Localization of electromagnetic waves in three-dimensional fractal cavities

Three-dimensional fractals called the Menger sponge, with a fractal dimension D=log(20/log(3, were fabricated from epoxy resin by stereolithography. Clear attenuation of both reflection and transmission intensity was observed at 12.8 GHz for a cubic specimen with an edge size of 27 mm that was constructed up to the third stage of the self-similar patterns. The electromagnetic field was found to be confined in the central part of the specimen at this frequency. The localization is not caused by the presence of a photonic band gap as in photonic crystals but should be attributed to a singular photon density of states realized in the fractal structure. This is the first report on such localization of electromagnetic waves in three-dimensional fractal cavities.     

Scaling behavior of two-dimensional domain growth: Computer simulation of vertex models

Computer simulations are performed for vertex models which are coarse-grained models for dynamical cellular patterns in two dimensions. By simulating large systems, we obtain conclusive evidence of scaling behavior, that is, a power law for the growth of the average cell size and the scaling properties for the distribution functions of edge number and size of cells. Several versions of the vertex models are obtained by making some approximations for the equation of motion of a vertex, and we compare the statistical properties of the patterns in the scaling regime.     

Voltammetry at microcylinder electrodes: Part I. Linear sweep voltammetry

An expression for reversible linear sweep voltammograms at stationary microcylinder electrodes is presented. From numerical calculations theoretical voltammograms are obtained for various values of the dimensionless parameter, p=(nFa²v/RTD)^{$\text{1}\text{2}$}, where a is the radius of the electrode, v the potential sweep rate and D the diffusion coefficient. The peak current and the peak potential are evaluated from the voltammograms as functions of p and are expressed by approximate equations with high precision. In order to examine the validity of the equations, an experimental study was made at platinum wire micro-electrodes (a=10?10) μm). The experimental voltammograms were in good agreement with the ones predicted theoretically for various values of the sweep rates and for several different radii of the electrodes.     

Unveiling the Biosynthetic Pathway of the Ribosomally Synthesized and Post‐translationally Modified Peptide Ustiloxin B in Filamentous Fungi

The biosynthetic machinery of the first fungal ribosomally synthesized and post‐translationally modified peptide (RiPP) ustiloxin B was elucidated through a series of gene inactivation and heterologous expression studies. The results confirmed an essential requirement for novel oxidases possessing the DUF3328 motif for macrocyclization, and highly unique side‐chain modifications by three oxidases (UstCF1F2) and a pyridoxal 5′‐phosphate (PLP)‐dependent enzyme (UstD). These findings provide new insight into the expression of the RiPP gene clusters found in various fungi.     

Extraction—Spectrophotometric determination of nickel with 2-hydroxy-1-naphthaldoxime

A method for the solvent extraction—spectrophotometric determination of nickel with 2-hydroxyl-1-naphthaldoxime (HNA) has been studied. The method is based upon the formation of a nickel—HNA complex which is extracted into chloroform from an aqueous solution of pH 5.8. The nickel—HNA complex in chloroform exhibits an absorption maximum at 410 nm with molar absorptivity of 8.1 × 10³ liters mol^?1 cm^?1. Beer's law is applicable in the range from 5 to 50 μg of nickel. The mole ratio of the complex and effect of interfering ions are described.     

An alternative synthetic route of [3(5)](1,2,3,4,5)cyclophane,and structural properties of multibridged [3(n)]cyclophanes and their charge-transfer complexes in the solid state

To develop an improved synthetic route to [3(6)](1,2,3,4,5,6)cyclophane (CP) 2, a more practical synthetic route to [3(5)](1,2,3,4,5)CP 3 than the original one was developed, which started from [3(2)](1,3)CP 7 via [3(4)](1,2,4,5)CP 5. The fundamental structural parameters of [3(n)]CPs (n = 3-6) in the solid state were elucidated, and the observed structures were in good agreement with the most stable conformers in solution and those predicted by the theoretical calculations. In the case of [3(6)]CP 2, the most stable C(6)(h) structure was observed in the crystal structure of the 2-TCNQ-F(4) (1:1) complex, whereas the highly strained structure with a D(6)(h) symmetry was observed in the crystal structure of 2 and the 2:TCNQ:benzene (1:1:1) complex because of a severe disorder problem. [3(n)]CPs (n > 3) showed reversible redox processes, and 2 (+0.39 V vs F(c)/F(c)(+), Cl(2)CHCHCl(2)) showed the lowest first half-wave oxidation potential [E(1/2) (I)] in [3(n)]CPs. The E(1/2) (I) data support the strong donating ability of 2 and its lower homologues. This is attributed to their molecular structures where effective hyperconjugation between the benzyl hydrogens and benzene ring is possible. By taking advantage of the strong electron-donating ability of [3(n)]CPs, their CT complexes with TCNE, TCNQ, and TCNQ-F(4) were prepared, and their crystal structural properties were examined. The single-crystal conductivity data of the CT complexes indicated that the TCNQ-F(4) complexes showed higher conductivities than the corresponding TCNQ complexes mainly due to a larger charge separation. Among the [3(n)]CP-TCNQ complexes, the [3(3)](1,3,5)CP 6-TCNQ-F(4) (1:1) complex showed the highest conductivity (10(-)(4) S cm(-)(1)), and this was ascribed to the formation of an infinite column of partially overlapped acceptors with a short acceptor-acceptor distance, while the formation of such a column was not observed in the 2-TCNQ-F(4) complex. Although the conductivities of the cyclophane-CT complexes are much lower than those of the TTF related complexes, this study successfully provides the basic knowledge for understanding the CT interactions in the solid state.     

Structure and redox properties of electropolymerized film obtained from iron meso‐tetrakis(3‐thienyl)porphyrin

Oxidative polymerization of bromoiron(III) meso‐tetrakis(3‐thienyl)porphyrin gave a novel polymeric porphyrin complex randomly crosslinked at the 2,5‐positions of the peripheral thienyl groups. The electrical semiconductivity of ca. 10^?5 S/cm after I₂ doping indicated that the polymer had a π‐conjugated structure with a moderate delocalization of π electrons over the thienylporphyrin units. PM3 calculations for free‐base models revealed that HOCO (the highest occupied crystal orbital) band width was reduced by introduction of the porphyrin moieties into the thienylene backbone and yet low HOCO‐LUCO (the lowest unoccupied crystal orbital) gap was maintained, which accounted for the relatively low electrical conductivity of the porphyrin polymer. The modified electrode prepared by electropolymerization was redox‐active due to the presence of iron(II/III) couple and the semiconductivity of the film, which served as a novel non‐enzymatic electrochemical sensor for superoxide anion radical based on the facile electrocatalytic oxidation of the superoxide. Copyright © 2005 John Wiley & Sons, Ltd.