Rate Response Characteristics Research Articles

Strain rate response and rheological characteristics of ZrCuNiAl bulk metallic glass in supercooled liquid region

In this study, the plastic deformation behavior of Zr55.7Cu22.4Ni7.2Al14.7 bulk metallic glass (BMG) in the supercooled liquid region (SLR) was studied by high temperature compression experiments at various strain rates. The results show that the high temperature plastic deformation behavior of the BMG in SLR is highly sensitive to the strain rate. With the decrease in strain rate, the steady-state flow stress and peak stress decreases, and the viscosity increases. Meanwhile the stress overshoot gradually disappears, the deformation of the BMG specimen changes from non-Newtonian flow to near-Newtonian flow, and there is a critical strain rate of 5 × 10−4 s−1. The surface deformation profile changes from an "S" shaped truncated cone to a true truncated cone. The plastic deformation of BMGs at room temperature is completed by the initiation and expansion of the shear bands, while the high temperature plastic deformation is caused by the generation and annihilation of free volume.

Effect of pore density on the compressive response of open-cell Al foams

The effects of pore density and matrix on the quasi-static and dynamic compressive behaviours of the high porosity open-cell aluminium foams were examined. The results show that pore density has little effect on the collapse strength of the samples under quasi-static conditions. However, as the strain rate increases, the collapse strength decreases with increasing pore density. The different matrix material also shows distinct strain rate response characteristics, which is related to their respective microstructures. The strain-rate sensitivity is mainly attributed to the micro-inertia effect caused by the larger aspect ratio of the cell edges, which was verified by the more transverse elongation of the dynamic compression samples. Moreover, the energy absorption capacity is also discussed in the present paper.

Dynamic fracture mechanics and energy distribution rate response characteristics of coal containing bedding structure.

To investigate the influence of bedding structure and different loading rates on the dynamic fracture characteristics and energy dissipation of Datong coal, a split Hopkinson bar was used to obtain the fracture characteristics of coal samples with different bedding angles. The process of crack initiation and propagation in Datong coal was recorded by the high-speed camera. The formula for the model I fracture toughness of the transversely isotropic material is obtained on the basis of the finite element method (FEM) together with the J-integral. By comparing the incident energy, absorbed energy, fracture energy and residual kinetic energy of Datong coal samples under various impact speeds, the energy dissipation characteristics during the dynamic fracture process of coal considering the bedding structure is acquired. The experimental results indicate that the fracture pattern of notched semi-circular bending (NSCB) Datong coal is tensile failure. After splitting into two parts, the coal sample rotates approximately uniformly around the contact point between the sample and the incident rod. The dynamic fracture toughness is 3.52~8.64 times of the quasi-static fracture toughness for Datong coal. Dynamic fracture toughness increases with increasing impact velocity, and the effect of bedding angle on fracture toughness then decreases. In addition, the residual kinetic energy of coal samples with the same bedding angle increases with the increase of impact speed. The energy utilization rate decreases continuously, and the overall dispersion of statistical data decreases gradually. In rock fragmentation engineering, the optimum loading condition is low-speed loading regardless of energy utilization efficiency or fracture toughness. These conclusions may have significant implications for the optimization of hydraulic fracturing process in coal mass and the further understanding of crack propagation mechanisms in coalbed methane extraction (CME). The anisotropic effect of coal should be fully considered in both these cases.

Experimental study on influence of wetting-drying cycle on dynamic fracture and energy dissipation of red-sandstone

To study the influence of the wetting-drying cycles and loading rate on dynamic fracture toughness and energy dissipation of rocks under the dynamic loads, the split Hopkinson pressure bar (SHPB) system was used to perform the dynamic impact tests on NSCB specimens of red sandstone after different wetting-drying cycles. The loading rate response characteristics of fracture toughness of specimens after different wetting-drying cycles were analyzed, and the energy dissipation law of dynamic fracture under the impact loads was obtained. The results show that under a given number of wetting-drying cycles, with the increase of loading rate, the dynamic fracture toughness shows an overall trend of increasing. When the critical loading rate K˙IC is exceeded, the dynamic fracture toughness no longer increases. At the fixed loading rate, the dynamic fracture toughness of red sandstone decreases linearly with the increase of wetting-drying cycles, and the higher the loading rate, the more sensitive the fracture toughness to the wetting-drying cycle. With the increase of the loading rate, the dynamic fracture energy increases exponentially and becomes more sensitive to the loading rate. Under the fixed wetting-drying cycles, the dynamic fracture toughness of red sandstone has a logarithmic relationship with the increase of fracture energy.

Robust Continuous Finite-Time Control of a Helicopter in Turbulence

This letter synthesizes a C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> smooth, continuous, output-tracking sliding mode controller for a full-scale helicopter operating in high-intensity turbulence. The closed-loop dynamics are required to satisfy ideal on-axis attitude and rate response characteristics. Additionally, robust command tracking and suppression of off-axis responses are required in the presence of matched and unmatched uncertainties. Lyapunov based theoretical proofs are utilized for the tracking problem via application of a continuous second-order sliding mode (SOSM) controller. A second order sliding mode observer is employed to estimate the higher derivatives of the sliding variable for the output feedback controller. Simulations in hover illustrate the continuity, smoothness, and robustness properties of the proposed controller as compared to a conventional sliding mode controller and a linear quadratic controller.

Heart Rate Response, Duration, Grip Strength, and Anthropometric Characteristics in Recreational Indoor Rock Climbers.

Smetanka, RG, Armenta, RF, Nessler, JA, and Newcomer, SC. Heart rate response, duration, grip strength, and anthropometric characteristics in recreational indoor rock climbers. J Strength Cond Res 36(3): 832-837, 2022-Despite the growing popularity of recreational indoor rock climbing, there is a lack of research on cardiovascular responses to rock climbing. In addition, although the importance of body composition and grip strength has been established in elite climbers, their effect on recreational climbing is unknown. Therefore, the purpose of this study was to characterize the physiological and anthropometric characteristics of indoor climbers engaging in climbing at a recreational or noncompetitive setting. We hypothesized that heart rates and climbing durations would meet the standards set by the American College of Sports Medicine (ACSM) and Center for Disease Control and Prevention (CDC) for eliciting health benefits and that grip strength would decrease over the course of a typical climbing session. One hundred twenty-one male and female adult recreational climbers participated in this study. Following informed consent, subjects were instrumented with a heart rate monitor (Polar V800) which recorded heart rate and duration. Preclimb and postclimb grip strength were evaluated using a hand grip dynamometer and used to calculate fatigue. Subjects were 30.9 ± 8.3 years old and had participated in climbing for 5.6 ± 6.5 years. The average heart rate during climbing sessions was 122.3 ± 14.5 b·min-1, and session duration was 90.6 ± 31.3 minutes. Mean grip strength was 49.9 ± 11.2 kg, whereas the strength to mass ratio was 0.71 ± 0.14, and fatigue was 13.1 ± 11.6%. Results from the current study suggest that recreational indoor climbing elicits exercise heart rates and durations that are consistent with the CDC and ACSM's recommendations for cardiovascular health. Grip strength data suggested that forearm muscle fatigue may limit climbing durations.

High strain rate response of bio-composites using split Hopkinson pressure bar and digital image correlation technique

ABSTRACTIn this research, high strain rate response and energy absorption characteristics under dynamic compression loading of five different bio-composites were studied using a compression split Hopkinson pressure bar (SHPB) and DIC (digital image correlation) technique. This study is to map suitability of plant-based materials instead of petroleum-based plastic as a constituent raw material in composites. Bio-composites panels were made from Southern yellow pine (SYP), Corn starch (CS), and Methylene diphenyl diisocyanate (MDI) using a Dieffenbacher hot press. The ability of non-contact DIC analysis served as a valuable tool to measure the strains over a large range of deformation in wood-based bio-composites subjected to high strain rate compressive loading. Among all, Material 2 bio-composite with high manufacturing pressure had highest peak strength, shows that material behaviour at high strain rates is strongly dependent on the manufacturing pressure during fabrication. Presence of corn starch marginally increased the energy absorption capacity.

Dose rate response of Digital Megavolt Imager detector for flattening filter-free beams.

In this study we investigated the dose rate response characteristics of the Digital Megavolt Imager (DMI) detector, including panel saturation, linearity, and imager ghosting effects for flattening filter‐free (FFF) beams. The DMI detector dose rate response characteristics were measured as a function of dose rate on a Varian TrueBeam machine. Images were acquired at dose rates ranging from 400 to 1400 MU/min for 6XFFF and 400 to 2400 MU/min for 10XFFF. Line profiles and central portal doses derived from the images were analyzed and compared. The linearity was verified by acquiring images with incremental Monitor Unit (MU) ranging from 5 to 500 MU. Ghosting effects were studied at different dose rates. Finally, for validation, test plans with optimal fluence were created and measured with different dose rates. All test plans were analyzed with a Gamma criteria of 3%‐3 mm and 10% dose threshold. Our study showed that there was no panel saturation observed from the profile comparison even at the maximum dose rate of 2400 MU/min. The central portal doses showed a slight decrease (1.013–1.008 cGy/MU for 6XFFF, and 1.020–1.009 cGy/MU for 10XFFF) when dose rate increased (400–1400 MU/min for 6XFFF, and 400–2400 MU/min for 10XFFF). The linearity of the DMI detector response was better than 0.5% in the range of 20–500 MU for all energies. The residual image was extremely small and statistically undetectable. The Gamma index measured with the test plans decreased from 100% to 97.8% for 6XFFF when dose rate increased from 400 to 1400 MU/min. For 10XFFF, the Gamma index decreased from 99.9% to 91.5% when dose rate increased from 400 to 2400 MU/min. We concluded that the Portal Dosimetry system for the TrueBeam using DMI detector can be reliably used for IMRT and VMAT QA for FFF energies.

Chronic Performance of a Leadless Cardiac Pacemaker: 1-Year Follow-Up of the LEADLESS Trial

BackgroundA leadless cardiac pacemaker (LCP) system was recently introduced to overcome lead-related complications of conventional pacing systems. To date, long-term results of an LCP system are unknown. ObjectivesThe aim of this study was to assess the complication incidence, electrical performance, and rate response characteristics within the first year of follow-up of patients implanted with an LCP. MethodsWe retrospectively assessed intermediate-term follow-up data for 31 of 33 patients from the LEADLESS trial cohort who had an indication for single-chamber pacing and received an LCP between December 2012 and April 2013. ResultsThe mean age of the cohort was 76 ± 8 years, and 65% were male. Between 3 and 12 months of follow-up, there were no pacemaker-related adverse events reported. The pacing performance results at 6- and 12-month follow-up were, respectively, as follows: mean pacing threshold (at a 0.4-ms pulse width), 0.40 ± 0.26 V and 0.43 ± 0.30 V; R-wave amplitude 10.6 ± 2.6 mV and 10.3 ± 2.2 mV; and impedance 625 ± 205 Ω and 627 ± 209 Ω. At the 12-month follow-up in 61% of the patients (n = 19 of 31), the rate response sensor was activated, and an adequate rate response was observed in all patients. ConclusionsThe LCP demonstrates very stable performance and reassuring safety results during intermediate-term follow-up. These results support the use of the LCP as a promising alternative to conventional pacemaker systems. Continued evaluation is warranted to further characterize this system. (Evaluation of a New Cardiac Pacemaker; NCT01700244)

Analysis on Vehicle Vibration Performance Based on Yaw Rate Response Characteristics

Abstract: Automotive vibration characteristic analysis is of great significance, the vibration influence of ride comfort, the working efficiency and good health.Therefore, measures should be taken to reduce the vibration of the vehicle and keep the working environment of comfort, to ensure the driving personnel under the condition of the motion of the complex and manipulated with good psychological state and accurate sensitive reaction.

Effect of Process Parameters on the Dynamic Modulus, Damping and Energy Absorption of Vertically Aligned Carbon Nano-Tube (VACNT) Forest Structures

Functionally graded materials (FGMs) are a new generation of engineered materials wherein the micro-structural details are spatially varied through non-uniform distribution of the reinforcement phase(s). The dynamic mechanical behavior and high-strain rate response characteristics of a functionally graded material system consisting of vertically aligned carbon nanotube ensembles grown on silicon wafer substrate (VACNT-Si) and processed at various temperatures have been characterized. Flexural rigidity (storage modulus) and the loss factor (damping) were measured with a dynamic mechanical analyzer in an oscillatory three-point bending mode. It was found that the functionally graded VACNT-Si processed at 770°C and 820°C exhibited higher damping without sacrificing flexural rigidity. A Split-Hokinson Pressure Bar (SHPB) was used for determining the dynamic response under high-strain rate compressive loading. It was again observed that the VACNT-Si specimens processed at 770°C and 820°C showed a large increase in specific energy absorption, compared with those processed at 720°C. Interfacial friction between individual VACNTs, caused by their alignment/entanglements under cyclic deformation, is believed to be the primary energy dissipation mechanism for such large improvement in loss factor (compared to base Silicon wafer substrate). The larger height of VACNT forest depositions for specimens processed at 770°C and 820°C may have caused more entanglements, as reflected in higher damping and specific energy absorption. It appears that the optimal processing temperature may be around 770°C for attaining the highest damping and specific energy absorption, in terms of height and alignment/entanglement of the VACNTs grown on Si-wafer substrate. doi:10.12783/issn. 2168-4286/2.2/Mantena

Firing-rate models for neurons with a broad repertoire of spiking behaviors

Instantaneous firing rates are commonly used to describe either the compound spiking activity of neuron ensembles (population rate) or the trial-averaged response of individual neurons to multiple repetitions of the same stimulus. The dynamics of firing rates is often studied by means of population or firing-rate models. The main motivation for using such models rather than spiking neuron models is to reduce the dimensionality and complexity of the microscopic dynamics to allow analytical tractability, efficient simulation, and intuitive understanding. In most cases, population models have to be treated as purely phenomenological descriptions. Only under simplifying assumptions can they be derived or extracted from the single-neuron dynamics. Previous studies in this field were mainly restricted to homogeneous populations of simple integrate-and-fire neurons which can, to some extent, mimic the rather stereotypical behaviour of regularly firing neurons (e.g., pyramidal cells in the neocortex). Electrophysiological studies have revealed a large diversity of neuron types with different dynamical behaviours, ranging from regular spiking to bursting cells, from accommodating to non-accommodating cells, from integrators to resonators, from depolarization- to hyperpolarization-activated cells, etc. So far, the effect of this neuron-type diversity on the dynamics of neural populations is unclear. Here, we investigate the rate-response characteristics for a variety of neuron types in simulation experiments. To this end, we extend previous work on simple integrate-and-fire neurons [1,2] to the multi-timescale adaptive threshold (MAT) [3] and the Izhikevich model [4]. The model neurons are probed by spike trains modeled as realizations of inhomogeneous Poisson or Gamma point processes with sinusoidally modulated intensity. Average rates, modulation amplitudes and phases of the period-averaged spike responses are measured for a broad range of stimulus, neuron and synapse parameters. The stationary and nonstationary response properties are parameterized by means of nonlinear activation functions and linear filter kernels, respectively, serving as ingredients for simple linear-nonlinear firing rate models. We show that linear-nonlinear rate models can accurately predict the population responses to novel test stimuli for a broad range of parameters and neuron types.

Energy Dissipation and the High‐Strain Rate Dynamic Response of Vertically Aligned Carbon Nanotube Ensembles Grown on Silicon Wafer Substrate

The dynamic mechanical behavior and high‐strain rate response characteristics of a functionally graded material (FGM) system consisting of vertically aligned carbon nanotube ensembles grown on silicon wafer substrate (VACNT‐Si) are presented. Flexural rigidity (storage modulus) and loss factor (damping) were measured with a dynamic mechanical analyzer in an oscillatory three‐point bending mode. It was found that the functionally graded VACNT‐Si exhibited significantly higher damping without sacrificing flexural rigidity. A Split‐Hopkinson pressure bar (SHPB) was used for determining the system response under high‐strain rate compressive loading. Combination of a soft and flexible VACNT forest layer over the hard silicon substrate presented novel challenges for SHPB testing. It was observed that VACNT‐Si specimens showed a large increase in the specific energy absorption over a pure Si wafer.

The Research of Steer by Wire System Based on Fuzzy Logic Control

This paper describes SBW system structure and principle, for different vehicle speed inputs and steering wheel angle step inputs, the simulation model run in Simulink, and obtain yaw rate response characteristics, so the steering system control requirements is proposed, establishes fuzzy logic control system. This control strategy can improve vehicle’s stability and fast respond characteristics. Simulations are carried out to gain a series of transmission ratio curves, show the validity of the proposed fuzzy logic control method.

A comparison of singles and doubles badminton: heart rate response, player profiles and game characteristics

Physiological demands of singles and doubles badminton were compared to assist coaches in evidence-based design of training programs. Sixteen male players (eight singles and eight doubles) were tested for physical and physiological characteristics. Heart rates were monitored during competition and games videoed to allow for lapsed-time analysis. Mean and peak heart rates were significantly greater in singles (88.8% and 96.8% of maximal heart rate respectively) than doubles (75.5% and 89.0%). Singles players took more steps per game (593.8 vs 314.5) and at a higher velocity. There were no differences in rally or game length. Singles players had greater predicted VO2max (50.6 vs 45.5 ml·kg-1 ·min-1) and flexibility, and lower body fat levels (15.5% vs 21.9%). There were no differences in power, speed or agility. Game analyses showed tactical differences, with 89.6% of shots in singles played to the extreme fore- and rear-court (clear, drop, lift or net shot) or a smash, and doubles involving a greater diversity of shots. Success in badminton may require focusing on specific discipline strategies. For example, singles training drills could focus on efficient movement about the court and doubles on a faster, more attacking game.

Genetic and Environmental Sources of Variation in Heart Rate Response to Infused Nicotine in Twins

The heart rate response to nicotine may be an important component of the process leading to dependence. The present study is the first to determine the extent to which genetic and environmental sources play a role in various components of the heart rate response. One hundred and ten monozygotic and 29 dizygotic twin pairs received an i.v. infusion of nicotine and cotinine over 30 min. Before, during, and for 30 min after infusion, heart rate was measured via an electronic monitor. The clearance of nicotine was determined as a measure of the rate of nicotine metabolism. Average resting heart rate before infusion was 64.7 beats per minutes (bpm), and at the termination of infusion, heart rate had increased to an average of 72.7 bpm. At 30 min after infusion, heart rate had decreased to 67.5 bpm. Age, current smoking status, body mass index, and nicotine clearance were associated significantly with heart rate levels over the full 60 min of measurement. After adjustment for several covariates, including dose of administered nicotine and rate of nicotine clearance, the variance in several characteristics of the heart rate response curve was examined for the relative contribution from genetic and environmental sources. In the total sample, as much as 30.3% of the variance in the acceleration of heart rate was due to additive genetic sources. In nonsmokers, 34.8% and 31.0% of variance in the acceleration and deceleration of heart rate, respectively, was due to genetic sources. Heart rate acceleration and deceleration may be a reflection of central nervous system responsiveness to nicotine. The contribution from genetic sources to heart rate response characteristics should be investigated further as a potential endophenotype for use in genetic studies of nicotine dependence.

RATE RESPONSE ASSESSMENT FROM VARIOUS GRANULAR VRT APPLICATORS

Variable-rate technology (VRT) adds complexity to application equipment, thereby confounding the assessmentof applicator performance. The intent of this investigation was to assess the rate response of various VRT granularapplicators: two spinner spreaders (A and B), and two pneumatic applicators (C and D). Variable-rate (VR) tests wereconducted to quantify the rate response characteristics (delay and transition times) for the applicators. A sigmoidal functionwas used to model the rate response for five of the six tests. Applicator A exhibited a linear response during decreasing ratechanges. Results indicated that only applicator B demonstrated consistent delay and transition times, enabling the use of asingle look-ahead time for rate response time correction. Contouring of prescription maps increased the transition timesfor applicator D by enlarging the adjustment area between management zones. Rate changes were quicker for the two newerVR control systems, signifying advancement in hydraulic control valve technology. This research illustrates the need forstandard testing protocols for VRT systems to help guide VRT software developers, equipment manufacturers, and end users.

KMP023 Recurrent pacemaker-related infection due to small colony variants (SCVs) of Staphylococcus aureus

A leadless cardiac pacemaker (LCP) system was recently introduced to overcome lead-related complications of conventional pacing systems. To date, long-term results of an LCP system are unknown.The aim of this study was to assess the complication incidence, electrical performance, and rate response characteristics within the first year of follow-up of patients implanted with an LCP.We retrospectively assessed intermediate-term follow-up data for 31 of 33 patients from the LEADLESS trial cohort who had an indication for single-chamber pacing and received an LCP between December 2012 and April 2013.The mean age of the cohort was 76 ± 8 years, and 65% were male. Between 3 and 12 months of follow-up, there were no pacemaker-related adverse events reported. The pacing performance results at 6- and 12-month follow-up were, respectively, as follows: mean pacing threshold (at a 0.4-ms pulse width), 0.40 ± 0.26 V and 0.43 ± 0.30 V; R-wave amplitude 10.6 ± 2.6 mV and 10.3 ± 2.2 mV; and impedance 625 ± 205 Ω and 627 ± 209 Ω. At the 12-month follow-up in 61% of the patients (n = 19 of 31), the rate response sensor was activated, and an adequate rate response was observed in all patients.The LCP demonstrates very stable performance and reassuring safety results during intermediate-term follow-up. These results support the use of the LCP as a promising alternative to conventional pacemaker systems. Continued evaluation is warranted to further characterize this system. (Evaluation of a New Cardiac Pacemaker; NCT01700244)

Control studies of steering characteristics of commercial three-axle vehicle for front and rear wheels steering

The mechanical model of a three-axle vehicle for front and rear wheels steering is established. The transfer functions of yaw rate, sideslip angle and lateral acceleration to front and rear wheel angles are derived under different feed-forward and feedback control strategies. The control laws are discussed in order to make the sideslip angle of steady state and transient state keep to zero during vehicle steering. Simulation results show that the yaw rate and lateral acceleration response characteristics of the steering wheel angle of a three-axle vehicle are satisfactory when the body sideslip angle in the transient state is controlled at zero. Based on the control strategy and control target for a three-axle vehicle the manoeuverability at low-speed and lateral stability at high-speed are improved. The relationship between manoeuverability and stability is good as expressed by the manoeuverability factor and stability factor when introduced.

Chloroplast movements in fern leaves: correlation of movement dynamics and environmental flexibility of the species

ABSTRACTThe movements of chloroplasts in response to varying levels and wavelengths of incident light were investigated in leaves of four fern species: Adiantum capillus‐veneris, Adiantum caudatum, Adiantum diaphanum and Pteris cretica. In all of the species studied blue light induced chloroplast redistribution resulting in face and profile patterns that were typical of low and high fluence rates, respectively. Fluence rate response characteristics and the kinetics of transmission changes accompanying these blue‐light‐induced movements were similar to those observed in the leaves of higher plants. Only in A. capillus‐veneris was the distribution of chloroplasts affected by red light. The response was of the weak‐light type, irrespective of the light intensity. The most effective fluence rate for red light was found to be below 7·2 μmol m–2 s–1 (1 W m–2). The effect of red light was far‐red reversible, indicating phytochrome involvement. Chloroplast responses were more dynamic in A. capillus‐veneris and P. cretica, the two species that exhibited higher environmental flexibility.