5,889 research outputs found
Convergence rates of the DPG method with reduced test space degree
This paper presents a duality theorem of the Aubin-Nitsche type for
discontinuous Petrov Galerkin (DPG) methods. This explains the numerically
observed higher convergence rates in weaker norms. Considering the specific
example of the mild-weak (or primal) DPG method for the Laplace equation, two
further results are obtained. First, the DPG method continues to be solvable
even when the test space degree is reduced, provided it is odd. Second, a
non-conforming method of analysis is developed to explain the numerically
observed convergence rates for a test space of reduced degree
Characterization of polyacrylonitrile ultrafiltration membranes
Various methods have been used to characterize ultrafiltration membranes, such as gas flux measurements, (field emission) scanning electron microscopy, permporometry and liquid-liquid displacement. Significant differences in the pore size distributions determined from permporometry and liquid-liquid displacement were found
A population of high-velocity absorption-line systems residing in the Local Group
Aims. We aim to investigate the ionisation conditions and distances of
Galactic high-velocity clouds (HVCs) in the Galactic halo and beyond in the
direction of the Local Group (LG) barycentre and anti-barycentre, by studying
spectral data of 29 extragalactic background sources obtained with Cosmic
Origins Spectropgraph (COS) installed on the Hubble Space Telescope (HST).
Methods. We model column-densities of low, intermediate, and high ions, such as
Si II, C II, Si III, Si IV, and C IV and use this to construct a set of Cloudy
ionisation models. Results. In total, we found 69 high-velocity absorption
components along the 29 lines of sight. The ones in the direction of the LG
barycentre span the entire range of studied velocities, 100 \lesssim
|v_{LSR}|\lesssim 400 km s^-1, while the anti-barycentre sample has velocities
up to about 300 km s^-1. For 49 components, we infer the gas densities. In the
direction of the LG barycentre, the gas densities exhibit a large range between
log n_H=-3.96 to -2.55, while in the anti-barycentre direction the densities
are systematically higher, log n_H>-3.25. The barycentre absorbers can be split
into two groups based on their density: a high density group with log
n_H>-3.54, which can be affected by the Milky Way radiation field, and a low
density group (log n_H \leq -3.54). The latter has very low thermal pressures
of P/k<7.3 K cm^-3. Conclusions. Our study shows that part of the absorbers in
the LG barycentre direction trace gas at very low gas densities and thermal
pressures. Such properties indicate that these absorbers are located beyond the
virial radius of the Milky Way. Our study also confirms results from earlier,
single-sightline studies, suggesting the presence of a metal-enriched
intragroup medium filling the LG near its barycentre.Comment: Accepted for publication in A&A. 12 pages, 11 figure
A General Overview of Environmental Liability and Pollution Prevention
This paper focusses mainly on environmental liability. However, when the behavioral consequences of liabilities are studied and strategic decision-making processes are described, other incentives to take environmental care are identified. As governments, like the Dutch government, increasingly aim to rely on changing the behavior of organizations by indirect and voluntary regulations, there is a need for more empirical data on actual decision-making processes within organizations and the way in which "environmental" aspects are dealt with. The paper describes some preliminary results of a study within the Dutch electricity sector
Soil survey and the study of water in unsaturated soil : simplified theory and some case studies
Stiboka onderzoe
Analysis of reinforced concrete structures with occurrence of discrete cracks at arbitrary positions
A nonlinear analysis of in-plane loaded plates is presented, which eliminates the disadvantages of the smeared crack approach. The elements used and the computational method are discussed. An example is shown in which one or more discrete cracks are dominant
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