Athermal arrayed waveguide gratings in silicon-on-insulator by overlaying a polymer cladding on narrowed arrayed waveguides

Athermal arrayed waveguide gratings (AWGs) in silicon-on-insulator (SOI) are experimentally demonstrated for the first time to our knowledge. By using narrowed arrayed waveguides, and then overlaying a polymer layer, the wavelength temperature dependence of the AWGs is successfully reduced to -1.5 pm/°C, which is more than 1 order of magnitude less than that of normal SOI AWGs. The athermal behavior of the AWGs is obtained with little degradation of their performance. For the central channel, the cross talk is less than -15 dB and the insertion loss is around 2.6 dB. Good characteristics can be maintained with temperatures up to 75 °C. The total size of the device is 350 μm × 250 μm.     

Luminous power efficiency optimization of a white organic light-emitting diode by tuning its spectrum and its extraction efficiency

We show an increase of the luminous power efficiency of a white organic light-emitting diode (LED) with three emitters by optimizing its spectrum and its extraction efficiency. To calculate this efficiency we use a model with four parameters: the spectra, extraction efficiencies, internal quantum efficiencies of three emitters, and the driving voltage. This luminous power efficiency increases by 30% by use of a spectrum close to the spectrum of the MacAdam limit. This limit gives the highest luminous efficacy for a given chromaticity. We also show that a white organic LED with an inefficient deep blue emitter can give the same luminous power efficiency as a white organic LED with a more efficient light blue emitter, because of their different fractions in the radiant flux. Tuning the extraction efficiency with a microcavity to the spectrum also increases the luminous power efficiency by 10%.     

Prediction of ruminal volatile fatty acid proportions of lactating dairy cows based on milk odd- and branched-chain fatty acid profiles: new models, better predictions

The volatile fatty acids (VFA) produced in the rumen and the proportions in which they are produced are important determinants of a ruminant's metabolism, but their monitoring requires rumen-fistulated animals, which is not feasible under practical conditions or in experimental setups at herd level. An alternative approach was suggested earlier, consisting of predicting the VFA proportions from measured odd- and branched-chain fatty acid concentrations in the milk with a linear model. Here, we have improved this strategy through the development and application of 2 new model structures: the quadratic model, containing quadratic terms and interactions, and the rational model, consisting of a ratio of linear expressions. Both were found to improve prediction accuracy significantly compared with the linear model. Although the quadratic model achieved the best prediction accuracy, the rational model has the interesting property that it takes the dependence of the 3 predicted VFA into account and guarantees that the 3 proportions add up to 1. Adding a study effect to correct for a possible study bias in the multi-study data improved prediction substantially for all 3 methods. Our results demonstrate the potential of using milk odd- and branched-chain fatty acid concentrations to predict rumen VFA proportions.     

Electrical discharge machining of ZrO2 toughened WC composites

The interrelationships between the dispersion of the ZrO₂ phase and the electrical discharge machining (EDM) behaviour of WC based composites with 0, 5 or 10 vol% of ZrO₂ are investigated. Special attention was given to the homogeneity of the ultrafine WC – nanometric ZrO₂ powder based composites which were fully densified by means of pulsed electric current sintering (PECS). X-ray photoelectron spectroscopy (XPS) measurements revealed the presence of a nanometric WO₃ layer on the EDM surface, confirming oxidation as the major material removal mechanism (MRM). The surface roughness after the final EDM finishing regime was strongly influenced by the composite homogeneity and could be reduced down to 0.15 μm (R_a) on agglomerate-free composites. Residual stress measurements indicated that EDM did not introduce a significant amount of surface stresses, especially not after the final finishing regime. XRD measurements of EDM surfaces however indicated surface depletion of ZrO₂ by the formation of ZrC and W₂C during spark erosion.     

Wear behavior of carbon fiber‐reinforced poly(phenylene sulfide)

On a pin‐on‐disc test rig, online measurements of the wear and friction of steel sliding against carbon fiber‐reinforced polyphenylene sulfide were done. Instead of the standard set‐up, a rotating composite disc and steel pin are used. The frictional behavior of this material pair results in a friction coefficient of 0.33, while a carbide film is formed in the wear track. This results in the lowering of the frictional behavior. The wear rate is rather low, but when the wear track is covered with a carbide film, suddenly the wear rate raises. This is not due to the wear of the composite material but only as a result of the start of terrible wear of the steel counter face. Moreover, the wear of the pin is strongly related to the wear track. The pin is flattened at the sides of the formed wear track, but in contact with the carbide film there is less wear, resulting in a pin with two flat sides, making contact with the original surface, and a rig in the middle of the pin following the roundness of the wear track. The frictional behavior is strongly dependent on the weft‐warp direction. POLYM. COMPOS., 27:92–98, 2006. © 2005 Society of Plastics Engineers     

Änderung der Gelenklagerkonstruktion des Sturmflutsperrwerks bei Rotterdam

Modification of the ball bearing of the storm surge barrier near Rotterdam (NL). A few years after the commissioning of the Stormbarrier near Rotterdam, the ball joint showed wear marks in the MoS₂ sliding surfaces. Analyses have been carried out to reveal the origin of the wear marks and a modification has been developed. The modification is based on a search for reducing maintenance costs by the use of other materials. A full redesign of the sliding surfaces led to pads of Ultra High Molecular Weight PE with carbon fibre rings against a sliding surface of zink alkyd primer. The design of this modification also included the manufacturing and erection tolerances and quality control.     

The influence of lateral carrier diffusion and surface recombination on the behavior of semiconductor optical amplifier (SOA)-based MMIs

The influence of lateral carrier diffusion and surface recombination on the self-imaging properties of semiconductor-optical-amplifier-based multimode interference couplers has been verified by simulations using a beam propagation method. It shows a significant degradation of the self-imaging properties of these devices. Buried heterostructures or deeply etched waveguide structures can decrease the impact when the degree of surface recombination is sufficiently low.     

Aggregating constraint satisfaction degrees expressed by possibilistic truth values

In information systems, one often has to deal with constraints in order to compel the semantics and integrity of the stored information or to express some querying criteria. Hereby, different constraints can be of different importance. A method to aggregate the information about the satisfaction of a finite number of constraints for a given data instance is presented. Central to the proposed method is the use of extended possibilistic truth values (to express the degree of satisfaction of a constraint) and the use of residual implicators and residual coimplicators (to model the impact and relevance of a constraint). The proposed method can be applied to any constraint-based system. A database application is discussed and illustrated.     

Comparison of different polymeric multimode star couplers forbackplane optical interconnect

This paper describes a comparison of three types of 8×8 multimode star couplers made in polymeric multimode waveguides. Their geometry was designed with a ray tracing tool, measurements show low loss for all designs, but a symmetrical design, based on a tree of Y-junctions yields the best uniformity     

Algorithms for the computation of T-transitive closures

We present two weight-driven algorithms for the computation of the T-transitive closure of a symmetric binary fuzzy relation on a finite universe X with cardinality n (or, equivalently, of a symmetric (n/spl times/n)-matrix with elements in [0, 1]), with T a triangular norm. The first algorithm is proven to be valid for any triangular norm T, whereas the second algorithm is shown to be valid when T is either the minimum operator or an Archimedean triangular norm. Furthermore, we investigate how these algorithms can be appropriately adapted to generate the T-transitive closure of nonsymmetric binary fuzzy relations (or matrices) as well.