Drop Height Research Articles

Biomechanics of step-off drop landings are affected by limb dominance and lead limb in task initiation

ABSTRACT This study examines the effects of limb dominance and lead limb in task initiation on the kinetics and kinematics of step-off drop landings. Nineteen male participants performed drop landings led by the dominant and non-dominant limbs at 45-cm and 60-cm drop heights. Ground reaction force (GRF) and lower body kinematic data were collected. Between-limb time differences at the initial ground contact were calculated to indicate temporal asymmetry. Statistical Parametric Mapping (SPM) was applied for waveform analysis while two-way repeated measures ANOVA was used for discrete parameters. SPM results revealed greater GRF and lesser ankle dorsiflexion in the lead limb compared to the trail limb in 3 out of 4 landing conditions. The dominant limb displayed a greater forefoot loading rate (45 cm: p=.009, η p 2 = 0.438; 60 cm: p=.035, η p 2 = 0.225) and greater ankle joint quasi-stiffness (45 cm: p < .001, η p 2 = 0.360; 60 cm: p < .001, η p 2 = 0.597) than the non-dominant limb. Not all 380 trials were lead-limb first landings, with a smaller between-limb time difference (p=.009, d = 0.60) at 60 cm (4.1 ± 2.3 ms) than 45 cm (5.6 ± 2.7 ms). In conclusion, the step-off drop landing is not an ideal protocol for examining bilateral asymmetry in lower limb biomechanics due to potential biases introduced by limb dominance and the step-off limb.

MFiX-TFM simulation of hydrodynamics of a dual fluidized bed system

The abundance and replenishable nature of biomass make it a suitable fuel for power generation. Among the various technologies, dual fluidized bed gasification (DFBG) is a suitable technology to generate high-quality syngas from biomass. However, the complexity of hydrodynamics and heat transfer with bed geometry, flow conditions as well as feedstock demands effective research for the design of such system. This study, therefore, focuses on the simulation of hydrodynamics of a dual fluidized bed gasification system. The 2-D two-fluid model (TFM) simulations were performed using Multiphase Flow with Interphase eXchanges (MFiX) software by varying the superficial air velocities for both the gasifier and riser. The influence of superficial air velocity on static pressure, pressure drop, axial and radial voidage, solid velocities, and granular temperature was evaluated. From the simulations, it was observed that with the increase in superficial air velocities, there was an increase in the effective height of pressure drop (66%), voidage, and solid velocities of the gasifier. For the simulation of the riser, similar trends in the profile of hydrodynamic parameters were also observed. The optimum velocity for the gasifier and riser has been suggested to be between 0.15 and 0.35 m/s and 6–7 m/s, respectively.

Compressive Strength of Midfoot Fusion Nail vs Midfoot Fusion Bolt and Role of Subtalar Fusion in Midfoot Charcot Fixation Model.

Operative management of midfoot Charcot arthropathy often involves an extended midfoot arthrodesis with intramedullary bolts for fixation, a method called "beaming." Recently intramedullary nails have been introduced for the same indication, presumably providing stronger fixation. This study compares midfoot fusion nails to bolts with regard to stiffness and compressive ability. Additionally, we assessed how the addition of a subtalar fusion affects the construct. Medial column fusions were performed on 10 matched cadaver foot specimens with either a midfoot fusion nail or bolt. Specimens underwent cyclical compression loading, and displacement was measured. Separately, compressive forces produced were compared between the 2 fixation constructs using a synthetic bone block model. Lastly, another 10 matched specimens with midfoot fusion nails were evaluated with or without subtalar fusions. No differences in stiffness were found in comparing matched specimens between nail vs bolt or comparing nail only without subtalar fusion (STF) vs nail with STF. The compressive force produced by the nail specimens was significantly and substantially greater than the bolted specimens (751.7 vs 139.0 N, P = .01). The accumulated height drop at the midfoot after cycling was 0.5 mm more in the nail group than in the bolt group (1.72 vs 1.22 mm, P = .008). The nail with STF group had greater initial height drop at the midfoot than the nail-only group (0.68 vs 0.34 mm, P = .035) with similar initial height drop at the ankle. However, there were no differences in strength among the matched pairs of midfoot nail-only vs midfoot nail with STF as measured by displacement after fatigue or maximum force at load to failure. The overall cadaveric comparisons between matched pairs of nails vs bolts, and nail-only vs nail with STF, did not provide noteworthy differences between the groups with regard to strength or stiffness. However, the compressive force of the midfoot fusion nail was far superior to the bolt in a synthetic bone model. These data provide valuable insight comparing implants used in Charcot midfoot arthrodesis.

Behavior of steel fiber-reinforced coal gangue concrete beams under impact load

In order to promote the use of new sustainable steel fibers (SF) reinforced coal gangue aggregates (CGA) concrete, impact tests were performed in this paper. The impact resistance of steel fiber-reinforced coal gangue concrete was investigated using a self-developed drop-weight facility. The test variables were the CGA replacement rate (0 %, 50 %, and 100 %), the SF volume content (0 %, 0.75 %, and 1.5 %), and the drop height of the drop-weight (0.5 m and 1.0 m). Using 15 kg of hard steel as a drop-weight, the drop-weight impact test was performed on steel fiber-reinforced coal gangue concrete beams with a span of 300 mm; the damage pattern, impact reaction force-time, displacement-time relationships, and energy absorbed by steel fiber-reinforced coal gangue concrete beams were studied. The test shows that, compared with natural aggregate, CGA reduces concrete's static mechanical properties and impact resistance, and adding SF improves the static mechanical properties and impact resistance of coal gangue concrete. As the CGA replacement rate increased from 0 % to 50 % and 100 %, the reaction force of impact of the specimens decreased by 2.54 %− 6.06 % and 3.69 %− 12.33 %. The SF volume content was increased from 0 % to 0.75 % and 1.5 %, and the reaction force of impact of the specimens was increased by 23.05 %− 32.34 % and 72.27 %− 81.84 %, respectively. The impact resistance of steel fiber-reinforced concrete beams under impact loading was investigated numerically using a nonlinear explicit finite element model in LS-DYNA. The Finite Element results were validated with experimental results. Based on the validated finite element model, a parametric study was carried out to investigate the effects of coal gangue replacement rate, steel fiber volume content, and drop height of the drop weight on the behavior of the beams. This study might provide a basis for the future engineering project applications of steel fiber-reinforced coal gangue concrete under impact conditions.

Mussel-inspired poly-norepinephrine coatings as “slippy-sticky interlayer” for fabricating high-energy insensitive energetic composites

Inspired by the super-adhesive properties in marine mussel, a desensitized energetic powder constituted of a slippy-sticky polynorepinephrine interlayer and CL-20 microcore is reported. The slow polymerization process enables the extremely smooth and multifunctional thin-coating formed onto the CL-20 surface. Based on the designed composites, the calculated electronic energy values of all 15 optimized structures reveals a spontaneous thermodynamic process and a stronger bonding strength with the increase of polymerization degree. The H50values of NE/CL-20 structure are calculated and show a significant increase for new composite, produced by the bonding of norepinephrine with CL-20, versus pure CL-20. The subsequent experimental results demonstrate that the slippy CL-20@polynorepinephrine structure exhibits a high drop height (H50, 35.5 cm) and a low explosion probability (60 %) than that of pure CL-20, even exhibits a considerable increase and decreases by 13.3 cm and 12 % in turn versus CL-20@polydopamine under the identical experimental conditions. The sensitive simulation results indicate that the shorter NN bond length and lower area percent in electrostatic potential of samples are positively correlated with the decreasing of impact sensitivity. Note that the ultrasmooth bionic interlayer gives the super-adhesive properties of energetic powder, greatly improves the coating degree of 2D material, thereby shows a lower sensitivity and a high detonation heat for the constructed double-coating composites (CL-20@PNE@GO). To sum up, this study will provide an innovative route to construct a high-safety powder based on a bionic sticky interlayer strategy.

Study on the free surface evolution and slamming pressure of curved-wedge water entry using a Riemann-smoothed particle hydrodynamics method

The present study aims to provide a deep understanding of curved wedge water entry. It involves a numerical simulation investigation into the kinematic and dynamic properties of water entry for two curved wedges with deadrise angles of 25° and 35°. The meshless Riemann-smoothed particle hydrodynamics (SPH) model embedded with an acoustic damper is developed to simulate these violent water entries. The validation of the Riemann-SPH accuracy is confirmed through comparison with experimental data, and subsequently, we make a systematical simulation study on curved wedge water entry, including a comparative study of free surface evolution and pressure distribution at different curvatures and drop heights. Furthermore, the kinematics analysis of velocity and displacement of curved wedges and time domain characteristics of slamming pressure loads on both sides of the wedge are investigated. It is revealed that the pressure distribution is symmetrical, with high-pressure regions forming near the bottom of the wedge and gradually propagating outward. The free surface profiles are symmetrical, with deeper depressions formed by sharper wedges. The entry depth and velocity are correlated with the initial theoretical entry velocity, and the rate of speed decline varies with the curvature of the wedge. The slamming pressure loads exhibit distinct time-domain patterns, with lower pressure loads by sharper wedges.

Banana fruit bruise detection using fractal dimension based image processing

The study used the fractal dimension (FD), browning incidence, and grayscale values using machine vision to describe the bruise magnitude and quality of mechanically damaged ‘Fard’ bananas bruised from 20, 40, 60 cm drop heights by 66, 98, and 110 g ball weights conditioned at different storage temperatures (5, 13, 22 °C) after 48 h. Conventional analyses like bruise area (BA), bruise volume (BV), and bruise susceptibility (BS) were also conducted. A correlation was performed to determine the relationship between image processing and conventional assessment of bruise damage in bananas. Weight, firmness, color, sugar content, and acidity were investigated. The results demonstrated that bananas bruised from the highest force and stored at 5 and 22 °C reported the lowest FD with values of 1.7162 and 1.7403, respectively. Increasing the level of damage reduced the fractal dimension and grayscale values and increased browning incidence and bruise susceptibility values after 48 h of storage. The total color change values showed a strong Pearson's correlation coefficient (r≥-0.81) with image analysis fractal dimension and grayscale values. The findings also indicated that higher bruising and temperature can induce weight loss, firmness reduction, lightness, and yellowness increment, and sugar and acidity changes. Overall, the fractal image analysis conducted in this study was highly effective in describing the bruising magnitude of bananas under different conditions.

Commercial Soccer Ball‐Integrated Triboelectric Nanogenerator

Triboelectric nanogenerators (TENG) are representative mechanical energy harvesters that can easily generate electricity based on contact electrification and electrostatic induction. However, most TENGs have low mechanical and electrical output stabilities because of their unstable structures, in which separate TENG devices are attached to the outside surface of commercial products/items for application. Herein, a commercial soccer ball‐integrated TENG (CSB‐TENG) is proposed as a potential solution. The CSB‐TENG is designed with an electrode‐fully packaged all‐in‐one structure; thus, it can have remarkable mechanical and electrical output stability for 160 000 cycles. For one bouncing motion, the CSB‐TENG generates a maximum peak power of 480 μW. The working mechanism of the CSB‐TENG is established by considering the actual motion of a soccer ball (kicking, bouncing, and rolling). The electrical output of the CSB‐TENG is evaluated and analyzed based on various design and environmental variables (ball material, shoe material, ground material, impact force, ball drop height, and electrode size) in daily life. The CSB‐TENG demonstrates applications, including LED array illumination and capacitor charging tests.

Measurement and Analysis of the Shock and Drop Levels Experienced by Small and Medium Packages in the Korean Parcel Delivery System

South Korea is one of the leading markets for the e-commerce industry. In line with the rapid growth of the e-commerce industry, the parcel delivery volume in Korea has also proliferated. Despite the developments in the Korean e-commerce and courier industries, consumers still experience a high package damage rate. In response, many packaging engineers in Korea have raised the need for new parcel shipping environment tests that reflect the Korean ground shipping environment in order to properly optimize packages. However, only limited information on the Korean parcel shipping environment is currently available. Therefore, this study focused on measuring and analyzing the shock and drop levels that parcels experience during ground shipping in Korea. Shock data were collected from a total of sixty one-way shipments for small, lightweight packages and medium, mid-weight packages. The findings revealed that the two types of boxes do not experience significantly different numbers of shock events or drop heights in the Korean parcel delivery environment. Furthermore, the number of shock events that occur in Korea is substantially less than the international testing standard and less than in previous studies conducted in both Europe and the USA. In contrast, however, the drop heights are higher than those in the international testing standard and previous studies. Shock events were found to occur most frequently on the edges and to be concentrated around the bottoms of the packages. Most shock events happen while packages are loaded and unloaded at hub terminals and sub terminals.

Spherical core-shell CL-20@LLM-105 composites with excellent mechanical sensibility obtained by Pickering emulsion

The effect of crystallization conditions on the morphology, particle size and dispersibility of 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) was investigated by solvent-nonsolvent method, and nano-LLM-105 was successfully prepared and used as a surfactant after modification with stearic acid. A spherical core-shell composites of CL-20@LLM-105 was prepared by Pickering emulsion method. The morphology, crystal structure, and thermal decomposition properties were characterized by scanning electron microscopy (SEM), powder X-ray diffractometry (XRD), differential scanning calorimetry (DSC), fourier transform infrared (FT-IR) tested for impact and friction sensibility. The results showed that the prepared composites had a particle size of 50–100 μm, a spherical core-shell structure, and nano-LLM-105 was encapsulated on its surface. The peak thermal decomposition temperature of the composites was 252.7 ℃, which was 9.4 ℃ higher than that of the raw material CL-20. Compared with the CL-20/LLM-105 mixture with the same ratio, the characteristic drop height (H50) of the CL-20@LLM-spherical compoe-shell site was increased by 13 cm, and the explosion probability (P) was reduced by 43%. The spherical core-shell composites prepared by this method is characterized by high energy and excellent mechanical sensibility, which is expected to provide new ideas for the design of explosive formulations containing CL-20 and nanoenergy-containing materials in the direction of high safety and high energy.

Developing and Assessing Performance of a Laboratory-Scale Fluidized Bed Dryer

A laboratory-scale batch fluidized bed dryer with 75 mm bed diameter was designed, fabricated and evaluated to study the hydrodynamics of river sand as well as the drying of cassava mash and bitter kola particulates. The hydrodynamics properties such as minimum fluidization velocity, effect of bed height and pressure drop across the bed, effect of particle size and density on minimum fluidization velocity and stability of the bed column of river sand were studied. Drying of cassava mash to edible garri was carried out at in fluidized bed dryer at controlled temperatures. Drying characteristics of the laboratory fluidized bed dryer was compared with the laboratory WiseVen oven (model number: WOF - 105) using bitter kola particulate material sample. The experimental results from laboratory-scale fluidized bed dryer showed that the minimum fluidization velocity increases as material density increases and the value of the minimum fluidization velocity obtained from the fluidized bed gave good agreement with other empirical correlation such as Kozeny-Carman Equation. The fluidized bed dryer showed high rates of moisture removal over the conventional oven with the ratio of 1:29 under the same operating conditions. Drying of cassava mash to edible garri was achieved at lower drying temperatures of 83 oC \(\pm\) 3 oC at 55 minutes when compared to conventional frying temperatures of cassava mash to edible at 180 – 200 oC thereby saving energy cost. Hence, this fluidized bed dryer is recommended for use in demonstrating hydrodynamics and drying of particulate materials in the laboratory.

Numerical contact line behavior prediction for drop-wall impact using Basilisk

Drop-wall impact and spray cooling have a wide technical application. There are still fundamental problems associated with wettability and its effect on the drop spreading. Experiments and direct numerical simulations are performed in a wide range of initial drop velocities (0.2–3.6 m/s). The 3D simulation is implemented by solving the incompressible Navier-Stokes equations along with the volume-of-fluid method in the Basilisk software. An adaptive mesh refinement near the interfacial surface provides a cell size of 5 µ m. The effect of the contact angle calculated using the Hoffman function on the minimum drop height and its maximum spreading is explored. The contact angle affects the dynamics of the contact line. Moreover, the mesh cell size and the initial velocity of a water drop before impact define the development of the drop rim instability when compared with experimental results. Experimental and numerical findings are compared to estimate quantitatively numerical model capabilities.

THE EFFICIENCY AND COEFFICIENT OF SPORTS BALLS RESTITUTION USING AN ACOUSTIC APPLICATION

Studying the efficiency of a sports ball and its coefficient of restitution is important for performance optimization, fairness, and consistency of play. This research paper is dedicated to studying the coefficient of restitution and bounce efficiency in sports ball. Ping Pong ball and tennis balls were used to show the relationship between the bounce height and drop height. This paper used standard laboratory equipment like meter ruler, retort stand, clamp and with the utilization of the acoustic program of the smartphone using PhyPhox. The result showed that the application was able to accurately measure the bounce height in relation to the drop height. This was showed in the straight-line graph plotted. There was a constant ball efficiency coefficient of restitution and have very small percent error from the standard. This experiment can boost the interest and confidence of students in the classroom. Being able to accurately measure the performance of different balls can help students understand the science and engineering principles behind how they work. This knowledge can benefit students by allowing them to make more informed decisions when purchasing sports equipment, as well as give them an opportunity to modify their playing methods and strategies.

Experimental and Numerical Prediction of Slamming Impact Loads Considering Fluid–Structure Interactions

Slamming impacts on water are common occurrences, and the whipping induced by slamming can significantly increase the structural load. This paper carries out an experimental study of the water entry of rigid wedges with various deadrise angles. The drop height and deadrise angle are parametrically varied to investigate the effect of the entry velocity and wedge shape on the impact dynamics. A two-way coupled approach combing CFD method software STAR-CCM+12.02.011-R8 and the FEM method software Abaqus 6.14 is presented to analyze the effect of structural flexibility on the slamming phenomenon for a wedge and a ship model. The numerical method is validated through the comparison between the numerical simulation and experimental data. The slamming pressure, free surface elevation, and dynamic structural response, including stress and strain, in particular, are presented and discussed. The results show that the smaller the inclined angle at the bottom of the wedge-shaped body, the faster the entry speed into the water, resulting in greater impact pressure and greater structural deformation. Meanwhile, studies have shown that the bottom of the bow is an area of concern for wave impact problems, providing a basis for the assessment of ship safety design.

Testing the shock protection performance of Type I construction helmets using impactors of different masses.

Wearing protective helmets is an important prevention strategy to reduce work-related traumatic brain injuries. The existing standardized testing systems are used for quality control and do not provide a quantitative measure of the helmet performance. To analyze the failure characterizations of Type I industrial helmets and develop a generalized approach to quantify the shock absorption performance of Type I industrial helmets based on the existing standardized setups. A representative basic Type I construction helmet model was selected for the study. Top impact tests were performed on the helmets at different drop heights using two different impactor masses (3.6 and 5.0 kg). When the helmets were impacted with potential impact energies smaller than the critical potential impact energy values, there was a consistent relationship between the peak impact force and the potential impact energy. When the helmets were impacted under potential impact energies greater than the critical potential impact energy values, the peak impact forces increased steeply with increasing potential impact energy. A concept of safety margin for construction helmets based on potential impact energy was introduced to quantify the helmets' shock absorption performance. The proposed method will help helmet manufacturers improve their product quality.

Use of an Impact Recording Device to Determine the Risk of Bruising in Packaged Potatoes

Handling potatoes individually or collectively in packages can create opportunities for potatoes to develop quality defects including blackspot and shatter bruise. Three trials were conducted to examine how handling packaged potatoes can influence the risk for physical damage including shatter and blackspot bruise. An impact recording device was used to record peak acceleration (max g-force) in common fresh market packaging options (boxes or bales) at four drop heights (15 to 91 cm) on to three different surface types. When boxed potatoes were dropped onto concrete or a plastic slip, the potatoes on the bottom of the box had the highest risk of damage (greater than 100 g-force). When drop heights were lowered, or when cushioning material was added to hard surfaces (e.g., wooden pallet on top of concrete floor), the risk for impact damage was decreased throughout the box. When palletizing boxed potatoes, the risk of bruise decreased after the first layer was stacked on the pallet. Drop heights need to be below 15 cm, especially when making the first layer in a palletized stack of packaged potatoes to reduce potential bruising. The risk of high peak accelerations was not seen in the dropped or stationary bales for any of the drop heights examined. This study provided information for educating personnel on handling packaged potatoes and determining situations in which robotic stacking equipment needs to be adjusted to lower drop heights of packaged potatoes.

Association between Sprint and Jump Performance and Maximum Strength in Standing Calf Raise or Squat in Elite Youth Soccer Players.

Soccer is a complex sports discipline that requires players to engage in diverse high-intensity and multidirectional activities. The optimization of strength and conditioning programs requires a comprehensive understanding of the physical attributes influencing player performance. While previous research has demonstrated the influence of knee and hip extensor muscles on the performance in sprints and other explosive movements, this study aimed to establish the relationship between plantar flexor muscle strength and high-intensity actions. Back squat (BS) and calf raise (CR) one-repetition maxima as well as linear sprint (5-, 10-, 30 m) and drop jump performance from different heights (15, 30, 45 and 60 cm) were measured in 45 elite youth players (age: 16.62 ± 1.1 years). Results showed significant negative correlations between BS strength and sprint times (r = -0.60 to -0.61), confirming the importance of lower limb extensor muscle strength in short-distance sprints. While no significant correlations were found with sprint performances, CR strength was significantly associated with drop jump test results from 45 and 60 cm drop height (r = 0.36 to 0.46). These findings demonstrate that isolated CR strength positively influences the performance in actions involving rapid stretch-shortening cycles, which suggests that current strength and conditioning programs for youth soccer players should be extended to also include exercises specifically targeting the plantar flexor muscles. While this cross-sectional study provides novel insights into the complex interplay between muscle strength and soccer-specific performance, its findings need to be corroborated in longitudinal studies directly testing the impact of plantar flexor strength training.

Optimizing pile bearing capacity prediction: Insights from dynamic testing and smart algorithms in geotechnical engineering

In contemporary mining and geotechnical projects, various approaches are employed to predict the bearing capacity of piles (Qu). However, accurately modeling pile behavior using numerical, experimental, analytical, and regression methods proves challenging and, at times, infeasible due to the intricate nature of geotechnical materials, uncertainties, and the interaction between soil and piles. Consequently, formulations are generally presented, incorporating assumptions and simplifications that deviate from the actual complexity of the problem. Moreover, despite the high accuracy of pile loading tests as a reliable method in various design stages, their high costs and time requirements deter designers from conducting field tests. To address these challenges, this study performed 50 dynamic tests (HSDT) on precast concrete piles in Indonesia, Pekanbaru, to generate the necessary datasets. To mitigate experimental costs, two optimization algorithms fruit fly optimization (FFO) and invasive weed optimization (IWO) were employed. These models incorporated pile set (S), drop height (H), hammer weight (W), cross-sectional area (A), and length (L) as input parameters. Finally, the models' accuracy was evaluated using squared correlation coefficient (R2), variance accounted for (VAF), mean square error (MSE), mean absolute percentage error (MAPE), and root mean square error (RMSE). The results revealed that the FFO algorithm achieved an accuracy range of 0.971–0.978. Similarly, the IWO algorithm exhibited an accuracy range of 0.984–0.988. Additionally, sensitivity analysis indicated that, among the input parameters, W had the most significant impact on the Qu in both algorithms.

Effects of Stroboscopic Vision on Depth Jump Motor Control: A Biomechanical Analysis.

Researchers commonly use the 'free-fall' paradigm to investigate motor control during landing impacts, particularly in drop landings and depth jumps (DJ). While recent studies have focused on the impact of vision on landing motor control, previous research fully removed continuous visual input, limiting ecological validity. The aim of this investigation was to evaluate the effects of stroboscopic vision on depth jump (DJ) motor control. Ground reaction forces (GRF) and lower-extremity surface electromyography (EMG) were collected for 20 young adults (11 male; 9 female) performing six depth jumps (0.51 m drop height) in each of two visual conditions (full vision vs. 3 Hz stroboscopic vision). Muscle activation magnitude was estimated from EMG signals using root-mean-square amplitudes (RMS) over specific time intervals (150 ms pre-impact; 30-60 ms, 60-85 ms, and 85-120 ms post-impact). The main effects of and interactions between vision and trial number were assessed using two-way within-subjects repeated measures analyses of variance. Peak GRF was 6.4% greater, on average, for DJs performed with stroboscopic vision compared to full vision (p = 0.042). Tibialis anterior RMS EMG during the 60-85 ms post-impact time interval was 14.1% lower for DJs performed with stroboscopic vision (p = 0.020). Vastus lateralis RMS EMG during the 85-120 ms post-impact time interval was 11.8% lower for DJs performed with stroboscopic vision (p = 0.017). Stroboscopic vision altered DJ landing mechanics and lower-extremity muscle activation. The observed increase in peak GRF and reduction in RMS EMG of the tibialis anterior and vastus lateralis post-landing may signify a higher magnitude of lower-extremity musculotendinous stiffness developed pre-landing. The results indicate measurable sensorimotor disruption for DJs performed with stroboscopic vision, warranting further research and supporting the potential use of stroboscopic vision as a sensorimotor training aid in exercise and rehabilitation. Stroboscopic vision could induce beneficial adaptations in multisensory integration, applicable to restoring sensorimotor function after injury and preventing injuries in populations experiencing landing impacts at night (e.g., military personnel).

A Novel Method of Improving the Mechanical Properties of Propellant Using Energetic Thermoplastic Elastomers with Bonding Groups.

The relatively poor mechanical properties of extruded modified double base (EMDB) propellants limit their range of applications. To overcome these drawbacks, a novel method was proposed to introduce glycidyl azide polymer-based energetic thermoplastic elastomers (GAP-ETPE) with bonding groups into the propellant adhesive. The influence of the molecular structure of three kinds of elastomers on the mechanical properties of the resultant propellant was analyzed. It was found that the mechanical properties of the propellant with 3% CBA-ETPE (a type of GAP-ETPE that features chain extensions using N-(2-Cyanoethyl) diethanolamine and 1,4-butanediol) were improved at both 50 °C and -40 °C compared to a control propellant without GAP-ETPE. The elongation and impact strength of the propellant at -40 °C were 7.49% and 6.58 MPa, respectively, while the impact strength and maximum tensile strength of the propellant at 50 °C reached 21.1 MPa and 1.19 MPa, respectively. In addition, all three types of GAP-ETPE improved the safety of EMDB propellants. The friction sensitivity of the propellant with 3% CBA-ETPE was found to be 0%, and its characteristic drop height H50 was found to be 39.0 cm; 126% higher than the traditional EMDB propellant. These results provide guidance for studies aiming to optimize the performance of EMDB propellants.