ESR study of Cu(II) ion complexes adsorbed on interlamellar surfaces of montmorillonite

Oriented films of Cu(II)-montmorillonite before and after adsorption of pyridine, glycine and $\text{b}\text{?}$-alanine showed markedly orientation-dependent ESR spectra. Complex formation of Cu(II) ions with the adsorbates was indicated by changes in ESR parameters. The ESR spectra and parameters suggest that the complexes formed on the interlamellar surfaces of montmorillonite have planar or axially elongated tetragonal structures and that the symmetry axes of the complexes are oriented perpendicularly to the aluminosilicate layers of the clay.     

N,N-Diethyl-3-toluamide Formulation Based on Ethanol Containing 0.1% 2-Hydroxypropyl-β-cyclodextrin Attenuates the Drug’s Skin Penetration and Prolongs the Repellent Effect without Stickiness

N,N-diethyl-3-toluamide (DEET) is one of the most widely used insect repellents in the world. It was reported that a solution containing 6–30% cyclodextrin (CD) as a solvent instead of ethanol (EtOH) provided an enhancement of the repellent action time duration of the DEET formulation, although the high-dose CD caused stickiness. In order to overcome this shortcoming, we attempted to prepare a 10% DEET formulation using EtOH containing low-dose CDs (β-CD, 2-hydroxypropyl-β-CD (HPβCD), methyl-β-CD, and sulfobutylether-β-CD) as solvents (DEET/EtOH/CD formulations). We determined the CD concentration to be 0.1% in the DEET/EtOH/CD formulations, since the stickiness of 0.1% CDs was not felt (approximately 8 × 10⁻³ N). The DEET residue on the skin superficial layers was prolonged, and the drug penetration into the skin tissue was decreased by the addition of 0.1% CD. In particular, the retention time and attenuated penetration of DEET on the rat skin treated with the DEET/EtOH/HPβCD formulation was significantly higher in comparison with that of the DEET/EtOH formulation without CD. Moreover, the repellent effect of DEET was more sustained by the addition of 0.1% HPβCD in the study using Aedes albopictus. In conclusion, we found that the DEET/EtOH/HPβCD formulations reduced the skin penetration of DEET and prolonged the repellent action without stickiness.     

Structural phase transitions at clean and metal-covered Si(111) surfaces investigated by RHEED spot analysis

Structural phase transitions between various kinds of superlattice structures formed on a Si(111) surface have been investigated by spot analysis of reflection high-energy electron diffraction (RHEED). Reversible transitions induced by temperature changes and irreversible ones induced by metal depositions were observed. Detailed discussions on the dynamics of the phase transitions are made by quantitative analyses of integrated spot intensity and profile. For a phase transition of 7′7  1′1 structures on a clean Si(111) surface, a hysteresis with temperature difference of 5°C. between in heating and cooling processes was found in the spot intensity change, indicating a first-order transition. Hysteresis was hardly recognized, on the other hand, for transitions of Au-induced superstructures (5×2-Au or ×-Au)  1×1-Au. The spot profiles were found to be broadened during the transition of Si(111)-×-Au  1×1-Au, which was a signature of a continuous transition, while the profiles remained unchanged during the transitions of the 7×7  1×1 and 5×2-Au  1×1-Au phases. Structural conversions induced by In adsorption on the Si(111) surface kept at constant temperatures were also analyzed. The conversions at room temperature were totally dependent on the initial substrate surface structures; the 7×7 surface did not show any structural conversion with In adsorption, while the ×-In surface successively converted to a 2×2 and a × phase with coverage increase. The structural transitions at elevated temperatures were sensitively dependent on the temperatures. Sequences of transitions among the 7×7, 4×1, ×, 1×, and ×4 were quantitatively revealed as changes in RHEED spot intensity.     

Reinvestigation of the thermoelectric properties of Ag8GeTe6

High‐density polycrystalline samples (above 98% of the theoretical density) of Ag₈GeTe₆ were prepared by solid‐state reactions of Ag₂Te, GeTe, and Te, followed by hot‐pressing. The thermoelectric properties were measured at temperatures ranging from room temperature to around 700 K. The thermal conductivity values were extremely low (0.25 Wm^–1 K^–1 at room temperature), and consequently Ag₈GeTe₆ exhibited a relatively high thermoelectric figure of merit, ZT = 0.48 at 703 K. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The anomalous behaviour of Gd atoms (Fe1−xMnx)2 compounds

The educed Gd atoms in the X-structure (Th₆Mn₂₃-type) of Gd(Fe_1−xMn_x)₂ were magnetically investigated by comparing with Gd₆(Fe_1−yMn_y)₂₃ whose structure is Th₆Mn₂₃-type. The magnetic properties of Gd(Fe_1−xMn_x)₂ (0.4≤x≤0.7) were observed to be quite similar to those of Gd₆(Fe_1−yMn_y)₂₃ (0.4≤y≤0.7).     

A characterization of certain irreducible symplectic 4-folds

 We give a characterization of irreducible symplectic fourfolds which are given as Hilbert scheme of points on a K3 surface. Received: 26 June 2002 / Revised version: 9 September 2002 Published online: 14 February 2003 Mathematics Subject Classification (2000): Primary 14J32, Secondary 32Q20     

Polymeric saturable-absorber mirror for passive Q-switching of a laser-diode-pumped Nd3+:YVO4 microchip laser

A polymeric multilayered mirror doped with a saturable dye worked as a passive Q-switch of a laser-diode-pumped Nd(3+):YVO4 microchip laser. The multilayered mirror consisted of alternately spin-coated layers of polyvinylcarbazole (PVK) and cellulose acetate on a glass substrate. A dye of bis-(dimethylaminodithiobenzil)-nickel was doped in one of the layers of PVK, providing the repetitively Q-switched pulses. The pulse width and repetition rate were 4 ns and 68 kHz, respectively, for a laser-cavity length of 5 mm, and the average and the peak power were 40 mW and 156 W, respectively, for the highest pump power of 435 mW. The dependence of the Q-switched characteristics on the pump power and on the concentration of the doped dye is described.     

Rapid wavelength scanning based on acousto-optically tuned external-cavity laser diode

High-speed, wide-range wavelength scanning is demonstrated using a laser diode with an antireflection coating and an external cavity employing an acousto-optic deflector. The narrow spectral width of 0.2 nm observed in the experiment indicates the availability of a highly coherent laser beam. The scanning range of 15 nm under rapid modulation is confirmed in the prototype system. A tuning rate of more than 100 kHz is achieved without any mode hops. To the best of our knowledge, no such high-speed wavelength tuning based on an acousto-optical configuration has been demonstrated thus far.