Vascularized subcutaneous human liver tissue from engineered hepatocyte/fibroblast sheets in mice

Subcutaneous liver tissue engineering is an attractive and minimally invasive approach used to curative treat hepatic failure and inherited liver diseases. However, graft failure occurs frequently due to insufficient infiltration of blood vessels (neoangiogenesis), while the maintenance of hepatocyte phenotype and function requires invivo development of the complex cellular organization of the hepatic lobule. Here we describe a subcutaneous human liver construction allowing for rapidly vascularized grafts by transplanting engineered cellular sheets consisting of human primary hepatocytes adhered onto a fibroblast layer. The engineered hepatocyte/fibroblast sheets (EHFSs) showed superior expression levels of vascularization-associated growth factors (vascular endothelial growth factor, transforming growth factor beta 1, and hepatocyte growth factor) invitro. EHFSs developed into vascularized subcutaneous human liver tissues contained glycogen stores, synthesized coagulation factor IX, and showed significantly higher synthesis rates of liver-specific proteins (albumin and alpha 1 anti-trypsin) invivo than tissues from hepatocyte-only sheets. The present study describes a new approach for vascularized human liver organogenesis under mouse skin. This approach could prove valuable for establishing novel cell therapies for liver diseases

Self-Turn-on-Free 5V Gate Driving for 1200V Scaled IGBT

Negative biasing of the gate voltage in a scaled insulated gate bipolar transistor (IGBT) during the off-state was modeled and found to be effective against self-turn-on failures. The required self-turn-on-free criteria were verified experimentally.31st IEEE International Symposium on Power Semiconductor Devices and ICs (ISPSD 2019), 19-23 May 2019, Shanghai, Chin

A Path to Writing : An Approach to Writing for Communication with EFL Students

I.本論文は大学・短大・高校教員による外国語教育の共同研究である。II.外国語でのcommunicationは,listening, speaking, reading及びwritingの円滑な学習が大切であるが,ここではwritingを軸にした演習指導方法について研究し検討したものである。III.研究教育についての構想 1.対象 : 高校生40名を被験者とした。(新高校学習指導要領により,1996年度は「ライティング」導入の初年度であった。)2.教材等 : 視聴覚を利用するauthentic教材を使用する。3.研究授業指導内容 (a)被験者は和文英訳型英作文の教育を受けてきたが,writingは未経験者である。journal writingをもって出発点とし,半ばよりessay writingを加える。 (b)研究期間は3ヵ月,週一度12回を予定する。 4.研究内容 (a)被験者は教材から自己の思考をいかにして造りあげるかを分析・検討する。 (b)書き手の責任として,読み手に,如何にして分かりやすくtextを作成するかの過程を分析・検討する。 IV.研究成果 1.被験者の思考過程を分析した結果,10の事項に整理した。2.漫然とwritingに参加するより,読み手を意識し意欲的な被験者は書き手として,予想を超え多彩なstrategyを展開した。3.語学力は,levelを問わずwriting教育を導入することによって向上する傾向がみられた。V.今後の課題 被験者の作品には,plagiarismの発生がみられ,今後,初期段階から引用符使用と書き換えの指導が要求される

Effects of nitrogen deficiency on electronic properties of AlGaN surfaces subjected to thermal and plasma processes

Effects of device processing on chemical and electronic properties of AlGaN surfaces were investigated. The X-ray photoelectron spectroscopy analysis showed serious deterioration such as stoichiometry disorder and nitrogen deficiency (N deficiency) at the AlGaN surfaces processed by high-temperature annealing, H2-plasma cleaning, dry etching in CH4/H2/Ar plasma and deposition of SiO2. This resulted in high density of surface states at the processed AlGaN surface. Furthermore, the N deficiency introduced a localized deep donor level related to N vacancy (VN) at AlGaN surfaces. Such electronic states governed by a VN-related deep donor and surface state continuum can cause strong Fermi level pinning at the AlGaN surface, reduction of the barrier height and excess leakage currents at the AlGaN Schottky interface and serious drain current collapse in AlGaN/GaN heterostructure field effect transistors. The SiNx- or A12O3-based passivation scheme with a combination of a remote N2-plasma treatment was found to be effective in suppressing formation of VN-related surface defects at AlGaN surfaces

Electron Beam Induced Current Characterization of Novel GaAs Quantum Nanostructures Based on Potential Modulation of Two-Dimensional Electron Gas by Schottky In-Plane Gates

The electron beam induced current (EBIC) technique was used for characterization of novel GaAs quantum nanostructures based on potential modulation of two dimensional electron gas (2DEG) by Schottky in-plane gates (IPGs). A simple theory on the EBIC signal from the basic Schottky IPG structure was developed and it was compared to experimental results. Excellent agreement is between theoretical and experimental results was obtained, indicating that the EBIC technique is a powerful means to detect electric field profiles in depletion layers of quantum nanostructures. The EBIC technique was also applied to Schottky IPG-based quantum wires, lateral superlattices and multi-quantum dot chains. The EBIC study revealed that effective potential control and electron confinement can be achieved by suitable design of Schottky IPG electrodes

Suppression of current collapse in insulated gate AlGaN/GaN heterostructure field-effect transistors using ultrathin Al2O3 dielectric

We investigated effects of electronic states at free surfaces of AlGaN/GaN heterostructure field-effect transistors (HFETs) on the inner current transport at the heterointerfaces. The analysis on transient currents for the air-exposed and H2-plasma-treated devices showed that N-vacancy-related near-surface traps play an important role in current collapse in AlGaN/GaN HFETs. An Al2O3-based surface passivation scheme including an N2-plasma surface treatment was proposed and applied to an insulated-gate HFET. A large conduction-band offset of 2.1 eV was achieved at the Al2O3/Al0.3Ga0.7N interface. No current collapse was observed in the fabricated Al2O3 insulated-gate HFETs under both drain stress and gate stress

Leakage mechanism in GaN and AlGaN Schottky interfaces

Based on detailed temperature-dependent current–voltage (I–V–T) measurements the mechanism of leakage currents through GaN and AlGaN Schottky interfaces is discussed. The experiments were compared to calculations based on thin surface barrier model in which the effects of surface defects were taken into account. Our simulation method reproduced the experimental I–V–T characteristics of the GaN and AlGaN Schottky diodes, and gave excellent fitting results to the reported Schottky I–V curves in GaN for both forward and reverse biases at different temperatures. The present results indicate that the barrier thinning caused by unintentional surface-defect donors enhances the tunneling transport processes, leading to large leakage currents through GaN and AlGaN Schottky interfaces

Mechanism of current leakage through metal/n-GaN interfaces

Detailed current–voltage–temperature (I–V–T) measurements were performed on the Schottky diodes fabricated on MOVPE-grown n-GaN layers. A large deviation from the thermionic emission (TE) transport was observed in the reverse I–V curves with a large excess leakage. From the calculation based on the thermionic-field emission (TFE) model, it was found that the tunneling plays an important role in the carrier transport across the GaN Schottky barrier even for doping densities as low as 1×10(17) cm(−3). A novel barrier-modified TFE model based on presence of near-surface fixed charges or surface states is proposed to explain the observed large reverse leakage currents

Computer simulation of current transport in GaN and AlGaN Schottky diodes based on thin surface barrier model

This paper attempts a rigorous computer simulation of the current transport in GaN and AlGaN Schottky diodes on the basis of the thin surface barrier (TSB) model recently proposed by the authors’ group. First, a computer program was developed which can calculate current transport through an arbitrary potential profile of Schottky barrier by a combined mechanism of thermionic emission (TE), thermionic-field emission (TFE) and field emission (FE). Then, from the view point of the TSB model, attempts were made to fit the theoretical temperature dependent current voltage (I–V–T) curves to the measured I–V–T data taken on Ni/n-GaN and Ni/n-AlGaN Schottky diodes changing the barrier profiles and the energy depth of the surface donor. As compared with the previous poor fitting using approximate analytic formulas, excellent fitting was obtained for both forward and reverse current, confirming the validity of the TSB model as the mechanism for anomalously large leakage currents in GaN and AlGaN Schottky diodes. Best fittings for GaN and Al 0.26 Ga 0.74 N were obtained for exponentially decaying distributions of surface defect donors with the peak density of 5 × 10(18) cm(−3) and 1 × 10(19) cm(−3), the characteristic decay depth of 11 nm and 11.5 nm and the energy depth of 0.25 eV and 0.37 eV, respectively