Feasibility of noncontacting electromagnetic despinning of asatellite by inducing eddy currents in its skin. I. Analyticalconsiderations

The servicing of disabled satellites requires that the units be despun before any repair can be done. This paper embarks on the feasibility study of an electromagnetically coupled despinning system based on inducing eddy currents in the satellite skin by an external dc magnetic field. The eddy current power input would act in such a way as to reduce the rotational energy of the satellite. The system does not contact the disabled satellite, and therefore, eliminates the hazards associated with physically attaching equipment, or astronauts with equipment, to the satellite. Two methods are investigated for inducing the eddy currents: (1) a large-diameter current loop positioned around the satellite such that the axis of the satellite rotation is in the plane of the loop, and (2) a magnet, either bar or U-shaped, positioned close to or surrounding the satellite. Closed-form solution for-the interacting magnetic flux, in terms of which the eddy current power input may be derived, is given for the two cases. Design parameters are evaluated for the two despinning systems in terms of input power and weight requirements     

On the performance of tubular surface coils in nuclear magneticresonance imaging and spectroscopy

Surface coils are important devices in the clinical application of nuclear magnetic resonance imaging and spectroscopy (NMRIS) because they have higher signal-to-noise ratios than body or head coils in superficial regions. This paper describes our theoretical and experimental study of the performances of tubular surface coils, aiding the effective application of such coils to NMRIS. We present formulas for the RF magnetic (H₁) fields produced by tabular surface coils placed over layered media, and for the self- and loaded-impedances of these coils. The calculated results show the dependence of the coil performances on the coil design parameters and the characteristics of the sample under test. We include the calculated results for the H₁ field phase shifts in conductive samples     

Measurement of the microwave conductivity of a polymeric materialwith potential applications in absorbers and shielding

The microwave conductivity of a new material, the polymer poly-p-phenylene-benzobis-thiazole (PBT) made conductive by ion-implantation doping with iodine, is measured at 9.89 GHz as a function of temperature using the cavity perturbation technique applicable to thin films of arbitrary shape. The DC and microwave conductivities of PBT are seen to approach asymptotically the low-temperature limit predicted by Mott's energy-dependent hopping model. The potential utilization of conductive polymers in microwave absorbers and electromagnetic interference (EMI) shielding is examined using layered media EM theory     

Channel quality estimation and rate adaptation for cellular mobileradio

We propose a technique to measure channel quality in terms of signal-to-interference plus noise ratio (SINR) for the transmission of signals over fading channels. The Euclidean distance (ED) metric, associated with the decoded information sequence or a suitable modification thereof, is used as a channel quality measure. Simulations show that the filtered or averaged metric is a reliable channel quality measure which remains consistent across different coded modulation schemes and at different mobile speeds. The average scaled ED metric can be mapped to the SINR per symbol. We propose the use of this SINR estimate for data rate adaptation, in addition to mobile assisted handoff (MAHO) and power control. We particularly focus on data rate adaptation and propose a set of coded modulation schemes which utilize the SINR estimate to adapt between modulations, thus improving the data throughput. Simulation results show that the proposed metric works well across the entire range of Dopplers to provide near-optimal rate adaptation to average SINR. This method of adaptation averages out short-term variations due to Rayleigh fading and adapts to the long-term effects such as shadowing. At low Dopplers, the metric can track Rayleigh fading and match the rate to a short-term average of the SINR, thus further increasing throughput     

A congestion control scheme for window flow controlled computer networks

In this paper we introduce a congestion control scheme that is appropriate for virtual circuit networks that use fixed routing and a window mechanism for end-to-end flow control. The scheme relies on the notion of balancing the flow of traffic at the local buffer pool of the outgoing links at every node of the network. The effectiveness of the scheme at the intermediate nodes of a network as well as at the network entry point and at the gateway node of interconnected networks is studied via simulation.     

Visualizing causal semantics using animations

Michotte's theory of ampliation suggests that causal relationships are perceived by objects animated under appropriate spatiotemporal conditions. We extend the theory of ampliation and propose that the immediate perception of complex causal relations is also dependent on a set of structural and temporal rules. We designed animated representations, based on Michotte's rules, for showing complex causal relationships or causal semantics. In this paper we describe a set of animations for showing semantics such as causal amplification, causal strength, causal dampening, and causal multiplicity. In a two part study we compared the effectiveness of both the static and animated representations. The first study (N=44) asked participants to recall passages that were previously displayed using both types of representations. Participants were 8% more accurate in recalling causal semantics when they were presented using animations instead of static graphs. In the second study (N=112) we evaluated the intuitiveness of the representations. Our results showed that while users were as accurate with the static graphs as with the animations, they were 9% faster in matching the correct causal statements in the animated condition. Overall our results show that animated diagrams that are designed based on perceptual rules such as those proposed by Michotte have the potential to facilitate comprehension of complex causal relations.