7,382 research outputs found
The build up of the correlation between halo spin and the large scale structure
Both simulations and observations have confirmed that the spin of
haloes/galaxies is correlated with the large scale structure (LSS) with a mass
dependence such that the spin of low-mass haloes/galaxies tend to be parallel
with the LSS, while that of massive haloes/galaxies tend to be perpendicular
with the LSS. It is still unclear how this mass dependence is built up over
time. We use N-body simulations to trace the evolution of the halo spin-LSS
correlation and find that at early times the spin of all halo progenitors is
parallel with the LSS. As time goes on, mass collapsing around massive halo is
more isotropic, especially the recent mass accretion along the slowest
collapsing direction is significant and it brings the halo spin to be
perpendicular with the LSS. Adopting the (FA)
parameter to describe the degree of anisotropy of the large-scale environment,
we find that the spin-LSS correlation is a strong function of the environment
such that a higher FA (more anisotropic environment) leads to an aligned
signal, and a lower anisotropy leads to a misaligned signal. In general, our
results show that the spin-LSS correlation is a combined consequence of mass
flow and halo growth within the cosmic web. Our predicted environmental
dependence between spin and large-scale structure can be further tested using
galaxy surveys.Comment: 9 pages, 7 figures, 2 tables, Accepted for publication in MNRA
Practical Fine-grained Privilege Separation in Multithreaded Applications
An inherent security limitation with the classic multithreaded programming
model is that all the threads share the same address space and, therefore, are
implicitly assumed to be mutually trusted. This assumption, however, does not
take into consideration of many modern multithreaded applications that involve
multiple principals which do not fully trust each other. It remains challenging
to retrofit the classic multithreaded programming model so that the security
and privilege separation in multi-principal applications can be resolved.
This paper proposes ARBITER, a run-time system and a set of security
primitives, aimed at fine-grained and data-centric privilege separation in
multithreaded applications. While enforcing effective isolation among
principals, ARBITER still allows flexible sharing and communication between
threads so that the multithreaded programming paradigm can be preserved. To
realize controlled sharing in a fine-grained manner, we created a novel
abstraction named ARBITER Secure Memory Segment (ASMS) and corresponding OS
support. Programmers express security policies by labeling data and principals
via ARBITER's API following a unified model. We ported a widely-used, in-memory
database application (memcached) to ARBITER system, changing only around 100
LOC. Experiments indicate that only an average runtime overhead of 5.6% is
induced to this security enhanced version of application
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