99 research outputs found
Large scale environmental bias of the QSO line of sight proximity effect
We analyse the proximity zone of the intergalactic matter around
high-redshift quasars in a cosmological environment. In a box of 64 h-1 Mpc
base length we employ dark matter only simulations. For estimating the hydrogen
temperature and density distribution we use the effective equation of state.
Hydrogen is assumed to be in photoionisation equilibrium with a model
background flux which is fit to recent observations of the mean optical depth
and transmission flux statistics. At redshifts z = 3, 4, and 4.8, we select
model quasar positions at the centre of the 20 most massive halos and 100 less
massive halos identified in the simulation. From each assumed quasar position
we cast 100 random lines of sight for two box length including the changes in
the ionisation fractions by the QSO flux field and derive mock Ly{\alpha}
spectra. The proximity effect describes the dependence of the mean normalised
optical depth {\xi} = {\tau}eff, QSO/{\tau}eff, Ly{\alpha} as a function of the
ratio of the ionisation rate by the QSO and the background field, {\omega} =
{\Gamma}QSO/{\Gamma}UVB, i.e. the profile {\xi} = (1 + {\omega}/a)-0.5, where a
strength parameter a is introduced. The strength parameter measures the
deviation from the theoretical background model and is used to quantify any
influence of the environmental density field. We reproduce an unbiased
measurement of the proximity effect which is not affected by the host halo
mass. The scatter between different lines of sight and different quasar host
positions increases with decreasing redshift. Around the host halos, we find
only a slight average overdensity in the proximity zone at comoving radii of 1
< rc < 10h-1 Mpc. However, a clear power-law correlation of the strength
parameter with the average overdensity in rc is found, showing an
overestimation of the ionising background in overdense regions and an
underestimation in underdense regions.Comment: Accepted by Monthly Notices of the Royal Astronomical Society. 15
pages, 12 figure
The evolution of HI and CIV quasar absorption line systems at 1.9 < z < 3.2
We have investigated the distribution and evolution of ~3100 intergalactic HI
absorbers with HI column densities log N(HI) = [12.75, 17.0] at 1.9 < z < 3.2,
using 18 high resolution, high S/N quasar spectra obtained from the ESO
VLT/UVES archive. We used two sets of Voigt profile fitting analysis, one
including all the available high-order Lyman lines to obtain reliable HI column
densities of saturated lines, and another using only the Ly-alpha lines. There
is no significant difference between the results from the two fits. Combining
our results with literature data, the mean number density at 0 < z < 4 is not
well described by a single power law and strongly suggests that its evolution
slows down at z < 1.5 at the high and low column density ranges. We also
divided our entire HI absorbers at 1.9 < z < 3.2 into two samples, the
unenriched forest and the CIV-enriched forest, depending on whether HI lines
are associated with CIV at log N(CIV) > 12.2 within a given velocity range. The
entire HI column density distribution function (CDDF) can be described as the
combination of these two well-characterised populations which overlap at log
N(HI) ~ 15. At log N(HI) < 15, the unenriched forest dominates, showing a
similar power-law distribution to the entire forest. The CIV-enriched forest
dominates at log N(HI) > 15, with its distribution function proportional to
N(HI)^(-1.45). However, it starts to flatten out at lower N(HI), since the
enriched forest fraction decreases with decreasing N(HI). The deviation from
the power law at log N(HI) = [14, 17] shown in the CDDF for the entire HI
sample is a result of combining two different HI populations with a different
CDDF shape. The total HI mass density relative to the critical density is
Omega(HI) ~ 1.6 x 10^(-6) h^(-1), where the enriched forest accounts for ~40%
of Omega(HI).Comment: 26 pages, 20 figures, accepted for AA, in pres
Micro Scale Tensile Behaviour of Thin Bitumen Films
The tensile behaviour of two types of viscoelastic bituminous films confined between mineral aggregates or steel as adherends, was investigated in the brittle and ductile regimes. Uniaxial specimens were fabricated employing a prototype set up allowing construction of micro-scale thin films and visualization of failure phenomena. The effect of key parameters, namely, temperature (23°C and −10°C), binder type (straight run and polymer modified), adherend type (stainless steel and mineral aggregate), and water conditioning were investigated sequentially. The results show that water sensitive aggregate-binder combinations in macro (150mm diameter) and mega (in service) scales also displayed reduced tensile strength in the micro scale when water conditioned. At 23°C ductile failure and at −10°C brittle fracture were observed. At 23°C phenomena, such as formation of striations during tensile mechanical loading, void nucleation and growth, filamentation and large ductile flow before fracture could be witnessed. When using proper surface preparation procedures, in all types of specimen investigated at 23°C only cohesive failure and at −10°C predominantly adhesive-cohesive failure were foun
Evaluation of accelerometers to determine pavement deflections under traffic loads
The purpose of this work was to study the use of accelerometers to measure pavement deflections due to traffic loads. To this end, accelerometers were embedded in two sites: the full scale load simulator Circular Test Track (CTT) and the A1 motorway in Switzerland. Deflections were derived from acceleration measurements using an algorithm that double integrates the measured signal and corrects any errors derived from the procedure. In the motorway, deflections were monitored using a set of three magnetostrictive deflectometers. Additionally, the pavement's material viscoelastic parameters determined in the laboratory were incorporated in Finite Element (FE) models to estimate the theoretical deflections. The calculated deflections were then compared to the measured and to the theoretical deflections. Deflections calculated from acceleration showed a reasonable qualitative correlation to those measured by magnetostrictive deflectometers. In addition, the FE models revealed the inability of the accelerometers to measure very slow or quasi-static motio
Triple-ionised carbon associated with the low-density neutral hydrogen gas at 1.7 < z < 3.3: the integrated N(HI)-N(CIV) relation
From the Voigt profile fitting analysis of 183 intervening CIV systems at 1.7
< z < 3.3 in 23 high-quality UVES/VLT and HIRES/Keck QSO spectra, we find that
a majority of CIV systems (~75%) display a well-characterised scaling relation
between integrated column densities of HI and CIV with a negligible redshift
evolution, when column densities of all the HI and CIV components are
integrated within a given (-150, +150) km/sec range centred at the CIV flux
minimum. The integrated CIV column density N(CIV, sys) increases with N(HI,
sys) at log N(HI, sys) = 14.0--15.5 and log N(CIV, sys) = 11.8--14.0, then
becomes almost independent of N(HI, sys) at log N(HI, sys) > 16, with a large
scatter: at log N(HI, sys) = 14--22, log N(CIV, sys) = C1 / (log(NHI, sys) +
C2) + C3, with C1 = -1.90+0.55, C2 = -14.11+0.19 and C3 = 14.76+0.17,
respectively. The steep (flat) part is dominated by SiIV-free (SiIV-enriched)
CIV systems. Extrapolating the N(HI, sys)-N(CIV, sys) relation implies that
most absorbers with log N(HI) < 14 are virtually CIV-free. The N(HI,
sys)-N(CIV, sys) relation does not hold for individual components, clumps or
the integration velocity range less than +-100 km/sec. It is expected if the
line-of-sight extent of CIV is smaller than HI and N(CIV, sys) decreases more
rapidly than N(HI, sys) at the larger impact parameter, regardless of the
location of the HI+CIV gas in the IGM filaments or in the intervening galactic
halos.Comment: Accepted for publication on MNRAS, 26 pages, 20 figures, 4 tables.
On-line materials are found in the submitted civ.tar.gz file: complete Table
2, complete Table 3, complete Table 4, velocity plots civ1.pdf, civ2.pdf,
civ3.pdf, civ4.pdf and civ5.pd
Enabling parallel computing in CRASH
We present the new parallel version (pCRASH2) of the cosmological radiative
transfer code CRASH2 for distributed memory supercomputing facilities. The code
is based on a static domain decomposition strategy inspired by geometric
dilution of photons in the optical thin case that ensures a favourable
performance speed-up with increasing number of computational cores. Linear
speed-up is ensured as long as the number of radiation sources is equal to the
number of computational cores or larger. The propagation of rays is segmented
and rays are only propagated through one sub-domain per time step to guarantee
an optimal balance between communication and computation. We have extensively
checked pCRASH2 with a standardised set of test cases to validate the
parallelisation scheme. The parallel version of CRASH2 can easily handle the
propagation of radiation from a large number of sources and is ready for the
extension of the ionisation network to species other than hydrogen and helium.Comment: Accepted by Monthly Notices of the Royal Astronomical Society. 18
pages, 20 figure
Schweizerisches Handbuch fuer die Konzeption des Strassenoberbaus. (Manuel suisse de conception des chaussées).
Le présent manuel de conception des chaussées s'adresse aux ingénieurs et aux techniciens oeuvrant dans le domaine de la construction et de l'entretien des chaussées en Suisse. L'ouvrage fournit les outils et conseils nécessaires au dimensionnement d'une chaussée, à la sélection de la structure offrant la solution économique optimale et à la sélection des techniques d'entretien et des matériaux adéquats, compte tenu du trafic, des conditions géométriques, topographiques et environnementales de l'ouvrage concerné. Il contient le savoir-faire d'experts de la construction et de l'entretien des chaussées en Suisse et fournit les informations utiles à la conception et à l'entretien des superstructures routières, qu'elles soient souples, semi- rigides ou en béton, mais ne comprend pas les ouvrages d'art. Il traite également des techniques et des matériaux innovants. Le manuel se veut complémentaire aux normes suisses et aux publications helvétiques en matière de conception et d'entretien des chaussées. Les normes reprises dans ce recueil sont complétées par les considérations pratiques en matière de construction et de maintenance des chaussées, en particulier pour le choix des structures, des techniques d'entretien et des matériaux. Le manuel doit fournir au praticien la solution technique et économique la mieux adaptée compte tenu des conditions locales de l'ouvrage considéré
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