Experimental and theoretical investigations on short-channel effects in 4H-SiC MOSFETs

In this paper, a fundamental investigation on short-channel effects (SCEs) in 4H-SiC MOSFETs is given. Planar MOSFETs with various channel lengths have been fabricated on p-type 4H-SiC (0001), (0001) and (1120) faces. In the fabricated MOSFETs, SCEs such as punchthrough behavior, decrease of threshold voltage, deterioration of subthreshold characteristics, and saturation of transconductance occur by reducing channel length. The critical channel lengths below which SCEs occur are analyzed as a function of p-body doping and oxide thickness by using device simulation. The critical channel lengths obtained from the device simulation is in good agreement with the empirical relationship for Si MOSFETs. The critical channel lengths in the fabricated SiC MOSFETs are slightly longer than simulation results. The dependence of crystal face orientations on SCEs is hardly observed. Impacts of interface charge on the appearance of SCEs are discussed.     

Efficient Persistent Room Temperature Phosphorescence in Organic Amorphous Materials under Ambient Conditions

Persistent emission with a long lifetime (>1 s) from organic materials can only be observed at a low temperature, because of the significant nonradiative deactivation pathway that occurs at room‐temperature (RT). If organic materials with persistent RT emission in air could be developed, they could potentially be utilized for a variety of applications. Here, organic host‐guest materials with efficient persistent RT phosphorescence (RTP) are developed by minimizing the nonradiative deactivation pathway of triplet excitons. The nonradiative deactivation pathway is dependent on both nonradiative deactivation of the guest and quenching by diffusional motion of the host. The rigidity and oxygen barrier properties of the steroidal compound used as the host suppressed the quenching, and the aromatic hydrocarbon used as the guest is highly deuterated to minimize nonradiative deactivation of the guest. Red‐green‐blue persistent RTP with a lifetime >1 s and a quantum yield >10% in air is realized for a pure organic material.     

Statistical Shape Model of the Liver and Its Application to Computer‐Aided Diagnosis of Liver Cirrhosis

In recent years, there has been increasing interest in statistical shape modeling of human anatomy. The statistical shape model can capture the morphological variations of human anatomy. Since liver cirrhosis will cause significant morphological changes, the authors propose a computer‐aided diagnosis method for liver cirrhosis based on statistical shape models. In the proposed method, the authors first construct a statistical shape model of the liver using 50 clinical CT datasets (25 sets of normal data and 25 sets of abnormal data). The authors apply the marching cubes algorithm to convert the segmented liver volume to a triangulated mesh surface containing 1000 vertex points. The coordinates of these vertex points are used to represent the 3D liver shape as a shape vector. After normalization and identification of correspondences between all datasets, principal component analysis (PCA) is employed to find the principal variation modes of the shape vectors. Then the authors propose a mode selection method based on class variations between the normal class and abnormal class. The authors found that the top two modes of class variations are most effective for the classification of normal and abnormal livers. The classification rate of abnormal livers and normal livers by the use of a simple linear discriminant function were 84% and 80%, respectively.     

Persulfate-induced photochemical decomposition of a fluorotelomer unsaturated carboxylic acid in water

The persulfate (S(2)O(8)(2-))-induced photochemical decomposition of C(3)F(7)CF=CHCOOH in water was investigated to develop a method to neutralize stationary sources of fluorotelomer unsaturated carboxylic acids (FTUCAs), which have recently been detected in the environment, and are considered to be more toxic than the environmentally persistent perfluorocarboxylic acids (PFCAs). Photolysis of S(2)O(8)(2-) produced highly oxidative sulfate radical anions (SO(4)(-)), which efficiently decomposed C(3)F(7)CF=CHCOOH to F(-) and CO(2) via C(3)F(7)COOH. With an initial S(2)O(8)(2-) concentration of 12.5mM and irradiation from a 200-W xenon-mercury lamp, C(3)F(7)CF=CHCOOH at a concentration of 680muM was completely decomposed within 5min. When 8.00mM S(2)O(8)(2-) was used, the initial rate of C(3)F(7)CF=CHCOOH decomposition induced by 254-nm light irradiation was 45 times as high as that with photolysis alone. The apparent quantum yield for the C(3)F(7)CF=CHCOOH decomposition with 6.25mM S(2)O(8)(2-) and 254-nm light was 2.4, indicating that virtually all SO(4)(-) anions produced by the photolysis of S(2)O(8)(2-) contribute to the decomposition of C(3)F(7)CF=CHCOOH.     

Cigarette smoke extract enhances oxytocin-induced rhythmic contractions of rat and human preterm myometrium

Although smoking during pregnancy is a major risk factor for preterm delivery, the underlying mechanism by which smoking stimulates uterine contractions is still poorly understood. In the present study, we tried to clarify the effects of smoking on myometrial contractility induced by oxytocin (OT) using cigarette smoke extract (CSE). Myometrial strips, which were taken from the rat on day 16 of pregnancy, and from human preterm and term delivery groups, were incubated overnight with several doses of CSE at 37 degrees C under non-hormonal conditions. The uterine contractile sensitivity and activity (force and frequency) upon exposure to OT were investigated. Furthermore, the expression levels of oxytocin receptor (OTR) mRNA in the myometrial strips were investigated by real-time PCR. Contractile sensitivity to OT in the rat CSE (10(-7) pieces/ml) group was found to be significantly higher than in the control group (P < 0.05). Contractile activity did not differ between the CSE and control groups. The expression levels of rat OTR mRNA in the CSE (10(-7) pieces/ml) group were significantly higher than in the control group (P < 0.01). Similarly, in preterm myometrial strips, the expression levels of human OTR mRNA in the CSE (10(-7) pieces/ml) group were significantly higher than in the control group (P < 0.05). These findings suggest that CSE directly increases the contractile sensitivity of preterm myometrium in response to OT by upregulating the expression of OTR mRNA and thereby increases the risk of preterm delivery in women, who smoke during pregnancy.     

Occurrence of estrogenic compounds in and removal by a swine farm waste treatment plant

The total estrogenic activity of the wastewater from a swine farm in Japan was quantitatively characterized, and the compounds responsible for the estrogenic activity were identified and quantified. The wastewater treatment process consisted of a series of an up-flow anaerobic sludge blanket (UASB) and a trickling filter. Samples were collected at each treatment step, and the total estrogenic activity was determined by use of an in vitro gene expression assay (MVLN; MCF-7 human breast cancer cell stably transfected with the pVit-tk-LUC receptor plasmid). Individual estrogenic compounds were identified and quantified using liquid chromatography-mass spectrometry (LC/MS) and liquid chromatography-tandem mass spectrometry (LC/ MS/MS). To further identify the compounds contributing to the estrogenic activity in the wastewater, the sample extracts were fractionated into 12 fractions (fractions 1-12) by HPLC. The rate of removal of estrogenic activity between the effluent and the influent was greater than 97%. The trickling filter removed the majority of the estrogenic activity. The removal rates of specific estrogenic compounds ranged from 44 to 99%. Estrogenic activity was detected mainly in the fractions containing estrone (El), 17beta-estradiol (betaE2), 17alpha-estradiol (alpha E2), estriol (E3), bisphenol A (alphaPA), and equol (EQ0). The ratios of betaE2-EQc (betaE2 equivalents derived from chemical analysis) to betaE2-EQB (betaE2 equivalent derived from bioassay) in the 12 fractions collectively were contributed by El (17-30%), betaE2 (23-30%), acE2 (<1%), E3 (1-2%), BPA (<1%), and EQO (2-3%) in the influent and El (16-37%), PE2 (<1-7%), alphaE2 (<1%), E3 (<1-3%), BPA (<1%), and EQO (<1%) in the effluent. The compounds responsible for most of the estrogenic activity measured in the bioassay were natural estrogens such as El and betaE2.     

Densification process of α′-sialon ceramics

The liquid-phase sintering process of -sialon ceramics has been investigated by high-temperature dilatometry and microstructural observation. In addition, isothermal shrinkage measurements have been performed to examine the densification kinetic parameter. It has been confirmed that densification kinetic parameters in the solution-reprecipitation stage are much larger than the rate exponent predicted for the classic liquid-phase sintering model, and are slightly smaller than that for the viscous flow process. Rapid shrinkage was observed in the solution-reprecipitation stage from the results of shrinkage rate, and corresponds to pore elimination by particle rearrangement and cooperative flow of particle/liquid mixture. These processes provide the major contribution to shrinkage. In addition, the liquid flow process occurs when the silica content in the raw powder increases, but it is retarded due to the formation of -sialon. It is anticipated that particle rearrangement and cooperative flow, as well as liquid-flow processes, take place in the solution-reprecipitation stage of sintering of Si₃N₄-based materials, and cause a large amount of shrinkage.     

Selective Triplet–Singlet Förster-Resonance Energy Transfer for Bright Red Afterglow Emission

Förster-resonance energy transfer (FRET_T-S) from the lowest excited triplet state (T₁) of a donating sensitizer to a fluorescence acceptor can be used to obtain bright room-temperature afterglow emission at long wavelengths. However, the energy transfer from the lowest excited singlet state of the donor to the acceptor is an undesirable deactivation pathway that prevents FRET_T-S. Herein, heteroatoms in chromophores are shown to allow selective and efficient FRET_T-S for enhanced triplet emission for bright room-temperature afterglow emission at long wavelengths. Different transition characteristics between the lowest singlet excited state and triplet states in heteroatom-containing chromophores accelerate triplet generation, enabling near-zero fluorescence yields. Out-of-plane vibrations of the heteroatoms in aromatic fused rings greatly enhance the radiative rate from T₁ by a factor of 88 relative to non-heteroatom-containing fused chromophore. The compatibility of the near-zero fluorescence and the enhanced triplet emission in a heteroatom-containing fused chromophore enable selective and efficient FRET_T-S pathways, resulting in room-temperature red afterglow emission with a yield of 17%. The bright emission at long-wavelengths allows distinguishable, multiple spectral signals in ambient white light.     

Polyether-segmented nylon hemodialysis membranes. III. Preparation and properties of new polyether-segmented nylon

In order to apply a blood-compatible polymer to hemodialysis membrane, a new polyether-segmented nylon which dissolved in common organic solvents was designed. The basic polyether-segmented nylon was synthesized by melt polycondensation from sebacic acid, m-xylenediamine, and α,ω-bisaminopropyl-poly(ethylene oxide). To improve the solubility, azelaic acid and hexamethylenediamine were copolycondensed with the basic copolymer. The solubility was correlated with the heat of fusion (ΔH_m) of the copolymer. When ΔH_m is < 30 mJ/mg, the polymer is soluble in dimethylsulfoxide and makes a stable solution. The nonthrombogenicity was investigated in the viewpoint of adhesion of platelet onto the copolymer surface. It is made clear that the surface of the block copolymer, having > 10 wt % of poly(ethylene oxide), suppresses the adhesion of platelet, and the composition of the nylon block has no effect on the adhesion of platelet. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1723–1729, 1997     

An image processing approach for two-phase interfaces visualized by a real time neutron radiography technique

An image enhancement technique for a visualization of gas–liquid metal two-phase interfaces is developed for a real time neutron radiography (RTNR) technique, where the dynamic motion of bubbles inside liquid metal cannot be observed optically. The proposed image enhancement technique consisted of noise reduction, pipe–fluid interface determination, and image smoothing procedures. The results show that the RTNR technique is able to visualize the dynamics of gas–liquid metal interfaces, and also is able to determine more accurate two-phase flow parameters such as void fraction.