Luminescence of Pr-doped LiCaAlF6 and LiSrAlF6 crystals

The spectral and kinetic parameters of LiCaAlF₆:Pr and LiSrAlF₆:Pr single crystals are studied at LHeT and room temperature (RT). Photon cascade emission (PCE), i.e., ¹S₀→¹I₆ and ³P₀→³H_j, ³F_j transitions after Pr³⁺ excitation via 4f²→4f 5d absorption results in the conversion of the vacuum ultraviolet photon to two visible photons. The excitation and photoemission spectra as well as decay times have been measured and compared with those for CaF₂:Pr and SrF₂:Pr crystals. X-ray luminescence was measured to study the emission origin from both ¹S₀ and ³P₀ states of Pr³⁺. An intense phosphorescence of LiSrAlF₆:Pr was observed in the visible range after X-irradiation at RT, contrary to LiCaAlF₆:Pr.     

Measurement of nitrogen atomic flux for RF-MBE growth of GaN and AlN on Si substrates

Production and measurement of active nitrogen atoms (N+N*), which consist of ground state nitrogen atoms N and excited state nitrogen atoms N*, in an inductively coupled radio frequency discharge for the growth of group III nitrides and their alloys using a molecular beam epitaxy (MBE) were studied. Two discharge modes of the low brightness (LB) and the high brightness (HB) used in this study to produce excited nitrogen molecules (N₂*) and dissociated active nitrogen atoms (N+N*). The flux of (N+N*) was measured by a Langumuir-like electrode due to the self-ionization of adsorbed (N+N*) on a negatively biased electrode. The self-ionization, which emits electrons from (N+N*), forms an atom current and is confirmed using different electrodes such as Pt and CuBe and different electrode area. The atom current was calibrated by the grown GaN thickness in a VG80H MBE machine. The calibrated flux of (N+N*) per atom current in the VG80H machine is 5.5×10⁻⁴ ML/s/nA, where ML is monolayer. The atom current is useful to monitor the flux of chemically active nitrogen atoms N+N* for growth of group III nitrides and their alloys. Activity modulation migration enhanced epitaxial growth (AM-MEE) was demonstrated as an application of the measurement of atom current for the growth of the group III nitrides.     

Ferroelectric domain phenomena and microdomain engineering in BaMgF4 single crystal

Ferroelectric domain phenomena and periodic domain patterning of orthorhombic as-grown BaMgF₄ single crystal were investigated in the present study. An isolated ferroelectric domain shows a hexagonal form and exhibits a high domain-wall anisotropy. Periodic domain patterning was demonstrated on the polar surface by a periodic macropoling technique. In-plane polarization switching-induced microdomain patterning was tailored by the lateral component of the inhomogeneous electric field through a biased atomic force microscope tip. Such in-plane domain switching behavior exhibits potential promise for periodic domain engineered phonon devices. PACS 77.80.Dj; 77.80.Fm; 07.79.Lh     

Assay of Angiotensin I-converting Enzyme-inhibiting Activity Based on the Detection of 3-Hydroxybutyrate with Water-soluble Tetrazolium Salt.

A newly synthesized substrate, 3-hydroxybutyrylglycyl-glycyl-glycine (3HB-GGG), was applied to the assay of ACE-inhibiting activity to overcome the smaller selectivity and sensitivity of the conventional method. In this study, an ACE-inhibiting assay was improved by the use of a water-soluble tetrazolium salt, 4-[3-(4-iodophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzene disulfonate sodium salt (WST-1), for the detection of 3-hydroxybutyrate, derived from 3HB-GGG. The optimized conditions were as follows: 0.333 mM NAD(+), 0.333 mM WST-1, 0.1 mM EDTA, 0.633 U ml(-1) diaphorase, and 0.700 U ml(-1) 3-hydroxybutyrate dehydrogenase. The developed assay was efficiently applicable to evaluate the ACE-inhibiting activity of practical ACE inhibitors.     

Selective oxidation of methane to formaldehyde over antimony oxide-loaded catalyst

A possibility of antimony oxide as a catalyst for the selective oxidation of methane with oxygen to formaldehyde was investigated. The activity measurement was carried out at an atmospheric pressure and at 873 K, where the homogeneous gas-phase reaction was negligible. Oxidized diamond (O-Dia)-supported antimony oxide catalyst produced 1.3 mmol h⁻¹ g-cat⁻¹ of formaldehyde with a formaldehyde selectivity of 23%. On the other hand, SiO₂ supported antimony oxide catalyst exhibited negligible catalytic activity. XRD and UV–vis analyses revealed that -Sb₂O₄ was formed on the oxidized diamond while Sb₆O₁₃ was formed on SiO₂. Selective oxidation of methane to formaldehyde seemed to proceed on -Sb₂O₄ with moderate activity and selectivity to formaldehyde, via a redox cycle of -Sb₂O₄ and Sb₂O_4−x. On the other hand, Sb₆O₁₃ on SiO₂ was stable under the reaction conditions and the selective oxidation occurred only slightly.     

Inhibition of angiogenesis by bleomycin and its copper complex.

The effects of bleomycin (BLM) and its copper complex on embryonic angiogenesis were studied in the chorioallantoic membranes of 4.5-day-old chick embryos. Copper-free BLM inhibited embryonic angiogenesis in a dose-dependent manner, with activity detectable at 1 ng/egg and maximal at 1000 ng/egg. Also, treatment with copper-BLM complex dose-dependently caused inhibition of embryonic angiogenesis in a lower dose range. Since tumor growth is believed to depend on angiogenesis, the present results may indicate that the antiangiogenic activity of BLM is, at least in part, implicated in the antitumor activity of the drug.     

First principles calculation of CH<Subscript>4</Subscript> decomposition on nickel (111) surface

The mechanism of the CH₄ decomposition on the nickel (111) surface is investigatedby first principles calculations. The activation energy of each reaction is calculatedusing nudged elastic band method. The activation energy of hydrogen dissociation from aCH₂ fragment isfound much lower than the one of a CH₃ fragment. This result is consistent with the fact,observed in our previous molecular dynamics (MD) simulations, that the CH₃ fragment is dissociated into aCH fragment and two hydrogen atoms spontaneously. The effects of finite temperatureat 1500 K on the decomposition reaction of a CH₄ molecule and its fragments are also investigated usingconstraint MD method. While the temperature effects are barely visible inCH₄ andCH₂ dissociationprocesses, they reduce the activation free energy of hydrogen dissociation fromCH₃ and CHfragments largely.