Microwave holographic metrology of large reflector antennas

A microwave holographic technique for the determination of amplitude and phase of the principal and cross-polarized aperture fields of large reflector antennas is described. The hologram formation process utilizes the elevation over azimuth scanning system normally associated with these antennas, and, in this respect, appears to be unique among other proposed methods of field probing. The present work describes the means used to obtain vital information on the antenna structure such asE- andH-plane phase centers of the feed, and rms values of the reflector surface profile errors. Accurate prediction ofE- andH-plane radiation patterns in the near- and far-field is also demonstrated.     

Voluminous oxidation of aluminium by continuous dissolution in a wetting mercury film

Aluminium, in its normal passivated state, does not react with mercury, i.e., it is not attacked and does not wet or readily dissolve. When the passivating surface layer is removed from high-purity aluminium, the metal can be easily wetted by mercury and upon exposure to air a spontaneous and rapid growth of a fibrous or ribbon-like product emanates from the wetted surfaces. In this work it was observed that the reaction product had little mechanical strength and readily disintegrated into a molecular-scale powder. It was identified as -Al₂O₃ which even after heating for 48 h at 750° C was still of the order of 60 to 70 Å in average particle size. By consideration of the Al-Hg phase diagram, thermodynamic data, and further experimental observations, a mechanism for the phenomenon has been proposed. The probably unique situation which exists at room-temperature in the Al-Hg system enables a spontaneous reaction to take place between the aluminium dissolved in the wetting mercury film and the water vapour and oxygen present in the atmosphere. The influences of several variables on the reaction product morphology and relative reaction rate were investigated. Also, other mercury-metal systems were investigated for possible similar reactions.     

Q-band (26?40 GHz) GaAs FET single-stage amplifier

The high-frequency S-parameters of a 0.3 ?m-gate-length GaAs FET have been measured and compared with the device equivalent circuit model. From the data a Q-band single-stage low noise (3.1 dB) amplifier was designed.     

Measurement of contrast enhancement in VDU screens

Contrast enhancement has been measured on three different VDUs with each of four different enhancement filters. The contrast enhancement filters are of different types — circular polarizing, mesh, neutral isotropically absorbing, and spectrally selective isotropic absorbing. For situations where the contrast reduction is caused by near-specular reflection of ambient light, the circular polarizing filter is considerably more effective than the others. For situations where the contrast reduction is caused by non-specular reflection of ambient light, the filters were all about equally effective. Thus, in an average situation where contrast of the unfiltered VDU image is reduced by both near-specular and non-specular reflections, it would be expected that the circular polarizer would enhance contrast to a noticeably greater extent than the other filters. Resolution was also measured through each of the filters which had been tested for contrast enhancement. The mesh filter noticeably degraded resolution, whereas the circular polarizer and the isotropically absorbing filters did not.     

Investigation of steel containment buckling under dynamic loads

Buckling of freestanding nuclear steel containment buildings from dynamic base excitation was investigated in a combined experimental/numerical program. A polycarbonate scale model of a containment building was excited with scaled earthquake transients and single-frequency harmonic transients to determine the peak base acceleration levels required to induce buckling. Buckling was identified using recorded signals from strain gages and accelerometers, with high-speed video records, and by audibility. Experimental results are compared with numerical results obtained by using a freezing-in-time technique. The results are preliminary, since several more tests are to be performed. However, the limited data obtained indicate that the freezing-in-time technique approximates the required acceleration levels reasonably well, although not conservatively. Additional experiments are described that will take containment asymmetries into account, as well as use instrumentation that will provide more accurate measures of the occurrence of buckling.     

Involvement of specific mechanism in plasmid DNA uptake by mouse peritoneal macrophages

Lamina-associated polypeptide (LAP)2, which directly interacts with B-type lamins and chromosomes, is an integral membrane protein specifically distributed along the inner nuclear membrane of the nuclear envelope. Multiple regions of its large nucleoplasmic domain promote this localization, including the first (residues 1-296) and the second (residues 298-409) halves of the LAP2 N terminus. The second half is involved in LAP2 association with the nuclear lamina [Furukawa, K., Panté, N., Aebi, U. & Gerace, L. (1995) EMBO J. 14, 1626-1636]. In this study to further define its role, we examined which domain of B-type lamin interacts with LAP2 by means of a binding assay with bacterially expressed proteins and a yeast two-hybrid system. We found that amino acids in the region of residues 78-258 of the lamin B1 rod domain directly bound with LAP2. The data suggest that LAP2 may modulate the assembly of nuclear lamins.