47,070 research outputs found
Formation of Quantum Shock Waves by Merging and Splitting Bose-Einstein Condensates
The processes of merging and splitting dilute-gas Bose-Einstein condensates
are studied in the nonadiabatic, high-density regime. Rich dynamics are found.
Depending on the experimental parameters, uniform soliton trains containing
more than ten solitons or the formation of a high-density bulge as well as
quantum (or dispersive) shock waves are observed experimentally within merged
BECs. Our numerical simulations indicate the formation of many vortex rings. In
the case of splitting a BEC, the transition from sound-wave formation to
dispersive shock-wave formation is studied by use of increasingly stronger
splitting barriers. These experiments realize prototypical dispersive shock
situations.Comment: 10 pages, 8 figure
Formation Splitting and Merging
This paper presents an approach to swarm split and rejoin
maneuvers of a system of multi-robots formations. A post split formation is split into low-degree sub-swarms when the swarm encounters an obstacle. The sub-swarms reestablish links with other sub-swarms and converge into its pre-split formation after avoiding collisions with the
obstacles. The leader-follower control strategy is used for maintaining formation shape in the sub-swarms. A set of artificial potential field functions is proposed for avoiding inter-robot, inter-formation and obstacle collisions and attraction to their designated targets. The Direct Method of Lyapunov is then used to establish stability of the given system. The effectiveness of the proposed nonlinear acceleration control laws is demonstrated through a computer simulation
Distributed Formation Control for Multi-Vehicle Systems With Splitting and Merging Capability
This letter develops a novel strategy for splitting and merging of agents travelling in formation. The method converts the formation control problem into an optimization problem, which is solved among the agents in a distributed fashion. The proposed control strategy is one type of Distributed Model Predictive Control (DMPC) which allows the system to cope with disturbances and dynamic environments. A modified Alternating Direction Method of Multipliers (ADMM) is designed to solve the trajectory optimization problem and achieve formation scaling. Furthermore, a mechanism is designed to implement path homotopy in splitting and merging of the formation, which examines the H-signature of the generated trajectories. Simulation shows that, by using the proposed method, the formation is able to automatically resize and dynamically split to better avoid obstacles, even in the case of losing communication among agents. Upon splitting the newly formed groups proceed and merge again when it becomes possible
A coincidence of disturbed morphology and blue UV colour: minor-merger driven star formation in early-type galaxies at z~0.6
We exploit multi-wavelength photometry of early-type galaxies (ETGs) in the
COSMOS survey to demonstrate that the low-level star formation activity in the
ETG population at intermediate redshift is likely to be driven by minor
mergers. Splitting the ETGs into galaxies that show disturbed morphologies
indicative of recent merging and those that appear relaxed, we find that ~32%
of the ETG population appears to be morphologically disturbed. While the
relaxed objects are almost entirely contained within the UV red sequence, their
morphologically disturbed counterparts dominate the scatter to blue UV colours,
regardless of luminosity. Empirically and theoretically determined major-merger
rates in the redshift range z<1 are several times too low to account for the
fraction of disturbed ETGs in our sample, suggesting that minor mergers
represent the principal mechanism driving the observed star formation activity
in our sample. The young stellar components forming in these events have ages
between 0.03 and 0.3 Myrs and typically contribute <10% of the stellar mass of
the remnant. Together with recent work which demonstrates that the structural
evolution of nearby ETGs is consistent with one or more minor mergers, our
results indicate that the overall evolution of massive ETGs may be heavily
influenced by minor merging at late epochs and highlights the need to
systematically study this process in future observational surveys.Comment: MNRAS in press (significant revisions to version 1
Formation and kinetics of transient metastable states in mixtures under coupled phase ordering and chemical demixing
We present theory and simulation of simultaneous chemical demixing and phase
ordering in a polymer-liquid crystal mixture in conditions where isotropic-
isotropic phase separation is metastable with respect to isotropic-nematic
phase transition. It is found that mesophase formation proceeds by a transient
metastable phase that surround the ordered phase, and whose lifetime is a
function of the ratio of diffusional to orientational mobilities. It is shown
that kinetic phase ordering in polymer-mesogen mixtures is analogous to kinetic
crystallization in polymer solutions.Comment: 17 pages, 5 figures accepted for publication in EP
Coalitional Games in MISO Interference Channels: Epsilon-Core and Coalition Structure Stable Set
The multiple-input single-output interference channel is considered. Each
transmitter is assumed to know the channels between itself and all receivers
perfectly and the receivers are assumed to treat interference as additive
noise. In this setting, noncooperative transmission does not take into account
the interference generated at other receivers which generally leads to
inefficient performance of the links. To improve this situation, we study
cooperation between the links using coalitional games. The players (links) in a
coalition either perform zero forcing transmission or Wiener filter precoding
to each other. The -core is a solution concept for coalitional games
which takes into account the overhead required in coalition deviation. We
provide necessary and sufficient conditions for the strong and weak
-core of our coalitional game not to be empty with zero forcing
transmission. Since, the -core only considers the possibility of
joint cooperation of all links, we study coalitional games in partition form in
which several distinct coalitions can form. We propose a polynomial time
distributed coalition formation algorithm based on coalition merging and prove
that its solution lies in the coalition structure stable set of our coalition
formation game. Simulation results reveal the cooperation gains for different
coalition formation complexities and deviation overhead models.Comment: to appear in IEEE Transactions on Signal Processing, 14 pages, 14
figures, 3 table
Anisotropic merging and splitting of dipolar Bose-Einstein condensates
We study the merging and splitting of quasi-two-dimensional Bose-Einstein
condensates with strong dipolar interactions. We observe that if the dipoles
have a non-zero component in the plane of the condensate, the dynamics of
merging or splitting along two orthogonal directions, parallel and
perpendicular to the projection of dipoles on the plane of the condensate are
different. The anisotropic merging and splitting of the condensate is a
manifestation of the anisotropy of the roton-like mode in the dipolar system.
The difference in dynamics disappears if the dipoles are oriented at right
angles to the plane of the condensate as in this case the Bogoliubov
dispersion, despite having roton-like features, is isotropic.Comment: 9 pages and 9 figure
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