3,670 research outputs found
Time evolution of intrinsic alignments of galaxies
Intrinsic alignments (IA), correlations between the intrinsic shapes and
orientations of galaxies on the sky, are both a significant systematic in weak
lensing and a probe of the effect of large-scale structure on galactic
structure and angular momentum. In the era of precision cosmology, it is thus
especially important to model IA with high accuracy. Efforts to use
cosmological perturbation theory to model the dependence of IA on the
large-scale structure have thus far been relatively successful; however, extant
models do not consistently account for time evolution. In particular, advection
of galaxies due to peculiar velocities alters the impact of IA, because galaxy
positions when observed are generally different from their positions at the
epoch when IA is believed to be set. In this work, we evolve the galaxy IA from
the time of galaxy formation to the time at which they are observed, including
the effects of this advection, and show how this process naturally leads to a
dependence of IA on the velocity shear. We calculate the galaxy-galaxy-IA
bispectrum to tree level (in the linear matter density) in terms of the evolved
IA coefficients. We then discuss the implications for weak lensing systematics
as well as for studies of galaxy formation and evolution. We find that
considering advection introduces nonlocality into the bispectrum, and that the
degree of nonlocality represents the memory of a galaxy's path from the time of
its formation to the time of observation. We discuss how this result can be
used to constrain the redshift at which IA is determined and provide Fisher
estimation for the relevant measurements using the example of SDSS-BOSS.Comment: 30 pages, 5 figures, 2 table
Migration, vulnerability and the complexity of violence: Experiences of documented non-EU migrants in Slovakia
Migration to East and Central Europe (ECE) remains under-researched, not least because of the relatively small number of migrants in the region. Exploring experiences of documented non-EU migrants in Slovakia with various forms of violence – including violence motivated by hate and associated with work exploitation – the paper uncovers patterns of violence and vulnerability across the migrant cohort. As a broader contribution to studies of migration, the research alerts scholars to the need for a greater attention to the experiences of smaller cohorts of migrants, which often remain under the radar because of their size. The second line of the argument highlights the complexity and relations between different kinds of violence. Several risk factors are identified as contributing to the risk of migrants’ exposure to various forms of abuse at the same time, providing with implications for preventive and supportive policies and practices. The analysis particularly emphasises the importance of ties between migrant communities and formal institutions for mitigating violence
High energy density fluctuations in terms of factorial moments and associated frequency moments
We propose to verify relations between quantities which characterize scaling
properties of high energy density fluctuations in terms of factorial moments
and newly introduced associated frequency moments. Typical examples are
presented in frame of systematics developed in the present paper. It involves
also several sorts of moments applied so far in the search for intermittency
and multifractality. Our approach takes the advantage of relations in which a
linear combination of associated frequency moments reduces statistical
fluctuations to the same extent as it is done by corresponding factorial
moments.Comment: 20 page
Assessment of Human Hemodynamics under Hyper- and Microgravity: Results of two Aachen University Parabolic Flight Experiments
Astronauts complain about fluid shifts from their lower extremities to their head caused by weightlessness during their flight into space. For a study of this phenomenon, RWTH Aachen University and Charité University Berlin participated in a joint project on two parabolic flight campaigns of the German Aerospace Centre (DLR) in September 2005 and June 2006. During these campaigns, the characteristics of the rapid fluid shifts during hyper- and micro gravity were measured by a combination of PPG and PPGI optoelectronic sensor concepts.
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