4,655 research outputs found
Variability of aliphatic glucosinolates in Arabidopsis thaliana (L.) – Impact on glucosinolate profile and insect resistance
The glucosinolate(GS)-myrosinase system of Brassicaceae, including the model plant Arabidopsis thaliana (L.), comprises a defence which is effective especially against generalist herbivores. Based on their side chain structure GS are grouped into aliphatic, aromatic, and indolyl GS. Indolyl GS are widely distributed among A. thaliana ecotypes and the Brassicaceae family, but the presence of aliphatic GS is variable and under strong genetic control. We investigated the effect of AOP gene expression on the side chain modifications of GS and the impact on insect resistance. AOP2 and AOP3 genes from Mr-0 and Sap-0 ecotypes, respectively, were crossbred into the methylsulfinyl GS producing Gie-0. Successful crosses were heterozygote plants which produced allyl (AOP2) or 3-hydroxypropyl GS (AOP3). After self-pollination, the chemical profile of the F3 generation of plants was screened to identify homozygote lines. Homozygote lines producing 3-hydroxypropyl GS were compared to methylsulfinyl GS, which were used to study the impact of GS structure on insect performance in first experiments. Our experiments revealed that methylsulfinyl GS containing ecotype lines were more resistant to the generalist caterpillar Spodoptera exigua (Hübner) and to the specialist caterpillar Pieris brassicae (L.) than the lines containing hydroxypropyl GS as main compounds
A steerable UV laser system for the calibration of liquid argon time projection chambers
A number of liquid argon time projection chambers (LAr TPC's) are being build
or are proposed for neutrino experiments on long- and short baseline beams. For
these detectors a distortion in the drift field due to geometrical or physics
reasons can affect the reconstruction of the events. Depending on the TPC
geometry and electric drift field intensity this distortion could be of the
same magnitude as the drift field itself. Recently, we presented a method to
calibrate the drift field and correct for these possible distortions. While
straight cosmic ray muon tracks could be used for calibration, multiple coulomb
scattering and momentum uncertainties allow only a limited resolution. A UV
laser instead can create straight ionization tracks in liquid argon, and allows
one to map the drift field along different paths in the TPC inner volume. Here
we present a UV laser feed-through design with a steerable UV mirror immersed
in liquid argon that can point the laser beam at many locations through the
TPC. The straight ionization paths are sensitive to drift field distortions, a
fit of these distortion to the linear optical path allows to extract the drift
field, by using these laser tracks along the whole TPC volume one can obtain a
3D drift field map. The UV laser feed-through assembly is a prototype of the
system that will be used for the MicroBooNE experiment at the Fermi National
Accelerator Laboratory (FNAL)
Experimental study of electric breakdowns in liquid argon at centimeter scale
In this paper we present results on measurements of the dielectric strength
of liquid argon near its boiling point and cathode-anode distances in the range
of 0.1 mm to 40 mm with spherical cathode and plane anode. We show that at such
distances the applied electric field at which breakdowns occur is as low as 40
kV/cm. Flash-overs across the ribbed dielectric of the high voltage
feed-through are observed for a length of 300 mm starting from a voltage of 55
kV. These results contribute to set reference for the breakdown-free design of
ionization detectors, such as Liquid Argon Time Projection Chambers (LAr TPC)
Relativistic nucleon optical potentials with isospin dependence in Dirac Brueckner Hartree-Fock approach
The relativistic optical model potential (OMP) for nucleon-nucleus scattering
is investigated in the framework of Dirac-Brueckner-Hartree-Fock (DBHF)
approach using the Bonn-B One-Boson- Exchange potential for the bare
nucleon-nucleon interaction. Both real and imaginary parts of isospin-dependent
nucleon self-energies in nuclear medium are derived from the DBHF approach
based on the projection techniques within the subtracted T -matrix
representation. The Dirac potentials as well as the corresponding Schrodinger
equivalent potentials are evaluated. An improved local density approximation is
employed in this analysis, where a range parameter is included to account for a
finite-range correction of the nucleon-nucleon interaction. As an example the
total cross sections, differential elastic scattering cross sections, analyzing
powers for n, p + 27Al at incident energy 100 keV < E < 250 MeV are calculated.
The results derived from this microscopic approach of the OMP are compared to
the experimental data, as well as the results obtained with a phenomenological
OMP. A good agreement between the theoretical results and the measurements can
be achieved for all incident energies using a constant value for the range
parameter.Comment: 10 pages, 16 figure
Measurement of the drift field in the ARGONTUBE LAr TPC with 266~nm pulsed laser beams
ARGONTUBE is a liquid argon time projection chamber (LAr TPC) with a drift
field generated in-situ by a Greinacher voltage multiplier circuit. We present
results on the measurement of the drift-field distribution inside ARGONTUBE
using straight ionization tracks generated by an intense UV laser beam. Our
analysis is based on a simplified model of the charging of a multi-stage
Greinacher circuit to describe the voltages on the field cage rings
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