6,086 research outputs found
Do the A4c60 Fullerides Have a Broken-Symmetry Ground State?
Band theory predicts both K3C60 and K4C60 to be metals; various experimental
probes show that while K3C60 is indeed metallic, K4C60 appears to be
insulating. The standard view of this apparent failure of the single-particle
picture is that electron correlation is predominant. We describe an alternative
scenario, motivated on theoretical grounds, which invokes a spin- or
charge-density-wave state to explain the observed insulating behavior.Comment: 9 pages + 3 figures, REVTeX 3.
Important role of alkali atoms in A4C60
We show that hopping via the alkali atoms plays an important role for the t1u
band of A4C60 (A=K, Rb), in strong contrast to A3C60. Thus the t1u band is
broadened by more than 40 % by the presence of the alkali atoms. The difference
between A4C60 and A3C60 is in particular due to the less symmetric location of
the alkali atoms in A4C60.Comment: 5 pages, revtex, 2 figures, submitted to Phys. Rev. B more
information at http://www.mpi-stuttgart.mpg.de/dokumente/andersen/fullerene
Reformulation of the LDA+U method for a local orbital basis
We present a new approach to the evaluation of the on-site repulsion energy U
for use in the LDA+U method of Anisimov and collaborators. Our objectives are
to make the method more firmly based, to concentrate primarily on ground state
properties rather than spectra, and to test the method in cases where only
modest changes in orbital occupations are expected, as well as for highly
correlated materials. Because of these objectives, we employ a differential
definition of U. We also define a matrix U, which we find is very dependent on
the environment of the atom in question. The formulation is applied to evaluate
U for transition metal monoxides from VO to NiO using a local orbital basis
set. The resulting values of U are typically only 40-65% as large as values
currently in use. We evaluate the U matrix for the e_g and t_{2g} subshells in
paramagnetic FeO, and illustrate the very different charge response of the e_g
and t_{2g} states. The sensitivity of the method to the choice of the d
orbitals, and to the basis set in general, is discussed.Comment: 6 figure
Bioinspired auditory sound localisation for improving the signal to noise ratio of socially interactive robots
In this paper we describe a bioinspired hybrid architecture for acoustic sound source localisation and tracking to increase the signal to noise ratio (SNR) between speaker and background sources for a socially interactive robot's speech recogniser system. The model presented incorporates the use of Interaural Time Differ- ence for azimuth estimation and Recurrent Neural Net- works for trajectory prediction. The results are then pre- sented showing the difference in the SNR of a localised and non-localised speaker source, in addition to presenting the recognition rates between a localised and non-localised speaker source. From the results presented in this paper it can be seen that by orientating towards the sound source of interest the recognition rates of that source can be in- creased
Depreciation, Deterioration and Obsolescence when there is Embodied or Disembodied Technical Change
The paper considers how to measure capital in a model where technical progress is either embodied in new units of capital or it is "disembodied" and simply causes the price of capital services to fall. The disembodied case is considered in sections 2-4. Sections 2 and 3 set out standard vintage capital aggregation models when there is no embodied technical progress. Section 4 discusses disembodied obsolescence in more detail. Section 5 introduces new (more efficient) models of the capital good so that technical progress is embodied in the new models. Section 6 shows how the parameters in the Jorgenson model of capital services could be estimated by statistical agencies if their investment surveys covered sales and retirements of used assets as well as purchases of new assets. Section 7 concludes.Aggregation of Capital, embodiment of technical progress, depreciation, deterioration, obsolescence, index number theory
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