# Rotator

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## rotator

[′rō‚tād·ər]
(anatomy)
A muscle that partially rotates a part of the body on the part's axis.
(electromagnetism)
A device that rotates the plane of polarization of a plane-polarized electromagnetic wave, such as a twist in a waveguide.
(mechanics)
A rotating rigid body.
(quantum mechanics)
A molecule or other quantum-mechanical system which behaves as the quantum-mechanical analog of a rotating rigid body. Also known as top.

## Rotator

a mechanical system consisting of a material point of mass μ held by a weightless fixed pivot at a constant distance r from a point O, which is fixed in space and constitutes the center of the rotator.

In classical mechanics, the permitted motion of the rotator is the rotation around the point O with a moment of inertia 7 = μr2. The motion of the rotator occurs in the plane perpendicular to the vector of the angular momentum M of the rotator. The energy of the rotator E = M2.

In quantum mechanics, the states of rotators are characterized by certain discrete values of the square of the orbital angular momentum Ml2 = ħ2l(l + 1) and of the projection of this momentum Mlz = mħ onto the quantization axis z ( ħ is Planck’s constant h divided by 2π), where the quantum number l of the orbital angular momentum can assume any nonnegative whole value 0, 1, 2, … and the magnetic quantum number m for a given l can assume any whole value between – l and +l. The permitted values of the energy of a rotator are E = ħ 2l(l + l)/27; that is, they do not depend on m. Thus, a (21 + l)-fold degeneration of levels occurs by values of the projection of the angular momentum.

The rotator is important as an idealized model used to describe the rotational motion of molecules and nuclei. In particular, the rotator model is used to describe the motion of diatomic molecules in which the distance between the atoms is a quantity that varies comparatively little. The energy states of the rotation of such a molecule as a whole (the rotational spectrum of the molecule) are described by the formula for the energy of a quantum rotator.

V. G. VAKS

References in periodicals archive ?
These abnormalities are possibly associated with the concentric and eccentric weakness found in the external rotator muscles relative to the concentric internal rotator muscles.
Many studies concentrated on the effect of strengthening exercises of hip abductor and external rotator muscles on female patients with PFPS.
Strain of the hip external rotator muscles is rare and should be in the differential diagnosis of proximal posterior thigh pain in athletes.
Trabold, "Modified "2-portal" kocher-langenbeck approach: a minimally-invasive procedure protecting the short external rotator muscles," Journal of Orthopaedic Trauma, vol.
Our result also showed that the external rotator muscles were significantly weaker on the throwing side compared with the internal rotation strength.
The lower activity of the external rotator muscle of the knee could be reason why females showed more internal rotation of the knee during single-leg drop landing.
Failure of reinserted short external rotator muscles after total hip arthroplasty.
3 show that patient 1 recovered best the mobility of flexor muscles, as compared to patient 2 who recovered best the rotator muscles. Comparison between the mobility recovery by the 2 patients
Quadratus femoris (QF), piriformis, obturator internus, obturator externus, and superior and inferior gemelli are the deep external rotator muscles of the hip joint (Fig).
Repeat 3 sets of 10, focusing on the butt and rotator muscles.
--strengthening exercises to strengthen the internal and external rotator muscles of the rotator cuff muscles by elastic bands fixed to wall bars with the patient standing and with elbow flexed at 90 degree closed to the body.

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