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Applications of Graphene
Published in Andre U. Sokolnikov, Graphene for Defense and Security, 2017
Precession is a change in the direction of the axis of rotation of a rotational body. There are two kinds of precession: torque-induced and torque-free. The Hanle effect implies reduction in the polarization of light: the atoms emitting the light are influenced by a magnetic field in a certain direction. The Larmor frequency refers to the rate of precession of the proton’s magnetic moment around the external magnetic field. The frequency of precession is connected with the strength of the magnetic field B0. The precession effect takes place when a magnetic field is perpendicular to the graphene device plane (Fig. 9.27 a)) and is applied so that the electron spin precesses at the Larmor frequency (Eq. 9.26). In Fig. 9.27 b) B = 100 mT. When the spin-up electrons are injected through electrode 3, they diffuse to electrode 2 and precess around the vertical magnetic field. The spin diffusion length was found between 1.5 and 2.0 µm41. A non-local magnetoresistance ΔRNL=130Ω was observed by tunneling spin injection from Co through MgO/TiO2 barrier42.
MRI
Published in John G Webster, Minimally Invasive Medical Technology, 2016
Precession is analogous to the way a top, while spinning, precesses about the vertical axis. Figure 6.1 shows that as protons precess in the presence of an external magnetic field, they may do so in two possible energy states: either excited (oriented antiparallel to the external magnetic field) or relaxed (aligned with the magnetic field).
The ship's master compass
Published in Laurie Tetley, David Calcutt, Electronic Navigation Systems, 2007
Precession is the term used to describe the movement of the axle of a gyroscope under the influence of an external force. If a force is applied to the rotor by moving one end of its axle, the gyroscope will be displaced at an angle of 90° from the applied force. Assume that a force is applied to the rotor in Figure 8.4 by lifting one end of its axle so that point A on the rotor circumference is pushed downwards into the paper. The rotor is rapidly spinning clockwise, producing gyroscopic inertia restricting the effective force attempting to move the rotor into the paper. As the disturbing force is applied to the axle, point A continues its clockwise rotation but will also move towards the paper. Point A will therefore move along a path that is the vector sum of its original gyroscopic momentum and the applied disturbing force. As point A continues on its circular path and moves deeper into the paper, point C undergoes a reciprocal action and moves away from the paper. The plane of rotation of the rotor has therefore moved about the H axis although the applied force was to the V axis.
Multibody system design based on reference dynamic characteristics: gyroscopic system paradigm
Published in Mechanics Based Design of Structures and Machines, 2023
Ayman A. Nada, Abdullatif H. Bishiri
A gyroscope is basically a symmetrical body mounted so that it can rotate about an axis in any direction. When gyrating, the gyroscope can resist any changes in the orientation of its rotational axis. Moreover, the gyroscope has the ability to undergo precession. In general terms, precession is the angular velocity component required to reconcile the angular momentum vector of the gyroscope with the torque acting on the system. The gyroscopic effect exerts influence on the performance and behavior of a wide range of mechanisms and machines to a large extent. In some applications, designers have to introduce ways to counterweigh its effect, whereas, in others, it can be employed to modulate mechanism performance.
Study on bearing force of marine propeller induced by longitudinal vibration of propulsion-shafting*
Published in Ships and Offshore Structures, 2020
Donglin Zou, Fangrui Lv, Na Ta, Zhushi Rao
When the shaft rotates, it has two kinds of rotation motions (Zhang 1990), as shown in Figure 1, namely the spin around the centre of the shaft and the precession around the bearing centre. In rotordynamics theories, the precession motion is also called the whirl motion. In fact, the amplitude of the whirl orbit is just the amplitude of bending vibrations.