1,830 research outputs found
Topological Phases of Sound and Light
Topological states of matter are particularly robust, since they exploit
global features insensitive to local perturbations. In this work, we describe
how to create a Chern insulator of phonons in the solid state. The proposed
implementation is based on a simple setting, a dielectric slab with a suitable
pattern of holes. Its topological properties can be wholly tuned in-situ by
adjusting the amplitude and frequency of a driving laser that controls the
optomechanical interaction between light and sound. The resulting chiral,
topologically protected phonon transport along the edges can be probed
completely optically. Moreover, we identify a regime of strong mixing between
photon and phonon excitations, which gives rise to a large set of different
topological phases. This would be an example of a Chern insulator produced from
the interaction between two physically very different particle species, photons
and phonons
Pattern phase diagram for 2D arrays of coupled limit-cycle oscillators
Arrays of coupled limit-cycle oscillators represent a paradigmatic example
for studying synchronization and pattern formation. They are also of direct
relevance in the context of currently emerging experiments on nano- and
optomechanical oscillator arrays. We find that the full dynamical equations for
the phase dynamics of such an array go beyond previously studied Kuramoto-type
equations. We analyze the evolution of the phase field in a two-dimensional
array and obtain a "phase diagram" for the resulting stationary and
non-stationary patterns. The possible observation in optomechanical arrays is
discussed briefly
Unjamming of Granular Packings due to Local Perturbations: Stability and Decay of Displacements
We study the mechanical response generated by local deformations in jammed
packings of rigid disks. Based on discrete element simulations we determine the
critical force of the local perturbation that is needed to break the mechanical
equilibrium and examine the generated displacement field. Displacements decay
as a power law of the distance from the perturbation point. The decay exponent
and the critical force exhibit nontrivial dependence on the friction: Both
quantities are nonmonotonic and have a sharp maximum at the friction
coefficient 0.1. We find that the mechanical response properties are closely
related to the problem of force-indeterminacy where similar nonmonotonic
behavior was observed previously. We establish direct connection between the
critical force and the ensemble of static force networks.Comment: 4 pages, 4 figure
Extent of force indeterminacy in packings of frictional rigid disks
Static packings of frictional rigid particles are investigated by means of
discrete element simulations. We explore the ensemble of allowed force
realizations in the space of contact forces for a given packing structure. We
estimate the extent of force indeterminacy with different methods. The
indeterminacy exhibits a nonmonotonic dependence on the interparticle friction
coefficient. We verify directly that larger force-indeterminacy is accompanied
by a more robust behavior against local perturbations. We also investigate the
local indeterminacy of individual contact forces. The probability distribution
of local indeterminacy changes its shape depending on friction. We find that
local indeterminacy tends to be larger on force chains for intermediate
friction. This correlation disappears in the large friction limit.Comment: 5 pages, 6 figure
Limit quantum efficiency for violation of Clauser-Horne Inequality for qutrits
In this paper we present the results of numerical calculations about the
minimal value of detection efficiency for violating the Clauser - Horne
inequality for qutrits. Our results show how the use of non-maximally entangled
states largely improves this limit respect to maximally entangled ones. A
stronger resistance to noise is also found.Comment: Phys. Rev. A in pres
Delivery actuator for a transcervical sterilization device
The use of delivery systems in the human body for positioning and deploying implants, such as closure devices, dilation balloons, stents, coils and sterilization devices, are gaining more importance to preclude surgical incisions and general anesthesia. The majorities of the non-surgical medical devices are delivered in a low profile into human body form and subsequently require specialized operations for their deployment and release. An analogous procedure for permanent female sterilization is the transcervical approach that does not require either general anesthesia or surgical incision and uses a normal body passage. The objective of this paper is to detail the design, development and verification of an ergonomic actuator for a medical application. In particular, this actuator is designed for the deployment and release of an implant to achieve instant permanent female sterilization via the transcervical approach. This implant is deployed under hysteroscopic visualization and requires a sequence of rotary and linear operations for its deployment and release. More specifically, this manually operated actuator is a hand held device designed to transmit the required forces in a particular sequence to effect both implant deployment and release at a target location. In order to design the actuator and to investigate its mechanical behavior, a three-dimensional (3D) Computer Aided Design (CAD) model was developed and Finite Element Method (FEM) was used for simulations and optimization. Actuator validation was performed following a number of successful bench-top in-air deployments and in-vitro deployments in animal tissue and explanted human uteri. During these deployments it was observed that the actuator applied the required forces to the implant resulting in successful deployment. Initial results suggest that this actuator can be used single handedly during the deployment phase. The ongoing enhancement of this actuator is moving towards “first-in- man” clinical trials
Pore Stabilization in Cohesive Granular Systems
Cohesive powders tend to form porous aggregates which can be compacted by
applying an external pressure. This process is modelled using the Contact
Dynamics method supplemented with a cohesion law and rolling friction. Starting
with ballistic deposits of varying density, we investigate how the porosity of
the compacted sample depends on the cohesion strength and the friction
coefficients. This allows to explain different pore stabilization mechanisms.
The final porosity depends on the cohesion force scaled by the external
pressure and on the lateral distance between branches of the ballistic deposit
r_capt. Even if cohesion is switched off, pores can be stabilized by Coulomb
friction alone. This effect is weak for round particles, as long as the
friction coefficient is smaller than 1. However, for nonspherical particles the
effect is much stronger.Comment: 10 pages, 15 figure
Covariant boost and structure functions of baryons in Gross-Neveu models
Baryons in the large N limit of two-dimensional Gross-Neveu models are
reconsidered. The time-dependent Dirac-Hartree-Fock approach is used to boost a
baryon to any inertial frame and shown to yield the covariant energy-momentum
relation. Momentum distributions are computed exactly in arbitrary frames and
used to interpolate between the rest frame and the infinite momentum frame,
where they are related to structure functions. Effects from the Dirac sea
depend sensitively on the occupation fraction of the valence level and the bare
fermion mass and do not vanish at infinite momentum. In the case of the kink
baryon, they even lead to divergent quark and antiquark structure functions at
x=0.Comment: 13 pages, 12 figures; v2: minor correction
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