1,502 research outputs found
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
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
Pulsed energy-time entangled twin-photon source for quantum communication
A pulsed source of energy-time entangled photon pairs pumped by a standard
laser diode is proposed and demonstrated. The basic states can be distinguished
by their time of arrival. This greatly simplifies the realization of 2-photon
quantum cryptography, Bell state analyzers, quantum teleportation, dense
coding, entanglement swapping, GHZ-states sources, etc. Moreover the
entanglement is well protected during photon propagation in telecom optical
fibers, opening the door to few-photon applications of quantum communication
over long distances.Comment: 8 pages, 4 figure
Collaborative hyperparameter tuning
International audienceHyperparameter learning has traditionally been a manual task because of the limited number of trials. Today's computing infrastructures allow bigger evaluation budgets, thus opening the way for algorithmic approaches. Recently, surrogate-based optimization was successfully applied to hyperparameter learning for deep belief networks and to WEKA classifiers. The methods combined brute force computational power with model building about the behavior of the error function in the hyperparameter space, and they could significantly improve on manual hyperparameter tuning. What may make experienced practitioners even better at hyperparameter optimization is their ability to generalize across similar learning problems. In this paper, we propose a generic method to incorporate knowledge from previous experiments when simultaneously tuning a learning algorithm on new problems at hand. To this end, we combine surrogate-based ranking and optimization techniques for surrogate-based collaborative tuning (SCoT). We demonstrate SCoT in two experiments where it outperforms standard tuning techniques and single-problem surrogate-based optimization
On Conversational Agents in Information Systems Research: Analyzing the Past to Guide Future Work
Conversational agents (CA), i.e. software that interacts with its users through natural language, are becoming increasingly prevalent in everyday life as technological advances continue to significantly drive their capabilities. CA exhibit the potential to support and collaborate with humans in a multitude of tasks and can be used for innovation and automation across a variety of business functions, such as customer service or marketing and sales. Parallel to the increasing popularity in practice, IS researchers have engaged in studying a variety of aspects related to CA in the last few years, applying different research methods and producing different types of theories. In this paper, we review 36studies to assess the status quo of CA research in IS, identify gaps regarding both the studied aspects as well as applied methods and theoretical approaches, and propose directions for future work in this research area
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