Search

X-Ray absorption fine structure (XAFS) studies were performed for cobalt(II) bromo complexes prepared for the ratio Br/Co from 0.0 to 4.0 and for their oxidized complexes with ozone in acetic acid solvent. The multivariate curve resolution method indicates the existence of two kinds of chemical species both before and after the oxidation. Before oxidation, the two species are cobalt(II) acetate and tetrahedral cobalt(II) complex coordinated by Br. The oxidized sample with ozone consists of cobalt(II) acetate and trinuclear cobalt(III) complex; however, cobalt(III) complexes including Br are not detected. The rate of the change from the cobalt(II) complex coordinated by Br to the trinuclear cobalt(III) complex is lower than that from cobalt(II) acetate complex. This indicates that the tetrahedral cobalt(II) complex coordinated by Br is more difficult to be oxidized than the octahedral cobalt(II) acetate complex.

Characterization studies of a mixed Ru-Co catalyst unsupported and supported on SiO{sub 2} were performed. The authors also examined the effect of the catalyst on hydrogenation of nitrile compounds. TPR shows that Co(II) in an unsupported Ru(OH)x/Co(OH)y precursor is easily reduced at around 473-573 K, whereas the hydrogen reduction of Co(II) in the Ru(OH)x-Co(OH)y/SiO{sub 2} did not occur even at 873 K. X-ray adsorption fine structure measurements indicated that both metals of the unsupported Ru/Co catalyst are reduced to their respective metallic state, and it is thought that Co{sup 0}-Ru{sup 0} alloy is formed. However, Ru and Co exist as Ru{sup 0} metal and Co oxide, respectively, in the case of a SiO{sub 2} supported catalyst. An unsupported Ru-Co catalyst shows higher activity for the hydrogenation of nitrile group and reductive amination of C=O group of isophoronenitrile and the hydrogenation of nitrile groups of adiponitrile, succinonitrile, and dicyanobenzene than the SiO{sub 2} supported catalyst does. It is suggested that this high performance of the unsupported catalyst is based on the formation of Ru{sup 0}-Co{sup 0} alloy. 16 refs., 12 figs., 6 tabs.

Experiments have been conducted for turbulent channel flow obstructed with a square rod placed perpendicular to the flow. The streamwise distributions of the similarity parameter 2St/Cf were examined for four different space ratios between the square rod and the channel wall. The dissimilarity between momentum transfer and heat transfer was intensified in the case when the square rod was slightly detached from the channel wall. Simultaneous measurements of velocity and temperature were taken by making use of hot-wire and cold-wire probes in the case when the space ratio, y'=0.7. Wavelet analysis applied to the velocity and temperature signals was found effective for the extraction of periodically changing patterns of flow and thermal fields. Through the analysis, heat transfer enhancement was related to the intensification of cold and hot interactions toward the wall and away from the wall, respectively, which occurs depending on the existence of periodical change of flow structure.

The crystal structures of the three title compounds, which were obtained during studies of the preparation and reactions of 5-8-5 fused-ring compounds, have been determined by X-ray diffraction.

The 5-8-5 fused ring compounds, synthesized by photocycloaddition, cis-cisoid-cis- and cis-transoid-cis-tricyclo[9.3.0.04,8]tetradecane-2,9-dione (1-A and 2-A) and cis-cisoid-cis-tricyclo[9.3.0.03,7]tetradecane-2,9-dione (3-A) were isomerized to trans isomers (1-B, 1-C, 2-B, 2-C, and 3-B) at ring junction under basic conditions. Their molecular structures except for 1-B were determined by X-ray crystallography. The eight-membered rings of these 5-8-5 fused ring compounds were found in various conformations, boat-chair, twist-boat (S4), chair, twist-boat-chair, and chair-chair forms. With regard to the conformations of their eight-membered rings the strain energies were calculated by MM2 and the predicted conformations were compared with those obtained by X-ray crystallography.

X-ray absorption fine structure (XAFS) studies are performed for a new Co(II) polyamine complex, N,N′-bis(3-aminopropyl)-1,3-propanediamine Co(II) complex (Co-APPD), and related complexes. The observed Co K-edge XANES spectra show that Co-APPD complex reacted with oxygen (Co-APPD( O2)) has a trivalent cobalt atom and has the octahedral structure around Co, whereas the difference in the structure between solid Co-APPD and Co-APPD dimethylsulfoxide (DMSO) solution is small. We also find the distortion from octahedral to tetrahedral structure with the increase of 2-furancarboxylic acid (FRA) concentration in DMSO solution. With the aid of short-range-order multiple scattering calculation, we study the Co K-edge X-ray absorption near edge structure (XANES) spectra of Co-APPD and Co-APPD ( O2) in more detail. From this theoretical study, we obtain information about oxygen bonding angle: the bond angle Co–O–O is about 120°.

The XAFS study is performed for a new Co(II) polyamine complex; N,N'-bis(3-aminopropyl) 1,3propanediamine Co(II) complex (Co-APPD), the Co-APPD reacted with oxygen (Co-APPD(O2)), and their solution in DMSO and DMSO with 2-furancarboxylic acid (FRA). The Co-APPD(O2) complex is found to be trivalent and has the similar local structure around Co to that in [Co(NH3)6]Cl3. The difference in the XANES between solid Co-APPD and Co-APPD DMSO solution is quite small. It is considered that the difference of geometrical and electronic structure around Co is also quite small by dissolving Co-APPD in DMSO. Addition of FRA to the Co-APPD DMSO solution changes octahedral structure around Co into tetrahedral structure.

An yeast, Hansenula jadinii, which was one of the best producers of CDP-choline on our system, lost its activity when cultured in jar fermenter. This phenomenon was also reproduced in flasks. Cells cultured aerobically in the medium containing 1 % of glucose (A-cells) could not phosphorylate nucleotides although development of mitochondria was observed, whereas cells cultured less aerobically in the medium containing 5% of glucose (D-cells) could phosphorylate CMP to CTP and finally produce CDP-choline although they had only poor mitochondria. Further study revealed that the A-cells were unstable in hexokinase activity, although they had the dense cytosol, whereas the D-cells remained stable, and they had many round particles. Glycolytic activity was about 4 times stronger in the D-cells than in the A-cells. The phenomenon that respiration (development of mitochondria) suppressed fermentation (glycolysis) has been known as the Pasteur effect. However, in our system, phosphofructokinase, the primary key en...

On presente un principe d'exclusion sur les equilibres pour le systeme de Lotka-Volterra. Par exemple, si l'equilibre du genre 1 et 2 est stable, alors l'equilibre du genre 1, 2 et 3 est instable meme s'il existe. Ceci est verifie, que l'interaction interspecifique soit competitive ou non

A transient process of a dynamical system is discussed in the phase plane R2. To each pair of vectors Xl and X2 in R2, their distance is introduced by the use of a positive definite symmetric matrix. To discriminate whether two trajectories passing through a neighborhood of a point X are approaching each other at that point of time or not, a repulsion rate D(x) is introduced; they are approaching each other if D(x)

The field of the randomly connected neural network is approximately formulated by Griffith's equation, regarding the network as being continuous. An integral representation of Griffith's equation is derived. If a relative refractory period can be ignored, it is X(x,t) =1 ∫ o ∞ ds ∫ −vs vs dn kv 2t e −avs X(x−n, t−s) − θ where X(x, t) corresponds to the firing rate and θ means the threshold of the neural firing, τ the absolute refractory period and v the velocity for the spike potential travelling down the axon. The above equation is formally analogous to Caianiello's equation, but the former describes the more macroscopic behaviour of the neural network than the latter. With the aid of computer simulation, appropriate solutions are successfully obtained. In regions where X = 1, neurones are firing at a high constant rate of 1 τ (active regions). In regions where X = 0, there is no firing of neurones (resting regions). In the neural net for which 0 a 2 τθ k , the net is generally a mixture of the active regions and of the resting regions. In the case that a large active region is in contact with a large resting region, the propagation velocity of boundary between the two regions tends to the velocity u given by u = (1 − 2a 2 τθ k )v . This expression of velocity u was deduced from the fact that there exists a solution of the type X(x, t) = 1 (ut − x) for equation (A). In the case of 0 a 2 τθ k , the active region grows and in the case of 0 · 5 a 2 τθ k , the resting region grows. A fatigue effect is introduced, for which it is hard for neurones to maintain firing states. In this case an active region of definite width L propagates with constant velocity u′. The dependence of L and u′ on characteristics of neural network and on the fatigue effect is investigated.

For a dynamical system \(\textbf{\itshape \dot{x}}{=}\textbf{\itshape F}(\textbf{\itshape x})\), an inflector C is defined by C={ x |( A -λ I ) F =0, | A -λ I |=0}, where the matrix A denotes ∂ F /∂ x . It is seen that C consists of inflection points of trajectories and singular points. The inflector C plays an important role for the threshold and shaping actions in many dynamical systems. As an example, the BVP model of an excitable membrane is investigated by means of the inflector C, and some knowledge about continuous threshold phenomena of the BVP model is obtained.