3,088 research outputs found
Interpreting the recent results on direct search for dark matter particles in terms of relic neutralino
The most recent results from direct searches for dark matter particles in the
galactic halo are examined in terms of an effective Minimal Supersymmetric
extension of the Standard Model at the electroweak scale without gaugino masses
unification. We show that the annual modulation effect at 8.2 C.L.
recently presented by the DAMA Collaboration, as the result of a combined
analysis of the DAMA/NaI and the DAMA/LIBRA experiments for a total exposure of
0.82 ton yr, fits remarkably well with what expected for relic neutralinos for
a wide variety of WIMP distribution functions. Bounds derivable from other
measurements of direct searches for dark matter particles are analyzed. We
stress the role played by the uncertainties affecting the neutralino--quark
couplings arising from the involved hadronic quantities. We also examine how
present data on cosmic antiprotons can help in constraining the neutralino
configurations selected by the DAMA effect, in connection with the values of
the astrophysical parameters.
Perspectives for measurement of antideuterons possibly produced in the
galactic halo by self--annihilation of neutralinos belonging to the DAMA
configurations are examined. Finally, we discuss how findings at LHC would
impact on these issues.Comment: 18 pages, 10 figures a few minor comments and two references adde
Autonomous control of underground mining vehicles using reactive navigation
Describes how many of the navigation techniques developed by the robotics research community over the last decade may be applied to a class of underground mining vehicles (LHDs and haul trucks). We review the current state-of-the-art in this area and conclude that there are essentially two basic methods of navigation applicable. We describe an implementation of a reactive navigation system on a 30 tonne LHD which has achieved full-speed operation at a production mine
"Hiccup" accretion in the swinging pulsar IGR J18245-2452
IGR J18245-2452 is the fifteenth discovered accreting millisecond X-ray
pulsar and the first source of this class showing direct evidence for
transition between accretion and rotational powered emission states. These
swing provided the strongest confirmation of the pulsar recycling scenario
available so far. During the two XMM-Newton observations that were carried out
while the source was in outburst in April 2013, IGR J18245-2452 displayed a
unique and peculiar variability of its X-ray emission. In this work, we report
on a detailed analysis of the XMM- Newton data and focus in particular on the
timing and spectral variability of the source. IGR J18245-2452 continuously
switches between lower and higher intensity states, with typical variations in
flux up to a factor of about 500 in time scales as short as few seconds. These
variations in the source intensity are sometimes associated to a dramatic
spectral hardening, during which the power-law photon index of the source
changes from Gamma=1.7 to Gamma=0.9. The pulse profiles extracted at different
count rates and energies show a complex variability. These phenomena are not
usually observed in accreting millisecond X-ray pulsars, at least not on such a
short time scale. Fast variability was also found in the ATCA radio
observations carried out for about 6 hours during the outburst at a frequency
of 5.5 and 9 GHz. We interpret the variability observed from IGR J18245-2452 in
terms of a "hiccup" accretion phase, during which the accretion of material
from the inner boundary of the Keplerian disk is reduced by the onset of
centrifugal inhibition of accretion, possibly causing the launch of strong
outflows. Changes across accretion and propeller regimes have been long
predicted and reproduced by MHD simulations of accreting millisecond X-ray
pulsars but never observed to produce an extreme variability as that shown by
IGR J18245-2452.Comment: A&A in press. Revised versio
Test of isospin symmetry via low energy H(,) charge exchange
We report measurements of the differential cross
sections at six momenta (104-143 MeV/c) and four angles (0-40 deg) by detection
of -ray pairs from decays using the TRIUMF
RMC spectrometer. This region exhibits a vanishing zero-degree cross section
from destructive interference between s-- and p--waves, thus yielding special
sensitivity to pion-nucleon dynamics and isospin symmetry breaking. Our data
and previous data do not agree, with important implications for earlier claims
of large isospin violating effects in low energy pion-nucleon interactions.Comment: 5 pages, 3 figures, submitted to Physical Review Letter
Facile fabrication of lateral nanowire wrap-gate devices with improved performance
We present a simple fabrication technique for lateral nanowire wrap-gate
devices with high capacitive coupling and field-effect mobility. Our process
uses e-beam lithography with a single resist-spinning step, and does not
require chemical etching. We measure, in the temperature range 1.5-250 K, a
subthreshold slope of 5-54 mV/decade and mobility of 2800-2500 --
significantly larger than previously reported lateral wrap-gate devices. At
depletion, the barrier height due to the gated region is proportional to
applied wrap-gate voltage.Comment: 3 pages, 3 figure
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