1,239 research outputs found
Glycine Receptors Support Excitatory Neurotransmitter Release in Developing Mouse Visual Cortex.
Glycine receptors (GlyRs) are found in most areas of the brain, and their dysfunction can cause severe neurological disorders. While traditionally thought of as inhibitory receptors, presynaptic-acting GlyRs (preGlyRs) can also facilitate glutamate release under certain circumstances, although the underlying molecular mechanisms are unknown. In the current study, we sought to better understand the role of GlyRs in the facilitation of excitatory neurotransmitter release in mouse visual cortex. Using whole-cell recordings, we found that preGlyRs facilitate glutamate release in developing, but not adult, visual cortex. The glycinergic enhancement of neurotransmitter release in early development depends on the high intracellular to extracellular Cl(-) gradient maintained by the Na(+)-K(+)-2Cl(-) cotransporter and requires Ca(2+) entry through voltage-gated Ca(2+) channels. The glycine transporter 1, localized to glial cells, regulates extracellular glycine concentration and the activation of these preGlyRs. Our findings demonstrate a developmentally regulated mechanism for controlling excitatory neurotransmitter release in the neocortex
Z boson decay to photon plus Kaluza-Klein graviton in large extra dimensions
In the large extra dimensional ADD scenario, Z bosons undergo a one-loop
decay into a photon and Kaluza-Klein towers of gravitons/gravi-scalars. We
calculate such a decay width, extending previous arguments about the general
form of the four-dimensional on-shell amplitude. The amplitudes calculated are
relevant to processes in other extra dimensional models where the Standard
Model fields are confined to a 4-brane.Comment: 47 pages, uses feynmp for diagrams. v2: typographical corrections for
letter-sized paper and to correct feynmf parsing error. v3: minor error in
polarisation averaging and reference corrected. v4: reflects changes for
published version; arithmetic error corrected and reference updated; section
on transversality conditions not present in published version retaine
The Photon Underproduction Crisis
We examine the statistics of the low-redshift Lyman-alpha forest from
smoothed particle hydrodynamic simulations in light of recent improvements in
the estimated evolution of the cosmic ultraviolet background (UVB) and recent
observations from the Cosmic Origins Spectrograph (COS). We find that the value
of the metagalactic photoionization rate required by our simulations to match
the observed properties of the low-redshift Lyman-alpha forest is a factor of 5
larger than the value predicted by state-of-the art models for the evolution of
this quantity. This mismatch results in the mean flux decrement of the
Lyman-alpha forest being underpredicted by at least a factor of 2 (a 10-sigma
discrepancy with observations) and a column density distribution of Lyman-alpha
forest absorbers systematically and significantly elevated compared to
observations over nearly two decades in column density. We examine potential
resolutions to this mismatch and find that either conventional sources of
ionizing photons (galaxies and quasars) must be significantly elevated relative
to current observational estimates or our theoretical understanding of the
low-redshift universe is in need of substantial revision.Comment: Submitted to ApJ Letters; 6 pages including 3 figure
Time evolution of a non-singular primordial black hole
There is growing notion that black holes may not contain curvature
singularities (and that indeed nature in general may abhor such spacetime
defects). This notion could have implications on our understanding of the
evolution of primordial black holes (PBHs) and possibly on their contribution
to cosmic energy. This paper discusses the evolution of a non-singular black
hole (NSBH) based on a recent model [1]. We begin with a study of the
thermodynamic process of the black hole in this model, and demonstrate the
existence of a maximum horizon temperature T_{max}, corresponding to a unique
mass value. At this mass value the specific heat capacity C changes signs to
positive and the body begins to lose its black hole characteristics. With no
loss of generality, the model is used to discuss the time evolution of a
primordial black hole (PBH), through the early radiation era of the universe to
present, under the assumption that PBHs are non-singular. In particular, we
track the evolution of two benchmark PBHs, namely the one radiating up to the
end of the cosmic radiation domination era, and the one stopping to radiate
currently, and in each case determine some useful features including the
initial mass m_{f} and the corresponding time of formation t_{f}. It is found
that along the evolutionary history of the universe the distribution of PBH
remnant masses (PBH-RM) PBH-RMs follows a power law. We believe such a result
can be a useful step in a study to establish current abundance of PBH-MRs.Comment: To appear in Int. J. Mod. Phys.
The Impact of Wind Scalings on Stellar Growth and the Baryon Cycle in Cosmological Simulations
Many phenomenologically successful cosmological simulations employ kinetic winds to model galactic outflows. Yet systematic studies of how variations in kinetic wind scalings might alter observable galaxy properties are rare. Here we employ GADGET-3 simulations to study how the baryon cycle, stellar mass function, and other galaxy and CGM predictions vary as a function of the assumed outflow speed and the scaling of the mass-loading factor with velocity dispersion. We design our fiducial model to reproduce the measured wind properties at 25 perâcent of the virial radius from the Feedback In Realistic Environments simulations
The Blue Tip of the Stellar Locus: Measuring Reddening with the SDSS
We present measurements of reddening due to dust using the colors of stars in
the Sloan Digital Sky Survey (SDSS). We measure the color of main sequence
turn-off stars by finding the "blue tip" of the stellar locus: the prominent
blue edge in the distribution of stellar colors. The method is sensitive to
color changes of order 18, 12, 7, and 8 mmag of reddening in the colors u-g,
g-r, r-i, and i-z, respectively, in regions measuring 90' by 14'. We present
maps of the blue tip colors in each of these bands over the entire SDSS
footprint, including the new dusty southern Galactic cap data provided by the
SDSS-III. The results disfavor the best fit O'Donnell (1994) and Cardelli et
al. (1989) reddening laws, but are well described by a Fitzpatrick (1999)
reddening law with R_V = 3.1. The SFD dust map is found to trace the dust well,
but overestimates reddening by factors of 1.4, 1.0, 1.2, and 1.4 in u-g, g-r,
r-i, and i-z, largely due to the adopted reddening law. In select dusty regions
of the sky, we find evidence for problems in the SFD temperature correction. A
dust map normalization difference of 15% between the Galactic north and south
sky may be due to these dust temperature errors.Comment: 18 pages, 22 figure
Percutaneous Liver Biopsy after Living Donor Liver Transplantation Resulting in Fulminant Hepatic Failure: The First Reported Case of Hepatic Compartment Syndrome
A 28-year-old female who underwent live donor liver transplantation 3 years prior presented after percutaneous liver biopsy with abdominal and shoulder pain, nausea, vomiting, and elevated liver enzymes. Computed tomography (CT) showed an intrahepatic and subcapsular hematoma. There was a progressive increase in liver enzymes, bilirubin, and INR and a decline in hemoglobin. Subsequent CT imaging revealed flattening of the portal vein consistent with compression by the enlarging hematoma. Liver failure ensued and the patient required urgent retransplantation. The explant demonstrated ischemic necrosis of greater than 90% of the liver parenchyma. We report this case of âHepatic Compartment Syndromeâ leading to fulminant hepatic failure
The clustering of intermediate redshift quasars as measured by the Baryon Oscillation Spectroscopic Survey
We measure the quasar two-point correlation function over the redshift range
2.2<z<2.8 using data from the Baryon Oscillation Spectroscopic Survey. We use a
homogeneous subset of the data consisting of 27,129 quasars with spectroscopic
redshifts---by far the largest such sample used for clustering measurements at
these redshifts to date. The sample covers 3,600 square degrees, corresponding
to a comoving volume of 9.7(Gpc/h)^3 assuming a fiducial LambdaCDM cosmology,
and it has a median absolute i-band magnitude of -26, k-corrected to z=2. After
accounting for redshift errors we find that the redshift space correlation
function is fit well by a power-law of slope -2 and amplitude s_0=(9.7\pm
0.5)Mpc/h over the range 3<s<25Mpc/h. The projected correlation function, which
integrates out the effects of peculiar velocities and redshift errors, is fit
well by a power-law of slope -1 and r_0=(8.4\pm 0.6)Mpc/h over the range
4<R<16Mpc/h. There is no evidence for strong luminosity or redshift dependence
to the clustering amplitude, in part because of the limited dynamic range in
our sample. Our results are consistent with, but more precise than, previous
measurements at similar redshifts. Our measurement of the quasar clustering
amplitude implies a bias factor of b~3.5 for our quasar sample. We compare the
data to models to constrain the manner in which quasars occupy dark matter
halos at z~2.4 and infer that such quasars inhabit halos with a characteristic
mass of ~10^{12}Msun/h with a duty cycle for the quasar activity of 1 per
cent.Comment: 20 pages, 18 figures. Minor modifications to match version accepted
by journa
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