6,083 research outputs found
The Distribution of Satellites Around Central Galaxies in a Cosmological Hydrodynamical Simulation
Observations have shown that the spatial distribution of satellite galaxies
is not random, but rather is aligned with the major axes of central galaxies
(CGs). The strength of the alignment is dependent on the properties of both the
satellites and centrals. Theoretical studies using dissipationless N-body
simulations are limited by their inability to directly predict the shape of
CGs. Using hydrodynamical simulations including gas cooling, star formation,
and feedback, we carry out a study of galaxy alignment and its dependence on
the galaxy properties predicted directly from the simulations.We found that the
observed alignment signal is well produced, as is the color dependence: red
satellites and red centrals both show stronger alignments than their blue
counterparts. The reason for the stronger alignment of red satellites is that
most of them stay in the inner region of the dark matter halo where the shape
of the CG better traces the dark matter distribution. The dependence of
alignment on the color of CGs arises from the halo mass dependence, since the
alignment between the shape of the central stellar component and the inner halo
increases with halo mass. We also find that the alignment of satellites is most
strongly dependent on their metallicity, suggesting that the metallicity of
satellites, rather than color, is a better tracer of galaxy alignment on small
scales. This could be tested in future observational studies.Comment: ApJ Letter, accepted. Four figures, no table. The resolution of Fig 1
was downgraded due to the limitation of file size. Updated to match the
version in pres
A gap between hyponormality and subnormality for block Toeplitz operators
AbstractThis paper concerns a gap between hyponormality and subnormality for block Toeplitz operators. We show that there is no gap between 2-hyponormality and subnormality for a certain class of trigonometric block Toeplitz operators (e.g., its co-analytic outer coefficient is invertible). In addition we consider the extremal cases for the hyponormality of trigonometric block Toeplitz operators: in this case, hyponormality and normality coincide
A Dynamic Programming Solution to Bounded Dejittering Problems
We propose a dynamic programming solution to image dejittering problems with
bounded displacements and obtain efficient algorithms for the removal of line
jitter, line pixel jitter, and pixel jitter.Comment: The final publication is available at link.springer.co
Properties of Central Caustics in Planetary Microlensing
To maximize the number of planet detections, current microlensing follow-up
observations are focusing on high-magnification events which have a higher
chance of being perturbed by central caustics. In this paper, we investigate
the properties of central caustics and the perturbations induced by them. We
derive analytic expressions of the location, size, and shape of the central
caustic as a function of the star-planet separation, , and the planet/star
mass ratio, , under the planetary perturbative approximation and compare the
results with those based on numerical computations. While it has been known
that the size of the planetary caustic is \propto \sqrt{q}, we find from this
work that the dependence of the size of the central caustic on is linear,
i.e., \propto q, implying that the central caustic shrinks much more rapidly
with the decrease of compared to the planetary caustic. The central-caustic
size depends also on the star-planet separation. If the size of the caustic is
defined as the separation between the two cusps on the star-planet axis
(horizontal width), we find that the dependence of the central-caustic size on
the separation is \propto (s+1/s). While the size of the central caustic
depends both on and q, its shape defined as the vertical/horizontal width
ratio, R_c, is solely dependent on the planetary separation and we derive an
analytic relation between R_c and s. Due to the smaller size of the central
caustic combined with much more rapid decrease of its size with the decrease of
q, the effect of finite source size on the perturbation induced by the central
caustic is much more severe than the effect on the perturbation induced by the
planetary caustic. Abridged.Comment: 5 pages, 4 figures, ApJ accepte
Nonequilibrium Steady States and Fano-Kondo Resonances in an AB Ring with a Quantum Dot
Electron transport through a strongly correlated quantum dot (QD) embedded in
an Aharonov-Bohm (AB) ring is investigated with the aid of the finite-U
slave-boson mean-field (SBMF) approach extended to nonequilibrium regime. A
nonequilibrium steady state (NESS) of the mean-field Hamiltonian is constructed
with the aid of the C*-algebraic approach for studying infinitely extended
systems. In the linear response regime, the Fano-Kondo resonances and AB
oscillations of the conductance obtained from the SBMF approach are in good
agreement with those from the numerical renormalization group technique (NRG)
by Hofstetter et al. by using twice larger Coulomb interaction. At zero
temperature and finite bias voltage, the resonance peaks of the differential
conductance tend to split into two. At low bias voltage, the split of the
asymmetric resonance can be observed as an increase of the conductance plateau.
We also found that the differential conductance has zero-bias maximum or
minimum depending on the background transmission via direct tunneling between
the electrodes.Comment: 24 pages,17 figure
Generation of T Follicular Helper Cells Is Mediated by Interleukin-21 but Independent of T Helper 1, 2, or 17 Cell Lineages
SummaryAfter activation, CD4+ helper T (Th) cells differentiate into distinct effector subsets. Although chemokine (C-X-C motif) receptor 5-expressing T follicular helper (Tfh) cells are important in humoral immunity, their developmental regulation is unclear. Here we show that Tfh cells had a distinct gene expression profile and developed in vivo independently of the Th1 or Th2 cell lineages. Tfh cell generation was regulated by ICOS ligand (ICOSL) expressed on B cells and was dependent on interleukin-21 (IL-21), IL-6, and signal transducer and activator of transcription 3 (STAT3). However, unlike Th17 cells, differentiation of Tfh cells did not require transforming growth factor Ī² (TGF-Ī²) or Th17-specific orphan nuclear receptors RORĪ± and RORĪ³ in vivo. Finally, naive T cells activated in vitro in the presence of IL-21 but not TGF-Ī² signaling preferentially acquired Tfh gene expression and promoted germinal-center reactions in vivo. This study thus demonstrates that Tfh is a distinct Th cell lineage
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