Gaining Ground Information Database

A Report on a New Internet Research Library of Innovative Land Use Laws, Regulations, and Practice

Volume MLS Ray Casting

The method of Moving Least Squares (MLS) is a popular framework for reconstructing continuous functions from scattered data due to its rich mathematical properties and well-understood theoretical foundations. This paper applies MLS to volume rendering, providing a unified mathematical framework for ray casting of scalar data stored over regular as well as irregular grids. We use the MLS reconstruction to render smooth isosurfaces and to compute accurate derivatives for high-quality shading effects. We also present a novel, adaptive preintegration scheme to improve the efficiency of the ray casting algorithm by reducing the overall number of function evaluations, and an efficient implementation of our framework exploiting modern graphics hardware. The resulting system enables high-quality volume integration and shaded isosurface rendering for regular and irregular volume data.Engineering and Applied Science

Reach and grasp by people with tetraplegia using a neurally controlled robotic arm

Paralysis following spinal cord injury (SCI), brainstem stroke, amyotrophic lateral sclerosis (ALS) and other disorders can disconnect the brain from the body, eliminating the ability to carry out volitional movements. A neural interface system (NIS)1–5 could restore mobility and independence for people with paralysis by translating neuronal activity directly into control signals for assistive devices. We have previously shown that people with longstanding tetraplegia can use an NIS to move and click a computer cursor and to control physical devices6–8. Able-bodied monkeys have used an NIS to control a robotic arm9, but it is unknown whether people with profound upper extremity paralysis or limb loss could use cortical neuronal ensemble signals to direct useful arm actions. Here, we demonstrate the ability of two people with long-standing tetraplegia to use NIS-based control of a robotic arm to perform three-dimensional reach and grasp movements. Participants controlled the arm over a broad space without explicit training, using signals decoded from a small, local population of motor cortex (MI) neurons recorded from a 96-channel microelectrode array. One of the study participants, implanted with the sensor five years earlier, also used a robotic arm to drink coffee from a bottle. While robotic reach and grasp actions were not as fast or accurate as those of an able-bodied person, our results demonstrate the feasibility for people with tetraplegia, years after CNS injury, to recreate useful multidimensional control of complex devices directly from a small sample of neural signals

Numerical study of the influence of interfacial roughness on the exchange bias properties of ferromagnetic/antiferromagnetic bilayers

International audienceExchange bias and coercivity are both studied numerically in antiferromagnetic/ferromagnetic (AFM/FM) bilayers in the presence of a rough interface. The roughness is modeled by an AFM atomic mesa of variable width, in a periodic bidimensional system. Unlike the flat interface case, roughness can favor the presence of magnetic interfacial frustration or the formation of sharp magnetic domain walls pinned within the first AFM planes, inside the AFM mesa, in a Peierls potential well. We demonstrate by using athermal steepest-descent calculations that irreversible processes can occur during the hysteresis loops, when the AFM mesa width is less than half of the system period. In this case, the depinning of the domain wall from the Peierls potential well during the descending branch is not followed by its rewinding in a certain range of the AFM anisotropy. This leads to a large increase of both exchange bias and coercivity at low temperature and to an athermal training effect. When the thermal activation is taken into account by using Monte Carlo simulations, we show that a random walk of the domain wall occurs within the AFM layer. These processes induce changes in the AFM spin configuration when the system is cycled several times and produce a thermally activated training effect. Our simulations, interpreted in the context of periodic Peierls potential, provide an explanation for two important features of the exchange bias phenomenon, i.e., the thermal variation of its characteristic fields and the different contributions giving rise to the training effect (AFM bulk vs interface). More generally, the presence of interfacial atomic roughness reduces both exchange bias and coercivity with respect to the perfect interface case

Magnetic domain wall coercivity and aftereffect in antiferromagnetic/ferromagnetic bilayers

Équipe 107 : Physique des plasmas chaudsInternational audienceExchange bias and coercivity are investigated in antiferromagnetic (AFM)/ferromagnetic (FM) bilayers by steepest descent and Monte Carlo simulations. For a given range of the AFM anisotropy, a magnetic domain wall parallel to the interface is created in the AFM layer. This domain wall propagates along the AFM thickness and eventually gets pinned at the negative saturation due to the intrinsic Peierls potential of the AFM material. We demonstrate that this pinning and its associated dissipation is one possible source of coercivity in such exchange coupled bilayers. Monte Carlo simulations were also carried out to investigate the influence of thermal fluctuations, which induce a random walk of the domain wall throughout the AFM layer, leading to magnetic aftereffect. Depending on the experimental characteristic measurement time and temperature, the domain wall can eventually be expelled from the AFM layer leading to the reversal of the entire AFM spin lattice. This contribution to the exchange bias phenomenon particularly explains quite well the enhancement of coercivity in exchange coupled bilayers at low temperature, even in polycrystalline samples

Contribution of the Peierls Potential to the Exchange Bias and Coercivity of Ferromagnetic-Antiferromagnetic Bilayers

Équipe 107 : Physique des plasmas chaudsInternational audienceA new contribution to the exchange bias phenomenon in antiferromagnetic-ferromagnetic bilayers is presented, based on the intrinsic Peierls potential experienced by narrow magnetic domain walls moving through the antiferromagnet crystal lattice. Although the model is developed in the ideal case of a perfect crystalline structure with an atomically flat interface, this new contribution is expected to play a significant role at the grain scale in polycrystalline realistic samples. The thermal variation of the hysteresis loss in such bilayers is interpreted by a random walk process of the domain wall through the antiferromagnet. This new contribution yields a relationship between exchange bias and coercivity

Singularity-Aware Design Optimization for Multi-Degree-of-Freedom Spatial Linkages

We introduce a singularity-aware design optimization method for spatial multi-degree-of-freedom mechanical linkages. At the core of our approach is an adversarial sampling strategy, which actively detects singular configurations within the targeted operation range. The detection of singularities in both forward and inverse kinematics allows for two-way bijective mappings between input and output trajectories on our optimized designs, thus enabling robust control. We demonstrate our approach on a set of simulation examples and provide additional validation on physical prototypes.ISSN:2377-376