Total Impulse Research Articles

Accelerator Grid Life Modeling of T6 Ion Thruster for BepiColombo

The T6 ion thruster is providing in-space propulsion for the BepiColombo mission, currently en route to Mercury. Simulations of the accelerator grid erosion during flight operation were carried out using the CEX2D and CEX3D codes in order to verify that the grid lifetime will be sufficient to impart the 5.75 total impulse per thruster required for the mission. Before calculating in-space erosion rates, the models were benchmarked against data from long-duration wear tests. Two-dimensional simulations tracked the time-dependent grid geometry and calculated changes in the electron backstreaming limit as the grids eroded. Sensitivity studies assessed the impact of uncertainty in the operating screen-to-accelerator grid gap on . Three-dimensional simulations employed a particle-in-cell model for the charge exchange ions and were able to accurately reproduce the nonaxisymmetric pits and grooves erosion pattern observed on the downstream face of the accelerator grid following ground testing. Charge exchange ion space charge effects were found to broaden the pit erosion features in flight, further reducing the peak erosion rate relative to that observed on the ground. The simulations predicted that T6 will have sufficient margin against both electron backstreaming and accelerator grid wearthrough over the duration of the mission.

Individual transducer impulse response characterization method to improve image quality of array-based handheld optoacoustic tomography.

The physical properties of each transducer element play a vital role in the quality of images generated in optoacoustic (photoacoustic) tomography using transducer arrays. Thorough experimental characterization of such systems is often laborious and impractical. A shortcoming of the existing impulse response correction methods, however, is the assumption that all transducers in the array are identical and therefore share one electrical impulse response (EIR). In practice, the EIRs of the transducer elements in the array vary, and the effect of this element-to-element variability on image quality has not been investigated so far, to the best of our knowledge. We hereby propose a robust EIR derivation for individual transducer elements in an array using sparse measurements of the total impulse response (TIR) and by solving the linear system for temporal convolution. Thereafter, we combine a simulated spatial impulse response with the derived individual EIRs to obtain a full characterization of the TIR, which we call individual synthetic TIR. Correcting for individual transducer responses, we demonstrate significant improvement in isotropic resolution, which further enhances the clinical potential of array-based handheld transducers.

Analysis and Design of One-Way Steel-Plate Composite Walls for Far-Field Blast Effects

AbstractThis paper presents the development of normalized total force-total impulse (P-I) diagrams for analyzing and designing steel-plate composite (SC) walls to resist far-field blast loads. The ...

Creatine supplementation attenuates the rate of fatigue development during intermittent isometric exercise performed above end-test torque.

What is the central question of this study? Does creatine supplementation augment the total torque impulse accumulated above end-test torque (IET) during severe-intensity knee-extensor exercise by attenuating the rate of decrease in peak potentiated twitch torque (PT)? What is the main finding and its importance? Creatine augmented the IET and attenuated the rate of decrease in both voluntary activation and PT during severe-intensity exercise. The IET was related to the rate of decrease in PT. These findings reveal an important role for the rates of neuromuscular fatigue development as key determinants of exercise tolerance within the severe domain. This study investigated the effect of creatine supplementation on exercise tolerance, total torque impulse accumulated above end-test torque (total IET) and neuromuscular fatigue development of the knee extensors during severe-intensity intermittent isometric exercise. Sixteen men were randomly allocated into Creatine (n=8, 20gday-1 for 5days) or Placebo (n=8) groups and performed knee-extensor maximal voluntary contraction (MVC) testing, all-out testing to determine end-test torque (ET) and the finite torque impulse accumulated above end-test torque (IET'), and three submaximal tests at ET+10%: (i) time to task failure without supplementation (Baseline); (ii) time to task failure after creatine or placebo supplementation; and (iii) time matched to Baseline after creatine (Creatine-Isotime) or placebo (Placebo-Isotime) supplementation. Creatine supplementation significantly increased the time to task failure (Baseline=572±144sversusCreatine=833±221s) and total IET (Baseline=5761±1710 Nms versus Creatine=7878±1903Nms), but there were no significant differences within the Placebo group. The percentage change pre- to postexercise in MVC, voluntary activation, peak potentiated twitch torque and integrated EMG during MVC were not significantly different between Baseline and Creatine but were all significantly attenuated in Creatine-Isotime compared with Baseline. There were no significant differences in these variables within the placebo group. The total IET was significantly correlated with the rates of change in potentiated twitch torque peak (r=0.83-0.87) and rate of torque development (r=-0.83 to -0.87) for the submaximal tests to task failure. These findings reveal an important role for the rates of neuromuscular fatigue development as key determinants of exercise tolerance during severe-intensity intermittent isometric exercise.

Utilising one minute and four minute recovery when employing the resistance training contrast method does not negatively affect subsequent jump performance in the presence of concurrent training.

BackgroundLittle is known about contrast training and post-activation performance enhancement (PAPE) in a same day concurrent training model. The aim of the current study was to examine the use of two short duration (1-min and 4-min) recovery periods on drop jump performance in same day concurrently trained athletes.MethodsTen professional Australian Rules footballers (age, 20.6 ± 1.9 yr; height, 184.8 ± 6.9 cm; body mass, 85.8 ± 8.4 kg) completed two resistance training sessions with different PAPE recovery durations; 1-min and 4-min, 1 h following a field-based endurance session. Baseline (pre) drop jumps were compared to post-test maximal drop jumps, performed after each set of three squats (where each participant was encouraged to lift as heavy as they could), to determine changes between 1-min and 4-min recovery periods. Data were analysed by fitting a mixed model (significance was set at P ≤ 0.05). Corrected Hedges’ g standardised effect sizes ±95% confidence limits were calculated using group means ± SDs.ResultsThere were no significant differences between baseline and experimental sets 1, 2 and 3 for reactive strength index (RSI), flight time, and total and relative impulse for either recovery duration. However, for contact time, 1-min baseline was significantly different from set 2 (mean difference; 95% CI [0.029; 0.000–0.057 s], P = 0.047, ES; 95% CI [−0.27; −1.20 to 0.66]). For RSI and flight time, 1-min was significantly higher than 4-min (RSI: 0.367; 0.091 to 0.642, P = 0.010, ES; 95% CI [0.52; −0.37 to 1.42]; flight time: 0.033; 0.003 to 0.063 s, P = 0.027, ES; 95% CI [0.86; −0.06 to 1.78]).DiscussionShort recovery periods of 1-min may be a time-efficient form of prescribing strength-power exercise in contrast loading schemes. Longer recovery periods do not appear to benefit immediate, subsequent performance.

Naphthalene as a Cubesat Cold Gas Thruster Propellant

The `cubesat' form factor (multiples of 10x10x10 cm^3 volume and 1.33 kg mass) has been adopted as the defacto standard for a cost effective and modular, nano-satellite platform. Many commercial options exist for nearly all components required to build such satellite; however, there is a limited range of thruster options that suit the power and size restrictions of a cubesat. This work presents the design, implementation and direct thrust measurements of a proof of concept cubesat cold gas thruster system using naphthalene (C10H8) as the propellant. The proposed design is optimised for simplicity to match the requirement of entry level cubesat missions, yet, due to the properties of naphthalene, it can achieve a total impulse in the order of tens of newton-seconds.

Relationship Between Internal and External Training Load in Field Hockey

Training load monitoring in team sports is important in order to plan and evaluate training strategies and ensure optimal performance. Integration of internal and external training load measures into a single training efficiency metric reduces the effect of confounding variables on training loads. The purpose of this study was to generate a training efficiency metric to evaluate in-season field hockey training. Further, the relationship between players’ perceived wellness the training efficiency metric was determined. Internal (training impulse and session rating of perceived exertion; TRIMP and sRPE) and external (total distance, high-speed distance, acceleration load, high-power distance, metabolic work, mechanical work, and impulse) training load was collected over a 6-week period for 11 male national level field hockey players (21.1 ± 1.2 years, 178.7 ± 8.6 cm, 4.6 ± 6.3 kg). The relationships between internal and external training load were assessed, and two training efficiency models were generated through mixed model analyses using sRPE and TRIMP. Subsequently, the relationships between training efficiency and perceived wellness were examined. The statistical analyses determined that total distance, high-speed distance, high-power distance, and metabolic work (r = 0.311-0.573) were included in the TRIMP training efficiency model. The sRPE training efficiency model included total distance, high-speed distance, high-power distance, metabolic work, and mechanical work (r = 0.329-0.757). Moreover, neither of the training efficiency models were related to daily cumulative wellness scores (TRIMP: r = -0.046; p = 0.336; sRPE: r = -0.034; p = 0.370). The study showed that the sRPE training efficiency model provided a better reflection of in-season field hockey training demands than the TRIMP model. Additionally, practitioners are not advised to adjust training based on acute changes in players’ perceived wellness.

Wave-in-deck experiments with focussed waves into a solid deck

This paper examines impact forces resulting from wave-in-deck processes from two separate series of experiments: one with a generic solid deck model, and the other with a combined jacket and deck model, both were conducted with and without an I-beam grillage in-place below the solid deck. A range of inundation levels from 2.1 to 7.1 cm at 1:80 scale is considered. The focus is on global impact forces, which are considered more relevant for integrity assessment of overall bottom-founded structures when survivability is in question and local slamming is not addressed. The objective is to characterise the resultant impact forces as well as to investigate whether there is any interaction between the flows through the jacket and hitting the deck. Focussed wave groups were generated to impinge on the models which were suspended from a carriage over a towing tank. The motion of the support carriage mimics uniform current in-line with the incident waves. Both undisturbed surface elevations as well as impact force time histories were measured. From the first series of tests, a large increase in peak forces as well as high frequency oscillations (force spikes) is observed with the grillage in-place. As soon as the jacket model is in-place for the second series of tests, albeit with a different mounting support arrangement, such a large difference vanishes, which could likely be due to the effect of frequency-dependent transfer functions. We provide experimental evidence of the presence of the jacket in modifying the wave impact on the deck through a significant reduction in the total horizontal impulse. The effects of current on the wave impact forces are also investigated. A simple analytical model based on a momentum argument is used to describe the scaling of horizontal peak force with currents and inundation levels. Finally, the importance of the short duration force spikes as well as vertical impact loads on a real structure at full-scale is discussed based on the same analytical model.

Hydroelasticity effects on water-structure impacts

Local and global loadings, which may cause the local damage and/or global failure and collapse of offshore structures and ships, are experimentally investigated in this study. The research question is how the elasticity of the structural section affects loading during severe environmental conditions. Two different experiments were undertaken in this study to try to answer this question: (i) vertical slamming impacts of a square flat plate, which represents a plate section of the bottom or bow of a ship structure, onto water surface with zero degree deadrise angle; (ii) wave impacts on a truncated vertical wall in water, where the wall represents a plate section of a hull. The plate and wall are constructed such that they can be either rigid or elastic by virtue of a specially designed spring system. The experiments were carried out in the University of Plymouth’s COAST Laboratory. For the cases considered here, elasticity of the impact plate and/or wall has an effect on the slamming and wave impact loads. Here the slamming impact loads (both pressure and force) were considerably reduced for the elastic plate compared to the rigid one, though only at high impact velocities. The total impact force on the elastic wall was found to reduce for the high aeration, flip-through and slightly breaking wave impacts. However, the impact pressure decreased on the elastic wall only under flip-through wave impact. Due to the elasticity of the plates, the impulse of the first positive phase of pressure and force decreases significantly for the vertical slamming impact tests. This significant effect of hydroelasticity is also found for the total force impulse on the vertical wall under wave impacts.Graphic abstractHydroelasticity effects on water-structure impacts: a impact pressures on dropped plates; b impact forces on dropped plates; c, d, e, f wave impact pressures on the vertical walls; g wave impact forces on the vertical walls; h wave force impulses on the vertical walls: elastic wall 1 vs. rigid wall (filled markers); elastic wall 2 vs. rigid wall (empty markers)

The Characterization Of The Transition Phase During A 180° Change Of Direction Task

The evaluation of change of direction ability should not merely rely on the measurement of total sprinting time, but it should focus also on the understanding of specific movement patterns. PURPOSE: To evaluate the transition phase (TP) during a 180° change of direction (COD) task. METHODS: 14 recreational basketball athletes (age: 21.4±2.6 years) were evaluated during a 10-m COD test. TP has been identified considering 3 consecutive steps (i.e., final decelerating foot contact [DFC], turning foot contact [TFC], first accelerating foot contact [AFC]), using two force platforms. Differences in total (TCT), braking (BCT), and propulsive (PCT) contact time, vertical braking (VBGRF) and propulsive (VPGRF) ground reaction force (relative to body mass), and vertical braking (VBI), propulsive (VPI), and total (VTI) impulse (relative to body mass) were evaluated in relation to leg preference, the 3 steps, and groups (slower vs. faster defined as those below and above the 50th percentile of total sprinting time). RESULTS: No differences emerged for leg preference. TP (1.199±0.11 s) contributed for an average of 42.6±3.4% to the total sprinting time (2.817±0.14 s), with DFC involving only a braking action, whilst TFC and AFC comprising both a braking and propulsive action. Differences (p<0.05) among the 3 steps emerged for TCT (DFC: 0.380±0.07 s; TFC: 0.525±0.06 s; and AFC: 0.303±0.04 s), VBGRF (DFC: 22.7±7.5 N·kg-1; TFC: 20.3±2.8 N·kg-1; and AFC: 8.1±2.7 N·kg-1), VBI (DFC: 2.1±0.4 m·s-1; TFC: 2.5±0.5 m·s-1; and AFC: 0.4±0.2 m·s-1), and VTI (DFC: 2.1±0.4 m·s-1; TFC: 5.6±0.6 m·s-1; and AFC: 2.6±0.3 m·s-1). Furthermore, differences (p<0.05) between TCF and AFC were evident for VPGRF (TFC: 14±1.2 N·kg-1; and AFC: 15.6±1.7 N·kg-1) and VPI (TFC: 3.1±0.6 m·s-1; and AFC: 2.2±0.4 m·s-1). Differences between groups emerged in the TFC only, with faster individuals demonstrating shorter TCT (0.489±0.1 s) and PCT (0.281±0.1 s), and lower VPI (2.8±0.5 m·s-1) compared to slower individuals (TCT: 0.542±0.1 s; PT: 0.339±0.1 s; and VPI 3.4±0.6 m·s-1). CONCLUSIONS: Findings revealed specific movement patterns during the TP of a COD task and the central role played by the turning step in differentiating faster and slower recreational basketball athletes, with potential further implications for future testing and training procedures.

Pushing the boundaries of optoacoustic microscopy by total impulse response characterization

Optical microscopy improves in resolution and signal-to-noise ratio by correcting for the system’s point spread function; a measure of how a point source is resolved, typically determined by imaging nanospheres. Optical-resolution optoacoustic (photoacoustic) microscopy could be similarly corrected, especially to account for the spatially-dependent signal distortions induced by the acoustic detection and the time-resolved and bi-polar nature of optoacoustic signals. Correction algorithms must therefore include the spatial dependence of signals’ origins and profiles in time, i.e. the four-dimensional total impulse response (TIR). However, such corrections have been so far impeded by a lack of efficient TIR-characterization methods. We introduce high-quality TIR determination based on spatially-distributed optoacoustic point sources (SOAPs), produced by scanning an optical focus on an axially-translatable 250 nm gold layer. Using a spatially-dependent TIR-correction improves the signal-to-noise ratio by >10 dB and the axial resolution by ~30%. This accomplishment displays a new performance paradigm for optoacoustic microscopy.

Influence of Nozzle Type, Divergence Angle and Area Ratio on Impulse of Pulse Detonation Engine

The influence of nozzle geometry on the impulse produced by the single cycle Pulse detonation engine (PDE) was experimentally investigated. For each experiment the nozzles were attached at the end of the engine. The impulse produced by the pulse detonation engine was calculated from the measured thrust. The thrust measurement was done by sliding the engine on the central bar of the thrust stand. The main structure of the basic PDE has a detonation tube with one terminal closed, a Schelkin spiral used as deflagration to detonation device, and a thrust stand to support the structure. Stoichiometric acetylene and oxygen mixture were used as detonation mixture. Various nozzles with a range of divergent angle and area ratios were tested. The calculations of the impulse were made from the thrust pulse for the duration it lasted. The effect of the type of nozzle, divergent angle and area ratio were observed. The bell shaped nozzle with large angle of divergence produced maximum specific impulse of 80 Sec with 20° divergence angle and area ratio of 6.942; maximum impulse was produced by the bell shaped nozzle with a small area ratio of 2.969 and 10° divergence angle. The maximum total impulse obtained was 1200 N-sec.

Muscle length: A new feature to investigate neural control of lengthening contractions.

Muscle length: A new feature to investigate neural control of lengthening contractions.

Design and Test of a Student Hybrid Rocket Engine with an External Carbon Fiber Composite Structure

The development of hybrid rockets offers excellent opportunities for the practical education of students at universities due to the high safety and relatively low complexity of the rocket propulsion system. During the German educational program Studentische Experimental-Raketen (STERN), students of the Technische Universität Braunschweig obtain the possibility to design and launch a sounding rocket with a hybrid engine. The design of the engine HYDRA 4X (HYbridDemonstrations-RaketenAntrieb) is presented, and the results of the first engine tests are discussed. The results for measured regression rates are compared to the results from the literature. Furthermore, the impact of the lightweight casing material carbon fiber-reinforced plastic (CFRP) on the hybrid engine mass and flight apogee altitude is examined for rockets with different total impulse classes (10 to 50 kNs). It is shown that the benefit of a lightweight casing material on engine mass decreases with an increasing total impulse. However, a higher gain on apogee altitude, especially for bigger rockets with a comparable high total impulse, is shown.

The Distribution of Match Activities Relative to the Maximal Mean Intensities in Professional Rugby League and Australian Football.

Johnston, RD, Thornton, HR, Wade, JA, Devlin, P, and Duthie, GM. The distribution of match activities relative to the maximal mean intensities in professional rugby league and Australian football. J Strength Cond Res 36(5): 1360-1366, 2022-This study determined the distribution of distance, impulse, and accelerometer load accumulated at intensities relative to the maximal mean 1-minute peak intensity within professional rugby league and Australian football. Within 26 rugby league (n = 24 athletes) and 18 Australian football (n = 38 athletes) games, athletes wore global navigation satellite system devices (n = 608 match files). One-minute maximal mean values were calculated for each athlete per game for speed (m·minP-1P), accelerometer load (AU·minP-1P), and acceleration (m·sP-2P). Volumes for each parameter were calculated by multiplying by time, specifying total distance, accelerometer load, and impulse. The distribution of intensity of which these variables were performed relative to the maximal mean was calculated, with percentages ranging from 0-110%, separated into 10% thresholds. Linear mixed models determined whether the distribution of activities within each threshold varied, and positional differences. Effects were described using standardized effect sizes (ESs), and magnitude-based decisions. Across both sports, the distribution of activity (%) largely reduced the closer to the maximal mean 1-minute peak and was highest at ∼60% of the maximal mean peak. When compared with Australian football, a higher percentage of total distance was accumulated at higher intensities (70-80% and 100-110%) for rugby league (ES range = 0.82-0.87), with similar, yet larger differences for accelerometer load >80% (0.78-1.07) and impulse >60% (1.00-2.26). These findings provide information of the volume of activities performed relative to the mean maximal 1-minute peak period, which may assist in the prescription of training.

Hybrid removal of end-of-life geosynchronous satellites using solar radiation pressure and impulsive thrusts

This paper proposes an analytical solution of removing end-of-life GEO satellites to the GEO graveyard region using solar radiation pressure (SRP) and impulsive thrusts. The dynamic model of a GEO satellite equipped with a solar sail is first built upon the magnitude comparisons of different accelerations exerted on the satellite. Then the dynamic system is constructed based on the Gauss’s Variation of Parameter (VOP) equations, and linearized along a nominal trajectory. Control angles of the sail and impulsive thrust vectors are generated using the proposed optimal hybrid disturbance-accommodation tracking maneuvers. Simulations indicate that, to remove a satellite in 360 days using only SRP with the proposed method, a minimal area-to-mass (A/M) ratio of 0.13 m2/kg is required. When the A/M ratio of spacecraft is smaller than the minimal value, impulsive thrusts are applied to assist the removal process. For a satellite with an A/M ratio of 0.1 m2/kg, a total impulse of 10.5 m/s is required.

A Synthetic Total Impulse Response Characterization Method for Correction of Hand-Held Optoacoustic Images.

The impulse response of optoacoustic (photoacoustic) tomographic imaging system depends on several system components, the characteristics of which can influence the quality of reconstructed images. The effect of these system components on reconstruction quality have not been considered in detail so far. Here we combine sparse measurements of the total impulse response (TIR) with a geometric acoustic model to obtain a full characterization of the TIR of a handheld optoacoustic tomography system with concave limited-view acquisition geometry. We then use this synthetic TIR to reconstruct data from phantoms and healthy human volunteers, demonstrating improvements in image resolution and fidelity. The higher accuracy of optoacoustic tomographic reconstruction with TIR correction further improves the diagnostic capability of handheld optoacoustic tomographic systems.

Metal Plasma Thruster for Small Satellites

This paper describes a metal plasma thruster (MPT) that is suited to nano- and microsatellites. The MPT uses solid metal propellant (hence requires no liquids, gases, flow valves, or flow controls), has no moving parts, generates approximately , and may be packaged into , 1-U, and multiple-U increments. A vacuum arc generates a metal plasma plume that accelerates into space at (platinum, Pt) to (magnesium, Mg) to generate thrust (). The range of specific impulse is from 693 s (Pt) up to 3119 s (Mg). Spacecraft interface is simple: the autonomous MPT requires only a DC input (7–28 V) and a start/stop control pulse from the satellite. The MPT is simpler and more rugged than ion engines and Hall thrusters, which are not easily scaled down in mass and power for satellites, and provides superior total impulse per kilogram. The MPT is easier to operate than equivalent-sized alternatives: field emission electric propulsion thruster, xenon gas radiofrequency thruster, and pulsed plasma thruster.

Investigation into the transient flow characteristics of noble gas propellants using the pulsed inductive discharge in electric propulsion

The Pulsed Inductive Thruster (PIT) has the advantages of repeatable startup, no corruption and in-situ propellant feed. To study the flow expansion and circuit characteristics of PITs, the circuit-fluid model is developed, and the high temperature thermodynamic and transport models are combined with the circuit-fluid model to predict the critical plasma parameters. The flow fields of initial mass of 2–8 mg and charge voltages of 10–14 kV are simulated. Comparison of the flow fields of argon and helium propellants suggests that, the flow field structures are similar. Slight differences exist on the magnitude of the density and magnetic field, caused by larger velocity in lighter atom case and difference on the ionization gap between adjacent ionization levels. Analysis of the circuit characteristics by the two-dimensional results indicates that the ratio of coil inductance to circuit inductance affects both the rise rate and phase of the plasma current, the larger the ratio, the greater the rise rate and the better the following characteristic. The calculations show that the magnetic energy obtained within the decoupling distance determines the overall performance the thruster can be obtained; self-induced field maintained by the thermal motion after the main pulse leads to the long attenuation process and difference on the total impulse when the angle of conical pylon is varied under constant coil dimension.

Numerical investigation on jet characteristics and performance of SparkJet actuator based on pressure wave behavior inside a cavity

Thrust and total impulse performance of a SparkJet actuator are affected by pressure waves inside the cavity, so it is important to understand these effects. The two objectives of the present study are to characterize the jet performance of a SparkJet actuator and to investigate pressure waves inside the cavity and correlate them with actuator performance. To this end, a SparkJet actuator is solved numerically based on equilibrium gas assumption. Loss of thrust occurs because of the pressure drop caused by the pressure wave, flow separation at the orifice throat, and vortex above the orifice exit. A fast Fourier transform of thrust reveals pressure wave components at two natural frequencies that originate from the pressure waves inside the cavity. The reflected pressure waves inside the cavity affect natural frequencies. The pressure wave reflected in the r-axis direction is affected by the energy deposition aspect ratio which influenced the total impulse by as much as ∼3.21%. The pressure wave reflected in the z-axis direction is affected by the effective height distance. However, this rarely affects the total impulse directly. The use of an appropriate taper angle affects the total impulse by as much as ∼8.49%. Approximately, 11% of the total impulse is originated from oscillations by the reflected wave in the r-axis direction, whereas 4% of it is from the reflected wave in the z-axis direction. This work contributes to improving the design of electrode and cavity configurations for SparkJet actuators and showing the importance of oscillations made by reflected pressure waves.