ディジタルオーディオ信号のサンプル欠けの位置推定と修復

ディジタルオーディオ信号データの転送の際，クロック同期の設定を誤ると，サンプルの欠けや重複を生じてしまう．本論文では，このうちサンプル欠けに焦点をしぼり，修復を行う方法について述べる．まず，同期ミスによって起こるサンプル欠けの型を分類した後，一つの評価関数で，サンプル欠けの位置推定，サンプル欠けの型の判定，失われた信号値の復元を行う方法を提案する．次に，評価関数を得る方法として，線形予測誤差を規範とする方法，スパース性を規範とする方法，エントロピーを規範とする方法の三つを定式化する．最後に，それら三つを実験的に比較し，エントロピーを規範とする方法が最も優れていることを示す

順位表に基づいた独立成分分析：rankICA

順位情報に基づいた新しい独立成分分析法（rankICA）を提案する．rankICAとは，まず，2信号の順位関係から順位表を作り，次に，順位表のすべてのデータペア間のマンハッタン距離のヒストグラムを作成し，最後に，そのヒストグラムをコントラスト関数で評価することで2信号間の独立性の尺度を得て独立成分分析を実行する方法である．本論文では，アルゴリズムの紹介をしたあと，どのようなコントラスト関数を用いるのが適当であるかを実験的に検討し，比較的良い結果が得られるコントラスト関数を提示する．また，既存の方法と本手法を比較し，データをその順位情報のみに置き換えても独立性判定の能力は下がらず，むしろ性能が良くなることもあること，そして，外れ値に対する耐性（ロバスト性）は向上することを示す．計算量の大きさを度外視すれば，rankICAは，現存する独立成分分析法の中で最も良い信号分離を実現できる可能性を秘めている

Pricing Currency Options with a Market Model of Interest Rates under Jump-Diffusion Stochastic Volatility Processes of Spot Exchange Rates

This paper proposes a pricing method of currency options with a market model of interest rates. Using a simple approximation and a Fourier transform method, we derive a formula of the option pricing under jump-diffusion stochastic volatility processes of spot exchange rates. As an application, we apply the formula to the calibration of volatility smiles in the JPY/USD currency option market. Moreover, using the approximate prices as a control variate, we achieve substantial variance reduction in Monte Carlo simulation.

"Pricing Currency Options with a Market Model of Interest Rates under Jump-Diffusion Stochastic Volatility Processes of Spot Exchange Rates"

This paper proposes a pricing method of currency options with a market model of interest rates. Using a simple approximation and a Fourier transform method, we derive a formula of the option pricing under jump-diffusion stochastic volatility processes of spot exchange rates. As an application, we apply the formula to the calibration of volatility smiles in the JPY/USD currency option market. Moreover, using the approximate prices as a control variate, we achieve substantial variance reduction in Monte Carlo simulation.

時間周波数平面を用いた音声が埋もれない音信号混合法の評価

本論文では，音のミキシングに時間周波数平面を用いることの有効性を示す．著者らは，時間周波数平面を用いた新しい音信号混合法を提案してきた．時間周波数平面を用いることで，各入力信号の特徴を捉え，信号間の特徴の相互関係に沿った緻密な処理が実現できる．この考えに立脚したミキシング手法として，音声とBGM(Background Music)とのミキシング時に，音声が埋もれない音信号混合法を提案してきた．本論文では提案法が時間周波数領域での処理であることの有効性を，聴取実験により検証する．具体的には，提案法での変化量を，周波数領域，時間領域での処理で近似し，了解度と主観評価を比較して評価する．これらの検討により，時間周波数平面を用いた音信号混合法の有効性を示す

How the Foot Modulates its Mechanics During Uphill and Downhill Walking

The foot\u27s biomechanical role in walking on sloped surfaces is currently unclear. While previous biomechanics studies have examined the hip, knee, and ankle, the foot is oversimplified as a rigid-body segment. This oversimplification overshadows its complex structure and function. In this project, we use an innovative multi-segment foot model to explore how the foot adapts its mechanics to incline and decline walking. Preliminary results have revealed that the foot is capable of adapting its mechanical work profile to both incline and decline walking. Specifically, the foot can increase its positive work output (i.e., increased energy generation) during inclined walking to help propel the body upwards, and it increases its negative work output (i.e., increased energy dissipation) during declined walking to help slow the body down. These results are informative for understanding the role the foot plays during walking, and may help in the design of prosthetic, orthotic, or exoskeletal devices that are supposed to mimic the foot’s function

Spin-polarized electronic structures and transport properties of Fe-Co alloys

The electrical resistivities of Fe-Co alloys owing to random alloy disorder are calculated using the Kubo-Greenwood formula. The obtained electrical esistivities agree well with experimental data quantitatively at low temperature. The spin-polarization of Fe50Co50 estimated from the conductivity (86%) has opposite sign to that from the densities of the states at the Fermi level (-73%). It is found that the conductivity is governed mainly by s-electrons, and the s-electrons in the minority spin states are less conductive due to strong scattering by the large densities of the states of d-electrons than the majority spin electrons.Comment: 3 pages, 4 figure

The foot and ankle structures reveal emergent properties analogous to passive springs during human walking

An objective understanding of human foot and ankle function can drive innovations of bio-inspired wearable devices. Specifically, knowledge regarding how mechanical force and work are produced within the human foot-ankle structures can help determine what type of materials or components are required to engineer devices. In this study, we characterized the combined functions of the foot and ankle structures during walking by synthesizing the total force, displacement, and work profiles from structures distal to the shank. Eleven healthy adults walked at four scaled speeds. We quantified the ground reaction force and center-of-pressure displacement in the shank’s coordinate system during stance phase and the total mechanical work done by these structures. This comprehensive analysis revealed emergent properties of foot-ankle structures that are analogous to passive springs: these structures compressed and recoiled along the longitudinal axis of the shank, and performed near zero or negative net mechanical work across a range of walking speeds. Moreover, the subject-to-subject variability in peak force, total displacement, and work were well explained by three simple factors: body height, mass, and walking speed. We created a regression-based model of stance phase mechanics that can inform the design and customization of wearable devices that may have biomimetic or non-biomimetic structures

A neuromechanics-based powered ankle exoskeleton to assist walking post-stroke: a feasibility study

Background: In persons post-stroke, diminished ankle joint function can contribute to inadequate gait propulsion. To target paretic ankle impairments, we developed a neuromechanics-based powered ankle exoskeleton. Specifically, this exoskeleton supplies plantarflexion assistance that is proportional to the user’s paretic soleus electromyography (EMG) amplitude only during a phase of gait when the stance limb is subjected to an anteriorly directed ground reaction force (GRF). The purpose of this feasibility study was to examine the short-term effects of the powered ankle exoskeleton on the mechanics and energetics of gait. Methods: Five subjects with stroke walked with a powered ankle exoskeleton on the paretic limb for three 5 minute sessions. We analyzed the peak paretic ankle plantarflexion moment, paretic ankle positive work, symmetry of GRF propulsion impulse, and net metabolic power. Results: The exoskeleton increased the paretic plantarflexion moment by 16% during the powered walking trials relative to unassisted walking condition (p \u3c .05). Despite this enhanced paretic ankle moment, there was no significant increase in paretic ankle positive work, or changes in any other mechanical variables with the powered assistance. The exoskeleton assistance appeared to reduce the net metabolic power gradually with each 5 minute repetition, though no statistical significance was found. In three of the subjects, the paretic soleus activation during the propulsion phase of stance was reduced during the powered assistance compared to unassisted walking (35% reduction in the integrated EMG amplitude during the third powered session). Conclusions: This feasibility study demonstrated that the exoskeleton can enhance paretic ankle moment. Future studies with greater sample size and prolonged sessions are warranted to evaluate the effects of the powered ankle exoskeleton on overall gait outcomes in persons post-stroke

Prosthetic energy return during walking increases after 3 weeks of adaptation to a new device

Background: There are many studies that have investigated biomechanical differences among prosthetic feet, but not changes due to adaptation over time. There is a need for objective measures to quantify the process of adaptation for individuals with a transtibial amputation. Mechanical power and work profiles are a primary focus for modern energystorage- and-return type prostheses, which strive to increase energy return from the prosthesis. The amount of energy a prosthesis stores and returns (i.e., negative and positive work) during stance is directly influenced by the user’s loading strategy, which may be sensitive to alterations during the course of an adaptation period. The purpose of this study was to examine changes in lower limb mechanical work profiles during walking following a three-week adaptation to a new prosthesis. Methods: A retrospective analysis was performed on 22 individuals with a unilateral transtibial amputation. Individuals were given a new prosthesis at their current mobility level (K3 or above) and wore it for three weeks. Kinematic and kinetic measures were recorded from overground walking at 0, 1.5, and 3 weeks into the adaptation period at a self-selected pace. Positive and negative work done by the prosthesis and sound ankle-foot were calculated using a unified deformable segment model and a six-degrees-of-freedom model for the knee and hip. Results: Positive work from the prosthesis ankle-foot increased by 6.1% and sound ankle-foot by 5.7% after 3 weeks (p = 0.041, 0.036). No significant changes were seen in negative work from prosthesis or sound ankle-foot (p = 0.115, 0.192). There was also a 4.1% increase in self-selected walking speed after 3 weeks (p = 0.038). Our data exhibited large inter-subject variations, in which some individuals followed group trends in work profiles while others had opposite trends in outcome variables. Conclusions: After a 3-week adaptation, 14 out of 22 individuals with a transtibial amputation increased energy return from the prosthesis. Such findings could indicate that individuals may better utilize the spring-like function of the prosthesis after an adaptation period