2,460 research outputs found
Local Voids as the Origin of Large-angle Cosmic Microwave Background Anomalies: The Effect of a Cosmological Constant
We explore the large angular scale temperature anisotropies in the cosmic
microwave background (CMB) due to homogeneous local dust-filled voids in a flat
Friedmann-Robertson-Walker universe with a cosmological constant. In comparison
with the equivalent dust-filled void model in the Einstein-de Sitter
background, we find that the anisotropy for compensated asymptotically
expanding local voids can be larger because second-order effects enhance the
linear integrated Sachs-Wolfe (ISW) effect. However, for local voids that
expand sufficiently faster than the asymptotic velocity of the wall, the
second-order effect can suppress the fluctuation due to the linear ISW effect.
A pair of quasi-linear compensated asymptotic local voids with radius
(2-3)*10^2 ~h^{-1} Mpc and a matter density contrast ~-0.3 can be observed as
cold spots with a temperature anisotropy Delta T/T~O(10^{-5}) that might help
explain the observed large-angle CMB anomalies. We predict that the associated
anisotropy in the local Hubble constant in the direction of the voids could be
as large as a few percent.Comment: 23 pages, 5 figures, version accepted for publication in ApJ with
minor revisio
A fluid-structure solver for confined microcapsule flows
We present a fluid-structure coupling method designed to study capsules
flowing in a confined environment. The fluid solver is based on the Finite Volume Method
and is coupled to a Finite Elements solid solver using the Immersed Boundary Method. We study the
relaxation of a spherical capsule, initially deformed into an ellipsoid, and released in a square
cross-section channel within a quiescent fluid environment. We perform a convergence
study in order to validate the numerical method and consider the effect of
the inertial forces on the capsule relaxation
On the Rees-Sciama effect: maps and statistics
Small maps of the Rees-Sciama (RS) effect are simulated by using an
appropriate N-body code and a certain ray-tracing procedure. A method designed
for the statistical analysis of cosmic microwave background (CMB) maps is
applied to study the resulting simulations. These techniques, recently proposed
--by our team-- to consider lens deformations of the CMB, are adapted to deal
with the RS effect. This effect and the deviations from Gaussianity associated
to it seem to be too small to be detected in the near future. This conclusion
follows from our estimation of both the RS angular power spectrum and the RS
reduced n-direction correlation functions for n<7.Comment: 11 pages, 13 figures, to appear in MNRA
CMB anisotropy: deviations from Gaussianity due to non-linear gravity
Non-linear evolution of cosmological energy density fluctuations triggers
deviations from Gaussianity in the temperature distribution of the cosmic
microwave background. A method to estimate these deviations is proposed. N-body
simulations -- in a CDM cosmology -- are used to simulate the strongly
non-linear evolution of cosmological structures. It is proved that these
simulations can be combined with the potential approximation to calculate the
statistical moments of the CMB anisotropies produced by non-linear gravity.
Some of these moments are computed and the resulting values are different from
those corresponding to Gaussianity.Comment: 6 latex pages with mn.sty, 3 eps figures. Accepted in MNRA
Integration of social aspects in decision support, based on life cycle thinking
Recently increasing attention has been paid to complementing environmental Life Cycle Assessment (LCA) with social aspects. The paper discusses the selection of social impacts and indicators from existing frameworks like Social Life Cycle Assessment (SLCA) and Social Impact Assessment (SIA). Two ongoing case studies, addressing sustainability assessment within decision support, were considered: (1) Integrated Water Resources Management (IWRM) in Indonesia; and (2) Integrated Packaging Waste Management in Spain and Portugal (FENIX). The focus was put on social impacts occurring due to decisions within these systems, such as choice of technologies, practices or suppliers. Thus, decision makers—here understood as intended users of the studies’ results—are not consumers that buy (or do not buy) a product, such as in recent SLCA case-studies, but mainly institutions that decide about the design of the water or packaging waste management system. Therefore, in the FENIX project, a list of social impacts identified from literature was sent to the intended users to be ranked according to their priorities. Finally, the paper discusses to what extent the entire life cycle is reflected in SLCA impact categories and indicators, and explains how both life-cycle and on-site-related social impacts were chosen to be assessed. However, not all indicators in the two projects will assess all stages of the life cycle, because of their varying relevance in the different stages, data availability and practical interest of decision makers
Local Voids as the Origin of Large-angle Cosmic Microwave Background Anomalies I
We explore the large angular scale temperature anisotropies in the cosmic
microwave background due to expanding homogeneous local voids at redshift z~1.
A compensated spherically symmetric homogeneous dust-filled void with radius
\~3*10^2 h^{-1}Mpc, and density contrast ~-0.3 can be observed as a cold spot
with a temperature anisotropy -1*10^{-5} surrounded by a slightly hotter ring.
We find that a pair of these circular cold spots separated by ~50 degree can
account both for the planarity of the octopole and for the alignment between
the quadrupole and the octopole in the cosmic microwave background (CMB)
anisotropy. The cold spot in the Galactic southern hemisphere which is
anomalous at the ~3sigma level can be explained by such a large void at z~1.
The observed north-south asymmetry in the large-angle CMB power can be
attributed to the asymmetric distribution of these local voids between the two
hemispheres. The statistical significance of the low quadrupole is further
reduced in this interpretation of the large angular scale CMB anomalies.Comment: 8 pages, 5 eps files, Version accepted for ApJ. New maps for
non-overlapping voids (Fig. 4) is adde
Estimating small angular scale CMB anisotropy with high resolution N-body simulations: weak lensing
We estimate the impact of weak lensing by strongly nonlinear cosmological
structures on the cosmic microwave background. Accurate calculation of large
multipoles requires N-body simulations and ray-tracing schemes with both
high spatial and temporal resolution. To this end we have developed a new code
that combines a gravitational Adaptive Particle-Particle, Particle-Mesh (AP3M)
solver with a weak lensing evaluation routine. The lensing deviations are
evaluated while structure evolves during the simulation so that all evolution
steps--rather than just a few outputs--are used in the lensing computations.
The new code also includes a ray-tracing procedure that avoids periodicity
effects in a universe that is modeled as a 3-D torus in the standard way.
Results from our new simulations are compared with previous ones based on
Particle-Mesh simulations. We also systematically investigate the impact of box
volume, resolution, and ray-tracing directions on the variance of the computed
power spectra. We find that a box size of Mpc is sufficient to
provide a robust estimate of the weak lensing angular power spectrum in the
-interval (2,000--7,000). For a reaslistic cosmological model the power
takes on values of a few in this
interval, which suggests that a future detection is feasible and may explain
the excess power at high in the BIMA and CBI observations.Comment: 49 pages, 13 figures, accepted for publication in Ap
Effect of Void Network on CMB Anisotropy
We study the effect of a void network on the CMB anisotropy in the
Einstein-de Sitter background using Thompson &Vishniac's model. We consider
comprehensively the Sacks-Wolfe effect, the Rees-Sciama effect and the
gravitational lensing effect. Our analysis includes the model of primordial
voids existing at recombination, which is realized in some inflationary models
associated with a first-order phase transition. If there exist primordial voids
whose comoving radius is larger than Mpc at recombination, not
only the Sachs-Wolfe effect but also the Rees-Sciama effect is appreciable even
for multipoles l\lsim1000 of the anisotropy spectrum. The gravitational
lensing effect, on the other hand, slightly smoothes the primary anisotropy;
quantitatively, our results for the void model are similar to the previous
results for a CDM model. All the effects, together, would give some constraints
on the configuration or origin of voids with high-resolution data of the CMB
anisotropy.Comment: 23 pages, latex, 12 eps figures, some calculations and discussions
are added, to appear in ApJ 510 (1999
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