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This paper proposes a new method for assessing individual differences in time series data from multiple subjects, based on the cluster scale using a data reduction method as a measure for quantitatively detecting differences over subjects. This evaluation method is based on a previously proposed method of measuring individual difference among subjects by a common cluster scale over the subjects. However, it is unique in that we can reduce significant amounts of data by extracting data that affect the obtained common clusters by defining a new distance between the target data and the common clusters using the idea of distance based on maximum likelihood estimation using fuzzy covariance. Also, we demonstrate the effectiveness of the proposed method by showing that measuring the data between different subjects on only the selected data on the common cluster scale yields similar results to those obtained when using all data before selection.

Ultrahigh resolution terahertz time-domain spectroscopy (TDS) is realized by a low-complexity system featuring a dual-comb mode-locked fiber laser and adaptive sampling. It breaks the TDS’s long-time performance bottleneck in spectral resolution with an affordable platform.

Terahertz dual-comb spectroscopy (THz-DCS) has the potential to be used as universal THz spectroscopy with high spectral resolution, high spectral accuracy, and broad spectral coverage; however, the requirement for dual stabilized femtosecond lasers hampers its versatility due to the bulky size, high complexity, and high cost. We here report the first demonstration of dual THz comb spectroscopy using a single free-running fiber laser. While greatly reducing the size, complexity, and cost of the laser source, THz-DCS maintains the spectroscopic performance comparable to a system equipped with dual stabilized fiber lasers, and can be effectively applied to gas spectroscopy.

Mode-resolved dual-comb spectroscopy (DCS) is an emerging spectroscopic tool with the potential to simultaneously achieve a broad spectral coverage and ultrahigh spectral resolution in terahertz (THz) spectroscopy. However, the need for two independently stabilized ultrafast lasers significantly hampers the potential application of DCS techniques. In this article, we demonstrate mode-resolved DCS in the THz region based on a free-running single-cavity dual-comb fiber laser with adaptive sampling. Low-pressure spectroscopy of acetonitrile gas with absorption features approaching the Doppler limit is demonstrated by comb-mode-resolved measurements with a spectral sampling spacing of 48.8 MHz, a spectral resolution of less than 5 MHz and a signal-to-noise ratio of ~50 dB. The successful demonstration of the proposed method clearly indicates the great potential for the realization of low-complexity, MHz-resolution THz spectroscopy instrumentation.

We demonstrate dual-THz-comb spectroscopy using a wavelength-multiplexed mode- locked fiber laser. While greatly reducing its size, complexity, and cost, the proposed system maintains the spectroscopic performance comparable to a system equipped with dual stabilized fiber lasers.

Dual THz comb spectroscopy has the potential to be used as universal THz spectroscopy with high spectral resolution, high spectral accuracy, and broad spectral coverage; however, the requirement for dual stabilized femtosecond lasers hampers its versatility due to the bulky size, high complexity, and high cost. We here report the first demonstration of dual THz comb spectroscopy using a single free-running fibre laser. By tuning the cavity-loss-dependent gain profile with an intracavity Lyot filter together with precise management of the cavity length and dispersion, dual-wavelength pulsed light beams with slightly detuned repetition frequencies are generated in a single laser cavity. Due to sharing of the same cavity, such pulsed light beams suffer from common-mode fluctuation of the repetition frequency, and hence the corresponding frequency difference between them is passively stable around a few hundred hertz within millihertz fluctuation. This considerably stable frequency difference enables dual THz comb spectroscopy with a single free-running fibre laser. While greatly reducing the size, complexity, and cost of the laser source by use of a single free-running fibre laser, the dual THz comb spectroscopy system maintains a spectral bandwidth and dynamic range of spectral power comparable to a system equipped with dual stabilized fibre lasers, and can be effectively applied to high-precision spectroscopy of acetonitrile gas at atmospheric pressure. The demonstrated results indicate that this system is an attractive solution for practical applications of not only THz spectroscopy but also THz-pulse-based measurements., Comment: 29 pages, 7 figures

ガラス製Y字型マイクロチャネルを用いて，酢酸－メタノールをモデル系として，それぞれを別々の入口から導入し，2流体が合流した混合部での物質移動を顕微レーザーラマン分光計により計測する実験を行った．まず，はじめに各物質の定量化実験を行い，濃度とラマンスペクトルの強度には比例関係があり，各物質のラマンスペクトル強度からその濃度を求められることを明らかにした．次に，チャネル幅wと深さdの比として定義されるアスペクト比（w/d）が3.2であるチャネルをX–Y–Zステージ上にのせ，ステージを動かしながら，ラマンスペクトルを測定することでチャネル内の濃度分布を観測した．異なった3種類の流速において，濃度分布の観測値と計算値が良好に一致したことから，顕微レーザーラマン分光計を用いた物質移動計測法とCFD（Computational Fluid Dynamics）解析法の両者の信頼性を相互に確認した．次に，CFD解析を用いて，アスペクト比w/dが異なる3数種のマイクロチャネルを取り上げ，チャネル下流域における酢酸とメタノールの界面の位置を調べた．その結果，アスペクト比w/dが1のチャネルでは，酢酸とメタノールの比重の差異から，重力の影響を受けて比重の大きい酢酸がメタノールの下部に潜り込む効果により，2液の界面は3次元的に斜めとなった．一方，アスペクト比が1と比べて大きい3.2であるチャネル，また小さい0.31であるチャネルでは，比重の差異による潜り込みの程度が穏やかであり，界面は垂直に近くなることがわかった．これより，1より離れたアスペクト比を持つチャネルが，潜り込みが抑えられ，深さ方向に対する濃度分布が少ない理由より，2次元濃度分布計測に適していることがわかった．

We have observed a coherent oscillation signal of the interlayer shearing phonon mode of highly oriented pyrolytic graphite by means of femtosecond pump-probe experiment. The optical polarization dependence reveals a nontrivial phase shift between Rayleigh and Raman components. The detailed analysis of the phase shift clarifies that the Raman component mainly comes from the real part of the dielectric function. The excitation density dependence of the coherent phonon shows the same saturation behavior as that of the electronic response and the generation process of the coherent phonon is attributed to the real excitation of the $\ensuremath{\pi}\ensuremath{-}{\ensuremath{\pi}}^{*}$ transition.

The purpose of this study is to develop wearable sensor system for gait evaluation using gyroscopes and accelerometers for application to rehabilitation, healthcare and so on. In this paper, simultaneous measurement of joint angles of lower limbs and stride length was tested with a prototype of wearable sensor system. The system measured the joint angles using the Kalman filter. Signals from the sensor attached on the foot were used in the stride length estimation detecting foot movement automatically. Joint angles of the lower limbs were measured with stable and reasonable accuracy compared to those values measured with optical motion measurement system with healthy subjects. It was expected that the stride length measurement with the wearable sensor system would be practical by realizing more stable measurement accuracy. Sensor attachment position was suggested not to affect significantly measurement of slow and normal speed movements in a test with the rigid body model. Joint angle patterns measured in 10 m walking with a healthy subject were similar to common patterns. High correlation between joint angles at some characteristic points and stride velocity were also found adequately. These results suggested that the wireless wearable inertial sensor system could detect characteristics of gait.