1,027 research outputs found
Follicle and Oocyte Relationships During Superovulation in the Heifer
As the female cow matures, the majority of her follicles become atretic and are lost as a store house of the female gamete (oocyte). Emphasis on in vitro fertilization to maximize the utilization of superior animals for transplant of frozen embryos is considerably limited by the number of viable mature oocytes that can be collected. Understanding the biochemical environment required to produce maximum numbers of mature, fertilizable oocytes is a prime requirement to utilize this technology in increasing meat animal production and efficiency.
The goal of these studies was to characterize the endocrine and biochemical events associated with follicle and oocyte maturation to establish the best environment for follicle development and maximize numbers
A multiple electrode carrier for chronic implantation in small animals
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32480/1/0000565.pd
The First Galaxies: Chemical Enrichment, Mixing, and Star Formation
Using three-dimensional cosmological simulations, we study the assembly
process of one of the first galaxies, with a total mass of 10^8 M_sun,
collapsing at z = 10. Our main goal is to trace the transport of the heavy
chemical elements produced and dispersed by a pair-instability supernova
exploding in one of the minihalo progenitors. To this extent, we incorporate an
efficient algorithm into our smoothed particle hydrodynamics code which
approximately models turbulent mixing as a diffusion process. We study this
mixing with and without the radiative feedback from Population III stars that
subsequently form in neighboring minihalos. Our simulations allow us to
constrain the initial conditions for second-generation star formation, within
the first galaxy itself, and inside of minihalos that virialize after the
supernova explosion. We find that most minihalos remain unscathed by ionizing
radiation or the supernova remnant, while some are substantially photoheated
and enriched to supercritical levels, likely resulting in the formation of
low-mass Population III or even Population II stars. At the center of the newly
formed galaxy, 10^5 M_sun of cold, dense gas uniformly enriched to 10^-3 Z_sun
are in a state of collapse, suggesting that a cluster of Population II stars
will form. The first galaxies, as may be detected by the James Webb Space
Telescope, would therefore already contain stellar populations familiar from
lower redshifts.Comment: 13 pages, 9 figures, published in Ap
Chiral Extrapolation of Lattice Data for Heavy Meson Hyperfine Splittings
We investigate the chiral extrapolation of the lattice data for the
light-heavy meson hyperfine splittings D^*-D and B^*-B to the physical region
for the light quark mass. The chiral loop corrections providing non-analytic
behavior in m_\pi are consistent with chiral perturbation theory for heavy
mesons. Since chiral loop corrections tend to decrease the already too low
splittings obtained from linear extrapolation, we investigate two models to
guide the form of the analytic background behavior: the constituent quark
potential model, and the covariant model of QCD based on the ladder-rainbow
truncation of the Dyson-Schwinger equations. The extrapolated hyperfine
splittings remain clearly below the experimental values even allowing for the
model dependence in the description of the analytic background.Comment: 14 pages, 4 figures, typos corrected, presentation clarifie
Stochastic Gravitational Wave Background from Cosmological Supernovae
Based on new developments in the understanding of supernovae (SNe) as
gravitational-wave (GW) sources we estimate the GW background from all cosmic
SNe. For a broad range of frequencies around 1 Hz, this background is crudely
comparable to the GW background expected from standard inflationary models.
While our estimate remains uncertain within several orders of magnitude, the SN
GW background may become detectable by second-generation space-based
interferometers such as the proposed Big-Bang Observatory (BBO). By the same
token, the SN GWs may become a foreground for searches of the inflationary GWs,
in particular for sub-Hz frequencies where the SN background is Gaussian and
where the BBO will be most sensitive. SN simulations lasting far beyond the
usual cutoff of about 1 second are needed for more robust predictions in the
sub-Hz frequency band. An even larger GW background can arise from a
hypothetical early population of massive stars, although their GW source
strength as well as their abundance are currently poorly understood.Comment: 9 revtex pages, 8 ps figures included, considerably extended version
with detailed discussion of uncertainties due to supernova physics and rate
Accretion onto black holes formed by direct collapse
One possible scenario for the formation of massive black holes (BHs) in the
early Universe is from the direct collapse of primordial gas in atomic-cooling
dark matter haloes in which the gas is unable to cool efficiently via molecular
transitions. We study the formation of such BHs, as well as the accretion of
gas onto these objects and the high energy radiation emitted in the accretion
process, by carrying out cosmological radiation hydrodynamics simulations. In
the absence of radiative feedback, we find an upper limit to the accretion rate
onto the central object which forms from the initial collapse of hot (~ 10^4 K)
gas of the order of 0.1 MSun per year. This is high enough for the formation of
a supermassive star, the immediate precursor of a BH, with a mass of the order
of 10^5 MSun. Assuming that a fraction of this mass goes into a BH, we track
the subsequent accretion of gas onto the BH self-consistently with the high
energy radiation emitted from the accretion disk. Using a ray-tracing algorithm
to follow the propagation of ionizing radiation, we model in detail the
evolution of the photoionized region which forms around the accreting BH. We
find that BHs with masses of the order of 10^4 MSun initially accrete at close
to the Eddington limit, but that the accretion rate drops to of order 1 percent
of the Eddington limit after ~ 10^6 yr, due to the expansion of the gas near
the BH in response to strong photoheating and radiation pressure. One signature
of the accretion of gas onto BHs formed by direct collapse, as opposed to
massive Pop III star formation, is an extremely high ratio of the luminosity
emitted in He II 1640 to that emitted in H_alpha (or Ly_alpha); this could be
detected by the James Webb Space Telescope. Finally, we briefly discuss
implications for the coevolution of BHs and their host galaxies.Comment: 16 pages; 17 figures, slightly reduced quality; MNRAS in pres
Prevalence of sexual harassment among Norwegian female elite athletes in relation to sport type
Although it is often assumed that the prevalence of sexual harassment is different in different sports, this assumption has not been empirically tested. This study considers whether the experience of sexual harassment varies by sport. The female elite athletes (N = 553) in the study participated in 56 different sport disciplines. These were grouped as follows :1) team or individual sports; 2) extent to which clothing required for competition is revealing ; 3) gender structure (male-or female dominated membership statistics); and 4) gender culture (masculine, gender-neutral, or feminine). The data show that sexual harassment occurs in every sport group. Female elite athletes who participated in âmasculineâ sports appear to experience more harassment than women in the other groups. We conclude that, when it comes to female athletesâ experiences of sexual harassment, sport type matters far less than sport participation per se
Excited Heavy Mesons Beyond Leading Order in the Heavy Quark Expansion
We examine the decays of excited heavy mesons, including the leading power
corrections to the heavy quark limit. We find a new and natural explanation for
the large deviation of the width of the from the heavy quark
symmetry prediction. Our formalism leads to detailed predictions for the
properties of the excited bottom mesons, some of which recently have been
observed. Finally, we present a detailed analysis of the effect of power
corrections and finite meson widths on the angular distributions which may be
measured in heavy meson decays.Comment: Uses REVTeX, 19 pages, 6 EPS figures embedded with epsf.st
Chiral extrapolation of lattice data for the hyperfine splittings of heavy mesons
Hyperfine splittings between the heavy vector (D*, B*) and pseudoscalar (D,
B) mesons have been calculated numerically in lattice QCD, where the pion mass
(which is related to the light quark mass) is much larger than its physical
value. Naive linear chiral extrapolations of the lattice data to the physical
mass of the pion lead to hyperfine splittings which are smaller than
experimental data. In order to extrapolate these lattice data to the physical
mass of the pion more reasonably, we apply the effective chiral perturbation
theory for heavy mesons, which is invariant under chiral symmetry when the
light quark masses go to zero and heavy quark symmetry when the heavy quark
masses go to infinity. This leads to a phenomenological functional form with
three parameters to extrapolate the lattice data. It is found that the
extrapolated hyperfine splittings are even smaller than those obtained using
linear extrapolation. We conclude that the source of the discrepancy between
lattice data for hyperfine splittings and experiment must lie in non-chiral
physics.Comment: 27 pages, 6 figure
A very brief description of LOFAR - the Low Frequency Array
LOFAR (Low Frequency Array) is an innovative radio telescope optimized for
the frequency range 30-240 MHz. The telescope is realized as a phased aperture
array without any moving parts. Digital beam forming allows the telescope to
point to any part of the sky within a second. Transient buffering makes
retrospective imaging of explosive short-term events possible. The scientific
focus of LOFAR will initially be on four key science projects (KSPs): 1)
detection of the formation of the very first stars and galaxies in the universe
during the so-called epoch of reionization by measuring the power spectrum of
the neutral hydrogen 21-cm line (Shaver et al. 1999) on the ~5' scale; 2)
low-frequency surveys of the sky with of order expected new sources; 3)
all-sky monitoring and detection of transient radio sources such as gamma-ray
bursts, x-ray binaries, and exo-planets (Farrell et al. 2004); and 4) radio
detection of ultra-high energy cosmic rays and neutrinos (Falcke & Gorham 2003)
allowing for the first time access to particles beyond 10^21 eV (Scholten et
al. 2006). Apart from the KSPs open access for smaller projects is also
planned. Here we give a brief description of the telescope.Comment: 2 pages, IAU GA 2006, Highlights of Astronomy, Volume 14, K.A. van
der Hucht, e
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