A Variant of the ORTHOMIN(2) Method for Singular Linear Systems

For singular linear systems A x=b, ORTHOMIN(2) is known theoretically to attain the minimum residual min _xR nb–A x₂ under a certain condition. However, in the actual computation with finite precision arithmetic, the residual is often observed to be reduced further than the theoretically expected level. Therefore, we propose a variant of ORTHOMIN(2), which is mathematically equivalent to the original ORTHOMIN(2) method, but uses recurrence formulas that are different from those of ORTHOMIN(2); they contain alternative expressions for the auxiliary vector and the recurrence coefficients. Although our implementation has the same computational costs as ORTHOMIN(2), numerical experiments on singular systems show that our implementation is more accurate and less affected by rounding errors than ORTHOMIN(2).     

Optical second harmonic generation in ammonium tartrate

Second harmonic generation was observed in ammonium tartrate single crystals by a phase matching technique at the fundamental wavelength 1.153 μm. The nonlinear coefficients were found to be comparable in magnitude to those of KDP. The optical transmission and the refractive indices were also measured.     

Lanthanide organometallic sandwich nanowires: formation mechanism

A molecular beam of europium-cyclooctatetraene sandwich nanowires Eu(n)()(COT)(m)() was produced by a laser vaporization synthesis method. The formation mechanism of the nanowires was quantitatively revealed by photoelectron and photoionization spectroscopies of the Eu-COT species, together with supporting theoretical calculations. From these results, it is confirmed that growth processes extending the length of Eu-COT nanowires involve a series of elementary reactions in which efficient charge transfer occurs at the terminal reaction sites. In every elementary step, the reaction proceeds between one reactant having low ionization energy and the other reactant having high electron affinity, probably via a "harpoon" mechanism.     

Allylation of epoxides with allylic indium reagents

Allylindium sesquihalide reacts with epoxide to give homoallyl alcohol via a 1,2-shift reaction. In contrast, allylindate gives the ring-opening product without rearrangement.     

Dual CCK-A and CCK-B receptor antagonists (II). Preparation and structure activity relationships of 5-alkyl-9-methyl-1,4-benzodiazepines and discovery of FR208419

In our continuing research for dual CCK-A and -B antagonists, according to our hypothesis that dual CCK-A and -B antagonists should be more efficacious than selective CCK-A antagonists for the treatment of pancreatitis, we have prepared various 5-alkyl-9-methyl-1,4-benzodiazepines. From the compounds prepared, 1-cyclohexyl-carbonylmethyl-5-ethyl-9-methyl-3- (m-tolylureido)-2-oxo-1,4-benzodiazepine, (40) was selected as a candidate for development due to its well-balanced high affinity for both receptors. The R-enantiomer of 40, (R)-40 (FR 208419), had 27-fold higher affinity for the CCK-A receptor and 8-fold more potent CCK-B receptor binding activity than (S)-40. The biological activity after p.o. administration of (R)-40, estimated from the ID50 value (0.23 mg/kg p.o.) obtained by preliminary evaluation by gastric emptying effects, is considered to be high enough for further development. This compound is now undergoing further biological evaluations with a view to clinical development.     

Mössbauer study on the CMR double perovskite AFe<Subscript>0.5</Subscript>Mo<Subscript>0.5</Subscript>O<Subscript>3 </Subscript>with A=(Ba,Sr) or (Sr,Ca): Chemical pressure effect

Summary The double perovskites, AFe_0.5Mo_0.5O₃with A=(Ba,Sr) or (Sr,Ca), were prepared by a sol-gel method, and the substitution effect at site A was studied by M?ssbauer spectrometry. In the M?ssbauer spectra of the double perovskite (Ba, Sr)Fe_0.5Mo_0.5O₃, the isomer shifts decreased fromδ=0.72 mm/s to δ=0.4 mm/s and the internal magnetic fields increased with the increase of the Sr content. The Ba-rich samples were shown to contain superparamagnetic components under the same preparation conditions. Better crystallinity and larger hyperfine fields were obtained when 5% of the Sr-content of SrFe_0.5Mo_0.5O₃was substituted by Ca as compared with substitution by Ba. Phonon density of states (DOS) of SrFe_0.5Mo_0.5O₃substituted with Ca or Ba were obtained by nuclear inelastic scattering. The peaks of phonon DOS were shifted, depending on chemical compression/expansion of the lattice. The chemical pressure effect could be observed in the M?ssbauer spectra and the phonon DOS spectra.     

γ-radiation-induced crosslinking of polystyrene

The γ-radiation-induced crosslinking of polystyrene was studied at 30–100°C in vacuo with a dose rate of 6.35 × 10⁵ rad/hr. The amount of hydrogen formation increased with increasing irradiation time, and the rate of the formation decreased with the time. The results were well described by the zero-order formation kinetics with respect to the hydrogen concentration combined with the first-order disappearance. The apparent rate constant for the formation of hydrogen increased somewhat with rising irradiation temperature, and the one for the disappearance was little affected by the temperature. The gel fraction increased with the time by the irradiation beyond the critical time for incipient gel formation, and the rate of gel formation decreased with the time. The gel formation was retarded by rising irradiation temperature, and only a little gel fraction was observed at 100°C. The G values for the crosslinking and main-chain scission were obtained from the gel data by using the Charlesby–Pinner equation. On the basis of these results, the mechanism of the γ-radiation-induced crosslinking of polystyrene was discussed.     

Characterization of perovskite related oxides by nuclear resonance inelastic scattering of synchrotron radiation

Resonant nuclear inelastic scattering (NIS) spectra of (Sr,Ca)(Fe,Co)O_{3- d} and (Ba,Ca)(Fe,Co)O_{3- d} were measured with the energy resolution of 3.5 MeV by detecting the 6.3 keV Fe K_a X-rays following after Mössbauer effect on ⁵⁷Fe transition excited by the monochromatized 14.41 keV synchrotron radiation. Both series of oxides annealed in air and in CO₂ were examined. Soft phonon peak arising at ~8 MeV in NIS spectra of (Sr_0.5Ca_0.5)(Fe_0.5Co_0.5)O_{3- d} and (Ba_0.5Ca_0.5)FeO_{3- d} was found to be correlated with the oxygen ordering into brownmillerite structure, whereas more complex multi-phonon structure was observed in the spectra of less oxygen-deficient oxides such as (Sr_0.95Ca_0.05)(Fe_0.5Co_0.5)O_{3- d} and (Sr_0.7Ca_0.3)(Fe_0.5Co_0.5)O_{3- d} showing rather random distrubution of the oxygen vacancies. The changes in phonon DOS after CO₂ absorbtion were also detected. Lam-Mössbauer factors of these oxides were calculated on the base of Debye Model.     

Stereochemistry and mechanism of the hydrogenation of substituted cyclopentenes

1,2- and 2,3-disubstituted cyclopentenes were hydrogenated with several transition metal catalysts. The hydrogenation of 1,2-disubstituted cyclopentenes gave preferably the cis products with Raney Ni, whereas 2,3-disubstituted cyclopentenes gave preferably the trans isomers. The trans products were favoured in the hydrogenation of 1,2- and 2,3-dialkylcyclopentenes with Pt or Pd catalysts. A detailed product analysis of the hydrogenation of 1,2-dialkylcyclopentenes indicates that the double bond migration occurred to form 2,3-dialkylcyclopentenes in advance of the hydrogenation. In contrast, 1-methyl-2-phenylcyclopentene gave predominantly the cis product irrespective of the kind of catalyst. These results suggest the formation of a π-benzylic species during the course of the reaction. The mechanism is discussed in terms of the modified Horiuti-Polanyi mechanism.