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高機能メタサーフェスの自動最適設計法の開発に関する研究
Get PDF室蘭工業大学Muroran Institute of Technology博士（工学）天然材料では得られない特性を実現可能なメタサーフェスに注目が集まっている．メタサーフェスは人間の手で創成された物質であり，人工的に波長オーダー以下の構成要素を配列することで，自然界には存在しない材料特性を実現することができる．特に，2次元的に形成されるメタサーフェスは半導体分野でのフォトリソグラフィ技術が適用可能で作製が比較的容易であることから，実用化を視野に入れた研究が活発になされている．
しかしながら，現時点ではメタサーフェスの設計は、設計者の知識や経験に頼るところが大きく，既存構造の改良や発見的な方法による報告が主であり，任意の構造から最適解を見いだせる自動最適設計についての報告は少ない．さらなるメタサーフェスの特性改善や新たな機能の創造に向けて，トポロジー最適設計を含めた自動最適設計の技術が求められている．
メタサーフェスの自動最適設計を行うには，周期構造を効率的に解析できる特性解析法と，大域的な探索を行いながら最適な構造を創出可能な最適設計法が必要である．そこで本研究では，まず，非相反動作を実現できる1次元磁性メタサーフェスの設計を例に基本的な検討を行った．特性解析手法には柔軟性と適合性の高いメッシュ分割により解析領域全体を精度良くモデリングできる有限要素法を採用し，最適設計法には，感度解析を必要としない進化的手法を採用した．これに加えて，目的関数の設定方法についての検討を行い，二目的問題を非線形関数を用いて単目的化することで，両方の目標を同時に達成する構造が比較的容易に得られることを示した．また，構造パラメータの一部を設計変数に加えた最適化も行い、入射角度特性を大幅に改善した設計結果を示した．
次に、磁性メタサーフェスの偏波無依存化を目的とし，特性解析には 3 次元の有限要素法を採用し，平面波入射と分散性を有する磁性材料の入力プログラムの実装と周期構造に対応した境界条件の設定を行った．構造表現には関数展開法を採用し，複数の関数の重ね合わせによって多媒質材料を扱う改良を行った，これに加え，特性解析の際のメッシュ分割の改良についての検討も行い、偏波無依存型の磁性メタサーフェスの設計結果を示した．
最後に軸対称メタレンズの初期検討を行った．特性解析には軸対称フルベクトル有限要素法を採用し周方向に対称な構造を考え，最適化手法に共分散行列適応進化戦略 (CMA-ES) を用い，構造表現には関数展開法を採用した最適設計を実施し，近似ベッセルビームを生成するメタレンズ等の最適設計が可能であることを示した．
本自動最適設計法は，2次元平面及び周方向に周期構造を持つメタサーフェスの効率的な特性解析が可能であり，設計者の知識によらずに所望の特性が得られ、比較的短時間で解析結果を得られることから，メタサーフェスの自動最適設計法とした場合にその有用性が高く，実用的な設計手法として活用できる．Metasurfaces are attracting a lot of attention because they can realize unique properties that cannot be achieved with ordinary materials. Metasurfaces are created materials by human knowledge, by artificially arranging the constituent elements below the wavelength order. In particular, metasurface with two-dimensional (2D) structure is easy to be fabricated by existing semiconductor fabrication process compared to three-dimensional (3D) metamaterials.
However, design of metasurfaces, now, rely on knowledge and experience of designers, their reports are mainly based on improvements to existing structures and heuristic methods. Few reports on automatic optimization techniques. In order to develop high-performance metasurfaces, now, computer simulations are widely used and automatic optimization techniques using them are also proposed.
In automatic optimal design methods for high-performance metasurfaces, we consider that we need characterization method for efficient analysis of periodic structures and optimal design method that can create optimal structures while conducting global search. In this study, in order to realize metasurface isolator with simple one dimensional (1D) periodic structure. In addition, we employ frequency domain finite element method with periodic boundary condition as a numerical simulation technique, and evolutionary method as an optimizer. We have designed 1D magneto-metasurfaces consist of InSb and SiO2. In order to satisfy two different objectives simultaneously, we improved the objective function by using nonlinear function. Then, in order to improve angular characteristics, we designed the structural parameters together and achieved wide angle operation.
Next, to achieve polarization independent isolator, 2D metasurface isolator is designed using function-expansion-based topology optimization method which is developed in the design of plane wave circuits. In this design, three materials are assumed to be used to enhance the nonreciprocity and the function expansion method is extended to be applicable to multiple materials. A 3D full-vectorial finite element method (3D-FVFEM) with periodic boundary condition (PBC) which has been originally developed is used for numerical analysis and design parameters are optimized using the covariance matrix adaptation evolution strategy (CMA-ES). Furthermore, in order to achieve efficient and accurate 3D FEM analysis, the boundary-fitted finite element mesh generation scheme is improved to suit multi-material function expansion method. We have shown that the polarization independent isolator with wide operation bandwidth around 0.9 THz is actually designed.
Finally, an initial study of axisymmetric meta-lenses was carried out. The axisymmetric full-vector finite element method was employed for the characteristic analysis, a circumferentially symmetric structure was considered, CMA-ES was used as the optimization method, and a function expansion method was employed for the structural representation.
This automatic optimum design method can efficiently analyze the characteristics of metasurfaces with periodic structures in the 2D plane and in the circumferential direction, obtain the desired characteristics without the designer's knowledge, and obtain analysis results in a relatively short time. It can be used as a practical design methods.doctoral thesi
高強度コンクリートの圧縮強度および収縮特性に及ぼすフライアッ シュ混和およびその減水作用の影響
Get PDF高強度コンクリートの圧縮強度および収縮特性に及ぼすフライアッシュの混和およびその減水作用の影響を明らかにするために，圧縮強度試験および収縮試験を実施し，単位水量を一定にしたものと減少させたものとの比較を行った。水結合材比は30%一定，フライアッシュの置換率は0%，10%，20%，30%と変化させた。その結果，フライアッシュ置換率が増加するほど圧縮強度および自己収縮は減少，乾燥収縮は増加
すること，単位水量を減少させることで，圧縮強度および自己収縮は若干増加，乾燥収縮は減少することがわかった。journal articl
高炉スラグ微粉末を主結合材とするセメントフリーモルタルの凝結および強度発現に及ぼす消石灰および無水石こうの影響
Get PDF高炉スラグ微粉末を主結合材とするセメントフリーモルタルの凝結および強度発現に及ぼす消石灰および無水石こうの影響について検討するため，水結合材比を50%一定とし，粉末度4000 の高炉スラグ微粉末に対して消石灰添加率を0, 0.1, 0.2, 0.5, 1%，無水石こうをSO3添加率で0, 0.1, 0.2, 0.5, 1, 2, 5%となるように設定し，凝結試験，粉末X 線回折試験および圧縮強度試験を行った。その結果，消石灰を0.2%から1%，無水石こうをSO3添加率で0.5%から5%程度用いることで，終結時間は基準セメントモルタルと同程度から1.6 倍程度になること，消石灰を0.1%から0.2%，無水石こうをSO3添加率で5%程度用いることで，圧縮強度は基準セメントモルタルの9 割程度得られることが明らかとなった。journal articl
Time Adverbs Indicating Duration and Progress in Ainu Language from a Japanese Perspective
Get PDF本稿ではアイヌ語の「時間関係の副詞」を、事態存続の時間量を表すもの、時間の中での事態の進展を表すもの、起動への時間量を表すものの三種類に分け、それらの意味と構文の特徴について記述した。事態存続の時間量を表す時間副詞は、形式上バリエーションが多く、構文上、動作動詞と共起する場合はその動作の持続時間を、変化動詞と共起する場合はその変化した結果の持続時間を表す。時間の中での事態の進展を表す時間副詞には、「uweepakta（だんだん）」、「usimne（日一日）」などがある。これらの時間副詞は変化動詞と共起する場合、変化の漸進的進展を表し、動作動詞と共起する場合は繰り返しの意味で解釈されることがあり、事態の進展性を示す。起動への時間量を表す時間副詞には、アイヌ語で「nisapno（急に）」、「ekuskonna（突然）」、「oykesne（しまいに）」などがあり、これらは各々異なる時間の長さを示しながらも、事態の起動や取り掛かりまでの所要時間量を表す。journal articl
Design of Polarization Beam Splitter Based on Rectangular Core Photonic Crystal Fiber Without Holes in the Cladding
Get PDFA new polarization beam splitter (PBS) based on
rectangular core photonic crystal fibers (RC-PCFs) is proposed.
Based on the full-vector finite element method, RC-PCFs without
holes in the cladding are introduced to improve the design
flexibility of multi-core PCF structure. An anisotropic lattice
distribution using staggered arrangement of silicon nitride rods
and air holes is employed in the core region to increase the
birefringence. Optimization of the rectangular core structure
is conducted to achieve single-polarization single-mode (SPSM)
property. Afterwards, utilizing two SPSM PCFs, in the proposed
PBS, two orthogonal polarization waves are only coupled to
corresponding PCFs with a device length of 185 μm, and the
crosstalk-free PBS is achieved.journal articl
Profit-Maximizing Service Function Chain Embedding in NFV-Based 5G Core Networks
Get PDFNetwork Function Virtualization (NFV) is a promising technology to make 5G networks more flexible and cost-efficient. With NFV, a 5G network service is implemented as several Virtual Network Functions (VNFs) that run on general machines, called a Service Function Chain (SFC). A recent survey has revealed that when multiple VNFs are colocated in the same machine, contention for shared physical resources will occur and hence degrade the throughput of a VNF and finally increase its processing delays by 50%, as compared to it runs in isolation. However, prior works fail to capture this important characteristic because they simply treat machines as a resource pool without any resource contention happening, making their approach inapplicable to the SFC embedding problem when resource contention is taken into consideration. To bridge that gap, in this paper, we study a contention-aware QoS-guaranteed SFC embedding problem and formulate it as an Integer Non-Linear Programming (INLP) under a couple of constraints. Given the formulated problem is challenging to solve due to high complexity, we propose a low-complexity approach, which can achieve a near-optimal result in a reasonable time. Numerical results reveal that the proposed approach has advantages in profit, delay, and execution time compared with other state-of-the-art approaches.journal articl
Creating a Framework for Encouraging Self-Regulated Learning: Applying Nudge Theory in Japanese Reading Classes
Get PDFThe purpose of this study was to investigate the following two key aspects within the context of Japanese reading classes for international students at a Japanese national university: i. Support for Japanese language learners to acquire academic reading skills, ii. Encouraging Japanese language learners' Self-Regulated Learning (SRL) in Japanese reading classes. In view of this, the following practices were specifically carried out: i. Creating a framework for Japanese reading classes by applying the nudge theory to foster Japanese language learners’ SRL, ii. Elucidating the phases of SRL in Japanese language learning through classwork, thereby nudging students to enhance their metacognitive awareness of SRL phases for Japanese language learning. The findings of this study indicate that the framework for Japanese reading classes that apply the nudge theory is effective in encouraging Japanese language learners' SRL in this case. However, further research is necessary on the formation process of SRL in individual learners.departmental bulletin pape
EVALUATION OF MISSING PROCESSING AND INFERENCE FOR PREDICTION OF WATER LEVEL USING SPARSE MODELING WITH HIGH MISSING RATE
Get PDF本論文では，欠測値を含むデータセットから直接学習可能な欠測対応スパースモデリング（HMLasso）による水位推論を提案し，その有効性を検証した．河川情報で生じる観測所の未観測，観測エラーなどによる欠測への対応手法として，HMLassoによる欠測処理の有用性を検証するため，令和4年8月に出水事例が報告された最上川を対象に，従来法と比較した．さらに，学習データの欠測率を最大50%まで人為的に増加させ評価した．その結果，HMLassoモデルはNash-Sutcliffe係数で，実測値で学習した場合で0.876に対し，50%欠測では0.842と，欠測率による性能低下が少ないとわかった．In this paper, we propose a inference model for prediction of water level using the HMLasso (least absolute shrinkage and selection operator with high missing rate) algorithm. The HMLasso algorithm enables the learning of models directly from data sets that contain missing values. In the collection of river data, there are several factors that can induce missing data. These factors encompass the closure of telemeter, their installation, and observation errors. We conducted a comparative analysis between conventional method and the HMLasso model. The analysis was carried out on the Mogami River during a flooding event in August 2022. To facilitate this comparison, we artificially increased the missing data rate up to a maximum of 50% and performed multiple analyses. As a result, when trained using actual values, the Nash-Sutcliffe coefficient was 0.876. However, even with a 50% data missingness rate, the coefficient reduced only marginally to 0.842. This results that the HMlasso model's performance degradation due to missingness rate is relatively minimal.journal articl
ユーザ中心の無線システムに向けて：カスタマイズと持続可能性のための再構成可能なインテリジェント表面の最適化
Get PDF室蘭工業大学Muroran Institute of Technology博士（工学）Reconfigurable intelligent surfaces (RISs) have emerged as a promising technology for future wireless communication systems due to their passive meta-elements, slim design, high integration, cost-effectiveness, and ease of deployment. However, optimizing beamforming at RISs, transmission power at access points (APs), deployment locations of multiple RISs, and association relationships between RISs and IoT devices are crucial for various RIS assisted wireless communication networks. Therefore, this dissertation presents effective solutions to maximize the achievable rates, enhance the coverage probability, minimize power consumption, and optimize the quality of experience (QoE).
In this dissertation, four major tasks are proposed on the various multi-RIS-assisted wireless communication scenarios. The first task investigates the influence of multiple RIS on the average achievable rate in indoor communication wireless networks. The second task focuses on exploring the relationships between coverage probability and deployment locations of multiple RIS in outdoor scenarios to maximize coverage while satisfying the network cost constraint. Moreover, the second task introduces a method based on approximate cell decomposition to calculate coverage probability quantitatively. The third task is to optimize power consumption, which consists of exploring the association relationships and minimizing the overall power consumption. Finally, the last task investigates the RIS deployed in the
wireless VR THz communication systems to maximize the QoE by jointly optimizing the beamforming vectors at multiple RISs, the transmit power of AP, and the rendering capacity allocation among VR users. To solve the issue, the issue is decomposed into two stages: stage-1 aims to minimize BER and maximize the data rate, while stage-2 aims to maximize rendering capacity among virtual objects.doctoral thesi
銀を用いる表面プラズモンセンシング基板へのポリマー薄膜成膜に関する研究
Get PDF室蘭工業大学Muroran Institute of Technology博士（工学）金属表面における自由電子の集団的な振動の量子は表面プラズモンと呼ばれ，表面近傍
の屈折率変化により，その振動の空間的な周波数（伝搬定数）が鋭敏な応答を示すことが知
られている．その屈折率感度は分子検出に適用できるほど高く，無修飾で測定が行うことが
でき，蛍光染色などを必要としないため，特に，生体関連分子の検出に広く用いられている．
表面プラズモンを励起するための典型的な手法として，高屈折率ガラスに金属薄膜を成
膜した基板を用いて，ガラス側から p 偏光の光を全反射条件で入射させる方法が一般的に
知られている．基板表面に対する，入射光の波数ベクトルの射影成分を入射角によって変化
させると，特定の空間周波数で反射光強度が低下し，ディップの形を示す空間周波数スペク
トルが得られる．このディップの位置の空間周波数が表面プラズモンの伝搬定数を示し，デ
ィップの幅の狭さが測定感度の高さに影響する．金属に銀を用いるとディップが最も狭く
なり，最高の測定感度が得られるが，一方で，硫化や酸化によって劣化が容易に生じる．そ
の対策として，これまでに，シリカや金で保護膜を形成する手法が報告されているが，シリ
カは特定の細胞の培養液で崩壊することも報告されており，金を用いる際にはディップの
広がりを避けることができない．そこで本研究では，新たな保護膜としてポリマーを用いる
ことを考えた．その中でも，光学的な透明性と化学的安定性を考慮し，poly(methyl metha
crylate) (PMMA) を用いることを提案した．
PMMAの厚さについて，表面プラズモンが形成する電場はエバネッセント波であるから，測
定感度の維持を行うため，PMMAを膜厚 〜15 nm 程度で成膜することとした．薄膜を形成す
る手法としてはスピンコート法が一般的であるが，銀表面で実行しようとすると，親水性の
低さが妨げとなる．そこで本研究では，銀表面の親水性を向上するための手段を検討し，大
気圧低温プラズマ処理が有効であることを発見した． そして，プラズマ処理された銀表面
にPMMAをスピンコートし，表面プラズモンの伝搬定数測定を行ったところ，PMMAを膜厚 〜
15 nm で成膜できることを実験で確認した．その膜厚均一性について，集束表面プラズモ
ン顕微鏡法を用いて，15 μm × 15 μm （64 点 × 64 点）の領域で伝搬定数分布を測定
すると，標準偏差は 10-4 程度であることを確認した．A flat metal surface can support the excitation of collective electron oscillations known as surface plasmons. Surface plasmons exhibit a dependence on the refractive indices in the optical near field on the surface, which changes their propagation constant. Optical sensors using surface plasmons exhibit high refractometry sensitivity, making them ideal for detecting intermolecular interactions between bio-related molecules without the need for labeling with fluorescent dyes.
A common method for exciting surface plasmons involves illuminating a metal film on a glass substrate with p-polarized light at an angle greater than the critical angle directed from the glass side. Surface plasmons are excited on the metal surface on the opposite side of the glass when the spatial frequency, which is the projected component of the wave vector of the incident light onto the metal surface, matches the propagation constant of the surface plasmons. The reflectance versus spatial frequency curve shows a dip at the point in which the spatial frequency coincides with the propagation constant. The narrowness of the dip enhances the measurement sensitivity of surface plasmon sensing. The narrowest dip was achieved using silver as the metal film. However, sulfidation or oxidation of the silver surface degrades the measurement sensitivity. To counteract this, a protective film is necessary. I have developed a deposition method for a polymer thin film to serve as a protective layer. Among various polymers, poly(methyl methacrylate) (PMMA) is particularly suitable as a protective film owing to its optical transparency and chemical stability.
The thickness of the PMMA layer was set at approximately 15 nm to maintain measurement sensitivity for refractive index sensing using surface plasmons, which exhibit evanescent decay on the silver surface. When I attempted to apply spin coating, a common method for polymer deposition on silver surfaces, I encountered a problem: the low hydrophilicity of the silver surface repelled the coating solution. To address this, I developed a method for enhancing the hydrophilicity of silver surface using atmospheric low-temperature plasma treatment.
After plasma treatment, a PMMA thin film was successfully deposited on the silver surface using spin coating. The thickness of PMMA was determined to be approximately 15 nm by measuring the propagation constants of the surface plasmons. The standard deviation of the propagation constants over an area of 15 × 15 μm was on the order of 10−4, indicating high microscopic uniformity.doctoral thesi