234,559 research outputs found
Stabilization Control of the Differential Mobile Robot Using Lyapunov Function and Extended Kalman Filter
This paper presents the design of a control model to navigate the
differential mobile robot to reach the desired destination from an arbitrary
initial pose. The designed model is divided into two stages: the state
estimation and the stabilization control. In the state estimation, an extended
Kalman filter is employed to optimally combine the information from the system
dynamics and measurements. Two Lyapunov functions are constructed that allow a
hybrid feedback control law to execute the robot movements. The asymptotical
stability and robustness of the closed loop system are assured. Simulations and
experiments are carried out to validate the effectiveness and applicability of
the proposed approach.Comment: arXiv admin note: text overlap with arXiv:1611.07112,
arXiv:1611.0711
Damping of nonlinear standing kink oscillations: a numerical study
We aim to study the standing fundamental kink mode of coronal loops in the
nonlinear regime, investigating the changes in energy evolution in the
cross-section and oscillation amplitude of the loop which are related to
nonlinear effects, in particular to the development of the Kelvin-Helmholtz
instability (KHI). We run idea, high-resolution three-dimensional (3D)
magnetohydrodynamics (MHD) simulations, studying the influence of the initial
velocity amplitude and the inhomogeneous layer thickness. We model the coronal
loop as a straight, homogeneous magnetic flux tube with an outer inhomogeneous
layer, embedded in a straight, homogeneous magnetic field. We find that, for
low amplitudes which do not allow for the KHI to develop during the simulated
time, the damping time agrees with the theory of resonant absorption. However,
for higher amplitudes, the presence of KHI around the oscillating loop can
alter the loop's evolution, resulting in a significantly faster damping than
predicted by the linear theory in some cases. This questions the accuracy of
seismological methods applied to observed damping profiles, based on linear
theory.Comment: 10 pages, 8 figure
Numerical simulations of transverse oscillations in radiatively cooling coronal loops
We aim to study the influence of radiative cooling on the standing kink
oscillations of a coronal loop. Using the FLASH code, we solved the 3D ideal
magnetohydrodynamic equations. Our model consists of a straight, density
enhanced and gravitationally stratified magnetic flux tube. We perturbed the
system initially, leading to a transverse oscillation of the structure, and
followed its evolution for a number of periods. A realistic radiative cooling
is implemented. Results are compared to available analytical theory. We find
that in the linear regime (i.e. low amplitude perturbation and slow cooling)
the obtained period and damping time are in good agreement with theory. The
cooling leads to an amplification of the oscillation amplitude. However, the
difference between the cooling and non-cooling cases is small (around 6% after
6 oscillations). In high amplitude runs with realistic cooling, instabilities
deform the loop, leading to increased damping. In this case, the difference
between cooling and non-cooling is still negligible at around 12%. A set of
simulations with higher density loops are also performed, to explore what
happens when the cooling takes place in a very short time (tcool = 100 s). We
strengthen the results of previous analytical studies that state that the
amplification due to cooling is ineffective, and its influence on the
oscillation characteristics is small, at least for the cases shown here.
Furthermore, the presence of a relatively strong damping in the high amplitude
runs even in the fast cooling case indicates that it is unlikely that cooling
could alone account for the observed, flare-related undamped oscillations of
coronal loops. These results may be significant in the field of coronal
seismology, allowing its application to coronal loop oscillations with observed
fading-out or cooling behaviour
Seagull and pion-in-flight currents in neutrino-induced and knockout
[Background] The neutrino-nucleus () cross section is a major source
of systematic uncertainty in neutrino-oscillation studies. A precise
scattering model, in which multinucleon effects are incorporated, is pivotal
for an accurate interpretation of the data. [Purpose] In interactions,
meson-exchange currents (MECs) can induce two-nucleon () knockout from the
target nucleus, resulting in a two-particle two-hole (2p2h) final state. They
also affect single nucleon () knockout reactions, yielding a one-particle
one-hole (1p1h) final state. Both channels affect the inclusive strength. We
present a study of axial and vector, seagull and pion-in-flight currents in
muon-neutrino induced and knockout reactions on C. [Method]
Bound and emitted nucleons are described as Hartree-Fock wave functions. For
the vector MECs, the standard expressions are used. For the axial current,
three parameterizations are considered. The framework developed here allows for
a treatment of MECs and short-range correlations (SRCs). [Results] Results are
compared with electron-scattering data and with literature. The strengths of
the seagull, pion-in-flight and axial currents are studied separately and
double differential cross sections including MECs are compared with results
including SRCs. A comparison with MiniBooNE and T2K data is presented.
[Conclusions] In the 1p1h channel, the effects of the MECs tend to cancel each
other, resulting in a small effect on the double differential cross section.
knockout processes provide a small contribution to the inclusive double
differential cross section, ranging from the knockout threshold into the
dip region. A fair agreement with the MiniBooNE and T2K data is reached.Comment: 16 pages, 10 figure
Electron-neutrino scattering off nuclei from two different theoretical perspectives
We analyze charged-current electron-neutrino cross sections on Carbon. We
consider two different theoretical approaches, on one hand the Continuum Random
Phase Approximation (CRPA) which allows a description of giant resonances and
quasielastic excitations, on the other hand the RPA-based calculations which
are able to describe multinucleon emission and coherent and incoherent pion
production as well as quasielastic excitations. We compare the two approaches
in the genuine quasielastic channel, and find a satisfactory agreement between
them at large energies while at low energies the collective giant resonances
show up only in the CRPA approach. We also compare electron-neutrino cross
sections with the corresponding muon-neutrino ones in order to investigate the
impact of the different charged-lepton masses. Finally, restricting to the
RPA-based approach we compare the sum of quasielastic, multinucleon emission,
coherent and incoherent one-pion production cross sections (folded with the
electron-neutrino T2K flux) with the charged-current inclusive
electron-neutrino differential cross sections on Carbon measured by T2K. We
find a good agreement with the data. The multinucleon component is needed in
order to reproduce the T2K electron-neutrino inclusive cross sections
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