4,395 research outputs found
Collective oscillations in spatially modulated exciton-polariton condensate arrays
We study collective dynamics of interacting centers of exciton-polariton
condensation in presence of spatial inhomogeneity, as modeled by diatomic
active oscillator lattices. The mode formalism is developed and employed to
derive existence and stability criteria of plane wave solutions. It is
demonstrated that wave number mode with the binary elementary cell on a
diatomic lattice possesses superior existence and stability properties.
Decreasing net on-site losses (balance of dissipation and pumping) or
conservative nonlinearity favors multistability of modes, while increasing
frequency mismatch between adjacent oscillators detriments it. On the other
hand, spatial inhomogeneity may recover stability of modes at high
nonlinearities. Entering the region where all single-mode solutions are
unstable we discover subsequent transitions between localized quasiperiodic,
chaotic and global chaotic dynamics in the mode space, as nonlinearity
increases. Importantly, the last transition evokes the loss of synchronization.
These effects may determine lasing dynamics of interacting exciton-polariton
condensation centers.Comment: 9 pages, 3 figure
Space-Time Complexity in Hamiltonian Dynamics
New notions of the complexity function C(epsilon;t,s) and entropy function
S(epsilon;t,s) are introduced to describe systems with nonzero or zero Lyapunov
exponents or systems that exhibit strong intermittent behavior with
``flights'', trappings, weak mixing, etc. The important part of the new notions
is the first appearance of epsilon-separation of initially close trajectories.
The complexity function is similar to the propagator p(t0,x0;t,x) with a
replacement of x by the natural lengths s of trajectories, and its introduction
does not assume of the space-time independence in the process of evolution of
the system. A special stress is done on the choice of variables and the
replacement t by eta=ln(t), s by xi=ln(s) makes it possible to consider
time-algebraic and space-algebraic complexity and some mixed cases. It is shown
that for typical cases the entropy function S(epsilon;xi,eta) possesses
invariants (alpha,beta) that describe the fractal dimensions of the space-time
structures of trajectories. The invariants (alpha,beta) can be linked to the
transport properties of the system, from one side, and to the Riemann
invariants for simple waves, from the other side. This analog provides a new
meaning for the transport exponent mu that can be considered as the speed of a
Riemann wave in the log-phase space of the log-space-time variables. Some other
applications of new notions are considered and numerical examples are
presented.Comment: 27 pages, 6 figure
Experimental evidence of planar channeling in a periodically bent crystal
The usage of a Crystalline Undulator (CU) has been identified as a promising
solution for generating powerful and monochromatic -rays. A CU was
fabricated at SSL through the grooving method, i.e., by the manufacturing of a
series of periodical grooves on the major surfaces of a crystal. The CU was
extensively characterized both morphologically via optical interferometry at
SSL and structurally via X-ray diffraction at ESRF. Then, it was finally tested
for channeling with a 400 GeV/c proton beam at CERN. The experimental results
were compared to Monte Carlo simulations. Evidence of planar channeling in the
CU was firmly observed. Finally, the emission spectrum of the positron beam
interacting with the CU was simulated for possible usage in currently existing
facilities
Study of Scintillator Strip with Wavelength Shifting Fiber and Silicon Photomultiplier
The performance of the cm plastic scintillator
strip with wavelength shifting fiber read-out by two novel photodetectors
called Silicon PhotoMultipliers (SiPMs) is discussed. The advantages of SiPM
relative to the traditional multichannel photomultiplier are shown. Light yield
and light attenuation measurements are presented. This technique can be used in
muon or calorimeter systems.Comment: 9 pages, 5 figure
Meson vacuum phenomenology in a three-flavor linear sigma model with (axial-)vector mesons
We study scalar, pseudoscalar, vector, and axial-vector mesons with
non-strange and strange quantum numbers in the framework of a linear sigma
model with global chiral symmetry. We perform a
global fit of meson masses, decay widths, as well as decay amplitudes. The
quality of the fit is, for a hadronic model that does not consider
isospin-breaking effects, surprisingly good. We also investigate the question
whether the scalar states lie below or above 1 GeV and find the
scalar states above 1 GeV to be preferred as states. Additionally,
we also describe the axial-vector resonances as states.Comment: 29 pages, 4 figures, 3 tables. v2 is the updated version after
referee remarks (dilaton field discussed, a new figure added
Dynamics and kinetics of reversible homo-molecular dimerization of polycyclic aromatic hydrocarbons
Physical dimerization of polycyclic aromatic hydrocarbons (PAHs) has been investigated via molecular dynamics (MD) simulation with the ReaxFF reactive force field that is developed to bridge the gap between the quantum mechanism and classical MD. Dynamics and kinetics of homo-molecular PAH collision under different temperatures, impact parameters, and orientations are studied at an atomic level, which is of great value to understand and model the PAH dimerization. In the collision process, the enhancement factors of homo-molecular dimerizations are quantified and found to be larger at lower temperatures or with smaller PAH instead of size independent. Within the capture radius, the lifetime of the formed PAH dimer decreases as the impact parameter increases. Temperature and PAH characteristic dependent forward and reverse rate constants of homo-molecular PAH dimerization are derived from MD simulations, on the basis of which a reversible model is developed. This model can predict the tendency of PAH dimerization as validated by pyrene dimerization experiments [H. Sabbah et al., J. Phys. Chem. Lett. 1(19), 2962 (2010)]. Results from this study indicate that the physical dimerization cannot be an important source under the typical flame temperatures and PAH concentrations, which implies a more significant role played by the chemical route
DANSSino: a pilot version of the DANSS neutrino detector
DANSSino is a reduced pilot version of a solid-state detector of reactor
antineutrinos (to be created within the DANSS project and installed under the
industrial 3 GW(th) reactor of the Kalinin Nuclear Power Plant -- KNPP).
Numerous tests performed at a distance of 11 m from the reactor core
demonstrate operability of the chosen design and reveal the main sources of the
background. In spite of its small size (20x20x100 ccm), the pilot detector
turned out to be quite sensitive to reactor antineutrinos, detecting about 70
IBD events per day with the signal-to-background ratio about unity.Comment: 16 pages, 11 figures, 3 tables. arXiv admin note: substantial text
overlap with arXiv:1304.369
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