Ultrafast all-optical switching by cross phase modulation induced wavelength conversion in silicon-on-insulator waveguides and ring resonators

We present new results on ultrafast alloptical wavelength conversion in Silicon-on-Insulator waveguides through cross phase modulation. We demonstrate sub-picosecond all-optical switching with 13dB on/off ratio by combining the nonlinear wavelength conversion in the port waveguide with passive filtering using an integrated SOI microring resonator.\u

A comparison of two techniques for bibliometric mapping: Multidimensional scaling and VOS

VOS is a new mapping technique that can serve as an alternative to the well-known technique of multidimensional scaling. We present an extensive comparison between the use of multidimensional scaling and the use of VOS for constructing bibliometric maps. In our theoretical analysis, we show the mathematical relation between the two techniques. In our experimental analysis, we use the techniques for constructing maps of authors, journals, and keywords. Two commonly used approaches to bibliometric mapping, both based on multidimensional scaling, turn out to produce maps that suffer from artifacts. Maps constructed using VOS turn out not to have this problem. We conclude that in general maps constructed using VOS provide a more satisfactory representation of a data set than maps constructed using well-known multidimensional scaling approaches

Cycling Pathways

In an effort to fight climate change, many cities try to boost their cycling levels. They often look towards the Dutch for guidance. However, historians have only begun to uncover how and why the Netherlands became the premier cycling country of the world. Why were Dutch cyclists so successful in their fight for a place on the road? Cycling Pathways explores the long political struggle that culminated in today’s high cycling levels. Delving into the archives, it uncovers the important role of social movements and shows in detail how these interacted with national, provincial, and urban engineers and policymakers to govern the distribution of road space and construction of cycling infrastructure. It discusses a wide range of topics, ranging from activists to engineering committees, from urban commuters to recreational cyclists and from the early 1900s to today in order to uncover the long and all-but-forgotten history of Dutch cycling governance

Determination of the pigment stoichiometry of the photochemical reaction center of photosystem II

AbstractThe stoichiometry of chlorophyll a, pheophytin α and β-carotene in the photochemical reaction center of Photosystem II was analyzed by reversed phase high-performance liquid chromatography (HPLC) with methanol as the mobile phase, and by the shape of spectra of extracts in 80% acetone. For the HPLC method the molar extinction coefficient of pheophytin a in methanol was redetermined, while for the spectroscopic method spectra of extracts in 80% acetone were simulated by fitting with spectra of isolated chlorophyll a, pheophytin a and β-carotene in 80% acetone. Both methods give internally consistent results, and suggest that the reaction center of Photosystem II isolated by a short Triton X-100 treatment binds 6 chlorophyll a per 2 pheophytin a molecules. We also present evidence that prolonged exposure of the Photosystem II reaction center complex to Triton X-100 does not result in the loss of chlorophyll from the complex. Based on a comparison with spectra reported in publications from other groups, we conclude that the chlorophyll to pheophytin ratio has previously been underestimated to sometimes very significant extents, and that, as yet, no Photosystem II reaction center particles have been purified that bind less than 5–6 chlorophyll a per 2 pheophytin a

Supramolecular organization of photosystem II and its light-harvesting antenna in partially solubilized photosystem II membranes

We present an extended analysis of the organization of green plant photosystem II and its associated light-harvesting antenna using electron microscopy and image analysis. The analysis is based on a large dataset of 16 600 projections of negatively stained PSII-LHCII supercomplexes and megacomplexes prepared by means of three different pretreatments. In addition to our previous work on this system [Boekema, E.J., van Roon, H., Calkoen, F., Bassi, R. and Dekker, J.P. (1999) Biochemistry 38, 2233-2239], the following results were obtained. The rotational orientation of trimeric LHCII at the S, M and L binding positions was determined. It was found that compared to the S trimer, the M and L trimers are rotationally shifted by about -20 degrees and -50 degrees, respectively. The number of projections with empty CP29, CP26 and CP24 binding sites was found to be about 0, 18 and 4%, respectively. We suggest that CP26 and CP24 are not required for the binding of trimeric LHCII at any of the three binding positions. A new type of megacomplex was observed with a characteristic windmill-like shape. This type III megacomplex consists of two C2S2 supercomplexes connected at their CP26 tips. Structural variation in the region of the central dimeric photosystem II complex was found to occur at one specific position near the periphery of the complex. We attribute this variation to the partial absence of an extrinsic polypeptide or one or more small intrinsic membrane proteins