On Centroidal Dynamics and Integrability of Average Angular Velocity

In the literature on robotics and multibody dynamics, the concept of average angular velocity has received considerable attention in recent years. We address the question of whether the average angular velocity defines an orientation framethat depends only on the current robot configuration and provide a simple algebraic condition to check whether this holds. In the language of geometric mechanics, this condition corresponds to requiring the flatness of the mechanical connection associated to the robotic system. Here, however, we provide both a reinterpretation and a proof of this result accessible to readers with a background in rigid body kinematics and multibody dynamics but not necessarily acquainted with differential geometry, still providing precise links to the geometric mechanics literature. This should help spreading the algebraic condition beyond the scope of geometric mechanics,contributing to a proper utilization and understanding of the concept of average angular velocity.Comment: 8 pages, accepted for IEEE Robotics and Automation Letters (RA-L

Changes in energy uxes during NPQ in LHCII and PSII-LHCII

PhD ThesisThe non-photochemical quenching of excess energy (NPQ) is a fast molecular adaptation of photosynthetic organisms to variations of sunlight intensities. In plants, the energy-dependent quenching (qE) is the main NPQ component, which promptly protects the thylakoid membrane components by dissipating the excess energy absorbed. While the trigger of this physiological process is known to be thylakoid DpH, the site in the membrane, the structural changes involved and the nature of the quencher pigment are still a subject of debate. In this thesis, I addressed these gaps in our knowledge of qE. The results presented here show that neither minor light harvesting antenna complexes nor reaction cores are sites of qE, which instead takes place entirely in major LHCII trimers. The nature of the change from a light-harvesting to a dissipative state in LHCII and its dependence on the binding of xanthophyll-cycle carotenoids was investigated. Zeaxanthin was found to exert no e ect on the quenching dynamics of single LHCII trimers, disproving its role as a quencher. However, it controls the kinetics of the transition to the quenched state by favouring LHCII aggregation. To determine the nature of the quencher species, transient absorption spectroscopy was applied to isolated LHCII. A mechanism was identi ed whereby chlorophylls donate energy to a carotenoid species, likely a lutein, leading to quick energy dissipation. Overall, this work reveals the self-regulatory nature of photosynthetic light harvesting, showing that in principle only trimeric LHCII and the proton gradient are su cient to enable qE in vivo. The protein PsbS and zeaxanthin exert an allosteric regulation of the process, that, by tuning the degree of antennae sensitivity to the amplitude of the proton gradient, assures a ne control of light harvestin

On centroidal dynamics and integrability of average angular velocity

\u3cp\u3eIn the literature on robotics and multibody dynamics, the concept of average angular velocity has received considerable attention in recent years. We address the question of whether the average angular velocity defines an orientation frame that depends only on the current robot configuration and provide a simple algebraic condition to check whether this holds. In the language of geometric mechanics, this condition corresponds to requiring the flatness of the mechanical connection associated with the robotic system. Here, however, we provide both a reinterpretation and a proof of this result accessible to readers with a background in rigid body kinematics and multibody dynamics but not necessarily acquainted with differential geometry, still providing precise links to the geometric mechanics literature. This should help spreading the algebraic condition beyond the scope of geometric mechanics, contributing to a proper utilization and understanding of the concept of average angular velocity.\u3c/p\u3

Protection of photosystem I during sudden light stress depends on ferredoxin:NADP(H) reductase abundance and interactions

International audienceAbstract Plant tolerance to high light and oxidative stress is increased by overexpression of the photosynthetic enzyme Ferredoxin:NADP(H) reductase (FNR), but the specific mechanism of FNR-mediated protection remains enigmatic. It has also been reported that the localization of this enzyme within the chloroplast is related to its role in stress tolerance. Here, we dissected the impact of FNR content and location on photoinactivation of photosystem I (PSI) and photosystem II (PSII) during high light stress of Arabidopsis (Arabidopsis thaliana). The reaction center of PSII is efficiently turned over during light stress, while damage to PSI takes much longer to repair. Our results indicate a PSI sepcific effect, where efficient oxidation of the PSI primary donor (P700) upon transition from darkness to light, depends on FNR recruitment to the thylakoid membrane tether proteins: thylakoid rhodanase-like protein (TROL) and translocon at the inner envelope of chloroplasts 62 (Tic62). When these interactions were disrupted, PSI photoinactivation occurred. In contrast, there was a moderate delay in the onset of PSII damage. Based on measurements of ΔpH formation and cyclic electron flow, we propose that FNR location influences the speed at which photosynthetic control is induced, resulting in specific impact on PSI damage. Membrane tethering of FNR therefore plays a role in alleviating high light stress, by regulating electron distribution during short-term responses to light

Prevalence and predictors of flare after immunosuppressant discontinuation in patients with systemic lupus erythematosus in remission

Patients with SLE are often exposed to prolonged immunosuppression since few data on flare recurrence in remitted patients who discontinued immunosuppressants are available. We aimed to assess the rate and predictors of flare after immunosuppressant withdrawal in SLE patients in remission

Prevalence, outcome and management of patients with SLE and secondary antiphospholipid antibody syndrome after aPL seroconversion

The withdrawal of oral anticoagulation (OAC) in patients with SLE and secondary aPL syndrome (SAPS) who become seronegative has not been clearly investigated to date. Our aim was to evaluate the prevalence of aPL seroconversion and the prognosis of SLE patients with SAPS who withdrew OAC after aPL negativization

Control of humanoid robot motions with impacts: numerical experiments with reference spreading control

This work explores the stabilization of desired dynamic motion tasks involving hard impacts at non-negligible speed for humanoid robots. To this end, a so-called reference spreading hybrid control law is designed showing promising results in simulation. The simulations are performed employing a dynamical model of an existing humanoid robot and impacts are assumed to be inelastic. The desired motion task consists of having the robot balancing on one foot while repeatedly making and breaking contact with a wall by means of one hand. The simulation results illustrate that the considered controller is suited to control humanoid robot motions with impacts

Unraveling the Excited-State Dynamics and Light-Harvesting Functions of Xanthophylls in Light-Harvesting Complex II Using Femtosecond Stimulated Raman Spectroscopy

Photosynthesis in plants starts with the capture of photons by light-harvesting complexes (LHCs). Structural biology and spectroscopy approaches have led to a map of the architecture and energy transfer pathways between LHC pigments. Still, controversies remain regarding the role of specific carotenoids in light-harvesting and photoprotection, obligating the need for high-resolution techniques capable of identifying excited-state signatures and molecular identities of the various pigments in photosynthetic systems. Here we demonstrate the successful application of femtosecond stimulated Raman spectroscopy (FSRS) to a multichromophoric biological complex, trimers of LHCII. We demonstrate the application of global and target analysis (GTA) to FSRS data and utilize it to quantify excitation migration in LHCII trimers. This powerful combination of techniques allows us to obtain valuable insights into structural, electronic, and dynamic information from the carotenoids of LHCII trimers. We report spectral and dynamical information on ground- and excited-state vibrational modes of the different pigments, resolving the vibrational relaxation of the carotenoids and the pathways of energy transfer to chlorophylls. The lifetimes and spectral characteristics obtained for the S1 state confirm that lutein 2 has a distorted conformation in LHCII and that the lutein 2 S1 state does not transfer to chlorophylls, while lutein 1 is the only carotenoid whose S1 state plays a significant energy-harvesting role. No appreciable energy transfer takes place from lutein 1 to lutein 2, contradicting recent proposals regarding the functions of the various carotenoids (Son et al. Chem.2019, 5 (3), 575-584). Also, our results demonstrate that FSRS can be used in combination with GTA to simultaneously study the electronic and vibrational landscapes in LHCs and pave the way for in-depth studies of photoprotective conformations in photosynthetic systems

Regulation of photosynthetic electron flow on dark to light transition by ferredoxin:NADP(H) oxidoreductase interactions

International audienceDuring photosynthesis, electron transport is necessary for carbon assimilation and must be regulated to minimize free radical damage. There is a longstanding controversy over the role of a critical enzyme in this process (ferredoxin:NADP(H) oxidoreductase, or FNR), and in particular its location within chloroplasts. Here we use immunogold labelling to prove that FNR previously assigned as soluble is in fact membrane associated. We combined this technique with a genetic approach in the model plant Arabidopsis to show that the distribution of this enzyme between different membrane regions depends on its interaction with specific tether proteins. We further demonstrate a correlation between the interaction of FNR with different proteins and the activity of alternative photosynthetic electron transport pathways. This supports a role for FNR location in regulating photosynthetic electron flow during the transition from dark to light