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• A two-step direct measurement method is used to obtain the biodynamic response. • The MI & VT of fingers-hand-arm system under zero-gravity environment are measured. • The zero-gravity environment is important for ground measurement of on-orbit HAV. This paper proposes a direct measurement method to obtain the mechanical impedance and vibration transmissibility of the fingers-hand-arm system when operating power tools based on zero-gravity environment simulations. A hand-transmitted vibration measurement system with a suspension device for zero-gravity simulation is first built. The two-step dynamic measurement method is used to measure the dynamic force and acceleration of fingers and palm directly. The forearm and upper arm's acceleration is also measured using the two-step dynamic measurement method. Based on eliminating the effect of the handle's effective mass on the mechanical impedance, the mechanical impedance and vibration transmissibility of the human fingers-hand-arm system during the actual operation of the power tool are calculated by using the measured data, and the biodynamic response characteristics of the fingers-hand-arm system at different frequencies are analyzed. The results show that, under the condition of the ISO standardized operating posture (ISO 10819, 2013), the mechanical impedance and vibration transmissibility curves obtained by direct measurement of 21 subjects have remarkable consistency respectively. Compared with the experimental data in the gravity environment, the mechanical impedance and the vibration transmissibility obtained based on the zero-gravity simulation are more consistent with the working conditions of the on-orbit maintenance power tools. [ABSTRACT FROM AUTHOR]

Background: Individualised bedside adjustment of mechanical ventilation is a standard strategy in acute coma neurocritical care patients. This involves customising positive end-expiratory pressure (PEEP), which could improve ventilation homogeneity and arterial oxygenation. This study aimed to determine whether PEEP titrated by electrical impedance tomography (EIT) results in different lung ventilation homogeneity when compared to standard PEEP of 5 cmH2O in mechanically ventilated patients with healthy lungs. Methods: In this prospective single-centre study, we evaluated 55 acute adult neurocritical care patients starting controlled ventilation with PEEPs close to 5 cmH2O. Next, the optimal PEEP was identified by EIT-guided decremental PEEP titration, probing PEEP levels between 9 and 2 cmH2O and finding the minimal amount of collapse and overdistension. EIT-derived parameters of ventilation homogeneity were evaluated before and after the PEEP titration and after the adjustment of PEEP to its optimal value. Non-EIT-based parameters, such as peripheral capillary Hb saturation (SpO2) and end-tidal pressure of CO2, were recorded hourly and analysed before PEEP titration and after PEEP adjustment. Results: The mean PEEP value before titration was 4.75 ± 0.94 cmH2O (ranging from 3 to max 8 cmH2O), 4.29 ± 1.24 cmH2O after titration and before PEEP adjustment, and 4.26 ± 1.5 cmH2O after PEEP adjustment. No statistically significant differences in ventilation homogeneity were observed due to the adjustment of PEEP found by PEEP titration. We also found non-significant changes in non-EIT-based parameters following the PEEP titration and subsequent PEEP adjustment, except for the mean arterial pressure, which dropped statistically significantly (with a mean difference of 3.2 mmHg, 95% CI 0.45 to 6.0 cmH2O, p < 0.001). Conclusion: Adjusting PEEP to values derived from PEEP titration guided by EIT does not provide any significant changes in ventilation homogeneity as assessed by EIT to ventilated patients with healthy lungs, provided the change in PEEP does not exceed three cmH2O. Thus, a reduction in PEEP determined through PEEP titration that is not greater than 3 cmH2O from an initial value of 5 cmH2O is unlikely to affect ventilation homogeneity significantly, which could benefit mechanically ventilated neurocritical care patients. [ABSTRACT FROM AUTHOR]

We consider the linear elasticity system for a body coated with a thin elastic layer. The effect of the thin layer on that body can be described through an impedance operator linking the displacement and the traction on the interface. This operator cannot be in general explicitly computed for an arbitrary shape. In this paper, we consider the case of a linear elastic slab with Hooke's law. We compute by the Fourier transform the exact symbol of the impedance operator and prove that it is a pseudodifferential operator of order one. Then, we give a Padé-like approximation at order three (with respect to the thickness of the layer) for the impedance operator. The pattern of this approximation will be a helpful guide for approximating the impedance operator for a body whose boundary has nonzero curvature. [ABSTRACT FROM AUTHOR]

Frequency-domain modeling is a core tool for the analysis of linear time-invariant structures. In a process that has been unclear, additional Dirac delta distributions can arise in the frequency-domain transfer functions of certain structures, beyond those seemingly given by the structural model—e.g., in the mechanical impedance of a linear spring. Previous analyses have manually appended these "hidden deltas" to the relevant transfer functions in to ensure that they remain causal, but questions remain as to their exact origin and behavior in in noncausal models. Here, we demonstrate that these hidden deltas arise from the theory of distributions and the solution of the distributional division equation. We demonstrate a rigorous and reliable method for deriving these hidden deltas in which the role of causality constraints are made clear. Furthermore, we demonstrate that the appropriate frequency-domain conditions for causality in such systems are generalized—not classical—Hilbert transform relations, and that the process of appending delta distributions is related to the analysis of causality via these generalized relations. [ABSTRACT FROM AUTHOR]

SUMMARY: It has been hypothesized that vacuolar occupancy in mature root cortical parenchyma cells regulates root metabolic cost and thereby plant fitness under conditions of drought, suboptimal nutrient availability, and increased soil mechanical impedance. However, the mechanistic role of vacuoles in reducing root metabolic cost was unproven. Here we provide evidence to support this hypothesis. We first show that root cortical cell size is determined by both cortical cell diameter and cell length. Significant genotypic variation for both cortical cell diameter (~1.1‐ to 1.5‐fold) and cortical cell length (~ 1.3‐ to 7‐fold) was observed in maize and wheat. GWAS and QTL analyses indicate cortical cell diameter and length are heritable and under independent genetic control. We identify candidate genes for both phenes. Empirical results from isophenic lines contrasting for cortical cell diameter and length show that increased cell size, due to either diameter or length, is associated with reduced root respiration, nitrogen content, and phosphorus content. RootSlice, a functional‐structural model of root anatomy, predicts that an increased vacuolar: cytoplasmic ratio per unit cortical volume causes reduced root respiration and nutrient content. Ultrastructural imaging of cortical parenchyma cells with varying cortical diameter and cortical cell length confirms the in silico predictions and shows that an increase in cell size is correlated with increased vacuolar volume and reduced cytoplasmic volume. Vacuolar occupancy and its relationship with cell size merits further investigation as a phene for improving crop adaptation to edaphic stress. Significance Statement: Cortical cell size is an important phene determining root metabolic cost, but the underlying physiological mechanism is unclear. Here, using in silico and empirical approaches, we provide evidence that supports the hypothesis that vacuolar occupancy in cortical parenchyma cells regulates root metabolic cost. We also show that vacuolar occupancy is associated with cortical cell diameter and cell length, phenes that are under distinct genetic control and hold the potential for improving crop yields under edaphic stress. [ABSTRACT FROM AUTHOR]

In this paper, a novel adjustable magnetorheological fluid (MRF) gradient material for low-frequency control is proposed, and the vibration isolation performance of this gradient material is investigated theoretically and experimentally. The gradient material has an excellent ability to control the sound waves and vibrations. However, the currently prepared gradient material does not have the parameter adjustability. At the same time, the MRF can change its material parameters according to the external magnetic field. After applying the traveling magnetic field (TMF) to the MRF with continuously varying and adjustable magnetic induction strength, its material parameters will also be continuously varying and adjustable to constitute an adjustable gradient material. In order to investigate the vibration transfer characteristics of this adjustable gradient material, this paper establishes a micro-mechanical model of MRF and theoretically investigates and numerically calculates the mechanical impedance and vibration transfer characteristics of the adjustable gradient material through the machine-electric analogy theory. At the same time, experimental research was conducted by building an experimental platform to conduct experiments. The results show that the novel adjustable gradient material composed of a TMF and MRF has a good vibration suppression effect in the low-frequency range (10 ∼ 60 Hz) with the vibration level difference of up to 30 dB or more, which has a broad application prospect in the field of vibration control. [ABSTRACT FROM AUTHOR]

This paper proposes a decentralized variable impedance control method of modular robot manipulators (MRM) with physical human-robot interaction (pHRI) using Gaussian process-based motion intention estimation. The dynamic model of MRM subsystem is established by using joint torque feedback (JTF) technique. Human limb dynamic model is regarded as mechanical impedance model, and human motion intention is estimated online based on Gaussian process. A variable impedance control method is proposed to make the MRM comply with human motion intention in the process of pHRI. A decentralized sliding mode control strategy is designed to achieve high performance position tracking and compensate the uncertainty of the controller. Based on Lyapunov theory, the uniform ultimately bounded of tracking error of each joint is proved. Finally, the effectiveness of the proposed control method under pHRI is verified by experiments. The experimental results show that the proposed method reduces the position tracking error by ∼ 10% and the interaction force by ∼ 20% compared with the existing control methods. [ABSTRACT FROM AUTHOR]

The identification of soybean genotypes tolerant to soil compaction makes it possible to reduce productivity loss under stress conditions. Added to this, the prior selection of these genotypes will result in greater assertiveness in the positioning of cultivars in the field. Thus, the objective was to evaluate the susceptibility of soybean genotypes to compaction in greenhouse and field conditions; verify which characteristics of seedlings under high resistance to root penetration are correlated with crop production in compacted soil; and to validate the substrate mechanical impedance method for evaluating the susceptibility of plant genotypes to soil compaction. Seeds of 20 genotypes were sown in a substrate mechanical impedance system under controlled conditions. The characteristics evaluated were total root length, total root surface area, mean root diameter, total root volume, taproot length, shoot length, root dry matter and seedling shoot dry matter. In the field experiment, half of the planting area was compacted, constituting two treatments, soil with and without compaction. The percentage of seedling emergence, initial plant height, stem diameter, number of nodes, internode length, number of lateral branches, shoot dry matter, final plant height, absolute and relative growth rate, number of pods, weight of 100 seeds and grain yield. In addition, the number of days between soybean sowing until plant flowering and grain harvest was recorded according to genotype and soil compaction level. In a controlled environment, genotypes tolerant to soil compaction show greater plasticity of root characteristics and smaller alterations in the shoot of seedlings. In the field, these genotypes show smaller reductions in growth rate, height, number of pods and grain yield. The shoot dry matter and the root dry matter of soybean seedlings in a mechanical impedance system present a positive and negative correlation, respectively, with soybean yield in compacted soil, indicating that the genetically determined susceptibility to soil compaction stress was similar throughout ontogenesis. The substrate mechanical impedance system used to evaluate the performance of soybean seedlings under stress, facilitates the decision‐making in breeding programs focused on identifying genotypes expressing soil compaction tolerance. [ABSTRACT FROM AUTHOR]

Due to their ability to buffer and attenuate vibrations, as well as their low cost, rubber-based isolators are widely used in military and civilian vessels. Since these isolators are part of a ship's structure, the accurate prediction of their static and dynamic performance is essential for overall structural design. In this paper, two kinds of marine shear-compression rubber isolators of different models in the same series are taken as the research objects, and the static and dynamic constitutive models of the rubber materials are obtained through material tests, which are used as inputs to accurately predict the static and dynamic characteristics of the isolators in the three translational directions through numerical calculations. The effects of size and preload force on the dynamic characteristics of the vibration isolators were analyzed as were the reasons for the peaks in the impedance curves. The results show that the preload force increases the amplitudes of the peak transfer impedance in the X direction and decreases it in the Z direction. On the other hand, as the size of the vibration isolator increases, the peak frequency of the transfer impedance in the X direction increases, while in the Y and Z directions, the first-order peak frequency decreases and the second-order peak frequency increases. The peaks of the transfer impedance curves appear due to the resonance of the embedded metal blocks, and the order of appearance of the resonance modes is fixed. [ABSTRACT FROM AUTHOR]

As the number of long-span bridges continues to grow, wind-induced vibration issues have become increasingly intensified. Among them, flutter is a serious wind-induced vibration that can lead to bridge collapse. To address this problem, this paper proposes inerter-based dampers as a solution for flutter control and compares their performance to traditional tuned mass dampers (TMDs). Firstly, eight distinct inerter-based dampers were proposed, based on various combinations of mass-inerter-spring-damper (MISD) components. Secondly, the equations of motion of the bridge-MISD system were derived based on the two-mode coupled flutter theory and the mechanical impedance analysis method. Thirdly, the flutter control performance of the eight proposed MISDs is examined using a simply supported beam, with the six better-performing dampers further evaluated using the Jiangyin Bridge. The results show that inerter-based dampers can effectively improve the critical flutter wind speed of bridges, with performance sensitive to frequency. Additionally, incorporating an inerter decreases the static displacement of the mass block, while increasing the mass of MISD and the distance between the damper and the section center improves flutter control performance. The optimal spring stiffness ratios for the six MISDs are identified, largely dependent on the damper's inertance and mass. In conclusion, this paper offers a promising solution to addressing flutter in long-span bridges and provides insights into the design and optimization of inerter-based dampers. [ABSTRACT FROM AUTHOR]

The impedance matching control, also known as approximate complex conjugate control (ACC), is one of the main strategies for improving the capture of energy by point absorber wave energy converters. Such a strategy shapes the mechanical impedance related to the floater dynamics via the control law. Since the traditional ACC is given by a linear control law, this work proposes a generalization denoted as nonlinear complex conjugate control (NCC) that considers the presence of nonlinear viscous damping in addition to the usual linear damping and stiffness. The energy maximization conditions for the proposed NCC are derived in the frequency domain through the describing function method. These conditions show that the ACC is a special case of the NCC when the total damping on the floater is approximated as a linear function of its velocity. From numerical simulations of a point absorber wave energy converters with nonlinear damping, which is based on the Archimedes wave swing prototype, it is shown that the NCC provides greater energy conversion than the ACC, as well as a robust performance in the presence of variations of the damping coefficient and the excitation force peak frequency. [ABSTRACT FROM AUTHOR]

Purpose: The suspension requires optimal parameters to achieve superior performance for different vibration frequency band. When the mechanical impedance of suspension is equal to that of other elements, the minimal vibration power is transmitted to the vehicle body. This paper aims to examine the relationship between vibration frequency and suspension performance focusing on the requirements of mechanical impedance matching and suspension performance for inerter, and provide guidance for suspension control strategies that can improve identification accuracy and suspension performance. Methods: The effect of the vibration frequency on the suspension performance is simulated and analyzed from the perspective of mechanical impedance matching and suspension performance. According to the electrical–mechanical analogy theory, the inerter is used in suspension to realize the mechanical impedance matching. A two-parameter frequency tracker is proposed and verified from forward and backward analysis. A two-parameter control strategy is developed and applied in semi-active suspension. The performance of semi-active suspension with two-parameter control strategy is simulated and compared with passive suspension. Results: The two-parameter frequency tracker can track the vibration frequency accurately and realize the suspension requirements for inerter from the mechanical impedance matching and performance. When applied to a semi-active suspension system, the two-parameter control strategy improves suspension performance, particularly in body acceleration and dynamic tire load. Compared with the passive suspension, the suspension with two-parameter control strategy improves the ride comfort (body acceleration) up to 7.09% and road handling (dynamic tire load) up to 4.05%. Conclusion: This paper proposes a two-parameter frequency tracker to optimize the identification algorithm and improves the identification accuracy. The suspension requirements for inerter from mechanical impedance matching and performance are conducted. A two-parameter frequency tracker is also applied in suspension and realized by a semi-active inerter, which derives a two-parameter control strategy. The two-parameter control strategy presents a superior performance. [ABSTRACT FROM AUTHOR]

Cartilage conduction hearing aids (CCHAs) are new devices that have attracted attention in recent years for external auditory canal atresia. In these devices, a vibrator is attached to the ear cartilage to transmit sound through vibration. In this study, we measure the mechanical impedance of the ear concha auriculae, which represents the mechanical load on the vibrator. To evaluate the output of the CCHAs, we develop a coupler simulating the ear cartilage that measures the sound pressure corresponding to the eardrum sound pressure of the normal ear. Consequently, the mechanical impedance of the developed coupler is several times larger than that of the human ear cartilage measured in this study; however, it is an acceptable value considering the difference in the contact area. The output sound pressure of the vibrator with the coupler simulating the ear cartilage roughly simulates the sound pressure in the ear canal with normal hearing (with the ear canal sealed). In this study, the measured mechanical impedance of the human ear cartilage is approximately 20 dB less than that of the mechanical coupler specified in IEC (International Electrotechnical Commission) 60318-6 for the evaluation of the bone conduction vibrator. [ABSTRACT FROM AUTHOR]

In this paper, we study Scholte's waves propagating along the interface of micropolar solid and liquid media, considering the effect of initial stress and impedance boundary surface. We obtained the phase velocities of basic elastic waves in both media and used them to derive the secular equation of Scholte's wave. We found that the initial stress in the solid material does not affect the speed of basic longitudinal waves. After solving the secular equation, we obtained the speed of Scholte's wave and the corresponding attenuation. We observed that Scholte's surface wave obtained at the micropolar solid–liquid interface is inhomogeneous and dispersive. We investigated the effects of initial stress, Tiersten's impedance boundary condition, and micropolar solid parameters on Scholte's wave and basic shear waves. Numerically, these effects are computed for a particular model using the appropriate value of the parameters, and the results are illustrated graphically. This paper also contributes to not only understanding the behavior of Scholte's waves in micropolar solid–liquid interfaces but also the factors that affect the propagation. [ABSTRACT FROM AUTHOR]

This paper presents a simplified method for launch vehicle coupled loads analysis (CLA) with spacecraft which is normally conducted in the process of the spacecraft development. The method allows spacecraft developers to calculate coupled vibration response of their own without performing transient analysis for the coupled whole system model. A new method, which allows us to obtain coupled vibration response by convolving non-loaded acceleration time history at the spacecraft boundary with corresponding impulse response of combined apparent mass matrices in frequency domain, has been proposed. The proposed method functions well in any CLA cases including lift-off forced events where loads accompany quasi-static component in nature. We propose a novel approach to escape the error caused in the process of convolution for the quasi-static event by making use of the method to convolve only dynamic acceleration response extracted from the original acceleration by inertia relief technique. Finally, we demonstrate the validity of the proposed method through the analysis using practical launch vehicle and spacecraft models.

Compaction disrupts soil structure, reducing root growth, nutrient and water uptake, gas exchange, and microbial growth. Root growth inhibition by soil compaction was originally thought to reflect the impact of mechanical impedance and reduced water availability. However, using a novel gas diffusion-based mechanism employing the hormone ethylene, recent research has revealed that plant roots sense soil compaction. Non-compacted soil features highly interconnected pore spaces that facilitate diffusion of gases such as ethylene which are released by root tips. In contrast, soil compaction stress disrupts the pore network, causing ethylene to accumulate around root tips and trigger growth arrest. Genetically disrupting ethylene signalling causes roots to become much less sensitive to compaction stress. Such new understanding about the molecular sensing mechanism and emerging root anatomical traits provides novel opportunities to develop crops resistant to soil compaction by targeting key genes and their signalling pathways. This expert view discusses these recent advances and the molecular mechanisms associated with root–soil compaction responses. [ABSTRACT FROM AUTHOR]

Humans substantially outperform robotic systems in tasks that require physical interaction, despite seemingly inferior muscle bandwidth and slow neural information transmission. The control strategies that enable this performance remain poorly understood. To bridge that gap, this study examined kinematically constrained motion as an intermediate step between the widely studied unconstrained motions and sparsely studied physical interactions. Subjects turned a horizontal planar crank in two directions (clockwise and counterclockwise) at three constant target speeds (fast, medium, and very slow) as instructed via visual display. With the hand constrained to move in a circle, nonzero forces against the constraint were measured. This experiment exposed two observations that could not result from mechanics alone but may be attributed to neural control composed of dynamic primitives. A plausible mathematical model of interactive dynamics (mechanical impedance) was assumed and used to "subtract" peripheral neuromechanics. This method revealed a summary of the underlying neural control in terms of motion, a zero-force trajectory. The estimated zero-force trajectories were approximately elliptical and their orientation differed significantly with turning direction; that is consistent with control using oscillations to generate an elliptical zero-force trajectory. However, for periods longer than 2-5 s, motion can no longer be perceived or executed as periodic. Instead, it decomposes into a sequence of submovements, manifesting as increased variability. These quantifiable performance limitations support the hypothesis that humans simplify this constrained-motion task by exploiting at least three primitive dynamic actions: oscillations, submovements, and mechanical impedance. [ABSTRACT FROM AUTHOR]

Detection of preload losses in bolts based on electromechanical impedance spectra The FOSTA research project P 1403 "Detection of preload losses in bolts based on electromechanical impedance spectra" aims at the development of a statistically validated method, which enables a cost‐efficient, continuous monitoring of bolt forces in preloaded HV connections based on electromechanical impedance spectra (EMI) within the framework of structural health monitoring (SHM). The EMI method is based on the indirect measurement of the frequency‐ and preload‐dependent mechanical impedance of the bolt. Within the framework of the project, it was possible to derive an indicator from the measurement data that correlates with the pretensioning force. Furthermore, additional effects on EMI spectra, which must be distinguished from the influence of the pretensioning force itself for reliable pretensioning force monitoring, were investigated, including the influence of temperature. In this publication, these influences are investigated in more detail. This is done on the one hand on the basis of simulations carried out with the help of FEM and on the other hand with the help of experiments. [ABSTRACT FROM AUTHOR]

Mooring systems are a critical component of all floating wave energy converter (WEC) systems, yet the impact of amooring system on the WEC dynamics is often neglected during the initial assessment of candidate designs. The purpose of this study was to investigate how the inclusion of mooring dynamics in the early stages of the WEC design process influences decisions regarding hydrodynamic features and control strategies. The study was executed within a mechanical circuit framework to represent the WEC response in the frequency domain. Thevenin's theorem was applied within this framework to transform a multi-body WEC into a single-body canonical form. This work specifically focused on self-reacting point absorbers and examined how four realistic mooring designs impact WEC intrinsic mechanical impedance across a range of common wave frequencies. We show how the mooring can easily be included in this framework, and a simple approach to identifying the mooring model parameters is described. It was observed that if mooring dynamics are considered within the WEC control design process, a 40% reduction in the required range of the controller physical variable can be achieved while yielding up to 16% more useful power. These results suggest that considering the mooring system early can enhance WEC design. [ABSTRACT FROM AUTHOR]

As a critical component of ultrasonic vibration systems, piezoelectric transducers play an essential role in various practical application scenarios. Recent advances in spherical transducers have been widely used in underwater sound and structural health monitoring, while the cascaded spherical piezoelectric transducer with arbitrary piezoceramic shell thickness has not been investigated. Here, we propose a radially cascaded spherical piezoelectric transducer (RCSPT) and derive its electromechanical equivalent circuit with mechanical losses, dielectric losses, and load mechanical impedances. The resulting device is composed of three concentric spherical metal shells and two radially polarized spherical piezoceramic shells. The underlying physical mechanism is the inverse piezoelectric effect, which converts electrical signals into mechanical vibrations. The effects of the spherical piezoceramic shell's thickness and location on the RCSPT are studied. We also analyze the effects of mechanical losses, dielectric losses, and load mechanical impedances on the modulus of input electric impedance of the cascaded spherical transducer. The experiments are conducted to verify the electromechanical characteristics of the resulting device, which are in good agreement with the simulated results and theoretical predictions. Our methodology will offer new possibilities for designing RCSPTs and may promote applications in various fields, such as underwater acoustic detection and structural health monitoring. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach for controlling variable end-point viscoelasticity in musculoskeletal robots to reduce contact forces during contact tasks. This is achieved by adjusting the desired end-point viscoelasticity in response to environmental contact, and by controlling the end-point viscoelasticity in muscle space. The musculoskeletal system of living bodies can adapt to the mechanical impedance of joints via the nonlinear properties of muscles, which are a significant factor in enhancing flexibility and safety during contact tasks. To take advantage of the characteristics of the musculoskeletal structure, we introduce nonlinear viscous properties into muscles and control the end-point viscosity by modulating the internal force. Numerical simulations are conducted to evaluate the proposed method, which demonstrates that the method successfully reduces contact forces during the crank-turning task while maintaining tracking performance. Overall, the proposed approach promises to achieve safer and more flexible interactions between robots and their environment. [ABSTRACT FROM AUTHOR]

Soil compaction has caused negative impacts on soybean productivity due to the excessive use of machinery and heavy agricultural implements in the cultivation areas. Effects of two levels of soil compaction were investigated on 60 soybean genotypes in a field experiment. Soil properties, weather conditions in the region and changes in agronomic characteristics of the crop were evaluated. The genotypes were divided into three groups according to the relative maturity group (RMG) and classified according to stress susceptibility. Compaction increased soil density and soil mechanical resistance to penetration, varying according to the registered rainfall regime. The genotype responses to compaction in the three groups, in general, were increased seedling emergence (EME), initial height (IH), number of nodes (NN), shoot dry matter (SDM), and final height (FH) of the plants. However, there was a reduction in the relative growth rate (RCR), in the number of pods (NP), and in grain yield (PROD). From the calculation of the stress susceptibility index (SSI) it was possible to identify tolerant and sensitive soybean genotypes to soil compaction stress. SSI and the relative trait change index (RTC) indicated the responses that the tolerant genotypes present under conditions of high mechanical impedance. Therefore, soil compaction provides greater seedling emergence and vegetative growth, but significant losses in soybean yield. Soil compaction‐tolerant genotypes show smaller reductions in relative growth rate, absolute growth rate, final height, number of pods, and grain yield. [ABSTRACT FROM AUTHOR]

This manuscript investigates the rotational mechanical impedance of the human hand–arm system with respect to vibration excitation around the gripping axis of the hand under the influence of body posture, gripping force, and push force. Knowledge of rotational mechanical impedance is required for deriving models of hand–arm biodynamics. These models are used in the validation of power tools to predict further vibrational human–machine interactions. In the current state of research, such models exist for translational but not rotational vibration excitation. Consequently, this study investigates the properties of a hand–arm system with respect to rotational vibration excitation. In the study, the rotational impedance of the hand–arm systems of 13 adults was measured at various gripping and push forces applied in different body postures. The setup of the test used in this study consisted of a shaker that applied rotational vibrations at certain frequencies to the subjects’ hand–arm systems via a cylindrical handle. The results of the study indicate a spring–damper dynamic of the hand–arm system. The gripping force strongly influences the magnitude of rotational impedance across the frequency spectrum. Regarding push force and posture, no corresponding influence could be determined. The results suggest that the frictional contact between the hand and handle might confer a damping effect.

Mechanical impedance (MI) defines the ability of a system to vibrate as a consequence of force application. In the recent years, the correlation of this parameter with tire-road noise and other characteristics has gained certain attention. Nevertheless, the information about this topic is still insufficient. Usually, the force is set through an impulse hammer as a master and the acceleration is measured through an accelerometer as a response in order to measure the corresponding Frequency Response Function (FRF). The objectives of the study presented in this paper are i) to analyse the differences between the axial mechanical impedance (complex ratio of force and velocity referred to the same point, named driving-point impedance) and the non-axial mechanical impedance (complex ratio of the force at the point i and velocity at the point j, named transfer impedance); ii) to analyse the effect of adding crumb rubber (2% by mixture weight) and of the percentage of bitumen on the mechanical impedance for the bituminous samples. Therefore, laboratory tests on asphalt concrete specimens have been performed, using an instrumentation system composed of i) an impact hammer reporting the impact force value; ii) an impedance head measuring the direct impact force and the direct acceleration at the hitting point location; iii) a piezoelectric accelerometer measuring the transfer acceleration at a certain distance from the hitting point location. Results demonstrate that the ratio between the repeatability and the average is quite constant, while for heights higher than 10 cm, also MI tends to be independent on the height. A number of recommendations have been made based on the results of the present research.

Due to their ability to buffer and attenuate vibrations, as well as their low cost, rubber-based isolators are widely used in military and civilian vessels. Since these isolators are part of a ship’s structure, the accurate prediction of their static and dynamic performance is essential for overall structural design. In this paper, two kinds of marine shear-compression rubber isolators of different models in the same series are taken as the research objects, and the static and dynamic constitutive models of the rubber materials are obtained through material tests, which are used as inputs to accurately predict the static and dynamic characteristics of the isolators in the three translational directions through numerical calculations. The effects of size and preload force on the dynamic characteristics of the vibration isolators were analyzed as were the reasons for the peaks in the impedance curves. The results show that the preload force increases the amplitudes of the peak transfer impedance in the X direction and decreases it in the Z direction. On the other hand, as the size of the vibration isolator increases, the peak frequency of the transfer impedance in the X direction increases, while in the Y and Z directions, the first-order peak frequency decreases and the second-order peak frequency increases. The peaks of the transfer impedance curves appear due to the resonance of the embedded metal blocks, and the order of appearance of the resonance modes is fixed.

Cartilage conduction hearing aids (CCHAs) are new devices that have attracted attention in recent years for external auditory canal atresia. In these devices, a vibrator is attached to the ear cartilage to transmit sound through vibration. In this study, we measure the mechanical impedance of the ear concha auriculae, which represents the mechanical load on the vibrator. To evaluate the output of the CCHAs, we develop a coupler simulating the ear cartilage that measures the sound pressure corresponding to the eardrum sound pressure of the normal ear. Consequently, the mechanical impedance of the developed coupler is several times larger than that of the human ear cartilage measured in this study; however, it is an acceptable value considering the difference in the contact area. The output sound pressure of the vibrator with the coupler simulating the ear cartilage roughly simulates the sound pressure in the ear canal with normal hearing (with the ear canal sealed). In this study, the measured mechanical impedance of the human ear cartilage is approximately 20 dB less than that of the mechanical coupler specified in IEC (International Electrotechnical Commission) 60318-6 for the evaluation of the bone conduction vibrator.

Incompatible interphases resulting from the irreconcilable contradiction between impedance and mechanical strength have become one of the major obstacles to the practical application of solid‐state lithium metal batteries (SSLMBs). With the employment of a decoupling strategy by rational topological design, herein a topological polymer‐reinforced interphase layer is in situ constructed using a synthesized solid polymer electrolyte. As a result, the constructed topological solid electrolyte interphase (SEI) layer harmonizes the enhanced mechanochemical stability and fast diffusion dynamics of Li+, which maintains the integrity and stability of the SEI layer during cycling. In addition, a highly stable and reversible Li nucleation/stripping behaviors exceeding 3000 h and the superior cycling performance of practical LiFePO4/Li metal battery beyond 500 cycles can be achieved by virtue of the formation of the topological interphase layer. This design strategy of constructing a topological interphase layer to decouple mechanical strength and the activation energy of Li+ transport provides a feasible paradigm for realizing practical SSLMBs. [ABSTRACT FROM AUTHOR]

Summary: A key trait conferring flood tolerance is the ability to grow adventitious roots as a response to submergence. The genetic traits of deepwater rice determining the development and characteristics of aquatic adventitious roots (AAR) had not been evaluated.We used near‐isogenic lines introgressed to test the hypothesis that the impressive shoot elongation ability of deepwater rice linked to quantitative trait loci 1 and 12 also promote the development of AAR.The deepwater rice genotype NIL‐12 possessed expanded regions at the stem nodes where numerous AAR developed as a response to submergence. Two types (AR1 and AR2) of roots with distinct timing of emergence and large differences in morphological and anatomical traits formed within 3 (AR1) to 7 (AR2) d of submergence. The mechanical impedance provided by the leaf sheath caused AR2 to emerge later promoting thicker roots, higher elongation capacity and higher desiccation tolerance. Upregulation of key genes suggests a joint contribution in activating the meristem in AAR enhancing the development of these in response to submergence.The morphological and anatomical traits suggested that AR2 is better adapted to long‐term flooding than AR1. We therefore propose that AR2 in deepwater rice functions as an evolutionary defence strategy to tackle periodic submergence. See also the Commentary on this article by Maric & Hartman, 238: 1337–1339. [ABSTRACT FROM AUTHOR]

Manholes are vital component of the sewerage system; they are often damaged due to concrete corrosion, hydrogen sulphide (H2S) gas released by sewage effluent and vehicular loading. Due to large number of accidents occurred on the road, there is need for supervision of manholes so that it can be replaced when it is about to damage. In this paper, three different manholes were tested according to Indian standard code IS 12592 (2002). At the same time, using electro mechanical impedance (EMI) technique, the damage quantification was done using root mean square deviation (RMSD) for the obtained signature of the manholes with different damage stages. Three PZT sensors were bonded using epoxy, one each on top and bottom of manhole cover and third at the frame of the manhole. It was found that the PZT bonded at bottom captures the damages well than the PZT bonded on the top of cover, but it shows large variation when the crack line passes through the PZT bonded place, the PZT bonded on the frame shows abrupt variations with the damage. Hence, PZT sensor pasted on top of manhole cover was found to be well correlated to the damage stages. The effective structural parameters were extracted using PZT sensor; moreover, for all the three manhole structures, the structural damping was identified for different damage states. A model was developed including all three manholes with more than 95% confidence level for estimating the remaining life of manhole. [ABSTRACT FROM AUTHOR]

Humans are adept at a wide variety of motor skills, including the handling of complex objects and using tools. Advances to understand the control of voluntary goal-directed movements have focused on simple behaviors such as reaching, uncoupled to any additional object dynamics. Under these simplified conditions, basic elements of motor control, such as the roles of body mechanics, objective functions, and sensory feedback, have been characterized. However, these elements have mostly been examined in isolation, and the interactions between these elements have received less attention. This study examined a task with internal dynamics, inspired by the daily skill of transporting a cup of coffee, with additional expected or unexpected perturbations to probe the structure of the controller. Using optimal feedback control (OFC) as the basis, it proved necessary to endow the model of the body with mechanical impedance to generate the kinematic features observed in the human experimental data. The addition of mechanical impedance revealed that simulated movements were no longer sensitively dependent on the objective function, a highly debated cornerstone of optimal control. Further, feedforward replay of the control inputs was similarly successful in coping with perturbations as when feedback, or sensory information, was included. These findings suggest that when the control model incorporates a representation of the mechanical properties of the limb, that is, embodies its dynamics, the specific objective function and sensory feedback become less critical, and complex interactions with dynamic objects can be successfully managed. [ABSTRACT FROM AUTHOR]

Pushing and gripping forces may contribute to Hand-Arm Vibration Syndrome but, thus far, have not been taken into account in vibratory dose assessment according to the current standards. To obtain a better understanding of the symptom onset, we developed a finite element model of the hand to replicate its vibratory behaviour in gripping and pushing actions. In a case study, Supersonic Shear Imaging measurements revealed the significant dependence of muscle stiffness and anisotropy on gripping. The use of these measurements in our model showed that muscle activation influences the driving-point mechanical impedance of the hand and local vibration propagation. [ABSTRACT FROM AUTHOR]

In acoustic-vibration coupling modeling and analysis, the damping loss factor (DLF) and coupling loss factor (CLF) are important parameters that can measure the damping characteristics of a system and determine its vibration energy dissipation capacity. Their accuracy directly affects the accuracy and reliability of model prediction. To improve the calculation accuracy and efficiency of the system loss factor, this study proposed a method for calculating the loss factor and CLF in a subsystem based on experimental measurement data. First, the quantitative relationship among the total loss factor, DLF, and CLF of a subsystem was deduced and established on the basis of an energy balance equation. Then, the total loss factor of the subsystem and the expressions between the average vibration energy and vibration signal under single-frequency excitation were derived in accordance with mechanical impedance theory. Second, the spectrum function of multipoint response under single-frequency excitation was measured with an experimental identification method, and the total loss factor of each subsystem of the coupling model and the CLF were calculated using the derived formula. Results show that the proposed method cannot only fully utilize the advantages of the transient attenuation and mean admittance methods, but can also avoid the error of response signal changing with time under steady-state excitation and reflect on the loss characteristics of a subsystem more comprehensively. This study provides a good reference for improving the prediction accuracy of the acoustic-vibration coupling of complex structures and guiding structural acoustic design. [ABSTRACT FROM AUTHOR]

In this article, a new capsule-like smart aggregate (CSA) is developed and verified for impedance-based stress monitoring in a pre-determined frequency range of less than 100 kHz. The pros and cons of the existing smart aggregate models are discussed to define the requirement for the improved CSA model. The conceptual design and the impedance measurement model of the capsule-like smart aggregate (CSA) are demonstrated for concrete damage monitoring. In the model, the interaction between the CSA and the monitored structure is considered as the 2-degrees of freedom (2-DOF) impedance system. The mechanical and impedance responses of the CSA are described for two conditions: during concrete strength development and under compressive loadings. Next, the prototype of the CSA is designed for impedance-based monitoring in concrete structures. The local dynamic properties of the CSA are numerically simulated to pre-determine the sensitive frequency bands of the impedance signals. Numerical and experimental impedance analyses are performed to investigate the sensitivity of the CSA under compressive loadings. The changes in the impedance signals of the CSA induced by the compressive loadings are analyzed to assess the effect of loading directions on the performance of the CSA. Correlations between statistical impedance features and compressive stresses are also made to examine the feasibility of the CSA for stress quantification. [ABSTRACT FROM AUTHOR]

A novel approach to design the controller of the active suspension is presented in light of the suspensions' mechanical impedance dynamics, where the sprung-mass kinematic states, including acceleration, velocity, and displacement are comprehensively modeled considering the concept of suspension mechanical impedance. The proposed impedance controller is designed by tracking the equilibrium trajectory error of the sprung-mass states. The approximate transfer function of the active suspension is derived for choosing the parameters of the virtual mechanical impedance system. The numerical simulation of the suspension amplitude–frequency response is carried out, which demonstrates that the virtual mass and damping parameters have greater influence than the virtual spring parameter. The ride comfort of the suspension controlled by the designed impedance control behaves well in a wide range of road conditions, and the road holding with it is even better than that with the Linear Quadratic Regulator (LQR) control especially around the second-order resonance frequency. The numerical simulation and experimental comparison all demonstrate that the proposed impedance control law, which does not strictly rely on the suspension parameters, could achieve a better power economy and road holding than that of the LQR control. [ABSTRACT FROM AUTHOR]

Mechanical impedance (MI) defines the ability of a system to vibrate as a consequence of force application. In the recent years, the correlation of this parameter with tire-road noise and other characteristics has gained certain attention. Nevertheless, the information about this topic is still insufficient. Usually, the force is set through an impulse hammer as a master and the acceleration is measured through an accelerometer as a response in order to measure the corresponding Frequency Response Function (FRF). The objectives of the study presented in this paper are i) to analyse the differences between the axial mechanical impedance (complex ratio of force and velocity referred to the same point, named driving-point impedance) and the non-axial mechanical impedance (complex ratio of the force at the point i and velocity at the point j, named transfer impedance); ii) to analyse the effect of adding crumb rubber (2% by mixture weight) and of the percentage of bitumen on the mechanical impedance for the bituminous samples. Therefore, laboratory tests on asphalt concrete specimens have been performed, using an instrumentation system composed of i) an impact hammer reporting the impact force value; ii) an impedance head measuring the direct impact force and the direct acceleration at the hitting point location; iii) a piezoelectric accelerometer measuring the transfer acceleration at a certain distance from the hitting point location. Results demonstrate that the ratio between the repeatability and the average is quite constant, while for heights higher than 10 cm, also MI tends to be independent on the height. A number of recommendations have been made based on the results of the present research. [ABSTRACT FROM AUTHOR]

A two-degree-of-freedom (two-DOF) equation of motion was derived in the frequency domain using a substructuring technique for efficiently calculating the in-structure response spectrum (ISRS) considering equipment–structure interaction. The model of the primary structure was condensed into a mechanical impedance function and combined with the equipment represented by a single-degree-of-freedom oscillator in the frequency domain. This condensed two-DOF system is applied to the efficient calculation of the ISRS considering the equipment–structure interaction without repeated analysis of the coupled model with full DOFs. This coupled analysis procedure was applied to a finite element model of an auxiliary building in a nuclear power plant to validate both the accuracy and impact on the equipment response. Finally, the adequacy of three representative decoupling criteria on the necessity of coupled analysis was investigated by applying those criteria to the auxiliary building example. [ABSTRACT FROM AUTHOR]

In this paper, a novel auxetic structure with rotating squares with holes is investigated. The unit cell of the structure consists of four units in the shape of a square with cut corners and holes. Finally, the structure represents a kind of modified auxetic structure made of rotating squares with holes or sheets of material with regularly arranged diamond and square cuts. Effective and dynamic properties of these structures depend on geometrical properties of the structure. The structures are characterized by an effective Poisson's ratio from negative to positive values (from about minus one to about plus one). Numerical analysis is made for different geometrical features of the unit cells. The simulations enabled the determination of the dynamic characteristic of the analyzed structures using vibration transmission loss, transmissibility, and mechanical impedance. Numerical calculations were conducted using the finite element method. In the analyzed cases of cellular auxetic structures, a linear elasticity model of the material is assumed. The dynamic characteristic of modified rotating square structures is strongly dependent not only on frequency. The dynamic behavior could also be enhanced by adjusting the geometric parameter of the structure. Auxetic and non-auxetic structures show different static and dynamic properties. The dynamic properties of the analyzed structures were examined in order to determine the frequency ranges of dynamic loads for which the values of mechanical impedance and transmissibility are appropriate. [ABSTRACT FROM AUTHOR]

Slips are side-shoots or fruit with large crowns that grow from buds on the pineapple (Ananas comosus L.) peduncle. The slips are widely used for pineapple vegetative propagation when crowns are left attached to the fruit that is marketed. There is a difference between the two most popular low-acid pineapple hybrids grown worldwide. The 'Pineapple Research Institute 73-50' (CO-2, MD-1) slips develop few roots when planted compared with 'Pineapple Research Institute 73-114' (MD2). The slow rooting of 73-50 leads to slow field establishment and can extend the crop cycle. Our objective was to determine the cause of this reduced rooting and evaluate treatments to increase the rooting rate. Rooting trials in moist, coarse vermiculite showed that larger slips and green slips with red hues also had a greater number of roots compared with smaller slips and green or yellow slips. Delaying harvesting of the slips after the fruit were harvested also resulted in a greater number of roots. Treatments including components frequently used for rooting cuttings did not significantly increase root numbers. An exception was a tendency for slips treated with potassium nitrate to have greater rooting during some tests. We present data that support the conclusion that the poor root development is associated with the mechanical impedance of the root from the tightly affixed basal leaf bracts. Removal of the lower ten bracts can lead to greater root numbers. When the slip with the bracts removed was tightly wrapped in plastic wrap and masking tape, rooting was reduced. The sizing and selection of slips that are green with a red hue and collected as late as possible after fruit harvest had the best rooting response. [ABSTRACT FROM AUTHOR]

Steer-by-wire (SBW) system has been introduced to reduce the number of parts in a vehicle by eliminating the mechanical link between the steering wheel and the road wheel. Even though intensive research has been conducted on the SBW system, the performance of the actuator system that provides the desired steering feel still needs improvement. Therefore, this article presents a compact size torque controllable steering wheel module for the SBW system, where the actuator that provides the steering feel to the driver is modularized with the gear mechanism and the spring. The steering torque sensing mechanism is compactly integrated by placing the spring inside the gear mechanism. Thanks to the advantage in the torque measurement and control ability by the spring mechanism, high gear-ratio transmission can be employed in the proposed module, which can also address the low inherent mechanical impedance problem that may cause fail-safety issues in the SBW system. To enhance the impedance rendering performance of the proposed module, an internal model compensator which is composed of inertia and friction compensation is applied. The kinematics, statics, and dynamics of the proposed module are theoretically analyzed, and a model-based control algorithm is proposed based on this analysis result. Finally, the increase in the inherent impedance and the torque control performance of the proposed module are verified through experiments. [ABSTRACT FROM AUTHOR]

Humans have an astonishing ability to extract hidden information from the movement of others. In previous work, subjects observed the motion of a simulated stick-figure, two-link planar arm and estimated its stiffness. Fundamentally, stiffness is the relation between force and displacement. Given that subjects were unable to physically interact with the simulated arm, they were forced to make their estimates solely based on observed kinematic information. Remarkably, subjects were able to correctly correlate their stiffness estimates with changes in the simulated stiffness, despite the lack of force information. We hypothesized that subjects were only able to do this because the controller used to produce the simulated arm's movement, composed of oscillatory motions driving mechanical impedances, resembled the controller humans use to produce their own movement. However, it is still unknown what motion features subjects used to estimate stiffness. Human motion exhibits systematic velocity-curvature patterns, and it has previously been shown that these patterns play an important role in perceiving and interpreting motion. Thus, we hypothesized that manipulating the velocity profile should affect subjects' ability to estimate stiffness. To test this, we changed the velocity profile of the simulated two-link planar arm while keeping the simulated joint paths the same. Even with manipulated velocity signals, subjects were still able to estimate changes in simulated joint stiffness. However, when subjects were shown the same simulated path with different velocity profiles, they perceived motions that followed a veridical velocity profile to be less stiff than that of a non-veridical profile. These results suggest that path information (displacement) predominates over temporal information (velocity) when humans use visual observation to estimate stiffness. Author summary: Stiffness of the arms or legs, the force evoked by displacement, plays an important role in managing physical interaction with objects in the world. Measuring stiffness fundamentally requires physical contact. Nevertheless, previous study showed that humans have a remarkable ability to estimate stiffness solely from visual observation of a computer simulation, with no physical contact. The present study extended that work and found that this ability was robust. In particular, the ability to estimate simulated stiffness was largely unaffected by changing the time course of simulated motion. This was surprising given the extensive prior research reporting that distorting velocity patterns influences motion perception. The results presented in this paper indicate that geometric information (path) predominates over temporal information (velocity) in the perception of stiffness. Given the highly-cited relationship between motor action and perception, it also suggests that the structure of the motor control system we used in the simulations is a reasonable approximation of the neural motor controller. This work provides insight into humans' representation of motor behavior and how humans interpret and learn from the motor actions of others. [ABSTRACT FROM AUTHOR]

It is of great significance to monitor the aging state and evaluate the useful life of stored solid‐rocket‐motor (SRM) propellant grains. In this work, the aging state of hydroxyl terminated polybutadiene (HTPB) propellant grains was studied based on the electromechanical impedance (EMI) method. The relationship between the complex modulus and the mechanical impedance of viscoelastic material was derived. The finite element analysis of the structure with different moduli was carried out. The results show that the peak value of electromechanical impedance increases with an increase of propellant modulus. This report focuses on experimental research on monitoring the aging of cylindrical SRMs based on the EMI method. It is found that the peak of electromechanical impedance spectrum increases with aging time, while the peak frequency decreases slightly. As an aging damage variable, the root mean squared error (RMSD) of electromechanical impedance increases with aging time, and its growth rate is large at first, then decreases, and finally increases. Finally, a tensile test of aging propellant specimens was carried out, and the results show that the rate of change (ROC) of the modulus can be fit by a linear relationship to the RMSD of the electromechanical impedance. [ABSTRACT FROM AUTHOR]

• A bonded PZT-rubber bearing structural dynamic interaction model was developed. • Shear stress effect on the electromechanical admittance (EMA) was analytically interpreted. • 3D finite element model of a full-sized rubber bearing was generated to detect shear stress. • Validated experiment was conducted on two plate rubber bearings for shear stress identification. • Analytical, numerical and experimental results indicated the effectiveness of the approach. This paper presented a preliminary study on the feasibility of shear stress identification in plate rubber bearings using surface-bonded piezoceramic (PZT) transducers. A PZT-rubber bearing structural dynamic interaction model was developed to analyze the shear stress effect on the electromechanical admittance (EMA, inverse of impedance) by introducing a mechanical impedance system consisting of parallel mechanical elements. 3D finite element (FE) model of a full-sized plate rubber bearing was generated to detect shear stress using the EMA signatures. Proof-of-concept experiment was finally conducted on two plate rubber bearings subjected to shearing force, during which the process was monitored by three PZT sheets arranged at different loci. Theoretical, numerical and experimental results demonstrated that identification results of PZT transducers were closely related to the PZT location, shear stress in rubber bearings were generally in linear relationship with the peak values of EMA spectrum and its statistically quantifiable indicators. [ABSTRACT FROM AUTHOR]

• The regulation pattern of the human arm endpoint impedance across a wide range is investigated by the perturbation method. The 3D impedance features including magnitude, shape, and orientation are summarized to reveal the independent influences of arm postures and muscle co-contraction level on the mechanical impedance of arm endpoint. • Inspired from these findings, the orientation of the impedance ellipsoid is determined by compact arm posture vectors, while the magnitude of the impedance ellipsoid is estimated from the muscle co-contraction by extreme learning machine. The proposed method provides accurate impedance estimation results and avoids complex computation of Jacobian matrix when estimating impedance in a wide range of arm motion. Transferring the mechanical impedance regulation skill from humans to robot systems can enhance the compliance, safety, and stability of the robots in interaction with external environments. To acquire human arm endpoint impedance, traditional methods employ perturbation-based approaches or muscle-driven models to conduct offline identification and online estimation, respectively. This paper proposes a simplified method for arm endpoint impedance estimation across a wide range of motion, which expands its application by eliminating the need for physiological parameter identification and Jacobian matrix calculation. Perturbation experiments were conducted to identify the common regulation pattern of the endpoint impedance in a wide range, considering various arm postures and muscle co-contraction intensities. The impedance magnitude and orientation are researched and found to be independently affected by the arm postures and the muscle co-contraction. Moreover, a consistent relationship is observed between the orientation of the impedance principal axes and the arm posture vectors. Inspired from these findings, the orientations of the principal axes are estimated based on arm posture vectors, resulting in an average error of approximately 10° for each axis. Additionally, the lengths of the principal axes are determined based on surface electromyography (sEMG) using the Extreme Learning Machine (ELM). The normalized root mean square error (nRMSE) of the length of principal axes for four subjects is below 20 %. The completeness and accuracy of the estimation result are demonstrated by the estimated impedance ellipsoid, which graphically represents the length and orientation of the impedance principal axes. [ABSTRACT FROM AUTHOR]