1,380 research outputs found
The crystal and molecular structure of Hydridotetrakis(diethyl phenylphosphonite)cobalt(I)
An X-ray structure determination of the title compound shows that the co-ordination about the cobalt atom is approximately trigonal bipyramidal; n.m.r. data indicate that the complex is non-rigid in solution
V4743 Sgr, a magnetic nova?
Two XMM Newton observations of Nova V4743 Sgr (Nova Sgr 2002) were performed
shortly after it returned to quiescence, 2 and 3.5 years after the explosion.
The X-ray light curves revealed a modulation with a frequency of ~0.75 mHz,
indicating that V4743 Sgr is most probably an intermediate polar (IP). The
X-ray spectra have characteristics in common with known IPs, with a hard
thermal plasma component that can be fitted only assuming a partially covering
absorber. In 2004 the X-ray spectrum had also a supersoft blackbody-like
component, whose temperature was close to that of the white dwarf (WD) in the
supersoft X-ray phase following the outburst, but with flux by at least two
orders of magnitude lower. In quiescent IPs, a soft X-ray flux component
originates at times in the polar regions irradiated by an accretion column, but
the supersoft component of V4743 Sgr disappeared in 2006, indicating a possible
origin different from accretion. We suggest that it may have been due to an
atmospheric temperature gradient on the WD surface, or to continuing localized
thermonuclear burning at the bottom of the envelope, before complete turn-off.
An optical spectrum obtained with SALT 11.5 years after the outburst showed a
prominent He II 4686A line and the Bowen blend, which reveal a very hot region,
but with peak temperature shifted to the ultraviolet (UV) range. V4743 Sgr is
the third post-outburst nova and IP candidate showing a low-luminosity
supersoft component in the X-ray flux a few years after the outburst.Comment: 9 pages, 5 figures, accepted to MNRA
DiagnĂłstico para identificação de demandas de pesquisa no setor produtivo de suĂnos e aves no Estado do ParĂĄ.
bitstream/item/63289/1/Oriental-Doc103.pd
Effects of Metformin With or Without Supplementation With Folate on Homocysteine Levels and Vascular Endothelium of Women With Polycystic Ovary Syndrome
OBJECTIVE: To evaluate whether the administration of metformin exerts any effects
on serum homocysteine (Hcy) levels in patients with polycystic ovary syndrome
(PCOS) and whether supplementation with folate enhances the positive effects of
metformin on the structure and function of the vascular endothelium.
RESEARCH DESIGN AND METHODS: A total of 50 patients affected by PCOS, without
additional metabolic or cardiovascular diseases, were enrolled in a prospective
nonrandomized placebo-controlled double-blind clinical study. They were grouped
into two treatment arms that were matched for age and BMI. Patients were treated
with a 6-month course of metformin (1,700 mg daily) plus folic acid (400 microg
daily; experimental group, n = 25) or placebo (control group, n = 25). Complete
hormonal and metabolic patterns, serum Hcy, folate, vitamin B12, endothelin-1
levels, brachial artery diameter at the baseline (BAD-B) and after reactive
hyperemia (BAD-RH), flow-mediated dilation, and intima-media thickness in both
common carotid arteries were evaluated.
RESULTS: After treatment, a significant increase in serum Hcy levels was observed
in the control group compared with the baseline values and the experimental
group. A beneficial effect was observed in the concentrations of BAD-B, BAD-RH,
flow-mediated dilation, intima-media thickness, and serum endothelin-1 in both
groups. However, the results were improved more significantly in the experimental
group than in the control subjects.
CONCLUSIONS: Metformin exerts a slight but significant deleterious effect on
serum Hcy levels in patients with PCOS, and supplementation with folate is useful
to increase the beneficial effect of metformin on the vascular endothelium
Optical observations of "hot" novae returning to quiescence
We have monitored the return to quiescence of novae previously observed in
outburst as supersoft X-ray sources, with optical photometry of the
intermediate polar (IP) V4743 Sgr and candidate IP V2491 Cyg, and optical
spectroscopy of these two and seven other systems. Our sample includes
classical and recurrent novae, short period (few hours), intermediate period
(1-2 days) and long period (symbiotic) binaries. The light curves of V4743 Sgr
and V2491 Cyg present clear periodic modulations. For V4743 Sgr, the modulation
occurs with the beat of the rotational and orbital periods. If the period
measured for V2491 Cyg is also the beat of these two periods, the orbital one
should be almost 17 hours. The recurrent nova T Pyx already shows fragmentation
of the nebular shell less than 3 years after the outburst. While this nova
still had strong [OIII] at this post-outburst epoch, these lines had already
faded after 3 to 7 years in all the others. We did not find any difference in
the ratio of equivalent widths of high ionization/excitation lines to that of
the Hbeta line in novae with short and long orbital period, indicating that
irradiation does not trigger high mass transfer rate from secondaries with
small orbital separation. An important difference between the spectra of RS Oph
and V3890 Sgr and those of many symbiotic persistent supersoft sources is the
absence of forbidden coronal lines. With the X-rays turn-off, we interpret this
as an indication that mass transfer in symbiotics recurrent novae is
intermittent.Comment: In press in Monthly Notices of the Royal Astronomical Societ
The X-ray emission from Nova V382 Velorum: I. The hard component observed with BeppoSAX
We present BeppoSAX observations of Nova Velorum 1999 (V382 Vel), done in a
broad X-ray band covering 0.1-300 keV only 15 days after the discovery and
again after 6 months. The nova was detected at day 15 with the BeppoSAX
instruments in the energy range 1.8-10 keV and we attribute the emission to
shocks in the ejecta. The plasma temperature was kT~6 keV and the unabsorbed
flux was F(x)~4.3 x 10(-11) erg/cm**2/s. The nebular material was affected by
high intrinsic absorption of the ejecta. 6 months after after the outburst, the
intrinsic absorption did not play a role, the nova had turned into a bright
supersoft source, and the hot nebular component previously detected had cooled
to a plasma temperature kT<=1 keV. No emission was detected in either
observation above 20 keV.Comment: 1 tex file, 2 figures as .ps, and 1 .sty file of MNRA
Dynamical noise can enhance high-order statistical structure in complex systems
Recent research has provided a wealth of evidence highlighting the pivotal
role of high-order interdependencies in supporting the information-processing
capabilities of distributed complex systems. These findings may suggest that
high-order interdependencies constitute a powerful resource that is, however,
challenging to harness and can be readily disrupted. In this paper we contest
this perspective by demonstrating that high-order interdependencies can not
only exhibit robustness to stochastic perturbations, but can in fact be
enhanced by them. Using elementary cellular automata as a general testbed, our
results unveil the capacity of dynamical noise to enhance the statistical
regularities between agents and, intriguingly, even alter the prevailing
character of their interdependencies. Furthermore, our results show that these
effects are related to the high-order structure of the local rules, which
affect the system's susceptibility to noise and characteristic times-scales.
These results deepen our understanding of how high-order interdependencies may
spontaneously emerge within distributed systems interacting with stochastic
environments, thus providing an initial step towards elucidating their origin
and function in complex systems like the human brain.Comment: 8 pages, 4 figures, 2 table
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