Magnetic braking

The most fashionable theories of cataclysmic variables evolution assume that mass transfer above the period gap is driven by magnetic braking (e.g. Lamb and Melia 1987, Hameury et al. 1987). Available magnetic braking laws give accretion rates that are dependent on the orbital period but are quite insensitive to other parameters of the binary system (Verbunt and Zwaan 1981, Mestel and Spruit 1987). In particular, the spread in the values of A observed at a given orbital period (Warner 1987), is significantly wider than predicted by the theory. 

The predictions of magnetic braking models (or the model itself) could be uncertain, or A changes as a function of time so that the spread is introduced by the time variability of M. 

Mouschovias T. Ch. (1991) Magnetic braking, ambipolar diffusion, cloud cores, and star formation natural length scales and protostellar masses. Astrophys. J. 373, 169-186. 

Magnetorque electric load brake Electric brake Rotor Aluminum fan Field assembly Spring mechanism Magnetic brakes Friction devices Brake shoes... 

The INTROS Flaw Detector is able to inspect ropes moving through the magnetic head at speed 0...2 m/s. Limit of sensitivity to wire brake is 1% of the rope meatallic cross-section area, the LMA measure accuracy is not less than 2%. 

Figure 6.55(a) A magnetic particle brake (Courtesy Dynaspede)... 

Figure 6.54 Electro-magnetic shoe brake (Courtesy BCM)...

Figure 6.55(b) Cross-section of a typical magnetic particle brake... 

Nissan s Hypermini concept EV is a two passenger EV (electric vehicle) that can go 60 miles per hour and travel about 75 miles on a single charge. It uses a neodynium magnet synchronous motor, with a maximum output of 20 kW at 15,000 rpm, lithium-ion batteries and an inductive charging system. Rear-wheel 2WD is used with front independent struts and rear independent parallel-link struts. The brakes are ventilated discs with an anti-lock system. 

The high hardness of chromium oxide resulting from its crystal structure is exploited in polishing agents for metals and in brake linings. Addition of a small amount of chromium oxide to magnetic materials of audio and video tapes imparts a self-cleaning effect to the sound heads. 

Tension Control Roil These type rolls provide the important function of material tension control. There is a proportional relationship between winding tension and lay-on-roll forces (eliminating areas were bumps, valleys, unwanted stretch, etc. develop). There are various tension control techniques available. The proper selection involves decisions on how to produce the tension, how to sense the tension, and how to control the tension. For instance, if the material has a very low tension requirement and if exact control is required, then perhaps, using a magnetic particle brake with an electrical transducer roll with appropriate electronic control is best. However, if the material is on large diameter rolls and moves at slow speed, then a roll follower system can be used effectively. 

Figure 6.29 Active magnetic bearing for a 23 OOOkW6300min 1 natural gas compressor drive. Mechanical backup bearings catch the rotor and brake it to standstill in case of active control malfunction.

The first flight of the Reel Down system took place on 15 September 1982 from the National Scientific Balloon Facility in Palestine, Texas. When the balloon was properly positioned for the descent phase of the experiments, a pin locking the suspended instrument cluster to the winching system was pulled and the controlled descent phase was initiated by releasing a magnetically controlled brake. Descent velocity was selectable by command from the ground. A line velocity of 7 1 m/sec was used for the experiment reported here. A full treatment of mechanical and electronic systems, as well as the data analysis regarding the dynamics of the system, appears elsewhere [19]. 

One high-volume application is the wheel speed detection for anti-lock braking (ABS) systems. Wheel speed information is also needed in modern vehicle dynamics control (VDC) and navigation systems. Both require, in addition to the wheel speed, the steering angle as an input value, which is also often provided by magnetic sensors. A classic field of application is the power train, in which magnetic sensors deliver information about the cam and crank shaft positions as well as the transmission speed. 

Besides these applications of very high volume, more and more position sensors, in particular in safety-relevant and drive-by-wire systems, are replaced by magnetic sensors, because these work without contact and thus without wear. Examples are pedal-position sensors for electronic gas and electrohydraulic braking. Additional quantities which are already sensed magnetically today or which will... 

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