80 research outputs found
Nova V1425 Aquilae 1995 - The Early Appearance of Accretion Processes in An Intermediate Polar Candidate
Continuous CCD photometry of Nova Aquilae 1995 was performed through the
standard B,V,R and I filters during three nights in 1995 and with the I filter
during 18 nights in 1996. The power spectrum of the 1996 data reveals three
periodicities in the light curve: 0.2558 d, 0.06005 d and 0.079 d, with
peak-to-peak amplitudes of about 0.012, 0.014 and 0.007 mag. respectively.
The two shorter periods are absent from the power spectrum of the 1995 light
curve, while the long one is probably already present in the light curve of
that year.
We propose that V1425 Aql should be classified as an Intermediate - Polar CV.
Accordingly the three periods are interpreted as the orbital period of the
underlying binary system, the spin period of the magnetic white dwarf and the
beat period between them. Our results suggest that no later than 15 months
after the outburst of the nova, accretion processes are taking place in this
stellar system. Matter is being transferred from the cool component, most
likely through an accretion disc and via accretion columns on to the magnetic
poles of the hot component.Comment: 7 pages, 4 eps. figures, Latex, accepted for publication in MNRA
Metformin mitigates the impaired development of skeletal muscle in the offspring of obese mice
Background: Maternal obesity is linked with offspring obesity and type 2 diabetes. Skeletal muscle (SM) insulin resistance is central to the development of diabetes. Adenosine monophosphate (AMP)-activated protein kinase (AMPK) is inhibited in SM of fetuses born to obese mothers
MACHO Alert 95-30 : First Real-Time Observation of Extended Source Effects in Gravitational Microlensing
We present analysis of MACHO Alert 95-30, a dramatic gravitational
microlensing event towards the Galactic bulge whose peak magnification departs
significantly from the standard point-source microlensing model. Alert 95-30
was observed in real-time by the Global Microlensing Alert Network (GMAN),
which obtained densely sampled photometric and spectroscopic data throughout
the event. We interpret the light-curve ``fine structure'' as indicating
transit of the lens across the extended face of the source star. This signifies
resolution of a star several kpc distant. We find a lens angular impact
parameter theta_{min}/theta_{source} = 0.715 +/- 0.003. This information, along
with the radius and distance of the source, provides an additional constraint
on the lensing system. Spectroscopic and photometric data indicate the source
is an M4 III star of radius 61 +/- 12 Rsun, located on the far side of the
bulge at 9 kpc. We derive a lens angular velocity, relative to the source, of
21.5 +/- 4.9 km/s/kpc, where the error is dominated by uncertainty in the
source radius. Likelihood analysis yields a median lens mass of
0.67{+2.53}{-0.46} Msun, located with 80% probability in the Galactic bulge at
a distance of 6.93{+1.56}{-2.25} kpc. If the lens is a main-sequence star, we
can include constraints on the lens luminosity. This modifies our estimates to
M_lens = 0.53{+0.52}{-0.35} Msun and D_lens = 6.57{+0.99}{-2.25} kpc. Spectra
taken during the event show that the absorption line equivalent widths of H
alpha and the TiO bands near 6700 A vary, as predicted for microlensing of an
extended source. This is most likely due to center-to-limb variation in the
stellar spectral lines. These data demonstrate the feasibility of using
microlensing limb crossings as a tool to probe stellar atmospheres directly.Comment: 32 pages including 6 tables, and 15 figures; Uses AASTeX 4.0;
submitted to The Astrophysical Journa
Regulation of Asymmetrical Cytokinesis by cAMP during Meiosis I in Mouse Oocytes
Mammalian oocytes undergo an asymmetrical first meiotic division, extruding half of their chromosomes in a small polar body to preserve maternal resources for embryonic development. To divide asymmetrically, mammalian oocytes relocate chromosomes from the center of the cell to the cortex, but little is known about the underlying mechanisms. Here, we show that upon the elevation of intracellular cAMP level, mouse oocytes produced two daughter cells with similar sizes. This symmetrical cell division could be rescued by the inhibition of PKA, a cAMP-dependent protein kinase. Live cell imaging revealed that a symmetrically localized cleavage furrow resulted in symmetrical cell division. Detailed analyses demonstrated that symmetrically localized cleavage furrows were caused by the inappropriate central positioning of chromosome clusters at anaphase onset, indicating that chromosome cluster migration was impaired. Notably, high intracellular cAMP reduced myosin II activity, and the microinjection of phospho-myosin II antibody into the oocytes impeded chromosome migration and promoted symmetrical cell division. Our results support the hypothesis that cAMP plays a role in regulating asymmetrical cell division by modulating myosin II activity during mouse oocyte meiosis I, providing a novel insight into the regulation of female gamete formation in mammals
Multiwavelength observations of short time-scale variability in NGC 4151. IV. Analysis of multiwavelength continuum variability
This paper combines data from the three preceding papers in order to analyze
the multi-waveband variability and spectral energy distribution of the
Seyfert~1 galaxy NGC~4151 during the December 1993 monitoring campaign. The
source, which was near its peak historical brightness, showed strong,
correlated variability at X-ray, ultraviolet, and optical wavelengths. The
strongest variations were seen in medium energy (1.5~keV) X-rays, with a
normalized variability amplitude (NVA) of 24\%. Weaker (NVA = 6\%) variations
(uncorrelated with those at lower energies) were seen at soft -ray
energies of 100~keV. No significant variability was seen in softer
(0.1--1~keV) X-ray bands. In the ultraviolet/optical regime, the NVA decreased
from 9\% to 1\% as the wavelength increased from 1275~\AA\ to 6900~\AA. These
data do not probe extreme ultraviolet (1200~\AA\ to 0.1~keV) or hard X-ray
(2--50~keV) variability. The phase differences between variations in different
bands were consistent with zero lag, with upper limits of \ls0.15~day between
1275~\AA\ and the other ultraviolet bands, \ls0.3~day between 1275~\AA\ and
1.5~keV, and \ls1~day between 1275~\AA\ and 5125~\AA. These tight limits
represent more than an order of magnitude improvement over those determined in
previous multi-waveband AGN monitoring campaigns. The ultraviolet fluctuation
power spectra showed no evidence for periodicity, but were instead well-fitted
with a very steep, red power-law ().
If photons emitted at a ``primary" waveband are absorbed by nearby material
and ``reprocessed" to produce emission at a secondary waveband, causality
arguments require that variations in the secondary band follow those in the
primary band. The tight interband correlation and limits on the ultraviolet andComment: 35 pages, LaTeX (including aaspp4), including 7 PostScript figures;
To appear in the ApJ (October 20, 1996) Vol. 47
Biodiesel production by esterification of oleic acid over zeolite Y prepared from kaolin
Zeolite Y, with a Si/Al ratio 3.1, was prepared using Iraqi kaolin and tested as a catalyst in the liquid-phase esterification of oleic acid (a simulated free fatty acid frequently used as a model reaction for biodiesel production). XRD confirmed the presence of the characteristic faujasite structure of zeolite Y, and further analysis was conducted using BET adsorption, FTIR spectroscopy, XRF, DLS particle size and SEM. A range of experimental conditions were employed to study the reaction; alcohol/oleic acid molar ratio, temperature, and catalyst mass loading. The optimum conditions for the reaction were observed at 70 Β°C, 5 wt% catalyst loading and 6:1 ethanol to oleic acid molar ratio. The oleic acid conversion using the zeolite prepared from kaolin was 85% after 60 min, while the corresponding value for a commercial sample of HY zeolite was 76%. Our findings show that low Si/Al ratio zeolite Y is a suitable catalyst for esterification, which is in contrast to the widespread view of the unsuitability of zeolites, in general, for such applications
Risk factors for preterm birth in an international prospective cohort of nulliparous women
To identify risk factors for spontaneous preterm birth (birth ,37 weeks gestation) with intact membranes(SPTB-IM) and SPTB after prelabour rupture of the membranes (SPTB-PPROM) for nulliparous pregnant women. DESIGN: Prospective international multicentre cohort. PARTICIPANTS: 3234 healthy nulliparous women with a singleton pregnancy, follow up was complete in 3184 of participants (98.5%). RESULTS: Of the 3184 women, 156 (4.9%) had their pregnancy complicated by SPTB; 96 (3.0%) and 60 (1.9%) in the SPTB-IM and SPTB-PPROM categories, respectively. Independent risk factors for SPTB-IM were shorter cervical length, abnormal uterine Doppler flow, use of marijuana pre-pregnancy, lack of overall feeling of well being, being of Caucasian ethnicity, having a mother with diabetes and/or a history of preeclampsia, and a family history of low birth weight babies. Independent risk factors for SPTB-PPROM were shorter cervical length, short stature, participantβs not being the first born in the family, longer time to conceive, not waking up at night, hormonal fertility treatment (excluding clomiphene), mild hypertension, family history of recurrent gestational diabetes, and maternal family history of any miscarriage (risk reduction). Low BMI (<20) nearly doubled the risk for SPTB-PPROM (odds ratio 2.64; 95% CI 1.07β6.51). The area under the receiver operating characteristics curve (AUC), after internal validation, was 0.69 for SPTB-IM and 0.79 for SPTB-PPROM. CONCLUSION: The ability to predict PTB in healthy nulliparous women using clinical characteristics is modest. The dissimilarity of risk factors for SPTB-IM compared with SPTB-PPROM indicates different pathophysiological pathways underlie these distinct phenotypes.Gustaaf Albert Dekker, Shalem Y. Lee, Robyn A. North, Lesley M. McCowan, Nigel A.B. Simpson and Claire T. Robert
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