Bibliothek

Notizen: The growth process, crystal structure, and optical properties of ultrathin GaAs and InAs wires (whiskers) as thin as 15–40 nm and about 2 μm long are reviewed and discussed. Experimental results for growing whiskers using Au as a growth catalyst during metalorganic vapor phase epitaxy (MOVPE) and the shape and growth direction of whiskers provide new insight into growth control of GaAs and InAs whiskers. The crystal structure of whiskers, Au behavior during MOVPE, and their growth mechanism are reviewed and discussed on the basis of transmission electron microscopic analysis. The photoluminescence spectra of GaAs wires are compared with those of a GaAs epitaxial layer, and the effect of surface treatment on the luminescence peak energy shift is discussed. The time dependent photoluminescence of GaAs wires is also discussed. The application of GaAs whiskers to light emitting devices is reviewed because a semiconductor wire structure employing quantum size effects is a very important element of electronic and optical devices. © 1995 American Institute of Physics.

Notizen: Blood flow stagnation is said to be an important factor for the incidence of dark eye circles, but there are few reports, which have studied dark eye circles and the relationship to blood flow. We have examined dark eye circles dermatologically using a non-invasive method and made clear the factor related to it. We have also studied the effect of newly developed cosmetics on improvement of dark eye circles. Melanin and haemoglobin content, haemoglobin oxygen saturation and blood flow rate were measured to compare dark eye circles with a normal control. An increased amount of haemoglobin and decreased haemoglobin oxygen saturation were observed at the site of dark eye circles. We also observed that the blood flow rate was slow at dark eye circles in comparison with cheek. From these results, blood flow stagnation seems to be one of the factors that could induce dark eye circles. In addition, the increase of melanin at dark eye circles was also observed in older subjects. It was considered that not only congestion but also an increase of melanin content in the skin could induce dark eye circles. On the basis of these results, we developed anti-dark eye circle cosmetics that can improve blood circulation, reduce melanin content and maintain high moisture retention in the skin. After 3 weeks’ usage of this product, it was confirmed that dark eye circles were improved, judging from the result of non-invasive instrumental measurements.

Notizen: Previous studies have shown that nanoparticle chain aggregates (NCA) of titania are elastic [S. K. Friedlander, H. D. Jang and K. H. Ryu, Appl. Phys. Lett. 72, 1 (1998)]. The NCA were a few tenths of a micron long and composed of (approximately) 7 nm primary particles. They were produced by thermal decomposition of titanium tetraisopropoxide vapor in nitrogen. The goal of this study was to see whether the elastic behavior depends on (a) the material properties, (b) primary particle size, and (c) method of NCA formation. For this purpose, titania, alumina, and iron oxide NCA were generated by laser ablation. Rotating metal foil targets were mounted in a small cylindrical chamber and exposed to an excimer laser beam. The resulting aerosol was swept out by an oxygen stream. The generator was operated to produce NCA with similar mobility diameter and primary particle size. The NCA were deposited on the carbon or formvar films of an electron micrograph grid. Under the electron beam a hole develops in the carbon film in the neighborhood of the deposited NCA. The NCA then stretch and contract as described in our earlier study [S. K. Friedlander, H. D. Jang and K. H. Ryu, Appl. Phys. Lett. 72, 1 (1998)]. The titania, alumina, and iron oxide NCA generated by laser ablation all showed elastic behavior for primary particles smaller than about 10 nm. However, titania NCA composed of 36 nm primary particles did not exhibit elastic behavior indicating that very small primary nanoparticles are needed for this phenomenon to occur. The small scale stretching and contraction of chain segments were studied by measuring changes in the bond angles between adjoining particles and in the lengths of the segments studied. The elastic behavior is probably associated with local folding of chain segments due to van der Waals forces. Under tension, folded chains straighten but when the tension is relaxed, folds tend to reform but not reversibly. Rotation and sliding probably occur at the boundaries between particles during stretching. We hypothesize that elastic behavior is a general property of NCA composed of transition metal oxides with primary particles smaller than 10–15 nm; the phenomenon has now been observed for NCA produced in two ways, thermal decomposition and laser ablation. These phenomena may play a role in the action of nanoparticle additives such as fumed silica and carbon black used to improve the properties of rubber. NCA elasticity may also contribute to the ductile properties of nanoparticle compacts. © 2000 American Institute of Physics.

Notizen: We fabricated screen-printed Ag-(Bi,Pb)2Sr2Ca2Cu3Ox monofilament and multifilament tapes with filament number 1≤N≤5. As N increases, the critical current Ic increases monotonically until it reaches 54 A (77 K, 0 T) for N=5, while the critical current density Jc is around 1.6×104 A/cm2 (77 K, 0 T) nearly independent of N. The bend strain tolerance is found to decrease with increasing N. For monofilament tapes the strain tolerance is 2%–3% strain while for multifilament tapes it decreases to ∼1% at N=3 and ∼0.4% at N=5. © 1995 American Institute of Physics.

Notizen: An in-plane gate field-effect transistor is characterized by ultrafast electro-optic sampling. The transistor is monolithically integrated with photoconductive switches in coplanar waveguide and 〈0.5 ps measurement time resolution is achieved. The gate-drain capacitance of the transistor is obtained as 1.8 fF at zero drain voltage from displacement current transients. The gate-drain capacitance is dominated by parasitic capacitance and the intrinsic gate-drain capacitance is estimated as less than 0.2 fF. © 1995 American Institute of Physics.

Notizen: A vital staining technique with fluorescein diacetate (FDA) and propidium iodide (PI) was used for determination of viability of myxosporean stage spores of Myxobolus artus and actinosporean stage spores of M. cultus. Viable spores stained green with FDA and non-viable spores stained red with PI were clearly distinguishable in M. artus myxosporean spores released from live infected fish, while the spores collected from pseudocysts were not well stained with FDA. Immediately after release from the oligochaete, Branchiura sowerbyi, actinosporean spores of M. cultus, stained bright green in the sporoplasms and red in the spore processes. In vitro survivability tests revealed that the longevity of M. artus spores was 5 months at 25°C and 15 months at 18°C. Drying and ultraviolet irradiation (36 000 mW s cm–2 for M. artus myxosporean spores, 600 mW s cm–2 for M. cultus actinosporean spores) were most effective as sporicidal treatments.

Notizen: Background  Barium sulphate, a stable inorganic material, has been used in contrast media and cosmetic products because of its stability. As a negative external electric potential accelerates the skin barrier repair after barrier disruption, we hypothesized that topical application of barium sulphate may affect the skin barrier recovery rate depending on its ζ potential.Objectives  To investigate whether barium sulphate particles in aqueous solution have different ζ potentials depending on their surface structure, and to investigate the possible relation between ζ potential and skin barrier recovery rate.Methods  Mice were subjected to tape stripping to disrupt barrier function, or were treated with acetone and kept in a dry environment to induce epidermal hyperplasia. They were then treated with different forms of barium sulphate, and barrier recovery was monitored by measurements of transepidermal water loss.Results  There was a significant correlation between the barrier recovery rate and ζ potential of barium sulphate applied topically. Barium sulphate with a negative ζ potential significantly accelerated barrier recovery, but barium sulphate with a positive ζ potential did not accelerate or even delayed barrier repair. Barium sulphate with a negative ζ potential had an X-ray diffraction pattern different from that with a positive potential. The distribution of calcium in the epidermis was also influenced by the polarity of ζ potential.Conclusions  These findings suggest a new pharmacological approach towards altering barrier function or epidermal hyperplasia with inorganic particles in healthy and diseased skin.

Notizen: Aim : To investigate the inhibitory effects on gastric acid secretion of three proton pump inhibitors, omeprazole, lansoprazole and rabeprazole, using a three-way crossover design in healthy Helicobacter pylori-negative,S-mephenytoin 4′-hydroxylase (CYP2C19) homo- and hetero-extensive metabolizers.Methods : Eight healthy Japanese male volunteers were enrolled. After the administration of rabeprazole (10 mg/day), lansoprazole (30 mg/day) or omeprazole (20 mg/day), intragastric pH monitoring was commenced from 24 h before the first proton pump inhibitor dose, and continued for days 1–3 after proton pump inhibitor administration. The pH electrode was used for 48 h and changed just before pH monitoring on day 2.Results : For the administration of 10 mg/day rabeprazole, the mean ratios of the 24-h pH ≥ 3 holding timewere 5.7 ± 1.1%,13.6 ± 2.2%, 35.3 ± 2.7% and 62.8 ± 3.1% for the pre-treatment day and days 1, 2 and 3, respectively. The same ratios for lansoprazole (30 mg/day) were 5.7 ± 0.7%, 7.4 ± 1.5%, 13.6 ± 3.4% and 26.6 ± 4.9%; the same ratios for 20 mg/day omeprazole were 5.9 ± 0.9%, 6.1 ± 1.2%, 11.4 ± 2.8% and 16.4 ± 4.6%. The mean ratio of the 24-h pH ≥ 3 holding time of days 1–3 increased significantly compared to the pre-treatment day (P 〈 0.01) with the administration of rabeprazole and lansoprazole. The magnitude of inhibition of gastric acid secretion after rabeprazole administration was stronger than that after lansoprazole. A significant elevation of the mean ratio of the 24-h pH ≥ 3 holding time was demonstrated on days 2 and 3 with omeprazole (P 〈 0.01).Conclusions : In H. pylori-negative CYP2C19 extensive metabolizers, rabeprazole (10 mg/day) shows a faster onset of rising intragastric pH and a stronger inhibition of gastric acid secretion than do lansoprazole (30 mg/day) or omeprazole (20 mg/day).

Notizen: Pathological changes in cultured tiger puffer, Takifugu rubripes, with emaciation disease in Kyushu, Japan were studied histologically. In most cases, diseased fish were heavily infected with at least one of three myxosporeans (Myxidium fugu, Myxidium sp. and Leptotheca fugu) and two unidentified hyperparasitic microsporeans, attached to, or in, the intestinal epithelium. Myxidium fugu attached to the surface of the epithelium, caused no noticeable effects on the host tissue, irrespective of its infection with the hyperparasite. Myxidium sp., which proliferated in the epithelium, induced severe pathological changes including accumulation of cell debris between the epithelium and lamina propria and resultant detachment of the epithelium. Leptotheca fugu, another histozoic myxosporean, induced degeneration of the epithelium, associated with massive infiltration of macrophages into the epithelium to encapsulate parasites. When L. fugu was infected with its hyperparasitic microsporean, shortened villi were also observed. This is probably because passage of macrophage-parasite aggregates through the basement membrane of the epithelium severely damaged the epithelial structure. It is evident histologically that, unlike epicellular M. fugu, histozoic Myxidium sp. and L. fugu with or without hyperparasitic microsporeans, were highly pathogenic to host fish. This strongly suggests that they are causative agents of the emaciation disease.