Morphology and kinetics of discontinuous precipitation and dissolution in an Fe-8.5Al-27Mn-1.0Si-0.92C alloy

The morphology and growth kinetics of discontinuous precipitation (DP) and discontinuous dissolution (DD) in an Fe-8.5Al-27Mn-1.0Si-0.92C alloy are investigated. The results indicate that the solid-solution-treated austenite phase decomposes into lamellar DP after aging at temperatures ranging from 900 to 1050 K. After the specimens of a preaged DP structure go through further aging at temperatures ranging from 1118 to 1173 K, the lamellar DP falls into dissolution because of the DD reaction. The lamellar spacings of the DP structure, as well as the reaction-front migration rates during DP and DD reactions, are measured. Based on Aaronson and Liu’s simplified kinetics model, the grain-boundary diffusivities are estimated. They are found to be slightly lower than the grain-boundary diffusion data of Mn in Fe and Fe in Fe as reported by Aaronson and Liu.     

Reduction of sidelobe and speckle artifacts in microwave imaging:the CLEAN technique

Large random thin arrays provide a high angular resolution microwave images but are plagued with artifacts (false targets and target breakup or speckle) caused by high sidelobe levels. The CLEAN algorithm for reducing the sidelobe-induced artifacts is extended to the coherent radiation field and the theory placed on a quantitative basis. The CLEAN technique decomposes the received echoes of a coherent multiple-target scene by iterative cancellation of the largest target found. At each step, cancellation information is used to create a target image. The image includes target intensities, phases, and directions. The process is designed for an imaging instrument consisting of a random thinned array. A condition is derived which, when satisfied, guarantees that all proper targets will be preserved in the cleaned image and all false targets discarded. An algorithm involving moving thresholds is derived to extract the target coordinates. It is shown that targets much weaker than the sidelobe level can be detected and displayed without the hazard of artifacts. The target dynamic range and the image contrast can be increased by up to twice the signal-to-noise ratio per element     

Mutational analysis of human papillomavirus type 11 E5a oncoprotein

In this study, we investigated the structural basis of human papillomavirus type 11 (HPV-11) E5a transforming activity at the amino acid level. The effects of insertion, deletion , and substitution mutations on teh E5a transforming activity were determined by the assay of anchorage-independent growth. In the conserved Cys-X-Cys structure, substitution of Ser for Cys-73 resulted in indistinguishable transforming activity, whereas substitution of Ser for Cys-75 or Ser for both Cys-73 and Cys-75 retained 50 and 42% transformation, respectively. This suggests that Cys at position 75 may be important for transformation. Charge and structural changes at teh COOH termini of several mutants impaired transformation significantly, but those at the middle region did so only mildly. In addition, the 16,000-molecular-weight pore-forming protein (16K protein) is known to associate with BPV-1, HPV-6, and HPV-16 E5 proteins. In this study, we investigated the correlation between E5a-16K binding affinity and the transforming activity of E5a by the use of 11 E5a mutants. Results show that E5a and these 11 E5a mutants could bind to the 16K protein when these proteins were coexpressed in COS cells, suggesting that simple binding of the 16K protein by E5a may not be sufficient for cell transformation.     

Tropospheric effects on design of line-of-sight space-diversity system

The successful application of space diversity to achieve a high propagation reliability over line-of-sight microwave links requires proper separation between diversity antennas, whereby the signals received at the antennas are sufficiently decorrelated. The multipath-propagation model is examined, and en expression is derived for the envelope correlation coefficient which is a function of antenna spacing and is dependent on the parameters of the troposphere.     

Spectral-domain analysis of circular patch frequency selective surfaces

A computationally efficient method is presented for analyzing the scattering from frequency selective surfaces (FSS) comprised of circular metal patches. The formulation is carried out in the spectral domain where the convolution form of the integral equation for the induced current reduces to an algebraic one and the spectral-Galerkin technique is used to solve the resulting equation. Entire-domain basis functions that satisfy the edge condition are introduced to expand the unknown induced current on the metal patches. Calculated results using this procedure show good agreement with data reported by other authors.     

Biosynthesis of phospholipids in subcellular particles from cultured cells of human tissue

A time study of the incorporation of³²P_i into the phospholipids of HeLa, KB, human heart, and liver tissue-culture cell lines has been carried out. The incorporation of³²P_i at various time-intervals into the phospholipids of nuclei, mitochondria, and microsomes of HeLa and KB cells was investigated. The labeling of the isotope into the phospholipids was divided into three groups. The first had two components: phosphatidyl inositol and polyglycerol phosphatides, which showed the greatest incorporation of the isotope as demonstrated in the specific activity values and the percentage of total radioactivity after 15 to 30 minutes of incubation. A second group was composed of the major phospholipids of all tissue-culture cell lines studied, phosphatidyl choline, and phosphatidyl ethanolamine. At first, there was a delayed labeling of these phospholipids; however, after one hour of incubation, a rapid increase was shown in the incorporation of³²P_i. A third group of lipids containing sphingomyelin and phosphatidyl serine demonstrated low specific activity values. The phospholipids of the subcellular fractions, nuclei, mitochondria, and microsomes, had a high degree of incorporation of the isotope into the individual phospholipids and probably represented an active process in the membranes of these cellular units or a renewal of the biological membrane structures. Part of a thesis submitted to the Graduate School of the University of North Dakota in partial fulfillment for the degree of Doctor of Philosophy.     

Radiation resistance of antennas in lossy media

Using the concept of modified power density, expressions are derived for the radiation resistance and efficiency of antennas in a dissipative medium.     

Comparison of Vibrio cholerae O1 isolates by polymerase chain reaction fingerprinting and ribotyping

AIM: To determine reproducibility and accuracy of the Nikon Retinomax autorefractor when used with children who were made cycloplegic. METHODS: Autorefraction and retinoscopy or subjectively refined retinoscopy (where, under the patient's direction, the refraction was varied until the best visual acuity was achieved) were performed on the right eye of 47 children, age 11-93 months. Autorefraction was performed using the Nikon Retinomax, which provides up to eight measured values of refractive error and one representative measurement of refractive error. RESULTS: Autorefractor measurements were successfully obtained from 7/9 children age 3 years or younger, and from all older children. Vector methods were used to calculate differences. Retinomax reproducibility averaged 0.43 D. Unbiased Retinomax and retinoscopy measurements differed by an average of 0.82 D. Unbiased Retinomax and subjectively refined retinoscopy differed by an average of 1.03 D. CONCLUSIONS: Reproducibility of Retinomax measured values in children is comparable with reproducibility of retinoscopy, subjective refraction, and autorefraction measurements in adults. Agreement between Retinomax and retinoscopy and agreement between Retinomax and subjective refinement in children is comparable with agreement between autorefraction and subjective refraction in adults. The study indicates that the Retinomax is a useful instrument for measuring refractive errors in young children.