897 research outputs found
COMPUTATION OF HIP AND SHOULDER TORQUES IN COMPETITIVE SWIMMING
The mechanisms of propulsion can be deduced from 3D video analysis of swimming. The basic hydrodynamic equation can be used to compute the total force for those particles. The shoulder torque was calculated by summation over hand, lower arm and upper arm of infinitesimal torques of displaced water particles. These muscle force moments were related to the velocity of the mass centre as a measure of the propulsion. However, a direct interrelation between velocity and torques cannot be established since the total resistance of the body in motion is unknown. Therefore, the aim was to determine individual differences in swimming technique, controlled by shoulder, hip torques and swimming velocity, at any state of one movement cycle. Recommendations for best propulsion techniques are derived
Spatio-temporal dynamics induced by competing instabilities in two asymmetrically coupled nonlinear evolution equations
Pattern formation often occurs in spatially extended physical, biological and
chemical systems due to an instability of the homogeneous steady state. The
type of the instability usually prescribes the resulting spatio-temporal
patterns and their characteristic length scales. However, patterns resulting
from the simultaneous occurrence of instabilities cannot be expected to be
simple superposition of the patterns associated with the considered
instabilities. To address this issue we design two simple models composed by
two asymmetrically coupled equations of non-conserved (Swift-Hohenberg
equations) or conserved (Cahn-Hilliard equations) order parameters with
different characteristic wave lengths. The patterns arising in these systems
range from coexisting static patterns of different wavelengths to traveling
waves. A linear stability analysis allows to derive a two parameter phase
diagram for the studied models, in particular revealing for the Swift-Hohenberg
equations a co-dimension two bifurcation point of Turing and wave instability
and a region of coexistence of stationary and traveling patterns. The nonlinear
dynamics of the coupled evolution equations is investigated by performing
accurate numerical simulations. These reveal more complex patterns, ranging
from traveling waves with embedded Turing patterns domains to spatio-temporal
chaos, and a wide hysteretic region, where waves or Turing patterns coexist.
For the coupled Cahn-Hilliard equations the presence of an weak coupling is
sufficient to arrest the coarsening process and to lead to the emergence of
purely periodic patterns. The final states are characterized by domains with a
characteristic length, which diverges logarithmically with the coupling
amplitude.Comment: 9 pages, 10 figures, submitted to Chao
Effects of Task Experience and Layout on Learning from Text and Pictures with or without Unnecessary Picture Descriptions
The presentation of extraneous (i.e., irrelevant or unnecessary) information may
hamper learning with multimedia. The present study examined whether people can
learn to ignore unnecessary information with increasing experience with the task and
whether this depends on the layout of that information. In two experiments,
participants learned about the process of mitosis from a multimedia slideshow, with
each slide presenting a combination of expository text and a picture on one of the
stages in the process. Slides either contained no unnecessary text (control condition)
or unnecessary text (i.e., merely describing the picture) either integrated in the picture
(integrated condition) or presented underneath the picture (separated condition).
Knowledge about the studied mitosis phase was tested immediately after each slide
using a cloze test. Across Experiments 1 and 2, we did not find a reliable negative effect
of the unnecessary text on cloze test performance. As a result, the question of whether
task experience would reduce or eliminate that negative effect could not be answered.
The eye movement data did confirm, however, that participants attended less to the
unnecessary information with increasing task experience, suggesting that students
can adapt their study strategy and learn to ignore unnecessary information
Особенности разработки палеозойских отложений Томской области
peer reviewedProton magnetic resonance spectroscopic data ((1)H-MR spectroscopy) of patients with 18q deletion syndrome have not yet been reported. (1)H-MR spectroscopy, performed in an affected 2-year-old girl with markedly delayed neuromotor development and typical supratentorial white-matter disease (WMD), showed an increase of choline and alpha-glutamate concentrations. Eight months later, simultaneously with clinical improvement, alpha-glutamate had normalised whereas choline remained slightly increased. Active demyelination or increased myelin turnover might contribute to the hitherto unexplained WMD of this rare disorder
Entanglement dynamics of two nitrogen vacancy centers coupled by a nanomechanical resonator
In this paper we study the time evolution of the entanglement between two remote NV Centers (nitrogen vacancy in diamond) connected by a dual-mode nanomechanical resonator with magnetic tips on both sides. Calculating the negativity as a measure for the entanglement, we find that the entanglement between two spins oscillates with time and can be manipulated by varying the parameters of the system. We observed the phenomenon of a sudden death and the periodic revivals of entanglement in time. For the study of quantum decoherence, we implement a Lindblad master equation. In spite of its complexity, the model is analytically solvable under fairly reasonable assumptions, and shows that the decoherence influences the entanglement, the sudden death, and the revivals in time
Climate-human-landscape interaction in the eastern foothills of Mt. Kilimanjaro (equatorial East Africa) during the last two millennia
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