584 research outputs found
Mechanosensitive Neurons on the Internal Reproductive Tract Contribute to Egg-Laying-Induced Acetic Acid Attraction in Drosophila
SummarySelecting a suitable site to deposit their eggs is an important reproductive need of Drosophila females. Although their choosiness toward egg-laying sites is well documented, the specific neural mechanism that activates femalesâ search for attractive egg-laying sites is not known. Here, we show that distention and contraction of femalesâ internal reproductive tract triggered by egg delivery through the tract plays a critical role in activating such search. We found that females start to exhibit acetic acid (AA) attraction prior to depositing each egg but no attraction when they are not laying eggs. Artificially distending the reproductive tract triggers AA attraction in non-egg-laying females, whereas silencing the mechanosensitive neurons we identified that can sense the contractile status of the tract eliminates such attraction. Our work uncovers the circuit basis of an important reproductive need of Drosophila females and provides a simple model for dissecting the neural mechanism that underlies a reproductive need-induced behavioral modification
Identification of valid reference genes during the differentiation of human myoblasts
<p>Abstract</p> <p>Background</p> <p>Analysis of RNA expression using real-time PCR (qRT-PCR) traditionally includes reference genes (RG) as an internal control. This practice is being questioned as it becomes increasingly clear that RG may vary considerably under certain experimental conditions. Thus, the validity of a particular RG must be determined for each experimental setting. We used qRT-PCR to measure the levels of six RG, which have been reported in the literature to be invariant. The RG were analyzed in human myoblast cultures under differentiation conditions. We examined the expression by qRT-PCR of mRNA encoding Beta-actin (ACTB), Beta-2-microglobulin (B2M), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), peptidylprolyl isomerase A (PPIA), TATA box binding protein (TBP) and ribosomal protein, large, P0 (RPLPO). The mRNA expression of the following genes of interest (GOI) were analyzed: skeletal muscle alpha 1 actin (ACTA1), myogenin/myogenic factor 4 (MYOG), embryonic skeletal muscle myosin heavy chain 3 (MYH3) and the activity of creatine phosphokinase (CK). The geNorm, NormFinder and BestKeeper software programs were used to ascertain the most suitable RG to normalize the RNA input.</p> <p>Results</p> <p>Using the geNorm program, RPLPO and TBP were found to be the most stable genes, additionally a suitable normalization factor (NF) was calculated. The NormFinder software showed that RPLPO was the most stable, whereas TBP ranked second. BestKeeper program also revealed that RPLPO and TBP as stable genes, but PPIA was the most stable reference gene, whereas GAPDH and ACTB were the worst ranked.</p> <p>Conclusion</p> <p>RNA expression analyses including three independent softwares revealed that RPLPO, TBP as reference genes or NF calculated by geNorm software, are suitable to normalize the mRNA expression in myoblast after culture under differentiation conditions. Significant correlations can be identified between the differentiations markers ACTA1, MYOG, MYH3 and creatine phosphokinase (CK) activity, when the expression is normalized with the NF calculated with RPLPO and TBP.</p
Inhibition of thermohaline mixing by a magnetic field in Ap star descendants: Implications for the Galactic evolution of 3He
To reconcile the measurements of 3He/H in Galactic HII regions with high
values of 3He in a couple of planetary nebulae, we propose that thermohaline
mixing is inhibited by a fossil magnetic field in red giant stars that are
descendants of Ap stars. We examine the effect of a magnetic field on the
salt-finger instability, using a local analysis. We obtain a threshold for the
magnetic field of 10^4 - 10^5 Gauss, above which it inhibits thermohaline
mixing in red giant stars located at or above the bump. Fields of that order
are expected in the descendants of the Ap stars, taking into account the
contraction of their core. We conclude that in a large fraction of the
descendants of Ap stars thermohaline mixing does not occur. As a consequence
these objects must produce 3He as predicted by the standard theory of stellar
evolution and as observed in the planetary nebulae NGC3242 and J320. The
relative number of such stars with respect to non-magnetic objects that undergo
thermohaline mixing is consistent with the statistical constraint coming from
observations of the carbon isotopic ratio in red giant stars. It also satisfies
the Galactic requirements for the evolution of the 3He abundance.Comment: Accepted for publication in A&A Letters (Vol.476
3C 220.3: a radio galaxy lensing a submillimeter galaxy
Herschel Space Observatory photometry and extensive multiwavelength followup
have revealed that the powerful radio galaxy 3C 220.3 at z=0.685 acts as a
gravitational lens for a background submillimeter galaxy (SMG) at z=2.221. At
an observed wavelength of 1mm, the SMG is lensed into three distinct images. In
the observed near infrared, these images are connected by an arc of 1.8" radius
forming an Einstein half-ring centered near the radio galaxy. In visible light,
only the arc is apparent. 3C 220.3 is the only known instance of strong
galaxy-scale lensing by a powerful radio galaxy not located in a galaxy cluster
and therefore it offers the potential to probe the dark matter content of the
radio galaxy host. Lens modeling rejects a single lens, but two lenses centered
on the radio galaxy host A and a companion B, separated by 1.5", provide a fit
consistent with all data and reveal faint candidates for the predicted fourth
and fifth images. The model does not require an extended common dark matter
halo, consistent with the absence of extended bright X-ray emission on our
Chandra image. The projected dark matter fractions within the Einstein radii of
A (1.02") and B (0.61") are about 0.4 +/- 0.3 and 0.55 +/- 0.3. The mass to
i-band light ratios of A and B, M/L ~ 8 +/- 4 Msun/Lsun, appear comparable to
those of radio-quiet lensing galaxies at the same redshift in the CASTLES, LSD,
and SL2S samples. The lensed SMG is extremely bright with observed f(250um) =
440mJy owing to a magnification factor mu~10. The SMG spectrum shows luminous,
narrow CIV 154.9nm emission, revealing that the SMG houses a hidden quasar in
addition to a violent starburst. Multicolor image reconstruction of the SMG
indicates a bipolar morphology of the emitted ultraviolet (UV) light suggestive
of cones through which UV light escapes a dust-enshrouded nucleus.Comment: 17 pages, 14 Figures, accepted for publication in Ap
Investigation of conduction band structure, electron scattering mechanisms and phase transitions in indium selenide by means of transport measurements under pressure
In this work we report on Hall effect, resistivity and thermopower
measurements in n-type indium selenide at room temperature under either
hydrostatic and quasi-hydrostatic pressure. Up to 40 kbar (= 4 GPa), the
decrease of carrier concentration as the pressure increases is explained
through the existence of a subsidiary minimum in the conduction band. This
minimum shifts towards lower energies under pressure, with a pressure
coefficient of about -105 meV/GPa, and its related impurity level traps
electrons as it reaches the band gap and approaches the Fermi level. The
pressure value at which the electron trapping starts is shown to depend on the
electron concentration at ambient pressure and the dimensionality of the
electron gas. At low pressures the electron mobility increases under pressure
for both 3D and 2D electrons, the increase rate being higher for 2D electrons,
which is shown to be coherent with previous scattering mechanisms models. The
phase transition from the semiconductor layered phase to the metallic sodium
cloride phase is observed as a drop in resistivity around 105 kbar, but above
40 kbar a sharp nonreversible increase of the carrier concentration is
observed, which is attributed to the formation of donor defects as precursors
of the phase transition.Comment: 18 pages, Latex, 10 postscript figure
Thermohaline mixing in evolved low-mass stars
Thermohaline mixing has recently been proposed to occur in low-mass red
giants, with large consequence for the chemical yields of low-mass stars. We
investigate the role of thermohaline mixing during the evolution of stars
between 1Msun and 3Msun, in comparison to other mixing processes acting in
these stars. We use a stellar evolution code which includes rotational mixing,
internal magnetic fields and thermohaline mixing. We confirm that during the
red giant stage, thermohaline mixing has the potential to decrease the
abundance of ^3He which is produced earlier on the main sequence. In our models
we find that this process is working on the RGB only in stars with initial mass
M \simle 1.5Msun. Moreover we report that thermohaline mixing is present also
during core helium burning and beyond, and has the potential to change the
surface abundances of AGB stars. While we find rotational and magnetic mixing
to be negligible compared to the thermohaline mixing in the relevant layers,
the interaction of thermohaline motions with the differential rotation may be
essential to establish the time scale of thermohaline mixing in red giants. To
explain the surface abundances observed at the bump in the luminosity function,
the speed of the mixing process needs to be more than two orders of magnitude
higher than in our models. However it is not clear if thermohaline mixing is
the only physical process responsible for these surface abundance anomalies.
Therefore, at this stage, it is not possible to calibrate the efficiency of
thermohaline mixing against the observations.Comment: 10 pages - Accepted for publication in A&
C, N and O abundances in red clump stars of the Milky Way
The Hipparcos orbiting observatory has revealed a large number of
helium-core-burning "clump" stars in the Galactic field. These low-mass stars
exhibit signatures of extra-mixing processes that require modeling beyond the
first dredge-up of standard models. The 12C/13C ratio is the most robust
diagnostic of deep mixing, because it is insensitive to the adopted stellar
parameters. In this work we present 12C/13C determinations in a sample of 34
Galactic clump stars as well as abundances of nitrogen, carbon and oxygen.
Abundances of carbon were studied using the C2 Swan (0,1) band head at 5635.5
A. The wavelength interval 7980-8130 A with strong CN features was analysed in
order to determine nitrogen abundances and 12C/13C isotope ratios. The oxygen
abundances were determined from the [O I] line at 6300 A. Compared with the Sun
and dwarf stars of the Galactic disk, mean abundances in the investigated clump
stars suggest that carbon is depleted by about 0.2 dex, nitrogen is enhanced by
0.2 dex and oxygen is close to abundances in dwarfs. Comparisons to
evolutionary models show that the stars fall into two groups: the one is of
first ascent giants with carbon isotope ratios altered according to the first
dredge-up prediction, and the other one is of helium-core-burning stars with
carbon isotope ratios altered by extra mixing. The stars investigated fall to
these groups in approximately equal numbers.Comment: 8 pages 6 figures Accepted for publication in MNRA
Concurrent Bounded Model Checking
The Definitive Version can be found in the ACM Digital Library here: http://dx.doi.org/10.1145/2693208.2693240issue_date: January 2015 numpages: 5 acmid: 2693240 keywords: Bounded Model Checking, Concurrency, Symbolic Executionissue_date: January 2015 numpages: 5 acmid: 2693240 keywords: Bounded Model Checking, Concurrency, Symbolic Executionissue_date: January 2015 numpages: 5 acmid: 2693240 keywords: Bounded Model Checking, Concurrency, Symbolic Executio
Thermohaline instability and rotation-induced mixing. I - Low- and intermediate-mass solar metallicity stars up to the end of the AGB
(abridged) Numerous spectroscopic observations provide compelling evidence
for non-canonical processes that modify the surface abundances of low- and
intermediate-mass stars beyond the predictions of standard stellar theory. We
study the effects of thermohaline instability and rotation-induced mixing in
the 1-4 Msun range at solar metallicity. We present evolutionary models by
considering both thermohaline and rotation-induced mixing in stellar interior.
We discuss the effects of these processes on the chemical properties of stars
from the zero age main sequence up to the end of the second dredge-up on the
early-AGB for intermediate-mass stars and up to the AGB tip for low-mass stars.
Model predictions are compared to observational data for
lithium,12C/13C,[N/C],[Na/Fe],16O/17O, and 16O/18O in Galactic open clusters
and in field stars with well-defined evolutionary status,as well as in
planetary nebulae. Thermohaline mixing simultaneously accounts for the observed
behaviour of 12C/13C,[N/C], and lithium in low-mass stars that are more
luminous than the RGB bump, and its efficiency is increasing with decreasing
initial stellar mass. On the TP-AGB,thermohaline mixing leads to lithium
production, although the 7Li yields remain negative. Although the 3He stellar
yields are much reduced thanks to this process, we find that solar-metallicity,
low-mass stars remain net 3He producers. Rotation-induced mixing is found to
change the stellar structure so that in the mass range between \sim 1.5 and 2.2
Msun the thermohaline instability occurs earlier on the red giant branch than
in non-rotating models. Finally rotation accounts for the observed star-to-star
abundance variations at a given evolutionary status, and is necessary to
explain the features of CN-processed material in intermediate-mass stars.Comment: 18 pages, 22 figures, accepted for publication in A&
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