Towards predicting removal rate and surface roughness during grinding of optical materials.

A series of controlled grinding experiments, utilizing loose or fixed abrasives of either alumina or diamond at various particle sizes, were performed on a wide range of optical workpiece materials [single crystals of Al2O3 (sapphire), SiC, Y3Al5O12 (YAG), CaF2, and LiB3O5 (LBO); a SiO2-Al2O3-P2O5-Li2O glass ceramic (Zerodur); and glasses of SiO2:TiO2 (ULE), SiO2 (fused silica), and P2O5-Al2O3-K2O-BaO (phosphate)]. The material removal rate, surface roughness, and morphology of surface fractures were measured. Separately, Vickers indentation was performed on the workpieces, and the depths of various crack types as a function of applied load was measured. Single pass grinding experiments showed distinct differences in the spatial pattern of surface fracturing between the loose alumina abrasive (isolated indent-type lateral cracking) and the loose or fixed diamond abrasive (scratch-type elongated lateral cracking). Each of the grinding methods had a removal rate and roughness that scaled with the lateral crack slope, s ℓ (i.e., the rate of increase in lateral crack depth with the applied load) of the workpiece material. A grinding model (based on the volumetric removal of lateral cracks accounting for neighboring lateral crack removal efficiency and the fraction of abrasive particles leading to fracture initiation) and a roughness model (based on the depth of lateral cracks or the interface gap between the workpiece and lap) are shown to quantitatively describe the material removal rate and roughness as a function of workpiece material, abrasive size, applied pressure, and relative velocity. This broad, multiprocess variable grinding model can serve as a predictive tool for estimating grinding rates and surface roughness for various grinding processes on different workpiece materials.

Convergent polishing: a simple, rapid, full aperture polishing process of high quality optical flats & spheres.

Convergent Polishing is a novel polishing system and method for finishing flat and spherical glass optics in which a workpiece, independent of its initial shape (i.e., surface figure), will converge to final surface figure with excellent surface quality under a fixed, unchanging set of polishing parameters in a single polishing iteration. In contrast, conventional full aperture polishing methods require multiple, often long, iterative cycles involving polishing, metrology and process changes to achieve the desired surface figure. The Convergent Polishing process is based on the concept of workpiece-lap height mismatch resulting in pressure differential that decreases with removal and results in the workpiece converging to the shape of the lap. The successful implementation of the Convergent Polishing process is a result of the combination of a number of technologies to remove all sources of non-uniform spatial material removal (except for workpiece-lap mismatch) for surface figure convergence and to reduce the number of rogue particles in the system for low scratch densities and low roughness. The Convergent Polishing process has been demonstrated for the fabrication of both flats and spheres of various shapes, sizes, and aspect ratios on various glass materials. The practical impact is that high quality optical components can be fabricated more rapidly, more repeatedly, with less metrology, and with less labor, resulting in lower unit costs. In this study, the Convergent Polishing protocol is specifically described for fabricating 26.5 cm square fused silica flats from a fine ground surface to a polished ~λ/2 surface figure after polishing 4 hr per surface on a 81 cm diameter polisher.

Postdeployment experiences of military mental health providers.

The deployment experiences of military mental health providers (MMHP) since September 2001 have been largely unexamined. MMHP are an integral part to the military health system and play a key role in maintaining a fit fighting force. MMHP deploy and are expected to help others manage their deployment experiences while being faced with their own emotional challenges during deployment and while transitioning home. This study examines two questions: First, how do MMHP experience reintegration to their families and jobs after being deployed, and second, how do MMHP assess and cope with their own postdeployment issues. In this study, 27 mental health professionals including social workers, psychiatrist, and psychologist were interviewed to examine their deployment and postdeployment experiences. Results indicated 81% of MMHP recognized some level of dysfunction in their lives, at home, at work, or at both, upon their return from deployment. The ability for MMHP to manage their own reintegration issues has significance for their own personal well-being as well as their ability to provide specialized care for others. Attention needs to be given to how MMHP are supported postdeployment and possibly tailor a transitional process for postdeployment reintegration based on the unique nature of their work.

Validation of the Canadian c-spine rule in the UK emergency department setting.

AIM: To determine the potential of the Canadian Cervical Spine Rule (CCR) to safely reduce the number of cervical spine (c-spine) radiographs performed in the UK emergency department setting. METHODS: The study was conducted in two UK emergency departments with a combined annual attendance of >150,000 adult patients. Over the 24 month trial period, 148 doctors were provided training in the use of the CCR and instructed to assess eligible patients presenting with potential c-spine injury. Doctors were instructed to manage patients according to existing practice and not according to the decision obtained from the rule. A subsample of patients was reassessed by a second doctor to test interobserver reliability. RESULTS: A total of 1420 patients were enrolled in the study (50.4% male). 987 (69.5%) had c-spine radiography performed, with 8 (0.6%) having a c-spine injury. If the decision for radiography had been made according to the outcome of the CCR, only 815 (57.4%) would have had c-spine radiography and all 8 abnormal cases would have undergone imaging. Doctors were comfortable using the rule in 91% of cases. Interobserver reliability was good (κ=0.75 95% CI 0.44 to 1.06). CONCLUSION: The CCR can be applied successfully in the UK. Had the CCR been in use during the study period, a 17.4% reduction in radiography could have been achieved without compromising patient care.

Can emergency nurses use the Canadian cervical spine rule to reduce unnecessary patient immobilisation?

The Canadian c-spine rule (CCR) allows safe, reproducible use of radiography in alert, stable patients with potential c-spine injury in the emergency setting [Stiell, I., Clement, C., McKnight, R., Brison, R., Schull, M., Lowe, B., Worthington, J., Eisenhauer, M., Cass, D., Greenberg, G., MacPhail, I., Dreyer, J., Lee, J., Bandiera, G., Reardon, M., Holroyd, B., Lesiuk, H., G. Wells, 2003. The Canadian c-spine rule versus the nexus low-risk criteria in patients with trauma. The New England journal of medicine 349 (26), 2510-2518; Stiell, I., Wells, G., Vandemheen, K., Clement, C., 2001. The Canadian c-spine rule for radiography in alert and stable trauma patients. JAMA 286 (15), 1841]. This paper reports on a study of emergency nurses' ability to identify patients requiring immobilisation using the CCR. Emergency department triage nurses (N = 112) were trained in the use of the CCR and then asked to use the tool over the following 14 months in the assessment of 460 patients who presented with potential c-spine injury. Trained medical staff repeated 55% of the clinical assessments independently using the rule. The level of agreement between nurse and medical judgement was calculated. The inter-rater reliability using the kappa statistic was 0.6 (95% CI 0.50-0.62 N = 254) indicating a 'good' level of agreement. The majority of nurses indicated they were comfortable using the rule. The results suggest that UK emergency department nurses were able to use the Canadian c-spine rule to successfully guide selective immobilisation. A 25% reduction in immobilisation rates would have been achieved if the rule had been followed. Further studies are needed to test the reduction in levels of immobilisation that could be achieved in clinical practice.