23 research outputs found
TECHNOLOGY FOR DECREASING ACTIVE DRAG AT THE MAXIMAL SWIMMING VELOCITY
The article describes the technology for decreasing active drag at the maximal swimming velocity. This technology can be used for both elite and sub-elite swimmers of different sex, age and qualification. It has been developed on the basis of optimal interaction between two functional systems of a swimmer (biomechanical and metabolic). The technology includes three components (training exercises; choice of training categories according to their international classification; use of special technical devices), as well as a set of concrete methods and technical procedures. The parameters, necessary for the research, have been measured by the method of small perturbations with the help of an additional hydrodynamic body
Thermodynamics of nanodomain formation and breakdown in Scanning Probe Microscopy: Landau-Ginzburg-Devonshire approach
Thermodynamics of tip-induced nanodomain formation in scanning probe
microscopy of ferroelectric films and crystals is studied using the
Landau-Ginzburg-Devonshire phenomenological approach. The local redistribution
of polarization induced by the biased probe apex is analyzed including the
effects of polarization gradients, field dependence of dielectric properties,
intrinsic domain wall width, and film thickness. The polarization distribution
inside subcritical nucleus of the domain preceding the nucleation event is very
smooth and localized below the probe, and the electrostatic field distribution
is dominated by the tip. In contrast, polarization distribution inside the
stable domain is rectangular-like, and the associated electrostatic fields
clearly illustrate the presence of tip-induced and depolarization field
components. The calculated coercive biases of domain formation are in a good
agreement with available experimental results for typical ferroelectric
materials. The microscopic origin of the observed domain tip elongation in the
region where the probe electric field is much smaller than the intrinsic
coercive field is the positive depolarization field in front of the moving
counter domain wall. For infinitely thin domain walls local domain breakdown
through the sample depth appears. The results obtained here are complementary
to the Landauer-Molotskii energetic approach.Comment: 35 pages, 8 figures, suplementary attached, to be submitted to Phys.
Rev.
Monotone traveling wavefronts of the KPP-Fisher delayed equation
In the early 2000's, Gourley (2000), Wu et al. (2001), Ashwin et al. (2002)
initiated the study of the positive wavefronts in the delayed
Kolmogorov-Petrovskii-Piskunov-Fisher equation. Since then, this model has
become one of the most popular objects in the studies of traveling waves for
the monostable delayed reaction-diffusion equations. In this paper, we give a
complete solution to the problem of existence and uniqueness of monotone waves
in the KPP-Fisher equation. We show that each monotone traveling wave can be
found via an iteration procedure. The proposed approach is based on the use of
special monotone integral operators (which are different from the usual Wu-Zou
operator) and appropriate upper and lower solutions associated to them. The
analysis of the asymptotic expansions of the eventual traveling fronts at
infinity is another key ingredient of our approach.Comment: 25 pages, 2 figures, submitte
Watching Domains Grow: In-situ studies of polarization switching by combined Scanning Probe and Scanning Transmission Electron Microscopy
Ferroelectric domain nucleation and growth in multiferroic BiFeO3 films is
observed directly by applying a local electric field with a conductive tip
inside a scanning transmission electron microscope. The nucleation and growth
of a ferroelastic domain and its interaction with pre-existing 71^{\circ}
domain walls are observed and compared with the results of phase-field
modeling. In particular, a preferential nucleation site and direction-dependent
pinning of domain walls is observed due to slow kinetics of metastable
switching in the sample without a bottom electrode. These in-situ
spatially-resolved observations of a first-order bias-induced phase transition
reveal the mesoscopic mechanisms underpinning functionality of a wide range of
multiferroic materials
Pushed traveling fronts in monostable equations with monotone delayed reaction
We study the existence and uniqueness of wavefronts to the scalar
reaction-diffusion equations with monotone delayed reaction term and . We are mostly interested in the situation when the graph of is not
dominated by its tangent line at zero, i.e. when the condition , is not satisfied. It is well known that, in such a case, a
special type of rapidly decreasing wavefronts (pushed fronts) can appear in
non-delayed equations (i.e. with ). One of our main goals here is to
establish a similar result for . We prove the existence of the minimal
speed of propagation, the uniqueness of wavefronts (up to a translation) and
describe their asymptotics at . We also present a new uniqueness
result for a class of nonlocal lattice equations.Comment: 17 pages, submitte
Saccadic latency in hepatic encephalopathy: a pilot study
Hepatic encephalopathy is a common complication of cirrhosis. The degree of neuro-psychiatric impairment is highly variable and its clinical staging subjective. We investigated whether eye movement response times—saccadic latencies—could serve as an indicator of encephalopathy. We studied the association between saccadic latency, liver function and paper- and pencil tests in 70 patients with cirrhosis and 31 patients after liver transplantation. The tests included the porto-systemic encephalopathy (PSE-) test, critical flicker frequency, MELD score and ammonia concentration. A normal range for saccades was established in 31 control subjects. Clinical and biochemical parameters of liver, blood, and kidney function were also determined. Median saccadic latencies were significantly longer in patients with liver cirrhosis when compared to patients after liver transplantation (244 ms vs. 278 ms p < 0.001). Both patient groups had prolonged saccadic latency when compared to an age matched control group (175 ms). The reciprocal of median saccadic latency (μ) correlated with PSE tests, MELD score and critical flicker frequency. A significant correlation between the saccadic latency parameter early slope (σE) that represents the prevalence of early saccades and partial pressure of ammonia was also noted. Psychometric test performance, but not saccadic latency, correlated with blood urea and sodium concentrations. Saccadic latency represents an objective and quantitative parameter of hepatic encephalopathy. Unlike psychometric test performance, these ocular responses were unaffected by renal function and can be obtained clinically within a matter of minutes by non-trained personnel
Patchy Invasion of Stage-Structured Alien Species with Short-Distance and Long-Distance Dispersal
Metabolic Power, Active Drag, Mechanical and Propelling Efficiency of Elite Swimmers at 100 Meter Events in Different Competitive Swimming Techniques
Eight elite swimmers—four females and four males—were studied, each of whom specialized in different swimming techniques and ranked among the top 10 in the world in the 100 m event in their swimming specialty. Methods included a complex of physiological, biomechanical and hydrodynamic procedures, as well as mathematical modeling. During the special preparation period for the 2017 Swimming World Championship, all subjects performed an 8 × 100 m swimming step-test using their main swimming technique. The relationships between velocity, mechanical and metabolic power were obtained and analyzed for each swimming technique. It was found that, at the last stage of the test, in all swimming techniques, men demonstrated higher values of metabolic power (Pai = 3346–3560 W) and higher mechanical efficiency (eg = 0.062–0.068) than women (Pai = 2248–2575 W; eg = 0.049–0.052). As for propelling efficiency, women (ep = 0.67–0.71) and men (ep = 0.65–0.71) did not differ from each other. Results showed that the frontal component of active drag force is the main reason for the existing differences in maximal swimming velocity between different techniques, since no relevant differences were observed for mechanical and propelling efficiencies among swimming techniques