Polyelectrolyte swelling of polyamidobenzimidazole

Conclusions An extreme character of the swelling of PABI fibres in DMAc-water mixtures has been detected. The maximum is observed in the region of a 10% water content.The peculiarity in swelling has been explained by the manifestation of a polyelectrolyte nature of the polymer.Translated from Khimicheskie Volokna, No. 5, pp. 34–35, September–October, 1987.     

A high-performance magnetic shield with large length-to-diameter ratio

We have demonstrated a 100-fold improvement in the magnetic field uniformity on the axis of a large aspect ratio, cylindrical, mumetal magnetic shield by reducing discontinuities in the material of the shield through the welding and re-annealing of a segmented shield. The three-layer shield reduces Earth's magnetic field along an 8 m region to 420 μG (rms) in the axial direction, and 460 and 730 μG (rms) in the two transverse directions. Each cylindrical shield is a continuous welded tube which has been annealed after manufacture and degaussed in the apparatus. We present both experiments and finite element analysis that show the importance of uniform shield material for large aspect ratio shields, favoring a welded design over a segmented design. In addition, we present finite element results demonstrating the smoothing of spatial variations in the applied magnetic field by cylindrical magnetic shields. Such homogenization is a potentially useful feature for precision atom interferometric measurements.     

Pulse response of linear dipole antenna

Applications of transient electromagnetics include nonnuclear electromagnetic pulse (EMP) effects on electronic systems to evaluate system vulnerability. A basic component used in the mathematical modeling of systems for EMP vulnerability is the linear dipole antenna. Wu has derived an approximate analytical solution for the pulse reflected from the feed point of a linear dipole antenna for an incident ideal step function of current. The solution does not include the part associated with the very high frequency components because of an approximation used in evaluating the integral describing the reflected pulse. The approximation is eliminated and a simple analytical solution is given that describes that portion of the step function response associated with the very high frequency components. Numerical evaluation of the solution demonstrates convergence with Wu's approximate solution.     

LSM control of Maglev vehicle ride quality

The ride quality of a high speed repulsion type magnetically levitated vehicle using linear synchronous motor (LSM) propulsion has been studied. Vehicle motion is dependent upon the active LSM forces, the passive magnetic lift and drag forces, the aerodynamic drag force, and the technique employed for control. Derivations of the passive lift and drag forces and of the active heave and propulsion control forces are presented. For a balanced three phase LSM, it is shown that harmonic force pulsations disappear, except for the sixth harmonic and its multiples. A control technique which stabilizes the surge motion and provides needed damping in heave to guarantee acceptable ride quality has been simulated. Transient responses, for a vehicle traveling at 120 m/s show stable well damped motion. At this velocity, sixth harmonic effects are completely negligible. Stochastic results show that the heave motion power spectral density response to a moderately rough guideway, i.e., A = 1.34 × 10^-5m, more than satisfies the UMTA ride quality specification.     

Optical Determination of Short-Wave Modulation by Long Ocean Gravity Waves

Time series short-wave spectra were produced from photographs acquired during the Joint North Sea Waves Project (JONSWAP). The feasibility of using this surface imagery to quantify the nature of short-wave modulation by long waves is demonstrated. Photographically obtained time series spectra are correlated to the long wave slope. The modulation transfer function of short-wave spectral energy versus long wave slope is measured to have a 9(slope)-1 magnitude with a 90° phase at a wind speed of 5 m/s in the short-wave spectral regime between 3 and 30 cm in wavelength. Comparison of these results with measurements by coherent radars and laser slope gauges indicates good agreement in the measured modulation magnitude but significant disagreement in measured phase. Modulation magnitude and phase predicted from the action balance model are shown to be significantly smaller than empiricaly measured results.     

Extreme localization of electrons in space and time

Electron emission from sharp metal tips can take place on sub-femtosecond time scales if the emission is driven by few cycle femtosecond laser pulses. Here we outline the experimental prerequisites in detail, discuss emission regimes and relate them to recent experiments in the gas phase (attosecond physics). We present a process that leads to single atom tip emitters that are stable under laser illumination and conclude with a discussion of how to achieve short electron pulses at a target.