Stiffness modeling of robotic manipulator with gravity compensator

The paper focuses on the stiffness modeling of robotic manipulators with gravity compensators. The main attention is paid to the development of the stiffness model of a spring-based compensator located between sequential links of a serial structure. The derived model allows us to describe the compensator as an equivalent non-linear virtual spring integrated in the corresponding actuated joint. The obtained results have been efficiently applied to the stiffness modeling of a heavy industrial robot of the Kuka family

Vanishing Hawking Radiation from a Uniformly Accelerated Black Hole

We consider quantum fields around uniformly accelerated black holes. At a particular value of the acceleration, the Bogolubov transformation which would be responsible for the late-time Hawking radiation, is found to be trivial. When this happens, Hawking's thermal radiation, Doppler-shifted or not, is absent to the asymptotic inertial observers despite the nonzero Hawking temperature, while the co-moving observers find the black hole radiance exactly balanced by the acceleration heat bath. After a brief comparison to the classical system of a uniformly accelerated charge, we close with two important comments. (Phys. Rev. Lett. 75 (1995) 382)Comment: LaTeX, 10pages, 2 figures (a typo in Eq.(3) corrected; minor revisions to accomodate the length limitation of the journal

Suppression of ferromagnetic ordering in doped manganites: Effects of the superexchange interaction

From a Monte Carlo study of the ferromagnetic Kondo lattice model for doped manganites, including the antiferromagnetic superexchange interaction ($J_{AF}$), we found that the ferromagnetic ordering was suppressed as $J_{AF}$ increased. The ferromagnetic transition temperature $T_c$, as obtained from a mean field fit to the calculated susceptibilities, was found to decrease monotonically with increasing $J_{AF}$. Further, the suppression in $T_c$ scales with the bandwidth narrowing induced by the antiferromagnetic frustration originating from $J_{AF}$. From these results, we propose that the change in the superexchange interaction strength between the $t_{2g}$ electrons of the Mn ions is one of the mechanisms responsible for the suppression in $T_c$ observed in manganites of the type (La$_{0.7-y}$Pr$_{y}$)Ca$_{0.3}$MnO$_3$.Comment: 5 pages, 6 figures. To appear in PR

Interaction induced ferro-electricity in the rotational states of polar molecules

We show that a ferro-electric quantum phase transition can be driven by the dipolar interaction of polar molecules in the presence a micro-wave field. The obtained ferro-electricity crucially depends on the harmonic confinement potential, and the resulting dipole moment persists even when the external field is turned off adiabatically. The transition is shown to be second order for fermions and for bosons of a smaller permanent dipole moment, but is first order for bosons of a larger moment. Our results suggest the possibility of manipulating the microscopic rotational state of polar molecules by tuning the trap's aspect ratio (and other mesoscopic parameters), even though the later's energy scale is smaller than the former's by six orders of magnitude.Comment: 4 pages and 4 figure

On the Nonlocal Equations and Nonlocal Charges Associated with the Harry Dym Hierarchy

A large class of nonlocal equations and nonlocal charges for the Harry Dym hierarchy is exhibited. They are obtained from nonlocal Casimirs associated with its bi-Hamiltonian structure. The Lax representation for some of these equations is also given.Comment: to appear in Journal of Mathematical Physics, 17 pages, Late

Anomalous spin susceptibility and magnetic polaron formation in the double exchange systems

The magnetic susceptibility and spin-spin correlation of the double-exchange model for doped manganites are investigated through the Monte Carlo calculations on the three-dimensional lattice model. Deviations of the susceptibility from the Curie-Weiss behavior above the ferromagnetic ordering temperature $T_c$ seem to indicate a formation of local ferromagnetic clusters in the vicinity of $T_c$, which is consistent with recent electron paramagnetic resonance experiments for La$_{2/3}$Ca$_{1/3}$MnO$_3$. A further analysis of the spin-spin correlations show the ferromagnetic cluster size to be three-to-four lattice spacings, suggesting that the charge carriers may form magnetic polarons.Comment: 5 pages, 5 figures, Late