Environmentally benign, non-catalytic, simple, and complete aromatic ring methylation of catechol derivatives by using 1,3,5-trioxane as the source of methyl groups was investigated in subcritical and supercritical water and under solvent-free conditions. Irrespective of the presence of subcritical and supercritical water as a reaction medium, catechol and 4-methylcatechol afforded the permethylation product 3,4,5,6-tetramethylcatechol. Only a small amount of 3,4,5,6-tetramethylcatechol (2% yield) was obtained under solvent-free conditions at 400 °C for 10 min. However, supercritical water considerably accelerated the formation of 3,4,5,6-tetramethylcatechol (13% yield) under the conditions of 400 °C, 10 min, and 0.35 g/mL water density.3

It is well known that wind-induced water waves generate formations of Langmuir circulation. This phenomenon is observed together with the high-speed and low-speed streaks, i.e., the convergence and divergence zones, respectively. Mass and momentum are transported significantly from the divergence zone toward the convergence zone, and consequently, strong downflows appear in the convergence zone. So, it is very important to study hydrodynamic properties of Langmuir circulation in natural lakes and ocean. In this study, stereoscopic PIV measurements were conducted in order to reveal the distributions of all thee components of velocity vectors. These experiments allowed us to investigate 3-D turbulent structure under the water waves and generation mechanism of large-scale circulations.

No abstract

Langmuir circulation is a large-scale secondary current which is generated by wind-induced water waves, and it plays some important roles on turbulence production and the transports of mass and momentum. Previously, many researchers have conducted studies on Langmuir circulation and related hydrodynamic phenomena. However, most of them focused on only hydrodynamic characteristics, e.g., generating mechanism and velocity streaks, and thus we lack for reliable information of the relation between a gas transfer and the Langmuir circulation. The goal of the present study is to obtain the relationship between a gas transfer velocity and the aspect ratio of the laboratory flume. So, in order to suggest a new physical model, DO measurements were conducted for each aspect ratio condition.

Wind-induced water waves play a vital role in the mass and momentum exchange across interface between air and water. They are closely related to various scaled problems such as global warming and water environment, and it is thus important to know the flow structure of them. So, many researchers have conducted intensively theoretical, experimental and numerical studies on this flow. In particular, Langmuir circulation is well highlighted, which is a large-scale secondary current with longitudinal axis.wave. However, most of previous studies using laboratory flume could not cover the longitudinal variations of current structure which has fetch-depending properties. Therefore, in the present study, stereoscopic PIV measurements were conducted at several fetches in order to reveal the fetch dependency of three dimensional current property and related turbulence structure.