9,331 research outputs found
An Observed Transition of Galaxy Spins on the Void Surfaces
In the linear theory, the galaxy angular momentum vectors which originate
from the initial tidal interactions with surrounding matter distribution
intrinsically develop perpendicular alignments with the directions of maximum
matter compression, regardless of galaxy mass. In simulations, however, the
galaxy spins exhibit parallel alignments in the mass-range lower than a certain
threshold, which depends on redshift, web type, and background cosmology. We
show that the observed three dimensional spins of the spiral galaxies located
on the void surfaces from the Sloan Digital Sky Survey indeed transit from the
perpendicular to the parallel alignments with the directions toward the nearest
void centers at the threshold zone, . This study presents a first direct
observational evidence for the occurrence of the mass-dependent spin transition
of the real galaxies with respect to the non-filamentary structures of the
cosmic web, opening a way to constrain the initial conditions of the early
universe by measuring the spin transition threshold.Comment: Accepted by ApJ Letters, 5 figures and 1 table, improved statistics
and data analysis after referee's revie
The Density Parity Model for the Evolution of the Subhalo Inner Spin Alignments with the Cosmic Web
We develop a new model within which the radius-dependent transition of the
subhalo inner spins with respect to the cosmic web and the variation of the
transition threshold radius () with subhalo mass (),
smoothing scale (), and redshift () can be coherently explained. The
key tenet of this model is that the competition between the pressure effect of
the inner mass and the compression effect of the local tidal field determines
which principal direction of the tidal field the inner spins are aligned with.
If the former predominates, then only the tidal torques turn on, resulting in
the alignments of the inner spins with the intermediate principal axes of the
tidal field. Otherwise, the subhalo spins acquire a tendency to be aligned with
the shortest axes of the subhalo shapes, which is in the major principal
directions of the tidal field. Quantifying the two effects in terms of the
densities, we make a purely analytical prediction for . Testing this model against the numerical results from a
high-resolution dark matter only N-body simulation in the redshift range of
on the galactic mass scale of for two different cases of and , we find excellent agreements of the model predictions with
the numerical results. It is also shown that this model naturally predicts the
alignments between the inner spins of the present subhalos with the principal
axes of the high- tidal field at the progenitors' locations.Comment: Accepted for publication in ApJ, revised version after a referee's
report, improved analysi
Reoriented Memory of Galaxy Spins for the Early Universe
Galaxy spins are believed to retain the initially acquired tendency of being
aligned with the intermediate principal axes of the linear tidal field, which
disseminates a prospect of using them as a probe of early universe physics.
This roseate prospect, however, is contingent upon the key assumption that the
observable stellar spins of the present galaxies measured at inner radii have
the same alignment tendency toward the initial tidal field as their dark matter
counterparts measured at virial limits. We test this assumption directly
against a high-resolution hydrodynamical simulation by tracing back the galaxy
component particles back to the protogalactic stage. It is discovered that the
galaxy stellar spins at have strong but {\it reoriented} memory for the
early universe, exhibiting a significant signal of cross-correlation with the
{\it major} principal axes of the initial tidal field at . An analytic
single-parameter model for this reorientation of the present galaxy stellar
spins relative to the initial tidal field is devised and shown to be in good
accord with the numerical results.Comment: Accepted for publication in ApJ, revised version, improved analysis
and more details about analytic modelin
On the sparse subset sum problem from Gentry-Halevi\u27s implementation of fully homomorphic encryption
In Gentry\u27s fully homoomrphic cryptosystem, a sparse subset sum problem is used and a big set is included in the public key. In the implementation of a variant of Gentry\u27s scheme, to reduce the size of the public key, Gentry and Halevi used a specific form of a sparse subset sum problem with geometric progressions. In this note, we show that their sparse subset sum challenges are rather easy given the aggressive choice of parameters. Our experiment shows that even their large instance of a sparse subset sum problem could be solved within two days with probability of about . A more conservative parameter choice can easily avoid our attack
NOD2/RICK-dependent β-defensin 2 regulation is protective for nontypeable Haemophilus influenzae-induced middle ear infection.
Middle ear infection, otitis media (OM), is clinically important due to the high incidence in children and its impact on the development of language and motor coordination. Previously, we have demonstrated that the human middle ear epithelial cells up-regulate β-defensin 2, a model innate immune molecule, in response to nontypeable Haemophilus influenzae (NTHi), the most common OM pathogen, via TLR2 signaling. NTHi does internalize into the epithelial cells, but its intracellular trafficking and host responses to the internalized NTHi are poorly understood. Here we aimed to determine a role of cytoplasmic pathogen recognition receptors in NTHi-induced β-defensin 2 regulation and NTHi clearance from the middle ear. Notably, we observed that the internalized NTHi is able to exist freely in the cytoplasm of the human epithelial cells after rupturing the surrounding membrane. The human middle ear epithelial cells inhibited NTHi-induced β-defensin 2 production by NOD2 silencing but augmented it by NOD2 over-expression. NTHi-induced β-defensin 2 up-regulation was attenuated by cytochalasin D, an inhibitor of actin polymerization and was enhanced by α-hemolysin, a pore-forming toxin. NOD2 silencing was found to block α-hemolysin-mediated enhancement of NTHi-induced β-defensin 2 up-regulation. NOD2 deficiency appeared to reduce inflammatory reactions in response to intratympanic inoculation of NTHi and inhibit NTHi clearance from the middle ear. Taken together, our findings suggest that a cytoplasmic release of internalized NTHi is involved in the pathogenesis of NTHi infections, and NOD2-mediated β-defensin 2 regulation contributes to the protection against NTHi-induced otitis media
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