Avenic acid,a new amino acid possessing an iron chelating activity

A new amino acid derivative possessing an iron chelating activity was isolated from root washings of water cultured $\text{Avena sativa}$ under iron deficient conditions. The structure of this compound, avenic acid A has been determined as 2(S),3′(S),3″(S)-N-[3-(3-hydroxy-3-carboxypropylamino)-3-carboxypropyl]-homoserine (1) on the basis of chemical and spectroscopic evidence.     

Non-Darcian effects on conjugate natural convection between horizontal concentric cylinders filled with a porous medium

An analysis is presented of steady conjugate free convection between two horizontal concentric cylinders filled with a fluid-saturated porous medium; the innermost cylinder surface is maintained at a high temperature and the outermost cylinder surface at a lower one. The velocity-pressure-gradient relation is taken to be nonlinear, with departure from the linear Darcy situation measured by a parameter F₀. The investigation is based on the numerical solution, by a finite-difference method, of the full momentum and energy equations. The streamline and isotherm patterns as well as the local and mean Nusselt numbers are plotted for several physical parameters to show some of the flow and heat transfer characteristics. It is found that all parameters play an important role in the flow and heat transfer characteristics. The model can be applied to a variety of engineering problems.     

Malliavin calculus, geometric mixing, and expansion of diffusion functionals

Under geometric mixing condition, we presented asymptotic expansion of the distribution of an additive functional of a Markov or an ε-Markov process with finite autoregression including Markov type semimartingales and time series models with discrete time parameter. The emphasis is put on the use of the Malliavin calculus in place of the conditional type Cramér condition, whose verification is in most case not easy for continuous time processes without such an infinite dimensional approach. In the second part, by means of the perturbation method and the operational calculus, we proved the geometric mixing property for non-symmetric diffusion processes, and presented a sufficient condition which is easily checked in practice. Accordingly, we obtained asymptotic expansion of diffusion functionals and proved the validity of it under mild conditions, e.g., without the strong contractivity condition. Received: 7 September 1997 / Revised version: 17 March 1999     

Polarization dependence of the optical absorption of single-walled carbon nanotubes

Anisotropic optical absorption properties of single-walled carbon nanotubes (SWNTs) are determined from a vertically aligned SWNT film for 0.5-6 eV. Absorption peaks at 4.5 and 5.25 eV are found to exhibit remarkable polarization dependence and have relevance to optical properties of graphite. A method for determining a nematic order parameter for an aligned SWNT film based on the collinear absorption peak at 4.5 eV is presented, followed by the determination of the optical absorption cross section.     

Highly planar amphiphilic porphyrins

A first synthesis of an asymmetric and amphiphilic β-substituted porphyrin is reported. The porphyrin can be integrated into various types of nanostructures with the amphiphilic characters in hydrophilic solvents. The one-dimensional integration may induce a magnetic interaction between the central metals.     

Rapid Separation of Hydrophobic Compounds by UPLC: in Case of Bisindolylmaleimides, Indolocarbazoles or Fullerene C60 Derivatives

Rapid separation of hydrophobic compounds such as bisindolylmaleimides, indolocarbazoles or fullerene C₆₀ derivatives by ultra performance liquid chromatography was developed. Bisindolylmaleimides and indolocarbazoles were separated within 7 and 5 min, respectively. The linear ranges for the determination of bisindolylmaleimides and indolocarbazoles were 1.25?500 pmol and 0.5?50 pmol per injection (r > 0.99), respectively. Fullerene C₆₀ derivatives were separated within 9 min, and the linear range for the determination of fullerene C₆₀ derivatives was 0.1?10 pmol per injection (r > 0.99).     

Helical Chiral Pyridine N‐Oxides: A New Family of Asymmetric Catalysts

Optically active chiral alkyl chlorides are valuable compounds because of their bioactivity and versatile synthetic utility. Accordingly, the ring opening of epoxides with a chloride nucleophile stands as an important goal in asymmetric catalysis. We describe herein recent advances in the design and development of chiral pyridine N‐oxide catalysts for the enantioselective synthesis of chlorohydrins.     

Chaotic mixing generated by acoustic streaming

The acoustic mixer presented in this paper is a closed cylinder containing chemical solutions. The ultrasound was generated in a water bath outside of the cylinder. The mixing efficiency was measured by using a laser-photodiode system and by mixing iodine and sodium thiosulfate. Iodine solution has a light brown color which becomes transparent if the solution is mixed with sodium thiosulfate. The unmixed regions of the solution in the container remain dark. Starch was used to make the solution darker. Considering the relative position between the cylinder and the transducer, it was shown that displacements parallel to the axes of the streaming have little effect on the mixing speed. Indeed, the distance of the cylinder from the center of the streaming is more important to obtain ideal mixing performances. The frequency and size of the transducers has been investigated too and little effect was found. In contrast, the wave amplitude seems to be the biggest factor in obtaining rapid mixing.