LOSS OF PHOTOREACTIVATION IN UV-IRRADIATED CULTURED FISH CELLS UNDER DIFFERENT CONDITIONS

Abstract— CAF-MM1 cells derived from a goldfish have photoreactivability for the damage induced by ultraviolet light (UV). When UV-irradiated cells were incubated in the dark at 26_AoC, the longest interval in which photoreactivation (PR) was observed (i.e. effective time for PR), measured by colony formation technique, was about 30 h after the UV irradiation. However, if the cells were incubated at 20_AoC, the effective time was prolonged. Since each time appeared to correspond to the doubling time of the cells at each temperature, the loss of photoreactivability is suggested to be closely related to cell growth or progression of cell cycle. The loss of PR was not observed in the cells held in confluence up to 48 h after UV irradiation, in support of the above suggestion. Photoreactivating enzyme in growing CAF-MM1 cells incubated in the dark for 24 h after UV irradiation was shown to be active, so that it is not possible that the cause of the loss of PR is change in the activity of photoreactivating enzyme.     

Imaging Analysis of Near-Field Recording Technique for Observation of Biological Specimens

We present an analysis of the properties of an imaging based on a near-field recording technique in comparison with simulation results. In the system, the optical field distributions localized near the specimens are recorded as the surface topographic distributions of a photosensitive film. It is possible to observe both soft and moving specimens, because the system does not require a scanning probe to obtain the observed image. The imaging properties are evaluated using fine structures of paramecium, and we demonstrate that it is possible to observe minute differences of refractive indices.     

Growth control of stoichiometry in LaMnO3 epitaxial thin films by pulsed laser deposition

We have studied structural, magnetic, and optical transport properties of LaMnO₃ (LMO) thin films grown on SrTiO₃. While the stoichiometric LMO is an insulating antiferromagnet, it tends to be a ferromagnetic insulator when grown as thin films. By exploring the majority of growth parameters, we have found that the bulk-like electronic and magnetic phases can be stabilized by growing thin films under reducing atmospheres and by using more energetic laser processes. These conditions are found to reduce the La deficiency in the film resulting in the greatly improved cation stoichiometry. Since oxides are prone to reduce the oxygen content and to alter the cation ratio under such growth conditions, it suggests that the cation and oxygen stoichiometries in complex oxide thin films can be improved by properly optimizing the growth parameters.     

Ground state valency and spin configuration of the Ni ions in nickelates

The ab initio self-interaction-corrected local-spin-density approximation is used to study the electronic structure of both stoichiometric and nonstoichiometric nickelates. From total energy considerations it emerges that, in their ground state, both LiNiO2 and NaNiO2 are insulators, with the Ni ion in the Ni3+ low-spin state (t(2g)(6)e(g)(1)) configuration. It is established that a substitution of a number of Li/Na atoms by divalent impurities drives an equivalent number of Ni ions in the NiO2 layers from the Jahn-Teller (JT)-active trivalent low-spin state to the JT-inactive divalent state. We describe how the observed considerable differences between LiNiO2 and NaNiO2 can be explained through the creation of Ni2+ impurities in LiNiO2. The indications are that the random distribution of the Ni2+ impurities might be responsible for the destruction of the long-range orbital ordering in LiNiO2.     

Permanence of delay competitive systems with weak Allee effects

This study discusses a multispecies delay competitive system with weak Allee effects. In the situation where the model is a single species, the weak Allee effect represents a biological mechanism in which an increase in population is beneficial for low densities, but detrimental for high densities. In other words, the per-capita growth rate of each species is formulated by a sign-changing function of population density. In this paper, an existence theorem of positive equilibrium is established using the Brouwer degree theory. For cases without intraspecific delays, it is shown that the system has the property of permanence. Furthermore, a sufficient condition for a positive equilibrium to be globally attractive is obtained by means of the Lyapunov method.     

Direct C2-trifluoromethylation of indole derivatives catalyzed by copper acetate

Direct C2-selective trifluoromethylation of indole derivatives was achieved with Togni’s hypervalent iodine reagent and CuOAc as a catalyst in MeOH under mild conditions, affording the desired C2-trifluoromethylated indoles in good yield (up to 90%).     

Giant dielectric susceptibility and magnetocapacitance effect in manganites at room temperature

Extremely high values of the relative permittivity up to 10⁷ and the magnetocapacitance up to 10⁵% have been found in La_{1 − x} Sr _x MnO₃ single crystals (x = 0.1, 0.11). These phenomena are observed even at room temperature. The observed behavior can be a consequence of the strong interaction among charge, spin, and lattice degrees of freedom, which leads to charge and phase separation in the regime before the percolation threshold.     

PHOTOREACTIVATION OF ULTRAVIOLET LIGHT-INDUCED DAMAGE IN CULTURED FISH CELLS AS REVEALED BY INCREASED COLONY FORMING ABILITY AND DECREASED CONTENT OF PYRIMIDINE DIMERS

Abstract— Cultured cells derived from a goldfish were irradiated with 254nm ultraviolet light. Cell survival and splitting of pyrimidine dimers after photoreactivation treatment with white fluorescent lamps were examined by colony forming ability and by a direct dimer assay, respectively. When UV-irradiated (5 J/m²) cells were illuminated by photoreactivating light, cell survival was enhanced up to a factor of 9 (40min) followed by a decline after prolonged exposures. Exposure of UV-irradiated (15 J/m²) cells to radiation from white fluorescent lamps reduced the amounts of thymine-containing dimers in a photoreactivating fluence dependent manner, up to about 60% reduction at 120 min exposure. Keeping UV-irradiated cells in the dark for up to 120min did not affect either cell survival or the amount of pyrimidine dimers in DNA, indicating that there were not detectable levels of a dark-repair system in the cells under our conditions. Correlation between photoreactivation of colony forming ability and photoreactivation of the pyrimidine dimers was demonstrated, at least at relatively low fluences of photoreactivating light.