47,350 research outputs found
Electron multiplier development /phase 1/
Fabrication of aluminum oxide thin film window for capillary type photomultiplier tube
A global approach for using kinematic redundancy to minimize base reactions of manipulators
An important consideration in the use of manipulators in microgravity environments is the minimization of the base reactions, i.e. the magnitude of the force and the moment exerted by the manipulator on its base as it performs its tasks. One approach which was proposed and implemented is to use the redundant degree of freedom in a kinematically redundant manipulator to plan manipulator trajectories to minimize base reactions. A global approach was developed for minimizing the magnitude of the base reactions for kinematically redundant manipulators which integrates the Partitioned Jacobian method of redundancy resolution, a 4-3-4 joint-trajectory representation and the minimization of a cost function which is the time-integral of the magnitude of the base reactions. The global approach was also compared with a local approach developed earlier for the case of point-to-point motion of a three degree-of-freedom planar manipulator with one redundant degree-of-freedom. The results show that the global approach is more effective in reducing and smoothing the base force while the local approach is superior in reducing the base moment
Quantum criticality out of equilibrium in the pseudogap Kondo model
We theoretically investigate the non-equilibrium quantum phase transition in
a generic setup: the pseudogap Kondo model where a quantum dot couples to
two-left (L) and right (R)-voltage-biased fermionic leads with power-law
density of states (DOS) with respect to their Fermi levels {\mu}_L/R,
{\rho}_c,L(R) ({\omega}) \propto |{\omega} - {\mu}_L(R) |r, and 0 < r < 1. In
equilibrium (zero bias voltage) and for 0 < r < 1/2, with increasing Kondo
correlations, in the presence of particle-hole symmetry this model exhibits a
quantum phase transition from a unscreened local moment (LM) phase to the Kondo
phase. Via a controlled frequency-dependent renormalization group (RG)
approach, we compute analytically and numerically the non-equilibrium
conductance, conduction electron T-matrix and local spin susceptibility at
finite bias voltages near criticality. The current-induced decoherence shows
distinct nonequilibrium scaling, leading to new universal non-equilibrium
quantum critical behaviors in the above observables. Relevance of our results
for the experiments is discussed.Comment: 4.1 pages, 2 figure
Extraction of nuclear matter properties from nuclear masses by a model of equation of state
The extraction of nuclear matter properties from measured nuclear masses is
investigated in the energy density functional formalism of nuclei. It is shown
that the volume energy and the nuclear incompressibility depend
essentially on , whereas the symmetry energy
and the density symmetry coefficient as well as symmetry incompressibility
depend essentially on , where
, and are the
neutron and proton chemical potentials respectively, the nuclear energy,
and the Coulomb energy. The obtained symmetry energy is ,
while other coefficients are uncertain within ranges depending on the model of
nuclear equation of state.Comment: 12 pages and 7 figure
Base reaction optimization of redundant manipulators for space applications
One of the problems associated with redundant manipulators which were proposed for space applications is that the reactions transmitted to the base of the manipulator as a result of the motion of the manipulator will cause undesirable effects on the dynamic behavior of the supporting space structure. It is therefore necessary to minimize the magnitudes of the forces and moments transmitted to the base. It is shown that kinematic redundancy can be used to solve the dynamic problem of minimizing the magnitude of the base reactions. The methodology described is applied to a four degree-of-freedom spatial manipulator with one redundant degree-of-freedom
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