Nuclear Inelastic X-Ray Scattering of FeO to 48 GPa

The partial density of vibrational states has been measured for Fe in compressed FeO (w\"ustite) using nuclear resonant inelastic x-ray scattering. Substantial changes have been observed in the overall shape of the density of states close to the magnetic transiton around 20 GPa from the paramagnetic (low pressure) to the antiferromagnetic (high pressure) state. Our data indicate a substantial softening of the aggregate sound velocities far below the transition, starting between 5 and 10 GPa. This is consistent with recent radial x-ray diffraction measurements of the elastic constants in FeO. The results indicate that strong magnetoelastic coupling in FeO is the driving force behind the changes in the phonon spectrum of FeO.Comment: 4 pages, 4 figure

Structural, Electronic, and Magnetic Properties of MnO

We calculate the structural, electronic, and magnetic properties of MnO from first principles, using the full-potential linearized augmented planewave method, with both local-density and generalized-gradient approximations to exchange and correlation. We find the ground state to be of rhombohedrally distorted B1 structure with compression along the [111] direction, antiferromagnetic with type-II ordering, and insulating, consistent with experiment. We show that the distortion can be understood in terms of a Heisenberg model with distance dependent nearest-neighbor and next-nearest-neighbor couplings determined from first principles. Finally, we show that magnetic ordering can induce significant charge anisotropy, and give predictions for electric field gradients in the ground-state rhombohedrally distorted structure.Comment: Submitted to Physical Review B. Replaced: regenerated figures to resolve font problems in automatically generated pd

Multi-agent motion planning for nonlinear Gaussian systems

In this paper, a multi-agent motion planner is developed for nonlinear Gaussian systems using a combination of probabilistic approaches and a rapidly exploring random tree (RRT) algorithm. A closed-loop model consisting of a controller and estimation loops is used to predict future distributions to manage the level of uncertainty in the path planner. The closed-loop model assumes the existence of a feedback control law that drives the actual system towards a nominal system. This ensures the uncertainty in the evolution does not grow significantly and the tracking errors are bounded. To trade conservatism with the risk of infeasibility and failure, we use probabilistic constraints to limit the probability of constraint violation. The probability of leaving the configuration space is included by using a chance constraint approach and the probability of closeness between two agents is imposed using an overlapping coefficient approach. We augment these approaches with the RRT algorithm to develop a robust path planner. Conflict among agents is resolved using a priority-based technique. Numerical results are presented to demonstrate the effectiveness of the planner

SANS experiments on micellar nematic mesophases

Lyotropic Nematics are liquid crystalline mixtures characterized by anisotropic aggregates of amphiphilic molecules with finite shape and long range orientational but no positional order. They are distinguished according to their macroscopic properties in positive and negative uniaxial nematics and in biaxial nematics. Very few notices are available on the structure and on the evolution of the micelles through the different nematic mesophases. We have studied by Small Angle Neutrons Scattering the potassium laurate, decylammonium hydrochloride, water system which was found to exhibit the three nematic phases as a function of temperature and concentration. SANS preliminary experiments were performed at PAXY spectrometer of Orphée reactor at Saclay on adequate combinations of fully deuterated components

Nanopores in track-etched polymer membranes characterized by small-angle x-ray scattering

International audienceNanochannels and nanowires with diameters ranging from 30 to 400 nm were produced by etching ion tracks in thin polyarylate and polycarbonate foils. The shape and the size distribution of dry and wet nanochannels, as well as of nanowires grown therein, were examined by small-angle x-ray scattering. The x-ray intensity as a function of the scattering vector exhibits pronounced oscillations showing that both the channels and the wires have a highly cylindrical geometry and a very narrow size distribution. UV exposure before chemical etching significantly improves the monodispersity of the nanopores. For fixed etching conditions, the scattering patterns provide evidence that the diameter of dry and water-filled channels as well as for embedded nanowires are identical, demonstrating that the pores in the polymer are completely filled. (Some figures in this article are in colour only in the electronic version