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.     

The equivalence problem of multidimensional multitape automata

This article considers the equivalence problem of multitape automata with multidimensional tapes, where the motion of the heads is monotone in all directions (no backward motion). It is shown that this problem can be reduced to the equivalence problem of ordinary multitape automata. Some applications of the result are adduced.     

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.<>     

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 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.     

Water and oxygen induced degradation of small molecule organic solar cells

Small molecule organic solar cells were studied with respect to water and oxygen induced degradation by mapping the spatial distribution of reaction products in order to elucidate the degradation patterns and failure mechanisms. The active layers consist of a 30 nm bulk heterojunction formed by the donor material zinc-phthalocyanine (ZnPc) and the acceptor material Buckminsterfullerene (C₆₀) followed by 30 nm C₆₀ for additional absorption. The active layers are sandwiched between 6 nm 4,7-diphenyl-1,10-phenanthroline (Bphen) and 30 nm N,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine p-doped with C₆₀F₃₆ (MeO-TPD:C₆₀F₃₆), which acted as hole transporting layer. Indium-tin-oxide (ITO) and aluminum served as hole and electron collecting electrode, respectively. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS) in conjunction with isotopic labeling using H₂¹⁸O and ¹⁸O₂ provided information on where and to what extent the atmosphere had reacted with the device. A comparison was made between the use of a humid (oxygen free) atmosphere, a dry oxygen atmosphere, and a dry (oxygen free) nitrogen atmosphere during testing of devices that were kept in the dark and devices that were subjected to illumination under simulated sunlight. It was found that water significantly causes the device to degrade. The two most significant degradation mechanisms are diffusion of water through the aluminum electrode resulting in massive formation of aluminum oxide at the BPhen/Al interface, and diffusion of water into the ZnPc:C₆₀ layer where ZnPc becomes oxidized. Finally, diffusion from the electrodes was found to have no or a negligible effect on the device lifetime.