Biomedical subjects

James E Harvey

Publications and source records attributed to James E Harvey.

5 recordsLinked to original sources

PubMed2006

The ecological condition of Gulf of Mexico resources from Perdido Key to Port St. Joe, Florida: Part II near-shelf coastal resources.

In 1999, the United States Environmental Protection Agency Gulf Ecology Division initiated a pilot study to assess the condition of nearshore coastal resources. Near-shelf areas associated with coastal beaches are susceptible to land based activities, but are not consistently monitored. Additionally, few or no marine water quality criteria exist for evaluating these waters. The goal of this pilot study was to assess the ecological condition of Gulf of Mexico near-shelf resources using a probability-based survey design. Data are used to generate a baseline assessment of condition in coastal nearshore areas and provide a comparative tool for evaluating future trends in condition. Water quality, sediment quality and benthic diversity data can provide a baseline assessment for managers to evaluate the potential for future problems such as nutrient over-enrichment, sediment contamination and degraded biological condition. We present results from a probability-based survey demonstration assessing near-shelf resources along the Florida panhandle.

Caribbean Region↗

PubMed2006

Nonparaxial scalar treatment of sinusoidal phase gratings.

Scalar diffraction theory is frequently considered inadequate for predicting diffraction efficiencies for grating applications where lambda/d>0.1. It has also been stated that scalar theory imposes energy upon the evanescent diffracted orders. These notions, as well as several other common misconceptions, are driven more by an unnecessary paraxial approximation in the traditional Fourier treatment of scalar diffraction theory than by the scalar limitation. By scaling the spatial variables by the wavelength, we have previously shown that diffracted radiance is shift invariant in direction cosine space. Thus simple Fourier techniques can now be used to predict a variety of wide-angle (nonparaxial) diffraction grating effects. These include (1) the redistribution of energy from the evanescent orders to the propagating ones, (2) the angular broadening (and apparent shifting) of wide-angle diffracted orders, and (3) nonparaxial diffraction efficiencies predicted with an accuracy usually thought to require rigorous electromagnetic theory.

Journal Article↗

PubMed2003

Aberrations of diffracted wave fields: distortion.

Near-field diffraction patterns are merely aberrated Fraunhofer diffraction patterns. These aberrations, inherent to the diffraction process, provide insight and understanding into wide-angle diffraction phenomena. Nonparaxial patterns of diffracted orders produced by a laser beam passing through a grating and projected upon a plane screen exhibit severe distortion (W311). This distortion is an artifact of the configuration chosen to observe diffraction patterns. Grating behavior expressed in terms of the direction cosines of the propagation vectors of the incident and diffracted orders exhibits no distortion. Use of a simple direction cosine diagram provides an elegant way to deal with nonparaxial diffraction patterns, particularly when large obliquely incident beams produce conical diffraction.

Journal Article↗

PubMed2002

Axial irradiance distribution throughout the whole space behind an annular aperture.

In many photonics and fiber-optics applications, the irradiance distribution in the very near field (z/D < 0.25) behind a circular or annular aperture is of interest. We present the results of detailed calculations of the irradiance distribution throughout the entire space behind an annular aperture. Included as a special case of the annular aperture is the circular aperture and the opaque circular disk. A log-log plot over many orders of magnitude in axial distance provides particular insight. The behavior throughout the Fresnel and Fraunhofer region is well known; however, we pay particular attention to the behavior in the near field. A variety of subtle effects in the near field are presented and discussed.

Journal Article↗

PubMed2002

Tolerance on defocus precisely locates the far field (exactly where is that far field anyway?).

The Fraunhofer criterion defines the location of the boundary between the Fresnel and the Fraunhofer diffraction regions and thus determines the location of that region commonly referred to as the far field. The Fraunhofer criterion is usually given as an axial distance much greater than some amount relative to the maximum dimension of the aperture. By recognizing that Fresnel diffraction patterns are merely defocused Fraunhofer diffraction patterns, we show that the Fraunhofer criterion can be written precisely in terms of an allowable tolerance on defocus. This new criterion provides insight that is useful to optical designers and engineers who routinely deal with such tolerances.

Journal Article↗