283 research outputs found
Plasticity of maritime pine (Pinus pinaster) wood-forming tissues during a growing season
Research• The seasonal effect is the most significant external source of variation affecting
vascular cambial activity and the development of newly divided cells, and hence
wood properties. Here, the effect of edapho-climatic conditions on the phenotypic
and molecular plasticity of differentiating secondary xylem during a growing season
was investigated.
• Wood-forming tissues of maritime pine (Pinus pinaster) were collected from the
beginning to the end of the growing season in 2003. Data from examination of fibre
morphology, Fourier-transform infrared spectroscopy (FTIR), analytical pyrolysis, and
gas chromatography/mass spectrometry (GC/MS) were combined to characterize the
samples. Strong variation was observed in response to changes in edapho-climatic
conditions.
• A genomic approach was used to identify genes differentially expressed during
this growing season. Out of 3512 studied genes, 19% showed a significant seasonal
effect. These genes were clustered into five distinct groups, the largest two representing
genes over-expressed in the early- or late-wood-forming tissues, respectively. The other
three clusters were characterized by responses to specific edapho-climatic conditions.
• This work provides new insights into the plasticity of the molecular machinery
involved in wood formation, and reveals candidate genes potentially responsible for
the phenotypic differences found between early- and late-wood
Towards a standard typology of endogenous landslide seismic sources
The objective of this work is to propose a standard classification of seismic
signals generated by gravitational processes and detected at close distances
(<1 km). We review the studies where seismic instruments have been
installed on unstable slopes and discuss the choice of the seismic
instruments and the network geometries. Seismic observations acquired at 13
unstable slopes are analyzed in order to construct the proposed typology. The
selected slopes are affected by various landslide types (slide, fall, topple
and flow) triggered in various material (from unconsolidated soils to
consolidated rocks). We investigate high-frequency bands (>1 Hz) where
most of the seismic energy is recorded at the 1 km sensor to source
distances. Several signal properties (duration, spectral content and
spectrogram shape) are used to describe the sources. We observe that similar
gravitational processes generate similar signals at different slopes. Three
main classes can be differentiated mainly from the length of the signals, the
number of peaks and the duration of the autocorrelation. The classes are the
“slopequake” class, which corresponds to sources potentially occurring
within the landslide body; the “rockfall” class, which corresponds to
signals generated by rock block impacts; and the “granular flow” class,
which corresponds to signals generated by wet or dry debris/rock flows.
Subclasses are further proposed to differentiate specific signal properties
(frequency content, resonance, precursory signal). The signal properties of
each class and subclass are described and several signals of the same class
recorded at different slopes are presented. Their potential origins are
discussed. The typology aims to serve as a standard for further comparisons
of the endogenous microseismicity recorded on landslides.</p
Performance of the First ANTARES Detector Line
In this paper we report on the data recorded with the first Antares detector
line. The line was deployed on the 14th of February 2006 and was connected to
the readout two weeks later. Environmental data for one and a half years of
running are shown. Measurements of atmospheric muons from data taken from
selected runs during the first six months of operation are presented.
Performance figures in terms of time residuals and angular resolution are
given. Finally the angular distribution of atmospheric muons is presented and
from this the depth profile of the muon intensity is derived.Comment: 14 pages, 9 figure
The ANTARES Optical Beacon System
ANTARES is a neutrino telescope being deployed in the Mediterranean Sea. It
consists of a three dimensional array of photomultiplier tubes that can detect
the Cherenkov light induced by charged particles produced in the interactions
of neutrinos with the surrounding medium. High angular resolution can be
achieved, in particular when a muon is produced, provided that the Cherenkov
photons are detected with sufficient timing precision. Considerations of the
intrinsic time uncertainties stemming from the transit time spread in the
photomultiplier tubes and the mechanism of transmission of light in sea water
lead to the conclusion that a relative time accuracy of the order of 0.5 ns is
desirable. Accordingly, different time calibration systems have been developed
for the ANTARES telescope. In this article, a system based on Optical Beacons,
a set of external and well-controlled pulsed light sources located throughout
the detector, is described. This calibration system takes into account the
optical properties of sea water, which is used as the detection volume of the
ANTARES telescope. The design, tests, construction and first results of the two
types of beacons, LED and laser-based, are presented.Comment: 21 pages, 18 figures, submitted to Nucl. Instr. and Meth. Phys. Res.
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