Spreading of a new surfactant in the presence of a pre-existing surfactant distribution is investigated both experimentally and theoretically for a thin viscous substrate. The experiments are designed to provide a better understanding of the fundamental interfacial and fluid dynamics for spreading of surfactants instilled into the lung. Quantitative measurements of spreading rates were conducted using a fluorescent new surfactant that was excited by argon laser light as it spread on an air-glycerin interface in a petri dish. It is found that pre-existing surfactant impedes surfactant spreading. However, fluorescent microspheres used as surface markers show that pre-existing surfactant facilitates the propagation of a surface-compression disturbance, which travels faster than the leading edge of the new surfactant. The experimental results compare well with the theory developed using lubrication approximations. An effective diffusivity of the thin film system is found to be Deff = (E*gamma)/(mu/H), which indicates that the surface-compression disturbance propagates faster for larger background surfactant concentration, gamma, larger constant slope of the sigma*-gamma* relation, -E*, and smaller viscous resistance, mu/H. Note that sigma* and gamma* are the dimensional surface tension and concentration, respectively, mu is fluid viscosity, and H is the unperturbed film thickness.

An examination of 56 inks with an argon-ion laser revealed the laser will sometimes stimulate infrared luminescence in inks which did not produce infrared luminescence under the video spectral comparator (VSC-1). This infrared luminescence was always at a higher range (usually 830 to 900 nm) than that found under the VSC-1. This indicates that laser-induced infrared luminescence may be a useful tool in differentiating between inks which otherwise appear similar.

There has been a recent increase in the use and availability of full-color copiers. With this increase comes a greater potential for criminal use. Research by the authors has shown that many products of full-color copiers can be differentiated by the use of microscopy, infrared luminescence, infrared reflectance, and laser luminescence.

Two experimental applications of digital image processing to the examination of questioned documents are evaluated. First is a comparison of digital image processing, electrostatic detection apparatus (ESDA) processing, side lighting, and photography in the decipherment of indented writing. Best results are achieved by first utilizing the ESDA, then digitally enhancing the ESDA lift using a high-pass sharpening filter. The second application is the use of image processing equipment to make fracture match comparisons to associate carbon film typewriter ribbons with questioned typescript. Split-screen images and image overlays are found to be very effective techniques for this kind of examination. Wenderoth [1] and Baier et al. [2] have reported on image processing as it relates to questioned document examination.