Biomedical subjects

Nicholas George

Publications and source records attributed to Nicholas George.

4 recordsLinked to original sources

PubMed2003

Fourier optical analysis of gradient-index array imaging.

We present theory and experiments in which Fourier optics and the generalized Fresnel-zone integral form are used to characterize the imaging both of a single gradient-index rod and an array of nine rods. For the unity magnification SELFOC imager, we show that it has both internal and external Fourier transform planes. Careful treatment of the aperture function for off-axis points leads to a theoretical point-spread function that is in close agreement with experiments. Experiments are presented to illustrate the Fourier transform patterns as well as the imaging for single rods and for the entire array.

Journal Article↗

PubMed2003

Direct coarse sampling of electronic holograms.

We describe a series of experiments in order to test a new sampling criterion for wavefront reconstruction from a carrier-frequency signal as obtained in electronic holography. Both a Fourier-transform configuration and a Fresnel-zone form of a digital holographic microscope are described. Direct coarse sampling of holograms with no phase-shifting elements can be used to obtain wavefront reconstruction, with the number of samples required reduced by the ratio f0/(2Bs), where f0 is the carrier frequency and 2Bs is the signal bandwidth.

Journal Article↗

PubMed2003

Holographic interference filters for infrared communications.

We demonstrate that high-quality interference filters for the wavelength range 1300-1600 nm can be holographically fabricated in DuPont HRF-800X001 photopolymer material by use of visible laser illumination. We also summarize a chain-matrix technique, which we call thin-film decomposition, that is useful for modeling multilayer films with an arbitrary index profile n(z). We use the thin-film-decomposition technique to create design curves that allow one to choose the proper exposure angle and film thickness with which to fabricate a holographic interference filter with a desired transmission efficiency and bandwidth at a particular wavelength. These curves are of general utility and are not confined to any particular holographic recording medium. Excellent agreement between theory and experiment is found.

Journal Article↗

PubMed2003

Inactivation of ompR promotes precocious swarming and flhDC expression in Xenorhabdus nematophila.

The response regulator OmpR is involved in numerous adaptive responses to environmental challenges. The role that OmpR plays in swarming behavior and swarm-cell differentiation in the symbiotic-pathogenic bacterium Xenorhabdus nematophila was examined in this study. Swarming began 4 h sooner in an ompR mutant strain than in wild-type cells. Precocious swarming was correlated with elevated expression of fliC, early flagellation, and cell elongation. The level of flhDC mRNA was elevated during the early period of swarming in the ompR strain relative to the level in the wild type. These findings show that OmpR is involved in the temporal regulation of flhDC expression and flagellum production and demonstrate that this response regulator plays a role in the swarming behavior of X. nematophila.

Bacterial Proteins↗