Academic literature on the topic 'Relative puese duration of the control signal'

A computer simulation of the amplitude change of the pulsed echo signal of a normal probe from a reflector in the form of a strip simulating a stratification in metal, the plane of which is parallel to the control surface, depending on the distance between the axis of the probe and the normal to the surface of the reflector in its center. The calculations used radiated pulses of various durations ‒ long, medium length and short. The expediency of using medium-length pulses has been established. The estimation of the linear conventional length of the stratification model by the method of reducing the amplitude of the echo signal from the largest by 20 dB showed that this size approximately corresponds to the size of the reflector used in calculations for the distance between the plane of the reflector and the control surface approximately equal to the three near fields of the probe.

Abstract In this paper, we study the diagnostics and identification of injection duration of common rail (CR) diesel pilot injectors of dual-fuel engines. In these pilot injectors, the injected volume is small and the repeatability of the injections and identification of the drifts of the injectors are important factors, which need to be taken into account in achieving good repeatability (shot-to-shot with every cylinder) and therefore a well-balanced engine and reduced overall wear. A diagnostics method based on analysis of CR pressure signal with experimental verification results is presented. Using the developed method, the relative duration of injection events can be identified. In the method, the pressure signal during the injection is first extracted after the control of each injection event. After that, the signal is normalized and filtered. Then a derivative of the filtered signal is calculated. Change in the derivative of the filtered signal larger than a predefined threshold indicates an injection event which can be detected and its relative duration can be identified. The efficacy of the proposed diagnostics method is presented with the experimental results, which show that the developed method detects drifts in injection duration and the magnitude of drift. According to the result, ≥ 10 μs change (2%, 500 μs) in injection time can be identified.

The electron valley pseudospin in two-dimensional hexagonal materials is a crucial degree of freedom for achieving their potential application in valleytronic devices. Here, bringing valleytronics to layered van der Waals materials, we theoretically investigate lightwave-controlled valley-selective excitation in twisted bilayer graphene (tBLG) with a large twist angle. It is demonstrated that the counter-rotating bicircular light field, consisting of a fundamental circularly-polarized pulse and its counter-rotating second harmonic, can manipulate the sub-cycle valley transport dynamics by controlling the relative phase between two colors. In comparison with monolayer graphene, the unique interlayer coupling of tBLG renders its valley selectivity highly sensitive to duration, leading to a noticeable valley asymmetry that is excited by single-cycle pulses. We also describe the distinct signatures of the valley pseudospin change in terms of observing the valley-selective circularly-polarized high-harmonic generation. The results show that the valley pseudospin dynamics can still leave visible fingerprints in the modulation of harmonic signals with a two-color relative phase. This work could assist experimental researchers in selecting the appropriate protocols and parameters to obtain ideal control and characterization of valley polarization in tBLG.

Introduction Neuromuscular electrical stimulation (NMES) is an innovative and effective (re)training strategy to improve or restore neuromuscular function (Maffiuletti et al., 2018). Contractions induced by NMES differ in many aspects from voluntary contractions, as motor unit (MU) recruitment is random, synchronous and spatially fixed (mostly superficial; Maffiuletti, 2010). Consequently, several limitations, such as higher fatigability (Vanderthommen et al., 1999) and discomfort (Delitto et al., 1992) might restrain its clinical implementation. The use of specific stimulation parameters may partly overcome these limitations. Indeed, the use of wide pulses (≥ 1 ms) delivered at low stimulation intensity leads to a preferential recruitment of Ia sensory axons (Veale et al., 1973) which may promote MU central (reflexive) recruitment. Furthermore, the high stimulation frequencies (> 80 Hz) would facilitate the temporal summation of post-synaptic excitatory potentials and reflexively activate spinal motoneurons through Ia afferents (Dideriksen et al., 2015), which may increase force production. Another potential advantage of wide pulse high frequency (WPHF) NMES is that low stimulation intensities are required to limit antidromic collision, and these lower intensities are associated with less discomfort (Delitto et al., 1992). Therefore, by stimulating at intensities expected to generate ~10% of the maximal voluntary contraction (MVC) force, WPHF NMES induces, in some individuals, a progressive increase in force during the stimulation, called ‘extra force’. It can reach up to 80% of the MVC force in plantar flexors (Neyroud et al., 2018) but the response to WPHF NMES in other muscle groups is less documented. Extra force is usually accompanied by a prolongation of the surface electromyographic (EMG) activity after cessation of the stimulation, also called ‘sustained EMG activity’ which is interpreted as MU recruited through the central pathway (Neyroud et al, 2018). The main aim of the present study was to explore the effect of varying stimulation parameters on the NMES-evoked force and sustained EMG activity in the plantar flexors, knee extensors and elbow flexors. It was hypothesized that the plantar flexors would show higher centrally-mediated responses to NMES than knee extensors and elbow flexors, especially with large pulse duration. Methods Sixteen volunteers, 2 women and 14 men (29 ± 6 yr, 177 ± 6 cm, 74 ± 11 kg) participated to three experimental sessions - one for each muscle group - in a randomized order. The experimental protocol was similar for the three muscle groups and included twelve 10-s NMES trains separated by at least 2 min of rest and delivered at an intensity set initially to evoke 10% of the maximal voluntary contraction force. Stimulation trains were randomly delivered with a combination of frequencies (20, 50, 100 and 147 Hz) and pulse durations (0.2, 1 and 2 ms). Force was collected using specific isometric ergometers and EMG activity was recorded with bipolar electrodes on the soleus, vastus lateralis and biceps brachii muscles. Extra force was calculated as the relative force difference between the last second and the 2nd second of stimulation. Sustained EMG activity was identified as the visible activity on the EMG after the end of the stimulation and quantified over 500 ms as the root mean square (RMS) of this signal normalized by the RMS of the EMG activity measured during the MVC. Results Stimulation frequency. Extra force was significantly higher for the plantar flexors than for the elbow flexors at 50 Hz (69 ± 68% vs 38 ± 53%, p = 0.025), 100 Hz (84 ± 71% vs 21 ± 72%, p < 0.001) and 147 Hz (75 ± 84% vs 16 ± 82%, p < 0.001), but not at 20 Hz (p = 0.649). For all the tested frequencies, extra force was not significantly different between plantar flexors and knee extensors (p = 0.065 - 0.743). Extra force was significantly higher for the knee extensors than for the elbow flexors at 100 Hz (63 ± 106% vs 21 ± 72%, p = 0.012), but not at the other frequencies (p = 0.156 - 0.388). Sustained EMG activity was significantly higher for the plantar flexors than for the elbow flexors at all frequencies (p < 0.001) as well as compared to the knee extensors at 50 Hz, 100 Hz and 147 Hz (p = 0.010, p = 0.009, p = 0.003 respectively) but not at 20 Hz (p = 0.483). Finally, sustained EMG activity was significantly higher for the knee extensors than for the elbow flexors at for all the tested stimulation frequencies (p < 0.05). Pulse duration. Extra force was significantly higher for the plantar flexors than for the elbow flexors with pulse durations of 1 ms (76 ± 74% vs 23 ± 48%, p < 0.001) and 2 ms (73 ± 70% vs 29 ± 88%, p < 0.001) but not with 0.2 ms (p = 0.064). Extra force was not significantly different between the plantar flexors and the knee extensors, and the knee extensors showed a higher extra force than elbow flexors with 1 ms (56 ± 99% vs 23 ± 48%, p = 0.002). Sustained EMG activity was significantly higher for the plantar flexors than the elbow flexors with all pulse durations (p < 0.001) and than the knee extensors with 1 and 2 ms (p < 0.001). Knee extensors showed a higher sustained EMG activity than elbow flexors with 0.2 ms and 2 ms (p < 0.001) but not with 1 ms. Discussion/Conclusion WPHF NMES is a promising tool for (re)training and the results of the present study suggest that its use to induce centrally-mediated force is more pertinent in lower limb muscles. The difference in responses between muscle groups could be explained by muscle typology and density in neuromuscular spindles. Indeed, muscles involved in precise movements and postural control have a greater number of neuromuscular spindles, which are mainly located in type 1 fibers (Botterman et al., 1978). The greater centrally-mediated responses in the plantar flexors compared with the elbow flexors can be explained by the difference in muscle typology (more type I muscle fibers in the postural lower limb muscles). It may also justify the absence of difference in extra force between plantar flexors and knee extensors as they both contribute to postural maintenance (Jusić et al., 1995). Since the effectiveness of NMES for neuromuscular adaptations depends on the amount of force generated during training (Maffiuletti et al., 2018), these results suggest that the use of WPHF NMES would be efficient on plantar flexors and knee extensors for training and rehabilitation and that wide pulses and high frequencies should be preferentially used when implementing this NMES modality in clinical settings. References Botterman, B. R., Binder, M. D., & Stuart, D. G. (1978). Functional anatomy of the association between motor units and muscle teceptors. American Zoologist, 18(1), 135–152. https://doi.org/10.1093/icb/18.1.135 Delitto, A., Strube, M. J., Shulman, A. D., & Minor, S. D. (1992). A study of discomfort with electrical stimulation. Physical Therapy, 72(6), 410–421. https://doi.org/10.1093/ptj/72.6.410 Dideriksen, J. L., Muceli, S., Dosen, S., Laine, C. M., & Farina, D. (2015). Physiological recruitment of motor units by high-frequency electrical stimulation of afferent pathways. Journal of Applied Physiology, 118(3), 365–376. https://doi.org/10.1152/japplphysiol.00327.2014 Jusić, A., Baraba, R., & Bogunović, A. (1995). H-reflex and F-wave potentials in leg and arm muscles. Electromyography and Clinical Neurophysiology, 35(8), 471–478. Maffiuletti, N. A., Gondin, J., Place, N., Stevens-Lapsley, J., Vivodtzev, I., & Minetto, M. A. (2018). Clinical Use of Neuromuscular Electrical Stimulation for Neuromuscular Rehabilitation: What Are We Overlooking? Archives of Physical Medicine and Rehabilitation, 99(4), 806-812. https://doi.org/10.1016/j.apmr.2017.10.028 Maffiuletti, N. A. (2010). Physiological and methodological considerations for the use of neuromuscular electrical stimulation. European Journal of Applied Physiology, 110(2), 223–234. https://doi.org/10.1007/s00421-010-1502-y Neyroud, D., Grosprêtre, S., Gondin, J., Kayser, B., & Place, N. (2018). Test–retest reliability of wide-pulse high-frequency neuromuscular electrical stimulation evoked force. Muscle & Nerve, 57(1), E70–E77. https://doi.org/10.1002/mus.25747 Vanderthommen, M., Gilles, R., Carlier, P., Ciancabilla, F., Zahlan, O., Sluse, F., & Crielaard, J. M. (1999). Human muscle energetics during voluntary and electrically induced isometric contractions as measured by 31P NMR spectroscopy. International Journal of Sports Medicine, 20(5), 279–283. https://doi.org/10.1055/s-2007-971131 Veale, J. L., Mark, R. F., & Rees, S. (1973). Differential sensitivity of motor and sensory fibres in human ulnar nerve. Journal of Neurology, Neurosurgery & Psychiatry, 36(1), 75–86.