Numerical Analysis for Light Absorption Spectra of the Base of DNA-Wrapped Single-Walled Carbon Nanotubes.

This study numerically demonstrates the light absorption spectra of each base of DNA-wrapped single-walled carbon nanotubes (SWCNTs). Previous experimental and theoretical studies show that the optical properties of these composites are different from the bare SWCNTs. In this work, we investigated the bases of DNA that influence optical properties. To obtain stable molecular states for studying optical properties, molecular dynamics calculations were performed. Additionally, light absorption spectra in the ultraviolet-to-near-infrared region of one type of base-wrapped (e.g., adenine-, thymine-, cytosine-, or guanine-wrapped) SWCNTs were investigated by utilizing the semi-empirical molecular orbital theory using SCIGRESS commercial software. This method can significantly reduce the calculation time compared to the ab initio molecular orbital method, making the handling of composites of bases and SWCNTs possible. We found that the largest peaks appear at a wavelength of around 300 nm for all the composites. Furthermore, we found that the light absorption spectra above 570 nm are strongly influenced by adenine and cytosine. Thus, our computational results provide insight into the optical properties and the effects of base-SWCNTs that are difficult to investigate experimentally under the influence of solvents and various molecules.

Differences in dynamic behavior of single diatom cells caused by changing wavelengths.

We investigate a motion of diatom cells stimulated by a halogen lamp irradiation. Diatom cells are single-celled organisms which have chloroplast. Chloroplast contains photosynthetic pigment which absorbs blue light (wave length of the light is 400 nm-450 nm) and red one (650 nm-700 nm). Light intensity of the halogen lamp is fixed about 500 Lx during the experiment. We used colored films to cut the blue or red light and observed motion of diatom cells by using the optical microscope. We found that the speed of diatom cells decreases when the colored film is inserted, and it increases after ejecting the film. It is noted that the light intensity is constant during the experiment, which means that we change wave length of the irradiated light. Our results show that the average speed of diatom cells is influenced by not the light intensity but the wave length of the light.

Use of a microchamber for analysis of thermal variation of the gliding phenomenon of single Navicula pavillardii cells.

In this study, we used a microchamber to observe and analyze the gliding phenomenon of Navicula pavillardii diatom cells at different temperatures. The temperature of the culture medium was varied from 17.0 to 30.0 °C to examine the effect of temperature on diatom movement. Movement of each cell at different temperatures was monitored by use of an inverted optical microscope and continuously recorded as video data, from which the velocities of each cell were calculated, by using dedicated software to perform two-dimensional trajectory analysis. The velocities of the same cell at different temperatures were thereby successfully compared. The results showed that the change in cell velocity was insignificant when the temperature was increased from 17.0 to 25.0 °C. When the temperature was increased from 17.0 to 27.5 °C, non-uniformly disrupted cell movement was observed. When the temperature was further increased to 30.0 °C, cell movement was clearly inhibited. By use of single-cell analysis, the effects of the temperature increases on diatom movement were successfully evaluated. Finally, we characterized the experimental data by performing t tests to evaluate the effects of variations of the movement of individual cells on the data analysis.

Flux-free conductance modulation in a helical Aharonov--Bohm interferometer.

A novel conductance oscillation in a twisted quantum ring composed of a helical atomic configuration is theoretically predicted. The internal torsion of the ring is found to cause a quantum phase shift in the wavefunction that describes the electron's motion along the ring. The resulting conductance oscillation is free from magnetic flux penetrating inside the ring, which is in complete contrast with the case for the ordinary Aharonov-Bohm effect observed in untwisted quantum rings.

Torsion-induced persistent current in a twisted quantum ring.

We describe the effects of geometric torsion on the coherent motion of electrons along a thin twisted quantum ring. The geometric torsion inherent in the quantum ring triggers a quantum phase shift in the electrons' eigenstates, thereby resulting in a torsion-induced persistent current that flows along the twisted quantum ring. The physical conditions required for detecting the current flow are discussed.