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Notes: Conductivity control of the boron and phosphorus ion implanted C60 films subjected to various doses with multiple energy has been investigated. Temperature dependent conductivity shows the semiconducting nature of the B+ and P+ implanted films. Fourier transform infrared spectra of the B+ and P+ implanted C60 films show the structural change of the C60 into amorphous carbon. Optical gaps of the implanted films have been observed as a function of implantation dose. The dramatic increase in the conductivity and the reduction in the optical gap on ion implantation are thought to be attributed to an increase in sp2 bounded states, lattice damage, and substitutional impurity doping with ion implantation. The B+ and P+ implantation into C60 and amorphous carbon suggests the possibility of fabricating carbon based homojunction solar cells. © 2001 American Institute of Physics.

Notes: Retinal derivatives were synthesized and their third-order nonlinear optical properties were measured by degenerate four-wave mixing with temporally incoherent nanosecond laser pulses. Fast optical nonlinearities, whose response time was shorter than 30 ps, were observed. The magnitudes of resonant third-order hyperpolarizability were found to be 10−31∼10−29 esu. The large optical nonlinearities were of electronic origin.

Notes: Electrical breakdown streamers have been triggered in atmospheric air by laser-induced ionization. Streamers were successfully triggered even when the voltage applied to the electrodes was too low for breakdown to occur by the influence of the electrical field alone. The lifetime of the observed triggering effect has been found to be no less than 1 ms. Laser-induced streamers were photographically studied and conveniently classified by their observed shapes. In addition, the statistics of the observed phenomena have been compiled according to the classified shape. The statistics indicate that the shape of streamer is likely to be determined by the degree of laser-induced ionization. It has also been found that the speed of streamer formation is strongly related to the degree of ionization.

Notes: The cathodoluminescence (CL) from porous silicon and thermal-oxidized porous silicon was examined by x-ray spectroscopy and photoluminescence (PL). Two dominant CL bands were observed at 460 nm (2.7 eV) and 650 nm (1.9 eV), respectively, which were not found in the PL spectrum. Electron beam irradiation caused degradation and/or increase in luminescence, and the two bands showed different variations. It has been concluded that electron beam excitation mainly occurs in amorphous SiO2, and the two bands are caused from different defects in amorphous SiO2 covering the porous silicon. © 1995 American Institute of Physics.

Notes: Resonant nonlinear optical response was measured in a crystalline cyanine dye MPER, 5-(5-morpholino-2,4-pentadienilydene)-3-ethylrhodanine, which had a broad reflection band due to large oscillator strength of an electronic excited state in the visible wavelength region. Nonlinear optical response measured by the change of reflectivity under optical pumping at the wavelength of the peak of the excited state was composed of fast and slow components. Response time of the fast component was less than 4 ps and its nonlinear optical coefficient χ(3) was evaluated to be (5±2)×10−15 m2/V2 [(4±2)×10−7 esu], which was one of the largest among organic materials.

Notes: Simultaneous surface topography and conductivity/potential measurements were carried out on low-field-emission (1 V/μm) carbon films by combining conductive atomic force microscopy and Kelvin probe force microscopy. The current image showed that highly conducting sites and nonconducting regions coexisted on a micro- and/or nanoscale. Further, in situ I–V characteristics of both regions demonstrated that the conducting sites have an Ohmic property, whereas nonconducting regions have a degenerated Schottky property. When combined with the current image, the contact potential difference image showed that the conducting sites have a highest contact potential difference of 0.5 V, which implies the existence of a graphite phase. It is revealed that the conducting channels play an important role in the low-field-emission process. It is also suggested that the combination of conductivity and surface-potential measurements is an effective method for investigating complex-phase nanostructural surfaces. © 1999 American Institute of Physics.

Notes: Ghrelin, a novel growth hormone (GH)-releasing peptide, was isolated from the rat stomach as an endogenous ligand to the growth hormone secretagogues receptor. It is known that ghrelin stimulates the release of GH from the rat anterior pituitary gland, but the intracellular signal cascade in somatotrophs has not yet been clarified. In this study, using an isolated cell perifusion system, we examined whether ghrelin- and growth hormone-releasing hormone (GHRH)-induced GH secretion from rat pituitary cells depends on intra- and extracellular Ca2+ and voltage-gated Ca2+ channels. For this purpose, we first measured ghrelin- or GHRH-stimulated GH concentration following treatment with reduced extracellular Ca2+ and/or thapsigargin, an endoplasmic reticulum Ca2+ ATPase inhibitor. Reductions in the extracellular Ca2+ concentration to 0.25 mM and to 0 mM resulted in decreases in ghrelin-stimulated GH secretion to 81% and 39% and decreases in GHRH-induced GH secretion to 83% and 13%, respectively, compared to the levels in the case of 2.5 mM Ca2+ concentration, suggesting that extracellular Ca2+ is essential for both ghrelin- and GHRH-induced GH secretion. Pretreatment with thapsigargin resulted in a reduction in ghrelin-induced GH secretion to approximately 60% of the control level, but GHRH treatment had not effect on the GH secretion. Moreover, preincubation with thapsigargin and 0 mM extracellular Ca2+ concentration resulted in significant inhibition of GHRH- and ghrelin-induced GH secretion. Subsequently, to determine whether ghrelin-stimulated GH secretion was induced through voltage-gated Ca2+ channels, we measured the ghrelin-stimulated GH concentration following treatment with nifedipine, an L-type Ca2+ channel inhibitor, and found that the amount of GH secretion was reduced to 44% of the control level. Furthermore, by replacement of extracellular Na2+ in the medium with N-methyl-d(–)-glucamine, an impermeable molecule, GH secretion was reduced to 47%. In this study, we demonstrated that the GH-stimulatory effect of ghrelin, unlike that of GHRH, is achieved through both intracellular and extracellular Ca2+ sources and that ghrelin-induced extracellular Ca2+ influx involves an L-type voltage-gated Ca2+ channel and Na+ influx.

Notes: Ghrelin, a novel growth hormone (GH)-releasing peptide, was recently isolated from the rat stomach as an endogenous ligand to growth hormone secretagogue receptor (GHS-R). Ghrelin specifically stimulates the release of GH from the rat anterior pituitary gland, but the regulational effect of ghrelin on GH secretion has not yet been clarified. We used a perifusion system to examine the single effect and combined effects of ghrelin with growth hormone-releasing hormone (GHRH) and somatostatin on GH secretion from rat anterior pituitary cells. The increase in GH concentration due to ghrelin stimulation showed a transitory peak that was almost the same as that previously reported for GHS, but apparently distinct from that of GHRH. Ghrelin (10−10 M to 10−8 M) stimulated GH secretion from the rat anterior pituitary cells in a dose-dependent manner. Serial ghrelin stimulation of the dispersed cells at 1-h intervals decreased the GH response, but the response recovered with stimulation at 3-h intervals, indicating that ghrelin strongly desensitized cells. Costimulation with ghrelin and GHRH elicited neither a synergistic nor an additive GH response from the rat pituitary cells. Furthermore, pretreatment to anterior pituitary cells with somatostatin strongly abolished ghrelin- and/or GHRH-stimulated GH secretion. In this study, we demonstrated that ghrelin caused weaker GH secretion than that caused by GHRH, and we also showed that costimulation with GHRH had no additive or synergistic effect on GH secretion, suggesting that ghrelin indirectly affects coordinated GH release from pituitary gland, as found in vivo.