2,097 research outputs found
Identification of stable endogenous reference genes for real-time PCR in the human fetal gonad using an external standard technique
Peer reviewedPostprin
Blindly detecting orbital modulations of jets from merging supermassive black holes
In the last few years before merger, supermassive black hole binaries will
rapidly inspiral and precess in a magnetic field imposed by a surrounding
circumbinary disk. Multiple simulations suggest this relative motion will
convert some of the local energy to a Poynting-dominated outflow, with a
luminosity 10^{43} erg/s * (B/10^4 G)^2(M/10^8 Msun)^2 (v/0.4 c)^2, some of
which may emerge as synchrotron emission at frequencies near 1 GHz where
current and planned wide-field radio surveys will operate. On top of a secular
increase in power on the gravitational wave inspiral timescale, orbital motion
will produce significant, detectable modulations, both on orbital periods and
(if black hole spins are not aligned with the binary's total angular momenta)
spin-orbit precession timescales. Because the gravitational wave merger time
increases rapidly with separation, we find vast numbers of these transients are
ubiquitously predicted, unless explicitly ruled out (by low efficiency
) or obscured (by accretion geometry f_{geo}). If the fraction of
Poynting flux converted to radio emission times the fraction of lines of sight
accessible is sufficiently large (f_{geo} \epsilon > 2\times 10^{-4}
for a 1 year orbital period), at least one event is accessible to future blind
surveys at a nominal 10^4 {deg}^2 with 0.5 mJy sensitivity. Our procedure
generalizes to other flux-limited surveys designed to investigate EM signatures
associated with many modulations produced by merging SMBH binaries.Comment: Submitted to ApJ. v1 original submission; v2 minor changes in
response to refere
Reactions at Polymer Interfaces: Transitions from Chemical to Diffusion-Control and Mixed Order Kinetics
We study reactions between end-functionalized chains at a polymer-polymer
interface. For small chemical reactivities (the typical case) the number of
diblocks formed, , obeys 2nd order chemically controlled kinetics, , until interfacial saturation. For high reactivities (e.g. radicals) a
transition occurs at short times to 2nd order diffusion-controlled kinetics,
with for unentangled chains while and
regimes occur for entangled chains. Long time kinetics are 1st order and
controlled by diffusion of the more dilute species to the interface: for unentangled cases, while and regimes
arise for entangled systems. The final 1st order regime is governed by center
of gravity diffusion, .Comment: 11 pages, 3 figures, uses poliface.sty, minor changes, to appear in
Europhysics Letter
Effect of FSH on testicular morphology and spermatogenesis in gonadotrophin-deficient hypogonadal mice lacking androgen receptors
Follicle stimulating hormone (FSH) and androgen act to stimulate and maintain spermatogenesis. FSH acts directly on the Sertoli cells to stimulate germ cell number and acts indirectly to increase androgen production by the Leydig cells. In order to differentiate between the direct effects of FSH on spermatogenesis and those mediated indirectly through androgen action we have crossed hypogonadal (hpg) mice which lack gonadotrophins with mice lacking androgen receptors (AR) either ubiquitously (ARKO) or specifically on the Sertoli cells (SCARKO). These hpg.ARKO and hpg.SCARKO mice were treated with recombinant FSH for 7 days and testicular morphology and cell numbers assessed. In untreated hpg and hpg.SCARKO mice germ cell development was limited and did not progress beyond the pachytene stage. In hpg.ARKO mice testes were smaller with fewer Sertoli cells and germ cells compared to hpg mice. Treatment with FSH had no effect on Sertoli cell number but significantly increased germ cell numbers in all groups. In hpg mice FSH increased numbers of spermatogonia and spermatocytes and induced round spermatid formation. In hpg.SCARKO and hpg.ARKO mice, in contrast, only spermatogonial and spermatocyte numbers were increased with no formation of spermatids. Leydig cell numbers were increased by FSH in hpg and hpg.SCARKO mice but not in hpg.ARKO mice. Results show that in rodents 1) FSH acts to stimulate spermatogenesis through an increase in spermatogonial number and subsequent entry of these cells into meiosis, 2) FSH has no direct effect on the completion of meiosis and 3) FSH effects on Leydig cell number are mediated through interstitial ARs
Kinetic Regimes and Cross-Over Times in Many-Particle Reacting Systems
We study kinetics of single species reactions ("A+A -> 0") for general local
reactivity Q and dynamical exponent z (rms displacement x_t ~ t^{1/z}.) For
small molecules z=2, whilst z=4,8 for certain polymer systems. For dimensions d
above the critical value d_c=z, kinetics are always mean field (MF). Below d_c,
the density n_t initially follows MF decay, n_0 - n_t ~ n_0^2 Q t. A 2-body
diffusion-controlled regime follows for strongly reactive systems (Q>Qstar ~
n_0^{(z-d)/d}) with n_0 - n_t ~ n_0^2 x_t^d. For Q<Qstar, MF kinetics persist,
with n_t ~ 1/Qt. In all cases n_t ~ 1/x_t^d at the longest times. Our analysis
avoids decoupling approximations by instead postulating weak physically
motivated bounds on correlation functions.Comment: 10 pages, 1 figure, uses bulk2.sty, minor changes, submitted to
Europhysics Letter
Accurate and efficient waveforms for compact binaries on eccentric orbits
Compact binaries that emit gravitational waves in the sensitivity band of
ground-based detectors can have non-negligible eccentricities just prior to
merger, depending on the formation scenario. We develop a purely analytic,
frequency-domain model for gravitational waves emitted by compact binaries on
orbits with small eccentricity, which reduces to the quasi-circular
post-Newtonian approximant TaylorF2 at zero eccentricity and to the
post-circular approximation of Yunes et al. (2009) at small eccentricity. Our
model uses a spectral approximation to the (post-Newtonian) Kepler problem to
model the orbital phase as a function of frequency, accounting for eccentricity
effects up to at each post-Newtonian order. Our approach
accurately reproduces an alternative time-domain eccentric waveform model for
eccentricities and binaries with total mass less than 12 solar
masses. As an application, we evaluate the signal amplitude that eccentric
binaries produce in different networks of existing and forthcoming
gravitational waves detectors. Assuming a population of eccentric systems
containing black holes and neutron stars that is uniformly distributed in
co-moving volume, we estimate that second generation detectors like Advanced
LIGO could detect approximately 0.1-10 events per year out to redshift , while an array of Einstein Telescope detectors could detect hundreds of
events per year to redshift .Comment: 12 pages, 6 figures, 1 appendix. Submitted to Phys. Rev. D. v2:
affiliations updated, one reference corrected. Accepted to Phys. Rev.
Observing IMBH-IMBH Binary Coalescences via Gravitational Radiation
Recent numerical simulations have suggested the possibility of forming double
intermediate mass black holes (IMBHs) via the collisional runaway scenario in
young dense star clusters. The two IMBHs formed would exchange into a common
binary shortly after their birth, and quickly inspiral and merge. Since
space-borne gravitational wave (GW) observatories such as LISA will be able to
see the late phases of their inspiral out to several Gpc, and LIGO will be able
to see the merger and ringdown out to similar distances, they represent
potentially significant GW sources. In this Letter we estimate the rate at
which LISA and LIGO will see their inspiral and merger in young star clusters,
and discuss the information that can be extracted from the observations. We
find that LISA will likely see tens of IMBH--IMBH inspirals per year, while
advanced LIGO could see ~10 merger and ringdown events per year, with both
rates strongly dependent on the distribution of cluster masses and densities.Comment: Accepted for publication in ApJL. Minor changes to reflect accepted
version. 4 pages in emulateapj, 3 figure
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