Key Agreement for Large-Scale Dynamic Peer Group

Many applications in distributed computing systems,such as IP telephony, teleconferencing, collaborative workspaces,interactive chats and multi-user games, involve dynamic peergroups. In order to secure communications in dynamic peergroups, group key agreement protocols are needed. In this paper,we come up with a new group key agreement protocol, composedof a basic protocol and a dynamic protocol, for large-scaledynamic peer groups. Our protocols are natural extensions ofone round tripartite Diffie-Hellman key agreement protocol. Inview of it, our protocols are believed to be more efficient thanthose group key agreement protocols built on two-party Diffie-Hellman key agreement protocol. In addition, our protocols havethe properties of group key secrecy, forward and backwardsecrecy, and key independence

高等学校物理教育の目標と教師の教育観の変遷 : 昭和30年代以降の学習指導要領改訂毎の時代区分による分析 <第2部 教科研究>

本研究は，教師の教育観，とりわけ物理教育の目的・目標に焦点をあてて，時代変遷や時代毎の特徴を明らかにしていくことを目的とした．はじめに学習指導要領にみられた理科教育の目的・目標の変遷を分析した後，日本物理教育学会の機関誌にみられた教師の教育観を文献調査した． 学習指導要領では物理教育の目標として4つの用語（「科学的な自然観」，「探究」，「科学的な考え方」と「基本的な概念，原理，法則」）が時代によらず用いられていた．また自然観と探究の用語は．時代や社会にあわせて意味が変化していると考えられた．本研究の調査では，教師が主眼においていた指導目標は，学習指導要領の改訂如何に関わらず，「（履修している）すべての生徒に物理を理解させること」にあった．また物理が必修科目として設定されて履修状況が高いときには，如何に知識（概念）を伝えるか，選択科目として履修状況が低いときには，思考や教育的価値観などに目的・目標を置く傾向がみられた．本研究では，履修方法（必修科目・選択科目）による生徒の状況の違いが教師の教育観にも影響を与える傾向がみられることが明らかになった．本研究はJSPS科研費 JP16H00173（高等学校物理の指導目標の変遷と教材の扱い方に関する基礎研究）の助成を受けて実施したものである

Underlying Assumptions and Designated Verifier Signatures

In this paper, we define an underlying computational problem and its decisional problem. As an application of their problems, we propose an efficient designated verifier signature (DVS) scheme without random oracles (related to symmetric pairings). We formally redefine the (Strong) Privacy of Signature\u27s Identity, and prove our DVS scheme satisfying security based on the difficulty of the problems. Also we prove that the difficulty of the computational problem is tightly equivalent to the Strong Unforgeability of our proposed conventional signature scheme (without random oracles) related to asymmetric pairings. We believe that our underlying problems are profitable to propose many efficient cryptographic schemes

Leakage of Mildly Flammable Refrigerants into a Room

The use of chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) has been widely restricted. They have been replaced with hydrofluorocarbons (HFCs) in order to protect the ozone layer. However, the leakage of refrigerant into air from active or end-of-life air conditioners has been a serious environmental issue owing to the high global warming potential (GWP). It has therefore been widely recognized that the replacement of HFCs with low-GWP refrigerants is a reasonable solution of the problem. In Japan, the low-GWP refrigerants such as R1234yf, R1234ze, and R32 are considered as candidate alternatives for conventional HFC refrigerants. However, these low-GWP refrigerants are often flammable. When refrigerants leak into a space, they tend to accumulate at the floor if they are heavier than air and ventilation is inadequate. If the refrigerant concentration is higher than the lower flammable limit (LFL), there is an ignition source, and the air velocity is lower than the burning velocity, the refrigerant may ignite. When leakage occurs from an air conditioner, there is always a region where the refrigerant concentration is higher than the LFL because the refrigerant concentration is about 100% near the outlet from the air conditioner. Thus, it is important to understand the diffusion phenomena of the low-GWP refrigerants when acquiring sufficient information for the safety standards to assess the risks in the usage of these refrigerants. Numerical analysis is an effective tool because it is very difficult to measure the diffusion of a refrigerant in a large space. In this study, diffusion phenomena were numerically analyzed when a refrigerant leaked from a room air conditioner (RAC), a package air conditioner (PAC) or a chiller into a large space where these were equipped. From the calculation results, the refrigerant concentration distributions, the volumes and positions of the flammable regions, and their changes in time were discussed