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"Critical velocity"

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
Bettina Karsten, Eneko Larumbe-Zabala, Gokhan Kandemir, Tahir Hazir, Andreas Klose, Fernando Naclerio
UNLABELLED: The objectives of this study were to examine the effects of a moderate intensity strength training on changes in critical velocity (CV), anaerobic running distance (D'), sprint performance and Yo-Yo intermittent running test (Yo-Yo IR1) performances. METHODS: two recreational soccer teams were divided in a soccer training only group (SO; n = 13) and a strength and soccer training group (ST; n = 13). Both groups were tested for values of CV, D', Yo-Yo IR1 distance and 30-m sprint time on two separate occasions (pre and post intervention)...
2016: PloS One
Mingming Ding, Xiaozheng Duan, Tongfei Shi
We study the flow-induced translocation of the star polymers through a nanopore using a hybrid simulation method that incorporates a lattice-Boltzmann approach for the fluid into a molecular dynamics model for the polymer. Our simulation demonstrates the existence of an optimal forward arm number of the star polymers captured by the nanopore, and illustrates its significance in determining the critical velocity flux of the star polymer translocation through the nanopore. Importantly, we find that the critical velocity flux of the star polymers is independent of the arm polymerization degree, but exhibits a linear dependence on the arm number...
March 21, 2016: Soft Matter
Michael P N Juniper, Arthur V Straube, Dirk G A L Aarts, Roel P A Dullens
We study the motion of colloidal particles driven by a constant force over a periodic optical potential energy landscape. First, the average particle velocity is found as a function of the driving velocity and the wavelength of the optical potential energy landscape. The relationship between average particle velocity and driving velocity is found to be well described by a theoretical model treating the landscape as sinusoidal, but only at small trap spacings. At larger trap spacings, a nonsinusoidal model for the landscape must be used...
January 2016: Physical Review. E
Marion Delehaye, Sébastien Laurent, Igor Ferrier-Barbut, Shuwei Jin, Frédéric Chevy, Christophe Salomon
We study the dynamics of counterflowing bosonic and fermionic lithium atoms. First, by tuning the interaction strength we measure the critical velocity v(c) of the system in the BEC-BCS crossover in the low temperature regime and we compare it to the recent prediction of Castin et al., C. R. Phys. 16, 241 (2015). Second, raising the temperature of the mixture slightly above the superfluid transitions reveals an unexpected phase locking of the oscillations of the clouds induced by dissipation.
December 31, 2015: Physical Review Letters
Arnau Vilà, Miguel González, Ricardo Mayol
The capture dynamics of a Ne atom by a superfluid helium nanodroplet (((4)He)N=1000; T = 0.37 K), Ne + ((4)He)N→ Ne@((4)He)N', was investigated using a quantum approach (TDDFT (helium) + quantum wave packet (Ne)) at zero angular momentum and a rather wide range of Ne atom initial mean velocities (〈v0〉: 90-1300 m s(-1)). This is probably the first quantum dynamics study focusing on the pick up process and the evolution of the dopant inside the nanodroplet and the second more detailed investigation on this topic...
January 21, 2016: Physical Chemistry Chemical Physics: PCCP
Pierre-François Duc, Michel Savard, Matei Petrescu, Bernd Rosenow, Adrian Del Maestro, Guillaume Gervais
In one of the most celebrated examples of the theory of universal critical phenomena, the phase transition to the superfluid state of (4)He belongs to the same three-dimensional (3D) O(2) universality class as the onset of ferromagnetism in a lattice of classical spins with XY symmetry. Below the transition, the superfluid density ρs and superfluid velocity v s increase as a power law of temperature described by a universal critical exponent that is constrained to be identical by scale invariance. As the dimensionality is reduced toward 1D, it is expected that enhanced thermal and quantum fluctuations preclude long-range order, thereby inhibiting superfluidity...
May 2015: Science Advances
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