1,009 research outputs found
Recommended from our members
Simulation of Laminated Object Manufacturing (LOM) with Variation of Process Parameters
A previously developed and verified thermal model for Laminated Object Manufacturing
(LOM) was used to investigate the effects of various processing parameters on the temperature
profile in a LOM part during the build cycle. The mathematical model, based on 3-dimensional
transient heat conduction in a rectangular geometry LOM part, allows calculation ofthe transient
temperature distribution within the part during the application of a new layer as well as during
other periods ofthe LOM build cycle. The parameters roller temperature, roller speed, chamber
air temperature, base plate temperature, and laser cutting time were independently varied, and the
LOM process response simulated. The results were analyzed in order to gain insight into
potential strategies for intelligent process control.Mechanical Engineerin
Magnetic field induced control of breather dynamics in a single plaquette of Josephson junctions
We present a theoretical study of inhomogeneous dynamic (resistive) states in
a single plaquette consisting of three Josephson junctions. Resonant
interactions of such a breather state with electromagnetic oscillations
manifest themselves by resonant current steps and voltage jumps in the
current-voltage characteristics. An externally applied magnetic field leads to
a variation of the relative shift between the Josephson current oscillations of
two resistive junctions. By making use of the rotation wave approximation
analysis and direct numerical simulations we show that this effect allows to
effectively control the breather instabilities, e. g. to increase (decrease)
the height of the resonant steps and to suppress the voltage jumps in the
current-voltage characteristics.Comment: 4 pages, 3 figure
Discrete breathers in classical spin lattices
Discrete breathers (nonlinear localised modes) have been shown to exist in
various nonlinear Hamiltonian lattice systems. In the present paper we study
the dynamics of classical spins interacting via Heisenberg exchange on spatial
-dimensional lattices (with and without the presence of single-ion
anisotropy). We show that discrete breathers exist for cases when the continuum
theory does not allow for their presence (easy-axis ferromagnets with
anisotropic exchange and easy-plane ferromagnets). We prove the existence of
localised excitations using the implicit function theorem and obtain necessary
conditions for their existence. The most interesting case is the easy-plane one
which yields excitations with locally tilted magnetisation. There is no
continuum analogue for such a solution and there exists an energy threshold for
it, which we have estimated analytically. We support our analytical results
with numerical high-precision computations, including also a stability analysis
for the excitations.Comment: 15 pages, 12 figure
Observation of breathers in Josephson ladders
We report on the observation of spatially-localized excitations in a ladder
of small Josephson junctions. The excitations are whirling states which persist
under a spatially-homogeneous force due to the bias current. These states of
the ladder are visualized using a low temperature scanning laser microscopy. We
also compute breather solutions with high accuracy in corresponding model
equations. The stability analysis of these solutions is used to interpret the
measured patterns in the I-V characteristics
Breathers in Josephson junction ladders: resonances and electromagnetic waves spectroscopy
We present a theoretical study of the resonant interaction between dynamical
localized states (discrete breathers) and linear electromagnetic excitations
(EEs) in Josephson junction ladders. By making use of direct numerical
simulations we find that such an interaction manifests itself by resonant steps
and various sharp switchings (voltage jumps) in the current-voltage
characteristics. Moreover, the power of ac oscillations away from the breather
center (the breather tail) displays singularities as the externally applied dc
bias decreases. All these features can be mapped to the spectrum of EEs that
has been derived analytically and numerically. Using an improved analysis of
the breather tail, a spectroscopy of the EEs is developed. The nature of
breather instability driven by localized EEs is established.Comment: 15 pages, 13 figure
Energy Flow Puzzle of Soliton Ratchets
We study the mechanism of directed energy transport for soliton ratchets. The
energy flow appears due to the progressive motion of a soliton (kink) which is
an energy carrier. However, the energy current formed by internal system
deformations (the total field momentum) is zero. We solve the underlying puzzle
by showing that the energy flow is realized via an {\it inhomogeneous} energy
exchange between the system and the external ac driving. Internal kink modes
are unambiguously shown to be crucial for that transport process to take place.
We also discuss effects of spatial discretization and combination of ac and dc
external drivings.Comment: 4 pages, 3 figures, submitted to PR
Conductance transition with interacting bosons in an Aharonov-Bohm cage
We study transport of interacting bosons through an Aharonov-Bohm cage - a
building block of flat band networks - with coherent pump and sink leads. In
the absence of interactions the cage is insulating due to destructive
interference. We find that the cage stays insulating up to a critical value of
the pump strength in the presence of mean field interactions, while the quantum
regime induces particle pair transport and weak conductance below the critical
pump strength. A swift crossover from quantum into the classical regime upon
further pump strength increase is observed. We solve the time dependent master
equations for the density matrix of the many body problem both in the
classical, pure quantum, and pseudoclassical regimes. We start with an empty
cage and switch on driving. We characterize the transient dynamics, and the
complexity of the resulting steady states and attractors. Our results can be
readily realized using experimental platforms involving interacting ultracold
atoms and photons on finetuned optical lattices.Comment: 5 pages, 4 figure
q-breathers in Discrete Nonlinear Schroedinger lattices
-breathers are exact time-periodic solutions of extended nonlinear systems
continued from the normal modes of the corresponding linearized system. They
are localized in the space of normal modes. The existence of these solutions in
a weakly anharmonic atomic chain explained essential features of the
Fermi-Pasta-Ulam (FPU) paradox. We study -breathers in one- two- and
three-dimensional discrete nonlinear Sch\"{o}dinger (DNLS) lattices --
theoretical playgrounds for light propagation in nonlinear optical waveguide
networks, and the dynamics of cold atoms in optical lattices. We prove the
existence of these solutions for weak nonlinearity. We find that the
localization of -breathers is controlled by a single parameter which depends
on the norm density, nonlinearity strength and seed wave vector. At a critical
value of that parameter -breathers delocalize via resonances, signaling a
breakdown of the normal mode picture and a transition into strong mode-mode
interaction regime. In particular this breakdown takes place at one of the
edges of the normal mode spectrum, and in a singular way also in the center of
that spectrum. A stability analysis of -breathers supplements these
findings. For three-dimensional lattices, we find -breather vortices, which
violate time reversal symmetry and generate a vortex ring flow of energy in
normal mode space.Comment: 19 pages, 9 figure
Topological Filters for Solitons in Coupled Waveguides Networks
We study the propagation of discrete solitons on chains of coupled optical
waveguides where finite networks of waveguides are inserted at some points. By
properly selecting the topology of these networks, it is possible to control
the transmission of traveling solitons: we show here that inhomogeneous
waveguide networks may be used as filters for soliton propagation. Our results
provide a first step in the understanding of the interplay/competition between
topology and nonlinearity for soliton dynamics in optical fibers
- …