Low-Cost Micromechanically Tunable Optical Devices: Strained Resonator Engineering, Technological Implementation and Characterization

The rapid growth of the optical communication branches and the enormous demand for more bandwidth require novel networks such as dense wavelength division multiplexing (DWDM). These networks enable higher bitrate transmission using the existing optical fibers. Micromechanically tunable optical microcavity devices like VCSELs, Fabry-Pérot filters and photodetectors are core components of these novel DWDM systems. Several air-gap based tunable devices were successfully implemented in the last years. Even though these concepts are very promising, two main disadvantages are still remaining. On the one hand, the high fabrication and integration cost and on the other hand the undesired adverse buckling of the suspended membranes. This thesis addresses these two problems and consists of two main parts: • PECVD dielectric material investigation and stress control resulting in membranes shape engineering. • Implementation and characterization of novel tunable optical devices with tailored shapes of the suspended membranes. For this purposes, low-cost PECVD technology is investigated and developed in detail. The macro- and microstress of silicon nitride and silicon dioxide are controlled over a wide range. Furthermore, the effect of stress on the optical and mechanical properties of the suspended membranes and on the microcavities is evaluated. Various membrane shapes (concave, convex and planar) with several radii of curvature are fabricated. Using this resonator shape engineering, microcavity devices such as non tunable and tunable Fabry-Pérot filters, VCSELs and PIN photodetectors are succesfully implemented. The fabricated Fabry-Pérot filters cover a spectral range of over 200nm and show resonance linewidths down to 1.5nm. By varying the stress distribution across the vertical direction within a DBR, the shape and the radius of curvature of the top membrane are explicitely tailored. By adjusting the incoming light beam waist to the curvature, the fundamental resonant mode is supported and the higher order ones are suppressed. For instance, a tunable VCSEL with 26 nm tuning range, 400µW maximal output power, 47nm free spectral range and over 57dB side mode suppresion ratio (SMSR) is demonstrated. Other technologies, such as introducing light emitting organic materials in microcavities are also investigated.

German consumers' attitudes and preferences with regard to organic food and food from different origins

In dieser Studie geht es darum, ein umfassendes Bild bezüglich der Konsumenteneinstellungen, Präferenzen und Zahlungsbereitschaften für ökologisch produzierte Lebensmittel und Lebensmittel verschiedener Herkünfte in Deutschland zu erhalten. Obwohl die regionale Herkunft von Lebensmitteln nicht offiziell und einheitlich geregelt ist und keiner Zertifizierung unterliegt wie die ökologische Produktion von Lebensmitteln, zeigen nationale und internationale Studien gleichermaßen, dass Konsumenten bereit sind, mehr für regionale als für ökologisch produzierte Lebensmittel zu bezahlen. Zur Erreichung des Forschungsziels wurde ein Kaufexperiment in Kombination mit einer Konsumentenbefragung, bestehend aus Fragen zum generellen Einkaufsverhalten, zu Einstellungen gegenüber regionalen und ökologisch produzierten Lebensmitteln und zu soziodemographischen Informationen durchgeführt. Im Kaufexperiment wurden die Attribute Produktherkunft, Produktionsweise und Preis anhand vier verschiedener Produkte (Äpfel, Butter, Mehl und Steaks) untersucht. Die Befragung, einschließlich des Experimentes, war durch Interviewer eines Marktforschungsinstituts initiiert, computergestützt und von den Konsumenten selbständig zu erledigen. Das Ziel war es 80 Konsumenten in jedem der acht Befragungsorte in verschiedenen Regionen Deutschlands zu befragen. Zur Auswertung des Experiments wurden RPL-Modell geschätzt, die die Konsumentenpräferenzen für die zu untersuchenden Produktattribute aufzeigen und die Berechnung von Zahlungsbereitschaften ermöglichen. Für die Gesamtheit der Konsumenten war die regionale Herkunft von Lebensmitteln wichtiger als die ökologische Produktion. Außerdem wurden Produktalternativen, die aus der Region stammen, immer stärker präferiert als Produkte aus Deutschland, aus einem Nachbarland und einem außereuropäischen Land. Weiterhin zeigte die Studie, dass Konsumentenpräferenzen produkt- und regionsspezifisch sind. Folglich wird empfohlen, in zukünftigen Studien unterschiedlich Produkte bzw. Produktgruppen und Konsumenten verschiedener Regionen einzubeziehen. Die zunehmenden Präferenzen und Zahlungsbereitschaften der Konsumenten für regionale Lebensmittel deuteten sowohl in dieser Dissertation als auch in vielen anderen nationalen und internationalen Studien darauf hin, dass es ein großes Potential für einen regionalen Lebensmittelmarkt gibt. Aus diesem Grund wird Produzenten und Vermarktern von ökologischen sowie konventionellen Produkten empfohlen, verstärkt in die Entwicklung von regionalen Versorgungsketten zu investieren.

Double burden malnutrition of preschool children and its association with brain development and milk consumption

Protecting the quality of children growth and development becomes a supreme qualification for the betterment of a nation. Double burden child malnutrition is emerging worldwide which might have a strong influence to the quality of child brain development and could not be paid-off on later life. Milk places a notable portion during the infancy and childhood. Thus, the deep insight on milk consumption pattern might explain the phenomenon of double burden child malnutrition correlated to the cognitive impairments. Objective: Current study is intended (1) to examine the current face of Indonesian double burden child malnutrition: a case study in Bogor, West Java, Indonesia, (2) to investigate the association of this phenomenon with child brain development, and (3) to examine the contribution of socioeconomic status and milk consumption on this phenomenon so that able to formulate some possible solutions to encounter this problem. Design: A cross-sectional study using a structured coded questionnaire was conducted among 387 children age 5-6 years old and their parents from 8 areas in Bogor, West-Java, Indonesia on November 2012 to December 2013, to record some socioeconomic status, anthropometric measurements, and history of breast feeding. Diet and probability of milk intake was assessed by two 24 h dietary recalls and food frequency questionnaire (FFQ). Usual daily milk intake was calculated using Multiple Source Method (MSM). Some brain development indicators (IQ, EQ, learning, and memory ability) using Projective Multi-phase Orientation method was also executed to learn the correlation between double burden child malnutrition and some brain development indicator. Results and conclusions: A small picture of child double burden malnutrition is shown in Bogor, West Java, Indonesia, where prevalence of Severe Acute Malnutrition (SAM) is 27.1%, Moderate Acute Malnutrition (MAM) is 24.9%, and overnutrition is 7.7%. This phenomenon proves to impair the child brain development. The malnourished children, both under- and over- nourished children have significantly (P-value<0.05) lower memory ability compared to the normal children (memory score, N; SAM = 45.2, 60; MAM = 48.5, 61; overweight = 48.4, 43; obesity = 47.9, 60; normal = 52.4, 163). The plausible reasons behind these evidences are the lack of nutrient intake during the sprout growth period on undernourished children or increasing adiposity on overnourished children might influence the growth of hippocampus area which responsible to the memory ability. Either undernutrition or overnutrition, the preventive action on this problem is preferable to avoid ongoing cognitive performance loss of the next generation. Some possible solutions for this phenomenon are promoting breast feeding initiation and exclusive breast feeding practices for infants, supporting the consumption of a normal portion of milk (250 to 500 ml per day) for children, and breaking the chain of poverty by socioeconomic improvement. And, the national food security becomes the fundamental point for the betterment of the next. In the global context, the causes of under- and over- nutrition have to be opposed through integrated and systemic approaches for a better quality of the next generation of human beings.