38,181 research outputs found
Recommended from our members
E-government: A comparison of strategies in local authorities in the UK and Norway
In Europe almost all countries have implemented some form of e-government, not to mention the UK and Norway which are now both well into their sixth year of e-government implementation. These six years have seen various strategic plans formulated, implemented and also intermittently postponed in the two countries. Although time may result in the amplification of e-government experience for Norway and the UK, the postponement of implementation deadlines indicates that not only political and social issues, but also strategic and organisational issues need to be addressed when formulating plans for deploying e-government. Using empirical research this paper examines the strategies adopted by the UK and Norway in the context of aligning central and local government plans for implementing e-government services. While technical, political and social issues are considered as key areas to be addressed in any e-government exploitation plan; this paper examines how different perspectives on e-government definition, strategy, awareness and related organisational change influence implementation. The need to align central and local e-government plans, guidelines for local level implementation, user centred solutions, strong leadership and a common understanding of the definition of e-government are highlighted in the paper as some of the key components of good e-government implementation practice
Extending the random-phase approximation for electronic correlation energies: The renormalized adiabatic local density approximation
The adiabatic connection fluctuation-dissipation theorem with the random
phase approximation (RPA) has recently been applied with success to obtain
correlation energies of a variety of chemical and solid state systems. The main
merit of this approach is the improved description of dispersive forces while
chemical bond strengths and absolute correlation energies are systematically
underestimated. In this work we extend the RPA by including a parameter-free
renormalized version of the adiabatic local density (ALDA) exchange-correlation
kernel. The renormalization consists of a (local) truncation of the ALDA kernel
for wave vectors , which is found to yield excellent results for the
homogeneous electron gas. In addition, the kernel significantly improves both
the absolute correlation energies and atomization energies of small molecules
over RPA and ALDA. The renormalization can be straightforwardly applied to
other adiabatic local kernels.Comment: 5 page
Static correlation beyond the random phase approximation: Dissociating H2 with the Bethe-Salpeter equation and time-dependent GW
We investigate various approximations to the correlation energy of a H
molecule in the dissociation limit, where the ground state is poorly described
by a single Slater determinant. The correlation energies are derived from the
density response function and it is shown that response functions derived from
Hedin's equations (Random Phase Approximation (RPA), Time-dependent
Hartree-Fock (TDHF), Bethe-Salpeter equation (BSE), and Time-Dependent GW
(TDGW)) all reproduce the correct dissociation limit. We also show that the BSE
improves the correlation energies obtained within RPA and TDHF significantly
for intermediate binding distances. A Hubbard model for the dimer allow us to
obtain exact analytical results for the various approximations, which is
readily compared with the exact diagonalization of the model. Moreover, the
model is shown to reproduce all the qualitative results from the \textit{ab
initio} calculations and confirms that BSE greatly improves the RPA and TDHF
results despite the fact that the BSE excitation spectrum breaks down in the
dissociation limit. In contrast, Second Order Screened Exchange (SOSEX) gives a
poor description of the dissociation limit, which can be attributed to the fact
that it cannot be derived from an irreducible response function
Bright bichromatic entanglement and quantum dynamics of sum frequency generation
We investigate the quantum properties of the well-known process of sum
frequency generation, showing that it is potentially a very useful source of
non-classical states of the electromagnetic field, some of which are not
possible with the more common techniques. We show that it can produce
quadrature squeezed light, bright bichromatic entangled states and symmetric
and asymmetric demonstrations of the Einstein-Podolsky-Rosen paradox. We also
show that the semiclassical equations totally fail to describe the mean-field
dynamics when the cavity is strongly pumped
Preferences for and comprehension of original and readability-adapted materials
Running title: Preferences and comprehensionIncludes bibliographical references (leaves 41-42)Performed pursuant to contract no. 400-81-0030 of the National Institute of Educatio
Quantum ultra-cold atomtronics
It is known that a semi-classical analysis is not always adequate for
atomtronics devices, but that a fully quantum analysis is often necessary to
make reliable predictions. While small numbers of atoms at a small number of
sites are tractable using the density matrix, a fully quantum analysis is often
not straightforward as the system becomes larger. We show that the fully
quantum positive-P representation is then a viable calculational tool. We
postulate an atomtronic phase-gate consisting of four wells in a Bose-Hubbard
configuration, for which the semi-classical dynamics are controllable using the
phase of the atomic mode in one of the wells. We show that the quantum
predictions of the positive-P representation for the performance of this device
have little relation to those found semi-classically, and that the performance
depends markedly on the actual quantum states of the initially occupied modes.
We find that initial coherent states lead to closest to classical dynamics, but
that initial Fock states give results that are quite different. A fully quantum
analysis also opens the door for deeply quantum atomtronics, in which
properties such as entanglement and EPR (Einstein-Podolsky-Rosen) steering
become valuable technical properties of a device.Comment: 12 pages, 6 figures, submitted to Phys. Rev
A quantum correlated twin atom laser from a Bose-Hubbard system
We propose and evaluate a method to construct a quantum correlated twin atom
laser using a pumped and damped Bose-Hubbard inline trimer which can operate in
a stationary regime. With pumping via a source condensate filling the middle
well and damping using either an electron beam or optical means at the two end
wells, we show that bipartite quantum correlations build up between the ends of
the chain, and that these can be measured either in situ or in the outcoupled
beams. While nothing similar to our system has yet been achieved
experimentally, recent advances mean that it should be practically realisable
in the near future.Comment: 15 pages, 8 figures, theory. Typos fixed and material added to
introductio
Excitons in van der Waals heterostructures: The important role of dielectric screening
The existence of strongly bound excitons is one of the hallmarks of the newly
discovered atomically thin semi-conductors. While it is understood that the
large binding energy is mainly due to the weak dielectric screening in two
dimensions (2D), a systematic investigation of the role of screening on 2D
excitons is still lacking. Here we provide a critical assessment of a widely
used 2D hydrogenic exciton model which assumes a dielectric function of the
form {\epsilon}(q) = 1 + 2{\pi}{\alpha}q, and we develop a quasi-2D model with
a much broader applicability. Within the quasi-2D picture, electrons and holes
are described as in-plane point charges with a finite extension in the
perpendicular direction and their interaction is screened by a dielectric
function with a non-linear q-dependence which is computed ab-initio. The
screened interaction is used in a generalized Mott-Wannier model to calculate
exciton binding energies in both isolated and supported 2D materials. For
isolated 2D materials, the quasi-2D treatment yields results almost identical
to those of the strict 2D model and both are in good agreement with ab-initio
many-body calculations. On the other hand, for more complex structures such as
supported layers or layers embedded in a van der Waals heterostructure, the
size of the exciton in reciprocal space extends well beyond the linear regime
of the dielectric function and a quasi-2D description has to replace the 2D
one. Our methodology has the merit of providing a seamless connection between
the strict 2D limit of isolated monolayer materials and the more bulk-like
screening characteristics of supported 2D materials or van der Waals
heterostructures.Comment: 14 pages, 13 figure
Multiquark Hadrons
A number of candidate multiquark hadrons, i.e., particle resonances with
substructures that are more complex than the quark-antiquark mesons and
three-quark baryons that are prescribed in the textbooks, have recently been
observed. In this talk I present: some recent preliminary BESIII results on the
near-threshold behavior of sigma(e+e- --> Lambda Lambda-bar) that may or may
not be related to multiquark mesons in the light- and strange-quark sectors;
results from Belle and LHCb on the electrically charged, charmoniumlike
Z(4430)^+ --> pi^+ psi ' resonance that necessarily has a four-quark
substructure; and the recent LHCb discovery of the P_c(4380) and P_c(4450)
hidden-charm resonances seen as a complex structure in the J/psi p invariant
mass distribution for Lambda_b --> K^-J/psi p decays and necessarily have a
five-quark substructure and are, therefore, prominent candidates for pentaquark
baryons.Comment: 12 pages, 9 figures, summary of a talk presented at the 12th
Conference on Hypernuclear and Strange Particle Physics (HYP2015), September
7-12, 2015 Sendai, JAPAN. To appear in the JPS Conference proceeding
- …