Large-Signal Transient Responses of a Switching Regulator

Analytical and experimental considerations of the large-signal transient responses of the buck-type switching regulator are described. The dynamic behavior under the large-signal condition is different from the small-signal operation because of the saturation characteristics of the pulsewidth modulator feedback controller. The effect of this nonlinearity is analyzed by dividing its operation into three modes. As a result the peak values of the inrush current and output voltage are obtained analytically both for the start-up and for the step change of the load condition.     

Large aerial bursts: an important class of terrestrial accretionary events

Large aerial bursts similar to the 1908 Tunguska bolide but much larger in magnitude have surely been responsible for many catastrophic events in the history of the Earth. Because aerial bursts produce shallow (or even negligible) craters, their existence is difficult to document in the geological record. Even aerial bursts as small as Tunguska deposit enough energy to melt approximately 1mm of dry soil. Silica-rich glass formed in such melts has the potential to survive in the soil for many Ma, thus a potential indicator of large aerial bursts is glass that was formed as thick regions within silicate melt sheets. The layered tektites from Southeast Asia and the Libyan desert glass may have formed by a combination of sedimentation and downslope flow of silicate melt heated by radiation from large aerial bursts. The alternative, formation of layered tektites as crater ejecta, cannot account for observations such as uniformly high 10Be contents, the orientation of the magnetic remanence field, and the absence of splash-form (e.g., teardrop or dumbbell) tektites in regions where layered tektites are common. The largest asteroids or comets make craters no matter what their strength. Recent reviews suggest that, for events in the energy range up to 10(19)-10(20) J (about two orders of magnitude larger than the Meteor Crater impact), aerial bursts are more likely than cratering events, and the layered tektites of Southeast Asia imply the existence of aerial bursts one to two orders of magnitude larger still.     

Does the centre of mass remain stable during complex human postural equilibrium tasks in weightlessness?

In normal gravity conditions the execution of voluntary movement involves the displacement of body segments as well as the maintenance of a stable reference value for equilibrium control. It has been suggested that centre of mass (CM) projection within the supporting base (BS) is the stabilised reference for voluntary action, and is conserved in weightlessness. The purpose of this study was to determine if the CM is stabilised during whole body reaching movements executed in weightlessness. The reaching task was conducted by two cosmonauts aboard the Russian orbital station MIR, during the Franco-Russian mission ALTAIR, 1993. Movements of reflective markers were recorded using a videocamera, successive images being reconstructed by computer every 40ms. The position of the CM, ankle joint torques and shank and thigh angles were computed for each subject pre- in- and post-flight using a 7-link mathematical model. Results showed that both cosmonauts adopted a backward leaning posture prior to reaching movements. Inflight, the CM was displaced throughout values in the horizontal axis three times those of pre-flight measures. In addition, ankle dorsi flexor torques inflight increased to values double those of pre- and post-flight tests. This study concluded that CM displacements do not remain stable during complex postural equilibrium tasks executed in weightlessness. Furthermore, in the absence of gravity, subjects changed their strategy for producing ankle torque during spaceflight from a forward to a backward leaning posture.     

PowerCore combining structure and batteries for increased energy toweight ratio

Much of the mass of a battery is comprised of nonreactive materials. In an NiH₂ battery, this includes the pressure vessel and 50% of the positive electrode. PowerCore reconfigures the battery materials to serve as a structural sandwich panel. The effective specific energy of the new device can exceed 100 Wh/kg. PowerCore is intended to handle power demands of low Earth orbiting communications satellites such as IRIDIUM. This paper describes the concept and development progress     

Programmable, multi-purpose opto-electronic sensor system

Optical fibre sensing is becoming increasingly attractive in both the smart structure sphere of interest as well as the medical and industrial concerns. Fibre-optic interferometric sensors can be designed as compact and robust transducers. In general, the transduction mechanism involves the phase modulation of coherent or monochromatic light propagating through a fibre-optic cable, and detecting the changes in the energy associated with this phase change. Sensors based on this technique can generally be configured to be quite sensitive and measurements of a wide variety of physical parameters are achievable. Intrinsic features of optical fibres, such as immunity to electromagnetic interference, flexibility, thinness, strength and weight, make this ideal for sensor technology. In the process of developing fibre-optic sensors for laboratory experimentation, as well as generalised research, an appropriate, easy to use opto-electronic drive and measurement system is required. This paper discusses the operation of a programmable opto-electronic drive and measurement system     

Phase Space Density Analysis of Energy Transport in the Earth’s Magnetotail

Two energetic events in the Earth’s magnetotail detected by Geotail are examined with detailed analysis of three-dimensional velocity phase space density. It is found that the occurrence of multiple ion components is high during these dynamic episodes. Different populations evolve independently of each other, suggesting particles from multiple activity sites contributing to the observed phase space density. The transport properties with consideration of multiple components are evaluated, with the result showing significant differences from those based on a single fluid approach. This comparison indicates that precise evaluation of the energy and magnetic flux transport of energetic events in the magnetotail requires resolving individual populations in the phase space density.     

The Effect of Interfering Signals on the Performance of Angle of Arrival Estimates

The performance of angle of arrival estimates using an array in the presence of interfering signals is evaluated using the Cramer-Rao bound. To do this, a model for interference is developed which presents the interference as narrowband, temporally white, but spatially correlated, noise. The bound is evaluated and it is shown to depend upon the ambiguity function of the array and spatial correlation matrix of the noise plus interference. Motivation of the model in the context of air traffic control and sonar surveillance is presented.