Driven Dynamics of Periodic Elastic Media in Disorder

We analyze the large-scale dynamics of vortex lattices and charge density waves driven in a disordered potential. Using a perturbative coarse-graining procedure we present an explicit derivation of non-equilibrium terms in the renormalized equation of motion, in particular Kardar-Parisi-Zhang non-linearities and dynamic strain terms. We demonstrate the absence of glassy features like diverging linear friction coefficients and transverse critical currents in the drifting state. We discuss the structure of the dynamical phase diagram containing different elastic phases very small and very large drive and plastic phases at intermediate velocity.Comment: 21 pages Latex with 4 figure

The use of airborne LiDAR data for the analysis of debris flow events in Switzerland

A methodology of magnitude estimates for debris flow events is described using airborne LiDAR data. Light Detection And Ranging (LiDAR) is a widely used technology to generate digital elevation information. LiDAR data in alpine regions can be obtained by several commercial companies where the automated filtering process is proprietary and varies from companies to companies. This study describes the analysis of geomorphologic changes using digital terrain models derived from commercial LiDAR data. The estimation of the deposition volumes is based on two digital terrain models covering the same area but differing in their time of survey. In this study two surveyed deposition areas of debris flows, located in the canton of Berne, Switzerland, were chosen as test cases. We discuss different grid interpolating techniques, other preliminary work and the accuracy of the used LiDAR data and volume estimates

MOTION PATTERN CONSISTENCY OF THE RIDER-HORSE SYSTEM

INTRODUCTION: Dressage riding is difficult to judge, because the aesthetics of the performance cannot be measured simply. The aim of this study was to show a method of visualizing and quantifying the harmony of the motion of a rider and a horse by evaluating their coordination. Rider and horse have a natural frequency when trotting; they can therefore be considered a system of coupled biological oscillators. The characteristics of such a system are determined by the innate and learned motion patterns, anatomy and physical condition of both participants. Any periodic motion can be described as a limit-cycleattractor in the phase space. The characteristics of an oscillator or a system of oscillators can be depicted as a phase plane diagram (PPD), which is a suitable method to visualize the characteristics (e.g., longterm behavior and limit-cycle) of a complex system, such as the ridden horse. METHODS: Twenty horses aged 4 to 22 years on different training levels were measured being ridden at trot by a professional rider and a hobby rider. The measurements were carried out from the right side, with six cameras (sample rate 120 Hz, resolution 240 x 833 points) tracing 20 reflecting spherical markers placed on the horse’s and rider’s right side. At least eight recordings of five seconds each were taken with the ExpertVision System of the Motion Analysis Corporation with the horse trotting on a 12 m long pressed sand track in an indoor riding arena. At least eight motion cycles of each rider-horse combination were analyzed. The 3-dimensional movements of the markers were used to deduce the angle between the linkages of rider’s head to rider’s back and of rider’s back to the horse’s head. Then the data were normalized to 100% of the length of the motion cycle. Angle velocity and angle acceleration were computed and from all three data-sets, scaled to 100% of the professional rider’s angle, angle velocity and angle acceleration; the trajectories in the phase-space were plotted and the lengths of the resulting vectors (LV) in the phase-space were computed. The mean and average deviation (variation of LV) of LV of every horse and rider were determined and grouped for each rider. The normal distribution of each group was tested with the Kolmogorov-Smirnov test. The Student test of paired samples and one-way analysis of variance were used to check the differences between the mean of the groups of LV and average deviation. RESULTS AND DISCUSSION: There was no significant difference in the mean of LV between the 2 riders, but there was a significant () difference in the average deviation of the LV, showing that the motion of the horse-professional rider system is more consistent than of the horse-hobby rider system. With this method the rhythm and the natural balance of the rider-horse system can be evaluated, and this information might prove a useful feedback for the education of riders

THE INFLUENCE OF THE RIDER ON THE TROTTING MOTION OF A HORSE

Introduction: The characteristics of trot, such as collection, impulsion, action of the hind quarter, the position of the head and the balance of the horse are described in the Rules of Dressage Events of the Federation Equestre International. Up to now, these characteristics were judged subjectively by dressage judges, but no objective measures have been developed to substantiate these judgments. The aim of our study was to establish measurable criteria that make possible the quantification of dressage characteristics, by comparing the motion pattern of trotting horses ridden by two riders of different skill and being led on hand. Materials and Methods: Twenty horses aged 4 to 22 years at different training levels were measured being ridden at trot by a professional rider and a hobby rider, as well as being trotted on hand. The measurements were carried out from the right side, with six cameras (sample rate 120 Hz, resolution 240 x 833 points) tracing 20 reflecting spherical markers placed on the horse’s and rider’s right side. At least eight recordings of five seconds each were taken with the ExpertVision System of Motion Analysis Corporation with the horse trotting on a 12 m long pressed sand track in an indoor riding arena. At least eight motion cycles of each rider-horse combination and of the horses being trotted on hand were analyzed. The 3-dimensional movement of the markers was calculated, and the stridelength, speed, and vertical movement of the fetlock joints were compared. The data were normalized to the trotting speed. The normal distribution of each group was tested using the Kolmogorov- Smirnov test, and the Student test of paired samples was used to check the differences between the means of the groups of the above described parameters. Results and Discussion: With the hobby rider the horses had the significantly lowest trotting speeds, the smallest stride length, the highest head position, the smallest vertical movement of the fetlock joint and the longest duration of stancephase when compared to when the horse is ridden by the professional rider and trotted on hand. Between the horse’s motion when ridden by the professional rider and trotted on hand no significant differences could be detected in the trotting speed and the duration of stance-phase, whereas significant differences were established for head position and stride length. The vertical movement of the fetlock joint did not differ significantly when ridden by the hobby rider and trotted on the hand, but both did differ significantly from the vertical movement of the fetlock joint when ridden by the professional rider. The results of this study show that some terms used by the Federation Equestre International can be translated into measurable quantities, and thus a more objective judgment of dressage may evolve

Rectification in Luttinger liquids

We investigate the rectification of an ac bias in Luttinger liquids in the presence of an asymmetric potential (the ratchet effect). We show that strong repulsive electron interaction enhances the ratchet current in comparison with Fermi liquid systems, and the I-V curve is strongly asymmetric in the low-voltage regime even for a weak asymmetric potential. At higher voltages the ratchet current exhibits an oscillatory voltage dependence.Comment: 5 pages, Revte

Non-universal ordering of spin and charge in stripe phases

We study the interplay of topological excitations in stripe phases: charge dislocations, charge loops, and spin vortices. In two dimensions these defects interact logarithmically on large distances. Using a renormalization-group analysis in the Coulomb gas representation of these defects, we calculate the phase diagram and the critical properties of the transitions. Depending on the interaction parameters, spin and charge order can disappear at a single transition or in a sequence of two transitions (spin-charge separation). These transitions are non-universal with continuously varying critical exponents. We also determine the nature of the points where three phases coexist.Comment: 4 pages, 3 figure