888 research outputs found
The air quality impact of cordon and distance based road user charging: an empirical study of Leeds, U.K
Traffic assignment, pollutant emission and dispersion models were applied to a major UK city so as to assess the air quality impacts of five road pricing schemes. Schemes were evaluated with reference to: exceedence of air quality standards for six pollutants; greenhouse gas emission; redistribution of pollution, an environmental justice concern; and road network performance as traffic speed and trip distance. Results were compared to alternatives of do nothing, network development and clean fuel promotion. The air quality benefits of a modest distance based charge are highlighted. However, whilst road pricing shows potential as an air quality management tool, its value and suitability are strongly sensitive to prior air quality and emission source apportionment in the application city
Parastatal development - institutional strengthening
When the World Bank financed BKS technical assistance team arrived at the Water and Sewerage Authority of Lesotho (WASA) in 1994 it was evident that the organisation was facing three main obstacles to the sustainability of the organisation:
âą absence of a proper planning function;
âą financial frailty; and
âą limited institutional capacity.
This paper illustrates the problems, discusses how solutions have been approached and the extent to which
strategies have been successful
Worst case and probabilistic analysis of the 2-Opt algorithm for the TSP
2-Opt is probably the most basic local search heuristic for the TSP. This heuristic achieves amazingly good results on âreal worldâ Euclidean instances both with respect to running time and approximation ratio. There are numerous experimental studies on the performance of 2-Opt. However, the theoretical knowledge about this heuristic is still very limited. Not even its worst case running time on 2-dimensional Euclidean instances was known so far. We clarify this issue by presenting, for every pâN , a family of L p instances on which 2-Opt can take an exponential number of steps.
Previous probabilistic analyses were restricted to instances in which n points are placed uniformly at random in the unit square [0,1]2, where it was shown that the expected number of steps is bounded by O~(n10) for Euclidean instances. We consider a more advanced model of probabilistic instances in which the points can be placed independently according to general distributions on [0,1] d , for an arbitrary dâ„2. In particular, we allow different distributions for different points. We study the expected number of local improvements in terms of the number n of points and the maximal density Ï of the probability distributions. We show an upper bound on the expected length of any 2-Opt improvement path of O~(n4+1/3â
Ï8/3) . When starting with an initial tour computed by an insertion heuristic, the upper bound on the expected number of steps improves even to O~(n4+1/3â1/dâ
Ï8/3) . If the distances are measured according to the Manhattan metric, then the expected number of steps is bounded by O~(n4â1/dâ
Ï) . In addition, we prove an upper bound of O(Ïâd) on the expected approximation factor with respect to all L p metrics.
Let us remark that our probabilistic analysis covers as special cases the uniform input model with Ï=1 and a smoothed analysis with Gaussian perturbations of standard deviation Ï with ÏâŒ1/Ï d
Crystallization of a classical two-dimensional electron system: Positional and orientational orders
Crystallization of a classical two-dimensional one-component plasma
(electrons interacting with the Coulomb repulsion in a uniform neutralizing
positive background) is investigated with a molecular dynamics simulation. The
positional and the orientational correlation functions are calculated for the
first time. We have found an indication that the solid phase has a
quasi-long-range (power-law) positional order along with a long-range
orientational order. This indicates that, although the long-range Coulomb
interaction is outside the scope of Mermin's theorem, the absence of ordinary
crystalline order at finite temperatures applies to the electron system as
well. The `hexatic' phase, which is predicted between the liquid and the solid
phases by the Kosterlitz-Thouless-Halperin-Nelson-Young theory, is also
discussed.Comment: 3 pages, 4 figures; Corrected typos; Double columne
Quasiparticlelike peaks, kinks, and electron phonon coupling at the pi,0 regions in the CMR oxide La2 2xSr1 2xMn2O7
Using Angle Resolved Photoemission ARPES , we present the first observation of sharp quasiparticle like peaks in a CMR manganite. We focus on the pi,0 regions of k space and study their electronic scattering rates and dispersion kinks, uncovering the critical energy scales, momentum scales, and strengths of the interactions that renormalize the electrons. To identify these bosons we measured phonon dispersions in the energy range of the kink by inelastic neutron scattering INS , finding a good match in both energy and momentum to the oxygen bond stretching phonon
Competition of charge, orbital, and ferromagnetic correlations in layered manganites
The competition of charge, orbital, and ferromagnetic interactions in layered
manganites is investigated by magneto-Raman scattering spectroscopy. We find
that the colossal magnetoresistance effect in the layered compounds results
from the interplay of the orbital and ferromagnetic double-exchange
correlations. Inelastic scattering by charge-order fluctuations dominates the
quasiparticle dynamics in the ferromagnetic-metal state. The scattering is
suppressed at low frequencies, consistent with the opening of a charge-density
wave pseudogap.Comment: 10 pages, 4 figure
On the spherical-axial transition in supernova remnants
A new law of motion for supernova remnant (SNR) which introduces the quantity
of swept matter in the thin layer approximation is introduced. This new law of
motion is tested on 10 years observations of SN1993J. The introduction of an
exponential gradient in the surrounding medium allows to model an aspherical
expansion. A weakly asymmetric SNR, SN1006, and a strongly asymmetric SNR,
SN1987a, are modeled. In the case of SN1987a the three observed rings are
simulated.Comment: 19 figures and 14 pages Accepted for publication in Astrophysics &
Space Science in the year 201
Work function changes in the double layered manganite La1.2Sr1.8Mn2O7
We have investigated the behaviour of the work function of La1.2Sr1.8Mn2O7 as
a function of temperature by means of photoemission. We found a decrease of 55
+/- 10 meV in going from 60 K to just above the Curie temperature (125 K) of
the sample. Above T_C the work function appears to be roughly constant. Our
results are exactly opposite to the work function changes calculated from the
double-exchange model by Furukawa, but are consistent with other measurements.
The disagreement with double-exchange can be explained using a general
thermodynamic relation valid for second order transitions and including the
extra processes involved in the manganites besides double-exchange interaction.Comment: 6 pages, 4 figures included in tex
Ab initio and finite-temperature molecular dynamics studies of lattice resistance in tantalum
This manuscript explores the apparent discrepancy between experimental data
and theoretical calculations of the lattice resistance of bcc tantalum. We
present the first results for the temperature dependence of the Peierls stress
in this system and the first ab initio calculation of the zero-temperature
Peierls stress to employ periodic boundary conditions, which are those best
suited to the study of metallic systems at the electron-structure level. Our ab
initio value for the Peierls stress is over five times larger than current
extrapolations of experimental lattice resistance to zero-temperature. Although
we do find that the common techniques for such extrapolation indeed tend to
underestimate the zero-temperature limit, the amount of the underestimation
which we observe is only 10-20%, leaving open the possibility that mechanisms
other than the simple Peierls stress are important in controlling the process
of low temperature slip.Comment: 12 pages and 9 figure
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