Solid-state postpolymerization of l-lactide was
studied by two different ways with 0.1 mol
% of stannous 2-ethyl hexanoate as the catalyst. In a two-step
method, the ordinary melt polymerization
of l-lactide was first performed at temperatures higher
than the crystallization temperature (T
c) of
poly(l-lactide) (PLLA), and then the postpolymerization was
continued around the T
c of PLLA. As
PLLA
crystallized in the second stage (e.g., when the temperature
was changed from 140 to 120 °C), the monomer
consumption was found to reach 100% because the monomer and catalyst
could be concentrated in the
amorphous part. Without the crystallization of PLLA occurring in
the postpolymerization, a homogeneous
supercooling state was formed to have a remaining monomer ratio
exceeding 5 wt %. In the alternative
one-step method where the polymerization was continued around the
T
c of PLLA, the polymer
crystallization was induced during the polymerization to promote the
monomer consumption to reach
100%. The kinetic analysis of this polymerization revealed that
the rate of monomer consumption is
inversely proportional to the square of the amorphous ratio of PLLA,
which is opposite to the crystal
ratio. However, the molecular weight did not increase with the
monomer consumption. This should be
because various oligomers are formed in the postpolymerization stage by
the ester interchange reaction.
The effects of conduction band grading in a Cu(In,Ga)Se2 (CIGS) thin film with an average bandgap of 1.4 eV on solar cell performance were investigated by changing the minimum bandgap (E
gmin) and its position, employing the software wxAMPS. The calculation was carried out, taking CdS/CIGS heterointerface recombination into account, by incorporating a thin defective layer into the interface. For CIGS with a flat conduction band profile, i.e., without conduction band grading, the effects of the valence band offset (ΔE
V) between a CdS layer and a CIGS layer with bandgaps from 1.05 to 1.6 eV were investigated. It was found that efficiency was increased by up to 3% by changing the conduction band profile from flat to double-graded, with a deep notch located in the vicinity of the CdS/CIGS interface. On the other hand, efficiency was increased by over 6% and reached 22% by increasing ΔE
V up to 0.3 eV in the case of CIGS with a bandgap of 1.35 eV. Finally, an efficiency of 23.4% was achieved by combining a single-graded conduction band profile with a ΔE
V of 0.3 eV. This result shows that a single-graded conduction band profile is required for high-efficiency wide-bandgap CIGS solar cells if the recombination at the CdS/CIGS heterointerface can be suppressed.
The valence band offsets at the heterointerfaces of the CdF2/CaF2/Si(111) structure grown by molecular beam epitaxy were evaluated using x-ray photoelectron spectroscopy, and the energy band diagram of this heterostructure was proposed. It was found that the interface of CdF2/CaF2 has large conduction band offset: 2.9 eV, and the energy level of CdF2 conduction band edge is below that of Si.
Background/Aims: Although colonic diverticular bleeding (CDB) often ceases spontaneously, re-bleeding occurs in about 30%. Bleeding diverticulum can be treated directly by endoscopic hemostasis; however, it is difficult to perform colonoscopy in all cases with limited medical resource and certain risks. The aim of this study was to clarify who should undergo colonoscopy as well as appropriate methods of initial management in CDB patients. Methods: A total of 285 patients who were diagnosed as CDB and underwent colonoscopy from March 2004 to October 2015 were retrospectively analyzed. First, the association between re-bleeding and various factors including patients’ background and initial management were analyzed. Second, the examination conditions that influenced bleeding point identification were analyzed. Results: Of 285 patients, 187 were men and 98 were women. Median age was 75 years, and the median observation period was 17.5 months. Re-bleeding was observed in 79 patients (28%). A history of CDB (OR 2.1, p = 0.0090) and chronic kidney disease (CKD; OR 2.3, p = 0.035) were risk factors, and bleeding point identification (OR 0.20, p = 0.0037) was a preventive factor for re-bleeding. Bleeding point identification significantly reduced approximately 80% of re-bleeding. Furthermore, extravasation on CT (OR 3.7, p = 0.031) and urgent colonoscopy (OR 5.3, p < 0.001) were predictors for identification of bleeding point. Compared to bleeding point identification of 11% in all patients who underwent colonoscopy, identification rate in those who had extravasation on CT and underwent urgent colonoscopy was as high as 70%. Conclusions: Contrast-enhanced CT upon arrival is suggested, and patients with extravasation on CT would be good candidates for urgent colonoscopy, as well as patients who have a history of CDB and CKD.
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