14,858 research outputs found
Damping-Antidamping Effect on Comets Motion
We make an observation about Galilean transformation on a 1-D mass variable
systems which leads us to the right way to deal with mass variable systems.
Then using this observation, we study two-bodies gravitational problem where
the mass of one of the bodies varies and suffers a damping-antidamping effect
due to star wind during its motion. For this system, a constant of motion, a
Lagrangian and a Hamiltonian are given for the radial motion, and the period of
the body is studied using the constant of motion of the system. Our theoretical
results are applied to Halley's comet.Comment: 19 pages, 5 figures. arXiv admin note: substantial text overlap with
arXiv:0910.468
Study of the double non linear quantum resonances in diatomic molecules
We study the quantum dynamics of diatomic molecule driven by a circularly
polarized resonant electric field. We look for a quantum effect due to
classical chaos appearing due to the overlapping of nonlinear resonances
associated to the vibrational and rotational motion. We solve the Schr\"odinger
equation associated with the wave function expanded in term of proper
stationary states, (vibrationalangular momentum
states). Looking for quantum-classic correspondence, we consider the Liouville
dynamics in the two dimensional phase space defined by the coherent -like state
of vibrational states, and it is found some similarities when the quantum
dynamics is pictured in terms of number and phase operators.Comment: 15 pages, 4 figure
A new sensorless method for switched reluctance motor drives
This paper describes a new method for indirect sensing of the rotor position in switched reluctance motors (SRMs) using pulse width modulation voltage control. The detection method uses the change of the derivative of the phase current to detect the position where a rotor pole and stator pole start to overlap, giving one position update per energy conversion. As no a priori knowledge of motor parameters is required (except for the numbers of stator and rotor poles), the method is applicable to most SRM topologies in a wide power and speed range and for several inverter topologies. The method allows modest closed-loop dynamic performance. To start up the motor, a feedforward stepping method is used which assures robust startup (even under load) from standstill to a predefined speed at which closed-loop sensorless operation can be applied. Experimental results demonstrate the robust functionality of the method with just one current sensor in the inverter, even with excitation overlap, and the sensorless operation improves with speed. The method is comparable to the back-EMF position estimation for brushless DC motors in principle, performance and cost. A detailed operation and implementation of this scheme is shown, together with steady-state and dynamic transient test results
An ab-initio converse NMR approach for pseudopotentials
We extend the recently developed converse NMR approach [T. Thonhauser, D.
Ceresoli, A. Mostofi, N. Marzari, R. Resta, and D. Vanderbilt, J. Chem. Phys.
\textbf{131}, 101101 (2009)] such that it can be used in conjunction with
norm-conserving, non-local pseudopotentials. This extension permits the
efficient ab-initio calculation of NMR chemical shifts for elements other than
hydrogen within the convenience of a plane-wave pseudopotential approach. We
have tested our approach on several finite and periodic systems, finding very
good agreement with established methods and experimental results.Comment: 11 pages, 2 figures, 4 tables; references expande
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