Biomedical subjects

Raymond A Shaw

Publications and source records attributed to Raymond A Shaw.

4 recordsLinked to original sources

PubMed2006

Phase signature for particle detection with digital in-line holography.

The spatial phase resulting from the digital reconstruction of an in-line hologram of a particle field is shown to yield a unique pattern that can be used for particle detection. This phase signature is present only when viewed along with the reference light. The existence of the phase pattern is verified computationally and confirmed in laboratory experiments with holograms of calibrated glass spheres. The phase signature provides an alternative to the widely used intensity method for particle detection.

Journal Article↗

PubMed2005

Depth-of-focus reduction for digital in-line holography of particle fields.

Poor axial precision caused, in part, by large depth of focus (tau) has been a vexing problem in extraction of particle position from digital in-line holograms. A simple method is proposed to combat this depth-of-focus difficulty. The method is based on decoupling of size and position information. With d, Delta, and lambda being particle diameter, CCD pixel size, and the wavelength, respectively, our main theoretical result is the reduction of tau from tau - d2/lambda to tau - Delta2/lambda for particles of known size. This result is confirmed in laboratory experiments with holograms of calibrated glass spheres.

Journal Article↗

PubMed2005

Heterogeneous surface crystallization observed in undercooled water.

We report laboratory observations of higher freezing temperatures when an ice-forming nucleus is near the surface of an undercooled water drop than when the nucleus is immersed in the drop. The nucleation rate at the water surface is a factor of 10(10) greater than in bulk water, thereby complementing and providing evidence for homogeneous surface crystallization, which has been hypothesized recently. Interpretation of the data via classical nucleation theory shows that the free energy of formation of a critical ice germ is decreased by a factor of approximately 2 when the substrate is near the air-water interface. Furthermore, the analysis suggests that the jump frequency of molecules from the liquid to the solid may be greatly enhanced at the interface.

Letter↗

PubMed2004

Airborne digital holographic system for cloud particle measurements.

An in-line holographic system for in situ detection of atmospheric cloud particles [Holographic Detector for Clouds (HOLODEC)] has been developed and flown on the National Center for Atmospheric Research C-130 research aircraft. Clear holograms are obtained in daylight conditions at typical aircraft speeds of 100 m s(-1). The instrument is fully digital and is interfaced to a control and data-acquisition system in the aircraft via optical fiber. It is operable at temperatures of less than -30 degrees C and at typical cloud humidities. Preliminary data from the experiment show its utility for studies of the three-dimensional spatial distribution of cloud particles and ice crystal shapes.

Journal Article↗