873 research outputs found
Nematic elastomers with aligned carbon nanotubes: new electromechanical actuators
We demonstrate, for the first time, the large electromechanical response in
nematic liquid crystalline elastomers filled with a very low (~0.01%)
concentration of carbon nanotubes, aligned along the nematic director at
preparation. The nanotubes create a very large effective dielectric anisotropy
of the composite. Their local field-induced torque is transmitted to the
rubber-elastic network and is registered as the exerted uniaxial stress of
order ~1kPa in response to a constant field of order ~1MV/m. We investigate the
dependence of the effect on field strength, nanotube concentration and
reproducibility under multiple field-on and -off cycles. The results indicate
the potential of the nanotube-nematic elastomer composites as electrically
driven actuators
Testing gravity law in the solar system
The predictions of General relativity (GR) are in good agreement with
observations in the solar system. Nevertheless, unexpected anomalies appeared
during the last decades, along with the increasing precision of measurements.
Those anomalies are present in spacecraft tracking data (Pioneer and flyby
anomalies) as well as ephemerides. In addition, the whole theory is challenged
at galactic and cosmic scales with the dark matter and dark energy issues.
Finally, the unification in the framework of quantum field theories remains an
open question, whose solution will certainly lead to modifications of the
theory, even at large distances. As long as those "dark sides" of the universe
have no universally accepted interpretation nor are they observed through other
means than the gravitational anomalies they have been designed to cure, these
anomalies may as well be interpreted as deviations from GR. In this context,
there is a strong motivation for improved and more systematic tests of GR
inside the solar system, with the aim to bridge the gap between gravity
experiments in the solar system and observations at much larger scales. We
review a family of metric extensions of GR which preserve the equivalence
principle but modify the coupling between energy and curvature and provide a
phenomenological framework which generalizes the PPN framework and "fifth
force" extensions of GR. We briefly discuss some possible observational
consequences in connection with highly accurate ephemerides.Comment: Proceedings of Journ\'ees 2010 "Syst\`emes de r\'ef\'erence
spatio-temporels", New challenges for reference systems and numerical
standards in astronom
Commissioning of the CMS Cryogenic System After Final Installation in the Underground Cavern
After having served for the surface tests of the Compact Muon Solenoid (CMS) magnet, the cold box and ancillaries of the CMS helium refrigerator have been dismantled, moved and re-installed in the USC55 cavern in 2007. The full re-commissioning in the cavern has been followed by several tests of the refrigerator to confirm its nominal performance before it was used for the magnet and detector tests in 2008. During these tests the safety modes of the refrigeration system have been tested and improved. After a nine-year project both, the magnet and the refrigeration system are now ready for the CMS operation
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