Biomedical subjects
Publications and source records attributed to K J Webb.
A Ag/SiO2 multilayer imaging structure is shown to have subwavelength performance. Loss is the major limitation, and selection of low-loss materials and suitable operating wavelengths has a significant impact on performance. The influence of the variables is presented, and vortices are shown to exist.
Communications wavelength waveguide mode conversion is demonstrated in an irregular metal-walled structure that was designed by using multiresolution optimization. Strong scatter and a large number of degrees of freedom allowed high-efficiency conversion in a device having a length of just a few wavelengths. The fabrication approach draws on standard semiconductor processing. Mode-selective reflectors, splitters, phase shifters, and other elements can be achieved by using this principle.
The importance of loss in the field solution for left-handed media, and in particular, the impact on what would otherwise be a purely evanescent field, is addressed. Using an equivalent electric current source, field solutions are constructed in semi-infinite and finite thickness left-handed media. In the slab case, field growth and power dissipation metrics with uniform amplitude and uniform power excitation, respectively, provide a means to evaluate the potential of a left-handed material lens. Power dissipation suggests that field growth will be adversely impacted.
The zero-mean circular complex Gaussian field statistics of a random medium are experimentally demonstrated in the optical domain, thus verifying this key assumption of statistical optics. Using a frequency-tunable laser source in a fixed-path-length interferometer, we obtain optical field fluctuations in the time and frequency domains that clearly show that the ensemble-averaged temporal intensity converges to the photon transit time distribution, which for the samples used is in excellent agreement with a diffusion model.
We demonstrate for the first time that the temporal response of a random medium can be obtained from optical intensity fluctuations. Our method uses third-order intensity correlations of measured speckle patterns from a multiple scattering random medium as a function of optical frequency. In particular, our experimental results for the temporal response extracted from third-order intensity correlations are in good agreement with the predictions of a diffusion model. Our results are valid for waves in random media where the scattered field is described by circular complex Gaussian statistics.
We report the synthesis of the fluorescent 2'-deoxycytidine analogue 5-methylpyrimidin-2-one nucleoside, its incorporation at three specified sites in a single 60-nucleotide DNA molecule, and the use of its total and polarized intrinsic fluorescence to characterize RecA-DNA complexes. [reaction: see text]
The composition of antioxidant enzymes, especially superoxide dismutase (SOD), was studied in one nontransgenic and three transgenic lines of nodulated alfalfa plants. Transgenic lines overproduced MnSOD in the mitochondria of nodules and leaves (line 1-10), MnSOD in the chloroplasts (line 4-6), and FeSOD in the chloroplasts (line 10-7). In nodules of line 10-7, the absence of transgene-encoded FeSOD activity was due to a lack of mRNA, whereas in nodules of line 4-6 the absence of transgene-encoded MnSOD activity was due to enzyme inactivation or degradation. Transgenic alfalfa showed a novel compensatory effect in the activities of MnSOD (mitochondrial) and FeSOD (plastidic) in the leaves, which was not caused by changes in the mRNA levels. These findings imply that SOD activity in plant tissues and organelles is regulated, at least partially, at the posttranslational level. All four lines had low CuZnSOD activities and an abundant FeSOD isozyme, especially in nodules, indicating that FeSOD performs important antioxidant functions other than the scavenging of superoxide radicals generated in photosynthesis. This was confirmed by the detection of FeSOD cDNAs and proteins in nodules of other legumes such as cowpea, pea, and soybean. The cDNA encoding alfalfa nodule FeSOD was characterized and the deduced protein found to contain a plastid transit peptide. A comparison of sequences and other properties reveals that there are two types of FeSODs in nodules.
A promoter tagging program in the legume Lotus japonicus was initiated to identify plant genes involved in the nitrogen-fixing symbiosis between legumes and rhizobia. Seven transformed plant lines expressing the promoterless reporter gene uidA (beta-glucuronidase; GUS) specifically in roots and/or nodules were identified. Four of these expressed GUS in the roots only after inoculation with nodule-forming Mesorhizobium loti. In one line (T90), GUS activity was found in the root epidermis, including root hairs. During seedling growth, GUS expression gradually became focused in developing nodules and disappeared from root tissue. No GUS activity was detected when a non-nodulating mutant of M. loti was used to inoculate the plants. The T-DNA insertion in this plant line was located 1.3 kb upstream of a putative coding sequence with strong homology to calcium-binding proteins. Four motifs were identified, which were very similar to the "EF hands" in calmodulin-related proteins, each binding one Ca2+. We have named the gene LjCbp1 (calcium-binding protein). Northern (RNA) analyses showed that this gene is expressed specifically in roots of L. japonicus. Expression was reduced in roots inoculated with non-nodulating M. loti mutants and in progeny homozygous for the T-DNA insertion, suggesting a link between the T-DNA insertion and this gene.
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