List of Tables viii List of Figures ix Chapters 1. Introduction 1 Background 1 Problem Statement 3 Dissertation Goal 4 Research Questions 4 Barriers and Issues 5 Assumptions, Limitations, and Delimitations 5 Definitions and Acronyms 6 Organization of the Study 8 2. Literature Review 9

The challenges of measuring optical properties of human tissues include the thickness of the sample, homogenization, or crystallization from freezing of the tissue. This investigation demonstrates a method to avoid these problems by growing optically thin samples of human keratinocytes as a substitute for ex vivo epidermis samples. Several methods of growth were investigated. Resulting samples were measured on a spectrophotometer for transmission between 300 nm and 2600 nm. The efficacy of the cell growth was confirmed with histological examination of several cultured keratinocyte samples. Limitations were the requirement to measure samples immediately after removal from the incubation environment, and the absence of the irregular structures of normal skin such as hair and glands.

Abstract. Human perception of 2.0-m infrared laser irradiation has become significant in such disparate fields as law enforcement, neuroscience, and pain research. Several recent studies have found damage thresholds for single-pulse and continuous wave irradiations at this wavelength. However, the only publication using multiple-pulse irradiations was investigating the cornea rather than skin. Literature has claimed that the 2.0-m light characteristic thermal diffusion time was as long as 300-ms. Irradiating the skin with 2.0-m lasers to produce sensation should follow published recommendations to use pulses on the order of 10 to 100 ms, which approach the theoretical thermal diffusion time. Therefore, investigation of the heating of skin for a variety of laser pulse combinations was undertaken. Temperatures of ex vivo pig skin were measured at the surface and at three depths from pulse sequences of six different duty factors. Differences were found in temperature rise per unit exposure that did not follow a linear relation to duty factor. The differences can be explained by significant heat conduction during the pulses. Therefore, the common heat modeling assumption of thermal confinement during a pulse may need to be experimentally verified if the pulse approaches the theoretical thermal confinement time.

Non-contact temperature measurement and imaging instruments are widely used in studies of laser interaction with tissue. For reliable results, independent verification of the instruments abilities and limitations is necessary. Two common types of heat measuring instruments are the LiTaO 3 type II pyrometer and the microbolometer array thermal imager. This study found that when considering the Signal to Noise Ratio, the temporal resolution, and the spatial dependency of the temperature measured by the instrument the microbolometer was superior for measurements of incident beams of 5 mm diameter and all pulse frequencies investigated.

The authors have developed a comprehensive history of instructional design and performance improvement. They methodically describe the theories that became the foundation of instructional design and then explain how instructional design led to other theories, including performance improvement. They also identify future research opportunities. The Instructional Design Knowledge Base: Theory, Research, and Practice (2011; 219 pages; ISBN13: 978‐0‐415‐80200‐0, hardcover, $163.00; ISBN13: 978‐0‐415‐80201‐7, paperback, $47.95; ISBN13: 978‐0‐203‐84098‐6, e‐book, $35.99 Kindle edition) is published by Taylor & Francis.