4,169 research outputs found
A multi-phenotypic cancer model with cell plasticity
The conventional cancer stem cell (CSC) theory indicates a hierarchy of CSCs
and non-stem cancer cells (NSCCs), that is, CSCs can differentiate into NSCCs
but not vice versa. However, an alternative paradigm of CSC theory with
reversible cell plasticity among cancer cells has received much attention very
recently. Here we present a generalized multi-phenotypic cancer model by
integrating cell plasticity with the conventional hierarchical structure of
cancer cells. We prove that under very weak assumption, the nonlinear dynamics
of multi-phenotypic proportions in our model has only one stable steady state
and no stable limit cycle. This result theoretically explains the phenotypic
equilibrium phenomena reported in various cancer cell lines. Furthermore,
according to the transient analysis of our model, it is found that cancer cell
plasticity plays an essential role in maintaining the phenotypic diversity in
cancer especially during the transient dynamics. Two biological examples with
experimental data show that the phenotypic conversions from NCSSs to CSCs
greatly contribute to the transient growth of CSCs proportion shortly after the
drastic reduction of it. In particular, an interesting overshooting phenomenon
of CSCs proportion arises in three-phenotypic example. Our work may pave the
way for modeling and analyzing the multi-phenotypic cell population dynamics
with cell plasticity.Comment: 29 pages,6 figure
Detecting high- galaxies in the Near Infrared Background
Emission from high- galaxies must unquestionably contribute to the
near-infrared background (NIRB). However, this contribution has so far proven
difficult to isolate even after subtracting the resolved galaxies to deep
levels. Remaining NIRB fluctuations are dominated by unresolved low-
galaxies on small angular scales, and by an unidentified component with unclear
origin on large scales (). In this paper, by analyzing mock
maps generated from semi-numerical simulations and empirically determined
relations, we find that fluctuations associated with
galaxies at amount to several percent of the unresolved NIRB flux
fluctuations. We investigate the properties of this component for different
survey areas and limiting magnitudes. In all cases, we show that this signal
can be efficiently, and most easily at small angular scales, isolated by
cross-correlating the source-subtracted NIRB with Lyman Break Galaxies (LBGs)
detected in the same field by {\tt HST} surveys. This result provides a fresh
insight into the properties of reionization sources.Comment: MNRAS in press, 8 pages, 7 figure
Schwinger boson mean field theory of the Heisenberg Ferrimagnetic Spin Chain
The Schwinger boson mean field theory is applied to the quantum ferrimagnetic
Heisenberg chain. There is a ferrimagnetic long range order in the ground
state. We observe two branches of the low lying excitation and calculate the
spin reduction, the gap of the antiferromagnetic branch, and the spin
fluctuation at . These results agree with the established numerical
results quite well. At finite temperatures, the long range order is destroyed
because of the disappearance of the Bose condensation. The thermodynamic
observables, such as the free energy, magnetic susceptibility, specific heat,
and the spin correlation at , are calculated. The has a
minimum at intermediate temperatures and the spin correlation length behaves as
at low temperatures. These qualitatively agree with the numerical
results and the difference is small at low temperatures.Comment: 15 pages, 5 figures. Accepted by Phys. Rev.
Triggering the formation of direct collapse black holes by their congeners
Direct collapse black holes (DCBHs) are excellent candidates as seeds of
supermassive black holes (SMBHs) observed at z \gsim 6. The formation of a
DCBH requires a strong external radiation field to suppress formation
and cooling in a collapsing gas cloud. Such strong field is not easily achieved
by first stars or normal star-forming galaxies. Here we investigate a scenario
in which the previously-formed DCBH can provide the necessary radiation field
for the formation of additional ones. Using one-zone model and the simulated
DCBH Spectral Energy Distributions (SEDs) filtered through absorbing gas
initially having column density , we derive the critical field
intensity, , to suppress formation and
cooling. For the SED model with cm,
cm and cm, we obtain
, 35 and 54, all much smaller than the critical
field intensity for normal star-forming galaxies (J_{\rm LW}^{\rm crit}\simgt
1000). X-ray photons from previously-formed DCBHs build up a high- X-ray
background (XRB) that may boost the . However, we find
that in the three SED models only increases to
, 170 and 390 respectively even when \dt{\rho}_\bullet reaches the
maximum value allowed by the present-day XRB level (yrMpc), still much smaller than the galactic value.
Although considering the XRB from first galaxies may further increase , we conclude that our investigation supports a scenario in
which DCBH may be more abundant than predicted by models only including
galaxies as external radiation sources.Comment: 18 pages, 14 figures, 5 tables, ApJ in pres
Ultra-faint high-redshift galaxies in the Frontier Fields
By combining cosmological simulations with Frontier Fields project lens
models we find that, in the most optimistic case, galaxies as faint as (AB magnitude at ) can be detected in the
Frontier Fields. Such faint galaxies are hosted by dark matter halos of mass
and dominate the ionizing photon budget over currently
observed bright galaxies, thus allowing for the first time the investigation of
the dominant reionization sources. In addition, the observed number of these
galaxies can be used to constrain the role of feedback in suppressing star
formation in small halos: for example, if galaxy formation is suppressed in
halos with circular velocity km s, galaxies fainter than
should not be detected in the FFs.Comment: 5 pages, 7 figures, accepted for publication in MNRAS Letter
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