3,763 research outputs found
Holographic Bosonic Technicolor
We consider a technicolor model in which the expectation value of an
additional, possibly composite, scalar field is responsible for the generation
of fermion masses. We define the dynamics of the strongly coupled sector by
constructing its holographic dual. Using the AdS/CFT correspondence, we study
the S parameter and the phenomenology of the light technihadrons. We find that
the S parameter is small over a significant region of the model's parameter
space. The particle spectrum is distinctive and includes a nonstandard Higgs
boson as well as heavier hadronic resonances. Technihadron masses and decay
rates are calculated holographically, as a function of the model's parameters.Comment: 20 Pages, 4 eps figures, REVTex. Minor corrections and comments adde
A Massive Protostar Forming by Ordered Collapse of a Dense, Massive Core
We present 30 and 40 micron imaging of the massive protostar G35.20-0.74 with
SOFIA-FORCAST. The high surface density of the natal core around the protostar
leads to high extinction, even at these relatively long wavelengths, causing
the observed flux to be dominated by that emerging from the near-facing outflow
cavity. However, emission from the far-facing cavity is still clearly detected.
We combine these results with fluxes from the near-infrared to mm to construct
a spectral energy distribution (SED). For isotropic emission the bolometric
luminosity would be 3.3x10^4 Lsun. We perform radiative transfer modeling of a
protostar forming by ordered, symmetric collapse from a massive core bounded by
a clump with high mass surface density, Sigma_cl. To fit the SED requires
protostellar masses ~20-34 Msun depending on the outflow cavity opening angle
(35 - 50 degrees), and Sigma_cl ~ 0.4-1 g cm-2. After accounting for the
foreground extinction and the flashlight effect, the true bolometric luminosity
is ~ (0.7-2.2)x10^5 Lsun. One of these models also has excellent agreement with
the observed intensity profiles along the outflow axis at 10, 18, 31 and 37
microns. Overall our results support a model of massive star formation
involving the relatively ordered, symmetric collapse of a massive, dense core
and the launching bipolar outflows that clear low density cavities. Thus a
unified model may apply for the formation of both low and high mass stars.Comment: 6 pages, 4 figures, 1 table, accepted to Ap
The Formation of the First Stars II. Radiative Feedback Processes and Implications for the Initial Mass Function
We consider the radiative feedback processes that operate during the
formation of the first stars, including the photodissociation of H_2, Ly-alpha
radiation pressure, formation and expansion of an HII region, and disk
photoevaporation. These processes may inhibit continued accretion once the
stellar mass has reached a critical value, and we evaluate this mass separately
for each process. Photodissociation of H_2 in the local dark matter minihalo
occurs relatively early in the growth of the protostar, but we argue this does
not affect subsequent accretion since by this time the depth of the potential
is large enough for accretion to be mediated by atomic cooling. However,
neighboring starless minihalos can be affected. Ionization creates an HII
region in the infalling envelope above and below the accretion disk. Ly-alpha
radiation pressure acting at the boundary of the HII region is effective at
reversing infall from narrow polar directions when the star reaches ~20-30Msun,
but cannot prevent infall from other directions. Expansion of the HII region
beyond the gravitational escape radius for ionized gas occurs at masses
~50-100Msun, depending on the accretion rate and angular momentum of the
inflow. However, again, accretion from the equatorial regions can continue
since the neutral accretion disk has a finite thickness and shields a
substantial fraction of the accretion envelope from direct ionizing flux. At
higher stellar masses, ~140Msun in the fiducial case, the combination of
declining accretion rates and increasing photoevaporation-driven mass loss from
the disk act to effectively halt the increase in the protostellar mass. We
identify this process as the mechanism that terminates the growth of Population
III stars... (abridged)Comment: 31 pages, including 10 figures, accepted to Ap
The Ubiquitin Ligase Adaptor NDFIP1 Selectively Enforces a CD8<sup>+</sup> T Cell Tolerance Checkpoint to High-Dose Antigen
Escape from peripheral tolerance checkpoints that control cytotoxic CD8+ T cells is important for cancer immunotherapy and autoimmunity, but pathways enforcing these checkpoints are mostly uncharted. We reveal that the HECT-type ubiquitin ligase activator, NDFIP1, enforces a cell-intrinsic CD8+ T cell checkpoint that desensitizes TCR signaling during in vivo exposure to high antigen levels. Ndfip1-deficient OT-I CD8+ T cells responding to high exogenous tolerogenic antigen doses that normally induce anergy aberrantly expanded and differentiated into effector cells that could precipitate autoimmune diabetes in RIP-OVAhi mice. In contrast, NDFIP1 was dispensable for peripheral deletion to low-dose exogenous or pancreatic islet-derived antigen and had little impact upon effector responses to Listeria or acute LCMV infection. These data provide evidence that NDFIP1 mediates a CD8+ T cell tolerance checkpoint, with a different mechanism to CD4+ T cells, and indicates that CD8+ T cell deletion and anergy are molecularly separable checkpoints.This work
was funded by NIH grant U19-AI100627, by an Australian Government
Research Training Program Domestic Scholarship (to M.V.W.), by a Sydney
Parker Smith Postdoctoral Research Fellowship from the Cancer Council of
Victoria (to J.M.M.), and by the National Health and Medical Research Council
(NHMRC) through Program Grants 1016953, 1113904, and 1054925, Australia
Fellowship 585490 (to C.C.G.), Senior Principal Research Fellowship 1081858
(to C.C.G.), CJ Martin Early Career Fellowship 585518 (to I.A.P.), and Independent
Research Institutes Infrastructure Support Scheme Grant 361646. Florey
Institute of Neuroscience and Mental Health and WEHI acknowledge the
strong support from the Victorian Government and in particular funding from
the Operational Infrastructure Support Grant
Head-Neck Dual-energy CT Contrast Media Reduction Using Diffusion Models
Iodinated contrast media is essential for dual-energy computed tomography
(DECT) angiography. Previous studies show that iodinated contrast media may
cause side effects, and the interruption of the supply chain in 2022 led to a
severe contrast media shortage in the US. Both factors justify the necessity of
contrast media reduction in relevant clinical applications. In this study, we
propose a diffusion model-based deep learning framework to address this
challenge. First, we simulate different levels of low contrast dosage DECT
scans from the standard normal contrast dosage DECT scans using material
decomposition. Conditional denoising diffusion probabilistic models are then
trained to enhance the contrast media and create contrast-enhanced images. Our
results demonstrate that the proposed methods can generate high-quality
contrast-enhanced results even for images obtained with as low as 12.5% of the
normal contrast dosage. Furthermore, our method outperforms selected competing
methods in a human reader study
Fragmentation of Massive Protostellar Disks
We examine whether massive-star accretion disks are likely to fragment due to
self-gravity. Rapid accretion and high angular momentum push these disks toward
fragmentation, whereas viscous heating and the high protostellar luminosity
stabilize them. We find that for a broad range of protostar masses and for
reasonable accretion times, massive disks larger than ~150 AU are prone to
fragmentation. We develop an analytical estimate for the angular momentum of
accreted material, extending the analysis of Matzner and Levin (2005) to
account for strongly turbulent initial conditions. In a core-collapse model, we
predict that disks are marginally prone to fragmentation around stars of about
four to 15 solar masses -- even if we adopt conservative estimates of the
disks' radii and tendency to fragment. More massive stars are progressively
more likely to fragment, and there is a sharp drop in the stability of disk
accretion at the very high accretion rates expected above 110 solar masses.
Fragmentation may starve accretion in massive stars, especially above this
limit, and is likely to create swarms of small, coplanar companions.Comment: 15 pages, 7 figures, accepted for publication in MNRAS, updated
version with minor changes to tex
The RNA-binding protein hnRNPLL induces a T cell alternative splicing program delineated by differential intron retention in polyadenylated RNA
BACKGROUND Retention of a subset of introns in spliced polyadenylated mRNA is emerging as a frequent, unexplained finding from RNA deep sequencing in mammalian cells. RESULTS Here we analyze intron retention in T lymphocytes by deep sequencing polyadenylated RNA. We show a developmentally regulated RNA-binding protein, hnRNPLL, induces retention of specific introns by sequencing RNA from T cells with an inactivating Hnrpll mutation and from B lymphocytes that physiologically downregulate Hnrpll during their differentiation. In Ptprc mRNA encoding the tyrosine phosphatase CD45, hnRNPLL induces selective retention of introns flanking exons 4 to 6; these correspond to the cassette exons containing hnRNPLL binding sites that are skipped in cells with normal, but not mutant or low, hnRNPLL. We identify similar patterns of hnRNPLL-induced differential intron retention flanking alternative exons in 14 other genes, representing novel elements of the hnRNPLL-induced splicing program in T cells. Retroviral expression of a normally spliced cDNA for one of these targets, Senp2, partially corrects the survival defect of Hnrpll-mutant T cells. We find that integrating a number of computational methods to detect genes with differentially retained introns provides a strategy to enrich for alternatively spliced exons in mammalian RNA-seq data, when complemented by RNA-seq analysis of purified cells with experimentally perturbed RNA-binding proteins. CONCLUSIONS Our findings demonstrate that intron retention in mRNA is induced by specific RNA-binding proteins and suggest a biological significance for this process in marking exons that are poised for alternative splicing.This work has been supported by grants from the National Health and Medical Research Council (Australia), the Wellcome Trust, the National Institutes of Health (USA) and the Biomedical Research Council (BMRC) of the Agency for Science, Technology and Research (A*STAR), Singapore
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