The loss of the polarization dependence of diffraction reflection in chiral photonic crystals in the presence of anisotropic defects

The properties of defect modes in chiral photonic crystals with anisotropic defects are considered. The problem has been solved using the modified method of Ambartsumyan layer addition. The influence of the defect layer thickness and the optical axis orientation on the properties of defect modes is analyzed. At a certain thickness of the defect layer, the medium loses its main property, namely, the polarization dependence of diffraction reflection.     

Applicability of X-ray reflectometry to studies of polymer solar cell degradation

Although degradation of polymer solar cells is widely acknowledged, the cause, physical or chemical, has not been identified. The purpose of this work is to determine the applicability of X-ray reflectometry for in situ observation of physical degradation mechanisms. We find that the rough interfaces of the polymer solar cell constituent layers seriously obstruct the sensitivity of the technique, rendering it impossible to elucidate changes in the layer/interface structure at the sub-nanometer level.     

Single-step buried waveguides in glass by field-assisted copper ion-exchange

Symmetric profile buried waveguides can be fabricated in glass by single-step electromigration of Cu/sup 2+/ ions from thin solid films. The theory of this process is given. The controllable process needs a molten multi-ionic anode to keep the glass surface background composition unchanged.<>     

Apparatus for viscoelastic thermal compression of wood

Viscoelastic Thermal Compression (VTC) of wood is a treatment which greatly improves material properties by means of densification with mechanical compression perpendicular to the grain. VTC is similar to other wood densification processes, but is designed for thin lamina and employs dynamic temperature and steam pressure conditions. A?device was constructed that is capable of producing VTC wood. Details of the construction and operation of the VTC device are presented. The device consists of a pressurized chamber with variable volume. Wood density may be modified from the initial density of the virgin wood up to approximately 1400?kg/m³. Control of steam pressure and temperature insures that the wood cell walls are not fractured during the process. The device is designed for batch operation and may be adapted to a conventional laboratory hot-press. An example operating schedule is described, but other procedures are possible within the design parameters of the device.     

Interdependence of Escherichia coli formate dehydrogenase and hydrogen-producing hydrogenases during mixed carbon sources fermentation at different pHs

The impact of the four membrane-bound [NiFe]-hydrogenases (Hyd) of Escherichia coli on total H₂-oxidizing activity during fermentation of a mixture of glucose, glycerol and formate at different pHs was examined. It was shown that Hyd-2 had a major contribution to total Hyd activity at pH 7.5 in early-stationary phase (24 h) cells, while the main contribution was made by Hyd-3 in late-stationary phase (72 h). Hyd-4-dependent Hyd activity could be demonstrated at pH 6.5 in cells lacking Hyd-1, Hyd-2 and Hyd-3. at pH 7.5 Hyd-4-dependent formate dehydrogenase (FDH-H) activity was demonstrated. Growth properties and fermentation end product patterns during 72 h demonstrated that the cells retained viability deep into stationary phase. Our findings emphasize the importance of formate in modulating H₂ metabolism, presumably by contributing to maintain redox, pH and pmf balance. This is important for regulating and enhancing H₂ production when a mixture of carbon sources is applied.     

The income return to entrepreneurship: theoretical model and outcomes for Swedish regions

This paper investigates the income return to entrepreneurship and wage employment by means of Lazear’s model of occupational choice. The paper has two major aims. The first is to develop a new theoretical framework for analyzing the income return to entrepreneurship by combining the Lazear model with the assumption that the skill profiles in a population are Fréchet-distributed. The second is to demonstrate that the resulting theoretical derivations can be used for a new type of regional analysis of the income return to entrepreneurship and wage employment. The empirical analysis is based on data for individuals with a Master of Science degree in Electrical Engineering. We compute their income return to self-employment and wage employment in three parts of Sweden: the Stockholm region, the combined Gothenburg and Malmö region, and the Rest of Sweden. The results show that the average return to self-employment is less than 5% in all regions and smaller in the Gothenburg and Malmö region than in the other two regions. The regional differences are explained by the differential supply curves and market values of entrepreneurial talent. The theoretical derivation of the income return to entrepreneurship is the main contribution of the paper. Another contribution is the derivation of regional supply curves for entrepreneurs.     

The Pyridyldiisopropylsilyl Group: A Masked Functionality and Directing Group for Monoselective ortho‐Acyloxylation and ortho‐Halogenation Reactions of Arenes

A novel, easily removable and modifiable silicon‐tethered pyridyldiisopropylsilyl directing group for C H functionalizations of arenes has been developed. The installation of the pyridyldiisopropylsilyl group can efficiently be achieved via two complementary routes using easily available 2‐(diisopropylsilyl)pyridine ( 5 ). The first strategy features a nucleophilic hydride substitution at the silicon atom in 5 with aryllithium reagents generated in situ from the corresponding aryl bromides or iodides. The second milder route exploits a highly efficient room‐temperature rhodium(I)‐catalyzed cross‐coupling reaction between 5 and aryl iodides. The latter approach can be applied to the preparation of a wide range of pyridyldiisopropylsilyl‐substituted arenes possessing a variety of functional groups, including those incompatible with organometallic reagents. The pyridyldiisopropylsilyl directing group allows for a highly efficient, regioselective palladium(II)‐catalyzed mono‐ortho‐acyloxylation and ortho‐halogenation of various aromatic compounds. Most importantly, the silicon‐tethered directing group in both acyloxylated and halogenated products can easily be removed or efficiently converted into an array of other valuable functionalities. These transformations include protio‐, deuterio‐, halo‐, boro‐, and alkynyldesilylations, as well as a conversion of the directing group into the hydroxy functionality. In addition, the construction of aryl‐aryl bonds via the Hiyama–Denmark cross‐coupling reaction is feasible for the acetoxylated products. Moreover, the ortho‐halogenated pyridyldiisopropylsilylarenes, bearing both nucleophilic pyridyldiisopropylsilyl and electrophilic aryl halide moieties, represent synthetically attractive 1,2‐ambiphiles. A unique reactivity of these ambiphiles has been demonstrated in efficient syntheses of arylenediyne and benzosilole derivatives, as well as in a facile generation of benzyne. In addition, preliminary mechanistic studies of the acyloxylation and halogenation reactions have been performed. A trinuclear palladacycle intermediate has been isolated from a stoichiometric reaction between diisopropyl(phenyl)pyrid‐2‐ylsilane ( 3a ) and palladium acetate. Furthermore, both C H functionalization reactions exhibited equally high values of the intramolecular primary kinetic isotope effect (k_H/k_D=6.7). Based on these observations, a general mechanism involving the formation of a palladacycle via a C H activation process as the rate‐determining step has been proposed.     

About Faraday rotation in bulk media,in a magneto-active layer and in a magneto-photonic crystal layer

ABSTRACT

In this paper, we studied the influence of medium parameters and the wavelength of incident light on Faraday’s rotation and on the ellipticity of polarization. The results of comparison of these dependencies for bulk (unbounded) media, for a layer of a magnetically active medium of finite thickness and, finally, for a magneto-photonic crystal layer are investigated. The dependences of the reflection on the same parameters are investigated too.