761,762 research outputs found
Deterministic coupling of a single silicon-vacancy color center to a photonic crystal cavity in diamond
Deterministic coupling of single solid-state emitters to nanocavities is the
key for integrated quantum information devices. We here fabricate a photonic
crystal cavity around a preselected single silicon-vacancy color center in
diamond and demonstrate modification of the emitters internal population
dynamics and radiative quantum efficiency. The controlled, room-temperature
cavity coupling gives rise to a resonant Purcell enhancement of the zero-phonon
transition by a factor of 19, coming along with a 2.5-fold reduction of the
emitter's lifetime
Robust Whole-Body Motion Control of Legged Robots
We introduce a robust control architecture for the whole-body motion control
of torque controlled robots with arms and legs. The method is based on the
robust control of contact forces in order to track a planned Center of Mass
trajectory. Its appeal lies in the ability to guarantee robust stability and
performance despite rigid body model mismatch, actuator dynamics, delays,
contact surface stiffness, and unobserved ground profiles. Furthermore, we
introduce a task space decomposition approach which removes the coupling
effects between contact force controller and the other non-contact controllers.
Finally, we verify our control performance on a quadruped robot and compare its
performance to a standard inverse dynamics approach on hardware.Comment: 8 Page
Control Synthesis for an Underactuated Cable Suspended System Using Dynamic Decoupling
This article studies the dynamics and control of a novel underactuated
system, wherein a plate suspended by cables and with a freely moving mass on
top, whose other ends are attached to three quadrotors, is sought to be
horizontally stabilized at a certain height, with the ball positioned at the
center of mass of the plate. The freely moving mass introduces a 2-degree of
underactuation into the system. The design proceeds through a decoupling of the
quadrotors and the plate dynamics. Through a partial feedback linearization
approach, the attitude of the plate and the translational height of the plate
is initially controlled, while maintaining a bounded velocity along the and
directions. These inputs are then synthesized through the quadrotors with a
backstepping and timescale separation argument based on Tikhonov's theorem
Chaos in classical string dynamics in deformed
We consider a circular string in deformed which is localized in the center of and winds around the two
circles of deformed . We observe chaos in the phase space of the
circular string implying non-integrability of string dynamics. The chaotic
behaviour in phase space is controlled by energy as well as the deforming
parameter . We further show that the point like object exhibits
non-chaotic behaviour. Finally we calculate the Lyapunov exponent for both
extended and point like object in support of our first result.Comment: 15 page
Globule-like conformation and enhanced diffusion of active polymers
We study the dynamics and conformation of polymers composed by active
monomers. By means of Brownian dynamics simulations we show that when the
direction of the self-propulsion of each monomer is aligned with the backbone,
the polymer undergoes a coil-to-globule-like transition, highlighted by a
marked change of the scaling exponent of the gyration radius. Concurrently, the
diffusion coefficient of the center of mass of the polymer becomes essentially
independent of the polymer size for sufficiently long polymers or large
magnitudes of the self-propulsion. These effects are reduced when the
self-propulsion of the monomers is not bound to be tangent to the backbone of
the polymer. Our results, rationalized by a minimal stochastic model, open new
routes for activity-controlled polymer and, possibly, for a new generation of
polymer-based drug carriers.Comment: 5 pages, 5 figures, Supplementary Materials 7 page
A minimal model for spontaneous cell polarization and edge activity in oscillating, rotating and migrating cells
How the cells break symmetry and organize their edge activity to move
directionally is a fun- damental question in cell biology. Physical models of
cell motility commonly rely on gradients of regulatory factors and/or feedback
from the motion itself to describe polarization of edge activity. Theses
approaches, however, fail to explain cell behavior prior to the onset of
polarization. Our analysis using the model system of polarizing and moving fish
epidermal keratocytes suggests a novel and simple principle of
self-organization of cell activity in which local cell-edge dynamics depends on
the distance from the cell center, but not on the orientation with respect to
the front-back axis. We validate this principle with a stochastic model that
faithfully reproduces a range of cell-migration behaviors. Our findings
indicate that spontaneous polarization, persistent motion, and cell shape are
emergent properties of the local cell-edge dynamics controlled by the distance
from the cell center.Comment: 8 pages, 5 figure
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