Regulation of Budding Yeast Mating-Type Switching Donor Preference by the FHA Domain of Fkh1

During Saccharomyces cerevisiae mating-type switching, an HO endonuclease-induced double-strand break (DSB) at MAT is repaired by recombining with one of two donors, HMLα or HMRa, located at opposite ends of chromosome III. MATa cells preferentially recombine with HMLα; this decision depends on the Recombination Enhancer (RE), located about 17 kb to the right of HML. In MATα cells, HML is rarely used and RE is bound by the MATα2-Mcm1 corepressor, which prevents the binding of other proteins to RE. In contrast, in MATa cells, RE is bound by multiple copies of Fkh1 and a single copy of Swi4/Swi6. We report here that, when RE is replaced with four LexA operators in MATa cells, 95% of cells use HMR for repair, but expression of a LexA-Fkh1 fusion protein strongly increases HML usage. A LexA-Fkh1 truncation, containing only Fkh1's phosphothreonine-binding FHA domain, restores HML usage to 90%. A LexA-FHA-R80A mutant lacking phosphothreonine binding fails to increase HML usage. The LexA-FHA fusion protein associates with chromatin in a 10-kb interval surrounding the HO cleavage site at MAT, but only after DSB induction. This association occurs even in a donorless strain lacking HML. We propose that the FHA domain of Fkh1 regulates donor preference by physically interacting with phosphorylated threonine residues created on proteins bound near the DSB, thus positioning HML close to the DSB at MAT. Donor preference is independent of Mec1/ATR and Tel1/ATM checkpoint protein kinases but partially depends on casein kinase II. RE stimulates the strand invasion step of interchromosomal recombination even for non-MAT sequences. We also find that when RE binds to the region near the DSB at MATa then Mec1 and Tel1 checkpoint kinases are not only able to phosphorylate histone H2A (γ-H2AX) around the DSB but can also promote γ-H2AX spreading around the RE region

Modeling and PreSizing Process for Hydrostatic Thrust Bearing with Special Consideration to Performance Robustness Within a Wide Temperature Range

International audienceThe research presented in this communication proposes a preliminary sizing approach of hydrostatic thrust bearings used in an embedded power system, which faces severe environmental and power consumption constraints. In particular, the hydrostatic thrust bearing shall be compliant with its specification within a wide temperature range and shall minimize the consumed flow. The performance of the thrust bearing is assessed in terms of static bearing force, consumed flow rate and stiffness. A particular attention is paid to the influence of the type of fixed hydraulic restriction. The short tube orifice is considered as an attractive solution that combines the advantages of both capillary tube and orifice types. In this attempt, a lumped parameter model of the short tube is proposed. The structure of the model is defined on basis an analytical approach while the model’s parameters are identified from computational fluid dynamics simulation. This new model enables the recess pressure to be calculated in order to compute the performances of the thrust bearing versus fluid temperature. Dimensionless results are used to facilitate the comparison of the sensitivity to temperature of the designs based on the above-mentioned types of hydraulic restrictions. The behavior – function of the temperature – of a given hydrostatic thrust bearing geometry is superimposed for the three hydraulic resistance models in order to emphasize the high contribution of the proposed short tube orifice model and sizing process to the global optimization

Modeling and PreSizing Process for Hydrostatic Thrust Bearing with Special Consideration to Performance Robustness Within a Wide Temperature Range

International audienceThe research presented in this communication proposes a preliminary sizing approach of hydrostatic thrust bearings used in an embedded power system, which faces severe environmental and power consumption constraints. In particular, the hydrostatic thrust bearing shall be compliant with its specification within a wide temperature range and shall minimize the consumed flow. The performance of the thrust bearing is assessed in terms of static bearing force, consumed flow rate and stiffness. A particular attention is paid to the influence of the type of fixed hydraulic restriction. The short tube orifice is considered as an attractive solution that combines the advantages of both capillary tube and orifice types. In this attempt, a lumped parameter model of the short tube is proposed. The structure of the model is defined on basis an analytical approach while the model’s parameters are identified from computational fluid dynamics simulation. This new model enables the recess pressure to be calculated in order to compute the performances of the thrust bearing versus fluid temperature. Dimensionless results are used to facilitate the comparison of the sensitivity to temperature of the designs based on the above-mentioned types of hydraulic restrictions. The behavior – function of the temperature – of a given hydrostatic thrust bearing geometry is superimposed for the three hydraulic resistance models in order to emphasize the high contribution of the proposed short tube orifice model and sizing process to the global optimization

Wigner matrix formalism for phase-modulated signals

International audienceLaser beam can carry multi-scales properties in space and time that impact the beam quality. The study of their evolution along complex optical sequences is of crucial interest, particularly in high intensity laser chains. For such analysis, results obtained with standard numerical calculus are strongly dependent of the sampling. In this paper, we develop an analytic model for a sinusoidal phase modulation inside a sequence of first order optics elements based on the Wigner matrix formalism. A Bessel decomposition of the Wigner function gives pseudo-Wigner functions that obey to the general ABCD matrix law transformation without approximations and sampling considerations. Applied to a Gaussian beam, explicit expressions are obtained for the projections of the Wigner function in the sub-spaces and gives a powerful tool for laser beam analysis. The formalism is established in the spatial and temporal domain and can be used to evaluate the impact of the phase noise to the beam properties and is not limited to small modulation depths. In a sake of illustration, the model is applied to the Talbot effect with the analysis of the propagation in the spatial and phase-space domain. A comparison with full numerical calculations evidences the high accuracy of the analytic model that retrieves all the features of the diffracted beam

Bond Graphs Aided development of Mechanical Power Transmission for Aerospace Electromechanical Actuators

International audienceThe Bond-graph formalism is used to support the model based development of mechanical power transmissions in aerospace electromechanical actuators. The effort placed in architecting models injects the genes of performance to make them “ready for” incremental modelling covering various engineering needs: power sizing, dynamics, power/energy consumption, response to failure, etc. The model topology is addressed with consideration to model decomposition, mechanical / energy balance, and fault injection. Standardized mechanical body and interface are presented to limit the impact of the topological choice on the model response and ensure the sub-models inter-connexion. The genericity of the model is increased at a little expense in complexity. These proposed concepts are illustrated using the example of a nut-screw. The nut-screw model is decomposed into perfect power transformation, frictional loss and compliance effect. Order of decomposition and causality at model’s interfaces are considered. The proposed generic architecture is consistent with top-level as well as detailed modelling: influence of velocity, transmitted force, preload and temperature on friction, single parameter for backlash and preloading, simple implementation of jamming and free-run failures. The detailed model based on standardized component is finally presented and discussed

Optimization of the Actuation System Sizing of a New Helicopter base on Global Modeling Approach

International audienceThe achievements presented in this communication propose a model based approach to propagate the Flight Control System requirements to the actuation system with the aim to identify each subsystem contribution and then think a global optimization of the actuation system architecture and sizing. Within the helicopter’s Flight Control System, many functions are encapsulated, making the global performance dependent of each subsystem. Hydraulic power generation and distribution impact the actuators performances, which dynamics are influencing the global helicopter control loop performances. After presenting some recommendations in terms of pipes and actuators sizing, the new global modeling approach is introduced. The actuation system model is described with its interfaces, including degrees of freedom on its architecture, and its key parameters. Open loop simulations – based on real flight data – and closed loop simulation – responses to commands needed for maneuvers – are detailed with their respective advantages. The contribution of this global modeling approach to the final design is presented and perspectives are given

Optimization of the Actuation System Sizing of a New Helicopter base on Global Modeling Approach

International audienceThe achievements presented in this communication propose a model based approach to propagate the Flight Control System requirements to the actuation system with the aim to identify each subsystem contribution and then think a global optimization of the actuation system architecture and sizing. Within the helicopter’s Flight Control System, many functions are encapsulated, making the global performance dependent of each subsystem. Hydraulic power generation and distribution impact the actuators performances, which dynamics are influencing the global helicopter control loop performances. After presenting some recommendations in terms of pipes and actuators sizing, the new global modeling approach is introduced. The actuation system model is described with its interfaces, including degrees of freedom on its architecture, and its key parameters. Open loop simulations – based on real flight data – and closed loop simulation – responses to commands needed for maneuvers – are detailed with their respective advantages. The contribution of this global modeling approach to the final design is presented and perspectives are given

Trajectory and design optimization of multirotor drones with system simulation

International audienc