794 research outputs found
Rapid Direct Action of Estradiol in GnRH Neurons: Findings and Implications
Estradiol plays a pivotal role in the control of gonadotropin-releasing hormone (GnRH) neuronal function and female reproduction. While positive and negative feedback actions of estradiol that enhance and suppress release of GnRH and LH are primarily mediated through estrogen receptor alpha located in interneurons, a series of recent studies in our laboratory indicate that rapid excitatory actions of estradiol also directly modify GnRH neuronal activity. We observed this phenomenon in cultured primate GnRH neurons, but similar rapid direct actions of estradiol are also described in cultured GnRH neurons and green fluorescent protein-labeled GnRH neurons of mice. Importantly, rapid direct action of estradiol in GnRH neurons is mediated through membrane or membrane associated receptors, such as GPR30, STX-sensitive receptors, and ERÎČ. In this review, possible implications of this rapid estradiol action in GnRH neurons are discussed
Geometrical Effects of Baryon Density Inhomogeneities on Primordial Nucleosynthesis
We discuss effects of fluctuation geometry on primordial nucleosynthesis. For
the first time we consider condensed cylinder and cylindrical-shell fluctuation
geometries in addition to condensed spheres and spherical shells. We find that
a cylindrical shell geometry allows for an appreciably higher baryonic
contribution to be the closure density (\Omega_b h_{50}^2 \la 0.2) than that
allowed in spherical inhomogeneous or standard homogeneous big bang models.
This result, which is contrary to some other recent studies, is due to both
geometry and recently revised estimates of the uncertainties in the
observationally inferred primordial light-element abundances. We also find that
inhomogeneous primordial nucleosynthesis in the cylindrical shell geometry can
lead to significant Be and B production. In particular, a primordial beryllium
abundance as high as [Be] = 12 + log(Be/H) is possible while still
satisfying all of the light-element abundance constraints.Comment: Latex, 20 pages + 11 figures(not included). Entire ps file with
embedded figures available via anonymous ftp at
ftp://genova.mtk.nao.ac.jp/pub/prepri/bbgeomet.ps.g
Moving on up: Second-Line Agents as Initial Treatment for Newly-Diagnosed Patients with Chronic Phase CML
The treatment of chronic myelogenous leukemia (CML) was revolutionized by the development of imatinib mesylate, a small molecule inhibitor of several protein tyrosine kinases, including the ABL1 protein tyrosine kinase. The current second generation of FDA-approved ABL tyrosine kinase inhibitors, dasatinib and nilotinib, are more potent inhibitors of BCR-ABL1 kinase in vitro. Originally approved for the treatment of patients who were refractory to or intolerant of imatinib, dasatinib and nilotinib are now also FDA approved in the first-line setting. The choice of tyrosine kinase inhibitor (ie, standard or high dose imatinib, dasatinib, nilotinib) to use for initial therapy in chronic-phase CML (CML-CP) will not always be obvious. Therapy selection will depend on both clinical and molecular factors, which we will discuss in this review
Big Bang Nucleosynthesis and Lepton Number Asymmetry in the Universe
Recently it is reported that there is the discrepancy between big bang
nucleosynthesis theory and observations (BBN crisis). We show that BBN
predictions agree with the primordial abundances of light elements, He4, D, He3
and Li7 inferred from the observational data if an electron neutrino has a net
chemical potential xi_{nu_e} due to lepton asymmetry. We estimate that
xi_{nu_e} = 0.043^{+0.040}_{-0.040} (95% C.L.) and Omega_bh^2 =
0.015^{+0.006}_{-0.003} (95% C.L.).Comment: 10 pages, using AAS LATEX and three postscript figure
Spin gap in the 2D electron system of GaAs/AlGaAs single heterojunctions in weak magnetic fields
We study the interaction-enhanced spin gaps in the two-dimensional electron
gas confined in GaAs/AlGaAs single heterojunctions subjected to weak magnetic
fields. The values are obtained from the chemical potential jumps measured by
magnetocapacitance. The gap increase with parallel magnetic field indicates
that the lowest-lying charged excitations are accompanied with a single spin
flip at the odd-integer filling factor nu=1 and nu=3, in disagreement with the
concept of skyrmions.Comment: as publishe
Super-sample covariance of the power spectrum, bispectrum, halos, voids, and their cross-covariances
We study the effect of super-sample covariance (SSC) on the power spectrum
and higher-order statistics: bispectrum, halo mass function, and void size
function. We also investigate the effect of SSC on the cross-covariance between
the statistics. We consider both the matter and halo fields. Higher-order
statistics of the large-scale structure contain additional cosmological
information beyond the power spectrum and are a powerful tool to constrain
cosmology. They are a promising probe for ongoing and upcoming high precision
cosmological surveys such as DESI, PFS, Rubin Observatory LSST, Euclid,
SPHEREx, SKA, and Roman Space Telescope. Cosmological simulations used in
modeling and validating these statistics often have sizes that are much smaller
than the observed Universe. Density fluctuations on scales larger than the
simulation box, known as super-sample modes, are not captured by the
simulations and in turn can lead to inaccuracies in the covariance matrix. We
compare the covariance measured using simulation boxes containing super-sample
modes to those without. We also compare with the Separate Universe approach. We
find that while the power spectrum, bispectrum and halo mass function show
significant scale- or mass-dependent SSC, the void size function shows
relatively small SSC. We also find significant SSC contributions to the
cross-covariances between the different statistics, implying that future
joint-analyses will need to carefully take into consideration the effect of
SSC.Comment: 8+2 pages, 4 figure
Finite temperature effects on cosmological baryon diffusion and inhomogeneous Big-Bang nucleosynthesis
We have studied finite temperature corrections to the baryon transport cross
sections and diffusion coefficients. These corrections are based upon the
recently computed renormalized electron mass and the modified state density due
to the background thermal bath in the early universe. It is found that the
optimum nucleosynthesis yields computed using our diffusion coefficients shift
to longer distance scales by a factor of about 3. We also find that the minimum
value of abundance decreases by while and
increase. Effects of these results on constraints from primordial
nucleosynthesis are discussed. In particular, we find that a large baryonic
contribution to the closure density (\Omega_b h_{50}^{2} \lsim 0.4) may be
allowed in inhomogeneous models corrected for finite temperature.Comment: 7 pages, 6 figures, submitted to Phys. Rev.
Inhomogeneous Neutrino Degeneracy and Big Bang Nucleosynthesis
We examine Big Bang nucleosynthesis (BBN) in the case of inhomogenous
neutrino degeneracy, in the limit where the fluctuations are sufficiently small
on large length scales that the present-day element abundances are homogeneous.
We consider two representive cases: degeneracy of the electron neutrino alone,
and equal chemical potentials for all three neutrinos. We use a linear
programming method to constrain an arbitrary distribution of the chemical
potentials. For the current set of (highly-restrictive) limits on the
primordial element abundances, homogeneous neutrino degeneracy barely changes
the allowed range of the baryon-to-photon ratio. Inhomogeneous degeneracy
allows for little change in the lower bound on the baryon-to-photon ratio, but
the upper bound in this case can be as large as 1.1 \times 10^{-8} (only
electron neutrino degeneracy) or 1.0 \times 10^{-9} (equal degeneracies for all
three neutrinos). For the case of inhomogeneous neutrino degeneracy, we show
that there is no BBN upper bound on the neutrino energy density, which is
bounded in this case only by limits from structure formation and the cosmic
microwave background.Comment: 6 pages, no figure
Probing neutrino decays with the cosmic microwave background
We investigate in detail the possibility of constraining neutrino decays with
data from the cosmic microwave background radiation (CMBR). Two generic decays
are considered \nu_H -> \nu_L \phi and \nu_H -> \nu_L \nu_L_bar \nu_L. We have
solved the momentum dependent Boltzmann equation in order to account for
possible relativistic decays. Doing this we estimate that any neutrino with
mass m > 1 eV decaying before the present should be detectable with future CMBR
data. Combining this result with other results on stable neutrinos, any
neutrino mass of the order 1 eV should be detectable.Comment: 8 pages, 4 figures, to appear in Phys. Rev.
Boron in Very Metal-Poor Stars
We have observed the B I 2497 A line to derive the boron abundances of two
very metal-poor stars selected to help in tracing the origin and evolution of
this element in the early Galaxy: BD +23 3130 and HD 84937. The observations
were conducted using the Goddard High Resolution Spectrograph on board the
Hubble Space Telescope. A very detailed abundance analysis via spectral
synthesis has been carried out for these two stars, as well as for two other
metal-poor objects with published spectra, using both Kurucz and OSMARCS model
photospheres, and taking into account consistently the NLTE effects on the line
formation. We have also re-assessed all published boron abundances of old disk
and halo unevolved stars. Our analysis shows that the combination of high
effective temperature (Teff > 6000 K, for which boron is mainly ionized) and
low metallicity ([Fe/H]<-1) makes it difficult to obtain accurate estimates of
boron abundances from the B I 2497 A line. This is the case of HD 84937 and
three other published objects (including two stars with [Fe/H] ~ -3), for which
only upper limits can be established. BD +23 3130, with [Fe/H] ~ -2.9 and
logN(B)_NLTE=0.05+/-0.30, appears then as the most metal-poor star for which a
firm measurement of the boron abundance presently exists. The evolution of the
boron abundance with metallicity that emerges from the seven remaining stars
with Teff < 6000 K and [Fe/H]<-1, for which beryllium abundances were derived
using the same stellar parameters, shows a linear increase with a slope ~ 1.
Furthermore, the B/Be ratio found is constant at a value ~ 20 for stars in the
range -3<[Fe/H]<-1. These results point to spallation reactions of ambient
protons and alpha particles with energetic particles enriched in CNO as the
origin of boron and beryllium in halo stars.Comment: 38 pages, 11 Encapsulated Postscript figures (included), uses
aaspp4.sty. Accepted for publication in The Astrophysical Journal. The
preprint is also available at: http://www.iac.es/publicaciones/preprints.htm
- âŠ