53 research outputs found
The Earliest Optical Observations of GRB 030329
We present the earliest optical imaging observations of GRB 030329 related to
SN 2003dh. The burst was detected by the HETE-2 satellite at 2003 March 29,
11:37:14.67 UT. Our wide-field monitoring started 97 minutes before the trigger
and the burst position was continuously observed. We found no precursor or
contemporaneous flare brighter than () in 32 s (64 s) timescale
between 10:00 and 13:00 UT. Follow-up time series photometries started at
12:51:39 UT (75 s after position notice through the GCN) and continued for more
than 5 hours. The afterglow was at min after burst.
Its fading between 1.2 and 6.3 hours is well characterized by a single
power-law of the form in -band. No significant flux variation was
detected and upper limits are derived as % in
minutes to hours timescales and % in seconds to
minutes timescales. Such a featureless lightcurve is explained by the smooth
distribution of circumburst medium. Another explanation is that the optical
band was above the synchrotron cooling frequency where emergent flux is
insensitive to the ambient density contrasts. Extrapolation of the afterglow
lightcurve to the burst epoch excludes the presence of an additional flare
component at minutes as seen in GRB 990123 and GRB 021211.Comment: ApJL, in pres
Intra-annual patterns of tracheid size in the Mediterranean tree Juniperus thurifera as an indicator of seasonal water stress
Because climate can affect xylem cell anatomy, series of intra-annual cell anatomical features have the potential to retrospectively supply seasonal climatic information. In this study, we explored the ability to extract information about water stress conditions from tracheid features of the Mediterranean conifer Juniperus thurifera L. Tracheidograms of four climatic years from two drought-sensitive sites in Spain were compared to evaluate whether it is possible to link intra-annual cell size patterns to seasonal climatic conditions. Results indicated site-specific anatomical adjustment such as smaller and thicker tracheids at the dryer site but also showed a strong climatic imprint on the intra-annual pattern of tracheid size. Site differences in cell size reflected expected structural adjustments against cavitation failures. Differences between intra-annual patterns, however, indicated a response to seasonal changes in water availability whereby cells formed under drought conditions were smaller and thicker, and vice versa. This relationship was more manifest and stable at the dryer sit
Múltiple (poemas) Florida, 1926/27.
Mode of access: Internet
Are neighboring trees in tune? Wood formation in Pinus pinaster
Neighboring trees growing under identical
environmental conditions can exhibit different dynamics
and periods of growth. Despite the recent advances in
cambial biology, the exogenous and endogenous factors
generating asynchronous xylem growths still remain
undetermined. This study investigated timings and duration
of xylem formation in maritime pine (Pinus pinaster Ait.)
from an even-aged plantation in Portugal growing under
Mediterranean climate. Cambial phenology and stem
diameter were monitored weekly, from March to December
2010, on two classes of trees divided according to the tree
ring widths of the last 15 years, but similar age and size:
fast- and slow-growing trees. We tested the hypothesis that
differences in tree ring widths result from cell production
which in turn affects timings of xylogenesis and that the
bimodal growth pattern, typical of the Mediterranean,
originates from a double reactivation of the cambium: in
spring and autumn. Cambial activity started earlier and
ended later in fast-growing trees, confirming that cell
production is a key factor determining the duration of xylogenesis.
Intra-annual variations in stem diameter recorded
by band dendrometers revealed two peaks of increment
occurring in spring and late summer. However, the number
of cambial cells did not increase in late summer, which
suggested that the second peak of increment was caused by
stem rehydration, rather than by a reactivation of cell
division. These results demonstrated that the variability in
the timings of xylem phenology observed among trees of
the same age and size and growing under similar environmental
conditions was closely related to cell production
and not to age or size per se.This study was supported by the Fundac¸a˜o para
a Cieˆncia e a Tecnologia, Ministe´rio da Educac¸a˜o e Cieˆncia (FCT) cofinanced
by Compete, through the project PTDC/AAC-AMB/111675/
2009. Joana Vieira was supported by a Ph.D. Grant (SFRH/BD/
48089/2008) and Filipe Campelo by a postdoctoral research grant
(SFRH/BPD/47822/2008), both grants from FCT with funds from
POPH (Portuguese Operational Human Potential Program) and
QREN Portugal (Portuguese National Strategic Reference Framework)
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