Birefringence in Injection-Molded Cyclic Olefin Copolymer Substrates and Its Impact on Integrated Photonic Structures.

This contribution quantifies the birefringence within injection-molded cyclic olefin copolymer plates and discusses its impact on the mechanical properties of the plates. It also focuses on the impact of birefringence on integrated waveguides and Bragg gratings and provides fabrication guidelines for such structures. The anisotropy in all three dimensions of the workpiece is examined by means of polarimetry and a prism coupler. It is found that the birefringence is inhomogenously distributed within the workpieces, whereas the maximum birefringence not only varies locally, but also depends on the observation direction. Overall, a maximum birefringence of 10 × 10-4 is found at the plate's surface near the injection gate. The anisotropy then reduces exponentially towards the center of the workpiece and saturates at 1.8 × 10-4, in a depth of 0.4 mm. Thus, the birefringence strongly affects near-surface photonic structures. It is found that, depending on their orientation and the local birefringence of the substrate, waveguides and Bragg gratings fabricated with comparable parameters behave completely differently in terms of polarization-dependent optical attenuation, cross-sectional intensity distribution and Bragg reflection signal. For example, the support of the TM mode can vary between total loss and an optical attenuation of 0.9 dB × cm-1. In consequence, this study underlines the importance of quantifying the birefringent state of an injection-molded cyclic olefin copolymer workpiece if it is supposed to serve as a substrate for integrated photonic structures. The study furthermore demonstrates that birefringence effects can be omitted by burying the photonic structures deeper into the volume of the thermoplastic.

Do children's health resources differ according to preschool physical activity programmes and parental behaviour? A mixed methods study.

Preschool can have positive effects on the development of a healthy lifestyle. The present study analysed to what extent different conditions, structures and behavioural models in preschool and family-children's central social microsystems-can lead to differences in children's health resources. Using a cross-sectional mixed methods approach, contrast analyses of "preschools with systematic physical activity programmes" versus "preschools without physical activity programmes" were conducted to assess the extent to which children's physical activity, quality of life and social behaviour differ between preschools with systematic and preschools without physical activity programmes. Differences in children's physical activity according to parental behaviour were likewise assessed. Data on child-related outcomes and parent-related factors were collected via parent questionnaires and child interviews. A qualitative focused ethnographic study was performed to obtain deeper insight into the quantitative survey data. Two hundred and twenty seven (227) children were interviewed at 21 preschools with systematic physical activity programmes, and 190 at 25 preschools without physical activity programmes. There was no significant difference in children's physical activity levels between the two preschool types (p = 0.709). However, the qualitative data showed differences in the design and quality of programmes to promote children's physical activity. Data triangulation revealed a strong influence of parental behaviour. The triangulation of methods provided comprehensive insight into the nature and extent of physical activity programmes in preschools and made it possible to capture the associations between systematic physical activity promotion and children's health resources in a differential manner.

Do preschools differ in promoting children's physical activity? An instrument for the assessment of preschool physical activity programmes.

BACKGROUND: Preschools offer high potential for preventive interventions. However, little is known about the structure of preschool programmes to promote physical activity (PA) in preschoolers although almost all children aged three to six years spend one third of the day at preschool. The aim of this study was to determine whether and to what extent preschools implement systematic PA promotion measures using an instrument specifically developed to assess and systematize preschool PA programmes. METHODS: In the cross-sectional study a baseline survey of preschool education policies was conducted to identify and assess the type and extent of PA programmes and opportunities in preschools in the State of Lower Saxony, Germany. An assessment instrument was developed to identify preschools with systematic PA programmes (type 1) and those without PA programmes (type 2) based on the following quality criteria: A) written PA policy, B) structured weekly PA offerings for all children; C) at least one qualified physical education teacher; D) PA-friendly indoor and outdoor facilities (exercise room, situational PA opportunities, outdoor areas, play equipment etc.), and E) structured PA promotion in place for at least two years. A third type of preschool that promotes PA in children to some extent (i.e., that meets the criteria partially but not completely) was classified as "preschools with limited PA programmes". RESULTS: 2415 preschools participated in the survey (response rate: 59%). The results show that 26% (n = 554) have a systematic PA programme while 3% (n = 64) have no PA programme. Most (71%, n = 1514) were classified as limited PA programme preschools. All three types of preschools differed significantly (p = .000) from each other in terms of size (small vs. large). Most of the preschools without PA programmes are small half-day preschools. CONCLUSIONS: The study investigated an assessment-instrument providing extensive insight into the nature, extent and routine practical implementation of PA promotion in preschools. The criteria used to evaluate preschool PA programmes are well-suited to identify the different preschool PA programme types and target areas in the field of PA promotion in which specific measures (teacher education, structured PA offerings, etc.) can be implemented in future interventions.