The ergonomics of command and control

Since its inception, just after the Second World War, ergonomics research has paid special attention to the issues surrounding human control of systems. Command and Control environments continue to represent a challenging domain for Ergonomics research. We take a broad view of Command and Control research, to include C2 (Command and Control), C3 (Command, Control and Communication), and C4 (Command, Control, Communication and Computers) as well as human supervisory control paradigms. This special issue of ERGONOMICS aims to present state-of-the-art research into models of team performance, evaluation of novel interaction technologies, case studies, methodologies and theoretical review papers. We are pleased to present papers that detail research on these topics in domains as diverse as the emergency services (e.g., police, fire, and ambulance), civilian applications (e.g., air traffic control, rail networks, and nuclear power) and military applications (e.g., land, sea and air) of command and control. While the domains of application are very diverse, many of the challenges they face share interesting similarities

Image encryption and the fractional Fourier transform

A number of method have been recently proposed in the literature for the encryption of 2-D information using optical systems based on the fractional Fourier fransform, FRT. In this paper a brief review of the methods proposed to date is presented. A measure of the strength/robustness of the level of encryption of the various techniques is proposed and a comparison is carried out between the methods. Optical implementations are discussed. Robustness of system with respect to misalignment and blind decryption are also discussed

NPDD model: A tool for photopolymer enhancement

The use of theoretical models to represent the photochemical effects present during the formation of spatially and temporally varying index structures in photopolymers, is critical in order to maximise a material’s potential. One such model is the Non-local Photo-Polymerization Driven Diffusion (NPDD) model. Upon application of appropriate physical constraints for a given photopolymer material, this model can accurately quantify all major photochemical processes. These include i) non-steady state kinetics, (ii) non-linearity iii) spatially non-local polymer chain growth, iv) time varying primary radical production, v) diffusion controlled effects, vi) multiple termination mechanisms, vii) inhibition, (viii) polymer diffusion and ix) post-exposure effects. In this paper, we examine a number of predictions made by the NPDD model. The model is then applied to an acrylamide/polyvinylalcohol based photopolymer under various recording conditions. The experimentally obtained results are then fit using the NPDD model and key material parameters describing the material’s performance are estimated. The ability to obtain such parameters facilitates material optimisation for a given application

Theoretical and Experimental Analysis of Chain Transfer Agents Behaviors in Photopolymer Material

The Non-local Photo-Polymerization Driven Diffusion (NPDD) model indicates how a material’s performance might be improved, and provides a tool for quantitive comparison of different material compositions and to predict their fundamental limits. In order to reduce the non-locality of polymer chain growth (i.e the non-local response parameter, σ) and to improve the spatial frequency response of a photopolymer material, we introduce the chain transfer agent (CTA). In the literature, extensive studies have been carried out on the improvements of the non-local response modifying by the CTA, sodium formate, in the polyvinyl alcohol-acrylamide (PVA/AA) material. In this article, i) based on the chemical reactions of CTA, we extended the CTA model in the literature; ii) we compare two different CTA materials, sodium formate and 1-mercapto-2-propanol without cross-linker in order to obtain the experimental confirmation of the reduction in the average polymer molecular weight is provided using a diffusion-based holographic technique; iii) we examine the non-local responses of several spatial frequencies with the two CTAs. Using the extended CTA model it is demonstrated that the CTA has the effect of decreasing the average length of the polyacrylamide (PA) chains formed, thus reducing the non-local response parameter, especially, in the high spatial frequency case

Recent developments in the NPDD model

An understanding of the photochemical and photo-physical processes, which occur during photo-polymerization, is of extreme importance when attempting to improve a photopolymer material’s performance for a given application. Recent work carried out on the modeling of photopolymers during- and post-exposure, has led to the development of a tool, which can be used to predict the behavior of a number of photopolymers subject to a range of physical conditions. In this paper, we explore the most recent developments made to the Non-local Photo-polymerization Driven Diffusion model, and illustrate some of the useful trends, which the model predicts and then analyze their implications on photopolymer improvement

Non-local spatial frequency response of photopolymer materials containing chain transfer agents: II. Experimental results

In part I of this paper the non-local photo-polymerization driven diffusion model was extended to include the kinetics of chain transfer and re-initiation, in order to analyse the effects of chain transfer agents on the system kinetics and to study their use in reducing the average polymer chain length in free-radical based photopolymer materials. Based on these results, it is proposed that one possible way to improve the material response at high spatial frequency is the addition of chain transfer agents. In this paper, the validity of the proposed model is examined by applying it to fit experimental data for an acrylamide/polyvinyl alcohol (AA/PVA) layer containing two different types of chain transfer agent (CTA): sodium formate (HCOONa) and 1-mercapto-2-propanol (CH3CH(OH)CH2SH). The effects on decreasing the average polymer chain length formed, by the addition of chain transfer agent, which in turn reduces the non-local response of the material, are demonstrated. These reductions are shown to be accompanied by improved high spatial frequency response. Key material parameters are extracted by numerically fitting experimentally measured refractive index modulation growth curves using the model. Further independent experimental confirmation of the reduction in the average polymer molecular weight is provided using a diffusion based holographic technique