Resonance splitting in gyrotropic ring resonators

We present the theoretical concept of an optical isolator based on resonance splitting in a silicon ring resonator covered with a magneto-optical polymer cladding. For this task, a perturbation method is derived for the modes in the cylindrical coordinate system. A polymer magneto-optical cladding causing a 0.01 amplitude of the off-diagonal element of the dielectric tensor is assumed. It is shown that the derived resonance splitting of the clockwise and counterclockwise modes increases for smaller ring radii. For the ring with a radius of approximately 1.5μm, a 29GHz splitting is demonstrated. An integrated optical isolator with a 10μm geometrical footprint is proposed based on a critically coupled ring resonator.     

ChemInform Abstract: Structure Determination of Gold Clusters by Trapped Ion Electron Diffraction: Au‐14—Au‐19.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Preconditioning of spectral methods via Birkhoff interpolation

High-order differentiation matrices as calculated in spectral collocation methods usually include a large round-off error and have a large condition number (Baltensperger and Berrut Computers and Mathematics with Applications 37(1), 41–48 1999; Baltensperger and Trummer SIAM J. Sci. Comput. 24(5), 1465–1487 2003; Costa and Don Appl. Numer. Math. 33(1), 151–159 2000). Wang et al. (Wang et al. SIAM J. Sci. Comput. 36(3), A907–A929 2014) present a method to precondition these matrices using Birkhoff interpolation. We generalize this method for all orders and boundary conditions and allowing arbitrary rows of the system matrix to be replaced by the boundary conditions. The preconditioner is an exact inverse of the highest-order differentiation matrix in the equation; thus, its product with that matrix can be replaced by the identity matrix. We show the benefits of the method for high-order differential equations. These include improved condition number and, more importantly, higher accuracy of solutions compared to other methods.     

Nanostructured Materials for Skeletal Repair

The treatment of bone and cartilage defects with bioengineered constructs of artificial scaffolds and autogenous cells became the main challenge of contemporary regenerative medicine. Early defect repair may prevent secondary injury. Recent studies could prove that bone and cartilage cells are sensitive to microscale and nanoscale patterns of surface topography and chemical structure. Nanostructured materials provide an environment for tissue regeneration mimicking the physiological range of extracellular matrix. The article reviews several studies substantiating the superiority of nanostructured materials for bone and cartilage repair along with own results on cell attachment.     

Technological Opportunities for the Implementation of Anti-Microbial Activities into Dry-Wet Shaped Cellulose Fibres

Metal cations are valuable antimicrobial additives for controlling of bacteria growth on textile fibres. By means of multiple actions they are able to suppress the undesirable microbe action also during wound healing. Dry-wet shaping technology offers numerous opportunities for implementation of antimicrobial activities into textile structures (fibres, yarn, fabrics). The degree of load, insertion step as well as type of additive (Ag, Cu, Zn) presents a broad field of physical modification of dry-wet spun cellulose fibres. The investigation of antimicrobial activities of manufactured fibres and yarns exhibit bactericide or bacteriostatic effects against typical pathogenic germs. Ag contents higher than 30 ppm in fibres and 0.06 per cent in yarns as well as Cu contents higher than 100 ppm in fibres and about 0.5 per cent in yarns are fairly effective for a permanent antimicrobial effect. Fabrics based on the developed fibres and yarns could already been successfully commercialised by innovative small and medium sized enterprises (SME).     

Hydrolysis of Cutin by PET-Hydrolases

Functionalisation of synthetic polymers by using enzymes has been recently demonstrated. The major advantage of enzymes over chemical processes lies in their surface specific and endo-wise mode of action. Surface hydrophilisation of PET with lipases and cutinases leads to a dramatic increase of the surfacial acid and hydroxyl group content while conventional chemical treatment does not cause any change. However, this PET-hydrolysing activity by enzymes from distinct classes has not yet been correlated to activity on natural polyesters. Here, we show that lipases, cutinases and a PHA-depolymerase are all capable of hydrolysing PET, while only lipases and cutinases also hydrolysed cutin to various degrees. Lipases showed a higher specificity for terminal fatty acids while the cutinases preferred hydroxy fatty acids during cutin hydrolysis.     

Quaternionic theta constants

We investigate the six quaternionic theta constants introduced by Freitag and Hermann. More precisely we investigate their restrictions to the Hermitian resp. Siegel half-space of degree 2. It turns out that these theta constants generate the graded ring of symmetric Hermitian modular forms for the principal congruence subgroup of level 1 + i over the Gaussian number field resp. of Siegel modular forms for the principal congruence subgroup of level 2 and even weight. As an application we obtain a simple construction of Igusa’s Siegel modular form of degree 2 and weight 30 with respect to the non-trivial character.     

Microbial Baeyer-Villiger oxidation: stereopreference and substrate acceptance of cyclohexanone monooxygenase mutants prepared by directed evolution

[reaction: see text] An array of random mutants of cyclohexanone monooxygenase (CHMO) from Acinetobacter sp. NCIMB 9871 was screened against a library of structurally diverse ketones for modifications in the substrate acceptance profile and stereopreference of the enzymatic Baeyer-Villiger biooxidation. While the set of mutant biocatalysts was initially evolved for the enantiocomplementary oxidation of 4-hydroxycyclohexanone, improved and/or divergent stereoselectivities were observed for several substrates. In addition, expanded substrate acceptance to facilitate biotransformation of sterically demanding ketones was found.