2,526 research outputs found
Results from HARP and their implications for neutrino physics
Recent results from the HARP experiment on the measurements of the
double-differential production cross-section of pions in proton interactions
with beryllium, carbon and tantalum targets are presented. These results are
relevant for a detailed understanding of neutrino flux in accelerator neutrino
experiments MiniBooNE/SciBooNE, for a better prediction of atmospheric neutrino
fluxes as well as for an optimization of a future neutrino factory design.Comment: Presented at the XLIInd Rencontres de Moriond on Electroweak
Interactions and Unified Theorie
Fast diffusion of graphene flake on graphene layer
Diffusion of a graphene flake on a graphene layer is analyzed and a new
diffusion mechanism is proposed for the system under consideration. According
to this mechanism, rotational transition of the flake from commensurate to
incommensurate states takes place with subsequent simultaneous rotation and
translational motion until the commensurate state is reached again, and so on.
The molecular dynamics simulations and analytic estimates based on ab initio
and semi-empirical calculations demonstrate that the proposed diffusion
mechanism is dominant at temperatures T ~ Tcom, where Tcom corresponds to the
barrier for transitions of the flake between adjacent energy minima in the
commensurate states. For example, for the flake consisting of ~ 40, 200 and 700
atoms the contribution of the proposed diffusion mechanism through rotation of
the flake to the incommensurate states exceeds that for diffusion of the flake
in the commensurate states by one-two orders of magnitude at temperatures 50 -
150 K, 200 - 600 K and 800 - 2400 K, respectively. The possibility to
experimentally measure the barriers to relative motion of graphene layers based
on the study of diffusion of a graphene flake is considered. The results
obtained are also relevant for understanding of dynamic behavior of polycyclic
aromatic molecules on graphene and should be qualitatively valid for a set of
commensurate adsorbate-adsorbent systems.Comment: 33 pages, 6 figure
Kalman Filter Track Fits and Track Breakpoint Analysis
We give an overview of track fitting using the Kalman filter method in the
NOMAD detector at CERN, and emphasize how the wealth of by-product information
can be used to analyze track breakpoints (discontinuities in track parameters
caused by scattering, decay, etc.). After reviewing how this information has
been previously exploited by others, we describe extensions which add power to
breakpoint detection and characterization. We show how complete fits to the
entire track, with breakpoint parameters added, can be easily obtained from the
information from unbroken fits. Tests inspired by the Fisher F-test can then be
used to judge breakpoints. Signed quantities (such as change in momentum at the
breakpoint) can supplement unsigned quantities such as the various chisquares.
We illustrate the method with electrons from real data, and with Monte Carlo
simulations of pion decays.Comment: 27 pages including 10 figures. To appear in NI
Molecular dynamics simulation of the self-retracting motion of a graphene flake
The self-retracting motion of a graphene flake on a stack of graphene flakes
is studied using molecular dynamics simulations. It is shown that in the case
when the extended flake is initially rotated to an incommensurate state, there
is no barrier to the self-retracting motion of the flake and the flake retracts
as fast as possible. If the extended flake is initially commensurate with the
other flakes, the self-retracting motion is hindered by potential energy
barriers. However, in this case, the rotation of the flake to incommensurate
states is often observed. Such a rotation is found to be induced by the torque
acting on the flake on hills of the potential relief of the interaction energy
between the flakes. Contrary to carbon nanotubes, telescopic oscillations of
the graphene flake are suppressed because of the high dynamic friction related
to the excitation of flexural vibrations of the flake. This makes graphene
promising for the use in fast-responding electromechanical memory cells.Comment: 24 pages, 8 figure
AA stacking, tribological and electronic properties of double-layer graphene with krypton spacer
Structural, energetic and tribological characteristics of double-layer
graphene with commensurate and incommensurate krypton spacers of nearly
monolayer coverage are studied within the van der Waals-corrected density
functional theory. It is shown that when the spacer is in the commensurate
phase, the graphene layers have the AA stacking. For this phase, the barriers
to relative in-plane translational and rotational motion and the shear mode
frequency of the graphene layers are calculated. For the incommensurate phase,
both of the barriers are found to be negligibly small. A considerable change of
tunneling conductance between the graphene layers separated by the commensurate
krypton spacer at their relative subangstrom displacement is revealed by the
use of the Bardeen method. The possibility of nanoelectromechanical systems
based on the studied tribological and electronic properties of the considered
heterostructures is discussed
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