Rotation around a fixed axis

About: Rotation around a fixed axis is a research topic. Over the lifetime, 4037 publications have been published within this topic receiving 52889 citations. The topic is also known as: rotational motion & rotary motion.

Light-driven monodirectional molecular rotor

Abstract: Attempts to fabricate mechanical devices on the molecular level1,2 have yielded analogues of rotors3, gears4, switches5, shuttles6,7, turnstiles8 and ratchets9. Molecular motors, however, have not yet been made, even though they are common in biological systems10. Rotary motion as such has been induced in interlocked systems11,12,13 and directly visualized for single molecules14, but the controlled conversion of energy into unidirectional rotary motion has remained difficult to achieve. Here we report repetitive, monodirectional rotation around a central carbon–carbon double bond in a chiral, helical alkene, with each 360° rotation involving four discrete isomerization steps activated by ultraviolet light or a change in the temperature of the system. We find that axial chirality and the presence of two chiral centres are essential for the observed monodirectional behaviour of the molecular motor. Two light-induced cis-trans isomerizations are each associated with a 180° rotation around the carbon–carbon double bond and are each followed by thermally controlled helicity inversions, which effectively block reverse rotation and thus ensure that the four individual steps add up to one full rotation in one direction only. As the energy barriers of the helicity inversion steps can be adjusted by structural modifications, chiral alkenes based on our system may find use as basic components for ‘molecular machinery’ driven by light.

Surgical instrument incorporating an articulation mechanism having rotation about the longitudinal axis

Abstract: A surgical instrument particularly suited to endoscopic articulates an end effector by including an end effector having a geared articulation mechanism that converts rotational motion from a handle portion. A hollow articulation drive tube transfers the rotation motion in some versions to a spear gear, bevel gear or snaggle tooth gear articulation mechanism. Alternatively, one or more threaded drive rod offset from a longitudinal axis engages a worm gear or flex-neck articulation mechanism.

Slender-body theory for particles of arbitrary cross-section in Stokes flow

Abstract: A rigid body whose length (2l) is large compared with its breadth (represented by R0) is straight but is otherwise of arbitrary shape. It is immersed in fluid whose undisturbed velocity, at the position of the body and relative to it, may be either uniform, corresponding to translational motion of the body, parallel or perpendicular to the body length, or a linear function of distance along the body length, corresponding to an ambient pure straining motion or to rotational motion of the body. Inertia forces are negligible. It is possible to represent the body approximately by a distribution of Stokeslets over a line enclosed by the body; and then the resultant force required to sustain translational motion, the net stresslet strength in a straining motion, and the resultant couple required to sustain rotational motion, can all be calculated. In the first approximation the Stokeslet strength density F(x) is independent of the body shape and is of order μUe, where U is a measure of the undisturbed velocity and e = (log 2l/R0)−1. In higher approximations, F(x) depends on both the body cross-section and the way in which it varies along the length. From an investigation of the ‘inner’ flow field near one section of the body, and the condition that it should join smoothly with the ‘outer’ flow which is determined by the body as a whole, it is found that a given shape and size of the local cross-section is equivalent, in all cases of longitudinal relative motion, to a circle of certain radius, and, in all cases of transverse relative motion, to an ellipse of certain dimensions and orientation. The equivalent circle and the equivalent ellipse may be found from certain boundary-value problems for the harmonic and biharmonic equations respectively. The perimeter usually provides a better measure of the magnitude of the effect of a non-circular shape of a cross-section than its area. Explicit expressions for the various integral force parameters correct to the order of e2 are presented, together with iterative relations which allow their determination to the order of any power of e. For a body which is ‘longitudinally elliptic’ and has uniform cross-sectional shape, the force parameters are given explicitly to the order of any power of e, and, for a cylindrical body, to the order of e3.

Nuclear Spin Relaxation in Ellipsoids Undergoing Rotational Brownian Motion

Abstract: The nuclear spin relaxation times T1 and T2 have been calculated for two identical nuclei of spin I = ½ fixed in an ellipsoid undergoing rotational Brownian motion. The ellipsoid is subject to small random changes in orientation in which the rotation probabilities about its three major axes are different. This anisotropic motion yields five nuclear correlation times; isotropic motion yields only one correlation time. The results are applicable provided that the static dipolar coupling is effectively averaged to small values by the rotational motion. For nonviscous liquids, T1 = T2. When the rotation probabilities about two axes are equal, the relaxation‐time expressions simplify a great deal, but they retain the essential relaxation features of anisotropic rotational motion; the number of nuclear correlation times is reduced to three; the relaxation times for rapid motion have been calculated as a function of the ratio of the two rotation probabilities for this case. The relaxation rates in ellipsoids of ...