2,045 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
BIOMECHANICAL ANALYSIS A SEQENCE OF ANGULAR VELOCITY AND COORDINATED MUSCLES ACTIVITY DURING BASEBALL HITTING
The purpose of this study was to analyse a sequence of rotations and coordinated muscles activities of upper body. Using kinematic and EMG data from 3 recreational university baseball players participating in this study, we computed the angular velocity of trunk, pelvis, bat and trunk-pelvis rotation angle and PMT of upper body muscles. Trunkpelvis rotation angle was 22 Β° before the bat-ball contact. The pelvis, trunk, and bat showed a sequence of angular velocity beginning with the hip, followed by the trunk, and end tip of the bat. Additionally, PMT of upper body muscles generated right pectoralis major(1.03 sec.), right external oblique(1.11 sec.), left thoracloumbar fasci(1.12 sec.), left external oblique(1.13 sec.), right latissimus dorsi(1.15 sec.), left latissimus dorsi(1.16 sec.), right thoracloumbar fascia(1.16 sec.), left pectoralis major(1.25 sec.), on at a time during baseball hitting motion. PMT of upper body muscles were related to the shifting and rotating of body segment and this action can be considered the coordinated muscle activities of upper body
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