11 research outputs found
GRB 050822: Detailed analysis of an XRF observed by Swift
We report on the temporal and spectral characteristics of the early X-ray
emission from the GRB 050822 as observed by Swift. This burst is likely to be
an XRF showing major X-ray flares in its XRT light-curve. The quality of the
data allows a detailed spectral analysis of the early afterglow in the X-ray
band. During the X-ray flares, a positive correlation between the count rate
and the spectral hardness (i.e. the higher the count rate, the harder the
spectrum) is clearly seen for the X-ray flares. This behaviour, similar to that
seen for Gamma-ray pulses, indicates that the energy peak of the spectrum is in
the XRT energy band and it moves towards lower energies with time. We show
evidence for the possible detection of the emergence of the forward-shock
emission, produced at a radius larger than 4x10^16 cm in the case of a CBM
afterglow model (a formation region clearly different from that producing the
prompt emission). Finally, we show that the null detection of a jet break up to
T_0 + 4x10^6 s in the X-ray light curve of this XRF can be understood: i) if
the jet seen on-axis is uniform with a large opening angle theta > 20 degrees);
or ii) if the jet is a structured Gaussian-like jet with the line-of-sight
outside the bright Gaussian core.Comment: Now accepted for publication in A&
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Trophoblast alterations in the placental bed in relation to physiological changes in spiral arteries
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Nanosized polymetallic resorcinarene-based host assemblies that strongly bind fullerenes
Polymetallic nanodimensional assemblies have been prepared via metal directed assembly of dithiocarbamate functionalized cavitand structural frameworks with late transition metals (Ni, Pd, Cu, Au, Zn, and Cd). The coordination geometry about the metal centers is shown to dictate the architecture adopted. X-ray crystallographic studies confirm that square planar coordination geometries result in "cagelike" octanuclear complexes, whereas square-based pyramidal metal geometries favor hexanuclear "molecular loop" structures. Both classes of complex are sterically and electronically complementary to the fullerenes (C-60 and C-70). The strong binding of these guests occurred via favorable interactions with the sulfur atoms of multiple dithiocarbamate moieties of the hosts. In the case of the tetrameric copper(II) complexes, the lability of the copper(II)-dithiocarbamate bond enabled the fullerene guests to be encapsulated in the electron-rich cavity of the host, over time. The examination of the binding of fullerenes has been undertaken using spectroscopic and electrochemical methods, electrospray mass spectrometry, and molecular modeling