Topological graph polynomials and quantum field theory, Part II: Mehler kernel theories

We define a new topological polynomial extending the Bollobas-Riordan one, which obeys a four-term reduction relation of the deletion/contraction type and has a natural behavior under partial duality. This allows to write down a completely explicit combinatorial evaluation of the polynomials, occurring in the parametric representation of the non-commutative Grosse-Wulkenhaar quantum field theory. An explicit solution of the parametric representation for commutative field theories based on the Mehler kernel is also provided.Comment: 58 pages, 23 figures, correction in the references and addition of preprint number

Dynamic Regulation of Public Good Quality

We investigate the design of incentives for public good quality provision in a dynamic regulation setting in which maintenance efforts and quality shocks have durable effects. When the regulator contracts with a sequence of agents, asymmetries of information can lead to over-provision of quality under optimal regulation, reflecting a dynamic rent extraction motive. When the regulator hires a single agent to manage public good quality, over-provision of quality can also occur as a result of quality pooling, which typically occurs if quality depreciates slowly and the discount factor is large. We further show that for small levels of asymmetric information, the regulator prefers to hire a single agent rather than to contract with a sequence of agents, provided all parties can commit to a long-term contract. When no such commitment is feasible, the fact that quality physically links periods together leads to a ratchet effect even when private information is recurring, and shorter franchises are beneficial from a social point of view.Quality, Regulation, Asymmetric Information

Online Drift Compensation for Chemical Sensors Using Estimation Theory

Sensor drift from slowly changing environmental conditions and other instabilities can greatly degrade a chemical sensor\u27s performance, resulting in poor identification and analyte quantification. In the present work, estimation theory (i.e., various forms of the Kalman filter) is used for online compensation of baseline drift in the response of chemical sensors. Two different cases, which depend on the knowledge of the characteristics of the sensor system, are studied. First, an unknown input is considered, which represents the practical case of analyte detection and quantification. Then, the more general case, in which the sensor parameters and the input are both unknown, is studied. The techniques are applied to simulated sensor data, for which the true baseline and response are known, and to actual liquid-phase SH-SAW sensor data measured during the detection of organophosphates. It is shown that the technique is capable of estimating the baseline signal and recovering the true sensor signal due only to the presence of the analyte. This is true even when the baseline drift changes rate or direction during the detection process or when the analyte is not completely flushed from the system

Improving situation awareness of a single human operator interacting with multiple unmanned vehicles: first results

In the context of the supervision of one or several unmanned vehicles by a human operator, the design of an adapted user interface is a major challenge. Therefore, in the context of an existing experimental set up composed of a ground station and heterogeneous unmanned ground and air vehicles we aim at redesigning the human-robot interactions to improve the operator's situation awareness. We base our new design on a classical user centered approach

Copepods use chemical trails to find sinking marine snow aggregates

Copepods are major consumers of sinking marine particles and hence reduce the efficiency of the biological carbon pump. Their high abundance on marine snow suggests that they can detect sinking particles remotely. By means of laboratory observations, we show that the copepod Temora longicornis can detect chemical trails originating from sinking marine snow particles (appendicularian houses). The chemical cue was detected by copepods from a distance of .25 particle radii, with the probability of detection decreasing with distance. The behavior of T. longicornis following the trail resembled the behavior of males tracking pheromone trails, although with a lower tracking velocity. Upon finding a house, the copepod would attach for a short period (10–30 s) and feed intensively. Due to short residence times, daily feeding rates were moderate. Our results demonstrate that even T. longicornis, a species usually considered a microparticle feeder, is able to detect and feed on marine snow aggregates. If similar behaviors are displayed by the more dedicated aggregate-feeding copepods, a topic that remains unexplored, the effect of copepods on vertical flux attenuation may be significant

Development and validation of a composite material law for crash simulations

International audienceMore and more structural parts are building using organic matrix composite materials in order to reduce the weight of aircraft structures. In order to reduce the number of tests required at the different scale of the building block approach, an increase of the knowledge regarding strain rate dependency of such materials is still a topic of interest. Particularly most of the strain rate dependent material laws are based on or validated with tests performed on split Hopkinson bars [1,2]. Few results are available in the literature concerning the intermediate strain rate, typically ranging between 10-3 s-1 and 100 s-1. Consequently, this study is first dedicated to the experimental characterisation of the rate effect for this specific range of strain rate. For that purpose, tensile tests have been performed on a servo-hydraulic jack on off-axis specimens. Various off-axis angles have been considered: 15°, 30°, 45°, 60°, 75° and 90°. The geometry of the coupon for each angle has been defined thanks to a numerical study in order to reduce stress concentration near to the tabs and maximise the stress field homogeneity within the specimens. Three different loading speeds with at least three specimens were tested in order to evaluate discrepancy. A Photron SA-X high speed camera has been used to evaluate strain using a Digital Image Correlation software (Aramis GOM). Moreover, as multiple failure locations are observed for high loading rate tests, high speed imaging allow the localisation of the first failure.These results have been used in order to include rate dependency in an advanced material law initially proposed by ONERA for quasi-static loadings. This model written at the ply scale is based on a visco-elastic behaviour law until a ply failure criterion is reached. A Hashin like failure criterion is used and two failure modes are considered: fibre failure and matrix failure. The degradation of the ply properties is obtained with 2 damage variables: d1 for fibre failure and d2 for matrix failure. Improvements regarding rate dependency of this material law have been studied for its three main aspects: the visco-elastic behaviour, the failure criterion and the damage evolution law. Regarding the visco-elastic behaviour, previous works [3] have shown that a bi-spectral visco-elastic model is required in order to take into account the short relaxation times required to accurately described rate dependency for high strain rate tests and long relaxation times for low strain rate tests. The main drawback of this model is its computational cost due to the important number of viscous mechanisms that have to be considered. As full-scale crash simulation is the targeted application case, a modified version of this model has been proposed. It still has an accurate prediction of the different modulus evolutions with the loading rate but it has a reduce computational cost. Concerning the loading speed dependency of the failure criterion, dynamic off-axis tensile tests will be used as input data to analyse and improve the failure criterion. Finally, improvements of the different damage evolution laws will be based on results available in the literature [4]. Finally, this material law has been implemented in an explicit finite element code in order to validate it on more complex coupons

Preface for the special issue on Microscopy of Semiconducting Materials 2019

This issue contains selected invited and contributed presentations from the 21st international conference on 'Microscopy of Semiconducting Materials' held at Fitzwilliam College, University of Cambridge, on 9–12 April 2019. The meeting was organised by the Institute of Physics, supported by the Royal Microscopical Society, the European Microscopy Society, attolight (Platinum sponsor), JEOL (Gold sponsor) and ThermoFisher Scientific (Silver sponsor)