371 research outputs found
Interactive Chemical Reactivity Exploration
Elucidating chemical reactivity in complex molecular assemblies of a few
hundred atoms is, despite the remarkable progress in quantum chemistry, still a
major challenge. Black-box search methods to find intermediates and
transition-state structures might fail in such situations because of the
high-dimensionality of the potential energy surface. Here, we propose the
concept of interactive chemical reactivity exploration to effectively introduce
the chemist's intuition into the search process. We employ a haptic pointer
device with force-feedback to allow the operator the direct manipulation of
structures in three dimensions along with simultaneous perception of the
quantum mechanical response upon structure modification as forces. We elaborate
on the details of how such an interactive exploration should proceed and which
technical difficulties need to be overcome. All reactivity-exploration concepts
developed for this purpose have been implemented in the Samson programming
environment.Comment: 36 pages, 14 figure
Dark matter directional detection with MIMAC
MiMac is a project of micro-TPC matrix of gaseous (He3, CF4) chambers for
direct detection of non-baryonic dark matter. Measurement of both track and
ionization energy will allow the electron-recoil discrimination, while access
to the directionnality of the tracks will open a unique way to distinguish a
geniune WIMP signal from any background. First reconstructed tracks of 5.9 keV
electrons are presented as a proof of concept.Comment: 4 pages, proc. of the 44th Rencontres De Moriond: Electroweak
Interactions And Unified Theories, 7-14 Mar 2009, La Thuile, Ital
In situ measurement of the electron drift velocity for upcoming directional Dark Matter detectors
Three-dimensional track reconstruction is a key issue for directional Dark
Matter detection and it requires a precise knowledge of the electron drift
velocity. Magboltz simulations are known to give a good evaluation of this
parameter. However, large TPC operated underground on long time scale may be
characterized by an effective electron drift velocity that may differ from the
value evaluated by simulation. In situ measurement of this key parameter is
hence needed as it is a way to avoid bias in the 3D track reconstruction. We
present a dedicated method for the measurement of the electron drift velocity
with the MIMAC detector. It is tested on two gas mixtures: CF4 and CF4 + CHF3.
The latter has been chosen for the MIMAC detector as we expect that adding CHF3
to pure CF4 will lower the electron drift velocity. This is a key point for
directional Dark Matter as the track sampling along the drift field will be
improved while keeping almost the same Fluorine content of the gas mixture. We
show that the drift velocity at 50 mbar is reduced by a factor of about 5 when
adding 30% of CHF3.Comment: 19 pages, 14 figures. Minor corrections, matches published version in
JINS
Measurement of the electron drift velocity for directional dark matter detectors
Three-dimensional track reconstruction is a key issue for directional Dark
Matter detection. It requires a precise knowledge of the electron drift
velocity. Magboltz simulations are known to give a good evaluation of this
parameter. However, large TPC operated underground on long time scale may be
characterized by an effective electron drift velocity that may differ from the
value evaluated by simulation. In situ measurement of this key parameter is
hence a way to avoid bias in the 3D track reconstruction. We present a
dedicated method for the measurement of the electron drift velocity with the
MIMAC detector. It is tested on two gas mixtures : and . We also show that adding allows us to lower the
electron drift velocity while keeping almost the same Fluorine content of the
gas mixture.Comment: Proceedings of the 4th international conference on Directional
Detection of Dark Matter (CYGNUS 2013), 10-12 June 2013, Toyama, Japa
Development and validation of a 64 channel front end ASIC for 3D directional detection for MIMAC
A front end ASIC has been designed to equip the {\mu}TPC prototype developed
for the MIMAC project, which requires 3D reconstruction of low energy particle
tracks in order to perform directional detection of galactic Dark Matter. Each
ASIC is able to monitor 64 strips of pixels and provides the "Time Over
Threshold" information for each of those. These 64 digital informations,
sampled at a rate of 50 MHz, can be transferred at 400MHz by eight LVDS serial
links. Eight ASIC were validated on a 2x256 strips of pixels prototype.Comment: proceedings of TWEPP-11, Vienna, Austria, 26-30 September 201
Quenching factor measurement in low pressure gas detector for directional dark matter search
There is considerable experimental effort dedicated to the directional
detection of particle dark matter. Gaseous mu-TPC detectors present the
privileged features of being able to reconstruct the track and the energy of
the recoil nucleus following the interaction. A precise measurement of the
recoil energy is a key point for the directional search strategy. Quenching has
to be taken into account, i.e. only a certain fraction of the recoil energy is
deposited in the ionization channel. Measurements of the ionization quenching
factor for different gas mixture at room temperature have been made with a
dedicated ion beam facility at the LPSC of Grenoble.Comment: Proceedings of the 3rd International conference on Directional
Detection of Dark Matter (CYGNUS 2011), Aussois, France, 8-10 June 201
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