Surrogate Assisted Computation of the Parametric Safety Margin for a Flexible Launcher

International audienceIn order to assess the robustness of dynamical systems, an approach is to demarcate the uncertain parameter space as safe set and unsafe set. Unsafe set represents the region within which the system lacks the required level of performance, or even loses its stability. However, determining the minimum distance metric for the unsafe set from the nominal operating point, the so-called parametric safety margin, for a higher dimensional dynamical system is not trivial and is often computationally demanding. In this paper, the parametric safety margin for a closed loop industrial standard launch vehicle simulator during its thrust vector control phase is computed. Imposing certain basic topological restrictions for the multi-dimensional uncertain parameter space, the computation of the parametric safety margin can be posed as a constrained nonconvex global optimization problem, and is thus extremely challenging in the case of high-fidelity aerospace simulators. Various performance requirements become the constraints in the optimization problem. An approach exploiting the use of nonintrusive polynomial surrogate modeling is proposed for the efficient computation of the parametric safety margin for the industrial standard launch vehicle simulator

Critère H-infini pour la commande de lanceurs flexibles

National audienc

Dynamics modeling and comparative robust stability analysis of a space launcher with constrained inputs

International audienceThis paper presents a comparative robust stability analysis using IQC-based and LMI-based tools. An LFR, resulting from the factorization of the equations of motion, allows assessing the robust stability of a space launcher in the face of inertia uncertainties and saturated inputs

Dosimetry for spectral molecular imaging of small animals with MARS-CT

The Medipix All Resolution Scanner (MARS) spectral CT is intended for small animal, pre-clinical imaging and uses an x-ray detector (Medipix) operating in single photon counting mode. The MARS system provides spectrometric information to facilitate differentiation of tissue types and bio-markers. For longitudinal studies of disease models, it is desirable to characterise the system’s dosimetry. This dosimetry study is performed using three phantoms each consisting of a 30 mm diameter homogeneous PMMA cylinder simulating a mouse. The imaging parameters used for this study are derived from those used for gold nanoparticle identification in mouse kidneys. Dosimetry measurement are obtained with thermo-luminescent Lithium Fluoride (LiF:CuMgP) detectors, calibrated in terms of air kerma and placed at different depths and orientations in the phantoms. Central axis TLD air kerma rates of 17.2 (± 0.71) mGy/min and 18.2 (± 0.75) mGy/min were obtained for different phantoms and TLD orientations. Validation measurements were acquired with a pencil ionization chamber, giving an air-kerma rate of 20.3 (±1) mGy/min and an estimated total air kerma of 81.2 (± 4) mGy for a 720 projection acquisition. It is anticipated that scanner design improvements will significantly decrease future dose requirements. The procedures developed in this work will be used for further dosimetry calculations when optimizing image acquisition for the MARS system as it undergoes development towards human clinical applications

PWM Modeling for Attitude Control of a Launcher During Ballistic Phase and Comparative Stability Analysis

International audienceThe present paper exposes a novel description of the effect of a pulse generator on a double integrator representing one axis of rotation for a space vehicle. By considering the difference between the angular velocity obtained with zero-order-hold (ZOH) actuator and the one with a PWM actuator, a perturbation operator expressing the influence of the PWM on the angular speed is defined. Using this configuration in a linear fractional representation (LFR), a stability analysis allows comparing LMI-based and IQC-based stability results for a one degree of freedom rotating body with uncertain PWM and saturation and permits dwelling on improvements to make for further analyses

Molecular characterization of O157:H7, O26:H11 and O103:H2 shiga toxin-producing escherichia coli isolated from dairy products

Pathogenic Shiga toxin-producing E. coli (STEC) are recognized worldwide as environment and foodborne pathogens which can be transmitted by ingestion of ready-to-eat food such as raw milk-derived products. STEC show a prevalence rate in dairy products of 0.9%, yet comparably few outbreaks have been related to dairy products consumption. In this study, we used rt-qPCR to identify the virulence potential of 0157, 026 and 0103 STEC strains isolated from raw-milk dairy products by analyzing virulence-related gene frequencies and associations with O-island (OI) 44, 01-48, 01-50, 01-57, 01-71 and 01-122. Results showed that 100% of STEC strains investigated harbored genes associated with EHEC-related virulence profile patterns (eae and stx, with either espK, espy, ureD and/or Z2098). We also found similarities in virulence-related gene content between O157:H7 and O103:H2 dairy and non-dairy STEC strains, especially isolates from human cases. The O26:H11-serotype STEC strains investigated harbor the arcA-allele 2 gene associated with specific genetic markers. These profiles are associated with high-virulence seropathotype-A STEC. However, the low frequency of stx2 gene associated with absence of other virulence genes in dairy isolates of O26:H11 remains a promising avenue of investigation to estimate their real pathogenicity. All O26:H11 attaching-effacing E. coli (AEEC) strains carried CRISPRo26:rni SP 026E but not genetic markers espK, espy, ureD and/or Z2098 associated with the emerging potentially high -virulence "new French clone". These strains are potentially as "EHEC-like" strains because they may acquire (or have lost) stx gene. In this study, O157:H7, O103:H2 and O26:H11 STEC strains isolated from dairy products were assigned as potential pathogens. However, research now needs to investigate the impact of dairy product environment and dairy processing on the expression of their pathogenicity

Growth and Survival of Acid-Resistant and Non-Acid-Resistant Shiga-Toxin-Producing Escherichia coli Strains during the Manufacture and Ripening of Camembert Cheese

Growth and survival of acid-resistant (AR) and non-acid-resistant (NAR) Shiga-toxin-producing Escherichia coli (STEC) strains were investigated during the manufacture and ripening of microfiltered milk Camembert cheeses. The induction of acid resistance of the STEC strains in cheeses was also studied. Six different mixtures of AR and/or NAR STEC strains were inoculated separately into microfiltered milk at a level of 103 CFU mL−1. The STEC counts (AR and NAR) initially increased by 1 to 2 log⁡10 CFU g−1 during cheese-making. Thereafter, the populations stabilized during salting/drying and then decreased during the early stages of ripening. Exposing the STEC strains in artificially inoculated cheeses to simulated gastric fluid (SGF - pH: 2.0) reduced the number of NAR strains to undetectable levels within 40 minutes, versus 120 minutes for the AR STEC strains. AR and NAR STEC were able to survive during the manufacture and ripening of Camembert cheese prepared from microfiltered milk with no evidence of induced acid tolerance in NAR STEC strains