventually be shown that at lower values of α or μ (chemical potential), the transverse diffusion coefficient is larger than the longitudinal one, and the speed of the heavy quark has minimal impact on the ratio.

Study on Impact Load Mitigation for High-Speed Water Entry Projectiles Using Aluminum Foam Buffering Structure

Abstract This paper investigated the fluid-solid coupling nonlinear problem of water entry by a high-speed projectile, considering cavitation, air cushion effect, and water vapor generated by the high-speed relative motion between the projectile and the fluid. To this end, a sandwich structure containing aluminum foam attached piston was studied and designed. The numerical simulation of the entry process was analyzed by LS-DYNA. The results show that the sandwich structure reduces the peak impact load. 87.47% reduction in peak force during water entry and aluminum foam has good cushioning effect.

Migration dynamics of molten droplets impacting on vertical solid surfaces

Droplet impact onto solid surfaces is a widespread phenomenon in various engineering applications, including metal droplet ejection three-dimensional (3D) printing, an innovative metal additive manufacturing technique. Despite extensive research on droplet behavior upon impact, the physics of molten droplets impacting on vertical or inclined substrates, particularly in the scenarios of omnidirectional deposition and conformal fabrication, remains understudied. This paper introduces a novel phenomenon termed “migration,” distinct from slipping and rolling, observed when a droplet impacts vertical surfaces. The study investigates the migration behavior of molten droplets on vertical substrates with varying roughness and wettability, elucidating the underlying mechanisms and influences of these surface properties on droplet migration. Meanwhile, the coupled effects of fluid dynamics and thermodynamics on the migration of the droplet are numerically analyzed. It was found that the migration results from the asymmetric spreading and receding along the longitudinal direction caused by gravity or gravity-induced lateral inertial forces. The migration distance of the droplet increases with the substrate's roughness and non-wettability, which resulting from a reduction in interfacial binding force. The migration dynamics depend on the interaction between the surface flow and rapid solidification, allowing control over the final form and migration displacement of droplets. These findings enhance our understanding of the minor migration phenomena in droplets impacting on the vertical substrates along the gravity direction, contributing valuable insights for practitioners aiming to minimize forming defects and improve the quality of metal droplet ejection 3D printing.

Investigation of wind tunnel experiments on nonlinear ground effect for flying cars

This research investigates the nonlinear aerodynamic characteristics of ground effect for flying cars, utilizing high-precision balance measurements to determine the lift and drag of flying cars and particle image velocimetry (PIV) in a closed-circuit low-speed recirculating wind tunnel. The ground effect's lift enhancement mechanism was revealed through analysis of aerodynamic results and flow field structures. Force measurement experiments demonstrated that ground effect significantly improves aerodynamic performance, with the lift coefficient showing a nonlinear trend as altitude decreases, undergoing the gentle force phase, the force increase phase, and the force reduction phase. PIV results indicated that the narrowing flow channel between the flying car and the ground at lower heights reduces airflow speed beneath the wing, converting kinetic energy into pressure potential energy, similar to a high-pressure air cushion. Consequently, airflow speed over the upper wing surface increases, enhancing lift. Additionally, ground effect causes the wingtip vortex structure to move upward and outward along the wing span, reducing downward induced velocity, weakening vortex strength, and increasing the effective aspect ratio of the three-dimensional wing. These changes reduce induced drag, thereby improving the overall performance of the flying car.

Pseudo-static analytical formulation for seismic thrust on cantilever retaining walls in C-Φ soils considering double failure planes

This study proposes a pseudo-static analytical formulation for calculating the active thrust force on cantilever retaining walls under seismic loads. The formula incorporates the effects of soil cohesion and failure surface shape and is applied to short-heel and long-heel cantilever walls. The results are compared to classic analytical methods and a numerical model. The proposed formula provides a good representation of wall behavior under low to medium seismic loads, with an extended range compared to classical methods. However, using 100% of the peak ground acceleration (PGA) overestimates the active force for medium to strong earthquakes, so reduced PGA values are recommended. The formula accurately predicts the failure surface inclination, with an accuracy of approximately 10°. Soil cohesion has no significant effect on the failure mechanism, but the heel length influences its effect on active force reduction. Overall, the study offers an improved analytical approach for assessing the seismic response of cantilever retaining walls.

Macro-Superlubricity Induced by Tribocatalysis of High-Entropy Ceramics.

Macroscale superlubricity has attracted considerable attention as a promising strategy to minimize frictional energy dissipation and achieve near-zero wear. However, realizing macroscale superlubricity with prolonged durability remains an immense challenge, particularly on engineering steels. Current superlubricants render steel surfaces susceptible to corrosion, causing severe wear and superlubrication failure. Herein, high-entropy ceramics (HEC) with catalytic properties are innovatively introduced to prevent corrosion of engineering steels and achieve macro-superlubricity through tribo-catalytic effect. Furthermore, this catalytically induced superlubricity system exhibits an ultra-low friction coefficient of 0.0037 under contact pressure up to 1.47 GPa, an ultra-long cycle lifetime of 1.25 × 106 cycles (corresponding sliding distance up to 5 km), and an extremely low wear rate of 3.032 × 10-10 mm3·N-1·m-1 on the HEC surface. Based on the experimental analysis and theoretical simulation, the in situ formed HEC nanocrystals reduce the Gibbs free energy of hydrolysis of PA molecules into inositol and phosphoric acid molecules in the lubricant. Notably, the hydrolysis products favorably contributed to the reduction of shear force in the lubrication system, which is essential for achieving macroscale superlubricity over a long time. This study provides a new perspective for designing robust superlubricity systems by harnessing the tribocatalytic effect of high-entropy materials.

Effects of Soil–Structure Interaction on the Seismic Response of RC Frame–Shear Wall Building Structures Under Far-Field Long-Period Ground Motions

This paper focuses on the effect of soil–structure interaction (SSI) on the seismic response of high-rise RC frame–shear wall structures under far-field long-period ground motions. Elastic–plastic time–history analyses were performed using ABAQUS. The effects of the ground motion type, soil type, and structural frequency on the seismic response are analyzed and quantitatively evaluated. On this basis, the influence mechanism of SSI on the seismic response under far-field long-period ground motions is discussed and revealed through a ground motion spectrum analysis. The results show that the consideration of the SSI effect leads to an increase in the displacement response and a decrease in the shear response. The SSI coefficient of the base shear is all less than 1, ranging from 0.5 to 1. The SSI effect under far-field long-period ground motions is more pronounced than that under ordinary ground motions. The shear force reduction in the current code may not be applicable to the structural design considering the SSI effect under far-field long-period ground motions. The displacement response amplification of the SSI effect on loess soil (Site 2) is more remarkable than that on sand soil (Site 1). The SSI effect can reduce the structural frequency, especially for the structures with fewer floors on the softer soil site. The “bimodal characteristic” of the acceleration response spectrum for far-field long-period ground motions may lead to shear force amplification when SSI is considered.

Seismic Behavior of Resilient Reinforced Concrete Columns with Ultra-High-Strength Rebars Under Strong Earthquake-Induced Multiple Reversed Cyclic Loading

The frequent occurrence of major earthquakes highlights the structural challenges posed by long-period ground motions (LPGMs). This study investigates the seismic performance and resilience of five reinforced concrete (RC) columns with different high-strength steel bars under LPGM-induced cyclic loading, both experimentally and numerically. The results show that low-bond and debonded high-strength steel bars significantly enhance self-centering capabilities and reduce residual drift, with lateral force reductions of 7.6% for normal cyclic loading and 19.2% for multiple reversed cyclic loading. The concrete damage in the hinge zone of the columns was increased; however, the significant inside damage of the concrete near the steel bars made it easier to restore the columns for the damage accumulation caused by multiple loading. Based on the experiment, a numerical model was developed for the columns, and a simplified model was proposed to predict energy dissipation capacity, providing practical design methods for resilient RC structures that may be attacked by LPGMs.

TRIBOLOGICAL PROPERTIES OF AAO COATINGSCATALYTICALLY MODIFIED WITH NICKEL

The purpose of this work is to determine the possibility of modifying oxide coating with nickel in the catalyticprocess and to verify the tribological properties of the coatings as a result of such modification. The coatingswere made on the EN AW-5251 aluminum alloy by electrochemical method. Nickel dispersions were obtainedthrough thermochemical treatment of the coatings. Tribological tests were carried out in a combination ofcoatings with polymer, cast iron, and steel, in a reciprocating motion on the T-17 tester. The paper presentsthe results of tribological tests and roughness of AAO coatings modified with nickel, before and after thetribological test. The results of tribological tests were supplemented with SEM tests and statistical analysis.The tests showed the possibility of modifying the AAO coatings with nickel compounds, which, in the case ofa sliding combination of the modified coating with steel, causes a significant reduction of friction forces bothin the case of technically dry friction and friction with lubrication.

Patient-specific gait pattern in individuals with patellofemoral instability reduces knee joint loads

Patellofemoral instability is influenced by morphological factors and associated with compensational alterations in gait pattern. Recent simulation studies investigated the impact of knee morphology on the stability and loading of the patellofemoral joint but neglected the patient-specific gait pattern. The aim of this study was to investigate the impact of patient-specific gait pattern on muscle forces and joint loading in individuals with patellofemoral instability. Musculoskeletal simulations with a model including a twelve degrees of freedom knee joint were performed based on three-dimensional motion capture data of 21 individuals with chronic patellofemoral instability and 17 healthy control participants. The patellofemoral instability group walked with a less flexed knee joint and reduced knee flexion and abduction moments compared to the control group, which required less quadriceps muscle forces. Lower quadriceps muscle forces resulted in a reduction of tibiofemoral and patellofemoral joint contact forces despite similar walking velocities between both groups. Furthermore, we observed decreased lateralizing patella forces in subjects with patella instability, which could potentially reduce the risk of patella dislocation. Our findings highlight the importance of accounting for the patient-specific gait pattern when analysing knee loads in individuals with patellofemoral instability.

An Experimental Investigation into the Enhancement of Surface Quality of Inconel 718 Through Axial Ultrasonic Vibration-Assisted Grinding in Dry and MQL Environments

Ultrasonic vibration-assisted grinding (UVAG) has proven to be beneficial for grinding difficult-to-machine materials. This work attempts to enhance the grinding performance of Inconel 718 through a comprehensive study of UVAG characteristics. Grinding experiments were performed in both dry and Minimum Quantity Lubrication (MQL) environments, and assessment of the grinding forces, specific energy, residual stress, and surface topography was done. A substantial reduction of both surface roughness and grinding force components was observed in UVAG compared to conventional grinding (CG). Utilizing UVAG with MQL at the maximum vibration amplitude led to a 64% reduction in tangential grinding force and a 51% decrease in roughness parameter, Ra, when compared to CG conducted in a dry environment. The high-frequency indentations of the abrasives in UVAG generated compressive residual stresses on the ground surface. Surface parameters pointed to uniform texture and SEM images showed widening of abrasive grain tracks on the workpiece surface during UVAG. The utilization of UVAG under MQL produced a synergistic impact and resulted in the lowest grinding forces, specific energy, and optimal surface quality among all the grinding conditions investigated. Overall analysis of the results indicated that the axial configuration of the vibration set-up is favorable for UVAG, and the high-frequency periodic separation-cutting characteristic of the process improves lubricating efficiency and grinding performance.

Tribological performance of TiO2 nanoparticle-oil-water emulsion in the hot rolling process

This study aims to evaluate the lubrication performance of a nano-TiO2 oil-in-water (O/W) emulsion during the hot rolling process. A series of O/W emulsions with varying concentrations of TiO2 nanoparticles (0.05, 0.1, 0.3, and 0.5 wt.%) were synthesized. Tribological tests were conducted under a load of 70 N for 10 minutes to determine the optimal concentration based on anti-frictional properties. The O/W nano-emulsion optimized with a 0.1 wt.% concentration of TiO2 applied in the hot rolling process of IS 2062 E250 grade steel. This application resulted in a reduction of rolling force (RF) and surface roughness, suggesting its potential as an alternative lubricant. The results indicated superior antifriction performance at a TiO2 concentration of 0.1 wt.%, leading to a 15% reduction in RF. Additionally, the use of the nano-emulsion contributed to a significant reduction in oxide scale formation. Surface roughness measurements of the rolled samples revealed a 19% decrease, with a roughness value of 2.125 µm, compared to samples rolled with a nano-free O/W emulsion. These findings suggest that nano-TiO2 O/W emulsions could serve as an effective alternative to conventional O/W emulsions in future industrial metalworking applications.

Magnesium Stearate Fatty Acid Composition, Lubrication Performance and Tablet Properties

Magnesium stearate (MgSt) is a common tablet lubricant. As variations in MgSt properties are known to influence tablet attributes, the impact of MgSt fatty acid composition, particularly the significance of the stearate and palmitate contents, and its effects on tablet properties warrant further investigation. This study investigated the effect of MgSt with different stearate and palmitate contents but comparable physical properties (e.g. particle size, crystallinity, specific surface area and morphology) on lubrication performance and resulting tablet quality attributes, including mechanical strength, disintegratability and drug release. The influence of MgSt concentration and blending duration on the resulting tablet properties was also examined. Tablets produced using the lower stearate content MgSt had slightly higher tensile strength. The effect of MgSt stearate content was more apparent in the disintegration time and drug release, whereby MgSt of lower stearate content resulted in tablets with longer disintegration time and slower drug release. The lower stearate content also resulted in a lower lubrication performance, leading to a lesser reduction in tablet ejection force. As expected, a longer blending time of the tablet formulation blend with MgSt yielded tablets with reduced tensile strength, shorter disintegration time and slower drug release. Tablets with higher MgSt concentration showed a greater reduction in tensile strength, longer disintegration time and faster drug release. The study findings reinforced observations by other researchers and provided a better understanding of the fatty acid composition effects of MgSt on lubrication performance and the resulting tablet properties.Graphical

Suicidal ideation and thoughts of self-harm during the COVID-19 pandemic among Swedish employees: a cohort study on the role of job instability and job insecurity

BackgroundSuicidal ideation may be a warning sign for suicide and previous work has indicated a higher prevalence of suicidal ideation during the COVID-19 pandemic. Job loss and job insecurity are potential risk factors for suicidal ideation, but their importance during the pandemic, and the role of organizational changes for suicidal ideation, is unclear. This study examined the association between various experiences associated with job loss and job insecurity during the pandemic and thoughts of suicide/self-harm in Sweden.MethodsThe study sample was drawn from the Swedish Longitudinal Occupational Survey of Health (SLOSH). Auxiliary data collections in February 2021 and 2022 assessed exposure to job loss/unemployment, furlough, workplace downsizing, or increased job insecurity versus stable employment and thoughts of suicide or self-harm (PHQ-9) during the pandemic. The analyses were based on 1558 individuals (2 349 observations) participating in either or both waves and who had been working before the pandemic. Logistic regression models with cluster-robust standard errors were fitted, including sociodemographic factors and prior mental health problems to control for potential confounding. Measures of personality based on a brief version of the Big-Five personality inventory were also added.ResultsThe results indicated an association between all experiences, except furlough, and thoughts of suicide/self-harm, when adjusting for sex, age, civil status, socioeconomic status and prior mental health (job loss odds ratio (OR) = 3.70, 95% confidence interval (CI) 1.79–7.63, downsizing OR = 2.41, CI 1.24–4.70, job insecurity OR = 2.77, CI 1.15–6.67). The associations for job loss and insecurity were attenuated by adjustment for personality, although it remained statistically significant for downsizing.ConclusionsThe results suggested a higher risk of suicidal ideation connected with loss of employment and survival of a downsizing, but not a forced reduction in working times/pay during the COVID-19 pandemic. The association for subjective job insecurity was less robust and may be partly explained by personality.

Modeling and Experimental Studies on Vibration-Induced Force Reduction During Needle Insertion of Thin Tissues

Modeling and Experimental Studies on Vibration-Induced Force Reduction During Needle Insertion of Thin Tissues

Loosening Phenomenon on Thin Plates Bolted Joint due to Offset Load

In this study, the new loosening behavior was discovered and investigated when offset loads were repeatedly applied to both ends of a bolted joint initially tightened to a thin plate made of high-tensile steel. In the experiments, the impact of offset distance on reduction of clamp force was investigated through multiple applications of symmetric offset axial load to the bolted joint assembly. The experimental results showed that even a slight offset load reduced the clamp force, and the larger the offset distance, the greater the reduction of the clamp force. It was also found that the decrease in clamp force depends not on the number of times the offset load is applied but on the magnitude of the offset load. Until now even if the thin plate bolted joint was subjected to an offset load, as long the plates do not deform significantly due to plastic deformation, it has been generally recognized that the clamp force is not reduced. This loosening phenomenon is new and its mechanism has not been elucidated yet. In order to clarify the mechanism that may lower the clamp force, this study conducted FE analysis using a simplified model of a bolted joint. In the FE model, the bolt and nut are considered as a single unit and the effect of slippage between the thread surfaces and the effect of plastic deformation is ignored by using elastic analysis. The results of the FE analysis showed that the main factor causing the reduction in clamp force was slippage between the thin plates to be joined, which was caused by offset load, and that the slippage didn't return to the original position resulting in the reduction in clamp force.

Nutritional support for cancer patients during chemoradiation treatment

An analysis of publications in the medical databases e-Library, PubMed, and Medline (2005–2024) was conducted to evaluate the impact of nutritional support on the tolerability of antitumor chemoradiotherapy. Based on the data collected, it was revealed that chemoradiotherapy is linked to a high risk of developing protein-energy malnutrition. Consequently, the initial nutritional deficiency and sarcopenia result in either a refusal to administer chemotherapy in favor of radiation treatment alone, a forced reduction in the dose of a cytostatic medication, or the disruption of the chemoradiotherapy course. Patients with malignancies of the head and neck who have received chemoradiotherapy with previous induction chemotherapy are in the “red zone” for the risk of developing protein-energy malnutrition. Nutritional support is one of the instruments that enhances the likelihood of treatment implementation and mitigates the risk of drug and radiation toxicity. The fundamental principles of nutritional support during chemoradiotherapy include timely prescription, adequacy, composition of a specialized mixture, and the choice of the most physiological way of its implementation. Supplementing nutritional support with feasible strength physical exercise triggers protein synthesis in skeletal muscles, increases muscular sensitivity to the anabolic properties of amino acids, and mitigates insulin resistance.

Research on the annular distribution state of resin and design of anchoring synergistic device

The resin anchoring method promotes the development of high-strength bolt (cable bolt) support, which simplifies the construction process while ensuring that the high-strength support force of the bolt (cable bolt) can be effectively exerted. And with the increase of engineering depth and the complexity and variation of geological conditions, higher requirements are put forward for resin anchoring performance. In view of the influence of the annular distribution state of resin on the anchoring performance, with the main line of “optimizing the annular thickness, improving the mixing efficiency and increasing the degree of compactness”, through the comprehensive research method combining theoretical analysis, numerical simulation, laboratory test and field test, an anchoring synergistic device with simple and convenient operation were developed, the mechanism of the synergistic device was revealed, and the universality of synergistic anchoring was verified. The results show that the annular distribution of resin has a great influence on the anchoring performance, when the bolt is unconstrained, the annular thickness distribution of resin is uneven, and the mixing uniformity and the compactness of the anchoring section cannot be guaranteed, resulting in the reduction of anchorage force and the easy failure of anchorage. This device can center the bolt to ensure the uniform distribution of the annular thickness of the resin, which is helpful to break the resin sealing bag, improve the efficiency of stirring the resin, effectively prevent the spillage of the resin. Besides, it can also ensure the compactness of the anchoring section and strengthen the anchoring performance. Through laboratory tests and on-site verification, compared with normal construction, the anchorage force of the synergistic anchoring is increased by about 40 %, and the deformation of the roof is reduced by about 57.5 %. The research results enhance the understanding of the mechanism of the annular distribution state of resin on the anchoring performance, and carry out innovative attempts to solve the problem, which effectively form a relatively stable anchorage structure of the soft and broken surrounding rock on the surface, which has a certain theoretical reference value for ensuring the quality of resin anchoring engineering under the condition of soft and broken coal and rock mass.

JAK inhibition with tofacitinib rapidly increases contractile force in human skeletal muscle.

Reduction in muscle contractile force associated with many clinical conditions incurs serious morbidity and increased mortality. Here, we report the first evidence that JAK inhibition impacts contractile force in normal human muscle. Muscle biopsies were taken from patients who were randomized to receive tofacitinib (n = 16) or placebo (n = 17) for 48 h. Single-fiber contractile force and molecular studies were carried out. The contractile force of individual diaphragm myofibers pooled from the tofacitinib group (n = 248 fibers) was significantly higher than those from the placebo group (n = 238 fibers), with a 15.7% greater mean maximum specific force (P = 0.0016). Tofacitinib treatment similarly increased fiber force in the serratus anterior muscle. The increased force was associated with reduced muscle protein oxidation and FoxO-ubiquitination-proteasome signaling, and increased levels of smooth muscle MYLK. Inhibition of MYLK attenuated the tofacitinib-dependent increase in fiber force. These data demonstrate that tofacitinib increases the contractile force of skeletal muscle and offers several underlying mechanisms. Inhibition of the JAK-STAT pathway is thus a potential new therapy for the muscle dysfunction that occurs in many clinical conditions.