Electromagnetic Brake Research Articles

Gravitational radiation from a solid-crust neutron star

The measured period derivative1–3 for the millisecond pulsar PSR1937 + 214 is Ṗ ≃ 1.05×10−19, whereas the present upper limit5 for PSR1953 + 296 is Ṗ<4.2×10−17. For electromagnetic braking, the combination of rapid rotation with such small period derivatives requires a small (∼108 G) magnetic field. A natural association between rapid rotation and small magnetic field is provided by accretion spin-up scenarios7–9. Here we address the analogous problem for gravitational radiation. Balancing gravitational radiation power against the rate of rotational energy loss, we find that if the effective triaxiality eeff exceeds emax∼10−9, gravitational radiation alone would spin a millisecond pulsar down at a faster rate than the observed Ṗ. We show that eeff<<emax, so that gravitational radiation is not likely to play a major role in the evolution of millisecond pulsars even in the absence of damping. Damping times for precession of the solid crust are estimated to be <2×l03 yr.

Cardiorespiratory dynamics during sinusoidal and impulse exercise in man.

Dynamic characteristics of ventilation, cardiac output, and gas exchange during sinusoidally varying work rates for the periods from 1 to 12 min and impulse work rate with a duration of 10 sec were studied on five healthy men in an upright position. Changes in work rate were given by controlling externally the electromagnetic braking system of a bicycle ergometer. Stroke volume, heart rate, and cardiac output during exercise were determined continuously by using an automated impedance cardiograph. Breath by breath determination in minute ventilation, respiratory frequency, tidal volume, oxygen consumption, carbon dioxide output, end-tidal pressures of oxygen and carbon dioxide, and gas exchange ratio were conducted. From these and steady-state response data amplitude and phase relations between each variable and the input work loads were obtained utilizing the frequency analysis techniques. The response characteristics to sinusoidal stimuli were well represented by first-order models with time constants for VE, VCO2, VO2, and Q averaging 75, 67, 52, and 36 sec, respectively. The kinetics of HR closely resembled that of Q. There was a close link between both the dynamics of VE and VCO2. On the other hand, the responses to impulse stimuli were better described by second-order models in which fast and slow response components were connected in parallel. However, the contribution of the fast component to total response was small. Although this response may support in its form the neuro-humoral concept to explain exercise hyperpnea, a tight linkage was observed between VE and VCO2 responses to impulse stimuli. Thus, hyperpnea during the unsteady-state of exercise may be explained by the cardiodynamic hypothesis.

Wind energy conversion system with electromagnetic stabiliser

The development of a novel medium-power (<50kW) w.e.c.s. is outlined. This device, composed of a constant-pitch rigid rotor and a double-stage generator, uses a particular electromagnetic braking to assure speed stabilisation.

Electric currents in the solar wind

The electric currents in the solar wind are described for the particular case of Parker's model, in which the sun's magnetic field is a dipole located at the center of the sun and inclined at an arbitrary angle to the sun's axis of rotation. The current consists of two components. The density of one depends only upon the sun's dipole moment, and that of the other depends upon the solar wind velocity and the sun's angular velocity as well as its dipole moment. The latter component flows in heliographic meridional planes. The electromagnetic forces of this component tend to accelerate the plasma in the leading half of a magnetic sector and to decelerate it in the following half. If the angle λ between the sun's spin axis and the dipole axis is different from either 0° or 90°, the electromagnetic force near the equatorial plane has a southward component in the positive sector and a northward component in the negative sector. The generalization to a more complicated solar magnetic field is discussed. The electromagnetic torque on the sun slows its rotation and for λ ≠ 0° or 90° also has oscillating components in the two directions perpendicular to the spin axis. These components tend to increase λ, indicating that the stable configuration is λ = 90°. For a given dipole moment, λ = 90° is also the orientation that maximizes the electromagnetic braking. Possible electromagnetic contributions to the sun's differential rotation are also considered.

Instability of the free-convection type in magnetohydrodynamics

The processes occurring in an electroconductive fluid in a magnetic field and subjected to an electric current flowing through it are discussed. In a fluid whose electrical conductivity rises with temperature, a phenomenon similar to free convection occurs when the entropy drops along the direction of the force j × B. The joint action of this phenomenon and the overheating instability which also stems from the temperature dependence of the electrical conductivity and the effect of electromagnetic braking is considered. In this case, the criterion of stability is obtained. Instability in the form of free convection also appears due to a Hall current jH flowing along the electrodes of a magnetohydrodynamic channel when a high temperature gradient occurs along the direction of the force jH × B. The instability arises near the cathode and the appearance of one is determined by the value of a dimensionless parameter identical to the Rayleigh number Ra = (dlnσ/dT) g̃l4 ‖∇T‖ /νχ where g̃ = jH B/ρ plays the role of the gravitational acceleration and dlnσ/dT plays the role of the expansion coefficient.

Modification of a stereotaxic guide for trans-nasal pituitary ablation.

Abstract A stereotaxic guide (the Todd-Wells apparatus) has been modified for use with a mobile X-ray image intensifier to allow rapid and precise positioning of a cannula within the pituitary fossa. The sagittal plane of the sella is determined in relation to external, radio-opaque skin markers by preliminary radiographs. The C-arm of the image intensifier is aligned with the sagittal plane of the hemicircular sighting arc of the stereotaxic frame. The patient's skull is fixed to the frame and rotated beneath the sighting arc until the sagittal planes of the sella and arc coincide. The intensifier C-arm is then linked in the horizontal position to the sighting arc by an extension bar and electromagnetic brakes. The patient's head and lateral sighting assembly are moved during screening until the centering mark lies at the chosen point within the sella. A surgical cannula represents a radius of the sighting arc and is passed through the nasal cavity and across the sphenoid bone to this point within the se...

Unipolar induction braking of thin metal sheets

The eddy currents due to the motion of a thin conducting strip in the airgap of a d.c.-excited electromagnet are analysed. This permits determination of the braking force exerted on the sheet. A general method for this type of problem is outlined. The current streamlines are shown, and a specific numerical example is given. The results should be of interest in view of the widespread use of electromagnetic braking and damping in measuring instruments, relays etc.

The design of a translator logic circuit for a three-phase stepping motor

A procedure is described for the design of a translator logic circuit, capable of operating a three-phase electrical stepping motor in the electromagnetic braking drive mode. The resulting logic circuit requires eighteen NAND logic elements and provides a 40 per cent reduction in the number of elements required, in comparison with an equivalent circuit whose design has been based on converting the outputs of a reversible ring counter circuit to the required drive sequence.

Swirls Produced in a ``Crowbarred'' Rotating Plasma

Hydromagnetic swirls develop in a rotating, gaseous plasma subjected to an electromagnetic braking action. Observations of these swirls and the effect of a conducting grid upon them are discussed.

Direct generation of electric power from a high-velocity gas jet

The possibility of generating electric power by the electromagnetic braking of a high-velocity gas jet is discussed. Outstanding problems are assessed and suggestions are put forward for the solution of some of them, but the need for more research is emphasized The continued economic expansion of our society depends upon the growing availability of distributable power, and most of the burden of this increase will fall upon the electric power generating industry. The output of electrical generating plant doubles about every 10 years, but the demand is still greater than the supply. In spite of the vast amount of electric energy (about 1012 kw-hr) produced every year, the efficiency of modern fossil fuel power stations is only about 35 per cent. Any method for increasing this efficiency would be of great importance. The major loss of energy in the conventional process occurs during the conversion of thermal energy in the working fluid to mechanical energy at the electric generator; i.e., in the turbine part of the system. This conversion efficiency could be increased by raising operating temperatures, but there is a practical limit in machines operating with high mechanical stresses.

10. Experimental study of plasmoids

A plasma source can be used to project ionized matter across a magnetic field. The configuration of plasma observed when an electromagnetic braking action is produced by the presence of low-pressure gas (about 1 μ) in the vacuum chamber provides an insight into the manner in which magnetic-field lines can be dragged and twisted. By firing several sources simultaneously, it is possible to simulate the production of spiral galaxies and barred spirals. The paper presented here forms an extension of earlier experiments performed by the author on plasmoids[1].

Experimental Study of Plasmoids

A plasma source can be used to project ionized matter across a magnetic field. The configuration of plasma observed when an electromagnetic braking action is produced by the presence of low-pressure gas (\ensuremath{\sim}1 \ensuremath{\mu}) in the vacuum chamber provides an insight into the manner in which magnetic-field lines can be dragged and twisted. By firing several sources simultaneously, it is possible to simulate in geometrical form the production of spiral galaxies and barred spirals.