Reaction kinetics and pathway of hydrothermal decomposition of aspartic acid

The kinetics and pathway of hydrothermal decomposition of aspartic acid were studied using a continuous‐flow tubular reactor. The reaction was carried out in the temperature range of 200–260°C and at a pressure of 20 MPa. Deamination was the primary reaction, indicated by the presence of significant amount of ammonia, fumaric acid, or maleic acid in the products. Other reaction products were pyruvic acid, malic acid, and traces of succinic and lactic acid. Traces of alanine were also detected, showing the possibility of decomposing high‐molecular weight amino acids to obtain simple amino acids such as glycine or alanine. Results on the effect of reaction parameters demonstrated that decomposition of aspartic acid is highly temperature dependent under hydrothermal conditions. For a slight temperature difference of 60°C (from 200 to 260°C), the first‐order reaction rate constants of 0.003 significantly increased to 0.231 s^?1. The activation energy was 144 kJ/mol, as calculated by the Arrhenius equation. No significant effect was exhibited by other reaction parameters such as pH and pressure. The results are useful in controlling the hydrolysis of proteinaceous materials toward high yield of aspartic acid under hydrothermal conditions. © 2007 Wiley Periodicals, Inc. 39: 175–180, 2007     

Bifurcations in the growth process of a vortex sheet in rotating superfluid

Vortex-sheet growth is considered. Broken symmetry bifurcations are found in the growth process. The collective elasticity theory for a well-developed vortex sheet is presented, which is similar to that of smectic liquid crystals. The bifurcations in the limit of a much folded vortex sheet correspond to the Helfrich instability in smectics and cholesterics.     

Microdetermination of hyaluronic acid in human urine by high performance liquid chromatography.

A high performance liquid chromatographic (HPLC) system is described for determination of the unsaturated disaccharide (delta Di-HA) derived from hyaluronic acid (HA) in human urine by digestion with hyaluronidase SD. The effects of eluents on the separation of delta Di-HA and delta Di-0S, which is derived from the reaction of chondroitin with the enzyme, have been studied. The established chromatographic conditions were as follows--column: a stainless steel tube (4 mm i.d. x 250 mm) packed with TSKgel NH2-60; eluent: a mixture of acetonitrile and 0.1 M Tris-HCl buffer containing 0.1 M boric acid and 10 mM sodium sulphate, pH 7.0 (64:36, v/v). The strong fluorescence of unsaturated disaccharide after the reaction with 2-cyanoacetamide in alkaline medium was used for post-column detection. The calibration curve for delta Di-HA was linear in the range 5 pmol-5nmol with a practical detection limit of 2 pmol. The assay coefficients of variation (n = 5) at 200 pmol for delta Di-HA and delta Di-0S were 1.7 and 1.5%, respectively. This HPLC system has been applied to the determination of HA in human urine.     

Isolation of acetic acid-tolerant Baker’s yeast variants in a turbidostat

A commercial baker’s yeast was subjected to selection in a continuous turbidostat cultivation with increasing concentration of acetic acid. The final acetic acid content in fresh medium was 0.6% or 0.8% v/v. Two of seven selected variants were stable over 15 sequential shake flask cultivations without selection pressure. After laboratory scale production of baker’s yeast, one of the variants also showed increased acetic acid tolerance in sour dough. The overall raising power (mL CO₂/h) in sour dough was improved 36%.     

Structural Transformations in Fe/Zr Bi- and Multilayers Induced by Ion-Beam Mixing

The Ar-ion-beam mixing of Fe/Zr bi- and multilayers is studied by conversion electron Mössbauer spectroscopy as a function of ion dose ranging from 1×10¹⁴ to 1×10¹⁷ at./cm². The mixing leads to amorphization of the Fe/Zr system. It was shown that the mixing process in bilayers depends strongly on the thickness of the Zr substrate. The amorphization is much more effective and occurs at lower ion doses in multilayers as compared to corresponding bilayers.     

Influence of relaxation on the profile of a nonlinear acoustic pulse

The influence of transverse relaxation on a nonlinear acoustic wave generated in the presence of the acoustic self-induced transparency (SIT) phenomenon is investigated. An explicit analytical equation for the profile of the nonlinear acoustic wave is derived by a perturbation theory developed on the basis of the inverse scattering problem. This equation provides a possible means for investigating experimentally the profile of an acoustic SIT pulse with allowance for relaxation effects, so that these results can be used to construct new types of acoustoelectronic devices. Zh. Tekh. Fiz. 68, 130–131 (May 1998)