1,213 research outputs found
Steady-state attitude control propulsion systems computer program documentation and user's manual, volume 1
Computer program documentation and user manual for steady state attitude control propulsion system - vol.
Tuning a Resonance in the Fock Space: Optimization of Phonon Emission in a Resonant Tunneling Device
Phonon-assisted tunneling in a double barrier resonant tunneling device can
be seen as a resonance in the electron-phonon Fock space which is tuned by the
applied voltage. We show that the geometrical parameters can induce a symmetry
condition in this space that can strongly enhance the emission of longitudinal
optical phonons. For devices with thin emitter barriers this is achieved by a
wider collector's barrier.Comment: 4 pages, 3 figures. Figure 1 changed, typos correcte
Fermi liquid to Luttinger liquid transition at the edge of a two-dimensional electron gas
We present experimental results on the tunneling into the edge of a two
dimensional electron gas (2DEG) obtained with a GaAs/AlGaAs cleaved edge
overgrown structure in a strong perpendicular magnetic field. While the 2DEG
exhibits typical fractional quantum Hall features of a very high mobility
sample, we observe the onset of a non-linear current-voltage characteristic in
the vicinity of nu=1. For filling factor nu<1 the system is consistent with a
non-Fermi liquid behavior, such as a Luttinger liquid, whereas for nu>1 we
observe an Ohmic tunneling resistance between the edge and a three dimensional
contact, typical for a Fermi liquid. Hence, at the edge, there is a transition
from a Luttinger liquid to a Fermi liquid. Finally, we show that the Luttinger
liquid exponent at a given filling factor is not universal but depends on
sample parameters.Comment: 4 pages, 4 figure
The SSTARS (STeroids and Stents Against Re-Stenosis) Trial : different stent alloys and the use of peri-procedural oral corticosteroids to prevent in-segment restenosis after percutaneous coronary intervention
Background
Stent design and technological modifications to allow for anti-proliferative drug elution influence restenosis rates following percutaneous coronary intervention (PCI). We aimed to investigate whether peri-procedural administration of corticosteroids or the use of thinner strut cobalt alloy stents would reduce rates of binary angiographic restenosis (BAR) after PCI.
Methods
This was a two centre, mixed single and double blinded, randomised controlled trial using a factorial design. We compared (a) the use of prednisolone to placebo, starting at least six hours pre-PCI and continued for 28 days post-PCI, and (b) cobalt chromium (CoCr) to stainless steel (SS) alloy stents, in patients admitted for PCI. The primary end-point was BAR at six months.
Results
315 patients (359 lesions) were randomly assigned to either placebo (n = 145) or prednisolone (n = 170) and SS (n = 160) or CoCr (n = 160). The majority (58%) presented with an ACS, 11% had diabetes and 287 (91%) completed angiographic follow up. BAR occurred in 26 cases in the placebo group (19.7%) versus 31 cases in the prednisolone group (20.0%) respectively, p = 1.00. For the comparison between SS and CoCr stents, BAR occurred in 32 patients (21.6%) versus 25 patients (18.0%) respectively, p = 0.46.
Conclusion
Our study showed that treating patients with a moderately high dose of prednisolone for 28 days following PCI with BMS did not reduce the incidence of BAR. In addition, we showed no significant reduction in 6 month restenosis rates with stents composed of CoCr alloy compared to SS
Measurement of the multi-TeV neutrino cross section with IceCube using Earth absorption
Neutrinos interact only very weakly, so they are extremely penetrating.
However, the theoretical neutrino-nucleon interaction cross section rises with
energy such that, at energies above 40 TeV, neutrinos are expected to be
absorbed as they pass through the Earth. Experimentally, the cross section has
been measured only at the relatively low energies (below 400 GeV) available at
neutrino beams from accelerators \cite{Agashe:2014kda, Formaggio:2013kya}. Here
we report the first measurement of neutrino absorption in the Earth, using a
sample of 10,784 energetic upward-going neutrino-induced muons observed with
the IceCube Neutrino Observatory. The flux of high-energy neutrinos transiting
long paths through the Earth is attenuated compared to a reference sample that
follows shorter trajectories through the Earth. Using a fit to the
two-dimensional distribution of muon energy and zenith angle, we determine the
cross section for neutrino energies between 6.3 TeV and 980 TeV, more than an
order of magnitude higher in energy than previous measurements. The measured
cross section is (stat.) (syst.)
times the prediction of the Standard Model \cite{CooperSarkar:2011pa},
consistent with the expectation for charged and neutral current interactions.
We do not observe a dramatic increase in the cross section, expected in some
speculative models, including those invoking new compact dimensions
\cite{AlvarezMuniz:2002ga} or the production of leptoquarks
\cite{Romero:2009vu}.Comment: Preprint version of Nature paper 10.1038/nature2445
Neutrinos below 100 TeV from the southern sky employing refined veto techniques to IceCube data
Many Galactic sources of gamma rays, such as supernova remnants, are expected
to produce neutrinos with a typical energy cutoff well below 100 TeV. For the
IceCube Neutrino Observatory located at the South Pole, the southern sky,
containing the inner part of the Galactic plane and the Galactic Center, is a
particularly challenging region at these energies, because of the large
background of atmospheric muons. In this paper, we present recent advancements
in data selection strategies for track-like muon neutrino events with energies
below 100 TeV from the southern sky. The strategies utilize the outer detector
regions as veto and features of the signal pattern to reduce the background of
atmospheric muons to a level which, for the first time, allows IceCube
searching for point-like sources of neutrinos in the southern sky at energies
between 100 GeV and several TeV in the muon neutrino charged current channel.
No significant clustering of neutrinos above background expectation was
observed in four years of data recorded with the completed IceCube detector.
Upper limits on the neutrino flux for a number of spectral hypotheses are
reported for a list of astrophysical objects in the southern hemisphere.Comment: 19 pages, 17 figures, 2 table
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