5,298 research outputs found
Non-damping oscillations at flaring loops
Context. QPPs are usually detected as spatial displacements of coronal loops
in imaging observations or as periodic shifts of line properties in
spectroscopic observations. They are often applied for remote diagnostics of
magnetic fields and plasma properties on the Sun. Aims. We combine imaging and
spectroscopic measurements of available space missions, and investigate the
properties of non-damping oscillations at flaring loops. Methods. We used the
IRIS to measure the spectrum over a narrow slit. The double-component Gaussian
fitting method was used to extract the line profile of Fe XXI 1354.08 A at "O
I" window. The quasi-periodicity of loop oscillations were identified in the
Fourier and wavelet spectra. Results. A periodicity at about 40 s is detected
in the line properties of Fe XXI, HXR emissions in GOES 1-8 A derivative, and
Fermi 26-50 keV. The Doppler velocity and line width oscillate in phase, while
a phase shift of about Pi/2 is detected between the Doppler velocity and peak
intensity. The amplitudes of Doppler velocity and line width oscillation are
about 2.2 km/s and 1.9 km/s, respectively, while peak intensity oscillate with
amplitude at about 3.6% of the background emission. Meanwhile, a quasi-period
of about 155 s is identified in the Doppler velocity and peak intensity of Fe
XXI, and AIA 131 A intensity. Conclusions. The oscillations at about 40 s are
not damped significantly during the observation, it might be linked to the
global kink modes of flaring loops. The periodicity at about 155 s is most
likely a signature of recurring downflows after chromospheric evaporation along
flaring loops. The magnetic field strengths of the flaring loops are estimated
to be about 120-170 G using the MHD seismology diagnostics, which are
consistent with the magnetic field modeling results using the flux rope
insertion method.Comment: 9 pages, 9 figures, 1 table, accepted by A&
Generalized L\"uscher Formula in Multi-channel Baryon-Meson Scattering
L\"uscher's formula relates the elastic scattering phase shifts to the
two-particle energy levels in a finite cubic box. The original formula was
obtained for elastic scattering of two massive spinless particles in the center
of mass frame. In this paper, we consider the case for the scattering of a spin
1/2 particle with a spinless particle in multi-channel scattering. A
generalized relation between the energy of two particle system and the
scattering matrix elements is established. We first obtain this relation using
quantum-mechanics in both center-of-mass frame and in a general moving frame.
The result is then generalized to quantum field theory using methods outlined
in Ref. \cite{Hansen:2012tf}. We verify that the results obtained using both
methods are equivalent up to terms that are exponentially suppressed in the box
size.Comment: One reference adde
Few-Body Systems Composed of Heavy Quarks
Within the past ten years many new hadrons states were observed
experimentally, some of which do not fit into the conventional quark model. I
will talk about the few-body systems composed of heavy quarks, including the
charmonium-like states and some loosely bound states.Comment: Plenary talk at the 20th International IUPAP Conference on Few-Body
Problems in Physics, to appear in Few Body Systems (2013
Suppressing nano-scale stick-slip motion by feedback
When a micro cantilever with a nano-scale tip is manipulated on a substrate
with atomic-scale roughness, the periodic lateral frictional force and
stochastic fluctuations may induce stick-slip motion of the cantilever tip,
which greatly decreases the precision of the nano manipulation. This unwanted
motion cannot be reduced by open-loop control especially when there exist
parameter uncertainties in the system model, and thus needs to introduce
feedback control. However, real-time feedback cannot be realized by the
existing virtual reality virtual feedback techniques based on the position
sensing capacity of the atomic force microscopy (AFM). To solve this problem,
we propose a new method to design real-time feedback control based on the force
sensing approach to compensate for the disturbances and thus reduce the
stick-slip motion of the cantilever tip. Theoretical analysis and numerical
simulations show that the controlled motion of the cantilever tip tracks the
desired trajectory with much higher precision. Further investigation shows that
our proposal is robust under various parameter uncertainties. Our study opens
up new perspectives of real-time nano manipulation.Comment: 8 pages, 10 figure
Interferometry signatures for QCD first-order phase transition in heavy ion collisions at GSI-FAIR energies
Using the technique of quantum transport of the interfering pair we examine
the Hanbury-Brown-Twiss (HBT) interferometry signatures for the
particle-emitting sources of pions and kaons produced in the heavy ion
collisions at GSI-FAIR energies. The evolution of the sources is described by
relativistic hydrodynamics with the system equation of state of the first-order
phase transition from quark-gluon plasma (QGP) to hadronic matter. We use
quantum probability amplitudes in a path-integral formalism to calculate the
two-particle correlation functions, where the effects of particle decay and
multiple scattering are taken into consideration. We find that the HBT radii of
kaons are smaller than those of pions for the same initial conditions. Both the
HBT radii of pions and kaons increase with the system initial energy density.
The HBT lifetimes of the pion and kaon sources are sensitive to the initial
energy density. They are significantly prolonged when the initial energy
density is tuned to the phase boundary between the QGP and mixed phase. This
prolongations of the HBT lifetimes of pions and kaons may likely be observed in
the heavy ion collisions with an incident energy in the GSI-FAIR energy range.Comment: 16 pages, 4 figure
Eta-mesic nuclei in relativistic mean-field theory
With the eta-nucleon (eta N) interaction Lagrangian deduced from chiral
perturbation theory, we study the possible eta-mesic nuclei in the framework of
relativistic mean-field theory. The eta single-particle energies are sensitive
to the eta N scattering length, and increase monotonically with the nucleon
number A. If the scattering length is in the range of a^{eta N}=0.75-1.05 fm
and the imaginary potential V_{0}-15 MeV, some discrete states of C, O and Ne
eta bound states should be identified in experiments. However, when the
scattering length a^{eta N} 30 MeV,
no discrete eta meson bound states could be observed in experiments.Comment: 6 page
- …