Hydrodynamic interaction and coalescence of two droplets under large step shear strains

We observed change in distance between two droplets in each step after application of large multi-step shear strains. Experiments were performed using a sliding plate apparatus. Large step shear strains were applied to two polyisobutylene droplets in poly(dimethyl siloxane) matrix in the same plane between the plates. The distance between the two droplets decreases with increasing the total shear strain, which is given by the product of the step strain magnitude and the number of application of the step strains. The two droplets coalesce when the distance becomes less than the diameter of the droplets. The slope for plots of the distance versus the total strain is independent of the step strain magnitude. This indicates that the effect per unit strain on the distance is the same, irrespective of the strain magnitude. It is suggested that a stronger hydrodynamic interaction between the droplets is the main cause for the droplet approach.     

Ideal crosslinked-polymers and their characterization in free-radical monovinyl-divinyl copolymerizations

The critical conditions in which the classical Flory-Stockmayer gelation theory (F-S theory) is applicable to monovinyl-divinyl copolymerizations were pursued in detail. The resulting prepolymers or precursors of ideal crosslinked-polymers were characterized as standard polymers for the discussion of network formation in free-radical monovinyl-divinyl copolymerizations. Methyl methacrylate was copolymerized with a small amount of ethylene dimethacrylate, butylene dimethacrylate or nonapropyleneglycol dimethacrylate in the presence of lauryl mercaptan, a chain transfer agent to reduce the occurrence of a thermodynamic excluded volume effect and intramolecular crosslinking as the primary and secondary factors, respectively, for the greatly delayed gelation in the free-radical monovinyl-divinyl copolymerizations and, moreover, to keep the primary chain length constant by inhibiting a gel effect. The ratio of the actual gel point to the theoretical one reached 1.1, supporting the validity of F-S theory. The resulting prepolymers were subjected to SEC-MALLS analysis to determine the molecular weights, the molecular-weight distributions and the radii of gyration; the correlations of molecular weight vs. elution volume and radius of gyration vs. molecular weight were useful for the characterization of the precursors of ideal network-polymers.     

Patients with ultrasonic coarse-nodular cirrhosis who are anti-hepatitis C virus-positive are at high risk for hepatocellular carcinoma

BACKGROUND: The relationship between echosonographic patterns of patients with cirrhosis who are antihepatitis C virus (HCV)-positive, the DNA synthesis of hepatocytes, and the risk for HCC were studied. METHODS: Thirty-eight patients with anti-C-100 antibody-positive and Child's grade A posthepatitic cirrhosis were studied. DNA synthesis activity was measured by a bromodeoxyuridine (BrdU, a thymidine analogue)-labeling index (LI), using the BrdU-anti-BrdU in vitro method, and the patients were followed prospectively by frequent liver ultrasonography for 3 years. The ultrasound patterns were classified into fine, coarse, and coarse-nodular (CN) patterns, and the reproducibility of the classification in practical use also was confirmed. RESULTS: Of the 21 patients with high DNA synthesizing cirrhosis (BrdU LI > or = 1.5%), 10 (48%) showed coarse-nodular, 5 (24%) coarse, and 6 (29%) fine pattern in ultrasonography. Conversely, of the 17 patients with low DNA synthesizing LC (BrdU LI < 1.5%), only 1 (6%) showed coarse-nodular, 2 (12%) coarse, and 14 (82%) fine pattern. A significant relationship was found between the two groups of BrdU LI and ultrasound imaging patterns (P < 0.05). The incidence of CN pattern was significantly higher (P < 0.01) in the high DNA synthesizing group than in low DNA synthesizing group. Of the 11 patients with CN pattern by ultrasound imaging, 10 (91%) were in the high DNA synthesizing group, and 9 (82%) developed HCC during the follow-up period, compared with 3 of 7 (43%) with coarse, and only one of 20 (5%) with fine pattern developed HCC. The incidence of HCC was significantly higher (P < 0.01) in patients with a CN cirrhosis pattern than in those with a fine pattern. CONCLUSIONS: In patients with cirrhosis who are anti-HCV-positive, the CN pattern by ultrasound imaging indicates increased DNA synthesis of hepatocytes and a high risk for developing HCC.     

Blue electroluminescent devices withSrGa2S4:Ce for full-color display

In order to realize full-color electroluminescent (EL) displays, which are expected as a dominant candidate for the future multimedia flat panel display, blue EL devices with SrGa₂S₄:Ce have been prepared by molecular beam epitaxy (MBE). This paper proposes a novel deposition method employing Sr metal and Ga₂S₄ compound as the source materials. A single-phase SrGa₂S₄ layer is obtained in a Ga₂S₃/Sr flux ratio of 60 and at the growth temperature of 560°C. We have obtained the well-saturated blue with CIE color coordinates of x=0.14, y=0.14 and brighter blue EL devices made by optimizing the growth conditions in MBE. The maximum luminance of 70 cd/m² in comparison with the 3 cd/m₂ of our previous EL devices, is achieved at a driving frequency of 1 kHz     

Room temperature pulsed operation of 1.5 μm GaInAsP/InPvertical-cavity surface-emitting laser

Room-temperature pulsed operation of a GaInAsP/InP vertical-cavity surface-emitting laser diode (VCSELD) with an emission wavelength near 1.55 μm is reported. A double heterostructure with a 34-pair GaInAsP (λ_g=1.4 μm)/InP distributed Bragg reflector (DBR) was grown by metalorganic chemical vapor deposition (MOCVD). The measured reflectivity of the semiconductor DBR is over 97% and threshold current is 260 mA for a 40-μmφ device with a 0.88-μm-thick active layer. Threshold current density is as low as 21 kA/cm² at room temperature     

Polyacene capacitors

We fabricated two types of polyacene capacitor with extremely stable polyacenic semiconductor (PAS) as the positive and negative electrodes. The first one is a coin-type PAS capacitor (six different sizes), which possesses large capacity with high reliability. Its capacity is much larger than that of the conventional electric double-layer capacitor which uses activated carbon as electrode. PAS capacitor can maintain more than 70% of the initial capacity even after 100 000 cycles. Moreover, this capacitor can be charged and discharged in a few minutes as well as at low rate. The second one is a cylinder-type PAS capacitor (diameter: 18 mm, height: 65 mm) which shows high capacity of 100 F and can discharge at the extremely high rate of 80 C. The coin-type PAS capacitor is currently used for memory back-up of electrical and communication equipment, and the cylinder-type is considered to be useful as power back-up for starting drive parts of electric equipment which needs high power density.     

Direct growth of CdTe on (100), (211), and (111) Si by metalorganic chemical vapor deposition

CdTe epilayers were grown directly on (100), (211), and (111) silicon substrates by metalorganic chemical vapor deposition (MOCVD). The crystallinity and the growth orientation of the CdTe film were dependent on the surface treatment of the Si substrate. The surface treatment consisted of exposure of the Si surface to diethyltelluride (DETe) at temperatures over 600°C prior to CdTe growth. Direct growth of CdTe on (100) Si produced polycrystalline films whereas (lll)B single crystals grew when Si was exposed to DETe prior to CdTe growth. On (211) Si, single crystal films with (133)A orientation was obtained when grown directly; but produced films with (211)A orientation when the Si surface was exposed to DETe. On the other hand, only (lll)A CdTe films were possible on (111) Si, both with and without Te source exposure, although twinning was increased after exposure. The results indicate that the exposure to a Te-source changes the initial growth stage significantly, except for the growth on (111) Si. We propose a model in which a Te atom replaces a Si atom that is bound to two Si atoms.