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"Critical velocity"

Dmitry Bratsun, Alexey Mizev, Elena Mosheva, Konstantin Kostarev
We report shock-wave-like structures that are strikingly different from previously observed fingering instabilities, which occur in a two-layer system of miscible fluids reacting by a second-order reaction A+B→S in a vertical Hele-Shaw cell. While the traditional analysis expects the occurrence of a diffusion-controlled convection, we show both experimentally and theoretically that the exothermic neutralization reaction can also trigger a wave with a perfectly planar front and nearly discontinuous change in density across the front...
November 2017: Physical Review. E
Guillaume Riboux, José Manuel Gordillo
A drop falling onto a solid substrate will disintegrate into smaller parts when its impact velocity V exceeds the so-called critical velocity for splashing, i.e., when V>V^{*}. Under these circumstances, the very thin liquid sheet, which is ejected tangentially to the solid after the drop touches the substrate, lifts off as a consequence of the aerodynamic forces exerted on it. Subsequently, the growth of capillary instabilities breaks the toroidal rim bordering the ejecta into smaller droplets, violently ejected radially outward, provoking the splash [G...
July 2017: Physical Review. E
Alexei Boulbitch, Yury M Gufan, Alexander L Korzhenevskii
Stress concentration at a crack tip generates a solid structural transformation in its vicinity, the process zone. We argue that its formation represents a local phase transition described by a multicomponent order parameter. We derive a system of equations describing the dynamics of the order parameter driven by an inhomogeneous, time-dependent stress field in the solid and show that it exhibits a bifurcation. The latter corresponds to the emergence of a process zone characterized by the distribution of the order parameter localized in the vicinity of the crack tip...
July 2017: Physical Review. E
Jesús Cuevas-Maraver, Panayotis G Kevrekidis, Anna Vainchtein, Haitao Xu
In this work, we provide two complementary perspectives for the (spectral) stability of solitary traveling waves in Hamiltonian nonlinear dynamical lattices, of which the Fermi-Pasta-Ulam and the Toda lattice are prototypical examples. One is as an eigenvalue problem for a stationary solution in a cotraveling frame, while the other is as a periodic orbit modulo shifts. We connect the eigenvalues of the former with the Floquet multipliers of the latter and using this formulation derive an energy-based spectral stability criterion...
September 2017: Physical Review. E
A Seguin, P Gondret
We measure experimentally and analyze the resisting force exerted by a bidimensional packing of small disks on a larger intruder disk dragged horizontally at constant velocity V_{0}. Depending on the vibration level of the packing that leads to a granular "cold" or "hot" packing, two force regimes are observed. At low vibration level ("cold" granular medium), the drag force F does not depend on V_{0}, whereas for high vibrations ("hot" granular medium), the drag force increases linearly with V_{0}. Both regimes can be understood by the balance of two "granular temperatures" that can be defined in the system: a bulk temperature T_{b} imposed by the external vibration to the overall packing and a local temperature T_{0} induced by the own motion of the intruder disk in its vicinity...
September 2017: Physical Review. E
Marceli Rocha Leite, Juliana Souza Uzeloto, Bruna Spolador de Alencar Silva, Ana Paula Coelho Figueira Freire, Fabiano Francisco de Lima, Eduardo Zapaterra Campos, Diego Giulliano Destro Christofaro, Carlos Augusto Kalva-Filho, Dionei Ramos, Ercy Mara Cipulo Ramos
BACKGROUND: Exercise training is an effective and low-cost tool for COPD rehabilitation. Thus, validating a non-exhaustive method to determine a patient's anaerobic threshold would be a very interesting tool in practical settings. We aimed to test the reproducibility of critical velocity values determined in a non-exhaustive manner (CVNE ) and tolerance for exercise performed at this physiological marker in subjects with COPD. METHODS: Twelve subjects with COPD were evaluated in this cross-sectional study...
March 2018: Respiratory Care
Mauryn C Nweke, R Graham McCartney, Daniel G Bracewell
Mechanical characterisation of agarose-based resins is an important factor in ensuring robust chromatographic performance in the manufacture of biopharmaceuticals. Pressure-flow profiles are most commonly used to characterise these properties. There are a number of drawbacks with this method, including the potential need for several re-packs to achieve the desired packing quality, the impact of wall effects on experimental set up and the quantities of chromatography media and buffers required. To address these issues, we have developed a dynamic mechanical analysis (DMA) technique that characterises the mechanical properties of resins based on the viscoelasticity of a 1ml sample of slurry...
December 29, 2017: Journal of Chromatography. A
Raz Halifa Levi, Yacov Kantor
We use Newtonian and overdamped Langevin dynamics to study long flexible polymers dragged by an external force at a constant velocity v. The work W performed by that force depends on the initial state of the polymer and the details of the process. The Jarzynski equality can be used to relate the nonequilibrium work distribution P(W) obtained from repeated experiments to the equilibrium free energy difference ΔF between the initial and final states. We use the power law dependence of the geometrical and dynamical characteristics of the polymer on the number of monomers N to suggest the existence of a critical velocity v_{c}(N), such that for v<v_{c} the reconstruction of ΔF is an easy task, while for v significantly exceeding v_{c} it becomes practically impossible...
August 2017: Physical Review. E
Mingming Ding, Xiaozheng Duan, Tongfei Shi
Using a hybrid simulation method that combines a lattice-Boltzmann approach for the flow and a molecular dynamics model for the polymer, we investigated the effect of solvent quality on the flow-induced polymer translocation through a nanopore. We demonstrate the nontrivial dependence of the translocation dynamics of polymers on the solvent quality, i.e., the enhancement in the polymer insolubility increases the critical velocity flux and shortens the translocation time. Accordingly, we propose a new strategy to separate polymers with different solubilities via their translocations in the nanopore by adjusting the velocity flux of the flow, which appears to be promising for the design of micro-scaled polymer separation devices...
October 18, 2017: Soft Matter
A Paris-Mandoki, J Shearring, F Mancarella, T M Fromhold, A Trombettoni, P Krüger
Superfluidity and superconductivity have been widely studied since the last century in many different contexts ranging from nuclear matter to atomic quantum gases. The rigidity of these systems with respect to external perturbations results in frictionless motion for superfluids and resistance-free electric current flow in superconductors. This peculiar behaviour is lost when external perturbations overcome a critical threshold, i.e. above a critical magnetic field or a critical current for superconductors...
August 22, 2017: Scientific Reports
Yu-Hsuan Kuo, Ching-Feng Cheng, Wei-Chieh Hsu, Del P Wong
This study's aim was to investigate the test-retest reliability of the 3-min all-out running test (3MRT) in hot environments. Twelve male sprinters (age 21.2 ± 1.8 years; height 1.78 ± 0.01 m; weight 71.0 ± 1.6 kg; [Formula: see text] 55.0 ± 1.0 mL kg(-1) min(-1)) performed an incremental exercise test in a laboratory, during which the first and second ventilatory thresholds (VT1 and VT2) and [Formula: see text] were determined. In addition, they performed two 3MRTs on an outdoor track in a hot environment, during which the critical velocity (CV) and anaerobic capacity (D') were estimated...
August 17, 2017: Research in Sports Medicine
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, M Travis Byrd, Jonathan R Switalla, Richard J Schmidt, Glen O Johnson
Bergstrom, HC, Housh, TJ, Cochrane-Snyman, KC, Jenkins, NDM, Byrd, MT, Switalla, JR, Schmidt, RJ, and Johnson, GO. A model for identifying intensity zones above critical velocity. J Strength Cond Res 31(12): 3260-3265, 2017-The purpose of this study was to describe the V[Combining Dot Above]O2 responses relative to V[Combining Dot Above]O2peak at 4 different intensities within the severe domain and, based on the V[Combining Dot Above]O2 responses, identify intensity zones above critical velocity (CV). Twelve runners (mean ± SD age = 23...
December 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
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