Atom-probe field-ion microscopy of GaAs and GaP

The atom-probe field-ion microscope (atom-probe FIM) was applied for the first time to GaAs and GaP which belong to the III–V compound semiconductors. The general character of the pulsed field-evaporation of GaAs and GaP was quite similar. Ga field-evaporated predominantly in the form of singly charged ions. As and P also field-evaporated mainly as singly charged ions, but their abundances were small compared with Ga⁺. It appears that As (or P) atoms can field-evaporate more easily in the form of AsO⁺ (or PO⁺) in the presence of oxygen on the surface. In all experiments, GaAsⁿ⁺ and GaPⁿ⁺ were rarely detected. After chemical etching the surfaces were covered with oxide films and various oxide ions were detected. The abundance of oxide ions dramatically decreased after field evaporation in hydrogen. No distinct difference between the 〈111〉 orientations of these materials which have zinc-blende structure could be observed. Most of the experimental results obtained were explained in terms of the existing theory of field evaporation. It was concluded that field penetration effects have a considerable influence on the field evaporation processes of these materials as well as on the field ionization processes.     

Ruthenium-catalyzed cycloaddition between propargylic alcohols and cyclic 1,3-dicarbonyl compounds via an allenylidene intermediate

Thiolate-bridged diruthenium complexes such as [Cp*RuCl(mu(2)-SR)(2)RuCp*Cl] (Cp* = eta(5)-C(5)Me(5); R = Me, (n)Pr, (i)Pr) and [Cp*RuCl(mu(2)-S(i)Pr)(2)RuCp*(OH(2))]OTf (OTf = OSO(2)CF(3)) promote the cycloaddition between propargylic alcohols and cyclic 1,3-dicarbonyl compounds to give either the corresponding 4,6,7,8-tetrahydrochromen-5-ones or 4H-cyclopenta[b]pyran-5-ones in high yields with complete regioselectivity. This catalytic cycloaddition provides a simple and one-pot synthetic protocol for a variety of substituted chromenones and cyclopenta[b]pyranones.     

Entrap-immobilization of biocatalysts on cellulose acetate-inorganic composite gel fiber using a gel formation ofcellulose acetate–metal (Ti, Zr) alkoxide

We developed a new entrap-immobilization method, using a gel formationof cellulose acetate and metal (Ti, Zr) alkoxide. Several biocatalysts(-galactosidase, -chymotrypsine, invertase, urease, lipase andSaccharomyces cereviciae) were successfullyentrap-immobilized on this composite gel fiber. The immobilization process wassimple and the resultant immobilized biocatalysts on the gel fiber were easy tohandle. It is considered that the biocatalysts are physically entrapped amongthe gel networks and distribute throughout the gel fiber. The gel fiber wasstable in phosphate buffer solution, electrolyte solution and organic solvent,because the gel formation was due to coordination interaction between celluloseand transition metal. Therefore, it can be applicable as a support for abiotransformation in various reaction media. We examined some enzyme reactionsand biotransformation using the immobilized biocatalysts on this gel fiber andevaluated this immobilization matrix in the reactions compared to the resultsobtained by the other immobilization method. The immobilized biocatalyst showedstable activity for repeated cycles and over a long period of time. Moreover,continuous reaction could be carried out in a column reactor packed with thisimmobilized biocatalyst.     

Statistics of velocity gradients in turbulence at moderate reynolds numbers

A direct numerical simulation of the Navier-Stokes equation is performed in order to investigate the small scale structure of turbulence at moderately large microscale Reynolds numbers 40–140, using the spectral method with 340³ modes starting from a high-symmetric flow. It is shown that the small scale motion is statistically isotropic. The probability density distribution of the velocity is Gaussian, while those of the velocity gradients and the vorticity are not Gaussian but have long exponential tails. The moments of the velocity gradients are expressed in terms of the gamma function, and the ratio of the moments of the velocity gradients of successive orders increases linearly with the order. A comparison is made with a laboratory experiment.     

Synthesis of an Optically Active Trisubstituted α,β-Butenolide, (S)-4, 6-Dihydroxy-2, 3-dimethyl-2-hexesoic Acid 1, 4-Lactone,from 2-Deoxy-D-ribose

The title compound has been synthesized efficiently from 2-deoxy-D-ribose. The synthesis involves : 1) an aldol like carbon-carbcr. bond formation of (S)-3, 5-dibenzyioxy-2-pentanor.e (8) with a lithium enolate of methyl propanoate, and 2) O-de-benzylation of the aldol adducts (11) for a γ-lactonization followed by β-elimination of the desired butenolide skeleton.     

Toxadocials B, C and toxadocic acid A: thrombin-inhibitory aliphatic tetrasulfates from the marine sponge, toxadocia cylindrica

Three new thrombin-inhibitory metabolites, toxadocial B (2), toxadocial C (3), and toxadocic acid A (4) have been isolated from the marine sponge Toxadocia cylindrica. The structures of these compounds were determined by spectroscopic and chemical methods.     

Faithful and unfaithful students in time series learning

A model neuron with delay line feedback connections can learna time series generated by another neuron. In the case thatboth neurons have identical transfer functions, a model neuron(student) is capable of reproducing the instruction sequencegenerated by another neuron (teacher), but the parameters arenot uniquely determined by learning a quasi-periodic time series.A student that has completed the learning can be either faithfulor unfaithful, depending on whether it continues mimicking theteacher's time series over a long interval after the learningor whether it departs from the teacher and eventually generatesa time series that bears no resemblance to the teacher's. Inthe case that both neurons have different transfer functions,a student is generally incapable of reproducing the instructionsequence. Each student readjusts its parameters so as to minimizethe mean-squared deviation between the instruction signal andits own output, but this parameter set is not uniquely determined.In this unrealizable learning, the degeneracy among faithfulstudents is lifted and there is no more distinction betweenfaithful and unfaithful students.