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Andrew G Cresswell - One of the best experts on this subject based on the ideXlab platform.
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effects of muscle activation on shear between human soleus and gastrocnemius muscles
Scandinavian Journal of Medicine & Science in Sports, 2017Co-Authors: Taija Finni, Glen A Lichtwark, Neil J Cronin, Dean L Mayfield, Andrew G CresswellAbstract:Lateral connections between muscles provide pathways for myofascial force transmission. To elucidate whether these pathways have functional roles in vivo, we examined whether activation could alter the shear between the soleus (SOL) and lateral gastrocnemius (LG) muscles. We hypothesized that selective activation of LG would decrease the stretch-induced shear between LG and SOL. Eleven volunteers underwent a series of knee joint manipulations where plantar flexion force, LG, and SOL muscle fascicle lengths and relative displacement of aponeuroses between the muscles were obtained. Data during a passive full range of motion were recorded, followed by 20° knee extension stretches in both passive conditions and with selective electrical stimulation of LG. During active stretch, plantar flexion force was 22% greater (P < 0.05) and relative displacement of aponeuroses was smaller than during passive stretch (P < 0.05). Soleus fascicle length changes did not differ between passive and active stretches but LG fascicles stretched less in the active than passive condition when the stretch began at angles of 70° and 90° of knee flexion (P < 0.05). The activity-induced decrease in the relative displacement of SOL and LG suggests stronger (stiffer) connectivity between the two muscles, at least at flexed knee joint angles, which may serve to facilitate myofascial force transmission.
S K Vartapetov - One of the best experts on this subject based on the ideXlab platform.
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application of dispersion compensating fiber with w type refractive index profile in Stretcher of ultrashort laser pulses at a wavelength of 1 03 µm
Journal of The Optical Society of America B-optical Physics, 2019Co-Authors: D V Khudyakov, D V Ganin, A D Lyashedko, M E Likhachev, A K Senatorov, M Y Salgansky, S K VartapetovAbstract:The application of a fiber with W-type refractive index profile as a Stretcher of ultrashort laser pulses for chirped pulse amplification is shown. As a result, pulses were obtained with energy of 3 µJ and duration of 270 fs, with high pulse contrast due to dispersion compatibility of the fiber Stretcher and compressor on diffraction gratings. A comparative analysis of several types of fibers for use as a Stretcher for amplification of chirped pulses is given in terms of their compatibility with the compressor.
Stephen N Stanley - One of the best experts on this subject based on the ideXlab platform.
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effect of passive stretching and jogging on the series elastic muscle stiffness and range of motion of the ankle joint
British Journal of Sports Medicine, 1996Co-Authors: Peter J Mcnair, Stephen N StanleyAbstract:Objective To determine the effect of stretching and jogging on the series elastic muscle stiffness of the plantar flexors and on the range of dorsiflexion at the ankle joint. Methods 24 healthy subjects participated in this study. Each subject undertook all of the following protocols, in random order: (1) stretching protocol: five 30 s static stretches with 30 s rest between stretches; (2) aerobic jogging protocol: subjects ran on a treadmill for 10 min at 60% of their maximum age predicted heart rate; (3) combined protocol: subjects ran first and then stretched. A damped oscillation technique was used to measure the series elastic stiffness of the plantar flexors. Dorsiflexion of the ankle was assessed with a weights and pulley system that moved the ankle joint from a neutral position into dorsiflexion passively. Electromyography was used to monitor the activity of the plantar and dorsiflexors during these procedures. The statistical analysis of these data involved an analysis of covariance Results For decreasing series elastic muscle stiffness running was more effective than stretching (P Conclusions Both jogging and static stretching exercises appear to be beneficial to individuals participating in sporting activities.
Mersedeh Tohidnezhad - One of the best experts on this subject based on the ideXlab platform.
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different frequency of cyclic tensile strain relates to anabolic catabolic conditions consistent with immunohistochemical staining intensity in tenocytes
International Journal of Molecular Sciences, 2020Co-Authors: Yusuke Kubo, Bernd Hoffmann, Katja Goltz, Uwe Schnakenberg, Holger Jahr, Rudolf Merkel, Gundula Schulzetanzil, Thomas Pufe, Mersedeh TohidnezhadAbstract:Tenocytes are mechanosensitive cells intimately adapting their expression profile and hence, their phenotype to their respective mechanomilieu. The immunolocalization and expression intensity of tenogenic, anabolic and catabolic markers in tenocytes in response to in vitro mechanical loading have not been monitored by immunohistochemical staining (IHC). Thus, we investigated the association between IHC intensities, different stimulation frequencies, and tenogenic metabolism using a versatile mechanical Stretcher. Primary tenocytes obtained from murine Achilles tendons were transferred to poly(dimethylsiloxane) (PDMS) elastomeric chamber. Chambers were cyclically stretched by 5% in uniaxial direction at a variation of tensile frequency (1 or 2 Hz) for 3 h. After stretching, cell physiology, IHC intensities of tendon-related markers, and protein level of the angiogenesis marker vascular endothelial growth factor (VEGF) were evaluated. Cell proliferation in tenocytes stimulated with 1 Hz stretch was significantly higher than with 2 Hz or without stretch, while 2 Hz stretch induced significantly reduced cell viability and proliferation with microscopically detectable apoptotic cell changes. The amount of scleraxis translocated into the nuclei and tenomodulin immunoreactivity of tenocytes treated with stretch were significantly higher than of non-stretched cells. The collagen type-1 expression level in tenocytes stretched at 1 Hz was significantly higher than in those cultivated with 2 Hz or without stretching, whereas the matrix metalloproteinase (MMP)-1 and MMP-13 immunoreactivities of cells stretched at 2 Hz were significantly higher than in those stimulated with 1 Hz or without stretching. The secreted VEGF-protein level of tenocytes stretched at 2 Hz was significantly higher than without stretching. Our IHC findings consistent with cell physiology suggest that appropriate stretching can reproduce in vitro short-term tenogenic anabolic/catabolic conditions and allow us to identify an anabolic stretching profile.
Almantas Galvanauskas - One of the best experts on this subject based on the ideXlab platform.
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compression of μj level fs pulses from a monolithic yb fiber amplifier at 1 μm wavelength in a hollow core photonic bandgap fiber
International Quantum Electronics Conference, 2013Co-Authors: A J Verhoef, Almantas Galvanauskas, Andrius Baltuska, T V Andersen, Tobias Flory, A. FernandezAbstract:Summary form only given. Yb-doped femtosecond fiber chirped pulse amplifiers (FCPAs) are extremely attractive to replace their solid-state counterparts in when it comes to robustness and ease of operation. However, in most Yb-doped FCPAs delivering high-energy output pulses the advantages of robustness and ease of operation are forfeited since free-space optical components are used to stretch and compress the pulses. The main bottleneck to obtain fiber based stretching and compression is to match the dispersion of the Stretcher and compressor. Recent advances have yielded good results with fiber-based Stretchers and free space compressors [1-3]. However, the free space compressors require rather large distances between the compressor elements, which reduces the robustness of the system. On the other hand, while anomalous dispersion solid-core fibers have been available, e.g. photonic crystal fibers [4] or higher-order mode fibers [5], such fibers are not suitable as compressor fibers for pulse energies exceeding several nJ, because of the high nonlinearities experienced in the solid core. The use of a hollow-core (HC) photonic bandgap fiber (PBF) can alleviate this problem, an approach that was demonstrated in Er-doped fiber lasers [6]. Short lengths of HC PBF have been used to compress pulses from Yb-fiber oscillators [7], but not yet in Yb-FCPA. Here, we present a μJ-level femtosecond Yb-FCPA that uses a dispersion-matched dispersion compensating fiber (DCF) Stretcher [8] and a HC PBF compressor.The Yb-fiber laser system consists of an all normal dispersion Yb-fiber oscillator operating at 40 MHz repetition rate, two PM single mode fiber (SMF) preamplifiers and a PM large mode area (LMA) fiber amplifier. The pulses from the oscillator are stretched in a hybrid fiber-pulse Stretcher that consists of 8 m of ClearLite 980 fiber followed by 5 m of DCF. After amplification, the pulses are compressed in 25 m of HC PBF. The measured group delay dispersion of the compressor at 1060 nm is about -2 ps2 resulting in a stretched pulse duration of ~30 ps. Because the effective area of the DCF is rather small (~6.7 μm2), the seed energy was limited to 0.2 nJ and the pulses were pre-stretched in the ClearLite 980 fiber in order to minimize the nonlinearities in the DCF Stretcher. After the first amplification stage a fiber pigtailed acousto-optic modulator (AOM) was used to reduce the repetition rate to 2 MHz. In preliminary test experiments, we used a large mode area (LMA) power amplifier as a final amplification stage. The LMA has a core diameter of 30 μm, corresponding to a mode field area of ~625 μm2. Free space coupling and mode conversion was used to couple the amplified pulses into the HC PBF. The output pulses from the compressor were characterized by second harmonic frequency resolved optical gating (SH FROG). The shortest compressed pulse duration was achieved by optimizing the fiber length of the pre-Stretcher. Figure 1 shows the retrieved pulse with a duration of 220 fs and its spectral phase for a pulse energy of 250 nJ. At the moment experiments using a power amplification stage utilizing a single mode fiber with 10 μm core diameter are underway. This will allow us to directly couple (by fusion-splicing) the light from the power amplifier to the HC PBF. The results from these experiments will be presented at the conference. We thank K. Jespersen and L. Gruner-Nielsen from OFS Denmark for their support, providing the fiber Stretcher and measuring the Stretcher and compressor dispersion.
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ytterbium fiber system using a dispersion compensating fiber Stretcher
European Quantum Electronics Conference, 2011Co-Authors: A J Verhoef, Kim G. Jespersen, A. Fernandez, L Zhu, Lars Grunernielsen, Almantas Galvanauskas, Andrius BaltuskaAbstract:Ytterbium doped fiber amplifiers (YDFA) delivering high-fidelity sub 200-fs pulses are very attractive scalable sources for seeding and pumping of CEP stable DFG OPAs [1]. Replacing the grating Stretcher optics by a fiber-Stretcher in YDFA is of key importance for achieving a robust turn-key alignment-free all-fiber integrated design. A major problem when designing a fiber Stretcher is to match the dispersion requirements of the compressor unit in the whole spectral range of the pulses. Two main approaches have been used in all-fiber integrated YDFA. One relies on nonlinear CPA [2] and uses a standard single mode fiber (SMF) Stretcher in combination with a pair of gratings. The main disadvantage of this scheme is that the pulse fidelity is strongly degraded with a considerably portion of the pulse energy in the pulse pedestal [3]. The other approach uses a longer polarization maintaining (PM) SMF Stretcher in combination with a grism compressor, while keeping the nonlinearities low throughout the amplifier, allowing for the generation of high-fidelity µJ level pulses [1,4]. In this contribution we report on a simplified monolithic YDFA scheme that uses a non-PM dispersion compensating fiber (DCF) Stretcher [5] specially designed to match the dispersion of a compressor unit consisting of a pair of 1480 lines/mm gratings. The system delivers high fidelity >5 µJ sub-165 fs pulses. The experimental setup is shown in Fig. 1. It consists of an Yb-fiber oscillator, two PM SMF preamplifiers and a PM large mode area (LMA) fiber amplifier. The seed pulses are stretched in a hybrid fiber-pulse Stretcher which consists of ∼8 m of PM980 fiber (pre-Stretcher) followed by 100m DCF. After the Stretcher a polarization controller and inline polarizer are used to ensure linear polarization in the amplifier.
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all fiber femtosecond pulse amplification circuit using chirped bragg gratings
Applied Physics Letters, 1995Co-Authors: Almantas Galvanauskas, M E Fermann, D Harter, Kate Sugden, Ian BennionAbstract:In‐fiber chirped Bragg gratings are used as Stretchers and compressors for distortionless amplification of femtosecond pulses in chirped pulse amplification system. It is shown that using opposite directions of pulse propagation the effects of higher order dispersion and grating irregularities can be eliminated and the original pulse shape and duration can be recovered. Using these gratings a compact all‐fiber system consisting of a mode‐locked fiber oscillator and an erbium‐doped fiber amplifier was built. 330 fs bandwidth‐limited pulses from a fiber oscillator were stretched to 30 ps, amplified and recompressed back to 408 fs. The maximum energy of the pulses after the amplifier was 6 nJ and was at the threshold of nonlinear effects for a 30 ps stretched pulse.
