5,387 research outputs found
Analytic study of the three-urn model for separation of sand
We present an analytic study of the three-urn model for separation of sand.
We solve analytically the master equation and the first-passage problem. We
find that the stationary probability distribution obeys the detailed balance
and is governed by the {\it free energy}. We find that the characteristic
lifetime of a cluster diverges algebraically with exponent 1/3 at the limit of
stability.Comment: 5pages, 4 figures include
Chaotic exploration and learning of locomotion behaviours
We present a general and fully dynamic neural system, which exploits intrinsic chaotic dynamics, for the real-time goal-directed exploration and learning of the possible locomotion patterns of an articulated robot of an arbitrary morphology in an unknown environment. The controller is modeled as a network of neural oscillators that are initially coupled only through physical embodiment, and goal-directed exploration of coordinated motor patterns is achieved by chaotic search using adaptive bifurcation. The phase space of the indirectly coupled neural-body-environment system contains multiple transient or permanent self-organized dynamics, each of which is a candidate for a locomotion behavior. The adaptive bifurcation enables the system orbit to wander through various phase-coordinated states, using its intrinsic chaotic dynamics as a driving force, and stabilizes on to one of the states matching the given goal criteria. In order to improve the sustainability of useful transient patterns, sensory homeostasis has been introduced, which results in an increased diversity of motor outputs, thus achieving multiscale exploration. A rhythmic pattern discovered by this process is memorized and sustained by changing the wiring between initially disconnected oscillators using an adaptive synchronization method. Our results show that the novel neurorobotic system is able to create and learn multiple locomotion behaviors for a wide range of body configurations and physical environments and can readapt in realtime after sustaining damage
Phenomenological Impacts of the CP-odd Rephase-Invariant Phase of the Chargino Mass Matrix in the Production of Light Chargino-Pair in Collisions
One CP--odd rephase-invariant phase appears in the chargino mass matrix in
the minimal Supersymmetric Standard Model. We investigate in detail the
phenomenological impacts of the CP-odd complex phase in the production of light
charginos in annihilation. The values of the chargino masses and the
mixing angles, determining the size of the wino and higgsino components in the
chargino wave functions, are so sensitive to the CP-odd phase that the
constraints on the supersymmetric parameters based on the conventional
assumptions for the parameters are recommended to be re-evaluated including the
CP-odd phase.Comment: 9 pages, latex with 3 eps figur
Anisotropic Dirac fermions in a Bi square net of SrMnBi2
We report the highly anisotropic Dirac fermions in a Bi square net of
SrMnBi2, based on a first principle calculation, angle resolved photoemission
spectroscopy, and quantum oscillations for high-quality single crystals. We
found that the Dirac dispersion is generally induced in the (SrBi)+ layer
containing a double-sized Bi square net. In contrast to the commonly observed
isotropic Dirac cone, the Dirac cone in SrMnBi2 is highly anisotropic with a
large momentum-dependent disparity of Fermi velocities of ~ 8. These findings
demonstrate that a Bi square net, a common building block of various layered
pnictides, provide a new platform that hosts highly anisotropic Dirac fermions.Comment: 5 pages, 4 figure
Superconductivity of metastable dihydrides at ambient pressure
Hydrogen in metals is a significant research area with far-reaching
implications, encompassing diverse fields such as hydrogen storage,
metal-insulator transitions, and the recently emerging phenomenon of
room-temperature (\textit{T_C}) superconductivity under high pressure.
Hydrogen atoms pose challenges in experiments as they are nearly invisible, and
they are considered within ideal crystalline structures in theoretical
predictions, which hampers research on the formation of meta-stable hydrides.
Here, we propose pressure-induced hydrogen migration from tetrahedral site
() to octahedral site (),forming
in cubic .Under decompression, it retains occupancy, and is
dynamically stable even at ambient pressure, enabling a synthesis route of
metastable dihydrides via compression-decompression process. We predict that
the electron phonon coupling strength of is enhanced with
increasing , and the associated \textit{T_C} reaches up to 10.8
at ambient pressure. Furthermore, we calculated stoichiometric
hydrogen migration threshold pressure (\textit{P_C}) for various
lanthanides dihydrides (, where =Y, Sc, Nd, and
Lu), and found an inversely linear relation between \textit{P_C} and ionic
radii of . We propose that the highest \textit{T_C} in the
face-centered-cubic dihydride system can be realized by optimizing the
/-site occupancies
Disturbance Observer
Disturbance observer is an inner-loop output-feedback controller whose role
is to reject external disturbances and to make the outer-loop baseline
controller robust against plant's uncertainties. Therefore, the closed-loop
system with the DOB approximates the nominal closed-loop by the baseline
controller and the nominal plant model with no disturbances. This article
presents how the disturbance observer works under what conditions, and how one
can design a disturbance observer to guarantee robust stability and to recover
the nominal performance not only in the steady-state but also for the transient
response under large uncertainty and disturbance
Factorization in graviton interactions
The study of factorization in the linearized gravity is extended to the
graviton scattering processes with a massive scalar particle, with a massless
vector boson and also with a graviton. Every transition amplitude is shown to
be completely factorized and the physical implications of their common factors
are discussed.Comment: 5 pages, Revtex 3.0, SNUTP 93-7
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