1,381 research outputs found

    Assessing the rider's seat and horse's behavior: difficulties and perspectives

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    correct seat and position are the basis for a good performance in horseback riding. This study aimed to measure deviations from the correct seat, test a seat improvement program (dismounted exercises), and investigate whether horse behavior was affected by the rider's seat. Five experienced trainers defined 16 seat deviations and scored the occurrence in 20 riders in a dressage test. Half the riders then carried out an individual training program; after 9 weeks, riders were again scored. The study took no video or heart-rate recordings of horses and riders. Panel members did not agree on the deviations in the rider's seat; the study detected no differencesÂżwith the exception of improvement of backward-tilted pelvisÂżbetween the groups. Horse behavior, classified as Âżevasive,Âż increased; horse heart rate decreased in the experimental group. Heart rates of riders in both groups decreased. Seven of 9 riders in the experimental group had the impression that the exercises improved their riding performance. There is a clear need to develop a robust system that allows trainers to objectively evaluate the rider's sea

    A Holder Continuous Nowhere Improvable Function with Derivative Singular Distribution

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    We present a class of functions K\mathcal{K} in C0(R)C^0(\R) which is variant of the Knopp class of nowhere differentiable functions. We derive estimates which establish \mathcal{K} \sub C^{0,\al}(\R) for 0<\al<1 but no K∈KK \in \mathcal{K} is pointwise anywhere improvable to C^{0,\be} for any \be>\al. In particular, all KK's are nowhere differentiable with derivatives singular distributions. K\mathcal{K} furnishes explicit realizations of the functional analytic result of Berezhnoi. Recently, the author and simulteously others laid the foundations of Vector-Valued Calculus of Variations in L∞L^\infty (Katzourakis), of L∞L^\infty-Extremal Quasiconformal maps (Capogna and Raich, Katzourakis) and of Optimal Lipschitz Extensions of maps (Sheffield and Smart). The "Euler-Lagrange PDE" of Calculus of Variations in L∞L^\infty is the nonlinear nondivergence form Aronsson PDE with as special case the ∞\infty-Laplacian. Using K\mathcal{K}, we construct singular solutions for these PDEs. In the scalar case, we partially answered the open C1C^1 regularity problem of Viscosity Solutions to Aronsson's PDE (Katzourakis). In the vector case, the solutions can not be rigorously interpreted by existing PDE theories and justify our new theory of Contact solutions for fully nonlinear systems (Katzourakis). Validity of arguments of our new theory and failure of classical approaches both rely on the properties of K\mathcal{K}.Comment: 5 figures, accepted to SeMA Journal (2012), to appea

    Convexity criteria and uniqueness of absolutely minimizing functions

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    We show that absolutely minimizing functions relative to a convex Hamiltonian H:Rn→RH:\mathbb{R}^n \to \mathbb{R} are uniquely determined by their boundary values under minimal assumptions on H.H. Along the way, we extend the known equivalences between comparison with cones, convexity criteria, and absolutely minimizing properties, to this generality. These results perfect a long development in the uniqueness/existence theory of the archetypal problem of the calculus of variations in L∞.L^\infty.Comment: 34 page

    An easy proof of Jensen's theorem on the uniqueness of infinity harmonic functions

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    We present a new, easy, and elementary proof of Jensen's Theorem on the uniqueness of infinity harmonic functions. The idea is to pass to a finite difference equation by taking maximums and minimums over small balls.Comment: 4 pages; comments added, proof simplifie

    A nonhomogeneous boundary value problem in mass transfer theory

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    We prove a uniqueness result of solutions for a system of PDEs of Monge-Kantorovich type arising in problems of mass transfer theory. The results are obtained under very mild regularity assumptions both on the reference set Ω⊂Rn\Omega\subset\mathbf{R}^n, and on the (possibly asymmetric) norm defined in Ω\Omega. In the special case when Ω\Omega is endowed with the Euclidean metric, our results provide a complete description of the stationary solutions to the tray table problem in granular matter theory.Comment: 22 pages, 2 figure

    Microsecond folding dynamics of the F13W G29A mutant of the B domain of staphylococcal protein A by laser-induced temperature jump

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    The small size (58 residues) and simple structure of the B domain of staphylococcal protein A (BdpA) have led to this domain being a paradigm for theoretical studies of folding. Experimental studies of the folding of BdpA have been limited by the rapidity of its folding kinetics. We report the folding kinetics of a fluorescent mutant of BdpA (G29A F13W), named F13W*, using nanosecond laser-induced temperature jump experiments. Automation of the apparatus has permitted large data sets to be acquired that provide excellent signal-to-noise ratio over a wide range of experimental conditions. By measuring the temperature and denaturant dependence of equilibrium and kinetic data for F13W*, we show that thermodynamic modeling of multidimensional equilibrium and kinetic surfaces is a robust method that allows reliable extrapolation of rate constants to regions of the folding landscape not directly accessible experimentally. The results reveal that F13W* is the fastest-folding protein of its size studied to date, with a maximum folding rate constant at 0 M guanidinium chloride and 45°C of 249,000 (s-1). Assuming the single-exponential kinetics represent barrier-limited folding, these data limit the value for the preexponential factor for folding of this protein to at least ≈2 x 10(6) s(-1)

    Boron Isotope Effect in Superconducting MgB2_2

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    We report the preparation method of, and boron isotope effect for MgB2_2, a new binary intermetallic superconductor with a remarkably high superconducting transition temperature TcT_c(10^{10}B) = 40.2 K. Measurements of both temperature dependent magnetization and specific heat reveal a 1.0 K shift in TcT_c between Mg11^{11}B2_2 and Mg10^{10}B2_2. Whereas such a high transition temperature might imply exotic coupling mechanisms, the boron isotope effect in MgB2_2 is consistent with the material being a phonon-mediated BCS superconductor.Comment: One figure and related discussion adde
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