Effects of impact ionization on I-Vcharacteristics of GaAs n-i-n structures including hole trap

Numerical simulations of GaAs n-i-n structures with Cr deep acceptors (hole trap) in the i-layer are performed by considering the impact ionization of carriers. At low voltages, I-V curves show sublinear or saturated features, because the voltage is entirely applied along the reverse-biased n-i junction. When the deep-acceptor density is low, a steep rise of current occurs due to trap filling, whereas when the deep-acceptor density becomes high, the steep current rise occurs due to impact ionization of carriers at the reverse-biased n-i junction. In this case, the voltage for current rise becomes lower as the acceptor density becomes higher     

Line-drawing interpretation using probabilistic relaxation

This paper shows that probabilistic relaxation is an effective method in the automatic interpretation of line drawings consisting of lines, symbols, and characters, such as electricity distribution diagrams superimposed on maps. The line interpretation problem has been newly formulated as a labeling problem in which probabilistic relaxation is used to obtain globally consistent results. The proposed automatic interpretation method consists of two stages. The first is segmentation and recognition of primitive components, such as symbols, characters, and long lines. The second is long-line interpretation, where probabilistic relaxation is introduced.     

Synthesis and photodegradation of copolyamides containing α-diketone linkage in the main chain

Copolyamides were prepared from 4,4′-dichloroformylbenzil, adipyldichloride and hexamethylenediamine. The melting points and solubilities of the copolyamides varied with benzil content. The copolyamides were irradiated by u.v. light in solution and in a film. The copolyamide irradiated in solution was still soluble but the copolyamide irradiated in a film was crosslinked. The mechanisms of the photochemical reactions are discussed.     

A Method of Study of Radioactive Tracer Kinetics

This paper presents an approach to the problem of estimating the number of exponential functions and the pertinent parameters in the output of a radioactive tracer kinetic process. In particular, application of a criterion called an information theoretical criterion (AIC) for the estimation of the number of exponential functions is proposed; AIC was introduced by Akaike for the estimation of the order of linear dynamical systems and has been successfully applied for statistical model identification in a wide range of fields. Also, the maximum likelihood method was applied in order to evaluate AIC and to estimate decay constants and coefficients.     

Comparison of miscibility in poly(N-vinylcarbazole)/polystyrene and polyoxyethylene blends by excimer fluorescence

Summary It is for the first time found that poly(N-vinylcarbazole)(PVCz)/polystyrene (PS) blends have lower miscibility on molecular level than that of PVCz/polyoxyethylene (PEO) blends. This is obtained from excimer fluorescence properties of PVCz in PVCz (9.1–100%)/PS and PVCz (9.6–100%)/PEO blends. Schematic diagrams of phase-separated structure of the PVCz blends are proposed consistent with emission properties and phase-contrast microscopic images. Received: 8 February 2000/Revised version: 21 March 2000/Accepted: 27 March 2000     

Adsorption mechanism of copper and cadmium onto defatted waste biomass

In this study, the amount of copper or cadmium adsorbed using waste biomass (i.e., coffee grounds (CG) and rice bran (RB)) was investigated. The amount of crude protein in defatted CG (D-CG) or RB (D-RB) was greater than that in CG or RB, respectively. The amount of copper or cadmium adsorbed using CG was greater than that using RB. Additionally, the amount of copper or cadmium adsorbed was not affected by the presence of fat in CG. Adsorption data was fitted to the Freundlich equation, and the correlation coefficients were in the range of 0.794-0.991. The main adsorption mechanism was thought to be monolayer adsorption onto the surface of the waste biomass. The adsorption rate data was fitted to the pseudo-second-order model, and the correlation coefficient average was in the range of 0.891-0.945. This result showed that the rate-limiting step may be chemisorption. Moreover, the amount of copper or cadmium desorbed from CG or RB using 0.01 mol/L or 1.00 mol/L HNO(3) was investigated. Desorption with 0.01 mol/L HNO(3) resulted in the recovery of 86-97% of the copper and cadmium, indicating that copper or cadmium that was adsorbed using waste biomass was recoverable.     

Phosphate adsorption ability of granular gibbsite and cerium hydroxide

In the present study, the phosphate adsorption abilities of granular materials, gibbsite (GB) and cerium hydroxide (CE), granulated with ethyl cellulose and ethanol, were investigated. For suitable granular conditions using GB or CE, the percentage of binder and amount of solvent were 10% and 3.25 mL/5 g for GB and 7.5% and 2.50 mL/5 g for CE. The amount of phosphate adsorbed by granular GB or CE was similar to that adsorbed by powdered GB or CE. The adsorption isotherms of phosphate were also similar for the granular and powdered materials. The results of a column experiment showed that when GB was used, the suitable concentration of sodium hydroxide as the desorption solution was 2 mmol/L. In these experiments, the amount of phosphate adsorbed was 31.4 mg/g, the amount of phosphate desorbed was 25.3 mg/g, and the recovery percentage was 80.5%. In contrast, when CE was used, the suitable concentration of sodium hydroxide was 500 mmol/L; the amount of phosphate adsorbed was 77.7 mg/g, the amount of phosphate desorbed was 57.8 mg/g, and the recovery percentage was 74.4%. Results also indicate that granular GB and CE could be used at least five times in a column without loss of absorption or desorption abilities. Moreover, granulation of GB and CE is possible using ethyl cellulose and ethanol.     

Low temperature preparation and machinability of porous ceramics from talc and foamed glass particles

Porous ceramics were prepared by firing mixtures of talc (Mg₃Si₄O₁₀(OH)₂) and foamed glass particles (ceramic balloons, CB) with and without LiCl as a sintering acid. The mixing ratios of the starting materials were talc:CB = 7:3, 8:2, 9:1 and 10:0, with additions of LiCl of 0, 2 and 5 mass%. The mixtures were formed into pellets and fired at 600–1000 °C. The pellets without LiCl showed very poor strength even when fired at 1000 °C but those containing LiCl were much stronger, even when fired at only 600 °C. The crystalline phases in these samples changed to enstatite (MgSiO₃) at ≥ 700 °C by decomposition of the talc under the fluxing action of the LiCl. The resulting samples were machinable and easily cut and drilled. The cutting rate decreased with increasing bending strength, for example, from 105 mm²/s and 6.3 MPa to 50 mm²/s and 16.3 MPa, respectively. The drilling rate of the present sample was found to be only slightly less than Teflon (polytetrafluoroethylene, PTFE) but much faster than graphite, glass ceramics, etc.     

Limited axillary thoracotomy vs video-assisted thoracoscopic surgery for spontaneous pneumothorax

BACKGROUND: Video-assisted thoracoscopic surgery (VATS) has been reported to have a higher pneumothorax recurrence rate than limited axillary thoracotomy (LAT). We investigated the cause of pneumothorax recurrence after VATS by comparing surgical results for VATS and LAT. METHODS: Ninety-five patients with spontaneous pneumothorax underwent resection of pulmonary bullae by VATS (n = 51) or LAT (n = 44). Operating duration, bleeding during surgery, number of resected bullae, duration of postoperative chest tube drainage, postoperative hospital stay, postoperative complication, and pneumothorax recurrence were analyzed to compare VATS and LAT in a retrospective study. RESULTS: The duration of surgery, postoperative chest tube drainage, and postoperative hospital stay was significantly shorter in VATS than in LAT cases (p < 0.0005 and p < 0.005). Bleeding during surgery was significantly less in VATS than in LAT cases (p < 0.005). Numbers of resected bullae were significantly lower in VATS (2.7 +/- 2.1) than in LAT cases (3.9 +/- 2.7) (p < 0.05). Postoperative pneumothorax recurrence was more frequent in VATS (13.7%) than in LAT cases (6.8%), but there was no significant difference. CONCLUSIONS: VATS has many advantages over LAT in treating spontaneous pneumothorax, although the pneumothorax recurrence rate in VATS cases was double that in LAT cases. The lower number of resected bullae in VATS than in LAT cases suggests that overlooking bullae in operation could be responsible for the high recurrence rate in VATS cases. We recommend additional pleurodesis in VATS for spontaneous pneumothorax to prevent postoperative pneumothorax recurrence.