321 research outputs found
Small-scale Intensity Mapping: Extended Ly, H and Continuum emission as a Probe of Halo Star Formation in High-redshift Galaxies
Lyman alpha halos are observed ubiquitously around star-forming galaxies at
high redshift, but their origin is still a matter of debate. We demonstrate
that the emission from faint unresolved satellite sources, , clustered around the central galaxies may play a major role in generating
spatially extended Ly, continuum () and H
halos. We apply the analytic formalism developed in Mas-Ribas & Dijkstra (2016)
to model the halos around Lyman Alpha Emitters (LAEs) at , for several
different satellite clustering prescriptions. In general, our UV and Ly
surface brightness profiles match the observations well at physical kpc from the centers of LAEs. We discuss how our profiles
depend on various model assumptions and how these can be tested and constrained
with future H observations by the James Webb Space Telescope (JWST).
Our analysis shows how spatially extended halos constrain (i) the presence of
otherwise undetectable satellite sources, (ii) the integrated, volumetric
production rates of Ly and LyC photons, and (iii) their
population-averaged escape fractions. These quantities are all directly
relevant for understanding galaxy formation and evolution and, for high enough
redshifts, cosmic reionization.Comment: 13 pages, 6 figures, edited to match accepted ApJ version. Results
unaffected. New descriptive flow-chart figure (Fig.6
Effect of fluid flow on vascular network organization in a multi-structural in vitro model
Introduction: Engineered tissues offer a great promise to the field of medicine as an alternative for donor tissues for which the supply is not meeting the demands. However, the integration of engineered tissues after implantation is limited due to the lack of a vascular network. Currently, strategies to include vascular networks rely on the spontaneous organization of vascular cells, or on the patterning of these cells. However, this results in either vascular networks that are not organized, or networks that lose their initial organization fast.1-3 In this project we will use interstitial flow as one of the main cues to control vascular organization and maturation in hydrogel-based tissues. Aim: To develop a microfluidic system to evaluate the effect of fluid flow profiles on vascular organization and maturation. Materials and Methods: We use a microfluidic 5-channel PDMS system that was developed in our group. The hydrogel channels are flanked by media channels and PDMS pillars to contain the Collagen I (5 mg/mL) (see Scheme 1). Additionally both hydrogel channels possess together four different diameters to analyze the effect of hydrogel thickness on endothelial cell sprouting. The media channels are coated with 0.1% Collagen I to improve the cell attachment and seeded with Human Umbilical Vein Endothelial Cells (HUVECs). One channel is filled with VEGF (50 ng/mL), which is known as one of the main angiogenic factors.4 Different fluid-flow profiles are applied to the cell seeded channels 24 hours later. The newly formed capillary network are analysed by ImageJ. Results and Conclusions: The GeltrexÂź (soluble form of basement membrane extracted from murine Engelbreth-Holm-Swarm tumors) based hydrogel channels shrink rapidly during the polymerization process, which further led to the formation of deep pores between the pillars. Due to the presence of the pores, the formation of a smooth HUVEC monolayer is disturbed. Therefore, it is better to use Collagen I hydrogel instead of GeltrexÂź, which could reduce the shrinking phenomenon during polymerization. Based on various fluid-flow profiles, hydrogel thicknesses and diffusion of VEGF within the hydrogel, different sprouting of HUVECs into the Collage I hydrogel channel is observed. Future Plans: Gradients of stiffness of different hydrogels (Collagen I, GeltrexÂź) will be generated and used in a designed mold with a 3-Channel system. To mimic the physiological state, different Endothelial cell types (e.g. HUVECs, HMECs, HIAEC) will be integrated into the fluid flow channels. This will allow us to see if different endothelial cell origins leads to a different sprouting behaviour or if the already described endothelial plasticity leads to similar results. References: 1. Levenberg et. al., Engineering vascularized skeletal muscle tissue. Nat Biotechnol, 2005. 23(7): 879-84. 2. Rivron et. al., Tissue deformation spatially modulates VEGF signaling and angiogenesis. Proc Natl Acad Sci U S A, 2012. 109(18): 6886-91. 3. Rivron et. al., Sonic Hedgehog-activated engineered blood vessels enhance bone tissue formation. Proc Natl Acad Sci U S A, 2012. 109(12): 4413-8. 4. Shibuya M., Vascular endothelial growth factor and its receptor system: physiological functions in angiogenesis and pathological roles in various diseases. J Biochem, 2013. 153(1):13-9. Acknowledgements This work is supported by an ERC Consolidator Grant under grant agreement n
Chemical defence by sterols in the freshwater ciliate Stentor polymorphus
Heterotrich ciliates typically retain toxic substances in specialized ejectable organelles, called extrusomes, which are used in predator-prey interactions. In this study, we analysed the chemical defence strategy of the freshwater heterotrich ciliate Stentor polymorphus against the predatory ciliate Coleps hirtus, and the microturbellarian flatworm Stenostomum sphagnetorum. The results showed that S. polymorphus is able to defend itself against these two predators by deploying a mix of bioactive sterols contained in its extrusomes. Sterols were isolated in vivo and characterized by liquid chromatography-mass spectrometry (LC-MS), and nuclear magnetic resonance (NMR), as ergosterol, 7-dehydroporiferasterol, and their two peroxidized analogues. The assessment of the toxicity of ergosterol and ergosterol peroxide against various organisms, indicated that these sterols are essential for the effectiveness of the chemical defence in S. polymorphus
Where can we really find the First Stars' Remnants today?
A number of recent numerical investigations concluded that the remnants of
rare structures formed at very high redshift, such as the very first stars and
bright redshift z~6 QSOs, are preferentially located at the center of the most
massive galaxy clusters at redshift z=0. In this paper we readdress this
question using a combination of cosmological simulations of structure formation
and extended Press-Schechter formalism and we show that the typical remnants of
Population III stars are instead more likely to be found in a group
environment, that is in dark matter halos of mass ~2x10^{13} h^{-1}M_sun.
Similarly, the descendants of the brightest z~6 QSOs are expected to be in
medium-sized clusters (mass of a few 10^{14} h^{-1}M_sun), rather than in the
most massive superclusters (M>10^{15} h^{-1}M_sun) found within the typical 1
Gpc^3 cosmic volume where a bright z~6 QSO lives. The origin of past claims
that the most massive clusters preferentially host these remnants is rooted in
the numerical method used to initialize their numerical simulations: Only a
small region of the cosmological volume of interest was simulated with
sufficient resolution to identify low-mass halos at early times, and this
region was chosen to host the most massive halo in the cosmological volume at
late times. The conclusion that the earliest structures formed in the entire
cosmological volume evolve into the most massive halo at late times was thus
arrived at by construction. We demonstrate that, to the contrary, the first
structures to form in a cosmological region evolve into relatively typical
objects at later times. We propose alternative numerical methods for simulating
the earliest structures in cosmological volumes.Comment: 18 pages, 5 figures, ApJ accepted, high resolution version of the
paper available at http://www.stsci.edu/~trenti/papers/halo_evolution.pd
The surface density profile of NGC 6388: a good candidate for harboring an intermediate-mass black hole
We have used a combination of high resolution (HST ACS-HRC, ACS-WFC, and
WFPC2) and wide-field (ESO-WFI) observations of the galactic globular cluster
NGC 6388 to derive its center of gravity, projected density profile, and
central surface brightness profile. While the overall projected profiles are
well fit by a King model with intermediate concentration (c=1.8) and sizable
core radius (rc=7"), a significant power law (with slope \alpha=-0.2) deviation
from a flat core behavior has been detected within the inner 1 arcsecond. These
properties suggest the presence of a central intermediate mass black hole. The
observed profiles are well reproduced by a multi-mass isotropic, spherical
model including a black hole with a mass of ~5.7x10^3 Msol.Comment: ApJ Letter in pres
Slow evolution of elliptical galaxies induced by dynamical friction
Many astrophysical problems, ranging from structure formation in cosmology to
dynamics of elliptical galaxies, refer to slow processes of evolution of
essentially collisionless self-gravitating systems. In order to determine the
relevant quasi-equilibrium configuration at time t from given initial
conditions, it is often argued that such slow evolution may be approximated in
terms of adiabatic evolution, for the calculation of which efficient
semi--analytical techniques are available. Here we focus on the slow process of
evolution, induced by dynamical friction of a host stellar system on a minority
component of "satellites", that we have investigated in a previous paper, to
determine to what extent an adiabatic description might be applied. The study
is realized by comparing directly N--body simulations of the stellar system
evolution (in two significantly different models) from initial to final
conditions in a controlled numerical environment. We demonstrate that for the
examined process the adiabatic description is going to provide incorrect
answers, not only quantitatively, but also qualitatively. The two classes of
models considered exhibit generally similar trends in evolution, with one
exception noted in relation to the evolution of the total density profile. This
simple conclusion should be taken as a warning against the indiscriminate use
of adiabatic growth prescriptions in studies of structure of galaxies.Comment: 13 pages, 5 figures, Accepted for publication in A&
Ivar, an interpretationâoriented tool to manage the update and revision of variant annotation and classification
The rapid evolution of Next Generation Sequencing in clinical settings, and the resulting challenge of variant reinterpretation given the constantly updated information, require robust data management systems and organized approaches. In this paper, we present iVar: a freely available and highly customizable tool with a userâfriendly web interface. It represents a platform for the unified management of variants identified by different sequencing technologies. iVar accepts variant call format (VCF) files and text annotation files and elaborates them, optimizing data organization and avoiding redundancies. Updated annotations can be periodically reâuploaded and associated with variants as historically tracked attributes, i.e., modifications can be recorded whenever an updated value is imported, thus keeping track of all changes. Data can be visualized through variantâcentered and sampleâcentered interfaces. A customizable search function can be exploited to periodically check if pathogenicityârelated data of a variant has changed over time. Patient recontacting ensuing from variant reinterpretation is made easier by iVar through the effective identification of all patients present in the database carrying a specific variant. We tested iVar by uploading 4171 VCF files and 1463 annotation files, obtaining a database of 4166 samples and 22,569 unique variants. iVar has proven to be a useful tool with good performance in terms of collecting and managing data from a mediumâthroughput laboratory
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