516 research outputs found
Laser ablation loading of a radiofrequency ion trap
The production of ions via laser ablation for the loading of radiofrequency
(RF) ion traps is investigated using a nitrogen laser with a maximum pulse
energy of 0.17 mJ and a peak intensity of about 250 MW/cm^2. A time-of-flight
mass spectrometer is used to measure the ion yield and the distribution of the
charge states. Singly charged ions of elements that are presently considered
for the use in optical clocks or quantum logic applications could be produced
from metallic samples at a rate of the order of magnitude 10^5 ions per pulse.
A linear Paul trap was loaded with Th+ ions produced by laser ablation. An
overall ion production and trapping efficiency of 10^-7 to 10^-6 was attained.
For ions injected individually, a dependence of the capture probability on the
phase of the RF field has been predicted. In the experiment this was not
observed, presumably because of collective effects within the ablation plume.Comment: submitted to Appl. Phys. B., special issue on ion trappin
Composing Trust Models towards Interoperable Trust Management
Part 2: Full PapersInternational audienceComputational trust is a central paradigm in today's Internet as our modern society is increasingly relying upon online transactions and social net- works. This is indeed leading to the introduction of various trust management systems and associated trust models, which are customized according to their target applications. However, the heterogeneity of trust models prevents exploiting the trust knowledge acquired in one context in another context although this would be beneficial for the digital, ever-connected environment. This is such an issue that this paper addresses by introducing an approach to achieve interoperability between heterogeneous trust management systems. Specifically, we define a trust meta-model that allows the rigorous specification of trust models as well as their composition. The resulting composite trust models enable heterogeneous trust management systems to interoperate transparently through mediators
On gravitational waves emitted by an ensemble of rotating neutron stars
We study the possibility to detect the gravitational wave background
generated by all the neutron stars in the Galaxy with only one gravitational
wave interferometric detector. The proposed strategy consists in squaring the
detector's output and searching for a sidereal modulation. The shape of the
squared signal is computed for a disk and a halo distribution of neutron stars.
The required noise stability of the interferometric detector is discussed. We
argue that a possible population of old neutron stars, originating from a high
stellar formation rate at the birth of the Galaxy and not emitting as radio
pulsars, could be detected by the proposed technique in the low frequency range
of interferometric experiments.Comment: 14 pages, 2 PostScript figures, RevTeX, accepted for publication in
Physical Review
Search for Doubly-Charged Higgs Boson Production at HERA
A search for the single production of doubly-charged Higgs bosons H^{\pm \pm}
in ep collisions is presented. The signal is searched for via the Higgs decays
into a high mass pair of same charge leptons, one of them being an electron.
The analysis uses up to 118 pb^{-1} of ep data collected by the H1 experiment
at HERA. No evidence for doubly-charged Higgs production is observed and mass
dependent upper limits are derived on the Yukawa couplings h_{el} of the Higgs
boson to an electron-lepton pair. Assuming that the doubly-charged Higgs only
decays into an electron and a muon via a coupling of electromagnetic strength
h_{e \mu} = \sqrt{4 \pi \alpha_{em}} = 0.3, a lower limit of 141 GeV on the
H^{\pm\pm} mass is obtained at the 95% confidence level. For a doubly-charged
Higgs decaying only into an electron and a tau and a coupling h_{e\tau} = 0.3,
masses below 112 GeV are ruled out.Comment: 15 pages, 3 figures, 1 tabl
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
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