Comment and Reply Why eye movements and perceptual factors have to be controlled in studies on "representational momentum”

In order to study memory of the final position of a smoothly moving target, Hubbard (e.g., Hubbard & Bharucha, 1988) presented smooth stimulus motion and used motor responses. In contrast, Freyd (e.g., Freyd & Finke, 1984) presented implied stimulus motion and used the method of constant stimuli. The same forward error was observed in both paradigms. However, the processes underlying the error may be very different. When smooth stimulus motion is followed by smooth pursuit eye movements, the forward error is associated with asynchronous processing of retinal and extraretinal information. In the absence of eye movements, no forward displacement is observed with smooth motion. In contrast, implied motion produces a forward error even without eye movements, suggesting that observers extrapolate the next target step when successive target presentations are far apart. Finally, motor responses produce errors that are not observed with perceptual judgments, indicating that the motor system may compensate for neuronal latencie

The LHCb RICH detectors

The LHCb experiment at the Large Hadron Collider has been optimised for high precision measurements of the charm and beauty quark sector. The different particle species produced in the high-energy collision are identified using two Ring-Imaging Cherenkov detectors

Atomistic Simulations of Basal Dislocations Interacting with Mg17_{17}Al12_{12} Precipitates in Mg

The mechanical properties of Mg-Al alloys are greatly influenced by the complex intermetallic phase Mg$_{17}$Al$_{12}$, which is the most dominant precipitate found in this alloy system. The interaction of basal edge and 30$^\text{o}$ dislocations with Mg$_{17}$Al$_{12}$ precipitates is studied by molecular dynamics and statics simulations, varying the inter-precipitate spacing ($L$), and size ($D$), shape and orientation of the precipitates. The critical resolved shear stress $\tau_c$ to pass an array of precipitates follows the usual $\ln((1/D + 1/L)^{-1})$ proportionality. In all cases but the smallest precipitate, the dislocations pass the obstacles by depositing dislocation segments in the disordered interphase boundary rather than shearing the precipitate or leaving Orowan loops in the matrix around the precipitate. An absorbed dislocation increases the stress necessary for a second dislocation to pass the precipitate also by absorbing dislocation segments into the boundary. Replacing the precipitate with a void of identical size and shape decreases the critical passing stress and work hardening contribution while an artificially impenetrable Mg$_{17}$Al$_{12}$ precipitate increases both. These insights will help improve mesoscale models of hardening by incoherent particles.Comment: 13 pages with 9 figures and 2 tables. Supplementary materia

On Extracting Mechanical Properties from Nanoindentation at Temperatures up to 1000∘^{\circ}C

Alloyed MCrAlY bond coats, where M is usually cobalt and/or nickel, are essential parts of modern turbine blades, imparting environmental resistance while mediating thermal expansivity differences. Nanoindentation allows the determination of their properties without the complexities of traditional mechanical tests, but was not previously possible near turbine operating temperatures. Here, we determine the hardness and modulus of CMSX-4 and an Amdry-386 bond coat by nanoindentation up to 1000$^{\circ}$C. Both materials exhibit a constant hardness until 400$^{\circ}$C followed by considerable softening, which in CMSX-4 is attributed to the multiple slip systems operating underneath a Berkovich indenter. The creep behaviour has been investigated via the nanoindentation hold segments. Above 700$^{\circ}$C, the observed creep exponents match the temperature-dependence of literature values in CMSX-4. In Amdry-386, nanoindentation produces creep exponents very close to literature data, implying high-temperature nanoindentation may be powerful in characterising these coatings and providing inputs for material, model and process optimisations

Mental and sensorimotor extrapolation fare better than motion extrapolation in the offset condition

Evidence for motion extrapolation at motion offset is scarce. In contrast, there is abundant evidence that subjects mentally extrapolate the future trajectory of weak motion signals at motion offset. Further, pointing movements overshoot at motion offset. We believe that mental and sensorimotor extrapolation is sufficient to solve the problem of perceptual latencies. Both present the advantage of being much more flexible than motion extrapolatio

LHCb RICH Online-Monitor and Data-Quality

The LHCb experiment at the LHC (CERN) has been optimised for high precision measurements of the beauty quark sector. Its main objective is to precisely determine and over-constrain the parameters of the CKM mixing matrix, and to search for further sources of CP violation and new physics beyond the Standard Model in rare B-decays. Efficient particle identification at high purities over a wide momentum range from around 1 to ~100GeV/c is vital to many LHCb analyses. Central to the LHCb particle identification strategy are two Ring Imaging CHerenkov (RICH) detectors which use Silica Aerogel and C4F10 and CF4 gas radiators. A rigorous quality control scheme is being developed to insure that the data recorded by the RICH detector meets the stringent requirements of the physics analyses. The talk summarises the LHCb RICH online monitoring and data-quality strategy. Multiple dedicated algorithms are deployed to detect any potential issue already during data-taking ranging from integrity checks, mis-alignments to changes in the refractive determined from changes in the radii of Cherenkov rings found using a Markov Chain approach. A further key ingredient is the online monitoring of the particle ID performance using multiple exclusively reconstructed decay channels where the particle identity can be determined from kinematic constraints. In addition, any re-calibration of the detector can be performed using a dedicated express stream covering a dedicated data-taking period. The same tests are performed during the reconstruction phase of the full statistics of the recorded data to verify the quality of the data before made available for physics analyses

On the structure of defects in the Fe7Mo6 μ\mu-Phase

Topologically close packed phases, among them the $\mu$-phase studied here, are commonly considered as being hard and brittle due to their close packed and complex structure. Nanoindentation enables plastic deformation and therefore investigation of the structure of mobile defects in the $\mu$-phase, which, in contrast to grown-in defects, has not been examined yet. High resolution transmission electron microscopy (HR-TEM) performed on samples deformed by nanoindentation revealed stacking faults which are likely induced by plastic deformation. These defects were compared to theoretically possible stacking faults within the $\mu$-phase building blocks, and in particular Laves phase layers. The experimentally observed stacking faults were found resulting from synchroshear assumed to be associated with deformation in the Laves-phase building blocks

Deep Intrinsically Motivated Continuous Actor-Critic for Efficient Robotic Visuomotor Skill Learning

In this paper, we present a new intrinsically motivated actor-critic algorithm for learning continuous motor skills directly from raw visual input. Our neural architecture is composed of a critic and an actor network. Both networks receive the hidden representation of a deep convolutional autoencoder which is trained to reconstruct the visual input, while the centre-most hidden representation is also optimized to estimate the state value. Separately, an ensemble of predictive world models generates, based on its learning progress, an intrinsic reward signal which is combined with the extrinsic reward to guide the exploration of the actor-critic learner. Our approach is more data-efficient and inherently more stable than the existing actor-critic methods for continuous control from pixel data. We evaluate our algorithm for the task of learning robotic reaching and grasping skills on a realistic physics simulator and on a humanoid robot. The results show that the control policies learned with our approach can achieve better performance than the compared state-of-the-art and baseline algorithms in both dense-reward and challenging sparse-reward settings