Predicting lubrication performance between the slipper and swashplate in axial piston hydraulic machines

Engineering of the sliding interfaces within swashplate type axial piston machines represents the most complex and difficult part of the design process. The sliding interfaces are subject to significant normal loads which must be supported while simultaneously preventing component wear to ensure long lasting operation. Proper lubrication design is essential to separate the solid bodies from each other, but the complexity of the physics involved makes this a difficult problem. This work focuses on lubrication and the resulting energy losses at the sliding interface between the slipper and swashplate. ^ To better understand the slipper lubrication performance, a numerical model has been developed to predict the behavior of a design. The numerical model considers the multi-physics, multi-scale, and transient nature of the lubrication problem by utilizing novel segmented physics solvers and numerical techniques. Partitioned solvers considering the fluid pressure and temperature distributions, structural deformation due to fluid pressure and viscous heating, as well as a solid body dynamics from transient loads have been originally developed and tightly coupled. Although the effort necessary to implement this was significant, by avoiding a more traditional co-simulation approach, high computational efficiency and model fidelity can be achieved. ^ To validate the developed numerical model, a specialized test rig was designed and manufactured. Miniature high-speed inductive position sensors were mounted inside the swashplate of a commercially manufactured pump with only minimal modifications. These six sensors measured the distance between the sensor face and the slipper land as the slipper passed over the sensor, effectively measuring the direct film thickness in real time. The thickness of lubrication represents the greatest unknown predicted by the model and provides the most rigorous validation as well as experimental insight into actual slipper operation. New slippers were installed in the test rig, measured, and then following a period of operation, were measured again. A significant change in film thickness behavior was measured due to the presence of a worn slipper surface during the second period of testing, and this same behavioral change was captured with the simulation model. ^ The developed numerical model was used to conduct case studies demonstrating the potential of virtual pump lubrication design. Slipper sensitivity to operating conditions and materials were explored. Operational changes such as slipper tipping and liftoff at high speeds were numerically observed and would serve to aid a designer in improving the robustness of a design. A multi-modeling approach using a surrogate model based upon a design of experiment study and the full numerical model explored the inter-dependence of variables in a multi-land slipper design. In particular, a decrease in total power loss while increasing the outer stabilizing land width at a constant hydrostatic balance factor was observed for low pressure operatio

Concurrent visuomotor behaviour improves form discrimination in a patient with visual form agnosia

It is now well established that the visual brain is divided into two visual streams, the ventral and the dorsal stream. Milner and Goodale have suggested that the ventral stream is dedicated for processing vision for perception and the dorsal stream vision for action [A.D. Milner & M.A. Goodale (1995) The Visual Brain in Action, Oxford University Press, Oxford]. However, it is possible that ongoing processes in the visuomotor stream will nevertheless have an effect on perceptual processes. This possibility was examined in the present study. We have examined the visual form-discrimination performance of the form-agnosic patient D.F. with and without a concurrent visuomotor task, and found that her performance was significantly improved in the former condition. This suggests that the visuomotor behaviour provides cues that enhance her ability to recognize the form of the target object. In control experiments we have ruled out proprioceptive and efferent cues, and therefore propose that D.F. can, to a significant degree, access the object's visuomotor representation in the dorsal stream. Moreover, we show that the grasping-induced perceptual improvement disappears if the target objects only differ with respect to their shape but not their width. This suggests that shape information per se is not used for this grasping task

On large-scale diagonalization techniques for the Anderson model of localization

We propose efficient preconditioning algorithms for an eigenvalue problem arising in quantum physics, namely the computation of a few interior eigenvalues and their associated eigenvectors for large-scale sparse real and symmetric indefinite matrices of the Anderson model of localization. We compare the Lanczos algorithm in the 1987 implementation by Cullum and Willoughby with the shift-and-invert techniques in the implicitly restarted Lanczos method and in the Jacobi–Davidson method. Our preconditioning approaches for the shift-and-invert symmetric indefinite linear system are based on maximum weighted matchings and algebraic multilevel incomplete LDLT factorizations. These techniques can be seen as a complement to the alternative idea of using more complete pivoting techniques for the highly ill-conditioned symmetric indefinite Anderson matrices. We demonstrate the effectiveness and the numerical accuracy of these algorithms. Our numerical examples reveal that recent algebraic multilevel preconditioning solvers can accelerate the computation of a large-scale eigenvalue problem corresponding to the Anderson model of localization by several orders of magnitude

First Forms of Art : Pt.2. Crystal Forms

2 v. : 80 leaves of plates ; 36 cm. Cover title. In portfolio. This collection of 156 different forms of crystals was produced by microphotography. Professor T.H. Schenk, of Austria, experimented several years in order to bring about interesting designs through the action of acids on various metals... --Pt. 2., cover page verso. Pt. 1. Nature -- Pt. 2. Crystal forms. Library has Pt. 2 only ; Plates: 1-20.https://digitalcommons.risd.edu/specialcollections_books_nature/1003/thumbnail.jp

The interaction of brain regions during visual search processing as revealed by transcranial magnetic stimulation

Although it has long been known that right posterior parietal cortex (PPC) has a role in certain visual search tasks, and human motion area V5 is involved in processing tasks requiring attention to motion, little is known about how these areas may interact during the processing of a task requiring the speciality of each. Using transcranial magnetic stimulation (TMS), this study first established the specialization of each area in the form of a double dissociation; TMS to right PPC disrupted processing of a color/form conjunction and TMS to V5 disrupted processing of a motion/form conjunction. The key finding of this study is, however, if TMS is used to disrupt processing of V5 at its critical time of activation during the motion/form conjunction task, concurrent disruption of right PPC now has a significant effect, where TMS at PPC alone does not. Our findings challenge the conventional interpretation of the role of right PPC in conjunction search and spatial attention

Investigating the familiarity effect in texture segmentation by means of event-related brain potentials

The familiarity effect (FE) refers to the phenomenon that it is easier to find an unfamiliar element on a background of familiar elements than vice versa. In this study, we examined the FE in texture segmentation while recording event-related brain potentials with the aim to find out which processing stages were influenced by familiarity. In two experiments, with different levels of texture homogeneity, the N1, the N2p and the P3 components were investigated. It was found that the FE in texture segmentation is associated with a modulation of the early N1 and of the intermediate N2p component for homogeneous textures. For inhomogeneous (jittered) textures, the FE was found for the intermediate N2p and for the late P3 components, but not for the N1 component. Our findings suggest that increasing texture inhomogeneity shifts the FE occurrence to later processing stages

A steerable UV laser system for the calibration of liquid argon time projection chambers

A number of liquid argon time projection chambers (LAr TPC's) are being build or are proposed for neutrino experiments on long- and short baseline beams. For these detectors a distortion in the drift field due to geometrical or physics reasons can affect the reconstruction of the events. Depending on the TPC geometry and electric drift field intensity this distortion could be of the same magnitude as the drift field itself. Recently, we presented a method to calibrate the drift field and correct for these possible distortions. While straight cosmic ray muon tracks could be used for calibration, multiple coulomb scattering and momentum uncertainties allow only a limited resolution. A UV laser instead can create straight ionization tracks in liquid argon, and allows one to map the drift field along different paths in the TPC inner volume. Here we present a UV laser feed-through design with a steerable UV mirror immersed in liquid argon that can point the laser beam at many locations through the TPC. The straight ionization paths are sensitive to drift field distortions, a fit of these distortion to the linear optical path allows to extract the drift field, by using these laser tracks along the whole TPC volume one can obtain a 3D drift field map. The UV laser feed-through assembly is a prototype of the system that will be used for the MicroBooNE experiment at the Fermi National Accelerator Laboratory (FNAL)