1,776 research outputs found
A cost-benefit analysis of tunnel investment and tolling alternatives in Antwerp
A proposal has been made to build a new tunnel under the Scheldt river near the centre of Antwerp in
order to relieve traffic congestion on the ring road and in an existing tunnel. The new tunnel is expected
to cost more than €1 billion, and tolls have been suggested to help finance construction and to manage
demand. This paper conducts a preliminary cost-benefit analysis of a new tunnel and three alternative
tolling schemes, and compares them with a do-nothing scenario and an option to toll the existing tunnel
without building a new one. The two tunnels are treated as imperfect substitutes, and a multi-year
accounting framework is adopted that accounts for emissions, accidents and noise externalities, road
damage, revenues accruing to the national and regional governments from existing transport user charges,
and the salvage value of the new tunnel. With the base-case parameter values it is found that building the
tunnel is worthwhile with all three tolling regimes and yields a higher benefit than not building the tunnel
and tolling the old one. Nevertheless, the net benefit from building the tunnel differs appreciably between
tolling regimes, and it is sensitive to the value assumed for the marginal cost of public funds
Oogst, opslag en voedering van snijmais in Noord-Italie : verslag van een studiereis in september 1972
Door de stormachtige ontwikkeling van snijmais komen veel vragen naar voren. Het is daarom nuttig zich te orienteren in landen waar de snijmaisteelt al jaren lang een grote omvang heeft. In dit artikel wordt een korte studiereis naar Italië beschreven. Deze reis werd gemaakt met het doel zich op de hoogte te stellen van de ontwikkelingen bij de oogst, de opslag en de voedering van snijmai
Properties of Semi-Chiral Superfields
Whenever the N=(2,2) supersymmetry algebra of non-linear sigma-models in two
dimensions does not close off-shell, a holomorphic two-form can be defined. The
only known superfields providing candidate auxiliary fields to achieve an
off-shell formulation are semi-chiral fields. Such a semi-chiral description is
only possible when the two-form is constant. Using an explicit example,
hyper-Kahler manifolds, we show that this is not always the case. Finally, we
give a concrete construction of semi-chiral potentials for a class of
hyper-Kahler manifolds using the duality exchanging a pair consisting of a
chiral and a twisted-chiral superfield for one semi-chiral multiplet.Comment: LaTeX, 17 page
Optical modeling of plasma-deposited ZnO films : electron scattering at different length scales
In this work, an optical modeling study on electron scattering mechanisms in plasma-deposited ZnO layers is presented. Because various applications of ZnO films pose a limit on the electron carrier density due to its effect on the film transmittance, higher electron mobility values are generally preferred instead. Hence, insights into the electron scattering contributions affecting the carrier mobility are required. In optical models, the Drude oscillator is adopted to represent the free-electron contribution and the obtained optical mobility can be then correlated with the macroscopic material properties. However, the influence of scattering phenomena on the optical mobility depends on the considered range of photon energy. For example, the grain-boundary scattering is generally not probed by means of optical measurements and the ionized-impurity scattering contribution decreases toward higher photon energies. To understand this frequency dependence and quantify contributions from different scattering phenomena to the mobility, several case studies were analyzed in this work by means of spectroscopic ellipsometry and Fourier transform infrared (IR) spectroscopy. The obtained electrical parameters were compared to the results inferred by Hall measurements. For intrinsic ZnO (i-ZnO), the in-grain mobility was obtained by fitting reflection data with a normal Drude model in the IR range. For Al-doped ZnO (Al:ZnO), besides a normal Drude fit in the IR range, an Extended Drude fit in the UV-vis range could be used to obtain the in-grain mobility. Scattering mechanisms for a thickness series of Al:ZnO films were discerned using the more intuitive parameter "scattering frequency" instead of the parameter "mobility". The interaction distance concept was introduced to give a physical interpretation to the frequency dependence of the scattering frequency. This physical interpretation furthermore allows the prediction of which Drude models can be used in a specific frequency range
A layered model for non-thermal radio emission from single O stars
We present a model for the non-thermal radio emission from bright O stars, in
terms of synchrotron emission from wind-embedded shocks. The model is an
extension of an earlier one, with an improved treatment of the cooling of
relativistic electrons. This improvement limits the synchrotron-emitting volume
to a series of fairly narrow layers behind the shocks. We show that the width
of these layers increases with increasing wavelength, which has important
consequences for the shape of the spectrum. We also show that the strongest
shocks produce the bulk of the emission, so that the emergent radio flux can be
adequately described as coming from a small number of shocks, or even from a
single shock.
A single shock model is completely determined by four parameters: the
position of the shock, the compression ratio and velocity jump of the shock,
and the surface magnetic field. Applying a single shock model to the O5 If star
Cyg OB2 No. 9 allows a good determination of the compression ratio and shock
position and, to a lesser extent, the magnetic field and velocity jump.
Our main conclusion is that strong shocks need to survive out to distances of
a few hundred stellar radii. Even with multiple shocks, the shocks needed to
explain the observed emission are stronger than predictions from time-dependent
hydrodynamical simulations.Comment: 10 pages, 5 figures, accepted by Astronomy and Astrophysic
Quasi-simultaneous XMM-Newton and VLA observation of the non-thermal radio emitter HD\168112 (O5.5III(f^+))
We report the results of a multiwavelength study of the non-thermal radio
emitter HD168112 (O5.5III(f^+)). The detailed analysis of two
quasi-simultaneous XMM-Newton and VLA observations reveals strong variability
of this star both in the X-ray and radio ranges. The X-ray observations
separated by five months reveal a decrease of the X-ray flux of ~30%. The radio
emission on the other hand increases by a factor 5-7 between the two
observations obtained roughly simultaneously with the XMM-Newton pointings. The
X-ray data reveal a hard emission that is most likely produced by a thermal
plasma at kT ~2-3 keV while the VLA data confirm the non-thermal status of this
star in the radio waveband. Comparison with archive X-ray and radio data
confirms the variability of this source in both wavelength ranges over a yet
ill defined time scale. The properties of HD168112 in the X-ray and radio
domain point towards a binary system with a significant eccentricity and an
orbital period of a few years. However, our optical spectra reveal no
significant changes of the star's radial velocity suggesting that if HD168112
is indeed a binary, it must be seen under a fairly low inclination.Comment: 17 pages, 11 figures (10 postscript + 1 gif
The Two Forms of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Activase Differ in Sensitivity to Elevated Temperature
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