1,686 research outputs found
A note on the metallization of compressed liquid hydrogen
We examine the molecular-atomic transition in liquid hydrogen as it relates
to metallization. Pair potentials are obtained from first principles molecular
dynamics and compared with potentials derived from quadratic response. The
results provide insight into the nature of covalent bonding under extreme
conditions. Based on this analysis, we construct a schematic
dissociation-metallization phase diagram and suggest experimental approaches
that should significantly reduce the pressures necessary for the realization of
the elusive metallic phase of hydrogen.Comment: 11 pages, 4 figure
Kinematic analysis of the 3-RPR parallel manipulator
The aim of this paper is the kinematic study of a 3-RPR planar parallel
manipulator where the three fixed revolute joints are actuated. The direct and
inverse kinematic problem as well as the singular configuration is
characterized. On parallel singular configurations, the motion produce by the
mobile platform can be compared to the Reuleaux straight-line mechanism
Working and Assembly Modes of the Agile Eye
This paper deals with the in-depth kinematic analysis of a special spherical
parallel wrist, called the Agile Eye. The Agile Eye is a three-legged spherical
parallel robot with revolute joints in which all pairs of adjacent joint axes
are orthogonal. Its most peculiar feature, demonstrated in this paper for the
first time, is that its (orientation) workspace is unlimited and flawed only by
six singularity curves (rather than surfaces). Furthermore, these curves
correspond to self-motions of the mobile platform. This paper also demonstrates
that, unlike for any other such complex spatial robots, the four solutions to
the direct kinematics of the Agile Eye (assembly modes) have a simple geometric
relationship with the eight solutions to the inverse kinematics (working
modes)
Diffusion Monte Carlo study of the equation of state of solid ortho-D
We present results of Diffusion Monte Carlo calculations for a system of
solid ortho-D_2 at different densities, for pressure ranging from 0 up to
350MPa. We compare the equation of state obtained using two of the most used
effective intermolecular potentials, i.e. the Silvera--Goldman and the Buck
potentials, with experimental data, in order to assess the validity of the
model interactions. The Silvera-Goldman potential has been found to provide a
satisfactory agreement with experimental results, showing that, as opposed to
what recently found for p-H_2, three--body forces can be efficiently accounted
for by an effective two--body term.Comment: 11 pages, 4 figure
Changing Assembly Modes without Passing Parallel Singularities in Non-Cuspidal 3-R\underline{P}R Planar Parallel Robots
This paper demonstrates that any general 3-DOF three-legged planar parallel
robot with extensible legs can change assembly modes without passing through
parallel singularities (configurations where the mobile platform loses its
stiffness). While the results are purely theoretical, this paper questions the
very definition of parallel singularities.Comment: 2nd International Workshop on Fundamental Issues and Future Research
Directions for Parallel Mechanisms and Manipulators, Montpellier : France
(2008
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