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1
Wzorek, Marek, Andrzej Czerwiński, Andrian V. Kuchuk, Jacek Ratajczak, Ania Piotrowska, and Jerzy Kątcki. "Ni-Based Ohmic Contacts to Silicon Carbide Examined by Electron Microscopy." Solid State Phenomena 186 (March 2012): 82–85. http://dx.doi.org/10.4028/www.scientific.net/ssp.186.82.
Повний текст джерелаАнотація:
Ni/Si multilayer contact structures to 4H-SiC after subsequent annealing steps are investigated with electron microscopy methods. After high temperature annealing step, specific defects in the contact structures are observed. The influence of phase transformations during annealings on the morphology on the contacts is discussed and the explanation of formation mechanism of voids within contact layer is proposed.
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Thierry-Jebali, Nicolas, Olivier Ménard, Arnaud Yvon, Emmanuel Collard, Miao Zhe, Olivier Dezellus, Christian Brylinski, and Jean Claude Viala. "Al-Si-Ti Ohmic Contacts on N-Type Gallium Nitride." Materials Science Forum 679-680 (March 2011): 812–15. http://dx.doi.org/10.4028/www.scientific.net/msf.679-680.812.
Повний текст джерелаАнотація:
Ohmic contacts represent a major technological brick for the development of high power devices on Gallium Nitride. Al(200 nm) Ti(70 nm) metallization on n+-GaN, annealed at 650 °C, provides a “Specific Contact Resistivity” (SCR) in the range mid 10-5 Ω.cm², which is low enough for the main switching power applications. However, the Al-Ti metallic compound phases formed during the annealing step result from solid-solid reactions, which may lead to high stress and / or poor cohesion, possibly deleterious to contact reliability. In this work, we have investigated several configurations of Ti-Al-Si based contacts, aiming at favoring liquid-solid reactions and / or Si element diffusion, in order to get better SCR and / or morphology and cohesion of the metallic phase. Surprisingly, only contacts annealed at low temperature (450 °C) provide low contact SCR, comparable to that of Ti-Al only contact, but systematically higher.
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Hak, Laura, Jaap H. van Dieën, Peter van der Wurff, and Han Houdijk. "Stepping Asymmetry Among Individuals With Unilateral Transtibial Limb Loss Might Be Functional in Terms of Gait Stability." Physical Therapy 94, no. 10 (October 1, 2014): 1480–88. http://dx.doi.org/10.2522/ptj.20130431.
Повний текст джерелаАнотація:
BackgroundThe asymmetry in step length in prosthetic gait is often seen as a detrimental effect of the impairment; however, this asymmetry also might be a functional compensation. An advantage of a smaller step length of the nonprosthetic leg, and specifically foot forward placement (FFP), might be that it will bring the center of mass closer to the base of support of the leading foot and thus increase the backward margin of stability (BW MoS).ObjectiveThe purpose of this study was to characterize differences in step length, FFP, and the concomitant difference in BW MoS between steps of the prosthetic and nonprosthetic legs (referred to as prosthetic and nonprosthetic steps, respectively) of people after transtibial amputation.DesignThis was an observational and cross-sectional study.MethodsTen people after transtibial amputation walked for 4 minutes on a self-paced treadmill. Step length and FFP were calculated at initial contact. The size of the BW MoS was calculated for the moment of initial contact and at the end of the double-support phase of gait.ResultsStep length (5.4%) and FFP (7.9%) were shorter for the nonprosthetic step than for the prosthetic step. The BW MoS at initial contact was larger for the nonprosthetic step, but because of a significant leg × gait event interaction effect, BW MoS did not differ significantly at the end of the double-support phase.LimitationsAll participants were relatively good walkers (score of E on the Special Interest Group in Amputee Medicine [SIGAM] scale).ConclusionsThe smaller step length and FFP of the nonprosthetic step help to create a larger BW MoS at initial contact for the nonprosthetic step compared with the prosthetic step. Hence, step length asymmetry in people after transtibial amputation might be seen as a functional compensation to preserve BW MoS during the double-support phase to cope with the limited push-off power of the prosthetic ankle.
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Kelkar, R., and G. A. Ateshian. "Contact Creep of Biphasic Cartilage Layers." Journal of Applied Mechanics 66, no. 1 (March 1, 1999): 137–45. http://dx.doi.org/10.1115/1.2789140.
Повний текст джерелаАнотація:
Integral transform methods are used to solve the contact creep problem between two identical cylindrical biphasic cartilage layers bonded to rigid impermeable subchondral bone substrates. The biphasic model employed for cartilage consists of a binary mixture of an incompressible porous-permeable solid phase and an incompressible fluid phase. Solutions are obtained as a function of time, from the instantaneous to the equilibrium responses of the tissue. A significant result of this analysis is that under application of a step load, fluid pressurization may support upward of 96 percent of the total applied load for more congruent joints, shielding the solid collagen-proteoglycan matrix of the tissue from excessive stresses during physiological loading durations. The protection imparted by interstitial fluid pressurization to the solid collagen-proteoglycan matrix of cartilage is investigated, and the influence of material properties and osteoarthritic changes on the potential loss of this protective effect is discussed.
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Gao, Lichao, Alexander Y. Fadeev, and Thomas J. McCarthy. "Superhydrophobicity and Contact-Line Issues." MRS Bulletin 33, no. 8 (August 2008): 747–51. http://dx.doi.org/10.1557/mrs2008.160.
Повний текст джерелаАнотація:
AbstractThe wettability of several superhydrophobic surfaces that were prepared recently by simple, mostly single-step methods is described and compared with the wettability of surfaces that are less hydrophobic. We explain why two length scales of topography can be important for controlling the hydrophobicity of some surfaces (the lotus effect). Contact-angle hysteresis (difference between the advancing, θA, and receding, θR, contact angles) is discussed and explained, particularly with regard to its contribution to water repellency. Perfect hydrophobicity (θA/θR = 180°/180°) and a method for distinguishing perfectly hydrophobic surfaces from those that are almost perfectly hydrophobic are described and discussed. The Wenzel and Cassie theories, both of which involve analysis of interfacial (solid/liquid) areas and not contact lines, are criticized. Each of these related topics is addressed from the perspective of the three-phase (solid/liquid/vapor) contact line and its dynamics. The energy barriers for movement of the three-phase contact line from one metastable state to another control contact-angle hysteresis and, thus, water repellency.
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Wu, Yanxue, Gaoxu Wu, Shichao Yang, Tian Yang, and Fei Liu. "Two-step gradient-assisted phase-shifting demodulation algorithm for fast 3D reconstruction." Measurement Science and Technology 33, no. 2 (December 7, 2021): 025204. http://dx.doi.org/10.1088/1361-6501/ac3677.
Повний текст джерелаАнотація:
Abstract The conventional multi-frequency heterodyne method is one of the most widely used methods in non-contact 3D measurement. However, it needs to project different phase-shifting patterns with different frequencies, so a large number of patterns are required. For most conventional methods, the fringe period number of the projected patterns is usually small due to its limited noise tolerance, though a larger fringe period number always means higher accuracy. We propose a two-step phase-shifting demodulation algorithm based on an intensitygradient. In this method, only two patterns for each frequency are required. With the intensity gradient of the two patterns, we obtain the wrapped phase of each frequency. Next, the absolute phase is retrieved from the three wrapped phases with the heterodyne algorithm. Because only two patterns are required for each frequency, the proposed method is more robust and has higher measuring speed compared with the traditional three-frequency four-step heterodyne method. Simulations and experiments prove the feasibility and effectiveness of the method, and demonstrate that the proposed method extends the noise tolerance and achieves highprecision with only half of the patterns required by the traditional three-frequency four-step method.
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Wu, Yucong, Yang Pan, Xiaokun Leng, and Zhicheng He. "Kid-size robot humanoid walking with heel-contact and toe-off motion." PeerJ Computer Science 7 (March 15, 2022): e797. http://dx.doi.org/10.7717/peerj-cs.797.
Повний текст джерелаАнотація:
Human-like features, like toe-off, heel-strike can enhance the performance of bipedal robots. However, few studies have considered the anthropomorphism of walking planning. Fewer studies have achieved their toe-off, heel-strike gait planning framework in a child-sized humanoid robot platform. This paper presents a human-like walking control framework based on the Divergent Component of Motion (DCM) com planning method that enables a child-sized humanoid robot to walk with a humanoid pattern with a speed of 0.6 s per step a strike of 30 cm. The control framework consists of three parts: the human-like gait generation of the center of mass (CoM) and swings foot trajectory, the dynamic replan in phase switch and the upper body stabilization controller. The dynamic replanning of the CoM and foot trajectory can efficiently decrease the vibration in the step-phase switch. The up-body stabilization controller can reduce the up-body swing in walking and increase the robot's stability while walking. The robot uses a mems-based inertial measurement unit (IMU) and joint position encoders to estimate the current state of the robot and use force-sensitive resistors (FSR) on the robot foot to identify the actual step phase of the robot. None of these solutions is high-cost or difficult to integrate with a child-size robot. Software simulations and walking experiments are using to verify the motion control algorithm. The effectiveness of the pattern generation and the controller can realize more human-like walking styles in a child-size robot are confirmed.
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Hayes, Heather Brant, Young-Hui Chang, and Shawn Hochman. "Stance-phase force on the opposite limb dictates swing-phase afferent presynaptic inhibition during locomotion." Journal of Neurophysiology 107, no. 11 (June 1, 2012): 3168–80. http://dx.doi.org/10.1152/jn.01134.2011.
Повний текст джерелаАнотація:
Presynaptic inhibition is a powerful mechanism for selectively and dynamically gating sensory inputs entering the spinal cord. We investigated how hindlimb mechanics influence presynaptic inhibition during locomotion using pioneering approaches in an in vitro spinal cord–hindlimb preparation. We recorded lumbar dorsal root potentials to measure primary afferent depolarization-mediated presynaptic inhibition and compared their dependence on hindlimb endpoint forces, motor output, and joint kinematics. We found that stance-phase force on the opposite limb, particularly at toe contact, strongly influenced the magnitude and timing of afferent presynaptic inhibition in the swinging limb. Presynaptic inhibition increased in proportion to opposite limb force, as well as locomotor frequency. This form of presynaptic inhibition binds the sensorimotor states of the two limbs, adjusting sensory inflow to the swing limb based on forces generated by the stance limb. Functionally, it may serve to adjust swing-phase sensory transmission based on locomotor task, speed, and step-to-step environmental perturbations.
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Messerschmidt, Emily L., Eric E. Hall, Caroline J. Ketcham, Kirtida Patel, and Srikant Vallabhajosula. "Gait Assessment in College Athletes: Do Concussion History, Symptoms, Gender, and Type of Sport Matter?" Journal of Sport Rehabilitation 30, no. 7 (September 1, 2021): 988–99. http://dx.doi.org/10.1123/jsr.2019-0331.
Повний текст джерелаАнотація:
Context: Though previous research has focused on examining the effects of concussion history using a dual-task paradigm, the influence of factors like symptoms (unrelated to concussion), gender, and type of sport on gait in college athletes is unknown. Objective: To examine the effect of concussion history, symptoms, gender, and type of sport (noncontact/limited contact/contact) individually on gait among college athletes. Design: Exploratory cross-sectional study. Setting: Laboratory. Participants: In total, 98 varsity athletes (age, 18.3 [1.0] y; height, 1.79 [0.11] m; mass, 77.5 [19.2] kg; 27 with concussion history, 58 reported at least one symptom, 44 females; 8 played noncontact sports and 71 played contact sports) walked under single- and dual-task (walking while counting backward by 7) conditions. Interventions: Not applicable. Main Outcome Measures: Dual-task cost (DTC; % difference between single task and dual task) of gait speed, cadence, step length and width, percentage of swing and double-support phases, symptom score, and total symptom severity score. Independent samples t tests and 1-way analysis of variance were conducted (α value = .05). Results: Self-reported concussion history resulted in no significant differences (P > .05). Those who reported symptoms at testing time showed significantly greater DTC of step length (mean difference [MD], 2.7%; 95% confidence interval [CI], 0.3% to 5.1%; P = .012), % of swing phase (MD, 1.0%; 95% CI, −0.2 to 2.1%; P = .042), and % of double-support phase (MD, 3.9%; 95% CI, 0.2% to 7.8%; P = .019). Females demonstrated significantly higher DTC of gait speed (MD, 5.3%; 95% CI, 1.3% to 9.3%; P = .005), cadence (MD, 4.0%; 95% CI, 1.4% to 6.5%; P = .002), % of swing phase (MD, 1.2%; 95% CI, 0.1% to 2.3%; P = .019), and % of double-support phase (MD, 4.1%; 95% CI, 0.4% to 7.9%; P = .018). Noncontact sports athletes had significantly greater step width DTC than contact sports athletes (MD, 14.2%; 95% CI, 0.9% to 27.6%; P = .032). Conclusions: Reporting symptoms at testing time may influence gait under dual-task conditions. Additionally, female athletes showed more gait changes during a dual task. Sports medicine professionals should be aware that these variables, while unrelated to injury, may affect an athlete’s gait upon analysis.
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Xu, Kai, Xiao Zhong Deng, Jian Jun Yang, and Guan Qiang Dong. "Tooth Contact Analysis of Planetary Gear Trains with Equally Spaced Planets." Applied Mechanics and Materials 43 (December 2010): 279–82. http://dx.doi.org/10.4028/www.scientific.net/amm.43.279.
Повний текст джерелаАнотація:
Based on Tooth Contact Analysis (TCA), a feasible approach for Transmission Error (TE) of planetary gear train is proposed in this paper. With a view to getting the total TE curve of the planetary gear train, a specific analysis of the TE from the planetary gear train with only one planet should be proceed firstly, the second step is to calculate each phase difference of planets in the gear train. The applicable conditions for the simplified calculation are spur gear or involute gear pairs in the gear train. Due to equal space between them, planets have the same phase angle.
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Paradisis, Giorgos P., Athanassios Bissas, and Carlton B. Cooke. "Combined Uphill and Downhill Sprint Running Training Is More Efficacious Than Horizontal." International Journal of Sports Physiology and Performance 4, no. 2 (June 2009): 229–43. http://dx.doi.org/10.1123/ijspp.4.2.229.
Повний текст джерелаАнотація:
Purpose:This study examined the effects of sprint running training on sloping surfaces (3°) on selected kinematic and physiological variables.Methods:Fifty-four sport and physical education students were randomly allocated to one of two training groups (combined uphill–downhill [U+D] and horizontal (H)) and a control group (C). Pre- and post training tests were performed to examine the effects of 8 wk of training on the maximum running speed (MRS), step rate, step length, step time, contact time, eccentric and concentric phase of contact time (EP, CP), fight time, selected posture characteristics of the step cycle, and 6-s maximal cycle sprint test.Results:MRS, step rate, contact time, and step time were improved significantly in a 35-m sprint test for the U+D group (P < .01) after training by 4.3%, 4.3%, -5.1%, and -3.9% respectively, whereas the H group showed smaller improvements, (1.7% (P < .05), 1.2% (P < .01), 1.7% (P < .01), and 1.2% (P < .01) respectively). There were no significant changes in the C group. The posture characteristics and the peak anaerobic power (AWT) performance did not change with training in any of the groups.Conclusion:The U+D training method was significantly more effective in improving MRS and the kinematic characteristics of sprint running than a traditional horizontal training method.
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Deng, Xiao, Xianmin Zhou, Muhammad Shahzad Kamal, Syed Muhammad Shakil Hussain, Mohamed Mahmoud, and Shirish Patil. "A Modified Contact Angle Measurement Process to Suppress Oil Drop Spreading and Improve Precision." Molecules 27, no. 4 (February 10, 2022): 1195. http://dx.doi.org/10.3390/molecules27041195.
Повний текст джерелаАнотація:
Static contact angle measurement is a widely applied method for wettability assessment. Despite its convenience, it suffers from errors induced by contact angle hysteresis, material heterogeneity, and other factors. This paper discusses the oil drop spreading phenomenon that was frequently observed during contact angle measurements. Experimental tests showed that this phenomenon is closely related to surfactants in the surrounding phase, the remaining oil on the rock surface, and oil inside the surrounding phase. A modified contact angle measurement process was proposed. In the modified method, deionized water was used as the surrounding phase, and a rock surface cleaning step was added. Subsequent measurements showed a very low chance of oil drop spreading and improved precision. A further comparison study showed that, when the surrounding phase was deionized water, the measured contact angle values tended to be closer to intermediate-wet conditions compared to the values measured in clean surfactant solutions. This difference became more significant when the surface was strongly water-wet or strongly oil-wet. As a result, the developed process has two prerequisites: that the in-situ contact angle values inside surfactant solutions are not required, and that the wettability alteration induced by the surfactant solution is irreversible.
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Santoro, Enrico, Antonio Tessitore, Chiang Liu, Chi-Hsien Chen, Chutimon Khemtong, Mauro Mandorino, Yi-Hua Lee, and Giancarlo Condello. "The Biomechanical Characterization of the Turning Phase during a 180° Change of Direction." International Journal of Environmental Research and Public Health 18, no. 11 (May 21, 2021): 5519. http://dx.doi.org/10.3390/ijerph18115519.
Повний текст джерелаАнотація:
The aim of this study was to characterize the turning phase during a modified 505 test. Forty collegiate basketball students, divided into faster and slower performers and high-playing-level and low-playing-level groups, were evaluated for the force-time characteristics (braking and/or propulsive phase) of the penultimate foot contact (PFC), final foot contact (FFC), and first accelerating foot contact (AFC), and for completion time and approach velocity. Based on the composition of the AFC, trials were classified as braking/propulsive or only propulsive. Regression analysis for the prediction of completion time was performed. The AFC contributed to reacceleration through shorter contact times and step length, and lower braking force production (p < 0.05). Faster performers and the high-playing-level group demonstrated (p < 0.05): lower completion times, higher approach velocities, longer steps length in the PFC and FFC, greater braking forces and impulses in the PFC; greater braking and propulsive forces, braking impulses, lower contact times in the FFC; greater braking and propulsive horizontal forces, horizontal impulses, lower contact times and vertical impulses in the AFC. Kinetic variables from only the FFC and AFC and approach velocity predicted 75% (braking/propulsive trials) and 76.2% (only-propulsive trials) of completion times. The characterization of the turning phase demonstrated the specific contribution of each foot contact and the possible implications for training prescription.
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Gerstle, Emily E., Kristian O’Connor, Kevin G. Keenan, and Stephen C. Cobb. "Foot and Ankle Kinematics During Descent From Varying Step Heights." Journal of Applied Biomechanics 33, no. 6 (December 1, 2017): 453–59. http://dx.doi.org/10.1123/jab.2016-0301.
Повний текст джерелаАнотація:
In the general population, one-third of incidences during step negotiation occur during the transition to level walking. Furthermore, falls during curb negotiation are a common cause of injury in older adults. Distal foot kinematics may be an important factor in determining injury risk associated with transition step negotiation. The purpose of this study was to identify foot and ankle kinematics of uninjured individuals during descent from varying step heights. A 7-segment foot model was used to quantify kinematics as participants walked on a level walkway, stepped down a single step (heights: 5 cm, 15 cm, 25 cm), and continued walking. As step height increased, landing strategy transitioned from the rearfoot to the forefoot, and the rearfoot, lateral and medial midfoot, and medial forefoot became more plantar flexed. During weight acceptance, sagittal plane range of motion of the rearfoot, lateral midfoot, and medial and lateral forefoot increased as step height increased. The changes in landing strategy and distal foot function suggest a less stable ankle position at initial contact and increased demand on the distal foot at initial contact and through the weight acceptance phase of transition step negotiation as step height increases.
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Bloch, R. J. "Clusters of neural cell adhesion molecule at sites of cell-cell contact." Journal of Cell Biology 116, no. 2 (January 15, 1992): 449–63. http://dx.doi.org/10.1083/jcb.116.2.449.
Повний текст джерелаАнотація:
I have examined the distribution of neural cell adhesion molecule (N-CAM) in cultured C2 myogenic cells and other cell lines to determine if N-CAM accumulates at sites of cell-cell contact. C2 cells growing in log phase display large clusters of neural cell adhesion molecule where they contact each other. These clusters are remarkably stable, do not form at cell-substrate contacts, and appear not to be enriched in a number of other cytoskeletal, membrane, or extracellular proteins. Thus, N-CAM clusters form preferentially in response to cell-cell contact and are specifically enriched in N-CAM. As C2 cultures mature and differentiate, clusters persist at contacts between aligning myoblasts and between myotubes, consistent with a role in myogenesis. N-CAM is also enriched at cell-cell contacts in cultures of PC12, NRK, and CHO cells. These cells have significant amounts of N-CAM as detected on immunoblots. Clusters are not seen in L929 cells, which do not have detectable amounts of N-CAM. Coculture of these cells with C2 cells results in the clustering of N-CAM at heterologous contacts between C2 cells and NRK, CHO, or PC12 cells, but not between C2 cells and L929 cells. These results suggest that N-CAM specifically accumulates where N-CAM-bearing cells contact one another. Clustering of N-CAM may be an important step in strengthening intercellular adhesion.
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Zhang, Songsong, and Haisong Huang. "Step Surface Profile Measurement Based on Fringe Projection Phase-Shifting Using Selective Sampling." Photonics 8, no. 12 (December 20, 2021): 592. http://dx.doi.org/10.3390/photonics8120592.
Повний текст джерелаАнотація:
Fringe projection is a non-contact optical method that is widely used in the optical precision measurement of complex stepped surfaces. However, the accuracy of the fringe phase extraction employed has a direct impact on the measurement precision of the surface shape. Where phase-shifting measurement is used, the classical equal step phase extraction algorithm can only be used to measure simple and smooth surfaces, and leads to measurement errors on complex stepped surfaces, which affects the accuracy of the phase extraction. In addition, the iterative process lasts for a long time, resulting in a low efficiency. This paper proposes a step-by-step phase-shifting extraction algorithm based on selective sampling to measure the contour of the stepped surface. Firstly, the fringe pattern is sampled at equal intervals to reduce the iterative calculation time. Finally, the accurate measurement phase is calculated by the alternating iteration method. The phase extraction accuracy and iteration times are compared in experimental measurements between classical iterative algorithms such as four-step phase-shifting algorithms and the variable phase shift phase interpolation algorithm based on selective sampling. It is shown that the variable frequency phase-shifting extraction algorithm based on selective sampling has a shorter operation time, smaller error, and higher accuracy than the traditional iterative algorithm in fringe projection measuring complex stepped surfaces.
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Hanson, Ashley M., Darin A. Padua, J. Troy Blackburn, William E. Prentice, and Christopher J. Hirth. "Muscle Activation During Side-Step Cutting Maneuvers in Male and Female Soccer Athletes." Journal of Athletic Training 43, no. 2 (March 1, 2008): 133–43. http://dx.doi.org/10.4085/1062-6050-43.2.133.
Повний текст джерелаАнотація:
Abstract Context: Female soccer athletes are at greater risk of anterior cruciate ligament (ACL) injury than males. Sex differences in muscle activation may contribute to the increased incidence of ACL injuries in female soccer athletes. Objective: To examine sex differences in lower extremity muscle activation between male and female soccer athletes at the National Collegiate Athletic Association Division I level during 2 side-step cutting maneuvers. Design: Cross-sectional with 1 between-subjects factor (sex) and 2 within-subjects factors (cutting task and phase of contact). Setting: Sports medicine research laboratory. Patients or Other Participants: Twenty males (age = 19.4 ± 1.4 years, height = 176.5 ± 5.5 cm, mass = 74.6 ± 6.0 kg) and 20 females (age = 19.8 ± 1.1 years, height = 165.7 ± 4.3 cm, mass = 62.2 ± 7.2 kg). Intervention(s): In a single testing session, participants performed the running-approach side-step cut and the box-jump side-step cut tasks. Main Outcome Measure(s): Surface electromyographic activity of the rectus femoris, vastus lateralis, medial hamstrings, lateral hamstrings, gluteus medius, and gluteus maximus was recorded for each subject. Separate mixed-model, repeated-measures analysis of variance tests were used to compare the dependent variables across sex during the preparatory and loading contact phases of each cutting task. Results: Females displayed greater vastus lateralis activity and quadriceps to hamstrings coactivation ratios during the preparatory and loading phases, as well as greater gluteus medius activation during the preparatory phase only. No significant differences were noted between the sexes for muscle activation in the other muscles analyzed during each task. Conclusions: The quadriceps-dominant muscle activation pattern observed in recreationally active females is also present in female soccer athletes at the Division I level when compared with similarly trained male soccer athletes. The relationship between increased quadriceps activation and greater incidence of noncontact ACL injury in female soccer athletes versus males requires further study.
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Sawyer, W. Gregory, and Thierry A. Blanchet. "Vapor-Phase Lubrication in Combined Rolling and Sliding Contacts: Modeling and Experimentation." Journal of Tribology 123, no. 3 (July 6, 2000): 572–81. http://dx.doi.org/10.1115/1.1308039.
Повний текст джерелаАнотація:
The in situ vapor-phase lubrication of M50 steel, in combined rolling and sliding contacts at 540°C using nitrogen atmospheres containing acetylene, is achieved. Acetylene partial pressures of 0.05 atmospheres are capable of providing continuous lubrication to combined rolling and sliding contacts through pyrolytic carbon deposition. In these tests, friction coefficients as low as μ=0.01 are found for contacts at 2.0 m/s rolling speed, 10 cm/s sliding speed, 100 N load (1.3 GPa Hertzian contact pressure), and ambient temperature of 540°C, with even lower values observed at more modest sliding speeds. One example of a model for vapor phase lubrication of combined rolling and sliding contacts is developed which predicts the lubricant steady-state fractional coverage of the contact surfaces, and from this makes friction coefficient predictions using a linear rule-of-mixture. Friction coefficient responses to step changes in acetylene partial pressure, sliding speed, and disk wear-track diameter are measured. Increased partial pressure of acetylene and increased area available for deposition are observed to be beneficial, while increased sliding speed is detrimental to lubrication performance. Shapes and trends of steady-state friction coefficient versus acetylene partial pressure, sliding speed, and disk wear-track diameter are described and curve-fit by the model. In combined rolling and sliding this example model predicts large regions of operating conditions over which friction coefficient is independent of rolling speed, as well as regions of independence of vapor partial pressure. In the special case of pure sliding, a region of friction coefficient independence of a ratio of partial pressure to sliding speed and another region of independence of a ratio of partial pressure to the product of sliding speed and normal load are predicted.
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Abd Alsamieh, Mohamed. "Numerical investigation of elastohydrodynamic contacts subjected to harmonic load variation." Industrial Lubrication and Tribology 71, no. 6 (August 12, 2019): 832–41. http://dx.doi.org/10.1108/ilt-12-2018-0461.
Повний текст джерелаАнотація:
Purpose The purpose of this paper is to study the behavior of elastohydrodynamic contacts subjected to forced harmonic vibrations including the effect of changing various working parameters such as frequency, load amplitude and entrainment speed. Design/methodology/approach The time-dependent Reynolds equation is solved using the Newton–Raphson technique. The film thickness and pressure distribution are obtained at every time step by simultaneous solution of the Reynolds equation and film thickness equation including elastic deformation. Findings The frequency of vibration, load amplitude and entrainment speed are directly related to the film thickness perturbation, which is formed during load increasing phase of the cycle. The film thickness formed during load increasing phase is larger than that formed during load decreasing phase with larger deviation at a higher frequency or load amplitude and vice versa for lower frequency or load amplitude. The entrainment speed of the contact has an opposite effect to that of the frequency of vibration or load amplitude. Originality/value Physical explanations for the behavior of elastohydrodynamic contact subjected to forced harmonic vibration are presented in this paper for various working parameters of frequency, load amplitude and entrainment speed.
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KO, BYUNG-WOO, and WON-KYUNG SONG. "EFFECT OF PHASE-SHIFTED AUDITORY CUE ON GAIT SYMMETRY AND TRUNK DISPLACEMENT DURING TREADMILL WALKING." Journal of Mechanics in Medicine and Biology 20, no. 10 (December 2020): 2040033. http://dx.doi.org/10.1142/s0219519420400333.
Повний текст джерелаАнотація:
This study investigated changes in gait symmetry with trunk displacement during phase-shifted auditory paced treadmill walking for effective training with auditory cueing provided in conventional gait training. Eighteen able-bodied participants walked at a comfortable speed on a treadmill and the measured cadence was set at 100% (baseline). The phase-shifted auditory cue was set to both phase advance and delay of 20% at 5% intervals based on the baseline with respect to matching foot contact to the auditory cue. Trunk displacement increased with the phase-shifted auditory cue, and the largest value was found in the 120% condition compared to baseline ([Formula: see text]). Step length, step time, and swing phase time symmetry ratio gradually increased with increasing phase delay and gradually decreased with increasing phase advance on the linear model. However, single support time and stance phase time symmetry ratio showed contrasting characteristics compared to above parameters. The results indicate that the phase-shifted auditory cue significantly changes gait symmetry and trunk displacement. Particularly, the 20% phase advance and delay cues yielded about a 5% change in the step length symmetry ratio. These results could be used to induce a symmetric gait pattern when an asymmetric gait appears in hemiplegia.
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Unger, Andreas, Walter Sextro, Simon Althoff, Paul Eichwald, Tobias Meyer, Florian Eacock, Michael Brökelmann, Matthias Hunstig, Daniel Bolowski, and Karsten Guth. "Experimental and Numerical Simulation Study of Pre-deformed Heavy Copper Wire Wedge Bonds." International Symposium on Microelectronics 2014, no. 1 (October 1, 2014): 000289–94. http://dx.doi.org/10.4071/isom-tp44.
Повний текст джерелаАнотація:
To implement a self-optimization technique for ultrasonic wire bonding machines, a model of the pre-deformation phase is essential. The local material characteristics change abruptly because of the cold work during deformation. Investigations confirm a significant influence on the material properties of the contact members during touchdown. In a first step this paper validates the importance of modeling the pre-deformation experimentally. In a second step, the paper presents a numerical study of the elasto-plastic deformation based on the finite element method. This model includes measured overshoots in the touchdown forces in order to achieve accurate model responses. A validation of the model with the resulting nominal contact area, surface pressure and penetration depth reveals the high model quality.
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Sinkjaer, T., J. B. Andersen, and B. Larsen. "Soleus stretch reflex modulation during gait in humans." Journal of Neurophysiology 76, no. 2 (August 1, 1996): 1112–20. http://dx.doi.org/10.1152/jn.1996.76.2.1112.
Повний текст джерелаАнотація:
1. The modulation of the short-latency stretch reflex during walking at different walking speeds was investigated and compared with the stretch reflex during standing in healthy human subjects. 2. Ankle joint stretches were applied by a system able to rotate the human ankle joint during treadmill walking in any phase of the step cycle. The system consisted of a mechanical joint attached to the subject's ankle joint and connected to a motor placed beside the treadmill by means of bowden wires. The weight of the total system attached to the leg of the subject was 900 g. 3. The short-latency soleus stretch reflex was modulated during a step. In the stance phase, the amplitude equaled that found during standing at matched soleus background electromyogram (EMG). In the transition from stance to swing, the amplitude was 0 in all subjects. In late swing, the stretch reflex amplitude increased to 45 +/- 27% (mean +/- SD) of the maximal amplitude in the stance phase (stretch amplitude 8 degrees, stretch velocity 250 degrees/s). 4. The onset (42 +/- 3.2 ms) and peak latencies (59 +/- 2.5 ms) of the stretch reflex did not depend on the phase in the step cycle at which the reflex was elicited. 5. When the ankle joint is rotated, a change in torque can be measured. The torque measured over the first 35 ms after stretch onset (nonreflex torque) was at a maximum during late stance, when the leg supported a large part of the body's weight, and at a minimum during the swing phase. At heel contact the nonreflex torque was 50% of its maximal value. 6. During the stance phase the maximal EMG stretch reflex had a phase lead of approximately 120 ms with respect to the maximal background EMG and a phase lead of approximately 250 ms with respect to the maximal nonreflex torque. 7. The constant latency of the stretch reflex during a step implied that the ankle extensor muscle spindles are always taut during walking. 8. The relatively high amplitude of the stretch reflex in late swing and at heel contact made it likely that the stretch reflex contributed to the activation of the ankle extensor muscles in early stance phase.
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Kadlečková, Markéta, Kateřina Skopalová, Barbora Ptošková, Erik Wrzecionko, Eliška Daďová, Karolína Kocourková, Aleš Mráček, et al. "Hierarchically Structured Surfaces Prepared by Phase Separation: Tissue Mimicking Culture Substrate." International Journal of Molecular Sciences 23, no. 5 (February 25, 2022): 2541. http://dx.doi.org/10.3390/ijms23052541.
Повний текст джерелаАнотація:
The pseudo 3D hierarchical structure mimicking in vivo microenvironment was prepared by phase separation on tissue culture plastic. For surface treatment, time-sequenced dosing of the solvent mixture with various concentrations of polymer component was used. The experiments showed that hierarchically structured surfaces with macro, meso and micro pores can be prepared with multi-step phase separation processes. Changes in polystyrene surface topography were characterized by atomic force microscopy, scanning electron microscopy and contact profilometry. The cell proliferation and changes in cell morphology were tested on the prepared structured surfaces. Four types of cell lines were used for the determination of impact of the 3D architecture on the cell behavior, namely the mouse embryonic fibroblast, human lung carcinoma, primary human keratinocyte and mouse embryonic stem cells. The increase of proliferation of embryonic stem cells and mouse fibroblasts was the most remarkable. Moreover, the embryonic stem cells express different morphology when cultured on the structured surface. The acquired findings expand the current state of knowledge in the field of cell behavior on structured surfaces and bring new technological procedures leading to their preparation without the use of problematic temporary templates or additives.
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Wahls, M. W. C., and J. C. Leyte. "Step-Scan FT-IR Photoacoustic Studies of a Double-Layered Polymer Film on Metal Substrates." Applied Spectroscopy 52, no. 1 (January 1998): 123–27. http://dx.doi.org/10.1366/0003702981942447.
Повний текст джерелаАнотація:
The influence of various metal substrates on the photoacoustic response of a double-layered polymer coating (polypropylene on a polybutylacrylate-adhesive) is demonstrated. The extended Rosencwaig–Gersho theory by Fernelius for a double-layered sample is used to discuss the step-scan Fourier transform infrared photoacoustic spectroscopy (FT-IR PAS) experimental results. A clear dependence of the photoacoustic phase φ on the thermal diffusivity α of the metal substrate is found. Therefore, the quality of the thermal contact between the polymer coating and the metal substrate influences the photoacoustic phase spectrum.
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van der Linden, Marleen H., Daniel S. Marigold, Fons J. M. Gabreëls, and Jacques Duysens. "Muscle Reflexes and Synergies Triggered by an Unexpected Support Surface Height During Walking." Journal of Neurophysiology 97, no. 5 (May 2007): 3639–50. http://dx.doi.org/10.1152/jn.01272.2006.
Повний текст джерелаАнотація:
An important phase in the step cycle is foot contact. When the moment of foot contact differs from the one expected, a fast response is needed. Such a mismatch can be caused by hitting a support surface earlier or later than expected. To study this, experiments were performed with healthy young adults who walked on a platform that was unexpectedly at a lowered (5 cm) or at a level height. Glasses blocked the lower visual field. In the unexpectedly lowered trials, the absence of expected heel contact triggered responses in the ipsilateral anti-gravity muscles [ipsilateral medial gastrocnemius (MGi), ipsilateral rectus femoris (RFi)] and contralateral flexor muscles [contralateral tibialis anterior (TAc), contralaterial biceps femoris (BFc)] with latencies of 47–69 ms. After the delayed heel contact, enhanced activity was found in the MGi, RFi, and TAc muscles. This specific muscle synergy was presumably activated to arrest the forward propulsion of the body. In contrast, when the surface was unexpectedly at level height, the subjects expected to step down, and the leg briefly yielded. A muscle synergy was activated at 46–81 ms that flexed the ipsilateral knee (TAi, BFi, RFi) and extended the contralateral one (MGc, BFc) to unload the perturbed leg and delay the contralateral swing phase. Both conditions triggered a fast functionally relevant muscle synergy because of a mismatch between the expected and actual sensory feedback at the moment of foot contact. The results are consistent with an internal model that compares the expected with the actual sensory feedback. The short latency of the response suggests a subcortical, possibly cerebellar pathway.
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Ghosh, AK, S. Ahmed, and MYA Mollah. "Synthesis and characterization of zeolite NaY using local rice husk as a source of silica and removal of Cr(VI) from wastewater by zeolite." Bangladesh Journal of Scientific and Industrial Research 48, no. 2 (July 21, 2013): 81–88. http://dx.doi.org/10.3329/bjsir.v48i2.15737.
Повний текст джерелаАнотація:
The Zeolite NaY in pure phase was synthesized from rice husk (RH) following a three step synthetic route. In the preliminary step seed gel was prepared from a mixture of silicate and Na-acetate solution. This step was then followed by the preparation of feedstock gel. The third or final step involved the mixing of seed gel (5%) and feedstock gel (95%) which produced the zeolite of desired phase, NaY. The synthesized zeolite was characterized by FT-IR, XRD, SEM and DLS particle size analyzer and used to treat wastewater containing Cr (VI). The adsorption of Cr(VI) was monitored as a function of pH of the solution, contact time and initial concentration of Cr(VI). The adsorption results revealed that after scaling up the methodology, the synthesized zeolite NaY could be used as a promising cost-effective adsorbent for the treatment of wastewater containing chromium. Bangladesh J. Sci. Ind. Res. 48(2), 81-88, 2013 DOI: http://dx.doi.org/10.3329/bjsir.v48i2.15737
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Davis-Belmar, Carol S., Mauricio Acosta, Valerie Schoen, George Rautenbach, and Cecilia Demergasso. "Effect of Contact with Organic Extractant LIX 84IC during Solvent Extraction Process on the Re-Establishment of Growth of Bioleaching Microorganisms." Advanced Materials Research 825 (October 2013): 340–43. http://dx.doi.org/10.4028/www.scientific.net/amr.825.340.
Повний текст джерелаАнотація:
Solvent extraction (SX) used for the recovery of copper is a primary low-cost hydrometallurgical process applied extensively in cases like commercial bioleaching operations. Bioleaching solutions during SX treatment are exposed to important concentrations of organic extractants, a step that has a detrimental impact on microbial activity. The following work studies and determines the effect of this exposure on the re-establishment of growth and activity of different bioleaching microorganisms after contact and phase separation. Different bioleaching iron and sulfur -oxidizing microorganisms were tested. After contact with an industrially utilized organic extractant (LIX 84IC as extractant and Oxform SX12 as solvent), cultures were grown and their substrate utilization monitored.Acidithiobacillus ferrooxidansshowed only a slight increase in doubling time without significant latency period. On the contrary, for bothSulfobacillusspecies studied,S. thermosulfidooxidansandS. thermotolerans, were strongly impacted showing important lag phases before growth could take place. Additionally, the SX reagent showed disruption of cell walls and protein liberation during contact with all the different strains studied.
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Herzog, W., and T. R. Leonard. "Dynamic Force Properties of Soleus, And Sensorimotor Interactions of Soleus, Medial Gastrocnemius, and Tibialis Anterior in the Freely Moving Cat." Journal of Musculoskeletal Research 01, no. 02 (December 1997): 95–109. http://dx.doi.org/10.1142/s0218957797000116.
Повний текст джерелаАнотація:
The dynamic properties of the cat soleus muscle were studied in freely walking animal preparations. The force and EMG responses of the soleus following supramaximal, ins tants of the step cycle. The sensorimotor interactions of soleus with the medial head of the gastrocnemius (a functional agonist of the soleus at the ankle) and the tibialis anterior (a functional antagonist of soleus at the ankle) were studied by measuring their force and EMG responses following the artifical stimulation of the soleus nerve. Supramaximal nerve stimulation showed distinct increases in the soleus forces during the entire swing phase and the second part (after peak forces had been reached) of the stance phase. Soleus forces could only be increased slightly in the first part of stance (from paw contact to peak force). These results suggest that force production of the soleus is virtually maximal during the early phases of stance but is submaximal for the remainder of the step cycle. Forces and EMGs of the medial gastrocnemius muscle were affected by the soleus nerve stimulation only in the latter part of the swing phase. In these cases, the force and EMG of the medial gastrocnemius were reduced significantly for the step cycle following the perturbation. The active force production of soleus during late swing causes an inhibition of medial gastrocnemius activity and force. Forces and EMGs of the tibialis anterior muscle were always affected by the soleus nerve stimulation during the swing phase of the step cycle. In these case, the force EMG of the medial gastrocnemius were reduced significantly for the step cycle following the perturbation. The active force production of soleus during late swing causes an inhibition of medial gastrocnemius activity and force. Forces and EMGs of the tibialis anterior muscle were always affected by the soleus nerve stimulation during the swing phase of the step cycle. In these instances, forces and EMGs of the tibialis anterior were significantly increased compared to step cycles preceding or following the perturbation. Part of the force enhancement is caused by the stretch of the activated tibialis anterior by the soleus, and part of the enhancement is caused by reflex activation. No effects on forces or EMGs of the tibialis anterior were observed when the soleus nerve stimulation showed its effects during the stance phase of the step cycle. The results of theis study suggest that the magnitude and the quality of ensorimotor interactions of soleus with medial gastrocnemius and tibialis anterior depend on the phase of the step cycle. The strongest interactions appear to exist during the swing phase; no observable interactions were found during stance.
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Rivadulla, Adrian, Xi Chen, Gillian Weir, Dario Cazzola, Grant Trewartha, Joseph Hamill, and Ezio Preatoni. "Development and validation of FootNet; a new kinematic algorithm to improve foot-strike and toe-off detection in treadmill running." PLOS ONE 16, no. 8 (August 9, 2021): e0248608. http://dx.doi.org/10.1371/journal.pone.0248608.
Повний текст джерелаАнотація:
The accurate detection of foot-strike and toe-off is often critical in the assessment of running biomechanics. The gold standard method for step event detection requires force data which are not always available. Although kinematics-based algorithms can also be used, their accuracy and generalisability are limited, often requiring corrections for speed or foot-strike pattern. The purpose of this study was to develop FootNet, a novel kinematics and deep learning-based algorithm for the detection of step events in treadmill running. Five treadmill running datasets were gathered and processed to obtain segment and joint kinematics, and to identify the contact phase within each gait cycle using force data. The proposed algorithm is based on a long short-term memory recurrent neural network and takes the distal tibia anteroposterior velocity, ankle dorsiflexion/plantar flexion angle and the anteroposterior and vertical velocities of the foot centre of mass as input features to predict the contact phase within a given gait cycle. The chosen model architecture underwent 5-fold cross-validation and the final model was tested in a subset of participants from each dataset (30%). Non-parametric Bland-Altman analyses (bias and [95% limits of agreement]) and root mean squared error (RMSE) were used to compare FootNet against the force data step event detection method. The association between detection errors and running speed, foot-strike angle and incline were also investigated. FootNet outperformed previously published algorithms (foot-strike bias = 0 [–10, 7] ms, RMSE = 5 ms; toe-off bias = 0 [–10, 10] ms, RMSE = 6 ms; and contact time bias = 0 [–15, 15] ms, RMSE = 8 ms) and proved robust to different running speeds, foot-strike angles and inclines. We have made FootNet’s source code publicly available for step event detection in treadmill running when force data are not available.
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Anichenko, E. V., V. S. Arykov, E. V. Erofeev, and V. A. Kagadei. "Copper-Metalized GaAs pHEMT with Cu/Ge Ohmic Contacts." International Journal of Microwave Science and Technology 2012 (June 9, 2012): 1–5. http://dx.doi.org/10.1155/2012/418264.
Повний текст джерелаАнотація:
The fully Cu-metalized GaAs pHEMT using developed Cu/Ge-based ohmic contacts and T-gate Ti/Mo/Cu with length of the 150 nm has been successfully fabricated for the high-frequency applications. The fabricated Cu-metalized pHEMT has a maximum drain current of 360 mA/mm, an off-state gate-drain breakdown of 7 V, and a transconductance peak of 320 mS/mm at Vds=3 V. The maximum stable gain value was about 15 dB at frequency 10 GHz. The current gain cutoff frequency of the copper-metalized device is about 60 GHz at Vds=3 V, and maximum frequency of oscillations is beyond 100 GHz. This work investigated in detail the formation of Cu/Ge ohmic contacts to n-GaAs with an atomic hydrogen preannealing step. It was shown that after the first preliminary annealing is carried out in a flow of atomic hydrogen with a flow density of atoms of 1013/1016 at. cm2 s−1 a reduction in specific contact resistance by 2/2.5 times is observed. The reduction in specific contact resistance is apparently caused by the action of the hydrogen atoms which minimise the rate of the oxidizing reactions and activate solid phase reactions forming the ohmic contact during the thermal treatment process.
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Panahi, P., MH Korayem, and H. Khaksar. "Manipulation of ellipsoidal nanoparticles considering roughness based on atomic force microscopy." Proceedings of the Institution of Mechanical Engineers, Part K: Journal of Multi-body Dynamics 233, no. 3 (February 28, 2019): 763–74. http://dx.doi.org/10.1177/1464419319832495.
Повний текст джерелаАнотація:
The contribution in this paper is to investigate the manipulation of ellipsoidal nanoparticles by atomic force microscopy, taking into consideration of roughness. For the first phase of manipulation, roughness was investigated just for the substrate, but for the second phase, it begins by particle movement substrate and particle roughness is considered. The particle is of gold material; moreover, tip and substrate are made of silicon. Having examined the effective parameters of the contact mechanics, including the indentation depth and contact area for the Hertz, Jamari and Jeng–Wang models, two Jamari and Jeng–Wang contact models were used to consider the particle–probe contact and the particle–substrate contact respectively. By these two models, the first phase of manipulation process is simulated. At the end of this step, the force and the time, by which the particle starts moving, are detected. The next phase of manipulation begins with particle movement initiation and ends when it reaches the target point, which is called the second phase of manipulation. In order to simulate the second phase of manipulation, the Wilson model is used. Also, due to the fact that no surface is completely smooth and it has roughness that affects the amount of friction force and consequently manipulation relations, in order to bring the results closer to reality, in this article the Rumpf and Rabinovich models are used. In the first phase of manipulation for modelling the substrate roughness, Rumpf and Rabinovich models are used. Moreover, Rumpf model is used for modelling the particle and substrate roughness in the second phase of manipulation. Finally, to validate the results of the manipulation simulation process, they are compared with the results of the existing researches. In the first phase of the manipulation, based on the simulation results, the critical time and force error for the sliding mode were 0.94 and 1.1%, respectively. Meanwhile, the critical time and force error for rotation mode are 1.3 and 1.7%, respectively. For manipulation, taking roughness into account, the critical time and force error for sliding and rotation modes in the first phase of manipulation are about 6%. The error for the second phase, using Wilson model, considering roughness for the particle and the substrate when the particle slides on the substrate is 3.2% as well. As a result, there is a good match between the simulation and the experimental results for both manipulation phases.
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Saidouni, Tarik, and Guy Bessonnet. "Generating globally optimised sagittal gait cycles of a biped robot." Robotica 21, no. 2 (February 26, 2003): 199–210. http://dx.doi.org/10.1017/s0263574702004691.
Повний текст джерелаАнотація:
The paper is aimed at generating optimal gait cycles in the sagittal plane of a biped, the locomotion system of which has anthropomorphic characteristics. Both single and double support phases are globally optimised, considering incompletely specified transition postural configurations from one phase to the other. An impactless heel-touch is prescribed. Full dynamic models are developed for both gait phases. They are completed by specific constraints attached to the unilaterality of contact with the supporting ground.A parametric optimisation method is implemented. The biped joint coordinates are approximated by cubic splines functions connected at uniformly distributed knots along the motion time. The finite set of unknowns consists of the joint coordinate values at knots, some gait pattern parameters at phase transitions, and the motion time of each phase. The step length is adjusted to the prescribed gait speed by the optimisation process. Numerical simulations concerning slow and fast optimal gaits are presented and discussed.
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Mosiałek, M., M. Dudek, and J. Wojewoda-Budka. "Composite La0.6Sr0.4Co0.8Fe0.2O3/Ag Cathode For SoFCs With Ce0.8Sm0.2O1.9 Electrolyte / Kompozytowa Katoda La0.6Sr0.4Co0.8Fe0.2O3/Ag Do Stało-Tlenkowych Ogniw Paliwowych Z Elektrolitem Ce0.8Sm0.2O1.9." Archives of Metallurgy and Materials 58, no. 1 (March 1, 2013): 275–81. http://dx.doi.org/10.2478/v10172-012-0185-2.
Повний текст джерелаАнотація:
Influence of the short time external polarization of silver electrode contacted Ce0.8Sm0.2O1.9 electrolyte was studied. Silver is moving along the Ce0.8Sm0.2O1.9 surface during the -0.5 V cathodic polarization at 600°C. It caused both the increase of the electrode - electrolyte contact area and the triple phase boundary length but also decrease of electrolyte and polarization resistances. Deposit of silver oxide was found at the place where the electrode polarized at the potential of 0.5 V contacted the electrolyte and around. The decrease of electrolyte and polarization resistance was smaller but more stable in this case. Composite cathodes were obtained on Ce0.8Sm0.2O1.9 electrolyte with the double step sintering procedure. Silver introduced into a La0.6Sr0.4Co0.8Fe0.2O3 cathode improved a performance of a La0.6Sr0:4Co0.8Fe0.2O3|Ce0.8Sm0.2O1.9|Ni cell by 33%.
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Tanel, Michelle R., Tyler B. Weaver, and Andrew C. Laing. "Standing Versus Stepping—Exploring the Relationships Between Postural Steadiness and Dynamic Reactive Balance Control." Journal of Applied Biomechanics 34, no. 6 (December 1, 2018): 488–95. http://dx.doi.org/10.1123/jab.2017-0205.
Повний текст джерелаАнотація:
While the literature has characterized balance control during quasi-static and/or dynamic tasks, comparatively few studies have examined relationships across paradigms. This study investigated whether quiet-stance postural steadiness metrics were associated with reactive control parameters (during both stepping and restabilization phases) following a lean-and-release perturbation. A total of 40 older adults participated. Postural steadiness (center of the pressure range, root mean square, velocity, and frequency) was evaluated in “feet together” and “tandem stance” positions. During the reactive control trials, the step length, step width, movement time, and reaction time were measured, in addition to the postural steadiness variables measured during the restabilization phase following the stepping response. Out of 64 comparisons, only 10 moderate correlations were observed between postural steadiness and reactive spatio-temporal stepping parameters (P ≤ .05, r = −.312 to −.534). However, postural steadiness metrics were associated with the center of pressure velocity and frequency during the restabilization phase of the reactive control trials (P ≤ .02, r = .383 to .775 for velocity and P ≤ .01, r = .386 to .550 for frequency). Although some elements of quasi-static center of pressure control demonstrated moderate associations with dynamic stepping responses, relationships were stronger for restabilization phase dynamics after foot-contact. Future work should examine the potential association between restabilization phase control and older adult fall-risk.
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Remelius, Jebb G., and Richard E. A. van Emmerik. "Time-To-Contact Analysis of Gait Stability in the Swing Phase of Walking in People With Multiple Sclerosis." Motor Control 19, no. 4 (October 2015): 289–311. http://dx.doi.org/10.1123/mc.2013-0106.
Повний текст джерелаАнотація:
This study investigated timing and coordination during the swing phase of swing leg, body center of mass (CoM) and head during walking people with multiple sclerosis (MS; n = 19) and controls (n = 19). The MS group showed differences in swing phase timing at all speeds. At imposed but not preferred speeds, the MS group had less time to prepare for entry into the unstable equilibrium, as the CoM entered this phase of swing earlier. Time-to-contact coupling, quantifying the coordination between the CoM and the swing foot, was not different between groups. The projection of head motion on the ground occurred earlier after toeoff and was positioned closer to the body in the MS group, illustrating increased reliance on visual exproprioception in which vision of the body in relation to the surface of support is established. Finally, prospective control, linking head movements to the swing foot time-to-contact and next step landing area, was impaired in the MS group at higher gait speeds.
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Mucheroni, Marcos Luiz. "Interface Tesseracto UI and the Hologram." International Journal of Creative Interfaces and Computer Graphics 10, no. 1 (January 2019): 56–64. http://dx.doi.org/10.4018/ijcicg.2019010105.
Повний текст джерелаАнотація:
Building Tesseracto UI-type holographic interfaces is one step significant interaction in interfaces of computational devices with interaction in 3D. This follows the idea that the best user interface is no interface device, in the space of the hypercube and the fourth dimension. The contact device detects haptic interfaces, at the same time the touch in a free space as contact is made from fine ultrasonic sensors corresponding to the hologram images. The prototype was developed using the vertical and horizontal ultrasonic devices and a display hologram. The device is still in the testing phase, but the connection with the computer screens is already possible, in a prototype environment.
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Li, Yufeng, and F. E. Talke. "Limitations and Corrections of Optical Profilometry in Surface Characterization of Carbon Coated Magnetic Recording Disks." Journal of Tribology 112, no. 4 (October 1, 1990): 670–77. http://dx.doi.org/10.1115/1.2920314.
Повний текст джерелаАнотація:
The thickness of a thin absorbing carbon step on a strongly absorbing magnetic layer is measured using contact stylus and noncontact optical profilometer instrumentation, The dependence of optical profilometer measurements on carbon film thickness and optical properties of both the magnetic layer and the carbon film is investigated, and the error in the optical measurement is evaluated as a function of the phase shift of the light reflected from the sample surface. A marked improvement in the accuracy of the step height measurement is obtained if account is taken of the phase shift of the light reflected from the carbon overcoat and the magnetic substrate, respectively. The measurement of surface roughness of thin films on strongly absorbing substrates is discussed and the use of a dual wavelength technique is proposed to enhance the accuracy of optical profilometry.
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GALLOUËT, THIERRY, JEAN-MARC HÉRARD, and NICOLAS SEGUIN. "NUMERICAL MODELING OF TWO-PHASE FLOWS USING THE TWO-FLUID TWO-PRESSURE APPROACH." Mathematical Models and Methods in Applied Sciences 14, no. 05 (May 2004): 663–700. http://dx.doi.org/10.1142/s0218202504003404.
Повний текст джерелаАнотація:
The present paper is devoted to the computation of two-phase flows using the two-fluid approach. The overall model is hyperbolic and has no conservative form. No instantaneous local equilibrium between phases is assumed, which results in a two-velocity two-pressure model. Original closure laws for interfacial velocity and interfacial pressure are proposed. These closures allow to deal with discontinuous solutions such as shock waves and contact discontinuities without ambiguity with the definition of Rankine–Hugoniot jump relations. Each field of the convective system is investigated, providing maximum principle for the volume fraction and the positivity of densities and internal energies are ensured when focusing on the Riemann problem. Two-finite volume methods are presented, based on the Rusanov scheme and on an approximate Godunov scheme. Relaxation terms are taken into account using a fractional step method. Eventually, numerical tests illustrate the ability of both methods to compute two-phase flows.
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Gündemir, Ozan, Dilek Olğun Erdikmen, and Çağla Parkan Yaramış. "Evaluation of the stance phases of warmblood sport horses on soft and hard surfaces by infrared optical sensors." Veterinarski arhiv 91, no. 2 (April 15, 2021): 109–16. http://dx.doi.org/10.24099/vet.arhiv.0907.
Повний текст джерелаАнотація:
The aim of the study was to assertain the differences in walking time of sport horses by investigating their stance phases on soft versus hard surfaces using infrared sensors. A total of 15 warmblood sport horses were used in the study. Three different stages of the stance phase were examined, including initial contact, foot flat and propulsion, alongside assessment of walking pace and step-length. It was observed that the horses were inclined to walk more slowly on soft surfaces compared to hard ground. The amount of time spent in the foot flat position constituted the majority of the stance phase on both surfaces. Propulsion length during the stance phase was shorter on soft surfaces in comparison to hard ground. While the ratio of contact length in forelimbs was lower on hard ground compared to soft surfaces, in hind limbs this ratio was higher on hard ground. Objective data obtained through gait analysis systems are thought to serve as a potential auxiliary diagnostic tool in diseases associated with the locomotor system manifested by lameness, particularly in equine veterinary medicine. In the future, the relevant systems that could offer rapid results through current technology are anticipated to provide accurate preliminary assumptions to evaluate the potential of horses regarding their walking, trotting, and leaping capacity before competitions through such studies.
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Frigo, Carlo Albino, Christian Wyss, and Reinald Brunner. "The Effects of the Rectus Femoris Muscle on Knee and Foot Kinematics during the Swing Phase of Normal Walking." Applied Sciences 10, no. 21 (November 6, 2020): 7881. http://dx.doi.org/10.3390/app10217881.
Повний текст джерелаАнотація:
The role of rectus femoris (RF) muscle during walking was analyzed through musculoskeletal models to understand the effects of muscle weakness and hyperactivity. Such understanding is fundamental when dealing with pathological gait, but the contribution of RF as a bi-articular muscle is particularly difficult to estimate. Anybody software was used for inverse dynamics computation, and SimWise-4D for forward dynamics simulations. RF force was changed in the range of 0 to 150%, and the resulting kinematics were analyzed. Inverse dynamics showed a short positive RF power in correspondence with the onset of knee extension in the swing phase. Forward dynamics simulations showed an increasing knee flexion and initial toe contact when the RF force was decreased, and increasing knee extension and difficult foot clearance when the RF force was increased. The step became shorter with both increased and reduced RF force. In conclusion, the RF actively contributes to the knee extension in the swing phase. RF also contributes to obtaining a proper step length and to preparing the foot for initial heel contact. So the effect of RF muscle as a bi-articular muscle seems fundamental in controlling the motion of distal segments. RF overactivity should be considered as a possible cause for poor foot clearance in some clinical cases, while RF weakness should be considered in cases with apparent equinus.
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Perez-Munuera, I., D. F. Lewis, and M. A. Lluch. "Microstructure Changes During the Xixona Turrón Manufacture Analyzed by Light Microscopy." Food Science and Technology International 7, no. 6 (December 2001): 473–78. http://dx.doi.org/10.1106/xl5d-xke5-0l00-q5a7.
Повний текст джерелаАнотація:
Xixona turrón [Xixona nougat] is a typical Spanish confectionery product made still according to the traditional craft method. This work analyzed the microstructural changes during Xixona turrón manufacture by light microscopy. Different sample preparation methods provided useful complementary information for the understanding of the Xixona turrón structure. A progressively closer contact between a ‘‘sugar phase’’ and a ‘‘fat phase’’ is observed during processing. Inside these phases were immersed many protein bodies and a lot of cellular debris from almond tissue. At the initial stages of mixing the toasted almond paste with the sugar and honey mass, the lipid and sugar phases were relatively discrete. However, as the process developed, the relatively large aerated sugar particles, and to some extent the almond cell debris and protein bodies, were trapped within the lipid phase. In the step when the paste is heated at 65°C, gently stirred, the sugar and plant cell wall material tended to become more finely dispersed. The finished product seemed to consist of twin continuous phases in which the sugar, plant cell wall and protein bodies have formed a ‘‘sugar phase’’ that is infiltrated by the lipid fraction or ‘‘fat phase’’. This structure could contribute to the relatively ‘‘crispy’’ texture of Xixona turrón although the ‘‘oily’’ feel of the product clearly stated that the lipid phase was not extensively encapsulated in the product.
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Kaysan, Gina, Alexander Rica, Gisela Guthausen, and Matthias Kind. "Contact-Mediated Nucleation of Subcooled Droplets in Melt Emulsions: A Microfluidic Approach." Crystals 11, no. 12 (November 26, 2021): 1471. http://dx.doi.org/10.3390/cryst11121471.
Повний текст джерелаАнотація:
The production of melt emulsions is mainly influenced by the crystallization step, as every single droplet needs to crystallize to obtain a stable product with a long shelf life. However, the crystallization of dispersed droplets requires high subcooling, resulting in a time, energy and cost intensive production processes. Contact-mediated nucleation (CMN) may be used to intensify the nucleation process, enabling crystallization at higher temperatures. It describes the successful inoculation of a subcooled liquid droplet by a crystalline particle. Surfactants are added to emulsions/suspensions for their stabilization against coalescence or aggregation. They cover the interface, lower the specific interfacial energy and form micelles in the continuous phase. It may be assumed that micelles and high concentrations of surfactant monomers in the continuous phase delay or even hinder CMN as the two reaction partners cannot get in touch. Experiments were carried out in a microfluidic chip, allowing for the controlled contact between a single subcooled liquid droplet and a single crystallized droplet. We were able to demonstrate the impact of the surfactant concentration on the CMN. Following an increase in the aqueous micelle concentrations, the time needed to inoculate the liquid droplet increased or CMN was prevented entirely.
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CHOI, EUI BUM, HYEONG MIN JEON, JAE HOON HEO, and GWANG MOON EOM. "COMPARISON OF ANKLE JOINT LOAD IN DIFFERENT FOOT STRIKE STRATEGIES DURING STAIR ASCENT." Journal of Mechanics in Medicine and Biology 19, no. 07 (November 2019): 1940043. http://dx.doi.org/10.1142/s0219519419400438.
Повний текст джерелаАнотація:
The purpose of this study was to find a foot strike strategy that can reduce the ankle joint load during stair ascent by comparing the ankle joint load in two strategies of initial contact during stair ascent. Twenty young subjects performed ascending stairs with two strategies, i.e., rearfoot strike (RFS) and forefoot strike (FFS). Kinematic data was measured from 12 cameras and the ground reaction force was measured by a force plate inserted in the second step of four-step stairs. Stance phase was divided into three phase, i.e., weight acceptance, pull up, and forward continuance. Four ankle related kinetic variables were derived from the measured data, i.e., joint reaction force, moment, and the magnitude and moment arm of ground reaction force. Root-mean-square (RMS) was used as the representative value of the variables during each phase was compared between strategies. In the weight acceptance phase, FFS resulted in greater values of all four kinetic variables than RFS. For the pull-up and forward continuance phases, joint reaction force and ground reaction force were not different between strategies but joint moment and moment arm was greater for FFS than RFS. In weight acceptance phase, greater ground reaction forces and longer moment arm of FFS may have resulted from faster weight transfer to the ipsilateral foot and the more anterior location of center of pressure, respectively. Both have contributed greater joint moment of FFS. In pull-up and forward continuance phases, greater ankle moment of FFS was affected mainly by longer moment arms, which may reflect the persistent farther location of center of pressure from the ankle joint. The results suggest that RFS would be more advantageous than FFS in terms of ankle joint load.
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González-Frutos, Pablo, Santiago Veiga, Javier Mallo, and Enrique Navarro. "Evolution of the Hurdle-Unit Kinematic Parameters in the 60 m Indoor Hurdle Race." Applied Sciences 10, no. 21 (November 4, 2020): 7807. http://dx.doi.org/10.3390/app10217807.
Повний текст джерелаАнотація:
The aims of this study were to compare the five hurdle-unit split times from the deterministic model with the hurdle-to-hurdle model and with the official time, to compare the step kinematics of each hurdle-unit intervals, and to relate these variables to their respective hurdle-unit split times. The temporal and spatial parameters of the 60 m hurdles race were calculated during the 44th Spanish and 12th IAAF World Indoor Championships (men: n = 59; women: n = 51). The hurdle-unit split times from the deterministic model showed a high correlation (r = 0.99; p < 0.001) with the split times of the hurdle-to-hurdle model and faster split times were related to shorter step and flight times in hurdle steps for both genders. At the first hurdle, male athletes tended to increase their flight and contact times while the tendency of female athletes was to decrease their contact and flight times. In addition, at the first hurdle, both genders presented shorter take-off distance, shorter landing distance, and greater step width than in the remaining hurdles of the race. Therefore, coaches should implement training programs that have an impact on these key variables according to the specific demands of each hurdle-unit phase and gender.
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Marsi, Noraini, Anika Zafiah Mohd Rus, Ibrahim Mohd Razali, Syahir Arif Samsuddin, and Azrin Hani Abdul Rashid. "The Synthesis and Surface Properties of Newly Eco-Resin Based Coconut Oil for Superhydrophobic Coating." Solid State Phenomena 266 (October 2017): 59–63. http://dx.doi.org/10.4028/www.scientific.net/ssp.266.59.
Повний текст джерелаАнотація:
The paper presents the synthesis of newly eco-resin based on coconut oil for superhydrophobic coating. Superhydrophobicity of the coating provide a self-cleaning or water-repellent characteristic that prevents peeling, thereby extend the life expectancy of the coating. The use of newly synthesized eco-resin offer a sustainable, eco-friendly and cost effective source of nature. The synthesis and formulation of different percentages of coconut oil which is 20, 40, 60 and 80 weight by weight percentage (wt/wt%) consists of three phases to form superhydrophobic coating. The first phase involved alcoholysis step, condensation step and third phase purification through alcoholysis. The adhesion test (ASTM D3359-03) results was obtained the highest classification grading of 5B for coating at 80% (wt/wt) of coconut oil with 9 layer whereas the rate of adhesion is 9.87% of the area affected. It is shows that the small flakes of coating are detached at intersections. Scratch resistance test was evaluated in terms of pencil hardness grade, which is increased from grade HB to 6H and there is minor scratch occurs for 9 layer coating. The water droplet test was demonstrated that the advancing water contact angle up to 60% of coconut oil at 169.22o with the smooth surface roughness at 0.2448 μm.
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Hurmuzlu, Y. "Dynamics of Bipedal Gait: Part I—Objective Functions and the Contact Event of a Planar Five-Link Biped." Journal of Applied Mechanics 60, no. 2 (June 1, 1993): 331–36. http://dx.doi.org/10.1115/1.2900797.
Повний текст джерелаАнотація:
Previous approaches to the problem of prescribing the motion of bipedal machines do not completely characterize the desired walking patterns in terms of coherent parameters. A well-structured parametric formulation that ties the objective functions to the resulting gait patterns has never been established. This article presents an approach that can be followed to formulate objective functions which can be used to prescribe the gait of a planar, five-element, bipedal automaton during single support phase. The motion of the biped is completely characterized in terms of progression speed, step length, maximum step height, and stance knee bias. Kinematic relations have been derived and the inverse problem has been solved to perform a parametric study that correlates the regions of the four-dimensional parameter space with the respective gait patterns. Major limitations include the assumptions of rigid elements and point contact between the lower limbs and the walking surface. Most importantly, the motion of the biped is assumed to perfectly conform with the objective functions at the instant of contact. The control and stability issues are presented in Part II of this paper.
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Wiśniewski, Łukasz, Jerzy Grygorczuk, Paweł Zajko, Mateusz Przerwa, Gordon Wasilewski, Joanna Gurgurewicz, and Daniel Mège. "Energy Dissipation during Surface Interaction of an Underactuated Robot for Planetary Exploration." Energies 14, no. 14 (July 15, 2021): 4282. http://dx.doi.org/10.3390/en14144282.
Повний текст джерелаАнотація:
The article summarizes research on essential contributors to energy dissipation in an actuator for an exemplary planetary exploration hopping robot. It was demonstrated that contact dynamics could vary significantly depending on the surface type. As a result, regolith is a significant uncertainty factor to the control loop and plays a significant contribution in the control system development of future planetary exploration robots. The actual prototype of the actuating mechanism was tested on a reference surface and then compared with various surfaces (i.e., Syar, quartz sand, expanded clay, and quartz aggregate) to estimate the dissipation of the energy in the initial phase of hopping. Test outcomes are compared with multibody analysis. The research enhances trajectory planning and adaptive control of future hopping robots by determining three significant types of energy losses in the system and, most importantly, determining energy dissipation coefficients in contact with the various surfaces (i.e., from 4% to 53% depending on the surface type). The actual step-by-step methodology is proposed to analyze energy dissipation aspects for a limited number of runs, as it is a case for space systems.
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Gorassini, M. A., A. Prochazka, G. W. Hiebert, and M. J. Gauthier. "Corrective responses to loss of ground support during walking. I. Intact cats." Journal of Neurophysiology 71, no. 2 (February 1, 1994): 603–10. http://dx.doi.org/10.1152/jn.1994.71.2.603.
Повний текст джерелаАнотація:
1. In the cat step cycle the electromyographic (EMG) activity in ankle extensor muscles commences approximately 70 ms before foot contact. There is a sharp peak between 10 and 25 ms after contact and the EMG then declines for the remainder of the stance phase. It has been posited that the abrupt transition in EMG after contact is the consequence of reflexes elicited by the large barrage of afferent input that signals foot touchdown. However, it is also possible that the basic profile might be generated within the CNS, with little modification by afferent input. 2. These ideas were tested in 11 normal cats. We compared EMG responses and hindlimb kinematics in steps with normal ground support and steps in which an actuator-controlled trap door unexpectedly opened, withdrawing ground support just before foot contact. 3. In the absence of ground support the transition in EMG activity was still present. The averaged EMG pattern was similar for at least 30 ms after the foot passed through the plane of the floor. We conclude that the basic extensor activation profile in this part of the cycle is generated centrally and is not substantially altered by afferent input. 4. Between 35 and 200 ms after contact the stance phase was aborted and the foot was lifted smartly out of the hole. This reaction varied both in latency and kinematic detail, suggesting a fairly complex corrective response.(ABSTRACT TRUNCATED AT 250 WORDS)
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Tsalouchos, Aris, and Maurizio Salvadori. "La pandemia del nuovo coronavirus 2019 ed il trapianto renale." Giornale di Clinica Nefrologica e Dialisi 32, no. 1 (May 6, 2020): 60–63. http://dx.doi.org/10.33393/gcnd.2020.2133.
Повний текст джерелаАнотація:
The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a major pandemic challenging health care. Infection has been reported in all ages, but older patients and immunosuppressant patients as the transplanted are at major risk. Prevention and treatment, whenever possible are the commonly used strategies. Three steps may be distinguished. In the first step prophylaxis is essential and based in avoiding any possible contact to infected people. Staying at home, masking the patient, carefully washing the hands are the most commonly used strategies. If the disease develops in a transplanted patient two steps must be added. In the first step the reduction of the immunosuppressive therapy must be considered together with the administration of antiviral drugs. In a second phase of the disease a severe lung involvement may develop mostly due to a inflammation citokine induced. In this phase in addition to a intensive ventilation requiring the intensive care unit, anticytokine drugs as tocilizumab should be considered.
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Zimmerman, Aukje W., Ben Joosten, Ruurd Torensma, Jane R. Parnes, Frank N. van Leeuwen, and Carl G. Figdor. "Long-term engagement of CD6 and ALCAM is essential for T-cell proliferation induced by dendritic cells." Blood 107, no. 8 (April 15, 2006): 3212–20. http://dx.doi.org/10.1182/blood-2005-09-3881.
Повний текст джерелаАнотація:
Abstract Interactions between T cells and antigen-presenting cells (APCs) are the first step in the induction of an adaptive immune response. Here, we show that CD6 and its ligand activated leukocyte cell adhesion molecule (ALCAM) are actively recruited to the antigen-induced dendritic cell (DC)–T-cell contact zone. Moreover, ALCAM-blocking antibodies interfere with DC–T-cell conjugate formation, demonstrating that CD6-ALCAM binding is essential for stable T-cell–APC contact. We now demonstrate that besides their role in establishing initial contacts, CD6-ALCAM interactions are also required during the proliferative phase of the T-cell response; the presence of CD6-blocking antibodies or recombinant ALCAM-Fc proteins results in a strong and sustained inhibition of T-cell proliferation. Furthermore, simultaneous crosslinking of CD6 and CD3 induces enhanced proliferation and transcriptional activity to a similar level as observed after CD3 and CD28 co-crosslinking, demonstrating that CD6 is an important costimulatory molecule. The stability of ALCAM-CD6 binding, which contrasts with transient homotypic ALCAM-ALCAM interactions, further supports the long-lasting effects observed on T-cell proliferation. Taken together, we demonstrate that CD6 and ALCAM form a key adhesive receptor-ligand pair that is not only involved in early DC-T-cell binding but also in sustaining DC-induced T-cell proliferation long after the initial contact has been established.