Screening effect diverts the swimming directions from diaphototactic to positive phototactic in a disk-shaped green flagellate Mesostigma viride

We found diaphototactic behavior (i.e. the cells swim perpendicularly with respect to the incident light) in a strain with colorless eyespot of a unicellular disk-shaped green flagellate Mesostigma viride. Lacking pigments completely in the eyespot, the screening effect in this strain was due only to the central part of the chloroplast whose cross section was thin. The diaphototaxis was most obvious when unilateral green stimulus light (520-580 nm) was given, whereas positive phototaxis appeared when given blue light (430-490 nm). The choice between diaphototaxis and (ordinary) phototaxis depended entirely on the transmission (%T) of the cell body against each wavelength of the stimulus: the green light penetrated well (%T > 90%), whereas the blue light was considerably shaded by the chloroplast (50% < %T < 70%). The fraction of positive phototactically behaving cells against each wavelength was in proportion to the front-to-back contrast value obtained at each individual wavelength. The fraction of diaphototaxis was inversely proportional to it. In addition, bilateral stimulus irradiations to wild-type cell with colored eyespot provided useful information about the principle of the diaphototactic steering.     

Massadine,a novel geranylgeranyltransferase type I inhibitor from the marine sponge Stylissa aff. massa

Massadine, a highly oxygenated alkaloid, was isolated from the marine sponge Stylissa aff. massa as an inhibitor of geranylgeranyltransferase type I (GGTase I). The structure of massadine has been deduced from spectral data. Massidine inhibited GGTase I from Candida albicans with an IC(50) value of 3.9 microM. [structure: see text]     

Delay-dependent and delay-independent stability criteria for a delay differential system

For a linear delay differential system with two coefficients and one delay, we establish some necessary and sufficient conditions on the asymptotic stability of the zero solution, which are composed of delay-dependent and delay-independent stability criteria. On the former criterion, the range of the delay is explicitly given.

     

Explosion hazards of ion exchange resin mixed with perchloric acid

On January 21, 2003, an explosion occurred while ion exchange resin (IER) was being used to separate impurities from uranium solution. To clarify the cause of the accident and go/no-go criteria of the explosion, elemental analysis of the IER, DSC analysis, and SIKAREX analysis (a screening tool for runaway reactions) were performed. Finally, experiments on the same scale as the accident were conducted in an explosion chamber. When HClO₄ was added to IER-NO₃, the IER violently exploded without any heating nor metal ions such as uranium. It was confirmed that the accident was caused by an incorrect procedure in the chemical process. From the standpoint of explosion safety, IER-NO₃ in particular should be kept away from perchloric acid in the laboratory.     

Observation of charged excitons in hole-doped carbon nanotubes using photoluminescence and absorption spectroscopy

We report the first observation of trions (charged excitons), three-particle bound states consisting of one electron and two holes, in hole-doped carbon nanotubes at room temperature. When p-type dopants are added to carbon nanotube solutions, the photoluminescence and absorption peaks of the trions appear far below the E11 bright exciton peak, regardless of the dopant species. The unexpectedly large energy separation between the bright excitons and the trions is attributed to the strong electron-hole exchange interaction in carbon nanotubes.