Multimode pumping of optical parametric oscillators

Cataloged from PDF version of article.Calculations suggest that optical parametric oscillators (OPO’s) can be efficiently pumped using multimode, divergent pump sources. The influence of pump beam divergence and mode structure upon OPO performance is measured for both noncritical phase-matching, and OPO’s with walkoff. Multimode OPO pumping is shown to be efficient, provided appropriate nonlinear crystals and OPO cavities are employed; the nonlinear crystal must have sufficient angular acceptance to tolerate a divergent pump; the OPO cavity must support modes that match the divergence and spatial intensity characteristics of the pump. For low-order pump modes, the OPO can be made to match the mode of the pump. Higher order pump modes reduce the OPO efficiency, and cause a saturation of efficiency with increasing pump power. The efficiency is degraded in a similar fashion in the presence of walkoff. Multimode pumping is more difficult in longer OPO cavities due to increased buildup time of higher order OPO modes

Its Not My Fault - Exploring Multi-Causal Factors for Educational and Societal Dropout in Asia and Europe

This symposium paper presentation provides an insight into the nature of causes of drop out in Norway, Denmark and the UK

Validity of self-assessment of hallux valgus using the Manchester scale

<p>Abstract</p> <p>Background</p> <p>Hallux valgus (HV) is a common condition involving the progressive subluxation of the first metatarsophalangeal joint due to lateral deviation of the hallux and medial deviation of the first metatarsal. The objective of this study was to evaluate the re-test reliability and validity of self-assessment of HV using a simple clinical screening tool involving four standardised photographs (the Manchester scale), in order to determine whether this tool could be used for postal surveys of the condition.</p> <p>Methods</p> <p>HV was assessed with the Manchester scale in 138 people aged 65 to 93 years of age (102 women and 36 men) as part of a larger randomised controlled trial. At the six month follow-up assessment, HV was reassessed to determine re-test reliability, and participants were asked to self-assess their degree of HV independent of the examiners. Associations between (i) baseline and follow-up assessments of the examiners and (ii) participant and examiner assessments were performed using weighted kappa statistics. Analyses were then repeated after HV was dichotomised as present or absent using unweighted kappa, and sensitivity and specificity of self-assessment of HV was determined.</p> <p>Results</p> <p>Re-test reliability of the examiners was substantial to almost perfect (weighted kappa = 0.78 to 0.90), and there was a substantial level of agreement between observations of the participants and the examiners (weighted kappa = 0.71 to 0.80). Overall, there was a slight tendency for participants to rate their HV as less severe than the examiners. When the Manchester scale scores were dichotomised, agreement was substantial to almost perfect for both re-test comparisons (kappa = 0.80 to 0.89) and substantial for comparisons between participants and examiners (kappa = 0.64 to 0.76). The sensitivity and specificity of self-assessment of HV using the dichotomous scale were 85 and 88%, respectively.</p> <p>Conclusions</p> <p>The Manchester scale demonstrates high re-test reliability, and self-assessment scores obtained by participants are strongly associated with scores obtained by examiners. These findings indicate that the tool can be used with confidence in postal surveys to document the presence and severity of HV.</p> <p>Trial registration</p> <p>ACTRN12608000065392</p

Intracorneal bacterial colonization in a crystalline pattern

We report the case of a 78-year-old woman who developed an intrastromal bacterial colonization 22 months after penetrating keratoplasty. Slit-lamp examination revealed discrete, finely branched, fernlike stromal opacities, which were histopathologically found to be large intrastromal aggregates of gram-positive cocci with almost no inflammatory cell response.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47391/1/417_2005_Article_BF02143065.pd

Self-similarity of contact line depinning from textured surfaces

The mobility of drops on surfaces is important in many biological and industrial processes, but the phenomena governing their adhesion, which is dictated by the morphology of the three-phase contact line, remain unclear. Here we describe a technique for measuring the dynamic behaviour of the three-phase contact line at micron length scales using environmental scanning electron microscopy. We examine a superhydrophobic surface on which a drop’s adhesion is governed by capillary bridges at the receding contact line. We measure the microscale receding contact angle of each bridge and show that the Gibbs criterion is satisfied at the microscale. We reveal a hitherto unknown self-similar depinning mechanism that shows how some hierarchical textures such as lotus leaves lead to reduced pinning, and counter-intuitively, how some lead to increased pinning. We develop a model to predict adhesion force and experimentally verify the model’s broad applicability on both synthetic and natural textured surfaces.National Science Foundation (U.S.) (CAREER Award 0952564)DuPont MIT AllianceNational Science Foundation (U.S.). Graduate Research Fellowship ProgramNational Science Foundation (U.S.) (Award ECS-0335765