37,094 research outputs found
Roles of progenitor cells for intervertebral disc regeneration in "healer" mice
Student Oral Presentation Session 1INTRODUCTION: Intervertebral disc (IVD) degeneration is a major cause of back pain that can also lead to sciatica, affecting the quality of life. Current treatments are limited to salvage surgical operations. Biological treatments to relieve symptoms or to restore disc are not available as we know little about the biology of IVD degeneration and its potential to regeneration. While most people will develop disc degeneration with aging, there are individuals who are protected even at the age (older than 50 years) when over 90% of the population would succumb to the problem, suggesting the presence of protective genes. Furthermore, maintenance of progenitor cells within the nucleus pulposus (NP) is thought …postprin
Structural basis for recruitment of mitochondrial fission complexes by Fis1
Mitochondrial fission controls mitochondrial shape and physiology, including mitochondrial remodeling in apoptosis. During assembly of the yeast mitochondrial fission complex, the outer membrane protein Fis1 recruits the dynamin-related GTPase Dnm1 to mitochondria. Fis1 contains a tetratricopeptide repeat (TPR) domain and interacts with Dnm1 via the molecular adaptors Mdv1 and Caf4. By using crystallographic analysis of adaptor-Fis1 complexes, we show that these adaptors use two helices to bind to both the concave and convex surfaces of the Fis1 TPR domain. Fis1 therefore contains two interaction interfaces, a binding mode that, to our knowledge, has not been observed previously for TPR domains. Genetic and biochemical studies indicate that both binding interfaces are important for binding of Mdv1 and Caf4 to Fis1 and for mitochondrial fission activity in vivo. Our results reveal how Fis1 recruits the mitochondrial fission complex and will facilitate efforts to manipulate mitochondrial fission
CMB Constraint on Radion Evolution in the Brane World Scenario
In many versions of brane model, the modulus field of extra dimensions, the
radion, could have cosmological evolution, which induces variation of the Higgs
vacuum expectation value, , resulting in cosmological variation of the
electron mass $m_e$. The formation of Cosmic Microwave Background (CMB)
anisotropies is thus affected, causing changes both in the peaks positions and
amplitudes in the CMB power spectra. Using the three-year Wilkinson Microwave
Anisotropies Probe (WMAP) CMB data, with the Hubble parameter $H_0$ fixed to be
the Hubble Space Telescope (HST) result 72 km s$^{-1}$ Mpc$^{-1}$, we obtain a
constraint on $\rho$, the ratio of the value of at CMB recombination to
its present value, to be [0.97, 1.02].Comment: 7 pages, 6 figures, minor changes of format to conform with PRD
forma
Cosmic ray feedback in the FIRE simulations: constraining cosmic ray propagation with GeV gamma ray emission
We present the implementation and the first results of cosmic ray (CR)
feedback in the Feedback In Realistic Environments (FIRE) simulations. We
investigate CR feedback in non-cosmological simulations of dwarf, sub-
starburst, and galaxies with different propagation models, including
advection, isotropic and anisotropic diffusion, and streaming along field lines
with different transport coefficients. We simulate CR diffusion and streaming
simultaneously in galaxies with high resolution, using a two moment method. We
forward-model and compare to observations of -ray emission from nearby
and starburst galaxies. We reproduce the -ray observations of dwarf and
galaxies with constant isotropic diffusion coefficient . Advection-only and streaming-only
models produce order-of-magnitude too large -ray luminosities in dwarf
and galaxies. We show that in models that match the -ray
observations, most CRs escape low-gas-density galaxies (e.g.\ dwarfs) before
significant collisional losses, while starburst galaxies are CR proton
calorimeters. While adiabatic losses can be significant, they occur only after
CRs escape galaxies, so they are only of secondary importance for -ray
emissivities. Models where CRs are ``trapped'' in the star-forming disk have
lower star formation efficiency, but these models are ruled out by -ray
observations. For models with constant that match the -ray
observations, CRs form extended halos with scale heights of several kpc to
several tens of kpc.Comment: 31 pages, 26 figures, accepted for publication in MNRA
Aqueous-phase photochemical oxidation and direct photolysis of vanillin – a model compound of methoxy phenols from biomass burning
We present here experimental results on aqueous-phase (A) photochemical
oxidation (with UV and OH radicals generated from H<sub>2</sub>O<sub>2</sub> photolysis)
and (B) direct photolysis (with only UV irradiation) of a methoxy phenol,
vanillin (VL), as a model compound from biomass burning. Both on-line
aerosol mass spectrometric (AMS) characterization and off-line chemical
analyses were performed. AMS analyses of dried atomized droplets of the bulk
reacting mixtures showed that VL almost entirely evaporates during the
drying process. Large amounts of organic mass remained in the particle phase
after reactions under both conditions. Under condition (A), AMS measured
organic mass first increased rapidly and then decreased, attributable to the
formation of non-volatile products and subsequent formation of smaller and
volatile products, respectively. The oxygen-to-carbon (O : C) ratio of the
products reached 1.5 after about 80 min, but dropped substantially
thereafter. In contrast, organic mass increased slowly under condition (B).
The O : C ratio reached 1.0 after 180 min. In off-line analyses, small
oxygenates were detected under condition (A), while hydroxylated products
and dimers of VL were detected under condition (B). Particle hygroscopic
growth factor (GF) and cloud condensation nuclei (CCN) activity of the
reacting mixtures were found to depend on both organic volume fraction and
the degree of oxygenation of organics. Results show that (1) aqueous-phase
processes can lead to the retention of a large portion of the organic mass
in the particle phase; (2) once retained, this portion of organic mass
significantly changes the hygroscopicity and CCN activity of the aerosol
particles; (3) intensive photochemical oxidation gave rise to an O : C ratio
as high as 1.5 but the ratio decreased as further oxidation led to smaller
and more volatile products; and (4) polymerization occurred with direct
photolysis, resulting in high-molecular-weight products of a yellowish
color. This study demonstrates that aqueous-phase reactions of a
methoxy phenol can lead to substantial amount of secondary organic aerosol
(SOA) formation. Given the vast amount of biomass burning input globally,
model representation of either the SOA budget or their subsequent effects
would not be adequate if the contribution of SOA formation from
aqueous-phase reactions of methoxy phenols is not considered
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