Redundant mechanical systems like humanoid robots are designed to fulfill multiple tasks at a time. A task, in velocity-resolved inverse kinematics, is a desired value for a function of the robot ...configuration that can be regulated with an ordinary differential equation (ODE). When facing simultaneous tasks, the corresponding equations can be grouped in a single system or, better, sorted in priority and solved each in the solutions set of higher priority tasks. This elegant framework for hierarchical task regulation has been implemented as a sequence of least-squares problems. Its limitation lies in the handling of inequality constraints, which are usually transformed into more restrictive equality constraints through potential fields. In this paper, we propose a new prioritized task-regulation framework based on a sequence of quadratic programs (QP) that removes the limitation. At the basis of the proposed algorithm, there is a study of the optimal sets resulting from the sequence of QPs. The algorithm is implemented and illustrated in simulation on the humanoid robot HRP-2.
Double perovskites are currently being intensively studied thanks to their highly relevant technological potential as materials with manifold properties. This contribution aims to the preparation of ...double perovskite oxide material BiBaFeZnO
6
, which is synthesized by the sol–gel method. The structural study shows that the sample is single phase and crystallizes in the rhombohedral system with the R
3
-
C space group. In addition, impedance spectroscopy was used to study the dielectric behavior of materials and the different physical phenomena at temperature range from 200 to 380 K and in a frequency range up to 1 MHz. The Nyquist diagram at different temperatures reveals the behavior of flat semi-circular, which has been modeled by an equivalent circuit including an RC element and an RQ element. The frequency-dependent behavior of Z” shows a peak inferring a relaxation. The electrical conductivity was determined by the Jonscher’s law, and the activation energy were calculated from modulus or DC conductivity. The obtained results have confirmed that the non-overlapping small polaron tunneling model (NSPT) is the appropriate model to explain the electrical conduction phenomenon.
Force myography (FMG) is increasingly gaining importance in gesture recognition because of it’s ability to achieve high classification accuracy without having a direct contact with the skin. In this ...study, we investigate the performance of a bracelet with only six commercial force sensitive resistors (FSR) sensors for classifying many hand gestures representing all letters and numbers from 0 to 10 in the American sign language. For this, we introduce an optimized feature selection in combination with the Extreme Learning Machine (ELM) as a classifier by investigating three swarm intelligence algorithms, which are the binary grey wolf optimizer (BGWO), binary grasshopper optimizer (BGOA), and binary hybrid grey wolf particle swarm optimizer (BGWOPSO), which is used as an optimization method for ELM for the first time in this study. The findings reveal that the BGWOPSO, in which PSO supports the GWO optimizer by controlling its exploration and exploitation using inertia constant to improve the convergence speed to reach the best global optima, outperformed the other investigated algorithms. In addition, the results show that optimizing ELM with BGWOPSO for feature selection can efficiently improve the performance of ELM to enhance the classification accuracy from 32% to 69.84% for classifying 37 gestures collected from multiple volunteers and using only a band with 6 FSR sensors.
•Collect FMG signal using a bracelet with 6 FSR sensors.•Investigate the performance of BGWOPSO as a feature selection and an optimizer for the ELM classifier and test it on real FMG data.•Comapre the classification of 37 gestures from the ASL using three swarm intelligence algorithms.
Safe localization of trains via GPS and wireless sensors is essential for railway traffic supervision. Especially for freight trains and because normally no power source is available on the wagons, ...special solutions for energy supply have to be developed based on energy harvesting techniques. Since vibration is available in this case, it provides an interesting source of energy. Nevertheless, in order to have an efficient design of the harvesting system, the existing vibration needs to be investigated. In this paper, we focus on the characterization of vibration parameters in railway application. We propose an electromagnetic vibration converter especially developed to this application. Vibration profiles from a train traveling between two German cities were measured using a data acquisition system installed on the train’s wagon. Results show that the measured profiles present multiple frequency signals in the range of 10 to 50 Hz and an acceleration of up to 2 g. A prototype for a vibration converter is designed taking into account the real vibration parameters, robustness and integrability requirements. It is based on a moving coil attached to a mechanical spring. For the experimental emulation of the train vibrations, a shaker is used as an external artificial vibration source controlled by a laser sensor in feedback. A maximum voltage of 1.7 V peak to peak which corresponds to a maximum of 10 mW output power where the applied excitation frequency is close to the resonant frequency of the converter which corresponds to 27 Hz.
Dielectric and conduction properties were investigated on La
1 −
x
Sr
x
FeO
3
(0 ≤
x
≤ 0.5) ceramics synthesized by solid-state reaction method. X-ray powder diffraction pattern of all prepared ...samples and their Rietveld refinement revealed that all samples crystallize in orthorhombic structure with Pnma space group. Sr substitution induced the volume unit cell to decrease and the crystallite size to vary in a non-monotonic manner. Scanning electron microscopy images revealed also Sr-dependent morphology of the studied ceramics. Fourier transform infrared (FTIR) spectra evidenced structural distortion effects on
ν
Fe–O–Fe
,
σ
Fe–O–Fe
and
ν
La–O
vibrations and showed the presence of the carbonate ion impurity for the compositions
x
= 0.2, 0.3, 0.4 and 0.5. Ac conductivity analysis was accomplished according to equation:
σ
ac
ω
=
σ
s
1
+
τ
2
ω
2
+
σ
∞
τ
2
ω
2
1
+
τ
2
ω
2
+
A
ω
n
for the parent compound and its doped one La
0.9
Sr
0.1
FeO
3
. However, this analysis was realized by using Jonscher law:
σ
ac
ω
=
σ
dc
+
A
ω
n
for the compositions
x
= 0.2, 0.3, 0.4 and 0.5. It revealed that the hopping process occurred through long distance for 0 ≤
x
≤ 0.3 compositions, whereas for
x
= 0.4 and 0.5 compositions the hopping occurred between neighboring sites. Complex impedance analysis performed on these ceramics by means of different electrical equivalent circuits owing to their different morphologies allowed probing grain boundary effect on ac conductivity.
La
0.6
Sr
0.4
FeO
3
ceramic was elaborated by solid-state route. Preliminary room-temperature structural analysis evidences the sample formation in the orthorhombic structure and its phase purity. ...Electrical properties of the studied ceramic have been investigated according to dielectric measurements in the frequency range 10
–1
- 10
6
Hz and the temperature range 93 - 313 K. Electrical conductivity curves exhibit a step-like behavior, at low temperatures, attributed to grain boundaries and grain contributions which are well described by the two Jonscher equations. The grains conduction mechanism is consistent with the thermally activated hopping of small polaron (SPH). Whereas, this mechanism is no longer satisfied for grain boundaries conduction mechanism at lower temperatures. Indeed, this latter is governed by the variable range hopping (VRH) model. This electrical conductivity analysis is further confirmed by the complex impedance formalism according to the obtained activation energies. Analysis of Nyquist plots at low temperatures has evidenced the presence of two grain boundaries effects attributed to the heterogeneous structure of La
0.6
Sr
0.4
FeO
3
grain boundary according to the morphological analysis
.
Such characteristic may be at the origin of the grain boundaries electrical conductivity mechanism change at low temperatures.
In this paper, an experiment has been conducted in order to record the ground temperature at different depths during 2006 in a suburb of Sfax (Tunisia) which represents an example of the ...South-Mediterranean climate. The temperature of the soil has also been calculated using a thermal model taking into account properties of the soil and meteorological conditions. Experimental results are compared with theoretical predictions. In order to estimate the influence of the soil properties on the ground temperature, different soil thermal conductivities are tested. A simplified model of an earth pipe system is developed. The cooling and heating capabilities produced by such a system are evaluated. This model is validated against an other published experimental model.
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