279 research outputs found
Gross shell structure at high spin in heavy nuclei
Experimental nuclear moments of inertia at high spins along the yrast line
have been determined systematically and found to differ from the rigid-body
values. The difference is attributed to shell effects and these have been
calculated microscopically. The data and quantal calculations are interpreted
by means of the semiclassical Periodic Orbit Theory. From this new perspective,
features in the moments of inertia as a function of neutron number and spin, as
well as their relation to the shell energies can be understood. Gross shell
effects persist up to the highest angular momenta observed.Comment: 40 pages total; 22 pages text, 19 figures sent as 27 .png file
Stiffness modelling of parallelogram-based parallel manipulators
International audienceThe paper presents a methodology to enhance the stiffness analysis of parallel manipulators with parallelogram-based linkage. It directly takes into account the influence of the external loading and allows computing both the non-linear ``load-deflection" relation and relevant rank-deficient stiffness matrix. An equivalent bar-type pseudo-rigid model is also proposed to describe the parallelogram stiffness by means of five mutually coupled virtual springs. The contributions of this paper are highlighted with a parallelogram-type linkage used in a manipulator from the Orthoglide family
Microscopic Evidence of Spin State Order and Spin State Phase Separation in Layered Cobaltites RBaCo2O5.5 with R=Y, Tb, Dy, and Ho
We report muon spin relaxation measurements on the magnetic structures of
RBaCo_2O_5.5 with R=Y, Tb, Dy, and Ho. Three different phases, one
ferrimagnetic and two antiferromagnetic, are identified below 300 K. They
consist of different ordered spin state arrangements of high-, intermediate-,
and low-spin Co^3+ of CoO_6 octahedra. Phase separation into well separated
regions with different spin state order is observed in the antiferromagnetic
phases. The unusual strongly anisotropic magnetoresistance and its onset at the
FM-AFM phase boundary is explained.Comment: 4 pages, accepted for publication in Phys. Rev. Let
Coupled spin-lattice fluctuations in a compound with orbital degrees of freedom: the Cr based dimer system Sr3Cr2O8
We report on an extended fluctuation regime in the spin dimer system Sr3Cr2O8
based on anomalies in Raman active phonons and magnetic scattering. The
compound has two characteristic temperatures, TS = 275 K, related to a
Jahn-Teller transition with structural distortions and orbital ordering and a
second, T*= 150 K, which is due to further changes in the orbital sector. Below
TS quasielastic scattering marks strong fluctuations and in addition phonon
anomalies are observed. For temperatures below T* we observe an exponential
decrease of one phonon linewidth and determine a gap of the orbital
excitations. At low temperatures the observation of two- and three-magnon
scattering allows the determination of the spin excitation gap.Comment: 7 pages, 4 figures, 1 tabl
Workspace and Singularity analysis of a Delta like family robot
Workspace and joint space analysis are essential steps in describing the task
and designing the control loop of the robot, respectively. This paper presents
the descriptive analysis of a family of delta-like parallel robots by using
algebraic tools to induce an estimation about the complexity in representing
the singularities in the workspace and the joint space. A Gr{\"o}bner based
elimination is used to compute the singularities of the manipulator and a
Cylindrical Algebraic Decomposition algorithm is used to study the workspace
and the joint space. From these algebraic objects, we propose some certified
three dimensional plotting describing the the shape of workspace and of the
joint space which will help the engineers or researchers to decide the most
suited configuration of the manipulator they should use for a given task. Also,
the different parameters associated with the complexity of the serial and
parallel singularities are tabulated, which further enhance the selection of
the different configuration of the manipulator by comparing the complexity of
the singularity equations.Comment: 4th IFTOMM International Symposium on Robotics and Mechatronics, Jun
2015, Poitiers, France. 201
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