Non-linear current–voltage characteristics related to native defects in SrTiO3 and ZnO bicrystals

SrTiO₃ and ZnO bicrystals with various types of boundaries were fabricated in order to examine their current–voltage characteristics across single grain boundaries. Their grain boundary structures were also investigated by high-resolution transmission electron microscopy. In Nb-doped SrTiO₃, electron transport behaviors depend on the type of boundaries. Random type boundaries exhibit highly non-linear current–voltage characteristics, while low angle boundaries show a slight non-linearity. On the contrary, undoped ZnO does not exhibit non-linear current–voltage characteristics in any type of boundaries including random ones. It is suggested that the differences observed in current–voltage properties between the two systems are mainly due to the difference in the accumulation behavior of acceptor-like native defects at grain boundaries. A clear non-linearity is obtained by means of Co-doping even for the highly coherent Σ1 boundary in a ZnO bicrystal. This is considered to result from the production of acceptor-like native defects by Co-doping.     

Phase and amplitude comparison between experiment and calculation of ultrabroad-band pulses generated in a taper fiber

Using a cross-correlation frequency-resolved optical gating apparatus, the phases and amplitudes of ultrabroad-band optical pulses from a taper fiber have been measured for various input pulse peak powers. The measured waveforms have been compared with calculated waveforms using a finite-difference in the frequency domain method, in which no envelope approximations were used and the variation of the taper shape was taken into account. Excellent agreement between the measured and the calculated waveforms was obtained when the additional dispersion of a normal fiber and an objective was considered.     

Epstein-Barr virus-positive multiple early gastric cancers and dysplastic lesions: a case report

Epstein-Barr virus (EBV) has been implicated as a causal virus of gastric cancer with episomal monoclonality, elevated antibodies and a unique morphologic expression in the early intramucosal stage, but the infection mechanisms have not been demonstrated. EBV has been shown only in the cancerous lesions by the highly sensitive EBV-encoded small RNA in situ hybridization (EBER-ISH) method, not in the dysplastic mucosa adjacent to the cancer. A case is presented of multiple EBV-positive gastric cancer and dysplastic epithelium observed in a 52-year-old man. Serial cut sections of the gastrectomy specimen showed four small cancerous lesions, three of which were EBER-positive, and three EBER-positive, minute, non-cancerous dysplastic lesions. The three cancerous lesions were intramucosal cancer, with one having minimal submucosal invasion forming a lymphoepithelioma-like histology. All of these EBER-positive cancerous and dysplastic lesions showed intense CD8 T-lymphocytic infiltration. There was no such findings in the EBV-negative cancerous lesion. It was concluded that EBV infection may occur in the epithelial cells of atrophic gastric mucosa, and progress to cancer with monoclonal expansion through the EBV-positive dysplastic change. Cytotoxic T-lymphocytic reactions can occur even in the dysplastic lesions. Multifocal EBV infection in the gastric mucosa may occur and, if necessary, total gastrectomy is recommended in such a case.     

Intramolecular triplet energy migration in poly(2-vinylnaphthalene) and poly(naphthylalkyl methacrylate)s in solid solution: Effects of side chain length

Summary The effect of side chain length on intramolecular triplet energy migration of naphthalene containing polymers was investigated by a delayed fluorescence (DF) spectroscopy for the solid solution of the polymers. The degree of triplet energy migration depends strongly on whether the chromophores are directly attached to the main chain or not.     

Photoresponsive peptide and polypeptide systems: part II. Photochromism of poly(l-ornithine) containing various azo-contents in side chains

Poly(L-ornithine)s having various azo-contents in the side chains were synthesized by the water-soluble carbodiimide procedure. The photochemical properties of the polypeptides poly[N^δ-p-(phenylazo)benzoyl-L-ornithine] (PPABLO) containing 3–77 mol% azobenzene were investigated by absorption and circular dichroism spectroscopy in hexafluoro-2-propanol (HFIP) or water, and in HFIP-water or methanol-water solvent mixtures. The photochromism of the dichroic bands of the PPABLOs containing 20–77 mol% azobenzene in the visible and ultraviolet wavelength regions was found to be mostly reversible as a function of irradiation time at different wavelengths due to the photostationary state (above 80% trans-cis photoisomerization) of the azo aromatic moieties. The PPABLO containing 3.2 mol% azobenzene in water exhibited conformational changes from random coil to helix by the addition of methanol or sodium dodecyl sulphate (SDS). The photo-induced conformational change was observed in HFIP-water-SDS solvent mixtures, while no conformational change was seen in water and HFIP-water solvent mixtures.     

Effect of ascorbic acid 2-0-alpha-glucoside on hydrocortisone-induced cataract formation in developing chick embryos: I. Comparison of the preventive effect of ascorbic acid derivatives

The effect of ascorbic acid 2-O-alpha-glucoside (AA-2G) on hydrocortisone (HC)-induced lens opacity in developing chick embryo was examined and compared with those of ascorbic acid (AsA) and ascorbic acid 2-phosphate (AA-2P). The opacity was dose-dependently inhibited by a single administration of 10 or 20 mumol/egg of AA-2G and by three repeated administrations of 1, 3 or 10 mumol/egg of AA-2G. AA-2G was the most effective among the three compounds. Glucose did not enhance the preventive effect of AsA against HC-induced opacity, and neither dehydro ascorbic acid nor glucose also prevented HC-induced cataract. In the histological study, we observed many small vacuoles in the nuclear region of the opaque lens treated with HC. AA-2G inhibited the formation of such vacuoles, an effect closely correlated with the prevention of cataract formation.     

Physical and functional association of cortactin with Syk in human leukemic cell line K562

Human leukemic cell line K562 is induced to differentiate into the megakaryocytic lineage by stimulation with 12-O-tetradecanoylphorbol-13-acetate (TPA). We demonstrate here that TPA stimulation increases tyrosine phosphorylation of an 80-kDa protein at an early stage of megakaryocytic differentiation and that this 80-kDa protein is identical with cortactin. Since tyrosine kinase Syk was activated by TPA stimulation, we examined the possibility that cortactin is a potential substrate of Syk in K562 cells. TPA-induced tyrosine phosphorylation of cortactin was decreased profoundly by overexpression of dominant-negative Syk. Furthermore, cortactin was associated with Syk even before TPA stimulation. Since cortactin was previously referred as an 80/85-kilodalton pp60src substrate, we examined the association between Src and cortactin, whereas its association could not be detected. These data suggest that Syk phosphorylates cortactin in K562 cells upon TPA treatment.