100 research outputs found
High-Current Field Emission from an Atomic Quantum Wire
Linear chains of carbon atoms have been proposed as the electron emitting
structures of open tip carbon nanotubes subject to an electric field. To better
understand the implications of the results of Smalley and collaborators, the
electromagnetic response of linear carbon chains to both static and dynamics
fields have been studied, making use of ab-initio methods. It is found that the
associated emission currents, plotted as a function of the bias potential,
follow Fowler-Nordheim intensity-voltage curves typical of the field emission
of metallic tips. Under standard bias conditions, linear carbon chains of one
nanometer of length are expected to deliver currents of the order of one
microampere. These systems behave, furthermore, as conducting needles in
photoabsorption processes. Linear carbon chains are thus likely to constitute
the ultimate atomic-scale realization of metallic wires.Comment: 10 pages, 4 figures, RevTe
Electron-Phonon Coupling in Charged Buckminsterfullerene
A simple, yet accurate solution of the electron-phonon coupling problem in
C_{60} is presented. The basic idea behind it is to be found in the
parametrization of the ground state electronic density of the system calculated
making use of ab-initio methods, in term of sp hybridized orbitals.
This parametrization allows for an economic determination of the deformation
potential associated with the fullerene's normal modes. The resulting
electron-phonon coupling constants are used to calculate Jahn-Teller effects in
C_{60}^-, and multiple satellite peaks in the corresponding photoemission
reaction. Theory provides an accurate account of the experimental findings.Comment: 11 pages, 3 figures. Accepted for publication in Chem. Phys. Let
Impact of Exchange Rate Deregulation on manufacturing Sector Performance in Nigeria
The study examined the impact of exchange rate
deregulation on manufacturing output performance in
Nigeria over the period 1980 to 2016. The normalized cointegration
technique was used to test for long-run
relationship between exchange rate and manufacturing
output while the granger causality test was used to ascertain
the direction of causality between them. Also, the error
correction mechanism (ECM) was used to calculate the
speed of adjustment of the model to short-run disequilibrium
condition. The empirical findings revealed that exchange
rate has non-significant positive long-run effect on
manufacturing industry output. However, unidirectional
causal impact of exchange rate on manufacturing output was
established using the pairwise granger causality test. Based
on the above result, it is recommended that in discharging
the mandate of exchange rate management, the monetary
authorities should aim at stabilizing exchange rate through
the use of appropriate monetary policy tools as well as
support export diversification programmes in order to
enhance foreign exchange inflo
Impact of Exchange Rate Deregulation on Manufacturing Sector Performance in Nigeria
The study examined the impact of exchange rate deregulation on manufacturing output performance in Nigeria over the period 1980 to 2016. The normalized co-integration technique was used to test for long-run relationship between exchange rate and manufacturing output while the granger causality test was used to ascertain the direction of causality between them. Also, the error correction mechanism (ECM) was used to calculate the speed of adjustment of the model to short-run disequilibrium condition. The empirical findings revealed that exchange rate has non-significant positive long-run effect on manufacturing industry output. However, unidirectional causal impact of exchange rate on manufacturing output was established using the pairwise granger causality test. Based on the above result, it is recommended that in discharging the mandate of exchange rate management, the monetary authorities should aim at stabilizing exchange rate through the use of appropriate monetary policy tools as well as support export diversification programmes in order to enhance foreign exchange inflow
Extreme current measurements using a fibre optics current sensor
We demonstrate that an optical fibre current sensor can measure current over 500 kA with an accuracy of 0.2%. This level of accuracy has never previously been achieved using a traditional non-optical senso
C in intense femtosecond laser pulses: nonlinear dipole response and ionization
We study the interaction of strong femtosecond laser pulses with the C
molecule employing time-dependent density functional theory with the ionic
background treated in a jellium approximation. The laser intensities considered
are below the threshold of strong fragmentation but too high for perturbative
treatments such as linear response. The nonlinear response of the model to
excitations by short pulses of frequencies up to 45eV is presented and analyzed
with the help of Kohn-Sham orbital resolved dipole spectra. In femtosecond
laser pulses of 800nm wavelength ionization is found to occur multiphoton-like
rather than via excitation of a ``giant'' resonance.Comment: 14 pages, including 1 table, 5 figure
Photoionization of the fullerene ion C60+
Photoionization cross section of the fullerene ion C60+ has been calculated
within a single-electron approximation and also by using a consistent many-body
theory accounting for many-electron correlations.Comment: 8 pages, 3 figure
Formalism for Multiphoton Plasmon Excitation in Jellium Clusters
We present a new formalism for the description of multiphoton plasmon
excitation processes in jellium clusters. By using our method, we demonstrate
that, in addition to dipole plasmon excitations, the multipole plasmons
(quadrupole, octupole, etc) can be excited in a cluster by multiphoton
absorption processes, which results in a significant difference between plasmon
resonance profiles in the cross sections for multiphoton as compared to
single-photon absorption. We calculate the cross sections for multiphoton
absorption and analyse the balance between the surface and volume plasmon
contributions to multipole plasmons.Comment: 29 pages, 1 figur
Ionic and electronic structure of sodium clusters up to N=59
We determined the ionic and electronic structure of sodium clusters with even
electron numbers and 2 to 59 atoms in axially averaged and three-dimensional
density functional calculations. A local, phenomenological pseudopotential that
reproduces important bulk and atomic properties and facilitates structure
calculations has been developed. Photoabsorption spectra have been calculated
for , , and to
. The consistent inclusion of ionic structure considerably
improves agreement with experiment. An icosahedral growth pattern is observed
for to . This finding is supported by
photoabsorption data.Comment: To appear in Phys. Rev. B 62. Version with figures in better quality
can be requested from the author
Application of time-dependent density functional theory to optical activity
As part of a general study of the time-dependent local density approximation
(TDLDA), we here report calculations of optical activity of chiral molecules.
The theory automatically satisfies sum rules and the Kramers-Kronig relation
between circular dichroism and optical rotatory power. We find that the theory
describes the measured circular dichroism of the lowest states in methyloxirane
with an accuracy of about a factor of two. In the chiral fullerene C_76 the
TDLDA provides a consistent description of the optical absorption spectrum, the
circular dichroism spectrum, and the optical rotatory power, except for an
overall shift of the theoretical spectrum.Comment: 17 pages and 13 PostScript figure
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