18,705 research outputs found
A unified approach to exact solutions of time-dependent Lie-algebraic quantum systems
By using the Lewis-Riesenfeld theory and the invariant-related unitary
transformation formulation, the exact solutions of the {\it time-dependent}
Schr\"{o}dinger equations which govern the various Lie-algebraic quantum
systems in atomic physics, quantum optics, nuclear physics and laser physics
are obtained. It is shown that the {\it explicit} solutions may also be
obtained by working in a sub-Hilbert-space corresponding to a particular
eigenvalue of the conserved generator ({\it i. e.}, the {\it time-independent}
invariant) for some quantum systems without quasi-algebraic structures. The
global and topological properties of geometric phases and their adiabatic limit
in time-dependent quantum systems/models are briefly discussed.Comment: 11 pages, Latex. accepted by Euro. Phys. J.
Influence of skew and cross-coupling on flux-weakening performance of permanent-magnet brushless AC machines
A method is proposed for predicting the flux-weakening performance of permanent-magnet (PM) brushless ac machines accounting for skew and d-q axis cross-coupling. The method is based on a d-q-axis flux-linkage model, a hybrid 2-D finite-element (FE)-analytical method being used to predict the d- and q-axis inductances. However, it only requires 2-D FE analysis of the magnetic field distribution over a cross section of the machine. The developed method is used to predict the torque-speed characteristic of an interior PM brushless ac machine with one stator slot-pitch skew. This is compared with predictions from a direct FE analysis of the machine and validated by measurements
Ultra-compact structure in intermediate-luminosity radio quasars: building a sample of standard cosmological rulers and improving the dark energy constraints up to
In this paper, we present a new compiled milliarcsecond compact radio data
set of 120 intermediate-luminosity quasars in the redshift range . These quasars show negligible dependence on redshifts and intrinsic
luminosity, and thus represents, in the standard model of cosmology, a fixed
comoving-length of standard ruler. We implement a new cosmology-independent
technique to calibrate the linear size of of this standard ruler as pc, which is the typical radius at which AGN jets become opaque
at the observed frequency GHz. In the framework of flat
CDM model, we find a high value of the matter density parameter,
, and a low value of the Hubble constant,
, which is in excellent
agreement with the CMB anisotropy measurements by \textit{Planck}. We obtain
, at 68.3% CL
for the constant of a dynamical dark-energy model, which demonstrates no
significant deviation from the concordance CDM model. Consistent
fitting results are also obtained for other cosmological models explaining the
cosmic acceleration, like Ricci dark energy (RDE) or Dvali-Gabadadze-Porrati
(DGP) brane-world scenario. While no significant change in with redshift is
detected, there is still considerable room for evolution in and the
transition redshift at which departing from -1 is located at .
Our results demonstrate that the method extensively investigated in our work on
observational radio quasar data can be used to effectively derive cosmological
information. Finally, we find the combination of high-redshift quasars and
low-redshift clusters may provide an important source of angular diameter
distances, considering the redshift coverage of these two astrophysical probes.Comment: 36 pages, 5 tables, 16 figures, A&A, in pres
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