高濃度ドープSiCショットキー接合における高電界輸送および非合金化オーミック接合の形成

付記する学位プログラム名: 京都大学卓越大学院プログラム「先端光・電子デバイス創成学」京都大学新制・課程博士博士(工学)甲第25295号工博第5254号京都大学大学院工学研究科電子工学専攻(主査)教授 木本 恒暢, 教授 白石 誠司, 准教授 船戸 充学位規則第4条第1項該当Doctor of Philosophy (Engineering)Kyoto UniversityDFA

Basal Cell Carcinoma of the Head and Neck

Basal cell carcinoma (BCC) is a malignant neoplasm derived from nonkeratinizing cells that originate from the basal layer of the epidermis and is the most frequent type of skin cancer in humans, with cumulative exposure to ultraviolet radiation as an important risk factor. BCC occurs most frequently at sun-exposed sites, with the head and neck being common areas. Tumors can be classified as nodular, superficial, morpheaform, infiltrating, metatypic, and fibroepithelioma of Pinkus. Several treatment options such as surgical excision and nonsurgical procedures are available. The choice of treatment should be determined based on the histological subtype of a lesion, cost, its size and location, patient age, medical condition of the patient, treatment availability, and the patient's wishes. The aim of any therapy selected for BCC treatment involving the head and neck is to ensure complete removal, the preservation of function, and a good cosmetic outcome

Dealing with Imbalanced Classes in Bot-IoT Dataset

With the rapidly spreading usage of Internet of Things (IoT) devices, a network intrusion detection system (NIDS) plays an important role in detecting and protecting various types of attacks in the IoT network. To evaluate the robustness of the NIDS in the IoT network, the existing work proposed a realistic botnet dataset in the IoT network (Bot-IoT dataset) and applied it to machine learning-based anomaly detection. This dataset contains imbalanced normal and attack packets because the number of normal packets is much smaller than that of attack ones. The nature of imbalanced data may make it difficult to identify the minority class correctly. In this thesis, to address the class imbalance problem in the Bot-IoT dataset, we propose a binary classification method with synthetic minority over-sampling techniques (SMOTE). The proposed classifier aims to detect attack packets and overcome the class imbalance problem using the SMOTE algorithm. Through numerical results, we demonstrate the proposed classifier's fundamental characteristics and the impact of imbalanced data on its performance

Early Detection of Nasopharyngeal Carcinoma

Nasopharyngeal carcinoma (NPC) is a unique disease with a clinical presentation, epidemiology, and histopathology differing from other squamous cell carcinomas of the head and neck. NPC is an Epstein-Barr virus-associated malignancy with a marked racial and geographic distribution. Specifically, it is highly prevalent in southern China, Southeast Asia, and the Middle East. To date, most NPC patients have been diagnosed in the advanced stage, but the treatment results for advanced NPC are not satisfactory. This paper provides a brief overview regarding NPC, with the focus on the early detection of initial and recurrent NPC lesions

Cellular Fragments as Biomaterial for Rapid In Vitro Bone-Like Tissue Synthesis

Current stem cell-based techniques for bone-like tissue synthesis require at least two to three weeks. Therefore, novel techniques to promote rapid 3D bone-like tissue synthesis in vitro are still required. In this study, we explored the concept of using cell nanofragments as a substrate material to promote rapid bone formation in vitro. The methods for cell nanofragment fabrication were ultrasonication (30 s and 3 min), non-ionic detergent (triton 0.1% and 1%), or freeze-dried powder. The results showed that ultrasonication for 3 min allowed the fabrication of homogeneous nanofragments of less than 150 nm in length, which mineralized surprisingly in just one day, faster than the fragments obtained from all other methods. Further optimization of culture conditions indicated that a concentration of 10 mM or 100 mM of beta-glycerophosphate enhanced, whereas fetal bovine serum (FBS) inhibited in a concentration-dependent manner, the mineralization of the cell nanofragments. Finally, a 3D collagen-cell nanofragment-mineral complex mimicking a bone-like structure was generated in just two days by combining the cell nanofragments in collagen gel. In conclusion, sonication for three min could be applied as a novel method to fabricate cell nanofragments of less than 150 nm in length, which can be used as a material for in vitro bone tissue engineering

Important roles of odontoblast membrane phospholipids in early dentin mineralization

The objective of this study was to first identify the timing and location of early mineralization of mouse first molar, and subsequently, to characterize the nucleation site for mineral formation in dentin from a materials science viewpoint and evaluate the effect of environmental cues (pH) affecting early dentin formation. Early dentin mineralization in mouse first molars began in the buccal central cusp on post-natal day 0 (P0), and was first hypothesized to involve collagen fibers. However, elemental mapping indicated the co-localization of phospholipids with collagen fibers in the early mineralization area. Co-localization of phosphatidylserine and annexin V, a functional protein that binds to plasma membrane phospholipids, indicated that phospholipids in the pre-dentin matrix were derived from the plasma membrane. A 3-dimensional in vitro biomimetic mineralization assay confirmed that phospholipids from the plasma membrane are critical factors initiating mineralization. Additionally, the direct measurement of the tooth germ pH, indicated it to be alkaline. The alkaline environment markedly enhanced the mineralization of cell membrane phospholipids. These results indicate that cell membrane phospholipids are nucleation sites for mineral formation, and could be important materials for bottom-up approaches aiming for rapid and more complex fabrication of dentin-like structures

Rapid bioinspired mineralization using cell membrane nanofragments and alkaline milieu

Bone is a sophisticated organic-inorganic hybrid material, whose formation involves a complex spatio-temporal sequence of events regulated by the cells. A deeper understanding of the mechanisms behind bone mineralization at different size scales, and using a multidisciplinary approach, may uncover novel pathways for the design and fabrication of functional bone tissue in vitro. The objectives of this study were first to investigate the environmental factors that prime initial mineralization using the secondary ossification center as an in vivo model, and then to apply the obtained knowledge for rapid in vitro synthesis of bone-like tissue. First, the direct and robust measurement of pH showed that femur epiphysis is alkaline (pH ≅ 8.5) at the initial mineral stage at post-natal day 6. We showed that the alkaline milieu is decisive not only for alkaline phosphatase activity, which precedes mineral formation at P6, but also for determining initial mineral precipitation and spherical morphology. Next, engineering approaches were used to synthesize bone-like tissue based on alkaline milieu and artificial chondrocyte membrane nanofragments, previously shown to be the nucleation site for mineral formation. Interestingly, mineralization using artificial cell membrane nanofragments was achieved in just 1 day. Finally, ex vivo culture of femur epiphysis in alkaline pH strongly induced chondrocyte burst, which was previously shown to be the origin of chondrocyte membrane nanofragments, and also enhanced mineral formation. Taken together, these findings not only shed more light on the microenvironmental conditions that prime initial bone formation in vivo, but they also show that alkaline milieu can be used as an important factor for enhancing methods for in vitro synthesis of bone tissue.Hara E.S., Okada M., Kuboki T., et al. Rapid bioinspired mineralization using cell membrane nanofragments and alkaline milieu. Journal of Materials Chemistry B, 6, 38, 6153. https://doi.org/10.1039/C8TB01544A

Re-Evaluation of Initial Bone Mineralization from an Engineering Perspective

Bone regeneration was one of the earliest fields to develop in the context of tissue regeneration, and currently, repair of small-sized bone defects has reached a high success rate. Future researches are expected to incorporate more advanced techniques toward achieving rapid bone repair and modulation of the regenerated bone quality. For these purposes, it is important to have a more integrative understanding of the mechanisms of bone formation and maturation from multiple perspectives and to incorporate these new concepts into the development and designing of novel materials and techniques for bone regeneration. This review focuses on the analysis of the earliest stages of bone tissue development from the biology, material science, and engineering perspectives for a more integrative understanding of bone formation and maturation, and for the development of novel biology-based engineering approaches for tissue synthesis in vitro. More specifically, the authors describe the systematic methodology that allowed the understanding of the different nucleation sites in intramembranous and endochondral ossification, the space-making process for mineral formation and growth, as well as the process of apatite crystal cluster growth in vivo in the presence of suppressing biomolecules. A detailed understanding of the developmental process of bone tissue leads to the acquisition of useful information for the bone tissue fabrication. This review summarizes the study of the calcification process of the calvaria and epiphyses from an engineering perspective and provides useful information for the realization of bone tissue biofabrication. Here, we describe the new mechanism of space formation for mineralization such as rupture of chondrocytes and disruption of cell-cell adhesion. We also describe the roles of nucleation site such as cell membrane nanofragments and matrix vesicles.Hara E.S., Okada M., Nagaoka N., et al. Re-Evaluation of Initial Bone Mineralization from an Engineering Perspective. Tissue Engineering - Part B: Reviews, 28, 1, 246. https://doi.org/10.1089/ten.teb.2020.0352