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"Critical velocity"

Alex Rizzato, Giuseppe Marcolin, Alessandro Rubini, Nicola Olivato, Simone Fava, Antonio Paoli, Gerardo Bosco
BACKGROUND: In swimming one of the most employed training speed among coaches is the non-invasive Theoretical Critical Velocity (TCV) defined as the velocity that can be maintained continuously without exhaustion. METHODS: We calculated the 4mmol/L lactate Critical Velocity (MCV) in a group of swimmers of different ages (Young, Elite and Master), and compared results to the predicted TCV defined starting from the 200 and 400 m freestyle best seasonal performances...
June 8, 2017: Journal of Sports Medicine and Physical Fitness
Frédéric Aitken, Ferdinand Volino, Luis Guillermo Mendoza-Luna, Klaus von Haeften, Jussi Eloranta
Electron mobility in superfluid helium is modeled between 0.1 and 2.2 K by a van der Waals-type thermodynamic equation of state, which relates the free volume of solvated electrons to temperature, density, and phase dependent internal pressure. The model is first calibrated against known electron mobility reference data along the saturated vapor pressure line and then validated to reproduce the existing mobility literature values as a function of pressure and temperature with at least 10% accuracy. Four different electron mobility regimes are identified: (1) Landau critical velocity limit (T ≈ 0), (2) mobility limited by thermal phonons (T < 0...
June 21, 2017: Physical Chemistry Chemical Physics: PCCP
Xiaochao Jin, Huawei Yang, Xueling Fan, Zhihua Wang, Xuefeng Shu
The cavity expansion theory is most widely used to predict the depth of penetration of concrete targets. The main purpose of this work is to clarify the differences between the spherical and cylindrical cavity expansion models and their scope of application in predicting the penetration depths of concrete targets. The factors that influence the dynamic cavity expansion process of concrete materials were first examined. Based on numerical results, the relationship between expansion pressure and velocity was established...
2017: PloS One
Ming-Ta Yang, Mien-Mien Lee, Shu-Ching Hsu, Kuei-Hui Chan
The purpose of this study was to compare the effects of high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) utilizing a canoeing ergometer on endurance determinants, as well as aerobic and anaerobic performances among flat-water canoeists. Fourteen well-trained male flat-water canoeists were divided into an HIIT group or an MICT group. All subjects performed a continuous graded exercise test (GXT) and three fixed-distance (200, 500, and 1000 m) performance tests on a canoeing ergometer to determine canoeing economy, peak oxygen uptake (VO2peak), and power at VO2peak, and to calculate the critical velocity (CV) and anaerobic work capacity before and after the training programmes...
August 2017: European Journal of Sport Science
Filipe Antônio de Barros Sousa, Natalia Almeida Rodrigues, Leonardo Henrique Dalcheco Messias, Jair Borges Queiroz, Fulvia Barros Manchado-Gobatto, Claudio Alexandre Gobatto
This study aims to propose and validate the tethered swimming lactate minimum test (TSLacmin) estimating aerobic and anaerobic capacity in one single test session, using force as measurement parameter. 6 male and 6 female young swimmers (age=15.7±1.1 years; height=173.3±9.5 cm; weight=66.1±9.5 kg) performed 4 sessions comprising i) an all-out 30 s test and incremental test (TSLacmin); ii) 30 min of tethered swimming at constant intensity (2 sessions); iii) free-swimming time trials used to calculate critical velocity...
May 2017: International Journal of Sports Medicine
Haley C Bergstrom, Terry J Housh, Kristen C Cochrane-Snyman, Nathaniel D M Jenkins, Travis Byrd, Jonathan R Switalla, Richard J Schmidt, Glen O Johnson
The purpose of this study was to describe the VO2 responses relative to VO2 peak at four different intensities within the severe domain and, based on the VO2 responses, identify intensity zones above critical velocity (CV). Twelve runners (mean ± SD age = 23.2 ± 3.0 years) performed an incremental treadmill test (ITT) to exhaustion to determine the VO2peak and velocity associated with VO2peak (vVO2peak). Critical velocity was determined from four, exhaustive, constant velocity, randomly ordered treadmill runs (V1, V2, V3, V4; V1 = highest, V4 = lowest)...
February 28, 2017: Journal of Strength and Conditioning Research
Han Yan, Wen-Ming Zhang, Hui-Ming Jiang, Kai-Ming Hu
In this article, the pull-in instability and dynamic characteristics of electrostatically actuated suspended microchannel resonators are studied. A theoretical model is presented to describe the pull-in effect of suspended microchannel resonators by considering the electrostatic field and the internal fluid. The results indicate that the system is subjected to both the pull-in instability and the flutter. The former is induced by the applied voltage which exceeds the pull-in value while the latter occurs as the velocity of steady flow get closer to the critical velocity...
January 8, 2017: Sensors
Francisco J Arias, Geoffrey T Parks
The thermal behavior of insoluble radiogenic particles at the solid-liquid interface of an advancing solidification front and its significance with regard to environmental impact are discussed. It is shown that, unlike classical particles, where the most probable behavior is engulfing by the solidification front, radiogenic particles are more likely to be rejected by the solidification front. Utilizing a simplified physical model, an adaptation of classical theoretical models is performed, where it is shown that, unlike classical particles, for radiogenic particles the mechanism is thermally driven...
February 2017: Journal of Environmental Radioactivity
Peng Zou, Joachim Brand, Xia-Ji Liu, Hui Hu
We investigate traveling solitons of a one- or two-dimensional spin-orbit-coupled Fermi superfluid in both topologically trivial and nontrivial regimes by solving the static and time-dependent Bogoliubov-de Gennes equations. We find a critical velocity v_{h} for traveling solitons that is much smaller than the value predicted using the Landau criterion due to spin-orbit coupling. Above v_{h}, our time-dependent simulations in harmonic traps indicate that traveling solitons decay by radiating sound waves. In the topological phase, we predict the existence of peculiar Majorana solitons, which host two Majorana fermions and feature a phase jump of π across the soliton, irrespective of the velocity of travel...
November 25, 2016: Physical Review Letters
Qiaoyue Chen, Lili Zhang, Mingming Ding, Xiaozheng Duan, Yineng Huang, Tongfei Shi
We study the effects of the nanopore size on the flow-induced capture of the star polymer by a nanopore and the afterward translocation, using a hybrid simulation method that couples point particles into a fluctuating lattice-Boltzmann fluid. Our simulation demonstrates that the optimal forward arm number decreases slowly with the increase of the length of the nanopore. Compared to the minor effect of the length of the nanopore, the optimal forward arm number obviously increases with the increase of the width of the nanopore, which can clarify the current controversial issue for the optimal forward arm number between the theory and experiments...
November 2016: European Physical Journal. E, Soft Matter
Christopher J Howland, Arnaud Antkowiak, J Rafael Castrejón-Pita, Sam D Howison, James M Oliver, Robert W Style, Alfonso A Castrejón-Pita
Droplets splash when they impact dry, flat substrates above a critical velocity that depends on parameters such as droplet size, viscosity, and air pressure. By imaging ethanol drops impacting silicone gels of different stiffnesses, we show that substrate stiffness also affects the splashing threshold. Splashing is reduced or even eliminated: droplets on the softest substrates need over 70% more kinetic energy to splash than they do on rigid substrates. We show that this is due to energy losses caused by deformations of soft substrates during the first few microseconds of impact...
October 28, 2016: Physical Review Letters
Henrique P Neiva, Mário C Marques, Tiago M Barbosa, Mikel Izquierdo, João L Viana, Ana M Teixeira, Daniel A Marinho
The aim of this study was to compare the effects of two different warm-up intensities on 100m swimming performance in a randomized controlled trial. Thirteen competitive swimmers performed two 100m freestyle time-trials on separate days after either control or experimental warm-up, in a randomized design. The control warm-up included a typical race-pace set (4x25m), while the experimental warm-up included an aerobic set (8x50m at 98-102% of critical velocity). Cortisol, testosterone, blood lactate ([La]), oxygen uptake (VO2), heart rate, core (Tcore and Tcorenet) and tympanic temperatures, and rating of perceived exertion (RPE) were monitored...
October 27, 2016: Journal of Strength and Conditioning Research
C H J Bong, T L Lau, A Ab Ghani, N W Chan
The understanding of how the sediment deposit thickness influences the incipient motion characteristic is still lacking in the literature. Hence, the current study aims to determine the effect of sediment deposition thickness on the critical velocity for incipient motion. An incipient motion experiment was conducted in a rigid boundary rectangular flume of 0.6 m width with varying sediment deposition thickness. Findings from the experiment revealed that the densimetric Froude number has a logarithmic relationship with both the thickness ratios ts/d and ts/y0 (ts: sediment deposit thickness; d: grain size; y0: normal flow depth)...
October 2016: Water Science and Technology: a Journal of the International Association on Water Pollution Research
Alexey N Boychuk, Dmitriy V Makarov, Alexander N Zakhlevnykh
We theoretically study the dynamics of the orientational structure of a ferronematic liquid crystal with soft planar coupling between the director and the magnetization in a rotating magnetic field. We determine critical parameters characterizing the boundary between synchronous and asynchronous rotation regimes. We show that the magnetic impurity increases the stability threshold of an asynchronous rotation regime. The critical angular velocity, the angles of the director and the magnetization rotation in each regime of orientational structure rotation are found for rigid planar coupling...
October 2016: European Physical Journal. E, Soft Matter
Conglin Dong, Chengqing Yuan, Lei Wang, Wei Liu, Xiuqin Bai, Xinping Yan
Frictional vibration and noise caused by water-lubricated rubber stern tube bearings, which are generated under extreme conditions, severely threaten underwater vehicles' survivability and concealment performance. This study investigates the effect of flaky and spherical MoS2 nanoparticles on tribological properties and damping capacity of water-lubricated rubber materials, with the aim of decreasing frictional noise. A CBZ-1 tribo-tester was used to conduct the sliding tests between rubber ring-discs and ZCuSn10Zn2 ring-discs with water lubrication...
October 7, 2016: Scientific Reports
Jin Chen, Bo Zhang, Wei Chen, Jian-Yi Kang, Kui-Jun Chen, Ai-Min Wang, Jian-Min Wang
The development of high-energy weapons could increase the velocity of projectiles to well over 1000 m/s. The nature of the injuries caused by the ballistic impact of projectiles at velocities much faster than 1000 m/s is unclear. This study characterizes the mechanical and biochemical alterations caused by high-speed ballistic impact generated by spherical steel ball to the hind limbs of the pig. That the local and distal injuries caused by hypervelocity ballistic impact to the living body are also identified...
2016: SpringerPlus
M Kafi, A Salar Elahi, M Ghoranneviss, M R Ghanbari, M K Salem
In a tokamak with a toroidal electric field, electrons that exceed the critical velocity are freely accelerated and can reach very high energies. These so-called `runaway electrons' can cause severe damage to the vacuum vessel and are a dangerous source of hard X-rays. Here the effect of toroidal electric and magnetic field changes on the characteristics of runaway electrons is reported. A possible technique for runaways diagnosis is the detection of hard X-ray radiation; for this purpose, a scintillator (NaI) was used...
September 1, 2016: Journal of Synchrotron Radiation
Fay B Horak, JoAnn Kluzik, Frantisek Hlavacka
Vestibular information is known to be important for postural stability on tilting surfaces, but the relative importance of vestibular information across a wide range of surface tilt velocities is less clear. We compared how tilt velocity influences postural orientation and stability in nine subjects with bilateral vestibular loss and nine age-matched, control subjects. Subjects stood on a force platform that tilted 6 deg, toes-up at eight velocities (0.25 to 32 deg/s), with and without vision. Results showed that visual information effectively compensated for lack of vestibular information at all tilt velocities...
September 1, 2016: Journal of Neurophysiology
Emmanuel N Millán, Diego R Tramontina, Herbert M Urbassek, Eduardo M Bringa
While at small collision velocities collisions of nanoparticles (NPs) are elastic, they become plastic at higher velocities. We study the elastic-plastic threshold and the onset of plasticity using molecular dynamics simulation for a Lennard-Jones material. The reasons behind the R^{-2/3} increase of the threshold velocity for small NP radii R found recently are discussed. At the threshold, NP orientation strongly influences the generation of plasticity, and averaging over many orientations is required to predict the critical velocity for dislocation generation...
June 2016: Physical Review. E
Mingming Ding, Qiaoyue Chen, Xiaozheng Duan, Tongfei Shi
We study the flow-induced polymer translocation through a nanopore from a confining nanotube, using a hybrid simulation method that couples point particles into a fluctuating lattice-Boltzmann fluid. Our simulation illustrates that the critical velocity flux of the polymer linearly decreases with the decrease in the size of the confining nanotube, which corresponds well with our theoretical analysis based on the blob model of the polymer translocation. Moreover, by decreasing the size of the confining nanotube, we find a significantly favorable capture of the polymer near its ends, as well as a longer translocation time...
May 7, 2016: Journal of Chemical Physics
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