L\'evy Processes on Uq(g)U_q(g) as Infinitely Divisible Representations

L\'evy processes on bialgebras are families of infinitely divisible representations. We classify the generators of L\'evy processes on the compact forms of the quantum algebras $U_q(g)$, where $g$ is a simple Lie algebra. Then we show how the processes themselves can be reconstructed from their generators and study several classical stochastic processes that can be associated to these processes.Comment: 13 pages, LATEX file, ASI-TPA/13/99 (TU Clausthal); 6/99 (Preprint-Reihe Mathmatik, Univ. Greifswald)

The functional subdivision of the visual brain : Is there a real illusion effect on action? A multi-lab replication study

Acknowledgements We thank Brian Roberts and Mike Harris for responding to our questions regarding their paper; Zoltan Dienes for advice on Bayes factors; Denise Fischer, Melanie Römer, Ioana Stanciu, Aleksandra Romanczuk, Stefano Uccelli, Nuria Martos Sánchez, and Rosa María Beño Ruiz de la Sierra for help collecting data; Eva Viviani for managing data collection in Parma. We thank Maurizio Gentilucci for letting us use his lab, and the Centro Intradipartimentale Mente e Cervello (CIMeC), University of Trento, and especially Francesco Pavani for lending us his motion tracking equipment. We thank Rachel Foster for proofreading. KKK was supported by a Ph.D. scholarship as part of a grant to VHF within the International Graduate Research Training Group on Cross-Modal Interaction in Natural and Artificial Cognitive Systems (CINACS; DFG IKG-1247) and TS by a grant (DFG – SCHE 735/3-1); both from the German Research Council.Peer reviewedPostprin

Effective "Penetration Depth" in the Vortex State of a d-wave Superconductor

The temperature and field dependence of the effective magnetic penetration depth in the vortex state of a d-wave superconductor, as measured by muon spin rotation experiments, is calculated using a nonlocal London model. We show that at temperatures below T^* \propto \sqrt{B}, the linear T-dependence of the effective penetration depth crosses over to a T^3-dependence. This could provide an explanation for the low temperature flattening of the effective penetration depth curves observed in a recent muon spin rotation experiment.Comment: 4 pages, RevTex, 3 Postscript figure

BIOMECHANICS OF HORSE JUMPING

INTRODUCTION: During jumping, a horse’s body changes its direction of angular movement twice and hence has to undergo the necessary accelerations/ decelerations in order to perform the jump. Clayton (1989) describes the terminology of horse jumping. The aim of this study was to calculate the angular acceleration of the horse’s body, the path of the center of gravity, and to provide an explanation of jump failures. METHODS: Videofilms were made during an international tournament. The fence chosen for this analysis was an oxer of 1.6m height and 1.2m distance between the elements (rails). A video camera Sony DXC-9100 (100 fr./s) and video software (Adobe Premiere 4.2) were used. For 33 horses we measured the angle of a reference line (crupper - withers) relative to the environment. The angular data set vs. time was splined (non-linear least squares, taking consideration of the linear segments) and first and second differentiations were performed to calculate the angular velocity and acceleration using Mathematica 3.0. The path of the center of gravity (constructed according to Sprigings and Leach, 1986) during the suspension phase was also analyzed by means of a parabolic function. RESULTS: Related to angular acceleration, 5 phases can be distinguished: phase 1: acceleration in order to lift the body, 1a) initiated by the front limbs and 1b) continued by the rear limbs, with zero acceleration during the short time interval between 1a and 1b. Phase 2: deceleration of body lift and acceleration of negative angular motion of the jump suspension (generated by the rear limbs). Phase 3: zero acceleration during jump suspension. Phase 4: deceleration of jump suspension and acceleration of body descent (front limbs). Phase 5: deceleration of body descent (rear limbs). The mean values of angular accelerations of phases 1-5 (in rad/s2) were: phase 1a: +30, phase 1b: +20, phase 2: -55, phase 3: 0, phase 4: +40, phase 5: -30. For positive acceleration, the ground reaction force vector is situated in front of the center of gravity, in negative acceleration, behind. The angular impulse (considering body mass, radius of gyration, Dangle and Dtime of the suspension phase) amounted to 200-250 Nms. The knocking down of the rails by the front limbs was mainly due to the jump-off position, the angular body lift and the path of the center of gravity. The knocking down of the rails by the hind limbs was due to flexion in the hip joint instead of extension. CONCLUSIONS: Decisive factors for horse jumping are acceleration during body lift (phases 1a and 1b), the take-off position, the path of the center of gravity, and limb movements, especially for high fences and high speeds (for a reduced winning time). The measurement of the mentioned parameters by means of a videotechnique is hence a valuable tool for aptitude tests. REFERENCES: Clayton, H. M. (1989). Terminology for the Description of Equine Jumping Kinematics. J. Eq. Vet. Sci. 9, 341-348. Sprigings, E., Leach, D. (1986). Standardised Technique for Determining the Centre of Gravity of Body and Limb Segments of Horses. Eq. Vet. J. 18, 43-49

How do we grasp (virtual) objects in three-dimensional space?

Jeannerod (1981,1984) studied extensively the relationships between object size and grasping parameters, which has been influential for the interpretation of grasping data. The maximum grip aperture (MGA) scales linearly with object size, but the slope is less than 1 (app. 0.82, cf. Smeets Brenner 99). Here, we investigated if the location of the object in three-dimensional space influences the MGA. As well we addressed the question if the grasping of virtual objects shows the same characteristics as natural prehension. Virtual environments could enable experimenters to easily vary objects after the movement onset and therefore to explore the mechanisms of online control in visually guided movements. A virtual disc (36, 40, or 44 mm in diameter) was rendered using stereo computer graphics in 27 positions in different heights and locations relative to the observer. Virtual, haptic feedback was given using two robot arms (PHANToM TM). One robot arm was connected to the index finger, one to the thumb. Ten participants grasped the discs and transported them to a goal area, where they dropped the discs. The stereoscopically rendered discs were viewed through a mirror, such that the visual and haptic feedback matched. The position of the finger tips was measured using the two robot arms and an Optotrak (TM), in order to test for the accuracy of the PHANToM devices. The MGA was dependent on the distance of the object with respect to the observers body but not on the height of the disc. Participants scaled their MGA according to the size of the virtual disc, but with a slightly smaller slope (0.64+/−0.06) compared to natural environments. This could indicate that tactile feedback (in addition to haptic feedback) is needed to perform natural grasping movements

TDC Chip and Readout Driver Developments for COMPASS and LHC-Experiments

A new TDC-chip is under development for the COMPASS experiment at CERN. The ASIC, which exploits the 0.6 micrometer CMOS sea-of-gate technology, will allow high resolution time measurements with digitization of 75 ps, and an unprecedented degree of flexibility accompanied by high rate capability and low power consumption. Preliminary specifications of this new TDC chip are presented. Furthermore a FPGA based readout-driver and buffer-module as an interface between the front-end of the COMPASS detector systems and an optical S-LINK is in development. The same module serves also as remote fan-out for the COMPASS trigger distribution and time synchronization system. This readout-driver monitors the trigger and data flow to and from front-ends. In addition, a specific data buffer structure and sophisticated data flow control is used to pursue local pre-event building. At start-up the module controls all necessary front-end initializations.Comment: 5 pages, 4 figure

BIOMECHANICAL FACTORS FOR THE ETIOLOGY OF NAVICULAR DISEASE IN SPORTS HORSES

INTRODUCTION: Navicular disease is a common syndrome in sports horses such as gallopers, jumpers and western horses (especially quarter horses; Stashak, 1987). This syndrome causes forelimb lameness due to pain of the navicular bone (distal sesamoid of the horse digit), navicular bursitis and deep flexor tendon (DFT) affection. When horses develop navicular disease, they can no longer be used for competitive purposes, although they may still be useful for breeding purposes. Yet navicular disease is hereditary, although the mechanisms are still unclear. Nevertheless, distinct morphological variations exist in the navicular bone which are also hereditary (Ueltschi et al., 1995). Our hypothesis on the transmission of navicular disease is that morphological variability causes differences in joint load and bone stress. The aim of this study was to analyze the biomechanical effects of morphological variations of the navicular bone. METHODS: We examined 87 horses radiographically. X-rays were taken of the lateral aspects of the front toes. In the radiographs, the rotation center (center of curvature) of the coffin joint (phalanx II-phalanx III and navicular bone-phalanx II) was determined. Based on this, we constructed the lever arms of the acting forces, taking into account the diameter of the DFT. The lever arms of the proximal DFT-force and of the force of the joint between phalanx III and the navicular bone were calculated relative to the lever arm of the distal DFT-force. Taking into consideration the joint angles, we calculated the tendon and joint forces, and joint surface stresses (quasi-static inverse-dynamic calculation). RESULTS: The decisive factor for the differences in navicular mechanics is the proximal DFT lever arm. The smaller it is - relative to the distal lever arm - the more pressure will be concentrated at the distal end of the navicular bone. The larger it is, the more the pressure maxima will be shifted to the middle, and the more favorable the pressure distribution will be. Unfavorable navicular mechanics will thus occur when the bone is over-stressed in its distal border region where the distal arteries enter the bone. CONCLUSIONS: The varying morphology of the navicular bone is therefore a further explanation for the multi-factorial genesis of navicular disease. This knowledge appears all the more important because selective breeding can prevent the hereditary transmission of unfavorable navicular morphology. The radiological examination of the navicular bone is therefore, besides the classic exterior examination, a sensible screening measure for breeding (Ueltschi et al. 1995). Further, radiological examination is a sensible complement to purchase or aptitude tests. REFERENCES: Stashak, T. S. (1987). Adams’ Lameness in Horses. Philadelphia: Lea & Febiger. Ueltschi, G., Hornig, I., Stornetta, D. (1995). Beobachtungen zur Genetik der Podotrochlose. In P. F. Knezevic (Ed.), Orthopädie bei Huf- und Klauentieren. Stuttgart: Schattauer

Distribution of equilibrium free energies in a thermodynamic system with broken ergodicity

At low temperatures the configurational phase space of a macroscopic complex system (e.g., a spin-glass) of $N\sim 10^{23}$ interacting particles may split into an exponential number $\Omega_s \sim \exp({\rm const} \times N)$ of ergodic sub-spaces (thermodynamic states). Previous theoretical studies assumed that the equilibrium collective behavior of such a system is determined by its ground thermodynamic states of the minimal free-energy density, and that the equilibrium free energies follow the distribution of exponential decay. Here we show that these assumptions are not necessarily valid. For some complex systems, the equilibrium free-energy values may follow a Gaussian distribution within an intermediate temperature range, and consequently their equilibrium properties are contributed by {\em excited} thermodynamic states. This work will help improving our understanding of the equilibrium statistical mechanics of spin-glasses and other complex systems.Comment: 7 pages, 2 figure

Anti-phase Modulation of Electron- and Hole-like States in Vortex Core of Bi2Sr2CaCu2Ox Probed by Scanning Tunneling Spectroscopy

In the vortex core of slightly overdoped Bi2Sr2CaCu2Ox, the electron-like and hole-like states have been found to exhibit spatial modulations in anti-phase with each other along the Cu-O bonding direction. Some kind of one-dimensionality has been observed in the vortex core, and it is more clearly seen in differential conductance maps at lower biases below +-9 mV

Disease spread through animal movements: a static and temporal network analysis of pig trade in Germany

Background: Animal trade plays an important role for the spread of infectious diseases in livestock populations. As a case study, we consider pig trade in Germany, where trade actors (agricultural premises) form a complex network. The central question is how infectious diseases can potentially spread within the system of trade contacts. We address this question by analyzing the underlying network of animal movements. Methodology/Findings: The considered pig trade dataset spans several years and is analyzed with respect to its potential to spread infectious diseases. Focusing on measurements of network-topological properties, we avoid the usage of external parameters, since these properties are independent of specific pathogens. They are on the contrary of great importance for understanding any general spreading process on this particular network. We analyze the system using different network models, which include varying amounts of information: (i) static network, (ii) network as a time series of uncorrelated snapshots, (iii) temporal network, where causality is explicitly taken into account. Findings: Our approach provides a general framework for a topological-temporal characterization of livestock trade networks. We find that a static network view captures many relevant aspects of the trade system, and premises can be classified into two clearly defined risk classes. Moreover, our results allow for an efficient allocation strategy for intervention measures using centrality measures. Data on trade volume does barely alter the results and is therefore of secondary importance. Although a static network description yields useful results, the temporal resolution of data plays an outstanding role for an in-depth understanding of spreading processes. This applies in particular for an accurate calculation of the maximum outbreak size.Comment: main text 33 pages, 17 figures, supporting information 7 pages, 7 figure