BIOMECHANICS OF SURFING: DEVELOPMENT AND VALIDATION OF AN INSTRUMENTED SURFBOARD TO MEASURE SURFBOARD KINETICS

The purpose of this study was to investigate the different relations between the actions of a surfer and the kinematic behaviour of his surfboard. An instrumented surfboard has been designed with a force platform synchronized with an inertial measurement unit and acquisition system. An experimental campaign has been carried out in situ, where different waves have been surfed to validate the device. Results revealed that measured efforts of the surfer and kinematics of his surfboard are consistent regarding the expected behaviour. Instrumented surfboards will help coaches by giving them a new performance analysis tool. It will also provide an experimental database for the development of numerical models about interactions Surfer/Surfboard/Wave

Monitoring DC anode current of a grounded-cathode photomultiplier tube

Abstract The Pierre Auger Observatories (PAO) for the highest energy cosmic rays will make use of both the Cherenkov and Air Fluorescence techniques. Surface Detectors (SD) and Fluorescence Detectors (FD) will have to operate in a desert-type environment during at least 15 years. In order to avoid dust deposition, due to electrostatics, and other practical inconveniences derived from biasing the cathode with a negative potential, the 15 000 PMTs of the FD will operate in the grounded cathode configuration. Despite the fact that the anodes will remain at high voltage with respect to ground, the DC anode current, which varies with background light, will have to be recorded. We have developed a current monitoring system based on a novel optocoupled feedback circuit that allows sensitive, linear, and temperature-independent measurements of the DC anode current. A distinctive feature of this circuit is that it uses optical coupling between passive components at high voltage and active components near the ground potential. This represents a substantial improvement over classical solutions which require the supply of power to an active circuit at high voltage. We report on the first tests performed with both active and passive biasing networks which demonstrate the validity of this new method

Contribution to the understanding of tribological properties of graphite intercalation compounds with metal chloride

Intrinsic tribological properties of lamellar compounds are usually attributed to the presence of van der Waals gaps in their structure through which interlayer interactions are weak. The controlled variation of the distances and interactions between graphene layers by intercalation of electrophilic species in graphite is used in order to explore more deeply the friction reduction properties of low-dimensional compounds. Three graphite intercalation compounds with antimony pentachloride, iron trichloride and aluminium trichloride are studied. Their tribological properties are correlated to their structural parameters, and the interlayer interactions are deduced from ab initio bands structure calculations

Superconductivity in the Intercalated Graphite Compounds C6Yb and C6Ca

In this letter we report the discovery of superconductivity in the isostructural graphite intercalation compounds C6Yb and C6Ca, with transition temperatures of 6.5K and 11.5K respectively. A structural characterisation of these compounds shows them to be hexagonal layered systems in the same class as other graphite intercalates. If we assume that all the outer s-electrons are transferred from the intercalant to the graphite sheets, then the charge transfer in these compounds is comparable to other superconducting graphite intercalants such as C8K 1,2 . However, the superconducting transition temperatures of C6Yb and C6Ca are up to two orders of magnitude greater. Interestingly, superconducting upper critical field studies and resistivity measurements suggest that these compounds are significantly more isotropic than pure graphite. This is unexpected as the effect of introducing the intercalant is to move the graphite layer further apart.Comment: 2 Figures. Please see accompanying theoretical manuscript, "Electronic Structure of the Superconducting Graphite Intercalates" by Csanyi et al., cond-mat/050356

Inducible NAD overproduction in Arabidopsis alters metabolic pools and gene expression correlated with increased salicylate content and resistance to Pst-AvrRpm1

Plant development and function are underpinned by redox reactions that depend on co-factors such as nicotinamide adenine dinucleotide (NAD). NAD has recently been shown to be involved in several signalling pathways that are associated with stress tolerance or defence responses. However, the mechanisms by which NAD influences plant gene regulation, metabolism and physiology still remain unclear. Here, we took advantage of Arabidopsis thaliana lines that overexpressed the nadC gene from E. coli, which encodes the NAD biosynthesis enzyme quinolinate phosphoribosyltransferase (QPT). Upon incubation with quinolinate, these lines accumulated NAD and were thus used as inducible systems to determine the consequences of an increased NAD content in leaves. Metabolic profiling showed clear changes in several metabolites such as aspartate-derived amino acids and NAD-derived nicotinic acid. Large-scale transcriptomic analyses indicated that NAD promoted the induction of various pathogen-related genes such as the salicylic acid (SA)-responsive defence marker PR1. Extensive comparison with transcriptomic databases further showed that gene expression under high NAD content was similar to that obtained under biotic stress, eliciting conditions or SA treatment. Upon inoculation with the avirulent strain of Pseudomonas syringae pv. tomato Pst-AvrRpm1, the nadC lines showed enhanced resistance to bacteria infection and exhibited an ICS1-dependent build-up of both conjugated and free SA pools. We therefore concluded that higher NAD contents are beneficial for plant immunity by stimulating SA-dependent signalling and pathogen resistance

Cosmic dust grains strike again

A detailed simulation of air showers produced by dust grains has been performed by means of the {\sc aires} Monte Carlo code with the aim of comparing with experimental data. Our analysis indicates that extensive dust grain air showers must yet be regarded as highly speculative but they cannot be completely ruled out.Comment: Improved revised version with comments by an anonymous referee. Accepted for publication in Physical review

Machina ex Deus? From Distributed to Orchestrated Agency

In this chapter, the author draws on a historical case study of the Australian wine industry to explore variations in collective agency. The inductively derived process model illustrates the emergence of a new profession of scientific win- emaking, which unfolds in three phases. Each phase is characterized by a dis- tinct form of agency: distributed agency during the earliest phase, coordinated agency during later phases, and orchestrated agency during consolidation. In addition to exploring the temporal shifts in agency, the study includes a detailed analysis of the early stages of distributed agency, examining how col- lective agency is achieved in the absence of shared intentions