110 research outputs found
Dissipative structures in optomechanical cavities
Motivated by the increasing interest in the properties of multimode
optomechanical devices, here we study a system in which a driven mode of a
large-area optical cavity is despersively coupled to a deformable mechanical
element. Two different models naturally appear in such scenario, for which we
predict the formation of periodic patterns, localized structures (cavity
solitons), and domain walls, among other complex nonlinear phenomena. Further,
we propose a realistic design based on intracavity membranes where our models
can be studied experimentally. Apart from its relevance to the field of
nonlinear optics, the results put forward here are a necessary step towards
understanding the quantum properties of optomechanical systems in the multimode
regime of both the optical and mechanical degrees of freedom.Comment: Updated version with a more general model and a specific
implementation proposal. Comments and (constructive) criticism are welcom
Generalized approach for enabling multimode quantum optics
We develop a universal approach enabling the study of any multimode quantum optical system evolving under a quadratic Hamiltonian. Our strategy generalizes the standard symplectic analysis and permits the treatment of multimode systems even in situations where traditional theoretical methods cannot be applied. This enables the description and investigation of a broad variety of key-resources for experimental quantum optics, ranging from optical parametric oscillators, to silicon-based micro-ring resonator, as well as opto-mechanical systems
MR imaging of entrapment neuropathies of the shoulder
LEARNING OBJECTIVES:
To describe the MRI features of most common entrapment neuropathies of the shoulder:
- Parsonage-Turner syndrome
- quadrilateral space syndrome (axillary neuropathy)
- suprascapular nerve syndrome
BACKGROUND:
Entrapment neuropathies are characterized by alteration of nerve function secondary to compression by mechanical or dynamic forces. The compression may be acute, chronic or intermittent.
Not infrequently compressive neuropathies are related to space-occupying lesions such as tumors, cysts, inflammatory processes, or post-traumatic conditions.
IMAGING FINDINGS:
The MR imaging appearance of Parsonage-Turner syndrome is quite characteristic, with marked edema in the affected muscles of the shoulder, most commonly those innervated by the suprascapular nerve, although deltoid muscle can also be compromised.
MR imaging of quadrilateral space syndrome may reveal fatty atrophy or edema isolated to the teres minor muscle.
MR imaging of suprascapular nerve syndrome is established when edema or fatty changes of supraspinatus and/or infraspinatus muscle is present along with a cyst or ganglion in the spinoglenoid or suprascapular notch.
CONCLUSION:
MRI is a powerful diagnostic imaging tool in the diagnosis of entrapment neuropathies of the shoulder and underlying causes, thus excluding other possible causes of shoulder pain. Moreover, MRI may recognize active changes of denervation in muscle from chronic denervation muscle changes or “fatty atrophy” in isolation, and therefore it may change treatment and management
Measuring nonclassicality of bosonic field quantum states via operator ordering sensitivity
We introduce a new distance-based measure for the nonclassicality of the
states of a bosonic field, which outperforms the existing such measures in
several ways. We define for that purpose the operator ordering sensitivity of
the state which evaluates the sensitivity to operator ordering of the Renyi
entropy of its quasi-probabilities and which measures the oscillations in its
Wigner function. Through a sharp control on the operator ordering sensitivity
of classical states we obtain a precise geometric image of their location in
the density matrix space allowing us to introduce a distance-based measure of
nonclassicality. We analyse the link between this nonclassicality measure and a
recently introduced quantum macroscopicity measure, showing how the two notions
are distinct
Cavity Light Bullets: 3D Localized Structures in a Nonlinear Optical Resonator
We consider the paraxial model for a nonlinear resonator with a saturable
absorber beyond the mean-field limit and develop a method to study the
modulational instabilities leading to pattern formation in all three spatial
dimensions. For achievable parametric domains we observe total radiation
confinement and the formation of 3D localised bright structures. At difference
from freely propagating light bullets, here the self-organization proceeds from
the resonator feedback, combined with diffraction and nonlinearity. Such
"cavity" light bullets can be independently excited and erased by appropriate
pulses, and once created, they endlessly travel the cavity roundtrip. Also, the
pulses can shift in the transverse direction, following external field
gradients.Comment: 4 pages, 3 figures, simulations files available at
http://www.ba.infn.it/~maggipin/PRLmovies.htm, submitted to Physical Review
Letters on 24 March 200
Spatial localization and pattern formation in discrete optomechanical cavities and arrays
We investigate theoretically the generation of nonlinear dissipative structures in optomechanical (OM) systems containing discrete arrays of mechanical resonators. We consider both hybrid models in which the optical system is a continuous multimode field, as it would happen in an OM cavity containing an array of micro-mirrors, and also fully discrete models in which each mechanical resonator interacts with a single optical mode, making contact with Ludwig and Marquardt (2013 Phys. Rev. Lett. 101, 073603). Also, we study the connections between both types of models and continuous OM models. While all three types of models merge naturally in the limit of a large number of densely distributed mechanical resonators, we show that the spatial localization and the pattern formation found in continuous OM models can still be observed for a small number of mechanical elements, even in the presence of finite-size effects, which we discuss. This opens new venues for experimental approaches to the subject
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