"Pricing Convertible Bonds with Default Risk: A Duffie-Singleton Approach"

We propose a new method to value convertible bonds(CBs). In particular, we explicitly take default risk into consideration based on Duffie-Singleton(1999), and provide a consistent and practical method for relative pricing of securities issued by a firm such as CBs, non-convertible corporate bonds and equities. Moreover, we show numerical examples using Japanese CBs' data, and compare our model with other practical models.

"Pricing Convertible Bonds with Credit Risk: A Duffie-Singleton Approach "(in Japanese)

This paper proposes a method to price convertible bonds with credit risk using Duffie-Singleton approach to handle credit risk. As such it also provides a method to replicate convertibles by trading common stocks and corporate bonds of the issuing company. Empirical comparison with existing models which incorporate credit risk is provided using Japanese convertible bond data.

酸素漂白条件下における炭水化物と活性酸素種との反応に関する研究

学位の種別:課程博士University of Tokyo(東京大学

Numerical Simulation of Rock Toughness Testing

The testing method of rock toughness is proposed by the international society of rock mechanics (ISRM), but the results may be influenced by the test pieces, and the details of the crack propagation and the stress intensity factors are not clarified through the testing. Also the experimental test requires tedious works for the preparation of test specimen and economical responsibility. The present study aims to simulate numerically the rock toughness testing which is proposed by ISRM. For this purpose, the authors propose a numerical method which can simulate the experimental testing, and they show the propriety of the proposed method by comparing the results with the experimental and other numerical methods. At the same time, they clarify the details of crack propagation behaviors in rocks, and show the change of the stress intensity factors. The proposed method is based on the displacement-type finite element method, and several techniques are introduced to obtain accurate solution of the mechanical behavior near the crack-tip area

A Phenotypic Analysis of Involucrin-Membrane-Bound Ovalbumin Mice after Adoptive Transfer of Ovalbumin-Specific CD8⁺ T Cells

To investigate the mechanism of autoimmunity and peripheral tolerance in the skin, several transgenic mouse strains expressing membrane-bound ovalbumin (mOVA) as an epidermal self-antigen under the control of keratinocyte-specific promotors, such as keratin 5 and keratin 14, were employed in combination with adoptive transfer of CD8⁺ T cells from OT-I mice (OT-I T cells) that recognize an ovalbumin-derived peptide. However, these strains showed bodyweight loss and required additional inflammatory stimuli, such as γ-irradiation and tape-stripping, to induce skin inflammation. In this study, we generated a mouse strain expressing mOVA under the control of human involucrin promoter (involucrin-mOVA mice). In contrast to previous strains, involucrin-mOVA mice spontaneously developed skin inflammation after the transfer of OT-I T cells in the absence of external stimuli without significant bodyweight loss. We focused on the skin infiltration process of OT-I T cells and found that transferred OT-I T cells accumulated around the hair follicles in the early phase of skin inflammation, and in the later phase, the skin inflammation spontaneously resolved despite the remaining OT-I T cells in the skin. Our involucrin-mOVA mice will provide a promising tool to investigate the pathogenesis and the tolerance mechanisms of cytotoxic skin autoimmunity

Angiomatous Nasal Polyp Diagnosed by Preoperative Imaging and Successfully Resected by Endonasal Endoscopic Surgery: A Case Report

Angiomatous polyp is a benign, nonneoplastic nasal polyp that accounts for 4-5% of all inflammatory nasal polyps but is rarely reported in the literature. It can grow rapidly and exhibit an aggressive clinical behavior that can simulate malignant sinonasal tumor. We herein report a case of a 13-year-old boy with a rapidly growing angiomatous polyp in the nasal cavity. We had followed up the patient without significant changes for two years, but the tumor had rapidly grown in the last six months. At first, the rapid growth of the tumor and the bone erosion of the maxilla were suggestive of a malignant tumor. However, with preoperative magnetic resonance imaging (MRI) and [18F]-2-fluoro-2-deoxy-D-glucose positron emission tomography imaging findings, we established the corrective diagnosis of an angiomatous polyp. After the diagnostic imaging, we performed an endoscopic endonasal surgery and totally resected the tumor without unnecessary excessive surgery. Recognition of this disease that can mimic malignancy is important to avoid excessive surgery such as en bloc resection by craniofacial approach, and we believe that MRI findings can be helpful for the imaging diagnosis

Inhibitory Effect of 1α-Hydroxyvitamin D3 on N-nitrosobis (2-oxopropyl)Amine-induced Cholangiocarcinogenesis in Syrian Hamsters

Sixty-three male 5-week-old Syrian hamsters received the carcinogen N-nitrosobis(2-oxopropyl)amine (BOP) s.c. in 5 weekly injections (the first, 70mg/kg body, and the remaining, 20mg/kg each). The hamsters that received BOP were given intragastric administration of 0.2ml of medium chain triglyceride (MCT) with or without 0.04μg of 1α-hydroxyvitamin D3 [1α(OH)D3] through a feeding tube for 12 weeks. Thus, 3 groups were assigned:Group 1;BOP alone (n＝20), Group 2;BOP＋MCT (n＝18) and Group 3;BOP＋1α(OH)D3 (n＝25). The mean body weight of Group 3 was lower than those of Groups 1 and 2 at the end of the experiment (p＜0.001,Tukey-Kramer HSD test). At the end of week 12, all surviving hamsters were put to sleep. The incidences of liver tumors were 80%, 72% and 32% in Groups 1, 2 and 3, respectively. The incidence of tumors in Group 3 was significantly lower than in Group 1 and Group 2 (p＜0.05, χ2-test). All tumors were cholangiocarcinoma. These results indicated that BOP-induced cholangiocarcinogenesis was suppressed by the supplemental administration of 1α(OH)D3

センチメント分析とトピック抽出によるマイクロブログからの評判傾向抽出

近年，政策やサービスなどの評判を調査するためにアンケート形式による調査が増加しているが，回収率が低落傾向にあることや，人的コストが増加するなどの問題が生じている．一方，Web上にはユーザの意見を含む評価情報が多数存在している．そこで本研究では，評判傾向予測システムの構築を目的として評判傾向の時間的変化とその原因をマイクロブログから抽出する評判傾向抽出エージェントの実現を目指す．特に本論文では，評判傾向の抽出と評判傾向が変化した原因の抽出に注力する．評価情報の感情を抽出するセンチメント分析に着目し，回帰式から評判傾向の変化点を抽出した後に，変化点におけるトピックをチャンキングにより抽出する手法を提案する．本手法は，従来の評価判定法であるp/n判定にセンチメント分析を組み合わせることで，p/n判定単体よりも人手による調査と相関の高い時系列変化を抽出できる点が特徴であり，政治及びテレビドラマに関するコンテンツを対象に実際の支持率，視聴率に対する評価実験を実施した結果，政治（自由度調整済決定係数R\u272（p/n判定単体：0.22，提案手法：0.60）），テレビドラマ（自由度調整済決定係数R\u272（p/n判定単体：0.26，提案手法：0.56））ともに相関の高い時系列変化を抽出できることが確認できた.In this paper, we propose reputation trend extraction method from microblogging using sentiment analysis and topic extraction. Microblogging is a new form of communication in which users can describe their current status in short texts. We analyze these contents by two approaches -- positive vs. negative determination and sentiment analysis. Moreover, we use the multiple regression is order to get the semantic orientations which have an impact to investigation objects, and we also use chunking is order to extract topics that cause reputation changes. We evaluated our method by applying it to the politics and the ratings of TV dramas

タグクラスタ多様化による未知性を考慮した推薦手法の提案

近年推薦システムの研究において，その有用性は予測精度（適合率，再現率）の高さとされていたが，既存の推薦方法では，ユーザは予測精度の高さだけでは満足しないということが報告されている．したがって，今後の推薦システムの課題として，未知性や意外性といった予測精度以外の新たな観点が重要とされている．こうした課題を踏まえ，本論文では推薦リストの未知性という観点に着目し，ユーザの嗜好に合致するが，まだ知らないコンテンツの発見を促す推薦手法を提案する．多面的に付与されたタグの話題単位で推薦リストを多様化することにより，予測精度を維持しつつ，未知性を向上させる．評価実験の結果，推薦リストの約6割に嗜好に合致し，かつ知らないコンテンツが含まれ，未知性の高い推薦が実現できていることを確認した．The traditional recommendation approaches are evaluated based on accuracy, i.e., precision and recall. However, by this approaches, it has been reported that a user is not satisfied only with the accuracy. Therefore, this paper focuses on novelty in order to recommend interesting and unknown items. By diversifying recommended list on topics of tag clusters, our approach improves not only accuracy but also novelty. According to our experimental results, there are about 60% interesting and unknown are recommended

インタラクションシーケンスに着目した商品検索目的抽出エージェントの開発

e-Commerceの急速な発展を背景に，Web検索結果への検索連動型広告（スポンサーリンクなど）が広告配信手段として注目されている．しかし，ユーザの検索意図と異なる広告の配信は，長期的に見てユーザの不快感を招き，逆効果となるリスクがある．そこで，ユーザの検索行動から検索の目的を推測し，適切な情報を提供することが重要となってきている．これまでも検索結果に対するユーザのブラウザ側の操作（インタラクション）に注目した研究は行われているが，一連のインタラクションの前後関係を考慮した研究は行われていない．そこで，本研究では商品検索結果に対するユーザのインタラクションシーケンスに着目し，検索の目的を購入目的か，情報収集目的かに分類するエージェントを提案する．実験により，先行手法と提案手法を組み合わせることにより，商品検索目的の抽出精度を10%以上向上できることを確認した．Search advertising like sponsor link on a search engine result page is now attracting attention as a new advertising solution according to the rapid growth of e-Commerce. However, if the advertising product does not match with a user\u27s search intension, it would cause uncomfortable feeling to the user, and an opposite effect for the advertising near future. Therefore, it\u27s increasingly important to extract the user\u27s search intension from his/her behavior, and fit the advertising to it. Although several studies have been done on extraction of the user\u27s search intention by checking the interactions with a browser, most of them lack of consideration of sequences of the interactions. Therefore, we focus on the user\u27s interaction sequences to the product search result, then try to classify the intentions to "buy" or "survey". Our experiment shows that combination of our method with a previous work raises more than 10% accuracy than the previous work alone