Positive muon behavior in KCl with and without F centers

Positive muon behavior in KCl containing F centers has been studied. The muon spin depolarization rate showed a maximum near 120 K, which was not found in pure KCl. This is probably due to the fact that free positive muons are trapped by F centers in KCl. However, the binding energy between a positive muon and an F center is not large, so that muons detrap again above 150 K.     

Magnetic dilution in the geometrically frustrated SrCr(9p)Ga(12-9p)O19 and the role of local dynamics: A muon spin relaxation study

We investigate the spin dynamics of SrCr(9p)Ga(12-9p)O19 for p below and above the percolation threshold p(c) using muon spin relaxation. Our major findings are as follows: (i) At T-->0 the relaxation rate is T independent and approximately p(3), (ii) the slowing down of spin fluctuation is activated with an energy U, which is also a linear function of p(3) and lim U as p-->0 = 8 K; this energy scale could stem only from a single ion anisotropy, and (iii) the p dependence of the dynamical properties is identical below and above p(c), indicating that they are controlled by local excitation.     

Oxidative transformation of tert-cyclobutanols by palladium catalysis under oxygen atmosphere

Palladium(II)-catalyzed oxidative reaction of tert-cyclobutanols involving the cleavage of a C-C bond via beta-carbon elimination under atmospheric pressure of oxygen is described. An alkylpalladium intermediate produced by beta-carbon elimination from a Pd(II) alcoholate gives a variety of products, depending on the substituents on the cyclobutane ring, in which reactions such as dehydrogenative ring opening, ring expansion and ring contraction are involved. For some substrates, the addition of a catalytic amount of ethyl acrylate dramatically accelerates the reaction. In all cases, the dehydrogenative products are obtained and the Pd(II)-hydride species produced at the final stage can be converted again to active Pd(II) species by molecular oxygen.     

Evaluation of Morphology and Size Distribution of Silicon and Titanium Oxide Nanoparticles Generated by Laser Ablation

Nanometer-sized particles of silicon and titanium oxide were generated by irradiating solid targets using a nanosecond pulsed-Nd : YAG laser in a low pressure atmosphere. A low pressure differential mobility analyzer (LP-DMA) was used to classify the size of the generated particles. The LP-DMA and electron microscopes (SEM and TEM) were used to measure the change in the size distribution and morphology of the generated particles with laser power density and system pressure. The size distribution of both silicon and titanium oxide ranged from two to one hundred nanometers in diameter depending on the laser power density and pressure. From the high resolution TEM observation and electron diffraction, it was found that the generated titanium oxide nanoparticles were composed of a core of faceted metallic single crystals with an oxide layer 'shell.     

Mutually pumped phase conjugate mirror using cross polarized photorefractive coupling

This paper presents a new proposal for a mutually pumped phase conjugate mirror (MPPCM) using cross polarization. In the cross polarized MPPCM, two light beams, whose polarizations are orthogonal to each other, incident on a photorefractive crystal, causing photorefractive interaction to generate phase conjugate waves with an orthogonal polarization to an incident beam. The use of Ar⁺ laser and BaTiO₃ crystal in an experiment for the cross polarized MPPCM found that diffraction efficiency for an extraordinary beam is about 20%. As opposed to a conventional parallel polarized MPPCM in which the use of a beam splitter is required to separate a diffraction beam, the cross polarized MPPCM can efficiently extract phase conjugate waves by means of a polarized beam splitter, demonstrating the advantage of substantially improved efficiency.     

Synthesis of biladienone and bilatrienone by coupled oxidation of tetraarylporphyrins

Tetraarylbiladien-ab-ones bearing various substituents (R) in the para position of the phenyl groups were preprared by coupled oxidation of tetraarylporphyrin iron complexes. The yields of 5,10,15-triaryl-19-aroyl-15-hydroxybiladien-ab-ones were 74% (R=H), 85% (R=OMe), 44% (R=COOMe), and 28% (R=CN). Kinetic studies of the iron porphyrin oxidation revealed that the reaction is accelerated by an electron-withdrawing substituent with the Hammett reaction constant rho=0.295. 5,10,15-Triaryl-19-aroyl-15-hydroxybiladien-ab-ones undergo the acid-catalyzed elimination reaction either by acetic acid or by mesoporous silica to afford 5,10,15-triaryl-19-aroylbilatrien-abc-one. The elimination reaction in acetic acid is accelerated by an electron-donating substituent with the Hammett reaction constant rho=-1.48.     

Photoelectrochemical reaction and H2 generation at zero bias optimized by carrier concentration of n-type GaN

The authors studied the photoelectrochemical properties dependent on carrier concentration of n-type GaN. The photocurrent at zero bias became the maximum value at the carrier concentration of 1.7x10(17) cm-3. Using the sample optimized carrier concentration, the authors achieved H2 gas generation at a Pt counterelectrode without extra bias for the first time. The authors also discussed the mechanism of the dependence of photocurrent on the carrier concentration of GaN.