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To capture vibration waveforms whose frequencies exceed the limitation set by sensing fiber length in OTDR distributed vibration sensing (DVS), we propose a sampling rate enhancement technique based on frequency-division-multiplexing (FDM). Our proposal, unlike conventional FDM-based sampling rate enhancement methods, directly eliminates inherent distortion by using complementary frequency concept with new probe pulse sequence. The proposed method can suppress the distortion of arbitrary waveforms in regular fiber without prior knowledge of the vibration. The proposal can accurately measure vibration waveforms and fully characterize the vibration on a standard single-mode fiber; it determines not only the frequency but also the correct amplitude and the exact shape of the vibration. Furthermore, our distortion compensation scheme incorporates a state-of-the-art FDM-based fading suppression technique, yielding high sampling rates and high sensitivity simultaneously. We demonstrate the validity of the proposal by proof-of-concept experiments in which the number of multiplexed frequencies is set to three for both sampling rate enhancement and fading suppression. In creating the experimental setup, we take the great care with the optical pulse shape and the carrier frequencies to avoid crosstalk. We successfully measure vibration waveforms with frequencies ranging from 1 kHz to 9 kHz on a sensing fiber with length of about 12 km.

To suppress coherent fading in Φ-OTDR distributed vibration sensing (DVS) with frequency-division-multiplexing (FDM), we propose an efficient methodology named the double averaging approach that processes complex vectors of Rayleigh scattered light on IQ plane. The double averaging approach rotates and averages complex vectors across the time domain as well as the optical frequency domain; this yields the final phase representing the vibration with less phase noise than the conventional method. This allows the proposal to prevent the phase unwrapping failures caused by the noise and improve the vibration detection sensitivity without incurring penalties in detection bandwidth or system complexity. The proposal is also effective in suppressing the vibration waveform distortion permitted by the conventional method. We confirm the effectiveness of the proposal through experiments in which we apply nϵ-level vibrations to an over 5 km sensing fiber and perform Φ-OTDR DVS by using FDM pulses composed of three optical frequencies.

We observe the waveform distortion in FDM-based sampling-rate-enhanced Φ -OTDR with pulse compression for the first time. We demonstrate that our complementary frequency approach is compatible and effective in suppressing the waveform distortion.

We present a field demonstration of distributed vibration sensing with FDM-Φ-OTDR in a deployed optical fiber cable network. Additionally, we propose and verify a vibration trace analysis technique that can localize telecommunication facilities.

Significance Imaging flow cytometry is a powerful tool for analyzing every single cell in a large heterogeneous population but relies on fluorescent labeling, which comes with cytotoxicity, nonspecific binding, and interference with natural cellular functions. This paper presents label-free multicolor chemical imaging flow cytometry based on stimulated Raman scattering (SRS), a highly sensitive method of molecular vibrational spectroscopy. With the help of deep learning, it demonstrates high-precision characterization and classification of microalgal cells and cancer cells without the need for fluorescent labeling., Combining the strength of flow cytometry with fluorescence imaging and digital image analysis, imaging flow cytometry is a powerful tool in diverse fields including cancer biology, immunology, drug discovery, microbiology, and metabolic engineering. It enables measurements and statistical analyses of chemical, structural, and morphological phenotypes of numerous living cells to provide systematic insights into biological processes. However, its utility is constrained by its requirement of fluorescent labeling for phenotyping. Here we present label-free chemical imaging flow cytometry to overcome the issue. It builds on a pulse pair-resolved wavelength-switchable Stokes laser for the fastest-to-date multicolor stimulated Raman scattering (SRS) microscopy of fast-flowing cells on a 3D acoustic focusing microfluidic chip, enabling an unprecedented throughput of up to ∼140 cells/s. To show its broad utility, we use the SRS imaging flow cytometry with the aid of deep learning to study the metabolic heterogeneity of microalgal cells and perform marker-free cancer detection in blood.

Cooling heat loss is one of the most dominant losses among the various engine losses to be reduced. Although many attempts to reduce it by insulating the combustion chamber wall have been carried out, most of them have not been successful. Charge air heating by the constantly high temperature insulating wall is a significant issue, because it deteriorates charging efficiency, increases the emissions of soot and NOx in diesel engines, and promotes the knock occurrence tendency in gasoline engines. A new concept heat insulation methodology which can reduce cooling heat loss without heating the charging air has been developed. Surface temperature of insulation coating on the combustion chamber wall changes rapidly, according to the quickly changing in-cylinder gas temperature in each engine stroke. During the compression and expansion stroke, the surface temperature of the insulation coating goes up rapidly, and consequently, the heat transfer becomes lower by the reduced temperature difference between the surface and the gas. During the intake stroke, the surface temperature goes down rapidly, and it prevents intake air heating from the wall. To realize the above-mentioned functionality, a thin coating layer with low thermal conductivity and low heat capacity was developed. It was applied on the pistons of diesel engines, and showed improvement in thermal efficiency. It also showed a reduction of unburnt fuel emission in low temperature engine starting condition. The energy balance analysis showed reduction of cooling heat loss and, on the contrary, increase in the brake power and the exhaust loss.

The FDM-based sampling rate enhancement method proposed herein detects vibration waveforms more accurately than previous methods while reducing phase unwrapping failures; it can measure vibrations with larger amplitude and higher frequency than heretofore.

For risk assessment of communication failure, Φ-OTDR vibration measurements are used to visualise optical fibre cable states. We reveal that conventional high-sensitive Φ-OTDR distort large vibration waveforms. The double-averaging method combined with frequency-division-multiplexing proposed herein is shown to well suppress the distortion.

High-speed label-free imaging with chemical contrast is effective for non-invasive analysis of the metabolic heterogeneity of single cells. Stimulated Raman scattering (SRS) microscopy enables high-speed label-free image acquisition with molecular vibrational specificity. While single-color SRS microscopy only acquires images at a certain vibrational frequency, multicolor SRS microscopy successively acquires SRS images at different vibrational frequencies, which then can be used to investigate the distributions of different intracellular molecules. However, its imaging speed remains an order of magnitude slower than that of single-color video-rate SRS microscopy. Previous approaches to circumvent this issue used either only two colors with limited chemical specificity or multiplex detection of SRS spectra using a photodiode array at the expense of imaging speed. Here we demonstrate high-speed four-color SRS imaging using a single photodiode by introducing fast wavelength-switched laser pulses. The fast wavelength switching is realized by the use of an optical intensity modulator as a time gate, a diffraction grating, and fiber delay lines. Using the developed system, we demonstrate motion-artifact-free multicolor SRS imaging of polymer beads and living cells. The results firmly support that our method is a powerful tool for the label-free analysis of living cells in microbiology, oncology, plant science, and medicine.

Microalgae have been receiving great attention for their ability to produce biomaterials that are applicable for food supplements, drugs, biodegradable plastics, and biofuels. Among such microalgae, Euglena gracilis has become a popular species by virtue of its capability of accumulating useful metabolites including paramylon and lipids. In order to maximize the production of desired metabolites, it is essential to find ideal culturing conditions and to develop efficient methods for genetic transformation. To achieve this, understanding and controlling cell-to-cell variations in response to external stress is essential, with chemically specific analysis of microalgal cells including E. gracilis. However, conventional analytical tools such as fluorescence microscopy and spontaneous Raman scattering are not suitable for evaluation of diverse populations of motile microalgae, being restricted either by the requirement for fluorescent labels or a limited imaging speed, respectively. Here we demonstrate video-rate label-free metabolite imaging of live E. gracilis using stimulated Raman scattering (SRS) – an optical spectroscopic method for probing the vibrational signatures of molecules with orders of magnitude higher sensitivity than spontaneous Raman scattering. Our SRS’s highspeed image acquisition (27 metabolite images per second) allows for population analysis of live E. gracilis cells cultured under nitrogen-deficiency - a technique for promoting the accumulation of paramylon and lipids within the cell body. Thus, our SRS system’s fast imaging capability enables quantification and analysis of previously unresolvable cell-to-cell variations in the metabolite accumulation of large motile E. gracilis cell populations.

Understanding metabolism in live microalgae is crucial for efficient biomaterial engineering, but conventional methods fail to evaluate heterogeneous populations of motile microalgae due to the labelling requirements and limited imaging speeds. Here, we demonstrate label-free video-rate metabolite imaging of live Euglena gracilis and statistical analysis of intracellular metabolite distributions under different culture conditions. Our approach provides further insights into understanding microalgal heterogeneity, optimizing culture methods and screening mutant microalgae. Label-free, video-rate metabolite imaging of live Euglena gracilis shows spatiotemporal intracellular metabolite distributions under different culture conditions.

Microbes, especially microalgae, have recently been of great interest for developing novel biofuels, drugs, and biomaterials. Imaging-based screening of live cells can provide high selectivity and is attractive for efficient bio-production from microalgae. Although conventional cellular screening techniques use cell labeling, labeling of microbes is still under development and can interfere with their cellular functions. Furthermore, since live microbes move and change their shapes rapidly, a high-speed imaging technique is required to suppress motion artifacts. Stimulated Raman scattering (SRS) microscopy allows for label-free and high-speed spectral imaging, which helps us visualize chemical components inside biological cells and tissues. Here we demonstrate high-speed SRS imaging, with temporal resolution of 0.14 seconds, of intracellular distributions of lipid, polysaccharide, and chlorophyll concentrations in rapidly moving Euglena gracilis, a unicellular phytoflagellate. Furthermore, we show that our method allows us to analyze the amount of chemical components inside each living cell. Our results indicate that SRS imaging may be applied to label-free screening of living microbes based on chemical information.

A series calculation method from injector nozzle internal flow to in-cylinder combustion in diesel engines has been developed. In this study, the calculation results of in-cylinder pressure, heat release rate, and NO concentration are compared with experimental results for conventional combustion conditions as well as an advanced combustion condition, which combines a high exhaust gas recirculation (EGR) rate, high boost pressure, and high pressure injection. The calculated pressure and heat release rate histories are in reasonable agreement with those of experiments, but the NO concentration is underestimated especially on the higher EGR rate condition. Therefore, an investigation to improve the quantitative accuracy of NO concentration is performed. The probability density function (PDF) method is one way to estimate the accurate mean reaction rate containing the reaction rate fluctuation by turbulence. In this study, the PDF method only applied for NO calculation is developed to balance the calculation accuracy and the computational cost. The result shows that the reaction rate fluctuation, on NO formation, has a small effect on conventional combustion conditions, but increases with decreasing combustion temperature.

The detection of rare cells in a large heterogeneous population of healthy cells has become an extremely important task in medical diagnostics, regenerative medicine, and drug discovery. The types of such rare cells include antigen- specific T cells, hematopoietic stem cells, fetal cells in maternal blood, and circulating tumor cells (CTCs) in blood. Particularly important among these cells are CTCs – precursors to cancer metastasis that circulate in the bloodstream of cancer patients [1, 2]. Unfortunately, conventional cell-screening methods fall short of providing sufficient sensitivity, specificity, and throughput required for identification of these cells with a reasonable statistical accuracy in a practical period of time. Next-generation medical instruments that should satisfy these requirements are expected to play a critical role for reducing medical costs (especially for the elderly) and hence improving their quality of life.

The effects of aromatic components in fuel on ignition and combustion of intermittent spray were examined experimentally. Four types of fuel with different aromatic components, and with similar cetane number and calorific value were used in this study. Fuels were injected into the high-temperature and high-pressure vessel with the injection pressures of 100 MPa and 60 MPa using an electronically controlled fuel injection system developed by the authors. Injection rate shaping applied to the experiments was rectangular, which is a typical injection rate shaping of a common rail type injection system. Images of spray flames were captured using an ICCD camera under ambient conditions corresponding to a turbo-charged diesel engine, 6.1 MPa and 1030 K. A two-color pyrometry technique was applied to the images of spray flame to quantify two-dimensional distributions of flame temperature and soot in flame. Through systematic experiments, it was explored that the aromatic components have little effects on ignition delay and combustion period. However, the aromatic components have significant effects on flame temperature and soot formation. The flame temperature and the amount of soot in flame become higher as the aromatic components in fuel increase. The injection pressure has a great effect on spray combustion, i.e., shorter combustion period and rapid soot oxidization with high injection pressure. However the effects of aromatic components on combustion were not changed qualitatively by the increased injection pressure.